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Title: Modern Machine-Shop Practice, Volumes I and II
Author: Rose, Joshua
Language: English
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| TRANSCRIBER'S NOTES |
| |
| Transcriptions used in this e-text: |
| italics text in the original work is presented here between |
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| the author uses the form 1-64, this form has been retained, |
| except in tables; |
| superscript texts are transcribed as in ^{text}; |
| subscript texts are transcribed as in _{text}; |
| single Greek letters are transcribed as [alpha], [beta], etc.; |
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| work have been transcribed as single-line in-line formulas and |
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| More extensive Transcriber's Notes will be found at the end of |
| this text. |
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[Illustration: _VOL. I. MODERN MACHINE-SHOP PRACTICE FRONTISPIECE_
_Copyright, 1887 by Charles Scribner's Sons._
=MODERN AMERICAN FREIGHT LOCOMOTIVE.=]
MODERN
MACHINE-SHOP PRACTICE
BY
JOSHUA ROSE, M.E.
ILLUSTRATED WITH MORE THAN 3000 ENGRAVINGS
VOLUME I.
NEW YORK
CHARLES SCRIBNER'S SONS
1887
COPYRIGHT, 1887, BY
CHARLES SCRIBNER'S SONS
Press of J. J. Little & Co.
Astor Place, New York.
PREFACE.
MODERN MACHINE-SHOP PRACTICE is presented to American mechanics as a
complete guide to the operations of the best equipped and best managed
workshops, and to the care and management of engines and boilers.
The materials have been gathered in part from the author's experience of
thirty-one years as a practical mechanic; and in part from the many
skilled workmen and eminent mechanics and engineers who have generously
aided in its preparation. Grateful acknowledgment is here made to all
who have contributed information about improved machines and details of
new methods.
The object of the work is practical instruction, and it has been written
throughout from the point of view, not of theory, but of approved
practice. The language is that of the workshop. The mathematical
problems and tables are in simple arithmetical terms, and involve no
algebra or higher mathematics. The method of treatment is strictly
progressive, following the successive steps necessary to becoming an
intelligent and skilled mechanic.
The work is designed to form a complete manual of reference for all who
handle tools or operate machinery of any kind, and treats exhaustively
of the following general topics: I. The construction and use of
machinery for making machines and tools; II. The construction and use of
work-holding appliances and tools used in machines for working metal or
wood; III. The construction and use of hand tools for working metal or
wood; IV. The construction and management of steam engines and boilers.
The reader is referred to the TABLE OF CONTENTS for a view of the
multitude of special topics considered.
The work will also be found to give numerous details of practice never
before in print, and known hitherto only to their originators, and aims
to be useful as well to master-workmen as to apprentices, and to owners
and managers of manufacturing establishments equally with their
employees, whether machinists, draughtsmen, wood-workers, engineers, or
operators of special machines.
The illustrations, over three thousand in number, are taken from modern
practice; they represent the machines, tools, appliances and methods now
used in the leading manufactories of the world, and the typical steam
engines and boilers of American manufacture.
The new PRONOUNCING AND DEFINING DICTIONARY at the end of the work, aims
to include all the technical words and phrases of the machine shop, both
those of recent origin and many old terms that have never before
appeared in a vocabulary of this kind.
The wide range of subjects treated, their convenient arrangement and
thorough illustration, with the exhaustive TABLE OF CONTENTS of each
volume and the full ANALYTICAL INDEX to both, will, the author hopes,
make the work serve as a fairly complete ready reference library and
manual of self-instruction for all practical mechanics, and will
lighten, while making more profitable, the labor of his fellow-workmen.
CONTENTS.
VOLUME I.
CHAPTER I.
=THE TEETH OF GEAR-WHEELS.=
PAGE
=Gear-Wheels.= Spur-wheels, bevel-wheels, mitre-wheels,
crown-wheels, annular or internal wheels 1
Trundle-wheels, rack and pinion-wheel and tangent screw, or
worm and worm-wheel 1
The diameter of the pitch circle of 1
=Gear-Wheel Teeth.= The face, the flank, the depth or height 1
The space, the pitch line, the point, the arc pitch, the chord
pitch, the line of centres 2
Rules for finding the chord pitch from the arc pitch; table of
natural sines; diametral pitch; finding the arc from the
diametral pitch; table of arc and diametral pitches 3
=Gear-Wheels.= The driver and follower, a train of gears 3
Intermediate gears 3
The velocity of compounded wheels 4
Finding the diameters of the pitch circles of 4
Considered as revolving levers 5
Calculating the revolutions of, and power transmitted by 5
The angular velocity of 6
=Gear-Wheels.= Hunting tooth in, stop motion of 7
=Gear-Wheel Teeth.= The requirements and nature of the teeth
curves 7
Cycloidal curves for the faces of; epicycloidal and involute
curves; the hypocycloidal curve; method of forming or
generating the epicycloidal and hypocycloidal curves for the
faces and flanks of gear teeth 8
Applications of the epicycloidal and hypocycloidal curves in
the formation of gear teeth 9
The diameter of the circle for generating the epicycloidal and
hypocycloidal curves; graphical demonstration that the flank
curves are correctly formed to work with the face curves of the
other wheel 10
Graphical demonstration that the curves are correct independent
of either the respective sizes of the wheels, or of the curve
generating circles 11
=Gear-Wheels.= Hand applications of the rolling or
generating circle to mark the tooth curves for a pair of wheels 12
=Gear-Wheel Teeth.= The variation of curve due to different
diameters of wheels or of rolling circles 12
Tracing the path of contact of tooth upon tooth in a pair of
gear-wheels; definition of the "arc of approach;" definition of
the "arc of recess;" demonstration that the flanks of the teeth
on the driver or driving-wheel have contact with the faces of
the driven wheel during the arc of approach, and with the
flanks of the driven wheel during the arc of recess 13
Confining the action of the teeth to one side only of the line
of centres, when motion rather than power is to be conveyed 13
Demonstration that the appearance or symmetry of a tooth has no
significance with regard to its action 14
Finding how many teeth will be in constant action, the diameter
of the wheels, the pitch of the teeth, and the diameter of the
rolling circle being given 15
Example of the variation of tooth form due to variation of
wheel diameter 15
=Gear Teeth.= Variation of shape from using different
diameters of rolling circles 16
Thrust on the wheel shafts caused by different shapes of teeth 16
=Gear-Wheels.= Willis' system of one size of rolling circle for
trains of interchangeable gearing 16
Conditions necessary to obtain a uniform velocity of 16
=Gear Teeth.= The amount of rolling and of sliding motion of 16
The path of the point of contact of 16
The arcs of approaching and of receding contact 16
Lengths of the arcs of approach and of recess 16
The influence of the sizes of the wheels upon the arcs of
contact 17
Influence of the size of the rolling circle upon the amount of
flank contact 18
Demonstration that incorrectly formed teeth cannot correct
themselves by wear 18
The smaller the diameter of the rolling circle, the less the
sliding motion 18
Influence of the size of the rolling upon the number of teeth
in contact in a given pair of wheels 19
Demonstration that the degrees of angle the teeth move through
exceed those of the path of contact, unless the tooth faces
meet in a point 19
Influence of the height of the teeth upon the number of teeth
in contact 20
Increasing the arc of recess without increasing the arc of
approach 20
Wheels for transmitting motion rather than power 21
Clock wheels 21
Forms of teeth having generating or rolling circles, as large
or nearly as large as the diameters of the wheels 21
=Gear-Wheels.= Bevel 21
The principles governing the formation of the teeth of bevel-
wheels 22
Demonstration that the faces of the wheels must be in line with
the point of intersection of the axis of the two shafts 22
=Gear Teeth.= Method of finding the curves of, for bevel
gear 22
=Gear-Wheels.= Internal or annular 23 to 27
Demonstration that the teeth of annular wheels correspond to
the spaces of spur-wheels 23
=Gear-Wheels Internal.= Increase in the length of the path
of contact on spur-wheels of the same diameter, and having the
same diameter of generating or rolling circle 23
Demonstration that the teeth of internal wheels may interfere
when spur-wheels would not do so 23
Methods of avoiding the above interference 23
Comparison of, with spur-wheels 23
The teeth of: demonstration that it is practicable to so form
the teeth faces that they will have contact together as well as
with the flanks of the other wheel 24
Intermediate rolling circle for accomplishing the above result 24
The application of two rolling circles for accomplishing the
above result 24
Demonstration that the result reached by the employment of two
rolling circles of proper diameter is theoretically and
practically perfect 24
Limits of the diameters of the two rolling circles 25
Increase in the arc of contact obtained by using two rolling
circles 25
Demonstration that the above increase is on the arc of recess
or receding contact, and therefore gives a smooth action 25
Demonstration that by using two rolling circles each tooth has
for a certain period two points of contact 25
The laws governing the diameters of the two rolling circles 25
Practical application of two rolling circles 26
Demonstration that by using two rolling circles the pinion may
contain but one tooth less than the wheel 26
The sliding and rolling motion of the teeth of 27
CHAPTER II.
=THE TEETH OF GEAR-WHEELS (Continued).=
=Worm and Worm-Wheel=, or wheel and tangent screw 28 to 31
General description of 28
Qualifications of 28
The wear of 28
=Worm-Wheel Teeth=, the sliding motion of 28
When straight have contact on the centres only of the tooth
sides 28
That envelop a part of the worm circumference 28
The location of the pitch line of the worm 28
The proper number of teeth in the worm-wheel 29
Locating the pitch line of the worm so as to insure durability 29
Rule for finding the best location for the pitch line of the
worm 29
Increasing the face of the worm to obtain a smoother action 29
=Worms=, to work with a square thread 29
=Worm-Wheels=, applications of 30
=Gear-Wheels= with involute teeth 31 to 34
=Gear Teeth.= Generating the involute curve 31
Templates for marking the involute curve 32
=Involute Teeth=, the advantages of 34
=Gear Teeth=, Pratt and Whitney's machine for cutting
templates for 35
CHAPTER III.
=THE TEETH OF GEAR-WHEELS (Continued).=
=Gear Teeth=, revolving cutters for 37
Pantagraph engine for dressing the cutters for 38
Numbers of cutters used for a train of wheels 39
=Gear-Wheel Teeth.= Table of equidistant value of cutters 41
Depth of, in the Brown and Sharpe system 42
Cutting the teeth of worm-wheels 42
Finding the angle of the cutter for cutting worm-wheels 43
The construction of templates for rolling the tooth curves 43
Rolling the curves for gear teeth 43
Forms of templates for gear teeth 44
Pivoted arms for tooth templates 44
Marking the curves by hand 45
Former or Template of the Corliss bevel gear-wheel engine or
cutting machine 45
The use of extra circles in marking the curves with compasses 46
Finding the face curves by geometrical constructions 47
The Willis odontograph for finding the radius for striking the
curves by hand 47
The method of using the Willis odontograph 48
Professor Robinson's odontograph 49
Method of using Professor Robinson's odontograph 49
Application of Professor Robinson's odontograph for trains of
gearing 51
Tabular values and setting numbers for Professor Robinson's
odontograph 51
Walker's patent wheel scale for marking the curves of cast
teeth 51
The amount of side clearance in cast teeth 53
Filleting the roots of epicycloidal teeth with radial flanks 53
Scale of tooth proportions given by Professor Willis 54
The construction of a pattern for a spur-wheel that is to be
cast with the teeth on 54
Template for planing the tooth to shape 54
Method of marking the curves on teeth that are to be glued on 55
Method of getting out the teeth of 56
Spacing the teeth on the wheel rim 56
Methods of accurately spacing the pattern when it has an even
number of teeth 58
Method of spacing the wheel rim when it has an odd number of
teeth 58
=Gear-Wheels, Bevel Pinion=, drawings for 59
Getting out the body for a bevel-wheel 59
Template for marking the division lines on the face of the
wheel 59
Marking the lines of the division on the wheel 60
=Gear-Wheels, Pinion=, with dovetail teeth 60
Testing the angle of bevel-wheels while in the lathe 60
=Gear-Wheels, Skew Bevel.= Finding the line of contact 61
Marking the inclination of the teeth 61
=Gear-Wheels, Bevel=, drawing for built up 61
=Gear-Wheels, Worm=, or endless screw 62
Constructing a pattern from which the worm is to be cast 62
Tools for cutting the worm in a lathe 62
Cutting the teeth by hand 62
=Gear-Wheels, Mortise= or cogged 63
Methods of fastening cogs 63
Methods of getting out cogs for 63
=Gear-Wheel Teeth=, calculating the strength of epicycloidal 64
Factors of safety for 64
Tredgold's rule for calculating the strength of 65
Cut, calculating the strength of 65
=Gear-Wheel Teeth.= The strength of cogs 66
The thickness of cogs 66
The durability of cogs 66
Table for calculating the strength of different kinds of 67
The contact of cast teeth 67
Table for determining the relation between pitch diameter,
pitch, and number of teeth in gear-wheels 68
Examples of the use of the above table 68
With stepped teeth 69
Angular or helical teeth 69
End thrust of angular teeth 69
Herring-bone angular teeth 69
For transmitting motion at a right angle by means of angular or
helical teeth 69
Cutting helical teeth in the lathe 69
For wheels whose shaft axes are neither parallel nor meeting 70
Elliptical 70
Elliptical, marking the pitch lines of 70
Elliptical, drawing the teeth curves of 73
For variable motion 74
Form of worm to give a period of rest 74
Various applications of 74
=Gear-Wheels=, arrangement of, for periodically reversing
the direction of motion 75
Watt's sun and planet motion 75
Arrangements for the rapid multiplication of motion 75
Arrangement of, for the steering gear of steam fire-engines 75
Various forms of mangle gearing 79
=Gear-Wheel and Rack=, for reciprocating motion 77
=Friction Wheels.= 77
The material for 77
Paper 78
For the feed motion of machines 78
The unequal wear upon grooved 79
Form of, for relieving the journals of strain 79
=Cams=, for irregular motion 80
Finding the pitch line of 80
Finding the working face of 80
The effect the diameter roller has upon the motion produced by
a cam 80
Demonstration of the different motion produced by different
diameters of rollers upon the same cam 80
Diagram of motion produced from the same cam with different
diameters of rollers 81
Return or backing 82
Methods of finding the shape of return or backing 82
=Cam Motion=, for an engine slide valve without steam lap 83
For a slide valve with steam lap 83
=Groove Cams=, proper construction of 84
The wear of 84
Brady's improved groove cam with rolling motion and adjustment
for wear 84
CHAPTER IV.
=SCREW-THREADS.=
=Screw Threads=, the various forms of 85
The pitch of 85
Self-locking 85
The Whitworth 86
The United States standard 86
The Common V 86
The requirements of 86
Tools for cutting 87
Variation of pitch from hardening 87
The wear of thread-cutting tools 88
Methods of producing 88
Alteration of shape of, from the wear of the tools they are cut
by 89
=Screw Thread Cutting Tools.= The wear of the tap and the die 89
Improved form of chaser to equalize the wear 90
Form of, to eliminate the effects of the wear in altering the
fit 90
Originating standard angles for 91
Standard micrometer gauge for the United States standard screw
thread 91
Standard plug and collar gauges for 91
Producing gauges for 92
Table of United States standard for bolts and nuts 93
Table of standard for the V-thread 93
United States standard for gas and steam pipes 93
Taper for standard pipe threads 95
Tables of the pitches and diameters at root of thread, of the
Whitworth thread 95
Table of Whitworth's screw threads for gas, water, and
hydraulic piping 96
Whitworth's standard gauges for watch and instrument makers 96
Screw-cutting hand tools 96
=Thread-Cutting Tools.= American and English forms of stocks
and dies 97
Adjustable or jamb dies 98
The friction of jamb dies 98
The sizes of hobs that should be used on jamb dies 99
Cutting right or left-hand thread with either single, double,
or treble threads with the same dies 99
Hobs for hobbing or threading dies 100
Various forms of stocks with dies adjustable to take up the
wear 101
Dies for gas and steam pipes 101
=Thread-Cutting Tool Taps.= The general forms of taps 102
Reducing the friction of 102
Giving clearance to 102
The friction of taper 103
Improved forms of 103
Professor J. E. Sweet's form of tap 104
Adjustable standard 104
The various shapes of flutes employed on taps 105
The number of flutes a tap should have 105
Demonstration that a tap should have four cutting edges rather
than three 106
The position of the square or driving end, with relation to the
cutting edges 106
Taper taps for blacksmiths 106
Collapsing taps for use in tapping machines 107
Collapsing tap for use in a screw machine 107
The alteration of pitch that occurs in hardening 108
Gauging the pitch after the hardening 108
Correcting the errors of pitch caused by the hardening 109
For lead 109
Elliptical in cross section 109
For very straight holes 109
Tap wrenches solid and adjustable 110
=Thread-Cutting.= Tapping 110
Appliances for tapping standard work 111
CHAPTER V.
=FASTENING DEVICES.=
=Bolts=, classification of, from the shapes of their heads 112
Classification of, from the shapes of their bodies 112
Countersunk 112
Holes for, classification of 112
For foundations, various forms of 113
Hook bolts 113
The United States standard for finished bolts and nuts 113
The United States standard for rough bolts and nuts, or black
bolts 114
The Whitworth standard for bolts and nuts 114
=Screws= 114
=Studs= 115
=Set Screws= 115
=Bolts= for quick removal 116
That do not pass through the work 117
That self-lock in grooves and are readily removable 117
Heads and their bedding 117
=Nuts=, the forms of, when they are to be steam tight 118
Various forms of 118
Jamb nuts and lock nuts 119
=Differential Threads= for locking purposes 119
For fine adjustments 119
=Nuts=, taking up the wear of 120
Securing devices 120
Securing by taper pins 121
Securing by cotters 121
Securing by notched plates 121
=Pins.= Securing for exact adjustments 121
And double eyes fitting 121
Fixed 122
Working 122
=Bolts=, removing corroded 122
=Nuts=, removing corroded 122
=Washers=, standard sizes of 122
=Wrench=, the proper angles of 123
Box 124
Monkey 125
Adjustable, various forms of 125
Sockets 125
Novel for carriage bolts 125
Pin 126
Improved form of 126
=Keys=, the various kinds of 126
The bearing surfaces of 126
=Set Screws=, application of, to hubs or bosses 127
=Keys=, with set-screws 127
The draught of 127
=Feathers=, and their applications 127
=Keys=, for parallel rods 128
=Taper Pins=, proper position of, for locking purposes 128
Improved method of fitting 128
CHAPTER VI.
=THE LATHE.=
=Lathe=, the importance and advantages of 129
Classification of lathes 129
Foot 130
Methods of designating the sizes of 130
Bench 130
Power 130
Hand 130
Slide Rest for 131
American form of, their advantages and disadvantages 132
English forms of 132
For spherical work 132
Methods of taking up lost motion of 133
=Engine Lathe=, general construction of 133
The construction of the shears of 134
Construction of the headstock 134
Construction of the bearings 134
Construction of the back gear 135
Means of giving motion to the feed spindle 135
Construction of the tailstock 135
Method of rapidly securing and releasing the tailstock 136
=Lathe Tailstock=, setting over for turning tapers 136
=Engine Lathe=, construction of carriage 137
Feed motion for carriage or saddle 137
=Lathe Apron=, Construction of the feed traverse 138
Construction of the cross-feed motion 138
=Engine Lathe=, lead screw and change wheels of 139
Feed spindle and lead screw bearings 139
Swing frame for lead screw 139
Lead screw nuts 140
With compound slide rest 140
Construction of compound slide rest 141
Advantages of compound slide rest 141
For taper turning 142
Taper-turning attachments 142
With compound duplex slide rest 143
Detachable slide rest 143
Three-tool slide rest for turning shafting 143
With flat saddle for chucking work on 143
=The Sellers Lathe= 143
Construction of the headstock and treble gear 144
Construction of the tailstock and method of keeping it in line 145
Construction of the carriage and slide rest 145
Methods of engaging and disengaging the feed motions 146
=Car Axle Lathe=, with central driving motion and two slide
rests 147
The feed motions of 148
=Self-Acting Lathe=, English form of 148
=Pattern Maker's Lathe= 148
Brake for cone pulley 149
With wooden bed 149
Slide rest for 149
=Chucking Lathe=, English 149
Feed motions of 150
=Pulley Lathe= 150
=Gap or Break Lathe= 151
=Extension Lathe= 151
=Wheel Lathe= 151
=Chucking Lathe= for boring purposes 152
=Lathe= for turning crank axles 152
Construction of the headstock 153
Construction of the feed motions 154
For turning crank, Arrangements of the slide rests 154
Application of the slide rest to a crank 155
CHAPTER VII.
=DETAILS IN LATHE CONSTRUCTION.=
=Live Spindle= of a lathe, the fit of 157
With coned journals 157
Methods of taking up the end motion of 158
Arranging the swing frame for the change gears 158
Taking up the wear of the back bearing 158
The wear of the front bearing of 158
=The Taper= for the live centre 159
=Methods= of removing the lathe centres 159
=Tapers= for the live centres 159
=Methods= of removing the dead centre 159
=Driving Cone=, arranging the steps of 159
Requirements of proportioning the steps of 159
Rules for proportioning the diameters of the steps of, when the
two pulleys are exactly alike and are connected by an open
belt 159 to 161
When the two pulleys are unlike 161 to 164
=Back Gear=, methods of throwing in and out 165
=Conveying= motion to the lead screw 165
=Attaching= the swing frame 166
=Feed Gear.= Arrangement for cutting worm threads or tangent
screws 167
=Feed Motion= for reversing the direction of tool traverse
in screw cutting 168
For lathe aprons 168
=Slide Rest=, weighted elevated 168
Double tool holder for 169
Gibbed elevating 169
=Examples= of feed motions 170
=Feed Regulators= for screw cutting 171
The star feed 172
=Ratchet Feeds= 173
=Tool Holding= devices, the various kinds of 173
=Tool Rest= swiveling 174
=Tool Holder= for compound slide rests 174
For octagon boring tools 175
=Lathe Lead and Feed Screws= 175
Lead screws, supporting, long 176
Position of the feed nut 177
Form of threads of lead screws 177
The effect the form of thread has in causing the nut to lock
properly or improperly 177
Example of a lead screw with a pitch of three threads per inch 177
Example of a lead screw with five threads per inch 178
Example with a lead screw of five threads per inch 179
Device for correcting the errors of pitch of 179
=Table= for finding the change wheels for screw cutting when
the teeth in the change wheels advance by four 180
For finding the change wheels when the teeth in the wheels
advance by six 180
Constructing a table to cut fractional threads on any lathe 181
Finding the change wheels necessary to enable the lathe to cut
threads of any given pitches 181
Finding the change wheels necessary to cut fractional pitches 181
=Determining= the pitches of the teeth for change wheels 182
=Lathe Shears= or beds 182
Advantages and disadvantages of, with raised V-guide-ways 182
Examples of various forms of 183
=Lathe Shears= with one V and one flat side 183
Methods of ribbing 184
The arrangement of the legs of 184
=Lathe Tailblock= 185
With rapid spindle motion 185
With rapid fastenings and releasing devices 185
The wear of the spindles of 185
Spindles, the various methods of locking 186
Testing, various methods of 187
CHAPTER VIII.
=SPECIAL FORMS OF THE LATHE.=
=Watchmaker's Lathes= 188
Construction of the headstock 188
Construction of chucks for 188
Expanding chucks for 188
Contracting chucks for 188
Construction of the tailblock 189
Open spindle tailstocks for 189
Filing fixture for 189
Fixture for wheel and pinion cutting 189
Jewelers' rest for 189
=Watch Manufacturers' Lathe= 190
Special chucks for 190
Pump centre rest 190
=Lathe=, hand 191
Screw slotting 192
With variable speed for facing purposes 192
Cutting-off machine 193
Grinding Lathes 193
With elevating rest 194
Universal 195
Special chucks for 196
The Morton Poole calender roll grinding lathe 196
The construction of the bed and carriages 197
Principles of action of the carriages 197, 198
Construction of the emery-wheel arbors and the driving
motion 198, 199
The advantages of 199
The method of driving the roll 200
Construction of the headstock 200
The transverse motion 200
=The Brown and Sharpe Screw Machine=, or screw-making lathe 200
Threading tools for 203
Examples of the use of 203
=The Secor Screw Machine=, construction of the headstock 204
The chuck 205
The feed gear 205
The turret 205
The cross slide 205
The stop motions 206
=Pratt and Whitney's Screw Machine= 206
Parkhurst's wire feed, construction of the headstock, chuck and
feed motion 207
Box tools for 208
Applications of box tools 208
Threading tool for 208
Cutting-off tool for 208
=Special Lathe= for wood working 208
The construction of the carriage and reducing knife 209
Construction of the various feed motions 209
Construction of the tailstock 209
=Lathes for irregular forms= 210
Axe-handle 210
Back knife gauge 210
Special, for pulley turning 211
=Boring and Turning= mill or lathe 211
Construction of the feed motions 213
Construction of the framing and means of grinding the lathe 214
Construction of the vertical feed motions 215
=The Morton Poole= roll turning lathe 215
Construction of the slide rest 216
The tools for 216
=Special Lathes= for brass work 216, 217
=Boring Lathe= with traversing spindle 218
For engine cylinders 219
Cylinder, with facing slide rests 219
With double heads and facing rests 220
=Lathe for turning Wheel= hubs 221
CHAPTER IX.
=DRIVING WORK IN THE LATHE.=
=Drivers=, carriers, dogs, or clamps, and their defects 222
Lathe clamps 222
Equalizing drivers 223
The Clements driver 223
Driver and face plate for screw cutting 223
Forms of, for bolt heads 224
Adjustable, for bolt heads 224
For threaded work 225
For steady rest work 225
For cored work 225
For wood 225
=Centres= for hollow work 226
For taper work 226
=Lathe Mandrels=, or arbors 227
Drivers for 227
For tubular work 227
Expanding mandrels 227
With expanding cones 228
With expanding pieces 228
Expanding, for large work 228
For threaded work 228
For nuts, various forms of 229
For eccentric work 229
=Centring devices= for crank axles 230
=The Steady Rest= or back rest 231
Steady rest, improved form of 232
Cone chuck 232
Steady rest for square and taper work 233
The cat head 233
Clamps for 233
Follower rests 234
=Chucks and Chucking= 234
Simple forms of chucks 234
Adjustable chucks for true work 235
Two-jawed chucks 236
Box body chucks 237
Reversible jawed chucks 237
Three and four-jawed chucks 237
Combination chucks 237
The wear of scroll chuck threads 237
Universal chucks 238
The wear of chucks 240
Special forms of chucks 241
Expanding chucks for ring-work 241
Cement chuck 241
Chucks for wood-working lathes 242
=Lathe Face Plates= 243
Face plates, errors in, and their effects 243
Work-holding straps 244
Face plate, clamping work on 245
Forms of clamps for 245
Examples of chucking work on 246, 247
For wood work 247
=Special Lathe Chuck= for cranks 248
=Face Plate Work=, examples of 249
Errors in chucking 250
Movable dogs for 250
The angle plate 251
Applications of 251
Angle plate chucking, examples of 251
Cross-head chucking 251-253
CHAPTER X.
=CUTTING TOOLS FOR LATHES.=
=Principles= governing the shapes of lathe tools 254
=Diamond-pointed=, or front tool 254
=Principles= governing use of tools 254
Front rake and clearance of front tools 254
Influence of the height of a tool upon its clearance and
keenness 255
Tools with side rake in various directions 256
The effect of side rake 256
The angle of clearance in lathe tools 257
Variation of clearance from different rates of feed and
diameters of work 257
=Round-nosed= tools 258
=Utmost Duty= of cutting tools 258
Judging the quantity of the tool from the shape of its cutting 259
=Square-nosed= tools 260
The height of lathe tools 260
Side tools for lathe work 261
Cutting-off or grooving tools 262
Facing tools or knife tools 262
Spring tools 263
=Brass Work=, front tools for 264
Side tools for 264
=Threading= tools 264
Internal threading tools 264
The length of threading tools 265
The level of threading tools 265
Gauges for threading tools 266
Setting threading tools 266
Circular threading tools 267
Threading tool holders 267
=Chasers= 268
Chaser holders 268
Setting chasers 268
=Square Threads=, clearance of tools for 269
Diameter at the roots of threads 269
Cutting coarse pitch square threads 269
Dies for finishing square threads 269
=Tool Holders= for outside work 270
For circular cutters 272
Swiveled 273
Combined tool holders and cutting-off tools 273
=Power Required= to drive cutting tools 273
CHAPTER XI.
=DRILLING AND BORING IN THE LATHE.=
=The Twist Drill= 274
Twist drill holders 274
The diametral clearance of twist drills 274
The front rake of twist drills 275
The variable clearance on twist drills as usually ground 275
Demonstration of the common error in grinding twist drills 276
The effects of improper grinding upon twist drills 276
Table of speeds and feeds for twist drills 277
Grinding twist drills by hand 279
Twist drills for wood work 279
=Tailstock Chucks= for drilled work 279
=Flat Drills= for lathe work 280
Holders for lathe work 281
=Half-round= bit or pod auger 281
With front rake for wrought iron or steel 281
With adjustable cutter 281
For very true work 281
=Chucking Reamer= 281
The number of teeth for reamers 282
Spacing the teeth of reamers 282
Spiral teeth for reamers 282
Grinding the teeth of reamers 282
Various positions of emery-wheel in grinding reamers 282
Chucking reamers for true work 283
Shell reamers 283
Arbor for shell reamers 283
Rose-bit or rose reamers 283
Shell rose reamers 284
Adjustable reamers 284
Stepped reamers for taper work 285
Half-round reamers 285
Reamers for rifle barrels 285
=Boring Tools= for lathe work 285
Countersinks 285
Shapes of lathe boring tools 285
Boring tools for brass work 286
The spring of boring tools 286
Boring tools for small work 287
Boring tool holders 287
=Boring Devices for Lathes= 288
=Boring Heads= 288
=Boring Bars= 289
Boring bar cutters 289
Three _versus_ four cutters for boring bars 290
Boring bars with fixed heads 290
With sliding heads 290
Bar cutters, the shapes of 291
Boring head with nut feed 291
Boring bars for taper work, various forms of 292
Boring double-coned work 293
Boring bar, centres for 293
=Cutting Speeds= and feeds for wrought iron 294
Examples of speeds taken from practice 295
CHAPTER XII.
=EXAMPLES IN LATHE WORK.=
=Technical Terms= used in the work 296
=Lathe Centres= 296
Devices for truing 297
Tools for testing the truth of, for fine work 298
Shapes of, for light and heavy work 299
=Centre Drilling=, attachment for lathes 300
The error induced by straightening work after 300
Machine 300
Combined centre-drill and countersink 300
Countersink with adjustable drill 300
Centring square 300
Centre-punch 300
Centre-punch guide 301
Centring work with the scribing block 301
Finding the centre of very rough work 301
Centre-drill chuck 302
The proper form of countersink for lathe work 302
Countersinks for lathe work 302
Various forms of square centres 303
The advantage of the square centre for countersinking 303
Novel form of countersink for hardened work 303
Chucks for centre-drilling and countersinking 303
Recentring turned work 304
=Straightening Work.= Straightening machine for bar iron 304
Hand device for straightening lathe work 305
Chuck for straightening wire 305
=Cutting Rods= into small pieces of exact length, tools for 305
=Roughing cuts=, the change of shape of work that occurs
from removing the surface by 306
Feeds for 306
Rates of feed for 307
=Finishing Work=, the position of the tool for 307
Finishing cast-iron with water 307
Specks in finished cast-iron work 307
Scrapers for finishing cast-iron work 307
Method of polishing lathe work 308
Filing lathe work 308
The use of emery paper on lathe work 308
The direction of tool feed in finishing long work 309
Forms of laps for finishing gauges or other cylindrical lathe
work 310
Forms of laps for finishing internal work 311
Grinding and polishing clamps for lathe work 311
Burnishing lathe work 311
=Taper Work=, turning 312
The wear of the centres of 312
Setting over the tailstock to turn 312
Gauge for setting over 313
Fitting 313
Grinding 313
The order of procedure in turning 313
The influence of the height of the tool in producing true 314
=Special Forms.= Curved work 314, 315
Standard gauges for taper work 316
Methods of turning an eccentric 317
Turning a cylinder cover 318
Turning pulleys 318
Chucking device for pulleys 318
=Cutting Screws= in the lathe 319
The arrangement of the change gears 319
The intermediate wheels 319
The compounded gears 320
Finding the change wheels to cut a given thread 320
Finding the change wheels for a lathe whose gears are
compounded 321
Finding the change gears for cutting fractional pitches 321
To find what pitch of thread the wheels already on the lathe
will cut 322
Cutting left-hand threads 322
Cutting double threads 322
Cutting screws whose pitches are given in the terms of the
metric system 322
Cutting threads on taper work 323
Errors in cutting threads on taper work 324
CHAPTER XIII.
=EXAMPLES IN LATHE WORK (Continued).=
=Ball Turning= with tubular saw 325
With a single tooth on the end of a revolving tube 325
With a removable tool on an arbor 325
Tool holder with worm feed 325
By hand 325
=Cams=, cutting in the lathe 326
Improved method of originating cams in the lathe 326
Motions for turning cams in the lathe 326, 327
Application of cam motions to special work 327
Cam chuck for irregular work 328
=Milling= or knurling tool 328
Improved forms of 328
=Winding Spiral Springs= in the lathe 329
=Hand Turning= 330
The heel tool 330
The graver and its applications 330, 331
Hand side tools 331
Hand round-nosed tools for iron 331
Hand finishing tool 331
=Hand Tools=, for roughing out brass work 332
Various forms and applications of scrapers 332, 333
Clockmakers' hand tool for special or standard work 334
Screw cutting with hand tools 334
Outside and inside chasers 334
Hobs and their uses 335
The application of chasers, and errors that may arise from
the position in which they are presented to the work 336
Errors commonly made in cutting up inside chasers 337
V-tool for starting outside threads 337
Starting outside threads 338
Cutting taper threads 338
Wood turning hand tools 338
The gauge and how to use it 338
The chisel and its use 339
The skew chisel and how to use it 339
Wood turners' boring tools for lathe work 340
CHAPTER XIV.
=MEASURING MACHINES, TOOLS AND DEVICES.=
=Standards of Measurements=, in various countries 341
Use of, by sight and by the sense of feeling 341
Variations in standard gauges 341
The necessity for accurate standards 341
The Rogers Bond standard measuring machine 342
Details of construction of 343, 344
The principle of construction of 344
The methods of using 345
The Whitworth measuring machine 345
The Betts Machine Company's measuring machine 346
Professor Sweet's measuring machine 347
Measuring machine for sheet metal 348
=Circle=, division of the 348
Troughton's method of dividing the circle 348, 349
Ramsden's dividing engine 349
The construction of 350, 351
Pratt and Whitney's dividing device 352
Practical application of 353
Index wheel, method of originating, by R. Hoe & Co. 353
Application of the index wheel (Hoe & Co.'s system) 353
=Classification= of the measuring tools used by workmen 354
=Micrometer Caliper= and its principle of construction 354, 355
=Gauges.= Standard plug and collar gauges 356
Methods of comparing standard plug and collar gauges 356
The effects of variations of temperature upon standard gauges 356
Plug and collar gauges for taper work 357
The Baldwin standards for taper bolts 359
Workmen's gauges for lathe work 359
=Calipers=, outside, the various forms of 360
Inside calipers 360
Calipers with locking devices 360
Spring calipers 360
The methods of holding and using 361, 362
Keyway calipers 363
The advantages of calipers 363
=Fitting.= The four kinds of fit in machine work 363
The influence of the diameter of the work in limiting the
application of standard gauges 363
The wear of tools and its influence upon the application of the
standard gauge system 364
The influence of the smoothness of the surface upon the
allowance to be made for drilling or hydraulic fits 365
Examples of allowance for hydraulic fits 365
Parallel holes and taper plugs for hydraulic fits 365
=Fitting.= Practicable methods of testing the fit of axle
brasses forced in by hydraulic pressure 366
Shrinkage or contraction fits 366
Allowances for 366
Gauge for 367
The shrinkage system at the Royal Gun Factory at Woolwich 367
Experiments by Thomas Wrightson upon the shrinkage of iron
under repeated heatings and coolings 368 to 374
Shrinking work, to refit it 374, 375
CHAPTER XV.
=MEASURING TOOLS.=
=End Measurements= of large lathe work 376
Template gauges for 376
Trammels or Trains 377
Adjustable gauges for 377
=Compasses=--Dividers 377
Compass calipers 378
=Key Seating= rule 378
=Surface Gauge= 378
Pattern makers' pipe gauge 379
=Squares.= The try square 379
The T square 379
Various methods of testing squares 379, 380
Bevel squares 380
=Bevel Protractors= 380
=Hexagon Gauge= 381
=Straight Edge= and its applications 381, 382
Winding strips and their application 382
=Surface Plate= or planimeter 383
=Templates= for curves 384
=Wire Gauges=, notch 384
Standard gauges for wire, &c. 384, 386
Gauge for music wire 386
Brown and Sharpe wire gauge 387
Birmingham wire gauge for rolled shell silver and gold 387
Sheet iron gauge, Russian 387
Galvanized iron 387
Belgian sheet zinc 387
American sheet zinc 387
=Rifle Bore= gauge 387
=Strength of Wire=, Kirkaldy's experiments 387, 388
CHAPTER XVI.
=SHAPING AND PLANING MACHINES.=
=General description= of a shaping machine 389
=Construction= of swivel head 389
Slide 390
Vice chuck 390
Feed motion 390
=Hand= shaping machine 392
=Quick Return Motion=, Whitworth's 392
=Vice Chucks=, the principles of construction of plain, for
planing machine 392
The proper methods of chucking work in 393
Holding taper work in 394
Various forms of 394
Swiveling 395
Rapid motion 396
For vice work 396
=Centres= for shaping machines 397
=Traveling Head= in shaping machine 397
=Planer Shapers= or shaping machines, having a tappet motion
for reversing the direction of motion 398, 399
=Quick Return Motion= shaping machines, link 399
The Whitworth 400
Comparisons of the link motion and Whitworth 401
=Simple Crank=, investigating the motion of 401
=Planing Machines=, or planer 402
The various motions of 402, 403
The table driving gear 404
Planing machine with double heads 404
Rotary planing machine 405
CHAPTER XVII.
=PLANING MACHINERY.=
=The Sellers= planing machine 406
The belt shifting mechanism 406, 407
The automatic feed motions 408
=Sliding Head= 408
=Cross Bar= 409
=Slides of Planers=, the various forms of construction of 410
=Wear of the Slides= of planer heads, various methods of
taking up the 410
=Swivel Heads= 411
=Tool Aprons= 411
=Swivel Tool-holding devices= for planers 411
=Planer Heads=, graduations of 412
Safety devices for 413
Feed motions for 414
V-guideways for 414
Flat guideways for 415
Oiling devices for 415
=Planing Machine Tables= 415
Slots and holes in planing machine tables 416
Forms of bolts for planer tables 417
Supplementary tables for planer tables 417
Angle plates for planer tables 418
Chucking devices for planer tables 418
=Planer Centres= 418
=Planer Chucks= 419
For spiral grooved work 419
For curved work 420
Chucking machine beds on planer tables 420
For large planing machines 422
Chucking the halves of large pulleys on a planer 423
=Gauges= for planing V-guideways in machine beds 421
Planing guideways in machine beds 422
Gauge for planer tools 424
=Planer Tools=, the shapes of 424
For coarse finishing feeds 424
The clearance of 424
For slotted work 424
=Planer Tool Holder=, with tool post 425
Various applications of 425
Simple and advantageous form of 426
Examples of application of 426
CHAPTER XVIII.
=DRILLING MACHINES.=
=Drilling Machines.= General description of a power drilling
machine 428
Lever feed 428
With automatic and quick return feed motions 428
Improved, with simple belt and uniform motion, two series of
rates of automatic feed, and guide for boring bar 429, 430
Radial 430, 431
For boiler shells 436
Cotter or keyway 438
Drilling Machine, three-spindle 434
Four-spindle 434
=Drilling and Boring= machine 431
Feed motion of 432
=Combined Drilling Machine= and lathe 433
=Boring Machine=, horizontal 433
For car wheels 438
For pulleys 438
=Quartering Machine= 434
=Drilling and Turning Machine= for boiler makers 435
Feed motions of 436
CHAPTER XIX.
=DRILLS AND CUTTERS FOR DRILLING MACHINES.=
=Jigs or Fixtures= for drilling machines 439
Limits of error in 439
Examples of, for simple work, as for links, &c. 440
Considerations in designing 440
For drilling engine cylinders 440 to 441
For cutting out steam ports 441
=Drills and Cutters= for drilling machines 442
Table of sizes of twist drills, and their shanks 442
Flat drills for drilling machines 442
Errors in grinding flat drills 443
The tit-drill 443
The lip drill 443
Cotter or keyway drills 446
=Drilling holes= true to location with flat drills 444
Drilling hard metal 444
Table of sizes of tapping holes 445
=Drill Shanks= and sockets 445
Improved form of drill shank 446
Square shanked drills and their disadvantages 446
=Drill Chucks= 446
=Stocks and Cutters= for drilling machines 447
Tube plate cutters 448
=Stocks and Cutters.= Adjustable stock and cutter 448
Facing tool with reamer pin 449
Counterbores for drilling machines 449
Drill and counterbore for wood work 449
Facing and countersink cutters 449
Device for drilling square holes 450
Device for drilling taper holes in a drilling machine 451
CHAPTER XX.
=HAND-DRILLING AND BORING TOOLS, AND DEVICES.=
=The Brad-awl= 452
=Bits.= The gimlet bit 452
The German bit 452
The nail bit 452
The spoon bit 452
The nose bit 453
The auger bit 453
Cook's auger bit 453
Principles governing the shapes of the cutting edges of auger
bits 453
Auger bit for boring end grain wood 453
The centre bit 454
The expanding bit 454
=Drills.= Drill for stone 454
The fiddle drill 455
The fiddle drill with feeding device 455
Drill with cord and spring motion 455
Drill stock with spiral grooves 455
Drill brace 455
Drill brace with ratchet motion 456
Universal joint for drill brace 456
Drill brace with multiplying gear and ratchet motion 456
Breast drill with double gear 456
Drilling levers for blacksmiths 457
Drill cranks 457
Ratchet brace 457
Flexible shaft for driving drills 458
Drilling device for lock work 459
Hand drilling machine 459
=Slotting Machine= 459
Sectional view of 460
Tool holders 460, 461
Tools 461, 462
CHAPTER XXI.
=THREAD-CUTTING MACHINERY AND BROACHING PRESS.=
=Pipe Threading=, die stock for, by hand 463
Die stock for, by power 463
Pipe threading machines, general construction of 463
=Bolt Threading= hand machine 464
With revolving head 465
Power threading machine 465
With automatic stop motion 466
Construction of the head 466
Construction of the chasers 466
Bolt threading machine with back gear 467
Single rapid bolt threading machine 467
Double rapid bolt threading machine 467
Construction of the heads of the rapid machines 468
Bolt threading machinery, the Acme 468
Construction of the head of 468 to 470
Capacity of 470
=Cutting Edges= for taps, the number of 471
Examples when three and when four cutting edges are used, and
the results upon bolts that are not round 471, 472
Demonstration that four cutting edges are correct for bar iron 472
=Positions of Dies=, or chasers in the heads of bolt cutting
machine 473
=Dies=, methods of hobbing, to avoid undue friction 473
The construction of, for bolt threading machines 473
Method of avoiding friction in thread cutting 474
Hob for threading 474
Cutting speeds for threading 474
=Nut Tapping= machine 475
Automatic socket for 475
Rotary 475
Three-spindle 475
=Pipe Threading Machine= 475 to 477
=Tapping Machine= for steam pipe fittings 478
=Broaching Press= 478
Principles of broaching 478
Examples in the construction of broaches 479
FULL-PAGE PLATES.
Volume I.
_Facing_
_Frontispiece._ MODERN LOCOMOTIVE ENGINE. TITLE PAGE
PLATE I. TEMPLATE-CUTTING MACHINES FOR GEAR TEETH. 34
" II. FORMS OF SCREW THREADS. 85
" III. MEASURING AND GAUGING SCREW THREADS. 93
" IV. END-ADJUSTMENT AND LOCKING DEVICES. 120
" V. EXAMPLES IN LATHE CONSTRUCTION. 148
" VI. CHUCKING LATHES. 150
" VII. TOOL-HOLDING AND ADJUSTING APPLIANCES. 174
" VIII. WATCHMAKER'S LATHE. 188
" IX. DETAILS OF WATCHMAKER'S LATHE. 188
" X. EXAMPLES OF SCREW MACHINES. 200
" XI. ROLL-TURNING LATHE. 215
" XII. EXAMPLES IN ANGLE-PLATE CHUCKING. 252
" XIII. METHODS OF BALL-TURNING. 325
" XIV. STANDARD MEASURING MACHINES. 341
" XV. DIVIDING ENGINE AND MICROMETER. 354
" XVI. SHAPING MACHINES AND TABLE-SWIVELING DEVICES. 398
" XVII. EXAMPLES OF PLANING MACHINES. 404
" XVIII. EXAMPLES IN PLANING WORK. 422
" XIX. LIGHT DRILLING MACHINES. 428
" XX. HEAVY DRILLING MACHINES. 430
" XXI. EXAMPLES IN BORING MACHINERY. 434
" XXII. BOILER-DRILLING MACHINERY. 436
" XXIII. NUT-TAPPING MACHINERY. 475
MODERN
MACHINE SHOP PRACTICE.
CHAPTER I.--THE TEETH OF GEAR-WHEELS.
A wheel that is provided with teeth to mesh, engage, or gear with
similar teeth upon another wheel, so that the motion of one may be
imparted to the other, is called, in general terms, a gear-wheel.
[Illustration: Fig. 1.]
When the teeth are arranged to be parallel to the wheel-axis, as in Fig.
1, the wheel is termed a spur-wheel. In the figure, A represents the
axial line or axis of the wheel or of its shaft, to which the teeth are
parallel while spaced equidistant around the rim, or face, as it is
termed, of the wheel.
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
When the wheel has its teeth arranged at an angle to the shaft, as in
Fig. 2, it is termed a bevel-wheel, or bevel gear; but when this angle
is one of 45°, as in Fig. 3, as it must be if the pair of wheels are of
the same diameter, so as to make the revolutions of their shafts equal,
then the wheel is called a mitre-wheel. When the teeth are arranged upon
the radial or side face of the wheel, as in Fig. 4, it is termed a
crown-wheel. The smallest wheel of a pair, or of a train or set of
gear-wheels, is termed the pinion; and when the teeth are composed of
rungs, as in Fig. 5, it is termed a lantern, trundle, or wallower; and
each cylindrical piece serving as a tooth is termed a _stave_,
_spindle_, or _round_, and by some a _leaf_.
[Illustration: Fig. 4.]
An annular or internal gear-wheel is one in which the faces of the teeth
are within and the flanks without, or outside the pitch-circle, as in
Fig. 6; hence the pinion P operates within the wheel.
[Illustration: Fig. 5.]
[Illustration: Fig. 6.]
When the teeth of a wheel are inserted in mortises or slots provided in
the wheel-rim, it is termed a mortised-wheel, or a cogged-wheel, and the
teeth are termed cogs.
When the teeth are arranged along a plane surface or straight line, as
in Fig. 7, the toothed plane is termed a _rack_, and the wheel is termed
a pinion.
A wheel that is driven by a revolving screw, or worm as it is termed, is
called a worm-wheel, the arrangement of a worm and worm-wheel being
shown in Fig. 8. The screw or worm is sometimes also called an endless
screw, because its action upon the wheel does not come to an end as it
does when it is revolved in one continuous direction and actuates a nut.
So also, since the worm is tangent to the wheel, the arrangement is
sometimes called a wheel and tangent screw.
The diameter of a gear-wheel is always taken at the pitch circle, unless
otherwise specially stated as "diameter over all," "diameter of
addendum," or "diameter at root of teeth," &c., &c.
[Illustration: Fig. 7.]
When the teeth of wheels engage to the proper distance, which is when
the pitch circles meet, they are said to be in gear, or geared together.
It is obvious that if two wheels are to be geared together their teeth
must be the same distance apart, or the same _pitch_, as it is called.
The designations of the various parts or surfaces of a tooth of a
gear-wheel are represented in Fig. 9, in which the surface A is the face
of the tooth, while the dimension F is the width of face of the wheel,
when its size is referred to. B is the flank or distance from the pitch
line to the root of the tooth, and C the point. H is the _space_, or
the distance from the side of one tooth to the nearest side of the next
tooth, the width of space being measured on the pitch circle P P. E is
the depth of the tooth, and G its thickness, the latter also being
measured on the pitch circle P P. When spoken of with reference to a
tooth, P P is called the pitch line, but when the whole wheel is
referred to it becomes the pitch circle.
[Illustration: Fig. 8.]
The points C and the surface H are true to the wheel axis.
The teeth are designated for measurement by the pitch; the height or
depth above and below pitch line; and the thickness.
The pitch, however, may be measured in two ways, to wit, around the
pitch circle A, in Fig. 10, which is called the arc or circular pitch,
and across B, which is termed the chord pitch.
[Illustration: Fig. 9.]
In proportion as the diameter of a wheel (having a given pitch) is
increased, or as the pitch of the teeth is made finer (on a wheel of a
given diameter) the arc and chord pitches more nearly coincide in
length. In the practical operations of marking out the teeth, however,
the arc pitch is not necessarily referred to, for if the diameter of the
pitch circle be made correct for the required number of teeth having the
necessary arc pitch, and the wheel be accurately divided off into the
requisite number of divisions with compasses set to the chord pitch, or
by means of an index plate, then the arc pitch must necessarily be
correct, although not referred to, save in determining the diameter of
the wheel at the pitch circle.
The difference between the width of a space and the thickness of the
tooth (both being measured on the pitch circle or pitch line) is termed
the clearance or side clearance, which is necessary to prevent the teeth
of one wheel from becoming locked in the spaces of the other. The amount
of clearance is, when the teeth are cut to shape in a machine, made just
sufficient to prevent contact on one side of the teeth when they are in
proper gear (the pitch circles meeting in the line of centres). But when
the teeth are cast upon the wheel the clearance is increased to allow
for the slight inequalities of tooth shape that is incidental to casting
them. The amount of clearance given is varied to suit the method
employed to mould the wheels, as will be explained hereafter.
The line of centres is an imaginary line from the centre or axis of one
wheel to the axis of the other when the two are in gear; hence each
tooth is most deeply engaged, in the space of the other wheel, when it
is on the line of centres.
There are three methods of designating the sizes of gear-wheels. First,
by their diameters at the pitch circle or pitch diameter and the number
of teeth they contain; second, by the number of teeth in the wheel and
the pitch of the teeth; and third, by a system known as diametral pitch.
[Illustration: Fig. 10.]
The first is objectionable because it involves a calculation to find the
pitch of the teeth; furthermore, if this calculation be made by dividing
the circumference of the pitch circle by the number of teeth in the
wheel, the result gives the arc pitch, which cannot be measured
correctly by a lineal measuring rule, especially if the wheel be a small
one having but few teeth, or of coarse pitch, as, in that case, the arc
pitch very sensibly differs from the chord pitch, and a second
calculation may become necessary to find the chord pitch from the arc
pitch.
The second method (the number and pitch of the teeth) possesses the
disadvantage that it is necessary to state whether the pitch is the arc
or the chord pitch.
If the arc pitch is given it is difficult to measure as before, while if
the chord pitch is given it possesses the disadvantage that the
diameters of the wheels will not be exactly proportional to the numbers
of teeth in the respective wheels. For instance, a wheel with 20 teeth
of 2 inch chord pitch is not exactly half the diameter of one of 40
teeth and 2 inch chord pitch.
To find the chord pitch of a wheel take 180 (= half the degrees in a
circle) and divide it by the number of teeth in the wheel. In a table of
natural sines find the sine for the number so found, which multiply by
2, and then by the radius of the wheel in inches.
Example.--What is the chord pitch of a wheel having 12 teeth and a
diameter (at pitch circle) of 8 inches? Here 180 ÷ 12 = 15; (sine of 15
is .25881). Then .25881 × 2 = .51762 × 4 (= radius of wheel) = 2.07048
inches = chord pitch.
TABLE OF NATURAL SINES.
+--------+--------++--------+--------++--------+--------+
|Degrees.| Sine. ||Degrees.| Sine. ||Degrees.| Sine. |
+--------+--------++--------+--------++--------+--------+
| 1 | .01745 || 16 | .27563 || 31 | .51503 |
| 2 | .03489 || 17 | .29237 || 32 | .52991 |
| 3 | .05233 || 18 | .30901 || 33 | .54463 |
| 4 | .06975 || 19 | .32556 || 34 | .55919 |
| 5 | .08715 || 20 | .34202 || 35 | .57357 |
| 6 | .10452 || 21 | .35836 || 36 | .58778 |
| 7 | .12186 || 22 | .37460 || 37 | .60181 |
| 8 | .13917 || 23 | .39073 || 38 | .61566 |
| 9 | .15643 || 24 | .40673 || 39 | .62932 |
| 10 | .17364 || 25 | .42261 || 40 | .64278 |
| 11 | .19080 || 26 | .43837 || 41 | .65605 |
| 12 | .20791 || 27 | .45399 || 42 | .66913 |
| 13 | .22495 || 28 | .46947 || 43 | .68199 |
| 14 | .24192 || 29 | .48480 || 44 | .69465 |
| 15 | .25881 || 30 | .50000 || 45 | .70710 |
+--------+--------++--------+--------++--------+--------+
The principle upon which diametral pitch is based is as follows:--
The diameter of the wheel at the pitch circle is supposed to be divided
into as many equal parts or divisions as there are teeth in the wheel,
and the length of one of these parts is the diametral pitch. The
relationship which the diametral bears to the arc pitch is the same as
the diameter to the circumference, hence a diametral pitch which
measures 1 inch will accord with an arc pitch of 3.1416; and it becomes
evident that, for all arc pitches of less than 3.1416 inches, the
corresponding diametral pitch must be expressed in fractions of an inch,
as 1/2, 1/3, 1/4, and so on, increasing the denominator until the
fraction becomes so small that an arc with which it accords is too fine
to be of practical service. The numerators of these fractions being 1,
in each case, they are in practice discarded, the denominators only
being used, so that, instead of saying diametral pitches of 1/2, 1/3, or
1/4, we say diametral pitches of 2, 3, or 4, meaning that there are 2,
3, or 4 teeth on the wheel for every inch in the diameter of the pitch
circle.
Suppose now we are given a diametral pitch of 2. To obtain the
corresponding arc pitch we divide 3.1416 (the relation of the
circumference to the diameter) by 2 (the diametral pitch), and 3.1416 ÷
2 = 1.57 = the arc pitch in inches and decimal parts of an inch. The
reason of this is plain, because, an arc pitch of 3.1416 inches being
represented by a diametral pitch of 1, a diametral pitch of 1/2 (or 2 as
it is called) will be one half of 3.1416. The advantage of discarding
the numerator is, then, that we avoid the use of fractions and are
readily enabled to find any arc pitch from a given diametral pitch.
Examples.--Given a 5 diametral pitch; what is the arc pitch? First
(using the full fraction 1/5) we have 1/5 × 3.1416 = .628 = the arc
pitch. Second (discarding the numerator), we have 3.1416 ÷ 5 = .628 =
arc pitch. If we are given an arc pitch to find a corresponding
diametral pitch we again simply divide 3.1416 by the given arc pitch.
Example.--What is the diametral pitch of a wheel whose arc pitch is
1-1/2 inches? Here 3.1416 ÷ 1.5 = 2.09 = diametral pitch. The reason of
this is also plain, for since the arc pitch is to the diametral pitch as
the circumference is to the diameter we have: as 3.1416 is to 1, so is
1.5 to the required diametral pitch; then 3.1416 × 1 ÷ 1.5 = 2.09 = the
required diametral pitch.
To find the number of teeth contained in a wheel when the diameter and
diametral pitch is given, multiply the diameter in inches by the
diametral pitch. The product is the answer. Thus, how many teeth in a
wheel 36 inches diameter and of 3 diametral pitch? Here 36 × 3 = 108 =
the number of teeth sought. Or, per contra, a wheel of 36 inches
diameter has 108 teeth. What is the diametral pitch? 108 ÷ 36 = 3 = the
diametral pitch. Thus it will be seen that, for determining the relative
sizes of wheels, this system is excellent from its simplicity. It also
possesses the advantage that, by adding two parts of the diametral pitch
to the pitch diameter, the outside diameter of the wheel or the diameter
of the addendum is obtained. For instance, a wheel containing 30 teeth
of 10 pitch would be 3 inches diameter on the pitch circle and 3-2/10
outside or total diameter.
Again, a wheel having 40 teeth of 8 diametral pitch would have a pitch
circle diameter of 5 inches, because 40 ÷ 8 = 5, and its full diameter
would be 5-1/4 inches, because the diametral pitch is 1/8, and this
multiplied by 2 gives 1/4, which added to the pitch circle diameter of 5
inches makes 5-1/4 inches, which is therefore the diameter of the
addendum, or, in other words, the full diameter of the wheel.
Suppose now that a pair of wheels require to have pitch circles of 5 and
8 inches diameter respectively, and that the arc pitch requires to be,
say, as near as may be 4/10 inch; to find a suitable pitch and the
number of teeth by the diametral pitch system we proceed as follows:
In the following table are given various arc pitches, and the
corresponding diametral pitch.
+----------------+----------+----------+----------------+
|Diametral Pitch.|Arc Pitch.|Arc Pitch.|Diametral Pitch.|
+----------------+----------+----------+----------------+
| | | Inch. | |
| 2 | 1.57 | 1.75 | 1.79 |
| 2.25 | 1.39 | 1.5 | 2.09 |
| 2.5 | 1.25 | 1.4375 | 2.18 |
| 2.75 | 1.14 | 1.375 | 2.28 |
| 3 | 1.04 | 1.3125 | 2.39 |
| 3.5 | .890 | 1.25 | 2.51 |
| 4 | .785 | 1.1875 | 2.65 |
| 5 | .628 | 1.125 | 2.79 |
| 6 | .523 | 1.0625 | 2.96 |
| 7 | .448 | 1.0000 | 3.14 |
| 8 | .392 | 0.9375 | 3.35 |
| 9 | .350 | 0.875 | 3.59 |
| 10 | .314 | 0.8125 | 3.86 |
| 11 | .280 | 0.75 | 4.19 |
| 12 | .261 | 0.6875 | 4.57 |
| 14 | .224 | 0.625 | 5.03 |
| 16 | .196 | 0.5625 | 5.58 |
| 18 | .174 | 0.5 | 6.28 |
| 20 | .157 | 0.4375 | 7.18 |
| 22 | .143 | 0.375 | 8.38 |
| 24 | .130 | 0.3125 | 10.00 |
| 26 | .120 | 0.25 | 12.56 |
+----------------+----------+----------+----------------+
From this table we find that the nearest diametral pitch that will
correspond to an arc pitch of 4/10 inch is a diametral pitch of 8, which
equals an arc pitch of .392, hence we multiply the pitch circles (5 and
8,) by 8, and obtain 40 and 64 as the number of teeth, the arc pitch
being .392 of an inch. To find the number of teeth and pitch by the arc
pitch and circumference of the pitch circle, we should require to find
the circumference of the pitch circle, and divide this by the nearest
arc pitch that would divide the circumference without leaving a
remainder, which would entail more calculating than by the diametral
pitch system.
The designation of pitch by the diametral pitch system is, however, not
applied in practice to coarse pitches, nor to gears in which the teeth
are cast upon the wheels, pattern makers generally preferring to make
the pitch to some measurement that accords with the divisions of the
ordinary measuring rule.
Of two gear-wheels that which impels the other is termed the driver, and
that which receives motion from the other is termed the driven wheel or
follower; hence in a single pair of wheels in gear together, one is the
driver and the other the driven wheel or follower. But if there are
three wheels in gear together, the middle one will be the follower when
spoken of with reference to the first or prime mover, and the driver,
when mentioned with reference to the third wheel, which will be a
follower. A series of more than two wheels in gear together is termed a
train of wheels or of gearing. When the wheels in a train are in gear
continuously, so that each wheel, save the first and last, both receives
and imparts motion, it is a simple train, the first wheel being the
driver, and the last the follower, the others being termed intermediate
wheels. Each of these intermediates is a follower with reference to the
wheel that drives it, and a driver to the one that it drives. But the
velocity of all the wheels in the train is the same in fact per second
(or in a given space of time), although the revolutions in that space
of time may vary; hence a simple train of wheels transmits motion
without influencing its velocity. To alter the velocity (which is always
taken at a point on the pitch circle) the gearing must be compounded, as
in Fig. 11, in which A, B, C, E are four wheels in gear, B and C being
compounded, that is, so held together on the shaft D that both make an
equal number of revolutions in a given time. Hence the velocity of C
will be less than that of B in proportion as the diameter,
circumference, radius, or number of teeth in C, varies from the
diameter, radius, circumference, or number of teeth (all the wheels
being supposed to have teeth of the same pitch) in B, although the
rotations of B and C are equal. It is most convenient, and therefore
usual, to take the number of teeth, but if the teeth on C (and therefore
those on E also) were of different pitch from those on B, the radius or
diameters of the wheels must be taken instead of the pitch, when the
velocities of the various wheels are to be computed. It is obvious that
the compounded pair of wheels will diminish the velocity when the driver
of the compounded pair (as C in the figure) is of less radius than the
follower B, and conversely that the velocity will be increased when the
driver is of greater radius than the follower of the compound pair.
[Illustration: Fig. 11.]
The diameter of the addendum or outer circle of a wheel has no influence
upon the velocity of the wheel. Suppose, for example, that we have a
pair of wheels of 3 inch arc or circular pitch, and containing 20 teeth,
the driver of the two making one revolution per minute. Suppose the
driven wheel to have fast upon its shaft a pulley whose diameter is one
foot, and that a weight is suspended from a line or cord wound around
this pulley, then (not taking the thickness of the line into account)
each rotation of the driven wheel would raise the weight 3.1416 feet
(that being the circumference of the pulley). Now suppose that the
addendum circle of either of the wheels were cut off down to the pitch
circle, and that they were again set in motion, then each rotation of
the driven wheel would still raise the weight 3.1416 feet as before.
It is obvious, however, that the addendum circle must be sufficiently
larger than the pitch circle to enable at least one pair of teeth to be
in continuous contact; that is to say, it is obvious that contact
between any two teeth must not cease before contact between the next two
has taken place, for otherwise the motion would not be conveyed
continuously. The diameter of the pitch circle cannot be obtained from
that of the addendum circle unless the pitch of the teeth and the
proportion of the pitch allowed for the addendum be known. But if these
be known the diameter of the pitch circle may be obtained by subtracting
from that of the addendum circle twice the amount allowed for the
addendum of the tooth.
Example.--A wheel has 19 teeth of 3 inch arc pitch; the addendum of the
tooth or teeth equals 3/10 of the pitch, and its addendum circle
measures 19.943 inches; what is the diameter of the pitch circle? Here
the addendum on each side of the wheel equals (3/10 of 3 inches) = .9
inches, hence the .9 must be multiplied by 2 for the two sides of the
wheel, thus, .9 × 2 = 1.8. Then, diameter of addendum circle 19.943
inches less 1.8 inches = 18.143 inches, which is the diameter of the
pitch circle.
Proof.--Number of teeth = 19, arc pitch 3, hence 19 × 3 = 57 inches,
which, divided by 3.1416 (the proportion of the circumference to the
diameter) = 18.143 inches.
If the distance between the centres of a pair of wheels that are in gear
be divided into two parts whose lengths are in the same proportion one
to the other as are the numbers of teeth in the wheels, then these two
parts will represent the radius of the pitch circles of the respective
wheels. Thus, suppose one wheel to contain 100 and the other 50 teeth,
and that the distance between their centres is 18 inches, then the pitch
radius or pitch diameter of one will be twice that of the other, because
one contains twice as many teeth as the other. In this case the radius
of pitch circle for the large wheel will be 12 inches, and that for the
small one 6 inches, because 12 added to 6 makes 18, which is the
distance between the wheel centres, and 12 is in the same proportion to
6 that 100 is to 50.
A simple rule whereby to find the radius of the pitch circles of a pair
of wheels is as follows:--
Rule.--Divide number of teeth in the large wheel by the number in the
small one, and to the sum so obtained add 1. Take this amount and divide
it into the distance between the centres of the wheels, and the result
will be the radius of the smallest wheel. To obtain the radius of the
largest wheel subtract the radius of the smallest wheel from the
distance between the wheel centres.
Example.--Of a pair of wheels, one has 100 and the other 50 teeth, the
distance between their centres is 18 inches; what is the pitch radius of
each wheel?
Here 100 ÷ 50 = 2, and 2 + 1 = 3. Then 18 ÷ 3 = 6, hence the pitch
radius of the small wheel is 6 inches. Then 18 - 6 = 12 = pitch radius
of large wheel.
Example 2.--Of a pair of wheels one has 40 and the other 90 teeth. The
distance between the wheel centres is 32-1/2 inches; what are the radii
of the respective pitch circles? 90 ÷ 40 = 2.25 and 2.25 + 1 = 3.25.
Then 32.5 ÷ 3.25 = 10 = pitch radius of small wheel, and 32.5 - 10 =
22.5, which is the pitch radius of the large wheel.
To prove this we may show that the pitch radii of the two wheels are in
the same proportion as their numbers of teeth, thus:--
Proof.--Radius of small wheel = 10 × 4 = 40
---- ----
radius of large wheel = 22.5 × 4 = 90.0
Suppose now that a pair of wheels are constructed, having respectively
50 and 100 teeth, and that the radii of their true pitch circles are 12
and 6 respectively, but that from wear in their journals or journal
bearings this 18 inches (12 + 6 = 18) between centres (or line of
centres, as it is termed) has become 18-3/8 inches. Then the acting
effective or operative radii of the pitch circles will bear the same
proportion to the 18-3/8 as the numbers of teeth in the respective
wheels, and will be 12.25 for the large, and 6.125 for the small wheel,
instead of 12 and 6, as would be the case were the wheels 18 inches
apart. Working this out under the rule given we have 100 ÷ 50 = 2, and 2
+ 1 = 3. Then 18.375 ÷ 3 = 6.125 = pitch radius of small wheel, and
18.375 - 6.125 = 12.25 = pitch radius of the large wheel.
The true pitch line of a tooth is the line or point where the face curve
joins the flank curve, and it is essential to the transmission of
uniform motion that the pitch circles of epicycloidal wheels exactly
coincide on the line of centres, but if they do not coincide (as by not
meeting or by overlapping each other), then a false pitch circle becomes
operative instead of the true one, and the motion of the driven wheel
will be unequal at different instants of time, although the revolutions
of the wheels will of course be in proportion to the respective numbers
of their teeth.
If the pitch circle is not marked on a single wheel and its arc pitch is
not known, it is practically a difficult matter to obtain either the arc
pitch or diameter of the pitch circle. If the wheel is a new one, and
its teeth are of the proper curves, the pitch circle will be shown by
the junction of the curves forming the faces with those forming the
flanks of the teeth, because that is the location of the pitch circle;
but in worn wheels, where from play or looseness between the journals
and their bearings, this point of junction becomes rounded, it cannot be
defined with certainty.
In wheels of large diameter the arc pitch so nearly coincides with the
chord pitch, that if the pitch circle is not marked on the wheel and the
arc pitch is not known, the chord pitch is in practice often assumed to
represent the arc pitch, and the diameter of the wheel is obtained by
multiplying the number of teeth by the chord pitch. This induces no
error in wheels of coarse pitches, because those pitches advance by 1/4
or 1/2 inch at a step, and a pitch measuring about, say, 1-1/4 inch
chord pitch, would be known to be 1-1/4 arc pitch, because the
difference between the arc and chord pitch would be too minute to cause
sensible error. Thus the next coarsest pitch to 1 inch would be 1-1/8,
or more often 1-1/4 inch, and the difference between the arc and chord
pitch of the smallest wheel would not amount to anything near 1/8 inch,
hence there would be no liability to mistake a pitch of 1-1/8 for 1 inch
or _vice versâ_. The diameter of wheel that will be large enough to
transmit continuous motion is diminished in proportion as the pitch is
decreased; in proportion, also, as the wheel diameter is reduced, the
difference between the arc and chord pitch increases, and further the
steps by which fine pitches advance are more minute (as 1/4, 9/32, 5/16,
&c.). From these facts there is much more liability to err in estimating
the arc from the measured chord pitch in fine pitches, hence the
employment of diametral pitch for small wheels of fine pitches is on
this account also very advantageous. In marking out a wheel the chord
pitch will be correct if the pitch circle be of correct diameter and be
divided off into as many points of equal division (with compasses) as
there are to be teeth in the wheel. We may then mark from these points
others giving the thickness of the teeth, which will make the spaces
also correct. But when the wheel teeth are to be cut in a machine out of
solid metal, the mechanism of the machine enables the marking out to be
dispensed with, and all that is necessary is to turn the wheel to the
required addendum diameter, and mark the pitch circle. The following are
rules for the purposes they indicate.
The circumference of a circle is obtained by multiplying its diameter by
3.1416, and the diameter may be obtained by dividing the circumference
by 3.1416.
The circumference of the pitch circle divided by the arc pitch gives the
number of teeth in the wheel.
The arc pitch multiplied by the number of teeth in the wheel gives the
circumference of the pitch circle.
Gear-wheels are simply rotating levers transmitting the power they
receive, less the amount of friction necessary to rotate them under the
given conditions. All that is accomplished by a simple train of gearing
is, as has been said, to vary the number of revolutions, the speed or
velocity measured in feet moved through per minute remaining the same
for every wheel in the train. But in a compound train of gears the speed
in feet per minute, as well as the revolutions, may be varied by means
of the compounded pairs of wheels. In either a simple or a compound
train of gearing the power remains the same in amount for every wheel in
the train, because what is in a compound train lost in velocity is
gained in force, or what is gained in velocity is lost in force, the
word force being used to convey the idea of strain, pressure, or pull.
In Fig. 12, let A, B, and C represent the pitch circles of three gears
of which A and B are in gear, while C is compounded with B; let E be the
shaft of A, and G that for B and C. Let A be 60 inches, B = 30 inches,
and C = 40 inches in diameter. Now suppose that shaft E suspends from
its perimeter a weight of 50 lbs., the shaft being 4 inches in diameter.
Then this weight will be at a leverage of 2 inches from the centre of E
and the 50 must be multiplied by 2, making 100 lbs. at the centre of E.
Then at the perimeter of A this 100 will become one-thirtieth of one
hundred, because from the centre to the perimeter of A is 30.
One-thirtieth of 100 is 3-33/100 lbs., which will be the force exerted
by A on the perimeter of B. Now from the perimeter of B to its centre
(or in other words its radius) is 15 inches, hence the 3-33/100 lbs. at
its perimeter will become fifteen times as much at the centre G of B,
and 3-33/100 × 15 = 49-95/100 lbs. From the centre G to the perimeter of
C being 20 inches, the 49-95/100 lbs. at the centre will be only
one-twentieth of that amount at the perimeter of C, hence 49-95/100 ÷ 20
= 2-49/100 lbs., which is the amount of force at the perimeter of C.
Here we have treated the wheels as simple levers, dividing the weight by
the length of the levers in all cases where it is transmitted from the
shaft to the perimeter, and multiplying it by the length of the lever
when it is transmitted from the perimeter of the wheel to the centre of
the shaft. The precise same result will be reached if we take the
diameter of the wheels or the number of the teeth, providing the pitch
of the teeth on all the wheels is alike.
Suppose, for example, that A has 60 teeth, B has 30 teeth, and C has 40
teeth, all being of the same pitch. Suppose the 50 lb. weight be
suspended as before, and that the circumference of the shaft be equal to
that of a pinion having 4 teeth of the same pitch as the wheels. Then
the 50 multiplied by the 4 becomes 200, which divided by 60 (the number
of teeth on A) becomes 3-33/100, which multiplied by 30 (the number of
teeth on B) becomes 99-90/100, which divided by 40 (the number of teeth
on C) becomes 2-49/100 lbs. as before.
[Illustration: Fig. 12.]
It may now be explained why the shaft was taken as equal to a pinion
having 4 teeth. Its diameter was taken as 4 inches and the wheel
diameter was taken as being 60 inches, and it was supposed to contain 60
teeth, hence there was 1 tooth to each inch of diameter, and the 4
inches diameter of shaft was therefore equal to a pinion having 4 teeth.
From this we may perceive the philosophy of the rule that to obtain the
revolutions of wheels we multiply the given revolutions by the teeth in
the driving wheels and divide by the teeth in the driven wheels.
Suppose that A (Fig. 13) makes 1 revolution per minute, how many will C
make, A having 60 teeth, B 30 teeth, and C 40 teeth? In this case we
have but one driving wheel A, and one driven wheel B, the driver having
60 teeth, the driven 30, hence 60 ÷ 30 = 2, equals revolutions of B and
also of C, the two latter being on the same shaft.
It will be observed then that the revolutions are in the same proportion
as the numbers of the teeth or the radii of the wheels, or what is the
same thing, in the same proportion as their diameters. The number of
teeth, however, is usually taken as being easier obtained than the
diameter of the pitch circles, and easier to calculate, because the
teeth will be represented by a whole number, whereas the diameter,
radius, or circumference, will generally contain fractions.
Suppose that the 4 wheels in Fig. 14 have the respective numbers of
teeth marked beside them, and that the upper one having 40 teeth makes
60 revolutions per minute, then we may obtain the revolutions of the
others as follows:--
Revolu- Teeth Teeth Teeth Teeth
tions. in first in first in second in second
driver. driven. driver. driven.
60 × 40 ÷ 60 × 20 ÷ 120 = 6-66/100
and a remainder of the reciprocating decimals. We may now prove this by
reversing the question, thus. Suppose the 120 wheel to make 6-66/100
revolutions per minute, how many will the 40 wheel make?
Revolu- Teeth Teeth Teeth Teeth
tions. in first in first in second in second
driver. driven. driver. driven.
6.66 × 120 ÷ 20 × 60 ÷ 40 = 59-99/100 =
revolutions of the 40 wheel, the discrepancy of 1/100 being due to the
6.66 leaving a remainder and not therefore being absolutely correct.
That the amount of power transmitted by gearing, whether compounded or
not, is equal throughout every wheel in the train, may be shown as
follows:--
[Illustration: Fig. 13.]
Referring again to Fig. 10, it has been shown that with a 50 lb. weight
suspended from a 4 inch shaft E, there would be 30-33/100 lbs. at the
perimeter of A. Now suppose a rotation be made, then the 50 lb. weight
would fall a distance equal to the circumference of the shaft, which is
(3.1416 × 4 = 12-56/100) 12-56/100 inches. Now the circumference of the
wheel is (60 dia. × 3.1416 = 188-49/100 cir.) 188-49/100 inches, which
is the distance through which the 3-33/100 lbs. would move during one
rotation of A. Now 3.33 lbs. moving through 188.49 inches represents the
same amount of power as does 50 lbs. moving through a distance of 12.56
inches, as may be found by converting the two into inch lbs. (that is to
say, into the number of inches moved by 1 lb.), bearing in mind that
there will be a slight discrepancy due to the fact that the fractions
.33 in the one case, and .56 in the other are not quite correct. Thus:
188.49 inches × 3.33 lbs. = 627.67 inch lbs., and
12.56 " × 50 " = 628 " "
Taking the next wheels in Fig. 12, it has been shown that the 3.33 lbs.
delivered from A to the perimeter of B, becomes 2.49 lbs. at the
perimeter of C, and it has also been shown that C makes two revolutions
to one of A, and its diameter being 40 inches, the distance this 2.49
lbs. will move through in one revolution of A will therefore be equal to
twice its circumference, which is (40 dia. × 3.1416 = 125.666 cir., and
125.666 × 2 = 251.332) 251.332 inches. Now 2.49 lbs. moving through
251.332 gives when brought to inch lbs. 627.67 inch lbs., thus 251.332 ×
2.49 = 627.67. Hence the amount of power remains constant, but is
altered in form, merely being converted from a heavy weight moving a
short distance, into a lighter one moving a distance exactly as much
greater as the weight or force is lessened or lighter.
[Illustration: Fig. 14.]
Gear-wheels therefore form a convenient method of either simply
transmitting motion or power, as when the wheels are all of equal
diameter, or of transmitting it and simultaneously varying its velocity
of motion, as when the wheels are compounded either to reduce or
increase the speed or velocity in feet per second of the prime mover or
first driver of the train or pair, as the case may be.
[Illustration: Fig. 15.]
In considering the action of gear-teeth, however, it sometimes is more
convenient to denote their motion by the number of degrees of angle they
move through during a certain portion of a revolution, and to refer to
their relative velocities in terms of the ratio or proportion existing
between their velocities. The first of these is termed the angular
velocity, or the number of degrees of angle the wheel moves through
during a given period, while the second is termed the velocity ratio of
the pair of wheels. Let it be supposed that two wheels of equal diameter
have contact at their perimeters so that one drives the other by
friction without any slip, then the velocity of a point on the perimeter
of one will equal that of a point on the other. Thus in Fig. 15 let A
and B represent the pitch circles of two wheels, and C an imaginary line
joining the axes of the two wheels and termed the line of centres. Now
the point of contact of the two wheels will be on the line of centres
as at D, and if a point or dot be marked at D and motion be imparted
from A to B, then when each wheel has made a quarter revolution the dot
on A will have arrived at E while that on B will have arrived at F. As
each wheel has moved through one quarter revolution, it has moved
through 90° of angle, because in the whole circle there is 360°, one
quarter of which is 90°, hence instead of saying that the wheels have
each moved through one quarter of a revolution we may say they have
moved through an angle of 90°, or, in other words, their angular
velocity has, during this period, been 90°. And as both wheels have
moved through an equal number of degrees of angle their velocity ratio
or proportion of velocity has been equal.
Obviously then the angular velocity of a wheel represents a portion of a
revolution irrespective of the diameter of the wheel, while the velocity
ratio represents the diameter of one in proportion to that of the other
irrespective of the actual diameter of either of them.
[Illustration: Fig. 16.]
Now suppose that in Fig. 16 A is a wheel of twice the diameter of B;
that the two are free to revolve about their fixed centres, but that
there is frictional contact between their perimeters at the line of
centres sufficient to cause the motion of one to be imparted to the
other without slip or lost motion, and that a point be marked on both
wheels at the point of contact D. Now let motion be communicated to A
until the mark that was made at D has moved one-eighth of a revolution
and it will have moved through an eighth of a circle, or 45°. But during
this motion the mark on B will have moved a quarter of a revolution, or
through an angle of 90° (which is one quarter of the 360° that there are
in the whole circle). The angular velocities of the two are, therefore,
in the same ratio as their diameters, or two to one, and the velocity
ratio is also two to one. The angular velocity of each is therefore the
number of degrees of angle that it moves through in a certain portion of
a revolution, or during the period that the other wheel of the pair
makes a certain portion of a revolution, while the velocity ratio is the
proportion existing between the velocity of one wheel and that of the
other; hence if the diameter of one only of the wheels be changed, its
angular velocity will be changed and the velocity ratio of the pair will
be changed. The velocity ratio may be obtained by dividing either the
radius, pitch, diameter, or number of teeth of one wheel into that of
the other.
Conversely, if a given velocity ratio is to be obtained, the radius,
diameter, or number of teeth of the driver must bear the same relation
to the radius, diameter, or number of teeth of the follower, as the
velocity of the follower is desired to bear to that of the driver.
If a pair of wheels have an equal number of teeth, the same pairs of
teeth will come into action at every revolution; but if of two wheels
one is twice as large as the other, each tooth on the small wheel will
come into action twice during each revolution of the large one, and will
work during each successive revolution with the same two teeth on the
large wheel; and an application of the principle of the hunting tooth is
sometimes employed in clocks to prevent the overwinding of their
springs, the device being shown in Fig. 17, which is from "Willis'
Principles of Mechanism."
For this purpose the winding arbor C has a pinion A of 19 teeth fixed to
it close to the front plate. A pinion B of 18 teeth is mounted on a stud
so as to be in gear with the former. A radial plate C D is fixed to the
face of the upper wheel A, and a similar plate F E to the lower wheel B.
These plates terminate outward in semicircular noses D, E, so
proportioned as to cause their extremities to abut against each other,
as shown in the figure, when the motion given to the upper arbor by the
winding has brought them into the position of contact. The clock being
now wound up, the winding arbor and wheel A will begin to turn in the
opposite direction. When its first complete rotation is effected the
wheel B will have gained one tooth distance from the line of centres, so
as to place the stop D in advance of E and thus avoid a contact with E,
which would stop the motion. As each turn of the upper wheel increases
the distance of the stops, it follows from the principle of the hunting
cog, that after eighteen revolutions of A and nineteen of B the stops
will come together again and the clock be prevented from running down
too far. The winding key being applied, the upper wheel A will be
rotated in the opposite direction, and the winding repeated as above.
[Illustration: Fig. 17.]
Thus the teeth on one wheel will wear to imbed one upon the other. On
the other hand the teeth of the two wheels may be of such numbers that
those on one wheel will not fall into gear with the same teeth on the
other except at intervals, and thus an inequality on any one tooth is
subjected to correction by all the teeth in the other wheel. When a
tooth is added to the number of teeth on a wheel to effect this purpose
it is termed a hunting cog, or hunting tooth, because if one wheel have
a tooth less, then any two teeth which meet in the first revolution are
distant, one tooth in the second, two teeth in the third, three in the
fourth, and so on. The odd tooth is on this account termed a hunting
tooth.
It is obvious then that the shape or form to be given to the teeth must,
to obtain correct results, be such that the motion of the driver will be
communicated to the follower with the velocity due to the relative
diameters of the wheels at the pitch circles, and since the teeth move
in the arc of a circle it is also obvious that the sides of the teeth,
which are the only parts that come into contact, must be of same curve.
The nature of this curve must be such that the teeth shall possess the
strength necessary to transmit the required amount of power, shall
possess ample wearing surface, shall be as easily produced as possible
for all the varying conditions, shall give as many teeth in constant
contact as possible, and shall, as far as possible, exert a pressure in
a direction to rotate the wheels without inducing undue wear upon the
journals of the shafts upon which the wheels rotate. In cases, however,
in which some of these requirements must be partly sacrificed to
increase the value of the others, or of some of the others, to suit the
special circumstances under which the wheels are to operate, the
selection is left to the judgment of the designer, and the
considerations which should influence his determinations will appear
hereafter.
[Illustration: Fig. 18.]
Modern practice has accepted the curve known in general terms as the
cycloid, as that best filling all the requirements of wheel teeth, and
this curve is employed to produce two distinct forms of teeth,
epicycloidal and involute. In epicycloidal teeth the curve forming the
face of the tooth is designated an epicycloid, and that forming the
flank an hypocycloid. An epicycloid may be traced or generated, as it is
termed, by a point in the circumference of a circle that rolls without
slip upon the circumference of another circle. Thus, in Fig. 18, A and B
represent two wooden wheels, A having a pencil at P, to serve as a
tracing or marking point. Now, if the wheels are laid upon a sheet of
paper and while holding B in a fixed position, roll A in contact with B
and let the tracing point touch the paper, the point P will trace the
curve C C. Suppose now the diameter of the base circle B to be
infinitely large, a portion of its circumference may be represented by a
straight line, and the curve traced by a point on the circumference of
the generating circle as it rolls along the base line B is termed a
cycloid. Thus, in Fig. 19, B is the base line, A the rolling wheel or
generating circle, and C C the cycloidal curve traced or marked by the
point D when A is rolled along B. If now we suppose the base line B to
represent the pitch line of a rack, it will be obvious that part of the
cycloid at one end is suitable for the face on one side of the tooth,
and a part at the other end is suitable for the face of the other side
of the tooth.
[Illustration: Fig. 19.]
A hypocycloid is a curve traced or generated by a point on the
circumference of a circle rolling within and in contact (without slip)
with another circle. Thus, in Fig. 20, A represents a wheel in contact
with the internal circumference of B, and a point on its circumference
will trace the two curves, C C, both curves starting from the same
point, the upper having been traced by rolling the generating circle or
wheel A in one direction and the lower curve by rolling it in the
opposite direction.
[Illustration: Fig. 20.]
To demonstrate that by the epicycloidal and hypocycloidal curves,
forming the faces and flanks of what are known as epicycloidal teeth,
motion may be communicated from one wheel to another with as much
uniformity as by frictional contact of their circumferential surfaces,
let A, B, in Fig. 21, represent two plain wheel disks at liberty to
revolve about their fixed centres, and let C C represent a margin of
stiff white paper attached to the face of B so as to revolve with it.
Now suppose that A and B are in close contact at their perimeters at the
point G, and that there is no slip, and that rotary motion commenced
when the point E (where as tracing point a pencil is attached), in
conjunction with the point F, formed the point of contact of the two
wheels, and continued until the points E and F had arrived at their
respective positions as shown in the figure; the pencil at E will have
traced upon the margin of white paper the portion of an epicycloid
denoted by the curve E F; and as the movement of the two wheels A, B,
took place by reason of the contact of their circumferences, it is
evident that the length of the arc E G must be equal to that of the arc
G F, and that the motion of A (supposing it to be the driver) would be
communicated uniformly to B.
[Illustration: Fig. 21.]
Now suppose that the wheels had been rotated in the opposite direction
and the same form of curve would be produced, but it would run in the
opposite direction, and these two curves may be utilized to form teeth,
as in Fig. 22, the points on the wheel A working against the curved
sides of the teeth on B.
To render such a pair of wheels useful in practice, all that is
necessary is to diminish the teeth on B without altering the nature of
the curves, and increase the diameter of the points on A, making them
into rungs or pins, thus forming the wheels into what is termed a wheel
and lantern, which are illustrated in Fig. 23.
[Illustration: Fig. 22.]
A represents the pinion (or lantern), and B the wheel, and C, C, the
primitive teeth reduced in thickness to receive the pins on A. This
reduction we may make by setting a pair of compasses to the radius of
the rung and describing half-circles at the bottom of the spaces in B.
We may then set a pair of compasses to the curve of C, and mark off the
faces of the teeth of B to meet the half-circles at the pitch line, and
reduce the teeth heights so as to leave the points of the proper
thickness; having in this operation maintained the same epicycloidal
curves, but brought them closer together and made them shorter. It is
obvious, however, that such a method of communicating rotary motion is
unsuited to the transmission of much power; because of the weakness of,
and small amount of wearing surface on, the points or rungs in A.
[Illustration: Fig. 23.]
[Illustration: Fig. 24.]
In place of points or rungs we may have radial lines, these lines,
representing the surfaces of ribs, set equidistant on the radial face of
the pinion, as in Fig. 24. To determine the epicycloidal curves for the
faces of teeth to work with these radial lines, we may take a generating
circle C, of half the diameter of A, and cause it to roll in contact
with the internal circumference of A, and a tracing point fixed in the
circumference of C will draw the radial lines shown upon A. The
circumstances will not be altered if we suppose the three circles, A, B,
C, to be movable about their fixed centres, and let their centres be in
a straight line; and if, under these circumstances, we suppose rotation
to be imparted to the three circles, through frictional contact of their
perimeters, a tracing point on the circumference of C would trace the
epicycloids shown upon B and the radial lines shown upon A, evidencing
the capability of one to impart uniform rotary motion to the other.
[Illustration: Fig. 25.]
To render the radial lines capable of use we must let them be the
surfaces of lugs or projections on the face of the wheel, as shown in
Fig. 25 at D, E, &c., or the faces of notches cut in the wheel as at F,
G, H, &c., the metal between F and G forming a tooth J, having flanks
only. The wheel B has the curves of each tooth brought closer together
to give room for the reception of the teeth upon A. We have here a pair
of gears that possess sufficient strength and are capable of working
correctly in either direction.
[Illustration: Fig. 26.]
But the form of tooth on one wheel is conformed simply to suit those on
the other, hence, neither two of the wheels A, nor would two of B, work
correctly together.
They may be qualified to do so, however, by simply adding to the tops
of the teeth on A, teeth of the form of those on B, and adding to those
on B, and within the pitch circle, teeth corresponding to those on A, as
in Fig. 26, where at K´ and J´ teeth are provided on B corresponding to
J and K on A, while on A there are added teeth O´, N´, corresponding to
O, N, on B, with the result that two wheels such as A or two such as B
would work correctly together, either being the driver or either the
follower, and rotation may occur in either direction. In this operation
we have simply added faces to the teeth on A, and flanks to those on B,
the curves being generated or obtained by rolling the generating, or
curve marking, circle C upon the pitch circles P and P´. Thus, for the
flanks of the teeth of A, C is rolled upon, and within the pitch circle
P of A; while for the face curves of the same teeth C is rolled upon,
but without or outside of P. Similarly for the teeth of wheel B the
generating circle C is rolled within P´ for the flanks and without for
the faces. With the curves rolled or produced with the same diameter of
generating circle the wheels will work correctly together, no matter
what their relative diameter may be, as will be shown hereafter.
[Illustration: Fig. 27.]
In this demonstration, however, the curves for the faces of the teeth
being produced by an operation distinct from that employed to produce
the flank curves, it is not clearly seen that the curves for the flanks
of one wheel are the proper curves to insure a uniform velocity to the
other. This, however, may be made clear as follows:--
In Fig. 27 let _a_ _a_ and _b_ _b_ represent the pitch circles of two
wheels of equal diameters, and therefore having the same number of
teeth. On the left, the wheels are shown with the teeth in, while on the
right-hand side of the line of centres A B, the wheels are shown blank;
_a_ _a_ is the pitch line of one wheel, and _b_ _b_ that for the other.
Now suppose that both wheels are capable of being rotated on their
shafts, whose centres will of course be on the line A B, and suppose a
third disk, Q, be also capable of rotation upon its centre, C, which is
also on the line A B. Let these three wheels have sufficient contact at
their perimeters at the point _n_, that if one be rotated it will rotate
both the others (by friction) without any slip or lost motion, and of
course all three will rotate at an equal velocity. Suppose that there is
fixed to wheel Q a pencil whose point is at _n_. If then rotation be
given to _a_ _a_ in the direction of the arrow _s_, all three wheels
will rotate in that direction as denoted by their respective arrows _s_.
Assume, then, that rotation of the three has occurred until the pencil
point at _n_ has arrived at the point _m_, and during this period of
rotation the point _n_ will recede from the line of centres A B, and
will also recede from the arcs or lines of the two pitch circles _a_
_a_, _b_ _b_. The pencil point being capable of marking its path, it
will be found on reaching _m_ to have marked inside the pitch circle _b_
_b_ the curve denoted by the full line _m_ _x_, and simultaneously with
this curve it has marked another curve outside of _a_ _a_, as denoted by
the dotted line _y_ _m_. These two curves being marked by the pencil
point at the same time and extending from _y_ to _m_, and _x_ also to
_m_. They are prolonged respectively to _p_ and to K for clearness of
illustration only.
The rotation of the three wheels being continued, when the pencil point
has arrived at O it will have continued the same curves as shown at O
_f_, and O _g_, curve O _f_ being the same as _m_ _x_ placed in a new
position, and O _g_ being the same as _m_ _y_, but placed in a new
position. Now since both these curves (O _f_ and O _g_) were marked by
the one pencil point, and at the same time, it follows that at every
point in its course that point must have touched both curves at once.
Now the pencil point having moved around the arc of the circle Q from
_n_ to _m_, it is obvious that the two curves must always be in contact,
or coincide with each other, at some point in the path of the pencil or
describing point, or, in other words, the curves will always touch each
other at some point on the curve of Q, and between _n_ and O. Thus when
the pencil has arrived at _m_, curve _m_ _y_ touches curve K _x_ at the
point _m_, while when the pencil had arrived at point O, the curves O
_f_ and O _g_ will touch at O. Now the pitch circles _a_ _a_ and _b_
_b_, and the describing circle Q, having had constant and uniform
velocity while the traced curves had constant contact at some point in
their lengths, it is evident that if instead of being mere lines, _m_
_y_ was the face of a tooth on _a_ _a_, and _m_ _x_ was the flank of a
tooth on _b_ _b_, the same uniform motion may be transmitted from _a_
_a_, to _b_ _b_, by pressing the tooth face _m_ _y_ against the tooth
flank _m_ _x_. Let it now be noted that the curve _y_ _m_ corresponds to
the face of a tooth, as say the face E of a tooth on _a_ _a_, and that
curve _x_ _m_ corresponds to the flank of a tooth on _b_ _b_, as say to
the flank F, short portions only of the curves being used for those
flanks. If the direction of rotation of the three wheels was reversed,
the same shape of curves would be produced, but they would lie in an
opposite direction, and would, therefore, be suitable for the other
sides of the teeth. In this case, the contact of tooth upon tooth will
be on the other side of the line of centres, as at some point between
_n_ and Q.
[Illustration: Fig. 28.]
In this illustration the diameter of the rolling or describing circle Q,
being less than the radius of the wheels _a_ _a_ or _b_ _b_, the flanks
of the teeth are curves, and the two wheels being of the same diameter,
the teeth on the two are of the same shape. But the principles governing
the proper formation of the curve remain the same whatever be the
conditions. Thus in Fig. 28 are segments of a pair of wheels of equal
diameter, but the describing, rolling, or curve-generating circle is
equal in diameter to the radius of the wheels. Motion is supposed to
have occurred in the direction of the arrows, and the tracing point to
have moved from _n_ to _m_. During this motion it will have marked a
curve _y_ _m_, a portion of the _y_ end serving for the face of a tooth
on one wheel, and also the line _k_ _x_, a continuation of which serves
for the flank of a tooth on the other wheel. In Fig. 29 the pitch
circles only of the wheels are marked, _a_ _a_ being twice the diameter
of _b_ _b_, and the curve-generating circle being equal in diameter to
the radius of wheel _b_ _b_. Motion is assumed to have occurred until
the pencil point, starting from _n_, had arrived at _o_, marking curves
suitable for the face of the teeth on one wheel and for the flanks of
the other as before, and the contact of tooth upon tooth still, at every
point in the path of the teeth, occurring at some point of the arc _n_
_o_. Thus when the point had proceeded as far as point _m_ it will have
marked the curve _y_ and the radial line _x_, and when the point had
arrived at _o_, it will have prolonged _m_ _y_ into _o_ _g_ and _x_ into
_o_ _f_, while in either position the point is marking both lines. The
velocities of the wheels remain the same notwithstanding their different
diameters, for the arc _n_ _g_ must obviously (if the wheels rotate
without slip by friction of their surfaces while the curves are traced)
be equal in length to the arc _n_ _f_ or the arc _n_ _o_.
[Illustration: Fig. 29.]
[Illustration: Fig. 30.]
In Fig. 30 _a_ _a_ and _b_ _b_ are the pitch circles of two wheels as
before, and _c_ _c_ the pitch circle of an annular or internal gear, and
D is the rolling or describing circle. When the describing point arrived
at _m_, it will have marked the curve _y_ for the face of a tooth on _a_
_a_, the curve _x_ for the flank of a tooth on _b_ _b_, and the curve
_e_ for the face of a tooth on the internal wheel _c_ _c_. Motion being
continued _m_ _y_ will be prolonged to _o_ _g_, while simultaneously _x_
will be extended into _o_ _f_ and _e_ into _h_ _v_, the velocity of all
the wheels being uniform and equal. Thus the arcs _n_ _v_, _n_ _f_, and
_n_ _g_, are of equal length.
[Illustration: Fig. 31.]
In Fig. 31 is shown the case of a rack and pinion; _a_ _a_ is the pitch
line of the rack, _b_ _b_ that of the pinion, A B at a right angle to
_a_ _a_, the line of centres, and D the generating circle. The wheel and
rack are shown with teeth _n_ on one side simply for clearness of
illustration. The pencil point _n_ will, on arriving at _m_, have traced
the flank curve _x_ and the curve _y_ for the face of the rack teeth.
[Illustration: Fig. 32.]
It has been supposed that the three circles rotated together by the
frictional contact of their perimeters on the line of centres, but the
circumstances will remain the same if the wheels remain at rest while
the generating or describing circle is rolled around them. Thus in Fig.
32 are two segments of wheels as before, _c_ representing the centre of
a tooth on _a_ _a_, and _d_ representing the centre of a tooth on _b_
_b_. Now suppose that a generating or rolling circle be placed with its
pencil point at _e_, and that it then be rolled around _a_ _a_ until it
had reached the position marked 1, then it will have marked the curve
from _e_ to _n_, a part of this curve serving for the face of tooth _c_.
Now let the rolling circle be placed within the pitch circle _a_ _a_ and
its pencil point _n_ be set to _e_, then, on being rolled to position 2,
it will have marked the flank of tooth _c_. For the other wheel suppose
the rolling wheel or circle to have started from _f_ and rolled to the
line of centres as in the cut, it will have traced the curve forming the
face of the tooth _d_. For the flank of _d_ the rolling circle or wheel
is placed within _b_ _b_, its tracing point set at _f_ on the pitch
circle, and on being rolled to position 3 it will have marked the flank
curve. The curves thus produced will be precisely the same as those
produced by rotating all three wheels about their axes, as in our
previous demonstrations.
The curves both for the faces and for the flanks thus obtained will vary
in their curvature with every variation in either the diameter of the
generating circle or of the base or pitch circle of the wheel. Thus it
will be observable to the eye that the face curve of tooth _c_ is more
curved than that of _d_, and also that the flank curve of _d_ is more
spread at the root than is that for _c_, which has in this case resulted
from the difference between the diameter of the wheels _a_ _a_ and _b_
_b_. But the curves obtained by a given diameter of rolling circle on a
given diameter of pitch circle will be correct for any pitch of teeth
that can be used upon wheels having that diameter of pitch circle. Thus,
suppose we have a curve obtained by rolling a wheel of 20 inches
circumference on a pitch circle of 40 inches circumference--now a wheel
of 40 inches in circumference may contain 20 teeth of 2 inch arc pitch,
or 10 teeth of 4 inch arc pitch, or 8 teeth of 5 inch arc pitch, and the
curve may be used for either of those pitches.
If we trace the path of contact of each tooth, from the moment it takes
until it leaves contact with a tooth upon the other wheel, we shall find
that contact begins at the point where the flank of the tooth on the
wheel that drives or imparts motion to the other wheel, meets the face
of the tooth on the driven wheel, which will always be where the point
of the driven tooth cuts or meets the generating or rolling circle of
the driving tooth. Thus in Fig. 33 are represented segments of two
spur-wheels marked respectively the driver and the driven, their
generating circles being marked at G and G´, and X X representing the
line of centres. Tooth A is shown in the position in which it commences
its contact with tooth B at B. Secondly, we shall find that as these
two teeth approach the line of centres X, the point of contact between
them moves or takes place along the thickened arc or curve C X, or along
the path of the generating circle G.
Thus we may suppose tooth D to be another position of tooth A, the
contact being at F, and as motion was continued the contact would pass
along the thickened curve until it arrived at the line of centres X. Now
since the teeth have during this path of contact approached the line of
centres, this part of the whole arc of action or of the path of contact
is termed the arc of approach. After the two teeth have passed the line
of centres X, the path of contact of the teeth will be along the dotted
arc from X to L, and as the teeth are during this period of motion
receding from X this part of the contact path is termed the arc of
recess.
That contact of the teeth would not occur earlier than at C nor later
than at L, is shown by the dotted teeth sides; thus A and B would not
touch when in the position denoted by the dotted teeth, nor would teeth
I and K if in the position denoted by their dotted lines.
[Illustration: Fig. 33.]
If we examine further into this path of contact we find that throughout
its whole path the face of the tooth of one wheel has contact with the
flank only of the tooth of the other wheel, and also that the flank only
of the driving-wheel tooth has contact before the tooth reaches the line
of centres, while the face of only the driving tooth has contact after
the tooth has passed the line of centres.
Thus the flanks of tooth A and of tooth D are in driving contact with
the faces of teeth B and E, while the face of tooth H is in contact with
the flank of tooth I.
These conditions will always exist, whatever be the diameters of the
wheels, their number of teeth or the diameter of the generating circle.
That is to say, in fully developed epicycloidal teeth, no matter which
of two wheels is the driver or which the driven wheel, contact on the
teeth of the driver will always be on the tooth flank during the arc of
approach and on the tooth face during the arc of recess; while on the
driven wheel contact during the arc of approach will be on the tooth
face only, and during the arc of recess on the tooth flank only, it
being borne in mind that the arcs of approach and recess are reversed in
location if the direction of revolution be reversed. Thus if the
direction of wheel motion was opposite to that denoted by the arrows in
Fig. 33 then the arc of approach would be from M to X, and the arc of
recess from X to N.
It is laid down by Professor Willis that the motion of a pair of
gear-wheels is smoother in cases where the path of contact begins at the
line of centres, or, in other words, when there is no arc of approach;
and this action may be secured by giving to the driven wheel flanks
only, as in Fig. 34, in which the driver has fully developed teeth,
while the teeth on the driven have no faces.
In this case, supposing the wheels to revolve in the direction of arrow
P, the contact will begin at the line of centres X, move or pass along
the thickened arc and end at B, and there will be contact during the arc
of recess only. Similarly, if the direction of motion be reversed as
denoted by arrow Q, the driver will begin contact at X, and cease
contact at H, having, as before, contact during the arc of recess only.
But if the wheel W were the driver and V the driven, then these
conditions would be exactly reversed. Thus, suppose this to be the case
and the direction of motion be as denoted by arrow P, the contact would
occur during the arc of approach, from H to X, ceasing at X.
Or if W were the driver, and the direction of motion was as denoted by
Q, then, again, the path of contact would be during the arc of approach
only, beginning at B and ceasing at X, as denoted by the thickened arc B
X.
The action of the teeth will in either case serve to give a
theoretically perfect motion so far as uniformity of velocity is
concerned, or, in other words, the motion of the driver will be
transmitted with perfect uniformity to the driven wheel. It will be
observed, however, that by the removal of the faces of the teeth, there
are a less number of teeth in contact at each instant of time; thus, in
Fig. 33 there is driving contact at three points, C, F, and J, while in
Fig. 34 there is driving contact at two points only. From the fact that
the faces of the teeth work with the flanks only, and that one side only
of the teeth comes into action, it becomes apparent that each tooth may
have curves formed by four different diameters of rolling or generating
circles and yet work correctly, no matter which wheel be the driver, or
which the driven wheel or follower, or in which direction motion occurs.
Thus in Fig. 35, suppose wheel V to be the driver, having motion in the
direction of arrow P, then faces a on the teeth of V will work with
flanks B of the teeth on W, and so long as the curves for these faces
and flanks are obtained with the same diameter of rolling circle, the
action of the teeth will be correct, no matter what the shapes of the
other parts of the teeth. Now suppose that V still being the driver,
motion occurs in the other direction as denoted by Q, then the faces C
of the teeth on V will drive the flanks C of the teeth on W, and the
motion will again be correct, providing that the same diameter (whatever
it may be) of rolling circle be used for these faces and flanks,
irrespective, of course, of what diameter of rolling circle is used for
any other of the teeth curves. Now suppose that W is the driver, motion
occurring in the direction of P, then faces E will drive flanks F, and
the motion will be correct as before if the curves E and F are produced
with the same diameter of rolling circle. Finally, let W be the driving
wheel and motion occur in the direction of Q, and faces G will drive
flanks H, and yet another diameter of rolling circle may be used for
these faces and flanks. Here then it is shown that four different
diameters of rolling circles may be used upon a pair of wheels, giving
teeth-forms that will fill all the requirements so far as correctly
transmitting motion is concerned. In the case of a pair of wheels having
an equal number of teeth, so that each tooth on one wheel will always
fall into gear with the same tooth on the other wheel, every tooth may
have its individual curves differing from all the others, providing that
the corresponding teeth on the other wheel are formed to match them by
using the same size of rolling circle for each flank and face that work
together.
[Illustration: Fig. 34.]
[Illustration: Fig. 35.]
It is obvious, however, that such teeth would involve a great deal of
labor in their formation and would possess no advantage, hence they are
not employed. It is not unusual, however, in a pair of wheels that are
to gear together and that are not intended to interchange with other
wheels, to use such sizes as will give to for the face of the teeth on
the largest wheel of the pair and for the flanks of the teeth of the
smallest wheel, a generating circle equal in diameter to the radius of
the smallest wheel, and for the faces of the teeth of the small wheel
and the flanks of the teeth of the large one, a generating circle whose
diameter equals the radius of the large wheel.
[Illustration: Fig. 36.]
It will now be evident that if we have planned a pair or a train of
wheels we may find how many teeth will be in contact for any given
pitch, as follows. In Fig. 36 let A, B, and C, represent three blanks
for gear-wheels whose addendum circles are M, N and O; P representing
the pitch circles, and Q representing the circles for the roots of the
teeth. Let X and Y represent the lines of centres, and A, H, I and K the
generating or rolling circle, whose centres are on the respective lines
of centres--the diameter of the generating circle being equal to the
radius of the pinion, as in the Willis system, then, the pinion M being
the driver, and the wheels revolving in the direction denoted by the
respective arrows, the arc or path of contact for the first pair will be
from point D, where the generating circle G crosses circle N to E, where
generating circle H crosses the circle M, this path being composed of
two arcs of a circle. All that is necessary, therefore, is to set the
compasses to the pitch the teeth are to have and step them along these
arcs, and the number of steps will be the number of teeth that will be
in contact. Similarly, for the second pair contact will begin at R and
end at S, and the compasses applied as before (from R to S) along the
arc of generating circle I to the line of centres, and thence along the
arc of generating circle K to S, will give in the number of steps, the
number of teeth that will be in contact. If for any given purpose the
number of teeth thus found to be in contact is insufficient; the pitch
may be made finer.
[Illustration: Fig. 37.]
When a wheel is intended to be formed to work correctly with any other
wheel having the same pitch, or when there are more than two wheels in
the train, it is necessary that the same size of generating circle be
used for all the faces and all the flanks in the set, and if this be
done the wheels will work correctly together, no matter what the number
of the teeth in each wheel may be, nor in what way they are
interchanged. Thus in Fig. 37, let A represent the pitch line of a rack,
and B and C the pitch circles of two wheels, then the generating circle
would be rolled within B, as at 1, for the flank curves, and without it,
as at 2, for the face curves of B. It would be rolled without the pitch
line, as at 3, for the rack faces, and within it, as at 4, for the rack
flanks, and without C, as at 5, for the faces, and within it, as at 6,
for flanks of the teeth on C, and all the teeth will work correctly
together however they be placed; thus C might receive motion from the
rack, and B receive motion from C. Or if any number of different
diameters of wheels are used they will all work correctly together and
interchange perfectly, with the single condition that the same size of
generating circle be used throughout. But the curves of the teeth so
formed will not be alike. Thus in Fig. 38 are shown three teeth, all
struck with the same size of generating circle, D being for a wheel of
12 teeth, E for a wheel of 50 teeth, and F a tooth of a rack; teeth E,
F, being made wider so as to let the curves show clearly on each side,
it being obvious that since the curves are due to the relative sizes of
the pitch and generating circles they are equally applicable to any
pitch or thickness of teeth on wheels having the same diameters of pitch
circle.
[Illustration: Fig. 38.]
In determining the diameter of a generating circle for a set or train
of wheels, we have the consideration that the smaller the diameter of
the generating circle in proportion to that of the pitch circle the more
the teeth are spread at the roots, and this creates a pressure tending
to thrust the wheels apart, thus causing the axle journals to wear. In
Fig. 39, for example, A A is the line of centres, and the contact of the
curves at B C would cause a thrust in the direction of the arrows D, E.
This thrust would exist throughout the whole path of contact save at the
point F, on the line of centres. This thrust is reduced in proportion as
the diameter of the generating circle is increased; thus in Fig. 40, is
represented a pair of pinions of 12 teeth and 3 inch pitch, and C being
the driver, there is contact at E, and at G, and E being a radial line,
there is obviously a minimum of thrust.
[Illustration: Fig. 39.]
[Illustration: Fig. 40.]
What is known as the Willis system for interchangeable gearing, consists
of using for every pitch of the teeth a generating circle whose diameter
is equal to the radius of a pinion having 12 teeth, hence the pinion
will in each pitch have radial flanks, and the roots of the teeth will
be more spread as the number of teeth in the wheel is increased. Twelve
teeth is the least number that it is considered practicable to use;
hence it is obvious that under this system all wheels of the same pitch
will work correctly together.
[Illustration: Fig. 41.]
Unless the faces of the teeth and the flanks with which they work are
curves produced from the same size of generating circle, the velocity of
the teeth will not be uniform. Obviously the revolutions of the wheels
will be proportionate to their numbers of teeth; hence in a pair of
wheels having an equal number of teeth, the revolutions will per force
be equal, but the driver will not impart uniform motion to the driven
wheel, but each tooth will during the path of contact move irregularly.
The velocity of a pair of wheels will be uniform at each instant of
time, if a line normal to the surfaces of the curves at their point of
contact passes through the point of contact of the pitch circles on the
line of centres of the wheels. Thus in Fig. 41, the line A A is tangent
to the teeth curves where they touch, and D at a right angle to A A, and
meets it at the point of the tooth curves, hence it is normal to the
point of contact, and as it meets the pitch circles on the line of
centres the velocity of the wheels will be uniform.
The amount of rolling motion of the teeth one upon the other while
passing through the path of contact, will be a minimum when the tooth
curves are correctly formed according to the rules given. But
furthermore the sliding motion will be increased in proportion as the
diameter of the generating circle is increased, and the number of teeth
in contact will be increased because the arc, or path, of contact is
longer as the generating circle is made larger.
[Illustration: Fig. 42.]
Thus in Fig. 42 is a pair of wheels whose tooth curves are from a
generating circle equal to the radius of the wheels, hence the flanks
are radial. The teeth are made of unusual depth to keep the lines in the
engraving clear. Suppose V to be the driver, W the driven wheel or
follower, and the direction of motion as at P, contact upon tooth A will
begin at C, and while A is passing to the line of centres the path of
contact will pass along the thickened line to X. During this time the
whole length of face from C to R will have had contact with the length
of flank from C to N, and it follows that the length of face on A that
rolled on C N can only equal the length of C N, and that the amount of
sliding motion must be represented by the length of R N on A, and the
amount of rolling motion by the length N C. Again, during the arc of
recess (marked by dots) the length of flank that will have had contact
is the depth from S to Ls, and over this depth the full length of tooth
face on wheel V will have swept, and as L S equals C N, the amount of
rolling and of sliding motion during the arc of recess is equal to that
during the arc of approach, and the action is in both cases partly a
rolling and partly a sliding one. The two wheels are here shown of the
same diameter, and therefore contain an equal number of teeth, hence the
arcs of approach and of recess are equal in length, which will not be
the case when one wheel contains more teeth than the other. Thus in Fig.
43, let A represent a segment of a pinion, and B a segment of a
spur-wheel, both segments being blank with their pitch circles, the
tooth height and depth being marked by arcs of circles. Let C and D
represent the generating circles shown in the two respective positions
on the line of centres. Let pinion A be the driver moving in the
direction of P, and the arc of approach will be from E to X along the
thickened arc, while the arc of recess will be as denoted by the dotted
arc from X to F. The distance E X being greater than distance X F,
therefore the arc of approach is longer than that of recess.
But suppose B to be the driver and the reverse will be the case, the arc
of approach will begin at G and end at X, while the arc of recess will
begin at X and end at H, the latter being farther from the line of
centres than G is. It will be found also that, one wheel being larger
than the other, the amount of sliding and rolling contact is different
for the two wheels, and that the flanks of the teeth on the larger wheel
B, have contact along a greater portion of their depths than do the
flanks of those on the smaller, as is shown by the dotted arc I being
farther from the pitch circle than the dotted arc J is, these two dotted
arcs representing the paths of the lowest points of flank contact,
points F and G, marking the initial lowest contact for the two
directions of revolution.
[Illustration: Fig. 43.]
Thus it appears that there is more sliding action upon the teeth of the
smaller than upon those of the larger wheel, and this is a condition
that will always exist.
In Fig. 44 is represented portion of a pair of wheels corresponding to
those shown in Fig. 42, except that in this case the diameter of the
generating circle is reduced to one quarter that of the pitch diameter
of the wheels. V is the driver in the direction the teeth of V that
will have contact is C N, which, the wheels, being of equal diameter,
will remain the same whichever wheel be the driver, and in whatever
direction motion occurs. The amount of rolling motion is, therefore, C
N, and that of sliding is the difference between the distance C N and
the length of the tooth face.
[Illustration: Fig. 44.]
If now we examine the distance C N in Fig. 42, we find that reducing the
diameter of generating circle in Fig. 44 has increased the depth of
flank that has contact, and therefore increased the rolling motion of
the tooth face along the flank, and correspondingly diminished the
sliding action of the tooth contact. But at the same time we have
diminished the number of teeth in contact. Thus in Fig. 42 there are
three teeth in driving contact, while in Fig. 44 there are but two,
viz., D and E.
[Illustration: Fig. 45.]
In an article by Professor Robinson, attention is called to the fact
that if the teeth of wheels are not formed to have correct curves when
new, they cannot be improved by wear; and this will be clearly perceived
from the preceding remarks upon the amount of rolling and sliding
contact. It will also readily appear that the nearer the diameter of the
generating to that of the base circle the more the teeth wear out of
correct shape; hence, in a train of gearing in which the generating
circle equals the radius of the pinion, the pinion will wear out of
shape the quickest, and the largest wheel the least; because not only
does each tooth on the pinion more frequently come into action on
account of its increased revolutions, but furthermore the length of
flank that has contact is less, while the amount of sliding action is
greater. In Fig. 45, for example, are a wheel and pinion, the latter
having radial flanks and the pinion being the driver, the arc of
approach is the thickened arc from C to the line of centres, while the
arc of recess is denoted by the dotted arc. As contact on the pinion
flank begins at point C and ends at the line of centres, the total depth
of flank that suffers wear from the contact is that from C to N; and as
the whole length of the wheel tooth face sweeps over this depth C N, the
pinion flanks must wear faster than the wheel faces, and the pinion
flanks will wear underneath, as denoted by the dotted curve on the
flanks of tooth W. In the case of the wheel, contact on its tooth flanks
begins at the line of centres and ends at L, hence that flank can only
wear between point L and the pitch line L; and as the whole length of
pinion face sweeps on this short length L S, the pinion flank will wear
most, the wear being in the direction of the dotted arc on the left-hand
side V of the tooth. Now the pinion flank depth C N, being less than the
wheel flank depth S L, and the same length of tooth face sweeping
(during the path of contact) over both, obviously the pinion tooth will
wear the most, while both will, as the wear proceeds, lose their proper
flank curve. In Fig. 46 the generating arcs, G and G´, and the wheel are
the same, but the pinion is larger. As a result the acting length C N,
of pinion flank is increased, as is also the acting length S L, of wheel
flank; hence, the flanks of both wheels would wear better, and also
better preserve their correct and original shapes.
It has been shown, when referring to Figs. 42 and 44, when treating of
the amount of sliding and of rolling motion, that the smaller the
diameter of rolling circle in proportion to that of pitch circle, the
longer the acting length of flank and the more the amount of rolling
motion; and it follows that the teeth would also preserve their original
and true shape better. But the wear of the teeth, and the alteration of
tooth form by reason of that wear, will, in any event, be greater upon
the pinion than upon the wheel, and can only be equal when the two
wheels are of equal diameter, in which case the tooth curves will be
alike on both wheels, and the acting depths of flank will be equal, as
shown in Fig. 47, the flanks being radial, and the acting depths of
flank being shown at J K. In Fig. 48 is shown a pair of wheels with a
generating circle, G and G´, of one quarter the diameter of the base
circle or pitch diameter, and the acting length of flank is shown at L
M. The wear of the teeth would, therefore, in this latter case, cause it
in time to assume the form shown in Fig. 49. But it is to be noted that
while the acting depth of flank has been increased the arcs of contact
have been diminished, and that in Fig. 47 there are two teeth in
contact, while in Fig. 48 there is but one, hence the pressure upon each
tooth is less in proportion as the diameter of the generating circle is
increased. If a train of wheels are to be constructed, or if the wheels
are to be capable of interchanging with other combinations of wheels of
the same pitch, the diameter of the generating circle must be equal to
the smallest wheel or pinion, which is, under the Willis system, a
pinion of 12 teeth; under the Pratt and Whitney, and Brown and Sharpe
systems, a pinion of 15 teeth.
[Illustration: Fig. 46.]
[Illustration: Fig. 47.]
But if a pair or a particular train of gears are to be constructed, then
a diameter of generating circle may be selected that is considered most
suitable to the particular conditions; as, for example, it may be equal
to the radius of the smallest wheel giving it radial flanks, or less
than that radius giving parallel or spread flanks. But in any event, in
order to transmit continuous motion, the diameter of generating circle
must be such as to give arcs of action that are equal to the pitch, so
that each pair of teeth will come into action before the preceding pair
have gone out of action.
[Illustration: Fig. 48.]
It may now be pointed out that the degrees of angle that the teeth move
through always exceeds the number of degrees of angle contained in the
paths of contact, or, in other words, exceeds the degrees contained in
the arcs of approach and recess combined.
[Illustration: Fig. 49.]
In Fig. 50, for example, are a wheel A and pinion B, the teeth on the
wheel being extended to a point. Suppose that the wheel A is the driver,
and contact will begin between the two teeth D and F on the dotted arc.
Now suppose tooth D to have moved to position C, and F will have been
moved to position H. The degrees of angle the pinion has been moved
through are therefore denoted by I, whereas the degrees of angle the
arcs of contact contain are therefore denoted by J.
The degrees of angle that the wheel A has moved through are obviously
denoted by E, because the point of tooth D has during the arcs of
contact moved from position D to position C. The degrees of angle
contained in its path of contact are denoted by K, and are less than E,
hence, in the case of teeth terminating in a point as tooth D, the
excess of angle of action over path of contact is as many degrees as are
contained in one-half the thickness of the tooth, while when the points
of the teeth are cut off, the excess is the number of degrees contained
in the distance between the corner and the side of the tooth as marked
on a tooth at P.
[Illustration: Fig. 50.]
With a given diameter of pitch circle and pitch diameter of wheel, the
length of the arc of contact will be influenced by the height of the
addendum from the pitch circle, because, as has been shown, the arcs of
approach and of recess, respectively, begin and end on the addendum
circle.
If the height of the addendum on the follower be reduced, the arc of
approach will be reduced, while the arc of recess will not be altered;
and if the follower have no addendum, contact between the teeth will
occur on the arc of recess only, which gives a smoother motion, because
the action of the driver is that of dragging rather than that of pushing
the follower. In this case, however, the arc of recess must, to produce
continuous motion, be at least equal to the pitch.
It is obvious, however, that the follower having no addendum would, if
acting as a driver to a third wheel, as in a train of wheels, act on its
follower, or the fourth wheel of the train, on the arc of approach only;
hence it follows that the addendum might be reduced to diminish, or
dispensed with to eliminate action, on the arc of approach in the
follower of a pair of wheels only, and not in the case of a train of
wheels.
To make this clear to the reader it may be necessary to refer again to
Fig. 33 or 34, from which it will be seen that the action of the teeth
of the driver on the follower during the arc of approach is produced by
the flanks of the driver on the faces of the follower. But if there are
no such faces there can be no such contact.
On the arc of recess, however, the faces of the driver act on the flanks
of the follower, hence the absence of faces on the follower is of no
import.
From these considerations it also appears that by giving to the driver
an increase of addendum the arc of recess may be increased without
affecting the arc of approach. But the height of addendum in machinists'
practice is made a constant proportion of the pitch, so that the wheel
may be used indiscriminately, as circumstances may require, as either a
driver or a follower, the arcs of approach and of recess being equal.
The height of addendum, however, is an element in determining the number
of teeth in contact, and upon small pinions this is of importance.
[Illustration: Fig. 51.]
In Fig. 51, for example, is shown a section of two pinions of equal
diameters, and it will be observed that if the full line A determined
the height of the addendum there would be contact either at C or B only
(according to the direction in which the motion took place).
With the addendum extended to the dotted circle, contact would be just
avoided, while with the addendum extended to D there would be contact
either at E or at F, according to which direction the wheel had motion.
This, by dividing the strain over two teeth instead of placing it all
upon one tooth, not only doubles the strength for driving capacity, but
decreases the wear by giving more area of bearing surface at each
instant of time, although not increasing that area in proportion to the
number of teeth contained in the wheel.
In wheels of larger diameter, short teeth are more permissible, because
there are more teeth in contact, the number increasing with the
diameters of the wheels. It is to be observed, however, that from having
radial flanks, the smallest wheel is always the weakest, and that from
making the most revolutions in a given time, it suffers the most from
wear, and hence requires the greatest attainable number of teeth in
constant contact at each period of time, as well as the largest possible
area of bearing or wearing surface on the teeth.
It is true that increasing the "depth of tooth to pitch line" increases
the whole length of tooth, and, therefore, weakens it; but this is far
more than compensated for by distributing the strain over a greater
number of teeth. This is in practice accomplished, _when circumstances
will permit_, by making the pitch finer, giving to a wheel, of a given
diameter, a greater number of teeth.
[Illustration: Fig. 52.]
When the wheels are required to transmit motion rather than power (as in
the case of clock wheels), to move as frictionless as possible, and to
place a minimum of thrust on the journals of the shafts of the wheels,
the generating circle may be made nearly as large as the diameter of the
pitch circle, producing teeth of the form shown in Fig. 52. But the
minimum of friction is attained when the two flanks for the tooth are
drawn into one common hypocycloid, as in Fig. 53. The difference between
the form of tooth shown in Fig. 52 and that shown in Fig. 53, is merely
due to an increase in the diameter of the generating circle for the
latter. It will be observed that in these forms the acting length of
flank diminishes in proportion as the diameter of the generating circle
is increased, the ultimate diameter of generating circle being as large
as the pitch circles.
[Illustration: Fig. 53.]
[1]This form is undesirable in that there is contact on one side only
(on the arc of approach) of the line of centres, but the flanks of the
teeth may be so modified as to give contact on the arc of recess also,
by forming the flanks as shown in Fig. 54, the flanks, or rather the
parts within the pitch circles, being nearly half circles, and the parts
without with peculiarly formed faces, as shown in the figure. The pitch
circles must still be regarded as the rolling circles rolling upon each
other. Suppose _b_ a tracing point on B, then as B rolls on A it will
describe the epicycloid _a_ _b_. A parallel line _c_ _d_ will work at a
constant distance as at _c_ _d_ from _a_ _b_, and this distance may be
the radius of that part of D that is within the pitch line, the same
process being applied to the teeth on both wheels. Each tooth is thus
composed of a spur based upon a half cylinder.
[1] From an article by Professor Robinson.
[Illustration: Fig. 54.]
Comparing Figs. 53 and 54, we see that the bases in 53 are flattest, and
that the contact of faces upon them must range nearer the pitch line
than in 54. Hence, 53 presents a more favorable obliquity of the line of
direction of the pressures of tooth upon tooth. In seeking a still more
favorable direction by going outside for the point of contact, we see by
simply recalling the method of generating the tooth curves, that tooth
contacts outside the pitch lines have no possible existence; and hence,
Fig. 53 may be regarded as representing that form of toothed gear which
will operate with less friction than any other known form.
[Illustration: Fig. 55.]
This statement is intended to cover fixed teeth only, and not that
complicated form of the trundle wheel in which the cylinder teeth are
friction rollers. No doubt such would run still easier, even with their
necessary one-sided contacts. Also, the statement is supposed to be
confined to such forms of teeth as have good practical contacts at and
near the line of centres.
Bevel-gear wheels are employed to transmit motion from one shaft to
another when the axis of one is at an angle to that of the other. Thus
in Fig. 55 is shown a pair of bevel-wheels to transmit motion from
shafts at a right angle. In bevel-wheels all the lines of the teeth,
both at the tops or points of the teeth, at the bottoms of the spaces,
and on the sides of the teeth, radiate from the centre E, where the axes
of the two shafts would meet if produced. Hence the depth, thickness,
and height of the tooth decreases as the point E is approached from the
diameter of the wheel, which is always measured on the pitch circle at
the largest end of the cone, or in other words, at the largest pitch
diameter.
The principles governing the practical construction of the curves for
the teeth of the bevel-wheels may be explained as follows:--
In Fig. 56 let F and G represent two shafts, rotating about their
respective axes; and having cones whose greatest diameters are at A and
B, and whose points are at E. The diameter A being equal to that of B
their circumferences will be equal, and the angular and velocity ratios
will therefore be equal.
[Illustration: Fig. 56.]
Let C and D represent two circles about the respective cones, being
equidistant from E, and therefore of equal diameters and circumferences,
and it is obvious that at every point in the length of each cone the
velocity will be equal to a point upon the other so long as both points
are equidistant from the points of intersection of the axes of the two
shafts; hence if one cone drive the other by frictional contact of
surfaces, both shafts will be rotated at an equal speed of rotation, or
if one cone be fixed and the other moved around it, the contact of the
surfaces will be a rolling contact throughout. The line of contact
between the two cones will be a straight line, radiating at all times
from the point E. If such, however, is not the case, then the contact
will no longer be a rolling one. Thus, in Fig. 57 the diameters or
circumferences at A and B being equal, the surfaces would roll upon each
other, but on account of the line of contact not radiating from E (which
is the common centre of motion for the two shafts) the circumference C
is less than that of D, rendering a rolling contact impossible.
[Illustration: Fig. 57.]
We have supposed that the diameters of the cones be equal, but the
conditions will remain the same when their diameters are unequal; thus,
in Fig. 58 the circumference of A is twice that of B, hence the latter
will make two rotations to one of the former, and the contact will still
be a rolling one. Similarly the circumference of D is one half that of
C, hence D will also make two rotations to one of C, and the contact
will also be a rolling one; a condition which will always exist
independent of the diameters of the wheels so long as the angles of the
faces, or wheels, or (what is the same thing, the line of contact
between the two,) radiates from the point E, which is located where the
axes of the shafts would meet.
[Illustration: Fig. 58.]
[Illustration: Fig. 59.]
The principles governing the forms of the cones on which the teeth are
to be located thus being explained, we may now consider the curves of
the teeth. Suppose that in Fig. 59 the cone A is fixed, and that the
cone whose axis is F be rotated upon it in the direction of the arrow.
Then let a point be fixed in any part of the circumference of B (say at
_d_), and it is evident that the path of this point will be as B rolls
around the axis F, and at the same time around A from the centre of
motion, E. The curve so generated or described by the point _d_ will be
a spherical epicycloid. In this case the exterior of one cone has rolled
upon the coned surface of the other; but suppose it rolls upon the
interior, as around the walls of a conical recess in a solid body; then
a point in its circumference would describe a curve known as the
spherical hypocycloid; both curves agreeing (except in their spherical
property) to the epicycloid and hypocycloid of the spur-wheel. But this
spherical property renders it very difficult indeed to practically
delineate or mark the curves by rolling contact, and on account of this
difficulty Tredgold devised a method of construction whereby the curves
may be produced sufficiently accurate for all practical purposes, as
follows:--
[Illustration: Fig. 60.]
In Fig. 60 let A A represent the axis of one shaft, and B the axis of
the other, the axes of the two meeting at W. Mark E, representing the
diameter of one wheel, and F that of the other (both lines representing
the pitch circles of the respective wheels). Draw the line G G passing
through the point W, and the point T, where the pitch circles E, F meet,
and G G will be the line of contact between the cones. From W as a
centre, draw on each side of G G dotted lines as _p_, representing the
height of the teeth above and below the pitch line G G. At a right angle
to G G mark the line J K, and from the junction of this line with axis B
(as at Q) as a centre, mark the arc _a_, which will represent the pitch
circle for the large diameter of pinion D; mark also the arc _b_ for the
addendum and _c_ for the roots of the teeth, so that from _b_ to _c_
will represent the height of the tooth at that end.
[Illustration: Fig. 61.]
Similarly from P, as a centre, mark (for the large diameter of wheel C,)
the pitch circle _g_, root circle _h_, and addendum _i_. On these arcs
mark the curves in the same manner as for spur-wheels. To obtain these
arcs for the small diameters of the wheels, draw M M parallel to J K.
Set the compasses to the radius R L, and from P, as a centre, draw the
pitch circle _k_. To obtain the depth for the tooth, draw the dotted
line _p_, meeting the circle _h_, and the point W. A similar line from
circle _i_ to W will show the height of the addendum, or extreme
diameter; and mark the tooth curves on _k_, _l_, _m_, in the same manner
as for a spur-wheel.
Similarly for the pitch circle of the small end of the pinion teeth, set
the compasses to the radius S L, and from Q as a centre, mark the pitch
circle _d_, outside of _d_ mark _e_ for the height of the addendum and
inside of _d_ mark _f_ for the roots of the teeth at that end. The
distance between the dotted lines (as _p_) represents the full height of
the teeth, hence _h_ meets line _p_, being the root of tooth for the
large wheel, and to give clearance, the point of the pinion teeth is
marked below, thus arc _b_ does not meet _h_ or _p_. Having obtained
these arcs the curves are rolled as for a spur-wheel.
A tooth thus marked out is shown at _x_, and from its curves between _b_
_c_, a template for the large diameter of the pinion tooth may be made,
while from the tooth curves between the arcs _e_ _f_, a template for the
smallest tooth diameter of the pinion can be made.
Similarly for the wheel C the outer end curves are marked on the lines
_g_, _h_, _i_, and those for the inner end on the lines _k_, _l_, _m_.
[Illustration: Fig. 62.]
Internal or annular gear-wheels have their tooth curves formed by
rolling the generating circle upon the pitch circle or base circle, upon
the same general principle as external or spur-wheels. But the tooth of
the annular wheel corresponds with the space in the spur-wheel, as is
shown in Fig. 61, in which curve A forms the flank of a tooth on a
spur-wheel P, and the face of a tooth on the annular wheel W. It is
obvious then that the generating circle is rolled within the pitch
circle for the face of the wheel and without for its flank, or the
reverse of the process for spur-wheels. But in the case of internal or
annular wheels the path of contact of tooth upon tooth with a pinion
having a given number of teeth increases in proportion as the number of
teeth in the wheel is diminished, which is also the reverse of what
occurs in spur-wheels; as will readily be perceived when it is
considered that if in an internal wheel the pinion have as many teeth as
the wheel the contact would exist around the whole pitch circles of the
wheel and pinion and the two would rotate together without any motion of
tooth upon tooth. Obviously then we have, in the case of internal
wheels, a consideration as to what is the greatest number (as well as
what is the least number) of teeth a pinion may contain to work with a
given wheel, whereas in spur-wheels the reverse is again the case, the
consideration being how few teeth the wheel may contain to work with a
given pinion. Now it is found that although the curves of the teeth in
internal wheels and pinions may be rolled according to the principles
already laid down for spur-wheels, yet cases may arise in which internal
gears will not work under conditions in which spur-wheels would work,
because the internal wheels will not engage together. Thus, in Fig. 62,
is a pinion of 12 teeth and a wheel of 22 teeth, a generating circle
having a diameter equal to the radius of the pinion having been used for
all the tooth curves of both wheel and pinion. It will be observed that
teeth A, B, and C clearly overlap teeth D, E, and F, and would therefore
prevent the wheels from engaging to the requisite depth. This may of
course be remedied by taking the faces off the pinion, as in Fig. 63,
and thus confining the arc of contact to an arc of recess if the pinion
drives, or an arc of approach if the wheel drives; or the number of
teeth in the pinion may be reduced, or that in the wheel increased;
either of which may be carried out to a degree sufficient to enable the
teeth to engage and not interfere one with the other. In Fig. 64 the
number of teeth in the pinion P is reduced from 12 to 6, the wheel W
having 22 as before, and it will be observed that the teeth engage and
properly clear each other.
[Illustration: Fig. 63.]
By the introduction into the figure of a segment of a spur-wheel also
having 22 teeth and placed on the other side of the pinion, it is shown
that the path of contact is greater, and therefore the angle of action
is greater, in internal than in spur gearing. Thus suppose the pinion to
drive in the direction of the arrows and the thickened arcs A B will be
the arcs of approach, A measuring longer than B. The dotted arcs C D
represent the arcs of receding contact and C is found longer than D, the
angles of action being 66° for the spur-wheels and 72° for the annular
wheel.
On referring again to Fig. 62 it will be observed that it is the faces
of the teeth on the two wheels that interfere and will prevent them from
engaging, hence it will readily occur to the mind that it is possible to
form the curves of the pinion faces correct to work with the faces of
the wheel teeth as well as with the flanks; or it is possible to form
the wheel faces with curves that will work correctly with the faces, as
well as with the flanks of the pinion teeth, which will therefore
increase the angle of action, and Professor McCord has shown in an
article in the London _Engineering_ how to accomplish this in a simple
and yet exceedingly ingenious manner which may be described as
follows:--
[Illustration: Fig. 64.]
It is required to find a describing circle that will roll the curves for
the flanks of the pinion and the faces of the wheels, and also a
describing circle for the flanks of the wheel and the faces of the
pinion; the curve for the wheel faces to work correctly with the faces
as well as with the flanks of the pinion, and the curve for the pinion
faces to work correctly with both the flanks and faces of the internal
wheel.
[Illustration: Fig. 65.]
[Illustration: Fig. 66.]
In Fig. 65 let P represent the pitch circle of an annular or internal
wheel whose centre is at A, and Q the pitch circle of a pinion whose
centre is at B, and let R be a describing circle whose centre is at C,
and which is to be used to roll all the curves for the teeth. For the
flanks of the annular wheel we may roll R within P, while for the faces
of the wheel we may roll R outside of P, but in the case of the pinion
we cannot roll R within Q, because R is larger than Q, hence we must
find some other rolling circle of less diameter than R, and that can be
used in its stead (the radius of R always being greater than the radius
of the axis of the wheel and pinion for reasons that will appear
presently). Suppose then that in Fig. 66 we have a ring whose bore R
corresponds in diameter to the intermediate describing circle R, Fig. 65
and that Q represents the pinion. Then we may roll R around and in
contact with the pinion Q, and a tracing point in R will trace the curve
M N O, giving a curve a portion of which may be used for the faces of
the pinion. But suppose that instead of rolling the intermediate
describing circle R around P, we roll the circle T around P, and it will
trace precisely the same curve M N O; hence for the faces of the pinion
we have found a rolling circle T which is a perfect substitute for the
intermediate circle Q, and which it will always be, no matter what the
diameters of the pinion and of the intermediate describing circle may
be, providing that the diameter of T is equal to the difference between
the diameters of the pinion and that of the intermediate describing
circle as in the figure. If now we use this describing circle to roll
the flanks of the annular wheel as well as the faces of the pinion,
these faces and flanks will obviously work correctly together. Since
this describing circle is rolled on the outside of the pinion and on the
outside of the annular wheel we may distinguish it as the exterior
describing circle.
[Illustration: Fig. 67.]
Now instead of rolling the intermediate describing circle R within the
annular wheel P for the face curves of the teeth upon P, we may find
some other circle that will give the same curve and be small enough to
be rolled within the pinion Q for its teeth flanks. Thus in Fig. 67 P
represents the pitch circle of the annular wheel and R the intermediate
circle, and if R be rolled within P, a point on the circumference of R
will trace the curve V W. But if we take the circle S, having a diameter
equal to the difference between the diameter of R and that of P, and
roll it within P, a point in its circumference will trace the same curve
V W; hence S is a perfect substitute for R, and a portion of the curve V
W may be used for the faces of the teeth on the annular wheel. The
circle S being used for the pinion flanks, the wheel faces and pinion
flanks will work correctly together, and as the circle S is rolled
within the pinion for its flanks and within the wheel for its faces, it
may be distinguished as the interior describing circle.
To prove the correctness of the construction it may be noted that with
the particular diameter of intermediate describing circle used in Fig.
65, the interior and exterior describing circles are of equal diameters;
hence, as the same diameter of describing circle is used for all the
faces and flanks of the pair of wheels they will obviously work
correctly together, in accordance with the rules laid down for spur
gearing. The radius of S in Fig. 69 is equal to the radius of the
annular wheel, less the radius of the intermediate circle, or the radius
from A to C. The radius of the exterior describing circle T is the
radius of the intermediate circle less the radius of the pinion, or
radius C B in the figure.
[Illustration: Fig. 68.]
[Illustration: Fig. 69.]
Now the diameter of the intermediate circle may be determined at will,
but cannot exceed that of the annular wheel or be less than the pinion.
But having been selected between these two limits the interior and
exterior describing circles derived from it give teeth that not only
engage properly and avoid the interference shown in Fig. 62, but that
will also have an additional arc of action during the recess, as is
shown in Fig. 68, which represents the wheel and pinion shown in Fig.
62, but produced by means of the interior and exterior describing
circles. Supposing the pinion to be the driver the arc of approach will
be along the thickened arc of the interior describing circle, while
during the arc of recess there will be an arc of contact along the
dotted portion of the exterior describing circle as in ordinary gearing.
But in addition there will be an arc of recess along the dotted portion
of the intermediate circle R, which arc is due to the faces of the
pinion acting upon the faces as well as upon the flanks of the wheel
teeth. It is obvious from this that as soon as a tooth passes the line
of centres it will, during a certain period, have two points of contact,
one on the arc of the exterior describing circle, and another along the
arc of R, this period continuing until the addendum circle of the pinion
crosses the dotted arc of the exterior describing circle at Z.
The diameters of the interior and exterior describing circles obviously
depend upon the diameter of the intermediate circle, and as this may, as
already stated, be selected, within certain limits, at will, it is
evident that the relative diameters of the interior and exterior
describing circles will vary in proportion, the interior becoming
smaller and the exterior larger, while from the very mode of
construction the radius of the two will equal that of the axes of the
wheel and pinion. Thus in Fig. 69 the radii of S, T, equal A B, or the
line of centres, and their diameters, therefore, equal the radius of the
annular wheel, as is shown by dotting them in at the upper half of the
figure. But after their diameters have been determined by this
construction either of them may be decreased in diameter and the teeth
of the wheels will clear (and not interfere as in Fig. 62), but the
action will be the same as in ordinary gear, or in other words there
will be no arc of action on the circle R. But S cannot be increased
without correspondingly decreasing T, nor can T be increased without
correspondingly decreasing S.
[Illustration: Fig. 70.]
Fig. 70 shows the same pair of gears as in Fig. 68 (the wheel having 22
and the pinion 12 teeth), the diameter of the intermediate circle having
been enlarged to decrease the diameter of S and increase that of T, and
as these are left of the diameter derived from the construction there is
receding action along R from the line of centres to T.
[Illustration: Fig. 71.]
In Fig. 71 are represented a wheel and pinion, the pinion having but
four teeth less than the wheel, and a tooth, J, being shown in position
in which it has contact at two places. Thus at _k_ it is in contact with
the flank of a tooth on the annular wheel, while at L it is in contact
with the face of the same tooth.
As the faces of the teeth on the wheel do not have contact higher than
point _t_, it is obvious that instead of having them 3/10 of the pitch
as at the bottom of the figure, we may cut off the portion X without
diminishing the arc of contact, leaving them formed as at the top of the
figure. These faces being thus reduced in height we may correspondingly
reduce the depth of flank on the pinion by filling in the portion G,
leaving the teeth formed as at the top of the pinion. The teeth faces of
the wheel being thus reduced we may, by using a sufficiently large
intermediate circle, obtain interior and exterior describing circles
that will form teeth that will permit of the pinion having but one tooth
less than the wheel, or that will form a wheel having but one tooth more
than the pinion.
The limits to the diameter of the intermediate describing circle are as
follows: in Fig. 72 it is made equal in diameter to the pitch diameter
of the pinion, hence B will represent the centre of the intermediate
circle as well as of the pinion, and the pitch circle of the pinion will
also represent the intermediate circle R. To obtain the radius for the
interior describing circle we subtract the radius of the intermediate
circle from the radius of the annular wheel, which gives A P, hence the
pitch circle of the pinion also represents the interior circle R. But
when we come to obtain the radius for the exterior describing circle
(T), by subtracting the radius of the pinion from that of the
intermediate circle, we find that the two being equal give O for the
radius of (T), hence there could be no flanks on the pinion.
[Illustration: Fig. 72.]
Now suppose that the intermediate circle be made equal in diameter to
the pitch circle of the annular wheel, and we may obtain the radius for
the exterior describing circle T; by subtracting the radius of the
pinion from that of the intermediate circle, we shall obtain the radius
A B; hence the radius of (T) will equal that of the pinion. But when we
come to obtain the radius for the interior describing circle by
subtracting the radius of the intermediate circle from that of the
annular wheel, we find these two to be equal, hence there would be no
interior describing circle, and, therefore, no faces to the pinion.
[Illustration: Fig. 73.]
The action of the teeth in internal wheels is less a sliding and more a
rolling one than that in any other form of toothed gearing. This may be
shown as follows: In Fig. 73 let A A represent the pitch circle of an
external pinion, and B B that of an internal one, and P P the pitch
circle of an external wheel for A A or an internal one for B B, the
point of contact at the line of centres being at C, and the direction of
rotation P P being as denoted by the arrow; the two pinions being
driven, we suppose a point at C, on the pitch circle P P, to be
coincident with a point on each of the two pinions at the line of
centres. If P P be rotated so as to bring this point to the position
denoted by D, the point on the external pinion having moved to E, while
that on the internal pinion has moved to F, both having moved through an
arc equal to C D, then the distance from E to D being greater than from
D to F, more sliding motion must have accompanied the contact of the
teeth at the point E than at the point F; and the difference in the
length of the arc E D and that of F D, may be taken to represent the
excess of sliding action for the teeth on E; for whatever, under any
given condition, the amount of sliding contact may be, it will be in the
proportion of the length of E D to that of F D. Presuming, then, that
the amount of power transmitted be equal for the two pinions, and the
friction of all other things being equal--being in proportion to the
space passed (or in this case slid) over--it is obvious that the
internal pinion has the least friction.
CHAPTER II.--THE TEETH OF GEAR-WHEELS.--CAMS.
WHEEL AND TANGENT SCREW OR WORM AND WORM GEAR.
In Fig. 74 are shown a worm and worm gear partly in section on the line
of centres. The worm or tangent screw W is simply one long tooth wound
around a cylinder, and its form may be determined by the rules laid down
for a rack and pinion, the tangent screw or worm being considered as a
rack and the wheel as an ordinary spur-wheel.
[Illustration: Fig. 74.]
Worm gearing is employed for transmitting motion at a right angle, while
greatly reducing the motion. Thus one rotation of the screw will rotate
the wheel to the amount of the pitch of its teeth only. Worm gearing
possesses the qualification that, unless of very coarse pitch, the worm
locks the wheel in any position in which the two may come to a state of
rest, while at the same time the excess of movement of the worm over
that of the wheel enables the movement of the latter, through a very
minute portion of a revolution. And it is evident that, when the plane
of rotation of the worm is at a right angle to that of the wheel, the
contact of the teeth is wholly a sliding one. The wear of the worm is
greater than that of the wheel, because its teeth are in continuous
contact, whereas the wheel teeth are in contact only when passing
through the angle of action. It may be noted, however, that each tooth
upon the worm is longer than the teeth on the wheel in proportion as the
circumference of the worm is to the length of wheel tooth.
[Illustration: Fig. 75.]
If the teeth of the wheel are straight and are set at an angle equal to
the angle of the worm thread to its axis, as in Fig. 75, P P
representing the pitch line of the worm, C D the line of centres, and
_d_ the worm axis, the contact of tooth upon tooth will be at the centre
only of the sides of the wheel teeth. It is generally preferred,
however, to have the wheel teeth curved to envelop a part of the
circumference of the worm, and thus increase the line of contact of
tooth upon tooth, and thereby provide more ample wearing surface.
[Illustration: Fig. 76.]
In this case the form of the teeth upon the worm wheel varies at every
point in its length as the line of centres is departed from. Thus in
Fig. 76 is shown an end view of a worm and a worm gear in section, _c_
_d_ being the line of centres, and it will be readily perceived that the
shape of the teeth if taken on the line _e_ _f_, will differ from that
on the line of centres _c_ _d_; hence the form of the wheel teeth must,
if contact is to occur along the full length of the tooth, be conformed
to fit to the worm, which may be done by taking a series of section of
the worm thread at varying distances from, and parallel to, the line of
centres and joining the wheel teeth to the shape so obtained. But if the
teeth of the wheel are to be cut to shape, then obviously a worm may be
provided with teeth (by serrating it along its length) and mounted in
position upon the wheel so as to cut the teeth of the wheel to shape as
the worm rotates. The pitch line of the wheel teeth, whether they be
straight and are disposed at an angle as in Fig. 75, or curved as in
Fig. 76, is at a right angle to the line of centres _c_ _d_, or in other
words in the plane of _g_ _h_, in Fig. 76. This is evident because the
pitch line must be parallel to the wheel axis, being at an equal radius
from that axis, and therefore having an equal velocity of rotation at
every point in the length of the pitch line of the wheel tooth.
If we multiply the number of teeth by their pitch to obtain the
circumference of the pitch circle we shall obtain the circumference due
to the radius of _g_ _h_, from the wheel axis, and so long as _g_ _h_ is
parallel to the wheel axis we shall by this means obtain the same
diameter of pitch circle, so long as we measure it on a line parallel to
the line of centres _c_ _d_. The pitch of the worm is the same at
whatever point in the tooth depth it may be measured, because the teeth
curves are parallel one to the other, thus in Fig. 77 the pitch measures
are equal at _m_, _n_, or _o_.
But the action of the worm and wheel will nevertheless not be correct
unless the pitch line from which the curves were rolled coincides with
the pitch line of the wheel on the line of centres, for although, if the
pitch lines do not so coincide, the worm will at each revolution move
the pitch line of the wheel through a distance equal to the pitch of the
worm, yet the motion of the wheel will not be uniform because,
supposing the two pitch lines not to meet, the faces of the pinion teeth
will act against those of the wheel, as shown in Fig. 78, instead of
against their flanks, and as the faces are not formed to work correctly
together the motion will be irregular.
[Illustration: Fig. 77.]
The diameter of the worm is usually made equal to four times the pitch
of the teeth, and if the teeth are curved as in figure 76 they are made
to envelop not more than 30° of the worm.
The number of teeth in the wheel should not be less than thirty, a
double worm being employed when a quicker ratio of wheel to worm motion
is required.
[Illustration: Fig. 78.]
[Illustration: Fig. 79.]
When the teeth of the wheel are curved to partly envelop the worm
circumference it has been found, from experiments made by Robert Briggs,
that the worm and the wheel will be more durable, and will work with
greatly diminished friction, if the pitch line of the worm be located to
increase the length of face and diminish that of the flank, which will
decrease the length of face and increase the length of flank on the
wheel, as is shown in Fig. 79; the location for the pitch line of the
worm being determined as follows:--
[Illustration: Fig. 80.]
The full radius of the worm is made equal to twice the pitch of its
teeth, and the total depth of its teeth is made equal to .65 of its
pitch. The pitch line is then drawn at a radius of 1.606 of the pitch
from the worm axis. The pitch line is thus determined in Fig. 76, with
the result that the area of tooth face and of worm surface is equalized
on the two sides of the pitch line in the figure. In addition to this,
however, it may be observed that by thus locating the pitch line the
arcs both of approach and of recess are altered. Thus in Fig. 80 is
represented the same worm and wheel as in Fig. 79, but the pitch lines
are here laid down as in ordinary gearing. In the two figures the arcs
of approach are marked by the thickened part of the generating circle,
while the arcs of recess are denoted by the dotted arc on the generating
circle, and it is shown that increasing the worm face, as in Fig. 79,
increases the arc of recess, while diminishing the worm flank diminishes
the arc of approach, and the action of the worm is smoother because the
worm exerts more pulling than pushing action, it being noted that the
action of the worm on the wheel is a pushing one before reaching, and a
pulling one after passing, the line of centres.
[Illustration: Fig. 81.]
It may here be shown that a worm-wheel may be made to work correctly
with a square thread. Suppose, for example, that the diameter of the
generating circle be supposed to be infinite, and the sides of the
thread may be accepted as rolled by the circle. On the wheel we roll a
straight line, which gives a cycloidal curve suitable to work with the
square thread. But the action will be confined to the points of the
teeth, as is shown in Fig. 81, and also to the arc of approach. This is
the same thing as taking the faces off the worm and filling in the
flanks of the wheel. Obviously, then, we may reverse the process and
give the worm faces only, and the wheel, flanks only, using such size of
generating circle as will make the spaces of the wheel parallel in their
depths and rolling the same generating circle upon the pitch line of the
worm to obtain its face curve. This would enable the teeth on the wheel
to be cut by a square-threaded tap, and would confine the contact of
tooth upon tooth to the recess.
The diameter of generating circle used to roll the curves for a worm and
worm-wheel should in all cases be larger than the radius of the
worm-wheel, so that the flanks of the wheel teeth may be at least as
thick at the root as they are at the pitch circle.
To find the diameter of a wheel, driven by a tangent-screw, which is
required to make one revolution for a given number of turns of the
screw, it is obvious, in the first place, that when the screw is
single-threaded, the number of teeth in the wheel must be equal to the
number of turns of the screw. Consequently, the pitch being also given,
the radius of the wheel will be found by multiplying the pitch by the
number of turns of the screw during one turn of the wheel, and dividing
the product by 6.28.
[Illustration: Fig. 82.]
When a wheel pattern is to be made, the first consideration is the
determination of the diameter to suit the required speed; the next is
the pitch which the teeth ought to have, so that the wheel may be in
accordance with the power which it is intended to transmit; the next,
the number of the teeth in relation to the pitch and diameter; and,
lastly, the proportions of the teeth, the clearance, length, and
breadth.
[Illustration: Fig. 83.]
When the amount of power to be transmitted is sufficient to cause
excessive wear, or when the velocity is so great as to cause rapid wear,
the worm instead of being made parallel in diameter from end to end, is
sometimes given a curvature equal to that of the worm-wheel, as is shown
in Fig. 82.
[Illustration: Fig. 84.]
[Illustration: Fig. 85.]
The object of this design is to increase the bearing area, and thus, by
causing the power transmitted to be spread over a larger area of
contact, to diminish the wear. A mechanical means of cutting a worm to
the required form for this arrangement is shown in Fig. 83, which is
extracted from "Willis' Principles of Mechanism." "A is a wheel driven
by an endless screw or worm-wheel, B, C is a toothed wheel fixed to the
axis of the endless screw B and in gear with another and equal toothed
gear D, upon whose axis is mounted the smooth surfaced solid E, which it
is desired to cut into Hindley's[2] endless screw. For this purpose a
cutting tooth F is clamped to the face of the wheel A. When the handle
attached to the axis of B C is turned round, the wheel A and solid wheel
E will revolve with the same relative velocity as A and B, and the tool
F will trace upon the surface of the solid E a thread which will
correspond to the conditions. For from the very mode of its formation
the section of every thread through the axis will point to the centre of
the wheel A. The axis of E lies considerably higher than that of B to
enable the solid E to clear the wheel A.
[2] The inventor of this form of endless screw.
"The edges of the section of the solid E along its horizontal centre
line exactly fit the segment of the toothed wheel, but if a section be
made by a plane parallel to this the teeth will no longer be equally
divided as they are in the common screw, and therefore this kind of
screw can only be in contact with each tooth along a line corresponding
to its middle section. So that the advantage of this form over the
common one is not so great as appears at first sight.
"If the inclination of the thread of a screw be very great, one or more
intermediate threads may be added, as in Fig. 84, in which case the
screw is said to be double or triple according to the number of separate
spiral threads that are so placed upon its surface. As every one of
these will pass its own wheel-tooth across the line of centres in each
revolution of the screw, it follows that as many teeth of the wheel will
pass that line during one revolution of the screw as there are threads
to the screw. If we suppose the number of these threads to be
considerable, for example, equal to those of the wheel teeth, then the
screw and wheel may be made exactly alike, as in Fig. 85; which may
serve as an example of the disguised forms which some common
arrangements may assume."
[Illustration: Fig. 86.]
In Fig. 86 is shown Hawkins's worm gearing. The object of this ingenious
mechanical device is to transmit motion by means of screw or worm
gearing, either by a screw in which the threads are of equal diameter
throughout its length, or by a spiral worm, in which the threads are not
of equal diameter throughout, but increase in diameter each way from the
centre of its length, or about the centre of its length outwardly.
Parallel screws are most applicable to this device when rectilinear
motions are produced from circular motions of the driver, and spiral
worms are applied when a circular motion is given by the driver, and
imparted to the driven wheel. The threads of a spiral worm instead of
gearing into teeth like those of an ordinary worm-wheel, actuate a
series of rollers turning upon studs, which studs are attached to a
wheel whose axis is not parallel to that of the worm, but placed at a
suitable inclination thereto. When motion is given to the worm then
rotation is produced in the roller wheel at a rate proportionable to the
pitch of worm and diameter of wheel respectively.
In the arrangement for transmitting rectilinear motion from a screw,
rollers may be employed whose axes are inclined to the axis of the
driving screw, or else at right angles to or parallel to the same. When
separate rollers are employed with inclined axes, or axes at right
angles with that of the main driving screw, each thread in gear touches
a roller at one part only; but when the rollers are employed with axes
parallel to that of the driving screw a succession of grooves are turned
in these rollers, into which the threads of the driving screw will be in
gear throughout the entire length of the roller. These grooves may be
separate and apart from each other, or else form a screw whose pitch is
equal to that of the driving screw or some multiple thereof.
In Fig. 86 the spiral worm is made of such a length that the edge of one
roller does not cease contact until the edge of the next comes into
contact; a wheel carries four rollers which turn on studs, the latter
being secured by cottars; the axis of the worm is at right angles with
that of the wheel. The edges of the rollers come near together, leaving
sufficient space for the thread of the worm to fit between any two
contiguous rollers. The pitch line of the screw thread forms an arc of a
circle, whose centre coincides with that of the wheel, therefore the
thread will always bear fairly against the rollers and maintain rolling
contact therewith during the whole of the time each roller is in gear,
and by turning the screw in either direction the wheel will rotate.
[Illustration: Fig. 87.]
To prevent end thrust on a worm shaft it may have a right-hand worm A,
and a left-hand one C (Fig. 87), driving two wheels B and D which are in
gear, and either of which may transmit the power. The thrust of the two
worms A and C, being in opposite directions, one neutralizes the other,
and it is obvious that as each revolution of the worm shaft moves both
wheels to an amount equal to the pitch of the worms, the two wheels B D
may, if desirable, be of different diameters.
[Illustration: Fig. 88.]
[Illustration: Fig. 89.]
Involute teeth.--These are teeth having their whole operative surfaces
formed of one continuous involute curve. The diameter of the generating
circle being supposed as infinite, then a portion of its circumference
may be represented by a straight line, such as A in Fig. 88, and if this
straight line be made to roll upon the circumference of a circle, as
shown, then the curve traced will be involute P. In practice, a piece of
flat spring steel, such as a piece of clock spring, is used for tracing
involutes. It may be of any length, but at one end it should be filed so
as to leave a scribing point that will come close to the base circle or
line, and have a short handle, as shown in Fig. 89, in which S
represents the piece of spring, having the point P´, and the handle H.
The operation is, to make a template for the base circle, rest this
template on drawing paper and mark a circle round its edge to represent
on the paper the pitch circle, and to then bend the spring around the
circle B, holding the point P´ in contact with the drawing paper,
securing the other end of the piece of steel, so that it cannot slip
upon B, and allowing the steel to unwind from the cylinder or circle B.
The point P´ will mark the involute curve P. Another way to mark an
involute is to use a piece of twine in place of the spring and a pencil
instead of the tracing point; but this is not so accurate, unless,
indeed, a piece of wood be laid on the drawing-board and the pencil held
firmly against it, so as to steady the pencil point and prevent the
variation in the curve that would arise from variation in the vertical
position of the pencil.
The flanks being composed of the same curve as the faces of the teeth,
it is obvious that the circle from which the tracing point starts, or
around which the straight line rolls, must be of less diameter than the
pitch circle, or the teeth would have no flanks.
A circle of less diameter than the pitch circle of the wheel is,
therefore, introduced, wherefrom to produce the involute curves forming
the full side of the tooth.
[Illustration: Fig. 90.]
The depth below pitch line or the length of flank is, therefore, the
distance between the pitch circle and the base circle. Now even
supposing a straight line to be a portion of the circumference of a
circle of infinite diameter or radius, the conditions would here appear
to be imperfect, because the generating circle is not rolled upon the
pitch circle but upon a circle of lesser diameter. But it can be shown
that the requirements of a proper velocity ratio will be met,
notwithstanding the employment of the base instead of the pitch circle.
Thus, in Fig. 90, let A and B represent the respective centres of the
two pitch circles, marked in dotted lines. Draw the base circle for B as
E Q, which may be of any radius less than that of the pitch circle of
B. Draw the straight line Q D R touching this base circle at its
perimeter and passing through the point of contact on the pitch circles
as at D. Draw the circle whose radius is A R forming the base circle for
wheel A. Thus the line R P Q will meet the perimeters of the two circles
while passing through the point of contact D at the line of centres (a
condition which the relative diameters of the base circles must always
be so proportioned as to attain).
If now we take any point on R Q, as P in the figure, as a tracing point,
and suppose the radius or distance P Q to represent the steel spring
shown in Fig. 89, and move the tracing point back to the base circle of
B, it will trace the involute E P. Again we may take the tracing point P
(supposing the line P R to represent the steel spring), and trace the
involute P F, and these two involutes represent each one side of the
teeth on the respective wheels.
[Illustration: Fig. 91.]
The line R P Q is at a right angle to the curves P E and P F, at their
point of contact, and, therefore, fills the conditions referred to in
Fig. 41. Now the line R P Q denotes the path of contact of tooth upon
tooth as the wheels revolve; or, in other words, the point of contact
between the side of a tooth on one wheel, and the side of a tooth on the
other wheel, will always move along the line Q R, or upon a similar line
passing through D, but meeting the base circles upon the opposite sides
of the line of centres, and since line Q R always cuts the line of
centres at the point of contact of the pitch circles, the conditions
necessary to obtain a correct angular velocity are completely fulfilled.
The velocity ratio is, therefore, as the length of B Q is to that of A
R, or, what is the same thing, as the radius of the base circle of one
wheel is to that of the other. It is to be observed that the line Q R
will vary in its angle to the line of centres A B, according to the
diameter of the base circle from which it is struck, and it becomes a
consideration as to what is its most desirable angle to produce the
least possible amount of thrust tending to separate the wheels, because
this thrust (described in Fig. 39) tends to wear the journals and
bearings carrying the wheel shafts, and thus to permit the pitch circles
to separate. To avoid, as far as possible, this thrust the proportions
between the diameters of the base circles D and E, Fig. 91, must be such
that the line D E passes through the point of contact on the line of
centres, as at C, while the angles of the straight line D E should be as
nearly 90° to a radial line, meeting it from the centres of the wheels
(as shown in the figure, by the lines B E and D E), as is consistent
with the length of D E, which in order to impart continuous motion must
at least equal the pitch of the teeth. It is obvious, also, that, to
give continuous motion, the length of D E must be more than the pitch in
proportion, as the points of the teeth come short of passing through the
base circles at D and E, as denoted by the dotted arcs, which should
therefore represent the addendum circles. The least possible obliquity,
or angle of D E, will be when the construction under any given
conditions be made such by trial, that the base circles D and E coincide
with the addendum circles on the line of centres, and thus, with a given
depth of both beyond, the pitch circle, or addenda as it is termed, will
cause the tooth contacts to extend over the greatest attainable length
of line between the limits of the addendum circles, thus giving a
maximum number of teeth in contact at any instant of time. These
conditions are fulfilled in Fig. 92,[3] the addendum on the small wheel
being longer than the depth below pitch line, while the faces of the
teeth are the narrowest.
[3] From an article by Prof. Robinson.
[Illustration: Fig. 92.]
In seeking the minimum obliquity or angle of D E in the figure, it is to
be observed that the less it is, the nearer the base circle approaches
the pitch circle; hence, the shorter the operative length of tooth flank
and the greater its wear.
In comparing the merits of involute with those of epicycloidal teeth,
the direction of the line of pressure at each point of contact must
always be the common perpendicular to the surfaces at the point of
contact, and these perpendiculars or normals must pass through the pitch
circles on the line of centres, as was shown in Fig. 41, and it follows
that a line drawn from C (Fig. 91) to any point of contact, is in the
direction of the pressure on the surfaces at that point of contact. In
involute teeth, the contact will always be on the line D E (Fig. 92),
but in epicycloidal, on the line of the generating circle, when that
circle is tangent at the line of centres; hence, the direction of
pressure will be a chord of the circle drawn from the pitch circle at
the line of centres to the position of contact considered. Comparing
involute with radial flanked epicycloidal teeth, let C D A (Fig. 91)
represent the rolling circle for the latter, and D C will be the
direction of pressure for the contact at D; but for point of contact
nearer C, the direction will be much nearer 90°, reaching that angle as
the point of contact approaches C. Now, D is the most remote legitimate
contact for involute teeth (and considering it so far as epicycloidal
struck with a generating circle of infinite diameter), we find that the
aggregate directions of the pressures of the teeth upon each other is
much nearer perpendicular in epicycloidal, than in involute gearing;
hence, the latter exert a greater pressure, tending to force the wheels
apart. Hence, the former are, in this respect, preferable.
It is to be observed, however, that in some experiments made by Mr.
Hawkins, he states that he found "no tendency to press the wheels apart,
which tendency would exist if the angle of the line D E (Fig. 92)
deviated more than 20° from the line of centres A B of the two wheels."
A method commonly employed in practice to strike the curves of involute
teeth, is as follows:--
In Fig. 93 let C represent the centre of a wheel, D D the full diameter,
P P the pitch circle, and E the circle of the roots of the teeth, while
R is a radial line. Divide on R, the distance between the pitch circle
and the wheel centre, into four equal parts, by 1, 2, 3, &c. From point
or division 2, as a centre, describe the semicircle S, cutting the wheel
centre and the pitch circle at its junction with R (as at A). From A,
with compasses set to the length of one of the parts, as A 3, describe
the arc B, cutting S at F, and F will be the centre from which one side
of the tooth may be struck; hence from F as a centre, with the compasses
set to the radius A B, mark the curve G. From the centre C strike,
through F, a circle T T, and the centres wherefrom to strike all the
teeth curves will fall on T T. Thus, to strike the other curve of the
tooth, mark off from A the thickness of the tooth on the pitch circle P
P, producing the point H. From H as a centre (with the same radius as
before,) mark on T T the point I, and from I, as a centre, mark the
curve J, forming the other side of the tooth.
[Illustration: Fig. 93.]
[Illustration: Fig. 94.]
In Fig. 94 the process is shown carried out for several teeth. On the
pitch circle P P, divisions 1, 2, 3, 4, &c., for the thickness of teeth
and the width of the spaces are marked. The compasses are set to the
radius by the construction shown in Fig. 93, then from _a_, the point
_b_ on T is marked, and from _b_ the curve _c_ is struck.
In like manner, from _d_, _g_, _j_, the centres _e_, _h_, _k_, wherefrom
to strike the respective curves, _f_, _i_, _l_, are obtained.
Then from _m_ the point _n_, on T T, is marked, giving the centre
wherefrom to strike the curve at _h_ _m_, and from _o_ is obtained the
point _p_, on T T, serving as a centre for the curve _e_ _o_.
A more simple method of finding point F is to make a sheet metal
template, C, as in Fig. 95, its edges being at an angle one to the other
of 75° and 30'. One of its edges is marked off in quarters of an inch,
as 1, 2, 3, 4, &c. Place one of its edges coincident with the line R,
its point touching the pitch circle at the side of a tooth, as at A, and
the centre for marking the curve on that side of the tooth will be found
on the graduated edge at a distance from A equal to one-fourth the
length of R.
[Illustration: Fig. 95.]
The result obtained in this process is precisely the same as that by the
construction in Fig. 93, as will be plainly seen, because there are
marked on Fig. 93 all the circles by which point F was arrived at in
Fig. 95; and line 3, which in Fig. 95 gives the centre wherefrom to
strike curve _o_, is coincident with point F, as is shown in Fig. 95. By
marking the graduated edge of C in quarter-inch divisions, as 1, 2, 3,
&c., then every division will represent the distance from A for the
centre for every inch of wheel radius. Suppose, for example, that a
wheel has 3 inches radius, then with the scale C set to the radial line
R, the centre therefrom to strike the curve _o_ will be at 3; were the
radius of the wheel 4 inches, then the scale being set the same as
before (one edge coincident with R), the centre for the curve _o_ would
be at 4, and arc T would require to meet the edge of C at 4. Having
found the radius from the centre of the wheel of point F for one tooth,
we may mark circle T, cutting point F, and mark off all the teeth by
setting one point of the compasses (set to radius A F) on one side of
the tooth and marking on circle T the centre wherefrom to mark the curve
(as _o_), continuing the process all around the wheel and on both sides
of the tooth.
This operation of finding the location for the centre wherefrom to
strike the tooth curves, must be performed separately for each wheel,
because the distance or radius of the tooth curves varies with the
radius of each wheel.
In Fig. 96 this template is shown with all the lines necessary to set
it, those shown in Fig. 95 to show the identity of its results with
those given in Fig. 93 being omitted.
The principles involved in the construction of a rack to work correctly
with a wheel or pinion, having involute teeth, are as in Fig. 97, in
which the pitch circle is shown by a dotted circle and the base circle
by a full line circle. Now the diameter of the base circle has been
shown to be arbitrary, but being assumed the radius B Q will be
determined (since it extends from the centre B to the point of contact
of D Q, with the base circle); B D is a straight line from the centre B
of the pinion to the pitch line of the rack, and (whatever the angle of
Q D to B D) the sides of the rack teeth must be straight lines inclined
to the pitch line of the rack at an angle equal to that of B D Q.
Involute teeth possess four great advantages--1st, they are thickest at
the roots, where they should be to have a maximum of strength, which is
of great importance in pinions transmitting much power; 2nd, the action
of the teeth will remain practically perfect, even though the wheels are
spread apart so that the pitch circles do not meet on the line of
centres; 3rd, they are much easier to mark, and truth in the marking is
easier attained; and 4th, they are much easier to cut, because the full
depth of the teeth can, on spur-wheels, in all cases be cut with one
revolving cutter, and at one passage of the cutter, if there is
sufficient power to drive it, which is not the case with epicycloidal
teeth whenever the flank space is wider below than it is at the pitch
circle. On account of the first-named advantage, they are largely
employed upon small gears, having their teeth cut true in a gear-cutting
machine; while on account of the second advantage, interchangeable
wheels, which are merely required to transmit motion, may be put in gear
without a fine adjustment of the pitch circle, in which case the wear of
the teeth will not prove destructive to the curves of the teeth. Another
advantage is, that a greater number of teeth of equal strength may be
given to a wheel than in the epicycloidal form, for with the latter the
space must at least equal the thickness of the tooth, while in involute
the space may be considerably less in width than the tooth, both
measured, of course, at the pitch circle. There are also more teeth in
contact at the same time; hence, the strain is distributed over more
teeth.
[Illustration: Fig. 96.]
These advantages assume increased value from the following
considerations.
In a train of epicycloidal gearing in which the pinion or smallest wheel
has radial flanks, the flanks of the teeth will become spread as the
diameters of the wheels in the train increase. Coincident with spread at
the roots is the thrust shown with reference to Fig. 39, hence under the
most favorable conditions the wear on the journals of the wheel axles
and the bearings containing them will take place, and the pitch circles
will separate. Now so soon as this separation takes place, the motion of
the wheels will not be as uniformly equal as when the pitch circles were
in contact on the line of centres, because the conditions under which
the tooth curves, necessary to produce a uniform velocity of motion,
were formed, will have become altered, and the value of those curves to
produce constant regularity of motion will have become impaired in
proportion as the pitch circles have separated.
[Illustration: Fig. 97.]
In a single pair of epicycloidal wheels in which the flanks of the teeth
are radial, the conditions are more favorable, but in this case the
pinion teeth will be weaker than if of involute form, while the wear of
the journals and bearings (which will take place to some extent) will
have the injurious effect already stated, whereas in involute teeth, as
has been noted, the separation of the pitch circles does not affect the
uniformity of the motion or the correct working of the teeth.
If the teeth of wheels are to be cut to shape in a gear-cutting machine,
either the cutters employed determine from their shapes the shapes or
curves of the teeth, or else the cutting tool is so guided to the work
that the curves are determined by the operations of the machine. In
either case nothing is left to the machine operator but to select the
proper tools and set them, and the work in proper position in the
machine. But when the teeth are to be cast upon the wheel the pattern
wherefrom the wheel is to be moulded must have the teeth proportioned
and shaped to proper curve and form.
Wheels that require to run without noise or jar, and to have uniformity
of motion, must be finished in gear-cutting machines, because it is
impracticable to cast true wheels.
When the teeth are to be cast upon the wheels the pattern-maker makes
templates of the tooth curves (by some one of the methods to be
hereafter described), and carefully cuts the teeth to shape. But the
production of these templates is a tedious and costly operation, and one
which is very liable to error unless much experience has been had. The
Pratt and Whitney Company have, however, produced a machine that will
produce templates of far greater accuracy than can be made by hand work.
These templates are in metal, and for epicycloidal teeth from 15 to a
rack, and having a diametral pitch ranging from 1-1/2 to 32.
The principles of action of the machine are that a segment of a ring
(representing a portion of the pitch circle of the wheel for whose teeth
a template is to be produced) is fixed to the frame of the machine. Upon
this ring rolls a disk representing the rolling, generating, or
describing circle, this disk being carried by a frame mounted upon an
arm representing the radius of the wheel, and therefore pivoted at a
point central to the ring. The describing disk is rolled upon the ring
describing the epicycloidal curve, and by suitable mechanical devices
this curve is cut upon a piece of steel, thus producing a template by
actually rolling the generating upon the base circle, and the rolling
motion being produced by positive mechanical motion, there cannot
possibly be any slip, hence the curves so produced are true epicycloids.
The general construction of the machine is shown in the side view, Fig.
98 (Plate I.), and top view, Fig. 99 (Plate I.), details of construction
being shown in Figs. 100, 101 (Plate I.), 102, 103, 104, 105, and 106. A
A is the segment of a ring whose outer edge represents a part of the
pitch circle. B is a disk representing the rolling or generating circle
carried by the frame C, which is attached to a rod pivoted at D. The
axis of pivot D represents the axis of the base circle or pitch circle
of the wheel, and D is adjustable along the rod to suit the radius of A
A, or what is the same thing, to equal the radius of the wheel for whose
teeth a template is to be produced.
When the frame C is moved its centre or axis of motion is therefore at D
and its path of motion is around the circumference of A A, upon the edge
of which it rolls. To prevent B from slipping instead of rolling upon A
A, a flexible steel ribbon is fastened at one end upon A A, passes
around the edge of A A and thence around the circumference of B, where
its other end is fastened; due allowance for the thickness of this
ribbon being made in adjusting the radii of A A and of B.
E´ is a tubular pivot or stud fixed on the centre line of pivots E and
D, and distant from the edge of A A to the same amount that E is. These
two studs E and E´ carry two worm-wheels F and F´ in Fig. 102, which
stand above A and B, so that the axis of the worm G is vertically over
the common tangent of the pitch and describing circles.
[Illustration: _VOL. I._ =TEMPLATE-CUTTING MACHINES FOR GEAR TEETH.=
_PLATE I._
Fig. 98.
Fig. 99.
Fig. 100.
Fig. 101.]
The relative positions of these and other parts will be most clearly
seen by a study of the vertical section, Fig. 102.[4] The worm G is
supported in bearings secured to the carrier C and is driven by another
small worm turned by the pulley I, as seen in Fig. 101 (Plate I.); the
driving cord, passing through suitable guiding pulleys, is kept at
uniform tension by a weight, however C moves; this is shown in Figs. 98
and 99 (Plate I.).
[4] From "The Teeth of Spur Wheels," by Professor McCord.
[Illustration: Fig. 102.]
Upon the same studs, in a plane still higher than the worm-wheels turn
the two disks H, H´, Figs. 103, 104, 105. The diameters of these are
equal, and precisely the same as those of the describing circles which
they represent, with due allowance, again, for the thickness of a steel
ribbon, by which these also are connected. It will be understood that
each of these disks is secured to the worm-wheel below it, and the outer
one of these, to the disk B, so that as the worm G turns, H and H´ are
rotated in opposite directions, the motion of H being identical with
that of B; this last is a rolling one upon the edge of A, the carrier C
with all its attached mechanism moving around D at the same time.
Ultimately, then, the motions of H, H´, are those of two equal
describing circles rolling in external and internal contact with a fixed
pitch circle.
[Illustration: Fig. 103.]
[Illustration: Fig. 104.]
In the edge of each disk a semicircular recess is formed, into which is
accurately fitted a cylinder J, provided with flanges, between which the
disks fit so as to prevent end play. This cylinder is perforated for the
passage of the steel ribbon, the sides of the opening, as shown in Fig.
103, having the same curvature as the rims of the disks. Thus when these
recesses are opposite each other, as in Fig. 104, the cylinder J fills
them both, and the tendency of the steel ribbon is to carry it along
with H when C moves to one side of this position, as in Fig. 105, and
along with H´ when C moves to the other side, as in Fig. 103.
This action is made positively certain by means of the hooks K, K´,
which catch into recesses formed in the upper flange of J, as seen in
Fig. 104. The spindles, with which these hooks turn, extend through the
hollow studs, and the coiled springs attached to their lower ends, as
seen in Fig. 102, urge the hooks in the directions of their points;
their motions being limited by stops _o_, _o´_, fixed, not in the disks
H, H´, but in projecting collars on the upper ends of the tubular studs.
The action will be readily traced by comparing Fig. 104 with Fig. 105;
as C goes to the left, the hook K´ is left behind, but the other one, K,
cannot escape from its engagement with the flange of J; which,
accordingly, is carried along with H by the combined action of the hook
and the steel ribbon.
On the top of the upper flange of J, is secured a bracket, carrying the
bearing of a vertical spindle L, whose centre line is a prolongation of
that of J itself. This spindle is driven by the spur-wheel N, keyed on
its upper end, through a flexible train of gearing seen in Fig. 99; at
its lower end it carries a small milling cutter M, which shapes the edge
of the template T, Fig. 105, firmly clamped to the framing.
[Illustration: Fig. 105.]
When the machine is in operation, a heavy weight, seen in Fig. 98 (Plate
I.), acts to move C about the pivot D, being attached to the carrier by
a cord guided by suitably arranged pulleys; this keeps the cutter M up
to its work, while the spindle L is independently driven, and the duty
left for the worm G to perform is merely that of controlling the motions
of the cutter by the means above described, and regulating their speed.
The centre line of the cutter is thus automatically compelled to travel
in the path R S, Fig. 105, composed of an epicycloid and a hypocycloid
if A A be the segment of a circle as here shown; or of two cycloids, if
A A be a straight bar. The radius of the cutter being constant, the edge
of the template T is cut to an outline also composed of two curves;
since the radius M is small, this outline closely resembles R S, but
particular attention is called to the fact that it is _not identical
with it, nor yet composed of truly epicycloidal curves of any generation
whatever:_ the result of which will be subsequently explained.
NUMBER AND SIZES OF TEMPLATES.
With a given pitch every additional tooth increases the diameter of the
wheel, and changes the form of the epicycloid; so that it would appear
necessary to have as many different cutters, as there are wheels to be
made, of any one pitch.
But the proportional increment, and the actual change of form, due to
the addition of one tooth, becomes less as the wheel becomes larger; and
the alteration in the outline soon becomes imperceptible. Going still
farther, we can presently add more teeth without producing a sensible
variation in the contour. That is to say, several wheels can be cut with
the same cutter, without introducing a perceptible error. It is obvious
that this variation in the form is least near the pitch circle, which is
the only part of the epicycloid made use of; and Prof. Willis many years
ago deduced theoretically, what has since been abundantly proved by
practice, that instead of an infinite number of cutters, 24 are
sufficient of one pitch, for making all wheels, from one with 12 teeth
up to a rack.
[Illustration: Fig. 106.]
Accordingly, in using the epicycloidal milling engine, for forming the
template, segments of pitch circles are provided of the following
diameters (in inches):
12, 16, 20, 27, 43, 100,
13, 17, 21, 30, 50, 150,
14, 18, 23, 34, 60, 300.
15, 19, 25, 38, 75,
In Fig. 106, the edge T T is shaped by the cutter T T, whose centre
travels in the path R S, therefore these two lines are at a constant
normal distance from each other. Let a roller P, of any reasonable
diameter, be run along T T, its centre will trace the line U V, which is
at a constant normal distance from T T, and therefore from R S. Let the
normal distance between U V and R S be the radius of another milling
cutter N, having the same axis as the roller P, and carried by it, but
in a different plane as shown in the side view; then whatever N cuts
will have R S for its contour, if it lie upon the same side of the
cutter as the template.
The diameter of the disks which act as describing circles is 7-1/2
inches, and that of the milling cutter which shapes the edge of the
template is 1/8 of an inch.
Now if we make a set of 1-pitch wheels with the diameters above given,
the smallest will have twelve teeth, and the one with fifteen teeth will
have radial flanks. The curves will be the same whatever the pitch; but
as shown in Fig. 106, the blank should be adjusted in the epicycloidal
engine, so that its lower edge shall be 1/16th of an inch (the radius of
the cutter M) above the bottom of the space; also its relation to the
side of the proposed tooth should be as here shown. As previously
explained, the depth of the space depends upon the pitch. In the system
adopted by the Pratt & Whitney Company, the whole height of the tooth is
2-1/8 times the diametral pitch, the projection outside the pitch circle
being just equal to the pitch, so that diameter of blank = diameter of
pitch circle + 2 × diametral pitch.
We have now to show how, from a single set of what may be called 1-pitch
templates, complete sets of cutters of the true epicycloidal contour may
be made of the same or any less pitch.
Now if T T be a 1-pitch template as above mentioned, it is clear that N
will correctly shape a cutting edge of a gear cutter for a 1-pitch
wheel. The same figure, reduced to half size, would correctly represent
the formation of a cutter for a 2-pitch wheel of the same number of
teeth; if to quarter size, that of a cutter for a 4-pitch wheel, and so
on.
But since the actual size and curvature of the contour thus determined
depend upon the dimensions and motion of the cutter N, it will be seen
that the same result will practically be accomplished, if these only be
reduced; the size of the template, the diameter and the path of the
roller remaining unchanged.
The nature of the mechanism by which this is effected in the Pratt &
Whitney system of producing epicycloidal cutters will be hereafter
explained in connection with cutters.
CHAPTER III.--THE TEETH OF GEAR-WHEELS (continued).
The revolving cutters employed in gear-cutting machines, gear-cutters,
or cutting engines (as the machines for cutting the teeth of gear-wheels
to shape are promiscuously termed), are of the form shown in Fig. 107,
which represents what is known as a Brown and Sharpe patent cutter,
whose peculiarities will be explained presently. This class of cutters
is made as follows:--
[Illustration: Fig. 107.]
A cast steel disk is turned in the lathe to the required form and
outline. After turning, its circumference is serrated as shown, so as to
provide protuberances, or teeth, on the face of which the cutting edges
may be formed. To produce a cutting edge it is necessary that the metal
behind that edge should slope or slant away leaving the cutting edge to
project. Two methods of accomplishing this are employed: in the first,
which is that embodied in the Brown and Sharpe system, each tooth has
the curved outline, forming what may be termed its circumferential
outline, of the same curvature and shape from end to end, and from front
to back, as it may more properly be termed, the clearance being given by
the back of the tooth approaching the centre of the cutter, so that if a
line be traced along the circumference of a tooth, from the cutting edge
to the back, it will approach the centre of the cutter as the back is
approached, but the form of the tooth will be the same at every point in
the line. It follows then that the radial faces of the teeth may be
ground away to sharpen the teeth without affecting the shape of the
tooth, which being made correct will remain correct.
This not only saves a great deal of labor in sharpening the teeth, but
also saves the softening and rehardening process, otherwise necessary at
each resharpening.
The ordinary method of producing the cutting edges after turning the
cutter and serrating it, is to cut away the metal with a file or rotary
cutter of some kind forming the cutting edge to correct shape, but
paying no regard to the shape of the back of the tooth more than to give
it the necessary amount of clearance. In this case the cutter must be
softened and reset to sharpen it. To bring the cutting edge up to a
sharp edge all around its profile, while still preserving the shape to
which it was turned, the pantagraphic engine, shown in Fig. 108, has
been made by the Pratt and Whitney Company. Figs. 109 and 110 show some
details of its construction.[5] "The milling cutter N is driven by a
flexible train acting upon the wheel O, whose spindle is carried by the
bracket B, which can slide from right to left upon the piece B, and this
again is free to slide in the frame F. These two motions are in
horizontal planes, and perpendicular to each other.
[5] From "The Teeth of Spur Wheels," by Professor McCord.
[Illustration: Fig. 108.]
"The upper end of the long lever P C is formed into a ball, working in a
socket which is fixed to P C. Over the cylindrical upper part of this
lever slides an accurately fitted sleeve D, partly spherical externally,
and working in a socket which can be clamped at any height on the frame
F. The lower end P of this lever being accurately turned, corresponds to
the roller P in Fig. 109, and is moved along the edge of the template T,
which is fastened in the frame in an invariable position.
"By clamping D at various heights, the ratio of the lever arms P D, P D,
may be varied at will, and the axis of N made to travel in a path
similar to that of the axis of P, but as many times smaller as we
choose; and the diameter of N must be made less than that of P in the
same proportion.
"The template being on the left of the roller, the cutter to be shaped
is placed on the right of N, as shown in the plan view at Z, because the
lever reverses the movement.
"This arrangement is not mathematically perfect, by reason of the
angular vibration of the lever. This is, however, very small, owing to
the length of the lever; it might have been compensated for by the
introduction of another universal joint, which would practically have
introduced an error greater than the one to be obviated, and it has,
with good judgment, been omitted.
"The gear-cutter is turned nearly to the required form, the notches are
cut in it, and the duty of the pantagraphic engine is merely to give the
finishing touch to each cutting edge, and give it the correct outline.
It is obvious that this machine is in no way connected with, or
dependent upon, the epicycloidal engine; but by the use of proper
templates it will make cutters for any desired form of tooth; and by its
aid exact duplicates may be made in any numbers with the greatest
facility.
[Illustration: Fig. 109.]
"It forms no part of our plan to represent as perfect that which is not
so, and there are one or two facts, which at first thought might seem
serious objections to the adoption of the epicycloidal system. These
are:
"1. It is physically impossible to mill out a _concave_ cycloid, by any
means whatever, because at the pitch line its radius of curvature is
zero, and a milling cutter must have a sensible diameter.
"2. It is impossible to mill out even a _convex_ cycloid or epicycloid,
by the means and in the manner above described.
[Illustration: Fig. 110.]
"This is on account of a hitherto unnoticed peculiarity of the curve at
a constant normal distance from the cycloid. In order to show this
clearly, we have, in Fig. 110, enormously exaggerated the radius C D, of
the milling cutter (M of Figs. 105 and 106). The outer curve H L,
evidently, could be milled out by the cutter, whose centre travels in
the cycloid C A; it resembles the cycloid somewhat in form, and presents
no remarkable features. But the inner one is quite different; it starts
at D, and at first goes down, _inside the circle whose radius is_ C D,
forms a cusp at E, then begins to rise, crossing this circle at G, and
the base line at F. It will be seen, then, that if the centre of the
cutter travel in the cycloid A C, its edge will cut away the part G E D,
leaving the template of the form O G I. Now if a roller of the same
radius C D, be rolled along this edge, its centre will travel in the
cycloid from A, to the point P, where a normal from G, cuts it; then the
roller will turn upon G as a fulcrum, and its centre will travel from P
to C, in a circular arc whose radius G P = C D.
"That is to say even a roller of the same size as the original milling
cutter, will not retrace completely the cycloidal path in which the
cutter travelled.
"Now in making a rack template, the cutter, after reaching C, travels in
the reversed cycloid C R, its left-hand edge, therefore, milling out a
curve D K, similar to H L. This curve lies wholly _outside_ the circle D
I, and therefore cuts O G at a point between F and G, but very near to
G. This point of intersection is marked S in Fig. 110, where the actual
form of the template O S K is shown. The roller which is run along this
template is _larger_, as has been explained, than the milling cutter.
When the point of contact reaches S (which so nearly corresponds to G
that they practically coincide), this roller cannot now swing about S
through an angle so great as P G C of Fig. 110; because at the root D,
the radius of curvature of D K is only equal to that of the cutter, and
G and S are so near the root that the curvature of S K, near the latter
point, is greater than that of the roller. Consequently there must be
some point U in the path of the centre of the roller, such, that when
the centre reaches it, the circumference will pass through S, and be
also tangent to S K. Let T be the point of tangency; draw S U and T U,
cutting the cycloidal path A R in X and Y. Then, U Y being the radius of
the new milling cutter (corresponding to N of Fig. 109), it is clear
that in the outline of the gear cutter shaped by it, the circular arc X
Y will be substituted for the true cycloid.
[Illustration: Fig. 111.]
THE SYSTEM PRACTICALLY PERFECT.
"The above defects undeniably exist; now, what do they amount to? The
diagram is drawn purposely with these sources of error greatly
exaggerated, in order to make their nature apparent and their existence
sensible. The diameters used in practice, as previously stated, are:
describing circle, 7-1/2 inches; cutter for shaping template, 1/8 of an
inch; roller used against edge of template, 1-1/8 inches; cutter for
shaping a 1-pitch gear cutter, 1 inch.
"With these data the writer has found that the _total length_ of the arc
X Y of Fig. 110, which appears instead of the cycloid in the outline of
a cutter for a 1-pitch rack, is less than 0.0175 inch; the real
_deviation_ from the true form, obviously, must be much less than that.
It need hardly be stated that the effect upon the velocity ratio of an
error so minute, and in that part of the contour, is so extremely small
as to defy detection. And the best proof of the practical perfection of
this system of making epicycloidal teeth is found in the smoothness and
precision with which the wheels run; a set of them is shown in gear in
Fig. 111, the rack gearing as accurately with the largest as with the
smallest. To which is to be added, finally, that objection taken, on
whatever grounds, to the epicycloidal form of tooth, has no bearing upon
the method above described of producing duplicate cutters for teeth of
any form, which the pantagraphic engine will make with the same facility
and exactness, if furnished with the proper templates.
"The front faces of the teeth of rotary cutters for gear-cutting are
usually radial lines, and are ground square across so as to stand
parallel with the axis of the cutter driving spindle, so that to
whatever depth the cutter may have entered the wheel, the whole of the
cutting edge within the wheel will meet the cut simultaneously. If this
is not the case the pressure of the cut will spring the cutter, and also
the arbor driving it, to one side. Suppose, for example, that the tooth
faces not being square across, one side of the teeth meets the work
first, then there will be as each tooth meets its cut an endeavour to
crowd away from the cut until such time as the other side of the tooth
also takes its cut."
It is obvious that rotating cutters of this class cannot be used to cut
teeth having the width of the space wider below than it is at the pitch
line. Hence, if such cutters are required to be used upon epicycloidal
teeth, the curves to be theoretically correct must be such as are due to
a generating circle that will give at least parallel flanks. From this
it becomes apparent that involute teeth being always thicker at the root
than at the pitch line, and the spaces being, therefore, narrower at the
root, may be cut with these cutters, no matter what the diameter of the
base circle of the involute.
To produce with revolving cutters teeth of absolutely correct
theoretical curvature of face and flank, it is essential that the cutter
teeth be made of the exact curvature due to the diameter of pitch circle
and generating circle of the wheel to be cut; while to produce a tooth
thickness and space width, also theoretically correct, the thickness of
the cutter must also be made to exactly answer the requirements of the
particular wheel to be cut; hence, for every different number of teeth
in wheels of an equal pitch a separate cutter is necessary if
theoretical correctness is to be attained.
This requirement of curvature is necessary because it has been shown
that the curvatures of the epicycloid and hypocycloid, as also of the
involute, vary with every different diameter of base circle, even
though, in the case of epicycloidal teeth, the diameter of the
generating circle remain the same. The requirement of thickness is
necessary because the difference between the arc and the chord pitch is
greater in proportion as the diameter of the base or pitch circle is
decreased.
But the difference in the curvature on the short portions of the curves
used for the teeth of fine pitches (and therefore of but little height)
due to a slight variation in the diameter of the base circle is so
minute, that it is found in practice that no sensible error is produced
if a cutter be used within certain limits upon wheels having a different
number of teeth than that for which the cutter is theoretically correct.
The range of these limits, however, must (to avoid sensible error) be
more confined as the diameter of the base circle (or what is the same
thing, the number of the teeth in the wheel) is decreased, because the
error of curvature referred to increases as the diameters of either the
base or the generating circles decrease. Thus the difference in the
curve struck on a base circle of 20 inches diameter, and one of 40
inches diameter, using the same diameter of generating circle, would be
very much less than that between the curves produced by the same
diameter of generating circle on base circles respectively 10 and 5
inches diameter.
For these reasons the cutters are limited to fewer wheels according as
the number of teeth decreases, or, per contra, are allowed to be used
over a greater range of wheels as the number of teeth in the wheels is
increased.
Thus in the Brown and Sharpe system for involute teeth there are 8
cutters numbered numerically (for convenience in ordering) from 1 to 8,
and in the following table the range of the respective cutters is shown,
and the number of teeth for which the cutter is theoretically correct is
also given.
BROWN AND SHARPE SYSTEM.
No. of cutter. Involute teeth. Teeth.
1 Used upon all wheels having from 135 teeth to a rack correct for 200
2 " " " " " 55 " to 134 teeth, 68
3 " " " " " 35 " to 54 " 40
4 " " " " " 26 " to 34 " 29
5 " " " " " 21 " to 25 " 22
6 " " " " " 17 " to 20 " 18
7 " " " " " 14 " to 16 " 16
8 " " " " " 12 " to 14 " 13
Suppose that it was required that of a pair of wheels one make twice the
revolutions of the other; then, knowing the particular number of teeth
for which the cutters are made correct, we may obtain the nearest
theoretically true results as follows: If we select cutters Nos. 8 and 4
and cut wheels having respectively 13 and 26 teeth, the 13 wheel will be
theoretically correct, and the 26 will contain the minute error due to
the fact that the cutter is used upon a wheel having three less teeth
than the number it is theoretically correct for. But we may select the
cutters that are correct for 16 and 29 teeth respectively, the 16th
tooth being theoretically correct, and the 29th cutter (or cutter No. 4
in the table) being used to cut 32 teeth, this wheel will contain the
error due to cutting 3 more teeth than the cutter was made correct for.
This will be nearer correct, because the error is in a larger wheel,
and, therefore, less in actual amount. The pitch of teeth may be
selected so that with the given number of teeth the diameters of the
wheels will be that required.
We may now examine the effect of the variation of curvature in
combination with that of the thickness, upon a wheel having less and
upon one having more teeth than the number in the wheel for which the
cutter is correct.
First, then, suppose a cutter to be used upon a wheel having less teeth
and it will cut the spaces too wide, because of the variation of
thickness, and the curves too straight or insufficiently curved because
of the error of curvature. Upon a wheel having more teeth it will cut
the spaces too narrow, and the curvature of the teeth too great; but, as
before stated, the number of wheels assigned to each cutter may be so
apportioned that the error will be confined to practically unappreciable
limits.
If, however, the teeth are epicycloidal, it is apparent that the spaces
of one wheel must be wide enough to admit the teeth of the other to a
depth sufficient to permit the pitch lines to coincide on the line of
centres; hence it is necessary in small diameters, in which there is a
sensible difference between the arc and the chord pitches, to confine
the use of a cutter to the special wheel for which it is designed, that
is, having the same number of teeth as the cutter is designed for.
Thus the Pratt and Whitney arrangement of cutters for epicycloidal teeth
is as follows:--
PRATT AND WHITNEY SYSTEM.
EPICYCLOIDAL TEETH.
[All wheels having from 12 to 21 teeth have a special cutter for each
number of teeth.][6]
Cutter correct for
No. of teeth.
23 Used on wheels having from 22 to 24 teeth.
25 " " " " 25 to 26 "
27 " " " " 26 to 29 "
30 " " " " 29 to 32 "
34 " " " " 32 to 36 "
38 " " " " 36 to 40 "
43 " " " " 40 to 46 "
50 " " " " 46 to 55 "
60 " " " " 55 to 67 "
76 " " " " 67 to 87 "
100 " " " " 87 to 123 "
150 " " " " 123 to 200 "
300 " " " " 200 to 600 "
Rack " " " " 600 to rack.
[6] For wheels having less than 12 teeth the Pratt and Whitney Co. use
involute cutters.
Here it will be observed that by a judicious selection of pitch and
cutters, almost theoretically perfect results may be obtained for
almost any conditions, while at the same time the cutters are so
numerous that there is no necessity for making any selection with a view
to taking into consideration for what particular number of teeth the
cutter is made correct.
For epicycloidal cutters made on the Brown and Sharpe system so as to
enable the grinding of the face of the tooth to sharpen it, the Brown
and Sharpe company make a separate cutter for wheels from 12 to 20
teeth, as is shown in the accompanying table, in which the cutters are
for convenience of designation denoted by an alphabetical letter.
24 CUTTERS IN EACH SET.
Letter A cuts 12 teeth.
B " 13 "
C " 14 "
D " 15 "
E " 16 "
F " 17 "
G " 18 "
H " 19 "
I " 20 "
J " 21 to 22 "
K " 23 " 24 "
L " 25 " 26 "
M " 27 " 29 "
N " 30 " 33 "
O " 34 " 37 "
P " 38 " 42 "
Q " 43 " 49 "
R " 50 " 59 "
S " 60 " 74 "
T " 75 " 99 "
U " 100 " 149 "
V " 150 " 249 "
W " 250 " Rack.
X " Rack.
In these cutters a shoulder having no clearance is placed on each side
of the cutter, so that when the cutter has entered the wheel until the
shoulder meets the circumference of the wheel, the tooth is of the
correct depth to make the pitch circles coincide.
In both the Brown and Sharpe and Pratt and Whitney systems, no side
clearance is given other than that quite sufficient to prevent the teeth
of one wheel from jambing into the spaces of the other. Pratt and
Whitney allow 1/8 of the pitch for top and bottom clearance, while Brown
and Sharpe allow 1/10 of the thickness of the tooth for top and bottom
clearance.
It may be explained now, why the thickness of the cutter if employed
upon a wheel having more teeth than the cutter is correct for,
interferes with theoretical exactitude.
[Illustration: Fig. 112.]
[Illustration: Fig. 113.]
First, then, with regard to the thickness of tooth and width of space.
Suppose, then, Fig. 112 to represent a section of a wheel having 12
teeth, then the pitch circle of the cutter will be represented by line
A, and there will be the same difference between the arc and chord pitch
on the cutter as there is on the wheel; but suppose that this same
cutter be used on a wheel having 24 teeth, as in Fig. 113, then the
pitch circle on the cutter will be more curved than that on the wheel as
denoted at C, and there will be more difference between the arc and
chord pitches on the cutter than there is on the wheel, and as a result
the cutter will cut a groove too narrow.
The amount of error thus induced diminishes as the diameter of the pitch
circle of the cutter is increased.
But to illustrate the amount. Suppose that a cutter is made to be
theoretically correct in thickness at the pitch line for a wheel to
contain 12 teeth, and having a pitch circle diameter of 8 inches, then
we have
3.1416 = ratio of circumference to diameter.
8 = diameter.
-------
Number of teeth = 12 ) 25.1328 = circumference.
-------
2.0944 = arc pitch of wheel.
If now we subtract the chord pitch from the arc pitch, we shall obtain
the difference between the arc and the chord pitches of the wheel; here
2.0944 = arc pitch.
2.0706 = chord pitch.
------
.0238 = difference between the arc and the chord pitch.
Now suppose this cutter to be used upon a wheel having the same pitch,
but containing 18 teeth; then we have
2.0944 = arc pitch.
2.0836 = chord pitch.
------
.0108 = difference between the arc and the chord pitch.
Then
.0238 = difference on wheel with 12 teeth.
.0108 = " " " 18 "
-----
.0130 = variation between the differences.
And the thickness of the tooth equalling the width of the space, it
becomes obvious that the thickness of the cutter at the pitch line being
correct for the 12 teeth, is one half of .013 of an inch too thin for
the 18 teeth, making the spaces too narrow and the teeth too thick by
that amount.
Now let us suppose that a cutter is made correct for a wheel having 96
teeth of 2.0944 arc pitch, and that it be used upon a wheel having 144
teeth. The proportion of the wheels one to the other remains as before
(for 96 bears the proportion to 144 as 12 does to 18).
Then we have for the 96 teeth
2.0944 = arc pitch.
2.0934 = chord pitch.
------
.0010 = difference.
For the 144 teeth we have
2.0944 = arc pitch.
2.0937 = chord pitch.
------
.0007 = difference.
We find, then, that the variation decreases as the size of the wheels
increases, and is so small as to be of no practical consequence.
If our examples were to be put into practice, and it were actually
required to make one cutter serve for wheels having, say, from 12 to 18
teeth, a greater degree of correctness would be obtained if the cutter
were made to some other wheel than the smallest. But it should be made
for a wheel having less than the mean diameter (within the range of 12
and 18), that is, having less than 15 teeth; because the difference
between the arc and chord pitch increases as the diameter of the pitch
circle increases, as already shown.
A rule for calculating the number of wheels to be cut by each cutter
when the number of cutters in the set and the number of teeth in the
smallest and largest wheel in the train are given is as follows:--
Rule.--Multiply the number of teeth in the smallest wheel of the train
by the number of cutters it is proposed to have in the set, and divide
the amount so obtained by a sum obtained as follows:--
From the number of cutters in the set subtract the number of the cutter,
and to the remainder add the sum obtained by multiplying the number of
the teeth in the smallest wheel of the set or train by the number of the
cutter and dividing the product by the number of teeth in the largest
wheel of the set or train.
Example.--I require to find how many wheels each cutter should cut,
there being 8 cutters and the smallest wheel having 12 teeth, while the
largest has 300.
Number of teeth in Number of cutters
smallest wheel. in the set.
12 × 8 = 96
Then
Number of cutters Number of
in set. cutter.
8 - 7 = 1
Then
Number of teeth in The number of the The number of the teeth
smallest wheel. cutter. in largest wheel.
12 × 8 ÷ 300
12
8
---
300 ) 960 ( 0.32
900
---
600
600
Now add the 1 to the .32 and we have 1.32, which we must divide into the
96 first obtained.
Thus
1.32 ) 96.00 ( 72
924
----
360
264
---
96
Hence No. 8 cutter may be used for all wheels that have between 72 teeth
and 300 teeth.
To find the range of wheels to be cut by the next cutter, which we will
call No. 7, proceed again as before, but using 7 instead of 8 as the
number of the cutter.
Thus
Number of teeth in Number of cutters in
smallest wheel. the set.
12 × 8 = 96
Then
Number of cutters Number of
in the set. cutters.
8 - 6 = 2
And
Number of teeth in The number of the The number of teeth
smallest wheel. cutter. in the largest wheel.
12 × 8 ÷ 300
Here
12
8
---
300 ) 960 ( 0.32
900
---
600
600
Add the 2 to the .32 and we have 2.32 to divide into the 96.
Thus
2.32 ) 96.00 ( 41
928
---
320
232
---
88
Hence this cutter will cut all wheels having not less than the 41 teeth,
and up to the 72 teeth where the other cutter begins. For the range of
the next cutter proceed the same, using 6 as the number of the cutter,
and so on.
By this rule we obtain the lowest number of teeth in a wheel for which
the cutter should be used, and it follows that its range will continue
upwards to the smallest wheel cut by the cutter above it.
Having by this means found the range of wheels for each cutter, it
remains to find for what particular number of teeth within that range
the cutter teeth should be made correct, in order to have whatever error
there may be equal in amount on the largest and smallest wheel of its
range. This is done by using precisely the same rule, but supposing
there to be twice as many cutters as there actually are, and then taking
the intermediate numbers as those to be used.
Applying this plan to the first of the two previous examples we have--
Number of teeth in the Number of cutters in
smallest wheel. the set.
12 × 16 = 192
Then
Number of cutters Number of the
in the set. cutter.
16 - 15 = 1
And
Number of teeth in The number of the The number of the teeth in
smallest wheel. cutter. the largest wheel.
12 × 15 ÷ 300
12
15
---
60
12
-----
300 ) 180.0 ( 0.6
1800
Then add the 1 to the .6 = 1.6, and this divided into 192 = 120.
By continuing this process for each of the 16 cutters we obtain the
following table:--
Number of Number of
Cutter. Teeth.
1 12
*2 13
3 14
*4 15
5 17
*6 18
7 20.61
*8 23
9 26
*10 30
11 35
*12 42
13 54
*14 75
15 120
*16 300
Suppose now we take for our 8 cutters those marked by an asterisk, and
use cutter 2 for all wheels having either 12, 13, or 14 teeth, then the
next cutter would be that numbered 4, cutting 14, 15, or 16 toothed
wheels, and so on.
A similar table in which 8 cutters are required, but 16 are used in the
calculation, the largest wheel having 200 teeth in the set, is given
below.
Number of Number of
Cutter. Teeth.
1 12.7
2 13.5
3 14.5
4 15.6
5 16.9
6 18
7 21
8 23.5
9 26.5
10 29
11 35
12 40.6
13 52.9
14 67.6
15 101
16 200
To assist in the selections as to what wheels in a given set the
determined number of cutters should be made correct for, so as to obtain
the least limit of error, Professor Willis has calculated the following
table, by means of which cutters may be selected that will give the same
difference of form between any two consecutive numbers, and this table
he terms the table of equidistant value of cutters.
TABLE OF EQUIDISTANT VALUE OF CUTTERS.
Number of Teeth.
Rack--300, 150, 100, 76, 60, 50, 43, 38, 34, 30, 27, 25, 23, 21, 20, 19,
17, 16, 15, 14, 13, 12.
The method of using the table is as follows:--Suppose it is required to
make a set of wheels, the smallest of which is to contain 50 teeth and
the largest 150, and it is determined to use but one cutter, then that
cutter should be made correct for a wheel containing 76; because in the
table 76 is midway between 50 and 150.
But suppose it were determined to employ two cutters, then one of them
should be made correct for a wheel having 60 teeth, and used on all the
wheels having between 50 and 76 teeth, while the other should be made
correct for a wheel containing 100 teeth, and used on all wheels
containing between 76 and 150 teeth.
In the following table, also arranged by Professor Willis, the most
desirable selection of cutters for different circumstances is given, it
being supposed that the set of wheels contains from 12 teeth to a rack.
+-----------+------------------------------------------------------+
|Number of | |
|cutters in | Number of Teeth in Wheel for which the Cutter is to |
|the set. | be made correct. |
+-----------+----+----+--------------------------------------------+
| 2 | 50 | 16 | |
| --+----+----+----+ |
| 3 | 75 | 25 | 15 | |
| --+----+----+----+----+ |
| 4 | 100| 34 | 20 | 14 | |
| --+----+----+----+----+----+----+ |
| 6 | 150| 50 | 30 | 21 | 16 | 13 | |
| --+----+----+----+----+----+----+----+----+ |
| 8 | 200| 67 | 40 | 29 | 22 | 18 | 15 | 13 | |
| --+----+----+----+----+----+----+----+----+----+----+ |
| 10 | 200| 77 | 50 | 35 | 27 | 22 | 19 | 16 | 14 | 13 | |
| --+----+----+----+----+----+----+----+----+----+----+----+
| | 300| 100| 60 | 43 | 34 |27 | 23 | 20 | 17 | 15 | 14 |
| 12 +----+----+----+----+----+----+----+----+----+----+----+
| | 13 | |
| --+----+----+----+----+----+----+----+----+----+----+----+
| | 300| 150| 100| 70 | 50 | 40 | 30 | 26 | 24 | 22 | 20 |
| 18 +----+----+----+----+----+----+----+----+----+----+----+
| | 18 | 16 | 15 | 14 | 13 | 12 | |
| --+----+----+----+----+----+----+----+----+----+----+----+
| |Rack| 300| 150| 100| 76 | 60 | 50 | 43 | 38 | 34 | 30 |
| +----+----+----+----+----+----+----+----+----+----+----+
| 24 | 27 | 25 | 23 | 21 | 20 | 19 | 18 | 17 | 16 | 15 | 14 |
| +----+----+----+----+----+----+----+----+----+----+----+
| | 13 | 12 | |
+-----------+----+----+--------------------------------------------+
Suppose now we take the cutters, of a given pitch, necessary to cut all
the wheels from 12 teeth to a rack, then the thickness of the teeth at
the pitch line will for the purposes of designation be the thickness of
the teeth of all the wheels, which thickness may be a certain proportion
of the pitch.
But in involute teeth while the depth of tooth on the cutter may be
taken as the standard for all the wheels in the range, and the actual
depth for the wheel for which the cutter is correct, yet the depth of
the teeth in the other wheels in the range may be varied sufficiently on
each wheel to make the thickness of the teeth equal the width of the
spaces (notwithstanding the variation between the arc and chord
pitches), so that by a variation in the tooth depth the error induced by
that variation may be corrected. The following table gives the
proportions in the Brown and Sharpe system.
+------------+-----------------+-----------------+
| Arc Pitch. | Depth of Tooth. | Depth in terms |
| | |of the arc pitch.|
+------------+-----------------+-----------------+
| inches. | inches. | inches. |
| 1.570 | 1.078 | .686 |
| 1.394 | .958 | .687 |
| 1.256 | .863 | .686 |
| 1.140 | .784 | .697 |
| 1.046 | .719 | .687 |
| .896 | .616 | .686 |
| .786 | .539 | .685 |
| .628 | .431 | .686 |
| .524 | .359 | .685 |
| .448 | .307 | .685 |
| .392 | .270 | .686 |
| .350 | .240 | .686 |
| .314 | .216 | .687 |
+------------+-----------------+-----------------+
To avoid the trouble of measuring, and to assist in obtaining accuracy
of depth, a gauge is employed to mark on the wheel face a line denoting
the depth to which the cutter should be entered.
Suppose now that it be required to make a set of cutters for a certain
range of wheels, and it be determined that the cutters be so constructed
that the greatest permissible amount of error in any wheel of the set be
1/100 inch. Then the curves for the smallest wheel, and those for the
largest in the set, and the amount of difference between them
ascertained, and assuming this difference to amount to 1/16 inch, which
is about 6/100, then it is evident that 6 cutters must be employed for
the set.
It has been shown that on bevel-wheels the tooth curves vary at every
point in the tooth breadth; hence it is obvious that the cutter being of
a fixed curve will make the tooth to that curve. Again, the thickness of
the teeth and breadth of the spaces vary at every point in the breadth,
while with a cutter of fixed thickness the space cut will be parallel
from end to end. To overcome these difficulties it is usual to give to
the cutter a curve corresponding to the curve required at the middle of
the wheel face and a thickness equal to the required width of space at
its smallest end, which is at the smallest face diameter.
The cutter thus formed produces, when passed through the wheel once, and
to the required depth, a tooth of one curve from end to end, having its
thickness and width of space correct at the smaller face diameter only,
the teeth being too thick and the spaces too narrow as the outer
diameter of the wheel is approached. But the position and line of
traverse of the cutter may be altered so as to take a second cut,
widening the space and reducing the tooth thickness at the outer
diameter.
By moving the cutter's position two or three times the points of contact
between the teeth may be made to occur at two or three points across the
breadth of the teeth and their points of contact; the wear will soon
spread out so that the teeth bear all the way across.
Another plan is to employ two or three cutters, one having the correct
curve for the inner diameter, and of the correct thickness for that
diameter, another having the correct curve for the pitch circle, and
another having the correct curve at the largest diameter of the teeth.
The thickness of the first and second cutters must not exceed the
required width of space at the small end, while that for the third may
be the same as the others, or equal to the thickness of the smallest
space breadth that it will encounter in its traverse along the teeth.
The second cutter must be so set that it will leave the inner end of the
teeth intact, but cut the space to the required width in the middle of
the wheel face. The third cutter must be so set as to leave the middle
of the tooth breadth intact, and cut the teeth to the required thickness
at the outer or largest diameter.
CUTTING WORM-WHEELS.
The most correct method of cutting the teeth of a worm-wheel is by means
of a worm-cutter, which is a worm of the pitch and form of tooth that
the working worm is intended to be, but of hardened steel, and having
grooves cut lengthways of the worm so as to provide cutting edges
similar to those on the cutter shown in Fig. 107.
The wheel is mounted on an arbor or mandril free to rotate on its axis
and at a right angle to the cutter worm, which is rotated and brought to
bear upon the perimeter of the worm-wheel in the same manner as the
working worm-wheel when in action. The worm-cutter will thus cut out the
spaces in the wheel, and must therefore be of a thickness equal to those
spaces. The cutter worm acting as a screw causes the worm-wheel to
rotate upon its axis, and therefore to feed to the cutter.
In wheels of fine pitch and small diameter this mode of procedure is a
simple matter, especially if the form of tooth be such that it is
thicker, as the root of the tooth is approached from the pitch line,
because in that case the cutter worm may be entered a part of the depth
in the worm-wheel and a cut be taken around the wheel. The cutter may
then be moved farther into the wheel and a second cut taken around the
wheel, so that by continuing the process until the pitch line of the
cutter worm coincides with that of the worm-cutter, the worm-wheel may
be cut with a number of light cuts, instead of at one heavy cut.
But in the case of large wheels the strain due to such a long line of
cutting edge as is possessed by the cutter worm-teeth springs or bends
the worm-wheel, and on account of the circular form of the breadth of
the teeth this bending or spring causes that part of the tooth arc above
the centre of the wheel thickness to lock against the cutter.
To prevent this, several means may be employed. Thus the grooves forming
the cutting edges of the worm-cutter may wind spirally along instead of
being parallel to the axis of the cutter.
The distance apart of these grooves may be greater than the breadth of
tooth a width of worm-wheel face, in which case the cutting edge of one
tooth only will meet the work at one time. In addition to this two
stationary supports may be placed beneath the worm-wheel (one on each
side of the cutter). But on coarse pitches with their corresponding
depth of tooth, the difficulty presents itself, that the arbor driving
the worm-cutter will spring, causing the cutter to lift and lock as
before; hence it is necessary to operate on part of the space at a time,
and shape it out to so nearly the correct form that the finishing cut
may be a very light one indeed, in which case the worm-cutter will
answer for the final cut.
The removal of the surplus metal preparatory to the introduction of the
worm-cutter to finish, may be made with a cutter-worm that will cut out
a narrow groove being of the thickness equal to the bottom of the tooth
space and cutting on its circumference only. This cutter may be fed into
the wheel to the permissible depth of cut, and after the cut is taken
all around the wheel, it may be entered deeper and a second cut taken,
and so on until it has entered the wheel to the necessary depth of
tooth. A second cutter-worm may then be used, it being so shaped as to
cut the face curve only of the teeth. A third may cut the flank curve
only, and finally a worm-cutter of correct form may take a finishing cut
over both the faces and the flanks. In this manner teeth of any pitch
and depth may be cut. Another method is to use a revolving cutter such
as shown in Fig. 107, and to set it at the required angle to the wheel,
and then take a succession of cuts around the wheel, the first cut
forming a certain part of the tooth depth, the second increasing this
depth, and so on until the final cut forms the tooth to the requisite
depth. In this case the cutter operates on each space separately, or on
one space only at a time, and the angle at which to set the cutter may
be obtained as follows in Fig. 114. Let the length of the line A A equal
the diameter of the worm at the pitch circle, and B B (a line at a right
angle to A A) represent the axial line of the worm. Let the distance C
equal the pitch of the teeth, and the angle of the line D with A A or B
B according to circumstances, will be that to which the cutter must be
set with reference to the tooth.
[Illustration: Fig. 114.]
If then a piece of sheet metal be cut to the lines A, D, and the cutter
so set that with the edge D of the piece held against the side face of
the cutter (which must be flat or straight across), the edge A will
stand truly vertical, and the cutter will be at the correct angle
supposing the wheel to be horizontal.
[Illustration: Fig. 115.]
[Illustration: Fig. 116.]
In making patterns wherefrom gear-wheels may be cast in a mould, the
true curves are frequently represented by arcs of circles struck from
the requisite centres and of the most desirable radius with compasses,
and this will be treated after explaining the pattern maker's method of
obtaining true curves by rolling segments by hand. If, then, the wheels
are of small diameter, as say, less than 12 inches in diameter, and
precision is required, it is best to turn in the lathe wooden disks
representing in their diameters the base and generating circles. But
otherwise, wooden segments to answer the same purpose may be made as
from a piece of soft wood, such as pine or cedar, about three-eighths
inch thick, make two pieces A and B, in Fig. 115, and trim the edges C
and D to the circle of the pitch line of the required wheel. If the
diameter of the pitch circle is marked on a drawing, the pieces may be
laid on the drawing and sighted for curvature by the eye. In the absence
of a drawing, strike a portion of the pitch circle with a pair of
sharp-pointed compasses on a piece of zinc, which will show a very fine
line quite clear. After the pieces are filed to the circle, try them
together by laying them flat on a piece of board, bringing the curves in
contact and sweeping A against B, and the places of contact will plainly
show, and may be filed until continuous contact along the curves is
obtained. Take another similar piece of wood and form it as shown in
Fig. 116, the edge E representing a portion of the rolling circle. In
preparing these segments it is an excellent plan to file the convex
edges, as shown in Fig. 117, in which P is a piece of iron or wood
having its surface S trued; F is a file held firmly to S, while its
surface stands vertical, and T is the template laid flat on S, while
swept against the file. This insures that the edge shall be square
across or at least at the same angle all around, which is all that is
absolutely necessary. It is better, however, that the edges be square.
So likewise in fitting A and B (Fig. 115) together, they should be laid
flat on a piece of board. This will insure that they will have contact
clear across the edge, which will give more grip and make slip less
likely when using the segments. Now take a piece of stiff drawing paper
or of sheet zinc, lay segment A upon it, and mark a line coincident with
the curved edge. Place the segment representing the generating circle
flat on the paper or zinc, hold its edge against segment A, and roll it
around a sufficient distance to give as much of the curve as may be
required; the operation being illustrated in Fig. 118, in which A is the
segment representing the pitch or base circle, E is the segment
representing the generating circle, P is the paper, C the curve struck
by the tracing point or pencil O.
[Illustration: Fig. 117.]
[Illustration: Fig. 118.]
This tracing point should be, if paper be used to trace on, a piece of
the _hardest_ pencil obtainable, and should be filed so that its edge,
if flat, shall stand as near as may be in the line of motion when
rolled, thus marking a fine line. If sheet zinc be used instead of paper
a needle makes an excellent tracing point. Several of the curves, C,
should be struck, moving the position of the generating segment a little
each time.
[Illustration: Fig. 119.]
On removing the segments from the paper, there will appear the lines
shown in Fig. 119; A representing the pitch circle, and O O O the curves
struck by the tracing point.
Cut out a piece of sheet zinc so that its edge will coincide with the
curve A and the epicycloid O, trying it with all four of the epicycloids
to see that no slip has occurred when marking them; shape a template as
shown in Fig. 120. Cutting the notches at _a_ _b_, acts to let the file
clear well when filing the template, and to allow the scriber to go
clear into the corner. Now take the segment A in Fig. 118, and use it as
a guide to carry the pitch circle across the template as at P, in Fig.
120. A zinc template for the flank curve is made after the same manner,
using the rolling segment in conjunction with the segment B in Fig. 115.
[Illustration: Fig. 120.]
But the form of template for the flank should be such as shown in Fig.
121, the curve P representing, and being of the same radius as the pitch
circle, and the curve F being that of the hypocycloid. Both these
templates are set to the pitch circles and to coincide with the marks
made on the wheel teeth to denote the thickness, and with a hardened
steel point a line is traced on the tooth showing the correct curve for
the same.
[Illustration: Fig. 121.]
An experienced hand will find no difficulty in producing true templates
by this method, but to avoid all possibility of the segments slipping on
coarse pitches, and with large segments, the segments may be connected,
as shown in Fig. 122, in which O represents a strip of steel fastened at
one end into one segment and at the other end to the other segment.
Sometimes, indeed, where great accuracy is requisite, two pieces of
steel are thus employed, the second one being shown at P P, in the
figure. The surfaces of these pieces should exactly coincide with the
edge of the segments.
[Illustration: Fig. 122.]
[Illustration: Fig. 123.]
[Illustration: Fig. 124.]
[Illustration: Fig. 125.]
[Illustration: Fig. 126.]
The curve templates thus produced being shaped to apply to the pitch
circle may be correctly applied to that circle independently of its
concentricity to the wheel axis or of the points of the teeth, but if
the points of the teeth are turned in the lathe so as to be true (that
is, concentric to the wheel axis) the form of the template may be such
as shown in Fig. 123, the radius of the arc A A equalling that of the
addendum circle or circumference at the points of the teeth, and the
width at B (the pitch circle) equaling the width of a space instead of
the thickness of a tooth. The curves on each side of the template may in
this case be filed for the full side of a tooth on each side of the
template so that it will completely fill the finished space, or the
sides of two contiguous teeth may be marked at one operation. This
template may be set to the marks made on the teeth at the pitch circle
to denote their requisite thickness, or for greater accuracy, a similar
template made double so as to fill two finished tooth spaces may be
employed, the advantage being that in this case the template also serves
to mark or test the thickness of the teeth. Since, however, a double
template is difficult to make, a more simple method is to provide for
the thickness of a tooth, the template shown in Fig. 124, the width from
A to B being either the thickness of tooth required or twice the
thickness of a tooth plus the width of a space, so that it may be
applied to the outsides of two contiguous teeth. The arc C may be made
both in its radius and distance from the pitch circle D D to equal that
of the addendum circle, so as to serve as a gauge for the tooth points,
if the latter are not turned true in the lathe, or to rest on the
addendum circle (if the teeth points are turned true), and adjust the
pitch circle D D to the pitch circle on the wheel.
The curves for the template must be very carefully filed to the lines
produced by the rolling segments, because any error in the template is
copied on every tooth marked from it. Furthermore, instead of drawing
the pitch circle only, the addendum circle and circle for the roots of
the teeth or spaces should also be drawn, so that the template may be
first filed to them, and then adjusted to them while filing the edges to
the curves.
Another form of template much used is shown in Fig. 125. The curves A
and B are filed to the curve produced by rolling segments as before, and
the holes C, D, E, are for fastening the template to an arm, such as
shown in Fig. 126, which represents a section of a wheel W, with a plug
P, fitting tightly into the hub H of the wheel. This plug carries at its
centre a cylindrical pin on which pivots the arm A. The template T is
fastened to the arm by screws, and set so that its pitch circle
coincides with the pitch circle P on the wheel, when the curves for one
side of all the teeth may be marked. The template must then be turned
over to mark the other side of the teeth.
The objection to this form of template is that the length of arc
representing the pitch circle is too short, for it is absolutely
essential that the pitch line on the template (or line representing the
arc of the addendum if that be used) be greater than the width of a
single tooth, because an error of the thickness of a line (in the
thickness of a tooth), in the coincidence of the pitch line of the
template with that of the tooth, would throw the tooth curves out to an
extent altogether inadmissible where true work is essential.
[Illustration: Fig. 127.]
To overcome this objection the template may be made to equal half the
thickness of a tooth and its edge filed to represent a radial line on
the wheel. But there are other objections, as, for example, that the
template can only be applied to the wheel when adjusted on the arm shown
in Fig. 126, unless, indeed, a radial line be struck on every tooth of
the wheel. Again, to produce the template a radial line representing the
radius of the wheel must be produced, which is difficult where segments
only are used to produce the curves. It is better, therefore, to form
the template as shown in Fig. 127, the projections at A B having their
edges filed to coincide with the pitch circle P, so that they may be
applied to a length of one arc of pitch circle at least equal to the
pitch of the teeth.
The templates for the tooth curves being obtained, the wheel must be
divided off on the pitch circle for the thickness of the teeth and the
width of the spaces, and the templates applied to the marks or points of
division to serve as guides to mark the tooth curves. Since, however, as
already stated, the tooth curves are as often struck by arcs of circles
as by templates, the application of such arcs and their suitability may
be discussed.
MARKING THE CURVES BY HAND.
In the employment of arcs of circles several methods of finding the
necessary radius are found in practice.
[Illustration: Fig. 128.]
In the best practice the true curve is marked by the rolling segments
already described, and the compass points are set by trial to that
radius which gives an arc nearest approaching to the true face and flank
curves respectively. The degree of curve error thus induced is
sufficient that the form of tooth produced cannot with propriety be
termed epicycloidal teeth, except in the case of fine pitches in which
the arc of a circle may be employed to so nearly approach the true curve
as to be permissible as a substitute. But in coarse pitches the error is
of much importance. Thus in Fig. 128 is shown the curve of the _former_
or _template_ attachment used on the celebrated Corliss Bevel Gear
Cutting Machine, to cut the teeth on the bevel-wheels employed upon the
line shafting at the Centennial Exhibition. These gears, it may be
remarked, were marvels of smooth and noiseless running, and attracted
wide attention both at home and abroad. The engraving is made from a
drawing marked direct from the _former_ itself, and kindly furnished me
by Mr. George H. Corliss. A A is the face and B B the flank of the
tooth, C C is the arc of a circle nearest approaching to the face curve,
and D D the arc of a circle nearest approaching the flank curve. In the
face curve, there are but two points where the circle coincides with the
true curve, while in the flank there are three such points; a circle of
smaller radius than C C would increase the error at _b_, but decrease it
at _a_; one of a greater radius would decrease it at _b_, and increase
it at _a_. Again, a circle larger in radius than D D would decrease the
error at _e_ and increase it at _f_; while one smaller would increase it
at _e_ and decrease it at _f_. Only the working part of the tooth is
given in the illustration, and it will be noted that the error is
greatest in the flank, although the circle has three points of
coincidence.
[Illustration: Fig. 129.]
In this case the depth of the _former_ tooth is about three and
three-quarter times greater than the depth of tooth cut on the
bevel-wheels; hence, in the figure the actual error is magnified three
and three-quarter times. It demonstrates, however, the impropriety of
calling coarsely pitched teeth that are found by arcs of circles
"epicycloidal" teeth.
When, however, the pitches of the teeth are fine as, say an inch or
less, the coincidence of an arc of a circle with the true curve is
sufficiently near for nearly all practical purposes, and in the case of
cast gear the amount of variation in a pitch of 2 inches would be
practically inappreciable.
To obtain the necessary set of the compasses to mark the curves, the
following methods may be employed.
First by rolling the true curves with segments as already described, and
the setting the compass points (by trial) to that radius which gives an
arc nearest approaching the true curves. In this operation it is not
found that the location for the centre from which the curve must be
struck always falls on the pitch circle, and since that location will
for every tooth curve lie at the same radius from the wheel centre it is
obvious that after the proper location for one of the curves, as for the
first tooth face or tooth flank as the case may be, is found, a circle
may be struck denoting the radius of the location for all the teeth. In
Fig. 129, for example, P P represents the pitch circle, A B the radius
that will produce an arc nearest approaching the true curve produced by
rolling segments, and A the location of the centre from which the face
arc B should be struck. The point A being found by trial with the
compasses applied to the curve B, the circle A C may be struck, and the
location for the centres from which the face arcs of each tooth must be
struck will also fall on this circle, and all that is necessary is to
rest one point of the compasses on the side of the tooth as, say at E,
and mark on the second circle A C the point C, which is the location
wherefrom to mark the face arc D.
If the teeth flanks are not radial, the locations of the centre
wherefrom to strike the flank curves are found in like manner by trial
of the compasses with the true curves, and a third circle, as I in Fig.
130, is struck to intersect the first point found, as at G in the
figure. Thus there will be upon the wheel face three circles, P P the
pitch circle, J J wherefrom to mark the face curves, and I wherefrom to
mark the flank curves.
When this method is pursued a little time may be saved, when dividing
off the wheel, by dividing it into as many divisions as there are teeth
in the wheel, and then find the locations for the curves as in Fig. 131,
in which 1, 2, 3 are points of divisions on the pitch circle P P, while
A, B, struck from point 2, are centres wherefrom to strike the arcs E,
F; C, D, struck also from point 2 are centres wherefrom to strike the
flank curves G, H.
[Illustration: Fig. 130.]
It will be noted that all the points serving as centres for the face
curves, in Fig. 130, fall within a space; hence if the teeth were rudely
cast in the wheel, and were to be subsequently cut or trimmed to the
lines, some provision would have to be made to receive the compass
points.
To obviate the necessity of finding the necessary radius from rolling
segments various forms of construction are sometimes employed.
[Illustration: Fig. 131.]
Thus Rankine gives that shown in Fig. 132, which is obtained as follows.
Draw the generating circle D, and A D the line of centres. From the
point of contact at C, mark on circle D, a point distance from C
one-half the amount of the pitch, as at P, and draw the line P C of
indefinite length beyond C. Draw a line from P, passing through the line
of centres at E, which is equidistant between C and A. Then multiply
the length from P to C by the distance from A to D, and divide by the
distance between D and E. Take the length and radius so found, and mark
it upon P C, as at F, and the latter will be the location of centre for
compasses to strike the face curve.
[Illustration: Fig. 132.]
Another method of finding the face curve, with compasses, is as follows:
In Fig. 133, let P P represent the pitch circle of the wheel to be
marked, and B C the path of the centre of the generating or describing
circle as it rolls outside of P P. Let the point B represent the centre
of the generating circle when that circle is in contact with the pitch
circle at A. Then from B, mark off on B C any number of equidistant
points, as D, E, F, G, H, and from A, mark on the pitch circle, points
of division, as 1, 2, 3, 4, 5, at the intersection of radial lines from
D, E, F, G, and H. With the radius of the generating circle, that is, A
B, from B, as a centre, mark the arc I, from D the arc J, from E the arc
K, &c., to M, marking as many arcs as there are points of division on B
C. With the compasses set to the radius of divisions 1, 2, step off on
arc M the five divisions, N, O, S, T, V, and V will be a point in the
epicycloidal curves. From point of division 4, step off on L four points
of division, as _a_, _b_, _c_, _d_, and _d_ will be another point in the
epicycloidal curve. From point 3 set off three divisions on K, from
point 2 two dimensions on L, and so on, and through the points so
obtained, draw by hand or with a scroll the curve represented in the cut
by curve A V.
[Illustration: Fig. 133.]
Hypocycloids for the flanks of the teeth may be traced in a similar
manner. Thus in Fig. 134 P P is the pitch circle, and B C the line of
motion of the centre of the generating circle to be rolled within P P,
and R a radial line. From 1 to 6 are points of equal division on the
pitch circle, and D to I are arc locations for the centre of the
generating circle. Starting from A, which represents the supposed
location for the centre of the generating circle, the point of contact
between the generating and base circles will be at B. Then from 1 to 6
are points of equal division on the pitch circle, and from D to I are
the corresponding locations for the centres of the generating circle.
From these centres the arcs J, K, L, M, N, O, are struck. From 6 mark
the six points of division from _a_ to _f_, and _f_ is a point in the
curve. Five divisions on N, four on M, and so on, give respectively
points in the curve which is marked in the figure from A to _f_.
There is this, however, to be noted concerning the constructions of the
last two figures. Since the circle described by the centre of the
generating circle is of different arc or curve to that of the pitch
circle, the chord of an arc having an equal length on each will be
different. The amount is so small as to be practically correct. The
direction of the error is to give to the curves a less curvature, as
though they had been produced by a generating circle of larger diameter.
Suppose, for example, that the difference between the arc N 5 (Fig. 133)
and its chord is .1, and that the difference between the arc 4 5, and
its chord is .01, then the error in one step is .09, and, as the point V
is formed in 5 steps, it will contain this error multiplied five times.
Point _d_ would contain it multiplied four times, because it has 4
steps, and so on.
The error will increase in proportion as the diameter of the generating
is less than that of the pitch circle, and though in large wheels,
working with large wheels (so that the difference between the radius of
the generating circle and that of the smallest wheel is not excessive),
it is so small as to be practically inappreciable, yet in small wheels,
working with large ones, it may form a sensible error.
[Illustration: Fig. 134.]
An instrument much employed in the best practice to find the radius
which will strike an arc of a circle approximating the true epicycloidal
curve, _and for finding at the same time_ the location of the centre
wherefrom that curve should be struck, is found in the Willis'
odontograph. This is, in reality, a scale of centres or radii for
different and various diameters of wheels and generating circles. It
consists of a scale, shown in Fig. 135, and is formed of a piece of
sheet metal, one edge of which is marked or graduated in divisions of
one-twentieth of an inch. The edge meeting the graduated edge at O is at
angle of 75° to the graduated edge.
On one side of the odontograph is a table (as shown in the cut), for the
flanks of the teeth, while on the other is the following table for the
faces of the teeth:
TABLE SHOWING THE PLACE OF THE CENTRES UPON THE SCALE.
CENTRES FOR THE FACES OF THE TEETH.
Pitch in Inches and Parts.
+------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|No. of|1/4|3/8|1/2|5/8|3/4| 1|1- |1- |1- | 2|2- |2- | 3|3- |
|Teeth | | | | | | |1/4|1/2|3/4| |1/4|1/2| |1/2|
|------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 12 | 1| 2| 2| 3| 4| 5| 6| 7| 9| 10| 11| 12| 15| 17|
| 15 | ..| ..| 3| ..| ..| ..| 7| 8| 10| 11| 12| 14| 17| 19|
| 20 | 2| ..| ..| 4| 5| 6| 8| 9| 11| 12| 14| 15| 18| 21|
| 30 | ..| 3| 4| ..| ..| 7| 9| 10| 12| 14| 16| 18| 21| 25|
| 40 | ..| ..| ..| ..| 6| 8| ..| 11| 13| 15| 17| 19| 23| 26|
| | | | | | | | | | | | | | | |
| 60 | ..| ..| ..| 5| ..| ..| 10| 12| 14| 16| 18| 20| 25| 29|
| 80 | ..| ..| ..| ..| ..| 9| 11| 13| 15| 17| 19| 21| 26| 30|
| 100 | ..| ..| ..| ..| 7| ..| ..| ..| ..| 18| 20| 22| ..| 31|
| 150 | ..| ..| 5| 6| ..| ..| ..| 14| 16| 19| 21| 23| 27| 32|
|Rack. | ..| 4| ..| ..| ..| 10| 12| 15| 17| 20| 22| 25| 30| 34|
+------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
The method of using the instrument is as follows: In Fig. 136, let C
represent the centre, and P the pitch circle of a wheel to contain 30
teeth of 3 inch arc pitch. Draw the radial line L, meeting the pitch
circle at A. From A mark on the pitch circle, as at B, a radius equal to
the pitch of the teeth, and the thickness of the tooth as A _k_. Draw
from B to C the radial line E. Then for the flanks place the slant edge
of the odontograph coincident and parallel with E, and let its corners
coincide with the pitch circle as shown. In the table headed _centres
for the flanks of the teeth_, look down the column of 3 inch pitch, and
opposite to the 30 in the column of numbers of teeth, will be found the
number 49, which indicates that the centre from which to draw an arc for
the flank is at 49 on the graduated edge of the odontograph, as denoted
in the cut by _r_. Thus from _r_ to the side _k_ of the tooth is the
radius for the compasses, and at _r_, or 49, is the location for the
centre to strike the flank curve _f_. For the face curve set the slant
edge of the odontograph coincident with the radial line L, and in the
table of centres for the faces of teeth, look down the column of 3-inch
pitch, and opposite to 30 in the number of teeth column will be found
the number 21, indicating that at 21 on the graduated edge of the
odontograph, is the location of the centre wherefrom to strike the curve
_d_ for the face of the tooth, this location being denoted in the cut at
R.
[Illustration: Fig. 135.
TABLE SHOWING THE PLACE OF THE CENTRES UPON THE SCALE.
+--------------------------------------------------------------+
| CENTRES FOR THE FLANKS OF THE TEETH. |
+--------------------------------------------------------------+
| PITCH IN INCHES AND PARTS. |
+------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|Number| | | | | | | | | | | | | | |
| of | | | | | | 1 | 1-| 1-| 1-| 2 | 2-| 2-| 3 | 3-|
|teeth.|1/4|3/8|1/2|5/8|3/4| |1/4|1/2|3/4| |1/4|1/2| |1/2|
+------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 13| 32| 48| 64| 80| 96|129|160|193|225|257|289|321|386|450|
| 14| 17| 26| 35| 43| 52| 69| 87|104|121|139|156|173|208|242|
| 15| 12| 18| 25| 31| 37| 49| 62| 74| 86| 99|111|123|148|173|
| 16| 10| 15| 20| 25| 30| 40| 50| 59| 69| 79| 89| 99|119|138|
| 17| 8| 13| 17| 21| 25| 34| 43| 50| 59| 67| 75| 84|101|117|
| 18| 7| 11| 15| 19| 22| 30| 37| 45| 52| 59| 67| 74| 89|104|
| 19|...| 10| 13| 17| 20| 27| 35| 40| 47| 54| 60| 67| 80| 94|
| 20| 6| 9| 12| 16| 19| 25| 31| 37| 43| 49| 56| 62| 74| 86|
| 22| 5| 8| 11| 14| 16| 22| 27| 33| 39| 43| 49| 54| 65| 76|
| 24|...| 7| 10| 12| 15| 20| 25| 30| 35| 40| 45| 49| 59| 69|
| 26|...|...| 9| 11| 14| 18| 23| 27| 32| 37| 41| 46| 55| 64|
| 28| 4| 6|...|...| 13|...| 22| 26| 30| 35| 40| 43| 52| 60|
| 30|...|...| 8| 10| 12| 17| 21| 25| 29| 33| 37| 41| 49| 58|
| 35|...|...|...| 9| 11| 16| 19| 23| 26| 30| 34| 38| 45| 53|
| 40|...| 5| 7|...|...| 15| 18| 21| 25| 28| 32| 35| 42| 49|
| 60| 3|...| 6| 8| 9| 13| 15| 19| 22| 25| 28| 31| 37| 43|
| 80|...| 4|...| 7|...| 12|...| 17| 20| 23| 26| 29| 35| 41|
| 100|...|...|...|...| 8| 11| 14|...|...| 22| 25| 28| 34| 39|
| 150|...|...| 5|...|...|...| 13| 16| 19| 21| 24| 27| 32| 38|
| Rack.| 2|...|...| 6| 7| 10| 12| 15| 17| 20| 22| 25| 30| 34|
+------+---+---+---+---+---+---+---+---+---+---+---+---+---+---+]
The requisite number on the graduated edge for pitches beyond 3-1/2 (the
greatest given in the tables), may be obtained by direct proportion from
those given in the tables. Thus for 4 inch pitch, by doubling the
numbers given for a 2 inch pitch, containing the same number of teeth,
for 4-1/2 inch pitch by doubling the numbers given for a 2-1/4 inch
pitch. If the pitch be a fraction that cannot be so obtained, no serious
error will be induced if the nearest number marked be taken.
[Illustration: Fig. 136.]
An improved form of template odontograph, designed by Professor Robinson
of the Illinois School of Industry, is shown in Fig. 137.
In this instrument the curved edge, having graduated lines, approaches
more nearly to the curves produced by rolling circles than can be
obtained from any system in which an arc of a circle is taken to
represent the curve; hence, that edge is applied direct to the teeth and
used as a template wherefrom to mark the curve. The curve is a
logarithmic spiral, and the use of the instrument involves no other
labor than that of setting it in position. The applicability of this
curve, for the purpose, arises from two of its properties: first, that
the involute of the logarithmic spiral is another like spiral with poles
in common; and, second, that the obliquity or angle between a normal and
radius sector is constant, the latter property being possessed by this
curve only. By the first property it is known that a line, lying tangent
to the curve C E H, will be normal or perpendicular to the curve C D B;
so that when the line D E F is tangent to the pitch line, the curve A D
B will coincide very closely with the true epicycloidal curve, or,
rather, with that portion of it which is applied to the tooth curve of
the wheel. By the second quality, all sectors of the spiral, with given
angle at the poles, are similar figures which admit of the same degree
of coincidence for all similar epicycloids, whether great or small, and
nearly the same for epicycloids in general; thus enabling the
application of the instrument to epicycloids in general.
To set the instrument in position for drawing a tooth face a table which
accompanies the instrument is used. From this table a numerical value is
taken, which value depends upon the diameters of the wheels, and the
number of teeth in the wheel for which the curve is sought. This tabular
value, when multiplied by the pitch of the teeth, is to be found on the
graduated edge on the instrument A D B in Fig. 137. This done, draw the
line D E F tangent to the pitch line at the middle of the tooth, and
mark off the half thickness of the tooth, as E, D, either on the tangent
line or the pitch line. Then place the graduated edge of the odontograph
at D, and in such a position that the number and division found as
already stated shall come precisely on the tangent line at D, and at the
same time so set the curved edge H F C so that it shall be tangent to
the tangent line, that is to say, the curved edge C H must just meet the
tangent line at some one point, as at F in the figure. A line drawn
coincident with the graduated edge will then mark the face curve
required, and the odontograph may be turned over, and the face on the
other side of the tooth marked from a similar setting and process.
For the flanks of the teeth setting numbers are obtained from a separate
table, and the instrument is turned upside down, and the tangent line D
F, Fig. 137, is drawn from the side of the tooth (instead of from the
centre), as shown in Fig. 138.
It is obvious that this odontograph may be set upon a radial arm and
used as a template, as shown in Fig. 126, in which case the instrument
would require but four settings for the whole wheel, while rolling
segments and the making of templates are entirely dispensed with, and
the degree of accuracy is greater than is obtainable by means of the
employment of arcs of circles.
The tables wherefrom to find the number or mark on the graduated edge,
which is to be placed coincident with the tangent line in each case, are
as follows:--
TABLE OF TABULAR VALUES WHICH, MULTIPLIED BY THE ARC PITCH OF THE TEETH,
GIVES THE SETTING NUMBER ON THE GRADUATED EDGE OF THE INSTRUMENT.
+--------------------+-----------------------------------------------------+
| | Number of Teeth in Wheel Sought; or, Wheel for |
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | 8 | 12 | 16 | 20 | 30 | 40 | 50 | 60 | 70 |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | _For Faces: Flanks Radial or Curved._ |
| RATIOS.[7] | Draw Setting Tangent at Middle of Tooth.-- |
| | Epicycloidal Spur or Bevel Gearing. |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| 1/12 = .083 | .32 | .39 | .46 | .51 | | | | | |
| 1/4 = .250 | .31 | .37 | .44 | .49 | .61 | .70 | .78 | .85 | .92 |
| 1/2 = .500 | .28 | .34 | .41 | .46 | .57 | .66 | .73 | .80 | .87 |
| 2/3 = .667 | .27 | .32 | .38 | .43 | .54 | .62 | .70 | .77 | .83 |
| 1 | .23 | .28 | .34 | .39 | .49 | .58 | .65 | .72 | .78 |
| 3/2 = 1.50 | .19 | .25 | .29 | .34 | .44 | .51 | .58 | .64 | .69 |
| 2 | .17 | .22 | .26 | .30 | .38 | .46 | .53 | .59 | .63 |
| 3 | | .16 | .19 | .23 | .31 | .38 | .44 | .49 | .53 |
| 4 | | .14 | .17 | .20 | .26 | .33 | .38 | .42 | .46 |
| 6 | | | | | .22 | .26 | .30 | .34 | .37 |
| 12 | | | | | | .20 | .23 | .25 | .28 |
| 24 | | | | | | | | | |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | Number of Teeth in Wheel Sought; or, Wheel for|
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| | 80 | 90 | 100 | 120 | 150 | 200 | 300 | 500 |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| | _For Faces: Flanks Radial or Curved._ |
| RATIOS.[7] | Draw Setting Tangent at Middle of Tooth.-- |
| | Epicycloidal Spur or Bevel Gearing. |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+
| 1/12 = .083 | | | | | | | | |
| 1/4 = .250 | .99 | 1.05| 1.11| 1.22| 1.36| 1.55| 1.94| 2.54|
| 1/2 = .500 | .93 | 1.00| 1.06| 1.15| 1.29| 1.50| 1.86| 2.41|
| 2/3 = .667 | .89 | .95| 1.01| 1.11| 1.24| 1.45| 1.79| 2.32|
| 1 | .83 | .89| .94| 1.03| 1.15| 1.36| 1.65| 2.10|
| 3/2 = 1.50 | .74 | .79| .84| .93| 1.05| 1.25| 1.53| 1.94|
| 2 | .68 | .72| .76| .84| .95| 1.13| 1.40| 1.81|
| 3 | .57 | .60| .63| .71| .82| .97| 1.23| 1.60|
| 4 | .49 | .53| .56| .63| .73| .87| 1.08| 1.42|
| 6 | .41 | .44| .47| .53| .61| .71| .90| 1.20|
| 12 | .30 | .32| .34| .37| .42| .49| .60| .82|
| 24 | | .19| .21| .23| .26| .31| .40| .57|
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+
+--------------------+-----------------------------------------------------+
| | Number of Teeth in Wheel Sought; or, Wheel for |
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | 8 | 12 | 16 | 20 | 30 | 40 | 50 | 60 | 70 |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | _For Flanks, when Curved._ |
| | Draw Setting Tangent at Side of Tooth.-- |
| | Epicycloidal Spur and Bevel Gearing. |
|D C | Faces of Internal, and Flanks of Pinion Teeth. |
|e u +-----+-----+-----+-----+-----+-----+-----+-----+-----+
|g F r { 1.5 slight.| .77 | .98 | 1.18| 1.36| 1.75| 2.05| 2.31| 2.56| 2.75|
|r l v { 2 good. | .44 | .54 | .63| .72 | .92| 1.09| 1.24| 1.38| 1.49|
|e a a { 3 more. | .20 | .28 | .35| .40 | .54| .65| .76| .86| .95|
|e n t { 4 much. | | .20 | .23| .25 | .34| .42| .51| .59| .66|
| k u { 6 | | | .16| .17 | .26| .32| .38| .43| .48|
|o r {12 | | | | | .19| .24| .28| .31| .34|
|f e {24 | | | | | | | | | |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | Number of Teeth in Wheel Sought; or, Wheel for|
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| | 80 | 90 | 100 | 120 | 150 | 200 | 300 | 500 |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| | _For Flanks, when Curved._ |
| | Draw Setting Tangent at Side of Tooth.-- |
| | Epicycloidal Spur and Bevel Gearing. |
|D C | Faces of Internal, and Flanks of Pinion Teeth.|
|e u +-----+-----+-----+-----+-----+-----+-----+-----+
|g F r { 1.5 slight.| 2.92| 3.08| 3.24| 3.52| 3.87| 4.51| 5.50| 7.20|
|r l v { 2 good. | 1.59| 1.79| 1.79| 1.98| 2.23| 2.67| 3.22| 4.50|
|e a a { 3 more. | 1.02| 1.10| 1.18| 1.31| 1.46| 1.67| 2.08| 2.76|
|e n t { 4 much. | .71| .77| .82| .92| 1.06| 1.25| 1.64| 2.15|
| k u { 6 | .52| .56| .60| .66| .76| .93| 1.20| 1.54|
|o r {12 | .36| .38| .40| .45| .52| .63| .80| .98|
|f e {24 | | | .22| .25| .28| .33| .47| .60|
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+
+--------------------+-----------------------------------------------------+
| | Number of Teeth in Wheel Sought; or, Wheel for |
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | 8 | 12 | 16 | 20 | 30 | 40 | 50 | 60 | 70 |
| +-----+-----+-----+-----+-----+-----+-----+-----+-----+
| _For Faces of Racks; and of Pinions for Racks and Internal Gears; for |
| Flanks of Internal and Sides of Involute Teeth._ |
| Draw Setting Tangent at Middle of Tooth, regarding Space as Tooth in |
| Internal Teeth. For Rack use Number of Teeth in Pinion. |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| Pinion. | .31 | .39 | .48 | .57 | .73 | .88 | 1.00| 1.10| 1.20|
| Rack. | .32 | .38 | .44 | .50 | .62 | .72 | .80| .87| .93|
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+
| | Number of Teeth in Wheel Sought; or, Wheel for|
| | Which Teeth are Sought. |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| | 80 | 90 | 100 | 120 | 150 | 200 | 300 | 500 |
| +-----+-----+-----+-----+-----+-----+-----+-----+
| _For Faces of Racks; and of Pinions for Racks and Internal Gears; |
| for Flanks of Internal and Sides of Involute Teeth._ |
|Draw Setting Tangent at Middle of Tooth, regarding Space as Tooth in|
| Internal Teeth. For Rack use Number of Teeth in Pinion. |
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+
| Pinion. | 1.30| 1.40| 1.48| 1.65| 1.85| 2.15| 2.65| 3.50|
| Rack. | .99| 1.03| 1.08| 1.16| 1.27| 1.49| 1.86| 2.44|
+--------------------+-----+-----+-----+-----+-----+-----+-----+-----+
[7] These ratios are obtained by dividing the radius of the wheel
sought by the diameter of the generating circle.
From these tables may be found a tabular value which, multiplied by the
pitch of the wheel to be marked (as stated at the head of the table),
will give the setting number on the graduated edge of the instrument,
the procedure being as follows:--
For the teeth of a pair of wheels intended to gear together only (and
not with other wheels having a different number of teeth).
For the face of such teeth where the flanks are to be radial lines.
Rule.--Divide the pitch circle radius of the wheel to have its teeth
marked by the pitch circle radius of the wheel with which it is to gear:
or, what is the same thing, divide the number of teeth in the wheel to
have its teeth marked by the number of teeth in the wheel with which it
is to gear, and the quotient is the "ratio." In the ratio column find
this number, and look along that line, and in the column at the head of
which is the number of teeth contained in the wheel to be marked, is a
number termed the tabular value, which, multiplied by the arc pitch of
the teeth, will give the number on the graduated edge by which to set
the instrument to the tangent line.
Example.--What is the setting number for the face curves of a wheel to
contain 12 teeth, of 3-inch arc pitch, and to gear with a wheel having
24 teeth?
Here number of teeth in wheel to be marked = 12, divided by the number
of teeth (24) with which it gears; 12 ÷ 24 = .5. Now in column of ratios
may be found 1/2 = .500 (which is the same thing as .5), and along the
same horizontal line in the table, and in the column headed 12 (the
number of teeth in the wheel) is found .34. This is the tabular value,
which, multiplied by 3 (the arc pitch of the teeth), gives 1.02, which
is the setting number on the graduated edge. It will be noted, however,
that the graduated edge is marked 1, 2, 3, &c., and that between each
consecutive division are ten subdivisions; hence, for the decimal .02 an
allowance may be made by setting the line 1 a proportionate amount below
the tangent line marked on the wheel to set the instrument by.
[Illustration: Fig. 137. NEW ODONTOGRAPH Full Size]
Required now the setting number for the wheel to have the 24 teeth.
Here number of teeth on the wheel = 24, divided by the number of teeth
(12) on the wheel with which it gears; 24 ÷ 12 = 2. Now, there is no
column in the "number of teeth sought" for 24 teeth; but we may find the
necessary tabular value from the columns given for 20 teeth and 30
teeth, thus:--opposite ratio 2, and under 20 teeth is given .30, and
under 30 teeth is given .38--the difference between the two being .08.
Now the difference between 20 teeth and 24 teeth is 4/10; hence, we take
4/10 of the .08 and add it to the tabular value given for 20 teeth,
thus: .08 × 4 ÷ 10 = .032, and this added to .30 (the tabular value
given for 20 teeth = .33, which is the tabular value for 24 teeth). The
.33 multiplied by arc pitch (3) gives .99. This, therefore, is the
setting number for the instrument, being sufficiently near to the 1 on
the graduated edge to allow that 1 to be used instead of .99.
[Illustration: Fig. 138.]
It is to be noted here that the pinion, having radial lines, the other
wheel must have curved flanks; the rule for which is as follows:--
CURVED FLANKS FOR A PAIR OF WHEELS.
Note.--When the flanks are desired to be curved instead of radial, it is
necessary to the use of the instrument to select and assume a value for
the degree of curve, as is done in the table in the column marked
"Degree for flank curving;" in which
1.5 slight--a slight curvature of flank.
2 good--an increased curvature of flank.
3 more--a degree of pronounced spread at root.
4 much--spread at root is a distinguishing feature of tooth form.
6--still increased spread in cases where the strength at root of
pinion is of much importance to give strength.
12--as above, under aggravated conditions.
24--undesirable (unless requirement of strength compels this degree),
because of excessive strain on pinion.
Rule.--For faces of teeth to have curved flanks.
Divide the number of teeth in the wheel to be marked by the number of
teeth in the wheel with which it gears, and multiply by the degree of
flank curve selected for the wheel with which that to be marked is to
gear, and this will give the ratio. Find this number in ratio column,
and the tabular number under the column of number of teeth of wheel to
be marked; multiply tabular number so found by arc pitch of wheel to be
marked, and the product will be the setting number for the instrument.
Example.--What is the setting number on the graduated edge of the
odontograph for the faces of a wheel (of a pair) to contain 12 teeth of
2-inch arc pitch, and to gear with a wheel having 24 teeth and a flank
curvature represented by 3 in "Degree of flank curving" column?
Here teeth in wheel to be marked (12) divided by number of teeth in the
wheel it is to gear with (24), 12 ÷ 24 = .5, which multiplied by 3
(degree of curvature selected for flanks of 24-teeth wheel), .5 × 3 =
1.5. In column of ratio numbers find 1.5, and in 12-teeth column is .25,
which multiplied by pitch (2) gives .5 as the setting number for the
instrument; this being the fifth line on the instrument, and half way
between the end and mark 1.
FOR CURVED FLANKS.
Rule.--Assume the degree of curve desired for the flanks to be marked,
select the corresponding value in the column of "Degrees of flank
curving," and find the tabular value under the number of teeth column.
Multiply tabular value so found by the arc pitch of the teeth, and the
product is the setting number on the instrument.
Example.--What is the setting number on the odontograph for the flanks
of a wheel to contain 12 teeth and gear with one having 24 teeth, the
degree of curvature for the flanks being represented by 4 in the column
of "Degree of flank curvature?"
Here in column of degrees of flank curvature on the 3 line and under 12
teeth is .20, which multiplied by pitch of teeth (2) is .20 × 2 = 40, or
4/10; hence, the fourth line of division on the curved corner is the
setting line, it representing 4/10 of 1.
FOR INTERCHANGEABLE GEARING (THAT IS, A TRAIN OF GEARS ANY ONE OF WHICH
WILL WORK CORRECTLY WITH ANY OTHER OF THE SAME SET).
Rule--both for the faces and for the flanks. For each respective wheel
divide the number of teeth in that wheel by some one number not greater
than the number of teeth in the smallest wheel in the set, which gives
the ratio number for the wheel to be marked. On that line of ratio
numbers, and in the column of numbers of teeth, find the tabular value
number; multiply this by the arc pitch of the wheel to be marked, and
the product is the setting number of the instrument.
Example.--A set of wheels is to contain 10 wheels; the smallest is to
contain 12 teeth; the arc pitch of the wheels is four inches. What is
the setting number for the smallest wheel?
Here number of teeth in smallest wheel of set is 10; divide this by any
number smaller than itself (as say 5), 10 ÷ 5 = 2 = the ratio number on
ratio line for 2; and under column for 12 is .17, which is the tabular
value, which multiplied by pitch (4) is .17 × 4 = 68, or 6/10 and 8/100;
hence, the instrument must be set with its seventh line of division just
above the tangent line marked on the wheel. It will be noted that, if
the seventh line were used as the setting, the adjustment would be only
the 2/100 of a division out, an amount scarcely practically appreciable.
Both for the faces and flanks, the second number is obtained in
_precisely_ the same manner for every wheel in the set, except that
instead of 10 the number of teeth in each wheel must be substituted.
RACK AND PINION.--_For radial flanks_ use for faces the two lower lines
of table. _For curved flanks_ find tabular value for pinion faces in
lowest line. For flanks of pinion choose degree of curving, and find
tabular value under "flanks," as for other wheels. For faces of rack
divide number of teeth in pinion by degree of curving, which take for
number of teeth in looking opposite "rack." Flanks of rack are still
parallel, but may be arbitrarily curved beyond half way below pitch
line.
INTERNAL GEARS.--For tooth curves within the pitch lines, divide radius
of each wheel by any number not greater than radius of pinion, and look
in the table under "flanks." For curves outside pitch line use lower
line of table; or, divide radii by any number and look under "faces." In
applying instrument draw tangents at middle and side of _space_, for
internal teeth.
INVOLUTE TEETH.--For tabular values look opposite "Pinion," under proper
number of teeth, for each wheel. Draw setting tangent from "base circle"
of involute, at middle of tooth. For this the instrument gives the whole
side of tooth at once.
In all cases multiply the tabular value by the pitch in inches.
BEVEL-WHEELS.--Apply above rules, using the developed normal cone bases
as pitch lines. For right-angled axes this is done by using in place of
the actual ratio of radii, or of teeth numbers, the square of that
ratio; and for number of teeth, the actual number multiplied by the
square root of one plus square of ratio or radii; the numerator of
ratio, and number of teeth, belonging to wheel sought.
When the first column ratio and teeth numbers fall between those given
in the table, the tabular values are found by interpolating as seen in
the following examples:
EXAMPLES OF TABULAR VALUES AND SETTING NUMBERS.
_Take a pair of 16 and 56 teeth; radii 5.09 and 17.82 inches
respectively; and 2 inches pitch._
+----------------+------+----------------+------+---------------+-------+
| |Number} | | First Column | Tab. |
|Kind of Gearing.| of } Kind of Flank. |Ratio | Ratio. | Val. |
| |Teeth.} |Radii.+--------+------+---+---+
| | | | | Flank. |Face. |[A]|[B]|
+----------------+------+----------------+------+--------+------+---+---+
|Epicycloidal, }|Small |Radial | .29 |Radial | .29 |.. |.44|
|Radial Flanks }|Large |Radial | 3.5 |Radial | 3.5 |.. |.44|
|Epicycloidal, } |Small |Curved 2 deg. | .29 | 2 | .87 |.63|.36|
|Curved Flanks.} |Large |Curved 3 deg. } | 3.5 | 3 | 7. |.82|.30|
|Epicycloidal, }|Small |"Sets," Divide} | 2. | 2 | 2. |.63|.26|
|Interchange'bl.}|Large |Radii by 2.55 } | 7. | 7 | 7. |.40|.30|
|Epicycloidal, } |Pinion|Curved 2 deg. | | 2 |Pinion|.63|.44|
|Internal. } |Wheel |Int. face 7 deg.| 3.5 |Pinion | 7[8] |.84|.39|
|Epicycloidal, }|Pinion|Curved 2 deg. | | 2 |Pinion|.63|.44|
|Rack & Pinion. }|Rack |Parallel | |Parallel|Rack |.. |.31|
|Involute } |Small |Face and Flank | | Pinion. | .44 |
|Gearing. } |Large |One Curve | | Pinion. | .84 |
+----------------+------+----------------+------+--------+------+-------+
Legend: A = Flank.
B = Face.
[8] The face being here internal, the tabular value is to be found
under "flanks." If bevels, use ratio radii .082 and 12.25; and teeth
numbers 16.6 and 203.8 respectively.
WALKER'S PATENT WHEEL SCALE.--This scale is used in many manufactories
in the United States to mark off the teeth for patterns, wherefrom to
mould cast gears, and consists of a diagram from which the compasses may
be set to the required radius to strike the curves of the teeth.
[Illustration: Fig. 139.]
The general form of this diagram is shown in Fig. 139. From the portion
A the length of the teeth, according to the pitch, is obtained. From the
portion B half the thickness of the tooth at the pitch line is obtained.
From the part C half the thickness at the root is obtained, and from the
part D half the thickness at the point is obtained.
[Illustration: Fig. 140.]
Each of these parts is marked with the number of teeth the wheel is to
contain, and with the pitch of the teeth as shown in Fig. 140, which
represents part C full size. Now suppose it is required to find the
thickness at the root, for a tooth of a wheel having 60 teeth of one
inch pitch, the circles from the point A, pitch line B and root C being
drawn, and a radial line representing the middle of the tooth being
marked, as is shown in Fig. 142, the compass points are set to the
distance F B, Fig. 140--F being at the junction of line 1 with line 60;
the compasses are then rested at G, and the points H I are marked. Then,
from the portion B, Fig. 139 of the diagram, which is shown full-size in
Fig. 141, the compasses may be set to half the thickness at the pitch
circle, as in this case (for ordinary teeth) from E to E, and the points
J K, Fig. 142, are marked. By a reference to the portion D of the
diagram, half the thickness of the tooth at the point is obtained, and
marked as at L M in Fig. 142. It now remains to set compasses to the
radius for the face and that for the flank curves, both of which may be
obtained from the part A of the diagram. The locations of the centres,
wherefrom to strike these curves, are obtained as in Fig. 142. The
compasses set for the face curve are rested at H, and the arc N is
struck; they are then rested at J and the arc O struck; and from the
intersection of N O, as a centre, the face curve H J is marked. By a
similar process, reference to the portion D of the diagram, half the
thickness of the tooth at the point is obtained, and marked as at L M in
Fig. 142. It now remains to set the compasses to the radius to strike
the respective face and flank curves, and for this purpose the operator
turns to the portion A, Fig. 139, of the diagram or scale, and sets the
compasses from the marks on that portion to the required radii.
[Illustration: Fig. 141.]
It now remains to find the proper location from which to strike the
curves.
[Illustration: Fig. 142.]
The face curve on the other side of the tooth is struck. The compasses
set to the flank radius is then rested at M, and the arc P is marked and
rested at K to mark the arc Q; and from the intersection of P Q, as a
centre, the flank curve K M is marked: that on the other side of the
tooth being marked in a similar manner.
Additional scales or diagrams, not shown in Fig. 139, give similar
distances to set the compasses for the teeth of internal wheels and
racks.
It now remains to explain the method whereby the author of the scale has
obtained the various radii, which is as follows: A wheel of 200 teeth
was given the form of tooth curve that would be obtained by rolling it
upon another wheel, containing 200 teeth of the same pitch. It was next
given the form of tooth that would be obtained by rolling upon it a
wheel having 10 teeth of the same pitch, and a line intermediate between
the two curves was taken as representing the proper curve for the large
wheel. The wheel having 10 teeth was then given the form of tooth that
would be obtained by rolling upon it another wheel of the same diameter
of pitch circle and pitch of teeth. It was next given the form of tooth
that would be given by rolling upon it a wheel having 200 teeth, and a
curve intermediate between the two curves thus obtained was taken as
representing the proper curve for the pinion of 10 teeth. By this means
the inventor does not claim to produce wheels having an exactly equal
velocity ratio, but he claims that he obtains a curve that is the
nearest approximation to the proper epicycloidal curve. The radii for
the curves for all other numbers of teeth (between 10 and 200) are
obtained in precisely the same manner, the pinion for each pitch being
supposed to contain 10 teeth. Thus the scale is intended for
interchangeable cast gears.
The nature of the scale renders it necessary to assume a constant height
of tooth for all wheels of the same pitch, and this Mr. Walker has
assumed as .40 of the pitch, from the pitch line to the base, and .35
from the pitch line to the point.
The curves for the faces obtained by this method have rather more
curvature than would be due to the true epicycloid, which causes the
points to begin and leave contact more easily than would otherwise be
the case.
For a pair of wheels Mr. Walker strikes the face curve by a point on the
pitch rolling circle, and the flanks by a point on the addendum circle,
fastening a piece of wood to the pitch circle to carry the tracing
point. The flank of each wheel is struck with a tracing point, thus
attached to the pitch circle of the other wheel.
The proportions of teeth and of the spaces between them are usually
given in turns of the pitch, so that all teeth of a given pitch shall
have an equal thickness, height, and breadth, with an equal addendum and
flank, and the same amount of clearance.
The term "clearance" as applied to gear-wheel teeth means the amount of
space left between the teeth of one wheel, and the spaces in the other,
or, in other words, the difference between the width of the teeth and
that of the spaces between the teeth.
This clearance exists at the sides of the teeth, as in Fig. 143, at A,
and between the tops of the teeth and the bottoms or roots of the spaces
as at B. When, however, the simple term clearance is employed it implies
the side clearance as at A, the clearance at B being usually designated
as _top and bottom clearance_. Clearance is necessary for two purposes;
first, in teeth cut in a machine to accurate form and dimensions, to
prevent the teeth of one wheel from binding in the spaces of the other,
and second, in cast teeth, to allow for the imperfections in the teeth
which are incidental to casting in a founder's mould. In machine-cut
teeth the amount of clearance is a minimum.
In wheels which are cast with their teeth complete and on the pattern,
the amount of clearance must be a maximum, because, in the first place,
the teeth on the pattern must be made taper to enable the extraction of
the pattern from the mould without damage to the teeth in the mould, and
the amount of this taper must be greater than in machine-moulded teeth,
because the pattern cannot be lifted so truly vertical by hand as to
avoid, in all cases, damage to the mould; in which case the moulder
repairs the mould either with his moulding tools and by the aid of the
eye, or else with a tooth and a space made on a piece of wood for the
purpose. But even in this case the concentricity of the teeth is
scarcely likely to be preserved.
It is obvious that by reason of this taper each wheel is larger in
diameter on one side than on the other, hence to preserve the true
curves to the teeth the pitch circle is made correspondingly smaller.
But if in keying the wheels to their shafts the two large diameters of a
pair of wheels be placed to work together, the teeth of the pair would
have contact on that side of the wheel only, and to avoid this and give
the teeth contact across their full breadth the wheels are so placed on
their shafts that the large diameter of one shall work with the small
one of the other, the amount of taper being the same in each wheel
irrespective of their relative diameters. This also serves to keep the
clearance equal in amount both top, and bottom, and sideways.
A second imperfection is that in order to loosen the pattern in the sand
or mould, and enable its extraction by hand from the mould, the pattern
requires to be _rapped_ in the mould, the blows forcing back the sand of
the mould and thus loosening the pattern. In ordinary practice the
amount of this rapping is left entirely to the judgment of the moulder,
who has nothing to guide him in securing an equal amount of pattern
movement in each direction in the mould; hence, the finished mould may
be of increased radius at the circumference in the direction in which
the wheel moved most during the rapping. Again, the wood pattern is apt
in time to shrink and become _out of round_, while even iron patterns
are not entirely free from warping. Again, the cast metal is liable to
contract in cooling more in one direction than in another. The amount of
clearance usually allowed for pattern-moulded cast gearing is given by
Professor Willis as follows:--Whole depth of tooth 7/10, of the pitch
working depth 6/10; hence 1/10 of the pitch is allowed for top and
bottom clearance, and this is the amount shown at B in Fig. 143. The
amount of side clearance given by Willis as that ordinarily found in
practice is as follows:--"Thickness of tooth 5/11 of the pitch; breadth
of space 6/11; hence, the side clearance equals 1/11 of the pitch, which
in a 3-inch pitch equals .27 of an inch in each wheel." Calling this in
round figures, which is near enough for our purpose, 1/4 inch, we have
thickness of tooth 1-1/4, width of space 1-3/4, or 1/2 inch of clearance
in a 3-inch pitch, an amount which on wheels of coarse pitch is
evidently more than that necessary in view of the accuracy of modern
moulding, however suitable it may have been for the less perfect
practice of Professor Willis's time. It is to be observed that the
rapping of the pattern in the founder's mould reduces the thickness of
the teeth and increases the width of the spaces somewhat, and to that
extent augments the amount of side clearance allowed on the pattern, and
the amount of clearance thus obtained would be nearly sufficient for a
small wheel, as say of 2 inches diameter. It is further to be observed
that the amount of rapping is not proportionate to the diameter of the
wheel; thus, in a wheel of 2 inches diameter, the rapping would increase
the size of the mould about 1/32 inch. But in the proportion of 1/32
inch to every 2 inches of diameter, the rapping on a 6-foot wheel would
amount to 1-1/16 inches, whereas, in actual practice, a 6-foot wheel
would not enlarge the mould more than at most 1/8 inch from the rapping.
[Illustration: Fig. 143.]
It is obvious, then, that it would be more in accordance with the
requirements to proportion the amount of clearance to the diameter of
the wheel, so as to keep the clearance as small as possible. This will
possess the advantage that the teeth will be stronger, it being obvious
that the teeth are weakened both from the loss of thickness and the
increase of height due to the clearance.
It is usual in epicycloidal teeth to fill in the corner at the root of
the tooth with a fillet, as at C, D, in Fig. 143, to strengthen it.
This is not requisite when the diameter of the generating circle is so
small in proportion to the base circle as to produce teeth that are
spread at the roots; but it is especially advantageous when the teeth
have radial flanks, in which case the fillets may extend farther up the
flanks than when they are spread; because, as shown in Fig. 47, the
length of operative flank is a minimum in teeth having radial flanks,
and as the smallest pinion in the set is that with radial flanks, and
further as it has the least number of teeth in contact, it is the
weakest, and requires all the strengthening that the fillets in the
corners will give, and sometimes the addition of the flanges on the
sides of the pinion, such gears being termed "shrouded."
The proportion of the teeth to the pitch as found in ordinary practice
is given by Professor Willis as follows:--
Depth to pitch line 3/10 of the pitch.
Working depth 6/10 " "
Whole depth 7/10 " "
Thickness of tooth 5/11 " "
Breadth of space 6/11 " "
The depth to pitch line is, of course, the same thing as the height of
the addendum, and is measured through the centre of the tooth from the
point to the pitch line in the direction of a radial line and not
following the curve of tooth face.
Referring to the working depth, it was shown in Figs. 42 and 44 that the
height of the addendum remaining constant, it varies with the diameter
of the generating circle.
[Illustration: Fig. 144. Scale of Proportions given by Willis]
From these proportions or such others as may be selected, in which the
proportions bear a fixed relation to the pitch, a scale may be made and
used as a gauge, to set the compasses by, and in marking off the teeth
for any pitch within the capacity of the scale. A vertical line A B in
Fig. 144, is drawn and marked off in inches and parts of an inch, to
represent the pitches of the teeth; at a right angle to A B, the line B
C is drawn, its length equalling the whole depth of tooth, which since
the coarsest pitch in the scale is 4 inches will be 7/10 of 4 inches.
From the end of line C we draw a diagonal line to A, and this gives us
the whole depth of tooth for any pitch up to 4 inches: thus the whole
depth for a 4-inch pitch is the full length of the horizontal line B C;
the whole depth for a 3-inch pitch will be the length of the horizontal
line running from the 3 on line A B, to line A C on the right hand of
the figure; similarly for the full depth of tooth for a 2-inch pitch is
the length of the horizontal line running from 2 to A C. The working
depth of tooth being 6/10 of the pitch a diagonal is drawn from A
meeting line C at a distance from B of 6/10 of 4 inches and we get the
working depth for any other pitch by measuring (along the horizontal
line corresponding to that pitch), from the line of pitches to the
diagonal line for working depth of tooth. The thickness of tooth is 5/11
of the pitch and its diagonal is distant 5/11 of 4 (from B) on line B C,
the thickness for other pitches being obtained on the horizontal line
corresponding to those pitches as before.
[Illustration: Fig. 145.]
The construction of a pattern wherefrom to make a foundry mould, in
which to cast a spur gear-wheel, is as shown in section, and in plan of
Fig. 145. The method of constructing these patterns depends somewhat on
their size. Large patterns are constructed with the teeth separate, and
the body of the wheel is built of separate pieces, forming the arms, the
hub, the rim, and the teeth respectively. Pinion patterns, of six inches
and less in diameter, are usually made out of a solid piece, in which
case the grain of the wood must lie in the direction of the teeth
height. The chuck or face plate of the lathe, for turning the piece,
must be of smaller diameter than the pinion, so that it will permit
access to a tool applied on both sides, so as to strike the pitch circle
on both sides. A second circle is also struck for the roots or depths of
the teeth, and also, if required, an extra circle for striking the
curves of the teeth with compasses, as was described in Fig. 130. All
these circles are to be struck on both sides of the pattern, and as the
pattern is to be left slightly taper, to permit of its leaving the
mould easily, they must be made of smaller diameter on one side than on
the other of the pattern; the reduction in diameter all being made on
the same side of the pattern. The pinion body must then be divided off
on the pitch line into as many equal divisions as there are to be teeth
in it; the curves of the teeth are then marked by some one of the
methods described in the remarks on curves of gear-teeth. The top of the
face curves are then marked along the points of the teeth by means of a
square and scribe, and from these lines the curves are marked in on the
other side of the pinion, and the spaces cut out, leaving the teeth
projecting. For a larger pinion, without arms, the hub or body is built
up of courses of quadrants, the joints of the second course _breaking
joint_ with those of the first.
[Illustration: Fig. 146.]
The quadrants are glued together, and when the whole is formed and the
glue dry, it is turned in the lathe to the diameter of the wheel at the
roots of the teeth. Blocks of wood, to form the teeth, are then planed
up, one face being a hollow curve to fit the circle of the wheel. The
circumference of the wheel is divided, or pitched off, as it is termed,
into as many points of equal division as there are to be teeth, and at
these points lines are drawn, using a square, having its back held
firmly against the radial face of the pinion, while the blade is brought
coincidal with the point of division, so as to act as a guide in
converting that point into a line running exactly true with the pinion.
All the points of division being thus carried into lines, the blocks for
the teeth are glued to the body of the pinion, as denoted by A, in Fig.
145. Another method is to dovetail the teeth into the pinion, as in Fig.
145 at B. After the teeth blocks are set, the process is, as already
described, for a solid pinion.
[Illustration: Fig. 147.]
The construction of a wheel, such as shown in Fig. 145, is as follows:
The rim R must be built up in segments, but when the courses of segments
are high enough to reach the flat sides of the arms they should be
turned in the lathe to the diameter on the inside, and the arms should
be let in, as shown in the figure at O. The rest of the courses of
segments should then be added. The arms are then put in, and the inside
of the segments last added may then be turned up, and the outside of the
rim turned. The hub should then be added, one-half on each side of the
arms, as in the figure. The ribs C of the arms are then added, and the
body is completed (ready to receive the teeth), by filleting in the
corners. An excellent method of getting out the teeth is as follows:
Shape A piece of hard wood, as in Fig. 146, making it some five or six
inches longer than the teeth, and about three inches deeper, the
thickness being not less than the thickness of the required teeth at the
pitch line. Parallel to the edge B C, mark the line A D, distant from B
C to an amount equal to the required depth of tooth. Mark off, about
midway of the piece, the lines A B and C D, distant from each other to
an amount equal to the breadth of the wheel rim, and make two saw cuts
to those lines. Take a piece of board an inch or two longer than the
radius of the gear-wheel and insert a piece of wood (which is termed a
box) tightly into the board, as shown in Fig. 147, E representing the
box. Let the point F on the board represent the centre of the wheel, and
draw a radial line R from F through the centre of the box. From the
centre F, with a trammel, mark the addendum line G G, pitch line H I,
and line J K for the depth of the teeth (and also a line wherefrom to
strike the teeth curves, as shown in Fig. 129 if necessary). From the
radial line R, as a centre, mark off on the pitch circle, points of
division for several teeth, so as to be able to test the accuracy of the
spacing across the several points, as well as from one point to the
next, and mark the curves for the teeth on the end of the box, as shown.
Turn the box end for end in the board, and mark out a tooth by the same
method on the other end of the box. The box being removed from the board
must now have its sides planed to the lines, when it will be ready to
shape the teeth in. The teeth are got out for length, breadth, and
thickness at the pitch line as follows: The lumber from which they are
cut should be very straight grained, and should be first cut into strips
of a width and thickness slightly greater than that of the teeth at the
pitch line. These strips (which should be about two feet long) should
then be planed down on the sides to very nearly the thickness of the
tooth at the pitch line, and hollow on one edge to fit the curvature of
the wheel rim. From these strips, pieces a trifle longer than the
breadth of the wheel rim are cut, these forming the teeth. The pieces
are then planed on the ends to the exact width of the wheel rim. To
facilitate this planing a number of the pieces or blank teeth may be set
in a frame, as in Figs. 148 and 149, in which A is a piece having the
blocks B B affixed to it. C is a clamp secured by the screws at S S, and
1, 2, 3, 4, 5, 6 are the ends of the blank teeth. The clamp need not be
as wide as the teeth, as in Fig. 148, but it is well to let the pieces
A and B B equal the breadth of the wheel rim, so that they will act as a
template to plane the blank teeth ends to. The ends of B B may be
blackleaded, so as to show plainly if the plane blade happens to shave
them, and hence to prevent planing B B with the teeth. The blank teeth
may now be separately placed in the box (Fig. 146) and secured by a
screw, as shown in that figure, in which S is the screw, and T the blank
tooth. The sides of the tooth must be carefully planed down equal and
level with the surface of the box. The rim of the wheel, having been
divided off into as many divisions as there are to be teeth in the
wheel, as shown in Fig. 150, at _a_, _a_, _a_, &c., the finished teeth
are glued so that the same respective side of each tooth exactly meets
one of the lines _a_. Only a few spots of glue should be applied, and
these at the middle of the root thickness, so that the glue shall not
exude and hide the line _a_, which would make it difficult to set the
teeth true to the line. When the teeth are all dry they must be
additionally secured to the rim by nails. Wheels sufficiently large to
incur difficulty of transportation are composed of a number of sections,
each usually consisting of an arm, with an equal length of the rim arc
on each side of it, so that the joint where the rim segments are bolted
together will be midway between the two arms.
[Illustration: Fig. 148.]
This, however, is not absolutely necessary so long as the joints are so
arranged as to occur in the middle of tooth spaces, and not in the
thickness of the tooth. This sometimes necessitates that the rim
sections have an unequal length of arc, in which event the pattern is
made for the longest segment, and when these are cast the teeth
superfluous for the shorter segments are stopped off by the foundry
moulder. This saves cutting or altering the pattern, which, therefore,
remains good for other wheels when required.
[Illustration: Fig. 149.]
When the teeth of wheels are to be cut in a gear-cutting machine the
accurate spacing of the teeth is determined by the index plate and
gearing of the machine itself; but when the teeth are to be cast upon
the wheel and a pattern is to be made, wherefrom to cast the wheel the
points of division denoting the thickness of the teeth and the width of
the spaces are usually marked by hand. This is often rendered necessary
from the wheels being of too large a diameter to go into dividing
machines of the sizes usually constructed.
To accurately divide off the pitch circle of a gear-wheel by hand,
requires both patience and skilful manipulation, but it is time and
trouble that well repays its cost, for in the accuracy of spaces lies
the first requisite of a good gear-wheel.
It is a very difficult matter to set the compasses so that by commencing
at any one point and stepping the compasses around the circle
continuously in one direction, the compass point shall fall into the
precise point from which it started, for if the compass point be set the
1-200th inch out, the last space will come an inch out in a circle
having 200 points of divisions. It is, therefore, almost impossible and
quite impracticable to accurately mark or divide off a circle having
many points of division in this manner, not only on account of the
fineness of the adjustment of the compass points, but because the
frequent trials will leave so many marks upon the circle that the true
ones will not be distinguishable from the false. Furthermore, the
compass points are apt to spring and fall into the false marks when
those marks come close to the true ones.
[Illustration: Fig. 150.]
In Fig. 151 is shown a construction by means of which the compass points
may be set more nearly than by dividing the circumference of the circle
by the number of divisions it is required to be marked into and setting
the compasses to the quotient, because such a calculation gives the
length of the division measured around the arc of the circle, instead of
the distance measured straight from point of division to point of
division.
[Illustration: Fig. 151.]
The construction of Fig. 151 is as follows: P P is a portion of the
circle to be divided, and A B is a line at a tangent to the point C of
the circle P P. The point D is set off distant from C, to an amount
obtained by dividing the circumference of P P by the number of divisions
it is to have. Take one-quarter of this distance C D, and mark it from
C, giving the point E, set one point of the compass at E and the other
at D, and draw the arc D F, and the distance from F to C, as denoted by
G, is the distance to which to set the compasses to divide the circle
properly. The compasses being set to this distance G, we may rest one
compass point at C, and mark the arc F H, and the distance between arc H
and arc D, measured on the line A B, is the difference between the
points C, F when measured around the circle P P, and straight across, as
at G.
[Illustration: Fig. 152.]
A pair of compasses set even by this construction will not, however, be
entirely accurate, because there will be some degree of error, even
though it be in placing the compass points on the lines and on the
points marked, hence it is necessary to step the compasses around the
circle, and the best method of doing this is as follows: Commencing at
A, Fig. 152, we mark off continuously one from the other, and taking
care to be very exact to place the compass point exactly coincident with
the line of the circle, the points B, C, D, &c., continuing until we
have marked half as many divisions as the circle is to contain, and
arriving at E, starting again at A, we mark off similar divisions (one
half of the total number), F, G, H, arriving at I, and the centre K,
between the two lines E, I, will be the true position of the point
diametrally opposite to point A, whence we started. These points are all
marked inside the circle to keep them distinct from those subsequently
marked.
[Illustration: Fig. 153.]
It will be, perhaps, observed by the reader that it would be more
expeditious, and perhaps cause less variation, were we to set the
compasses to the radius of the circle and mark off the point K, as shown
in Fig. 153, commencing at the point A, and marking off on the one side
the lines B, C, and D, and on the other side E, F, and G, the junction
or centre, between G and D, at the circle being the true position of the
point K. For circles struck upon flat surfaces, this plan may be
advantageous; and in cases where there are not at hand compasses large
enough, a pair of trammels may be used for the purpose; but our
instructions are intended to apply also to marking off equidistant
points on such circumferences as the faces of pulleys or on the outsides
of small rings or cylinders, in which cases the use of compasses is
impracticable. The experienced hand may, it is true, adjust the
compasses as instructed, and mark off three or four of the marks B, C,
&c., in Fig. 152, and then open out the compasses to the distance
between the two extreme marks, and proceed as before to find the centre
K, but as a rule, the time saved will scarcely repay the trouble; and
all that can be done to save time in such cases is, if the holes come
reasonably close together, to mark off, after the compasses are
adjusted, three or four spaces, as shown in Fig. 154. Commencing at the
point A, and marking off the points B, C, and D, we then set another
pair of compasses to the distance between A and D, and then mark, from D
on one side and from A on the other, the marks from F to L and from M to
T, thus obtaining the point K. This method, however expeditious and
correct for certain work, is not applicable to circumferential work of
small diameter and in which the distance between two of the adjacent
points is, at the most, 1/20 of the circumference of the circle; because
the angle of the surface of the metal to the compass point causes the
latter to spring wider open in consequence of the pressure necessary to
cause the compass point to mark the metal. This will be readily
perceived on reference to Fig. 155 in which A represents the stationary,
and B the scribing or marking point of the compasses.
[Illustration: Fig. 154.]
The error in the set of the compasses as shown by the distance apart of
the two marks E and I on the circle in Fig. 152 is too fine to render it
practicable to remedy it by moving the compass legs, hence we effect the
adjustment by oilstoning the points on the outside, throwing them closer
together as the figure shows is necessary.
[Illustration: Fig. 155.]
Having found the point K, we mark (on the outside of the circle, so as
to keep the marks distinct from those first marked) the division B, C,
D, Fig. 156, &c., up to G, the number of divisions between B and G being
one quarter of those in the whole circle. Then, beginning at K, we mark
off also one quarter of the number of divisions arriving at M in the
figure and producing the point 3. By a similar operation on the other
side of the circle, we get the true position of point No. 4. If, in
obtaining points 3 and 4, the compasses are not found to be set dead
true, the necessary adjustment must be made; and it will be seen that,
so far, we have obtained four true positions, and the process of
obtaining each of them has served as a justification of the distance of
the compass points. From these four points we may proceed in like
manner to mark off the holes or points between them; and the whole will
be as true as it is practicable to mark them off upon that size of
circle. In cases, however, where mathematical precision is required upon
flat and not circumferential surfaces, the marking off may be performed
upon a circle of larger diameter, as shown in Fig. 157. If it is
required to mark off the circle A, Fig. 157, into any even number of
equidistant points, and if, in consequence of the closeness together of
the points, it becomes difficult to mark them (as described) with the
compasses, we mark a circle B B of larger diameter, and perform our
marking upon it, carrying the marks across the smaller circle with a
straightedge placed to intersect the centres of the circles and the
points marked on each side of the diameter. Thus, in Fig. 157, the lines
1 and 2 on the smaller circle would be obtained from a line struck
through 1 and 4 on the outer circle; and supposing the larger circle to
be three times the size of the smaller, the deviation from truth in the
latter will be only 1/3 of whatever it is in the former.
[Illustration: Fig. 156.]
[Illustration: Fig. 157.]
In this example we have supposed the number of divisions to be an even
one, hence the point K, Fig. 152, falls diametrically opposite to A,
whereas in an odd number of points of division this would not be the
case, and we must proceed by either of the two following methods:--
[Illustration: Fig. 158.]
In Fig. 158 is shown a circle requiring to be divided by 17 equidistant
points. Starting from point 1 we mark on the outside of the
circumference points 2, 3, 4, &c., up to point 9. Starting again from
point 1 we mark points 10, 11, &c., up to 17. If, then, we try the
compasses to 17 and 9 we shall find they come too close together, hence
we take another pair of compasses (so as not to disturb the set of our
first pair) and find the centre between 9 and 17 as shown by the point
A. We then correct the set of our first pair of compasses, as near as
the judgment dictates, and from point A, we mark with the second
compasses (set to one half the new space of the first compasses) the
points B, C. With the first pair of compasses, starting from B, we mark
D, E, &c., to G; and from I, we mark divisions H, I, &c., to K, and if
the compasses were set true, K and G would meet at the circle. We may,
however, mark a point midway between K and G, as at 5. Starting again
from points C and I, we mark the other side of the circle in a similar
manner, producing the lines P and Q, midway between which (the compasses
not being set quite correct as yet) is the true point for another
division. After again correcting the compasses, we start from B and 5
respectively, and mark point 7, again correcting the compasses. Then
from C and the point between P and Q, we may mark an intermediate point,
and so on until all the points of division are made. This method is
correct enough for most practical purposes, but the method shown in Fig.
159 is more correct for an odd number of points of division. Suppose
that we have commenced at the point marked I, we mark off half the
required number of holes on one side and arrive at the point 2; and
then, commencing at the point I again, we mark off the other half of the
required number of holes, arriving at the point 3. We then apply our
compasses to the distance between the points 2 and 3; and if that
distance is not exactly the same to which the compasses are set, we make
the necessary adjustment, and try again and again until correct
adjustment is secured.
[Illustration: Fig. 159.]
It is highly necessary, in this case, to make the lines drawn at each
trial all on the same side of the circle and of equal length, but of a
different length to those marked on previous trials. For example, left
the lines A, B, C, D, in Fig. 159 represent those made on the first
trial, and E, F, G, H, those made on the second trial; and when the
adjustment is complete, let the last trial be made upon the outside or
other side of the circle, as shown by the lines I, J, K, L. Having
obtained the three true points, marked 1, 2, 3, we proceed to mark the
intermediate divisions, as described for an even number of divisions,
save that there will be a space, 2 and 3, opposite point 1, instead of a
point, as in case of a circle having an even number of divisions.
[Illustration: Fig. 160.]
The equal points of division thus obtained may be taken for the centres
of the tooth at the pitch circle or for one side of the teeth, as the
method to be pursued to mark the tooth curves may render most desirable.
If, for example, a template be used to mark off the tooth curves, the
marks may be used to best advantage as representing the side of a tooth,
and from them the thickness of the tooth may be marked or not as the
kind of template used may require. Thus, if the template shown in Fig.
21 be used, no other marks will be used, because the sides of a tooth on
each side of a space may be marked at one setting of the template to the
lines or marks of division. If, however, a template, such as shown in
Fig. 81 be used, a second set of lines marked distant from the first to
a radius equal to the thickness of a tooth becomes necessary so that the
template may be set to each line marked. If the Willis odontograph or
the Robinson template odontograph be used the second set of lines will
also be necessary. In using the Walker scale a radial line, as G in Fig.
142, will require to be marked through the points of equal division, and
the thickness of the tooth at the points on the pitch circle and at the
root must be marked as was shown in Fig. 142.
But if the arcs for the tooth curves are to be marked by compasses, the
location for the centres wherefrom to strike these arcs may be marked
from the points of division as was shown in Fig. 130.
To construct a pattern wherefrom to cast a bevel gear-wheel.--When a
pair of bevel-wheels are in gear and upon their respective shafts all
the teeth on each wheel incline, as has been shown, to a single point,
hence the pattern maker draws upon a piece of board a sketch
representing the conditions under which the wheels are to operate. A
sketch of this kind is shown in Fig. 160, in which A, B, C, D, represent
in section the body of a bevel pinion. F G is the point of a tooth on
one side, and E the point of a tooth on the other side of the pinion,
while H I are pitch lines for the two teeth. Thus, the cone surface, the
points, the pitch lines and the bottom of the spaces, projected as
denoted by the dotted lines, would all meet at X, which represents the
point where the axes of the shafts would meet.
[Illustration: Fig. 161.]
In making wooden patterns wherefrom to cast the wheels, it is usual,
therefore, to mark these lines on a drawing-board, so that they may be
referred to by the workman in obtaining the degree of cone necessary for
the body A B C D, to which the teeth are to be affixed. Suppose, then,
that the diameter of the pinion is sufficiently small to permit the body
A B C D to be formed of one piece instead of being put together in
segments, the operation is as follows: The face D C is turned off on the
lathe, and the piece is reversed on the lathe chuck, and the face A B is
turned, leaving a slight recess at the centre to receive and hold the
cone point true with the wheel. A bevel gauge is then set to the angle A
B C, and the cone of the body is turned to coincide in angle with the
gauge and to the required diameter, its surface being made true and
straight so that the teeth may bed well. While turning the face D C in
the lathe a fine line circle should be struck around the circumference
of the cone and near D C, on which line the spacing for the teeth may be
stepped off with the compasses. After this circle or line is divided off
into as many equidistant points as there are to be teeth on the wheel,
the points of division require to be drawn into lines, running across
the cone surface of the wheel, and as the ordinary square is
inapplicable for the purpose, a suitable square is improvised as
follows: In Fig. 161 let the outline in full lines denote the body of a
pinion ready to receive the teeth, and A B the circle referred to as
necessary for the spacing or dividing with the compasses. On A B take
any point, as C, as a centre, and with a pair of compasses mark
equidistant on each side of it two lines, as D, D. From D, D as
respective centres mark two lines, crossing each other as at F, and draw
a line, joining the intersection of the lines at F with C, and the last
line, so produced, will be in the place in which the teeth are to lie;
hence the wheel will require as many of these lines as it is to contain
teeth, and the sides of the teeth, being set to these lines all around
the pinion, will be in their proper positions, with the pitch lines
pointing to X, in Fig. 160.
[Illustration: Fig. 162.]
To avoid, however, the labor involved in producing these lines for each
tooth, two other plans may be adopted. The first is to make a square,
such as shown in Fig. 162, the face _f_ _f_ being fitted to the surface
C, in Fig. 161, while the edges of its blade coincide with the line
referred to; hence the edge of the blade may be placed coincident
successively with each point of division, as D D, and the lines for the
place of the length of each tooth be drawn. The second plan is to divide
off the line A B before removing the body of the pinion from the lathe,
and produce, as described, a line for one tooth. A piece of wood may
then be placed so that when it lies on the surface of the hand-rest its
upper surface will coincide with the line as shown in Fig. 163, in which
W is the piece of wood, and A, B, C, &c., the lines referred to. If the
teeth are to be glued and bradded to the body, they are first cut out in
blocks, left a little larger every way than they are to be when
finished, and the surfaces which are to bed on the cone are hollowed to
fit it. Then blocks are glued to the body, one and the same relative
side of each tooth being set fair to the lines. When the glue is dry,
the pinion is again turned on the lathe, the gauge for the cone of the
teeth being set in this case to the lines E, F, G in Fig. 160. The pitch
circles must then be struck at the ends of the teeth. The turned wheel
is then ready to have the curves of the teeth marked. The wheel must now
again be divided off on the pitch circle at the large end of the cone
into as many equidistant points as there are to be teeth on the wheel,
and from these points, and on the same relative side of them, mark off a
second series of points, distant from the points of division to an
amount equal to the thickness the teeth are required to be. From these
points draw in the outline of the teeth (upon the ends of the blocks to
form the teeth) at the large end of the cone. Then, by use of the
square, shown in Fig. 162, transfer the points of the teeth to the small
end of the cone, and trace the outline of the teeth at the small end,
taking centres and distances proportionate to the reduced diameter of
the pitch circle at the small end, as shown in Fig. 160, where at J are
three teeth so marked for the large end, and at K three for the small
end, P P representing the pitch circle, and R R a circle for the compass
points. The teeth for bevel pinions are sometimes put on by dovetails,
as shown in Fig. 164, a plan which possesses points of advantage and
disadvantage. Wood shrinks more across the grain than lengthwise with
it, hence when the grain of the teeth crosses that of the body with
every expansion or contraction of the wood (which always accompanies
changes in the humidity of the atmosphere) there will be a movement
between the two, because of the unequal expansion and contraction,
causing the teeth to loosen or to move. In the employment of dovetails,
however, a freedom of movement lengthways of the tooth is provided to
accommodate the movement, while the teeth are detained in their proper
positions. Again, if in making the founders' mould, one of the mould
teeth should break or fall down when the pattern is withdrawn, a tooth
may be removed from the pattern and used by the moulder to build up the
damaged part of the mould again. And if the teeth of a bevel pinion are
too much undercut on the flank curves to permit the whole pattern from
being extracted from the mould without damaging it, dovetailed teeth may
be drawn, leaving the body of the pattern to be extracted from the mould
last. On the other hand, the dovetail is a costly construction if
applied to large wheels. If the teeth are to be affixed by dovetails,
the construction varies as follows: Cut out a wooden template of the
dovetail, leaving it a little narrower than the thickness of the tooth
at the root, and set the template on the cone at a distance from one of
the lines A, B, C, Fig. 163, equal to the margin allowed between the
edge of the dovetail and the side of the root of the tooth, and set it
true by the employment of the square, shown in Fig. 162, and draw along
the cone surface of the body lines representing the location of the
dovetail grooves. The lines so drawn will give a taper toward X (Fig.
160), providing that, the template sides being parallel, each side is
set to the square. While the body is in the lathe, a circle on each end
may be struck for the depth of the dovetails, which should be cut out to
gauge and to template, so that the teeth will interchange to any
dovetail. The bottom of the dovetails need not be circular, but flat,
which is easier to make. Dovetail pieces or strips are fitted to the
grooves, being left to project slightly above the face of the cone or
body. They are drawn in tight enough to enable them to keep their
position while being turned in the lathe when the projecting points are
turned down level with the cone of the body. The teeth may then be got
out as described for glued teeth, and the dovetails added, each being
marked to its place, and finally the teeth are cut to shape.
[Illustration: Fig. 163.]
[Illustration: Fig. 164.]
[Illustration: Fig. 165.]
In wheels too large to have their cones tested by a bevel gauge, a
wooden gauge may be made by nailing two pieces of wood to stand at the
required angle as shown in Fig. 165, which is extracted from _The
American Machinist_, or the dead centre C and a straightedge may be used
as follows. In the figure the other wheel of the pair is shown dotted in
at B, and the dead centre is set at the point where the axes of A and B
would meet; hence if the largest diameter of the cone of A is turned to
correct size, the cone will be correct when a straightedge applied as
shown lies flat on the cone and meets the point of the dead centre E.
The pinion B, however, is merely introduced to explain the principle,
and obviously could not be so applied practically, the distance to set
_e_, however, is the radius _a_.
Skew Bevel.[9]--When the axles of the shaft are inclined to each other
instead of being in a straight line, and it is proposed to connect and
communicate motion to the shafts by means of a single pair of
bevel-gears, the teeth must be inclined to the base of the frustra to
allow them to come into contact.
[9] From the "Engineer and Machinists' Assistant."
[Illustration: Fig. 166.]
To find the line of contact upon a given frustrum of the tangent-cone;
let the Fig. 166 be the plane of the frustrum; _a_ the centre. Set off
_a_ _e_ equal to the shortest distance between the axes (called the
_eccentricity_), and divide it in _c_, so that _a_ _c_ is to _e_ _c_ as
the mean radius of the frustrum to the mean radius of that with which it
is to work; draw _c_ _p_ perpendicular to _a_ _e_, and meeting the
circumference of the conical surface at _m_; perform a similar operation
on the base of the frustrum by drawing a line parallel to _c_ _m_ and at
the same distance _a_ _c_ from the centre, meeting the circumference in
_p_.
The line _p_ _c_ is then plainly the line of direction of the teeth. We
are also at liberty to employ the equally inclined line _c_ _q_ in the
opposite direction, observing only that, in laying out the two wheels,
the pair of directions be taken, of which the inclinations correspond.
[Illustration: Fig. 167.]
Fig. 167 renders this mode of laying off the outlines of the wheels at
once obvious. In this figure the line _a_ _e_ corresponds to the line
marked by the same letters in Fig. 166; and the division of it at _c_ is
determined in the manner directed. The line _c_ _m_ being thus found in
direction, it is drawn indefinitely to _d_. Parallel to this line and
from the point _c_ draw _e_ to _e_, and in this line take the centre of
the second wheel. The line _c_ _m_ _d_ gives the direction of the teeth;
and if from the centre _a_ with radius at _c_ a circle be described, the
direction of any tooth of the wheel will be a tangent to it, as at _c_,
and similarly if a centre _e_ be taken in the line _e_ _d_, and with
radius _e_ _d_, _c_ _e_ a circle be drawn, the direction of the teeth of
the second wheel will be tangents to this last, as at _d_.
Having thus found the direction of the teeth, these outlines may be
formed as in the case of ordinary bevel-wheels and with equal exactness
and facility, all that is necessary being to find the curves for the
teeth as described for bevel-wheels, and follow precisely the same
construction, except that the square, Fig. 162, marking the lines across
the cones, requires to be set to the angle for the tooth instead of at a
right angle, and this angle may be found by the construction shown in
Fig. 167, it being there represented by line _d_ _c_. It is obvious,
however, that the bottoms of the blocks to form the teeth must be curved
to bed on the cone along the line _d_ _c_, Fig. 167, and this may best
be done by bedding two teeth, testing them by trial of the actual
surfaces.
[Illustration: Fig. 168.]
Then two teeth may be set in as No. 1 and No. 6 in the box shown in Fig.
148, the intermediate ones being dressed down to them.
Where a bevel-wheel pattern is too large to be constructed in one piece
and requires to be built up in pieces, the construction is as in Fig.
168, in which on the left is shown the courses of segments 1, 2, 3, 4,
5, &c., of which the rim is built up (as described for spur wheels), and
on the right is shown the finished rim with a tooth, _c_, in position.
The tooth proper is of the length of face of the wheel as denoted by _b
b´_; now all the lines bounding the teeth must converge to the point X.
Suppose, then, that the teeth are to be shaped for curve of face and
flank in a box as described for spur-wheel teeth in Fig. 146, then in
Fig. 168 let _a_, _a_ represent the bottom and _b b´_ the top of the
box, and _c_ a tooth in the box, its ends filling the opening in the box
at _b b´_ then the curve on the sides of the box at _b´_ must be of the
form shown at F, and the curve on the sides of the box (at the point _b_
of its length) must be as shown at G, the teeth shown in profile at G
and U representing the forms of the teeth at their ends, on the outside
of the wheel rim at _b´_, and on the inside at _b_; having thus made a
box of the correct form on its sides, the teeth may be placed in it and
planed down to it, thus giving all the teeth the same curve.
The spacing for the teeth and their fixing may be done as described for
the bevel pinion.
[Illustration: Fig. 169.]
To construct a pattern wherefrom to cast an endless screw, worm, or
tangent screw, which is to have the worm or thread cut in a lathe.--Take
two pieces, each to form one longitudinal half of the pattern; peg and
screw them together at the ends, an excess of stuff being allowed at
each end for the accommodation of two screws to hold the two halves
together while turning them in the lathe, or dogs, if the latter are
more convenient, as they might be in a large pattern. Turn the piece
down to the size over the top of the thread, after which the core prints
are turned. The body thus formed will be ready to have the worm or
thread cut, and for this purpose the tools shown in Figs. 169 and 140
are necessary.
That shown in Fig. 169 should be flat on the face similar to a parting
tool for cast iron, but should have a great deal more bottom rake, as
strength is not so much an object, and the tool is more easily
sharpened. It has also in addition two little projections A B like the
point of a penknife, formed by filing away the steel in the centre;
these points are to cut the fibres of the wood, the severed portion
being scraped away by the flat part of the tool.
[Illustration: Fig. 170.]
The degree of side rake given to the tool must be sufficient to let the
tool sides well clear the thread or worm, and will therefore vary with
the pitch of the worm.
The width of the tool must be a shade narrower than the narrowest part
of the space in the worm. Having suitably adjusted the change wheels of
the lathe to cut the pitch required the parting tool is fed in until the
extreme points reach the bottom of the spaces, and a square nosed
parting tool without any points or spurs will finish the worm to the
required depth. This will have left a square thread, and this we have
now to cut to the required curves on the thread or worm sides, and as
the cutting will be performed on the end grain of the wood, the top face
of the tool must be made keen by piercing through the tool a slot A,
Fig. 170, and filing up the bevel faces B, C and D, and then carefully
oilstoning them. This tool should be made slightly narrower than the
width of the worm space, so that it may not cut on both sides at once,
as it would have too great a length of cutting edge.
[Illustration: Fig. 171.]
Furthermore, if the pattern is very large, it will be necessary to have
two tools for finishing, one to cut from the pitch line inwards and the
other to complete the form from the pitch line outwards. It is advisable
to use hard wood for the pattern.
If it is decided to cut the thread by hand instead of with these lathe
tools, then, the pattern being turned as before, separate the two halves
by taking out the screws at the ends; select the half that has not the
pegs, as being a little more convenient for tracing lines across. Set
out the sections of the thread, A, B, C, and D, Fig. 171, similar to a
rack; through the centres of A, B, C, and D, square lines across the
piece; these lines, where they intersect the pitch line, will give the
centres of teeth on that side: or if we draw lines, as E, F, through the
centres of the spaces, they will pass through the centres of the teeth
(so to speak) on the other side; in this position complete the outline
on that side. It will be found, in drawing these outlines, that the
centres of some of the arcs will lie outside the pattern. To obtain
support for the compasses, we must fit over the pattern a piece of board
such as shown by dotted lines at G H.
[Illustration: Fig. 172.]
It now remains to draw in the top of the thread upon the curved surface
of the half pattern; for this purpose take a piece of stiff card or
other flexible material, wrap it around the pattern and fix it
temporarily by tacks, we then trim off the edges true to the pattern,
and mark upon the edges of the card the position of the tops of the
thread upon each side; we remove the card and spread it out on a flat
surface, join the points marked on the edges by lines as in Fig. 172,
replace the card exactly as before upon the pattern, and with a fine
scriber we prick through the lines. The cutting out is commenced by
sawing, keeping, of course, well within the lines; and it is facilitated
by attaching a stop to the saw so as to insure cutting at all parts
nearly to the exact depth. This stop is a simple strip of wood and may
be clamped to the saw, though it is much more convenient to have a
couple of holes in the saw blade for the passage of screws. For
finishing, a pair of templates, P and Q, Fig. 173, right and left, will
be found useful; and finally the work should be verified and slight
imperfections corrected by the use of a form or template taking in three
spaces, as shown at R in Fig. 173. In drawing the lines on the card, we
must consider whether it is a right or left-handed worm that we desire.
In the engraving the lines are those suitable for a right-handed thread.
Having completed one half of the pattern, place the two halves together,
and trace off the half that is uncut, using again the card template for
drawing the lines on the curved surface. The cutting out will be the
same as before.
[Illustration: Fig. 173.]
As the teeth of cast wheels are, from their deviation from accuracy in
the tooth curves and the concentricity of the teeth to the wheel centre,
apt to create noise in running, it is not unusual to cast one or both
wheels with mortises in the rim to receive wooden teeth. In this case
the wheel is termed a mortise wheel, and the teeth are termed _cogs_. If
only one of a pair of wheels is to be cogged, the largest of the pair is
usually selected, because there are in that case more teeth to withstand
the wear, it being obvious that the wear is greatest upon the wheel
having the fewest teeth, and that the iron wheel or pinion can better
withstand the wear than the mortise wheel. The woods most used for cogs
are hickory, maple, hornbeam and locust. The blocks wherefrom the teeth
are to be formed are usually cut out to nearly the required dimensions,
and kept in stock, so as to be thoroughly well-seasoned when required
for use, and, therefore less liable to come loose from shrinkage after
being fitted to the mortise in the wheel. The length of the shanks is
made sufficient to project through the wheel rim and receive a pin, as
shown in Fig. 174, in which B is a blank tooth, and C a finished tooth
inserted in the wheel, the pin referred to being at P. But, if a mortise
should fall in an arm of the wheel, this pin-hole must pass through the
rim, as shown in the mortise A. The wheel, however, should be designed
so that the mortises will not terminate in the arms of the wheel.
[Illustration: Fig. 174.]
[Illustration: Fig. 175.]
Another method of securing the teeth in the mortises is to dovetail them
at the small end and drive wedges between them, as shown in Fig. 175, in
which C C are two contiguous teeth, R the wheel rim and W W two of the
wedges. On account of the dovetailing the wedges exert A pressure
pressing the teeth into the mortises. This plan is preferable to that
shown in the Fig. 174 inasmuch as from the small bearing area of the
pins they become loose quicker, and furthermore there is more elasticity
to take up the wear in the case of the wedges.
[Illustration: Fig. 176.]
The mortises are first dressed out to a uniform size and taper, using
two templates to test them with, one of which is for the breadth and the
other for the width of the mortise. The height above the wheel requires
to be considerably more than that due to the depth of the teeth, so that
the surface bruised by driving the cogs or when fitting them into the
mortises may be cut off. To avoid this damage as much as possible, a
broad-face hammer should be employed--a copper, lead, lignum vitæ, or a
raw hide hammer being preferable, and the last the best. The teeth are
got out in a box and two guides, such as shown in Figs. 176, 177, and
178, similar letters of reference denoting the same parts in all three
illustrations.
In Fig. 176, X is a frame or box containing and holding the operative
part of the tooth, and resting on two guides C D. The height of D from
the saw table is sufficiently greater than that of C to give the shank G
the correct taper, E F representing the circular saw. T is a plain piece
of the full size of the box or frame, and serving simply to close up on
that side the mortise in the frame. The grain of T should run at a right
angle to the other piece of the frame so as to strengthen it. S is a
binding screw to hold the cog on the frame, and H is a guide for the
edge of the frame to slide against. It is obvious, now, that if the
piece D be adjusted at a proper distance from the circular saw E F, and
the edge of the frame be moved in contact with the guide H, one side of
the tooth shank will be sawn. Then, by reversing the frame end for end,
the other side of the shank may be sawn. Turning the frame to a right
angle the edges of the cog shank can be sawn from the same box or frame,
and pieces C, D, as shown in Fig. 177.
[Illustration: Fig. 177.]
The frame is now stood on edge, as in Fig. 178, and the underneath
surfaces sawed off to the depth the saw entered when the shank taper was
sawn. This operation requires to be performed on all four sides of the
tooth.
After this operation is performed on one cog, it should be tried in the
wheel mortises, to test its correctness before cutting out the shanks on
all the teeth.
[Illustration: Fig. 178.]
The shanks, being correctly sawn, may then be fitted to the mortises,
and let in within 1/8 of butting down on the face of the wheel, this
amount being left for the final driving. The cogs should be numbered to
their places, and two of the mortises must be numbered to show the
direction in which the numbers proceed. To mark the shoulders (which are
now square) to the curvature of the rim, a fork scriber should be used,
and the shanks of the cogs should have marked on them a line coincident
with the inner edge of the wheel rim. This line serves as a guide in
marking the pin-holes and for cutting the shanks to length; but it is to
be remembered that the shanks will pass farther through to the amount of
the distance marked by the fork scriber. The holes for the pins which
pass through the shanks should be made slightly less in their distances
(measured from the nearest edge of the pin-hole) from the shoulders of
the cogs than is the thickness of the rim of the wheel, so that when the
cogs are driven fully home the pin-holes will appear not quite full
circles on the inside of the wheel rim; hence, the pins will bind
tightly against the inside of the wheel rim, and act somewhat as keys,
locking and drawing the shanks to their seats in the mortises.
In cases where quietness of running is of more consequence than the
durability of the teeth, or where the wear is not great, both wheels may
be cogged, but as a rule the larger wheel is cogged, the smaller being
of metal. This is done because the teeth of the smaller wheel are the
most subject to wear. The teeth of the cogged wheel are usually made the
thickest, so as to somewhat equalise the strength of the teeth on the
two wheels.
Since the power transmitted by a wheel in a given time is composed of
the pressure or weight upon the wheel, and the space a point on the
pitch circle moves through in the given time, it is obvious that in a
train of wheels single geared, the velocities of all the wheels in the
train being equal at the pitch circle, the teeth require to be of equal
pitch and thickness throughout the train. But when the gearing is
compounded the variation of velocity at the pitch circle, which is due
to the compounding, has an important bearing upon the necessary strength
of the teeth.
Suppose, for example, that a wheel receives a tooth pressure of 100 lbs.
at the pitch circle, which travels at the velocity of 100 feet per
minute, and is keyed to the same shaft with another wheel whose velocity
is 50 feet per minute. Now, in the power transmitted by the two wheels
the element of time is 50 for one wheel and 100 for the other, hence the
latter (supposing both wheels to have an equal number of teeth in
contact with their driver or follower as the case may be) will be twice
as strong in proportion to the duty, and it appears that in compounded
gearing the strength in proportion to the duty may be varied in
proportion as the velocity is modified by compounding of the wheels.
Thus, when the velocity at the pitch circle is increased its strength is
increased, and per contra when its velocity is decreased its strength is
decreased, when considered in proportion to the duty. When, however, the
wheels are upon long shafts, or when they overhang the bearing of the
shaft, the corner contact will from tension of the shaft, continue much
longer than when the shaft is maintained rigid.
It is obvious that if a wheel transmits a certain amount of power, the
pressure of tooth upon tooth will depend upon the number of teeth in
contact, but since, in the case of very small wheels, that is to say,
pinions of the smallest diameter of the given pitch that will transmit
continuous motion, it occurs that only one tooth is in continuous
contact, it is obvious that each single tooth must have sufficient
strength to withstand the whole of the pressure when worn to the limits
to which the teeth are supposed to wear. But when the pinion is so small
that it has but one tooth in continuous contact, that contact takes
place nearer the line of centres and to the root of the tooth, and
therefore at a less leverage to the line of fracture, hence the ultimate
strength of the tooth is proportionately increased. On the other hand,
however, the whole stress of the wheel being concentrated on the arc of
contact of one tooth only (instead of upon two or more teeth as in
larger wheels), the wear is proportionately greater; hence, in a short
time the teeth of the pinion are found to be thinner than those on the
other wheel or wheels. The multiplicity of conditions under which small
wheels may work with relation to the number of teeth in contact, the
average leverage of the point of contact from the root of the tooth, the
shape of the tooth, &c., renders it desirable in a general rule to
suppose that the whole strain falls upon one tooth, so that the
calculation shall give results to meet the requirements when a single
tooth only is in continuous contact.
It follows, then, that the thickness of tooth arrived at by calculation
should be that which will give to a tooth, when worn to the extreme
thinness allowed, sufficient strength (with a proper margin of safety)
to transmit the whole of the power transmitted by the wheel.
The margin (or factor) of safety, or in other words, the number of times
the strength of the tooth should exceed the amount of power transmitted,
varies (according to the conditions under which the wheels work) between
5 and 10.
The lesser factor may be used for slow speeds when the power is
continuously and uniformly transmitted. The greater factor is necessary
when the wheels are subjected to violent shocks and the direction of
revolution requires to be reversed.
[Illustration: Fig. 179.]
In pattern-cast teeth, contact between the teeth of one wheel and those
of the other frequently occurs at one corner only, as shown in Fig. 179,
and the line of fracture is in the direction denoted by the diagonal
dotted lines. The causes of this corner contact have been already
explained, but it may be added that as the wheels wear, the contact
extends across the full breadths of the teeth, and the strength in
proportion to the duty, therefore, steadily increases from the time the
new wheels have action until the wear has caused contact fully across
the breadth. Tredgold's rule for finding the proper thickness of tooth
for a given stress upon cast-iron teeth loaded at the corner as in Fig.
179 and supposed to have a velocity of three feet per second of time, is
as follows:--
Rule.--Divide the stress in pounds at the pitch circle by 1500, and the
square root of the quotient is the required thickness of tooth in inches
or parts of an inch.
In the results obtained by the employment of this rule, an allowance of
one-third the thickness for wear, and the margin for safety is included,
so that the thickness of tooth arrived at is that to be given to the
actual tooth. Further, the rule supposes the breadth of the tooth to be
not less than twice the height of the same, any extra breadth not
affecting the result (as already explained), when the pressure falls on
a corner of the tooth.
In practical application, however, the diameter of the wheel at the
pitch circle is generally, or at least often a fixed quantity, as well
as the amount of stress, and it will happen as a rule that taking the
stress as a fixed element and arriving at the thickness of the tooth by
calculation, the required diameter of wheel, or what is the same thing,
its circumference, will not be such as to contain the exact number of
teeth of the thickness found by the calculation, and still give the
desired amount of side clearance. It is desirable, therefore, to deal
with the stress upon the tooth at the pitch circle, and the diameter,
radius, or circumference of the pitch circle, and its velocity, and
deduce therefrom the required thickness for the teeth, and conform the
pitch to the requirements as to clearance from the tooth thickness thus
obtained.
To deduce the thickness of the teeth from these elements we have
Robertson Buchanan's rule, which is as follows:--
Find the amount of horse-power employed to move the wheel, and divide
such horse-power by the velocity in feet per second of the pitch line of
the wheel. Extract the square root of the quotient, and three-fourths of
this root will be the least thickness of the tooth. To the result thus
obtained, there must be added the allowance for wear of the teeth and
the width of the space including the clearance which will determine the
number of teeth in the wheel.
In conforming strictly to this rule the difficulty is met with that it
would give fractional pitches not usually employed and difficult to
measure on an existing wheel. Cast wheels kept on hand or in stock by
machinists have usually the following standard:--
Beginning with an inch pitch, the pitches increase by 1/8 inch up to
3-inch pitch, from 3 to 4-inch pitches the increase is by 1/4 inch, and
from 4-inch pitch and upwards the increase is by 1/2 inch. Now, under
the rule the pitches would, with the clearance made to bear a certain
proportion to the pitch, be in odd fractions of an inch.
It appears then, that, if in a calculation to obtain the necessary
thickness of tooth, the diameter of the pitch circle is not an element,
the rule cannot be strictly adhered to unless the diameter of the pitch
circle be varied to suit the calculated thickness of tooth; or unless
either the clearance, factor of safety, or amount of tooth thickness
allowed for wear be varied to admit of the thickness of tooth arrived at
by the calculation. But if the diameter of the pitch circle is one of
the elements considered in arriving at the thickness of tooth requisite
under given conditions, the pitch must, as a rule, either be in odd
fractions, or else the allowance for wear, factor of safety, or amount
of side clearance cannot bear a definite proportion to the pitch. But
the allowance for clearance is in practice always a constant proportion
of the pitch, and under these circumstances, all that can be done when
the circumstances require a definite circumference of pitch circle, is
to select such a pitch as will nearest meet the requirements of tooth
thickness as found by calculation, while following the rule of making
the clearance a constant proportion of the pitch. When following this
plan gives a thinner tooth than the calculation calls for, the factor of
safety and the allowance for wear are reduced. But this is of little
consequence whenever more than one tooth on each wheel is in contact,
because the rules provide for all the stress falling on one tooth. When,
however, the number of teeth in the pinion is so small that one tooth
only is in contact, it is better to select a pitch that will give a
thicker rather than a thinner tooth than called for by the calculation,
providing, of course, that the pitch be less than the arc of contact, so
that the motion shall be continuous.
But when the pinions are shrouded, that is, have flanges at each end,
the teeth are strengthened; and since the wear will continue greater
than in wheels having more teeth in contact, the shrouding may be
regarded as a provision against breakage in consequence of the reduction
of tooth thickness resulting from wear.
In the following table is given the thickness of the tooth for a given
stress at the pitch circle, calculated from Tredgold's rule for teeth
supposed to have contact when new at one corner only.
+-------------------+--------------------+---------------------+
| Stress in lbs. at | Thickness of tooth | Actual pitches to |
| pitch circle. | in inches. | which wheels may be |
| | | made. |
+-------------------+--------------------+---------------------+
| 400 | .52 | 1-1/8 to 1-1/4 |
| 800 | .75 | 1-1/2 " 1-5/8 |
| 1,200 | .90 | 1-7/8 " 2 |
| 1,600 | 1.03 | 2 " 2-1/8 |
| 2,000 | 1.15 | 2-1/4 " 2-3/8 |
| 2,400 | 1.26 | 2-1/2 " 2-5/8 |
| 2,800 | 1.36 | 2-5/8 " 2-3/4 |
| 3,200 | 1.43 | 2-7/8 " 3 |
| 3,600 | 1.56 | 3-1/8 " 3-1/4 |
| 4,000 | 1.63 | 3-1/4 " 3-3/8 |
| 4,400 | 1.70 | 3-3/8 " 3-1/2 |
| 4,800 | 1.78 | 3-1/2 " 3-5/8 |
| 5,200 | 1.86 | 3-5/8 " 3-3/4 |
| 5,600 | 1.93 | 3-3/4 " 4 |
| 6,000 | 2.00 | 4 " 4-1/4 |
+-------------------+--------------------+---------------------+
In wheels that have their teeth cut to form in a gear-cutting machine
the thickness of tooth at any point in the depth is equal at any point
across the breadth; hence, supposing the wheels to be properly keyed to
their shafts so that the pitch line across the breadth of the wheel
stands parallel to the axis of the shaft, the contact of tooth upon
tooth occurs across the full breadth of the tooth.
As the practical result of these conditions we have three important
advantages: first, that the stress being exerted along the full breadth
of the tooth instead of on one corner only, the tooth is stronger (with
a given breadth and thickness) in proportion to the duty; second, that
with a given pitch, the thickness and therefore the margin for safety
and allowance for wear are increased, because the tooth may be increased
in thickness at the expense of the clearance, which need be merely
sufficient to prevent contact on both sides of the spaces so as to
prevent the teeth from locking in the spaces; and thirdly, because the
teeth will not be subject to sudden impacts or shocks of tooth upon
tooth by reason of back lash.
[Illustration: Fig. 180.]
In determining the strength of cut gear-teeth we may suppose the weight
to be disposed along the face at the extreme height of the tooth, in
which case the theoretical shape of the tooth to possess equal strength
at every point from the addendum circle to the root would be a parabola,
as shown by the dotted lines in Fig. 180, which represents a tooth
having radial flanks. In this case it is evident that the ultimate
strength of the tooth is that due to the thickness at the root, because
it is less than that at the pitch circle, and the strength, as a whole,
is not greater than that at the weakest part. But since teeth with
radial flanks are produced, as has been shown, with a generating circle
equal in diameter to the radius of the pinion, and since with a
generating circle bearing that ratio of diameter to diameter of pitch
circle the acting part of the flank is limited, it is usual to fill in
the corners with fillets or rounded corners, as shown in Fig. 129;
hence, the weakest part of the tooth will be where the radial line of
the flank joins the fillet and, therefore, nearer the pitch circle than
is the root. But as only the smallest wheel of the set has radial flanks
and the flanks thicken as the diameter of the wheels increase, it is
usual to take the thickness of the tooth at the pitch circle as
representing the weakest part of the tooth, and, therefore, that from
which the strength of the tooth is to be computed. This, however, is not
actually the case even in teeth which have considerable spread at the
roots, as is shown in Fig. 181, in which the shape of the tooth to
possess equal strength throughout its depth is denoted by the parabolic
dotted lines.
[Illustration: Fig. 181.]
Considering a tooth as simply a beam supporting the strain as a weight
we may calculate its strength as follows:--
Multiply the breadth of the tooth by the square of its thickness, and
the product by the strength of the material, per square inch of section,
of which the teeth are composed, and divide this last product by the
distance of the pitch line from the root, and the quotient will give a
tooth thickness having a strength equal to the weight of the load, but
having no margin for safety, and no allowance for wear; hence, the
result thus obtained must be multiplied by the factor of safety (which
for this class of tooth may be taken as 6), and must have an additional
thickness added to allow for wear, so that the factor of safety will be
constant notwithstanding the wear.
Another, and in some respects more convenient method, for obtaining the
strength of a tooth, is to take the strength of a tooth having 1-inch
pitch, and 1 inch of breadth, and multiply this quantity of strength by
the pitch and the face of the tooth it is required to find the strength
of, both teeth being of the same material.
Example.--The safe working pressure for a cast-iron tooth of an inch
pitch, and an inch broad will transmit, being taken as 400 lbs., what
pressure will a tooth of 3/4-inch pitch and 3 inches broad transmit with
safety?
Here 400 lbs. × 3/4 pitch × 3 breadth = 900 = safe working pressure of
tooth 3/4-inch pitch and 3 inches broad.
Again, the safe working pressure of a cast-iron tooth, 1 inch in breadth
and of 1-inch pitch, being considered as 400 lbs., what is the safe
working pressure of a tooth of 1-inch pitch and 4-inch breadth?
Here 400 × 1 × 4 = 1600.
The philosophy of this is apparent when we consider that four wheels of
1-inch pitch and an inch face, placed together side by side, would
constitute, if welded together, one wheel of an inch pitch and 4 inches
face. (The term _face_ is applied to the wheel, and the term breadth to
the tooth, because such is the custom of the workshop, both terms,
however, mean, in the case of spur-wheels, the dimension of the tooth in
a direction parallel to the axis of the wheel shaft or wheel bore.)
The following table gives the safe working pressures for wheels having
an inch pitch and an inch face when working at the given velocities,
S.W.P. standing for "safe working pressure:"--
+------------+------------+------------+------------+--------------+
| Velocity of| | | | |
|pitch circle| S.W.P. for | S.W.P. for |S.W.P. for | S.W.P. |
| in feet | cast-iron |spur mortise| cast-iron | for bevel |
|per second. |spur gears. | gears. |bevel gears.|mortise gears.|
+------------+------------+------------+------------+--------------+
| 2 | 368 | 178 | 258 | 178 |
| 3 | 322 | 178 | 225 | 157 |
| 6 | 255 | 178 | 178 | 125 |
| 12 | 203 | 142 | 142 | 99 |
| 18 | 177 | 124 | 124 | 87 |
| 24 | 161 | 113 | 113 | 79 |
| 30 | 150 | 105 | 105 | 74 |
| 36 | 140 | 98 | 98 | 69 |
| 42 | 133 | 93 | 93 | 65 |
| 48 | 127 | 88 | 88 | 62 |
+------------+------------+------------+------------+--------------+
For velocities less than 2 feet per second, use the same value as for 2
feet per second.
The proportions, in terms of the pitch, upon which this table is based,
are as follows:--
Thickness of iron teeth .395 of the pitch.
" wooden " .595 "
Height of addendum .28 "
Depth below pitch line .32 "
The table is based upon 400 lbs. per inch of face for an inch pitch, as
the safe working pressure of mortise wheel teeth or cogs; it may be
noted that there is considerable difference of opinion. They are claimed
by some to be in many cases practically stronger than teeth of cast
iron. This may be, and probably is, the case when the conditions are
such that the teeth being rigid and rigidly held (as in the case of
cast-iron teeth), there is but one tooth on each wheel in contact. But
when there is so nearly contact between two teeth on each wheel that but
little elasticity in the teeth would cause a second pair of teeth to
have contact, then the elasticity of the wood would cause this second
contact. Added to this, however, we have the fact that under conditions
where violent shock occurs the cog would have sufficient elasticity to
give, or spring, and thus break the shock which cast iron would resist
to the point of rupture. It is under these conditions, which mainly
occur in high velocities with one of the wheels having cast teeth, that
mortise wheels, or cogging, is employed, possessing the advantage that a
broken or worn-out tooth, or teeth, may be readily replaced. It is
usual, however, to assign to wooden teeth a value of strength more
nearly equal to that of its strength in proportion to that of cast iron;
hence, Thomas Box allows a wood tooth a value of about 3/10ths the
strength of cast iron; a value as high as 7/10ths is, however, assigned
by other authorities. But the strength of the tooth cannot exceed that
at the top of the shank, where it fits into the mortise of the wheel,
and on account of the leverage of the pressure the width of the mortise
should exceed the thickness of the tooth.
In some practice, the mortise teeth, or cogs, are made thicker in
proportion to the pitch than the teeth on the iron wheel; thus Professor
Unwin, in his "Elements of Machine Design," gives the following as "good
proportions":--
Thickness of iron teeth 0.395 of the pitch.
" wood cogs 0.595 " "
which makes the cogs 2/10ths inch thicker than the teeth.
The mortises in the wheel rim are made taper in both the breadth and the
width, which enables the tooth shank to be more accurately fitted, and
also of being driven more tightly home, than if parallel. The amount of
this taper is a matter of judgment, but it may be observed that the
greater the taper the more labor there is involved in fitting, and the
more strain there is thrown upon the pins when locking the teeth with a
given amount of strain. While the less the taper, the more care required
to obtain an accurate fit. Taking these two elements into consideration,
1/8th inch of taper in a length of 4 inches may be given as a desirable
proportion.
[Illustration: Fig. 182.]
As an evidence of the durability of wooden teeth, there appeared in
_Engineering_ of January 7th, 1879, the illustration shown in Fig. 182,
which represents a cog from a wheel of 14 ft. 1/2 in. diameter, and
having a 10-inch face, its pinion being 4 ft. in diameter. This cog had
been running for 26-1/2 years, day and night; not a cog in the wheel
having been touched during that time. Its average revolutions were 38
per minute, the power developed by the engine being from 90 to 100
indicated horse-power. The teeth were composed of beech, and had been
greased twice a week, with tallow and plumbago ore.
Since the width of the face of a wheel influences its wear (by providing
a larger area of contact over which the pressure may be distributed, as
well as increasing the strength), two methods of proportioning the
breadth may be adopted. First, it may be made a certain proportion of
the pitch; and secondly, it may be proportioned to the pressure
transmitted and the number of revolutions. The desirability of the
second is manifest when we consider that each tooth will pass through
the arcs of contact (and thus be subjected to wear) once during each
revolution; hence, by making the number of revolutions an element in the
calculation to find the breadth, the latter is more in proportion to the
wear than it would be if proportioned to the pitch.
It is obvious that the breadth should be sufficient to afford the
required degree of strength with a suitable factor of safety, and
allowance for wear of the smallest wheel in the pair or set, as the case
may be.
According to Reuleaux, the face of a wheel should never be less than
that obtained by multiplying the gross pressure, transmitted in lbs., by
the revolutions per minute, and dividing the product by 28,000.
In the case of bevel-wheels the pitch increases, as the perimeter of
the wheel is approached, and the maximum pitch is usually taken as the
designated pitch of the wheel. But the mean pitch is that which should
be taken for the purposes of calculating the strength, it being in the
middle of the tooth breadth. The mean pitch is also the diameter of the
pitch circle, used for ascertaining the velocity of the wheel as an
element in calculating the safe pressure, or the amount of power the
wheel is capable of transmitting, and it is upon this basis that the
values for bevel-wheels in the above table are computed.
In many cases it is required to find the amount of horse-power a wheel
will transmit, or the proportions requisite for a wheel to transmit a
given horse-power; and as an aid to the necessary calculations, the
following table is given of the amount of horse-power that may be
transmitted with safety, by the various wheels at the given velocities,
with a wheel of an inch pitch and an inch face, from which that for
other pitches and faces may be obtained by proportion.
TABLE SHOWING THE HORSE-POWER WHICH DIFFERENT KINDS OF GEAR-WHEELS OF
ONE INCH PITCH AND ONE INCH FACE WILL SAFELY TRANSMIT AT VARIOUS
VELOCITIES OF PITCH CIRCLE.
+------------+------------+------------+-------------+-------------+
|Velocity of | | | | |
|Pitch Circle|Spur-Wheels.|Spur Mortise|Bevel-Wheels.|Bevel Mortise|
|in Feet per | H.P. | Wheels. | H.P. | Wheels. |
|Second. | | H.P. | | H.P. |
+------------+------------+------------+-------------+-------------+
| 2 | 1.338 | .647 | .938 | .647 |
| 3 | 1.756 | .971 | 1.227 | .856 |
| 6 | 2.782 | 1.76 | 1.76 | 1.363 |
| 12 | 4.43 | 3.1 | 3.1 | 2.16 |
| 18 | 5.793 | 4.058 | 4.058 | 2.847 |
| 24 | 7.025 | 4.931 | 4.931 | 3.447 |
| 30 | 8.182 | 5.727 | 5.727 | 4.036 |
| 36 | 9.163 | 6.414 | 6.414 | 4.516 |
| 42 | 10.156 | 7.102 | 7.102 | 4.963 |
| 48 | 11.083 | 7.680 | 7.680 | 5.411 |
+------------+------------+------------+-------------+-------------+
In this table, as in the preceding one, the safe working pressure for
1-inch pitch and 1-inch breadth of face is supposed to be 400 lbs.
In cast gearing, the mould for which is made by a gear moulding machine,
the element of draft to permit the extraction of the pattern is reduced:
hence, the pressure of tooth upon tooth may be supposed to be along the
full breadth of the tooth instead of at one corner only, as in the case
of pattern-moulded teeth. But from the inaccuracies which may occur from
unequal contraction in the cooling of the casting, and from possible
warping of the casting while cooling, which is sure to occur to some
extent, however small the amount may be, it is not to be presumed that
the contact of the teeth of one wheel will be in all the teeth as
perfect across the full breadth as in the case of machine-cut teeth.
Furthermore, the clearance allowed for machine-moulded teeth, while
considerably less than that allowed for pattern-moulded teeth, is
greater than that allowed for machine-cut teeth; hence, the strength of
machine-moulded teeth in proportion to the pitch lies somewhere between
that of pattern-moulded and machine-cut teeth--but exactly where, it
would be difficult to determine in the absence of experiments made for
the purpose of ascertaining.
It is not improbable, however, that the contact of tooth upon tooth
extends in cast gears across at least two-thirds of the breadth of the
tooth, in which case the rules for ascertaining the strength of cut
teeth of equal thickness may be employed, substituting 2/3rds of the
actual tooth breadth as the breadth for the purposes of the calculation.
If instead of supposing all the strain to fall upon one tooth and
calculating the necessary strength of the teeth upon that basis (as is
necessary in interchangeable gearing, because these conditions may exist
in the case of the smallest pinion that can be used in pitch), the
actual working condition of each separate application of gears be
considered, it will appear that with a given diameter of pitch circle,
all other things being equal, the arc of contact will remain constant
whatever the pitch of the teeth, or in other words is independent of the
pitch, and it follows that when the thickness of iron necessary to
withstand (with the allowances for wear and factor of safety) the given
stress under the given velocity has been determined, it may be disposed
in a coarse pitch that will give one tooth always in contact, or a finer
pitch that will give two or more teeth always in contact, the strength
in proportion to the duty remaining the same in both cases.
In this case the expense of producing the wheel patterns or in trimming
the teeth is to be considered, because if there are a train of wheels
the finer pitch would obviously involve the construction and dressing to
shape of a much greater number of teeth on each wheel in the train, thus
increasing the labor. When, however, it is required to reduce the pinion
to a minimum diameter, it is obvious that this may be accomplished by
selecting the finer pitch, because the finer the pitch, the less the
diameter of the wheel may be. Thus with a given diameter of pitch circle
it is possible to select a pitch so fine that motion from one wheel may
be communicated to another, whatever the diameter of the pitch circle
may be, the limit being bounded by the practicability of casting or
producing teeth of the necessary fineness of pitch. The durability of a
wheel having a fine pitch is greater for two reasons: first, because the
metal nearest the cast surface of cast iron is stronger than the
internal metal, and the finer pitch would have more of this surface to
withstand the wear; and second, because in a wheel of a given width
there would be two points, or twice the area of metal, to withstand the
abrasion, it being remembered that the point of contact is a line which
partly rolls and partly slides along the depth of the tooth as the wheel
rotates, and that with two teeth in contact on each wheel there are two
of such lines. There is also less sliding or rubbing action of the
teeth, but this is offset by the fact that there are more teeth in
contact, and that there are therefore a greater number of teeth
simultaneously rubbing or sliding one upon the other.
But when we deal with the number of teeth the circumstances are altered;
thus with teeth of epicycloidal form it is manifestly impossible to
communicate constant motion with a driving wheel having but one tooth,
or to receive motion on a follower having but one tooth. The number of
teeth must always be such that there is at all times a tooth of each
wheel within the arc of action, or in contact, so that one pair of teeth
may come into contact before the contact of the preceding teeth has
ceased.
In the construction of wheels designed to transmit power as well as
simple motion, as is the case with the wheels employed in machine work,
however, it is not considered desirable to employ wheels containing a
less number of teeth than 12. The diameter of the wheel bearing such a
relation to the pitch that both wheels containing the same number of
teeth (12), the motion will be communicated from one to the other
continuously.
It is obvious that as the number of teeth in one of the wheels (of a
pair in gear) is increased the number of teeth in the other may be
(within certain limits) diminished, and still be capable of transmitting
continuous motion. Thus a pinion containing, say 8 teeth, may be capable
of receiving continuous motion from a rack in continuous motion, while
it would not be capable of receiving continuous motion from a pinion
having 4 teeth; and as the requirements of machine construction often
call for the transmission of motion from one pinion to another of equal
diameters, and as small as possible, 12 teeth are the smallest number it
is considered desirable for a pinion to contain, except it be in the
case of an internal wheel, in which the arc of contact is greater in
proportion to the diameters than in spur-wheels, and continuous motion
can therefore be transmitted either with coarser pitches or smaller
diameters of pinion.
For convenience in calculating the pitch diameter at pitch circle, or
pitch diameter as it is termed, and the number of teeth of wheels, the
following rules and table extracted from the _Cincinnati Artisan_ and
arranged from a table by D. A. Clarke, are given. The first column gives
the pitch, the following nine columns give the pitch diameters of wheels
for each pitch from 1 tooth to 9. By multiplying these numbers by 10 we
have the pitch diameters from 10 to 90 teeth, increasing by _tens_; by
multiplying by 100 we likewise have the pitch diameters from 100 to 900,
increasing by _hundreds_.
TABLE FOR DETERMINING THE RELATION BETWEEN PITCH DIAMETER, PITCH, AND
NUMBER OF TEETH IN GEAR-WHEELS.
+-----+------------------------------------------------------------------+
| | NUMBER OF TEETH. |
|Pitch.------+------+------+------+------+-------+-------+-------+-------+
| | 1. | 2. | 3. | 4. | 5. | 6. | 7. | 8. | 9. |
+-----+------+------+------+------+------+-------+-------+-------+-------+
|1 | .3183| .6366| .9549|1.2732|1.5915| 1.9099| 2.2282| 2.5465| 2.8648|
|1-1/8| .3581| .7162|1.0743|1.4324|1.7905| 2.1486| 2.5067| 2.8648| 3.2229|
|1-1/4| .3979| .7958|1.1937|1.5915|1.9894| 2.3873| 2.7852| 3.1831| 3.5810|
|1-3/8| .4377| .8753|1.3130|1.7507|2.1884| 2.6260| 3.0637| 3.5014| 3.9391|
| | | | | | | | | | |
|1-1/2| .4775| .9549|1.4324|1.9099|2.3873| 2.8648| 3.3422| 3.8197| 4.2971|
|1-5/8| .5173|1.0345|1.5517|2.0690|2.5862| 3.1035| 3.6207| 4.1380| 4.6552|
|1-3/4| .5570|1.1141|1.6711|2.2282|2.7852| 3.3422| 3.8993| 4.4563| 5.0134|
|1-7/8| .5968|1.1937|1.7905|2.3873|2.9841| 3.5810| 4.1778| 4.7746| 5.3714|
| | | | | | | | | | |
|2 | .6366|1.2732|1.9099|2.5465|3.1831| 3.8197| 4.4563| 5.0929| 5.7296|
|2-1/8| .6764|1.3528|2.0292|2.7056|3.3820| 4.0584| 4.7348| 5.4112| 6.0877|
|2-1/4| .7162|1.4324|2.1486|2.8648|3.5810| 4.2972| 5.0134| 5.7296| 6.4457|
|2-3/8| .7560|1.5120|2.2679|3.0239|3.7799| 4.5359| 5.2919| 6.0479| 6.8038|
| | | | | | | | | | |
|2-1/2| .7958|1.5915|2.3873|3.1831|3.9789| 4.7746| 5.5704| 6.3662| 7.1619|
|2-5/8| .8355|1.6711|2.5067|3.3422|4.1778| 5.0133| 5.8499| 6.6845| 7.5200|
|2-3/4| .8753|1.7507|2.6260|3.5014|4.3767| 5.2521| 6.1274| 7.0028| 7.8781|
|2-7/8| .9151|1.8303|2.7454|3.6605|4.5757| 5.4908| 6.4059| 7.3211| 8.2362|
| | | | | | | | | | |
|3 | .9549|1.9099|2.8648|3.8197|4.7746| 5.7296| 6.6845| 7.6394| 8.5943|
|3-1/4|1.0345|2.0690|3.1035|4.1380|5.1725| 6.2070| 7.2415| 8.2760| 9.3105|
|3-1/2|1.1141|2.2282|3.3422|4.4563|5.5704| 6.6845| 7.7986| 8.9126|10.0268|
|3-3/4|1.1937|2.3873|3.5810|4.7746|5.9683| 7.1619| 8.3556| 9.5493|10.7429|
| | | | | | | | | | |
|4 |1.2732|2.5465|3.8197|5.0929|6.3662| 7.6394| 8.9127|10.1839|11.4591|
|4-1/2|1.4324|2.8648|4.2972|5.7296|7.1619| 8.5943|10.0267|11.4591|12.8915|
|5 |1.5915|3.1831|4.7746|6.3662|7.9577| 9.5493|11.1408|12.7324|14.3240|
|5-1/2|1.7507|3.5014|5.2521|7.0028|8.7535|10.5042|12.2549|14.0056|15.7563|
|6 |1.9099|3.8196|5.7295|7.6394|9.5493|11.4591|13.3690|15.2788|17.1887|
+-----+------+------+------+------+------+-------+-------+-------+-------+
The following rules and examples show how the table is used:
Rule 1.--Given ---- number of teeth and pitch; to find ---- pitch
diameter.
Select from table in columns opposite the given pitch--
First, the value corresponding to the number of units in the number of
teeth.
Second, the value corresponding to the number of tens, and multiply this
by 10.
Third, the value corresponding to the number of hundreds, and multiply
this by 100. Add these together, and their sum is the pitch diameter
required.
Example.--What is the pitch diameter of a wheel with 128 teeth, 1-1/2
inches pitch?
We find in line corresponding to 1-1/2 inch pitch--
Pitch diameter for 8 teeth 3.8197
" " 20 " 9.549
" " 100 " 47.75
--- -------
" " 128 " 61.1187
Or about 61-1/8". Answer.
Rule 2.--Given ---- pitch diameter and number of teeth; to find
---- pitch.
First, ascertain by Rule 1 the pitch diameter for a wheel of 1-_inch
pitch_, and the given _number of teeth_.
Second, divide _given pitch diameter_ by the _pitch diameter_ for
1-_inch pitch_.
The quotient is the pitch desired.
Example.--What is the pitch of a wheel with 148 teeth, the pitch
diameter being 72"?
First, pitch diameter for 148 teeth, 1-inch pitch, is--
8 teeth 2.5465
40 " 12.732
100 " 31.83
--- -------
148 " 47.1085
Second, 72/47.1 = 1.53 inch equal to the pitch.
This is nearly 1-1/2-inch pitch, and if possible the diameter would be
reduced or the number of teeth increased so as to make the wheel exactly
1-1/2-inch pitch.
Rule 3.--Given ---- pitch and pitch diameter; to find ---- number of
teeth.
First, ascertain from table the _pitch diameter_ for 1 _tooth_ of the
given _pitch_.
Second, divide the _given pitch diameter_ by the _value_ found in table.
The quotient is the number required.
Example.--What is the number of teeth in a wheel whose pitch diameter is
42 inches, and pitch is 2-1/2 inches?
First, the pitch diameter, 1 tooth, 2-1/2-inch pitch, is 0.7958 inches.
42
Second. ------ = 52.8. Answer.
0.7958
This gives a fractional number of teeth, which is impossible; so the
pitch diameter will have to be increased to correspond to 53 teeth, or
the pitch changed so as to have the number of teeth come an even number.
Whenever two parallel shafts are connected together by gearing, the
distance between centres being a fixed quantity, and the speeds of the
shafts being of a fixed ratio, then the pitch is generally the best
proportion to be changed, and necessarily may not be of standard size.
Suppose there are two shafts situated in this manner, so that the
distance between their centres is 84 inches, and the speed of one is
2-1/2 times that of the other, what size wheels shall be used? In this
case the pitch diameter and number of teeth of the wheel on the
slow-running shaft have to be 2-1/2 times those of the wheel on the
fast-running shaft; so that 84 inches must be divided into two parts,
one of which is 2-1/2 times the other, and these quantities will be the
pitch radii of the wheels; that is, 84 inches are to be divided into
3-1/2 equal parts, 1 of which is the radius of one wheel, and 2-1/2 of
which the radius of the other, thus 84"/3-1/2 = 24 inches. So that 24
inches is the pitch radius of pinion, pitch diameter = 48 inches; and
2-1/2 × 24 inches = 60 inches is the pitch radius of the wheel, pitch
diameter = 120 inches. The pitch used depends upon the power to be
transmitted; suppose that 2-5/8 inches had been decided as about the
pitch to be used, it is found by Rule 3 that the number of teeth are
respectively 143.6, and 57.4 for wheel and pinion. As this is
impossible, some whole number of teeth, nearest these in value, have to
be taken, one of which is 2-1/2 times the other; thus 145 and 58 are the
nearest, and the pitch for these values is found by Rule 2 to be 2.6
inches, being the best that can be done under the circumstances.
[Illustration: Fig. 183.]
[Illustration: Fig. 184.]
The forms of spur-gearing having their teeth at an angle to the axis, or
formed in advancing steps shown in Figs. 183 and 184, were designed by
Dr. Hooke, and "were intended," says the inventor, "first to make a
piece of wheel work so that both the wheel and pinion, though of never
so small a size, shall have as great a number of teeth as shall be
desired, and yet neither weaken the wheels nor make the teeth so small
as not to be practicable by any ordinary workman. Next that the motion
shall be so equally communicated from the wheel to the pinion that the
work being well made there can be no inequality of force or motion
communicated.
"Thirdly, that the point of touching and bearing shall be always in the
line that joins the two centres together.
"Fourthly, that it shall have _no manner of rubbing_, nor be more
difficult to make than common wheel work."
The objections to this form of wheel lies in the difficulty of making
the pattern and of moulding it in the foundry, and as a result it is
rarely employed at the present day. For racks, however, two or more
separate racks are cast and bolted together to form the full width of
rack as shown in Fig. 185. This arrangement permits of the adjustment of
the width of step so as to take up the lost motion due to the wear of
the tooth curves.
Another objection to the sloping of the teeth, as in Fig. 183, is that
it induces an end pressure tending to force the wheels apart
_laterally_, and this causes _end_ wear on the journals and bearings.
[Illustration: Fig. 185.]
[Illustration: Fig. 186.]
To obviate this difficulty the form of gear shown in Fig. 186 is
employed, the angles of the teeth from each side of the wheel to its
centre being made equal so as to equalize the lateral pressure. It is
obvious that the stepped gear, Fig. 184, is simply equivalent to a
number of thin wheels bolted together to form a thick one, but
possessing the advantage that with a sufficient number of steps, as in
the figure, there is always contact on the line of centres, and that the
condition of constant contact at the line of centres will be approached
in proportion to the number of steps in the wheel, providing that the
steps progress in one continuous direction across the wheel as in Fig.
184. The action of the wheels will, in this event, be smoother, because
there will be less pressure tending to force the wheels apart.
But in the form of gearing shown in Fig. 183, the contact of the teeth
will bear every instant at a single point, which, as the wheels revolve,
will pass from one end to the other of the tooth, a fresh contact always
beginning on the first side immediately before the preceding contact has
ceased on the opposite side. The contact, moreover, being always in the
plane of the centres of the pair, the action is reduced to that of
rolling, and as there is no sliding motion there is consequently no
rubbing friction between the teeth.
[Illustration: Fig. 187.]
[Illustration: Fig. 188.]
A further modification of Dr. Hooke's gearing has been somewhat
extensively adopted, especially in cotton-spinning machines. This
consists, when the direction of the motion is simply to be changed to an
angle of 90°, in forming the teeth upon the periphery of the pair at an
angle of 45° to the respective axes of the wheels, as in Figs. 187 and
188; it will then be perceived that if the sloped teeth be presented to
each other in such a way as to have exactly the same horizontal angle,
the wheels will gear together, and motion being communicated to one axis
the same will be transmitted to the other at a right angle to it, as in
a common bevel pair. Thus if the wheel A upon a horizontal shaft have
the teeth formed upon its circumference at an angle of 45° to the plane
of its axis it can gear with a similar wheel B upon a vertical axis. Let
it be upon the driving shaft and the motion will be changed in direction
as if A and B were a pair of bevel-wheels of the ordinary kind, and, as
with bevels generally, the direction of motion will be changed through
an equal angle to the sum of the angles which the teeth of the wheels of
the pair form with their respective axes. The objection in respect of
lateral or end pressure, however, applies to this form equally with that
shown in Fig. 183, but in the case of a vertical shaft the end pressure
may be (by sloping the teeth in the necessary direction) made to tend to
lift the shaft and not force it down into the step bearing. This would
act to keep the wheels in close contact by reason of the weight of the
vertical shaft and at the same time reduce the friction between the end
of that shaft and its step bearing. This renders this form of gearing
preferable to skew bevels when employed upon vertical shafts.
It is obvious that gears, such as shown in Figs. 187 and 188 may be
turned up in the lathe, because the teeth are simply portions of spirals
wound about the circumference of the wheel. For a pair of wheels of
equal diameter a cylindrical piece equal in length to the required
breadth of the two wheels is turned up in the lathe, and the teeth may
be cut in the same manner as cutting a thread in the lathe, that is to
say, by traversing the tool the requisite distance per lathe revolution.
In pitches above about 1/4 inch, it will be necessary to shape one side
of the tooth at a time on account of the broadness of the cutting edges.
After the spiral (for the teeth are really spirals) is finished the
piece may be cut in two in the lathe and each half will form a wheel.
To find the full diameter to which to turn a cylinder for a pair of
these wheels we proceed as in the following example: Required to cut a
spiral wheel 5 inches in diameter and to have 30 teeth. First find the
diametral pitch, thus 30 (number of teeth) ÷ 5 (diameter of wheel at
pitch circle) = 6; thus there are 6 teeth or 6 parts to every inch of
the wheel's diameter at the pitch circle; adding 2 of these parts to the
diameter of the wheel, at the pitch circle we have 5 and 2/6 of another
inch, or 5-2/6 inches, which is the full diameter of the wheel, or the
diameter of the addendum, as it is termed.
[Illustration: Fig. 189.]
[Illustration: Fig. 190.]
It is now necessary to find what change wheels to put on the lathe to
cut the teeth out the proper angle. Suppose then the axes of the shafts
are at a right angle one to the other, and that the teeth therefore
require to be at an angle of 45° to the axes of the respective wheels,
then we have the following considerations. In Fig. 189 let the line A
represent the circumference of the wheel, and B a line of equal length
but at a right angle to it, then the line C, joining A, B, is at an
angle of 45°. It is obvious then that if the traverse of the lathe tool
be equal at each lathe revolution to the circumference of the wheel at
the pitch circle, the angle of the teeth will be 45° to the axis of the
wheel.
Hence, the change wheels on the lathe must be such as will traverse the
tool a distance equal to the circumference at pitch circle of the wheel,
and the wheels may be found as for ordinary screw cutting.
If, however, the axes of the shafts are at any other angle we may find
the distance the lathe tool must travel per lathe revolution to give
teeth of the required angle (or in other words the pitch of the spiral)
by direct proportion, thus: Let it be required to find the angle or
pitch for wheels to connect shafts at an angle of 25°, the wheels to
have 20 teeth, and to be of 10 diametral pitch.
Here, 20 ÷ 10 = 2 = diameter of wheel at the pitch circle. The
circumference of 2 inches being 6.28 inches we have, as the degrees of
angle of the axes of the shafts are to 45°, so is 6.28 inches (the
circumference of the wheels, to the pitch sought).
Here, 6.28 inches × 45° ÷ 25° = 11.3 inches, which is the required pitch
for the spiral.
When the axes of the shafts are neither parallel nor meeting, motion
from one shaft to another may be transmitted by means of a double gear.
Thus (taking rolling cones of the diameters of the respective pitch
circles as representing the wheels) in Fig. 190, let A be the shaft of
gear _h_, and B _b_ that of wheel _e_. Then a double gear-wheel having
teeth on _f_, _g_ may be placed as shown, and the face _f_ will gear
with _e_, while face _g_ will gear with _h_, the cone surfaces meeting
in a point as at C and D respectively, hence the velocity will be equal.
When the axial line of the shafts for two gear-wheels are nearly in line
one with the other, motion may be transmitted by gearing the wheels as
in Fig. 191. This is a very strong method of gearing, because there are
a large number of teeth in contact, hence the strain is distributed by a
larger number of teeth and the wear is diminished.
[Illustration: Fig. 191.]
[Illustration: Fig. 192.]
Fig. 192 (from Willis's "Principles of Mechanism") is another method of
constructing the same combination, which admits of a steady support for
the shafts at their point of intersection, A being a spherical bearing,
and B, C being cupped to fit to A.
Rotary motion variable at different parts of a rotation may be obtained
by means of gear-wheels varied in form from the true circle.
[Illustration: Fig. 193.]
The commonest form of gearing for this purpose is elliptical gearing,
the principles governing the construction of which are thus given by
Professor McCord. "It is as well to begin at the foundation by defining
the ellipse as a closed plane-curve, generated by the motion of a point
subject to the condition that the sum of its distances from two fixed
points within shall be constant: Thus, in Fig. 193, A and B are the two
fixed points, called the _foci_; L, E, F, G, P are points in the curve;
and A F + F B = A E + E B. Also, A L + L B = A P + P B = A G + G B. From
this it follows that A G = L O, O being the centre of the curve, and G
the extremity of the minor axis, whence the foci may be found if the
axes be assumed, or, if the foci and one axis be given, the other axis
may be determined. It is also apparent that if about either focus, as B,
we describe an arc with a radius greater than B P and less than B L, for
instance B E, and about A another arc with radius A E = L P-B E, the
intersection, E, of these arcs will be on the ellipse; and in this
manner any desired number of points may be found, and the curve drawn by
the aid of sweeps.
"Having completed this ellipse, prolong its major axis, and draw a
similar and equal one, with its foci, C, D, upon that prolongation, and
tangent to the first one at P; then B D = L P. About B describe an arc
with any radius, cutting the first ellipse at Y and the line L at Z;
about D describe an arc with radius D Z, cutting the second ellipse in
X; draw A Y, B Y, C X, and D X. Then A Y = D X, and B Y = C X, and
because the ellipses are alike, the arcs P Y and P X are equal. If then
B and D are taken as fixed centres, and the ellipses turn about them as
shown by the arrows, X and Y will come together at Z on the line of
centres; and the same is true of any points equally distant from P on
the two curves. But this is the condition of rolling contact. We see,
then, that in order that two ellipses may roll together, and serve as
the pitch-lines of wheels, they must be equal and similar, the fixed
centres must be at corresponding foci, and the distance between these
centres must be equal to the major axis. Were they to be toothless
wheels, if would evidently be essential that the outlines should be
truly elliptical; but the changes of curvature in the ellipse are
gradual, and circular arcs may be drawn so nearly coinciding with it,
that when teeth are employed, the errors resulting from the substitution
are quite inappreciable. Nevertheless, the rapidity of these changes
varies so much in ellipses of different proportions, that we believe it
to be practically better to draw the curve accurately first, and to find
the radii of the approximating arcs by trial and error, than to trust to
any definite rule for determining them; and for this reason we give a
second and more convenient method of finding points, in connection with
the ellipse whose centre is R, Fig. 193. About the centre describe two
circles, as shown, whose diameters are the major and minor axes; draw
any radius, as R T, cutting the first circle in T, and the second in S;
through T draw a parallel to one axis, through S a parallel to the
other, and the intersection, V, will lie on the curve. In the left hand
ellipse, the line bisecting the angle A F B is normal to the curve at F,
and the perpendicular to it is tangent at the same point, and bisects
the angles adjacent to A F B, formed by prolonging A F, B F.
[Illustration: Fig. 194.]
"To mark the pitch line we proceed as follows:--
"In Fig. 194, A A and B B are centre lines passing through the major and
minor axes of the ellipse, of which _a_ is the axis or centre, _b_ _c_
is the major and _a_ _e_ half of the minor axis. Draw the rectangle _b_
_f_ _g_ _c_, and then the diagonal line _b_ _e_; at a right angle to _b_
_e_ draw line _f_ _h_ cutting B B at _i_. With radius _a_ _e_ and from
_a_ as a centre draw the dotted arc _e_ _j_, giving the point _j_ on the
line B B. From centre _k_, which is on line B B, and central between _b_
and _j_, draw the semicircle _b_ _m_ _j_, cutting A A at _l_. Draw the
radius of the semicircle _b_ _m_ _j_ cutting _f_ _g_ at _n_. With radius
_m_ _n_ mark on A A, at and from _a_ as a centre, the point _o_. With
radius _h_ _o_ and from centre _h_ draw the arc _p_ _o_ _q_. With radius
_a_ _l_ and from _b_ and _c_ as centres draw arcs cutting _p_ _o_ _q_ at
the points _p_ _q_. Draw the lines _h_ _p_ _r_ and _h_ _q_ _s_, and also
the lines _p_ _i_ _t_ and _q_ _v_ _w_. From _h_ as centre draw that part
of the ellipse lying between _r_ and _s_. With radius _p_ _r_ and from
_p_ as a centre draw that part of the ellipse lying between _r_ and _t_.
With radius _q_ _s_ and from _q_ draw the ellipse from _s_ to _w_. With
radius _i_ _t_ and from _i_ as a centre draw the ellipse from _t_ to
_b_. With radius _v_ _w_ and from _v_ as a centre draw the ellipse from
_w_ to _c_, and one half the ellipse will be drawn. It will be seen that
the whole construction has been performed to find the centres _h_ _p_
_q_ _i_ and _v_, and that while _v_ and _i_ may be used to carry the
curve around the other side or half of the ellipse, new centres must be
provided for _h_ _p_ and _q_; these new centres correspond in position
to _h_ _p_ _q_.
"If it were possible to subdivide the ellipse into equal parts it would
be unnecessary to resort to these processes of approximately
representing the two curves by arcs of circles; but unless this be done,
the spacing of the teeth can only be effected by the laborious process
of stepping off the perimeter into such small subdivisions that the
chords may be regarded as equal to the arcs, which after all is but an
approximation; unless, indeed, we adopt the mechanical expedient of
cutting out the ellipse in metal or other substance, measuring and
subdividing it with a strip of paper or a steel tape, and wrapping back
the divided measure in order to find the points of division on the
curve.
"But these circular arcs may be rectified and subdivided with great
facility and accuracy by a very simple process, which we take from Prof.
Rankine's "Machinery and Mill Work," and is illustrated in Fig. 195. Let
O B be tangent at O to the arc O D, of which C is the centre. Draw the
chord D O, bisect it in E, and produce it to A, making O A = O E; with
centre A and radius A D describe an arc cutting the tangent in B; then O
B will be very nearly equal in length to the arc O D, which, however,
should not exceed about 60°; if it be 60°, the error is theoretically
about 1/900 of the length of the arc, O B being so much too short; but
this error varies with the fourth power of the angle subtended by the
arc, so that for 30° it is reduced to 1/16 of that amount, that is, to
1/14400. Conversely, let O B be a tangent of given length; make O F =
1/4 O B; then with centre F and radius F B describe an arc cutting the
circle O D G (tangent to O B at O) in the point D; then O D will be
approximately equal to O B, the error being the same as in the other
construction and following the same law.
[Illustration: Fig. 195.]
"The extreme simplicity of these two constructions and the facility with
which they may be made with ordinary drawing instruments make them
exceedingly convenient, and they should be more widely known than they
are. Their application to the present problem is shown in Fig. 196,
which represents a quadrant of an ellipse, the approximate arcs C D, D
E, E F, F A having been determined by trial and error. In order to space
this off, for the positions of the teeth, a tangent is drawn at D, upon
which is constructed the rectification of D C, which is D G, and also
that of D E in the opposite direction, that is, D H, by the process just
explained. Then, drawing the tangent at F, we set off in the same manner
F I = F E, and F K = F A, and then measuring H L = I K, we have finally
G L, equal to the whole quadrant of the ellipse.
[Illustration: Fig. 196.]
"Let it now be required to lay out 24 teeth upon this ellipse; that is,
6 in each quadrant; and for symmetry's sake we will suppose that the
centre of one tooth is to be at A, and that of another at C, Fig. 196.
We therefore divide L G into six equal parts at the points 1, 2, 3, &c.,
which will be the centres of the teeth upon the rectified ellipse. It is
practically necessary to make the spaces a little greater than the
teeth; but if the greatest attainable exactness in the operation of the
wheel is aimed at, it is important to observe that backlash, in
elliptical gearing, has an effect quite different from that resulting in
the case of circular wheels. When the pitch-curves are circles, they are
always in contact; and we may, if we choose, make the tooth only half
the breadth of the space, so long as its outline is correct. When the
motion of the driver is reversed, the follower will stand still until
the backlash is taken up, when the motion will go on with a perfectly
constant velocity ratio as before. But in the ease of two elliptical
wheels, if the follower stand still while the driver moves, which must
happen when the motion is reversed if backlash exists, the pitch-curves
are thrown out of contact, and, although the continuity of the motion
will not be interrupted, the velocity ratio will be affected. If the
motion is never to be reversed, the perfect law of the velocity ratio
due to the elliptical pitch-curve may be preserved by reducing the
thickness of the tooth, not equally on each side, as is done in circular
wheels, but wholly on the side not in action. But if the machine must be
capable of acting indifferently in both directions, the reduction must
be made on both sides of the tooth: evidently the action will be
slightly impaired, for which reason the backlash should be reduced to a
minimum. Precisely what _is_ the minimum is not so easy to say, as it
evidently depends much upon the excellence of the tools and the skill of
the workmen. In many treatises on constructive mechanism it is variously
stated that the backlash should be from one-fifteenth to one-eleventh of
the pitch, which would seem to be an ample allowance in reasonably good
castings not intended to be finished, and quite excessive if the teeth
are to be cut; nor is it very obvious that its amount should depend upon
the pitch any more than upon the precession of the equinoxes. On paper,
at any rate, we may reduce it to zero, and make the teeth and spaces
equal in breadth, as shown in the figure, the teeth being indicated by
the double lines. Those upon the portion L H are then laid off upon K I,
after which these divisions are transferred to curves. And since under
that condition the motion of this third line, relatively to each of the
others, is the same as though it rolled along each of them separately
while they remained fixed, the process of constructing the generated
curves becomes comparatively simple. For the describing line, we
naturally select a circle, which, in order to fulfil the condition, must
be small enough to roll within the pitch ellipse; its diameter is
determined by the consideration, that if it be equal to A P, the radius
of the arc A F, the flanks of the teeth in that region will be radial.
We have, therefore, chosen a circle whose diameter, A B, is
three-fourths of A P, as shown, so that the teeth, even at the ends of
the wheels, will be broader at the base than on the pitch line. This
circle ought strictly to roll upon the true elliptical curve, and
assuming as usual the tracing-point upon the circumference, the
generated curves would vary slightly from true epicycloids, and no two
of those used in the same quadrant of the ellipse would be exactly
alike. Were it possible to divide the ellipse accurately, there would be
no difficulty in laying out these curves; but having substituted the
circular arcs, we must now roll the generating circle upon these as
bases, thus forming true epicycloidal teeth, of which those lying upon
the same approximating arc will be exactly alike. Should the junction
of two of these arcs fall within the breadth of a tooth, as at D,
evidently both the face and the flank on one side of that tooth will be
different from those on the other side; should the junction coincide
with the edge of a tooth, which is very nearly the case at F, then the
face on that side will be the epicycloid belonging to one of the arcs,
its flank a hypocycloid belonging to the other; and it is possible that
either the face or the flank on one side should be generated by the
rolling of the describing circle partly on one arc, partly on the one
adjacent, which, upon a large scale and where the best results are aimed
at, may make a sensible change in the form of the curve.
[Illustration: Fig. 197.]
"The convenience of the constructions given in Fig. 194 is nowhere more
apparent than in the drawing of the epicycloids, when, as in the case
in hand, the base and generating circles may be of incommensurable
diameters; for which reason we have, in Fig. 197, shown its application
in connection with the most rapid and accurate mode yet known of
describing those curves. Let C be the centre of the base circle;
B that of the rolling one; A the point of contact. Divide the
semi-circumference of B into six equal parts at 1, 2, 3, &c.; draw the
common tangent at A, upon which rectify the arc A2 by process No. 1,
then by process No. 2 set out an equal arc A2 on the base circle, and
stepping it off three times to the right and left, bisect these spaces,
thus making subdivisions on the base circle equal in length to those on
the rolling one. Take in succession as radii the chords A1, A2, A3, &c.,
of the describing circle, and with centres 1, 2, 3, &c., on the base
circle, strike arcs either externally or internally, as shown
respectively on the right and left; the curve tangent to the external
arcs is the epicycloid, that tangent to the internal ones the
hypocycloid, forming the face and flank of a tooth for the base circle.
"In the diagram, Fig. 196, we have shown a part of an ellipse whose
length is 10 inches and breadth 6, the figure being half size. In order
to give an idea of the actual appearance of the combination when
complete, we show in Fig. 198 the pair in gear, on a scale of 3 inches
to the foot. The excessive eccentricity was selected merely for the
purpose of illustration. Fig. 198 will serve also to call attention to
another serious circumstance, which is that although the ellipses are
alike, the wheels are not; nor can they be made so if there be an even
number of teeth, for the obvious reason that a tooth upon one wheel must
fit into a space on the other; and since in the first wheel, Fig. 196,
we chose to place a tooth at the extremity of each axis, we must in the
second one place there a space instead; because at one time the major
axes must coincide, at another the minor axis, as in Fig. 191. If then
we use even numbers, the distribution and even the forms of the teeth
are not the same in the two wheels of the pair. But this complication
may be avoided by using an odd number of teeth, since, placing a tooth
at one extremity of the major axis, a space will come at the other.
"It is not, however, always necessary to cut teeth all round these
wheels, as will be seen by an examination of Fig. 199, C and D being the
fixed centres of the two ellipses in contact at P. Now P must be on the
line C D, whence, considering the free foci, we see P B is equal to P C,
and P A to P D; and the common tangent at P makes equal angles with C P
and P A, as is also with P B and P D; therefore, C D being a straight
line, A B is also a straight line and equal to C D. If then the wheels
be overhung, that is, fixed on the ends of the shafts outside the
bearings, leaving the outer faces free, the moving foci may be connected
by a rigid link A B, as shown.
[Illustration: Fig. 198.]
"This link will then communicate the same motion that would result from
the use of the complete elliptical wheels, and we may therefore dispense
with most of the teeth, retaining only those near the extremities of the
major axes which are necessary in order to assist and control the motion
of the link at and near the dead-points. The arc of the pitch-curves
through which the teeth must extend will vary with their eccentricity:
but in many cases it would not be greater than that which in the
approximation may be struck about one centre, so that, in fact, it would
not be necessary to go through the process of rectifying and subdividing
the quarter of the ellipse at all, as in this case it can make no
possible difference whether the spacing adopted for the teeth to be cut
would "come out even" or not if carried around the curve. By this
expedient, then, we may save not only the trouble of drawing, but a
great deal of labor in making, the teeth round the whole ellipse. We
might even omit the intermediate portions of the pitch ellipses
themselves; but as they move in rolling contact their retention can do
no harm, and in one part of the movement will be beneficial, as they
will do part of the work; for if, when turning, as shown by the arrows,
we consider the wheel whose axis is D as the driver, it will be noted
that its radius of contact, C P, is on the increase; and so long as this
is the case the other wheel will be compelled to move by contact of the
pitch lines, although the link be omitted. And even if teeth be cut all
round the wheels, this link is a comparatively inexpensive and a useful
addition to the combination, especially if the eccentricity be
considerable. Of course the wheels shown in Fig. 198 might also have
been made alike, by placing a tooth at one end of the major axis and a
space at the other, as above suggested. In regard to the variation in
the velocity ratio, it will be seen, by reference to Fig. 199, that if D
be the axis of the driver, the follower will in the position there shown
move faster, the ratio of the angular velocities being PD/PB; if the
driver turn uniformly the velocity of the follower will diminish, until
at the end of half a revolution, the velocity ratio will be PB/PD; in
the other half of the revolution these changes will occur in a reverse
order. But P D = L B; if then the centres B D are given in position, we
know L P, the major axis; and in order to produce any assumed maximum or
minimum velocity ratio, we have only to divide L P into segments whose
ratio is equal to that assumed value, which will give the foci of the
ellipse, whence the minor axis may be found and the curve described. For
instance, in Fig. 198 the velocity ratio being nine to one at the
maximum, the major axis is divided into two parts, of which one is nine
times as long as the other; in Fig. 199 the ratio is as one to three, so
that, the major axis being divided into four parts, the distance A C
between the foci is equal to two of them, and the distance of either
focus from the nearer extremity of the major axis equal to one, and from
the more remote extremity equal to three of these parts."
[Illustration: Fig. 199.]
Another example of obtaining a variable motion is given in Fig. 200. The
only condition necessary to the construction of wheels of this class is
that the sum of the radii of the pitch circles on the line of centres
shall equal the distance between the axes of the two wheels. The pitch
curves are to be considered the same as pitch circles, "so that," says
Willis, "if any given circle or curve be assumed as a describing (or
generating) curve, and if it be made to roll on the inside of one of
these pitch curves and on the outside of the corresponding portion of
the other pitch curve, then the motion communicated by the pressure and
sliding contact of one of the curved teeth so traced upon the other will
be exactly the same as that effected by the rolling contact (by
friction) of the original pitch curves."
[Illustration: Fig. 200.]
It is obvious that on B the corner sections are formed of simple
segments of a circle of which the centre is the axis of the shaft, and
that the sections between them are simply racks. The corners of A are
segments of a circle of which the axis of A is the centre, and the
sections between the corners curves meeting the pitch circles of the
rack at every point as it passes the line of centres.
Intermittent motion may also be obtained by means of a worm-wheel
constructed as in Fig. 201, the worm having its teeth at a right angle
to its axis for a distance around the circumference proportioned to the
required duration of the period of rest; or the motion may be made
variable by giving the worm teeth different degrees of inclination (to
the axis), on different portions of the circumference.
In addition to the simple operation of two or more wheels transmitting
motion by rotating about their fixed centres and in fixed positions, the
following examples of wheel motion may be given.
[Illustration: Fig. 201.]
[Illustration: Fig. 202.]
In Fig. 202 are two gear-wheels, A, which is fast upon its stationary
shaft, and B, which is free to rotate upon its shaft, the link C
affording journal bearing to the two shafts. Suppose that A has 40
teeth, while B has 20 teeth, and that the link C is rotated once around
the axis of A, how many revolutions will B make? By reason of there
being twice as many teeth in A as in B the latter will make two
rotations, and in addition to this it will, by reason of its connection
to the arm C, also make a revolution, these being two distinct motions,
one a rotation of B about the axis of A, and the other two rotations of
B upon its own axis.
A simple arrangement of gearing for reversing the direction of rotation
of a shaft is shown in Fig. 203. I and F are fast and loose pulleys for
the shaft D, A and C are gears free to rotate upon D, N is a clutch
driven by D; hence if N be moved so as to engage with C the latter will
act as a driver to rotate the shaft B, the wheel upon B rotating A in
an opposite direction to the rotation of D. But if N be moved to engage
with A the latter becomes the driving wheel, and B will be caused to
rotate in the opposite direction. Since, however, the engagement of the
clutch N with the clutch on the nut of the gear-wheels is accompanied
with a violent shock and with noise, a preferable arrangement is shown
in Fig. 204, in which the gears are all fast to their shafts, and the
driving shaft for C passes through the core or bore of that for A, which
is a sleeve, so that when the driving belt acts upon pulley F the shaft
B rotates in one direction, while when the belt acts upon E, B rotates
in the opposite direction, I being a loose pulley.
[Illustration: Fig. 203.]
If the speed of rotation of B require to be greater in one direction
than in the other, then the bevel-wheel on B is made a double one, that
is to say, it has two annular toothed surfaces on its radial face, one
of larger diameter than the other; A gearing with one of these toothed
surfaces, and C with the other. It is obvious that the pinions A C,
being of equal diameters, that gearing with the surface or gear of
largest diameter will give to B the slowest speed of rotation.
[Illustration: Fig. 204.]
Fig. 205 represents Watt's sun-and-planet motion for converting
reciprocating into rotary motion; B D is the working beam of the engine,
whose centre of motion is at D. The gear A is so connected to the
connecting rod that it cannot rotate, and is kept in gear with the wheel
C on the fly-wheel shaft by means of the link shown. The wheel A being
prevented from rotation on its axis causes rotary motion to the wheel C,
which makes two revolutions for one orbit of A.
[Illustration: Fig. 205.]
An arrangement for the rapid increase of motion by means of gears is
shown in Fig. 206, in which A is a stationary gear, B is free to rotate
upon its shaft, and being pivoted upon the shaft of A, at D, is capable
of rotation around A while remaining in gear with C. Suppose now that
the wheel A were absent, then if B were rotated around C with D as a
centre of motion, C and its shaft E would make a revolution even though
B would have no rotation upon its axis. But A will cause B to rotate
upon its axis and thus communicate a second degree of motion to C, with
the result that one revolution of B causes two rotations of C.
The relation of motion between B and C is in this case constant (2 to
1), but this relation may be made variable by a construction such as
shown in Fig. 207, in which the wheel B is carried in a gear-wheel H,
which rides upon the shaft D. Suppose now that H remains stationary
while A revolves, then motion will be transmitted through B to C, and
this motion will be constant and in proportion to the relative diameters
of A and C. But suppose by means of an independent pinion the wheel H be
rotated upon its axis, then increased motion will be imparted to C, and
the amount of the increase will be determined by the speed of rotation
of H, which may be made variable by means of cone pulleys or other
suitable mechanical devices.
[Illustration: Fig. 206.]
Fig. 208 represents an arrangement of gearing used upon steam
fire-engines and traction engines to enable them to turn easily in a
short radius, as in turning corners in narrow streets. The object is to
enable the driving wheel on either side of the engine to increase or
diminish its rotation to suit the conditions caused by the leading or
front pair of steering wheels.
[Illustration: Fig. 207.]
In the figures A is a plate wheel having the lugs L, by means of which
it may be rotated by a chain. A is a working fit on the shaft S, and
carries three pinions E pivoted upon their axes P. F is a bevel-gear, a
working fit on S, while C is a similar gear fast to S. The pinions B, D
are to drive gears on the wheels of the engine, the wheels being a
working fit on the axle. Let it now be noted that if S be rotated, C and
F will rotate in opposite directions and A will remain stationary. But
if A be rotated, then all the gears will rotate with it, but E will not
rotate upon P unless there be an unequal resistance to the motion of
pinions D and B. So soon, however, as there exists an inequality of
resistance between D and B then pinions E operate. For example, let B
have more resistance than D, and B will rotate more slowly, causing
pinion E to rotate and move C faster than is due to the motion of the
chain wheel A, thus causing the wheel on one side of the engine to
retard and the other to increase its motion, and thus enable the engine
to turn easily. From its action this arrangement is termed the
equalizing gear.
[Illustration: Fig. 208.]
In Figs. 209 to 214 are shown what are known as mangle-wheels from their
having been first used in clothes mangling machines.
[Illustration: Fig. 209.]
[Illustration: Fig. 210.]
The mangle-wheel[10] in its simplest form is a revolving disc of metal
with a centre of motion C (Fig. 209). Upon the face of the disc is fixed
a projecting annulus _a_ _m_, the outer and inner edges of which are cut
into teeth. This annulus is interrupted at _f_, and the teeth are
continued round the edges of the interrupted portion so as to form a
continued series passing from the outer to the inner edge and back
again.
[10] From Willis's "Principles of Mechanism."
A pinion B, whose teeth are of the same pitch as those of the wheel, is
fixed to the end of an axis, and this axis is mounted so as to allow of
a short travelling motion in the direction B C. This may be effected by
supporting this end of it either in a swing-frame moving upon a centre
as at D, or in a sliding piece, according to the nature of the train
with which it is connected. A short pivot projects from the centre of
the pinion, and this rests in and is guided by a groove B S _f_ _t_ _b_
_h_ K, which is cut in the surface of the disc, and made concentric to
the pitch circles of the inner and outer rays of teeth, and at a normal
distance from them equal to the pitch radius of the pinion.
Now when the pinion revolves it will, if it be on the outside, as in
Fig. 209, act upon the spur teeth and turn the wheel in the opposite
direction to its own, but when the interrupted portion _f_ of the teeth
is thus brought to the pinion the groove will guide the pinion while it
passes from the outside to the inside, and thus bring its teeth into
action with the annular or internal teeth. The wheel will then receive
motion in the same direction as that of the pinion, and this will
continue until the gap _f_ is again brought to the pinion, when the
latter will be carried outwards and the motion again be reversed. The
_velocity ratio_ in either direction will remain constant, but the ratio
when the pinion is inside will differ slightly from the ratio when it is
outside, because the pitch radius of the annular or internal teeth is
necessarily somewhat less than that of the spur teeth. However, the
change of direction is not instantaneous, for the form of the groove S
_f_ _t_, which connects the inner and outer grooves, is a semicircle,
and when the axis of the pinion reaches S the velocity of the
mangle-wheel begins to diminish gradually until it is brought to rest at
_f_, and is again gradually set in motion from _f_ to _t_, when the
constant ratio begins; and this retardation will be increased by
increasing the difference between the radius of the inner and outer
pitch circles.
The teeth of a mangle-wheel are, however, most commonly formed by pins
projecting from the face of the disc as in Fig. 210. In this manner the
pitch circles for the inner and outer wheels coincide, and therefore the
velocity ratio is the same within and without, also the space through
which the pinion moves in shifting is reduced.
[Illustration: Fig. 211.]
[Illustration: Fig. 212.]
This space may be still further reduced by arranging the teeth as in
Fig. 211, that is, by placing the spur-wheel within the annular or
internal one; but at the same time the difference of the two velocity
ratios is increased.
If it be required that the velocity ratio vary, then the pitch lines of
the mangle-wheel must no longer be concentric.
Thus in Fig. 212 the groove _k_ _l_ is directed to the centre of the
mangle-wheel, and therefore the pinion will proceed during this portion
of its path without giving any motion to the wheel, and in the other
lines of teeth the pitch radius varies, hence the angular velocity ratio
will vary.
In Figs. 209, 210, and 211 the curves of the teeth are readily obtained
by employing the same describing circle for the whole of them. But when
the form Fig. 212 is adopted, the shape of the teeth requires some
consideration.
Every tooth of such a mangle-wheel may be considered as formed of two
ordinary teeth set back to back, the pitch line passing through the
middle. The outer half, therefore, appropriated to the action of the
pinion on the outside of the wheel, resembles that portion of an
ordinary spur-wheel tooth that lies beyond its pitch line, and the inner
half which receives the inside action of the pinion resembles the half
of an annular wheel that lies within the pitch circle. But the
consequence of this arrangement is, that in both positions the action of
the driving teeth must be confined to the approach of its teeth to the
line of centres, and consequently these teeth must be wholly within
their pitch line.
To obtain the forms of the teeth, therefore, take any convenient
describing circle, and employ it to describe the teeth of the pinion by
rolling within its pitch circle, and to describe the teeth of the wheel
by rolling within and without its pitch circle, and the pinion will then
work truly with the teeth of the wheel in both positions. The tooth at
each extremity of the series must be a circular one, whose centre lies
on the pitch line and whose diameter is equal to half the pitch.
[Illustration: Fig. 213.]
If the reciprocating piece move in a straight line, as it very often
does, then the mangle-_wheel_ is transformed into a _mangle-rack_ (Fig.
213) and its teeth may be simply made cylindrical pins, which those of
the mangle-wheel do not admit of on correct principle. B _b_ is the
sliding piece, and A the driving pinion, whose axis must have the power
of shifting from A to _a_ through a space equal to its own diameter, to
allow of the change from one side of the rack to the other at each
extremity of the motion. The teeth of the mangle-rack may receive any of
the forms which are given to common rack-teeth, if the arrangement be
derived from either Fig. 210 or Fig. 211.
But the mangle-rack admits of an arrangement by which the shifting
motion of the driving pinion, which is often inconvenient, may be
dispensed with.
[Illustration: Fig. 214.]
B _b_ Fig. 214, is the piece which receives the reciprocating motion,
and which may be either guided between rollers, as shown, or in any
other usual way; A the driving pinion, whose axis of motion is fixed;
the mangle rack C _c_ is formed upon a separate plate, and in this
example has the teeth upon the inside of the projecting ridge which
borders it, and the guide-groove formed within the ring of teeth,
similar to Fig. 211.
This rack is connected with the piece B _b_ in such a manner as to allow
of a short transverse motion with respect to that piece, by which the
pinion, when it arrives at either end of the course, is enabled by
shifting the rack to follow the course of the guide-groove, and thus to
reverse the motion by acting upon the opposite row of teeth.
The best mode of connecting the rack and its sliding piece is that
represented in the figure, and is the same which is adopted in the
well-known cylinder printing-engines of Mr. Cowper. Two guide-rods K C,
_k_ _c_ are jointed at one end K _k_ to the reciprocating piece B _b_,
and at the other end C _c_ to the shifting-rack; these rods are moreover
connected by a rod M _m_ which is jointed to each midway between their
extremities, so that the angular motion of these guide-rods round their
centres K _k_ will be the same; and as the angular motion is small and
the rods nearly parallel to the path of the slide, their extremities C
_c_ may be supposed to move at a right angle to that path, and
consequently the rack which is jointed to those extremities will also
move upon B _b_ in a direction at a right angle to its path, which is
the thing required, and admits of no other motion with respect to B _b_.
[Illustration: Fig. 215.]
To multiply plane motion the construction shown in Fig. 215 is
frequently employed. A and B are two racks, and C is a wheel between
them pivoted upon the rod R. A crank shaft or lever D is pivoted at E
and also (at P) to R. If D be operated C traverses along A and also
rotates upon its axis, thus giving to B a velocity equal to twice that
of the lateral motion of C.
The diameter of the wheel is immaterial, for the motion of B will always
be twice that of C.
Friction gearing-wheels which communicate motion one to the other by
simple contact of their surfaces are termed friction-wheels, or
friction-gearing. Thus in Fig. 216 let A and B be two wheels that touch
each other at C, each being suspended upon a central shaft; then if
either be made to revolve, it will cause the other to revolve also, by
the friction of the surfaces meeting at C. The degree of force which
will be thus conveyed from one to the other will depend upon the
character of the surface and the length of the line of contact at C.
[Illustration: Fig. 216.]
These surfaces should be made as concentric to the axis of the wheel and
as flat and smooth as possible in order to obtain a maximum power of
transmission. Mr. E. S. Wicklin states that under these conditions and
proper forms of construction as much as 300 horse-power may be (and is
in some of the Western States) transmitted.
In practice, small wheels of this class are often covered with some
softer material, as leather; sometimes one wheel only is so covered, and
it is preferred that the covered wheel drive the iron one, because, if a
slip takes place and the iron wheel was the driver, it would be apt to
wear a concave spot in the wood covered one, and the friction between
the two would be so greatly diminished that there would be difficulty in
starting them when the damaged spot was on the line of centre.
If, however, the iron wheel ceased motion, the wooden one continuing to
revolve, the damage would be spread over that part of the circumference
of the wooden one which continued while the iron one was at rest, and if
this occurred throughout a whole revolution of the wooden wheel its
roundness would not be apt to be impaired, except in so far as
differences in the hardness of the wood and similar causes might effect.
"To select the best material for driving pulleys in friction-gearing has
required considerable experience; nor is it certain that this object
has yet been attained. Few, if any, well-arranged and careful
experiments have been made with a view of determining the comparative
value of different materials as a frictional medium for driving iron
pulleys. The various theories and notions of builders have, however,
caused the application to this use of several varieties of wood, and
also of leather, india-rubber, and paper; and thus an opportunity has
been given to judge of their different degrees of efficiency. The
materials most easily obtained, and most used, are the different
varieties of wood, and of these several have given good results.
"For driving light machinery, running at high speed, as in sash, door,
and blind factories, basswood, the linden of the Southern and Middle
States (_Tilia Americana_) has been found to possess good qualities,
having considerable durability and being unsurpassed in the smoothness
and softness of its movement. Cotton wood (_Populus monilifera_) has
been tried for small machinery with results somewhat similar to those of
basswood, but is found to be more affected by atmospheric changes. And
even white pine makes a driving surface which is, considering the
softness of the wood, of astonishing efficiency and durability. But for
all heavy work, where from twenty to sixty horse-power is transmitted by
a single contact, soft maple (_Acer rubrum_) has, at present, no rival.
Driving pulleys of this wood, if correctly proportioned and well built,
will run for years with no perceptible wear.
"For very small pulleys, leather is an excellent driver and is very
durable; and rubber also possesses great adhesion as a driver; but a
surface of soft rubber undoubtedly requires more power than one of a
less elastic substance.
"Recently paper has been introduced as a driver for small machinery, and
has been applied in some situations where the test was most severe; and
the remarkable manner in which it has thus far withstood the severity of
these tests appears to point to it as the most efficient material yet
tried.
"The proportioning, however, of friction-pulleys to the work required
and their substantial and accurate construction are matters of perhaps
more importance than the selection of material.
"Friction-wheels must be most accurately and substantially made and kept
in perfect line so that the contact between the surfaces may not be
diminished. The bodies are usually of iron lagged or covered with wooden
segments.
"All large drivers, say from four to ten feet diameter and from twelve
to thirty inch face, should have rims of soft maple six or seven inches
deep. These should be made up of plank, one and a half or two inches
thick, cut into 'cants,' one-sixth, eighth, or tenth of the circle, so
as to place the grain of the wood as nearly as practicable in the
direction of the circumference. The cants should be closely fitted, and
put together with white lead or glue, strongly nailed and bolted. The
wooden rim, thus made up to within about three inches of the width
required for the finished pulley, is mounted upon one or two heavy iron
'spiders,' with six or eight radial arms. If the pulley is above six
feet in diameter, there should be eight arms, and two spiders when the
width of face is more than eighteen inches.
"Upon the ends of the arms are flat 'pads,' which should be of just
sufficient width to extend across the inner face of the wooden rim, as
described; that is, three inches less than the width of the finished
pulley. These pads are gained into the inner side of the rim; the gains
being cut large enough to admit keys under and beside the pads. When the
keys are well driven, strong 'lag' screws are put through the ends of
the arm into the rim. This done, an additional 'round' is put upon each
side of the rim to cover bolt heads and secure the keys from ever
working out. The pulley is now put to its place on the shaft and keyed,
the edges trued up, and the face turned off with the utmost exactness.
"For small drivers, the best construction is to make an iron pulley of
about eight inches less diameter and three inches less face than the
pulley required. Have four lugs, about an inch square, cast across the
face of this pulley. Make a wooden rim, four inches deep, with face
equal to that of the iron pulley, and the inside diameter equal to the
outer diameter of the iron. Drive this rim snugly on over the rim of the
iron pulley having cut gains to receive the lugs, together with a hard
wood key beside each. Now add a round of cants upon each side, with
their inner diameter less than the first, so as to cover the iron rim.
If the pulley is designed for heavy work, the wood should be maple, and
should be well fastened by lag screws put through the iron rim; but for
light work, it may be of basswood or pine, and the lag screws omitted.
But in all cases, the wood should be thoroughly seasoned.
"In the early use of friction-gearing, when it was used only as backing
gear in saw-mills, and for hoisting in grist-mills, the pulleys were
made so as to present the head of the wood to the surface; and we
occasionally yet meet with an instance where they are so made. But such
pulleys never run so smoothly nor drive so well as those made with the
fibre more nearly in a line with the work."[11]
[11] By E. S. Wicklin.
[Illustration: Fig. 217.]
[Illustration: Fig. 218.]
The driving friction may be obtained from contact of the radial surfaces
in two ways: thus, Fig. 217 represents three discs, A, B, and C; the
edge of A being gripped by and between B and C, which must be held
together by a spiral spring S or other equivalent device. These wheels
may be made to give a variable speed of rotation by curving the surfaces
of the pair B C as in the figure. By means of suitable lever-motion A
may be made to advance towards or recede from the centre of B and C,
giving to their shaft an increased or diminished speed of revolution.
[Illustration: Fig. 219.]
A similar result may be obtained by the construction shown in Fig. 218,
in which D and E are two discs fast upon their respective shafts, and C
are discs of leather clamped in E. It is obvious that if D be the driver
the speed of revolution of E will be diminished in proportion as it is
moved nearer to the centre of D, and also that the direction of
revolution of D remaining constant, that of E will be in one direction
if on the side B of the centre of D, and in the other direction if it is
on the side A of the centre of D, thus affording means of reversing the
motion as well as of varying its speed. A similar arrangement is
sometimes employed to enable the direction of rotation of the driver
shaft to be reversed, or its motion to cease. Thus, in Fig. 219, R is a
driving rope driving the discs A, B, and _c_, _d_, _e_, _f_, _g_ are
discs of yellow pine clamped between the flanges _h_ _i_; when these
five discs are forced (by lifting shaft H), against the face of a motion
occurs in one direction, while if forced against B the direction of
motion of H is reversed.
For many purposes, such as hoisting, for example, where considerable
power requires to be transmitted, the form of friction wheels shown in
Fig. 220 is employed, the object being to increase the line of contact
between wheels of a given width of face. In this case the strain due to
the length of the line of contact partly counteracts itself, thus
relieving to that extent the journals from friction. Thus in Fig. 221 is
shown a single wedge and groove of a pair of wheels. The surface
pressure on each side will be at a right angle to the face, or in the
direction described by the arrows A and B. The surface contact acts to
thrust the bearings of the two shafts apart. The effective length of
surface acting to thrust the bearings apart being denoted by the dotted
line C. The relative efficiency of this class of wheel, however, is not
to be measured by the length of the line C, as compared to that of the
two contacting sides of the groove, because it is increased from the
wedge shape of the groove, and furthermore, no matter how solid the
wheels may be, there will be some elasticity which will operate to
increase the driving power due to the contact. It is to preserve the
wedge principle that the wedges are made flat at the top, so that they
shall not bottom in the grooves even after considerable wear has taken
place. The object of employing this class of gear is to avoid noise and
jar and to insure a uniform motion. The motion at the line of contact of
such wheels is not a rolling, but, in part, a sliding one, which may
readily be perceived from a consideration of the following. The
circumference of the top of each wedge is greater than that of the
bottom, and, in the case of the groove, the circumference of the top is
greater than that of the bottom; and since the top or largest
circumference of one contacts with the smallest circumference of the
other, it follows that the difference between the two represents the
amount of sliding motion that occurs in each revolution. Suppose, for
example, we take two of such wheels 10 inches in diameter, having wedges
and grooves 1/4 inch high and deep respectively; then the top of the
groove will travel 31.416 inches in a revolution, and it will contact
with the bottom of the wedge which travels (on account of its lesser
diameter) 29.845 inches per revolution.
[Illustration: Fig. 220.]
[Illustration: Fig. 221.]
Fig. 222 shows the construction for a pair of bevel wheels on the same
principle.
[Illustration: Fig. 222.]
[Illustration: Fig. 223.]
[Illustration: Fig. 224.]
A form of friction-gearing in which the journals are relieved of the
strain due to the pressure of contact, and in which slip is impossible,
is shown in Fig. 223. It consists of projections on one wheel and
corresponding depressions or cavities on the other. These projections
and cavities are at opposite angles on each half of each wheel, so as to
avoid the end pressure on the journals which would otherwise ensue.
Their shapes may be formed at will, providing that the tops of the
projections are narrower than their bases, which is necessary to enable
the projections to enter and leave the cavities. In this class of
positive gear great truth or exactness is possible, because both the
projections and cavities may be turned in a lathe. Fig. 224 represents a
similar kind of gear with the projections running lengthways of the
cylinder approaching more nearly in its action to toothed gearing, and
in this case the curves for the teeth and groves should be formed by the
rules already laid down for toothed gearing. The action of this latter
class may be made very smooth, because a continuous contact on the line
of centres may be maintained by reason of the longitudinal curve of the
teeth.
[Illustration: Fig. 225.]
Cams may be employed to impart either a uniform, an irregular, or an
intermittent motion, the principles involved in their construction being
as follows:--Let it be required to construct a cam that being revolved
at a uniform velocity shall impart a uniform reciprocating motion. First
draw an inner circle O, Fig. 225, whose radius must equal the radius of
the shaft that is to drive it, plus the depth of the cam at its
shallowest part, plus the radius of the roller the cam is to actuate.
Then from the same centre draw an outer circle S, the radius between
these two circles being equal to the amount the cam is to move the
roller. Draw a line O P, and divide it into any convenient numbers of
divisions (five being shown in the figure), and through these points
draw circles. Divide the outer circle S into twice as many equal
divisions as the line O P is divided into (as from 1 to 10 in the
figure), and where these lines pass through the circles will be points
through which the pitch line of the cam may be drawn.
[Illustration: Fig. 226.]
Thus where circle 1 meets line 1, or at point A, is one point in the
pitch line of the cam; where circle 2 meets line 2, or at B, is another
point in the pitch line of the cam, and so on until we reach the point
E, where circle 5 meets line 5. From this point we simply repeat the
process, the point E where line 6 cuts circle 4, being a point on the
pitch line, and so on throughout the whole 10 divisions, and through the
points so obtained we draw the pitch line.
[Illustration: Fig. 227.]
[Illustration: Fig. 228.]
If we were to cut out a cam to the outline thus obtained, and revolve it
at a uniform velocity, it would move a point held against its perimeter
at a uniform velocity throughout the whole of the cam revolution. But
such a point would rapidly become worn away and dulled, which would, as
the point broadened, vary the motion imparted to it, as will be seen
presently. To avoid this wear a roller is used in place of a point, and
the diameter of the roller affects the action of the cam, causing it to
accelerate the cam action at one and retard it at another part of the
cam revolution, hence the pitch line obtained by the process in Fig. 225
represents the path of the centre of the roller, and from this pitch
line we may mark out the actual cam by the construction shown in Fig.
226. A pair of compasses are set to the radius of the roller R, and from
points (such as at A, B, E, F), as the pitch line, arcs of circles are
struck, and a line drawn to just meet the crowns of these arcs will give
the outline of the actual cam. The motion of the roller, however, in
approaching and receding from the cam centre C, must be in a straight
line G G that passes through the centre C of the cam. Suppose, for
example, that instead of the roller lifting and falling in the line G G
its arm is horizontal, as in Fig. 227, and that this arm being pivoted
the roller moves in an arc of a circle as D D, and the motion imparted
to the arm will no longer be uniform. Furthermore, different diameters
of roller require different forms of cam to accomplish the same motion,
or, in other words, with a given cam the action will vary with different
diameters of roller. Suppose, for example, that in Fig. 228 we have a
cam that is to operate a roller along the line A A, and that B
represents a large and C a small roller, and with the cam in the
position shown in the figure, C will have contact with the cam edge at
point D, while B will have contact at the point E, and it follows that
on account of the enlarged diameter of roller B over roller C, its
action is at this point quicker under a given amount of cam motion,
which has occurred because the point of contact has advanced upon the
roller surface--rolling along it, as it were. In Fig. 229 we find that
as the cam moves forward this action continues on both the large and the
small roller, its effect being greater upon the large than upon the
small one, and as this rolling motion of the point of contact evidently
occurs easily, a quick roller motion is obtained without shock or
vibration. Continuing the cam motion, we find in Fig. 230 that the point
of contact is receding toward the line of motion on the large roller and
advancing upon the small one, while in Fig. 231 the two have contact at
about the same point, the forward motion being about completed.
[Illustration: Fig. 229.]
[Illustration: Fig. 230.]
[Illustration: Fig. 231.]
[Illustration: Fig. 232.]
To compare the motions of the respective rollers along the line of
motion A A we proceed as in Fig. 232, in which the two dots M and N are
the same distance apart as are the centres of the two rollers B and C
when in the positions they occupy in Fig. 228; hence a pair of compasses
set to the radius from the axis of the cam to that of roller B will, if
rested at N, strike the arc marked 1 above the line of motion A A, while
a pair of compasses set to the radius from the axis of the cam to that
of roller C in Fig. 228 will, if rested at M in Fig. 232, mark the arc 1
below the line of motion A A. Continuing this process, we set the
compasses to the radius from the axis of the cam to that of roller B in
Fig. 229, and mark this radius at arc 2 above the line A A in Fig. 232;
hence the distance apart of these two arcs is the amount the roller
travelled along the line A A while the cam moved from its position in
Fig. 228 to its position in Fig. 229. Next we set the compasses from the
axis of the cam to that of the large roller in Fig. 230, and then mark
arc 3 above the line in Fig. 232, and repeat the process for Fig. 233,
thus using the centre N for all the positions of the large roller and
marking its motion above the line A A. To get the motion of the small
roller C, we set the compasses to the radius from the axis of the cam to
the small roller in Fig. 228, and then resting one point of these
compasses on centre M in Fig. 232, we mark arc 1 below the line A A.
Turning to Fig. 229 we set the compasses from the cam axis to the centre
of roller C, and from centre N in Fig. 232 mark arc 2 below line A. From
Figs. 230 and 231 proceed in the same way to get lines 3 and 4 below
line A in Fig. 232, and we may at once compare the two motions. Thus we
find that while the cam moved from the position in Fig. 228 to that in
Fig. 229, the large roller moved twice as far as the small one, while at
230 the motions were rapidly equalizing again, the equalization being
completed at 231.
[Illustration: Fig. 233.]
[Illustration: Fig. 234.]
[Illustration: Fig. 235.]
We may now consider the return motion, and in Fig. 233 we find that the
order of things is reversed, for the small roller has contact at O,
while the large one has contact at P; hence the small one leads and
gives the most rapid motion, which it continues to do, as is shown in
Figs. 234, 235, and 236, and we may plot out the two motions as in Fig.
237--that for the large roller being above and that for the small one
below the line A A. First we set a pair of compasses to the radius from
the axis of the large and small roller when in the position shown in
Fig. 231 (which corresponds to the same radius in Fig. 228), and mark
two centres, M and N, as we did in Fig. 232. Of these N is the centre
for plotting the motion of the large roller and M the centre for
plotting the motion of the small one. We set a pair of compasses to the
radius from the axis of the cam and that of the large roller in Fig.
231, and then resting the compasses at N we mark arc 5 above the line A
A, Fig. 237. The compasses are then set from the cam to the roller axis
in Fig. 233, and arc 6 is marked above line A A. From Figs. 234, 235,
and 236 we get the radii to mark arcs 7, 8, 9 above A A, and the motion
of the large roller is plotted. We proceed in the same way for the small
one, but use the centre M, Fig. 237, to mark the arcs 5, 6, 7, 8, and 9
below the line A A, and find that the small roller has moved quickest
throughout. It appears, then, that the larger the roller the quicker the
forward motion and the slower the return one, which is advantageous,
because the object is to move the roller out quickly and close it
slowly, so that under a quick speed the cam shall not run away from the
roller as it is apt to do in the absence of a return or backing cam,
which consists of a separate cam for moving the roller on its return
stroke, thus dispensing with the use of springs or weights to keep the
roller upon the cam and making the motion positive.
[Illustration: Fig. 236.]
[Illustration: Fig. 237.]
[Illustration: Fig. 238.]
The return or backing cam obviously depends for its shape upon the
forward cam, and the latter having been determined, the requisite form
for the return cam may be found as follows. In Fig. 238 let A represent
the forward cam fastened in any suitable or convenient way to a disc of
paper, or, what is better, sheet zinc, B. The cam is pivoted by a pin
passing through it and the zinc, and driven into the drawing-board. A
frame F is made to carry two rollers R and R´, whose width apart exactly
equals the extreme length of the forward cam. The faces D D of the frame
F are in a line with a line passing through the centres of the rolls R
R´, and the cam is also pivoted on this line, so that when the four pins
P are driven into the drawing-board, the frame F will be guided by them
to move in a line that crosses the centre of the cam A. Suppose then
that, the pieces occupying the position shown in the engraving, we slide
F so that roller R touches the edge of cam A, and we may then take a
needle and mark an arc or line around the edge of R´. We then revolve
cam A a trifle, and, being fast to B, the two will move together, and
with R against A we mark a second arc, coincident with the edge of
roller R´. By continuing this process we mark the numerous short arcs
shown upon B, and the crowns of these arcs give us the outline of the
return cam. It is obvious that, while the edge of the cam A will not let
roller R (and therefore frame F) move to the right, roller R´ being
against the edge of the backing or return cam as marked upon B, prevents
the frame F from moving to the left; hence neither roll can leave its
cam.
[Illustration: Fig. 239.]
We have in this example supposed that the frame carrying the rollers is
guided to move in a straight line, and it remains to give an example in
which the rollers are carried on a pivoted shaft or rocking arm. In Fig.
239 we have the same cam A with a sheet of paper B fastened to it, the
rollers R R´ being carried in a rock shaft pivoted at X. It is essential
in this case that the rollers R and R´ and the centre upon which the cam
revolves shall all three be in the arc of a circle whose centre is the
axis of X, as is denoted by the arc D. The cam A is fastened to the
piece of stiff paper or of sheet zinc B, and the two are pivoted by a
pin passing through the axis E of the cam and into the drawing-board,
while the lever is pivoted at X by a pin passing into the drawing-board.
The backing or return cam is obviously marked out the same way as was
described with reference to Fig. 238.
[Illustration: Fig. 240.]
In Fig. 240 we have as an example the construction of a cam to operate
the slide valve of an engine which is to have the steam supply to the
cylinder cut off at one-half the piston stroke, and that will admit the
live steam as quickly as a valve having steam lap equal to, say,
three-fourths the width of the port. In Fig. 240 let the line A
represent a piston stroke of 24 inches, the outer circle B the path of
the outer edge of the cam, and the inner circle C the inner edge of the
cam, the radius between these circles representing the full width of the
steam port. Now, in a valve having lap equal to three-fourths the width
of the steam port, and travel enough to open both ports fully, the
piston of a 24-inch-stroke engine will have moved about 2 inches before
the steam port is fully opened, and to construct a cam that will effect
the same movement we mark a dot D, distant from the end E of piston
stroke 2/26 of the length of the line A, and by erecting the line F we
get at point G, the point at which the cam must attain its greatest
throw. It is obvious, therefore, that as the roller is at R the valve
will be in mid-position, as shown at the bottom of the figure, and that
when point G of the cam arrives at E the edge P of the valve will be
moved fair with edge S of the steam port T, which will therefore be full
open. To cut off at half stroke the valve must again be closed by the
time point N of the cam meets the roller R; hence we may mark point N.
We may then mark in the cam curve from N to M, making it as short as it
will work properly without causing the roller to fail to follow the
curve or strike a blow when reaching the circle C. To accomplish this
end in a single cam, it is essential to make the curve as gradual as
possible from point M to O, so as to start the roller motion easily. But
once having fairly started, its motion may be rapidly accelerated, the
descent from O to Q being rapid. To prevent the roller from meeting
circle C with a blow, the curve from Q to N is again made gradual, so as
to ease and retard the roller motion. The same remarks apply to the
curve from R to G, the object being to cause the roller to begin and end
its passage along the cam curve as slowly as the length of cam edge
occupied by the curve will permit. There is one objection to starting
the curve slowly at G, which is that the port S will be opened
correspondingly slowly for the live steam. This, however, may be
overcome by giving the valve an increased travel, as shown in Fig. 241,
which will simply cause the valve edge to travel to a corresponding
amount over the inside edge of the port. The increased travel is shown
by the circles Y and Z, and it is seen that the cam curve from W to R is
more gradual than in Fig. 240, while the roller R will be moved much
more quickly in the position shown in Fig. 241 than it will in that
shown in Fig. 240, both positions being that when the piston is at the
end of the stroke and the port about to open. While that part of the cam
curve from G to M in Fig. 241 is moving past the roller R, the valve
will be moving over the bridge, the steam port remaining wide open, and
therefore not affecting the steam distribution. After point M, Fig. 241,
has passed the roller, we have from M to T to start the roller
gradually, so that when it has arrived at T and the port begins to close
for the cut-off it may move rapidly, and continue to do so until the
point N reaches the roller and the cut-off has occurred, after which it
does not matter how slowly the valve moves; hence we may make the curve
from N to the circle Y as gradual as we like.
[Illustration: Fig. 241.]
[Illustration: Fig. 242.]
Fig. 242 represents a cam for a valve having the amount of lap
represented by the distance between circles C and Y, the cam occupying
the position it would do with the piston at one end of the stroke, as at
E. Obviously, a full port is obtained when point G reaches the roller,
and as point N is distant from E three-quarters of the diameter of the
outer circle, the cut-off occurs at three-quarter stroke, and we have
from N to Y to make the curve as gradual as we like, and from W to R in
moving the valve to open the port. We cannot, however, give more gradual
curves at G and at M without retarding the roller motion, and therefore
opening and closing the port slower, and it would simply be a matter of
increase of speed to cause the roller to fail to follow the cam surface
at these two points unless a return cam be employed.
We have in these engine cams considered the steam supply and point of
cut-off only, and it is obvious that a second and separate cam would be
required to operate the exhaust valves.
[Illustration: Fig. 243.]
Fig. 243 represents a groove-cam, and it is to be observed that the
roller cannot be maintained in a close fit in the groove, because the
friction on its two sides endeavours to drive it in opposite directions
at the same time, causing an abrasion that soon widens the groove and
reduces the roller diameter; furthermore, when the grooves are made of
equal width all the way down (and these cams are often made in this way)
the roller cannot have a rolling action only, but must have some sliding
motion. Thus, referring to Fig. 243, the amount of sliding motion will
be equal to the differences in the circumferences of the outer circle A
and the inner one B. To obviate this the groove and roller must be made
of such a taper that the axis of the cam and of the roller will meet on
the line of the cam axes and in the middle of the width, as is shown in
Fig. 244; but even in this case the cam will grind away the roller to
some extent, on account of rubbing its sides in opposite directions. To
obviate this, Mr. James Brady, of Brooklyn, N. Y., has patented the use
of two rollers, as in Fig. 245, one acting against one side and the
other against the other side of the groove, by which means lost motion
and rapid wear are successfully avoided.
[Illustration: Fig. 244.]
[Illustration: Fig. 245.]
In making a cam of this form, the body of the cam is covered by a
sleeve. The groove is cut through the sleeve and into the body, and is
made wider than the diameter of the roller. When the rollers are in
place on the spindle or journal, the sleeve is pushed forward, or rather
endways, and fastened by a set-screw. This gives the desired bearing on
both sides of the groove, while each roller touches one side only of the
groove. The edges of the sleeve are then faced off even with the cam
body, the whole appearing as in the figure.
[Illustration: _VOL. I._ =FORMS OF SCREW THREADS.= _PLATE II._
THE [V]-THREAD.
Fig. 246.
THE UNITED STATES STANDARD THREAD.
Fig. 247.
THE WHITWORTH, OR ENGLISH STANDARD THREAD.
Fig. 248.
THE SQUARE THREAD.
Fig. 249.
THE PITCH OF A THREAD.
Fig. 250.
A DOUBLE THREAD.
Fig. 251.
A RATCHET THREAD.
Fig. 252.
A "DRUNKEN" THREAD.
Fig. 253.
RIGHT AND LEFT HAND THREAD.
Fig. 254.]
CHAPTER IV.--SCREW THREAD.
Screw threads are employed for two principal purposes--for holding or
securing, and for transmitting motion. There are in use, in ordinary
machine shop practice, four forms of screw thread. There is, first, the
sharp [V]-thread shown in Fig. 246; second, the United States standard
thread, the Sellers thread, or the Franklin Institute thread, as it is
sometimes called--all three designations signifying the same form of
thread. This thread was originally proposed by William Sellers, and was
afterward recommended by the Franklin Institute. It was finally adopted
as a standard by the United States Navy Department. This form of thread
is shown in Fig. 247. The third form is the Whitworth or English
standard thread, shown in Fig. 248. It is sometimes termed the round top
and bottom thread. The fourth form is the square thread shown in Fig.
249, which is used for coarse pitches, and usually for the transmission
of motion.
The sharp [V]-thread, Fig. 246, has its sides at an angle of 60° one to
the other, as shown; or, in other words, each side of the thread is at
an angle of 60° to the axial line of the bolt. The United States
Standard, Fig. 247, is formed by dividing the depth of the sharp
[V]-thread into 8 equal divisions and taking off one of the divisions at
the top and filling in another at the bottom, so as to leave a flat
place at the top and bottom. The Whitworth thread, Fig. 248, has its
sides at an angle of 55° to each other, or to the axial line of the
bolt. In this the depth of the thread is divided into 6 equal parts, and
the sides of the thread are joined by arcs of circles that cut off one
of these parts at the top and another at the bottom of the thread. The
centres from which these arcs are struck are located on the second lines
of division, as denoted in the figure by the dots. Screw threads are
designated by their pitch or the distance between the threads. In Fig.
250 the pitch is 1/4 inch, but it is usual to take the number of threads
in an inch of length; hence the pitch in Fig. 250 would generally be
termed a pitch of 4, or 4 to the inch. The number of threads per inch of
length does not, however, govern the true pitch of the thread, unless it
be a "single" thread.
A single thread is composed of one spiral projection, whose advance upon
the bolt is equal in each revolution to the apparent pitch. In Fig. 251
is shown a double thread, which consists of two threads. In the figure,
A denotes one spiral or thread, and B the other, the latter being
carried as far as C only for the sake of illustration. The true pitch is
in this case twice that of the apparent pitch, being, as is always the
case, the number of revolutions the thread makes around the bolt (which
gives the pitch per inch), or the distance along the bolt length that
the nut or thread advances during one rotation. Threads may be made
double, treble, quadruple and so on, the object being to increase the
motion without the use of a coarser pitch single thread, whose increased
depth would weaken the body of the bolt.
The "ratchet" thread shown in Fig. 252 is sometimes used upon bolts for
ironwork, the object being to have the sides A A of the thread at a
right angle to the axis of the bolt, and therefore in the direct line of
the strain. Modifications of this form of thread are used in coarse
pitches for screws that are to thread direct into woodwork.
A waved or drunken thread is one in which the path around the bolt is
waved, as in Fig. 253, and not a continuous straight spiral, as it
should be. All threads may be either left hand or right, according to
their direction of inclination upon the bolt; thus, Fig. 254 is a
cylinder having a right-hand thread at A and a left-hand one at B. When
both ends of a piece have either right or left-hand threads, if the
piece be rotated and the nuts be prevented from rotating, they will move
in the same direction, and, if the pitches of the threads are alike, at
the same rate of motion; but if one thread be a right and the other a
left one, then, under the above conditions, the nuts will advance toward
or recede from each other according to the direction of rotation of the
male thread.
[Illustration: Fig. 255.]
In Fig. 255 is represented a form of thread designed to enable the nut
to fit the bolt, and the thread sides to have a bearing one upon the
other, notwithstanding that the diameter of the nut and bolt may differ.
The thread in the nut is what may be termed a reversed ratchet thread,
and that in the bolt an undercut ratchet thread, the amount of undercut
being about 2°. Where this form of thread is used, the diameter of the
bolt may vary as much as 1-32d of an inch in a bolt 3/4 inch in
diameter, and yet the nut will screw home and be a tight fit. The
difference in the thread fit that ordinarily arises from differences in
the standards of measurement from wear of the threading tools, does not
in this form affect the fit of the nut to the bolt. In screwing the nut
on, the threads conform one to the other, giving a bearing area
extending over the full sides of the thread. The undercutting on the
leading face of the bolt thread gives room for the metal to conform
itself to the nut thread, which it does very completely. The result is
that the nut may be passed up and down the bolt several times and still
remain too tight a fit to be worked by hand. Experiment has demonstrated
that it may be run up and down the bolt dozens of times without becoming
as loose as an ordinary bolt and nut. On account of this capacity of the
peculiar form of thread employed, to adapt itself, the threads may be
made a tight fit when the threading tools are new. The extra tightness
that arises from the wear of these tools is accommodated in the
undercutting, which gives room for the thread to adjust itself to the
opposite part or nut.
In a second form of self-locking thread, the thread on the bolt is made
of the usual [V]-shape United States standard. The thread in the nut,
however, is formed as illustrated in Fig. 256, which is a section of a
3/4-inch bolt, greatly enlarged for the sake of clearness of
illustration. The leading threads are of the same angle as the thread on
the bolt, but their diameters are 3/4 and 1-16th inch, which allows the
nut to pass easily upon the bolt. The angle of the next thread following
is 56°, the succeeding one 52°, and so on, each thread having 4° less
angle than the one preceding, while the pitch remains the same
throughout. As a result, the rear threads are deeper than the leading
ones. As the nut is screwed home, the bolt thread is forced out or up,
and fills the rear threads to a degree depending upon the diameter of
the bolt thread. For example, if the bolt is 3/4 inch, its leading or
end thread will simply change its angle from that of 60° to that of 44°,
or if the bolt thread is 3/4 and 1-64th inch in diameter, its leading
thread will change from an angle of 60° to one of 44°. It will almost
completely fill the loose thread in the nut. The areas of spaces between
the nut threads are very nearly equal, although slightly greater at the
back end of the nut, so that if the front end will enter at all, the nut
will screw home, while the thread fit will be tight, even under a
considerable variation in the bolt itself. From this description, it is
evident that the employment of nuts threaded in this manner is only
necessary in order to give to ordinary bolts all the advantages of
tightness due to this form of thread.
The term "diameter" of a thread is understood to mean its diameter at
the top of the thread and measured at a right angle to the axis of the
bolt. When the diameter of the bottom or root of the thread is referred
to it is usually specified as diameter at the bottom or at the root of
the thread.
The depth of a thread is the vertical height of the thread upon the
bolt, measured at a right angle to the bolt axis and not along the side
of the thread.
A true thread is one that winds around the bolt in a continuous and even
spiral and is not waved or drunken as is the thread in Fig. 253. An
outside or male thread is one upon an external surface as upon a bolt;
an internal or female thread is one produced in a bore or hole as in a
nut.
[Illustration: Fig. 256.]
The Whitworth or English standard thread, shown in Fig. 248, is that
employed in Great Britain and her colonies, and to a small extent in the
United States. The [V]-thread fig. 246 is that in most common use in the
United States, but it is being displaced by the United States standard
thread. The reasons for the adoption of the latter by the Franklin
Institute are set forth in the report of a committee appointed by that
Institute to consider the matter. From that report the following
extracts are made.
"That in the course of their investigations they have become more deeply
impressed with the necessity of some acknowledged standard, the
varieties of threads in use being much greater than they had supposed
possible; in fact, the difficulty of obtaining the exact pitch of a
thread not a multiple or sub-multiple of the inch measure is sometimes a
matter of extreme embarrassment.
"Such a state of things must evidently be prejudicial to the best
interests of the whole country; a great and unnecessary waste is its
certain consequence, for not only must the various parts of new
machinery be adjusted to each other, in place of being interchangeable,
but no adequate provision can be made for repairs, and a costly variety
of screwing apparatus becomes a necessity. It may reasonably be hoped
that should a uniformity of practice result from the efforts and
investigations now undertaken, the advantages flowing from it will be so
manifest, as to induce reform in other particulars of scarcely less
importance.
"Your committee have held numerous meetings for the purpose of
considering the various conditions required in any system which they
could recommend for adoption. Strength, durability, with reference to
wear from constant use, and ease of construction, would seem to be the
principal requisites in any general system; for although in many cases,
as, for instance, when a square thread is used, the strength of the
thread and bolt are both sacrificed for the sake of securing some other
advantage, yet all such have been considered as special cases, not
affecting the general inquiry. With this in view, your committee decided
that threads having their sides at an angle to each other must
necessarily more nearly fulfil the first condition than any other form;
but what this angle should be must be governed by a variety of
considerations, for it is clear that if the two sides start from the
same point at the top, the greater the angle contained between them, the
greater will be the strength of the bolt; on the other hand, the greater
this angle, supposing the apex of the thread to be over the centre of
its base, the greater will be the tendency to burst the nut, and the
greater the friction between the nut and the bolt, so that if carried to
excess the bolt would be broken by torsional strain rather than by a
strain in the direction of its length. If, however, we should make one
side of the thread perpendicular to the axis of the bolt, and the other
at an angle to the first, we should obtain the greatest amount of
strength, together with the least frictional resistance; but we should
have a thread only suitable for supporting strains in one direction, and
constant care would be requisite to cut the thread in the nut in the
proper direction to correspond with the bolt; we have consequently
classed this form as exceptional, and decided that the two sides should
be at an angle to each other and form equal angles with the base.
"The general form of the thread having been determined upon the above
considerations, the angle which the sides should bear to each other has
been fixed at 60°, not only because this seems to fulfil the conditions
of least frictional resistance combined with the greatest strength, but
because it is an angle more readily obtained than any other, and it is
also in more general use. As this form is in common use almost to the
exclusion of any other, your committee have carefully weighed its
advantages and disadvantages before deciding to recommend any
modification of it. It cannot be doubted that the sharp thread offers us
the simplest form, and that its general adoption would require no
special tools for its construction, but its liability to accident,
always great, becomes a serious matter upon large bolts, whilst the
small amount of strength at the sharp top is a strong inducement to
sacrifice some of it for the sake of better protection to the remainder;
when this conclusion is reached, it is at once evident a corresponding
space may be filled up in the bottom of the thread, and thus give an
increased strength to the bolt, which may compensate for the reduction
in strength and wearing surface upon the thread. It is also clear that
such a modification, by avoiding the fine points and angles in the tools
of construction, will increase their durability; all of which being
admitted, the question comes up, what form shall be given to the top and
bottom of the thread? for it is evident one should be the converse of
the other. It being admitted that the sharp thread can be made
interchangeable more readily than any other, it is clear that this
advantage would not be impaired if we should stop cutting out the space
before we had made the thread full or sharp; but to give the same shape
at the bottom of the threads would require that a similar quantity
should be taken off the point of the cutting tool, thus necessitating
the use of some instrument capable of measuring the required amount, but
when this is done the thread having a flat top and bottom can be quite
as readily formed as if it was sharp. A very slight examination sufficed
to satisfy us that in point of construction the rounded top and bottom
presents much greater difficulties--in fact, all taps and screws that
are chased or cut in a lathe require to be finished or rounded by a
second process. As the radius of the curve to form this must vary for
every thread, it will be impossible to make one gauge to answer for all
sizes, and very difficult, in fact impossible, without special tools, to
shape it correctly for one.
"Your committee are of opinion that the introduction of a uniform system
would be greatly facilitated by the adoption of such a form of thread as
would enable any intelligent mechanic to construct it without any
special tools, or if any are necessary, that they shall be as few and as
simple as possible, so that although the round top and bottom presents
some advantages when it is perfectly made, as increased strength to the
thread and the best form to the cutting tools, yet we have considered
that these are more than compensated by ease of construction, the
certainty of fit, and increased wearing surface offered by the flat top
and bottom, and therefore recommend its adoption. The amount of flat to
be taken off should be as small as possible, and only sufficient to
protect the thread; for this purpose one-eighth of the pitch would seem
to be ample, and this will leave three-fourths of the pitch for bearing
surface. The considerations governing the pitch are so various that
their discussion has consumed much time.
"As in every instance the threads now in use are stronger than their
bolts, it became a question whether a finer scale would not be an
advantage. It is possible that if the use of the screw thread was
confined to wrought iron or brass, such a conclusion might have been
reached, but as cast iron enters so largely into all engineering work,
it was believed finer threads than those in general use might not be
found an improvement; particularly when it was considered that so far as
the vertical height of thread and strength of bolt are concerned, the
adoption of a flat top and bottom thread was equivalent to decreasing
the pitch of a sharp thread 25 per cent., or what is the same thing,
increasing the number of threads per inch 33 per cent. If finer threads
were adopted they would require also greater exactitude than at present
exists in the machinery of construction, to avoid the liability of
overriding, and the wearing surface would be diminished; moreover, we
are of opinion that the average practice of the mechanical world would
probably be found better adapted to the general want than any
proportions founded upon theory alone."
* * * * *
[Illustration: Fig. 257.]
[Illustration: Fig. 258.]
The principal requirements for a screw thread are as follows: 1. That it
shall possess a strength that, in the length or depth of a nut, shall be
equal to the strength of the weakest part of the bolt, which is at the
bottom of the bolt thread. 2. That the tools required to produce it
shall be easily made, and shall not alter their form by reason of wear.
3. That these tools shall (in the case of lathe work) be easily
sharpened, and set to correct position in the lathe. 4. That a minimum
of measuring and gauging shall be required to test the diameter and form
of the thread. 5. That the angles of the sides shall be as acute as is
consistent with the required strength. 6. That it shall not be unduly
liable to become loose in cases where the nut may require to be fastened
and loosened occasionally.
Referring to the first, by the term "the strength of a screw thread," is
not meant the strength of one thread, but of so many threads as are
contained in the nut. This obviously depends upon the depth or thickness
of the nut-piece. The standard thickness of nut, both in the United
States and Whitworth systems, as well as in general practice, or where
the common [V]-thread is used, is made equal to the diameter of the top
of the thread. Therefore, by the term "strength of thread" is meant the
combined strength of as many threads as are contained in a nut of the
above named depth. It is obvious, then, when it is advantageous to
increase the strength of a thread, that it may be done by increasing the
depth of the nut, or in other words, by increasing the number of threads
used in computing its strength. This is undesirable by reason of
increasing the cost and labor of producing the nuts, especially as the
threading tools used for nuts are the weakest, and are especially liable
to breakage, even with the present depth of nuts.
It has been found from experiments that have been made that our present
threads are stronger than their bolts, which is desirable, inasmuch as
it gives a margin for wear on the sides of the threads. But for threads
whose nuts are to remain permanently fastened and are not subject to
wear, it is questionable whether it were not better for the bolts to be
stronger than the threads. Suppose, for instance, that a thread strips,
and the bolt will remain in place because the nut will not come off the
bolt readily. Hence the pieces held by the bolt become loosened, but not
disconnected. If, on the other hand, the bolt breaks, it is very liable
to fall out, leaving the piece or pieces, as the case may be, to fall
apart, or at least become disconnected, so far as the bolt is concerned.
But since threads are used under conditions where the threads are liable
to wear, and since it is undesirable to have more than one standard
thread, it is better to have the threads, when new, stronger than the
bolts.
[Illustration: Fig. 259.]
Referring to the second requirement, screw threads or the tools that
produce them are originated in the lathe, and the difficulty with making
a round top and bottom thread lies in shaping the corner to cut the top
of the thread. This is shown in Fig. 257, where a Whitworth thread and a
single-toothed thread-cutting tool are represented. The rounded point A
of the tool will not be difficult to produce, but the hollow at B would
require special tools to cut it. This is, in fact, the plan pursued
under the Whitworth system, in which a hob or chaser-cutting tool is
used to produce all the thread-cutting tools. A chaser is simply a
toothed tool such as is shown in Fig. 258. Now, it would manifestly be
impracticable to produce a chaser having all the curves, A and B, at the
top and at the bottom of the teeth alike, by the grinding operations
usually employed in the workshop, and hence the employment of the hob.
Fig. 259 represents a hob, which is a threaded piece of steel with a
number of grooves such as shown at A, A, A, which divide the thread into
teeth, the edges of which will cut a chaser, of a form corresponding to
that of the thread upon the hob. The chaser is employed to produce taps
and secondary hobs to be used for cutting the threads in dies, &c., so
that the original hob is the source from which all the thread-cutting
tools are derived.
[Illustration: Fig. 260.]
For the United States standard or the common [V]-thread, however, no
standard hob is necessary, because a single-pointed tool can be ground
with the ordinary grinding appliances of the workshop. Thus, for the
United States standard, a flat-pointed tool, Fig. 260, and for the
common [V]-thread, a sharp-pointed tool, Fig. 260, may be used. So far
as the correctness of angle of pitch and of thread depth are concerned,
the United States standard and the common [V]-thread can both be
produced, under skilful operation, more correctly than is possible with
the Whitworth thread, for the following reasons:--
To enable a hob to cut, it must be hardened, and in the hardening
process the pitch of the thread alters, becoming, as a general rule
(although not always) finer. This alteration of pitch is not only
irregular in different threads, but also in different parts of the same
thread. Now, whatever error the hob thread receives from hardening it
transfers to the chaser it cuts. But the chaser also alters its form in
hardening, the pitch, as a general rule, becoming coarser. It may happen
that the error induced in the hob hardening is corrected by that induced
by hardening the chaser, but such is not necessarily the case.
[Illustration: Fig. 261.]
The single-pointed tool for the United States standard or for the common
[V]-thread is accurately ground to form after the hardening, and hence
need contain no error. On the other hand, however, the rounded top and
bottom thread preserves its form and diameter upon the thread-cutting
tools better than is the case with threads having sharp corners, for the
reason that a rounded point will not wear away so quickly as a sharp
point. To fully perceive the importance of this, it is necessary to
consider the action of a tool in cutting a thread. In Fig. 261 there is
shown a chaser, A, applied to a partly-formed thread, and it will be
observed that the projecting ends or points of the teeth are in
continuous action, cutting a groove deeper and deeper until a full
thread is developed, at which time the bottoms of the chaser teeth will
meet the perimeter of the work, but will perform no cutting duty upon
it. As a result, the chaser points wear off, which they will do more
quickly if they are pointed, and less quickly if they are rounded. This
causes the thread cut to be of increased and improper diameter at the
root.
[Illustration: Fig. 262.]
The same defect occurs on the tools for cutting internal threads, or
threads in holes or bores. In Fig. 262, for example, is shown a tool
cutting an internal thread, which tool may be taken to represent one
tooth of a tap. Here again the projecting point of the tool is in
continuous cutting action, while this, being a single-toothed tool, has
no bottom corners to suffer from wear. As a result of the wear upon the
tools for cutting internal threads, the thread grooves, when cut to
their full widths, will be too shallow in depth, or, more correctly
speaking, the full diameter of the thread will be too small to an amount
corresponding to twice the amount of wear that the tool point has
suffered. In single-pointed tools, such as are used upon lathe work,
this has but little significance, because it is the work of but a minute
or two to grind up the tool to a full point again, but in taps and solid
dies, or in chasers in heads (as in some bolt-cutting machines) it is
highly important, because it impairs the fit of the threads, and it is
difficult to bring the tools to shape after they are once worn.
[Illustration: Fig. 263.]
The internal threads for the nuts of bolts are produced by a tap formed
as at T in Fig. 263. It consists of a piece of steel having an external
thread and longitudinal flutes or grooves which cut the thread into
teeth. The end of the thread is tapered off as shown, to enable the end
of the tap to enter the hole, and as it is rotated and the nut N held
stationary, the teeth cut grooves as the tap winds through, thus forming
the thread.
[Illustration: Fig. 264.]
The threads upon bolts are usually produced either by a head containing
chasers or by a solid die such as shown at A in Fig. 264, B representing
a bolt being threaded. The bore of A is threaded and fluted to provide
cutting teeth, and the threads are chamfered off at the mouth to assist
the cutting by spreading it over several teeth, which enables the bolt
to enter the die more easily.
We may now consider the effect of continued use and its consequent wear
upon the threads or teeth of a tap and die or chaser.
The wear of the corners at the tops of the thread (as at A B in Fig.
265) of a tap is greater than the wear at the bottom corners at E F,
because the tops perform more cutting duty.
[Illustration: Fig. 265.]
First, the top has a larger circle of rotation than has the bottom, and,
therefore, its cutting speed is greater, to an amount equal to the
difference between the circumferences of the thread at the top and at
the bottom. Secondly, the tops of the teeth of tap perform nearly all
the cutting duty, because the thread in the nut is formed by the tops
and sides of the tap, which on entering cut a groove which they
gradually deepen, until a full thread is formed, while the bottoms of
the teeth (supposing the tapping hole to be of proper diameter and not
too small) simply meet the bore of the tapping hole as the thread is
finished. If, as in the case of hot punched nuts, the nut bore contains
scale, this scale is about removed by the time the bottoms of the top
teeth come into action, hence the teeth bottoms are less affected by the
hardness of the scale.
In the case of the teeth on dies and chasers, the wear at the corners C
D, in Fig. 266, is the greatest. Now, the tops of the teeth on the tap
(A B, in Fig. 265) cut the bottom or full diameter of the thread in the
nut, while the tops of the teeth (C D, in Fig. 266) in the die cut the
bottom of the thread on the bolt; hence the rounded corners cut on the
work by the tops of the teeth in the one case, meet the more square
corners left by the tops of the teeth in the other, and providing that
under these circumstances the thread in the nut were of equal diameter
to that on the bolt the latter would not enter the former.
If the bolt were made of a diameter to enable the nut to wind a close
fit upon the bolt, the corners only of the threads would fit, as shown
in Fig. 267, which represents at N a thread in a portion of a nut and at
S a portion of a thread upon a tap or bolt, the two threads being
magnified and shown slightly apart for clearness of illustration. The
corners A, B of the nut are then cut by the corners A B of the tap in
Fig. 265, and the corners C, C, D correspond to those cut by the corners
C, D of the die teeth in Fig. 266; corners E, F, Fig. 267, are cut by
corners C, D, in Fig. 266, and corners G, H are cut by corners G, H in
Fig. 266, and it is obvious that the roundness of the corners A, B, C,
and D in Fig. 267 will not permit the tops of the thread on the bolt to
meet the bottoms of the thread in the nut, but that the threads will
bear at the corners only.
[Illustration: Fig. 266.]
[Illustration: Fig. 267.]
So far, however, we have only considered the wear tending to round off
the sharp corners of the teeth, which wear is greater in proportion as
the corners are sharp, and less as they are rounded or flattened, and we
have to consider the wear as affecting the diameters of the male and
female thread at their tops and bottoms respectively.
Now, since the tops of the tap teeth wear the most, the diameter of the
thread decreases in depth, while, since the tops of the die teeth wear
most, the depth of the thread in the die also decreases. The tops of the
tap teeth cut the bottom of the thread in the nut and the tops of the
die teeth cut the bottoms of the thread upon the bolt.
Let it be supposed then that the points of the teeth of a tap have worn
off to a depth of the 1-2000th part of an inch, which they will by the
time they become sufficiently dulled to require resharpening, and that
the teeth of a die have become reduced by wear by the same amount, and
the result will be the production of threads such as shown in Fig. 268,
in which the diameter of the bolt is supposed to be an inch, and the
proper thread depth 1-10th inch. Now, the diameter at the root of the
thread on the bolt will be .802 inch in consequence of the wear, but the
smallest diameter of the nut thread is .800 inch, and hence too small to
admit the male or bolt thread. Again, the full diameter of the bolt
thread is 1 inch, whereas the full diameter of the nut thread is but
.998 inch, or, again, too small to admit the bolt thread. As a result,
it is found in practice that any standard form of thread that makes no
allowance for wear, cannot be rigidly adhered to, or if it is adhered
to, the tap must be made when new above the standard diameter, causing
the thread to be an easy fit, which fit will become closer as the
thread-cutting tools wear, until finally it becomes too tight
altogether. The fit, however, becomes too tight at the top and bottom,
where it is not required, instead of at the sides, where it should
occur. When this is the case, the nuts will soon wear loose because of
their small amount of bearing area.
[Illustration: Fig. 268.]
[Illustration: Fig. 269.]
It may be pointed out, however, that from the form in which the chasers
or solid dies for bolt machines, and also that in which taps are made,
the finishing points of the teeth are greatly relieved of cutting duty,
as is shown in Figs. 269 and 270. In the die the first two or three
threads are chamfered off, while in the tap the thread is tapered off
for a length usually equal to about two or three times the diameter for
taps to be used by hand, and six or seven times the diameter for taps to
be used in a machine. The wear of the die is, therefore, more than that
of the tap, because the amount of cutting duty to produce a given
length of thread is obviously the same, whether the thread be an
internal or an external one, and the die has less cutting edges to
perform this duty than the tap has. The main part of the cutting is, it
is true, in both cases borne by the beveled surfaces at the top of the
chamfered teeth of the cutting tools, but the fact remains that the
depth of the thread is finished by the extreme tops of the teeth, and
these, therefore, must in time suffer from the consequent wear, while
the bottoms of the teeth perform no cutting duty, providing that the
hole in the one case and the bolt in the other are of just sufficient
diameter to permit of a full thread being formed, as should be the case.
In threads cut by chasers the same thing occurs; thus in Fig. 271 is
shown at A a chaser having full teeth, as it must have when a full
thread is to pass up to a shoulder, as up to the head of a bolt. Here
the first tooth takes the whole depth of the cut, but if from wear this
point becomes rounded, the next tooth may remedy the defect. When,
however, a chaser is to be used upon a thread that terminates in a stem
of smaller diameter, as C in Fig. 271, then the chaser may have its
teeth bevelled off, as is shown on B.
[Illustration: Fig. 270.]
The evils thus pointed out as attending the wear of screw-cutting tools
for bolts and nuts, may be overcome by a slight variation in the form of
the thread. Thus in Fig. 272, at A is shown a form of thread for the
tools to cut internal threads, and at B a form of thread for dies to cut
external threads. The sides of the thread are in both cases at the same
angle, as say, 60°. The depth of the thread, supposing the angle of the
sides to meet in a point, is divided off into 11, or any number of equal
divisions. For a tap one of these divisions is taken off, forming a flat
top, while at the bottom two of these divisions are taken off, or if
desirable, 1-1/2 divisions may be taken off, since the exact amount is
not of primary importance. On the external thread cutting tool B, as say
a solid die, two divisions are taken off at the largest diameter, and
one at the smallest diameter, or, if any other proportion be selected
for the tap, the same proportion may be selected for the die, so long as
the least is taken off the largest diameter of the tap thread, and of
the smallest diameter of the die thread.
[Illustration: Fig. 271.]
The diameter of the tap may still be standard to ring or collar gauge,
as in the Franklin Institute thread, the angle at the sides being simply
carried in a less distance. In the die the largest diameter of the
thread has a flat equal to that on the bottom of the tap, while the
smallest diameter has a flat equal to that on the tops of the tap teeth,
the width or thickness of the threads remaining the same as in the
Franklin Institute thread at each corresponding diameter in its depth.
[Illustration: Fig. 272.]
The effect is to give to the threads on the work a certain amount of
clearance at the top and bottom of the thread, leaving the angles just
the same as before, and insuring that the contact shall be at the sides,
as shown in Fig. 273.
This form of thread retains the valuable features of the Franklin
Institute that it can be originated by any one, and that it can be
formed with a single-toothed or single-pointed tool. Furthermore, the
wear of the threading tools will not impair the diametral fit of the
work, while the permissible limit of error in diameter will be
increased.
By this means great accuracy in the diameters of the threads is rendered
unnecessary, and the wear of the screw-cutting tools at their corners is
rendered harmless, nor can any confusion occur, because the tools for
external threads cannot be employed upon internal ones. The sides only
of the thread will fit, and the whole contact and pressure of the fit
will be on those sides only.
[Illustration: Fig. 273.]
This is an important advantage, because if the tops of the thread are
from the wear of the dies and taps of too large or small diameter,
respectively, the threads cannot fit on the sides. Thus, suppose a bolt
thread to be loose at the sides, but to be 1-1000 of an inch larger in
diameter than the nut thread, then it cannot be screwed home until that
amount has been worn or forced off the thread diameter, or has been
bruised down by contact with the nut thread, and it would apparently be
a tight fit at the sides. Suppose a thread to have been cut in the
lathe to the correct diameter at the bottom of the thread, the sides of
the thread being at the correct angle, but let the diameter at the top
of the thread (a Franklin Institute thread is here referred to), be
1-1000 too large, then the nut cannot be forced on until that 1-1000 is
removed by some means or other, unless the nut thread be deepened to
correspond.
Now take this last bolt and turn the 1-1000 inch off, and it will fit,
turn off another 1-1000 or 1-64 inch, and it will still fit, and the fit
will remain so nearly the same with the 1-64 inch off that the
difference can scarcely be found. Furthermore, with a nut of a fit
requiring a given amount of force to screw it upon the bolt, the area of
contact will be much greater when that contact is on the sides than when
it is upon the tops and bottoms of the thread, while the contact will be
in a direction better to serve as an abutment to the thrust or strain.
In very fine pitches of thread such as are used in the manufacture of
watches, this plan of easing or keeping free the extremities of the
thread is found to be essential, and there appears every probability
that its adoption would obviate the necessity of using check nuts.
It has been observed that the threads upon tools alter in pitch from the
hardening operation, and this is an objection to the employment of
chasers cut from hobs.
Suppose, for instance, that a nut is produced having a thread of true
and uniform pitch, then after hardening, the pitch may be no longer
correct. The chasers cut from the hob will contain the error of pitch
existing in the hob, and upon being hardened may have added to it errors
of its own. If this chaser be used to produce a new hob, the latter will
contain the errors in the chaser added to whatever error it may itself
obtain in the hardening. The errors may not, it is true, all exist in
one direction, and those of one hardening may affect or correct those
caused by another hardening, but this is not necessarily the case, and
it is therefore preferable to employ a form of thread that can be cut by
a tool ground to correct shape after having been hardened, as is the
case with the [V]-thread and the United States standard.
[Illustration: Fig. 274.]
It is obvious that in originating either the sharp [V] or the United
States standard thread, the first requisite is to obtain a correct angle
of 60°, which has been done in a very ingenious manner by Mr. J. H.
Heyer for the Pratt and Whitney Company, the method being as follows.
Fig. 274 is a face and an end view of an equilateral triangle employed
as a guide in making standard triangles, and constructed as
follows:--Three bars, A, A, A, of steel were made parallel and of
exactly equal dimensions. Holes X were then pierced central in the width
of each bar and the same distance apart in each bar; the method of
insuring accuracy in this respect being shown in Figs. 275 and 276, in
which S represents the live spindle of a lathe with its face-plate on
and a plug, C, fitted into the live centre hole. The end of this plug is
turned cylindrically true, and upon it is closely fitted a bush, the
plug obviously holding the bush true by its hole. A rectangular piece
_e_ is provided with a slot closely fitting to the bush.
The rectangular piece _e_ is then bolted to the lathe face-plate and
pierced with a hole, which from this method of chucking will be exactly
central to its slot, and at a right angle to its base. The bush is now
dispensed with and the piece _e_ is chucked with its base against the
face-plate and the hole pierced as above, closely fitting to the pin on
the end of the plug _c_, which, therefore, holds _e_ true.
[Illustration: Fig. 275.]
The bars A are then chucked one at a time in the piece _e_ (the outer
end resting upon a parallel piece _f_), and a hole is pierced near one
end, this hole being from this method of chucking exactly central to the
width of the bar A, and at a right angle to its face.
[Illustration: Fig. 276.]
The parallel piece _f_ is then provided with a pin closely fitting the
hole thus pierced in the bar. The bars were turned end for end with the
hole enveloping the pin in _f_ (the latter being firmly fixed to the
face-plate), and the other end laid in the slot in _e_, while the second
hole was pierced. The holes (X, Fig. 274) must be, from this method of
chucking, exactly an equal distance apart on each bar. The bars were
then let together at their ends, each being cut half-way through and
closely fitting pins inserted in the holes X, thus producing an
equilateral triangle entirely by machine work, and therefore as correct
as it can possibly be made, and this triangle is kept as a standard
gauge whereby others for shop use may be made by the following
process:--
Into the interior walls of this triangle there is fitted a cylindrical
bush B, it being obvious that this bush is held axially true or central
to the triangle, and it is secured in place by screws _y_, _y_, _y_,
passing through its flange and into bars A.
At one end of the bush B, is a cylindrical part D, whose diameter is 2
inches or equal to the length of one side of an equilateral triangle
circumscribed about a circle whose diameter is 1.1547 inches, as shown
in Fig. 278 and through this bush B passes a pin P, having a nut N. A
small triangle is then roughed out, and its bore fitting to the stem of
pin P, and by means of nut N, the small triangle is gripped between the
under face of D and the head of P. The large triangle is then held to an
angle-plate upon a machine while resting upon the machine-table, and the
uppermost edge of the small triangle is dressed down level with the
cylindrical stem D, which thus serves as a gauge to determine how much
to take off each edge of the small triangle to bring it to correct
dimensions.
The truth of the angles of the small triangle depends, of course, also
upon the large one; thus with face H resting upon the machine-table,
face G is cut down level with stem D; with face F upon the table, face E
is cut down level with D; and with face L upon the table, face K is
dressed down level with D. And we have a true equilateral triangle
produced by a very ingenious system of chuckings, each of which may be
known to be true.
The next operation is to cut upon the small triangle the flat
representing the top and bottom of the United States standard thread,
which is done by cutting off one-eighth part of its vertical height, and
it then becomes a test piece or standard gauge of the form of thread.
The next step is to provide a micrometer by means of which tools for
various pitches may be tested both for angle and for width of flat, and
this is accomplished as follows:--
[Illustration: _VOL. I_ =MEASURING AND GAUGING SCREW THREADS.= _PLATE
III._
Fig. 279.
Fig. 280.
Fig. 281.
Fig. 282.
Fig. 285.
Fig. 286.
Fig. 283.
Fig. 284.
Fig. 287.]
In Fig. 278 F is a jaw fixed by a set screw to the bar of the
micrometer, and E is a sliding jaw; these two jaws being fitted to the
edges of the triangle or test piece T in the figure which has been made
as already described. To the sliding jaw E is attached the micrometer
screw C, which has a pitch of 40 threads per inch; the drum A upon the
screw has its circumference divided into 250 equidistant divisions,
hence if the drum be moved through a space equal to one of these
divisions the sliding jaw E will be moved the 1-250th part of 1-40th of
an inch, or in other words the 1-10,000th of an inch. To properly adjust
the position of the zero piece or pointer, the test piece T is placed in
the position shown in Fig. 278, and when the jaws were so adjusted that
light was excluded from the three edges of the test piece, the pointer
R, Fig. 277, was set opposite to the zero mark on the drum and fastened.
[Illustration: Fig. 277.]
To set the instrument for any required pitch of thread of the United
States standard form the micrometer is used to move the sliding jaw E
away from the fixed jaw F to an amount equal to the width of flat upon
the top and bottom, of the required thread, while for the sharp
[V]-thread the jaws are simply closed. The gauge being set the tool is
ground to the gauge.
[Illustration: Fig. 278.]
Referring to the third requirement, that the tools shall in the case of
lathe work be easily sharpened and set to correct position in the lathe,
it will be treated in connection with cutting screws in the lathe.
Referring to the fourth requirement, that a minimum of measuring and
gauging shall be required to test the diameter and form of thread, it is
to be observed that in a Whitworth thread the angle and depth of the
thread is determined by the chaser, which may be constantly ground to
resharpen without altering the angles or depth of the thread, hence in
cutting the tooth the full diameter of the thread is all that needs to
be gauged or measured. In cutting a sharp [V]-thread, however, the
thread top is apt to project (from the action of the single-pointed
tool) slightly above the natural diameter of the work, producing a
feather edge which it becomes necessary to file off to gauge the full
diameter of the thread. In originating a sharp [V]-thread it is
necessary first to grind the tool to correct angle; second, to set it at
the correct height in the latter, and with the tool angles at the proper
angle with the work (as is explained with reference to thread cutting in
the lathe) and to gauge the thread to the proper diameter. In the
absence of a standard cylindrical gauge or piece to measure from, a
sheet metal gauge, such as in Fig. 279, may be applied to the thread;
such gauges are, however, difficult to correctly produce.
So far as the diameter of a thread is concerned it may be measured by
calipers applied between the threads as in Figs. 280 and 281, a plan
that is commonly practised in the workshop when there is at hand a
standard thread or gauge known to be of proper diameter; and this method
of measuring may be used upon any form of thread, but if it is required
to test the form of the thread, as may occur when its form depends upon
the workman's accuracy in producing the single-pointed threading tools,
then, in the case of the United States standard thread, the top, the
bottom, and the angle must be tested. The top of the thread may (for all
threads) be readily measured, but the bottom is quite difficult to
measure unless there is some standard to refer it to, to obtain its
proper diameter, because the gauge or calipers applied to the bottom of
the thread do not stand at a right angle to the axis of the bolt on
which the thread is cut, but at an angle equal to the pitch of the
thread, as shown in Fig. 282.
Now, the same pitch of thread is necessarily used in mechanical
manipulation upon work of widely varying diameters, and as the angle of
the calipers upon the same pitch of thread would vary (decreasing as the
diameter of the thread increases), the diameter measured at the bottom
of the thread would bear a constantly varying proportion to the diameter
measured across the tops of the thread at a right angle to the axial
line of the work. Thus in Fig. 282, A A is the axial line of two
threaded pieces, B, C. D, D represents a gauge applied to B, its width
covering the tops of two threads and measuring the diameter at a right
angle to A A, as denoted by the dotted line E. The dotted line F
represents the measurement at the bottom of the thread standing at an
angle to E equal to half the pitch. The dotted line G is the measurement
of C at the bottom of the thread.
Now suppose the diameter of B to be 1-1/2 inches at the top of the
thread, and 1-1/8 inches at the bottom, while C is 1-1/8 inches on the
top and 3/4 at the bottom of the thread, the pitches of the two threads
being 1/4 inch; then the angle of F to E will be 1/8 inch (half the
pitch) in its length of 1-1/8 inches. The angle of G to E will be 1/8
inch (half the pitch) in 3/4 (the diameter at the bottom or root of the
thread).
It is obvious, then, that it is impracticable to gauge threads from
their diameters at the bottom, or root.
On account of the minute exactitude necessary to produce with lathe
tools threads of the sharp [V] and United States standard forms, the
Pratt and Whitney Company manufacture thread-cutting tools which are
made under a special system insuring accuracy, and provide standard
gauges whereby the finished threads may be tested, and since these tools
are more directly connected with the subject of lathe tools than with
that of screw thread, they are illustrated in connection with such
tools. It is upon the sides of threads that the contact should exist to
make a fit, and the best method of testing the fit of a male and female
thread is to try them together, winding them back and forth until the
bright marks of contact show. Giving the male thread a faint tint of
paint made of Venetian red mixed with lubricating oil, will cause the
bearing of the threads to show very plainly.
Figs. 283 and 284 represent standard reference gauges for the United
States standard thread. Fig. 283 is the plug or male gauge. The top of
the thread has, it will be observed, the standard flat, while the bottom
of the thread is sharp. In the collar, or female gauge, or the template,
as it may be termed, a side and a top view of which are shown in Fig.
284, and a sectional end view in Fig. 285, the flat is made on the
smallest diameter of the thread, while the largest diameter is left
sharp; hence, if we put the two together they will appear as in Fig.
286, there being clearance at both the tops and bottoms of the threads.
This enables the diameters of the threads to be in both cases tested by
standard cylindrical gauges, while it facilitates the making of the
screw gauges. The male or plug gauge is made with a plain part, A, whose
diameter is the standard size for the bottoms of the threads measured
at a right angle to the axis of the gauge and taking the flats into
account. The female gauge or template is constructed as follows:--A
rectangular piece of steel is pierced with a plain hole at B, and a
standard thread hole at A, and is split through at C. At D is a pin to
prevent the two jaws from springing, this being an important element of
the construction. E is a screw threaded through one jaw and abutting
against the face of the other, while at F is another screw passing
through one jaw and threaded into the other, and it is evident that
while by operating these two screws the size of the gauge bore A may be
adjusted, yet the screws will not move and destroy the adjustment,
because the pressure of one acts as a lock to the other. It is obvious
that in adjusting the female gauge to size, the thread of the male gauge
may be used as a standard to set it by.
To produce sheet metal templates such as was shown in Fig. 279, the
following method may be employed, it being assumed that we have a
threading tool correctly formed.
[Illustration: Fig. 288.]
[Illustration: Fig. 289.]
Suppose it is required to make a gauge for a pitch of 6 per inch, then a
piece of iron of any diameter may be put in the lathe and turned up to
the required diameter for the top of the thread. The end of this piece
should be turned up to the proper diameter for the bottom of the thread,
as at G, in Fig. 287. Now, it will be seen that the angle of the thread
to the axis A of the iron is that of line C to line A, and if we require
to find the angle the thread passes through in once winding around the
bolt, we proceed as in Fig. 288, in which D represents the circumference
of the thread measured at a right angle to the bolt axis, as denoted by
the line B in Fig. 287. F, Fig. 288 (at a right angle to D), is the
pitch of the thread, and line C therefore represents the angle of the
thread to the bolt axis, and corresponds to line C in Fig. 287. We now
take a piece of iron whose length when turned true will equal its
finished and threaded circumference, and after truing it up and leaving
it a little above its required finished diameter, we put a pointed tool
in the slide-rest and mark a line A A in Fig. 289, which will represent
its axis. At one end of this line we mark off below A A the pitch of the
thread, and then draw the line H J, its end H falling below A to an
amount equal to the pitch of the thread to be cut. The piece is then put
in a milling machine and a groove is cut along H J, this groove being to
receive a tightly-fitting piece of sheet metal of which a thread gauge
is to be made. This piece of sheet metal must be firmly secured in the
groove by set-screws. The piece of iron is then again put in the lathe
and its diameter finished to that of the required diameter of thread.
Its two ends are then turned down to the required diameter for the
bottom of the thread, leaving in the middle a section on which a full
thread can be cut, as in Fig. 290, in which F F represents the sheet
metal for the gauge. After the thread is cut, as in Fig. 290, we take
out the gauge and it will appear as in Fig. 291, and all that is
necessary is to file off the two outside teeth if only one tooth is
wanted.
[Illustration: Fig. 290.]
The philosophy of this process is that we have set the gauge at an angle
of 90°, or a right angle to the thread, as is shown in Fig. 289, the
line C representing the angle of the thread to the axis A A, and
therefore corresponding to the line C in Fig. 287. A gauge made in this
way will serve as a test of its own correctness for the following
reasons: Taking the middle tooth in Fig. 291, it is clear that one of
its sides was cut by one angle and the other by the other angle of the
tool that cut it, and as a correctly formed thread is of exactly the
same shape as the space between two threads, it follows that if the
gauge be applied to any part of the thread that was cut in forming it,
and if it fits properly when tried, and then turned end for end and
tried again, it is proof that the gauge and the thread are both correct.
Suppose, for example, that the tool was correct in its shape, but was
not set with its two angles equal to the line of lathe centres, and in
that case the two sides of the thread will not be alike and the gauge
will not reverse end for end and in both cases fit to the thread. Or
suppose the flat on the tool point was too narrow, and the flat at the
bottom of the thread will not be like that at the top, and the gauge
will show it.
[Illustration: Fig. 291.]
Referring to the fifth requirement, that the angles of the sides of the
threads shall be as acute as is consistent with the required strength,
it is obvious that the more acute the angles of the sides of the thread
one to the other the finer the pitch and the weaker the thread, but on
the other hand, the more acute the angle the better the sides of the
thread will conform one to the other. The importance of this arises from
the fact that on account of the alteration of pitch, already explained,
as accompanying the hardening of screw-cutting tools, the sides of
threads cut even by unworn tools rarely have full contact, and a nut
that is a tight fit on its first passage down its bolt may generally be
caused to become quite easy by running it up and down the bolt a few
times. Nuts that require a severe wrench force to wind them on the bolt,
may, even though they be as large as a two-inch bolt, often be made to
pass easily by hand, if while upon the bolt they are hammered on their
sides with a hand hammer. The action is in both cases to cause the sides
of the thread to conform one to the other, which they will the more
readily do in proportion as their sides are more acute. Furthermore, the
more acute the angles the less the importance of gauging the threads to
precise diameter, especially if the tops and bottoms of the male and
female thread are clear of one another, as in Fig. 273.
Referring to the sixth requirement, that the nut shall not be unduly
liable to become loose of itself in cases where it may require to be
fastened and loosened occasionally, it may be observed, that in such
cases the threads are apt from the wear to become a loose fit, and the
nuts, if under jar or vibration, are apt to turn back of themselves upon
the bolt. This is best obviated by insuring a full bearing upon the
whole area of the sides of the thread, and by the employment of as fine
pitches as is consistent with sufficient strength, since the finer the
pitch the nearer the thread stands at right angle to the bolt axis, and
the less the tendency to unscrew from the pressure on the nut face.
The pitches, diameters, and widths of flat of the United States
standard thread are as per the following table:--
UNITED STATES STANDARD SCREW THREADS.
+-------------+-----------+-----------------+----------+
| Diameter of | Threads | Diameter at | Width of |
| Screw. | per inch. | root of Thread. | Flat. |
+-------------+-----------+-----------------+----------+
| 1/4 | 20 | .1850 | .0063 |
| 5/16 | 18 | .2403 | .0069 |
| 3/8 | 16 | .2938 | .0078 |
| 7/16 | 14 | .3447 | .0089 |
| 1/2 | 13 | .4001 | .0096 |
| 9/16 | 12 | .4542 | .0104 |
| 5/8 | 11 | .5069 | .0114 |
| 3/4 | 10 | .6201 | .0125 |
| 7/8 | 9 | .7307 | .0139 |
| | | | |
| 1 | 8 | .8376 | .0156 |
| 1-1/8 | 7 | .9394 | .0179 |
| 1-1/4 | 7 | 1.0644 | .0179 |
| 1-3/8 | 6 | 1.1585 | .0208 |
| 1-1/2 | 6 | 1.2835 | .0208 |
| 1-5/8 | 5-1/2 | 1.3888 | .0227 |
| 1-3/4 | 5 | 1.4902 | .0250 |
| 1-7/8 | 5 | 1.6152 | .0250 |
| 2 | 4-1/2 | 1.7113 | .0278 |
+-------------+-----------+-----------------+----------+
The standard pitches for the sharp [V]-thread are as follows:--
SIZE OF BOLT.
---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
1/4| 5/|3/8| 7/|1/2|5/8|3/4|7/8| 1 | 1-| 1-| 1-| 1-| 1-| 1-| 1-| 2
| 16| | 16| | | | | |1/8|1/4|3/8|1/2|5/8|3/4|7/8|
---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
NUMBER OF THREADS TO INCH.
---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
20| 18| 16| 14| 12| 11| 10| 9 | 8 | 7 | 7 | 6 | 6 | 5 | 5 | 4-| 4-
| | | | | | | | | | | | | | |1/2|1/2
---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---
The following table gives the threads per inch, pitches and diameters at
root of thread of the Whitworth thread. The table being arranged from
the diameter of the screw as a basis.
+----------+---------+--------+----------------+
| Diameter | Threads | | Diameter at |
| of | per | Pitch. | Root or Bottom |
| Screw. | Inch. | | of Thread. |
+----------+---------+--------+----------------+
| | | Inch. | Inch. |
| 1/8 | 40 | .025 | .0929 |
| 3/16 | 24 | .041 | .1341 |
| 1/4 | 20 | .050 | .1859 |
| 5/16 | 18 | .056 | .2413 |
| 3/8 | 16 | .063 | .2949 |
| 7/16 | 14 | .071 | .346 |
| 1/2 | 12 | .083 | .3932 |
| 9/16 | 12 | .083 | .4557 |
| 5/8 | 11 | .091 | .5085 |
| 11/16 | 11 | .095 | .571 |
| 3/4 | 10 | .100 | .6219 |
| 13/16 | 10 | .100 | .6844 |
| 7/8 | 9 | .111 | .7327 |
| 15/16 | 9 | .111 | .7952 |
| 1 | 8 | .125 | .8399 |
| 1-1/8 | 7 | .143 | .942 |
| 1-1/4 | 7 | .143 | 1.067 |
| 1-3/8 | 6 | .167 | 1.1615 |
| 1-1/2 | 6 | .167 | 1.2865 |
| 1-5/8 | 5 | .200 | 1.3688 |
| 1-3/4 | 5 | .200 | 1.4938 |
| 1-7/8 | 4-1/2 | .222 | 1.5904 |
| 2 | 4-1/2 | .222 | 1.7154 |
| 2-1/8 | 4-1/2 | .222 | 1.8404 |
| 2-1/4 | 4 | .250 | 1.9298 |
| 2-3/8 | 4 | .250 | 2.0548 |
| 2-1/2 | 4 | .250 | 2.1798 |
| 2-5/8 | 4 | .250 | 2.3048 |
| 2-3/4 | 3-1/2 | .286 | 2.384 |
| 2-7/8 | 3-1/2 | .286 | 2.509 |
| 3 | 3-1/2 | .286 | 2.634 |
| 3-1/4 | 3-1/4 | .308 | 2.884 |
| 3-1/2 | 3-1/4 | .308 | 3.106 |
| 3-3/4 | 3 | .333 | 3.356 |
| 4 | 3 | .333 | 3.574 |
| 4-1/4 | 2-7/8 | .348 | 3.824 |
| 4-1/2 | 2-7/8 | .348 | 4.055 |
| 4-3/4 | 2-3/4 | .364 | 4.305 |
| 5 | 2-3/4 | .364 | 4.534 |
| 5-1/4 | 2-5/8 | .381 | 4.764 |
| 5-1/2 | 2-5/8 | .381 | 5.014 |
| 5-3/4 | 2-1/2 | .400 | 5.238 |
| 6 | 2-1/2 | .400 | 5.488 |
+----------+---------+--------+----------------+
The standard degree of taper, both for the taps and the dies, is 1/16
inch per inch, or 3/4 inch per foot, for all sizes up to 10-inch bore.
The sockets or couplings, however, are ordinarily tapped parallel and
stretched to fit the pipe taper when forced on the pipe. For bores of
pipe over 10 inches diameter the taper is reduced to 3/8 inch per foot.
The pipes or casings for oil wells are given a taper of 3/8 inch per
foot, and their couplings are tapped taper from both ends. There is,
however, just enough difference made between the taper of the socket and
that of the pipe to give the pipe threads a bearing at the pipe end
first when tried with red marking, the threads increasing their bearing
as the pieces are screwed together.
The United States standard thread for steam, gas and water pipe is given
below, which is taken from the Report of the Committee on Standard Pipe
and Pipe Threads of The American Society of Mechanical Engineers,
submitted at the 8th Annual Meeting held in New York, November-December,
1886.
"A longitudinal section of the tapering tube end, with the screw-thread
as actually formed, is shown full size in Fig. 291_a_ for a nominal
2-1/2 inch tube, that is, a tube of about 2-1/2 inches internal
diameter, and 2-7/8 inches actual external diameter.
[Illustration: Fig. 291_a_.]
"The thread employed has an angle of 60°; it is slightly rounded off
both at the top and at the bottom, so that the height or depth of the
thread, instead of being exactly equal to the pitch, is only four fifths
of the pitch, or equal to 0.8 × 1/_n_ if _n_ be the number of threads
per inch. For the length of tube end throughout which the screw thread
continues perfect, the empirical formula used is (0.8_D_ + 4.8) × 1/_n_,
where _D_ is the actual external diameter of the tube throughout its
parallel length, and is expressed in inches. Further back, beyond the
perfect threads, come two having the same taper at the bottom, but
imperfect at the top. The remaining imperfect portion of the screw
thread, furthest back from the extremity of the tube, is not essential
in any way to this system of joint; and its imperfection is simply
incidental to the process of cutting the thread at a single operation.
The standard thicknesses of the pipes and pitches of thread are as
follows:--
STANDARD DIMENSIONS OF WROUGHT IRON WELDED TUBES.
+-----------------------------+-----------+--------------------+
| DIAMETER OF TUBE. | | SCREWED ENDS. |
+---------+---------+---------+ THICKNESS +----------+---------+
| Nominal | Actual | Actual | OF | Number |Length of|
| Inside. | Inside. | Outside.| METAL. |of Threads| Perfect |
| | | | |per Inch. | Screw. |
+---------+---------+---------+-----------+----------+---------+
| Inches. | Inches. | Inches. | Inch. | No. | Inch. |
| 1/8 | 0.270 | 0.405 | 0.068 | 27 | 0.19 |
| 1/4 | 0.364 | 0.540 | 0.088 | 18 | 0.29 |
| 3/8 | 0.494 | 0.675 | 0.091 | 18 | 0.30 |
| 1/2 | 0.623 | 0.840 | 0.109 | 14 | 0.39 |
| 3/4 | 0.824 | 1.050 | 0.113 | 14 | 0.40 |
| 1 | 1.048 | 1.315 | 0.134 | 11-1/2 | 0.51 |
| 1-1/4 | 1.380 | 1.660 | 0.140 | 11-1/2 | 0.54 |
| 1-1/2 | 1.610 | 1.900 | 0.145 | 11-1/2 | 0.55 |
| 2 | 2.067 | 2.375 | 0.154 | 11-1/2 | 0.58 |
| 2-1/2 | 2.468 | 2.875 | 0.204 | 8 | 0.89 |
| 3 | 3.067 | 3.500 | 0.217 | 8 | 0.95 |
| 3-1/2 | 3.548 | 4.000 | 0.226 | 8 | 1.00 |
| 4 | 4.026 | 4.500 | 0.237 | 8 | 1.05 |
| 4-1/2 | 4.508 | 5.000 | 0.246 | 8 | 1.10 |
| 5 | 5.045 | 5.563 | 0.259 | 8 | 1.16 |
| 6 | 6.065 | 6.625 | 0.280 | 8 | 1.26 |
| 7 | 7.023 | 7.625 | 0.301 | 8 | 1.36 |
| 8 | 8.982 | 8.625 | 0.322 | 8 | 1.46 |
| 9 | 9.000 | 9.688 | 0.344 | 8 | 1.57 |
| 10 | 10.019 | 10.750 | 0.366 | 8 | 1.68 |
+---------+---------+---------+-----------+----------+---------+
The taper of the threads is 1/16 inch in diameter for each inch of
length or 3/4 inch per foot.
WHITWORTH'S SCREW THREADS FOR GAS, WATER, AND HYDRAULIC IRON PIPING.
NOTE.--The Internal and External diameters of Pipes, as given below, are
those adopted by the firm of Messrs. JAMES RUSSELL & SONS, in Pipes of
their manufacture.
+---------------------------------------+
| GAS AND WATER PIPING. |
+-------------+-------------+-----------+
| Internal | External | No. of |
| Diameter of | Diameter of | Threads |
| Pipe. | Pipe. | per Inch. |
+-------------+-------------+-----------+
| 1/8 | .385 | 28 |
| 1/4 | .520 | 19 |
| 3/8 | .665 | 19 |
| 1/2 | .822 | 14 |
| 3/4 | 1.034 | 14 |
| 1 | 1.302 } | |
| 1-1/8 | 1.492 } | |
| 1-1/4 | 1.650 } | |
| 1-3/8 | 1.745 } | |
| 1-1/2 | 1.882 } | |
| 1-5/8 | 2.021 } | |
| 1-3/4 | 2.047 } | |
| 1-7/8 | 2.245 } | |
| 2 | 2.347 } | |
| 2-1/8 | 2.467 } | |
| 2-1/4 | 2.587 } | 11 |
| 2-3/8 | 2.794 } | |
| 2-1/2 | 3.001 } | |
| 2-5/8 | 3.124 } | |
| 2-3/4 | 3.247 } | |
| 2-7/8 | 3.367 } | |
| 3 | 3.485 } | |
| 3-1/4 | 3.698 } | |
| 3-1/2 | 3.912 } | |
| 3-3/4 | 4.125 } | |
| 4 | 4.339 } | |
+-------------+-------------+-----------+
+----------------------------------------------------+
| HYDRAULIC PIPING. |
+----------+----------+------------------+-----------+
| Internal | External | Pressure in lbs. | No. of |
| Diameter | Diameter | per Square | Threads |
| of Pipe. | of Pipe. | Inch. | per Inch. |
+----------+----------+------------------+-----------+
| | { 5/8 | 4,000} | |
| 1/4 | { 3/4 | 6,000} | 14 |
| | { 7/8 | 8,000} | |
| | {1 | 10,000} | |
| | | | |
| | { 3/4 | 4,000} | |
| 3/8 | { 7/8 | 6,000} | 14 |
| | {1 | 8,000} | |
| | {1-1/8 | 10,000} | |
| | | | |
| | {1 | 4,000} | 14 |
| 1/2 | {1-1/8 | 6,000} | |
| | {1-1/4 | 8,000 } | 11 |
| | {1-3/8 | 10,000 } | |
| | | | |
| | {1-1/8 | 4,000 | 14 |
| 5/8 | {1-1/4 | 6,000} | |
| | {1-3/8 | 8,000} | 11 |
| | {1-1/2 | 10,000} | |
| | | | |
| | {1-1/4 | 4,000} | |
| 3/4 | {1-3/8 | 6,000} | 11 |
| | {1-1/2 | 8,000} | |
| | {1-5/8 | 10,000} | |
| | | | |
| | {1-3/8 | 4,000} | |
| 7/8 | {1-1/2 | 6,000} | 11 |
| | {1-5/8 | 8,000} | |
| | {1-3/4 | 10,000} | |
| | | | |
| | {1-1/2 | 4,000} | |
| 1 | {1-5/8 | 6,000} | 11 |
| | {1-3/4 | 8,000} | |
| | {1-7/8 | 10,000} | |
| | | | |
| | {1-5/8 | 4,000} | |
| 1-1/8 | {1-3/4 | 6,000} | 11 |
| | {1-7/8 | 8,000} | |
| | {2 | 10,000} | |
| | | | |
| | {1-3/4 | 4,000} | |
| 1-1/4 | {1-7/8 | 6,000} | 11 |
| | {2 | 8,000} | |
| | {2-1/8 | 10,000} | |
| | | | |
| | {1-7/8 | 4,000} | |
| 1-3/8 | {2 | 6,000} | 11 |
| | {2-1/8 | 8,000} | |
| | {2-1/4 | 10,000} | |
| | | | |
| | {2 | 4,000} | |
| | {2-1/8 | 6,000} | |
| 1-1/2 | {2-1/4 | 8,000} | 11 |
| | {2-3/8 | 10,000} | |
| | {2-1/2 | 10,000} | |
| | | | |
| | {2-1/8 | 4,000} | |
| 1-5/8 | {2-1/4 | 6,000} | 11 |
| | {2-3/8 | 8,000} | |
| | {2-1/2 | 10,000} | |
| | | | |
| | {2-1/4 | 3,000} | |
| | {2-3/8 | 4,000} | |
| 1-3/4 | {2-1/2 | 6,000} | 11 |
| | {2-5/8 | 8,000} | |
| | {2-3/4 | 10,000} | |
| | | | |
| | {2-3/8 | 3,000} | |
| | {2-1/2 | 4,000} | |
| 1-7/8 | {2-5/8 | 6,000} | 11 |
| | {2-3/4 | 8,000} | |
| | {2-7/8 | 10,000} | |
| | | | |
| | {2-1/2 | 3,000} | |
| | {2-5/8 | 4,000} | |
| 2 | {2-3/4 | 6,000} | 11 |
| | {2-7/8 | 8,000} | |
| | {3 | 10,000} | |
+----------+----------+------------------+-----------+
The English pipe thread is a sharp [V]-thread having its sides at an
angle of 60°, and therefore corresponds to the American pipe thread
except that the pitches are different.
The standard screw thread of The Royal Microscopical Society of London,
England, is employed for microscope objectives, and the nose pieces of
the microscope into which these objectives screw.
The thread is a Whitworth one, the original standard threading tools now
in the cabinet of the society having been made especially for the
society by Sir Joseph Whitworth. The pitch of the thread is 36 per inch.
The cylinder, or male gauge, is .7626 inch in diameter.
The following table gives the Whitworth standard of thread pitches and
diameters for watch and mathematical instrument makers.
WHITWORTH'S STANDARD GAUGES FOR WATCH AND INSTRUMENT MAKERS, WITH SCREW
THREADS FOR THE VARIOUS SIZES, 1881.
+---------------------+-------------+-------------+
| No. of each | Size in | Number of |
| size in thousandths | decimals of | Threads per |
| of an inch. | an inch. | inch. |
+---------------------+-------------+-------------+
| 10 | .010 | 400 |
| 11 | .011 | " |
| 12 | .012 | 350 |
| 13 | .013 | " |
| 14 | .014 | 300 |
| 15 | .015 | " |
| 16 | .016 | " |
| 17 | .017 | 250 |
| 18 | .018 | " |
| 19 | .019 | " |
| 20 | .020 | 210 |
| 22 | .022 | " |
| 24 | .024 | " |
| 26 | .026 | 180 |
| 28 | .028 | " |
| 30 | .030 | " |
| 32 | .032 | 150 |
| 34 | .034 | " |
| 36 | .036 | " |
| 38 | .038 | 120 |
| 40 | .040 | " |
| 45 | .045 | " |
| 50 | .050 | 100 |
| 55 | .055 | " |
| 60 | .060 | " |
| 65 | .065 | 80 |
| 70 | .070 | " |
| 75 | .075 | " |
| 80 | .080 | 60 |
| 85 | .085 | " |
| 90 | .090 | " |
| 95 | .095 | " |
| 100 | .100 | 50 |
+---------------------+-------------+-------------+
For the pitches of the threads of lag screws there is no standard, but
the following pitches are largely used.
+-----------+-----------+
|Diameter of| Threads |
| Screw. | per Inch. |
+-----------+-----------+
| Inch. | |
| 1/4 | 10 |
| 5/16 | 9 |
| 3/8 | 8 |
| 7/16 | 7 |
| 1/2 | 6 |
| 9/16 | 6 |
| 5/8 | 5 |
| 11/16 | 5 |
| 3/4 | 5 |
| 7/8 | 4 |
| 1 | 4 |
+-----------+-----------+
SCREW-CUTTING HAND TOOLS.
For cutting external or male threads by hand three classes of tools are
employed.
The first is the screw plate shown in Fig. 292. It consists of a
hardened steel plate containing holes of varying diameters and threaded
with screw threads of different pitches. These holes are provided with
two diametrically opposite notches or slots so as to form cutting edges.
[Illustration: Fig. 292.]
This tool is placed upon the end of the work and slowly rotated while
under a hand pressure tending to force it upon the work, the teeth
cutting grooves to form the thread and advancing along the bolt at a
rate determined by the pitch of the thread.
The screw plate is suitable for the softer metals and upon diameters of
1/8 inch and less, in which the cutting duty is light; hence the holes
do not so rapidly wear larger.
The second class consists of a stock and dies such as shown in Fig. 293.
For each stock there are provided a set of dies having different
diameters and pitches of thread.
In this class of tool the dies are opened out and placed upon the bolt.
The set screw is tightened up, forcing the dies to their cut, and the
stock is slowly rotated and a traverse taken down the work.
[Illustration: Fig. 293.]
In some cases the dies are then again forced to the work by the set
screw, and a cut taken by winding the stocks up the bolt, the operation
being continued until the thread is fully developed and cut to the
required diameter. In other cases the cut is carried down the bolt, only
the dies being wound back to the top of the bolt after each cut is
carried down. The difference between these two operations will be shown
presently.
[Illustration: Fig. 294.]
The thread in dies which take successive cuts to form a thread may be
left full clear through the die, and will thus cut a full thread close
up to the head collar or shoulder of the work. It is usual, however, to
chamfer off the half threads at the ends of the dies, because if left of
their full _height_ they are apt to break off when in use. It is
sometimes the practice, however, to chamfer off the first two threads on
one side of the dies, leaving the teeth on the other side full, and to
use the chamfered as the leading side in all cases in which the thread
on the work does not require to be cut up to a shoulder, but turning the
dies over with the full threaded teeth as the leading ones when the
thread _does_ require to be carried up to a head or shoulder on the
work.
To facilitate the insertion and extraction of the dies in and from their
places in the stock, the Morse Twist Drill Co. employ the following
construction. In Figs. 294 and 295 the pieces A, A´ which hold the dies
are pivoted in the stock at B, so as to swing outward as in Fig. 295,
and receive the dies which are slotted to fit them. These pieces are
then swung into position in the stock. The lower die is provided with a
hole to fit the pin C, hence when that die is placed home C acts as a
detaining piece locking the pieces A, A´ through the medium of the
bottom die.
[Illustration: Fig. 295.]
[Illustration: Fig. 296.]
In other dies of this class the two side pieces or levers which hold the
dies are pivoted at the corner of the angle, as in Fig. 296. In the
bottom of the stock is a sliding piece beveled at its top and meeting
the bottom face of the levers; hence, by pressing this piece inwards the
side pieces recede into a slot provided in the stock, and leave the
opening free for the dies to pass into their places, when the pin is
released and a spring brings the side pieces back. Now, since the bottom
die rests upon the bottom angle of the side pieces the pressure of the
set screw closes the side pieces to the dies holding them firmly.
[Illustration: Fig. 297.]
In Fig. 297 is shown Whitworth's stocks and dies, the cap that holds the
guide die _a_ and the two chasers _b_, _c_ in their seats or recesses in
the stock being removed to expose the interior parts. The ends of the
chasers _b_, _c_ are beveled and abut against correspondingly beveled
recesses in the key _d_, so that by operating the nut _e_ on the end of
the key the dies are caused to move longitudinally. The principles of
action are more clearly shown in Fig. 298. The two cutting chasers B and
C move in lines that would meet at D, and therefore at a point behind
the centre or axis of the bolt being threaded; this has the effect of
preserving their clearance. It is obvious, for example, that when these
chasers cut a thread on the work it will move over toward guide A on
account of the thread on the work sinking into the threads on A, and
this motion would prevent the chasers B, C from cutting if they moved in
a line pointing to the centre of the work. This is more clearly shown in
Fig. 299, in which the guide die A and one of the cutting dies or
chasers B is shown removed from the stock, while the bolt to be threaded
is shown in two positions--one when the first cut is taken, and the
other when the thread is finished. For the first cut the centre of the
work is at E, for the last one it is at G, and this movement would, were
the line of motion as denoted by the dotted lines, prevent the chaser
from cutting, because, while the line of chaser motion would remain at
J, pointing to the centre of work for the first cut, it would require a
line at K to point to that centre for the last one; hence, when
considered with relation to the work, the line of chaser motion has been
moved forward, presenting the cutting edges at an angle that would
prevent their cutting. By having their motion as shown in Fig. 299,
however, the clearance of the chasers is preserved.
[Illustration: Fig. 298.]
[Illustration: Fig. 299.]
[Illustration: Fig. 300.]
Referring now to the die A, it acts as a guide rather than as a cutting
chaser, because it has virtually no clearance and cannot cut so freely
as B and C; hence it offers a resistance to the moving of the bolt, or
of the dies upon the bolt, in a lateral direction when the chaser teeth
meet either a projection or a depression upon the work. The guide
principle is, however, much more fully carried out in a design by
Bodmer, which is shown in Fig. 300. Here there is but one cutting chaser
C, the bush G being a guide let into a recess in the stock and secured
thereon by a pin _p_. The chaser is set in a stock, D also let into a
recess in the stock, and this recess, being circular, permits of stock D
swinging. At S are two set-screws, which are employed to limit the
amount of motion permitted to D. the handle E screws through D, and acts
upon the edge of chaser C to put on the cut. The action of the tool is
shown in Fig. 301, where it is shown upon a piece of work. Pulling the
handle E causes D to swing in the stock, thus giving the chaser
clearance, as shown. When the cut is carried down, a new cut may be put
on by means of E, and on winding the stock in the opposite direction, D
will swing in its seat, and cant or tilt the chaser in the opposite
direction, giving it the necessary clearance to enable it to cut on the
upward or back traverse. Another point of advantage is that the cutting
edges are not rubbed by the work during the back stroke, and their
sharpness is, therefore, greatly preserved. A die of this kind will
produce work almost as true as the lathe, and, in the case of long,
slender work, more true than the lathe; but it is obvious that, on
account of the friction caused by the pressure of the work to the guide
G, the tool will require more power to operate than the ordinary stock
and die or the solid die.
[Illustration: Fig. 301.]
In adjustable dies which require to take more than one cut along the
bolt to produce a fully developed thread, there is always a certain
amount of friction between the sides of the thread in the die and the
grooves being cut, because the angle of the thread at the top of a
thread is less than the angle at the bottom. Thus in Fig. 302 the pitch
at the top of thread (at A, B) is the same as at the bottom (C, D). Now
suppose that in Fig. 303 _a_ _b_ represents the axial line of a bolt,
and _c_ _d_ a line at a right angle to _a_ _b_. The radius _e_ _f_ being
equal to the circumference of the top of the thread, the pitch being
represented by _b_; then _k_ represents the angle of the top of the
thread to the axial line _a_ _b_. Now suppose that the radius _e_ _g_
represents the circumference at the bottom of the thread and to the
pitch; then _l_ is the angle of the bottom of the thread to the axial
line of the work, and the difference in angle between _k_ and _l_ is the
difference in angle between the top and bottom of the thread in the dies
and the thread to be cut on the work.
[Illustration: Fig. 302.]
Now the tops of the teeth on the die stand at the greatest angle _l_, in
Fig. 303, when taking the first cut on the bolt, but the grooves they
cut will be on the full diameter of the bolt, and will, therefore, stand
at the angle _k_, hence the lengths of the teeth do not lie in the same
planes as the grooves which they cut.
[Illustration: Fig. 303.]
In cutting [V]-threads, however, the angle of the die threads gradually
right themselves with the plane of the grooves attaining their nearest
coincidence when closed to finish the thread.
Since, however, the full width of groove is in a square thread cut at
the first cut taken by the dies, it is obvious that a square thread
cannot be cut by this class of die, because the sides of the grooves
would be cut away each time the dies were closed to take another cut.
[Illustration: Fig. 304.]
[Illustration: Fig. 305.]
Dies of this class require to have the threaded hole made of a larger
diameter than is the diameter of the bolt they are intended to thread,
the reason being as follows:--
Suppose the threaded hole in the dies to be cut by a hob or master tap
of the same diameter as the thread to be cut by the dies; when the dies
are opened out and placed upon the work as in Fig. 304, the edges A, B
will meet the work, and there will be nothing to steady the dies, which
will, therefore, wobble and start a drunken thread, that is to say, a
thread such as was shown in Fig. 253.
[Illustration: Fig. 306.]
Instances have been known in the use of dies made in this manner,
wherein the workman using a right-hand single-threaded pair of dies has
cut a right or left-hand double or treble thread; the teeth of the dies
acting as chasers well canted over, as shown in Fig. 305. It is
necessary to this operation, however, that the diameter of the work be
larger than the size of hob the dies were threaded with.
In Fig. 306 is shown a single right-hand and a treble left-hand thread
cut by the author with the same pair of dies.
All that is necessary to perform this operation is to rotate the dies
from left to right to produce a right-hand thread, and from right to
left for a left-hand thread, exerting a pressure to cause the dies to
advance more rapidly along the bolt than is due to the pitch of the
thread. A double thread is produced when the dies traverse along the
work twice as fast as is due to the pitch of the thread in the dies, and
so on.
[Illustration: Fig. 307.]
It is obvious, also, that a piece of a cylindrical thread may be used to
cut a left-hand external thread. Thus in Fig. 307 is shown a square
piece of metal having a notch cut in on one side of it and a piece of an
external thread (as a tap inserted) in the notch. By forcing a piece of
cylindrical work through the hole while rotating it, the piece of tap
would cut upon the work a thread of the pitch of the tap, but a
left-handed thread, which occurs because, as shown by the dotted lines
of the figure, the thread on one side of a bolt slopes in opposite
directions to its direction on the other, and in the above operation the
thread on one side is taken to cut the thread on the other.
These methods of cutting left-hand threads with right-handed ones are
mentioned simply as curiosities of thread cutting, and not as being of
any practical value.
To proceed, then: to avoid these difficulties it is usual to thread the
dies with a hob or master tap of a diameter equal to twice the depth of
the thread, larger than the size of bolt the dies are to thread. In this
case the dies fit to the bolt at the first cut, as shown in Fig. 308, C,
D being the cutting edges. The relation of the circle of the thread in
the dies to that of the work during the final cut is shown in Fig. 309.
[Illustration: Fig. 308.]
[Illustration: Fig. 309.]
There is yet another objection to tapping the dies with a hob of the
diameter of the bolt to be threaded, in that the teeth fit perfectly to
the thread of the bolt when the latter is threaded to the proper
diameter, producing a great deal of friction, and being difficult to
make cut, especially when the cutting edges have become slightly dulled
from use.
Referring now to taking a cut up the bolt or work as well as down, it
will be noted that supposing the dies to have a right-hand thread, and
to be rotating from left to right, they will be passing down the bolt
and the edges C, D (Fig. 308) will be the cutting ones. But when the
dies are rotated from right to left to bring them to the end of the bolt
again, C, D will be rubbed by the thread, which tends to abrade them and
thus destroy their sharpness.
[Illustration: Fig. 310.]
In some cases two or more pairs of dies are fitted to the same stock, as
shown in Fig. 310, but this is objectionable, because it is always
desirable to have the hole in the dies central to the length of the
stock, so that when placed to the work the stock shall be balanced,
which will render it easier to start the thread true with the axial line
of the bolt.
[Illustration: Fig. 311.]
From what has been said with reference to Fig. 303, it is obvious that a
square thread cannot be cut by a die that opens and closes to take
successive cuts along the work, but such threads may be cut upon work
that is of sufficient strength to withstand the twisting pressure of the
dies, by making a solid die, and tapering off the threads for some
distance at the mouth of the die, so as to enable the die to take its
bite or grip upon the work, and start itself. It is necessary, however,
to give to the die as many flutes (and therefore cutting edges), as
possible, or else to make flutes wide and the teeth as short as will
leave them sufficiently strong, both these means serving to avoid
friction.
[Illustration: Fig. 312.]
The teeth for adjustable dies, such as shown in Fig. 293, are cut as
follows:--There is inserted between the two dies a piece of metal,
separating them when set together to a distance equal to twice the depth
of the thread, added to the distance the faces of the dies are to be
apart when the dies are set to cut to this designated or proper
diameter. The tapping hole is then drilled (with the pieces in place) to
the diameter of the bolt the die is for. The form of hob used by the
Morse Twist Drill & Machine Company, to cut the thread, is shown in Fig.
311. The unthreaded part at the entering end is made to a diameter equal
to that of the work the dies are to be used in; the thread at the
entering end is made sunk in one half the height of the full thread, and
is flattened off one half the height of a full thread, so that the top
of the thread is even with the diameter of the unthreaded part at the
entering end. The thread then runs a straight taper up the hob until a
distance equal to the diameter of the nut is reached, and the length of
hob equal to its diameter is made a full and parallel thread for
finishing the die teeth with. The thread on the taper part has more
taper at the root of the thread than it has at the top of the same, and
the diameter of the full and parallel part at the shank end of the
thread is made of a diameter equal to twice the height or depth of a
full thread, larger than the diameter at the entering end of the hob.
The hob thus becomes a taper and relieved tap cutting a full thread at
one passage through the dies. If the hob is made parallel and a full
thread from end to end, as in Fig. 312, the dies must traverse up and
down the hob, or the hob through the dies to form a full thread.
The third class of stock and die is intended to cut a full thread at one
passage along the work, while at the same time provision is made,
whereby, to take up the wear due to the abrasion of the cutting edges,
which wear would cause the diameter of thread cut to be above the
standard.
In Fig. 313 is shown the Grant adjustable die made by the Pratt &
Whitney Company. It consists of four chasers or toothed cutting tools,
inserted in radial recesses or slots in an iron disc or collet encircled
by an iron ring. Each chaser is beveled at its end to fit a
corresponding bevel in the ring, and is grooved on one of its side faces
to receive the hardened point of a screw that is inserted in the collet
to hold the chaser in its adjusted position. Four screws extend up
through the central flange or body of the collet, two of which serve to
draw down the ring, and by reason of the taper on the ring move the
chasers equally towards the centre and reduce the cutting diameter of
the die, while the other two hold the ring in the desired position, or
force it upward to enlarge the cutting diameter of the die. The range of
adjustment permitted by this arrangement is 1-32 inch. The dies may be
taken out and ground up to sharpen.
[Illustration: Fig. 313.]
The object of cutting grooves in the sides of the chasers is that the
fine burrs formed by the ends of the set screws do not prevent the
chasers from moving easily in the collet during the process of
adjustment; the groove also acts as a shoulder for the screw end to
press the chaser down to its seat. These chasers are marked to their
respective places in the collet, and are so made that if one chaser
should break, a new one can be supplied to fit to its place, the teeth
of the new one falling exactly in line with the teeth on the other
three, whereas under ordinary conditions if one chaser breaks, a full
set of four new ones must be obtained.
In this die, as in all others which cut a full thread at one passage
along the work, the front teeth of the chasers are beveled off as shown
in the cut; this is necessary to enable the dies to take hold of or
"bite" the work, the chamfer giving a relief to the cutting edge, while
at the same time forming to a certain extent a wedge facilitating the
entrance of the work into the die.
Fig. 314 represents J. J. Grant's patent die, termed by its makers
(Wiley and Russel) the "lightening die." In this, as in other similar
stocks, several collets with dies of various pitches and diameters of
thread, fit to one stock. The nut of the stock is split on one side, and
is provided with lugs on that side to receive a screw, which operates to
open and enlarge the bore to release a collet, or close thereon and
grip it, as may be required when inserting or extracting the same. The
dies are formed as shown in Fig. 315, in which A, A are the dies, and B
the collet. To open the dies within the collet, the screws E are
loosened and the screws D are tightened, while to close the dies D, D
are loosened and E are tightened; thus the adjustment to size is
effected by these four screws, while the screws D also serve to hold the
dies to the collet B. The collets are provided with a collar having a
bore F, through which the work passes, so that the dies may be guided
true when starting upon the work; but if it is required to cut a thread
close up to a head or shoulder, the stock is turned upside down, not
only to have the collet out of the way of the head or shoulder, but also
because the thread of the dies on the collet side are chamfered off (as
is necessary in all solid dies, or dies which cut a full thread at one
traverse down the work) so as to enable them to grip or bite the work,
and start the thread upon it as before stated.
[Illustration: Fig. 314.]
[Illustration: Fig. 315.]
In Fig. 316 is shown Stetson's die, which cuts a full thread at one
passage, is adjustable to take up its wear, and has a guide to steady it
upon the work and assist it in cutting a true thread. The guide piece
consists of a hub (through which the work passes) having a flange
fitting into the dies and being secured thereto by the two screws shown.
The holes in the flanges are slotted to permit of the dies being closed
(to take up wear) by means of the small screws shown at the end of the
die, which screws pass through one die in a plain hole and screw into
the other.
[Illustration: Fig. 316.]
In Fig. 317 is shown Everett's stocks and dies. In this tool the dies
are set up by a cam lever, the dies being set to standard size when the
lever arm stands parallel with the arm of the stock. By turning the
straight side of the cam lever opposite to the dies, the latter may be
instantly removed and another size of die inserted. The dies may be used
to cut on their passage up and down the bolt or by operating the cam.
When the dies are at the end of a cut the dies may be opened, lifted to
the top of the work and another cut taken, thus saving the time
necessary to wind the stock back. When the final cut is taken the dies
may be opened and lifted off the work.
[Illustration: Fig. 317.]
The hardening process usually increases the thickness of these dies,
making the pitch of the thread coarser. The amount of expansion due to
hardening is variable, but increases with the thickness of the die. The
hob as a rule shortens during the tempering, but the amount being
variable, no rule for its quantity can be given.[12]
[12] See also page 108.
Stocks and dies for pipe work are made in the form shown in Fig. 318, in
which B is the stock having the detachable handles (for ease of
conveyance) A, H, the latter being shown detached. The solid
screw-cutting dies C are placed in the square recess at B, and are
secured in B by the cap D, which swings over (upon its pivoted end as a
centre) and is locked by the thumbscrew E. To guide the stocks and cause
them to cut a true thread, the bushes F are provided. These fit into the
lower end of B and are locked in position by four set screws G. The
bores of the bushes F are made an easy fit to the outside of the pipe to
be threaded, there being a separate bush for each size of pipe.
[Illustration: Fig. 318.]
The dies employed in stocks for threading steam and gas pipes by hand
are sometimes solid, as in Fig. 318 at C, and at others adjustable. In
Fig. 319 is shown Stetson's adjustable pipe die containing four chasers
or toothed thread-cutting tools. These are set to cut the required
diameter by means of a small screw in each corner of the die, while they
are locked in their adjusted position by four screws on the face.
The tap is a tool employed to cut screw threads in internal surfaces, as
holes or bores. A set of taps for hand use usually consist of three: the
taper tap, Fig. 320; plug tap, Fig. 321; and bottoming tap, Fig. 322.
(In England these taps are termed respectively the taper, second, and
plug tap.) The taper tap is the first to be inserted, and (when the
hole to be threaded passes entirely through the work) rotated until it
passes through the work, thus cutting a thread parallel in diameter
through the full length of the hole. If, however, the hole does not pass
through the work, the taper tap leaves a taper-threaded hole containing
more or less of a fully developed thread according to the distance the
tap has entered.
[Illustration: Fig. 319.]
[Illustration: Fig. 320.]
[Illustration: Fig. 321.]
[Illustration: Fig. 322.]
To further complete the thread the plug tap is inserted, it being
parallel from four or five threads from the entering end of the tap to
the other end. If the work will admit it, this tap is also passed
through, which not only saves time in many cases, by avoiding the
necessity to wind the tap back, but preserves the cutting edge which
suffers abrasion from being wound back. To cut a full thread as near as
possible to the bottom of a hole the bottoming tap is used, but when the
circumstances will admit, it is best to drill the hole rather deeper
than is actually necessary, to avoid the trouble incident to tapping a
hole clear to the bottom.
On wrought iron and steel, which are fibrous and tough, the tap, when
used by hand, will not (if the hole be deeper than the diameter of the
tap) readily operate by a continuous rotary motion, but requires to be
rotated about half a revolution back occasionally, which gives
opportunity for the oil to penetrate to the cutting edges of the tap,
frees the tap and considerably facilitates the tapping operation,
especially if the hole be a deep one.
[Illustration: Fig. 323.]
When the tap is intended to pass entirely through the work with a
continuous rotary motion, as is the case, for example, in tapping nuts
in a tapping machine, it is made of similar form to the taper hand tap,
but longer, as shown in Fig. 323, the thread being full and parallel at
the shank end for a distance at least equal to the full diameter of the
tap measured across the tops of the thread.
If the thread of a tap be in diametral section a full circle, the sides
of the thread rub against the grooves cut by the teeth, producing a
friction which augments as the sharp edge of the teeth become dulled
from use, but the tap cuts a thread of great diametral accuracy.
To reduce this friction to a minimum as much as is consistent with
maintaining the standard size of the tapped hole, taps are sometimes
given clearance in the thread, that is to say, the back of each tooth
recedes from a true circle, as shown in Fig. 324, in which A A
represents a washer, and B A tap in the same, the back of the teeth
receding at C, D, E, from the true circle of the bore of A A, the tap
cutting when revolved in the direction of the arrow. The objection to
this is that when the tap is revolved backwards, as it must be to
extract it unless the hole passes clear through the work, the cuttings
lodge between the teeth and the thread in the work, rendering the
extraction of the tap difficult, unless, indeed, the clearance be small
enough in amount to clear the sides of the thread in the work
sufficiently to avoid friction without leaving room for the cuttings to
enter. If an excess of clearance be allowed upon taps that require to be
used by hand, the tap will thread the hole taper, the diameter being
largest at the top of the hole. This occurs because the tap is not so
well steadied by its thread, which fails to act as a guide, and it is
impossible to revolve the tap steadily by hand. Taps that are revolved
by machine tools may be given clearance because both the taps and the
work are detained in line, hence the tap cannot wobble.
[Illustration: Fig. 324.]
[Illustration: Fig. 325.]
In some cases clearance is given by filing or cutting off the tops of
the threads along the middle of the teeth, as shown in Fig. 325 at A, B,
C, which considerably reduces the friction. If clearance were given to a
tap after this manner but extended to the sides and to the bottom of the
thread, it would produce the best of results (for all taps that do not
pass entirely through the hole), reducing the friction and leaving no
room for the cuttings to jam in the threads when the tap is being backed
out. The threads of Sir Joseph Whitworth's taper hand taps are made
parallel, measured at the bottom of the thread, and parallel at the tops
of the thread for a distance equal to the diameter of the tap at the
shank end; thence, to the entering end of the tap, the tops of the
thread are turned off a straight taper, the amount of taper being
slightly more than twice the depth of the thread: hence, the thread is
just turned out at the entering end of the tap, and that end is the
exact proper size for the tapping hole.
This enables the tap to enter the tapping hole for a distance enveloping
one or perhaps two of the tap threads, leaving the extreme end of the
tap with the thread just turned out. In the practice of some tap makers
the diameter of the thread at the top is made the same as in the
Whitworth system, but there is more depth at the root of the thread and
near the entering end of the tap, hence the bottoms of the thread at
that end perform no cutting duty. This is done to enable the tap to take
hold of, and start a thread in, the work more readily, which it does for
the following reasons. In Fig. 326 is a piece of work with a tap A,
having a tapered thread, and a tap B, in which the taper is given by
turning off the thread. In the case of A the teeth points cut a groove
that is gradually widened and deepened as the tap enters, until a full
thread is finally produced. In the case of B the teeth cut at first a
wide groove, leaving a small projection, that is a part of the actual
finished thread, and the groove gets narrower as the tap enters; so that
in the one case no part of the thread is finished until the tap has
entered to its full diameter, while in the other the thread is finished
as it is produced. On entering, therefore, more cutting duty is
performed by B than by A, because a greater length of cutting edge is in
operation and more metal is being removed, and as a result B requires
more power to start it, so that in practice it is necessary to exert a
pressure upon it, tending to force it into the hole while rotating it.
The cutting duty on B decreases as the tap enters, because it gets less
width and area of groove to cut, while the cutting duty on A increases
as the tap enters, because it gets a greater width and area of groove to
cut. In the latter case the maximum of pressure falls on the tap when it
has entered the hole deepest, and hence can be operated steadiest,
which, independent of its entering easiest, is an advantage. When,
however, the bottom of a thread is taper (as must be the case to enable
it to cut as at A), the cutting edge of each tooth does not cut a groove
sufficiently large in diameter to permit the tooth itself to pass
through. In Fig. 327, for example, is shown a tap which is taper and has
a full thread from end to end (as is necessary for pipe tapping). Its
diameter increases as the thread proceeds from the end towards the line
A B. Now take the tooth O P, which stands lengthwise, in the plane C D.
Its cutting edge is at P, but the diameter of the tap at P is less than
it is at O, while O has to pass through the groove that P cuts. To
obviate this difficulty the tap is given clearance, as shown in Fig.
324, the amount being slightly more than the difference in the diameter
of the tap at O and at P in that figure. It follows, therefore, that a
tap having taper from end to end and a full thread also, as shown in the
lower tap in Fig. 328, is wrong in principle, and from the unsteady
manner in which it operates is undesirable, even though its thread be
given clearance.
[Illustration: Fig. 326.]
[Illustration: Fig. 327.]
In some cases the thread is made parallel at the tops and turned taper
for a distance of 1/3 or 1/2 the length of the tap, the root of the
thread at the taper part being deepened and the tops being given a
slight clearance. This answers very well for shallow holes, because the
taper tap cuts more thread on entering a given depth so that the second
tap can follow more easily, but the tap will not operate so steadily as
when the taper part is longer.
[Illustration: Fig. 328.]
It is on account of the tops of the teeth performing the main part of
the cutting that a tap taper may be sharpened by simply grinding the
teeth tops. In the Pratt and Whitney taps, the hand taper tap is made
parallel at the shank end for a distance equal in length to the diameter
of the tap.
The entering end of the taper tap is made straight or parallel for a
distance equal in length to one half the diameter of the tap, the
diameter at this end being the exact proper size of tapping hole. The
parallel part serves as a guide, causing the tap to enter and keep
axially true with the hole to be tapped. The plug and bottoming taps are
made parallel in the thread, the former being tapered slightly at and
for two or three threads from the entering, as shown in Fig. 328. The
threads are made parallel at the roots.
The Pratt and Whitney taper taps for use in machines are of the
following form:--
The entering end of the tap is equal in diameter to the diameter of the
tapping hole into which the tap will enter for a distance of two or
three threads. The thread at the shank end is parallel both at the top
and at the root for a distance equal, in length, to twice the diameter
of the tap. The top of the thread has a straight taper running from the
parallel part at the shank to the point or entering end, while the roots
of the thread are made along this taper twice the taper that there is at
the top of the thread, which is done to make the tap enter and take hold
of the nut more easily.
[Illustration: Fig. 329.]
A form of tap that cuts very freely on account of the absence of
friction on the sides of the thread is shown in Fig. 329. The thread is
cut in parallel steps, increasing in size towards the shank, the last
step (from D to E in the figure) being the full size. The end of the tap
at A being the proper size for the tapping hole, and the flutes not
being carried through A, insures that the tap shall not be used in holes
too small for the size of the tap, and thus is prevented a great deal of
tap breakage. The bottom of the thread of the first parallel step (from
A to B) is below the diameter of A, so as to relieve the sides of the
thread of friction and cause the tap to enter easily. The first tooth
of each step does all the cutting, thus acting as a turning tool, while
the step within the work holds the tooth to its cut, as shown in Fig.
330, in which N represents a nut and T the tap, both in section. The
step C holds the tap to its work, and it is obvious that, as the tooth B
enters, it will cut the thread to its own diameter, the rest of the
teeth on that step merely following frictionless until the front tooth
on the next step takes hold. Thus, to sharpen the tap equal to new, all
that is required is to grind away the front tooth on each step, and it
becomes practicable to sharpen the tap a dozen times without softening
it at all. As a sample of duty, it may be mentioned that, at the
Harris-Corliss Works, a tap of this class, 2-7/8 inches diameter, with a
4 pitch, and 10 inches long, will tap a hole 5 inches deep, passing the
tap continuously through without any backing motion, two men performing
the duty with a wrench 4 feet long over all, the work being of cast
iron.
[Illustration: Fig. 330.]
[Illustration: Fig. 331.]
[Illustration: Fig. 332.]
Another form of free cutting tap especially applicable to taps of large
diameter has been designed by Professor Sweet. Its principles may be
explained as follows:--
In the ordinary tap, with the taper four or five diameters in length,
there are far more cutting-edges than are necessary to do the work; and
if the taper is made shorter, the difficulty of too little room for
chips presents itself. The evil results arising from the extra cutting
edges are that, if all cut, then it is cutting the metal uselessly
fine--consuming power for nothing; or if some of the cutting edges fail
to cut, they burnish down the metal, not only wasting power, but making
it all the harder for the following cutters. One plan to avoid this is
to file away a portion of the cutting edges; but the method adopted in
the Cornell University tap is still better. Assume that it is desired to
make three following cutters, to remove the stock down to the dotted
line in Fig. 331. Instead of each cutter taking off a layer one-third
the thickness and the full width, the first cutter is cut away on each
side to about one-third its full width, so that it cuts out the centre
to its full depth, as shown in Fig. 331, the next cutter cutting out the
metal at A, and so on. This is accomplished by filing, or in any other
way cutting away the sides of one row of the teeth all the way up; next
cutting away the upper sides of the next row and the lower sides of the
third, leaving the fourth row (if it be a four-fluted tap) as it is left
by the lathe, to insure a uniform pitch and a smooth thread.
[Illustration: Fig. 333.]
Figs. 333, 334 and 335 represent an adjustable tap designed by C. R.
French, of Providence, R. I., to thread holes accurate in diameter.
The plug tap, Fig. 333, has at its end a taper screw, and the tap is
split up as far as the flutes extend, a second screw binds the two sides
of the tap together, hence by means of the two screws the size of the
tap may be regulated at will. In the third or bottoming tap, Fig. 334,
the split extends farther up the shank, and four adjusting screws are
used as shown, hence the parallelism of the tap is maintained.
In the machine tap, Fig. 335, there are six adjusting screws, two of
those acting to close the tap being at the extreme ends so as to
strengthen it as much as possible.
[Illustration: Fig. 334.]
[Illustration: Fig. 335.]
In determining the number, the width, the depth, and the form of flutes
for a tap, we have the following considerations. In a tap to be used in
a machine and to pass entirely through the work, as in the case of
tapping nuts, the flute need not be deep, because the taper part of the
tap being long the cutting teeth extend farther along the tap; hence,
each tooth takes a less amount of cut, producing less cuttings, and
therefore less flute is required to hold them. In taps of this class,
the thread being given clearance, the length of the teeth may be a
maximum, because they are relieved of friction; on the other hand,
however, the shallower and narrower the flute the stronger the tap, so
long as there is room for the cuttings so that they shall not become
wedged in the flutes. Taps for general use by hand are frequently used
to tap holes that do not pass entirely through the work; hence, the
taper tap must have a short length of taper so that the second tap may
be enabled to carry a full thread as near as possible to the bottom of
the hole without carrying so heavy a cut as to render it liable to
breakage, and the second or plug tap must in turn have so short a length
of its end tapered that it will not throw too much duty upon the
bottoming tap. Now, according as the length of the taper on the taper
tap is reduced, the duty of the teeth is increased, and more room is
necessary in the flute to receive the cuttings, and supposing the tap
to be rotated continuously to its duty the flute must possess space
enough to contain all the cuttings produced by the teeth, but on account
of the cuttings filling the flutes and preventing the oil fed to the tap
from flowing down the flute to the teeth it is found necessary in hand
taps (when they cannot pass through the work, or when the depth of the
hole is equal to more than about the tap diameter), to withdraw the tap
and remove the cuttings. On account of the tap not being accurately
guided in hand-tapping it produces a hole that is largest at its mouth,
and it is found undesirable on this account to give any clearance to
hand taps, because such clearance gives more liberty to the tap to
wobble in the hole and to enlarge its diameter at the mouth. It is
obvious also, that the less of the tap circumference removed to form the
flutes the longer the tap-teeth and the more steadily the tap may be
operated. On the other hand, however, the longer the teeth the greater
the amount of friction between them and the thread in the hole and the
more work there is involved in the tapping, because the tap must
occasionally be rotated back a little to ease its cut, which it is found
to do.
[Illustration: Fig. 336.]
[Illustration: Fig. 337.]
Fig. 336 represents a form of flute recommended by Brown and Sharp. The
teeth are short, thus avoiding friction, and the flutes are shallow,
which leaves the tap strong. The inclination of the cutting edges, as A
B (the cutting direction of rotation being denoted by the arrow), is
shown by the dotted lines, being in a direction to curve the chip or
cutting somewhat upward and not throw them down upon the bottom of the
flute. A more common form, and one that perhaps represents average
American practice, is shown in Fig. 337, the cutting edges forming a
radial line as denoted by the dotted line. The flute is deeper, giving
more room for the chips, which is an advantage when the tap is required
to cut a thread continuously without being moved back at all, but the
tap is weaker on account of the increased flute depth, the teeth are
longer and produce more friction, and the flutes are deeper than
necessary for a tap having a long taper or that requires to be removed
to clear out the cuttings. Fig. 338 shows the form of flute in the Pratt
and Whitney Company's hand taps, the cutting edges forming radial lines
and the bottoms of the flutes being more rounded than is usual. It may
here be remarked that if the flutes have comparatively sharp corners, as
at C in Fig. 339, the tap will be liable to crack in the hardening
process. The form of flute employed in the Whitworth tap is shown in
Fig. 340; here there being but three flutes the teeth are comparatively
long, and on this account there is increased friction. But, on the other
hand, such a tap produces, when used by hand, more accurate work, the
threaded hole being more parallel and of a diameter more nearly equal to
that of the tap, it being observed that even though a hand tap have no
clearance it will usually tap a hole somewhat larger than itself so that
it will unwind easily. If a hand tap is given clearance not only will it
cut a hole widest at the mouth, but it will cut a thread larger than
itself in an increased degree, and, furthermore, when the tap requires
to be wound back to extract it the fine cuttings will become locked in
the threads and the points of the tap teeth are liable to become broken
off. To ease the friction of long teeth, therefore, it is preferable to
do so either as in Fig. 325 at A, B, C, or as in Fig. 341. In Fig. 325
the tops of the teeth are shown filed away, leaving each end full, so
that the cuttings cannot get in, no matter in which direction the tap is
rotated; but the clearance is not so complete as in Fig. 341, in which
the teeth are supposed to be eased away within the area enclosed by
dotted lines, which gives clearance to the bottom as well as to the tops
and sides of the thread and leaves the ends of each tooth a full thread.
[Illustration: Fig. 338.]
[Illustration: Fig. 339.]
[Illustration: Fig. 340.]
[Illustration: Fig. 341.]
Concerning the number of flutes in taps, it is to be observed that the
duty the tap is to be put to, has much influence in this respect. In
hand tapping the object is to tap as parallel and straight as possible
with the least expenditure of power. Now, the greater the number of
flutes the less the tap is guided, because more of the circumferential
guiding surface is cut away. But on the other hand, the less the number
of flutes, and therefore the less the number of cutting edges, the more
power it takes to operate the tap on account of the greater amount of
friction between the tap and the walls of the hole. In hand tapping on
what may be termed frame work (as distinguished from such loose work as
nuts, &c.), the object is to tap the holes as parallel as possible with
the least expenditure of power while avoiding having to remove the tap
from the hole to clear it of the cuttings. Obviously the more flutes and
cutting edges there are the more room there is for the cuttings and the
less frequent the tap requires to be cleaned. If the tapping hole is
round and straight the tapping may be made true and parallel if due care
is taken, whatever the number of flutes, but less care will be required
in proportion as there are less flutes, while, as before noted, more
power and more frequent tap removals will be necessary. But if the hole
is not round, other considerations intervene.
[Illustration: Fig. 342.]
Thus in Fig. 342 we have a three-flute tap in a hole out of round at A,
and it is obvious that when a cutting edge meets the recess at A, all
three teeth will cease to cut; hence there will be no inducement for the
tap to move over toward A. But in the case of the four-flute tap in Fig.
343, when the teeth come to A there will be a strain tending to force
the teeth over toward the depression A. How much a given tap would
actually move over would, of course, depend upon the amount of
clearance; but whether the tap has clearance or not, the three-flute tap
will not move over, while with four flutes the tap would certainly do
so. Again, with an equal width of flute there is more of the
circumference tending to guide and steady the three-flute than the
four-flute tap. If the hole has a projection instead of a depression, as
at B, Figs. 344 and 345, then the advantage still remains with the
three-flute tap, because in the case of the three flutes, any lateral
movement of the tap will be resisted at the two points _c_ and D,
neither of which are directly opposite to the location of the projection
B; hence, if the projection caused the tap to move laterally, say,
1-100th inch, the effect at _c_ and D would be very small, whereas in
the four-flute, Fig. 345, the effect at E would be equal to the full
amount of lateral motion of the tap.
[Illustration: Fig. 343.]
[Illustration: Fig. 344.]
[Illustration: Fig. 345.]
In hand taps the position of the square at the head of the tap with
relation to the cutting-edges is of consequence; thus, in Fig. 346,
there being a cutting-edge A opposite to the handle, any undue pressure
on that end of the handle would cause A to cut too freely and the tap to
enlarge the hole; whereas in Fig. 347 this tendency would be greatly
removed, because the cutting-edges are not in line with the handle. In a
three-flute tap it makes but little difference what are the relative
positions of the square to the flutes, as will be seen in Fig. 348,
where one handle of the wrench comes in the most favorable and the other
in the most unfavorable position. Taps for use by hand and not intended
to pass through the work are sometimes made with the shank and the
square end which receive the wrench of enlarged diameter. This is done
to avoid the twisting of the shank which sometimes occurs when the tap
is employed in deep holes, giving it much strain, and also to avoid as
much as possible the wearing and twisting of the square which occurs,
because in the course of time the square holes in solid wrenches enlarge
from wear, and the larger the square the less the wear under a given
amount of strain.
[Illustration: Fig. 346.]
Brass finishers frequently form the heads of their taps as in Fig. 349,
using a wrench with a slot in it that is longer than the flat of the tap
head.
[Illustration: Fig. 347.]
The thickness of the flat head at A is made equal for all the taps
intended to be used with the same wrench. By this means one wrench may
be used for many different diameters of taps.
[Illustration: Fig. 348.]
For gas, steam pipe, and other connections made by means of screw
threads, and which require to be without leak when under pressure, the
tap shown in Fig. 350 is employed. It is made taper and full threaded
from end to end, so that the fittings may be entered easily into their
places and screwed home sufficiently to form a tight joint.
[Illustration: Fig. 349.]
[Illustration: Fig. 350.]
The standard degree of taper for steam-pipe taps is 3/4 inch per foot of
length, the taper being the same in the dies as on the taps. The
threading tools for the pipes or casings for petroleum oil wells are
given a taper of 3/8 inch per foot, because it was not found practicable
to tap such large fittings with a quick taper, because of the excessive
strain upon the threading tools. Ordinary pipe couplings are, however,
tapped straight and stretch to fit when screwed home on the pipe.
Oil-well pipe couplings are tapped taper from both ends, and there is
just enough difference in the taper on the pipe and that in the socket
to show a bearing mark at the end only when the pipe and socket are
tested with red marking.
PITCHES OF TAP THREADS IN USE IN THE UNITED STATES.
+-----------+---------+----------------+
| | | No. of Threads |
| Diameter. | Length. | to Inch. |
+-----------+---------+----------------+
| 1/4 | 2-3/4 | 16, 18 & 20 |
| 5/16 | 2-7/8 | 16 & 18 |
| 3/8 | 3-1/2 | 14 & 16 |
| 7/16 | 3-13/16 | 14 & 16 |
| 1/2 | 4-5/16 | 12, 13 & 14 |
| 9/16 | 4-3/4 | 12 & 14 |
| 5/8 | 5-1/8 | 10, 11 & 12 |
| 11/16 | 5-3/8 | 11 & 12 |
| 3/4 | 5-13/16 | 10, 11 & 12 |
| 13/16 | 6 | 10 |
| 7/8 | 6-1/8 | 9 & 10 |
| 15/16 | 6-3/8 | 9 |
| 1 | 6-13/16 | 8 |
| 1-1/8 | 7-1/4 | 7 & 8 |
| 1-1/4 | 8 | 7 & 8 |
+-----------+---------+----------------+
Fig. 351 represents the form of tap employed by blacksmiths for rough
work, and for the axles of wagon wheels. These taps are given a taper of
1/2 inch per foot of length, and are made with right and left-hand
threads, so that the direction of rotation on both sides of a wagon
wheel shall be in a direction to screw up the nuts and not to unscrew
the nut, as would be the case if both ends of the axle were provided
with right-hand threads.
[Illustration: Fig. 351.]
Taps that are used in a machine are sometimes so constructed that upon
having tapped the holes to the required depth, the pieces containing the
tap teeth recede from the walls of the hole, so that the tap may be
instantly withdrawn from the hole instead of requiring to be rotated
backwards. This is an advantage, not only on account of the time saved,
but also because the cutting edges of the teeth are saved from the
abrasion and its consequent wear which occur in rotating a tap
backwards.
[Illustration: Fig. 352.]
Figs. 352 and 353 represent a collapsing tap that is much used in
manufactories of pipe fittings.
[Illustration: Fig. 353.]
A is driven by the spindle of the machine, and drives B through the
medium of the pin H. In B are three chasers C, fitting into the dovetail
and taper grooves D. These chasers are provided with lugs fitting into
an annular groove E sunk in A, so that if the piece H rises, the chasers
will not rise with it, but will simply close together by reason of the
lifting or rising of the core B, with its taper dovetail grooves; or, on
the other hand, if the core B descends, the taper grooves in B force the
chasers outward, increasing their cutting diameter.
When the tap is cutting, it is driven as denoted by the arrow, and the
pin H is driven by the ends of the grooves, of which there are two, one
diametrically opposite the other, inclined in the same direction. But
when the tap has cut a thread to the required depth on the work, the
handles H may be pulled or pushed the working way, passing along the
grooves I, and causing B to lift within A, and allowing the chasers to
close away from the thread just cut, and the tap may be instantly
withdrawn, and handles H pushed back to expand the chasers, ready for
the next piece of work.
[Illustration: Fig. 354.]
Fig. 354 represents a collapsing tap used in Boston, Massachusetts, at
the Hancock Inspirator Works, in a monitor or turret lathe. It consists
of an outer shell A carrying three chasers B, pivoted to A at C, having
a small lug E at one end, and being coned at the inner end D. The inner
shell F is reduced along part of its length to receive the lug E of the
chaser, and permit the chasers to open out full at their cutting end. F
has a cone at the end G, fitting to the internal cone on the chasers at
D. At the other end of F is a washer H, against which abuts the spiral
spring shown, the other end of this spring abutting against a shoulder
provided in A. The washer H is bevelled on its outer or end face to
correspond with the bevel on a notch provided in lever I, as is shown.
Within the inner tube F is the stem J, into the end of which is fitted
the piece K, and on which is fixed the cone L. Piece K, and therefore L,
is prevented from rotating by a spline in K, into which spline the pin M
projects.
The operation is as follows. In the position in which the parts are
shown in the engraving, F is pushed forward so that its coned end G has
opened out the chaser to its fullest extent, which opening is governed
by contact of the lug E with the reduced diameter of F. Suppose that the
tap is operating in the work, then, when the foot N of K meets with a
resistance (as the end of the hole being tapped), J, and therefore L,
will be gradually pushed to the right, until, finally, the cone on L
will raise the end of lever I until the notch on I is clear of H, when
the spiral spring, acting against H, will force F to the right, and the
shoulder on F, at X, will lift the end E of the chaser, causing the
cutting end to collapse within A, the pivot C being its centre of
motion. The whole device may then be withdrawn from the work. To open
the chasers out again the rod J is forced, by hand, to the left, the
cone-piece L meeting the face of H and pushing it to the left until cone
G meets cone D, when the chasers open until the end E meets the body of
F, as in the cut. The rod J is then pulled to the right until L again
meets the curved end of lever I and all the parts assume the positions
shown in the cut. To regulate the depth of thread the tap shall cut, the
body A is provided with a thread to receive the nut O, by means of which
the collar P may be moved along A. This collar carries the pivots Q for
levers I, so that, by shifting O, the position of I is varied, hence the
point at which L will act upon the end of I and lift it to release H is
adjustable.
When used upon steel, wrought iron, cast iron, copper, or brass, a tap
should be freely supplied with oil, which preserves its cutting edge as
well as causes it to cut more freely, but for cutting the soft metals
such as tin, lead, &c., oil is unnecessary.
The diameters of tapping holes should be equal to the diameter of the
thread at the root, but in the case of cast iron there is much
difference of opinion and practice. On the one hand, it is claimed that
the size of the tapping hole should be such as to permit of a full
thread when it is tapped; on the other hand, it is claimed that
two-thirds or even one-half of a full thread is all that is necessary in
holes in cast iron, because such a thread is, it is claimed, equally as
strong as a full one, and much easier to tap. In cases where it is not
necessary for the thread to be steamtight, and where the depth of the
thread is greater by at least 1/8 inch than the diameter of the bolt or
stud, three-quarters of a full thread is all that is necessary, and can
be tapped with much less labor than would be the case if the hole were
small enough to admit of a full thread, partly because of the diminished
duty performed by the tap, and partly because the oil (which should
always be freely supplied to a tap) obtains so much more free access to
the cutting edges of the tap. If a long tap is employed to cut a
three-quarter full thread, it may be wound continuously down the hole,
without requiring to be turned backwards at every revolution or so of
the tap, to free it from the tap cuttings or shavings, as would be
necessary in case a full thread were being cut. The saving of time in
consequence of this advantage is equal to at least 50 per cent. in favor
of the three-quarter full thread.
As round bar iron is usually rolled about 1/32 inch larger than its
designated diameter, a practice has arisen to cut the threads upon the
rough iron just sufficiently to produce a full thread, leaving the
latter 1/32 inch above the proper diameter, hence taps 1/32 inch above
size are required to thread nuts to fit the bolts. This practice
should be discountenanced as destroying in a great measure the
interchangeability of bolts and nuts, because 1/32 inch is too small a
measurement to be detected by the eye, and a measurement or trial of the
bolt and nut becomes necessary.
A defect in taps which it has been found so far impracticable to
eliminate is the alteration of pitch which takes place during the
hardening process. The direction as well as the amount of this variation
is variable even with the most uniform grades of steel, and under the
most careful manipulation. Mr. John J. Grant, in reply to a
communication upon this subject, informs me that, using Jones and
Colver's (Sheffield) steel, which is very uniform in grade, he finds
that of one hundred taps, about 5 per cent. will increase in length, the
pitch of the thread becoming coarser; 15 per cent. will suffer no
appreciable alteration of pitch, and 80 per cent. will shrink in length,
the pitch becoming finer, and these last not alike. But it must be borne
in mind that with different steel the results will be different, and the
greater the variation in the grade of the steel the greater the
difference in the alteration of pitch due to hardening.
It is further to be observed that the expansion or contraction of the
steel is not constant throughout the same tap; thus the pitches of three
or four consecutive teeth may measure correct to pitch, while the next
three or four may be of too coarse or too fine a pitch.
There is no general rule, even using the same grade of steel, for the
direction in which the size of a tap may alter in hardening, as is
attested by the following answers made by Mr. J. J. Grant to the
respective questions:--
"Do the taps that shorten most in length increase the most in diameter?"
Answer.--"Not always; sometimes a tap that shortens by hardening becomes
also smaller in diameter, while sometimes a tap will increase in length,
and also in diameter from hardening."
"Do taps that remain of true pitch after hardening remain true, or
increase or diminish in diameter?"
Answer.--"They will generally be of larger diameter."
"Do small taps alter more in diameter from hardening than large ones?"
Answer.--"No; the proportion is about the same, and is about .002 per
inch of diameter."
"What increase in diameter do you allow for shrinkage in hardening of
hob taps for tapping solid dies?"
Answer.--"As follows:--
Diameter of Shrinkage
Hob Tap about
1/4 inch .003
1/2 " .003
3/4 " .005
1 " .008"
"Suppose a tap that had been hardened and tempered to a straw color
contained an error 1/1000 inch both in diameter and in pitch, was
softened again, would it when soft retain the errors, or in what way
would softening affect the tap?"
Answer.--"We have repeatedly tried annealing or softening taps that were
of long or short pitch caused by tempering, and invariably found them
about the same as before the annealing. The second tempering will
generally shorten them more than the first. Sometimes, however, a second
tempering will bring a long pitch nearer correct."
"Do you soften your taps after roughing them out in the lathe?"
Answer.--"Never, if we can possibly avoid it. Sometimes it is necessary
because of improper annealing at first. The more times steel is annealed
the worse the results obtained in making the tool, and the less durable
the tool."
The following are answers to similar questions addressed to the Morse
Twist Drill and Machine Co.:--
"The expansion of taps during hardening varies with the diameter. A
1-inch tap would expand in diameter from 1/1000 to 3/1000 inch."
"Taps above 1/2 inch diameter expand in diameter to stop the gauge every
time."
"The great majority of taps contract in pitch during the hardening, they
seldom expand in length."
"The shortening of the pitch and the expansion in diameter have not much
connection necessarily, though steel that did not alter in one direction
would be more likely to remain correct in the other."
"There does not seem to be any change in the diameter or pitch of taps
if measured after hardening (and before tempering) and again after
tempering them."
"Taps once out in length seem to get worse at every heating, whether to
anneal or to harden."
[Illustration: Fig. 355.]
It will now be obvious to the reader that the diameter of a tap, to give
a standard sized bolt a required tightness of fit, will, as a general
rule, require to vary according to the depth of hole to be tapped,
because the greater that depth the greater the error in the pitch.
Suppose a tap, for example, to get of finer pitch to the amount of .002
per inch of length, then a hole an inch deep and tapped with that tap
would err .002 in its depth, while a hole two inches deep would err
twice as much in its depth.
[Illustration: Fig. 356.]
Therefore a bolt that would be a hand fit (that is, screw in under hand
pressure) in the hole an inch deep would require more force, and
probably the use of a wrench, to wind it through the hole 2 inches deep;
hence in cases where a definite degree of fit is essential, the
reduction in diameter of the male screw or thread necessary to
compensate for the error in the tap pitch must vary according to the
depth of the hole, and the degree of error in the tap.
[Illustration: Fig. 357.]
It is obvious that the longer a tap is the greater the error induced by
hardening, and it often becomes a consideration how to tap a long hole,
and obtain a thread true to pitch. This may be accomplished as follows.
Several taps are made of slightly different diameters, the largest being
of the required finished size. Each tap is made taper for a distance of
two or three threads only, and is hardened at this tapered end, but left
soft for the remainder of its length. The smallest tap is used first,
and when it has tapped a certain distance, a larger one is inserted, and
by continuing this interchange of taps and slightly varying the length
of the taper, the work may be satisfactorily done.
To test the accuracy, or rather the uniformity, of a thread that has
been hardened, a sheet metal gauge, such as at G or at G´ (Fig. 355),
may be used, there being at _a_ and _b_ teeth to fit the threads. If the
edge of the gauge meets the tops of the threads, then their depth is
correct. If it is desired to test only the pitch, then the gauge may be
made as at G´, where, as is shown in the figure, the edge of the gauge
clears the tops of the threads, and in this way may be tried at various
points along the thread length.
[Illustration: Fig. 358.]
A method of truing hardened threads proposed by the author of this work
in 1877, and since employed by the Pratt and Whitney Company to true
their hardened steel plug-thread gauges, is as follows:--A soft steel
wheel about 3-1/2 inches in diameter, whose circumference is turned off
to the shape of the thread, is mounted upon the slide rest of a lathe,
and driven by a separate belt after the manner of driving emery wheels;
this wheel is charged with diamond dust, which is pressed into its
surface by a roller, hence it grinds the thread true.
The amount allowed for grinding is 3/1000 inch measured in the angles of
the thread, as was shown in Figs. 280 and 281.
In charging the wheel with diamond dust it is necessary to use a roller
shaped as in Fig. 356, so that the axis of the roller R and wheel W
shall be at a right angle, as denoted by the dotted lines. If the roller
is not made to the correct cone its action will be partly a rolling and
partly a sliding one, and it will strip the diamond dust from the wheel
rather than force it in, the reasons for this being shown in Figs. 57
and 58 upon the subject of bevel-wheels.
[Illustration: Fig. 359.]
Taps for lead and similar soft metal are sometimes made with three flat
sides instead of grooves. The tapping holes may in this case be made of
larger diameter than the diameter of the end of the tap thread, because
the metal in the hole will compress into the tap thread, and so form a
full thread. Taps for other metal have also been made of half-round
section. Fig. 357 represents a tap of oval cross section, having two
flutes, as shown, but it may be observed that neither half-round nor
oval taps possess any points of advantage over the ordinary forms of
three or four fluted taps, while the former are more troublesome and
costly to manufacture.
[Illustration: Fig. 360.]
When it is required to tap a hole very straight and true, it is
sometimes the practice to provide a parallel stem to the tap, as shown
in figure at C. This stem is made a neat working fit to the tapping
hole, so that the latter serves as a guide to the tap, causing it to
enter and to operate truly.
TAP WRENCH.--Wrenches for rotating a tap are divided into two principal
classes, single and double wrenches. The former has the hole which
receives the squared end of the tap in the middle of its length, as
shown in Fig. 358 at E, there being a handle on each side to turn it by.
[Illustration: Fig. 361.]
The single wrench has its hole at one end, as shown in Fig. 359 at D,
and is employed for tapping holes in locations where the double wrench
could not be got in.
[Illustration: Fig. 362.]
[Illustration: Fig. 363.]
In some cases double tap wrenches are made with two or three sizes of
square holes to serve as many different sizes of taps, but this is
objectionable, because unless the handles of the wrench extend equally
on each side of the tap, the overhanging weight on one side of the tap
exerts an influence to pull the tap over to one side and tap the hole
out of straight. For taps that have square heads the wrench should be a
close but an easy fit to the tap head, otherwise the square corners of
the tap become rounded. For the smaller sizes of taps, adjustable
wrenches, such as shown in Fig. 360, are sometimes employed. These
contain two dies; the upper one, which meets the threaded end of C,
being a sliding fit, and the joint faces being formed as shown at A, B.
By rotating the handle C its end leaves the upper die, which may be
opened out, leaving the square hole between the dies large enough to
admit the squared tap end. After the wrench is placed on the tap, C is
rotated so as to close the dies upon the tap.
[Illustration: Fig. 364.]
[Illustration: Fig. 365.]
When the location of the tapping hole leaves room for the wrench to
rotate a full circle, C is screwed up so that the dies firmly grip the
tap head, which preserves the tap head; but when the wrench can only be
rotated a part of a revolution, C is adjusted to leave the dies an easy
fit to the tap head, so as to enable the wrench to be removed from the
tap head with facility and again placed upon the tap head. C is operated
by a round lever or pin introduced in a hole in the collar, or the
collar may be squared to receive a wrench.
To insure that a tap shall tap a hole straight, the machinist, in the
case of hand tapping, applies a square to the work and the tap, as shown
in Fig. 361, in which W represents a piece of work, T a tap, and S S two
squares. If the tap is a taper one the square is sighted with the shank
of the tap, as shown in position 1, but if the thread of the tap is
parallel, the square may be applied to the thread of the tap, as in
position 2. If the tap leans over to one side, as in Fig. 362, it is
brought upright by exerting a pressure on the tap wrench handle B (on
the high side) in the direction of the arrow A, while the wrench is
rotated; but if the tap leans much to one side it is necessary to rotate
the tap back and forth, exerting the pressure on the forward stroke
only.
[Illustration: Fig. 366.]
[Illustration: Fig. 367.]
It is necessary to correct the errors before the tap has entered the
hole deeply, because the deeper the tap has entered the greater the
difficulty in making the correction. If the pressure on the tap wrench
be made excessive, it is very liable to cause the tap to break,
especially in the case of small taps, that is to say, those of 5/8 inch
or less in diameter. The square should be applied as soon as the tap has
entered the hole sufficiently to operate steadily, and should be applied
several times during the tapping operation.
When the tap does not pass through the hole it may be employed with a
guide which will keep it true, as shown in Fig. 363, in which W is a
piece of work, T the tap, and S a guide, the latter being bolted or
clamped to the work at B. In this case the shank of the tap is made
fully as large in diameter as the thread. In cases where a number of
equidistant holes require tapping, as in the case of cylinder ends, this
device saves a great deal of time and insures that the tapping be
performed true, the hole to receive the bolt B and that to receive the
tap being distant apart to the same amount as are the holes in the work.
In shops where small work is made to standard gauge, and on the
interchangeable system, devices are employed, by means of which a piece
that has been threaded will screw firmly home to its place, and come to
some definite position, as in the following examples. In Fig. 364 let it
be required that the stud A shall screw in the slide S; the arm A to
stand vertical when collar B is firmly home, and a device such as in
Fig. 365 may be employed. P is a plate on which is fixed a chuck C to
receive the slide S. In plate P is a groove G to hold the head H at a
right angle to the slideway in C, there being a projection beneath H and
beneath C to fit into G. The tap T is threaded through H, but not fluted
at the part that winds through H when the tapping is being done, so as
not to cause the thread in H to wear. H acts as a guide to the tap and
causes it to start the thread at the same point in the bore of each
piece S, and the stem will be so threaded that the screw starts at the
same point in the circumference of each piece.
[Illustration: Fig. 368.]
A second example of uniform tapping is shown in Figs. 366, 367, and 368.
The piece, Fig. 366, is to have its bore A tapped in line with the slot
C, and the thread is to start at a certain point in its bore. In Fig.
367 this piece is shown chucked on a plate D. F is a chuck having a lug
E fitting into the slot (C, Fig. 366) of the work. This adjusts the work
in one direction. The face D of the plate adjusts the vertical height of
the work, and the alignment of the hole to the axis of the tap is
secured in the construction of the chuck, as is shown in Fig. 369. A lug
K is at a right angle to the face B of the chuck and stands in a line
with lug E, as denoted by the dotted line _g_ _g_, and as lug K fits
into the slot G, Fig. 367, the work will adjust itself true when bolted
to the plate.
[Illustration: Fig. 369.]
Fig. 368 shows a method of tapping or hobbing four chasers (as for a
bolt cutter), so that if the chasers are marked 1, 2, 3 and 4, as shown,
any chaser of No. 1 will work with the others, although not tapped at
the same operation. C is a chuck with four dies (A, B, C, D) placed
between the chasers. By tightening the set-screws S, the dies and
chasers are locked ready for the tapping. N is a hub to receive a
guide-pin P, which is passed through to hold the chasers true while
being set in the chuck, and it is withdrawn before the tapping
commences; _d_ _e_ _f_ are simply to take hold of when inserting and
removing the dies. It is obvious that a chuck such as this used upon a
plate, as in Fig. 365, with the hob guided in the head H there shown,
would tap each successive set of chasers alike as a set, and
individually alike, provided, of course, that the hob guide or head H is
at each setting placed the same distance from the face of the chuck, a
condition that applies to all this class of work. In the case of work
like chasers, where the tap or hob does not have much bearing to guide
it in the work, a three-flute hob should be used for four chasers, or a
four-flute hob for three chasers, which is necessary so that the hob may
work steadily and tap all to the same diameter.
CHAPTER V.--FASTENING DEVICES.
Bolts are usually designated for size by their diameters measured at the
cylindrical stem or body, and by their lengths measured from the inner
side of the head to the end of the thread, so that if a nut be used, the
length of the bolt, less the thickness of the nut and washer (if the
latter be used), is the thickness of work the bolt will hold. If the
work is tapped, and no nut is used, the full length of the bolt stem is
taken as the length of the bolt.
A _black_ bolt is one left as forged. A finished bolt has its body, and
usually its head also, machine finished, but a finished bolt sometimes
has a black head, the body only being turned.
A square-headed bolt usually has a square nut, but if the nut is in
a situation difficult of access for the wrench, or where the head
of the bolt is entirely out of sight (as secluded beneath a flange) the
nut is often made hexagon. A machine-finished bolt usually has a
machine-finished and hexagon nut. Square nuts are usually left black.
[Illustration: Fig. 370.]
The heads of bolts are designated by their shapes, irrespective of
whether they are left black or finished. Fig. 370 represents the various
forms: _a_, square head; _b_, hexagon head; _c_, capstan head; _d_,
cheese head; _e_, snap head; _f_, oval head, or button head; _g_,
conical head; _h_, pan head; _i_, countersink head.
The square heads _a_ are usually left black, though in exceptional cases
they are finished. Hexagon heads are left black or finished as
circumstances may require; when a bolt head is to receive a wrench and
is to be finished, it is usually made hexagon. Heads _c_ and _d_ are
almost invariably finished when used on operative parts of machines, as
are also _e_ and F. Heads _g_ are usually left black, while _h_ and _i_
are finished if used on machine work, and left black when used as rivets
or on rough unfinished work.
The heads from _e_ to _i_ assume various degrees of curve or angle to
suit the requirements, but when the other end of the bolt is threaded to
receive a nut, some means is necessary to prevent them from rotating in
their holes when the nut is screwed up, thus preventing the nut from
screwing up sufficiently tight. This is accomplished in woodwork by
forging either a square under the head, as in Fig. 371, or by forging
under the head a tit or stop, such as shown in Figs. 372 and 373 at P.
Since, however, forging such stops on the bolt would prevent the heads
from being turned up in the lathe, they are for lathe-turned bolts put
in after the bolts have been finished in the lathe, a hole being
subsequently drilled beneath the head to receive the pin or stop, P,
Fig. 372, which may be tightly driven in. A small slot is cut in the
edge of the hole to receive the stop.
[Illustration: Fig. 371.]
[Illustration: Fig. 372.]
[Illustration: Fig. 373.]
Bolts are designated for kinds, as in Fig. 374, in which _k_ is a
machine bolt; _l_ a collar bolt, from having a collar on it; _m_ a
cotter bolt, from having a cotter or key passing through it to serve in
place of a nut; _n_ a carriage bolt, from having a square part under the
head to sink in the wood and prevent the bolt from turning with the nut;
and _o_ a countersink bolt for cases where the head of the bolt comes
flush.
[Illustration: Fig. 374.]
The simple designation "machine bolt" is understood to mean a black or
unfinished bolt having a square head and nut, and threaded, when the
length of the bolt will admit it, and still leave an unthreaded part
under the bolt head, for a length equal to about four times the diameter
of the bolt head. If the bolt is to have other than a square head it is
still called a machine bolt, but the shape of the head or nut is
specially designated as "hexagon head machine bolt," this naturally
implying that a hexagon nut also is required.
In addition to these general names for bolts, there are others applied
to special cases. Thus Fig. 375 represents a patch bolt or a bolt for
fastening patches (as plate C to plate D), its peculiarity being that it
has a square stem A for the wrench to screw it in by. When the piece the
patch bolt screws into is thin, as in the case of patches on steam
boilers, the pitch of the thread may, to avoid leakage, be finer than
the usual standard.
In countersink head bolts, such as the patch bolt in Fig. 375, the head
is very liable to come off unless the countersink in the work (as in C)
is quite fair with the tapped hole (as in D) because the thread of the
bolt is made a tight fit to the hole, and all the bending that may take
place is in the neck beneath the head, where fracture usually occurs.
These bolts are provided with a square head A to screw them in by, and
are turned in as at B to a diameter less than that at the bottom of the
thread, so that if screwed up until they twist off, they will break in
the neck at B.
[Illustration: Fig. 375.]
[Illustration: Fig. 376.]
Instead of the hole being countersunk, however, it may be cupped or
counterbored, as in Fig. 376, in which the names of the various forms of
the enlargement of holes are given. The difference between a faced and a
counterbored hole is that in a counterbored hole the head or collar of
the pin passes within the counterbore, the use of the counterbore being
in this case to cause the pin to stand firmly and straight. The
difference between a dished and a cupped is merely that cupped is deeper
than dished, and that between grooved and recessed is that a recess is a
wide groove.
Eye bolts are those having an eye in place of a head, as in Fig. 377,
being secured by a pin passing through the eye, or by a second bolt, as
in the figure. When the bolt requires to pivot, that part that is
within the eye may be made of larger diameter than the thread, so as to
form a shoulder against which the bolt may be screwed firmly home to
secure it without gripping the eye bolt.
[Illustration: Fig. 377.]
[Illustration: Fig. 378.]
Fig. 378 represents a foundation bolt for holding frames to the stone
block of a foundation. The bolt head is coned and jagged with chisel
cuts. It is let into a conical hole (widest at the bottom) in the stone
block, and melted lead is poured around it to fill the hole and secure
the bolt head.
[Illustration: Fig. 379.]
[Illustration: Fig. 380.]
Another method of securing a foundation bolt head within a stone block
is shown in Fig. 379; a similar coned hole is cut in the block, and
besides the bolt head B a block W is inserted, the faces of the block
and bolt being taper to fit to a taper key K, so that driving K locks
both the bolt and the block in the stone. When the bolt can pass
entirely through the foundation (as when the latter is brickwork) it is
formed as in Fig. 380, in which B is a bolt threaded to receive a nut at
the top. At the bottom it has a keyway for a key K, which abuts against
the plate P. To prevent the key from slackening and coming out, it has a
recess as shown in the figure at the sectional view of the bolt on the
right of the illustration, the recess fitting down into the end of the
keyway as shown.
[Illustration: Fig. 381.]
Another method is to give the bolt head the form at B in Fig. 381, and
to cast a plate with a rectangular slot through, and with two lugs A C.
The plate is bricked in and a hole large enough to pass the bolt head
through is left in the brickwork. The bolt head is passed down through
the brickwork in the position shown at the top, and when it has passed
through the slot in the plate it is given a quarter turn, and then
occupies the position shown in the lower view, the lugs A C preventing
it from turning when the nut is screwed home. The objection to this is
that the hole through the brickwork must be large enough to admit the
bolt head. Obviously the bolt may have a solid square head, and a square
shoulder fitting into a square hole in the plate, the whole being
bricked in.
[Illustration: Fig. 382.]
[Illustration: Fig. 383.]
Figs. 382 and 383 represent two forms of hook bolt for use in cases
where it is not desired to have bolt holes through both pieces of the
work. In Fig. 382 the head projects under the work and for some distance
beneath and beyond the washer, as is denoted by the dotted line, hence
it would suspend piece A from B or piece B from A. But in Fig. 383 the
nut pressure is not beneath the part where the hook D grips the work,
hence the nut would exert a pressure to pull piece B in the direction of
the arrow; hence if B were a fixed piece the bolt would suspend A from
it, but it could not suspend B from A.
In woodwork the pressure of the nut is apt to compress the wood, causing
the bolt head and nut to sink into the wood, and to obviate this, anchor
plates are used to increase the area receiving the pressure; thus in
Fig. 384 a plate is tapped to serve instead of a nut, and a similar
plate may of course be placed under the bolt head.
[Illustration: Fig. 384.]
The Franklin Institute or United States Standard for the dimensions of
bolt heads and nuts is as follows. In Fig. 385, D represents the
diameter of the bolt, J represents the short diameter or width across
flats of the bolt head or of the nut, being equal to one and a half
times the diameter of the bolt, plus 1/16 inch for finished heads or
nuts, and plus 1/8 inch for rough or unfinished heads or nuts. K
represents the depth or thickness of the head or nut, which in finished
heads or nuts equals the diameter of the bolt minus 1/16 inch, and in
rough heads equals one half the distance between the parallel sides of
the head, or in other words one half the width across the flats of the
head.
H represents the thickness or depth of the nut, which for finished nuts
is made equal to the diameter of the bolt less 1/16 inch, and therefore
the same thickness as the finished bolt head, while for rough or
unfinished nuts it is made equal to the diameter of the bolt or the same
as the rough bolt head. I represents the long diameter or diameter
across corners, which, however, is a dimension not used to work to, and
is inserted in the following tables merely for reference:--
[Illustration: Fig. 385.]
TABLE OF THE FRANKLIN INSTITUTE STANDARD DIMENSIONS FOR THE HEADS OF
BOLTS AND FOR THEIR NUTS, WHEN BOTH HEADS AND NUTS ARE OF HEXAGON FORM,
AND ARE POLISHED OR FINISHED.
+------------+-------------+-----------+---------------+-----------+
| Diameter | Diameter at | Number of | Diameter | Thickness |
| at top | bottom of | Threads | across Flats, | or |
| of Thread. | Thread. | per inch. | or short | Depth. |
| | | | diameter. | |
+------------+-------------+-----------+---------------+-----------+
| 1/4 | .185 | 20 | 7/16 | 3/16 |
| 5/16 | .240 | 18 | 17/32 | 1/4 |
| 3/8 | .294 | 16 | 5/8 | 5/16 |
| 7/16 | .345 | 14 | 23/32 | 3/8 |
| 1/2 | .400 | 13 | 13/16 | 7/16 |
| 9/16 | .454 | 12 | 29/32 | 1/2 |
| 5/8 | .507 | 11 | 1 | 9/16 |
| 3/4 | .620 | 10 | 1-3/16 | 11/16 |
| 7/8 | .731 | 9 | 1-3/8 | 13/16 |
| 1 | .837 | 8 | 1-9/16 | 15/16 |
| 1-1/8 | .940 | 7 | 1-3/4 | 1-1/16 |
| 1-1/4 | 1.065 | 7 | 1-15/16 | 1-3/16 |
| 1-3/8 | 1.160 | 6 | 2-1/8 | 1-5/16 |
| 1-1/2 | 1.284 | 6 | 2-5/16 | 1-7/16 |
| 1-5/8 | 1.389 | 5-1/2 | 2-1/2 | 1-9/16 |
| 1-3/4 | 1.491 | 5 | 2-11/16 | 1-11/16 |
| 1-7/8 | 1.616 | 5 | 2-7/8 | 1-13/16 |
| 2 | 1.712 | 4-1/2 | 3-1/16 | 1-15/16 |
| 2-1/4 | 1.962 | 4-1/2 | 3-7/16 | 2-3/16 |
| 2-1/2 | 2.176 | 4 | 3-13/16 | 2-7/16 |
| 2-3/4 | 2.426 | 4 | 4-3/16 | 2-11/16 |
| 3 | 2.629 | 3-1/2 | 4-9/16 | 2-15/16 |
| 3-1/4 | 2.879 | 3-1/2 | 4-15/16 | 3-3/16 |
| 3-1/2 | 3.100 | 3-1/4 | 5-5/16 | 3-7/16 |
| 3-3/4 | 3.377 | 3 | 5-11/16 | 3-13/16 |
| 4 | 3.567 | 3 | 6-1/16 | 3-15/16 |
| 4-1/4 | 3.798 | 2-7/8 | 6-7/16 | 4-3/16 |
| 4-1/2 | 4.028 | 2-7/8 | 6-13/16 | 4-7/16 |
| 4-3/4 | 4.256 | 2-5/8 | 7-3/16 | 4-11/16 |
| 5 | 4.480 | 2-1/2 | 7-9/16 | 4-15/16 |
| 5-1/4 | 4.730 | 2-1/2 | 7-15/16 | 5-3/16 |
| 5-1/2 | 4.953 | 2-3/8 | 8-5/16 | 5-7/16 |
| 5-3/4 | 5.203 | 2-3/8 | 8-11/16 | 5-11/16 |
| 6 | 5.423 | 2-1/4 | 9-1/16 | 5-15/16 |
+------------+-------------+-----------+---------------+-----------+
Note that square heads are supposed to be always unfinished, hence there
is no standard for their sizes if finished.
The Franklin Institute standard dimensions for hexagon and square bolt
heads and nuts when the same are left unfinished or rough, as forged,
are as follows:--
+----------+-------------+-------------+---------------+-----------+
| | Diameter | Diameter | Short | Thickness |
| Bolt | across | across | diameter, | or |
| Diameter | corners, or | corners or | or diameter | depth for |
| in | long | long | across flats | square or |
| Inches. | diameter of | diameter of | for square or | hexagon |
| | hexagon | square | hexagon heads | heads. |
| | heads. | heads. | and nuts. | |
+----------+-------------+-------------+---------------+-----------+
| | Inch. | Inch. | Inch. | Inch. |
| 1/4 | 37/64 | 7/10 | 1/2 | 1/4 |
| 5/16 | 11/16 | 10/12 | 19/32 | 19/64 |
| 3/8 | 51/64 | 63/64 | 11/16 | 11/32 |
| 7/16 | 9/10 | 1-7/64 | 25/32 | 25/64 |
| 1/2 | 1 | 1-15/64 | 7/8 | 7/16 |
| 9/16 | 1-1/8 | 1-23/64 | 31/32 | 31/64 |
| 5/8 | 1-7/32 | 1-1/2 | 1-1/16 | 17/32 |
| 3/4 | 1-7/16 | 1-49/64 | 1-1/4 | 5/8 |
| 7/8 | 1-21/32 | 2-1/32 | 1-7/16 | 23/32 |
| 1 | 1-7/8 | 2-19/64 | 1-5/8 | 13/16 |
| 1-1/8 | 2-2/32 | 2-9/16 | 1-13/16 | 29/32 |
| 1-1/4 | 2-5/16 | 2-53/64 | 2 | 1 |
| 1-3/8 | 2-17/32 | 3-3/32 | 2-3/16 | 1-3/32 |
| 1-1/2 | 2-3/4 | 3-23/64 | 2-3/8 | 1-3/16 |
| 1-5/8 | 2-31/32 | 3-5/8 | 2-9/16 | 1-9/32 |
| 1-3/4 | 3-3/16 | 3-57/64 | 2-3/4 | 1-3/8 |
| 1-7/8 | 3-13/32 | 4-5/32 | 2-15/16 | 1-15/32 |
| 2 | 3-5/8 | 4-27/64 | 3-1/8 | 1-9/16 |
| 2-1/4 | 4-1/16 | 4-61/64 | 3-1/2 | 1-3/4 |
| 2-1/2 | 4-1/2 | 5-31/64 | 3-7/8 | 1-15/16 |
| 2-3/4 | 4-29/32 | 6 | 4-1/4 | 2-1/8 |
| 3 | 5-3/8 | 6-17/32 | 4-5/8 | 2-5/16 |
| 3-1/4 | 5-13/16 | 7-1/16 | 5 | 2-1/2 |
| 3-1/2 | 6-7/64 | 7-39/64 | 5-3/8 | 2-11/16 |
| 3-3/4 | 6-21/32 | 8-1/8 | 5-3/4 | 2-7/8 |
| 4 | 7-3/32 | 8-41/64 | 6-1/8 | 3-1/16 |
| 4-1/4 | 7-9/16 | 9-3/16 | 6-1/2 | 3-1/4 |
| 4-1/2 | 7-31/32 | 9-3/4 | 6-7/8 | 3-7/16 |
| 4-3/4 | 8-13/32 | 10-1/4 | 7-1/4 | 3-5/8 |
| 5 | 8-27/32 | 10-49/64 | 7-5/8 | 3-13/16 |
| 5-1/4 | 9-9/32 | 11-23/64 | 8 | 4 |
| 5-1/2 | 9-23/32 | 11-7/8 | 8-3/8 | 4-3/16 |
| 5-3/4 | 10-5/32 | 12-3/8 | 8-3/4 | 4-3/8 |
| 6 | 10-19/32 | 12-15/16 | 9-1/8 | 4-9/16 |
+----------+-------------+-------------+---------------+-----------+
The depth or thickness of both the hexagon and square nuts when left
rough or unfinished is, according to the above standard, equal to the
diameter of the bolt.
The following are the sizes of finished bolts and nuts according to the
present Whitworth Standard. The exact sizes are given in decimals, and
the nearest approximate sizes in sixty-fourths of an inch:--
+-------------+------------------------+----------------------+
| Diameter of | Width of nuts across | Height of bolt |
| bolts. | flats. | heads. |
+-------------+----------+-------------+--------+-------------+
| 1/8 | .338 | 21/64 _f_ | .1093 | 7/64 |
| 3/16 | .448 | 29/64 _b_ | .1640 | 5/32 |
| 1/4 | .525 | 33/64 _f_ | .2187 | 7/32 |
| 5/16 | .6014 | 19/32 _f_ | .2734 | 17/64 |
| 3/8 | .7094 | 45/64 _f_ | .3281 | 21/64 |
| 7/16 | .8204 | 53/64 _b_ | .3828 | 3/8 _f_ |
| 1/2 | .9191 | 29/32 _b_ | .4375 | 7/16 |
| 9/16 | 1.011 | 1-1/64 _b_ | .4921 | 31/64 _f_ |
| 5/8 | 1.101 | 1-3/32 _f_ | .5468 | 35/64 |
| 11/16 | 1.2011 | 1-13/64 _b_ | .6015 | 19/32 _f_ |
| 3/4 | 1.3012 | 1-19/64 _f_ | .6562 | 21/32 |
| 13/16 | 1.39 | 1-25/64 _b_ | .7109 | 45/64 _f_ |
| 7/8 | 1.4788 | 1-31/64 _b_ | .7656 | 49/64 |
| 15/16 | 1.5745 | 1-37/64 _b_ | .8203 | 13/16 _f_ |
| 1 | 1.6701 | 1-43/64 _b_ | .875 | 7/8 |
| 1-1/8 | 1.8605 | 1-55/64 _f_ | .9843 | 63/64 |
| 1-1/4 | 2.0483 | 2-3/64 _f_ | 1.0937 | 1-3/32 |
| 1-3/8 | 2.2146 | 2-7/32 _b_ | 1.2031 | 1-13/64 |
| 1-1/2 | 2.4134 | 2-13/32 _f_ | 1.3125 | 1-5/16 |
| 1-5/8 | 2.5763 | 2-37/64 _b_ | 1.4128 | 1-27/64 |
| 1-3/4 | 2.7578 | 2-3/4 _f_ | 1.5312 | 1-17/32 |
| 1-7/8 | 3.0183 | 3-1/16 _f_ | 1.6406 | 1-41/64 |
| 2 | 3.1491 | 3-5/32 _b_ | 1.75 | 1-3/4 |
| 2-1/8 | 3.337 | 3-11/32 _b_ | 1.8523 | 1-55/64 |
| 2-1/4 | 3.546 | 3-35/64 _b_ | 1.9687 | 1-31/32 |
| 2-3/8 | 3.75 | 3-3/4 | 2.0781 | 2-5/64 |
| 2-1/2 | 3.894 | 3-57/64 _f_ | 2.1875 | 2-3/16 |
| 2-5/8 | 4.049 | 4-3/64 _f_ | 2.2968 | 2-19/64 |
| 2-3/4 | 4.181 | 4-3/16 _b_ | 2.4062 | 2-13/32 |
| 2-7/8 | 4.3456 | 4-11/32 _f_ | 2.5156 | 2-33/64 |
| 3 | 4.531 | 4-17/32 _b_ | 2.625 | 2-5/8 |
+-------------+----------+-------------+--------+-------------+
The thickness of the nuts is in every case the same as the diameter of
the bolts: _f_ = full, _b_ = bare.
When bolts screw directly into the work instead of passing through it
and receiving a nut, they come under the head of either tap bolts, set
screws, cap screws, or machine screws. A tap bolt is one in which the
full length of the stem or body is threaded, and differs from a set
screw, which is similarly threaded, in the respect that in a set screw
the head is square and its diameter is the same as the square bar of
steel or iron (as the case may be) from which the screw was made, while
in the tap bolt the head is larger in diameter than the bar it was made
from. Furthermore a tap bolt may have a hexagon head, which is usually
left unfinished unless ordered to be finished, as is also the case with
set screws.
Cap screws are made with heads either hexagon, square, or round, and
also with a square head and round collar, as in Fig. 386, the square
heads being of larger diameter than the iron from which they were made.
When the heads of cap screws are finished they are designated as "milled
heads."
[Illustration: Fig. 386.]
[Illustration: Fig. 387.]
A machine screw is a small screw, such as in Fig. 387, the diameter of
the body being made to the Birmingham wire gauge, the heads being formed
by upsetting the wire of which they are made. They have saw slots S for
a screw driver, the threads having special pitches, which are given
hereafter. The forms of the heads are as in Fig. 387, A being termed a
Fillister, B a countersink, and C a round head. The difference between a
Fillister head of a machine screw and the same form of head in a cap
screw is that the former is upset cold, and the latter is either forged
or cut out of the solid metal.
When the end of a screw abuts against the work to secure it, it is
termed a set screw. The ordinary form of set screw is shown in Fig. 389,
the head being square and either black or polished as may be required.
The ends of the set screws of commerce, that is to say, that are kept on
sale, are usually either pointed as at A, Fig. 388, slightly bevelled as
at B, or cupped as at D. If left flat or only slightly bevelled as at B,
they are liable, if of steel and not hardened, or if of iron and
case-hardened only, to bulge out as at C. This prevents them from
slacking back easily or prevents removal if necessary, and even though
of hardened steel they do not grip very firmly. On this account their
points are sometimes made conical, as at A. This form, however,
possesses a disadvantage when applied to a piece of work that requires
accurate adjustment for position, inasmuch as it makes a conical
indentation in the work, and unless the point be moved sufficiently to
clear this indentation the point will fall back into it; hence the
conical point is not desirable when the piece may require temporary
fixture to find the adjustment before being finally screwed home. For
these reasons the best form of set screw end is shown at D, the outside
of the end being chamfered off and the inside being cupped, as denoted
by the dotted lines. This form cuts a ring in the work, but will hold
sufficiently for purposes of adjustment without being screwed home
firmly.
In some cases the end of the set screw is tapped through the enveloping
piece (as a hub) and its end projects into a plain hole in the internal
piece of the work, and in this case the end of the thread is turned off
for a distance of two or three threads, as at A in Fig. 390. Similarly,
when the head of the screw is to act or bear upon the work, the thread
may be turned off as at B in the figure.
When a bolt has no head, but is intended to screw into the work at one
end, and receive a nut at the other, it is termed a stud or standing
bolt. The simplest form of standing bolt is that in which it is parallel
from end to end with a thread at each end, and an unthreaded part in the
middle, but since standing bolts or studs require to remain fixed in the
work, it is necessary to screw them tightly into their places, and
therefore firmly home. This induces the difficulty that some studs may
screw a trifle farther into the work than others, so that some of the
stud ends may project farther through the nuts than others, giving an
appearance that the studs have been made of different lengths. The
causes of this may be slight variations in the tapping of the holes and
the threading of the studs. If those that appear longest are taken out
and reduced to the lengths of the others, it will be found sometimes
that the stud on the second insertion will pass farther into the work
than at the first, and the stud will project less through the nut than
the others. To avoid this those protruding most may be worked backward
and forward with the wrench and thus induced to screw home to the
required distance, but it is better to provide to the stud a shoulder
against which it may screw firmly home; thus in Fig. 391 is a stud,
whose end A is to screw into the work, part B is to enter the hole in
the work (the thread in the hole being cut away at the mouth to receive
B). In this case the shoulder between B and C screwing firmly against
the face of the work, all the studs being made of equal length from this
shoulder to end E, then the thickness of the flange or work secured by
the nut being equal, the nuts will pass an equal distance on end D, and
E will project equally through all the nuts. The length of the plain
part C is always made slightly less than the thickness of the flange or
foot of the work to be bolted up, so that the nut shall not meet C
before gripping the flange surface.
There are, however, other considerations in determining the shape and
size of the parts A and C of studs.
Thus, suppose a stud to have been in place some time, the nut on end E
being screwed firmly home on the work, and perhaps somewhat corroded on
E. Then the wrench pressure applied to the nut will be in a direction to
unscrew the stud out of the work, and if there be less friction between
A and the thread in the work than there is between D and the thread in
the nut, the stud and not the nut will unscrew. It is for this purpose
that the end A requires firmly screwing into the work. But in the case
of much corrosion this is not always sufficient, and the thread A is
therefore sometimes made of a larger diameter than the thread at D. In
this case the question at once arises, What shall be the diameter of the
plain part C?
[Illustration: Fig. 388.]
[Illustration: Fig. 389.]
[Illustration: Fig. 390.]
[Illustration: Fig. 391.]
If it be left slightly larger than D, but the depth of the thread less
than A, then it may be held sufficiently firmly by the fit of the
threads (without the aid of screwing against a shoulder) to prevent
unscrewing when releasing the nut, and may be screwed within the work
until its end projects the required distance; thus all the studs may
project an equal distance, but there will be the disadvantage that when
the studs require removing and are corroded the plain part is apt to
twist off, leaving the end A plugging the hole. The plain part C may be
left of same diameter as A, both being larger than D; but in this case
the difficulty of having all the studs project equally when screwed
home, as previously mentioned, is induced; hence C may be larger than A,
and a shoulder left at B, as in the figure; this would afford excellent
facility for unscrewing the stud to remove it, as well as insuring equal
projection of E. The best method of all is, so far as quality goes, to
make the plain part C square, as in Fig. 392, which is an English
practice, the square affording a shoulder to screw up against and secure
an equal projection while serving to receive a wrench to put in or
remove the stud. In this case the holes in the flange or piece bolted up
being squared, the stud cannot in any case unscrew with the nut. The
objection to this squared stud is that the studs cannot be made from
round bar iron, and are therefore not so easily made, and that the
squaring of the holes in the flange or part of the work supported by the
stud is again extra work, and for these reasons studs with square
instead of cylindrical mid-sections have not found favor in the United
States.
[Illustration: Fig. 392.]
[Illustration: Fig. 393.]
An excellent method of preventing the stud from unscrewing with the nut
is to make the end A longer than the nut end, as in Fig. 393, so that
its threads will have more friction; and this has the further advantage
that in cast iron it serves also to make the strength of the thread
equal to that of the stud. As the faces of the nuts are apt when screwed
home to score or mark the face of the work, it adds to the neatness of
the appearance to use a washer W beneath the nut, which distributes the
pressure over a greater area of work surface.
In some practice the ends A of studs are threaded taper, which insures
that they shall fit tight and enables their more easy extraction.
[Illustration: Fig. 394.]
An excellent tool for inserting studs of this kind to the proper
distance is shown in Fig. 394. It consists of a square body _a_ threaded
to receive the stud whose end is shown at _c_. The upper end is threaded
to receive an adjusting screw _b_, which is screwed in so that its end
_d_ meets the end _c_ of the stud. It is obvious that _b_ may be so
adjusted that when _a_ is operated by a wrench applied to its body until
its end face meets the work and the stud is inserted to the proper
depth, all subsequent studs may be put into the same depth.
[Illustration: Fig. 395.]
When the work pivots upon a stem, as in Fig. 395, the bolt is termed a
standing pin, and as in such cases the stem requires to stand firm and
true it is usual to provide the pin with a collar, as shown in the
figure, and to secure the pivoted piece in place with a washer and a
taper pin because nuts are liable to loosen back of themselves.
Furthermore, a pin and washer admit of more speedy disconnection than a
nut does, and also give a more delicate adjustment for end fit.
In drilling the tapping holes for standing bolts, it is the practice
with some to drill the holes in cast iron of such a size that the tap
will cut three-quarters only of a full thread, the claim being that it
is as strong as a full thread. The difference in strength between a
three-quarter and a full thread in cast iron is no doubt practically
very small indeed, while the process of tapping is very much easier for
the three-quarter full thread, because the tap may, in that case, be
wound continuously forward without backing it at every quarter or half
revolution, as would otherwise be necessary, in order to give the oil
access to the cutting edges of the tap--and oil should always be used in
the process of tapping (even though on cast iron it causes the cuttings
to clog in the flutes of the tap, necessitating in many cases that the
tap be once or twice during the operation taken out, and the cuttings
removed) because the oil preserves the cutting edges of the tap teeth
from undue abrasion, and, therefore, from unnecessarily rapid dulling.
With a tap having ordinarily wide and deep flutes, and used upon a hole
but little deeper than the diameter of the tap, the cuttings due to
making a three-quarter full thread will not more than fill the flutes of
the tap by the time its duty is performed. We have also to consider that
with a three-quarter full thread it is much easier to extract the
standing bolt when it is necessary to do so, so that all things
considered it is permissible to have such a thread, providing the
tapping hole does not pass through into a cylinder or chamber requiring
to be kept steam-tight, for in that case the bolt would be almost sure
to leak. As a preventive against such leakage, the threads are sometimes
cut upon the standing bolts without having a terminal groove, and are
then screwed in as far as they will go; the termination of the thread
upon the standing bolt at the standing or short end being relied upon to
jam into and close up the thread in the hole. A great objection to this,
however, is the fact that the bolts are liable to screw into the holes
to unequal depths, so that the outer ends will not project an equal
distance through the nuts, and this has a bad appearance upon fine work.
It is better, then, in such a case, to tap the holes a full thread, the
extra trouble involved in the tapping being to some extent compensated
for in the fact that a smaller hole, which can be more quickly drilled,
is required for the full than for the three-quarter thread.
The depth of the tapping hole should be made if possible equal to one
and a half times the diameter of the tap, so that in case the hole
bottoms and the tap cannot pass through, the taper, and what is called
in England the second, and in the United States the plug tap, will
finish the thread deep enough without employing a third tap, for the
labor employed in drilling the hole deeper is less than that necessary
to the employment of a third tap. If the hole passes through the work,
its depth need not, except for cast-iron holes, be greater than 1/8 inch
more than the diameter of the bolt thread, which amount of excess is
desirable so that in case the nut corrodes, the nut being as thick as
the diameter of the tap, and therefore an inch less than the depth of
the hole at the standing end, will be more likely to leave the stud
standing than to carry it with it when being unscrewed.
[Illustration: Fig. 396.]
When it is desirable to provide that bolts may be quickly removed, the
flanges may be furnished with slots, as in Fig. 396, so that the bolts
may be passed in from the outside, and in this case it is simply
necessary to slacken back the nut only. It is preferable, however, in
this case to have the bolt square under the head, as in Fig. 397, so as
to prevent the bolt from turning when screwing up or unscrewing the nut.
The bolt is squared at A, which fits easily into the flange. The
flanges, however, should in this case be of ample depth or thickness to
prevent their breakage, twice the depth of the nut being a common
proportion.
[Illustration: Fig. 397.]
[Illustration: Fig. 398.]
In cases where it is inconvenient for the bolt head to pass through the
work a [T] groove is employed, as in Fig. 398. In this case the bolt
head may fit easily at A B to the sides A B of the groove, so that while
the bolt head will slide freely along the groove, the head, being
square, cannot turn in the slot when the nut is screwed home. This,
however, is more efficiently attained when there is a square part
beneath the bolt head, as in Fig. 399, the square A of the bolt fitting
easily to the slot B of the groove.
[Illustration: Fig. 399.]
[Illustration: Fig. 400.]
When it is undesirable that the slots run out to the edge of the work
they may terminate in a recess, as at A in Fig. 400, which affords
ingress of the bolt head to the slot; or the bolt head may be formed as
in Fig. 401, the width A B of the bolt head passing easily through the
top A B of the slot, and the bolt head after its insertion being turned
in the direction of the arrow, which it is enabled to do by reason of
the rounded corners C D. In this case, also, there may be a square under
the head to prevent the bolt head from locking in the slot, but the
corners of the square must also be rounded as in Fig. 402.
[Illustration: Fig. 401.]
[Illustration: Fig. 402.]
The underneath or gripping surface of a bolt head should be hollow, as
at A in Fig. 403, rather than rounding as at B, because, if rounding,
the bolt will rotate with the nut when the latter grips the work
surface. It should also be true with the axial line of the bolt so as to
bear fairly upon the work without bending. The same remarks apply to the
bedding surface of the nut, because to whatever amount the face is out
of true it will bend the threaded end of the bolt, and this may be
sufficient to cause the bolt to break.
[Illustration: Fig. 403.]
In Fig. 404, for example, is shown a bolt and nut, neither of which bed
fair, being open at A and B respectively, and it is obvious that the
strain will tend to bend or break the bolt across the respective dotted
lines C, D. In the case of the nut there is sufficient elasticity in the
thread to allow of the nut forcing itself to a bed on the work, the bolt
bending; but in the case of the bolt head the bending is very apt to
break off the bolt short in the neck under the head. In a tap bolt where
the wrench is applied to the bolt head, the rotation, under severe
strain, of the head will usually cause it to break off in all cases
where the bolt is rigidly held, so that it cannot cant over and allow
the head to bed fair.
[Illustration: Fig. 404.]
A plain tap bolt should be turned up along its body, because if out of
true the hole it passes through must be made large enough to suit the
eccentricity of the bolt, or else a portion of the wrench pressure will
be expended in rotating the bolt in the hole instead of being expended
solely in screwing the bolt farther into the work.
It is obvious therefore, that if a tap bolt be left black the hole it
passes through must be sufficiently large to make full allowance for the
want of truth in the bolt. For the same reasons the holes for tapped
bolts require to be tapped very true.
Black studs possess an advantage (over tap bolts) in this respect,
inasmuch as that if the holes are not tapped quite straight the error
may be to some extent remedied by screwing them fully home and then
bending them by hammer blows.
Nuts are varied in form to suit the nature of the work. For ordinary
work, as upon bolts, their shape is usually made to conform to the shape
of the bolt head, but when the nut is exposed to view and the bolt head
hidden, the bolt end and the nut are (for finished work) finished while
the bolt heads are left black.
[Illustration: Fig. 405.]
[Illustration: Fig. 406.]
The most common form of hexagon nut is shown in Fig. 405, the upper edge
being chamfered off at an angle of about 40°. In some cases the lower
edge is cut away at the corners, as in Fig. 405 at A, the object being
to prevent the corners of the nut from leaving a circle of bearing marks
upon the work, but this gives an appearance at the corners that the nut
does not bed fair. Another shape used by some for the end faces of deep
nuts, that is to say, those whose depth exceeds the diameter of the
bolt, is shown in Fig. 406. Nuts of extra depth are used when, from the
nut being often tightened and released, the thread wear is increased,
and the extra thread length is to diminish the wear.
To avoid the difficulty of having some of the bolt ends project farther
through some nuts than others on a given piece of work, as is liable to
occur where the flanges to be bolted together are not turned on all four
radial faces, the form of nut shown in Fig. 407 is sometimes employed,
the thread in the nut extending beyond the bolt end.
[Illustration: Fig. 407.]
[Illustration: Fig. 408.]
As an example of the application of this nut, suppose a cylinder cover
to be held by bolts, then the cylinder flange not being turned on its
back face is usually of unequal thickness; hence to have the bolt ends
project equally through the nuts, each bolt would require to be made of
a length to suit a particular hole, and this would demand that each hole
and bolt be marked so that they may be replaced when taken out, without
trying them in their places. Another application of this nut is to make
a joint where the threads may be apt to leak. In this case the mouth of
the hole is recessed and coned at the edge; the nut is chamfered off
with a similar cone, and a washer W, Fig. 408, is placed beneath the nut
to compress and conform to the coned recess; thus with the aid of a
cement of some kind, as red or white lead (usually red lead), a tight
joint may be made independent of the fit of the threads.
When the hole through which the bolt passes is considerably larger in
diameter than the bolt, the flange nut shown in Fig. 409 is employed,
the flange covering the hole. A detached washer may be used for the same
purpose, providing that its hole fit the bolt and it be of a sufficient
thickness to withstand the pressure and not bend or sink into the hole.
[Illustration: Fig. 409.]
[Illustration: Fig. 410.]
Circular nuts are employed where, on account of their rotating at high
speed, it is necessary that they be balanced as nearly as possible so as
not to generate unbalanced centrifugal force. Fig. 410 represents a nut
of this kind: two diametrically opposite flat sides, as A, affording a
hold for the wrench. Other forms of circular nuts are shown in Figs. 411
and 412. These are employed where the nuts are not subject to great
strain, and where lightness is an object.
[Illustration: Fig. 411.]
[Illustration: Fig. 412.]
That in Fig. 411 is pierced around its circumference with cylindrical
holes, as A, B, C, to receive a round lever or rod or a wrench, such as
shown in Fig. 459.
That shown in Fig. 412 has slots instead of holes in its circumference,
and the form of its wrench is shown in Fig. 461.
When nuts are employed upon bolts in which the strain of the duty is
longitudinal to the bolt, and especially if the direction of motion is
periodically reversed, and also when a bolt is subject to shocks or
vibrations, a single nut is liable to become loose upon the bolt, and a
second nut, termed a check nut, jamb nut, or safety nut, becomes
necessary, because it is found that if two nuts be employed, as in Fig.
413, and the second nut be screwed firmly home against the first, they
are much less liable to come loose on the bolt.
Considerable difference of practice exists in relation to the thickness
of the two nuts when a check nut is employed. The first or ordinary nut
is screwed home, and the second or check nut is then screwed home. If
the second nut is screwed home as firmly as the first, it is obvious
that the strain will fall mainly on the second. If it be screwed home
more firmly than the first, the latter may be theoretically considered
to be relieved entirely of the strain, while if it be screwed less
firmly home, the first will be relieved to a proportionate degree of the
strain. It is usual to screw the second home with the same force as
applied to the first, and it would, therefore, appear that the first
nut, being relieved of strain, need not be so thick as the first, but it
is to be considered that, practically, the first nut will always have
some contact with the bolt threads, because from the imperfections in
the threads of ordinary bolts the area and the force of contact is not
usually the same nor in the same direction in both nuts, unless both
nuts were tapped with the same tap and at about the same time.
When, for example, a tap is put into the tapping machine, it is at its
normal temperature, and of a diameter due to that temperature, but as
its work proceeds its temperature increases, notwithstanding that it may
be freely supplied with oil, because the oil cannot, over the limited
area of the tap, carry off all the heat generated by the cutting of a
tap rotated at the speeds usually employed in practice. As a result of
this increase of temperature, we have a corresponding increase in the
diameter of the tap, and a variation in the diameter of the threads in
the nuts. The variation in the nuts, however, is less than that in the
tap diameter, because as the heated tap passes through the nut it
imparts some of its heat to the nut, causing it also to expand, and
hence to contract in cooling after it has been tapped, and, therefore,
when cold, to be of a diameter nearer to that of the tap.
Furthermore, as the tap becomes heated it expands in length, and its
pitch increases, hence here is another influence tending to cause the
pitches of the nut threads to vary, because although the temperature of
the tap when in constant use reaches a limit beyond which, so long as
its speed of rotation is constant, it never proceeds; yet, when the tap
is taken from the machine to remove the tapped nuts which have collected
on its shank, and it is cooled in the oil to prevent it from becoming
heated any more than necessary, the pitch as well as the diameter of the
tap is reduced nearer to its normal standard.
[Illustration: Fig. 413.]
[Illustration: Fig. 414.]
So far, then, as theoretical correctness, either of pitch or diameter in
nut threads, is concerned, it could only be attained (supposing that the
errors induced by hardening the tap could be eliminated) by employing
the taps at a speed of rotation sufficiently slow to give the oil time
to carry off all the heat generated by the cutting process. But this
would require a speed so comparatively slow as not to be commercially
practicable, unless followed by all manufacturers. Practically, however,
it may be considered that if two nuts be tapped by a tap that has become
warmed by use, they will be of the same diameter and pitch, and should,
therefore, have an equal area and nature of contact with the bolt
thread, supposing that the bolt thread itself is of equal and uniform
pitch. But the dies which cut the thread upon the bolt also become
heated and expanded in pitch. But if the temperature of the dies be the
same as that of the tap, the pitches on both the bolt and in the nut
will correspond, though neither may be theoretically true to the
designated standard.
In some machines for nut tapping the tap is submerged in oil, and thus
the error due to variations of temperature is practically eliminated,
though even in this case the temperature of the oil will gradually
increase, but not sufficiently to be of practical moment.
Let it now be noted that from the hardening process the taps shrink in
length and become of finer pitch, while the dies expand and become of
coarser pitch, and that this alone precludes the possibility of having
the nut threads fit perfectly to those on the bolt. It becomes apparent,
then, that only by cutting the threads in the lathe, and with a
single-toothed lathe tool that can be ground to correct angle after
hardening, can a bolt and nut be theoretically or accurately threaded.
Under skilful operation, however, both in the manufacture of the
screw-cutting tools and in their operation, a degree of accuracy can be
obtained in tapped nuts and die-threaded bolts that is sufficient with a
single nut for ordinary uses, but in situations in which the direction
of pressure on the nut is periodically reversed, or in which it is
subject to shocks or vibrations, the check nut becomes necessary, as
before stated.
An excellent method of preventing a nut from slackening back of itself
is shown in the safety nut in Fig. 414; it consists of a second nut
having a finer thread than the first one, so that the motion of the
first would in unscrewing exceed that of the second, hence the locking
is effectually secured.
[Illustration: Fig. 415.]
Work may be very securely fastened together by the employment of what
are called differential screws, the principle of whose action may be
explained with reference to Fig. 415, which is extracted from
"Mechanics." It represents a piston head and piston rod secured together
by means of a differential screw nut. The nut contains an internal
thread to screw on the rod, and an external one to screw into the piston
head, but the internal thread and that on the rod differ from the
external one, and that in the head by a certain amount, as say one tenth
of the pitch. The nut itself is furnished with a hexagonal head, and
when screwed into place draws the two parts together with the same power
as a screw having a pitch equal to the difference between the two
pitches.
[Illustration: Fig. 416.]
When putting the parts together the nut is first screwed upon the rod B.
The outside threads are then entered into the thread in the piston C,
and by means of a suitable wrench the nut is screwed into the proper
depth. As shown in the engraving, the nut goes on to the rod a couple of
threads before it is entered in the piston. The tightening then takes
place precisely as though the nut had a solid bearing on the piston and
a fine thread on the rod, the pitch of which is equal to the difference
between the pitches of the two threads. Fig. 416 shows its application
to the securing of a pump plunger upon the end of a piston-rod. In this
case, as the rod does not pass through the nut, the latter is provided
with a cap, which covers the end of the rod entirely.
[Illustration: Fig. 417.]
The principle of the differential screw may be employed to effect very
fine adjustments in place of using a very fine thread, which would soon
wear out or wear loose. Thus in Fig. 417 is shown the differential foot
screws employed to level astronomical instruments. C D is a foot of the
instrument to be levelled. It is threaded to receive screw A, which is
in turn threaded to receive the screw B, whose foot rests in the recess
or cup in E F. Suppose the pitch of screw A is 30 per inch, and that of
B is 40, and we have as follows. If A and B are turned together the foot
C D is moved the amount due to the pitch of A. If B is turned within a
the foot is moved the amount due to the pitch of B. If A is turned the
friction of the foot of B will hold B stationary, and the motion of C D
will equal the difference between the pitches of the threads of A and B.
Thus one revolution of A forward causes it to descend through C D 1/30
inch (its pitch), tending to raise C D 1/30 inch. But while doing this
it has screwed down upon the thread of B 1/40 inch (the pitch of B) and
this tends to lower C D, hence C D is moved 1/120 inch, because
1/30-1/40 = 1/120.
To cause a single nut to lock itself and dispense with the second or
jamb nut, various expedients have been employed. Thus in Fig. 418 is
shown a nut split on one side; after being threaded the split is closed
by hammer blows, appearing as shown in the detached nut. Upon screwing
the nut upon the bolt the latter forces the split nut open again by
thread pressure, and this pressure locks the nut. Now there will be
considerable elasticity in the nut, so that if the thread compresses on
its bearing area, this elasticity will take up the wear or compression
and still cause the threads to bind. Sometimes a set screw is added to
the split, as in Fig. 419, in which case the split need not be closed
with the hammer.
Another method is to split the nut across the end as shown in Fig. 420,
tapping the nut with the split open, then closing the split by hammer
blows. Here as before the nut would pass easily upon the bolt until the
bolt reached the split, when the subsequent threads would bind. In yet
another design, shown in Fig. 421, four splits are made across the end,
while the face of the nut is hollowed, so that a flat place near each
corner meets the work surface. The pressure induced on these corners by
screwing the nut home is relied on in this case to spring the nut,
causing the thread at the split end to close upon and grip the bolt
thread.
Check nuts are sometimes employed to lock in position a screw that is
screwed into the work, thus screws that require to be operated to effect
an adjustment of length (as in the case of eccentric rods and eccentric
straps) are supplied with a check nut, the object being to firmly lock
the screw in its adjusted position.
The following are forms of nuts employed to effect end adjustments of
length, or to prevent end motion in spindles or shafts that rotate in
bearings.
Fig. 422 shows two cylindrical check nuts, the inner one forming a
flange for the bearing. The objection to this is that in screwing up the
check nut the adjustment of the first nut is liable to become altered in
screwing up the second one, notwithstanding that the first be held by a
lever or wrench while the second is screwed home.
Another method is to insert a threaded feather in the adjustment nut and
having at its back a set screw to hold the nut in its adjusted position,
as in Fig. 423. In this case the protruding head of the set screw is
objectionable. In place of the feather the thread of the spindle may be
turned off and a simple set screw employed, as in Fig. 424; here again,
however, the projecting set screw head is objectionable. The grip of an
adjustment nut may be increased by splitting it and using a pinching or
binding screw, as in Fig. 425, in which case the bore of the thread is
closed by the screw, and the nut may be countersunk to obviate the
objection of a projecting head. For adjusting the length of rods or
spindles a split nut with binding screws, such as shown in Fig. 426, is
an excellent and substantial device. The bore is threaded with a
right-hand thread at one end and a left-hand one at the other, so that
by rotating the nut the rod is lengthened or shortened according to the
direction of rod rotation. Obviously a clamp nut of this class, but
intended to take up lost motion or effect end adjustment, may be formed
as in Fig. 427, but the projecting ears or screw are objectionable.
[Illustration: Fig. 429.]
Where there is sufficient length to admit it an adjustment nut, such as
in Fig. 428, is a substantial arrangement. The nut A is threaded on the
spindle and has a taper threaded split nut to receive the nut B. Nut A
effects the end adjustment by screwing upon the spindle, and is
additionally locked thereon by screwing B up the taper split nut,
causing it to close upon and grip the spindle.
[Illustration: Fig. 430.]
Lost motion in square threads and nuts may be taken up by forming the
nut in two halves, A and B, in Fig. 429 (A being shown in section) and
securing them together by the screws C C. The lost motion is taken up by
letting the two halves together by filing away the joint face D of
either half, causing the thread in the nut to bear against one side only
of the thread of the screw. The same end may be accomplished in nuts for
[V]-shaped threads by forming the nut either in two halves, as shown in
Fig. 430, in which A is a cap secured by screws B, the joint face C
being filed away to take up the lost motion. Or the nut may be in one
piece with the joint C left open, the screws B crossing the nut upon the
screw by pressure. In this case the nut closes upon the circumference of
the thread, taking up the wear by closing upon both sides of the thread
instead of on one side only as in the case of the square thread.
[Illustration: Fig. 431.]
[Illustration: Fig. 432.]
[Illustration: Fig. 433.]
In cases where nuts are placed under rapid vibration or motion they are
sometimes detained in their places by pins or cotters. The simplest form
of pin used for this purpose is the split pin, shown in Fig. 431. It is
made from half round wire and is parallel, and does not, therefore,
possess the capability of being tightened when the nut has become
loosened from wear. As the wire from which these pins are made is not
usually a full half circle the pins should, if the best results are to
be obtained, be filed to fit the hole, and in doing this, care should be
taken to have the pin bear fully in the direction of the split which is
longitudinal to the bolt, as shown in Fig. 432, where the pin is shown
with its ends opened out as is required to prevent the pin from coming
out. If the pin bears in a direction across the bolt as at A D, in Fig.
433, it will soon become loose.
[Illustration: _VOL. I._ =END-ADJUSTMENT AND LOCKING DEVICES.= _PLATE
IV_.
Fig. 418.
Fig. 419.
Fig. 420.
Fig. 421.
Fig. 422.
Fig. 423.
Fig. 424.
Fig. 425.
Fig. 426.
Fig. 427.
Fig. 428.]
Pins of this class are sometimes passed through the nut itself as well
as through the bolt; but when this is the case, there is the objection
that the nut cannot be screwed up to take up any wear, because in that
case the hole in the nut would not come fair with that in the bolt, and
the pin could not be inserted. When, therefore, such a pin passes
through the nut, lost motion must be taken up by placing an additional
or a thicker washer behind the nut. The efficiency of this pin as a
locking device is much increased by passing it through the nut, because
its bearing, and, therefore, wearing area, is increased, and the pin is
prevented from bending after the manner shown in Fig. 434, as it is apt
to do under excessive wear, with the result that the end pressure of the
nut almost shears or severs the pin close to the perimeter of the bolt.
[Illustration: Fig. 434.]
[Illustration: Fig. 435.]
To enable the pin to take up the wear, it is a good plan to file on it a
flat place, which must be parallel to the sides of the pin-head and
placed against the nut-face. The hole in the bolt is in this case made
to fall slightly under the nut, as in Fig. 435, so that the flat place
is necessary to enable the pin to enter. By filing the flat place taper,
the lost motion that may ensue from wear may be taken up by simply
driving the pin in farther.
[Illustration: Fig. 436.]
[Illustration: Fig. 437.]
In place of this class of split pin, solid taper pins are sometimes
used, but these, if employed in situations where they are subject to jar
and vibration, are apt sometimes to come loose, especially if they be
given much taper, because in that case they do not wedge so tightly in
the hole. But if a taper pin be made too nearly parallel, it will drive
through too easily, and has less capability to take up the play due to
wear. An ordinary degree of taper is about 5/8 inch per foot of length,
but in long pins having ample bearing area, 1/2 inch per foot of length
is ample. To prevent taper pins from coming loose from vibration, they
are sometimes forged split at the small end, as in Fig. 436, and opened
out at that end after the manner shown in Fig. 432. This forms a very
secure locking device, and one easily applied. The split ends are closed
by hammer blows to remove the pin, and it is found that such pins may be
opened and closed many times without breaking, even though made of cast
steel. The heads and ends are rounded so as to prevent them from
swelling from the hammer blows necessary to drive them in and out. When
a taper pin is passed through a nut and bolt, it simply serves as a
locking device to secure the nut in position, and the lost motion due to
wear must be taken up by the application of a washer beneath the nut, as
already described. If, however, the taper pin be applied outside the
nut, it may be made to take up the wear, by filing on it a flat place,
and locating the hole in the bolt so that it will fall partly beneath
the nut, as shown in Fig. 435. In this case, the nut may be screwed up
to take up the wear, and the pin by being driven farther in will still
bear against the nut and prevent its slacking back.
Another and excellent locking device for bolts or nuts, is the cotter
shown in Fig. 437, which is sometimes forged solid and sometimes split,
as in the figure. By being made taper from A to B, it will take up the
wear if driven farther in. Its width gives it strength in the direction
in which it acts to lock, the overhanging head is to drive it out by,
and the bevelled corner C is to enable its easy insertion, because if
left sharp it would be liable to catch against the edge of the
cotter-way and burr up. If made split, its ends are opened out after it
is inserted, as shown at D. When closing the ends of either split
cotters or split pins to extract them it is better to close one side
first and bend it over a trifle too much, so that, when closing the
other side, by the time the pin is straightened the two ends will be
closed together, and extraction becomes easy.
[Illustration: Fig. 438.]
A very safe method in the case of a single nut or bolt head is to
provide a separate plate, as in Fig. 438. The plate P is provided with
three sides, corresponding to the sides of the hexagon, as shown, and in
the middle of these sides are cut the notches A B C, so that by giving
the nut N one-twelfth of a turn its corners D E would be held by the
notches B C, S being a small screw to hold P. It is obvious that a
simple set screw passed through the walls of the nut would grip the bolt
thread and serve to hold the nut, but this would damage the bolt thread,
and, furthermore, that thread would under jar or vibration compress and
let the set screw come loose.
A better plan than this is to provide a thick washer beneath the nut and
let a set screw pass through the washer and grip the bolt, fastening or
setting up the set screw after the nut is screwed home. This, however,
makes the washer a gripping piece and in no wise serves to lock the nut.
In addition to the washer a pin may project through the radial face of
the washer and into the work surface, which will prevent, in connection
with the set screw, both the bolt and the washer from turning.
When a bolt has no thread but is secured by a taper pin, set screw,
cotter, or device other than a nut, it is termed a pin. So, likewise, a
cylindrical piece serving as a pivot, or to hold two pieces together and
having no head, is termed a pin.
The usual method of securing a pin is by a set screw or by a taper pin
and a washer; and since the term pin applying to both may lead to
misunderstanding, the term bolt will here be applied to the large and
the term pin to the small or securing pin only.
The object of pins and washers is to secure an exact degree of fit and
permit of rapid connection or disconnection. An application of a taper
pin and washer to a double eye is shown in Fig. 439. It is obvious, in
this case, the pin E will drive home until it fills the hole through the
bolt, and hence always to the same spot, so that the parts may be taken
apart and put together again rapidly, while the fit is self-adjusting,
providing that the pin fills the hole, bears upon the groove in the
washer, and is driven home, so that by first letting the pin bind the
washer W slightly too tight, and then filing the radial faces of the
joint to a proper fit (which will ease the bearing of the pin on the
washer), an exact degree of fit and great accuracy may be obtained,
whereas when a nut is used it is difficult to bring the nut to the exact
same position when screwing it home. When the joints are to be thus
fitted, it is a good plan to drill the pin-hole (through the bolt) so
that its centre falls coincident with the face of the washer; to then
file out the grooves in the washer not quite deep enough. The pin may
then be filed to fit the hole through the bolt, but left slightly too
large, so that it shall not pass quite far enough through the bolt. The
joint faces may then be filed true, and when finished, the parts may be
put together, and the groove through the washer and hole through the
bolt may be simultaneously finished by reaming with a taper reamer. This
will leave the job a good fit, with a full bearing, without much
trouble, the final reaming letting the taper pin pass to its proper
distance through the bolt.
[Illustration: Fig. 439.]
[Illustration: Fig. 440.]
Taper pins are sometimes employed to secure in position a bolt that
rotates, or one that requires locking in position, in situations in
which there is no room for the bolt end to project and receive a nut or
washer. Examples of these kinds are shown in section in Figs. 440 and
441. In 441, B is a stud pin, to rotate in the bore of A. C is a semi
circular groove in B, and P a taper pin entering one-half in the groove
C and one-half in B, thus preventing B from moving endwise in A, while
at the same time permitting its free rotation. In this case it is best
to fit B to its place, a fit tight enough to hold it firmly while the
pin-hole is drilled and reamed through A and B simultaneously, then B
can be put in the lathe, and the groove cut in to coincide with the
half-hole or groove caused in the pin by the drilling, and after the
groove is turned the stud pin may be eased to the required degree of
working fit. The process for Fig. 440 is precisely the same, except that
no groove turning or easing of the pin will be necessary, because the
pin being locked in position may be left a tight fit. If, however, it is
considered desirable to give the taper pin in Fig. 440 a little draft,
so that any looseness (that may occur to the pin or stud) from wear may
be taken up, then after the taper pin-hole has been drilled and reamed,
the pin or stud (D in the figure) may be taken out, and its taper
pin-hole _in the arm E_ may be filed out all the way through on one
side, as denoted by the dotted half-circle. This will give draft to the
pin and allow it to drive farther through and grip the pin as it wears
smaller.
If a bolt and nut fit too tightly in their threads the nut may be wound
back and forth upon the bolt under free lubrication, which will ease the
fit by wearing away or compressing that part of the thread surface that
is in contact. If this should not suffice we may generally ease a nut
that fits so tight that it cannot be screwed upon the bolt with an
ordinary wrench, by screwing the nut on a thread or two, then rest it on
an iron block, and lightly hammer its sides; it will loosen its fit, and
if continued, the nut may be made to pass down the bolt comparatively
easily. Now, in this operation, it is not that the nut has been
stretched, but that the points of contact on the threads have become
compressed and imbedded; we have, in other words, caused the shape of
each thread to conform nearer to that of the other than it is
practicable to make them, because of reasons explained in the remarks on
screw threads, and on taps.
[Illustration: Fig. 441.]
To remove nuts or bolts that have become corroded in their places, we
may adopt the following methods:--
If the nuts are so corroded that they will not unscrew with an ordinary
wrench, we may, if the standing bolts and the wrench are strong enough
to stand it, place a piece of gas or other pipe on the end of the
wrench, so as to get a longer leverage; and, while applying the power to
the wrench, we may strike the end face of the nut a few sharp blows with
the hammer, interposing a set chisel, if the nut is a small one, so as
to be sure to strike the nut in the proper place, and not rivet the
screw end. If the joint is made with tap bolts we may strike the bolt
heads with the hammer direct, using as before a light hammer and sharp
blows, which will, in a majority of cases, start the thread, after which
the wrench alone will usually suffice to unscrew it. If, however, this
is not effective, we should take a thick washer, large enough in its
bore to pass over the nut, and heat it to a yellow heat and place it
over the nut, and the nut heating more rapidly than the stud or standing
bolt, will be proportionately expanded and loosened; and, furthermore,
the iron becomes stronger by being heated, providing the temperature
does not exceed about 400°. If standing bolts or studs are employed on
the joint, the heating is still advantageous, for the increase of
strength more than compensates for the expansion. In this case the
heating, however, may be performed more slowly, so that the hole may
also become heated, and the bolt, therefore, not made a tighter fit by
its excessive expansion. So also, in taking out the standing bolts or
studs, heating them will often enable one to extract them without
breaking them off in the hole, which would necessitate drilling out the
broken piece or part. If, however, this should become necessary, we may
drill a hole a little smaller than the diameter of the bottom of the
bolt thread, and then drive into the hole a taper square reamer, as
shown in Fig. 442, in which W represents the work, R the square reamer,
and S the drilled screw end, and then, with a wrench applied to the
reamer, unscrew the bolt thread. If this plan fails there is no
alternative, after drilling the hole, but to take a round-nosed cape or
cross-cut chisel and cut out the screw as nearly as possible, then pick
out the thread at the entrance of the hole, and insert a plug tap to cut
out the remaining bolt thread.
To take out a standing bolt, take two nuts and screw them on the bolt
end; then hold the outer one still with a wrench and unscrew the inner
one tightly against it. We may then remove the wrench from the outer or
top nut, and unscrew the bolt by a wrench applied to the bottom or inner
one. If the thread of a standing bolt has become damaged or burred, we
can easily correct the evil by screwing a solid die or die nut down it,
applying a little oil to preserve the cutting edge of the nut. If it is
found impossible to take off a corroded nut without twisting off the
standing bolt, it is the better plan to sacrifice the nut in order to
save the bolt; and we may first hold a hammer beneath the nut, and take
a cold chisel, and holding it so that the cutting edge stands parallel
with the chamfered edge of the nut, and slanting it at an angle obtuse
to the direction in which the nut in unscrewing would travel, strike it
a few sharp blows, using a light hand-hammer; and this will often start
it, especially if the nut is heated as before directed. The hammer held
beneath the nut should be a heavy one, and should be pressed firmly
against the square or hexagon side of the nut, the object being to
support it, and thus prevent the standing bolt from bending or breaking,
as it would otherwise be very apt to do. If this plan succeeds, the nut
may, for rough work, be used over again, the burr raised by the chisel
head being hammered down to close it as much as possible before filing
it off. By holding the chisel precisely as directed, the seating of the
nut acts to support it, and thus aids the heavy hammer in its duty. If
this procedure fails we may cut the nut off, and thus preserve the bolt.
[Illustration: Fig. 442.]
To do this, we must use a cross-cut or cape chisel, and cut a groove
from the end face to the seating of the nut--a narrow groove will do,
and two may be cut if necessary; light cuts should be taken, and the
chisel should be ground at a keen angle, so that it will keep to its cut
when held at an angle, as nearly parallel to the centre line of the
length of the bolt as possible, in which case the force of the blows
delivered upon the chisel head will be in a direction not so liable to
bend the bolt. The groove or grooves should be cut down nearly to the
tops of the bolt threads, and then a wrench will unscrew the nut or else
cause it to open if one, and break in halves, if two grooves were cut.
After the nuts are all taken off, we may take a hammer and two or three
wedges, or chisels (according to the size of the joint), and drive them
an equal distance into the joint, striking one chisel first, and the
diametrically opposite one next, and going over all the wedges to keep
an equal strain upon each. If the joint resists this method, we may take
a hammer and strike blows between the standing bolts on the outside
face, interposing a block of hard wood to prevent damage to the face,
and holding the wood so that the hammer strikes it endwise of the grain;
and this will, in most cases, loosen the material of which the joint is
made, and break the joint. If, however, the joint, after repeated
trials, still resists, we may employ the hammer without the
interposition of the wood, using a copper or lead hammer, if one is at
hand, so as not to cause damage to the face of the work. To facilitate
the entrance of the wedges, grooves should be cut in the joint of one
face, their widths being about an inch, and their depth 1/16 inch.
WASHERS.--Washers are placed upon bolts for the following purposes.
First, to provide a smooth seating for the nut in the case of rough
castings. Second, to prevent the nut corners from marking and marring
the surface of finished work. Thirdly, to give a neat finish, and in
some cases to increase the bearing area of the nut and provide an
elastic cushion to prevent the nut from loosening. Washers are usually
of wrought iron, except in the case of brass nuts, when the washers also
are of brass. The standard sizes adopted by the manufacturers in the
United States for wrought iron washers is given in the following
table:--
MANUFACTURERS' STANDARD LIST.
Adopted by "The Association of Bolt and Nut Manufacturers of the United
States," at their meeting in New York, December 11th, 1872.
+-----------+---------+-------------+---------+
| Diameter. | Size of | Thickness | Size of |
| | Hole. | Wire Gauge. | Bolt. |
+-----------+---------+-------------+---------+
| 1/2 | 1/4 | No. 18 | 3/16 |
| 5/8 | 5/16 | " 16 | 1/4 |
| 3/4 | 5/16 | " 16 | 1/4 |
| 7/8 | 3/8 | " 16 | 5/16 |
| 1 | 7/16 | " 14 | 3/8 |
+-----------+---------+-------------+---------+
| 1-1/4 | 1/2 | " 14 | 7/16 |
| 1-3/8 | 9/16 | " 12 | 1/2 |
| 1-1/2 | 5/8 | " 12 | 9/16 |
+-----------+---------+-------------+---------+
| 1-3/4 | 11/16 | " 10 | 5/8 |
| 2 | 13/16 | " 10 | 3/4 |
+-----------+---------+-------------+---------+
| 2-1/4 | 15/16 | " 9 | 7/8 |
| 2-1/2 | 1-1/16 | " 9 | 1 |
| 2-3/4 | 1-1/4 | " 9 | 1-1/8 |
| 3 | 1-3/8 | " 9 | 1-1/4 |
| 3-1/2 | 1-1/2 | " 9 | 1-3/8 |
+-----------+---------+-------------+---------+
[Illustration: Fig. 443.]
[Illustration: Fig. 444.]
The various forms of wrenches employed to screw nuts home or to remove
them are represented in the following figures. Fig. 443 represents what
is known as a solid wrench, the width between the jaws a being an easy
fit to the nuts across the flats. The opening between the jaws being at
an angle to the body enables the wrench to be employed in a corner which
would be too confined to receive a wrench in which the handle stood in a
line with the jaws, because in that common form of wrench the position
of the jaws relative to the handle would be the same whether the wrench
be turned over or not, whereas with the jaws at an angle as in the
figure, the wrench may be applied to the nut, rotating it a certain
distance until its handle meet an abutting piece, flange, or other
obstruction, and then turned over and the jaw embracing the same two
sides of the nut the handle will be out of the way and may again operate
the nut.
[Illustration: Fig. 445.]
In some cases each end of the wrench is provided with jaws, those at one
end standing at the same angle but being on the opposite side of the
wrench.
The proper angle of the jaws to the centre line of the jaws may be
determined as follows:--The most desirable angle is that which will
enable the wrench to operate the nut with the least amount of
wrench-motion, an object that is of great importance in cases where an
opening has to be provided to admit the wrench to the nut, it being
desirable to leave this opening as small as possible so as to impair the
solidity of the work as little as practicable. For a hexagon nut this
angle may be shown to be one of 15°, as in Fig. 444.
[Illustration: Fig. 446.]
[Illustration: Fig. 447.]
In Fig. 445, for example, the wrench is shown in the position in which
it will just engage the nut, and at the first movement it will move the
nut to the position shown in Fig. 446. The wrench is then turned upside
down and placed upon the nut as in Fig. 447, and moved to the position
shown in Fig. 448, thus moving the nut the sixth part of a revolution,
and bringing it to a position corresponding to that in Fig. 445, except
that it has moved the nut around to a distance equal to one of its
sides. Since the wrench has been moved twice to move the nut this
distance, and since there are six sides, it will take twelve movements
to give the nut a full revolution, and, there being 360° in the circle,
each movement will move the nut 30°, or one-twelfth of 360°, and
one-half of this must be the angle of the gripping faces of the jaws to
the body of the wrench. The width of the opening in the work to admit
the wrench in such a case as in Fig. 445 must be not less than 30°, plus
the width of the wrench handle, at the radius of the outer corner of the
opening.
[Illustration: Fig. 448.]
In the case of wrenches for square nuts it is similarly obvious that
when the nut makes one-eighth of a revolution its sides will stand in
the same position to receive the wrench that the nut started from, and
in one-eighth of a revolution there are 45°. As the wrench is applied
twice to the same side of the nut, its jaws must stand at one half this
angle (or 22-1/2°) to the handle.
[Illustration: Fig. 449.]
When a nut is in such a position that it can only be operated upon from
the direction of and in a line with the axis of the bolt, a box wrench
such as shown in Fig. 449, is employed, the cavity at B fitting over
the bolt head; but if there is no room to admit the cross handle, a hub
or boss is employed instead, and this hub is pierced with four radial
holes into which the point of a round lever may be inserted to turn the
wrench. Adjustable wrenches that may be opened and closed to suit the
varying sizes of nuts are represented in Figs. 450, 451, and 452. In
Fig. 450, A is the fixed jaw solid upon the square or rectangular bar E,
and passing through the wooden handle D. B is a sliding jaw embracing E,
and operated thereon by the screw C, whose head is serrated to afford a
good finger grip. Various modifications of this form of wrench are made;
thus, for example, in Fig. 451 A is the jaw, B a slotted shank, C the
handle, all made in one piece. D is the movable jaw having a sleeve
extension D´, and recesses which permit the jaw to slide on the shank
longitudinally, but which prevent it from turning. The movable jaw is
run to and from the nut or bolt head to be turned, by means of the screw
G.
[Illustration: Fig. 450.]
[Illustration: Fig. 451.]
In another class of adjustable wrench the jaws slide one within the
other; thus in Fig. 452, the fixed jaw of the wrench forms a part of the
handle, and is hollowed out and slotted to receive the stem of the loose
jaw, which plays therein, being guided by ribs in the slot, which take
into grooves in the stem of the loose jaw. A screw with a milled head
and a grooved neck serves to propel the loose jaw, being stopped from
moving longitudinally by a partly open fixed collar on the fixed jaw,
which admits the screw and engages the grooved neck of the same. The
threaded extremity of the screw engages a female screw in the loose jaw,
and while the same are engaged the screw cannot be released from the
embrace of the fixed collar, as it requires considerable lateral
movement to accomplish this.
[Illustration: Fig. 452.]
[Illustration: Fig. 453.]
Adjustable wrenches are not suited for heavy work because the jaws are
liable to spring open under heavy pressure and thus cause damage to the
edges of finished nuts, and indeed these wrenches are not suitable for
ordinary use on finely finished work unless the duty be light.
Furthermore, the jaws being of larger size than the jaws of solid
wrenches, will not pass so readily into corners, as may be seen from the
[S] wrench shown in Fig. 453. In the adjustable [S] wrench in Fig. 454,
each half is provided with a groove at one end and a tongue in the
other, so that when put together the tongues are detained in the
grooves. To open or close the wrench a right and left-hand screw is
tapped into the wrench as shown, the head being knurled or milled to
afford increased finger-grip.
[Illustration: Fig. 454.]
[Illustration: Fig. 455.]
In all wrenches the location of contact and of pressure on the nut is
mainly at the corners of the nut, and unless the wrench be a very close
fit, the nut corners become damaged. A common method of avoiding this is
to interpose between the wrench jaw and the nut a piece of soft metal,
as copper, sheet zinc, or even a piece of leather. The jaws of the
wrench are also formed to receive babbitt metal linings which may be
renewed as often as required. To save the trouble of adjusting an
accurately fitting wrench to the nut, Professor Sweet forms the jaws as
in Fig. 455, so that when moved in one direction the jaws will pass
around the nut without gripping it, but when moved in the opposite
direction the jaws will grip the nut but not damage the corners, while
to change the direction of a nut rotation it is simply necessary to turn
the wrench over.
[Illustration: Fig. 456.]
Fig. 456 represents a key wrench which is suitable for nuts of very
large size. The sliding jaw J is held by the key or wedge S, which is
operated by hammer blows. The projection at R is necessary to give
sufficient bearing to the sliding jaw.
[Illustration: Fig. 457.]
For use in confined places where but little handle-motion is obtainable,
the ratchet wrench is employed, consisting of a lever affording journal
bearing to a socket that fits the head of the bolt. The socket is
provided with a ratchet or toothed wheel in which a catch or pawl
engages. Fig. 457 represents the Lowell Wrench Company's ratchet wrench
in which a lag screw socket is shown affixed. The socket is removable so
that various sizes and shapes may be used with the same wrench. Each
socket takes two sizes of square and one of hexagon heads or nuts. So
long as the screw runs easily, it can be turned by the wooden handle
more conveniently and faster than by the fingers, and independently of
the ratchet motion. When this can no longer be done with ease, the
twelve-inch handle is brought into use to turn the screw home.
For carriage bolts used in woodwork that turn with the nut
notwithstanding the square under the head (as they are apt to do from
decay of the wood or from the bolt gradually working loose) the form of
wrench shown in Fig. 458 is exceedingly useful, it is driven into the
wood by hammer blows at A. The bevelled edges cause the jaws to close
upon the head in addition to the handle-pressure.
[Illustration: Fig. 458.]
For circular nuts such as was shown in Fig. 411, the pin wrench or
spanner wrench shown in Fig. 459 is employed, the pin P fitting into the
holes in the nut circumference. The pin P should be parallel and slope
very slightly in the direction of A, so that it may not meet and bruise
the mouths of the pin-holes, A, B, C. The pin must, of course, pass
easily into the pin-holes, and would, if vertical, therefore meet the
edge of the hole at the top, bruising it and causing the wrench to
spring or slip out, as would be the case if the pin stood in the
direction of B.
[Illustration: Fig. 459.]
[Illustration: Fig. 460.]
It is obvious that to reverse the motion of the nut it is necessary to
reverse the position of the wrench, because the handle end must, to
enable the wrench to grip the work, travel in advance of the pin end. To
avoid this necessity Professor Sweet forms the wrench as in Fig. 460, in
which case it can operate on the nut in either direction without being
reversed.
When a circular nut has its circumference provided with notches as was
shown in Fig. 412 the wrench is provided with a rectangular piece as
shown in Fig. 461. This piece should slope in the direction of a for the
reasons already explained with reference to the cylindrical pin in Fig.
459. It is obvious, however, that this wrench also may be made upon
Professor Sweet's plan, in which case the pin should be straight.
[Illustration: Fig. 461.]
KEYS AND KEYWAYS.--Keys and keyways are employed for two purposes--for
locking permanently in a fixed position, and for locking and adjusting
at the same time. Keys that simply permanently lock are usually simply
embedded in the work, while those that adjust the parts and secure them
in their adjusted position usually pass entirely through the work. The
first are termed sunk keys and keyways, the latter adjusting keys and
through keyways.
[Illustration: Fig. 462.]
The usual forms of sunk keyways are as follows:--Fig. 462 represents the
common sunk key, the head _h_ forming a gib for use in extracting the
key, which is done by driving a wedge between the head and the hub of
the work.
[Illustration: Fig. 463.]
The flat key, sunk key, and feather shown in Fig. 463, are alike of
rectangular form, their differences being in their respective
thicknesses, which is varied to meet the form of key way which receives
them. The flat key beds upon a flat place upon the shaft, the sunk key
beds in a recess provided in the shaft, and the feather is fastened
permanently in position in the shaft. The hollow key is employed in
places where the wheel or pulley may require moving occasionally on the
shaft, and it is undesirable that the latter have any flat place upon it
or recess cut in it. The flat key is used where it is necessary to
secure the wheel more firmly without weakening the shaft by cutting a
keyway in it. The sunk key is that most commonly used; it is employed in
all cases where the strain upon the parts is great. The feather is used
in cases where the keyway extends along the shaft beyond the pulley or
wheel, the feather being fast in the wheel, and its protruding part a
working fit in the shaft keyway. This permits the wheel to be moved
along the shaft while being driven through the medium of the feather
along the keyway or spline. The heads of the taper keys are sometimes
provided with a set screw as in Fig. 464, which may be screwed in to
assist in extracting the key.
[Illustration: Fig. 464.]
[Illustration: Fig. 465.]
Fig. 465 represents an application of keys to a square shaft that has
not been planed true. The wheel is hung upon the shaft and four
temporary gib-headed keys are inserted in the spaces _a_, _a_, _a_, _a_,
in Fig. 465. (It may be mentioned here that similar heads are generally
forged upon keys to facilitate their withdrawal while fitting them to
their seats, the heads being cut off after the key is finally driven
home.) These sustain the wheel while the permanent keys, eight in
number, as shown in the figure at _b_, _b_, _b_, _b_, _b_, _b_, _b_,
_b_, are fitted, the wheel being rotated and tested for truth from a
fixed point, the fitting of the keys being made subservient to making
the wheel run true.
The proportions of sunk keys are thus given by the Manchester (England)
rule. The key is square in cross section and its width or depth is
obtained by subtracting 1/2 from the diameter of the shaft and dividing
the sum thus obtained by 8, and then adding to the subtrahend 1/4.
Example.--A shaft is 6 inches in diameter, what should be the cross
section dimensions of its key diameter of shaft?
6 - 1/2 = 5-1/2, 5-1/2 ÷ 8 = .687, and .687 + .25 = 937/1000 inch.
In general practice, however, the width of a key is made slightly
greater than its depth, and one-half its depth should be sunk in the
shaft.
[Illustration: Fig. 466.]
[Illustration: Fig. 467.]
Taper keys are tapered on their surfaces A and B in Fig. 466, and are
usually given 1/8-inch taper per foot of length. There is a tendency
either in a key or a set screw to force the hub out of true in the
direction of the arrow. It therefore causes the hub bore to grip the
shaft, and this gives a driving duty more efficient than the friction of
the key itself. But the sides also of the key being a sliding fit they
perform driving duty in the same manner as a feather which fits on the
sides A, D in Fig. 467, but are clear either top or bottom. In the
figure the feather is supposed to be fast in the hub and therefore free
at C, but were it fast in the shaft it would be free on the top face.
[Illustration: Fig. 468.]
[Illustration: Fig. 469.]
Fig. 468 represents a shaft held by a single set screw, the strain being
in the direction of the arrow, hence the driving duty is performed by
the end of the set screw and the opposite half circumference of the bore
and shaft. On account, however, of the small area of surface of the set
screw point the metal of the shaft is apt, under heavy duty and when the
direction of shaft rotation is periodically reversed, to compress (as
will also the set screw point unless it is of steel and hardened),
permitting the grip to become partly released no matter how tightly the
set screw be screwed home. On this account a taper key will under a
given amount of strain upon the hub perform more driving duty, because
the increased area of contact prevents compression. Furthermore, the
taper key will not become loose even though it suffer an equal amount of
compression. Suppose, for example, that a key be driven lightly to a
fair seating, then all the rest of the distance to which the key is
driven home causes the hub to stretch as it were, and even though the
metal of the key were to compress, the elasticity thus induced would
take up the compression, preventing the key from coming loose. It is
obvious, then, that set screws are suitable for light duty only, and
keys for either heavy or light duty. It is advanced by some authorities
that keys are more apt to cause a wheel or pulley to run out of true
than a set screw, but such is not the case, because, as shown in Figs.
466 and 468, both of them tend to throw the wheel out of true in one
direction; but a key may be made with proper fitting to cause a wheel to
run true that would not run true if held by a set screw, as is explained
in the directions for fitting keys given in examples in vice work.
If two set screws be used they should both be in the same line (parallel
to the shaft axis) or else at a right angle one to the other as in Fig.
469, so that the shaft and bore may drive by frictional contact on the
side opposite to the screws. Theoretically the contact of their surface
will be at a point only, but on account of the elasticity of the metal
the contact will spread around the bore in the arc of a circle, the
length of the arc depending upon the closeness of fit between the pulley
bore and the shaft. If the bore is a close fit to the shaft it is by
reason of the elasticity of the metal relieved of contact pressure on
the side on which the set screw or key is to an amount depending upon
the closeness of the bore fit, but this will not in a bore or driving
fit to the shaft be sufficient to set the wheel out of true.
If two set screws are placed diametrally opposite they will drive by the
contact of their ends only, and not by reason of their inducing
frictional contact between the bore and the shaft.
A very true method of securing a hub to a shaft is to bore it larger
than the shaft and to a taper of one inch to the foot. A bushing is then
bored to fit the shaft and turned to the same taper as the hub is
turned, but left, say, 1/100 inch larger in diameter and 1/4 or 3/8
longer. The bush is then cut into three pieces and these pieces are
driven in the same as keys, but care must be taken to drive them equally
to keep the hub true.
[Illustration: Fig. 470.]
[Illustration: Fig. 471.]
Feathers are used under the following conditions:--When the wheel driven
by a shaft requires to slide along the shaft during its rotation, in
which case the feather is fast in the wheel and the shaft is provided
with a keyway or spline (as it is termed when the sliding action takes
place), of the necessary length, the sides of the feather being a close
but sliding fit in the spline while fixed fast in the wheel.
It is obvious that the feather might extend along the shaft to the
requisite distance and the spline or keyway be made in the wheel: but in
this case the work is greater, because the shaft would still require
grooving to receive the feather, and the feather instead of being the
simple width of the wheel would require to be the width of the wheel
longer than the traverse of the wheel on the shaft. Nor would this
method be any more durable, because the keyway's bearing length would be
equal to the width of the wheel only.
When a feather is used to enable the easy movement of a wheel from one
position to another a set screw may be used to fix the wheel in position
through the medium of the feather as is shown in Fig. 470.
Through keys and keyways are employed to lock two pieces, and sometimes
to enable the taking up of the wear of the parts. Fig. 471 represents an
example in which the key is used to lock a taper shaft end into a socket
by means of a key passing through both of them. When the keyway is
completely filled by the key as in the figure it is termed a solid key
and keyway, indicating that there is no draft to the keyway. Fig. 472
represents a key and keyway having draft. One edge, A C, of the key
binds against the socket edges only, and the other edge E binds against
the edge B of the enveloped piece or plug, so that by driving in the key
with A hammer the two parts are forced together. The space or distance
between the edge D and the key, and between edges E and F, is termed the
draft. The amount of this draft is made equal to the taper of the key,
hence, when the key is driven in so that its head comes level with the
socket or work surface, the draft will be all taken up and the key will
fill the keyway.
[Illustration: Fig. 472.]
Draft is given to ensure all the strain of the key forcing the parts
together, to enable the key to be driven in to take up any wear and to
adjust movable parts, as straps, journal boxes or brasses, &c. When the
bore of the socket and the end of the rod are parallel, the end of the
rod F, Fig. 473, should key firmly against the end E of the socket,
while the end D of the socket should be clear of the shoulder on the
rod; otherwise instead of the key merely compressing the metal at F it
will exert a force tending to burst the end F from G of the rod,
furthermore, the area of contact at the shoulder D being small the metal
would be apt to compress and the key would soon come loose.
In some cases two keys are employed passing through a sleeve, the
arrangement being termed a coupling, or a butt coupling.
[Illustration: Fig. 473.]
The usual proportions for this class of key, when the rod ends and
socket boxes are parallel, is width of key equals diameter of socket
bore, thickness of key equals one-fourth its width, with a taper
edgeways of about 1/4 inch in 10 inches of length.
[Illustration: Fig. 474.]
[Illustration: Fig. 475.]
As the keys in through keyways often require to be driven in very tight,
and as the parts keyed together often remain a long time without being
taken apart and in some situations become rusted together, it is often a
difficult matter to get them apart. First, it is difficult to drive it
out because the blows swell the end of the key so that it cannot pass
through the keyway, and secondly, driving the socket off the plug of the
two parts keyed together often damages the socket and may bend the rod
to which it is keyed. Furthermore, as the diameter of the socket is
usually not more than half as much again as the diameter of the plug,
misdirected blows are apt to fall upon the rod instead of upon the
socket end and damage it. Hence, a piece of copper, of lead, or a block
of wood should always be placed against the socket end to receive the
hammer blows. To force a plug out of a socket, we may use reverse keys.
These are pieces formed as shown in Fig. 474. A, A and B, B are edge and
face views respectively of two pieces of metal, formed as shown, which
are inserted in the keyway as shown in Fig. 475, in which A is the plug
or taper end of a rod and B the socket, C is one and D the other of the
reverse keys, while E is a taper key inserted between them, B driving E
through the keyway, A and B are forced apart. The action of the reverse
keys is simply to reverse the direction of the draft in the keyway so
that the pressure due to driving E through the keyway is brought to bear
upon the rod end in the part that was previously the draft side of the
keyway, and in like manner upon the keyway in the socket on the side
that previously served as draft.
Reverse keys are especially serviceable to take off cross heads, piston
heads, keyed crank-pins, and parts that are keyed very firmly together.
[Illustration: Fig. 476.]
[Illustration: Fig. 477.]
Hubs are sometimes fastened to their shafts by pins passing through both
the hub and the shaft. These pieces may be made parallel or taper, but
the latter obviously secures the most firmly. If the pin is located as
in Fig. 476, its resisting strength is that due to its cross sectional
area at A and B. But if the pin be located as in Fig. 477 it secures the
hub more firmly, because it draws the bore (on the side opposite to the
pin) against the shaft, causing a certain amount of friction, and,
furthermore, the area resisting the pressure of the hub is increased,
and that pressure is to a certain degree in a crushing as well as a
shearing direction.
[Illustration: Fig. 478.]
If unturned pins are used and the holes are rough or drilled but not
reamed, it is better that two sides of the pin should be eased off with
a file or on the emery wheel, so that all the locking pressure of the
pin shall fall where it is the most important that it should--that is,
where it performs locking duty. This is shown in Fig. 478, the hole
being round and the pin being very slightly oval (not, of course, so
much as shown in the drawing), so that it will bind at A B, and just
escape touching at C, D, so that all the pressure of contact is in the
direction to bind the hub to the shaft.
CHAPTER VI.--THE LATHE.
The lathe may be justly termed the most important of all metal-cutting
machine tools. Not only on account of the rapidity of its execution
which is due to its cutting continuously while many others cut
intermittently, but also because of the great variety of the duty it
will perform to advantage. In the general operations of the lathe,
drilling, boring, reaming, and other processes corresponding to those
performed by the drilling machine, are executed, while many operations
usually performed by the planing machine, or planer as it is sometimes
termed, may be so efficiently performed by the lathe that it sometimes
becomes a matter of consideration whether the lathe or the planer is the
best machine to use for the purpose.
The forms of cutting tools employed in the planer, drilling machine,
shaping machine, and boring machine, are all to be found among lathe
tools, while the work-holding devices employed on lathe work include,
substantially, very nearly all those employed on all other machines and,
in addition, a great many that are peculiar to itself. In former times,
and in England even at the present day, an efficient turner (as a lathe
operator is termed), or lathe hand, is deemed capable of skilfully
operating a planer, boring machine, screw-cutting machine, drilling
machine, or any of the ordinary machine tools, whereas those who have
learned to operate any or all of those machine tools would prove
altogether inefficient if put to operate a lathe.
[Illustration: Fig. 479.]
In almost all the mechanic arts the lathe in some form or other is to be
found, varying in weight from the jewellers' lathe of a few pounds to
the pulley or fly-wheel lathe of the engine builder, weighing many tons.
The lathe is the oldest of machine tools and exists in a greater variety
of forms than any other machine tool. Fig. 479 represents a lathe of
primitive construction actually in use at the present day, and
concerning which the "Engineering" of London (England), says, "At the
Vienna Exhibition there were exhibited wood, glasses, bottles, vases,
&c., made by the Hucules, the remnant of an old Asiatic nation which had
settled at the time of the general migration of nations in the remotest
parts of Galicia, in the dense forests of the Carpathian Mountains. The
lathe they are using has been employed by them from time immemorial.
They make the cones _b_, _b_ (of maple) serve as centres, one being
fixed and the other movable (longitudinally). They rough out the work
with a hatchet, making one end _a_ cylindrical, to receive the rope for
giving rotary motion. The cross-bar _d_ is fastened to the trees so as
to form a rest for the cutting tool, which consists of a chisel." C, of
course, is the treadle, the lathe or pole being a sapling.
In other forms of ancient lathes a wooden frame was made to receive the
work-centres, and one of these centres was carried in a block capable of
adjustment along the frame to suit different lengths of work. In place
of a sapling a pole or lath was employed, and from this lath is probably
derived the term lathe.
It is obvious, however, that with such a lathe no cutting operation can
be performed while the work is rotating backwards, and further, that
during the period of rest of the cutting tool it is liable to move and
not meet the cut properly when the direction of work rotation is
reversed and cutting recommences, hence the operation is crude in the
extreme, being merely mentioned as a curiosity.
The various forms in which the lathe appears in ordinary machine shop
manipulation may be classified as follows:--
The _foot lathe_, signifying that the lathe is driven by foot.
The _hand lathe_, denoting that the cutting tools must be held in the
hands, there being no tool-carrying or feeding device on the lathe.
The _single-geared lathe_, signifying that it has no gear-wheels to
reduce the speed of rotation of the live spindle from that of the cone.
The _back-geared lathe_, in which gear-wheels at the back of the
headstock are employed to reduce the speed of the lathe.
The _self-acting lathe_, or _engine lathe_, implying that there is a
slide rest actuated automatically to traverse the tool to its cut or
feed.
The _screw-cutting lathe_, which is provided with a _lead_ screw, by
means of which other screws may be cut.
The _screw-cutting lathe with independent feed_, which denotes that the
lathe has two feed motions, one for cutting threads and another for
ordinary tool feeding; and
The _chucking lathe_, which implies that the lathe has a face plate of
larger diameter than usual, and that the bed is somewhat short, so as to
adapt it mainly to work held by being chucked, that is to say, held by
other means than between the lathe centres.
There are other special applications of the lathe, as the boring lathe,
the grinding lathe, the lathe for irregular forms, &c., &c.
This classification, however, merely indicates the nature of the lathe
with reference to the individual feature indicated in the title; thus,
although a foot lathe is one run by foot, yet it may be a single or
double gear (back-geared) lathe, or a hand or self-acting lathe, with
lead screw and independent feed motion.
Again, a hand lathe may have a hand slide rest, and in that case it may
also be a back-geared lathe, and a back-geared lathe may have a hand
slide rest or a self-acting feed motion or motions.
Fig. 480 represents a simple form of foot lathe. The office of the
shears or bed is to support the headstock and tailstock or tailblock,
and to hold them so that the axes of their respective spindles shall be
in line in whatever position the tailstock may be placed along the bed.
The duty of the headstock is to carry the live spindle, which is driven
by the cone, the latter being connected by the belt to the wheel upon
the crank shaft driven by the crank hook and the treadle, which are
pivoted by eyes W to the rod X, the operation of the treadle motion
being obvious. The work is shown to be carried between the live centre,
which is fitted to the live spindle, and the dead centre fitting into
the tail spindle, and as it has an arm at the end, it is shown to be
driven by a pin fixed in the face plate, this being the simplest method
of holding and driving work. The lathe is shown provided with a hand
tool rest, and in this case the cutting tools are supported upon the top
of the tool rest N, whose height may be adjusted to bring the tool edge
to the required height on the work by operating the set screw S, which
secures the stem of N in the bore of the rest.
To maintain the axes of the live and dead spindles in line, they are
fitted to a slide or guideway on the shears, the headstock being fixed
in position, while the tailstock is adjustable along the shears to suit
the length of the work.
To lock the tailstock in its adjusted position along the shears, it has
a bolt projecting down through the plate C, which bolt receives the hand
nut D. To secure the hand rest in position at any point along the
shears, it sets upon a plate A and receives a bolt whose head fits into
a [T]-shaped groove, and which, after passing through the plate P
receives the nut N, by which the rest is secured to the shears.
To adjust the end fit of the live spindle a bracket K receives an
adjusting screw L, whose coned end has a seat in the end J of the live
spindle, M being a check nut to secure L in its adjusted position.
[Illustration: Fig. 480.]
The sizes of lathes are designated in three ways, as follows:--First by
the _swing_ of the lathe and the total length of the bed, the term
_swing_ meaning the largest diameter of work that the lathe is capable
of revolving or swinging. The second is by the _height of the centres_
(from the nearest corner of the bed) and the length of the shears. The
height of the centres is obviously equal to half the swing of the lathe,
hence, for example, a lathe of 28-inch swing is the same size as one of
14-inch centres. The third method is by the swing or height of centres
and by the greatest length of work that can be held between the lathe
centres, which is equal to the length of the bed less the lengths of the
head and tailstock together.
The effective size of a lathe, however, may be measured in yet another
way, because since the hand rest or slide rest, as the case may be,
rests upon the shears or bed, therefore the full diameter of work that
the lathe will swing on the face plate cannot be held between the
centres on account of the height of the body of the hand rest or slide
rest above the shears.
Fig. 481 shows a hand lathe by F. E. Reed, of Worcester, Massachusetts,
the mechanism of the head and tail stock being shown by dotted lines.
The live spindle is hollow, so that if the work is to be made from a
piece of rod and held in any of the forms of chucks to be hereafter
described, it may be passed through the spindle, which saves cutting the
rod into short lengths. The front bearing of the headstock has two
brasses or boxes, A and B, set together by a cap C.
The rear bearing has also a bearing box, the lower half D being threaded
to receive an adjustment screw F and check nut G to adjust the end fit
of the spindle in its bearings. In place of grooved steps for the belt
the cone has flat ones to receive a flat belt.
The tail spindle is shown, in Fig. 482, to be operated by a screw H,
having journal bearing at I, and threaded into a nut fast in the tail
spindle at J. To hold the tail spindle firmly the end of the tail stock
is split, and the hand screw K may be screwed up to close the split and
cause the bore at L to clasp the tail spindle at that end.
To lock the tail stock to the shears the bolt M receives the lever N at
one end and at the other passes through the plate or clamp O, and
receives the nut P, so that the tail stock is gripped to or released
from the shears by operating N in the necessary direction. The hand
rest, Fig. 483, has a wheel W in place of a nut, which dispenses with
the use of a wrench.
What are termed bench lathes are those having very short legs, so that
they may for convenience be mounted on a bench or fastened to a second
frame, as shown in Fig. 484.
It is obvious that when work is turned by hand tools, the parallelism of
the work depends upon the amount of metal cut off at every part of its
length, which to obtain work of straight outline, whether parallel or
taper, involves a great deal of testing and considerable skill, and to
obviate these disadvantages various methods of carrying and accurately
guiding tools are employed. The simplest of these methods is by means of
a slide rest, such as shown in Fig. 485.
The tool T is carried in the tool post P, being secured therein by the
set screw shown, which at the same time locks the tool post to the upper
slider. This upper slider fits closely to the cross slide, and has a
nut projecting down into the slot shown in the same, and enveloping the
cross feed screw, whose handle is shown at C, so that operating C
traverses the upper slider on the cross slide and regulates the depth to
which the tool enters the work, or in other words, the depth of cut.
[Illustration: Fig. 481.]
The cross slide is formed on the top of the lower slider, which has
beneath a nut for the feed screw, whose handle is shown at A, hence
rotating A will cause the lower slider to traverse along the lower slide
and carry the tool along the work to its cut. To maintain the fit of the
sliders to the slides a slip of metal is inserted, as at _e_ and at _c_,
and these are set up by screws as at _f_, _f_ and _b_, _b_.
[Illustration: Fig. 482.]
The lower or feed traverse slide is pivoted to its base B, so that it
may be swung horizontally upon the same, and is provided with means to
secure it in its adjusted position, which is necessary to enable it to
turn taper as well as parallel work. To set this lower slide to a given
degree of angle it may be marked with a line and the edge of base B may
be divided into degrees as shown at D.
[Illustration: Fig. 483.]
When a piece of work is rotated between the lathe centres its axis of
rotation may be represented by an imaginary straight line and the lower
slides must, to obtain parallel work, be set parallel to this straight
line, while for taper work the slide rest must be set at an angle to it.
Now, in the form of slide rest shown in figure the cross slide is
carried by the lower or feed traverse slide, hence setting the lower
slide out of parallel with the work axis sets the cross slide out of a
right angle to the work axis, with the result that when a taper piece of
work is turned that has a collar or flange on it, the face of that
collar or flange will be turned not at a right angle to the work axis as
it should be, but at a right angle to the surface of the cone. Thus in
Fig. 486 A represents the axis of a piece of work, and the slide nut
having been set parallel to the work axis, the face C will be at a right
angle to the surface B or axis A, but with the slide nut set at an angle
to turn the cone D, the cross slide will be at an angle to A, hence the
face E will be undercut as shown, and at a right angle to the surface D
instead of to A A. This may be obviated by letting the cross slide be
the lower one as in the English form of slide rest shown in Fig. 487, in
which the upper slide is pivoted at its centre to the cross slide and
may be swung at an angle thereto and secured in its adjusted position by
the bolt at F. The projection at the bottom of the lower slider fits
between the shears of the lathe and holds the lower slider parallel with
the line of lathe centres, which causes the slide rest to cut all faces
at a sight angle to the work axis whether the feed traverse slide be set
to turn parallel or taper. In either case, however, there is nothing to
serve as a guide to set the feed traverse slide parallel to the work
axis, and this must, therefore, be done as near as may be by the eye and
by taking a cut and testing its parallelism.
[Illustration: Fig. 484.]
[Illustration: Fig. 485.]
[Illustration: Fig. 486.]
The rest may be set approximately true by bringing the operator's eye
into such a position that the edge _a_ _a_, Fig. 488, of the slide rest
come into line with the edge _b_ _b_ of the lathe shears, because that
edge is parallel to the line of lathe centres, and therefore to the work
axis.
Slide rests which have a slide for traversing the tool along the work to
its cut are but little used in the United States, being confined to very
small lathes, and then (except in the case of watchmakers' lathes whose
forms of slide rest will be shown hereafter), mainly as an expedient to
save expense in the cost of the lathe, it being preferred to feed the
tool for the feed traverse (as the motion of the cutting tool along the
work is termed) by mechanism operated from the live spindle and to be
hereafter described. In England, however, slide rests are much used, a
specimen construction being shown in Fig. 489. The end face A of the
rest comes flush so that the tool shall be carried firmly when taking
facing cuts in which solidity in the rest is of most importance. The
tool is held by two clamps instead of by single tool posts, because the
slide rest is employed to take heavy cuts, and when this is the case
with boring tools whose cutting edges stand far out from the slide rest,
a single tool post will not hold the tool sufficiently firm.
[Illustration: Fig. 487.]
[Illustration: Fig. 488.]
The gib _e_, Fig. 485, is sometimes placed on the front side of the
slider, as in the figure, and at others on the back; when it is placed
in the front the strain of the cut causes it to be compressed against
the slide, and there is a strain placed upon the screws _f_ which lifts
them up, whereas if placed on the other side the screws are relieved of
strain, save such as is caused by the setting of the gib up.
[Illustration: Fig. 489.]
On the other hand, the screws are easier to get at for adjustment if
placed in front. When the screws _b_ of the upper gib _c_, Fig. 485, are
on the right-hand side, as in that figure, there is considerable strain
on the screws when a boring tool is used to stand far out, as for boring
deep holes. On the other hand, however, the screws can be readily got at
in this position, and may therefore be screwed up tightly to lock the
upper slider firmly to the cross slide, which will be a great advantage
in boring and also in facing operations. But the screws must not in this
case have simple saw slot heads, such as shown on a larger scale in
Fig. 490, but should have square heads to receive a wrench, and if these
four screws are used, the two end ones may be set to adjust the slicing
fit of the slider, while the two middle ones may be used to set the
slider form on its slide when either facing or boring. The corners of
the gibs as well as those of the slider and slide may with advantage be
rounded so that they may not become bruised or burred, and, furthermore,
the slider is strengthened, and hence less liable to spring under the
pressure of a heavy cut.
[Illustration: Fig. 490.]
A slide rest for turning spherical work is shown in Fig. 491. A is the
lower slide way on which is traversed the slide B, upon which is fitted
the piece C, pivoted by the bolt D; there is provided upon C a
half-circle rack, shown at E, and into this rack gears a worm-wheel
having journal bearing on B, and operated by the handle F. As F is
rotated C would rotate on D as a centre of motion, hence the tool point
would move in an arc of a circle whose radius would depend upon the
distance of the tool point from D as denoted by J, which should be
coincident with the line of centres of the lathe.
[Illustration: Fig. 491.]
The slide G is constructed in the ordinary manner, but the way on which
it slides should be short, so as not to come into contact with the work.
If the base slide way A be capable of being traversed along the lathe
shears S S by a separate motion, then the upper slide way and slide may
be omitted, G and C being in one piece. It is to be noted in a rest of
this kind, however, that the tool must be for the roughing cut set too
far from D to an amount equal to about the depth of cut allowed to
finish with, and for the finishing cut to the radius of the finished
sphere in order to obtain a true sphere, because if B be operated so
that D does not stand directly coincident with the line of lathe
centres, the centre of motion, or of the circle described by the tool
point, will not be coincident with the centre on which the work rotates,
hence the work though running true would not be a true sphere but an
oval. This oval would be longest in the direction parallel with the line
of centres whenever the pivot D was past the line of centres, and an
oval of largest diameter at the middle or largest diameter turned by the
tool whenever the pivot D was on the handle H side of the line of
centres. To steady C it may be provided with a circular dovetail, as
shown at the end I, provision being made (by set screw or otherwise) for
locking C in a fixed position when using the rest for other than
spherical work.
To construct such a rest for turning curves or hollows whose outline
required to be an arc of a circle, the pivot D would require to be
directly beneath the tool post, which must in this case occupy a fixed
position. The radius of the arc would here again be determined by the
distance of the tool point from the centre of rotation of the pivot, or,
what would be the same thing, from that of the tool post.
Next to the hand slide rest lathe comes the self-acting or engine lathe.
These are usually provided with a feed motion for traversing the slide
rest in the direction of the length of the bed, and sometimes with a
self-acting cross feed, that is to say, a feed motion that will traverse
the tool to or from the line of centres and at a right angle to the
same.
In an engine lathe the parallelism or truth of the work depends upon the
parallelism of the line of centres with the shears of the lathe, and
therefore upon the truth of the shears or bed, and its alignment with
the cone spindle and tail spindle, while the truth of the radial faces
on the turned work depends upon the tool rest moving on the cross slide
at a true right angle to the line of centres.
[Illustration: Fig. 492.]
Fig. 492 represents an 18-inch engine (or self-acting) lathe designed by
and containing the patented improvements of S. W. Putnam, of the Putnam
Tool Company, of Fitchburg, Massachusetts. The lathe has an elevating
slide rest self-acting feed traverse and self-acting cross feed, both
feeds being operative in either direction. It has also a feed rod for
the ordinary tool feeding and a lead screw for screw-cutting purposes.
Fig. 493 represents a cross-sectional view of the shears beneath the
headstock; A A are the shears or bed having the raised [V]s marked V´
and V on which the headstock and tailstock rest, and V´´ and V´´´ on
which the carriage slides. A and A´ are the shears connected at
intervals by cross girts or webs B to stiffen them. C C are the bolts to
secure the headstock to the shears. D is a bracket bolted to A´ and
affording at E journal bearing for the spindle that operates the
independent feed spindle. E is split at _f_ and a piece of soft wood or
similar compressible material is inserted in the split. The bolt F is
operated to close the split, and, therefore, to adjust the bore E to
properly fit the journal of the feed spindle, and as similar means are
provided in various parts of the lathe to adjust the fits of journals
and bearings the advantages of the system may here be pointed out.
First, then, the fit of the bearing may be adjusted by simply operating
the screw, and, therefore, without either disconnecting the parts or
performing any fitting operation, as by filing. Secondly, the presence
of the wood prevents the ingress of dust, &c., which would cause the
bearings and journals to abrade; and, thirdly, the compression of the
wood causes a resistance and pressure on the adjusting screw thread,
which pressure serves to lock it and prevent it from loosening back of
itself, as such screws are otherwise apt to do.
[Illustration: Fig. 493.]
As the pressure of the tool cut falls mainly on the front side of the
carriage, and as the weight of the carriage itself is greatest on that
side, the wear is greatest; this is counteracted by forming the front
[V], marked V´´´ in figure, at a less acute angle, which gives it more
wearing area and causes the rest to lower less under a given amount of
wear.
The rib A´´ which is introduced to strengthen the shears against
torsional strains, extends the full length of the shears.
[Illustration: Fig. 494.]
Fig. 494 is a sectional side elevation of the headstock; A A´ represents
the headstock carrying the bearing boxes B and B´, which are capable of
bore closure so as to be made to accurately fit the spindle S by the
construction of the front bearing B, being more clearly shown in Fig.
495; B is of composition brass, its external diameter being coned to fit
the taper hole in the head; it is split through longitudinally, and is
threaded at each end to receive the ring nuts C and C´. If C be loosened
from contact with the radial face of A, then C´ may be screwed up,
drawing B through the coned hole in A, and, therefore, causing its bore
to close upon S.
At the other end of S, Fig. 496, C´´ is a ring nut for drawing the
journal box B´ through _a´_ to adjust the bore of B´ to fit the journal
of S, space to admit the passage of B´ being provided at _e_. D is a box
nut serving to withdraw B´ or to secure it firmly in its adjusted
position, and also to carry the end adjusting step E. F is a check nut
to lock E in its adjusted position.
The method of preventing end motion to S is more clearly shown in Fig.
496, in which _h_ is a steel washer enveloping S, having contact with
the radial face of B´ and secured in its adjusted position by the check
nuts _g_, hence it prevents S from moving forward to the right. _f_ is a
disk of raw hide let into E; the latter is threaded in D and is squared
at the end within F to admit of the application of a wrench, hence E may
be screwed in until it causes contact between the face of _f_ and the
end of S, thus preventing its motion to the left. By this construction
the whole adjustment laterally of S is made with the short length from
_h_ to _f_, hence any difference of expansion (under varying
temperature) between the spindle and the head A A´, or between the boxes
and the spindle S, has no effect towards impairing the end fit of S in
its bearings.
The method of adjusting the bearings to the spindle is as follows:--C´´
and C´ are slackened back by means of a "spanner wrench" inserted in the
holes provided for that purpose. C and D are then screwed up,
withdrawing B and B´ respectively, and leaving the journal fit too easy.
C´ is then screwed up until B is closed upon the spindle sufficiently
that the belt being loose on the cone pulley, the latter moved by the
hand placed upon the smallest step of the cone can just detect that
there is contact between the bore of B and the spindle, then, while
still moving the cone, turn C´ back very slowly and a very little, the
object being to relieve the bore of B from pressure against S. C may
then be screwed up, firmly locking B in its adjusted position. C´´ may
then be operated to adjust B´ in a similar manner, and D screwed up to
lock it in its adjusted position. Before, however, screwing up D it is
better to remove F and release E from pressure against _f_, adjusting
the end pressure of E after D has been screwed home against A´.
To prevent B and B´ from rotating in the head when the ring nuts are
operated, each is provided with a pin, _q_, grooves _c_ and _c´_
permitting of the lateral movement of B and B´ for adjustment. The boxes
B, B´ admit of being rotated in their sockets in A and A´ so as to
assume different positions, the pins _q_ and _q´_ being removable from
one to another of a series of holes in the boxes B, B´ when it is
desired to partly rotate those boxes. The tops of the boxes are provided
with oil holes, and the oil ways shown at _r_, _s_ being the oil groove
through the head and _a_ simply a stopper to prevent the ingress of
dust, &c.
[Illustration: Fig. 495.]
The thread on S at Z, Fig. 494, is to receive and drive the face plates,
chucks, &c., which are bored and threaded to fit over Z. To cause the
radial faces of such face plates or chucks to run true, there is
provided the plain cylindrical part _l_, to which the bore in the hub of
the face plate or chuck is an accurate fit when the radial face of that
hub meets the radial face _m_.
Referring again to Fig. 494, G´ is the pinion to drive the back gear
while G receives motion from the back-gear pinion. The object of the
back gear is to reduce the speed of rotation of S and to enable it to
drive a heavier cut, which is accomplished as follows:--G´ is secured
within the end K of the cone and is free to rotate with the cone upon S;
at the other end the cone is secured to M, which is free to rotate upon
S so far as its bore is concerned. G is fixed upon S and hence rotates
at all times with it; but G may be locked to or released from M as
follows:--
[Illustration: Fig. 496.]
In G is a radial slot through which passes a bolt I provided with a cap
nut H, in M is an annular groove J. When I is lifted its head passes
into a recess in M, then H is screwed up and G is locked to M. This is
the position of I when the back gear is not in use, the motion of the
cone being communicated to S through I. But if H be loosened and I be
moved inwards towards S, the head of I passes into the annular groove J,
and the cone is free to rotate upon S while the latter and G remain
stationary unless the back gear is put into operation. In this latter
case the pinion G´ rotating with the cone drives the large gear of the
back gear and the small pinion of the latter drives G, whose speed of
rotation is reduced by reason of the relative proportions of the gear
wheels.
In this case it is obvious that since the pulley rotates upon the
spindle it requires lubrication, which is accomplished through the oil
hole tubes L.
The means of giving motion to the feed spindle and lead screw are as
follows:--N, Fig. 494, is a pinion fast upon S and operating the gear O,
which is fast upon the spindle P, having journal bearing in a stem in A´
and also at G´´. P drives the three-stepped cone R, which is connected
by belt to a similar cone fast upon the independent feed spindle. The
seat for the driving gear of the change wheels for the lead screw is on
P at V. To provide ample bearing surface for P in A´ the bush or sleeve
shown is employed, but this sleeve also serves to pivot the swing frame
W which carries the studs for the change wheels that go between the
wheel on V and that on the lead screw; _x_ _y_ are simply oil holes to
lubricate P in its bearings.
To provide a wider range of tool feed than that obtainable by the steps
on the feed cones, as R, they are provided at their ends with seats for
change wheels, the swing frame W carrying the intermediate wheels for
transmitting motion from V to a similar seat on the cone on the feed
spindle.
Fig. 497 represents the tailstock (or tailblock as it is sometimes
termed), shown in section. A represents the base which slides upon the
raised [V]s on the bed and carries the upper part B, in which slides the
tail spindle C, which is operated longitudinally by the tail screw D,
having journal bearing in E, and threaded through the nut F which is
fast in C. The hand wheel G is for rotating D, whose thread operating in
the nut F, causes C to slide within B in a direction determined by the
direction of rotation of G. To lock C in its adjusted position the
handled nut H is employed in connection with the bolt I, which is shown
in dotted lines; C is split as shown by the dotted lines at _f_; J is
the dead centre fitting accurately into a conical hole in C. When it is
required to remove J from C the wheel G is operated to withdraw C
entirely within B, and the end _d_ of D meets the end _e_ of J and
forces J from the coned hole in C.
The method of securing the tailstock to the shears or releasing it from
the same is as follows. A vertical prolongation of B affords at B´´ a
bearing surface for the nut-handle L and washer M. K is a bolt threaded
into L passing through M, B´´ and N, the latter of which it carries. N
spans the shears beneath the two [V]s on which the tailstock slides.
Moving or rather partly rotating the handle L in the necessary direction
lifts K and causes N to rise, and grip the shears beneath, while the
pressure of M on B´´ causes B to grip A and the latter to grip the
raised [V]s on the shears. If L be rotated in the opposite direction it
will cause N to fall, leaving A free to slide along the shears. To
prevent N from partly rotating when free, its ends are shaped to fit
loosely between the shears as shown at _n_.
To give to N sufficient rise and fall to enable it to grip or fall
entirely free from the shears with the small amount of rotary motion
which the handle-lever L is enabled from its position to have, the
following device is provided. M is a washer interposed between L and
B´´. This washer has upon it steps of different thickness as shown at M
and _m_, the two thicknesses being formed by an incline as shown. The
face of L has, as shown, similar steps; now as shown in the cut the step
_l_ on lever L meets the steps _m_ of the washer, the handle having
receded to the limit of its motion. The bolt K then has fallen to the
amount due to unscrewing the threaded or nut end of L, and also to the
amount of the difference of thickness at M and at _m_ of the washer, the
plate N being clear of the lathe-shears. But suppose the handle L be
pulled towards the operator, then the surface _l_ passing from a thin
section on to a thick one as M of the washer, will lift the bolt K,
causing N to meet the under surface of the shears, and then the motion
of L continuing the pressure of the thread will bind or lock N to the
bed.
[Illustration: Fig. 497.]
The surface A´ in Fig. 497 affords a shelf or table whereon tools, &c.,
may be placed instead of lying on the lathe bed, where they may cause or
receive damage.
Fig. 498 represents an end view of the tailstock viewed from the dead
centre end, the same letters of reference applying to like parts that
are shown in Fig. 497. The split at _f_ is here shown to be filled with
a piece of soft wood which prevents the ingress of dust, &c. At _d_ is a
cup or receptacle for oil, _e_ being a stopper, having attached to it a
wire pin flattened and of barb shape at the end, the object being to
cause the wire to withdraw from the cup a drop of oil to lubricate the
dead centre and centre in the work. The proximity of _e_ to the dead
centre makes this a great convenience, while the device uses much less
oil than would be used by an oil can.
[Illustration: Fig. 498.]
The method of setting over the upper part B to enable the turning of the
diameter of work conical or taper instead of parallel is shown in Fig.
498: P and P´ are square-headed screws threaded into the walls of A and
meeting at their ends the surface of B´. In A there is at _a_ a wide
groove or way, and on B there is at _b_ a projection fitting into the
way _a_ so as to guide B when it slides across A, as it will when P is
unscrewed in A and P´ is screwed into A. This operation is termed
setting over the tailstock, and its effect is as follows:--Suppose it be
required to turn a piece of work of smaller diameter at the end which
runs on the dead centre, then, by operating the screw P towards the
front of the lathe (or to the left as shown in the cut) and screwing P´
farther into A, the end of P´ will meet the surface of B´, causing B´ to
move over, and the centre of the dead centre J (which is the axis of
rotation of the work at that end) will be nearer to the point of the
cutting tool. Or suppose the work requires to be turned a taper having
its largest diameter at the end running on the dead centre, then P´
would be unscrewed and P screwed farther into A, carrying B farther
towards the back of the lathe.
The [V] grooves Q and Q´ fit upon the inner raised [V]s shown at V, V´
in Fig. 499.
[Illustration: Fig. 499.]
Fig. 499 is a side view of the slide rest for holding and traversing the
cutting tool. A represents the carriage resting upon the raised [V]s
marked V´´ and V´´´ and prevented from lifting by its own weight, and in
front also by the gib _a_ secured to A by the bolt _b_ and having
contact at _c_ with the shears. A carries at _d_ a pivot for the cross
slide B and at _e_ a ball pivot for the cross slide elevating screw C.
This screw is threaded through the end of B so that by operating it that
end of B may be raised or lowered to adjust the height of the cutting
tool point to suit the work. To steady B there is provided (in addition
to the pivots at _d_) on A two lugs _f_, between the vertical surfaces
of which B is a close working fit. The upper surface of B is provided
with a [V]-slide-way _g_, to which is fitted the tool rest D (the
construction being more clearly shown in Fig. 500).
[Illustration: Fig. 500.]
The means for traversing D along the slide _g_ on B is as follows:--
A nut _i_ is secured to D by the screw bolt _j_, and threaded through
the nut _i_ is the cross-feed screw E, which has journal bearing in the
piece _k_, which is screwed into the end face of B; there is a collar on
E which meets the inner end of _k_, and the handle F being secured by
nut to that end of E its radial face forms a shoulder at _m_ which with
the collar prevents any end motion of E, so that when F is rotated E
rotates and winds through the nut _i_ which moves D along B.
An end view of A, B, and D is shown in Fig. 500, in which the letters of
reference correspond to those in Fig. 499. B´ and B´´ are the
projections that pass into A and receive the pivoting screws _d_ and
_d_. To adjust the fit and take up any wear that may ensue on the slide
_g_, on B and on the corresponding surface on D, the piece _n_ is
provided, being set up by the adjusting screws O.
To adjust the fit and take up the wear at the pivots _d_ they are made
slightly taper, fitting into correspondingly taper holes in B.
The dotted circle T´, represents a pinion fast upon the cross-feed screw
(E, Fig. 499); the similar circles T and S´´ also represent pinions, the
three composing a part of the method of providing an automatic or
self-acting cross feed or cross traverse to D by rotating it through a
gear-wheel motion derived from the rotation of the independent feed
spindle, as is described with reference to Fig. 501.
_m_ in Fig. 500 represents a cavity or pocket to receive wool, cotton or
other elastic or fibrous material to be saturated with oil and thus
lubricate the raised [V]s while keeping dirt from passing between the
rest and the [V]s. The shape of these pockets is such as to enable them
to hold the cotton with a slight degree of pressure against the slides,
thus insuring contact between them.
The mechanical devices for giving to the carriage a self-acting traverse
in either direction along the bed, so as to feed the tool automatically
to its cut, and for giving to the tool rest (D, Fig. 499) traverse
motion so as to feed the tool to or from the line of centres along the
cross slide, are shown in Fig. 501, which presents two views of the feed
table or apron. The lower view supposes the feed table to be detached
from the carriage and turned around so as to present a side elevation of
the mechanism. The upper view is a plan of the same with two pinions (N
and N´), omitted. A represents the part of the lathe carriage shown at A
in Fig. 500. It has two bolts _p_ and _p´_, which secure the apron G,
Fig. 501, to A. At H is the independent feed spindle or feed rod
operated by belt from the cone pulley R, Fig. 494, or by a gear on stud
P at V. H is carried in bearings fixed to each end of the lathe shears
or bed, both of these bearings being seen in Fig. 492. H is also
provided with a bearing fixed on the feed apron as seen in Fig. 501, and
is splined as shown at _h_. At I is a bracket fast upon the apron G and
affording journal bearing to J, which is a bevel pinion having a hub
which has journal bearing in the bracket I. The fit of the bearing to
the journal is here again adjusted by a split in the bearing with a
screw passing through the split and threaded in the lower half (similar
to the construction of D in Fig. 493); J is bored to receive H, and is
driven by means of a feather projecting into the spline _h_. When
therefore, the carriage A is moved it carries with it the apron G, and
this carries the bracket I holding the bevel pinion J, which is in gear
with the bevel-wheel K, and therefore operates it when H has rotary
motion. At the back of K, and in one piece with it, is a pinion K´, both
being carried upon the stud L; pivoted upon this same stud is a plate
lever M, carrying two pinions N and N´ in gear together, but N only is
in gear with K´, hence K´ drives N and N drives N´. Now in the position
shown neither N or N´ is in gear with the gear-wheel O, but either of
them may be placed in gear with it by means of the following
construction:--
At the upper end of M there is provided a handle stud M´ passing through
the slot M´´ in G. Screwing up this stud locks M fast by binding it
against the surface of G. Suppose, then, M´ to be unscrewed, then if it
be moved to the right in the slot M´´, N will be brought into gear with
O and the motion will be transmitted in the direction of the arrows, and
screwing up N would retain the gear in that position. But suppose that
instead of moving M´ to the right it be moved to the left, then N´ will
be brought into gear with O and the direction of rotation of O will be
reversed.
[Illustration: Fig. 501.]
Thus, then, O may be made to remain stationary or to rotate in either
direction according to the position of M´ in the slot M´´, and this
position may be regulated at will.
The gear O contains in its radial face a conical recess, and upon the
same stud or pin (P) upon which O is pivoted, there is fixed the disk
P´, which is in one piece with the pinion P´´; the edge of P´ is coned
to fit the recess in the wheel O, so that if the stud P is operated to
force the disk P´ into the coned recess in O the motion of wheel O will
be communicated to disk P´, by reason of the friction between their two
coned surfaces. Or if P be operated to force the coned edge of the disk
out of contact with the coned bore or recess in gear O, then O will
rotate while P´ and P´´ will remain stationary. Suppose the coned
surfaces to be brought (by operating _x_) into contact and P´ to rotate
with O, then P´´ being in gear with wheel Q will cause it to rotate. Now
Q is fast to the pinion Q´, hence it will also rotate, and being in
contact with the rack which is fixed along the shears of the lathe and a
section of which is shown in the cut, the whole feed table or apron will
be made to traverse along the lathe shears.
The direction in which this traverse will take place depends upon the
adjusted position of M´ in M´´, or in other words upon whether N or N´
be the pinion placed in gear with O. As shown in the cut neither of them
is in gear, and motion from H would be communicated to N and N´ and
would there cease; but if M´ be raised in the slot M´´, N would drive O,
and supposing P´ to be held to O, the motion of all the gears would be
as denoted by the arrows, and the lathe carriage A would traverse along
the lathe bed in the direction of arrow Q´´. But if N´ be made to drive
O all the motions would be in the opposite directions. The self-acting
feed motion thus described is obviously employed to feed the cutting
tool, being too slow in its operation for use to simply move the
carriage from one part of the lathe bed to another; means for this
purpose or for feeding the carriage and cutting tool by hand are
provided as follows:--R is a pinion in gear with Q and fast upon the
stud R´, which is operated by the handle R´´. The motion of R´´ passes
from R to Q and Q´ which is in gear with the rack. But Q´ being in gear
with P´´ the latter also rotates, motion ceasing at this point because
the cone on P´ is not in contact with the coned recess in O. When,
however, P´ and O are in contact and in motion, that motion is
transmitted to R´´, which cannot then be operated by hand.
It is often necessary when operating the cross feed to lock the carriage
upon the lathe bed so that it shall not move and alter the depth of the
tool-cut on the radial face of the work. One method of doing this is to
throw off the belt that operates the feed spindle H, place N in gear
with O and P´ in contact with O, so that the transverse feed motion will
be in action, and then pull by hand the cone pulley driving H, thus
feeding the tool to its necessary depth of cut. The objection to this
method, however, is that when the operator is at the end of the lathe,
operating the feed cone by hand he cannot see the tool and can but
guess how deep a cut he has put on. To overcome this difficulty a brake
is provided to the pinion R as follows:--
The brake whose handle is shown at V has a hub V´ enveloping the hub
R´´´ which affords journal bearing to the stud R´. In the bore of this
hub V´ is an eccentric groove, and in R´´´ is a pin projecting into the
eccentric groove and meeting at its other end the surface of the stud
R´. When, therefore, V is swung in the required direction (to the left
as presented in the cut), the cam groove in V´ forces _r_ inwards,
gripping it and preventing it from moving, and hence the movement of R
which also locks Q and Q´.
It remains now to describe the method of giving rotary motion to the
cross-feed screw E (Fig. 499) so as to enable it to self-act in either
direction. S is a lever pivoted upon the hub of O and carrying at one
end the pinion S´´, while at the other end is a stud S´ passing through
a slot in G. The pinion S´´ is in gear with O and would therefore
receive rotary motion from it and communicate such motion to pinion T,
which in turn imparts rotary motion to T´. Now T´ is fast upon the
cross-feed screw as shown in Fig. 499 and the cross-feed screw E in that
figure would by reason of the nut _i_ in figure cause the tool rest D to
traverse along the cross-slide in a direction depending upon the
direction of motion of T´, which may be governed as follows:--
If S´ be moved to the left S´´ will be out of gear with T and the
cross-feed screw may be operated by the handle (F, Fig. 499). If S´ be
in the position shown in cut and M´´ also in the position there shown
(Fig. 501), operating the feed screw by its handle would cause its
pinion T´ to operate T, S´´, and O; hence S´ should always be placed to
disconnect S´´ from T when the cross-feed screw is to be operated by
hand, and S´ operated to connect them only when the self-acting cross
feed is to operate. In this way when the cross feed is operated by hand
T´ and T will be the only gears having motion. It has been shown that
the direction of motion of O is governed by the position of M´, or in
other words, is governed by which of the two pinions N or N´ operates,
and as O drives S´´ its motion, and therefore that of T´, is reversible
by operating M´.
The construction of S´ is as follows:--Within the apron as shown in the
side elevation it consists of what may be described as a crank, its pin
being at _t_; in the feed table is a slot through which the shaft of the
crank passes; _s_ is a handle for operating the crank. By rotating _s_
the end S´ of S is caused to swing, the crank journal moving in the slot
to accommodate the motion and permit S to swing on its centre.
The device for forcing the cone disk P´ into contact with or releasing
it from O is as follows:--The stud P is fast at the other end in P´ and
has a collar at _b_; the face of this collar forms one radial face, and
the nut W affords the other radial face, preventing end motion to _x_
without moving P endwise. If _x_ be rotated its thread at _x´_ causes it
to move laterally, carrying P with it, and P being fast to P´ also moves
it laterally. P´ is maintained from end motion by a groove at O´ in
which the end of a screw _a_ projects, _a_ screwing through W and into
the groove O´.
[Illustration: Fig. 502.]
The lead screw of a lathe is a screw for operating the lathe carriage
when it is desired to cut threads upon the work. It is carried parallel
to the lathe shears after the same manner as the independent feed
spindle, and is operated by the change wheels shown in Fig. 492 at the
end of the lathe. These wheels are termed change wheels on account of
their requiring to be changed for every varying pitch of thread to be
cut, so that their relative diameters, or, what is the same thing, their
relative number of teeth, shall be such as to give to the lead screw the
speed of rotation per lathe revolution necessary to cut upon the work a
thread or screw of the required pitch.
The construction of the bearings which carry the lead screw in the S. W.
Putnam's improved lathe is shown in Fig. 502, in which A represents the
bearing box for the headstock end of the lathe, having the foot A´ as a
base to bolt it to the lathe shears. L represents the lead screw, having
on one side of A the collar L´ and on the other the nut and washer N and
N´. The seat for the change wheel that operates the lead screw is at
L´´, the stop pin _l_ fitting into a recess in the change wheel so as to
form a driving pin to the lead screw. The washer N´ is provided with a
feather fitting into a recess into L so that it shall rotate with L and
shall prevent the nut N from loosening back as it would be otherwise apt
to do. End motion to L is therefore prevented by the radial faces of L´
and N´.
[Illustration: Fig. 503.]
At the other end of the lathe there are no collars on the lead screw,
hence when it expands or contracts, which it will do throughout its
whole length under variations of atmospheric temperature, it is free to
pass through the bearing and will not be deflected, bent, or under any
tension, as would be the case if there were collars at the ends of both
bearings. The amount of this variation under given temperatures depends
upon the difference in the coefficients of expansion for the metal of
which the lead screw and the lathe shears are composed, the shears being
of cast iron while lead screws are sometimes of wrought iron and
sometimes of steel.
The bearings at both ends are split, with soft wood placed in the split
and a screw to close the split and adjust the bearing bore to fit the
journal, in the manner already described with reference to other parts
of this lathe.
The construction of the swing frame for carrying the change wheels that
go between the driving stud V, Fig. 494, and that on the seat L´´, Fig.
502, are as follows:--
Fig. 503 represents the change wheel swing frame, an edge view of which
is partly shown at W in Fig. 494. S is a slot narrower at _a_ than at
_b_. Into this slot fit the studs for carrying the change wheels.
By enabling a feed traverse in either direction the lathe carriage may
be traversed back (for screw-cutting operations) without the aid of an
extra overhead pulley to reverse the direction of rotation of the lathe,
but in long screws it is an advantage to have such extra overhead pulley
and to so proportion it as to make the lathe rotate quicker backwards
than forward, so as to save time in running the carriage back.
The mechanical devices for transmitting motion from the lead screw to
the carriage are shown in Fig. 504, representing a view from the end and
one from the back of the lathe. B is a frame or casting bolted by the
bolt _b_ to the carriage A of the lathe. C is a disk having a handle C´
and having rotary motion from its centre. Instead of being pivoted at
its centre, however, it is guided in its rotary motion by fitting at _d_
_d_ into a cylindrical recess provided in B to receive it. C contains
two slots D and D´ running entirely through it. These slots are not
concentric but eccentric to the centre of motion of C. Through these
slots there pass two stud bolts E and E´ shown by dotted lines in Fig.
504, and these bolts perform two services: first by reason of the nuts F
and F´ they hold C to its place in B, and next they screw into and
operate the two halves G and G´ of a nut.
[Illustration: Fig. 504.]
Suppose, now, that the handle C´ be operated or moved towards arrow _e_,
then the dot at _f_ being the centre of its motion and the slots D and
D´ gradually receding from _f_ as their ends _g_ are approached they
will cause E to move vertically upward and E´ to move vertically
downward, a slot in B (which slot is denoted by the dotted lines _h_)
guiding them and permitting this vertical movement.
Since E and E´ carry the two halves of the nut which envelops the lead
screw L it is obvious that operating C´ will either close or release the
half nuts from L according to which direction it (C´) is moved in.
The screws H and H´ screw tightly into B, and the radial faces of their
heads are made to have a fair and full bearing against the underside of
the shears, so that they serve as back gibs to hold the carriage to the
shears and may be operated to adjust the fit or to lock the carriage to
the bed if occasion may require. This lathe is made with a simple tool
rest as shown in the engravings or with a compound slide rest. In some
sizes the rest is held to the carriage by a weight upon a principle to
be hereafter described. The bed is made (as is usual) of any length to
suit the purposes for which the lathe is to be used.
The next addition to the lathe as it appears in the United States is
that of a compound slide rest.
[Illustration: Fig. 505.]
Fig. 505 represents a 28-inch swing lathe by the Ames Manufacturing
Company, of Chicopee, Massachusetts. It is provided with the usual
self-acting feed motion and also with a compound slide rest. The swing
frame for the studs carrying the change wheels for screw cutting here
swings upon the end of the lead screw, the same spindle that carries the
driving cone for the independent feed rod which is in front of the
lathe, also carries the driving gear for the change wheels used for
screw cutting.
The construction of the compound rest is shown in Figs. 506 and 507. N
is the nut for the cross-feed screw (not shown in the cut) and is
carried in the slide A. A and the piece L above it are virtually in one,
since the latter is made separate for convenience of construction and
then secured to it firmly by screws. B is made separate from C also for
convenience of construction and fixed to it by screws; L is provided
with a conical circular recess into which the foot B of C fits. E is a
segment of a circle operated by the set screw F to either grip or
release B. The bolt D simply serves as a pivot for piece B C; at its
foot C is circular and is divided off into the degrees of a circle to
facilitate setting it to any designated angle.
If, then, F be unscrewed, C may be rotated and set to the required
angle, in which position screwing up F will lock it through the medium
of E. G is the feed nut for the upper slider H, which operates along a
slide way provided on C, the upper feed screw having journal bearing at
C´. I is the tool post, having a stepped washer J, by means of which the
height of the tool K may be regulated to suit the work.
[Illustration: Fig. 506.]
[Illustration: Fig. 507.]
Suppose, now, that it be required to turn a shaft having a parallel and
a taper part; then the carriage may be traversed to turn the parallel
part, and the compound slide C may be set to turn the taper part, while
the lower feed screw operating in N may be used to turn radial faces.
[Illustration: Fig. 508.]
The object of making A and L in two pieces is to enable the boring and
insertion of B, which is done as follows:--The front end of L as L´ is
planed out, leaving in it a groove equal in diameter and depth to the
diameter and depth of B, so that B may be inserted laterally along this
groove to its place in L. The segment E is then inserted and a piece is
then fitted in at L´ and held fast to A by screws. It is into this piece
that the set screw F is threaded.
Various forms of construction are designed for compound rests, but the
object in all is to provide an upper sliding piece carrying the tool
holder, such sliding piece being capable of being so set and firmly
fixed that it will feed the tool at an angle to the line of the lathe
centres.
Another and valuable feature of the compound rest is that it affords an
excellent method of putting on a very fine cut or of accurately setting
the depth of cut to turn to an exact diameter; this is accomplished by
setting the upper slide at a slight angle to the line of centres and
feeding the tool to the depth of cut by means of the screw operating the
upper slide. In this way the amount of feed screw handle motion is
increased in proportion to the amount to which the tool point moves
towards the line of lathe centres, hence a delicate adjustment of depth
of cut may be more easily made.
Suppose, for example, that a cut be started and that it is not quite
sufficiently deep, then, while the carriage traverse is still
proceeding, the compound rest may be operated to increase the cut depth,
or if it be started to have too deep a cut the compound rest may be
operated to withdraw the tool and lessen its depth of cut. Or it may be
used to feed the tool in sharp corners when the feed traverse is thrown
out, or to turn the tops of collars or flanges when the tailstock is
set over to turn a taper.
It is obvious, however, that comparatively short tapers only can be
conveniently turned by a compound slide rest; but most tapers, however,
are short.
To turn long tapers the tailstock of the lathe is set over as described
with reference to the Putnam lathe, but for boring deep holes the slide
rest must either be a compound one or a taper turning former or
attachment must be employed.
[Illustration: Fig. 509.]
When, however, the tailstock is set over, the centres in the work are
apt to wear out of true and move their location (the causes of which
will be hereafter explained).
In addition to this, however, the employment of a taper turning
attachment enables the boring of taper holes without the use of a
compound slide rest, thus increasing the capacity of the lathe not
having a simple or single rest.
In Fig. 508 is shown a back view of a Pratt and Whitney weighted lathe
having a Slate's taper turning attachment, the construction of which is
as follows:--Upon the back of the lathe shears are three brackets having
their upper surfaces parallel with and in the same plane as the surface
of the lathe shears. Pivoted to the middle bracket is a bar which has at
each end a projection or lug fitting into grooves provided in the end
brackets, these grooves being arcs of a circle whose centre is the axis
of the pivot in the middle bracket.
The end brackets are provided with handled nuts upon bolts, by which
means the bar may be fixed at any adjusted angle to the lathe shears.
Upon the upper surface of the bar is a groove or way in which slides a
sliding block or die, so that this die in traversing the groove will
move in a straight line but at an angle to the lathe bed corresponding
to the angle at which the bar may be adjusted. The slide rest upon being
connected by a bar or rod to the die or sliding block is therefore made
to travel at the same angle to the lathe bed or line of centres as that
to which the bar is set. The method of accomplishing this in the lathe,
shown in Fig. 508, is as follows:--
In Fig. 509 A is the bar pivoted at C upon the centre bracket B; E is
the sliding block pivoted to the nut bar F. This nut bar carries the
cross-feed nut, which in turn carries the feed screw and hence the tool
rest. When the nut bar is attached to the sliding block to turn a taper
it is free to move endways upon the lower part of the carriage in which
it slides, but when the taper attachment is not in use the bar is
fastened to the lower part of the carriage by a set screw.
The screw at D is provided to enable an accurate adjustment for the
angle of the bar A. G and H are screws simply serving to adjust the
diameter to which the tool will turn after the manner shown in Fig. 588,
G being for external and H for internal work.
When the lathe has a bed of sufficient length to require it, a slide is
provided to receive the brackets, which may be adjusted to any required
position along the slide, as shown in Fig. 510. This is a gibbed instead
of a weighted lathe, and the method of attaching the sliding block to
the lathe rest is as follows:--
A separate rod is pivoted to the sliding block. This rod carries at its
other end a small cross head which affords general bearing to the end of
the cross-feed screw, which has a collar on one side of the cross head
and a fixed washer on the other, to prevent any end motion of the said
screw.
[Illustration: Fig. 510.]
The cross-feed nut is attached to the traversing cross slide. The other
or handle end of the cross-feed screw has simple journal bearing in the
slide rest, but no radial faces to prevent end motion, so that one may
from the rod attached to the sliding-block traverse the cross-feed
slide, which will carry with it the feed screw. As a result, the line of
motion of the tool rest is governed by the sliding die, but the diameter
to which the tool will turn is determined by the feed screw in the usual
manner. When it is not required to use the taper attachment, the rod or
spindle is detached from the sliding die and is locked by a clamp, when
the rest may be operated in the usual manner.
Fig. 511 represents a compound duplex lathe of a design constructed by
Sir Joseph Whitworth, of Manchester, England. The two rests are here
operated on the same cross slide by means of a right and left-hand
cross-feed screw.
The tool for the back rest is here obviously turned upside down.
The lead screw is engaged at two places by the feed nut, which is in two
pieces attached to levers; while at a third point in its circumference
it is supported by a bracket, bolted to the lathe bed.
[Illustration: Fig. 511.]
Fig. 512 represents the New Haven Manufacturing Company's three tool
slide rest, for turning shafting. It is provided with a follower rest,
in front of which are two cutting tools for the roughing cuts, and
behind which is a third tool for the finishing cut. The follower rest
receives bushes, bored to the requisite diameter, to leave a finishing
cut. The first tool takes the preliminary roughing cut; the second tool
turns the shaft down to fit the bush or collar in the follower rest;
and, as stated, the last tool finishes the work.
Fig. 513 represents a 44-inch swing lathe, showing an extra and
detachable slide rest, bolted on one side of the carriage and intended
for turning work of too large a diameter to swing over the slide rest.
By means of this extra rest the cutting tool can be held close in the
rest, instead of requiring to stand out from the tool-post to a distance
equal to the width of the work. The ordinary tool post is placed in this
extra rest.
[Illustration: Fig. 512.]
When it is desired to bolt work on the lathe carriage and rotate the
cutting tools, as in the case of using boring bars, the cross slide is
sunk into instead of standing above the top surface of the carriage so
as to leave a flat surface to bolt the work to, and [T]-shaped slots are
provided in the carriage, to receive bolts for fastening the work to the
carriage, an example of this kind being shown in Fig. 514.
[Illustration: Fig. 513.]
Fig. 515 represents a self-acting slide or engine lathe by William
Sellers and Co., of Philadelphia. These lathes are made in various sizes
from 12 inches up to 48 inches swing on the same general design,
possessing the following features:--The beds or shears are made with
flat tops, the carriage being gibbed to the edges of the shears, these
edges being at a right angle to the top face of the bed. The dead centre
spindle is locked at each end of its bearing in the tailstock, thus
securing it firmly in line with the live spindle. The ordinary tool feed
is operated by a feed rod in front of the lathe, and this rod is
operated by a disc feed, which may be altered without stopping the lathe
so as to vary the rate of tool feed; and an index is provided whereby
the operator may at once set the discs to give the required rate of
feed. The lead screw for screw cutting is placed in a trough running
inside the lathe bed, so that it is nearer to the cutting tool than if
placed outside that bed, while it is entirely protected from the lathe
cuttings and from dirt or dust; and the feed-driving mechanism is so
arranged that both may be in gear with the live spindle, and either the
rod feed or screw-cutting feed may be put into action instantly, while
putting one into action throws the other out, and thus avoid the
breakage that occurs when both may be put into action at the same time.
The direction of the turning feed is determined by the motion of a lever
conveniently placed on the lathe carriage, and the feed may be stopped
or started in either direction instantly. The mechanism for putting the
cross feed in action is so constructed (in those lathes having a
self-acting cross feed) that the cross feed cannot be in action at the
same time as the turning feed or carriage traverse by rod feed.
Lathes of 12 and 16 inches swing are back-geared, affording six changes
of speed, and the lathe tool has a vertical adjustment on a single slide
rest. Lathes of 20 inches swing are back-geared with eight changes of
speed. Lathes of 25 inches and up to 48 inches swing inclusive are
triple-geared, affording fifteen changes of speed, having a uniformly
progressive variation at each change.
The construction of the live head or headstock for a 36-inch lathe is
shown in the sectional side view in Fig. 516, and in the top view in
Fig. 517, and it will be seen that there are five changes of speed on
the cone, five with the ordinary back-gear, and five additional ones
obtained by means of an extra pinion on the end of the back-gear
spindle, and gearing with the teeth on the circumference of the face
plate, the ordinary pinion of the back-gear moving on the back-gear
spindle so as to be out of the way and clear the large gear on the cone
spindle when the wheel of the extra back-gear pinion is in use, as shown
in Fig. 517.
[Illustration: Fig. 514.]
The front bearing of the live spindle is made of large diameter to give
rigidity, and the usual collar for the face plate to screw against is
thus dispensed with. End motion to the live spindle is prevented by a
collar of hardened steel, this collar being fast on the live spindle and
abutting on one side against the end face of the back bearing and on the
other against a hardened steel thrust collar.
[Illustration: Fig. 515.]
All these parts are enclosed in a tight cast-iron tail-block, which
serves as an oil well to insure constant and perfect lubrication. The
surfaces which confine the revolving collar back and front are so
adjusted as to allow perfect freedom of rotary motion to the spindle and
collar, but no perceptible end motion. The securing of the live spindle
endwise is thus confined to the thickness of the steel collar only, and
this is so enclosed in a large mass of cast iron as to insure uniformity
of temperature in all its parts, hence there is no liability for the
live spindle to stick or jam in its bearings, while the expansion of the
live spindle endways from this collar (if it expands more than the lathe
head) is allowed for in freedom of end motion through the front journal,
which is a little longer than the bearing it runs in. In turning work
held between the lathe centres the end thrust is taken against the
hardened steel collar on the live spindle, and the hardened steel collar
at the back of it, while in turning work chucked to the face plate the
spindle is held in place endways by the confinement of the steel collar
on the spindle between the steel collar behind it and the back end of
the back bearing. With this arrangement of the spindle the change from
turning between the lathe centres and turning chucked work requires no
thought or attention to be given to any adjustment of the live spindle
to accommodate it for the changed condition of end pressure between
turning between the centres and turning chucked work, as is the case in
ordinary lathes.
The double-geared lathes, as those of 12, 16 and 20 inches swing, are
provided with face plates that unscrew from the live spindle to afford
convenience for changing from one size of face plate to another, and all
such lathes have their front live spindle journal made of sufficiently
enlarged diameter above that of the screw, to afford a shoulder for the
face plate to abut against. The nose of the live spindle is not threaded
along its entire length, but a portion next to the shoulder is made
truly cylindrical but without any thread upon it, and to this unthreaded
part the face plate accurately fits so that it is held true thereby, and
the screw may fit somewhat loosely so that all the friction acts to hold
the face plate true and hard up against the trued face of the spindle
journal. Face plates fitted in this way may be taken off and replaced as
often as need be, with the assurance that they will be true when in
place unless the surfaces have been abused in their fitting parts.
[Illustration: Fig. 516.]
The construction of the tailstock or poppet-head, as it is sometimes
termed, is shown in Figs. 518, 519, and 520. To hold it in line with the
live spindle it is fitted between the inner edges of the bed, and it
will be seen that one of the bed flanges (that on the left of the
figure) is provided on its under side with a [V], and the clamp is
provided with a corresponding [V], so that in tightening up the bolt
that secures the tailstock to the bed the tailstock is drawn up to the
edge of the shears, and therefore truly in line with the live spindle,
while when this bolt is released the tailstock is quite free to be moved
to its required position in the length of the bed. As a result of this
form of design there is no wear between the clamp and the underneath
[V], and the tailstock need not fit tightly between the edges of the
bed, hence wear between these surfaces is also avoided, while the
tailstock is firmly clamped against one edge of the bed as soon as the
clamp is tightened up by the bolt on that side.
[Illustration: Fig. 517.]
Fig. 520 shows the method of locking the tailstock spindle and of
preventing its lateral motion in the bearing in the tailstock. At the
front or dead centre end of this bearing there is between the spindle a
sleeve enveloping the spindle, and coned at its outer end, fitting into
a corresponding cone in the bore of the tailstock. Its bore is a fit to
the dead spindle, and it is split through on the lower side. Its inner
end is threaded to a sleeve that is within the headstock, and whose end
is coned to fit a corresponding cone at the inner end of the bore of the
tailstock.
[Illustration: Fig. 518.]
To this second sleeve the line shown standing vertically on the left of
the hand wheel is attached, so that operating this handle revolves the
second sleeve and the two sleeves screw together, their coned ends
abutting in their correspondingly coned seats in the tailstock bore, and
thus causing the first-mentioned and split sleeve to close upon the dead
centre spindle and yet be locked to the tailstock.
[Illustration: Fig. 519.]
As the bore of the tailstock is exactly in line with the live spindle,
it follows that the dead spindle will be locked also in line with it.
Figs. 521 and 522 represent sectional views of the carriage and slide
rest of these lathes of a size over 16 inches swing. On the feed rod
there are two bevel pinions P, one on each side of the bevel-wheel A,
and by a clutch movement either of these wheels may be placed in gear
with bevel-wheel A.
The clutch motion is operated by a lever which, when swung over to the
right, causes the bevel pinion on the right to engage with the
bevel-wheel A, and the carriage feeds to the right, while with the lever
swung over to the left the carriage feeds to the left.
On the inclined shaft is a worm, or, as the makers term it, a spiral
pinion of several teeth which gears into a straight toothed spur
gear-wheel, giving a smooth and rolling tooth contact, and therefore
producing an even and uniform feed motion.
This spur gear is fast on a shaft C, which is capable of end motion and
is provided on each of its side faces with an annular toothed clutch. On
each side of this spur-wheel is a clutch, one of which connects with the
train of gears for the turning feed, and the other with the cross-feed
gear B.
[Illustration: Fig. 520.]
When the shaft (whose end is shown at C, and to which the spur gear
referred to is fast) is pulled endways outwards from the lathe bed, its
front annular clutch engages with the clutch that sets the cross-feed
gear B in motion, and B engages with a pinion which forms the nut of the
cross-feed screw.
When shaft C is moved endways inwards its other annular clutch engages
the clutch on that side of it, and the turning feed is put into
operation. The method of operating shaft C endways is as follows:--
In a horizontal bearing D is a shaft at whose end is a weighted lever L,
and on the end of this shaft is a crank pin shown engaging a sleeve E
which affords journal bearing to the outer end of shaft C, so that
operating the weighted lever L operates E, and therefore shaft C with
the spur gear receiving motion from the worm. A simple catch confines
lever L to either of its required limits of motion, and allows the free
motion of the operating lever to start or stop either the longitudinal
or the cross feed, either of which is started or stopped by this lever,
but no mistake can occur as to which feed is operated, because the catch
above mentioned requires to be shifted to permit the feed to be
operated.
The lower end of the bell crank F engages with the sleeve E, so that
when the shaft C is operated outwards the horizontal arm of bell crank F
is depressed and the spur pinion of the cross-feed nut is free to
revolve, being driven by the cross-feed motion. When the lever F is
moved towards the lathe bed (which occurs when the stop or catch is set
to allow the longitudinal feed to be used) the nut of the cross feed is
locked fast by the horizontal arm of the bell crank F. This device makes
the whole action from one direction of feed to another automatic, and
the attention of the workman is not needed for any complicated
adjustment of parts preparatory to a change from one feed to the other.
At H is a hand wheel for hand feeding, the pinion R meshing into the
rack that extends along the front of the lathe bed; back of the hand
wheel and at H´ a clamp is provided whereby the saddle or carriage may
be locked to the lathe bed when the cross feed is being used, thus
obviating the use of a separate clamp on the bed.
The top slide of the compound rest is long and its guideway is short,
the nut being in the stationary piece G, and it will be observed that by
this arrangement at no time does the bearing surfaces of the slides
become exposed to the action of chips or dirt.
[Illustration: Fig. 521.]
Fig. 523 is a sectional view of the carriage and slide rest as arranged
for 12 and 16-inch lathes when not provided with a self-acting cross
feed. In this case end motion to shaft C is given by lever H, which is
held in its adjusted position by the tongue T. In this lathe the
screw-cutting and the turning feed cannot be put into gear at the same
time.
[Illustration: Fig. 522.]
The tool nut is arranged to enable the tool to be adjusted for height
after it is fastened in the tool post by pivoting it to the cross slide,
a spring S forcing it upwards at its outer end, thus holding the tool
point down and in the direction in which the pressure of the cut forces
it, thus preventing the wear of the pivot from letting the tool move
when it first meets the cut. The nut N is operated to adjust the tool
height, and at the same time enables the depth of cut to be adjusted
very minutely. A trough catches the water, cuttings, &c., and thus
protects the slides and slideways from undue wear.
In all these lathes the feeding mechanism is so arranged that there are
no overhanging or suspended shaft pins or spindles, each of such parts
having a bearing at each end and not depending on the face surface of a
collar or pin, as is common in many lathes. Furthermore, in these
lathes the handle for the hand carriage feed moves to the right when the
carriage moves to the right; the cross-feed screw (and the upper screw
also in compound slide rests) has a left-hand thread, so that the nut
being fixed the slides move in the same direction as though the nut
moved as in ordinary lathes. The tailstock or poppet-head screw is a
right hand because the nut moves in this case. The object of employing
right-hand screws in some cases, and left-hand ones in others, is that
it comes most natural in operating a screw to move it from right to left
to unscrew, and from left to right to screw up a piece, this being the
action of a right-hand screw, left-hand screws being comparatively
rarely used in mechanism, save when to attain the object above referred
to.
[Illustration: Fig. 523.]
Fig. 524 represents the Niles Tool Works car axle lathe, forming an
example in which the work is driven from the middle of its length,
leaving both ends free to be operated upon simultaneously by separate
slide rests.
[Illustration: Fig. 524.]
The work being driven from its centre enables it to rotate upon two dead
centres, possessing the advantage that both being locked fast there is
no liberty for the work to move, as is the case when an ordinary lathe
having one live or running spindle is used, because in that case the
live spindle must be held less firmly and rigidly than a dead centre, so
as to avoid undue wear in the live spindle bearings; furthermore, the
liability of the workman to neglect to properly adjust the bearings to
take up the wear is avoided in the case of two dead centres, and no
error can occur because of either of the centres running out of true, as
may be the case with a rotating centre.
The cone pulley and back gear are here placed at the head of the lathe
driving a shaft which runs between the lathe shears and drives a pinion
which gears with the gear on the work driving head shown to stand on the
middle of the shears. This head is hollow so that the axle passes
through it. On the face of this gear is a Clement's equalizing driver
constructed upon the principle of that shown hereafter in Fig. 756.
The means for giving motion to the feed screw and for enabling a quick
change from the coarse roughing feed to a finer finishing feed to the
cutting tool without requiring to change the gears or alter their
positions, is shown in Fig. 525. _a_ and _b_ are two separate pinions
bored a working fit to the end of the driving shaft S, but pierced in
the bore with a recess and having four notches or featherways _h_. The
end of the driving shaft S is pierced or bored to receive the handled
pin _i_, and contains four slots to receive the four feathers _j_ which
are fast in _i_. In the position shown in the figure these feathers
engage with neither _a_ nor _b_, hence the driving shaft would remain
motionless, but it is obvious that if pin _i_ be pushed in the feathers
would engage _b_ and therefore drive it; or if _i_ were pulled outwards
the feathers would engage _a_ and drive it, because _a_ and _b_ are
separate pinions with a space or annular recess between them sufficient
in dimensions to receive the feathers. The difference in the rate of
feed is obviously obtained through the difference in diameters of the
pair of wheels _a_, _c_ and the pair _d_, _b_, the lathe giving to the
lead screw the slowest motion and, therefore, the finest feed.
The means for throwing the carriage in and out of feed gear with the
feed screw and of providing a hand feed for operating the tool in
corners or for quickly traversing the carriage, is shown in Fig. 526, in
which S represents the feed screw and B a bracket or casting bolted to
the carriage and carrying the hand wheel and feed mechanism shown in the
general cut figure.
[Illustration: Fig. 525.]
B provides a slide way denoted by the dotted lines at _b_, for the two
halves N and N´ of the feed nut. It also carries a pivot pin shown at
_p_ in the front elevation, which screws into B as denoted by _p´_ in
the end view; upon this pivot operates the piece D, having the handle
_d_. In D are two cam grooves _a_ _a_; two pins _n_, which are fast in
the two half-nuts N N´, pass through slots _c_ _c_ in B, and into the
cam grooves _a_ _a_ respectively.
[Illustration: Fig. 526.]
As shown in the cut the handle _d_ of D is at its lowest point, and the
half-nuts N´ and N are in gear upon the feed screw; but suppose _d_ be
raised, then the grooves _a_ _a_ would force their respective pins _n_
up the slots _c_, and these pins _n_ being each fast to a half of the
nut, the two half-nuts would be opened clear of the feed screw, and the
carriage would cease to be fed.
The hand-feed or guide-carriage traverse motion is accomplished as
follows:--B provides at _e_ journal bearing to a stud on which is the
hand wheel shown in the general cut; attached to this hand wheel is a
pinion operating a large gear (also seen in general cut) whose pitch
line is seen at _g_, in figure. The stud carrying _g_ has journal
bearing at _f_, and carries a pinion whose pitch circle is at _h_ and
which gears with the rack.
Fig. 527, which is taken from _The American Machinist_, represents an
English self-acting lathe capable of swinging work of 12 inches diameter
over the top of the lathe shears, which are provided with a removable
piece beneath the live centre, which when removed leaves a gap,
increasing the capacity of the lathe swing. The gears for reversing the
direction of feed screw motion are here placed at the end of the live
head or headstock, the screw being used for feeding as well as for screw
cutting.
Fig. 528 represents a pattern-maker's lathe, by the Putnam Tool Co., of
Fitchburg, Massachusetts. This lathe is provided with convenient means
of feeding the tool to its cut by mechanism instead of by hand, as is
usually done by pattern-makers, and this improvement saves considerable
time, because the necessity of frequently testing the straightness of
the work is avoided.
It is provided with an iron extension shears, the upper shears sliding
in [V]-ways provided in the lower one. The hand-wheel is connected with
a shaft and pinion, which works in a rack, and is used for the purpose
of changing the position of the upper bed, which is secured in its
adjusted position by means of the tie bolts and nuts, as shown on the
front of the lower shears. This enables the gap in the lower shears to
be left open to receive work of large diameter, and has the advantage
that the gap need be opened no more than is necessary to receive the
required length of work. The slide-rest is operated by a worm set at an
angle, so as to operate with a rolling rather than a sliding motion of
the teeth, and the handle for operating the worm-shaft is balanced. The
carriage is gibbed to the bed. The largest and smallest steps of the
cone pulley are of iron, the intermediate steps being of wood, and a
brake is provided to enable the lathe to be stopped quickly. This is an
excellent improvement, because much time is often lost in stopping the
lathe while running at a high velocity, or when work of large diameter
is being turned. The lathe will swing work of 50 inches within the gap,
and the upper shears will move sufficiently to take in 4 additional feet
between the centres.
In the general view of the lathe, Fig. 528, the slide-rest is shown
provided with a [T]-rest for hand tools, but as this sets in a clip or
split bore, it may readily be removed and replaced by a screw tool,
poppet for holding a gauge, or other necessary tool. To enable the
facing of work when the gap is used, the extra attachment shown in Figs.
529 and 530 is employed. It consists of an arm or bar A, bolted to the
upper shears S by a bolt B, and clamp C, in the usual manner, and is
provided with the usual slideway and feed-screw _f_ for operating the
lower slide T, which carries a hollow stem D; over D fits a hub K, upon
the upper slide E, which hub is split and has a bolt at F, by means of
which the upper slide may be clamped to its adjusted angle or position.
The upper slider H receives the tool-post, which is parallel and fits in
a split hub, so that when relieved it may be rapidly raised or lowered
to adjust the height of the tool.
The construction of the brake for the cone pulley is shown in Figs. 531
and 532, in which P represents the pulley rim, L the brake lever, S a
wooden shoe, and W a counter-weight. The lever is pivoted at G to a lug
R, provided on the live headstock, and the brake obviously operates on
the lowest part of the cone flange; hence the lever handle is depressed
to put the brake in action.
[Illustration: _VOL. I._ =EXAMPLES IN LATHE CONSTRUCTION.= _PLATE V._
Fig. 527.
Fig. 528.
Fig. 529.]
The construction of the front and back bearings for the live spindle is
the same as that shown in Figs. 495 and 496.
[Illustration: Fig. 530.]
Wood turners sometimes have their lathes so made that the headstock can
be turned end for end on the lathe shears, so that the face plate may
project beyond the bed, enabling it to turn work of large diameter. A
better method than this is to provide the projecting end of the lathe
with a screw to receive the face plate as shown in Fig. 533, which
represents a lathe constructed by Walker Brothers of Philadelphia. At
the end of the lathe is shown a hand rest upon a frame that can be moved
about the floor to accommodate the location, requiring to be turned upon
the work.
[Illustration: Fig. 531.]
For very large work, wood-workers sometimes improvise a facing lathe, as
shown in Fig. 534, in which A is a headstock bolted to the upright B; C
is the cone pulley, and E a face plate built up of wood, and fastened to
an iron face plate by bolts. The legs A, of the tripod hand rest, Fig.
535, are weighted by means of the weights B.
[Illustration: Fig. 532.]
In Fig. 536 is shown a chucking lathe, especially adapted for boring and
facing discs, wheels, &c. The live spindle is driven by a worm-wheel,
provided around the circumference of the face plate. The driving worm
(which runs in a cup of oil) is on a driving shaft, running across the
lathe and standing parallel with the face of the face plate. This shaft
is driven by a pulley as shown, changes of speed being effected by
having a cone pulley on the counter-shaft and one on the line of
shafting.
[Illustration: Fig. 533.]
This lathe is provided with two compound slide rests. One of which may
be used for boring, while the other is employed for facing purposes.
These rests are adjustable for location across the bed of the lathe by
means of bolts in slots, running entirely across the lathe bed.
These slide rests are given a self-acting motion by the following
arrangement of parts: at the back of the live spindle is an eccentric
rod, operating a connecting rod, which is attached at its lower end to
the arm of a shaft running beneath the bed, and parallel to the lathe
spindle. This shaft passes beyond the bed where it carries a bevel
gear-wheel, which meshes with a bevel gear-wheel upon a cross shaft.
This cross shaft carries three arms, one at each end and inside its
journal bearings in the bed, and one beneath and at a right angle to the
other two. These receive oscillating motion by reason of the eccentric
connecting rod, &c.
For each compound rest there are provided two handles as usual, and in
addition an [L] lever, one arm of the latter being provided with a
series of holes, while the other carries a weight.
[Illustration: Fig. 534.]
The [L] lever carries a pawl which operates a ratchet wheel, placed on
the handle end of the slide rest cross feed screw. If then a chain be
attached to one of the holes of the [L] lever, and to the oscillating
arm, the motion in one direction of the latter will be imparted to the
[L] lever (when the chain is pulled). On the return motion of the
oscillating arm, the chain hangs loose, and the weight on the [L] lever
causes that lever arm to fall, taking up the slack of the chain, the
feed taking place (when the pawl is made to engage with the ratchet
wheel) during the motion of the oscillating arm from right to left, or
while pulling the chain.
The rate of feed is varied by attaching the chain to different holes in
the [L] lever.
To operate the rests in a line parallel to the lathe spindle, a similar
[L] lever is attached by chain to the third oscillating arm, which is
placed on the cross shaft, mid-way of the bed, or between the two slide
rests. It is obvious then that with an [L] lever attachment on each feed
screw, both slides of each rest may be simultaneously operated, while
either one may be stopped either by detaching the chain or removing the
[L] lever.
For operating the rests by hand, the usual feed-screw handles are used.
Fig. 537 represents a 90-inch swing lathe by the Ames Manufacturing
Company of Chicopee, Massachusetts.
[Illustration: Fig. 535.]
The distinguishing feature of this lathe is that the tailstock spindle
is made square, to better enable it to bear the strain due to carrying
cutting tools in place of the dead centre; and by means of a pulley
instead of a simple hand wheel for operating the tail spindle, that
spindle may be operated from an overhead countershaft, and a tool may be
put in to cut key-ways in pulleys, wheels, &c., chucked on the face
plate (which of course remains stationary during the operation), thus
dispensing with the necessity of cutting out such key-ways by hammer,
chisel, and file, in wheel bores too large and heavy to be operated upon
in a slotting machine.
[Illustration: Fig. 538.]
On account of the weight of the tailstock it is fitted with rollers,
which may be operated to lift it from the bed when it is to be moved
along the lathe bed.
[Illustration: _VOL. I._ =CHUCKING LATHES.= _PLATE VI._
Fig. 536.
Fig. 537.]
Fig. 538 represents a 50-inch swing lathe by the New Haven
Manufacturing Company of New Haven, Connecticut. The compound rest is
here provided with automatic feed so that it may be set at an angle to
bore tapers with a uniform feed. The tailstock is provided with a
bracket, carrying a pinion in gear with the hand-feed rack, so as to
move the tailstock along the bed by means of the pinion. The feed screw
is splined to give an independent feed, and the swing frame is operated
by a worm as shown.
[Illustration: Fig. 539.]
GAP LATHE OR BREAK LATHE.
The gap lathe is one in which the bed is provided with a gap beneath the
face plate, so as to enable that plate or the chucks to swing work of
larger diameter, an example being given in Fig. 539.
[Illustration: Fig. 540.]
It is obvious, however, that the existence of the gap deprives the slide
rest of support on one side, when it is used close to the face plate.
This is obviated in some forms of gap lathes by fitting into the gap a
short piece of bed that may be taken out when the use of the gap is
required.
The gap lathe has not found favor in the United States, the same result
being more frequently obtained by means of the extension lathe, which
possesses the advantages of the gap lathe, while at the same time
enabling the width of the gap to be varied to suit the length of the
work. Fig. 540 represents an extension lathe by Edwin Harrington and
Son, of Philadelphia. There are two beds A and B, the former sliding
upon the latter when operated by the hand-wheel E, which is upon the end
of a screw that passes between the two beds, has journal bearing in the
upper bed, and engages a nut in the lower one, so that as the screw is
operated the wheel moves longitudinally with the upper bed. C is the
feed rod which communicates motion to the feeding screw D, which has
journal bearing on the upper bed and therefore travels with it when it
is moved or adjusted longitudinally. The cross slide has sufficient
length to enable the slide rest to face work of the full diameter that
will swing in the gap, and to support the slide rest when moved outwards
to the full limit, it is provided with a piece F, which slides at its
base upon the guideway or slide G.
Fig. 541 represents a double face plate lathe such as is used for
turning the wheels for locomotives. The circumference of both the face
plates are provided with spur teeth, so that both are driven by pinions,
which by being capable of moving endways into or out of gear, enable
either face plate to be used singly, if required, as for boring
purposes.
The slide rests are operated by ratchet arms for the self feed, these
arms being operated by an overhead shaft, with arms and chains.
[Illustration: Fig. 541.]
Fig. 542 represents a chucking lathe adapted more especially for boring
purposes. Thus the cone pulley is of small diameter and the parts are
light, so that the lathe is more handy than would be the case with a
heavier built lathe, while at the same time it is sufficiently rigid for
large work that is comparatively light.
[Illustration: Fig. 542.]
The compound rest is upon a pedestal that can be bolted in any required
position on the lower cross slide, and is made self-acting for the feed
traverse by the change wheels and feed screw, while the self-acting
cross feed is operated by a ratchet handle, actuated by a chain from an
overhead reciprocating lever; the latter being actuated from the crank
pin at A, which is adjustable in a slot in the crank disk B. A lathe of
this kind is very suitable for brass work of unusually large diameter,
because in such work the cuts and feeds are light, and the cutting speed
is quick, hence a heavy construction is not essential.
Figs. 543 and 544 represent a large lathe built by Thomas Shanks and
Co., of Johnstone, near Glasgow, Scotland; all the figures of this lathe
being from _The American Machinist_.
Fig. 543 shows the headstock and two of the slide rests, while Fig. 544
represents the remainder of the bed, the tailstock, and two of the slide
rests.
It will be seen from the figures that there are a compound rest and a
column or pillar rest both at the front and at the back of the lathe,
and that there is an additional rest on the front end of the tailstock
which may be used for facing the ends of the work.
Fig. 545 represents a section through, and a partial plan of the
headstock, and it will be seen that the live spindle is free from the
cone pulley and from the gearing, the chuck plate being driven from a
pinion engaging an internal gear at the back of the chuck plate. By this
construction the balancing of such work as crank shafts is facilitated,
because the chuck plate is not affected by the friction of the driving
gears, and may therefore be easily revolved to test the balance of the
work.
Fig. 546 represents a cross section through the bed, and through one of
the compound rests, and one of the pillar rests, the latter rests being
made thin so that they may pass between the cheeks of crank shafts, to
turn their faces and the crank journals.
Fig. 547 represents a view from the back end of the headstock, and Fig.
548 a view of the lathe from the tailstock end.
Figs. 549 and 550 represent a plan and a side view of the headstock and
the two slide rests nearest to it. The lathe being shown at work on the
crank shaft of the steamship service, which is shown in dotted lines,
and it will be seen that for turning the stem of the shaft all the rests
can be used at once, those at the back of the lathe having their
cutting tools turned upside down (as will be more clearly seen in the
cross-sectional view of the rests in Fig. 546).
[Illustration: Fig. 543.]
Figs. 551 and 552 represent a plan and a side view of the other half of
the lathe in operation upon the same crank shaft, which is again shown
in dotted lines.
[Illustration: Fig. 544.]
Referring now to the general construction of the lathe, the headstock or
live spindle has a front journal bearing 18 inches diameter and 24
inches long, and a back bearing 12 inches diameter and 15 inches long,
the bearings being parallel. The driving cone has five changes of speed
for a 6-inch belt, and is carried on an independent spindle. The cone is
turned inside as well as outside, so as to be in balance at high speeds.
[Illustration: Fig. 545.]
The face plate is 12 feet diameter, cast with internal gear at the back.
It is provided with [T]-slots and square holes for fixing work. It is
bolted to a large flange in one piece with the spindle, and fitted with
four steel expanding gripping jaws worked with screws and toothed
blocks. These are for doing chuck work, or for gripping work to be
driven, as the collars of propeller or crank shafts, or work of a
similar character. By the system of gearing adopted, when desired, the
face plate can be revolved almost free, which facilitates balancing for
turning crank shafts, as well as other operations. The thrust against
the live spindle is taken by an adjustable steel tail piece.
[Illustration: Fig. 546.]
[Illustration: Fig. 547.]
[Illustration: Fig. 548.]
[Illustration: Fig. 549.]
The beds are double, 10 feet in width over all, the sections being
joined together by massive ground plates and bolts. They are made with
square lips to resist the upward strain of cutting. The front bed is
fitted with two saddles, each carrying a compound slide rest having the
following movements: First, screw-cutting, by means of a leading screw,
situated inside the bed, with a sliding disengaging nut and reversing
motion for right or left-hand threads, or for instantaneously stopping
the longitudinal movement of the saddle. This is accomplished by a set
of clutch mitres placed inside the bed at headstock end, and actuated by
a lever in front: Second, a self-acting surfacing motion to slide rest
by means of a longitudinal shaft at the front of the bed, and clutch
mitres for reversing the saddle screw.
[Illustration: Fig. 550.]
Third, power motion for moving the saddles quickly to position along the
bed. This is done through the fast and loose pulleys at the headstock
end of lathe.
Fourth, hand rack motion to saddle. The back bed is fitted with two
saddles, each carrying a pillar rest, fitted for all movements in plain
turning like the front rests, and also with swiveling motion for corner
turning.
[Illustration: Fig. 551.]
The tailstock has a spindle 9 inches diameter. It is fitted in [V]s on
the bed, and held down by three [T]-head bolts on each side. The top
section is adjustable for turning tapers. It is moved along the ways by
engaging a nut with the main screw. An end-cutting rest is fitted to the
tailstock, which is adapted for operating on flanged couplings and
similar work.
There is a separate set of change wheels for each saddle, so arranged as
to cut standard pitches up to 3-inch pitch, and for self-acting feeds
down to 50 per inch. By this means, when both tools are in operation on
a piece of work, one tool may be used with coarse feed for roughing out,
while the other may be taking a fine or finishing cut either on the same
or a different part of the piece; or one tool may be cutting towards and
the other from the face plate, always maintaining the balance of a front
and back cut.
[Illustration: Fig. 552.]
Complete counter driving motion, consisting of wall brackets, shaft,
cone, and sets of fast and loose pulleys for quick reversing motion in
screw cutting, also belt bar shipping motion, and full set of
case-hardened wrenches are provided.
CHAPTER VII.--DETAILS IN LATHE CONSTRUCTION.
Although in each class of lathe the requirements may be practically the
same, yet there is a variety of different details of construction by
means of which these requirements may be met or filled, and it may be
profitable to enter somewhat into these requirements and the different
constructions generally employed to meet them.
[Illustration: Fig. 553.]
The cone spindle or live spindle of a lathe should be a close working
fit to its boxes or bearings, so that it will not lift under a heavy
cut, or lift and fall under a cut of varying pressure. This lifting and
falling may occur even though the work be true, and the cut therefore of
even depth all around the work, because of hard seams or spots in the
metal.
It is obvious that the bearings should form a guide, compelling the live
spindle to revolve in a true circle and in a fixed plane, the axis of
revolution being in line with the centre line of the tail spindle and
that means should be provided to maintain this alignment while
preserving the fit, or in other words taking up the wear. The spindle
journals must, to produce truly cylindrical work, be cylindrically true,
or otherwise the axis of its revolution will change as it revolves, and
this change will be communicated through the live centre to the work, or
through the chuck plate to the work, as the case may be.
The construction of the bearings should be such, that end motion to the
spindle is prevented in as short a length of the spindle as possible,
the thrust in either direction being resisted by the mechanism contained
in one bearing.
In Fig. 553 is a form of construction for the front bearing (as that
nearest to the live centre is called), in which end motion to the
spindle is prevented at the same time as the diametral fit is adjusted.
The spindle is provided with a cone at C and is threaded at T to receive
two nuts N which draw the spindle cone within the bearing. In this case
the journal at the back end may be made parallel, so that if the spindle
either expands or contracts more under variations of temperature than
the frame or head carrying the bearings or bearing boxes, it will not
bind endwise, nor will the fit be impaired save inasmuch as there may be
an inequality of expansion in the length of the front journal and its
box. In this case, however, the end pressure caused by holding the work
between the lathe centres acts to force the spindle into its bearing and
increase the tightness of its fit, hence it is not unusual to provide at
the back bearing additional means to resist the thrust of the dead
centre.
[Illustration: Fig. 554.]
Fig. 554, which is taken from "Mechanics," represents Wohlemberg's
patent lathe spindle, in which both journals are coned, fitting into
bushes which can be replaced by new ones when worn; the end thrust is
here taken by a steel screw, while the end fit is adjusted by means of a
ring nut which binds the face of the large cone gear against the inside
face of the front bearing and by the face of the gear that drives the
change gears. It may be pointed out, however, that in this construction
the spindle must be drawn within to adjust the fit of the front bearing,
which can only be done by adjusting the pinion that drives the change
gears, or by screwing up the nut that is inside the cone, and therefore
cannot be got at. The back bearing can be adjusted by means of the ring
nuts provided at each of its ends.
[Illustration: Fig. 555.]
Fig. 555 represents another design of cone bearing, in which the spindle
is threaded to receive the nuts A which draw it within the front bearing
and thus adjust the fit, and at the same time prevent end motion. The
back bearing is provided with a bush parallel outside, and furnished
with a nut at B to adjust the fit of the end bearing. To prevent the end
pressure of the dead centre from forcing the spindle cones too tightly
within their bearings a cross piece P is employed (being supported by
two studs provided in the head), and through P passes an adjusting screw
D, having nuts N and C, one on each side of P. Between the end of D and
of the lathe spindle a washer of leather or of raw hide is placed to
prevent the end faces from abrading. A similar device for taking up the
end thrust is often provided to lathes in which the journals are both
parallel, fitting in ordinary boxes, a top view of the device being
illustrated in Fig. 556, in which B is the back bearing box, S S two
studs supporting cross-piece P, and N and C are adjusting nuts. G is the
gear for driving the change wheels for screw cutting or for ordinary
feeding as the case may be. In this design the gear wheel G remains
fixed and the combinations of gears necessary to cut various pitches of
thread must be made on the lead screw and on the swing frame, which must
be long enough to permit the change gear stud to pass up to permit the
smallest change wheel to gear with wheel G, and which is provided with
two grooves E and F, Fig. 557, for two studs to carry two compounded
pairs of change wheels. This compounding in two places on the swing
frame enables gear G to be comparatively large, and thus saves the teeth
from rapid wear, while it facilitates the cutting of left-hand threads,
because it affords more convenience for putting in a gear to change the
direction of feed screw revolution.
[Illustration: Fig. 556.]
In many lathes of American design the journals are made parallel, and
the end play is taken up at the back bearing, an example being given in
Fig. 558, in which the back bearing boxes are made in two halves A and
B, the latter having a set screw (with check nut) threaded through it
and bearing against a washer that meets the end of the spindle.
[Illustration: Fig. 557.]
A simple method of preventing end motion is shown in Fig. 559, a bracket
B affording a support for a threaded adjusting screw, which is sometimes
made pointed and at others flat. When pointed it acts to support the
spindle, but on the other hand it also acts to prevent the journal from
bedding fairly in the boxes. In some cases of small lathes the back
bearing is dispensed with, and a similar pointed adjusting screw takes
its place, which answers very well for very small work.
Since the strain of the cut carried by the cutting tool falls mainly
upon the live centre end of the cone spindle, it is obvious that the
bearing at that end has a greater tendency to wear.
[Illustration: Fig. 558.]
In addition to this the weight of the cone itself is greatest at that
end, and furthermore the weight of the face plate or chuck, and of the
work, is carried mainly at that end. If, however, one journal and
bearing wears more than the other, the spindle is thrown out of line
with the lathe shears, and with the tail block spindle. The usual method
of obviating this as far as possible is to give that end a larger
journal-bearing area.
[Illustration: Fig. 559.]
The direction in which this wear will take place depends in a great
measure upon the kind of work done in the lathe; thus in a lathe running
slowly and doing heavy work carried by chucks, or on the face plate, the
wear would be downwards and towards the operator, the weight of the
chuck, &c., causing the downward, and the resistance or work-lifting
tendency of the cut causing the lateral wear. As a general rule the wear
will be least in a lateral direction towards the back of the lathe, but
the direction of wear is so variable that provision for its special
prevention or adjustment is not usually made. In the S. W. Putnam lathe,
provision is made that the bearing boxes may be rotated in the head, so
that when the lathe is used on a class of work that caused the live
spindle to wear the bearing boxes on one side more than on another, the
boxes may be periodically partly rotated in the head so that further
wear will correct the evil.
The coned hole to receive the live centre should run quite true, so that
the live centre will run true without requiring, when inserted, to be
placed in exactly the same position it occupied when being turned up at
its conical point. But when this hole does not run true a centre punch
dot is made on the end of the spindle, and another on the centre, so
that by placing the two dots to coincide at all times, the centre will
run true.
The taper given to lathe centres varies from 9/16 per foot to 1 inch per
foot. In the practice of Pratt and Whitney a taper of 9/16 per foot is
given to all lathes, the lengths of the tapers for different sizes of
lathes being as follows:
Length of Taper Socket
Swing of Lathe. for Live Centre.
13 inches 5 inches.
16 " 3-3/4 "
18 and 19 inches 7-11/16 "
" " with hollow spindle 5 inches long
and 1-1/16 diameter at the small end.
The less the amount of taper the more firmly the centre is held, but the
more difficult it becomes to remove the centre when necessary.
[Illustration: Fig. 560.]
The principal methods of removing live centres are shown in Fig. 560, in
which is shown at B a square part to receive a wrench, it being found
that if not less than about 1/2-inch taper per foot of length be given
to the live spindle socket, then revolving the centre with a wrench will
cause it to release itself, enabling it to be removed by hand. Another
method employed on small lathes is to drill a hole through the live
spindle to receive a taper pin P, the live centre end being shown at C.
Another and excellent plan for large lathes, is to thread the centre and
provide it with a nut M, which on being screwed against the end face of
the live spindle will release the centre. The objection to the use of
the pin P is that it is apt to become mislaid, and it is not advisable
to use a hammer about the parts of the lathe, especially in such an
awkward place as between the journal bearing and the cone, which is
where the pin hole requires to be located. The square section is,
therefore, the best method for small lathes, and the nut for large ones.
In cases where the live spindle is made hollow a bar may be passed
through from the rear end to remove the centre; this also enables rods
of iron to be passed through the spindle, leaving the end projecting
through the chuck for any length necessary for the work to be turned out
of its exposed end.
The dead centre may be extracted from the tail spindle by a pin and hole
as in Fig. 560, or, what is better, by contact with the end of the tail
screw as described when referring to the tail stock of the S. W. Putnam
lathe.
The cone pulley should be perfectly balanced, otherwise at high speeds
the lathe will shake or tremble from the unbalanced centrifugal motion,
and the tremors will be produced to some extent on the work. The steps
of the cone should be amply wide, so that it may have sufficient power,
without overstraining the belt, to drive the heaviest cut the lathe is
supposed to take without the aid of the back gear.
In some cases, as in spinning lathes, the order of the steps is
reversed, the smallest step of the cone being nearest to the live
centre, the object being to have the largest step on the left, and
therefore more out of the way.
The steps of the cone should be so proportioned that the belt will shift
from one to the other, and have the same degree of tension, while at the
same time they should give a uniform graduation or variation of speed
throughout, whether the lathe runs in single gear or with the back gear
in. This is not usually quite the case although the graduation is
sufficiently accurate for practical purposes. The variation in the
diameter of the steps of a lathe cone varies from an inch for lathes of
about 12-inch swing, up to 2 inches for lathes of about 30-inch swing,
and 3 inches for lathes of 5 or more feet of swing.
To enable the graduation of speed of the cone to be uniform throughout,
while the tension of the belt is maintained the same on whatever step
the cone may be, the graduation of the steps may be varied, and this
graduation may be so proportioned as to answer all practical purposes if
the overhead or countershaft cone and that on the lathe are alike.
The following on this subject is from the pen of Professor D. E. Klein,
of Yale College.
"The numbers given in the following tables are the differences between
the diameters of the adjacent steps on either cone pulley, and are
accurate within half a hundredth of an inch, which is a degree of
accuracy sufficient for practical purposes.
By simply omitting a step at each end of the cone, the two tables given
will be found equally well adapted for determining the diameters of
cones having four and three steps respectively.
The following are examples in the use of the tables. Suppose the centres
of a pair of pulley shafts to be 60 inches apart, and that the
difference of diameter between the adjacent steps is to be as near to
2-1/2 inches as can be, to obtain a uniformity of speed graduation and
belt tension, also that each cone is to have six steps, the smallest of
which is to be of five inches diameter.
To find the diameters for the remaining steps, we look in Table I.
(corresponding to cone pulleys with six steps), under 60 in. and
opposite 2-1/2 in. and obtain the differences,
2.37 2.43 2.50 2.57 2.63
Each of these differences is _subtracted_ from the _larger_ diameter of
the two adjacent steps to which it corresponds, thus:
17.50 = 1st step.
Difference of 1st and 2nd = 2.37
-----
15.13 = 2nd "
" 2nd " 3rd = 2.43
-----
12.70 = 3rd "
" 3rd " 4th = 2.50
-----
10.20 = 4th "
" 4th " 5th = 2.57
-----
7.63 = 5th "
" 5th " 6th = 2.63
-----
5.00 = 6th "
EXAMPLE 2. If we suppose the same conditions as in Example 1, with the
exception that each cone is to have four steps instead of six, the
largest diameter will, in this case, equal 12-1/2 in. and we may obtain
the remaining diameters by omitting the end differences of the above
example, and then subtracting the remaining differences as follows:
12.50 = 2nd step.
Difference of 2nd and 3rd = 2.43
-----
10.07 = 3rd "
" 3rd " 4th = 2.50
-----
7.57 = 4th "
" 4th " 5th = 2.57
-----
5.00 = 5th "
The 2nd, 3rd, 4th, and 5th steps of the table correspond respectively to
the 1st, 2nd, 3rd, and 4th steps of the cone, having but four steps. If
the smallest diameter had not been assumed equal to 5 in. we might have
dropped a step at each end of the six-step cone of the preceding
example, and employed the remaining four diameters, 15.13 in. 12.70 in.
10.20 in. and 7.63 in. for one four-step cone.
The present and the previous examples show that we can assume the size
of the smallest step anything that we please, and, other things being
equal, can make the required cones large or small.
I.--TABLE FOR FINDING CONE PULLEY DIAMETERS WHEN THE TWO PULLEYS ARE
CONNECTED BY AN OPEN BELT, AND ARE EXACTLY ALIKE.
The numbers given in table are the differences between the diameters of
the adjacent steps on either cone pulley, and can be employed when there
are either six or four steps on a cone. When there are six steps, the
largest is the first, and the smallest the sixth step of the table. When
there are four steps, the largest is the second, and the smallest the
fifth step of the table.
+-------------+-----------+------------------------------
| Average | Adjacent | DISTANCE BETWEEN THE CENTRES
| difference | steps, | OF CONE PULLEYS.
| between | whose +----+----+----+----+----+----+
| the | diffe- | | | | | | |
| adjacent | rence is | 10 | 20 | 30 | 40 | 50 | 60 |
| steps. | given in | i n c h e s. |
| | table. | | | | | | |
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|0.87|0.94|0.96|0.97|0.98|0.98|
| |2nd " 3rd|0.94|0.97|0.98|0.98|0.99|0.99|
| 1 inch |3rd " 4th|1.00|1.00|1.00|1.00|1.00|1.00|
| |4th " 5th|1.06|1.03|1.02|1.02|1.01|1.01|
| |5th " 6th|1.13|1.06|1.04|1.03|1.02|1.02|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.21|1.36|1.40|1.43|1.44|1.45|
| |2nd " 3rd|1.36|1.43|1.45|1.46|1.47|1.48|
| 1-1/2 inch |3rd " 4th|1.50|1.50|1.50|1.50|1.50|1.50|
| |4th " 5th|1.64|1.57|1.55|1.54|1.53|1.52|
| |5th " 6th|1.79|1.64|1.60|1.57|1.56|1.55|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.47|1.74|1.83|1.87|1.90|1.92|
| |2nd " 3rd|1.74|1.87|1.92|1.93|1.95|1.96|
| 2 inches |3rd " 4th|2.00|2.00|2.00|2.00|2.00|2.00|
| |4th " 5th|2.26|2.13|2.08|2.07|2.05|2.04|
| |5th " 6th|2.53|2.26|2.17|2.13|2.10|2.08|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.66|2.10|2.23|2.30|2.34|2.37|
| |2nd " 3rd|2.10|2.30|2.37|2.40|2.42|2.43|
|2-1/2 inches |3rd " 4th|2.50|2.50|2.50|2.50|2.50|2.50|
| |4th " 5th|2.90|2.70|2.63|2.60|2.58|2.57|
| |5th " 6th|3.34|2.90|2.77|2.70|2.66|2.63|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.76|2.42|2.62|2.71|2.77|2.81|
| |2nd " 3rd|2.42|2.71|2.81|2.86|2.88|2.90|
| 3 inches |3rd " 4th|3.00|3.00|3.00|3.00|3.00|3.00|
| |4th " 5th|3.58|3.29|3.19|3.14|3.12|3.10|
| |5th " 6th|4.24|3.58|3.38|3.29|3.23|3.19|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |3.95|3.31|3.49|3.59|3.66|
| |2nd " 3rd|2.94|3.49|3.66|3.75|3.80|3.83|
| 4 inches |3rd " 4th|4.00|4.00|4.00|4.00|4.00|4.00|
| |4th " 5th|5.06|4.51|4.34|4.25|4.20|4.17|
| |5th " 6th| |5.05|4.69|4.51|4.41|4.34|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |3.33|3.92|4.20|4.36|4.47|
| |2nd " 3rd|3.31|4.19|4.47|4.60|4.68|4.74|
| 5 inches |3rd " 4th|5.00|5.00|5.00|5.00|5.00|5.00|
| |4th " 5th|6.69|5.81|5.53|5.40|5.32|5.26|
| |5th " 6th| |6.67|6.09|5.80|5.64|5.53|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |3.52|4.42|4.83|5.08|5.23|
| |2nd " 3rd| |4.83|5.23|5.42|5.54|5.62|
| 6 inches |3rd " 4th| |6.00|6.00|6.00|6.00|6.00|
| |4th " 5th| |7.17|6.77|6.58|6.46|6.38|
| |5th " 6th| |8.48|7.58|7.17|6.92|6.77|
+-------------+-----------+----+----+----+----+----+----+
+-------------+-----------+-----------------------------+
| Average | Adjacent | DISTANCE BETWEEN THE CENTRES|
| difference | steps, | OF CONE PULLEYS. |
| between | whose +----+----+----+----+----+----+
| the | diffe- | | | | | | |
| adjacent | rence is | 70 | 80 | 90 | 100| 120| 240|
| steps. | given in | i n c h e s. |
| | table. | | | | | | |
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|0.98|0.98|0.99|0.99|0.99|1.00|
| |2nd " 3rd|0.99|0.99|0.99|0.99|1.00|1.00|
| 1 inch |3rd " 4th|1.00|1.00|1.00|1.00|1.00|1.00|
| |4th " 5th|1.01|1.01|1.01|1.01|1.00|1.00|
| |5th " 6th|1.02|1.02|1.01|1.01|1.01|1.00|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.46|1.46|1.47|1.47|1.48|1.49|
| |2nd " 3rd|1.48|1.48|1.49|1.49|1.49|1.49|
| 1-1/2 inch |3rd " 4th|1.50|1.50|1.50|1.50|1.50|1.50|
| |4th " 5th|1.52|1.52|1.51|1.51|1.51|1.51|
| |5th " 6th|1.54|1.54|1.53|1.53|1.52|1.51|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.93|1.93|1.94|1.95|1.96|1.98|
| |2nd " 3rd|1.96|1.97|1.97|1.97|1.98|1.99|
| 2 inches |3rd " 4th|2.00|2.00|2.00|2.00|2.00|2.00|
| |4th " 5th|2.04|2.03|2.03|2.03|2.02|2.01|
| |5th " 6th|2.07|2.07|2.06|2.05|2.04|2.02|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|2.39|2.40|2.41|2.42|2.43|2.47|
| |2nd " 3rd|2.44|2.45|2.46|2.46|2.47|2.49|
| 2-1/2 inches|3rd " 4th|2.50|2.50|2.50|2.50|2.50|2.50|
| |4th " 5th|2.56|2.55|2.54|2.54|2.53|2.51|
| |5th " 6th|2.61|2.60|2.59|2.58|2.57|2.53|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|2.84|2.86|2.87|2.88|2.90|2.95|
| |2nd " 3rd|2.92|2.93|2.94|2.94|2.95|2.98|
| 3 inches |3rd " 4th|3.00|3.00|3.00|3.00|3.00|3.00|
| |4th " 5th|3.08|3.07|3.06|2.06|3.05|3.02|
| |5th " 6th|3.16|3.14|3.13|3.12|3.10|3.05|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|3.71|3.75|3.78|3.80|3.83|3.91|
| |2nd " 3rd|3.85|3.87|3.88|3.89|3.91|3.96|
| 4 inches |3rd " 4th|4.00|4.00|4.00|4.00|4.00|4.00|
| |4th " 5th|4.15|4.13|4.12|4.11|4.09|4.04|
| |5th " 6th|4.29|4.25|4.22|4.20|4.17|4.09|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|4.55|4.60|4.64|4.68|4.74|4.87|
| |2nd " 3rd|4.77|4.80|4.82|4.84|4.86|4.93|
| 5 inches |3rd " 4th|5.00|5.00|5.00|5.00|5.00|5.00|
| |4th " 5th|5.23|5.20|5.18|5.16|5.14|5.07|
| |5th " 6th|5.45|5.40|5.36|5.32|5.26|5.13|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|5.34|5.42|5.49|5.55|5.62|5.80|
| |2nd " 3rd|5.67|5.71|5.75|5.77|5.81|5.90|
| 6 inches |3rd " 4th|6.00|6.00|6.00|6.00|6.00|6.00|
| |4th " 5th|6.33|6.29|6.25|6.23|6.19|6.10|
| |5th " 6th|6.66|6.58|6.51|6.45|6.38|6.20|
+-------------+-----------+----+----+----+----+----+----+
EXAMPLE 3. Let distance apart of the centres = 30 in. the average
difference between adjacent steps = 2 in. the diameter of the smallest
step = 4 in., and the number of steps on each of the cones = 5. The
largest step will then equal 12 in., and from Table II., under 30 in.
and opposite 2 in., we obtain the differences
1.87 1.96 2.04 2.13
and then subtracting as before we get the required diameters
12 in. 10.30 in. 8.17 in. 6.13 in. 4 in.
EXAMPLE 4. Let the conditions be as in the preceding example, the cone
pulley having, however, three steps instead of five, the largest
diameter will then equal 8 in.; and by dropping the end differences and
subtracting
8.00 = 2nd step.
Difference of 2nd and 3rd = 1.96
-----
6.04 = 3rd "
" 3rd " 4th = 2.04
-----
4.00 = 4th "
we get the diameters 8 in., 6.04, and 4 in., which correspond
respectively to 2nd, 3rd, and 4th steps of the table, and to the 1st,
2nd, and 3rd steps of the three-step cone.
EXAMPLE 5. Let the distance apart of the centres be 60 in., the average
difference between the adjacent steps be 2-1/8 in., the smallest step 7
in. and the number of steps = 5. The largest step will then be 7 in. +
(4 × 2-1/8) = 15-1/2 inches.
Now an inspection of Table II. will show that it contains no horizontal
lines corresponding to the average difference 2-1/8 inches, we cannot,
therefore, as heretofore, obtain the required differences directly, but
must interpolate as follows: since 2-1/8 inches is quarter way between 2
inches and 2-1/2 inches, the numbers corresponding to 2-1/8 inches (for
any given distance apart of the centres), will be quarter way between
the numbers of the table corresponding to 2 inches and 2-1/2 inches.
Thus, in Table II., we have under 60 inches,
and opposite 2-1/2 in.: 2.40 2.47 2.53 2.60
" 2 1.93 1.98 2.02 2.07
---- ---- ---- ----
.47 .49 .51 .53
Dividing these differences by 4, we get:
.12 .12 .13 .13
to which we add,
1.93 1.98 2.02 2.07
and get for the differences corresponding to 2-1/8 inches
2.05 2.10 2.15 2.20
and subtracting as before,
15.5 1st step.
difference of 1st and 2nd = 2.05
-----
13.45 = 2nd "
" 2nd " 3rd = 2.10
-----
11.35 = 3rd "
" 3rd " 4th = 2.15
-----
9.20 = 4th "
" 4th " 5th = 2.20
-----
7.00 = 5th "
Thus far, however, we have considered only the case where the two cone
pulleys were exactly alike. Now although this case occurs much more
frequently than the case in which the cone pulleys are unlike, it is
nevertheless true that unlike cone pulleys occur with sufficient
frequency to make it desirable that convenient means be established for
obtaining the diameters of their steps rapidly and accurately, and Table
III. was calculated by the writer for this purpose; its accuracy is more
than sufficient for the requirements of practice, the numbers in the
table being correct to within a unit of the fourth decimal place (_i.e._
within .0001). It should be noticed that the tabular quantities are not
the diameters of the steps, but these diameters divided by the distance
between the centres of the cone pulleys; in other words, the tabular
quantities are the effective diameters of the steps only when the
centres of the pulleys are a unit's distance apart. By thus expressing
the tabular quantities in terms of the distance apart of the axis, the
table becomes applicable to all cone pulleys whatever their distance
from each other, the effective diameters of the steps being obtained by
multiplying the proper tabular quantities by the distance between the
centres of the pulleys.
II.--TABLE FOR FINDING CONE PULLEY DIAMETERS WHEN THE TWO PULLEYS ARE
CONNECTED BY AN OPEN BELT, AND ARE EXACTLY ALIKE.
The numbers given in table are the differences between the diameters of
the adjacent steps on either cone pulley, and can be employed when there
are either five or three steps on a cone.
+-------------+-----------+-----------------------------+
| Average | Adjacent | DISTANCE BETWEEN THE CENTRES|
| difference | steps, | OF CONE PULLEYS. |
| between | whose +----+----+----+----+----+----+
| the | diffe- | | | | | | |
| adjacent | rence is | 10 | 20 | 30 | 40 | 50 | 60 |
| steps. | given in | i n c h e s. |
| | table. | | | | | | |
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|0.90|0.95|0.97|0.98|0.98|0.98|
| |2nd " 3rd|0.97|0.98|0.99|0.99|0.99|0.99|
| 1 inch |3rd " 4th|1.03|1.02|1.01|1.01|1.01|1.01|
| |4th " 5th|1.10|1.05|1.03|1.02|1.02|1.02|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.28|1.39|1.43|1.45|1.46|1.46|
| |2nd " 3rd|1.43|1.46|1.48|1.48|1.48|1.49|
| 1-1/2 inch |3rd " 4th|1.57|1.54|1.52|1.52|1.52|1.51|
| |4th " 5th|1.72|1.61|1.57|1.55|1.54|1.54|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.61|1.81|1.87|1.90|1.92|1.93|
| |2nd " 3rd|1.87|1.94|1.96|1.97|1.97|1.98|
| 2 inches |3rd " 4th|2.13|2.06|2.04|2.03|2.03|2.02|
| |4th " 5th|2.39|2.19|2.13|2.10|2.08|2.07|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.89|2.20|2.30|2.35|1.38|2.40|
| |2nd " 3rd|2.30|2.40|2.43|2.45|2.46|2.47|
| 2-1/2 inches|3rd " 4th|2.70|2.60|2.57|2.55|2.54|2.53|
| |4th " 5th|3.11|2.80|2.70|2.65|2.62|2.60|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|2.10|2.57|2.71|2.78|2.83|2.86|
| |2nd " 3rd|2.71|2.86|2.90|2.93|2.94|2.95|
| 3 inches |3rd " 4th|3.29|3.14|3.10|3.07|3.06|3.05|
| |4th " 5th|3.90|3.43|3.29|3.22|3.17|3.14|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |3.22|3.49|3.62|3.69|3.75|
| |2nd " 3rd|3.48|3.74|3.83|3.87|3.90|3.91|
| 4 inches |3rd " 4th|4.52|4.26|4.17|4.13|4.10|4.09|
| |4th " 5th| |4.78|4.51|4.38|4.31|4.25|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |3.77|4.20|4.40|4.52|4.60|
| |2nd " 3rd|4.19|4.60|4.73|4.80|4.84|4.87|
| 5 inches |3rd " 4th|5.81|5.40|5.27|5.20|5.16|5.13|
| |4th " 5th| |6.23|5.80|5.60|5.48|5.40|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd| |4.21|4.83|5.13|5.31|5.42|
| |2nd " 3rd|4.82|5.42|5.62|5.71|5.77|5.81|
| 6 inches |3rd " 4th|7.18|6.58|6.38|6.29|6.23|6.19|
| |4th " 5th| |7.79|7.17|6.87|6.69|6.58|
+-------------+-----------+----+----+----+----+----+----+
+-------------+-----------+-----------------------------+
| Average | Adjacent | DISTANCE BETWEEN THE CENTRES|
| difference | steps, | OF CONE PULLEYS. |
| between | whose +----+----+----+----+----+----+
| the | diffe- | | | | | | |
| adjacent | rence is | 70 | 80 | 90 | 100| 120| 240|
| steps. | given in | i n c h e s. |
| | table. | | | | | | |
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|0.99|0.99|0.99|0.99|0.99|1.00|
| |2nd " 3rd|0.99|1.00|1.00|1.00|1.00|1.00|
| 1 inch |3rd " 4th|1.01|1.00|1.00|1.00|1.00|1.00|
| |4th " 5th|1.01|1.01|1.01|1.01|1.01|1.00|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.47|1.47|1.48|1.48|1.48|1.49|
| |2nd " 3rd|1.49|1.49|1.49|1.49|1.49|1.49|
| 1-1/2 inch |3rd " 4th|1.51|1.51|1.51|1.51|1.51|1.51|
| |4th " 5th|1.53|1.53|1.52|1.52|1.52|1.51|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|1.94|1.95|1.96|1.96|1.97|1.98|
| |2nd " 3rd|1.98|1.98|1.99|1.99|1.99|1.99|
| 2 inches |3rd " 4th|2.02|2.02|2.01|2.01|2.01|2.01|
| |4th " 5th|2.06|2.05|2.04|2.04|2.03|2.02|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|2.41|2.42|2.43|2.44|2.45|2.47|
| |2nd " 3rd|2.47|2.47|2.48|2.48|2.48|2.49|
| 2-1/2 inches|3rd " 4th|2.53|2.53|2.52|2.52|2.52|2.51|
| |4th " 5th|2.59|2.58|2.57|2.56|2.55|2.53|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|2.87|2.89|2.90|2.91|2.93|2.96|
| |2nd " 3rd|2.96|2.96|2.97|2.97|2.98|2.99|
| 3 inches |3rd " 4th|3.04|3.04|3.03|3.03|3.02|3.01|
| |4th " 5th|3.13|3.11|3.10|3.09|3.07|3.04|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|3.78|3.81|3.83|3.84|3.87|3.94|
| |2nd " 3rd|3.92|3.94|3.94|3.95|3.96|3.98|
| 4 inches |3rd " 4th|4.08|4.06|4.06|4.05|4.04|4.02|
| |4th " 5th|4.22|4.19|4.17|4.16|4.13|4.06|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|4.66|4.71|4.73|4.76|4.80|4.90|
| |2nd " 3rd|4.89|4.90|4.91|4.92|4.93|4.96|
| 5 inches |3rd " 4th|5.11|5.10|5.09|5.08|5.07|5.04|
| |4th " 5th|5.34|5.29|5.27|5.24|5.20|5.10|
+-------------+-----------+----+----+----+----+----+----+
| |1st and 2nd|5.51|5.57|5.62|5.66|5.71|5.86|
| |2nd " 3rd|5.83|5.86|5.87|5.88|5.90|5.95|
| 6 inches |3rd " 4th|6.17|6.14|6.13|6.12|6.10|6.05|
| |4th " 5th|6.49|6.43|6.38|6.34|6.29|6.14|
+-------------+-----------+----+----+----+----+----+----+
Before describing and applying the table, we will call attention to the
term "effective" diameter. The effective radius--as is well
known--extends from the centre of the pulley to the centre of the belt;
the effective diameter, being twice this effective radius, must also
equal the actual diameter plus thickness of belt.
The table is so arranged that the diameter (divided by distance between
centres) of one step of a belted pair will always be found in the
extreme right-hand column; while its companion step will be found on the
same horizontal line, and in that vertical column of the table
corresponding to the length of belt employed. For example, if column 14
of the table corresponded to the length of belt employed, some of the
possible pairs of diameters would be as follows:
.7118 .5813 .42 .2164 .0474
.06 .24 .42 .60 .72
The upper row of this series of pairs being taken from column 14, and
the lower row from the extreme right-hand column, the numbers in each
pair being on the same horizontal line. If the distance between the
centers of the pulleys were 60 ins. the effective diameters of the steps
corresponding to the above pairs would be:
42.71 34.88 25.2 12.98 2.84 ins.
3.6 14.4 25.2 36.0 43.20
being obtained by multiplying the first series of pairs by 60; the
length of belt which would be equally tight on each of these pairs would
be 3.3195 × 60 ins. = 199.17 ins.
III.--TABLE FOR FINDING THE EFFECTIVE DIAMETERS OF THE STEPS OF CONE
PULLEYS, WHEN THE PULLEYS ARE CONNECTED BY AN OPEN BELT AND ARE UNLIKE.
Each vertical cone of the table corresponds to a given length of belt,
and the numbers in these columns are the required effective diameters of
the steps when the centres of the pulleys are a Unit's distance apart.
+--------------------------------------------------------------+------+
| LENGTH OF BELT WHEN THE CENTRES OF THE CONE PULLEYS ARE A | |
| UNIT'S DISTANCE APART. | |
+------+------+------+------+------+------+------+------+------+ |
|2.0942|2.1885|2.2827|2.3770|2.4712|2.5655|2.6597|2.7540|2.8482| |
+------+------+------+------+------+------+------+------+------+ [A] |
| =1= | =2= | =3= | =4= | =5= | =6= | =7= | =8= | =9= | |
+------+------+------+------+------+------+------+------+------+------+
| .0594| .1177| .1750| .2313| .2867| .3413| .3950| .4479| .5000| 0.00 |
| .03 | .0894| .1477| .2050| .2613| .3167| .3713| .4250| .4779| 0.03 |
| | .06 | .1194| .1777| .2350| .2913| .3467| .4013| .4550| 0.06 |
| | .0294| .09 | .1494| .2077| .2650| .3213| .3767| .4313| 0.09 |
| | | .0594| .12 | .1794| .2377| .2950| .3513| .4067| 0.12 |
| | | .0275| .0894| .15 | .2094| .2677| .3250| .3813| 0.15 |
| | | | .0575| .1194| .18 | .2394| .2977| .3550| 0.18 |
| | | | .0244| .0875| .1494| .21 | .2694| .3277| 0.21 |
| | | | | .0544| .1175| .1794| .24 | .2994| 0.24 |
| | | | | .0200| .0844| .1475| .2094| .27 | 0.27 |
| | | | | | .0500| .1144| .1775| .2394| 0.30 |
| | | | | | .0140| .0800| .1444| .2075| 0.33 |
| | | | | | | .0440| .1100| .1744| 0.36 |
| | | | | | | .0064| .0740| .1400| 0.39 |
| | | | | | | | .0364| .1040| 0.42 |
| | | | | | | | | .0664| 0.45 |
| | | | | | | | | .0271| 0.48 |
+------+------+------+------+------+------+------+------+------+------+
+--------------------------------------------------------------+------+
| LENGTH OF BELT WHEN THE CENTRES OF THE CONE PULLEYS ARE A | |
| UNIT'S DISTANCE APART. | |
+------+------+------+------+------+------+------+------+------+ |
|2.9425|3.0367|3.1310|3.2252|3.3195|3.4137|3.5080|3.6022|3.6965| |
|------+------+------+------+------+------+------+------+------+ [A] |
| =10= | =11= | =12= | =13= | =14= | =15= | =16= | =17= | =18= | |
+------+------+------+------+------+------+------+------+------+------+
| .5514| .6020| .6518| .7010| .7495| .7974| .8447| .8913| .9373| 0.00 |
| .5300| .5814| .6320| .6818| .7310| .7795| .8274| .8747| .9213| 0.03 |
| .5079| .5600| .6114| .6620| .7118| .7610| .8095| .8574| .9047| 0.06 |
| .4850| .5379| .5900| .6414| .6920| .7418| .7910| .8395| .8874| 0.09 |
| .4613| .5150| .5679| .6200| .6714| .7220| .7718| .8210| .8695| 0.12 |
| .4367| .4913| .5450| .5979| .6500| .7014| .7520| .8018| .8510| 0.15 |
| .4113| .4667| .5213| .5750| .6279| .6800| .7314| .7820| .8318| 0.18 |
| .3850| .4413| .4967| .5513| .6050| .6579| .7100| .7614| .8120| 0.21 |
| .3577| .4150| .4713| .5267| .5813| .6350| .6879| .7400| .7914| 0.24 |
| .3294| .3877| .4450| .5013| .5567| .6113| .6650| .7179| .7700| 0.27 |
| .30 | .3594| .4177| .4750| .5313| .5867| .6413| .6950| .7479| 0.30 |
| .2694| .33 | .3894| .4477| .5050| .5613| .6167| .6713| .7250| 0.33 |
| .2375| .2994| .36 | .4194| .4777| .5350| .5913| .6467| .7013| 0.36 |
| .2044| .2675| .3294| .39 | .4494| .5077| .5650| .6213| .6767| 0.39 |
| .1700| .2344| .2975| .3594| .42 | .4794| .5377| .5950| .6513| 0.42 |
| .1340| .2000| .2644| .3275| .3894| .45 | .5094| .5677| .6250| 0.45 |
| .0964| .1640| .2300| .2944| .3575| .4194| .48 | .5394| .5977| 0.48 |
| .0571| .1264| .1940| .2600| .3244| .3875| .4494| .51 | .5694| 0.51 |
| .0160| .0871| .1564| .2240| .2900| .3544| .4175| .4794| .54 | 0.54 |
| | .0460| .1171| .1864| .2540| .3200| .3844| .4475| .5094| 0.57 |
| | .0029| .0760| .1471| .2164| .2840| .3500| .4144| .4775| 0.60 |
| | | .0329| .1060| .1771| .2464| .3140| .3800| .4444| 0.63 |
| | | | .0629| .1360| .2071| .2764| .3440| .4100| 0.66 |
| | | | .0174| .0929| .1660| .2371| .3064| .3740| 0.69 |
| | | | | .0474| .1229| .1960| .2671| .3364| 0.72 |
| | | | | | .0774| .1529| .2260| .2971| 0.75 |
| | | | | | .0292| .1074| .1829| .2560| 0.78 |
| | | | | | | .0592| .1374| .2129| 0.81 |
| | | | | | | .0081| .0892| .1674| 0.84 |
| | | | | | | | .0381| .1192| 0.87 |
| | | | | | | | | .0681| 0.90 |
| | | | | | | | | .0138| 0.93 |
+------+------+------+------+------+------+------+------+------+------+
+--------------------------------------------------------------+------+
| LENGTH OF BELT WHEN THE CENTRES OF THE CONE PULLEYS ARE A | |
| UNIT'S DISTANCE APART. | |
+------+------+------+------+------+------+------+------+------+ |
|3.7907|3.8850|3.9792|4.0735|4.1677|4.2620|4.3562|4.4504|4.5447| |
|------+------+------+------+------+------+------+------+------+ [A] |
| =19= | =20= | =21= | =22= | =23= | =24= | =25= | =26= | =27= | |
+------+------+------+------+------+------+------+------+------+------+
| .9828|1.0277|1.0721|1.1159|1.1593|1.2021|1.2444|1.2861|1.3274| 0.00 |
| .9673|1.0128|1.0577|1.1021|1.1459|1.1893|1.2321|1.2744|1.3161| 0.03 |
| .9513| .9973|1.0428|1.0877|1.1321|1.1759|1.2193|1.2621|1.3044| 0.06 |
| .9347| .9813|1.0273|1.0728|1.1177|1.1621|1.2059|1.2493|1.2921| 0.09 |
| .9174| .9647|1.0113|1.0573|1.1028|1.1477|1.1921|1.2359|1.2793| 0.12 |
| .8995| .9474| .9947|1.0413|1.0873|1.1328|1.1777|1.2221|1.2659| 0.15 |
| .8810| .9295| .9774|1.0247|1.0713|1.1173|1.1628|1.2077|1.2521| 0.18 |
| .8618| .9110| .9595|1.0074|1.0547|1.1013|1.1473|1.1928|1.2377| 0.21 |
| .8420| .8918| .9410| .9895|1.0374|1.0847|1.1313|1.1773|1.2228| 0.24 |
| .8214| .8720| .9218| .9710|1.0195|1.0674|1.1147|1.1613|1.2073| 0.27 |
| .8000| .8514| .9020| .9518|1.0010|1.0495|1.0974|1.1447|1.1913| 0.30 |
| .7779| .8300| .8814| .9320| .9818|1.0310|1.0795|1.1274|1.1747| 0.33 |
| .7550| .8079| .8600| .9114| .9620|1.0118|1.0610|1.1095|1.1574| 0.36 |
| .7313| .7850| .8379| .8900| .9414| .9920|1.0418|1.0910|1.1395| 0.39 |
| .7067| .7613| .8150| .8679| .9200| .9714|1.0220|1.0718|1.1210| 0.42 |
| .6813| .7367| .7913| .8450| .8979| .9500|1.0014|1.0520|1.1018| 0.45 |
| .6550| .7113| .7667| .8213| .8750| .9279| .9800|1.0314|1.0820| 0.48 |
| .6277| .6850| .7413| .7967| .8513| .9050| .9579|1.0100|1.0614| 0.51 |
| .5994| .6577| .7150| .7713| .8267| .8813| .9350| .9879|1.0400| 0.54 |
| .57 | .6294| .6877| .7450| .8013| .8567| .9113| .9650|1.0179| 0.57 |
| .5394| .60 | .6594| .7177| .7750| .8313| .8867| .9413| .9950| 0.60 |
| .5075| .5694| .63 | .6894| .7477| .8050| .8613| .9167| .9713| 0.63 |
| .4744| .5375| .5994| .66 | .7194| .7777| .8350| .8913| .9467| 0.66 |
| .4400| .5044| .5675| .6294| .69 | .7494| .8077| .8650| .9213| 0.69 |
| .4040| .4700| .5344| .5975| .6594| .72 | .7794| .8377| .8950| 0.72 |
| .3664| .4340| .5000| .5644| .6275| .6894| .75 | .8094| .8677| 0.75 |
| .3271| .3964| .4640| .5300| .5944| .6575| .7194| .78 | .8394| 0.78 |
| .2860| .3571| .4264| .4940| .5600| .6244| .6875| .7494| .81 | 0.81 |
| .2429| .3160| .3871| .4564| .5240| .5900| .6544| .7175| .7794| 0.84 |
| .1974| .2729| .3460| .4171| .4864| .5540| .6200| .6844| .7475| 0.87 |
| .1492| .2274| .3029| .3760| .4471| .5164| .5840| .6500| .7144| 0.90 |
| .0981| .1792| .2574| .3329| .4060| .4771| .5464| .6140| .6800| 0.93 |
| .0438| .1281| .2092| .2874| .3629| .4360| .5071| .5764| .6440| 0.96 |
| | .0738| .1581| .2392| .3174| .3929| .4660| .5371| .6064| 0.99 |
| | .0157| .1038| .1881| .2692| .3474| .4229| .4960| .5671| 1.02 |
| | | .0457| .1338| .2181| .2992| .3774| .4529| .5260| 1.05 |
| | | | .0757| .1638| .2481| .3292| .4074| .4829| 1.08 |
| | | | .0131| .1057| .1938| .2781| .3592| .4374| 1.11 |
| | | | | .0431| .1357| .2238| .3081| .3892| 1.14 |
| | | | | | .0731| .1657| .2538| .3381| 1.17 |
| | | | | | .0050| .1031| .1957| .2838| 1.20 |
| | | | | | | .0350| .1331| .2257| 1.23 |
| | | | | | | | .0650| .1631| 1.26 |
| | | | | | | | | .0950| 1.29 |
| | | | | | | | | .0200| 1.32 |
+------+------+------+------+------+------+------+------+------+------+
+-----------------------------------------+------+
| LENGTH OF BELT WHEN THE CENTRES OF THE | |
|CONE PULLEYS ARE A UNIT'S DISTANCE APART.| |
+------+------+------+------+------+------+ |
|4.6389|4.7332|4.8274|4.9217|5.0159|5.1102| |
|------+------+------+------+------+------+ [A] |
| =28= | =29= | =30= | =31= | =32= | =33= | |
+------+------+------+------+------+------+------+
|1.3682|1.4085|1.4484|1.4877|1.5266|1.5650| 0.00 |
|1.3574|1.3982|1.4385|1.4784|1.5177|1.5566| 0.03 |
|1.3461|1.3874|1.4282|1.4685|1.5084|1.5477| 0.06 |
|1.3344|1.3761|1.4174|1.4582|1.4985|1.5384| 0.09 |
|1.3221|1.3644|1.4061|1.4474|1.4882|1.5285| 0.12 |
|1.3093|1.3521|1.3944|1.4361|1.4774|1.5182| 0.15 |
|1.2959|1.3393|1.3821|1.4244|1.4661|1.5074| 0.18 |
|1.2821|1.3259|1.3693|1.4121|1.4544|1.4961| 0.21 |
|1.2677|1.3121|1.3559|1.3993|1.4421|1.4844| 0.24 |
|1.2528|1.2977|1.3421|1.3859|1.4293|1.4721| 0.27 |
|1.2373|1.2828|1.3277|1.3721|1.4159|1.4593| 0.30 |
|1.2213|1.2673|1.3128|1.3577|1.4021|1.4459| 0.33 |
|1.2047|1.2513|1.2973|1.3428|1.3877|1.4321| 0.36 |
|1.1874|1.2347|1.2813|1.3273|1.3728|1.4177| 0.39 |
|1.1695|1.2174|1.2647|1.3113|1.3573|1.4028| 0.42 |
|1.1510|1.1995|1.2474|1.2947|1.3413|1.3873| 0.45 |
|1.1318|1.1810|1.2295|1.2774|1.3247|1.3713| 0.48 |
|1.1120|1.1618|1.2110|1.2595|1.3074|1.3547| 0.51 |
|1.0914|1.1420|1.1918|1.2410|1.2895|1.3374| 0.54 |
|1.0700|1.1214|1.1720|1.2218|1.2710|1.3195| 0.57 |
|1.0479|1.1000|1.1514|1.2020|1.2518|1.3010| 0.60 |
|1.0250|1.0779|1.1300|1.1814|1.2320|1.2818| 0.63 |
|1.0013|1.0550|1.1079|1.1600|1.2114|1.2620| 0.66 |
| .9767|1.0313|1.0850|1.1379|1.1900|1.2414| 0.69 |
| .9513|1.0067|1.0613|1.1150|1.1679|1.2200| 0.72 |
| .9250| .9813|1.0367|1.0913|1.1450|1.1979| 0.75 |
| .8977| .9550|1.0113|1.0667|1.1213|1.1750| 0.78 |
| .8694| .9277| .9850|1.0413|1.0967|1.1513| 0.81 |
| .84 | .8994| .9577|1.0150|1.0713|1.1267| 0.84 |
| .8094| .87 | .9294| .9877|1.0450|1.1013| 0.87 |
| .7775| .8394| .90 | .9594|1.0177|1.0750| 0.90 |
| .7444| .8075| .8694| .93 | .9894|1.0477| 0.93 |
| .7100| .7744| .8375| .8994| .96 |1.0194| 0.96 |
| .6740| .7400| .8044| .8675| .9294| .99 | 0.99 |
| .6364| .7040| .7700| .8344| .8975| .9594| 1.02 |
| .5971| .6664| .7340| .8000| .8644| .9275| 1.05 |
| .5560| .6271| .6964| .7640| .8300| .8944| 1.08 |
| .5129| .5860| .6571| .7264| .7940| .8600| 1.11 |
| .4674| .5429| .6160| .6871| .7564| .8240| 1.14 |
| .4192| .4974| .5729| .6460| .7171| .7864| 1.17 |
| .3681| .4492| .5274| .6029| .6760| .7471| 1.20 |
| .3138| .3981| .4792| .5574| .6329| .7060| 1.23 |
| .2557| .3438| .4281| .5092| .5874| .6629| 1.26 |
| .1931| .2857| .3738| .4581| .5392| .6174| 1.29 |
| .1250| .2231| .3157| .4038| .4881| .5692| 1.32 |
| .0500| .1550| .2531| .3457| .4338| .5181| 1.35 |
| | .0800| .1850| .2831| .3757| .4638| 1.38 |
| | | .1100| .2150| .3131| .4057| 1.41 |
| | | .0255| .1400| .2450| .3431| 1.44 |
| | | | .0555| .1700| .2750| 1.47 |
| | | | | .0855| .2000| 1.50 |
+------+------+------+------+------+------+------+
Legend: [A] = Assumed diameter of steps, divided by distance between the
centres of Cone Pulleys.
To get the actual diameters of these steps when thickness of belt = 7/32
= 0.22 in., we have simply to subtract 0.22 in. from the effective
diameters just given, thus:
42.49 34.66 24.98 12.76 2.62 in.
3.38 14.18 24.98 35.78 42.98
would be the series of pairs of actual diameters.
In solving problems relating to the diameters of cone pulleys by means
of the accompanying table, we must have, besides the distance between
centres, sufficient data to determine the column representing the length
of belt. The length of belt is seldom known because it is of small
practical importance to know its exact length; but it may be estimated
approximately, and then the determination of suitable diameters of the
steps becomes an extremely simple matter, as may be seen from what has
already preceded. When the length of the belt is not known, and has not
been assumed, we indirectly prescribe the length of belt by assuming the
effective diameters of the two steps of a belted pair; thus, in the
following Figure (561), the length of belt is prescribed when the
distance A B, and any one of the pairs of steps D_{1}_d__{1},
D_{2}_d__{2}, D_{3}_d__{3} and D_{4}_d__{4} are given. We will show in
the following examples how the length of belt and its corresponding
column of diameter may be found when a pair of steps (like
D_{1}_d__{1}), are given.
[Illustration: Fig. 561.]
EXAMPLE 1. Given the effective diameters
4.5 in. 9 in. 15 in. 21 in. on cone A,
-- -- 15 in. -- " B,
and the distance between centres equal to 50 inches.
Required the remaining diameters on cone B.
Since in this example the steps of the given pair are equal, we look for
15/50 = 0.30, in the extreme right-hand column of table; we will find it
in the 11th line from the top; now looking along this line for the
diameter of the other step, = 15/50 = 0.30, we will find it in column
10; consequently the numbers of this column may be taken as the
diameters of the steps which are the companions or partners of those in
the extreme right-hand column.
We can now easily determine the remaining members of the pairs to which
4.5 in., 9 in., and 21 in. steps respectively belong. To find the
partner of the 4.5 step, we find 4.5/50 = 0.09 in the right-hand column,
and look along the horizontal line on which 0.09 is placed till we come
to column 10, in which we will find the number 0.4850; 0.4850 × 50 in. =
24.25 in. will be the effective diameter of the companion to the 4.5 in.
step.
To find the partner to the 9 in. step, we proceed as before, looking for
9/50 = 0.18 in the right-hand column, and then along the horizontal line
of 0.18 to column 10, then will 0.4113 × 50 in. = 20.57 in. be the
required companion to the 9 in. step of cone A.
In like manner for the partner of the 21 in. step we get 0.1700 × 50 in.
= 8.5 in. The effective diameter therefore will be,
4.5 in. 9 in. 15 in. 21 in. on cone A,
24.25 20.57 15 in. 8.5 " B.
If the thickness of belt employed were 0.25 in. the _actual_ diameters
of steps would be,
4.25 8.75 14.75 20.75 on cone A,
24.00 20.32 14.75 8.25 " B,
and the length of belt would be 2.9425 × 50 = 147.125 in.
EXAMPLE 2. Given the effective diameters
6 in. 12 in. 18 in. 24 in. on cone A,
30 in. -- -- -- " B,
and the distance between centres = 40 in.
Required the unknown diameters on cone B.
We must, as before, first find the vertical column corresponding to the
length of belt which joins the pair of steps 6 in/30 in. We find the
number 6/40 = .15 in the right-hand column, and then look along its
horizontal line for its partner 30/40 = 0.75. Since we do not find any
number exactly equal to .7500, we must interpolate. For the benefit of
those not familiar with the method of interpolation we will give in
detail the method of finding intermediate columns of the table. On the
aforesaid horizontal line we find in column 16 a number 0.7520, larger
than the required 0.7500, and in column 15 a number 0.7014, smaller than
0.7500; evidently the intermediate column, containing the required
0.7500, must lie between columns 16 and 15. To find how far the required
column is from column 16, we subtract as follows:
0.7520 0.7520
0.7500 0.7014
------ ------
.0020 0.0506
then the fraction .0020/.00506 = 0.04 nearly will represent the position
of the required intermediate column; namely, that its distance from
column 16 is about 4/100 of the distance between the adjacent columns,
15 and 16.
To find other numbers in this intermediate column we have only to
multiply the difference between the adjacent numbers of columns 16 and
15 by 0.04, and subtract the product from the number in column 16. But
it is not necessary to find as many numbers of the intermediate columns
as are contained in either of the adjacent columns; it is only necessary
to find as many numbers as there are steps in each of the cone pulleys.
We will now illustrate what has preceded, by finding the partner to the
12 in. step of cone A. Find, as before, the horizontal line
corresponding to 12/40 = 0.30, then take the difference between the
numbers 0.6413 and 0.5867 of columns 16 and 15, and multiply this
difference, 0.0546, by 0.04; this product = 0.0022 subtracted from
0.6413, will give 0.6391, a number of the intermediate columns
corresponding to the length of belt of the present problem. Multiplying
by the distance between the axes = 40 in. we get 0.6391 × 40 = 25.56,
for the diameter of the step of cone B which is partner to the 12 in.
step of cone A.
To find the companion to the 18 in. step, we proceed in the same manner,
looking for the horizontal line 18/40 = 0.45, and interpolating as
follows:
0.5094 - (0.5094 - 0.4500) × 0.04 = 0.5070.
Consequently, 0.5070 × 40 in. = 20.28 in. will be the required partner
of the 18 in. step.
In like manner, for the 24 in. step, we have
0.3500 - (0.3500 - 0.2840) × 0.04 = 0.3474, and 0.3474 × 40 = 13.90.
The effective diameters are therefore
6 in. 12 in. 18 in. 24 in. on cone A.
30 25.56 20.28 13.9 " B.
The actual diameters, when thickness of belt = 0.20 in., are:
5.8 11.8 17.8 23.8 on cone A.
29.8 25.36 20.08 13.7 " B.
And the length of belt will be:
[3.5080 - (3.5080 - 3.4137) × 0.04] × 40 in. = 140.17 in.
EXAMPLE 3. Given the effective diameters:
12 in. 18 in. 24 in. 30 in. on cone A,
33 in. -- -- -- " B,
and the distance between the centres = 60 in.
Required the remaining diameters on cone B.
The horizontal corresponding to 12/60 = 0.20 lies 2/3rd way between the
horizontal line, corresponding to 0.18 and 0.21; the number 33/60 =
0.5500, corresponding to the companion of the 12 in. step, will
therefore lie 2/3rd way between the horizontal lines 0.18 and 0.21. We
have now to find two numbers on this 2/3rd line, of which one will be
less and the other greater than 0.5500. An inspection of the table will
show that these greater and less numbers must lie in columns 13 and 12.
The numbers on the 2/3rd line itself may now be found as follows:
In column 13, 0.5750 - 2/3(0.5750 - 0.5513) = 0.5592.
In column 12, 0.5213 - 2/3(0.5213 - 0.4967) = 0.5049.
0.5592 will be the number on the 2/3rd line, which is greater than
0.5500, and 0.5049 will be the one which is less than 0.5500. The
position of the intermediate column, corresponding to the length of belt
of the present example, may now be found, as before, briefly. It is:
0.5592 - 0.5500 = 0.0092
= 0.17.
0.5592 - 0.5049 = 0.0543
Consequently the required column lies nearest column 13, 17/100th way
between columns 13 and 12. To find any other number in the required
column, we have only to multiply the difference between two adjacent
numbers of columns 13 and 12 by 17/100, and subtract the product from
the number in column 13. For example, to find the diameter of the
partner to the 18 in. step of cone A, we find the numbers 0.4750 and
0.4177 of columns 13 and 12, which lie on the horizontal line
corresponding to 18/60 = 0.30; the difference, 0.0573, between the two
numbers is multiplied by 0.17, and the product, 0.0573 × 0.17 = 0.0097,
subtracted from 0.4750. This last difference will equal 0.4653, and will
be the number sought. If we now multiply by 60, we will get 27.92 in. as
the effective diameter of that step on cone B which is the partner to
the 18 in. step of cone A.
To find the companion of the 24 in. step, we proceed after the same
fashion; the horizontal line 24/60 = 0.40 lies 1/3rd way between 0.39
and 0.42; hence,
In column 13, 0.3900 - 1/3(0.3900 - 0.3594) = 0.3798;
In column 12, 0.3294 - 1/3(0.3294 - 0.2975) = 0.3188;
And 0.3798 - (0.3798 - 0.3188) × 0.17 = 0.3694.
The required effective diameter of the step, which is partner to the 24
in. step, will therefore be 0.3694 × 60 = 22.16 in.
In like manner we obtain partner for the 30 in. step, thus:
In column 13, 0.2944 - 2/3(0.2944 - 0.2600) = 0.2715.
In column 12, 0.2300 - 2/3(0.2300 - 0.1940) = 0.2060.
Also 0.2715 - (0.2715 - 0.2060) × 0.17 = 0.2604, and 0.2604 × 60 in. =
15.62 in. = diam. of step belonging to the same belted pair as the 30
in. step of cone A.
The effective diameters will be:
12 in. 18 in. 24 in. 30 in. on cone A,
33 27.92 22.16 15.62 " B,
and the actual diameters when belt is 0.22" thick:
11.78 17.78 23.78 29.78 in.
32.78 27.70 21.94 15.40
and the length of belt is found to be:
[3.2252 - (3.2252 - 3.1310) × 0.17] × 60 in. = 192.55 in.
In all the preceding problems it should be noticed that we arbitrarily
assumed _all_ the steps on one cone, and _one_ of the steps on the other
cone. It will be found that all of the practical problems relating to
cone-pulley diameters can finally be reduced to this form, and can
consequently be solved according to the methods just given.
For those who find difficulty in interpolating, the following procedure
will be found convenient: Estimate approximately the necessary length of
belt, then divide this length by the distance between the centres of the
cone pulleys; now find which one of the 33 lengths of belt (per unit's
distance apart of the centres) given in the table is most nearly equal
to the quotient just obtained, and then take the vertical column, at the
head of which it stands, for the companion to the right-hand column.
Those numbers of these companion columns which are on the same
horizontal line will be the companion steps of a belted pair. The table
is so large, that in the great majority of cases not only exact, but
otherwise satisfactory values can be obtained by this method, without
any interpolation whatever."
[Illustration: Fig. 562.]
The teeth of the back gear should be accurately cut so that there is no
lost motion between the teeth of one wheel, and the spaces of the other,
because on account of the work being of large diameter or of hard metal
(so as to require the slow speed), the strain of the cut is nearly
always heavy when the back gear is in use, and the strain on the teeth
is correspondingly great, causing a certain amount of spring or
deflection in the live spindle and back gear spindle. Suppose then, that
at certain parts of the work there is no cut, then when the tool again
meets the cut the work will meet the tool and stand still until the lost
motion in the gear teeth and the spring of the spindles is taken up,
when the cut will proceed with a jump that will leave a mark on the work
and very often break the tool. When the cut again leaves the tool a
second jump also leaving a mark on the work will be made. If the teeth
of the gears are cut at an angle to the axial line of the spindle, as is
sometimes the case, this jumping from the play between the teeth will be
magnified on account of a given amount of play, affording more back lash
in such gears.
The teeth of the wheels should always be of involute and not of
epicycloidal form, for the following reasons. The transmission of motion
by epicycloidal teeth is exactly uniform only when their pitch circles
exactly coincide, and this may not be the case in time because of wear
in the parts as in the live spindle journals and the bearings, and the
back gear spindle and its bearings, and _every variation of speed_ in
the cut, however slight it may be, produces a corresponding mark upon
the work. In involute teeth the motion transmitted will be smooth and
equal whether the pitch lines of the wheels coincide or not, hence the
wear of the journals and bearings does not impair their action.
The object of cutting the teeth at an angle is to have the point of
contact move or roll as it were from one end to the other of the teeth,
and thus preserve a more conterminous contact on the line of centres of
the two wheels, the supposition being that this would remove the marks
on the work produced by the tremor of the back gear. But such tremor is
due to errors in the form of the teeth, and also in the case of
epicycloidal teeth from the pitch lines of the teeth not exactly
coinciding when in gear.
The pitch of the teeth should be as fine as the requisite strength, with
the usual allowance of margin for wear and safety will allow, so as to
have as many teeth in continuous contact as possible.
Various methods of moving the back gear into and out of gear with the
cone spindle gears are employed. The object is to place the back gears
into gear to the exact proper depth to hold them securely in position,
and to enable the operator to operate the gears without passing to the
back of the lathe. Sometimes a sliding bearing box, such as shown in
Fig. 562, is employed; _a_ is the back gear spindle, _b_ its bearing
box, and _d_ a pin which when on the side shown holds _b_ in position,
when the back gear is in action. To throw it out of action _d_ is
removed, _b_ pushed back, and _d_ inserted in a hole on the right hand
of _b_; the objection is that there is no means of taking up the wear of
_b_, and it is necessary to pass to the back of the lathe to operate the
device.
[Illustration: Fig. 563.]
Another plan is to let the back gear move endwise and bush its bearing
holes with hardened steel bushes. This possesses the advantage that the
gear is sure, if made right, to keep so, but it has some decided
disadvantages: first, the pinion A, Fig. 563, must be enough larger than
the smallest cone-step B to give room between B and C for the belt, and
this necessitates that D also be larger than otherwise; secondly, the
gear-spindle F projects through the bearing at _f_, and this often comes
in the way of the bolt-heads used for chucking work to the face plate.
The method of securing the spindle from end motion is as follows: On the
back of the head is pivoted at _i_, a catch G, and on the gear shaft F
are two grooves. As shown in the sketch, G is in one of these grooves
while H is the other, but when the back gear is in, G would be in H.
[Illustration: Fig. 564.]
Sometimes a simple eccentric bush and pin is used as in Fig. 564, in
which _a_ is the spindle journal, _b_ a bush having bearing in the lathe
head, and _d_ a taper pin to secure _b_ in its adjusted position.
[Illustration: Fig. 565.]
In large heavy lathes having many changes of speed, there are various
other constructions, as will be seen upon the lathes themselves in the
various illustrations concerning the methods of throwing the back gear
in and out. The eccentric motion shown in Fig. 573 of the Putnam lathe,
is far preferable to any means in which the back-gear spindle moves
endways, because, as before stated, the end of the back-gear spindle
often comes in the way of the bolts used to fasten work to the large
face plate. This occurs mainly in chucked work of the largest diameter
within the capacity of the lathe.
[Illustration: Fig. 566.]
In many American lathes the construction of the gearing that conveys
motion from the live spindle is such that facility is afforded to throw
the change gears out of action when the lathe is running fast, as for
polishing purposes, so as to save the teeth from wear. Means are also
provided to reverse the direction of lead screw or feed screw
revolution. An example of a common construction of this kind is shown in
Fig. 565, in which the driving wheel A is on the inner side of the back
bearing as shown. It drives (when in gear) a pair of gears, one only of
which is seen in the figure at B, which drives C, and through R, D, I,
and S, the lead screw. A side view of the wheel A and the mechanism in
connection therewith is shown in Fig. 566, in which S represents the
live spindle and R is a spindle or shaft corresponding to R in Fig. 565.
L is a lever pivoted upon R and carrying two pinions B and E; pinion B
is of larger diameter than E, so that B gears with both C and E (C
corresponding to wheel C in Fig. 565), while E gears with B only.
[Illustration: Fig. 567.]
With the lever L in the position shown, neither B nor E engages with A,
hence they are at rest; but if lever L be raised as in Fig. 567, B will
gear with wheels A and C, and motion will be conveyed from A to C, wheel
E running as an idle wheel, thus C will revolve in the same direction as
the lathe spindle.
But if lever L be lowered as in fig. 568, then wheel E will gear with
and receive motion from A, which it will convey to B, and C will revolve
in the opposite direction to that in which the lathe spindle runs. To
secure lever L in position, a pin F passes through it and into holes as
I, J, provided in the lathe head. Lever L is sometimes placed inside the
head, and sometimes outside as in Fig. 569, and it will be obvious that
it may be used to cut left-hand threads without the use of an extra
intermediate change gear, which is necessary in the construction shown
in Fig. 570, in order to reverse the direction of lead screw revolution.
Sometimes the pin F is operated by a small spring lever attached
to L, so that the hand grasps the end of L and the spring lever
simultaneously, removing F from the hole in H, and therefore freeing L,
so as to permit its operation. By relaxing the pressure on the small
spring lever pin F finds its own way into the necessary hole in H, when
opposite to it, without requiring any hand manipulation.
In larger lathes the lever L is generally attached to its stud outside
the end bearing of the head H.
[Illustration: Fig. 568.]
It is preferable, however, that the device for changing the direction of
feed traverse be operative from the lathe carriage as in the Sellers
lathe, so that the operator need not leave it when it is necessary to
reverse the direction of traverse.
[Illustration: Fig. 569.]
The swing frame, when the driving gear D is outside of the back bearing
(as it is in Fig. 570), is swung from the axis of the lead screw as a
centre of motion, and has two slots for receiving studs for change
wheels. But when the driving gear is inside the back bearing as in Fig.
571, the swing frame may be suspended from the spindle (R, Fig. 565)
that passes through the lathe head, which may also carry the cone for
the independent feed as shown in Fig. 571, no matter on which side of
the lathe the lead screw and feed rod are. This affords the convenience
that when both lead screw and feed rod are in front of the lathe, the
feed may be changed from the screw cutting to the rod feed, or _vice
versâ_, by suitable mechanism in the apron, without requiring any change
to be made in the driving gears.
[Illustration: Fig. 570.]
In the lathe shown in Fig. 572, which is from the design of S. W.
Putnam, of the Putnam Tool Company of Fitchburg, Massachusetts, the cone
pinion for the back gear, and that for driving the feed motion, are of
the same diameter and pitch, so that the gear-wheel L in Fig. 573 may
(by means of a lever shown dotted in) be caused to engage with either of
them. When the latter is used in single gear it would obviously make no
difference which wheel drives L, but when the back gear is put in and L
is engaged with the cone pinion, its speed corresponds to that of the
cone, which being nine times faster than the live spindle, enables the
cutting of threads nine times as coarse as if the back gear was not in
use. This affords very great advantages for cutting worms and threads of
coarse pitches.
An excellent method of changing the direction of feed motion, and of
starting or stopping the same, is shown in Fig. 574, which represents
the design of the Ames Manufacturing Company's lathe.
[Illustration: Fig. 571.]
In the figure, A is the small step of the lathe cone, B the pinion to
drive the back gear, C a pinion to drive the feed gear, giving motion to
D, which drives E, the latter being fast to G and rotating freely upon
the shaft F, G drives H, which in turn drives I. The clutch J has a
featherway into which fits the feather _c_, on the shaft F, so that when
the clutch rotates it rotates J through the medium of _c_; K is a
circular fork in a groove in J, and operated by a lever operated by a
rod running along the front of the lathe bed. This rod is splined so
that a lever carried by the apron or feed-table, having a hub and
enveloping the rod, may by means of a feather filling into the spline
operate the rod by partly rotating it, and hence operate K. Suppose now
that this lever stands horizontal, then the clutch J would stand in the
position shown in the cut, and D, E, G, H, and I, would rotate, while F
would remain stationary. By lifting the lever, however, J would be moved
laterally on F (by means of K) and the lug _a_ on J would engage with
lug _b_ on G, and G would drive J, which through _c_ would drive F, on
which is placed a change gear at L, thus traversing the carriage
forward. To traverse it backward the lever would be lowered or depressed
below the horizontal level moving K, and therefore J, to the right, so
that lug _a_ would engage with lug _b_ on I, hence F would be driven by
I, whose motion is in an opposite direction to G, as is denoted by the
respective arrows.
[Illustration: Fig. 572.]
To throw all the feed motion out of gear, to run the lathe at its
quickest for polishing, &c., the operation is as follows.
[Illustration: Fig. 573.]
M is tubular and fast in N and affords journal bearing to wheel D.
Through M passes stud O, having a knob handle at P. At the end of the
hub of D is a cap fast in D, the latter being held endways between the
shoulder shown on O and the washer and nut T. If then P be pulled
outwards O will slide through M, and through the medium of T will cause
D to slide over M, in the direction of the arrow, and pass out of gear
from C, motion therefore ceasing at C.
Q is the swing frame for the studs to carry the change wheels, and R a
bolt for securing Q in its adjusted position. S is a journal and bearing
for H.
If it be considered sufficient the feed motion on small lathes (instead
of feeding in both directions on the lateral and cross feeds as in the
Putnam Lathe), may feed in the direction from the dead to the live
centre, and in one direction only on the cross slide.
[Illustration: Fig. 574.]
An example of a feed motion of this kind is shown in Figs. 575 and 576;
_f_ _f_ is the feed spindle splined and through the medium of a feather
driving the bevel pinion A having journal bearing in B. Pinion A drives
the bevel gear C, which is in one piece with pinion D. The latter drives
gear F, which drives pinion K, which is carried on a lever L, pivoted on
the stud which carries F, so that by operating L, pinion K is brought
into gear with pinion P, which is fast upon the cross-feed screw, and
therefore rotates it to effect the automatic cross feed.
[Illustration: Fig. 575.]
[Illustration: Fig. 576.]
As shown in the cut, the lever L is in such a position as to throw K out
of gear with P, and the cross feed screw is free to be operated by the
handle by hand. At M is a slot in L in which operates a cam or
eccentric, one end of which projects into L, while at the other end is
the round handle R, Fig. 575, which is rotated to raise or lower that
end of L so as to operate K. To operate the saddle or carriage the
motion is continued as follows:--at the centre of F is a pinion gear G
which operates a gear H, which is in one piece with the pinion I, and
the latter is in gear with the rack running along the lathe bed.
If the motion from A to I was continuous, the carriage feed or traverse
would be continuous, but means are provided whereby motion from F to I
may be discontinued, as follows:--A hand traverse or feed is provided.
J, Figs. 575 and 576, is carried by a stud having journal bearing in a
hub on X and receiving the handle Q; hence by operating Q, J is rotated,
operating the gear H, upon which is the pinion I, which is in gear with
the rack running along the lathe bed.
To lock the carriage in a fixed position, as is necessary when operating
the cross feed on large radial surfaces, the following device is
provided:--N is a stud fixed in a hub on X, and having a head which
overlaps the rim of H, as shown in figure. On the other side of that rim
is a washer Z on the same stud having a radial face also overlapping the
rim of H, but its back face is bevelled to a corresponding bevel on the
radial face on the hub of lever O (the hub of O being pivoted on the
same stud). When therefore O is depressed the two-bevel face of the hub
of O forces the washer Z against the face of the wheel H, whose radial
faces at the rim are therefore gripped between the face of the collar N
and that of the washer Z, hence H is locked fast. By raising the end of
lever O, Z is released and H is free to rotate.
Both the carriage feed and cross feed can only be traversed in one
direction so far as these gears and levers are concerned, but means are
provided on the lathe headstock for reversing the direction of motion of
the feed spindle _f_ so as to reverse the direction of the feeds. It
will be observed that so long as _f_ rotates, A, C, D, and F rotate, the
remaining motions only operating when S is screwed up.
In order to obtain a delicate tool motion from the handle Q it is
necessary to reduce the motion between J and I as much as possible, a
point in which a great many lathes as at present constructed are
deficient, because Q, although used to simply traverse the carriage
along the bed, in which case rapid motion of the latter is desirable, is
also used to feed the tool into corners when the lathe has no compound
rest to put on light cuts on radial faces, hence it should be capable of
giving a delicate tool motion.
[Illustration: Fig. 577.]
On account of the deficiency referred to it is often necessary to put on
a fine radial cut by putting the feed traverse in gear, and, throwing
the feed screw gear out of contact with the other change wheels, pull it
around by hand to put on the cut. In compound slide rests these remarks
do not apply, because the upper part of the rest may be used instead of
the handle Q.
Many small lathes are provided with a tool rest known as the _elevating
rest_, or weighted lathe.
An excellent example of an elevating rest for a weighted lathe is shown
in Figs. 577 and 578, which represent the construction in the Pratt and
Whitney lathe. A is the lathe shears upon which slides the carriage
provided with [V] slideways R for the sliding piece B, and provided at
the other end with the guides H. The cross slide S is pivoted upon B at
D, and fits at the other end between the guides H. At E is the elevating
screw which when operated raises or lowers that end of the elevating
rest to adjust the tool height. This also affords an excellent means of
making a minute adjustment for depth of tool cut. The tool rest F is
bolted to S.
[Illustration: Fig. 578.]
The weight W is suspended from S and, therefore, holds one end of S to
B, the lathe to C, and C to A; at the other end the weight holds S to C
(through the medium of the elevating screw E) and C to A. The cross feed
nut N is fast to S, the cross feed screw being operated by hand wheel G.
B is provided with the [V] slideways R, which slide upon corresponding
[V] slides R´ upon C; P is a lug cast upon C, and K is a screw threaded
in B. When the end of screw K abuts against P the motion of S, and,
therefore, of the cutting tool T, towards the work is arrested, hence
when the tool is adjusted to the proper depth of cut, K is operated to
abut firmly against P, and successive pieces may be turned to the same
diameter without requiring each piece to be measured for diameter. N is
the handle for opening and closing the nut for the feed screw Q, and Z
is the wheel for the hand feed traverse. The length of cross feed motion
is determined by the length of the cross [V] slides R´.
This class of rest possesses the advantage that no lost motion in the
slides occurs by reason of the wear, because the weight keeps the parts
in constant contact notwithstanding such wear; on the other hand,
however, the slide [V]s sustain the extra wear due to the weight W in
addition to the weight of the carriage. Lathes of this class are
intended for light work, and are less suited for boring than for plain
turning; they are, however, very convenient, and are preferred by many
to any other kind of lathe for short and light work.
[Illustration: Fig. 579.]
The tool rest being removable may be supplanted by other special forms
of rest. Thus Figs. 579 and 580 represent a special rest for carrying
two tools to cut pieces of work to the exact same length. Bolts D and E
are to secure the rest A to the elevating rest, and C C are the clamps
for the two tools B.
[Illustration: Fig. 580.]
Fig. 581 represents a cross sectional view of the Putnam Tool Company's
gibbed elevating rest, there being a gib on the underneath side of the
front shear. The elevating screw is pivoted by a ball joint. By
employing a gib instead of a weight, the bed may be provided with cross
girts or ribs joining the two sides of the shear, thus giving much
greater stiffness to it.
Figs. 582, 583, and 584 represent a lathe feed motion by William Munzer,
of New York. The object in this motion is to insure that no two feeds
can be put into operation simultaneously, because putting the feed in
motion in one direction throws it out of gear for either of the others.
Another object is to have the transmitting motion as direct as possible
so as to avoid the rotation of any wheels not actually necessary for the
transmission of the motion; and a third object is to enable the throwing
out of gear of all wheels (when no feed motion at all is required)
without leaving the apron.
The means employed to effect these objects are as follows:--
In Fig. 582 _f_ represents the independent feed spindle and S the
lead-screw: _f_ is splined to drive A, A´ and A´´, which is a sleeve in
one piece, and consists of a circular rack at A, a bevel pinion at A´,
and a second bevel pinion at A´´. This sleeve may be operated in either
direction along _f_ by rotating the pinion B. As shown in the cut A´ and
A´´ are both out of gear with the bevel-wheel C, but if B be rotated to
the right then A´ will be in gear with C, or if it be operated to the
left then A´´ will be in gear with C. Now the direction of rotation of C
will be governed by which pinion, A´ or A´´, drives it, and these are
the means by which the direction of the feed traverse and also of the
cross feed is determined.
If none of the feeds are required to operate, the sleeve occupies the
position shown in the cut, and the circular rack at A simply rotates
while B and all other parts remain at rest. On the same central pin as C
is the pinion D driving a spur gear E´´. On the same centre pin as E is
the gear F driving G, which is on the same central pin as C and D. The
gear H is fixed to and rotates with G and drives I; all these gears
serving to reduce the speed of motion when operating to feed the
carriage traverse in either direction.
A gear J is carried on the end of a lever K, being pivoted at L. In the
position shown J is out of gear with all gears, but it may be swung to
the right so as to engage with wheel I and wheel M, and convey the
motion of I to M. Upon the same spindle as M is the pinion N, engaging
with the rack O, which is fast on the lathe bed. This completes the
automatic feed traverse.
For a hand feed traverse, pinion P is employed to drive M, which is fast
to N. The cross feed is self-acted by moving lever K to the left,
causing it to engage with pinion Q as well as with T, Q being fast on
the cross feed screw. To lock J in either of its three positions there
is provided on lever K a spring locking pin R, shown clearly in Fig.
584, which represents an irregular section of the gearing viewed from
the headstock of the lathe. The pin R is pressed inward by the spiral
spring shown, and has a conical end fitting into holes provided in the
apron to receive it. There are three of these holes, shown in dotted
lines at _a_ _b_ _c_ in Fig. 582. When the pin is in _a_ the lever K,
and therefore wheel J, Fig. 582, is locked out of gear; when it is in
hole _b_ wheel J is locked in gear with I and M, and when it is in _c_
the wheel J is in gear with T and Q, and the cross feed is actuated.
[Illustration: Fig. 581.]
[Illustration: Fig. 582.]
A similar locking device is provided for the pinion B for actuating A;
thus in Fig. 582 B is the lever, the spring pin being at R´´; or
referring to Fig. 584, X is the lever fast at _x_ on the pin driving B,
and R´´ is the spring pin.
The nut for the lead screw is secured either in or out of gear with the
screw in the same manner, _x´_, Fig. 583, being the lever and R´ the
spring pin.
In screw cutting the cutting tool requires to be withdrawn from the
thread while the carriage traverses back, and it is somewhat difficult
to know just how far to move the tool in again in order to put on a
proper depth of cut. To facilitate this the device shown in Fig. 585
(which is taken from the "American Machinist,") is sometimes employed.
It consists of a ring C inserted between the cross slide D and the
handle hub B having journal bearing on and rotating with the latter.
When the first cut is put on, the mark on C is coincident with that on
D, and the ring is then, while the first cut is traversing, moved
(supposing the cross feed screw to have a right-hand thread) to the
left, as shown in the figure, to the amount the handle will be required
to move to the right to put on the next cut, and when the next cut is
put on the handle will be moved the distance it was moved to withdraw
the tool for the back traverse, and in addition enough to make the marks
coincide, then while the second cut is being taken the ring is again
moved to the left, as in the cut, to give the depth of cut for the next
traverse, and so on.
[Illustration: Fig. 583.]
If the cross feed screw has a left-hand thread, the mark on the ring
would require to be moved to the right instead of to the left of the
mark on D. It is obvious that this answers the same purpose, but is more
exact than the chalk mark before referred to, and, indeed, that chalk
mark could be used in the same way, leaving the chalk mark D and rubbing
out that on C while the cut is proceeding and making a new one for the
next cut.
[Illustration: Fig. 584.]
Another device for use on lathes specially designed for screw-cutting is
shown in Fig. 586, in which A represents the cross feed screw. It is
fast to the notched wheel B, and is operated by it in the usual way. C
is a short screw which provides journal bearing for the screw A by a
plain hole. It is screwed on the outside, and the plate in which it fits
acts as its nut. It is fast to the handle D, and is in fact operated by
it. The handle or lever is provided with a catch E, pivoted in the
enclosed box F, which also contains a means of detaining the catch in
the notches of the wheel, or of holding it free from the same when it is
placed clear. If, then, the lever D be moved back and forth the feed
screw A, and hence the slide rest, will be operated; while, if the catch
be placed in one of the notches on the wheel B, both the screws, A and
C, will act to operate the rests. When, therefore, the tool is set to
touch the diameter of the work, the catch E is lifted and the feed wheel
B rotated, putting on the cut until the catch E will fall into the next
notch in B, the lever D resting in the meantime on the stud G. When the
cut is carried along the work to the required distance the tool is
withdrawn by moving D over until it rests upon stud or stop H. While the
slide rest is traversing back E is lifted and B rotated so that E will
fall into the next notch, and when the tool starts forward again D is
moved over from H to G, as shown in the figure, and the tool cut is put
on.
[Illustration: Fig. 585.]
When the device is not required to be used E is thrown out, D rests on
E, and the feed is operated in the ordinary manner.
[Illustration: Fig. 586.]
A simple attachment for regulating on a slide rest the depth of tool cut
in screw cutting or for adjusting the cut to a requisite diameter when a
number of pieces are to be turned to diameter by a finishing cut, is
shown in Fig. 587, in which B represents the slide rest carriage, and E
the cross slide on which the slide rest A is traversed by means of the
cross feed screw _f_. A screw is screwed into the rest, as shown,
carrying the two circular milled edge nuts R P; the screw passes an easy
fit through the piece C, which is capable of being fixed in any position
along the slide E by means of the set screw S; the nut R is set in such
a position on the screw that it will abut against C when the tool is
clear of the work surface (for the back traverse) while P may be used in
two ways:--First it may be set so that when it comes against C the
thread is cut to the required depth, and thus act as stop to give the
thread depth without trying the gauge: or it may be used to answer the
same purpose and in the same way as the ring C in Fig. 585.
[Illustration: Fig. 587.]
The use of this device as a stop to gauge the thread depth is confined
to such lengths of work as enable the tool to cut several pieces without
requiring regrinding, because when the tool is removed to grind it, it
is impracticable to set it exactly the same distance out from the tool
post, hence the adjustment of P becomes destroyed. It is better,
therefore, in most cases where a number of threads of equal pitch and
diameter are to be cut, to rough them all out, cutting the threads a
little above the gauge diameter so as to leave a finishing cut to be
taken. In roughing out, however, the nut P may still be used to regulate
the depth.
For the finishing cut the tool may be ground and P adjusted to give the
requisite depth of cut, taking a single traverse over each thread to
finish it. This, of course, preserves the tool and enables it to finish
a larger number of threads without regrinding, and the consequent
readjustment of P.
It is obvious that the nut P may be employed in the same manner to turn
a number of plain pieces to an equal diameter.
[Illustration: Fig. 588.]
It is preferable in a device of this kind, however, to employ the two
adjusting nuts P and Q in Fig. 588, Q being a clamp nut that can be
closed by a screw so as to firmly grip the threaded stud. Q is adjusted
so that when P abuts against it the tool will cut to the correct
diameter when it is moved in as far as nuts P Q will permit. The use of
the second nut P is as follows:--Suppose a first cut has been taken and
P may be screwed up to just meet the face of clamp C. Then while the
carriage is traversing, P may be screwed back towards Q sufficiently to
put on the next cut, and so on, so that P is used to adjust the depths
of the roughing, and Q that of the finishing cut.
Sometimes a feed motion to a slide rest is improvised by what is known
as the _star feed_, the principle of action of which is as follows: Upon
the outer end of the feed screw of the boring bar or slide rest, as the
case may be, is fastened a piece of iron plate, which, from having the
form in which stars are usually represented, is called the star. If the
feed is for a slide rest a pin is fastened to the lathe face plate or
other revolving part, in such a position that during the portion of the
revolution in which it passes the star it will strike one of the star
wings, and move it around sufficiently to bring the next wing into
position to be struck by the pin during its succeeding revolution. When
the feed is applied to a revolving boring bar the construction is the
same, but in this case the pin is stationary and the star revolves with
the feed screw of the bar.
In Fig. 589 is shown a star feed applied to a slide rest. A is the slide
rest, upon the end of the feed screw of which the star, B, is fitted. C
is a pin attached to the face plate of the lathe, which, as it revolves,
strikes one of the star wings, causing it to partly rotate, and thus
move the feed screw. The amount of rotation of the feed screw will
depend upon the size of the star and how far the circle described by the
pin C intersects the circle described by the extreme points of the star
wings. Thus the circles denoted by D E show the path of the pin C; the
circle F H the path of the star points, and the distance from F to G the
amount which one intersects the other. It follows that at each
revolution of C an arm or wing of the star will be carried from the
point G to point F, which, in this case, is a sixth of a revolution. If
more feed is required, we may move the pin C, so that it may describe a
smaller circle than D E, and cause it to intersect F H to a greater
extent, in which case it will move the star through a greater portion of
its revolution, striking every other wing and doubling the amount of
feed.
It will be observed that the points F and G are both below the
horizontal level of the slide rest's feed screw, and therefore that the
sliding motion of the pin C upon the face of the star wings will be from
the centre towards the points. This is better, because the motion is
easier and involves less friction than would be the case if the pin
contact first approached and then receded from the centre, a remark
which applies equally to all forms of gearing, for a star feed is only a
form of gearing in which the star represents a tooth wheel, and the pin
a tooth in a wheel or a rack, according to whether its line of motion is
a circle or a straight line.
[Illustration: Fig. 589.]
It is obvious that in designing a star feed, the pitch of the feed screw
is of primary importance. Suppose, for example, that the pitch of a
slide rest feed screw is 4 to an inch, and we require to feed the tool
an inch to every 24 lathe revolutions; then the star must have 6 wings,
because each revolution of the screw will move the rest 1/6 in., while
each revolution of the pin C will move the star 1/6 of a revolution, and
4 × 6 = 24. To obtain a very coarse feed the star attachment would
require to have two multiplying cogs placed between it and the feed
screw, the smaller of the cogs being placed upon the feed screw.
In many lathes of European design, the feeds or some of them, are
actuated by ratchet handles, operated by an overhead shaft, having arms
which rock back and forth. Thus in Fig. 590 is a lathe on which there is
provided at A crank disc, carrying in a dovetail slot a pin P, for
rocking the overhead shaft from whose arms a chain is attached which may
be connected to the ratchet handle shown on the cross-feed screw, the
weight being for the purpose of carrying that handle down while the
chain pulls it up. To regulate the amount of feed the pin P is adjusted
in the slot in A, or the chain may be attached in different positions
along the length of the ratchet arm, the weight being provided with a
set screw so that it may be set in any required position along the
ratchet arm.
[Illustration: Fig. 590.]
TOOL-HOLDING DEVICES.--Perhaps no part of a lathe is found in American
practice with so many different forms of construction as the device for
holding the cutting tool. The requirements for a lathe to be used on
light work and where frequent changes in the position of the tool are
necessary, are quite different from those for a lathe intended to take
as heavy a cut as the lathe will properly drive, and wherein tools
having the cutting edge at times standing a long way out from the tool
post (as sometimes occurs in the use of boring tools). In the former
case a single holding screw will suffice, possessing the advantage that
the tool may be quickly inserted, adjusted for height and set to one
side or the other, with a range of motion which often permits of a tool
that has taken a parallel cut being moved in position to capacitate it
to take a facing one, which would not be the case were its capacity for
side adjustment limited.
In the case of the common American lathe having a self-acting feed and
no compound rest, the tool post is usually employed, the rest being
provided with a [T] slot such as shown in Fig. 577. This enables the
tool post to be moved from side to side of the tool rest, and swing
around in any required position. In connection with such tool posts
various contrivances are employed to enable the height of the cutting
edge of the tool to be readily adjusted. Thus in the Fig. 591, the tool
post is surrounded by a cupped washer W, and through the slot in the
tool post passes a gib G, which may be moved endways in the slot and
thus elevates or depresses the tool point.
The objection to this is that the tool is not lifted parallel, or in
other words is caused to stand out of its proper horizontal position
which alters the clearance of the tool, and by presenting the angles
forming the tool edge in an improper position, with relation to the
work, impair its cutting qualification, as will be shown hereafter when
treating of lathe cutting tools.
An improvement on this form has been pointed out by Professor John E.
Sweet, whose device is shown in Fig. 592. Here the washer or ring is
rounded and the bottom surface of the gib is hollowed, so that chips or
dirt will to a great extent fall off, and every time the tool post is
swung the gib acts to push off whatever dirt may lodge on the washer.
In the design shown in Fig. 593, the tool rests upon two washers W that
are tapered, and its height is adjusted by revolving one of these
washers, it being obvious that the limit of action to depress the tool
point is obtained when the two thin sides of the washers are placed
together, and on the same side of the tool post as the cutting edge of
the tool, while the limit of action to raise the tool point is obtained
when the washers have their thick sides together and nearest to the tool
point.
Here again the tool is thrown out of level, and to obviate this
difficulty the stepped washer shown in Fig. 594 may be used, the steps
on opposite sides of the washer being of an equal height. This enables
the tool to be raised or lowered without being set out of the horizontal
position; but it has the defect that the adjustment cannot be made any
finer than the height of the steps, and if the height is made to vary
but slightly, in order to refine, as it were, the adjustment, the range
of tool elevation or depression is correspondingly limited. Another form
of stepped washer is shown in Fig. 595, in which no two steps are of the
same height. This affords a wider range of adjustment, because the same
two steps will alter the height of the tool by simply turning the washer
one-half revolution. It has two defects, however; first, the least
amount of adjustment is that due to the difference in height of the
steps; and, second, when the tool is elevated it grips the washer at A,
so that the tool is not supported across the full width of face of the
washer, as it should be.
A defect common to all devices in which the tool is thrown out of level,
is that the binding screw does not bed fair upon the tool, and as a
result it is apt, if screwed home very firmly, as is necessary to hold
boring tools that stand far out from the tool post, to spread the screw
end as in Fig. 596, or to bend it.
A very convenient tool-adjusting device is shown in Fig. 597. It
consists of a threaded ring N receiving the threaded bush M, the tool
height being adjusted by screwing or unscrewing one within the other.
The objection to this is, that it occupies so much vertical height that
there is not always room to admit it, which occurs, for example, in
compound slide rests on small lathes.
On these rests, therefore, a single washer is more frequently used,
which answers very well when the tool post is in a slot, so that it can
be moved from side to side of the rest as occasion may require. When,
however, the position of the tool post is fixed it has the disadvantage
that the point P, Fig. 598, where the tool takes its leverage, is too
far removed, and the tool is therefore liable to bend or spring from the
pressure of the cut.
In Fig. 599 is an elevating device sometimes used on the compound rests
of large lathes. The top of the rest is provided with a hub H, threaded
externally to receive a ring nut R, around whose edge there are numerous
holes to receive a pin for operating the nut. The tool-post is situated
central in the hub. When the tool is loose the ring nut can be operated
by hand or the tool may be gripped lightly and the ring nut operated by
a pin. The level of the tool is here maintained; it is supported to
about the edge of the rest on account of the large diameter of the ring
nut, and a very delicate adjustment for height can be made, but such a
device is only suitable for large lathes on account of the depth of the
ring nut and hub.
[Illustration: Fig. 607.]
On small slide-rests the device shown in Fig. 600 is often found. It
consists of a holder H, in which is cut a seat for the tool, this seat
being inclined to give the piece of steel used as a tool a certain
constant degree of angle, and at the same time to permit of the tool
being moved endwise in the holder to set it for height; but, as the tool
requires to be pushed farther and farther through the holder to raise
it, it is not so well supported as is desirable when slight tools are
used, unless the holder is made long, so as to pass through the tool
post with the tool. Again, it does not support the tool sideways unless
the tool steel is dressed up and closely fits the groove in the holder.
In Fig. 601 W W are two inverted wedges which afford an accurate
adjustment, but the range is limited, because if the wedges have much
taper they are apt to move endways when the tool is fastened.
A convenient device for the compound rests of small lathes is shown in
Fig. 602. It consists of a holder pivoted upon a central post and
carrying two tool-binding screws, hence it can be revolved to set the
tool in any required position. A similar device is shown in Fig. 603, in
which the central post is slotted at A to receive the tool, and also
carries a plate C, held by the nut N, and provided with tool-holding
screws B and B´, which abut against the top of the rest, a top view of
the device being shown in Fig. 604. Plate C may thus be swung around to
set the tool in any required position on either side of the rest.
In Maudslay's slide rest, the tool clamp shown in Fig. 605 is employed.
Screws A are employed to grip the tool moderately firm, and a turn of
screws B (whose ends abut against the top of the slide rest) very firmly
secures the tool, since it moves the clamp C as a lever, whose fulcrum
is the screw A.
Figs. 606 and 607 represent the Whitworth tool clamp, the clamping
plates of which change about upon the four studs, and are supported at
their inner ends by a block equal in height to the height of the tool
steel.
Figs. 608, 609, 610, and 611 represent the "Lipe" tool post, so called
from the name of its inventor. The top of the cross slide is
cylindrical, and is bored to receive the tool post which has a
cylindrical stem. The cylindrical part of the tool post is split
vertically, and has two lips, the bolt D passing through one lip and
threading into the other, so that by operating bolt D the tool post may
be gripped very firmly or released, so that it may be revolved to bring
the tool into any required position after it is fastened in the tool
post, which is a great advantage because the tool is brought to a solid
seating in the post before its height is adjusted, and will not
therefore be altered in height by setting up the set screws as often
occurs in ordinary tool posts. From the shape of the tool post, the tool
may be gripped by one set screw only, when required for light duty, or
by two set screws for heavy duty or for boring, while in either case it
is supported clear to the edge of the rest.
[Illustration: Fig. 608.]
[Illustration: _VOL. I._ =TOOL-HOLDING AND ADJUSTING APPLIANCES.= _PLATE
VII._
Fig. 591.
Fig. 592.
Fig. 593.
Fig. 594.
Fig. 595.
Fig. 596.
Fig. 597.
Fig. 598.
Fig. 599.
Fig. 600.
Fig. 601.
Fig. 602.
Fig. 603.
Fig. 604.
Fig. 605.
Fig. 606.]
Fig. 608 shows the tool in position, held by a single screw, for work
requiring the tool to be close up to the work driver. In Fig. 609 a tool
is shown held as is required by work between centres, but both
set-screws are used. Fig. 610 shows a tool in position for boring, two
set-screws being used. Fig. 611 shows a tool being held for the same
purpose, but by a single screw, and it will be observed that the
advantage of the second set-screw is obtained without in any way
sacrificing the handiness of the post, when used with a single screw.
Whether one or two set-screws are used, the boring tool may be forged
from a single bar of octagon steel, which can be seated in a piece like
that shown at E in Fig. 610, which is grooved so as to receive and hold
the tool. As is well known, boring tools are the most troublesome both
to forge and to adjust in the lathe, and, as the result, a light tool is
often used because no other is at hand and it is costly to make a new
one. When, however, the tool can be forged from a plain piece of steel,
these objections are overcome, and a sufficient number of tools may be
had so that one can always be found suitable for any ordinary sized
hole, the object being to use as rigid a tool as can be got into the
hole bored. The feature of maintaining the tool level is of great
importance in boring work, because when the tool requires to be set out
of level to adjust its height, it will generally strike against the
mouth of the hole if the latter is of much depth. This annoyance is also
frequently met with in boring tools which are forged out of rectangular
steel, because the rounded stem is generally left taper. The largest end
of the taper is generally nearest the tool post. Hence the capacity to
use octagon steel and keep it level while adjusting its height, added to
the fact that the tool is supported clear to the edge of the tool rest,
and the tool post is so blocked as to virtually become a part of the
rest, constitute a very important advantage.
[Illustration: Fig. 609.]
[Illustration: Fig. 610.]
A common device on large lathes is shown in Fig. 612, the two clamps
being shown in position for outside turning, and being changed (so as to
stand at a right angle to the position they occupy in the figure) for
holding boring tools. The bolts are enveloped by spiral springs which
support the clamps.
Figs. 613 and 614 represent the tool holders employed in the Brown and
Sharpe small screw machines. In the front rest, Fig. 613, the piece R
receives two adjusting and tool-gripping screws S, upon which sits the
gib G, and upon this the tool is placed. The surface E at the top of the
tool post slot is curved so that it will bear upon the top of the tool
at a point only. The tool is here supported along the full length of the
gib, and there is no set-screw at the top of the tool post, which
enables a much more unobstructed view of the tool.
Fig. 614 is the tool post used at the back of the rest, the piece B
passing through the tool post slot. The tool rests upon the top of screw
E and upon the top of B at F, and is secured by set-screw S; its height
is therefore adjusted by means of screw E, which is threaded in B. The
set-screw S is not in this case objectionable, because it is at the back
of the rest, and therefore does not obstruct the view of the work, while
it is at the same time convenient to get at.
When the screw for traversing a lathe carriage is used for plain
feeding, it is termed the feed screw, but when it is used to cut threads
it is termed the lead screw.
A lead screw should be used for screw cutting only, so that it may be
preserved as much as possible from wear. As the greater portion of
threads cut in a lathe of a given size are short in comparison with the
length of the lathe, it follows that the part of the lead screw that is
in operation when the carriage or saddle is traversing over short work
is most worn, while the other end is least worn, hence it is not unusual
to so construct the screw and its bearings that it may be changed end
for end in the lathe, to equalize the wear. By turning a lead screw end
for end, therefore, to equalize the wear, the middle of the length of
the screw will become the least worn, and, therefore, the most true.
Hence it is better to use one end of the lead screw for general work,
and to reverse it and use the other end only for screws requiring to be
of very correct pitch.
[Illustration: Fig. 611.]
[Illustration: Fig. 612.]
[Illustration: Fig. 613.]
[Illustration: Fig. 614.]
To obviate the wear as much as possible the feed nut should embrace as
great a length of the screw as convenient, and should be of a material
that will suffer more from wear than the lead screw, or in other words
shall relieve the feed screw from wear as much as possible. The wear on
the nut being equal from end to end, the wearing away of one side of its
thread does not vary its pitch; hence the only consideration as to its
wearing qualification are the expense of its renewal and the length of
time that may occur between its being engaged with the lead screw and
giving motion to the lathe carriage, this time increasing in proportion
as the nut thread is worn. Under quick speeds or when the lathe is in
single gear, the rotation of the feed screw is so quick that not much
time is lost before the carriage feeds, but when the back gear is in
operation at the slowest speeds, the loss of time due to a nut much worn
is an item of importance.
In some lathes the feed screw is employed for screw cutting and for
operating an independent feed also. This is accomplished by cutting a
feather way or spline along it, so that a worm having journal bearing in
the apron of the rest carriage may envelop the lead screw and be driven
by it, through the medium of a feather fast into the worm gear. The
motion obtained from the worm gear is transferred through suitable
gearing to the rack pinion.
The spline is cut deeper than the thread, so as to prevent the latter as
far as possible from wear, by reason of the friction of the spline.
The lead screw if long should be supported, to prevent its sagging of
its own weight. In some cases the lead screw is supported in a trough
along its whole length, as is done in the Sellers lathe. In other cases,
bearings hanging from the [V]-slides, and movable along the bed, are
employed.
It is desirable that the feed screw and nut be as near the middle of the
carriage as possible, so that it shall pull the carriage at as short a
leverage as possible, thus avoiding the liability to tilt or twist the
carriage; but it is not practicable to place it midway between the lathe
shears, because in that case the cuttings, &c., from the work would fall
upon it, and cause excessive and rapid wear of the screw and nut.
In general the lead screw is located either in front, or at the back of
the lathe, and in considering the more desirable of the two locations,
we have as follows:
The feed nut should obviously remain axially true with the lead screw,
as by reason of the extra weight of the front of the carriage, both it
and the lathe shears wear most at the front, and the carriage,
therefore, falls to the amount of its own wear and the wear of the
shears. If the lead screw is used to feed with (as it should not be),
the nut wears coincidently with the carriage and the shears, and the
screw alignment is not impaired; but with an independent feed, only a
small portion of the carriage traversing is done with the lead screw,
hence the carriage lowers from the wear due to the independent feeding,
and when the lead screw comes to be used its nut is not in true
alignment with it. It is obviously preferable, then, to place the lead
screw at the back, where the carriage and shears wear the least.
Furthermore, this relieves the carriage front from the weight of the
nut, &c., tending to equalize the back and front wear, while removing
the nut-operating device from the front to the back of the shears, and
thus reducing the number of handles in front, and thus avoid
complication in small lathes.
LATHE LEAD SCREWS.--Lead screws have their pitches in terms of the inch
throughout all parts of the world; or, in other words, the lead screws
of all lathes contain so many full threads per inch of length.
Lead screws are usually provided with square threads of the usual form,
or with threads whose sides have about fifteen degrees of angle, so that
the two halves of the feed nut may be let together to take up the wear.
It is obvious that in a [V]-thread or in a thread whose sides are at an
angle, the feeding strain tends to force the two halves of the feed nut
apart, and therefore places a strain on the feed-nut operating mechanism
that does not exist in the case of a square thread. Furthermore it can
be shown that with a [V]-thread the opportunities to lock the carriage
on a wrong place, after traversing it back by hand in screw cutting, are
increased, thus augmenting the liability to cut intermediate and
improper threads.
[Illustration: Fig. 615.]
In Fig. 615, for example, we have a pitch of lead screw of three threads
per inch, and the gears arranged to cut six threads per inch on the
work. As the bottom wheel has twice as many teeth as the top one, it is
clear that, while the top one makes one, the bottom one will make half
revolution, and the lead screw will make half a turn for every turn the
work makes. Now, suppose the tool point to stand opposite to space A,
and the nut (supposing it to have but one thread only, which is all that
is required for our purpose), stand opposite to space D. Suppose,
further, that the lathe makes one revolution, and space B on the work
will have moved to occupy the position occupied by space A, or, rather,
there will still be a place at A fully in front of the tool, as should
be the case, but the lead screw will have made half revolution, the top
_e_ of the thread coming opposite to the feed nut, as in the position of
tool and nut shown in the figure at T and N; hence the nut would not
engage, without moving the lathe carriage sideways, and thus throwing
the tool to one side of the thread in the work. When, however, the work
had made another revolution, both the feed screw and the work would
again come into position for the tool and nut to engage properly, and it
follows that in this case the tool will always fall into proper position
for the nut to be locked.
It is obvious, however, that had the lead screw thread been a square
one, and the nut thread to accurately fit to the lead screw thread, so
as to completely fill it, then the nut could not engage with the lead
screw until the lathe had made a complete revolution, at which time the
work will have made two full or complete revolutions, and the tool
would, therefore, fall into proper position to follow in the groove or
part of a thread cut at the first tool traverse.
[Illustration: Fig. 616.]
In Fig. 616, we have the same lead screw geared to cut five or an odd
number of threads per inch. The tool and the nut are shown in position
to properly engage, but suppose, the nut being disengaged, that the work
makes one revolution, and during this period the lead screw will have
made 3/5ths of a revolution, hence the nut will not be in position to
engage properly, because, although space B will have travelled forward
so as to occupy the position of space A in the figure (that is, there
will be a space fairly in front of the tool point), yet the nut will not
engage properly, because the nut point will not be opposite to the
bottom of the lead screw thread. When the work has made its second
revolution, and space C moves to the position occupied by A, the lead
screw will have made 6/5 or 1-1/5 revolutions, and the nut cannot engage
properly; when the lathe has made its third revolution, the lead screw
will have made 1-4/5 revolutions and the nut will still fall to one side
of the thread space, and will not lock properly. The work having made
its fourth turn, the lead screw will have made 2-2/5 turns, and the nut
will not be in position to lock fairly. The work having made its fifth
turn, however, the lead screw will have made three turns, and the
threads will fall into the same position that they occupy in the figure,
and both tool and feed nut will fall into their proper positions in
their respective threads. It does not follow, however, that, the lead
screw having a [V]-shaped thread, the nut cannot be forced to engage but
once in every five turns of the lead screw, because, were this the case,
it would be impossible to lock the nut in an improper position.
[Illustration: Fig. 617.]
Suppose, for example, that we have in Fig. 617, the same piece of work
and lead screw as in Fig. 616, and that a first groove, A, has been cut
with the tool in the position shown, and the nut engaged in the position
marked 1. Now, suppose the nut be disengaged and the work allowed to
make one revolution, then the lead screw will, during this revolution,
revolve 3/5 of a revolution, and the position of the nut point with
relation to the lead screw will be as at position 2. If, then, the nut
was forced into the lead screw thread, it would, acting on the wedge
principle, move the carriage to the right sufficiently to permit the nut
to engage fully in thread G, and the tool would then cut a second groove
on thread B. If the nut then be withdrawn from thread G, and the work
allowed to make another revolution, the nut will stand in a precisely
similar position with relation to the lead screw thread as it did in
position 2, and by forcing it down into thread H the carriage would be
again forced to the right, causing a third thread, C, to be cut. By
repeating the operation of withdrawing the nut, letting the work make
another revolution and then engaging the nut again, it will seat in
thread K, and a fourth thread D will be cut. On again repeating the
operation, however, the nut will come into position 5, and, on being
drawn home into thread, or, rather, into space L, the tool will fall
into groove A again. Thus there will be four threads, each having a
pitch equal to that of the lead screw. The second (B) of these four will
fall to the left of thread A to an amount or distance equal to 2/5 of
the pitch of the lead screw, because, in forcing the nut from position 2
down into the lead screw, the slide rest, and therefore the tool, will
be moved to the right 2/5 of the pitch of the lead screw. The third
thread C will fall to the left of thread B also to an amount equal to
2/5 of the pitch of the lead screw, because, in forcing the thread to
seat itself into thread H from position 3, the slide rest was again
moved (to that amount) to the right. The fourth thread D will fall to
the left of thread C to the same amount and for the same reason.
But in this case, as before, if the lead screw had a square thread and
the nut threads completely filled the spaces between the lead screw
threads, then the nut could not engage at the 2nd, 3rd, or 4th work
revolution, hence the false threads B, C, and D, could not have been
cut, even though the feed nut was disengaged and the lathe carriage was
traversed back by hand.
Now, suppose that two threads on the work measure less than the amount
the lead screw advances during the time that the work makes a
revolution, and if the lead screw has a [V]-shaped thread, the case is
altered. We have, for example, in Fig. 618, a pitch of lead screw of 3
to cut 12 and 13 threads respectively. In the case of the 13 threads it
will be seen that, supposing there to have been a first cut taken on the
work, and the feed nut to be disengaged while the work makes a
revolution, then the lead screw will revolve 3/13 revolution and the
point A on the lead screw will have moved up to point B, and the nut
point remaining at N, seating it in the thread, would cause it to engage
with the same thread that it did before, and no second thread would be
cut. If the nut be then released, the work allowed to make another
revolution and the nut again closed, the operation would be the same as
before, and no error would be induced, and so on. Suppose, further, that
after the nut was disengaged the lathe was permitted to make two
revolutions, and the lead screw would make 6/13, or less than half a
turn, and closing it would still cause it to pass back into the same
thread on the lead screw and produce correct work. But if after the nut
was released the work made three turns, the lead screw would make 9/13
of a turn, and the nut would fall on the right-hand side of the lead
screw thread, and in closing would move the lathe carriage to the right,
causing the tool to cut a second thread. Now, the same operation that
occurred with the first thread would during the next three trials occur
with the second thread, and at the next or seventh trial a third thread
would be cut, which would be again operated upon during the next
succeeding three trials. At the eleventh trial a fourth thread would be
cut, but on the next three trials the tool would again fall into the
groove first cut and the work proceed correctly. In the case of the 12
threads, the thread cut at the first and second trials would be correct.
At the third trial the nut would seat itself in the groove C of the lead
screw, causing the carriage to move to the right to a distance equal to
twice the pitch of thread being cut, but the tool would still fall into
the same groove in the work, as it also would on the fourth. At the
fifth trial the process would be repeated, and so on, so that no second
thread would be cut.
[Illustration: Fig. 618.]
It may now be noted that if we draw the lead screw and the thread to be
cut as in the figure, and draw the dotted lines shown, then those that
meet the bottom of the thread on the lead screw, and also meet the
groove cut on the work, at the first trial, represent the cases in which
the nut will fall naturally into its proper position for the tool to
fall into the correct groove, while whenever the nut is being forced
home it seats in a groove in the lead screw, the bottom of which groove
meets a line drawn from the first thread cut; the results obtained will
be made correct by reason of the movement given to the slide nut when
artificially seating the nut. This is shown to be the case in Fig. 619,
which represents a lead screw having an even number of threads per inch,
and from which it appears that in cutting 12 threads (an even number
also) the nut cannot be engaged wrong, whereas in the case of 13 threads
it can be engaged right three times in 13 trials, and 10 times wrong,
the latter causing the tool to cut three wrong threads.
[Illustration: Fig. 619.]
To prevent end motion of a lead screw it should have collars on both
sides of one bearing, and not one at each bearing. By this means the
screw will be permitted to expand and contract under variations of
atmospheric temperature, without binding against the bearing faces.
When a lead screw is long it requires to be supported, otherwise, either
its weight will be supported or lifted by the feed nut in gear, or if
that nut does not lift the screw, the thread cut will be finer than that
due to the pitch of the lead screw, by reason of its deflection or sag.
A lead screw should preferably be as near as possible to the middle of
the lathe shears, and as close to the surface as possible, so as to
bring it as nearly in line with the strain on the tool as possible, but
on account of the cuttings, which falling upon the screw would cause it
to wear rapidly, it is usual to locate it on one side, so as to protect
it from the cuttings. It is better to locate it on the front side of the
lathe rather than on the back, because the strain of the cut falls
mainly on the front side (especially in work of large diameter when this
strain is usually greatest) and it is desirable to pull the carriage as
near in a line with the resistance of the cut as possible, because the
farther off the feed nut from the cutting tool point, the greater the
tendency to twist the carriage on the shears.
To preserve the nut from wear, it should be made as long as convenient,
as, say, five or six times the diameter of the lead screw; it is usually
made, however, three or four diameters.
It is obvious that the pitch of the thread should be as accurate as
possible, but it has not as yet been found practicable to produce a
screw so accurate that it would not show an error, if sufficient of its
length be tested, as, say, several feet.
If the error in a screw be equal, and in the same direction at all parts
of its length, various devices may be employed to correct it. Thus Fig.
620 represents a device employed by the Pratt and Whitney Co.
It was first ascertained by testing the lathe that its lead screw was
too short by 7/100ths of a revolution in a length of 2 feet, the pitch
of its thread being 6 to an inch. Now in 2 feet of the screw there would
be 144 threads, and since 7/100ths (the part of a revolution the thread
was too short) × 1/6 (the pitch of the thread) = 7/600ths (which was
called 1/85th), the error amounted to 1/85th inch in 144 turns of the
screw. The construction of the device employed to correct this error is
as follows: In Fig. 620, A represents the bearing of the feed screw of
the lathe, and B _b_ a sleeve, a sliding fit upon A, prevented from
revolving by the pin _h_, while still having liberty to move endways. C
represents a casing affording journal bearing to B _b_, having a fixed
gear-wheel at its end C´, and an external thread upon a hub at that end.
D is the flange of C to fasten the device to the shears of the latter,
being held by screws. E represents an arm fast upon the collar of the
feed screw, and carrying the pinion F, the latter being in gear with the
pinion C´, and also with G, which is a pinion containing two internal
threads, one fitting to B at _b_, and the other fitting to C at _c_, the
former having a pitch of 27 threads to an inch, the latter a pitch of 25
to an inch.
[Illustration: Fig. 620.]
The operation is as follows:--The ordinary change wheels are connected
to the feed screw, or lead screw, as it is sometimes termed, at J in the
usual manner. The arm E being fast to the feed screw will revolve with
it, and cause the pinion F to revolve around the stationary gear-wheel
C´. F also gears with G. Now, F is of 12 diametrical pitch and contains
26 teeth, C´ is of 12 diametrical pitch and contains 37 teeth, and G is
of 12 diametrical pitch and contains 36 teeth. It follows that the
pinion F, while moving around the fixed gear C´, will revolve the pinion
G (which acts as a nut), to an amount depending upon the difference in
the number of its teeth and those of fixed gear C´ (in this case as 36
is to 37), and upon the difference in the pitches of the two threads, so
that at each revolution G will move the feed screw ahead of the speed
imparted by the change gears, the end of the sleeve B abutting against
the collar of the feed screw to move it forward.
In this case there are 36 turns of the feed screw A for one turn of the
nut pinion G, the thread on sleeve B being 27, and that on the hub of C
being 25 to the inch; hence, 36 turns of the feed screw gives an end
motion to the sleeve B of 1/25 minus 1/27 = 2/675, and 1/36 of that =
1/12150 of an inch = the amount of sliding motion of the sleeve _b_, for
each revolution of the lathe feed screw. By varying the proportions
between the number of teeth in C´ and G and the pitches of the two
threads in a proper and suitable ratio, the device enables the cutting
of a true thread from any untrue one in which the variation is regular.
It is usual to fasten to the side of the lathe head stock a brass plate,
giving a table of threads, and the wheels that will cut them, and
obviously such tables vary according to the pitch of the lead screw, but
a universal table may be constructed, such as the following table
(prepared by the author) that will serve for any lathe.
At the top of the table is the number of teeth in wheels, advancing by
four from 12 to 80 teeth, but it may be carried as much beyond 80 as
desired. On the left hand of the table is a column of the same wheels.
At the bottom of the scale are pitches of lead screw from 3 up to 20
threads per inch. Over each lead screw pitch are thread pitches, thus on
lead screw pitch 4 we have 20, 19, 18, and so on.
The use of the table is as follows:--
Find the pitch of the lead screw, and at the head of that column is the
number of teeth for the lathe stud or mandril. Then find in that column
the number of threads to be cut, and on the same line, but at the left
hand, will be found the number of teeth for the lead screw.
NUMBERS OF TEETH FOR WHEEL TO GO ON LATHE SPINDLE, LATHE STUD, OR
MANDRIL.
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
Lead |12|16|20|24|28|32|36| 40| 44| 48| 52| 56| 60| 64| 68| 72| 76| 80
Screw.| | *| | | | | | | | | | | | | | | |
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
12 | 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
16 | 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
20 | 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
24 | 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
28 | 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
32 | 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
36 | 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
40 |10|10|10|10|10|10|10| 10| 10| 10| 10| 10| 10| 10| 10| 10| 10| 10
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
44 |11|11|11|11|11|11|11| 11| 11| 11| 11| 11| 11| 11| 11| 11| 11| 11
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
48 |12|12|12|12|12|12|12| 12| 12| 12| 12| 12| 12| 12| 12| 12| 12| 12
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
*52 |13|13|13|13|13|13|13| 13| 13| 13| 13| 13| 13| 13| 13| 13| 13| 13
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
56 |14|14|14|14|14|14|14| 14| 14| 14| 14| 14| 14| 14| 14| 14| 14| 14
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
60 |15|15|15|15|15|15|15| 15| 15| 15| 15| 15| 15| 15| 15| 15| 15| 15
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
64 |16|16|16|16|16|16|16| 16| 16| 16| 16| 16| 16| 16| 16| 16| 16| 16
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
68 |17|17|17|17|17|17|17| 17| 17| 17| 17| 17| 17| 17| 17| 17| 17| 17
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
72 |18|18|18|18|18|18|18| 18| 18| 18| 18| 18| 18| 18| 18| 18| 18| 18
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
76 |19|19|19|19|19|19|19| 19| 19| 19| 19| 19| 19| 19| 19| 19| 19| 19
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
80 |20|20|20|20|20|20|20| 20| 20| 20| 20| 20| 20| 20| 20| 20| 20| 20
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
Lead | | | | | | | | | | | | | | | | | |
Screw |3.|4.|5.|6.|7.|8.|9.|10.|11.|12.|13.|14.|15.|16.|17.|18.|19.|20.
Pitch | | | | | | | | | | | | | | | | | |
------+--+--+--+--+--+--+--+---+---+---+---+---+---+---+---+---+---+---
EXAMPLE.--The lead screw has a pitch of 4, and I require to cut 13
threads per inch. At the head of the column is 16, and on a line with
the 13 of the column, but on the left is 52, each number being marked by
a * hence the 16 and 52 are the wheels; if we have not those wheels,
multiply both by 2 and 32, and 104 will answer.
If the pitch of the lead screw is 2 threads per inch, the wheels must
advance by 6 teeth, as indicated below:--
NUMBERS OF TEETH FOR WHEEL TO GO ON LATHE STUD, LATHE SPINDLE OR
MANDRIL.
+-----+--------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |Lead |12|18|24|30|36|42|48|54|60|66|72|78|84|90|96|
| |Screw. | | | | | | | | | | | | | | | |
|NUM- +--------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
|BER | 12 | 2| 2| 2| 2| 2| 2| 2| 2| 2| 2| 2| 2| 2| 2| 2|
|OF | 18 | 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3| 3|
|TEETH| 24 | 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4| 4|
|FOR | 30 | 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5| 5|
|WHEEL| 36 | 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6| 6|
|TO | 42 | 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7| 7|
|GO | 48 | 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8| 8|
|ON | 54 | 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9| 9|
|LEAD | 60 |10|10|10|10|10|10|10|10|10|10|10|10|10|10|10|
|SCREW+--------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| |Pitch of| | | | | | | | | | | | | | | |
| |Lead | 2| 3| 4| 5| 6| 7| 8| 9|10|11|12|13|14|15|16|
| |Screw. | | | | | | | | | | | | | | | |
+-----+--------+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
This table may be used for compound lathes by simply dividing the pitch
of the lead screw by the ratio of the compounded pair of wheels. For
example, for the wheels to cut 8 threads per inch, the pitch of lead
screw being 4 and the compounded gears 2 to 1, as the ratio of the
compounded pair is 2 to 1, we divide the pitch of lead screw by 2, which
gives us 2, and we thus find the wheels in the column of pitch of lead
screw 2, getting 12 and 48 as the required wheels, the 12 going on top
of the lathe because it is at the top of the table, and the 48 on the
lead screw because it is at the left-hand end of the table, and the lead
screw gear is at the left-hand end of the lathe.
The table may be made for half threads as well as whole ones by simply
advancing the left-hand column by two teeth, instead of by four, thus:--
+------+--------------------------------------------------------------+
|Teeth | Teeth for Wheel on Stud. |
| for |------+------+------+------+------+------+------+------+------+
|Wheel | | | | | | | | | |
| on | 12 | 16 | 20 | 24 | 28 | 32 | 36 | 40 | 44 |
| Lead | | | | | | | | | |
|Screw.| | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+
| 12 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 | 3 |
+------+------+------+------+------+------+------+------+------+------+
| 14 | 3-1/2| 3-1/2| 3-1/2| 3-1/2| 3-1/2| 3-1/2| 3-1/2| 3-1/2| 3-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 16 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 | 4 |
+------+------+------+------+------+------+------+------+------+------+
| 18 | 4-1/2| 4-1/2| 4-1/2| 4-1/2| 4-1/2| 4-1/2| 4-1/2| 4-1/2| 4-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 20 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 | 5 |
+------+------+------+------+------+------+------+------+------+------+
| 22 | 5-1/2| 5-1/2| 5-1/2| 5-1/2| 5-1/2| 5-1/2| 5-1/2| 5-1/2| 5-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 24 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 |
+------+------+------+------+------+------+------+------+------+------+
| 26 | 6-1/2| 6-1/2| 6-1/2| 6-1/2| 6-1/2| 6-1/2| 6-1/2| 6-1/2| 6-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 28 | 7 | 7 | 7 | 7 | 7 | 7 | 7 | 7 | 7 |
+------+------+------+------+------+------+------+------+------+------+
| 30 | 7-1/2| 7-1/2| 7-1/2| 7-1/2| 7-1/2| 7-1/2| 7-1/2| 7-1/2| 7-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 32 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
+------+------+------+------+------+------+------+------+------+------+
| 34 | 8-1/2| 8-1/2| 8-1/2| 8-1/2| 8-1/2| 8-1/2| 8-1/2| 8-1/2| 8-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 36 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 9 | 9 |
+------+------+------+------+------+------+------+------+------+------+
| 38 | 9-1/2| 9-1/2| 9-1/2| 9-1/2| 9-1/2| 9-1/2| 9-1/2| 9-1/2| 9-1/2|
+------+------+------+------+------+------+------+------+------+------+
| 40 |10 |10 |10 |10 |10 |10 |10 |10 |10 |
+------+------+------+------+------+------+------+------+------+------+
| 42 |10-1/2|10-1/2|10-1/2|10-1/2|10-1/2|10-1/2|10-1/2|10-1/2|10-1/2|
+------+------+------+------+------+------+------+------+------+------+
|Pitch | | | | | | | | | |
| of | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 |11 |
| Lead | | | | | | | | | |
|Screw.| | | | | | | | | |
+------+------+------+------+------+------+------+------+------+------+
For quarter threads we advance the left-hand column by one tooth, or for
thirds of threads by three teeth, and so on.
If we require to find what wheels to provide for a lathe, we take the
pitch of the lead screw for the numerator, and the pitch required for
the denominator, and multiply them first by 2, then by 3, then by 4, and
so on, continuing until the numerator or denominator is as large as it
can be to give the required proportion of teeth, and not exceed the
greatest number that the largest wheel can contain.
For example: A lathe has single gear, and its lead screw pitch is 8 per
inch, what wheels will cut 18, 17, 16, 15, 14, or 13 threads per inch?
Wheels.
Pitch of lead screw 8 16 24 32
-- × 2 = -- -- --
Pitch required 18 36 54 72
Pitch of lead screw 8 16 24 32
-- " -- -- --
Pitch required 17 34 51 68
Pitch of lead screw 8 16 24 32
-- " -- -- --
Pitch required 16 32 48 64
Pitch of lead screw 8 16 24 32
-- " -- -- --
Pitch required 15 30 45 60
Pitch of lead screw 8 16 24 32
-- " -- -- --
Pitch required 14 28 42 56
Pitch of lead screw 8 16 24 32 40
-- " -- -- -- --
Pitch required 13 26 39 52 65
If we suppose that the greatest number of teeth permissible in one wheel
is not to exceed 100, then in this table we have all the combinations of
wheels that can be used to cut the given pitches; and having made out
such a table, comprising all the pitches to be cut, we may select
therefrom the least number of wheels that will cut those pitches. The
whole table being made out it will be found, of course, that the
numerators of the fractions are the same in each case; that is, in this
case, 16, 18, 24, 32, and so on as far as we choose to carry the
multiplication of the numerator. We shall also find that the
denominators diminish in a regular order: thus taking the fractions
whose numerators are in each case 16, we find their denominators are, as
we pass down the column, 36, 34, 32, 30, 28, and 26, respectively, thus
decreasing by 2, which is the number we multiplied the left-hand column
by to obtain them. Similarly in the fractions whose numerators are 24,
the denominators diminish by 3, being respectively 54, 51, 48, 45, 42,
and 39; hence the construction of such a table is a very simple matter
so far as whole numbered threads are concerned, as no multiplication is
necessary save for the first line representing the finest pitch to be
cut.
For fractional threads, however, instead of using the pitch of the lead
screw for the numerator, we must reduce it to terms of the fraction it
is required to cut. For example, for 5-1/2 threads we proceed as
follows. The pitch of the lead screw is 8, and in 8 there are 16 halves,
hence we use 16 instead of 8, and as in the 5-1/2 there are 11 halves we
use the fraction 16/11 and multiply it first by 2, then by 3, and then
by 4, and so on, obtaining as follows: 16/11, 32/22, 48/33, 64/44,
obtaining as before three sets of wheels either of which will cut the
required pitch. In selecting from such a table the wheels to cut any
required number of pitches, the set must, in order to cut a thread of
the same pitch as the lead screw, contain two wheels having the same
number of teeth.
Now, suppose that the pitch of the lead screw was 6 instead of 8 threads
per inch, and the table will be as follows:--
6 12 18 24
-- -- -- --
18 36 54 72
6 12 18 24
-- -- -- --
17 34 51 68
6 12 18 24
-- -- -- --
16 32 48 64
6 12 18 24
-- -- -- --
15 30 45 60
6 12 18 24
-- -- -- --
14 28 42 56
6 12 18 24
-- -- -- --
13 26 39 52
Here, again, we find that in the first vertical column the denominators
decrease by two for each thread less per inch, in the second column they
decrease by three, and in the third by four; this decrease equalling the
number the first fraction was multiplied by.
But suppose the lead screw pitch is an odd one, as, say, 3 threads per
inch, and we construct the table as before, thus--
Pitch of lead screw 3 6 9 12 15
-- -- -- -- --
Pitch to be cut 18 32 54 72 90
Now it is useless to multiply by 2 or by 3, because they give a less
number of teeth than the smallest wheel should have, hence the first
multiplier should be 4, giving the following table:--
3 12 15 18
-- -- -- ---
18 72 90 108
3 12 15 18
-- -- -- ---
17 68 85 102
3 12 15 18
-- -- -- --
16 64 80 96
3 12 15 18
-- -- -- --
15 60 75 90
By continuing the table for other pitches we shall find that in the
first vertical column the denominators diminish by 4, the second column
by 5, and the third by 6; and it is seen that by diminishing the pitch
of the lead screw, we have rendered necessary one of two things, which
is, that either larger wheels containing more teeth must be used, or the
change gears must be compounded.
Assuming that the pitch of the lead screw was 5 per inch, the table
would be as follows:--
5 15 20 25
-- × 3 = -- -- --
18 54 72 90
5 15 20 25
-- " -- -- --
17 51 68 85
5 15 20 25
-- " -- -- --
16 48 64 80
The wheels in the first column here decrease by 3, the second by 4, and
the third by 5.
In nearly all lathes the advance or decrease is by 4 or by 6. In
determining this rate of advance or decrease, there are several
elements, among which are the following. Suppose the lathe to be geared
without compounding, then the distance between the lathe spindle and the
lead screw will determine what shall be the diameters of the largest and
of the smallest wheel in the set, it being understood that the smallest
wheel must not contain less than 12 teeth. Assume that in a given case
the distance is 10 inches, and it is obvious that the pitch of the teeth
at once commands consideration, because the finer the pitch the smaller
the wheel that will contain 12 teeth, and the larger the wheel on the
lead screw may be made. Of course the pitch must be coarse enough to
give the required tooth strength.
Let it be supposed that the arc pitch is 3/4-inch, then the pitch
circumference of a 12-toothed wheel would be 9 inches and its radius
1.432 in.; this subtracted from the 10 leaves 8.568 in. as the radius,
or 17.136 in. as the largest diameter of wheel that can be used on the
lead screw, supposing there to be no intermediate gears. Now a wheel of
this diameter would be capable of containing more than 75 teeth, but
less than 76. But from the foregoing tables it will be seen that it
should contain a number of teeth divisible either by 4 or by 6 without
leaving a remainder, and what that number should be is easily determined
by means of a table constructed as before explained. Thus from the
tables it would be found that 72 teeth would be best for a lead screw
having a pitch of either 8, 6, 5, or 3 threads per inch, and the
screw-cutting capacity of the lathe would (unless compounded) be
confined to such pitches as may be cut with wheels containing between 12
and 72 teeth both inclusive.
But assume that an arc pitch of 3/8-inch be used for the wheel teeth,
and we have as follows: A wheel of this pitch and containing 12 teeth
will have a radius of 7-16/1000 inches, leaving 9.284 in. as the radius
of the largest wheel, assuming it to gear direct with the 12-tooth
pinion. With this radius it would contain 155 teeth and a fraction of a
tooth; we must, therefore, take some less number, and from what has been
said, it will be obvious that this lesser number should be one divisible
by either 4 or 6. If made divisible by 6, the number will be 150,
because that is the highest number less than 155 that is divisible by 6
without leaving a remainder. But if made divisible by 4, it may contain
152 teeth, because that number is divisible by 4 without leaving a
remainder. With 150 teeth the latter could cut a thread 12-1/2 times as
fine as the lead screw, because the largest wheel contains 12-1/2 times
as many teeth as the smallest one; or it would cut a thread 12-1/2 times
as coarse as the lead screw, if the largest wheel be placed on the
mandril and the smallest on the lead screw. With 152 teeth the lathe
would be able to cut a thread 12-84/100 times as fine or as coarse as
the lead screw. Unless, however, the lathe be required to cut fractional
pitches, it is unnecessary that the largest wheel have more teeth than
divisible, without leaving a remainder, by the number of teeth in the
smallest wheel, which being 12 we have 144 as the number of teeth for
the largest wheel. In the United States standard pitches of thread,
however, there are several pitches in fractions of an inch, hence it is
desirable to have wheels that will cut these pitches.
LATHE SHEARS OR BEDS.--The forms of the shears and beds may be
classified as follows.
The term shear is generally applied when the lathe is provided with
legs, while the term bed is used when there are no legs; it may be
noted, however, that by some workmen the two terms of _shear_ and _bed_
are used indiscriminately.
The forms of shears in use on common lathes are, in the United States,
the raised [V], the flat shear and the shear, with the edge at an angle
of 90° or with parallel edges. In England and on the continent of
Europe, the flat shear is almost exclusively employed.
Referring to the raised [V] it possesses an important advantage in that,
first, the slide rest does not get loosely guided from the wear; and
second, the wear is in the direction that least affects the diameter of
the work.
[Illustration: Fig. 621.]
In Fig. 621, for example, is a section of a lathe shear, with a slide
rest shown in place, and it will be observed that the wear of the [V]
upon the lathe bed, and of the [V]-groove in the slide rest, will cause
the rest to fall in the direction of arrow A, and that a given amount of
motion in that direction will have less effect in altering the diameter
than it would in any other direction. This is shown on the right hand of
the figure as follows: Suppose the cutting point of the tool is at _a_,
and the work will be of the diameter shown by the full circle in the
figure. If we suppose the tool point to drop down to _f_, the work would
be turned to the diameter denoted by dotted arc _g_, while if the tool
were moved outwards from _a_ to _c_ the work would be turned to the
diameter _e_. Now since _f_ and _c_ are equidistant from the point _a_,
therefore the difference in the diameters of _e_ and _g_ represents the
difference of effect between the wear letting the rest merely fall, or
moving it outwards, and it follows that, as already stated, the diameter
of the work is less affected by a given amount of wear, when this wear
is in the direction of A, than when it is in the direction of B. When
the carriage is held down by a weight as is shown in Figs. 577 and 578,
there is therefore no lost motion or play in the carriage, which
therefore moves steadily upon the shears, unless the pressure of the cut
is sufficient in amount, and also in a direction to lift the carriage
(as it is in the case of boring with boring tools); but to enable the
carriage to remain firm upon the shears under all conditions, it is
necessary to provide means to hold it down upon the [V]s, which is done
by means of gibs G, G, which are secured to the carriage, and fit
against the bottom of the bed flange as shown.
Now since lathes are generally used much more frequently on short than
on long work, therefore the carriage traverses one part of the shears
more than another, and the [V]s wear more at the part most traversed,
and it follows that if gibs G are set to slide properly at some parts
they will not be properly set at another or other parts of the length of
the shears; hence the carriage will in some parts have liberty to move
from the bed, there being nothing but the weight of the carriage, &c.,
to hold it down to the [V]s. Now, the wear in the direction of A acts
directly to cause this inequality of gib fit, whereas that in the
direction of B does so to a less extent, as will appear hereafter.
Meantime it may be noted that when the carriage is held down by a
suspended weight the shears cannot be provided with cross girts, and are
therefore less rigid and more subject to torsion under the strain of the
cut; furthermore the amount of the weight must be sufficient to hold the
carriage down under the maximum of cut, and this weight acts
continuously to wear the [V]s, whether the carriage is under cutting
duty or not, but the advantage of keeping the carriage firmly down upon
the [V]s is sufficiently great to cause many to prefer the weighted
carriage for light work driven between the lathe centres.
[Illustration: Fig. 622.]
Fig. 622 represents the flat shear, the edges being at an angle and the
fit of the carriage to the shears being adjusted by the gibs at _a_ _a_,
which are set up by bolts _c_ _c_ and _d_ _d_. In this case there is a
large amount of wearing surface at _b_ _b_, to prevent the fall of the
carriage _c_, but the amount of end motion (in the direction of B, Fig.
621), permitted to the carriage by reason of the wear of the gibs and
shear edges, is greater than the amount of the wear because of the edges
being at an angle. It is true that the amount of fall of the carriage on
the raised [V] is also (on account of the angle of the [V]) greater than
the actual amount of the wear, but the effect upon the work diameter is
in this case much greater, as will be readily understood from what has
already been said. The wearing surface of the raised [V] may obviously
be increased by providing broader [V]s, or two [V]s instead of having
four. This would tend to keep the lathe in line, because the wear due to
moving the tailblock would act upon those parts of the shear length that
are less acted upon by the carriage, and since the front journal and
bearing of the live spindle wear the most, the alignment of the lathe
centres would be more nearly preserved.
[Illustration: Fig. 623.]
Fig. 623 represents another form of parallel edged shears in which the
fit of the carriage to the shears is effected at the front end only, the
other or back edge being clear of contact with the carriage, but
provided with a gib to prevent the carriage from lifting. This allows
for any difference in expansion and contraction between the carriage and
the shears, while maintaining the fit of the carriage to the bed.
[Illustration: Fig. 624.]
A modification of this form (both these forms being taken from
"Mechanics") is shown in Fig. 624, in which the underneath side of the
front edge is beveled so that but one row of screws is required to
effect the adjustment.
[Illustration: Fig. 625.]
Fig. 625 represents a form of bed in which the fit adjustment is also
made at the front end only of the bed, and there is a flange or slip at
_a_, which receives the thrust outwards of the carriage; and a similar
design, but with a bevelled edge, is shown in Fig. 626.
[Illustration: Fig. 626.]
[Illustration: Fig. 627.]
In Fig. 627 is shown a lathe shear with parallel edges, the fit being
adjusted by a single gib D, set up by set-screws S. In this case the
carriage will fall or move endwise, to an amount equal to whatever the
amount of the wear may be, and no more, but it may be observed that in
all the forms that admit of wear endways (that is to say in the
direction of B in Fig. 621), the straightness of the shears is impaired
in proportion as its edges are more worn at one part than at another.
[Illustration: Fig. 628.]
A compromise between the flat and the raised [V]-shear is shown in Fig.
628, there being a [V]-guide on one side only, as at J. When the
carriage is moved by mechanism on the front side of the lathe, and close
to the [V], this plan may be used, but if the feed screw or other
mechanism for traversing the carriage is within the two shears, the
carriage should be guided at each end, or if the operating mechanism is
at the back of the lathe, the carriage should be guided at the back end,
if not at both ends.
In flat shear lathes the tailstock is fitted between the inside edges of
the two shears, and the alignment of the tailstock depends upon
maintaining a proper fit notwithstanding the wear that will naturally
take place in time. The inside edges of the shears are sometimes
tapered; this taper makes it much easier to obtain a correct fit of the
tailstock to the shears, but at the same time more hard to move the
tailstock along the bed. To remedy this difficulty, rollers are
sometimes mounted upon eccentrics having journal bearing in the
tailstock, so that by operating these eccentrics one half a turn, the
rollers will be brought down upon the upper face of the shears, lifting
the tailstock and enabling it to be easily moved along the bed to its
required position.
In many of the watchmakers' lathes the outer edges are beveled off as in
Fig. 629, the bearing surfaces being on the faces _b_ as well as on the
edges _a_. As a result, edges _a_ are relieved of weight, and therefore
to some extent of wear also, and whatever wear faces _b_ have helps the
fit at _a_ _a_.
In the Barnes lathe, as in several other forms in which the lathe is
made (as, for example, in screw-making lathes) the form of bed in Fig.
630 is employed. The tailblock may rest on the surfaces A, A´, B, C, D,
and E, or as in the Barnes lathe the tailstock may fit to angles A B,
but not to E D, while the carriage fits to B E, and C D, but not to A,
the intention being to equalize the wear as much as possible.
[Illustration: Fig. 629.]
The shears of lathes require to be as rigid as possible, because the
pressure of the cut, as well as the weight of the carriage, slide rest,
and tailstock, and of the work, tends to bend and twist them.
[Illustration: Fig. 630.]
The pressure of the dead centre against the end of the work considered
individually, is in a direction to bend the lathe shears upward, but the
weight of the work itself acts in an opposite direction.
The strain due to the cut falls in a direction variable with the shape
of the cutting tool, but mainly in a direction towards the operator,
and, therefore, tending to twist the shears. To resist these strains,
lathe shears are usually given the [I] form shown in the cuts.
[Illustration: Fig. 631.]
[Illustration: Fig. 632.]
Figs. 631 and 632 represent the ribbing in the Putnam Tool Company's
lathe; a middle rib running the entire length, which greatly stiffens
it.
The legs supporting lathe shears are, in lathes of ordinary length,
placed at each end of the bed, so that the weight of the two heads, that
of the work, and that of the carriage and slide rest, as well as the
downward pressure of the cut, act combined to cause it to deflect or
bend. It is necessary, therefore, in long beds to provide intermediate
resting or supporting points to prevent this deflection.
[Illustration: Fig. 633.]
Professor Sweet has pointed out that a lathe shears will be more truly
supported on three than on four resting points, if the foundation on
which the legs rest do not remain permanently level, and in lathes
designed by him has given the right-hand end of the shears a single
supporting point, as shown at _a_ in Fig. 633.
[Illustration: Fig. 634.]
J. Richards in an article in "Engineering," has pointed out also that,
when the lathe legs rest upon a floor that is liable from moving loads
upon it to move its level, it is preferable that the legs be shaped as
in Fig. 634, being narrowest at the foot, whereas when upon a permanent
foundation, in which the foundation is intended to impart rigidity to
the legs, they should be broader at the base, as in Fig. 635.
[Illustration: Fig. 635.]
The rack on a lathe bed should be a cut one, and not simply a cast one,
because when a cutting tool is running up to a corner as against a
radial face, the self-acting motion must be stopped and the tool fed
into the corner by hand. As a very delicate tool movement is required to
cut the corner out just square, it should be capable of easy and steady
movement, but in the case of cast racks, the rest will, from defects in
the rack teeth, move in little jumps, especially if the pitch of the
teeth be coarse. On the other hand it is difficult to cast fine pitches
of teeth perfectly, hence the racks as well as the gear teeth should be
cut gear and of fine pitch.
The tailblock of a lathe should be capable of easy motion for adjustment
along the shears, or bed of the lathe, and readily fixable in its
adjusted position. The design should be such as to hold the axial line
of its spindle true with the axial line of the live spindle. If the
lathe bed has raised [V]s there are usually provided two special [V]s
for the tailblock to slide on, the slide rest carriage sliding on two
separate ones. In this case the truth of the axial line of the tail
spindle depends upon the truth of the [V]s.
If the lathe bed is provided with ways having a flat surface, as was
shown in Fig. 622, the surfaces of the edges and of the projection are
apt in time to wear, permitting an amount of play which gives room for
the tailblock to move out of line. To obviate this, various methods are
resorted to, an example being given in the Sellers lathe, Fig. 518.
In wood turners' lathes, where tools are often used in place of the dead
centre, and in which a good deal of boring is done by such use of the
tail spindle, it is not unusual to provide a device for the rapid motion
of that spindle. Such a device is shown in Fig. 636; it consists of an
arm A to receive the end C of the lever B, C being pivoted to A. The
spindle is provided with an eye at E, the wheel W is removed and a pin
passed through D and E, so that by operating the handle the spindle can
be traversed in and out without any rotary motion of the screw.
When the tailblock of a lathe fits between the edges of the shears,
instead of upon raised [V]s, it is sometimes the practice to give them
a slight taper fitting accurately a corresponding taper on the edges of
the shears. This enables the obtenance of a very good fit between the
surfaces, giving an increased area of contact, because the surfaces can
be filed on their bearing marks to fit them together; but this taper is
apt to cause the tailstock to fit so tightly between the shears as to
render it difficult to move it along them, and in any event the friction
is apt to cause the fit to be destroyed from the wear. An excellent
method of obviating these difficulties is by the employment of rollers,
such as shown at R in Figs. 637 and 638, which represent the tailstock
of the Putnam Tool Company's lathe. In some cases such rollers are
carried on eccentric shafts so that they may be operated to lift the
tailstock from the bed when moving it.
[Illustration: Fig. 636.]
[Illustration: Fig. 637.]
[Illustration: Fig. 638.]
[Illustration: Fig. 639.]
A very ready method of securing or releasing a small tailstock to a
lathe shears is shown applied to a wood turner's hand rest in Fig. 639,
in which A A represents the lathe shears, B the hand rest, C the
fastening bolt, D a piece hinged at each end and having through its
centre a hole to receive the fastening bolt, and a counter-sink or
recess to receive the nut and prevent it unscrewing. E represents a
hinged plate, and F a lever, having a cam at its pivoted end. A slot for
the fastening bolt to pass through is provided in the plate E. In this
arrangement a very moderate amount of force applied to bring up the cam
lever will cause the plate D to be pressed down, carrying with it the
nut, and binding the tailstock or the tool rest, as the case may be,
with sufficient force for a small lathe.
When a piece of work is driven between the lathe centres, the weight of
the work tends to deflect or bend down the tail spindle. The pressure of
the cut has also to be resisted by the tail spindle, but this pressure
is variable in direction, according to the shape of the tool and the
direction of the feed; usually it is laterally towards the operator and
upwards. In any event, however, the spindle requires locking in its
adjusted position, so as to keep it steady. The pressure on the conical
point of the dead centre is in a direction to cause the tail screw to
unwind, unless it be a left-hand thread, as is sometimes the case.
If the spindle and the bore in which it operates have worn, the
resulting looseness affords facility for the spindle to move in the bore
as the pressure of the cut varies, especially when the spindle is far
out from the tailstock.
Now, in locking the tail spindle to obviate these difficulties, it is
desirable that the locking device shall hold that spindle axially true
with the live spindle of the lathe, notwithstanding any wear that may
have taken place. The spindle is released from the pressure of the
locking device whenever it is adjusted to the work, whether the cut be
proceeding or not. Hence, the wear takes place on the bottom of the
spindle and of the hole, wear only ensuing on the top of the spindle and
bore when the spindle is operated under a slight locking pressure, while
the cut is proceeding in order to take up the looseness that may have
arisen from wear in the work centres.
In all cases the feed of the cut should be stopped while the centre is
adjusted, so as to relieve the spindle and bore from undue wear; but
most workmen pay little heed to this; hence the wear ensues, being, as
already stated, mainly at the bottom. It is obvious, then, that, if the
spindle is to be locked to the side of the bore on which it slides, it
will be held most truly in line if it be locked to that side which has
suffered least from wear, and this has been shown to be at the top.
[Illustration: Fig. 640.]
[Illustration: Fig. 641.]
The methods usually employed to effect this locking are as follows:--In
Fig. 640, S is the tail spindle, B part of the tailblock in section, R a
ring-bolt, and H a handled nut. Screwing up the nut H causes R to clamp
S to the upper part of the bore of B; while releasing H leaves S free to
slide. There are three objections to this plan. The ring R tends to
spring or bend S. The weight of R tends to produce wear upon the top of
the spindle, and the spindle is not gripped so near to its dead centre
end as it might be. If S is a close fit in B the pressure of R could not
spring or bend S; but, so soon as wear has taken place, S becomes simply
suspended at R, having the pressure of R, and the weight of the work
tending to bend it. Another locking device is shown in Fig. 641. It
consists of a shoe placed beneath S, and a wedge-bolt beneath it,
operated by the handled nut C. Here the pressure is again in a direction
to lift S, as denoted by the arrow; but when the wedge W is released the
shoe falls away from S, hence the locking device produces no wear upon
S. This device may be placed nearer to the end of B, since the wedge may
pass through the front leg of the tailstock instead of to the right of
it, as in Fig. 640. But S is still suspended from the point of contact
of the shoe, and the weight of the work still bends it as much as its
play in B will permit.
[Illustration: Fig. 642.]
Another clamping device is shown in Fig. 642. In this the cylindrical
part B of the tailblock is split on one side, and is provided with two
lugs. A handled screw passes through the upper lug, and is threaded into
the lower one, so that by operating the handle C, the bore may be
closed, so as to grip S, or opened to relieve it. This possesses the
advantages: First, that it will cause S to be gripped most firmly at the
end of B, and give a longer length of bearing of B upon S; and,
secondly, that it will grip S top and bottom, and, therefore, prevent
its springing from the weight of the work. But, on the other hand, B
will close mainly on the side of the split, as denoted by the dotted
half-circle, and therefore tend to throw S somewhat in the direction of
the arrow, which it will do to an amount answerable to the amount of
looseness of S in B. In the Pratt and Whitney lathes this device is
somewhat modified, as is shown in Fig. 643. A stud E screws into the
lower lug D, having a collar at E let into the upper lug, with a square
extending above the upper lug so that the stud may be screwed into D,
exerting sufficient pressure to close the bore of B to a neat working
fit to the spindle. The handled nut, when screwed up, causes B to grip
the spindle firmly; but when released, leaves the spindle a neat working
fit and not loose to the amount of the play; hence, the locking device
may be released, and the centre adjusted to take up the wear in the work
centres while the cut is proceeding, without any movement of the spindle
in B, because there is no play between the spindle and B.
[Illustration: Fig. 643.]
[Illustration: Fig. 644.]
In the design shown in Fig. 644, the end B of the tailblock is threaded
and is provided with a handled cap nut A A. In the end of the tailblock
where the spindle emerges, is provided a cone, and into this cone fits a
wedge-shaped ring, as shown. This ring is split quite through on one
side, while there are two other slots nearly but not quite splitting the
wedge-ring. When the handle C is pulled towards the operator it screws A
up on the end B, and forces the wedge-ring up in the conical bore in B.
From the split the ring closes upon the spindle S, and grips it. Now, as
the ring is weakened by slots in two places besides the split, it closes
more nearly cylindrically true than if it had only a split, there being
three points where the ring can spring when closing upon S; and from the
cone being axially true with the live spindle of the lathe, S is held
axially true, notwithstanding any wear of the spindle, because the
locking device, being at the extreme end of B, is as near to the dead
centre as it is possible to get it; and, furthermore, when C is operated
for the release, the wedge-ring opens clear of S, so that S does not
touch it when moved laterally. The wear of the bore of B has, therefore,
no effect to throw S out of line, nor has the gripping device any
tendency to bend or spring S, while the latter is held as close to the
work as possible; hence the weight of the work has less influence in
bending it. The pitch of the thread and the degree of cone are so
proportioned that less than one-quarter rotation of A will suffice to
grip or release S, the handle C being so placed on A as to be about
vertical when the split ring binds S; hence C is always in a convenient
position for the hand to grasp.
[Illustration: Fig. 645.]
In this case, however, the spindle being locked at the extreme end of
the hole, there is more liability of the other end moving from the
pressure of the cut, or from the weight of the work; hence it would seem
desirable that a tail spindle should be locked in _two_ places; one at
the dead centre end of the hole, and the other as near the actuating
wheel, or handle, as possible, and also that each device should either
hold it central to the original bore, notwithstanding the wear, an end
that is attained in the Sellers lathes already described.
Slide rests for self-acting or engine lathes are divided into seven
kinds, termed respectively as follows: simple, or single, elevating,
weighted, gibbed, compound, duplex, and duplex compound. A simple, or
single, slide rest contains a carriage and one cross slide, as in Fig.
621. An elevating slide rest is one capable of elevation at one end to
adjust the cutting tool height, as in Fig. 499. A weighted slide rest is
one held to the shears by a weight, as in Fig. 577. A gibbed slide rest
is held to the shears by gibs, as in Fig. 621. A compound slide rest has
above the cross slide, a second slide carrying the tool holder, this
second slide pivoting to stand at any required angle, as in Fig. 505. A
duplex slide rest has two rests on the same cross slide, and in a
compound duplex both these two rests are compound, as in Fig. 511. The
rest shown on the Putnam lathe in Figs. 492 and 499, is thus an
elevating gibbed single rest.
TESTING A LATHE.--To test a lathe to find if its live and dead spindles
are axially in line one with the other and with the guides on the lathe
bed, the following methods may be employed in addition to those referred
to under the heading of Erecting.
To test if the live spindle is true with the bed or shear guides, a
piece such as in Fig. 645 may be turned up between the lathe centres,
the end A fitting into the live spindle in place of the live centre, and
the collars B C being turned to an equal diameter, and the end face D
squared off true. The end A must then be placed in the lathe in place of
the live centre, the dead centre being removed from contact with the
work; with the lathe at rest a tool point may be set to just touch
collar C, and if when the carriage is moved to feed the tool past
collar B, the tool draws a line along it of equal depth to that it drew
along C, the live head is true; the dead centre may then be moved up to
engage the work end D, and the lathe must be revolved so that (the tool
not having been moved at all by the cross-feed screw) the tool may be
traversed back to draw another line along C, and if all three lines are
of equal depth the lathe is true. The tool should be fine pointed and
set so as to mark as fine a line as possible.
[Illustration: Any View.
Fig. 646.]
[Illustration: Side View.
Fig. 647.]
[Illustration: Side View.
Fig. 648.]
[Illustration: Top View.
Fig. 649.]
Another method is to turn up two discs, such as in Fig. 646, their stems
A and B fitting in place of the live and dead centres. One of these
discs is put in the place of the live, and the other in that of the dead
centre, and if then the lathe tailstock be set up so that the face of B
meets that of A, their coincidence will denote the truth of the live and
dead spindles. The faces of the discs may be recessed to save work and
to meet at their edges only, but their diameters must be equal. If the
discs come one higher than the other, as in Fig. 647, the centres are of
unequal height. If the faces meet at the top and are open at the bottom,
as in Fig. 648, it shows that the back bearing of the live spindle is
too high, or that the tail spindle is too low at the dead centre end. If
the discs, when viewed from above, come as in Fig. 649, it is proof that
either the live spindle or the tail spindle does not stand true with the
lathe shears. If the disc faces come so nearly fair that it is difficult
to see if they are in contact all around, four pieces of thin paper may
be placed equidistant between them, and the grip upon them tested by
pulling.
If the tailstock has been set over to turn taper and it is required to
set it back to turn parallel again, place a long rod (that has been
accurately centred and centre-drilled) between the lathe centres, and
turn up one end for a distance of an inch or two.
Then turn it end for end in the lathe and let it run a few moments so
that the work centre, running on the dead centre of the lathe, may wear
to a proper bed or fit to the lathe centre, and then turn up a similar
length at the dead centre end, taking two cuts, the last a fine
finishing cut taken with a sharp tool, and feeding the finishing cut
from left to right, so that it will be clear of the work end when the
cut is finished. Without moving the cross-feed screw of the lathe after
the finishing cut is set, take the bar out of the lathe and wind the
slide rest carriage, so that the turning tool will stand close to the
live centre. Place the bar of iron again in the lathe, with the turned
end next to the live centre, and move the lathe carriage, so that the
tool is on the turned end of the bar.
Rotate the bar by hand, and if the tool just touches the work without
taking a cut the line of centres is parallel with the ways. If there is
space between the tool point and the turned end of the bar, the
tailstock requires setting over towards the back of the lathe, while if
the tool takes a cut the tailstock requires to be set over towards the
operator. If a bar is at hand that is known to be true, a pointed tool
may be adjusted to just make a mark on the end of the bar when the slide
rest is traversed. On the bar being reversed, the tool should leave,
when traversed along the bar, a similar mark on the bar.
To test the workmanship of the back head or tailstock, place the
forefinger on the spindle close to the hub whence it emerges, and
observe how much the hand wheel can be moved without moving the spindle;
this will show how much, if any, lost motion there is between the screw
and the nut in the spindle. Next wind the back spindle about three
quarters of its length out of the tailstock, take hold of the dead
centre and pull it back and forth laterally, when an imperfect fit
between the spindle and the hole in which it slides will be shown by the
lateral motion of the dead centre. Wind the dead centre in again, and
tighten and loosen the spindle clamp, and see if doing so moves the
spindle in the socket.
To examine the slide rest, move the screw handles back and forth to find
how much they may be moved without giving motion to the slides; this
will determine the amount of lost motion between the collars of the
screws and between the screws themselves and the nuts in which they
operate. To try the fit of the slide rest slides, in the stationary
sliding ways or [V]s, remove the feed screws and move the slide so that
only about one-half inch is in contact with the [V]s, then move the
slide back and forth laterally to see if there is any play. Move the
slide to the other end of the [V]s, and make a similar test, adjusting
the slide to take up any play at either end. Then clean the bearing
surfaces and move the slide back and forth on the [V]s, and the marks
will show the fit, while the power required to move the slide will show
the parallelism of the [V]s.
If the lathe carriage have a rack feed, operate it slowly by hand, to
ascertain if it can be fed slowly and regularly by hand, which is of
great importance. Then put the automatic feed in gear, and operate the
feed gear back and forth, to determine how much it can be moved without
moving the slide rest. To test the fit of the feed screw to the feed
nut, put the latter in gear and operate the rack motion back and forth.
To determine whether the cross slide is at a right angle with the ways
or shears, take a fine cut over a radial face, such, for example, as the
largest face plate, and test the finished plate with a straight edge. If
the face plate runs true and shows true with a straight edge, so that it
is unnecessary to take a cut over it, grind a piece of steel a little
rounding on its end, and fasten it in the tool post or clamp, with the
rounded end next to the face plate. Let the rounded end be about 1/4 in.
away from the face plate, and then put the feed motion into gear, and,
with the steel near the periphery of the face plate, let the carriage
feed up until the rounded steel end will just grip a piece of thin paper
against the face plate tight enough to cause a slight strain in pulling
the paper out, then wind the tool in towards the lathe centre and try
the friction of the paper there; if equal, the cross slide is true.
To find the amount of lost motion in the screw feed gear, adjust it
ready to feed the saddle, and pull the lathe belt so as to revolve the
cone spindle backward, until the slide rest saddle begins to move, then
mark a fine line on the lathe bed making the line coincident with the
end of the lathe saddle or carriage. Then revolve the cone spindle
forward, and note how much the cone spindle rotates before the saddle
begins to traverse.
If the lathe has an independent feed motion it may be tested in the same
manner as above.
In large lathes this is of great consideration, because the work
revolves very slowly, and if there is much lost motion in the feed gear,
it may take considerable time after the feed is put in gear before the
carriage begins to travel. Suppose, for example, a 14-foot pulley is
being turned, and that the tool cuts at 15 feet per minute, it will take
nearly three minutes for the work to make a revolution.
CHAPTER VIII.--SPECIAL FORMS OF THE LATHE.
The lathe is made in many special or limited forms, to suit particular
purposes, the object being to increase its efficiency for those
purposes, which necessarily diminishes its capacity for general work.
In addition to this, however, there are machine tools whose construction
varies considerably from the ordinary form of lathe, which nevertheless
belong to the same family, and must, therefore, be classified with it,
because they operate upon what is essentially lathe work. Thus boring
and turning mills are essentially what may be termed horizontal lathes.
Figs. 650 to 655 inclusive, represent the American Watch Tool Company's
special lathes for watch-makers, which occupy a prominent position in
Europe, as well as in the United States.
In lathes of this class, refinement of fit, alignment, truth, and
durability of parts are of the first importance, because of the
smallness of the work they perform, and the accuracy to which that work
must be made. Furthermore, such lathes must be constructed to hold and
release the work as rapidly as possible, because in such small work the
time occupied by the tools in cutting is less, while that occupied in
the insertion and removal of it is greater in comparison than in larger
jobs; it often takes longer to insert and remove the work than to
perform it.
These facts apply with equal force to all such parts as require the
removal to or from the lathe-bed, or frequent adjustment upon the same.
Thus the devices for holding and releasing the tool post or hand rest
and tailblock are each so constructed that they may be set without the
use of detached wrenches.
Fig. 650 represents a general view of the lathe, while Fig. 651
represents a sectional view of the headstock. The live spindle consists
of two parts, an outer sleeve A A, having journal bearing in the head,
and an inner hollow spindle B B, threaded at its front end _e_, to
receive the chucks. The main spindle at the front end works in a journal
box _c_, that is cylindrical to fit the headstock, but double coned
within to afford journal bearing to the spindle A. The inner step of
this double cone is relied upon mainly to adjust the diametral fit of
the bearing, while the outer step is relied upon mainly to adjust the
end fit of the spindle; but it is obvious in both cases there is an
action securing simultaneously the diametral and the end fit. In the
back bearing there are two cones. The outer one _r_ is cylindrical
outside where it fits into the head, and coned in its bore to receive
the second cone _s_, which rotates with spindle A. The nut F is threaded
upon A, so that by operating F, A is drawn within _c_, and S is
simultaneously moved within _r_, so that both bearings are
simultaneously adjusted. D D are _dust_ rings, being ring-caps which
cover the ends of the bearings and the oil holes so as to prevent the
ingress of dust.
The inner spindle B has a bearing in A at the back end to steady it, and
a bearing at end _e_, and is provided with the hand wheel H, by which it
may be rotated to attach the chucks which screw into its mouth at _e_.
To rotate or drive the chucks there is in A a feather at _g_, the chucks
having a groove to receive this feather and screwing into B at E, when B
is rotated.
The mouth of A is coned, as shown at _h_, and the chucks are provided
with a corresponding male cone, as shown at _h_ in Figs. 652 and 653, so
that the chucks are supported and guided by the cone, and are therefore
as close to the work as possible while having a bearing at _g_. But the
cone on the chucks being split, (as is shown in Fig. 652), rotating B
while holding A stationary (which may be done by means of the band
pulley P), causes the chucks to move endwise in A, and if the motion is
in the direction to draw the chuck within A, the cone _h_ causes the
chuck to close upon and grip the work. Thus in Fig. 652 is shown a step
chuck. The thread at J enters the end _e_ of B, in Fig. 651, which
screws upon it. Cone _h_ fits mouth _h_ in Fig. 651, and _l_ represents
the splits in the chuck, which enable it to close when the cone _h_ is
drawn within the mouth _h_ of spindle A.
The chuck is employed to hold cylindrical plates or discs, such as
wheels and barrels, and the various steps are to suit the varying
diameters of these parts in different sizes of watches.
Fig. 653 represents a wire chuck, having the cone at _h_, and the three
splits at _l_, as before, the cone-mouth _h_ closing the chuck as the
latter is drawn within the spindle A.
In both the chucks thus far described, the construction has been
arranged to close the splits and thus grip the circumferences of
cylindrical bodies, but in Fig. 654 is shown the arrangement for
enabling the chuck to expand and grip the bores of hollow work, such as
rings, &c.
The outer spindle A corresponds to the outer spindle A in Fig. 651, and
the inner one to spindle B in that figure. The chuck is here made in two
separate parts, a sleeve V fitting in and driven by A, and a plug X
fitting into a cone in the mouth of V, and screwing into the end of
drawing spindle B. But while V is driven by and prevented from rotating
within A by means of the feather at _g_, so likewise X is prevented from
rotating within V by means of a feather _h_ fast in X and fitting into a
groove or featherway in V. It follows then that when B is rotated X may
be traversed endways in V, to open or close the steps Y according to the
direction of rotation of B.
It will now be apparent that in the case of chucks requiring to grip
external diameters, the gripping jaws of the chucks will, when out of
the lathe, be at their largest diameter, the splits _l_ being open to
their fullest, and that when by the action of the cones, they are closed
to grip the work, such closure must be effected against a slight spring
or resistance of the jaws, and this it is that enables and causes the
chuck to open out of itself, when the enveloping cone permits it to do
so.
But in the case of the opening or expanding chuck, the reverse is the
case, and the chuck is at its smallest diameter (the splits _l_ being at
their closest) when the chuck is removed from the lathe, as is obviously
necessary. In reality the action is the same in both cases, for the
chuck moves to grip the work under a slight resistance, and this it is
that enables it to readily release the work when moved in the necessary
endwise direction.
The band pulley P is fast upon A, and is provided with an index of 60
holes on its face G, and which are adjusted for any especial work by a
pin Q, so that a piece of work may have marked on it either 60, 30, 20,
15, 12, 10, 6, 5, 4, 3, or 2 equidistant lines of division, each of
those numbers being divisors of 60. In marking such lines of division
upon the work a sharp point may be used, supported by the face of the
hand rest as a guide; or a sharp-pointed tool may be placed in the slide
rest to cut a deeper line upon the work. The index plates used for
cutting wheels and pinions may be placed on the rear end of A, the pawl
being secured to the work-bench. The wheel H is for rotating spindle B
to screw the chucks on or off the same.
[Illustration: _VOL. I._ =WATCHMAKER'S LATHE.= _PLATE VIII._
Fig. 650.
Fig. 651.
Fig. 652.
Fig. 653.
Fig. 654.]
[Illustration: _VOL. I._ =DETAILS OF WATCHMAKER'S LATHE.= _PLATE IX._
Fig. 655.
Fig. 656.
Fig. 657.
Fig. 658.
Fig. 659.
Fig. 660.
Fig. 661.
Fig. 662.]
Fig. 655 represents an end view from the tailstock end of the lathe; A´
is the bed having the angles _a_ _a_ to align the heads and rests. The
means of holding or releasing the tailstock, on the lathe-bed, is the
same as that for holding the headstock, the construction being as
follows: _b_ is the shoulder of a bolt through which passes the shaft
_c_, with a lever _d_ to operate it. This shaft is eccentric where it
passes through the bolt, so that by using the lever aforesaid the bolt
secures or releases the head according to the direction in which it is
moved. A very small amount of motion is needed for this. The standard
for the hand rest is split, and a screw is used to tighten it in an
obvious manner, the screw being operated by the handle _e´_. An end view
of the rest, showing the device for securing the foot _h_ to the bed, is
shown in Fig. 656, _f_ is a shoe spanning the bed and fitting to the bed
angles _a_. Through _f_ passes the bolt _g_, its head passing into the
[T]-shaped groove _h_; N´ is a hand wheel for operating bolt _g_. At S
is a spiral spring, which by exerting an end pressure on washer _w_ and
nut N´, pulls _g_ and the head _h_ down upon _f_, and therefore _f_ down
upon the bed, whether the rest be locked to the bed or not; hence when
N´ is released to remove or adjust the rest, neither dust nor fine
cuttings can pass either between the rest and shoe or the shoe and the
lathe-bed, and the abrasion that would otherwise occur is thus avoided.
Two qualities of these lathes are made: in the better quality all the
working parts are hardened and afterwards ground true. In the other the
parts are also ground true, but the parts (which in either case are of
steel) are left soft for the sake of reducing the cost. In all, the
parts are made to gauge and template, so that a new head, tailstock, or
any other part in whole or in detail may be obtained from the factory,
either to make additions to the lathe or to replace worn parts.
Two styles of slide rest are made with these lathes: in the first, shown
in Fig. 657, the swivel for setting the top slide at an angle for taper
turning is at the base of the top slide, hence the lower slide turns all
radial faces at a right angle to the line of lathe centres. In the
second, Fig. 658, there is a third slide added at the top, so that the
bottom slide turns radial faces to a right angle with the line of lathe
centres, the next slide turns the taper and the top slide may be used to
turn a radial face at a right angle to the surface of the taper, and not
at a right angle to the axis of the work. Both these rests are provided
with tool post clamps, to hold tools made of round wire, such clamps
being shown in position in figure 657.
Fig. 659 represents an additional tailstock for this lathe, the tail
spindle lying in open bearings so that it can be laid in, which enables
the rapid employment of several spindles holding tools for performing
different duties, as drilling, counter-boring, chamfering, &c.
Fig. 660 represents a filing fixture to be attached to the bed in the
same manner as the slide rest. It consists of a base supporting a link,
carrying two hardened steel rolls, upon which the file may rest, the
rolls rotating by friction during the file strokes, and serving to keep
the file flat and fair upon the work.
Fig. 661 represents a fixture for wheel and pinion cutting; it is
attached to the slide rest. When the cutter spindle is vertical the belt
runs directly to it from the overhead counter shaft, but when it is
horizontal the belt passes over idler pulleys, held above the lathe. The
cutter spindle is carried on a frame, pivoted to the sliding piece on
the vertical slide, so that it may be swivelled to set in either the
vertical or horizontal position.
Fig. 662 represents a jewelers' rest for this lathe. It fits on the bed
in the place of the tailstock, and is used for cutting out the seats for
jewels, in plates, or settings. It is especially constructed so as to
receive the jewel at the top and bore the seating to the proper
diameter, without requiring any measurements or fitting by trial, and
the manner in which this is accomplished is as follows:--
[Illustration: Fig. 663.]
[Illustration: Fig. 664.]
[Illustration: Fig. 665.]
Fig. 663 is a side elevation, Fig. 664 an end elevation, and Fig. 665 a
plan view of this rest, and similar letters of reference indicate like
parts in each of the three figures. A is the base, held to the lathe bed
by the bolt B, whose operation is the same as that already described for
the head and tailstocks.
In one piece with A is the arm C, carrying at its head three gauge
tongues or pieces D E F, which are adjustable by means of the screws _d_
_e_ _f_, which move the gauge tongues horizontally. Through a suitable
guide I is a standard or head; pivoted to A at J J, and carrying at its
top three gauge tongues K L M.
Midway between pivots J J and the ends of the gauge tongues, is the
centre or tool carrying spindle O. If a piece of work, as a jewel, be
placed between the tongues F and M, Fig. 664 [swinging M, and with it I
(which is pivoted at J), laterally], then the point of the centre N will
be thrown out of line with the lathe live spindle half the diameter of
the jewel, because from J to the centre N, of O, is exactly one half of
the vertical distance from J to the jewel. If then a tool be placed in
the dead centre and its cutting edge is in line with the axis of spindle
O, it will bore a hole that will just fit the jewel. Hence placing the
jewel between the two tongues sets the diameter to which the tool will
bore and determines that it shall equal the diameter of the jewel.
The object of having three pair of gauge tongues is to enable the
obtaining of three degrees of fit; thus with a piece placed between D K
the hole may be bored to fit the piece easily, with it placed between E
L the fit may be made barely movable, while with it placed between F M
the fit may be too tight to be a movable one save by pressure or
driving, each degree of fit being adjusted by means of the screws _e_
_f_ _g_.
The tool is fed by moving spindle O by hand, the screw P being adjusted
so that its end abuts against stop Q, when the hole is bored to the
requisite depth; R is simply a guide for the piece S, which being
attached to O, prevents it from rotating.
In watch manufactories special chucks and appliances are necessary to
meet their particular requirements. There is found to exist, for
example, in different rods of wire of the same nominal diameter, a
slight variation in the actual diameter, and it is obvious that with the
smaller diameters of wire the split chucks will pass farther within the
mouth _h_ of A, Fig. 651, because the splits of the chucks will close to
a greater extent, and the cones on the chucks therefore become reduced
in diameter.
If then it be required to turn a number of pieces of work to an exact
end measurement, or a number of flanges or wheels to equal thicknesses,
without adjusting the depth of cut for each it becomes necessary to
insure that the successive pieces of work shall enter the chucks to an
equal distance, notwithstanding any slight variation in the work
diameter at the place or part where it is gripped by the chuck.
To accomplish this end what is termed a sliding-spindle head is
employed. In this the _outer spindle_ has the end motion necessary to
open and close the chuck, the chuck having no end motion.
[Illustration: Fig. 666.]
The construction of this sliding-spindle head is shown in Fig. 666, in
which a wire chuck is shown in position in the spindles; L is the live
spindle passing through parallel bearings, so that it may have end
motion when the nut M is operated. The inner spindle N to which the
chucks are screwed is prevented from having end motion by means of the
collar _p_ and nut _q_ at the rear bearing. When nut M is rotated and N
is held stationary by means of the pulley P, L slides endways, and the
chuck opens or closes according to the direction in which the nut moves
the spindle L.
To regulate the exact distance to which the work shall be placed within
the chuck, a piece of wire rod may be placed within the hollow spindle N
being detained in its adjusted position by the set screw S.
The construction whereby the nut is permitted to revolve with spindle L,
and be operated by hand to move spindle L when the lathe is at rest, is
as follows.
The cylindrical rim _t_ of the nut is provided with a series of notches
arranged around its circumference. R is a lever whose hub envelops nut
M, but has journal bearing on V. R receives the pin S, which rests upon
a spiral spring T. When, therefore, S is pushed down it depresses the
spring T and its end W enters some one of the notches in the rim _t_,
and operates the nut after the manner of a ratchet. But so soon as the
end pressure on R is released, the spiral spring lifts it and M is free
to revolve with L as before. The inner spindle is driven by means of the
feather G.
Pulley P has two steps Y for the belt, and a friction step _z_, around
which passes a friction band operated by the operator's foot to stop the
lathe quickly. This performs two functions, as follows. The thread of M
is a left-hand one so that the inertia of the nut will not, when the
lathe is started, operate to screw the nut back, and release the chuck
jaws from the work, by moving spindle L endwise. Per contra, however, in
stopping the lathe suddenly by means of the brake, there is a tendency
of nut M to stop less quickly than spindle L, and this operates to
unscrew nut N and release the work. To assist this R is sometimes in
lathes for watch manufactories provided with a hand wheel whose weight
is made sufficient for the purpose.
[Illustration: Fig. 667.]
[Illustration: Fig. 668.]
Figs. 667 and 668 represent a pump centre head for watch manufactories,
being a device for so chucking a piece of work that a hole may be
chucked true and enlarged or otherwise operated upon, with the assurance
that the work will be chucked true with the hole. Suppose two discs be
secured together at their edges, their centres being a certain distance
apart, as, for example, a top and bottom plate of a watch movement, and
that the holes of one plate require to be transferred to the other, then
by means of this head they may be transferred with the assurance that
they shall be axially in line one with the other, and at a right angle
to the faces of the plates, as is necessary in setting jewels in a watch
movement.
In holes of such small diameters as are used in watch work, it is
manifestly very difficult to set them true by the ordinary methods of
chucking and it is tedious to test if they are true, and it is to
obviate these difficulties that the pump centre head is designed. Its
operation is as follows.
There are in this case three spindles A, B, and C, in Fig. 667; A
corresponds to spindle A in Fig. 651, driving the chuck D which screws
on A as shown; B simply holds the work against the face _d_ of D, and C
holds the work true by means of the centre _e_, which enters the hole or
centre in the work and is withdrawn when the work is secured by spindle
B.
The chuck D is open on two sides as shown at E E in Fig. 668, which is
an end face view of the chuck, and through these openings the work is
admitted to the chuck. The rod or spindle C is then pushed, by hand,
endwise, its centre _e_ entering the hole or centre in the work (so as
to hold the same axially true) and forcing the work against the inside
faces _d_, spindle B is then operated, the face _p_ forcing the work
against face _d_, and between these two faces _d_ _p_ the work is held
and driven by friction. The spindle C and its centre _e_ is then
withdrawn by hand, leaving the hole in the work free to be operated
upon.
The journal bearings for spindle A are constructed as described for A in
Fig. 666; spindle B is operated endways within A as follows. A is
threaded at G to receive the hub H of wheel I, at the end of B is a
collar which is held to and prevented from end motion within the hub H:
hence when wheel I is rotated and A is held stationary (by means of the
band pulley), H traverses on G and carries B with it. Operating I in one
direction, therefore moves _p_ against the work, while operating it in
the other direction releases face _p_ from contact with the work.
It is obviously of the first importance that the spindle C be held and
maintained axially true, notwithstanding any wear, and that it be a
close fit within B so as to remain in any position when the lathe is
running, and thus obviate requiring to remove it. To maintain this
closeness of fit the following construction is designed. Between spindle
A and spindle B, at the chuck end of the two, is a steel bush which can
be replaced by a new one when any appreciable wear has taken place.
Between B and C are two inverted conical steel bushes, which can also be
replaced by new ones, to take up any wear that may have taken place.
[Illustration: Fig. 669.]
Fig. 669 represents an improved hand lathe by the Brown and Sharpe
Manufacturing Company, of Providence, R. I. It is specially designed for
the rapid production of such cylindrical work as may be held in a chuck,
or cut from a rod of metal passing through the live spindle, which is
hollow, so that the rod may pass through it. Short pieces may be driven
by the chuck or between the centres of a face plate (shown on the floor
at _e_) screwing on in the ordinary manner. When, however, this face
plate is removed a nut _d_ screws on in its stead, to protect the thread
on the live spindle.
The chuck for driving work in the absence of face plate _e_ (as when the
rod from which the work is to be made is passed through the live
spindle) may be actuated to grip or release the work without stopping
the lathe. The pieces _j_ _j_ are to support the hand tool shown in
Figs. 1313 and 1314, in connection with hand turning, the tool stock or
handle being shown at _k_ on the floor. The lever for securing the
tailstock to or releasing it from the shears is shown at _t_. The tail
spindle is operated by a lever pivoted at _g_ so that it may be operated
quickly and easily, while the force with which the tail spindle is fed
may be more sensitively felt than would be the case with the ordinary
wheel and screw, this being a great advantage in small work. The tail
spindle is also provided with a collar _r_, that may be set at any
desired location on the spindle to act as a stop, determining how far
the tail spindle can be fed forward, thus enabling it to drill holes,
&c., of a uniform depth, in successive pieces of work.
The live spindle is of steel and will receive rods up to 1/2 inch in
diameter. Its journals are hardened and ground cylindrically true after
the hardening. It runs in bearings which are split and are coned
externally, fitting into correspondingly coned holes in the headstock.
These bearings are provided with a nut by means of which they may be
drawn through the headstock to take up such wear in the journal and
bearing fit, as may from time to time occur.
[Illustration: Fig. 670.]
It is obvious that the lathe may be removed from the lower legs and
frame and bolted to a bench, forming in that case a bench lathe.
Fig. 670 represents a special lathe or screw slotting machine, as it is
termed, for cutting the slots in the heads of machine or other screws.
The live spindle drives a cutter or saw _e_, beneath which is the device
for holding the screws to be slotted, this device also being shown
detached and upon the floor.
The screw-holding end of the lever _a_ acts similarly to a pair of
pliers, one jaw of which is provided on handle _a_, while the other is
upon the piece to which _a_ is pivoted. The screw to be slotted is
placed between the jaws of _a_ beneath _e_; handle _a_ is then moved to
the left, gripping the screw stem; by depressing _a_, the screw head is
brought up to the cutter _e_ and the slot is cut to a depth depending
upon the amount to which _a_ is depressed, which is regulated by a screw
at _b_; hence after _b_ is properly adjusted, all screw heads will be
slotted to the same depth.
The frame carrying the piece to which _a_ is pivoted may be raised or
lowered to suit screws having different thicknesses of head by means of
a screw, whose hand nut is shown at _d_.
The frame for the head of the machine is hollow, and is divided into
compartments as shown, in which are placed the bushings used in
connection with the screw-gripping device, to capacitate it for
different diameters of screws, and also for the wrenches, cutters, &c.
[Illustration: Fig. 671.]
[Illustration: Fig. 672.]
[Illustration: Fig. 673.]
Figs. 671, 672, and 673, represent a lathe having a special feed motion
designed and patented by Mr. Horace Lord, of Hartford, Connecticut. Its
object is to give to a cutting tool a uniform rate of cutting speed
(when used upon either flat or spherical surfaces), by causing the
rotations of the work to be retarded as the cutting tool traverses from
the centre to the perimeter of the work, or to increase as the tool
traverses from a larger to a smaller diameter. If work of small diameter
be turned at too slow a rate of cutting speed, it is difficult to obtain
a true and smooth surface; hence, as the tool approaches the centre, it
is necessary to increase the speed of rotation. As lathes are at present
constructed, it is necessary to pass the belt from one step to another
of the driving cone, to increase the speed. In this two disadvantages
are met with. First, that the increase of speed occurs suddenly and does
not meet the requirements with uniformity. Second, that the strain upon
the cutting tool varies with the alteration of cutting speed. As a
result, the spring of the parts of the lathe, as well as of the cutting
tool, varies, so that the cut shows plainly where the sudden increase or
decrease (as the case may be) of cutting speed has occurred. The
greatest attainable degree of trueness is secured when the cutting speed
and the strain due to the cut are maintained constant, notwithstanding
variations of the diameter.
This, Mr. Lord accomplishes by the following mechanism: Instead of
driving the lathe from an ordinary countershaft, he introduces a pair of
cones which will vary the speed of the lathe as shown in Fig. 672 as
applied to ball turning. L is a belt cone upon the counter-shaft driven
from the line shaft. L drives H, which may be termed the lathe
countershaft, and from the stepped cone K the belt is connected to the
lathe in the usual manner. P is a shipper bar to move the belt N upon
and along the belt cones, and thus vary the speed. R is a vertical shaft
extending up at the end of the lathe and carrying a segment. This
segment is connected to the belt shipper bar P by two cords, one passing
from _r_^{1} around half the segment to _r_^{2}, and the other passing
from _r_^{3} to _r_^{4}, so that if the segment be rotated, say to the
right, it and the bar will move as denoted by the dotted lines, or if
moved in an opposite direction, the bar motion will correspond and move
the belt N along the cones respectively left or right.
At the back of the lathe is a horizontal shaft S, similar to an ordinary
feed spindle, and connected to the segment shaft by a pair of bevel
gears S^{2}. Between the two ears _e_ _e_, at the rear of the lathe
carriage, is a pinion _t_, which drives the splined shaft S, which works
in a rack T´. The tool rest is pivoted directly beneath the ball, to be
turned after the usual manner of spherical slide rests, and carries a
gear _a_^{2}, which, as the rest turns, rotates a gear _a_^{3}. Upon the
face of the latter is a pin _a_^{4} working in a slot _a_^{5} at the end
of the rack T´; hence as the tool rest feeds, motion is transmitted from
_a_^{2} through _a_^{3}, _a_^{4}, _a_, T´, T, and _s_ _s_^{2} to R,
which operates the belt shipper P. As it is the rate of tool feed that
governs the speed of these motions, the effect is not influenced by
irregularity in feeding; hence the speed of the work will be equalized
with the tool feed under all conditions. The direction of motion of all
the parts will correspond to that of the tool feed from which their
motion is directed, and therefore the work speed will augment or
diminish automatically to meet the requirements.
[Illustration: Fig. 674.]
Fig. 673 illustrates the action of the mechanism when used for surfaces,
like a lathe face plate. In this case the two gears and the rack T´
simply traverse with the cross-feed slider, and the mechanism is
actuated as before. In Fig. 674 a different method of actuating the belt
shipper is illustrated. A pulley is attached to the intermediate stud of
the change gears, being connected by belt to the shipper, which is
threaded as shown at _d_, the belt guiding forks, as _p_^{2}, being
carried on a nut actuated by the screw _d_.
CUTTING-OFF MACHINE.--The cutting-off machine is employed to cut up into
the requisite lengths pieces of iron from the bar. As the cutting is
done by a tool, the end of the work is left true and square and a great
saving of time is effected over the process of heating and cutting off
the pieces in the blacksmith's forge, in which case the pieces must be
cut off too long and the ends left rough.
[Illustration: Fig. 675.]
Fig. 675 represents Hyde's cutting-off machine, which consists of a
hollow live spindle through which the bar of iron is passed and gripped
by the chucks C C. At G is a gauge rod whose distance from the tool rest
R determines the length of the work. F is a feed cone driven by a
corresponding cone on the live spindle and driving the worm W, which
actuates the self-acting tool feed, which is provided with an automatic
motion, which throws the feed out of action when the work is cut off
from the bar. The stand S is movable and is employed to support the ends
of long or heavy bars.
To finish work smooth and more true than can be done with steel cutting
tools in a lathe, what are known as grinding lathes are employed. These
lathes are not intended to remove a mass of metal, but simply to reduce
the surfaces to cylindrical truth, to true outline and to standard
diameter, hence the work is usually first turned up in the common lathe
to the required form and very nearly to the required diameter, and then
passed to the grinding lathe to be finished. The grinding lathe affords
the best means we have of producing true and smooth cylindrical parallel
work, and in the case of hardened work the only means. In place of steel
cutting tools an emery wheel, revolved at high speed from an
independent drum or wide pulley, is employed, the direction of rotation
of the emery wheel being opposite to that of the work.
[Illustration: Fig. 676.]
Fig. 676 represents Pratt and Whitney's weighted grinding lathe. The
headstock and tailstock are attached to the bed in the usual manner, the
frame carrying the emery wheel is bolted to the slide rest as shown, the
rest traversing by a feed spindle motion. The carriage traverse is
self-acting and has three changes of feed, by means of the feed cones
shown.
To enable the lathe to grind taper work (whether internal or external)
the lathe is fitted with the Slate taper attachment shown in Figs. 508
and 509.
It is obvious that in a lathe of this kind, there must be an extra
overhead shaft, driving a drum of a length equal to the full traverse of
the lathe carriage, or of the plate carrying the head and tailstocks,
and the arrangement of this drum with its belt connection to the pulley
on the emery wheel arbor, is sufficiently shown in figure. To protect
the ways of the bed from the abrasion that would be caused by the emery
and water falling upon them, guards are attached to the carriage
extending for some distance over the raised [V]s.
[Illustration: Fig. 677.]
It is essential that the work revolve in a direction opposite to that of
the emery wheel, for the following reasons. In Fig. 677 let A represent
a reamer and B a segment of an emery wheel. Now suppose A and B to
revolve in the direction that would exist if one drove the other from
frictional contact of the circumferential surfaces, then the pressure of
the cut would cause the reamer A to spring vertically and a wedging
action between the reamer and wheel would take place, the reamer
vibrating back and forth under varying degrees of this wedging; as a
result the surface of A would show waves and would be neither round nor
smooth.
[Illustration: Fig. 678.]
In the absence of a proper grinding lathe, an ordinary lathe is
sometimes improvised for grinding purposes, by attaching to the slide
rest a simple frame and emery wheel arbor with pulley attached as in
Fig. 678, in which A is the emery wheel, C the pulley for driving the
arbor, and B the frame, D being a lug for a bolt hole to hold the frame
to the lathe rest.
In some cases the work may remain stationary and the emery wheel only
rotate. Thus, suppose it was required to grind the necessary clearance
to relieve the cutting edge C of the reamer, then A could be rotated
until C stood in the required position with relation to B, and the
revolving emery wheel may either be traversed along, or the work may
traverse past the wheel, according to the design of the grinding lathe,
but in either case A remains stationary during each cut traverse; after
each successive traverse A may be rotated sufficiently to give a cut for
the next traverse.
Fig. 679 represents Brown and Sharpe's universal grinding lathe.
[Illustration: Fig. 679.]
This lathe is constructed to accomplish the following ends. First, to
have the lathe centres axially true with the work when grinding tapers,
so that the lathe centres shall not wear and gradually throw the work
out of true from the causes explained in the remarks on turning tapers
in a lathe of ordinary construction.
Second, to have the headstock B capable of lateral swing, so as to
enable the grinding of taper holes.
The manner in which these results are accomplished is as follows:
The headstock B and the tailstock are attached to the bed or table A,
which is pivoted at its centre to a table beneath it, this latter table
being denoted by C. This permits table A to swing laterally upon C and
stand at any required angle. To enable a delicate adjustment of this
angle, a screw _a_ having journal bearing in a lug on C is threaded
through a piece carried in projection on the end of A.
The table C traverses back and forth past the emery wheel, after the
manner of an ordinary iron planing machine, the mechanical parts
effecting this motion being placed within the bed upon which C slides.
The carriage supporting the emery frame and table D remains stationary
in its adjusted position, while C (carrying A with it) traverses back
and forth.
Now, if A be adjusted so that the line of centres is parallel with the
line of motion of C, then the work will be ground parallel, but if _a_
be operated to move A upon its pivoted centre and draw the tailstock end
of A towards the operator, then the work will be ground of larger
diameter at the tailblock end. Conversely, by operating screw _a_ in the
opposite direction, it will be of smaller diameter at that end.
But whatever the degree of angle of A to C, the line of centres of the
head and tailstocks will be axially true with the axial line of the
work, hence the work centres are not liable to wear off true, as is the
case when the tailstock only sets over (as will be fully explained in
the remarks on taper turning).
To grind conical holes the headstock B is pivoted at its centre upon a
piece held by bolts to the table A, so that it is capable of being swung
laterally to the degree requisite for the required amount of taper in
the work bore, and of being locked in that adjusted position, the work
being held in a chuck screwed upon the spindle in the usual manner. The
pulley _d_ being removed to enable the grinding of cones, chamfers, or
tapers of too great an angle to permit of A setting over to the required
degree. The line of cross-feed motion of the emery wheel may be set to
the required angle as follows.
The frame carrying the emery wheel arbor is fixed to a table D, which is
capable of being operated (in a direction across the table A) upon a
carriage beneath A. This carriage, or saddle (as it may perhaps be more
properly termed), is pivoted so as to allow of its movement and
adjustment in a horizontal plane, and since D operates in the slide of
the carriage, its line of motion in approaching or receding from the
line of centres will be that to which the saddle is set. This enables
the grinding of such short cones as the circumferences of bevelled
cutters, chamfers, &c., at whatever angle the saddle may be set,
however, D may be operated from the feed screw disc and handle _f_.
The lever handle at the left hand is for operating or rather traversing
C by hand; _b_ is a pan to catch the grit and water, the water being led
to the back of machine into a pail; _c_ is a back rest to steady the
work when it is slight and liable to deflection.
The slot and stops shown upon the edge of C are to regulate the points
of termination of the traverse (in the respective directions) of C. A
guard is placed over the emery wheel to arrest and collect the water
cuttings, &c., which would otherwise fly about.
A large amount of work which has usually been filed in a lathe, can be
much more expeditiously and accurately finished by grinding in this
machine.
Work to be ground may obviously be held in the same chucks or
work-holding appliances as would be required to hold it to turn it with
cutting tools, or where a quantity of similar work is to be done special
chucks may be made.
[Illustration: Fig. 680.]
Fig. 680 (from _The American Machinist_) shows a special chuck for
grinding the faces of thin discs, such as very thin milling cutters,
which could not be held true by their bores alone. The object of the
device is to hold the cutter by its bore and then draw it back against
the face of the chuck, which, therefore, sets it true on the faces. The
construction of the chuck is as follows. The hub screws upon the lathe
like an ordinary face plate, and has a slot running diametrically
through it. Upon its circumference is a knurled or milled nut C, which
is threaded internally to receive the threaded wings of the bush B. A
collar behind C holds it in place upon the hub. To admit piece B the
front of the chuck is bored out, and after B is inserted and its
threaded wings are engaged in the ring nut C a collar is fitted over it
and into the counter-bore to prevent B from having end motion unless C
is revolved. D is a split bushing that fits into B, its stem fitting the
bore of the disc, or cutter to be ground: the enlarged end of D is
countersunk to receive the head of the screw E, whose stem passes
through D and threads at its end into B, so that when E is screwed up
its head expands D and causes it to grip the bore of the disc or cutter
to be ground. After E is screwed up the ring nut C is revolved, drawing
B within the chuck and therefore bringing the inside face of the disc or
cutter against the face of the chuck or face plate, and truing it upon
the bushing D. All that is necessary therefore in using the chuck is to
employ a bushing of the necessary diameter for the bore of the cutter,
insert it in B, then screw up the screw E and then revolve the ring nut
C until the work is brought to bear evenly and fair against the face of
the chuck, and to insure this it is best not to screw E very tightly up
until after the ring nut C has been operated and brought the work up
fair against the chuck face.
[Illustration: Fig. 681.]
Fig. 681 represents the J. Morton Poole calender roll grinding lathe,
which has attained pre-eminence both in Europe and the United States
from the great accuracy and fine finish of the work it produces.
In all other machine tools, surfaces are made true either by guiding the
tool to the work or the work to the tool, and, in either case,
guide-ways and slides are employed to determine the line of motion of
the tool or the work, as the case may be. These guideways and slides are
usually carried by a framing really independent of the work, so that the
cutting depends entirely upon the truth or straightness of the
guideways, and is not determined by the truth, straightness, or
parallelism of the work itself. As a result, the surface produced
depends for its truth upon the truth of the tool-guiding ways. In the
Poole lathe, however, while guideways are necessarily employed to guide
the emery wheels in as straight a line as is possible, by means of such
guides, the roll itself is employed as a corrective agent to eliminate
whatever errors may exist in the guide. The rolls come to this machine
turned (in the lathe Fig. 730), and with their journals ground true (on
dead centres).
Fig. 681 represents a perspective view of the machine, as a whole. It
consists of a driving head, answering to the headstock of an ordinary
lathe. B B are bearings in which the rolls are revolved to be ground. C
is a carriage answering to the carriage of an ordinary lathe, but seated
in sunken [V]-guideways, corresponding to those on an ordinary iron
planing machine. Referring to Fig. 682, F is a swing-frame suspended by
four links at G, H, I, J, which are upon shafts having at their ends
knife edges resting in small [V]-grooves on the surface of standards S,
which are fixed to carriage C. The frame F being thus suspended and
being in no way fixed to C, it may be swung back and forth crosswise of
the latter, the links at G, H, I, J, swinging as pendulums. At the top
of F are two slide rests A A, one on each end, carrying emery or
corundum wheels W, and the roll R, which rests in the bearings B,
rotates between these emery wheels. The carriage C is fed along the bed
as an ordinary lathe carriage, and the emery wheels are revolved from an
overhead countershaft. Now, it will be found that from this form of
construction the surface of the roll, when ground true, serves as a
guide to determine the line of motion of the emery wheels, and that the
emery wheels may be compared to a pair of grinding calipers that will
operate on such part of the roll length as may be of larger diameter
than the distance apart of the perimeters of the emery wheels, and
escape such parts in the roll length as may be of less diameter than the
width apart of those perimeters; hence parallelism in the roll is
inevitable, because it is governed solely by the width apart of the
wheel perimeters, which remain the same, while the wheels traverse the
roll, except in so far as it may be affected by wear of emery-wheel
diameters in one traverse along the roll.
[Illustration: Fig. 682.]
Supposing now that we have a roll R (Fig. 683), placed in position and
slowly revolved, and that the carriage C is fed along by feed screw E,
then the line of motion of the emery wheels will be parallel to the axis
of the roll, provided, of course, that the bearings B (Figs. 681 and
687) are set parallel to the [V]-guideways in the bed, and that these
guideways are straight and parallel. But the line of travel of the emery
wheels is not guided by the [V]s except in so far as concerns their
height from those [V]s, because the swing-frame is quite free to swing
either to the right or to the left, as the case may be. Its natural
tendency is, from its weight, to swing into its lowest position, and
this it will obviously do unless some pressure is put on it in a
direction tending to swing it. Suppose, then, that instead of the roll
running true, it runs eccentrically, or out of true, as it is termed, as
shown in Fig. 683, when the high side meets the left-hand wheel it will
push against it, causing the carriage C to swing to the left and to
slightly raise. The pressure thus induced between the emery wheel and
the roll causes the roll surface to be ground, and the grinding will
continue until the roll has permitted the swing-frame to swing back to
its lowest and normal position. When the high side of the roll meets the
right-hand emery wheel it will bear against it, causing the swing-frame
to move to the right, and the pressure between the wheel and the roll
will again cause the high side of the latter to be reduced by grinding.
This action will continue so long as the roll runs out of true, but when
it runs true both emery wheels will operate, grinding it to a diameter
equal to the distance between the emery-wheel perimeters, which are, of
course, adjusted by the slide rests A A. If the roll is out of true in
the same direction and to the same amount throughout its length, the
emery wheel will act on an equal area (for equal lengths of roll)
throughout the roll length; but the roll may be out in one direction at
one part and in another at some other part of the length; still the
emery wheel will only act on the high side, no matter where that high
side may be or how often it may change in location as the carriage and
wheels traverse along the roll. Now, the roll does not run true until
its circumference is equidistant at every point of its surface from the
axis on which the roll revolves, and obviously when it does run true its
circumference is parallel to the axis of revolution of the roll, because
this axis is the line which determines whether the roll runs true or
not, and therefore the swing-frame is actually guided by the axis of
revolution of the roll, and will therefore move parallel to it.
[Illustration: Fig. 683.]
It is obvious that if by any means the swinging of frame F is slightly
resisted, as by a plate between it and C, with a spring to set up the
plate against F, then the emery wheels will be capacitated to take a
deeper cut than if the frame swing freely, this plan being adopted until
such time as the roll is ground true, when both wheels will act
continuously and simultaneously, and F may swing freely.
A screw may be used to set up the spring and plate when they are
required to act.
Suppose now that the roll was not set exactly level with the
[V]-guideways of the bed, there being a slight error in the adjustment
of the roll journals in the bearings on B, and the emery-wheels would
vary in height with relation to the height of the roll axis, and
theoretically they would grind the roll of larger diameter at one end
than at the other.
[Illustration: Fig. 684.]
This, however, is a theoretical, rather than a practical point, as may
be perceived from Fig. 684, in which R is a part of a section of a roll,
and W a part of a section of a wheel. Now, assuming that the [V]-ways
were as much as even a sixteenth out of true, so far as height is
concerned, all the influence of the variation in height is shown by the
second line of emery-wheel perimeter, shown in the figure, the two arcs
being drawn from centres, one of which is 1/16th inch higher than the
other. It is plain, then, that with the ordinary errors found in such
[V]-guideways, which will not be found to exceed 1/30th of an inch, no
practical effect will be produced upon the roll. Again, if one [V] is
not in line with the other, no practical effect is produced, because if
the carriage C were inclined at an angle, though the plane of rotation
of the emery-wheel would be varied, its face would yet be parallel to
the roll axis. If the [V]s were to vary in their widths apart (the
angles of the [V]s being 45° apart), all the effect it would have would
be to raise or lower the carriage C to one-half the amount the [V]s were
in error. It will be thus perceived that correctness of the roll both
for parallelism and cylindricity is obtained independent of absolute
truth in the [V]-guides.
Referring now to some of the details of construction of the lathe, the
slide rest A, Fig. 683, is bored to receive sockets D D, Fig. 685, and
is provided with caps, so that the sockets may be firmly gripped and
held axially true one with the other. The socket-bores are taper, to
receive the taper ends of the arbor _x_, and are provided with oil
pockets at each end. There is a driving pulley on each side of the
emery-wheel, and equal belt-speed is obtained as follows: Two belt
driving drums M N are employed, and each belt passes over both, as in
Figs. 683 and 685, and down around the pulleys P. The diameter of the
drum N is less than the diameter of the drum M by twice the thickness of
the belt, thus equalizing inside and outside belt diameters, since they
both pass over the pulley of the emery-arbor. The piece T is a guard to
catch the water from the emery-wheels, and is hinged at the back so that
the top is a lid that may be swung back out of the way when necessary.
[Illustration: Fig. 685.]
[Illustration: Fig. 686.]
The method of securing the emery-wheels is shown in Fig. 686. Two
flanges Z (made in halves) are let into the wheel, and clamp the wheel
by means of the screws shown. The bore of these flanges Z is larger than
the diameter of pulleys P, so that the emery-wheels may be changed on
the arbor without removing the pulley. Fig. 687 represents an end view
of the bearings B for the roll to revolve in, being provided with three
pieces, the two side ones of which are adjustable by the set-screws, so
as to facilitate setting the roll parallel with the bed of the lathe.
The height is adjusted by means of screws K, K, which may also be used
in grinding a roll of large diameter at the middle of its length, by
occasionally raising the roll as the carriage C proceeds along the roll
(the principle of this action is hereafter explained with reference to
turning tapers on ordinary lathe work). When the wheels have traversed
half the length of the roll, the screws K are operated to lower it
again, it being found that the effect of a slight operating of the
screws K is so small that the workman's judgment may be relied upon to
use them to give to a roll with practical accuracy any required degree
of enlarged diameter at the middle of its length with sufficient
accuracy for all practical purposes.
[Illustration: Fig. 687.]
There are, however, other advantages of this system, which may be noted
as follows. When a single emery-wheel is used there is evidently twice
the amount of wear to take a given amount of metal off (per traverse)
that there is when two wheels are used, and furthermore the reduction of
every wheel diameter per traverse is evidently twice as great with one
wheel as it is with two. From some experiments made by Messrs. Morton
Poole, it was found that using a pair of 10-inch emery-wheels it would
take 40,000 wheel traverses along an average sized calender roll, to
reduce its diameter an inch, hence the amount of error due to the
reduction of the emery-wheel diameters, per traverse, may be stated as
1/40000 of an inch per traverse, for the two wheels.
[Illustration: Fig. 688.]
Now referring to Fig. 688, let R represent a roll and W W the two
emery-wheels.
Suppose the wheels being at the end of a traverse, the roll is 1/40000
inch larger at that end on account of the wear of the emery-wheels, then
each wheel will have worn 1/40000 inch diameter or 1/80000 inch radius,
hence the increase of roll diameter is equal to the wear of wheel
diameter.
[Illustration: Fig. 689.]
Now, suppose that one wheel be used as in Fig. 689, and its reduction of
_diameter_ will be equal to that of the two wheels added together, or
1/20000 inch, this would be 1/40000 in the radius of the wheel,
producing a difference of 1/20000 difference in the diameter of the
wheel.
There is another advantage, however, in that a finer cut can be easier
put on in the Poole system, because if a feed be put on of 1/100th inch,
the roll is only reduced 1/100th inch in diameter, but if the same
amount of feed be put on with a single wheel, it will reduce the roll
1/50th inch, hence for a given amount of feed or movement of emery-wheel
towards the roll axis, the amount of cut taken is only half as much as
it would be if a single wheel is used. This enables a minimum of feed to
be put on the wheel, wear being obviously reduced in proportion as the
feed is lighter and the duty therefore diminished.
The method of driving the roll is as follows: Shaft _t_, Fig. 681, runs
in bearings in the head, and spindle _r r´_ passes through, and is
driven by shaft _t_. A driving pulley is fitted on the spindle at end
_r´_, at the other end is a driving chuck _p_ for driving the roll
through the medium of a _wabbler_, whose construction will be shown
presently. Spindle _r_ may be adjusted endwise in _t_, so that it may be
adjusted to suit different lengths of rolls without moving the bearing
blocks B.
The wabbler is driven by _p_ and receives the end of the roll to be
ground, as shown in Fig. 690, the end of the roll being a taper square
and fitting very loosely in a square taper hole in the end of the
wabbler; similarly _p_ may have a taper square hole loosely fitting the
squared end of the wabbler. The looseness of fit enables the wabbler to
drive the roll without putting any strain on it tending to lift or twist
it in its bearings in block B, and obviates the necessity for the axis
of the rolls to be dead in line with the axis of _r r´_. Various lengths
of wabblers may be used to suit the lengths of roll and avoid moving
blocks B, and it is obvious also that if the ends of the roll are round
instead of square, two set-screws may be used to hold the roll end being
set diametrically opposite, and if set screws are used in _p_ to drive
the wabbler they should be two in number, set diametrically opposite,
and at a right angle to the two in the wabbler, so that it may act as a
universal joint.
[Illustration: Fig. 690.]
The method of automatically traversing the carriage C is as follows:
Referring to Fig. 681, two gears _a_, _b_ are fast upon shaft _t_, gear
_a_ drives _c_ which is on the same shaft as _e_, gear _b_ drives _d_
which drives a gear not seen in the cut, but which we will term _x_, it
being on the same shaft as _c_ and _e_. Now if _e_ is driven through the
medium of _a_ _c_, it runs in one direction, while if it is driven
through the medium of _b_ _d_ _x_, it revolves _e_ in the opposite
direction, and since _e_ drives _g_ and _g_ is on the end of the feed
screw (E, Fig. 682) the direction of motion of carriage C is determined
by which of the wheels _a_ or _b_ drives _e_. At _h_ is a stand
affording journal bearing to a shaft _n_, whose end engages a clutch
upon the shaft of wheels _c_, _x_ and _e_. On the outer end of shaft _n_
is ball lever _l´´_, whose lower end is attached to a rod _k_, upon
which are stops _l l´_ adjustable along rod _k_ by means of set-screws.
At _m_ is a bracket embracing rod _k_.
Now suppose carriage C to traverse to the left, and _m_ will meet _l_
moving rod _k_ to the left, the ball _i_ will move up to a vertical
position and then fall over to the right, causing the clutch to
disengage from gear _c_ and engage with the unseen gear _x_, reversing
the motion of _e_ and of _g_, and therefore of carriage C, which moves
to the right until _m_ meets _l´_ and pushes it to the right, causing
_i_ to move back to the position it occupies in the engraving, the
clutch engaging _c_, which is then the driving wheel for _e_.
SCREW MACHINE.--The screw machine is a special form of lathe in which
the work is cut direct from the bar, without the intervention of forging
operations, and it follows therefore that the bar must be large enough
in diameter to suit the largest diameter of the work, the steps or
sections of smaller diameter being turned down from the full size of the
bar. The advantages of the screw machine are, that the work requires no
centring since it is held in a chuck, that forging operations are
dispensed with, that any number of pieces may be made of uniform
dimensions without any measuring operations save those necessary when
adjusting the tool for the first piece, and that it does not require
skilled labor to operate the machine after the tools are once set.
The capacity of the screw machine is, therefore, many times greater than
that of a lathe, while the diameters and lengths of the various parts of
the work will be more uniform than can be done by caliper measurements,
being in this case varied by the wear of the cutting edges of the tools
only, which eliminates the errors liable to independent caliper
measurement. Hollow work, as nuts and washers, may be equally operated
on being driven by a mandril held in the chuck.
Fig. 691 represents Brown and Sharpe's Number 1 screw machine, which is
designed for the rapid production of small work.
Three separate tool-holding devices may be employed: first, cutting
tools may be placed in the holes shown to pierce (horizontally) the
circular head F; second, tools may be fixed in the tool posts shown in
the double slide rest, which has two slides (one in the front and one at
the back of the line of centres); and third, tools may be placed in what
may be termed the screw-cutting slide-rest J.
F is a head pierced horizontally with seven holes, and is capable of
rotation upon L; when certain mechanism is operated L slides on D and
the mechanism of these three parts is arranged to operate as follows.
The lever arms K traverse L in D. When K is operated from right to left,
L advances towards the live spindle until arrested at some particular
point by a suitable stop motion, this stop motion being capable of
adjustment so as to allow F to approach the live spindle a distance
suitable for the work in hand.
When, however, K is operated from left to right L moves back, and when
it has traversed a certain distance, the head F rotates 1/7 of a
rotation, and becomes again locked so far as rotation is concerned. Now
the relation between the seven holes in F is such that when F has
rotated its 1/7 rotation, one of the seven holes is in line with the
live spindle. Suppose then seven cutting tools to be secured in the
holes in F, then K may be operated from right to left, traversing L and
F forward, and one of the cutting tools will operate upon the work until
L meets the stop; K may then be moved from left to right, L and F will
traverse back, then F will rotate 1/7 rotation and L and F may be
traversed by K, and a second tool will operate upon the work, and so on.
The diameter of the work is determined by the distance of the cutting
edge of the tool from the line of centres, when such tool is in line
with the work, or, in other words, is in position to operate upon the
work. The end measurements of the work are secured by placing the
cutting edges of the tools the requisite distance out from F, when L is
moved forward as far as the stop motion will permit. But it is evident
that the length of cut taken along the work, would under these simple
conditions vary with the distance of the end of the work from the face
of the chuck driving it, but this is obviated as follows:--
The live spindle is made hollow so that the rod of metal, of which the
work is to be made, may pass through that spindle. A chuck on the
spindle holds the work or releases it in the usual manner. Suppose then
the chuck to be open and the bar free to be moved, then there is placed
in the hole in F, that is in line with the work, a stop instead of a
cutting tool. The end of the work may then, for the first piece turned,
be squared up by a tool placed in the slide rest and then released from
the chuck and pushed through the live spindle until it abuts against the
stop so adjusted and affixed in the hole in F; K may then be operated to
act on the work. The first tool may reduce the work to its largest
required diameter, the second turn down a plain shoulder, the third may
be a die cutting a thread a certain distance up the work, the fourth may
be a tool turning a plain part at the beginning of the thread, the fifth
may round off the end of the work, and the sixth may be a drill to
pierce a hole a certain distance up the end of the work.
[Illustration: _VOL. I._ =EXAMPLES OF SCREW MACHINES.= _PLATE X._
Fig. 691.
Fig. 692.]
Now suppose the work to require its edge at the other end to be
chamfered, then there may be placed in the slide rest tool posts a tool
to sever the work from the bar out of which it has been made, while the
other may be used to chamfer the required edge, or to round it if needs
be to any required form.
Work held in the chuck but not formed from a rod may be, of course,
operated upon in a similar manner.
In the case, however, of work of large diameter requiring to be
threaded, the threading tool may be held and operated differently and
more rigidly as follows. I is a lever carrying under its bend and over
the projecting end of the live spindle, a segment of a nut whose thread
must equal in pitch the pitch of thread to be given to the work. A
collar or ring, oftentimes called the leader, having a thread of the
same pitch, is then secured upon the live spindle, so as to rotate with
it, and have no end motion; when therefore I is depressed, the nut will
come into work with the collar or ring, and I will be traversed at a
speed proportioned to the pitch of the threads on the collar and nut.
Now I is attached to a shaft having journal bearing (and capable of end
motion) at the back of the lathe head, and on this bar is attached the
slide rest J, in which the turning or threading tool may be placed. The
shaft above referred to having end motion, may be operated (when the nut
in the lever I is lifted clear of the collar) laterally by means of the
lever I; hence to traverse J to the right, or for the back traverse, I
is raised and pulled to the right, I is then lowered, the nut engages
with the collar, and the tool is traversed to the cut. The cut is
adjusted for diameter by the slide rest, which is provided with an
adjustable stop to determine the depth to which the tool shall enter the
work.
It is obvious that this part of the machine, may be employed for
ordinary turning operations, if the collar be of suitable pitch for the
feed.
[Illustration: Fig. 693.]
Figs. 692 and 693 represent A screw machine for general work.
A is a chuck with hardened steel [V]-shaped jaws. It is fast on the
hollow arbor of the machine. B is a steadying chuck on the rear end of
the arbor. The arbor has a two and one-sixteenth hole through it and its
journals are very large and stiff. It is of steel, and runs in gun-metal
boxes. The cone pulley and back gear is of the full proportion and power
of an eighteen-inch lathe. C is an ordinary lathe carriage fitted to
slide on the bed, and be operated by hand-wheel D and a rack pinion as
usual. Across this carriage slides a tool rest E operated by screw as
usual, and having two tool posts, one to the front and one to the rear
of the work. This tool rest, instead of sliding directly in the carriage
as is the case with lathes, slides on an intermediate slide which fits
and slides in the carriage. This intermediate slide is moved in and out,
a short distance only, by means of cam lever G. An apron on the front
end of this slide carries the lead screw nut H. When the cam lever is
raised it brings the slide outward about half an inch, and the tool rest
E comes out with it and at the same time the nut leaves the lead screw.
The inward movement of the slide is always to the same point, thus
engaging the lead screw and resetting the tool. In cutting threads with
a tool in the front tool post the tool is set by moving the tool rest as
usual, and at the end of the cut the cam lever serves to quickly
withdraw the tool and lead screw nut so that the carriage can be run
back. The tool rest is then advanced slightly and the new cut taken. By
this means threads are cut without any false motions, and the threads
may be cut close up to a shoulder.
I is the lead screw. This screw does not extend, as is usual, to the
head of the machine. It is short and is socketed into a shaft which runs
to the head of the machine and is driven by gearing as usual. The lead
screw is thus a plain shaft with a short, removable, threaded end. The
gearing is never changed. Different lead screws are used for different
threads, thus permitting threads to be cut without running back. The
lead screws are changed in an instant by removing knob J. The lead screw
nut H is a sectional nut, double ended, so that each nut will do for two
pitches, by turning end for end in the apron. L is an adjustable stop
which determines the position of the carriage in cutting off, facing,
&c. K is an arm pivoted to the rear of the carriage and carrying three
open dies like a bolt cutter head. At M is a block sliding or capable of
being fed along the bed. N is a gauge screw attached to this block and
provided with two nuts. The stop lever shown in the cut turns up to
straddle this screw, and the position of the nuts determines how far
each way the block may slide. O is the turret fitted to turn on the
block. It has six holes in its rim to receive sundry tools. It can be
turned to bring any of these tools into action, and is secured by the
lock lever P.
[Illustration: Fig. 694.]
The turret slide is moved quickly by hand, by means of the capstan
levers U, which, by an in-and-out motion, also serve to lock the turret
at any point. The turret slide is fed, in heavy work, by the crank-wheel
R on its tail screw. This tail screw carries, inside the crank-wheel,
two gears S, which are driven at different speeds by a back shaft behind
the machine. These two gears are loose on the tail screw, and a clutch
operated by lever T locks either one to the screw. Both the carriage and
turret are provided with oil pots not shown in the cuts.
[Illustration: Fig. 695.]
A top view of the turret is shown in Fig. 694, a set of tools being
shown in place.
The end gauge which is shown removed from the chuck in Fig. 695, is
composed of a hollow shank A fitting the hole in the turret, and a gauge
rod B fitting the bore of the shank. The shank A may be set farther in
or out of the turret, and the rod B may be set farther in or out of the
shank, the two combined being so set that when the turret is clear back
against its stop the end of the rod B will gauge the proper distance
that the bar iron requires to project outwards from the chuck of the
machine. The centre shown in Fig. 696 corresponds to an ordinary lathe
centre, and is only used when chasing long work in steel.
[Illustration: Fig. 696.]
The turner shown removed from the chuck in Fig. 697, consists of a
hollow shank A, fitting the turret and having at its front end a
hardened bushing B secured to A by a set screw. It has also a heavy
mortised bolt C in the front lug of the shank; an end-cutting tool D
shaped like a carpenter's mortising chisel, and clamped by the mortised
bolt; a collar screw E to hold the tool endwise; and a pair of
set-screws F to swivel the tool and its bolt. Bushing B is to suit the
work in hand. The tool D is a piece of square steel hardened throughout.
It is held by its bolt with just the proper clearance on its face. It
cuts with its end without any springing, and will on this account stand
a very keen angle of cutting edge. There is hardly any limit to its
cutting power. It will cut an inch bar away at one trip with a coarse
feed. It does not do smooth work, and is, therefore, used only to remove
the bulk of the metal, leaving the sizer to follow.
[Illustration: Fig. 697.]
[Illustration: Fig. 698.]
The sizer Fig. 698, consists of a hollow shank A fitting the turret and
carrying in its front end a hardened bushing B and a flat cutting tool
C. The sizer follows the turner and takes a light finishing cut with oil
or water, giving size and finish with a coarse feed, and having only a
light and clean duty it maintains its size.
[Illustration: Fig. 699.]
The die holder shown in Figs. 699 and 700, is arranged to automatically
stop cutting when the thread is cut far enough along the work. It will
cut a full thread cleanly up against a solid shoulder. It consists of a
hollow shank A fitting the turret; a sleeve B fitted to revolve and
slide on the front end of the shank C; a groove E bored inside the
sleeve; a pin D on the shank fitting freely in the groove E; a keyway F
at one point in the groove and leading out each way from it; and a
thread die G held in the front end of the sleeve. When the turret is
run forward, the thread die takes hold of the bolt to be cut, but it
revolves idly instead of standing still to cut, until the pin D comes
opposite the keyway F when, the turret still being moved forward, the
pin enters the back of the keyway. The sleeve now stands still, the die
cuts the thread and pulls the turret along by the friction of the pin in
the keyway. Finally the turret comes against its front stop and can move
forward no farther. Consequently the sleeve is drawn forward on its
shank C, and the instant the pin D reaches the groove E the die and
sleeve commence to revolve with the work and cease cutting. The machine
is then run backward, and the turret moved back a trifle. This causes
the pin to catch in the front end of the keyway and the sleeve is again
locked. The die then unscrews, and, in doing so, pushes the turret back.
A tap holder may be inserted in place of the die, and plug taps may be
run to an exact depth without danger.
[Illustration: Fig. 700.]
[Illustration: Fig. 701.]
Drills and other boring tools are held in suitable sockets, which fit
into the turret.
[Illustration: Fig. 702.]
The following are the operations necessary to produce in this machine an
hexagon-headed bolt.
First operation: The bar is inserted through the open chuck.
Second operation: Turret being clear back against its stop and revolved
to bring present the end gauge, the bar is set against the end gauge,
and the chuck is tightened. This chucks the bar and leaves the proper
length projecting from the chuck.
Third operation: Front tool in the carriage, a bevelled side tool cones
the end of the bar so turret tools will start nicely.
Fourth operation: Turret being revolved to present the turner, the bar
is reduced, at one heavy cut, to near the proper size, the turret stop
determining the length of the reduced portion.
Fifth operation: Turret being revolved to present the sizer, the body of
the bolt is brought to exact size by a light, quick, sliding cut.
Sixth operation: Open die arm being brought down, the bolt is threaded;
the left carriage stop indicating the length of the threaded part.
Seventh operation: Turret being revolved to present the die holder, the
solid die is run over the bolt, bringing it to exact size with a light
cut, and cutting _full thread to the exact point desired_.
Eighth operation: Front tool in the carriage chamfers off the end
thread.
Ninth operation: Back tool of carriage, a parting tool, cuts off the
bolt; the left carriage stop determining the proper length of head.
Tenth operation: Bolt being reversed in chuck, the top of the head is
water cut finished by a front tool in the carriage. This operation is
deferred till all the bolts of the lot are ready for it.
Fig. 703 represents a general view of a screw machine designed by Jerome
B. Secor, of Bridgeport, Connecticut. The details of the machine are
shown in Figs. 704, 705, 706, 707, 708, 709, 710, and 711.[13] The live
spindle is of steel and is hollow, and its journals are ground. The
boxes are lined with babbitt, so that no other metal touches the
spindle, and may, by a special device, be re-babbitted and bored exactly
parallel with the planing of the bed.
[13] From _Mechanics_.
A steel collar J, Fig. 704, between the front end of the forward box and
the spindles, receives the thrust due to the cut, and a nut on the
spindle acts against the cone to adjust it forward on a feather K in the
spindle to take up end wear. The wire or rod from which the work is to
be made is passed through the spindle and collar on the stand, and is
held by a thumb-screw in the collar, which is influenced by the weight
and cords, so that when the wire is released in the chuck the weight
pulls the collar and wire forward, forcing the wire out through the
front end of the chuck until it comes against the stop in the turret,
which gauges the length needed to make the piece required. From time to
time, as the rod is used up, the thumb-screw in the sliding collar is
loosened, and the collar is shoved back on the rod as far as it will go,
and the set-screw is again tightened.
[Illustration: Fig. 703.]
[Illustration: Fig. 704.]
Fig. 704 shows in section the front bearing and the automatic chuck. M
is a hollow spindle within which is the hollow spindle H, through which
the rod or wire to make the work passes. It is prevented from end motion
by the cone hub on one side and the collar J on the other side of the
bearing, while H may be operated endwise within M by means of the
hand-lever shown on the left-hand of the headstock in the general view.
The core A of the chuck screws upon M, and is threaded to receive the
adjustment nut B, which receives and holds the adjustment wedges C at
their ends by the talon shown. The shell D is secured to H by the screws
I, which pass through slots in A, and therefore move endwise when H is
operated by its hand-lever. Now the mouth of D, against which the
adjustment wedges C rest, is coned 2-1/2°, as marked; hence the end
motion of D to the left causes C, and therefore F, to approach the axis
of the chuck and grip the rod or wire, while its motion to the right
causes C, and therefore F, to recede from the chuck axis and to release
the wire. Since B is screwed upon A, and C is guided at the end by B,
and since also F is detained endwise in A, the motions of C and of F are
at a right angle to the chuck axis. Hence in gripping the rod or wire
there is no tendency to move it endways, as there is where the gripping
jaws have, as in many machines, a certain amount of end motion while
closing. When this end motion exists, tightening the jaws upon the work
draws it away from the stop in the turret and impairs the adjustment for
length of work. The gripping jaws are closely guided in slots in D and
in A, and three sets of these jaws are necessary to cover a range of
work from the full diameter of the bore of H down to zero. The capacity
of each of these sets of jaws, however, may be varied as follows: The
adjustment ring B is threaded upon A, and may be operated along A to
move C endwise by means of the tangent screw E, whose threads engage
with teeth parallel to the axis of B, and running across its width all
around its circumference, hence rotating E, rotates B, causing it to
move along A, and carry C beneath F. By this method of adjustment F need
be given only enough motion to and from the chuck axis to grip and
release the work, and the reduction of motion between the hand-lever
operating H and the motion of F is so great, that with a very moderate
force at the lever the wire may be held so that its projecting end may
be twisted off without slipping the wire within the jaws or impairing
the jaw grip.
[Illustration: Fig. 705.]
Fig. 705 is a sectional and end view of the core A of the chuck, and
Fig. 706 a sectional and end view of the shell D.
[Illustration: Fig. 706.]
Fig. 707 represents a sectional side view and an end view of the cross
slide, or cutting-off slide, which carries two tool posts, and therefore
two cutting tools, one of which is at the back of the rest. In place of
a feed screw and nut, or of a hand lever and link, it is provided with a
segment of a gear-wheel P operating in a rack R, which avoids the
tendency to twist the cross slides in its guides which exists when a
hand lever and link is used.
[Illustration: Fig. 707.]
The cross slide is adjusted to fit in its guideway by a jaw S^{1}, Fig.
707, which is firmly screwed to and recessed into R. To take up the
wear, the face of S^{1} is simply reduced. This possesses a valuable
advantage, because it is rigid and solid, does not admit of improper
adjustment, nor can the adjustment become impaired at the hands of the
operator.
To adjust the position of the cross slide upon the shears a screw passes
between the shears and is threaded into the stud Q. This screw is
operated by a hand wheel shown in the general view, Fig. 703, beneath
the rear bearing of the headstock.
A special and excellent feature of the machine is the stop device for
the motion of the cross slide which is shown in Fig. 707.
The screw S has one collar C, solid on it, and the screwed end is tapped
into the sliding sleeve T, which is held from turning by the stud A.
Between the solid collar C and the loose collar B there is a short,
stiff spiral spring, as shown; by means of the fast and loose collars,
the spring and the screwed thimble D, a strong friction is had on the
collar B, which is ample to keep the screw from turning while in use as
a stop, although it permits the screw to turn easily enough when a
wrench is applied to the square end. Precisely the same device is used
at the other end of the slide to stop it in the opposite direction.
[Illustration: Fig. 708.]
Details of the mechanism of the turret and turret slide are shown in
Figs. 708, 709, and 710. Fig. 708 is an end sectional view of the turret
slide, which is traversed on its base by a segment D of a gear operating
in a rack R (in the same manner as the cutting-off slide), the segment
being connected by stud N to handle M. O represents the body of the
slide, which is grooved at the sides to receive the gibs X, which secure
it to the base P on which it slides. P is clamped to its adjusted
position on the shears or bed by means of the gib, shown in dotted
lines, which is pulled laterally forward by the screw S, which is tapped
into the stem of the gib. The method of rotating the slide and of
locking it in position is shown in Fig. 709, which is a top view of the
turret head, and Fig. 710, which shows O removed from P and turned
upside down. Pivoted to segment D is a rod E having at K a pin that as
motion proceeds falls into S and rotates T, which is fast to the bottom
of the turret. Upon the handle M being moved backward the segment begins
its motion forward, as indicated by the arrow in Fig. 710, thereby
moving the slide backward upon the gibs by the working of its cogs into
the rack R, Fig. 708, which is attached to the base P. When the segment
D has accomplished about one-half its motion the pin H, which is on the
upper side of the segment D, comes in contact with the projection or lug
on the side of the cam F, as shown by the arrow head in Fig. 710,
bringing the opposite side of the cam against the pin G, Fig. 709,
thereby moving it backward, compressing the spring U, and drawing the
bolt L from its seat in the disc V. This operation is completed before
the motion of the segment brings the pin K in contact with the
ratchet-wheel T. The segment D in continuing its motion after the pin K
is brought into the notch S, begins the revolution of the turret on its
axis. As will be seen by the inspection of Fig. 710, the pin H works
upon a much longer radius than the projection upon the cam with which it
comes in contact, and therefore, after a given part of its motion is
complete, gets beyond the reach of the cam, thereby releasing its hold
and allowing the bolt L, Fig. 709, to be forced against the disc V by
the expansion of the spring U, which occurs soon after the turret has
commenced its revolution by the contact of pin K with the wheel T. The
completion of the movement of the handle M (and the segment D) completes
the revolution of the turret one-sixth of its circumference, thereby
allowing the bolt L, by the further expansion of the spring U, to be
forced into its next opening or seat in the disc V. The forward motion
of the handle M brings the turret forward to its position at the work
and restores the parts to their former positions, as shown in the
illustrations.
[Illustration: Fig. 709.]
[Illustration: Fig. 710.]
The stop motion for the forward motion of M, and that therefore
determines the length of turret traverse forward, and hence the distance
each tool shall carry its cut along the work, is shown in Fig. 711. The
end of the screw A abuts against the stop B in the usual manner; it is,
however, threaded through the eye of a bolt C, as well as through the
end of the turret slide, so that it may be locked by simply operating
the nut D. Thus the use of a wrench is obviated, and the adjustment is
more readily effected.
[Illustration: Fig. 711.]
Figs. 712 and 713 represent a screw machine by the Pratt and Whitney
Company, of Hartford, Connecticut, and having Parkhurst's patent wire or
rod feed for moving the work through the hollow spindle and into
position to be operated upon by the tools. The reference letters
correspond in both figures.
At A is the front and at B the back bearing, affording journal bearing
to a hollow spindle C, which carries the shell D of the work-gripping
chuck, the clutch ring H and a collar I, in which is pivoted, at J, the
clutch levers G. This collar is threaded upon C and is locked in
position by a ring lock nut J´. The clutch arm K slides upon a rod X,
and has a feather projecting into a spline in X. The core E of the
work-gripping chuck is fast upon the inner spindle F, which revolves
with the outer one C. The left-hand end of F abuts against the short
arms of the clutch levers G, and it is obvious that when K is operated
back and forth upon X, it moves the clutch H endways upon C, and the
cone upon H operates the levers G, causing them to move the inner
spindle F endways and the inner cone E of the chuck to open or close.
Suppose, for example, that K (and hence H) is moved to the right, and
the long ends of G will be released and may close moving their short
ends away from the end of F, and therefore releasing E from its grip
upon the work. In moving K to the right the sleeve L is also moved to
the right, and its serrations at L´ being engaged with the tongue P, the
sleeve M is pulled forward. Now the bar or rod of which the work is made
is held at one end by the chuck, it is supported by the bushing Z in the
end of spindle C, and in the bushing S in the arm of sleeve M, while it
has fast upon it a collar T. When therefore M is pulled forward or to
the right, its arm meets T and pulls the rod or bar for the work through
the chuck E.
[Illustration: Fig. 712.]
[Illustration: Fig. 713.]
On the other hand when K and therefore H, L, and M, are moved to the
left, levers G are opened at their long ends by the cone of H. The short
ends of G push the inner spindle F to the right, E passes through D, and
being split, closes upon the work and grips it, the parts occupying the
positions shown in the figure. The same motion of K passes L through the
sleeve M (the teeth at N raise the catch P, allowing L´ to pass through
M) so that at the next movement of K to the right, M will be pulled a
second step forward, again passing the work through the chuck. Q is
merely a pin wherewith to lift P and enable M to be moved back, when
putting in a new rod for the work; K is operated by a link from U to V,
the handle for moving this link being shown at W in the general view.
To prevent the sleeve M from moving back with L it is provided with a
shoe O, pressed by the spring R against X, thus producing a friction
between M and X that holds M while L slides through it. R´ is to
regulate the tension of the spring at R. _y_ is merely a sleeve to
protect the clutch mechanism from dust, &c.
Box tools for screw machines are used for a great variety of special
work. They are simply boxes or heads carrying tools and a work-steadying
rest.
Fig. 714 represents a box tool for a screw machine. The cylindrical stem
fits into the turret holes and contains a steadying piece or rest G to
support the work and keep it to its cut. In the box tool shown in the
figure, there are four cutting tools set in to the depth of cut by the
screws A, B, C, and D respectively, and a fifth for rounding off the end
of the work is shown at E.
[Illustration: Fig. 714.]
Fig. 715 represents a top view, Fig. 715_a_ a front view, and Fig.
715_b_ an end view, of a box tool for shaping the handles for the wheels
of the feeding mechanism of machines. The work is first turned true and
to its required diameter, and the rest is set to just bear against the
work to steady it and hold it against the pressure of the cut. The
cutter is cylindrical with a gap cut in it at G, so as to give a cutting
edge. By grinding the face of this gap the tool is sharpened without
altering its shape, as is explained with reference to circular or disc
tools for lathe work. The cutter is provided with a stem by which it is
held in the slide, through the medium of the clamp. The slide is
operated by an eccentric on the spindle or rod R, which is operated by
the handle H. The stop obviously arrests the motion of the slide when it
meets the box B, and this determines the diameter of the work, which is
represented by W in the end view figure.
[Illustration: Fig. 715.]
[Illustration: Fig. 715_a_.]
[Illustration: Fig. 715_b_.]
Fig. 716 represents the die holder and die for the Pratt and Whitney
Co.'s screw machine. The die is cut through on four sides, and is
enveloped by a split ring having a screw through its two lugs, so that
by operating the screw the die may be closed to take up the wear and
adjust it for diameter. It is secured in a collar by the set-screw
shown, and this collar is clutch shaped on its back face, engaging a
similar clutch face on the shoulder of the arbor, the object of this
arrangement being as follows. Suppose it is required to cut a thread a
certain distance, as say, 3/4 inch, along a stud, and that the depth of
the clutch is 1/4 inch. Suppose that when the turret is fed forward
sufficiently the thread is cut half an inch along the work at the moment
that the turret meets its stop and comes to rest, then the die will
continue to feed forward one-quarter of an inch, moving along the body
or stem of the holder until its clutch face disengages, when the die
will revolve with the work.
[Illustration: Fig. 716.]
[Illustration: Fig. 717.]
Fig. 717 represents a cutting-off tool and holder for a screw machine.
The tool fits into a dovetail groove in the split end of the holder, and
is ground taper in thickness to give the necessary clearance on the
sides. It is held by the screw shown, which closes the split and grips
the dovetail; obviously the top face only is ground to resharpen it.
[Illustration: Fig. 718.]
Fig. 718 represents a special lathe for wood work designed and
constructed by Charles W. Wilder, of Fitchburg, Massachusetts. It is
intended to produce small articles in large quantities, cutting them to
duplicate form and size without any further measurements than those
necessary to set the tools in their proper respective positions. It is
employed mainly for such work as druggists' boxes, tool handles,
straight spokes for toy vehicles, piano pins, balls, rings, and similar
work.
Its movements are such that the tools are guided by stops determining
the length and the diameter of the work so as to make it exactly
uniform, while the form of the cutting tools determines the form of the
work, which must therefore be uniform.
The lathe may be described as one having a carriage rest spanning the
bed of the lathe, which rest holds the work axially true with the lathe
centres without the aid of the dead centre, while it at the same time
trues the end of the work and leaves it free to be operated upon by
other tools, which, after once being set and adjusted, shape any number
of pieces of work to exact and uniform diameter and shape.
[Illustration: Fig. 719.]
The manner in which this is accomplished is as follows: Fig. 718 is a
general external view of the lathe; Fig. 719 is an end elevation view of
the rest from the cone spindle end, and Fig. 720 is an end view of the
rest viewed from the tailstock end of the lathe. A is a ring fastened in
the rest R by the set-screw B. The mouth C of the ring which first meets
the work is coned, or beveled, as shown, and an opening on one side of
the ring admits a cutting tool T. Now the work is placed one end in the
cone driving chuck on the lathe spindle, and the other end in the cone
or mouth C, Fig. 719, being kept up to the driving chuck by the end
pressure of C. As the work rotates, the tool T cuts it to the diameter D
of the ring bore, the carriage or rest R traversing along the lathe bed
as fast as tool cuts; hence the bore D serves as a guide to hold the
work and make it run true, this bore being axially true with the lathe
centres. The cone surface of C thus operates the same as the sole of an
ordinary carpenter's plane, the tool T cutting more or less rapidly
according as its cutting edge is set to project more or less in advance
of the surface of the cone or recess C. This admits of the tool cutting
at a rate of feed that may best suit the diameter of the work and the
nature of the wood. The tool T, is operated laterally to increase or
diminish the rate of feed by the screw E, which also serves as a pivot,
so that by operating the thumb-screw F, the tool point may be adjusted
for distance from the centre of the bore D, or in other words the
diameter to which the tool T will turn the work is adjusted by the
thumb-screw F. G is the head of the pivot screw that the swing tool
holder H works upon, and this swing motion carries the forming tool or
cutter X, which shapes the work to the required form. I is a shaft upon
which a lever, carrying the tool holder J, works, the latter carrying
the severing tool K, which severs the finished work from the stick of
wood from which the work is made.
The tool holders H and J are connected by means of the arms L and M to
the stud O, fast in wheel P, operated by a knee lever Q, which is
pivoted at S to _u_, which is fast to one of the gibs that hold the
carriage to the lathe [V]s. The knee lever Q is connected to the wheel P
by a raw-hide strap, or belt V, so that the operator, by pressing his
knee upon the end of the lever Q, causes the wheel P, to partly rotate,
carrying O with it (O being fast in P), and gives a forward radial
motion to tool holder H and cutter X, causing the latter to enter the
work until such time as the stud O and the screw stud W are in line,
horizontally with the centre of the wheel P, after which tool holder H
will move back, while the severing tool K (which has a continuous upward
or vertical movement) is cutting off the finished work, which has been
formed to shape, and reduced to the required diameter by the forward
movement of the tool or cutter X. The object of the backward or retiring
motion of H is to relieve the shaping tool X from contact with the work,
while K cuts it off, or otherwise the work might meet X when cut off,
and receive damage from contact with it. The stud W, connecting tool
holder H with the wheel P, is threaded with a right and left-hand screw,
by operating which the tool X may be operated to reduce the work to any
required diameter.
The rest or carriage R traverses along the lathe shears or bed Z,
carrying with it all the levers and tools, so far described.
[Illustration: Fig. 720.]
The tailstock, or back head, carries a tool holder in the rear of the
spindle, in which fits also a drill bit or other cutting tool. The
method of traversing and operating the carriage R and the back head is
as follows:
At the back of the bed or shears is a table, shown at T, in Fig. 718.
Upon this table is a stand to which is pivoted the end of a lever, as is
shown at 1 in figure. This lever has a joint at 2, and is connected to
the tailstock spindle at a joint marked 3. It is obvious that by
operating the lever laterally, joint 2 will double, and the tail spindle
will be moved along the bed. If the tail spindle is not locked it will
simply feed through the tailstock and the tool in the spindle will
operate, but if it is locked (by the ordinary screw shown), then the
handle will slide the whole tailstock and the tool in the holder at the
back of the tail spindle may operate.
[Illustration: Fig. 721.]
At 4 is an adjusting screw, which, by coming into contact with the
carriage R causes it also to traverse, which it will do until it meets
against a screw on the other side, marked 5, in Fig. 718, which,
standing farther out than the chuck prevents the cutting tool from
meeting the chuck.
The movement of the carriage continues until the stop-gauge 6 meets the
end of the work, hence the length of the work is from the cutting-off
tool to the face of stop 6. The adjustment for the length of the work is
made by means of screw 4, which will slide the carriage R, as soon as it
meets it, independent of what distance the stop 6 may be from the work
end. The tailstock carries two tool holders, similar to those on an
ordinary lathe. When the cutting tools are used to cut completely over
the end of the work, as in ball turning or a round ended handle, the
stop 6 is not used, the tool which rounds the end acting as a stop of
itself.
When bits are used they are held in the tail spindle and are made of a
proper length to give the required depth of hole, or sometimes the face
of the bit-holder may be used as a stop.
When the tools, cutters, and belts are all properly adjusted in position
to cut to the required respective diameters or lengths the operator has
simply to place a stick of wood in the lathe and operate the respective
handles or levers in their proper consecutive order, and the work will
be finished and cut off, the operation being repeated until the stick is
used up, when a new one may be inserted, and so on.
LATHES FOR IRREGULAR FORMS.--In lathes for irregular forms (which are
chiefly applied to wood and very rarely to metal turning), the work is
performed by rotary cutting tools carried in a rapidly rotating head.
The work itself is rotated slowly, and the carriage or frame carrying
the cutting tools is caused to follow the outline of the pattern or
_former_ at every point in its circumference as well as in its length.
The principle of action by means of which these ends are attained is
represented in Fig. 721, in which S represents a slide which carries the
sliding head, affording journal bearing to the rotating head H, driven
by the belt E, and carrying the cutters, and also the wheel W. F
represents the pattern or former, and B a piece of wood requiring to be
turned to the same form as that of F. Suppose then that F be slowly
rotated by A and C, receiving rotary motion from A (through the medium
of D), then the rotations of C will equal those of F, because the
diameter of A is equal to that of C. The diameter of the circle
described by the cutters at H is also equal to the diameter of W, hence
the motion of the extremities of the cutters is precisely the same as
that of the circumference of W, and as W receives its motion from F it
is obvious that the cutters will reduce G to the same form and size as
F, and if the head be traversed in the same direction as the axis of F,
then the diameter and form of B will be made to correspond to that of F
at every corresponding point throughout its length. Contact between W
and F is maintained by means of a weight or spring, the rotation of F
being sufficiently slow to insure its being continuous, while the
necessary rapidity of cutting speed for the tools is attained by
rotating H at the required speed of rotation.
This class of lathe is termed the "Blanchard" lathe from the name of the
inventor, or "Lathe for irregular forms," from the chief characteristic
of the work, but is sometimes designated from the special article it is
intended to turn, as "The Shoe-last lathe," "Axe-handle lathe," "Spoke
lathe," &c., &c.
[Illustration: Fig. 722.]
Let Fig. 722 represent a lathe of this kind provided with a frame A
affording journal bearing to the shaft of the drum B, which is driven by
the pulleys C. Let E represent a pulley receiving motion from B by the
belt D. The cutting tools are carried by the head F which is rotated by
pulley E. Let the carriage or frame carrying the shaft of E carry a dull
pointed tracer, with continuous contact with the _former_ H by means of
a weight or spring, the carriage being so connected to the way N on
which it traverses that it is capable of rocking motion, and if H be
rotated the carriage will, by reason of the tracing point, have a motion
(at a right angle to the axis of H) that will be governed by the shape
of H; hence since G rotates equally with H, the form of the blank work G
will be similar to that of H, but modified by reason of the tracing
point being at a greater distance than F from the centre of rocking
motion.
All that is necessary to render this motion positive throughout the
lengths of G and H is to connect them together by gears of equal
diameter, and traverse the carriage along N for the full length of the
pieces. But the effect will be precisely the same if the frame carrying
G and H be pivoted below, capable of a rocking motion, and H be kept
against the tracing point by means of a spring or weight, in which case
the carriage may travel in a straight line upon N and without any
rocking motion. This would permit of the carriage operating in a slide
way on N enabling it to traverse more steadily.
To maintain continuous contact between the tracing point and the
_former_ H, the rotations of H are slow, the necessary rapidity of tool
cutting action being obtained by means of the rapid rotation of the head
and cutters F.
Since motion from the line shaft to the machine is communicated at C it
is obvious that the gears or devices for giving motion to H and G may be
conveniently derived from the shaft carrying C and B, for which purpose
it extends beyond the frame at one end as shown. Lathes of this kind are
made in various forms, but the principles of action in all are based
upon the principles above described.
[Illustration: Fig. 723.]
BACK KNIFE GAUGE LATHE.--This lathe, Fig. 723, has a carriage similar to
that described with reference to Fig. 718, and carries similar tools
upon the tailstock. It is further provided, however, with a self-acting
feed traverse to the carriage, and by means of a rope and a weight, with
a rapid carriage feed back or from left to right on the bed, and also
with a knife at the back. This knife stands, as seen in the engraving,
at an angle, and is carried (by means of an arm at each end) on a
pivoted shaft that can be revolved by the vertical handle shown. The
purpose of this knife is first to shape the work and then to steady and
polish the wood or work. Obviously when the knife is brought over upon
the work its cutting edge meets it at an angle and cuts it to size and
to shape; the surface behind the cutting edge having no clearance rubs
against the work, thus steadying it while polishing it at the same time.
These lathes are used for turning the parts of chairs, balusters, and
other parts of household furniture, the beads or other curves or members
being produced on the work by suitably shaped knives, which obviously
cut the work to equal shape and length as well as diameter, and it is
from this qualification that the term "gauge" is applied to it.
Fig. 724 represents the Niles Tool Works special pulley turning lathe,
in which motion from the cone spindle to the live spindle is conveyed by
means of a worm on the cone spindle and a worm-wheel on the live
spindle. Two compound slide rests are provided, the tool on the rear one
being turned upside down as shown. These rests may be operated singly or
simultaneously, and by hand or by a self-acting motion provided as
follows:--A screw running parallel to the cone spindle is driven by
suitable gearing from the cone spindle. At each end of this screw it
gears into a worm-wheel having journal bearing on the end of the slide
rest feed screw as shown. By a small hand wheel on the end of the slide
rest feed screw the worm-wheel may be caused to impart motion to the
feed screw by friction causing the slide rest to feed. But releasing
this hand wheel or circular nut releases its grip upon the feed screw,
and permits of its being operated by the handle provided at the other
end. The rail carrying the slide rest is adjustable in and out to suit
varying diameters of pulleys, being secured in its adjusted position by
the bolts shown.
The cut is put on by means of the upper part of the compound rest. To
turn a crowning pulley the rails carrying the slide rests are set at an
angle, the graduations shown on the edge of the ways to which they are
bolted being to determine the degree of angle. When the pulley surface
of the pulley is to be "straight" both tools may commence to operate on
one edge of the pulley surface, the advance tool taking a roughing and
the follower tool a finishing cut; but for crowning pulleys the tools
may start from opposite edges of the pulley, the cuts meeting at the
middle of the face; hence the angles at which the respective rails are
set will be in opposite directions.
The pulleys to be turned are placed upon mandrels and driven by two arms
engaging opposite arms of the pulley. To drive both arms with an equal
pressure, as is necessary to produce work cylindrically true, an
equalizing driver on Clements' principle (which is explained in Fig.
756, and its accompanying remarks) is employed.
For driving the pulleys to polish them after they are turned the cone
spindle is hollow at the rear end and receives a mandrel. The high speed
at which the cone spindle runs renders this possible, which would not be
the case if wheels and pinions, instead of worm-gear, were employed to
communicate motion from the cone to the live spindle. A wheel shown in
position for polishing is exhibited in the cut, the pivoted arm in front
affording a rest for the polishing stick or lever.
BORING AND TURNING MILLS.--The boring and turning mill patented in
England by Bodmer in 1839, has developed into its present improved form
in the United States, being but little known in other countries. It
possesses great advantages over the lathe for some kinds of turning and
boring, as wheels, pulleys, &c.
The principal advantages of its form of construction are:--
[Illustration: Fig. 724.]
[Illustration: Fig. 725.]
1st. That its work table is supported by the bed at its perimeter as
well as at its centre, whereas in a lathe the weight of the chuck plate
as well as that of the work overhangs a journal of comparatively small
diameter, and is therefore more subject to spring or deflection and
vibration.
2nd. It will carry two slide rests more readily adjustable to an angle,
and more readily operated simultaneously, than a lathe slide rest.
3rd. It is much more easy to chuck work on a boring mill table than on a
lathe, because on the former the work is more readily placed upon the
table, and rests upon the table, so that in wedging up or setting any
part of the circumference of the work to the work table, there is no
liability to move the work beneath the other holding plates; whereas in
a lathe the work standing vertical is apt when moving or setting one
part to become unset at other points, and furthermore requires to be
held and steadied while first being gripped by the chucking dogs,
plates, or other holding devices.
Figs. 725, 726, 727, 728, and 729 represent the design of the Niles Tool
Works (of Hamilton, Ohio), boring and turning mill. In this design
provision is made to raise the table so that it takes its bearing at the
centre spindle only when used upon small work where a quick speed of
rotation is necessary, or it may be lowered so as to take its
circumferential bearing for large heavy work where slower speeds and
greater pressure are to be sustained.
The bearing surfaces are, in either case, protected from dust, &c., and
provided with ample means of lubrication. Each tool bar is so balanced
that the strain due to the balancing weights is in a line parallel to
the bar axis in whatever position and at whatever angle to the work
table the bar may be set. This prevents the friction that is induced
between the bar and its bearings when the balancing strain is at an
angle to the bar axis, and consequently pulls the bar to one side of or
in a line to twist the bar. The bar is therefore more easily operated,
and the feed gear is therefore correspondingly relieved of strain and
wear.
The general construction of the machine is shown in Fig. 725. It
consists of a base or bed, affording journal bearing and support to a
horizontal work table, rotated by devices carried upon the bed. To each
side of the bed are attached uprights or standards, forming a rigid
support to a cross slide or rail for the two sliding heads carrying the
tool bars.
The various motions of the machine are as follows: There are 16 speeds
of work table, 8 with the single, and the same with the back gear. The
cross slide is capable of being raised or lowered, to suit the height of
the work, by an automatic motion. Both tool rests are capable of hand or
automatic feed motion at various rates of speed, in a line parallel to
the surface of the work table. Both are also capable of automatic or
hand feed motion, either vertically or at any required angle to the work
table, and have a quick return motion for raising them, while each may
be firmly locked while taking radial or surfacing cuts, thus preventing
spring or vibration to the tool bar. In addition to this, however, there
is provided, when required, a tailstock, carrying a dead centre after
the manner of a lathe, so that the work may be steadied from above as
well as by the work table. In Figs. 726 and 727 are shown the devices
for raising the work table and those for actuating the feed screws and
the feed rod; thus operating the sliding heads horizontally and the tool
bars vertically. A is the base or bed supporting the work carrying table
B´, and affording its spindle journal bearing at D´. A step within and
at the foot of D´ rests upon the wedge F´ so that when the wedge is
caused to pass within D´ it lifts the step, which in turn lifts the
table spindle, and hence the table, sufficiently to relieve its contact
with the outer diameter of the bed. F´ is operated as follows: The lever
G´ is pivoted at E´ and carries at its upper end a nut H´, operated by a
screw on the end of the bolt I´; hence rotating I´, operates wedge F´.
For operating the automatic feed motions, _f_ is a disc upon a shaft
that is rotated by suitable gears beneath the work table; _g_ is a disc
composed of two plates, having a leather disc between them, the
perimeter of the disc having sufficient frictional contact with _f_ to
cause _g_ to rotate when _f_ does so: _g_ drives the vertical spindle
_i_, which has a worm at J´ driving a worm-wheel which rotates the gears
upon the feed spindles V, F, W, in the figures; _f_ rotates in a
continuous direction, but the spindle _i_ is caused to rotate in either
direction, according to whether it has contact with the top or bottom of
the face of _f_, it being obvious that the motion of _f_ above its
centre is in the opposite direction to that below its centre of
rotation. The means of raising and lowering _g_ to effect this reversal
of rotative direction is as follows: It is carried on a sleeve _g´_
which is provided with a rack operated by a pinion that is rotated by
means of hand wheel _h_; hence, operating _h_ raises or lowers _g´_, and
therefore _g_; _h´_ is a hand wheel for locking the pinion, and hence
detaining the rack (and therefore _g_) in its adjusted position. This
design is an excellent example of advanced American practice for
obtaining a variable rate of feed motion in either direction, it being
obvious that _g_, being driven by the radial face of _f_, its speed of
rotation will be greater according as it is nearer to the perimeter of
_f_ and less as it approaches the centre of _f_, at which point the
rotary motion of _g_ would cease. Here, then, we have a simple device,
by means of which the direction and rate of feed may be governed at will
with the mechanism under continuous motion, and conveniently situated
for the operator, without his requiring to move from the position he
naturally occupies when working the machine.
[Illustration: Fig. 726.]
The means of raising or lowering the height of the rail R on the side
standards Z are as follows: K is a pulley driven by belt from the
countershaft and operating pinion _l_, which operates pinion _n_,
driving _m_. O is a gear on the shaft driving the pinions _p_, _p_,
which operate the gears _q_, _q_, on the vertical screws which engage
with nuts attached to R; _m_ and _n_ are carried on a bell-crank _r_
pivoted on the shaft of pulley K. Pinion _n_ is always in gear with
pinion _l_, and pinion _m_ is always in gear with pinion _n_ (and not
with pinion _l_). With the bell-crank in one position, motion passes
from _l_ to _n_ and to O; but with it in the other position, motion
passes from _l_ to _n_, thence to _m_, and from it to O. The motion of
_m_, therefore, is always in a direction opposite to that of _n_; hence
O, and gears _p_ and _q_, may be operated in either direction by
regulating which of the two gears _n_, _m_ shall drive O, and this is
accomplished as follows: The bell-crank _r_ is connected by an arm to
rod _s_, and the latter is connected by a strap to an eccentric _t_,
operated by the handle shown. When this handle stands horizontally, both
_m_ and _n_ are disengaged from pinion O; but if the handle be raised,
rod _s_ is raised, and _m_ is brought into gear with O. If, however, it
be lowered from the horizontal position, _n_ is brought into gear with
O, and _m_ becomes an idle wheel.
[Illustration: Fig. 727.]
There are two feed screws--one for operating each boring bar-head, and a
spindle for operating the vertical feeds of the bars in the sliding
heads. Fig. 728 shows the arrangement for engaging and disengaging the
feed nuts of these heads. A is the slide that traverses the rail. It
carries a nut made in two halves, N and N´, which are carried in a guide
or slide-way, and which open from or close upon the screw F when the
handle O is operated in the necessary direction. Each half of the nut is
provided with a pin projecting into eccentric slots _x_ in the face of a
pivoted plate (shown dotted in), to which the handle O is attached. W, W
represent bearings for the vertical feed spindle W in Fig. 726. _a_ is
the annular groove for the bolts _b_ in Fig. 729.
[Illustration: _VOL. I._ =ROLL-TURNING LATHE.= _PLATE XI._
Fig. 730.
Fig. 731.]
For a quick hand traverse for the head the ratchet, P is provided,
operating a pinion _s_, which engages with a rack T, running along the
underneath side of the cross-rail R. To adjust the fit of A to the rail
the gibs _y_ and _y´_ and the wedge _x_ are employed.
[Illustration: Fig. 728.]
Fig. 729 represents the automatic feed motion within the head for
operating the tool bars vertically. R is the cross rail on which slides
A carrying B, and permitting it to swivel at any angle by means of bolts
_b_, whose heads pass within an annular groove, _a_ in A. In B is
carried the boring bar G, having the rack shown. P is a pinion to
operate the rack. W is the feed-rod driving the worm H, which drives the
worm-wheel I. This worm-wheel is provided with a coned recess, into
which the friction plate C fits, so that when the two are forced
together rotary motion from I is communicated to C, and thence to C´
(which is a sleeve upon C), where it drives pinion P by means of pin P´.
_i_ rotates upon and is supported by the stud J, which is threaded into
C^{2} (the latter being also a continuation of C); hence when hand-wheel
K is operated in one direction, C^{2} acting as a nut causes J to clamp
I to C, and the tool bar to therefore feed. Conversely, when K is
operated in the opposite direction, I is released from C, and may,
therefore, rotate while C remains at rest. For feeding the tool bar G by
hand, or for moving it rapidly, the hand-wheel M is provided, being fast
to the sleeve at its section C^{2}, and, therefore, capable of rotating
pinion P. D affords journal bearing to C at its section C´. The chain
from the weights which counterbalance the bars G pass over sheaves which
are fixed to the piece B in which the bar slides, so that they occupy
the same position with relation to the axis of the bar at whatever angle
the latter may be set, and thus the counterbalancing weight is delivered
upon the bar in a line parallel to its axis. As an example of the
efficiency of the machine, it may be mentioned that at the Buckeye
Engine Co.'s Works, at Salem, Ohio, a pulley 12 feet in diameter,
weighing 8860 pounds, and having a 27-inch face, was bored and turned on
one of these machines in 17 hours, taking three cuts across the face,
turning the edge of the rim facing off the hub and recessing the bore in
the middle of its length for a distance of several inches, the bore
being in all 18 inches deep. The machine is made in different sizes, and
with some slight variations in each, but the main features of the
design, as clearly shown in our engravings, are common to all sizes.
Fig. 730 represents a lathe for turning chilled rolls such as are used
for paper calendering machines, and is constructed by the J. Morton
Poole Company of Wilmington, Delaware.
In the figure a roll is shown in position in the lathe. The journals of
the rolls are first turned in a separate lathe, and form the guide by
which the body of the roll is turned in the lathe shown in the figure.
The lathe consists of a bed plate P, at one end of which is mounted the
driving head. Upon this bed plate are also mounted three standards or
vertical frames, to the two end ones of which are pivoted the binder
arms shown. These frames hold the bushes at L and N, in which the
journals of the roll revolve. They also carry the bar G, secured to the
arm W of the frame by clamps _a_, _a_, _a_. Upon the bar G are two slide
rests, consisting of a tool rest E, a tool clamp A, and a feed yoke B,
which is screwed up by a wrench applied to the nuts as shown on the
right-hand tool rest in the figure. The binder arm is adjusted to hold
the bushings L N (which are varied to suit the size of the roll journal)
a fair working fit upon the roll journals, the bolts S holding the
binder arms firmly against the enormous pressure due to the cut. It is
obvious that the frames W may be adjusted anywhere along the bed plate P
to suit the length of roll to be turned, and that the slide rests may be
moved to any required position along the bar G. Further details of the
construction are as follows. Fig. 731 is an end, and Fig. 732 is a top
view of the tool rest; A is the tool clamp securing the tool to the rest
E, R representing a section of the roll, B is the feed yoke, which to
put on a cut is screwed inwards by operating the nuts D. The pins C are
fast in B, and their ends abut against the tool, which is fed in under
the full pressure of the clamp A. The tool is shown at F in figure, and
also at F in Fig. 733, which is a view of the rest with the clamp A
removed. The form of tool employed is shown in Fig. 734, its length
varying from five to six inches. As the tool feeds in and does not
traverse along the roll it is obvious that it cuts along its entire
length, the cuttings coming off like a bundle of fine ragged needles.
[Illustration: Fig. 729.]
When the tool has been fed in cutting the roll to the required diameter
the rest is moved along the bar G, a distance equal to the length of the
tool, and the operation is repeated until the full length of the roll
has been turned. It is obvious that to feed the tool in parallel, both
nuts D of the tool rest are operated. The tool is held as close in to
the rest as the depth of cut to be taken will permit, and is used at a
cutting speed varying from about 2-1/3 feet to 5 feet per minute
according to the hardness of the roll. The tool has four cutting edges,
and each cutting edge will carry in at least one cut, and may sometimes
be used for a second one. The tools are used dry and the amount of
clearance is just sufficient to clear the roll and no more.
The rolls are driven by a socket bolted to the lathe face plate, and
containing a square hole, in which fits loosely the square end of the
roll. The object of this arrangement is to permit the roll to be guided
entirely by the bearings in which it rotates, uninfluenced by the
guiding effect that accompanies the use of centres in the ordinary
method of turning.
[Illustration: Fig. 732.]
Fig. 735 represents a lathe designed and constructed by the American
Tool and Machine Company, of Boston, Mass. This class of lathe is
strictly of American origin, and has become the most important tool in
the brass finishing shop.
[Illustration: Fig. 733.]
In its design the following advantages are obtained:--
1st. The front of the lathe is entirely unobstructed by the ordinary
lathe carriage and slide rest, hence the work may be more easily chucked
and examined, while in the case of work requiring to be ground together,
while one part is in the chuck, the trouble of moving the slide rest out
of the way is entirely obviated.
2nd. In place of the single cutting tool carried in a slide rest and of
the tailstock of the ordinary lathe, there is provided, what is known as
a turret, or turret rest, carrying 6 tools, each of which can be
successively brought into action upon the work by the simple motion of a
lever or handle.
[Illustration: Fig. 734.]
3rd. The rest for traversing single pointed screw cutting tools or
chasers (for internal threads) is at the back of the lathe where it is
out of the way.
4th. In place of the usual change wheels required to operate the lead
screw, the chasing bar is operated by a single threaded collar or hob,
which is more easy of application and removal.
5th. The slide rest carrying the screw cutting tool is capable of such
adjustment, that the tool will thread successive pieces of duplicate
work to an exactly equal diameter, so as to obviate the necessity of
either measuring or trying the work after the tool has been accurately
set for the first piece.
6th. When the threading tool has traversed to the end of its cut it may
be lifted from the same and pulled back by hand, ready to take a second
cut, thus avoiding the loss of time involved in traversing it back by a
lead screw or its equivalent.
7th. Each of the tools in the turret may be set so as to operate to an
equal depth and diameter upon successive pieces of work.
[Illustration: Fig. 735.]
In the particular lathe shown in our example, there is another and
special advantage as follows:--
In lathes operating upon small work and upon the softer metals, as
composition, brass, &c., the time occupied in traversing the cutting
tool is comparatively short, and from the comparative softness of the
metal the speed of lathe rotation is quick, and the tool motions must be
correspondingly quick. In addition to this the work being so much more
quickly performed, changes and readjustments of the parts are
necessarily more frequent, hence the rests traverse the bed more rapidly
as well as more frequently and the wear of the [V]s on the lathe, and
the corresponding [V]-grooves in the tool rest, slide rest, or turret,
is increased; as a result, tools carried in the tailstock or the turret,
as the case may be, which tools should for a great many purposes stand
axially true with the live spindle, stand below it, and hence instead of
boring a hole equal to their own diameter, bore one of larger diameter.
In the case of tools, however, which, as in the case of drills,
endeavour to find their own centre in the work, this action takes place
to some extent as the tool enters the work, and as a result the hole is
made a taper, whose largest diameter is at the mouth. This induces
another evil in that it dulls the advance edge of the drill flute, and
wears away the clearance which is of such vital importance to the free
action of the drill.
The manner in which these advantages are obtained is as follows:--
In place of the ordinary tailstock a back head is provided which has a
cross slide operating after the manner of the ordinary slide rest; this
carries an upper slide, thus forming a compound slide rest. On the top
of this rest is carried a rotating head or turret head, serving the same
purpose as the head shown in Fig. 694, and carrying a series of tool
holders. These tool holders may be operated by the feed screw of the
compound rest, or may be operated by the hand lever shown standing
horizontally. In addition to the ordinary back gear for reducing the
live spindle speed there is provided on the live spindle a second small
pinion, driving at the back of the lathe head a shaft, on the left-hand
end of which is a seat for collars or hobs, operating a bar running
along the back of the lathe, and forming what is termed the screw
apparatus, whose operation is as follows:--
This bar carries the slide rest shown, a handle or lever for partly
rotating the slide rest, spanning the bed of the lathe. When this handle
is lifted, the bar at the back of the lathe rotates in its journals. On
this bar is an arm which carries a segment of a circle, containing a
thread corresponding in pitch to the thread on the collar or hob. When
the lever is raised the segment moves away from the hob, and the bar may
be moved laterally by hand, but when the lever is lowered the arm falls,
and the segment comes into contact with the hob thread, which therefore
feeds the bar; all that is necessary for thread cutting is, therefore,
to place on the lathe a hob having the required pitch for the thread to
be cut, and place in the slide rest a chaser or single-pointed threading
tool, and set the tool to the work by means of the slide rest,
depressing the lever to cause the tool to feed forward, and elevating it
to move the bar back by a lateral hand pressure. To put on successive
cuts the slide rest is operated, the lever always being lowered till it
meets the surface of the lathe bed. To cause the slide rest to cut
successive threads to the same diameter, a suitable stop motion is
provided to the slide rest, and when the rest has been operated as far
as the stop will permit it, the thread is cut to the required depth and
diameter.
A stop motion is also provided to the lateral motion of the turret, so
that the tools being set to enter the work to their respectively
required distances, all pieces will be turned to equal depths or
lengths.
To enable the centres of the tool holders to maintain true alignment
with the live spindle, notwithstanding the wear of the lathe bed and
back head, the bed is made in two parts. One of them carries the
headstock, and on the vertical face of this part is a slide in which the
end of the second part fits, so that by means of adjusting screws the
second part may be elevated to effect the true alignment when necessary.
Fig. 736 represents a square arbor brass-finisher's lathe. The object of
the square arbor or tail spindle is to enable it to carry cutting tools
in place of the dead centre. A cross slide is provided to the tailstock,
and upon this slide the head of the tailstock is pivoted so as to bore
taper holes; the tailstock thus virtually becomes a compound slide rest.
This lathe is provided at the back of the bed with a bar carrying a
slide rest, operated in the same way and for the same purpose as that
described with reference to Fig. 735. Both these lathes are furnished
with separate compound slide rests, and with a hand rest.
[Illustration: Fig. 736.]
When work of considerable weight requires to be bored with holes of
moderate diameter, it is more convenient that it remain fixed upon a
table, and that the boring tools rotate, and a machine constructed by
the Ames Manufacturing Company for this purpose is shown in Fig. 737; a
standard occupies the position of the ordinary tailstock. It carries an
horizontal table, or angle plate, on which the work may be chucked. This
table is capable of a vertical and a cross shear movement, so that when
the work is chucked upon it, holes whose axes are parallel, but situated
in different locations upon the same surface, may be drilled or bored by
so moving the table as to bring each successive hole into line with the
live spindle. The feed motions are as follows:--
[Illustration: Fig. 737.]
At the back of the smallest step on the cone and fast on the cone
spindle is a gear-wheel gearing into a pinion, which drives the lower
shaft shown behind the back bearing, and on this shaft are two pinions.
One drives the upper feed cone, shown at the back of the back bearing,
which cone connects by belt to the feed cone below, which operates a
traverse feed for the work table; the other drives the tool holding
spindle which passes through the cone spindle. This tool holding or
driving spindle is threaded at its back end, passing through a nut which
causes it to self-feed from left to right, or in other words, towards
the work table. To throw this feed out of operation the pinion on the
end of the lower or feed driving spindle is moved laterally out of gear
with the pinion driving it.
To provide a quick hand-feed traverse the shaft or spindle, shown with a
hand-wheel, is provided, being connected to the tool driving spindle by
gearing.
When employed to operate a boring bar, a bearing to support the bar at
the tail or footstock end may be bolted to the table, such bearing
carrying a bushing which may be changed to suit the diameter of the
boring bar.
[Illustration: Fig. 738.]
Fig. 738 represents a cylinder boring lathe. D is the driving cone, on
whose shaft is the worm W, driving the worm-wheel G, which is fast upon
the boring bar _g_, having journal bearing in the standards H and H´,
the latter of which must be moved out of the way to get the work over
the bar. _h_ is a head provided with slots to carry the cutting tools;
_h_ is a close sliding fit to the bar _g_, and is traversed along _g_ as
follows:--_g_ is hollow and there passes through it a feed screw, which
operates a nut on _h_, which nut passes through a longitudinal opening
in the bar _g_. At the end of this feed screw is the gear-wheel D. Now
fast upon the end of _g_, and therefore rotating with it, is the gear A,
driving gear B, which is fast on the same sleeve as C, which it
therefore drives; C drives D. The diameter of A is less than that of B,
while that of C is less than that of D; hence the rotation of D is
slower than that of A, and the difference in the relative velocities of
D and A causes the feed screw to rotate upon its axis and feed the head
_h_ along the bar. If C be placed out of gear with D, the feed screw
(and hence the head H) may be operated by the handle E.
[Illustration: Fig. 739.]
There are several objections to this form of machine, as will be seen
when comparison is made with Fig. 739, which represents a special
cylinder boring lathe, designed and constructed by William Sellers and
Co., of Philadelphia, Pennsylvania. The boring bar is here supported in
two heads, and is hollow, the feed screw for traversing the head
carrying the boring cutters being within the bar. The feed is effected
through the medium of the train of gearing shown at the end. The two
face plates shown which drive the boring bar, also carry two slide rests
which are used to face off the ends of cylinders while the boring bar is
in operation, these slide rests being operated by a star feed, acting on
the principle described with reference to Fig. 589. The boring bar in
this case being driven from each side of the work the torsion due to the
strain of the cut is divided between the two halves of the bar; or in
other words, when a boring bar is driven from one end the strain due to
the cut falls upon that part of the bar that lies between the
boring-head and the point at which the bar is driven; but when the bar
is driven from each end then the strain is divided between the two ends,
causing a bar of a given strength to operate more steadily and take a
heavier cut for roughing, and a smoother one for finishing. A greater
advantage, however, is that it gives to the bar a rigidity, enabling it
to carry a cutter having a long cutting edge without chattering, thus
allowing a very coarse finishing feed, which will finish a bore with
less wear to the tool edge (and therefore more parallel) because for a
given amount of work the cutting-edge is under duty for a less period of
time, the cutting speed remaining the same, or even slower than would be
desirable for a fine feed. The driving-cone, which is shown to be below
the boring-bar, is so situated to accomplish two objects, which are to
operate the two face plates by a shaft having two pinions (within the
bed) gearing with the circumferential teeth on the face plates, and to
operate at the same time the table (shown on the bed between the
face-plates) to which the cylinder is bolted.
In a boring machine it is of the utmost consequence that the bar shall
be as free from vibration as possible, while lost motion, or looseness
from wear, is especially to be avoided. By carrying the bar in two
bearings, as it were, the wear is greatly reduced.
The duty of facing the cylinder ends is sometimes done by facing cutters
carried in the head. Such cutters, however, must have a cutting edge
equal to the breadth of the surface faced by them, because the cutter
cannot be fed radially to its cut. Furthermore, the cut is carried by
the bar at a considerable leverage, and as a result it is very difficult
indeed to make the radial faces true or even nearly true, the cutter
dipping into the softer parts of the iron or into spongy places if there
are any. In any event springing away from its cut, resisting it until
forced to cut, and then cutting deeper than should be, so that on a
finished surface it is often apparent to the eye where the cutter began
and left off. When, however, the radial faces are operated upon by a
slide rest, as in the Sellers machine, the tool is more firmly held, and
may be fed radially to the cut, producing true faces, and saving a great
deal of time in making the cylinder cover joints, as well as in the
boring and facing operations.
Fig. 740 represents a double boring and facing lathe by G. A. Gray,
Junior, of Cincinnati, Ohio. Two driving heads are provided, each having
a main spindle, but holding the boring bar after the manner of an
ordinary lathe, and within each spindle is another capable of
longitudinal traverse. The main spindle is provided with a head
corresponding to a slide rest and carrying a cutting tool for facing
purposes, the feed being obtained by means of a _star-feed_. The work is
bolted to the carriage and fed to the cut for boring purposes. It is
provided with an automatic feed and also with hand feed. When facing is
to be done the carriage may be firmly locked to the lathe shears.
In boring and facing a steam pump centre, or other similar piece, the
casting is fastened to the carriage in a special fixture. The carriage
is then moved so that the work will come nearly in contact with tool in
the fast head, the loose head is moved up to the work, and both the
carriage and loose head are clamped.
[Illustration: Fig. 740.]
Both ends of the casting may be operated upon at the same time or
separately, as occasion requires, the object being, however, to work
upon as many places at one time as the nature of the work will permit;
this being the main point in the economical performance of work. It is
evident also that if the machine is true, and the piece is finished at
one setting, the work will be true.
[Illustration: Fig. 741.]
In the detail engravings, Fig. 741 represents boring, tapping, and
facing steam pump centres, in which operations the carriage is locked.
[Illustration: Fig. 742.]
[Illustration: Fig. 743.]
Fig. 742 illustrates the manner of boring and facing cylinders and
similar pieces, the loose head stock being used as a tailstock and the
fast headstock as the driver. The facing is done either before or after
the boring, all the work obviously being done at one chucking.
Fig. 743 shows a longitudinal cross section of the headstocks showing
the main and the internal spindles.
Fig. 744 represents a lathe constructed by the Defiance Machine Works
for turning the hubs for carriage and wagon wheels.
[Illustration: Fig. 744.]
The blank from which the hub is turned is driven by a mandrel having a
square stem fitting in the live or driving-spindle, this mandrel being
supported at the other end by the ordinary dead centre operated by the
upper hand-wheel. The bed is provided (between the driving-spindle and
tailstock) with the usual raised [V]s on which rests a carriage carrying
a cross slide. This cross slide carries, at the back of the lathe, a
head or stock containing the roughing-knives, and at the front a table
carrying the finishing-knives, hence, by operating the large hand-wheel
(which gives transverse motion to the cross slide) in one direction the
roughing-knives are brought into operation, while by operating it in the
opposite direction the finishing-knives are brought into operation (the
roughing-knives receding). By suitable stops, the motion of the roughing
and finishing-knives respectively are arrested when those knives have
cut the blanks to the desired diameter, the finishing-knives shaping the
work correctly by reason of their form of outline. Upon the same cross
slide are the equalizing-knives, one on each side of the front table.
These knives operate simultaneously with the finishing-knives, cutting
the hubs to uniform length. Thus the hubs are cut to exact uniformity of
diameter, shape and length, by simply operating the large hand-wheel
first in one direction and then in the other.
If it be required to cup the hubs, as in the case of standard wagon
hubs, suitable cutters carried in a bar (having sliding motion in a
guide way on the tailstock) are caused to do such cupping, the
cupper-bar being operated by the left-hand lever.
The live, or driving, spindle is started and stopped by a tight and
loose pulley, the belt being passed from one to the other by means of
the lever on the right, which simultaneously operates a brake attached
to the belt stopper, operating upon the tight pulley. By this means the
lathe can be started and stopped more quickly than would be the case
with a cone pulley, whose extra weight and inertia would take time to
overcome.
CHAPTER IX.--DRIVING WORK IN THE LATHE.
The devices employed to drive work that is suspended between the lathe
centres are shown in the following illustrations.
They are termed lathe dogs, drivers, or carriers. It is to be observed,
however, that since the term dog is also applied to a device for holding
work to the lathe face plate, as well as to the jaws of chucks, either
the term driver or the English term carrier is preferable to the term
dog.
[Illustration: Fig. 745.]
[Illustration: Fig. 746.]
Fig. 745 represents a lathe dog, driver, or carrier D, in position to
drive a piece of work in the lathe. It is obvious that the work is
secured within the carrier or driver by means of the set-screw shown.
The tail of the driver here shown is bent around to pass within the slot
provided in the face plate, a plan which is convenient, but is
objectionable, because in this manner of driving the work two improper
strains are induced, both of which act to spring or bend the work. The
first of these strains is caused by the carrier being driven at a
leverage to the work, as shown at A in the figure, which causes the live
centre to act as a fulcrum, from which the work may be bent by the
strain caused by the cut.
[Illustration: Fig. 747.]
The second strain is caused by driving the carrier from one side or end
only, and is shown in Fig. 746, where the dog receives the face-plate
pressure at the point A, and the cut or resistance being on the opposite
side of the work, the leverage of the driving point causes a tendency to
lift the work in the direction of the arrow C. The direction of this
latter strain, however, varies as the work revolves. For example, in
Fig. 747 the dog is shown in position at another point in its
revolution, and the point A, where the power is applied to the carrier,
is here on the same side as the tool cut; hence there is less tendency
to spring the work. It becomes obvious then, that work driven in this
manner will be liable to be oval, or out of round, as it is commonly
termed.
[Illustration: Fig. 748.]
The methods of overcoming these two sources of error are as follows:
Instead of the end of the dog being bent around to pass within the slot
in the face plate, as in Fig. 745, the leverage A in that figure may be
avoided by the means shown in Fig. 748, in which a driver having
straight ends is used, and a pin P is fastened to the face plate to
drive the carrier. But this does not remove the tendency (shown in Fig.
746) acting to spring the work from the pressure of the cut; hence, to
obviate this latter tendency, two driving-pins P P, in Fig. 749, are
sometimes used with the idea of driving the work from both sides, and
thus equalizing the strain. But this is effective only when each pin is
in working contact with the dog. This condition is difficult to secure
for several reasons. First, suppose the two ends of the carrier to be of
equal thickness, and the driving-pins to be of equal diameter, while the
work receiving hole of the carrier is quite central to these two ends,
then the work also must be true, in order to cause the pins to act
equally on the ends of the carrier. Hence, this method is only
applicable, even if all the above conditions be fulfilled, to the
finishing cuts, and these would have to be taken on work that had been
sprung in the roughing cuts, so that it would be difficult to obtain
accurate results. A nearer approach to correctness is therefore sought
by various means. Thus, Fig. 750 represents a face plate provided with
an annular [T]-groove, having a cut at H to admit two nuts into which
the pins P are screwed. These pins may be tightened lightly, so that
they will slip under the pressure of the roughing cut, and thus come to
an equal bearing upon the carrier or work, as in case of the arms of a
pulley where a carrier is not used. When the pins have adjusted
themselves to have as near as may be an equal driving bearing, they may
be tightened up. By this means the pins are compelled to act at an equal
leverage upon the carrier or work, but there is no assurance of an equal
degree of pressure of the pins P.
Another method is shown in Fig. 751, in which a clamp in two parts is
employed, the driving-pins P fitting into two holes equidistant from the
lathe centre, while loosening one bolt, J or K, and tightening the other
is resorted to, to equalize the driving contact on the two arms, but in
this case again there is no certainty that the two pins will drive
equally, and there is danger of drawing the work somewhat out of true.
Another form is shown in Fig. 752, the idea being to equalize the
pressure of the driving pins, by means of the four screws, but here
again, there is no means of knowing whether the driving pressure is
equalized.
[Illustration: Fig. 749.]
The best form of driver is shown in Fig. 753, which represents a
Clement's driver. The driving-plate F has four slots; two of them, A and
B, pass entirely through this plate to admit bolts C D, which have a
shoulder, so that they may be secured firmly to the lathe face plate,
but which are an easy fit in the plate F, so as to permit it to move
upon the lathe face plate. The other two are [T]-shaped slots to receive
nuts, into which the pins P P are to be screwed. The bolts C D drive F,
and the pins P drive the work, the freedom of the plate E to move upon
the lathe face plate permitting this strain-equalizing action of the
driving-plate and driving-pins.
[Illustration: Fig. 750.]
[Illustration: Fig. 751.]
[Illustration: Fig. 752.]
Sometimes, as in cutting screws, the work requires to be revolved
backwards, without having any lost motion between the arm and carrier,
or in other words, the carrier must revolve backwards as soon as the
face plate does. To accomplish this, a common plan is to tie the driver
or carrier to the driving-pin, but a better plan is to employ a bent
tailed dog and secure its end in the face-plate slot. A convenient form
of face plate for this purpose is shown in Fig. 754, A, B, C, and D,
being slots, and E a set-screw for binding the dog as shown in Fig. 755.
[Illustration: Fig. 753.]
For special lathes in which the work is of uniform diameter, the driving
pins P, Fig. 753, may be replaced by solid jaws, thus in Fig. 756 is a
Clement driver, such as is used on axle lathes, C C being driving lugs
in place of the pins P in figure.
To prevent the ends of the set-screw or screws of the driver from
damaging the surface of finished work, the form of driver shown in Fig.
757 has been patented in England. It consists of a disc arched to
receive a lever C, which is pivoted in the disc at D. A set-screw
provided in the disc binds one end of the lever to the work, and as the
pressure to drive the work is applied at the other end of the same
lever, it serves to assist (to some extent) the set-screw in binding the
lever to the work. The work is held between a [V] in the disc and one on
the lever, the object being to provide a large area of contact, and thus
prevent the damage to finished work which screw ends are apt to cause.
[Illustration: Fig. 754.]
The same end may be obtained for ordinary drivers by using a copper or
brass ring, such as shown in Fig. 758, which may be opened or closed,
within certain limits, to suit the diameter of the work, being placed on
the end of the work, and within the dog, to receive the pressure of the
set-screws.
[Illustration: Fig. 755.]
One such ring will serve for several diameters of work, springing open
when forced, under hand pressure, upon the work, or closing upon the
work as the pressure of the dog set-screw is received. It is obvious
that the split of the ring should be placed diametrally opposite to the
dog set-screw.
[Illustration: Fig. 756.]
In very small lathes the driver is sometimes driven by the device shown
in Fig. 759, which consists of a small chuck, screwed on the live
spindle, and containing the live centre and a driving arm B, which
passes through the chuck, and is set to any required distance out, by
the set-screw C. The objection to this is, first, that either the live
centre must be very short, or the arm B must be very long; and, second,
if the chuck wears out of true, it carries the live centre also out of
true; hence this class of driver is but little used, even in foot
lathes.
[Illustration: Fig. 757.]
[Illustration: Fig. 758.]
In small drivers of this kind it is sometimes the practice to cut away
rather more than one quarter of the thread on each side of the live
spindle as shown in Fig. 760 at A, and to then cut away one quarter of
the thread on each side of the bore of the driver as at B in the figure.
This enables the driver to be passed upon the spindle and screwed home
with one quarter of a turn, thus saving time in putting on and taking
off the driver.
Fig. 761 illustrates a work driver very convenient for turning bolts. It
consists of a piece of iron or plate P bolted to the lathe face plate F,
and having jaws so as to fit to the sides of the bolt B and drive it.
This not only saves the time that would otherwise be required to put on
a driver or carrier but leaves the underneath face of the bolt clear to
be faced up by the turning tool, an example of its use being shown in
connection with the knife tool or facing tool.
[Illustration: Fig. 759.]
[Illustration: Fig. 760.]
Fig. 762 represents a driver of this kind having a sliding jaw so that
it may be set for different sizes of bolt heads. When the driving end of
the work is threaded an ordinary dog or driver cannot be used because
its screw would damage the thread on the work. A common method of
overcoming this difficulty is to place over the ring a split ring of
copper, or to place on it two nuts, putting a common dog on the end nut.
It is better, however, to use a driver, threaded part of the way
through, as in figure 762 (from _The American Machinist_) and to screw
it upon the work.
[Illustration: Fig. 761.]
Fig. 763 represents a very useful form of work driver designed by Mr.
William A. Lorenz. It consists of two jaws A, A held together by two
screws, and threaded to receive two driving screws D, E in the figure,
which enable it to be used to hold work to the live centre as is
necessary when using the steady rest, as is shown in the figure, in
which B represents the work and C the jaws of the steady rest. It is
obvious that the dog may be thus employed to chuck work independently of
the steady rest, because the live centre may be removed, and the face of
the work held against the face of the chuck, the short screws H being
used instead of the long ones D, E.
[Illustration: Fig. 762.]
If the carrier is used to simply drive the work without clamping it to
the live centre or face plate, one or both of the screw pins J, K may be
used in place of bolts D, E, the carrier being balanced when both are
used.
[Illustration: Fig. 763.]
[Illustration: Fig. 764.]
Fig. 764 represents a driver, carrier, or dog threaded in its bore to
drive threaded work, which the screw of the ordinary dog would obviously
damage.
[Illustration: Fig. 765.]
[Illustration: Fig. 766.]
[Illustration: Fig. 767.]
Fig. 765 represents an excellent driver for cored work such as the piece
W. Its hub A is screwed on the live spindle in place of the face plate,
and carries the rods B, B´, both of which are adjustable in the distance
they stand out from A, so that B may be set to suit the work, and B´ set
out sufficiently to balance B and D. The driving arm D is adjustable
along B, and by being bent to the form shown is more out of the way, and
obviates the necessity of using a dog on many kinds of work. The other
end of the work is shown supported by a cone centre C, whose
construction is shown in Figs. 766 and 767. Its object is to avoid the
wear that occurs at the mouth of the hole in cored work, when it is run
on the dead centre, and to avoid the necessity of plugging the hole to
provide a temporary centre. In the figures, A represents a stem (fitting
into the tailstock spindle S, in place of the ordinary dead centre),
having a collar B and carrying the cone C. The work is supported upon C,
which revolves upon the stem of A. At E is a raw-hide washer, intended
to prevent the abrasion which would occur on the faces of B and C. The
pin F prevents C from coming off D, one half of its cross section being
in C, and the other half in a semicircular groove running around D. An
oil groove is provided through the collar B, and passes along the stem
D. This is an exceedingly handy device for cored work, and may also be
used to sustain work against the lathe face plate, while chucking the
work true by its bore.
[Illustration: Fig. 768.]
The work drivers employed by wood turners, for work held between the
lathe centres, are as follows:--
Fig. 768 represents two views of a fork centre to be placed in the cone
spindle of the lathe, and serve as a live centre, while also driving the
work; C is a sharp conical point, which should run true, because it
serves to centre the work; D, E are two wings which enter the wood to
drive it. This device answers well for work that can be finished without
taking it in and out of the lathe, it being difficult to place the work
in the lathe so as to run true after removal therefrom; in case,
however, that this should become necessary, the work should be replaced
so that each wing falls into its original impression. For heavy work
this device is unsuitable, hence the two plates shown in Fig. 769 are
employed, being termed centre plates. They are composed of iron and are
held to the work by screws passing through the respective holes shown at
the corners of the plates. The plate having the round centre hole is for
the dead centre end of the work, while that having the rectangular slot
is for the live centre end of the work. The rectangular slot is made a
close fit to the wings of the fork centre shown in figure. Figs. 770 and
771 represent a spur centre designed to hold pieces of soft wood, that
may be liable to split from the pressure of the centres. The spurs are
made parallel on their outer surfaces, while the inner ones are at an
angle, so as to close the wood around the central point, and not spread
the wood outwards. The plate for the dead centre is formed on the same
principle as is shown in figure 769.
[Illustration: Fig. 769.]
[Illustration: Fig. 770.]
Another form of chuck centre or driving centre for wood work is shown in
Fig. 772, being especially useful when the work cannot be supported by
the lathe dead centre. The body A screws on to the thread on the live
spindle of the lathe, while the work screws on the pointed screw B,
which will hold disc-shaped pieces of moderate diameter, as about 4 or 5
inches, leaving its face to be operated on as may be desired. To prevent
B from splitting the work, or when hard wood is to be turned, a small
hole may be bored up the work to permit B to enter sufficiently easily.
[Illustration: Fig. 771.]
[Illustration: Fig. 772.]
When a piece of work to be turned between the lathe centres is of such a
form that there is no place to receive centres, provision must be made
to supply the deficiency.
[Illustration: Fig. 773.]
In Fig. 773, for example, a temporary centre B is fitted into the socket
to receive the centre.
In small work that has been drilled or bored, a short mandrel is used
instead of the piece B.
[Illustration: Fig. 774.]
If a half-round piece is to be turned it should be forged with a small
projecting piece to receive the lathe centre, as in Fig. 774.
[Illustration: Fig. 775.]
When the end of the work is flat and not in line with the axial line of
the main body of the work, a piece of metal to contain the centre may be
held to the work by a driving clamp, as in Fig. 775, in which A
represents the end of the work and B a temporary piece containing the
centre C. In this case it is best to make the centre C after the piece B
is clamped to the work.
[Illustration: Fig. 776.]
To provide a temporary centre for a piece having a taper hole, a taper
plug is used, as shown in Fig. 776, W representing the work and P the
plug, which must be an accurate fit to the taper of the hole, and must
not reach to the bottom of the hole.
MANDRELS OR ARBORS.--Work (of about 6 inches and less in diameter) that
is bored is driven by the aid of the mandrel or arbor, which is held
between the lathe centres, as in Fig. 777, in which W represents a
washer and M the mandrel, driven into the washer bore so as to drive it
by friction. At A is a flat place to receive the set-screw of the driver
or lathe dog, and at B a flat place upon which the diameter of the
mandrel is marked. The mandrel diameter is made slightly larger at D
than at C, so as to accommodate any slight variation in the diameter of
holes bored by standard reamers, which gradually reduce in diameter by
wear; thus if a reamer be made 1-1/1000 inch diameter, with a limit of
wear of 1/1000 inch, then the mandrel may be made 1 inch at C and
1-1/1000 inch at D. It is well to taper the end of the mandrel from C to
E about 1/2000 inch, so that it may enter the work easily before being
driven in. Instead, however, of driving mandrels into work, it is better
to force them in under a press. If driving be resorted to a lead hammer,
or for very light mandrels a raw-hide mallet, may be used.
[Illustration: Fig. 777.]
[Illustration: Fig. 778.]
In the absence of a lead hammer, a driver, such as in Fig. 778, is a
good substitute, consisting of a socket containing babbitt or some other
soft metal at B (the mandrel being represented by M). If copper be used
instead of babbitt a hole may be drilled through it, as denoted by the
dotted lines.
[Illustration: Fig. 779.]
[Illustration: Fig. 780.]
The centres of mandrels should either have an extra countersink, as at A
in Fig. 779, or else the cut should be recessed as at B, Fig. 780.
Mandrels are best made of steel hardened and ground up after hardening.
If the bore of the work is coned, and of too great a cone to permit the
mandrel to be driven, and drive the work by friction, the cone mandrel
shown in Fig. 781 may be used. M is the mandrel in one piece with the
collar C. The work W is held between two cones A, A, which slide a close
fit upon the mandrel, and grip the work by screwing up the nut N, there
being a thread upon the mandrel, as at S, to receive the nut. It is
obvious, however, that work having a parallel bore may also be held by
the cone mandrel, as shown in Fig. 782.
[Illustration: Fig. 781.]
[Illustration: Fig. 782.]
To obviate the necessity of having the large number of mandrels that
would be necessary so as to have on hand a mandrel of any size that
might happen to be required, mandrels with provision for expanding or
contracting the diameter of the parts used to hold the work are made.
[Illustration: Fig. 783.]
Thus in Fig. 783 is shown Le Count's expanding mandrel, in which G H is
the body of the mandrel, turned parallel along a certain distance, to
fit the bore of the sleeve A, which is a close-sliding fit on this
parallel part of E.
From the end H of the mandrel there extends towards the end G four
dovetail grooves, which receive four keys B. The heads of these four
keys are enclosed and fit into an annular groove provided in the head C
of the sleeve A, so that moving the sleeve A along the mandrel causes
the four keys to slide simultaneously in their respective grooves.
Now these grooves, while concentric at any one point in their transverse
section to the axis of the mandrel, are taper to that axis, so that
sliding the sleeve A along the parallel part of the mandrel increases or
decreases (according to the direction in which A is moved) the diameter
of the keys.
If the sleeve be moved towards the end G, the keys while sliding in
their taper grooves recede from the axis of the mandrel, while if moved
towards H they approach the axis of the mandrel, or what is the same
thing, if the sleeve be held stationary and the body of the mandrel be
moved, the keys open or close in diameter in the same manner; hence all
that is necessary is to insert the mandrel in the bore of the work, and
drive the end G, when the keys will expand radially and grip the work
bore.
The keys, it will be observed, are stepped on their diametral or
work-gripping surfaces, which is done to increase the capacity of the
tool, since each step will expand to the amount equal to the whole
movement of the keys in their grooves or slots.
Mandrels or arbors are sometimes made adjustable for diameter by forcing
a split cone upon a coned plug, examples being given in the following
figures, which are extracted from _Mechanics_. In Fig. 784, A is a cone
having the driving head extending on both sides of the centre so as to
balance it. Over its coned body fits the shell B, which is split, as
shown in Fig. 785, the splits C, D being at a right angle to splits E,
F.
It is obvious that the range of adjustment for such a shell is small,
but several diameters of shell may be fitted to one cone, the thickness
being increased to augment the diameter. The diameter of the shell
should be made to enter the work without driving, the tightening being
effected by screwing the nut up to force the shell up the cone.
[Illustration: Fig. 784.]
[Illustration: Fig. 785.]
[Illustration: Fig. 786.]
[Illustration: Fig. 787.]
[Illustration: Fig. 788.]
[Illustration: Fig. 789.]
[Illustration: Fig. 790.]
Figs. 786, 787, 788, and 789 represent an expanding mandrel designed by
Mr. Hugh Thomas, of New York City. The body B of the mandrel is
provided with a taper section _g_, and either three or four gripping
pieces _a_, _a_, _a_, _a_, let through mortises or slots in a sleeve C,
which fits the body of the mandrel at each end.
This sleeve when forced up the mandrel by the nut D, carries the
gripping pieces along the cone at _g_, and causes them to expand
outwards and grip the bore of the work, which is shown in the end view
in Fig. 788 to be a ring or washer W.
The advantage of this form is that the cone at _g_ can be easily turned
or ground to keep it true, and the gripping pieces _a_ may be fastened
in their mortises by means of the screws shown at _h_ in the end view,
and thus kept true. It is obvious that for long work there may be
gripping pieces at each end of the mandrel, as in Fig. 789, and the work
will be held true whether its bore be parallel, stepped, or taper, a
valuable feature not usually found in expanding mandrels.
[Illustration: Fig. 791.]
When a mandrel is used upon work having its bore threaded the mandrel
also must be threaded, and must abut against a radial face, as at _a_,
in Fig. 790, because otherwise the pressure of the cut would hold the
work still while the mandrel revolved, thus causing the work to traverse
along the mandrel. If the thread of the mandrel be made so tight a fit
that it will drive the work by friction it will require considerable
force to remove the work from the mandrel, so much so, in fact, that
finished pieces would be much damaged in the operation. It is better
therefore to have the work such a fit that it can be just screwed home
against the radial face of the mandrel under heavy hand pressure (if the
work be not too heavy for this, in which case a clamp may be employed).
Small work, as nuts, &c., are turned on a mandrel of this kind, which
has a stem, and fits into the cone or live spindle in the same manner as
the live centre, which will drive work up to about 1 inch in diameter
without fear of slipping. Threaded mandrels that are in frequent use
soon become a loose fit to the work by reason of the thread wear, with
the result that if the face of the work is not true with the thread, it
meets the mandrel shoulder, as in Fig. 791, and as the nut cants over,
one side as T in the figure, is turned too thick. When the nut is
reversed on the mandrel, the turned face will screw up fair against the
mandrel shoulder, and the faces of the nut, though true one with the
other, are not square with the axis of the thread, and will not
therefore bed fair when placed in position upon the work.
[Illustration: Fig. 792.]
To obviate this difficulty we have Boardman's device, which is shown in
Fig. 792. It consists of a threaded mandrel provided with a ring, with
two rounded projections A, A and B, B, on each radial face, those on one
side being at a right angle to those on the other. This ring adapts
itself to the irregular surface of the nut and by equally distributing
the pressure on each side of the nut destroys the tendency to cant over,
hence the nut may be turned true, notwithstanding any irregularity of
its radial faces, and independently of its fitting the arbor or mandrel
thread tightly.
[Illustration: Fig. 793.]
Another form of mandrel for the same purpose is shown in Fig. 793, the
mandrel being turned spherical, instead of having a square shoulder, and
the washer W being cupped to fit, so that the washer will cant over and
conform to the nut surface.
[Illustration: Fig. 794.]
The mandrel thread may be caused to fill the nut thread better if it be
provided with three or more splits A, B, C, Fig. 794, a hole D being
drilled up the centre of the mandrel, the thread may then be turned
somewhat large, the splits permitting the thread to close from the nut
thread pressure.
[Illustration: Fig. 795.]
When a mandrel is fitted to the sockets for the lathe centre, it should
have a thread and nut, as shown in Fig. 795, so as to enable its
extraction from the socket without striking it, as has been described
with reference to lathe centres.
[Illustration: Fig. 796.]
[Illustration: Fig. 797.]
Mandrels may be employed to turn work, requiring its outside diameter to
be eccentric to the bore, by the following means:--In Fig. 796, let the
centre C represent the centre of the mandrel, and D a centre provided in
each end of the mandrel, distant from C to one half the amount the work
is required to be eccentric. The mandrel must be placed with the centres
D receiving the lathe centres. In this operation great care must be
taken that a radial line drawn on each end of the mandrel, and passing
through the centre of the centres D, shall exactly meet and coincide
with the line L drawn parallel to the axis of the mandrel. If this be
not the case the work will be less eccentric at one end than at the
other. As it is a somewhat difficult matter to test this and ascertain
if the mandrel has become out of true from use, it is an excellent plan
to turn such a mandrel down at each end, as shown in Fig. 797, and draw
on it the lines L, L, which correspond to the line L L in Fig. 796. If
then a steel point be put in the lathe rest and fed in to the work, so
that revolving the latter just causes the tool point to touch the lines
L at each end, or if the tool point makes long lines as at _a_, _a_, the
two lines L, L, should intersect the lines _a_, _a_ at the centre of
their respective lengths. The lines L L should be marked as fine as
possible, but deep enough to remain permanently, so that the truth of
the eccentricity of the mandrel may be tested at any time. An equivalent
device is employed in turning the journals of crank shafts, as is shown
in Figs. 798 and 799, in which D, D are two pieces fitted on the ends of
the crank shaft, being equal in thickness to the crank throw, as shown
at A, B in the figure, so that when D, D lie in the same plane as the
crank cheeks (as when all will lie level on a plate, as in the figure)
the centres C will be in line with the journal in the crank throw.
Pieces D are broadened at one end to counterbalance the weight of the
crank, which will produce more true work than counterbalancing by means
of weights bolted to the face plate of the lathe, as is sometimes done,
causing the crank throw to be turned oval instead of round. In the case
of a double crank, however, the centre pieces cannot be widened to
counterbalance, because what would counterbalance when the centres A in
Fig. 799 were used, would throw the crank more out of balance when
centres B were used for the throw B. In this case, therefore, the centre
pieces are provided with seats for the bars E, E, which may be bolted on
to carry the counterbalancing weights, the bars being changed on the
centre pieces when the centres are changed. The bars, for example, are
shown in their position when the centres A are being used to turn up the
journal A, the necessary amount of weight for counterbalancing being
bolted on them with a set-screw through the weight.
[Illustration: Fig. 798.]
[Illustration: Fig. 799.]
The centres are steel plugs screwed tightly into the pieces D, and are
hardened after being properly centre-drilled and countersunk.
[Illustration: Fig. 800.]
To enable the pieces D to be easily put on and taken off, it is a good
plan to make the bore a tight fit to the shaft and then cut it away as
at E, as shown in Fig. 801, using set-screws to hold it.
[Illustration: Fig. 801.]
Great care is necessary in putting in the work centres, since they must,
if the crank throws are to be at a right angle one to the other, as for
steam engines, be true to the dotted lines in figure, these dotted lines
passing through the centre of the axle and being at a right angle one to
the other. If the thickness of the centre pieces are greater than the
crank throws they may be adjusted as in Fig. 800, in which B, B´
represent the centre pieces, and C the crank, while S is a
straight-edge; the edge surfaces of B, B being made true planes parallel
to each other on each arm, and parallel to the axial line of the bore
fitting the end of the crank axle.
The straight-edge is pressed at one end, as at F, firmly to an edge face
of B, the other end being aslant so as not to cover the edge of the
piece B´ at the opposite end of the crank (as shown at G, Fig. 801).
While being so pressed the other end must be swung over the end arm of
B´ at the opposite end of the crank, when the edge of the straight-edge
should just meet and have slight contact with the surface of the edge
of B´. This test should be applied to all four edges of B, and in two
positions on each, as at G, H--I, J, and for great exactitude may be
applied from each end of the crank. It is to be observed, however, that
the tests made on the edges standing vertical, as at I, J, will be the
most correct, because the straightness of the straight-edge is when
applied in those positions not affected by deflection of the
straight-edge from its own weight.
In shops where such a job as this is a constantly recurring one
attachments are added to a press of some kind, so that the axle and the
pieces B may be guided automatically and forced to their proper places,
without requiring to be tested afterwards.
[Illustration: Fig. 802.]
When the work is sufficiently long or slender to cause it to sag and
bend from its own weight, or bend from the pressure of the cut, it is
supported by means of special guides or rests. Fig. 802 represents a
steady rest of the ordinary pattern; its construction being as
follows:--F is a base fitting to the [V]s of the lathe shears at F, and
capable of being fastened thereto by the bolt C, nut N, and clamp A. F´
is the top half of the frame, being pivoted at P to F, the bolt P´
forming the pivot for both halves (F and F´), of the frame, which may be
secured together by the nut of P´. On the other side of the frame the
bolt is pivoted at _b_ to F. This bolt passes through an open slot in
F´, so that its nut being loose, it may swing out of the way as denoted
by the arrow _e_, and the top half frame _f´_ may be swung over in the
direction of arrow _g_, the centre of motion or pivot being on the bolt
P´. With F´ out of the way the work may be placed within the frame, the
nut of B and also that of P´ may be tightened up so as to lock the two
halves of the frame firmly together.
On this frame and forming a part of it are the three ways, G G´ G´´,
which contain cavities or slide ways to which are fitted and in which
may slide the respective jaws J, and to operate these jaws are the
respective square-headed screws S, which are threaded through the tops
of the respective ways G, G´, and G´´. The screws are operated until the
ends of the jaws J have contact with the work W, and hold it axially
true with the line of centres of the lathe, or otherwise, as the nature
of the work may require. When adjusted the jaws are locked to the frame
by means of the bolts D, which are squared to fit in the rectangular
openings, shown at _h_ in the respective jaws, so as to prevent the
bolts from rotating when their locking nuts _d_ are screwed home.
As an example of the use of this device as a steadying rest, suppose a
long shaft to require turning from end to end and to be so slight as to
require steadying, then a short piece of the shaft situated somewhat
nearer the live centre than the middle of the length of the work is
turned upon the work, so that this place shall be round and true to
receive the jaws, or plates _p_, and revolve smoothly in them. The jaws
are then adjusted to fit the turned part a close sliding fit, but not a
tight fit, as that would cause the jaws to score the work. To prevent
this even under a light pressure of contact, oil should be occasionally
supplied. This steadies the work at its middle, preventing it from
springing or trembling when under the pressure of the cut.
By placing the steady rest to one side of the middle of the work length,
at least one half of that length may be turned before reversing the work
in the lathe centres. After reversing the work end for end in the lathe
centres, the jaws, or plates _p_, are adjusted to the turned part, and
the turning may be completed.
In adjusting the plates _p_ to the work, great care is necessary or they
will spring the work out of its normal line of straightness, and cause
it to be out of parallel, or to run out of true in the middle of its
length, as explained in the remarks referring to the cat head shown in
Fig. 809.
The plates _p_ should be gripped to the frame by the nuts with
sufficient force to permit them to be moved by the set-screw S under a
slight pressure, which will help their proper adjustment. They should
also be adjusted to just touch the work, without springing it, the two
lower ones being set up to the work first, so that their contact shall
serve to relieve the work of its spring or deflection, due to its own
weight. This is especially necessary in long slender spindles, in which
the deflection may occur to a sensible degree.
If the work does not require turning on its full length, the steady rest
may be applied but a short distance from the length of the part to be
turned, so as to hold the work more steadily against the pressure of the
cuts.
Steady rests are often used to support the end of work without the aid
of the dead centre, but it is not altogether suitable for this class of
work, because it has no provision to prevent the work from moving
endways and becoming loose on the dead centre. A provision of this kind
is sometimes made by tying the work driver to the face plate or to the
pins driving the work driver or dog, or bolts and plates holding the
work driver towards the lathe face plate; but these are all
objectionable in that unless the pressure thus exerted be equal, it
tends to spring or bend the work.
Another method of preventing this is to drive the work by means of a
universal chuck; but this again is objectionable, because the jaws of
these chucks do not keep dead true under the wear, and indeed if made to
run concentrically true (in cases where the chuck has provision for that
purpose) the gripping surfaces of the chuck jaws have more wear at the
outer than at the inner ends, hence those surfaces become in time
tapering. Again the jaws wear in time so easy a fit in their radial
slots that they spring under pressure, and the wear not being equal, the
amount of spring is not equal, so that it is impracticable to do dead
true work chucked in this way.
The reasons that the chuck jaws do not wear equal in the radial slots
may be various, as the more frequent presence of grit in one than in the
other, less perfect lubrication, inequalities in the fit, less perfect
cleaning, and so on, so that it is not often that the wear is precisely
equal. In addition to these considerations there are others rendering
the use of the steady rest in some cases objectionable; suppose, for
example, a piece of cylindrical work, say 6 feet long, to have in one
end a hole of 2 inches diameter, which requires to be very true (as, for
example, the cone spindle for a lathe). Now let the face plate end be
driven as it may, it will be a difficult matter to set the steady rest
so as to hold the other end of the work in perfect line, so that its
axial line shall be dead true with the line of lathe centres, because
the work will run true though its axial line does not stand true in the
lathe.
Here it may be added that it will not materially aid the holding of the
work true at the live centre end, by placing it on the live centre and
then tightening the universal chuck jaws on it, because the pressure of
those jaws will spring it away to some extent from the live centres.
This will occur even though the work be placed between the two lathe
centres, and held firmly by screwing up the dead centre tight upon the
work, before tightening the chuck jaws upon the work, because so soon as
the pressure of the dead centre is removed, the work will to some extent
relieve its contact with the live one.
If the jaws of the chuck are not hardened, they may be trued up to suit
a job of this kind as follows:--A ring (of such a size that when gripped
in the outer steps of the chuck jaws, the inner steps will be open to an
amount about equal to the diameter of the work at the live centre end)
may be fastened in the chuck, and the inner ends of the jaws may be
turned up with a turning tool, in which case the jaws will be made true
while under pressure, and while in the locations upon the chuck in which
they will stand when gripping the work, under which conditions they
ought to hold the work fairly upon the live centre. But even in this
case the weight of the work will aid to spring it, and relieve it from
contact with the live centre.
[Illustration: Fig. 803.]
Now let us suppose that the piece of work is taper on its external
diameter at each end, even truing of the chuck jaws will be of no avail,
nor will the steady rest be of avail, if the taper be largest at the
dead centre end. Another form of steady rest designed to overcome these
objectionable features is shown in Fig. 803. In this case the stand that
is bolted to the lathe bed is bored to receive a ring. This ring is made
with its middle section of enlarged diameter, as denoted by the dotted
circle C. Into the wide part of the stand fits a ring F, its external
diameter fitting into C. The ring carries the jaws, hence the ring is
passed over the work, and is then inserted into the stand, while the
work is placed between the lathe centres.
The ring revolves with the work and has journal bearing in the stand,
the enlarged diameter C preventing end motion. There is nothing here to
take up the lost motion that would in time ensue from the wear of the
radial faces of the ring, hence it is better to use the cone-plate shown
in Fig. 805.
[Illustration: Fig. 804.]
When, however, the work will admit of being sufficiently reduced in
diameter, it may be turned down, leaving a face F in Fig. 804, that may
bear against the radial faces of the jaws of the steady rest; or a
collar may be set upon the work as in Fig. 804 at C. But these are
merely makeshifts involving extra labor and not producing the best of
results, because the radial face is difficult to keep properly
lubricated, and the work is apt to become loose on the live centre.
[Illustration: Fig. 805.]
For these reasons the cone plate shown in Fig. 805 is employed; A is a
standard fitting the shears or bed of the lathe and carrying the
circular plate C by means of the stud B, which is fitted so as to just
clamp the plate C firmly to the frame A when the nut of B is screwed
firmly home with a wrench.
The plate C contains a number of conical holes, 1, 2, 3, &c., (as shown
in section at D) of various diameters to suit varying diameters of work.
The frame is fitted to the lathe bed so that the centre stud B stands
sufficiently out of the line of lathe centres to bring the centres of
the conical holes true with the line of lathe centres. The centres of
the conical holes are all concentric to B. Around the outer diameter of
the cone plate are arranged taper holes G, so situated with reference to
the coned holes that when the pin, shown at G in the sectional view,
will pass through the plate and into the frame A as shown, one of the
coned holes will stand axially true with the line of lathe centres.
Hence it is simply necessary to place one end of the work in the live
centre, with a work driver attached in the usual manner; to select a
coned hole of suitable size; to move the frame A along the lathe bed
until it supports the overhanging end of the work in a suitably sized
coned hole without allowing the work any end motion, and to then fasten
the frame A to the lathe bed, and the work will be ready to operate on.
The advantages of this device are that the pin shown at G in the
sectional view holds the conical hole true, and thus saves all need of
adjustment and liability to error, nor will the work be sprung out of
true, furthermore the tool feed may traverse back and forth, without
pulling the work off the live centre. With this device a coarse pitch
left-hand internal thread may be cut as easily as if it were an external
thread and the work was held between the lathe centres, heavy cuts being
taken which would scarcely be practicable in the ordinary form of steady
rest.
The pins B and G and the coned holes should be of cast steel hardened,
so as to avoid wear as much as possible. The plate may be made of cast
iron with hardened steel bushes to fit the coned holes.
It is obvious that the radial face of the work at the cone plate end, as
well as the circumference, must be trued up, so that the work end may
have equal contact around the bore of the coned rings.
[Illustration: Fig. 806.]
[Illustration: Fig. 807.]
Figs. 806 and 807 represent a class of work that it would be very
difficult to chuck and operate on without the aid of a cone plate. The
former requires to have a left-hand thread cut in its bore A, and the
latter a similar thread in end A. A universal chuck cannot be used to
drive the work, because in the former case it would damage its thin
edge, and in the latter the jaws would force the work out of the chuck;
a steady rest cannot be used on the former on account of its being
taper, while if used on the latter there would be nothing to prevent the
work from moving endwise, unless a collar be improvised on the stem,
which on account of the reduced diameter of the stem would require to
be made in two halves. It can, however, be driven on the live centre by
a driver or dog, and supported at the other end by the cone plate
without any trouble, and with an assurance of true work.
[Illustration: Fig. 808.]
Fig. 808 represents a form of steady rest designed by Wm. MacFaul, of
the Freeland Tool Works, for taper work. The frame affords journal
bearing to a ring A, having four projections B, to which are a close but
easy sliding fit, the steadying jaws C. These are held to the work or
cue blank W by the spiral springs shown in the projections or sockets B,
which act against the ends of C. It will be observed that the work being
square could not move in any direction without moving sideways the two
of the steadying jaws C which stand at a right angle to that direction.
But the jaws C fit the bore of the sockets, and cannot, therefore, move
sideways; hence it is evident that the work is firmly supported,
although the steadying jaws are capable of expanding or contracting to
follow the taper of the blank cue or other piece of work. This enables
the steady rest to lead the cutting tool instead of following it, so
that the work is steadied on both sides of the tool. Obviously, the
stand may be fastened to the leading side of the lathe carriage or
fitted upon the cross-slide, as may be most convenient.
[Illustration: Fig. 809.]
To steady work that is unturned and of so great a length that it springs
too much to permit of its being turned true, the sleeve or cat head
shown in Fig. 809 is employed; it may contain three or four screws C, to
true it upon the work. The body B is turned true.
The set-screws are so adjusted upon the work, that the outside runs
quite true from end to end. The jaws of the steady rest are then set to
just touch the circumference of the sleeve, care being taken that their
pressure does not spring the axial line of the work out of its normal
straight line. If the shaft is to be turned from end to end, the cat
head should be placed sufficiently to one side of the centre of the
length of the work and nearer the live centre, that the lathe tool may
turn up the work for a distance of at least half its length, or slightly
more than half. One half of the work being turned, the shaft is reversed
end for end in the lathe, when the cat head may be moved to envelop the
turned part, and again set true, or the jaws of the steady rest may be
set direct upon the work; in this latter case, however, the friction
between the jaws and the work will be apt to leave rings or marks upon
the latter.
If the cat head is not set to run quite true upon the work, the latter
will not run true when the steady rest is removed, and if the jaws of
the steady rest spring the axial line of the work out of its normal
straightness, the work will be turned either larger or smaller in
diameter in the middle of its length, according to the direction in
which the work is sprung.
Suppose, for example, that the work is sprung laterally towards the tool
point, then the work will be turned smaller in the middle, or if the
work were sprung laterally in the opposite direction, it would be turned
larger in the middle than at the ends. If the work is sprung vertically
so as to approach or recede from the lathe bed, the amount of the error
will be less than if it were sprung laterally, and the nature of the
error will depend upon the height of the cutting tool with relation to
the work. If, for example, the point is above the centre of the work,
and the latter is sprung towards the lathe bed, the work will turn of
largest diameter in the middle of its length; or with the tool point
placed at the centre of the work, the same result will follow, whether
the work be sprung up or down; but if the work be sprung up or away from
the lathe bed, and the tool point be placed above the centre, the
diameter of the work will be turned smaller than that at the ends.
[Illustration: Fig. 810.]
When the work is to be turned from end to end or for a considerable
distance, a follower rest such as shown in Fig. 810 should be employed,
being similar to the steady rest shown in Fig. 802, except that it is
open in front, and being fastened to the slide rest carriage, of course
travels with the tool; hence the plates P may be either directly in
front of the tool or following it, but if the work W has been turned
true and parallel, the plates P may be in front of the tool, or rather
may lead it.
[Illustration: Fig. 811.]
[Illustration: Fig. 812.]
The follower rest should always be set to the work when as near as
practicable to the dead centre, in which case it will be easier to set
it without springing the work.
For work of small diameter for which the plates P would be too large,
and therefore in the way, the plate P, Fig. 811, may be used, being
bolted to the follower rest. For work of larger diameter the device
shown in Fig. 812 is sometimes used. It consists of a plate P with a
cap C, and bolts for holding the bearings B, B. These bearings are bored
slightly larger in diameter than the finished diameter of the work.
The advantage of the use of this device is that bearings of the
requisite bore having been selected they may be inserted and adjusted a
proper fit to the work before P is fastened to the follower rest, thus
avoiding the liability of being either too tight or too loose as may
happen when the plates cannot be moved or rotated to test the fit.
Another and great advantage is that if after the adjustment of the
bearings B, B to the work, the plate P is carefully bolted to the
follower rest, the liability of springing the work is eliminated, hence
truer work will be produced.
[Illustration: Fig. 813.]
A representative of another class of follower rest is shown in Fig. 813,
the hub H is accurately bored to receive collars or rings of various
diameters of bore to suit the work. The bore of H may be made to stand
axially true with the lathe centres, and thus avoid the trouble of
setting, by employing the steady pin S, which, being a close fit in the
follower rest and in the lathe carriage will bring the rest to its
proper distance from the lathe centres, where it may be secured by the
bolt B, which may screw into the metal of the carriage or operate to
lift a wedge or guide slip so as to grip the [V]-slide of the carriage
and take up any lost motion between the slide in the rest and that in
the lathe carriage.
[Illustration: Fig. 814.]
Fig. 814 shows a follower rest in position on the cross slide of a
lathe.
CHUCKS AND CHUCKING.
There is a large class of small work that could be held between the
lathe centres, but that can be more conveniently held in chucks. Chucks
are devices for holding work to the live spindle, and may be divided
into classes as follows:
1st. Those in which the work is secured by a simple set-screw.
2nd. Drill chucks, which are applied mainly to drive drills, but which
may also be used to drive very small work to be operated upon by cutting
tools, the mechanism causing the jaws to move simultaneously to grip or
release the work.
3rd. Independent chucks, in which the jaws are operated separately.
4th. Universal chucks, which are larger than drill chucks, and in which
the jaws operate simultaneously.
5th. Combination chucks, in which the jaws may be operated either
separately or simultaneously as may be required.
[Illustration: Fig. 815.]
Referring to the first, Fig. 815 represents a simple form of set-screw
chuck, the stem S fitting into the live centre hole, and the outer end
being pierced to receive a drill shank, and the iron from which a piece
of work may require to be turned, which is secured in the chuck by the
set-screw B. In the case of drill or other cutting tools, however, it is
better that they be provided with a flat place A, to receive the
set-screw pressure, and enable it to hold them more securely. The
objections to this class of chuck are threefold: First, each chuck is
suitable for one diameter of work only; secondly the screw head B is in
the way; and thirdly, the set-screw pressure is in a direction to set
the work out of true, which it will do unless the work is a tight fit to
the bore of the chuck. In this case, however, it is troublesome to
insert and remove the drill, unless the bore of the socket is relieved
on the half circumference nearest to the set-screw, as shown at C in the
end view, in which case the efficiency of the chuck is greatly enhanced.
[Illustration: Fig. 816.]
Referring to the second class they are made to contain either two or
three jaws.
[Illustration: Fig. 817.]
When two jaws are employed they are made to slide in one slideway, and
are operated therein by a right and left-handed screw, causing them to
simultaneously advance or recede from the chuck axis. Fig. 816
represents a chuck of this class, the jaws fitting one into the other to
maintain each other in line, and prevent their tilting over from the
pressure.
In scroll chucks the mechanism for operating the jaws is constructed
upon two general principles. The first may be understood from Fig. 817,
in which the body of the chuck is provided upon its end face with a
scroll C, with which the ends of the jaws A engage. These jaws fit into
radial slots in the shell E, which is capable of rotation upon B and is
held thereto by the cap D; hence rotating E carries around the jaws A,
and the thread C causes them to approach or recede from the chuck axis,
according to their direction of rotation.
[Illustration: Fig. 818.]
The second general principle upon which small drill chucks are
constructed may be understood from Fig. 818, in which C may be taken to
represent the end of a lathe spindle or a stem fitting into the live
centre hole in the same. At the other end it is to receive the shell D
which screws upon it. D is coned at the outer end of its bore, and the
jaws E are made to fit the cone, and it is obvious that if D be rotated
to screw farther upon C, the coned bore of D will act to force the jaws
E nearer to the chuck axis and cause them to close upon and grip the
work. To operate D it is knurled or milled at G, or it may have pin
spanner holes as at H. In this class of chuck it is essential that the
direction of rotation of D to close the jaws must be opposite to that in
which the drill rotates, otherwise the resistance of the work against
the jaws would cause D to rotate upon C, and the work to become released
from the jaw grip. Furthermore, as the larger the work the more severe
the duty in driving it, it is usually provided by the construction of
such chucks that the jaws shall be opened to their maximum when at their
nearest approach to the body (as C) of the chuck, and shall close as
they move outward or away from the same. This principle of moving the
jaws radially by means of a cone sliding upon a cone is applied in
numerous ways, thus sometimes the jaws are provided with wings that
slide upon a cone or in slide ways that are at an angle to the chuck
axis.
[Illustration: Fig. 819.]
[Illustration: Fig. 820.]
[Illustration: Fig. 821.]
Figs. 819, 820, and 821 represent Gage's patent chuck, in which the
gripping surfaces of the jaws are serrated to increase the grip, and to
further secure the same object the jaws move at an angle instead of in a
radial line, so that the body of the jaws is more directly in the line
of strain, and therefore resists it better. The serrations are
left-handed, so that the tendency is to force the drill forward and
toward the cut, supposing them to act as a nut and screw upon the drill
shank. The jaws are supported by the central cylindrical piece that
contains them out to the extreme end, and have in addition a lug which
slides in radial grooves. Fig. 819 is a side elevation, with a piece of
the shell removed to show the jaw and its slide way, and an end view
showing the arrangement of the jaws. Fig. 820 is a sectional side
elevation, and Fig. 821, two views of the jaws removed from the chuck; A
represents the jaws with the lug E to slide in the radial slots provided
in B. The wings A´ of the jaws slide in the ways in B, the ways passing
through the opening F in Fig. 821; C is the cone for causing the jaws to
open and close radially. The driving piece H has A left-hand thread
operating in B. It also has a collar abutting over one side against the
end of B, and secured on the other by the cap I, which threads into the
shell G. A pin in C secures it to the cap I, so that if rotated both
move together. On the other hand, if H be rotated and G is held
stationary, the thread on H operates on B as a nut, causing it to slide,
carrying the jaws with it, and the jaws are simultaneously opened or
closed according to the direction of rotation of H. Fig. 819 shows the
jaws screwed partly out, and therefore partially closed, while in Fig.
820 the jaws are shown within the chuck, and therefore opened to their
fullest extent.
[Illustration: Fig. 822.]
Figs. 822 and 823 represent a chuck employed by the Hancock Inspirator
Co., of Boston, for very true work. This chuck will not get out of true
by wear, and holds brass work against a good lathe-cut without indenting
it.
Fig. 822 shows the chuck complete. Fig. 823 is a mid-section of chuck
complete. Fig. 824 is a side and an end of the work-gripping piece. The
chuck is composed of three pieces, A, B and C. Piece A screws upon the
lathe spindle and is bored to receive C; piece B screws upon A and
receives the outer end of C, which is provided with a double cone D E,
and is split nearly its full length at three places, one of which is
shown at F, so that when B is screwed upon A the two cones upon A, B
compress C, and cause the diameter of its bore to decrease and grip the
work. The splits F are made long, so that C shall not close at its outer
end only, but on both sides of the cones, and thus grip the work
parallel.
There are several advantages in this form of construction; thus the
parallel bore of A, in which C fits, is not subject to strain or wear,
and therefore remains true and holds C true. Furthermore, B has no
tendency to wear out of true, because it fits upon A at the part G, as
well as at its threaded end, while the cone E of C also acts to keep it
true. As B is screwed up with a wrench fitting its hexagon exterior, the
work can be held against any amount of cut that the lathe will drive.
[Illustration: Fig. 823.]
It is obvious that the capacity of the chuck, so far as taking in range
of different diameters, is quite limited, but the excellence of its
execution far more than compensates for this when work is to be turned
out true and correct to standard gauge.
To increase the range of capacity of the chuck, the split piece only
needs to be changed. Before hardening the split piece the jaws should be
sprung well apart, so that they will spring open when released by
unscrewing the outside shell to release the work and insert another
piece.
[Illustration: Fig. 824.]
In proportion as the diameter of the work is increased it requires to be
more firmly held, and the chucks are made with jaws moved by screws
operated by wrench power. These chucks are made with two, three, or four
jaws, and the bite of the jaw is shaped to suit the nature of the work,
the gripping area being reduced for very small work, and serrated
parallel to the chuck axis so as to form gripping teeth for firmly
gripping rough work, as shown in some of the following examples:--
[Illustration: Fig. 825.]
[Illustration: Fig. 826.]
Figs. 825 and 826 represent the Horton two-jawed chucks with false or
slip jaws, which are removable so that jaws of various shapes in the
bore may be fitted to the same chuck, thus enabling the jaws to be
varied to suit the shape of the work to be held. The jaws are secured in
place by the pins shown.
[Illustration: Fig. 827.]
Fig. 827 shows a two-jawed solid jaw chuck, the bite of the jaws being
made hollow, so as not to mark the surface of the work, while they will
hold it very firmly.
In Fig. 828 is shown what is termed a box-body two-jawed chuck, which is
mainly used by brass turners. The object of this form of body is to
permit the flanges, &c., of castings escaping the face of the chuck.
Fig. 829 also represents a two-jawed chuck, the body being cylindrical,
and having a [V]-groove at A to receive the work. The screws C, D may
act independently of each other, or a continuous screw may be used,
having, as in the figure, a left-hand thread at C, and a right-hand one
at D, so that the jaws move simultaneously when the screw is operated.
The difference between these two methods being as follows:--
When one screw is used the jaws will hold the work so that the centre of
rotation will be midway between the points of contact of the jaws of the
chuck and the work, hence work cannot be set eccentrically, unless
pieces of iron are inserted between it and one of the jaws. When two
screws are used the jaws may be operated separately, and one jaw may be
set to such distance from the centre of rotation as the necessities of
the work may require; but in this case more adjustment is required to
set either square or cylindrical work to rotate on its axis than when
the jaws operate simultaneously as with a right and left-hand screw. It
is obvious that the axial line of the screw or screws must stand
parallel with the plane of the face F. It will be observed that the back
of each jaw is cut away at B: this serves two purposes, first it permits
of a piece of work having a small flange, head or projection being held
in the [V]s of the jaws; and secondly, it equalizes the wear on the jaws
of the chuck, because in jaw chucks generally there is more wear at the
outer than at the inner end of the jaws, because work shorter than the
length of the jaws, or requiring to be held as far out from the jaws as
possible, does not have contact at the back end of the work holding jaw
faces, hence the jaws are apt to wear, in course of time, taper. By
cutting away the jaws at the back, the tendency to unequal wear is
greatly reduced, hence this plan is adopted to a more or less degree in
the dogs or jaws of all chucks, being in many cases merely a small
recess from 1/16 to 1/8 inch deep only.
[Illustration: Fig. 828.]
When the jaws have a [V]-groove as in the cut, the face F of the chuck
does not form a guide in setting the work, the truth of the [V]-grooves
being solely relied upon for that purpose.
[Illustration: Fig. 829.]
[Illustration: Fig. 830.]
The form of two-jawed chuck shown in Fig. 830 is intended for square or
rectangular work, and is mainly used by wood workers. It may be operated
by a right and left-hand screw, but is generally preferred with
independent screws. The face F of the chuck may be employed to serve as
a guide in setting the work as shown in the cut, in which W represents a
piece of work held between the jaws A, A, and resting against the face
F, which therefore serves as a guide against which to set the work to
insure that its axial line shall stand parallel with the face F, or in
other words at a right angle to the line of centres of the lathe.
[Illustration: Fig. 831.]
In Fig. 831 is an example of a machinist's two-jawed chuck. The jaws are
operated simultaneously by a right and left-hand screw. The jaws are
provided with slides to receive the two separate pieces shown in figure,
which may be made to suit the form of special work. The two screws shown
on each side of the chuck face are to support a piece of work that is
too large to be otherwise held firmly by the chuck. These screws may be
operated by screw-driver wrench, to enable the face of the work to rest
on them, and therefore be supported parallel or true with the chuck
face. The jaws may be turned end for end in their slide ways as shown in
Fig. 833, to enable them to grip work of small diameter, the separate
pieces shown in Fig. 832, being placed on the jaws for such small pieces
as drills, &c.
[Illustration: Fig. 832.]
In the larger sizes, lathe chucks are provided with either three or
four jaws, which are caused to operate either independently or
simultaneously, and in some cases the construction is such that the same
chuck may be used as an independent or as a universal one at will, in
which case they are termed combination chucks. Concerning the number of
jaws it may be observed that a three-jawed chuck will hold the work with
an equal pressure on all three jaws, whether it be cylindrical or not,
but in a four-jawed chuck the jaws will not have an equal grip upon the
work, unless the same be either cylindrically true or square, hence it
is obvious that a three-jawed chuck is less liable to wear out of true,
and is also preferable for holding unturned cylindrical work, while it
is equal to a four-jawed one for true, but unsuitable for square work.
[Illustration: Fig. 833.]
[Illustration: Fig. 834.]
Fig. 834 represents the construction of the Horton chuck. Upon the
screws that operate the jaws are placed pinions that gear into a
circular rack, so that by operating one jaw with a wrench the rack is
revolved and the remaining jaws are operated simultaneously. The chuck
being constructed in two halves, the rack may be removed and the jaws
operated separately, or independently as it is termed.
[Illustration: Fig. 835.]
Fig. 835 represents one of the jaws with its operating screw and pinion
removed from the chuck. The gripping surfaces of the steps in the jaws
are serrated to increase their grip upon the work, and the nuts A, A,
against which the works rests, are ground true with the face of the
chuck. The corner between the faces A and the bite or gripping surfaces
of the jaws are recessed so that the work cannot bind in them, but will
bed fairly against the faces A, A, which serve to set the work against
and hold it true instead of the face of the chuck.
[Illustration: Fig. 836.]
Fig. 836 represents a Horton chuck for work up to four inches diameter.
[Illustration: Fig. 837.]
Fig. 837 represents a similar chuck for all sizes between 4 and 15
inches, the designated sizes of the chuck being 6, 9, and 12 inches,
these diameters being the largest the chucks will take in.
[Illustration: Fig. 838.]
Fig. 838 represents a Horton chuck with outside bites for opening out to
grip the bores of rings or other hollow work.
The term scroll chuck is applied to universal chucks in which the jaws
are operated throughout their full range by means of a scroll thread
such as was shown in Fig. 817. The objection to this form is that the
threads on the jaws cannot be made to have a full bearing in the scroll
thread.
[Illustration: Fig. 839.]
In Fig. 839, for example, let A A and B B represent grooves between the
scroll threads, and if the thread on the jaws be made to the curve and
width of A A, it would not pass in that of B B, and _vice-versâ_, and it
would take but five revolutions of the thread to pass a nut thread from
A to B. To overcome this difficulty the jaw threads are not made correct
to either curvature but so formed as to fit at points C, D, E, when in
the groove A and at points F, G, H, when in groove B. This obviously
reduces their bearing area and therefore their durability. To avoid this
defect the jaws of many universal chucks are operated by screws in the
same way as independent jaw chucks, but provision is made whereby the
operation of any one of the jaw screws will simultaneously operate all
the others, so that all the jaws are moved by the operation of one
screw.
Thus in the following figures is shown the Sweetland chuck.
[Illustration: Fig. 840.]
Fig. 840 represents the chuck partly cut away to show the mechanism,
which consists of a pinion on each jaw screw, and a circular rack
beneath. The rack is shown in gear with a pinion at O, and out of gear
with a pinion at C, which is effected as follows:--
The rack is stepped, being thicker at its outer diameter, and the thin
part forms a recess and the shoulder between the thick and thin part
forms a bevel or cone. Between this circular rack and the face of the
plate at the back of the chuck is placed, beneath each jaw, a cam block
bevelled to correspond with the bevelled edge of the recess in the ring.
The cam block stem passes through radial slots in the face of the chuck,
so that it can be moved to and from the centre of the chuck. When it is
moved in, its cam head passes into the recess in the ring rack, which
then falls out of gear with the jaw screw pinion; but when it is moved
outward the cam head slides (on account of the bevelled edges) under the
ring rack and puts it in gear with the jaw screw pinion. Thus, to change
the chuck from an independent one to a universal one all that is
necessary is to push out the bolt heads on the cam block stems, the said
heads being outside the chuck. The washers beneath these heads are
dished to give them elasticity and enable them to steady the cams
without undue friction.
[Illustration: Fig. 841.]
To enable the setting of the jaws true for using the chuck as a
universal one, after it has been used as an independent one, a ring is
marked on the face, and to this ring the edges of all the jaws must be
set before operating the cams radially to put the rack ring in gear. In
Fig. 841 a three-jawed chuck on this principle is shown acting as an
independent one to hold an eccentric. On account of the spring of the
parts, which occurs when the strain is transmitted from one part to
another, it is desirable when using the chuck as a universal one to
first operate one screw to grip the work and then pass to the others and
operate them so that they may receive the pressure direct from the screw
head and not entirely through the medium of the rack, and there will be
found enough movement of the screws when thus operated to effect the
object of relieving the rack to some extent from strain.
[Illustration: Fig. 842.]
[Illustration: Fig. 843.]
[Illustration: Fig. 844.]
Figs. 842, 843, 844, and 845 represent Cushman's patent combination
chuck, in which each jaw may be operated independently by means of its
screw thread, or a circular rack may be made to engage with the
respective pinions, as shown in Fig. 844, in which case operating any
one of the screws operates simultaneously all the jaws. The method of
engaging and disengaging is shown in Fig. 845. C represents the circular
rack and D a circular ring beneath it. This ring is threaded on its
circumference, screwing into the body of the chuck, so that revolving it
in one direction moves the circular rack forward and into mesh with the
pinions, while revolving it backward causes the rack to recede from the
pinions. To operate this ring the lug shown near the top of the chuck in
figure is simply pushed in the required direction, while to lock the
ring when out of gear with the pinions the spring catch shown on the
left of that figure is moved radially. When the rack is in gear, the
chuck is a universal one, all the jaws moving simultaneously and
equally, whether they be set in such position in their slots as may be
necessary to grip an oval or round piece of work; when the rack is out
of gear the jaws may be moved by their respective screws so as to run
true as for round work, or to hold the work to any degree of
eccentricity required.
[Illustration: Fig. 845.]
The jaws may be reversed in their slots and operated simultaneously as a
universal chuck, or independently as a simple jaw chuck.
It is obvious that the truth of the jaws for concentricity may be
adjusted within the degree of accuracy due to the number of teeth in one
pinion divided into the pitch of the jaw operating screw, because each
screw may be revolved separately to bring each successive tooth into
mesh until the greatest obtainable jaw truth is secured.
[Illustration: Fig. 846.]
Fig. 846 represents a front, and Fig. 847 a sectional view, of the
Westcott combination chuck. F is the main body of the chuck screwing on
to the lathe spindle. F carries the annular ring D, which has a thread
on its face, as shown. D is kept in place by the ring E, which screws in
an annular recess provided in the back of the chuck. C is a box fitting
in the radial slots of the chuck. The back of the box C meshes into the
radial thread on D, hence, when D is revolved, the boxes C move radially
in the slots. Now the boxes C afford journal bearing to, and carry the
worm or screws B as well as the chuck jaws A, hence revolving D operates
the jaws simultaneously and concentrically as in a scroll or universal
chuck. By means of the screws B, the jaws may be operated individually
(the boxes C and ring D remaining stationary) as in an independent jaw
chuck.
[Illustration: Fig. 847.]
Suppose, now, the jaws to have been used independently, and that they
require to be set to work simultaneously and concentric to the centre of
the chuck, then the screws B may be operated until the jaws at their
outer edge are even with the circumference of the chuck (or, if the jaws
are nearer the centre of the chuck, they may be set true with a
pointer), and the ring D may be operated. In like manner, if a number of
pieces of work are eccentric, the screws B may be used to chuck the work
to the required eccentricity, and when the next piece is to be chucked
the ring D may be operated, and the chuck will be used as a universal
one, although the shape of the work be irregular, all that is necessary
being to place the same part of the work to the same jaw on each
occasion.
[Illustration: Fig. 848.]
The faces of the jaws of jaw chucks when they are true with the face of
the chuck (or what is the same thing, run true, and are at a right angle
to the axial line of the lathe centres), form guides wherefrom to set
the work true, but this will only be the case when they remain true,
notwithstanding the pressure of the jaws upon the work. Their truth,
however, is often impaired by their wear in the chuck slots which gives
them play and permits them to cant over. Thus in Fig. 848 is shown a
chuck gripping a piece of work W, and it is obvious that to whatever
extent the jaws may spring, or have lost motion in the ways or slots in
the chucks, the jaws will move in the direction of the dotted lines A A,
the face of the jaw then standing in the direction of dotted lines B B,
instead of being parallel to the chuck face. If the spring or wear of
the mechanism were equal for each jaw, the work would be held true,
notwithstanding that the jaws be out of line, but such is not found to
be the case, and as a result the work cannot be set quite true.
[Illustration: Fig. 849.]
When the jaws are applied within the work, as in Fig. 849 (representing
the jaws of the chuck within the bore of a ring or piece of work W), the
jaws spring in the opposite direction as denoted by dotted lines C, C,
and when the jaws are locked to the work the latter moves in the
direction of D and away from the chuck face. It will be observed that
there is no true surface to put the face of the work against in either
case.
[Illustration: Fig. 850.]
This is remedied in independent dog chucks by the construction shown in
Fig. 850, in which each jaw has a square A, fitting in the grooves of
the chuck, and a nut and washer at B secure the jaw to the face of the
chuck so that the lost motion due to wear of the parts may be taken up.
[Illustration: Fig. 851.]
[Illustration: Fig. 852.]
The Judson patent chuck is designed to overcome this difficulty, and is
constructed as shown in Figs. 851 and 852, the former being a face view
and the latter a sectional edge view of the chuck.
The jaws A of the chuck are hollow, and the nut instead of being solid
in the jaw is a separate piece, having two wings, the outer of which
bears upon a pin in the jaw, while the inner bears upon an inclined
surface as plainly shown in the cut, so that the pressure of the screw
is distributed equally upon the pin and the inclined surface. The nut B
being below the centre of the pin and inclined surface causes the
pressure to throw the jaw fair against the face of the chuck, hence the
faces of the jaws will serve (equally as well as the surface of the
chuck) as a guide to set the work against.
From the short length of gripping surface on the jaws of jaw chucks,
they are incapable of holding work of any greater length than, say,
about 6 inches, without the aid of the dead centre at the other end of
the work; but if the dead centre be used in this way the work will be
out of true, unless the jaws of the chuck be quite true, which is not
always the case, especially after the chuck has been much in use.
Furthermore, it is at times a difficult if not even an impracticable job
to set work quite true in this way.
For special work made in quantities the form of the chuck may be varied
to conform to the special requirements of the work. The variety of
chucks that may thus be formed is obviously as infinite as the
variations in form of the work. Thus threaded work may be screwed into
threaded chucks, or cylindrical work may be driven into bored blocks
forming chucks, or a ring may be chucked and then used as a mandrel to
drive the work by friction.
[Illustration: Fig. 853.]
An excellent example of special chuck is shown in Fig. 853, representing
a chuck for holding piston rings. It resembles a face plate screwing on
the live spindle at B, and having 8 radial dogs or jaws A, let into the
face D, and secured thereto, when adjusted by the bolts and nuts E. A
mandrel is fast in the centre of the chuck carrying the cone C, upon
which rest the cone surfaces on the ends of the dogs A, so that screwing
up C, by means of the nut shown, throws the dogs A outwards, causing
them to grip the inside of the piston ring as shown in the face view of
the chuck.
[Illustration: Fig. 854.]
In Fig. 854 is shown Swazey's expanding chuck. B is the body of the
chuck driven on an arbor A. The hub of B is turned taper to receive a
disc C, which is split partly through in three places, and wholly
through at Z. By means of the nut and washer D E, the disc is forced up
the taper hub and caused to expand in diameter and grip the bore of the
work, or ring R, the face of B serving to set the face of the ring
against to hold it true sideways.
The chucks employed by wood workers for driving work without, the aid of
the back or dead centre of the lathe are as follows:--On account of the
fast speed at which the wood-workers' lathe revolves, it would be
undesirable to have their chucks of iron, because of the time it would
take the lathe to start them to full speed, and also to stop them after
shifting the belt from the driving to the loose pulley of the
countershaft, and further because of the damage the tool edges would
receive if they accidentally came into contact with the face of the
chuck. For these reasons wood workers' chucks are usually built up upon
small iron face plates.
[Illustration: Fig. 855.]
Fig. 855 represents a cement chuck, consisting of a disc of hard wood A,
screwed firmly to the face plate B; at C is a round steel point located
at the axis of the chuck.
This chuck is employed to drive very thin work by the adhesion between
the surface of the work and that of the chuck. The surface of the chuck
is coated with a mixture of 8 parts of resin to one part of beeswax run
into sticks. The chuck is waxed or cemented by rotating it at high
velocity while holding the sticks against it. The whole surface of the
chuck being thus coated, the centre of the work is forced on the steel
point C, and the lathe is kept running until the surface of the work
nearly touches that of the chuck, when the belt is passed to the loose
pulley overhead and the work forced against the chuck surface until it
stops or else revolves the work against the hand pressure, the friction
between the surfaces having melted the wax or cement, and cemented the
work to the chuck. This leaves the face and the circumference of the
work free to be operated upon. The work is removed from the chuck by the
gradual insertion between the two of a long thin-bladed knife.
For work of large diameter, however, a mere disc of wood will not
answer, it being too weak across the grain: and here it may be remarked
that the work often supports the chuck, and therefore we should always,
in fixing, make the grain of the work cross that of the chuck, because
the centrifugal force due to the high velocity is so great that both the
chuck and the work have before now been rent asunder by reason of the
non-observance of this apparently small matter. When it is considered
that the chuck has not sufficient strength across the grain, battens
should be screwed on at the back; but a chuck so strengthened will
require truing frequently on account of the strains to which its fibres
will be subjected from the unequal expansion or contraction of its
component parts. Fig. 856 shows the back of a chuck strengthened by the
battens A, A, A.
[Illustration: Fig. 856.]
[Illustration: Fig. 857.]
Another and superior method of making a chuck suitable for work of about
the same diameter is shown in Fig. 857. Its construction enables it to
better resist outward strains in every direction, while the strains to
which it must necessarily be subject, from variations of temperature and
humidity, are less than in the former. It will also be found that it can
be trued with greater facility, especially on the diameter, as the
turning tool will not be exposed to the end grain of the wood.
The crossed bars at the back of the chuck are half checked, as shown at
A, so that both pieces may extend clear across the chuck and not
terminate at the centre. They are fastened together at the centre by
glue, and also with screws. Upon these bars as a frame, the four pieces
composing the body or face of the chuck are fastened by both glue and
screws. These pieces need not extend clear to the centre, but may leave
an open square as shown, because the centre of a large chuck rarely
requires to be used.
[Illustration: Fig. 858.]
For very large chucks a cross of this kind would not afford sufficient
strength, hence, the form shown in Fig. 858 is employed. The arms are
bolted to an iron face plate, as shown, their number increasing with the
diameter of the chuck. To keep the chuck true, the arms should have a
level and fair bed upon the face plate, the segments composing the rim
being fairly bedded to the arms and well jointed at the ends. They
should be both glued and screwed, care being taken that the points of
the screws do not meet the face of the chuck, in which case they would
damage the turning tools used to true the chuck.
As wooden chucks are liable to warp and become out of true it is
requisite to test them on each occasion before use, and true them if
necessary. The work is fastened to these chucks by means of screws whose
heads are sunk beneath the work surface a sufficient depth so that there
is no danger of their coming into contact with the turning tools. In
other cases the work is glued to the chuck, a piece of paper being
interposed between the work and the chuck, which, by being damped, will
enable the more ready removal of the work from the chuck.
[Illustration: Fig. 859.]
Another form of chuck used by wood workers is shown in Fig. 859. It
consists of a disc of wood A; screwed to the face plate and carrying
the two pieces B, B. The pieces C, C are wedges which slide endways to
grip the work. This chuck is especially handy for small work of
rectangular form.
From the shape of some work, it cannot be chucked in jaw chucks of any
description, and this is especially the case with work of large
diameter, hence, large lathes, as, say those that will swing more than
three feet, are not usually provided with universal chucks, although
sometimes provided with independent jaw-chucks. So likewise in small
lathes there are many forms of work that cannot be chucked in jaw
chucks, and yet other forms that can be more conveniently held or
chucked on face or chuck plates, &c.
If, for example, the surface of the chuck requires to be used in setting
the work, the jaws will often be in the way of the tools or instruments
employed to set the work. Again, there may be projections on the work
which will require the body of the work to be held too far from the face
of the chuck to enable its jaws to grip the work.
To meet the requirements of these classes of work chucking devices,
which may be classified as follows, are employed:--
1st. Chucking by bolting work to the face plate or chuck plate with
bolts and plates.
2nd. Chucking between dogs movable about the face chuck plate, and
holding the work from that plate.
3rd. Chucking with the aid of the angle plate, or with the angle plate
employed in conjunction with the chuck plate.
[Illustration: Fig. 860.]
The chuck plate is simply a face as large in diameter as the lathe will
swing, and is sometimes termed the large face plate. Chuck plates for
smaller lathes, as 30 inches swing, or less, are sometimes provided with
numerous round or square holes to receive the bolts which hold the work,
but usually with slots and holes as in Fig. 860. The larger sizes of
chuck plates are similarly formed, but are sometimes provided with short
slots that meet the circumference of the plate as in Fig. 861, which
represents a chuck plate of the Whitworth pattern. The face of the chuck
plate must be maintained true in order that true work may be produced,
and it is necessary when putting it upon the lathe to carefully clean
its threads and those of the live spindle, as, on account of its large
diameter, a very little dirt between it and the live spindle will throw
it considerably out of truth at the circumference.
[Illustration: Fig. 861.]
It is better if there be any error in a chuck plate or face plate that
it be hollow rather than rounding when tested with a straightedge,
because in that case a given amount of error in the plate will produce
less error in the work.
[Illustration: Fig. 862.]
[Illustration: Fig. 863.]
[Illustration: Fig. 864.]
In Fig. 862, for example, A represents a chuck plate hollow across the
face, and B a link requiring to be bored through its double eye C, the
centre line of the lathe being line E E, and the centre line of the hole
in the hub D of the link being denoted by F, and as E and F are not
parallel one to the other it is obvious that the holes will not be
parallel. Suppose, now, that the chuck face was rounding, and the centre
line of D would stand at G G, and the holes in C and D would be out of
true in the opposite direction. In this case the error would be equal,
but suppose we have a ring or disc such as B in Fig. 863 to chuck by
bolts and plates C, D and it will be chucked true, notwithstanding that
the face of the plate is hollow. But were the face of the plate rounding
the disc may be chucked as in Fig. 864, the face F of the work not being
held at a right angle to the line of centres E as it is in Fig. 863. The
truth of the chucking in Fig. 864 depends upon whether the clamps C were
screwed up with equal force upon the work. A hollow chuck plate will
lose this advantage in proportion as the work covers more of one side of
the chuck plate than it does of the other, but in any event it will
chuck more true than a rounding one. Suppose we have, for example, a
ring chucked eccentrically as in Figs. 865 and 866, the chuck being as
much hollow in the one case as it is rounding in the other, and that
shown in Fig. 866 will stand out of true to an amount greater than the
chuck is in an equal amount of its radius. While that shown in Fig. 865
would be nearer true than the chuck is in an equal length of its radius,
both amounts being in proportion to the length of the line A to that of
line B.
[Illustration: Fig. 865.]
[Illustration: Fig. 866.]
If the chuck plate is known to be either rounding or hollow, pieces of
paper of sufficient thickness to remedy the error may be placed at C and
D respectively. It is better, however, to true up the faces of plates so
that the surface of the work bolted against it will be true and stand at
a right angle to the line of lathe centres.
In truing up a face plate, the bearings of the live spindle should be
adjusted so that there is no play on them, and the screw or other device
used to prevent end motion to the live spindle should be properly
adjusted.
A bar or rod of iron should also be placed between the lathe centres to
further steady the live spindle, and the square holes or radial slots
should have the edges rounded or bevelled off, as shown in Fig. 867, so
that when the tool point strikes the sides A of the holes or slots it
will leave its cut gradually and not with a sudden jerk or jump, while,
when it again takes its cut on the side B, it will also meet it
gradually and will not meet the sand or hard skin on the face of the
casting, which would rapidly dull the tool.
[Illustration: Fig. 867.]
In facing or truing up a chuck plate, the feed nut should be put in gear
with the feed screw or feed spindle, and the cut should be put on by
revolving the feed spindle or feed screw. This will take up any lost
motion in the feeding mechanism, after which the carriage may, if there
are devices for the purpose, be locked to the lathe bed so as to prevent
its moving.
It is better that the thread of the chuck be not too tight a fit upon
that on the lathe spindle, the radial face of the chuck hub and of the
cone spindle collar being relied upon to set the chuck true, because it
is somewhat difficult to produce threads so true as to hold the faces
true.
To preserve the threads both upon the chuck bore and the lathe spindle
from undue wear, the chuck when taken off the lathe should be stood on
edge so that falling dust may not accumulate in the thread. Before
putting the chuck upon the lathe spindle the threads of both and the
radial faces of the chuck hub and cone spindle collar should be
carefully cleaned, because the presence of any dirt or dust on those
faces will throw the face of the chuck plate out of true to an amount
that may be of importance at and near the chuck's circumference.
[Illustration: Fig. 868.]
[Illustration: Fig. 869.]
As an example of simple chucking on a face plate, or chuck plate, let it
be required to bore, cut a thread in the bore, and recess the piece of
work shown in Fig. 868, the radial faces being already true planes not
requiring to be turned.
[Illustration: Fig. 870.]
This could be held as shown in Fig. 869, in which C is the chuck plate,
W the work, S a strap plate, and B, B are bolts and nuts, a face view of
the work already chucked being shown in Fig. 870. The surface of the
work being bolted direct against the face of the chuck plate will be
held true to that face, and all that is necessary is to set it true
concentrically. While performing this setting, the work should not be
bolted too firmly, but just firm enough to permit of its being moved on
the chuck plate by light blows, the final tightening of the clamps being
effected after the work is set true. The bolts should be tightened upon
the work equally, otherwise one end of the plate will grip the work
firmly, while the other being comparatively slack, the work will be apt
to move under the pressure of a heavy cut.
A form of strap not unusually employed for work chucked in this manner
is shown in Fig. 871, its advantage being that it is capable of more
adjustment about the chuck plate, because the slots afford a greater
range for the bolts to come even with the holes in the chuck plate.
If the work be light, it may be held to the face plate while the holding
or clamping plates are applied as shown in Fig. 872, in which F is the
face plate or chuck plate, W the work, P a plate of iron, D a rod, and C
the back lathe centre. The latter is forced out by the hand wheel of the
tailstock with sufficient force to hold the work by friction while the
bolts and plates are applied. It is obvious, however, that if the work
has no hole in its centre, the plate P may be dispensed with, and that
if a strap plate, such as shown in Fig. 871, be employed, it must first
be hung on the tail spindle so that it may be passed over the rod D to
the work. Strap plates are suitable for work not exceeding about 6
inches in diameter. For larger work, bolts and plates are used, as
shown, for example, in Fig. 873, which represents a piece of work W held
to the chuck plate by plates P and bolts B, there being at E E packing
pieces or pieces of iron to support those ends of the clamps or clamping
plates P. It is necessary that these packing pieces E be of such a
height as to cause the plates P to stand parallel to the face of the
chuck for the following reasons:--
[Illustration: Fig. 871.]
[Illustration: Fig. 872.]
[Illustration: Fig. 873.]
Suppose that in Fig. 874, W is a piece of work clamped to the chuck
plate, and that packing piece E is too high, and packing piece E´ is too
low, as shown, both pieces throwing the plates P out of level, then in
setting the hole in the work to run true it will be found difficult to
move it in the direction of the arrow, because moving it in that
direction acts to force it farther under plate P´, and therefore, to
tighten its nut. In the case of plate P, the packing piece E will be
gripped by the plate more firmly than the work is, which will be held
too loosely, receiving so little of the plate pressure as to be liable
to move under the pressure of the tool cut. It is better, however, that
the packing piece be slightly above, rather than below the level of the
work surface. The position of the plates with relation to the work
should be such as to drive rather than to pull it, which is accomplished
in narrow work by placing them as in Fig. 873.
[Illustration: Fig. 874.]
The position of the bolts should be as close as possible or convenient
to the work, because in that case a larger proportion of its pressure
falls upon the work than upon the packing piece. For the same reason,
the packing piece should be placed at the end of the plates. This
explains one reason why it is preferable that the packing piece be
slightly above rather than below the level of the work surface, because,
the bolt being nearer to the work than to the packing piece, will offset
in its increased pressure on the work the tendency of the packing piece
to take the most bolt pressure on account of standing the highest.
If a packing piece of the necessary height be not at hand, two or more
pieces may be used, one being placed upon the other. Another plan is to
bend the end of the clamping plate around, as in Fig. 875, in which case
a less number of packing pieces will be required, or, in case the part
bent around is of the right length or height, packing pieces may be
dispensed with altogether. This is desirable because it is somewhat
difficult to hold simultaneously the plate in its proper position and
the packing pieces in place while the nut is screwed up, there being too
many operations for the operator's two hands. To facilitate this
handling, the nuts upon the bolts should not be a tight fit, because, in
that case, the bolt will turn around in the bolt holes or slot of the
chuck, requiring a wrench to hold the head of the bolt while the nut is
screwed up, which, with holding the plate, would be more than one
operator could perform. If the holes in the chuck plate are square, as
they should be, the bolt may be made square under the head, as in Fig.
876 at A, which will prevent it from turning in the hole. This, however,
necessitates that the head of the bolt be placed at the back of the
chuck, the nut end of the bolt being on the work side, which is
permissible providing that the bolt is not too long, for in that case
the end of the bolt projecting beyond the nut would prevent the slide
rest from traversing close up to the work, which would necessitate that
the cutting tools stand farther out from the slide rest, which is always
undesirable. Bolts that are not square under the head should, therefore,
be placed with the head in the work side of the chuck plate, because it
is of little consequence if the bolt ends project beyond the nuts at the
back of the chuck plate.
[Illustration: Fig. 875.]
[Illustration: Fig. 876.]
The heads of the bolts should be of larger diameter than the nuts,
because the increased area under the head will tend to prevent the bolt
from turning when the nut is screwed up.
[Illustration: Fig. 877.]
It sometimes happens that a projection on the work prevents the surface
that should go against the surface of the chuck plate from meeting the
latter. In this case, what are known as parallel pieces are employed.
These are pieces of metal, such as shown in Fig. 877, the thickness A
varying from the width B so as to be suitable for work requiring to
stand at different distances from the chuck plate surface, it being
always desirable to have the work held as near as possible to the chuck
plate so that it may not overhang the live spindle bearings any more
than necessary.
[Illustration: Fig. 878.]
An example of chucking with bolts and plates and with parallel pieces is
given in Fig. 878, in which the work has projections _a_, _a_ and _b_,
_b_, which prevent it going against the face of the chuck; E, E are the
parallel pieces which, being of equal thickness, hold the inside face of
the work parallel to the chuck face.
[Illustration: Fig. 879.]
Another example of the employment of parallel pieces is shown in Fig.
879, which represents a connecting rod strap with its brasses in place,
and chucked to be bored. B is a small block of iron inserted so that the
key may bind the brasses in the strap and P P is one parallel piece, the
other being hidden beneath the key and gib. The object in this case is
to chuck the brasses true with the face A of the strap, the plates S
being placed directly above or over the parallel pieces. This is a point
requiring the strictest attention, for otherwise the pressure of the
clamping plates will bend both the work and the chuck plate.
[Illustration: Fig. 880.]
In Fig. 880, for example, the parallel pieces being placed at _p_, _p_,
and the clamping plates at P, P, the pressure of the latter will bend
the work as denoted by the dotted lines, and the chuck plate in the
opposite direction, and in this case the work being weaker than the
chuck plate will bend the most.
As a result the face of the work will not be true when released from the
pressure of the bolts and nuts holding it. Parallel pieces should
therefore always be placed directly beneath the clamping plates,
especially in the case of light work, because if they be but an inch
away the work will be bent, or spring as it is termed, from the holding
plate pressure. In very large work the want of truth thus induced would
be practically discernible, even though the work be quite thick, as,
say, three inches, if the parallel pieces were as much as, say, 6 inches
from the holding plates.
[Illustration: Fig. 881.]
Fig. 881 shows an example of chucking by means of parallel strips in
conjunction with parallel pieces. B, B are a pair of brasses clamped by
the strips S, S, which are bolted together by the bolts A, A; P, P are
the parallel pieces.
The strips being thus held parallel to the surface of the chuck plate,
all that is necessary is to set the flanges of the work fair against the
surface of the strips and true with the dotted circle, and the brass
bore will be bored at a true right angle to the inside face of the
flange. If the inside face of the brasses was true, the parallel pieces
might be omitted, but this is rarely the case.
An excellent example of bolt and plate chucking is given in a heavy ring
of, say, three feet diameter, and 5 or 6 inches cross section, requiring
to be turned quite true, and of equal thickness all over. This job may
be chucked in three different ways; for example, in Fig. 882, A, B, C, D
are four-chucking dogs, so holding the work that its two radial faces
and outside diameter may be turned. This being done, four more dogs may
be placed to grip the diameter of the work, and the inside ones may then
be removed and the bore turned out. In this way the work would not be
unchucked until finished. There is danger, however, that the dogs
applied outside may spring the work out of true, in which case it would
require setting by a pointer in the slide rest.
Another plan would be to hold the work by dogs applied on the outside,
and turn the bore and both of the faces. To these fasten four plates on
the chuck plate, and turn their ends to the size of the bore and place
the work on them, as in Fig. 883, in which A, B, C, D are the four
plates, and are clamping plates. This plan is often employed, but it is
not a desirable one in heavy work, because the weight of the work is
quite apt to move the plates during its setting. A better plan than
either of these is to first turn off one face and then turn the work
around in the lathe and hold it as in Fig. 884. The bore may then be
turned, and all that part of the face not covered by the plates. Four
holding plates must then be applied with the bolts within the bore, and
when screwed firmly down the outside plates may be removed, leaving the
work free to have the remainder of its face and its circumference turned
up. In this way the work may be turned more true than by either of the
two previously described methods, because it has no opportunity to move
or become out of true.
[Illustration: Fig. 882.]
Cylindrical work to be chucked with its axis parallel to the face plate
is chucked by wood workers as shown in Fig. 885, in which B, B are two
blocks screwed to the chuck C, and having [V]s in to receive the work as
shown; the work is held to the blocks B, by means of the straps S, S,
which are held to B, B by screws. An example of a different class of
chucking by bolts and clamps may be given in the engine crank. A common
method of chucking such a crank is to level the surface of the crank in
a planing machine, and to hold that surface to the chuck-plate by bolts
and plates, while boring both the holes, merely reversing the crank end
for end for the second chucking.
This method has several inherent defects, especially in the case of
large cranks. First, it is a difficult matter to maintain large chuck
plates quite true, and as a result by this method of chucking any want
of truth in the surface of the chuck will be doubled in the want of
parallelism in the bores of the crank.
[Illustration: Fig. 883.]
Suppose, for example, that the chuck surface is either slightly hollow
or rounding as tested with a straight-edge placed across its face, then
the axial line of the hole bored in the crank will not be at a true
right angle with the planed surface of the crank. When the crank is
turned end for end on the chuck-plate and again bolted with its plain
surface against the surface of the chuck, the second hole bored will
again not stand at a true right angle to the planed surface, and
furthermore the error in one hole will be in a directly opposite
direction to that of the other hole, so that the error in the crank will
be double the amount that it is on the chuck surface. To this it may be
answered that if such an error is known to exist it may be corrected by
placing a piece of paper of the requisite thickness at the necessary end
of the crank for both chuckings. But this necessitates testing the chuck
on each occasion of using it, and the selection of a sheet of paper of
the exact proper thickness, which is labor thrown away so long as an
equally easy and more true way of chucking can be found. Furthermore
there is a second and more important element than want of truth in the
chuck to be found, which is that of the alteration of form which occurs
in the crank (as each part of its surface is cut away) as explained in
the remarks with which the subject of chucking is prefaced.
[Illustration: Fig. 884.]
First, the planed surface of the crank will alter in truth so soon as
the crank is released from the pressure of the holding devices on the
planer or planing machine; second, that surface will again alter in form
and truth from the removal of the metal around the surface of the hole
first bored; and third, the planed surface will be _to some extent_
sprung from the pressure of the plates holding the crank to the chuck
plate, hence the following method is far preferable.
[Illustration: Fig. 885.]
If it is intended to plane the back surface of the crank let that be
done first as before, and let it be held to the face-plate by bolts and
plates as before, while the hole and its radial face at the large end of
the crank are turned and finished. In doing this, however, first rough
out the radial face, and then rough out the hole, so that if the work
alters in form a fine finishing cut on both the radial face and the bore
will correct the evil. Then release the crank from the pressure of the
holding plates; and it is obvious that however the planed surface may
have altered in truth from removing the surface metal, the radial face
just turned will be true with the bore turned at the same chucking. Now
to chuck the crank to bore the second hole, turn it end for end as in
Fig. 886, and bolt the face already turned to the chuck plate (as at A
in the figure) with one or more bolts and strap plates. To steady the
other end of the crank, and prevent it from moving under the pressure of
the cut, take two bolts and plates B, and place a washer between them
and the chuck surface as shown at C, then bolt the plates to the chuck
plate, so adjusting them that their ends just have contact with the
crank when it is set true. In setting it true it may be moved by
striking the outer ends of the plates.
[Illustration: Fig. 886.]
In this method of chucking, we have the following advantages:--
1st. If the chuck plate is not true we may place a piece of paper
beneath the crank surface A, to correct the error as in the former
method, or if this is neglected, the second hole bored will be out of
true to an amount answerable to the want of truth in the chuck, and not
to twice as much as in the former method.
2nd. Any alteration of form that may take place during the first
chucking does not affect the truth of the second chucking as in the
other case.
3rd. The crank being suspended during the second chucking, any
alteration of form that may accompany the boring of the second hole will
be corrected by the finishing cut, hence the crank will be bored with
its two holes as axially true as they can be produced in the lathe.
It now remains to explain the uses of the pieces W in Fig. 886, simply
weights termed counterbalances bolted to the chuck plate to balance it
against the overhanging weight of the crank on one side of the chuck
plate. If these weights are omitted the holes in the work will be bored
oval, because the centrifugal force generated by the revolution of the
work will take up any lost motion there may be between the cone spindle
journal and its bearings, or if there be no such lost motion the
centrifugal force will in many cases be sufficient to spring the cone
spindle.
In selecting these weights it is well to have them as nearly as possible
heavy enough to counterbalance the work when placed at the same distance
from the lathe centre as the outer end of the work. The proper
adjustment of the weight is ascertained by revolving the lathe and
letting it slowly come to rest, when, if the outer end, or overhanging
end as it termed, of the work comes to rest at the bottom of the circle
of revolution on two or three successive trials the weight of the
counterbalance must be increased by the addition of another weight, or
the weight may be moved farther from the lathe centre.
To enable a piece of work, such as a crank for example, to have two or
more holes bored at one chucking, a class of chuck such as shown in Fig.
887 is sometimes employed. S is a slide in one piece with the hub that
screws on the live spindle and standing at a true right angle with the
axial line of the cone spindle and made as long as will swing over the
lathe bed. It contains a dovetail groove (as shown in the edge view)
into which a bar _t_, running across the back of the face plate P,
passes. To cause the bar _t_ to accurately fit the dovetail,
notwithstanding any wear of the surfaces, a slip G is introduced, being
set up to _t_ by set-screws passing through that side of the dovetailed
piece. The work, as the crank C, is bolted to the face plate, and the
set-screws on G are eased so that the plate can be moved to set the work
true; when true, the set-screws are tightened, and the first hole may be
bored. To bore the second hole all that is necessary is to slacken the
set-screws on G, move the plate, which will slide in the dovetail
groove, and set the work; when the set-screws are again set up tight,
the boring may again be proceeded with. In this way both holes may be
bored without unclamping the work. The whole truth of the job, _before
being unclamped from the chuck plate_, depends in this case upon the
dovetail groove being at a true right angle to the axial line of the
lathe cone spindle, it being of no consequence whether the face plate
stands true or not. But suppose the removal of the metal to have
released strains in the casting or forging, then the clamping plates
will have prevented the crank from quite assuming its normal shape after
the release of those strains, and the crank, when finished, though true
while clamped, will change its form the instant the clamping plates are
removed, and the holes bored will in all probability not have their
axial lines true one with the other. Another objection is that throwing
the chuck plate out of balance on the lathe spindle as well as the crank
induces the evils due to the centrifugal motion. This may be offset by
increased counterbalancing, of course, but the counterbalancing becomes
cumbersome, and is not so easy a matter. For these reasons, chucks of
this class are not desirable unless it may be for comparatively small
and light work. It is obvious that the dovetail groove may be provided
with a screw, and the back of the plate with a nut, so as to move the
plate along the groove by revolving the screw. This will assist in
adjusting or setting the work, but it will increase the amount of weight
requiring to be counterbalanced.
[Illustration: Fig. 887.]
When a number of pieces are to be bored with their holes of equal
diameters and of the same distance apart, the chucking should be
performed as in Figs. 888 and 889; one and the same end of each link
should be bored and faced, the links being held by the stem, placed on
parallel pieces with plates. A pin such as shown in Fig. 889 should then
be provided, its diameter across A being a close sliding fit into the
bores of the links; while the length of A should be slightly less than
the length of the hole in the link, the part D should be made to
accurately fit the hole bored by any suitably sized reamer; a washer B
should be provided, and each end should be threaded to receive nuts.
There should then be provided in the chuck plate a hole whose distance
from the centre of the chuck must exactly equal the distance apart the
holes in the links are required to be, and into whose bore the end D of
the pin shown in Fig. 889 must drive easily. The pin should be locked in
this hole by a nut as shown in Fig. 889. The bored ends of the links may
then be placed on the pin and fastened by a nut as in Fig. 888, which
will regulate the distance apart of the holes.
[Illustration: Fig. 888.]
[Illustration: Fig. 889.]
It is obvious that the pin may be passed through one of the radial slots
in the chuck, and set the required distance from the centre, but in this
case the pin would be liable to become moved in its position in the
slot.
Side plates to prevent the link from moving should of course be applied
as at D, D in the figure.
The whole process of the second chucking will thus consist of fastening
the links on the pin, and setting the free end to the circle made to
mark its location. This is done as shown in Fig. 890, which represents
the free end of a link, D is the circle marked to set the link by, and P
a pointed tool held firmly in the slide rest tool post. The link is
obviously set true when the dotted circle on its end face runs true, the
pointer merely serving to test the dotted circle.
[Illustration: Fig. 890.]
When, however, one or two links only require to be turned it will not
pay to make the pins shown in Fig. 888, especially if the holes of the
different links vary in diameter, hence the work must be set by lines.
In the promiscuous practice of the general workshop, where it may and
often does happen that two pieces of work are rarely of the same shape
and size, lines whereby to set the work are an absolute necessity, not
only to set the work by in chucking it, but also to denote the quantity
of metal requiring to be taken off one face in order to bring its
distance correct with relation to other faces. An example of this kind
is given in Fig. 891, which represents a lever to be bored and faced at
the two ends, the radial faces standing at different distances from the
centre of the lever stem as denoted by the lines (defined by centre
punch dots) E, F, G, H, I, J, K, L. It will be noted that at H, I, F,
and E there is but little metal to be taken off, while there is ample at
L. Suppose then that the face L were the first one turned, and it was
only just trued up, then when F or H were turned there would be no metal
to turn, for they may be too near the plane of L already.
[Illustration: Fig. 891.]
The necessity for these lines now being shown, we may proceed to show
how they should be located and their services in setting the work. The
line A is called the centre line, it passing through the centre of the
thickness of the link body on both edges of the link. From it all the
other lines, as J, F, L, G, E, K, and H, I, are marked.
The first question that arises in the chucking is, which of the holes B,
C, or D, shall be bored first. Now the faces K and L are those that
project farthest from the centre line A, hence if the hole at that end
be bored and the faces K, L, be turned first, we may bolt those faces
against the chuck plate, and thus insure that all three holes shall
stand axially true one with the other. If the holes B or C were bored
first, L projecting beyond J and F (which are the faces of holes B, C)
would prevent the radial face first turned from serving as a guide in
the subsequent chuckings, unless a parallel piece were placed between
the face and the chuck. In this case, however, there is not only the
extra trouble of using the parallel piece, but there would obviously be
more liability of error, as from the parallel piece not being dead true
and the amount of the error multiplying in the length of the lever, and
so on.
The hole D is the one, therefore, to be bored first, the chucking
proceeding as follows:--Two parallel pieces of sufficient thickness to
keep L clear of the chuck plate should be placed one on each side of the
hub E, and bolts and plates placed directly over them. The work must be
set so that the line A on each side of the link stands exactly parallel
with the face of the chuck, the parallelism being tried at each end of
the line, because any error that may be made in setting the work by the
full length of the line will have a less effect upon the work than the
same amount of error in a shorter length of line. For this reason the
centre line should always be marked as long as possible and used to set
by, unless there is a longer line running parallel to it and marked on
both sides of the link, as would be the case if the dotted line at J
and that at L were equidistant from A, in which event they may
preferably be used.
The work is set true to the lines by a scribing block, or surface gauge,
but as that instrument is more used in setting work with chuck dogs its
application will be shown in connection with chucking by dogs; hence to
proceed: To set the work true to the line A it may be necessary to place
a thickness of paper, a piece of sheet tin, or the equivalent, beneath
one of the parallel pieces to bring A parallel with the chuck plate
surface. This being done, however, and the circle D being set to run
true, the hole may be bored and the radial face L turned off so as to
just split the dotted line at L, and this radial face may be used
instead of the line A for all subsequent chuckings, so as to avoid the
errors that might occur in referring to the line, and from the
alterations that might occur in the form of the work from removing the
surface metal.
[Illustration: Fig. 892.]
Fig. 892 represents a view of the end L as held for the second chucking.
C is a section of the chuck plate, and O O represents the line of
centres of the lathe, and it is obvious that the radial face of the
lever end (which is here represented by L) being used for all but the
first chucking, the holes will all stand axially true one with the
other, no matter how many chuckings and holes there may be, hence it
becomes obvious that the face that will meet the chuck plate is the one
that should be turned at the first chucking. It is of no consequence in
the case of a single lever whether the pin fits the hole in the end of
L, Fig. 892, or not, because the dotted circles at B, C, D in Fig. 891
form the guides whereby to set the holes for distance apart, and any
bolt may be used to clamp the work.
It is usual in an example of this kind to turn the stem of the lever to
its proper thickness for a short distance from the hubs, so as to have
the stem true with the bores, and form a guide whereby to set the lever
in the planer or shaper when cutting down the lever stem to size. The
rules of chucking and the balance weighting described with reference to
chucking a crank, of course also apply to this example.
It will now be observed that in all cases in which work is chucked by
bolts and plates, the whole of the faces cannot be turned at one
chucking unless the shape of the work is such that it will permit the
plates and the bolts to pass or be below the level of the work surface.
It will further be noticed that if one face of the work is held against
the chuck surface it cannot be turned at the same chucking that the
other face is turned at. Now it may be very desirable that a part or the
whole of the back face as well as the front one be turned at the same
chucking as that at which the hole is bored, so as to have the hole and
those two faces true without incurring the errors that might arise from
a second chucking. Again, the diameter of the work may be equal to that
of the chuck so as to preclude the possibility of using bolts and plates
outside of the circumference, and though there be cavities or slots
running through the work through which the bolts might be passed, yet
the presence of the plates would prevent the face from being turned.
[Illustration: Fig. 893.]
To meet these and many other requirements that might be named, chucking
by the aid of chucking dogs is resorted to, one of these dogs being
shown in Fig. 893. B represents a section of the chuck plate with a
piece broken out to show the stem A of the dog, which is squared to
prevent its revolving when the nut D, which holds the dog to the chuck
plate, is tightened, the holes of the chuck, of course, being square
also; E is the set-screw which holds the work, its end at E being turned
down below the thread, and the head squared to receive a wrench.
[Illustration: Fig. 894.]
Fig. 894 represents an example of chucking by dogs, it being required to
face the work off to the dotted line F F. Three of the four dogs used
are shown at D, D, D. To set the work the scribing block shown in the
figure is employed, the point of the needle being set to the line at any
one spot, and the scribing block or surface gauge carried around the
work rested with its base against the chuck plate and the needle point
tried for coincidence with the line at various points in the work's
circumference. The work is not at first held too firmly by the dogs, so
that light blows will suffice to so move the work that the surface gauge
needle point applied as shown and at any point around the work will
coincide with the line. It will here be observed that using the dogs
obviates the necessity for parallel pieces, when the work has
projections at the back face as shown in the cut.
[Illustration: Fig. 895.]
Fig. 895 represents another example in chucking by dogs. It is required
to surface the whole of the surfaces shown, to bore the hole C and to
face a face similar to A, but on the other side or chuck side of the
work. Then the work is placed so that its outer face will project beyond
the extreme surface of the dogs, and the whole of the operations can be
performed at one chucking. It will be observed that in this case the
surface of the chuck plate does not automatically serve to guide the
work in the chucking, because there is no contact between the two, but
the chuck surface can be used as a guide whereby to chuck the work as
has just been shown. Or suppose the work to require to be set as true as
can be to its exposed face, then the work end of the surface gauge is
applied as shown in Fig. 896 at E.
[Illustration: Fig. 896.]
[Illustration: Fig. 897.]
[Illustration: Fig. 898.]
The surface gauge may indeed be dispensed with if the work is
sufficiently light that the lathe can be swung around by pulling the
chuck plate with the hand, and the work merely requires to be set to run
true on its exposed radial face. A pointer held in the slide rest, and
applied as in Fig. 890, will denote the setting of the work, which must
be tapped until the pointer touches it equally on four equidistant
points of the surface; but if it is essential to take as little as
possible off the face while truing it up, the tool point should be held
stationary, while the work should be so set that the four most distant
points (in that circle on the work which is equivalent in radius to the
radius to which the tool point stands from the chuck centre) are
equidistant as measured by a rule from the tool point. The philosophy of
this will be understood from a reference to Fig. 894 and the remarks
thereon, this being a parallel case, but applied to a radial face
instead of to a circumference.
Now suppose we have the piece of work shown in Fig. 897, which requires
to have its surfaces A and B parallel and at a right angle to C and D,
the end faces E and F parallel to each other, and at a right angle to
both A, B, C, and D, the hole at G is to be axially true with the
surfaces A, B, C, and D, as well as with the pin at I, and the hole at H
at a dead right angle to that at G.
We may put a plug in G and turn up the surfaces E and F, and turn the
pin I; this, however, would leave the hole G unbored, whereas it should
be bored when the surface E is turned; again, after these surfaces are
turned they are of no advantage as guides in the subsequent chuckings.
We may grip the surfaces E and F in a jaw chuck to turn the surfaces A,
B, C and D, but depending upon the face jaws of the dogs to set the work
surface true by; but this would not be apt to produce true work on
account of the spring of the jaws, as explained in the remarks upon jaw
chucks; furthermore, the work, supposing it to be a foot long, could not
be held in a dog chuck sufficiently firmly to enable the turning of the
end face E or the pin I, and this brings us to that most excellent
adjunct to a general chucking lathe, the angle plate shown in Fig. 898.
It is simply a plate of the form shown in the figure, having two flat
and true surfaces, one at a right angle to the other; one of these
surfaces bolts to the chuck plate, while the other is to fasten the work
on. The slots shown are to pass the bolts through to fasten the angle
plate to the chuck plate, and the work surface of the plate contains
similar slots and holes to receive the bolts used to fasten the work.
[Illustration: Fig. 899.]
Suppose, then, we fasten the piece of work to the angle plate as shown
in Fig. 899, and face off the surface C, and bore the hole H, the work
being set true with its surface, or to a line, by the aid of a surface
gauge, as may be required. We then turn surface C down to meet the
surface of the angle plate, fasten it to the same with bolts and plates
and setting it as before, and on turning its surface A we shall have the
two surfaces A and C at a right angle to one another. We then turn the
surface A down upon the angle plate and bolt it again as before. But we
have now to set it so that the surface C shall be quite parallel with
the surface of the chuck plate. This we may do by placing one or more
parallel strips behind it, as at S S, in the plan view, Fig. 900,
setting the work so that it binds the parallel strips tight against the
chuck plate along their full lengths; or we may measure the distance of
C from the chuck plate surface with a pair of inside calipers; or we may
turn the bent end of a surface-gauge needle outwards and gauge the work
as shown in the plan view, trying the work all along. On turning the
surface D, Fig. 897, we shall have three of the surfaces done at right
angles and with C and D parallel.
[Illustration: Fig. 900.]
It is obvious that the surface D may be turned down on the angle plate
and bolted as before, the surface A being set parallel to the chuck
plate surface as before, and all four of these surfaces will be finished
true as required. Next come the two end surfaces and the pin I. For F
and the pin I we chuck the work on the angle plate, as shown in the plan
view, Fig. 901, P, P representing the clamping-plates. The angle plate
will here again serve to hold the work true one way, and all we have to
do to set it true the other way is to fasten a pointer in the tool post
and bring it up to just touch the corners of the work at the outer end,
as at K. Now run the carriage up so as to bring the pointer to position
L, and when the work is so set that all four corners just touch the
pointer, tried in their two positions, _without touching the cross-feed
screw_, the work is true, and the end surface E and hole G may be
turned; E will then be at a true right angle to the four faces, A, B, C,
D, while G will be axially true with them.
[Illustration: Fig. 901.]
We may, instead of using the pointer at K and L, or in addition to so
using it, apply a square against the chuck plate and bring the blade
against the work, as shown at R.
We have now to turn the pin I and end face, and to do this we simply
reverse the work, end for end, and bolt it as before. But we may now
employ the trued surface E as an aid in setting by causing it to abut
against the chuck plate surface, and, as an aid to finding that it abuts
fair, we may put two strips of the same piece of paper behind it, one on
each side of the square, and, after the work is bolted, see that both
are held firm; but it is necessary to test with the pointer as before,
as well as with the square.
It is obvious that the angle plate requires counterbalancing, which is
done by means of the weight W. (Fig. 900).
An excellent example of angle plate chucking is furnished in a pipe bend
requiring both flanges to be turned up. The method of chucking is shown
in Figs. 902 and 903, the flanges being simply bolted to the angle
plate. The work may be set true to the body of the bend close to the
neck of the flange or by the circumference of the flange. The face of
the flange will be held true one way by the face on the angle plate, but
must be set true the other way. The truest flange should be the one
first bolted to the angle plate.
[Illustration: Fig. 902.]
[Illustration: Fig. 903.]
[Illustration: Fig. 904.]
A common but good example of angle plate chucking is shown in Fig. 904,
which represents a cross head requiring to have its two holes bored one
at a right angle to the other, the jaws faced inside and outside, and
the hub or boss turned.
[Illustration: Fig. 905.]
It would be proper to mark the cross-head out by lines, giving dotted
circles to set the work by, and dotted lines to give the thickness of
the jaws. In thus marking out two centre lines A A and B B in Fig. 905
would be used to locate the centres of the holes; and the thickness of
the jaws would be marked from the line B B. In marking these lines the
cross head should be rested upon a table or plate as in Fig. 905, and
the line A A should be made with the jaws of the cross head lying flat
on the table, that is without the interposition of any packing or paper
between them and the plate, so that the edges of the jaws on that side
will be true with the line A A, and will therefore serve to apply a
square against when chucking to bore the hole through the jaws. If the
jaw edges are not sufficiently true to permit of their lying on the
table, they should be made so by filing a flat place on them, so that
when a square is applied to them as in Fig. 906, the edges C, C will be
parallel with the axis A A of the holes in the chucks or jaws. The first
chucking should be as in Fig. 907, the cross head being bolted to an
angle plate set true by the circle on the end face of its hub D, and a
square being applied to the centre line A, as in Fig. 908, and to the
dotted lines on the jaws as shown in Fig. 909. A balance weight W, Fig.
907, is necessary to counterbalance the weight of the angle plate.
[Illustration: Fig. 906.]
The second chucking to bore the cheeks and face them inside and out to
the required thickness would be as in Fig. 910, a single plate and two
bolts being used to hold the cross head to the angle plate. To set the
cross head true in one direction, the outer circle shown marked upon the
face of the cheek is used.
It remains to so set the face of the cheeks that the hole through them
shall be central with that already bored through the hub D and all that
is necessary to accomplish this is to set the edge true as shown in the
top view in Fig. 911, in which S is a square rested against the face of
the chuck and applied to the edges of the cheeks, these edges being
those that were rested on the plate when marking the line A A in Fig.
905, or that were filed square if it was found necessary as already
mentioned.
[Illustration: Fig. 912.]
The inside faces of the cheeks are turned to the dotted lines shown in
Fig. 909, and the outside faces being turned each to the proper
thickness measured from the outside ones, the job will be complete and
true in every direction.
[Illustration: _VOL. I._ =EXAMPLES IN ANGLE-PLATE CHUCKING.= _PLATE XII._
Fig. 907.
Fig. 908.
Fig. 909.
Fig. 910.
Fig. 911.]
An excellent example of angle plate chucking is shown in Fig. 912--the
actual dimension of the piece, measuring, say, 24 inches in length. It
is required to have the cylindrical stems A, B turned parallel to each
other, of equal diameters, equidistant from the central hole C, and true
with the hub D. A large piece of work of this kind would be marked off
with lines defined by centre-punch dots, as shown. The ends of A, B, D
would require dotted circles to set them by. Now, in all work of this
kind it is advisable to turn that surface first that will afford the
greatest length of finished surface, to serve as a guide for the
subsequent chucking, which in this case is the hub D, and the face on
that side as denoted by the dotted line which has to be cut to that
line. The method of chucking would, for this purpose, be as in Fig. 913.
[Illustration: Fig. 913.]
[Illustration: Fig. 914.]
[Illustration: Fig. 915.]
The second chucking would be as in Fig. 914 to bore the hole at C,
while, at the same time, the surface from F to G may be turned. Either
inside calipers or a surface gauge may be employed to set E E parallel
to the chuck plate surface. It is supposed that the location C is
defined by a dotted circle, by which the work may be set for
concentricity, as should be the case. At the next chucking it will
simply be necessary to move the work on the angle plate to the position
shown in Fig. 915, setting the circle on the end of A to run true, and
the surface E parallel to the chuck surface as before. The third
chucking is made by simply moving the work on the angle plate again, and
setting as in the last instance.
CHAPTER X.--CUTTING TOOLS FOR LATHES.
The cutting tools for lathes are composed of a fine grain of cast steel
termed "tool-steel," and are made hard, to enable them to cut, by
heating them to a red heat and dipping them in water, and subsequently
reheating them to temper them or lower their degree of hardness, which
is necessary for weak tools.
These cutting tools may be divided into two principal classes, viz.,
slide rest tools, or those held in the slide rest, and hand tools, which
are held by hand.
The latter, however, have lost most of their former importance in the
practice of the machine shop, by reason of the employment of self-acting
lathes.
The proper shape for lathe slide rest tools depends upon--
1st. The kind of metal to be cut.
2nd. Upon the amount of metal to be cut off.
3rd. Upon the purpose of the cut, as whether to rough out or to finish
the surface.
4th. Upon the degree of hardness of the metal to be cut.
5th. Upon the distance the tool edge is required to stand out from the
tool clamp, or part that supports it.
Lathe tools are designated either from the nature of their duty, or from
some characteristic peculiar to the tool itself.
The term "diamond point" is given because the face of the tool is
diamond shaped; but in England and in some practice in the United States
the same tool is termed a front tool, because it is employed on the
front of external work.
A side tool is one intended for use on the side faces of the work, as
the side of a collar or the face of a face plate. An outside tool is one
for use on external surfaces, and an inside one for internal, as the
walls or bores of holes, &c.
A spring tool is formed to spring or yield to excessive pressure rather
than dig or jump into the work.
A boring tool is one used for boring purposes.
[Illustration: Fig. 916.]
[Illustration: Fig. 917.]
The principal forms of cutting tools for lathes are the diamond points
or front tools, the side tools (right and left), and the cutting off or
parting tool. The cutting edges of lathe tools are formed by grinding
the upper surface, as _a_ in Fig. 916, and the bottom or side faces as
_b_, so that the cutting edges _c_ and _d_ shall be brought to a clean
and sharp edge, the figure representing a common form of front tool. The
manner in which this tool is used to cut is shown in Fig. 917, in which
the work is supposed to be revolved between the lathe centres in the
manner already described with reference to driving work in the lathe.
The tool is firmly held in the tool post or tool clamp, as the case may
be, and is fed into the work by the cross-feed screw taking a cut to
reduce the work diameter and make it cylindrically true; the depth to
which the tool enters the work is the depth of the cut. The tool is
traversed, or fed, or moved parallel to the work axis, and the motion in
that is termed the feed, or feed traverse.
[Illustration: Fig. 918.]
The cutting action of the tool depends upon the angles one to the other
of faces B, D (Fig. 918), and the position in which they are presented
to the work, and in discussing these elements the face D will be termed
the top face, and its inclination or angle above an horizontal line, or
in the direction of the arrow in Fig. 918, will be termed the rake, this
angle being considered with relation to the top A A, or what is the same
thing, the bottom E E of the tool steel. The angle of the bottom face B
to the line C is the bottom rake, or more properly, the clearance.
[Illustration: Fig. 919.]
In the form of diamond point or front tool, shown in Fig. 916, there is
an unnecessary amount of surface to grind at _b_, hence the form shown
in Fig. 919 is also employed on light work, while it is in its main
features also employed on large work, hence it will be here employed in
preference to that shown in Fig. 916, the cutting action of the two
being precisely alike so long as the angles of the faces are equal in
the two tools.
The strength of the cutting edge is determined by the angles of the rake
and clearance, but in this combination the clearance has the greater
strength value. On the other hand the keenness of the tool though
dependent in some degree upon the amount of clearance, is much more
dependent upon the angle of the top face.
It follows therefore that for copper, tin, lead, and other metals that
may be comparatively easily severed, a tool may be given a maximum of
top rake, and it is found in practice that top rake can be employed to
advantage upon steel, wrought iron, and cast iron, but the amount must
be decreased in proportion as the nature of either of those metals is
hard.
For the combinations of copper and tin which are generally termed brass
or composition, either no top rake or negative top rake is employed
according to the conditions.
[Illustration: Fig. 920.]
It may be pointed out, however, that in a given tool the cutting
qualification is governed to a great extent by the position in which the
tool is presented to the work, thus in Fig. 920, let C represent a piece
of work and B, B, B, B, four tools having their top and bottom faces
ground at the same angle to each other. In position 1, the top face of
the tool is at an acute angle below the radial line A, hence the tool
possesses top rake, the amount being about suitable for hard steel or
hard cast iron.
In position 2 the top face is at an acute angle above the radial line A,
hence the tool has negative top rake, the amount being about suitable
for brass work under some conditions.
In position 3 the top face has no rake of any kind, and the tool is
suitable (in this respect) for ordinary brass work.
In position 4 the tool possesses an amount of top rake about suitable
for ordinary wrought-iron work.
If the tool was presented to brass work in positions 1 or 4 it would rip
or tear the metal instead of cutting it, while if the tool was presented
to iron or steel (of an ordinary degree of hardness) in positions 2 or
3, it would force rather than cut the metal.
Furthermore it will be readily perceived that though each tool may have
its faces, whose junction forms the cutting edge, at the same angles,
yet the strength of the cutting edge is varied by the position in which
the tool is presented to the work, thus the edge in position 2, will be
weaker than that in position 4.
We have now to consider another point bearing upon the proper
presentment of top rake and the presentment of the tool to the work. It
is obvious that the strain of the cut falls upon the top face of the
tool, and therefore the direction in which this strain is exerted is the
direction in which the tool will endeavour to move if the strain is
sufficient to bend the tool and cause motion.
[Illustration: Fig. 921.]
In Fig. 921 let W represent the work having a cut C being taken off by
the tool T; let E represent the slide rest, and F the extreme point at
which the tool is supported; then the pressure placed by C on the top
face of the tool will be at a right angle to the plane of that top face,
or in the direction of the arrow B; to whatever amount therefore the
tool sprung under the cut pressure (its motion being in an arc of a
circle, of which F is the centre) it would enter the work deeper, and as
a result, the rough work not being cylindrically true, the tool will dip
farthest beyond its proper line of work where the cut is deepest, and
therefore will not cut the work cylindrically true; as this, however,
naturally leads to a variation in the direction of the top rake, and as
the cutting action of the point of such a tool differs from that of the
side edge, which also leads to a variation in the direction of the top
rake, it becomes necessary to consider just what the cutting action is
both at the point and on the side of the tool.
Suppose, then, that the tool carries so fine a cut that it cuts at the
point only, and the pressure will be as denoted by the arrow B in Fig.
921.
[Illustration: Fig. 922.]
If the tool be given no traverse, but be merely moved in towards the
centre of the work, the cut will move outward and in a line with the
body of the tool, the cutting coming off as shown in Fig. 922.
So soon, however, as the tool is fed to its feed traverse the form of
the cutting alters to the special form shown in Fig. 917, and moves to
one side of the tool, as well as outwards from the work.
[Illustration: Fig. 923.]
Fig. 923 is a top view of a tool and piece of work, and the arrow A
denotes the direction of the resistance of the work to the cut, being at
a right angle to plane of the cutting edge.
Now the duty of the side edge is simply to remove metal, while that of
the point is to finish the surface, and it is obvious that for finishing
purposes the most important part of the tool edge is the point, and this
it is that requires to be kept sharp, hence the angle or rake should be
in the direction of the point. But when the object is to remove metal
and prepare the work for the finishing cut the duty falls heavily on the
side edge of the tool, and the angle of the top face and the direction
of its rake may be varied with a view to increase the efficiency of the
side edge, and at the same time to diminish the amount of power
necessary to pull the tool along to its feed traverse. This may be
accomplished by altering the top rake from front to side rake, which is
done in varying degrees according to the nature of the work.
[Illustration: Fig. 924.]
In Fig. 924 the angle of the top face in the direction of A is the
front, and that in the direction of B is the side rake.
In small work where the cuts are not great, and where but one roughing
cut is taken, it is an object to have the roughing cut leave the work
with as smooth a surface as possible, and the amount of side rake may be
small as in Fig. 924. For heavy deep cuts, however, a maximum of side
rake may be used.
[Illustration: Fig. 925.]
Thus in Fig. 925 is an engraving of a tool used for roughing in the
Morgan Iron Works, its top rake being all side rake.
When a tool has side rake, its cutting capacity is obviously increased
on one side only, hence it should be fed to cut on that side only. It is
for this reason that no side rake is given to tools for very small and
short work, because it is then more convenient to traverse the tool to
cut in either direction at will.
In long and large work, however, where the motion of the slide rest is
slow, tools having right and left-hand side rake are used. The tools in
Figs. 924 and 925 are right-hand tools, their direction of feed travel
being to the left.
[Illustration: Fig. 926.]
In Fig. 926 is a left-hand tool, its direction of feed traverse being
from left to right; hence edge G is the cutting one, edge F being dulled
by the side angle B.
[Illustration: Fig. 927.]
It is obvious that various combinations of side rake and front rake may
be given to produce the same degree of keenness to the tool. For
example, a tool may have its keenness from side rake alone, or it may
have the same degree of keenness by using less side rake and some front
rake. The principles governing the selections of these combinations are
as follows:--
Suppose that in addition to say 20 degrees of side rake a tool is given
a certain amount of front rake as denoted in Fig. 927 by E E, and
suppose that the tool is moved in to its cut by the cross feed screw.
During this motion and until the tool point meets the work surface the
contact between the cross feed screw and feed nut will be on the sides
of the threads facing the line of lathe centres, and all the play
between those threads will be on their other sides, but so soon as the
tool meets the cut it will jump forward and into the work to the amount
that the play between the threads will allow it, and this is very apt to
cause the tool to break. Furthermore the point of the tool is apt from
its extreme keenness to become dulled quickly.
[Illustration: Fig. 928.]
The amount of side rake may, however, be considerably increased if the
heel D, Fig. 928, be made higher than the point A in that figure, the
plane of the middle being denoted by the arrow at A; a view of the other
side of this tool is shown in Fig. 929, the plane of the cutting edge
being denoted by the dotted line.
[Illustration: Fig. 929.]
A tool thus formed will require a slight cross feed screw pressure to
force it to its cut, thus causing the cross feed nut to have contact
with the sides of the thread in contact when winding the tool into its
cut, hence the tendency to jump into the depth of cut is eliminated, and
regulating the depth of the cut is much more easily accomplished.
In proportion as a tool is given side rake, it is more easily traversed
to its cut, as will be perceived from the following:--
[Illustration: Fig. 930.]
[Illustration: Fig. 931.]
Fig. 930 represents a section of a tool T, whose feed traverse is in the
direction of A. Now all the force that is expended in bending the
cutting C out of the straight line, or in other words the pressure on
the top face of the tool, acts to a great extent to force the tool to
the left, and therefore traverse it to its feed. The more side rake a
tool has the nearer the thickness of its cutting will accord to the
thickness of the feed traverse. For example, if a tool having a side
rake of say 35 degrees of angle feeds forward 1/32 inch per work
revolution, the thickness of the cutting will but slightly exceed 1/32
inch, but if no top rake at all be given, as shown in Fig. 931, then the
cutting will come off nearly straight, will be considerably thicker than
1/32 inch, and will be ragged and broken up, and it follows that the
thickening and the bending of the cutting has required an expenditure of
the driving power of the lathe, diminishing the depth of cut the lathe
will be capable of driving. With such a tool the pressure of the cut
will fall downwards as denoted by the arrow B.
[Illustration: Fig. 932.]
In the practice of many tool makers in the Eastern States the tool is
ground to a point A, Fig. 932, that is, ground sharp and merely rounded
off with an oil-stone. This may serve when the lathe has an exceedingly
fine feed, and the strain being in that case very slight the tool point
may be made to stand well above the level of the body of the steel, as
in the figure, and thus save forging; but this is a slow method of
procedure, and produces no better work than a tool which is rounded at
the point, and therefore capable of producing smoother work with a much
coarser feed.
The diameter of the curls of the cutting, shaving, or chip produced by a
turning and also the direction in which it moves after leaving the tool,
depends upon the amount of the top rake and the direction in which it is
provided. The greater the amount of rake, whether it be front or side
rake, the larger the coils of the cutting, and, therefore, the less the
amount of power expended in bending it. Furthermore, it may be remarked
that the thickness of the cutting is always greater than is due to the
amount of feed traverse, and it requires power to produce this
thickening of the cutting. The larger the coils of the cutting the
nearer the thickness accords with the rate of feed.
[Illustration: Fig. 933.]
In these considerations we have referred to the angle of the top face
only, but if we consider the angle of the two faces one to the other we
shall see that they form a wedge, and that all cutting tools are simply
wedges which enter the material the more easily in proportion as the
angles are more acute, providing always that they are presented to the
work in the most desirable position, as was explained with reference to
Fig. 920.
[Illustration: Fig. 934.]
We may now consider the degree of a bottom rake or clearance desirable
for a tool, and this it can be shown depends entirely upon the
conditions of work, diameter, and rate of tool traverse, and cannot,
therefore, be made a constant degree of angle. This is shown in Fig.
934, in which a tool T is represented in three positions, marked
respectively 1, 2, and 3. Line A A is at a right angle to the axis of
the work W, and the side of the tool is given in each case 5° of angle
from this line A A. In position 1 the tool has 3° of clearance from the
side of the cut; in position 2 it has 2° clearance, but in position 3 it
would require to have 2° more clearance given to it to enable the
cutting-edge to meet the side of the cut, without even then having the
clearance necessary to enable it to cut. This occurs because the side of
the cut is not at a right angle to the work axis, but at an angle the
degree of which depends upon the rate of feed.
[Illustration: Fig. 935.]
Thus in Fig. 935 the three tools have the same amount of clearance, and
if they are supposed to be facing off the work they will maintain that
clearance under all conditions of work, diameter, and rate of feed, but
if they were traversed along instead of across the work the angle of the
tool (both on the top and bottom face) to the cut will become changed,
and will continue to change with every change of work diameter, so that
the same tool stands at a different angle at each successive cut taken
off the work, even though the lathe were used at or possessed but one
rate of feed. But lathe tools are used at widely varying rates of feed,
and we may therefore take an example in which a tool is at work taking a
cut of the same diameter and depth at different rates of feed.
[Illustration: Fig. 936.]
This is shown in Fig. 936, tool 1 taking the coarsest, and 2 the finest
feed, and it is seen that the finer the rate of feed the more clearance
the tool has with a given degree of side clearance (for all the three
tools have 7° of side angle). The only way to obtain an equal degree of
clearance from the cut, therefore, clearly lies in giving to a tool a
different angle for every variation, either in work diameter or in rate
of feed traverse, and to show how much this will affect the shape of the
tool, we have Fig. 937, in which the same rate of feed is used for all
three cuts, and the tool is given in each position 5° of clearance from
the cut. In position 1 the tool side stands at 8-1/2° of angle from line
A, which is at a right angle to the work axis. In position 2 it stands
at 10-1/2°, and in position 3 at 15° of angle from line A, a variation
of 6-1/2°. Referring now to the top face of the tool, the variations
occur to the same extent and from the same causes. It is in a fine
degree of perception of these points that constitutes the skill of
expert workmen in grinding their lathe tools, varying the angle of the
tool at every grinding to suit the varying requirements.
[Illustration: Fig. 937.]
It has been shown that for freedom of cutting and ease of driving a
given cut, the direction of top rake as well as its degree needs to be a
maximum that the nature of the material and its degree of hardness will
admit; but this is not the only consideration, because in a finishing
cut the surface requires to be left as smooth and clean cut as possible,
and it remains to consider how this may best be accomplished. Now let it
again be considered that it is that part of the cutting edge that lies
at a right angle to the axial line of the work that removes the metal,
while it is that part that lies parallel to the work axis (or in other
words parallel to the finished work surface) that performs the finishing
cutting duty.
[Illustration: Fig. 938.]
Now, in proportion as the length of the cutting edge is disposed
parallel to the work axis, the tool has a tendency to spring (under an
increase of cut) into the work, and also to dip into soft places or
seams in the work, and the amount of its front rake must be decreased,
because such rake causes a pressure pulling the tool deeper into its
cut, as was explained with reference to Fig. 921. Round-nosed front
tools, therefore, such as in Fig. 938, cannot be given so much front
rake as ordinary ones, such as in the preceding figures.
[Illustration: Fig. 939.]
Round-nosed tools are used to cut out round corners, and the roughing
tools are given a less curvature than that to be formed on the work,
thus in Fig. 939 is an ordinary form of small round nose shown operating
in what is termed a hollow corner, the directions of tool feed being
marked by arrows. The tool may be fed by the feed traverse, and the tool
gradually withdrawn, thus forming the work to the required curve.
The amount of cut a lathe will drive, the degree of hardness which the
tool may be given, the length of time the tool will last without
grinding, the speed at which the work may run, and the cleanness and
truth of the cut, depend almost entirely upon the perfect adaptability
of the tool to the conditions under which it is to be used. Upon the
same kind of work, and using the same kind of tools, some workmen will
give a tool from 20° to 30° more angle than others.
[Illustration: Fig. 940.]
It is a difficult matter to determine at just what point the utmost duty
is being obtained from cutting tools, because the conditions of use are
so variable; but one good general guide is the speed at which the tool
cuts, and another is the appearance of the cuttings or chips.
[Illustration: Fig. 941.]
Both these guides, however, can only be applied to metal not unusually
hard, and to tools rigidly held, and having their cutting edges
sufficiently close to the tool point or clamp that the tool itself will
not bend and spring from the pressure of the cut. The cutting speed for
chilled cast-iron rolls, such, for example, as calender rolls, is but
about 7 feet per minute, and the angles one to the other of the tool
faces is about 75 degrees, the top face being horizontally level, and
standing level with the axis of the roll.
When a tool has front rake only, the form of its cutting will depend
upon the depth of its cut. With a very fine cut the cutting will come
off after the manner shown in Fig. 940, while as the depth of the cut is
increased, the cutting becomes a coil such as shown in Fig. 941. These
coils lie closer together in proportion as the top face of the tool is
given less rake, as is necessary for steel and other hard metal. Thus
Fig. 940 represents a cutting from steel, the tool having front rake
only, while Fig. 941 represents a cutting from a steel crank pin, the
tool having side rake. The following observations apply generally to the
cuttings.
[Illustration: Fig. 942.]
The cleaner the surface of a cutting, and the less ragged its edges are,
the keener the tool has cut; thus, in Fig. 941, the raggedness shows
that the tool was slightly dulled, although not sufficiently so to
warrant the regrinding of the tool. Such a cutting, however, taken off
wrought iron would show a tool too much dulled, or else possessing too
little top rake to cut to the best advantage. In wrought iron, the tool
having a keener top face, the cuttings will coil larger, and the
direction in which they coil and move as they leave the tool will depend
upon the shape of the tool and its height to the work.
[Illustration: Fig. 943.]
[Illustration: Fig. 944.]
In Fig. 942, for example, is a tool having front and side angle in about
an equal degree, and its cutting is shown in Fig. 943, the side angle
causing it to move to the right, and the front angle causing it to move
towards the tool post.
The tool in Fig. 944 has side rake mainly, and the point is slightly
depressed, hence its cutting would leave the work moving horizontally
and towards the right hand.
[Illustration: Fig. 945.]
[Illustration: Fig. 946.]
In Fig. 945 the point of the tool is made considerably lower than the
point B, and as a result the cutting would rise somewhat vertically as
in Fig. 946. Indeed the heel B may be raised so as to cause the cutting
to move but little to the right, but rise up almost vertically, being
thrown over towards the work, and in extreme cases the cutting will rub
against the surface of the work and the friction will prevent the
cutting from moving to the right, hence it will roll up forming a ball,
the direction of the rotation occasionally changing.
Whatever irregularities may appear in the coil of the cuttings will, if
the tool is not dulled from use, arise from irregularities in the work
and not from any cause attributable to the tool.
The strength of a cutting forms to a great extent a guide as to the
quality of the tool, since the stronger the cutting the less it has
become disintegrated, and therefore less power has been expended in
removing it from the work.
The cutting speed for wrought iron should be sufficiently great that
water being allowed to fall upon the work in a quick succession of drops
as, say, three per second, the cuttings will leave the work so hot as to
be almost unbearable in the hands, if the cut is a heavy one, as, say,
reducing the work diameter 1/2 inch at a cut.
If wrought-iron cuttings break off in short pieces it may occur from
black seams in the work, but if they break off short and show no
tendency to coil, the tool has too little rake. If the tool gets dull
too quickly and the cutting speed is not excessive, then the tool has
too much clearance. If the tool edge breaks there is too much rake
(providing of course that the tool has not been burnt in the forging or
hardening), a fine feed will generally produce longer and closer coiled
cuttings (that is of smaller diameter) than a coarse feed, especially
if the work be turned dry or without the application of water.
[Illustration: Fig. 947.]
Aside from these general considerations which apply to all tools, there
are peculiar characteristics of particular metals; thus, for example,
cast iron will admit of the tool having a greater width of cutting edge
in a line with the finished surface of the metal than either steel,
wrought iron, copper or brass, which renders it possible to use a
finishing tool of the form shown in Fig. 947, whose breadth of cutting
edge A, lying parallel with the line of feed traverse, may always exceed
that for other metals, and may in the case of cast iron be increased
according to the rigidity of the work, especially when held close in to
the tool post.
[Illustration: Fig. 948.]
The corners B C may for roughing the work be rounded so as to be more
durable, but for finishing cuts they should be bevelled as shown,
because by this means face A can more easily be left straight than would
be the case with a rounded corner. In the absence of the bevels there
would be a sharp corner that would soon become dull. For finishing
purposes the corners need not be so much bevelled as in figure, but may
be very slightly relieved at the corners A and B, in Fig. 948, the width
of the flat nose being slightly greater than the amount of feed per
lathe revolution. Such tools produce the quickest and best work without
chattering when the conditions are such that the work and the tool are
held sufficiently rigid, and in that case may be used for the harder and
tougher metals, as wrought iron and steel.
We have now to consider the height of the tool with relation to the
work, which is a very important point.
[Illustration: Fig. 949.]
In Fig. 949, for example, let E be the washer or ring under the tool,
and F therefore the fulcrum from which the tool will bend. Let the
horizontal dotted line a represent the centre of the work, and it is
plain that to whatever amount the tool may spring under the pressure of
the cut, its motion from this spring will be in the direction of the
dotted arc H, causing the tool to dip deeper into the work in proportion
as the tool point is set above the work centre line A. Now the amount of
tool spring will even under the most rigid conditions vary in a heavy
cut with every variation in the depth of cut or in the hardness of the
metal. Furthermore, as the cutting edge of the tool becomes dulled from
use, its spring will increase, because the pressure required to force it
to its cut becomes greater, and as a result when the conditions are such
that a perceptible amount of tool spring or deflection occurs, the work
will not be turned cylindrically true. Obviously the work under these
conditions will be most true when the tool point is set level with the
line A, passing through the work axis.
[Illustration: Fig. 950.]
There are two advantages, however, in setting the tool above the work
centre: first it severs the metal easier; and second, it enables the
employment of more bottom rake without increasing the bottom clearance.
[Illustration: Fig. 951.]
Thus in Figs. 950 and 951 the diameters of the work W and the top rake
of the respective tools are equal, but the tool that is set above the
centre, Fig. 950, has more bottom rake but no more clearance, which
occurs from the manner in which the cutting edge is presented to the
work; the dotted lines represent the line of severance for each, and it
is obvious that in Fig. 950, being of the shortest length for the depth
of the cut will require least power to drive, because it is, as
presented to the work, the sharpest wedge, as will be perceived by
referring to Fig. 952, in which the tool shown in Fig. 950 is simply
placed below the work centre, all other conditions as angle, &c., being
equal.
From these considerations it appears that while for roughing cuts it is
advantageous to set the tool above the centre, it is better where great
cylindrical truth is required to set it at the centre for finishing cut.
[Illustration: Fig. 952.]
It may also be observed that if the lathe bed be worn it will usually be
most worn at the live centre end, where it is most used, and a tool set
above the centre will gradually fall as the cut proceeds towards the
live centre, entering the work farther, and therefore reducing its
diameter. This can be offset by setting the tailstock over, but in this
case the wear of the work centres is increased, and the work will be
more liable to gradually run out of true, as explained with reference to
turning taper work. Sir Joseph Whitworth recommends that the tool edge
be placed at the "centre" of the work, while at the same time on a line
with the middle of the body of the steel. To accomplish this result it
is necessary that the form of the tool be such as shown in Fig. 953, in
which W represents a piece of work, R the slide rest, A the fulcrum of
the tool support, the dotted line the centre of the work, and the arrow
the direction in which the tool point would move from its deflection or
spring. Now take the conditions shown in Fig. 954, and it will be
perceived at once that the least tool deflection will have an
appreciable effect in causing the tool point to advance into the work in
the direction denoted by the arrow. This would impair the cylindrical
truth of the work, because metals are not homogeneous but contain in
forged metals seams and harder and softer places, and in cast metals
different degrees of density, that part laying at the bottom of the
mould being densest (and therefore hardest) by reason of having
supported the weight of the metal above it when cooling in the mould.
[Illustration: Fig. 953.]
This brings us to another consideration, inasmuch as supposing the tool
edge to be set level with the work centre (as in Figs. 951 and 953), the
arc of deflection of the tool point will vary in its direction with
relation to the work according to the vertical distance of the top of
the tool rest (R in Figs. 953 and 954) from the horizontal centre of the
work.
Thus the vertical distance between the point A in Fig. 953 and the work
centre is less than that between A and the horizontal work centre in
Fig. 954, as may be measured by prolonging the dotted lines in both
figures until they pass over A, and then measuring the respective
vertical distances between A and those dotted lines. It is to be noted
that this distance is governed by the vertical distance of the top of
the tool rest R from the work centre, but where this distance is
required or desired to be reduced a strip of metal may be placed beneath
the tool and between it and the slide rest.
[Illustration: Fig. 954.]
It will now be obvious that to produce work as nearly cylindrical as
possible, the tool edge should stand as near to the slide rest as the
circumstances will permit, which will hold the tool more firmly and
prevent, as far as possible, its deflection or spring from the cut
pressure. Both in roughing out and in finishing, this is of great
importance, influencing in many cases the depth of cut the tool will
carry as well as the cylindrical truth of the work.
We may now present some others of the ordinary forms of tools used in
the slide rests on external or outside work, bearing in mind, however,
that these are merely the principal forms, and that the conditions of
practice require frequent changes in their forms, to suit the conditions
of access to the work, &c.
Fig. 955 represents a diamond point tool much used by eastern tool
makers. The sides are ground flat and the point is merely oil-stoned to
take off the sharp corner. This tool is used with very fine feeds as,
say, 180 work revolutions to an inch of tool traverse, taking very fine
cuts, and in sharpening it the top face only is ground; hence as the
height of the tool varies greatly before it is worn out, the tool
elevating device must have a great range of action.
[Illustration: Fig. 955.]
In Fig. 956 is shown a side tool for use on wrought iron; it is bent
around so that its cutting edge A may be in advance of the side of the
steel, and thus permit the cutting edge to pass up into a corner. When
it is bent to the left as in the figure, it is termed a right-hand side
tool, and per contra when bent to the right it is a left-hand tool. The
edge A must form an acute angle to edge B, so that when in a corner the
point only will cut, or when the edge A meets a radial face, as in Fig.
957, the cutting edge B will be clear of the work as shown.
[Illustration: Fig. 956.]
If the angle of A to B is such that both those edges cut at once, the
pressure due to such a broad cutting surface would cause the tool to
spring or dip into the work, breaking off the tool point and perhaps
forcing the work from between the lathe centres.
This tool may be fed from right to left on parallel work, or inwards and
outwards on radial faces, but it produces the truest work when fed
inwards on radial faces, and to the left on parallel work, while it cuts
the smoothest in both cases when fed in the opposite direction.
[Illustration: Fig. 957.]
It is a very desirable tool on small work, since it may be used on both
the stem of the work, and on the radial face, which saves the trouble of
having to put in a front tool to turn the stem, and a separate tool for
the radial face.
In cutting down a radial face with this tool, it is best (especially if
much metal is to be cut off), if the face of the metal is hard, to carry
the cut from the circumference to the centre, as shown in the plan view
in Fig. 958, in which _a_ is the cutting edge of the tool, B a collar
on a piece of work, _c_ the depth of the cut, and D a hard skin surface.
Thus the point of the tool cuts beneath the hard surface, which breaks
away without requiring to be actually cut.
[Illustration: Fig. 958.]
[Illustration: Fig. 959.]
Fig. 959 represents a cutting off or parting tool for wrought iron, its
feed being directly into the metal, as denoted by the arrow. This tool
should be set exactly level with the work centre when it is desired to
completely sever the work. When, however, it is used to merely cut a
groove, it may be set slightly above the centre.
[Illustration: Fig. 960.]
[Illustration: Fig. 961.]
When the tool is very narrow at _c_, Fig. 960, or long as in Fig. 961,
it may be strengthened by being deepened, the bottom B projecting below
the level of the tool steel, which will prevent undue spring and the
chattering to which this tool is liable.
[Illustration: Fig. 962.]
[Illustration: Fig. 963.]
To enable the sides of the tool to clear the groove it cuts, the width
at _c_ should slightly exceed that at D, and the thickness along the top
_a_ should slightly exceed that at the bottom B.
When the tool is used to cut a wide groove as, say, 3/8-inch wide, in a
small lathe, it is necessary to carry down two cuts, making the tool
about 1/4 inch wide at _c_, which is a convenient size, affording
sufficient strength for ordinary uses.
[Illustration: Fig. 964.]
[Illustration: Fig. 965.]
When used on wrought iron the top face may, with advantage, be given top
rake as in Fig. 962, which on account of causing the tool to cut easier,
will reduce the spring of the work W in the direction of arrow A. For
brass work, however, the top should be ground in an opposite direction,
as in Figs. 963 and 964, which will enable it to cut smoother and with
less liability to rip into the metal, especially if the tool requires to
be held far out from the tool post. To capacitate the tool to cut a
groove close up to a shoulder, it should be forged to the shape shown in
Fig. 965. As it is very subject to spring, it should not, unless the
conditions are such as to give rigidity to both the work and the tool,
be set above the work centres.
[Illustration: Fig. 966.]
When a grooving or parting tool is to be used close up to the lathe dog,
its cutting end may be bent at an angle, as in Fig. 966, so that it may
be adjusted on the lathe rest, so that the work driver will not strike
against the slide rest.
[Illustration: Fig. 967.]
In Figs. 967, 968, and 969, are represented the facing tool, side tool,
or knife tool, as it is promiscuously termed, which is sometimes made
thicker at the bottom as in Fig. 969. It is mainly used for squaring up
side faces, as upon the ends of work or the sides of heads or collars. A
is the cutting edge which may be ground so as to cut at and near the
end, for large work in which it is necessary to feed the tool in with
the cross slide, or to cut along its full length for small work in which
the longitudinal feed is used. To facilitate the grinding, the bottom
may be cut away, as at B in Fig. 968.
[Illustration: Fig. 968.]
[Illustration: Fig. 969.]
In some practice the bottom B, Fig. 969, of the tool, is made thicker
than the top A, which is, however, unnecessary, unless for heavy cuts,
for which the tool would be otherwise unsuitable on account of weakness.
For all ordinary facing purposes, it should be made of equal thickness,
which will reduce the area to be ground in sharpening the tool.
[Illustration: Fig. 970.]
[Illustration: Fig. 971.]
On small work the edge A A should be ground straight, and set at a right
angle to the work, so that it may face off the whole surface at once,
but for work of large diameter it should be ground and set as in Figs.
970 and 971, so that it will cut deepest at the end E, enabling it to
carry a finishing cut from the circumference to the centre, by feeding
it with the cross-feed screw.
[Illustration: Fig. 972.]
The cutting edge should be level with the centre of the work, the angle
of the top face D being about 35 degrees in the direction of the arrow C
for wrought iron, and level if used for brass. When this tool is to be
used for a face close to the work driver it should be bent at an angle
as in Fig. 972, so as to enable the driver to clear the slide rest, and
when used for countersunk head bolts, it may be bent at an angle as in
Fig. 973, so that when it is once set to give the head the correct
degree of taper, it will turn successive heads to the correct taper
without requiring each head to be fitted to its place.
[Illustration: Fig. 973.]
In Fig. 974 is shown the spring tool which is employed to finish
smoothly round corners or sweeps, which it will do to better advantage
than any other slide rest tool, because it is capable of carrying a
larger amount of cutting edge in simultaneous operation. This property
is due to the shape of the tool, the bend or curve serving as a spring
to enable the tool to bend rather than dig into the work.
[Illustration: Fig. 974.]
This form of tool is sometimes objected to on the ground that it does
not turn true, but this is not the case if the tool is properly formed
and placed at the correct height with relation to the work. In the first
place the top face should, even on wrought iron, have but very little
top rake, and indeed none at all if held far out from the tool post,
while for brass, negative top rake may be employed to advantage. The
height of the cutting edge B should be level with the top of the tool
steel as denoted by the dotted line in the figure, and in no case should
it stand above that level. The cutting edge should be placed about
level with the horizontal centre of the work, but in no case above it.
It is from this error that the tool is frequently condemned, because if
placed above, the broad cutting edge causes the tool to spring slightly
and dig into the metal, whereas when placed at the middle of the height
of the work the spring will not have that effect, as already explained
when referring to front tools. Furthermore, the spring of the tool (from
inequalities in the texture or from seams in the metal) will be in a
line so nearly coincident with the work surface that the latter will be
practically true, and from the smoothness and the evenness of the curve
this tool will produce a much better work than any other tool, unless
indeed the curve be of a very small radius, as, say, about 1/4 inch
only, in which case a hand tool such as shown in Fig. 1292 may be
employed; spring tools are intended to finish only, and not to rough out
the work.
[Illustration: Fig. 975.]
The curves, as B in Fig. 974 for a round corner and C for a bead, should
be carefully and smoothly finished to the required curve and the top
face only ground to sharpen the tool, so as to maintain the curve as
nearly as possible; but if the curve is a very large one, the tool will
require to be a part of the curve only, and must be operated by the
slide rest around the curve.
For finishing the curves or round corners in cast-iron work the spring
tool is especially advantageous, as it will produce a polished clean
surface of exquisite finish if used with water, and the cutting speed is
exceedingly slow, as about 7 feet per minute.
LATHE SLIDE REST TOOLS FOR BRASS WORK.
Nearly all the tools used in the slide rest upon iron work may be
employed upon brass work, but the top faces should not have rake, that
is to say, they should have their top faces lying in the same plane as
the bottom plane of the tool steel which rests on the slide rest. For if
the top face is too keen it rips rather than cuts the brass, giving it a
patchy, mottled appearance.
[Illustration: Fig. 976.]
Fig. 975 represents a front tool for brass, which is used for carrying
cuts along outside work or for facing purposes, corresponding, so far as
its use is concerned, to the diamond point or front tool for iron. The
top face of this tool must in no case be given rake of any kind, as that
would cause it to tear rather than to cut the metal, and also to
chatter. The point A should be slightly rounded and the width at B and
depth at C must be regulated to suit the depth of cut taken, the rule
being that slightness in either of these directions causes the tool to
chatter. When held far out from the tool post or under other conditions
in which the tool cannot be rigidly held, the top face should be ground
away towards the end, thus depressing the point A, after the manner
shown with reference to the cutting-off tool for brass in Fig. 963. The
manner in which the cuttings come off brass work when a front tool is
used, depends upon the hardness of the brass and the speed at which the
tool cuts.
[Illustration: Fig. 977.]
[Illustration: Fig. 978.]
In the harder kinds of brass, such as that termed gun metal,
composition, or bell metal, the cuttings will fly off the tool in short
angular grains, such as indicated in Fig. 976, travelling a yard or two
after leaving the tool if a fairly quick cutting speed is used. But if
the cutting speed is too slow the cuttings will come off slowly and fly
but a few inches. In the softer kinds of brass, such as yellow brass,
the cuttings are longer and inclined to form short curls, which will, if
cut at a high speed, fly a few inches only after leaving the tool.
In Fig. 977 is shown a right-hand side tool for brass work. It is used
to carry cuts along short work, and to carry facing cuts at the same
time, thus avoiding the necessity to move the position of the tool to
enable it to carry a facing cut, as would be necessary if a front tool
for brass were used. It is peculiarly adapted, therefore, for brass
bolts, or other short work having a head or collar to be faced
especially; hence, it may be traversed to its cut in either direction
without requiring to be moved in the tool post. It may also be used to
advantage for boring purposes. It will be found that this tool will cut
smoother and will be less liable to chatter if its top face is ground
slightly down towards the point and if it be not forged too slight
either in depth or across B. Its clearance on the side is given by
forging it to the diamond shape shown in the sectional view. To make the
tool a left-handed one it must be bent to the right, the clearance being
in any case on the inside of the curve.
[Illustration: Fig. 979.]
The forms of single-pointed slide rest tools employed to cut [V]-threads
in the lathe are shown in Fig. 978, which represents a tool for
external, and Fig. 979, which represents one for an internal [V]-thread,
the latter being a tool ground to accurate shape and secured in a holder
by the set screw S.
It is obvious that a Whitworth thread might be cut with a single-pointed
tool such as shown in Fig. 980, the corner at B being rounded to cut the
rounded tops of the thread. It is more usual, however, to employ a
chaser set in the tool point in the same manner as a single-pointed
tool, or in a holder fixed in the tool post. When a single-pointed tool
is employed to cut a thread, the angles of its sides are not the same as
the angle of the thread it produces, which occurs because the tool must
have clearance to enable it to cut. In Fig. 981, for example, is a
single-pointed tool without any clearance, and, as a result, it cannot
enter the work to cut it. In Fig. 982 the tool is shown with clearance,
and, as a result, the angle of the cutting edge is not the same angle as
the sides of the tool are, because the top face is not at a right angle
to the sides of the tool. It is obvious that the angle of the sides of
the tool must be taken along the dotted line in Fig. 982.
[Illustration: Fig. 980.]
It follows then that a tool whose sides are at a given angle will cut a
different angle of thread for every variation in the amount of
clearance. But whatever the amount of clearance may be, the tool will
produce correct results providing that the gauge to which the tool is
ground is held level, as in Fig. 983 at A, and not at an angle as at B.
The tool, however, must be set at the correct height with relation to
the work, and its top surface must point to the work axis to produce
correct results.
[Illustration: Fig. 981.]
[Illustration: Fig. 982.]
Suppose, for example, that in Fig. 984 A is a piece of work, its
horizontal centre being represented by the dotted line C, and its centre
of revolution being at C. Now suppose D is a screw-cutting tool cutting
a depth of thread denoted by E. G is another lathe tool having teeth of
the same form and angle as D, but lifted above the horizontal centre of
the work. The depth of thread cut by G is denoted by F, which is
shallower, though it will be seen that the point of G has entered the
work to the same depth or distance (of the tool point) as D has. It is
obvious, however, that for any fixed height, a tool suitable to cut any
required depth or angle can be made, but it would be difficult to gauge
when the tool stood at its proper height.
[Illustration: Fig. 983.]
To facilitate setting the height of the tool, a gauge such as shown in
Fig. 985 may be used, the height of the line A from the base equalling
the height or distance between the top surface of the cross slides and
the axial line of the lathe centres. If the lathe, however, have an
elevating slide rest, the rest must be set level before applying the
gauge. Or in place of using the gauge, the tool stool or tool holder, as
the case may be, may be made of such height that when level in the tool
post its top face points to the axis of the lathe centre, the tool being
sharpened on the angles and not ground on the top face.
[Illustration: Fig. 984.]
[Illustration: Fig. 985.]
But in the case of a tool holder, or of a chaser holder, the tool may be
ground on the top face, and adjusted for height by any suitable means,
the top of the holder serving as a guide to set the tool by.
[Illustration: Fig. 986.]
The line of the cutting edge of the tool must, to obtain correct
results, be presented to the work in the same manner as it was presented
to the gauge to which its angles were ground, so that if the tool were
in position in the tool post, and the gauge were applied, it would point
to the axis of the lathe centre, for if this is not the case the thread
cut will not be of correct angle or depth. Thus, in Figs. 986 and 987
the tool T would cut threads too shallow, although placed at the correct
height, because the cutting edges are at an angle to the radial lines C
C.
[Illustration: Fig. 987.]
It becomes obvious, then, that it is improper to set the height of a
screw-cutting tool by means of any tool elevating or setting-device that
throws it out of the horizontal position. To enable the correct setting
of threading tools, and to avoid having to grind the angles correct to
gauge every time the tool requires sharpening, various kinds of tool
holders have been designed by means of which the tool may be ground on
the top face, and set at correct height and in the proper plane.
[Illustration: Fig. 988.]
[Illustration: Fig. 989.]
To facilitate grinding the tools to a correct angle, the gauge shown in
Fig. 988 is employed, the various notches being for the pitches of
thread for which they are respectively marked, but, the edge of the
gauge being circular, does not afford much guide to the eye in grinding
the angles equal from the sides of the body of the tool; hence the form
of gauge shown in Fig. 989 is preferable, because the tool can be so
ground that the edge of the gauge stands parallel with the side of the
tool steel, so that the tool will, when in correct position, point
straight to the work axis. To insure correctness in setting the tool, it
may then be set with a square S in Fig. 990, held firmly with its back
against the side of the tool, which may be adjusted in the tool post
until the blade B comes fair with the work.
[Illustration: Fig. 990.]
Another method of setting the tool is with a gauge as in Fig. 991, which
sets it true with the angle independent of whether the angle is true
with the side of the tool or not. In Fig. 992 is a form of gauge that
will serve to grind the tool by to correct angle, and also to set it in
the lathe by the angles, independent of the side of the tool.
The same gauge may be used for setting internal threading tools by first
facing the work quite true and then applying the gauge as in Fig. 993.
[Illustration: Fig. 991.]
[Illustration: Fig. 992.]
[Illustration: Fig. 993.]
By reason of the comparatively sharp points of thread-cutting tools,
they are more readily dulled than the rounder pointed ordinary lathe
tool, and by reason of their cutting edges extending along a greater
length of the work, and therefore causing it to spring or bend more from
the strain of the cut, they cannot be employed to take such heavy cuts
as ordinary tools. Hence, in all thread cutting, it is necessary to turn
the work down to the finished diameter before using the threading tool,
so that the thread will be finished when it is cut to the proper depth.
To test that depth on a piece of work having a United States standard,
or a sharp [V]-thread, a gauge such as shown in Fig. 994 may be used,
consisting of a piece of sheet steel about 1/50 inch thick, having a
single tooth formed correct for the space of the thread, so that the
edge of the gauge will meet the tops of the thread when the space is cut
to admit the tooth on the gauge; the most accurate method of producing
such a gauge having been described in the remarks upon screw threads.
[Illustration: Fig. 994.]
If the tool is known to be ground to the correct angle and is set
properly, the gauge for depth may be dispensed with by turning the body
of the work to correct diameter, and also turning a small part, as a in
Fig. 995, down to the correct diameter for the bottom of the thread, so
that when the tool point meets A the thread will be cut to correct
depth.
[Illustration: Fig. 995.]
Figs. 996 and 997 represent a method of cutting a round top and bottom,
or any other form of thread, by means of a single-pointed circular
cutting tool, which is mounted on a holder. On the circumference of the
cutter is cut a single thread, and a piece is cut out at E to form a
cutting edge. To cut a right-hand thread on the work, a left-hand one
must be cut on the cutter, so as to make its thread slant in the proper
direction. The tool is sharpened by grinding the top face, and moved on
the holding pin to set it to the proper height or in position to enable
it to cut. A top view of the tool and holder is shown in figure 997.
[Illustration: Fig. 996.]
It is obvious that two gaps may be cut in the wheel or cutter so as to
provide two cutting edges, one of which may be used for roughing, and
the other for finishing cuts.
[Illustration: Fig. 997.]
In roughing out coarse threads, a single-pointed tool, formed as in Fig.
998, and set considerably above the centre as shown, may be used to
great advantage. It will carry a heavy cut and throw off a cutting but
very little curved; hence but little power is absorbed in bending the
cutting. To preserve the cutting edge, the point of the tool should be
slightly rounded. Such a tool, however, requires to be rigidly held, and
requires experience to use it to the best advantage.
[Illustration: Fig. 998.]
An English tool holder for a single-pointed tool for cutting coarse
pitch threads, such as square threads, is shown in Fig. 999. The stem of
the holder is cylindrical, and is held between two clamping pieces,
while the short piece of steel used as a tool (which is thinnest at the
bottom, so as to provide for the clearance without grinding it) is
clamped in a swiveled post, so that it may be set at the angle sideways
required for the particular pitch of thread to be cut, as is shown in
the end view.
[Illustration: Fig. 999.]
[Illustration: Fig. 1000.]
[Illustration: Fig. 1001.]
The difficulty of adjusting the height of threading tools that are
ground on their top faces to sharpen them is obviated in a very
satisfactory manner by the tool holder patented by the Pratt and Whitney
Company, and represented in Figs. 1000 and 1001. A is the body of the
holder, C is the tool clamp, and B the set screw for C; D is a pin fast
in A and projecting into C to adjust it square upon A. The threading
tool G has a groove H, into which the projection E fits, so that the
tool is held accurately in position. F is the screw which adjusts the
height of the tool, being threaded into A and partly into G, as is shown
at I. The holder once being set in correct position, the threading tool
may be removed for grinding, and reset with accuracy. The face K of the
holder is made at 30° to the front or leading face of the holder, so
that the stem or body of the holder will be at an angle and out of the
way of the work driver.
[Illustration: Fig. 1002.]
If a chaser instead of a single-pointed tool be used to cut a thread,
the thread requires to be gauged for its full diameter only, because
both the angles of the thread sides and the thread depth are determined
by the chaser itself. Chasers are also preferable to a single-pointed
tool when the work does not require to be cut to an exact diameter, nor
to have a fully developed thread clear up to a shoulder; but when such
is the case a single-pointed tool is preferable, because if the leading
tooth should happen to run against the shoulder the whole of the teeth
dig into the work, and more damage is done to it than with a
single-pointed tool. When the thread does not run up to a shoulder, or
in cases where the thread may be permitted to run gradually out, and,
again, where the thread is upon a part of enlarged diameter, a chaser
may have its efficiency increased in two ways, the first of which is
shown in Fig. 1002. When the chaser is set and formed as at A in the
figure, the leading tooth takes all the cut, and the following tooth
will only cut as it is permitted to do so from the wear of the leading
bolt. This causes the tooth to wear, but the teeth may be caused to each
take a proportion of the cut by chamfering them as at B in the figure,
which will relieve the front tooth of a great part of its duty and let
the following teeth perform duty, and thus preserve the sharpness of the
cutting edges. We are limited in the degree of chamfer that may be given
to the teeth, first, because as the cutting edge is broader and the
strain of the cut is greater it causes the tool to spring or bend more
under the cut pressure; and secondly, because if the tool be given many
teeth in order to lengthen the chamfer, then the pitch is altered to a
greater extent by reason of the expansion which accompanies the
hardening of the chaser.
[Illustration: Fig. 1003.]
[Illustration: Fig. 1004.]
A chaser thus chamfered may be set square in the tool post by placing a
scale against the work as at S in Fig. 1003, and setting the bottoms of
the chaser teeth fair with the outer edge of the scale as in the figure.
The second method of increasing the efficiency of a chaser is to grind
the top face at an angle as from A to B in Fig. 1004, and set it so that
the last tooth B is at or a little above the work axis D. This causes
the last tooth B to stand sufficiently nearer the work axis than the
other teeth to enable it to take a light scraping cut, producing a
smooth cut, because the duty on the last tooth being light it preserves
its cutting edge, and therefore its form.
Chasers are often in shops, doing general work, formed in one piece in
the same way as an ordinary tool, but it is preferable to use short
chasers and secure them in holders.
[Illustration: Fig. 1005.]
Figs. 1005 and 1006 show a convenient form of holder, the chaser A being
accurately fitted into a recess in the holder D, so that it may be set
square in the holder without requiring to be adjusted to come fair with
the thread grooves after having been ground to resharpen it. The short
chasers are held by the clamp B, which has at C a projection fitting
into a recess in the holder to cause the clamp to adjust itself fairly.
In setting a chaser to correct position in a tool post the points of the
teeth may be set to the surface of the work as in Fig. 1007, or if the
thread is partly produced and the lathe has a compound slide rest, the
tool may be set to the tops of the thread as in Fig. 1008, and then
brought into position to meet the thread grooves by operating the slide
rest.
[Illustration: Fig. 1006.]
[Illustration: Fig. 1007.]
[Illustration: Fig. 1008.]
It is obvious that the height and position of a chaser require to be as
accurately set as a single-pointed tool, but it is more difficult to set
it because it can only be sharpened by grinding the top face, and this
alters the height at each grinding.
Thus, suppose that when new its teeth are of correct height, when the
bottom face I, Fig. 1009, lies upon the rest R, the face H being in line
with the centre B B of the work, then as face H is ground the tool must
be lifted to adjust its height. On account, however, of the curve of the
teeth it is very difficult to find when the chaser is in the exact
proper position, which in an ordinary chaser will be when it has just
sufficient clearance to enable it to cut, as is explained with reference
to cutting up chasers and using them by hand.
[Illustration: Fig. 1009.]
To obviate these difficulties, an excellent form of chaser holder is
shown in Figs. 1010 and 1011. Its top face C being made of such a height
that when the holder rests on the surface of the slide rest and is in
the tool box, C will stand horizontally level with the horizontal centre
of the work, as denoted by the horizontal line D E; then the tool proper
may have long teeth as denoted by A, and the surface of the teeth may
always be brought up level with the top surface of the tool holder as
tested with a straight-edge. This is a ready and accurate mode of
adjustment. A top view of the tool holder is shown in Fig. 1011, in
which A is the tool holder, B the threading tool, with a clamp to hold
B, and a screw to tighten the clamp.
[Illustration: Fig. 1010.]
It may now be pointed out that a common sharp [V]-chaser may be used to
cut a United States standard thread by simply grinding off the necessary
flats at the points of the teeth, because when the chaser has entered
the work to the proper depth it will leave the necessary flat places at
the top of the thread, as is shown in Fig. 1012.
In cutting internal, inside, or female threads (these terms being
synonymous) the diameter of the bore or hole requires to be made of the
diameter of the male thread _at the root_.
[Illustration: Fig. 1011.]
Since, however, it is impracticable to measure male threads at the root,
it becomes a problem as to the proper size of hole to bore for any given
diameter and pitch of thread. This, however, may be done by the
following rules:--
To find the diameter at the roots or bottom of the thread of United
States standard threads:
Rule.--Diameter - (1.299 ÷ pitch) = diameter at root.
Example.--What is the diameter at the root of a United States standard
thread measuring an inch in diameter at the top of the thread and having
an 8 pitch?
Here 1.299 ÷ 8 = .162375.
/ 1.000000 \
Then 1 - .162375 | .162375 | = .8376.
| -------- |
\ .837635 /
For the sharp [V]-thread the following rule is employed:
Rule.--Diameter - (1.73205 ÷ pitch) = diameter at root.
Example.--What is the diameter at the root of a sharp [V]-thread of 8
pitch, and measuring 1 inch diameter at the top of the thread?
Here 1.73205 ÷ 8 = .21650.
/ 1.0000 \
Then 1 - .2165 | .2165 | = .7835.
| ------ |
\ .7835 /
For cutting square threads the class of tool shown in Fig. 1013 is
employed, being made wider at the cutting point C than at B or at D, so
that the cutting may be done by the edge C, and the sides _a_ may clear,
which is necessary to reduce the length of cutting edge and prevent an
undue pressure of cut from springing the work.
[Illustration: Fig. 1012.]
The sides of the tool from _a_ to B must be inclined to the body of the
tool steel, as shown in Fig. 1014, the degree of the inclination
depending upon the pitch of thread to be cut. It may be determined,
however, by the means shown in Fig. 1015.
[Illustration: Fig. 1013.]
[Illustration: Fig. 1014.]
[Illustration: Fig. 1015.]
Draw the line A, and at a right angle to it line B, whose length must
equal the circumference of the thread to be cut and measured at its
root. On the line A set off from B the pitch of thread to be cut as at
C, then draw the diagonal D, which will represent the angle of the
bottom of the thread to the work axis, and the angle of the tool sides
must be sufficiently greater to give the necessary clearance. The width
of the point C of the tool should be made sufficiently less than the
width of the thread groove to permit of the sides of the thread being
pinched (after the thread is cut to depth) with a tool such as was shown
in Fig. 968.
[Illustration: Fig. 1016.]
For coarser pitches the thread is cut as shown in Fig. 1016. The tool
is made one-half the width of the thread groove, and a groove, _a_, _a_,
_a_, is cut on the work. The tool is then moved laterally and a second
cut as at B B is taken, this second cut being shown in the engraving to
have progressed as far as C only for clearness of illustration. When the
thread has in this manner been cut to its proper depth, the side tools
are introduced to finish the sides of the thread. If the thread is a
shallow one each side may be finished at one cut by a side tool ground
and set very true; but in the case of a deep one the tool may be made to
cut at and wear its end only, and after taking a cut, the tool fed in
and another cut taken, and so on until, having begun at the top of the
thread, the tool operated or fed, after each traverse, by the cross
feed, finally reaches the bottom of the thread. If a very fine or small
amount of cut is taken, both sides of the thread may in this way be
finished together, the tool being made to the exact proper width.
[Illustration: Fig. 1017.]
[Illustration: Fig. 1018.]
When used on wrought iron the tool is sometimes given top rake, which
greatly facilitates the operation, as the tool will then take a heavier
as well as a cleaner cut.
[Illustration: Fig. 1019.]
After the first thread cut is taken along the work, it is usual to
remove it from the lathe and drill, at the point where it is desired
that the thread shall terminate, a hole equal in diameter to the width
of the thread groove, and in depth to the depth of the thread. This
affords relief to the cutting tool at the end of the cut, enables the
thread to end abruptly, and leaves a neat finish.
[Illustration: Fig. 1020.]
On account of the broad cutting edge on a screw-cutting tool, the lathe
is always run at a slower speed than it would be on the same diameter of
work using an ordinary turning tool. After the tool is set to just clear
the diameter of the work it is moved (for a right-hand thread) past the
end of the work at the dead centre, and a cut is put on by operating the
cross-feed screw. The feed nut is then engaged with the feed screw and
the tool takes its cut as far along the work as the thread is to be,
when the tool is rapidly withdrawn from the work and the lathe carriage
traversed back again, ready to take another cut. If, however, the thread
to be cut runs close up to a shoulder, head, or collar, the lathe may be
run slower as the tool approaches that shoulder by operating the belt
shipper and moving the overhead belt partly off the tight pulley and on
to the loose one, or the lathe may be stopped when the tool is near the
shoulder and the belt pulled by hand.
An excellent method of finishing square threads after having cut them in
the lathe to very nearly the finished dimensions is with an adjustable
die in a suitable stock, such as in Figs. 1017 and 1018, in which S is a
stock having handle H, and containing a die D, secured by a cap C,
pivoted at P. To adjust the size of the die, two screws, _a_ and _b_,
are used, _a_ passing through the top half of the die and threading into
the half below the split, while _b_ threads into the lower half and
abuts against the face of the split in the die, so that, by adjusting
these two screws, the wear may be taken up and the size maintained
standard. This device is used to take a very light finishing cut only,
and is found to answer very well, because it obviates the necessity of
fine measurement in finishing the thread. The die D is seated in a
recess at the top and at the bottom so as to prevent it moving sideways
and coming out.
LATHE TOOL HOLDERS FOR OUTSIDE TOOLS.--When a lathe cutting tool is made
from a rectangular bar of steel it requires to be forged to bring it to
the required shape at the cutting end, and to avoid this labor, and at
the same time attain some other advantages which will be referred to
presently, various forms of tool holders are employed.
These holders fasten in the tool post, or tool clamp, and carry short
tools, which, from their shapes and the manner in which they are
presented to the work, require no forging, and maintain their shapes
while requiring a minimum of grinding.
Fig. 1019 represents a side view of Woodbridge's tool holder at work in
the lathe, and Fig. 1020 is a view of the same set at an angle to the
tool rest. Fig. 1021 is an end view of the tool and holder removed from
the lathe.
The tool seat A is at an angle of about 4 degrees to the base of holder
(a greater degree being shown in the cut for clearness of illustration),
so that the side J of the tool will stand at an angle and have clearance
without requiring such clearance to be produced by grinding. The seat B
of the cap C upon the tool is curved, so that the cap will bind the
middle of the tool and escape the edges, besides binding the tool fair
upon its seat A. The top face is formed at the angle necessary for free
and clean cutting, and the tools are, when the cutting edge is provided
at one end only, hardened for half their length.
The holder, and therefore the tool, may obviously be swung at any chosen
angle of the work or to suit the requirements.
[Illustration: Fig. 1021.]
[Illustration: Fig. 1022.]
[Illustration: Fig. 1023.]
Fig. 1022 shows a right and left-hand diamond-point tool in position in
the holder with the cap removed, the cutting edge being at G, the angle
of the top face being from F to E. The tool, it will be observed from
the dotted line, is supported close up to its cutting corner.
[Illustration: Fig. 1024.]
Fig. 1023 shows a right and left-hand side tool in position, the dotted
line showing that it is supported as close to the cutting edge D as the
nature of facing work will permit. When left-hand tools are used the
holder is turned end for end, so as to support the tools in the same
manner as for right-hand ones, and for this purpose it is that the
holder is beveled off at each end.
By grinding both ends of one tool, however, to the necessary shape and
angle, one tool may be made to serve for both right and left, the tool
holder being simply reversed end for end in the tool post. There are,
however, furnished with each holder a right and left-hand diamond point
and a right and left-hand side tool, each being hardened for half its
full length.
It is obvious, however, that there is no front rake to the tool, and
that it therefore derives its keenness from the amount of side rake,
which may be regulated to suit the conditions.
When tool holders of this class are employed, the end face only of the
tool requires grinding to resharpen the cutting edges; hence the area of
metal requiring to be ground is much less than that on forged tools, and
therefore the grinding occupies less time; and if the workman grinds the
tools, he is enabled to run more lathes and not keep them idle so long
while grinding the tool. Or if the tools are kept ground in stock (about
200 of the tools or cutters serving to run 24 lathes a week) the workman
has but to slip in a new tool as the old one becomes dull, no adjustment
for height being necessary as in the forged tool.
When the tool requires to be set to an exact position, as in the case of
screw cutting, it is desirable that the tool holder be so constructed
that the tool may be removed therefrom and replaced without disturbing
the position of the tool holder in the tool post or tool clamp; and
means must therefore be provided for securing the tool to the holder
independently of the tool post or clamp screw. Fig. 1024 represents a
tool holder possessing these features: H is the holder provided with a
clamp C, secured by a screw B, T representing the tool, which is in this
case a chaser, having teeth down the full length of its front face; K is
a key or feather fast in the holder H, and fitting into a groove
provided in the side of the tool. The vertical angle of this feather
obviously determines the angle of clearance at which the tool shall
stand to the work.
The Pratt and Whitney Company, who are the manufacturers of this holder,
make this angle of clearance 15 degrees. The height of the tool in the
holder is adjusted by the screw S, which has journal bearing in the
holder, and threads to the end edge of the tool.
Now it is obvious that the holder H, once being set to its proper
position in the tool post, the tool T may be removed from and replaced
in the exact same position, both in the holder and with reference to the
work.
In Fig. 1025, for example, is a top view of the holder with a
single-pointed threading tool T in place. W represents a piece of work
supposed to be in the lathe, and G a tool-setting gauge; and it is
obvious that, if the holder is not moved, the tool T may be removed,
ground up, and replaced with the assurance that it will stand in the
exact same position as before, producing the exact same effect upon the
work, providing that the height is maintained equal, and the tool is not
altered in shape by the grinding. To maintain the height equal, all that
is necessary is to have the upper face (H, Fig. 1024) of the holder
horizontally level and in line with the line of centres of the lathe,
and to set the top face of the tool level with that of the holder. In
sharpening the tool the top face only is ground; hence the angles are
not altered.
Fig. 1026 represents the holder with a tool in position to true up a
lathe centre, the angle of the tool holder to the line of centres being
the same as in Fig. 1025; and Fig. 1027 represents various forms of
tools for curves. All these serve to illustrate the advantages of such a
tool holder.
[Illustration: Fig. 1025.]
If, for example, a piece of work requires the use of two or more such
tools, and the holder is once set, the tools may be removed and
interchanged with a certainty that each one put into place will stand at
the exact angle and position required, not only with relation to the
work, but also in relation to the other tools that have preceded it.
Each hollow or round will not only be correct in its sweep, but will
also stand correct in relation to the other sweeps and curves, no matter
how often the tools may be changed. Inasmuch as the tool is ground at
the top only for the purpose of resharpening, it maintains a correct
shape until worn out.
[Illustration: Fig. 1026.]
The pin shown at _f_ in Fig. 1024 is fast in the holder, and fits
loosely in clamp C to prevent it from swinging around on B when B is
loosened.
When the tool requires to preserve its exact shape it may also be made
circular with the required form for the cutting edge formed round the
perimeter. Thus Figs. 1028 and 1029, which are extracted from _The
American Machinist_, represent tool holders with circular cutting tools.
[Illustration: Fig. 1027.]
The holder A fits the lathe tool post, carrying the cutting tool B,
which is bolted to the holder and has at F a piece cut out to form the
cutting edge.
To facilitate the grinding, holes are drilled at intervals through B. A
plan view of this tool and holder is shown at C, the shape of the
cutting edge being shown at D. The cutting edge is shown in the side
view to be level with the centre of the tool holder height, but it may
be raised to the level of the top of the tool steel by raising the hole
to receive the bolt that fastens the cutter, as is shown at E; or the
cutter may be mounted on top of the holder as shown at H, having a stem
passing down through the holder, and capable of being secured by the
taper pin I. A plan view of this arrangement is shown at J.
[Illustration: Fig. 1028.]
[Illustration: Fig. 1029.]
[Illustration: Fig. 1030.]
[Illustration: Fig. 1031.]
Another form of circular cutter is shown in Fig. 1030. It consists of a
disk or cutter secured to a holder fitted to the tool post, the cutter
edge being formed by a gap in the disk, as shown in the figure, which
represents a cutter for a simple bead or round corner. The front end of
the holder has a face A, whose height is level with the line of lathe
centre when the holder is set level in the tool post. Hence the top face
of the cutting edge may be known to be set level with the line of
centres when it is fair with the face A of the holder. The bottom
clearance is given by the circular shape of the cutter, while side
clearance may be given by inclining the face B of the holder (against
which the face of the cutter is bolted) to the necessary angle from a
vertical line. The face C is ground up to resharpen the cutting edge,
and may be reground until the circumference of the wheel is used up.
Figs. 1031, 1032, 1033, and 1034 represent lathe tool holders by Messrs.
Bental Brothers, of Fullbridge Works, Maldon, England. The holder
consists of a bar A, having at the front end a hub H, containing a bush
in two halves, through which the tool T passes; this tool consisting of
a piece of [V]-shaped steel. A set screw on top of the hub clamps the
two half-bushes together, and these, as their faces do not meet, grip
the tool.
[Illustration: Fig. 1032.]
[Illustration: Fig. 1033.]
[Illustration: Fig. 1034.]
The advantage possessed by this form of holder is that the top face of
the tool may be given any desired degree of side rake or angle required
by the nature of the work by simply revolving the bushes in the hub of
the holder. Thus, in Fig. 1034 the top face of the tool stands level, as
would be required for brass work; in Fig. 1032 the tool is canted over,
giving its top face angle a rake in the direction necessary when cutting
wrought iron and feeding toward the dead centre; and in Fig. 1033 the
tool is in position for carrying a cut on wrought iron, the feed being
toward the live centre of the lathe. This capacity to govern the angle
of the top face of the tool is a great advantage, and one not possessed
by ordinary tool holders, especially since it does not sensibly alter
the height of the tool point with relation to the work. Again, the
[V]-shape of the tool steel causes the bushes to grip and support the
tool sideways, and, by reducing the area of tool surface requiring to be
ground, facilitates the tool grinding to that extent. Altogether, this
is an exceedingly handy device. It is obvious, however, that it cannot
be moved from side to side of the tool rest unless a right and left-hand
tool holder be used; that is to say, there must be two holders having
the hub on the opposite side of the body A.
[Illustration: Fig. 1035.]
[Illustration: Fig. 1036.]
Figs. 1035, 1036, 1037, and 1038 represent tool holders in which the
tools consist of short pieces of steel held end-wise and at a given
angle, so that the amount of clearance is constant. The holders Figs.
1035 and 1036 are split, and the tool is secured by the screw shown.
Fig. 1037 represents a tool holder in which the tool is held by a clamp,
whose stem passes through the body of the holder so as to bring the
fastening nut out at the end, where it is more convenient to get at than
are the screw heads in Figs. 1035 and 1036. It is obvious, however, that
such a holder is weak and unsuitable for any tools save those used for
very light duty indeed, while all this class of holders is open to the
objection that the side of the holder prevents the tool from passing up
into a corner, hence the cut cannot be carried up to a shoulder on the
work. This may, however, be accomplished by bending the end of the
holder round; but in this case two holders, a right and a left, will be
necessary.
Fig. 1038 represents a form of tool holder of this kind in which the
tool may be set for height by a set screw beneath it.
[Illustration: Fig. 1037.]
Fig. 1039 represents a tool holder and work-steadying device combined.
The holder is held in the lathe tool rest in the usual manner, and
affords slideway to a slide operated by the handle shown at the
right-hand end.
[Illustration: Fig. 1038.]
The tool is carried at the other end of this slide, there being shown in
the figure a cutting-off tool in position. At the end of the holder is a
hub and three adjusting screws whose ends steady the work, and which are
locked in their adjusted position by the chuck nuts shown.
[Illustration: Fig. 1039.]
THE POWER REQUIRED TO DRIVE CUTTING TOOLS.--From experiments made by Dr.
Hartig, he concluded that by multiplying the weight of the metal
cuttings removed per hour by certain decimal figures (or constants) the
horse-power required to cut off that quantity of metal might be
obtained. These decimal constants are as follows:
Lbs. of metal cut off per hour, cast iron × .0314 = horse-power required
to drive the lathe.
" " " wrought iron × .0327 = "
" " " steel × .4470 = "
FOR PLANING TOOLS.
Lbs. of steel cut off per hour × .1120 = horse-power required to drive planer.
" wrought iron " × .0520 = " "
" gun metal " × .0127 = " "
CHAPTER XI.--DRILLING AND BORING IN THE LATHE.
For drilling in the lathe, the twist drill is employed not only on
account of its capacity to drill true, straight, and smooth holes, but
also because its flutes afford free egress to the cuttings and obviate
the necessity of frequently withdrawing the drill to clear the hole of
the cuttings.
In the smaller sizes of twist drill, the stem or shank is made parallel,
as in Fig. 1040, while in the larger sizes it is made taper, as in Fig.
1041, for reasons which will appear hereafter.
[Illustration: Fig. 1040.]
The taper shanks of twist drills are given a standard degree of taper of
5/8 inch per foot of length, which is termed the Morse taper. A former
standard, termed the American standard, is still used to a limited
extent, its degree of taper being 9/16 inch per foot.
[Illustration: Fig. 1041.]
Parallel shanked twist drills are driven by chucks, while taper, shanked
ones, are driven by sockets, such as in Fig. 1042, from C to D, fitting
into the lathe centre hole, while the bore at the other end is the Morse
standard taper, to receive the drills E E, which have a projection such
as shown at A, which by fitting into a slot that meets the end of the
taper holes in the socket, lock the drill and prevent its revolving in
the socket, while affording a means of forcing the drill out by
inserting a key K, as shown in the figure.[14]
[14] See also Shanks and Sockets for Drills used in the Drilling
Machine.
[Illustration: Fig. 1042.]
Each socket takes a certain number of different sized drills, the shanks
of the smaller drills being in some cases longer than the drill body.
Number 1 socket receives drills from 1/8 to 19/32 inch inclusive.
" 2 " " 5/8 " 29/32 " "
" 3 " " 15/16 " 1-1/4 " "
" 4 " " 1-9/32 " 2 " "
" 5 " " 2-1/32 " 2-1/2 " "
These sockets are manufactured ready to receive the drills, but are left
unturned at the shank end so that they may be fitted to the particular
lathe or machine in which they are to be used, no standard size or
degree of taper having as yet been adopted.
A twist drill possesses three cutting edges marked A, B, C respectively
in Fig. 1043, and of these C is the least effective, because it cannot
be made as keen as is desirable for rapid and clean cutting, and
therefore necessitates that the drill be given an unusually fine rate of
feed as compared with other cutting tools.
The _land_ of the drill--or, in other words, the circumference between
the flutes--is backed off to give clearance, as is shown in Fig. 1044, a
true circle being marked with a dotted line, and the drill being of full
diameter from A to B only. The object of this clearance is to prevent
the drill from seizing or grinding against the walls of the hole, as it
would otherwise be apt to do when the outer corner wore off, as is
likely to be the case.
[Illustration: Fig. 1043.]
[Illustration: Fig. 1044.]
Twist drills having three and more flutes have been devised and made,
but the increased cost and the weakness induced by the extra flutes have
been found to more than counterbalance the gain due to an increase in
the number of cutting edges, Further, the increase in the number of
flutes renders the grinding of the drill a more delicate and complicated
operation.
The keenness and durability of the cutting edge of a twist drill are
governed by the amount of clearance given by the grinding to the cutting
edge, by the angle of one cutting edge to the other, and by the degree
of twist of the flute. Beginning with the angle of the front face, we
shall find that it varies at every point in the diameter of the drill,
being greatest at the outer corner and least at the centre of the drill,
whatever degree of spirality the groove or flute may possess. In Fig.
1045, for example, we may consider the angle at the corner C and at the
point F in the length of the cutting edge. The angle or front rake of
the corner C is obviously that of the outer edge of the spiral C D,
while that of the point F is denoted by the line F _f_, more nearly
parallel to the drill axis, and it is seen that the front rake increases
in proportion as the corner C is approached, and diminishes as the drill
centre or point is approached.
[Illustration: Fig. 1045.]
[Illustration: Fig. 1046.]
[Illustration: Fig. 1047.]
It follows, then, that if the angle of the bottom face of the drill be
the same from the centre to the corner of the drill, and we consider the
cutting edge simply as a wedge and independent of its angle presentation
to the work, we find that it has a varying degree of acuteness at every
point in its length. This may be seen from Fig. 1046, in which the end
face is ground at a constant angle from end to end to the centre line of
the drill, and it is seen that the angle A represents the wedge at point
C and the angle B the wedge at the point F in the length of the cutting
edge, and it follows that the wedge becomes less acute as the centre of
the drill is approached from the point C. If, then, we give to the end
face a degree of clearance best suited for the corner C, it will be an
improper one for the cutting edge near the drill point; or if we adopt
an angle suitable for the point, it will be an improper one for the
corner C.
This corner performs the most cutting duty, because its path of
revolution is the longest, or rather of the greatest circumference, and
it operates at the highest rate of cutting speed for the same reason,
hence it naturally wears and gets dull the quickest.
As this wear proceeds the circumferential surface near this corner
grinds against the walls of the hole, causing the drill to heat and
finally to cease cutting altogether.
For these reasons it is desirable that the angle of the end face, or the
angle of clearance, be made that most suitable to obtain endurance at
this corner. It may be pointed out, however, that the angle of one
cutting edge to the other, or, what is the same thing, its angle to the
centre line of the drill, influences the keenness of this corner. In
Fig. 1045, for example, each edge is at an angle of 60° to the drill
axis, this being the angle given to drills by the manufacturers as most
suitable for general use. In Fig. 1047, the angle is 45°, and it will be
clearly seen that the corner C is much less acute; an angle of 45° is
suitable for brass work or for any work in which the holes have been
cored out and the drill is to be used to enlarge them.
[Illustration: Fig. 1048.]
Referring again to the angle of clearance of the end faces, it can be
shown that in the usual manner of grinding twist drills the conditions
compel the amount of clearance to be made suitable for the point of the
drill, and therefore unsuitable for the corner C, giving to it too much
clearance in order to obtain sufficient clearance for the remainder of
the cutting edge. Suppose, for example, that we have in Fig. 1048 a
spiral representing the path of corner C during one revolution, the rate
of feed being shown magnified by the distance P, and the spiral will
represent the inclination of that part of the bottom of the hole that is
cut by corner C, and the angle of the end face of the drill to the drill
axis will be angle R. The actual clearance will be represented by the
angle between the end face S of the drill and the spiral beneath it, as
denoted by T. But if we take the path of the point F, Fig. 1045, during
the same revolution, which is represented by the spiral in Fig. 1049, we
find that, in order to clear the end of the hole, it must have more
angle to the centre line of the drill, as is clearly shown, in order to
have the clearance necessary to enable the point F to cut, because of
the increased spiral. It follows that, if the same degree of clearance
is given throughout the full length of the cutting edge, it must be made
suitable for the point of the drill, and will therefore be excessive for
the corner C.
This fault is inseparable from the method of grinding drills in ordinary
drill-grinding machines, which is shown in Fig. 1050, the line A A
representing the axis of the motion given to the drill in these
machines. It is obvious that the line A A being parallel to the face of
the emery-wheel, the angle of clearance is made equal throughout the
whole length of the cutting edge. This is, perhaps, made more clear in
Fig. 1051, in which we have supposed the drill to take a full revolution
upon the axis A A, and as a result it would be ground to the cylinder
represented by the dotted lines. We may, however, place the axis on
which the drill is moved to grind it at an angle to the emery-wheel
face, as at B, Fig. 1052, and by this means we shall obtain two
important results: (1) The angle of B may be made such that the
clearance will be the same to the actual surface it cuts at every point
in the length of the cutting edge, making every point in that length
equally keen and equally strong, the clearance being such as it is
determined is the most desirable. (2) The clearance may be made to
increase as the heels of each end face are approached from the cutting
edge. This is an advantage, inasmuch as it affords freer access to the
oil or other lubricating or cooling material. If we were to prolong the
point of the drill sufficiently, and give it a complete revolution on
the axis B, we should grind it to a cone, as shown by the dotted lines
in Fig. 1052.
[Illustration: Fig. 1049.]
[Illustration: Fig. 1050.]
[Illustration: Fig. 1051.]
[Illustration: Fig. 1052.]
[Illustration: Fig. 1053. Top View.]
[Illustration: Fig. 1054. Sectional View.]
In Fig. 1053 we have a top, and in Fig. 1054 a sectional, view of a
conical recess cut by a drill, with a cylinder R lying in the same. P
represents in both views the outer arc or circle which would be
described by the outer corner, Fig. 1045, of the drill, and Q the path
or arc described or moved through by the point at F, Fig. 1045, of the
drill. At V and W are sectional views of the cylinder R, showing that
the clearance is greater at V than at W. The cylinder obviously
represents the end of a drill as usually ground. In Figs. 1055 and 1056
we have two views of a cone lying in a recess cut by a drill, the arcs
and circles P and Q corresponding to those shown in Fig. 1055, and it is
seen that in this case the amount of clearance between V and P and
between W and Q are equal, V representing a cross-section of the cone at
its largest end, and W a cross-section at the point where the cone
meets the circle Q. It follows, therefore, that drills ground upon this
principle may be given an equal degree of clearance throughout the full
length of each cutting edge, or may have the clearance increase or
diminished towards the point at will, according to the angle of the line
B in Fig. 1052.
In order that the greatest possible amount of duty may be obtained from
a twist drill, it is essential that it be ground perfectly true, so that
the point of the drill shall be central to the drill and in line with
the axis on which it revolves. The cutting edges must be of exactly
equal length and at an equal degree of angle from the drill axis. To
obtain truth in these respects it is necessary to grind the drill in a
grinding machine, as the eye will not form a sufficiently accurate guide
if a maximum of duty is to be obtained. The cutting speeds and rates of
feed recommended by the Morse Twist Drill and Machine Company are given
in the following table.
[Illustration: Fig. 1055. Top View.]
[Illustration: Fig. 1056. Sectional View.]
The following table shows the revolutions per minute for drills from
1/16 in. to 2 in. diameter, as usually applied:--
+----------+------+------+------++----------+------+------+------+
| Diameter |Speed |Speed |Speed || Diameter |Speed | Speed|Speed |
|of Drills.| for | for | for ||of Drills.| for | for | for |
| |Steel.|Iron. |Brass.|| |Steel.| Iron.|Brass.|
+----------+------+------+------++----------+------+------+------+
| inch. | | | || inch. | | | |
| 1/16 | 940 | 1280 | 1560 || 1-1/16 | 54 | 75 | 95 |
| 1/8 | 460 | 660 | 785 || 1-1/8 | 52 | 70 | 90 |
| 3/16 | 310 | 420 | 540 || 1-3/16 | 49 | 66 | 85 |
| 1/4 | 230 | 320 | 400 || 1-1/4 | 46 | 62 | 80 |
| 5/16 | 190 | 260 | 320 || 1-5/16 | 44 | 60 | 75 |
| 3/8 | 150 | 220 | 260 || 1-3/8 | 42 | 58 | 72 |
| 7/16 | 130 | 185 | 230 || 1-7/16 | 40 | 56 | 69 |
| 1/2 | 115 | 160 | 200 || 1-1/2 | 39 | 54 | 66 |
| 9/16 | 100 | 140 | 180 || 1-9/16 | 37 | 51 | 63 |
| 5/8 | 95 | 130 | 160 || 1-5/8 | 36 | 49 | 60 |
| 11/16 | 85 | 115 | 145 || 1-11/16 | 34 | 47 | 58 |
| 3/4 | 75 | 105 | 130 || 1-3/4 | 33 | 45 | 56 |
| 13/16 | 70 | 100 | 120 || 1-13/16 | 32 | 43 | 54 |
| 7/8 | 65 | 90 | 115 || 1-7/8 | 31 | 41 | 52 |
| 15/16 | 62 | 85 | 110 || 1-15/16 | 30 | 40 | 51 |
| 1 | 58 | 80 | 100 || 2 | 29 | 39 | 49 |
+----------+------+------+------++----------+------+------+------+
To drill one inch in soft cast iron will usually require: For 1/4 in.
drill, 125 revolutions; for 1/2 in. drill, 120 revolutions; for 3/4 in.
drill, 100 revolutions; for 1 in. drill, 95 revolutions.
The rates of feed for twist drills are thus given by the same Company:--
Diameter of Revolutions per inch
drill. depth of hole.
1/16 inch 125
1/4 " "
3/8 " 120 to 140
1/2 " " "
3/4 " 1 inch feed per minute
1 " " " " "
1-1/2 " " " " "
Taking an inch drill as an example, we find from this table that the
rate of feed is for iron 1/100th inch per drill revolution, and as the
drill has two cutting edges it is obvious that the rate of feed for each
edge is 1/200th inch per revolution. But it can be shown that this will
only be the case when the drill is ground perfectly true; or, in other
words, when the drill is so ground that each edge will take a separate
cut, or so that one edge only will cut, and that in either case the rate
of feed will be diminished one-half.
In Fig. 1057, for example, is shown a twist drill in which one cutting
edge (_e_) is ground longer than the other, and the effect this would
produce is as follows. First, suppose the drill to be fed automatically,
the rate of feed being 1/100th inch, and the whole of this feed would
fall on cutting edge _e_, and, being double what it should be, would in
the first place cause the corner _c_ to dull very rapidly, and in the
second place be liable to cause the drill to break when _c_ became dull.
[Illustration: Fig. 1057.]
[Illustration: Fig. 1058.]
In the second place the drill would make a hole of larger diameter than
itself, because the point of the drill will naturally be forced by the
feed to be the axis or centre of cutting edge revolution, which would
therefore be on the line _b_ _b_. This would cause the diameter of hole
drilled to be determined by the radius of the cutting edge _e_ rather
than by the diameter of the drill. Again, the side of the drill in line
with corner _c_ would bind against the side of the hole, tending to
grind away the clearance at the corner _c_, which, it has been shown, it
is of the utmost importance to keep sharp. But assuming 1/200th inch to
be the proper feed for each cutting edge, and the most it can carry
without involving excessive grinding, then the duty of the drill can
only be one-half what it would be were both cutting edges in action.
In Fig. 1058 is shown a twist drill in which one cutting edge is ground
longer than the other, and the two cutting edges are not at the same
angle to the axis _a_ _a_ of the drill.
Here we find that the axis of drill rotation will be on the line _b_
from the point of the drill as before, but both cutting edges will
perform some duty. Thus edge _e_ will drill a hole which the outer end
of _f_ will enlarge as shown. Thus the diameter of hole drilled will be
determined by the radius of corner _c_, from the axis of drill
revolution, and will still be larger than the drill. A drill thus ground
would drill a more true and round hole than one ground as in Fig. 1057,
because as both cutting edges perform duty the drill would be steadied.
[Illustration: Fig. 1059.]
The rate of feed, however, would require to be governed by that length
of cutting edge on _f_ that acts to enlarge the hole made by _e_, and
therefore would be but one-half what would be practicable if the drill
were ground true. Furthermore, the corner _c_ would rapidly dull because
of its performing an undue amount of duty, or in other words, because it
performs double duty, since it is not assisted by the other corner as it
should be. In both these examples the drill if rigidly held would be
sprung or bent to the amount denoted by the distance between the line
_a_ _a_, representing the true axis of the drill, and line _b_ _b_,
representing the line on which the drill point being ground and
one-sided compels the drill to revolve; hence one side of the drill
would continuously rub against the walls of the hole the drill produced,
acting, as before observed, to grind away the clearance that was shown
in figure and also to dull corner _c_.
Fig. 1059 shows a case in which the point of the drill is central to the
drill axis _d_ _d_, but the two cutting edges are not at the same angle.
As a result all the duty falls on one cutting edge, and the hole drilled
will still be larger in diameter than the drill is, because there is a
tendency for the cutting edge _e_ to push or crowd the drill over to the
opposite side of the hole.
It will be obvious from these considerations that the more correctly the
drill is ground, the longer it will last without regrinding, the greater
its amount of feed may be to take an equal depth of cut, and the nearer
the diameter of the hole drilled to that of the drill--the most correct
results being obtained when the drill will closely fit into the hole it
has drilled and will not fall through of its own gravity, a result it is
somewhat difficult to attain.
Professor John E. Sweet advocates grinding twist drills as in Fig. 1060
(which is from _The American Machinist_), the object being to have a
keener cutting edge at the extreme point of the drill.
In a paper on cutting tools read before the British Institution of
Mechanical Engineers the following examples of the efficiency of the
twist drill are given--
Referring to a 1/2 inch twist drill, it is said:
"The time occupied from the starting of each hole in a hammered
scrap-iron bar till the drill pierced through it varied from 1 minute 20
seconds to 1-1/2 minutes. The holes drilled were perfectly straight. The
speed at which the drill was cutting was nearly 20 feet per minute in
its periphery, and the feed was 100 revolutions per inch of depth
drilled. The drill was lubricated with soap and water, and went clean
through the 2-3/4 inches without being withdrawn, and after it had
drilled each hole it felt quite cool to the hand, its temperature being
about 75°. It is found that 120 to 130 such holes can be drilled before
it is advisable to resharpen the twist drill. This ought to be done
immediately the drill exhibits the slightest sign of distress. If
carefully examined after this number of holes has been drilled, the
prominent cutting parts of the lips which have removed the metal will be
found very slightly blunted or rounded to the extent of about 1/100th
inch, and on this length being carefully ground by the machine off the
end of the twist drill, the lips are brought up to perfectly sharp
cutting edges again.
"The same sized holes, 1/2 inch diameter and 2-3/4 inches deep, have
been drilled through the same hammered scrap-iron at the extraordinary
speed of 2-3/4 inches deep in 1 minute and 5 seconds, the number of
revolutions per inch being 75. An average number of 70 holes can be
drilled in this case before the drill requires resharpening. The writer
considers this test to be rather too severe, and prefers the former
speed.
"In London, upward of 3000 holes were drilled 5/8 inch diameter and 3/8
inch deep through steel bars by one drill without regrinding it. The
cutting speed was in this instance too great for cutting steel, being
from 18 to 20 feet per minute, and the result is extraordinary. Many
thousands of holes were drilled 1/8 inch diameter, through cast iron
7/16ths inch deep with straight-shank twist drills gripped by an
eccentric chuck in the end of the spindle of a quick-speed drilling
machine. The time occupied for each hole was from 9 to 10 seconds only.
Again, 1/4-inch holes have been drilled through wrought copper 1-3/8
inches thick at the speed of one hole in 10 seconds. With special twist
drills, made for piercing hard Bessemer steel, rail holes, 13/16ths inch
deep and 29/32nds inch diameter, have been drilled at the rate of one
hole in 1 minute and 20 seconds in an ordinary drilling machine. Had the
machine been stiffer and more powerful, better results could have been
obtained. A similar twist drill, 29/32nds inch in diameter, drilled a
hard steel rail 13/16ths inch deep in 1 minute, and another in 1 minute
10 seconds. Another drill, 5/8 inch diameter, drilled 3/4 inch deep in
38 seconds, the cutting speed being 22 feet per minute. This speed of
cutting rather distressed the drill; a speed of 16 feet per minute would
have been better. The steel rail was specially selected as being one of
the hardest of the lot."
[Illustration: Fig. 1060.]
Drills ground by hand may be tested for angle by a protractor, as in
Fig. 1061, and for equal length of cutting edge by resting them upon a
flat surface, as B in Fig. 1062, and applying a scale as at S in the
figure. In the case of very small drills, it is difficult to apply
either the protractor or the scale, as well as to determine the amount
of clearance on the end face. This latter, however, may be known from
the appearance of the cutting edge at the point A in Fig. 1063, for if
the line A is at a right angle to E, there is no clearance, and as
clearance is given this line inclines as shown at B in the figure, the
inclination increasing with increased clearance, as is shown at C. When
this part of the edge inclines in the opposite direction, as at D in the
figure, the curved edges _e_ _f_ stand the highest, and the drill cannot
cut. The circumferential surface of a drill should never be ground, nor
should the front face or straight side of the flute be ground unless
under unusual conditions, such as when it is essential, as in drilling
very thin sheet metal, to somewhat flatten the corner (C in Fig. 1062),
in order to reduce its tendency to run forward, in which case care must
be taken not to grind the front face sufficiently to reduce the full
diameter. In Fig. 1064, for example, that part of the circumference
lying between A and B being left of full circle, the faces of the flutes
might be ground away as denoted by the dotted lines C D without
affecting the drill diameter.
[Illustration: Fig. 1061.]
[Illustration: Fig. 1062.]
[Illustration: Fig. 1063.]
[Illustration: Fig. 1064.]
[Illustration: Fig. 1065.]
[Illustration: Fig. 1066.]
Fig. 1065 represents the Farmer lathe drill, in which the flutes are
straight and not spiral, by which means the tendency to run forward when
emerging through the work is obviated.
[Illustration: Fig. 1067.]
When a twist drill is to be used for wood and is driven by a machine it
is termed a bit, and is provided with a conical point to steady it, and
two wings or spurs, as in Fig. 1066, which sever the fibres of the wood
in advance of their meeting the main cutting edges and thus produce a
smooth hole. The sharp conical point is used in place of the conical
screw of the ordinary wood auger to avoid the necessity of revolving the
drill or bit backwards to release the screw in cases in which the hole
is not bored entirely through the work.
[Illustration: Fig. 1068.]
When the drill revolves and the work is to be held in the hands a rest
or table whereon to rest the work and hold it fair is shown in Fig.
1067, the taper shank fitting in the dead centre hole and the tailstock
spindle being fed up by hand to feed the drill to its cut. The face A A
of the chuck is at a right angle to the shank, and a coned recess is
provided at the centre, as denoted by the dotted lines, to permit the
drill point to pass through the work without cutting the chuck.
[Illustration: Fig. 1069.]
For larger work a table, such as shown in Fig. 1068, is used, the cavity
C permitting the drilling tool to pass through the work, there being a
hole H provided for that purpose. The stem S fits in place of the dead
centre. For cylindrical work the rest or chuck shown in Figs. 1069 and
1070 may be employed. It consists of a piece fitted to the tail spindle
in place of the dead centre, its end being provided with [V]-grooves.
These grooves are made true with the line of centres of the lathe, so
that when the work is laid in them it will be held true. It is obvious
that one groove would be sufficient, but two are more convenient--one
for large work and one for small work--so that the side of the shaft to
be drilled shall not pass within the fork, but will protrude, so that
the progress of the work can be clearly seen. In Fig. 1070 an end view
of this chuck is shown. It may be observed, however, that when starting
the drill care must be taken to have it start true, or the drill may
bend, and thus throw the work out of the true. For this reason the
drills should be as short as possible when their diameters are small.
For square work this class of work table or chuck may be formed so as to
envelop the work and prevent its revolving, thus relieving the fingers
of that duty, and it may be so formed as to carry the work back or off
the drill when the latter is retired after the drilling is performed.
[Illustration: Fig. 1070.]
Another and quite convenient method of holding work to be drilled by a
revolving drill in the lathe is shown in Fig. 1071. It consists of
simply a bracket, _a_ _b_, fitted to the tool-box of the slide rest,
carrying a spindle with one end screwed to receive any face plates or
chucks that fit the lathe live spindle. The bracket is kept in position
by two pins in the under side of it, fitting into holes in the bottom
piece of tool-box. If it be required to drill a straight row of holes,
the spindle is fixed by the set-screws in its bracket, and the work is
bolted to the face plate at the proper level, and traversed across
opposite the drill in the lathe mandrel, by the cross screw of the slide
rest, while it is fed up to the drill by the upper screw or the rack and
pinion.
For circular rows of holes the centre line of the spindle is adjusted
parallel with and at a proper distance from that of the mandrel. For
holes in the edge of the work, the whole top of slide rest is turned
round till the spindle is at right angles with the mandrel.
[Illustration: Fig. 1071.]
Work merely requiring to be held fast for drilling is bolted on one side
of the face plate, and can then be adjusted exactly to the drill by the
combined motions of the cross screw and the face plate on its centre.
Small round work, while drilled in the end, can be held in a scroll
chuck screwed on the spindle the same as a face plate.
The convenience of this device consists in this, that the work turned on
the chuck may be drilled without moving it from the chuck, which may be
so set as to cause the drilled holes to be at any required angle to the
work surface, which is quite difficult of accomplishment by other
ordinary means.
On account of the readiness with which a flat drill may be made to suit
an odd size or employed to recess work with a flat or other required
shape of recess, flat drills are not uncommonly used upon lathe work,
and in this case they may be driven in the drill chucks already shown. A
very convenient form of drill chuck for small drills is shown in Fig.
1072. It consists of a cylindrical chuck fitting from A to B into the
coned hole in the live spindle so as to be driven thereby. At the
protruding end C there is drilled a hole of the diameter of the wire
forming the drill. At the end of this hole there is filed a slot D
extending to the centre of the chuck. The end of the drill is filed half
round and slightly taper, as shown in Fig. 1073 at D, so that the
half-round end of the drill will pass into the slot of the chuck,
therefore forming a driving piece which effectually prevents the drill
from slipping, as is apt to occur with cylindrical stem or shank drills.
If one size of wire be used for all drills, and the drill size be
determined by the forging, the drill will run true, being held quite
firmly, and may be very readily inserted in or removed from the chuck.
[Illustration: Fig. 1072.]
But the flat drill possesses several disadvantages: thus, referring to
figure, it must be enough smaller at A than at B to permit the cuttings
to find egress, and this taper causes the diameter of the drill to be
reduced at each drill grinding. The end B may, it is true, be made
parallel for a short distance, but in this case the cuttings will be apt
to clog in the hole unless the drill be frequently removed from deep
holes to clear the cuttings. For these reasons the fluted drill or the
twist drill is preferable, especially as their diameters are maintained
without forging. For deep holes, as, say, those having a depth equal to
more than twice the diameter, the flat drill, if of small diameter, as,
say, an inch or less, is unsuitable because of the frequency with which
it must be removed from the hole to clear it of cuttings.
[Illustration: Fig. 1073.]
For fluted or twist drills the lathe may run quicker than for a flat
drill, which is again an advantage. It sometimes becomes convenient in
the exigencies which occur in the work of a general machine shop to hold
a drill in a dog or clamp and feed it into the work with the lathe dead
centre. In this case the drill should be held very firmly against the
dead centre, or otherwise the drill may, when emerging through the back
of the hole, feed itself forward, slipping off the dead centre, and
causing the drill to catch and break, or moving the work in the chuck,
to avoid which the drill should have a deep and well countersunk centre.
[Illustration: Fig. 1074.]
A very effective drill for holes that are above two inches in diameter
and require enlarging is shown in Fig. 1074. It consists of a piece of
flat steel A, with the pieces of wood B fastened on the flat faces, the
wood serving to steady the drill and prevent it from running to one side
in the work. This drill is sometimes used to finish holes to standard
size, in which case the hole to be bored or drilled should be trued out
a close fit to the drill for a distance equal to about the diameter of
the drill, and the face at the entrance of the hole should be true up.
This is necessary to enable the drill to start true, which is
indispensable to the proper operation of the drill.
This drill is made by being turned up in the lathe, and should have at
the stock end a deep and somewhat large centre, so that when in use it
may not be liable to slip off the dead centre of the lathe. The drill is
held at the stock end by being placed in the lathe dead centre and is
steadied, close to the entrance of the hole in the work, by means of a
hook which at one end embraces the drill, as shown in Fig. 1075, in
which A represents the hook and B the drill.
[Illustration: Fig. 1075.]
This drill will bore a parallel hole, but if the same be a long or a
deep one it is apt to bore gradually out of true unless the bore of the
hole is first trued from end to end with a boring tool before using the
drill. It is often employed to enlarge a hole so as to admit a stout
boring tool, and to remove the hard surface skin from which the boring
tool is apt to spring away.
[Illustration: Fig. 1076.]
[Illustration: Fig. 1077.]
HALF-ROUND BIT OR POD AUGER.--For drilling or enlarging holes of great
depth (in which case it is difficult to drill straight holes with
ordinary drills), the half-round bit--Figs. 1076 and 1077--is an
excellent tool. Its diameter D is made that of the required hole, the
cutting being done at the end only from A to B, from B to C being ground
at a slight angle to permit the edge from A to B to enter the cut. When
a half-round bit is to be used on iron or steel, and not upon brass, it
may be made to cut more freely by giving the front face rake as at E F,
Fig. 1078.
[Illustration: Fig. 1078.]
[Illustration: Fig. 1079.]
To enable a bit of this kind to be adjusted to take up the wear, it may
be formed as in Fig. 1079, in which a quarter of the circumference is
cut away at _a_, and a cutter _c_ is bolted in position projecting into
a recess at _b_ to secure the cutter in addition to the bolts. Pieces of
paper may be inserted at _b_ to set out the cutter.
An excellent form of boring bar and cutter is shown in Figs. 1080 and
1081.
Fig. 1082 shows a side view of the cutter removed from the bar; Fig.
1081 an end, and Fig. 1080 a side view of the bar and cutter. The cutter
is turned at A and B to fit the bore of the bar. The cutting edge C
extends to the centre of the bar, while that at D does not quite reach
the centre. These edges are in a line as shown in the end view. On
account of the thickness of the cutter not equaling the diameter of the
bore through the bar there is room for a stream of water to be forced
through the bar, thus keeping it cool and forcing out the cuttings which
pass through the passages G and H in the bar. The cutter drives lightly
into the bar. By reason of one cutting edge not extending clear to the
centre of the cutter there is formed a slight projection at the centre
of the hole bored which serves as a guide to keep the cutter true,
causing it to bore the hole very true.
[Illustration: Fig. 1080.]
For finishing the walls of holes more true, smooth, and straight, and of
more uniform diameter than it is found possible to produce them with a
drill, the reamer, or rymer, is employed. It consists of a hardened
piece of steel having flutes, at the top of which are the cutting edges,
the general form of solid reamer for lathe work being shown in Fig.
1083. The reamer is fed end-ways into the work at a cutting speed of
about 15 to 18 feet per minute.
[Illustration: Fig. 1081.]
[Illustration: Fig. 1082.]
The main considerations in determining the form of a reamer are as
follows:--
1. The number of its cutting edges.
2. The spacing of the teeth.
3. The angles of the faces forming the cutting edges.
4. Its maintenance to standard diameter.
[Illustration: Fig. 1083.]
As to the first, it is obvious that the greater the number of cutting
edges the more lines of contact there are to steady it on the walls of
the hole; but in any case there should be more than three teeth, for if
three teeth are used, and one of them is either relieved of its cut or
takes an excess of cut by reason of imperfections in the roundness of
the hole, the other two are similarly affected and the hole is thus made
out of round.
An even number of teeth will not work so steadily as an odd one, for the
following reasons.
In Fig. 1084 is represented a reamer having 6 teeth and each of these
teeth has a tooth opposite to it; hence, if the hole is out of round two
teeth only will operate to enlarge its smallest diameter. In Fig. 1085
is a reamer having 7 teeth, and it will be seen that if any one tooth
cuts there will be two teeth on the opposite side of the reamer that
must also cut; hence, there are three lines of contact to steady the
reamer instead of two only as in the case of the 6 teeth. An even number
of teeth, however, may be made to operate more steadily by spacing the
teeth irregularly, and thus causing three teeth to operate if the hole
is out of round. Thus, in Fig. 1086 the teeth are spaced irregularly,
and it will be seen that as no two teeth are exactly opposite, if a
tooth on one side takes a cut there must be two on the opposite side
that will also cut. The objection to irregular spacing is that the
diameter of the reamer cannot be measured by calipers. Another method of
obtaining steadiness, however, is to make the flutes and the cutting
edges spiral instead of parallel to the axis, but in this case the
spiral must be left-handed, as in Fig. 1087, or else the cutting edges
acting on the principle of a screw thread will force the reamer forward,
causing it to feed too rapidly to its cut. If, however, a reamer have
considerable degree of taper, it may be given right-hand flutes, which
will assist in feeding it.
[Illustration: Fig. 1084.]
[Illustration: Fig. 1085.]
[Illustration: Fig. 1086.]
[Illustration: Fig. 1087.]
Referring to the second, the spacing of the teeth must be determined to
a great extent by the size of the reamer, and the facility afforded by
that size to grind the cutting edges to sharpen them.
[Illustration: Fig. 1088.]
The method employed to grind a reamer is shown in Fig. 1088, in which is
shown a rapidly-revolving emery-wheel, above the reamer, and also a
gauge against which the front face of each tooth is held while its top
or circumferential face is being sharpened. The reamer is held true to
its axis and is pushed end-ways beneath the revolving emery-wheel. In
order that the wheel may leave the right-hand or cutting edge the
highest (as it must be to enable it to cut), the axis of the emery-wheel
must be on the left hand of that of the reamer, and the spacing of the
teeth must be such that the periphery of the emery-wheel will escape
tooth B, for otherwise it would grind away its cutting edge. It is
obvious, however, that the less the diameter of the emery-wheel the
closer the teeth may be spaced; but there is an objection to this,
inasmuch as that the top of the tooth is naturally ground to the
curvature of the wheel, as is shown in Fig. 1089, in which two
different-sized emery-wheels are represented operating on the same
diameter of reamer. The cutting edge of A has the most clearance, and is
therefore the weakest and least durable; hence it is desirable to employ
as large a wheel as the spacing of the teeth will allow, there being at
least four teeth, and preferably six, on small reamers, and their number
increasing with the diameter of the reamer.
[Illustration: Fig. 1089.]
It would appear that this defect might be remedied by placing the
emery-wheel parallel to the teeth as in Fig. 1090; but if this were
done, the wear of the emery-wheel would cause the formation of a
shoulder at S in the figure, which would round off the cutting edge of
the tooth. This, however, might be overcome by giving the emery-wheel
enough end motion to cause it to cross and recross the width of the top
facet; or the reamer R may be presented to the wheel W at an angle to
the plane of wheel rotation, as in Fig. 1091, which would leave a
straight instead of a curved facet, and, therefore, a stronger and more
durable cutting edge.
[Illustration: Fig. 1090.]
[Illustration: Fig. 1091.]
Another method of accomplishing the same object would be to mount the
emery-wheel as in Fig. 1092, using its side face, which might be
recessed on the side, leaving an annular ring of sufficient diameter to
pass clear across the tooth, and thus prevent a shoulder from forming on
the side face of the wheel.
Yet another method is to use an emery-wheel bevelled on its edge, and
mount it as in Fig. 1093, in which case it would be preferable to make
the bevel face narrow enough that all parts would cross the facet of the
tooth.
[Illustration: Fig. 1092.]
[Illustration: Fig. 1093.]
Referring to the third, viz., the angles of the faces forming the
cutting edges, it is found that the front faces, as A and B in Fig.
1094, should be a radial line, for if given rake as at C, the tooth will
spring off the fulcrum at point E in the direction of D, and cause the
reamer to cut a hole of larger diameter than itself, an action that is
found to occur to some extent even where the front face is a radial
line. As this spring augments with any increase of cut-pressure, it is
obvious that if a number of holes are to be reamed to the same diameter
it is essential that the reamer take the same depth of cut in each, so
that the tooth spring may be equal in each case. This may be
accomplished to a great extent by using two reamers, one for equalizing
the diameters of the holes, and the other for the final finishing. The
clearance at the top of the teeth is obviously governed by the position
of the reamer with relation to the wheel, and the diameter of the wheel,
being less in proportion as the reamer is placed farther beneath the
wheel, and the wheel diameter is increased. In some forms of reamer the
teeth are formed by circular flutes, such as at H in Fig. 1094, and but
three flutes are used. This leaves the teeth so strong and broad at the
base that the teeth are not so liable to spring; but, on the other hand,
the clearance is much more difficult to produce and to grind in the
resharpening.
[Illustration: Fig. 1094.]
[Illustration: Fig. 1095.]
[Illustration: Fig. 1096.]
As to the maintenance of the reamer to standard diameter, it is a matter
of great importance, for the following reasons: The great advantage of
the standard reamer is to enable holes to be made and pieces to be
turned to fit in them without requiring any particular piece to be
fitted to some particular hole, and in order to accomplish this it is
necessary that all the holes and all the pieces be exactly alike in
diameter. But the cutting edges of the reamer begin to wear--and the
reamer diameter, therefore, to reduce--from the very first hole that it
reams, and it is only a question of time when the holes will become too
small for the turned pieces to enter or fit properly. In all pieces that
are made a sliding or a working fit, as it is termed when one piece
moves upon the other, there must be allowed a certain latitude of wear
before the one piece must be renewed.
One course is to make the reamer when new enough larger than the proper
size to bore the holes as much larger as this limit of wear, and to
restore it to size when it has worn down so that the holes fit too
tightly to the pieces that fit them. But this plan has the great
disadvantage that the pieces generally require to have other cutting
operations performed on them after the reaming, and to hold them for
these operations it is necessary to insert in them tightly-fitting
plugs, or arbors, as they are termed. If, therefore, the holes are not
of equal diameter the arbor must be fitted to the holes, whereas the
arbor should be to standard diameter to save the necessity of fitting,
which would be almost as costly as fitting each turned piece to its own
hole. It follows, therefore, that the holes and arbors should both be
made to a certain standard, and the only way to do this is to so
construct the reamer that it may be readily adjusted to size by moving
its teeth.
It is obvious that a reamer must, to produce parallel holes, be held
axially true with the holes, or else be given liberty to adjust itself
true. Fig. 1095 shows a method of accomplishing this object. The reamer
is made to have a slight freedom or play in the sleeve, being 1/32 inch
smaller, and the hole for the pin is also made large so that the reamer
may adjust itself for alignment.
For short holes the shell reamer shown in Fig. 1096 may be employed. Its
bore is coned so that it will have sufficient friction upon its driving
arbor to prevent its coming off; when it is to be withdrawn from the
work it is provided with two slots into which fit corresponding lugs on
the driving arbor. Fig. 1097 shows the Morse Twist Drill and Machine
Company's arbor.
[Illustration: Fig. 1097.]
[Illustration: Fig. 1098.]
The rose reamer, or rose bit, has its cutting edges on the end only, as
shown in Fig. 1098, the grooves being to supply lubricating material (as
oil or water) only, and, as a result, will bore a more parallel hole
than the ordinary reamer in cases in which the reamer has liberty to
move sideways, from looseness in the mechanism driving it. Furthermore,
when the work is composed of two parts, the outer one, through which the
reamer must pass before it meets the inner one, guides the reamer
without becoming enlarged by reason of the reamer having cutting edges,
which is especially advantageous when the inner hole requires to be made
true with the outer one, or in cases where a piece has two holes with a
space between them, and one hole requires to be made true with the
other, and both require to be made to the same diameter as the reamer.
Fig. 1099 represents the Morse Twist Drill Company's shell rose reamer
for short holes, corresponding in principle to the solid rose reamer,
but fitting to an arbor for the same purposes as the shell reamer.
Instead of having upon a reamer a flat tooth top to provide clearance,
very accurate and smooth work may be produced by letting the back of the
tooth, as A in Fig. 1100, proceed in a straight line to B, leaving the
reamer, when soft, too large, so that after hardening it may be ground
by an emery-wheel to size; and the clearance may be given by simply
oilstoning the top of each tooth lengthwise, the oilstone marks barely
effacing the emery marks at the cutting edge and removing slightly more
as the back of the tooth is approached from the cutting edge. This
produces cutting edges that are very easily fed to the cut, which must
obviously, however, be a light one, as should always be the case for
finishing, so that the wear of the teeth may be a minimum, and the
reamer may therefore maintain its standard diameter as long as possible.
[Illustration: Fig. 1099.]
[Illustration: Fig. 1100.]
When a solid reamer has worn below its required diameter, the same may
be restored by upsetting the teeth with a set chisel, by driving it
against the front face; and in determining the proper diameter for a
reamer for work to be made to gauge under the interchangeable system the
following considerations occur.
Obviously the diameter of a reamer reduces as it wears; hence there must
be determined a limit to which the reamer may wear before being restored
to its original diameter. Suppose that this limit be determined as
1/1000 inch, then as the reamer wears less in diameter the bolts to fit
the holes it reams must also be made less as the reamer wear proceeds,
or otherwise they will not enter the reamed holes. But it is to be
observed that while the reamer wears smaller, the standard gauges to
which the pins or bolts are turned wear larger, and the wear is here
again in a direction to prevent the work from fitting together. It is
better then to make the reamer when new too large to the amount that has
been determined upon as the limit of wear, so that when the work begins
to go together too tight, the reamer requires resharpening and
restoring.
[Illustration: Fig. 1101.]
A still better plan, however, is to use reamers adjustable for diameter,
so that the wear may be taken up, and also the reamer sharpened, without
being softened, which always deteriorates the quality of the steel.
Reamers that are too small to be made adjustable for size by a
combination of parts may be constructed as in Fig. 1101, in which the
reamer is drilled and threaded, and countersunk at the end to receive a
taper-headed screw S, which may be screwed in to expand the reamer,
which contains three longitudinal splits to allow it to open. To cause S
to become locked in its adjusted position a plug screw P is inserted for
the end of S to abut against. It is obvious that in this form the reamer
is expanded most at the end.
Fig. 1102 represents a single-tooth adjustable reamer, in which the body
A is ground to the standard diameter, and the wear of the cutter C is
taken up by placing paper beneath the cutter. In this case the reamer
cannot, by reason of the wear of the cutting edge, ream too small,
because the body A forms a gauge of the smallest diameter to which the
reamer will cut. The cutter may, however, be set up to the limit allowed
for wear of cutting edge, which for work to fit should not be more than
1/5000 inch.
[Illustration: Fig. 1102.]
An adjustable reamer designed and used by the author for holes not less
than 1-1/2 inches in diameter, is shown in Fig. 1103, in which A
represents the body of the reamer containing dovetail grooves tapered in
depth with the least depth at the entering end. The grooves receive
cutters B, having gib heads. C is a ring or washer interposed between
the gib heads of the cutter and the face or shoulder of A, the cutters
being locked against that face by a nut and a washer E. By varying the
thickness of C, the cutters are locked in a different position in the
length of the grooves, whose taper depth therefore causes the cutters to
vary in diameter. Suppose, for example, that with a given thickness of
washer C, the cutters are adjusted in diameter so as to produce a hole a
tight working fit to a plug turned to a 2-inch standard gauge: a
slightly thinner washer may be used, setting the cutters so as to bore a
hole an easy working fit to the plug; or a slightly thicker washer may
be employed so as to produce a hole a driving fit to the same plug.
Three or more washers may thus be used for every standard size, their
thickness varying to suit the nature of the fit required.
[Illustration: Fig. 1103.]
It will be noted that it is mentioned that three _or more_ washers may
be used, and this occurs because a diameter of fit that would be a
driving fit for a hole of one length would be too tight for a driving
fit of a much longer hole, the friction of course increasing with the
length of hole, because of the increase of bearing area.
For large sizes, a reamer of this description is an excellent tool,
because if it be required to guide the reamer by means of a plain
cylindrical shank, a washer, or sleeve, having a bore to fit the shank
at the termination of the thread, may be used, but such a reamer is not
suitable for small diameters, because of the reduction of shank
necessary to provide for the nut and thread.
Reamers for roughing out taper holes may be made with steps, as in Fig.
1104, which is taken from _The American Machinist_, there being a
cutting edge where each step meets a flute. Such a reamer may be used to
enlarge parallel holes, or to rough out taper ones, and the flutes (if
not to be used for brass work) may be spiral, as in the figure. The end
step being guided by the hole serves as a guide to the first cutting
edge; the second step serves as a guide for the cutting edge that
follows it, and so on.
[Illustration: Fig. 1104.]
[Illustration: Fig. 1105.]
The steps are best turned a trifle larger, say 1/1000 inch larger, at
the cutting end. Half-round taper reamers, such as shown in Fig. 1105,
are used for finishing holes. The flat face is cut down, leaving rather
more than a half circle; the clearance being filed or ground on the
cutting side so as to enable the reamer to cut, and extending from the
cutting edge to nearly half-way to the bottom of the reamer.
For holes, however, that are large enough to admit a tool of sufficient
strength, the single-pointed boring tool produces the most true work.
Brass finishers use square taper reamers, which produce upon brass more
true work than the half-round reamer.
[Illustration: Fig. 1106.]
[Illustration: Fig. 1107.]
For reaming the bores of rifles, a square reamer, such as shown in Fig.
1106, is employed; the edges A B are the cutting ones, the edges C D
being rounded off; E is a piece of wood, beneath which slips of paper
are placed to restore the size as the wear proceeds. The entering end of
the reamer is slightly tapered. On account of the extreme length of this
reamer in proportion to its diameter, it is fed to its cut by being
pulled instead of pushed as is usually the case, the pull placing the
rod of the reamer under tension and thus stiffening it; the line of pull
is of course true with the axis of the rifle bore. The reamer is
revolved at high speed and freely supplied with oil.
[Illustration: Fig. 1108.]
By means of the slips of paper successive cuts and minute increases of
diameter may be taken with the same reamer.
Fig. 1107 represents a class of rose bit employed to reduce pins to a
uniform diameter, and face off the shoulder under the head, or it may be
used to cut a recess round a pin, or to cut a recess and leave a pin.
For making a recess round a hole, or, in other words, for cutting a
flat-bottom countersink, a facing countersink, Fig. 1108, may be used,
its cutting edges being at A, B, C, &c. The clearance is given at the
ends of the teeth only, being shown from B to D. The pin P steadies the
tool, and is made a working fit to the hole in the work. Or if too
small, a ferrule may be placed upon it, thus increasing the capacity of
the tool. When a tool of this kind is to be used on iron, steel, or
copper, and not upon brass, the front face of the teeth may be given
rake by cutting the grooves at an angle, as in Fig. 1109.
BORING TOOLS FOR LATHE WORK.--The principal object in forming a boring
tool to be held in a slide rest is to have the body of the tool as large
as can be conveniently got into the size of the hole to be bored; hence
the cutting edge should not stand above the level of the top of the
steel. By this means the tool will be as stiff as possible, and less
liable to spring away from its cut, as boring tools are apt to do,
especially when the cut or hole is a long one.
It is so difficult a matter to bore a long hole parallel with a long
boring tool that cutters of various forms are usually preferred, and
these will be described hereafter.
[Illustration: Fig. 1109.]
[Illustration: Fig. 1110.]
The boring tool is, upon cast iron and brass, exceedingly liable to
chatter, but this may always be avoided by making the angles forming the
cutting edge less acute: thus, in Fig. 1110 are three boring tools, A,
B, C, operating in a piece of work D. Now the lateral pressure of a cut
is exerted upon the tool at a right angle to the length of the cutting
edge; hence (in addition to the vertical pressure) the lateral pressure
of the tool A will be in the direction of the dotted line and arrow A,
that on B in the direction of dotted line and arrow B, and that on C in
the direction of dotted line and arrow C; hence the pressure of the cut
would tend to force A towards the centre of the hole and off or away
from its cut, B back from its cut, and C deeper into its cut. Now as the
cut proceeds, the tool edge dulls, hence it would appear that a
compromise between C and B would be the most desirable, as giving to the
tool enough of the tendency to deepen its cut to compensate for the
tendency to spring away from its cut, as the cutting edge dulls (which
it does from the moment the cut begins). This is quite practicable in
tools to be used on wrought iron, as shown in Fig. 1111, which
represents the most desirable form.
In this form the part of the cutting edge performing duty under a deep
cut will be mainly in front of the tool, but in light cuts the cutting
edge would be farther back, where it is more nearly parallel to the line
of the work bore, and will hence cut smoother.
[Illustration: Fig. 1111.]
[Illustration: Fig. 1112.]
Where a boring tool is intended for light cuts only on wrought iron it
may have all, or nearly all, its rake at the top, as shown in Fig. 1112,
from _a_ to B representing the cut, and C the tool.
Under ordinary conditions that in the form of tool shown in Fig.
1113[15] is best for brass work, the face A being horizontal or slightly
depressed towards the point. Boring tools require very little bottom
rake, and the cutting points should be as rounded as they can be made
without chattering. On wrought iron the top rake may be as much as is
consistent with strength, and water should be freely applied to the cut.
For cast iron the best form of tool is that shown in Fig. 1114, the edge
A being parallel with the bore of the hole, and the feed being a coarse
one, taking a very light cut when finishing.
[15] From "The Complete Practical Machinist."
[Illustration: Fig. 1113.]
[Illustration: Fig. 1114.]
In cases, however, where the tool point requires to cut up to a sharp
corner, the form of tool shown in Fig. 1115 (which represents a top and
end view) may be used. Its end face C is at an obtuse angle to the
length of the tool, so that on passing up a bore and meeting a radial
face the point only will meet that face. This angle, however, gives to
the tool a keenness that will cause chattering on brass work unless the
top face be bevelled to the tool body, as is A to B in the figure.
[Illustration: Fig. 1115.]
It frequently happens in boring cast iron that the skin or the surface
of the metal is very hard, rapidly dulling the tool and forcing it away
from its cut, unless the cut is deep enough to allow the point of the
tool to cut beneath it, as shown in Fig. 1116, in which the hardness is
supposed to extend from the bore to the dotted line.
In this case a tool formed as at C is employed, the point cutting in
advance of the rest of the tool, and entering the soft metal beneath the
hard metal; the hard metal will then break away in lumps or pieces,
without requiring to be absolutely cut into chips or turnings, because
of being undercut, as shown at B.
The cross slider or tool rest of a lathe should be adjusted to closely
fit the cross slide of the lathe if true and parallel work is to be
bored, because any lost motion that may exist in the slide is multiplied
by the length the tool stands out from the tool post. Thus the centre of
motion of the rest if it has play, as at B, Fig. 1117, and the direction
of motion at the tool point, will be an arc of a circle of which B is
the centre, the bend of the tool from the pressure of the cut will have
its point of least motion or fulcrum at A; hence, both tend to cause the
tool point to dip and spring unequally under the varying cut pressure
that may arise from hard or soft places in the metal, and from
inequalities in the cut depth.
[Illustration: Fig. 1116.]
The pressure of the cut increases as the tool point loses its sharpness,
and this makes sufficient difference for the amount of tool spring in
light boring tools or in long holes to cause the tool to bore a larger
hole at the beginning than it does at the end of its feed traverse; or,
in other words, to bore a taper hole, whose largest end is that at which
the cut was started. If, therefore, the cut is traversed from the front
to the back of the hole the latter will be of the smallest diameter at
the back, and conversely if the cut proceeds from the back to the front
of the hole the front will be of smallest diameter. The amount of the
taper so caused (or in other words the error from parallelism) will
obviously increase with the length of the hole.
To obviate this taper, the slide of the rest should for the finishing
cut be set up firmly, and the tool after being sharpened should take a
finishing cut through the hole, and then let traverse back, which can be
done providing that care be taken not to bore the hole too large.
[Illustration: Fig. 1117.]
A boring tool will take a smoother cut and chatter less if the final cut
be from the back to the front of the hole, and for the following
reasons: When the tool is fed in, the strain or pressure of the cut is
in a direction to partly compress and partly bend the steel which is
being pushed to its cut, but when it is fed in the opposite direction it
is pulled to its cut and the strain is in a direction to stretch the
steel, and this the tool is more capable of resisting, hence it does not
so readily vibrate to cause chattering.
In consequence, however, of the liability of a boring tool to spring
away from its cut, it is far preferable to finish holes with standard
cutters, reamers, or bits, in which case the boring tool may be
employed to rough out and true up the hole, leaving a _fine_ cut for the
finishing cutter or bit, so as to wear its cutting edge as little as
possible. To further attain this latter object, the cutter or bit should
be used at a slow cutting speed and with a coarse feed.
[Illustration: Fig. 1118.]
[Illustration: Fig. 1119.]
If cutters or bits are not at hand, tool holders are desirable, and the
forms of these depend upon the nature, or rather the diameter, of the
hole to be bored. In all cases, however, the best results will be
obtained when the diameter of the tool holder is as near that of the
hole to be bored as will give it clearance. This occurs on account of
the rigidity of the holder being greater than that of the tool.
[Illustration: Fig. 1120.]
[Illustration: Fig. 1121.]
For large work tool holders are desirable, in that the tools, being
short, are easier to forge, to handle, and to grind.
For example, a tool holder of a cross section of two inches square may
contain a tool whose cross section is 1 by 3/4 inch, in which case it is
necessary to forge, grind, &c., the small tool only, whereas in the
absence of the holder the tool would require to be of a cross section
equal to that of the holder to obtain an equal degree of rigidity.
A boring tool holder suitable for holes of from 2 to 4 or 5 inches is
shown in Fig. 1118, in which A represents a round bar shaped at the end
B to fit into the tool post of the slide rest, and having a groove
across the diameter of the end C D to receive a short tool. The slot and
tool may be either square or [V]-shaped, the tool being locked by a
wedge. It is obvious that instead of shaping the end B as shown, the bar
may be held (if the slide-rest head is provided with a clamp instead of
a tool post) by two diametrically opposite flat faces.
For holes of a greater diameter a holder such as shown in Fig. 1119
should be used, the body being a square bar, and the tool being held in
the box A A by two set screws B. For holes of small diameter, as, say,
less than 1-1/2 inches, a tool holder is especially desirable, because
when a boring tool is forged out of a piece of tool steel, its length is
determined, and in order to have tools suitable for various depths of
hole a number of tools of varying lengths are requisite. Suppose, for
example, that a piece of steel be forged into a boring tool suitable for
a hole of an inch diameter, and 4 inches deep, then the steel must be
forged round for a distance of at least 4 inches from the cutting end,
and if such a tool were applied to a hole, say, two inches deep, the
cutting edge would stand out from the tool post at least two inches more
than is necessary, which would cause the employment of a tool weaker
than necessary for the work. To enable the use of one tool for various
depths of work, and yet hold it in each case as close to the tool post
as the work depth admits, tool-clamping devices, such as in Fig. 1120
(which are extracted from _The American Machinist_), are employed. 1 and
2 are pieces of steel fitting in the tool post and clamping the tool,
which for very small holes is made of octagon or round forged steel. The
tool may be passed to any required distance through the clamp, so as to
project only to the amount necessary for the particular depth of hole
requiring to be bored. These clamping pieces 1 and 2 should bed upon the
tool fairly along their full length; or, what is better, they may bed
the firmest at their extremities, which will insure that the tool is
gripped firmly as near to the cutting edge as possible.
In place of a steel tool, a tool holder turned cylindrically true and
parallel may be used to carry a short boring tool, as shown in Fig.
1121, in which A is the tool secured by the set-screw B into the holder
C. The latter may be provided with a line running true longitudinally,
and may have a fine groove similar to a thread, and having a pitch
measuring some part of an inch, as 1/8, 1/4, 1/2 inch, &c., so that the
distance the tool projects from the holder may be known without
measuring the same. But when a tool and holder of this description are
used, the tool cannot be employed unless the hole passes entirely
through the work, which occurs because of the presence of the set-screw
B.
It is obvious that for a tool-holding bar such as this, a clamping
device such as shown in Fig. 1120 is requisite, and that the position of
the clamping device may be adjusted to suit the work by setting it more
or less through the tool post.
The manner in which the deflection of a boring tool will affect the bore
of the work depends upon the height of the boring tool in the work. If
the tool is above the horizontal centre of the work, as in Fig. 1122,
the spring vertically will cause it to leave the cut, and bore the hole
to a corresponding amount smaller; and since the tool gets duller as the
wear proceeds, it will spring more at the latter end of each tool
traverse, leaving the end of the hole last cut of smallest diameter.
If, on the other hand, the tool be below the horizontal centre, as in
Fig. 1123, the vertical spring will be in a direction to increase the
amount of the cut, and thus offset the tapering effect of the increased
tool spring due to the wear of the tool. Furthermore, the shaving will
be easier bent if the tool be below than if above the horizontal centre,
because the metal will be less supported by the metal behind it. It is
always desirable therefore to have the cutting edge of a boring tool
used on small work below rather than above the horizontal centre of the
work. On large work, however, as say, having a bore of 6 inches and
over, the curve of the bore in the length of the circumference affected
by the cut or bending of the cut is so small, that the height of the
tool is of less consequence.
[Illustration: Fig. 1122.]
To enable the use of a stout-bodied boring tool, while keeping its
cutting edge below the centre, the top face of the tool may be
depressed, as shown in Fig. 1123.
[Illustration: Fig. 1123.]
An excellent attachment for boring parallel holes is shown in Figs. 1124
and 1125, in which there is fixed to the cross slide A the bracket B,
which is bored to receive a number of bushes C, whose bores are made to
suit varying diameters of boring-bars or reamers D. The hub of the
bracket is split on one side to enable it to be closed (by the bolt _e_)
upon the bush C and grip it firmly, the bush also being split at _f_.
The bracket B is provided with a taper pin G, which brings it in
position upon the slide so that the bushes C are true with the line of
lathe centres. It is also provided with the screws H, which lock it
firmly to the cross slide and prevent any spring or movement from play
or looseness.
When the bracket is adjusted and the bar fastened up (by screw _e_), the
lathe-carriage feeds the boring tool to the cut in the usual manner. Now
suppose that, as shown in our illustrations, a pulley P requires to be
bored, and the boring tool or reamer may be set to have its cutting end
stand out just as far as the length of the hub requires, and no farther,
so that the bar will be held and supported as close to the pulley hub as
is possible from the nature of the job. There need not be a separate
bush for every size of reamer, because the bodies of several size bars
may fit to one size of bush, especially if the set of reamers for every
size of bush be made with its smallest size equal to the bore of the
bush; because in that case the whole of the set may be adjusted to bore
any required depth of hole by sliding the reamer through the bush to the
required distance. If there are a number of lathes in a shop, each lathe
may have its own bracket B, all these brackets being bored to receive
the same bushes, and therefore the same boring-bars or reamers.
[Illustration: Fig. 1124.]
[Illustration: Fig. 1125.]
A bracket or stand of this kind may obviously be used to carry a bar,
having a head such as is shown in Fig. 1126, each dovetail groove
carrying a cutting tool, and for wrought iron or steel work these
grooves may be at an angle to the bar axis, as in the figure, to give
each cutter front rake, and increase its keenness.
[Illustration: Fig. 1126.]
BORING BARS FOR LATHE WORK.--Boring bars for lathe work are of two
kinds, those in which the cutters are held in a fixed position in the
length of the bar, and those in which the cutters are held in a head
which traverses along the work. The former are the least desirable,
because they require to be more than twice the length of the work, which
must be on one side of the cutter at the commencement of the cut, and on
the other at the termination of the same. But to traverse the head
carrying the tools along the bar necessitates a feed screw either within
the bar or outside of it. If within, the metal removed to give it place
weakens the bar, while in small holes there is no room for it; hence
solid bars with fixed cutting tools are used for small holes, and tools
held in a traversing head for those sufficiently large to give room for
a head without weakening the bar too much. A boring bar is best driven
from both ends.
[Illustration: Fig. 1127.]
"The boring bar is one of the most important tools to be found in a
machine shop, because the work it has to perform requires to be very
accurately done; and since it is a somewhat expensive tool to make, and
occupies a large amount of shop room, it is necessary to make one size
of boring bar answer for as many sizes of hole as possible, which end
can only be attained by making it thoroughly stiff and rigid. To this
end a large amount of bearing and close fitting, using cast iron as the
material, are necessary, because cast iron does not spring or deflect so
easily as wrought iron; but the centres into which the lathe centres fit
are, if of cast iron, very liable to cut and shift their position, thus
throwing the bar out of true. It is, therefore, always preferable to
bore and tap the ends of such bars, and to screw in a wrought-iron or
steel plug, taking care to screw it in very tightly, so that it shall
not at any time become loose. The centres should be well drilled and of
a comparatively large size, so as to have surface enough to suffer
little from wear, and to well sustain the weight of the bar. The end
surface surrounding the centres should be turned off quite true to keep
the latter from wearing away from the high side, as they would do were
one side higher than the other."[16]
[16] From "The Complete Practical Machinist."
[Illustration: Fig. 1128.]
The common form of the smaller sizes of boring bar is that shown in Fig.
1127. A A being the bar, D D the lathe centres, B the cutter passing
through a slot or keyway in the bar, and C a key tapered (as is also the
back edge of the cutter) to wedge or fasten the cutter to the bar. It is
obvious that, if the cutter is turned up in the bar, and is of the exact
size of the hole to be bored, it will require to stand true in the bar,
and will therefore be able to cut on both ends, in which case the work
may be fed up to it twice as fast as though only one edge were
performing duty. To facilitate setting the cutter quite true, a flat and
slightly taper surface should be filed on the bar at each end of the
keyway, and the cutter should have a recess filed in it, as shown in
Fig. 1128, the recess being shown at A, and the edges B B forming the
diameter of the cutters. The backing off is shown at C, from which it
will be observed that the cutting duty is performed by the edge C, and
not along the edge B, further than is shown by the backing off. The
recess must be made taper, and to fit closely to the flat places filed
on the bar. Such a cutter, if required to be adjustable, must not be
provided with the recess A, but must be left plain, so that it may be
made to extend out on one side of the bar to cut any requisite size of
bore; it is far preferable, however, to employ the recess and have a
sufficient number of cutters to suit any size of hole, since, as already
stated (there being in that case two cutting edges performing duty), the
work may be fed up twice as fast as in the former case, in which only
one cutting edge operates.
Messrs. Wm. Sellers and Co. form the cutters for their celebrated car
wheel boring bar machine as in Fig. 1129, the bottom or plain edge
performing the cutting. By this means the recess to fit the bar is not
reduced in depth from sharpening the tool. The tool is sharpened by
grinding the ends of the lower face as shown by the unshaded parts, and
the cutter is said to work better after the cutting part has begun to be
oblique from grinding.
[Illustration: Fig. 1129.]
The cutter is hardened at the ends and left soft in the middle, so that
the standard size of the cutter may be restored when necessary, by
pening and stretching the soft metal in the middle. These cutters will
bore from 50 to 250 car wheels, without appreciable reduction of size.
The description of bar shown in Fig. 1127 may be provided with several
slots or keyways in its length, to facilitate facing off the ends of
work which requires it. Since the work is fed to the cutter, it is
obvious that the bar must be at least twice the length of the work,
because the work is all on one side of the cutter at the commencement,
and all on the other side at the conclusion of the boring operation. The
excessive length of bar, thus rendered necessary, is the principal
objection to this form of boring bar, because of its liability to
spring. There should always be a keyway, slot, or cutter way, near to
the centre of the length of the bar, so as to enable it to bore a hole
as long as possible in proportion to the length of the boring bar, and a
keyway or cutter way at each end of the bar, for use in facing off the
end faces of the work.
If a boring bar is to be used only for work that does not require facing
at the ends, the cutter, slot, or keyway should be placed in such
position in the length of the bar as will best suit the work (keeping in
mind the desirability of having the bar as short as possible), and the
bar should be tapering from the middle towards each end, as shown in
Fig. 1130. This will make the bar stronger in proportion to its weight,
and better able to resist the pressure of the cut and the tendency to
deflect. The parallel part at A is to receive the driving clamp, but
sometimes a lug cast on at that end is used instead of a clamp.
For bores too large to be bored by the bar alone, a tool-carrying head
is provided, being sometimes fixed upon the bar by means of a locking
key, and at others fed along the bar by a feed screw provided on the
bar.
[Illustration: Fig. 1130.]
When the head is fixed on the bar the latter must be twice as long as
the bore of the work, as the work is on one side of the head at the
beginning, and on the other at the end of a cut; hence it follows that
the sliding or feeding head is preferable, being the shortest, and
therefore the most rigid, unless the bar slides through bearings at each
end of the head.
Fig. 1131 represents a bar with a fixed head in operation in a cylinder,
and having three cutting tools, and it will be observed that if tool A
meets a low spot and loses its cut, the pressure on tools B and C, both
being on the opposite side of the head, would cause the bar to spring
over towards A, producing a hole or bore out of round, and it follows
that four tools are preferable.
Fig. 1132 is a side view of a bar with four cutters, and Fig. 1133 an
end view of the same shown within a cylinder, and it will be seen that
should one of the cutters lose its cut, the two at right angles to it
will steady the bar.
[Illustration: Fig. 1131.]
[Illustration: Fig. 1132.]
When the cutters require to stand far out from the head, the bar will
work more steadily if the cutters, instead of standing radially in the
head, are placed as in Fig. 1134, so that they will be pulled rather
than pushed to their cut.
[Illustration: Fig. 1133.]
[Illustration: Fig. 1134.]
An excellent form of boring bar fixed head, employed by Messrs. Wm.
Sellers and Co. on their horizontal cylinder boring machine, is shown in
Fig. 1135. The boring head is split at A, so that by means of the bolt B
it may be gripped firmly to the bar D, or readily loosened and slid
along it. The head is provided with cutters C (of which there are four
in the latest design of bar), fitting into the radial slots E. These
cutters are secured to the head by the clamps and nuts at G.
Fig. 1136 represents a boring bar, with a sliding head fed by a feed
screw running along the bar, and having at its end a pinion that meshes
upon a gear or pinion upon the dead centre of the lathe.
[Illustration: Fig. 1135.]
The tools employed for the roughing cuts of boring bars should, for
wrought iron, cast iron, steel, or copper, have a little front rake, the
cutting corner being at A in Fig. 1137.
If the cutters are to be used for one diameter of bore only, they will
work more steadily if but little or no clearance is given them on the
end B, Fig. 1138, but it is obvious that if they are to be used on
different diameters of bores they must have clearance on these ends. The
same tool may be used both for roughing and finishing cuts.
[Illustration: Fig. 1136.]
The lip or top rake must, in case the bar should tremble during the
finishing cut, be ground off, leaving the face level; and if, from the
bar being too slight for its duty, it should still either chatter or
jar, it will pay best to reduce the revolutions per minute of the bar,
keeping the feed as coarse as possible, which will give the best results
in a given time. In cases where, from the excessive length and smallness
of the bar, it is difficult to prevent it from springing, the cutters
must be made as in Fig. 1139, having no lip, and but a small amount of
cutting surface; and the corner A should be bevelled off as shown. Under
these conditions, the tool is the least likely to chatter or spring into
the cut.
The shape of the cutting corner of a cutter depends entirely upon the
position of its clearance or rake. If the edge forming the diameter has
no clearance upon it, the cutting being performed by the end edges, the
cutter may be left with a square, slightly rounded, or bevelled corner;
but if the cutter have clearance on its outside or diametrical edge, as
shown on the cutters in Fig. 1137, the cutting corner should be bevelled
or rounded off, otherwise it will jar in taking a roughing cut, and
chatter in taking a moderate cut. The principle is that bevelling off
the front edge of the cutter, as shown in Fig. 1139, tends greatly to
counteract a disposition to either jarring or chattering, especially as
applied to brass work.
[Illustration: Fig. 1137.]
The only other precaution which can be taken to prevent, in exceptional
cases, the spring of a boring bar is to provide a bearing at each end of
the work, as, for instance, by bolting to the end of the work four iron
plates, the ends being hollowed to fit the bar, and being so adjusted as
to barely touch it; so that, while the bar will not be sprung by the
plates, yet, if it tends to spring out of true, it will be prevented
from doing so by contact with the hollow ends of the plates, which
latter should have a wide bearing, and be kept well lubricated.
[Illustration: Fig. 1138.]
It sometimes happens that, from play in the journals of the machine, or
from other causes, a boring bar will jar or chatter at the commencement
of a bore, and will gradually cease to do so as the cut proceeds and the
cutter gets a broader bearing upon the work. Especially is this liable
to occur in using cutters having no clearance on the diametrical edge;
because, so soon as such a cutter has entered the bore for a short
distance, the diametrical edge (fitting closely to the bore) acts as a
guide to steady the cutter. If, however, the cutter has such clearance,
the only perceptible reason is that the chattering ceases as soon as the
cutting edge of the tool or cutter has lost its fibrous edges. The
natural remedy for this would appear to be to apply the oil-stone; this,
however, will either have no effect or make matters worse. It is,
indeed, a far better plan to take the tool (after grinding) and rub the
cutting edge into a piece of soft wood, and to apply oil to the tool
during its first two or three cutting revolutions. The application of
oil will often remedy a slight existing chattering of a boring bar, but
it is an expedient to be avoided, if possible, since the diameter or
bore cut with oil will vary from that cut dry, the latter being a trifle
the larger.
The considerations, therefore, which determine the shape of a cutter to
be employed are as follows: Cutters for use on a certain and unvarying
size of bore should have no clearance on the diametrical edges, the
cutting being performed by the end edge only. Cutters intended to be
adjusted to suit bores of varying diameter should have clearance on the
end and on the diametrical edges. For use on brass work the cutting
corner should be rounded off, and there should be no lip given to the
cutting edge. For wrought iron the cutter should be lipped, and oil or
soapy water should be supplied to it during the operation. A slight lip
should be given to cutters for use on cast iron, unless, from slightness
in the bar or other cause, there is a tendency to jarring, in which case
no lip or front rake should be given.
[Illustration: Fig. 1139.]
"In boring work chucked and revolved in the lathe, such, for instance,
as axle boxes for locomotives, the bar shown in Fig. 1140 is an
excellent tool. A represents a cutter head, which slides along, at a
close working fit, upon the bar D D, and is provided with the cutters B,
B, B, which are fastened into slots provided in the head A by the keys
shown. The bar D D has a thread cut upon part of its length, the
remainder being plain, to fit the sliding head. One end is squared to
receive a wrench, which resting against the bed of the lathe, prevents
the bar from revolving upon the lathe centres F, F, by which the bar is
held in the lathe. G, G, G are plain washers, provided to make up the
distance between the thread and plain part of the bar in cases where the
sliding head A requires considerable lateral movement, there being more
or less washers employed according to the distance along which the
sliding head is required to move. The edges of these washers are
chamfered off to prevent them from burring easily. To feed the cutters,
the nut H is screwed up with a wrench.
"The cutter head A is provided in its bore with two feathers, which
slide in grooves provided in the bar D D, thus preventing the head from
revolving upon the bar. It is obvious that this bar will, in consequence
of its rigidity, take out a much heavier cut than would be possible with
any boring tool, and furthermore that, there being four cutters, they
can be fed up four times as fast as would be possible with a single tool
or cutter. Care must, however, be exercised to so set the cutters that
they will all project true radially, so that the depth of cut taken by
each will be equal, or practically so; otherwise the feeding cannot
progress any faster than if one cutter only were employed."[17]
[17] From Rose's "Complete Practical Machinist."
[Illustration: Fig. 1140.]
For use on bores of a standard size, the cutters may be made with a
projecting feather, fitting into a groove provided in the head to
receive it, as shown in Fig. 1141, which shows the boring bar and head,
the nuts and washers being removed. A, A represent cutters, B the bar, C
the sliding head, and D, D keys which fasten the cutters in the head.
The cutters should be fitted to their places, and each marked to its
place; so that, if the keyways should vary a little in their radius from
their centre of the bar, they will nevertheless be true when in use, if
always placed in the slot in which they were turned up when made. By
fitting in several sets of cutters and turning them up to standard
sizes, correctness in the size of bore may be at all times insured, and
the feeding may be performed very fast indeed.
For boring cannon the form of bar shown in Fig. 1142 is employed. The
cannon is attached to the carriage or saddle of the lathe and fed to the
boring bar. The working end only of the bar is shown in the figure, the
shank stem or body of the bar being reduced in diameter to afford easy
access to the cuttings. The cutters occupy the positions indicated by
the letters A, A, A, being carefully adjusted as to distance from the
axis of the bar by packing them at the back with very thin paper. As may
be observed they are arranged in two sets of three each, of which the
first set performs almost the whole of the work, the second being
chiefly added as a safeguard against error in the size of the bore on
account of wear of the cutting edges, which takes place to a small but
an appreciable extent in the course of even a single boring. Following
the cutters is a series of six guide-bars (B B B), arranged spirally,
which are made exactly to fit the bore. Provided that the length of
these is sufficient, and their fit perfect, it is evident that the
cutters cannot advance except in a straight line. The spiral arrangement
of the cutters is employed to steady the bar and to give it front rake.
[Illustration: Fig. 1141.]
[Illustration: Fig. 1142.]
[Illustration: Fig. 1143.]
[Illustration: Fig. 1144.]
BORING TAPERS WITH A BORING BAR OR ATTACHMENT.--In cases where the
degree of taper is very great a live centre may be bolted to a chuck
plate, as in Fig. 1143, by which means any degree of taper may be bored.
Instead of a star feed, a gear feed may be provided by fastening one
gear, as A, on the dead centre, and another, as B, on the feed-screw.
The cutting tool must stand on the side of the sliding-head--that is,
farthest from the line of lathe centres.
[Illustration: Fig. 1145.]
[Illustration: Fig. 1146.]
Small holes may readily be bored taper with a bar set over as in Fig.
1144, the work being carried by a chuck. The head H carries the cutting
tool, having a feather which projects into the spline S to prevent the
head from rotating on the bar. To prevent the bar from rotating, it is
squared on the end F to receive a wrench. The head is fed by the nut N,
which is screwed upon the bar. W, W, W, W are merely washers used to
bring the nut N at the end of the thread when the head is near the mouth
of the work, their number, therefore, depending upon the depth of the
work. A bar of this kind is more rigid than a tool held in the tool
post.
Instead of setting the dead centre of the lathe over, the bar may be set
over, as in Fig. 1145, in which the boring tool is carried in the
sliding head at T, and is fed by a screw having a star feed on its end.
At B is a block sliding in the end of the bar and capable of movement
along the same, to adjust the degree of taper by means of the screw
shown in the end view, Fig. 1146. N is a nut to secure B in its adjusted
position.
In this case the work must be bolted to the lathe carriage, and the tool
feeds to the cut, and the largest end of the hole bored will be at the
live spindle end of the lathe.
But we may turn the bar around, as in Fig. 1147, driving the work in a
chuck, and holding the dead centre end of the bar stationary, feeding
the sliding head to the cut by the feed screw F.
To increase the steadiness of the sliding head it may with advantage,
be made long, as in Fig. 1148, in which S is a long sleeve fitting to
the bar B at the head end H, and recessed as denoted by the dotted
lines. The short cutting tool C may be fastened to H by a set-screw in
the end of H, or by a wedge, as may be most desirable. The bar may
obviously set over to bore tapers as in the cut, and the sliding head
may be prevented from turning by a driver resting on the top of the tool
rest, and pushed by a tool secured to the tool post, the self-acting
carriage feed being put in operation.
[Illustration: Fig. 1147.]
[Illustration: Fig. 1148.]
It is obvious that when a boring bar is set over to bore a taper, the
lathe centres do not bed fair in the work centres, hence the latter are
subject to excessive wear and liable to wear to one side more than to
another, thus throwing the bar out of true and altering the taper it
will bore. This, however, may be prevented by fitting to the bar at each
end a ball-and-socket centre, such as shown in section in Fig. 1149. A
spherical recess is cut in the bar, a spherical piece is fitted to this
recess and secured therein by a cap as shown, the device having been
designed by Mr. George B. Foote.
[Illustration: Fig. 1149.]
BORING DOUBLE TAPERS.--To prevent end play in journal bearings where it
is essential to do so, the form of journal shown in Fig. 1150 is
sometimes employed, hence the journal bearing requires to be bored to
fit.
[Illustration: Fig. 1150.]
[Illustration: Fig. 1151.]
Fig. 1151 represents a bearing box for such a journal, the brasses A, B
having flanges fitting outside the box as shown. The ordinary method of
doing such a job would be to chuck the box on the face plate of the
lathe, setting it true by the circle (marked for the purpose of setting)
upon the face of the brasses, and by placing a scribing point tool in
the lathe tool post and revolving the box, making the circle run true to
the point, which would set the box one way, and then setting the flanges
of the box parallel with the face plate of the lathe to set the box true
the other way; to then bore the box half way through from one side and
then turn it round upon the face plate, reset it and bore the other
half; thus the taper of the slide rest would not require altering. This
plan, however, is a tedious and troublesome one, because, as the flanges
protrude, parallel pieces have to be placed between them and the lathe
face plate to keep them from touching; and as the face of the casting
may not be parallel with the slide ways, and will not be unless it has
been planed parallel, pieces of packing, of paper or tin, as the case
may be, must be placed to true the ways with the face plate, and the
setting becomes tedious and difficult. But the two tapers may be bored
at one chucking, as shown in Fig. 1152, in which A represents the lathe
chuck, and B is a sectional view of the bearing chucked thereon, C, C
being the parallel pieces. Now it will be observed that the plane of the
cone on the front end and on one side stands parallel with the plane of
the cone on the back end at an exactly opposite diameter, as shown by
the dotted lines D and E. If then the top slide of the lathe rest be set
parallel with those lines, we may bore the front end by feeding the tool
from the front of the bore to the middle as marked from F to G, and
then, by turning the turning tool upside down, we may traverse or feed
it along the line from H to J, and bore out the back half of the double
cone without either shifting the set of the lathe rest or chucking the
box after it is once set.
[Illustration: Fig. 1152.]
In considering the most desirable speed and feed for the cutting tools
of lathes, it may be remarked that the speeds for boring tools are
always less than those for tools used on external diameters, and that
when the tool rotates and the work is stationary, the cutting speed is a
minimum, rarely exceeding 18 feet per minute, while the feed, especially
upon cast iron, is a maximum.
The number of machines or lathes attended by one man may render it
desirable to use a less cutting speed and feed then is attainable, so as
to give the attendant time to attend to more than one, or a greater
number of lathes. In the following remarks outside work and a man to one
lathe is referred to.
The most desirable cutting speeds for lathe tools varies with the
rigidity with which the tool is held, the rigidity of the work, the
purpose of the cut, as whether to remove metal or to produce finish and
parallelism, the hardness of the metal and stoutness of the tool, the
kind of metal to be cut, and the length the tool may be required to
carry the cut without being reground. The more rigid the tool and the
work the coarser the feed may be, and the more true and smooth the work
requires to be the finer the feed. In a roughing cut the object is to
remove the surplus metal as quickly as possible, and prepare the work
for the finishing cut, hence there is no objection to removing the tool
to regrind it, providing time is saved. Suppose, for example, that at a
given speed and feed the tool will carry a cut 12 inches along the work
in 20 minutes, and that the tool would then require regrinding, which
would occupy four minutes, then the duty obtained will be 12 inches
turned in 24 minutes; suppose, however, that by reducing the speed of
rotation, say, one-half, the tool would carry a cut 24 inches before
requiring to be reground, then the rate of tool traverse remaining the
same per lathe revolution, it would take twice as long (in actual
cutting time) to turn a foot in length of the work. If we take the
comparison upon two feet of work length, we shall have for the fast
speed 24 inches turned in 40 minutes of actual cutting time, and 10
minutes for twice grinding the tool, or 24 inches in 50 minutes; for the
slow speed of rotation we shall have 24 inches turned in 80 minutes.
In this case therefore, it would pay to run the lathe so fast that the
tool would require to be ground after every foot of traverse. But in the
case of the finishing cut, it is essential that the tool carry the cut
its full length without regrinding, because of the difficulty of
resetting the tool to cut to the exact diameter. It does not follow from
this that finishing cuts in all cases require to be taken at a slower
rate of cutting speed, because, as a rule, the opposite is the case,
because of the lightness of the cut; but in cases where the work is
long, the rate of cutting speed for the finishing cut should be
sufficiently slow to enable the tool to take a cut the whole work length
without grinding, if this can be done without an undue loss of time,
which is a matter in which the workman must exercise his judgment,
according to the circumstances. In tools designed for special purposes,
and especially upon cast iron the work being rigid the tool may be
carried so rigidly that very coarse feeds may be used to great
advantage, because the time that the cutting edge is under cutting duty
is diminished, and the cutting speed may be reduced and still obtain a
maximum of duty; but the surfaces produced are not, strictly speaking,
smooth ones, although they may be made to correct diameter measured at
the tops of the tool marks, or as far as that goes at the bottom of the
tool marks also, if it be practicable.
In the following table of cutting feeds and speeds, it is assumed that
the metals are of the ordinary degree of hardness, that the conditions
are such that neither the tool nor the work is unduly subject to spring
or deflection, and that the tool is required to carry a cut of at least
12 inches without being reground; but it may be observed that the 12
inches is considered continuous, because on account of the tool having
time to cool, it would carry more than the equivalent in shorter cuts,
thus if the work was 2 inches long and the tool had time to cool while
one piece of work was taken out and another put in the lathe, it would
probably turn up a dozen such pieces without suffering more in sharpness
than it would in carrying a continuous cut of 12 inches long. The rates
of feed here given are for work held between the lathe centres in the
usual manner.
CUTTING SPEEDS AND FEEDS.
FOR WROUGHT IRON.
+---------+--------+-----------+-------------+-----------+------------+
| Work |Roughing| Roughing |Feed as lathe| Finishing | Finishing |
|diameter.| cuts. | cuts. | revolutions |cuts. Lathe| cuts. Lathe|
| Inches. |Feet per| Lathe | per inch of |revolutions| revolutions|
| | minute.|revolutions| tool travel.|per minute.| per inch |
| | |per minute.| | |tool travel.|
|---------+--------+-----------+-------------+-----------+------------|
| 1/2 | 40 | 305 | 30 | 305 | 60 |
| 1 | 35 | 133 | 30 | 133 | 60 |
| 1-1/2 | 30 | 76 | 30 | 76 | 60 |
| 2 | 28 | 53 | 25 | 53 | 60 |
| 2-1/2 | 28 | 42 | 25 | 42 | 50 |
| 3 | 28 | 35 | 25 | 35 | 50 |
| 3-1/2 | 26 | 28 | 25 | 30 | 50 |
| 4 | 26 | 24 | 20 | 26 | 50 |
| 5 | 25 | 18 | 20 | 21 | 50 |
| 6 | 25 | 15 | 20 | 16 | 50 |
| CAST IRON. |
| 1 | 45 | 163 | 30 | 163 | 40 |
| 1-1/2 | 45 | 135 | 25 | 135 | 30 |
| 2 | 40 | 76 | 25 | 76 | 25 |
| 2-1/2 | 40 | 61 | 20 | 61 | 20 |
| 3 | 35 | 44 | 20 | 50 | 16 |
| 3-1/2 | 35 | 38 | 18 | 43 | 16 |
| 4 | 35 | 33 | 18 | 38 | 16 |
| 4-1/2 | 30 | 25 | 16 | 28 | 14 |
| 5 | 30 | 22 | 16 | 26 | 14 |
| 5-1/2 | 30 | 20 | 14 | 24 | 12 |
| 6 | 30 | 19 | 14 | 22 | 12 |
| BRASS. |
| 1/2 | 120 | 910 | 25 | 910 | 40 |
| 3/4 | 110 | 556 | 25 | 556 | 40 |
| 1 | 100 | 382 | 25 | 382 | 40 |
| 1-1/4 | 90 | 275 | 25 | 275 | 40 |
| 1-1/2 | 80 | 203 | 25 | 203 | 40 |
| 1-3/4 | 80 | 174 | 25 | 174 | 40 |
| 2 | 75 | 143 | 25 | 143 | 40 |
| 2-1/2 | 75 | 114 | 25 | 114 | 40 |
| 3 | 70 | 89 | 25 | 89 | 40 |
| 3-1/2 | 70 | 76 | 25 | 76 | 40 |
| 4 | 70 | 66 | 25 | 66 | 40 |
| 4-1/2 | 65 | 55 | 25 | 55 | 40 |
| 5 | 65 | 50 | 25 | 50 | 40 |
| 5-1/2 | 65 | 45 | 25 | 45 | 40 |
| 6 | 65 | 41 | 25 | 41 | 40 |
| TOOL STEEL. |
| 3/8 | 24 | 245 | 60 | 245 | 60 |
| 1/2 | 24 | 184 | 60 | 184 | 60 |
| 5/8 | 24 | 147 | 50 | 147 | 60 |
| 3/4 | 24 | 122 | 40 | 122 | 60 |
| 7/8 | 20 | 87 | 30 | 87 | 60 |
| 1 | 20 | 76 | 30 | 76 | 60 |
| 1-1/4 | 20 | 61 | 25 | 61 | 50 |
| 1-1/2 | 18 | 45 | 25 | 45 | 50 |
| 2 | 18 | 34 | 25 | 34 | 50 |
| 2-1/2 | 18 | 27 | 25 | 27 | 50 |
| 3 | 18 | 22 | 25 | 22 | 40 |
| 3-1/2 | 18 | 19 | 25 | 19 | 40 |
| 4 | 18 | 17 | 25 | 17 | 40 |
| 4-1/2 | 18 | 15 | 25 | 15 | 40 |
+---------+--------+-----------+-------------+-----------+------------+
These cutting speeds and feeds are not given as the very highest that
can be attained under average conditions, but those that can be readily
obtained, and that are to be found used by skilful workmen. It will be
observed that the speeds are higher as the work is smaller, which is
practicable not only on account of the less amount of work surface in a
given length as the diameter decreases, but also because with an equal
depth of cut the tool endures less strain in small work, because there
is less power required to bend the cutting, as has been already
explained.
When it is required to remove metal it is better to take it off at a
single cut, even though this may render it necessary to reduce the
cutting speed to enable the tool to stand an increase of feed better
than excessive speed. Suppose, for example, that a pulley requires 1/4
inch taken off its face, whose circumference is 5 feet and width 8
inches. Now the tool will carry across a cut reducing the diameter 1/8
inch, at a cutting speed of 40 feet per minute, or 10 lathe revolutions
per minute; but if the speed be reduced to about 35 feet per minute, the
tool would be able to stand the full depth of cut required, that is, 1/8
inch deep, reducing the diameter of the pulley 1/4 inch. Now with the
fast speed two cuts would be required, while with the slow one a single
cut would serve; the difference is therefore two to one in favor of the
deep cut, so far as depth of cut is concerned.
The loss of time due to the reduced rotative speed of work would of
course be in proportion to that reduction, or in the ratio of 35 to 50.
It is apparent then that the tool should, for roughing cuts, be set to
take off all the surplus metal at one cut, whenever the lathe has power
enough to drive the cut, and that the cutting speed should be as fast as
the depth of cut will allow.
Concerning the rate of feed, it is advisable in all cases, both for
roughing and finishing cuts, to let it be as coarse as the conditions
will permit, the rates given in the table being in close approximation
of those employed in the practice of expert lathe hands.
It is to be observed, however, that under equal conditions, so far as
the lathe and the work is concerned, it is not unusual to find as much
difference as 30 per cent. in the rate of cutting speed or lathe
rotation, and on small work 50 per cent. in the rate of tool traverse
employed by different workmen, and here it is that the difference is
between an indifferent and a very expert workman.
An English authority (Mr. Wilson Hartnell), who made some observations
(in different workshops and with different workmen) on this subject,
stated that taking the square feet of work surface _tooled_ over in a
given time, he had often found as much as from 100 to 200 per cent.
difference, and that he had found the rate of _tooling_ small fly-wheels
vary from 2 to 8 square feet per hour without any sufficient reason. The
author has himself observed a difference of as much as 20 feet of work
rotation per minute on work of 18 and less inches in diameter, and as
much as 50 per cent. in the rate of tool traverse per lathe revolution.
It is only by keeping the speed rotation at the greatest consistent with
the depth of cut, and by exercising a fine discretion in regulating the
rotations of feed and cutting speed, that a maximum of duty can under
any given conditions be obtained.
It has hitherto been assumed that the workman's attention is confined to
running one lathe, but cases are found in practice where the lathes,
having automatic feed and stop motions, one man can attend to several
lathes, and in this case the feeds and speeds may be considerably
reduced, so as to give the operator time to attend to a greater number
of lathes. As an example, in the use of automatic lathes, several of
which are run by one man, the following details of the practice in the
Pratt and Whitney Company's tap and die department are given.
[Illustration: Fig. 1153.]
Lathe Number 1.--Lathe turning tool steel 3/8 inch in diameter and 1-1/4
long, reducing the diameter of the work 1/8 inch. Revolutions of work
per minute 125. Feed one inch of tool travel to 200 lathe revolutions.
Lathe Number 2.--Turning tool steel 2 inches long and 1/2 inch diameter,
reducing diameter 1/8 inch. Revolutions of work 100 per minute. Feed 200
lathe revolutions per inch of tool travel.
Lathe Number 3.--Turning tool steel 4 inches long and 7/8 inch in
diameter, reducing the diameter 1/8 inch. Revolutions of work 40 per
minute. Feed 200 lathe revolutions per inch of tool travel.
Lathe Number 4.--Turning tool steel 6 to 8 inches long and 1-3/16
diameter, reducing work 1/8 inch in diameter. Revolutions of work 35 per
minute. Feed 200 lathe revolutions per inch of tool travel.
Lathe Number 5.--Turning tool steel 8 to 10 inches long, and 2 inches in
diameter, reducing diameter 1/8 inch. Lathe revolutions 30 per minute.
Feed 200 lathe revolutions per inch of tool travel.
Lathe Number 6.--Turning tool steel 5 inches long and 3-1/2 inches
diameter, reducing diameter 3/16. Lathe revolutions 19 per minute. Feed
200 lathe revolutions per inch of tool travel.
The power required to drive the work under a given depth of cut varies
greatly with the following elements:--
1st. The diameter of the work, all other conditions being equal.
2nd. The degree of hardness of the metal, all other conditions being
equal.
3rd. Upon the shape of the cutting tool; and--
4th. Upon the quality of the steel composing the cutting tool, and the
degree of its hardness.
That the diameter of the work is an important element in small work may
be shown as follows:--
[Illustration: Fig. 1154.]
[Illustration: Fig. 1155.]
In Fig. 1153 let W represent a piece of work having a cut taken off it,
and the line of detachment of the metal from the body of the work will
be represented by the part of the dotted line passing through the depth
of the cut (denoted by C). Let Fig. 1154 represent a similar tool with
the same depth of cut on a piece of work of larger diameter, and it will
be observed that the dotted line of severance is much longer, involving
the expenditure of more power.
In boring these effects are magnified: thus in Fig. 1155 let W represent
a washer to be bored with the tool T, and let the same depth of cut be
taken by the tool, the diameter of the work being simply increased. It
is manifest that the cutting would require to be bent considerably more
in the case of the small diameter of work than in that of the large, and
would thus require more power for an equal depth of cut.
Again, from a reference to Figs. 950 and 952, it will be observed that
the height of the tool will make a difference in the power required to
drive a given depth of cut, the shaving being bent more when the tool is
above the centre in the case of boring tools, and below the centre in
the case of outside tools. But when the diameter of the work exceeds
about 6 inches, it has little effect in the respects here enumerated.
The following, however, are the general rules applicable when
considering the power required for the cutting of metal with lathe or
planer tools. The harder the metal, the more power required to cut off a
given weight of metal. The deeper the cut the less power required to cut
off a given weight of metal. The quicker the feed the less power
required to cut off a given weight of metal. The smaller the diameter of
outside work, and the larger the diameter of inside or bored work, the
less power required.
Copper requires less power than brass; yellow, and other brass
containing zinc, less than brass containing a greater proportion of tin.
Brass containing lead requires less power than that not containing it.
Cast iron requires more power than brass, but less than wrought iron;
steel requires more power than wrought iron.
CHAPTER XII.--EXAMPLES IN LATHE WORK.
TECHNICAL TERMS USED WITH REFERENCE TO LATHE WORK.--Work held between
the lathe centres is said to run true, when a fixed point set to touch
its perimeter will have an equal degree of contact all around the
circumference, and at any part of the length of the same when the work
is cylindrical and is rotated. When such a fixed point has contact at
one part more than at another of the work circumference, it is said to
run "out of true," "out of truth," or not to run true.
Radial or side faces (as they are sometimes called) also run true when a
fixed point has equal contact (at all parts of the revolution) with the
work surface.
Work that is held in chucks is said to be set true when it is adjusted
in the intended position.
To true up is to take off the work a cut of sufficient depth to cause a
fixed point to touch the work surface equally at each point in the
revolution.
To clean work up is to take off it a cut sufficiently deep to cause it
to run true, and at the same time removes the rough surface or scale
from the metal.
Roughing out work is taking off a cut which reduces it to nearly the
finishing size, leaving sufficient metal to take a finishing cut, and
reduce it to the proper size.
_Facing_ a piece of work is taking a cut off its radial face.
When a radial face or surface is convex, it is said to be _rounding_ or
_round_, and when it is concave it is said to be _hollow_.
When a radial face is at a right angle to a cylindrical parallel
surface, it is said to be _square_; but in taper work, it is said to be
_square_ when it is at a right angle to the axis of the taper.
_Outside work_ includes all operations performed on a piece of work
except those executed within the bores of holes or recesses, which is
termed inside or internal work.
_Jarring_ or _chattering_ is the term applied to a condition in which
the tool does not cut the work smooth, but leaves a succession of
elevations and depressions on it, these forming sometimes a regular
pattern on the work. In this case the projections only will have contact
with the measuring tools, or with the enveloped or enveloping work
surface, when the two pieces are put together.
Jarring or chattering more commonly occurs in the bores of holes or upon
radial surfaces, than upon plain cylindrical surfaces, unless the latter
be very long and slender. It occurs more also upon brass than upon iron
work, and more upon cast than upon wrought iron or steel. It is caused
mainly by vibrations of either the work or the tool.
It is induced by weakness (or want of support) in the work, by weakness
in the tool, or by its being improperly formed for the duty. Thus, if a
tool have too broad a cutting surface it will jar; if it be held out far
from the tool post it may jar; if it have too keen a top face for the
conditions it will jar.
Jarring may almost always be remedied on brass work by reducing the
keenness of the top face, giving it if necessary negative rake, as shown
in Fig. 964. On iron or steel work it may be avoided by using as stiff a
cutting tool as possible, holding its cutting edge as close to the tool
post as convenient, and reducing the length of cutting edge to a
minimum.
It may be prevented sometimes by simply placing the finger or a weight
upon the tool, or by applying oil to the work, but if this be done it
should be supplied continuously throughout the cut, as a tool will cut
to a different depth when dry from what it will when lubricated.
In using hand tools such as scrapers, too thin a tool may cause jarring,
which may be obviated by keeping the tool rest as close to the work as
possible, and placing a piece of leather between the work and the rest.
EXAMPLES IN LATHE WORK.--The simplest class of lathe work is that cut
from rods or short lengths of rod metal, which may be turned by being
held in a small chuck, or between the lathe centres.
Such work is usually of small diameter and short length, and is
therefore difficult to get at if turned between the lathe centres,
because the dog that drives it, the lathe face plate, and the dead
centre are in the way; such work may be more conveniently driven by a
small chuck.
It is usually made of round wire or rod, cut into lengths to suit the
conditions; thus if the lathe have a hollow spindle, the rod lengths may
be so long as to pass entirely through the spindle, otherwise the
lengths may be passed through the chuck, and as far as possible into the
live spindle centre hole.
In any event it is desirable to let the rod project so far out from the
chuck as to enable its being finished and cut off, without removal from
or moving it in the chuck, because such chucks are apt in course of time
to wear, so that the jaws do not grip the work quite concentric to the
line of centres; hence, if the work be moved in the chuck after having
been turned, it is apt to run out of true.
Sometimes, however, the existence of a collar on the work prevents it
from being trued for fit at both ends without being cut off from the
rod, in which case, if it requires correction after being cut off, it
must be rechucked, and it may be necessary at this rechucking to grip it
in several successive positions (partly rotating it in the chuck at each
trial) before it will run true.
Sometimes the length of work that may advantageously be driven by such a
chuck is so great as to render the use of the dead centre to support one
end necessary, in which case the rod should be removed from the chuck
before each piece is turned, so as to centre drill the dead centre end.
There is one special advantage in driving small work in a chuck of this
kind, inasmuch as the work can be tried for fit without removing it from
the lathe, while in some cases operations can be performed on it which
would otherwise require its removal to the vice; suppose, for example, a
thread of very small diameter and pitch requires to be cut on the work
end, then a pair of dies or a screw plate may be placed on it, and the
lathe pulled round by the belt; after the dies have commenced to start
the thread, they may be released and allowed to rotate with the lathe,
which will show if they are starting the thread true upon the work.
In cases also where the end of the work requires fitting to a seat, or
where it requires turning to a conical point, there is the advantage
that the work can be tried to the seat, or turned to the point without
taking from the lathe, or without any subsequent operations, whereas in
the case of a conical point, the existence of a work centre would
necessitate turning the cone some distance from the end, and cutting off
the work centre.
As the size of the work increases, the form of the chuck is varied to
make it more powerful and strong to resist the strains, but when the
size of the chuck becomes so large that it is as much in the way as the
face place would be, it is better to turn the work between the lathe
centres.
For work to be turned between the lathe centres, it is essential that
those centres run true, and be axially in line, and that both centres be
turned to the same degree of angle or cone, which is usually for small
lathes an angle of 60°, and for lathes of about 30 inches swing and over
an angle of about 70°. Both centres should be of an equal angle, for the
following reasons.
It is obvious that the work centres wear to fit the dead centre, because
of the friction between the two. Now in order to turn a piece of work
from end to end, it is necessary to reverse it in the lathe, because at
the first turning one end is covered by the carrier or driver driving
it. At the first turning one work centre only will have worn to fit the
lathe centre; hence when at the second, the other work centre wears to
fit the dead centre and in the process of such wearing moves (as it
always does to some degree) its location, the part first turned will no
longer run true. To obviate this difficulty it is proper at the first
turning to cut the work down to nearly the finished size, and then
reverse it in the lathe and turn up the other end. At this second
turning the work will have had both work centres worn to fit the dead
centre, hence if it be of the same angle as the live centre, the work
will properly bed to both centres, otherwise it will plainly not bed
well to the live centre, and in consequence will be apt to run in some
degree out of true at the live centre end.
The lathe centres should, for parallel work, stand axially true one with
the other, and this can only be the case when the live centre runs true.
If the live centre does not run true the following difficulties are met
with.
[Illustration: Fig. 1156.]
If one end only of the work requires to be turned and it can be
completely finished without moving the work driver, the work will be
true (assuming the live spindle to run true in its bearings and to fit
the same). It will also run true if the work be taken from the lathe and
replaced without moving the driver or carrier, providing that the driver
be so placed as to receive the driving pressure at the same end as it
did when the work was driven; and it is therefore desirable, on this
account alone, to always so place the work in the lathe that the driver
is driven by its tail end, and not from the screw or screw head. But if
the work be turned end for end it will not run true, because the work
centre at the unturned end of the work will not be true or central to
the turned part of the work.
It is obvious then that lathe centres should run true. But this will not
be the case unless the holes into which they fit in the lathe are
axially true one with the other and with the lathe spindles. If these
holes are true, and the centres are turned true and properly cleaned
before insertion, the centres may be put into their places without any
adjustment of position. Otherwise, however, a centre punch mark is made
on the radial or end face of the live spindle, and another is made on
the live centre, so that both for turning up and for subsequent use the
centre will run true when these centre punch marks are exactly opposite
to each other.
The best way to true lathe centres is with an emery-wheel. In some
lathes there are special fixtures for emery grinding, while in others an
attachment to go in the tool post is used. Fig. 1156 shows such an
attachment.
In the figure A is a frame to be fastened in the slide rest tool post at
the stem A´. It affords journal bearing to the hand wheel B, to the
shaft of which is attached the gear-wheel C, which drives a pinion D, on
a shaft carrying the emery-wheel E, the operation being obviously to
rotate wheel B, and drive the emery-wheel E, through the medium of the
multiplying gear-wheels C, D.
The emery-wheel is fed to its depth of cut on the lathe centre P, by the
cross feed screw of the lathe, and is traversed by pulling or pushing
the knob F, the construction of this part of the device being as
follows: G and H are two bushes, a sliding fit in the arms of frame A,
but having on top flat places I and J, against which touch the ends of
the two set-screws _k_, _l_, to prevent them from rotating. The
emery-wheel and gear pinion D are fast together, and a pin passes
through and holds G and H together. Hence the knob F pushes or pulls, as
the case may be, the bushes through the bearings G, H, in the frame A,
the pinion and emery-wheel traversing with them. Hence pinion D is
traversed to and fro by hand, and it is to admit of this traverse that
it requires its great length. The stem A is at such an angle that, if it
be placed true with the line of cross feed, the lathe centre will be
ground to the proper angle.
Fig. 1157 represents a centre grinding attachment by Trump Brothers, of
Wilmington, Delaware. In this device the emery-wheel is driven by belt
power as follows. A driving wheel A is bolted to the lathe face plate,
and a stand carries at its top the over-head belt pulleys, and at its
base the emery-wheel and spindle. This stand at C sets over the tool
post, and is secured by a bar passing through C and through the tool
post, whose set-screw therefore holds the stand in position. On the end
of the emery-wheel spindle is a feed lever, by means of which the
emery-wheel may be fed along the lathe centre. Cup piece B is for
enabling wheel A to be readily set true on the lathe face plate, one end
of B fitting the hub of A, while the other receives the dead centre
which is screwed up so that B will hold A in place, while it is bolted
to the lathe face plate, and at the same time will hold it true.
In the absence of a centre grinding attachment, lathe centres may be
turned true with a cutting tool, and finished with water applied to the
tool so as to leave a bright and true surface. They should not, for the
finest of work, be finished by filing, even though the file be a dead
smooth one, because the file marks cause undue wear both to the lathe
centres and the work centres.
The dead centres should be hardened to a straw color, and the live
centre to a blue; the former so as to have sufficient strength to resist
the strain, and enough hardness to resist abrasion, and the latter to
enable it to be trued up without softening it.
[Illustration: Fig. 1157.]
When, after turning them up, the centres are put into their places, the
tailstock may be moved up the bed so that the dead centre projects but
very little from the tailstock, and is yet close to the live centre, and
the lathe should be run at its fastest speed to enable the eye to
perceive if the live centre runs true, and whether the dead centre is in
line with the live one, and the process repeated so that both centres
may be tested.
A more correct test, however, may be made with the centre indicator.
[Illustration: Fig. 1158.]
CENTRE INDICATORS.--On account of the difficulty of ascertaining when a
centre runs quite true, or when a very small hole or fine cone as a
centre punch mark runs true when chucked in a lathe, the centre
indicator is used to make such tests, its object being to magnify any
error, and locate its direction. Fig. 1158, from _The American
Machinist_, represents a simple form of this tool, designed by Mr. G. B.
Foote, for testing lathe centres. A is a piece of iron about 8 inches
long to fit the lathe tool post, B is a leather disk secured to A by a
plate C, and serving to act as a holding fulcrum to the indicator
needle, which has freedom of movement on account of the elasticity of
the leather washer, and on account of the hole shown to pass through A.
It is obvious that if the countersunk end of the needle does not run
true, the pointed end will magnify the error by as many times as the
distance from the needle point to the leather washer is greater than
that from the leather washer to the countersunk end of the needle. It is
necessary to make several tests with the indicator, rotating the lathe
centre a quarter turn in its socket for each test, so as to prove that
the centre runs true in any position in the lathe spindle. If it does
not run true the error should be corrected, or the centre and the lathe
spindle end may be marked by a centre punch done to show in what
position the centre must stand to run true.
[Illustration: Fig. 1159.]
The tension of the leather washer serves to keep the countersunk against
the lathe centre without a very minute end adjustment. Or the same end
may be attained by the means shown in Fig. 1159, which is a design
communicated by Mr. C. E. Simonds to _The American Machinist_. The
holder is cupped on one side to receive a ball as shown, and has a
countersink on the other to permit a free vibration of the needle. The
ball is fitted to slide easily upon the needle, and between the ball and
a fixed collar is a spiral spring that keeps the ball in contact with
its seat in the holder.
[Illustration: Fig. 1160.]
One end of the needle is pointed for very small holes or conical
recesses, while the other is countersunk for pointed work, as lathe
centres. The countersink of the needle may be made less acute than the
lathe centre, so that the contact will be at the very point of the lathe
centre, the needle not being centre-drilled. The end of the needle that
is placed against the work should be as near to the ball or fulcrum as
convenient, so as to multiply the errors of work truth as much as
possible.
In some forms of centre indicators the ball is pivoted, so that the
needle only needs to be removed to reverse it end for end, or for
adjusting its distance, it being made a close sliding fit through the
ball. Thus, in Fig. 1160 the ball E is held in a bearing cut half in the
holder A, and half in cap B, which is screwed to A by screws C D.
Or the ball may be held in a universal joint, and thus work more
frictionless. Thus, in Fig. 1161 it is held by the conical points of two
screws diametrically opposite in a ring which is held by the conical
points of two screws threading through an outer ring, these latter
screws being at a right angle to those in the inner ring. The outer ring
is held to the holder by the conical points of two screws, all the
conical points seating in conical recesses.
[Illustration: Fig. 1161.]
It is obvious that the contact of the point of the needle and the work
may be more delicately made when there is some elasticity provided, as
is the case with the spiral spring in Fig. 1159.
Indicators of this class may be used to test the truth of cylindrical
work: thus, in Fig. 1162 is an application to a piece of work between
the lathe centres, there being fitted to one end of the needle a fork
_a_ that may be removed at pleasure.
[Illustration: Fig. 1162.]
One of the difficulties in turning up a lathe centre to run true arises
from the difference in cutting speed at the point and at the full
diameter of the cone, the speed necessary to produce true smooth work at
the point being too fast for the full diameter. This may be remedied on
centres for small work, as, say, three inches and less in diameter, by
cutting away the back part of the cone, leaving but a short part to be
turned up to true the centre.
To permit the cutting off or squaring tool to pass close up to the
centre, and thus prevent leaving a burr or projection on the work end,
the centre may be thus relieved at the back and have a small parallel
relief, as in Fig. 1164 at A, the coned point being left as large as
possible, but still small enough to pass within the countersink.
In centres for large and heavy work it is not unusual to provide some
kind of an oil way to afford means of lubrication, and an excellent
method of accomplishing this object is to drill a hole A, Fig. 1163, to
the axis of the centre and let it pass thence to the point as denoted by
the dotted line; there may also be a small groove at B in the figure to
distribute the oil along the centre, but grooves of this kind make the
returning of the centre more difficult and are apt to cause the work
centres to enlarge more from wear, especially in turning tapers with the
tailstock set over the lathe centre, these being out of line with the
work centre.
To enable a broad tool such as a chaser to meet work of smaller diameter
than the lathe centre, the latter is cut away on one side as in Fig.
1164. It is obvious also that the flat place being turned uppermost,
will facilitate the use of the file on work of smaller diameter than the
lathe centre, and that placed in the position shown in the cut, it will
permit a squaring tool to pass clear down to the centre and avoid
leaving the projecting burr which is left when the tool cannot pass
clear down the face to the edge of the countersink of the work centre.
[Illustration: Fig. 1163.]
[Illustration: Fig. 1164.]
The method to be employed for centring work depends upon its diameter,
and upon whether its ends are square or not. When the pieces are cut
from a rod or bar in a cutting-off machine, the ends are square, and
they may be utilized to set the work by in centring it. Thus, in Fig.
1165 is a top, and in Fig. 1166 is an end view of a simple device, or
lathe attachment for centre drilling. S is a stand bolted to the lathe
shears and carrying two pins P, which act as guides to the cup chuck or
work guide G; between the heads of pins P and the hubs of G are spiral
springs, forcing it forward, but permitting it to advance over the drill
chuck; the work W is fed forward to the drill. At the dead centre end
the work is supported by a female cone centre D in the tail spindle T.
The work rests in mouths of G and D, and as the pieces are cut from the
rod they are sufficiently straight, and being cut off in a cutting-off
machine the ends are presumably square; hence the coned chucks will hold
them sufficiently true with the ends, and the alignment of the centre
drilled holes will not be impaired by any subsequent straightening
processes; for it is to be observed, that if work is centre-drilled and
straightened afterwards, the straightening throws the centre holes out
of line one with the other, and the work will be more liable to
gradually run out of true as its centres wear.
[Illustration: Fig. 1165.]
Thus, in Fig. 1167, let W represent a bent piece of work centre-drilled,
and the axis of the holes will be in line as denoted by the dotted line,
but after the piece is straightened the holes will lie in the planes
denoted by the dotted line in Fig. 1168, and there will be a tendency
for the work centres to move over towards the sides C D as the wear
proceeds.
[Illustration: Fig. 1166.]
In Fig. 1169 is shown a centre-drilling machine, which consists of a
live spindle carrying the centre-drilling tool, and capable of end
motion for the drill feed. The work is held in a universal chuck, and if
long is supported by a stay as shown in the figure. The axis of the work
being in line with that of the chuck, the work requires no setting.
[Illustration: Fig. 1167.]
In this case the centre hole will be drilled true with that part of the
work that is held in the chuck, and the alignment of the centre hole
will depend upon the length of the rod being supported with its axis in
line with the live spindle. If the work is not straightened after
drilling, the results produced are sufficiently correct for the
requirements; but it follows from what has been said, that work which
requires to be straightened and tried for straightness in the lathe
should be centred temporarily and not centre-drilled until after the
straightening has been done.
[Illustration: Fig. 1168.]
In Fig. 1170 is shown a combined centre-drill and countersink not
unfrequently used in centring machines. The objection to it is, that the
cutting edges of the drill get dull quicker than those of the
countersink, and in regrinding them the drill gets shorter. Of course
the drill may be made longer than necessary so as to admit of successive
grindings, but this entails drilling the centre holes deeper than
necessary, until such time as the drill has worn to its proper length.
To overcome this difficulty the countersink may be pierced to receive a
drill as in Fig. 1171, the drill being secured by a set-screw S.
[Illustration: Fig. 1169.]
Among the devices for centring work by hand, or of pricking the centre
preparatory for centre-drilling, are the following:--
[Illustration: Fig. 1170.]
[Illustration: Fig. 1171.]
In Fig. 1172 is a centre-marking square. A B C D represents the back and
E the blade of the square. Suppose then that the dotted circle F
represents the end of a piece of work, and we apply the square as shown
in the cut and mark a line on the end of the work, and then moving the
square a quarter turn around the work, draw another line, the point of
contact of these two lines (as at G in the cut) will be the centre of
the work, or if the work is of large diameter as denoted by the circle H
H, by a similar process we obtain the centre E. In this case, however,
the ends A B of the square back must be of equal lengths, so that the
end faces at A B will form a right angle to the edge of the blade, and
this enables the use of the square for ordinary purposes as well as for
marking centres.
[Illustration: Fig. 1172.]
The point _a_ of the centre punch shown in Fig. 1173 is then placed at
the intersection of the two lines thus marked, and a hammer blow
produces the required indentation. The centre punch must be held upright
or it will move laterally while entering the metal. The part _b_ of the
centre punch is tapered so as to obstruct the vision as little as
possible, while it is made hexagon or octagon at the upper end to afford
a better grip. By increasing the diameter at C, the tool is stiffened
and is much less liable to fly out of the fingers when the hammer blow
does not fall quite fair.
[Illustration: Fig. 1173.]
In Fig. 1174 is shown a device for guiding the centre punch true with
the axis of the work, so as to avoid the necessity of finding the same
by lines for the centres. It consists of a guide piece B and a parallel
cylindrical centre punch A, C representing a piece of work. B is pierced
above with a parallel hole fitting and guiding the centre punch, and
has a conical hole at the lower end to rest on the work, so that if the
device be held upright and pressed down upon the end of the work, and
the top of the centre punch is struck with the hammer, the indentation
made will be central to the points of contact of the end of the work
with the coned hole of B. If then the end of the work has no projecting
burrs the centring will be centred true.
[Illustration: Fig. 1174.]
[Illustration: Fig. 1175.]
In the absence of these devices, lines denoting the location for the
conical recess or centre may be made, when either of the following
methods may be pursued.
[Illustration: Fig. 1176.]
[Illustration: Fig. 1177.]
[Illustration: Fig. 1178.]
In Fig. 1175 is shown what is known as a pair of hermaphrodite calipers,
which consists of two legs pivoted at the upper end; the bent leg is
placed against the perimeter of the work, as shown, and held steadily,
while with the point a line is marked on the work. This operation is
performed from four equidistant (or thereabouts) points on the work,
which will appear as shown in Fig. 1176, providing the radius to which
the point was set be equal to the radius of the work. The point at which
the lines meet is in this case the location for the centre. If, however,
the radius to which the points are set is less than the radius of the
work, the lines will appear as in Fig. 1177, in which case the location
is in the centre of the inscribed square, as denoted by the dot; or if
the radius be set too great the lines will appear as in Fig. 1178, and
the location for the centre will again be as denoted by the dot.
[Illustration: Fig. 1179.]
Another and very old method of marking these lines is to place the work
on a pair of parallel pieces and draw the lines across it, as shown in
Fig. 1179, in which W represents the work, P, P the parallel pieces of
equal thickness, S a stand (termed a scribing block) carrying a needle
N, which is held by a thumb screw and bolt at B. The point of the needle
is adjusted for the centre of the work, a line is drawn, the work is
then rotated, another line drawn, and so on, until the four lines are
drawn as in Fig. 1180, when the work may be turned end for end if light,
or if heavy the scribing block may be moved to the other end of the
work.
[Illustration: Fig. 1180.]
The centre locations are here made true with the part of the work that
rests on the parallel pieces, and this is in some cases an essential
element in the centring.
Thus, in Fig. 1181, it is required to centre a piece true with the
journals A B, and it is obvious that those journals may be rested on
parallel pieces P, P, and the centres marked by the scribing block on
the faces E, F in the manner before described.
[Illustration: Fig. 1181.]
If there is a spot in the length of a long piece of work where the metal
is scant and out of round, so that it is necessary to centre the work
true by that part, the surface gauge and parallel pieces may be used
with advantage, but for ordinary centring it is a slow process. When a
piece of work is not cylindrical, and it is doubtful if it will clean
up, the centring requires care, for it must not always be assumed, that
if two diametrically opposite points meet the turning tool at an equal
depth of cut, the piece is centred so as to true up to the largest
possible diameter.
[Illustration: Fig. 1182.]
This is pointed out in Fig. 1182, which is extracted from an article by
Professor Sweet. "In a piece of the irregular form A, the points _a_ and
_b_ might be even and still be no indication of the best location for
the centre, and in the piece B it is evident that if _c_ and _d_ were
even, nothing like the largest cylinder could be got from it. In the
case of shape A, the two points _e_ and _f_ should be equidistant from
the centre, and in the case of shape B, the three points _g_, _h_, _i_
should be equidistant from the centre."
The depth of the centre drill holes should be such as to leave them in
the work after it is cut off to its proper length, and will, therefore,
be deeper as the amount to be cut off is greater.
The diameter of the centre drill is larger as the size of the work
increases, and may be stated as about 3/64 for work of about 1/2 inch,
increasing up to 1/8 inch for work of about an inch, and up to three
inches in diameter; for work of a foot or over the centre drill may be
3/16 inch in diameter.
[Illustration: Fig. 1183.]
The centre drilling and countersinking may, when the work is cut to
length, be performed at one operation, but when it requires to be cut to
length in the lathe, that should be done before the countersinking. A
very simple chuck for centre drilling is shown in Fig. 1183, with a
twist drill (which is an excellent tool for centre-drilling). If the
work is held in the hand and fed to the drill by the lathe dead centre,
the weight of the work will cause the hole to be out of straight with
the work axis, unless the grip is occasionally relaxed, and the work
made to rotate a half or a quarter turn as the drilling proceeds.
After the work is centre-drilled and cut off to length, it must be
finally countersunk, so as to provide ample bearing area for the lathe
centres.
[Illustration: Fig. 1184.]
The countersinking should be true to the centre hole; and it is
sometimes made to exactly fit the lathe centres, and in other cases it
is made more acute than the lathe centre, so that the oil may pass up
the countersink, while it is bedding itself to the lathe centres.
If the countersinking is done before the end of the work is squared, it
will not be true with the centre-drilled hole.
In order that the countersinking may wear true with the centre-drilled
hole, it may be made of a more obtuse angle (as, say, one degree) than
the lathe centre, as in Fig. 1184, so that the hole may form a guide to
cause the lathe centre to wear the countersinking true to the hole, and
thus correct any error that may exist.
[Illustration: Fig. 1185.]
If the countersink is made more acute than the lathe centre, as shown in
Fig. 1185, the wear of its mouth will act as a guide, causing the centre
to be true with the countersinking; and when the bearing area extends to
the centre-drilled hole, there will be introduced, if that hole does not
run true, an element tending to cause the work to run out of true again,
because the countersinking will have more bearing area on one side than
on the other.
It is to be observed, however, that if the difference between the
countersink angle and that of the lathe centre be not more than about
one degree, the work centre will bed itself fully to the lathe centre
very rapidly, and usually before the first cut is carried over the work,
unless the work centres have been made to have unduly large
countersinks.
[Illustration: Fig. 1186.]
Fig. 1186 represents a half-round countersink, in which the cutting edge
is produced by cutting away the coned point slightly below the dotted
axial line. This secures two advantages: first, it gives the cutting
edge clearance without requiring the grinding or filing such clearance;
and, secondly, the cone being the same angle as the lathe centres,
filing away more than half of it causes it to give the lathe centre at
first a bearing at the small end of the countersink, as in Fig. 1184,
and this secures the advantage mentioned with reference to that figure.
It is obvious that such a reamer, however, does not produce strictly a
cone countersink, as is shown in Fig. 1187, where the cutting away of
the cone is carried to excess simply to explain the principle, and the
cone becomes an hyperbolic curve.
The small amount, however, that it is necessary to carry the face below
the line of centres, practically serves to make the cone somewhat less
acute, and is not therefore undesirable.
[Illustration: Fig. 1187.]
Another method of forming the half-round countersink is shown in Fig.
1188, in which the cone is of the same angle as the lathe centres; the
back A is ground away to avoid its contact with the work and give
clearance, while clearance to the cutting edge is obtained by filing or
grinding a flat surface B at the necessary angle to the upper face of
the cone. In this case it is assumed that the centre-drilling and
countersinking are true one with the other. Yet another form of
countersink is shown in Fig. 1189, consisting of a cone having three or
four teeth. It may be provided with a tit, which will serve as a guide
to keep the countersink true with the hole, and this tit may be made a
trifle larger in diameter than the hole, and given teeth like a reamer,
so as to ream the hole out while the countersinking is proceeding.
[Illustration: Fig. 1188.]
[Illustration: Fig. 1189.]
Unless one side of a half-round reamer is filed away so as to give the
cutting edge alone contact with the bore of the hole, an improper strain
is produced both upon the work and the countersink.
In Fig. 1190, for example, is shown, enlarged for clearness of
illustration, a hole, and a half-round countersink in section, and it is
evident that if the countersink is set central to the hole, it will have
contact at A and at B, and A cannot enter the metal to cut without
springing towards C.
[Illustration: Fig. 1190.]
[Illustration: Fig. 1191.]
But when the lathe has made rather more than one-half a revolution, the
forcible contact at B will be relieved, and either the work or the
countersink will move back towards D. This may be remedied by setting
the countersink to one side, as in Fig. 1191, or by cutting it away on
one side, as in Fig. 1192, when the half-round reamer will, if the work
be rigidly held while being countersunk, act as a cutting tool. But it
is more troublesome to hold the work rigidly while countersinking it
than it is to simply hold it in the hands, and for these reasons the
square centre is an excellent tool to produce true countersinking.
[Illustration: Fig. 1192.]
[Illustration: Fig. 1193.]
[Illustration: Fig. 1194.]
Fig. 1193 represents a square centre, the conical end being provided
with four flat sides, two of which appear at A B, or it may have three
flat sides which will give it keener cutting edges, and will serve
equally well to keep it true with the drilled hole. But it is
questionable whether it is not an advantage not to have the cutting
edges so keen as is given by the three flat faces, because the less keen
the cutting edges are, the more true the countersinking will be with the
hole, the extra pressure required to feed the square centre tending to
cause it to remain true with the hole notwithstanding any unequal
density of the metal on different sides of the hole. An objection to the
square centre is that it involves more labor in the grinding to
resharpen it, and is not so easy to grind true, but for fine work this
is more than compensated for in the better quality of its work.
[Illustration: Fig. 1195.]
[Illustration: Fig. 1196.]
This labor, however, may be lessened in two ways: first, the faces may
be fluted, as in Fig. 1194, at A and at B, or its diameter may be turned
down, as in Fig. 1195. In using the square centre it is placed in the
position of the live centre and revolved at high speed, all the cutting
edges operating simultaneously; the work is fed up by the dead centre
and held in the hand.
To prevent the weight of the work from causing the countersinking being
out of true with the hole, the work should be occasionally allowed (by
relaxing the grip upon it) to make part of a revolution, as explained
with reference to centre-drilling without a work guide. Another and
simple form of square centre for countersinking is shown in Fig. 1196.
It consists of a piece of square steel set into a stock or holder.
[Illustration: Fig. 1197.]
Work that is to be hardened and whose centres are, therefore, liable to
warp in the hardening, may be countersunk as in Fig. 1197, there being
three indentations in the countersink as shown. This insures that there
shall be three points of contact, and the work will run steadily and
true. Furthermore, the indentations form passages for the oil,
facilitating the lubrication and preventing wear both to the work and to
the lathe centres.
[Illustration: Fig. 1198.]
These indentations are produced after the countersinking by the punch,
shown in Fig. 1198. Except when tapers are turned by setting the lathe
centres out of line with the lathe shears (as in setting the tailstock
over), all the wear falls on the dead centre end of the work, as there
is no motion of the work centre on the live centre, hence the work
centres will not have worn to a full bearing until the work has been
reversed end for end in the lathe.
[Illustration: Fig. 1199.]
[Illustration: Fig. 1200.]
If it be attempted to countersink a piece of work whose end face is not
square, the countersinking will not be true with the centre hole, and
furthermore the causes producing this want of truth will continue to
operate to throw the work out of true while it is being turned. Thus, in
Fig. 1199, _a_ represents a piece of work and B the dead centre; if the
side C is higher than side D of the work end, the increased bearing area
at C will cause the most wear to occur at D, and the countersink in the
work will move over towards D, and it follows that the face of a rough
piece of work should be faced before being countersunk. Professor Sweet
designed the centre-drilling device shown in Fig. 1200, which consists
of a stock fitting the holes for the lathe centres, and carrying what
may be called a turret head, in which are the centre drills, facing
tools, and countersinks. The turret has 6 holes corresponding to the
number of tools it carries, and each tool is held in position by a pin,
upon a spring, which projects into the necessary hole, the construction
being obvious. The facing tool is placed next to the drill and is
followed by a countersink, in whatever direction the turret is rotated
to bring the next tool into operation. The work should, on account of
the power necessary for the facing, be driven in a chuck.
[Illustration: Fig. 1201.]
A similar tool, which may, however, be used for other work besides
centring and countersinking, is shown in Fig. 1201. It consists of a
stem fitting into the hole of the tail spindle, and carrying a base
having a pin D, on which fits a cap having holes _b_, and set-screws C
for fastening drills, countersinks, or cutting tools. The cap is pierced
with six taper holes, and a pin projects through the base into these
holes to lock the cap in position, this pin being operated by the spring
lever shown.
[Illustration: Fig. 1202.]
Work that has already been turned, but has had its centres cut off, may
be recentred as follows. One end may be held and driven by a chuck,
while the other end is held in a steady rest such as was shown in Fig.
802, and the centre may then be formed in the free end by a half-round
reamer, such as shown in Fig. 1190, placed in the position of the dead
centre, or the square centre may be used in place of the dead centre,
being so placed that one of its faces stands vertically, and therefore
that two of its edges will operate to cut. The location for the work
centre should be centre punched as accurately as possible, and the work
is then placed in the lathe with a driver on it, as for turning it up; a
crotch, such as shown in Fig. 1202, is then fastened in the lathe tool
post, and fed up by the cross-feed screw until it causes the work to run
true, and the square centre should then be fed slowly up and into the
work, with a liberal supply of oil. If the work runs out of true, the
crotch should be fed in again, but care must be taken not to feed it too
far. So long as the square centre is altering the position of the centre
in the work, it will be found that the feed-wheel of the tailstock will
feed by jumps and starts; and after the feeding feels to proceed evenly,
the crotch may be withdrawn and the work tried for being true. The
crotch, as well as the square centre, should be oiled to prevent its
damaging the work surface. It is obvious that in order to prevent the
lathe dead centre point from seating at the point or bottom of the work
centre, the square centre should be two or three degrees more acute in
angle than the lathe dead centre. If the work is tried for truth while
running on the square centre, the latter is apt to enlarge the work
centre, while the work will not run steadily, hence it is better (and
necessary where truth is a requisite) to try the work with the dead
centre in place of the square one.
In thus using a square centre to true work, great care should be taken
not to cut the work centres too large, and this may be avoided by making
the temporary centre-punch centres small, and feeding the crotch rapidly
up to the work, until the latter runs true, while the square centre is
fed up only sufficiently to just hold the work steady.
[Illustration: Fig. 1203.]
To test the truth of a piece of rough work, it may, if sufficiently
light, be placed between the lathe centres with a light contact, and
rotated by drawing the hand across it, a piece of chalk being held in
the right hand sufficiently near to just touch the work, and if the
chalk mark extends all round the work, the latter is as true as can be
tested by so crude a test, and a more correct test may be made by a tool
held in the tool rest. If the test made at various positions in the
length of the work shows the work to be bent enough to require
straightening, such straightening may be done by a straightening lever.
In shops where large quantities of shafting are produced, there are
special straightening tools or devices: thus, Figs. 1203 and 1204
represent two views of a straightening machine. The shaft to be
straightened is rotated by the friction caused by its own weight as it
lies between rollers, which saves the trouble of placing the shaft upon
centres. Furthermore, the belt that is the prime mover of the gears
driving these rollers is driven from the line shaft itself without the
aid of any belt pulley. The tension of this driving belt is so adjusted
that it will just drive the heaviest shaft the machine will straighten;
but if the operator grasps the shaft in his hand, the driving mechanism
will stop and the belt will slip, the shaft remaining stationary until
the operator sets it in motion again with his hand, when the belt ceases
to slip and the mechanism again acts to drive the shaft.
Fig. 1203 represents the mechanism for driving the shaft S, to be
straightened, which lies upon and between two rollers, R, R´. Upon the
shafts of these rollers are the gear-wheels A and B, which are in gear
with wheel C, the latter being driven by gear-wheel D. Motion to D is
derived from a pair of gears, the pinion of which is driven by the belt
from the line shaft. H is a head carrying all these gears (and the
rollers) except D. There are two of these heads, one at each end of the
machine, the two wheels D being connected by a rod running between the
shears, but the motion is communicated at one end only of this rod, the
shaft is driven between four rollers, of which two, R R´, are shown in
the engraving.
[Illustration: Fig. 1204.]
[Illustration: Fig. 1205.]
In Fig. 1204 the straightening device is shown. A frame consisting of
two parts, F, F´, is gibbed to the edge of the shears at G and H. The
upper part of this frame carries a square-threaded screw I, and is
capable of sliding across the shears upon the part F´. It rests upon the
shears through the medium of four small rollers (which are encased), two
of which are at J, K, and two are similarly situated at the back of the
frame F´. The motion of F across the machine is provided so that the
upper part F may be pushed back out of the way, to permit the shaft
being easily put on and taken off the friction rollers R R´. The motion
along the shears is provided to enable the straightening device to be
moved to the required spot along the shaft S´. The shaft S is laid on
two pieces N, P, and a similar piece _r_ is placed above to receive the
pressure of the screw I, which is operated by a hand lever to perform
the straightening. The pieces N, P rest upon two square taper blocks V,
which are provided with circular knobs at their outer ends to enable
them to be held and pushed in or pulled out so as to cause N, P to meet
the shaft before I is operated. This is necessary to accommodate the
different diameters of shaft S. The operator simply marks the rotating
shaft with chalk in the usual manner to show where it is out of true,
and then straightens wherever it is found necessary.
Fig. 1205 represents a similar device for straightening rods or shafts
while they are in the lathe. A is a frame or box which is fitted to rest
on the [V]s of the lathe shears, the straightening frame resting on the
box. Instead, however, of simply adjusting the height of the pieces P to
suit different diameters of the shaft, the whole frame is adjusted by
means of the wedge W, which is inserted between the frame F and the
upper surface of the box A. At H is a hole to admit the operator's hand
to move A along the lathe shears.
[Illustration: Fig. 1206.]
A method of straightening wire or small rods that are too rigid to be
straightened by hand, and on which it is inadvisable to use hammer
blows, is shown in Fig. 1206. It consists of a head revolved in a
suitable machine, and having a hole passing endways through it. In the
middle is a slot and through the body pass the pins A, being so located
that their perimeters just press the rod or wire when it is straight,
and in line with the axis of the bore through the head, each successive
pin A touching an opposite side of the wire or rod. It is obvious that
these pins in revolving force out any crooks or bent places in the wire
or rod, and that as the work may be pulled somewhat rapidly through the
head or frame, the operation is a rapid one.
When pieces of lathe work are to be made from rod or bar iron, they
should be cut off to the proper length in a cutting-off machine, such as
described in special forms of the lathe, and for the reasons set forth
in describing that machine.
An excellent tool, however, for cutting up rods of not more than 1/2
inch in diameter, is Elliott's cutting-off tool shown in Fig. 1207. It
consists of a jaw carrying steadying pieces for the rod to be cut up,
these pieces being adjusted to fit the rod by the screw and nut shown.
On the same jaw is pivoted a tool-holder, carrying a cutting-off tool,
which is fed to its cut by the upper handle being pressed towards the
lower one.
An adjustable stop or gauge is attached, by means of a small rod, to the
swinging arm which carries the cutting tool, and can be removed when its
use is not desirable.
[Illustration: Fig. 1207.]
The operation of this tool is as follows:--The rod to be cut up is held
in the lathe chuck, projecting beyond any desired distance, and arranged
to revolve at the same speed as for turning. The tool is placed upon the
rod, and the movable jaw of the rest adjusted to a bearing. If several
pieces are to be cut to a length, the gauge is adjusted, the tool moved
along the rod till the gauge-stop comes in contact with the end, the
handles pressed together, which moves the cutting tool up to the work in
such a way that it will come exactly to the centre, thus cutting the
piece entirely off, no adjustment of the tool ever being necessary to
provide for its cutting to the centre, except keeping the cutting edge
(which is not in this respect changed by grinding) at a distance
specified in the directions from the part in which it is clamped. As the
tool is moved up to cut, by the same operation the gauge is moved back
out of contact with the end. When the pressure on the handles is
removed, a spring returns the cutting tool to its original position, and
also brings the gauge in position for determining the length of the next
piece to be cut. The operation is repeated by simply moving the tool
along the rod, the cutting up being done with great rapidity and
accuracy. It will be noticed that all the appliances for cutting,
gauging, &c., being a part of the tool itself, if the rod runs out of
truth--in other words, wabbles--it will have no effect on the cutting,
the rod to be cut forming the gauge for all the operations required;
also that comparatively no time is lost in adjustment between the
several pieces to be cut from a rod.
The cutting tool is a piece of steel of the proper thickness, cleared on
the sides by concave grinding. It is held in place by a clamp and two
small screws, and requires grinding on the end only.
When the work is centred, it should, for reasons already explained, have
its end faces trued up.
In doing this, however, it is desirable in some cases to cut off the
work to its exact finished length. This possesses the advantage, that
when the work is finished, the work centres will be left intact, and the
work may be put into the lathe at any time, and it will run true to the
original centres. But this is not always the best plan; suppose, for
example, that there are a number of collars or flanges on the work, then
it is better to leave a little extra length to the work when truing up
the ends, so that if any of the collars are scant of metal, or if it be
desirable to turn off more on one side of a collar than on another, as
may be necessary to turn out a faulty place in the material, the end
measurements on the work may be conformed to accommodate this
requirement, and not confined to an exact measurement from the end of
the work.
Again, in the case of work having a taper part to be fitted, it is very
difficult to obtain the exact proper fit and entrance of taper to an
exact distance, hence it is best to leave the work a little too long,
with its collars too thick, and to then fit the taper properly and
adjust all other end measurements to suit the taper after it is fitted.
Before any one part of a piece of work turned between the lathe centres
is finished to diameter, all the parts to be turned should be roughed
out, and for the following reasons, which apply with additional force to
work chucked instead of being turned between the lathe centres.
It is found, that all iron work changes its form if the surface metal be
removed from it. Thus, though the lathe centres be true, and a piece of
work be turned for half its length in the lathe, after it has been
turned end for end in the lathe to turn the other half of its length,
the part already turned will run out of true after the second half is
turned up. This occurs from the tension and unequal internal strains
which exist in the metal from its being forged or rolled at a constantly
diminishing temperature, and from the fact that the surface of the metal
receives the greatest amount of compression during the forging.
In castings it is caused by the unequal and internal strains set up by
the unequal cooling of the casting in the mould, because of one part
being thicker than another.
When the whole of the work surfaces have been cut down to nearly the
finished size, this alteration will have taken place, and the finishing
may be proceeded with, leaving the work as true as possible. In chucked
work, or the most of it rather, it is impracticable (from being too
troublesome) to rough out all over before finishing; hence at each
chucking all the work to be done at that chucking is finished.
The roughing cuts on a piece of work should always be taken with as
coarse a feed as possible, because the object is to remove the mass of
the metal to be cut away rather than to produce a finish, and this may
be most quickly done by a deep cut and coarse feed. Theoretically also
the finishing should be done with a coarse feed, since the coarser the
feed, the less the length of time the cutting edge is in action. But the
length of cutting edge in action, with a given tool and under a given
depth of cut, increases as that edge is made longer to carry the coarse
feed, and the long cutting edge produces a strain that tends to spring
or bend the work, and that causes the tool to dip into seams or soft
spots, or into spongy or other places, where the cutting strain is
reduced, and also to spring away from hard spots or seams, where the
cutting strain is increased. The most desirable rate of feed, therefore,
is that which is as coarse as can be used without springing either the
work or the tool, and this will depend upon the rigidity of the work of
the lathe, and of the cutting tool. Short or slight work may be turned
very true by a light cut fine feed and quick cutting speed, but the
speed must obviously be slower in proportion as the length of the work
increases, because the finishing cut should be taken without taking the
tool out to resharpen it, since it is very difficult to set the tool to
the exact proper depth a second time.
Since the cutting edge will, at any given rate of cutting speed, retain
its keenness better for a given surface of work in proportion as the
time it is under duty is diminished, it follows, therefore, that the
coarser the feed the better (so long as both the work and the tool are
sufficiently rigid to withstand the rate of feed without springing).
Under conditions of rigidity that are sufficiently favorable a tool,
such as in Fig. 948, may be used on wrought or cast iron, at a feed of
1/2 or even 3/4 inch of traverse per lathe revolution, producing true
and smooth work, providing that the tool be given a very slight degree
of clearance, that its cutting edge is ground quite straight, that it is
set parallel to the line of feed, or what is the same thing, to the work
axis, and that the length of cutting edge is greater than the amount of
tool traverse per lathe revolution, as is shown in the figure, the
amount of tool traverse per lathe revolution obviously being from A to
B. It may also be observed that the leading corner of the tool may with
advantage be very slightly rounded as shown, so that there shall be no
pointed corner to dull rapidly.
In proportion as the work is light and the pressure of the cut may
spring it, the feed must be lessened, so that on very slender work a
feed of 100 lathe revolutions per inch of tool travel may be used. On
cast-iron work the feeds may be coarser than for wrought-iron, the other
conditions being equal, because cast iron cuts easier and therefore
springs the work less for a given depth of cut. But since cast iron is
apt to break out, exposing the pores of the metal, and thus leaving
small holes plainly visible on the work surface, the finishing cut
should be of very small depth, indeed a mere scrape; and if the surface
is to be polished, a fine feed and a quick speed will leave a cleaner
cut surface, and one that will require the least polishing operations to
produce a clean and spotless surface. Brass work also is best finished
with a fine feed and a quick speed.
It is obvious that the top face of the tool should be given more rake
for wrought iron than for cast iron or steel, and that in the case of
the very fine feeds, the form of tool shown in figure is the best for
finishing these metals.
In turning a number of pieces requiring to be of the same diameter, it
is to be borne in mind that a great part of the time is consumed in
accurately setting the tool for the finishing cut, and that if one piece
is finished at a time, this operation will require to be done separately
for each piece.
It is more expeditious, therefore, to rough all the pieces out, leaving
enough metal for a fine finishing cut to be taken, and then finish these
pieces without moving the tool; which may be done, after the tool is
once set, by letting the tool stand still at the end of the first
finishing cut, and taking the work out of the lathe. The carriage is
then traversed back to the dead centre, and another piece of work is put
in, and it is obvious that as the cross-feed screw is not operated after
the tool is once set, the work will all be turned to the same diameter
without any further measuring than that necessary for the first piece.
If the tool is traversed back to the dead centre before the lathe is
stopped or before the work is removed from the lathe, one of two results
is liable to follow. If the lathe is left running, the tool will
probably cut a spiral groove on the work, during its back traverse; or
if the lathe be stopped, the tool point will mark a line along the work,
and the contact of the tool point with the work will dull the cutting
edge of the tool. The reason of this is as follows: When the slide rest
and carriage are traversing in one direction, the resistance between the
tool and the cut causes all the play in the carriage and rest, and all
the spring or deflection of those parts, to be in an opposite direction.
Now if the play and spring were precisely equal for both directions, the
tool should cut to an equal diameter with the carriage traversed in
either direction, but the carriage in feeding is fed by the feed nut or
friction feed device, while when being traversed back the traversing
handle is used; thus the power is applied to the carriage in the two
cases at two different points, hence the spring of the parts, whether
from lost motion, or play from wear, or from deflection, is variable.
Again, even with the tool fed both to its cut and on the back traverse
with the hand feed handle, the play is, from the altered direction of
resistance of the cut, reversed in direction, and the depth of cut is
therefore altered.
Thus, in Fig. 1208, let S S represent the cross slide on the carriage
and R R the cross slide of the tool rest shown in section, and suppose
the tool to be traversing towards the live centre, then to whatever
amount there may be play or spring between the slide and the slide way,
the slide will from the pressure of the cut twist over, bearing against
the slide way at A and B, and being clear of it at G and H. On reversing
the direction of traverse of the rest, so as to feed the tool towards
the dead centre, the exactly opposite condition will set in, that is,
the pressure of the cut will force the slides in the opposite direction,
or in other words, the contact will be as in Fig. 1209, at C, D, and the
play at E, F. During the change of location of bearing between the
slides and the way, there will have been a certain amount of tool motion
altering the distance of the tool point from the line of centres, and
therefore the diameter to which it will cut. The angle at which the body
of the tool stands will influence the effect: thus, if when traversing
towards the live centre the tool stands at an angle pointing towards the
live centre, it would recede and cause the tool to clear the cut, if
removed on the back traverse without being moved to or from the line of
centres. Conversely, if the body of the tool was at an angle, so that it
pointed towards the dead centre, and a cut was taken towards the live
centre, and the tool was traversed back without being moved in or out,
it would take another cut while being moved back.
The conditions, however, are so uncertain, that it is always advisable
to be on the safe side, and either wind the tool out from its cut before
winding the rest and carriage back (thus destroying its set for
diameter), or else to stop the lathe and remove the work before
traversing the carriage back as already directed. If the latter plan is
followed the trouble of setting the tool is avoided and much time is
saved, while greater accuracy of work diameter is obtained. It is
obvious that this plan may be adopted for roughing cuts in cases where
two cuts only are to be taken, so as to leave finishing cuts of equal
depths; or if three cuts are to be taken, it may advantageously be
followed for the second and last cuts, the depth of the first cut being
of less importance in this case.
The following rules apply to all tools and metals:
[Illustration: Fig. 1208.]
[Illustration: Fig. 1209.]
When the pressure between the tool and the work is sufficient, from the
proportions of the work, to cause the work to spring or bend, the length
of acting cutting edge on the tool should be reduced.
As the diameter and rigidity of the work increases, the length of tool
cutting edge may increase. The cutting edge of the tool should be kept
as close as the work will conveniently admit to the slide rest tool
post, 1/4 _inch even_ of this distance being _important_.
The slide rest tool should always be resharpened to take the finishing
cut, with which, for wrought iron or steel, soapy water with soda in it
should be used, the soda serving to prevent the dripping water from
rusting the parts of the lathe.
Cast iron will cut with an exquisite polish if finished at a _very slow_
rate of cutting speed, and turned with a spring tool, such as was shown
in Fig. 974, and water is used. But being a slow process it is not usual
to finish it in this manner, though for round corners, curves, &c., this
method is highly advantageous.
For cast iron the tool should be as keen as the hardness of the metal of
the work will permit. If an insufficiently keen tool, or too deep a cut,
or too coarse a feed be taken, the metal will break out instead of
cutting clean, and numerous fine holes will be perceived over the whole
surface, impairing that dead flatness which is necessary to an even and
fine polish.
To remove these specks or holes in cylindrical work, the file may be
used, but for radial faces hand-scrapers, such as shown in Fig. 1295,
are used, the work rotating in either case at high speed. Such scrapers
are oilstoned and held with the handle end above the horizontal level.
The _rest_ should be so conformed to suit the shape of the work, that
the scraper will be supported close to the work, which will prevent
chattering, and a piece of leather should (as a further preventive of
chattering) be placed beneath the scraper. A very good method of using a
scraper is to adjust it to the work, and holding it still on the rest,
traverse the slide rest to move the scraper to its cut.
After the scraping, three methods of polishing radial faces are commonly
employed; the first is to use emery paper only, and the second is by the
use first of grain, emery, and oil, and the subsequent use of emery
paper or cloth, and the third is by the use of emery wheels and crocus
cloth.
If the work is finished by emery paper only, and it requires much
application of the same to efface the scraper marks, the evil will be
induced that the emery cuts out the metal most where it is most porous,
so that the finished surface is composed of minute hills and hollows,
and the polish, though bright and free from marks, will not have that
dead flat smooth appearance necessary to a really fine polish and
finish; indeed, the finish is in this case to some extent sacrificed to
obtain the polish.
It is for this reason that stoning the work (as hereafter described) is
resorted to, and that grain emery and lead is employed, which is done as
follows:--
For a flat radial face, a flat piece of lead, say 3/8 inch thick, and of
a size to suit the work, may be pivoted to the end of a piece of wood of
convenient length and used with grain emery and oil, the work rotating
quickly. To afford a fulcrum for the piece of wood, a lever or rest of
some kind, as either a hand rest or a piece fastened in the tool post,
is used.
The rest should be placed a short distance from the work surface and the
lever held partly vertical until the lead meets the work surface, when
depressing the lever end will force the lead against the work. The lever
end must be quickly moved laterally, so that the lead will approach and
then recede from the work centre; this is necessary for two reasons.
First, to prevent the emery from cutting rings in the work surface, and
secondly, to prevent the formation of grooves behind any hollow spots or
specks the work may contain. The reason of the formation of these
grooves is that the emery lodges in them and works out from the contact
of the lead, so that if on working out they move always in the same line
they cut grooves.
When a lathe is provided with belt motion to run both ways, it is an
excellent plan to apply the lead with the lathe running forward and then
with it running backward.
When by this means the scraper marks are removed, the next object is to
let the marks left by the lead be as fine and smooth as possible, for
which purpose flour emery should be used; but towards the last no emery,
but oil only, should be applied, the lead being kept in constant lateral
motion, first quickly and then slowly, so that the marks on the work
cross and recross it at different angles.
For round or hollow corners the lead need not be pivoted to the stick,
but should be spherical at the end, the marks being made to cross by
partly rotating the lever first in one direction and then in the other.
Sometimes the end of the lever is used without the addition of lead, but
this does not produce so flat a surface, as it cuts out hollows in the
pores of the metal.
For polishing to be done entirely in the lathe, emery paper and crocus
may follow the lead, being used dry and kept also in constant lateral
motion. Each successive grade of emery paper must entirely remove all
marks existing on the work at the time of its (the paper's) first
application, and, furthermore, each successive grade should be continued
until it is well worn, because of two pieces of emery paper of the same
grade that most worn will cut the smoothest and polish the best. For the
final polishing a piece of the finest emery paper should be prepared in
the manner hereafter described for polishing plain cylindrical surfaces.
The radial faces of wrought iron must be finished as smoothly and true
as possible, because being harder than cast iron the emery acts less
rapidly upon it. For radial faces on brass the surfaces should be
finished as smooth as possible with the slide rest tool, which should be
round nosed, with the round flattened somewhat where the tool cuts, and
the tool should not, under any condition, have any rake on its top face,
while the feed should be fine as, say, 32 revolutions per inch of tool
travel. Under skillful manipulation scraping may then be dispensed with,
although it may be used to a slight extent without impairing the truth.
Very small radial surfaces of brass may best be finished by the scraper
and polished with emery paper, while large ones may be finished with dry
emery paper.
Round corners on brass work should be finished with a spring tool, such
as shown in Fig. 974, but having negative top rake; but if the corners
are of small radius a well oilstoned hand-scraper is best.
To enable the smooth and true turning of all radial faces of large
diameter, the lathe head should, when it is possible, be steadied for
end motion by placing a rod between the lathe centres, but if the radial
face is solid at the centre so that such a rod cannot be put in, the end
motion adjusting device of the lathe should be adjusted. The slides of
the lathe should also be set up to have good firm contact, and the tool
should be brought up to the work by putting the feed motion in gear and
operating it by hand at the cone pulley, or gear-wheel on the feed
spindle. If the lathe has no compound rest, the cut should be put on by
this means, but otherwise the tool may be brought near the work by the
feed motion and the cut put on by the compound rest, the object in both
cases being to take up all lost motion and hold the rest firmly or
steadily on the lathe shears, so that it shall not move back as the cut
proceeds.
Work of cast iron or brass and of small dimensions and irregular or
curved outline should be finished with scraping tools, such as shown in
Figs. 1303 and 1310, polished with emery cloth or paper. But whenever
scrapers are made with curves to suit the form of the work, such tool
curves should be so formed (for all metals) as not to cut along the
whole length of cutting edge at once, unless the curve be of very small
length as, say, 1/4 inch. This is necessary, because if the cutting edge
operates on too great a length it will jar or chatter.
For convex surfaces the curve on the scraper should be of greater radius
than that of the work, while in the case of concave curves the tool
should have a less radius. In both cases the tool will require a lateral
movement to cause it to operate over the full width of work curve.
If the work curves are sufficiently large, and the same is sufficiently
rigid that a slide rest tool may be used, the length of cutting edge may
be increased, so that under very favorable conditions of rigidity the
tool edge may cut along its whole length without inducing either jarring
or chattering, but the best results will always be obtained when with a
broad cutting edge the tool is of the spring tool form shown in Fig.
974.
Work of wrought iron or steel of small dimensions and of irregular form,
must also be finished by hand tools, such as the graver shown in Figs.
1285 and 1286, and the finishing tool shown in Figs. 1289 and 1292, the
shape of the tool varying to suit the shape of the work.
Round corners or sweeps cannot on any kind of work be finished by a
file, because the latter is apt to pin and cut scratches in the work.
For the final tool finishing of lathe work of plain cylindrical outline,
no tool equals the flat file if it be used under proper conditions,
which are, that the work be turned true and smooth with slide rest
tools, the marks left by these tools being exceedingly shallow and
smooth.
A dead smooth file that has been used enough to wear down the projecting
teeth (which would cut scratches) should then be used, the work rotating
at as fast a speed as the file teeth will stand without undue wear. The
file strokes should be made under a light pressure, which will prevent
the cuttings from clogging its teeth, and the cuttings should be cleaned
from the file after every few strokes. Under these conditions work of
moderate diameter may be turned to the greatest degree of smoothness and
truth attainable with steel cutting tools, providing that the work makes
several revolutions during each file stroke, and it therefore follows
that the file strokes may be more rapid as the diameter of the work
decreases, and should be more slow as that diameter increases. Allowing
the greatest speed of the filed surface permissible, without too rapid
destruction of the file teeth, to be 200 feet per minute, and the
slowest speed of file stroke that will prevent the file teeth from being
ground away or from becoming pinned (when used on wrought iron) to be
one stroke in two seconds, the greatest diameter of work that can be
finished by filing under the condition that the work must make more than
one rotation per file stroke, is about 25 inches in diameter, running
about 30 revolutions per minute. The same diameter and speed may be also
taken for cast iron, but brass may be filed under increased speed,
rendering it practicable to file it up to a diameter of about 36 inches
under the above conditions of work rotation and file stroke speed.
Supposing, however, that from hardness of the metal or from its
increased diameter the work cannot make a rotation per file stroke
unless that stroke be more slowly performed, then the cuttings gather in
the teeth of the file, become locked and form projections, termed pins,
above the file teeth, and these projections cut scratches in the work,
and this it is that renders it impracticable to hold the file still
while the work rotates. But suppose the file be applied to work of such
a diameter that, with a stroke in two seconds and the work surface
rotating at 200 feet per minute, each stroke acts on a fraction of the
circumference only, then there can be no assurance that the filed
surface will be cylindrical, because there is no means of applying the
file equally over the whole surface. But it is to be noted,
nevertheless, that the file acts with greater effect in proportion as
the area filed is decreased, and that as the tool marks are filed out
the area of surface operated upon is increased. Suppose, then, that
starting from any point on the work circumference a file stroke be
taken, and that it extends around one-third of the circumference, that
the second file stroke extends around one-third also, but that there is
an unfiled space of, say, two inches between the area of surface filed
by these two strokes, and that at the third file stroke the file starts
on the surface filed at the first stroke, passes over the two inches
previously unfiled and terminates on the surface filed by the second
stroke; then the conditions will be as follows:--
Part of the surface filed at the first stroke will have been filed
twice, part of the surface filed at the second stroke will also have
been filed twice, while the two inches will have been filed once only.
But this latter part will have had much more taken off it during the
third stroke than did the rest of the surface filed at that stroke,
because it operated on the ridges or tool marks where, being unfiled,
their area in contact with the file teeth was at a minimum. This
condition will prevail until the tool marks are effaced, and tends to
preserve the truth of the work up to that point, hence the necessity of
leaving very fine tool marks becomes obvious.
Apart from these considerations, however, there is the fact that filing
work in the lathe is a very slow operation, and therefore inapplicable
to large work; and furthermore, on large work the surface is not needed
to be so smooth as in small work; for example, tool feed marks 1/1000
inch deep would upon work of 1/2 inch diameter leave a surface appearing
very uneven, and the wearing away of those ridges or marks would destroy
the fit of the piece; but in a piece, say, six feet in diameter, tool
marks of that depth would not appear to much disadvantage, and their
wearing away would have but little effect upon the fit of the piece.
Finishing with the file, therefore, is usually applied to work of about
24 inches in diameter, and less, larger work being finished with the
cutting tool or by emery grinding, where a greater degree of finish is
required.
Small work--as, say, of six inches, or less, in diameter--may be
finished with the file so cylindrically true, that no error can be
discovered by measurement with measuring tools of the calipering class,
though the marks of contact if made apparent by gently forcing the work
through a closely fitting ring-gauge may not appear to entirely cover
the surface.
To produce filed work thus true, all that is necessary is to set the
cutting edge of the finishing tool at the horizontal centre of the work,
properly adjust the live spindle of the lathe for fit to its bearings,
adjust the slides of the slide rest so that there is no lost motion, and
follow the rules already given with reference to the shape of the tool
cutting edge, employing a cutting speed not so fast as to dull the tool
before it has finished its cut, using a fine feed except in the case of
cast iron, as already explained.
The requirement that the tool shall not become dull before it has
finished its cut, brings us to the fact that the length of work that can
be thus accurately turned is limited, as the diameter of the work
increases.
Indeed, the length of the work in proportion to its diameter is a very
important element. Thus, it would be very difficult indeed to turn up a
spindle of an inch in diameter and, say, 14 feet long, and finish it
cylindrically true, parallel, and smooth, because
1st. The slightness of the work would cause it to spring or deflect from
the pressure or strain due to the cut. This may to some extent be
remedied by steadying the work in a follower rest, but the bore of such
follower itself wears as the cut proceeds, though the amount may be so
small as to be almost inappreciable.
2nd. The work being better supported (by the lathe centres) at the two
ends than in the middle of its length, the duty placed on the follower
rest will increase as the middle of the work length is approached, hence
the spring or deflection of the follower rest will be a disturbing
element.
3rd. The tool gets duller as the cut proceeds, causing more strain from
the cut, and, therefore, placing more strain on the follower rest; and,
4th. It would be necessary, on account of the length of the cut, to
resharpen the tool before the cut was carried from end to end of the
spindle, and it would be almost impracticable to set the reground tool
to cut to the exact diameter.
The second, third, and fourth of the above reasons operate together in
causing increased work spring as the tool approaches the middle of the
work length; thus the deflection of the follower rest, the increased
weakness of the work, and the comparative dullness of the tool would all
operate to cause the work to gradually increase in diameter as the cut
proceeded towards the work centre (of length).
Suppose, for example, a cut to have been carried from the dead centre,
say, five feet along the work; at the end of this five feet the tool
will be at its dullest, the shaft at its weakest, and supported the
least from the dead centre and follower rest.
Suppose, then, that the reground tool be placed in the rest again and
set to just meet the turned surface without cutting it, then when it
meets the cut to carry it farther along the work the cut will produce
(on account of the tool being sharper) less strain on the work, which
will therefore spring or deflect less. Precisely what effect this may
have upon the diameter to which the tool will turn the work will depend
upon various conditions: thus, if the top face of the tool be
sufficiently keen to cause the strain due to bending the shaving cut or
chip to pull the work forward, the tool would turn to a smaller
diameter. If the depth of the cut be sufficient to cause the work to
endeavor to lift, and the tool edge be above the centre of the work, it
would be cut to smaller diameter. If the tool cutting edge were below
the centre, or if its top face be at an angle tending to force the work
away from the tool point, the diameter of the work would be increased.
From these considerations it is obvious that the finishing cut should be
started at the centre of the work length, and carried towards the lathe
centres, because in this case the tool will be sharpest, and therefore
will produce less tensional strain on the work at the point where the
latter is the weakest, while the resisting strength of the work would
increase as the cut proceeded, and the tool became dull from use.
Furthermore, if it were necessary to regrind the tool, it would be reset
nearer to the lathe centres, where the work would be more rigidly held;
hence the tool could be more accurately set to the diameter of the
finishing cut.
By following this plan, however, it becomes necessary to have the shaft
as near true and parallel as possible before taking the finishing cut,
for the following reasons:--
Let the diameter of the spindle before the finishing cut be 1-1/32
inches, leaving 1/32 inch to be taken off at the finishing cut, then the
ring in the follower rest must be at starting that cut 1-1/32 inch bore,
and if the rest is to follow the cut the bush must be changed (so soon
as it meets the finishing cut) to one of an inch bore. But if the
spindle be turned as true and parallel as possible before the finishing
cut the rest may lead the tool, in which case the bush need not be
changed. There are differences of opinion as to the desirability of
either changing the bush or letting the tool follow the rest, but there
can be no dispute that (from the considerations already given) a spindle
turned as true and parallel as may be with the tool started from the
dead centre and carried forward can be improved by carrying yet another
cut from the middle towards the dead centre. In any event, however, work
liable to spring or too long to be finished at one cut without removing
the tool to grind it, can be more accurately finished by grinding in a
lathe, such as was shown in Figs. 676 or 679, than by steel-cutting
tools, and for the following reasons:--
[Illustration: Fig. 1210.]
If it be attempted with steel tools to take a very fine cut, as, say,
one of sufficient depth to reduce a diameter, say 1/500 inch, the tool
is apt to turn an uneven surface. There appears, indeed, to be a
necessity to have the cut produce sufficient strain to bring the bearing
surfaces of the rest into close contact and to place a slight strain on
the tool, because under very light cuts, such as named above, the tool
will generally momentarily leave the cut or take a reduced cut, and
subsequently an increased one.
It may be accepted that from these causes a finishing cut taken with a
steel tool should not be less than that sufficient to reduce the
diameter of the work 1/64 inch. Now an emery-wheel will take a cut whose
fineness is simply limited by the wear of the wheel in the length of the
cut. Some experiments made by Messrs. J. Morton Poole and Sons, of
Wilmington, Delaware, upon this subject led to the conclusion that with
corundum wheels of the best quality the cut could be made so fine that a
12-inch wheel used upon a piece of work (a calender roll) 16 inches in
diameter and 6 feet long, would require about forty thousand traverses
to reduce the diameter of the work an inch, leading to the conclusion
that the wear of the wheel diameter was less than one eighty-thousandth
part of an inch per traverse.
Now the strain placed upon the work of an emery-wheel taking a cut of,
say, 1/1000 inch, is infinitely less than that caused by a cutting tool
taking a cut of 1/120 inch in diameter; hence the accuracy of grinding
consists as much in the small amount of strain and, therefore, of
deflection it places upon the work, as upon the endurance of the wheel
itself.
Since both in finishing and in polishing a piece of work the object is
to obtain as true and smooth a surface as possible, the processes are to
a certain extent similar, but there is this difference between the two:
where polishing alone is to be done, the truth of the work or refined
truth in its cylindrical form or parallelism may be made subservient to
the convenience of polish. Thus, in the case of the stem of the
connecting rod that has been turned and filed and finished as true as
possible, the polishing processes may be continued with emery-cloth,
&c., producing the finest of polish without impairing the quality of the
work, whereas the degree of error in straightness or parallelism induced
by the polishing may impair the degree of truth desirable for a piston
rod.
The degree of finish or polish for any piece of work is, therefore,
governed to some extent by the nature of its use. Thus a piston rod may
be finished and polished to the maximum degree consistent with
maintaining its parallelism and truth, while a connecting rod stem may
be polished to any required attainable degree.
In finishing for truth, as in the case of journal bearings, the work,
being turned as true and smooth as possible, may be filed with the
finest of cut files, and polished with a fine grade of emery-cloth or
paper; the amount of metal removed by filing and polishing being so
small as not to impair to any practically important degree the truth of
the work: a journal so finished will be as true as it is possible to
make it without the use of a grinding lathe.
Instead of using emery-paper, grain emery and oil may be used, but the
work will not be so true, because in this case much more metal will be
removed from the work in the finishing or polishing process.
When it is required to polish and to keep the work as true and parallel
as possible, these ends may be simultaneously obtained by means of
clamps, such as shown in Fig. 1210, which represents a form of grinding
and polishing clamp used by the Pratt and Whitney Company for grinding
their standard cylindrical gauges. A cast-iron cylindrical body A is
split partly through at B and entirely through at C, being closed by the
screw D to take up the wear. The split B not only weakens the body A and
enables its easy closure, but it affords ingress to the grinding
material. It may be noted that cast iron is the best metal that can be
used for this purpose, not only on account of the dead smooth surface it
will take, but also because its porosity enables it to carry the oil
better than a closer grained metal. For work of larger diameter, as,
say, 2 or 3 inches, the form of lap shown in Fig. 1211 is used for
external grinding, there being a hinge B C instead of a split, and
handles are added to permit the holding and moving of the lap. The bore
of this clamp is sometimes recessed and filled with lead. It is then
reamed out to fit the work and used with emery and oil, the lathe
running at about 300 feet per minute.
[Illustration: Fig. 1211.]
For grinding and polishing the bores of pieces, many different forms of
expanding grinding mandrels have been devised, in most of which the
mandrel has been given a slight degree of curvature in its length; or in
other words, the diameter is slightly increased as the middle of the
mandrel length is approached from either end. But with this curvature of
outline, as small as it may be, it rather increases the difficulty of
grinding a bore parallel instead of diminishing it. When expanding
mandrels are caused to expand by a wedge acting upon split sections of
the mandrel, they rarely expand evenly and do not maintain a true
cylindrical form.
Fig. 1212 represents a superior form of expanding mandrel for this
purpose. The length A is taper and contains a flute C. The lead is cast
on and turned upon the mandrel, the metal in the flute C driving the
lead. The diameter of the lap is increased by driving the taper mandrel
through it, and the lead is therefore maintained cylindrically true.
While these appliances are supplied with the flour emery and oil, their
action is to grind rather than to polish, but as they are used without
the addition of emery, the action becomes more a polishing one.
[Illustration: Fig. 1212.]
Fig. 1213 represents at A A a wooden clamp for rough polishing with
emery and oil. It consists of two arms hinged by leather at B and having
circular recesses, as C, D, to receive the work. At J J is represented a
similar grinding and polishing clamp for more accurate work. G and H are
screws passing through the top arm and threaded into the lower, while E,
F are threaded into the lower arm, and abut at their ends against the
face of the upper arm. It is obvious that by means of these screws the
clamp may be set to size, adjusted to give the required degree of
pressure, and held firmly together. Lead bushes may be inserted in the
bores as grinding laps. As this clamp is used by hand, it must be moved
along the work at an exactly even speed of traverse, or else it will
operate on the work for a longer period of time at some parts than at
others; hence the greatest care is necessary in its use.
The best method of polishing cylindrical work to be operated on entirely
in the lathe, the primary object being the polish, is by means of emery
paper, and as follows:--
In all polishing the lathe should run at a fast speed; hence special
high speeded lathes, termed speed lathes, are provided for polishing
purposes only.
The emery paper or cloth should be of a fine grade, which is all that is
necessary if the work has been properly filed, if cylindrical, and
scraped if radial or of curved outline.
In determining whether emery paper or cloth should be used, the
following is pertinent:--
The same grade of emery cuts more freely on cloth than on paper, because
the surface of the cloth is more uneven; hence the emery grains project
in places, causing them to cut more freely until worn down. If, then,
the surface is narrow, so that there is no opportunity to move the emery
cloth endways on the work, emery paper should be used. It should be
wrapped closely (with not more than one, or at least two folds) around a
_smooth_ file, and not a coarse one, whose teeth would press the emery
to the work at the points of its coarse teeth only. The file should be
given short, rapid, light strokes.
For work of curved outline emery cloth should be used, because it will
bend without cracking, and the cloth should be moved quickly backwards
and forwards across, and not round, the curve; and when the work is long
enough to permit it, the emery paper or cloth should be moved rapidly
backwards and forwards along the work so that its marks cross and
recross at an obtuse angle.
Now, suppose the grade of emery paper first used to be flour emery, and
the final polish is to be of the highest order, then 0000 French emery
paper will be required to finish, and it is to be observed that nothing
will polish a metal so exquisitely as an impalpable powder of the metal
itself: hence, while performing the earlier stages of polishing, it is
well to prepare the final finishing piece, so as to give it a glaze of
metal from the work surface.
When, therefore, all the file marks are removed by the use of the flour
emery cloth, the surface of the work should be slightly oiled and then
wiped, so as not to appear oily and yet not quite dry, with a piece of
rag or waste, then the piece of 0000 emery paper, or, what is equally as
good, a piece of crocus cloth, to be used for the final finishing should
be applied to the work, and the slightly oily surface will cause the
cuttings to clog and fill the crocus cloth. The cloth should be
frequently changed in position so as to bring all parts of its surface
in contact with the work and wear down all projections on the cloth as
well as filling it with fine cuttings from the work. Then a finer grade,
as, say, No. 0 French emery paper, must be used, moving it rapidly
endwise of the work, as before, and using it until all the marks left by
the flour emery have been removed.
One, or at most two drops of lard oil should then be put on the work,
and spread over as far as it will extend with the palm of the hand, when
the finishing crocus may again be applied and reversed as before in
every direction; 00 emery paper may then be used until all the marks of
the 0 are removed, and with the work left quite dry the crocus for final
finishing may again be applied; 000 emery paper may then be used to
efface all the marks left by the 00. This 000 emery paper should be used
until it is very much worn, the final finish being laid with the glazed
crocus.
If this crocus has been properly prepared, its whole surface will be
covered with a film of fine particles of metal, so that if the metal be
brass the crocus surface will appear like gold leaf. If cast iron, the
crocus surface will appear as though polished with plumbago or
blacklead, while in any case the crocus surface will be polished and
quite dry. The crocus should be pressed lightly to the work, so that its
polishing marks will not be visible to the naked eye.
If emery paper be applied to work finished to exact diameter it should
be borne in mind that the process reduces to some extent the size of the
work, and that the amount under proper conditions though small is yet of
importance, where preciseness of diameter is a requisite.
In the practice, however, of some of the best machine shops of the
United States, the lathe alone is not relied upon to produce the best of
polish. Thus, in the engine works of Charles H. Brown, of Fitchburg,
Massachusetts, whose engines are unsurpassed for finish and polish, and
which the majority of mechanics would suppose were finely silver plated,
the following is the process adopted for polishing connecting rods.
[Illustration: Fig. 1213.]
The rod is carefully tool-finished with a fine feed. The tool marks are
then erased with a fine smooth file, and these file marks by a
dead-smooth file, the work rotating at a quick speed, little metal being
left, so as to file as little as possible. Next comes _fine_ emery cloth
to smooth down and remove the file marks. The lathe is then stopped and
the rod stoned lengthwise with Hindostan stone and benzine, removing all
streaks. The Scotch stone used with water follows, until the surface is
without scratches or marks, as near perfect as possible. The next
process is, for the finest work, the burnisher used by hand. But if not
quite so exquisite a polish is required, the rod is finished by the use
of three grades of emery cloth, the last being very fine.
Sometimes, however, the streaks made by polishing with emery paper used
before the application of the stones are too difficult to remove by
them. In this case, for a very fine finish, the lathe is stopped and
draw-filing with the finest of files is performed, removing all streaks;
and the stones then follow the draw-filing. All stoning is done by hand
with the work at rest, as is also all burnishing.
After the burnisher comes fine imported crocus cloth, well worn, which
makes the surface more even and dead than that left by the burnisher.
The crocus is used with the lathe at its quickest speed, and is moved as
slowly and as evenly as possible, the slower and more even the crocus
movement along the rod, the more even the finish. If the rod has
filleted corners, such corners are in all cases draw-filed before the
stoning.
The method of polishing a cylinder cover at the Brown Engine Works is as
follows.
[Illustration: Fig. 1214.]
The finishing cut is taken with a feed of 32 lathe-revolutions per inch
of tool traverse, and at as quick a cutting speed as the hardness of the
iron will permit. This is necessary in order to have the tool-edge cut
the metal without breaking it out as a coarse one would do. With the
fine feed and quick speed the pores of the iron do not show; with a
coarse feed the pores show very plainly and are exposed for quite a
depth.
After the lathe-tool comes a well oil-stoned hand-scraper, with a piece
of leather between it and the tool rest to prevent the scraper from
chattering. The scraper not only smooths the surface, but it cuts
without opening the pores. It is used at a quick speed, as quick indeed
as it will stand, which varies with the hardness of the metal, but is
always greater than is possible with a slide-rest tool.
After the scraper the cover is removed from the lathe, and all flat
surfaces are filed as level as possible with a second-cut file, and then
stoned with soft Hindostan stone, used with benzine or turpentine, so as
to wash away the cuttings and prevent them from clogging the stone or
forming scratches. In using all stones the direction of motion is
frequently reversed so as to level the surface. Next comes stoning with
Scotch stone (Water of Ayr), used with water; in this part of the
operation great care must be taken, otherwise the cuttings will induce
scratches. When the Scotch stone marks have removed all those left by
the Hindostan stone, and left the surface as smooth as possible, the
cover is again put in the lathe and the grain is laid and finished with
very fine emery cloth and oil. The emery cloth is pressed lightly to the
work and allowed to become well worn so as to obtain a fine lustre
without leaving any streaks.
[Illustration: Fig. 1215.]
It will be noticed here that the use of the emery stick and oil is
entirely dispensed with; but for a less fine polish it may be used,
providing it be kept in quick motion radially on the work. The objection
to its use is that if there be any speck on the work it is apt to cut a
streak or groove following the spot like a comet's tail.
TURNING TAPERS.--There are five methods of turning outside tapers; 1st,
by setting over the tailstock of the lathe; 2nd, by the use of a former
or taper turning attachment such as was shown in Fig. 508; 3rd, by the
use of a compound slide rest; 4th, by means of a lathe in which the head
and tailstock are upon a bed that can be set at an angle to the lathe
shears on which the lathe carriage slides; and 5th, by causing the
cross-feed screw to operate simultaneously with the feed traverse.
Referring to the first method, it is objectionable, inasmuch as that the
work axis is thrown at an angle to the axis of the lathe centres, which
causes the work centres to wear rapidly, and this often induces them to
move their positions and throw the work out of true. Furthermore, the
tailstock has to be moved back in line with the live spindle axis for
turning parallel again, and this is a troublesome matter, especially
when the work is long.
Fig. 1214 shows the manner in which the lathe centres and the work
centres have contact, L being the live and B the dead centre; hence C C
is the axis of the live spindle which is parallel to the lathe shear
slides, which are represented by G; obviously A is the work axis. The
wear is greatest at the dead centre end of the work, but there is some
wear at the live centre end, because there is at that end also a certain
amount of motion of the work centre upon the live centre. Thus, in Fig.
1215, let _c_ represent the live centre axis, _a_ the work axis, D the
lathe face plate, and E F the plane of the driver or dog upon the work,
and it is obvious that the tail of the driver will when at one part of
the lathe revolution stand at E, while when diametrically opposite it
will stand at F; hence, during each work revolution the driver moves,
first towards and then away from the face plate D, and care must be
taken in adjusting the position of the driver to see that it has liberty
to move in this direction, for if obstructed in its motion it will
spring or bend the work.
[Illustration: Fig. 1216.]
To determine how much the tailstock of a lathe must be set over to turn
a given taper, the construction shown in Fig. 1216 may be employed. Draw
the outline of the work and mark its axis D, draw line C parallel to one
side of the taper end, and the distance A between this line and the work
axis is the amount the tailstock requires to be set over. This
construction is proved in Fig. 1217, in which the piece of work is shown
set over, C representing the line of the lathe ways, with which the side
F of the taper must be parallel. D is the line of the live spindle, and
E that of the work, and the distance B will be found the same as
distance A in Fig. 1216.
It may be remarked, however, that in setting the tailstock over it is
the point of the dead centre when set adjusted to the work length that
must be measured, and not the tailblock itself.
[Illustration: Fig. 1217.]
Other methods of setting tailstocks for taper turning are as follows: If
a new piece is to be made from an old one, or a duplicate of a piece of
work is to be turned, the one already turned, or the old piece as the
case may be, may be put in the lathe and we may put a tool in the tool
post and set the tailstock over until the tool traversed along the work
(the latter remaining stationary) will touch the taper surface from end
to end.
If, however, the taper is given as so much per foot, the distance to set
the tailstock over can be readily calculated.
Thus, suppose a piece of work has a taper part, having a taper of an
inch per foot, the work being three feet long, then there would be three
inches of taper in the whole length of the piece and the tailstock
requires to be set over one-half of the three inches, or 1-1/2 inches.
It will not matter how long the taper part of the work is, nor in what
part of the work it is, the rule will be found correct so long as the
tailstock is set over one-half the amount obtained by multiplying the
full length of the work per foot by the amount of taper per foot.
If we have no pattern we may turn at each end of the part that is to be
taper a short parallel place, truing it up and leaving it larger to the
same amount at each end than the finished size, and taking care that the
parallel part at the small end will all turn out in the finishing. We
then fasten a tool in the lathe tool post, place it so that it will
clear the metal of the part requiring to be turned taper, and placing it
at one extreme end of said part, we take a wedge, or a piece of metal
sufficiently thick, and place it to just contact with the turned part of
the work and the tool point (adjusting the tool with the cross-feed
screw), we then wind the rest to the other end of the required taper
part, and inserting same wedge or piece of iron, gauge the distance from
the tool point to the work, it being obvious that when the tool point
wound along is found to stand at an equal distance from each end of the
turned part, the lathe is set to the requisite taper.
[Illustration: Fig. 1218.]
Figs. 1218 and 1219 illustrate this method of setting. A represents a
piece of work requiring to be turned taper from B to C, and turned down
to within 1/32 inch of the required size at E and F. If then we place
the tool point H first at one end and then at the other, and insert the
piece I and adjust the lathe so that the piece of metal I will just fit
between the tool point and the work at each extreme end of the required
taper part, the lathe will be set to the requisite taper as near as
practicable without trying the work to the taper hole. The parallel part
at the small end of the work should be turned as true as possible, or
the marks may not be obliterated in finishing the work.
Fig. 1220 (from _The American Machinist_) represents a gauge for setting
the tailstock over for a taper. A groove is cut as at E and D, these
diameters corresponding to the required taper; a holder A is then put in
the tool point, and to this holder is pivoted the gauge B. The tailstock
is set over until the point of B will just touch the bottom of the
groove at each end of the work.
[Illustration: Fig. 1219.]
To try a taper into its place, we either make a chalked stripe along it
from end to end, smoothing the chalked surface with the finger, or else
apply red marking to it, and then while pressing it firmly into its
place, revolve it backwards and forwards, holding it the while firmly to
its seat in the hole; we move the longest outwardly projecting end up
and down and sideways, carefully noting at which end of the taper there
is the most movement. The amount of such movement will denote how far
the taper is from fitting the hole, while the end having the least
movement will require to have the most taken off it, because the fulcrum
off which the movement takes place is the highest part, and hence
requires the greatest amount of metal to be taken off.
Having fitted a taper as nearly as possible with the lathe tool, that is
to say, so nearly that we cannot find any movement or unequal movement
at the ends of the taper (for there is sure to be movement if the tapers
do not agree, or if the surfaces do not touch at more than one part of
their lengths), we must finish it with a fine smooth file as follows:
After marking the inside of the hole with a very light coat of red
marking, taking care that there is no dirt or grit in it, we press the
taper into the hole firmly, forcing it to its seat while revolving it
backwards and forwards.
By advancing it gradually on the forward stroke, the movement will be a
reciprocating and yet a revolving one. The work must then be run in the
lathe at a high speed, and a smooth file used to ease off the mark
visible on the taper, applying the file the most to parts or marks
having the darkest appearance, since the darker the marks the harder the
bearing has been. Too much care in trying the taper to its hole cannot
be taken, because it is apt to mark itself in the hole as though it were
a correct fit when at the same time it is not; it is necessary therefore
at each insertion to minutely examine the fit by the lateral and
vertical movement of projecting part of the taper, as before directed.
A taper or cone should be fitted to great exactitude before it is
attempted to grind it, the latter process being merely intended to make
the surfaces even.
For wrought-iron, cast-iron, or steel work, oil and emery may be used as
the grinding materials (for brass, burnt sand and water are the best).
The oil and emery should be spread evenly with the finger over the
surfaces of the hole and the taper; the latter should then be placed
carefully in its place and pressed firmly to its seat while it is being
revolved backwards and forwards, and slowly rotated forward by moving it
farther during the forward than during the backward movement of the
reciprocating motion.
After about every dozen strokes the taper should be carefully removed
from the hole and the emery again spread evenly over the surfaces with
the finger, and at and during about every fourth one of the back strokes
of the reciprocating movement the taper should be slightly lifted from
its bed in the hole, being pressed lightly home again on the return
stroke, which procedure acts to spread the grinding material and to make
the grinding smooth and even. The emery used should be about number 60
to 70 for large work, about 80 to 100 for small, and flour emery for
very fine work.
Any attempt to grind work by revolving it steady in one direction will
cause it to cut rings and destroy the surface.
[Illustration: Fig. 1220.]
Referring to the second method, all that is necessary in setting a
former or taper attachment bar is to set it out of line with the lathe
shears to half the amount of taper that is to be turned, the bar being
measured along a length equal to that of the work. Turning tapers with a
bar or taper-turning attachment possesses the advantage that the
tailstock not being set over, the work centres are not thrown out of
line with the live centres, and the latter are not subject to the wear
explained with reference to Fig. 1214. Furthermore, the tailstock being
kept set to turn parallel, the operator may readily change from turning
taper to turning parallel, and may, therefore, rough out all parts
before finishing any of them, and thus keep the work more true, whereas
in turning tapers by setting the tailstock over we are confronted by the
following considerations:--
If we turn up and finish the plain part first, the removing of the skin
and the wear of the centres during the operation of turning the taper
part will cause the work to run out of true, and hence it will not, when
finished, be true; or if, on the other hand, we turn up the taper part
first, the same effects will be experienced in afterwards turning the
plain part. We may, it is true, first rough out the plain part, then
rough out the taper part, and finish first the one and then the other;
to do this, however, we shall require to set the lathe twice for the
taper and once for the parallel part.
It is found in practice that the work will be more true by turning the
taper part the last, because the work will alter less upon the lathe
centres when changed from parallel to taper turning than when changed
from the latter to the former. In cases, however, in which the parts
fitting the taper part require turning, it is better to finish the
parallel part last, and to then turn up the work fastened upon the
taper part while it is fast upon its place: thus, in the case of a
piston rod and piston, were we to turn up the parallel part of the rod
first and the taper last, and the centres altered during the last
operation, when the piston head was placed upon the rod, and the latter
was placed in the lathe, the plain part or stem would not run true, and
we should require to true the centres to make the rod run true before
turning up the piston head. If, however, we first rough out the plain
part or stem of the rod, and then rough out and finish the taper part,
we may then fasten the head to its place on the rod, and turn the two
together; that is to say, rough out the piston head and finish its taper
hole; then rough out the parallel part of the rod, but finish its taper
end. The rod may then be put together and finished at one operation;
thus the head will be true with the rod whether the taper is true with
the parallel part of the rod or not. With a taper-turning attachment the
rod may be finished separately, which is a great advantage.
[Illustration: Fig. 1221.]
If, however, one part of the length of a taper turning attachment is
much more used than another, it is apt to wear more, which impairs the
use of the bar for longer work, as it affects its straightness and
causes the slide to be loose in the part most used, and on account of
the wear of the sliding block it is proper to wind the tool out from its
cut on the back traverse, or otherwise the tool may cut deeper on the
back than on the forward traverse, and thus leave a mark on the work
surface.
[Illustration: Fig. 1222.]
Referring to the third method, a compound slide rest provides an
excellent method of turning tapers whose lengths are within the capacity
of the upper slide of the compound rest, because that slide may be used
to turn the taper, while the ordinary carriage feed may be used for the
parallel parts of the work, and as the tailstock does not require to set
over, the work centres are not subject to undue wear.
If the seat for the upper slide of the rest is circular, and the taper
is given in degrees of angle, a mark may be made on the seat, and the
base of the upper slide may be marked in degrees of a circle, as shown
in Fig. 1221, which will facilitate the setting; or the following
construction, which is extracted from _Mechanics_, may be employed.
Measure the diameter of the slide rest seat, and scribe on a flat
surface a circle of corresponding diameter. Mark its centre, as A in
Fig. 1222, and mark the line A B. From the centre A mark the point B,
whose radius is that of the small end of the hole to be bored. Mark the
length of the taper to be turned on the line A G and draw the line G D
distant from A B equal to the diameter of the large end of the hole to
be bored. Draw the line B D. Then the distance E F is the amount the
rest must be swiveled to turn the required taper.
It is obvious that the same method may also be used for setting the
rest.
[Illustration: Fig. 1223.--Top View.]
Referring to the fourth method, by having an upper bed or base plate for
the head and tailstock, so that the line of lathe centres may be set at
the required angle to the [V]s or slides on which the carriage
traverses, it affords an excellent means of turning tapers, since it
avoids the disadvantages mentioned with regard to other systems, while
at the same time it enables the turning of tapers of the full length of
the carriage traverse, but it is obvious that the head and tailstock are
less rigidly supported than when they are bolted direct to the lathe
shears.
[Illustration: Fig. 1224.--End View.]
In turning tapers it is essential that the tool point be set to the
exact height of the work axis, or, in other words, level with the line
of centres. If this is not the case the taper will have a curved outline
along its length. Furthermore, it may be shown that if a straight taper
be turned and the tool be afterwards either raised or lowered, the
amount of taper will be diminished as well as the length being turned to
a curve.
Figs. 1223 and 1224 demonstrate that the amount of taper will be changed
by any alteration in the height of the tool. In Fig. 1223, A B
represents the line of centres of the spindle of a lathe, or, in other
words, the axis of the work W, when the lathe is set to turn parallel; A
C represents the axis of the work or cone when the lathe tailstock is
set over to turn the taper or cone; hence the length of the line C B
represents the amount the tailstock is set over. Referring now to Fig.
1224, the cone is supposed to stand level, as it will do in the end
view, because the lathe centres remain at an equal height from the lathe
bed or [V]s, notwithstanding that the tailstock is set over. The tool
therefore travels at the same height throughout its whole length of
feed; hence, if it is set, as at T, level with the line of centres, its
line of feed while travelling from end to end of the cone is shone by
the line A B. The length of the line A B is equal to the length of the
line B C Fig. 1223. Hence, the line A B, Fig. 1224, represents two
things: first, the line of motion of the point of tool T as it feeds
along the cone, and second its length represents the amount the work
axis is out of parallel with the line of lathe centres. Now, suppose
that the tool be lowered to the position shown at I; its line of motion
as it feeds will be the line C D, which is equal in length to the line A
B. It is obvious, therefore, that though the tool is set to the diameter
of the small end, it will turn at the large end a diameter represented
by the dotted circle H. The result is precisely the same if the taper is
turned by a taper-turning attachment instead of setting the tailstock
out of line.
[Illustration: Side View. Fig. 1225. End View.]
The demonstration is more readily understood when made with reference to
such an attachment as the one just mentioned, because the line A B
represents the line of tool feed along the work, and its length
represents the amount the attachment causes the tool to recede from the
work axis. Now as this amount depends upon the set-over of the
attachment it will be governed by the degree of that set over, and is,
therefore, with any given degree, the same whatever the length of the
tool travel may be. All that is required, then, to find the result of
placing the tool in any particular position, as at I in the end view, is
to draw from the tool point a line parallel to A B and equal in length
to it, as C D. The two ends of that line will represent in their
distances from the work axis the radius the work will be turned to at
each end with the tool in that position. Thus, at one end of the line C
D is the circle K, representing the diameter the tool I would turn the
cone at the small end, while at the other end the dotted circle H gives
the diameter at the large end that the tool would turn to when at the
end of its traverse. But if the tool be placed as at T, it will turn the
same diameter K at the small end, and the diameter of the circle P at
the large end.
We have here taken account of the diameters at the ends only of the
work, without reference to the result given at any intermediate point
along the cone surface, but this we may now proceed to do, in order to
prove that a curved instead of a straight taper is produced if the tool
be placed either above or below the line of lathe centres.
In Fig. 1225, D E F C represents the complete outline of a straight
taper, whose diameter at the ends is represented in the end view by the
outer and inner circles. Now, a line from A to B will represent the axis
of the work, and also the line of tool point motion or traverse, if that
point is set level with the axis. The line I K in the end view
corresponds to the line A B in the side view, in so far that it
represents the line of tool traverse when the tool point is set level
with the line of centres. Now, suppose the tool point to be raised to
stand level with the line G H, instead of at I K, and its line of feed
traverse be along the line G H, whose length is equal to that of I K. If
we divide the length of G H into six equal divisions, as marked from 1
to 6, and also divide the length of the work in the side view into six
equal divisions (_a_ to _f_), we shall have the length of line G H in
the first division in the end view (that is, the length from H to G),
representing the same amount or length of tool traverse as from the end
B of the cone to the line A in the side view. Now, suppose the tool
point has arrived at 1; the diameter of work it will turn when in that
position is evidently given by the arc or half-circle _h_, which meets
the point 1 on G H. To mark that diameter on the side view, we first
draw a horizontal line, as _h_ _p_, just touching the top of _h_; a
perpendicular dropped from it cutting the line A B, gives the radius of
work transferred from the end view to the side view. When the tool point
has arrived at 2 on G H in the end view, its position will be shown in
the side view at the line _b_, and the diameter of work it will turn is
shown in the end view by the half-circle _k_. To transfer this diameter
to the side view we draw the line _k_ _g_, and where it cuts the line
_b_ in the side view is the radius of the work diameter when the tool
has arrived at the point _b_ in the side view. Continuing this process,
we mark half-circles, as _l_, _m_, _n_, _o_, and the lines _l_ _r_, _m_
_s_, _n_ _t_, _o_ _u_, by means of which we find in the side view the
work radius when the tool has arrived at _c_, _d_, _e_, and _f_
respectively. All that remains to be done is to draw on the side view a
line, as _u_ E, that shall pass through the points. This line will
represent the outline of the work turned by the tool when its height is
that denoted by G H. Now, the line _u_ E is shown to be a curve, hence
it is proved that with the tool at the height G H a curved, and not a
straight, taper will be turned.
It may now be proved that if the tool point is placed level with the
line of centres, a straight taper will be turned. Thus its line of
traverse will be denoted by A B in the side view and the line I K in the
end view; hence we may divide I K into six equal divisions, and A B into
six equal divisions (as _a_, _b_, _c_, &c.). From the points of division
I K, we may draw half-circles as before, and from these half-circles
horizontal lines, and where the lines meet the lines of division in the
side view will be points in the outline of the work, as before. Through
these points we draw a line, as before, and this line C F, being
straight, it is proven that with the tool point level with the work
axis, it will turn a straight taper.
[Illustration: Top View. Fig. 1226. End View.]
It may now be shown that it is possible to turn a piece of work to a
curve of equal curvature on each side of the middle of the work length.
Suppose, for example, that the cutting tool stands on top of the work,
as in the end view in Fig. 1226, and that while the tool is feeding
along the work it also has a certain amount of motion in a direction at
right angles to the work axis, so that its line of motion is denoted by
the line B B in the top view. The outline of the work turned will be a
curve, as is shown in Fig. 1227, in which the line of tool traverse is
the line C D. Now the amount of tool motion that occurs during this
traverse in a direction at right angles to the work axis is represented
by the line F E, because the upper end is opposite to the upper end of C
D, while the lower end is opposite the lower end of C D. We may then
divide one-half of the length of F E into the divisions marked from 1 to
6. Now, as we have taken half the length of F E, we must also take half
the length of the work and divide it into six equal divisions marked
from _a_ to _f_. Now, suppose the tool point to stand in the line F S in
the end view, its position in the top view will be at C. When it is at 1
on the end view it will have arrived at _p_ in the top view. The radius
of work it will then turn is shown in the end view by the length of line
running from 1 to the work centre. Take this length, and from _a_ in the
work axis set it off on the line _a_ _h_, and make the length equal the
height of 1 S. In like manner, when the tool point has arrived at 2, the
radius it will cut the work is shown by the length of line _i_; hence
from 2 on the work axis we may set off the length of 2 S, making 2 S and
_b_ _i_ of equal length. Continuing this process, we make the length of
_c_ _k_ equal that of 3 S, the length of _d_ _l_ equal 4 S, and so on.
All that remains then is to draw a line, _o_ _g_, that shall meet the
tops of these lines. This line will show the curve to which that half of
the work length will be turned to. The other half of the work length
will obviously be turned to the same curvature.
[Illustration: Fig. 1227.]
[Illustration: Fig. 1228.]
It is obvious that the curvature of the work outline will be determined
by the proportion existing between the length of the work and the amount
of tool motion in a direction at right angles to the work axis, or, in
other words, between the length of the work and that of the line F E. It
is evident, also, that with a given amount of tool motion across the
work, the curvature of outline turned will be less in proportion as the
work length is greater. Now, suppose that the smaller and the larger
diameter of the work, together with its length, are given, and it is
required to find how much curvature the tool must have, we may find this
and work out the curve it will cut by the construction shown in Fig.
1228, in which the circle K is the smallest and the circle P the largest
diameter. The line _m_ C is drawn to just touch the perimeter of K, and
this at once gives the amount of cross-motion for the tool. Hence, we
may draw the line _m_ B and C B, and from their extremities draw the
line B B representing the path of traverse of the tool point. We may
then obtain the full curve on one side of the work by dividing one-half
the length of _m_ C into six equal divisions and proceeding as before,
except that we have here added the lines of division in the second half
as from _f_ to _l_. It will be observed that the centre of the curve is
at the point where the tool point crosses the axis of the work; hence,
by giving to the tool more traverse on one side than on the other of the
work axis, the location of the smallest point of work diameter may be
made to fall on one side of the middle of the work length.
In either turning or boring tapers that are to drive or force in or
together, the amount to be allowed for the fit may be ascertained, so
that the work may be made correct without driving each piece to its
place to try its fit.
Suppose, for example, that the pieces are turned, and the holes are to
be reamed, then the first hole reamed may be made to correct diameter by
fit and trial, and a collar may be put on the reamer to permit it to
enter the holes so far and no farther.
A taper gauge may then be made as in Fig. 1229, the line a representing
the bore of the hole, and line B the diameter of the internal piece, the
distance between the two being the amount found by trial to be necessary
for the forcing or driving. The same gauge obviously serves for testing
the taper of the holes reamed.
CHUCKED OR FACE PLATE WORK.--This class of work requires the most
skillful manipulation, because the order in which the work may most
advantageously proceed and the method of chucking are often matters for
mature consideration.
[Illustration: Fig. 1229.]
In a piece of work driven between the lathe centres, the truth of any
one part may be perceived at any time while operating upon the others,
but in chucked work, such is not always the case, and truth in the work
is then only to be obtained by holding it truly. Again, the work is apt
to be sprung or deflected by the pressure of the devices holding it, and
furthermore the removal of the skin or surface will in light work
sometimes throw it out of true as the work proceeds, the reason being
already given, when referring to turning plain cylindrical work.
TO TURN A GLAND.--There are three methods of turning a gland: first, the
hole and the face on the outside of the flange may be turned first, the
subsequent turning being done on a mandrel; second, the hole only may be
bored at the first chucking, all the remaining work being done on a
mandrel; and, third, the hole, hub, and one radial face may be turned at
one chucking, and the remaining face turned at a separate chucking.
If the first plan be adopted, any error in the truth of the mandrel will
throw the hole out of true with the hub, which would be a serious
defect, causing the gland to jamb against one side of the piston rod,
and also of the gland bore. The same evil is liable to result from the
second method; it is best, therefore, to chuck the gland by the hub in a
universal chuck, and simply face the outer face of the flange, and also
its edge. The gland may then be turned end for end, and the hole, the
hub, the inside radial flange face, and the hub radial face, may then
all be turned at one chucking; there is but one disadvantage in this
method, which is that the gland must be unchucked to try its fit in the
gland hole, but if standard gauges are used such trial will not be
necessary, while if such is not the case and an error of measurement
should occur, the gland may still be put on a mandrel and reduced if
necessary.
In either method of chucking, the fit of the hole to the rod it is
intended for cannot be tested without removing the gland from the chuck.
TO TURN A PLAIN CYLINDRICAL RING ALL OVER IN A UNIVERSAL CHUCK.--Three
methods may be pursued in doing this simple job: first, the hole may be
bored at one chucking, and the two radial faces and the circumference
turned at a second chucking; second, the diameter may be turned, first
on the hole and two radial faces turned at a second chucking; and third
the hole and one radial face may be turned at one chucking, and the
diameter and second radial face at a second chucking. The last method is
best for the following reasons. The tool can pass clear over the
surfaces at each chucking without danger of coming into contact with the
chuck jaws, which would cause damage to both; second, at the last
chucking, the chuck jaws being inside the ring, the latter may be tested
for truth with a pointer fixed in the tool rest, and therefore set quite
true.
It is obvious that at neither chucking should the ring be set so far
within the chuck jaws that there will be danger of the tool touching
them when turning the radial face.
In the case of a ring too thin to permit this, and of too large a bore
to warrant making a mandrel for it, the ring may be held on the outside
and bored, and both radial faces turned to within a short distance of
the chuck jaws; at the second chucking, the chuck jaws being within the
ring bore, the work may be set true with a pointer, as before, and
finished.
If, however, a number of such rings were to be turned, it would pay to
turn up another and thicker ring, and use it as a mandrel after the bore
and one radial face of the ring had been turned.
TO TURN AN ECCENTRIC STRAP AND ECCENTRIC.--The eccentric strap should be
turned first, because it can then be taken apart and its fit to the
eccentric tried while the latter is in the lathe, which is not the case
with the eccentric. The strap should first be held in a universal chuck
bolted to the face plate, or held in dogs such as shown in Fig. 893 at
C, and one face should be turned. It should then be turned round on the
chuck to bore it, and face the other side.
If the shape of the strap will admit it, it is best chucked by plates
and bolts holding the face first turned to the face plate, because in
this case there will be no pressure tending to spring the straps out of
their natural shape; otherwise, however, it may be held in a universal
or independent jaw chuck, or if too large for insertion in chucks of
this kind (which are rarely made for large lathes) it may be held in
dogs such as shown in Fig. 893 at C.
[Illustration: Fig. 1230.]
[Illustration: Fig. 1231.]
If after an eccentric strap is bored, and the bolts that hold its two
halves together have been slackened, its diameter at A and at C, Fig.
1230, be measured, it will be found that A is less than C. The cause of
this is partly explained under the head of tension of castings; but it
is necessary to add that the diameters at A and at C in the figure are
equal while the strap is in the lathe, or until the bolts holding the
two halves of the strap together are released, yet so soon as this is
done the diameter at A will reduce, the bore becoming an oval.[18]
[18] This occurs in all castings of similar form, as brasses, &c.
Now, it is obvious that the eccentric must be turned to the diameter at
C, or otherwise it will have lost motion in the strap. If, however, the
eccentric be turned to the diameter of C, the strap cannot be tried on,
as it will bind at the corners, as shown in Fig. 1231. To remedy this
evil it is usual to put a piece of sheet tin or metal between the joint
faces of the two halves of the eccentric straps before they are chucked
to turn them, and to bore them too large to the amount of the thickness
of sheet metal so employed. After the straps are bored these pieces of
metal are removed, and the strap halves bolted together as in Fig. 1230,
the diameter at C being that to which the eccentric must be turned.
If the sheet metal so inserted were thick enough, the strap bore will
measure the same at A as at C, Fig. 1230. If it were too thick the
diameter at A will be greatest, while if too thin the diameter at A will
be the least. There is no rule whereby the necessary thickness for a
given size of strap may be known, and the workman is usually governed by
his experience on castings of similar metal, or from the same moulding
shop.
He prefers, however, to be on the safe side by not putting in too great
a thickness, because it is easier to scrape away the bore at the joint
than it is to file away the joint faces. The following thicknesses for
the respective diameters may be considered safe for castings that have
not been reheated after casting.
Diameter Thickness of metal to
of place between the
bore. strap valves.
Inches. Inch.
6 1/64
12 1/32
18 3/64
24 1/8
In turning a new strap for an old eccentric, it will be necessary, when
taking the diameter of the eccentric, to take a piece of tin of the same
thickness as that placed between the eccentric lugs or jaws, and place
it between the caliper leg and the eccentric, so that the diameter of
the strap across C, Fig. 1230, may be made equal when the tin is removed
to the diameter of the eccentric.
In turning up the eccentric, the plain face should be faced first,
setting it true, or nearly so, with the circumference of the eccentric,
as will be the case if the circumference is held in a universal chuck,
but if the hub is so long that this cannot be done because the chuck
jaws cannot reach the circumference, the hub itself may be held in an
independent jaw chuck.
The face turned may then be turned round, so as to meet the face of the
chuck against which it should bed fairly, so as to run true. At this
chucking the hole bore, the hub, and the radial faces should be turned,
all these surfaces being roughed out before any one surface is finished.
The eccentric must then be again reversed, so that the face of the hub
meets, the face plate being held by bolts as shown for a crank in
figure, when the work being set to the lines marked (so as to give it
the correct amount of throw) may be turned to fit the bore of the strap,
the strap being taken apart so as to try it on, which this method of
chucking will readily permit.
Now, in an eccentric, the surfaces requiring to be most true one with
the other are those of the bore and of the circumference where the strap
fits, and since the latter was turned with the hub face to the chuck,
and that hub face was turned at the same chucking as the hole was bored
(and must, therefore, be true to the bore), the bore and circumference
will be as true as it is practicable to get them, because upon the truth
of the last chucking alone will the truth of the work depend.
Small eccentrics may be held for all their chuckings in jaw chucks, but
not so truly as if chucked on a face plate, because of the difficulty of
keeping the radial faces of such jaws true, which occurs by reason of
the causes explained with reference to Figs. 848 and 849.
Eccentrics having so much throw upon them as to render it difficult to
hold them for the last chucking by the method above given (by bolts
through the bore), usually have openings through them on the throw side,
and in this case parallel pieces may be placed behind the radial face
(on the hub side of the eccentric), such parallel pieces being thick
enough to keep the hub face clear of the chuck face, and bolts may be
passed through the said opening to hold the eccentric. Another method
would be as follows:--
The outside diameter of the eccentric may be gripped in a dog chuck, if
the dogs of the chuck project out far enough to reach it (otherwise the
dogs may grip the hub of the eccentric), while the hole is bored and the
plain face of the eccentric turned. The eccentric must then be reversed
in the lathe, and the hub and the radial face on that side must be
turned. Then the plain face of the eccentric must be bolted to the face
plate by plates placed across the spaces which are made to lighten the
eccentric, and by a plate across the face of the hub. The eccentric,
being set true to the lines, may then be turned on its outside diameter
to fit the strap; to facilitate which fitting, thin parallel strips may
be placed between the face plate and the plain face of the eccentric at
this last chucking. It will be observed that, in either method of
chucking, the outside diameter of the eccentric (that is to say, the
part on which the strap fits) is turned with the face which was turned
at the same chucking at which the hole was bored, clamped to the face
plate. In cases where a number of eccentrics having the same size of
bore and the same amount of throw are turned, there may be fitted to the
face plate of the lathe a disk (such as shown in Fig. 888), of
sufficient diameter to fit the hole of the eccentric, the said disk
being fastened to the face plate at the required distance from the
centre of the lathe to give the necessary amount of throw to the
eccentric. The best method of fastening such a disk to the face plate is
to provide it with a plain pin turned true with the disk, and let it fit
a hole (bored in the face plate to receive it) sufficiently tightly to
be just able to be taken in and out by the hand, the pin being provided
with a screw at the end, so that it can be screwed tight by a nut to the
face plate. The last chucking of the eccentric is then performed by
placing the hole of the eccentric on the disk, which will insure the
correctness of the throw without the aid of any lines on the eccentric
which may be set as true as the diameter of the casting will permit, and
then turned to fit the strap.
TO TURN A CYLINDER COVER.--A cylinder cover affords an example of
chucking in which the work done at one chucking requires to be very true
with that done at a subsequent chucking, thus the gland hole which is on
one side requires to be quite true with the diameter that fits into the
cylinder bore, this diameter being on the opposite side.
If the polished or gland side of the cover be turned first, the hole for
the packing ring and that for the gland may be bored with the assurance
that one will be true with the other, while the polished outside face
may be turned at the same chucking.
But when the cover is turned round in the lathe to turn the straight
face, though the hole may be set true as far as can be ascertained in
its short length, yet that length is too short to be an accurate guide,
and the hole for the packing ring may appear true, while that for the
gland, being longer, will have any error in the setting, multiplied by
reason of its greater length. It is better, therefore, to turn the plain
face first, gripping the cover by the gland flange so that the plain
radial face, the step that fits the cylinder bore, and the outer edge of
the cover flange may be turned at one chucking; then when the cover is
turned round in the chuck, the flat face may be set true by resting
against the radial surface of the chuck jaws, and the concentric truth
may be set by the outer edge of the flange, which, being of the extreme
diameter of the cover, will most readily show any want of truth in the
setting. If in this case a universal chuck be used, and the work does
not run quite true, it may be corrected by slacking the necessary dog or
jaw on one side, and tightening up again from the screw of the necessary
jaw on the other.
This occurs because from the wear, &c., there is always some small
amount of play or lost motion in the jaw screws, and in the mechanism
operating them, and by the above means this is taken advantage of to
true the work.
If from any cause the work cannot be held for the first chucking by
means of the gland hole flange, it must be held by the circumferential
edge of the cover, letting the jaws envelop as small a distance over
that edge as possible, the protruding part of it may then be turned up
as close to the chuck jaws as possible, and this turned part may still
be used to set the cover concentrically true at the second chucking.
In a very small cover the gland hole may have a mandrel fitted to it and
be turned therefrom on both radial faces, or on one face only, the other
being turned at the chucking at which the holes were bored.
In a cover too large to be held in a jaw chuck, the cover may be held in
chucking dogs such as shown at C in Fig. 893, the edge protruding as
much as possible from the dog screws, and being turned half way across
at one chucking, and finished at the second chucking. To set the radial
face at the second chucking, the surface gauge, applied as shown in Fig.
894, may be employed. If the bore of the packing ring or piston rod hole
is large enough to permit it, that hole and the gland hole may be bored
at the same chucking as that at which the plain face and step that fits
in the cylinder bore is turned, thus ensuring truth in all the essential
parts of the cover.
But in this case these operations should be performed at the last of the
two chuckings, so as to eliminate any error that might arise from the
casting altering its shape by reason of the removal of the metal on the
radial face of the gland hole side of the cover.
TO TURN A PULLEY.--A pulley affords an excellent example of lathe work,
because it may be operated upon by several different methods: thus, for
boring it may be held, if small, in a dog chuck, with the jaws inside
the rim; in a dog chuck with the jaws outside the rim; in a dog chuck by
the hub itself (if the hub is long enough). A larger pulley may be
chucked for boring by the rim held in a jaw chuck; by the rim held by
bolts and plates, or by the rim held by dogs, such as shown in Fig. 893,
or by the arms rested on pieces placed between them and the chuck, and
then bolts and plates applied to those arms.
The rim may be turned by placing the pulley on a mandrel and driving
that mandrel by a dog or carrier; by placing it on a mandrel and driving
it by a Clements driver such as shown in Fig. 753, and having two
diametrically opposite driving pins, placed to bear against
diametrically opposite arms; by holding the arms to the chuck as before
described, and performing the boring and facing at one chucking; or by
holding the rim on its inside by the chuck jaws, so as to turn and bore
the pulley at one chucking, which can be done when the inside of the rim
is parallel, or not sufficiently coned to cause it to slip off the jaws,
or when the jaws will reach to the centre of the rim width.
The advantages and disadvantages of these various methods are as
follows:--
From the weakness of the pulley rim it is apt to distort when held with
sufficient chuck-jaw pressure to enable the turning of the rim face and
edge. But this would not affect the truth of the hole; hence the rim may
be gripped in a chuck to bore the hole and face the hub. If so held it
should be held true to the inside face of the rim, so that the bore will
be true to the same, and then in turning the outside diameter it will be
made as true as possible with the rim, which will preserve the balance
of the pulley as much as possible. For these reasons the inside of the
rim should be the part set to run true, whatever method of chucking be
employed; hence, if the circumstances will permit of holding the hub to
bore it, an independent jaw chuck should be employed (that is, of
course, a chuck capable of independent jaw movement).
If the pulley be chucked by the arms, it is well-nigh impossible to
avoid springing those arms from the pressure of the bolts, &c., holding
them, and as a result the pulley face, though turned true, will not be
true of itself, nor true with the hole, when the arms are released from
such pressure.
If the pulley is of such a large size that its rim must be held by bolts
and plates while the boring is progressing, such bolts, &c., must be
placed on the outside of the rim, so as not to be in the way when
setting the pulley true to the inside of the rim.
A small pulley may be turned on a mandrel driven by a dog, which is the
truest method of turning, because the rim is in this case strained by
the pressure of the cut only. But a dog will not drive a cut at such a
leverage as exists at the rim of a pulley above about 18 inches in
diameter; furthermore, in a large wheel there would not be sufficient
friction between a mandrel and the pulley bore to drive the roughing cut
on the pulley face.
It is necessary, therefore, to drive the pulley from the arms, while
holding it on a mandrel, but if it be driven by one arm the whole strain
due to driving will fall on that one arm, and on one side of the pulley
only, and this will have a tendency to cause the rim at and near its
junction with that arm to spring or deflect from its natural position,
and, therefore, to be not quite true; all that can be done, therefore,
is to drive by two arms with a Clements driver, so as to equalize the
pressure on them.
An excellent method of chucking a pulley, and one that with care avoids
the disadvantages mentioned in the foregoing methods, is shown in Figs.
1232 and 1233. It consists of a clamping dog, Fig. 1234, that fastens to
the lathe face plate, and secures the pulley by its arms, while
supporting the rim and preventing it from chattering, if it is weak or
slight.
[Illustration: Fig. 1232.]
This dog is bolted to the face plate by the two studs A and B. At C is a
set screw for clamping the pulley arms against the screw D, and at F is
a screw that steadies the pulley rim between the arms.
[Illustration: Fig. 1233.]
CUTTING SCREWS IN THE LATHE WITH SLIDE REST TOOLS.--In order to cut a
thread in the lathe with a slide rest tool, it is necessary that the
gear-wheels which transmit motion from the cone spindle to the feed
screw shall be of the proportions necessary to give to the lathe
carriage and slide rest sufficient lateral movement or traverse for
lathe revolution to cut a thread of the desired pitch.
[Illustration: Fig. 1234.]
Suppose now that the feed screw makes a revolution in the same time that
the cone spindle does, and it is evident that the thread cut by the
slide rest tool will be of the same pitch as is the pitch of the lathe
feed screw. If the feed screw gear-wheels of the lathe are what is
called single geared (which means that no one stud in the change gearing
carries more than one gear-wheel), it does not matter what are the sizes
or how many teeth there are in the wheels used to convey or transmit
motion from the cone spindle to the feed screw, for so long as the
number of teeth on the cone spindle gear and that on the feed screw are
equal, the feed screw will make one revolution in the same time as the
cone spindle makes a revolution, and the cutting tool will travel a
lateral distance equal to the pitch of the lead screw.
[Illustration: Fig. 1235.]
Suppose, for example, that Fig. 1235 represents the screw cutting gear
or change wheels of a lathe, wheel D being the driver, I an intermediate
wheel for transmitting motion from the driver D to the lead-screw wheel
S. Suppose, also, that D has 32, I 80, and S 32 teeth, and we have a
simple or single-geared lathe. In this case it may first be proved that
we need not concern ourselves with the number of teeth in the
intermediate I, because its number of teeth is of no consequence. For
example, the 32 teeth in D will in a revolution move 32 of the teeth in
I past the line of centres, and it is obvious that I will move the 32
teeth in S past the line of centres, causing it to make one revolution
the same as D. If any other size of wheel be used for an intermediate,
the effect will be precisely the same, the revolutions of D and of S
remaining equal. Under these conditions the lathe would cut a thread
whose pitch would be the same as that of the thread on the lead screw.
[Illustration: Fig. 1236.]
Now let us turn to Fig. 1236, representing an arrangement of gearing
common in American practice, and we have within the lathe-head three
gears, A, B, and C, which cannot be changed. Of these, B and C are
simply intermediate wheels, the respective diameters of which have no
effect upon the revolutions of the lead screw, except that they convey
the motion to D. To demonstrate this, suppose the wheels to have the
number of teeth marked respectively against them in the end view of the
figure, C and D having each 20 teeth, and the one revolution of the live
spindle wheel A will cause the lead-screw wheel to make one revolution,
because A and S contain the same number of teeth. This may be made plain
as follows: The 20 teeth in A will in one revolution cause B to make two
revolutions, because B has but half as many teeth as A. The two
revolutions of B will cause C to make but one revolution, because C has
twice as many teeth as B has. Now, C and D are fast on the same shaft R;
hence they revolve together, the one revolution of C simply being
conveyed by the shaft R to D, and it is clear that the one revolution of
A has been conveyed without change to D, and that, therefore, D may be
considered to have simply taken the place of A, unaffected by the wheels
B, C. Wheel I is again an intermediate, so that, whatever its diameter
or number of teeth, one revolution of D will cause one revolution of S.
Thus in this arrangement the lead screw will again revolve at the same
speed as the live spindle, and the thread cut will be of the same pitch
as the pitch of the lead screw. Practically, then, all the wheels
between A and S, as thus arranged, act as simple intermediates, the same
as though it were a single-geared lathe, which occurs because C and D
have the same number of teeth, and we have, therefore, made no use of
the shaft R to compound the gearing.
[Illustration: Fig. 1237.]
The term "compounded" as applied to the change gears of a lathe, means
that there exists in it a shaft or some equivalent means by which the
velocity of the wheels may be changed. Such a shaft is shown at R in
Fig. 1236, and it affords a means of compounding by placing on its outer
end, as at D, a wheel that has a different number of teeth to that in
wheel C. In Fig. 1237 this change is made, wheel D having 40 teeth
instead of the 20 it had before. As in the former case, however, it will
make one revolution to one of C or one of A, but having 40 teeth it will
move 40 of the teeth in I past the line of centres, and this will cause
the lead screw wheel S to make two revolutions, because it has 20 teeth
only. Thus, the compounding of C and D on shaft R has caused S to make
two revolutions to one of A, or, what is the same thing, one revolution
of A will in this case cause S to make two revolutions, and the thread
cut would be twice as coarse as the lead-screw thread. In the case of a
lathe geared as in either Fig. 1235 or 1236, all the wheels that we
require to consider in calculating the change wheels are D and S. Now,
the shaft R is called the "mandrel," the "stud," or the "spindle," all
three terms being used, and the wheel D is the wheel on the stud,
mandrel, or spindle, while in every case S is that on the lead screw,
and the revolutions of this wheel D and those of the lead screw will be
in the same proportion as exists between their numbers of teeth. In
considering their revolutions it is to be borne in mind that when D has
more teeth than S the speed of the lead screw is increased, and the
lathe will cut a thread coarser than that of its lead screw, or when D
has less teeth than S the speed of the lead screw is diminished, and the
pitch of thread cut will be finer than that of the lead screw.
[Illustration: Fig. 1238.]
Another method of compounding is shown in Fig. 1238, the compounded pair
C D being on a stud carried in the swing frame F. Now, suppose A has 32,
C 64, D 32, and S 64 teeth, the revolution being in the same proportion
as the numbers of teeth, C will make one-half a revolution to one
revolution of A, and D, being fast to the same stud as C, will also make
one-half revolution to one revolution of A. This one-half revolution of
D will cause S to make one-quarter of a revolution; hence the thread cut
will be four times as fine as the pitch of the thread on the lead screw,
because while the lathe makes one turn the lead screw makes one-quarter
of a turn. In this arrangement we are enabled to change wheel C as well
as wheel D (which could not be done in the arrangement shown in Fig.
1236), and for this reason more changes can be made with the same number
of wheels. When the wheel C makes either more or less revolutions than
the driver A, it must be taken into account in calculating the change
wheels. As arranged in Fig. 1236, it makes the same number as A, which
is a very common, arrangement, but in Fig. 1238 it is shown to have
twice as many teeth as A; hence it makes half as many revolutions. In
the latter case we have two pairs of wheels, in each of which the driven
wheel is twice the size of the driver; hence the revolutions are reduced
four times.
Suppose it is required to cut a thread of eight to an inch on a lathe
such as shown in Fig. 1235, the lead screw pitch being four per inch,
and for such simple trains of gearing we have a very simple rule, as
follows:--
_Rule._--Put down the pitch of the lead screw as the numerator, and the
pitch of thread you want to cut as the denominator of a vulgar fraction,
and multiply both by the pitch of the lead screw, thus:
Pitch of
lead
screw. {the number of teeth for the
Pitch of lead screw 4 4 16 = {wheel on the spindle.
- × - = --
Pitch to be cut 8 4 32 = {the number of teeth for the
{wheel on the lead screw.
There are three things to be noted in this rule; and the first is, that
when the pitch of the lead screw and the pitch of thread you want to cut
is put down as a fraction, the numerator at once represents the wheel to
go on the stud, and the denominator represents the wheel to go on the
lead screw, and no figuring would require to be done providing there
were gear-wheels having as few teeth as there are threads per inch in
the lead screw, and that there was a gear-wheel having as many teeth as
the threads per inch required to be cut. For example, suppose the lathe
in Fig. 1236 to have a lead screw of 20 per inch, and that the change
wheels are required to cut a pitch 40, then we have 20/40, the 20 to go
on at D in Fig. 1236 and the 40 to go on the lead screw. But since lead
screws are not made of such fine pitch, but vary from two threads to
about six per inch, we simply multiply the fraction by any number we
choose that will give us numbers corresponding to the teeth in the
change wheels. Suppose, for example, the pitch of lead screw is 2, and
we wish to cut 6, then we have 2/6, and as the smallest change wheel
has, say, 12 teeth we multiply the fraction by 6, thus: 2/6 × 6/6 =
12/36. If we have not a 12 and a 36 wheel, we may multiply the fraction
by any other number, as, say, 8; thus: 2/6 × 8/8 = 16/48 giving us a 16
wheel for D, Fig. 1236, and a 48 wheel for the lead screw.
The second notable feature in this rule is that it applies just the same
whether the pitch to be cut is coarser or finer than the lead screw;
thus: Suppose the pitch of the lead screw is 4, and we want to cut 2. We
put these figures down as before 4/2, and proceed to multiply, say, by
8; thus: 4/2 × 8/8 = 32/16, giving a 32 and a 16 as the necessary
wheels.
The third feature is, that no matter whether the pitch to be cut is
coarser or finer than the lead screw, the wheels go on the lathe just as
they stand in the fraction; the top figure goes on top in the lathe, as,
for example, on the driving stud, and the bottom figures of the fraction
are for the teeth in the wheel that goes on the bottom of the lathe or
on the lead screw. No rule can possibly be simpler than this. Suppose
now that the pitch of the lead screw is 4 per inch and we want to cut
1-1/2 per inch. As the required pitch is expressed in half inches, we
express the pitch of the lead in half inches, and employ the rule
precisely as before. Thus, in four there are eight halves; hence, we put
down 8 as the numerator, and in 1-1/2 there are three halves, so we put
down 3 and get the fraction 8/3. This will multiply by any number, as,
say, 6; thus: (8/3) × (6/6) = (48/18), giving us 48 teeth for the wheel
D in Fig. 1236, and 18 for the lead screw wheel S.
In a lathe geared as in Fig. 1235 the top wheel D could not be readily
changed, and it would be more convenient to change the lead screw wheel
S only. Suppose, then, that the lead screw pitch is 2 per inch, and we
want to cut 8. Putting down the fraction as before, we have 2/8, and to
get the wheel S for the lead screw we may multiply the number of teeth
in D by 8 and divide it by 2; thus: 32 × 8 = 256, and 256 ÷ 2 = 128;
hence all we have to do is to put on the lead screw a wheel having 128
teeth. But suppose the pitch to be cut is 4-1/4, the pitch of the lead
screw being 2. Then we put both numbers into quarters, thus: In 2 there
are 8 quarters, and in 4-1/4 there are 17 quarters; hence the fraction
is 8/17. If now we multiply both terms of this 8/17 by 4 we get 32/68,
and all we have to do is to put on the lead screw a wheel having 68
teeth.
When we have to deal with a lathe compounded as in Fig. 1238, in which
the combination can be altered in two places--that is, between A and C
and between D and S--the wheel A remaining fixed, and the pitch of the
lead screw is 2 per inch, and it is required to cut 8 per inch--this
gives us the fraction 2/8, which is at once the proportion that must
exist between the revolutions of the wheel A and the wheel S. But in
this case the fraction gives us the number of revolutions that wheel S
must make while the wheel A is making two revolutions, and it is more
convenient to obtain the number that S requires to make while A is
making one revolution, which we may do by simply dividing the pitch
required to be cut by the pitch of the lead screw, as follows: Pitch of
thread required, 8; pitch of lead screw, 2; 8 ÷ 2 = 4 = the revolutions
S must make while A makes one. We have then to reduce the revolutions
four times, which we may do by putting on at C a wheel with twice as
many teeth in it as there are in A, and as A has 32, therefore C must
have 64 teeth. When we come to the second pair of wheels, D and S, we
may put any wheel we like in place of D, providing we put on S a wheel
having twice as many.
But suppose we require to cut a fractional pitch, as, say, 4-1/8 per
inch, the pitch of lead screw being 2, all we have to do is to put the
pitch of the lead screw into eighths, and also put the number of teeth
in A into eighths; thus: In two there are 16 eighths, and in the pitch
required there are 33 eighths; hence for the pitch of the lead screw we
use the 16, and for the thread required we use the 33, and proceed as
before; thus:
Pitch of thread Pitch of lead
required. screw.
33 ÷ 16 = 2-1/16 = the revolution which A
must make while wheel B
makes one revolution.
The simplest method of doing this would be to put on at C a wheel having
2-1/16 times as many teeth as there are in A. Suppose then that A has 32
teeth, and one sixteenth of 32 = 2, because 32 ÷ 16 = 2. Then twice 32
is 64, and if we add the 2 to this we get 66; hence, if we give wheel C
66 teeth, we have reduced the motion the 2-1/16 times, and we may put on
D and S wheels having an equal number of teeth. Or we may put on a wheel
at C having the same number as A has, and then put on any two wheels at
D and C, so long as that at S has 2-1/16 times as many teeth as that at
D.
Again, suppose that the pitch of a lead screw is 4 threads per inch, and
that it be required to find what wheels to use to cut a thread of 11/16
inch pitch, that is to say, a thread that measures 11/16 inch from one
thread to the other, and not a pitch of 11/16 threads per inch: First we
must bring the pitch of the lead screw and the pitch to be cut to the
same terms, and as the pitch to be cut is expressed in sixteenths we
must bring the lead screw pitch to sixteenths also. Thus, in an inch of
the length of the lead screw there are 16 sixteenths, and in this inch
there are 4 threads; hence each thread is 4/16 pitch, because 16 ÷ 4 =
4. Our pitch of lead screw expressed in sixteenths is, therefore, 4, and
as the pitch to be cut is 11/16 it is expressed in sixteenths by 11;
hence we have the fraction 4/11, which is the proportion that must exist
between the wheels, or in other words, while the lathe spindle (or what
is the same thing, the work) makes 4 revolutions the lead screw must
make 11.
Suppose the lathe to be single geared, and not compounded, and we
multiply this fraction and get--
4 × 4 16 = wheel to go on lead screw.
-- - = --
11 × 4 44 = " " stud or mandrel.
4 × 5 20 = wheel to go on lead screw.
Or, -- - = --
11 × 5 55 = " " stud or mandrel.
4 × 6 24 = wheel to go on lead screw.
Or, -- - = --
11 × 6 66 = " " stud or mandrel.
But suppose the lathe to be compounded as in Fig. 1235, and we may
arrange the wheels in several ways, and in order to make the problem
more practical, we may suppose the lathe to have wheels with the
following numbers of teeth, 18, 24, 36, 36, 48, 60, 66, 72, 84, 90, 96,
102, 108, and 132.
[Illustration: Fig. 1239.]
Here we have two wheels having each 36 teeth; hence we may place one of
them on the lathe spindle and one on the lead screw, as in Fig. 1239;
and putting down the pitch of the lead screw, expressed in sixteenths as
before, and beneath it the thread to cut also in sixteenths, we have:
4 × 6 24 = wheel to be driven by lathe spindle,
-- - = --
11 × 6 66 = " to drive lead screw wheel;
the arrangement of the wheels being shown in Fig. 1239.
We may prove the correctness of this arrangement as follows: The 36
teeth on the lathe spindle will in a revolution cause the 24 wheel to
make 1-1/2 revolutions, because there are one and a half times as many
teeth in the one wheel as there are in the other; thus: 36 ÷ 24 = 1-1/2.
Now, while the 24 wheel makes 1-1/2, the 66 will also make 1-1/2,
because they are both on the same sleeve and revolve together. In
revolving 1-1/2 times the 66 will cause the 36 on the lead screw to make
2-3/4 turns, because 99 ÷ 36 = 2-3/4 (or expressed in decimals 2.75),
and it thus appears that while the lathe spindle makes one turn, the
lead screw will make 2-3/4 turns.
Now, the proportion between 1 and 2-3/4 is the same as that existing
between the pitch of the lead screw and the pitch of the thread we want
to cut, both being expressed in sixteenths; thus:
Pitch of lead screw in sixteenths 4 }
}, and 11 ÷ 4 = 2-3/4;
" to be cut in sixteenths 11 }
that is to say, 11 is 2-3/4 times 4.
Suppose it is required, however, to find what thread a set of gears
already on the lathe will cut, and we have the following rule:
_Rule._--Take either of the driven wheels and divide its number of teeth
by the number of teeth in the wheel that drives it, then multiply by the
number of teeth in the other driving wheel, and divide by the teeth in
the last driven wheel. Then multiply by the pitch of the lead screw.
[Illustration: Fig. 1240.]
_Example._--In Fig. 1240 are a set of change wheels, the first pair of
which has a driving wheel having 36 teeth, and a driven wheel having 18
teeth. The second pair has a driving wheel of 66 teeth, and a driven
wheel of 48.
Let us begin with the first pair and we have 36 ÷ 18 = 2, and this
multiplied by 66 is 132. Then 132 ÷ 48 = 2.75, and 2.75 multiplied by 4
is 11, which is the pitch of thread that will be cut. Now, whether this
11 will be eleven threads per inch, or as in our previous examples a
pitch of 11/16 inch from one thread to another or to the next one,
depends upon what the pitch of the lead screw was measured in.
[Illustration: Fig. 1241.]
If it is a pitch of 4 threads per inch, the wheels will cut a thread of
11 per inch, while if it were a thread of 4/16 pitch, the thread cut
will be 11/16 pitch.
Let us now work out the same gears beginning from the lead screw pair,
and we have as follows:
Number of teeth in driver is 66, which divided by the number in the
driven, 48, gives 1.375. This multiplied by the number of teeth in the
driver of the other pair = 36 gives 49.5, which divided by the number of
teeth in the driven wheel of the first pair gives 2.75, which multiplied
by the pitch of the lead screw 4 gives 11 as before.
Taking now the second example as in Fig. 1240, and beginning from the
first pair of gears, we have, according to the rule, 36 ÷ 48 × 66 ÷ 18 ×
4 = 11 = pitch the gears will cut; or proceeding from the second pair of
gears, we have by the rule, 66 ÷ 18 × 36 ÷ 48 × 4 = 11 = the pitch the
gears will cut. It is not often, however, that it is required to
determine what threads the wheels already on a lathe will cut, the
problem usually being to find the wheels to cut some required pitch. But
it may be pointed out that when the problem is to find the result
produced by a given set of wheels, it is simpler to begin the
calculation from the wheel already on the lathe spindle, rather than
beginning with that on the lead screw, because in that case we begin at
the first wheel and calculate the successive ones in the same order in
which we find them on the lathe, instead of having to take the last pair
in their reverse order, as has been done in the examples, when we began
at the wheel on the lead screw, which we have termed the second pair.
The wheels necessary to cut a left-hand thread are obviously the same as
those for a right-hand one having an equal pitch; all the alteration
that is necessary is to employ an additional intermediate wheel, as at I
in Fig. 1241, which will reverse the direction of motion of the lead
screw. For a lathe such as shown in Fig. 1235, this intermediate wheel
may be interposed between wheels D and I or between I and S. In Fig.
1236, it may be placed between D and I or between I and S, and in Fig.
1238 it may be placed between A and C or between D and S.
[Illustration: Fig. 1242.]
Here it may be well to add instructions as to how to arrange the change
wheels to cut threads in terms of the French centimètre. Thus, an inch
equals 254/100 of a centimètre, or, in other words, 1 inch bears the
same proportion to a centimètre as 254 does to 100, and we may take the
fraction 254/100 and reduce it by any number that will divide both terms
of the fraction without leaving a remainder; thus, 254/100 ÷ 2 = 127/50.
If, then, we take a pair of wheels having respectively 127 and 50 teeth,
they will form a compound pair that if placed as in Fig. 1242 will
enable the cutting of threads in terms of the centimètre instead of in
terms of the inch.
Thus, for example, to cut 6 threads to the centimètre, we use the same
change wheels on the stud and on the lead screw that would be used to
cut 6 threads to the inch, and so on throughout all other pitches.
CUTTING DOUBLE OR OTHER MULTIPLE THREADS IN THE LATHE.--In cutting a
double thread the change wheels are obviously arranged for the pitch of
the thread, and one thread, as A in Fig. 251 is cut first, and the
other, B, afterwards. In order to insure that B shall be exactly midway
between A, the following method is pursued. Suppose the pitch of the
lead screw is 4 threads per inch, and that we require to cut a double
thread, whose actual pitch is 8 per inch, and apparent pitch 16 per
inch, then the lead screw requires to make half a turn to one turn of
the lathe spindle; or what is the same thing, the lathe spindle must
make two turns to one of the lead screw, hence the gears will be two to
one, and in a single-geared lathe we may put on a 36 and a 72, as in
Fig. 1243, in which the intermediate wheels are omitted, as they do not
affect the case. With these wheels we cut a thread of 8 per inch and
then, leaving the lead screw nut still engaged with the lead screw and
the tool still in position to cut the thread already formed, we make on
the change wheels a mark as at S T, and after taking off the driving
gear we make a mark at space _u_, which is 18 teeth distant from S, or
half-way around the wheel. We then pull the lathe around half a turn and
put the driving gear on again with the space _u_ engaged with the tooth
T, and the lathe will cut the second thread exactly intermediate to the
first one. If it were three threads that we require to cut, we should
after the driving gear was taken off give the lathe one-third a
revolution, and put it back again, engaging the twelfth space from S
with tooth T, because one-third of 36 is 12.
[Illustration: Fig. 1243.]
It is obviously necessary, in cutting multiple threads in this way, to
so select the change wheels that the driving gear contains a number of
teeth that is divisible without leaving a remainder by the thread to be
cut: thus, for a double thread the teeth must be divisible by two, hence
a 24, 30, 34, 36, or any even number of teeth will do. For a triple
thread the number of teeth in the driving gear must be divisible by 3,
and so on.
But suppose the driving gear is fast upon the lathe spindle and cannot
be taken off, and we may then change the position of the lead screw gear
to accomplish the same object as moving the lathe spindle. Thus for a
double thread we would require to remove the driving gear as before, and
then pull round the lead screw so that the eighteenth tooth from T would
engage with space S, which is obviously the same thing as moving the
driving gear round 18 teeth.
In short work of small diameter the tool will retain its sharpness so
long, that one tool will rough out and finish a number of pieces without
requiring regrinding, and in this case the finishing cuts can be set by
noting the position of the feed screw handle when the first piece is
finished to size and the tool is touching the work, so that it may be
brought to the same position in taking finishing cuts on the succeeding
pieces; but the calipers should nevertheless be used, being applied to
the threads as in Figs. 1244 and 1245, which is the best method when
there is a standard to set the calipers by.
[Illustration: Fig. 1244.]
After a threading tool has carried its cut along the required length of
the work, the carriage must be traversed back, so that the second cut
may be started. In short work the overhead cross belt that runs the
lathe backwards is sufficiently convenient and rapid for this purpose,
but in long screws much time would be lost in waiting while the carriage
runs back. In the Ames lathe there is a device that enables the carriage
to be traversed back by hand, and the feed nut to be engaged without
danger of cutting a double thread, or of the tool coursing to one side
of the proper thread groove, which is a great convenience.
The construction of this device is shown in Fig. 574. In lathes not
having a device for this purpose, the workman makes a chalk mark on the
tail of the work driver, and another on the top of the lead screw gear,
and by always moving the carriage back to the same point on the lathe
bed, and engaging the lead screw nut when these two chalk marks are at
the top of their paths of revolution, the tool will fall into its
correct position and there will be no danger of cutting a double thread.
[Illustration: Fig. 1245.]
In cutting [V] threads of very coarse pitch it will save time, if the
thread is a round top and bottom one, to use a single-pointed slide rest
tool, and cut up the thread to nearly the finished depth, leaving just
sufficient metal for the chaser to finish the thread.
In using the single-pointed tool _on_ the roughing cuts of very coarse
pitches, it is an advantage to move the tool laterally a trifle, so that
it will cut on one side or edge only. This prevents excessive tool
spring, and avoids tool breakage.
This lateral movement should be sufficient to let the follower side or
edge of the tool just escape the side of the thread, and all the cut be
taken by the leading side or edge of the tool.
This is necessary because the tool will not cut so steadily on the
follower as on the leading cutting edge, for the reason that the
pressure of the cut assists to keep the feed screw nut against the sides
of the feed screw thread, taking up the lost motion between them,
whereas the pressure of a cut taken on the follower side of the thread
tends to force the thread of the feed nut away from the sides of the
feed screw thread and into the space between the nut thread afforded by
the lost motion, and as a result the slide rest will move forward when
the tool edges meet exceptionally hard places or spots in the metal of
the work, while in any event the tool will not operate so steadily and
smoothly.
If the screw is a long one, the cutting should be done with a liberal
supply of oil or water to keep it cool, otherwise the contraction of the
metal in cooling will leave the thread finer than it was when cut. This
is of special importance where accuracy of pitch is requisite.
[Illustration: Fig. 1246.]
In cutting a taper thread in a lathe, it is preferable that the taper be
given by setting over the lathe tailstock, rather than by operating the
cross slider from a taper-turning attachment, because the latter causes
the thread to be cut of improper pitch. Thus, in Fig. 1246 is a piece of
work between the lathe centres, and it will be readily seen that
supposing the lathe to be geared to cut, say, 10 threads per inch, and
the length A of the work to be 2 inches long, when the tool has
traversed the distance A it will have cut 20 threads, and it will have
passed along the whole length of the side B of the work and have cut 20
threads upon it, but since the length of line B is greater than that of
A, the pitch of the thread cut will be coarser than that due to the
change wheels. The amount of the error is shown by the arc C, which is
struck from D as a centre; hence from C to E is the total amount of
error of thread pitch.
[Illustration: Fig. 1247.]
But if the lathe tailstock sets over as in Fig. 1247, then the pitch of
the thread will be cut correct, because the length of B will equal the
length of tool traverse; hence at each work revolution the tool would
advance one-twentieth of the length of the surface on which the thread
is cut, which is correct for the conditions.
[Illustration: _VOL. I._ =METHODS OF BALL TURNING.= _PLATE XIII._
Fig. 1248.
Fig. 1249.
Fig. 1250.
Fig. 1251.
Fig. 1252.
Fig. 1253.
Fig. 1254.
Fig. 1255.]
CHAPTER XIII.--EXAMPLES IN LATHE WORK.
BALL TURNING.--One of the best methods of turning balls of the softer
materials, such as wood, bone, or ivory, is shown in Figs. 1248 and
1249, in which are shown a blank piece of material and a tubular saw,
each revolving in the direction denoted by the respective arrows. The
saw is fed into the work and performs the job, cutting the ball
completely off. In this case the saw requires to be revolved quicker
than the work--indeed, as quickly as the nature of the material will
permit, the revolving of the work serving to help the feed. Of course,
the teeth of such a saw require very accurate sharpening if smooth work
is to be produced, but the process is so quickly performed that it will
pay to do whatever smoothing and polishing may be required at a separate
operation. This method of ball cutting undoubtedly gave rise to the idea
of using a single tooth, as in Fig. 1250. But when a single tooth is
employed the work must revolve at the proper cutting speed, while the
tooth simply advances to the feed. If the work was cut from a
cylindrical blank the cutter would require to be advanced toward the
work axis to put on a cut and then revolved to carry that cut over the
work, when another cut may be put on, and so on until the work is
completed. The diameter of ball that can be cut by one cutter is here
obviously confined to that of the bore of the cutter, since it is the
inside edge of the cutter that does the finishing.
This naturally suggests the employment of a single-pointed and removable
tool, such as in Fig. 1251, which can be set to turn the required
diameter of ball, and readily resharpened. To preserve the tool for the
finishing cut several of such tools and holders may be carried in a
revolving head provided to the lathe or machine, as the case may be. In
any event, however, a single-pointed tool will not give the smoothness
and polish of the ball cutter shown in Fig. 1252, which produces a
surface like a mirror. It consists of a hardened steel tube C, whose
bore is ground cylindrically true after it has been hardened. The ball B
is driven in a chuck composed of equal parts of tin and lead, and the
cutter is forced to the ball by hand. The ball requires to revolve at a
quick speed (say 100 feet per minute for composition brass), while the
cutter is slowly revolved.
A simple attachment for ball turning in an ordinary lathe is shown in
Fig. 1253. It consists of a base A, carrying a plate B, which is pivoted
in A; has worm-wheel teeth provided upon its circumference and a
slideway at S, upon which slides a tool rest R, operated by the
feed-screw handle H. The cut is put on by operating H, and the feed
carried around by means of the screw at W. The base plate A may be made
suitable to bolt on the tool rest, or clamped on in place of the tool,
as the circumstances may permit; or in some cases it might be provided
with a stem to fit in place of the dead centre. For boring the seats for
balls or other curved internal surfaces the device shown in Fig. 1254
may be used. It consists of a stem or socket S, fitting to the dead
spindle in place of the dead centre, and upon which is pivoted a wheel
W, carrying a tool T. R is a rack-bar that may be held in the lathe tool
post and fed in to revolve wheel W and feed the tool to its cut. At P is
a pin to maintain the rack in gear with the wheel. Obviously, a
set-screw may be placed to bear against the end of the tool to move it
endwise and put on the cut. An equivalent device is shown in Fig. 1255,
in which the tool is pivoted direct into the stem and moved by a bar B,
held in the tool post. The cut is here put on by operating the tail
spindle, a plan that may also be used in the device shown in Fig. 1254.
The pins P upon the bar are for moving or feeding the tool to its cut.
It is obvious that in all these cases the point of the tool must be out
of true vertically with the axis of the work.
[Illustration: Fig. 1256.]
[Illustration: Fig. 1257.]
In turning metal balls by hand it is best to cast them with a stem at
each end, as in Fig. 1257.
[Illustration: Fig. 1258.]
[Illustration: Fig. 1259.]
To rough them out to shape, a gauge or template, such as in Fig. 1256,
is used, being about 1/32 inch thick, which envelops about one-sixth of
the ball's circumference. After the ball is roughed out as near as may
be to the gauge, the stems may be nicked in, as in Fig. 1257, and broken
off, the remaining bits, A, B, being carefully filed down to the
template. The balls are then finished by chucking them in a chuck such
as shown in Fig. 1258,[19] and a narrow band, shown in black in the
figure, is scraped, bringing the ball to the proper diameter. The ball
is then reversed in the chuck, as in Fig. 1259, and scraped by hand
until the turning marks cross those denoted by the black band. The ball
is then reversed, so that the remaining part of the black band that is
within the chuck in Fig. 1259 may be scraped down, and when by
successive chuckings of this kind the lightest of scrape marks cross and
recross each other when the ball is reversed, it may be finished by the
ball cutter, applied as shown in Fig. 1252, and finally ground to its
seat with the red-burnt sand from the foundry, which is better than
flour emery or other coarser cutting grinding material.
[19] From _The American Machinist_.
[Illustration: Fig. 1260.]
[Illustration: Fig. 1261.]
CUTTING CAMS IN THE LATHE.--Fig. 1260 represents an end view of cam to
be produced, having four depressions alike in form and depth, and
arranged equidistant round the circumference, which is concentric to the
central bore. The body of a cam is first turned up true, and one of the
depressions is filed in it to the required form and curvature. On its
end face there is then drilled the four holes, A, B, C, D, Fig. 1261,
these being equidistant from the bore E. A similar piece is then turned
up in the lathe, and in its end is fitted a pin of a diameter to fit the
holes A, B, &c., it being an equal distance from bore E. These two
pieces are then placed together, or rather side by side, on an arbor or
mandrel, with the pin of the one fitting into one of the holes, as A.
Two tool posts are then placed in position, one carrying a dull-pointed
tool or tracer, and the other a cutting tool. The dull-pointed tracer is
set to bear against the cam shown in Fig. 1262, while the cutting tool
is set to take a cut off the blank cam piece. The cross feed screw of
the lathe is disengaged, and a weight W, Fig. 1262, attached to the
slider to pull the tracer into contact with the cam F. As a result, the
slide rest is caused to advance to and recede from the line of lathe
centres when the cam depression passes the tracer point, the weight W
maintaining contact between the two. Successive cuts are taken until the
tool cuts a depression of the required depth. To produce a second cam
groove, the piece is moved on the mandrel so that the pin will fall into
a second hole (as, say, B, Fig. 1261), when, by a repetition of the
lathe operation, another groove is turned. The whole four grooves being
produced by the same means, they must necessarily be alike in form, the
depths being equal, provided a finishing cut were taken over each
without moving the cutting tool.
[Illustration: Fig. 1263.]
It will be observed that this can be done in any lathe having a slide
rest, and that the grooves cut in one piece will be an exact duplicate
of that in the other, or guide groove, save such variation as may occur
from the thickness of the tracer point, which may be allowed for in
forming the guide or originating groove. From the wear, however, of the
tracer point, and from having to move the cutting tool to take
successive depths of cut, this method would be undesirable for
continuous use, though it would serve excellently for producing a single
cam. An arrangement for continuous use is shown in Fig. 1263, applied to
a lathe having a feed spindle at its back, with a cam G upon it. This
cam G may be supposed to have been produced by the method already
described. A tracer point H, or a small roller, may be attached to the
end of the slide-rest and held against G by the weight W, which may be
within the lathe shears if they have no cross girts, as in the case of
weighted lathes. The slide-rest may be arranged to have an end motion
slightly exceeding the motion, caused by the cam, of the tracer H.
Change gears may then be used to cause the cam G to make one rotation
per lathe rotation, cutting four recesses in the work; or by varying the
rotations of G per lathe rotation, the number of recesses cut by the
tool T may be varied. Successive depths of cut may then be put on by
operating the feed screw in the ordinary manner. In this arrangement the
depth and form of groove cut upon the work will correspond to the form
of groove upon the cam-roller G; or each groove upon G being of a
different character, those cut on the work will correspond. The wear on
the cross slide will, in this case, be considerable, however, in
consequence of the continuous motion of the tool-carrying slider, and to
prevent this another arrangement may be used, it being shown in Fig.
1264 as applied to a weighted and elevating slide rest. The elevating
part of the slide rest is here pivoted to the lathe carriage at I, the
weight W preventing play (from the wear) at I. A bracket J is shown fast
to the elevating slide of the rest, carrying a roller meeting the
actuating cam G. In this arrangement the cut may be put on by the feed
screw traversing the slider in the usual manner, or the elevating screw
K may be operated, causing the roller at the end of J to gradually
descend as each cut is put on into more continuous contact with G as the
latter rotates. The form of groove cut by the tool does not, in this
case, correspond to the form on G, because the tool lifts and falls in
the arc of a circle of which pivot I is the centre of motion, and its
radius from I being less than the radius of G, its motion is less. But
in addition to this the direction of its motion is not that of
advancing and receding directly toward and away from the line of lathe
centres, and the cam action is reduced by both these causes.
[Illustration: Fig. 1264.]
[Illustration: Fig. 1265.]
The location of pivot I is of considerable importance, since the nearer
it is to the line of centres the less the action of the cam G is reduced
upon the work. As this is not at first sight apparent, a few words may
be said in explanation of it. It is obvious that the farther the pivot I
is from the tool point the greater will be the amount of motion of the
tool point, but this motion is not in a direction to produce the
greatest amount of effect upon the work, as is demonstrated in Fig.
1265; referring to which, suppose line A B C to represent a lever
pivoted at B, and that end A be lifted so that the lever assumes the
position denoted by the dotted lines D and E, then the end of C will
have moved from circle F to circle G, as denoted by arc H; arm C of the
lever being one-half the length of arm A B, and from circle F to circle
G, measured along the line H, being one-half the distance between A and
the end of the line D, the difference in the diameters of circles F and
G will represent the effect of the cam motion on the tool under these
conditions. Now, suppose A J is a lever pivoted at K, and that end A is
raised to the dotted line D, then arm J, being one-half the length of A
K, will move half as much as end A, and will assume the position denoted
by dotted line L, and the difference in the diameter of circles F and M
will represent the cam motion upon the tool motion under these
conditions. From this it appears that the more nearly vertical beneath
the tool point the pivoted point is, the greater the effect produced by
a given amount of cam motion. On this account, as well as on account of
the direction of motion, the shape of the actuating cam may be more
nearly that of the form required to be produced in proportion as the
pivoted centre falls directly beneath the tool point. But, on the other
hand, the wear of the pivot, if directly beneath the tool point, would
cause more unsteadiness to the tool; hence it is desirable that it be
somewhere between points K and B, the location being so made that (B
representing the pivoted point of the rest) the line B C forms an angle
of 50° with the line B A. It is obvious that when the work is to be
cam-grooved on a radial face the pivoted design is unsuitable, and
either that in Fig. 1262 or 1263 is suitable.
Similar cam motions may be given to the cross feed of a lathe: thus, the
Lane and Bodley Company of Cincinnati, Ohio, employ the following method
for turning the spherical surfaces of their swiveling bearings for line
shafting.
[Illustration: Fig. 1266.]
[Illustration: Fig. 1267.]
The half bearing B, Fig. 1266, is chucked upon a half-round mandrel, C
being the spherical surface to be turned, a sectional view of C being
shown in Fig. 1267.
[Illustration: Fig. 1268.]
In Fig. 1268 is a plan view of the chuck, work, and lathe rest; D is a
former attachment bolted to the slider of the rest, and E a rod passing
through the lathe block. The weight W, Fig. 1269, is suspended by a cord
attached to the slide rest so as to keep the former D firmly against the
end of E.
As the slider is operated, the rest is caused by E to slide upon the
lathe bed, and the cutting tool forms a spherical curve corresponding to
the curve on the former D. The weight W of course lifts or falls
according to the direction of motion of the slider.
The cut is put on by operating handle G, thus causing E to advance.
The weight W causes any play between the slider and the cross slide to
be taken up in the same direction as the tool pressure would take it up,
hence the cut taken is a very smooth one. The half-round mandrel being
fixed to the lathe face plate will remain true, obviating the liability
of the centre of the spherical surface being out of line with the axis
of the bearing-bore.
A method of producing cams without a lathe especially adopted for the
purpose is shown in Figs. 1270 and 1272, which are extracted from
_Mechanics_. The apparatus consists of a frame E, which fits on the
cross ways of an ordinary lathe. The cross-feed screw is removed, so
that E may slide backwards and forthwards freely. The frame E carries
the worm-wheel A and the worm-gear B, which is operated by the crank F.
The cam C to be cut is bolted on to the face of the worm-wheel, which
faces the headstock of the lathe. The form for the cam, which may be
made of sheet steel, or thicker material, according to the wear it is to
have, is fastened to the face of the cam.
[Illustration: Fig. 1269.]
[Illustration: Fig. 1270.]
[Illustration: Fig. 1271.]
[Illustration: Fig. 1272.]
A cutter, like a fluted reamer, such as is shown in Fig. 1271, is then
put in the live centre of the lathe. Care must be taken that the shank
is the same size as the fluted part, and that the flutes are not cut up
farther than the thickness that the cam grooves are to be cut in the
blank. Having attached a cord to the back of E, pass it over a pulley H,
fastened on the rear of the lathe, and hang on a weight G. Fig. 1272 is
an edge view of the device, looking from the back of the lathe. It shows
the worm A, blank C, and former D all bolted together, while the cutter
I is ready in its place on a line with the centre of the worm, and just
at back of the former. The machine is operated by turning the crank F,
which causes the worm A, also C and D, to revolve slowly, while the
cutter I has a rather rapid rotation. The weight causes the cutter to be
held firmly against the form F, and to follow its curves in and out.
[Illustration: Fig. 1273.]
[Illustration: Fig. 1274.]
[Illustration: Fig. 1275.]
KNURLING OR MILLING TOOLS.--In Fig. 1273 is shown the method of using
the knurling tool in the slide rest of a lathe. It represents the tool
at work producing the indentations which are employed to increase the
hand grip of screw heads, or of cylindrical bodies, as shown in the
figure by the crossed lines. Fig. 1274 is an end view of the tool, which
consists of a holder to go in the slide rest tool post, and carrying two
small hardened steel wheels, each of which is serrated all round its
circumference, the serrations of one being in an opposite direction to
those of the other. The method of using the tool is shown in Fig. 1275,
where it is represented operating upon a cylindrical piece of work. If
the knurling is to be carried along the work to a greater length than
the thickness of the knurl wheels, the lathe slide rest is slowly
traversed the same as for a cutting tool.
As the knurling tool requires to be forced against the work with
considerable pressure, there is induced a strain tending to force the
tool directly away from the work, as denoted by the arrow in Fig. 1276,
and this, in a weighted lathe, acts to raise the lathe carriage and
weight. This is avoided by setting the tool at an angle, as in Fig.
1277, so that the direction of strain is below and not above the pivot
on which the cross slide rests. This is accomplished by pivoting the
piece carrying the wheels to the main body of the stem, as shown in Fig.
1277.
For use by hand the knurling or milling tool is fitted to a holder and
handle, as in Fig. 1278, and the hand tool rest is placed some little
distance from the work so that the knurl can pass over it, and below the
centre of the work.
Knurls for screw heads are made convex, concave, or parallel, to fit the
heads of the screws, and may be indented with various patterns.
[Illustration: Fig. 1276.]
[Illustration: Fig. 1277.]
[Illustration: Fig. 1278.]
WINDING SPIRAL SPRINGS IN THE LATHE.--Spiral springs whose coils are
close, and which therefore act on distension only, may be wound by
simply starting the first coil true, and keeping the wire as it winds on
the mandrel close to that already wound thereon.
[Illustration: Fig. 1279.]
Spiral springs with open coils may be best wound as shown in Fig. 1279,
in which is shown a mandrel held between the lathe centres and driven by
a dog that also grips one end of the wire W, of which the spring is to
be made. The wire is passed through two blocks B, which, by means of the
set-screw in the lathe tool post, place a friction on it sufficient to
place it under a slight tension which keeps it straight. The change
gears of the lathe are arranged as they would be to cut a screw of a
pitch equal to the thickness of the wire added to the space there is to
be between the coils of the spring. The first turn of the lathe should
wind a coil straight round the mandrel when the self-acting feed motion
is put in operation and the winding proceeds, and when the spring is
sufficiently long, the feed motion is disconnected, and the last coil is
allowed to wind straight round the mandrel, thus giving each end of the
spring a flat or level end.
If the wire is of brass it will be necessary to close it upon the
mandrel with blows from a lead mallet to prevent it from uncoiling on
the mandrel when the end is released, which it will do to some extent in
any event.
[Illustration: Fig. 1280.]
If it is of steel it may be necessary to heat the coil red-hot to
prevent its uncoiling, and in the coiling it will, if of stout wire,
require to be bent against the mandrel during winding with a piece of
steel placed in the tool post, as in Fig. 1280, in which A represents
the mandrel, B the spring wire, and D the lathe tool post.
[Illustration: Fig. 1281.]
[Illustration: Fig. 1282.]
In the absence of a lathe with a self-acting feed motion, the mandrel
may have a spiral groove in it and the piece of steel or other hard
metal shown in figure must be used, the feed screw of the slide rest
being removed so that the wire can feed itself along as the mandrel
rotates. Near one end of the mandrel a small hole is drilled through,
there being sufficient space between the hole and the end of the mandrel
to admit of a loose washer being placed thereon; the bore of this washer
requires to be rather larger in diameter than the outside diameter of
the spring, when wound upon the mandrel, and also requires to be
provided with a keyway and key. The washer D (Fig. 1281), is slipped
over the mandrel, the end of the wire C is inserted in the hole B and
the spring being wound, the washer is passed up to the end, and the key
driven home as in Fig. 1282; when the wire is cut off and the mandrel
may be taken from the lathe with the spring closely wound round it to be
hammered if of brass, and heated if of steel. The hammering should be
done over the whole circumference, not promiscuously, but beginning at
one end and following along the wire with the blows delivered not more
than 1/4 of an inch apart; for unless we do this we cannot maintain any
definite relation between the size of the mandrel and the size of the
spring.
When a grooved mandrel is used, its diameter should be slightly less
than the required diameter of spring, as when released the coils expand
in diameter.
[Illustration: Fig. 1283.]
If it is not essential that the coils be exactly true, take a plain
mandrel, such as shown in Fig. 1283, and a hook, such as shown at A,
fasten the end of the wire either round the lathe dog, or in a hole in
the mandrel as before, and wind one full coil of the spring upon the
mandrel, then force this coil open until the hook end of A can be
inserted between it and over the mandrel, the other end hanging down
between the lathe shears, which will prevent it from rotating, starting
the lathe while holding the unwound end of the wire against the hook
with a slight pressure, and the winding will proceed as shown in the
figure, the thickness of A regulating the width apart of the coils. It
is obvious that if the coil is to be a right-handed one and is started
at the carrier end, the lathe must revolve backwards.
Spiral springs for railroad cars are wound while red-hot in special
spring-winding lathes and with special appliances.
TOOLS FOR HAND TURNING.--Many of the tools formerly used in hand turning
have become entirely obsolete, because they were suitable for larger
work than any to which hand turning is now applied; hence, reference to
such tools will be omitted, and only such hand tools will be treated of
as are applicable to foot lathes and wood turning, their purposes being
those for which hand tools are now used.
To the learner, practice with hand tools is especially advantageous,
inasmuch as the strain due to the cut is felt by the operator; hence,
the effects of alterations in the shape of the tools, its height or
position with relation to the work, and also the resistance of the metal
to severance, are more readily understood and appreciated than is the
case where the tool is held in a slide rest or other mechanical device.
If under certain conditions the hand tool does not operate to advantage,
these conditions may be varied by a simple movement of the hands,
altering the height of the tool to the work, the angle of the cutting
edges to the work, or the rate of feed, as the case may be, and
instantly perceiving the effects; whereas with tools held by mechanical
means, such alterations would involve the expenditure of considerable
time in loosening, packing, and fastening the tool, and adjusting it to
position.
Small work that is turned by hand may, under exceptionally expert
manipulation, be made as interchangeable and more accurate in dimensions
than it could be turned by tools operated in special machines. That is
to say, it is possible to turn by hand a number of similar small pieces
that will be when finished as true, more nearly corresponding in
dimensions, and have a finer finish, than it is practicable to obtain
with tools operated or guided by parts of a machine. This occurs because
of the wear of the cutting tools, which upon small work may be
compensated for in the hand manipulation in cases where it could not be
in machine manipulation. But with ordinary skill, and under ordinary
conditions, the liability to error in hand work induces greater
variation in the work than is due to the wear of the tool cutting edges
in special machine work; hence, the practical result is that work made
by special machinery is more uniform and true to size and shape than
that made by hand, while also the quantity turned out by special
machines is very much greater.
[Illustration: Fig. 1284.]
The most desirable form of tool for taking a heavy hand cut is the heel
tool shown in Fig. 1284, which, it may be remarked, is at present but
little used on account of the greater expedition of tools held in slide
rests. It consists of a steel bar, about 3/8 or 1/2 inch square, forged
with a heel at F, so that it may firmly grip the hand rest, and having a
cutting edge at E. This bar is about 8 inches long, and is held in a
groove in a wooden stock by a strap passing over it, and having a stem
which passes down through the handle D, in which is fixed a nut, so that
by screwing up or unscrewing D the bar is gripped or released, as the
case may be, in a groove in the stock. In use, the end H of the stock is
held firmly against the operator's shoulder, the left hand grasps the
stock and presses the tool firmly down upon the face of the hand rest,
while with the right the handle D is moved laterally, causing the tool
to move to its cut. The depth of the cut is put on and regulated by
elevating the end H of the stock. The heel F is placed close enough to
the work to keep E F nearly vertical, for if it inclines too much in any
direction the tool gets beyond the operator's control. The position of
the heel F is moved from time to time along the hand rest to carry the
cut along.
A cut of 1/8 inch deep, that is, reducing the work diameter 1/4 inch,
may readily be taken with this tool, which, however, requires skilful
handling to prevent it from digging into the work.
The shorter the distance from the face E to the heel F the more easily
the tool can be controlled; hence, as F serves simply as a sharp and
gripping fulcrum it need not project much from the body of the steel;
indeed, in many cases it is omitted altogether, the bottom of the steel
bar being slightly hollowed out instead. No oil or water is required
with the heel tool.
The hand rest should be so adjusted for height that the cutting edge of
the tool stands slightly above the horizontal level of the work, a rule
which obtains with all hand tools used upon wrought iron and steel.
[Illustration: Fig. 1285.]
The graver is the most useful of all hand turning tools, since it is
applicable to all metals, and for finishing as well as roughing out the
work. It is formed by a square piece of steel whose end is ground at an
angle, as shown in the top and the bottom view, Fig. 1285, A A being the
cutting edges, C C the points, and D D the heels.
It is held in a wooden handle, which should be long enough to grasp in
both hands, so that the tool may be held firmly. For cutting off a
maximum of metal in roughing out the work the graver is held as in Fig.
1286, the heel being pressed down firmly upon the tool rest. The cut is
carried along the work by revolving the handle upon its axis, and from
the right towards the left, at the same time that the handle is moved
bodily from the left towards the right. By this combination of the two
movements, if properly performed, the point of the graver will move in a
line parallel to the centres of the lathe, because, while the twisting
of the graver handle causes the graver point to move away from the
centre of the diameter of the work, the moving of the handle bodily from
left to right causes the point of the graver to approach the centre of
that diameter; hence the one movement counteracts the other, producing a
parallel movement, and at the same time enables the graver point to
follow up the cut, using the heel as a pivotal fulcrum, and hence
obviating the necessity of an inconveniently frequent moving of the heel
of the tool along the rest. The most desirable range of these two
movements will be very readily observed by the operator, because an
excess in either of them destroys the efficacy of the heel of the graver
as a fulcrum, and gives it less power to cut, and the operator has less
control over the tool.
[Illustration: Fig. 1286.]
[Illustration: Fig. 1287.]
[Illustration: Fig. 1288.]
For finishing or smoothing the work the graver is held as in Fig. 1287,
the edge being brought parallel to the work surface. For brass work the
top faces of the graver should be slightly bevelled in the direction
shown in Fig. 1288.
The graver cuts most efficiently with the work revolving at a fast
speed, or, say, at about 60 feet per minute, and for finishing wrought
iron or steel requires an application of water.
[Illustration: Fig. 1289.]
To finish work that has been operated upon by a heel tool or by a
graver, the finishing tool shown in Fig. 1289 may be employed. It is
usually made about 5/8 or 3/4 inch wide, as the graver is employed for
shorter work. It is ground so as not to let the extreme corners cut, and
is used at a slow speed with water. The edge of this tool is sometimes
oilstoned, causing it to cut with a clean polish. The tool is held
level, brought up to the work, and a cut put on by elevating the handle
end. To carry the cut forward, the tool is moved along the hand rest to
nearly the amount of its width, and is brought to its cut by elevating
the handle as before. When the work has been finished as near as may be
with this tool, it may be finished by fine filing, the lathe running at
its quickest speed; or the file may be used to show the high spots while
using the finishing tool.
[Illustration: Fig. 1290.]
For facing the ends of work the tool shown in Fig. 1290, or that shown
in Fig. 1291, may be used, either of them being made from an old
three-cornered file. The cutting edge at A, Fig. 1290, should be
slightly curved, as shown. The point of the tool is usually brought to
cut at the smallest diameter of the work, with the handle end of the
tool somewhat elevated. As the cut is carried outwards the handle end of
the tool is depressed, and the point correspondingly elevated. It may be
used dry or with water, but the latter is necessary for finishing
purposes.
[Illustration: Fig. 1291.]
Another form of this tool is shown in Fig. 1291. It has two cutting
edges A A, one of which rests on the hand rest while the other is
cutting, the tool being shown in position for cutting a right-and a
left-hand face, the face nearest to the work being shown in the lower
view. This face should be placed against the radial face of the work,
and the cut put on by turning the upper edge over towards the work while
pressing the tool firmly to the lathe rest.
[Illustration: Fig. 1292.]
For cutting out a round corner the tool shown in Fig. 1292, employed
either for roughing or smoothing purposes (water being used with it for
the latter), the heel causes it to grip the hand rest firmly, and acts
as a pivotal fulcrum from which the tool may be swept right and left
round the curve, or a portion of it.
This tool, as in the case of all tools used upon wrought iron or steel,
should not cut all round its edge simultaneously, as in that case,
unless indeed it is a very narrow tool, the force placed upon it by the
cut will be too great to enable the operator to hold and control it;
hence the cut should be carried first on one side and then on the other,
and then at the point, or else the handle end should be moved laterally,
so that the point sweeps round the work. It should be brought to its cut
by placing its heel close to the work, and elevating the handle end
until the cutting edge meets the work.
The point or nose of the tool may obviously be made straight or square,
as it is termed, to suit the work, the top rake being omitted for brass
work.
[Illustration: Fig. 1293.]
In using this tool for cutting a groove it is better (if it be a deep
groove, and imperative if it be a broad one, especially if the work be
slight and apt to spring) to use a grooving tool narrower in width than
the groove it is to cut, the process being shown in Fig. 1293, in which
W represents a piece of work requiring the two grooves at A and B cut in
it. For a narrow groove as A the tool is made about half as wide as the
groove, and a cut is taken first on one side as at C, and then on the
other as at D. For a wider groove three or more cuts may be made, as at
E, F, G. In all cases the tool while sinking the groove is allowed to
cut on the end face only; but when the groove is cut to depth, the side
edges of the tool may be used to finish the sides of the groove, but the
side and end edge must not cut simultaneously, or the tool will be
liable to rip into the work.
[Illustration: Fig. 1294.]
HAND TOOLS FOR BRASS WORK.--In addition to the graver as a roughing-out
tool for brass work, we have the tool shown in Fig. 1294, the cutting
edge being at the rounded end A. It is held firmly to the rest, which is
not placed close to the work (as in the case of other tools), so as to
give the tool a wide range of movement, and hence permit of the cut
being carried farther along without moving its position on the rest. It
may be used upon either internal or external work.
For finishing brass work, tools termed scrapers are employed.
[Illustration: Fig. 1295.]
Fig. 1295 represents a flat scraper, the two end edges A and the side
edges along the bevel forming the cutting edges.
[Illustration: Fig. 1296.]
[Illustration: Fig. 1297.]
[Illustration: Fig. 1298.]
[Illustration: Fig. 1299.]
In this tool the thickness of the end A is of importance, since if it be
too thin it will jar or chatter. This is especially liable to occur when
a broad scraper is used, having a great length of cutting edge in
operation. This may be obviated to some extent by inclining the scraper
as in Fig. 1296, which has the same effect as giving the top face
negative rake, causing the tool to scrape rather than cut. The dividing
line between the cutting and scraping action of a tool is found in the
depth of the cut, and the presentation of the tool to the work, as well
as in the shape of the tool. Suppose, for example, that we have in Fig.
1297, a piece of work W and a tool S, and the cut being light will be a
scraping one. Now suppose that the relative positions of the size of the
work and of the tool remain the same, but that the cut be deepened as in
Fig. 1298, and the scraping action is converted into that class of
severing known as shearing, or we may reduce the depth of cut as in Fig.
1299, and the action will become a cutting one.
[Illustration: Fig. 1300.]
But let the depth of cut be what it may, the tool will cut and not
scrape whenever the angle of its front face is more than 90° to the line
of tool motion if the tool moves, or of work motion if the work moves to
the cut. In Fig. 1300, for example, the tool is in position to cut the
angle of the front face, being 110° to the direction of tool motion.
We may consider this question from another stand-point, however,
inasmuch as that the tool action is a cutting one whenever the pressure
of the cut is in a direction to force the tool deeper into the work, and
a scraping one whenever this pressure tends to force the tool away from
the work, assuming of course that the tool has no front rake, and that
the cut is light or a "mere scrape," as workmen say. This is illustrated
in Fig. 1301, the tool at A acting to cut, and at B to scrape, and the
pressure of the cut upon A acting to force the tool into the work as
denoted by the arrow D, while that upon B acts to force it in the
direction of arrow C, or away from the work.
In addition to these distinctions between a cutting and a scraping
action we have another, inasmuch as that if a tool is pulled or dragged
to its cut its action partakes of a scraping one, no matter at what
angle its front face may stand with relation to the work.
The end face of a flat scraper should be at a right angle to the body of
the tool, so that both edges may be equally keen, for if otherwise, as
in Fig. 1302, one edge as A will be keener than the other and will be
liable to jar or chatter.
[Illustration: Fig. 1301.]
[Illustration: Fig. 1302.]
The flat scraper can be applied to all surfaces having a straight
outline, whether the work is parallel or taper, providing that there is
no obstruction to prevent its application to the work.
[Illustration: Fig. 1303.]
[Illustration: Fig. 1304.]
[Illustration: Fig. 1305.]
[Illustration: Fig. 1306.]
Thus, in Fig. 1303 we have a piece of work taper at _a_ and C, parallel
at _e_, and with a collar at _d_, the scraper S being shown applied to
each of these sections, and it is obvious that it cannot be applied to
section _a_ because the collar _d_ is in the way. This is remedied by
grinding the scraper as in Fig. 1304, enabling it to be applied to the
work as in Fig. 1305. Another example of the use of a bevelled scraper
is shown in Fig. 1306, the scraper S having its cutting edge parallel to
the work and well clear of the arm H.
[Illustration: Fig. 1307.]
The round-nosed scraper is used for rounding out hollow corners, or may
be made to conform to any required curve or shape. It is limited in
capacity, however, by an element that affects all scraping tools, that
if too great a length of cutting edge is brought into action at one
time, chattering will ensue, and to prevent this the scraper is only
made of the exact curvature of the work when it is very narrow, as at S
in Fig. 1307.
For broad curves it is made of more curvature, so as to limit the length
of cutting edge, as is shown in the same figure at S´, and is swept
round the work so as to carry the cut around the curve.
There are, however, other means employed to prevent chattering, and as
these affect the flat scraper as well as the round-nosed one, they may
as well be explained with reference to the flat one.
First, then, a thin scraper is liable to chatter, especially if used
upon slight work. But the narrower the face on the end of the scraper,
the easier it is to resharpen it on the oilstone, because there is less
area to oilstone. A fair thickness is about 1/20 inch; but if the
scraper was no thicker than this throughout its whole length, it would
chatter violently, and it is for this reason that it is thinned at its
cutting end only. Chattering is prevented in small and slight work by
holding the scraper as in Fig. 1308, applying it to the top of the work;
and to reduce the acting length of cutting edge, so as to still further
avoid chattering, it is sometimes held at an angle as in the top view in
Fig. 1309, S being the scraper and R the tool rest.
When the scraper is applied to side faces, or in other cases in which a
great length of cutting edge is brought into action, a piece of leather
laid beneath the scraper deadens the vibration and avoids chattering.
[Illustration: Fig. 1308.]
[Illustration: Fig. 1309.]
[Illustration: Fig. 1310.]
It is obvious that the scraper may be given any required shape to meet
the work, Fig. 1310 representing a scraper of this kind; but it must in
this case be fed endways only to its cut, if the work is to be cut to
fit the scraper.
[Illustration: Fig. 1311.]
[Illustration: Fig. 1312.]
In Fig. 1311 is shown a half-round scraper, which is shown in Fig. 1312
in position to scrape out a bore or hole. This tool is made by grinding
the flat face and the two edges of a worn-out half-round smooth file,
and is used to ease out bores that fit too tightly. The cutting edges
are carefully oilstoned, and the work revolved at a very quick feed.
[Illustration: Fig. 1313.]
[Illustration: Fig. 1314.]
[Illustration: Fig. 1315.]
When a number of small pieces of duplicate form are to be turned by
hand, a great deal of measuring may be saved and the work very much
expedited by means of the device shown in Fig. 1313. It consists of a
tool stock or holder, the middle of which, denoted by A, is square, and
contains three or four square slots, with a set-screw to each slot to
hold different turning tools. Each end of the stock is turned parallel,
as denoted by B, C. In Figs. 1313 and 1314, D, E, and F are the tools,
and G, H, are the set-screws.
Fig. 1315 represents top and side view of a plate, of which there must
be two, one to fasten on the headstock and one on the tailstock of the
lathe, as shown in Fig. 1316. In Fig. 1317 the manner of using the tool
is shown, similar letters of reference denoting similar parts in all the
figures.
The plates P P are bolted by screws to the headblock H and the tailstock
T of the lathe. The tool holder is placed so that the cylindrical ends
B, C, rest on the ends of these plates, and in the angles P´ P´. The
cutting tool D is sustained, as shown, upon the lathe rest R. In use the
operator holds the stock A in his hands in the most convenient manner,
using the tool E as a handle when there is a tool in the position of E.
The cutting point of the tool is pressed up to the work W, and the feed
is carried along by hand. It is obvious, however, that when the
perimeters of A B meet the shoulders O O, Fig. 1315, of the plates P P,
the tool cannot approach any nearer to the diametrical centre of the
work; hence the diameter to which the tool will turn is determined by
the distance of the shoulder O of the plate P from the centre of the
lathe centres, as shown in Fig. 1316 by the line L. In carrying the cut
along it is also obvious that the lateral travel of the stock or holder
must end when the end of the square part A comes against the side face
of either of the plates. In the engraving we have shown the tool D
cutting a groove in the work W, while the shoulder of the holder is
against the plate fastened to the lathe tailstock T; and so long as the
operator, in each case, keeps the shoulder against that plate, the
grooves upon each piece of work will be cut in the same position, for it
will be observed that the position in the length of the work performed
by each tool is determined by the distance of the cutting part of each
tool from the end of the square part A of the tool holder. All that is
necessary, then, is to adjust each tool so that it projects the proper
distance to turn the requisite diameter and stands the required distance
from the shoulders of the square to cut to the desired length, and when
once set error cannot occur.
[Illustration: Fig. 1316.]
This plain description of the device, however, does not convey an
adequate idea of its importance. Suppose, for example, that it is
required to turn a number of duplicate pieces, each with a certain
taper: all that is necessary is to adjust the plates P in their
distances from the lathe centres. If the large end of the taper on the
work is required to stand nearest the lathe headstock A, the plate P on
the headstock must be moved until its shoulder O is farther from the
lathe centre. If, however, the work requires to be made parallel, the
plates P must be set the same distance for the axial line of the
centres. If it be desired to have a parallel and a taper in proximity
upon the same piece of work, the tool must have one of its cylindrical
ends taper and use it upon the taper part of the work.
[Illustration: Fig. 1317.]
In Fig. 1317 the tool D is shown cutting a square groove. The tool at F
serves to turn the parallel part X, and the tool E would cut the
[V]-shaped groove I.
All kinds of irregular work may be turned by varying the parallelism and
form of the cylindrical ends B C; but in this event the shoulders O O,
Fig. 1315, should be made [V]-shaped and hardened to prevent them from
rapid wear.
[Illustration: Fig. 1318.]
[Illustration: Fig. 1319.]
SCREW CUTTING WITH HAND TOOLS.--Screw threads are cut by hand in the
lathe with chasers, of which there are two kinds, the outside and the
inside chaser. In Fig. 1319 is shown an outside, or male, and in Fig.
1318 an inside, or female chaser. The width of a chaser should be
sufficient to give at least four teeth, and for the finer thread pitches
it is better to have six or eight teeth, the number increasing as the
pitch is finer, and the length of the work will permit. The leading
tooth should be a full one, or otherwise it will break off, and if in
cutting up the chaser a half or less than a full tooth is formed it
should be ground off. The tooth points should not be in a plane at a
right angle to the chaser length, but slightly diagonal thereto, as in
Fig. 1319, so that the front edge of the chaser will clear a bolt head
or shoulder, and permit the leading tooth to pass clear up to the head
without fear of the front edge of the steel meeting the shoulder.
[Illustration: Fig. 1320.]
[Illustration: Fig. 1321.]
[Illustration: Fig. 1322.]
The method of producing a chaser from a hob is shown in Fig. 1320, in
which H is a hob, which is a piece of steel threaded and serrated, as
shown, to give cutting edges to act, as the hob rotates, upon the chaser
C. If the chaser is cut while held in a constant horizontal plane, its
teeth will have the same curvature as the hob, or, in other words, they
will fit its circumference. Suppose that the chaser, being cut up by the
hob and then hardened, is applied to a piece of work of the same
diameter as the hob and held in the same vertical plane, as in Fig.
1320, it is obvious that, there being no clearance, the teeth cannot
cut. Or, suppose it be applied to a piece of work of smaller diameter,
as in Fig. 1324, it cannot cut unless its position be lowered, as in
Fig. 1322, or else it must be elevated, as in Fig. 1323. In either case
the angle of the thread cut will be different from the angle of the
sides of the chaser teeth, and the thread will be of improper depth.
Thus, on referring to Fig. 1321, it will be seen that the chaser C has a
tooth depth corresponding to that on the work W along the horizontal
dotted line E only, because the true depth of thread on the work is its
depth measured along a radial line, as line F or G, and the chaser teeth
are, at the cutting edge, of a different angle. This becomes more
apparent if we suppose the chaser thickness to be extended up to the
dotted line H, and compare that part of its length that lies within the
two circles I J, representing the top and bottom of the thread, with the
length of radial line G, that lies within these circles. If, then, the
chaser be lowered, to enable it to act, it will cut a thread whose sides
will be of more acute angle than are the sides of the chaser teeth or of
the hob from which it was cut. The same effect is caused by using a
chaser upon a larger diameter of work than that of the hob from which
the chaser was cut, because the increased curvature of the chaser teeth
acts to give the teeth less contact with the work, as is shown in Fig.
1325, for the teeth cannot cut without either the lower corners A of the
teeth being forced into the metal, or else the chaser being tilted to
relieve them of contact. To obviate these difficulties and enable a
chaser to be used upon various diameters of work, it is, while being cut
up by the hob, moved continuously up and down, as denoted in Fig. 1326,
by A and B, which represent two positions of the chaser. The amount of
this movement is sufficient to make the chaser teeth more straight in
their lengths, and to give them a certain amount of clearance, an
example of the form of chaser thus produced being shown in Fig. 1327,
applied to two different diameters of work, as denoted by the circle A
and segment of a circle B, C representing the chaser.
[Illustration: Fig. 1323.]
[Illustration: Fig. 1324.]
[Illustration: Fig. 1325.]
[Illustration: Fig. 1326.]
To obtain the most correct results with such a chaser, it must be
applied to the work in such a way that it has as little clearance as
will barely enable it to cut, because it follows from what has been said
with reference to single-pointed threading tools that to whatever amount
the chaser has clearance, a corresponding error of thread angle and
depth is induced. In hand use, therefore, it does not matter at what
height the chaser is applied so long as it is elevated sufficiently to
barely enable it to cut.
[Illustration: Fig. 1327.]
[Illustration: Fig. 1328.]
After the chaser is cut on the hob, its edges, as at C, and the corner,
as at D, in Fig. 1328, should be rounded off, so that they may not catch
in any burr which the heel of the hand tools may leave on the surface of
the hand rest.
[Illustration: Fig. 1329.]
For roughing out the threads on wrought iron or steel the top face
should be hollowed out, as shown in Fig. 1328, which will enable the
chaser to cut very freely. For use on cast iron the top face should be
straight, as shown in Fig. 1328 at A, while for use on soft metal, as
brass, the top face must be ground off, as shown in Fig. 1329.
[Illustration: Fig. 1330.]
The Pratt and Whitney Co. cut up chasers by the following method: In
place of a hob, a milling cutter is made, having concentric rings
instead of a thread. The cutters are revolved on a milling machine in
the ordinary manner. The chaser is fastened in a chuck fixed on the
milling machine table, and stands at an angle of 15°. It is traversed
beneath the milling cutter, and thus cut up with teeth whose lengths are
at a right angle to the top and bottom faces of the chaser; hence the
planes of the length of the teeth are not in the same plane as that of
the grooves of the thread to be cut. Thus, let _a_, _b_, _c_, and _d_,
Fig. 1330, represent the planes of the thread on the work, and _e_, _f_,
_g_, _h_, will be the planes of the lengths of the chaser teeth.
The chaser, however, is given 15° of bottom rake or clearance, and this
causes the sides of the chaser teeth to clear the sides of the thread.
[Illustration: Fig. 1331.]
Now, suppose the top face A, Fig. 1331, of the chaser to be parallel
with the face of the tool steel, and to lie truly horizontal and in the
same plane as the centre of the work. This clearance will cause the
thread cut by the chaser to be deeper than the natural depth of the
chaser teeth. Thus, in Fig. 1331 is shown a chaser (with increased
clearance to illustrate the point desired), the natural depth of whose
thread is represented by the line F, but it is shown on the section of
work that the thread cut by the tool will be of the depth of the line D,
which is greater than the length or depth of F, as may be more clearly
observed by making a line E, which, being parallel to A, is equal in
length to D, but longer than F. Hence, the clearance causes the chaser
under these conditions to cut a thread of the same pitch, but deeper
than the grooves of the hub, and this would alter the angles of the
thread. This, however, is taken into account in forming the angles of
the thread upon the milling cutter, and, therefore, of the chaser, which
are such that with the tool set level with the work centre, the thread
cut will be of correct angle, notwithstanding the clearance given to the
teeth.
[Illustration: Fig. 1332.]
In order to enable the cutting of an inside chaser from a hub, it
requires to be bent as in Fig. 1332, in which H is the hub, R the lathe
rest, and C the chaser. After the chaser is cut, it has to be
straightened out, as shown in Fig. 1318, in which is represented a
washer being threaded and shown in section; C is the chaser and R the
lathe rest, while P is a pin sometimes let into the lathe rest to act as
a fulcrum for the back of the chaser to force it to its cut, the handle
end of the chaser being pressed inwards.
[Illustration: Fig. 1333.]
[Illustration: Fig. 1334.]
When an inside chaser is cut from a hub (which is the usual method) or
male thread, its teeth slant the same as does the male thread on the
side of the hub on which it is cut, and in an opposite direction to that
of the thread on the other side of the hub. Thus, in Fig. 1333, H is the
hub, C the chaser, and R the lathe rest. The slope of the chaser-teeth
is shown by the dotted line B. Now, the slant of the thread on the half
circumference of the hub not shown or seen in the cut will be in an
opposite direction, and in turning the chaser over from the position in
which it is cut (Fig. 1333) to the position in which it is used (Fig.
1334), and applying it from a male to a female thread, we reverse the
direction with relation to the work in which the chaser-teeth slant; or,
in other words, whereas the teeth of the chaser should lie as shown in
Fig. 1334 at A A, they actually lie as denoted in that figure by the
dotted line B B. As a consequence, the chaser has to be tilted over
enough to cause the sides of the chaser-teeth to clear the sides of the
thread being cut, which, as they lie at opposite angles, is sufficient
to cause the female thread cut by the chaser to be perceptibly shallower
than the chaser-teeth, for reasons which have been explained with
reference to Fig. 1321. It may be noted however, that an inside chaser
cannot well be used with rake, hence the tilting in this case makes the
thread shallower instead of deeper.
To obviate these difficulties the hub for cutting a right-hand inside
chaser should have a left-hand thread upon it, and _per contra_, an
inside chaser for cutting a left-hand thread should be cut from a hub
having a right-hand thread.
The method of starting an outside thread upon wrought iron or steel to
cut it up with a chaser is as follows:--
[Illustration: Fig. 1335.]
The work is turned up to the required diameter, and the [V]-tool shown
in Fig. 1335 is applied; the lathe is run at a quick speed, and the heel
of the tool is pressed firmly to the face of the lathe rest, the handle
of the tool must be revolved from right to left at the same time as it
is moved laterally from the left to the right, the movement being
similar to that already described for the graver, save that it must be
performed more rapidly. It is in fact the relative quickness with which
these combined movements are performed which will determine the pitch of
the thread. The appearance of the work after striking the thread will be
as shown in Fig. 1336, A being the work, and B a fine groove cut upon it
by the [V]-tool.
The reason for running the lathe at a comparatively fast speed is that
the tool is then less likely to be checked in its movement by a seam or
hard place in the metal of the bolt, and that, even if the metal is soft
and uniform in its texture, it is easier to move the tool at a regular
speed than it would be if the lathe ran comparatively slowly.
[Illustration: Fig. 1336.]
If the tool is moved irregularly or becomes checked in its forward
movement, the thread will become waved or "drunken"--that is, it will
not move forward at a uniform speed;[20] and if the thread is drunken
when it is started, the chaser will not only fail to rectify it, but, if
the drunken part occurs in a part of the iron either harder or softer
than the rest of the metal, the thread will become more drunken as the
chaser proceeds. It is preferable, therefore, if the thread is not
started truly, to try again, and, if there is not sufficient metal to
permit of the starting groove first struck being turned out, to make
another farther along the bolt. It takes much time and patience to learn
to strike the requisite pitch at the first trial; and it is therefore
requisite for a beginner to leave the end of the work larger in diameter
than the required finished size, as shown in Fig. 1336, so as to have
sufficient metal to turn out the groove cut by the [V]-tool at the first
trial cut, and try again.
[20] See Fig. 253, Plate II., Vol. I.
If the thread is to be cut on brass the [V]-tool must not have any top
rake. Some turners start threads upon brass by placing the chaser itself
against the end of the work and sweeping it rapidly from left to right
(for a right-hand thread), thus obviating the use of the [V]-tool.
In all cases the work should be rounded off at the end to prevent the
chaser-teeth from catching.
In applying the chaser to the groove cut by the [V]-tool the leading
tooth should be held just clear of the work at first, and only be
brought to touch the work after the rear teeth have found and are
traversing in the groove. By this means the chaser will carry the thread
forward more readily and true. The thread must be carried forward but a
short distance at each passage of the chaser, gradually deepening the
thread while carrying it forward.
To start an inside thread the corner of the hole at its entrance should
be rounded off and the back teeth of the chaser placed to touch the bore
while the front teeth are clear. The lathe is to be run at a quick
speed, and the chaser moved forward at as near the proper speed as can
be judged. When the chaser is moved at the proper speed, the rear teeth
will fall into the fine grooves cut by the advance ones, and start a
thread, while otherwise promiscuous grooves only will be cut. It is an
easy matter, however, to start a double thread with an inside chaser;
hence, when the thread is started the lathe should be stopped and the
thread examined.
The chaser should be placed with its top face straight above the
horizontal level of the work and held quite horizontal, and the handle
end then elevated just sufficient to give the teeth clearance enough to
enable them to cut; otherwise, with a chaser having top rake, the thread
cut will be too deep, and its sides will be of improper angle one to the
other.
[Illustration: Fig. 1337.]
Thus, in Fig. 1337, W represents a piece of work, R the lathe rest, and
T the chaser. The depth of the thread cut in this case will be from the
circle A to the circle B; whereas the depth of the chaser teeth, and
therefore the proper depth for the thread, is from C to D. Thus tilting
the handle end of the chaser too much has caused the chaser teeth to cut
a thread too deep. If on brass work the chaser has its top face ground
off as in figure, tilting the handle too much will cause the thread cut
to be too shallow, and in both cases the error in thread depth induces a
corresponding error in the angles of the sides of the thread one to the
other and relative to the axial line of the bolt or work.
If the chaser teeth are held at an angle to the work surface, the thread
cut will be of finer pitch than the chaser, and the angles of the sides
of the thread on the work will not be the same as those of the teeth. It
is permissible, however, during the early cuts taken with a hand chaser
to give the chaser a slight degree of such angle, because it diminishes
the length of cutting edge, and causes the chaser to cut more freely,
especially when the pitch of the thread is coarse and the chaser is
becoming dull.
In the case of a taper thread the same rule, that the thread may be
roughed out with the chaser teeth at an angle to the surface lengthways
of the work, but must be finished with the teeth parallel to the
surface, holds good.
[Illustration: Fig. 1338.]
Thus, in Fig. 1338 is a taper plug fitting in a ring having a threaded
taper bore, the threads matching, and having the thread sides in both
cases at an equal angle to the surface, lengthways of the work, though
the tops and bottoms of the thread are not parallel with the axial line
of the work.
WOOD TURNING TOOLS.--Wood turning in the ordinary lathe is generally
performed by hand tools, and of these the principal is the gouge, which
in skillful hands may be used to finish as well as to rough out the work
(although there are other more useful finishing tools to be hereafter
described).
It is used mainly, however, to rough out the work and to round out
corners and sweeps. The proper form for this tool is shown in Fig. 1339,
the bevel on the end of the back or convex side being carried well round
at the corners, so as to bring those corners up to a full sharp cutting
edge on the convex or front side.
The proper way to hold a gouge is shown in Fig. 1340, in which the cut
taken by the tool is being carried from right to left, the face plate of
the lathe being on the left side, so that by holding it in the manner
shown the body and arms are as much as possible out of the way of the
face plate, which is a great consideration in short work. But if the cut
is to be carried from left to right, the relative position of the hands
may be changed.
When the work runs very much out of true, or has corners upon it, as in
the case of square wood, the forefinger may be placed under the hand
rest, and the thumb laid in the trough of the gouge, pressing the latter
firmly against the lathe rest to prevent the tool edge from entering the
work too far, or, in other words, to regulate the depth of the cut, and
prevent its becoming so great as to force the tool from the hands or
break it, as is sometimes the case under such circumstances. When the
gouge is thus held, its point of rest upon the lathe rest may be used as
a fulcrum, the tool handle being moved laterally to feed it to the cut,
which is a very easy and safe plan for learners to adopt, until practice
gives them confidence. The main point in the use of the gouge is the
plane in which the trough shall lie. Suppose, for example, that in Fig.
1341 is shown a piece of work with three separate gouge cuts being taken
along it, that on the right being carried in the direction of the arrow.
Now the gouge merely acts as a wedge, and the whole of the pressure
placed by the cut on the trough side or face of the gouge is tending to
force the gouge in the direction of the arrow, and therefore forward
into its cut, and this it does, ripping along the work and often
throwing it out of the lathe. To avoid this the gouge is canted, so that
when cutting from right to left it lies as shown at B, in which case the
pressure of the cut tends rather to force the gouge back from the cut,
rendering a slight pressure necessary to feed it forward. The gouge
trough should lie nearly horizontal lengthwise, the cutting edge being
slightly elevated. The gouge should never (for turning work) be ground
in the trough (as the concave side is termed), and should always be
oilstoned, the trough being stoned with a slip of stone lying flat along
the trough, the back being rotated upon a piece of flat stone, and held
with the ground surface flat on the surface of the stone, and so pressed
to it as to give most pressure at and near the cutting edge.
[Illustration: Fig. 1339.]
[Illustration: Fig. 1340.]
[Illustration: Fig. 1341.]
[Illustration: Fig. 1342.]
For finishing flat surfaces, the chisel shown in Fig. 1342 is employed.
It should be short, as shown. It should be held to the work in a
horizontal position, or it is apt to dig or rip into the work,
especially when it is used upon soft wood. Some expert workmen hold it
at an angle for finishing purposes, which makes it cut very freely and
clean, but increases the liability to dig into the work; hence learners
should hold it as shown.
[Illustration: Fig. 1343.]
[Illustration: Fig. 1344.]
Another excellent finishing tool is the skew-chisel, Fig. 1343, so
called because its cutting edge is at an angle, or askew with the body
of the tool. This tool will cut very clean, leaving a polish on the
work. It also has the advantage that the body of the tool may be kept
out of the way of flanges or radial faces when turning cylindrical work,
or may, by turning it on edge, be used to finish radial faces. It is
shown in Fig. 1343 by itself, and in Fig. 1344 turning up a stem. It is
held so that the middle of the edge does the cutting, and this tends to
keep it from digging into the work. The bevels forming the cutting edge
require to be very smoothly oilstoned.
The whole secret of the skillful and successful use of this valuable
tool lies in giving it the proper inclination to the work. It is shown
in Fig. 1344, at E, in the proper position for taking a cut from right
to left, and at F in position for taking a cut from left to right. The
face of the tool lying on the work must be tilted over, for E as denoted
by line A, and for F as denoted by the line B, the tilt being only
sufficient to permit the edge to cut. If tilted too much it will dig
into the work; if not tilted, the edge will not meet the work, and
therefore cannot cut. For cutting down the ends of the work, or down a
side face, it must be tilted very slightly, as denoted in figure by C D,
the amount of the tilt regulating the depth of the cut, so that when the
cutting edge of the tool has entered the wood to the requisite depth,
the flat face of the tool will prevent the edge from entering any
deeper. In cutting down a radial face the acute corner of the tool leads
the cut, whereas in in plain cylindrical work the obtuse is better to
lead.
For cutting down the ends, for getting into small square corners, and
especially for small work, the skew chisel is more handy than the
ordinary chisel, and leaves less work for the sand-paper to do.
Beginners will do well to practise upon black walnut, or any wood that
is not too soft, roughly preparing it with an axe to something near a
round shape.
[Illustration: Fig. 1345.]
For finishing hollow curves the tool shown in Fig. 1345 is employed, the
cutting edge being at B; the degree of the curve determines the width of
the tool, and, for internal work the tool is usually made long and
without a handle.
[Illustration: Fig. 1346.]
[Illustration: Fig. 1347.]
The tool shown in Fig. 1346 is employed in place of the gouge in cases
where the broad cutting edge of the latter would cause tremulousness. It
may be used upon internal or external work, being usually about two feet
long. For boring purposes, the tools shown in Fig. 1347 are employed,
the cutting edges being from the respective points along the edges C, D,
respectively. But when the bore is too small to admit of the application
of tools having their cutting edges on the side, the tool shown in Fig.
1347 at E is employed, which has its cutting edge on the end.
[Illustration: _VOL. I._ =THE ROGERS-BOND UNIVERSAL COMPARATOR.= _PLATE
XIV._
Fig. 1348.
Fig. 1349.]
CHAPTER XIV.--MEASURING MACHINES, TOOLS, AND DEVICES.
Measurements are primarily derived in Great Britain and her colonies,
and in the United States, from the English Imperial or standard yard.
This yard is marked upon a bar of "Bailey's metal" (composed of 16 parts
copper, 2-1/2 parts tin, and 1 part zinc), an inch square and 38 inches
long. One inch from each end is drilled a hole about three-quarters
through the whole depth of the bar, into which are fitted gold plugs,
whose upper end faces are level with the axis of the bar. Across each
plug is marked a fine line, and the distance between these lines was
finally made the standard English yard by an Act of Parliament passed in
1855. A copy of this bar is in the possession of the United States
Government at Washington, and all the standard measuring tools for feet,
inches, &c., are derived from subdivisions of this bar.
The standard of measurement in France and her colonies, Italy, Germany,
Portugal, British India, Mexico, Roumania, Greece, Brazil, Peru, New
Granada, Uruguay, Chili, Venezuela, and the Argentine Confederation, is
the French mètre, which is also partially the standard in Austria,
Bavaria, Wurtemberg, Baden, Hesse, Denmark, Turkey, and Switzerland. It
consists of a platinum bar, called the "mètre des archives," whose end
faces are parallel, and the length of this bar is the standard mètre.
But as measuring from the ends of this bar would (from the wear) impair
its accuracy, a second bar, composed of platinum and iridium, has been
made from the "mètre des archives." This second bar has ruled upon it
two lines whose distance apart corresponds to the length of the "mètre
des archives," and from the distance between these lines the
subdivisions of the mètre have been obtained.
As all metals expand or contract under variations of temperature, it is
obvious that these standards of length can only be accurate when at some
given temperature: thus the English bar gives a standard yard when it is
at a temperature of 62° Fahr., while the French standard bar is standard
at a temperature of 32° Fahr., which corresponds to 0 in the centigrade
thermometer. But if a bar is copied from a standard, and is found to be
too short, it is obvious that if its amount of expansion under an
increase of temperature be accurately known, it will be an accurate
standard at some higher temperature, or in other words, at a temperature
sufficiently higher to cause it to expand enough to compensate for its
error, and no more.
As all bars of metal deflect from their own weight, it is obvious that
the bar must be supported at the same points at which it rested when the
lines were marked, and it has been determined by Sir George Airy, that
the best position for the points of support for any bar may be obtained
as follows: Multiply the number of the points of support by itself (or,
as it is commonly called, "square it"), and from the sum so obtained
subtract 1. Then subtract the square root of the remainder, which gives
a sum that divided into the length of the bar will represent the
distance apart for the points of support. It will be obvious that the
points of support must be at an equal distance from each end of the bar.
Measurement may be compared in two ways, by sight and by the sense of
feeling. Measurement by sight is made by comparing the coincidence of
lines, and is called "line measurement." Measurement by feeling or touch
is called "end measurement," because the measurement is taken at the
ends. If, for example, we measure the diameter of a cylindrical bar, it
is an end measurement, because the measurement is in a line at a right
angle to the axis of the bar, and the points of touch on each side of
the bar are the ends of the measurement, which is supposed to have no
width.
In measuring by sight we may, for rude measurements, trust to the
unaided eye, as in using the common foot rule, but for such minute
comparisons as are necessary in subdividing or transferring a standard,
we may call in the aid of the microscope.
The standard gauges, &c., in use in the United States have been obtained
from Sir Joseph Whitworth, or duplicated from those made by him with the
aid of measuring and comparing machines. It has been found, however,
that different sets of these gauges did not measure alike, the
variations being thus given by Mr. Stetson, superintendent of the Morse
Twist Drill and Machine Co.
At the time the Government established the use of the standard system of
screw threads in the navy yards, ten sets of gauges were ordered from a
manufacturer. His firm procured a duplicate set of these and took them
to the navy yard in Boston and found that they were practically
interchangeable. He also took them to the Brooklyn Yard Navy. The
following tabular statement shows the difference between them:--
---------------------------------------------------------------
| |Morse Twist|
|Navy Yard |Drill and | Morse Twist Drill and
Size. |Male Gauge. |Machine Co.| Machine Co.
| |Male Gauge.| Female Gauge.
-------+------------+-----------+------------------------------
1/4 | 0.25 | 0.25 | Interchanged
5/16 | .313 | .313 | "
3/8 | .375 | .3759 |
7/16 | .437 | .437 | Interchanged
1/2 | .505 | .505 | "
9/16 | .562 | .564 (-)| "
5/8 | Damaged | .626 | "
3/4 | .7505 | .751 | "
7/8 | .876 | .8758 | "
1 | 1.00075 | 1.00075 | "
| | | { Navy Yard M. T. D. & M. Co.
1-1/8 | 1.125 (+)| 1.125 (-)| { --------- -----------------
| | | { (+) (-)
1-1/4 | 1.25 | 1.25 | Interchanged
1-3/8 | 1.375 | 1.375 | "
1-1/2 | 1.5 | 1.5 (-)| (-)
1-5/8 | 1.6245 | 1.624 | (-)
1-3/4 | 1.749 | 1.749 | Interchanged
1-7/8 | 1.8745 | 1.874 | (-)
2 | 1.999 | 1.999 |
---------------------------------------------------------------
The sign (-) means that the piece is small, but not enough to measure.
The sign (+) means that the piece is large, but not enough to measure.
The advantages to be derived from having universally accepted standard
subdivisions of the yard into inches and parts of an inch are as
follows:--
When a number of pieces of work of the same shape and size are to be
made to fit together, then, if their exact size is not known and there
is no gauge or test piece to fit them to, each piece must be fitted by
trial and correction to its place, with the probability that no two
pieces will be of exactly the same size. As a result, each piece in a
machine would have to be fitted to its place on that particular machine,
hence each machine is made individually.
Furthermore, if another lot of machines are afterwards to be made, the
work involved in fitting the parts together in the first lot of machines
affords no guide or aid in fitting up the second lot. But suppose the
measurements of all the parts of the first lot are known to within the
one ten-thousandth part of an inch, which is sufficiently accurate for
practical purposes, then the parts may be made to measurement, each part
being made in quantities and kept together throughout the whole process
of manufacture, so that when all the parts are finished they may go to
the assembling or erecting room, and one piece of each part may be taken
indiscriminately from each lot, and put together to make a complete
machine. By this means the manufacture of the machine may be greatly
simplified and cheapened, and the fit of any part may be known from its
size, while at the same time a new part may be made at any time without
reference to the machine or the part to which it is to fit.
Again, work made to standard size in one shop will fit to that made to
standard size in another, providing the standard gauges agree.
The Pratt and Whitney Company, of Hartford, Connecticut, in union with
Professor Rogers, of Cambridge University, in Massachusetts, determined
to inspect the Imperial British yard, to obtain a copy of it, and to
make a machine that would subdivide this copy into feet and inches, as
well as transfer the line measurements employed in the subdivisions into
end measures for use in the workshops, the degree of accuracy being
greater than is necessary in making the most refined mechanism, made
under the interchangeable or standard gauge system. The machine made
under these auspices is the Rogers-Bond Universal Comparator; Mr. Bond
having been engaged in conjunction with Professor Rogers in its
construction.
The machine consists of two cylindrical guides, upon which are mounted
two heads, carrying microscopes which may be reversed in the heads, so
as to be used at the front of the machine for line measurements and on
the back for end measurements.
Fig. 1348 is a front, and Fig. 1349 a rear view of the machine, whose
details of construction are more clearly shown in the enlarged views,
Fig. 1350 and 1352.
[Illustration: Fig. 1350.]
[Illustration: Fig. 1351.]
[Illustration: Fig. 1352.]
Fig. 1350 is a top view, and Fig. 1352 a front view, the upper part of
the machine being lifted up for clearness of illustration. X, X, are the
cylindrical guides, upon which are the carriages I, K, for the
microscopes. The construction of these carriages is more fully seen in
Fig. 1351, which represents carriage K. It is provided with a hand-wheel
R, operating a pinion in a rack (shown at T in the plan view figure of
the machine) and affording means to traverse the carriage along the
cylindrical guides. The microscope may be adjusted virtually by the
screw M^{4}. The base upon which the microscope stands is adjustable
upon a plate N, by means of the two slots and binding screws shown, and
the plate N fits in a slideway running across the carriage. U is one of
the stops used in making end measurements, the other being fixed upon
the frame of the machine at V in the plan view, Fig. 1350. The
micrometric arrangement for the microscope is shown more clearly in Fig.
1353. The screw B holds the box in position, the edge of the circular
base on which it sits being graduated, so that the position of M may be
easily read. In the frame M is a piece of glass having ruled upon it the
crossed lines, or in place of this a frame may be used, having in it
crossed spider web lines. These lines are so arranged as to be exactly
in focus of the upper glass of the microscope, this adjustment being
made by means of the screw S. The lines upon the bar are in the focus of
the lower glass; hence, both sets of lines can be seen simultaneously,
and by suitable adjustment of the microscope can be brought to coincide.
[Illustration: Fig. 1353.]
Beneath the cylindrical guides, and supported by the rack T that runs
between and beneath them, are the levers P, in Fig. 1352, upon which
weights may be placed to take up the flexure or sag of the cylindrical
guides.
In Fig. 1352, H, H, are heads that may be fixed to the cylindrical
guides at any required point, and contain metallic stops, against which
corresponding stops on the microscope carriages may abut, to limit and
determine the amount to which these carriages may be moved along the
cylindrical guides.
The pressure of contact between the carriage and the fixed stops is
found to be sufficiently uniform or constant if the carriage is brought
up to the stops (by means of the hand-wheel R, Fig. 1351) several times,
and a microscope reading taken for each time of contact. But this
pressure of contact may be made uniform or constant for all readings by
means of an electric current applied to the carriage through the
metallic stops on heads H, H, and those on the carriage.
We have now to describe the devices for supporting the work and
adjusting it beneath the microscopes.
[Illustration: Fig. 1354.]
Referring, then, to Fig. 1352, E is a bed or frame that may be raised or
lowered by means of the hand-wheel C, so as to bring the plate S (on
which rests the bar whose line measure is to be compared) within range
of the microscopes. The upper face of E is provided with raised [V]
slideways, which are more clearly seen in the end view of this part of
the machine shown in Fig. 1354. Upon these raised [V]s are the devices
for adjusting the height of the eccentric rollers S^{3}, upon which the
bars to be tested are laid, S^{2} representing one of these bars. To
adjust the bars in focus under the microscope, these eccentric rollers
are revolved by means of levers S^{4}. At S^{5} is a device for giving
to the table a slight degree of longitudinal movement in the base plate
that rests upon the raised [V]s; on the upper face of E and at S^{6} is
a mechanism for adjusting the height of that end of the plate S. The
base plate may be moved along the raised [V]s of E by the hand-wheel D.
To test whether the cylindrical guides are deflected by their own weight
or are level, a trough of mercury may be set upon the eccentric rollers
S^{3}, Fig. 1352, and the fine particles of dust on its surface may be
brought into focus in the microscope, whose carriage may then be
traversed to various positions along the cylindrical guides, and if
these dust particles remain in focus it is proof that the guides are
level with the mercury surface.
[Illustration: Fig. 1355.]
The methods of using the machine are as follows: The standard bar has
marked upon its upper face (which is made as true as possible and highly
polished) a line B (Fig. 1355), which is called the horizontal line, and
is necessary in order to set the bar parallel to the cylindrical guides
of the machine. The lines A, A, are those defining the measurement as a
yard, a foot, or whatever the case may be, and these are called the
vertical lines or lines of measurement. Now, suppose we require to test
a bar with the standard and the lines on its face are marked to
correspond to those on the standard.
The first operation will be to set the standard bar on the eccentric
rollers S^{3} in Fig. 1352, and it and the microscopes are so adjusted
that the spider web lines in the microscope exactly intersect the lines
A and B on the standard, when the microscope carriage abuts against the
heads H, Fig. 1352. The standard bar is then replaced by the bar to be
tested, which is adjusted without altering the microscope adjustment or
the heads H, and if the spider web lines in the microscope exactly
coincide with and intersect the lines A and B, the copy corresponds to
the standard. But if they do not coincide, then the amount of error may
be found by the micrometer wheel G, Fig. 1353.
[Illustration: Fig. 1356.]
In this test the carriage is moved up against the stops H several times,
and several readings or tests are made, so as to see that the force of
the contact of the carriage against the stops H is uniform at each test,
and if any variation is found, the average of a number of readings is
taken. It is found, however, that with practice the carriage may be
moved against the head H by means of the hand-wheel with such an equal
degree of force that an error of not more than one fifty-thousandth of
an inch is induced. It is found, however, that if too much time is
occupied in this test, the heat of the operator's body will affect the
temperature of the bars, and therefore expand them and vitiate the
comparison. But in this connection it may be noted that if a bar is at a
temperature of 40°, and is placed in an ice bath, it does not show any
contraction in less than one minute, and that when it does so, the
contraction is irregular, taking place in sudden movements or impulses.
Professor Rogers' methods of testing end measures are as follows: To
compare a line with an end measure, a standard bar is set upon the
machine, its horizontal and vertical lines being adjusted true to the
cylindrical guides by the means already described, and the microscope
carriage is so adjusted that the spider web lines of the microscope
coincide with the horizontal and vertical lines marked on the standard,
while at the same time the stop (U, Fig. 1350) on the carriage K has
contact with the fixed stop (V, Fig. 1350.) Carriage K is then moved
along the cylindrical guides so as to admit the bar (whose end measure
is to be compared with the lines on the standard) between the two stops,
and if, with the bar touched by both stops U and V, the microscope
spider lines intersect the vertical and horizontal line on the standard
bar, then the end measure corresponds to the line measure; whereas, if
such is not the case, the amount of error may be found by noting how
much movement of the micrometer wheel of the microscope is required to
cause the lines to intersect.
It is obvious that in this test, if the cylindrical guides had a
horizontal curvature, the test would not be perfect.
THE HORIZONTAL CURVATURE.--The copy or bar to be tested may be set
between the stops, and the standard bar may be placed on one side of it,
as in Fig. 1356, and the test be made as already described. It is then
set the same distance from the bar to be tested, but on the other side
of it, as in figure, and again adjusted for position and tested, and if
the readings on the standard bar are the same in both tests, it is proof
that the measurements are correct.
Suppose, for example, that the cylindrical guides were curved as in Fig.
1356, it is evident that the vertical lines would appear closer together
on the standard bar when in the first position than when in the second
position.
In the Rogers machine the amount of error due to curvature in the
cylindrical guides in this direction is found to be about 1/5000 part of
an inch in 39 inches, corresponding to a radius of curvature of five
miles.
[Illustration: Fig. 1357.]
[Illustration: Fig. 1358.]
Another method of testing an end with a line measure is as follows: The
bar to be measured is shaped as in Fig. 1357, the end measurement being
taken at A, and the projection B at each end serving to preserve the end
surfaces A from damage. The standard bar is then set upon the machine
and its horizontal and vertical lines adjusted in position as before
described. In connection with this adjustment, however, the bar to be
tested is set as in Fig. 1358; C being a block of metal (having marked
centrally upon it horizontal and vertical lines), placed between the bar
and the fixed stop U, its vertical line being in line with the vertical
line on the standard. This adjustment being made, the block C is removed
and placed at the other end of the bar, as shown in Fig. 1359, when, if
the end measure on the bar corresponds with the line measure on the
standard, the vertical line at the other end of the standard will
correspond with the vertical line on block C.
[Illustration: Fig. 1359.]
To prove that the vertical line is exactly equidistant from each end of
the block C, all that is necessary is to place it between the bar and
the fixed stop U, Fig. 1350, adjust the microscope to it and then turn
it end for end, and if its vertical line is still in line with the
spider web of the microscope it is proof that it is central on the
block, while if it is not central the necessary correction may be made.
It is obvious that it is no matter what the length of C may be so long
as its vertical line is central in its length.
In this process the coincidence of the vertical lines on the standard
and on the piece C are employed to test the end measure on the bar with
the line measure on the standard.
[Illustration: Fig. 1360.--General View.]
[Illustration: Fig. 1361.--Plan.]
Figs. 1360 and 1361 represent the Whitworth Millionth Measuring Machine,
in which the measurement is taken by the readings of an index wheel, and
the contact is determined from the sense of touch and the force of
gravity.
It is obvious that in measuring very minute fractions of an inch one of
the main difficulties that arise is that the pressure of contact between
the measuring machine and the surfaces measured must be maintained
constant in degree, because any difference in this pressure vitiates the
accuracy of the measurement. This pressure should also be as small as is
consistent with the assurance that contact actually exists, otherwise
the parts will spring, and this would again impair the accuracy of the
measurement.
If the degree of contact is regulated by devices connected with the
moving mechanism of the machine it is indirect, and may vary from causes
acting upon that mechanism. But if it is regulated between the work and
the moving piece that measures it, nothing remains but to devise some
means of making its degree or amount constant for all measurements; so
that if a duplicate requires to be compared with a standard, the latter
may first be measured and the duplicate be afterwards measured for
comparison.
All that is essential is that the two be touched with an equal degree
of contact, and the most ingenious and delicate method yet devised to
accomplish this result is that in the Whitworth machine, whose
construction is as follows:--
In a box frame A, is provided a slide-way for two square bars, B, C,
which are operated by micrometer screws, one of which is shown at J (the
cap over B being removed to expose B and J to view). The bars B, C, are
made truly square, and each side a true plane. The groove or slide-way
in which they traverse is made with its two sides true planes at a right
angle to each other; so that the bars in approaching or receding from
each other move with their axes in a straight line. At the two ends of
the frame the micrometer screws are afforded journal bearings. The ends
of the bars B, C, are true planes at a right angle to the axes of B, C.
Bar B is operated as follows: Its operating screw J has a thread of 1/20
inch pitch; or in other words, there are twenty threads in an inch of
its length. It is rotated by the hand-wheel F, whose rim-face is
graduated by 250 equidistant lines of division. Moving F through a
distance equal to that between, or from centre to centre of its lines of
division, moves B through a distance equal to one five-thousandth part
of an inch.
The screw in head I for operating bar C also has a pitch of 1/20 inch
(or twenty threads in an inch of its length), and is driven by a
worm-wheel W, having 200 teeth. This worm-wheel W is driven by a worm or
tangent-screw H, having upon its stem a graduated wheel G, having 250
equidistant lines marked upon the face of its rim.
Suppose, then, that wheel G be moved through a distance equal to that
between its lines of division, that is 1/250th of a rotation, then the
worm H will move through 1/250th of a rotation, and the worm-wheel on
the micrometer screw will be rotated 1/250th part of its pitch expressed
in inches; because a full rotation of G would move the worm one
rotation, and thus would move the worm-wheel on the screw one tooth
only, whereas it has 200 teeth in its circumference; hence it is obvious
that moving graduated wheel G, through a distance equal to one of its
rim divisions will move the bar C the one-millionth of an inch; because:
Pitch of Rotation of Rotation of
thread worm-wheel graduated wheel
1/20 inch × 1/200 × 1/250 = 1/1000000
[Illustration: Fig. 1362.]
Fixed pointers, as K, Fig. 1362, enable the amount of movement or
rotation of the respective wheels F, G, to be read.
A peculiarly valuable feature of this machine is the means by which it
enables an equal pressure of contact to be had upon the standards, and
the duplicates to be tested therewith. This feature is of great
importance where fine and accurate measurements are to be taken. The
means of accomplishing this end are as follows:--
In the figures, D is a piece in position to be measured, and between it
and the bar C is a feeler consisting of a small flat strip of steel, E
E, having parallel sides, which are true planes.
When the pressure of contact upon this piece E E is such that if one end
be supported independently the other will just be supported by friction,
and yet may be easily moved between D and C by a touch of the finger,
the adjustment is complete. At the sides of the frame A are two small
brackets, shown at K, in the end view, Fig. 1362, E E being shown in
full lines resting upon them, and in dotted lines with one end
suspended. The contact-adjustment may thus be made with much greater
delicacy and accuracy than in those machines in which the friction is
applied to the graduated wheel-rim, because in the latter case, whatever
friction there may be is multiplied by the difference in the amount of
movement of the graduated rim and that of the bar touching the work.
All that is necessary in the Whitworth machine is to let E E be easy of
movement under a slight touch, though capable of suspending one end by
friction, and to note the position of the lines of graduation on C with
reference to its pointer. By reason of having two operative bars, B, C,
that which can be most readily moved may be operated to admit the piece
or to adjust the bars to suit the length of the work, while that having
the finer adjustive motion, as C, may be used for the final measuring
only, thus preserving it from use, and therefore from wear as much as
possible; or coarser measurements may be made with one bar, and more
minute ones with the other.
So delicate and accurate are the measurements taken with this machine,
that it is stated by C. P. B. Shelley, C.E., in his "Workshop
Appliances," that if well protected from changes of temperature and from
dust, a momentary contact of the finger-nail will suffice to produce a
measurable expansion by reason of the heat imparted to the metal. In an
iron bar 36 inches long, a space equal to half a division on the wheel G
having been rendered distinctly measurable by it, this space indicating
an amount of expansion in the 36-inch bar equals the one two-millionth
part of an inch!
The following figures, which are taken from _Mechanics_, represent a
measuring machine made by the Betts Machine Company, of Wilmington,
Delaware.
[Illustration: Fig. 1363.]
Fig. 1363 shows a vertical section through the length of the machine,
which consists of a bed carrying a fixed and an adjustable head, the
fixed head carrying the measuring screw and vernier while the adjustable
one carries a screw for approximate adjustment in setting the points of
the standard bars.
These screws have a pitch of ten threads per inch, and the range of the
measuring screw has a range of 4 inches, and the machine is furnished
with firm standard steel bars (4-inch, 6-inch, 18-inch, and 24-inch).
The measuring points of the screws are of hardened steel, secured
axially in line with the screws, and of two forms, with spherical and
flat points, one set of each being used at a time. The larger wheel C is
indexed to 1000 divisions, each division representing the ten-thousandth
of an inch at the points; the smaller wheel has 100 divisions, each
representing the one-thousandth part of an inch at the points. Beside,
and almost in contact with, the larger wheel is a movable or adjustable
pointer E, upon which the error of the screw is indexed for each inch of
its length; the screw error is of the utmost importance when positive
results are desired. The screw is immersed in oil to maintain a uniform
temperature throughout its length, and to avoid particles of dust
accumulating on its surface.
[Illustration: Fig. 1364.]
As stated above, the readings are indexed to the ten-thousandth part of
an inch, but variations to the hundred-thousandth part of an inch can be
indicated. The machine will take in pieces to 24 inches in length, and
to 4 inches in diameter. In measuring, the points are brought into easy
contact and then expanded by turning the larger wheel, counting the
revolutions or parts of revolutions to determine the distance between
the points or the size of what is to be measured. The smaller machine is
constructed so as to indicate by means of vernier attachment to the
ten-thousandth part of an inch, and is of value in tool-rooms where
standard and special tools are continually being prepared. By its use,
gauges and other exact tools can be made, and at the same time keep
gauges of all kinds to standard size by detecting wear or derangement.
The machine consists of a frame with one fixed head; the other head is
moved by a screw; on both heads are hardened steel points. As with the
larger machine, the screw error is indicated in such a manner as to
permit the operator to guard against reproducing its error in its work.
These machines are used for making gauges, reamers, drills, mandrels,
taps, and so on.
The errors that may exist in the pitch of the measuring screw are taken
into account as follows: The points of the measuring machine should be
brought into light contact, the position of index-wheel, vernier, and
the adjustable pointer which has the screw error indexed upon it should
be as in Fig. 1364; that is, the zeros on index-wheel and vernier should
be in exact line, the vernier covering half of the zero line on pointer.
To measure 1/2 inch, for illustration, five complete revolutions of
index-wheel should produce 1/2 inch, and would if we had a perfect
screw, but the screw is not perfect, and we must add to the measurement
already obtained one-half of the space, stamped upon corrective devise,
0-1. This space 0-1 represents the whole error in the screw from zero to
1 inch. The backlash of the screw should always be taken up.
[Illustration: Fig. 1365.]
[Illustration: Fig. 1366.]
[Illustration: Fig. 1367.]
[Illustration: Fig. 1368.]
The details of this machine are as follows:--
In Fig. 1363 the points G are those between which the measuring is done,
and the slide held by the nut K in position is adjusted by means of inch
bars to the distance to be measured; H, the hand-wheel for moving one
point, and F the wheel which moves the other. Fig. 1366 is a cross
section of the movable head through the nut K and stud M, by which the
movable head is adjusted, and Fig. 1365 is a cross section through the
fixed head. The bars used in setting the machine are shown in Fig. 1367,
and in Fig. 1368 the points of the measuring screws are shown on a large
scale. The other figures show various details of the machine and their
method of construction. The vernier, it will be observed, is a double
one. This is shown in Fig. 1364, and is so arranged that the zero is
made movable in order to correct the errors of the screw itself. These
errors are carefully investigated and a record made of each. Thus, in
Fig. 1363 the arm E is graduated so as to show the true zero for
different parts of the screw; D can then be adjusted to a correct
reading, and the divisions on the large wheel will then be correct to an
exceedingly small fraction. This method of construction enables the
machine to be used for indicating very minute variations of length.
[Illustration: Fig. 1369.]
In Fig. 1369 is shown a measuring machine designed by Professor John E.
Sweet, late of Cornell University. The bed of the machine rests on three
feet, so that the amount of support at each leg may remain the same,
whether the surface upon which it rests be a true plane or otherwise.
This bed carries a headstock and a tailstock similar to a lathe. The
tailstock carries a stationary feeler, and the headstock a movable one,
operated horizontally by a screw passing through a nut provided in the
headstock, the axial lines of the two feelers being parallel and in the
same plane. The diameters of the two feelers are equal at the ends, so
that each feeler shall present the same amount of end area to the work.
The nut for the screw operating the headstock feeler is of the same
length as the screw itself, so that the wear of the screw shall be
equalized as near as possible from end to end, and not be the most at
and near the middle of its length, as occurs when the thread on the
screw is longer than that in the nut.
The pitch of the thread on the screw is 16 threads in an inch of length,
hence one revolution of the screw advances the feeler 1/16 inch. The
screw carries a wheel whose circumference is marked or graduated by 625
equidistant lines of division. If, therefore, this wheel be moved
through a part of a rotation equal to one of these divisions, the feeler
will move a distance equal to 1/625 of the 1/16th of an inch, which is
the ten thousandth part of an inch, and as the bed of the machine is
long enough to permit the feelers to be placed 12 inches apart, the
machine will measure from zero to 12 inches by the ten-thousandth of an
inch.
To assist the eye in reading the lines of division, each tenth line is
marked longer than the rest, and every hundredth, still longer. The
pitch of the screw being 16 threads to an inch enables the feeler to be
advanced or retired (according to the direction of the rotation of the
wheel) a sixteenth inch by a simple rotation of the wheel, an eighth
inch by two wheel rotations, a thirty-second inch by a quarter rotation,
and so on; and this renders the use of that machine very simple for
testing the accuracy of caliper gauges, that are graduated to 1/8, 1/16,
1/32, 1/64th inch, and so on, such a gauge being shown (in the cut)
between the feelers.
The bar or arm shown fixed to the headstock and passing over the
circumference of the wheel at the top affords a fixed line or point
wherefrom to note the motion of the wheel, or in other words, the number
of graduations it moves through at each wheel movement. It is evident
that in a machine of this kind it is essential that the work to be
measured have contact with the feelers, but that it shall not be
sufficient to cause a strain or force that will spring or deflect either
the work itself (if it be slight) or the parts of the machine. It is
also essential that at excessive measurements the feelers shall touch
the work with the same amount of force. The manner of attaining this end
in Professor Sweet's machine is as follows: Upon the same shaft as the
wheel is an arm having contact at both ends with the edge of the wheel
rim whose face is graduated. This arm is free to rotate upon the shaft
carrying the graduated wheel, which it therefore drives by multiple
friction on its edges at diametrically opposite points; by means of a
nut the degree of this friction may be adjusted so as to be just
sufficient to drive the wheel without slip when the wheel is moved
slowly. So long, then, as the feelers have no contact with the piece to
be measured, the arm will drive the graduated wheel, but when contact
does take place the wheel will be arrested and the arm will slip. The
greatest accuracy will therefore be obtained if the arm be moved at an
equal speed for all measurements.
[Illustration: Fig. 1370.]
Fig. 1370 represents a Brown and Sharpe measuring machine for sheet
metal. It consists of a stand A with a slotted upright having an
adjusting screw C above, and a screw D, with a milled head and carrying
a dial, passing through its lower part. One turn of the screw, whose
threads are 1/10th inch apart, causes one rotation of the dial, the edge
of which is divided into one hundred parts, enabling measurements to be
made to thousandths of an inch. The sheet-metal to be gauged is inserted
in the slot of the upright. The adjusting-screw is set so that when the
points of the two screws meet, the zero of the dial shall be opposite an
index or pointer which shows the number of divisions passed over, and is
firmly secured by a set-screw.
Next in importance to line and end measurements is the accurate division
of the circle, to accomplish which the following means have been taken.
What is known as "Troughton's" method (which was invented by Edward
Troughton about 1809) is as follows: A disk or circle of 4 feet radius
was accurately turned, both on its face and its inner and outer edges. A
roller was next provided of such diameter that it revolved sixteen times
on its own axis, while rolling once round the outer edge of the circle.
This roller was pivoted in a framework which could be slid freely, yet
tightly, along the circle, the roller meanwhile revolving by frictional
contact on the outer edge. The roller was also, after having been
properly adjusted as to size, divided as accurately as possible into
sixteen equal parts by lines parallel to its axis. While the frame
carrying the roller was moved once round along the circle, the points of
contact of the roller divisions with the circle were accurately observed
by two microscopes attached to the frames, one of which commanded the
ring on the circle near its edge, which was to receive the divisions,
and the other viewed the roller divisions. The exact points of contact
thus ascertained were marked with faint dots, and the meridian circle
thereby divided into 256 very nearly equal parts.
The next part of the operation was to find out and tabulate the errors
of these dots, which are called apparent errors, because the error of
each dot was ascertained on the supposition that all its neighbors were
correct. For this purpose two microscopes, which we shall call A and C,
were taken with cross-wires and micrometer adjustments, consisting of a
screw and head divided into 100 divisions, 50 of which read in the one
and 50 in the opposite direction. These microscopes, A and B, were fixed
so that their cross-wires respectively bisected the dots 0 and 128,
which were supposed to be diametrically opposite. The circle was now
turned half way round on its axis, so that dot 128 coincided with the
wire of A, and should dot 0 be found to coincide with B, then the dots
were sure to be 180° apart. If not, the cross-wire of B was moved till
it coincided with the dot 0 and the number of divisions of micrometer
head noted. Half this number gave clearly the error of dot 128 and was
tabulated plus or minus according as the arcual distance between 0 and
128 was found to exceed or fall short of the removing part of the
circumference. The microscope B was now shifted, A remaining opposite
dot 0 as before, till its wire bisected dot 64, and by giving the circle
one-quarter of a turn on its axis, the difference of the arcs between
dots 0 and 64, and between 64 and 128 was obtained. The half of this
distance gave the apparent error of dot 64, which was tabulated with its
proper sign. With the microscope A still in the same position, the error
of dot 192 was obtained, and in the same way, by shifting B to dot 32,
the errors of dots 32, 96, 160 and 224 were successively ascertained. By
proceeding in this way the apparent errors of all the 256 dots were
tabulated.
In order to make this method fully understood, we have prepared the
accompanying diagrams, which clearly show the plan pursued.
[Illustration: Fig. 1371.]
Fig. 1371 illustrates the plan of dividing the large circle by means of
the roller B.
[Illustration: Fig. 1372.]
Fig. 1372 shows the general adjustment of the microscope for the purpose
of proving the correctness of the divisions.
[Illustration: Fig. 1373.]
Fig. 1373 shows the location of the microscope over the points 0 and
128.
[Illustration: Fig. 1374.]
Fig. 1374 shows the circle turned half-way round, the points 0 and 128
coinciding with the cross threads of the microscope.
[Illustration: Fig. 1375.]
Fig. 1375 shows a similar reading, in which the points do not coincide
with the cross threads of the microscope.
[Illustration: Fig. 1376.]
Fig. 1376 shows the microscope adjusted for testing by turning the
circle a quarter revolution.
Fig. 1377 represents one of the later forms of Ramsden's dividing
engine.[21] It consists first of a three-legged table, braced so as to
be exceedingly stiff. Upon this is placed a horizontal wheel with deep
webs, and a flat rim. The webs stiffen the wheel as much as possible,
and one of these webs, which runs round the wheel about half-way between
the centre and the circumference, rests upon a series of rollers which
support it, and prevent, as far as possible, the arms from being
deflected by their own weight. An outer circle, which receives the
graduation, is laid upon the rim of the wheel and secured in place. The
edge of this circle is made concave. A very fine screw, mounted in boxes
and supported independently, is then brought against this hollow edge,
and, being pressed against it, the screw, when revolved, of course cuts
a series of teeth in the circumference, and this tooth-cutting,
facilitated by having the screw threads made with teeth, was continued
until perfect [V]-shaped teeth were cut all around the edge of the
wheel. This Mr. Ramsden calls ratching the wheel. The number of teeth,
the circumference of the wheel, and the pitch of the screw were all
carefully adjusted, so that by using 2160 teeth, six revolutions of the
screw would move the wheel the space of 1°. When this work was finished,
and the adjustment had been made as perfect as possible, a screw without
teeth--that is, one in which the thread was perfect--was put in the
place of that which had cut the teeth from the wheel, and the machine
was perfected. The wheel A B C in the drawings is made of bell metal,
and turns in a socket under the stand, which prevents the wheel from
sliding from the supporting or friction rolls Z, Z. The centre R,
working against the spindle M, is made so as to fit instruments of
various sizes. The large wheel has a radius of 45 inches, and has 10
arms. The ring B is 24 inches in diameter by 3 inches deep. The ring C
is of very fine brass, fitting exactly on the circumference of the
wheel, and fastened by screws, which, after being screwed home, were
well riveted. Great care was taken in making the centre on which the
wheel worked exceedingly true and perfect, and in making the socket for
the wheel fit as exactly as possible. The revolving mechanism is all
carried on the pillar P, resting on the socket C´. We may state here
that the machine, as shown in the engravings, now in the possession of
the Stevens Institute, is in some respects slightly improved on that
shown in the original drawings published in "Rees' Cyclopædia" in 1819.
After the wheel was put on its stand, and the pulleys in place, the
instrument was ready for the turning mechanism. The upper part of this
pillar P carries the framework in which the traversing screw revolves.
[21] From _Mechanics_.
In Fig. 1378 D is the head of this pillar, P the screw which turns the
wheel. E^{1} E^{1} are the boxes, which are made conical so as to
prevent any shake and to hold the screw firmly. Circles of brass, F and
V, are placed on the arbor of the screw, and as their circumference is
divided into 60 parts, each division consequently amounts to a motion of
the wheel of 10 seconds, and 60 of them will equal 1 minute. Revolution
is given to the screw by means of the treadle B´ and the cord Y, which
runs over the guiding screw W, Fig. 1379, and is finally attached to the
box U. A spring enclosed in the box U causes it to revolve, and winds up
the slack of the cord whenever the treadle is relieved. In the original
drawing the head of the pillar P was carried in a parallel slip in the
piece surrounding its head. The construction as shown in Fig. 1379 is
somewhat different. The result attained, however, is identical, and the
spindles and attachments are held so as to have no lateral motion. The
wheels V and X have stops upon them, so arranged that the screw may be
turned definitely to a given point and stopped. These wheels are at the
opposite ends of the screw W. A detail of one of them is shown at V in
Fig. 1380, where X is the ratchet-wheel. This figure also illustrates
the construction of the bearings for the screw arbor. We have not space
to explain the method by which the perfection of the screw was obtained,
nor to discuss the means by which was obtained the success of so
eliminating the errors as to make the division of the instrument more
perfect than anything which had been attempted previously. Success,
however, was obtained, and by means of the first or tooth-cutting screw
the teeth were brought to such a considerable uniformity that, together
with the fact that the screw took hold of a number of teeth at one time,
most of the errors which would have been expected from this method of
operation were eliminated. The method of ruling lines upon the
instrument was most ingenious. The frame L L, is connected to the head
D, of the pillar P in front, by the clamps I and K, and to the centre M
by the block R. A frame N N stiffens the back. The blocks O, O on the
frame Q´ are secured to the frame L L, by set-screws C, C.
[Illustration: Fig. 1377.]
Fig. 1381 shows a side view of the frame Q´, which it is seen carries a
[V]-shaped piece Q, which in turn carries another [V]-shaped piece S,
Fig. 1378. The piece Q is supported on pointed screws _d_, _d_, and the
piece S is supported on two similar screws _f_, _f_. The point of this
piece S carries the cutting tool E, Fig. 1378. Of course S can move only
in a radial line from the centre M towards the circumference. If the
sextant, octant, or other instrument be fastened to the large wheel A,
with its centre at M, and the large wheel be rotated by the screw, all
lines drawn upon it by E will be radial, and the distances apart will be
governed by the number of turns made by the screw. This improvement, we
think, was originated by Mr. Ramsden, and was a very great advance over
the old method of the straight-edge, and has been used in some of the
Government comparators and dividing engines. The following is Mr.
Ramsden's own description of the graduation of the machine, and of his
method of operating it. It shows the extreme care which he took in
correcting the mechanical errors in the construction:--
"From a very exact centre a circle was described on the ring C, about
4/10 inch within where the bottom of the teeth would come. This circle
was divided with the greatest exactness I was capable of, first into
five parts, and each of these into three. These parts were then bisected
four times; that is to say, supposing the whole circumference of the
wheel to contain 2160 teeth, this being divided into five parts, and
these again divided into three parts, each third part would contain 144,
and this space, bisected four times, would give 72, 36, 18, 9;
therefore, each of the last divisions would contain 9 teeth. But, as I
was apprehensive some error might arise from quinquesection and
trisection, in order to examine the accuracy of the divisions, I
described another circle on the ring C, Fig. 1378, 1/10 inch within the
first, and divided it by continual bisection, as 2160, 1080, 540, 270,
135, 67-1/2, 33-3/4, and, as the fixed wire (to be described presently)
crossed both the circles, I could examine their agreement at every 135
revolutions (after ratching could examine it at every 33-3/4); but not
finding any sensible difference between the two sets of divisions, I,
for ratching, made choice of the former, and, as the coincidence of the
fixed wire with an intersection could be more exactly determined with a
dot or division, I therefore made use of intersections on both sides,
before described.
"The arms of the frame L, Fig. 1381, were connected by a thin piece of
brass, 3/4 inch broad, having a hole in the middle 4/10 inch in
diameter; across this hole a silver wire was fixed, exactly in a line to
the centre of the wheel; the coincidence of this wire with the
intersections was examined by a lens of 1/10 inch focus, fixed in a tube
which was attached to one of the arms L. Now (a handle or winch being
fixed on the end of the screw) the division marked 10 on the circle F
was set to its index, and, by means of a clamp and adjusting-screw for
that purpose, the intersection marked I on the circle C´ was set exactly
to coincide with the fixed wire. The screw was then carefully pressed
against the circumference of the wheel by turning the finger-screw _h_;
then, removing the clamp, I turned the screw by its handle nine
revolutions, till the intersection marked 240 came nearly to the wire.
Then, turning the finger-screw _h_, I released the screw from the wheel,
and turned the wheel back till the intersection marked 2 exactly
coincided with the wire, and by means of the clamp before mentioned, the
division 10 on the circle being set to its index, the screw was pressed
against the edges of the wheel by the finger-screw _h_, the clamps were
removed, and the screw turned nine revolutions, till the intersection
marked I nearly coincided with the fixed wire; the screw was released
from the wheel by turning finger-screw _h_ as before, the wheel was
turned back till intersection marked 3 coincided with the fixed wire;
the division 10 in the circle being set to its index, the screw was
pressed against the wheel as before, and the screw turned nine
revolutions, till intersection 2 was nearly coincident with the fixed
wire, and the screw released, and I proceeded in this manner till the
teeth were marked round the whole circumference of the wheel. This was
repeated three times round to make the impressions deeper. I then
ratched the wheel round continuously in the same direction, without ever
disengaging the screw, and, in ratching the wheel about 300 times round,
the teeth were finished.
[Illustration: Fig. 1378.]
"Now, it is evident that if the circumference of the wheel was even one
tooth, or ten minutes, greater than the screw would require, this error
would, in the first instance, be reduced by 1/240 part of a revolution,
or two seconds and a half, and these errors or inequalities of the teeth
were equally distributed round the wheel at the distance of nine teeth
from each other. Now, as the screw in ratching had continual hold of
several teeth at the same time and thus constantly changing, the
above-mentioned irregularities soon corrected themselves, and the teeth
were reduced to a perfect equality. The piece of brass which carried the
wire was now taken away, and the cutting-screw was also removed, and a
plain one put in its place. At one end of the screw arbor, or mandrel
was a small brass circle F, having its edge divided into 60 parts,
numbered at every sixth division, as before mentioned. On the other end
of the screw is a ratchet-wheel V (X, Fig. 1380) having 60 teeth,
covered by the hollow circle (V, Fig. 1380), which carries two clicks
that catch upon opposite sides of the ratchet-wheel. When the screw is
to be moved forward, the cylinder W turns on a strong steel arbor E´´,
which passes through the piece X´; this piece, for greater firmness, is
attached to the screw-frame by the braces _w_. A spiral groove or thread
is cut upon the outside of the cylinder W, which serves both for holding
the string and also giving motion to the lever I on its centre, by means
of a steel tooth _v_, that works between the threads of the spiral. To
the lever is attached a strong steel pin _m_, on which a brass socket
turns; this socket passes through a slit in the piece _u_, and may be
tightened in any part of the slit by the finger-nut _y_. This piece
serves to regulate the number of revolutions of the screw for each tread
of the treadle B´."
[Illustration: Fig. 1379.]
[Illustration: Fig. 1380.]
[Illustration: Fig. 1381.]
[Illustration: Fig. 1382.]
Figs. 1382, 1383, and 1384 represent a method adopted to divide a circle
by the Pratt and Whitney Company. The principle of the device is to
enable the wheel to be marked, to be moved through a part of a
revolution equal to the length of a division, and to test the accuracy
of the divisions by the coincidence of the line first marked with that
marked last when the wheel has been moved as many times as it is to
contain divisions. By this means any error in the division multiplies,
so that the last division marked will exhibit it multiplied by as many
times as there are divisions in the whole wheel. The accuracy of this
method, so long as variations of temperature are avoided, both in the
marking and the drilling of the wheel, appears to be beyond question. In
the figures, W represents a segment of the wheel to be divided, and C
what may be termed a dividing chuck. The wheel is mounted on an arbor in
a gear-cutting machine. On the hub of the wheel (which has been turned
up for the purpose) there is fitted, to a close working fit, a bore at
the end of an arm, the other end of the arm being denoted by A in the
figures. The dividing chuck is fitted to the slide S of the gear-cutting
machine, and is of the following construction.
Between two lugs, B and B´, it receives the end of arm A. These lugs are
provided with set-screws, the distance between the ends of which
regulate the amount of movement of the end of arm A. Upon A is the slide
D, carrying the piece E, in which is the marking tool F, the latter
being lifted by a spring G, and, therefore, having no contact with the
wheel surface until the spring is depressed. H is an opening through the
arm A to permit the marking tool F to meet the wheel face, as shown in
Fig. 1384, which is an end view of the slide showing the arm A in
section. The face of the wheel rests upon the chuck on each side of the
arm at the points I, J, and may be clamped thereto by the clamps K. The
arm may be clamped to the wheel by the clamp shown dotted in at L, the
bolt passing up and through the screw handle M. N is simply a lever with
which to move the arm A, or arm A and the wheel. Suppose all the parts
to be in the position shown in the cuts, the clamps being all tightened
up, the slide D may be moved forward towards K, while the spring is
depressed, and F will mark a line upon the wheel. The handle M may then
be released and arm A moved until it touches the set-screw in B´, when M
may be tightened and another line marked. Clamps K are then tightened,
and the wheel, with the arm A fast to it, moved back to the position
shown in the cut, when the clamps may be tightened again and another
line marked, the process being continued all round the wheel. To detect
and enable the correction of any discoverable error in a division, there
is provided the plate P, having upon it three lines of division (which
have been marked simultaneously with three of the lines marked on the
wheel). This plate is supported by an arm or bracket Q, on the rear edge
of which are three notches R to hold a microscope, by means of which the
lines on P may be compared with those on the wheel face, so that if any
discrepancy should appear it may be determined which line is in error.
The labor involved in the operation of marking a large wheel is very
great. Suppose, for example, that a wheel has 200 lines of division, and
that after going round the wheel as described it is found that the last
division is 100th inch out; then in each division the error is the
two-hundredth part of this 100th inch, and that is all the alteration
that must be made in the distance between set-screws B and B´.
[Illustration: Fig. 1383.]
[Illustration: Fig. 1384.]
Figs. 1385 and 1386 represent a method of originating an index wheel,
adopted by R. Hoe and Co., of New York City.
In this method the plan was adopted of fitting round a wheel 180
tapering blocks, which should form a complete and perfect circle. These
blocks were to serve the same purpose as is ordinarily accomplished by
holes perforated on the face of an index wheel. In their construction,
means of correcting any errors that might be found, without the
necessity of throwing away any portion of the work done, would also be
provided. Further, this means would provide for taking up wear, should
any occur in the course of time, and thus restore the original truth of
the wheel.
Fig. 1385 of the engravings shows the originating wheel mounted upon a
machine or cutting engine. Upon the opposite end of the shaft is the
worm-wheel in the process of cutting. After the master worm-wheel has
been thus prepared by means of the originating wheel, it is used upon
the front end of the shaft, in the position now occupied by the
originating wheel, and operated by a worm in the usual manner.
Subdivisions are made by change wheels. The construction of the
originating wheel will be understood by the smaller engravings.
Fig. 1386 is an enlarged section of a segment of the wheel, while Fig.
1387 is an edge view of this segment. Fig. 1388 is a view of one of the
blocks employed in the construction of the wheel, drawn to full size.
In the rim of the originating wheel there was turned a shoulder, C, Fig.
1387, 5 feet in diameter. Upon this shoulder there were clamped 180
blocks, of the character shown in Fig. 1386, as indicated by the
section, Fig. 1387. These blocks were secured to the face of the wheel D
by screws E, and were held down to the shoulder by the screw and clamp G
F, shown in Fig. 1387. (They are omitted in Fig. 1385 for clearness of
illustration.) In the preparation of these blocks each was fitted to a
template T, in Fig. 1388, and was provided with a recess B, to save
trouble in fitting and to insure each block seating firmly on the
shoulder C. The shoulder, after successive trials, was finally reduced
to such a diameter that the last block exactly filled the space left for
it when it was fully seated on the shoulder C. The wheel thus prepared
was mounted on a Whitworth cutting engine, as shown in Fig. 1385. The
general process of using this wheel is as follows: The blocks forming
the periphery of the originating wheel are used in place of the holes
ordinarily seen in the index plates. One of them is removed to receive a
tongue, shown in the centre of Fig. 1385, which, exactly filling the
opening or notch thus made, holds the wheel firmly in place. After a
tooth has been cut in the master worm-wheel, shown at the back of Fig.
1385, the block in the edge of the originating wheel corresponding to
the next tooth to be cut is removed. The tongue is withdrawn from the
first notch, the wheel is revolved, and the tongue is inserted in the
second position. The block first removed is then replaced, and the
cutting proceeds as before. This operation is repeated until all the
teeth in the master wheel have been cut. The space being a taper, the
tongue holds the originating wheel more firmly than is possible by means
of cylindrical pins fitting into holes. The number of blocks in the
originating wheel being 180, the teeth cut in the master wheel may be
180 or some exact divisor of this number.
The advantages of this method of origination are quite evident. Since
180 blocks were made to fill the circle, the edges of each had 2° taper.
This taper enabled the blocks to be fitted perfectly to the template,
because any error in fit would be remedied by letting the block farther
down into the template. Hence, it was possible to correct any error that
was discovered without throwing the block away. Further, as the blocks
themselves are removed to form a recess for locking the originating
wheel in position while cutting the worm-wheel, the truth of the work is
not subject to the errors that creep in when holes or notches require to
be pierced in the originating wheel. Such errors arise from the heating
due to the drilling or cutting, from the wear of the tools or from their
guides, from soft or hard spots in the metal and other similar causes.
To avoid any error from the heating due to the cut on the worm-wheel, in
producing master wheels, Messrs. Hoe and Co. allowed the wheel to cool
after each cut. The teeth were cut in the following order: The first
three were cut at equidistant points in the circumference of the wheel.
The next three also were at equidistant points, and midway between
those first cut. This plan was continued until all the teeth were cut,
thus making the expansion of the wheel from the heat as nearly equal as
possible in all directions.
There is one feature in this plan that is of value. It is that a certain
number of blocks, for example six, may be taken out at two or three
different parts of the originating wheel and interchanged, thus
affording a means of testing that does not exist in any other method of
dividing.
The tools applied by the workmen to measure or to test work may be
divided into classes.
1st. Those used to determine the actual size or dimension of the work,
which may be properly termed measuring tools.
2nd. Those used as standards of a certain size, which may be termed
gauges.
3rd. Those used to compare one dimension with another, as in the common
calipers.
4th. Those used to transfer measurements or distances defined by lines.
5th. Those used to test the accuracy of plane or flat surfaces, or to
test the alignment of one surface to another.
Referring to the first, their distinctive feature is that they give the
actual dimensions of the piece, whether it be of the required dimension
or not.
The second determine whether the piece tested is of correct size or not,
but do not show what the amount of error is, if there be any.
The third show whatever error there may be, but do not define its
amount; and the same is true of the fifth and sixth.
Fig. 1389 represents a micrometer caliper for taking minute end
measurements. This instrument is capable of being set to a standard
measurement or of giving the actual size of a piece, and is therefore
strictly speaking a combined measuring tool and a gauge. The [U]-shaped
body of the instrument is provided with a hub _a_, which is threaded to
receive a screw C, the latter being in one piece with the stem D, which
envelops for a certain distance the hub _a_. The thread of C has a pitch
of 40 per inch; hence one revolution of D causes the screw to move
endways 1/40 of an inch.
The vertical lines of division shown on the hub _a_ are also 1/40 of an
inch apart, hence the bevelled edge of the sleeve advances one of the
divisions on _a_ at each rotation.
This bevelled edge is divided into 25 equal divisions round its
circumference, as denoted by the lines marked 5, 10, &c. If, then, D be
rotated to an amount equal to one of its points of division, the screw
will advance 1/25 of 1/40 of an inch. In the cut, for example, the line
5 on the sleeve coincides with the zero line which runs parallel to the
axial line of the hub. Now suppose sleeve D to be rotated so that the
next line of division on the bevelled edge of D comes opposite to the
zero line, then 1/25 part of a revolution of D will have been made, and
as a full revolution of D would advance the screw 1/40 of an inch, then
1/25 of a revolution will advance it 1/25 of 1/40 inch, which is 1/1000
inch.
The zero line being divided by lines of equal division into 40ths of an
inch, then, as shown in the cut, the instrument is set to measure
3/40ths and 5/25ths of a fortieth.
It is to be observed that to obtain correct measurements the work must
be held true with the face of the foot B, and the contact between the
end of screw _c_ and the work must be just barely perceptible, otherwise
the pressure of the screw will cause the [U]-piece to bend and vitiate
the accuracy of the measurement. Furthermore, if the screw be rotated
under pressure upon the work, its end will wear and in time impair the
accuracy of the instrument. To take up any wear that may occur, the
foot-piece B is screwed through the hub, holding it so that it may be
screwed through the hub to the amount of the wear.
To avoid wear as much as possible, the screws of instruments of this
kind are sometimes hardened, and to correct the error of pitch induced
in the hardening, each screw is carefully tested to find in what
direction the pitch of the hardened thread has varied, and provision is
made for the correction as follows:--
The zero line on the hub _a_ stands, if the thread is true to pitch,
parallel to the axis of the screw C, but if the pitch of the thread has
become coarser from hardening, this zero line is marked at an angle, as
shown in Fig. 1390, in which A A represents the axial line of the screw
and B the zero line.
If the screw pitch becomes finer from hardening, the zero line is made
at an angle in the opposite direction, as shown in Fig. 1391, the amount
of the angle being that necessary to correct the error in the screw
pitch. The philosophy of this is, that if the pitch has become coarser a
less amount of movement of the screw is necessary, while if it has
become finer an increased movement is necessary. It is obvious, also,
that if the pitch of the thread should become coarser at one end and
finer at the other the zero line may be curved to suit.
[Illustration: Fig. 1392.]
[Illustration: Fig. 1393.]
[Illustration: _VOL. I._ =DIVIDING ENGINE AND MICROMETER.= _PLATE XV._
Fig. 1385.
Fig. 1386.
Fig. 1387.
Fig. 1388.
Fig. 1389.
Fig. 1390.
Fig. 1391.]
Fig. 1392 represents a vernier caliper, in which the measurement is read
by the coincidence of ruled lines upon the following principle. The
vernier is a device for subdividing the readings of any equidistant
lines of division. Its principle of action may be explained as follows:
Suppose in Fig. 1393 A to be a rule or scale divided into inches and
tenths of an inch, and B a vernier so divided that its ten equidistant
divisions are equal to nine of the divisions on A; then the distance
apart of the lines of division on A will be 1/10 inch; but, as the whole
ten divisions on B measure less than an inch, by 1/10 inch, then each
line of division is a tenth part of the lacking tenth less than 1/10
inch apart. Thus, were we to take a space equal to the 1/10 inch between
9 and 10 on A, and divide it into 10 equal parts (which would give ten
parts each measuring 1/100th of an inch) and add one of said parts to
each of the distances between the lines of division on B, then the whole
of the lines on A would coincide with those on B. It becomes evident,
then, that line 1 on B is 1/100 inch below line 1 on A, that line 2 on B
is 2/100 inch below line 2 on A, line 3 on the vernier B is 3/100 inch
below line 3 on the rule A, and so on, until we arrive at line 10 on the
vernier, which is 10/100 or 1/10 inch below line 10 on A. Suppose, then,
the rule or scale to rest vertically on a truly surfaced plate, and a
piece of metal be placed beneath B, the thickness of the piece will be
shown by which of the lines on B coincides with a line on A. For more
minute divisions it is simply necessary to have more lines of division
in a given length on A and B. Thus, if the rule be divided into inches
and fiftieths, and the vernier is so divided that it has 20 equidistant
lines of division to 19 lines on the rule, it will then lack one
division, or 1/50 inch in 20/50 inch, each division on the vernier will
then be the one-twentieth of a fiftieth too short, and as 1/20 of 1/50
is 1/1000, the instrument will read to one-thousandth of an inch.
Let it now be noted that, instead of making the lines of division closer
together to obtain minute measurements, the same end may be obtained by
making the vernier longer. For example, suppose it be required to
measure to 1/2000 part of an inch, then, if the rule or scale be
graduated to inches and fiftieths, and the vernier be graduated to have
40 equidistant lines of division, and 39 of the lines on the scale, the
reading will be to the 1/2000 part of an inch. But, in any event, the
whole of the readings on the vernier may be read, or will be passed
through, while it is traversing a division equal to one of the divisions
on the scale or rule.
In Fig. 1392 is shown a vernier caliper, in which the vernier is
attached to and carried by a slide operating against the inside edge of
the instrument. The bar is marked or graduated on one side by lines
showing inches and fiftieths of an inch, with a vernier graduated to
have 20 equidistant lines of division in 19 of the lines of division on
the bar, and therefore measuring to the 1/1000th of an inch, while the
other side is marked in millimètres with a vernier reading to 1/40th
millimètre, there being also 20 lines of division on the vernier to 19
on the bar.
The inside surfaces of the feet or jaws are relieved from the bar to
about the middle of their lengths, so as to confine the measuring
surfaces to dimensions sufficiently small to insure accurate
measurement, while large enough to provide a bearing area not subject to
rapid wear. If the jaw surface had contact from the point to the bar, it
would be impossible to employ the instrument upon a rectangular having a
burr, or slight projection, on the edge. Again, by confining the bearing
area to as small limits as consistent with the requirements of
durability a smaller area of the measured work is covered, and the
undulations of the same may be more minutely followed.
To maintain the surface of the movable jaw parallel with that of the
bar-jaw, it is necessary that the edge of the slide carrying the vernier
be maintained in proper contact with the edge of the instrument, which,
while adjusting the vernier, should be accomplished as follows:--
The thumb-screw most distant from the vernier should be set up tight, so
that that jaw is fixed in position. The other thumb-screw should be set
so as to exert, on the small spring between its end and the edge of the
bar, a pressure sufficient to bend that spring to almost its full limit,
but not so as to let it grip the bar. The elasticity of the spring will
then hold the edge of the vernier slide sufficiently firmly to the under
edge of the bar to keep the jaw-surfaces parallel; to enable the correct
adjustment of the vernier, and to permit the nut-wheel to move the slide
without undue wear upon its thread, or undue wear between the edge of
the slide and that of the bar, both of which evils will ensue if the
thumb-screw nearest the vernier is screwed firmly home before the final
measuring adjustment of the vernier is accomplished.
When the measurement is completed the second thumb-screw must be set
home and the reading examined again, for correctness, to ascertain if
tightening the screw has altered it, as it would be apt to do if the
thumb-screw was adjusted too loose.
The jaws are tempered to resist wear, and are ground to a true plane
surface, standing at a right angle to the body of the bar. The method of
setting the instrument to a standard size is as follows:--
The zero line marked 0 on the vernier coincides with the line 0 on the
bar when the jaws are close together; hence, when the 0 line on the
vernier coincides with the inch line on the bar, the instrument is set
to an inch between the jaws. When the line next to the 0 line on the
vernier coincides with the line to the left of the inch line on the bar,
the instrument is set to 1-1/1000 inches. If the vernier slide then be
moved so that the second line on the vernier coincides with the second
line, on the left of the inch on the bar, the instrument is set to
1-2/1000 inches, and so on, the measurement of inches and fiftieths of
an inch being obtained by the coincidence of the zero line on the
vernier with the necessary line on the bar, and the measurements of
one-thousands being taken as described.
But if it is required to measure, or find the diameter of an existing
piece of work, the method of measuring is as follows:--
The thumb-screws must be so adjusted as to allow the slide to move
easily or freely upon the work without there being any play or looseness
between the slide and the bar. The slide should be moved up so as to
very nearly touch the work when the latter is placed between the jaws.
The thumb-screw farthest from the vernier should then be screwed home,
and the other thumb-screw operated to further depress the spring without
causing it to lock upon the bar. The nut-wheel is then operated so that
the jaws, placed squarely across the work, shall just have perceptible
contact with it. (If the jaws were set to grip the work tight they would
spring from the pressure, and impair the accuracy of the measurements.)
The thumb-screw over the vernier may then be screwed home, and the
adjustment of the instrument to the work again tried. If a correction
should be found necessary, it is better to ease the pressure of the
thumb-screw over the vernier before making such correction, tightening
it again afterwards. The reading of the measurement is taken as
follows:--
If the 0 line on the vernier coincides with a line on the bar, the
measurement will, of course, be shown by the distance of that line from
the 0 line on the bar, the measurement being in fiftieths of inches, or
inches and fiftieths (as the case may be), but if the 0 line on the
vernier does not coincide with any line of division on the bar, then the
measurement in inches and fiftieths will be from the next line (on the
bar) to the right of the vernier, while the thousandths of an inch may
be read by the line on the vernier which coincides with a line on the
bar.
Suppose, for example, that the zero line of the vernier stands somewhere
between the 1 inch and the 1-1/50 inch line of division on the bar, then
the measurement must be more than an inch, but less than 1-1/50 inches.
If the tenth or middle line on the vernier is the one that coincides
with a line on the bar, the reading is 1-10/1000 inches. If the line
marked 5 on the vernier is the one that coincides with a line on the
bar, the measurement is an inch and 5/1000, and so on.
For measuring the diameters of bores or holes, the external edges of the
jaws are employed; the width of the jaw at the ends being reduced in
diameter to enable the jaw ends to enter a small hole. These edges are
formed to a circle, having a radius smaller than the smallest diameter
of hole they will enter when the jaws are closed, which insures that the
point of contact shall be in the middle of the thickness of each jaw. In
this case the outside diameter of the jaws must be deducted from the
measurement taken by the vernier, or if it be required to set the
instrument to a standard diameter, the zero line on the vernier must be
set to a distance on the bar less than that of the measurement required
to an amount equal to the diameter of the jaw edges when the jaws are
closed. This diameter is, as far as possible, made to correspond to the
lines of division on the bar. Thus in the instrument shown in Fig. 1392,
these lines of division are 1/50 inch; hence the diameter across the
closed bars should, to suit the reading (for internal measurements) on
the bar, be measurable also in fiftieths of an inch; but the other side
of the bar is divided into millimètres, hence to suit internal
measurements (in millimètres or fractions thereof) the width of the
jaws, when closed, should be measurable in millimètres; hence, it
becomes apparent that the diameter of the jaws used for internal
measurements can be made to suit the readings on one side only of the
bar, unless the divisions on one side are divisible into those on the
other side of the bar. When the diameter of the jaws is measurable in
terms of the lines of division on the bar, the instrument may be set to
a given diameter by placing the zero of the vernier as much towards the
zero on the bar as the width of the jaws when closed. Thus, suppose that
width (or diameter, as it may be termed) be 10/50 of an inch, and it be
required to set the instrument for an inch interval or bore measurement,
then the zero on the vernier must be placed to coincide with the line on
the bar which denotes 40/50 of an inch, the lacking 10/50 inch being
accounted for in the diameter or width of the two jaws.
But when the width of the jaws when closed is not measurable in terms
of the lines of division on the bar, the measurement shown by the
vernier will, of course, be too small by the amount of the widths of the
two jaws, and the measurement shown by the vernier must be reduced to
the terms of measurement of the width of the jaws, or what is the same
thing, the measurement of the diameter of the jaws must be reduced to
the terms of measurement on the bar, in order to subtract one from the
other, or add the two together, as the case may require.
For example: Suppose the diameter of the jaws to measure, when they are
close together, 250/1000 of an inch, and that the bar be divided into
inches and fiftieths. Now set the zero of the vernier opposite to the
line denoting 49/50 inch on the bar. What, then, is the measurement
between the outside edges of the jaws? In this case we require to add
the 250/1000 to the 49/50 in order to read the measurement in terms of
fiftieths and thousandths of an inch, or we may read the measurement to
one hundredths of an inch, thus: 49/50 equal 98/100, and 250/1000 equal
25/100, and 98/1000 added to 25/100 are 123/100, or an inch and 23/100.
To read in 1/1000ths of an inch, we have that 49/50 of an inch are equal
to 980/1000, because each 1/50 inch contains 20/1000 inch, and this
added to 250/1000 makes 1230/1000, that is 1-230/1000 inches.
The accuracy of the instrument may be maintained, notwithstanding any
wear which may in the course of time take place on the inside faces of
the jaws, by adjusting the zero line on the vernier to exactly coincide
with the zero line on the bar, but the fineness of the lines renders
this a difficult matter with the naked eye, hence it is desirable to
read the instrument with the aid of a magnifying glass. If the outer
edges of the jaws should wear, it is simply necessary to alter the
allowance made for their widths.
[Illustration: Fig. 1394.]
Fig. 1394 represents standard plug and collar gauges. These tools are
made to represent exact standard measurements, and obviously do no more
than to disclose whether the piece measured is exactly to size or not.
If the work is not to size they will not determine how much the error or
difference is, hence they are gauges rather than measuring tools. It is
obvious, however, that if the work is sufficiently near to size, the
plug or male gauge may be forced in, or the collar or female gauge may
be forced on, and in this case the tightness of the fit would indicate
that the work was very near to standard size. But the use of such gauges
in this way would rapidly wear them out, causing the plug gauge and also
the collar to get smaller than its designated size, hence such gauges
are intended to fit the work without friction, and at the same time
without any play or looseness whatever. Probably the most accurate
degree of fit would be indicated when the plug gauge would fit into the
collar sufficiently to just hold its own weight when brought to rest
while within the collar, and then slowly fall through if put in motion
within the collar. It is obvious that both the plug and the collar
cannot theoretically be of the same size or one would not pass within
the other, but the difference that is sufficient to enable this to be
done is so minute that it is practically too small to measure and of no
importance.
[Illustration: Fig. 1395.]
When these gauges are used by the workmen, to fit the work to their wear
is sufficient to render it necessary to have some other standard gauge
to which they can be from time to time referred to test their accuracy,
and for this purpose a standard such as in Fig. 1395 may be employed. It
consists of a number of steel disks mounted on an arbor and carefully
ground after hardening each to its standard size.
But a set of plug and collar gauges provide within themselves to a
certain extent the means of testing them. Thus we may take a collar or
female gauge of a certain size and place therein two or three plug
gauges whose added diameters equal that of the female or collar gauge.
[Illustration: Fig. 1396.]
In Fig. 1396, for example, the size of the female gauge A being 1-1/2
inches, that of the male B may be one inch, and that of C 1/2 an inch,
and the two together should just fit the female. On the other hand, were
we to use instead of B and C two males, 7/8 and 5/8 inches respectively,
they should fit the female; or a 1/2 inch, a 5/8 inch and a 3/8 inch
male gauge together should fit the female. By a series of tests of this
description, the accuracy of the whole set may be tested; and by
judicious combinations, a defect in the size of any gauge in the set may
be detected.
The wear of these gauges is the most at their ends, and the fit may be
tested by placing the plug within the collar, as in Fig. 1397, and
testing the same with the plug inserted various distances within the
collar, exerting a slight pressure first in the direction of A and then
of B, the amount of motion thus induced in the plug denoting the
closeness of the fit.
In trying the fit of the plug by passing it well into or through the
collar, the axis of the plug should be held true with that of the
collar, and the plug while being pressed forward should be slightly
rotated, which will cause the plug to enter more true and therefore more
easily. The plug should be kept in motion and not allowed to come to
rest while in the collar, because in that case the globules of the oil
with which the surfaces are lubricated maintain a circular form and
induce rolling friction so long as the plug is kept in motion, but
flatten out, leaving sliding friction, so soon as the plug is at rest,
the result being that the plug will become too tight in the collar to
permit of its being removed by hand.
[Illustration: Fig. 1397.]
The surfaces of both the plug and the collar should be very carefully
cleaned and oiled before being tried together, it being found that a
film of oil will be interposed between the surfaces, notwithstanding the
utmost accuracy of fit of the two, and this film of oil prevents undue
abrasion or wear of the surfaces.
When great refinement of gauge diameter is necessary, it is obvious that
all the gauges in a set should be adjusted to diameter while under an
equal temperature, because a plug measuring an inch in diameter when at
a temperature of, say, 60° will be of more than an inch diameter when
under a temperature of, say, 90°.
It follows also that to carry this refinement still farther, the work to
be measured if of the same material as the standard gauge should be of
the same temperature as the gauge, when it will fit the gauge if applied
under varying temperatures; but if a piece of work composed, say, of
copper, be made to true gauge diameter when both it and the gauge are at
a temperature of, say, 60°, it will not be to gauge diameter, and will
not fit the gauge, if both be raised to 90° of temperature, because
copper expands more than steel.
To carry the refinement to its extreme limit then, the gauge should be
of the same metal as the work it is applied to whenever the two fitting
parts of the work are of the same material. But suppose a steel pin is
to be fitted as accurately as possible to a brass bush, how is it to be
done to secure as accurate a fit as possible under varying temperatures?
The two must be fitted at some equal temperature; if this be the lowest
they will be subject to, the fit will vary by getting looser, if the
highest, by getting tighter; in either case all the variation will be in
one direction. If the medium temperature be selected, the fit will get
tighter or looser as the temperature falls or rises. Now in workshop
practice, where fit is the object sought and not a theoretical standard
of size, the range of variation due to temperature and, generally, that
due to a difference between the metals, is too minute to be of practical
importance. To the latter, however, attention must, in the case of work
of large diameter, be paid: thus, a brass piston a free fit at a
temperature of 100° to a 12-inch cast-iron cylinder, will seize fast
when both are at a temperature of, say, 250°. In such cases an allowance
is made in conformity with the co-efficients of expansion.
In the case of the gauges, all that is practicable for ordinary
work-shop variation of temperature is to make them of one kind and
quality of material--as hard as possible and of standard diameter, when
at about the mean temperature at which they will be when in use. In this
case the limit of error, so far as variation from temperature is
concerned, will be simply that due to the varying co-efficients of
expansion of the metals of which the work is composed.
[Illustration: Fig. 1398.]
To provide a standard of lineal measurement which shall not vary under
changes of temperature it has been proposed to construct a gauge such as
shown in Fig. 1398, in which A and B are bars of different metals whose
lengths are in the inverse ratio of their co-efficients of expansion. It
is evident that the difference of their lengths will be a constant
quantity, and that if the two bars be fastened together at one end, the
distance from the free end of B to the free end of A will not vary with
ordinary differences in temperature.
Plug and collar gauges may be used for taper as well as for parallel
fits, the taper fit possessing the advantage that the bolt or pin may be
let farther into its hole to take up the wear. In a report to the Master
Mechanics Association upon the subject of the propriety of recommending
a standard taper for bolts for locomotive work, Mr. Coleman Sellers
says:--
"As the commission given to me calls for a decision as to the taper of
bolts used in locomotive work, it presupposes that taper bolts are a
necessity. In our own practice we divide bolts into several classes, and
our rule is that in every case where a through bolt can be used it must
be used. If we cannot use a through bolt we use a stud, and where a stud
cannot be used we put in a tap bolt, and the reason why a tap bolt comes
last is because it is part and parcel of the machine itself. There are
also black bolts and body bound bolts, the former being put into holes
1/16 inch larger than the bolt. It is possible in fastening a machine or
locomotive together to use black bolts and body bound bolts. With body
bound bolts it is customary for machine builders to use a straight
reamer to true the hole, then turn the bolt and fit it into its place.
It is held by many locomotive builders that the use of straight bolts is
objectionable, on the score that if they are driven in tight there is
much difficulty in getting them out, and where they are got out two or
three times they become loose, and there is no means of making them
tighter.
"There is no difficulty in making two bolts of commercially the same
size. But there is a vast difference between absolute accuracy and
commercial accuracy. Absolute accuracy is a thing that is not
obtainable. What we have to strive for, then, is commercial accuracy.
What system can we adopt that will enable workmen of limited capacity to
do work that will be practically accurate? The taper bolt for certain
purposes presents a very decided advantage. Bolts may be made
practically of the same diameter, but holes cannot be made practically
of the same diameter. Each one is only an approximation to correctness.
We have here an ordinary fluted reamer (showing an excellent specimen of
Betts Machine Company's make). That reamer is intended to produce a
straight hole, but having once passed through a hole the reamer will be
slightly worn. The next time you pass it through it is a little duller,
and every time you pass it through the hole must become smaller. There
have been many attempts made to produce a reamer that should be
adjustable. That, thanks to the gentlemen who are making such tools a
speciality, has added a very useful tool to the machine shop--a reamer
where the cutters are put in tapered and can be set up and the reamer
enlarged and made to suit the gauge. This will enable us to make and
maintain a commercially uniform hole in our work. But the successful use
of a reamer of this kind depends upon the drill that precedes this
reamer being made as nearly right as possible, so that the reamer will
have little work to do. The less you give a reamer to do the longer it
will maintain its size.
"The question of tapered bolts involves at once this difficulty: that we
have to drill a straight hole, then the tapered reamer must take out all
the metal that must be removed in order to convert a straight into a
tapered hole. The straight hole is maintained in its size by taking out
the least amount of metal. It follows that the tapered reamer would be
nearest right which would also take out the least amount of metal.
"Then you come to the question of the shape of the taper. When I was
engaged building locomotives in Cincinnati, a great many years ago, we
used bolts the taper of which was greater than I shall recommend to you.
In regard to the compression that would take place in bolts, no piece of
iron can go into another piece of iron without being smaller than the
hole into which it is intended to go. If it is in any degree larger, it
must compress the piece itself or stretch the material that is round
it. So, if you adopt a tapered bolt, you cannot adopt a certain distance
that it shall stand out before you begin to drive it, for there will be
more material to compress in a large piece than in a small one. Metal is
elastic. Within the elastic limit of the metal you may assume the
compression to be a spring. In a large bolt you have a long spring, and
in a short one you have a short spring. If you drive a half-inch bolt
into a large piece of iron, it is the small bolt which you compress;
therefore the larger the bolt the more pressure you can give to produce
the same result. Hence, if you adopt the taper bolt, you will have to
use your own discretion, unless you go into elaborate experiments to
show how far the bolt head should be away from the metal when you begin
to drive it.
[Illustration: Fig. 1399.]
"Certain builders of locomotives put their stub ends together with
tapered bolts, but do not use tapered bolts in any other part of the
structure. The Baldwin Works use tapered bolts wherever they are body
bound bolts. They make a universal taper of 1/16 inch to the foot. An
inch bolt 12 inches long would be 1-1/16 inches diameter under the head.
They make all their bolts under 9 inches long 1/16 larger under the head
than the name of the bolt implies. Thus a 3/4 inch bolt would be 13/16
inch under the head, provided it was 9 inches long or under. Anything
over 9 inches long is made 1/8 inch larger under the head, and still
made a taper of 1/16 inch to the foot. A locomotive builder informs me
that a taper of 1/8 inch to the foot is sometimes called for, and the
Pennsylvania road calls for 3/32 inch to the foot. But the majority of
specifications call for 1/16 inch to the foot. The advantage of 1/16
inch taper lies in the fact that a bolt headed in the ordinary manner
can be made to fill the requirements, provided it is made of iron. You
may decide that bolts should be tapered, for the reason that when a
tapered bolt is driven into its place it can be readily knocked loose,
or if that bolt, when in its place, proves to be too loose, you have
merely to drive it in a little farther: these are arguments in favor of
tapered bolts, showing their advantage. It is easier to repair work that
has tapered bolts than work that has straight bolts. If you adopt a
tapered bolt, say, with a taper of 1/16 inch to the foot, you are going
to effect the making of those bolts and the boring of those holes in a
commercially accurate manner, so that they can be brought into the
interchangeable system. To carry this out, you require some standard to
start with, and the simplest system that one can conceive is this: Let
us imagine that we have a steel plug and grind it perfectly true. We
have the means of determining whether that is a taper of 1/16 inch,
thanks to the gentlemen who are now making these admirable gauges. We
have a lathe that can turn that taper. I think if you go into the
manufacture of these bolts, you will be obliged to use a lathe which
will always turn a uniform taper. Having made a female gauge, Fig. 1399,
8 inches long and 1-1/16 inches diameter with a taper of 1/16 inch to
the foot, this is the standard of what? The area of the bolt, not of the
hole it goes into. We now make a plug, Fig. 1399. Taking that tapered
plug we should be able to drop it into the hole. Your taper reamer is
made to fit this, but you require to know how deep the hole should be.
Remember, I said this is the gauge that the bolts are made by. Now let
us suppose that we have this as a standard, and to that standard these
reamers are made. We decide by practice how much compression we can put
upon the metal. For inch bolts, and, say, all above 1/2 inch, we might,
say, allow the head to stand up 1/8 of an inch. Let us make another
female gauge like Fig. 1399, but turned down 1/8 of an inch shorter. We
then shall have the hole smaller than it was before. It is this degree
smaller, .0065 of an inch; that is a decimal representing how much
smaller that hole is when you have gone down 1/8 of an inch on a taper
of 1/16 inch to the foot.
[Illustration: Fig. 1400.]
"Having got this tapered plug, you then must have the means of making
the bolts commercially accurate in the shop. For that purpose you must
have some cast-iron plugs. Those are reamed with a reamer that has no
guard on it, but is pushed into it until the plug--this standard
plug--is flush with the end of it. If you go in a little too far it is
no matter. Having produced that gauge, we gauge first the one that is
used on the lathe for the workman to work by, and he will fit his bolt
in until the head will be pushed up against it. If you have a bolt to
make from a straight piece of iron, I should advise its being done in
two lathes. Here are those beautiful gauges of the Pratt and Whitney
Company, which will answer the present purpose; one of these gauges
measuring what the outside of the bolt will be, the other gauge 1/16 of
an inch larger will mark the part under the head. Messrs. Baldwin have a
very good system of gauges. All the cast-iron plugs which they use for
this purpose are square. Holes are cut in the blocks the exact size of
the bolts to be turned up, as shown in Fig. 1400. The object of this is
that there shall be no mistake as to what the gauge is. These gauges can
be readily maintained, because they have to go back into the room to the
inspector. He puts this plug in. If it goes in and fits flush, it is all
right. If the plug goes in too far, it is worn. He then turns a little
off the end and adjusts it.
"Now practically through machine shops we find that we have to use
cast-iron gauges. We take, for instance, 2-inch shafting. Shafting can
only be commercially accurate. Therefore we make cast-iron rings and if
those rings will go on the shafting it is near enough accurate for
merchantable purposes. But this ring will wear in a certain time.
Therefore it must not be used more than a certain number of days or
hours. Here you have a system that is simple in the extreme. You have
all this in two gauges, one gauge being made as a mere check on that
tapered plug which is the origin of all things, the origin being 1/8 or
7/16, or 1/4 of an inch shorter if the bolt is very large. There is
where you have to use your own judgment. But having adopted something
practical you then can use your reamer which is necessary to produce a
hole of a given size. If this reamer wears, you then turn off this
wrought-iron collar far enough back to let it go in that much farther. I
know of no other way by which you can accomplish this result so well as
by that in use at the Baldwin Locomotive Works. I think that the system
originated with Mr. Baldwin himself.
"I do not feel disposed to recommend to you any particular taper to be
adopted, because it is not a question like that of screw-threads. In
screw-threads we throw away the dies that are used upon bolts, which are
perishable articles. The taper that has once been adopted in locomotive
establishments is a perpetual thing. If the Pennsylvania railroad and
all its branches have adopted 3/32, it is folly to ask them to change it
to 1/16 of an inch, because their own connections are large enough to
make them independent of almost any other corporation, and the need of
absolute uniformity in their work would cause them to stick to that
particular thing. Any of you having five, six, seven, or two or three
hundred engines, must make up your minds what you will do. When we adopt
a standard for screw-threads, a screw-thread is adopted which has a
manifest advantage. A bolt that has one screw thread can be used on any
machine. But once having adopted a taper on a road, it is very difficult
to make a change; and whether it is wisdom for this Association to say
that thus-and-so shall be the standard taper, is a question I am unable
to answer. Therefore I am unwilling to present any taper to you, and
only present the facts, but will say that 1/16 inch is enough. The less
taper you have the less material you have to cut away. But to say that
1/16 inch is preferable to 1/32 inch is folly, because no human being
could tell the difference. If a bolt has 5° taper on the side, it may
set in place; if it has 7°, it may jump out. That is the angle of
friction for iron or other metals. Five degrees would be an absurd angle
for a taper bolt. Anything, then, that will hold; that is, if you drive
the bolt it will set there.
"This presentation may enable you to arrive at some conclusion. Nothing
is more desirable than an interchangeable system. In making turning
lathes we try to make all parts interchangeable, and we so fit the
sliding spindle. Every sliding spindle in the dead head of the lathe has
to be fitted into its own place. We know of no method of making all
holes of exactly the same size that shall be commercially profitable.
The only way we could surmount that difficulty was to put two conical
sleeves in that should compress. We have so solved the problem. We now
make spindles that are interchangeable, and we do not fit one part to
the other. But that is not the case with bolts. You cannot put the
compressing thimbles on them, therefore, you have to consider the
question, How can you make holes near enough, and how can you turn the
bolts near enough alike?"
[Illustration: Fig. 1401.]
Fig. 1401 represents, and the following table gives the taper adopted by
the Baldwin Locomotive Works.
Bolt threads, American standard, except stay bolts and boiler studs,
[V]-threads, 12 per inch; valves, cocks and plugs, [V]-threads, 14 per
inch, and 1/8 inch taper per 1 inch.
Standard bolt taper 1/16 inch per foot.
Length of bolts from head to end of thread equals A.
Diameter of bolt under the head as follows:--
3/64 inch larger at B for 9 inch and under
1/16 " " over 9 inch to 12 inch
3/32 " " " 12 " to 18 "
1/8 " " " 18 " to 24 "
5/32 " " " 24 " to 30 "
3/16 " " " 30 " to 36 "
[Illustration: Fig. 1402.]
It is obvious that a plug or collar gauge simply determines what is the
largest dimension of the work, and that although it will demonstrate
that a piece of work is not true or round yet it will not measure the
amount of the error. The work may be oval or elliptical, or of any other
form, and yet fit the gauge so far as the fit can be determined by the
sense of feeling. Or suppose there is a flat place upon the work, then
except in so far as the bearing marks made upon the work by moving it
within the gauge may indicate, there is no means of knowing whether the
work is true or not. Furthermore, in the case of lathe work held between
the lathe centres it is necessary to remove the work from the lathe
before the collar gauge can be applied, and to obviate these
difficulties we have the caliper gauge shown in Fig. 1402. The caliper
end is here shown to be for 3/4 inch, and the plug end for 13/16 inch.
If the two ends were for the same diameter one gauge only would be used
for measuring external and internal work of the same diameter, but in
this case the male cannot be tested with the female gauge; whereas if
the two ends are for different diameters the end of one gauge may be
tested with that of another, and their correctness tested, but the
workman will require two gauges to measure an external and internal
piece of the same diameter.
[Illustration: Fig. 1403.]
For small lathe work of odd size as when it is required to turn work to
fit holes reamed by a worn reamer that is below the standard size, a
gauge such as in Fig. 1403, is sometimes used, the mouth A serving as a
caliper and the hole B as a collar gauge for the same diameter of work.
It is obvious that such a gauge may be applied to the work while it is
running in the lathe, and that when the size at A wears too large the
jaw may be closed to correct it; a plan that is also pursued to rectify
the caliper gauge shown in Fig. 1402.
[Illustration: Fig. 1404.]
On large work, as, say, of six inches in diameter, a gauge, such as in
Fig. 1404, is used, being short so that it may be light enough to be
conveniently handled; or sometimes a piece such as in Fig. 1405 is used
as a gauge, the ends being fitted to the curvature of the bore to be
tested. Gauges of these two kinds, however, are generally used more in
the sense of being templates rather than measuring tools, since they
determine whether a bore is of the required size rather than determine
what that size is.
[Illustration: Fig. 1405.]
[Illustration: Fig. 1406.]
[Illustration: Fig. 1407.]
For gauging work of very large diameter, as, say, several feet, to
minute fractions of an inch, as is necessary, for example, for a
shrinkage fit on a locomotive tire, the following method is employed. In
Fig. 1406 let A represent a ring, say, 5 feet bore, and requiring its
bore to be gauged to within, say, 1/100 inch. Then R represents a rod
made, say, 1/2 inch shorter than the required diameter of bore, and W,
Fig. 1407, represents a wedge whose upper surface C D is curved, its
lower surface being a true plane. The thickness at the end C is made,
say, 51/100 inch, while that at D is 48/100 inch; or in other words,
there is 3/100 of an inch taper in the length of the wedge. Suppose then
that the rod R is placed in the bore of A as in figure, and that the
wedge just has contact with the work bore and with the end of the rod
when it has entered as far as E in Fig. 1407, and that point E is
one-third of the length of the wedge, then the bore of A will measure
the length of the rod R plus 49/100 of an inch. But if the wedge passed
in to line F, the latter being two-thirds the length of the wedge from
D, then the bore would be 50/100 larger than the length of the rod R. It
is obvious that with this method the work may be measured very minutely,
and the amount of error, if there be any, may be measured.
The rod must be applied to the work in the same position in which its
measurement was made, otherwise its deflection may vitiate the
measurement. Thus, if the rod measures 4 feet 11-1/2 inches when
standing vertical, it must be applied to the work standing vertical; but
if it was measured lying horizontal, it must be applied to the work
lying horizontal, as there will be a difference in its length when
measured in the two positions, which occurs on account of variations in
its deflection from its own weight.
[Illustration: Fig. 1408.]
[Illustration: Fig. 1409.]
For simply measuring a piece of work to fit it to another irrespective
of its exact size as expressed in inches and parts of an inch the common
calipers are used. Fig. 1408 represents a pair of spring calipers, the
bow acting as a spring to keep the two legs apart, and the screw and nut
being used to close them against the spring pressure. The slightness of
the legs enables these calipers to be forced or to spring over the work,
and thus indicate by the amount of pressure it requires to pass them
over the work how much it is above size, and therefore how much it
requires to be reduced. But, on the other hand, this slightness renders
it somewhat difficult to measure with great correctness. A better form
of outside calipers is shown in Fig. 1409, in which in addition to the
stiffness of the pivoted joint a bow spring acts to close the caliper
legs, which are operated, to open or close them, by operating the hand
screw shown, the nuts in which the screw operates being pivoted to the
caliper legs. The advantage of this form is that the calipers may be set
very readily, while there is no danger of the set or adjustment of the
calipers altering from any slight blow or jar received in laying them
down upon the bench.
[Illustration: Fig. 1410.]
Fig. 1410 gives views of a common pair of outside calipers such as the
workman usually makes for himself. When this form is made with a
sufficiently large joint, and with the legs broad and stiff as in the
figure, they will serve for very fine and accurate adjustments.
[Illustration: Fig. 1411.]
Fig. 1411 represents a pair of inside calipers for measuring the
diameters of holes or bores. The points of these calipers should be at
an angle as shown in the Fig. 1412, which will enable the points to
enter a long distance in a small hole, as is denoted by the dotted lines
in the figure. This will also enable the extreme points to reach the
end of a recess, as in Fig. 1413, which the rounded end calipers, such
as in this figure, will not do.
[Illustration: Fig. 1412.]
[Illustration: Fig. 1413.]
[Illustration: Fig. 1414.]
Fig. 1414 represents a pair of inside calipers with an adjustment screw
having a right-hand screw at A and a left-hand one at B, threaded into
two nuts pivoted into the arms, so that by operating the screw the legs
are opened or closed, and are locked in position, so that they cannot
move from an accidental blow. But as the threads are apt to wear loose,
it is preferable to provide a set screw to one of the nuts so as to take
up the wear and produce sufficient friction to prevent looseness of the
legs.
[Illustration: Fig. 1415.]
[Illustration: Fig. 1416.]
Calipers are sometimes made double, that is to say, the inside and the
outside calipers are provided in the one tool, as in Fig. 1415, which
represents a pair of combined inside and outside calipers having a set
screw at C to secure the legs together after the adjustment is made. The
object of this form is to have the measuring points equidistant from the
centre of the pivot A in Fig. 1416, so that when the outside legs are
set to the diameter of the work as at B, the inside ones will be set to
measure a hole or bore of the same diameter as at C.
This, however, is not a desirable form for several reasons, among which
are the following:--
In the first place outside calipers are much more used than inside ones,
hence the wear on the points are greatest. Again, the pivot is apt to
wear, destroying the equality of length of the points from the centre of
the pivot; and in the third place the shape of the points of calipers as
usually made vitiates the correctness of the measurements.
[Illustration: Fig. 1417.]
Fig. 1417, for example, represents the ordinary form, the points being
rounded; hence, when the legs are closed the point of contact between
the inside and outside calipers will be at A, while when they are opened
out to their fullest the points of contact will be at B. This may,
however, be remedied to a great extent by bevelling off the ends from
the outside as shown in Fig. 1416.
[Illustration: Fig. 1418.]
The end faces of outside calipers should be curved in their widths, as
in Fig. 1418, so that contact shall occur at the middle, and it will
then be known just where to apply the points of the inside calipers when
testing them with the outside ones.
Inside and outside calipers are capable of adjustment for very fine
measurements; indeed, from some tests made by the Pratt and Whitney
Company among their workmen it was found that the average good workman
could take a measurement with them to within the twenty-five thousandth
part of an inch. But the workman of the general machine shop who has no
experience in measuring by thousandths has no idea of the accuracy with
which he sets two calipers in his ordinary practice. The great
difference that the one-thousandth of an inch makes in the fit of two
pieces may be shown as in Fig. 1419, which represents a collar gauge of
5/8 inch in diameter, and a plug 1/1000 inch less in diameter, and it
was found that with the plug inserted 1/8 inch in the collar it could be
moved from A to B, a distance of about 5/16 inch, which an ordinary
workman would at once recognise as a very loose fit.
If the joints of outside calipers are well made the calipers may upon
small work be closed upon the work as in Fig. 1420, and the adjustment
may be made without requiring to tap or lightly knock the caliper legs
against the work as is usually done to set them. But to test the
adjustment very finely the work should be held up to the light, as in
Fig. 1421, the lower leg of the calipers rested against the little
finger so as to steady it and prevent it from moving while the top leg
is moved over the work, and at the same time moving it sideways to find
when it is held directly across the work. For testing the inside and
outside calipers together they should for small diameters be held as in
Fig. 1422, the middle finger serving to steady one inside and one
outside leg, while one leg only of either calipers is grasped in the
fingers.
[Illustration: Fig. 1419.]
[Illustration: Fig. 1420.]
[Illustration: Fig. 1421.]
[Illustration: Fig. 1422.]
For larger dimensions, as six or eight inches, it is better, however, to
hold the calipers as in Fig. 1423, the forefinger of the left hand
serving to rest one leg of each pair on the contact being thus tested
between the legs that are nearest to the operator.
The adjustment of caliper legs should be such that contact between the
caliper points and the work is scarcely, if at all, perceptible. If with
the closest of observation contact is plainly perceptible, the outside
calipers will be set smaller than the work, while in the case of inside
calipers, they would be set larger; and for this reason it follows that
if a bore is to be measured to have a plug fitted to it, the inside
calipers should have barely perceptible contact with the work bore, and
the outside calipers should have the same degree of contact, or, if
anything, a very minute degree of increased contact. On the other hand,
if a bore is to be fitted to a cylindrical rod the outside calipers
should be set to have the slightest possible contact with the rod, and
the inside ones set to have as nearly as possible the same degree of
contact with the outside ones, or, if anything, slightly less contact.
For if in any case the calipers have forcible contact with the work the
caliper legs will spring open and will therefore be improperly set.
Calipers should be set both to the gauge and to the work in the same
relative position. Let it be required, for example, to set a pair of
inside calipers to a bore, and a pair of outside calipers to the inside
ones, and to then apply the latter to the work. If the legs of the
inside calipers stand vertical to the bore for setting they should stand
vertical while the outside calipers are set to them, and if the outside
calipers are held horizontally while set to the inside ones they should
be applied horizontally to the work, so as to eliminate any error due to
the caliper legs deflecting from their own weight.
[Illustration: Fig. 1423.]
To adjust calipers so finely that a piece of work may be turned by
caliper measurement to just fit a hole; a working or a driving fit
without trying the pieces together, is a refinement of measurement
requiring considerable experience and skill, because, as will be readily
understood from the remarks made when referring to gauge measurements,
there are certain minute allowances to be made in the set of the
calipers to obtain the desired degree of fit.
In using inside calipers upon flat surfaces it will be found that they
can be adjusted finer by trusting to the ear than the eye. Suppose, for
example, we are measuring between the jaws of a pillow-block. We hold
one point of the calipers stationary, as before, and adjust the other
point, so that, by moving it very rapidly, we can just detect a scraping
sound, giving evidence of contact between the calipers and the work. If,
then, we move the calipers slowly, we shall be unable, with the closest
scrutiny, to detect any contact between the two.
Calipers possess one great advantage over more rigid and solid gauges,
in that the calipers may be forced over the work when the degree of
force necessary to pass them on indicates how much the work is too
large, and therefore how much it requires reducing. Thus, suppose a
cylindrical piece of work requires to be turned to fit a hole, and the
inside calipers are set to the bore of the latter, then the outside
calipers may be set to the inside ones and applied to the work, and when
the work is reduced to within, say, 1/100 inch the calipers will spring
open if pressed firmly to the work, and disclose to the workman that the
work is reduced to nearly the required size. So accustomed do workmen
become in estimating from this pressure of contact how nearly the work
is reduced to the required diameter, that they are enabled to estimate,
by forcing the calipers over the work, the depth of the cut required to
be taken off the work, with great exactitude, whereas with solid gauges,
or even caliper gauges of solid proportions, this cannot be done,
because they will not spring open.
The amount to which a pair of calipers will spring open without altering
their set depends upon the shape: thus, with a given joint they will do
so to a greater extent in proportion as the legs are slight, whereas
with a given strength of leg they will do so more as the diameter of the
joint is large and the fit of the joint is a tight one. But if the joint
is so weak as to move too easily, or the legs are so weak as to spring
too easily, the calipers will be apt in one case to shift when applied
to the work, and in the other to spring so easily that it will be
difficult to tell by contact when the points just touch the work and yet
are not sprung by the degree of contact. For these reasons the points of
calipers should be made larger in diameter than they are usually made:
thus, for a pair of calipers of the shape shown in Fig. 1410, the joint
should be about 1-1/4 inches diameter to every 6 inches of length of
leg. The joint should be sufficiently tight that the legs can just be
moved when the two legs are taken in one hand and compressed under heavy
hand pressure.
[Illustration: Fig. 1424.]
For measuring the distance of a slot or keyway from a surface, the form
of calipers shown in Fig. 1424 is employed; the straight leg has its
surface a true plane, and is held flat against the surface B of the slot
or keyway, and the outside or curved leg is set to meet the distance of
the work surface measuring the distance C. These are termed keyway
calipers.
There are in general machine work four kinds of fit, as follow: The
working or sliding fit; the driving fit; the hydraulic press fit; and
the shrinkage fit. In the first of these a proper fit is obtained when
the surfaces are in full contact, and the enveloped piece will move
without undue friction or lost motion when the surfaces are oiled. In
the second, third, and fourth, the enveloped piece is made larger than
the enveloping piece, so that when the two pieces are put together they
will be firmly locked.
It is obvious that in a working or sliding fit the enveloped piece must
be smaller than that enveloping it, or one piece could not pass within
the other. But the amount of difference, although too small to be of
practical importance in pieces of an inch or two in diameter and but few
inches in length, is appreciable in large work, as, say, of two or more
feet in diameter. A journal, for example, of 1/10 inch diameter, running
in a bearing having a bore of 1/1000 inch larger diameter, and being two
diameters in length, would be instantly recognised as a bad fit; but a
journal 6 inches in diameter and two diameters or 12 inches long would
be a fair fit in a bearing having a bore of 6-1/1000 inches. In the one
case the play would be equal to one one-hundredth of the shaft's
diameter, while in the other case the play would equal but one
six-thousandth part of the shaft's diameter. In small work the limit of
wear is so small, and the length of the pieces so short, that the 1/1000
of an inch assumes an importance that does not exist in larger work.
Thus, in watch work, an error of 1/1000 inch in diameter may render the
piece useless; in sewing machine work it may be the limit to which the
tools are allowed to wear; while in a steamship or locomotive engine it
may be of no practical importance whatever.
A journal 1/10 inch in diameter would require to run, under ordinary
conditions, several years to become 1/1000 inch loose in its bearing.
Some of this looseness, and probably nearly one half of it, will occur
from wear of the bearing bore; hence, if a new shaft of the original
standard diameter be supplied the looseness will be reduced by one-half.
But a 6-inch journal and bearing would probably wear nearly 1/1000 inch
loose in wearing down to a bearing which may take but a week or two, and
for these reasons among others, standard gauges and measuring tools are
less applicable to large than to small work.
The great majority of fits made under the standard gauge system consist
of cylindrical pieces fitting into holes or bores. Suppose then that we
have a plug and a collar gauge each of an inch diameter, and a reamer to
fit the collar gauge, and we commence to ream holes and to turn plugs to
fit the collar gauge, then as our work proceeds we shall find that as
the reamer wears, the holes it makes will get smaller, and that as the
collar gauge wears, its bore gets larger, and it is obvious that the
work will not go together. The wear of the gauge obviously proceeds
slowly, but the wear of the reamer begins from the very first hole that
it reams, although it may perform considerable duty before its wear
sensibly affects the size of the hole. Theoretically, however, its size
decreases from the moment it commences to perform cutting duty until it
has worn out, and the point at which the wearing-out process may have
proceeded to its greatest permissible limit is determined by its
reduction of size rather than by the loss of its sharpness or cutting
capacity. Obviously then either the reamer must be so made that its size
may be constantly adjusted to take up the wear, as in the adjustable
reamer, or else if solid reamers are used there must be a certain limit
fixed upon as the utmost permissible amount of wear, and the reamer must
be made above the standard size to an amount equal to the amount of this
limit, so that when the reamer has worn down it will still bore a hole
large enough to admit the plug gauge. To maintain the standard there
should be in this case two sets of gauges, one representing the correct
standard and the other the size to which the reamer is to be made when
new or restored to its proper size.
The limit allowed for reamer wear varies in practice from 1/1000 to
1/10000 of an inch, according to the requirements of the work. As
regards the wear of the standard gauges used by the workmen they are
obviously subject to appreciable wear, and must be returned at intervals
to the tool room to be corrected from gauges used for no other purpose.
To test if a hole is within the determined limit of size a limit gauge
may be used. Suppose, for example, that the limit is 1/1000 of an inch,
then a plug gauge may be made that is 1/1000 of an inch taper, and if
the large end of this plug will enter the hole, the latter is too large,
while if the small end will not enter, the hole is too small.
When only a single set of plug and collar gauges are at hand the plug or
the collar gauge may be kept to maintain the standard, the other being
used to work to, both for inside and outside work. Suppose, for example,
that a plug and collar gauge are used for a certain piece of work and
that both are new, then the reamer may be made from either of them,
because their sizes agree, but after they have become worn either one or
the other must be accepted as the standard of size to make the reamer
to. If it be the collar gauge, then the plug gauge is virtually
discarded as a standard, except in that if the plug gauge be not used at
all it may be kept as a standard of the size to which the collar gauge
must be restored when it has worn sufficiently to render restoration to
size necessary. If this system be adopted the size of the reamer will be
constantly varying to suit the wear of the collar gauge, and the
difficulty is encountered that the standard lathe arbors or mandrels
will not fit the holes produced, and it follows that if standard
mandrels are to be used the reamers must when worn be restored to a
standard size irrespective of the wear of the gauges, and that the
standard mandrels must be made to have as much taper in their lengths as
the limit of wear that is allowed to the reamers. Suppose, for example,
that it is determined to permit the reamer to wear the 1/2000 of an inch
before restoring it to size, then in an inch mandrel the smallest end
may be made an inch in diameter and the largest 1-1/2000 inch in
diameter, so that however much the reamer may be worn within the limit
allowed for wear the hole it produces will fit at some part in the
length of the standard mandrel. But as the reamer wears smaller its size
must be made as much above its designated standard size as the limit
allowed for wear; hence, when new or when restored to size, the reamer
would measure 1-1/2000 inches, and the hole it produced would fit the
large end of the mandrel. But as the reamer wore, the hole would be
reamed smaller and would not pass so far along the mandrel, until
finally the limit of reamer wear being reached the work would fit the
small end of the mandrel. The small end of the mandrel is thus the
standard of its size, and the wear of the collar gauge is in the same
direction as that of the reamer. Thus, so long as the collar gauge has
not worn more than the 1/2000 of an inch it will, if placed upon the
mandrel, fit it at some part of its length.
Now suppose that the plug gauge be accepted as the standard to which the
reamer is to be made, and that to allow for reamer wear the reamer is
made, say, 1/2000 inch larger than the plug gauge, the work being made
to the collar gauge. Then with a new reamer and new or unworn gauges the
hole will be reamed above the standard size to the 1/2000 inch allowed
for reamer wear. As the reamer wears, the hole it produces will become
smaller, and as the collar gauge wears, the work turned to it will be
larger, and the effect will be that, to whatever extent the collar gauge
wears, it will reduce the permissible amount of reamer wear, so that
when the collar gauge had worn the 1/2000 inch the work would not go
together unless the reamer was entirely new or unworn.
In a driving fit one piece is driven within the other by means of hammer
blows, and it follows that one piece must be of larger diameter than the
other, the amount of the difference depending largely upon the diameter
and length of the work.
It is obvious, however, that the difference may be so great that with
sufficiently forcible blows the enveloping piece may be burst open. When
a number of pieces are to be made a driving fit, the two pieces may be
made to fit correctly by trial and correction, and from these pieces
gauges may be made so that subsequent pieces may be made correct by
these gauges, thus avoiding the necessity to try them together.
In fitting the first two pieces by fit and trial, or rather by trial and
correction, the workman is guided as to the correctness of the fit by
the sound of the hammer blows, the rebound of the hammer, and the
distance the piece moves at each blow. Thus the less the movement the
more solid the blow sounds, and the greater the rebound of the hammer
the tighter the fit, and from these elements the experienced workman is
enabled to know how tightly the pieces may be driven together without
danger of bursting the outer one.
What the actual difference in diameter between two pieces may require to
be to make a driving fit is governed, as already said, to a great extent
by the dimensions of the pieces, and also by the nature of the material
and the amount of area in contact. Suppose, for example, that the plug
is 6 inches long, and the amount of pressure required to force it within
the collar will increase with the distance to which it is enveloped by
the collar. Or suppose one plug to be 3 inches and another to be 6
inches in circumference, and each to have entered its collar to the
depth of an inch, while the two inside or enveloped pieces are larger
than the outside pieces by the same amount, the outside pieces being of
equal strength in proportion to their plugs, so that all other elements
are equal, and then it is self-evident that the largest plug will
require twice as much power as the small one will to force it in another
inch into the collar, because the area of contact is twice as great. It
is usual, therefore, under definite conditions to find by experiment
what allowance to make to obtain a driving or a forcing fit. Thus, Mr.
Coleman Sellers, at a meeting of the Car Builders Association, referring
to the proper amount of difference to be allowed between the diameters
of car axles and wheel bores in order to obtain a proper forcing or
hydraulic fit, said, "Several years ago some experiments were made to
determine the difference which should be made between the size of the
hole and that of the axle. The conclusion reached was that if the axle
of standard size was turned 0.007 inch larger than the wheel was bored
it would require a pressure of about 30 tons to press the axle into the
wheel." The wheel seat on the axle here referred to was 4-7/8 inches in
diameter and 7 inches long. It is to be remarked, however, that the
wheel bore being of cast iron and the axle of wrought iron the friction
between the surfaces was not the same as it would be were the two
composed of the same metal. This brings us to a consideration of what
difference in the forcing fit there will be in the case of different
metals, the allowance for forcing being the same and the work being of
the same dimensions.
Suppose, for example, that a wrought-iron plug of an inch in diameter is
so fitted to a bore that when inserted therein to a distance of, say, 2
inches, it requires a pressure of 3 lbs. to cause it to enter farther,
then how much pressure would it take if the bore was of cast iron, of
yellow brass, or of steel, instead of wrought iron. This brings us to
another consideration, inasmuch as the elasticity and the strength of
the enveloping piece has great influence in determining how much to
allow for a driving, forcing, or a shrinkage fit.
Obviously the allowance can be more if the enveloping piece be of
wrought iron, copper, or brass, than for cast iron or steel, because of
the greater elasticity of the former. Leaving the elasticity out of the
question, it would appear a natural assumption that the pieces, being of
the same dimensions, the amount of force necessary to force one piece
within the other would increase in proportion as the equivalents of
friction of the different metals increased.
This has an important bearing in practice, because the fit of pieces not
made to standard gauge diameter is governed to a great extent by the
pressure or power required to move the pieces. Thus, let a steel
crosshead pin be required to be as tight a fit into the crosshead as is
compatible with its extraction by hand, and its diameter in proportion
to that of the bore into which it fits will not be the same if that bore
be of wrought iron, as it would be were the bore of steel, because the
coefficient of friction for cast steel on cast iron is not the same as
that for steel on wrought iron. In other words, the lower the
coefficient of friction on the two surfaces the less the power required
to force one into the other, the gauge diameters being equal. In this
connection it may be remarked that the amount of area in contact is of
primary importance, because in ordinary practice the surfaces of work
left as finished by the steel cutting tools are not sufficiently true
and smooth to give a bearing over the full area of the surfaces.
This occurs for the following reasons. First, work to be bored must be
held (by bolts, plates, chuck-jaws, or similar appliances) with
sufficient force to withstand the pressure of the cut taken by the
cutting tool, and this pressure exerts more or less influence to spring
or deflect the work from its normal shape, so that a hole bored true
while clamped will not be so true when released from the pressure of the
holding clamps.
To obviate this as far as possible, expert workmen screw up the holding
devices as tight as may be necessary for the heavy roughing cuts, and
then slack them off before taking the finishing cuts.
Secondly, under ordinary conditions of workshop practice, the steel
cutting tools do not leave a surface that is a true plane in the
direction of the length of the work, but leave a spiral projection of
more or less prominence and of greater or less height, according to the
width of that part of the cutting edge which lies parallel to the line
of motion of the tool feed, taken in proportion to the rate of feed per
revolution of the work.
Let the distance, Fig. 1424A, A to B lie in the plane of motion of the
tool feed, and measure, say, 1/4 inch, the tool moving, say, 5/16 inch
along the cut per lathe revolution. Suppose the edge from B to D to lie
at a minute angle to the line of tool traverse, and the depth of the cut
to be such that the part from B to C performs a slight cutting or
scraping duty, then the part from B to C will leave a slight ridge on
the work plainly discernible to the naked eye in what are termed the
tool marks.
The obvious means of correcting this is to have the part A B of greater
width than the tool will feed along the cut, during one revolution of
the work (or the cutter, as the case may be); but there are practicable
obstacles to this, especially when applied to wrought iron, steel, or
brass, because the broader the cutting edge of a tool the more liable it
is to spring, as well as to jar or chatter, leaving a surface showing
minute depressions lying parallel to the line of tool feed.
If the cutting tool be made parallel and cylindrical on its edges, and
clearance be given on the front end of its diameter only, so as to cut
along a certain distance only of its cylindrical edge, the rest being a
close fit to the bore of the work, the part having no cutting edge, that
is, the part without clearance, will be apt to cause friction by rubbing
the bore of the work as the tool edge wears, and the friction will cause
heat, which will increase as the cut proceeds, causing the hole to
expand as the cut proceeds, and to be taper when cooled to an equal
degree all over. This may be partly obviated by giving the tool a slow
rate of cutting speed, and a quick rate of feed, which will greatly
reduce the friction and consequently the heating of the tool and the
work. On cast iron it is possible to have a much broader cutting edge to
the tool, without inducing the chattering referred to, than is the case
with wrought iron, steel, or brass, especially when the finishing cut is
a very light one. If the finishing cut be too deep, the surface of the
work, if of cast iron, will be pitted with numerous minute holes, which
occur because the metal breaks out from the strain placed on it (and due
to the cut) just before it meets the cutting edge of the tool.
Especially is this the case if the tool be dull or be ground at an
insufficiently acute angle.
When the work shows the tool marks very plainly, or if of cast iron
shows the pitting referred to (instead of having a smooth and somewhat
glossy appearance), there will be less of its surface in contact with
the surface to which it fits, and the fit will soon become destroyed,
because the wearing surface or the gripping surface, as the case may be,
will the sooner become impaired, causing looseness of the fit. In the
one case the abrasion which should be distributed over the whole area of
the fitting parts is at first confined to the projections having
contact, which, therefore, soon wear away. In the other case the
projecting area in contact compresses, causing looseness of the fit.
Hydraulic press or forcing fits.--For securing pieces together by
forcing one within the other by means of an hydraulic press, the plug
piece is made a certain amount larger than the bore it is to enter, this
amount being termed the allowance for forcing. What this allowance
should be under any given conditions for a given metal, will depend upon
the truth and smoothness of the surfaces, and on this account no
universal rule obtains in general practice. From some experiments made
by William Sellers & Co., it was determined that if a wheel seat (on an
axle) measuring 4-7/8 inches in diameter and 7 inches long was turned
7/1000 of an inch larger than the wheel bore, it would require a
pressure of about thirty tons to force the wheel home on the axle.
At the Susquehanna shops of the Erie railroad the measurements are
determined by judgment, the operatives using ordinary calipers. If an
axle 3-1/2 diameter and 6 inches long requires less than 25 tons it is
rejected, and if more than 35 tons it is corrected by reducing the axle.
In order to insure a proper fit of pieces to be a driven or forced fit
it is sometimes the practice to make them taper, and there is a
difference of opinion among practical mechanics as to whether taper or
parallel fits are the best. Upon this point it may be remarked that it
is much easier to measure the parts when they are parallel than when
they are taper, and it is easier to make them parallel than taper.
On the elevated railroads in New York city, the wheel bores being 4-1/8
inches in diameter and 5 inches long, the measurements are taken by
ordinary calipers, the workmen judging how much to allow, and the rule
is to reject wheels requiring less than about 26 tons, or more than
about 35 tons, to force them on. These wheels form excellent examples,
because of the excessive duty to which they are subjected by reason of
the frequency of their stoppage under the pressure of the vacuum brake.
The practice with these wheels is to bore them parallel, finishing with
a feed of 1/4 inch per lathe revolution, and to turn the axle seats
taper just discernible by calipers.
This may, at first sight, seem strange, but examination makes it
reasonable and plain. Let a wheel having a parallel bore be forced upon
a parallel axle, and then forced off again, and the bore of the wheel
will be found taper to an appreciable amount, but increasing in
proportion as the surface of the hole varied from a dead smoothness; in
other words, varying with the depth of the tool marks in the bore and
the smoothness of the cut.
Let the length of the wheel bore be 7 inches long, and the amount
allowed for forcing be .004 inch, and one end of the wheel bore will
have been forced (by the time it is home on the axle) over the length of
7 inches of the axle-seat, whose diameter was .004 larger than the bore:
a condensation, abrasion, or smoothing of the metal must have ensued.
[Illustration: Fig. 1424A.]
Now the other end of the same bore, when it takes its bearing on the
shaft, is just iron, and iron without having suffered any condensation.
If the tool marks be deep, those on one end will be smoothed down while
those at the other remain practically intact. Clearly then, for a
parallel hole, a shaft having as much taper as the wheel bore will get
in being forced over the shaft best meets the requirements; or, for a
parallel shaft or seat, and a taper hole (the taper being proportioned
as before), the small end of the taper hole should be first entered on
the shaft, and then when home both the axle and the wheel-bore will be
parallel.
It may be remarked that the wheel seat on the axle will also be
affected, which is quite true, but the axle is usually of the hardest
metal and has the smoothest surface, hence it suffers but little; not an
amount of any practical importance.
In an experiment upon this point made in the presence of the author by
Mr. Howard Fry and the master mechanic of the Renovo shops of the
Philadelphia and Erie railroad, an axle seat finished by a Whitney
"doctor," and parallel in diameter, was forced into a wheel having a
parallel bore, and removed immediately. On again measuring the axle, the
wheel-seat was found to be 1/1000 taper in its length.
The wheel-bore was found to be but slightly affected in its diameter,
which is explained because it being very smooth, while the turning marks
in the axle were plainly visible, the abrasion fell mainly upon the
latter.
When the enveloping piece or bore is not solid or continuous, but is
open on one side, the degree of the fit may be judged from the amount
that it opens under the pressure of the plug piece.
[Illustration: Fig. 1425.]
Thus the axle brasses of American locomotives are often made circular at
the back, as shown in Fig. 1425, and are forced in endways by hydraulic
pressure. The degree of tightness of the brass within the box may, of
course, be determined by the amount of pressure it requires to force it
in, but another method is to mark a centre punch dot as at J, and before
the brass is put in mark from this dot as a centre an arc of a circle as
L L. When the brass is home in the box a second arc K is marked, the
distance between L and K showing how much the brass has sprung the box
open widening at H. In an axle box whose bore is about 4 inches to 5
inches in diameter, and 6 inches long, 1/32 inch is the allowance
usually made.
Shrinkage fits are employed when a hole or bore requires to be very
firmly and permanently fastened to a cylindrical piece as a shaft. The
bore is turned of smaller diameter than its shaft, and the amount of
difference is termed the allowance for shrinkage. The enveloping piece
is heated so as to expand its bore; the shaft is then inserted and the
cooling of the bore causes it to close or contract upon the shaft with
an amount of force varying of course with the amount allowed for
contraction. If this allowance is excessive, sufficient strain will be
generated to burst the enveloping piece asunder, while if the allowance
for shrinking is insufficient the enveloping piece may become loose.
The amount of allowance for shrinkage varies with the diameter
thickness, and kind of the material; but more may be allowed for wrought
iron, brass, and copper, than for cast iron or steel.
Again, the smoothness and truth of the surfaces is an important element,
because the measurement of a bore will naturally be taken at the tops of
the tool marks, and these will compress under the shrinkage strain,
hence less allowance for contraction is required in proportion as the
bore is smoother.
In ordinary workshop practice, therefore, no special rule for the amount
of allowance for shrinkage obtains, the amount for a desultory piece of
work generally being left to the judgment of the workman, while in cases
where such work is often performed on particular pieces, the amount of
allowance is governed by experience, increasing it if the pieces are
found in time to become loose, and decreasing it if it is found
impossible to get the parts together without making the enveloping piece
too hot, or if it is found to be liable to split from the strain.
The strength of the enveloping piece is again an element to be
considered in determining the amount to be allowed for shrinkage. It is
obvious, for example, that a ring of 8 inches thick, and having a bore
of, say, 6 inches diameter, would be less liable to crack from the
strain due to an allowance of 1/50 inch for contraction, than would a
ring of equal bore and one inch thick having the same allowance. The
strength or resistance to compression of the piece enveloped in
proportion to that enveloping it, is yet another consideration.
The tires for railway wheels are usually contracted on, and Herr Krupp
states the allowance for contraction to be for steel tires 1/100 inch
for every foot of diameter; in American practice, however, a greater
amount is often employed. Thus upon the Erie railroad a 5 foot tire is
given 1/16 inch contraction. The allowance for wrought iron or brass
should be slightly more than it is for steel or cast iron, on account of
the greater elasticity of those metals.
Examples of the practice at the Renovo shops of the Pennsylvania road
are as follows:
Class E, diameter of wheel centre, 44 inches; bore of steel tire,
43-15/16 inches.
Class D, diameter of wheel, 50 inches; bore of tire, 49-9/16 inches.
It is found that the shrinkage of the tire springs or distorts the wheel
centre, hence the tires are always shrunk on before the crank-pin holes
are bored.
Much of the work formerly shrunk on is now forced on by an hydraulic
press. But in many cases the work cannot be taken to an hydraulic press,
and shrinkage becomes the best means. Thus, a new crank pin may be
required to be shrunk in while the crank is on the engine shaft, the
method of procedure being as follows: In heating the crank, it is
necessary to heat it as equally as possible all round the bore, and not
to heat it above a _very dark_ red. In heating it some dirt will
necessarily get into the hole, and this is best cleaned out with a piece
of emery paper, wrapped round a half-round file, carefully blowing out
the hole after using the emery paper. Waste or rag, whether oiled or
not, is not proper to clean the hole with, as the fibres may burn and
lodge in the hole; indeed, nothing is so good as emery paper.
It is desirable to heat the crank as little as will serve the purpose,
and it is usual to heat it enough to allow the pin to push home by hand.
It is better, however, to overheat the crank than to underheat it,
providing that the heat in no case exceeds a barely perceptible red
heat. If, however, the crank once grips the pin before it is home, in a
few seconds the pin will be held so fast that no sledge hammer will move
it. It is well, therefore, to have a man stationed on each side of the
crank, each with a sledge hammer, and to push the crank pin in with a
slam, giving the man in front orders to strike it as quickly as possible
at a given signal; but if the pin does not move home so rapidly at each
blow as to make it appear certain that it will go home, the man at the
rear, who should have a ten-pound sledge, should be signalled to drive
out the crank pin as quickly as he possibly can for every second is of
consequence. All this should be done so quickly that the pin has not
had time to get heated to say 100° at the part within the crank.
So soon as the pin is home, a large piece of wetted cotton waste should
be wrapped round its journal, and a stream of water kept running on it,
to keep the crank pin cold. At the other end water should be poured on
the pin end in a fine stream, but in neither case should the water run
on the crank more than can be avoided. Of course, if the crank is off
the shaft, the pin may be turned downward, and let project into water.
The reasons for cooling the pin and not the crank are as follows: If the
crank be of cast iron, sudden cooling it would be liable to cause it to
split or crack. If the crank pin is allowed to cool of itself, the pin
will get as hot as the crank itself, and in so doing will expand,
placing a strain on the crank that will to some extent stretch it.
Indeed, when the pin has become equally hot with the crank it is as
tight a fit as it will ever be, because after that point both pieces
will cool together, and shrink or contract together, and hence the fit
will be a looser or less tight one to the amount that the pin expanded
in heating up to an equal temperature with the crank.
The correct process of shrinking is to keep the plug piece as cold as
possible, while the outside is cooled as rapidly as can be without
danger of cracking or splitting.
The ends of crank pins are often riveted after being shrunk in, in which
case it is best to recess the end, which makes the riveting easier, and
causes the water poured upon its face to be thrown outward, thus keeping
it from running down the crank face and causing the crank to crack or
split.
It sometimes becomes necessary and difficult to take out a piece that
has been shrunk in, and in this event, as also in the case of a piece
that has become locked before getting fully home in the shrinking
process, there is no alternative but to reheat the enveloping piece
while keeping the enveloped piece as cold as can be by an application of
water.
The whole aim in this case is to heat the enveloping piece as quickly as
possible, so that there shall be but little time for its heat to be
transmitted to the piece enveloped. To accomplish this end melted metal,
as cast iron, is probably the most efficient agent; indeed it has been
found to answer when all other means failed.
[Illustration: Fig. 1426.]
[Illustration: Fig. 1427.]
The fine measurements necessary for shrinkage purposes render it
necessary, where pieces of the same form and kind are shrunk on, to
provide the workmen with standard gauges with which the work may be
correctly gauged. These often consist of simple rods or pieces of iron
wire of the required length. Figs. 1426 and 1427, however, represent an
adjustable shrinkage gauge designed by H. S. Brown, of Hartford,
Connecticut. Fig. 1427 is a sectional, and Fig. 1426 a plan side view of
the gauge. A is a frame, containing at its lower end a fixed measuring
piece B, and provided at its upper end with a threaded and taper split
hub to receive externally the taper-threaded screw cap C, and threaded
internally to receive a tube E, which is plugged at the bottom by the
fixed plug F. The adjustable measuring leg G is threaded with the tube
E, so as to be adjustable for various diameters of boxes, but it is
locked when adjusted by the jamb-nut H. The operation is as follows: The
cap-nut C and jamb-nut H are loosened and screwed back, allowing stem G
and tube E to be adjusted to the exact size of the shaft for which a
shrinkage fit is to be bored, as, say, in an engine crank. In setting
the gauge to the diameter of the shaft, the cap end C and jamb-nut H are
screwed home, so as to obtain a correct measurement while all parts are
locked secure. The cap-nut C draws the split hub upon the tube E, and
the jamb-nut H locks up G to E, so that the shaft measurement is taken
with all lost motion, play and spring of the mechanism taken into
account, so that they shall not vitiate the measurement. This being
done, C is loosened so that E can be rotated, and raised up (by
rotating) to admit the shrinkage gauge-piece J, whose thickness equals
the amount to be allowed for the size of borer to be shrunk on the
shaft. J being inserted, E is rotated back so as to bind J between the
end of E and the foot piece B, when C is screwed down, clamping E again.
Thus the measuring diameter of the gauge is increased to an amount due
to the thickness of the gauge-piece J. At the right of Fig. 1426 an edge
and side elevation of J is shown, the 12/1000 indicating its thickness,
which is the amount allowed for shrinkage, and the 6-inch indicating
that this gauge-piece is to be used for bores of 6 inches in diameter.
The dotted circle K K L L represents a bore to which the gauge is shown
applied.
The system of shrinking employed at the Royal Gun Factory at Woolwich,
England, is thus described by Colonel Maitland, superintendent of that
factory:--
"The inside diameter of the outer tube, when cold, must be rather
smaller than the outside diameter of the inner tube: this difference in
the diameter is called the 'shrinkage.' While the outer coil is cooling
and contracting it compresses the inner one: the amount by which the
diameter of the inner coil is decreased is termed the 'compression.'
Again, the outer coil itself is stretched on account of the resistance
of the inner one, and its diameter is increased; this increase in the
diameter of an outer coil is called 'extension.' The shrinkage is equal
to compression plus the extension, and the amount must be regulated by
the known extension and compression under certain stresses and given
circumstances. The compression varies inversely as the density and
rigidity of the interior mass; the first layer of coils will therefore
undergo more compression than the secondhand the second more than the
third, and so on.
"Shrinking is employed not only as an easy and efficient mode of binding
the successive coils of a built-up gun firmly together, but also for
regulating as far as possible the tension of the several layers, so that
each and all may contribute fairly to the strength of the gun.
"The operation of shrinking is very simple; the outer coil is expanded
by heat until it is sufficiently large to fit easily over the inner coil
or tube (if a large mass, such as the jacket of a Fraser gun, by means
of a wood fire, for which the tube itself forms a flue; if a small mass,
such as a coil, in a reverberatory furnace at a low temperature, or by
means of gas). It is then raised up by a travelling crane overhead and
dropped over the part on to which it is to be shrunk, which is placed
vertically in a pit ready to receive it.
"The heat required in shrinking is not very great. Wrought iron, on
being heated from 62° Fahr. (the ordinary temperature) to 212°, expands
linearly about 1-1000th part of its length; that is to say, if a ring of
iron 1000 inches in circumference were put into a vat of boiling water,
it would increase to 1001 inches, and according to Dulong and Petit the
coefficient of expansion, which is constant up to 212°, increases more
and more from that point upward, so that if the iron ring were raised
150° higher still (_i.e._ to 362°) its circumference would be more than
1002 inches. No coil is ever shrunk on with so great a shrinkage as the
2-1000th part of its circumference or diameter, for it would be strained
beyond its elastic limit. Allowing, therefore, a good working margin, it
is only necessary to raise a coil to about 500° Fahr.,[22] though in
point of fact coils are often raised to a higher degree of temperature
than this in some parts, on account of the mode of heating employed.
Were a coil plunged in molten lead or boiling oil (600° Fahr.) it would
be uniformly and sufficiently expanded for all the practical purposes of
shrinking, but as shrinkings do not take place in large numbers or at
regular times, the improvised fire or ordinary furnace is the more
economical mode, and answers the purpose very well.
[22] The temperature may be judged by color; at 500° F. iron has a
blackish appearance; at 575° it is blue; at 775° red in the dark; at
1,500° cherry red, and so on, getting lighter in color, until it
becomes white, or fit for welding, at about 3,000°.
"Heating a coil beyond the required amount is of no consequence,
provided it is not raised to such a degree of temperature that scales
would form; and in all cases the interior must be swept clean of ashes,
&c., when it is withdrawn from the fire. With respect to the modes of
cooling during the process of shrinking, care must be taken to prevent a
long coil or tube cooling simultaneously at both ends, for this would
cause the middle portion to be drawn out to an undue state of
longitudinal tension. In some cases, therefore, water is projected on
one side of a coil so as to cool it first. In the case of a long tube of
different thickness, like the tube of a R. M. L. gun, water is not only
used at the thick end, but a ring of gas or a heated iron cylinder is
applied at the thin or muzzle end, and when the thick end cools the gas
or cylinder is withdrawn from the muzzle, and the ring of water raised
upward slowly to cool the remainder of the tube gradually.
"As a rule, the water is supplied whenever there is a shoulder, so that
that portion may be cooled first and a close joint secured there; and
water is invariably allowed to circulate through the interior of the
mass to prevent its expanding and obstructing or delaying the operation;
for example, when a tube is to be shrunk on a steel barrel, the latter
is placed upright on its breech end, and when the tube is dropped down
on it, a continual flow of cold water is kept up in the barrel by means
of a pipe and syphon at the muzzle. The same effect is produced by a
water jet underneath, when it is necessary to place the steel tube
muzzle downward for the reception of a breech coil. As to the absolute
amount of shrinkage given when building up our guns, let us take the
12-1/2-inch muzzle-loading gun of 38 tons as an example.
SHRINKAGES OF COILS OF 12.5 INCH R. M. L. GUNS.
-------------+---------------------------+---------------------------
| Shrinkages. |
+-------------+-------------+
| | In terms of |
Coils. | In Inches. | diameter. | Remarks.
+------+------+------+------+
| Rear.|Front.| Rear.|Front.|
-------------+------+------+------+------+---------------------------
| | | D | D |
Breech-piece| .022 | .026 | --- | --- | Shrunk on A tube.
| | | 857 | 807 |
| | | | |
| | | D | D |
B coil | .055 | .01 | --- | --- | " "
| | | 561 | 190 |
| | | | |
| | | D | |
B tube | .035 | nil. | --- | nil. | " "
| | | 668 | |
| | | | |
| | | D | D |
C coil | .03 | .06 | ---- | --- | Shrunk on to breech piece
| | | 1134 | 729 | and rear end of 1 B coil."
-------------+------+------+------+------+---------------------------
The objections to fitting work by contraction where accuracy is required
in the work are, that if the enveloping piece is of cast iron its form
is apt to change from being heated. Furthermore, if the enveloping
piece, which is always the piece to be heated, is of unequal thickness
all round the bore, the thin parts are apt to become heated the most,
and to therefore give way to the strain induced by contraction when
cooling, which, while not, perhaps, impairing the fit, may vitiate the
alignment of parts attached to it. Thus, a crank pin may be thrown out
of true by the alteration of form induced first by unequal heating of
the metal round the crank eye, enveloping the shaft; and secondly,
because of the weakest side of the eye giving way, to some extent, to
the pressure of the contracting strain. To counteract this, the
strongest part of the enveloping piece should be heated the most, or if
the enveloping piece be of equal strength all round its bore, it should
be heated equally all round. To effect this object heated liquids, as
boiling water, or heated fluids, as melted lead, may advantageously be
employed.
In some practice, locomotive wheel tires are heated for shrinking in
boiling water. The allowance for shrinkage is from .075 millimètre to
every mètre in diameter, which is .02952 inch to every 39.37079 inches
of diameter.
The employment of hot water, however, necessitates that the tires be
bored very smoothly and truly, and that the wheel rim be similarly true
and smooth, otherwise the amount of expansion thus obtained will be
insufficient to maintain a permanent fit under the duty to which a wheel
tire is submitted.
Shrinking is often employed to strengthen a weak place or part, or one
that has cracked. The required size is, in this case, a cylindrical
surface that is not a true cylinder, obtained by a rolling wheel rotated
by friction over the surface to be enveloped by the band. Or if the
surface is of a nature not to admit of this, a strip of lead or piece of
lead wire may be lapped round it to get the necessary measurements.
The bands for this purpose are usually of wrought iron, and require in
the case of irregular surfaces to be driven on by hammer blows, so that
the fit may be correct. As the band is forced on a heavy hammer is held
against it, to prevent its moving back and off the work as the other
parts are forced on.
[Illustration: Fig. 1428.]
Very slight bands may be forced on by levers: thus, wagon makers use a
lever or jack, such as in Fig. 1428, for forcing the tires on their
wheels. The wheel is laid horizontally on a table as shown, and the tire
A forced out by the vertical lever, the arm B affording a fulcrum for
the lever, and itself resting against the hub C of the wheel.
The following extracts are from a paper read by Thomas Wrightson, before
the Iron and Steel Institute of Great Britain.
"The large amount of attention bestowed upon the chemical properties of
metals, and the scientific methods adopted for their investigation, have
led to the most brilliant results in the history of iron and steel
industries. It must not, however, be overlooked that iron and steel have
highly important properties other than those which can be examined by
chemical methods. The cause for so little having been done in accurate
observation of the physical properties of iron is twofold: 1. The
molecular changes of the metals are so slow, when at ordinary
temperatures and when under ordinary conditions of strain, that reliable
observations, necessarily extending over long periods, are difficult to
obtain: 2. When the temperatures are high--at which times the greatest
and most rapid molecular changes are occurring--the difficulties of
observation are multiplied to such an extent that the results have not
the scientific accuracy which characterizes the knowledge we have of the
chemical properties of metals.
"The object of the present paper is to draw attention to some phenomena
connected with the physical properties of iron and steel, and to record
some experiments showing the behavior of these metals under certain
conditions.
"In experimenting the author has endeavored to adopt methods which
would, as far as possible, eliminate the two great difficulties
mentioned.
"It is obvious that the possible conditions under which experiments may
be made are so numerous that all which any one experimenter can do is to
record faithfully and accurately his observations, carefully specifying
the exact conditions of each observation, and this must eventually lead
to a more complete knowledge of the physical properties of the metals.
"The author's observations have been led in the following directions:--
"1. The changes in wrought and cast iron when subjected to repeated
heatings and coolings.
"2. The effect upon bars and rings when different parts are cooled at
different rates.
"3. These changes occurring in molten iron when passing from the solid
to the liquid state, and _vice versâ_.
PART I.
"To illustrate the practical importance of knowing the effects of
reiterated heating and cooling on iron plates, one of the most obvious
examples is the action of heat upon the plates of boilers which are
alternately heated and cooled, as in use or otherwise. When in use, the
plates above the fire are subjected to the fierce flame of the furnace
on one side, and on the other side to a temperature approximating to
that of the steam and water in the boiler. Where the conducting surfaces
of the metal are thickened at the riveted seams, a source of danger is
frequently revealed in the appearance of what are known as 'seam-rips.'
"The long egg-ended boilers, much used in the North of England, are very
subject to this breaking away of the seams. From some tests made by the
writer on iron cut from the plates of two different boilers which had
ripped at the seams, and one of which seam-rips had led to an explosion
resulting in the destruction of much property, though happily of no
lives, it was found that the heat acting on the bottom of the boiler
had, through time, so affected the iron at the seam as to make it
brittle, apparently crystalline in fracture, and of small tensile
strength. Farther from the seam the iron appeared in both cases less
injuriously affected. But although the alternate heating and cooling of
the plates over a long period had produced this change in the molecular
condition of the iron, a method of restoration presents itself in the
process of annealing. In subjecting the pieces cut from the seam-rips to
a dull red heat, and then allowing them to cool slowly in sawdust, the
writer found that the fibrous character of the iron appeared again, and
renewed testing showed that the ductility and tensile strength were
restored.
"The same process of annealing is equally effectual in restoring the
tenacity of iron in chains rendered brittle, and apparently crystalline,
by long use, and is periodically applied where safety depends upon
material in this form. Thus the heating and cooling of iron may be
looked upon as the bane or the antidote according to the conditions
under which the process is carried out. This affords an example of the
importance of the physical effects produced by repeated changes of
temperature. The change effected by one heating and cooling is so small
that a cumulative method of experiment is the only one by which an
observable result can be obtained, and this is the method adopted by the
writer in the investigation now to be described.
"It is well known that if a wrought-iron bar be heated to redness, a
certain expansion takes place, which is most distinctly observed in the
direction of its length. It is also known, although not generally so,
that if a bar be thus heated and then suddenly cooled in water, a
contraction in length takes place, the amount of this contraction
exceeding that of the previous expansion, insomuch that the bar when
cooled is permanently shorter than it originally was. If this process of
heating and cooling be repeated, a further amount of contraction is
found to follow for many successive operations.
"Experiments Nos. 1 and 2 were made to verify this, and to show the
increment of contraction after each operation.
"EXPERIMENTS ON WROUGHT-IRON BARS 1-1/8 IN. SQUARE BY 30.05 IN. LONG,
HEATED TO A DULL RED, THEN COOLED SUDDENLY IN WATER.
------------------+------------------------+------------------------
| EXPERIMENT NO. 1. | EXPERIMENT NO. 2.
| Common Iron. | Best Iron.
+------------+-----------+------------+-----------
| |Percentage | |Percentage
|Contraction.|on original|Contraction.|on original
| | length. | | length.
------------------+------------+-----------+------------+-----------
| Inches. | | Inches. |
After 1st cooling | .04 | .13 | .04 | .13
" 2nd " | .10 | .33 | .10 | .33
" 3rd " | .16 | .53 | .14 | .46
" 4th " | .17 | .56 | .16 | .53
" 5th " | .23 | .76 | .20 | .66
" 6th " | .28 | .93 | .24 | .80
" 7th " | .31 | 1.03 | .27 | .89
" 8th " | .33 | 1.10 | .30 | 1.00
" 9th " | .40 | 1.33 | .33 | 1.10
" 10th " | .47 | 1.56 | .39 | 1.30
" 11th " | .52 | 1.73 | .42 | 1.40
" 12th " | .54 | 1.80 | .47 | 1.56
" 13th " | .58 | 1.93 | .51 | 1.70
" 14th " | .62 | 2.06 | .54 | 1.80
" 15th " | .68 | 2.26 | .56 | 1.86
------------------+------------+-----------+------------+-----------
"The Table of Experiment No. 5 shows that at the twenty-fifth cooling a
contraction of 3.05 per cent. had taken place, or an average of .122 per
cent. after each cooling. This is almost identically the same average
result as shown in Experiment No. 1 with straight bars.
"The above experiments only having reference to the permanent
contraction of the iron in the direction of its length, the author made
the following experiments to ascertain the effect in the other
dimensions, and to see whether the specific gravity of the iron was
affected in the reduction of dimensions.
[Illustration: Fig. 1429.]
"_Experiment No. 6._--Wrought-iron plate, .74 inch thick, planed on both
surfaces and all edges to a form nearly rectangular, and of the
dimensions given in Fig. 1429.
"_Specific Gravity._--Two small samples were cut out of different parts
of the same piece of plate from which the experimental piece was planed,
and the specific gravity determined as follows:--
No. 1 piece 7.629 }
No. 2 piece 7.651 } Mean, 7.64.
"_Quality._--Subjecting a piece to tensile strain in the direction of
the grain, it broke at 21.2 tons per square inch of section, the
ductility being such that an elongation of 8.3 per cent. occurred before
fracture, with a reduction of 9.6 per cent. of the area of fracture.
This may be looked upon as representing a fairly good quality of iron.
"A bar of wrought iron, 1-1/8 inches square and 30.00 inches long, was
heated to redness, and then allowed to cool gradually in air.
Measurements after each of five coolings showed no perceptible change of
length.
"_Experiment No. 4._--Wrought-iron bar, 1-1/8 inches square by 30 inches
long, heated to a white heat and cooling gradually in air.
------------------+------------+----------------+----------------
|Contraction.| Percentage on | Remarks.
| |original length.|
------------------+------------+----------------+----------------
| Inches. | |
After 1st cooling | No change. | | ----
" 2nd " | " | | ----
" 3rd " | .02 | .07 | ----
" 4th " | .05 | .17 | ----
" 5th " | .05 | .17 | ----
------------------+------------+----------------+----------------
"It may be remarked, that if the bars be heated to white heat a slight
contraction does occur, as shown by Experiment No. 4, where a bar of the
same dimensions as No. 3 contracted .17 per cent. after the fifth
cooling. As, however, the further remarks on this subject have only
reference to bars heated to redness and then cooled, the writer would
summarize the results of Experiments Nos. 1, 2, and 3, by stating that
wrought-iron bars heated to redness permanently contract in their length
along the fibre when cooled in water of ordinary temperature; but when
cooled in air, they remain unchanged in length.
"To show that this is true as applied to circular hoops, Experiment No.
5 was made upon a wrought-iron bar of 1-1/8 inches square in section,
welded into a circular hoop, 57.7 inches outside circumference.
"_Experiment No. 5._--Wrought-iron hoop, 1-1/8 inches square by 57.7
inches outside circumference, heated to a dull red, then cooled suddenly
in water.
------------------+------------+--------------+-----------------------
| |Percentage of |
|Contraction.| original | Remarks.
| |circumference.|
------------------+------------+--------------+-----------------------
| Inches. | |
After 1st cooling | .06 | .10 | Red heat.
" 2nd " | .06 | .10 | This was nearly white,
" 3rd " | .16 | .28 | but before cooling
" 4th " | .26 | .45 | red hot.
" 5th " | .35 | .61 |
" 6th " | .46 | .80 |
" 7th " | .54 | .93 |
" 8th " | .60 | 1.04 |
" 9th " | .68 | 1.18 |
" 10th " | .76 | 1.32 |
" 11th " | .80 | 1.38 |
" 12th " | .87 | 1.51 |
" 13th " | .94 | 1.63 |
" 14th " | 1.00 | 1.73 |
" 15th " | 1.08 | 1.90 |
" 20th " | 1.30 | 2.25 | On opposite edge 1.66;
" 25th " | 1.76 | 3.05 | hoop splitting.
------------------+------------+--------------+-----------------------
"This hoop was heated to redness and cooled in water twenty-five times,
the circumference of the hoop being accurately measured after each
cooling.[23]
[23] The lengths of circumference were taken, in this and other hoops,
after each cooling, by encircling the periphery with a very fine piece
of "crinoline" steel, the ends of which were made just to meet round
the original hoop. By again encircling the hoop with the same piece of
steel the expansion was shown by a gap between the ends, and a
contraction by an overlap, either of which was measured with great
accuracy by means of a finely divided scale.
"Two wrought-iron bars, 1-1/8 inches square and 30.05 inches long, were
selected.[24] No. 1 was of common "Crown" quality; No. 2 of a superior
quality known as "Tudhoe Crown." These bars were heated to redness in a
furnace and then plunged into water of ordinary temperature, the length
being accurately measured after each cooling. After fifteen heatings and
coolings the permanent contraction on No. 1 bar was 2.26 per cent. of
the original length, and that on No. 2 bar 1.86 per cent., or an average
on the two bars of about .13 per cent. after each cooling, the increment
of contraction being nearly equal after each successive operation. It is
noticeable that after the first two coolings the better quality of iron
did not contract quite so much as the common quality, and that in the
latter the contraction was going on as vigorously at the fifteenth as at
the first cooling.
[24] In some of these experiments the original sizes of the iron were
only measured with an ordinary foot-rule, in which case the dimensions
are given in the ordinary fraction used in expressing the mercantile
sizes of iron. When accurate measurement was taken decimals are
invariably used both in this paper and the Tables of Experiment.
"Similar bars of wrought iron, heated to redness and then allowed to
cool in air at ordinary temperature, do not appear to suffer any
permanent change in their length.
"Experiment No. 3 was made to verify this.
"_Experiment No. 3._--Wrought-iron bar, 1-1/8 inches square by 30 inches
long heated to a dull red and cooled gradually in air.
------------------+------------+----------------+-----------
|Contraction.| Percentage on |
| |original length.| Remarks.
------------------+------------+----------------+-----------
After 1st cooling | No change. | ---- | ----
" 2nd " | " | ---- | ----
" 3rd " | " | ---- | ----
" 4th " | " | ---- | ----
" 5th " | " | ---- | ----
------------------+------------+----------------+-----------
[Illustration: _Wrought iron rectangular plate. 14" thick × 11" 995 ×
598 planed on both surface and edges. Heated to redness, and cooled in
water 50 times. The dotted lines show original form, the black lines the
form after the experiment._
(Two-ninths of full size.)
Fig. 1430.]
The plate was subjected to fifty heatings to redness and subsequent
coolings in water of ordinary temperature. At every tenth cooling
accurate measurements were taken of the contraction in superficial
dimensions, and Fig. 1430 shows the final form after fifty coolings. The
intermediate measurements at every tenth cooling showed a uniform and
gradual decrease in the superficial dimensions, but the thicknesses were
only measured after the fifty coolings had been completed. The thickness
appears to have varied considerably; in some places, notably towards the
centre and outside edges, being much reduced. Between the centre and
outside edges the thickness appears to have increased, and in some few
places the plate has been split open. The average dimensions in inches
before and after the experiment were as follows (dimensions of cracks
being allowed for):--
----------------------+---------+----------+----------+-----------
| | | | Cubic
| Average | Average | Average | inches
| length. | breadth. |thickness.|capacity.
+---------+----------+----------+----------
| Inches. | Inches. | Inches. |
Original | 11.995 | 5.98 | .74 | 53.08
After 50 coolings | 11.25 | 5.59 | .774 | 48.72
Per cent. variation { |Decrease |Decrease | Increase | Decrease
from original { | of | of | of | of
{ |6.2 p. c.|6.52 p. c.| 4.6 p. c.| 8.2 p. c.
----------------------+---------+----------+----------+----------
"Three triangular pieces of iron were then cut out of the plate from
positions indicated on the diagram; No. 1A from the part most reduced in
thickness, No. 3A from the part most increased in thickness, and No. 2A
from a part where the thickness was a mean between the thickest and
thinnest part. The specific gravities were accurately determined as
follows:--
No. 1A 7.552 thinnest part.
No. 2A 7.574 average thickness.
No. 3A 7.560 thickest part.
"The average of these specific gravities is 7.562.
"The average before experiment was 7.64. Hence the average loss in
specific gravity has been 1.02 per cent.
"The small triangular piece No. 1A, specific gravity 7.552 (already
subjected to fifty heatings when forming part of the solid plate), was
next heated and cooled fifty times more. The specific gravity at the end
of the one hundred total coolings was 7.52, being .43 per cent. lower
than after fifty heatings in plate, and 1.57 per cent. lower than 7.64,
the original mean specific gravity of the plate.
"The same piece, 1A, was then heated twenty-five times more, making 125
in all. On taking the specific gravity it was found to be 7.526, or
practically the same as after 100 total heatings and coolings.
"It thus appears that there is an undoubted decrease in specific gravity
on repeated heating and cooling as described up to one hundred coolings,
the specific gravity decreasing as much as 1.57 per cent.; that this
percentage appears to be less when the pieces of iron operated upon are
very small; that while there is a decrease of specific gravity there is
also a decrease of total volume.
[Illustration: Fig. 1431.]
"From the above it was evident that the volume was affected by several
causes:--
"1. By the permanent contraction of the outer skin, either the volume
would be lessened, or relief by bulging out the sides must occur.
"2. By the decrease of specific gravity an increase of volume must
occur, which could also find relief in bulging.
"3. A diminution of the whole mass must occur through scaling of the
surface.
"Having determined the change in specific gravity by Experiment 6, we
only now want to determine the loss of volume due to surface scaling,
and we can then infer the actual contraction of the outer skin.
"_Experiment No. 7._--To ascertain the amount of scaling which took
place in heating and cooling under same conditions as Experiment No. 6,
a wrought-iron plate was cut from the same piece as No. 6, thickness .74
in., planed on both surfaces and all edges to a form nearly rectangular,
and to the dimensions given in Fig. 1431.
"The only difference (except the very small difference in the
dimensions) between this and 1430, was that the principal grain of the
iron was in 1431 in the direction of the arrow, whereas in the other it
was lengthwise of the plate.
"This piece was subjected to fifty heatings to redness and sudden
coolings in water of ordinary temperature, as in the case of No. 6. The
change in form was exactly the same in general character, but the
contraction was not quite so great either in length or breadth; the
increase in thickness, however, was proportionately greater, the volume
(measured by displacement of water) after fifty heatings being 48.6
cubic inches, which is nearly the same as in No. 6 after the same number
of heatings. The weight of the piece:--
Avoirdupois.
lbs. oz. dr.
Before heating 14 10 15
After fifty heatings 13 5 10
------------
Difference 1 1 5
"This represents a loss of 9.07 per cent. of the original weight by
scaling, and upon the whole original surface (sides and edges)
represents a thickness of .0284 of an inch for the fifty immersions, or
.00057 of an inch for the thickness of the film lost at each immersion
over the whole surface.
"Calculating the weight of No. 6 before and after experiment from the
volumes and specific gravities, we find the following:--
Mean Weight of
specific cubic inch
Volume. gravity. water. Pounds.
Weight before heating should be 53.08 × 7.64 × .036 = 14.599
" after " " 48.72 × 7.562 × .036 = 13.262
------
Difference in weight 1.337
the ascertained difference in the case of No. 7 being 1.332, thus
sufficiently accounting for the discrepancy between specific gravity and
change of volume by the scaling.
"By Experiment 7 it has been shown that the loss of thickness due to
scaling after fifty immersions was .0284 inch over the whole surface
(sides and edges.) Therefore, assuming this scaling as uniform over the
surface, the girth, whether measured lengthwise or breadthwise, should
be eight times .0284, or .23 inch less after immersion than before. Now
the gross loss of girth is:--
--------------------------------------+-----------+------------
|Lengthwise.|Breadthwise.
--------------------------------------+-----------+------------
| Inches. | Inches.
In No. 6 | 1.38 | .86
In No. 7 | 1.2 | .52
+-----------+------------
Or for both experiments a mean of | 1.29 | .69
Deducting from them the loss of | |
girth due to scaling | .23 | .23
+-----------+------------
Net contraction after fifty immersions| 1.06 | .46
Or in percentage of original girths, | |
which were | 25.46 | 13.43
| per cent. | per cent.
We have a percentage of | 4.16 | 3.42
Or for each immersion an average of | .083 | .07
--------------------------------------+-----------+------------
"Comparing these results with those of Experiments Nos. 1, 2, and 5, we
find that the contraction of the skin of the plate is less for each
immersion than that of a bar or hoop, in the proportion of .125 to .083.
This is what might be expected, as the contraction of the plate is
resisted by the volume of heated matter inside, which is eventually
displaced by bulging, while the bar finds relief endwise without having
to displace the interior.
"We have now before us the following facts, substantiated by the
experiments described:--
"1. That in heating to redness, and then cooling suddenly in water at
ordinary temperatures, bars and plates of wrought iron, a reduction of
specific gravity takes place, the amount being about 1 per cent. after
fifty immersions, and 1.57 per cent. after one hundred immersions,
further heatings and coolings not appearing to produce further change.
"2. That a reduction of the surface takes place after each heating and
cooling, this being due to two causes:--
"_a._ The scaling of the surface, which is shown to amount to a film
over the (sides and edges) entire area of .00057 inch in thickness for
each immersion, or 0.284 inch for fifty immersions (Experiment 7).
"_b._ A persistent contraction, which takes place after each immersion.
This varies according to the form of the iron, being in plates from .07
per cent. to 0.83 per cent. (Experiment 6), while in long bars it varies
from .122 to .15 per cent. (Experiments 1, 2, and 5). This contraction
continues vigorously up to fifty immersions, and probably much farther.
"3. That in the case of plates a bulging takes place on the largest
surfaces, increasing the thickness towards the centres, although the
edges diminish in thickness.
"4. That wrought-iron bars heated to redness, and allowed to cool slowly
in air, do not show any change in dimensions (Experiment 3).
"The reduction of specific gravity, and the bulging out of the sides,
have been explained as follows by the learned Secretary of the Royal
Society, Professor Stokes, who has taken considerable interest in these
experiments, and who has kindly allowed the author to publish the
explanation:
"'When the heated iron is plunged into water, the skin tends everywhere
to contract. It cannot, however, do so to any significant extent by a
contraction which would leave it similar to itself, because that would
imply a squeezing in of the interior metal, which is still expanded by
heat, and is almost incompressible. The endeavor, then, of the skin to
contract is best satisfied, consistently with the retention of volume of
the interior, by a contraction of the skin in the two longish lateral
directions, combined with a bulging out in the short direction. The
still plastic state of the interior permits of this change.
"'Conceive an india-rubber skin of the form of the plate in its first
state, the skin being free from tension, and having its interior filled
with water, treacle, or pitch. I make abstraction of gravity. It would
retain its shape. But suppose, now, the india-rubber to be endowed with
a tension the same everywhere similar to that of india-rubber that has
been pulled out, what would take place? Why, the flat faces of
considerable area, being comparatively weak to resist the interior
pressure, would be bulged out, and the vessel would contract
considerably in the long directions, increasing in thickness. This is
just what takes place with the iron in the first instance. But when the
cooling has made further progress, and the solidified skin has become
comparatively thick and strong, the further cooling of the interior
tends to make it contract. But this it cannot well do, being encased in
a strong hide, and accordingly the interior tends to be left in a porous
condition.'
"The reduction by scaling does not require any explanation. The only
fact which appears unaccounted for is this persistent contraction of the
cooled iron skin, which does not appear to be explicable on any
mechanical grounds; and we are, therefore, obliged to look upon it as
the result of a change in the distance of the molecules of the iron,
caused by the sudden change of temperature in the successive coolings.
"Our next subject is the curious effect of cooling bars or rings by
partial immersion in water. Bearing in mind the results at which we have
arrived, viz., that wrought iron contracts when immersed in water after
heating, and that when allowed to cool in air it remains of the same
dimensions, let us ask what would be the behavior of a bar or circular
hoop of iron cooled half in water and half in air, the surface of the
water being parallel to the fibre and at right angles to the axis of the
hoop?
"Arguing from the results of Experiments 1, 2, and 5, it might be
expected that the lower portion cooled in water would suffer permanent
contraction; and, arguing from Experiment 3, that the upper or
air-cooled edge would not alter. This apparently legitimate conclusion
is completely disproved by experiments. This will be seen by a reference
to Experiments 8, 9, and 10.
[Illustration: Fig. 1432.--Experiments with a circular hoop of wrought
iron. Appearance of the hoop at the beginning.]
"In No. 8 a circular hoop of wrought iron was forged out of a 3-1/2-inch
by 1/2-inch bar, the external diameter being about 18 inches, the
breadth, 1/2 inch, being parallel to the axis of the hoop. This hoop,
Fig. 1432, was heated to redness, then plunged into cold water half its
depth, the upper half cooling in air. The changes in the external
circumference of the hoop were accurately measured after each of twenty
successive coolings, at the end of which the external circumference of
the water-cooled edge had increased 1.24 inches, or 2.14 per cent. of
its original length, and the air-cooled edge had contracted 7.9 inches,
or 13.65 per cent.
"_Experiment No. 8._--Wrought-iron hoop, 3-1/2 inches by 1/2 inch by
about 18 inches in diameter, or exactly 57.85 inches in circumference at
top, and 57.95 inches at bottom edge.
-------------+--------------------+--------------------+--------------
| Top Edge. | Bottom Edge. |
+--------+-----------+--------+-----------+
|Contrac-|Percentage | Expan- |Percentage |
| tion. |of original| sion. |of original|
| | circum- | | circum- | Remarks.
| | ference. | | ference. |
-------------+--------+-----------+--------+-----------+--------------
| Ins. | | Ins. | |
After 1st dip| .50 | .86 | .08 | .14 |
" 2nd " | .99 | 1.71 | .08 | .14 |
" 3rd " | 1.47 | 2.54 | .26 | .45 |
" 4th " | 1.92 | 3.32 | .30 | .52 |
" 5th " | 2.30 | 3.97 | .34 | .59 |
" 6th " | 2.60 | 4.49 | .40 | .70 |Slight crack
| | | | |in expanded
| | | | |edge.
" 7th " | 2.94 | 5.25 | .44 | .76 |
" 8th " | 3.40 | 5.98 | .50 | .86 |
" 9th " | 3.70 | 6.39 | .56 | .96 |
" 10th " | 4.40 | 7.60 | .62 | 1.07 |
" 11th " | 4.42 | 7.64 | .66 | 1.14 |
" 12th " | 4.85 | 8.40 | .70 | 1.22 |
" 13th " | 5.24 | 9.02 | .78 | 1.34 |
" 14th " | 5.74 | 9.92 | .80 | 1.39 |
" 15th " | 6.00 | 10.37 | .86 | 1.49 |
" 20th " | 7.90 | 13.65 | 1.24 | 2.14 |After de-
| | | | |ducting for a
| | | | |crack .06 inch
| | | | |wide which
| | | | |appeared at
| | | | |sixth dip.
-------------+--------+-----------+--------+-----------+--------------
"It will be observed that we have here two remarkable phenomena: 1. The
reversal of the expansion and contraction as described. 2. The very
large amount of contraction on the upper edge compared with what was
exhibited in Experiment 5 of entire submersion.
"The table showing Experiment 5 gives a contraction of 2.25 per cent.
after the twentieth cooling, whereas the contraction on the air-cooled
edge of Experiment 8 is 13.65 per cent., or six times the contraction of
an entirely submerged hoop.
[Illustration: Fig. 1433.--Condition of the hoop after the twentieth
cooling.]
"To ascertain whether these unexpected phenomena had any connection with
the circular form of the hoop, Experiment 9 was made with a straight bar
of iron 3-1/2 inches deep by 1/2 inch thick by 28.4 inches long.
"_Experiment No. 9._--Wrought-iron bar, 3-1/2 inches by 1/2 inch by 28.4
inches long, heated to a dull red, then quenched half its depth in
water.
------------------+--------------------+--------------------
| Bottom Edge. | Top Edge.
+--------+-----------+--------+-----------
| Expan- |Percentage |Contrac-|Percentage
| sion. |on original| tion. |on original
| | length. | | length.
------------------+--------+-----------+--------+-----------
| Inches.| | Inches.|
After 1st cooling | .05 | .18 | .26 | .91
" 2nd " | .10 | .35 | .43 | 1.51
" 3rd " | .10 | .35 | .54 | 1.90
" 4th " | .14 | .49 | .75 | 2.64
" 5th " | .20 | .70 | .92 | 3.24
" 6th " | .30 | 1.05 | 1.25 | 4.40
" 7th " | .34 | 1.20 | 1.50 | 5.28
" 8th " | .38 | 1.34 | 1.56 | 5.53
" 9th " | .39 | 1.37 | 1.66 | 5.84
" 10th " | .40 | 1.40 | 1.76 | 6.19
" 11th " | .41 | 1.43 | 1.84 | 6.48
" 12th " | .44 | 1.55 | 1.96 | 6.90
------------------+--------+-----------+--------+-----------
"This was cooled half in air and half in water, and the length of the
two edges measured accurately after each of twelve coolings. At the end
of this experiment the air-cooled edge had contracted 6.9 per cent.,
while the water-cooled edge had expanded 1.55 per cent. of the original
length. The effect on the bar was to make it gradually curve, the
water-cooled or extended edge becoming convex, the air-cooled or
contracted edge concave.
[Illustration: Fig. 1434.--Experiments with a wrought-iron bar.
Appearance of the piece before heating.]
"Experiment No. 10 was made in order to show the effect of reversing
this cooling process. After five coolings, a bar of iron, 28 inches
long, 3-1/2 inches deep, and 1/2 inch thick, was curved so that the
versed sine of its air-cooled edge was 1-1/2 inches. The coolings were
then reversed, what was the air-cooled edge being then immersed in
water. After five more coolings the bar was restored to within 1/8 inch
of being straight, and the eleventh cooling threw the concavity on the
other side of the bar.
[Illustration: Fig. 1435.--Appearance of the bar after the twelfth
cooling.]
"_Experiment No. 10._--Wrought-iron flat bar, 28 inches long by 3-1/2
inches by 1/2 inch, heated to dull red, then quenched half its depth in
water, up to five heats, then the opposite edge dipped.
-----------+-----------+------------+------------------
| | | Reversed Cooling.
| | +------------------
|Versed sine| | Versed sine
|of concave,| | of concave,
| _i.e._ | | _i.e._ now
|air-cooled | | water-cooled
| edge. | | edge.
-----------+-----------+------------+------------------
| Inches. | | Inches.
1st cooling| 5/16 | 6th cooling| 1-3/16
2nd " | 9/16 | 7th " | 7/8
3rd " | 13/16 | 8th " | 3/4 scant.
4th " | 1-3/8 | 9th " | 3/8 full.
5th " | 1-1/2 |10th " | 1/8
| |11th | Brought concavity
| | | 1/8 in. on other
| | | side.
-----------+-----------+------------+------------------
[Illustration: Fig. 1436.--After the preceding experiment the same bar
was reheated and reversed in the water, the eleventh cooling resulting
in the above form, the bar bending in the opposite direction from that
previously shown.]
"When the author had proceeded thus far, these curious results were
shown to several leading scientific men, who expressed interest in the
subject, which encouraged the author to extend his experiments under
varied conditions with a view of ascertaining the cause for these
anomalous effects. These experiments (Nos. 11 to 17) are fully recorded,
and the results shown on the diagrams; the actual rings are also on the
table before you.
"_Experiment No. 11._--Wrought-iron hoop, turned and bored, 37.1 inches,
outside circumference, by 2.95 inches deep by .44 inch thick, the grain
of the iron running the short way of the bar from which the hoop was
made, heated to redness, then cooled half its depth in water (see Fig.
1437 at A for final form of hoop after ten heatings and coolings).
-----------------+--------------------+--------------------
| Top Edge. | Bottom Edge.
+--------+-----------+--------+-----------
|Contrac-|Percentage | Expan- |Percentage
| tion. |on original| sion. |on original
| | length. | | length.
-----------------+--------+-----------+--------+-----------
| Inches.| | Inches.|
After 1st cooling| .3 | .83 | .05 | .13
" 2nd " | .64 | 1.72 | .12 | .32
" 3rd " | 1.02 | 2.75 | .22 | .60
" 4th " | 1.38 | 3.72 | .30 | .80
" 5th " | 1.62 | 4.37 | .37 | 1.00
" 10th " | 3.14 | 8.46 | .76 | 2.05
-----------------+--------+-----------+--------+-----------
"_Experiment No. 12._--Wrought-iron hoop, turned and bored, 6 inches
diameter (18.85 inches circumference) outside, by 2 inches deep by .375
inch thick, heated to redness, then cooled, with lower edge barely
touching the water (see Fig. 1437 at B for final form of hoop after
twenty heatings and coolings).
-----------------+--------------------+--------------------
| Top Edge. | Bottom Edge.
+--------+-----------+--------+-----------
|Contrac-|Percentage |Contrac-|Percentage
| tion. |of original| tion. |of original
|Outside | circum- |Outside | circum-
|circum- | ference. |circum- | ference.
|ference.| |ference.|
-----------------+--------+-----------+--------+-----------
| Inches.| | Inches.|
After 5th cooling| .10 | .53 | .16 | .85
" 10th " | .22 | 1.17 | .34 | 1.80
" 15th " | .32 | 1.70 | .48 | 2.54
" 20th " | .48 | 2.54 | .62 | 3.30
-----------------+--------+-----------+--------+-----------
"_Experiment No. 13._--Wrought-iron hoop, turned and bored, 6 inches
diameter (18.85 inches circumference) outside by 2 inches deep by .375
inch thick, heated to redness, then cooled one-fourth its depth in water
(see Fig. 1437 at C for final form of hoop after twenty heatings and
coolings).
-----------------+--------------------+--------------------------------
| Top Edge. | Bottom Edge.
+--------+-----------+-------------------+-----------
|Contrac-|Percentage | |Percentage
| tion. |of original| |of original
| | circum- | Extension. | circum-
| | ference. | | ference.
-----------------+--------+-----------+-------------------+-----------
| Inches.| | Inches. |
After 1st cooling| .06 | .32 | .02 | .10
" 5th " | .28 | 1.50 {|A hair's breadth |
| | {|contraction. |
" 10th " | .56 | 3.00 { |Returned to origi- |
| | { |nal circumference. |
" 15th " | .78 | 4.14 | .02 contraction. | .10
" 20th " | 1.12 | 6.00 | .02 contraction. | .10
-----------------+--------+-----------+-------------------+-----------
"_Experiment No. 14._--Wrought-iron hoop, turned and bored. 6 inches
diameter (18.85 inches circumference) outside by 2 inches deep by .375
inch thick, heated to redness, then cooled one-half its depth in water
(see Fig. 1437 at D for final form of hoop after twenty heatings and
coolings).
-----------------+--------------------+--------------------
| Top Edge. | Bottom Edge.
+--------+-----------+--------+-----------
|Contrac-|Percentage | Expan- |Percentage
| tion. |of original| sion. |of original
|Outside | circum- |Outside | circum-
|circum- | ference. |circum- | ference.
|ference.| |ference.|
-----------------+--------+-----------+--------+-----------
| Inches.| | Inches.|
After 5th cooling| .46 | 2.44 | .06 | .32
" 10th " | .96 | 5.00 | .09 | .48
" 15th " | 1.34 | 7.10 | .18 | .96
" 20th " | 1.80 | 9.10 | .26 | 1.38
-----------------+--------+-----------+--------+-----------
"_Experiment No. 15._--Wrought-iron hoop turned and bored, 6 inches in
diameter (18.85 inches circumference) outside by 2 inches deep by .375
inch thick, heated to redness, then cooled three-fourths its depth in
water (see Fig. 1437 at E for final form of hoop after twenty heatings
and coolings).
-----------------+--------------------+-------------------------------
| Top Edge. | Bottom Edge.
+--------+-----------+-------------------+-----------
|Contrac-|Percentage | |Percentage
| tion. |of original| |of original
| | circum- | Expansion. | circum-
| | ference. | | ference.
-----------------+--------+-----------+-------------------+-----------
| Inches.| | Inches. |
After 1st cooling| .05 | .26 | .015 | .08
" 5th " | .30 | 1.60 | .02 | .10
" 10th " | .56 | 3.00 {| A hair's breadth |
| | {| contraction. |
" 15th " | .74 | 3.92 { | .02 |} .10
| | { | contraction. |}
" 20th " | 1.02 | 5.40 {| .03 | } .10
| | {| contraction. | }
-----------------+--------+-----------+-------------------+-----------
"_Experiment No. 16._--Cast-copper ring, turned and bored to same
dimensions as Nos. 12, 13, 14, and 15, heated to redness, then cooled
half its depth in water (see Fig. 1437 at F for final form of hoop after
twenty heatings and coolings).
-----------------+--------------------+--------------------
| Top Edge. | Bottom Edge.
+--------+-----------+--------+-----------
|Contrac-|Percentage | Expan- |Percentage
| tion. |of original| sion. |of original
| | circum- | | circum-
| | ference. | | ference.
-----------------+--------+-----------+--------+-----------
| Inches.| | Inches.|
After 1st cooling| .01 | .05 | .05 | .26
" 2nd " | .01 | .05 | .08 | .42
" 3rd " | .02 | .10 | .14 | .75
" 4th " | .02 | .10 | .17 | .90
" 5th " |} No change from | .22 | 1.17
" 10th " |} original size | .40 | 2.13
" 15th " |} from 5th to | .56 | 3.00
" 20th " |} 20th cooling. | .70 | 3.70
-----------------+--------------------+--------+-----------
[Illustration: Fig. 1437.]
"It will be unnecessary to occupy much time in analyzing the
experiments, as any one who takes a practical interest in the subject
will have full information in the diagrams and tables. Professor Stokes
drew attention to the fact that, in 1863, similar phenomena had been
noticed by Colonel Clark, of the Royal Engineers. His experiments, made
at the Royal Arsenal, Woolwich, were published in the 'Proceedings of
the Royal Society,' and Professor Stokes had himself attached an
explanatory note, the outline of which was as follows:--
"Imagine a cylinder divided into two parts by a horizontal plane at the
water-line, and in this state immersed after heating. The under part,
being in contact with water, would rapidly cool and contract, while the
upper part would cool but slowly. Consequently by the time the under
part had pretty well cooled, the upper part would be left jutting out;
but when both parts had cooled their diameters would again agree. Now in
the actual experiments the independent motion of the two parts is
impossible on account of the continuity of the metal; the under part
tends to pull in the upper, and the upper to pull out the under. In this
contest the cooler metal, being the stronger, prevails, and so the upper
part gets pulled in a little above the water-line while still hot. But
it has still to contract in cooling, and this it will do to the full
extent due to its temperature, except in so far as it may be prevented
by its connection with the rest. Hence, on the whole, the effect of this
cause is to leave a permanent contraction a little above the water-line,
and it is easy to see that the contraction must be so much nearer to the
water-line as the thickness of the metal is less, the other dimensions
of the hollow cylinder and the nature of the metal being given. When the
hollow cylinder is very short, so as to be reduced to a mere hoop, the
same cause operates, but there is not room for more than a general
inclination of the surface, leaving the hoop bevelled.
"The expansion of the bottom edge was not noticed in Colonel Clark's
paper, perhaps owing to the much smaller hoops which he used in
experimenting. Accepting Professor Stokes' explanation of the top
contraction, it appears that expansion of the bottom may be accounted
for by the reacting strain put on the cooled edge when forcing in the
top edge, acting in such a way as to prevent the cooled edge coming
quite to its natural contraction, and this, when sufficiently great,
expresses itself in the form of a slight expansion.
"_Experiment No. 14._--Forged steel hoop, turned and bored, 18.53 inches
in circumference outside by 2.375 inches deep by .27 inch thick, heated
to redness, then cooled one-half its depth in water (see Fig. 1437 at G
for final form of hoop after three heatings and coolings).
-----------------+--------------------+-------------------+-------------
| Top Edge. | Bottom Edge. |
+--------+-----------+-------+-----------+
|Contrac-|Percentage | Expan-|Percentage |
| tion. |of original| sion. |of original|
| | length. | | length. |
-----------------+--------+-----------+-------+-----------+-------------
| Inches.| |Inches.| |
| | | | {|Cracked at
| | | | {|water-
After 1st cooling| .06 | .32 | -- | -- {|cooled
| | | | {|edge one-
| | | | {|third depth
| | | | {|of ring.
| | | | |
" 2nd " | .12 | .64 | -- | -- |
| | | | |
| | | | {|After allow-
| | | | {|ing for
" 3rd " | .20 | 1.08 | .05 | .27 {|three small
| | | | {|cracks in
| | | | {|bottom edge."
-----------------+--------+-----------+-------+-----------+-------------
The shrinkage of iron and steel by cooling rapidly is sometimes taken
advantage of by workmen to refit work, the principles involved in the
process being as follows:--
Suppose in Fig. 1438 _a_ _a_ represents a piece of wrought-iron tube
that has been heated to a bright red and immersed in cold water _c_ _c_
from the end B to D, _until that end is cold_. The part submerged and
cold will be contracted to its normal diameter and have regained its
normal strength, while the part above the water, remaining red-hot,
will be expanded and weak. There will be, then, a narrow section of the
tube, joining the heated and expanded part to the cooled and contracted
part, and its form will be conical, as shown at D D. Now, suppose the
tube to be slowly lowered in the water, the cold metal below will
compress the heated metal immediately above the water-line, the cone
section D being carried up into the metal before it has had time to
cool; and the tube removed from the water when cold will be as shown in
Fig. 1438, from _c_ to D, representing the part first immersed and
cooled. To complete the operation the tube must be heated again from the
end _c_ to a short distance past D, and then immersed from E nearly to
D, and held still until the submerged part is cold, when the tube must
be slowly lowered to compress the end _c_ D, making the tube parallel,
but smaller in diameter and in bore, while leaving it of its original
length, but thickening its wall.
[Illustration: Fig. 1438.]
[Illustration: Fig. 1439.]
This process may, in many cases, be artificially assisted. Suppose, for
example, a washer is too large in its bore; it should have its hole and
part of its radial faces filled with fire-clay, as shown in Fig. 1439,
in which A is the washer and B B the clay, _c_ _c_ being pieces of wire
to hold the fire-clay and prevent its falling off. The washer should be
heated to a clear red and plunged in the water D D, which will cool and
shrink the exterior and exposed metal in advance of the interior, which
will compress to accommodate the contraction of the outer metal, hence
the hole will be reduced. This operation may be repeated until the hole
be entirely closed.
[Illustration: Fig. 1440.]
[Illustration: Fig. 1441.]
Another method of closing such a piece as an eye of large diameter
compared to its section, is shown in Fig. 1440; first dipping the heated
eye at A and holding it there till cold and then slowly lowering it into
the water, which would close the diameter across C, and, after
reheating, dipping at D till cold, and then slowly immersing, which
would close the eye across E. To shrink a square ring, the whole ring
would require to be heated and a side of the square dipped, as shown in
Fig. 1441, until quite cold, and then immersed slowly for about an inch,
the operation being performed with a separate heating for each side.
Connecting rod straps, wheel-tires, and a large variety of work may be
refitted by this process, but in each case the outside diameter will be
reduced.
CHAPTER XV.--MEASURING TOOLS.
[Illustration: Fig. 1442.]
[Illustration: Fig. 1443.]
For what may be termed the length measurements of lathe work it is
obvious that caliper gauges, such as shown in Fig. 1402, may be
employed. Since, however, these length measurements rarely require to be
so accurate as the diametrical measurements, the ordinary lineal rule is
very commonly employed in work not done under the standard gauge system.
It is obvious, however, that when a number of pieces are to be turned to
corresponding lengths, a strip of sheet iron, or of iron rod made to the
required length, may be employed; a piece of sheet iron filed to have
the necessary steps being used where there are several steps in the
work; but if the lineal measuring rule is used, and more than one
measurement of length is to be taken, some one point, as one end of the
work, should be taken wherefrom to measure all the other distances.
Suppose, for example, that Fig. 1442 represents a crank pin requiring to
have its end collar 1/4 inch thick, the part A 2 inches long, part B 3
inches long, collar C 1/2 inch thick, and the part D 7 inches long. If
the length of each piece were taken separately and independently of the
others, any errors of measurement would multiply; whereas, if some one
point be taken as a point wherefrom to measure all the other distances,
error is less liable to occur, while at the same time an error in one
measurement would not affect the correctness of the others. In the case
of the crank pin shown, the collar C would be the best point wherefrom
to take all the other measurements. First, it would require to be made
to its proper thickness, and the lengths of B, A, and the end collar
should be measured from its nearest radial face. The length of D should
then be measured from the same radial face, the thickness of the collar
being added to the required length of D, or D may be measured from the
nearest radial face of C, providing C be of its exact proper thickness.
In measuring the length of the taper part D, a correct measurement will
not be obtained by laying the rule along its surface, because that
surface does not lie parallel to its axis, hence it is necessary to
apply the measuring rule, as shown in Fig. 1443, in which S is a
straight-edge held firmly against the radial face of the crank pin (the
radial face being of course turned true), and R is the measuring rule
placed true with the axial line of the crank pin. Whenever the diameters
of the lengths to be measured vary, this mode of measuring must be
employed. On small work, or on short distances requiring to be very
exact, a gauge such as shown in Fig. 1444 at A may be employed, which
will not only give more correct results, but because it is more
convenient, as it can be conveniently held or tried to the work with one
hand while the other hand is applied to the feed screw handle to
withdraw the cutting tool at the proper moment, and to the feed nut to
unlock it and stop the feed.
[Illustration: Fig. 1444.]
[Illustration: Fig. 1445.]
On long work a wooden strip is the best, especially if the work has
varying diameters and a number of pieces of work require to be made
exactly alike. In Fig. 1445 S represents the wooden strip, and W the
work. The strip is marked across by lines representing the distances
apart the shoulders of the work require to be; thus the lines A, B, C,
D, E, F, G, represent the distances apart of the radial faces _a_, _b_,
_c_, _d_, _e_, _f_, _g_, on the work, and these lines will be in the
same plane as the shoulders if the latter are turned to correct lengths.
To compare the radial faces with the lines, a straight-edge must be held
to each successive shoulder (as already described) that is of smaller
diameter than the largest radial face on the work.
If the wooden strip be made the full length of the work the dog or clamp
driving the work will require to be removed every time the wooden gauge
is applied, and since the work must be turned end for end in the lathe
to be finished, it would be as well to let the length of the wood gauge
terminate before reaching the work driver, as, say, midway between E and
F.
When a lineal distance is marked by lines, and this distance is to be
transferred to another piece of work and marked thereon by lines, the
operation may be performed, for short distances or radii, by the common
compasses employed to mark circles, but for greater distances where
compasses would be cumbersome, the trammels are employed.
Fig. 1446 represents a pair of trammels made entirely of metal, and
therefore suitable for machinists' use, in which the points require to
be pressed to the work to mark the lines. A A represents a bar of square
steel; or for very long trammels wood may be used. B represents a head
fastened tightly to one end, and through B passes the leg or pointer C,
which is thus adjustable as to its projecting distance, as C can be
fastened in any position by the thumb-screw D. The head E is made to a
good sliding fit upon the bottom and two side faces of A A; but at the
top there is sufficient space to admit a spring, which passes through E.
F is the leg screwed into E, which is locked in position by the
thumb-screw G. The head E is thus adjustable along the whole length of
the bar or rod A A. The object of the spring is as follows:--If the head
E were made to fit the bar A A closely on all four sides, the burrs
raised upon the top side of the rod A A by the end of the thumb-screw G
would be likely to impede its easy motion. Then again, when the sliding
head E has worn a trifle loose upon the bar A A, and is loosened for
adjustment, it would be liable to hang on one side, and only to right
itself when the screw G brought it to a proper bearing upon the under
side of the bar A A, and thus tightening the head E would alter the
adjustment of the point. The spring, however, always keeps the lower
face of the square hole through E bearing evenly against the
corresponding face of the bar, so that tightening the screw G does not
affect the adjustment, and, furthermore, the end of the set-screw,
bearing against the spring instead of against the top of the rod,
prevents the latter from getting burred.
[Illustration: Fig. 1446.]
The flat place at I I is to prevent the burrs raised by the thumb-screw
end from preventing the easy sliding of leg C through B.
[Illustration: Fig. 1447.]
In some cases a gib is employed, as shown at A in Fig. 1447, instead of
a spring, the advantage being that it is less liable to come out of
place when moving the head along the bar.
The trammels should always be tried to the work in the same relative
position as that in which they were set, otherwise the deflection of the
bar may vitiate the correctness of the measurement; thus, if the rod or
bar stood vertical when the points were adjusted for distance to set
them to the required distance, it should also stand vertical upon the
work when applied to transfer that distance, otherwise the deflection of
the bar from its own weight will affect the correctness of the
operation. Again, when applied to the work the latter should be
suspended as nearly as convenient in the same position as the work will
occupy when erected to its place.
Thus, suppose the trammels be set to the crank pin centres of a
locomotive, then the bar will stand horizontally. Now the side rod, or
coupling rod, as it may be more properly termed, should be stood on edge
and should rest on its ends, because its bearings wherever it will rest
when on the engine are at the ends; thus the deflection of the trammel
rod will be in the same direction when applied to the work as it was
when applied to the engine, and the deflection of the coupling rod will
be in the same direction when tried by the trammel as when on the
engine. The importance of this may be understood when it is mentioned
that if the coupling rod be a long one, resting it on its side and
supporting it in the middle instead of at its ends will cause a
difference of 1/50th inch in its length.
[Illustration: Fig. 1448.]
Another lineal measuring gauge employed in the machine shop is shown in
Fig. 1448. It is employed to measure the distance between two faces, and
therefore in place of inside calipers, in cases where from the extreme
distance to be measured it would require the use of inside calipers too
large to be conveniently handled. Its application is more general upon
planing machine work than any other, although it is frequently used by
the lathe hand or turner, and by the vice hand and erector. It consists
of two legs A and B, held together by the screws C D, which screw into
nuts. These nuts should have a shoulder fitting into the slots in both
legs, so as to form a guide to the legs. The screws are set up so as to
just bind both legs together but leaving them free enough to move under
a slight friction. The gauge is then set to length by lightly striking
the ends E, and when adjusted the screws C D are screwed firmly home.
The ends E are rounded somewhat, as is shown, to prevent them from
swelling or burring by reason of the blows given to adjust them.
For striking circles we have the compasses or dividers, which are made
in various forms.
[Illustration: Fig. 1449.]
Thus, Fig. 1449 represents a pair of spring dividers, the bow spring at
the head acting to keep the points apart, and the screw and nut being
employed to close and to adjust them.
[Illustration: Fig. 1450.]
Another form is shown in Fig. 1450, the legs being operated by a right
and left-hand screw, which may be locked in position by the set-screw
shown.
For very small circles the fork scriber shown in Fig. 1451 is an
excellent tool, since it may be used with great pressure so as to cut a
deep line in the surface of the work. This tool is much used by boiler
makers, but is a very useful one for the machinist for a variety of
marking purposes, which will be described with reference to vice work.
For larger work we have the compasses, a common form of which is shown
in Fig. 1452, in which the leg A is slotted to receive the arc piece C,
which has a threaded stem passing through E, and is provided with a nut
at B; at D is a spring which holds the face of the nut B firmly against
the leg E; at A is a thumb-screw for securing the leg to the arm C. The
thumb-screw A being loosened, the compass legs may be rudely adjusted
for distance apart, and A is then tightened. The adjustment is finally
made by operating the nut B, which, on account of its fine thread,
enables a very fine adjustment to be easily made.
[Illustration: Fig. 1451.]
[Illustration: Fig. 1452.]
[Illustration: Fig. 1453.]
It is often very convenient to be able to set one leg of a pair of
dividers to be longer than the other, for which purpose a socket B, Fig.
1453, is provided, being pierced to receive a movable piece A, and split
so that by means of a set-screw C the movable piece A may be gripped or
released at pleasure.
[Illustration: Fig. 1454.]
For finding the centres of bodies or for testing the truth of a centre
already marked, the compass calipers shown in Fig. 1454, are employed.
It is composed of one leg similar to the leg of a pair of compasses,
while the other is formed the same as the leg of an inside caliper. The
uses of the compass calipers are manifold, the principal being
illustrated as follows:--
[Illustration: Fig. 1455.]
Let it be required to find the centre of a rectangular block, and they
are applied as in Fig. 1455, the curved leg being rested against the
edge and a mark being made with the compass leg. This being done from
all four sides of the work gives the centre of the piece.
[Illustration: Fig. 1456.]
In the case of a hole its bore must be plugged and the compass calipers
applied as in Fig. 1456.
[Illustration: Fig. 1457.]
For marking a line true with the axial line of a cylindrical body, we
have the instrument W in Fig. 1457, which is shown applied to a shaft S.
The two angles of the instrument are at a right angle one to another, so
that when placed on a cylindrical body the contact will cause the edge
of W to be parallel with the axis of the shaft. The edge is bevelled, as
shown, so that the lines of division of inches and parts may come close
to the work surface, and a scriber may be used to mark a line of the
required length. A scriber is a piece of steel wire having a hardened
sharp point wherewith to draw lines.
On account of the instrument W finding its principal application in
marking key seats upon shafts, it is termed the "key-seat rule."
[Illustration: Fig. 1458.]
For marking upon one surface a line parallel to another surface, the
scribing block or surface gauge shown in Fig. 1458 is employed. It
consists of a foot piece or stand D, carrying a stem. In the form shown
this stem contains a slot running centrally up it. Through this slot
passes a bolt whose diameter close to the head is larger than the width
of the slot, so that it is necessary to file flat places on the side of
the slot to permit the bolt to pass through it.
On the stem of the bolt close to the head, and between the bolt head and
the stem of the stand, passes the piece shown at F. This consists of a
piece of brass having a full hole through which the bolt passes clear up
to the bolt head. On the edge view there is shown a slot, and on each
side of the slot a section of a hole to receive a needle. A view of the
bolt is given at E, the flat place to fit the slot in the stem being
shown in dotted lines, and the space between the flat place and the bolt
head is where the piece of brass, shown in figure, passes. This piece of
brass being placed on the bolt, and the bolt being passed through the
slot in the stem, the needle is passed through the split in the brass,
and the thumb-nut is screwed on so that tightening up the thumb-nut
causes the needle to be gripped in the brass split in any position in
the length of the stem slot in which the bolt may be placed. The
advantage of this form over all others is that the needle may be made of
a simple piece of wire, and therefore very readily. Again, the piece of
brass carrying the needle may be rotated upon the pin any number of
consecutive rotations backwards and forwards, and there is no danger of
slacking the thumb-nut, because the needle is on the opposite side of
the stem to what the thumb-nut is, and the flat place prevents the bolt
from rotating. Furthermore, the needle can be rotated on the bolt for
adjustment for height without becoming loosened, whereas when the
thumb-nut is screwed up firmly the needle is held very fast indeed, and
finally all adjustments are made with a single thumb-nut.
The figure represents a view of this gauge from the bolt head and needle
side of the stem, the thumb-nut being on the opposite side.
This tool finds its field of application upon lathe work, planer work,
and, indeed, for one purpose or another upon all machine tools, and in
vice work and erecting, examples of its employment being given in
connection with all these operations.
[Illustration: Fig. 1459.]
Fig. 1459 represents a scribing block for marking the curves to which to
cut the ends of a cylindrical body that joins another, as in the case of
a [T]-pipe. It is much used by pattern-makers. In the figure A is a stem
on a stand E. A loose sleeve B slides on A carrying an arm C, holding a
pencil at D. A piece of truly surfaced wood or iron W, has marked on it
the line J. Two [V]s, G, G, receive the work P. Now, if the centres of
G, G and of the stand E all coincide with the line J then E will stand
central to P, and D may be moved by the hand round P, being allowed to
lift and fall so as to conform to the cylindrical surface of P, and a
line will be marked showing where to cut away the wood on that side, and
all that remains to do is to turn the work over and mark a similar line
diametrically opposite, the second line being dotted in at K.
[Illustration: Fig. 1460.]
The try square, Fig. 1460, is composed of a rectangular back F, holding
a blade, the edges of the two being at a right angle one to the other
and as straight as it is possible to make them. The form shown in the
figure is an [L]-square.
[Illustration: Fig. 1461.]
Fig. 1461 represents the [T]-square, whose blade is some distance from
the end of the back and is sometimes placed in the middle. When the
square edges are at a true right angle the square is said to be true or
square, the latter being a technical term meaning at practically a true
right angle.
The machinists' square is in fact a gauge whereby to test if one face
stands at a right angle to another. It is applied by holding one edge
firmly and fairly bedded against the work, while the other edge is
brought to touch at some part against the face to be tested.
If in applying a square it be pressed firmly into the corner of the
work, any error in the latter is apt to escape observation, because the
square will tilt and the error be divided between the two surfaces
tested. To avoid this the back should be pressed firmly against one
surface of the work and the square edge then brought down or up to just
touch the work, which it will do at one end only if the work surface is
out of square or not at a right angle to the face to which the square
back is applied.
[Illustration: Fig. 1462.]
An application of the [T]-square is shown in Fig. 1462, in which W is a
piece of work requiring to have the face A of the jaw C at a right angle
to the face B C. Sometimes the [L]-square is employed in conjunction
with a straight-edge in place of the [T]-square. This is usually done in
cases where the faces against which the square rests are so far apart as
to require a larger [T]-square than is at hand. It is obvious that if
the face A of the work is the one to be tested, the edge B is the part
pressed to the work; or per contra, if B C is the face to be tested, the
edge of the blade is pressed to the work.
[Illustration: Fig. 1463.]
The plane of the edges of a square should, both on the blade and on the
back, stand at a right angle to the side faces of the body or stock, and
the side of the blade should be parallel to the sides of the back and
not at an angle to either side, nor should it be curved or bent, because
if under these conditions the plane of the square edge is not applied
parallel with the surface of the work the square will not test the work
properly. This is shown in Fig. 1463, in which W is a piece of work, and
S a square having its blade bent or curved and applied slightly out of
the vertical, so that presuming the plane of the blade edge to be a
right angle to the stock or back of the square the plane of the blade
edge will not be parallel with the plane of the work, hence it touches
the work at the ends A B only, whereas if placed vertically the blade
edge would coincide with the work surface all the way along. It is
obvious then that by making the edge of the blade at a right angle,
crossways as well as in its length, to the stock, the latter will serve
as a guide to the eye in adjusting the surface of the blade edge
parallel to that of the work by placing the stock at a right angle to
the same.
[Illustration: Fig. 1464.]
There are three methods of testing the angle of a square blade to the
square back. The first is shown in Fig. 1464, in which A is a surface
plate having its edge a true plane. The square S is placed in the
position shown by full lines pressed firmly to the edge of the surface
plate and a fine line is drawn with a needle point on the face of the
surface plate, using the edge of the square blade as denoted by the
arrow C as a guide. The square is then turned over as denoted by the
dotted lines and the edge is again brought up to the line and the
parallelism of the edge with the line denotes the truth, for whatever
amount the blade may be out of true will be doubled in the want of
coincidence of the blade edge with the line.
[Illustration: Fig. 1465.]
A better plan is shown in Fig. 1465, in which A is the surface plate, B
a cylindrical piece of iron turned true and parallel in the lathe and
having its end face true and cupped as denoted by the dotted lines so as
to insure that it shall stand steadily and true. The surface of A and
the vertical outline of B forming a true right angle we have nothing to
do but make the square S true to them when placed in the position shown.
[Illustration: Fig. 1466.]
[Illustration: Fig. 1467.]
[Illustration: Fig. 1468.]
If we have two squares that are trued and have their edges parallel, we
may test them for being at a right angle by trying them together as in
Figs. 1466 and 1467, in which A, B, are the two squares which, having
their back edges pressed firmly together (when quite clean), must
coincide along the blade edges; this being so we may place them on a
truly surfaced plate as shown in Fig. 1468, in which S is one square and
S´ the other, P being the surface plate. Any want of truth in the right
angle will be shown doubled in amount by a want of coincidence of the
blade edges.
[Illustration: Fig. 1469.]
For some purposes, as for marking out work on a surface plate, it is
better that the square be formed of a single piece having the back and
blade of equal thickness, as shown in Fig. 1469, which represents a side
and edge view of an [L]- and [T]-square respectively.
[Illustration: Fig. 1470.]
For angles other than a right angle we have the bevel or bevel square
(as it is sometimes called), shown in Fig. 1470, A representing the
stock or back, and B the blade, the latter being provided with a slot so
that it may be extended to any required distance (within its scope) on
either side of the stock. C is the rivet, which is made sufficiently
tight to permit of the movement by hand of the blade, and yet it must
hold firmly enough to be used without moving in the stock. Instead of
the rivet C, however, a thumb-screw and nut may be employed, in which
case, after the blade is set to the required angle, it may be locked in
the stock by the thumb-screw.
Fig. 1471 represents a Brown and Sharpe bevel protractor, with a pivot
and thumb-nut in the middle of the back with a half-circle struck from
the centre of the pivot and marked to angular degrees. The pointer for
denoting the degrees of angle has also a thumb-screw and nut so that the
blade may, by loosening the pivot and pointer, be moved to project to
the required distance on either side of the back.
[Illustration: Fig. 1471.]
[Illustration: Fig. 1472.]
Swasey's improved protractor, however, is capable of direct and easy
application to the work, forming a draughtsman's protractor, and at the
same time a machinist's bevel or bevel square, while possessing the
advantage that there is no protruding back or set-screw to prevent the
close application of the blade to the work. This instrument is shown in
Fig. 1472. The blade A is attached to the circular piece D, the latter
being recessed into the square B B, and marked with the necessary
degrees of angle, as shown, while the mark F upon the square B serves as
an index point. The faces of A, B B, and D are all quite level, so that
the edges will meet the lines upon the work and obviate any liability to
error. The piece D is of the shape shown in section at G, which secures
it in B B, the fit being sufficient to permit of its ready adjustment
and retain it by friction in any required position. The dotted lines
indicate the blade as it would appear when set to an angle, the point E
being the centre of D, and hence that from which the blade A operates.
[Illustration: Fig. 1473.]
On account, however, of the numerous applications in machine work of the
hexagon (as, for instance, on the sides of both heads and nuts), a
special gauge for that angle is requisite, the usual form being shown in
Fig. 1473. The edges A, B, form a hexagon gauge, and edges C, D, form a
square, while the edge E serves as a straight-edge.
All these tools should be made of cast steel, the blades being made of
straight saw blade, so that they will not be apt to permanently set from
an ordinary accidental blow; while, on the other hand, if it becomes, as
it does at times, necessary to bend the blade over to the work, it will
resume its straightness and not remain bent.
For testing the straightness, in one direction only, of a surface the
straight-edge is employed. It consists in the small sizes of a piece of
steel whose edges are made straight and parallel one to the other. When
used to test the straightness of a surface without reference to its
alignment with another one, it is simply laid upon the work and sighted
by the eye, or it may have its edge coated with red marking, and be
moved upon the work so that its marking will be transferred to the high
spots upon the work. The marking will look of the darkest colour in the
places where the straight-edge bears the hardest. The most refined use
of the straight-edge is that of testing the alignment of one surface to
the other, and as this class of work often requires straight-edges of
great length, as six or ten feet, which if made of metal would bend of
its own weight, therefore they are made of wood.
[Illustration: Fig. 1474.]
Fig. 1474 represents an example of the use of straight-edge for
alignment purposes. It represents a fork and connecting rod, and it is
required to find if the side faces of the end B are in line with the
fork jaws. A straight-edge is held firmly against the side faces of B in
the two positions S and S´, and it is obvious that if they are in line
the other end will be equidistant from the jaw faces, at the two
measurements.
[Illustration: Fig. 1475.]
[Illustration: Fig. 1476.]
[Illustration: Fig. 1477.]
Figs. 1474, 1475, 1476, 1477, and 1478 represent the process of testing
the alignment of a link with a straight-edge. First to test if the
single eye E is in line with the double eye F at the other end, the
straight-edge is pressed against the face of E, as in Fig. 1475, and the
distance I is measured. The straight-edge is then applied on the other
side of E, as in Fig. 1476, and the distance H is measured, and it is
clear that if distances H and I are equal, then E is in line with the
double eye. To test if the double eye F is in line with the single eye
E, the straight-edge is pressed against the face of the double eye in
the positions shown in Figs. 1477 and 1478, and when distances J and K
measure equal the jaws of the double eye F are in line with those of the
single eye E.
[Illustration: Fig. 1478.]
[Illustration: Fig. 1479.]
[Illustration: Fig. 1480.]
[Illustration: Fig. 1481.]
[Illustration: Fig. 1482.]
[Illustration: Fig. 1483.]
It is obvious, however, that we have here tested the alignment in one
direction only. But to test in the other direction we may use a pair of
straight-edges termed winding strips, applying them as in Fig. 1479, to
test the stem, and as in Fig. 1480 to test the eye E, and finally
placing the winding strip C on the eye of F while strip D remains upon
E, as in Fig. 1480. The two strips are sighted together by the eye, as
is shown in Fig. 1481, in which S and S´´ are the strips laid upon a
connecting rod, their upper edges being level with the eye, hence if
they are not in line the eye will readily detect the error. Fig. 1482
represents an application to a fork ended connecting rod. Pattern-makers
let into their winding strips pieces of light-coloured wood as at C, C,
C, C, in Fig. 1483, so that the eye may be assisted in sighting them.
It is obvious that in using winding strips they should be parallel one
to the other; thus, for example, the ends A, B, in Fig. 1481, should be
the same distance apart as ends C, D.
If less than three straight-edges or parallel strips are to be trued
they must be trued to a surface plate or its equivalent, but if a pair
are to be made they should have the side faces made true, and be riveted
together so that their edges may be trued together, and equal width may
be more easily obtained. For this purpose copper rivets should be used,
because they are more readily removable, as well as less likely to
strain the work in the riveting.
By riveting the straight-edges together the surface becomes broader and
the file operates steadier, while the edges of the straight-edge are
left more square. Furthermore parallelism is more easily obtained as one
measurement at each end of the batch will test the parallelism instead
of having to measure each one separately at each end. If three
straight-edges are to be made they may be riveted together and filed as
true as may be with the testing conveniences at hand, but they should be
finally trued as described for the surface plate.
In using straight-edges to set work, the latter is often heated to
facilitate the setting, and in this case the straight-edge or parallel
strips should be occasionally turned upside down upon the work, for if
the heated work heats one side of the straightedge more than the other
the increased expansion of the side most heated will bend the
straight-edge or strips, and throw them out of true.
In applying a straight-edge to test work it must never be pressed to the
work surface, because in that case it will show contact with the work
immediately beneath the parts where such pressure is applied. Suppose,
for example, a true straight-edge be given a faint marking, and be
applied to a true surface, the straight-edge itself being true; then if
the hands are placed at each end of the straight-edge, and press it to
the work while the straight-edge is given motion, it will leave the
heaviest marks at and near the ends as though the work surface was
slightly hollow in its length; while were the hand pressure applied to
the middle of the length of the straight-edge the marks on the work
would show the heaviest in the middle as though the work surface were
rounding. This arises from the deflection due to the weakness of the
straight-edge.
For testing the truth of flat or plane surfaces the machinist employs
the surface plate or planometer. The surface plate is a plate or casting
having a true flat surface to be used as a test plate for other
surfaces. It is usually made of cast iron, and sometimes of chilled cast
iron or hardened cast steel, the surface in either of these two latter
cases being ground true because their hardness precludes the possibility
of cutting them with steel tools. A chilled or hardened surface plate
cannot, however, be so truly surfaced as one that is finished with
either the scraper or the file.
The shape of the surface plate is an element of the first importance,
because as even the strongest bars of metal deflect from their own
weight, it is necessary to shape the plate with a view to make this
deflection as small as possible in any given size and weight of plate.
In connection, also, with the shape we must consider the effect of
varying temperatures upon the metal, for if one part of the plate is
thinner than another it will, under an increasing temperature, heat more
rapidly, and the expansion due to the heating will cause that part to
warp the plate out of its normal form, and hence out of true. The amount
that a plate will deflect of its own weight can only be appreciated by
those who have had experience in getting up true surfaces, but an idea
may be had when it is stated that it can be shown that it is easily
detected, in a piece of steel three inches square and a foot long.
Now this deflection will vary in direction according to the points upon
which the plate rests. For instance, take two plates, clean them
properly, and rest one upon two pieces of wood, one piece under each
end, and then place another plate upon the lower one and its face will
show hollow, and, if the upper plate is moved backwards and forwards
laterally it will be found to move from the ends as centres of motion.
Then rest the lower plate upon a piece of wood placed under the middle
of its length, and we shall find that (if the plates are reasonably
true) the top one will move laterally with the middle of its length as a
centre of motion. Now although this method of testing will prove
deflection to exist, it will not show its amount, because the top plate
deflects to a certain extent, conforming itself to the deflection of the
lower one, and if the test is accurately made it will be found that the
two plates will contact at whatever points the lower one is supported.
If plates, tested in this manner, show each other to have contact all
along however the lower one is supported, it is because they are so
light that the upper one will readily bend to suit the deflection of the
lower one, and true work is, with such a plate, out of the question.
To obviate these difficulties the body of the plate is heavily ribbed,
and these ribs are so arranged as to be of equal lengths, and are made
equal in thickness to the plate, so that under variations of temperature
the ribs will not expand or contract more quickly or slowly than the
body of the plate, and the twisting that would accompany unequal
expansion is avoided.
[Illustration: Fig. 1484.]
In Fig. 1484 is shown the form of surface plate designed by Sir Joseph
Whitworth for plates to be rested upon their feet. The resting points of
the plate are small projections shown at A, B, and C. The object of this
arrangement of feet is to enable the plate to rest with as nearly as
possible an equal degree of weight upon each foot, the three feet
accommodating themselves to an uneven surface. It is obvious, however,
that more of the weight will fall upon C than upon A or B, because C
supports the whole weight at one end, while at the other end A and B
divide the weight.
[Illustration: Fig. 1485.]
Fig. 1485 shows the form of plate designed by Professor Sweet.
[Illustration: Fig. 1486.]
In Fig. 1486 is shown a pair of angle surface plates resting upon a flat
one. The angle plates may be used for a variety of purposes where it is
necessary to true a surface standing at a true right angle to another.
The best methods of making surface plates are as follows:--
The edges of the plates should be planed first, care being taken to make
them square and flat. The surfaces should then be planed, the plates
being secured to the planer _by the edges_, which will prevent as far as
possible the pressure necessary to hold them against the planing tool
cut from springing, warping, or bending the plates. Before the finishing
cut is taken, the plates or screws holding the surface plate should be
slackened back a little so as to hold them as lightly as may be, the
finishing cut being a very light one, and under these circumstances the
plates may be planed sufficiently true that one will lift the other from
the partial vacuum between them.
After the plates are planed, and before any hand work is done on them,
they should be heated to a temperature of at least 200° Fahr., so that
any local tension in the casting may be as far as possible removed.
[Illustration: Fig. 1487.]
Surface plates for long and narrow surfaces are themselves formed long
and narrow, as shown in Fig. 1487, which represents the straight-edge
surface plate made at Cornell University.
[Illustration: Fig. 1488.]
The Whitworth surfacing straight-edge, or long narrow surface plate, is
ribbed as in Fig. 1488, so as to give it increased strength in
proportion to its weight, and diminish its deflection from its own
weight. The lugs D are simply feet to rest it on.
Straight-edges are sometimes made of cast steel and trued on both edges.
These will answer well enough for small work, but if made of a length to
exceed about four feet their deflection from their own weight seriously
affects their reliability. The author made an experiment upon this point
with a very rigid surface plate six feet long, and three cast steel
straight-edges 6 feet long, 4-1/2 inches wide, and 1/2 inch thick. Both
edges of the straight-edges were trued to the surface plate until the
light was excluded from between them, while the bearing surface appeared
perfect; thin tissue paper was placed between the straight-edges and
the plate, and on being pulled showed an equal degree of tension. The
straight-edges were tried one with the other in the same way and
interchanged without any apparent error, but on measuring them it was
found that each was about 1/50 inch wider in the middle of its length
than at the ends, the cause being the deflection. They were finished by
filing them parallel to calipers, using the bearing marks produced by
rubbing them together and also upon the plate; but, save by the caliper
test, the improvement was not discernible.
In rubbing them together no pressure was used, but they were caused to
slide under their own weight only.
A separate and distinct class of gauge is used in practice to copy the
form of one piece and transfer it to another, so that the one may
conform to or fit the other. To accomplish this end, what are termed
male and female templates or gauges are employed. These are usually
termed templates, but their application to the work is termed gauging
it.
[Illustration: Fig. 1489.]
Suppose, for example, that a piece is to be fitted to the rounded corner
of a piece F, Fig. 1489, and the maker takes a piece of sheet metal A,
and cuts it out to the line B C D, leaving a female gauge E, which will
fit to the work F. We then make a male gauge G, and apply this to the
work, thus gauging the round corner.
[Illustration: Fig. 1490.]
Fig. 1490 represents small templates applied to a journal bearing, and
it is seen that we may make the template as at T, gauging one corner
only, or we may make it as at T´, thus gauging the length of the journal
as well as the corners.
[Illustration: Fig. 1491.]
[Illustration: Fig. 1492.]
Fig. 1491 represents a female gauge applied to the corner of a bearing
or brass for the above journal, it being obvious that the male and
female templates when put together will fit as in Fig. 1492.
For measuring the diameters of metal wire and the thickness of rolled
sheet metal, measuring instruments termed wire gauges and sheet metal
measuring machines are employed. A simple wire gauge is usually formed
of a piece of steel containing numerous notches, whose widths are equal
to the intended thickness to be measured in each respective notch. These
notches are marked with figures denoting the gauge-number which is
represented by the notch.
For wire, however, a gauge having holes instead of notches is sometimes
employed, the wire being measured by insertion in the hole, an operation
manifestly impracticable in the case of sheet metal.
In Fig. 1493 is shown one of Brown and Sharpe's notch wire-gauges, the
notches being arranged round the edge as shown:
[Illustration: Fig. 1493.]
The thickness of a given number of wire-gauge varies according to the
system governing the numbering of the gauge, which also varies with the
class of metal or wire for which the gauge has been adopted by
manufacturers. Thus, in the following table are given the gauge-numbers
and their respective sizes in decimal parts of an inch, as determined by
Holtzapffel in 1843, and to which sizes the Birmingham wire-gauge is
made. The following table gives the numbers and sizes of the Birmingham
wire-gauge.
BIRMINGHAM WIRE GAUGE.
-----+------++------+------++------+------++------+------
Mark.| Size.|| Mark.| Size.|| Mark.| Size.|| Mark.| Size.
-----+------++------+------++------+------++------+------
36 | .004 || 26 | .018 || 16 | .065 || 6 | .203
35 | .005 || 25 | .020 || 15 | .072 || 5 | .220
34 | .007 || 24 | .022 || 14 | .083 || 4 | .238
33 | .008 || 23 | .025 || 13 | .095 || 3 | .259
32 | .009 || 22 | .028 || 12 | .109 || 2 | .284
31 | .010 || 21 | .032 || 11 | .120 || 1 | .300
30 | .012 || 20 | .035 || 10 | .134 || 0 | .340
29 | .013 || 19 | .042 || 9 | .148 || 00 | .380
28 | .014 || 18 | .049 || 8 | .165 || 000 | .425
27 | .016 || 17 | .058 || 7 | .180 || 0000 | .454
-----+------++------+------++------+------++------+------
In this gauge it will be observed that the progressive wire gauge
numbers do not progress by a regular increment.
This gauge is sometimes termed the Stubs wire-gauge, Mr. Stubs being a
manufacturer of instruments whose notches are spaced according to the
Birmingham wire-gauge. Since, however, Mr. Stubs has also a wire-gauge
of his own, whose numbers and gauge-sizes do not correspond to those of
the Birmingham gauge, the two Stubs gauges are sometimes confounded. The
second Stubs gauge is employed for a special drawn steel wire, made by
that gentleman to very accurate gauge measurement for purposes in which
accuracy is of primary importance.
From the wear of the drawing dies in which wire is drawn, it is
impracticable, however, to attain absolute correctness of gauge
measurement. The dies are made to correct gauge when new, and when they
have become worn larger, to a certain extent, they are renewed. As a
result the average wire is slightly larger than the designated
gauge-number. To determine the amount of this error the Morse
Twist-Drill and Machine Company measured the wire used by them during an
extended period of time, the result being given in table No. 2, in which
the first column gives the gauge-number, the second column gives the
thickness of the gauge-number in decimal parts of an inch, and the third
column the actual size of the wire in decimal parts of an inch as
measured by the above Company.
DIAMETER OF STUBS'S DRAWN STEEL WIRE IN FRACTIONAL PARTS OF AN INCH.
-------+-------+--------++-------+-------+--------++-------+-------+--------
No. by |Stubs's|Measure-||No. by |Stubs's|Measure-||No. by |Stubs's|Measure-
Stubs's|Dimen- |ment by ||Stubs's|Dimen- |ment by ||Stubs's|Dimen- |ment by
wire- |sions. | Morse || wire- |sions. | Morse || wire- |sions. | Morse
gauge. | | Twist- ||gauge. | | Twist- ||gauge. | | Twist-
| | Drill || | | Drill || | | Drill
| | and || | | and || | | and
| |Machine || | |Machine || | |Machine
| | Co. || | | Co. || | | Co.
-------+-------+--------++-------+-------+--------++-------+-------+--------
1 | .227 | .228 || 23 | .153 | .154 || 45 | .081 | .082
2 | .219 | .221 || 24 | .151 | .152 || 46 | .079 | .080
3 | .212 | .213 || 25 | .148 | .150 || 47 | .077 | .079
4 | .207 | .209 || 26 | .146 | .148 || 48 | .075 | .076
5 | .204 | .206 || 27 | .143 | .145 || 49 | .072 | .073
6 | .201 | .204 || 28 | .139 | .141 || 50 | .069 | .070
7 | .199 | .201 || 29 | .134 | .136 || 51 | .066 | .067
8 | .197 | .199 || 30 | .127 | .129 || 52 | .063 | .064
9 | .194 | .196 || 31 | .120 | .120 || 53 | .058 | .060
10 | .191 | .194 || 32 | .115 | .116 || 54 | .055 | .054
11 | .188 | .191 || 33 | .112 | .113 || 55 | .050 | .052
12 | .185 | .188 || 34 | .110 | .111 || 56 | .045 | .047
13 | .182 | .185 || 35 | .108 | .110 || 57 | .042 | .044
14 | .180 | .182 || 36 | .106 | .106 || 58 | .041 | .042
15 | .178 | .180 || 37 | .103 | .104 || 59 | .040 | .041
16 | .175 | .177 || 38 | .101 | .101 || 60 | .039 | .040
17 | .172 | .173 || 39 | .099 | .100 || 61 | .038 | .039
18 | .168 | .170 || 40 | .097 | .098 || 62 | .037 | .038
19 | .164 | .166 || 41 | .095 | .096 || 63 | .036 | .037
20 | .161 | .161 || 42 | .092 | .094 || 64 | .035 | .036
21 | .157 | .159 || 43 | .088 | .089 || 65 | .033 | .035
22 | .155 | .156 || 44 | .085 | .086 || | |
-------+-------+--------++-------+-------+--------++-------+-------+--------
The following table represents the letter sizes of the same wire:--
LETTER SIZES OF WIRE.
A. 0.234 | J. 0.277 | S. 0.348
B. 0.238 | K. 0.281 | T. 0.358
C. 0.242 | L. 0.290 | U. 0.368
D. 0.246 | M. 0.295 | V. 0.377
E. 0.250 | N. 0.302 | W. 0.386
F. 0.257 | O. 0.316 | X. 0.397
G. 0.261 | P. 0.323 | Y. 0.404
H. 0.266 | Q. 0.332 | Z. 0.413
I. 0.272 | R. 0.339 |
By an Order in Council dated August 23rd, 1883, and which took effect on
March 1st, 1884, the standard department of the British Board of Trade
substituted for the old Birmingham wire-gauge the following:--
+-------------+--------------++---------------------------+
| Descriptive | Equivalents || Descriptive | Equivalents |
| number | in parts || number | in parts |
| B. W. G. | of an inch. || B. W. G. | of an inch. |
+-------------+--------------++-------------+-------------+
| No. | Inch. || No. | Inch. |
| 7/0 | 0.500 || 23 | 0.024 |
| 6/0 | .464 || 24 | .022 |
| 5/0 | .432 || 25 | .020 |
| 4/0 | .400 || 26 | .018 |
| 3/0 | .372 || 27 | .0164 |
| 2/0 | .348 || 28 | .0148 |
| 0 | .324 || 29 | .0136 |
| 1 | .300 || 30 | .0124 |
| 2 | .276 || 31 | .0116 |
| 3 | .252 || 32 | .0108 |
| 4 | .232 || 33 | .0100 |
| 5 | .212 || 34 | .0092 |
| 6 | .192 || 35 | .0084 |
| 7 | .176 || 36 | .0076 |
| 8 | .160 || 37 | .0068 |
| 9 | .144 || 38 | .0060 |
| 10 | .128 || 39 | .0052 |
| 11 | .116 || 40 | .0048 |
| 12 | .104 || 41 | .0044 |
| 13 | .092 || 42 | .0040 |
| 14 | .080 || 43 | .0036 |
| 15 | .072 || 44 | .0032 |
| 16 | .064 || 45 | .0028 |
| 17 | .056 || 46 | .0024 |
| 18 | .048 || 47 | .0020 |
| 19 | .040 || 48 | .0016 |
| 20 | .036 || 49 | .0012 |
| 21 | .032 || 50 | .0010 |
| 22 | .028 || | |
+-------------+--------------++-------------+-------------+
[Illustration: Fig. 1494.]
[Illustration: Fig. 1495.]
The gauge known as the American Standard Wire-Gauge was designed by
Messrs. Brown and Sharpe to correct the discrepancies of the old
Birmingham wire-gauge by establishing a regular proportion of the
thirty-nine successive steps between the 0000 and 36 gauge-number of
that gauge. In the American Standard (which is also called the Brown and
Sharpe gauge) the value of 0.46 or 46/100 has been taken as that for
0000 or the largest dimension of the gauge. Then by successive and
uniform decrements, each number following being obtained from
multiplying its predecessor by 0.890522 (which is the same thing as
deducting 10.9478 per cent.), the final value for number 36 is reached
at 0.005, which corresponds with number 35 of the Birmingham wire-gauge.
The principle of the gauge is shown in Fig. 1495, which represents a
gauge for jewelers, having an angular aperture with the gauge-numbers
marked on the edge, the lines and numbers being equidistant.
The advantage of this system is that the instrument is easy to produce,
the difference between any two gauge-numbers being easily found by
calculation; and the gauge is easy to originate, since the opening,
being of the proper width at the open end, the sides terminating at the
proper distance and being made straight, the intermediate gauge-sizes
may be accurately marked by the necessary number of equidistant lines.
Wire, to be measured by such a gauge, is simply inserted into and passed
up the aperture until it meets the sides of the same, which gives the
advantage that the size of the wire may be obtained, even though its
diameter vary from a gauge-number. This could not be done with a gauge
in which each gauge-number and size is given in a separate aperture or
notch. A comparison between the Brown and Sharpe and the Birmingham
wire-gauge is shown in Fig. 1494, in which a piece of wire is inserted,
showing that No. 15 by the Birmingham gauge is No. 13 by the Brown and
Sharpe gauge.
The gauge-numbers and sizes of the same in decimal parts of an inch, of
the American standard or Brown and Sharpe gauge, are given in the table
following:--
------+--------------------------++------+--------------------------
|American or New Standard. || | American or New Standard.
+--------------------------++ +------------+-------------
No. of|Size of each| Difference ||No. of|Size of each| Difference
Wire- | number in | between ||Wire- | number in | between
Gauge.| decimal | consecutive ||Gauge.| decimal | consecutive
| parts of | numbers in || | parts of | numbers in
| an inch. |decimal parts|| | an inch. |decimal parts
| | of an inch. || | | of an inch.
------+------------+-------------++------+------------+-------------
0000 | .460 | ---- || 19 | .03589 | .00441
000 | .40964 | .05036 || 20 | .03196 | .00393
00 | .36480 | .04484 || 21 | .02846 | .00350
0 | .32495 | .03994 || 22 | .02535 | .00311
1 | .28930 | .03556 || 23 | .02257 | .00278
2 | .25763 | .03167 || 24 | .0201 | .00247
3 | .22942 | .02821 || 25 | .0179 | .00220
4 | .20431 | .02511 || 26 | .01594 | .00196
5 | .18194 | .02237 || 27 | .01419 | .00174
6 | .16202 | .01992 || 28 | .01264 | .00155
7 | .14428 | .01774 || 29 | .01126 | .00138
8 | .12849 | .01579 || 30 | .01002 | .00123
9 | .11443 | .01406 || 31 | .00893 | .00110
10 | .10189 | .01254 || 32 | .00795 | .00098
11 | .09074 | .01105 || 33 | .00708 | .00087
12 | .08081 | .00993 || 34 | .0063 | .00078
13 | .07196 | .00885 || 35 | .00561 | .00069
14 | .06408 | .00788 || 36 | .005 | .00061
15 | .05707 | .00702 || 37 | .00445 | .00055
16 | .05082 | .00625 || 38 | .00396 | .00049
17 | .04525 | .00556 || 39 | .00353 | .00043
18 | .0403 | .00495 || 40 | .00314 | .00039
------+------------+-------------++------+------------+-------------
This gauge is now the standard by which rolled sheet brass and seamless
brass tubing is made in the United States. It is also sometimes used as
a gauge for the copper wire used for electrical purposes, being termed
the American Standard; but unless the words "American Standard" are
employed, the above wire is supplied by the Birmingham wire-gauge
numbers. The brass wire manufacturers have not yet adopted the Brown and
Sharpe gauge; hence, for brass wire the Birmingham gauge is the
standard.
Gauges having simple notches are not suitable for measuring accurately
the thickness of metal, because the edges of the sheets or plates
frequently vary from the thickness of the body of the plate. This may
occur from the wear of the rolls employed to roll out the sheet, or
because the sheets have been sheared to cut them to the required width,
or to remove cracks at the edges, which shearing is apt to form a burr
or projection on one side of the edge, and a slight depression on the
other.
Again, a gauge formed by a notch requires to slide over the metal of the
plate, and friction and a wear causing an enlargement of the notch
ensues, which destroys the accuracy of the gauge. To avoid this source
of error the form of gauge that was shown in Fig. 1370 may be used, it
having the further advantage that it will measure thicknesses
intermediate between the sizes of two contiguous notches, thus measuring
the actual thickness of the sheet when it is not to any accurate sheet
metal gauge thickness.
It is to be observed that in the process of rolling, the sheet is
reduced from a greater to a lesser thickness, hence the gauge will not
pass upon the plate until the latter is reduced to its proper thickness.
In applying the gauge, therefore, there is great inducement for the
workman to force the gauge on to the sheet, in order to ascertain how
nearly the sheet is to the required size, and this forcing process
causes rapid wear to the gauge.
It follows, therefore, that a gauge should in no case be forced on, but
should be applied lightly and easily to the sheet to prevent wear. Here
may be mentioned another advantage of the Brown and Sharpe gauge, in
that its gauge-number measurements being uniform, it may be more readily
known to what extent a given plate varies from its required gauge
thickness.
Suppose, for example, a sheet requiring to be of Number 1 Birmingham
gauge is above the required thickness, but will pass easily through the
0 notch of the gauge, the excessive variation of those two gauge numbers
(over the variations between other consecutive numbers of the gauge)
leaves a wider margin in estimating how much the thickness is excessive
than would be the case in using the Brown and Sharpe gauge. Indeed, if
the edge of the plate be of uniform thickness with the body of the
plate, the variation from the required thickness may be readily
ascertained by a Brown and Sharpe gauge, by the distance the plate will
pass up the aperture beyond the line denoting the 0 gauge number, or by
the distance it stands from the 1 on the gauge when passed up the
aperture until it meets both sides of the same.
In addition to these standard gauges, some firms in the United States
employ a standard of their own; the principal of these are given in
comparison with others in the table following.
DIMENSIONS OF SIZES, IN DECIMAL PARTS OF AN INCH.
------+---------+--------+----------+---------+---------+------------
Number| American|Birming-| Washburn | Trenton | G. W. |Old English,
of | or Brown| ham, | & Moen |Iron Co.,|Prentiss,| from Brass
Wire | & | or | Mfg. Co.,| Trenton,| Holyoke,| Manu-
Gauge.| Sharpe. |Stubs's.|Worcester,| N. J. | Mass. | facturers'
| | | Ms. | | | List.
------+---------+--------+----------+---------+---------+------------
000000| ---- | ---- | .46 | ---- | ---- | ----
00000| ---- | ---- | .43 | .45 | ---- | ----
0000| .46 | .454 | .393 | .4 | ---- | ----
000| .40964 | .425 | .362 | .36 | .3586 | ----
00| .3648 | .38 | .331 | .33 | .3282 | ----
0| .32495 | .34 | .307 | .305 | .2994 | ----
1| .2893 | .3 | .283 | .285 | .2777 | ----
2| .25763 | .284 | .263 | .265 | .2591 | ----
3| .22942 | .259 | .244 | .245 | .2401 | ----
4| .20431 | .238 | .225 | .225 | .223 | ----
5| .18194 | .22 | .207 | .205 | .2047 | ----
6| .16202 | .203 | .192 | .19 | .1885 | ----
7| .14428 | .18 | .177 | .175 | .1758 | ----
8| .12849 | .165 | .162 | .16 | .1605 | ----
9| .11443 | .148 | .148 | .145 | .1471 | ----
10| .10189 | .134 | .135 | .13 | .1351 | ----
11| .090742 | .12 | .12 | .1175 | .1205 | ----
12| .080808 | .109 | .105 | .105 | .1065 | ----
13| .071961 | .095 | .092 | .0925 | .0928 | ----
14| .064084 | .083 | .08 | .08 | .0816 | .083
15| .057068 | .072 | .072 | .07 | .0726 | .072
16| .05082 | .065 | .063 | .061 | .0627 | .065
17| .045257 | .058 | .054 | .0525 | .0546 | .058
18| .040303 | .049 | .047 | .045 | .0478 | .049
19| .03539 | .042 | .041 | .039 | .0411 | .04
20| .031961 | .035 | .035 | .034 | .0351 | .035
21| .028462 | .032 | .032 | .03 | .0321 | .0315
22| .025347 | .028 | .028 | .027 | .029 | .0295
23| .022571 | .025 | .025 | .024 | .0261 | .027
24| .0201 | .022 | .023 | .0215 | .0231 | .025
2S| .0179 | .02 | .02 | .019 | .0212 | .023
26| .01594 | .018 | .018 | .018 | .0194 | .0205
27| .014195 | .016 | .017 | .017 | .0182 | .01875
28| .012641 | .014 | .016 | .016 | .017 | .0165
29| .011257 | .013 | .015 | .015 | .0163 | .0155
30| .010025 | .012 | .014 | .014 | .0156 | .01375
31| .008928 | .01 | .0135 | .013 | .0146 | .01225
32| .00795 | .009 | .013 | .012 | .0136 | .01125
33| .00708 | .008 | .011 | .011 | .013 | .01025
34| .006304 | .007 | .01 | .01 | .0118 | .0095
35| .005614 | .005 | .0095 | .009 | .0109 | .009
36| .005 | .004 | .009 | .008 | .01 | .0075
37| .004453 | ---- | .0085 | .00725 | .0095 | .0065
38| .003965 | ---- | .008 | .0065 | .009 | .00575
------+---------+--------+----------+---------+---------+------------
In the Whitworth wire-gauge, the mark or number on the gauge simply
denotes the number of 1/1000ths of an inch the wire is in diameter; thus
Number 1 on the gauge is 1/1000 inch, Number 2 is 2/1000ths inch in
diameter, and so on.
Below is given the Washburn and Moen Manufacturing Company's music
wire-gauge.
SIZES OF THE NUMBERS OF STEEL MUSIC WIRE-GAUGE.
+--------+------------------++--------+------------------+
| No. of | Size of each No. || No. of | Size of each No. |
| Gauge. | in decimal parts || Gauge. | in decimal parts |
| | of an inch. || | of an inch. |
+--------+------------------++--------+------------------+
| 12 | .0295 || 21 | .0461 |
| 13 | .0311 || 22 | .0481 |
| 14 | .0325 || 23 | .0506 |
| 15 | .0343 || 24 | .0547 |
| 16 | .0359 || 25 | .0585 |
| 17 | .0378 || 26 | .0626 |
| 18 | .0395 || 27 | .0663 |
| 19 | .0414 || 28 | .0719 |
| 20 | .043 || ---- | ---- |
+--------+------------------++--------+------------------+
These sizes are those used by the Washburn and Moen Manufacturing
Company, of Worcester, Mass., manufacturers of steel music wire.
In the following table is the French Limoges wire-gauge.
-------+-----------+-------++--------+-----------+------
Number | Diameter, | Inch. || Number | Diameter, | Inch.
on | milli- | || on | milli- |
gauge. | mètre. | || gauge. | mètre. |
-------+-----------+-------++--------+-----------+------
0 | .39 | .0154 || 13 | 1.91 | .0725
1 | .45 | .0177 || 14 | 2.02 | .0795
2 | .56 | .0221 || 15 | 2.14 | .0843
3 | .67 | .0264 || 16 | 2.25 | .0886
4 | .79 | .0311 || 17 | 2.84 | .112
5 | .90 | .0354 || 18 | 3.40 | .134
6 | 1.01 | .0398 || 19 | 3.95 | .156
7 | 1.12 | .0441 || 20 | 4.50 | .177
8 | 1.24 | .0488 || 21 | 5.10 | .201
9 | 1.35 | .0532 || 22 | 5.65 | .222
10 | 1.46 | .0575 || 23 | 6.20 | .244
11 | 1.68 | .0661 || 24 | 6.80 | .268
12 | 1.80 | .0706 || | |
-------+-----------+-------++--------+-----------+------
The following table gives the Birmingham wire-gauge for rolled sheet
silver and gold.
+---------+------------++---------+------------+
| Gauge | Thickness. || Gauge | Thickness. |
| number. | || number. | |
+---------+------------++---------+------------+
| | Inch. || | Inch. |
| 1 | .004 || 19 | .064 |
| 2 | .005 || 20 | .067 |
| 3 | .008 || 21 | .072 |
| 4 | .010 || 22 | .074 |
| 5 | .013 || 23 | .077 |
| 6 | .013 || 24 | .082 |
| 7 | .015 || 25 | .095 |
| 8 | .016 || 26 | .103 |
| 9 | .019 || 27 | .113 |
| 10 | .024 || 28 | .120 |
| 11 | .029 || 29 | .124 |
| 12 | .034 || 30 | .126 |
| 13 | .036 || 31 | .133 |
| 14 | .041 || 32 | .143 |
| 15 | .047 || 33 | .145 |
| 16 | .051 || 34 | .148 |
| 17 | .057 || 35 | .158 |
| 18 | .061 || 36 | .167 |
+---------+------------++---------+------------+
The following table gives the gauge thickness of Russia sheet iron,[25]
the corresponding numbers by Birmingham wire gauge, and the thicknesses
in decimal parts of an inch.
[25] This iron comes in sheets 28 × 56 inches = 10.88 square feet of
area.
+----------+------------+-------------------+
| Russia | Birmingham | Thickness in |
| gauge | wire-gauge | decimal |
| number. | number. | parts of an inch. |
+----------+------------+-------------------+
| 7 | 29 | .013 |
| 8 | 28 | .014 |
| 9 | 27 | .016 |
| 10 | 26 | .018 |
| 11 | 25 | .020 |
| 12 | 24-1/2 | .021 |
| 13 | 24 | .022 |
| 14 | 23-1/4 | ---- |
| 15 | 22-3/8 | ---- |
| 16 | 21-1/2 | ---- |
+----------+------------+-------------------+
The following table gives the gauge numbers to which galvanized iron is
made.[26]
[26] Galvanized iron is made to the Birmingham wire-gauge, the
thickness includes the galvanizing, the sheets being rolled thinner to
allow for it.
+---------+------------++---------+------------+
| Gauge | Thickness. || Gauge | Thickness. |
| number. | || number. | |
+---------+------------++---------+------------+
| | Inch. || | Inch. |
| 14 | .083 || 23 | .025 |
| 16 | .065 || 24 | .022 |
| 17 | .058 || 25 | .02 |
| 18 | .049 || 26 | .018 |
| 19 | .042 || 27 | .016 |
| 20 | .035 || 28 | .014 |
| 21 | .032 || 29 | .013 |
| 22 | .028 || | |
+---------+------------++---------+------------+
In the following table is given the American gauge sizes and their
respective thicknesses for sheet zinc.
--------------------------------++--------------------------------
Gauge and Thickness. || Gauge and Thickness.
-------+-----------+------------++-------+-----------+------------
Number.|Approximate|Thickness in||Number.|Approximate|Thickness in
|Birmingham |fractions of|| |Birmingham |fractions of
|wire-gauge.| an inch. || |wire-gauge.| an inch.
-------+-----------+------------++-------+-----------+------------
1 | ---- | 0.0039 || 16 | ---- | 0.0447
5 | ---- | 0.0113 || 17 | ---- | 0.0521
6 | ---- | 0.0132 || 18 | ---- | 0.0596
7 | ---- | 0.0150 || 19 | ---- | 0.0670
8 | 28 | 0.0169 || 20 | ---- | 0.0744
9 | 27 | 0.0187 || 21 | ---- | 0.0818
10 | 26 | 0.0224 || 22 | ---- | 0.0892
11 | 25 | 0.0261 || 23 | ---- | 0.0966
12 | 24 | 0.0298 || 24 | ---- | 0.1040
13 | ---- | 0.0336 || 25 | ---- | 0.1114
14 | ---- | 0.0373 || 26 | ---- | 0.1189
15 | ---- | 0.0410 || | |
-------+-----------+------------++-------+-----------+------------
The Belgian sheet zinc gauge is as follows:
+---------+-------------++---------+-------------+
| Gauge | Thickness in|| Gauge | Thickness in|
| number. |decimal parts|| number. |decimal parts|
| | of an inch. || | of an inch. |
+---------+-------------++---------+-------------+
| 1 | .004 || 14 | .037 |
| 2 | .006 || 15 | .041 |
| 3 | .008 || 16 | .045 |
| 4 | .009 || 17 | .052 |
| 5 | .011 || 18 | .059 |
| 6 | .013 || 19 | .067 |
| 7 | .015 || 20 | .074 |
| 8 | .017 || 21 | .082 |
| 9 | .019 || 22 | .089 |
| 10 | .022 || 23 | .097 |
| 11 | .026 || 24 | .104 |
| 12 | .030 || 25 | .111 |
| 13 | .034 || 26 | .120 |
+---------+-------------++---------+-------------+
The gauge sizes of the bores of rifles are given in the following
table,[27] in which the first column gives the proper gauge diameter of
bore, and the second the actual diameter containing the errors found to
exist from errors of workmanship. The standard diameters are supposed to
be based upon the number of spherical bullets to the pound weight, if of
the same diameter as the respective gauge sizes.
[27] From _The English Mechanic_.
No. of Diameter of Bore.
Gauge.
4 varies from 1.052 to 1.000
6 " .919 " .900
8 " .835 " .820
10 " .775 " .760
12 " .729 " .750
14 " .693 " .680
16 " .662 " .650
20 " .615 " .610
24 " .579 " .577
28 " .550 " .548
The following table gives the result of some recent experiments made by
Mr. David Kirkaldy, of London, to ascertain the tensile strength and
resistance to torsion of wire made of various materials:
+-----------------------+--------------------------+
| |Pulling stress per sq. in.|
| Kind of wire tested. +-------------+------------+
| | Unannealed. | Annealed. |
+-----------------------+-------------+------------+
| | Pounds. | Pounds. |
|Copper | 63,122 | 37,002 |
|Brass | 81,156 | 51,550 |
|Charcoal iron | 65,834 | 46,160 |
|Coke iron | 64,321 | 61,294 |
|Steel | 120,976 | 74,637 |
|Phosphor bronze, No. 1 | 159,515 | 58,853 |
| " No. 2 | 151,119 | 64,569 |
| " No. 3 | 139,141 | 54,111 |
| " No. 4 | 120,900 | 53,381 |
+-----------------------+-------------+------------+
+-----------------------+------------+----------------------+
| | Ultimate | No. of twists in |
| Kind of wire tested. |extension in| 5 inches. |
| | per cent. +-----------+----------+
| | Annealed. |Unannealed.| Annealed.|
+-----------------------+------------+-----------+----------+
|Copper | 34.1 | 86.8 | 96 |
|Brass | 36.5 | 14.7 | 57 |
|Charcoal iron | 28 | 48 | 87 |
|Coke iron | 17 | 26 | 44 |
|Steel | 10.9 | [28] | 79 |
|Phosphor bronze, No. 1 | 46.6 | 13.3 | 66 |
| " No. 2 | 42.8 | 15.8 | 60 |
| " No. 3 | 44.9 | 17.3 | 53 |
| " No. 4 | 42.4 | 13 | 124 |
+-----------------------+------------+-----------+----------+
[28] Of the eight pieces of steel tested, three stood from forty to
forty-five twists, and five stood one and a half to four twists.
The following, on some experiments upon the elasticity of wires, is from
the report of a committee read before the British Association at
Sheffield, England.
"The most important of these experiments form a series that have been
made on the elastic properties of very soft iron wire. The wire used was
drawn for the purpose, and is extremely soft and very uniform. It is
about No. 20 B.W.G., and its breaking weight, tested in the ordinary
way, is about 45 lbs. This wire has been hung up in lengths of about 20
ft., and broken by weights applied, the breaking being performed more or
less slowly.
"In the first place some experiments have been tried as to the smallest
weight which, applied very cautiously and with precautions against
letting the weight run down with sensible velocity, will break the wire.
These experiments have not yet been very satisfactorily carried out, but
it is intended to complete them.
"The other experiments have been carried out in the following way: It
was found that a weight of 28 lbs. does not give permanent elongation to
the wire taken as it was supplied by the wire drawer. Each length of the
wire, therefore, as soon as it was hung up for experiment, was weighted
with 28 lbs., and this weight was left hanging on the wire for 24 hours.
Weights were then added till the wire broke, measurements as to
elongation being taken at the same time. A large number of wires were
broken with equal additions of weight, a pound at a time, at intervals
of from three to five minutes--care being taken in all cases, however,
not to add fresh weight if the wire could be seen to be running down
under the effect of the weight last added. Some were broken with weights
added at the rate of 1 lb. per day, some with 3/4 lb. per day, and some
with 1/2 lb. per day. One experiment was commenced in which it was
intended to break the wire at a very much slower rate than any of these.
It was carried on for some months, but the wire unfortunately rusted,
and broke at a place which was seen to be very much eaten away by rust,
and with a very low breaking weight. A fresh wire has been suspended,
and is now being tested. It has been painted with oil, and has now been
under experiment for several months.
"The following tables will show the general results of these
experiments. It will be seen, in the first place, that the prolonged
application of stress has a very remarkable effect in increasing the
strength of soft iron wire. Comparing the breaking weights for the wire
quickly broken with those for the same wire slowly broken, it will be
seen that in the latter case the strength of the wire is from two to ten
per cent. higher than in the former, and is on the average about five or
six per cent. higher. The result as to elongation is even more
remarkable, and was certainly more unexpected. It will be seen from the
tables that, in the case of the wire quickly drawn out, the elongation
is on the average more than three times as great as in the case of the
wire drawn out slowly. There are two wires for which the breaking
weights and elongations are given in the tables, both of them 'bright'
wires, which showed this difference very remarkably. They broke without
showing any special peculiarity as to breaking weight, and without known
difference as to treatment, except in the time during which the
application of the breaking weight was made. One of them broke with
44-1/4 lbs., the experiment lasting one hour and a half; the other with
47 lbs., the time occupied in applying the weight being 39 days. The
former was drawn out by 28.5 per cent. on its original length, the
latter by only 4.79 per cent.
"It is found during the breaking of these wires that the wire becomes
alternately more yielding and less yielding to stress applied. Thus from
weights applied gradually between 28 lbs. and 31 lbs. or 32 lbs., there
is very little yielding, and very little elongation of the wire. For
equal additions of weight between 33 lbs. and about 37 lbs. the
elongation is very great. After 37 lbs. have been put on, the wire seems
to get stiff again, till a weight of about 40 lbs. has been applied.
Then there is a rapid running down till 45 lbs. has been reached. The
wire then becomes stiff again, and often remains so till it breaks. It
is evident that this subject requires careful investigation."
TABLES SHOWING THE BREAKING OF SOFT IRON WIRES AT DIFFERENT SPEEDS.
I.--WIRE QUICKLY BROKEN.
+------------------------+-----------+---------------+
| | Breaking | Per cent. of |
| Rate of adding weight. | weight in | elongation on |
| | pounds. | original |
| | | length. |
+------------------------+-----------+---------------+
| _Dark Wire._[29] | | |
| 0-1/4 lb. per minute | 45 | 25.4 |
| 1 " 5 minutes | 45-1/4 | 25.9 |
| " 5 " | 45-1/4 | 24.9 |
| " 4 " | 44-1/4 | 24.58 |
| " 3 " | 44-1/4 | 24.88 |
| " 3 " | 45-1/4 | 29.58 |
| " 5 " | 44-1/4 | 27.78 |
| _Bright Wire._[29] | | |
| 1 lb. per 5 minutes | 44-1/4 | 28.5 |
| " 5 " | 44-1/4 | 27.0 |
| " 4 " | 44-1/4 | 27.1 |
+------------------------+-----------+---------------+
[29] The wire used was all of the same quality and gauge, but the
"dark" and "bright" wire had gone through slightly different
processes for the purpose of annealing.
II.--WIRE SLOWLY BROKEN.
+--------------------+------------+--------------------+
| Weight added and | Breaking | Per cent. of |
| number of | weight in | elongation on |
| experiment. | pounds. | original length. |
+--------------------+------------+--------------------+
| 1. 1 lb. per day | 48 | 7.58 |
| 2. " " | 46 | 8.13 |
| 3. " " | 47 | 7.05 |
| 4. " " | 47 | 6.51 |
| 5. " " | 47 | 8.62 |
| 6. " " | 47 | 5.17 |
| 7. " " | 46 | 5.50 |
| 8. " " | 47 | 6.92 bright wire |
| 1. 3/4 lb. per day | 49 | 8.50 |
| 2. " " | 48-1/4 | 8.81 |
| 3. " " | Broken by accident. |
| 4. " " | 46 | 7.55 |
| 5. " " | 46 | 6.41 |
| 6. " " | 45-1/2 | 6.62 |
| 1. 1/2 lb. per day | 48 | 8.26 |
| 2. " " | 50 | 8.42 |
| 3. " " | 49 | 7.18 |
| 4. " " | 47 | 4.79} |
| 5. " " | 46-1/2 | 6.00} bright wires |
+--------------------+------------+--------------------+
The American Standard diameters of solid drawn or seamless brass and
copper tube are as in the following table.
+----------+-----------------+---------------+---------------+
| Outside |Thickness Stubs's| Weight per | Weight per |
|diameter. | wire-gauge. | running foot. | running foot. |
| | | Brass tubes. | Copper tubes. |
+----------+-----------------+---------------+---------------+
| 5/8 | 18 | 3/8 | 3/8 |
| 3/4 | 17 | 1/2 | 1/2 |
| 13/16 | 17 | 9/16 | 9/16 |
| 7/8 | 17 | 5/8 | 5/8 |
| 15/16 | 16 | 11/16 | 11/16 |
| 1 | 16 | 3/4 | 3/4 |
| 1-1/8 | 16 | 7/8 | 7/8 |
| 1-1/4 | 12 and 14 | 1-1/4 | 1-1/4 |
| 1-3/8 | 12 " 14 | 1-3/8 | 1-3/8 |
| 1-1/2 | 12 " 14 | 1-1/2 | 1-6/10 |
| 1-5/8 | 12 " 14 | 1-5/8 | 1-7/10 |
| 1-3/4 | 12 " 14 | 1-3/4 | 1-8/10 |
| 1-13/16 | 12 " 14 | 1-13/16 | 1-9/10 |
| 1-7/8 | 12 " 14 | 1-7/8 | 1-15/16 |
| 1-15/16 | 12 " 14 | 2 | 2-1/10 |
| 2 | 12 " 14 | 2-1/8 | 2-1/4 |
| 2-1/8 | 12 " 14 | 2-1/4 | 2-3/8 |
| 2-1/4 | 12 " 14 | 2-3/8 | 2-1/3 |
| 2-3/8 | 12 " 14 | 2-1/2 | 2-2/3 |
| 2-1/2 | 11 " 13 | 2-3/4 | 3 |
| 2-5/8 | 11 " 13 | 3 | 3-1/8 |
| 2-3/4 | 11 " 13 | 3-1/8 | 3-1/4 |
| 2-7/8 | 11 " 13 | 3-1/4 | 3-3/8 |
| 3 | 11 " 13 | 3-3/8 | 3-1/2 |
| 3-1/8 | 11 " 13 | 3-1/2 | 3-3/4 |
| 3-1/4 | 11 " 13 | 3-7/8 | 4-1/8 |
| 3-3/8 | 11 " 13 | 4-1/8 | 4-1/4 |
| 3-1/2 | 11 " 13 | 4-1/4 | 4-3/8 |
| 4 | 11 " 13 | 5 | 5-1/4 |
| 4-1/4 | 11 " 13 | 6 | 6-1/2 |
| 5 | 10 " 12 | 7 | 8 |
| 6 | 10 " 12 | 9 | 10 |
+----------+-----------------+---------------+---------------+
CHAPTER XVI.--SHAPING AND PLANING MACHINES.
The office of the shaping machine is to dress or cut to shape such
surfaces as can be most conveniently cut by a tool moving across the
work in a straight line.
The positions occupied among machine tools at the present time by
shaping and planing machines are not as important as was the case a few
years ago, because of the advent of the milling machine, which requires
less skill to operate, and produces superior work.
All the cutting tools used upon shaping and planing machines have
already been described with reference to outside tools for lathe work,
and it may be remarked that a great deal of the chucking done on the
shaping and planing machine corresponds to face plate chucking in the
lathe. Both shaping machines and small planing machines, however, are
provided with special chucks and work-holding appliances that are not
used in lathe work, and these will be treated of presently. On large
planing machines chucks are rarely used, on account of the work being
too large to be held in a chuck. Shaping machines are also known as
shapers and planing machines as planers.
[Illustration: Fig. 1496.]
The simplest form of shaping machine, or shaper as it is usually termed
in the United States, is that in which a tool-carrying slide is
reciprocated across the work, the latter moving at the end of each back
stroke so that on the next stroke the tool may be fed to its cut on the
work. Fig. 1496 represents a shaper of this kind constructed by Messrs.
Hewes and Phillips, of Newark, New Jersey, in which P is a cone pulley
receiving motion from a countershaft, and driving a pinion which
revolves the gear-wheel Q, whose shaft has journal bearing in the frame
of the machine. This shaft drives a bevel pinion gearing with a
bevel-wheel in one piece with the eccentric spur-wheel S, which is upon
a shaft having at its lower end the bevel-wheel B to operate the
work-feeding mechanism. S drives an eccentric gear wheel R, fast upon
the upper face of which is a projection E, in which is a [T]-shaped
groove to receive and secure a wrist or crank pin which drives a
connecting rod secured to the slide A by means of a bolt passing through
A, and secured to the same by a nut D.
When the gear-wheel R revolves, the connecting rod causes slide A to
traverse to and fro endways in a guideway, provided on the top of the
frame at X. On the end of this slide is a head carrying a cutting tool
T, which, therefore, moves across the work, the latter being held in the
vise V, which is fast upon a table W upon a carriage saddle or slider
_p_, which is upon a horizontal slide that in turn fits to a slide
vertical upon the front of the machine, and may be raised or lowered
thereon by means of an elevating screw driven by a pair of mitre-wheels
at F. The slider and table W (and therefore the vise and the work) are
moved along the horizontal slide to feed the work to the tool cut as
follows. A short horizontal shaft (driven by the bevel pinions at B),
drives at its outer end a piece C, having a slot to receive a crank pin
driving the feed rod N, which operates a pawl K engaging a ratchet wheel
which is fast upon the horizontal screw that operates slider _p_.
[Illustration: Fig. 1497.]
The diameters of the eccentric gear-wheels E and S are equal; hence, C
makes a revolution and the cross feed is actuated once for every cutting
stroke. The swivel head H is bolted to the end of the slide or ram, as
it is sometimes called, A, and is provided with a slide I upon which is
a slider J, carrying an apron containing the tool post holding the
cutting tool, the construction of this part of the mechanism being more
fully shown in Fig. 1497. The eccentric gear-wheels R S are so geared
that the motion of the slide A during the cutting stroke (which is in
the direction of the arrow) is slower than the return stroke, which on
account of being accelerated is termed a quick return. Various
mechanisms for obtaining a quick return motion are employed, the object
being to increase the number of cutting strokes in a given time, without
accelerating the cutting speed of the tool, and some of these mechanisms
will be given hereafter.
[Illustration: Fig. 1498.]
Referring again to the mechanism for carrying the cutting tool and
actuating it to regulate the depth of cut in Fig. 1497, G is the end of
the slide a to which the swivel head H is bolted by the bolts _a_ _b_.
The heads of these bolts pass into [T]-shaped annular grooves in G, so
that H may be set to have its slides at any required angle. I is a
slider actuated on the slide by means of the vertical feed screw which
has journal bearing in the top of H, and passes through a nut provided
in I. To I is fastened the apron swivel J, being held by a central bolt
not seen in the cut, and also by the bolt at _c_. In J is a slot, which
when _c_ is loosened permits J to be swung at an angle. The apron K is
pivoted by a taper pin L, which fits into both J and K. During the
cutting stroke the apron K beds down upon J, but during the back stroke
the tool may lift the apron K swinging upon the pivot L. This prevents
the cutting edge of the tool from rubbing against the work during the
return stroke.
Thus in Fig. 1498 is a piece of work, and it is supposed that a cut is
being carried down the vertical face or shoulder at A; by setting the
apron swivel at an angle and lifting the tool during the return stroke,
its end will move away from the face of the shoulder. The slider I
obviously moves in a vertical line upon slides M.
[Illustration: Fig. 1499.]
To take up the wear of the sliding bar A, various forms of guideways and
guides are employed, a common form being shown in Fig. 1499. There are
two gibs, one on each side of the bar, and these gibs are set up by
screws to adjust the fit. In some cases only one gib is used, and in
that event the wear causes the slide to move to one side, but as the
wear proceeds exceedingly slowly in consequence of the long bearing
surface of the bar in its guides, this is of but little practical
moment. On the other hand, when two gibs are used great care must be
taken to so adjust the screws that the slide bar is maintained in a line
at a right angle to the jaws of the work-holding vice, so that the tool
will cut the vertical surfaces or side faces of the work at a right
angle to the work surface that is gripped by the vice.
To enable the length of stroke of slide A, Fig. 1496, to be varied to
suit the length of the work, and thus not lose time by uselessly
traversing that slide, E is provided with a [T]-slot as before stated,
and the distance of the wrist pin (in this slot) from the centre of
wheel E determines the amount of motion imparted to the connecting rod,
and therefore to slide A. The wrist pin is set so as to give to A a
rather longer stroke than the work requires, so that this tool may pass
clear of the work on the forward stroke, and an inch or so past the work
on the return stroke, the latter giving time to feed the tool down
before it meets the work.
The length of the stroke being set, the crank piece E (for its slot and
wrist pin correspond to a crank) is, by pulling round the pulley P,
brought to the end of a stroke, the connecting rod being in line with
slide A. The nut D is then loosened and slide A may then be moved by
hand in its slideway until the tool clears the work at the end
corresponding to the connecting rod position when nut D is tightened and
the stroke is set.
[Illustration: Fig. 1500.]
Now suppose it is required to shape or surface the faces _f_ and _f´_,
the round curve S and the hollow curve C of the piece of work shown held
in a vice chuck in Fig. 1500, and during the cutting stroke the slide
_a_ will travel in the direction of _n_ in the figure, while during its
return stroke it will traverse back in the direction of _i_. The sliding
table W in Fig. 1496 would continuously but gradually be fed or moved
(so much per tool traverse, and by the feeding mechanism described with
reference to Fig. 1501) carrying with it the vice chuck, and therefore
the work. When this feeding brought the surface of curve S, Fig. 1500,
into contact with the tool, the feed screw handle in figure would be
operated by hand so much per feed traverse, thus raising the slider, and
therefore the tool, in the direction of _l_, and motion of the work to
the right and the left of the tool (by means of the feed handle) would
(if the amount of tool lift per tool stroke is properly proportioned to
the amount of work feed to the right) cause the tool to cut the work to
the required curvature. When the work had traversed until the tool had
arrived at the top of curve S, the direction of motion of the feed-screw
handle Z in Fig. 1496 must be reversed, the tool being fed down so much
per tool traverse (in the direction of _m_) so as to cut out the curves
from the top of S to the bottom of _c_, the face _f´_ being shaped by
the automatic feed motion only.
The feed obviously occurs once for each cutting stroke of the tool and
for the vertical motion of the tool, or when the tool is operated by the
hand feed-screw handle in Fig. 1496, the handle motion, and therefore
the feed should occur at the end of the back stroke and before the tool
again meets the work, so as to prevent the cutting edge of the tool from
scraping against the work during its back traverse.
In this connection it may be remarked that by setting the apron swivel
over, as in Fig. 1498, the tool is relieved from rubbing on the back
stroke for two reasons, the first having been already explained, and the
second being that to whatever amount the tool may spring, bend, or
deflect during the cutting stroke (from the pressure of the cut), it
will dip into the work surface and cut deeper; hence on the back stroke
it will naturally clear the surface, providing that the next cut is not
put on until the tool has passed back and is clear of the work.
[Illustration: Fig. 1501.]
Referring now to the automatic feed of the sliding table W, in Fig.
1496, the principle of its construction may be explained with reference
to Fig. 1501, which may be taken to represent a class of such feeding
mechanisms. A is a wheel corresponding to the wheel marked M in Fig.
1496, or, it may be an independent wheel in gear with the feed wheel. On
the same shaft as A is pivoted an arm B having a slot S at one end to
receive a pin to which the feed rod E may connect. F is a disk rotated
from the driving mechanism of the shaping machine, and having a
[T]-shaped slot G G, in which is secured a pin to actuate the rod E. As
F rotates E is vibrated to and fro and the catch C on one stroke falls
into the notches or teeth in A and causes it to partly rotate, while on
the return stroke of E it lifts over the teeth, leaving A stationary.
The amount of motion of B, and therefore the quantity of the feed, may
be regulated at either end of E; as, for example, the farther the pin
from the centre of G the longer the stroke of E, or the nearer the pin
in S is to the centre of B the longer the stroke, but usually this
provision is made at one end only of E.
To stop the feed motion from actuating, the catch C may be lifted to
stand vertically, as shown in dotted lines in position 2, and to actuate
the feed traverse in an opposite direction, C may be swung over so as to
occupy the position marked 3, and to prevent it moving out of either
position in which it may be set a small spring is usually employed.
Now suppose that the tool-carrying slide A, Fig. 1496, is traversing
forward and the tool will be moving across the work on the cutting
stroke, as denoted by the arrow _k_ in Fig. 1502, the line of tool
motion for that stroke being as denoted by the line _c_ _a_. At _a_ is
the point where the tool will begin its return stroke, and if the work
is moved by the feeding mechanism in the direction of arrow _e_, then
the line of motion during the return stroke will be in the direction of
the dotted line _a_ _b_, and as a result the tool will rub against the
side of the cut.
[Illustration: Fig. 1502.]
It is to obviate the friction this would cause to the tool edge, and the
dulling thereto that would ensue, that the pivot pin L for the apron is
employed as shown in Fig. 1497, this pin permitting the apron to lift
and causing the tool to bear against the cut with only such force as the
weight of the apron and of the tool may cause. Now suppose that in Fig.
1503 we have a piece of work whose edge A A stands parallel to the line
of forward tool motion, there being no feed either to the tool or the
work, and if the tool be set to the corner _f_ its line of motion during
a stroke will be represented by the line _f_ _g_. Suppose that on the
next stroke the feed motion is put into action and that feeding takes
place during the forward stroke, and the amount of the feed per stroke
being the distance from _g_ to _h_, then the dotted line from _f_ to _h_
represents the line of cut. On the return stroke the line of tool motion
will be from _h_ along the dotted line _h_ _k_, and the tool will rest
against the cut as before. Suppose again that the feed is put on during
the return stroke, and that _c_ _c´_ represents the line of tool motion
during a cutting stroke, and the return stroke will then be along the
line from _c´_ to _b_, from _c_ to _b_ representing the amount of feed
per stroke; hence, it is made apparent that the tool will rub against
the cut whether the feed is put on during the cutting or during the
return stroke. Obviously then it would be preferable to feed the work
between the period that occurs after the tool has left the work surface
on the return stroke and before it meets it again on the next cutting
stroke. It is to be observed, however, that by placing the pin actuating
the rod E, Fig. 1501, on the other side of the centre of the slot G in
F, the motion of E will be reversed with relation to the motion J of the
slide; hence, with the work feeding in either direction, the feed may be
made to occur during either the cutting or return stroke at will by
locating the driving pin on the requisite side of the centre of G.
[Illustration: Fig. 1503.]
An arrangement by Professor Sweet, whereby the feed may be actuated
during the cutting or return stroke (as may be determined in designing
the machine), no matter in which direction the work table is being fed,
is shown in Fig. 1504. Here there are two gears A and D, and the pawl or
catch C may be moved on its pivoted end so as to engage either with A or
D to feed in the required direction.
[Illustration: Fig. 1504.]
Suppose the slide to be on its return stroke in the direction of L, and
F be rotated as denoted by the arrow, then the pawl C will be actuating
wheel A as denoted by its arrow, but if C be moved over so as to engage
D as denoted by the dotted outline, then with the slide moving in the
same direction, C will pull D in the direction of arrow K´, and wheel A
will be actuated in the opposite direction, thus reversing the direction
of the feed while still causing it to actuate on the return stroke.
Since the feed wheel A must be in a fixed position with relation to the
work table feed screw, and since the height of this table varies to meet
the work, it is obvious that as the work table is raised the distance
between the centres of A and F in the figure is lessened, or conversely
as that table is lowered the distance between those centres is
increased; hence, where the work table has much capacity of adjustment
for height, means must be provided to adjust the length of rod E to suit
the conditions. This may be accomplished by so arranging the
construction that the rod may pass through its connection with wheel F,
in the figure, or to pass through its connection with B.
Fig. 1505 represents a shaper that may be driven either by hand or by
belt power. The cone pulley shaft has a pinion that drives the
gear-wheel shown, and at the other end of this gear-wheel shaft is a
slotted crank carrying a pin that drives a connecting rod that actuates
the sliding bar, or ram, as it is sometimes termed. The fly-wheel also
affords ready means of moving the ram to any required position when
setting the tool or the work.
Fig. 1506 represents a shaping machine by the Hewes and Phillips Iron
Works, of Newark, N.J. The slide or ram is operated by the Whitworth
quick return motion, whose construction will be shown hereafter. The
vice sets upon a knee or angle plate fitting to vertical slideways on
the cross slide, and may be raised or lowered thereon to suit the height
of the work by means of the crank handle shown in front. The vice may be
removed and replaced by the supplemental table shown at the foot of the
machine. Both the vice and the supplemental table are capable of being
swivelled when in position on the machine. The machine is provided with
a device for planing circular work, such as sectors, cranks, &c., the
cone mandrel shown at the foot of the machine bolting up in place of the
angle plate.
[Illustration: Fig. 1505.]
[Illustration: Fig. 1506.]
HOLDING WORK IN THE SHAPER OR PLANER VICE.--The simplest method of
holding work in a shaper is by means of a shaper vice, which may be
employed to hold almost any shape of work whose size is within the
capacity of the chuck. Before describing, however, the various forms of
shaper vices, it may be well to discuss points to be considered in its
use.
The bottom surface _a_ _a_, Fig. 1507, of a planer vice is parallel with
the surfaces _d_, _d´_ and as surface _a_ is secured to the upper face
of the slider table shown in figure, and this face is parallel to the
line of motion of the slide A, and also parallel with the cross slide in
that figure, it follows that the face _d_ is also parallel both with the
line of motion of slide A and with the surface of the slider table.
Parallel work to be held in the vice may therefore be set down upon the
surface _d_ (between the jaws), which surface will then form a guide to
set the work by. The work-gripping surfaces _b_ and _e_, Fig. 1507, of
the jaws are at a right angle to surface _a_, and therefore also to _d_,
therefore the upper surface of work that beds fair upon _d_, or beds
fair against _b_, will be held parallel to the line of motion X of the
tool and the line Z of the feed traverse. Similarly the upper surfaces
A, B of the gripping jaws are parallel to _a_ _a_, hence they may be
used to set the work true with the line of feed traverse. The sliding
jaw, however, must be a sufficiently easy fit to the slideways that
guide it to enable it to be moved by the screw that operates it, and as
a result it has a tendency to lift upon its guideways so that its face
_e_ will not stand parallel to _b_ or at a right angle to _d_. In Fig.
1508, for example, is a side view of a vice holding a piece of work W,
the face _f_ of the work being at an angle. As a consequence there is a
tendency to lift in the direction of C. If the jaw does lift or spring
in this direction it will move the work, so that instead of its lower
face bedding down upon face _d_, Fig. 1507, it will lie in the direction
of H, Fig. 1508, while its face parallel to _f_, instead of bedding fair
against the face of jaw J, will lie as denoted by the line _g_, and as a
result the work will not be held fair with either of those faces and the
value of faces _b_, _d_ and _e_ in Fig. 1507 is impaired.
This lifting of the movable or sliding jaw is prevented in some forms of
chuck, to be hereafter described, by bolts passing through which hold it
down, but the tendency is nevertheless present, and it is necessary to
recognise it in treating of chucking or holding work in such vices.
[Illustration: Fig. 1507.]
[Illustration: Fig. 1508.]
The work gripping face _b_, Fig. 1507, of the fixed jaw, however, is not
subject to spring, hence it and the surface _d_ are those by which the
work may be set. The work, however, is held by the force of the screw
operating the sliding jaw, hence the strain is in the direction of the
arrow P in Fig. 1508, which forces it against the face of the fixed jaw.
All the pressure that can be exerted to hold work down upon the surface
_d_, Fig. 1507, is that due to the weight of the work added to whatever
effort in that direction there may be induced by driving the work down
by blows upon surface _d_ after the jaws are tightened upon the work.
This, however, is not to be relied upon whenever there is any tendency
for the work not to bed down fair. It follows, then, that surface _b_ of
the work-gripping jaw is that to be most depended upon in setting the
work, and that the surface that is to act as a guide at each chucking
should be placed against this surface unless there are other
considerations that require to be taken into account.
[Illustration: Fig. 1509.]
For example, suppose we have a thin piece of work, as in Fig. 1509, and
the amount of surface bearing against the fixed jaw is so small in
comparison to its width between the jaws that _e_ would form no
practical guide in setting the work. If then the edges of such a piece
of work were shaped first the face or faces may or may not be made at a
right angle to them, or _square_ as it is termed. But if the faces were
shaped first, then when the work was held by them to have the edges
shaped there would be so broad an area of work surface bedding against
the jaw surface, that the edges would naturally be shaped square with
the faces.
In cases, therefore, where the area of bedding surface of the work
against the faces of the jaws is too small to form an accurate guide and
the work is not thick enough to rest upon the surface _d_, Fig. 1507, it
is set true to that surface by a parallel piece.
If the work is wide or long enough to require it, two parallel pieces
must be used, both being of the same thickness, so that they will keep
the work true with the surface _d_.
[Illustration: Fig. 1510.]
Pieces such as P, Fig. 1510, are also used to set work not requiring to
be parallel. Thus in figure are a number of keys placed side by side and
set to have their edges shaped, and piece P is inserted not only to lift
the narrow ends of the keys up, but also to maintain their lower edges
fair one with the other, and thus insure that the keys shall all be made
of equal width.
They are also serviceable to interpose between the work and the vice
jaws when the work has a projection that would receive damage from the
jaw pressure.
[Illustration: Fig. 1511.]
Thus in Fig. 1511 the work W has such a projection and a parallel piece
P is inserted to take the jaw pressure. By placing the broadest work
surface _g_ against the fixed jaw the work will be held true whether the
movable jaw springs or not, because there will be surface _g_ and
surface H guiding it.
[Illustration: Fig. 1512.]
But if the work were reversed, as in Fig. 1512, with the broadest
surface against K, then if K sprung in the direction of C, the work
would not be shaped true.
[Illustration: Fig. 1513.]
When the work is very narrow, however, the use of a parallel piece to
regulate its height is dispensed with, and the top surface B of the jaw,
in Fig. 1513, is used to set the work by. A line is marked on the work
surface to set it by and a surface gauge is set upon the face B, its
needle point being set to the line in a manner similar to that already
explained with reference to chucking work in the lathe.
All work should be so set that the tool will traverse across the longest
length of the work, as denoted by the tool in Fig. 1502, and the arrow
marking its direction of traverse.
The general principles governing the use of the shaper vice having been
explained, we may now select some examples in its use.
Fig. 1514 represents a simple rectangular piece, and in order to have
the tool marks run lengthwise of each surface (which is, as already
stated the most expeditious) they must be in the direction of the
respective arrows. In a piece of such relative proportions there would
be little choice as to the order in which the surfaces should be shaped,
but whatever surface be operated on first, that at a right angle to it
should be shaped second; thus, if _a_ be first, either _b_ or _d_ should
be second, for the following reasons.
[Illustration: Fig. 1514.]
All the surfaces have sufficient area to enable them to serve as guides
in setting the work, hence the object is to utilize them as much as
possible for that purpose. Now, suppose that surface _a_ has been trued
first, and if _c_ be the next one, then the bedding of surface _a_ upon
the vice surface or the parallel pieces must be depended upon to set _a_
true while truing _c_. Now the surfaces _b_ and _d_ may both, or at
least one of them, may be untrue enough to cause the work to tilt or
cant over, so that _a_ will not bed fair, and _c_ will then not be made
parallel to _a_. It will be preferable then to shape _a_ first and at
the second chucking to set _a_ against the stationary jaw of the vice,
so that it may be held true.
[Illustration: Fig. 1515.]
The sliding jaw will in this case be against face _c_, and if that face
is out of true enough to cant the work so that _a_ will not bed fair,
then a narrow parallel piece may be inserted between the sliding jaw and
the work, which will cause _a_ to bed fair. The third face should be
face _c_, in which case face _a_ will rest on one surface and face _b_
will be against the fixed jaw, and there will be two surfaces to guide
the work true while _c_ is being trued. In this case also, however, it
is better to use a parallel piece P, Fig. 1515, between the work and the
sliding jaw, so as to insure that the work shall bed fair against the
fixed jaw; and if necessary to bring up the top surface above the jaws,
a second parallel piece P´ should be used.
[Illustration: Fig. 1516.]
Suppose now that we have a connecting rod key to shape, and it is to be
considered whether the faces or the edges shall be shaped first. Now if
the side faces are out of parallel it will take more filing to correct
them than it will to correct the same degree of error in the edges;
hence it is obviously desirable to proceed with a view to make all
surfaces true, but more especially the side faces. As the set of the key
while shaping these faces is most influenced by the manner in which the
fixed jaw surface meets the work, and as an edge will be the surface to
meet the fixed jaw faces when the side faces are shaped, it will be best
to dress one edge first, setting the key or keys, as the case may be, as
was shown in Fig. 1510, so as to cut them with the tool operating
lengthways of the key; one edge being finished, then one face of each
key must be shaped, the key being set for this purpose with the surfaced
edge against the fixed jaw. As the width of the key is taper, either a
chuck with a taper attachment that will permit the sliding jaw to
conform itself to the taper of the key must be used (vices having this
construction being specially made for taper work as will be shown
hereafter), or else the key must be held as in Fig. 1516, in which K
represents the key with its trued edge against the fixed jaw, at P is a
piece put in to compensate for the taper of the key, and to cause the
other edge to bed firmly and fairly against the fixed jaw.
The first side face being trued, it should be placed against the fixed
jaw while the other edge is shaped. For the remaining side face we shall
then be able to set the key with a trued edge against the fixed jaw, and
a true face resting upon a parallel piece, while the other edge will be
true for the piece P, Fig. 1516, to press against, and all the elements
will be in favor of setting the key so that the sides will be parallel
one to the other, and the edges square with the faces.
In putting in the piece P, Fig. 1516, the key should be gripped so
lightly that it will about bear its own weight; piece P may then be
pushed firmly in with the fingers, and the vice tightened up.
[Illustration: Fig. 1517.]
If there are two keys the edges and one face may be trued up as just
described, and both keys K, Fig. 1517, chucked at once by inverting
their tapers as shown in figure. But in this case unless the edges are
quite true they may cause the keys not to bed fair on the underneath
face, and the faces therefore to be out of parallel on either or both of
the keys. If there are a number of keys to be cut to the same thickness
it may be done as follows:--
[Illustration: Fig. 1518.]
Plane or shape first one edge of all the keys; then plane up one face,
chucking them with one planed edge against each vice jaw, and put little
blocks (A, B, C, D, Fig. 1518) between the rough edges; then turn them
over, chuck them the same way and plane the other face, resting them on
parallel pieces; then plane the other edges last.
In place of the small blocks A, B, C, D, a strip of lead, pasteboard, or
wood, or for very thin work a piece of lead wire, may be used.
[Illustration: Fig. 1519.]
[Illustration: Fig. 1520.]
Cylindrical work may be held in a vice chuck, providing that the top of
the vice jaws is equal in height to the centre of the work, as in Fig.
1519, a parallel piece being used to set the work true. When, however,
the work is to be shaped at one end only, it is preferable to hold it as
in Fig. 1520, letting its end project out from the side of the chuck. In
some vices the jaws are wider than the body of the chuck, so that
cylindrical work may be held vertical, as in Fig. 1521, when the end is
to be operated upon.
Fig. 1522 represents a simple form of shaper or planer chuck, such
chucks being used upon small planing machines as well as upon shaping
machines.
[Illustration: Fig. 1521.]
[Illustration: Fig. 1522.]
The base A is bolted to the work table, and is in one piece with the
fixed jaw B. The movable jaw C is set up to meet the work by hand, and
being free to move upon A may be used for either taper or parallel work.
To fasten C upon the work, three screws threaded through F abut against
the end of C; F being secured to the upper surface of A by a key or
slip, which fits into a groove in F, and projects down into such of the
grooves in the upper surface of A as may best suit the width of work to
be held in the vice; C is held down by the bolts and nuts at G.
The operation of securing work in such a chuck is as follows:--The
screws both at F and at G being loosened, and jaw C moved up to meet the
work and hold it against the fixed jaw B, then nuts G should be set up
lightly so that the sliding jaw will be set up under a slight pressure,
screws F may then be set up and finally nuts G tightened.
[Illustration: Fig. 1523.]
This is necessary for the following reasons:--The work must, in most
cases, project above the level of the jaws so that the tool may travel
clear across it; hence, the strain due to holding the work is above the
level of the three screws, and the tendency, therefore, is to turn the
jaw C upwards, and this tendency the screws G resist. A similar chuck
mounted upon a circular base so that it may be swivelled without moving
the base on the work table is shown in Fig. 1523. The capacity to swivel
the upper part of the chuck without requiring the base of the chuck to
be moved upon the table is a great convenience in many cases.
[Illustration: Fig. 1524.]
Fig. 1524 represents an English chuck in which the fixed jaw is composed
of two parts, A which is solid with the base G, and D which is pivoted
to A at F. The movable jaw also consists of two parts, B which carries
the nut for the screw that operates B, and C which is pivoted to B at E.
The two pivots E, F being above the surface of the gripping jaws C, D,
causes them to force down upon the surface of G as the screw is
tightened, the work, if thin, being rested, as in the case of the chuck
shown in Fig. 1523, upon parallel pieces.
[Illustration: Fig. 1525.]
Fig. 1525 represents a chuck made by W. A. Harris, of Providence. The
jaws in this case carry two pivoted wings A, B, between the ends of
which the work C is held, and the pivots being above the level of the
work the tendency is here again to force the work down into the chuck,
the strain being in the direction denoted by the arrows.
Here the work rests on four pins which are threaded in the collars H, so
that by rotating the pins they will stand at different heights to suit
different thicknesses of work, or they may be set to plane tapers by
adjusting their height to suit the amount of taper required. The spiral
springs simply support the pins, but as the jaws close the pins lower
until the washer nuts H meet the surface of recess I.
[Illustration: Fig. 1526.]
[Illustration: Fig. 1527.]
Figs. 1526 and 1527 represent Thomas's patent vice, which possesses some
excellent conveniences and features.
In Fig. 1526 it is shown without, and in Fig. 1527 with a swivel motion.
The arrangement of the jaws upon the base in Fig. 1526 is similar to
that of the chuck shown in Fig. 1522, but instead of there being a key
to secure the piece F to the base, there is provided on each side of the
base a row of ratchet teeth, and there is within F a circular piece G
(in Fig. 1528) which is serrated to engage the ratchet teeth. This
piece may be lifted clear of the ratchet teeth by means of the pin at H,
and then the piece F may be moved freely by hand backwards or forwards
upon the base and swung at any required angle, as in Fig. 1528, or set
parallel as in Fig. 1527; F becoming locked, so far as its backward
motion is concerned, so soon as H is released and G engages with the
ratchet teeth on the base. But F may be pushed forward toward the fixed
jaw without lifting H, hence the adjustment of the sliding jaw to the
work may be made instantaneously without requiring any moving or setting
of locking keys or other devices.
[Illustration: Fig. 1528.]
It is obvious that it is the capability of G to rotate in their sockets
that enables F to be set at an angle and still have the teeth of G
engage properly with those on the base plate.
[Illustration: Fig. 1529.]
[Illustration: Fig. 1530.]
The mechanism for swivelling the upper part or body upon the base and
for locking it in its adjusted position is shown in Figs. 1529 and 1530.
The body D is provided with an annular ring fitting into the bore of the
base, which is coned at Q. The half-circular disks R fit this cone and
are held to the body of the chuck by four bolts N, which are adjusted to
admit disks R to move without undue friction. K is a key having on it
the nut V, which receives a screw whose squared end is shown at S. By
operating S in one direction key K expands disks R, causing them to
firmly grip the base at the bevel Q, hence the base and the body are
locked together. By operating S to unscrew in the nut V, K is moved in
the opposite direction and R, R release their grip at Q and the body D
may be swung round in any position, carrying with it all the mechanism
except base P.
To enable the body to be readily moved a quarter revolution, or in other
words, moved to a right angle, there is provided a taper pin, the base
having holes so situated that the body will have been moved a quarter
revolution when the pin having been removed from one hole in the base is
seated firmly home in the other.
Referring again to Fig. 1526, there are shown one pair of parallel
pieces marked respectively A, having bevelled edges, and another pair
marked respectively B. Both pairs are provided with a small rib fitting
into a groove in the jaws of the chuck, as shown in the figure.
[Illustration: Fig. 1531.]
These ribs and grooves are so arranged that the upper pair (A, A) may be
used in the place of the lower ones, and the uses of these pieces are as
follows:--
Suppose a very thin piece of work is to be planed, and in order to plane
it parallel, which is ordinarily a difficult matter, it must bed fair
down upon the face of the vice, which it is caused to do when chucked as
in Fig. 1531, in which the work is shown laid flat upon the face of the
vice, and gripped at its edges by the pieces A, A.
[Illustration: Fig. 1532.]
These pieces, it may be noted, do not bed fair against the gripping
faces of the jaws, but are a trifle open at the bottom as at _e_, _e_,
hence when they are pressed against the work they cant over slightly and
press the work down upon the chuck face causing it to bed fair.
Furthermore, the work is supported beneath its whole surface, and has,
therefore, less tendency to spring or bend from the holding pressure;
and as a result of these two elements much thinner work can be planed
true and parallel than is possible when the work is lifted up and
supported upon separate parallel pieces, because in the latter case the
work, being unsupported between the parallel pieces, has more liberty to
bend from the pressure due to the tool cut, as well as from the holding
pressure.
[Illustration: Fig. 1533.]
Fig. 1532 shows the chuck holding a bracket, having a projection or eye.
The work rests on pieces B, B, and is gripped by pieces A, A. It will be
observed that A, A being beveled enables the cut to be carried clear
across the work.
Fig. 1533 represents the chuck in use for holding a piece of shafting S
to cut a keyway or spline in it. In this case a bevelled piece J is
employed, its bevelled face holding the work down upon the chuck face.
[Illustration: Fig. 1534.]
Fig. 1534 represents a chuck termed shaper centres, because the work is
held between centres as in the case of lathe work. The live spindle is
carried in and is capable of motion in a sleeve, the latter having upon
it a worm-wheel, operated by a worm, so that it can be moved through any
given part of a circle, and has index holes upon its face to determine
when the wheel has been moved to the required amount.
For work that is too large to be operated upon in the class of shaping
machine shown in Fig. 1506, and yet can be more conveniently shaped than
planed, a class of machine is employed in which the tool-carrying slide
is fed to the work, which is chucked to a fixed table or to two tables.
[Illustration: Fig. 1535.]
Fig. 1535 represents a machine of this class. The tool-carrying slide A,
in this case, operates in guideways provided in B, the latter being
fitted to a slideway running the full length of the top of the frame M.
The base slider B is fed along the bed by means of a screw operating in
a nut on the under side of B, this screw being operated once during each
stroke of the tool-carrying slide A, by means of a pawl feeding
arrangement at F, which corresponds to the feeding device shown in Fig.
1501.
Two vertical frame pieces D, D are bolted against the front face of the
machine, being adjustable along any part of the bed or frame length,
because their holding bolts have heads capable of being moved (with the
frame pieces D) along the two [T]-shaped grooves shown, their [T]-shape
being visible at the end of the frame or bed. To frames D are bolted the
work-holding tables E, E, the bolts securing them passing into vertical
[T]-grooves in D, so that E may be adjusted at such height upon D as may
be found necessary to bring the work within proper range of the cutting
tool. The work tables E, E are raised or lowered upon D by means of a
vertical screw, which is operated by the handle H, this part of the
mechanism accomplishing the same end as the elevating mechanism shown in
Fig. 1496. The swivel head J is here provided at its top with a segment
of a worm-wheel which may be actuated to swivel that head by the worm G.
The swivel head may thus be operated upon its pivot, causing the tool
point to describe an arc of a circle of which the pivot is the centre.
To steady the swivel head when thus actuated, there is behind the worm
segment a [V]-slide that is an arc, whose centre is also the centre of
the pivot.
The tool-carrying slide A is operated as follows: The driving pulley P
rotates a shaft lying horizontal at the back of the machine. Along this
shaft there is cut a featherway or spline driving a pinion which
operates a link mechanism such as described with reference to Fig. 1550.
The means of adjusting the distance the head of A shall stand out from
B, are similar to that described for Fig. 1496, a bolt passing through
A, and in both cases attaching to a connecting rod or bar.
At K is a cone mandrel such as has been described with reference to
lathe work upon which is chucked a cross-head C. By means of suitable
mechanism, this mandrel is rotated to feed the circular circumference of
the cross-head jaws to the cut, the slider B remaining in a fixed
position upon the bed M.
To support the outer end of the cone mandrel a beam L is bolted to the
two tables E, E. On L is a slideway for the piece P. At S is a lug upon
E through which threads a screw R, which adjusts the height of the piece
P, while Q is a bolt for securing P in its adjusted position. This cone
mandrel and support is merely an attachment to be put on the machine as
occasion may require.
Fig. 1536 represents a shaping machine by the Pratt and Whitney Company.
In this machine a single sliding head is used and the work remains
stationary as in the case of the machine shown in Fig. 1535. The vice is
here mounted on a slide which enables the work to be finely adjusted
beneath the sliding bar independently of that bar, which is provided
with a Whitworth quick-return motion.
As the tool-carrying slide of a shaping machine leaves its guideways
during each stroke, the tool is less rigidly guided as the length of
slide stroke is increased, and on this account its use is limited to
work that does not require a greater tool stroke than about 18 inches,
and in small machines not to exceed 12 inches. The capacity of the
machine, however, is obviously greatest when the length of the work is
parallel to the line of motion of the feed traverse. Work whose
dimension is within the limit of capacity of the shaper can, however, be
more expeditiously shaped than planed because the speed of the cutting
tool can be varied to suit the nature of the work, by reason of the
machine having a cone pulley, whereas in a planing machine the cutting
speed of the tool is the same for all sizes of work, and all kinds of
metal. In shaping machines such as shown in Fig. 1537, or in similar
machines in which the work table is capable of being traversed instead
of the head, the efficiency of the work-holding table and of the
chucking devices may be greatly increased by constructing the table so
that it will swivel, as in Fig. 1538, which may be done by means of the
employment of Thomas's swivelling device in Fig. 1530. By this means the
ends of the work may be operated upon without removing it from the
chuck. Or the work may be shaped taper at one part and parallel at
another without unchucking it.
Fig. 1539 shows a circular table swivelled by the same device, sitting
upon a work table also swivelled.
[Illustration: Fig. 1540.]
Fig. 1540 represents a general view of a shaping machine having the
motion corresponding in effect to a planing machine, the object being to
give a uniform rate of speed to the tool throughout, both on its cutting
and return stroke. The feed always takes place at the end of the return
stroke, so as to preserve the edge of the tool, and the length of the
stroke may be varied, without stopping the machine, by simply adjusting
the tappets or dogs, the range of stroke being variable from 1/4 inch to
20 inches, while the return stroke is 40 per cent. quicker than the
cutting one. There are two different rates of cutting speed, one for
steel and the other for the softer metals.
[Illustration: Fig. 1541.]
The ram or bar is provided with a rack (Z, Fig. 1545) which engages with
a pinion S, Fig. 1541, H being the driving shaft driven by the belt
cones A and B. These two cones are driven by separate belts, but from
the same counter-shaft, one being an open and the other a crossed belt.
The open belt drives either the largest step of pulley B, giving a
cutting speed suitable for steel, or the smaller step, giving a cutting
speed for softer metals, as cast iron, &c. The crossed belt drives, in
either case, the pulley A for the quick-return stroke, and this pulley
revolve upon a sleeve or hub C, which revolves upon the shaft H. The
sleeve or hub C is in one piece with a pulley C, whose diameter is such
as to leave an annular opening between its face and the bore of the
largest step of cone pulley B, and pulley A is fast to the hub or sleeve
C. It will be seen that as the driving belts from the counter-shaft are
one open and one crossed, therefore pulley A runs constantly in one
direction, while pulley B runs constantly in the other, so that the
direction of motion of the driving shaft H depends upon whether it is
locked to pulley A or to pulley B.
[Illustration: Fig. 1542.]
[Illustration: _VOL. I._ =SHAPING MACHINES AND TABLE-SWIVELING DEVICES.=
_PLATE XVI._
Fig. 1536.
Fig. 1537.
Fig. 1538.
Fig. 1539.]
In the annular space left between the face of pulley C and the cone B is
a steel band G, Fig. 1542, forming within a fraction a complete circle,
and lined inside and out with leather, and this band is brought, by
alternately expanding and contracting it, into contact with either the
bore of the largest cone step of B or with the outside face of pulley C.
The ends of this band are pivoted upon two pins F, which are fast in two
arms E and D, in Fig. 1542. Arm E is fastened to the driving shaft H,
and its hub has two roller studs K, Fig. 1541, these being diametrically
opposite on the said hub. The hub of arm D is a working fit upon the
hub of E, and has two slots to admit the above rollers. Hub D is also
provided with two studs and rollers placed midway between the studs K.
These latter rollers project into the spiral slots K´ of the ring in
Fig. 1543, this ring enveloping the hub of D and being enveloped by the
sleeve M, which contains two spiral grooves diametrically opposite, and
lying in an opposite direction to grooves K´, Fig. 1543. Sleeve M is
prevented from revolving by rollers on the studs O, which are screwed
into the bearing bush R, and carry rollers projecting into the slots in
M.
[Illustration: Fig. 1543.]
It is evident that if the ring L, Fig. 1543, is moved endways with M,
then the arms E, D, together with the band G, will be expanded or
contracted according to the direction of motion of the ring, because the
motion of M, by means of its spiral grooves, gives a certain amount of
rotary motion to the ring L, and the spiral grooves in the ring give a
certain amount of rotary motion to the arms D and E, Fig. 1542. When
this rotary motion is in one direction the band is expanded; while when
it is reversed it is contracted, and the direction of motion of shaft H
is reversed.
[Illustration: Fig. 1544.]
[Illustration: Fig. 1545.]
The outer sleeve M carries the rod T, Figs. 1544 and 1545, which is
connected to the lever U, the upper arm of which is operated by the
tappets or dogs X on the ram or sliding bar, and it is obvious that when
U is vibrated sleeve M is operated in a corresponding direction, and the
ring L also is moved endwise in a corresponding direction, actuating the
band as before described, the direction of motion being governed,
therefore, by the direction in which U is moved by the tappets or dogs.
A certain degree of friction is opposed to the motion of lever U in
order to keep it steady, the construction being shown in Fig. 1546,
where it is seen that there is on each side of its nut a leather washer,
giving a certain amount of elasticity to the pressure of the nut holding
it in place on the shaft U.
[Illustration: Fig. 1546.]
The mechanism for actuating the feed at the end of the return stroke
only, is shown in Fig. 1547. The shaft V (which is also seen in a dotted
circle in Fig. 1545) carries a flange _c_, on each side of which is a
leather disk, so that the pressure of the bolts which secure _b_ to the
sleeve _a_ causes _c_ to revolve under friction, unless sleeve _a_,
slotted bar _b_, and flange _c_ all revolve together, or, in other
words, _c_ revolves under friction when it revolves within _a_ _b_.
[Illustration: Fig. 1547.]
[Illustration: Fig. 1548.]
Fig. 1548 is an end view of Fig. 1547.
[Illustration: Fig. 1549.]
Fig. 1549 gives a cross-sectional view of the shaft sleeve, &c. The
sleeve _a_ is provided with two pins _i_, _i_, and a pin _k_ is fast in
the frame of the machine, and it is seen that _a_ and V may revolve
together in either direction until such time as one of the pins _i_
meets the stationary pin _k_, whereupon the further revolving of _a_
will be arrested and V will revolve within _a_, and as flange _c_, Fig.
1547, revolves with V, it will do so under the friction of the leather
washers. The pins _i_ and the pin _k_ are so located that _a_ can have
motion only when the ram or sliding-bar is at the end of the return
stroke, and the feed-rod _f_, being connected to _b_, is therefore
actuated at the same time.
Among the various mechanisms employed to give a quick return to the
tool-carrying slide of shaping machines, those most frequently employed
are a simple crank, a vibrating link, and the Whitworth quick-return
motion, the latter being the most general one.
The principle of action when a vibrating link is employed may be
understood from Fig. 1550, in which P is a pinion driven by the cone
pulley and imparting motion to D. At L is a link pivoted at C. At A is a
link block or die capable of sliding in the slot or opening in the link
and a working fit upon a pin which is fast in the wheel D. As D rotates
the link block slides in the slot and the link is caused to travel as
denoted by the dotted lines. R is a rod connecting the tool-carrying
slide S to the upper end of link L, and therefore causing it to
reciprocate with L. But S being guided by its slide in the guideway
traverses in a straight line.
[Illustration: Fig. 1550.]
Since the rotation of P and D is uniform, the vibrations of the link L
will vary in velocity, because while the link block is working in the
lower half of the link slot it will be nearer to the centre of motion C
of the link, and the upper end of C will move proportionately faster.
The arrangement is such that during this time the tool-carrying slide is
moved on its return stroke, the cutting stroke being made while the link
block is traversing the upper half of the slot, or in other words,
during the period in which the crank pin in A is above the horizontal
centre of wheel D.
Now suppose the arrangement of the parts is such that the front of the
machine or the cutting tool end of the slide is at the end K of S, then
S will be pushed to its cut by the rod R at an angle which will tend to
lift S in the slideways. But suppose the direction of rotation of wheel
D instead of being as denoted by the arrow at D be as denoted by the
arrow at E, then S will be on its back stroke, the front of the machine
being at J. In this case rod R will pull S to the cut, and S will, from
the angularity of R, be pulled down upon the bed of the slideway guiding
it, and will therefore be more rigidly held and less subject to spring,
because the tendency to lift is resisted on one side by the adjustable
gib only, and on the other by the projecting V, whereas the tendency to
be pulled downwards is resisted by the strength of the frame of the
machine.
Furthermore, as the pressure on the cutting tool is below the level of
the tool-carrying slide it tends to force that slide down upon the
slideway, and it will therefore be more rigidly and steadily guided when
the force moving the slide and the tool pressure both act in the same
direction.
To vary the length of stroke of S pin A is so attached to wheel D that
it may be adjusted in its distance from the centre of D.
[Illustration: Fig. 1551.]
The Whitworth quick-return motion is represented in Fig. 1551. At P is
the pinion receiving motion from the cone pulley or driving pulley of
the machine and imparting motion to the gear-wheel G, whose bearing is
denoted by the dotted circle B. Through B passes a shaft C, which is
eccentric to B and carries at its end a piece A in which is a slot to
receive the pin X, which drives rod R whose end Z is attached to the ram
of the machine. At D is a pin fast in gear-wheel G and passing into a
slot in A.
Taking the position the parts occupy in the figures, and it is seen that
the axis of B is the centre of motion of G and is the fulcrum from which
the pin D is driven, the power being delivered at X. The path of motion
of the driving pin D is denoted by the dotted circle H´, and it is
apparent that as it moves from the position shown in the figure it
recedes from the axis of C, and as the motion of G is uniform in
velocity therefore D will move A faster while moving below the line M
than it will while moving above it, thus giving a quick return, because
the cutting stroke of the ram occurs while D is above the line M and the
return stroke occurs while D is below M.
In some constructions the pin X and pin D work in opposite ends of the
piece A, as shown in Fig. 1552. This, however, is an undesirable
construction because the shaft C becomes the fulcrum, and as the power
and resistance are on opposite ends of the lever A, the wheel G is
therefore forced against its bearing, and this induces unnecessary
friction and wear.
We may now consider the tool motion given by other kinds of slide
operating mechanism.
In Fig. 1553 is a diagram of the tool motion given when the slide is
operated by a simple crank C, the thickened line R representing the rod
actuating the slide and line on the line of motion of the cutting tool.
The circle H denotes the path of revolution of the crank pin, and the
black dots 1, 2, 3, 4, &c., equidistant positions of the crank pin.
[Illustration: Fig. 1552.]
Line _m_ represents the path of motion of the cutting tool.
If a pair of compasses be set to the full length of the thick line R,
that is from the centre of the crank pin to end B of line R, and these
compasses be then applied to the centre of crank pin position 1, and to
the line _m_, they will meet _m_ at a point denoted by line _a_, which
will, therefore, represent the position of the tool point when the crank
pin was in position 1. To find how far the tool point is moved while the
crank pin moves from position 1 to position 2, we place the compass
point on the centre of crank pin position 2 and mark line _b_. For crank
position 3 we have by the same process line _c_, and so on, the twelve
lines from _a_ to _l_ representing crank positions from 1 to 12.
Now let it be noted that since the path of the crank pin is a circle,
the tool point will on the backward stroke occupy the same position when
the crank pin is at corresponding positions on the forward and backward
strokes. For example, when the crank pin is in position 7 the tool point
will be at point _g_ on the forward stroke, and when the crank pin is in
position 17 the tool will be at point _g_ on the backward stroke, as
will be found by trial with the compasses; and it follows that the lines
_a_, _b_, _c_, &c., for the forward stroke will also serve for the
backward one, which enables us to keep the engraving clear, by marking
the first seven positions on one side of line _m_, and the remaining
five on the other side of _m_, as has been done in the figure.
[Illustration: Fig. 1553.]
Obviously the distances apart of the lines _a_, _b_, _c_, _d_, &c.,
represent the amount of tool motion during equal periods of time,
because the motion of the crank pin being uniform it will move from
position 1 to position 2 in the same time as it moves from position 2 to
position 3, and it follows that the cutting speed of the tool varies at
every instant in its path across the work, and also that since the crank
pin operates during a full one-half of its revolution to push the tool
forward, and during a full one-half to pull it backward, therefore the
speed of the two strokes are equal.
[Illustration: Fig. 1554.]
We may now plot out the motion of the link quick return that was shown
in Fig. 1550, the dotted circle H´, in Fig. 1554, representing the path
of the pin A, and the arc H representing the line of motion of the upper
end of link L, and lines N, O, its centre line at the extreme ends of
its vibrating motion. In Fig. 1554 the letters of reference refer to the
same parts as those in Fig. 1550. We divide the circle H´ of pin motion
into twenty-four equidistant parts marked by dots, and through these we
draw lines radiating from centre C and cutting arc H, obtaining on the
arc H the various positions for end Z of rod R, these positions being
marked respectively 1, 2, 3, 4, &c., up to 24. With a pair of compasses
set to the length of rod R from 1 on H, as a centre, we mark on the line
of motion of the slide line _a_, which shows where the other end of the
rod R will be (or, in other words, it shows the position of bolt B in
Fig. 1550), when the centre of A, Fig. 1550, is in position 1, Fig.
1554.
From 2 on arc H, we mark with the compasses line _b_ on line M, showing
that while the pin moved from 1 to 2, the rod R would move slide S, Fig.
1550, from _a_ to _b_, in Fig. 1554. From 3 we mark _c_, and so on, all
these marks being above the horizontal line M, representing the line of
motion, and being for the forward stroke. For the backward stroke we
draw the dotted line from position 17 up to arc H, and with the
compasses at 17 mark a line beneath the line M of motion, pursuing the
same course for all the other pin positions, as 18, 19, &c., until the
pin arrives again at position 24, and the link at O, and has made a full
revolution, and we shall have the motion of the forward stroke above and
that of the backward one below the line of motion of the slide.
On comparing this with the crank and with the Whitworth motion hereafter
described, we find that the cutting speed is much more uniform than
either of them, the irregularity of motion occurring mainly at the two
ends of the stroke.
In Fig. 1555 we have the motion of the Whitworth quick return described
in Fig. 1551, H´ representing the path of motion of the driving-pin D
about the centre of B, and H´ the path of motion of X about the centre
C, these two centres corresponding to the centres of B and C
respectively in Fig. 1551. Let the line M correspond to the line of
motion M in Fig. 1551. Now, since pin D, Fig. 1551, drives, and since
its speed of revolution is uniform, we divide its circle of motion H´
into twenty-four equal divisions, and by drawing lines radiating from
centre B, and passing through the lines of division on H´, we get on
circle H twenty-four positions for the pin X in Fig. 1551. Then setting
the compasses to the length of the rod (R, Fig. 1551), we mark from
position 1 on circle H as a centre, line _a_; from position 2 on H we
mark line _b_, and so on for the whole twenty-four positions on circle
H, obtaining from _a_ to _n_ for the forward, and from _n_ to _y_ for
the motion during the backward stroke. Suppose, now, that the mechanism
remaining precisely the same as before, the line M of motion be in a
line with the centres C, B, instead of at a right angle to it, as it is
in Fig. 1551, and the motion under this new condition will be as in Fig.
1556, the process for finding the amount of motion along M from the
motion around H being precisely as before.
[Illustration: Fig. 1555.]
[Illustration: Fig. 1556.]
The iron planing machine, or iron planer as it is termed in the United
States, is employed to plane such surfaces as may be operated upon by
traversing a work table back and forth in a straight line beneath the
cutting tool. It consists essentially of a frame or bed A, Fig. 1557,
provided on its upper surface with guideways, on which a work carrying
table T may be moved by suitable mechanism back and forth in a straight
line.
This frame or bed carries two upright frames or stanchions B, which
support a cross-bar or slide C, to which is fitted a head which carries
the cutting tool.
To enable the setting of the tool at such a height from the table as the
height of the work may require, the cross slide C may be raised higher
upon the uprights B by means of the bevel gears F, G, H, and T, the
latter being on a shaft at the top of the machine, and operating the
former, which are on vertical screws N, which pass down through nuts
that are fast upon the cross slide C.
To secure C at its adjusted height, the uprights are provided with
[T]-shaped slots H H, and bolts pass through C, their heads being in the
[T]-grooves, and their nuts exposed so that a wrench may be applied to
them.
The faces of the cross slide C are parallel one to the other, and stand
at a right angle to the [V]-guideways on which the work table (or platen
as it is sometimes termed) slides; hence the cross slide will, if the
table is planed true or parallel with this cross slide, be parallel with
the table at whatever height above the table it is set, providing that
the elevating screws, when operated, lift each end of C equally.
The construction of the head D corresponds to that of the head shown in
Figs. 1497 and 1498 for a shaper, except that in this case the swivel
head is secured to a saddle that slides along C, being provided with a
nut operated by a feed screw J, which moves D along C.
The mechanism for operating the work table or platen T is as follows:--P
P´ are two loose pulleys and P´´ is a driving pulley fast on the same
shaft. This shaft drives, within the casing at Q, a worm operating a
worm-wheel, which actuates inside the frame A and beneath the work table
a train of gears, the last of which gears with a rack, provided on the
underneath side of the table.
The revolutions of this last wheel obviously cause the work table to
slide back and forth while resting on the [V]-guideways provided on top
of the frame A, the direction of table motion being governed by the
direction in which the wheel revolves.
This direction is periodically reversed as follows:--The pulley P is
driven by a crossed belt, while pulley P´ is driven by an open or
uncrossed one, hence the direction of revolution of the driving pulley
P´´ will be in one direction if the belt is moved from P to P´´, and in
the other if the belt is moved from P´ to P´´. Mechanism is provided
whereby first one and then the other of these belts is moved so as to
pass over upon P´´ and drive it, the construction being as follows:--
To the edge of the work table there is fixed a stop R, which as the
table traverses to the right meets and moves a lever arm S, which
through the medium of a second lever operates the rod X, which operates
a lever _u_, which has a slot through which one of the driving belts
passes. The lever _u_ operates a second lever _w_ on the other side of
the pulleys, and this lever also has a slot through which the other
driving belt passes.
When the stop R moves the lever arm S levers _u_ and _w_ therefore move
their respective belts, one moving from the tight pulley P´´ to a loose
one as P, and the other moving its belt from the loose pulley as P´ to
the tight one P´´, and as the directions of belt motions are opposite
the direction of revolution of P´´ is reversed by the change of belt
operating it. There are two of the stops R, one on each side of the
lever S, hence one of these stops moves the lever S from left to right
and the other from right to left.
Suppose, then, that the table is moving from right to left, which is its
cutting stroke, and the driving belt will be on the pulley P´´ while the
other belt will be on pulley P. Then as the stop R moves S and operates
X the arm _u_ will move its belt from P´´ to P´, and arm _w_ will move
its belt from P to P´´, reversing the direction of motion of P´´, and
therefore causing the table T to move from left to right, which it will
continue to do until the other stop corresponding to R meets S and moves
it from right to left, when the belts will be shifted back again. The
stroke of the table, therefore, is determined by the distance apart of
the stops R, and these may be adjusted as follows:--
They are carried by bolts whose heads fit in a dovetail groove Z
provided along the edge of the table, and by loosening a set screw may
therefore be moved to any required location along the bed.
To give the table a quick return so that less time may be occupied for
the non-cutting stroke, all that is necessary is to make the
countershaft pulley that operates during the back traverse of larger
diameter than that which drives during the cutting traverse of the
table.
In order that one belt may have passed completely off the driving pulley
P´´ before the other moves on it the lever motions of _u_ and _w_ are so
arranged that when the belt is moving from P´´ to P lever _u_ moves in
advance of lever _w_, while when the other belt is being moved from P´´
to P´ lever _w_ moves in advance of lever _u_.
To enable the work table to remain at rest, one driving belt must be
upon P and the other upon P´, which is the case when the lever arm S is
in mid position, and to enable it to be moved to this position it is
provided with a handle K forming part of lever S.
To cause the tool to be fed to its cut before it meets the cut and thus
prevent it from rubbing against the side of the cut, as was described
with reference to Fig. 1503, the feed takes place when the table motion
is reversed from the back or return stroke to the cutting or forward
stroke by the following mechanism:--
[Illustration: Fig. 1557.]
At _a_ is a rack that is operated simultaneously with S and by the same
stop R. This rack operates a pinion _b_, which rotates the slotted piece
_c_, in which is a block that operates the vertical rod _d_, which is
attached to a segmental rack _e_, which in turn operates a pinion which
may be placed either upon the cross-feed screw J, or upon the rod above
it; the latter operates the vertical feed of the tool through mechanism
within the head D and not therefore shown in the engraving. Thus the
self-acting tool feed may take place vertically or across the work table
at will by simply placing the pinion upon the cross-feed screw or upon
the feed rod, as the case may be.
[Illustration: Fig. 1558.]
Fig. 1558 represents a planer by David W. Pond, of Worcester,
Massachusetts, in which the rod _x_ is connected direct from S to a
pivoted piece _y_ in which is a cam-shaped slot through which pass pins
from the belt-moving arms _u_ and W. The shape of the slot in _y_ is
such as to move the belt-moving arms one in advance of the other, as
described with reference to Fig. 1566.
The feed motions are here operated by a disk C, which is actuated
one-half a revolution when the work table is reversed. This disk is
provided on its face with a slide-way in which is a sliding block that
may be moved to or from the centre of C by the screw shown, thus varying
at will the amount of stroke imparted to the rod which moves the rack by
means of which the feed is actuated through the medium of the
gear-wheels at _f_. The handle _g_ is for operating the feed screw when
the self-acting feed is thrown out of operation, which is done by means
of a catch corresponding in its action to the catch shown in Fig. 1501.
S and S´ are in one piece, S´ being to move the two driving belts on to
the loose pulleys so as to stop the work table from traversing.
The size of a planer is designated from the size of work it will plane,
and this is determined by the greatest height the tool can be raised
above the planer table, the width between the stanchions, and the length
of table motion that can be utilized while the tool is cutting; which
length is less than the full length of table stroke, because in the
first place it is undesirable that the rack should pass so far over the
driving wheel or pinion that any of the teeth disengage, and,
furthermore, a certain amount of table motion is necessary to reverse
after the work has passed the tool at the end of each stroke.
Fig. 1559 represents a method employed in some English planing machines
to drive the work table and to give it a quick return motion. In this
design but one belt is used, being shifted from pulley A, which operates
the table for the cutting stroke, to pulley J, which actuates the table
for the return stroke. The middle pulley K is loose upon shaft B, as is
also pulley J, which is in one piece with pinion J´. Motion from A is
conveyed through shaft B and through gear C, D, E to F, and is reduced
by reason of the difference in diameter between D and E and between F
and G. Motion for the quick return passes from J direct to F without
being reduced by gears D, E, hence the difference between the cutting
speed and the speed of the return stroke is proportionate to the
relative diameters or numbers of teeth in D and E, and as E contains 12
and D 20 teeth, it follows that the return is 8/12 quicker than the
cutting stroke.
In this design the belt is for each reversal of table motion moved
across the loose pulley K from one driving pulley to the other, and
therefore across two pulleys instead of across the width of one pulley
only as in American machines.
[Illustration: Fig. 1559.]
[Illustration: Fig. 1560.]
In American practice the rack R, Fig. 1559, is driven by a large gear
instead of by a pinion, so that the strain on the last driving shaft S,
in Fig. 1560, shall be less, and also the wheel less liable to vibration
than a pinion would be, because in the one case, as in Fig. 1559, the
power is transmitted through the shaft, while in the other, as in Fig.
1560, it is transmitted through the wheel from the pinion P to the rack
R.
[Illustration: Fig. 1561.]
Fig. 1561 represents a planer, designed for use in situations where a
solid foundation cannot be obtained, hence the bed is made of unusual
depth to give sufficient strength and make it firm and solid on unstable
foundations, such as the floors in the upper stories of buildings. In
all other respects the machine answers to the general features of
improved planing machines.
[Illustration: Fig. 1562.]
As the sizes of planing machines increase, they are given increased
tool-carrying heads; thus, Fig. 1562 represents a class in which two
sliding heads are used, so that two cutting tools may operate
simultaneously. Each head, however, is capable of independent operation;
hence, one tool may be actuated automatically along the cross slide to
plane the surfaces of the work, while the other may be used to carry a
cut down the sides of the work, or one tool may take the roughing and
the other follow with the finishing cut, thus doubling the capacity of
the machine.
In other large planers the uprights are provided with separate heads as
shown in the planer in Fig. 1563, in which each upright is provided with
a head shown below the cross slide. Either or both these heads may be
employed to operate upon the vertical side faces of work, while the
upper surface of the work is being planed.
The automatic feed motion for these side heads is obtained in the
Sellers machine from a rod actuated from the disk or plate in figure,
this rod passing through the bed and operating each feed by a pawl and
feed wheel, the latter being clearly seen in the figure.
To enable the amount of feed to be varied the feed rod is driven by a
stud capable of adjustment in a slot in the disk.
[Illustration: _VOL. I._ =EXAMPLES OF PLANING MACHINES.= _PLATE XVII._
Fig. 1561.
Fig. 1563.]
Fig. 1563 represents a planing machine designed by Francis Berry & Sons,
of Lowerby Bridge, England. The bed of the machine is, it will be seen,
[L]-shaped, the extension being to provide a slide to carry the
right-hand standard, and permit of its adjustment at distances varying
from the left-hand standard to suit the width of the work. This
obviously increases the capacity of the machine, and is a desirable
feature in the large planers used upon the large parts of marine
engines.
[Illustration: Fig. 1564.]
ROTARY PLANING MACHINE.--Fig. 1564 is a rotary planing machine. The
tools are here carried on a revolving disk or cutter head, whose spindle
bearing is in an upper slide with 2 inches of motion to move the bearing
endways, and thereby adjust the depth of cut by means of a screw. The
carriage on which the spindle bearing is mounted is traversed back and
forth (by a worm and worm-wheel at the back of the machine) along a
horizontal slide, which, having a circular base, may be set either
parallel to the fixed work table or at any required angle thereto.
By traversing the cutter head instead of the work, less floor space is
occupied, because the head requires to travel the length of the work
only, whereas when the work moves to the cut it is all on one side of
the cutter at the beginning of the cut, and all on the other at the end,
hence the amount of floor space required is equal to twice the length of
the work.
The disk or cutter head is in one piece with the spindle, and carries
twenty-four cutters arranged in a circle of 36 inches in diameter. These
cutters are made from the square bar, and each cutting point should have
the same form and position as referred to one face, side, or square of
the bar, so that each cutter may take its proper share of the cutting
duty; and it is obvious that all the cutting edges must project an equal
distance from the face of the disk, in which case smooth work will be
produced with a feed suitable for the whole twenty-four cutters, whereas
if a tool cuts deeper than the others it will leave a groove at each
passage across the work, unless the feed were sufficiently fine for that
one tool, in which case the advantage of the number of tools is lost.
The cutters may be ground while in their places in the head by a
suitable emery-wheel attachment, or if ground separately they must be
very carefully set by a gauge applied to the face of the disk.
CHAPTER XVII.--PLANING MACHINERY.
[Illustration: Fig. 1565.]
Fig. 1565 represents a planer by William Sellers and Co., of
Philadelphia, Pennsylvania. This planer is provided with an automatic
feed to the sliding head, both horizontally and vertically, and with
mechanism which lifts the apron, and therefore the cutting tool, during
the backward stroke of the work table, and thus prevents the abrasion of
the tool edge that occurs when the tool is allowed to drag during the
return stroke. The machine is also provided with a quick return motion,
and in the larger sizes with other conveniences to be described
hereafter.
The platen or table is driven by a worm set at such an angle to the
table rack as to enable the teeth of the rack to stand at a right angle
to the table length, and as a result the line of thrust between the worm
and the rack is parallel to the [V]-guideways, which prevents wear
between the [V]s of the table and of the bed.
The driving pulleys are set at a right angle to the length of the
machine, their planes of revolution being, therefore, parallel to the
plane of revolution of the line or driving shaft overhead, and parallel
with the lathes and other machines driven from the same line of
shafting, thus taking up less floor space, while the passage ways
between the different lines of machines is less obstructed.
By setting the worm driving shaft at an angle the teeth of the worm
rotate in a plane at a right angle to the length of the work-table rack,
and as a result the teeth of the worm have contact across the full width
of the rack teeth instead of in the middle only, as is the case when the
axis of a worm is at a right angle to the axis of the wheel or rack that
it drives.
Furthermore, by inclining the worm shaft at an angle the teeth of the
rack may be straight (and not curved to suit the curvature of the worm
after the manner of worm-wheels), because the contact between the worm
and rack teeth begins at one side of the rack and passes by a rolling
motion to the other, after the manner and possessing the advantages of
Hook's gearing as described in the remarks made with reference to
gear-wheel teeth.
By inclining the worm shaft, however, the side thrust incidental to
Hook's gearing is avoided, the pressure of contact of tooth upon tooth
being in the same direction and in line with the rack motion. As the
contact between the worm teeth and the rack is uniform in amount and is
also continuous, a very smooth and uniform motion is imparted to the
work table, and the vibration usually accompanying the action of
spur-gearing is avoided.
The worm has four separate spirals or teeth, hence the table rack is
moved four teeth at each worm revolution, and a quick belt motion is
obtained by the employment of pulleys of large diameter.
It is desirable that the belt motion of a planing machine be as quick as
the conditions will permit, because the amount of power necessary to
drive the machine can thus be obtained by a narrower belt, it being
obvious that since the driving power of the belt is the product of its
tension and velocity the greater the velocity the less the amount of
tension may be to transmit a given amount of power.
The mechanism for shifting the belt to reverse the direction of table
motion is shown in Fig. 1566 removed from all the other mechanism.
To the bracket or arm B are pivoted the arms or belt guides C and D and
the piece G. In the position occupied by the parts in the figure the
belt for the forward or cutting stroke would be upon the loose pulley
P´, and that for the quick return stroke would be upon the loose pulley
P, hence the machine table would remain at rest. But suppose the rod F
be moved by hand in the direction of arrow _f_, then G would be moved
upon its pivot X, and its lug _h_ would meet the jaw _i_ of C, moving C
in the direction of arrow _a_, and therefore carrying the belt from
loose pulley P´ on to the driving pulley P´´, which would start the
machine work table, causing it to move in the direction of arrow W until
such time as the stop A meets the lug R, operating lever E and moving
rod F in the direction of arrow _d_. This would move G, causing its lug
_h_ to meet the jaw _j_, which would move C from P´´ back to the
position it occupies in the figure, and as the motion of G continued its
shoulder at _g´_ would meet the shoulder or lug T of K (the latter being
connected to D) and move arm D in the direction of _b_, and therefore
carrying the crossed belt upon P, and causing the machine table to run
backward, which it would do at a greater speed than during the cutting
traverse, because of the overhead pulley on the countershaft being of
greater diameter than that for the cutting stroke.
It is obvious that since each belt passes from its loose pulley to the
fast one, the width of the overhead or countershaft pulleys must be
twice as wide as the belt, and also that to reverse the direction of
pulley revolution one driving belt must be crossed; and as on the
countershaft the smallest pulley is that for driving the cutting stroke,
its belt is made the crossed one, so as to cause it to envelop as much
of the pulley circumference as possible, and thereby increase its
driving power. The arrangement of the countershaft pulleys and belts is
shown in Fig. 1567, in which S is the countershaft and N, O the fast and
loose pulleys for the belt from the line shaft pulley; Q´ is the pulley
for operating the table on the cutting stroke (with the crossed belt),
while Q is the pulley for operating the table on its return stroke. The
difference in the speed of the table during the two strokes is obviously
in the same proportions as the diameters of pulleys Q´ and Q.
The feed rod, and feed screw, and rope for lifting the tool on the back
stroke are operated as follows:--
Fig. 1568 is an end view of the mechanism viewed from the front of the
machine, and Fig. 1569 is a side view of the same.
The shaft of the driving pulleys (P P´ and P´´, Fig. 1567) drives a
pinion operating the gear wheel W, upon the face of which is a serrated
internal wheel answering to a ratchet wheel, and with which a pawl
engages each time the direction of pulley revolution (or, which is the
same thing, the direction of motion W) reverses, and causes the pawl and
the shaft, to which the plate P, Fig. 1569, is fast, to make one-half a
revolution, when the pawl disengages and all parts save the wheel W come
to rest.
From this plate P the feed motions are actuated, and the tool is lifted
during the back traverse of the work table by the following mechanisms.
[Illustration: Fig. 1566.]
[Illustration: Fig. 1567.]
[Illustration: Fig. 1568.]
[Illustration: Fig. 1569.]
[Illustration: Fig. 1570.]
Referring to Fig. 1570, upon the plate P is pivoted a lever Q, carrying
a universal joint at Z, and a nut pivoted at V, and it is obvious that
at each half-revolution of P, the rod R is moved vertically. This rod
connects to a universal joint J (shown in Fig. 1571) that is pivoted in
a toothed segment (K, in the same figure) which engages with a pinion on
the feed screw, this pinion being provided with a ratchet and feed pawl
(of the usual construction) for reversing the direction of the feed or
throwing it out of action.
The amount of feed is regulated as follows:--
Referring to Figs. 1569 and 1570, the amount of vertical motion of rod R
is obviously determined by the distance of the universal joint Z from
the centre of the plate P, and this is set by operating the hand wheel
T, which revolves the screw Y in the nut V.
For lifting the tool during the return motion of the work and work
table, there is provided in the plate P, Fig. 1570, a pin which actuates
the rod B, which in turn actuates the grooved segment C.
[Illustration: Fig. 1571.]
From this segment a cord is stretched passing over the grooved pulley D,
Fig. 1571, thence over pulley E, and after taking a turn around the
pulley F, Fig. 1571, it passes to the other end of the cross slide,
where it is secured.
This pulley F is therefore revolved at each motion of the plate P, Figs.
1569 or 1570, or in other words each time the work table reverses its
motion.
In reference to Figs. 1571 and 1572, F, Fig. 1571, is fast upon a pin
_g_, at whose other end is a pinion operating a gear-wheel _h_. Upon the
face of this gear-wheel is secured a steel plate shown at _m_ in Fig.
1572, which is a vertical section of the sliding head. In a cam groove
in _m_, projects a pin that is secured to the sleeve _n_, which envelops
the vertical feed screw O. This sleeve _n_ has frictional contact at _p_
with the bar _q_, whose lower end receives the bell crank _r_, which on
each return stroke is depressed, and thus moves the tool apron _s_, and
with it the tool, which is therefore relieved from contact with the cut
upon the work.
The self-acting vertical feed is actuated as follows:--
Referring to Figs. 1571 and 1572 the gear segment K operates a pinion
upon the squared end of the feed rod L, this pinion L having the usual
pawl and ratchet for reversing the direction of rod revolution.
The splined feed rod L actuates the bevel pinion M, which is in gear
with bevel pinion N, the latter driving pinion P, which is threaded to
receive the vertical feed screw O; hence when P is revolved it moves the
feed screw O endways, and this moves the vertical slide R upon which is
the apron box T and the apron _s_. To prevent the possibility of the
friction of the threads causing the feed screw O to revolve with the
pinion P, the journal _e_ of the feed screw O is made shorter than its
bearing in R, so that the nut _f_ may be used to secure the feed screw O
to the slide R.
PLANER SLIDING HEADS.--In order that the best work may be produced, it
is essential that the sliding head of a planer or planing machine be
constructed as rigid as possible, and it follows that the slides and
slideways should be of that form that will suffer the least from wear,
resist the tool strain as directly as possible, and at the same time
enable the taking up of any wear that may occur from the constant use of
the parts.
Between the tool point that receives the cutting strain and the cross
bar or cross slide that resists it there are the pivoted joint of the
apron, the sliding joint of the vertical feed, and the sliding joint of
the saddle upon the cross slide, and it is difficult to maintain a
sliding fit without some movements or spring to the parts, especially
when, as in the case of a planer head, the pressure on the tool point is
at considerable leverage to the sliding surfaces, thus augmenting the
strain due to the cut.
The wear on the cross slide is greater at and towards the middle than at
the ends, but it is also greater at the end nearest to the operator than
at the other end, because work that is narrower than the width of the
planing machine table is usually chucked on the side nearest to the
operator or near the middle of the table width, because it is easier to
chuck it there and more convenient to set the tool and watch the cut,
for the reason that the means for stopping and starting the machine, and
for pulling the feed motions in and out of operation, are on that side.
The form of cross bar usually employed in the United States is
represented in Fig. 1573, and it is clear that the pressure of the cut
is in the direction of the arrow _c_, and that the fulcrum off which the
strain will act on the cross bar is at its lowest point _d_, tending to
pull the top of the saddle or slider in the direction of arrow _e_,
which is directly resisted by the vertical face of the gib, while the
horizontal face _f_ of the gib directly resists the tendency of the
saddle to fall vertically, and, therefore, the amount of looseness that
may occur by reason of the wear cannot exceed the amount of metal lost
by the wear, which may be taken up as far as possible by means of the
screws _a_ and _b_, which thread through the saddle and abut against the
gib. The gib is adjusted by these screws to fit to the least worn and
therefore, the tightest part of the cross bar slideway, and the saddle
is more loosely held at other parts of the cross bar in proportion as
its slideway is worn.
[Illustration: Fig. 1572.]
In this construction the faces of the saddle are brought to bear over
the whole area of the slideways surface of the cross bar, because the
bevel at _g_ brings the two faces at _m_ into contact, and the set-screw
_b_ brings the faces in together. Instead of the screws _a_ and _b_
having slotted heads for a screw driver, however, it is preferable to
provide square-headed screws, having check nuts, as in Fig. 1574, so
that after the adjustment is made the parts may be firmly locked by the
check nuts, and there will be no danger of the adjustment altering.
The wear between the slider and the raised slideways S is taken up by
gibs and screws corresponding to those at _a_ and _c_ in the Fig. 1575,
and concerning these gibs and screws J. Richards has pointed out that
two methods may be employed in their construction, these two methods
being illustrated in Figs. 1575 and 1576, which are taken from
"Engineering."
In Fig. 1575 the end _s_ of the adjustment screw _a_ is plain, and is
let into the gib _c_ abutting against a flat seat, and as a result while
the screw pressure forces the gib _c_ against the bevelled edge of the
slideway it does not act to draw the surfaces together at _m_ _m_ as it
should do. This may be remedied by making the point of the screw of such
a cone that it will bed fair against gib _c_, without passing into a
recess, the construction being as in Fig. 1576, in which case the screw
point forces the gib flat against the bevelled face and there is no
tendency for the gib to pass down into the corner _e_, Fig. 1575, while
the pressure on the screw point acts to force the slide _a_ down upon
the slideway, thus giving contact at _m_ _m_.
The bearing area of such screw points is, however, so small that the
pressure due to the tool cut is liable to cause the screw to indent the
gib and thus destroy the adjustment, and on this account a wedge such as
shown in Fig. 1577 is preferable, being operated endwise to take up the
wear by means of a screw passing through a lug at the outer or exposed
end of the wedge.
The corners at _i_, Figs. 1575 and 1576, are sometimes planed out to the
dotted lines, but this does not increase the bearing area between the
gib _c_ and the slide, while it obviously weakens the slider and renders
it more liable to spring under heavy tool cuts.
Fig. 1578 represents a form of cross bar and gib found in many English
and in some American planing machines. In this case the strain due to
the cut is resisted directly by the vertical face of the top slide of
the cross bar, the gib being a triangular piece set up by the screws at
_a_, and the wear is diminished because of the increased wearing
surface of the gib due to its lower face being diagonal.
[Illustration: Fig. 1573.]
[Illustration: Fig. 1574.]
[Illustration: Fig. 1575.]
[Illustration: Fig. 1576.]
On the other hand, however, this diagonal surface does not directly
resist the falling of the saddle from wear, and furthermore in taking up
the wear the vertical face of the saddle is relieved from contact with
the vertical face of the cross bar, because the screws _a_ when set up
move the top of the saddle away from the cross bar, whereas in Fig.
1573, setting up screw _b_ brings the saddle back upon the vertical face
of the cross bar slideway.
[Illustration: Fig. 1577.]
[Illustration: Fig. 1578.]
[Illustration: Fig. 1579.]
Fig. 1579 is a front view, and Fig. 1580 a sectional top view, of a sunk
vertical slide, corresponding to that shown in Figs. 1573 and 1578, but
in this case the gib has a tongue _t_, closely fitted into a recess or
channel in the vertical slider S, and to allow room for adjustment, the
channel is made somewhat deeper than the tongue requires when newly
fitted. The adjustment is effected by means of two sets of screws, _a_
and _b_, of which the former, being tapped into the gib, serve to
tighten, and the latter, being tapped into the slide, serve to loosen
the gib. By thus acting in opposite directions the screws serve to check
each other, holding the gib rigidly in place. To insure a close contact
of the gib against the vertical surface of the slide, the screws _b_ are
placed in a line slightly outside of the line of the screws _a_.
Fig. 1581 represents a similar construction when the slideways on the
swing frame project outwards, instead of being sunk within that frame.
Fig. 1582 represents the construction of the Pratt & Whitney Company's
planer head, in which the swivel head instead of pivoting upon a central
pin and being locked in position by bolts, whose nuts project outside
and on the front face of the swing frame, is constructed as follows:--
A circular dovetail recess in the saddle receives a corresponding
dovetail projection on the swivel head or swing frame, and the two are
secured together at that point by a set-screw A. In addition to this the
upper edge B of the saddle is an arc of a circle of which the centre is
the centre of the dovetail groove, and a clamp is employed to fasten the
swivel head to the saddle, being held to that head by a bolt, and
therefore swinging with it. Thus the swivel head is secured to its
saddle at its upper edge, as well as at its centre, which affords a
better support.
The tool box is pivoted upon the vertical slider, and is secured in its
adjusted position by the bolts _n_ in Fig. 1573, the object of swinging
it being to enable the tool to be lifted on the back stroke and clear
the cut, when cutting vertical faces, as was explained with reference to
shaping machines.
The tool apron is in American practice pivoted between two jaws, which
prevent its motion sideways, and to prevent any play or lost motion
that might arise from the wear of the taper pivoting pin _b_, in Fig.
1583, the apron beds upon a bevel as at _a_, so that in falling to its
seat it will be pulled down, taking up any lost motion upon _b_.
[Illustration: Fig. 1580.]
[Illustration: Fig. 1581.]
[Illustration: Fig. 1582.]
[Illustration: Fig. 1583.]
[Illustration: Fig. 1584.]
[Illustration: Fig. 1585.]
The bevel at _a_ would also prevent any side motion to the apron should
wear occur between it and the jaws. In addition to this bevel, however,
there may be employed two vertical bevels _c_ in the top view in Fig.
1584. In English practice, and especially upon large planing machines,
the apron is sometimes made to embrace or fit the outsides of the tool
box, as in Fig. 1585, the object being to spread the bearings as wide
apart as possible, and thus diminish the effect of any lost motion or
wear of the pivoting pin, and to enable the tool post or holder to be
set to the extreme edge of the tool box as shown in the figure.
It is desirable that the tool apron bed as firmly as possible back
against its seat in the tool box, and this end is much more effectively
secured when it is pivoted as far back as possible, as in Fig. 1585,
because in that case nearly all the weight of the apron, as well as that
of the tool and its clamp, acts to seat the apron, whereas when the
pivot is more in front, as _m_, in Fig. 1573, it is the weight of the
tool post and tool only that acts to keep the apron seated.
In small planing machines it is a great advantage to provide an extra
apron carrying two tool posts, as in Fig. 1586, so that in planing a
number of pieces, that are to be of the same dimension, one tool may be
used for roughing and one for finishing the work. The tools should be
wider apart than the width of the work, so that the finishing tool will
not come into operation until after the roughing tool has carried its
cut across.
When the roughing tool has become dulled it should, after being ground
up, be set to the last roughing cut taken, so that it will leave the
same amount of finishing cut as before.
The advantage of this system is that the finishing tool will last to
finish a great many pieces without being disturbed, and as a result the
trouble of setting its cut for each piece is avoided; on which account
all the pieces are sure to be cut to the same dimension without any
further measuring than is necessary for the first piece, whereas if one
tool only is used it rapidly dulls from the roughing cut, and will not
cut sufficiently smooth for the finishing one, and must therefore be
more frequently ground up to resharpen it, while it must be accurately
set for each finishing cut. A double tool apron of this kind is
especially serviceable upon such work as planing large nuts, for it will
save half the time and give more accurate work.
In some planing machines, and notably those made by Sir Joseph
Whitworth, a swiveling tool holder is made so that at each end of the
stroke the cutting tool makes half a revolution, and may therefore be
used to cut during both strokes of the planer table. A device answering
this purpose is shown in Fig. 1587. The tool-holding box is pivoted upon
a pin A, and has attached to it a segment of a circular rack or
worm-wheel, operated by a worm upon a shaft having at its upper end the
pulley shown, so that by operating this pulley, part of a revolution at
the end of each work-table stroke, one or the other of the two tools
shown in the tool box, is brought into position to carry the cut along.
Thus two tools are placed back to back, and it is obvious that when the
tool box is moved to the right, the front tool is brought into position,
while when it is moved to the left, the back or right-hand tool is
brought into position to cut, the other tool being raised clear of the
work.
[Illustration: Fig. 1586.]
[Illustration: Fig. 1587.]
The objections to either revolving one tool or using two tools so as to
cut on both strokes are twofold: first, the tools are difficult to set
correctly; and, secondly, the device cannot be used upon vertical faces
or those at an angle, or in other words, can only be used upon surfaces
that are nearly parallel to the surface of the work table.
[Illustration: Fig. 1588.]
[Illustration: Fig. 1589.]
Figs. 1588 and 1589 represent the sliding head of the large planer at
the Washington Navy Yard, the sectional view, Fig. 1589, being taken on
the line X X in Fig. 1588. C is the cross bar and S the saddle, F being
the swing frame or fiddle, as some term it, and S´ the vertical slider;
B is the tool box, and A the apron.
The wear of the cross slider is taken up by the set screws _a_, and that
of the vertical slide by the screws _b_.
The graduations of the degrees of a circle for setting over the swing
frame F, as is necessary when planing surfaces that are at an angle to
the bed and to the cross slide, are marked on the face of the saddle,
and the pointer (_f_, Fig. 1578) is fastened to the edge of the swing
frame. When the swing frame is vertical the pointer is at 90° on the
graduated arc, which accords with English practice generally. In
American practice, however, it is customary to mark the graduations on
the edge of the swing frame as in Fig. 1590, so that the pointer stands
at the zero point _o_ when the swing frame is vertical, and the
graduations are marked on the edge of the swing frame as shown, the zero
line _o_ being marked on the edge of the saddle.
In the English practice the swing frame is supposed to stand in its
neutral or zero position when it is vertical, and all angles are assumed
to be measured from this vertical zero line, so that if the index point
be set to such figure upon the graduated arc as the angle of the work is
to be to a vertical line, correct results will be obtained.
Thus in Fig. 1591 (which is from _The American Machinist_) the pointer
is set to 40° and the bevelled face is cut to an angle of 40° with the
vertical face as marked. But if the head be graduated as in Fig. 1592,
the face of the planer table being taken as the zero line _o_, then the
swing frame would require to be set over to 30° out of its normal or
neutral vertical position as is shown in figure, the bevelled face being
at an angle of 50° from a vertical, and 40° from a horizontal line,
hence the operator requires to consider whether the number of degrees of
angle are marked on the drawing from a zero line that is vertical on one
that is horizontal.
[Illustration: Fig. 1590.]
[Illustration: Fig. 1591.]
[Illustration: Fig. 1592.]
[Illustration: Fig. 1593.]
[Illustration: Fig. 1594.]
Referring again to Fig. 1588 the slots for the tool post extend fully
across the apron, so that the tool posts may be set at any required
point in the tool-box width, and the tool or tool holder may be set
nearer to the edge of the tool box than is the case when fixed bolts, as
in Fig. 1590, are used, because these bolts come in the way.
This is mainly important when the tool is required to carry a deep
vertical cut, in which case it is important to keep the tool point as
close in to the holder as possible so that it may not bend and spring
from the pressure of the cut.
The tool or holder may be held still closer to the edge of the head, and
therefore brought still closer to the work, when the apron embraces the
outside of the tool box, as was shown in Fig. 1585, and referred to in
connection therewith.
[Illustration: Fig. 1595.]
[Illustration: Fig. 1596.]
A sectional side view and a top view of Fig. 1588 through the centre of
the head is given in Figs. 1595 and 1596, exposing the mechanism for the
self-acting feed traverse, and for the vertical feed. For the feed
traverse the feed screw (_m_, Fig. 1588) passes through the feed nut N.
For the vertical feed the feed rod (_n_, Fig. 1588) drives a pair of
bevel-gears at P, which drives a second pair at Q, one of which is fast
on a spindle which passes through the vertical feed screw, and is
secured thereto by the set screw _e_. The object of this arrangement is
that if the self-acting vertical feed should be in action and the tool
or swing frame S´ should meet any undue obstruction, the set screw _e_
will slip and the feed would stop, thus preventing any breakage to the
gears at P or Q. The feed screw is threaded into the top of S´. At E is
the pin on which the tool box pivots to swing it at an angle.
The mechanism for actuating the cross-feed screw and the feed rod is
shown in the top view, Fig. 1597, and the side view, Fig. 1598, in which
A is a rod operated vertically and actuated from the stop (corresponding
to stop R in Fig. 1558) that actuates the belt shifting gear. Upon A is
the sleeve B, which actuates rod C, which operates the frame D. This
frame is pivoted upon a stud which is secured to the cross bar C, and is
secured by the nut at E. Frame D carries pawls F and G, the former of
which engages gear-wheel H, which drives the pinion _n_, Fig. 1598, that
is fast on the feed rod, while the latter drives the gear K, which in
turn drives pinion P, which is fast upon the feed screw in Fig. 1588.
The feeds are put into or thrown out of action as follows:--On the same
shaft or pin as the pawls G and F, is secured a tongue T, Fig. 1599,
whose end is wedge shaped and has a correspondingly shaped seat in a
plate V, whose cylindrical stem passes into a recess provided in D, and
is surrounded by a spiral spring which acts to force V outwards from the
recess.
[Illustration: Fig. 1597.]
[Illustration: Fig. 1598.]
[Illustration: Fig. 1599.]
In the position shown in the figure the end of T is seated in the groove
in V, and the pressure of the spring acts to hold T still and keep the
pawl G from engaging with the teeth of gear-wheel H. But suppose the
handle W (which is fast on the pawl G) is pulled upwards, and T will
move downwards, disengaging from the groove in V, and the upper end of
pawl G will engage with the teeth of H, actuating in the direction of
the arrow during the upward motion of rod A, and thus actuating pinion
_n_ and putting the vertical feed in motion in one direction. When the
rod A makes its downward stroke the pawl G will slip over the teeth of
H, because there is nothing but the spiral spring to prevent the end of
the pawl from slipping over these teeth. To place the vertical feed in
action in the other direction, handle W is pressed downwards, causing
the bottom end X of the pawl to engage with the teeth of H.
PLANER BEDS AND TABLES.--The general forms of the beds of small planers
are such as in Figs. 1557 and 1558, and those of the larger sizes such
as shown in Fig. 1563.
It is of the first importance that the [V]-guideways in these beds
should be straight and true, and that the corresponding guides on the
planer table should fit accurately to those in the bed; for which
purpose it is necessary, if the greatest attainable accuracy is to be
had, that the guideways in the bed first be made correct, and those on
the table then fitted, using the bed to test them by.
The angle of these guides and guideways ranges from about 60° in the
smallest sizes to about 110° in the largest sizes of planers. Whatever
the angle may be, however, it is essential that all the angles be
exactly equal, in order that the fit of the table may not be destroyed
by the wear.
In addition to this, however, it is important that each side of the
guides stand at an equal height, or otherwise the table will not fit,
notwithstanding that all the angles may be equal.
[Illustration: Fig. 1600.]
Suppose, for example, that in Fig. 1600 all the sides are at an equal
angle, but that side _e_ was planed down to the dotted line _e_, then
all the weight of the table would fall on side _a_, and, moreover, the
table would be liable to rock in the guideways, for whenever the
combined weight of the table and the pressure of the cut was greatest on
the right-hand of the middle _x_ of the table width and the feed was
carried from right to left, then the table would move over, as shown
exaggerated in Fig. 1601, because the weight would press guide _g_ down
into its guideways, and guide _h_ would then rise up slightly and not
fit on one side at all, while on the other side it would bear heaviest
at point _p_. Great care is therefore necessary in planing and fitting
these guides and ways, the processes for which are explained under the
respective headings of "Examples in Planer Work," and "Erecting
Planers."
In some designs the bed and table are provided with but one
[V]-guideway, the other side of the table being supported on a flat
side, and in yet another form the table is supported on two flat
guideways.
Referring to the former the bearing surface of the [V] and of the flat
guide must be so proportioned to that of the [V] that the wear will let
the table down equally, or otherwise it would become out of parallel
with the cross slide, and would plane the work of unequal thickness
across its width.
[Illustration: Fig. 1601.]
[Illustration: Fig. 1602.]
Referring to the second, which is illustrated in Fig. 1602, it possesses
several disadvantages.
[Illustration: Fig. 1603.]
Thus, if there be four gibs as at A, B, and E, F, set up by their
respective set-screws, the very means provided to take up the wear
affords a means of setting the bed out of line, so that the slots in the
table (and, therefore, the chucks fitting to these slots) will not be in
the line of motion of the table, and the work depending upon these
chucks will not be true. This may be avoided by taking up the wear on
two edges only, as in Fig. 1603 at A, B, but in this case the bearing at
E and F would eventually cease by reason of the wear.
Suppose, for example, that the pressure of the tool cut tends to throw
the table in the direction of arrow J, and the surfaces at A and F
resist the thrust and both will wear. But when the strain on the table
is in the direction of arrow K, the surfaces B, E, will both wear; hence
while the width apart of the table slides becomes greater, the width
apart of the bed slideways wears less, and the fit cannot be maintained
on the inner edges of the guideways. It is furthermore to be noted that
with flat guideways the table will move sideways very easily, since
there is nothing but the friction of the slides to prevent it, but in
the case of [V]-guides the table must lift before it can move sideways;
hence, it lies very firmly in its seat, its weight resisting any side
motion.
[Illustration: Fig. 1604.]
It is found in practice that the wear of the guides and guideways in
planer tables and beds is greatest at the ends, and the reason of this
is as follows:--
In Fig. 1604 is a top view of a planer table, the cutting tool being
assumed to be at T, and as the driving gear is at G forcing the table in
the direction of the arrow A, and the resistance is at T, the tendency
is to throw the table around in the direction of arrows B and C. When
the tool is on the other side of the middle of the table width as at F,
the tendency is to throw the table in the opposite direction as denoted
by the arrows D and E, which obviously causes the most wear to be at the
ends of the slides.
As the feed motions are placed on the right-hand side of the machines
the operator stands on that side of the machine at X, and starts the cut
from that side of the table; hence unless the work is placed in the
middle of the table width, the wear will be most in the direction of
arrows B and C.
The methods of fitting the guideways and guides of planer beds and
tables is given in the examples of erecting.
[Illustration: Fig. 1605.]
A very good method of testing them, however, is as follows:--Suppose
that we have in Fig. 1605 a plate that has been planed on both edges G,
H, and that in consequence of a want of truth in the planer guideways
edge G is rounding and edge H hollow, the plate being supposed to lie
upon the planer table in the position in which it was planed.
[Illustration: Fig. 1606.]
Now, suppose that it be turned over on the planer, as in Fig. 1606, the
rounding edge, instead of standing on the right-hand side of the planer
table, will stand on the left-hand side, so that if that edge were
planed again in its new position it would be made hollow instead of
rounding in its length. It is obvious, therefore, that if a planed edge
shows true when turned over on the planer table, the [V]s of the planer
are true, inasmuch as the table moves in a straight line in one
direction, which is that affecting the truth of all surfaces of the work
that are not parallel to the cross feed of the tool, or, what is the
same thing, parallel to the surface of the planer table.
PLANING MACHINE TABLES.--In order that the guides on the table of a
planer may not unduly wear, it is essential that they be kept well
lubricated, which is a difficult matter when the table takes short
strokes and has work upon it that takes a long time to perform, in which
case it is necessary to stop the planing operations and run the work
back so as to expose the guideways in the bed, so that they may be
cleaned and oiled.
[Illustration: Fig. 1607.]
It will often occur that the work will not pass beneath the cross slide,
and in that case it should be raised out of the ways to enable proper
oiling, because insufficient lubrication frequently causes the guides
and guideways to tear one another, or cut as it is commonly termed.
[Illustration: Fig. 1608.]
The means commonly employed for oiling planer [V]s or guideways are as
follows:--At the top of the guideways small grooves, _g_ _g_, Fig. 1609,
are provided, and at the bottom a groove _x_. In the guides on the table
there are provided pockets or slots in which are pivoted pendulums of
the form shown in Fig. 1607 at A. Each pendulum passes down to the
bottom of groove _x_ in which the oil lies, and is provided on each side
with recesses _e_, which are also seen in the edge view on the right of
the figure.
The pendulums are provided with a long slot to enable them when the
table motion reverses to swing over and drag in the opposite direction
(as shown in Fig. 1607); as they drag on the bottom of groove _x_ of the
bed they lift the oil it contains, which passes up the sides of the
pendulum as denoted by the arrow, and into grooves provided on the
surface of the table guide, as at _h_ in Fig. 1608, in which V´ is the
table guide, V the guideway in the bed, _g_ oil grooves, (see sectional
view, Fig. 1613), _x_ the oil groove at the bottom of the bed V, and _h_
_h_ the oil grooves which receive the oil the pendulum lifts.
The oil grooves _h_ on the table guide run into the grooves _g_ in the
[V]-guideway in the bed, hence grooves _g_ _g_ become filled with oil.
But after the end of the table has passed and left the bed V exposed,
the oil flows out of grooves _g_ down the sides of the guideway, and
constant lubrication is thus afforded at all times when the stroke of
the table is sufficient to enable the pendulums to force the oil
sufficiently far along oil way _h_. When the table reverses the pendulum
will swing over and lift the oil up into grooves or oil ways _h´_.
[Illustration: Fig. 1609.]
[Illustration: Fig. 1610.]
Another and excellent method of oiling, also invented by Mr. Hugh
Thomas, of New York, is shown in Figs. 1609 and 1610, in which P
represents an oiling roll or wheel, [V]-shaped, to correspond to the
shape of the [V]s. This roll is laced with cotton wick or braid, as
shown by the dark zigzag lines, and is carried in a frame _f_, capable
of sliding vertically in a box C, which is set in a pocket in the bed V,
and contains oil. By means of a screw S, the roll P is set to touch the
face of the table [V], and the friction between the roll and the [V], as
the table traverses, rotates the roll, which carries up the oil and
lubricates the table [V] over its whole surface. The dust, &c., that may
get into the oil settles in the bottom of the box C, which can
occasionally be cleaned out. In this case the oil is not only presented
to the oil grooves (_h_, Fig. 1608), but spread out upon the [V]s; but
it is nevertheless advisable to have the grooves _h_ so as to permit of
an accumulation of oil that will aid in the distribution along the [V]s
of the bed.
This method of oiling has been adopted in some large and heavy planers
built by R. Hoe & Co., and has been found to operate admirably, keeping
the guides and guideways clean, bright, and well lubricated.
Mr. Thomas has also patented a system of forced oil circulation for
large planers. In this system a pump P, Fig. 1611, draws the oil from
the cellars C (which are usually provided on the ends of planer beds)
and delivers it through pipes passing up to the sides of the [V]s, thus
affording a constant flow of oil. A reservoir at the foot of the pump
enables the dirt, &c., in the oil to settle before it enters the pump,
which can be operated from any desirable part of the planer mechanism.
The pendulums are also used in connection with the forced circulation.
As the work is fastened to the upper face of a planing machine table
either directly or through the intervention of chucking devices, the
table must be pierced with holes and grooves to receive bolts or other
appliances by means of which the work or chuck, as the case may be, may
be secured.
For receiving the heads of bolts, [T]-shaped grooves running the full
length of the table are provided, and in addition there are sometimes
provided short [T]-grooves, to be shown presently.
For receiving stops and other similar chucking devices, the tables are
provided with either round or square holes.
In Fig. 1612 is shown a section of a table provided with [T]-grooves and
rows of round holes, _a_, _b_, _c_, _d_, _e_, which pass entirely
through the table, and hence must not be placed so that they will let
dirt fall through to the [V]-guides or the rack. Tables with this
arrangement of holes and grooves are usually used upon small planers in
the United States, and sometimes to large ones also.
[Illustration: Fig. 1611.]
[Illustration: Fig. 1612.]
[Illustration: Fig. 1613.]
It is obvious that the dirt, fine cuttings, &c., will pass through the
holes and may find its way to the [V]-guideways. Especially will this be
the case when water is used upon the tool to take smooth cuts upon
wrought iron and steel. To obviate this the construction shown in Fig.
1613 is employed.
Fig. 1613 represents a section of one guideway of a table and bed. On
each side of the table [V] there is cut a groove leaving projecting ribs
_b_, _c_, and whatever water, oil, or dirt may pass through the holes
(Fig. 1612), will fall off these points _b_, _c_, Fig. 1613, and thus
escape the guideways, while falling dust will be excluded by the wings
_b_, _c_, from the [V]s.
[Illustration: Fig. 1614.]
The capacity of a planer table may be increased by fitting thereto two
supplementary short tables, as shown in Fig. 1614, several applications
of its use being given with reference to examples in planer work. These
supplementary tables are secured to the main table by set-screws at A,
and have been found of great value for a large variety of work,
especially upon planing machines in which the table width is
considerably less than the width between the uprights or stanchions.
[Illustration: Fig. 1615.]
Fig. 1615 represents the arrangement of square holes and [T]-grooves
employed upon large planers. The square holes are cast in the table, and
are slightly tapered to receive taper plugs or stops against which the
work may abut, or which may be used to wedge against, as will be
hereafter described, one of these stops being shown at S in the figure.
[Illustration: Fig. 1616.]
The [T]-shaped slots _f_, _g_, _h_, are to receive the heads of bolts as
shown in Fig. 1616. The bolt head is rounded at corners _a_, _b_, and
the square under the head has the corresponding diagonal corners as _c_
also rounded, so that the width of the head being slightly less than
that of the slot it may be passed down in the slot and then given a
quarter revolution in the direction of the arrow, causing the wings of
the head to pass under the recess of the [T]-groove, as shown in Fig.
1617, which is a sectional end view of the groove with the bolt in
place. The square corners at _e_ and at _f_ prevent the bolt from
turning round more than the quarter revolution when screwing up the bolt
nut, and when the nut is loosened a turn the bolt can be rotated a
quarter revolution and lifted out of the groove.
Now it is obvious that these slots serve the same purpose as the
longitudinal [T]-grooves, since they receive the bolt heads, and it
might therefore appear that they could be dispensed with, but it is a
great convenience to be able to adjust the position of the bolt across
the table width, which cannot be done if longitudinal grooves only are
employed. Indeed, it might easily occur that the longitudinal grooves
be covered by the work when the short transverse ones would serve to
advantage, and in the wide range of work that large planers generally
perform, it is desirable to give every means for disposing the bolts
about the table to suit the size and shape of the work.
[Illustration: Fig. 1617.]
It is obvious that the form of bolt head shown in Fig. 1616 is equally
applicable to the longitudinal grooves as to the cross slots, enabling
the bolt to be inserted, notwithstanding that the work may cover the
ends of the longitudinal slots.
The round holes _a_, _b_, _c_, &c., in Fig. 1612, are preferable to the
square ones, inasmuch as they weaken the table less and are equally
effective. Being drilled and reamed parallel the plugs that fit them may
be passed through them to any desirable distance, whereas the square
plugs being taper must be set down home in their holes, necessitating
the use of plugs of varying length, so that when in their places they
may stand at varying heights from the table, and thus suit different
heights of work. Whatever kind of holes are used it is obvious that they
must be arranged in line both lengthways of the table and across it, so
that they will not come in the way of the ribs R, which are placed
beneath it to strengthen it.
The longitudinal grooves are planed out to make them straight and true
with the [V]-guides and guideways, so that chucking appliances fitting
into the grooves may be known to be set true upon the table.
[Illustration: Fig. 1618.]
[Illustration: Fig. 1619.]
In Fig. 1618, for example, is shown an angle piece A having a projection
fitting into a longitudinal groove, the screws whose heads are visible
passing through A into nuts that are in the widened part of the groove,
so that operating the screws secures A to the table. The vertical face
of A being planed true, a piece of work, as a shaft S, may be known to
be set in line with the table when it is clamped against A by clamps as
at P, or by other holding devices. Angle pieces such as A are made of
varying lengths and heights to suit different forms and sizes of work.
In some planing machine tables a [V]-groove is cut along the centre for
the purpose of holding spindles to have featherways or splines cut in
them, the method of chucking being shown in Fig. 1619. This, however, is
not a good plan, as the bolts and plates are apt to bend the shaft out
of straight, so that the groove cut in the work will not be straight
when the spindle is removed from the clamp pressure. The proper method
of chucking such work will, however, be given in connection with
examples on planer work.
For the round holes in planer tables several kinds of plugs or stops are
employed, the simplest of them being a plain cylindrical plug or stop.
[Illustration: Fig. 1620.]
Fig. 1620 represents a stop provided with a screw B. The stem A fits
into the round holes, and the screw is operated to press against the
work. By placing the screw at an angle, as shown, its pressure tends to
force the work down upon the planer table.
[Illustration: Fig. 1621.]
A similar stop, termed a bunter screw, S, Fig. 1621, may be used in the
longitudinal slots, the shape of its hook enabling it to be readily
inserted and removed from the slot. These screws may be applied direct
to the work when the circumstances will permit, or a wedge W may be
interposed between the screw and the work, as shown.
[Illustration: Fig. 1622.]
Fig. 1622 represents a form of planer chuck used on the smaller sizes of
planers, and commonly called planer centres. A is the base or frame
bolted to the planer table at the lugs L; at B is a fixed head carrying
what may be termed the live centre D, and C is a head similar to the
tailstock of a lathe carrying a dead centre; F is an index plate having
worm-teeth on its edge and being operated by the worm G. At S is a
spring carrying at its end the pin for the index holes. To bring this
pin opposite to the requisite circle of holes, the bolt holding S to A
is eased back and S moved as required. On the live centre D is a clamp
for securing the work or mandrel holding dog. Head C is split as shown,
and is held to the surface of A by the bolt H, which is tapped into the
metal on one side of the split.
It is obvious that polygons may be planed by placing the work between
the centres and rotating it by means of G after each successive side of
the polygon has been planed or shaped, the number of sides being
determined by the amount of rotation of the index plate.
[Illustration: Fig. 1623.]
Fig. 1623 shows a useful chuck for holding cylindrical work, such as
rolls. The base is split at E, so that by means of the bolt and nut D
the [V]-block a may be gripped firmly; B and C are screws for adjusting
the height of the [V]-block A. At F is the bolt for clamping the chuck
to the planer table, and G is a cap to clamp the work W in the block A.
It will be seen that this chuck can be set for taper as well as parallel
work.
[Illustration: Fig. 1624.]
[Illustration: Fig. 1625.]
Fig. 1624 represents a chucking device useful for supporting or packing
up work, or for adjusting it in position ready to fasten it to the work
table, it being obvious that its hollow seat at A enables it to set
steadily upon the table, and that its screw affords a simple means of
adjusting its height. It may also be used between the jaws of a
connecting rod strap or other similar piece of work to support it, as in
Fig. 1625, and prevent the jaws from springing together under the
pressure of the tool cut.
[Illustration: Fig. 1626.]
Another and very useful device for this purpose is shown in Fig. 1626,
consisting of a pair of inverted wedges, of which one is dovetailed into
the other and having a screw to operate them endwise, the purpose being
to hold the two jaws the proper distance apart and prevent their closure
under pressure of the planer vice jaws. It is obvious that the device in
Fig. 1625 is most useful for work that has not been faced between the
jaws, because the device in Fig. 1626 would, upon rough work that is not
true, be apt to spring the work true with the inside faces, which may
not be true with the outside ones, and when the wedges were removed the
jaws would spring back again, and the work performed while the inverted
wedges were in place would no longer be true when they were removed.
[Illustration: Fig. 1627.]
Fig. 1627 represents a centre chuck to enable the cutting of spirals.
The principle of the design is to rotate the work as it traverses, and
this is accomplished as follows:--
Upon the bed of the machine alongside of the table is bolted the rack A
A, into which gears the pinion B, which is fixed to the same shaft as
the bevel-gear C, which meshes with the bevel-wheel D. Upon the same
shaft as D is the face plate E, and in the spindle upon which D and E
are fixed is a centre, so that the plate E answers to the face plate of
a lathe. F is a bearing for the shaft carrying B and C, and G is a
bearing carrying the spindle to which E and D are fixed. H is a standard
carrying the screw and centre, shown at I, and hence answers to the
tailstock of a lathe. K represents a frame or plate carrying the
bearings F and G, and the standard H. L represents the table of the
planing machine to which K is bolted. The reciprocating motion of the
table L causes the pinion B to revolve upon the rack A A. The pinion B
revolves C, which imparts its motion to D, and the work W being placed
between the centres as shown, is revolved in unison with E, revolving in
one direction when the table K is going one way, and in the other when
the motion of the table is reversed; hence a tool in the tool post will
cut a spiral groove in the work.
To enable the device to cut grooves of different spirals or twist, all
that is necessary is to provide different sizes of wheels to take the
places of C and D, so that the revolutions of E, and hence of the work
W, may be increased or diminished with relation to the revolutions of B;
or, what is the same thing, to a given amount of table movement, or a
stud may be put in so as to enable the employment of change gears.
[Illustration: Fig. 1628.]
Figs. 1628 and 1629 represent a universal planer chuck, designed and
patented by John H. Greenwood, of Columbus, Ohio, for planing concave or
convex surfaces, as well as ordinary plane ones, with the cross feed of
the common planer.
The base L of the chuck is bolted to the planer work table in the
ordinary manner.
The work-holding frame or vice is supported, for circular surfaces, by
being pivoted to the base at O, O, and by the gibbed head D, which has
journal bearing at E. The work is held between the stationary jaw _b_ or
_b´_ (at option) and the movable jaw C which may face either _b_ or _b´_
(by turning C round). Suppose then, that while the chuck is passing the
cutting tool, end I of the work-holding frame is raised, lifting that
end of the work above the horizontal level (the work-holding frame
swinging at the other end on the pivots O, O), then the tool will
obviously cut a convex surface. Or if end I of the work-holding frame be
lowered while the cut is proceeding, the tool will cut a concave
surface.
[Illustration: Fig. 1629.]
Now end I is caused to rise or lower as follows:--The head D is adjusted
by means of its gibs to be a sliding fit on the bar G in Fig. 1629,
which bar is rigidly fixed at P to the planer bed; hence as the planer
table and the chuck traverse, D slides along bar G. If this bar is fixed
at an angle to the length of the planer head, D must travel at that same
angle, causing end I of the work-holding frame to rise or lower (from O,
O, as a centre of motion) as it traverses according to the direction of
motion of the planer table.
Suppose that in Fig. 1629, the planer table is moving on the back or
non-cutting stroke, then head D will be moving towards the point of
suspension P of the bar G, and will therefore gradually lower as it
proceeds, thus lowering end I of the work-holding frame and causing the
curved link to pass beneath the tool with a curved motion or suppose the
table to be on its cutting traverse, then head D will be raised as the
table moves and the cut proceeds, and the surface cut by the tool will
be concave.
Now, suppose that the bar G were fixed at an angle, with its end, that
is towards the back end of the planer, inclined towards the table
instead of away from it as in Fig. 1629, and then on the cutting
traverse head D would cause end I (Fig. 1628) of the work-holding vice
or frame to lower as the cut proceeded, and the tool would therefore
plane a convex surface.
Thus the direction of the angle in which G is fixed governs whether the
surface planed shall be a concave or a convex one, and it is plain that
the amount of concavity or convexity will be governed and determined by
the amount of angle to which G is set to the planer table.
When the chuck is not required to plane curved surfaces the bar G is
altogether dispensed with, and the chuck becomes an ordinary one
possessing extra facilities for planing taper work.
Thus for taper work the work-holding frame may be set out of parallel
with the base of the chuck to an amount answering to the required amount
of taper, being raised or lowered (as may be most convenient) at one end
by means of the gears M, of which there is one on each side meshing into
the segmental rack shown, the work-holding frame being secured in its
adjusted position by means of a set bolt.
To set the work-holding frame parallel for parallel planing, a steady
pin is employed, the frame being parallel to the base when that pin is
home in its place.
The construction of the chuck is solid, and the various adjustments may
be quickly and readily made, giving to it a range of capacity and
usefulness that are not possessed by the ordinary forms of planer
chucks.
PLANING MACHINE BEDS.--In long castings such as lathe or planer beds,
the greatest care is required in setting the work upon the planer table,
because the work will twist and bend of its own weight, and may have
considerable deflection and twist upon it notwithstanding that it
appears to bed fair upon the table. To avoid this it is necessary to
know that the casting is supported with equal pressure at each point of
support. In all such work the surface that is to rest upon the
foundation or legs should be planed first.
[Illustration: Fig. 1630.]
Thus supposing the casting in Fig. 1630 to represent a lathe shears, the
surfaces _f_ whereon the lathe legs are to be bolted should be planed
first, the method of chucking being as follows:--
[Illustration: Fig. 1631.]
The bed is balanced by two wedges A, in Fig. 1630, one being placed at
each end of the bed, and the position of the wedges being adjusted so
that it lies level. A line coincident with the face of the bed (as face
_d_) is then drawn across the upper face of each wedge. Wedges (as B,
C,) are then put in on each side of the bed until they each just meet
the bed, and a line coincident with the bed surface is drawn across
their upper surfaces. Wedge B is then driven in until it relieves A of
the weight of the bed, and a second line is drawn across its upper face.
It is then withdrawn to the first line, and the wedge on the opposite
side of the bed is driven in until A is relieved of the weight, when a
second line is drawn on this wedge's face. The wedges at the other end
(as C) are then similarly driven in and withdrawn, being also marked
with two lines, and then the four wedges (B, C, and the two
corresponding ones on the opposite side of the bed) are withdrawn,
having upon their surfaces two lines each (as A, B, in Fig. 1631).
Midway between these two lines a third (as C) is drawn, and all four
wedges are then driven in until line C is coincident with the bed
surface, when it may be assumed that the bed is supported equally at all
the four points. When the bed is turned over, surfaces _f_ may lie on
the table surface without any packing whatever, as they will be true.
Another excellent method is to balance the bed on three points, two at
one end and one at the other, and to then pack it up equally at all four
corners.
To test if the surface of a piece of such work has been planed straight,
the following plan may be pursued:--
[Illustration: Fig. 1632.]
Suppose that surface E, Fig. 1632, is to be tested, it having been
planed in the position it occupies in the figure, and the casting may be
turned over so that face E stands vertical, as in Fig. 1632, and a tool
may be put in the tool post of the planer, the bed being adjusted on the
planer table so that the tool point will just touch the surface at each
end of the bed. The planer table is then run so that the tool point may
be tried with the middle of the bed length, when, if the face E is true,
it will just meet the tool point at the middle of its length as well as
at the ends.
In the planing of the [V]-guides and guideways of a bed for a machine
tool, such as, for example, a planer bed and table, the greatest of care
is necessary, the process being as follows:--
Beginning with the bed it has been shown in Fig. 1601 that the sides of
the guideways must all be of the same height as well as at the same
angle, and an excellent method of testing this point is as follows:--
[Illustration: Fig. 1633.]
In Fig. 1633 is shown at A a male gauge for testing the [V]-guideways in
the bed, and at B a female gauge for testing those on the table. These
two gauges are accurately made to the correct angle and width, and
fitted together as true as they can be made, being corrected as long as
any error can be found, either by testing one with the other or by the
application of a surface plate to each separate face of the guides and
guideways. The surfaces C and D of the respective gauges are made
parallel with the [V]-surfaces, a point that is of importance, as will
be seen hereafter. It is obvious that the female gauge B is turned
upside down when tried upon the table.
[Illustration: Fig. 1634.]
Suppose it is required to test the sides _e_, _f_, of the bed guideways
in Fig. 1634, and the gauge must be pulled over in the direction of the
arrow so that it touches those two sides only; a spirit-level laid upon
the top of the gauge will then show whether the two faces _e_, _f_, are
of equal height. It is obvious that to test the other two faces the
gauge must be pulled over in the opposite direction.
This test must be applied while fitting the [V]s to the gauge. Suppose,
for example, that when the gauge is applied and allowed to seat itself
in the ways, the two outside angles _e_, _g_, are found to bear while
the two inside ones do not touch the gauge at all, then by this test it
can be found whether the correction should be made by taking a cut off
_e_ or off _g_, for if the spirit-level stood level when the gauge was
pulled in either direction, then both faces would require to be operated
upon equally, but suppose that the gauge and spirit-level applied as
shown proved end _e_ to be high, then it would be the one to be operated
on, or if when the gauge was pulled over in the opposite direction end
_g_ was shown (by the spirit-level) to be high, then it would be the one
to be operated upon.
By careful operation the table and bed may thus be made to fit more
perfectly than is possible by any other method. To test the fit of the
gauge to the [V]s it is a good plan to make a light chalk mark down each
[V] and to then apply the gauge, letting it seat itself and moving it
back and forth endways, when if it is a proper fit it will rub the chalk
mark entirely out. It may be noted, however, that a light touch of red
marking is probably better than chalk for this purpose.
It is of importance that the [V]s be planed as smooth as possible, and
to enable this a stiff tool holder holding a short tool, as in Fig. 1635
should be used, the holder being held close up to the tool box as shown.
It will be obvious that when the head is set over to an angle it should
be moved along the cross slide to plane the corresponding angle on the
other side of the bed.
Fig. 1636 represents a planer chuck by Mr. Hugh Thomas. The angle piece
A is made to stand at an angle, as shown, for cylindrical work, such as
shafts, so that the work will be held firmly down upon the table. The
base plate B has ratchet teeth at each end C, into which mesh the pawls
D, and has slotted holes for the bolts which hold it down to the table,
so that it has a certain range of movement to or from the angle piece A,
and may therefore be adjusted to suit the diameter or width of the work.
The movable jaw E is set up by the set-screw F and is held down by the
bolts shown. The pawls D are constructed as shown in Fig. 1637, the pin
or stem S fitting the holes in the planer table and the tongue P being
pivoted to the body R of the pawl. As the pawls can be moved into any of
the holes in the table, the base plate B may be set at an angle,
enabling the chuck to be used for taper as well as for parallel work,
while the chuck has a wide range of capacity.
In Fig. 1614 is shown a supplementary table for increasing the capacity
of planer tables, and which has already been referred to, and Fig. 1638
represents an application of the table as a chucking device. A, A, &c.,
are frames whose upper surfaces are to be planed. An angle plate is
bolted to the planer table and the supplementary table is bolted to the
angle plate. The first frame is set against the vertical face of the
supplementary table, and the remaining ones set as near as possible, B,
B, &c., being small blocks placed between the frames which are bolted to
the planer table as at C.
[Illustration: Fig. 1635.]
In many cases this method of chucking possesses great advantages. Thus
in the figure there are six frames to be planed, and as they would be
too long to be set down upon the planer table, only three or four could
be done at a time, and a good deal of measuring and trying would be
necessary in order to get the second lot like the first. This can all be
avoided by chucking the whole six at once, as in figure.
Another application of the same tables as useful chucking devices is
shown in Fig. 1639, where two frames E, F, are shown bolted to the
machine table and supported by the supplementary tables T, which are
bolted to the main table and supported by angle-pieces _b_, _b_. Work
that stands high up from the planer table may be very effectively
steadied in this way, enabling heavier cuts and coarser feeds while
producing smoother work.
[Illustration: Fig. 1640.]
As horizontal surfaces can be planed very much quicker than vertical
ones, it frequently occurs that it will pay to take extra trouble in
order to chuck the work so as to plane it horizontally, an excellent
example being the planing of the faces of the two halves of a large
pulley, the chucking of which is illustrated in Fig. 1640.
Four pieces, as at A, are made to engage the rims of the two halves of
the pulley and hold them true, one with the other. The two plates T´ and
T´´ are set under the pulley halves to level the upper faces, and wooden
clamps C, C, are bolted up to hold the pulleys together at the top, W
representing wedges between the hubs. S represents supports to block up
the pulley near its upper face, and at P are clamps to hold the two
halves to the table. It is found that by this method of chucking more
than half the time is saved, and the work is made truer than it is
possible to get it by planing each half separately and laying them down
on the table.
Supplemental tables may also be made in two parts, the upper one being
capable of swiveling as in Fig. 1641, the swiveling device corresponding
to that shown for the Thomas shaper chuck in Fig. 1530. This enables the
work to be operated upon on several different faces without being
released from the chuck. Thus in figure the segment could be planed on
one edge and the upper table swiveled to bring the other edge in true
with the table, which would be a great advantage, especially if the face
it is chucked by has not been trued.
Figs. 1642 and 1643 show other applications of the same swiveling
device.
It is obvious that the chuck shown in Fig. 1636 can be mounted on a
supplemental and swiveling table as shown in Fig. 1644, thus greatly
facilitating the chucking of the work and facilitating the means of
presenting different surfaces or parts of the work to the tool without
requiring to unchuck it. The pawls, also, may in heavy work have two
pins to enter the work-table holes and be connected by a strap as in
Fig. 1645.
In the exigencies of the general machine shop it sometimes happens that
it is required to plane a piece that is too wide to pass between the
uprights of the planing machine, in which case one standard or upright
may be taken down and the cross slide bolted to the other, as in Fig.
1646, the blocks _a_, _a_, being necessary on account of the arched form
of the back of the cross slide. In the example given the plates to be
planed were nearly twice as wide as the planer table and were chucked as
shown, the beam D resting on blocks E, F, and forming a pathway for the
piece C, which was provided with rollers at each end so as to move
easily upon D. The outer end of the plate was clamped between B and C,
and the work was found to be easily and rapidly done. In this chucking,
however, it is of importance that beam D be carefully levelled to stand
parallel with the planer table face, while its height must be so
adjusted that it does not act to cant or tilt the table sideways as that
would cause one [V] of the planer ways to carry all or most of the
weight, and be liable to cause it to cut and abrade the slide surfaces.
[Illustration: _VOL. I._ =EXAMPLES IN PLANING WORK.= _PLATE XVIII._
Fig. 1636.
Fig. 1637.
Fig. 1638.
Fig. 1639.]
[Illustration: Fig. 1641.]
[Illustration: Fig. 1642.]
[Illustration: Fig. 1643.]
[Illustration: Fig. 1644.]
[Illustration: Fig. 1645.]
[Illustration: Fig. 1646.]
CUTTING TOOLS FOR SHAPING AND PLANING MACHINES.--All the cutting tools
forged to finished shape from rectangular bar steel, and described in
connection with lathe work, are used in the planer and in the shaper,
and the principles governing the rake of the top face remain the same.
But in the matter of the clearance there is the difference that in a
planing tool it may be made constant, because the tool feeds to its cut
after having left the work surface at the end of the back stroke, hence
the clearance remains the same whatever the amount or rate of feed may
be.
[Illustration: Fig. 1647.]
On this account it is desirable to use a gauge as a guide to grind the
tool by, the application of such a gauge being shown in Fig. 1647. It
consists of a disk turned to the requisite taper and laid upon a plate,
whereon the tool also may be laid to test it. The tool should not be
given more than 10° of clearance, unless in the case of broad flat-nosed
tools for finishing, for which 5° are sufficient.
[Illustration: Fig. 1648.]
[Illustration: Fig. 1649.]
The principle of pulling rather than pushing the tool to its cut, can,
however, be more readily and advantageously carried out in planer than
in lathe tools, because the spring of the tool and of the head carrying
it only need be considered, the position of the tool with relation to
the work being otherwise immaterial. As a consequence it is not unusual
to forge the tools to the end of pulling, rather than of pushing the
cutting edge.
[Illustration: Fig. 1650.]
In Figs. 1648 and 1649, for example, are two tools, W representing the
work, and A the points off which the respective tools will spring in
consequence of the pressure; hence the respective arrows denote the
direction of the tool spring. As a result of this spring it is obvious
the tool in Fig. 1648 will dip deeper into the work when the pressure of
the cut increases, as it will from any increase of the depth of the cut
in roughing out the work, or from any seams or hard places in the metal
during the finishing cut. On the other hand, however, this deflection or
spring will have the effect of releasing the cutting edge of the tool
from contact with the work surface during the back stroke, thus
rendering it unnecessary to lift the tool to prevent the abrasion, on
its back stroke, from dulling its cutting edge.
[Illustration: Fig. 1651.]
[Illustration: Fig. 1652.]
It will be noted that the radius from the point of support A is less for
the tool in Fig. 1649 than for that in Fig. 1648, although both tools
are at an equal height from the work, which enables that in Fig. 1649 to
operate more firmly. In these two figures the extremes of the two
systems are shown, but a compromise between the two is shown in Fig.
1650, the cutting edge coming even with the centre of the body of the
steel, which makes the tool easier to forge and grind, and keeps the
cutting edge in plainer view when at work, while avoiding the evils
attending the shape shown in Fig. 1648.
It is sometimes necessary, however, that a tool of the form in Fig. 1652
be used, as, for example, to shape out the surface of a slot, and when
this is the case the tool should be shaped as in Fig. 1651, the bottom
face having ample clearance (as, say, 15°) from the heel A to about the
point B, and about 3° from B to the front end. The front face should
have little or no clearance, because it causes the tool to dig into the
work. A tool so shaped will clear itself well on the back stroke,
whereas if but little clearance and front rake be given as in Fig. 1652,
the tool will not only dig in, but its cutting edge will rub on the back
or return stroke.
[Illustration: Fig. 1653.]
For broad feed finishing cuts the shape of tool shown in Fig. 1653 is
employed, the cutting edge near the two corners being eased off very
slightly with the oilstone. The amount of clearance should be very
slight indeed, only just enough to enable the tool to cut as is shown in
the figure, by the line A A. The amount of front rake may be varied to
suit the nature and hardness of the metal, and the tool should be held
as close in as possible to the tool clamp.
Smoother work may be obtained in shaping and in planing machine tools
when the tool is carried in a holder, such as in Fig. 1654, which is
taken from _The American Machinist_ because in this case any spring or
deflection either in the tool or in the shaper head acts to cause the
tool to relieve itself of the cut instead of digging in, as would be the
case were the tool put in front of the tool post as in Fig. 1654. In
finishing large curves this is of great importance, because to obtain
true and smooth curves it is necessary to shape the tool to cut upon the
whole of the curve at once, and this gives so great a length of cutting
edge, that the tool is sure to chatter if held in front of the tool
post.
[Illustration: Fig. 1654.]
It is essential, therefore, to carry the tool at the back of the tool
post as shown, and for curves that are arcs of circles tools such as in
Fig. 1655 may be employed, or a circular disk will answer, possessing
the advantage that its shape may be maintained by grinding its flat face
to resharpen it.
Cutters of the kind shown in Fig. 1655 may be made to possess several
important advantages aside from their smooth action: thus they may be
made after the principle explained with reference to the Brown & Sharpe
rotary cutters for gear-teeth, in which case the front face only need be
ground to resharpen them, and their shapes will remain unaltered, and
they may be given different degrees of front rake by placing packing
between one side and the holder, and any number of different shaped
cutters may be fitted to the same stock.
[Illustration: Fig. 1655.]
TOOL HOLDERS FOR PLANING MACHINES.--The advantages of tool holders for
planing machines are equally as great as those already described for
lathes, but as applied to planing machines there is the additional
advantage that the clearance necessary on the tool is less variable for
planer work than for lathe work, because in lathe work the diameter of
the work as well as the rate of tool feed affects the tool clearance,
whereas in planer work the tool feed is put on before the tool begins
its cutting action; hence the degree of clearance is neither affected by
the size of the work nor by the rate of feed, and as a result the tools
may be given a definite and constant amount of clearance.
[Illustration: Fig. 1656.]
Fig. 1656 represents a planer tool holder (by Messrs. Smith & Coventry),
in which what is, in effect, a swivel tool post is attached to the end
of the holder, thus enabling the tool to be used on either the right or
left-hand of the holder at will. The shape of the tool steel is shown in
section on the right-hand of the engraving, being narrow at the bottom,
which enables the tool to be very firmly held and reduces the area to be
ground in sharpening the tool. A side and end view of the holder is
shown in Fig. 1657, in which it is seen that the tool may be given top
rake or angle to render it suitable for wrought iron or steel or may be
set level for brass work.
[Illustration: Fig. 1657.]
In Fig. 1658 the tool and holder are shown in position on the planer
head, the front rake on the tool being that suitable for wrought iron.
[Illustration: Fig. 1658.]
It is to be noted, however, that the amount of front rake should, to
obtain the best results, be less for steel than for wrought iron, and
less for cast iron than for wrought, while for brass there should be
none; hence the tool post should be made to accomplish these different
degrees of rake in order to capacitate such holders for the four
above-named metals. It is an advantage, however, that by inclining the
tool to give the top rake, this rake may be kept constant by grinding
the end only of the tool to sharpen it, and as the end may be ground to
a gauge it is very easy to maintain a constant shape of tool.
Furthermore as the tool is held by one binding screw only, it may be
more readily adjusted in position for the work than is the case when the
two apron clamp nuts require to be operated.
[Illustration: Fig. 1659.]
[Illustration: Fig. 1660.]
Figs. 1659 to 1661, show this tool-holder applied to various kinds of
work, thus in Fig. 1659 the tool is planing under the underneath side of
a lathe bed flange, while in Fig. 1660 it is acting upon a [V]-slideway
and escaping an overhanging arm, and in Fig. 1661 it is shown operating
on a [V]-slideway and in a [T]-groove.
[Illustration: Fig. 1661.]
Fig. 1662 represents a tool holder by Messrs. Bental Brothers, the tool
being held in a swivelled tool post, so that it may be used as a right
or left-hand tool. In this case the front rake must be forged or ground
on the tool, and there is the further objection common to many tool
holders, that the tool if held close in to the tool post is partly
hidden from view, thus increasing the difficulty of setting it to the
depth of cut.
[Illustration: Fig. 1662.]
Another form of planer or shaper tool-holder is shown in Fig. 1663, in
which a tool post is mounted on a tool bar, and may be used as a right
or left-hand tool at will.
[Illustration: Fig. 1663.]
[Illustration: Fig. 1664.]
Fig. 1664 represents a tool holder in which two tools may be held as
shown, or a single tool right-hand or left-hand as may be required, or
the tool may be held at the end of the holder as in Fig. 1665. The
advantage of such a holder is well illustrated in the case of cutting
out a [T]-shaped groove, because with such a holder a straight tool can
be used for the first cuts, its position being shown in Fig. 1665,
whereas in the absence of such a holder a tool bent as in Fig. 1666
would require to be used, this bend giving extra trouble in the forging,
rendering the tool unfit for ordinary plain work, and being unable to
carry so heavy a cut or to cut so smooth as the straight tool in Fig.
1665. In cutting out the widest part of such a groove the advantage of
the holder is still greater, because by its use a tool with one bend, as
in Fig. 1667, will serve, whereas without a holder the tool must have
two bends, as shown in the figure, and would be able to carry a very
light cut, while liable to dig into the work and break off.
[Illustration: Fig. 1665.]
[Illustration: Fig. 1666.]
The tool itself should be so forged that one side is flush with the side
of the tool steel as shown at A in Fig. 1668, for if there is a
shoulder, as at C, it sometimes prevents the tool from entering the work
as shown in the figure.
[Illustration: Fig. 1667.]
Other examples in the use of this tool holder are given in Figs. 1669
and 1670.
[Illustration: Fig. 1668.]
In Fig. 1669, we have the case of cutting out the [V]-slideways of a
planer bed, and it is seen that the tool point may be held close to the
holder, the side of the tool box still clearing the side of the
[V]-slideway, whereas in the absence of the holder the tool would
require to have a considerable bend in it, or else would have to stand
out from the bottom of the tool apron to a distance equal to the length
of one side of the slideway.
[Illustration: Fig. 1669.]
[Illustration: Fig. 1670.]
In Fig. 1670 it is also seen that by the use of the holder the tool
point may also be held as close as necessary to the holder, and still
permit the side of the vertical slide S´ and the tool box B to clear the
vertical face of the work.
In all planer work it is an essential in the production of true and
smooth surfaces that the tool be held as close in to the tool clamp or
tool box as possible, and this forms one of the main advantages of tool
holders.
CHAPTER XVIII.--DRILLING MACHINES.
POWER DRILLING MACHINES.--The drilling machine consists essentially of a
rotating spindle to drive the drill, a work-holding table, and means of
feeding the drill to its cut. The spindle speed and the force with which
it is driven are varied to suit the work. The feeding is sometimes given
to the spindle, and at others to the work table. In either case,
however, the feeding mechanism should be capable of varying the rate of
feed and of permitting a quick withdrawal of the drill. The spindle
should be supported as near to its drill-holding end as possible. When
the table feeds to the work the spindles may be held rigidly, because of
their not requiring to pass so far out or down from the bearing
supporting them; but when the spindle feeds, it must either pass through
its bearings, or the bearing, or one of them, must either be capable of
travel with the spindle or adjustable with relation to the machine
framing.
In using small drills in a machine it is of the first importance that
the amount of pressure necessary to feed the drill be plainly
perceptible at the hand lever or other device for feeding the drill or
the work, as the case may be, as any undue pressure causes the drills to
break. To attain sensitiveness in this respect the parts must be light
and easy both to move and to operate.
Fig. 1671 represents the American Tool Company's delicate drilling
machine for holes of 1/4 inch and less in diameter. It consists of a
head fixed upon a cylindrical column and affording journal bearing to
the drill-driving spindle, which is driven by belt. The table on which
the work is placed is carried by a knee that may be fixed at any
required height upon the same round column. The knee and table may be
swung out of the way, the column serving as a pivot. The table has
journal bearing in the knee, and is fed upwards by the small lever
shown.
Fig. 1672 represents Elliott's drilling machine for drills from 1/32
inch to 3/4 inch in diameter. The work table may be revolved in the arm
that carries it, and this arm may be swung round the column or post. It
is operated upwards for the feed by the hand lever shown. The conical
chuck shown lying on the work table fits into the hole that is central
in the table, and is used to receive the end of cylindrical work and
hold it true while the upper end is operated upon.
The construction of the live spindle and its cone are shown in Fig.
1673. The drill chuck Q is attached to and driven by a one-inch steel
spindle 19 inches long, which is accurately fitted through the sleeve
bearings, within which it is free to move up and down, but is made to
revolve with the cone by means of the connection O, one end of which
slides upon the rods L. The drill is held up by means of the spiral
spring M acting from the bottom of cone to the collar O. The weight of
cone and spindle is carried upon a raw-hide washer, beneath which is the
cupped brass P which retains the oil. The thrust of the feed lever G is
also taken by a raw-hide washer R.
The machine is provided with a hand and a foot feed by means of the
compound lever W Z, Fig. 1674, actuating the feed rod J, which passes up
within the column and connects to the lever K, the latter being
suspended by a link H.
Fig. 1675 represents Slate's sensitive drilling machine, in which the
lower bearing for the live spindle is carried in a head H that fits to a
slide on the vertical face of the frame, so that it may be adjusted for
height from the work table W to suit the height of the work. L is a
lever operating a pinion engaging a rack on the sleeve S to feed the
spindle. The table W swings out of the way and a conically recessed cup
chuck C is carried in a bracket fitting into a guideway in the vertical
bed G. The cone of the cup chuck is central to or axially in line with
the live spindle, hence cylindrical work may have its end rested in the
cone of the cup chuck, and thus be held axially true with the live
spindle.
[Illustration: Fig. 1676.]
Fig. 1676 represents a drilling machine in which the spindle has four
changes of feed, and is fed by a lever handle operating a pinion that
engages a rack placed at the back of a sleeve forming the lower journal
bearing for the spindle. This lever is provided with a ratchet so that
it may be maintained in a handy position for operating. The work table
is raised or lowered by a pinion operating in a rack fast upon the face
of the column, a pawl and ratchet wheel holding it in position when its
height has been set. A lever is used to operate the pinion, being
inserted in a hub fast upon the same spindle that carries the pinion and
the ratchet wheel.
Fig. 1677 represents a drilling machine by Prentice Brothers, of
Worcester, Massachusetts. Motion for the cone pulley A is received by
pulleys B and is conveyed by belt to cone pulley C, which is provided
with back gear, as shown; the driving spindle D drives the bevel pinion
E, which gears with the bevel-wheel F, which drives the drill spindle G
by means of a feather fitting in a keyway or spline that runs along that
spindle. Journal bearing is provided to the upper end of the spindle at
H and to the lower end by bearings in the head J, which may be adjusted
to stand at, and be secured upon any part of the length of the slideway
K. By this arrangement the spindle is guided as near as possible to the
end L to which the drill is fixed and upon which the strain of the
drilling primarily falls. This tends to steady the spindle and prevent
the undue wear that occurs when the drill spindle feeds below or through
the lower bearing.
[Illustration: _VOL. I._ =LIGHT DRILLING MACHINES.= _PLATE XIX._
Fig. 1671.
Fig. 1672.
Fig. 1673.
Fig. 1674.
Fig. 1675.]
The feed motions are obtained as follows:--
On the drill spindle is a feed cone M which is connected by belt to cone
N, which drives a pinion O, that engages a gear P upon the feed spindle
Q, which has at its lower end a bevel pinion, which drives a bevel gear
upon the worm shaft R. The worm shown on R drives the worm-wheel S,
whose spindle has a pinion in gear with the rack T, which is on a sleeve
U on the drill spindle G. It is obvious that when the rack T is
operated by its pinion the sleeve U is moved endways, carrying the feed
spindle with it and therefore feeding the drill to its cut, and that as
the feed cone M has three steps there are three different rates of
automatic feed.
To throw the self-feed into or out of action the following construction
is employed:--
The worm-wheel S has on its hub face teeth after the manner of a clutch,
and when these teeth are disengaged from the clutch sleeve W the
worm-wheel S rides or revolves idly upon its shaft or spindle, which
therefore remains at rest. Now the clutch sleeve S has a feather fitting
to its spindle or shaft, so that the two must, if motion takes place,
revolve together, hence when W is pushed in so as to engage with S, then
S drives W and the latter drives the spindle, whose pinion operates the
rack T.
A powerful hand feed to the drill spindle is provided as follows:--
[Illustration: Fig. 1677.]
The worm shaft R is hollow, and through it passes a rod having at one
end the hand nut V and at the other a friction disk fitting to the bevel
gear shown at the right-hand end of the worm-shaft. This friction disk
is fast upon the worm-shaft and serves to lock the bevel gear to the
worm-shaft when the nut V is screwed up, or to release it from that
shaft when V is unscrewed.
Suppose, then, that V is unscrewed and shaft R will be unlocked from the
bevel-wheel and may be operated by the hand wheel X, which is fast upon
the worm-shaft, and therefore operates it and worm-wheel S, so that W
being in gear with S the hand feed occurs when X is operated and V is
released. But as the motion of S is, when operated by its worm, a very
slow one, a second and quick hand feed or motion is given to the spindle
G as follows, this being termed the quick return, as it is mainly useful
in quickly removing the drill from a deep hole or bore.
The spindle carrying S and W projects through on the other side of the
head J and has at its end the lever Y, hence W being released from S,
lever Y may be operated, thus operating the pinion that moves rack T,
one revolution of Y giving one revolution to the pinion, both being on
the same shaft or spindle.
The work is carried and adjusted in position beneath the drill as
follows:--
The base of the column or frame is turned cylindrically true at _a_, and
to it is fitted a knee _b_ which carries a rack _c_. The knee _b_
affords journal bearing to a spindle which has a pinion gearing with the
rack _c_, and at the end of this spindle is a ratchet-wheel _d_ operated
by the lever shown. A catch may be engaged with or disengaged from
ratchet _d_. When it is disengaged the lever may be operated, causing
the pinion to operate on rack _c_ and the knee _b_ to raise or lower on
_a_ according to the direction in which the lever is operated. As the
knee _b_ carries the rack the knee may be swung entirely from beneath
the drill spindle and the work be set upon the base plate _e_ if
necessary, or it may be set upon the work table _f_ which has journal
bearing in the knee _b_, so that it may be revolved to bring the work in
position beneath the drill.
[Illustration: Fig. 1678.]
In the Sellers drilling machine, Fig. 1678, the drill spindle when in
single gear is driven by belt direct, producing a uniform and smooth
motion that is found of great advantage in drilling the smaller sizes of
holes. The back gear is arranged to drive the spindle direct without the
power requiring to be transmitted through a shaft, which induces
vibration. The drill spindle is provided with variable rates of
self-acting feed, but may also be moved rapidly by hand, and is
counterbalanced. The work table is capable of revolving upon its axis,
and the arm on which it is carried is pivoted in a slide upon a vertical
slideway on the front of the main frame, so that the table and the arm
may be swung out of the way for work that can be more advantageously
rested on the base plate of the machine. A central hole is bored in the
table, being true to the drill spindle when the arm is in its mid
position, and clamps are provided to secure the circular table against
rotation when it is set to place, and also to secure the swinging
bracket to any required position. This form of table, like the compound
table, has the advantage of permitting all parts of the table being
brought in turn under the drill, but the motion is not in right lines.
Holes are provided in the circular table to admit holding-down bolts.
The rates of feed are proportioned to the kind of drilling to be done.
When the back gear is not in use and small drills are to be driven, the
range of feeds is through a finer series than when the back gear is
being used, and large drills or boring bars are to be driven.
Fig. 1679 represents a drilling machine of English design. The cone
pulley A is provided with back gear B placed beneath it, the live
spindle driving the drill spindle through the bevel gears C, one of
which is fast upon a sleeve D through which the drill spindle E passes.
The feed motions are obtained as follows:--I is the feed cone driving
cone J, which drives a worm and worm-wheel at K. In one piece with the
worm-wheel is a ratchet wheel L, and at M is a handle with a pawl that
may be engaged with or disengaged from ratchet-wheel L. When it is
engaged the handle, which is fast upon the vertical feed spindle N, is
revolved by the worm-wheel and the automatic feed is put in operation;
but when the pawl is disengaged the worm and worm-wheel revolve in the
bearing while the spindle N remains at rest, unless it be operated by
the handle M, which obviously revolves the spindle N more quickly than
the worm and gives to a corresponding extent a quick motion to the drill
spindle. Spindle N is provided with the gear-wheel O, which drives gear
P, which is threaded upon the feed screw F and has journal bearing at Q.
The sleeve D has journal bearing at G and at H. At R is a hand wheel
upon a horizontal shaft at whose other end is a bevel gear engaging with
a bevel gear on the vertical screw for the knee T which fits to the
vertical slides V. The work table W is fitted to a horizontal slide upon
the arm X, which is pivoted to the knee T at Y, the handle for operating
the screw of the table being at Z.
[Illustration: Fig. 1680.]
RADIAL DRILLING MACHINE.--Fig. 1680 represents a radial drilling
machine, the column of which envelops a sleeve round which it may be
swung or revolved, the sleeve extending some distance up from the base
plate. The arm fits to the column and may be raised or lowered to any
desired height to suit the work, the construction being as follows:--
[Illustration: _VOL. I._ =HEAVY DRILLING MACHINE.= _PLATE XX._
Fig. 1679.]
[Illustration: Fig. 1681.--Front View.]
[Illustration: Fig. 1682.]
[Illustration: Fig. 1683.--Side Elevation.]
[Illustration: Fig. 1684.--Front Elevation.]
Motion by belt is given to the spindle shown extending above the top of
the column, and the pair of gears beneath it convey motion to the pair
of bevels which drive the upper cone pulley which connects by belt to
the lower one, which is provided with back gears to give the necessary
changes of speed and power for the wide range of work the machine is
intended for; the live spindle of the lower cone pulley extends past the
collar and runs beneath the horizontal arm, giving motion to the drill
spindle, which is carried in a sliding head. The spindle may be set at
any required angle to the arm.
The vertical screw on the right hand of the column passes through a nut
in the column, so that by throwing the gearing at the upper end of the
screw into action, the arm may be raised or lowered by power.
The vertical rod appearing in the front of the column and having an arm
at its top, is for putting this gearing in or out of action, the arm
being raised or lowered according to the direction in which the rod is
operated by the lever handle shown upon it, and in front of the column.
The gearing at the top of the raising and lowering screw is constructed
on the principle that was shown in Fig. 566, for reversing the direction
of a lathe feed.
The capacity to swing the drill spindle at an angle enables the drilling
of long work such as the flanges of pipes, by setting the pipe at an
angle and swinging the spindle so as to stand parallel to it, while the
facility with which the arm may be moved to any required position makes
it easier to move the arm to the work, so that the latter will require
but one chucking or setting.
Radial drilling machines are of various constructions. In some the
drilling head is carried by an arm standing at a right angle to the main
column or frame, and is capable of being moved to any required position
upon the length of this arm. The arm itself is sometimes made capable of
swinging upon its own axis, as shown in Fig. 1682.
It is also capable of being adjusted at any height from the bed or base
plate upon which the upright or main frame sits, or above the work table
when one is used as in the figure.
The advantage given by these facilities is that a heavy piece of work
may be set upon the base plate or work table, and be drilled in various
places without requiring to be moved.
Figs. 1681 and 1682 represent a radial drilling machine, in which the
radial arm is carried on a head, which fits a vertical slideway provided
on the face of the upright column, and may be moved to any required
height on this slideway by means of a rack and worm gear, the latter
being shown in the front view.
The seat of the arm on this head is cylindrical, the head being pivoted
upon it in order that it may permit of its being rotated to hold the
drill at an angle. The drill spindle is carried in a head sliding on the
radial arm as already stated, and is driven as follows:--
Motion from the shop driving shaft is communicated by belt to the cone
pulley shown at the base of the upright column.
The spindle of this cone pulley drives a belt which passes up the column
over an idle pulley on the sliding head that carries the radial arm;
hence it passes along the front of the radial arm and partly round a
pulley on the drill spindle, two idle pulleys holding it in contact with
the drill spindle pulley. Hence it passes over a small pulley at the
outer end of the radial arm, and returns along that arm through the
sliding head, over an idle pulley to the pulley seen at the head of the
vertical column, and from this pulley it passes to the pulley that is on
the cone spindle shaft at the base of the column. The drill is provided
with an automatic feed actuated by the worm shown on the drill spindle.
In Figs. 1683, 1684, and 1685 is represented a combined drilling and
boring machine.
It is provided with an horizontal as well as with a vertical spindle,
either of which may be used for boring as well as for drilling. In the
case of the vertical spindle the boring bar may extend down and have
journal bearing in a block, or bearing secured to the base plate I.
Each spindle has eight changes of speed, four in single, and four in
double gear, that is when the back gears at _a_ are in operation.
Motion from the pulley K on the cone spindle is conveyed by belt B to
pulley L, whose hub extends through the frame at R and affords journal
bearing to that end of spindle S which has a feed motion at H. Motion is
conveyed from the cone spindle to vertical spindle _m_ as follows:--
[Illustration: Fig. 1685.]
Referring to Fig. 1685, bevel-wheel _f_ is on the end of the cone
spindle and drives bevel-wheel _g_, which drives spindle _m_. This
spindle is provided with an automatic as well as a hand-feed motion, the
construction being as follows:--
Referring first to the automatic feed, the cone pulley E´, Fig. 1685,
which is upon the main cone spindle of the machine, drives cone E, Fig.
1683, and the latter operates a worm W, Fig. 1684, engaging a worm-wheel
W, which drives the bevel gear _a_, shown by dotted circles in Fig.
1685; _a_ drives the bevel gear _c_ upon the sleeve _o_, which has
journal bearing (in the frame A of the machine) both at its upper end
and immediately above C. The upper end of the sleeve _o_ is threaded to
receive an inner sleeve _n_, within which is a spindle _v_, having
journal bearing at each end of _n_ and being fast to _m_, so as to
revolve with it. End motion to _n_ is prevented by a collar at its upper
end _r_ and by three steel washers at _i_, the latter taking the thread
when the drill spindle _m_ is in operation. The inner sleeve _n_ is
prevented from revolving by means of a lug or projection which passes
into a slot or groove running vertically in the bore of the outer casing
A; hence when _o_ is revolved by _a_ it acts as a nut to _n_, causing
the latter to move endways and feed the drill spindle _m_.
To enable the engagement or disengagement of the automatic feed, there
is at F, Fig. 1684, a friction disk, the female half of which is fast
upon the spindle that drives bevel gear _a_ in Fig. 1685, while the male
half is in one piece with the hand wheel Z, Fig. 1684, which has journal
bearing upon the spindle of _a_. G is a hand nut for engaging or
disengaging the friction disks. In addition to the ordinary work table
T, the knee U carries on a projection X a work-holding vice V, which is
a great convenience, especially for cylindrical work. The base of the
machine is provided with a plate upon which work may be secured
independent of the work table T, or the lower end of a boring bar may be
steadied by a step bolted to the base plate.
The construction of the machine, as will be seen, is very substantial
throughout, since all the strains are central, the spindles are well
supported, and there is a commendable absence of springs, pull-pins, and
other light parts that are liable to get out of order from the wear and
tear of the ordinary machine-shop tool. It may also be remarked that the
combination of the two spindles is effected without impairing either the
usefulness or handiness of the vertical spindle.
[Illustration: Fig. 1686.]
In Fig. 1686, which is taken from _Mechanics_, is illustrated a combined
drilling and turning machine. In this machine the motion for both
drilling and turning is received by belt on the cone pulley shown on the
right, which is provided with back gear similar to that of a lathe. The
live spindle thus driven has a face plate at the left-hand end, whereon
work may be chucked to be operated upon by a tool in the compound slide
rest shown on the cylindrical column. Motion to the drill spindle is
conveyed by belt from a pulley on this same live spindle, hence the same
cone pulley and back gear are utilized for either drilling or turning.
The self-acting feed for the drill spindle is actuated by an eccentric
on that spindle operating an arm, having a pawl engaging with the
ratchet wheel on the lower end of the vertical feed spindle. Obviously
when the pawl is thrown out of engagement with the ratchet wheel, the
horizontal hand wheel may be used to feed the drill spindle by hand or
to withdraw it, as the case may be.
The work table for drilling operations has motion laterally in two
directions (one at a right angle to the other) by means of being carried
on slides, and is fitted to a vertical slide on the face of the column
so that it may be raised and lowered to suit the height of the work by
means of the worm and worm-wheel shown, the latter being on the same
shaft as a pinion engaging with a vertical rack on the face of the
upright frame or column.
In Fig. 1687 is represented a horizontal drilling and boring machine. In
this machine the work-holding table is provided with a hand feed, and
the drilling or boring spindle with hand and self-acting feed, the
latter being variable to suit different kinds of work. The table has a
compound motion upon suitable slideways and rests upon a frame or knee
that is elevated by two vertical screws that are operated by hand wheel.
This knee fits to a vertical slideway on the main frame, so that its
upper face, and therefore the face also of the work table, is maintained
parallel with the drill spindle at whatever height it may be set from
it.
The arbor that carries the drill spindle is arranged with a face plate
so that the machine can be used as a facing lathe. The feeds are
arranged in two separate series, a fine and a coarse, and both of these
series are applicable to any speed or any size of drill. The value of
the coarse feed will be felt in all kinds of boring with bars and
cutters, inasmuch as it is possible to rough out with a fine feed and
finish with a light cut and a very coarse feed.
For work that is too large to be conveniently lifted to the table of a
machine the floor boring machine is employed.
Fig. 1688 represents a machine of this class, which consists of two
heads that may be moved about upon, and secured to, any part of its base
or bed plate to which the work is secured. The boring bar it will be
seen stands horizontal, and may be set at any height from the base plate
between the limits of 14 inches and 6 feet 4 inches, the driving head
being raised on its slideway on the face of its standard or column by
automatic mechanism. The feed is automatic and variable in amount to
suit the nature of the duty.
The bar has eight speeds, four in single and four in double gear.
In order to insure that the crank pins of locomotive driving wheels
shall stand with their axes parallel to that of the wheel shaft, and
that they shall also stand 90° apart when measured on the wheel circle,
it is necessary that the holes for these pins be bored after the wheels
are upon their shaft, it being found that if the crank pin holes are
bored before the wheels are upon the shaft they are liable to be out of
parallel and out of quarter.
[Illustration: Fig. 1690.]
To avoid these errors a quartering machine is employed, such as shown in
Fig. 1689. This machine consists of two heads carrying stationary or
dead centres to hold the wheel axle, as in a lathe. Each of these heads
is provided with a boring bar having an automatic and adjustable feed,
the axes of these bars being 90°, or one quarter of a circle, apart.
As both crank pin holes are bored simultaneously and with the wheel
rigidly fixed and held upon centres the work will obviously be true.
This machine may also be used as an ordinary horizontal boring machine.
[Illustration: Fig. 1691.]
Multiple drilling machines are employed for two general purposes: first,
those in which a number of holes may be advantageously drilled
simultaneously; and second, where a number of operations require to be
performed upon one and the same hole. When the object is to drill a
number of holes spaced a certain distance apart in one piece of work,
the spindles may be so constructed that their distances one from the
other may be adjustable, so that they may be set to drill the holes
equally or unequally spaced as may be required.
In such machines it will be more convenient to feed the work to the
drill, so as to have but one feed motion, instead of having a separate
feed motion to each drill spindle. When, however, a number of separate
operations are to be performed upon the same hole, it is preferable to
rotate the table so that the work may be carried from one spindle to the
other, the spindles feeding automatically and simultaneously.
Fig. 1690 represents a three-spindle drilling machine. The main driving
spindle is vertical and within the top of the column, having three
pulleys to connect by belt to the vertical drill driving spindles, whose
driving pulleys are of different diameters to vary the speed to suit
different diameters of drilling tools. A foot feed is provided by means
of the treadle, and a hand feed by means of the lever, the weight of the
work table being balanced by means of the ball weight shown. The work
table is adjustable for height in a main table, that is adjustable for
height on the face of the column. Similar machines are made with four or
more spindles.
Fig. 1691 represents a four-spindle machine, in which each spindle has a
separate and independent feed, which may be operated in unison or
separately as may be required.
[Illustration: _VOL. I._ =EXAMPLES IN BORING MACHINERY.= _PLATE XXI._
Fig. 1687.
Fig. 1688.
Fig. 1689.]
The four spindles are driven by means of a gear-wheel engaging with a
gear on the central or main driving spindle. The work-holding table
rotates about the column of the machine, and is arranged with a stop
motion that locks the table in position when the work-holding chucks are
exactly in line with the drill spindles. Suppose, then, one spindle to
drive a drill, the second driving an enlarging drill, a third driving a
countersink, and a fourth a reamer. A piece of work may then be fastened
beneath the first spindle and be drilled. The table may then be rotated
one-fourth of a revolution, bringing it beneath the enlarging drill,
while a second piece of work is placed beneath the first or piercing
drill. The table may then be given another quarter rotation, bringing
the piece of work first put in beneath the countersink, the second
beneath the enlarging drill, while a third piece may be placed beneath
the first or piercing drill. The table being again given one-quarter
rotation the first piece will be brought beneath the reamer, the second
beneath the countersink, the third beneath the enlarging drill,
and a fourth may be placed beneath the piercing drill; all that will
then be necessary is to remove the first piece when it arrives at the
piercing drill and insert a new piece; the four spindles operating
simultaneously, and the process continuing, the four operations proceed
together.
Thus the piece of work is finished without being released from the
holding devices, which insures truth while requiring a minimum of
attendance. The amount of feed being equal for all four spindles the
depth to which each tool will operate is gauged by the distance it
stands down from the feeding head, each spindle being capable of
independent adjustment in this respect, so that the tool requiring to
move the farthest through the work will meet it the first, and so on.
[Illustration: Fig. 1692.]
Figs. 1692 and 1693 represent a combined drilling and turning machine
for boiler-maker's use. The machine consists of two uprights or drill
standards which can be traversed along horizontal slides on beds which
are fixed at right angles one to the other. The work to be drilled is
carried on a turntable or work-holding table, the pivot and carrying
frame of which can be traversed along a third set of guides lying
between the other two and forming an angle of 45° with either of them.
Thus, by adjusting the relative positions of the turntable and the drill
standards (each of which carries two drills), either a large or a small
boiler can be conveniently operated on. Worm-gear is provided for
revolving the turntable, either to divide the pitch of the holes, or
when the machine is used for turning the edges of flanged plates, or for
boring the large holes for flue tubes. Longitudinal seams may be drilled
by laying the boiler horizontally on chucks alongside one of the beds,
and traversing the drill standard from hole to hole.
Referring especially to Fig. 1693, A^{1} and A^{2} are the two wings of
the bed plate, each being provided with [V]-slides to carry the uprights
or standards B^{1}, B^{2}, on each of which is a drilling head C^{1},
C^{2}, these being each adjustable vertically on its respective standard
by means of rack and pinion and hand wheels D^{1} and D^{2}. The heads
are balanced so that the least possible exertion is sufficient to adjust
them. The vertical standards B^{1} and B^{2} are provided at their bases
with a gear wheel operated by means of pinions at G^{1}, G^{2}, so that
they may be rotated upon the sliders E^{1} and E^{2}, by means of which
they may be traversed along their respective bed slides. The drilling
heads are composed of a slider on a vertical slide on the face of the
vertical standard or upright, rotary motion and the feed being operated
as follows: Power is applied to the machine through the cones K^{1} and
K^{2}, working the horizontal and vertical shafts L^{1} and L^{2}, &c.
On the vertical shafts are fitted coarse pitch worms sliding on feather
keys, and carried with the heads C^{1} and C^{2}, &c. The worms gearing
with the worm-wheels M^{1} and M^{2} are fitted on the sleeves of the
steel spindles N^{1} and N^{2}. The spindles are fitted with self-acting
motions O^{1} and O^{2}, which are easily thrown in and out of gear.
The shell to be drilled is placed upon the circular table H, which is
carried by suitable framework adjustable by means of screw on the
[V]-slide I, placed at an angle of 45° with the horizontal bed plates.
By this arrangement, when the table is moved along I it will approach to
or recede from all the drills equally. J^{1} and J^{2} are girders
forming additional bearings for the framework of the table. The bed
plates and slides for the table are bolted and braced together, making
the whole machine very firm and rigid.
The machine is also used for turning the edge of the flanges which some
makers prefer to have on the end plates of marine boilers. The plates
are very readily fixed to the circular table H, and the edge of the
flange trued up much quicker than by the ordinary means of chipping.
When the machine is used for this purpose, the cross beam P, which is
removable, is fastened to the two upright brackets R^{1} and R^{2}. The
cross beam is cast with [V]-slides at one side for a little more than
half its length from one end, and on the opposite side for the same
length, but from the opposite end. The [V]-slides are each fitted with a
tool box S^{1} and S^{2}, having a screw adjustment for setting the tool
to the depth of cut, and adjustable on the [V]-slides of the cross beam
to the diameter of the plate to be turned. This arrangement of the
machine is also used for cutting out the furnace mouths in the boiler
ends. The plate is fastened to the circular table, the centre of the
hole to be cut out being placed over the centre of table; one or both of
the tool boxes may be used. There is sufficient space between the
upright brackets R^{1} and R^{2} to allow that section of a boiler end
which contains the furnace mouths to revolve while the holes are being
cut out; the plate belonging to the end of a boiler of the largest
diameter that the machine will take in for drilling. The holes cut out
will be from 2 ft. 3 in. diameter and upwards. Power for using the
turntable is applied through the cone T. The bevel-wheels, worms,
worm-wheels and pinions for driving the tables are of cast steel, which
is necessary for the rough work of turning the flanges.
[Illustration: Fig. 1693.]
As to the practical results of using the machine, the drills are driven
at a speed of 34 feet per minute at the cutting edges. A jet of soapsuds
plays on each drill from an orifice 1/32 in. in diameter, and at a
pressure of 60 lbs. per square inch. A joint composed of two 1-inch
plates, and having holes 1-1/8 in. in diameter, can be drilled in about
2-1/2 minutes, and allowing about half a minute for adjusting the drill,
each drill will do about 20 holes per hour. The machine is designed to
stand any amount of work that the drills will bear. The time required
for putting on the end of a boiler and turning the flange thereon (say,
14 ft. diameter), is about 2-1/2 hours; much, however, depends on the
state of the flanges, as sometimes they are very rough, while at others
very little is necessary to true them up. The time required for putting
on the plate containing the furnace mouths and cutting out three holes 2
ft. 6 in. in diameter, the plate being 1-1/8 inches thick, is three
hours. Of course, if several boilers of one size are being made at the
same time, the holes in two or more of these plates can be cut out at
once. The machine is of such design that it can be placed with one of
the horizontal bed plates (say A^{1}) parallel and close up to a wall of
the boiler shop; and when the turning apparatus is being used, the
vertical arm B^{2} can be swivelled half way round on its square box
E^{2}, and used for drilling and tapping the stay holes in marine boiler
ends after they are put together; of course sufficient room must be left
between bed plate A^{2} and the wall of boiler shop parallel with it, to
allow for reception of the boiler to be operated upon.
[Illustration: _VOL. I._ =BOILER-DRILLING MACHINERY.= _PLATE XXII._
Fig. 1694.
Fig. 1695.]
[Illustration: Fig. 1696.--CAR-WHEEL BORING MACHINE.]
[Illustration: Fig. 1697.--PULLEY-BORING MACHINE.]
[Illustration: Fig. 1698.--COMBINED DRILLING AND COTTER-DRILLING
MACHINE.]
In Figs. 1694 and 1695 is represented a machine which is constructed for
the drilling of shells of steam boilers, to effect which the boiler is
set upon a table, round which are placed four standards, each carrying a
drilling head, so that four holes may be drilled simultaneously, and is
provided with a dividing motion that enables the table to be revolved a
certain distance, corresponding to and determining the pitch of the
rivet holes.
It is capable of drilling locker shells of any diameter between four and
eight feet. The feed motion to each drill is driven from one source of
power, but each drill is adjustable on its own account. The depth of
feed is regulated by a patent detent lever which engages with the teeth
of a ratchet wheel, till released therefrom by contact with the
adjustable stop. The drill spindle is then instantly forced back by the
spiral spring and the forward feed motion continues.
It is the duty of the attendant to turn his dividing apparatus handle
the required distance for the next hole, directly the drills are
withdrawn, the amount of clearance between the drill point and the
boiler shell being such as to give him proper time for this purpose, but
no more. Self-acting water jets to the drills, and reflectors to enable
the operator to see each drill, will be provided, but were not in action
at the time views of the machine were made.
With an ordinary boiler shell formed in three plates, the three drills
work simultaneously, and the one movement of the dividing apparatus, of
course, applies to all. If the object to be drilled be not divisible
into multiples of three, any other divisions can be produced by the
dividing gear, either one, two, or three drills being used, as the
circumstances may permit. Two heads can be shifted round from the angle
of 120°, at which they are shown, to positions diametrically opposite,
as may be desired, and the third can be used or disused as wished.
Vertical gauge rods are provided, duly marked out to the various pitches
that may be needed for the vertical rows of holes, and the movement of
the drill spindle saddles is so simple and steady that accurate
adjustment can be made without the least difficulty. In the same way
when the drill would, in its natural course, come in contact with one of
the bolts by which the plates are held together, the attendant can run
all the drills downwards a couple of inches or so, then turn the
dividing apparatus two pitches instead of one, and on raising the three
drills again he can continue the circular row as before. The entire
control of the machine is governed by the attention of one man to two
levers and the one dividing handle, which are all conveniently placed
for the purpose.
In Fig. 1696 is represented a machine for boring car wheels. The chuck
is driven by a crown gear operated beneath by a pinion on the cone
spindle. The feed motion for the boring bar is operated from the small
cone shown on the cone spindle, there being three rates of automatic
feed, which are communicated to the bar by a worm and worm-wheel
operating a spindle carrying a pinion in gear with a rack on the back of
a boring bar.
The worm-wheel is provided with a friction disk operated by the small
hand-wheel shown, to start and stop the automatic feed, the large
hand-wheel operating the rack spindle direct, and therefore giving a
rapid hand-feed or quick return motion for the boring bar. The boring
bar is counterbalanced by a weight within the frame. On the side of the
frame is a small crane for handing the car wheels.
Fig. 1697 represents a special machine for boring pulleys, &c. The
advantage possessed by this class of machine is fully set forth in the
remarks upon Boring and Turning Mills, and with reference to Fig. 725.
The tool bar is fed vertically to the rotating pulley, and has three
changes of feed; viz. .0648, .0441, and .0279 of an inch per rotation of
the work. Its weight is counterbalanced.
The speed of rotation of the work table or chuck plate may, by means of
the four steps on the cone pulley, be varied as follows:--63, 43, 19, or
10 revolutions per minute, which speeds are suitable for work bores
ranging from 1 to 7-1/2 inches in diameter, the power exerted at the
tool-point being for the latter diameter 1800 lbs.
The tool bar feed is operated by the upper cone pulley, and the worm and
worm-wheel shown, the small wheel giving the automatic feed by a
suitable friction plate, and the large hand wheel operating the bar
quickly to elevate it after it has carried its cut through. When the
drill is given a traverse back and forth, it obviously cuts out a slot
or keyway whose width is equal to the diameter of the drill, and whose
length equals the amount of traverse given to the drill. Special forms
of drill are used for this purpose, and their forms will be shown
hereafter. The machines for using these drills are termed traverse or
cotter drilling machines. In Fig. 1698 is represented a combined
drilling and cotter drilling machine. This machine consists essentially
of a drilling machine provided with automatic feed motions for cotter
drilling; these motions consisting of a self-acting traverse to the
sliding head carrying the drill spindle, and a vertical feed, which
occurs at the end of each traverse, and during a short period of rest
given to the sliding head carriage, or saddle as it is promiscuously
termed. The slideway for this head stands vertical and extends across
the top of the frame.
The belt motion is conveyed up one end and then on the top of the
slideway, driving the spindle direct by means of a pulley. The traverse
of the head or saddle in cotter drilling is accomplished by means of a
peculiar arrangement of screws and adjustable nuts, which can be
instantly set to the required length of slot, and insures a uniform
motion, back and forth, at each stroke, the length of the stroke being
uniform, as is also the rate of its advance. The vertical position of
the drill spindle is of great advantage in cotter drilling wrought iron
or steel, as the slot in process of cutting can be kept full of oil.
The feed motions for cotter drilling may be instantly thrown out of gear
when not required, remaining at rest and leaving the machine a simple
traverse drill with automatic feeds.
CHAPTER XIX.--DRILLS AND CUTTERS FOR DRILLING MACHINES.
DRILLING JIGS, GUIDES, OR FIXTURES.--When a large number of pieces are
to be drilled alike, as in the case when work is done to special gauges,
special chucking devices called jigs, or fixtures, are employed to guide
the drill, and insure that the holes shall be pierced accurately in the
required location, and test pieces or gauges are provided to test the
work from time to time to insure that errors have not arisen by reason
of the wear of these drill-guiding devices.
[Illustration: Fig. 1699.]
[Illustration: Fig. 1700.]
Suppose, for example, that we have a link, such as in Fig. 1699, and
that we require to have the holes throughout a large number of them of
equal diameter at each end and the same distance apart, and if we could
prevent the wear of the tools, and so continue to produce any number of
links all exactly alike, we could provide a simple test gauge, such as
shown in the figure, making it pass the proper distance apart, and of a
diameter to fit the holes; but as we cannot prevent wear to the tools we
must fix a limit to which such wear may be permitted to occur, and
having reached that point they must be restored and corrected. We must
at the same time possess means of testing in what direction the wear has
induced error. Let it be assumed that the bore at A should be 1/2 inch
and that at B 3/8 inch in diameter, that their distance from centre is
to be, say, six inches, and that either bore may vary in diameter to the
amount of 1/1000 inch, while the distance from centre to centre of the
bores may also vary 1/1000 inch. Now let it be noted that if one piece
be made 1/2000 inch too short, and another 1/2000 inch too long we have
reached the extent of the limit, there being 1/1000 inch difference
between them, although neither piece varies more than 1/2000 inch from
the standard. Similarly in the bore diameters, if the bore, say at A, is
1/2000 inch too large in one piece and 1/2000 too small in another,
there is a difference of 1/1000 between them, although each varies only
the 1/2000 inch from the standard. In making test gauges for the holes,
therefore, we must consider in what direction the tool will wear; thus,
suppose that the finishing reamer for the holes is made when new to the
standard diameter, and it can only wear smaller, hence a plug gauge of
the standard diameter and 1/1000 inch smaller would serve thus, as so
long as the smaller one will go in the limit of wear is not reached;
when it will not go in sufficiently easily the reamer must be restored
to fit the standard gauge. On the other hand, the reamer when new may be
made 1/1000 inch above the standard size and restored when it has worn
down to the standard size. In this case the bore diameter is still
within the limit as long as the small gauge will enter; but when it fits
too tight the reamer must be restored to the large plug gauge, the forms
of these gauges being shown in Fig. 1700.
[Illustration: Fig. 1701.]
[Illustration: Fig. 1702.]
In Figs. 1701 and 1702 we have a jig or fixture for holding the link
during the drilling process. It consists of two parts, C and D, between
which the link is held by the screws E and F. The two hubs, G and H, are
provided with hardened steel bushes, I and J, which are pierced with
holes to receive and guide the drilling tool or reamer, and it is
evident that in time the bore of these bushes will wear, and if they
wear on one side more than on another they may wear longer or shorter
between the centres or axis; hence we require gauges such as shown in
Fig. 1703, one being longer between centres and the other shorter, in
each case to the amount of the prescribed limit. In this case, so long
as the holes are kept within the prescribed limit of diameter, the
distance apart of the two holes will be within the limit so long as
neither of the limit gauges will enter; and when they will enter the
bushes I J must be restored.
It is to be remarked, however, that the variation in the diameter of the
holes affects these standards, since if the holes are made sufficiently
large either gauge would enter, although the axis of the holes and of
the pins on the gauge might be the proper distance apart; hence the
gauging for length depends to some degree upon the degree of accuracy in
gauging for diameter.
[Illustration: Fig. 1703.]
Referring now to the construction of the jig, or fixture for drilling
the link shown in Figs. 1701 and 1702: the base piece is provided with
two short hubs, R and S, upon which the link is to sit, and it is
obvious that these hubs must be faced off true with the bottom face of
the base, while the link must also be faced so that it will be level,
and not be bent or sprung when clamped by the screws E F. It is obvious
that the hubs R and S may be omitted, and the link be flat on the base
plate; but this would not be apt to hold the link so steadily, and
greater care would be required to keep the surface clean. It is also
obvious that in the form of jig shown there is a tendency of the screws
E and F to bend the piece D; but in the case of small pieces, as, say,
not exceeding 8 inches long, piece D may be made strong enough to resist
the screw pressure without bending. If, however, the link were, say, 18
inches long, it would be preferable to have projections in place of the
hubs R, S, and to let these projections extend some distance along each
end of the link, using four holding screws, and clamping the piece D on
the inside of the hubs H G. To facilitate the rapid insertion and
removal of the link into and from the jig cap-piece, D is pivoted on
screw F, while a slot V is cut at the other end, so that when the two
screws E, F are loosened, the cap-piece D may be swung out of the way
without entirely removing it.
[Illustration: Fig. 1704.]
[Illustration: Fig. 1705.]
[Illustration: Fig. 1706.]
[Illustration: Fig. 1707.]
In Fig. 1704 we have a link in which a hole is to be bored at one end at
a certain distance from a pin at the other, and the fixture, or jig for
drilling, is shown in the sectional view, Fig. 1705, the side view, Fig.
1706, and the top view, Fig. 1707. It is obvious that the pin P and the
face W of the link must be made true, and that a hardened steel bush may
be placed in the hub to receive the pin P. The screw E binds one end of
the cap D, and eye-bolts with thumb-nuts F bind the other, these bolts
being pivoted at their lower ends, and passing through slots in D, so
that as soon as nuts F are loosened, their bolts may be swung out clear
of the cap, which may be swung on one side from the pin N as a pivot.
[Illustration: Fig. 1708.]
[Illustration: Fig. 1709.]
In Fig. 1708 we have a piece containing three holes, which are to be
drilled in a certain position with regard to each other, and with regard
to the face A. This brings us to the consideration that in all cases the
work must be chucked or held true by the faces to which it is necessary
that the holes must be true, and as in this case it is the face A, the
jig must be made to hold the piece true by A, the construction being as
in Fig. 1709, which represents a top view, and a sectional side view.
The upper plate D carries three hardened steel bushes, A, B, and C, to
receive the drilling tools, and thus determine that the holes shall be
drilled at their proper positions with relation to each other, and is
provided with a face N, against which the face (A, Fig. 1708) may be
secured by the screw H, and thus determine the positions of the holes
with, regard to that face. At E, F, and G are eye-bolts for clamping the
work between the cap and the base plate, which is made large so that it
may lie steadily on the table of the drilling machine. When the nuts E,
F, and G and the screw H are loosened the cap D may be lifted off and
the work removed.
If the holes are required to be made very exact in their positions with
relation to one edge, as well as to the face A of the work, two screws K
would be required, one binding the cap against the lug M of the base,
and the other binding the edge of the work against the same lug.
The usefulness of jigs, or fixtures, is mainly confined to small work in
which a great many duplicate pieces are to be made, and their designing
calls for a great deal of close study and ingenuity. They can obviously
be applied to all kinds of small work, and as a general principle the
holes and pins of the work are taken as the prime points from which the
work is to be held.
Drilling fixtures may, however, be applied with great advantage to work
of considerable size in cases where a number of duplicate parts are to
be made, an example of this kind being given in the fixtures for
drilling the bolt holes, &c., in locomotive cylinders.
[Illustration: Fig. 1710.]
For drilling the cylinder covers and the tapping holes in the cylinder,
the following device or fixture is employed: The flanges of the cylinder
covers are turned all of one diameter, and a ring is made, the inside
diameter of which is, say, an inch smaller than the bore of the
cylinder; and its outside diameter is, say, an inch larger than the
diameter of the cover. On the outside of the ring is a projecting flange
which fits on the cover, as in Fig. 1710, _a_ being the cylinder cover,
and _b_ _b_ a section of the ring, which is provided with holes, the
positions in the ring of which correspond with the required positions of
the holes in the cover and cylinder; the diameter of these holes (in the
ring, or template, as it is termed) is at least one quarter inch larger
than the clearing holes in the cylinder are required to be. Into the
holes of the template are fitted two bushes, one having in its centre a
hole of the size necessary for the tapping drill, the other a hole the
size of the clearing drill; both these bushes are provided with a handle
by which to lift them in and out of the template, as shown in Fig. 1711,
and both are hardened to prevent the drill cutting them, or the borings
of the drill from gradually wearing their holes larger. The operation is
to place the cover on the cylinder and the template upon the cover, and
to clamp them together, taking care that both cover and template are in
their proper positions, the latter having a flat place or deep line
across a segment of its circumference, which is placed in line with the
part cut away on the inside of the cover to give free ingress to the
steam, and the cover being placed in the cylinder so that the part so
cut away will be opposite to the port in the cylinder, by which means
the holes in the covers will all stand in the same relative position to
any definite part of the cylinder, as, say, to the top or bottom, or to
the steam port, which is sometimes of great importance (so as to enable
the wrench to be applied to some particular nut, and prevent the latter
from coming into contact with a projecting part of the frame or other
obstacle): the positions of the cylinder, cover, template, and bush,
when placed as described, being such as shown in Fig. 1712, _a_ _a_
being the cylinder, B the steam port, C the cylinder cover, D the
template, and E the bush placed in position. The bush E having a hole in
it of the size of the clearance hole, is the one first used, the drill
(the clearance size) is passed through the bush, which guides it while
it drills through the cover, and the point cuts a countersink in the
cylinder face. The clearing holes are drilled all round the cover, and
the bush, having the tapping size hole in it, is then brought into
requisition, the tapping drill being placed in the drilling machine, and
the tapping holes drilled in the cylinder flange, the bush serving as a
guide to the drill, as shown in Fig. 1712, thus causing the holes in the
cover and those in the cylinder to be quite true with each other. A
similar template and bush is provided for drilling the holes in the
steam chest face on the cylinder, and in the steam chest itself. While,
however, the cylinder is in position to have the holes for the steam
chest studs drilled, the cylinder ports may be cut as follows:--
[Illustration: Fig. 1711.]
[Illustration: Fig. 1712.]
[Illustration: Fig. 1713.]
The holes in the steam chest face of the cylinder being drilled and
tapped, a false face or plate is bolted thereon, which plate is provided
with false ports or slots, about three-eighths of an inch wider and
three-fourths of an inch longer than the finished width and length of
the steam ports in the cylinder (which excess in width and length is to
allow for the thickness of the die). Into these false ports or slots is
fitted a die to slide (a good fit) from end to end of the slots. Through
this die is a hole, the diameter of which is that of the required
finished width of the steam ports of the cylinder; the whole appliance,
when in position to commence the operation of cutting out the cylinder
ports, being as illustrated in Fig. 1713, _a_ _a_ being the cylinder, B
B the false plate, C the sliding die, and D D the slots or false ports
into which the die C fits. Into the hole of the die C is fitted a
reamer, with cutting edges on its end face and running about an inch up
its sides, terminating in the plain round parallel body of the reamer,
whose length is rather more than the depth of the die C. The operation
is to place the reamer into the drilling machine, taking care that it
runs true. Place the die in one end of the port, as shown in Fig. 1713,
and then wind the reamer down through the die so that it will cut its
way through the port of the cylinder at one end; the spindle driving the
drill is then wound along. The reamer thus carries the die with it, the
slot in the false face acting as a guide to the die.
In the case of the exhaust port, only one side is cut out at a time. It
is obvious that, in order to perform the above operation, the drilling
machine must either have a sliding head or a sliding table, the sliding
head being preferable.
[Illustration: Fig. 1714.]
The end of the slot at which the die must be placed when the reamer is
wound down through the die and cylinder port, that is to say, the end of
the port at which the operation of cutting it must be commenced, depends
solely on which side of the port in the cylinder requires most metal to
be cut off, since the reamer, or cutter, as it may be more properly
termed, must cut underneath the heaviest cut, so that the heaviest cut
will be forcing the reamer back, as shown in Fig. 1714, _a_ being a
sectional view of the cutter, B the hole cast in the cylinder for the
port, _c_ the side of the port having the most cut taken off, D the
direction in which the cutter _a_ revolves, and the arrow E the
direction in which the cutter _a_ is travelling up to its cut. If the
side F of the port were the one requiring the most to be cut off, the
cutter _a_ would require to commence at the end F, and to then travel in
the direction of the arrow G. The reason for the necessity of observing
these conditions, as to the depth of cut and direction of cutter travel,
is that the pressure of the cut upon the reamer is in a direction to
force the reamer forward and into its cut on one side, and backward and
away from its cut on the other side, the side having the most cut
exerting the most pressure. If, therefore, the cutter is fed in such a
direction that this pressure is the one tending to force the cutter
forward, the cutter will spring forward a trifle, the teeth of the
cutter taking, in consequence, a deep cut, and, springing more as the
cut deepens, terminate in a pressure which breaks the teeth out of the
cutter.
If, however, the side exerting the most pressure upon the reamer is
always made the one forcing the cutter back, as shown in Fig. 1714, by
reason of the direction in which the cutter is travelled to its cut, the
reamer, in springing away from the undue pressure, will also spring away
from its cut, and will not, therefore, rip in or break, as in the former
case.
[Illustration: Fig. 1715.]
In cutting out the exhaust port, only one side, in consequence of its
extreme width, may be cut at one operation; hence there are two of the
slots D, Fig. 1713, provided in the false plate or template for the
exhaust port. The cutter _a_ must, in this case, perform its cut so that
the pressure of the cut is in a direction to force the cutter backwards
from its cut. The time required to cut out the ports of an ordinary
locomotive cylinder, by the above appliance, is thirty minutes, the
operation making them as true, parallel, and square as can possibly be
desired.
DRILLS AND CUTTERS FOR DRILLING MACHINES.--In the drilling machine, as
in the lathe, the twist drill is the best tool that can be used for all
ordinary work, since it produces the best work with the least skill, and
is the cheapest in the end. As, however, the twist drill has been fully
discussed with reference to its use upon lathe work, it is unnecessary
to refer to it again more than to say that it possesses even greater
advantages when used in the drilling machine than it does when used in
the lathe; because as the drill stands vertical the flat drill will not
relieve itself of the cuttings, and in deep holes must be occasionally
withdrawn from the hole in order to permit the cuttings to be extracted,
an operation that often consumes more time than is required for the
cutting duty. Furthermore, as flat drills rarely run true they place
excessive wear upon the drilling machine spindle, causing it to wear
loose in its bearings, which is a great detriment to the machine.
Fig. 1715 represents a piece of work that can be readily drilled with a
twist drill but not with a flat one, such work being very advantageous
in cutting out keyways. All that is necessary is to drill the three
holes B first, and if the drill runs true and the work is properly held
and the drill fed slowly while run at a quick speed the operation may be
readily performed.
The speeds and feeds for twist drills are given in connection with the
use of the drill in the lathe, but it may be remarked here that more
duty may be obtained by hand than by automatically feeding a drill,
because in hand feeding the resistance of the feed motion indicates the
amount of pressure on the drill, and the feed may be increased when the
conditions (such as soft metal) permits, and reduced for hard spots or
places, thus preserving the drill. Furthermore, the dulling of the drill
edges becomes more plainly perceptible under hand feeding.
The commercial sizes of both taper and straight shank twist drills are
as follows:--
--------+-------++-------+-------++-------+-------++--------+-------
Dia- |Length.|| Dia- |Length.|| Dia- |Length.|| Dia- |Length.
meter. | ||meter. | ||meter. | ||meter. |
--------+-------++-------+-------++-------+-------++--------+-------
1/4 | 6-1/8 || 25/32| 9-7/8 ||1-5/16 |14-1/4 ||1-27/32 |16-3/8
9/32 | 6-1/4 || 13/16|10 ||1-11/32|14-3/8 ||1-7/8 |16-1/2
5/16 | 6-3/8 || 27/32|10-1/4 ||1-3/8 |14-1/2 ||1-29/32 |16-1/2
11/32 | 6-1/2 || 7/8 |10-1/2 ||1-13/32|14-5/8 ||1-15/32 |16-1/2
3/8 | 6-3/4 || 29/32|10-5/8 ||1-7/16 |14-3/4 ||1-31/32 |16-1/2
13/32 | 7 || 15/16|10-3/4 ||1-15/32|14-7/8 ||2 |16-1/2
7/16 | 7-1/4 || 31/32|10-7/8 ||1-1/2 |15 ||2-1/32 |16-1/2
15/32 | 7-1/2 ||1 |11 ||1-17/32|15-1/8 ||2-1/16 |17
1/2 | 7-3/4 ||1-1/32 |11-1/8 ||1-9/16 |15-1/4 ||2-1/8 |17
17/32 | 8 ||1-1/16 |11-1/4 ||1-19/32|15-3/8 ||2-3/16 |17
9/16 | 8-1/4 ||1-3/32 |11-1/2 ||1-5/8 |15-1/2 ||2-1/4 |17-1/2
19/32 | 8-1/2 ||1-1/8 |11-3/4 ||1-21/32|15-5/8 ||2-5/16 |17-1/2
5/8 | 8-3/4 ||1-5/32 |11-7/8 ||1-11/16|15-3/4 ||2-3/8 |18
21/32 | 9 ||1-3/16 |12 ||1-23/32|15-7/8 ||2-7/16 |18-1/2
11/16 | 9-1/4 ||1-7/32 |12-1/8 ||1-3/4 |16 ||2-1/2 |19
23/32 | 9-1/2 ||1-1/4 |12-1/2 ||1-25/32|16-1/8 || |
3/4 | 9-3/4 ||1-9/32 |14-1/8 ||1-13/16|16-1/4 || |
--------+-------++-------+-------++-------+-------++--------+-------
Twist drills are also made to the Stubs wire gauge as follows:--
+-----------------+---------++-----------------+--------+
|Numbers by gauge.| Length. ||Numbers by gauge.| Length.|
+-----------------+---------++-----------------+--------+
| 1 to 5 | 4 || 31 to 35 | 2-5/8 |
| 6 " 10 | 3-11/16 || 36 " 40 | 2-7/16 |
| 11 " 15 | 3-1/2 || 41 " 45 | 2-1/4 |
| 16 " 20 | 3-1/4 || 46 " 50 | 2-1/16 |
| 21 " 25 | 3-1/16 || 51 " 60 | 1-3/4 |
| 26 " 30 | 2-13/16 || 61 " 70 | 1-1/2 |
+-----------------+---------++-----------------+--------+
[Illustration: Fig. 1716.]
Fig. 1716 represents the flat drill, which has three cutting edges, A,
B, and C. The only advantages possessed by the flat drill are that it
will stand rougher usage than the twist drill, and may be fed faster,
while it can be more easily made. Furthermore, when the work is
unusually hard the flat drill can be conveniently shaped and tempered to
suit the conditions.
The drill is flattened out and tapered thinnest at the point C. The side
edges that form the diameter of the drill are for rough work given
clearance, but for finer work are made nearly cylindrical, as in the
figure.
The flattening serves two purposes: first, it reduces the point of the
drill down to its proper thinness, enabling it to enter the metal of the
work easily, and secondly, it enables the cuttings to pass upward and
find egress at the top of the hole being drilled.
The cutting edges are formed by grinding the end facets at an angle as
shown, and this angle varies from 5° for drilling hard metal, such as
steel, to 20° for soft metal, such as brass or copper.
[Illustration: Fig. 1717.]
The angle of one cutting edge to the other varies from 45° for steel to
about 35° or 40° for soft metals. The object of these two variations of
angles is that in hard metal the strain and abrasion is greatest and the
cutting edge is stronger with the lesser degree of angle, while in
drilling the softer metals the strain being less the cutting edge need
not be so strong and the angles may be made more acute, which enables
the drill to enter the metal more easily. The most imperfect cutting
edge in a drill is that running diagonally across the point, as denoted
by A in Fig. 1717, because it is less acute than the other cutting
edges, but this becomes more acute and, therefore, more effective, as
the angles of the facets forming it are increased as denoted by the
dotted lines in the figure. It is obvious, however, that the more acute
these angles the weaker the cutting edge, hence an angle of about 5° is
that usually employed.
It is an advantage to make the cutting edge at A, Fig. 1717, as short as
possible, which may be done by keeping the drill point thin; but if too
thin it will be apt either to break or to operate in jumps (especially
upon brass), drilling a hole that is a polygon instead of a true circle.
The cutting edges should not only stand at an equal degree of angle to
the axial line of the drill, but should be of equal lengths, so that the
point of the drill will be in line with the axial line of the drill. If
the drill runs true the point will then be in the axial line of
rotation, and the diameter of hole drilled will be equal to the diameter
of the drill.
If, however, one cutting edge is longer than the other the hole drilled
will be larger than is due to the diameter of the drill.
[Illustration: Fig. 1718.]
Suppose, for example, the drill to be ground as in Fig. 1718, the
cutting edge F being the longest and at the least angle, then the point
G of the drill, when clear of the work, will naturally revolve in a
circle around the axial line H of the drill's rotation. But when the
drilling begins, the point of the drill meets the metal first and
naturally endeavours to become the centre of rotation, drilling a
straight conical recess, the work moving around with the point of the
drill. If the work is prevented from moving, either the drill will
spring or bend, the point of the drill remaining (at first) the centre
of rotation at that end of the drill, or else the recess cut by the
drill will be as in the figure, and the hole will be larger in diameter
than the drill.
[Illustration: Fig. 1719.]
[Illustration: Fig. 1720.]
If, however, the drill is ground as shown in Fig. 1719, the edge E being
nearest to a right angle to the axial line H of the drill, the drilling
will be performed as shown in the figure, the edge E cutting the cone L,
the edge F serving simply to enlarge the hole drilled by E. Here, again,
if the work is held so that it cannot move, the point of the drill will
revolve in a circle, and in either case, so soon as the point of the
drill emerges the diameter of the hole drilled will decrease, the
finished hole being conical as shown in Fig. 1720 at A.
It may be remarked that the eye of the workman is (for rough work, such
as tapping or clearing holes) sufficient guide to enable the grinding of
the drill true enough to partly avoid the conditions shown in these two
figures (in which the errors are magnified for clearness of
illustration), because when the want of truth is less in amount than the
thickness of the drill point, the centre of motion of the drill point
when the drill has entered the work to its full diameter becomes neither
at the point of the drill nor in the centre of its diameter, but
intermediate between the two.
[Illustration: Fig. 1721.]
[Illustration: Fig. 1722.]
Thus, in Fig. 1721, A is the centre of the diameter of the drill, but
the cutting edge C being shorter than D throws the point of the drill
towards E, hence the extra pressure of D on the incline of the recess it
cuts, over the like pressure exerted by C tends to throw the centre of
rotation towards E, the natural endeavor of the drill point to press
into the centre of the recess acting in the same direction. This is in
part resisted by the strength of the drill, hence the centre of rotation
is intermediate as at B in figure. The dotted circle is drawn from the
axial line of the drill as a centre, while the full circle is drawn from
B as a centre. The result of this would be that the point of the drill
would perform more duty than is due to its thickness, and the recess cut
would have a flat place at the bottom, as shown in Fig. 1722 at O. This,
from the want of keenness of the cutting edge running diagonally across
the drill point, would cause the drill to cut badly and require more
power to drive and feed.
[Illustration: Fig. 1723.]
The edges at the flat end of the drill, as at A, A in Fig. 1723, should
have a little clearance back from the cutting edge though they may be
left the full circle as, at A, A, but in any event they should not have
clearance sufficient to form them as at B, B, Fig. 1723, because in that
case the side edges C, C would cut the sides of the hole. In large
drills, especially, it is necessary that the edges have but little
clearance, and that the form of the clearance be as shown in Fig. 1044,
with reference to twist drills. When no edge clearance whatever is given
the edges act to a certain extent as guides to the drill, but if the
drill is not ground quite true this induces a great deal of friction
between the edges of the drill and the side of the hole.
In any case of improper grinding the power required to drive the drill
will be increased, because of the improper friction induced between the
sides of the drill and the walls of the hole.
For use on steel, wrought iron, and cast iron the lip drill shown in
Fig. 1724 is a very efficient tool. It is similar to the flat drill but
has its cutting edge bent forward. It possesses the keenness of the
twist drill and the strength of the flat drill, but as in the case of
all drills whose diameters are restored by forging and hand grinding, it
is suitable for the rougher classes of work only, and requires great
care in order to have it run true and keep both cutting edges in action.
It is sometimes attempted to give a greater cutting angle to a flat
drill by grinding a recess in the front face, as at A in Fig. 1725, but
this is a poor expedient.
Fig. 1726 represents what is known as the tit drill. It is employed to
flatten the bottoms of holes, and has a tit T which serves to steady it.
The edges A, B of this drill may be turned true and left without
clearance, which will also serve to steady the drill. The tit T should
be tapered towards the point, as shown, which will enable it to feed
more easily and cut more freely. The speed of the drill must be as slow
again as for the ordinary flat drill, and not more than one-third as
fast as the twist drill.
To enable a drill to start a hole in the intended location the
centre-punch recess in the centre of that location should be large
enough in diameter at the top to admit the point of the drill, that is
to say, the recess should not be less in diameter at the top than the
thickness of the drill point.
[Illustration: Fig. 1724.]
[Illustration: Fig. 1725.]
[Illustration: Fig. 1726.]
[Illustration: Fig. 1727.]
If the drill does not enter true the alteration is effected as shown in
Fig. 1727, in which A represents the work, B a circle of the size of the
hole to be drilled, and C the recess cut by the drill, while D is a
recess cut with a round-nosed chisel, which recess will cause the drill
to run over in that direction.
[Illustration: Fig. 1728.]
It is a good plan when the hole requires to be very correctly located to
strike two circles, as shown in Fig. 1728, and to define them with
centre-punch marks so that the cuttings and oil shall not erase them, as
is apt to be the case with lines only. The outer circle is of the size
of hole to be drilled, the inner one serves merely as a guide to true
the drilling by.
If the work is to be clamped to the work table an alteration in the
location of the recess cut by the drill point may be made by moving the
work. In this case the point of the drill may be fed up so as to enter
into and press against the centre-punch mark made in the centre of the
location of the hole to be drilled, which, if the drill runs true will
set the work true enough to clamp it by. The alteration to the recess
cut by the drill when first starting to bring the hole in its true
position should be made as soon as a want of truth is discernible,
because the shallower the recess the more easily the alteration may be
made.
Sometimes a small hole is drilled as true to location as may be, and
tested, any error discovered being corrected by a file; a larger drill
is then used and the location again tested, and so on; in this way great
precision of location may be obtained.
The more acute angle the cutting edges form one to the other, or in
other words, the longer the cutting edges are in a drill of a given
diameter, the more readily the drill will move over if one side of the
recess be cut out as in Fig. 1727, and from some experiments made by
Messrs. William Sellers and Co., it was determined that if the angle of
one cutting edge to the other was more than 104° the drill would cease
to move over.
In drilling wrought iron or the commoner qualities of steel the drill
should be liberally supplied with either water or oil, but soapy water
is better than pure. This keeps the drill cool and keeps the cutting
edge clean, whereas otherwise the cuttings under a coarse feed are apt
to stick fast to the drill point if the speed of the drill is great.
Furthermore, under excessive duty the drill is apt to become heated and
softened.
For cast steel oil is preferable, or if the steel be very hard it will
cut best dry under a slow speed and heavy pressure.
For brass and cast iron the drill should run dry, otherwise the cuttings
clog and jam in the hole. When the drill squeaks either the cutting edge
is dulled and the drill requires regrinding, or else the cuttings have
jammed in the hole, and either defect should be remedied at once.
As soon as the point of the drill emerges through the work the feed
should be lessened, otherwise the drill is apt to force through the
weakened metal and become locked, which will very often either break or
twist the drill. This may be accomplished when there is any end play to
the drilling machine spindle by operating the feed motion in a direction
to relieve the feed as soon as the point of the drill has emerged
through the bottom of the hole, thus permitting the weight of the
spindle to feed the drill. In a drilling machine, however, in which the
weight of the spindle is counterbalanced, the feed may be simply reduced
while the drill is passing through the bottom of the hole.
Drills for work of ordinary hardness are tempered to an orange purple,
but if the metal to be cut is very hard a straw color is preferable, or
the drill may be left as hard as it leaves the water; that is to say
hardened, but not tempered. In these cases the speed of the drill must
be reduced.
To assist a drill in taking hold of hard metal it is an excellent plan
to jag the surface of the metal with a chisel which will often start the
drill to its cut when all other means have failed. It is obvious from
previous remarks that the harder the drill the less the angle of the end
facets.
In cases of extreme hardness two drills may with advantage be used
intermittently upon the same hole; one of these should have its cutting
edges ground at a more acute angle one to the other than is the case
with the other drill, thus the cutting edge will be lessened in length
while the drill will retain the strength due to its diameter, so that a
maximum of pressure may be placed upon it. When one drill has cut deep
enough to bring its full length of cutting edge into action, it may be
removed and the other drill employed, and so on.
The drill (for hard steel) should be kept dry until it has begun to cut,
when a very little oil may be employed, but for chilled cast iron it
should be kept dry.
Small work to be drilled while resting upon a horizontal table may
generally be held by hand, and need not therefore be secured in a chuck
or to the table, because the pressure of the drill forces the work
surface to the table, creating sufficient friction to hold the work from
rotating with the drill. For large holes, however, the work may be
secured in chucks or by bolts and plates as described for lathe and
planer work, or held in a vice.
The following table for the sizes of tapping holes is that issued by the
Morse Twist Drill and Machine Co. In reply to a communication upon the
subject that company states. "If in our estimate the necessary diameter
of a tap drill to give a full thread comes nearest to a 1/64 inch
measurement, we give the size of the drill in 64ths of an inch. If
nearest to a 32nd size of drill we give the drill size in 32nds of an
inch."
In the following table are given the sizes of tapping drills, to give
full threads, the diameters being practically but not decimally
correct:--
-------+-----------------+-----------------------
Dia- | Number | Drill for
meter | threads | [V]-thread.
of tap.| to inch. |
-------+-----------------+-----------------------
1/4 |16 18 20| 5/32 5/32 11/64
9/32 |16 18 20| 3/16 13/64 13/64
5/16 |16 18 --| 7/32 15/64 --
11/32|16 18 --| 1/4 17/64 --
3/8 |14 16 18| 1/4 9/32 9/32
13/32|14 16 18| 19/64 21/64 21/64
7/16 |14 16 --| 21/64 11/32 --
15/32|14 16 --| 23/64 3/8 --
1/2 |12 13 14| 3/8 25/64 25/64
17/32|12 13 14| 13/32 27/64 27/64
9/16 |12 14 --| 7/16 29/64 --
19/32|12 14 --| 15/32 31/64 --
5/8 |10 11 12| 15/32 1/2 1/2
21/32|10 11 12| 1/2 17/32 17/32
11/16|11 12 --| 9/16 9/16 --
23/32|11 12 --| 19/32 19/32 --
3/4 |10 11 12| 19/32 5/8 5/8
25/32|10 11 12| 5/8 21/32 21/32
13/16|10 -- --| 21/32 -- --
27/32|10 -- --| 11/16 -- --
7/8 | 9 10 --| 45/64 23/32 --
29/32| 9 10 --| 47/64 3/4 --
15/16| 9 -- --| 49/64 -- --
21/32| 9 -- --| 51/64 -- --
1 | 8 -- --| 13/16 -- --
1-1/32 | 8 -- --| 53/64 -- --
1-1/16 | 8 -- --| 55/64 -- --
1-3/32 | 8 -- --| 57/64 -- --
1-1/8 | 7 8 --| 29/32 15/16 --
1-5/32 | 7 8 --| 15/16 31/32 --
1-3/16 | 7 8 --| 31/32 1 --
1-7/32 | 7 8 --|1 1-1/32 --
1-1/4 | 7 -- --|1-1/32 -- --
1-9/32 | 7 -- --|1-1/16 -- --
1-5/16 | 7 -- --|1-3/32 -- --
1-11/32| 7 -- --|1-1/8 -- --
1-3/8 | 6 -- --|1-1/8 -- --
1-13/32| 6 -- --|1-5/32 -- --
1-7/16 | 6 -- --|1-5/32 -- --
1-15/32| 6 -- --|1-3/16 -- --
1-1/2 | 6 -- --|1-15/64 -- --
1-17/32| 6 -- --|1-9/32 -- --
1-9/16 | 6 -- --|1-9/32 -- --
1-19/32| 6 -- --|1-5/16 -- --
1-5/8 | 5 5-1/2 --|1-9/32 1-5/16 --
1-21/32| 5 5-1/2 --|1-5/16 1-11/32 --
1-11/16| 5 5-1/2 --|1-11/32 1-3/8 --
1-23/32| 5 5-1/2 --|1-3/8 1-13/32 --
1-3/4 | 5 -- --|1-13/32 -- --
1-25/32| 5 -- --|1-7/16 -- --
1-13/16| 5 -- --|1-15/32 -- --
1-27/32| 5 -- --|1-1/2 -- --
1-7/8 | 4-1/2 5 --|1-17/32 1-17/32 --
1-29/32| 4-1/2 5 --|1-9/16 1-9/16 --
1-15/16| 4-1/2 5 --|1-19/32 1-19/32 --
1-31/32| 4-1/2 5 --|1-5/8 1-5/8 --
2 | 4-1/2 -- --|1-21/32 -- --
-------+-----------------+-----------------------
-------+---------------------+--------------------
Dia- | Drill for U.S.S. | Drill for
meter | thread. | Whitworth
of tap.| | thread.
-------+---------------------+--------------------
1/4 | -- -- 3/16| -- -- 3/16
9/32 | -- -- -- | -- -- --
5/16 | -- 1/4 -- | -- 15/64 --
11/32| -- -- -- | -- -- --
3/8 | -- 9/32 -- | -- 9/32 --
13/32| -- -- -- | -- -- --
7/16 | 11/32 -- -- | 11/32 -- --
15/32| -- -- -- | -- -- --
1/2 | -- 13/32 -- | 3/8 -- --
17/32| -- -- -- | -- -- --
9/16 | 7/16 -- -- | -- -- --
19/32| -- -- -- | -- -- --
5/8 | -- 1/2 -- | -- 1/2 --
21/32| -- -- -- | -- -- --
11/16| -- -- -- | -- -- --
23/32| -- -- -- | -- -- --
3/4 | 5/8 -- -- | 5/8 -- --
25/32| -- -- -- | -- -- --
13/16| -- -- -- | -- -- --
27/32| -- -- -- | -- -- --
7/8 | 23/32 -- -- | 23/32 -- --
29/32| -- -- -- | -- -- --
15/16| -- -- -- | -- -- --
21/32| -- -- -- | -- -- --
1 | 27/32 -- -- | 27/32 -- --
1-1/32 | -- -- -- | -- -- --
1-1/16 | -- -- -- | -- -- --
1-3/32 | -- -- -- | -- -- --
1-1/8 | 15/16 -- -- | 15/16 -- --
1-5/32 | -- -- -- | -- -- --
1-3/16 | -- -- -- | -- -- --
1-7/32 | -- -- -- | -- -- --
1-1/4 |1-1/16 -- -- |1-1/16 -- --
1-9/32 | -- -- -- | -- -- --
1-5/16 | -- -- -- | -- -- --
1-11/32| -- -- -- | -- -- --
1-3/8 |1-5/32 -- -- |1-5/32 -- --
1-13/32| -- -- -- | -- -- --
1-7/16 | -- -- -- | -- -- --
1-15/32| -- -- -- | -- -- --
1-1/2 |1-9/32 -- -- |1-9/32 -- --
1-17/32| -- -- -- | -- -- --
1-9/16 | -- -- -- | -- -- --
1-19/32| -- -- -- | -- -- --
1-5/8 | -- 1-3/8 -- |1-23/64 -- --
1-21/32| -- -- -- | -- -- --
1-11/16| -- -- -- | -- -- --
1-23/32| -- -- -- | -- -- --
1-3/4 |1-1/2 -- -- |1-1/2 -- --
1-25/32| -- -- -- | -- -- --
1-13/16| -- -- -- | -- -- --
1-27/32| -- -- -- | -- -- --
1-7/8 | -- 1-5/8 -- |1-37/64 -- --
1-29/32| -- -- -- | -- -- --
1-15/16| -- -- -- | -- -- --
1-31/32| -- -- -- | -- -- --
2 |1-23/32 -- -- |1-45/64 -- --
-------+---------------------+--------------------
To drive all drills by placing them directly in the socket of the
drilling machine spindle would necessitate that all the drills should
have their shanks to fit the drilling machine socket. This would involve
a great deal of extra labor in making the drills, because the socket in
the machine spindle must be large enough to fit the size of shank that
will be strong enough to drive the largest drill used in the machine,
hence the small drills would require to be forged down from steel equal
to the full diameter of the shank of the largest drill. To obviate this
difficulty the sockets already described with reference to drilling in
the lathe are used.
The employment of these sockets preserves the truth of the bore of the
drilling machine spindle by greatly diminishing the necessity to insert
and remove the shank from the drill spindle, because each socket
carrying several sizes of drills (as given with reference to lathe work)
the sockets require less frequent changing.
[Illustration: Fig. 1729.]
Drill shanks are sometimes made parallel, with a flat place as at A in
Fig. 1729, to receive the pressure of the set-screw by which it is
driven. To enable the shank to run true it must be a close fit to the
socket and should be about five diameters long. The objection to this
form is that the pressure of the set-screw tends to force the drill out
of true, as does also the wear of the socket bore.
These objections will obviously be diminished in proportion as the drill
shank is made a tight fit to the socket, and to effect this and still
enable the drill to be easily inserted and removed from the socket, the
drill shank may be first made a tight fit to the socket bore, and then
eased away on the half circumference on the side of the flat place,
leaving it to fit on the other half circumference which is shown below
the dotted line B in the end view in the figure. The set-screw is also
objectionable, since it requires the use of a wrench, and is in the way
and liable to catch the operator's clothing.
There is, however, one advantage in employing a set-screw for twist
drills, inasmuch as that, on account of the front rake on a twist drill,
there is a strong tendency for the drill, as soon as the point emerges
through the work, to run forward into the work and by ripping in become
locked. This is very apt to be the case if there is any end play in the
driving spindle, because the pressure of the cut forces the spindle back
from the cut; but so soon as the drill point emerges and the pressure is
reduced, the weight of the spindle acting in concert with the front rake
on the drill causes the spindle to drop, taking up the lost motion in
the opposite direction. In addition to this the work will from the same
cause lift and run up the drill, often causing an increase in the duty
sufficient to break the drill.
If the spindle has no lost motion and the work is bolted or fastened to
the table or in a chuck, the drill if it has a taper shank only will
sometimes run forward and slip loose in the driving socket. This,
however, may be obviated by feeding the drill very slowly after its
point emerges through the work.
Yet another form in which the cylindrical shanks of drills have been
driven is shown in Fig. 1730. The shank is provided with a longitudinal
groove turning at a right angle; at its termination the socket is
provided with a screw whose point projects and fits into the shank
groove. The drill is inserted and turned to the right, the end of the
screw driving the drill and preventing it from coming out or running
forward.
Flat drills are usually provided with a square taper shank such as shown
in Fig. 1730, an average amount of taper being 1-1/4 inches per foot.
There are several disadvantages in the use of a square shank.
1st. It is difficult to forge the drill true and straight with the
shank.
2nd. It is difficult to make the square socket true with the axial line
of the machine spindle, and concentric with the same from end to end.
3rd. It is difficult to fit the shank of the drill to the socket and
have its square sides true with the axial line of the drill.
4th. It is an expensive form of shank to fit. It is a necessity,
however, when the cutting duty is very heavy, as in the case of stocks
carrying cutters for holes of large diameter.
In order to properly fit a square shank to a socket it should be pressed
into the socket by hand only, and pressed laterally in the direction of
each side of the square. If there is no lateral movement the shank is a
fit, and the spindle may be revolved to see if the drill runs true, as
it should do if the body of the drill is true with the shank (and this
must always be the case to obtain correct results). The drill must be
tried for running true at each end of the cylindrical body of the drill,
which, being true with the square shank, may be taken as the standard of
truth in grinding the drill, so that supposing the hole in the driving
spindle to be true and the drill shank to be properly fitted, the drill
will run true whichever way inserted. If the body of the drill runs out
of true it will cause a great deal of friction by rubbing and forcing
the cuttings against the sides of holes, especially if the clearance be
small or the hole a deep one.
[Illustration: Fig. 1730.]
In fitting the shank, the fitting or bearing marks will show most
correctly when the shank is driven very lightly home, for if driven in
too firmly the bearing marks will extend too far in consequence of the
elasticity of the metal. If the hole in the spindle is not true with the
axial line of the spindle, or if the sides of the hole are not a true
square or are not equidistant from the axial line of the spindle, the
drill must be fitted with one side of its square shank always placed to
the same side of the square in the socket, and these two sides must
therefore be marked so as to denote how to insert the drill without
having to try it in the socket. Usually a centre-punch mark, as at E,
Fig. 1731, is made on the drill and another on the collar as at _f_.
To enable the extraction of the drill from the socket the latter is
provided with a slot, shown in figure at C, the slot passing through the
spindle and the end of the drill protruding into the slot, so that a key
driven into the slot will force the drill from the socket. The key
employed for this purpose should be of some soft metal, as brass or hard
composition brass, so that the key shall not condense or press the metal
of the keyway, and after the key is inserted it should be lightly tapped
with a hammer, travelling in the direction of the line of the spindle
and not driven through the keyway.
The drill should not be given a blow or tap to loose it in the spindle,
as this is sure in time to make its socket hole out of true.
[Illustration: Fig. 1731.]
[Illustration: Fig. 1732.]
The thread shown on the end of the drill spindle in figure is to receive
chucks for holding and driving drills.
[Illustration: Fig. 1733.]
The various forms of small drill chucks illustrated in connection with
the subject of lathe chucks are equally suitable for driving drills in
the drilling machine.
Fig. 1732, however, represents an excellent three-jawed chuck for
driving drills, the bite being very narrow and holding the drill with
great firmness.
Fig. 1733 represents a two-jawed drill chuck in which the screws
operate a pair of dies for gripping parallel shank drills, the screws
being operated independently.
In other forms of similar chucks the bite is a [V] recess parallel to
the chuck axis, the only difference between a drill chuck for a drilling
machine and one for a lathe being that for the former the jaws do not
require outside bites nor to be reversible.
[Illustration: Fig. 1734.]
Holes that are to be made parallel, straight, cylindrically true in the
drilling machine, are finished by the reamer as already described with
reference to lathe work, and it is found as in lathe work that in order
that a reamer may finish holes to the same diameter, it is necessary
that it take the same depth of finishing cut in each case, an end that
is best obtained by the use of three reamers, the first taking out the
irregularities of the drilled hole, and the second preparing it for the
light finishing cut to be taken by the third.
All the remarks made upon the reamer when considered with reference to
lathe work apply equally to its use in the drilling machine.
Another tool for taking a very light cut to smooth out a hole and cut it
to exact size is the shell reamer shown in Fig. 1734, which fits on a
taper mandrel through which passes a square key fitting into the square
slot shown in the shell reamer.
[Illustration: Fig. 1735.]
Reamers may be driven by drill chucks, but when very true and parallel
work is required, and the holes are made true before using the reamer,
it is preferable to drive them by a socket that permits of their moving
laterally. Especially is this the case with rose-bits. Fig. 1735, which
is taken from _The American Machinist_, represents a socket of this
kind, being pivoted at its driving or shank end, and supported at the
other by two small spiral springs. The effect is that if the socket does
not run quite true the reamer is permitted to adjust itself straight and
true in the hole being reamed, instead of rubbing and binding against
its walls, which would tend to enlarge its mouth and therefore impair
its parallelism.
Cotter drills, slotting drills, or keyway drills, three names
designating the same tool, are employed to cut out keyways, mortises, or
slots.
Fig. 1736 represents a common form of cotter or keyway drill, the
cutting edges being at A, A, and clearance being given by grinding the
curve as denoted by the line C. In some cases a stock S and two
detachable bits or cutters C, C, are used as in Fig. 1737, the bits
being simple tools secured in slots in the stock by set-screws, and thus
being adjustable for width so that they may be used to cut keyways of
different widths.
The feed of keyway drills should be light, and especial care must be
taken where two spindles are used, to keep them in line, or otherwise
the keyway will not come fair, as is shown in Fig. 1738, where the half
drilled from side A and that drilled from side B are shown not to come
fair at their point of junction C. This is more apt to occur when a deep
keyway is drilled one half from each side. Hence in such a case great
care must be exercised in setting the work true, because the labor in
filing out such a keyway is both tedious and expensive.
[Illustration: Fig. 1736.]
[Illustration: Fig. 1737.]
In producing holes of above or about two inches in diameter, cutters
such as shown in Fig. 1739 may be employed. A is a stock carrying a
cutter B secured in place by a key C. Holes are first drilled to receive
the pin D, which serves as a guide to steady the stock. The amount of
cutting duty is obviously confined to the production of the holes to
receive the pin and the metal removed from the groove cut by the
cutters, so that at completion of the cutter duty there comes from the
work a ferrule or annular ring that has been cut out of the work.
[Illustration: Fig. 1738.]
For use on wrought iron or steel the front faces of the cutters may be
given rake as denoted by the dotted line at E, and smooth and more rapid
duty may be obtained if the cutter be set back, as in Fig. 1740, the
cutting edge being about in a line with line A, in which case the front
face may be hollowed out as at B, and take a good cut without the
digging in and jumping that is apt to occur in large holes if the cutter
is not thus set back. The larger the diameter of the work the greater
the necessity of setting the cutting edge back, thus in Fig. 1741 the
cutter is to be used to cut a large circle out of a plate P, as, say, a
man-hole in a boiler sheet. The cutter C is carried in a bar B secured
in the stock A by a screw, and unless the cutter is set well back it is
liable to dip into the work and break.
[Illustration: Fig. 1739.]
[Illustration: Fig. 1740.]
[Illustration: Fig. 1741.]
It is obvious that the pin E in the figure must be long enough to pass
into the hole in the plate before the cutter meets the plate surface and
begins to cut, so that the pin shall act as a guide to steady the
cutter, and also that in all cutters or cutter driving stocks the shank
must be either of large diameter or else made square, in order to be
able to drive the cut at the increased leverage over that in drilling.
[Illustration: Fig. 1742.]
In these forms of tube plate cutters it is necessary to drill a hole to
receive the pin D. But this necessity may be removed by means of a
cutter, such as shown in Fig. 1742, which is given simply as a
representative of a class of such cutters. A is a cutter stock having
the two cutters B B fitted in slots and bolted to it. C is a spiral
spring inserted in a hole in A and pressing upon the pin D, which has a
conical point. The work is provided with a deep centre-punch mark
denoting the centre of the hole to be cut. The point of D projects
slightly beyond the cutting edges of the cutters, and as it enters the
centre-punch mark in the work it forms a guide point to steady the
cutters as they rotate. As the cutters are fed to their cut, the pin D
simply compresses the spiral spring C and passes further up the cutter
stock. Thus the point of D serves instead of a hole and pin guide.
[Illustration: Fig. 1743.]
A simple form of adjustable cutter is shown in Figs. 1743 and 1744. It
consists of a stock A A with the shank B, made tapering to fit the
socket of a boring or drilling machine. Through the body of the stock is
a keyway or slot, in which is placed the cutter C, provided in the
centre of the upper edge with a notch or recess. Into this slot fits the
end of the piece D, which is pivoted upon the pin E. The radial edge of
D has female worm teeth upon it. F is a worm screw in gear with the
radial edge of D. Upon the outer end of F is a square projection to
receive a handle, and it is obvious that by revolving the screw F, the
cutter C will be moved through the slot in the stock, and hence the size
of the circle which the cutter will describe in a revolution of the
stock A may be determined by operating the screw F. Thus the tool is
adjustable for different sizes of work, while it is rigidly held to any
size without any tendency whatever either to slip or alter its form. The
pin G is not an absolutely necessary part of the tool, but it is a
valuable addition, as it steadies the tool. This is necessary when the
spindle of the machine in which it is used has play in the bearings,
which is very often the case with boring and drilling machines. The use
of G is to act as a guide fixed in the table upon which the work is
held, to prevent the tool from springing away from the cut, and hence
enabling it to do much smoother work. It is usual to make the width of
the cutter C to suit some piece of work of which there is a large
quantity to do, because when the cutter is in the centre of the stock
both edges may perform cutting duty; in which case the tool can be fed
to the cut twice as fast as when the cutter is used for an increased
diameter, and one cutting edge only is operative. The tool may be put
between the lathe centres and revolved, the work being fastened to the
lathe saddle. In this way it is exceedingly useful in cutting out plain
cores in half-core boxes.
[Illustration: Fig. 1744.]
In addition to its value as an adjustable boring tool this device may be
used to cut out sweeps and curves, and is especially adapted to cutting
those of double eyes. This operation is shown in Fig. 1744, in which D
is the double eye, A is the tool stock, F is the adjusting screw, and C
is the cutter. The circular ends of connecting rod strips and other
similar work also fall within the province of this tool, and in the case
of such work upon rods too long to be revolved this is an important
item, as such work has now to be relegated to that slowest and most
unhandy of all machine tools, the slotting machine.
It is obvious that any of the ordinary forms of cutter may be used in
this stock.
[Illustration: Fig. 1745.]
For enlarging a hole for a certain distance the counterbore is employed.
Fig. 1745 represents a counterbore or pin drill, in which the pin is cut
like a reamer, so as to ream the hole and insure that the pin shall fit
accurately. The sides are left with but little clearance and with a dull
edge, so that they will not cut, the cutting edges being at _e_, _c_ and
the clearance on the end faces.
[Illustration: Fig. 1746.]
For counterboring small holes or for facing the metal around their ends,
the form of counterbore shown in Fig. 1746 is employed. The pin must be
an accurate fit to the hole, and to capacitate one tool for various
sizes of holes the bit is made interchangeable. The stock has a flat
place on it to receive the pressure of the screw that secures the
counterbore, and the end of the stock is reduced in diameter, so that
the counterbore comes against a shoulder and cannot push up the stock
from the pressure of the feed; the end of the counterbore is bored to
receive the tit pin, thus making it permissible to exchange the pin, and
use various sizes in the same counterbore.
[Illustration: Fig. 1747.]
[Illustration: Fig. 1748.]
Twist drills for use in wood work are given a conical point, as was
shown with reference to lathe drills, and when the holes are to be
countersunk, an attachment, such as shown in Fig. 1747, may be used. It
is a split and threaded taper, so that by operating the nut in one
direction it may be locked to the drill, while by operating it in the
other it will be loosened, and may be adjusted to any required distance
from the point of the drill, as shown in Fig. 1748.
[Illustration: Fig. 1749.]
For larger sizes of holes a stock and cutter, such as shown in Fig.
1749, may be employed, receiving a facing of counterboring cutter such
as A, or a countersink bit such as B, and the bit may be made to suit
various sizes of holes by making its diameter suitable for the smallest
size of hole the tool is intended for, and putting ferrules to bring it
up to size for larger diameters.
The cutters are fastened into the stock by a small key or wedge, as
shown. By having the cutter a separate piece from the stock, the cutting
edges may be ground with greater facility, while one stock may serve for
various sizes of cutters. The slot in the stock should be made to have
an amount of taper equal to that given to the key, so that all the
cutters may be made parallel in their widths or depths, and thus be more
easily made, while at the same time the upper edge will serve as a guide
to grind the cutting edges parallel to, and thus insure that they shall
stand at a right angle to the axis of the stock, and that both will
therefore take an equal share of the cutting duty.
When cutters of this kind are used to enlarge holes of large diameter it
is necessary that the pin be long enough to pass down into a bushing
provided in the table of the machine, and thus steady the bar or stock
at that end.
For coning the mouths of holes the countersink is employed, being
provided with a pin, as shown in Fig. 1750; and it is obvious that the
pin may be provided with bushings or ferrules. The smaller sizes of
countersinks are sometimes made as in Fig. 1751, the coned end being
filed away slightly below the axis so as to give clearance to the
cutting edge.
[Illustration: Fig. 1750.]
[Illustration: Fig. 1751.]
[Illustration: Fig. 1752.]
Fig. 1752 refers to a device for drilling square holes. The chuck for
driving the drill is so constructed as to permit to the drill a certain
amount of lateral motion, which is rendered necessary by the peculiar
movement of the cutting edges of the drill which does not rotate on a
fixed central point, but diverges laterally to a degree proportional to
the size of the hole. For the chuck the upper part of the cavity of a
metal cylinder is bored out so as to fit on the driving spindle. Below
this bore a square recess is made, and below this latter and coming well
within the diameter of the square recess, is a circular hole passing
through the end of the chuck. The drill holder or socket is in a
separate piece, the bottom portion of which is provided with a square or
round recess for holding the drill shanks, and is held firmly in its
socket by means of a set-screw. The upper part of the socket consists
first of a screw (Fig. 1752) at S; secondly, of a squared shoulder B;
thirdly, of a cylindrical shoulder D, and the circular part E, the drill
shank being inserted at H. N is a nut holding the drill socket in the
chuck. The socket being inserted in the chuck, the loose square collar
C, which has an oblong rectangular slot in it, is put in, passing over
the squared part of the socket. The nut N is then screwed up, bringing
the face of E up to the face of the chuck, but not binding C, because C
is thinner than the recess in which it lies. When this is done the
socket will readily move in a horizontal plane to such a distance as the
play between the two sides of the loose collar C and two of the sides of
the recess will permit, while in the other direction it will move in a
horizontal plane such distance as the play between the two sides of the
square shoulder of the socket and the ends of the rectangular slot in
the loose collar C will permit. The amount of this horizontal motion is
varied to suit the size of the square hole to be drilled. Near to the
lower end or cutting edges of the drill, there is fixed above the work a
metal guide plate F having a square hole of the size requiring to be
drilled. The drill is made three-sided, as shown, the dimensions of the
three sides being such that the distance from the base to the apex of
the triangle is the same as the length of the sides of the hole to be
drilled. The drill may then be rotated through F as a guide, when it
will drill a square hole.
The method of operation is as follows: The three-sided drill being fixed
in the self-adjusting chuck, the guide bar with the square guide hole
therein rigidly fixed above the point in the work where it is required
to drill, the drilling spindle carrying the chuck drill is made to
revolve, and is screwed or pressed downwards, upon which the drill works
downwards through the square guide hole, and drills holes similar in
size and form to that in the guide. The triangular drill for drilling
dead square holes may also be used without the self-adjusting drill
chuck in any ordinary chuck, when the substance operated upon is not
very heavy nor stationary; then, instead of the lateral movement of the
drill, such lateral movement will be communicated by the drill to the
substance operated upon.
In making oblong dead square-cornered holes, either the substance to be
operated upon must be allowed to move in one direction more than
another, or the hole in the guide plate must be made to the shape
required, and the drill chuck made to give the drill greater play in one
direction.
[Illustration: Fig. 1753.]
The boring bars and cutters employed in drilling and boring machines are
usually solid bars having fixed cutters, the bars feeding to the cut.
[Illustration: Fig. 1754.]
[Illustration: Fig. 1755.]
[Illustration: Fig. 1756.]
Figs. 1753, 1754, 1755, and 1756, however, represent a bar having a
device for boring tapers in a drilling or boring machine. It consists of
a sleeve A fixed to the bar S, and having a slideway at an angle to the
bar axis. In this slideway is a slide carrying the cutting tool and
having at its upper end a feed screw with a star feed. Fig. 1753 shows
the device without, and Fig. 1754 with, the boring bar. A is a sleeve
having ribs B to provide the slideway C for the slide D carrying the
cutting-tool T. The feed screw F is furnished with the star G between
two lugs H K. A stationary pin bolted upon the work catches one arm of
the star at each revolution of the bar, and thus puts on the feed. To
take up the wear of the tool-carrying slide, a gib M and set-screws P
are provided, and to clamp the device to the boring-bar it is split at Q
and furnished with screws R. The boring-bar S, furthermore, has a collar
at the top and a nut N at the bottom. The tool, it will be observed, can
be closely held and guided, the degree of taper of the hole bored being
governed by the angle of the slideway C to the axis of the sleeve.
CHAPTER XX.--HAND DRILLING AND BORING TOOLS AND DEVICES.
HAND DRILLING AND BORING TOOLS.--The tools used for piercing holes in
wood are generally termed boring tools, while those for metal are termed
drilling tools when they cut the hole from the solid metal, and boring
tools when they are used to enlarge an existing hole. Wood-boring tools
must have their cutting edges so shaped that they sever the fibre of the
wood before dislodging it, or otherwise the cutting edges wedge
themselves in the fibre. This is accomplished, in cutting across the
grain of the wood, in two ways: first, by severing the fibre around the
walls of the hole and in a line parallel to the axial line of the boring
tool, and removing it afterwards with a second cutting edge at a right
angle to the axis of the boring tool; or else by employing a cutting
edge that is curved in its length so as to begin to cut at the centre
and operate on the walls of the hole, gradually enlarging it, as in the
case of Good's auger bit (to be hereafter described), the action being
to cut off successive layers from the end of the grain or fibre of the
wood. Tools for very small holes or holes not above one-quarter inch in
diameter usually operate on this second principle, as do also some of
the larger tools, such as the nail bit or spoon bit and the German bit.
[Illustration: Fig. 1757.]
[Illustration: Fig. 1758.]
The simplest form of wood-piercing tool is the awl or bradawl, shown in
Figs. 1757 and 1758, its cutting end being tapered to a wedge shape
whose width is sometimes made parallel with the stem and at others
spread, as at C D in figure. It is obvious that when the end is spread
the stem affords less assistance as a guide to pierce the hole straight.
It is obvious that the action of an awl is that of wedging and tearing
rather than of cutting, especially when it is operating endways of the
grain.
Thus in Fig. 1758 is shown an awl operating, on the right, across the
grain, and, on the left, endwise of the same. In the former position it
breaks the grain endwise, while in the latter it wedges it apart. Awls
are used for holes up to about three-sixteenths of an inch in diameter.
[Illustration: Fig. 1759.]
Fig. 1759 represents the gimlet bit having a spiral flute at F and a
spiral projection at S S, which, acting on the principle of a screw,
pulls the bit forward and into its cut. These bits are used in sizes
from 1/16 inch to 1/2 inch. The edge of the spiral flute or groove here
does the cutting, producing a conical hole and cutting off successive
layers of the fibre until the full diameter of hole is produced. The
upper part of the fluted end is reduced in diameter so as to avoid its
rubbing against the walls of the hole and producing friction, which
would make the tool hard to drive.
[Illustration: Fig. 1760.]
[Illustration: Fig. 1761.]
Figs. 1760 and 1761 represent the German bit, which is used for holes
from 1/16 inch to 3/8 inch in diameter. This, as well as all other bits
or augers, have a tapered square by which they are driven with a brace,
the notch shown at N being to receive the spring catch of the brace that
holds them in place. The cutting edges at A and B are produced by
cutting away the metal behind them.
[Illustration: Fig. 1762.]
[Illustration: Fig. 1763.]
Fig. 1762 represents the nail bit, which is used for boring across the
grain of the wood. Its cutting edge severs the fibre around the walls of
the hole, leaving a centre core uncut, which therefore remains in the
hole unless the hole is pierced entirely through the material. If used
to bore endways or parallel with the direction of the fibre or grain of
the wood it wedges itself therein.
The groove of the nail bit extends to the point, as shown by the dotted
line in the figure. Nail bits are used in sizes from 1/16 to 3/8 inch.
Fig. 1763 represents the spoon bit whose groove extends close to the
point, as shown by the dotted line C.
[Illustration: Fig. 1764.]
Fig. 1764 represents the pod or nose bit, whose cutting edge extends
half way across its end and therefore cuts off successive layers of the
fibres, which peculiarly adapts it for boring endways of the grain,
making a straight and smooth hole. It is made in sizes up to as large as
four inches, and is largely used for the bores of wooden pipes and
pumps, producing holes of great length, sometimes passing entirely
through the length of the log.
[Illustration: Fig. 1765.]
Fig. 1765 represents the auger bit, which is provided with a conical
screw S which pulls it forward into the wood. Its two wings W have
cutting edges at D, D, which, being in advance of the cutting edges A,
B, sever the fibre of the wood, which is afterwards cut off in layers
whose thickness is equal to the pitch of the thread upon its cone S. The
sides of the wings W obviously steady the auger in the hole, as do also
the tops T of the twist. This tool is more suitable for boring across
the grain than lengthways of it, because when boring lengthways the
wings W obviously wedge themselves between the fibres of the wood.
[Illustration: Fig. 1766.]
This is obviated in Cook's auger bit, shown in Fig. 1766, in which the
cutting edge is curved, so that whether used either across or with the
grain the cutting edge produces a dished seat and cuts the fibre endways
while removing the material in a spiral layer. The curve of the cutting
edge is such that near the corners it lies more nearly parallel to the
stem of the auger than at any other part, which tends to smooth the
walls of the hole. This tool while very serviceable for cross grain is
especially advantageous for the end grain of the wood.
[Illustration: Fig. 1767.]
[Illustration: Fig. 1768.]
In the smaller sizes of auger bits the twist of the spiral is made
coarser, as in Fig. 1767, which is necessary to provide sufficient
strength to the tool. For the larger sizes the width of the top of the
flute (T, Fig. 1765), or the land, as it is termed, is made narrow, as
in Fig. 1768, for holes not requiring to be very exact in their
straightness, while for holes requiring to be straight and smooth they
are made wider, as at D, in Fig. 1769, and the wings A, B in the figure
extend farther up the flutes so as to steady the tool in the walls of
the hole and make them smoother. It is obvious that the conical screw
requires to force or wedge itself into the wood, which in thin work is
apt to split the wood, especially when it is provided with a double
thread as it usually is (the top of one thread meeting the cutting edge
A in Fig. 1765, while the top of the other thread meets cutting edge B).
[Illustration: Fig. 1769.]
[Illustration: Fig. 1770.]
In boring end-grain wood, or in other words lengthways of the grain of
the wood, the thread is very apt to strip or pull out of the wood and
clog the screw of the auger; especially is this the case in hard woods.
This may be to a great extent avoided by cutting a spiral flute or
groove along the thread, as in Fig. 1770, which enables the screw to cut
its way into the wood on first starting, acts to obviate the stripping
and affords an easy means of cleaning. The groove also enables the screw
to cut its way through knots and enables the auger to bore straight.
In boring holes that are parallel with the grain or fibre of the wood,
much more pressure is required to keep the auger up to its cut and to
prevent the thread cut by the auger point from pulling or stripping out
of the wood, in which case it clogs the thread of the auger point and is
very difficult to clean it out, especially in the case of hard woods.
[Illustration: Fig. 1771.]
[Illustration: Fig. 1772.]
Furthermore, after the thread has once stripped it is quite difficult to
force the auger to start its cut again. To obviate these difficulties,
the screw is fluted as shown. It is obvious also that this flute by
imparting a certain amount of cutting action, and thereby lessening the
wedging action of the screw, enables it to bore, without splitting it,
thinner work than the ordinary auger. But it will split very thin work
nevertheless; hence for such work as well as for holes in any kind of
wood, when the hole does not require to be more than about twice as deep
as that diameter, the centre bit shown in Figs. 1771 and 1772 is
employed, being an excellent tool either for boring with the grain or
across it. The centre B is triangular and therefore cuts its way into
the work, and the spur or wing A extends lower than the cutting edge C,
which on account of its angle cuts very keenly.
[Illustration: Fig. 1773.]
Fig. 1773 represents the twist drill which is used by the wood-worker
for drilling iron, its end being squared to fit the carpenter's brace.
[Illustration: Fig. 1774.]
[Illustration: Fig. 1775.]
Fig. 1774 represents an extension bit, being adjustable for diameter by
reason of having its cutting edge upon a piece that can be moved endways
in the holder or stem. This piece is ruled with lines on its face so
that it may be set to the required size. Its upper edge is serrated with
notches into which a dish screw or worm meshes, so that by revolving the
worm the bit piece is moved farther out on the spur or wing side or end,
it being obvious that the spur must meet the walls of the hole. A better
form of extension bit for the end grain of wood is shown in Fig. 1775,
the cutting edge being a curve to adapt it to severing the fibre in
end-grained wood, as was explained with reference to Good's auger bit.
[Illustration: Fig. 1776.]
Fig. 1776 represents a drill for stone work, whose edge is made curved
to steady it. This tool is caused to cut by hammer blows, being slightly
revolved upon its axis after each blow, hence the curved shape of its
cutting edge causes it to sink a dish-shaped recess in the work which
holds that end steady. The end of the tool is spread because the corners
are subject to rapid wear, especially when used upon hard stone, and the
sides of the drill would bend or jam in the walls of the hole in the
absence of the clearance caused by the spread. To prevent undue abrasion
water is used.
In soft stones the hammer blows must be delivered lightly or the cutting
edge will produce corrugations in the seat or bottom of the hole, and
falling into the same recesses when revolved after each blow the
chipping action is impaired and finally ceases. To prevent this the
cutting edge is sometimes curved in its length so that the indentations
cross each other as the drill is revolved, which greatly increases the
capacity of the drill, but is harder to forge and to grind.
[Illustration: Fig. 1777.]
The simplest hand-drilling device employed for metal is the fiddle bow
drill shown in Fig. 1777. It consists of an elastic bow B, having a cord
C, which passes around the reel R, at one end of which is the drill D,
and at the other a stem having a conical or centre point fitting into a
conical recess in a curved breast-plate. The operator presses against
this plate to force the drill to cut, and by moving the bow back and
forth the cord revolves the drill.
[Illustration: Fig. 1778.]
As the direction of drill revolution is reversed at each passage of the
bow, its cutting edges must be formed so as to cut when revolved in
either direction, the shape necessary to accomplish this being shown in
the enlarged side and edge views at the foot of the engraving. It is
obvious that a device of this kind is suitable for small holes only, as,
say, those having a diameter of one-eighth inch or less. But for these
sizes it is an excellent tool, since it is light and very sensitive to
the drill pressure, and the operator can regulate the amount of pressure
to suit the resistance offered to the drill, and therefore prevent the
drill from breakage by reason of excessive feed. In place of the
breast-plate the bow drill may be used with a frame, such as in Fig.
1778. the frame being gripped in a vice and having a pin or screw A. If
a pin be used, its weight may give the feed, or it may be pressed down
by the fingers, while if a screw is used it must be revolved
occasionally to put on the feed.
[Illustration: Fig. 1779.]
Fig. 1779 represents a hand-drilling device in which the cord passes
around a drum containing a coiled spring which winds up the cord, the
latter passing around the drill spindle, so that pulling the cord
revolves the spindle and the drill, the drum and spiral spring revolving
the drill backwards.
[Illustration: Fig. 1780.]
Fig. 1780 represents a drilling device in which the drill is carried in
a chuck on the end of the spindle which has right and left spiral
grooves in it, and is provided with a barrel-shaped nut, which when
operated up and down the spindle causes it to revolve back and forth.
The nut or slide carries at one hand a right-hand, and at the other a
left-hand nut fitting into the spindle grooves, and cut like a ratchet
on their faces. Between these is a sleeve, also ratchet cut, but
sufficiently short that when one nut engages, the other is released,
with the result that the drill is revolved in one continuous direction
instead of back and forth, and can therefore be shaped as an ordinary
flat drill instead of as was shown in Fig. 1777. The drill is fed to its
cut by hand pressure on the handle or knob at the top.
[Illustration: Fig. 1781.]
Fig. 1781 represents Backus' brace for driving bits, augers, &c., the
construction of the chuck being shown in Fig. 1782. The two tongues are
held at their inner ends by springs and are coned at their outer ends,
there being a corresponding cone in the threaded sleeve, so that
screwing up this sleeve firmly grips the tool shank and thus holds it
true, independent of the squared end which fits into the inner tongue
that drives it.
In another form this brace is supplied with a ratchet between the chuck
and the cranked handle, as shown in Fig. 1783, the construction of the
ratchet being shown in Fig. 1784. The ring is provided on its inner edge
with three notches, so that by pulling it back and setting it in the
required notch the ratchet will operate the chuck in either direction or
lock it for use as an ordinary brace. The ratchet enables the tool to be
used in a corner in which there would be no room to turn the crank a
full revolution. This end may, however, be better accomplished by means
of the Backus' patent angular wrench shown in Fig. 1785, which consists
of a frame carrying a ball-and-socket joint between it and the chuck, as
shown.
[Illustration: Fig. 1782.]
[Illustration: Fig. 1783.]
[Illustration: Fig. 1784.]
[Illustration: Fig. 1785.]
[Illustration: Fig. 1786.]
[Illustration: Fig. 1787.]
Figs. 1786 and 1787 represent the brace arranged to have a gear-wheel
connected or disconnected at will, the object of this addition being to
enable a quick speed to the chuck when the same is advantageous.
[Illustration: Fig. 1788.]
For drilling small holes in metal, the breast drill shown in Fig. 1788
is employed. It consists of a spindle having journal bearing in a
breast-plate at the head, and in a frame carrying a bevel gear-wheel
engaging with two gear-pinions that are fast upon the spindle, this
frame and the bevel gear-wheel being steadied by the handle shown on the
right. At the lower end of the spindle is a chuck for holding and
driving the drill, which is obviously operated by revolving the handled
crank which is fast upon the large bevel gear. The feed is put on by
pressing the body against the breast-plate.
It is obvious that but one bevel pinion would serve, but it is found
that if one only is used the spindle is apt to wear so as to run out of
true, and the bore of the gear-wheel rapidly enlarges from the strain
falling on one side only. To avoid this the spindle is driven by two
pinions, one on each side of the driving gear as in figure.
Breast-drills do not possess enough driving power to capacitate them for
drills of above about quarter inch in diameter, for which various forms
of drill cranks are employed.
[Illustration: Fig. 1789.]
Fig. 1789 represents a drill crank which receives the drill at A, and is
threaded at B to receive a feed screw C, which is pointed at D; at E is
a loose tube or sleeve that prevents the crank from rubbing in the
operator's hands when it is revolved.
[Illustration: Fig. 1790.]
To use such a drill crank a frame A, Fig. 1790, is employed, being held
in a vice and having at T a table whereon the work W may be rested. The
feed is put on by unscrewing the screw S in this figure against the
upper jaws of A; holes of about half inch and less in diameter may be
drilled with this device.
[Illustration: Fig. 1791.]
A very old but a very excellent device for hand drilling when no
drilling machine is at hand is the drilling frame shown in Fig. 1791,
which consists of two upright posts A, and two B, placed side by side
with space enough between them to receive and guide the fulcrum lever
and the lifting lever. The fulcrum lever is pivoted at C, and has an
iron plate at E, and suspends a weight at its end which serves to put on
the feed. The lifting lever is pivoted at D, and at F hooks on to the
fulcrum lever. At its other end is a rope and eye G, and it is obvious
that the effect of the weight upon the fulcrum lever is offset by any
pressure applied to G, so that by applying the operator's foot at G the
weight of drill feed may be regulated to suit the size of hole and
strength of drill being used. The work is rested on a bench, and a drill
crank or other device such as a ratchet brace may be used to drive the
drill. This drill frame is capable of drilling holes up to about two
inches in diameter, but it possesses the fault that the upper end of the
brace or drilling device moves as the drill passes into the work in an
arc H of a circle, of which the pin C is the centre. The posts A are
provided with numerous holes for the pin C, so that the fulcrum lever
may be raised or lowered at that end to suit the height of the work
above the work bench. Another objection to this device is, it takes up a
good deal of shop room.
Ratchet braces are employed to drill holes that are of too large a bore
to be drilled by tread drills, and that cannot be conveniently taken to
a drilling machine.
[Illustration: Fig. 1792.]
In Fig. 1792 is represented a self-feeding ratchet brace. A is the body
of the brace, having a taper square hole in its end to receive the
square shank of the drill. L is a lever pivoted upon A, and having a
pawl or catch B, which acts upon ratchet teeth provided upon A. When the
lever L is moved backward the pawl B being pivoted rides over the
ratchet teeth, but when L is pulled forward B engages the ratchet teeth
and rotates A and therefore the drill. At F is a screw threaded into A,
its pointed end abutting against some firm piece, so that unscrewing F
forces the drill forward and into its cut. These features are essential
to all forms of ratchet braces, but the peculiar feature of this brace
consists in its exceedingly simple self-feeding devices, the feed screw
F requiring in ordinary braces to be operated by hand when the drill
requires to be fed.
The construction and operation of the self-feeding device is as follows:
The feed screw F is provided with a feather way or spline and with a
feed collar C, operated by the pawl E. The feed-collar C has at D a
groove, into which a flange on pawl E fits, and on its side face there
is a groove receiving an annular ring on the face of lever L, these two
keeping it in place. The pawl E is a double one, and may be tripped to
operate C in opposite directions to feed or release the drill, as the
case may be, or it may be placed in hind position to throw the feed
off--all these operations being easily performed while the lever L is in
motion. Collar C is in effect a double ratchet, since its circumference
is provided with two sets of notches, one at _g_ and the other at _h_.
Each set is equally spaced around the circumference, but one set or
circle is coarser spaced than the other, while both are finer spaced
than is the ratchet operated by pawl B. Suppose, now, that the lever L
is at the end of a back stroke, and pawl E will fall into one of the
notches on side _g_ of the feed-ratchet, and when lever L is moved on
its forward stroke it will operate the feed ratchet and move it forward,
A standing still until such time as pawl B meets a tooth of the ratchet
on A. The feed screw F is provided with a left-hand thread, and the feed
ratchet has a feather projecting into the spline in the feed screw;
hence moving the feed ratchet at the beginning of the forward motion of
L and before A is operated, puts a feed on, and the amount of this feed
depends upon how much finer the notches into which pawl E falls are than
those into which B falls. The feed takes place, be it noted, at the
beginning of the lever stroke, and ceases so soon as pawl B operates A
and the drill begins to cut.
As shown in the figure, the feed collar is set for large drills (which
will stand a coarser feed than small ones), because the notches are
finer spaced at _g_ than at _h_. For small drills and finer feeds the
collar is slipped off the screw and reversed so that side _h_ will fall
under E, it being obvious that the finer the notches are spaced the more
feed is put on per stroke. The spacings are made to suit very moderate
feeds, both for large and small drills, because the operator can
increase the feed at any stroke quite independently of the spacings on
the feed ratchet. All he has to do is to give the lever handle a short
stroke and more feed is put on; if still more feed is wanted, another
short stroke may be made, and so on, the least possible amount of feed
being put on when the longest strokes are made. In any event, however,
there will be a certain amount of average feed per stroke if equal
length of strokes is taken, the spacing being made to suit such ordinary
variations of stroke as are met within every-day practice. When it is
desired to stop feeding altogether, or to release the drill entirely
from the cut, all that is necessary is to trip the feed-pawl E (without
stopping the lever motion), and it will operate the feed screw in the
opposite direction sufficiently to release the drill in a single
backward stroke of the lever. The range of feed that is obtainable with
a single feed ratchet is sufficient for all practical purposes, although
it is obvious that if any special purpose should require it, a special
feed ratchet may be made to suit either an unusually fine or coarse rate
of feed. The feed screw is not provided with either a squared head or
with the usual pin holes, because the feed ratchet is so readily
operated that these, with their accompanying wrench or pin, are
unnecessary.
[Illustration: Fig. 1793.]
[Illustration: Fig. 1794.]
Figs. 1793 and 1794 represent a self-feeding ratchet brace for hand
drilling in which the feed is obtained as follows: The inside or feed
sleeve B, which screws upon the drill spindle, is fitted with a friction
or outer sleeve A, in the head of which is secured a steel chisel-shaped
pin C, the lower end of which is pointed and rests upon a hardened steel
bearing D, fixed in the head of the inner sleeve B. This sleeve, with
its bearing D, revolves upon the point of the pin C, and within the
friction sleeve A. Having thus described its construction, we will now
describe the operation of the self-feeding device. The head of the pin C
being chisel-shaped, prevents the pin and the outer sleeve A from
revolving. If the thumb or friction screw F is unscrewed, it will permit
the inner sleeve B to rotate freely upon the bearing of pin C, and
within the friction sleeve A. As the screw F is tightened, the friction
upon the inner sleeve B is increased, causing it to remain stationary,
and consequently causing the screw on the drill spindle to feed the
drill until the friction on the drill becomes greater than the friction
on the sleeve B. This then commences to rotate again within the outer
sleeve A, and continues until the chip which the drill has commenced to
cut is finished, when the same operation is repeated, thus giving a
continuous feed, capable of being instantly adjusted to feed fast or
slow as desired, by tightening or loosening the friction screw F,
thereby causing a greater or less friction upon the inside or feed
sleeve B.
[Illustration: Fig. 1795.]
To afford a fulcrum or point of resistance for the chisel-piece C, or
the pointed centre used in the common forms of ratchet brace feed
screws, various supporting arms, or stands are employed. Thus Fig.
1795[30] represents a boiler shell _a_, to which is attached an angle
frame or knee _b_, carrying the angle piece _c_ (which may be adjusted
for vertical height on _b_ by means of the bolt shown) affording a
fulcrum for the feed sleeve _d_. This sleeve is sometimes made hexagonal
on its outside to receive a wrench or to be held by the hand when
feeding, or it may have holes near its centre end to receive a small pin
or piece of wire; _e_ is a chain to pass around the boiler to secure _b_
to it, which is done by means of the device at _f_.
[30] From _The American Machinist_.
For many purposes a simple stand having an upright cylindrical bar
carrying an arm that may be set at any height and set to its required
position on the bar by a set-screw is sufficient, the base of the stand
being secured to the work by a clamp or other convenient device.
Fig. 1796 represents a flexible shaft for drilling holes inaccessible to
a drilling machine, and in situations or under conditions under which a
ratchet brace would otherwise require to be used. It consists of a shaft
so constructed as to be capable of transmitting rotary motion though the
shaft be bent to any curve or angle. A round belt driven from a line
shaft rotates the grooved pulley, and the shaft transmits the rotary
motion to bevel-wheels contained in a portable drilling frame, the
fulcrum for the feed being afforded by a drilling post after the manner
employed in ratchet drilling. The shaft is built up of several layers of
wire (as shown in the view to the left), the number of layers depending
upon the size and strength of shaft required, wound one upon the other
helically. The layers are put on in groups of three to eight wires,
parallel to each other, each successive layer containing groups of
varying numbers of wires, thus giving a different pitch to the helices
for each layer, the direction of each twist or helix being the reverse
of the one upon which it is wound. When the shaft is laid up in this
manner, the wires at each end for a short distance are brazed solidly
together, and to these solidified ends the piercers are secured for the
attachment of the pulley and tool which it is to drive.
This construction, it will be readily seen, produces a shaft which will
have considerable transverse elasticity, while it must necessarily offer
great resistance to torsional strain, the reversed helices forming a
kind of helical trussing, which effectually braces it against torsion.
The case within which it turns is simply an elastic tube of leather or
other suitable material, within which is wound a single helix of wire
fitting its inside tightly, the inside diameter of the helix being a
little greater than the outside diameter of the shaft, and wound in a
contrary direction to the outer helices of the shaft. This forms a
continuous bearing for the shaft; or at least serves as a bearing at the
points of contact between the shaft and case which are brought about in
the various bending of the whole when in use.
[Illustration: Fig. 1796.]
In order to give to the instrument all the transverse elasticity
possible, that end of the shaft carrying the pulley is made with a
feather so that it may slide endways in the pulley, while the latter is
secured to the case, the case, however, not rotating with it. It will be
readily seen that this is a necessary precaution, inasmuch as in the
varying curves given to the instrument in use a difference will occur in
the relative lengths of the shaft and tube.
It might be supposed that the friction of the shaft within the tube
would be so considerable as to militate against the success of the
apparatus; but in practice, and under test for the determination of
this, it has been found that the friction generated by running it when
bent at a right angle does not exceed that when used in a straight line
more than 15 per cent. of the latter.
In the running of it in a bent position, not only will there be friction
between the shaft and tube, but there must also be some little motion of
the layers of wire one upon another in the shaft itself; and to provide
against the wear and friction which would otherwise occur in this way,
provision is made for not only oiling the bearings at the ends, but also
for confining a small quantity of oil within the tube, by which all
motion of the wires upon one another, or the shaft upon the interior of
the tube, is made easy by its being well lubricated.
In the figure the shaft is shown complete with a wood-boring auger in
place at the shaft end. Shafts of similar but very light construction
are employed by dentists for driving their dental drills and plugging
tools, many of them having ingenious mechanical movements derived from
the rotary motion of the shaft.
[Illustration: Fig. 1797.]
In Fig. 1797 is represented a drilling device in position for drilling a
hole from the inside of a steam boiler. A represents a base piece made
with a journal stud _b_. This base piece is provided with radial arms
_a_, with threaded ends and nuts made with conical projecting ends, as
shown at _a_^{2}. One of these pieces is used at each end of the machine
when convenient, their use for centring and holding the frame being
apparent. When not convenient to use two of them, one end of the frame
is sustained as shown in the engraving, or in some other manner that may
suggest itself. The casting B is made in two pieces, and is provided
with a bearing for the pin _b_, and holds the ends of the rods C C. The
actuating shaft G carries the bevel-wheel _g_, more clearly seen in the
figure at side, which drives the drill spindle, whose ends are of
different lengths, for convenience in reaching to different distances.
The cross-head E may be slid along as required on the rods, and the
revolving frame and drill turned around to different positions.
[Illustration: Fig. 1798.]
Fig. 1798 represents a small hand drilling machine to be fastened to a
work bench. A suitable frame affords journal bearing to the upright
spindle, upon which is a bevel-gear G, which is driven by a gear upon
the same shaft as the wheel W. The spindle is threaded at S and is fed
by the hand wheel F, which is threaded upon the screw S and has journal
bearing in the cap C.
Fig. 1799 represents a hand drilling machine for fixture against a post,
the larger wheel serving as a fly-wheel and the smaller one being to
feed with.
SLOTTING MACHINE.--In the slotting machine the cutting tools are carried
in a ram or slide that operates vertically, and the work table lies
horizontal and beneath the ram.
Fig. 1800 represents a slotting machine, and Fig. 1801 is a sectional
view of the same machine.
The cone spindle shaft has a pinion which drives a spur-wheel upon an
horizontal shaft above. Upon the inside face of this spur gear is a cam
groove for operating the feed motions, at the other end of the shaft is
a Whitworth quick-return motion, such as has already been described with
reference to shaping machines. The connecting rod from the quick-return
motion attaches to the ram, which operates on a guide passing through a
way provided at the upper end of the main frame, and bolting to the
front face of the main body of the frame. The object of this arrangement
is that by adjusting the height of this guide to suit the height of the
work, the ram will be guided as close to the top of the work as the
height of the latter will permit; whereas when the guide for the ram is
fixed in position on the frame the ram passes as far through the guide
when doing this as it does when doing thick work, and is therefore less
closely guided than is necessary so far as the work is concerned.
[Illustration: Fig. 1799.]
[Illustration: Fig. 1800.]
The ram, or slotting bar as it is sometimes termed, is counterbalanced
by the weighted lever shown, so that the ram is always held up, and
there is no jump when the tool post meets the work, because the tool
motion is always taken up by the lever.
[Illustration: Fig. 1801.]
The work is held upon a circular table capable of being revolved upon
its axis to feed the work to the cut. This table is carried upon a
compound slide having two horizontal motions, one at a right angle to
the other. The lower of these is operated by a rod running through the
centre of the machine, as seen in the sectional view in Fig. 1801. The
upper is operated through the larger of the two gear-wheels, seen at the
side of the machine in the general view of the machine in Fig. 1800. The
upper and smaller of these wheels operates a worm, which engages with
worm-teeth cut on the periphery of the circular table to rotate the
latter. Either or all of these feed motions may be put in simultaneous
action, or all may be thrown out and the feeds operated by hand.
As the tool is in many cases rigid on the ram or bar of a slotting
machine, it is preferable that the feed should occur while the tool is
at the top of its stroke and before it meets the work, so that it may
not rub on the return stroke, and thus become rapidly dulled.
Fig. 1802 represents a slotting machine in which the guideway for the
slotting bar or ram is fixed in position, and the feed motions are
entirely on the outside of the machine. In this case the worm-gear
pinion is on the side of the machine not seen in the engraving.
The cutting tools for slotting machines are carried in one of these
ways: first, bolted direct to the slotting bar or ram, in which case
they stand vertically; secondly, in a box that is bolted to the end of
the ram and standing horizontally; and thirdly, held in a tool bar, in
which case the tool may stand either horizontally or vertically.
Fig. 1803 shows a tool B secured in a hole provided in a stout bar A by
the set-screw C. The tool in this case being rigidly held the cutting
edge is apt to rub against the work during the upward stroke and become
rapidly dulled. To avoid this, various devices have been employed, but
before describing them it will be well to point out that the shape of
the tool has an important bearing upon this point.
In Fig. 1804, for example, is a tool T bolted to the box B at the end of
the slide S. W is a piece of work having the cut C taken off it. Now
suppose that A is the centre of motion or fulcrum from which the spring
of the tool takes place (and there is sure to be a little spring under a
heavy cut), then the point of the tool will spring in the direction of
the arrow E, and will cut deeper to the amount of its spring; but during
the up stroke the tool being released from pressure will not spring, and
therefore will partly or quite clear the cut according to the amount of
the spring. This desirable action may be increased by giving the face of
the tool which meets the cutting a slight degree of side rake, as shown
in Fig. 1805, in which S is the slide, T the tool, B the box, and F the
direction of the tool spring, which takes place in this case from the
pressure of the cutting in its resistance to being bent out of the
straight line.
[Illustration: Fig. 1802.]
[Illustration: Fig. 1803.]
[Illustration: Fig. 1804.]
In Fig. 1806 is a device for obviating to some extent this defect. A A
is the tool box or bar containing a tool-holding piece pivoted at C, the
tool being secured therein by the set-screw E B. A spiral spring
sustains the weight of the pivoted piece and of the tool. During the
down stroke the spiral spring holds the pivoted piece against the box or
bar A, while during the up stroke the pivoted piece allows the tool to
swing from the pivot C as denoted by the arrow D. In this case the
friction on the tool edge is that due to overcoming the resistance of
the spring only.
[Illustration: Fig. 1805.]
[Illustration: Fig. 1806.]
[Illustration: Fig. 1807.]
In round-nose tools that are slight, and which from having a maximum
length of cutting edge are very subject to spring, additional strength
may be given the tool by swelling it out at the back, as denoted by the
dotted line B in Fig. 1807.
[Illustration: Fig. 1808.]
Excessively heavy cuts may be taken by the form of tool shown in Fig.
1808, in which A is the tool, B the tool box, and C the work, the depth
of cut being from D to E, which may be made 2-1/3 inches if necessary.
The face F of the tool is ground at an angle in the direction of I, so
that the tool shall take its cut gradually, and that the whole length of
the tool cutting edge shall not strike the cut at the same instant,
which would cause a sudden strain liable to break either the tool or
some part of the machine itself. So likewise the tool will leave its cut
gradually and not with a jump. As shown in the cut, but a small part of
the cutting edge would first meet the work, exerting for an instant of
time only enough pressure and resistance to bring all the working parts
of the machine up to a bearing, and as the tool descends (as denoted by
the arrow G), the strain would increase until the whole length of tool
cutting edge was in operation. For such heavy duty as this the tool is
tempered down to a purple to give it strength.
CHAPTER XXI.--THREAD CUTTING.--BROACHING PRESS.
In Fig. 1809 is represented a front view of a patent die stock for
threading pipe up to six inches in diameter. In the figure the three
bits or chasers are shown locked in position by the face plate, which is
shown removed in Fig. 1810. Fig. 1811 shows the machine with the face
plate removed, the bit or chasers having pins in them which fit into the
slots in the face plate, so that by rotating the plate the chasers may
be set to size.
[Illustration: Fig. 1809.]
[Illustration: Fig. 1810.]
[Illustration: Fig. 1811.]
[Illustration: Fig. 1812.]
The head carrying the chasers is revolved by means of the gear-wheel and
pinion, and Fig. 1812 represents a ratchet lever for revolving the
pinion, and is useful when the pipe is in the ground and the die stock
is used to cut it off and thread it without lifting it from its
position.
[Illustration: Fig. 1813.]
The method of gripping the pipe is shown in Fig. 1813, in which the
machine is represented as arranged for operating by belt power, the
pinion being operated by a worm and worm-gear.
[Illustration: Fig. 1814.]
Referring to the pipe-gripping vice it is seen in the figure that the
back of the machine is provided with ways in which the gripping jaws
slide. The lower jaw is adjusted for height to suit the size of pipe to
be operated upon, and is firmly locked in its adjusted position. It is
provided with an index pointer, and the face of the slideway is marked
by lines to suit the different diameters of pipe, so that this jaw may
at once be set to the proper height to bring the pipe central to the
bits. The lower jaw being set, all that is necessary is, by means of the
hand wheel, to operate the upper one to firmly grip the pipe. Fig. 1814
shows the front of the machine when arranged for belt power.
The No. 1 die stock threads pipe from one to two inches in diameter, but
has no cut-off. The large gear has cut teeth, and the pinion is of
steel, working in gun-metal bearings. The gripping jaws are fitted with
cast-steel faces, hardened.
By a simple change the stock may be used to cut left-hand as well as
right-hand threads, this change consisting in putting in left-hand bits
and in replacing the right-hand screw ring with a left-hand one. After a
piece of pipe has been threaded, all that is necessary is to turn the
head in the opposite direction, and the bits retire from the pipe
thread, so that the pipe may at once be withdrawn, which preserves the
cutting edges of the bits as well as saves the time usually lost in
winding the dies back.
In threading machines the bolt (or pipe, as the case may be) may be
revolved and the die held stationary, or the die may be revolved and the
pipe held from revolving, the differences between the two systems being
as follows, which is from _The American Machinist_:--
Fig. 1815 may be taken to represent a machine in which the pipe is held
and the die revolved, and Fig. 1816 one in which the pipe is revolved
and the dies are held in a head, which allows them to move laterally to
suit the pipe that may not run true, while it prevents them from
revolving.
In the former figure the bolt or pipe is shown to be out of line with
the die driving spindle, and the result will be that the thread will not
be parallel with the axis of the pipe. Whereas in Fig. 1816 the thread
will be true with the axis of the work, because the latter revolves, and
as the die is permitted more lateral motion it can move to accommodate
itself to the eccentric motion of the work, if the latter should not run
true.
If the end of a piece of pipe is not cut off square or at a right angle
to the pipe axis, and the die has liberty to move, it will thread or
take hold of one part, the longest one, of the pipe circumference first,
and the die will cant over out of square with the pipe axis, and the
thread cut will not be in line with the pipe axis.
[Illustration: Fig. 1815.]
[Illustration: Fig. 1816.]
The two important points in operating threading machines is to keep the
dies sharp and to well lubricate them with oil. When dies are run at a
maximum speed and continuously at work they should be sharpened once or,
if the duty is heavy, twice a day, a very little grinding sufficing.
In nut tapping the oil lubrication is of the utmost importance, and is
more difficult because the cuttings are apt to clog the tap flutes and
prevent the oil from flowing into the cutting teeth.
When the tap stands vertical and the nuts are put on at the upper end
(the point of the tap being uppermost), the cuttings are apt to pass
upwards and prevent perfect lubrication by the descending oil. When the
taps stand horizontally, gravity does not assist the oil to pass into
the nut, and it falls rapidly from the tap, hence it is preferable that
the tap should stand vertical with its point downwards, and running in
oil and water.
In machines which cut the bolt threads with a solid die, it is obvious
that after the thread is cut upon the bolt to the required distance, the
direction of rotation of the bolt or die, as the case may be, requires
to be reversed in order to remove the bolt from the die, and during this
reversal of rotation the thread upon the bolt is apt to rub against and
impair the cutting edges of the chasers or die teeth.
To obviate this difficulty in power machines the dies are sometimes
caused to open when the bolt is threaded to the required distance, which
enables the instant removal of the finished work, and this saves time as
well as preserving the cutting edges of the die or chaser teeth.
In machines in which the bolt rotates, the machine must be stopped to
take out each finished bolt and insert the blank one, which is
unnecessary when the bolt is stationary, because so soon as the bolt is
threaded to the required distance the dies may open automatically, the
carriage holding the bolt at once withdrawn and a new one inserted.
When the dies open automatically the further advantage is secured that
the bolts will all be threaded to an equal distance or length without
care on the part of the operator.
[Illustration: Fig. 1817.]
A hand machine for threading bolts from 1/4 inch to 3/4 inch in diameter
is shown in Fig. 1817. It consists of a head carrying a live spindle
revolved by hand, by the lever shown at the right-hand end of the
machine, being secured to the live spindle by a set-screw, so that the
handle may be used at a greater or less leverage to suit the size of the
thread to be cut; on the front end of this spindle are the dies,
consisting of four chasers held in a collet that is readily removable
from the spindle, being held by a spring bolt which, when pressed
downwards, frees the collet from the spindle.
The work is held in a pair of vice jaws operated by the hand wheel
shown, and this vice is moved endwise in its slideways on the bed by
means of the vertical lever shown. The bolt being stationary, the small
diameter of the die enables it to thread bent or crooked pieces, such as
staples, &c.
For bolts of larger diameter requiring more force than can be exerted by
a hand lever, a geared hand bolt cutter is employed.
[Illustration: Fig. 1818.]
In Fig. 1818 is represented a hand bolt cutter. In this cutter the bolt
is rotated, being held in a suitable chuck. The revolving spindle is
hollow in order to receive rods of any length, and is operated by
bevel-wheels as shown, so as to increase the driving power of the
spindle by decreasing its speed of rotation. To provide for a greater
speed of rotation than that due to the diameters of the bevel-pinion and
wheel, the lever is made to slide through the pinion, effecting the same
object and convenience as described for the machine shown in Fig. 1817.
The threading dies are held in collets carried by a head or cylinder
mounted horizontally on a carriage capable of being moved along the bed
by means of a rack and pinion, the latter being operated by a handle
passing through the side of the bed as shown. The cylinder also carries
a collet adapted for recessed plates so as to receive square or hexagon
nuts of different sizes for tapping purposes, the taps being held in the
rotating chuck. The collets are capable of ready and separate
extraction, and by removing the collet that is opposite to the one that
is at work, the end of a bolt may pass if necessary entirely through the
head or cylinder threading the work to any required length or distance.
To insure that the die shall stand axially true with the revolving
spindle, bolt holes are drilled in the lower part of the cylinder, and a
pin passes through the carriage carrying the head, and projects into
these holes, which are so situated that when the pin end projects into a
hole and locks the head a collet is in line with the spindle.
The dies consist of four chasers inserted in radial slots in collets
held in place and bound together by a flat steel ring, which is let into
the face of the collet and the external radial face of the chasers, and
secured to the collet by screws. One chaser only is capable of radial
motion for adjusting the diameter of thread the die will cut, and this
chaser is adjusted and set by a screw in the periphery of the collet.
The other two chasers being held rigidly in a fixed position in the ring
act as back rests and cut to the diameter or size to which they are
made, or according to the adjustment of the first chaser. The shanks of
the collets are secured in the cylindrical head by means of either a
bolt and key or by a set-screw.
The chasers are sharpened by grinding the face on an ordinary grindstone
or emery wheel.
[Illustration: Fig. 1819.]
The chasers are numbered to their places and are so constructed that if
a single chaser of a set of three should require renewal, a chaser can
be obtained from the manufacturers that will match with the remaining
two of the set, the threads on the one falling exactly in line with
those on the other two, whereas in other dies the renewal of one chaser
involves the renewal of the whole number contained in the die. This is
accomplished by so threading the dies that the thread starts from the
same chaser (as No. 1) in each set.
In Fig. 1819 is represented one of these machines, which is intended for
threads from 3/8 to 1 inch in diameter. It is arranged to be driven by
belt power, being provided with a pulley having three steps; on this
pulley spindle is a pinion operating a gear-wheel on the die driving
spindle, as shown.
The oil and cuttings fall into a trough provided in the bed of the
machine, but the oil drains through a strainer into the cylindrical
receiver shown beneath the bed, whence it may be drawn off and used over
again.
[Illustration: Fig. 1820.]
In Fig. 1820 is represented a bolt threading machine which is designed
for bolts from 3/16 to 1 inch in diameter.
The bolt to be threaded is gripped in the vice L, operated by hand by
the hand wheel M, and is moved by hand up to the head D, by the hand
wheel Q operating the pinion in the rack shown at the back of the
machine. When the dies or chasers have cut or threaded the bolt to the
required distance, the threading dies are opened automatically as
follows:--
At H is a clutch ring for opening and closing the threading chasers, and
at N is the lever operating the shoes in the groove of the clutch ring.
This lever is upon a shaft running across the machine and having at its
end the catch piece P; at Z is a catch for holding P upright against the
pressure of a spring that is beneath the bed of the machine, and presses
on an arm on the same shaft as the catch piece P. On the back jaw of the
vice L is a bracket carrying a rod R, and the bolt or work is threaded
until the end of rod R lifts catch Z, when the before-mentioned spring
pulls lever N and clutch ring H forward, opening the dies and therefore
stopping the threading operation. The length of thread cut upon the work
is obviously determined by adjusting the distance rod R projects through
V. The handle W is upon the same shaft as catch piece P and clutch lever
N, and therefore affords means of opening the dies by hand.
The operation of the machine obviously consists of gripping the work in
vice L, moving it up to the head D by the hand wheel Q, setting the rod
R to open the dies when the bolt is threaded to the required length, and
moving the vice back to receive a subsequent piece of work.
[Illustration: Fig. 1821.]
[Illustration: Fig. 1822.]
The construction of the head D and clutch and ring H is shown in Figs.
1821 and 1822.
The body F is bolted by the flange I to a face plate in the live spindle
or shaft of the machine, and through slots in this body pass the holders
or cases C containing the chasers or dies. Upon F is the piece D
provided with a slot to receive the die cases and a tongue to move them.
This slot and tongue, which are shown at E´, are at an angle to the axis
of F; hence if D be moved endways upon F the cases and dies are operated
radially in or through the body F. To operate D laterally or endwise
upon F the clutch ring H and the toggles G are provided, the latter
being pivoted in the body F, and H being operated endwise upon F by the
lever shown at N in the general view, Fig. 1820. The amount to which the
dies will be closed is adjustable by means of the adjusting screws E,
which are secured in their adjusted position by the set-screws R, Fig.
1821; it being obvious that when H meets the shoulder S of G and
depresses that end of the toggle, head D is moved to the right and the
dies are closed when the end of G meets E, and ceases to close when G
has seated itself in F and can no longer move E. The backward motion of
the clutch ring H, and therefore the amount to which the dies are
opened, is regulated by the screw B and stop A in Fig. 1822, it being
obvious that when B meets A the motion of H and D to the left upon F
ceases and the dies are fully opened. The amount of their opening is
therefore adjustable by means of screw B. J is simply a cap to hold the
dies and cases in their places.
[Illustration: Fig. 1823.]
In the end view, Fig. 1823, E, E are the adjustment screws for the
amount of die closure, and B, B those for the amount they will open to,
T representing the screws for the cap J, which is removed for the
insertion and extraction of the dies and die cases.
[Illustration: Fig. 1824.]
The construction of the dies P and cases C is shown in Fig. 1824. Two
screws at N secure the dies in their cases and a screw M adjusts them
endways so as to set them forward when recutting them. By inserting the
dies in cases they may be made of simple pieces of rectangular steel,
saving cost in their renewal when worn too short.
[Illustration: Fig. 1825.]
Fig. 1825 shows the machine arranged with back gear for bolts from 2 to
2-1/2 inches in diameter, the essential principles of construction being
the same as in Fig. 1820.
[Illustration: Fig. 1826.]
In Fig. 1826 is represented a single and in Fig. 1827 a double "rapid"
machine, constructed for sizes up to 5/8 inch in diameter, the double
machine having a pump to supply oil to the dies. This pump is operated
by an eccentric upon the end of the shaft of the cone pulley.
The construction of the head of this machine is shown in Fig. 1827A. Z
is the live or driving spindle, upon which is fast the head A. In A are
pivoted at M the levers L which carry the dies D, which are secured in
place in the levers by the set-screws B and adjusted to cut to the
required diameter by the screws E. The levers L are closed upon the
clutch C by means of the springs R and S, each of these springs acting
upon two diametrically opposite levers, hence the action of the springs
is to open the dies D. The clutch C has a cone at T and slides endways
upon the live spindle Z. The clutch lever and shoes are upon a shaft
running across the machine and actuated by a rod corresponding to the
rod R in Fig. 1820. When the clutch and levers L are in the position
shown in the figures the dies are closed for threading the bolt, and
when this threading has proceeded to the required distance along the
work, clutch C is moved by the aforesaid rod and lever in the direction
of arrow W, and the springs R, S close the ends P of lever L down upon
the body X of the clutch opening the dies and causing the threading to
cease.
[Illustration: Fig. 1827.]
[Illustration: Fig. 1827A.]
Fig. 1828 represents a "double" rapid machine for threading work up to
four inches in diameter, and therefore having back gear so as to provide
sufficient power. The gauge rod from the carriage here disengages a bell
crank from the end of the long lever shown, and thus prevents the spring
to operate the cross shaft and open the dies.
In Fig. 1829 is represented a bolt threading machine or bolt cutter,
which consists of a head carrying a live spindle upon which is a head
carrying four bits or chasers that may be set to cut the work to the
required diameter, and opened out after the work is threaded to the
required length and the bolt withdrawn without losing the time that
occurs when the dies require to run backward to release the work, and
also preventing the abrasion and wear that occurs to the cutting edges
of the die bits or chasers when revolved backward upon the work. This
head is operated by the upright lever shown in the figure, this lever
being connected to the clutch shown upon the live spindle. The details
of construction of the clutch and of the head are shown in Figs. 1830,
1831, 1832, and 1833. The work to be threaded is gripped between jaws
operated by the large hand wheel shown, while the vice moves the work up
to or away from the head by means of the small hand wheel which operates
pinions geared with racks on each side of the bed of the machine as
clearly shown in the figure.
Fig. 1830 is a longitudinal section of the head, and Fig. 1831 an end
view of the same. P are the threading dies or chasers held in slots in
the body _a_ by the annular ring face plate K. The ends of the dies are
provided with [T]-shaped caps T fitting into corresponding grooves or
slideways in the die ring B, and it is obvious that as the heads of
their caps are at an angle therefore sliding the ring B along _a_ and to
the right of the position it occupies in the figure will cause the dies
P to close concentrically towards the centre or axis of the head _a_. At
C is a ring capable of sliding upon _a_ and operated by the upright
lever shown in the general view in Fig. 1829.
The connection between the die ring B and the clutch ring C is shown in
Figs. 1832 and 1833, the former being also a longitudinal sectional view
of the head, but taken in a different plane from that in Fig. 1830. The
barrel or body _a_ _a_ of the head is provided with two diametrically
opposite curved rocking levers which are pivoted in recesses in _a_ _a_.
The clutch ring C envelops body _a_ and passes between the curved ends
of these rocking levers. The upper of the two rocker levers shown in the
engraving connects with a lever E, which connects to a stud or plunger
P, threaded to receive the adjusting screw I, which is threaded into the
die ring B. Obviously when C is moved to the right along _a_ it operates
the rocking lever and causes B to move to the right and to close the
dies upon the work. The amount of die closure, and therefore the
diameter to which the dies will thread the work, is adjustable by means
of the adjusting screw I, which has a coarse thread in B and a finer one
in P, hence screwing up I draws B to the left and farther over the
plunger P, thus shortening the distance between the centre of the curved
lever and limiting the motion of B to the right. On the other hand,
unscrewing I moves B to the right, and it is obvious that in doing this
the cap T in Fig. 1830 is forced down by the groove in B and the dies
are moved endwise towards the axis _a_ _a_, or in other words, closed.
It will be clear that a greater amount of power will be necessary to
hold the dies to their cut than to release them from it, and on that
account the lower curved rocking arm D connects through E to a solid
plunger G, the screw H abutting against the end of G and not threading
into it, because G is only operative in pushing B forward in conjunction
with P, while P pulls B backward, the duty being light. It is obvious,
however, that after the adjustment screw I is operated to set the dies
to cut to the proper diameter, adjustment screw H must be operated to
bring the ring B fair and true upon _a_ _a_ and prevent any lateral
strain that might otherwise ensue.
[Illustration: Fig. 1828.]
[Illustration: Fig. 1829.]
These two adjustments being made the clutch ring C is operated to the
left to its full limit of motion to open the dies and to its full limit
to the right to close them.
It will be seen, by the lines that are marked to pass through the
pivoting pins of the rocking lever D, that the joints marked 2 in Fig.
1832 are below these lines, and as a result the links E form in effect a
toggle joint locking firmer in proportion as the strain upon them is
greater.
Fig. 1834 represents a bolt threading machine having two heads each of
which is capable of threading bolts from 1/2 up to 1-1/2 inches in
diameter.
[Illustration: Fig. 1830.]
[Illustration: Fig. 1831.]
[Illustration: Fig. 1832.]
[Illustration: Fig. 1833.]
[Illustration: Fig. 1834.]
The levers for operating the clutch rings are here placed horizontal,
so that they may extend to the end of the machine and be convenient to
operate, and a pump is employed to supply oil to the dies.
The capacity of a double machine of this kind is about one ton of
railroad track bolts per day of 10 hours' working time.
In American practice it is usual to employ four cutting dies, bits, or
chasers, in the heads of bolt threading machines, while in European
practice it is common to employ but three. Considering this matter
independently of the amount of clearance given to the teeth, we have as
follows:--
If a die or internal reamer, the cutting points of which were all
equidistant from a common centre, were placed over a piece of work, as a
bar of iron shown in Fig. 1835, and set to take a certain cut, as shown
by the circle outside the section, it is evident that if revolved, but
left free to move laterally, or "wabble," the cutter would tend to
adjust itself at all times in a manner to equalize the cutting
duty--that is, if the die had two opposite cutting edges or points, and
the piece operated upon were not of circular form, then, when one cutter
reached the part that was not round, it would have either more or less
cutting to do than before, and hence, the opposite cutter having the
same amount, the tendency would be for the two cutting edges to travel
over and equalize the cuts, and hence the pressure. With three cutting
points, no two being opposite, the tendency would all the while be to
equalize the cuts taken by all three; with four, spaced equally, the
tendency would always be to equalize the cuts of those diametrically
opposite; with five, the tendency would be to equalize the duty on each,
and so on. Thus it will be noticed that there is a difference between
the acting principle of a die having an even or an odd number of
cutters, independent of the difference in the actual number of cutting
edges, or points, as we are now considering them.
[Illustration: Fig. 1835.]
[Illustration: Fig. 1836.]
To take an example, in Fig. 1835 is represented a die having four
cutting points, placed upon a piece of iron of a round section, with the
exception of a flat place, as shown. Now, in this position each one of
the cutting points A, B, C, and D, is in contact with the true
cylindrical part of the work only; hence, if the die were set to take
the amount of cut shown, each point would enter the iron an equal
distance, and the inner circle through the points would be the smallest
diameter of the die. Upon revolving the die in the direction denoted by
the arrow, an equal cut would continue to be taken off, and hence the
circular form maintained, until cutter D had reached the edge _x_ of the
flat, the opposite one B, being at _y_ (A at _r_ and C at _v_),
proceeding as D moved from _x_ towards A, its cutting duty would
continually become less and its pressure decrease, but as it is the
cutting pressure of D that holds the opposite point B to its cut, as the
pressure in D, after reaching _x_, continually becomes less, the die
would gradually travel over so as to carry D toward the centre and cause
it to take more cut, while B, on the opposite side, would travel out a
corresponding distance and take less, thus keeping the duty equalized
until the cutter D had reached H, the lowest part of the flat, when the
die would have moved the greatest distance off the centre, assuming the
position shown by dotted lines. Thus the cutting point at H has passed
inside the true circle that all the cutters commenced to follow, while F
has passed outside. Meanwhile, as H and F have shifted over, E and G
have, of course, moved an equal amount and in the same direction, but
the diameter of E and G being at right angles to that of H and F, the
distances of E and G from the centre would be changed but an
infinitesimal amount; hence, they would virtually continue to follow the
true circle, notwithstanding the deviation of the other pair. As the die
continues to revolve and H passes toward A, the lateral motion is
reversed, the die tending to resume its original central position, which
it does upon the completion of another quarter of a revolution, when the
cutter that started at D has passed to H and finally to A. A cutting has
now been removed from the entire circumference of the iron, leaving it
of a form shown approximately in Fig. 1836, where A _z_, B _y_, C _v_,
and D _x_, are the four true circular portions cut respectively by the
points A, B, C, and D, before the flat place was reached. After the flat
place was reached _x_ A is the depression cut by D, _y_ C the elevation
formed by B, and _z_ B and _v_ D are the arcs, differing almost
imperceptibly from the true circular ones cut by A and C.
[Illustration: Fig. 1837.]
[Illustration: Fig. 1838.]
Fig. 1837 represents a die having three instead of four cutting
points--that is, the point C of Fig. 1835 is left out, and the remaining
ones A, B, and D, are equally spaced. This, placed upon a similar bar
and taking an equal cut, would produce a truly circular form until D had
reached _x_--with A and B at _z_ and _y_--after which the die would move
laterally, tending to carry D toward the centre of the work and A and B
away from it, so as to equalize the cuts on all three. Hence, when D had
reached H and the three-cutter die attained the position shown by dotted
lines in Fig. 1837, H would have made an indentation inside the true
circle, while E and F have travelled away from it, thus forming
protuberances. From H to A the lateral movement is reversed, and finally
upon the completion of a third of a revolution, the die is again central
and a cut has been carried completely around the bar, leaving it as
shown in Fig. 1838. Comparing this with Fig. 1836, it will be seen that
there are three truly cylindrical portions--viz., A _z_, B _y_, and D
_x_ instead of four in Fig. 1836, but each one is longer; that there is
a depressed place, _x_ A, of equal length to that in Fig. 1836, and two
elevations, _z_ B and _y_ D, each of equal length to the one (_y_ C) in
Fig. 1836.
[Illustration: Fig. 1839.]
[Illustration: Fig. 1840.]
[Illustration: Fig. 1841.]
Now, suppose the bar to have an equal flat place on its opposite side,
becoming of a section shown in Fig. 1839, upon applying the dies and
pursuing a similar course of reasoning, the die with four points would
reduce the bar to the size and shape shown in Fig. 1840, or a true
cylinder, while the triple-pointed cutter would produce the form shown
in Fig. 1841, which is a sort of hexagon, coinciding with the true
circle in six places--A, _z_, B, _y_, D, and _x_--while between A and
_z_, and opposite, between _y_ and D, there is an elevation; also from
_z_ to B and from D to _x_. A flattened portion, A _x_, with a similar
one B _y_, opposite, completes the profile. Suppose, now, that a bar of
the form shown in Fig. 1842, having two flat places not opposite, be
taken, and the four-cutter and three-cutter dies are applied. The
product of the four is shown in Fig. 1843, and that produced by the
three-cutter die in Fig. 1844. The section cut with four coincides with
the true circle at four points, A, B, C, D, and differs from it almost
imperceptibly at _z_, _y_, _v_, and _x_. There are two elevations
between A and B and between B and C; also two depressions between C and
D and between D and A. The section from the three-cutter die is the
perfect circular form between A _z_, B _y_, and D _x_, with a projection
from _z_ to B and two depressions from _y_ to D and from _x_ to A. The
four-die, applied to a section having three flats like Fig. 1845, would
produce Fig. 1846, which does not absolutely coincide with the true
circle at any point, although the difference is inconsiderable at A,
_z_, _y_, C, _v_ and _x_; three equidistant sections A _z_, _y_ C, and
_v_ _x_, are elevated and the three alternate ones depressed.
[Illustration: Fig. 1842.]
[Illustration: Fig. 1843.]
[Illustration: Fig. 1844.]
[Illustration: Fig. 1845.]
[Illustration: Fig. 1846.]
[Illustration: Fig. 1847.]
The three-cutter die would in this case cut the perfectly circular form
of Fig. 1847.
Now, suppose both of the dies to have been made or set to some certain
diameter--in fact, presume them to be made by taking a ring of steel
having a round hole of the required diameter, say 1 inch, and removing
the metal shown by the dotted lines, Fig. 1848, and leaving only the
four cutting points in one case (and the three in the other). Then it is
evident that our dies are both of the same diameter, and likewise both
of the assumed diameter, or 1 inch; then it is fair to presume that the
plugs or sections just cut by either one of the dies should enter a
round hole of the same diameter as the dies; but it is obvious that only
two, Figs. 1840 and 1847, will do so, all the rest being considerably
too large, from their irregularity of form, notwithstanding the fact
that the diameter of any of those cut by four cutters is never more than
that of the die, while any one of the equal radii, taken at equal
distances on any of the forms cut by the three-cutter die, will not
exceed the radius of the die. Now, six of the pieces being too large
when referred to the standard of a round hole of the size of the die,
while two are of the correct size, it is obvious that if the four-die,
for example, which cut Fig. 1846, were reduced enough to make Fig. 1843
just enter the standard, that, Fig. 1840, which is now just correct in
size and form, would, when cut, be altogether too small. The same would
be the case also with the three-cutter die.
Now let us consider the two productions (Figs. 1840 and 1847) that
answer the requirements, the two different sections (Figs. 1839 and
1845) from which they were cut, and also the other two pieces (Figs.
1841 and 1846) that were cut from the same bars at the same time. The
general shape of Fig. 1839, is oval or four-sided, and while the four
cutters operated upon it to produce perfectly circular work, the three
cutters reproduced the general shape started with, only somewhat
modified, as Fig. 1841 plainly shows. Upon the blank, Fig. 1845, the
general shape of which is triangular, the very opposite is the case, for
the three cutters now produce a perfect circle, while the four modify
only the figure that they commenced to operate upon.
[Illustration: Fig. 1848.]
Considering that every irregular form may be approximated by a square,
an equilateral triangle, or in general by either a parallelogram or a
regular polygon, it will be found that from a flat, oval, or square
piece of metal the four cutters will produce a true circle; from a
triangular piece the three; from a heptagon neither will do so, while
from a hexagon both the three and four cutters are calculated to do so.
Following in the same manner, and increasing the sides, it will be found
that the four cutters will produce a true circle from every
parallelogram, whether all the sides are equal or not, while the three
cutters will produce a true circle also from every regular polygon the
number of sides of which is a multiple of three--that is, four cutters
would operate correctly upon a figure having 4, 6, 8, 10, 12, &c.,
parallel sides, while the three would do so upon a figure having 3, 6,
9, 12, 15, &c., equal sides. Thus, for regular forms varying between
these two series neither one would be adapted. Hence, if the general
form of the work is represented by the first series, the four cutters
are the best; if the general and average form of the material to be
operated upon corresponds to the second series, then the three dies are
the best adapted, so far as their two principles of action, mentioned at
the outset, are concerned; hence, if it is considered that the material
or bars of metal to be wrought vary from a circular form indifferently,
then there is no choice between an even and an odd number merely on that
account.
Placing the same dies that cut these six irregular figures upon their
respective productions would not serve to correct their form; as, for
instance, if the die that cut Fig. 1846 were revolved around it--even if
set up or reduced in diameter to take a cut--it would remove an equal
amount all round and leave the same figure still. Similarly with, say,
Fig. 1841, cut by the three; but if the three were run over Fig. 1846,
cut by the four, it would tend to correct the errors, and likewise if
the four were run over Fig. 1841, the tendency would be to modify the
discrepancies left by the three that cut it.
[Illustration: Fig. 1849.]
As regards the number of cutting points, suppose that there were a
certain number, as three, shown in Fig. 1849, all taking an equal cut;
then, when the position indicated by the dotted lines was reached,
where cutter H runs out, the entire duty would be only two-thirds as
much as it was, and the die would shift laterally in the direction of
the arrow enough to equalize this smaller amount of duty on all three,
or make H, E, and D each cut two-thirds as much as at first. With four
as shown in Fig. 1850 when H reached the depression where its cut would
run out, the entire duty would be three-fourths of what it was at first,
and the die would travel laterally in the direction of the arrow
sufficiently to equalise the pressure upon H and F, and upon E and G.
With five, as shown in Fig. 1851, in similar position the entire duty
would be four-fifths as much; with six, five-sixths, and so on. Thus it
can be seen that the variation between the least amount to be cut and
the full amount is relatively less, the greater the number of cutting
points that it is divided between, and hence the lateral movement would
be less; therefore the general tendency of an increase in the number of
cutting points would be to promote true work.
[Illustration: Fig. 1850.]
[Illustration: Fig. 1851.]
Hence, from these considerations it appears that it is not material
whether the number is odd or even merely on that account; so four would
be preferable to three only on account of being one more, and, in turn,
five would be better than four, and six better than five, and so on. It
is found, however, that bar iron usually inclines to the elliptical
form, and that an even number is, therefore, preferable.
Thus far the cutting edges of the die have been assumed to be points
equidistant about a circle--that is, it has been supposed to have
absolute clearance, so that its movements would be regulated entirely by
the depth of cut taken, in order to ascertain the inherent tendency to
untruth caused by an odd or an even, a greater or a less, number of
cutters. This tendency is, of course, modified in each case by the
amount of clearance.
[Illustration: Fig. 1852.]
[Illustration: Fig. 1853.]
[Illustration: Fig. 1854.]
The position of the dies in the head and with relation to the work is,
in bolt cutting machines, a matter of great importance, and in all cases
the dies should be held in the same position when being hobbed (that is,
having their teeth cut by the hob or master tap) as they will stand in
when put to work, and the diameter of the hob must be governed by the
position of the dies in the head. If they are placed as in Fig. 1852 the
diameter of the hob must be 1/32 inch larger than the diameter of bolt
the dies are intended to thread, so that the point or cutting edge may
meet the work first and the heel may have clearance, it being borne in
mind that the clearance is less at the tops than it is at the bottoms of
the teeth, because of their difference in curvature. In this position
the teeth are keen and yet retain their strength, acting somewhat as a
chaser. If placed in the position shown in Fig. 1853 the hob or master
tap must be 1/32 inch smaller than the diameter of bolt they are to
thread, so as to give the teeth clearance. In this case the dies are
somewhat harder to feed into their cut and do not cut quite so freely,
but on the other hand they work more steadily as the bolt is better
guided, while left-hand dies may be used in the same head. If placed as
in Fig. 1854 they must be cut with a hob 1/32 inch larger in diameter
than the bolt they are to thread, so that the teeth will have less
curvature than the work, and will, therefore, have clearance. In this
position the dies do not cut so freely as in Fig. 1852.
The dies should be broad enough to contain at least as many teeth as
there are in a length of bolt equal to its diameter, and should be thick
enough to withstand the pressure of the cut without perceptible spring
or deflection.
[Illustration: Fig. 1855.]
The cutting edges of dies may be brought in their best cutting position
and the dies placed in radial slots in the head by forming the dies as
in Fig. 1855. Face X is at an angle of 18° to the leading or front face
of the die steel, and the heel is filed off at an angle of 45° and
extends to the centre line of the die. This gives a strong and a keen
die, and by using a hob 1/32 inch smaller than the diameter of bolt to
be cut, the clearance is sufficiently maintained.
[Illustration: Fig. 1856.]
The heel of the die should not when the cutting edge is in front extend
past the axis of the work, but should be cut off so as to terminate at
the work axis as denoted by the dotted line G in Fig. 1856.
[Illustration: Fig. 1857.]
In hobbing the dies it is necessary that they be all of equal length so
that the hob may cut an equal depth in each, and may, therefore, work
steadily and hob them true. After the dies are hobbed their front ends
should be reamed with a taper reamer as in Fig. 1857, chamfering off not
more than three threads, and the chamfered teeth must then be filed,
just bringing the front edges up to a cutting edge, but filing nothing
off them, the reamed chamfer acting as a guide to file them by.
This will cause each tooth to take its proper share of the cut, thus
preserving the teeth and causing the dies to cut steadily. Back from the
cutting edge towards the heels of the teeth the clearance may gradually
increase so that the heel will not meet the work and cause friction.
The chasers or dies are obviously changed for each diameter of bolt, and
it follows that as the chasers all fit in the same slots in the head
they must all be made of the same size of steel whatever diameter of
bolt they are intended to cut, and this leads to the following
considerations.
Suppose the capacity of the machine is for bolts between 1/4 inch and
1-1/4 inches in diameter, and the size of the chaser or die will be
1-1/4 inches wide and 1/2 inch thick.
The width of a die or chaser should never be less than the diameter of
bolt it is to thread, so that it may contain as many threads as are
contained in a length of bolt equal to the bolt diameter. Now the
1-1/4-inch chaser equals in width the diameter of bolt it is to cut,
viz. 1-1/4 inches; but if the chaser for 1/4-inch bolts was threaded
parallel and left its full width it would be five times as wide as the
diameter of the bolt and the thread cut would be imperfect, because the
chasers alter their pitches in the hardening process, as was explained
with reference to taps, and it is found that the error induced in the
hardening varies in amount and sometimes in direction: thus of the four
chasers three may expand and become of coarser pitch, each varying in
degree from the other two, and the other may remain true, or contract
and become of finer pitch.
[Illustration: Fig. 1858.]
As a rule the dies expand, but do not so equally. The more teeth there
are in the die the more the pitch error from the hardening; or in other
words, there is obviously more error in an inch than there is in half an
inch of length. Suppose then that we have a die for 20 threads per inch,
and as the chaser is 1-1/4 inches wide, it will contain 25 teeth, and
the amount of pitch error due to 1-1/4 inches of length; and this amount
not being equal in all the chasers, the result is that the dies cut the
sides of the thread away, leaving it sharp at the top but widened at the
bottom, as shown in Fig. 1858, weakening it and impairing its durability
while placing excessive duty on the dies and on the machine.
[Illustration: Fig. 1859.]
[Illustration: Fig. 1860.]
[Illustration: Fig. 1861.]
A common method of avoiding this is to cut away all the teeth save for a
width of die equal to the diameter of the bolt, as shown in Fig. 1859.
An equally effective and much simpler plan is to form the dies as in
Fig. 1860, the diameter at the back B being slightly larger than that at
the mouth A, so that the back teeth are relieved of cutting duty. This
enables the dies to undergo more grindings and still retain sufficient
teeth. For example, the chamfer at A may be ground farther towards B,
and still leave in action sufficient teeth to equal in width of chaser
the diameter of the bolt. To enable the threading of dies in this manner
the hobs or master taps employed to thread them are formed as in Fig.
1861, the proportions of the master taps for the different sizes of
bolts being as given in the following table:--
------+-----------------------+---------------+-----------------------------
Dia- | | |
meter| | |
of | | | Length
bolt.| ---- | ---- |at A.|at B.|at C.|at D.|at E.
------+-----------------------+---------------+-----+-----+-----+-----+-----
1/4 |Dia. from G to H 15/64 |At J 7/32 | 1/2|1 |1 |1-1/2| 1/2
5/16| " " 19/64 | " 9/32 | 1/2|1 |1 |1-1/2| 1/2
3/8 | " " 23/64 | " 11/32 | 1/2|1 |1 |1-1/2| 1/2
7/16| " " 27/64 | " 13/32 | 1/2|1 |1 |1-1/2| 1/2
1/2 | " " 31/64 | " 15/32 | 1/2|1-1/2|1-1/2|1-1/2| 3/4
5/8 | " " 39/64 | " 19/32 | 1/2|1-1/2|1-1/2|1-1/2| 3/4
3/4 | " " 47/64 | " 23/32 | 1/2|1-1/2|2 |1-1/2| 3/4
7/8 | " " 55/64 | " 27/32 | 1/2|1-1/2|2 |1-1/2| 3/4
1 | Dia. at G 31/32 |At J 1/100 less| 1/2|4 |4 |1-1/2|1
1-1/8 | " 1-3/32 | ---- |1 |4 |4 |1-1/2|1
1-1/4 | " 1-7/32 | ---- |1 |4 |4 |1-1/2|1
1-3/8 | " 1-11/32| ---- |1 |4 |4 |1-1/2|1
1-1/2 | " 1-15/32| ---- |1 |4 |4 |1-1/2|1-1/4
1-5/8 | " 1-19/32| ---- |1 |5 |5 |2 |1-1/2
1-3/4 | " 1-23/32| ---- |1 |5 |5 |2 |1-1/2
1-7/8 | " 1-27/32| ---- |1 |6 |6 |2 |1-3/4
2 | " 1-31/32| ---- |1 |6 |6 |2 |1-3/4
------+-----------------------+---------------+-----+-----+-----+-----+-----
All over 2 in. same length as the 2 in. Shanks J turned to bottom of
last thread.
The cutting speeds for the dies and taps are as given in the following
table, in which it will be seen that the speeds for bolt factories are
greater than for machine shops. This occurs on account of the greater
experience of the operators and the greater care taken in lubricating
the dies and keeping them sharp:--
--------+-----------+-----------+--------+-----------+------------
Diameter|Revolutions|Revolutions|Diameter|Revolutions|Revolutions
of bolt.|of dies for|of dies for|of bolt.|of dies for|of dies for
| machine | bolt | | machine | bolt
| shops. | factories.| | shops. | factories.
--------+-----------+-----------+--------+-----------+------------
inch. | | | inch. | |
1/8 | 450 | 600 | 1-5/8 | 33 | 48
1/4 | 230 | 300 | 1-3/4 | 30 | 45
3/8 | 150 | 200 | 1-7/8 | 28 | 40
1/2 | 100 | 150 | 2 | 25 | 38
5/8 | 75 | 125 | 2-1/8 | 23 | 36
3/4 | 65 | 100 | 2-1/4 | 22 | 34
7/8 | 55 | 85 | 2-3/8 | 21 | 32
1 | 45 | 75 | 2-1/2 | 20 | 30
1-1/8 | 42 | 65 | 2-5/8 | 18 | 25
1-1/4 | 40 | 60 | 2-3/4 | 15 | 20
1-3/8 | 38 | 55 | 2-7/8 | 12 | 18
1-1/2 | 35 | 50 | 3 | 10 | 15
--------+-----------+-----------+--------+-----------+------------
Taps same speed as dies.
[Illustration: _VOL. I._ =NUT-TAPPING MACHINERY.= _PLATE XXIII._
Fig. 1864.
Fig. 1865.
Fig. 1866.
Fig. 1867.]
[Illustration: Fig. 1862.]
In Fig. 1862 is represented a nut threading or tapping machine. The
vertical spindles have spring sockets in which the taps are held, so
that they can be inserted or removed without stopping the machine. The
nuts are fed down the slots of the inclined plates shown on the upper
face of the circular base, and the spindles are raised and lowered by
the pivoted levers shown. The nuts lie in a dish that contains water up
to the level of the bottom of the nuts, the object being to prevent the
taps from getting hot and therefore expanding in diameter. Upon the top
of the water floats a body of oil about 1/2 inch deep, which lubricates
the cutting edges of the tap. These machines are also made with six
instead of four spindles, which in both machines run at different speeds
to suit different sizes of nuts, and which are balanced by weights
hanging inside the central hollow column or frame.
[Illustration: Fig. 1863.]
Fig. 1863 represents the socket for driving the tap, so devised that
when the tap is strung for its intended length with nuts, the top nut
releases the tap of itself, the construction being as follows: S is the
socket that fits into the driving spindle of the machine; its bore,
which fits the stem of the tap easily, receives two headless screws B, a
pin P, which is a sliding fit, and the screw A. R is a ring or sleeve
fitting easily to the socket, and is prevented from falling off by screw
A. The tap is provided with an annular groove G. The flattened end of
the tap passes up between and is driven by the ends of screws B, the
weight of the collar ring or sleeve R forcing pin P into the groove G,
thus holding the tap up. When the tap is full of nuts the top nut meets
face V of ring R, lifting this ring upon the socket and relieving pin P
of the weight of R, the weight of the tap and the nuts then causes the
tap to be released. By this construction the tap can be inserted or
removed while the machine is in motion.
In Fig. 1864 is represented a rotary nut tapper, and in Fig. 1865, is
also represented a sectional view of the same machine.
The tap driving spindles are driven from a central vertical shaft S,
driven by bevel-gear B. The horizontal driving shaft operates a worm C,
to drive a worm-wheel in a vertical shaft, which drives a pinion _a_,
driving a spur wheel W in the base of the spindle head, by which means
this head is revolved so as to bring the successive spindles in front of
the operator. A trough is provided at T to cool the tap with oil and
water after it has passed through the nut.
Fig. 1866 represents a nut tapping machine designed for light work, the
spindles are raised after each nut is tapped by the foot levers and rods
shown, the latter connecting to a shoe fitting into a groove in a collar
directly beneath the driving pulleys of the spindles.
Fig. 1867 represents a three-spindle nut tapping machine, in which the
spindles are horizontal and the nuts are held in three separate heads or
horizontal slideways and are traversed by the ball levers shown, and a
self-acting pump supplies them with oil. The three spindles are driven
by a cone pulley having four changes of speed to suit different
diameters of taps.
PIPE THREADING MACHINERY.--In Fig. 1868 is represented a machine for
threading and cutting off pipe of large diameter. This machine consists
of a driving head corresponding to the headstock of a lathe, but having
a hollow spindle through which the pipe may pass. The pipe is driven by
a three-jawed chuck, and the threading and cutting off tools are carried
on a carriage which has a threading head for ordinary lengths of pipe,
and one for short pieces such as nipples, the latter swinging out of the
way when not in use. Between these two is a pair of steadying jaws for
the pipe. A side view of the front of the carriage is shown in Fig.
1869, H H, &c., representing the threading dies used for nipples. It is
movable along a slideway E and pivoted upon its slider. The dies are
carried in a chuck G, and are opened or closed by the lever N; at L is
the handle for the screw that operates the guide jaws A A.
[Illustration: Fig. 1868.]
[Illustration: Fig. 1869.]
The threading head at H (right-hand end of Fig. 1868), is represented in
Fig. 1870, being pivoted so that it also can be swung out of the way to
permit of the removal of the pipe. The dies C are opened or closed by
the hand wheel B, operating a worm meshing into a segment of a
worm-wheel upon the body of the head, the amount of motion being
regulated by the stop screw at F, which therefore regulates the size to
which the dies can be closed, and therefore the diameter of thread the
dies will cut. The construction of the cutting-off head is shown in Fig.
1871, T representing the cutting tool which is operated by the hand
wheel K. The carriage is fed or traversed by means of two pinions
operated by the six-handled wheel shown at W, Fig. 1868; these two
pinions engaging racks beneath the carriage, and near the inside edges
of the bed, one of them being seen at the extreme right-hand end of Fig.
1868.
[Illustration: Fig. 1870.]
[Illustration: Fig. 1871.]
[Illustration: Fig. 1872.]
In Fig. 1872 is represented a machine for threading or tapping the
fittings for steam and gas pipe. The tap is carried in the end of the
vertical spindle, and the work may be held in the vice upon the work
table, or if too large the table may be swung out of the way.
The general design of the machine corresponds somewhat to that of a
drilling machine.
BROACHING PRESS.--Broaching consists in forcing cutters through keyways
or apertures, to dress their sides to shape.
In Fig. 1873 is represented a broaching press. Its driving gear which is
within the box frame is so constructed that it may be started and
stopped instantly, notwithstanding its heavy fly wheel.
Figs. 1874 to 1877 represent the method of cutting out a keyway by
broaching.
[Illustration: Fig. 1873.]
[Illustration: Fig. 1874.]
In Fig. 1874 A represents the end of a connecting rod having three
holes, B, C, and D, pierced through it, their diameters nearly equalling
the total finished width of keyway required. The punch D´ is first
forced through, thus making the three holes into one.
[Illustration: Fig. 1875.]
[Illustration: Fig. 1876.]
[Illustration: Fig. 1877.]
The [V]-shape of the end of the cutting punch D´ tends to steady it
while in operation, forces the cut outwards into the next hole,
preventing them from jambing, and causes the strain upon the punch to
begin and end gradually; thus it prevents violent action during the
ingress and egress of the cutting punch. This roughing out process
dispenses with the use of the hammer and chisel, and saves much time,
since it is done at one stroke of the press. The next part of the
process is the introduction of a series of broaches such as shown in
Fig. 1875, the principles involved being as follow: It is obvious that
from the large amount of cutting edge possessed by a single tooth
extending all around such a broach, it would be impracticable to take
much of a cut at once; hence a succession of broaches is used, some of
them performing duty on the sides only, others at the ends only, but the
last and final broach is usually made to take a very fine cut all over.
All these broaches are made slightly taper; that is to say, the breadth
of the lower tooth at A in Fig. 1875 is made less than that at B, the
amount allowed varying according to the dimensions and depth of the
keyway.
The smallest of the set of broaches is entered first and forced through
until its end stands level with the upper face of the work. Each broach
is provided with a conical teat at one end and a corresponding conical
recess at the other, so that when the second broach is placed on top of
the first, the teat fitting into the recess below it, will hold the two
broaches central one to the other.
The head of each broach is made somewhat conical or tapered, and sets in
a corresponding recess in the driving head in the machine, which,
therefore, holds the broaches parallel one to the other. A succession of
these broaches is used, each requiring one stroke of the press to force
it within the keyway, and another to force it out.
The following is an example of broaching, relating to which, the dotted
lines shown on the broaches, Fig. 1876, indicate the depths and shapes
of the teeth. The small end of each broach corresponds to the large end
of the one that preceded it, which is necessary in order to permit it to
enter easily. Of the ten broaches used the first two operate to
straighten the side walls of the hole, No. 3 being the first to operate
upon the circular corners, which are not cut to the rectangle until No.
8 has passed through. But as the duty in cutting out the corners
diminishes, the walls and ends of the hole are operated upon to finish
them to size; thus broach No. 3 leaves the hole 1-1/8 or 1.125 inches
wide, and 2.7501 inches long, which No. 4 increases to 1.1354 inches
wide and 2.7605 inches long. This increase of width and depth, or
breadth, as it may more properly be termed, continues up to the last or
tenth cutter, which is parallel and of the same dimensions as the large
end of cutter No. 9. Fig. 1877 gives two views of the No. 10 broach.
Broaches require a very free lubrication in order to prevent them from
tearing the walls of the hole, and to enable them to cut easily and
smoothly; hence it is found highly advantageous after the teeth are cut
to cut out grooves or passages lengthways of the broach, and extending
nearly to the bottom of the teeth, which eases the cut as well as
affords the required lubrication; but it is obvious that the finishing
cutter must not have such oil ways.
MODERN
MACHINE-SHOP
PRACTICE
[Illustration]
ILLUSTRATED
MODERN
MACHINE-SHOP
PRACTICE
[Illustration: _Vol. II MODERN MACHINE-SHOP PRACTICE FRONTISPIECE_
COMPOUND MARINE ENGINE.]
MODERN
MACHINE-SHOP PRACTICE
BY
JOSHUA ROSE, M.E.
ILLUSTRATED WITH MORE THAN 3000 ENGRAVINGS
VOLUME II.
NEW YORK
CHARLES SCRIBNER'S SONS
1888
COPYRIGHT, 1887, 1888.
BY CHARLES SCRIBNER'S SONS.
Press of J. J. Little & Co.
Astor Place, New York.
CONTENTS.
VOLUME II.
PAGE
CHAPTER XXII.
=MILLING MACHINERY AND MILLING TOOLS.=
=The Milling Machine=; Advantages possessed by 1
The hand milling machine 1
Power milling machine 2
Universal milling machines 2, 3
The Brown and Sharpe Universal Milling Machine, general view of 4
The construction of the bearings and of the head 5
Sectional view of head 6
The dividing mechanism 6
The index plate 7
Table of index holes for gear cutting 7
The automatic feed motion 8, 9
Special index plate for gear cutting 9
The Brainard Milling Machine 9
The various attachments of 10
The rotary vise 10
Universal head and back centre 10
Universal head for gear cutting 11
The head for cutting spirals 12
The cam cutting attachment 12
The Lipe Universal Milling Machine 12
Sectional view of the Lipe machine 13
The feed motions of the Lipe machine 13
The index head of the Lipe machine 14
The adjustable centre rest 14
The Universal Milling Machine for heavy work 15
Construction of the driving gear and feed motion 15
Pratt and Whitney's double spindle milling machine 16
=Milling Cutters or Mills= 16 to 24
Cutters with spiral teeth 17
Table of sizes of Brown and Sharpe standard cutters 17
Table of standard sizes of Brainard cutters 17
Face cutters 17
Twin cutters and right and left hand cutters 18
Advantages and disadvantages of face cutters 18
Angular cutters 19
Right and left angular cutters 19
The Brown and Sharpe patent cutters 19
Shank cutters 19
The direction of the feed for shank cutters 20
Applications of shank cutters 21
Sizes of shank cutters 21
Fly cutters 21
Different methods of making fly cutters, and the advantages and
defects of each method 21
Circular cutters, and holders for fly cutters 22
Matched cutters; methods of matching cutters 23
Gang or composite cutters; cutters with inserted teeth 24
=Cutter Arbors= 25
=Milling= 25 to 30
Comparison of the advantages of end milling, face milling,
and twin milling 25
The length of feed in face milling 26
Cutting grooves in cylindrical work 27
Angular cutters for groove cutting 27
The crowding of grooving cutters and how to avoid it 27
The direction of the feed in cutting spiral grooves 27
Setting angular grooving cutters 28
Cutting right and left hand grooves and determining the
direction of the feed for the same 29
Fluting twist drills 29
Finding the angle of the cutter in cutting spiral grooves 29
Producing different shaped grooves with the same cutter 29, 30
Holding work on the milling machine; milling taper work 30
=Chucks for Milling Machines= 31
=Vertical Milling Machine= 31
=Profiling Machine= 31, 32
=Grinding Machine=, for milling cutters 32 to 37
Fixture for grinding parallel cutters 32
Errors in grinding milling cutters 32
Grinding thin cutters 33
Grinding taper cutters 33
Fixture for grinding taper work 33
Fixture for taper cutters and for face cutters 34
The position of the emery wheel and clearance on the cutter 35
Grinding the teeth of spiral cutters 36
Positions of emery wheels in cutter grinding as affecting the
strength of the cutting edges 36, 37
CHAPTER XXIII.
=EMERY WHEELS AND GRINDING MACHINERY.=
=Grinding Operations=; Classification of 38
The qualifications of emery wheels 38
Cements used in the manufacture of emery wheels 38
Grades of coarseness and fineness of emery wheels 38
Grades of wheels and the work they are suitable for 39
Speeds of emery wheels 39
Balancing emery wheels 39
=Emery Grinding Machines= 40
The Sellers drill grinding machine 41
The construction of the drill holding chuck 41
Varying the drill position to suit the diameter of the drill,
and thus maintain equal conditions for all diameters of
drills 41
Errors of construction in ordinary drill grinding machines 41
The construction whereby the Sellers machine maintains an equal
degree of clearance from end to end of the cutting edge upon
all sizes of drills 41, 42, 43, 44
The Sellers attachment for thinning the points of large twist
drills 44
The front rake of twist drills 44
Emery grinder for true surfaces 45
For engine guide bars 45
For car axle boxes 45
Emery grinder with traversing emery wheel 46
For rough work 46
For planing machine knives or cutters 46
Emery wheel swing frame for dressing large castings, &c. 46
Emery belt grinding machine 47
Presenting emery wheels to the work, or the work to the wheels 47
Annular emery wheels 48
Recessed emery wheel 48
The wear of emery wheels 48
=Polishing Wheels= 49 to 51
The construction of 49
Lapping the leather on 49
Method of keeping them true 50
Charging with emery 50
The speed of 50
Polishing materials for 50
Brush wheels for polishing 50
Speed of brush wheels 50
Polishing materials for brush wheels for brass work 50
Solid leather wheels 51
Rag polishing wheels 51
Polishing materials for rag wheels 51
Polishing device for engravers' steel plates 51
=Grindstones= and Tool Grinding 51
The various kinds of 51
Suitable for wood working tools 52
Suitable for saws or iron plates 52
The speeds of 52
The changes of pulley diameter necessary as the diameter of the
stone decreases in order to maintain a nearly uniform
circumferential speed of grindstone 52
Arrangement of, for saw plates 52
Hacking 53
Device for truing 53
Automatic traversing device for 53
Considerations that determine the position in which the work
should be applied to 53
=Oil-stones=, the various kinds of 54
Truing oil-stones 54
Removing the feather edge left by 54
Oil-stoning edge tools 54
CHAPTER XXIV.
=GEAR CUTTING MACHINES.=
=Gear Cutters=--The Brainard Automatic 55
Plan view of the mechanism 55
Method of operating the cutter slide 55
The arrangement of the positive feed shipping motion 55
Arrangement and construction of the dividing mechanism 55
The Brainard half automatic gear cutting machine 56
Gear cutting engine with vertical cutter spindle 56
Gear planing machine 56
Piat's French gear cutting machine 56 to 61
CHAPTER XXV.
=VISE WORK.=
=Definition of Vise Work= 62
=The Vise= 62
The height of vise jaws 62
The wood-worker's vise 62
The Stephens vise 62
Swivelling vises 62
The Prentiss vise 62
Leg vise with parallel motion 63
Various forms of vise clamps 64
=Hammers= 64
The effects of the speed of a hammer blow 65
Experiments by Robert Sabine on the duration of a blow 65
Machinists' hand hammers 66
Shapes of hammer eyes 66
The proper method of putting handles in 67
Paning of pening hammers 68
The plate straightener's and saw maker's hammers 69
The principles involved in straightening plates 69
The dog-head hammer 69
The effects of hammer blows upon plates 69
Saw straightening and saw hammering 70, 71
Machinist's sledge hammer 71
The file cutter's hammers 71
Riveter's hammer 71
The cooper's hammer 71
The mallet 72
Pening or paning 72
Applications of pening to straighten work or refit it 72
Riveting crank pins 73
=Chisels= 73
Forms of bar steel for chisels 73
The widths and thicknesses of the cutting ends of 74
Angles of the cutting edges of 74
Shapes of the cutting edges of 74
Chisel holders 74
Cape or cross-cut 74
Round nosed 75
The cow-mouthed 75
Curved or oil groove 76
The diamond point chisel 76
Applications of machinists' chisels 76
The carpenter's chisel 77
The angle of presentation of chisels 77
=Plane Blades= 77
The form of, necessary to produce a given shape of moulding 77
Finding the shape of knives, plane blades, or cutters necessary
to produce given shapes upon the work 78 to 83
Scale for marking out the necessary shapes of moulding knives 83
Instruments for 84
=Files= 85
Shapes of file teeth 85
The cut of files 85
Sizes and kinds of flat files 86
Groubet files 87
Rasps, the kinds and cut of 88
The names of files 88, 89
Round, half-round, and three-square files 90
Knife files, cross files, reaper files, tumbler files 91
The selection of files 91
Putting handles on files 92
Instruction on holding files 92
Slim files 92
The warping of files 93
Using bent files 93
Cross filing 93
Draw filing 94
Cleaning files 94
Filing out round corners 95
Using round files 95
Files for soft metals 95
Resharpening files 95
The Sand Blast process 96
=Red Marking= for vise work 96
=Hack Saw= 97
=Screw Drivers= and their proper shape 97
=Scrapers= for true surfaces 97
Angles for the facets of scrapers 97
Various forms of scrapers 97
=Reamers= 98
The spacing of reamer teeth 98
Odd and even numbers of reamer teeth 98
Adjustable reamers 98
Taper reamers 99
Reamers for framing 99
Half-round reamers 99
Square reamers 99
CHAPTER XXVI.
=VISE WORK= (Continued).
=Examples in Vise Work= 100 to 113
The use of chisels 100
File cutting 100
Cutting key seats 101
Sinking feathers in shafts 101
Methods of securing feathers 102
Filing up a double eye or knuckle joint 103
Filing pins 103
Blocks for filing pins 104
Hand vise 104
Filing bolt heads and nuts 104, 105
Making outside calipers 105, 106
Fitting keys 107
Cutting keyways by hand 108
Cutting out keyways by drifts 109
Forms of drifts 109
Methods of using drifts 109
Templates 110
Making male and female templates 110 to 112
CHAPTER XXVII.
=VISE WORK= (Continued).
=Examples in Vise Work= 113 to 127
The various form of connecting rods 113
Solid ended connecting rods 113
Clip ended connecting rod 114
Strap ended connecting rod 115
Double gibbed connecting rod 115
Locomotive connecting rod 115
Bolted connecting rod straps 115
Marine engine connecting rod 116
Tapered connecting rod ends and their advantages 117
Stepped connecting rod straps and their advantages 117
Fitting up connecting rods 117, 119
Welding up stub ends of connecting rods 118
Aligning welded connecting rods 118
Fitting on connecting rod straps 119
Filing out connecting rod keyways 119
Fitting the keys and gibs 119
Fitting connecting rod brasses to their straps 120, 122
The joint faces of connecting rod straps 121
Disadvantages of joints left open to take up the wear 121
Obviating this disadvantage 121
Marking the lengths of connecting rods 122
Fitting up a fork end connecting rod 122
Aligning fork end connecting rods 123
Repairing connecting rods 124
Setting connecting rod brasses together 125
Lining up connecting rod brasses 126
Adjusting the lengths of connecting rods 126
Setting up the keys of connecting rods 126
Shapes of the crowns of brasses 127
Fitting up a link motion 127
Templates for filing the link slot 127
=Case-hardening= 128 to 133
Sheehan's case-hardening process 128
Preparing work for 129
Setting work after 129
Fitting brasses to pillow blocks or axle-boxes 130
Bedding brasses 132
The proper shape for the patterns of brasses 132
=Originating a True Plane= 133
Finding which of three surfaces is the nearest to a true plane 133
Methods of testing the surfaces 134
A new process of originating surface plates 134
The deflection of surface plates 134
=The Friction of Plane Surfaces= 135
=Oiling True Surfaces= 135
CHAPTER XXVIII.
=ERECTING.=
=Spirit-level= 136
=Plumb-level= 136
=Joints= 136 to 141
Filing or making joints 137
Ground joints 137
Scraped joints 137
Cylinder covered joints 137
Making a scraped joint with the studs in their places 138
Joints for rough surfaces 138
Gauze wire joints 138
Water joints 138
Joints to withstand great heat 138
Rubber joints 139
Boiler fitting joints 139
Easily removable joints 140
Rust or caulked joints; caulking tools 141
Thimble joints 141
Expansion joint 141
=Pipes, Cocks and Plugs= 141 to 145
Pipe cutters 141
Pipe vises 141
Pipe tongs 143
Erecting pipe work 144
Refitting leaky cocks and plugs 144
Grinding cocks and-plugs 145
=Boxes and Brasses= 145 to 149
Fitting brasses to their journals 145
Various forms of bearings and brasses or boxes 147
Locomotive axle boxes 148
Lead lined brasses 148
Open brasses 149
=Lubrication= 149 to 154
Examples of oil cavities and oil grooves for brasses 150
Qualities of lubricants 151
Testing lubricants 151
Best method of using thin oils 152
The influence of the atmosphere on oils 153
Longevity of lubricants 153
Testing oils for salts and acids 153
Swiss watchmakers' oil tests 153
The blotting paper oil test 154
=Friction and Wear= 154
Morin's experiments on 154
Order of the value of metals to resist wear 154
White metal or babbitt metal lined boxes 155
Methods of babbitting boxes 156
The pressure on journals 156
=Cranks= 156
Placing at right angles 156, 157
=Engine Cylinders= 158 to 161
Fitting 158
Setting 159
Reboring cylinders in their places 160
Scraping out cylinder ends 161
CHAPTER XXIX.
=ERECTING ENGINES AND MACHINERY.=
=Engine Guide Bars= 162
Setting 162
The spring of 162
Testing 163
Setting by stretched lines 163
=Heating and Knocking of Engines= 164
The ordinary causes of 164, 166
=Aligning New Engines= 166 to 171
Classification of the errors in engine alignment 166
Testing the alignment of the crank 167
Showing separately the causes of beating and pounding 168
Methods of discovery and determining the errors of alignment 169
Errors of alignment in crank pins 170
Methods of discovering errors of crank pin alignment 170
Remedying errors of crank pin alignment 171, 172
=Slide Valves= 173 to 175
Finding the dead centre of the crank 173
Taking up the lost motion when setting the valve 174
Measuring the valve lead 174
Finding the dead centre with a spirit level 174
=Setting Eccentrics= on crank shafts 175
Setting double eccentrics by lines 175
=Erecting the Framework= of machinery 176, 177
=Repairing and Patching= broken frames 178
=Erecting an Iron Planer= 179
Foundations for an iron planer 180
Fitting up and erecting a lathe 181
=Testing Lathes= 181
Instruments for testing lathes 182
Testing lathe carriages 183
=Erecting Line Shafting= 184 to 186
CHAPTER XXX.
=LINE SHAFTING.=
=Line Shafting= 187 to 190
Sizes of 187
Cold rolled shafting 187
Distance between bearings of line shafting 187
Tests of hot rolled and cold rolled shafting 188
Collars for shafting 189
Diameters of line shafting 189
The strength of line shafting 190
Speeds for shafting 190
=Counter Shafts= 191
=Friction Clutches= 192
=Shafting Hangers= 193
Various forms of 193
Open-sided 193
Wall hangers 194
=Pillow Blocks= for shafting 194
=Couplings= 194 to 199
For line shafts 194
With split sleeves 195
Errors in 196
Self-adjusting 196
Plate 196
Clamp 197, 198
For light shafting 199
Universal 199
CHAPTER XXXI.
=PULLEYS.=
=Classification= 200, 201
Wood pulleys 200
Solid and split pulleys 200
Expansion pulleys 200
Self-oiling pulleys 200
Crowned pulleys 201
=Fastening= pulleys to their shafts 201
=Balancing= pulleys 202
=The Transmitting Power= of pulleys 204
Size of pulleys for countershafts 205
=Calculating the Speeds= of pulleys 206
CHAPTER XXXII.
=LEATHER BELTING.=
=Hides= 207, 208
The parts of a hide used for belting 207
The thickness and stretch of the parts of a hide 207
Experiments on the strength of the parts of a hide 208
=Single and double= belts 208
=Grain Side of Leather= 208
Weakness of the 208
Why the grain side should go next to a pulley 208
=Belts= 209 to 217
The length of 209
Belt clamp 210
The sag of belts 210
Belt connection at an angle 211
Guide pulleys for belts 211
The tension and creep of belts 212
Methods of joining the ends of belts 213
Forms of belt lacings 214
Covers for belt lacings 215
Lap joints for belts 215
Joining thin belts 215
Bevelled joints for belts 215
Pegged belts 215
Belt hooks and belt screws 216
Angular or V-belts 217
The line of motion of belts 217
Changing or shipping belts 217
Automatic belt replacer 218
Pull of a belt 218
The Sellers experiments on transmission of power 218 to 225
Belt 5-1/2" wide by 7/32" thick 219
Belt 2-1/4" wide by 5/16" thick 219
Rawhide belt 4" by 9/32" 220
Double oak tanned belt 4" by 5/16" 220, 221
Oak tanned belt 2" by 3/16" 222
Coefficient of friction and velocity of slip 222
Torsional moment 223
Increase of tensions 224
CHAPTER XXXIII.
=FORGING.=
=Testing Iron= by bending it 226
Testing machines 227, 228
=Tools for Blacksmiths= 228 to 232
Forges 228, 229
Chisels, &c. 230
Anvils 230
Swages 230, 231
Spring swages 231
Swage blocks 232
=Swaging= 232, 233
=Examples in Welding= 233, 235
Iron 233, 234
Steel to iron 234
Best method of 234, 237
=Examples in Forging= 238 to 252
Device for bolt forging 238
Forging turn buckles 239
Methods of bending iron 240
Device for bending iron 240, 241
Forging steel forks 241
Forging under the hammer 242, 243
Forging rope sockets 243, 244
Forging wrought iron wheels for locomotives 244, 245
Forging rudder frames 245, 246
Welding scrap iron for large shafts 247
Construction of furnace for heating scrap 247
Forging crank shafts 248, 249
Forging large crank shafts 249, 252
Forging machines 252 to 263
Foot-power hammer or Oliver 252, 253
Standish's foot-power hammer 252, 253
Power hammers and steam hammers 252, 253
Bradley's cushioned hammer 252, 253
Corr's power hammer 254, 255
Kingsley's trip hammer 255
The drop hammer 255, 256
Steam hammers 257, 258
Double frame steam hammer 258
Double frame steam drop hammer 258
Double frame steam drop hammer for locomotive and car axles
and truck bars 259
The Edgemore Iron Works' hydraulic forging press 260
Dies for forging eye bars 260
Nail forging machine 260
Rolls for forming knife blades 261
Machine for forging threads on rods 261, 262
Finishing machine for horseshoes 262, 263
Circular saw for cutting hot iron 263
CHAPTER XXXIV.
=WOOD WORKING.=
=Pattern Making= 264, 267
Choice and preservation of wood for 264
=Bending Timber= 265, 266
The bending block 265, 266
Steaming wood for bending 266, 267
=Wood Working Tools= 267 to 274
Planes for pattern making 267
Compass planes 268
Stanley's iron frame block plane 269
Stanley's bull-nose rabbet plane 269
Bailey's patent adjustable planes 269
The combination plane 269, 270
The beading bit 270, 271
Tool for cutting material into parallel slips 271
The chisel and chisel handles 271
Firmer and paring chisels and gouges 272
Rip saws 272, 273
Cross cut saw 273
Common gauges for marking off work 274
Mortise gauge 274
Cutting gauge 274
=Wood Joints= 274, 275
Mortise joint 274
Tenon joint 274
Dovetail joint 275
Mitre joint 275
Half check joint 275
=Examples of Pattern Making= 275 to 285
Patterns for piston gland 275
Construction of piston gland pattern 276, 277
Rapping small cast gears 277
Casting pillow block 277
Pattern for pillow block 277
Pulley pattern 278, 279
Building up segments for patterns 278, 279
Getting out arms for pulleys 280
Making pipe patterns 280, 281
Globe valve pattern 281, 282
Angle valve pattern 283, 284
Branch pipes 284 to 286
CHAPTER XXXV.
=WOOD WORKING MACHINERY.=
=Classification= 287
=Circular Saws= 287 to 305
Gauges for circular saws 287
Table of diameters 287
Thickness 287
Size of mandrel hole 287
Shingle saw 287, 288
Concave saw 287, 288
Stretching of circular saws by heat 288
The tension of circular saws 288
Causes of alteration of tension and method of discovering the
same 288
Truth of circular saws 288
Various effects of circular saws heating 288
Truing circular saws 288
Sharpening the teeth of circular saws 289, 290
The gumming, gulleting or chamfering machine 290
Inserted teeth of saws 290
Chisel teeth saws 290, 291
Inserting teeth in circular saws 290, 291
Swing frame saws 290, 292
Fence for swing frame saws 293
Examples of work done on swing frame machine 293
Swing machine with fixed table 294
Double saw machine 294, 295
Gauges for sawing machine 294
Method of employing the mitre gauge 294
Cropping and gauging gauge 296
Bevel or mitre sawing machines 296, 298
Roll feed circular saw machine 298, 300
Segmental circular saws 300
Fastening saw segments to their disks 301
Gang edging machines 301
Rack feed saw bench 301
Construction of the feed motion 301 to 304
Fibrous packing for circular saw 305
=Tubular Saw Machine= 305
=Cross Cutting or Gaining Machine= 305, 306
=Scroll Sawing Machine= 306
Construction of various scroll sawing machines 306, 307
=Band Sawing Machine= 308 to 312
Various kinds of teeth for band saws 308, 309
Pitch of teeth for band saws 309
The adjustment of the saws of band saw machines 309, 310
Filing the teeth of band saw machines 309
Re-sawing band saw machine 309, 310
To regulate the tension of band saws 310, 311
Construction of band saw guides 311
Various band saw machines 311, 312
=Reciprocating Cross Cutting Saw= 312
Construction of 312
=Horizontal Saw Frame Machine= 312 to 315
Construction of the saw driving mechanism 314
Construction of the feed motion 315
Construction of the saw 315
=Planing Machines= 315 to 341
Buzz planer 315
Construction of the work table 316
Construction of the cutter head 316
Skew knives 316
Roll feed wood planing machine 317
The construction of the feed rolls 317
Adjustment of the feed rolls 317
Construction of the pressure bars 317
Adjustment of the roll pressure 318
Adjustment of the work table 318
The roll driving mechanism 319
The cutter head 320
Three feed roll wood planing machine 322, 323
Pony planer 323
Construction of the feed mechanism 324
Balancing cutter heads and knives 324, 326
Farrar planing machine 326, 327
Planing and matching machine 328
Construction of the feed rolls 329
Construction of the upper cylinder 329
Construction of the lower cylinder 329
Construction of a matcher hanger 329
The timber planer 330, 331
Construction of parts of the timber planer 331
How the timber planer operates 331, 332
Panel planing and trying up machine 332, 334
Moulding machine 334
Double head panel raiser and double sticker 335, 336
Moulding cutters 336, 337
Cutter heads and circular cutters 337
The Shimer head 337
Head for producing match board grooves 337, 338
Jointing machine 338
Knives of jointing machine 338
Speed of cutter head or disc 338
Stroke jointers 338, 339
Machine for cutting mitre joints 339
Moulding or friezing machines 339
Important points of friezing machines 339
Construction of moulding and friezing machines 340, 341
Shape of cutters for moulding and friezing machine 341
Rotary cutters for all kinds of work, and for edge moulding
and friezing machine 341 to 343
=Boring Machines= 342
Fences for 342
Augers or bits for 342
Boring machines for heavy work 343
=Mortising Machines= 344
Tools used in mortising machines 344
Motion of chisel bar and auger 344
Construction of bed 344
Adjustment of carriage 344
=Tenoning Machines= 344, 345
Construction of revolving heads 344, 345
Tenoning machine for heavy work 346
=Sand-papering Machines= 346, 349
Construction of sand-papering machines 347, 348
Movements of sand-papering machine 347
Cylinder sand-papering machines 348
Self-feeding sand-papering machine 348
Sizes of machines 348
Construction of feed rolls 348
Finishing and roughing cylinders 348
Brush attachment 348
Double wheel sanding machines 348, 349
CHAPTER XXXVI.
=STEAM BOILERS.=
=Strength of Boiler Shells= 350
=Strength of Boiler Plate= 351
Explanation of pressure in steam boilers 351
=Boiler Joints or Seams= 351 to 357
Forms of rivet joints 351
Single riveted lap joint 351
Double riveted lap joint 352
Single riveted butt joint with straps 352
Double riveted butt joint with straps zigzag riveted 352
Triple riveted lap joint zigzag riveted 352
Lap joint with covering plate 352
Double riveted lap joint chain riveted 353
Double riveted butt joints with double straps 353
Treble riveted butt joint with double straps 353, 354
Rules for spacing the rivets in boiler seams 353
Rule for finding diagonal pitch of riveted joints 353
High percentage joint 353
Rivets unevenly pitched 354
Rule for calculating the percentage strength of joint with
unevenly pitched rivets 354
Strength of circumferential seams of stationary engine boilers
354, 355
Table of additions to be made to the factor of safety for
various constructions of riveted joints 355
Table of diameter of rivets for single riveted lap joints 356
Rule for making rivet and plate area equal 336
Table of rivet diameter and pitch for single riveted lap joints 356
Rule for finding the pitch for double, diagonal riveted lap
joints 356
Example in the use of rule for diagonal pitch of rivets 356
Rule for finding distance V where the diagonal pitch has been
found 357
Comparing chain with zigzag riveted joints 357
=Interior of Boilers= 358 to 364
The internally fired flue boiler 358, 359
Boiler with Field tubes 350
Vertical water tube boiler 360
Construction of field tubes 360
Arrangement of field tubes 360
Vertical boilers with external uptakes 361
Horizontal return tubular boiler 361, 362
Construction of horizontal return tubular boiler 362, 363
Various arrangements of tubes in boilers 364
=Setting Boilers= 364, 366
Ground plan of brickwork 365
Setting full arch front boilers 365
Table of measurements for setting tubular stationary boilers
with full arch front 366
Table of measurements for setting stationary boilers with half
arch front 366
=The Evaporative Efficiencies of Boilers= 366 to 368
Table of the pressure, temperature and volume of steam 367
Calculating the evaporation of a boiler 368
=Care and Management of Boilers= 368 to 371
Examining safety valves 368
Water gauge glass 368
Gauge cocks 368
Lighting boiler fires 368
The thickness of the fire for boilers 368
Managing the fire 368
Shaking grate bars 369
The slice bar 369
The hoe 369
The poker 369
The clinker hook 369
The rake 369
The quantity of water in a boiler 369
Leaving the fire for the night 369
Leaving the safety valve for the night 369
Regulating the boiler feed 369
Dirty feed water 370
Defective feed pumps 370
Scale in boilers 370
Preventing the formation of scale 370
Feed water heaters 370
Low water in boilers 370
Priming or foaming 370
The known causes of priming 370
Wastefulness of priming 370
The detection of priming 370
To prevent or stop priming 370
Surface blow off cock or mechanical boiler cleaner 370
Blowing off a boiler 370
Blowing down a boiler 370
Washing out a boiler 371
Cleaning a boiler 371
Scaling a boiler 371
Examining a boiler 371
CHAPTER XXXVII.
=STEAM ENGINES.=
=Engine Cylinders= 372 to 374
The bores of 372
Sizes of 372
Wear of 372
Counterbore of 372
Clearance in 372
Lubrication of 373
The cocks of 373
Relief valves of 373
The steam ports of 373
Lagging 374
Jacketed cylinders 374
=Engine Pistons= 374
The speeds of 374
With releasing gears 374
With positive valve gears 374
The rings of 374
The follower 374
Testing the rings of 374
=Engine Piston Rods= 375
Methods of securing 375
Packing 375
Glands for 375
=Engine Cross Heads= 375
=Engine Guide Bars= 375
=Engine Connecting Rods= 375
Connecting rod keys 375
Angularity of 375
The lengths of 375
=Valves= 376 to 378
The D-valve 376
The point of cut off 376
Period of expansion of the steam 376
Point of release of the steam 376
Point of compression of the steam 376
Lead of 376
Point of admission of the steam 376
The lip 376
Exhaust lap 376
Steam lap 376
Tracing the action of 376
Double ported valves 377
The Allen valve 377
Webb's patent valve 377
Balanced valves 377
Circular valves 377
Piston valves 378
Separate cut off valves 378
Meyer's cut off valves 378
Gonzenback's cut off valve 378
=Eccentrics= 378
Shifting eccentrics 378
The action of 378
The angular advance of 378
=Designing Slide Valves= 380
=Valve Motions= 381
Diagram for designing 381
=Link Motion= 383
In full gear forward 383
In full gear backward 383
The action of 383
Setting the valves 383
=Governors= 384
Fly ball or throttling 384
Isochronal 384
Dancing 384
Speed of 384
Spring adjustment of 384
Sawyer's valve for 384
Speeder for 384
=Starting a Slide Valve Engine= 384
Crank position in 384
=Examination of an Engine= 385, 387
Adjusting connecting rod brasses 385
Adjusting main bearing 386
Taking a lead 386
Squaring a valve 386
Heating, to avoid 386
Setting a valve 386
Leaky throttle valves 386
Freezing an engine, prevention of 386, 387
=Pumps= 387, 388
Lift and force 387
Plunger 387
Rotary 387
Single-acting 387
Double-acting 387
Displacement of 387
Principles of action of 387, 388
Speed of 388
Capacity of 388
Air chamber of 388
Belt 388
CHAPTER XXXVIII.
=THE LOCOMOTIVE.=
=Modern Freight Locomotive= 389, 390
General construction 389
Course of steam from boiler to smoke stack 389
Boiler feed 389
Position of parts for starting 389
Steam supply to injectors 389
Oil supply to slide valve and cylinder 389
Control of safety valve 389
Pop valve 389
Automatic air brake 390
Draught of fire 390
Sand valves 390
=American Passenger Locomotive= 390 to 393
General construction 390
Steam reversing gear 390, 391
Link motion in full gear forward 391
In mid gear 392
In full gear backward 392
Reversing gear 392
Changing gear of link motion 393
Running forward 393
Running backward 393
=Special Operations= 394
Setting the slide valves 394
Getting the length of eccentric rods 394
Setting the lead 394
Backward eccentric 394
Marking sector notches 394
Setting Allen valves 395
=Special Parts= 395 to 400
The injector 395 to 397
Westinghouse automatic air brake 398 to 400
=Locomotive Running= 400 to 404
General discussion 400
Getting the engine ready 400
Laying the fire 400
Banking the fire 401
Starting up a banked fire 401
Examining the engine 401
Oiling the engine 401
Starting the engine 401
Saving fuel 402
Methods of firing 402
Examples of trips 402
=Accidents on the Road= 402
Knocking out cylinder heads 402
Heating of piston rods 403
Throwing off a wheel tire 403
Throwing off a driving wheel 403
Breaking a spring 403
Bursted tubes 403
Slipping eccentrics 403
Hot axle boxes 403
Breaking a lifting link 403
Breaking the saddle pin 403
Adjusting the wedges of the axle boxes 404
CHAPTER XXXIX.
=THE MECHANICAL POWERS.=
=Power= 405
=Lever= 405
The principles of 405
Wheels and pulleys considered as levers 405, 406
Power transmitted by gear wheels and pulleys combined 407
=Horse Power= 407
Calculating the horse power of an engine 407
Testing the horse power of an engine 408
=Safety Valve Calculations= 409
=Heat= 410
Latent heat 410
=Water= 410
=Steam= 410
Saturated 410
Superheated 410
Expansion of 411
Absolute pressure of 411
Weight of 411
Volume and pressure of 411
=Heat= 411
Conversion of heat into work 411
Joule's equivalent 411
Mechanical equivalent of heat 411
Mariotte's law 411
Radiation of heat 412
Conduction of heat 412
Convection of heat 412
CHAPTER XL.
=THE INDICATOR.=
=Computations from Indicator Diagrams= 413
=Indicators= 413
Description of 413
Thompson indicator 413
Tabor indicator 413
Diagrams 414
Admission of steam to indicator 414
Expansion line or curve 414
Exhaust line 414
Back pressure line 414
Atmospheric line 414
Theoretical diagram 414
Compression line or curve 415
Condensing engine diagram 415
Vacuum line of indicator diagram 415
(Barometer, construction of) 415
(Barometer, graduation of) 416
Indicator springs 416
Tables of springs for indicators 416
Attachment of indicators to an engine 416, 417
Pantagraph motions 417
Expansion curve, testing of 417, 418
Theoretical expansion curve 417, 418
Calculations from diagrams 418 to 421
Horse power 418, 419
Area 419
Rule for calculating horse power 419
Mean effective pressure 420
Steam used in engines 420
Water consumption 420, 421
Defective diagrams of engines 421
Excessive lead of engines 421
Theoretical compression curve of engines 422
CHAPTER XLI.
=AUTOMATIC CUT-OFF ENGINES.=
=Definition= 423
=Corliss Automatic Cut-off Engine= 423, 424
Valve gear of 424, 425
Governor of 425, 426
Admission of steam into 426
Lap of valve of 426, 427
=High Speed Automatic Engines= 427, 428
Speed of 427
Wheel governors for 427, 428
=Straight Line Automatic Engine= 428, 429
Important details of 429, 430
=Steam Fire Engine= 430, 431
Boilers of 430, 433
Pumps 431, 432
Heaters for 432, 433
CHAPTER XLII.
=MARINE ENGINES.=
=Various Kinds of Marine Engines= 434 to 451
High pressure engines 434
Compound condensing engines 434, 435
Triple expansion engines 436
Donkey engines 442
Trunk engines 446
Oscillating engines 446
Geared engine 446
Compound engine of the steamship _Poplar_ 447, 450, 451
=Arrangement of Marine Engine Pumps= 436
=Boilers of Marine Engines, Arrangement of= 436, 437
=Various Parts of Marine Engines, etc.= 438 to 449
Valve for intermediate cylinder of triple expansion engines 438
Link motions for triple expansion engines 438
Auxiliary or by-pass valve 438, 439
Oiling apparatus 439, 440
Surface condensers 440
Circulating pumps 440
The snifting valve 440
The blow-through valve 440
Air pumps 441
The air chamber 441
Feed escape or feed relief valve 441
Bilge injections for marine engines 441, 442
Surface condensing, advantages of 442
Valves of the surface condensing engine 442
Case hardening 442
Link motion for marine engines 443
The separate expansion valve 443
Friction of slide valves 443
Double beat valves 443
The siphon 443
Steam lubricators 444
Marine engine valves that are worked by hand 444
Vacuum gauge 444
Condenser, to find the total pressure in the 444
Paddle wheels 444, 445
Screw propeller 445
The thrust bearing 445
Marine engine, the principal parts of 445
Lagging marine engines 446
Propeller cylinders 446
Fuel required 446
Freezing of pipes 446
Failure of engine to start, causes of 446, 447
Defective vacuum, causes of 447
Heating, causes of 447
Construction of a triple expansion engine 447 to 449
CHAPTER XLIII.
=MARINE BOILERS.=
=Plates for Marine Boilers= 452
Iron 452
Steel 452
Strength of 452
=Boiler Stays= 452
Methods of securing 452
=Boiler Tubes= 452
Methods of securing 452
Causes of leaks 452
Repairing leaks 452
=The Up-take= 453
=The Receiver= 453
=The Fittings and their Uses= 453, 454
Valves 453, 454
Gauges 453, 454
Cocks 454
=Important Features and Facts= 454, 455
Boiler scale 454
The salinometer 454
Priming, the prevention of 454
Supplemental parts 454, 455
The superheater 454
The draught 455
Wasting of plates 455
Fuel, the quantity of 455
=To Relieve the Boiler in Case of Accident= 455
=Steel Marine Boiler= 456
=The "Martin" Boiler= 456
=Testing and Examining Boilers= 456 to 459
Hydraulic tests 456
Related to stays 456, 457
On new and old boilers 456, 457
Internal examinations 458
Preparation for 458
Safety valves 458
Bottom of the boiler 458
Bottom and sides of the furnace 458
Boxes and stays 458
Use of chipping hammer 458
Pit holes in the bottom of a furnace 458
Drilling through the plates 458
Flanges of furnaces 458
Deposits on the necks of stays 458
Man-hole door 458
Superheater 459
Proportions for grate surface 459
Outside examination 458
Cement beds for boilers 458
Proportions for circular tubular boilers 459
CHAPTER XLIV.
=HARDENING AND TEMPERING.=
=Purposes= 460
To resist wear 460
To increase elasticity 460
To provide a cutting edge 460
=Manufacturer's Temper= 460
=Blacksmith's Temper= 460
=Color Tempering= 460
=Practical Processes= 461 to 464
The muffle 461
Warping 461
Rapidity of reduction of temper 461
Brown and Sharpe's practice 461
Waltham Watch Co.'s practice 461
Pratt and Whitney Co.'s practice 461
Morse Twist Drill Co.'s practice 461
Outside hardening 462
Heating in fluxes 462
Monitor Sewing Machine Co.'s practice 462
Hardening saws 462
Drawing the temper 462
1. Lying in an open furnace 462
2. Stretched in a frame 462
3. Between dies 462
Stiffening saws 463
Tomlinson Carriage Spring Co.'s practice 463
Columbia Car Spring Co.'s practice 463
New Haven Clock Co.'s practice 464
APPENDIX.
=Part I.--Test Questions for Engineers= 467
=Part II.--Dictionary of Workshop Terms= 473
FULL-PAGE PLATES.
VOLUME II.
_Facing_
_Frontispiece._ COMPOUND MARINE ENGINE. TITLE PAGE
PLATE I. EXAMPLE OF MILLING MACHINE. 10
" II. EXAMPLES OF MILLING MACHINES. 12
" III. EXAMPLES OF MILLING MACHINES. 16
" IV. EMERY GRINDING MACHINERY. 45
" V. GRINDSTONE GRINDING. 54
" VI. FULL AUTOMATIC GEAR CUTTER. 55
" VII. GEAR CUTTING MACHINES. 56
" VIII. THE HAMMER AND ITS USES. 71
" IX. SCRAPERS AND SCRAPING. 97
" X. OIL-TESTING MACHINES. 153
" XI. TESTING PLANER BEDS AND TABLES. 180
" XII. EXAMPLES OF PULLEYS. 200
" XIII. THE ACTION OF SAW TEETH. 273
" XIV. EXAMPLE IN PATTERN WORK. 276
" XV. EXAMPLES IN STEAM HAMMER WORK. 232
" XVI. EXAMPLES IN HAND FORGING. 239
" XVII. FORGING UNDER THE HAMMER. 249
" XIX. DIMENSION SAWING MACHINE. 292
" XIX. RACK-FEED SAW BENCH. 302
" XX. PLANTATION SAW MILL. 305
" XXI. GAINING OR GROOVING MACHINE. 306
" XXII. BAND SAW WITH ADJUSTABLE FRAME. 311
" XXIII. BAND SAW MILL. 311
" XXIV. LOG CROSS-CUTTING MACHINE. 312
" XXV. HORIZONTAL SAW FRAME. 314
" XXVI. TRYING-UP MACHINE. 333
" XXVII. SANDING MACHINES. 348
" XXVIII. BOILER FOR STATIONARY ENGINES. 360
" XXIX. AMERICAN FREIGHT LOCOMOTIVE. 388
" XXX. AMERICAN PASSENGER LOCOMOTIVE. 390
" XXXI. LOCOMOTIVE LINK MOTION. 392
" XXXII. INJECTOR AS APPLIED TO A LOCOMOTIVE. 395
" XXXIII. LOCOMOTIVE AIR BRAKES. 396
" XXXIV. THE CORLISS VALVE GEAR. 425
" XXXV. STEAM FIRE ENGINE. 430
" XXXVI. COMPOUND MARINE ENGINE. 436
" XXXVII. TRIPLE EXPANSION MARINE ENGINE. 440
MODERN
MACHINE SHOP PRACTICE.
CHAPTER XXII.--MILLING MACHINERY AND MILLING TOOLS.
THE MILLING MACHINE.--The advantages of the milling machine lie first in
its capacity to produce work as true and uniform as the wear of cutting
edges will permit (which is of especial value in work having other than
one continuous plane surface); second, in the number of cutting edges
its tools will utilize in one tool or cutter; and third, in its
adaptability to a very wide range of work, and in the fact that when the
work and the cutters are once set the operator may turn out the best
quality of work without requiring to be a skilled machinist.
The extended use of the milling machine, which is an especial feature of
modern machine shop practice, is due, in a very large degree, to the
solid emery wheel, which provides a simple method of sharpening the
cutters without requiring them to be annealed and rehardened, it being
found that annealing and rehardening reduces the cutting qualifications
of the steel, and also impairs the truth of the cutting edges by reason
of the warping or distortion that accompanies the hardening process.
Rotary cutters are somewhat costly to make, but this is more than
compensated for in the uniformity of their action, since in the case of
the cutter the expense is merely that involved in forming the cutting
edges with exactitude to shape; once shaped the cutter will produce a
great quantity of work uniform in shape, whereas in the absence of such
cutters each piece of work would require, to bring it to precise form,
as much precision and skill as is required in shaping the cutter.
If a piece of work is shaped in a planing machine, the different steps,
curves, or members must be cut or acted upon by the tool separately, and
the dimensions must be measured individually, giving increased liability
to error of measurement, and requiring a fine adjustment of the cutting
tool for each step or member. Furthermore, neither a planing machine or
any other machine tool can have in simultaneous cutting operation so
great a length of cutting edge as is possible with a rotary cutter.
Again, in the planing machine each cut requires to be set individually,
and cannot be so accurately gauged for its depth, whereas with a rotary
cutter an error in this respect is impossible, because the diameters of
the various steps on the cutter determine the depth of the respective
cuts or steps in the work.
In a milling machine the cut is carried continuously from its
commencement to its end, whereas in a shaping or planing machine the
tool does not usually cut during the back or return stroke. In either of
these machines, therefore, the operator's skill is required as much in
measuring the work, setting the tools feeds, &c., as in shaping the
tools, whereas in the milling machine all the skill required lies in the
chucking and adjustment of the work to the cutter, rather than in
operating the machine, which may therefore be operated by comparatively
unskilled labor.
The multiplicity of cutting edges on a rotary cutter so increases its
durability, and the intervals at which it must be sharpened are so
prolonged, that, with the aid of the present improved cutter grinding
machines, one tool maker can make and keep in order the cutters for many
machines.
The speed at which milling cutters are run varies very widely in the
practice in different workshops. Thus upon cast iron, cutting speeds of
15 circumferential feet per minute will be employed upon the same class
of work that in another shop would be done at a cutting speed of as high
as fifty feet per minute. With the quick speeds, however, lighter feeds
are employed. As the teeth of milling cutters are in cutting action
throughout but a small portion of a revolution, they have ample time to
cool, and may be freely supplied with oil, which enables them to be used
at a higher rate of cutting speed than would otherwise be the case. Yet
another element of importance in this connection is that when the cut is
once started on a plain cutter, the cutting edges do not meet the
surface skin of the metal, this skin always being hard and destructive
to the cutting edges.
[Illustration: Fig. 1878.]
The simplest form in which the milling machine appears is termed the
hand milling machine, and an example of this is shown in Fig. 1878. This
machine consists of a head carrying a live spindle which drives the
cutting tools, which latter are called cutters or mills. The front of
the head is provided with a vertical slideway for the knee or bracket
that carries an upper compound slide upon which the work-holding devices
or chucks are held. The work is fed to the revolving cutter by the two
levers shown, the end one of which is for the vertical and the other for
the horizontal motion, which is in a direction at a right angle to the
live spindle axis.
In other forms of the hand milling machine the live spindle is capable
of end motion by a lever.
[Illustration: Fig. 1878_a_.]
In Fig. 1878_a_ is shown Messrs. Brown and Sharpe's _plain_ milling
machine, or in other words a milling machine having but one feed motion,
and therefore suitable for such work only as may be performed by feeding
the work in a straight line under the cutter, the line of feed motion
being at a right angle to the axis of the cutter spindle.
Machines of this class are capable of taking heavy cuts because the
construction admits of great rigidity of the parts, there being but one
slideway, and therefore but one place in the machine in which the
rigidity is impaired by the necessity for a sliding surface.
The construction of this machine is as follows: The head A which carries
the cutter spindle is pivoted at C to a stiff and solid projection on
the frame F, and means are provided to solidly clamp the two together.
A bracket B supports the outer end of the head; at its upper end B is
split so that by means of a bolt it may firmly clamp the cylindrical end
of A, which carries the dead centre piece D. The two lower ends of B are
bolted to the frame F.
The work table T is gibbed to slideways in F, and is provided with
suitable automatic feed and stop motion, and of course with a hand feed
also.
To adjust the height of the cutter, the lower ends of B are released
from F and the head A is swung on its centre C.
It is obvious that a machine of this class is suitable for cases where a
large quantity of work of one kind is to be done and frequent changes of
the adjustments are not required, and that for such work the solidity of
the construction and the convenience of having all the handles employed
in operating the machine accessible from one position are desirable
elements obtained by a very simple construction.
Fig. 1879 represents Pratt & Whitney's _power_ milling machine. The cone
and live spindle are here carried in boxes carried in vertical slideways
in the headstock, so as to be adjustable in height from the work table,
and is provided with a footstock for supporting the outer end of the
live spindle, which is necessary in all heavy milling. The carriage is
adjustable along the bed, being operated by a screw whose operating hand
wheel is shown at the left-hand end of the bed.
The automatic feed is obtained as follows: The large gear on the right
of the main driving cone operates a pinion driving a small four-step
cone connected by belt to the cone below, which, through the medium of a
pair of spur-gears, drives the feed rod, on which is seen a long worm
engaging a worm-wheel which drives the feed screw. A suitable stop
motion is provided.
What is termed a universal milling machine is one possessing the
capacity to cut spiral grooves on either taper or parallel work, and is
capable of cutting the teeth of spur and bevel-gears or similar work
other than that which can be held in an ordinary vice. These features
may be given to a machine by devices forming virtually an integral part
of the machine, or by providing the machine with separate devices which
are attachable to the work table.
In Fig. 1880 is represented a small size universal milling machine, in
which A is the frame that affords journal bearing to the live spindle,
in the coned mouth _a_ of which the mandrel carrying the rotary cutter
is fitted, means being afforded for taking up the wear of the live
spindle journal and bearings. B is the cone pulley for driving _a_. Upon
the front face of A is a vertical slide upon which may be traversed the
knee or table C, which by being raised, regulates the depth to which
the cutters enter the work. To operate C the vertical screw _b_ is
provided, it being operated (by bevel-gears) from a horizontal shaft
whose handle end is shown at _c_.
[Illustration: Fig. 1879.]
[Illustration: Fig. 1880.]
The nut for elevating screw _b_ is formed by a projecting lug from or on
the main frame A. To enable C to be raised to a definite height so that
the cutters shall enter successive pieces of work to an equal depth, a
stop motion is provided in the rod _d_, which passes through a plain
hole in the lug on A that forms a nut for _b_. Rod _d_ is threaded and
is provided with a nut and chuck nut whose location on the length of the
rod determines the height to which C can be raised, which ceases when
the faces of the nuts meet the face of the projecting lug.
The upper surface of C is provided with a slide on which is a slider D,
which, by means of a feed screw whose handle end is shown at _e_, may be
traversed in a line parallel to the axial line of the live spindle or
arbor, as it is more often termed, this motion being employed to set the
width of the work in the necessary position with relation to the rotary
cutters. To D is attached E, which is pivoted at its centre so as to be
capable of swinging horizontally, means being provided to fasten it to D
in its adjusted position. This is necessary to enable the line of
traverse of the work to be at other than a right angle to the axial line
of the cutter spindle when such is desired, as in the case of cutting
spirals; E serves as a guide to the carriage F, the latter being
operated endwise by means of a screw whose handle is shown at _e´´_, the
nut being attached to E, handle _e´´_ being to traverse E by hand. To
feed F automatically gear-wheel _f_ is attached to the other end of the
same screw, this automatic feed being actuated as follows:--
At the rear end of the live spindle is a three-stepped cone pulley
attached by belt to cone pulley G, which connects by rod to and drives
gear _f_. The construction of the rod is so designed as to transmit the
rotary motion from G to F without requiring any adjustment of parts when
C is raised or lowered or _f_ traversed back or forth, which is
accomplished as follows:--
At _g_ _g_ are two universal joints attached respectively to G and F,
and to two shafts which are telescoped one within the other. The inner
rod is splined to receive a feather in the outer. The rotary motion is
communicated from G to the universal joint, through that joint to the
outer or enveloping shaft which drives the inner shaft, the latter
driving a universal joint which drives _f_, the inner shaft passing
freely within the outer or sliding out from it (while the rotary motion
is continuing) to suit the varying distance from and position of _f_
with relation to G. This automatic feed motion may be adjusted to cease
at any point in the traverse of E by a stop and lever provided for the
purpose, so that if an attendant operates more than one machine, or if
the feed require to be carried a definite distance, it will stop
automatically when that point has been reached.
The carriage F may carry various chucks or attachments to suit the
nature of the work. As shown in the cut it carries a tailblock I and
head J, both fitting into a way provided in F so that they will be in
line one with the other at whatever part in the length of F they may be
set or fixed. Both I and J carry centres between which the work may be
held, as in the case of lathe work. Part _j_ is pivoted to J so that it
may be set at an angle if required, thus setting the centre, which fits
in the hole at _h_, above the level of that in I, as may be necessary in
milling taper work, the raising of _j_ answering to the setting over of
the tailstock of a lathe for taper turning.
[Illustration: Fig. 1881.]
To enable the accurate milling of a polygon, the spindle _h_ may be
rotated through any given portion of a circle by means of the index
wheel at _i_, it being obvious that if a piece of work be traversed
beneath the cutter, and _h_ be rotated a certain portion of a circle
after each traverse, the work will be cut to a polygon having a number
of sides answering to the portion of a circle through which _h_ is
rotated after each traverse. Means are also provided to rotate _h_ while
F is traversing beneath the cutter; hence when these two feed motions
act simultaneously the path of the work beneath the cutter is a spiral,
and the action of the cutter in the work is therefore spiral; hence
spiral grooves may be cut or spiral projections left on the work, as may
be determined by the shape of the cutters. K is a chuck that may be
connected to _h_ to drive the work, and H a work-holding vice, that may
be used instead upon F in place of heads I J.
The countershaft shown at the foot of the machine has two loose pulleys
and a tight one between them, this being necessary because, in cutting
spiral work, the work must rotate while on the back traverse as well as
on the forward one, hence a crossed as well as an open belt is
necessary.
Fig. 1881 represents a large Brown & Sharp universal milling machine, in
which the cone spindle is provided with back gear, and a supporting arm
is also provided for the outer end of the cutter arbor. The feed motions
for this machine correspond to those already described for the smaller
one, Fig. 1880, the construction of the important parts being shown in
the following figures.
[Illustration: Fig. 1882.]
[Illustration: Fig. 1883.]
The construction of the bearings for the cutter driving spindle of the
machine is as in Figs. 1882 and 1883. A is the spindle having a double
cone to fit corresponding cones in the sleeve B, the fit of one to the
other being adjusted by means of the nut C, which is threaded upon A.
The mouth of A is coned to receive the arbors or mandrels for driving
the mills or cutters. At the back bearing, Fig. 1883, the journal A´,
and bore of the sleeve B´, is parallel, this sleeve being split at the
top so that when it is (by means of nut D) drawn within the head E its
coned exterior will cause it to close to a proper fit upon A´, by which
means the wear of the parts may be taken up as they become perceptible.
[Illustration: Fig. 1884.]
[Illustration: Fig. 1885.]
The head J, Fig. 1880, is used (in connection with the foot block I) to
suspend or hold work by or between centres, its centre fitting into the
spindle at _h_, which is capable of being revolved continuously (to
enable the cutting of spirals), by means of change gears, and
intermittently through a given part of a circle by means of the index
wheel _i_. The block _j_ carrying the spindle is also capable of
elevation for conical or taper work, two examples of such uses being
shown in Figs. 1884 and 1885, in which C is the cutter and W the work.
[Illustration: Fig. 1886.]
[Illustration: Fig. 1887.]
Fig. 1886 is a sectional view in a vertical plane through the centre of
the head, and showing the construction of the spindle and the means of
elevating the block _j_; _h_ is the spindle having journal bearing in
_j_, and secured from end motion by the cone at _a_ and the nut _b_; its
bore is coned at the front end to receive the arbor C carrying the
centre D, upon which is the piece E for driving the work dog, which is
secured within E by the set-screw _f_. Fast upon spindle _h_ is a
worm-wheel F made in two halves, which are secured together by the
screws _g_. At G is the worm-wheel (for driving F) fast upon the shaft
H´.
It is obvious that the block _j_ may be raised at its centre end upon H
as a centre of motion, the worm F simply moving around upon G. At V is a
bolt to lock _j_ to J, and thus secure it in its adjusted position. W W
are lugs or blocks fitting into the slot in the work table, and serving
to secure the head, being in line with the foot block (shown at 1 in
Fig. 1880). A sleeve Z is used to cover the thread and protect it when a
chuck is not used.
[Illustration: Fig. 1888.]
[Illustration: Fig. 1888_a_.]
Fig. 1887 is an end view partly in section to show the construction of
the worm shaft and the index plate. H is a sleeve upon which _j_ pivots,
and H´ the worm shaft, which may be revolved by hand by the lever L, or
automatically by means of the bevel-gear K, which connects with the
train of change gears; these change gears being thrown out of operation
when gear K (and therefore _h_) is not required to revolve automatically
nor continuously. L is an arm for carrying the index pin _l_ for the
index plate _i_. The pin _l_ is adjustable for radius from the centre of
H (so as to come opposite to the necessary circle of holes on the plate
_i_), the arm L being slotted to permit of this adjustment, and being
secured in its adjusted position by the nut on the end of H´. Pin _l_ is
pushed into the index holes by means of the spiral spring coiled around
_l_ at _m_, which permits _l_ to be withdrawn from _i_ under an end
pressure, but pushes it into _i_ when that pressure is released. To
indicate the amount of rotation of _i_, without counting the number of
holes, a sector N N´ is employed, it having two arms adjustable for
their widths apart so as to embrace any given number of holes on the
required circle. At R´ is a pin which is pulled forward and into holes
provided in the plate _i_ to prevent its turning when using the lever L.
N and N´ are held to the face of _i_ by the friction of the spring Q. A
face view of index plate _i_ is shown in Fig. 1888, the lever L, Fig.
1887, being removed to expose N and N´.
The surface of the plate is provided with rings of holes marked
respectively 20, 19, 18, &c., the holes in each ring or circle being
equidistantly spaced.
The sector arms N and N´ may be opened apart or closed together so as to
embrace any required number of holes in either of the circles. As shown
in the cut they embrace one quarter of the circle of 20, there being
five divisions between the holes S and _t_. The screw W secures them in
their adjustment apart. Suppose that pin _l_ (Fig. 1887), is in S, and
arm N´ is moved up against it, the arm N leaves _t_ open, and indicates
that _t_ is the next hole for pin _l_, which is withdrawn from S, and
lever L (Fig. 1887) is moved around until the pin will enter _t_, and
the sector is then moved into the position shown in Fig. 1888A,
indicating that hole _u_ is the next one for the pin. This obviates the
necessity of counting the holes, and prevents liability to error in the
counting. Three of these index plates are provided, each having
different numbers of holes in the circles, and in the following tables
are given those specially prepared for use in cutting the teeth of
gear-wheels:
------+-------+------------++------+-------+------------
No. of| Index |No. of turns||No. of| Index |No. of turns
teeth.|circle.| of index. ||teeth.|circle.| of index.
------+-------+------------++------+-------+------------
2 | ANY | 20 || 35 | 49 | 1-7/49
3 | 39 | 13-13/39 || 36 | 27 | 1-3/27
4 | ANY | 10 || 37 | 37 | 1-3/37
5 | " | 8 || 38 | 19 | 1-1/19
6 | 39 | 6-26/39 || 39 | 39 | 1-1/39
7 | 49 | 5-35/49 || 40 | ANY | 1
8 | ANY | 5 || 41 | 41 | 40/41
9 | 27 | 4-12/27 || 42 | 21 | 20/21
10 | ANY | 4 || 43 | 43 | 40/43
11 | 33 | 3-21/33 || 44 | 33 | 30/33
12 | 39 | 3-13/39 || 45 | 27 | 24/27
13 | 39 | 3-3/39 || 46 | 23 | 20/23
14 | 49 | 2-42/49 || 47 | 47 | 04/47
15 | 39 | 2-26/39 || 48 | 18 | 15/18
16 | 20 | 2-10/20 || 49 | 49 | 20/49
17 | 17 | 2-6/17 || 50 | 20 | 16/20
18 | 27 | 2-6/27 || 52 | 39 | 30/39
19 | 19 | 2-2/19 || 54 | 27 | 20/27
20 | ANY | 2 || 55 | 33 | 24/33
21 | 21 | 1-19/21 || 56 | 49 | 35/49
22 | 33 | 1-27/37 || 58 | 29 | 20/29
23 | 23 | 1-17/23 || 60 | 39 | 26/39
24 | 39 | 1-26/39 || 62 | 31 | 20/31
25 | 20 | 1-12/20 || 64 | 16 | 10/16
26 | 39 | 1-21/39 || 65 | 39 | 24/39
27 | 27 | 1-13/27 || 66 | 33 | 20/33
28 | 49 | 1-21/49 || 68 | 17 | 10/17
29 | 29 | 1-11/29 || 70 | 49 | 28/49
30 | 39 | 1-13/39 || 72 | 27 | 15/27
31 | 31 | 1-9/31 || 74 | 37 | 20/37
32 | 20 | 1-5/20 || 75 | 15 | 8/15
33 | 33 | 1-7/33 || 76 | 19 | 10/19
34 | 17 | 1-3/17 || 78 | 39 | 20/39
------+-------+------------++------+-------+------------
------+-------+------------++------+-------+------------
No. of| Index |No. of turns||No. of| Index |No. of turns
teeth.|circle.| of index. ||teeth.|circle.| of index.
------+-------+------------++------+-------+------------
80 | 20 | 10/20 || 164 | 41 | 10/41
82 | 41 | 20/41 || 165 | 33 | 8/33
84 | 21 | 10/21 || 168 | 21 | 5/21
85 | 17 | 8/17 || 170 | 17 | 4/17
86 | 43 | 20/43 || 172 | 43 | 10/43
88 | 33 | 15/33 || 180 | 27 | 6/27
90 | 27 | 12/27 || 184 | 23 | 5/23
92 | 23 | 10/23 || 185 | 37 | 8/37
94 | 47 | 20/47 || 188 | 47 | 10/47
95 | 19 | 8/19 || 190 | 19 | 4/19
98 | 49 | 20/49 || 195 | 39 | 8/39
100 | 20 | 8/20 || 196 | 49 | 10/49
104 | 39 | 15/39 || 200 | 20 | 4/20
108 | 27 | 10/27 || 205 | 41 | 8/41
110 | 33 | 12/33 || 210 | 21 | 4/21
115 | 23 | 8/23 || 215 | 43 | 8/43
116 | 29 | 10/29 || 216 | 27 | 6/27
120 | 39 | 13/39 || 220 | 33 | 6/33
124 | 31 | 10/31 || 230 | 23 | 4/23
128 | 16 | 6/16 || 232 | 29 | 5/29
130 | 39 | 12/39 || 235 | 47 | 8/47
132 | 33 | 10/33 || 240 | 18 | 3/18
135 | 27 | 8/27 || 245 | 49 | 8/49
136 | 17 | 5/17 || 248 | 31 | 5/31
140 | 49 | 14/49 || 260 | 39 | 6/39
144 | 18 | 5/18 || 264 | 33 | 5/33
145 | 29 | 8/29 || 270 | 27 | 4/27
148 | 37 | 10/37 || 280 | 49 | 7/49
150 | 15 | 4/15 || 290 | 29 | 4/29
152 | 19 | 5/19 || 296 | 37 | 5/37
155 | 31 | 8/31 || 300 | 15 | 2/15
156 | 39 | 10/39 || 310 | 31 | 4/31
160 | 20 | 5/20 || 312 | 39 | 5/39
------+-------+------------++------+-------+------------
[Illustration: Fig. 1889.]
A plan view of one-half of the head is shown in Fig. 1889, the edge of J
being graduated for a guide in elevating the head at an angle, at V is
the bevel-gear for driving K, and at S is a pinion receiving motion from
the change gears.
The feed motions for the traversing table (F, Fig. 1880) is shown in
Figs. 1889, 1890, and 1891, _g_ represents the universal joint rotating
continuously the spindle _a_, which provides journal bearing to bevel
pinion _b_ and the clutch _c_, these two being fixed together; _d_ is a
clutch which rotates with _a_, but is capable of a certain amount of end
motion on or along _a_ to enable it to engage or disengage with its mate
_c_. When _d_ engages with _c_ the rotary motion of _a_ is transmitted
through _d_, _c_, _b_, to _f_, which actuates the feed screw A, while
when _d_ is disengaged from _c_, it rotates, leaving _c_ _b_ _f_ idle.
_d_ is operated to engage with or disengage from _c_, its hub is
enveloped by the fork _e_, which is attached to rod _h_, which is
provided with a recess to receive one end of the bell crank _l_, the
other end of which lies in a recess in the rod _m_, to the end of which
is connected the lever handle _n_, which is pivoted at O; hence
operating _n_ laterally as denoted by the arrows, throws _d_ in or out
of gear with _c_, according to the direction of motion, direction _p_
being that to throw it out of, and _q_ to throw it into gear or
engagement. At _r_ is a stop that can be fixed at any adjusted position
or desired location along the bed upon which the feed table or carriage
(F, Fig. 1880) slides, so that when that carriage is being self-actuated
it will traverse until the inner end of _n_ meets the stop, whereupon
the stop will move _n_ and thereby disengage _d_ from _c_, causing the
automatic feed to cease. All that is necessary, therefore, is to set _r_
in such a position along the bed that it will operate _n_ when the
milling cutter has operated to the required distance along or over the
work; _s_ is the stud arm that carries wheel _t_ to engage with and
drive the pinions shown in Fig. 1889, and _u_ is the stud for carrying
the wheels for giving the required changes of rotation to K, Fig. 1889,
the wheels on _u_ receiving motion from a gear placed at the seat V on
the feed screw A. The stud arm _s_ being slotted, can be moved forward,
transmitting motion from the change wheels on _u_ to wheel S, Fig. 1890,
causing the automatic spiral feed to actuate; or by moving _s_ outwards,
this feed is thrown out of action, and either the hand feed of handle W
or the self-acting feed traverse may be employed.
Thus the hand, and all the automatic feed motions are driven from the
feed screw A, and each of the automatic feed motions may be started or
stopped by operating the lever _n_, while the stop _r_ causes each of
them to cease when the work has traversed to the required distance
beneath the milling cutter.
Fig. 1892 represents an attachment to this machine to facilitate cutting
the teeth of gears, which it does because its index plate operates the
work-holding mandrel direct, and may, therefore, be set quicker. The
base bolts to the machine table and the index head and tailblock are
traversed in the base by means of the four-levered handle shown.
[Illustration: Fig. 1890.]
Figs. from 1893 to 1899 represent a universal milling machine. This
machine is so constructed that all the features essential to a universal
milling machine are obtained by means of attachments (each complete in
itself) which may be removed, leaving the work table clear, and,
therefore, serviceable for large work, or work which may be more
conveniently held without the use of attachments.
The [T]-slots in the table are furnished to standard size, and are at
right angles, so that the attachments will be held exactly parallel
with, or at a right angle, as the case may be, to the live spindle of
the machine; hence the machine will accomplish all the varied results
required in the tool room or for machine work generally.
Thus for the cutting of spirals, a fixture capable of originating any
spiral right or left hand, from 2 inches to 6 feet pitch, is provided.
Two bolts secure it to the machine table, and when the job is finished
it is removed. Similarly for the cutting of cams, an attachment fastened
to the work table by three bolts is used, which cuts either cylinder or
face cams of considerable size, and as conveniently as a machine built
solely for cam cutting. A gear-cutting device is also applied in the
same manner, as well as plain or universal work-holding centres.
The essential features of the machine are a standard A, Fig. 1894, with
spreading base, carrying upon its top a driving cone B, which is fully
back-geared like an engine lathe. The driving cone operates also the
feed mechanism. Above the driving cone is an arch C, in which is
inserted an arm D for supporting the outer end of the mill arbor when
used for heavy work. Upon the face or front of the standard slides a
knee E, which in its turn supports a carriage F, which traverses
crosswise upon it and carries above it the work table, which is provided
with an automatic feed at right angles with the movement of the
carriage. These three movements, vertical, cross, and longitudinal,
cover all that is usually required in a universal milling machine.
[Illustration: Fig. 1891.]
[Illustration: Fig. 1892.]
Coming to details we start with the spindle or arbor, the front end of
which runs in bearings of bronze. These are made in two parts, tapering
upon the outside and straight upon the inside, a corresponding taper
hole to receive the spindle bearings being bored in the solid iron of
the standard. A check nut upon each end of the bushing or bearing abuts
against the end faces of the standard bearing, and by drawing the
bushing or bearing through the taper hole in the standard, produces the
exact required closeness of fit between the spindle journal and its
bearing bore, and thus compensates for the wear of either the spindle
journal or its bearing or bushing bore, the front check nut also
providing a dust cap.
The back journal of the spindle runs in a bushing of considerable
length. Upon the back end of the spindle is secured a train of feed
gears G, the lower of which is upon a shaft that on its other end
carries the first feed cone H. The corresponding feed cone I is fixed to
the longer shaft J, carrying a worm (or tangent screw) K, which engages
with the worm-gear L connected directly with the feed screw, for the
longitudinal motion of the work table.
This whole feed work is shown fully in outline in Fig. 1894. The arm M
that supports the two lower feed gears pivots upon the outboard end of
the back bushing, hence its centre coincides with that of the spindle.
At its lower end a projection inwards forms a hub upon which a second
lug or arm N is pivoted. The lower end of this arm is bored out to
receive the threaded end of a lug O with the bearing of the second feed
cone I. This threaded end carries a milled or hand nut P, so that to
tighten or loosen the feed belt a turn of the nut is sufficient, the
effect being to increase or diminish the distance between the feed cones
H and I. The front end of the feed rod is supported in a drop box Q, and
is splined to allow the worm K to travel upon it. It will be seen,
therefore, that the feed mechanism is undisturbed either by the vertical
movement of the knee, or the cross motion of the carriage, or the
longitudinal feed of the table. The feed gears are covered with a shield
R, a part of which is shown broken away. The knee with its appendages is
actuated vertically by means of a crank connected with bevel gearing at
S, which moves a perpendicular screw T under the centre of the knee.
Rotating with this crank-shaft is a finger U held by friction. This
finger is in close proximity to a dial V graduated to thousandths of an
inch, and as one revolution of the finger indicates 1/8 of an inch of
elevation to the knee E, the ordinary subdivisions of an inch are
obtained either with or without an inner circle of graduations on the
dial. A similar dial upon the cross feed motion (not shown in the
engraving) is also put on, which likewise reads to thousandths of an
inch.
The feed of the work table is accomplished by means of a screw whose
thread is in shape a half [V] and does not bear upon the bottom of the
thread in the feed nut, which is in halves, with provision for closing
up to compensate for wear, while check nuts on one end of the feed screw
take up all end play.
The automatic feed is self-stopping (so as to enable one attendant to
operate several machines) by means of the following construction:--
In the general view, Fig. 1893, there is seen a stop that is secured in
the required position in the [T]-groove shown at X in the outline view,
Fig. 1894, and when this stop meets the bell crank Y it unlatches it
from a lug which is on the drop box Q, Fig. 1893, hence this box falls
and with it that end of the worm shaft J, throwing it out of gear with
the worm-wheel L, and therefore stopping the feed.
The attachments giving to this machine its universal qualifications are
as follows:--
The rotary vice is shown on the work table in the general view, Fig.
1893; and requires but little description. Upon the underside of the
base is a circular projection having beneath it a projection fitting
into the [T]-slots in the work table. Two segmental slots in the base
admit of a rotary movement of the vice within a range of 90°, and it is
held to the table by two bolts. The crank or handle of the vice is made
more convenient by means of two square holes that fit the end of the
screw that actuates the movable jaw. Using the central hole allows the
handle to clear the work table, but when the vice jaws need to be closed
with considerable force the handle is shifted to the end or outer hole,
thus doubling the leverage.
[Illustration: _VOL. II._ =EXAMPLE OF MILLING MACHINE.= _PLATE I._
Fig. 1893.
Fig. 1894.]
THE UNIVERSAL HEAD AND BACK CENTRE.--This tool is used for making
milling cutters either straight or angular, cutting small gears either
spur or bevel, fluting taps or reamers, finishing nuts or bolt-heads,
and a multitude of other jobs too numerous to particularise. The head
consists, as seen in Fig. 1895, of a swinging block mounted centrally
between the two upright sides or jaws of a base, and is clamped in any
position by a set-screw on either side. The face of one side or jaw is
laid out in degrees, and a finger or pointer on the block indicates its
angle of elevation. On the front end of the spindle is secured a
worm-wheel divided longitudinally, each half being used as a corrector
(in the making) for the other half till all errors are eliminated. A
dial is fixed upon the bushing through which passes the shaft that
actuates the worm, and consequently revolves the worm-gear and the
spindle. A pointer arm carrying a handle with a pointer and appendages
is secured to the end of this shaft. Under it are the usual spaces for
laying off or indicating the proper number of index holes for the
required fraction of a circle the spindle is to be moved through. The
spindle is hollow and has a screw on the outer end for taking a chuck or
face plate. It has a taper hole for receiving the proper centre, which
carries a lug for holding the dog used when the work to be finished is
held between centres. Three index dials, which are made interchangeable,
provide for most divisions except a few prime numbers to 360.
[Illustration: Fig. 1895.]
[Illustration: Fig. 1896.]
To prevent or take up lost motion between the worm and the worm-gear the
entire bracket carrying the worm and indexing mechanism is made
adjustable as follows:--
Through the base of the bracket thread two sleeves whose ends abut
against the top of the block, and therefore determine the engagement of
the worm with the worm-wheel. Through these sleeves pass the bolts which
thread into the block and lock the bracket in its adjusted position. A
simple screw bolts the back end of the bracket. The degree of fit
between the worm and the wheel may be very sensitively made by revolving
the worm spindle by hand.
The block carrying the back centre has some peculiar features, which
enable it to be set in line with the axis of the work, whether the
latter be parallel or taper, so as to suit the elevation or depression
of the head, and enable the centre to fill the countersink of work held
on centres, keeping it central and avoiding wear to one side. It
consists of a block held between two uprights or jaws, and clamped
thereto by two screw bolts. The block is slotted entirely through from
side to side, the front slot being only wide enough to receive the bolt
and making a changeable centre for the block to partially rotate upon.
The rear slot is wider and is a segment of a circle. The screw bolts
being slackened the back centre is raised, lowered, or tilted to any
required position to bring the centre in line with the work axis, and is
then clamped in place. One bolt holds this part of the machine to the
work table. The centre is adjusted to place in the end of the work in
the ordinary way, with a hand nut, &c.
For gear cutting, the universal head is enlarged and somewhat modified
in design, as is shown in Fig. 1896, the worm and worm-wheel being much
larger in diameter and exceedingly accurate by the following method
having been adopted to test them: Two cast-iron disks were placed side
by side on an arbor or mandrel held between the centres, and lines of
division were marked across the edges of both of them (the index plate,
of course, being used for the division). The disks were then separated
and one of them moved and the lines of division again compared with a
microscope, and no sensible errors were apparent.
The provisions for taking up the wear of the worm and its bearings, and
of the worm and its wheel, are as follows: The worm-shaft runs in
compensating bearings of phosphor bronze, and the bracket carrying the
worm-shaft is adjustable towards the worm-wheel by the means already
described for the ordinary universal head, and this head is said to be
capable of making divisions as fine as one minute of an arc, or dividing
the circle into 21,600 parts.
The employment of a worm and a worm-wheel necessitates that the index
pointer arm be given a certain number of revolutions, in order to move
the spindle the requisite amount for all divisions except those equal in
number to the number of teeth contained in the worm-wheel, and to avoid
any mistake in counting the number of revolutions of this index pointer
arm the following device is employed: On the worm shaft is a pin, and to
the right of the index plate is a dial plate which is clearly shown in
the engraving. The circumference of the latter is cut with ratchet
teeth, and the length of the pin on the worm-shaft is such that at each
revolution it moves one tooth of the dial plate. In front of the dial
plate is a fixed pointer, and as the face of the ratchet wheel is
graduated and marked 1, 2, 3, &c., it is obvious that the pointer shows
how many revolutions the dial plate, and therefore the worm shaft, has
made. After the requisite number has been made and the index pin has
been set in the index wheel, the small lever, shown on the right of the
dial plate, is moved and a spring brings the dial plate back so that its
zero number comes back to the pointer ready to count the number of
revolutions when the worm-shaft is revolved for the next division or
movement of the worm and wheel. For this head there are three index
plates drilled with 23 circles of holes, making, in combination with the
worm and wheel, all divisions up to 90, all even divisions up to 180,
with most of the other divisions between 90 and 180, or 135 divisions
and multiples of these divisions up to 16,200. The index plates are
interchangeable, and additional ones for other divisions may obviously
be added.
[Illustration: Fig. 1897.]
The device for cutting spirals as arranged for hand feeding is shown in
Fig. 1897, while in Fig. 1898 it is shown arranged for automatic
feeding, and is shown in position on the machine.
Referring to Fig. 1897 the hand wheel operates a worm engaging with a
worm-wheel on the shaft of the largest gear shown in the engraving. From
this gear motion is conveyed through intermediate wheels to the pinion
on the same shaft as the first bevel-gear, which obviously drives the
bevel-gear shown on the end of the head. The back face of this latter
gear is provided with index holes, and the usual index arm and pin are
provided.
The change gears provided for this device are sufficient to cut twelve
different pitches, ranging from one turn in 2 inches to one turn in 6
feet. Obviously right or left-hand spirals are produced according to the
direction of revolution of the hand wheel.
In the general view, Fig. 1898, the device is placed upon a box bolted
to the work table, and obtains its automatic feed through the medium of
the worm for the table feed.
[Illustration: Fig. 1899.]
The cam-cutting attachment, Fig. 1899, consists of a base bolted to the
machine table and adjustable to any required position thereon. This base
has a slide way in which a gibbed slide carrying a head is free to
travel longitudinally. The pattern or former cam and the work are
carried on the live spindle of the head, and the former cam is supported
by circumferential contact with a roll carried on the vertical bracket
shown on the right of the engraving. As shown, the device is arranged
for cutting face cams, the cam-holding spindle being placed in line with
the machine spindle. All that is necessary for cutting _cylinder_ cams
is to set the device with its spindle at a right angle to the machine
spindle and move the supporting bracket so that its roller will meet the
perimeter of the former cam. In either case the slide carrying the head
is pulled forward by weights suspended over the wheel shown on the end
of the base, and the feed is put on by revolving the spindle by means of
the worm and worm-wheel shown in the engraving, the ordinary crank
handle of the machine fitting the worm shaft.
A hand feed for cam cutters is preferable to the automatic feed, because
in turning corners or curves the rate of the feed requires to be reduced
in order to obtain smooth work.
Fig. 1900 represents a universal milling machine. The live spindle head
is fitted to a horizontal slide on the top of the main frame, and may
therefore be moved on that slideway to adjust the cutters to the work,
the motion being effected by a pinion operating a rack on the underside
of the head, as shown in Fig. 1901, which is a sectional view of the
machine.
[Illustration: _VOL. II._ =EXAMPLES OF MILLING MACHINES.= _PLATE II._
Fig. 1898.
Fig. 1900.]
At the handle end of the pinion shaft there is provided a dial (which is
seen in the general view of the machine) having an outer circle
graduated to sixty-fourths of an inch, and an inner one graduated to
fortieths of an inch. The driving shaft is at a right angle to the live
spindle, and drives it by means of a hardened steel worm operating a
bronze worm-wheel fast on the live spindle, and which runs in a trough
of oil to provide ample lubrication.
[Illustration: Fig. 1901.]
The spindle is hollow and has tapered journals. The arm for supporting
the outer end of the cutter arbor is cylindrical, and fits to a bore
provided in the top of the frame of the head, which is split and has two
binding screws. When these screws are loosened the arm may be readily
adjusted for position, while when they are screwed up they lock the arm
in its adjusted position. By this means the arm only projects out as far
as the particular work in hand requires.
The knee for carrying the work table and chucking devices terminates at
its top in a circular box cast open on top. This box is covered with a
circular cap, in the upper face of which are the slideways or guides for
the work table. The cap is recessed into the box so as to be kept
central, and is fastened therein by an expanding ring operated by a
single stud which projects through the walls of the box. This ring has a
[V]-shaped groove on its periphery, which in expanding closes over
corresponding bevelled ledges on the inside of both the cap and the box.
The edge of the cap is graduated for cutting spirals.
By this arrangement the table can be set to move at any required angle
with the live spindle and quickly clamped in position, while the ring
being of larger diameter and bearing evenly around the entire circle,
the cap is rigidly held. In this box, securely protected from the
cuttings or dirt, is a large worm-gear secured to a short vertical
shaft, on the upper end of which is a pinion projecting through the cap
and engaging with a rack upon the underneath side or face of the work
table. This shaft also carries a bevel-pinion which meshes with a pinion
on the end of the short shaft seen projecting through the front of the
box and provided with a hand crank, the hand lever shown behind this
crank being for securing or releasing the cap to or from the box. The
gearing is so arranged that one revolution of the hand crank traverses
the work table a distance of 2 inches, thus providing for the rapid
motion of the table to expedite putting in and taking out the work.
The knee is operated vertically by a pair of bevel-gears, the shaft for
operating which is shown on the left-hand side of the knee. On this
shaft is a pointer for an indexed dial, which has two graduated circles,
the outer of which is divided so that each division corresponds to a
knee motion of 1/32 of an inch, while the inner one denotes a knee
motion of 1/1000 inch.
Automatic feed motion for the work table is provided as follows: The
cone shaft projects through the live head and carries a leather-covered
friction disk which drives a vertical shaft carried by a bracket hinged
to the head. A small pulley splined on this shaft, and held at any point
by a spring-pressed catch, bears against the leather-covered face of the
disk, and it is obvious that the nearer to the centre of the disk the
pulley is set the slower the latter will be revolved, and therefore the
finer the feed will be, while the direction of revolution of the small
pulley will be reversed if it be set on the upper half or above the
centre of the disk, thus providing for reversing the direction of feed.
By this arrangement both the rate and direction of the feed can be set
without stopping the machine.
This vertical feed shaft carries a splined worm driving a worm-gear
splined on a horizontal shaft which is carried by the knee, which has a
projecting arm or bracket for carrying the back end of the shaft, so
that the latter rises or falls with the knee. A worm on this horizontal
shaft engages a large worm-wheel within the box and fast upon the short
upright shaft, whose pinion engages the table rack and thus completes
the feed motion.
It will be seen in the sectional view that the worm-wheel for the
automatic feed is in one piece, with a smaller bevel-wheel engaging with
a bevel-pinion for the hand feed.
A clutch joint near the centre of the horizontal shaft affords the means
for putting the automatic feed either into or out of action.
The table can be fed its full length in either direction, and when
placed so that one end will pass the main frame or column may be swung
around parallel to the spindle, thus enabling the machine to be used as
a boring mill for short holes, or by turning the table a half revolution
work may be done on both sides of a piece at one chucking, thus insuring
perfect parallelism.
[Illustration: Fig. 1902.]
[Illustration: Fig. 1903.]
The construction of the index head of this machine is as follows: Fig.
1902 represents it on a plate with a back centre and a centre rest, and
Fig. 1903 represents the head elevated. The head is a hollow box, the
outline of which is about two-thirds of a circle. The opening, in front
or chord side, is surrounded by a flange, and bored out as large as
permissible. This forms the front bearing of the spindle and face plate,
which is cast in one piece. A rear and smaller bearing is provided on
the circular part of the case. The end of the spindle projects through
the case, and is held from coming out by a recessed nut and washer. The
spindle also carries an accurately-divided steel gear of sixty teeth.
This gear is made as large as will go through the opening in front, or
about 6 inches in diameter. Directly under this gear the box is pierced
from the side. In this opening is inserted a long bush, through which a
steel worm engages with the gear. An index plate secured to the outer
end of the bush, and an adjustable arm and index pin attached to the
projecting end of the worm, complete the dividing mechanism. Substantial
but delicate adjustments are provided for eliminating lost motion.
On the periphery of the case is turned a dovetail shoulder, which slides
around in a corresponding groove in the quadrant-shaped base. The case
is graduated on its edge, and may be clamped at any angle of elevation
from 15 degrees below a horizontal line to a vertical position, being
equally stable in all positions. The face plate is no farther from the
bed in one position than another, and being seated to the case, and
adapted to hold work directly on its face, forms a stiff and substantial
device for cutting bevel-gears and other work requiring angular motion.
The tail centre is also of a strong and substantial design.
An adjustable centre rest of novel design also accompanies the outfit,
and an extra bed or table, with straps for securing it to the table of
the machine. With the centres arranged on this bed the line of centres
may be set at any angle with the sliding table, A sufficient number of
index plates are provided to divide all numbers up to 100 and all even
numbers to 200.
Fig. 1904 represents a machine in which the base column and the head are
constructed upon the same design as that in Fig. 1900, but the circular
top and cap are replaced with a larger and heavier knee of rectangular
form, and the table is longer. A cross sectional view of the head is
shown in Fig. 1905. The bearings for the live spindle are solid bushes
slightly tapered, and are driven into the head from each end up to and
against the flanges.
The spindle is of tool steel 3-1/2 inches in diameter at the front
bearing, tapering uniformly 3/4 inch per foot to the back end. This
simple construction allows the spindle to be perfectly ground, and
accurately fitted to the boxes by scraping. After this is done the
spindle is withdrawn about the 1/100 part of an inch, and a flat babbitt
metal washer fitted to exactly the space between the shoulder on the
spindle and the front box. A check nut and sliding collar on the back
end holds the spindle in place. A perfectly uniform space for oil is
thus formed between the spindle and bearings. The worm-gear is forced
tightly on the taper spindle with a nut, and keyed to prevent turning.
The spindle has a hole 1-9/16 inches through its centre, tapering in
front to receive the arbor to 1-7/8 inches. The taper is made 1/2 inch
per foot, and for ordinary work is sufficient to prevent the arbor
turning, but for driving gangs or large mills an arbor is used having a
hexagon enlargement just outside the spindle. A cap to screw over the
end of the spindle, having a hexagon opening in it to fit the arbor,
completes a positive driver that has none of the objections to cutting a
mortise or keyway in the spindle or otherwise disfiguring it. This cap
protects the thread on the spindle, and may be readily removed for a
face plate or large facing mills.
[Illustration: Fig. 1904.]
[Illustration: Fig. 1905.]
The cone shaft and its bearings are made independent of the head. A long
sleeve, which is provided with a large flange, projects through cored
openings in the side of the head. The bosses around these openings are
faced off square and parallel, and a large flat ring threaded on the
end of the sleeve draws the flange against the opposite face. The large
end of the sleeve is counterbored to receive the worm, and is cut away
on the under side to allow the worm to drop into mesh with the gear. The
worm is feathered on the shaft, the thrust of the worm being taken in
one direction against the shoulder in the sleeve, and in the opposite
direction (the machine can be driven either right or left-handed)
against the end of a bush, which is screwed in the sleeve and forms one
bearing for the cone shaft. Friction washers are placed to form the
step, and all wear or lost motion can be removed by screwing in the
bearing, which, when adjusted, is prevented from turning by a small
set-screw. The cone-shaft bearings are babbitt lined, but the spindle
bearings are made of cast iron, in which steel scrap has been melted.
The worm-gear has 40 teeth, and the worm is triple threaded, thus making
a back gear equivalent to 40-3, or 13-1/3 to 1. As the sleeve does not
fit the openings in the head, the worm and gear may be readily adjusted
to each other at all times, and held firmly and squarely in place by
drawing the flange tight against the side of the head. Set-screws
through the head prevent accidental displacement of the sleeve after
being adjusted.
[Illustration: Fig. 1906.]
Fig. 1906 represents a double spindle milling machine. The second
spindle is for driving the finishing cutters, so that as the two
spindles are capable of independent adjustment, the work may be finished
at one feed traverse, thus avoiding the necessity of removing the work
or making special adjustments.
Fig. 1907 represents a milling machine for globe valves and other
similar work. Here there are two cutter-driving spindles, one on each
end of the bed, and the work is held vertically. It is provided with an
index wheel for milling squares, hexagons, or octagons, and the pen for
the index wheel is operated by treadle. The work is fed across the bed,
the chucking devices being carried on a slide rest. In the figure a
globe valve is shown chucked between two plugs or arbors fitting its
bore, but it is obvious that centres or other work-holding appliances
may be used to suit the kind of work.
Fig. 1908 represents an eighty-inch milling machine, the table of which
has longitudinal motion; and provision for vertical and crosswise
movements are made in the head which carries the driving mechanism.
The machine table sets low on a bed supported by four box legs, and is
actuated by a steel screw driven by a worm and worm-gear connected with
a pair of spur-gears. The gearing is outside the bed, and therefore
accessible, and is protected by a shield, as shown in cut. The
arrangement for belting to feed works is also shown too plainly to need
description. The head upon which the spindle carrier is mounted travels
in ways upon the bed, and is adjusted crosswise on it by means of a
screw connected with a hand wheel, partially shown at the left of
engraving. For convenience and ease in fine adjustment this wheel, and
also the wheel at top of machine, connected with the elevating screw,
are worked by a hand lever, the wheels having sockets in their periphery
for this purpose.
The carrier, upon which is mounted the driving spindle, is gibbed to the
head, and has a vertical range sufficient to allow work 18 inches high
to pass under centres. From this carrier projects a large arm for
outside centre support of mill spindle, intended for use on work where a
back stand is not admissible. There is, however, as may be seen, a back
stand or tailstock of a very solid character. The arm is readily
removable, when desired, or the tailstock can be slid off its seat if
required. In most cases, however, the arm need not be removed, the yoke
on it being swung up out of the way, leaving the centre of mill arbor
free to engage with that on the back stand. This combination provides
for operating on a wide range of work.
As shown in the engraving, the space between head and tailstock is about
24 inches, but if required the tailstock can be made to travel in line
with the head, and its support be extended to any distance desired.
The method of driving the spindle is simple and strong, and allows of
free adjustment of the spindle without disarrangement of the driving and
feed belts.
The cone, which is made for 3-1/2 inch belt, is mounted in a stirrup
which is pivoted to the bed, and the pinion which engages with the
driving gear on the spindle is held at correct distance by a connecting
yoke, and is driven by a feather.
The machine has longitudinal feed only, but where it is desired an
automatic feed motion can be applied to the elevating screw in the head,
giving feed in a vertical direction.
The table is arranged to be run back rapidly by power, by a device which
is not seen in the engraving. As the table weighs one ton, the relief to
the operator by this improvement is obvious.
All the operations of the machine are intended to be conducted from the
front side, without any change in the position of the operator. The feed
can be thrown out by hand at any moment by means of a rod which connects
with the latch shown in the front of the cut, and the power quick-return
applied; or the table can be run back by hand, and the feed thrown in by
a foot lever, which lifts the drop box shown in front of cut. Adjustable
dogs automatically drop the feed motion at any point.
The machine is massive in all its parts, and is intended for heavy
milling of any description, but more particularly for shafting,
railroad, or engineering shops, being specially adapted for key-seating
long and heavy shafting, finishing guide bars, connecting rods, &c.
Its weight is 7,500 pounds. The work table is 7 feet long by 20 inches
wide; length of longitudinal feed, 84 inches; distance between uprights,
24 inches. The cast-steel spindle is 4 inches in diameter, and the mill
arbor 2-1/2 inches diameter. Arm for outer centre support 5 inches
diameter at its smallest part.
[Illustration: Fig. 1909.]
[Illustration: _VOL. II._ =EXAMPLES OF MILLING MACHINES.= _PLATE III._
Fig. 1907.
Fig. 1908.]
MILLING CUTTERS OR MILLS.--The simplest form of milling cutter is that
shown in Fig. 1909, the teeth being equidistantly arranged upon the
circumference only. Its size is usually designated by its length, which
is termed the face. Thus a cutter having its teeth parallel to its axis
and an inch long would be said to have 1 inch face. Cutters of more than
about half an inch face usually, however, have their teeth cut spirally,
as in Fig. 1910; the degree of spiral is one turn in a length of 3 feet
for cutters between 2-1/4 and 4 inches in diameter. For cutters of less
than 2-1/4 the degree in the spiral is increased; thus for an inch
cutter, the degree is one turn in 15 inches, while for 6 inches one turn
in about 60 inches is used.
[Illustration: Fig. 1910.]
In the following table is given the sizes of cutters as made by one
company, the bores being 1 inch.
+---------+-----------------------++---------+-----------------------+
| Width of| || Width of| |
| face. | Diameter of cutter. || face. | Diameter of cutter. |
+---------+-------+-------+-------++---------+-------+-------+-------+
| inch. | inch. | inch. | inch. || inch. | inch. | inch. | inch. |
| 1/8 | 2-1/2 | 3 | 4 || 15/16 | 2-1/2 | 3 | 4 |
| 3/16 | 2-1/2 | 3 | 4 || 1 | 2-1/2 | 3 | 4 |
| 1/4 | 2-1/2 | 3 | 4 || 1-1/8 | 2-1/2 | 3 | 4 |
| 5/16 | 2-1/2 | 3 | 4 || 1-1/4 | 2-1/2 | 3 | 4 |
| 3/8 | 2-1/2 | 3 | 4 || 1-1/2 | 2-1/2 | 3 | 4 |
| 7/16 | 2-1/2 | 3 | 4 || 1-3/4 | 2-1/2 | 3 | 4 |
| 1/2 | 2-1/2 | 3 | 4 || 2 | 2-1/2 | 3 | 4 |
| 9/16 | 2-1/2 | 3 | 4 || 2-1/4 | 2-1/2 | 3 | 4 |
| 5/8 | 2-1/2 | 3 | 4 || 2-1/2 | 2-1/2 | 3 | 4 |
| 11/16 | 2-1/2 | 3 | 4 || 3 | 2-1/2 | 3 | 4 |
| 3/4 | 2-1/2 | 3 | 4 || 3-1/2 | 2-1/2 | 3 | 4 |
| 13/16 | 2-1/2 | 3 | 4 || 4 | 2-1/2 | 3 | 4 |
| 7/8 | 2-1/2 | 3 | 4 || | | | |
+---------+-------+-------+-------++---------+-------+-------+-------+
The keyways are semicircular, the key being composed of a piece of No.
25 Stubbs steel wire.
The following is a table of the sizes of milling cutters made by another
company.
+----------+------------+---------++----------+------------+---------+
| | | || | | |
| Width of | Diameter | Size of || Width of | Diameter | Size of |
| face. | of cutter. | hole. || face. | of cutter. | hole. |
+----------+------------+---------++----------+------------+---------+
| inch. | inch. | inch. || inch. | inch. | inch. |
| 1/8 | 2-1/4 | 1 || 3/4 | 2-7/8 | 1 |
| 3/16 | 2-1/4 | 1 || 7/8 | 2-7/8 | 1 |
| 1/4 | 2-1/2 | 1 || 1 | 2-1/2 | 1 |
| 5/16 | 2-1/2 | 1 || 1-1/4 | 2-1/2 | 1 |
| 3/8 | 2-5/8 | 1 || 1-1/2 | 2-1/2 | 1 |
| 7/16 | 2-5/8 | 1 || 1-3/4 | 2-1/2 | 1 |
| 1/2 | 2-3/4 | 1 || 2 | 2-1/2 | 1 |
| 9/16 | 2-3/4 | 1 || 2-1/2 | 2-1/2 | 1 |
| 5/8 | 2-3/4 | 1 || 3 | 2-1/2 | 1 |
| 11/16 | 2-7/8 | 1 || | | |
+----------+------------+---------++----------+------------+---------+
Cutters of 1 inch face and over have teeth of a spiral form.
The object of providing spiral teeth is to maintain a uniformity of
cutting duty at each instant of time.
Suppose, for example, that the teeth are parallel to the cutter axis,
when the cutter first meets the work the tooth will take its cut along
its full length at the same instant, causing in wide cuts a jump to the
work because of the spring of the various parts of the work-holding
devices, and of the cutter driving spindle; furthermore as the cutter
revolves the number of teeth in action upon the work varies. Thus in
Fig. 1912 it is seen that one tooth only is in action, but when the
cutter has revolved a little more there will be two teeth in action, as
shown in Fig. 1913. This variation causes a corresponding variation of
spring or give to the machine, producing a surface very slightly marked
by undulations. But if the teeth are cut spiral the cut begins at one
end of the tooth and proceeds gradually along it, thus avoiding violent
shock, and after the cut is fairly started across the work the length of
cutting edge in action is maintained uniform, producing smoother work,
especially in the case of wide surfaces and deep cuts.
[Illustration: Fig. 1911.]
[Illustration: Fig. 1912.]
[Illustration: Fig. 1913.]
When the cutter is required to cut on the sides of the work as well as
on its upper face it is termed a face cutter, and its side faces are
provided with teeth, as shown in Fig. 1914; and when these cutters are
arranged in pairs as in Fig. 1915, so as to cut in the side faces only
of the work D, they are termed twin or straddle mills, both being of the
same diameter.
[Illustration: Fig. 1914.]
In mills or cutters used in this way the cutting duty is excessive on
the outer corners of the teeth, which, therefore, rapidly dull; hence it
is usual to provide teeth on both sides of the cutter, as in Fig. 1916,
so that after having been used in the position shown in the engraving
until the teeth are dull the positions of cutters may be changed,
bringing the unused cutting edges into use.
[Illustration: Fig. 1915.]
Twin or heading cutters are right and left hand, a right-hand one being
that in which the teeth at the top of the wheel revolves towards the
right, while a left-hand one revolves (at the top) towards the left.
[Illustration: Fig. 1916.]
[Illustration: Fig. 1917.]
If the machine is belted so that it can be revolved in either direction,
both sides of the cutter may be utilised by taking the cutters off the
arbor, turning them around and then replacing them in their original
positions on the same. Thus in Fig. 1917 we have at A a left-hand cutter
that if reversed upon its arbor would be a right-hand one as at B, and
it is obvious that the direction of revolution must be in each case as
denoted by the arrows F G, which are in opposite directions. In this
case the direction of work feed must be reversed, the work for A feeding
in the direction of C, and that for B in the direction of D. It is to be
observed, however, that the cutter could not be reversed if it was
driven by an arbor that screwed upon the driving spindle of the milling
machine. For if the machine has a right-hand thread then the cutter must
revolve in the direction of G, and the work feed must be in that of C;
whereas if the machine spindle drives its chucks, arbors, &c., by a
left-hand thread, then the direction of cutter revolution must be as at
F, and that of work feed as at D. But if the cutters are upon an arbor
that is driven by a conical seat in the machine spindle, or by any other
means enabling the arbor to revolve in either direction without becoming
released from that spindle, then the cutter may be simply turned around
and the feed direction reversed, as already explained. The reason for
reversing the direction of feed when the direction of cutter revolution
is reversed is as follows:--
[Illustration: Fig. 1918.]
In Fig. 1918 A and B represent two pieces of work of which B is to be
fed in the direction of arrow C, so that the pressure of the cut tends
to force the work back from under the cutter, whereas in the case of the
work A, feeding in the direction of D, the teeth act to pull the work
beneath the cutter, which causes tooth breakage.
Suppose, for example, that in Fig. 1919 P is a piece of work fastened to
the table T, feeding in the direction of A, the cutter W revolving in
the direction of arrow B, N representing the feed nut operated by the
feed screw S. Now while the table is being pulled in the direction of A,
the sides C of the feed screw thread will bear against the sides of the
thread in the nut, and whatever amount of looseness there may be between
the threads of the screw and nut will in this case be on the sides D of
the threads. So soon, therefore, as the wheel meets the work P, it will
suddenly pull the work forward to the amount of the play or looseness on
the sides D of the threads, and this in addition to the feed given by
the rotating screw S, would cause the wheel to lock upon the work
surface.
[Illustration: Fig. 1919.]
In all milling operations, therefore, the work is fed against the cutter
as at B, in Fig. 1918, unless, in the case of twin mills, it is fed (as
at E and F in the same figure) in the middle of the cutters, in which
case it is preferable to present it as at F, so that the pressure of the
cut will tend to hold the work down to the table, and the table down
upon its guideways. This position of the work presents some advantages
for small work which will be explained hereafter.
[Illustration: Fig. 1920.]
Fig. 1920 represents angular cutters, the teeth being at an angle to the
cutter axis. These cutters are made right and left as at A and B in Fig.
1921, the teeth of A being cut in the opposite direction to those at B,
so as to be able to cut equal angles on the work when these angles lie
in opposite directions, as C and D in the figure. Furthermore these
cutters are sometimes screwed to their arbors, and can therefore be
revolved in one direction only, which prevents their being turned around
end for end, even though the machine be so belted as to be capable of
revolving its spindle in either direction.
[Illustration: Fig. 1921.]
The angular cutters shown in Fig. 1921 have their teeth arranged for a
Brainard milling machine, in which the live spindle has a right-hand
thread for driving the chucks, arbors, &c.; hence the direction of
cutter revolution, and the arrangement of the teeth are as in the
figure.
[Illustration: Fig. 1922.]
[Illustration: Fig. 1923.]
In Fig. 1922 are segments of two wheels, A and B (corresponding to A and
B in Fig. 1921), but with their teeth arranged for a Brown and Sharpe
milling machine, in which the machine spindle has a left-hand thread;
hence the direction of cutter revolution is reversed, as denoted by the
arrows in the two figures.
[Illustration: Fig. 1924.]
Fig. 1923 represents a round edge cutter; and it is obvious that the
curvature or roundness of the cutting edges may be made to suit the
nature of the work, whether the same be of regular or irregular form. In
cutters of this description it would be a difficult matter to resharpen
the teeth by grinding their backs, hence they are ground on the front
faces; and to maintain the form or profile of the cutting edges,
notwithstanding the grinding, we have a patent form of cutter, an
example of which is shown in the gear tooth cutter in Fig. 1924. The
backs of the teeth are of the same form throughout their entire length,
so that grinding away the front face to sharpen the cutting edge does
not alter the contour or shape of the cutting edge. This is of especial
advantage in cutters for gear teeth, and those for irregular forms,
Figs. 1925, 1926, and 1927 forming prominent examples.
[Illustration: Fig. 1925.]
End mills or shank cutters are formed as in Fig. 1928, the shank
sometimes being made parallel with a flat place at A, to receive the
set-screw pressure, and at others taper, the degree of taper being 1/2
inch per foot. The hole at the end facilitates both the cutting of the
tooth in the making and also the grinding. Shank cutters may be used to
cut their way into the work, with the teeth on the end face, and then
carry it along, bringing the circumferential teeth into operation; or
the end teeth may be used to carry the cut after the manner of a face
cutter.
[Illustration: Fig. 1926.]
[Illustration: Fig. 1927.]
Shank cutters are rarely made above an inch in diameter, and are largely
used for cutting grooves or recesses, and sometimes to dress out slots
or grooves that have been cast in the work, as in the case of the steam
and exhaust ports of steam engine cylinders. In work of this kind the
direction of the feed is of great importance and must be varied
according to the depth of cut taken on the respective sides of the
cutter. Suppose, for example, that the conditions are such as
illustrated in Fig. 1929, the cut being deepest on the side A of the
slot, and the cutter must be entered at the end of the slot and fed in
the direction of D, so that the pressure of the cut may tend to push the
cutter back, it being obvious that on the side B the cutter has a
tendency to walk or move forward too rapidly to its cut, and if the cut
was heaviest on that side it would do, this increasing the cut rapidly
and causing tooth breakage.
[Illustration: Fig. 1928.]
[Illustration: Fig. 1929.]
This tendency, however, is resisted by the pressure on the side A of the
slot, which acts, as already stated, to push the cutter back. In
starting the cutter therefore, it is necessary to do so at that end of
the slot that will cause the deepest cut to act in the direction to
retard the feed. Suppose, for example, that the heaviest or deepest cut,
instead of being on the side A of the slot, as in Fig. 1929, was on the
side B, and in that case it would be necessary to start the cut from the
other end of the slot as in Fig. 1930, the arrow C denoting the
direction of feed.
[Illustration: Fig. 1930.]
[Illustration: Fig. 1931.]
Similarly when a groove has been roughed out from the solid, and it is
determined to take a finishing cut, the direction of the feed for the
latter is of importance. Suppose, for example, a [T]-groove is to be
cut, and that a slot is first cut with a shank cutter as in Fig. 1931,
leaving a light finishing cut of, say, 3/64 inch to finish the neck to
the dotted lines A B, and entering to within 1/16 inch of the full depth
as denoted by line C. The enlarged part of the groove may then be cut
out, leaving about 3/64 inch at the top and bottom, D and E, the cutter
having a plain shank (as in Fig. 1933), whose diameter should just clear
the narrow part of the groove already roughed out. The work will then be
ready for the finishing cutter, formed as in Fig. 1932, whose teeth (on
both the shank and the enlarged end) should have a diameter of 3/32 less
than that of the finished slot. In taking the finishing cut this cutter
must be set first to cut the sides B E to finished size, the direction
of the feed being such that the pressure of the cut acts to push the
cutter back as already explained, and when the cut is finished on this
side the finishing cut may be put on the side A D, without traversing
the cutter back, or in other words the feed must be carried in the
opposite direction, so that the cutter will run under the cut and be
pushed back by it, so as to prevent it from running forward as explained
with reference to figure.
[Illustration: Fig. 1932.]
For ordinary work not requiring great truth, however, the first cutter,
Fig. 1931, may be made of the finished diameter, and be followed by a
cutter such as in Fig. 1933, also of the finished diameter.
[Illustration: Fig. 1933.[31]]
[31] Figs. 1928, 1931, 1932, 1933, are from an article by John J.
Grant, in _The American Machinist_.
When a shank-cutter is required to enter solid metal endways, as in the
case of cutting grooves around the circumferential surface of a
cylinder, it is necessary to drill a hole to admit the cutter, leaving a
light finishing cut for the diameter of the cutter, and sufficient in
the depth to let the end face of the cutter remove or square up the cone
seat left by the drill. Shank cutters may obviously be made taper, or
to any other required angle or curvature, Figs. 1934 and 1935 being
examples which can be used in situations where other cutters could not,
as for example on the arms or spokes of wheels.
[Illustration: Fig. 1934.[32]]
[32] Figs. 1934, 1935, 1936, are from articles by John J. Grant, in
_The American Machinist_.
Fig. 1936, from _The American Machinist_, represents an example of the
employment of shank cutters, the work being a handle for a lathe
cross-feed screw, and it is obvious that the double cornering cutter may
be used upon both edges, and the cut being carried around the hub by the
parallel part of the cutter; the whole of the work on the handle
including the boring, if the hole is cast in, may be done by the shank
cutter, the handle end being finished and the boring done first, the hub
being finished on an arbor.
[Illustration: Fig. 1935.]
Shank mills may obviously be made of various shapes; thus in Fig. 1937
is shown two applications of an end or shank mill, one for cutting a
dovetailed groove and the other an angular one. In the case of the
dovetail groove the cutter will work equally well, whether it be used on
straight or spiral grooves; but this is not the case with angular
grooves for reasons which are explained with reference to angular
cutters and spiral groove cutting.
[Illustration: Fig. 1936.]
Shank cutters are provided with finer teeth than ordinary cutters, the
following being the numbers of teeth commonly employed for the
respective diameters:--
Diameter of cutter 1/8 or 3/16 inch, number of teeth 6
" " 1/4 " " " 7
" " 3/8 " " " 8
" " 1/2 " " " 8
" " 5/8 " " " 10
" " 3/4 " " " 10
" " 7/8 " " " 12
" " 1 " " " 14
The front faces of the teeth are radial as in other cutters, the angle
of the back of the tooth being 40° for the smaller, 50° for the medium,
and 60° for an inch cutter.
[Illustration: Fig. 1937.]
Fly cutters are single-toothed cutters, or rather tools, that are
largely used by watchmakers for cutting their fine pitches of gear
wheels.
Fig. 1938 represents a fly cutter in place in its holder or arbor, its
front face D being in line with the axis C of the arbor.
[Illustration: Fig. 1938.]
Let it be required to make a fly cutter for a very fine pitch of gear
tooth, such as used for watches, and a template, shown greatly magnified
at T in Fig. 1939, is made to fill a space and one half of each of the
neighboring teeth. From this template a cutting tool is made, being
carefully brought to shape with an oil-stone slip and a magnifying
glass. This tool is used for the production of fly cutters, and may be
employed by either of the following methods:--
[Illustration: Fig. 1939.]
The piece of steel to form the cutter is fastened in an arbor back from
the centre, as at D in Fig. 1940, and is then cut to shape by the tool
before referred to. It is then set for use in the milling machine, or in
such other machine as it may be used in, in the position shown in Fig.
1938, its front face D being in line with the axis C of the arbor. The
change of position has the effect of giving the tool clearance, thus
enabling it to cut while being of the same shape throughout its whole
thickness; face D may be ground to resharpen the cutter without altering
the shape it will produce. It is this capacity to preserve its shape
that makes the fly cutter so useful as a milling machine tool, since it
obviates the necessity of making the more expensive milling cutters,
which, unless made on the principle of the Brown and Sharpe cutters, do
not preserve their shapes.
[Illustration: Fig. 1940.]
It is to be observed, however, that a fly cutter made as above does not
produce work to exactly correspond to the template it was made from,
because moving it from the position it was made in (Fig. 1938) to the
position it is used in (Fig. 1940) causes it to cut slightly shallower,
but does not affect its width.
[Illustration: Fig. 1941.]
Another method of cutting up a fly cutter by the tool made to the
template is shown in Fig. 1941. The blank cutter is placed at an angle
to an arbor axis, and is cut to shape by the tool. For use it is placed
in line with the arbor axis as in Fig. 1942, the change of position here
again giving clearance as shown by the dotted arcs, the inside ones
showing the arc the cutter revolved on when it was in the arbor in Fig.
1938. Here again, however, the change of position causes the fly cutter
to produce a shape slightly different from the template to which the
first tool was made, hence the best method is as follows:--
[Illustration: Fig. 1942.]
The blank is let into an arbor of small diameter, as in Fig. 1943, its
face D being in line with the arbor axis. It is then cut up with the
tool made from the template. For use it is set in a larger arbor, as in
Fig. 1944, the difference in its path of revolution giving it the
necessary clearance. Thus, in the figure the inner dotted arcs show the
path of revolution of the cutter when it was in the small arbor, and the
outer arc of the path in the large arbor. The front face can be ground
without altering the shapes; the cutter will produce this front face,
being kept in line with the arbor axis by grinding the body of the steel
as much as the front face is ground when it is resharpened. Curves or
irregular shapes may be readily produced and preserved by fly cutters.
[Illustration: Fig. 1943.]
[Illustration: Fig. 1944.]
It is obvious, however, that when the tool made to the original template
is worn out, another must be made, and to avoid this trouble and
preserve the original shape beyond possible error, we have recourse to
the following additional method:--
[Illustration: Fig. 1945.]
With the tool made from the template we may cut up a wheel, such as in
Fig. 1945, and this wheel we may use as a turning tool to cut up fly
cutters, the principle of the wheel cutter having been shown in
connection with lathe tools. It may here be pointed out, however, that
if a wheel or circular cutter, as it is termed, is to be used, we may
make the template, and the master tool we make from it, for one side of
a tooth only, and use the master tool to cut up one side only of the
corner of the circular cutter, as shown in Fig. 1945.
[Illustration: Fig. 1946.]
[Illustration: Fig. 1947.]
The method of using the circular cutter is illustrated in Fig. 1946, in
which H is a holder, whose end face P is level with the axis of the
cutter, which is held to the holder by a screw. The side face of the
holder is out of the vertical so as to give the cutter side clearance. A
second holder has its side face inclined in the opposite direction, thus
enabling the one edge of the circular cutter to be used as a right or as
a left-hand tool and insuring uniformity, because the same edge of the
circular cutter is used in both cases, so that if used for say a tool
for a gear tooth, both sides of the tool will be cut from the same side
of the circular cutter.
It is obvious that instead of having one continuous cutter, the
necessary breadth of cutter face may be obtained by means of two or more
cutters placed side by side. Thus to mill a piece of work two inches
wide we may use two cutters of an inch face each (both of course being
of equal diameter), or we may use one cutter, of 1-1/4 inch and another
of 3/4 inch face. It is preferable, however, to use two cutters of an
inch face each, and to set one beam left-hand and the other right-hand
spiral teeth, because spiral teeth have considerable tendency to draw
the machine spindle endways in its bearings, because the teeth
correspond to a certain extent to a screw, and the work to a nut. A
cutter with a left-hand spiral exerts end pressure tending to draw the
driving spindle out from its bearings, while a right-hand one tends to
push it within them; hence by making the two cutters of equal length and
of the same degree of spiral, the effect of one cutter offsets that of
the other. Furthermore, it is found that the tendency to chatter which
increases with an increase in the width of the work, is diminished by
using right and left spiral cutters side by side.
[Illustration: Fig. 1948.]
In order that the cutting edges of cutters placed side by side in this
way may be practically continuous so as not to leave a line on the
finished work, the teeth may be made to overlap in two ways as in Fig.
1948, both representing magnified portions of cutters. In the method
shown on the left of the figure the usefulness of either cutter to be
used singly is not impaired, all that is necessary to insure the
overlapping being to cut the keyways in different positions with
relation to the teeth; whereas on the left of the figure neither cutter
would be efficient if used singly, except upon work as narrow as the
narrowest part of the cutter. On the other hand, however, it affords
excellent facilities for grinding, since the two cutters may be ground
together, thus ensuring that they be of equal diameters except in so far
as may be influenced by the wear of the emery wheel, which is, however,
almost inappreciable even in cutters of considerable width of face. In
the method shown on the left there is the further advantage that as the
teeth are not in line the cutting action is more continuous and less
intermittent, the arrangement having in a modified degree the same
advantage as the spiral cutter.
[Illustration: Fig. 1949.]
In both methods some latitude is given to adjust the total width of face
by placing paper washers between the cutters. If the plan on the right
is employed the projections may occupy one-fourth of the circumference,
there being two projections and two depressions on one end of the
cutter. When cutters of different diameters and shapes are put together
side by side on the same arbor the operation is termed gang milling.
[Illustration: Fig. 1950.]
Thus, in Fig. 1949 is shown a sectional view of a gang of three mills or
cutters, A, B, and C, of which A and C are recessed to admit of the ends
of B passing within them. The heavy black line representing a paper
washer inserted to adjust the distance apart of A and C, it being
obvious that this gives a means of letting them together after their
side teeth at D and E have been ground. As shown in the figure, A has
teeth on one only of its sides, while C has them on both sides as well
as in its circumference, while all three are of different widths of
face. This would capacitate A only for the inside cutter, as in the
figure, while B would be serviceable only when there was a cutter on
each side of it; or if used singly, only when its face overlapped the
width of the work on each side. But C, being cut on each side, could be
used singly for grooving or recessing, or for plain milling, or in the
position of B or A in the figure; hence it is preferable in gang milling
for general purposes to provide teeth on both sides as well as on the
circumference of the mill or cutter. But if a gang of mills are to be
made for some special purpose, and used for no other, the teeth may be
provided on the sides or not, as the circumstances may require.
[Illustration: Fig. 1951.]
Suppose, for example, that steps, such as shown in Fig. 1950, were
required to be cut in a piece of brass work, and that, the work
requiring to be very true, a set of roughing and one of finishing
cutters be used, then the latter may be put together as in Fig. 1951,
there being eight separate cutters, and their ends being slightly
recessed but without teeth. Such cutters would wear a long time and may
be readily sharpened, and there being no side teeth, the widths of the
cutters, individually and collectively, would not be altered by the
grinding; hence no readjustment with washers would be necessary. The
tooth corners must, however, be kept sharp, for in proportion as they
get dull or blunt, the sides of the cutter wedge in the work, causing
friction and extra power to drive them as well as producing inferior
work.
[Illustration: Fig. 1952.]
Fig. 1952, which is from an article by John J. Grant, represents a gang
of cutters arranged to mill out the jaws and the top faces of a head for
a lathe; and it is obvious that a number of such heads may be set in
line and all milled exactly alike.
THE NUMBER OF TEETH IN MILLS OR CUTTERS.--The teeth of cutters must
obviously be spaced wide enough apart to admit of the emery wheel
grinding one tooth without touching the next one, and the front faces of
the teeth are always made in the plane of a line radiating from the axis
of the cutter.
In cutters up to 3 inches in diameter, it is good practice to provide 8
teeth per inch of diameter, while in cutters above that diameter the
spacing may be coarser, as follows:--
Diameter of cutter 6 inches, number of teeth in cutter 40
" " 7 " " " 45
" " 8 " " " 50
[Illustration: Fig. 1953.]
MILLING CUTTERS WITH INSERTED TEETH.--When it is required to use milling
cutters of a greater diameter than about 8 inches, it is preferable to
insert the teeth in a disk or head, so as to avoid the expense of making
solid cutters and the difficulty of hardening them, not merely because
of the risk of breakage in hardening them, but also on account of the
difficulty in obtaining the uniform degree of hardness or temper. The
requirements for the heads for inserted teeth are, that the teeth shall
be locked firmly in position without lost motion, and be easily set to
gauge, ease of insertion and of removal being of secondary
consideration, as such teeth should be ground in their places in the
head, and are therefore rarely removed. The manner in which these
requirements are attained in the Brainard heads are, as shown in Fig.
1953. A disk of wrought iron of suitable thickness and diameter is
turned and squared, then a circle of index holes corresponding to the
number of teeth required is drilled in its face; this circle of holes is
used to insure the accurate spacing of the dovetail seats for the teeth,
and to attain accuracy in grinding the teeth. All the teeth are a
driving fit, and being milled are, of course, interchangeable. In order
to obtain a larger number of teeth in a given size of head than could be
got into the face, only one-half of the teeth are dovetailed into the
periphery of the head and the other half into its face, but yet all the
teeth are effective for face cutting, the construction being as
follows:--
Between each pair of face teeth is a slit sleeve, which meets them and
has a taper base, through which passes a taper bolt having a nut on the
back face of the head. Tightening this nut expands the sleeve, thus
locking the pair of teeth in their dovetail grooves. The circumferential
teeth are each counter-based to receive a screw tapped in the head, and
are firmly locked thereby. This affords a simple and reliable means of
inserting and adjusting other teeth with the certainty that they will be
true with those already in use.
The large size of some of these heads makes it convenient and desirable
to grind them in their places on the machine, and for this purpose a
special grinder is made by the same company. This grinder sets upon the
machine table and has a point or pin for the index holes or the cutter
head; by this means the grinding may be made as accurate as in small
milling cutters.
The head shown in figure represents one that has been in use ten years,
its cutters having been renewed but once; it is 28 inches in diameter,
contains 84 teeth, and weighs 400 lbs.
Arbors for milling cutters may be driven in two ways. In the first the
shank is made taper to fit the taper bore of the live spindle. The
standard taper is 1/2 inch per foot of length. The keyway is
semicircular, as shown at G in Fig. 1954, the key consisting of a piece
of No. 25 Stubbs steel wire, which being of uniform diameter enables a
number of keys of different lengths to be easily obtained or made, and
the nut is usually cylindrical, having two flat sides, A.
Fig. 1955 (from _The American Machinist_) represents an arbor, having a
cone at A, so that the cutter bore being coned to correspond, the cutter
will run true, notwithstanding that it may not fit the stem B. It is
obvious, however, that the nut and washer must be made quite true or the
cutter will be thrown out of line with the arbor axis and therefore out
of true, and also that such an arbor is not suitable for cutters of a
less width of face than the length of the cone A.
[Illustration: Fig. 1954.]
[Illustration: Fig. 1955.]
[Illustration: Fig. 1956.]
Shank cutters that have parallel shanks as in Fig. 1928 should have
their sockets eased away on the upper half of the bore as denoted by the
dotted arc D in Fig. 1956, which will enable the cutter shanks to be
made the full size of the socket bore proper, and thus run true while
enabling their easy insertion and extraction from the socket. Or the
same thing may be accomplished by leaving the socket bore a true circle
fitting the cutter shanks in tight, and then easing away that half of
the circumference that is above the centre line C in the figure. It is
preferable, however, to ease away the bore of the socket, which entails
less work than easing away the shanks of all the cutters that fit to the
one socket. When the cutter is held in a socket of this kind it allows
it to be set further in or out, to suit the convenience of the work in
hand, which cannot be done when the cutter has a taper shank fitting
into the coned bore of the machine spindles.
[Illustration: Fig. 1957.]
It is obvious that when the cutter requires to pass within the work, or
cut its way, as in the case of milling out grooves, a nut cannot be
used; hence, inch cutters are driven by a key as usual, but secured by a
screw, as in Fig. 1957, which is from the pen of John J. Grant, in _The
American Machinist_.
[Illustration: Fig. 1958.]
[Illustration: Fig. 1959.]
In many cases it becomes a question whether it is better to do a piece
of work with plain mills, with an end mill, or with face mills, a common
hexagon nut forming an example. Thus, in Fig. 1958, we have a nut being
operated upon by a plain mill; in Fig. 1959 by an end mill, and in Fig.
1960 by a pair of twin face mills.
In the case of the plain mill, it is obvious that only one side of the
nut is operated upon at a time, and as the whole of the pressure of the
cut falls on one side of the work it acts to spring or bend the mandrel
or arbor used to hold the nut, and this spring is sufficient, if several
nuts are milled at once on the same arbor, to make the arbor bend and
cause the nuts in the middle to be thicker than those at the ends of the
arbor. In the case of hand-forged nuts in which there may be more metal
to take off some nuts or some sides of nuts than off others, the extra
spring due to an increased depth of cut will make a sensible difference
to the size the work is milled to. In the case of the end mill the
pressure of the cut falls in line with the arbor axis and downwards;
hence the arbor spring is less and does not affect the depth of the cut.
In the case of the face mills the pressure of the cut falls on both
sides of the work, and the spring is mainly endways of the nut arbor;
hence, it does not affect the depth of the cut nor the truth of the
work. Furthermore, in both the end and the face mills, the work will be
true notwithstanding that the cutter may not be quite true, because each
point of the work surface is passed over by every tooth in the cutter,
so that the work will be true whether the cutter runs true or not;
whereas in the plain mill or cutter each tooth does its individual and
independent proportion of finishing. This is shown in Figs. 1961 and
1962. In Fig. 1961 we have the plain mill, and it is obvious that the
tooth does the finishing on the vertical line B, that being the lowest
point in its revolution. After a tooth has passed that point the work in
feeding moves forward a certain distance before the next tooth comes
into action; hence to whatever amount a tooth is too high it leaves its
mark on the work in the form of a depression, or _vice versâ_, a low
tooth will leave a projection.
[Illustration: Fig. 1960.]
[Illustration: Fig. 1961.]
[Illustration: Fig. 1962.]
In Fig. 1962 we have a piece of work being operated on by a face mill,
and it is obvious that while the teeth perform cutting duty throughout
the distance A, yet after the work has fed past the line A it is met by
the cutter teeth during the whole time that the work is feeding a
distance equal to A on the other side; hence the prolonged action of the
teeth insures truth in the work. On the other hand, however, it is clear
that the work requires to feed this extra distance before it is
finished.
[Illustration: Fig. 1963.]
Suppose, however, that the cutter being dead true the cutting action
ceases on the centre line, and therefore exists through the distance A
only, and if we take a plain cutter of the same diameter as in Fig. 1963
we see that its period of feed only extends through the length B, and it
becomes apparent that to perform an equal amount of work the face cutter
is longer under feed, and therefore does less work in a given time than
the plain cutter, the difference equalling twice that between A and B in
the two figures, because it occurs at the beginning and at the end of
the cut.
There is, however, another question to be considered, inasmuch as that
the face cutter must necessarily be of larger diameter than the plain
one, because the work must necessarily pass beneath the washer (C, Fig.
1915), that is between the two cutters; hence the cutter is more
expensive to make.
[Illustration: Fig. 1964.]
We may in very short work overcome this objection by feeding the work,
as at K in Fig. 1964, the face L to be milled requiring to feed the
length of the teeth instead of the distance H in the figure. In the end
mill the amount of feed also is greater for a given length of finished
surface than it is in the plain cutter, as will be readily understood
from what has already been said with reference to face mills.
Face milling possesses the following points of advantage and
disadvantage, in addition to those already enumerated: If the work is
sprung by the pressure of the holding devices it is in a line with the
plane of motion of the teeth, hence the truth of the work is not
impaired. On the other hand, the teeth meet the scale or skin of the
work at each cut, whereas in a cylindrical cutter this only occurs when
the cutter first meets the work surface.
The strain of the cut has more tendency to lift the work table than in
the case of a cylindrical cutter. The work must be held by end pressure;
hence the chuck or holding jaws must be narrower than the work,
rendering necessary more work-holding devices. Since, however, both
sides of the work are simultaneously operated on, there is no liability
of error in parallelism from errors in the second chucking, as is the
case with plain cutters.
[Illustration: Fig. 1965.]
[Illustration: Fig. 1966.]
To cut [V]-shaped grooves in cylindrical work, when it is required that
one face or side of the groove shall be a radial line from the centre of
the work, two methods may be employed. First we may form the cutter, as
in Fig. 1965, the side B of the cutter being straight and the point of
the cutter being set over the centre of the work. The objection to this
is that the finished groove will have a projection or burr on the radial
side of the groove, as shown at D in the figure, entailing the extra
labor of filing or grinding, to remove it; furthermore, that face will
have fine scored marks upon it, as denoted by the arcs at C, these
scores showing very plainly if the cutter has any high teeth upon it,
and more especially in the case of cutting spirals, as will appear
presently. The reason of this is that the side B of the cutter being
straight or flat the whole of the teeth that are within the groove have
contact with the side C of the groove, that is to say, all the teeth
included in the angle E in the figure, because the teeth on the side A
tend, from the pressure of the cut to force the cutter over towards the
side C of the groove. The second method referred to, which is that
commonly adopted for cutting the flutes of tapes, reamers, milling
cutters, &c., is to form the cutter on the general principle illustrated
in Fig. 1966, and set it to one side of the centre of the work so that
one of its faces forms a radial line, as shown in the figure, the
distance to which it is set to one side depending upon the angle of its
cutting edge to the face of the cutter.
[Illustration: Fig. 1967.]
Fig. 1967 represents a common form of cutter of this class that is used
for cutting spiral grooves on milling cutters up to 3 inches in
diameter, which contain eight teeth per inch of diameter. The angle of
the teeth on B is 12° to the side face A of the cutter, and the angle of
the teeth at C is 40° to the face D.
The effect produced by making face B at an angle instead of leaving it
straight, or in other words, instead of cutting the teeth on the face A,
may be shown as follows:--
[Illustration: Fig. 1968.]
Suppose that in Fig. 1968 we have a sectional view taken through the
middle of the thickness of a cutter for a rectangular groove, the
circumferential surface being at a right angle to the side faces, and it
is evident that the teeth, at every point in their length across the
cutter, except at the extreme corner that meets the side faces as C,
will have contact with the seat of the groove while passing through the
angle F only (which is only one half of the angle E in Fig. 1965); or in
other words, each tooth will have contact with the seat of the groove as
soon as it passes the line G, which passes through the axis of the
cutter; whereas, when the teeth are parallel with the side of the
cutter, as was shown in Fig. 1965, the teeth continue to have contact
with the side walls of the groove after passing the line G.
By forming the cutter as in Fig. 1967, therefore, we confine the action
to the angle F, Fig. 1968, the teeth having contact with the walls of
the groove as soon as they pass the line G.
[Illustration: Fig. 1969.]
In cutting spiral grooves this is of increased importance, for the
following reasons: In Fig. 1969 we have a cutter shown in section, and
lying in a spiral groove. Now suppose a tooth to be in action at the
bottom of the groove, and therefore on the line G G, and during the time
that it moves from that line until it has moved above the level of the
top of the groove, the work will have performed some part of a
revolution in the direction of the arrow, and has therefore moved over
towards that side of the cutter; hence, if that side of the cutter had
teeth lying parallel, as shown at B in Fig. 1965, the walls of the
groove would be scored as at C in that figure, whereas by placing the
teeth at an angle to the side face, they recede from the walls after
passing line G, and therefore produce smoother work.
A cutter of this kind must, for cutting the teeth of cutters, be
accurately set to the work, and the depth of cut must be accurate in
order to cut the grooves so that one face shall stand on a radial line,
and the top of the teeth shall not be cut to a feather edge. If the
teeth were brought up to a sharp edge the width of the groove at the top
would be obtained with sufficient accuracy by dividing the circumference
of the work by the number of flutes or teeth the work is to contain, but
it is usual to enter the cutter sufficiently deep into the work to bring
the teeth tops up to not quite a sharp edge. The method of setting the
cutter is to mark on the end of the work a central line R, Fig. 1970,
and make the distance E in same figure equal to about one tenth the
diameter of the work.
[Illustration: Fig. 1970.]
[Illustration: Fig. 1971.]
Obviously the cutter is set on opposite sides of the work centre,
according to which side of the groove is to have the radial face. Thus
for example, in Fig. 1970, the cutter is set to the left of line R, the
radial face of the groove being on the left, while in Fig. 1971 the
cutter is set on the right of line R, because the radial face is on the
right hand side of it, the work consisting (in these examples) in
cutting up a right and a left-hand mill or cutter.
The acting cutter J may in both cases be used to cut either a right or a
left-hand flute, according to the direction in which the work W is
revolved, as it is fed beneath the cutter J.
[Illustration: Fig. 1972.]
In Fig. 1972 we have an example of cutting straight grooves or teeth,
with an angular cutter having one side straight, and it is seen that we
may use the operating or producing cutter in two ways: first, so that
the feed is horizontal, as at A, or vertical, as at B; the first
produces a right-hand, and the second a left-hand cutter, as is clearly
seen in the plan, or top view. The feeds must, however, be as denoted by
the respective arrows being carried upwards for B, so that the cutter
may run under the cut and avoid cutter breakage.
[Illustration: Fig. 1973.]
The number of grooves or flutes producible by an angular cutter depends
upon the depth of the groove and the width of land or tooth between the
grooves. Thus Fig. 1973 represents a cutter producing in one case four
and in the other eight flutes with the same form of cutter, the left
being for taps, and the right for reamers.
For cutting the teeth of cutters or mills above 3 inches in diameter,
the angles of the acting or producing cutter are changed from the 12°
and 40° shown in Fig. 1967, to 12° as before on one side, and a greater
number on the other; thus in the practice of one company it is changed
to 12° and 48°, the 12° giving the radial face as before, and the 48°
giving a stronger and less deep tooth, the deep tooth in the small
cutters being necessary to facilitate the grinding of the teeth to
sharpen them.
In cutting angular grooves in which the angle is greater on one side
than on the other of the groove, the direction of cutter revolution and
the end of the work at which the groove is started; or in other words,
the direction of the feed, is of importance, and it can be shown that
the feed should preferably be so arranged that the side of the groove
having the least angle to the side of the cutter should be the one to
move away from the cutter after passing the lowest point of cutter
revolution.
[Illustration: Fig. 1974.]
In Fig. 1974, for example, we have at R a cylinder with a right-hand
groove in it, whose side C, representing the face of a tooth, is
supposed to be a radial line from the cylinder axis, the side B
representing the back of a cutter tooth, being at an angle of 40°.
Now if the work revolves in the direction of arrow A, and the cut be
started at end G (as it must to cut a right-hand groove with the work
revolving as at A), then the side C of the groove will move over towards
and upon the side of the cutter for the reasons explained with reference
to Fig. 1969, and the teeth on this side being at the least angle to the
side of the cutter, do not clear the cut so well, the teeth doing some
cutting after passing their lowest point of revolution--or in other
words, after passing the line G in Fig. 1968. The effect of this is to
cause the cutter to drag, as it is termed, producing a less smooth
surface on that side (C) of the groove or tooth.
We may, however, for a right-hand groove revolve cylinder R, as denoted
by arrow E, and start the cut at end D. The result of this is that the
side C of the groove, as the roller revolves, moves away from the side
of the cutter, whose teeth therefore do no cutting after passing their
lowest point of revolution (G, Fig. 1968), and the dragging action is
therefore avoided, and the cut smoother on this which is the most
important side of the tooth, since it is the one possessing the cutting
edge. When "dragging" takes place the burr that was shown in Fig. 1965
at D, is formed, and must, as stated with reference to that figure, be
removed either by filing or grinding.
Obviously if the direction of cutter revolution and of feed is arranged
to cause side C to move away from the side of the cutter, then side B
will move over towards the other side of the cutter; but on account of
the cutter teeth on this side being at a greater angle to the side of
the cutter, they clear better, as was explained with reference to Fig.
1968, and the dragging effect caused by the revolving of the work is
therefore reduced.
[Illustration: Fig. 1975.]
We have now to examine the case of a left-hand groove, and in Fig. 1975
we have such a groove in a cylinder L. Let it be supposed that the
direction of its revolution is as denoted by arrow F, and if the cutter
is started at H (as it must be to cut a left-hand groove if the work
revolves as at F), then the side C moves over towards the cutter, and
the dragging or crowding action occurs on that side; whereas if the
direction of revolution is as at K, and the cutter starts at N and feeds
to H, then side B of the groove moves towards the cutter; hence face C
of the groove is cut the smoothest. Obviously then the direction of
cutter and work revolution and of feed, in cutting angular grooves in
which one angle of the cutter is at a greater degree of angle than the
other to the side of the cutter, should be so arranged that the work
revolves towards that side of the cutter on which its teeth have the
greater angle, whether the spiral be a right-hand or a left-hand one. In
cutting grooves not truly circular the same principle should be
observed.
[Illustration: Fig. 1976.]
In Fig. 1976, for example, it is better if the side B is the one that
moves towards the cutter, the direction of revolution being as denoted
by the arrow, whether the groove be a right-hand or left-hand
(supposing, of course, that the cutter starts from end E of the work).
Obviously, also, the greater the degree of spiral the more important
this is, because the work revolves faster in proportion to the rate of
feed, and therefore moves over towards the outer faster.
In cutting spirals it is necessary first to put on such change gears as
are required to revolve the work at the required speed for the given
spiral, and to then set the work at such an angle that the cutter will
be parallel to the groove it cuts, for if this latter is not the case
the groove will not be of the same shape as the cutter that produces it.
[Illustration: Fig. 1977.]
In Fig. 1977 we have a spiral so set, the centre of the cutter and of
the groove being in the line O O, and the work axis (which is also the
line in which the work feeds beneath the cutter) being on the line C C.
The degrees of angle between the centre of the cutter, or line O O, and
the axis of the work, or line C C, are the number of degrees it is
necessary to set the work over to bring the cutter and the groove
parallel, this number being shown to be 20 in the example.
[Illustration: Fig. 1978.]
To find this angle for any given case we have two elements: first, the
pitch of the spiral, or in other words, the length or distance in which
it makes one complete turn or revolution; and second, the circumference
of the work; for in a spiral of a given pitch the angle is greater in
proportion as the diameter is increased as may be seen in Fig. 1978, in
which the pitch of the spirals is that in Fig. 1977, while the angle is
obviously different.
To find the required angle for any given case we may adopt either of two
plans, of which the first is to divide the circumference of the work in
inches by the number of inches which the spiral takes to make one turn.
This gives us the tangent of angle of the spiral.
The second method of setting the work to cut a given spiral is to chuck
the work and put on the necessary change gears. The cutter is then set
to just touch the work and the machine is started, letting the work
traverse beneath the cutter just as though the work was set at the
required angle to the cutter:
When the cutter has arrived at the end of the work it will have marked
on it a line, as in Fig. 1979, this line representing the spiral it will
cut with those change gears, and all that remains to do is to swing the
work over so that this line is parallel with the face of the cutter, as
shown in Fig. 1980. If the diameter of the cutter is small we may
obviously secure greater accuracy by placing a straight-edge upon the
side of the cutter so as to have a greater length to sight by the eye in
bringing the line fair with the cutter. This being done it remains to
merely set the cutter in its required position with reference to the
work diameter.
If an error be made in setting the angle of the work to the cutter the
form of groove cut will not correspond to that of the cutter. This is
shown in Fig. 1981, in which the cutter being at an angle to the groove
the latter is wider than the cutter thickness, and it is obvious that by
this means different shapes of grooves may be produced by the same
cutter. In proportion, however, as the cutter is placed out of true the
cutting duty falls on the cutting edges on one side only of the cutter,
which is the leading side C in the figure, while the duty on the other
side, B, is correspondingly diminished.
[Illustration: Fig. 1979.]
[Illustration: Fig. 1980.]
[Illustration: Fig. 1981.]
The simplest method of holding work to be operated upon in the milling
machine is either between the centres or in the vice that is provided
with the machine. The principles involved in holding work in the vise so
as to keep it true and avoid springing it for milling machine work, are
the same as those already described with reference to shaping machine
vises.
In milling tapers the work, if held in centres, should be so held that
its axial line is in line with the axes of both centres, for the
following reasons:--
[Illustration: Fig. 1982.]
[Illustration: Fig. 1983.]
[Illustration: Fig. 1984.]
In Figs. 1982 and 1983 we have a piece of work in which the axes of the
centres and of the work are not in line, and it is clear that the horn
_d_ of the dog D will, in passing from the highest to the lowest point
in its revolution, move nearer to the axis of the work. Suppose, then,
that the driver E is moved a certain portion of a revolution with tail
_d_ at its highest point, and is then moved through the same portion of
a revolution with _d_ at its lowest point in its path of revolution, and
being at a greater distance or leverage when at the top than when at the
bottom it will revolve the work less. Or if the tail _d_ of the dog is
taper in thickness, then in moving endways in the driver E (as it does
when the work is revolved) it will revolve the work upon the centres.
Suppose, then, that the piece of work in the figures required to be
milled square in cross-section, and the sides would not be milled to a
right angle one to another. This is avoided by the construction of the
Brainard back centre, shown in Fig. 1984, in which T represents the
surface of the work table and H the back centre. The block B is fitted
within head H, and has two slots A A, through which the bolts S S pass,
these bolts securing B in its adjusted position in H. The centre slide C
operates in B; hence B, and therefore C, may be set in line with the
work axis.
[Illustration: Fig. 1985.]
For heads in which the back centre cannot thus be set in line, the form
of dog shown in Fig. 1985 (which is from _The American Machinist_) may
be employed to accommodate the movement of the tail or horns through the
driver. Its horn or tail B is made parallel so as to lie flat against
the face of the slot in the driver. The other end of tail B is pivoted
into a stud whose other end is cylindrical, and passes into a hub
provided in one jaw of the dog, the set-screw A being loosened to permit
this sliding motion. This locks the horn in the clamp and permits the
dog to adjust itself to accommodate the motion endwise that occurs when
it is revolved. The amount of this motion obviously depends upon the
degree of taper, it being obvious (referring to Fig. 1982) that horn _d_
would pass through the chuck, as denoted by the dotted lines, when at
the bottom of its path of revolution.
[Illustration: Fig. 1986.]
It is obvious that when the head or universal head of the machine is
elevated so that it stands vertical, it may have a chuck screwed on and
thus possess the capacity of the swiveled vise. It is preferable,
however, to have a separate swiveled chuck, such as in Fig. 1986 (from
_The American Machinist_), which will not stand so high up from the
machine bed, and will therefore be more solid and suitable for heavy
work.
[Illustration: Fig. 1987.]
Another very handy form of chuck for general work is the angle chuck
shown in Fig. 1987, which is from an article by John J. Grant, in _The
American Machinist_. The work-holding plate has [T]-grooves to chuck the
work on and is pivoted at one end, while at the other is a segment and
bolt to secure it in its adjusted angle. Two applications of the chuck
are shown in the figure.
[Illustration: Fig. 1988.]
[Illustration: Fig. 1989.]
Fig. 1988 represents a top, and Fig. 1989 an end view of a chuck to hold
rectangular bars that are to be cut into pieces by a gang of mills. A,
A, A, are grooves through the chuck jaws through which the cutters pass,
severing the bar through the dotted lines. Each piece of the bar is held
by a single screw on one side and by two screws on the other, which is
necessary in order to obtain equal pressure on all the screws and
prevent the pieces from moving when cut through, and by moving, gripping
the cutters and causing them to break.
In chucking the bar the two end screws D D must be the first to be set
up to just meet the bar: next the screws B C on the other side must be
set up, holding the bar firmly. The two screws between D D are then set
up to just bind the bar, and then the middle four on the other side are
screwed up firmly. By this method all the screws will hold firmly and
the pieces cannot move.
VERTICAL MILLING, DIE SINKING, OR ROUTING MACHINE.--Fig. 1990 represents
Warner & Swazey's die sinking machine. The cutter driving spindle is
here driven by belt direct, imparting a smooth motion. The knee is
adjustable for height on the vertical slideway on the face of the
column, which is provided with a stop adjustable to determine how high
the knee and work-holding devices can be raised, and, therefore, the
depth to which the cutter can enter the work, and a _former_ pin is
placed 6 inches behind the cutter to act as a stop against which a
pattern may be moved when work is to be copied from a _former_ or
pattern piece. The work-holding device consists of a compound rest and a
vise capable of being swiveled to any angle or of being revolved to feed
the work to the cutter, hence the work may be moved in any required
direction, in either a straight line, in a circle, or in any irregular
manner to suit the shape of the work.
PROFILING MACHINE.--The profiling machine is employed mainly to cut the
edges of work, and to sink recesses or grooves in the upper surface of
the same to correspond to a pattern. A provisional template of the form
of the work is fastened on the bed of the machine, and from this is cut
in the machine a thicker one termed the "former," which is then used to
copy the work from.
Fig. 1991 represents Pratt & Whitney's profiling machine. On the cross
slide are two separate sliding heads, each of which carries a live
spindle for the cutting tool, and beside it a spindle to receive a pin,
which by being kept against the pattern or _former_ causes the work to
be cut to the same shape as the former.
The work is fastened to the table, which is operated upon the raised
[V]s shown by the handle on the left, which operates a pinion geared to
a rack on the underneath side of the table. The handle on the right
operates the heads along the cross slide also by a rack and pinion
motion. The gearing and racks in both cases are double, so that by two
independent adjusting screws the wear of the teeth may be taken up and
lost motion prevented. By means of these two handles the work may be
moved about the cutter with a motion governed by the form or shape of
the _former_, of which the work is thus made a perfect pattern both in
size and shape. The tool used is a shank or end mill, such as was shown
in Fig. 1928. In some profiling machines the spindle carrying the guide
or former pin is stationary, in which case the provisional template is
put beneath it and the _former_ is cut by the live spindle, and for use
must be moved from the position in which it was cut and reset beneath
the _former_ spindle. This machine, however, is provided with
Parkhurst's improvement, in which the _former_ spindle is provided with
a gear-wheel, by which it may be revolved from the live spindle, hence
the provisional template may be set beneath the live spindle in which
the guide pin is then placed. The cutter is then placed in the _former_
spindle, and the _former_ cut to shape from the provisional template
while in the actual position it will occupy when used.
[Illustration: Fig. 1990.]
[Illustration: Fig. 1991.]
[Illustration: Fig. 1992.]
Fig. 1992 represents Brainard's machine for grinding milling cutters. It
consists of a threaded column A to which is fitted the knee B, which as
it fits the top of the threads on the column may be swung or revolved
about the column without being altered in its height upon the same
except by means of the threaded ring C. At D is a lever for clamping the
knee B to the column after adjustment; W represents the emery wheel
mounted on the end of the horizontal spindle having journal bearing at
the top of the column. The face of the knee B has a slideway _d_ for the
fixtures, &c., which hold the cutters to be ground, and at E is a lug
pierced to receive an arbor whereon to place cutters to be ground, the
lug being split and having a binding screw to lock the arbor firmly in
place. F is a slide for receiving the grinding attachments, one of which
is shown at K carrying a milling cutter in position to be ground on the
face.
Fig. 1993 shows the fixture employed to grind parallel cutters, S
representing a stand upon slide F (which corresponds to slide F in the
general view of the machine in Fig. 1992) in which is fixed the arbor H.
The cutter C is slid by hand along arbor H and beneath the emery wheel,
the method of guiding the cutter to the wheel being shown in Fig. 1994,
which represents a front view of the machine. At E is the lug (shown
also at E in the general view) which has a hole to receive a rod P, and
is split through at S, so that operating binding screw L locks rod P in
E. At R is a rod secured to the rod P, and G is a gauge capable of
swivelling in the end of R and of being secured in its adjusted
position. The end of this gauge is adjusted to touch the front face of
the tooth to be ground on the cutter C, which must be held close against
the end of the gauge in order to grind the cutting edge to a straight
line parallel to its axis.
A not uncommon error is to place the gauge G against the tooth in front
of that which is being ground, as in Fig. 1995, the gauge being against
tooth C while tooth B is the one being ground. In this case the truth of
the grinding depends upon the accuracy of the tooth spacing. Suppose,
for example, that teeth B and C are too widely spaced, tooth C being
too far ahead, and this error of spacing would cause tooth B to be too
near the centre of the emery wheel and its cutting edge to be ground too
low.
[Illustration: Fig. 1993.]
[Illustration: Fig. 1994.]
[Illustration: Fig. 1995.]
The object of feeding the cutter by hand along the arbor H is twofold:
first, the amount of cut must be very light and the feed very delicate,
for if the grinding proceeds too fast the cutting edge will be what is
termed burned, that is to say, enough heat will be generated to soften
the extreme cutting edge, which may be discovered by holding the front
face of the tooth to the light, when a fine blue tint will be found
along the cutting edge, showing that it has been softened in the
grinding, and this will cause it to dull very rapidly.
[Illustration: Fig. 1996.]
The second object is to insure parallelism in the cutter. Suppose, for
example, that the cutter C was fast upon arbor H and was fed to the
wheel by moving slide F, and if the arbor H stood at an angle, as in
Fig. 1996, to the slide upon which F moved, the cutter would be ground
taper, whereas if the cutter is fed along the arbor it will be ground
parallel whether the arbor is true or not with the slideway of F, the
only essential being that the arbor H be parallel and straight, which is
much easier to test and to maintain than it is in the slideway (D, Fig.
1992). Here it may be noted that oil should not be applied either to
arbor H or to the cutter bore or slideway D, as lubrication only
increases the wear of the parts, causing the fine emery particles that
inevitably fall upon them to cut more freely.
As thin cutters would not have sufficient length of bore to steady them
upon the arbor and insure parallelism, the cutter sleeve shown in Fig.
1997, which is from _The American Machinist_, is employed to hold them.
It is provided with a collar, is threaded at T for the nut N to hold the
cutter against collar C, and is bored to fit the cutter arbor H, which
corresponds to H in Fig. 1993.
This device also affords an excellent means of holding two or more thin
cutters requiring to be ground of exactly equal diameters.
It follows from what has been said that taper tools, such as taper
reamers, must be held with their upper face parallel to the line of
their motion in being fed to the wheel, as in Fig. 1998, in which line M
represents this line of motion, line N the axis of the reamer, and line
O the line on which the fixture that holds the reamer must move, O being
parallel to M.
Fig. 1999 represents Slate's fixture for this class of work. A is a
stand that bolts upon the slideway _d_ in Fig. 1992. Upon A is fixed a
rectangular bar B, upon which (a sliding fit) is the shoe C. Upon C fits
the piece D, which is pivoted to shoe C by the pin at E. At the other
end of D is a lug, against which abuts the end of screw G, which is
threaded through the end of C, so that by operating the screw G, D may
be set to any required angle upon C, and at F is a set-screw threaded
through D and abutting against C, so as to lock D in its adjusted
position. At P is a pointer for the graduations on C, which are marked
to correspond with the graduations upon the taper turning attachment of
a lathe.
[Illustration: Fig. 1997.]
[Illustration: Fig. 1998.]
[Illustration: Fig. 1999.]
The work is held between centres, the head H fitting to a slideway on
the top of D, and being secured in its adjusted position by the screw I.
The work should obviously be set so that its upper face lies horizontal,
and is fed to the wheel by moving shoe C by hand along bar B, the long
bearing keeping C steady, and the lightness of the moving parts making
the feeding more sensitive than it would be were it required to move bar
B.
The tooth being ground is held by hand against the gauge G in Fig. 1994,
as was described with reference to that figure, and the reamer,
therefore, in the case of having spiral grooves, revolves upon its
centre while being fed to the emery wheel.
For tapers that are beyond the capacity of this device, and also for
holding cutters to have their face teeth ground, the device shown in
Fig. 2000 is employed. Upon the slide F is fixed knee K (the
corresponding parts to which are seen in the general view, Fig. 1992),
whose disk face at R is graduated as shown. Piece S is pivoted by a pin
passing through the hub of K and having a nut T to secure it in its
adjusted position. S is bored to receive the cutter arbor H, and is
split through so that by means of the screw at V the arbor may be
gripped and locked in S. The stud W for holding the gauge G passes into
a bore in the bracket X, and is secured therein by the screw at Y, the
lugs through which Y passes being split through into the bore for W. As
shown in the figure, the arbor H is set for grinding the side teeth of
the cutter, but it is obvious that S being pivoted to K may be swung out
of the vertical and to any required angle, so as to bring the face of
the tooth that is to be ground horizontally beneath the emery wheel, as
shown in Fig. 2001, which represents an angular cutter in position. We
have now to consider the adjustment of the cutter to the emery wheel,
necessary in order that the cutting edges may be given the necessary
clearance.
First, then, suppose in Fig. 2002 that the line A A represents the line
of centres of the emery-wheel spindle and the cutter arbor, and if the
front face B of the tooth be set coincident with this line, as in the
figure, then the top of the tooth partaking of the curvature of the
wheel that grinds it would have its heel C the highest; hence the edge
at B could not cut.
If, however, the line A A in Fig. 2003, still representing the line of
centres, we so set the gauge (G, Fig. 1994) that the heel C of the
tooth comes up to line A A, then the curvature of the emery wheel would
give clearance to the heel C, and therefore a cutting edge to face B of
the tooth.
[Illustration: Fig. 2000.]
[Illustration: Fig. 2001.]
[Illustration: Fig. 2002.]
The amount of clearance that may be given in this way is limited by the
spacing of the teeth and the diameter of the emery wheel, as is seen
from Fig. 2004, it being obvious that when tooth A is being ground the
emery wheel must clear the rear tooth B or it will grind its edge off,
and it is obvious that the smaller the emery-wheel diameter the more the
tooth to be ground may be set in advance of the line of centres of the
wheel and spindle. It may be pointed out, however, that there are two
methods of adjusting the cutter to the wheel.
In Fig. 2005, for example, let A A represent the line of centres of the
cutter and the wheel, and line B the plane of the front face of the
tooth being ground; and in Fig. 2006 let line A represent a vertical
line from the axis of the wheel, and B a vertical line passing through
the axis of the cutter, the tooth edge C occupying the same position in
both figures. Now suppose we employ cutting edge C as a centre and swing
the cutter until its axis or centre moves along the arc D to the dot E,
and it is evident that during this motion the heel of the tooth will
have approached the axis of the emery wheel and that more clearance will
therefore have been given to the cutting edge C.
The actual curve of the top face, as C, Fig. 2007, of the tooth T will
remain the same in either case, but its position with relation to the
front face will be altered. As this curve is greater in proportion as
the diameter of the emery wheel is diminished, and as the curvature
weakens the cutting edge of the tooth, it is obviously desirable to
employ a wheel of as large a diameter as possible.
To eliminate this curvature it would appear that the position of the
emery wheel might be reversed, as in Fig. 2008, but as the emery wheel
would wear only where in contact with the tooth, it would gradually
assume the shape in Fig. 2009, there being a shoulder at S that would
destroy the cutting edge of the tooth.
This may to a great extent be remedied by presenting the cutter
diagonally to the wheel, as in Fig. 2010, employing a wheel so thin that
the whole of its face will cross the tooth top during a revolution. Or
if the side faces of the wheel be recessed, leaving only a narrow
annular grinding ring at the circumference, the wheel might be mounted
as in Fig. 2011, thus making the top of the tooth quite flat. It may be
observed, however, that the usual plan is to revolve the wheel at a
right angle to the work axis, as was shown in Fig. 1994.
[Illustration: Fig. 2003.]
[Illustration: Fig. 2004.]
[Illustration: Fig. 2005.]
[Illustration: Fig. 2006.]
[Illustration: Fig. 2007.]
[Illustration: Fig. 2008.]
[Illustration: Fig. 2009.]
[Illustration: Fig. 2010.]
[Illustration: Fig. 2011.]
In grinding cutters having their teeth a right-hand spiral, care must be
taken that in grinding one tooth the emery wheel does not touch the
cutting edge of the next tooth.
Thus in Fig. 2013 it is seen that the corner C of the emery wheel is
closer than corner D, and being at the back of the wheel and out of
sight it is apt to touch at C unless a thin emery wheel be used.
In a left-hand spiral, Fig. 2012, it is the corner D that is apt to
touch the next tooth, the liability obviously being greatest in cutters
of large diameter.
The emery wheel should be of a grade of not less than 60 or more than
70. If it is too coarse it leaves a rough edge, which may, however, be
smoothed with an oilstone slip. If the wheel is too fine it is apt to
_burn_ the cutter, or in other words, to soften the cutting edge, which
may be known by a fine blue burr that may be seen on the front face of
the tooth, the metal along this line being softened.
The diameter of the wheel may be larger for small cutters than for large
ones, since the teeth of small cutters clear the wheel better. The
larger the wheel the less the curvature on the top of the tooth.
[Illustration: Fig. 2012.]
[Illustration: Fig. 2013.]
For general work a diameter of 2-1/2 inches will serve well, the
thickness being about 5/16 inch or 3/8 inch. The speed of a wheel of
this diameter varies in practice from 3,000 to 4,500 revolutions per
minute, but either too fast or too slow a speed will cause the wheel to
burn the cutter, and the same thing will occur if the cutter is fed too
fast to the wheel, or if too deep a cut is taken. The finishing cut
should obviously be very small in amount, especially in cutters of large
diameter, for otherwise the wear in the diameter of the wheel will
sensibly affect the teeth height, those last ground being the highest.
CHAPTER XXIII.--EMERY WHEELS AND GRINDING MACHINERY.
EMERY WHEELS AND GRINDING.--Emery grinding operations may be divided
into four classes as follow:--
1st. Tool or cutter grinding, in which the emery wheel is used to
sharpen tools which, from their shape, were formerly softened and
sharpened by the file, already largely treated in the preceding chapter.
2nd. Cylindrical grinding, in which both the work and the emery wheel
are revolved, as has been explained with reference to grinding-lathes.
3rd. Flat surface grinding, in which the emery wheel takes the place of
the ordinary steel cutting tool; and
4th. Surface grinding, in which the object is to remove metal or to
smoothen surfaces.
The distinctive feature of the various makes of solid emery wheels lies
in the material used to cement the emery together, and much thought and
experiment are now directed to the end of discovering some cementing
substance which will completely meet all the requisite qualifications.
Such a material must bind the emery together with sufficient strength to
withstand the centrifugal force due to the high speeds at which these
wheels must be run to work economically; and it must neither soften by
heat nor become brittle by cold. It must not be so hard as to project
above the surface of the wheel; or in other words, it should wear away
about as fast as does the emery. It must be capable of being mixed
uniformly throughout the emery, so that the wheel may be uniform in
strength, texture, and density. It must be of a nature that will not
spread over the surface of the emery, or combine with the cuttings and
form a glaze on the wheel, which will prevent it from cutting. This
glazing is, in fact, one of the most serious difficulties to be
encountered in the use of emery wheels for grinding purposes, while it
is a requisite for polishing uses, as will be explained farther on. Many
of the experiments to prevent glazing have been in the direction of
discovering a cement which would wear away under about the same amount
of duty as is necessary to wear away the cutting angles of the grains of
emery, thus allowing the emery to become detached from the wheel, rather
than to remain upon it in a glazed condition.
With the same grade of emery the wheel will cut more freely and glaze
less in proportion as the cementing material leaves the wheel softer,
but the softer the wheel the more rapidly it will wear away; indeed it
is the dislodgement of the emery points as soon as they have become
dulled that produces freedom from glazing. It may be remarked, however,
that the nature of the material operated upon has a good deal to do with
the glazing; thus wrought iron will glaze a wheel more quickly than
hardened steel, and brass more quickly than wrought iron, while on the
other hand soft cast iron has less tendency than either of them to
glaze. Glazing occurs more readily in all cases upon fine than upon
coarse wheels. Glazing is more apt to occur as the work is pressed more
firmly to the wheel, and with broad and flat surfaces rather than with
cylindrical ones. An excellent material for removing the glaze from an
emery wheel is a piece of ordinary pumice stone.
The principal cements used in the manufacture of emery wheels are as
follows, each representing the cement for one make of wheel:--
1. Hard rubber. 2. Chemical charcoal (leather cut down by acid and used
to prevent shrinkage), and glue. 3. Oxychloride of zinc. 4. Shellac. 5.
Linseed oil and litharge. 6. Silicate of soda and chloride of calcium.
7. Celluloid. 8. Oxychloride of magnesium. 9. Infusoria. 10. Ordinary
glue.
The vitrified emery wheel is made with a cement which contracts slightly
while cooling, leaving small pores or cells through which water,
introduced at the centre, is thrown (by centrifugal force) to the
surface. This causes, when the wheel is rotating, a constant flow of
water from the centre to the surface, carrying off the cuttings and the
detached emery.
In order that an emery wheel shall run true with its bore it must fit
the driving spindle, and in order that it may do this closely the wheel
bore is sometimes filled with lead, the latter being bored out to fit
the spindle. If the bore of the emery wheel itself were made a tight fit
to the spindle it would abrade the spindle in being put on, and the
pressure of the fit if any would tend to split the wheel. A common
method of securing emery wheels to their spindles is to fill the bore of
the wheel with lead, and bore it out to fit the spindle of the emery
grinding machine. The flanges between which the wheel is held are
recessed so as to grip the wheel at and near their perimeters only.
Between the flange and the wheel a thin disk of sheet-rubber is
sometimes used to afford a good bedding for the flange.
The forms of the perimeters of emery wheels are conformed to suit the
form of the work to be ground, and it is found that from the great
strength of the emery wheel it can be used to a degree of thinness that
cannot be approached in any kind of grinding stone. For instance,
vulcanite emery wheels 18 inches in diameter and having 3/16 inch
thickness, or face as it is commonly termed, are not unfrequently used
at a speed of some 5,000 feet of circumferential feet per minute,
whereas it would be altogether impracticable to use a grindstone of such
size and shape, because the side pressure would break it, no matter at
what speed it were run. Indeed, in the superior strength of the emery
wheels of the smaller sizes lies their main advantage, because they can
be made to suit narrow curvatures, sweeps, recesses, &c., and run at any
requisite speed under 5,000 feet per minute, and with considerable
pressure upon either their circumferential or radial faces.
GRADES OF COARSENESS OR FINENESS OF EMERY WHEELS.--Emery is found in the
form of rock, and is crushed into the various grades of fineness. The
crushing is done either between rollers or by means of stamps, the
latter, however, leaves the corners of the grains the sharpest, and
hence the best for cutting, though not for polishing purposes. The
grades of emery are determined by passing the crushed rock through
sieves or wire cloths having from eight to ninety wires to the inch;
thus, emery that will pass through a sieve of sixty wires to the inch is
called No. 60 grade.
The finest grade obtained from the manufactory is that which floats in
the atmosphere of the stamping room, and is deposited on the beams and
shelves, from where it is occasionally collected. Washed emery is used
by plate-glass workers, opticians, and others that require a greater
degree of fineness than can be obtained by the sieve.
The numbers representing the grades of emery run from 8 to 120, and the
degree of smoothness of surface they leave may be compared to that left
by files as follows:
8 and 10 represent the cut of a wood rasp
16 " 20 " " coarse rough file
24 " 30 " " ordinary rough file
36 " 40 " " bastard "
46 " 60 " " second cut "
70 " 80 " " smooth "
90 " 100 " " superfine "
120, F & FF " " dead smooth "
The F and FF emery is flour emery which has been washed to purify it.
The following are the kinds of wheel suitable for the respective
purposes named:--
Kind of work. Kind of wheel.
For rough grinding, such as on the edges of iron }
or steel plates, for removing the protuberances on } Coarse grain and
castings or on narrow surfaces where rough grinding } hard texture.
is sufficient. }
For narrow surfaces, such as moulding knives, lathe } Medium grain and
tools, saw gumming, &c. } hard texture.
For free cutting without gumming on broad surfaces } Medium grain and
on iron, steel, or brass. } soft texture.
For grinding fine tools, such as milling machine }
cutters, or for work in which the duty is not great } Fine grain and
while the wheel requires to keep its shape and keep } soft texture.
true. }
For smooth grinding on soft metals, as cast iron } Fine grain and
and brass. } hard texture.
[Illustration: Fig. 2014.]
When the work is presented to the wheel unguided, the wheel wears out of
true, because the work can follow the wheel, hence it becomes necessary
to true the wheel occasionally. This can be done by a tool such as in
Fig. 2014, which is applied by hand on the hand rest, and corresponds to
the tool shown in Fig. 2061 for grindstones, or by the use of a diamond
set in a tool to be held by hand or in a slide rest. The diamond
produces the most true and smooth work, but the cut of the wheel is at
first impaired by the action of the diamond, which is not the case with
the tool in Fig. 2014.
Corundum is a mineral similar to emery, and corundum wheels are made and
used in the same manner as emery wheels. Their cutting qualifications
are, however, superior to those of the emery wheel, both cutting more
freely and being more durable with less liability to glaze.
SPEEDS FOR EMERY WHEELS.--The speed at which an emery wheel may be run
without danger of bursting varies according to the thickness or breadth
of face of the wheel, as well as according to the quality of the
cementing material and excellence of manufacture. Hence, although a
majority of manufacturers recommend a speed of about 5,000
circumferential feet per minute, that speed may be largely exceeded in
some cases, while it would be positively dangerous in others. It is, in
fact, impracticable in the operations of the workshop to maintain a
stated circumferential speed, because that would entail a constant
increase of revolutions to compensate for the wear in the diameter of
the wheel. Suppose, for example, that a wheel when new is a foot in
diameter: a speed of about 1,600 revolutions per minute would equal
about 5,000 circumferential feet; whereas, when worn down to 2 inches in
diameter, the revolutions would require, to maintain the same
circumferential speed, to be about 9,500 per minute, entailing so many
changes of pulleys and counter-shafting as to be impracticable. In
practice, therefore, a uniform circumferential speed does not exist, the
usual plan adopted being to run the large-sized wheels, when new, at
about the speed recommended by the manufacturer of the kind of wheel
used, and to make such changes in the speed of the wheel during wear as
can be accomplished by changing the belt upon a three-stepped cone
pulley, and perhaps one, or at most two, changes of pulley upon the
counter-shaft. It is sometimes practicable to use wheels of a certain
diameter upon machines speeded to suit that diameter, and to transfer
them to faster speeded machines as they diminish in diameter. Even by
this plan, however, only an approximation to a uniform speed can in most
cases be obtained, because as a rule certain machines are adapted to
certain work, and the breadth of face and form of the edge of the emery
wheel are very often made to suit that particular work. Furthermore, a
new wheel is generally purchased of such a size, form, and grade of
emery as are demanded by the work it is intended at first to perform.
Neither is it, as a rule, practicable to transfer the work with the
diametrically reduced wheel to the lighter and faster-speeded grinding
machine. So that, while it is desirable to run all emery wheels as fast
as their composition will with safety admit, yet there are practical
objections to running small wheels at a rate of speed sufficient to make
their circumferential velocities equal to those of large wheels. The
speeds recommended for the various kinds of wheels now in use vary from
about 2,700 to 5,600 circumferential feet per minute; but the speeds
obtaining in workshops average between 2,000 and 4,000 feet for wheels 3
inches and less in diameter, and from about 3,000 to 5,600 feet for
wheels above 12 inches in diameter. Wheels above 15 inches in diameter,
and of ample breadth of face, are not unfrequently run at much greater
velocities.
On account of the high velocity at which emery wheels operate, it is
necessary that they be very accurately balanced, otherwise the unequal
centrifugal motion causes them to vibrate very rapidly, every vibration
leaving its mark upon the work.
The method of balancing adopted by one firm is as follows: The arbors
are of cast iron, and are cast standing vertical so as to induce equal
density in the metal, it having been found that if the arbors were cast
horizontally the lower part of the metal would from the weight of the
molten metal be more dense than that at the top of the casting. In
casting the arbors upright, the difference in the density of metal
simply causes one end of the arbor to be more dense than the other, and
the difference being at a right angle to the plane of revolution has no
tendency to cause vibration. The driving pulleys are cast horizontal to
obtain equal density, and after being turned are carefully balanced. The
driving pulleys are held to the arbors by being bored a driving fit, and
are driven on so as to avoid the use of keys, which would throw the
wheels out of balance.
The centrepiece and flange to hold the wheel to the arbor are turned and
balanced. The nut to hold the wheel is a round one, which is easier to
balance than a hexagon nut. After the centrepiece is put on the arbor,
the whole is tried for balance, and corrected if necessary. The pulley
is then put on and the whole is again balanced, and so on, the arbor
being balanced after each piece is added, so that while each piece is
balanced of itself the whole is balanced after the addition of each
separate piece.
[Illustration: Fig. 2015.]
[Illustration: Fig. 2016.]
The emery or corundum wheel is then put on the arbor and tried for being
in balance. The method of correcting the balance of the wheel is as
follows: The arbor with the wheel on is placed in the lathe, the wheel
turned true with a diamond tool (the wheel revolving at a comparatively
slow speed). The arbor is then revolved at its proper speed (5,000
circumferential feet per minute), and a point applied to just meet the
circumference will touch the wheel where it is heaviest, leaving a line
as shown in Fig. 2015 at A. The centre of the arbor is then moved over
towards this line as shown in Fig. 2016, in which W is the wheel, the
location of the line A (marked as above) being as denoted by the arc A,
and C represents the arbor whose centre is moved over towards the arc A.
When therefore the arbor is again put in the lathe, it will run out of
true by reason of the centre at one end having been altered. A cut is
taken down that radial face of the wheel which faces the end of the
arbor that has had its centre moved so that the wheel is turned thinner
where the mark (A, Fig. 2016) is. The amount of cut to be taken off is a
matter of judgment and trial, since it must be just sufficient to
compensate for the greater density of the wheel on that side. This
greater density, be it noted, occurs from the difficulty in mixing the
corundum or other abrasive grains with the cementing material with
entire uniformity throughout the mass.
By this method of balancing, the wheel will remain in true balance
notwithstanding its wear, because the balancing proceeds equally from
the perimeter towards the centre of the wheel.
[Illustration: Fig. 2017.]
EMERY GRINDING MACHINES. (For grinding-lathes and roll grinding, see
article on Lathes.)--Fig. 2017 represents Brown & Sharpe's grinding
machine. The bed, the table, and the cross-feed motion of this machine
closely resemble those of the planing machine, but its work is far more
smoothly and accurately done than can be performed in a planing machine.
The table traverses to and fro, accurately guided in ways, and the
revolving emery wheel takes the place of the ordinary cutting tool,
being carried in a sliding head upon a cross slide or cross bar. The
drum for driving the emery wheel is at the back of the machine, as shown
in the cut.
[Illustration: Fig. 2018.]
The vertical feed motion for adjusting the depth of cut of the emery
wheel is capable of very minute adjustment, thus avoiding a difficulty
commonly experienced in iron planing machines on account of the
coarseness of feed-screw pitch, which coarseness is necessary to insure
their durability. The means by which this capability of minute
adjustment is effected is shown in Fig. 2018, in which D is the cross
head of the machine and C the sliding head having the arm C´, which
provides at B a pivot for the wheel-carrying arm A. F is a stud fast in
C and carrying E, which forms the nut for the feed screw. Outside this
nut is the spiral spring S, whose force steadies the upper end of A.
Now suppose the feed wheel G be operated a full rotation, and the
motion of that end of A will be that due to the pitch of the feed screw,
but the motion at the centre H of the emery wheel will be the pitch of
the screw divided by the difference between the length from the centre
of H to the centre of the feed screw, and that from the centre of H to
the centre of B. But even this diminished motion at H is still further
reduced, so far as the depth of cut put on is concerned, because the
motion of H is not directly vertical but an arc P, of which B is the
centre.
The standards carrying the cross slide are segments of a circle struck
from the centre of the driving drum, which is necessary to enable the
raising and lowering of the cross slide, and maintain a uniform tension
on the belt driving the emery wheel without employing an idler wheel or
belt tightener.
[Illustration: Fig. 2019.]
Fig. 2019 represents Wm. Sellers & Co.'s drill-grinding machine, in
which the drill is held in a chuck operated by the hand wheel A. The
jaws of the chuck grip the drill at the outer corners of the cutting
edge as shown in Fig. 2020, and so as to grind the point of the drill
central to those corners. In order to give to the cutting edges a
suitable degree of clearance in their lengths, and to allow for the
difference in thickness at their points between large and small drills,
the following construction is employed.
[Illustration: Fig. 2020.]
Fig. 2020 represents the jaws J J holding on the left a small, and on
the right a large drill. The line of motion of the right-hand jaw in
opening and closing to grip the drill is along the line _r_, while that
of the left-hand is along the line _p_ _p_, the centre upon which the
chuck is revolved to grind the drill being denoted by the small circle
at S. _x´_ represents the centre line of the large drill when held in
the chuck, and it is seen that the action of the jaws in closing upon
small drills is to lift the drill point closer to the centre S upon
which the chuck revolves (the cutting edge being ground to be on the
line _y´_ _y´_). The reason for this peculiar and simple but exceedingly
ingenious construction is, as before remarked, to maintain the cutting
edge in its proper relation to the thickness of the drill point (which
thickness varies in different diameters of drills), and to maintain a
proper degree of clearance at every point along the length of the
cutting edge. In other drill grinding machines the drill when rotated to
grind the clearance is moved on the axis A A in Fig. 2022 as a centre of
motion, and as this line is parallel to the face of the emery wheel it
follows that if the drill were given a full revolution its circumference
would be ground to a cylinder as shown in Fig. 2021 by the dotted lines.
In this machine the drill is rocked on the line B, Fig. 2023, as a
centre of motion, this line corresponding to the axis of the shaft of
lever F in Fig. 2019 upon which the chuck swings, and to the line B in
Fig. 2024. As a result the surface is ground to the form of a cone as
denoted by the dotted lines in Fig. 2024. The results of the two systems
are shown in Figs. 2025 and 2026, which represent the conical holes made
by a drill.
[Illustration: Fig. 2021.]
[Illustration: Fig. 2022.]
[Illustration: Fig. 2023.]
[Illustration: Fig. 2024.]
In Fig. 2025 a cylinder R is shown lying in a conical recess, and end
views of the cylinder are shown at V and W. Now suppose the line of
contact of the roll or cylinder upon the recess represents the cutting
edge of the drill, and that we consider the clearance at the outer end,
and at that part that in revolving would describe the circle Q, and on
referring to circle V and the outer circle of the recess, and also to
circles W and Q, it is seen that there is more clearance for V than
there is for W, and that the clearance of the latter would be still less
if Q were of smaller diameter, and it follows that the clearance is less
in proportion as the point of the drill is approached. In determining
the amount of clearance, therefore, we are compelled to make it
sufficient for the point of the drill, and this under this system of
grinding is excessive for the outer diameter of the drill, causing it to
dull quickly, it being borne in mind that as the outer corner of the
cutting edge of a drill describes the largest circle of any point of the
cutting edge it obviously performs the most cutting duty in removing
metal, and furthermore revolves at the highest rate of cutting speed,
both of which cause it to dull the most rapidly. In Fig. 2026 we have a
cone R lying in the coned recess, an end view of the cone being shown at
V and W, and if we again consider the line of contact of the cone on the
recess to represent the cutting edge and the circumferential surface of
the cone as the end surface of the drill, we observe in the end views V
and W that the clearance is equal for the two positions, or by varying
the degree of taper of the cone we may regulate the amount of clearance
at will. It is found preferable, however, to give more clearance as the
point of the drill is approached so as to increase the cutting capacity;
hence, in this case, the outer corner of the drill has the least
clearance, which greatly increases its endurance for the reasons already
mentioned, and which were further pointed out in the remarks upon
drilling in the lathe. There remains, however, an additional advantage
in this method of grinding which may be pointed out, inasmuch as that
the clearance produced by the method shown in Fig. 2019, while capable
of being governed from end to end of the cutting edge, yet increases as
the heel of the _land_ is approached, making the central cutting edge
(C, Fig. 2028) more curved in its length so that it approaches the form
of cutting edge of the fiddle drill and this enhances its cutting
capability.
[Illustration: Fig. 2025.]
Referring again to the general view of the machine in Fig. 2019, the
chuck is supported or carried by the shaft having the ball lever F,
which is clearly seen in the rear view, Fig. 2027, and the rod carrying
the sleeve B (which holds the centre for supporting the shank end of the
drill) is secured to the back of the chuck, as seen in the same figure.
When, therefore, lever F is moved over, the drill is moved through an
arc of a circle of which the axis of the shaft of F is the centre, and
this it is that gives clearance to the cutting edge of the drill.
The drill being chucked, the emery wheel is brought up to it by means of
the hand wheel E, which moves the frame C laterally, the grinding being
done by the side face of the emery wheel. On the same shaft as E is a
lever which may be used in connection with the stop or pin (against
which it is shown lying) to enable an adjustment of the depth of cut
taken by the wheel separately when grinding each lip, and yet to permit
both cutting edges of the drill to be gauged to the same length.
Suppose, for example, that the point of a drill has been broken so that
it requires several cuts or traverses of the emery wheel to bring it up
to a point again; then when this has been done on one cutting edge the
lever may be set to the stop, so that when the grinding of the second
cutting edge has proceeded until the lever meets the stop both edges
will be known to be ground of the same length, and will, therefore,
perform equal cutting duty when at work.
The depth of cut being adjusted, the lever D is operated to pass the
side face of the emery wheel back and forth along the cutting edge of
the drill, this lever rocking the frame C on which the emery wheel is
mounted back and forth in a line parallel to the cutting edge of the
drill. Different angles of one cutting edge of the drill to the other
are obtained by swivelling the frame carrying the shaft of lever F. The
emery wheel is cased in except at a small opening where it operates upon
the drill, and may, therefore, be liberally supplied with water without
the latter splashing over. Water is continuously supplied to the emery
wheel by an endless belt pump, which also delivers water on the end of
the drill, enabling heavy grinding cuts to be taken without danger of
softening the drill at the cutting edge, which is otherwise apt to
occur. The following is the method of operating the machine: Open the
jaws of the chuck by means of the hand wheel A, insert the drill from
the back of the chuck towards the face of the stone, letting the end of
the drill rest on the lower jaw, with the cutting edge just touching the
end stop; close the jaws temporarily, while the back centre B is run up
and clamped; then release the jaws, hold the drill back against the back
centre B with the left hand, at the same time rotating hard against the
two side stops on the jaws; then tightly closing the jaws, clamp the
drill by means of the hand wheel A, using the right hand for this
purpose. Throw ball-handle F part way back, and by means of hand wheel E
feed up the stone until it just touches the drill. Bring ball-handle F
forward and give additional feed; pass the stone over the face of the
drill, back and forth, by lever D, moving ball-handle F back a little
between each two cuts. This slices off the stock to be removed; then
when entirely over the face of the lip being ground, hold lever D
stationary, and rotate the drill against the stone by means of
ball-handle F. By this means a heavy slicing cut can be taken and a
final smooth finish obtained without any risk of drawing the temper of
the drill.
When one lip has been thus formed, slack up the jaws of the chuck, turn
the drill half around, pressing its lips as before against the side
stops on jaws, and at the same time be sure to hold the drill firmly
back against the back centre B (pay no attention to the end stop, which
is only used in locating the drill endways in the first setting),
tighten chuck, and grind the second lip without any readjustment of the
stone. The lips will then be of equal length. During all these
manipulations the stop that is arranged in connection with hand wheel E
can be slack, and may rest against the pin in the bed made to receive
it.
[Illustration: Fig. 2026.]
Fig. 2027 represents a rear view of the machine, at which there is an
attachment for thinning the point of the drill, which is advantageous
for the following reasons. In Fig. 2028 we have a side and an end view
of a twist drill, and it can be shown that the angular piece of cutting
edge C that connects the two edges A and B cannot be given sufficient
angle to make it efficient as a cutting edge without giving clearance
and angle excessive to the edges A and B.
In Fig. 2029 we may consider the angle of the cutting edge at the corner
H and at the points F and G. First, then, it is obvious that the front
face for the point H is represented by the line H _h_, that for F by
line F _f_, and that for G by G _g_, and it appears that on account of
the spiral of the flute the front face has less angle to the drill axis
as the point of the drill is approached.
[Illustration: Fig. 2027.]
Considering the end of the drill, therefore, as a cutting wedge, and
considering the cutting edge at the two points C and E, in Fig. 2030,
the end face being at the same angle, we see that the point C has the
angle A and point E the angle B; at the drill point there will be still
less cutting angle, and it has, therefore, the least cutting capacity.
To remedy this the attachment shown in the figure is employed,
consisting of a frame or head carrying a thin emery wheel, and capable
of adjustment to any angle to suit the degree of spiral of the drill
flute.
[Illustration: Fig. 2028.]
By means of this emery wheel a groove is cut in the flute at the point
of the drill, as shown in Fig. 2031, at A and B, thus reducing the
length of C, and therefore increasing the cutting capacity and
correspondingly facilitating the feed of the drill. It is found, indeed,
that by this means the drill will perform 15 per cent. more duty.
[Illustration: Fig. 2029.]
[Illustration: Fig. 2030.]
[Illustration: Fig. 2031.]
It is obvious, however, that as the thickness of drills at the point
increases in proportion to the diameter of the drill, this improvement
is of greater advantage with large than with small drills. The reason
for augmenting the thickness at the centre with the drill diameter is
that the pressure of the cut acts to unwind the spiral of the drill, and
if the drill were sufficiently weak at its axis this unwinding would
occur, sensibly enlarging the diameter of hole drilled, more especially
when the drill became partly dulled and the resistance of the cut
increased. By means of the small grooves A and B, however, the point is
thinned while the strength of the drill is left unimpaired.
[Illustration: _VOL. II._ =EMERY GRINDING MACHINERY.= _PLATE IV._
Fig. 2032.
Fig. 2033.]
Fig. 2032 represents Brown & Sharpe's surfacing grinder, designed to
produce true and smooth surfaces by grinding instead of by filing. In
truing surfaces with a file a great part of the operator's time is
occupied in testing the work for parallelism, and applying it to the
surface plate to test its flatness or truth, whereas in a machine of
this kind both the parallelism and the truth of the work are effected by
the accurate guiding of the machine table in its guideways. Furthermore,
a high order of skill is essential to the production of work by filing
that shall equal for parallelism and truth work that is much more easily
operated upon in the machine. The machine is provided with two feed
motions, the first of which is in a line parallel with the axis of the
emery wheel driving spindle, and is communicated (by means of the small
hand wheel on the right) to the lower table, which moves in [V]-guides
provided upon the base plate of the machine. Upon this lower, and what
may be termed cross-feed table slides, in suitable guideways, the
work-holding or upper table, which is operated (by the large hand wheel)
to traverse the work back and forth beneath the grinding wheel. Both
these feed motions are operated by hand, automatic feed motions being
unnecessary for work of the size intended to be operated upon in this
machine. The grinding wheel spindle is carried in a bearing carried in a
vertical slide, and is fed to its depth of cut by means of the vertical
feed screw and hand wheel shown. The spindle passes through the bearing
and carries a pulley at the back of the machine, which pulley is driven
by a belt passing over idler pulleys at the back of the machine, by
means of which the tension of the driving belt may be regulated.
Fig. 2033 represents The Tanite Co.'s machine for surface grinding such
work as locomotive guide bars. The emery wheel N is mounted beneath a
table T, whose upper surface is planed true, and which has two
cylindrical stems C D fitting into the bored guides E. The stems are
threaded at their lower ends to receive a screw, on the lower end of
which is a bevel-gear F meshing into a similar gear G on the shaft
actuated by the hand wheel W, hence by operating W the height of the
table face may be adjusted to suit the diameter of the wheel.
The surface to be ground is laid upon the face of the table, and the
operator moves it by hand, slowly passing it over the emery wheel, which
projects slightly through the opening shown through the centre of the
table. The operator stands at the end of the machine so as to be within
reach of the wheel, and the direction of rotation is towards him, so
that the work requires to be pushed to the cut and is not liable to be
pulled too quickly across the table by the emery wheel.
[Illustration: Fig. 2034.]
Fig. 2034 represents an emery grinding machine for grinding the bores of
railroad car axle-boxes. The circumference of the emery wheel is dressed
to the curvature of the box bore by a diamond tool A which swings on a
centre in its frame, and can be adjusted to any arc. Once set, it can
only turn the prescribed arc with accuracy. In order to avoid the
necessity of the foreman having to set the tool, a gauge is also
furnished. This consists of a spindle adjustable with a nut in such a
way that its two points rest in the centres on which the diamond tool
revolves. It is only necessary for a disk B turned accurately to the
diameter of the bearing, to be prepared, and this the apprentice can
place on the spindle, adjust the latter, and screw down the diamond tool
until it touches the periphery of the disk. A nut is then fastened on
the diamond tool, and the frame is lifted on the ways beneath the wheel,
when the moving of the handle turns the face of the wheel to the exact
circle desired.
To adjust the brass in the chuck C, it is first set on the axle D. The
chuck is then placed on frame E, in such a way that the [V]s fit. Handle
F then moves a cam that clamps the brass between the jaws G, one set of
which swings on a pivot at H. The brass is thus adjusted in such a
manner that, despite the imperfections in moulding, it is ground
accurately with the least removal of metal. The chuck C fits into planed
guides on the table I, and is thus brought in exact line with the motion
of the wheel. The crank J serves to move the table to and fro on the
rods K, and the table also rises and falls on planed ways, being pressed
up by springs. The hand wheel gives vertical adjustment to the whole bed
by means of a chain beneath it. There is a pulley by which a suction
fan, to remove dust, &c., may be driven. The machine is capable of
fitting from 150 to 500 car brasses per day.
[Illustration: Fig. 2035.]
Fig. 2035 represents an emery planing machine. The emery wheel, which
takes the place of the cutting tool of an ordinary shaping machine, is
upon a spindle driven by the pulley A upon the spindle B, which is
traversed endways by means of the connecting rod which is actuated by a
crank E driven by the cone pulley C. The work-holding table G is
traversed by the handle K or automatically through wheel H, which
through suitable gearing drives the spindle I. The blower or fan is to
draw off the cuttings and emery. It is obvious that any of the usual
forms of work-holding devices may be employed.
[Illustration: Fig. 2036.]
Fig. 2036 represents an ordinary form of emery grinding machine for
general purposes. A represents the frame affording journal bearing for
the driving spindle driven by the cone pulley P, having the fast flanges
_f_ and collars C, which are screwed up to hold the emery wheel by the
nut N, the direction of spindle rotation being denoted by the arrows.
The thread at the end K of the spindle must be a right-hand one, and
that at the other end L must be a left-hand, so that the resistance
against the nut shall in both cases be in a direction to screw the nuts
up and cause them to bind or grip the wheels more firmly, and not
unscrew and release the wheels. Upon the frame A are the lugs D to carry
the hand rests R and S, which are adjustable, and are secured in their
adjusted position by the handle nuts E. The rest S is of the same form
and construction as a lathe hand rest, while that at R is angular, to
support the tool while applying it to the side as well as to the
circumference of the wheel.
Fig. 2037 represents a machine for grinding the knives for wood-planing
machines, and having a hand feed only. It consists of an emery wheel
mounted upon a spindle and with a slide rest in front of it. Mounted on
the slide rest is a frame for holding the knife, and a set-screw for
adjusting the angle of the knife to the wheel. The slide rest is
traversed by means of the hand wheel operating a pinion in the rack
shown.
Fig. 2038 represents a swing frame for carrying and driving an emery
wheel to be used on the surfaces of castings, its construction
permitting it to be moved about the casting to dress its surface. The
overhead countershaft carries the grooved driving wheel A. At B is a
vertical shaft pivoted at I by the forked bearing which swings upon the
countershaft. The fork L at the lower end of shaft B carries a shaft on
which is the fork C´, C having journal bearing on it, and the driving
pulley J. Fork D has journal bearing on the same shaft as pulley J, and
is fast upon the rod or arm E, which affords journal bearing to the
emery wheel K on a shaft having handles H H. Motion to the emery wheel
is conveyed through the belts F and G. To counterbalance the frame the
weight W is employed, permitting the frame to be readily swung. The
upper fork carrying B, being pivoted to the shaft of A, permits B to
swing to any required position. The pivot at I permits B to rotate in a
vertical plane; the pivot of C´ C at D affords vertical movement to E;
the pivot at D allows E to rotate about its own axis, hence the wheel K
can be moved about laterally, raised, lowered, or have its plane of
revolution varied at will by simply swinging the handles H H to the
required plane. The emery-wheel shaft is pivoted upon the fork carrying
it, so that the emery wheel can be turned to stand in a horizontal plane
if desired.
[Illustration: Fig. 2037.]
Fig. 2039 represents an emery belt machine, in which the belt runs
vertically and its tension is adjusted by the idler pulley shown at the
top of the frame.
[Illustration: Fig. 2038.]
It is obvious that if a piece of work, as A in Fig. 2040, be held
steadily upon the rest R, its end will be ground to the curvature of the
emery wheel W, and that if it be required to grind the surface flat the
piece must be raised and lowered as denoted by the dotted lines, the
amount of this motion being determined by the thickness of the piece.
Furthermore, if the piece of work be of a less width than the thickness
of the wheel, as in the top view in Fig. 2041, the work A will wear a
groove on the wheel, and its side edges will therefore become rounded
off unless it be given sufficient motion in the direction of D and E to
cause it to traverse across the full width of the wheel face, and as
this motion would require to be simultaneous with the vertical motion
explained with reference to Fig. 2040, it is not practicable to grind
true level surfaces upon the perimeter of the wheel. As the sides of the
wheel are flat, however, it is self-suggestive to apply the work to the
side faces. But in this case, also, that part of the wheel surface that
performs grinding duty will gradually wear away, leaving a shoulder or
projecting surface upon the wheel.
Suppose, for example, that in Fig. 2042 the duty has been confined to
that part of the wheel face from A to the perimeter and the wheel would
wear as shown, the result being the same whether the width or distance
from the shoulder A to the perimeter of the wheel represents the width
of the work held steadily against the wheel or the traverse of a
narrower piece of work.
This difficulty may be overcome by recessing the wheel face, as in Fig.
2043, in which the wheel is shown in section.
In some cases, as for grinding the knives for wood-working machines,
hollow cylindrical wheels, such as in Fig. 2044. are used, the duty
being performed on the end face B B of the wheel, and the work being
traversed in the direction of the arrows. The wheel is here gripped
between the flange F and the collar C, which fits accurately to the end
of the driving spindle S, so as to be held true, and secured by screws
passing through C and into F, or the end of S may be threaded to receive
a nut to screw against C.
The circumferential surface of a wheel may be employed to grind a flat
surface, providing that the work be traversed to the wheel, as in the
side view in Fig. 2045. In this case, however, the cut must be taken
while the work P is travelling in the direction denoted by the arrow J,
and no cutting must be done while the work is travelling back in the
direction of K. After the work has traversed back in the direction of K,
and is clear of the wheel, the cut is carried farther across the work by
moving or feeding the work in the direction of the arrow in the front
view, Fig. 2046. In this case the whole surface of the work passes
beneath the wheel thickness, and the wheel face wears parallel to the
wheel axis, producing a true plane (supposing the work to be moved in
straight lines), save in so far as it may have been affected by the
reduction of the diameter of the emery wheel from wear, which is not
found sufficient to be of practical importance. If the whole surface of
the work does not pass across or beneath the wheel thickness the wheel
face may wear taper. Suppose, for example, that in Fig. 2047, P is a
piece of work requiring to have produced in it a groove whose bottom is
to be parallel to the lower surface F. Then the upper work surface being
taper the thick side A would wear away the side B of the wheel, and the
groove ground would not be parallel to F.
[Illustration: Fig. 2039.]
[Illustration: Fig. 2040.]
[Illustration: Fig. 2041.]
[Illustration: Fig. 2042.]
[Illustration: Fig. 2043.]
[Illustration: Fig. 2044.]
Another method of grinding flat surfaces is to mount the emery wheel
beneath a table T in Fig. 2048, letting the top of the wheel emerge
through an opening in the table, and sliding the work upon the trued
upper surface of the table. The surface of the table thus becomes a
guide for the work. To obtain true work in this way, however, it is
necessary that the cut taken by the emery wheel be a very light one, as
will be perceived from the following considerations.
[Illustration: Fig. 2045.]
[Illustration: Fig. 2046.]
[Illustration: Fig. 2047.]
In Fig. 2049 T represents a table and B a guide bar thereon. The depth
of cut taken will be equal to the height the emery wheel projects above
the surface A of the table, hence when the bar has been moved nearly
half-way across the table its surface will be as in Fig. 2050, the bar
occupying the position shown in Fig. 2051. Now the part of the bar that
has passed over the table will not rest upon it as is shown in Fig.
2051. When the bar has passed over the emery wheel more than half of the
bar length, its end F, Fig. 2052, will fall to meet the half D of the
table, and end E will lift from the half C of the table, causing the bar
surface to be ground rounding in its length. If, however, the cut taken
be a very light one the surface may be ground practically true, because
the bar will bend of its own weight and lap down to fit the table at
both ends. Furthermore it will be noted that in the case of a large
surface in which the wheel might sensibly wear in diameter before it had
operated over the whole of the work surface, the table may be lowered or
the wheel may be raised (according to the construction of the machine),
to offset the wear of the wheel, or rather to take it up as it were.
[Illustration: Fig. 2048.]
[Illustration: Fig. 2049.]
[Illustration: Fig. 2050.]
POLISHING WHEELS.--For polishing purposes as distinguished from that of
grinding, various forms of polishing wheels are employed. For the
rougher class of polishing, wooden wheels covered with leather coated
with fine emery that is allowed to glaze are employed. For a finer
degree of polish the wheels are covered with lead to which various
polishing materials are occasionally applied, while for the finest
polishing rag or buff wheels are the best. Wooden polishing wheels are
built up of sections of soft wood fastened together by gluing, and with
wooden pegs in place of nails or screws.
[Illustration: Fig. 2051.]
[Illustration: Fig. 2052.]
[Illustration: Fig. 2053.]
[Illustration: Fig. 2054.]
[Illustration: Fig. 2055.]
The joints of the sections or segments are broken--that is to say,
suppose in Fig. 2053 that 1, 2, 3, &c., up to 6, represent the joints of
the six sections of wood forming one layer of the wheel, the next six
sections would have their joints come at the dotted lines A, B, C, &c.,
up to F. To prevent them from warping after being made into a wheel it
is advisable to cut out the sections somewhere near the size in the
rough and allow them to lie a day or two before planing them up and
fitting them together; the object being to allow any warping that may
take place to do so before the pieces are worked up into the wheel,
because if the warping takes place afterwards it will be apt to throw
the wheel out of true, whereas it is necessary that these wheels be very
true, not only so that they may not prove destructive to their shaft
bearings, but that they may run steady, and not shake or terrible, and
because the work can be made much more true and smooth with a true than
with an untrue wheel. Only one layer of segments should be put on in one
day, and they should be put on as quickly as possible after the glue is
applied, so that the latter shall not get cold. So soon as each segment
is put into its place it should be clamped firmly to its seat and driven
firmly up to the joint of the next one, and when the layer is completed
it should be left clamped all night to dry. In the morning one clamp
should be removed, and that section fastened by boring small holes and
driving therein round and slightly tapered soft-wood pegs of about 1/4
inch diameter. The whole of the sections being pegged the next layer of
segments may be added, and so on until the required width of wheel is
attained. The whole wheel should then be kept two days before it is
turned, and as little as possible should be taken off in the turning
process. The circumferential surface should be turned slightly rounding
across its width, and as smoothly as possible. It is practicable to
proceed with the construction of the wheel without waiting between the
various operations so long as here advised, but the wheel will in that
case be more apt to get, in time, out of true. To cover the
circumference of the wheel sole leather is used, its thickness being
about 1/4 inch; it should be put on soft and not hardened by hammering
at all, and with the flesh side to the wood. The joint of the leather
should not be made straight but diagonal with the wheel face, the
leather at the edge of the joint being chamfered off, as shown in Fig.
2054 at A, and the joint made diagonal, as shown in Fig. 2055 at A.
If the leather were put on with a square butt joint there would likely
be a crease in the joint, and the emery or other polishing material
would then strike the work with a blow, as well as presenting a keener
cutting edge, which would make marks in the work no matter what pains
might be taken to prevent it. This, indeed, is found to occur to a
slight extent upon very fine polishing, even when the joint of the
leather is made as above; and the means taken to obviate it is to not
put any polishing material on the immediate joint and to wipe off any
that may get there, leaving 1/10 inch clear of polishing material. It is
obvious that in fastening the wheel to its shaft it should be put on so
that it will run in the direction of the arrow, providing the operator
works with the wheel running from him, as is usually the case with large
wheels, that is to say, wheels over 18 inches in diameter. In any event,
however, the wheel should be put on so that the action of the work is to
smooth the edge of the leather joint down upon the wheel, and not catch
against the edge of the joint, which would tend to rough it up and tear
it apart. The leather should be glued to the wheel, which may be
slightly soaked first in hot water. The glue should be applied very hot,
and the leather applied quickly and bound tightly to the wheel with a
band. One end of the leather may be first glued to the wheel and
fastened with a few tacks to hold it while it is stretched tightly round
the wheel; the leather itself should be softened by an application of
hot water, but not too much should be applied. After the leather is
glued to the wheel it is fastened with soft wooden pegs, about 3/16 inch
in diameter, driven through the leather into the wood and cut off
slightly below the surface of the leather.
[Illustration: Fig. 2056.]
[Illustration: Fig. 2057.]
Wheels of this kind are sometimes made as large as 5 or 6 feet in
diameter, in which case the truth of the wheel may be preserved by
letting in a wrought-iron ring, as shown in Fig. 2056, fastening the
rings with wood screws. The wheels thus constructed are covered with
emery of grades varying from No. 60 to 120, and flour emery. The coarser
grades perform considerable cutting duty as well as polishing. The
manner of putting the emery, and fastening it, upon the wheel is as
follows:--The face of the wheel is well supplied with hot glue of the
best quality, and some roll the wheel in the emery, in which case the
emery does not adhere so well to the leather as it does when the
operation is performed as follows:--Let the wheel either remain in its
place upon the shaft, or else rest it upon a round mandrel, so that the
wheel can revolve upon the same. Then apply the hot glue to about a foot
of the circumference of the wheel, and cover it as quickly as possible
with the emery. Then take a piece of board about 3/4 inch thick and 28
inches long, the width being somewhat greater than that of the polishing
wheel, and placing the flat face of the board upon the circumferential
surface of the wheel, work it by hand, and under as much pressure as
possible, back and forth, so that each end will alternately approach the
circumference of the wheel, as illustrated in Fig. 2057, the movement
being indicated by the dotted lines. By adopting this method the whole
pressure placed upon the board is brought to bear upon a small area of
the emery and leather, and the two hold much more firmly together than
would be the case if the circumference of the wheel were glued and then
rolled in a trough of emery, because the time occupied in spreading the
glue evenly and properly over the whole wheel surface would permit it to
cool before receiving the emery, whereas it is essential that the glue
be hot so that it may conform itself to the shape of the grains of emery
and hold them firmly.
The speed at which such wheels are used is about 7,000 feet per minute.
The finest of emery applied upon such wheels is used for cast iron,
wrought iron, and steel, to give to the work a good ordinary machine
finish; but if a high polish or glaze is required, the wheels are coated
with flour emery, and the wheel is made into a glaze-wheel by wearing
the emery down until it gets glazed, applying occasionally a little
grease to the surface of the wheel. Another kind of glaze-wheel is made
by covering the wooden wheel with a band of lead instead of a band of
leather, and then applying to the lead surface a mixture of rouge,
crocus and wax, worn smooth by applying to it a piece of sheet steel or
a piece of flint-stone before applying the work. Others add to this
composition a little Vienna lime. For flat surfaces, or those requiring
to have the corners or edges kept sharp, it is imperative that such
wheels as above described--that is to say, those having an unyielding
surface--be used; but where such a consideration does not exist, brush
and rag wheels may be used. In Europe comparatively large flat surfaces
requiring a high polish are finished upon wooden wheels made of soft
wood and not emeried, the polishing material employed being Vienna lime.
The lime for ordinary use is mixed with water, and is applied by an
assistant on the opposite side of the wheel to the operator. For
superfine surfaces the Vienna lime is mixed with alcohol, which
increases its efficiency; and here it may be as well to note that Vienna
lime rapidly deteriorates from exposure to the air, so that it should be
kept as little exposed as possible.
BRUSH-WHEELS.--These are polishing wheels of wood with a hair brush
provided around the circumference. These wheels are excellent
appliances, whether employed upon iron, steel, or brass. Their sizes run
from 1-1/2 inch to about 8 inches in diameter, and the hair of the brush
should not exceed from 1 to 1-1/4 inches in length. The speed at which
they should be run is about 2,500 for the largest, and up to 4,500
revolutions per minute for the smaller sizes. In ordinary grinding and
polishing practice in the United States, brush wheels are used with
Vienna lime in all cases in which the lime is used by itself--that is to
say, unmixed with wax, crocus, or rouge, or a mixture of the same. In
watchmaking, however, and for other purposes in which the truth of the
work is an important element, Vienna lime is applied to wooden or even
metal, such as steel, polishing wheels, which are in this latter case
always of small diameter. An excellent polishing composition is formed
of water 1 gill, sperm oil 3 drops, and sufficient Vienna lime to well
whiten the mixture. The brush may be let run dry during the final
finishing. For polishing articles of intricate shape, brush wheels are
superior to all others. If the articles to be polished are of iron, or
steel, the first stage of the process is performed with a mixture of oil
and emery, Vienna lime being used for final finishing only. The wheels
to which Vienna lime is applied should not be used with any other
polishing material, and should be kept covered when not in use, so as to
keep them free from dust.
For brass work, brush wheels are used with crocus, with rouge, or with a
mixture of the two, with sufficient water, and sometimes with oil, to
cause the material to hold to the brush and not fly off from the
centrifugal force. For very fine brass polishing, the first stages are
performed with powdered pumice-stone mixed with sufficient oil to hold
it together. This material has considerable cutting qualifications. The
next process is with rouge and crocus mixed, and for very fine finishing
rotten-stone.
Solid leather wheels are much used by brass-finishers. The wheels are
made of walrus hide glued together in disks, so as to obtain the
necessary thickness of wheel. The disks are clamped between pieces of
board so soon as the glue is applied, so as to make a good joint, and
also keep the wheel flat and prevent it from warping during the drying
process. Such wheels may be run at a velocity of 8,000 feet per minute,
and with any of the polishing materials already referred to. After the
wheel is made and placed upon its spindle or mandrel it may be turned
true with ordinary wood-turning tools--and it may here be remarked that
rag wheels may be trued in the same way. The spongy nature of these
wheels renders them very efficient for polishing purposes, for the
following reasons: The polishing materials become imbedded in the
leather and are retained, and become mixed and glazed with a fine film
of the material being polished, which film possesses the very highest
polishing qualifications. These walrus wheels may be used with pumice,
crocus, rouge, or Vienna lime, according to the requirements of the
case, or even with a mixture of flour emery and oil; and they possess
the advantage of being less harsh than leather or lead-covered wheels,
while they are more effectual than the latter, and will answer very well
for flat surfaces.
Rag polishing wheels are formed of disks of rags, either woollen or
strong cotton, placed loosely side by side, and clamped together upon
the mandrel at the centre only. Their sizes range usually from 4 to 8
inches in diameter, and they are run at a speed of about 7,000 feet per
minute. They assume a disk form when in motion from the centrifugal
force generated from the great speed of rotation. They are used for the
fine polishing only, and not upon work requiring the surfaces to be kept
very flat or the corners very sharp. For use upon steel or iron, they
are supplied with a polishing material composed of Vienna lime 3 parts,
crocus 3 parts, beeswax 3 parts, boiled up together, allowed to cool
off, and then cut into cakes. These cakes are dipped in oil at the end,
which is then applied to the rag wheel occasionally during the polishing
process. For brass-work, an excellent polishing composition is composed
of crocus 2 parts, wax 1 part, rouge 1/8 part, the wax being melted, and
the ingredients thoroughly mixed. This mixture gives to the metal a rich
color. It is dipped in oil and then applied to the rag wheel. It may be
used to polish fine nickel-plating, for which purpose it is an excellent
material. Nickel-plated articles having sharp corners should be polished
with fine rouge mixed with clear water and a drop of oil, the mixture
being applied to the rag wheel with the finger of the operator. Any of
the compositions of rouge, crocus, and rotten-stone may be used for
brass, copper, or nickel-plated work upon rag wheels, while for iron or
steel work the same materials, separate or in combination, may be used,
though they are greatly improved by the addition of Vienna lime. When,
however, either of these materials is used singly, it should be applied
to the rag wheels with a brush; and if it is used dry, it must be at a
greatly reduced speed for the wheel, which is sometimes resorted to for
very fine polishing.
[Illustration: Fig. 2058.]
Fig. 2058 represents a polishing device used to polish the surface of
engravers' plates. It consists of a spindle D, carried in bearings B,
and, having no collars, it is capable of end motion through those
bearings. The spindle is pressed downward by a spring A, carrying at its
end a piece C, which is capped to receive the end of the spindle D and
the piece E which threads into the spindle, thus making a sort of
universal joint. The spindle D is run by the pulley P, and carries a
piece of stone S, the work W resting upon the plate or table T. The
stone being set to one side of the centre of the spindle, each part of
its surface describes a circle, the centre of which is outside of the
stone, thus making the effectiveness of the centre of the stone greater
by increase of motion. To raise the stone from the work the spindle is
raised by means of the chord F, or the table T may have a simple lever
motion. The work is moved about and around and beneath the revolving
stone. Water, oil, benzine or alcohol is used to keep the stone clear
and wash away the cuttings. The device saves a good deal of hand work in
the preparatory stages of grinding, although it can be used only with
soft stones.
GRINDSTONES AND TOOL GRINDING.--The general characteristics of
grindstones are as follow:--
For rapid grinding a coarse and an open grit is the most effective. The
harder the grit the more durable the stone, but the liability of the
stone to become coated or glazed with particles of the metal ground from
the work is increased. With a given degree of coarseness a soft grit
stone will grind a smoother surface than a hard grit one.
The finer the grit the smoother the surface it will grind. In all
stones, however, it is of prime importance that the texture be even
throughout the stone, because the soft or open-grained part will wear
more rapidly than the close or hard grained. All grindstones are softer
when water-soaked than when dry, and will cut more freely, because the
water washes away the particles of metal ground from the work, and
prevents them from glazing the stone. It follows from this, however,
that a stone should not be allowed to rest overnight with its lower part
resting in water, as the wear of the stone will be unequal until such
time as it has become equally saturated. Furthermore the balance of the
stone is destroyed, and if run at a maximum speed, as in the case of
stones used to grind up large edge tools, the unbalanced centrifugal
force generated on the water-soaked side may cause the stone to burst.
The following stones are suitable for the class of work named:--
FOR GRINDING MACHINISTS' TOOLS.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.|Color of stone.
----------------+-------------+-----------------+----------------
Nova Scotia. |All kinds, |All kinds, from |Blue or
|from finest |hardest to |yellowish grey.
|to coarsest. |softest. |
| | |
Bay Chaleur |Medium to |Soft and sharp. |Uniformly light
(New Brunswick).|finest. | |blue.
| | |
Liverpool or |Medium to |Soft, with sharp |Reddish.
Melling. |fine. |grit. |
----------------+-------------+-----------------+----------------
FOR WOOD-WORKING TOOLS.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.|Color of stone.
----------------+-------------+-----------------+----------------
Wickersly. |Medium to |Very soft. |Greyish yellow.
|fine. | |
| | |
Liverpool or |Medium to |Soft, with sharp |Reddish.
Melling. |fine. |grit. |
| | |
Bay Chaleur |Medium to |Soft and sharp. |Uniform light
(New Brunswick).|finest. | |blue.
| | |
Huron, Michigan.|Fine. |Soft and sharp. |Uniform light
| | |blue.
----------------+-------------+-----------------+----------------
FOR GRINDING BROAD SURFACES, AS SAWS OR IRON PLATES.
----------------+-------------+-----------------+----------------
Name of stone. |Kind of grit.|Texture of stone.| Color of stone.
----------------+-------------+-----------------+----------------
Newcastle. |Coarse to |The hard ones. |Yellow.
|medium. | |
| | |
Independence. |Coarse. |Hard to medium. |Greyish white.
| | |
Massillon. |Coarse. |Hard to medium. |Yellowish white.
----------------+-------------+-----------------+----------------
The flanges for grindstones should be trued on both faces, and should
pass easily over the grindstone shaft, and there should be between these
collars and the stone an elastic disk, as of wood or felt, which will
bed fully against the surface of the stone. It is preferable also if the
under faces of these collars be recessed to within an inch of their
perimeters so as to confine the grip to the outer edges of the faces.
The process of grinding large surfaces is entirely distinct from that of
small ones, because of the difficulty in the former of getting rid of
the cuttings. As an illustration of this point it may be remarked that a
stone that has become dulled and glazed from operating upon a broad area
of surface, as say a large plate, may be both cleaned of the cuttings
and sharpened by grinding upon it a roller of, say, 1 or 1-1/4 inches in
diameter. This roller is laid across the "horn" or rut of the stone, and
pressed firmly against it, the bar being allowed to slowly rotate. What
is commonly termed grinding is the class of grinding that is followed as
a trade, such as file grinding, saw grinding, plate grinding, edge tool
and cutlery grinding. In all this class of grinding the speeds of the
stones is very much greater than for machine-shop tool grinding. For all
the above, save cutlery grinding, the stones when new are of a diameter
from 5 to 8 feet, and of a width of from 8 to 15 inches. The stones used
by cutlers are about 15 inches in diameter, and from 1/2 inch to 3
inches thick. The average speed of grindstones in workshops may be given
as follows:--
Circumferential speed
of stone.
For grinding machinists' tools, about 900 feet per minute.
" carpenters' " 600 "
The speeds of stones for file grinding and other similar rapid grinding
is thus given in the "Grinders' List."
Diameter of
stone.
Revolutions
ft. in. per minute.
8 0 135
7 6 144
7 0 151
6 6 166
6 0 180
5 6 196
5 0 216
4 6 240
4 0 270
3 6 308
3 0 360
These speeds are obviously obtained by reducing the diameter of the
pulley on the grindstone shaft each time the stone has worn down 6
inches less in diameter, and give a uniform velocity of stone if the 8
feet stone be driven with a pulley 32 inches in diameter. Each shift (or
change of pulley) giving a pulley 2 inches less in diameter.
The following table (from the _Mechanical World_) is for the diameter of
stones and the number of revolutions they should run per minute (not to
be exceeded), with the diameter of change or shift pulleys required,
varying each shift or change 2-1/2 inches, 2-1/4 inches, or 2 inches in
diameter for each reduction of 6 inches in the diameter of the stone:--
+-------------+-------------+-----------------------------+
| | | Shift of pulleys in inches. |
| Diameter of | Revolutions +---------+---------+---------+
| stone. | per minute. | 2-1/2 | 2-1/4 | 2 |
+-------------+-------------+---------+---------+---------+
| ft. in. | | | | |
| 8 0 | 135 | 40 | 36 | 32 |
| 7 6 | 144 | 37-1/2 | 33-3/4 | 30 |
| 7 0 | 154 | 35 | 31-1/2 | 28 |
| 6 6 | 166 | 32-1/2 | 29-1/4 | 26 |
| 6 0 | 180 | 30 | 27 | 24 |
| 5 6 | 196 | 27-1/2 | 24-3/4 | 22 |
| 5 0 | 216 | 25 | 22-1/2 | 20 |
| 4 6 | 240 | 22-1/2 | 20-1/4 | 18 |
| 4 0 | 270 | 20 | 18 | 16 |
| 3 6 | 308 | 17-1/2 | 15-3/4 | 14 |
| 3 0 | 360 | 15 | 13-1/2 | 12 |
+-------------+-------------+---------+---------+---------+
| 1 | 2 | 3 | 4 | 5 |
+-------------+-------------+---------+---------+---------+
"Columns 3, 4, and 5 are given to show that if you start an 8 feet stone
with, say, a countershaft pulley driving a 40 inch pulley on the
grindstone spindle, and the stone makes the right number (135) of
revolutions per minute, the reduction in the diameter of the pulley on
the grinding-stone spindle, when the stone has been reduced 6 inches in
diameter, will require to be also reduced 2-1/2 inches in diameter, or
to shift from 40 inches to 37-1/2 inches, and so on similarly for
columns 4 and 5. Any other suitable dimensions of pulley may be used for
the stone when 8 feet in diameter, but the number of inches in each
shift named, in order to be correct, will have to be proportional to the
number of revolutions the stone should run, as given in column 2 of the
table."
[Illustration: Fig. 2059.]
[Illustration: Fig. 2060.]
In all grinding operations it is necessary that the stone should run
true. This is sometimes accomplished by so mounting the stones in their
frames that their perimeters touch at the back of each stone, one stone
running slightly faster than the other. Or sometimes the work is placed
between the two stones, as in Fig. 2059, which represents a plan
frequently used to grind circular saws; _c_ in the figure represents the
grinding-stone and _a_ the saw. Long saws are mounted vertically as in
Fig. 2060, _a_ representing a frame to which the upper end of the saw is
attached and driven by a disk crank and connecting rod as shown, the two
stones _c_ _e_ may, in this case, be of equal diameter.
[Illustration: Fig. 2061.]
Fig. 2061 represents a grindstone truing device (for tool-grinding
stones) in which a series of serrated disks are employed in place on a
threaded roll. The disks are fed to the stone by the hand wheel and
screw, and are traversed back and forth across the stone face by means
of the lever handle shown.
The fast running grindstones used for heavy and coarse grinding are
trued by a process known as hacking. The high spots of the stone are
marked by holding a piece of coal to the stone while it revolves slowly,
and a tool similar to an adze is used to cut or chop indentations in the
stone. The highest spots will be most plainly marked by the coal, and
the hacking is spaced closer together in these places, the hacking marks
crossing each other and varying in depth to suit, obviously being
deepest where the marks are blackest. The hacking also sharpens the
stone. To prevent the stone from wearing uneven across its face the file
grinder mounts the stone in a very ingenious manner, causing it to
traverse automatically, back and forth, while rotating.
[Illustration: Fig. 2062.]
This device is shown in Fig. 2062, in which A represents the grindstone
spindle having journal bearing at B B, but as there are no collars on
the journals, A can move endwise through B B. Fast to A are the collars
C and C´ (sometimes the face of the pulley hub is made to serve instead
of C´); S is a sleeve fitting easily to A, and containing a return
groove, as shown; D is a fixed arm carrying a pin which projects down
into the groove of S, as shown; P is the pulley driving A, and W W are
suspended weights. The operation is self-acting, as follows: The shaft
revolving causes the sleeve to revolve by friction, and the pin causes
the sleeve to move endwise; its end face abutting against the face of
the collar on one side, or the face of the pulley on the other side, as
the case may be, causing the shaft to travel in that lateral direction.
When the pin has arrived at the end of the groove, the stone ceases
lateral motion (there being left a little play between the faces of the
sleeve and of the collar and pulley face for this special purpose),
while the cam travels in the opposite lateral direction, getting fairly
in motion until it strikes the face, when it slowly crowds the face
over. In travelling to the right it crowds against the face of the
collar C´, and in traveling to the left, as shown in the figure, against
the face of the collar C. The swing thus given to the stone is a slow
and very regular one, the motion exciting surprise from its simplicity
and effectiveness, especially when it is considered that the friction of
the rotation of a shaft about 2-1/2 inches diameter in a smooth hole
about 6 inches long is all that is relied upon to swing a ponderous
stone.
The following are the considerations that determine in grinding tools or
pieces held by the hands to the grindstone. Upon the edge of a tool that
last receives the action of the stone there is formed what is termed a
feather-edge, which consists of a fine web of metal that bends as the
tool is ground, and does not become detached from the tool in the
grinding. The amount or length of this feather-edge increases as the
work is thinner, and is greater in soft than in hardened steel. It also
increases as the tool or piece is pressed more firmly to the stone.
To prevent its formation on such tools as plane blades or others having
thin edges, the tool is held as at G in Fig. 2063, the top of the stone
running towards the workman, and the tool is held lightly to the stone
during the latter part of the grinding operation. With the tool held on
the other side of the stone as at C, and pressed heavily to the stone, a
feather-edge extending as long as from D to E may be formed if the tool
has a moderate degree only of temper, as, say, tempered to a dark
purple. The feather-edge breaks off when the tool is put to work, or
when it is applied to an oil-stone, leaving a flat place instead of a
sharp cutting edge. In well-hardened and massive tools, such as the
majority of lathe tools, the amount of feather-edge is very small and of
little moment, but in thin tapered edges, even in well-hardened tools,
it is a matter of importance.
After a tool is ground it is often necessary to remove the feather-edge
without having recourse to an oil stone. This may be accomplished by
pressing the edge into a piece of wood lengthways with the grain of the
wood, and while holding the cutting edge parallel with the line of
motion, draw it towards you and along the grain of the wood, which
removes the feather-edge without breaking it off low down, as would be
the case if the length of the cutting edge stood at a right angle to the
line of motion.
The positions in which to hold cutting tools while grinding them are as
follows: The bottom faces of lathe tools and the end faces of tools such
as scrapers should be ground with the tool laid upon the grindstone rest
as in Fig. 2064, the stone running in the direction of the arrow. The
best position for thin work as blades is at F providing the stone runs
true, for otherwise the tool edge will be liable to catch in the stone.
With an untrue stone the position shown in Fig. 2065 is the best, the
blade being slowly reciprocated across the face of the stone.
If the facet requires to be ground rounding and not flat the position at
C, Fig. 2064, is the best, the work being moved to produce the roundness
of surface. If the tool is to be ground hollow or somewhat to the
curvature of the stone, as in Fig. 2066, the curve being from _b_ to
_c_, the position at B is the best. At position D the tool cannot be
held steadily; hence, that position is altogether unsuitable for tool
grinding purposes.
For grinding the top faces of lathe or planer tools or other similar
shaped pieces that must be held with their length at a right angle (or
thereabouts) to the plane of the rotation of the stone, the tool is held
in the hands, and the hands are supported by the grindstone rest as in
Fig. 2067, the fingers being so placed that should the tool catch in the
stone it will slip from between the fingers and not carry them down with
it upon the tool rest.
Tools to be ground to a sharp point should be ground at the back of the
stone, that is to say, with the top of the stone running away from the
operator, and the point should be slowly moved across the width of the
stone to prevent wearing grooves in its surface.
To produce a finer edge than is possible with the grindstone, the
oil-stone is brought into requisition, the shape of the oil-stone being
varied to suit the shape of the tool. Three kinds of oilstone are in
general use, Turkey stone, Arkansas stone, and Washita stone, the latter
being softer and of inferior quality to the two former. The best quality
of Arkansas stone is of a milky white color, of very fine and even
grain, and very hard, being impervious to a file; but there are softer
grades. An oil-stone should be of even grain throughout, so that it may
wear even throughout, and produce a smooth and unscored edge. Arkansas
stone is rarely obtainable in lengths above 6 inches, on account of the
presence of fine seams of hard quartz, which wears less than the stone,
and forms a projection that scores the cutting edge of the tool, and the
same applies to the Turkey stones.
For tools fully hardened and not tempered the hardest oilstones are
best; but for tools that are tempered, as tools for woodwork, a softer
grade of stone is preferable, since it will cut the most free.
When an oil-stone has worn out of shape it may be dressed on a
grindstone; but if a flat surface is required it is best to true it by a
piece of coarse sand-paper laid upon a flat true surface.
The action of an oil-stone is to smooth the surfaces; but while doing
this the oil-stone itself forms what is termed a wire-edge, which
resembles a feather-edge, except that it is smoother and more
continuous. It is caused by the weak edge of the blade giving way under
the pressure with which it is held to the stone. To reduce the wire-edge
as much as possible the tool is pressed very lightly to the oil-stone
during the latter part of the stoning, and is frequently turned over. If
the motion of the tool upon the oil-stone is parallel with the line of
cutting edge, the wire-edge will be greater than if the line of motion
were at a right angle to it.
Again, the strokes performed while the cutting edge is advancing upon
the oil-stone produce less wire-edge than the return strokes, hence the
finishing process consists of a few light strokes upon one and then upon
the other facet repeated several times. Now let it be observed that, the
wire-edge will never be turned toward the facet last oil-stoned, and
cannot be obviated by the most delicate use of the stone; but after the
stoning proper is finished, the operator will lay one facet quite level
with the face of the stone, and then give to the blade, under a very
light pressure, forward diagonal motion, and then perform the same
operation with the other facet upon the stone, the last facet operated
upon being usually the straight and not the bevelled one. To still
further reduce the wire-edge for very fine work, the operator sometimes
uses a piece of leather belt, either glued to a piece of wood, as upon
the lid of the oil-stone box, or some attach it at each end to
projecting pieces of wood, while yet others lap the tool upon the palm
of the hand. In giving an edge to a razor, the process may be carried
forward in the usual way by means of straps, the first strokes being
long ones made under a slight pressure, the strokes getting shorter and
the pressure lighter as the process proceeds, until at last the motion
and contact are scarcely perceptible.
[Illustration: Fig. 2068.]
When, as in the case of plane blades and carpenters' chisels, the area
of face is large, it is advantageous to grind the face somewhat concave,
as in Fig. 2068, so that the heel and the point only of the tool has
contact with the oil-stone, thus reducing the area to be stoned and
steadying the tool, because, the area being small, the heel as well as
the edge may be allowed to rest upon the oil-stone without unduly
prolonging the stoning operation.
[Illustration: _VOL. II._ =GRINDSTONE GRINDING.= _PLATE V._
Fig. 2063.
Fig. 2064.
Fig. 2065.
Fig. 2066.
Fig. 2067.]
[Illustration: _VOL. II._ =FULL AUTOMATIC GEAR CUTTER.= _PLATE VI._
Fig. 2069.
Fig. 2070.]
CHAPTER XXIV.--GEAR-CUTTING MACHINES.
[Illustration: Fig. 2071.]
The Brainard automatic gear cutter, Figs. 2069, 2070, 2071 and 2072 is
arranged to cut spur, bevel, and worm-wheels, and is of that class where
the manipulations required in gear cutting are all performed by the
machine itself, thus dispensing with the care of an attendant except to
place the wheels in position and set the machine for the proper depth
and length of cut. The manner in which these results are accomplished
will be seen from the following description, reference being had to the
engravings. The wheel to be cut (_a_, Fig. 2070) is held upon a mandrel
_b_ fitted to the spindle _c_, which is mounted in firm bearings upon a
column or standard _d_. To the face of the standard is gibbed a sliding
knee _e_. Upon this knee is placed the cutter slide _f_, which is
arranged to be inclined for bevel-gear cutting, and to be swung aside in
cutting worm-wheels. Rotary cutters are carried on arbors fitted to the
cutting spindle (_g_, Fig. 2071). Power for driving the cutter is
applied to the pulley _h_, mounted upon the cutter spindle.
The cutter slide _f_ is operated through the medium of a screw and
bevel-gears from a shaft _h_^{1}, which is arranged to revolve
alternately in opposite directions from a continuous motion of the
driving cone pulley _t_, receiving, motion from the feed pulley _i_,
through the means of a swinging arm, carrying a receiving pulley and
cone as is shown in Fig. 2069.
The method of obtaining these opposite motions of the shaft _h_^{1} will
be seen in Fig. 2071. To the block _h_^{2} which supports the shaft
_h_^{1} is secured a gear _h_^{3}, which engages with a pinion _h_^{4}
mounted loosely on the cone pulley _i_^{1}. Side by side with this gear
is placed a second gear _h_^{5} also engaging with the pinion _h_^{4}
and having one tooth less than the gear _h_^{3}. This gear is mounted
loosely on the shaft _h_^{1} and is sleeved through the block _h_^{2},
and to it is secured a ratchet clutch _j_.
This arrangement produces a motion analogous to that of worm gearing;
the revolution of the cone _i_^{1} carrying the pinion _h_^{4}, causes
the gear _h_^{5} to be moved in the opposite direction to that of the
cone _i_^{1}, and at a speed of one tooth for each revolution of the
cone. The cone _i_^{1} carries on its outer end a second clutch _j_^{1}.
The shaft _h_^{1} is made hollow, and two clutches are secured to a rod
playing loosely on the hollow shaft, and arranged to be engaged
alternately with the clutches _j_ and _j_^{1}. This engagement is
effected by means of a bell crank _k_, operated by a shipper rod _k_^{1}
on which adjustable dogs are placed, arranged to be operated by the
cutter slide _f_.
This arrangement of feed shipping motion is very positive in its action,
and allows of a very quick return of the cutter slide. The parts are so
proportioned that the slide returns thirty-three times as fast as the
forward motion, and yet on the very fastest speeds there is no
perceptible jar of the parts. The entire mechanism can be disconnected
from the feed screw, when desired, by disengaging the clutch _j_^{3} on
the feed screw. The means employed for spacing the wheel blank are shown
in Figs. 2070 and 2072. At the rear end of the spindle _c_ is secured a
worm-wheel _l_. This worm-wheel is made in two parts screwed firmly
together. By this construction the wheel is made very accurately. The
screw holes in the ring _l_^{1} are slightly elliptic. After the wheel
has been hobbed out the position of the ring is changed and the wheel
re-hobbed, and so on until the teeth will match perfectly in any
position of the ring, when the ring is pinned and screwed on
permanently. This wheel is driven by a worm _m_ in connection with
change gearing _m_^{1}, _m_^{2}, in such a way that one turn of the
shaft _m_^{3} serves for all divisions. To the shaft _m_^{3} is secured
a graduated plate _o_, to which is secured a latch plate _o_^{1} by
means of a [T]-slot and bolts. The latch plate _o_^{1} is secured in
this manner in order that the plate _o_ may be turned any desired amount
of "set over" in bevel-gear cutting, without disturbing the change
gearing or latch. This dividing mechanism is driven by an independent
belt from the countershaft to the pulley P, which is secured to a pinion
P^{1}, running loose on a stud. The pinion P^{1} engages with a gear
P^{2} mounted loosely on the shaft _m_^{3}. This gear is made to drive
the latch plate _o_^{1} at the proper time by means of friction plates,
which are set to the required tension by check nuts. The latch plate
_o_^{1} is held by a spring latch _v_, which is secured to an arm
_v_^{1} mounted loosely on a stud. The arm _v_^{1} is moved by a disk
_v_^{2} carrying a secondary latch _v_^{3}. This secondary latch _v_^{3}
has on one side a roll which engages with a fixed cam _v_^{4} which
trips the latch _v_^{3} from its connection with the arm _v_^{1}, thus
allowing the spring on the latch _v_ to return it to its seat in the
latch plate _o_^{1}.
The disk _v_^{2} is moved by a steel ribbon (S, Fig. 2070) which is
connected to a pair of plates, _t_ _t_^{1}, held together by a [T]-slot
and bolts, and mounted loosely upon the carriage which carries the
cutter slide _f_. The object of the double plates is to take up the
slack ribbon, in any required position of the carriage, on the knee _e_.
To the inside plate _t_^{1} is connected a shipper rod _t_^{2}, which
carries a dog and is operated by the return motion of the cutter slide
_f_. A spiral spring coiled on the stud supporting the disk _v_^{2}
returns the disk to its original position on the forward motion of the
cutter slide _f_ and reseats the secondary latch _v_^{3} in its seat in
the arm _v_^{1}. This arrangement of dividing mechanism requiring but
one turn of the shaft _m_^{3} possesses some very decided advantages
over the ordinary way of simple gearing and multiplied turns. The latch
_v_ is tripped immediately after leaving its seat in the plate _o_^{1},
and is returned by its spring against the periphery of the plate, and is
surely seated by means of a lip on the upper side of the plate. Should
it, however, fail by reason of any accident no harm will be done as the
gear will be correctly spaced whenever the latch is seated, only one or
more spaces will have been missed. Another advantage is that the feed
gear can be disconnected and the latch withdrawn, thus allowing the gear
to be revolved for the purpose of examination without any necessity for
remembering the exact number of turns. When the latch is again seated
the gear will be always properly spaced.
[Illustration: Fig. 2072.]
Fig. 2073 represents the same machine made half automatic, or in other
words the feed is automatic, but when the cut is through, the worm that
actuates the feed is thrown out of gear by a catch which lets the box or
bearing at the left hand of the worm shaft drop vertically, this catch
being operated by a stop on the side of the cutter slide. The method of
arranging the feed mechanism so that it shall remain undisturbed, and
require no alteration or adjustment at whatever height the knee carrying
the cutter slide may be, is substantially the same as that already
described with reference to the universal milling machine in Fig. 1893,
while the dividing mechanism and other general features are the same as
in the full automatic, with the exception of the mechanism for operating
the cutter during the return stroke, and operating the dividing
mechanism, both of which operations are done by hand in the
half-automatic machine.
Fig. 2074 represents a Whitworth machine in which the cutter is carried
in a vertical spindle carried in a sliding head. A is the driving
pulley, B a pair of bevel-gears, and C a pinion driving the cutter
spindle D, the cutter being at E. The cutter spindle has journal bearing
at each end in arms upon the sliding head F, which is operated along the
slideway of H by the gear-wheel G, receiving motion from the worm at C;
at K is the index wheel, the wheel to be cut being carried on its shaft
at M. The head N, carrying the index-wheel shaft, may be moved along the
bed on which it slides by the handle P, which operates a screw within
the bed, and engaging a nut on the under side of N. The worm for the
worm-wheel K is carried beneath the wheel by a bracket from N, and being
on a splined shaft moves with N. P is the handle for the divisions, the
latter being obtained by means of change wheels at J, which connect with
the worm shaft. By employing change gears the handle P makes a complete
turn for any division, and is locked in a recess, which determines when
an exact turn has been made. The range of a machine of this design is
very great, because of the length of the bed on which the head N slides,
which may be longer than would be practical if it stood upright.
Fig. 2075 represents a gear planing machine, shown with a bevel-gear in
place. The main spindle is horizontal upon a fixed head, and has its
dividing mechanism at the back of the machine. A single pointed tool is
used in a slide rest, operated (by crank motion) upon the horizontal
slideway shown, which may be set at any required angle for bevel-wheels.
The cut is carried from the point to the flank of the tooth, and is put
on by a rod and ratchet motion, the rod striking against the stop seen
beneath the cross slide for the slide rest, and on the side of the
horizontal slideway.
Figs. 2076, 2077, 2078, 2079, 2080, 2081, and 2082 represent different
views of a gear-cutting machine, which consists of a bed plate A A,
Figs. 2077, 2078, and 2079, having an extension at end A^{2}, to support
the hollow cylindrical column A^{3}, which carries an overhead shaft
_a_, at one end of which is a four-step cone A^{3}, for driving the
cutter feed motions. At the other end are the tight and loose pulleys
for driving this shaft, upon which is also a series of grooved pulleys
_a_^{5}, arranged in the form of a cone. The object of this is to drive
the cutter. At the base of the column A^{3} is a corresponding series of
grooved pulleys, also arranged in the form of a cone _a_^{6}. A round
belt is employed. The shaft on which _a_^{6} is placed extends through
the column, and on its opposite end a grooved pulley is also placed.
This serves to drive a belt which, passing over a series of idle
pulleys, as will be seen by reference to Figs. 2076 and 2077, drives the
rotary cutter.
The wheel to be cut is carried as follows: Upon the bed-plate of the
machine is placed a head B, Fig. 2078, corresponding to the headstock of
a lathe, opposite which is a head B´, answering to the tailstock of a
lathe. These two carry a mandrel D, to which is fastened a face-plate D´
against which the work is chucked. At the end of D´´ is fixed, in the
usual manner, the worm-wheel for the dividing mechanism. The cutting
arbor is held in a head that is carried in a cross slide C^{2}, Fig.
2077, this cross slide being a carriage that may be fed along the side
extension of the bed, which is broken off in the plan view of the
machine, Fig. 2078. The two slides thus provided in this machine form in
effect a longitudinal and cross feed, answering to the feeds of a lathe
carriage and tool rest.
[Illustration: _VOL. II._ =GEAR-CUTTING MACHINES.= _PLATE VII._
Fig. 2074.
Fig. 2075.]
The cutter head M, Fig. 2077, is composed of two parts, C and M.
Provision is made to swing the head in two directions, one of which is
noted by the plain arrow and the other by the feathered arrow in the
engravings. Between the two the cutter arbor, it will be perceived, may
be set at an angle in whatever direction the nature of the work may
require. Referring to Figs. 2076 and 2077, it will be seen that the
cutter-driver mechanism operates as follows: The tight pulley _a_^{1},
driven in the direction noted by the arrow, turns the cone _a_^{6} which
drives the pulley _b_. The belt from _b_ passes over grooved idlers,
_b_^{1}, _b_^{2}, _b_^{3}, &c., to the grooved pulley _b_^{8}, which is
fast on its shaft and drives a train of gearing that operates the cutter
arbor, the train being best shown in Fig. 2077. The train of gearing
thus driven is composed of gears _c_^{1}, _c_^{2} and _c_^{5}, the
latter being on the cutter arbor. The object of this arrangement is to
obtain a high belt velocity. It will be seen that all these gears have
their teeth at an angle to their axes, a feature that has been
introduced to obtain smoothness of action. To maintain equal tension of
belt at whatever angle the cutter may be set, the idle pulley _b_^{2}
acts as a belt tightener, being carried by the rods _t_ and _t_^{1}.
[Illustration: Fig. 2073.]
Referring now to the feed motions, the machine is provided with a quick
return for the cutter, the mechanism of which is as follows: The cone
pulley _a_^{4}, Fig. 2077, is mounted upon a driver shaft _d_, Fig.
2079. Upon this shaft are two loose bevelled pinions _d_^{2} _d_^{4},
between which, and splined to the shaft, is a clutch _f_. For the feed
traverse the clutch _f_ is moved to engage with the pinion D^{4}, while
for the quick return it engages with _d_^{2}. This device corresponds to
the old-style quick-return motion used in some of the heavy English
planing machines. The clutch _f_ is operated by a rod _l´_, and drives
the bevelled pinions _d_^{2} _d_^{4} by friction. The hub of the clutch
is coned to fit a coned recess in the hubs of the two pinions. A pair of
gears, _d_^{6} _d_^{7}, transmit the motion of _d_^{5} to the shaft
_d_^{1}, on the end of which is the pinion _e_^{1}, Motion is conveyed
from this pinion to the feed-screw _e_, Fig. 2081, by the intermediate
gears e^{2}, _e_^{3}, _e_^{4} and _e_^{5}, and also by the helical
pinions _e_^{6} and _e_^{7}, the latter two being also shown in Fig.
2081.
Referring to the dividing mechanism, E, Fig. 2077, is an index-wheel
operated by a worm. E^{1} is an arm with a locking tongue. Motion from E
is conveyed to the shaft _g_ through a swing-frame, shown in dotted
lines in Fig. 2077, and a train of gears _g_^{2}, _g_^{3}, _g_^{4},
_g_^{5}, _g_^{6}. On shaft _g_, Fig. 2078, is a pair of angular-toothed
beveled pinions, _h_^{1} _h_^{2}, and on shaft _h_, Fig. 2080, is a
pinion _h_^{3}, driving a pinion _h_^{4}, which in turn drives pinions
_i_ _i_^{1}. The latter drive the worm H´ which operates the wheel H.
The two shafts carrying _i_ _i_^{1} are supported by a piece F, the arm
of which appears in section. This is fixed on the large toothed wheel G,
indicated by the dotted lines in the same figure. The piece F above
referred to is not fully shown in the engraving, portions of it having
been omitted in order to show the mechanism previously mentioned. The
wheel H is mounted on shaft D´´, and is used to revolve the face plate
D´, all as shown in Fig. 2078. The wheels _g_^{2} _g_^{3} are change
wheels, whose relative diameters determine the number of turns the wheel
E must make for a given pitch. The arm E^{1}, Fig. 2077, is provided
with a spring to hold the index pin into the notch of the index wheel.
From this description it is obvious that when the number of the teeth of
the wheel to be cut is a multiple of that of the wheel H, the number of
turns to be given to the tangent screw H´, Fig. 2080, is exactly
determined by the ratio existing between these two numbers. On the other
hand, where the number of teeth required is not a multiple of the teeth
in the wheel H, the number of turns to be given to the screw will be
equal to _n_ plus a fraction. In the first case, if all the intermediate
gears between the dividing apparatus and the tangent screw are arranged
to transmit to the former a number of definite turns, it will suffice to
make the crank describe the number of turns indicated by the ratio the
wheel E bears to the worm-wheel. In the second case, in order to give
the tangent screw _n_ turns plus a fraction by giving the crank _n_ +
turns, it is necessary to employ several wheels, for which the ratio
must be calculated. If the division so obtained is not an exact divisor
of the number of teeth of the wheel H, it is necessary that one of the
wheels forming the combination shall have a number of teeth which is a
multiple of the division mentioned.
[Illustration: Fig. 2076.]
Another consideration with reference to the number of turns to be given
to the crank of the dividing apparatus is mentioned in the inventor's
description of this machine. The smaller the number the greater will be
the chance of error in the result; for example, if it be supposed that a
division corresponding to one turn of the tangent screw is to be made,
if only one turn of the crank is made, the play unavoidable where easy
movement is secured will be repeated and multiplied in the same way that
an error is produced after a certain number of divisions. If, on the
contrary, the mechanism be arranged so that the number of turns of the
crank is multiplied in obtaining one turn of the tangent screw, the
error will be appreciably reduced. It is therefore recommended by the
designer of this machine to arrange the train of gears so as to give a
certain number of full turns to the crank in all cases. If, after having
cut the teeth in the blank, it is desirable to go over them again, it is
simply necessary to turn the screw _j_ which engages with the gear-wheel
J^{1}.
The next feature to be described is the adjustment of the cutter. In
some cases it is necessary to incline the cutter in such a way that the
axis of the shaft carrying it forms a certain angle with the vertical.
This is the case in cutting angle teeth, as shown in Fig. 2076. In order
to produce the necessary angle for such teeth, it is only necessary to
turn the worm _k_ that engages with the worm-wheel _k_^{1}, Fig. 2077.
This wheel is fast on to the piece M, and the latter, when set to the
desired inclination, is kept in place by means of bolts O, Figs. 2077
and 2081. In some cases it is necessary to incline the cutter in such a
way that the axis of the shaft that carries it does not cease to be in
a vertical plane perpendicular to the shaft D, this being the case as
illustrated in Fig. 2082. In order to obtain this obliquity the small
shaft _m_ is turned, and the movement so obtained is transmitted by
means of two small pinions _m_^{2} _m_^{3} to the shaft carrying at its
extremity the screw _n´_. This screw gears with the segment _n´´_. The
latter is fixed to a piece J, furnished with bearings for the reception
of the shaft that drives the cutter spindle, which is adjusted endways
by means of the nuts shown.
[Illustration: Fig. 2077.]
If it is desired to produce a wheel with angle teeth it is necessary,
after having arranged the cutter as shown in Fig. 2076, and while the
forward motion of the carriage takes place, that the wheel R shall turn
with a slow, regular movement until the tooth operated upon is finished.
After this the tool retraces its path at a somewhat higher speed. This
automatic motion is obtained from a shaft (Fig. 2076), on which are
placed the pinions _e_^{2} _e_^{3}. This shaft carries a third pinion
_p_^{2}, which, by means of one or more pairs of wheels mounted two by
two on a swinging frame _p_, as shown by _p_^{3} _p_^{4} _p_^{5}, turns
the shaft _p´_ (Fig. 2080), which carries at one of its extremities the
wheel _p_^{5} and at the other the screw _h_^{3}. This screw, by proper
intermediates, operates the toothed wheel G, Fig. 2080, which in its
rotation carries along the piece F, with all the parts supported by it.
In this movement the pinion _h_^{3} does not turn, nor does the second
pinion _h_^{4}, which slides on the former. The screw H´ slightly turns
the large wheel H, which, as previously mentioned, is mounted on the
shaft D, Fig. 2078. When the special tooth operated upon is finished the
movement is reversed by operating the lever _l_. The table and the wheel
R, Fig. 2077, then move in the opposite direction. When the original
position is reached by the cutter, the reversing lever is thrown out of
gear; the handle E´ is then used so as to effect the proper division,
and the machine is again started.
As has been shown, only a small portion of the circumference of the
wheel G is subjected to wear. In this way it would be possible to limit
the operation of cutting the teeth to a certain length of arc only. In
that case, however, considerable wear would be produced; for this reason
the constructor has preferred to provide the whole circumference with
teeth, in order to change the working point from time to time, so as to
distribute the wear. In order to permit this displacement it is
necessary to disengage the worm K (Fig. 2076), which is accomplished by
turning the hand wheel _v_, mounted on the shaft _v´_, Fig. 2078. This
shaft carries at each extremity small pinions, _v_^{2}, _v_^{3}, gearing
with other pinions fixed at the extremity of each of the supports of the
shaft _p´_.
[Illustration: Fig. 2078.]
[Illustration: Fig. 2079.]
[Illustration: Fig. 2080.]
In order to make the operation of this machine better understood, we
will conclude our description by some practical examples of the
calculations required in making helical teeth. It will be observed that
the two small movements necessary in cutting an angle tooth in a given
inclination are obtained first by the screw _e_, Fig. 2077, feeding the
cutter head, and second by the tangent screw K, Fig. 2076, that governs
the rotary motion of the wheel G, and consequently of the shaft D,
carrying the face plate and the blank to be cut. The second wheel H,
mounted on this shaft, is driven by the endless screw H´, Fig. 2080, the
supports of which are fixed on the wheel G. It will be observed at the
same time that the speed of the screw _e_ acting upon the tool holder is
the same as that of the shaft carrying the wheels _e_^{2} _e_^{3} and
_p_^{2}, since the wheels _e_^{4} _e_^{5} _e_^{6} _e_^{7} have the same
number of teeth. It is obvious, therefore, that that ratio of speed
which will exist between the tangent screw K and the shaft of wheels
_e_^{2} _e_^{3} and _p_^{2} will have to be the same as that between the
driving screw _e_ of the cutter head and the tangent screw K.
Consequently, the combinations of wheels that connect this tangent screw
K to the shaft _e_^{2} _e_^{3} and _p_^{2} will produce the same effect
as if they were connected directly with the feed screw _e_. This being
established, the general formulæ determining the gearing to be employed
in order to produce helical teeth inclined at a certain angle are
obtained in the following manner: It should here be observed that the
teeth produced will be what in the United States are called angle teeth,
corresponding, however, so nearly to the helix as to be considered
helical. Suppose that the number of teeth in the wheel G is 300, and
that the pitch of the driving screw of the cutter head is 5 mm., using
for convenience the French system of measurements. Let _x_/_y_ be the
ratio of the four wheels that it is necessary to mount. Let M designate
the degrees of inclination of the teeth. Let P equal the pitch of the
desired helix, and D the diameter of the wheel to be operated upon. We
then have cotan. M = P/(D × 3.14), from which we find P = cotan. M × D ×
3.14, and in order to make the cutter head run over a distance
corresponding to this pitch, the driving screw _e_ must make a number of
turns equal to
cotan. M × D × 3.141
--------------------
5
But while the cutter head passes over a distance equal to the pitch,
the wheel G makes one turn and the tangent screw 300 turns;
consequently, the ratio to be established between the speed of the
tangent screw and between that of the screw driving the carriage will be
represented by
_x_ 1500
--- = --------------------
_y_ cotan. M × D × 3.141
[Illustration: Fig. 2081.]
[Illustration: Fig. 2082.]
Thus, for a wheel with a diameter of 1.75 inches, the machine ought to
have an inclination of 15° to the primitive circumference, and we would
have, for the ratio to be established between the tangent screw and the
driving screw,
_x_ 1500 1500
--- = ------------------------- = --------
_y_ cotan. 15° × 1.75 × 3.141 20.51778
It should be remarked that, according as the angle should be either to
right or to left, one or two intermediate pieces are placed on the
swing-frame, the slide of which is nearly horizontal. The speed of the
driving shaft, supported by the column mentioned in introductory
remarks, is 120 revolutions; that of cutter equals from 20 to 30
revolutions; that of screw of cutter head, advance from 1 to 42
revolutions, return from 7 to 66 revolutions.
CHAPTER XXV.--VICE WORK.
Vice work may be said to include all those operations performed by the
machinist that are not included in the work done by machine tools. In
England vice work is divided into two distinct classes, viz., fitting
and erecting. The fitter fits the work together after it has been
operated upon by the lathe planer and other machine tools, and the
erector receives the work from the fitter and erects it in place upon
the engine or machine. Fitting requires more skill than turning, and
erecting still more than fitting, but it is at the same time to be
observed that the operations of the erector includes a great many of
those of the fitter. In treating of the subjects of vice work and
erecting, it appears to the author desirable to treat at the same time
of some operations that are not usually included in those trades,
because they are performed with tools similar to those used by the
fitter, and may be treated equally as well in this way as in any other,
while a knowledge of them cannot fail to be of great service to both the
fitter and erector. Among the operations here referred to are some of
the uses of the hammer; such, for example, as in straightening metal
plates.
The vice used by the machinist varies both in construction and size
according to the class of work it is to hold. For ordinary work the vice
may possess the conveniences of swiveling and a quick return motion, but
when heavy chipping constitutes a large proportion of the work to be
done the legged vice is preferable.
The height of vice jaws from the floor is usually greater for very small
work than for the ordinary work of the machine shop, because the work
needs to be more clearly observed without compelling the operator to
stoop to examine it. The gripping surfaces of vice jaws are usually made
to meet a little the closest at the top, so as to grip the work close to
the top and enable work cut off with a chisel to be cut clean and level
with the jaws.
[Illustration: Fig. 2083.]
The jaws of the wood-worker's vice are made then as in Fig. 2083, and
reach higher above the screw than the vices used for iron work, because
the work is often of considerable depth, and being light will not lie
still of its own weight, as is the case with iron.
[Illustration: Fig. 2084.]
An example of the ordinary vice of the machine shop is shown in Fig.
2084, which represents partly in section a patent swivel vice. A is the
jaw in one piece with the body of the vice, and B is the movable jaw,
being the one nearest to the operator. The movable jaw is allowed to
slide freely through the fixed one (being pushed or pulled by hand), or
is drawn upon and grips the work by operating the handle or lever H. The
means of accomplishing this result are as follows: As shown in the cut,
B is free to be moved in or out, but if H be pulled away from the vice,
the shoulder C, meeting the shoulder _n_, will move the toggle G, and
this, through the medium of G´, moves the tooth bar _t_, so as to engage
with the teeth on the side of the movable jaw bar shown at T. As soon as
the teeth _t_ meet the teeth T the two travel together, and the jaw B
closes on and grips the work. But as the motion is small in amount, the
jaw B should be placed so to nearly or quite touch the work before H is
operated. To unloose the work, the handle H is operated in an opposite
direction, and the hook M meets _m_ and pulls _t_ to the position shown.
The spring S operates upon a hook at U, to engage the teeth _t_, with
the rack T, as soon as the handle H is moved in the tightening
direction. The vice grips with great force, because during the
tightening the toggle, G is nearly straight, and its movement less than
would be the case with a screw-vice having the ordinary pitch of thread
and under an equal amount of handle movement.
[Illustration: Fig. 2085.]
In this vice the fixed jaw is made to fasten permanently to the work
bench, but in others having a similar tightening mechanism the fixed jaw
is so attached to the bench as to allow of being swivelled. The method
of accomplishing this is shown in Fig. 2085, in which S is the foot of
the vice bored conical to receive a cone on the casting R, which is
fastened to the bench B. W is a washer and H the double arm nut.
Loosening this nut permits of the vice being rotated upon R.
When handle H is operated to release the movable jaw it can be moved
rapidly to open and receive the work, and to close upon the work, when
by a second handle movement the work can be gripped, the operation being
much quicker than when the movable jaw is traversed by a screw and nut.
In this vice the gripping surface of the jaws are always parallel one to
the other, and attachments are employed to grip taper work as wedges.
[Illustration: Fig. 2086.]
[Illustration: Fig. 2087.]
In Fig. 2086 is represented a patent adjustable jaw vice, which is also
shown in Fig. 2087 with the adjustable jaw removed and upside down. From
the construction it is apparent that the groove G, being an arc of a
circle of which C is the centre, the jaw is, as it were, pivoted
horizontally, and can swing so as to let the plane of the jaw surfaces
conform to the plane of the work; hence a wedge can be gripped all along
the length enveloped by the jaws, and not at one corner or end only.
When the pin A is inserted the jaw stands fixed parallel to the sliding
jaw. The pin A engages in a ratchet in the base below it to secure the
back vice jaw in position when it is set to any required angle.
A second convenience in this vice is that the whole vice can be
swivelled upon the base that bolts to the bench, which is provided with
a central hole and annular groove into which the base of the field jaw
pivots; at B is a spring pin passing into holes in the bench plate, so
that by lifting the pin B, the whole vice can be swung or rotated upon
the base or bench plate, until the pin B falls into another hole in the
base plate, which is provided with eight of these holes. The movable jaw
is here operated by a screw and nut.
[Illustration: Fig. 2088.]
Fig. 2088 represents a form of leg vice for heavy work. In the ordinary
forms of this class of vice the two gripping surfaces of the jaws, only
stand parallel and vertical when at one position, because the movable
leg is pivoted at P; but in that shown in the figure the movable jaw is
supported by the arm A, passing through the fixed leg L, which carries a
nut N. A screw S, having journal bearing in the movable leg, screws
through the nut N, and is connected to the upper screw by the chain C,
which passes around a chain wheel provided on each screw, so that the
movable leg moves in an upright position and the jaw faces stand
parallel, no matter what the width of the work. This is a very
substantial method of obtaining a desirable and important object, and
greatly enhances the gripping capability of the vice. Fig. 2089
represents a sectional view of another patent vice. A is the sliding and
B the fixed jaw. P is the bed plate carrying the steel rack plate H.
Attached to each side of the base of the handle is a disk. These disks
are carried on the outer end of the movable jaw A, and are held in place
by the friction straps T, adjusted by the screws S. On the radial face
of the disk is the pin K, which, when the handle or lever is lifted or
raised, depresses the end of lever J, which at its other end raises the
clutch G, disengaging the same from the rack H, as shown in the
engraving. The jaw A is thus free to be moved by hand, so as to have
contact with the work. To tighten the vice the handle is depressed,
whereon K releases J and the latter permits the toothed clutch G to
engage with the teeth of H. At the same time the bar D, which is pivoted
to the disks, is drawn outward. The end of the bar D, meeting the
surface of the lug shown on A, acts (in conjunction with the toothed
clutch H) as a toggle fulcrum from which the disks may force the movable
jaw to grip the work.
[Illustration: Fig. 2089.]
This action may be more minutely described as follows: The end _d_ of D
is pivoted upon the disks, as shown; hence when the handle is depressed
the effort of the end _d_ is to move to the right, but D being fixed at
the other end the pressure is exerted to force the movable jaw to the
left, and therefore upon the work. The amount of jaw movement due to the
depression of the handle is such that if that jaw is pushed near or
close to the work the handle will stand about vertical downward when the
vice firmly grips the work.
For vices whose jaws cannot be swiveled horizontally to enable them to
conform to taper work, attachments for the jaws are sometimes provided,
these attachments having the necessary swiveling feature. So likewise
for gripping pipes, and similar purposes, attachments are made having
circular recesses to receive the pipes.
[Illustration: Fig. 2090.]
[Illustration: Fig. 2091.]
To prevent the vice jaws from damaging the work surface, and also to
hold some kinds of work more firmly, various forms of clamps, or
coverings for the vice jaws are used. Thus Figs. 2090 and 2091 represent
clamps for holding round or square pins. In the former the grooves pass
entirely through the clamp jaws, so as to receive long pieces of wire,
while in the latter the recesses are short, so as to form an abutment
for the end of the pins, and act as a gauge in filing or cutting them
off to length.
[Illustration: Fig. 2092.]
An excellent form of pin clamp is shown in Fig. 2092, the spring bow at
the bottom acting to hold the jaws open and force the faces against the
vice jaws when the latter are opened. The flanges at B B rest upon the
tops of the vice jaws; hence it will be seen that the clamp is not
liable to fall off when the vice is opened to receive the work, which is
placed either in the hole at A or that at B, as may be most desirable.
[Illustration: Fig. 2093.]
Fig. 2093 shows such a clamp holding a screw, the clamp jaws being
forced against the screw by the vice jaw pressure, when the vice jaws
are opened the spring of the bow will cause the clamp jaws to open and
release the screw.
Clamps such as shown in Figs. 2090 and 2091, but without the pin holes,
are also provided, being made one pair of copper and another of lead,
the latter being preferable for highly finished work. As the filings are
apt to imbed in the copper, and, furthermore, as the copper gradually
hardens upon its surface, the copper clamps require to be annealed
occasionally, which may be done by heating them to a low red heat and
dipping them in water. Lead clamps will hold small work very firmly, and
are absolutely essential for triangular or other finished work having
sharp corners, and also for highly finished cylindrical work, which may
be held in them sufficiently firmly to be clipped without suffering
damage from the vice jaws. A piece of thick leather, such as sole
leather, also forms a very good clamp for finished work, but to prevent
its falling off the vice jaws it is necessary to cut it nearly through
on the outside and at the bent corner.
The hammer in some form or other is used in almost all kinds of
mechanical manipulation, and in each of these applications it assumes a
form varied to suit the nature of its duty, and of the material to be
operated upon. In the machine shop it is used to drive, to stretch, and
to straighten.
The most skilful of these operations are those involving stretching
operations, as saw and plate straightening, examples of which will be
given.
In using a hammer to drive, the weight and velocity of the hammer head
are the main considerations. For example, the force of a blow delivered
by a hammer weighing 1 lb., and travelling 40 feet in a second, will be
equal to that weighing 2 lbs, and travelling 20 feet in a second; but
the mechanical effects will be different. If received on the same area
of impact the effects will sink deeper into the metal with the greater
velocity, and they will extend to a less radius surrounding the area of
impact. Thus in driving out a key that is fast in its seat, a quick blow
is more effective than a slow one, both being assumed to have at the
moment of impact an equal amount of mechanical force stored up in them.
On the other hand, for riveting the reverse will be the case. In the
stretching processes the hammer requires to fall with as dead a blow as
possible. Thus the hammer handle is, for saw stretching, placed at such
an angle to the length of the hammer that the latter stands about
vertical when the blow is delivered. In straightening, the blow is
varied to accommodate the nature of the work; thus a short crook or bend
would be best straightened by a quick blow with a light hammer, and a
long one by a slower blow with a heavier hammer, which would cause the
effects of the blow to affect a greater radius around the part receiving
the impact.
As an example of the difference in mechanical effect between a number of
blows aggregating a given amount of energy and a single blow having an
equal amount of energy, suppose the case of a key requiring a given
amount of power to start it from its seat, and every blow delivered upon
it with insufficient force to loosen its hold simply tends to swell and
rivet it more firmly in the keyway.
Probably the most expert use of the hammer is required in the
straightening of engravers' plates, as bank-note plates; and next to
this comes the ornamental repoussé work of the manufacturing jeweller.
The most expert hammer process of the machine shop is that of
straightening rifle barrels and straightening saws and sheet metal
plates.
In straightening rifle barrels, the operator is guided as to the
straightness as follows: A black line is drawn across a piece of glass
elevated to the light, and the straightener looks through the bore at
this line, which throws a dark line of shadow along the rifle bore. If
this line appears straight while the barrel is rotated the bore is
straight; but if the line waves the barrel requires straightening, the
judgment of the operator being relied upon to determine the amount of
the error, its location, and the force and nature of the blow necessary
to rectify it.
The following information on the duration of a blow is taken from
_Engineering_, the results having been obtained from some experiments by
Mr. Robert Sabine. These experiments, which were intended as preliminary
to a more extended inquiry, were made with a view to find approximately
how the duration of a blow varied with the weight of the hammer, its
velocity of descent, and with the materials. An iron ball weighing 1/4
lb. was suspended by a fine wire from an insulated support upon the
ceiling; so that when it hung vertically it just grazed the vertical
face of an ordinary blacksmith's anvil placed upon its side on a table.
By raising the ball and letting it swing against the face of the anvil a
blow of varying force could be struck. On rebounding, the ball was
arrested whilst the excursion of the galvanometer needle was observed.
By measuring the angle through which the ball was separated, its
vertical fall and final velocity could be easily deduced. In this way
the greatest vertical height from which the iron ball was let fall on to
the face of the iron anvil was 4 ft., the least about 1/80 inch. Six
readings were taken for each height, and they were invariably found to
agree amongst each other. The averages only are given in the following
records:
Vertical fall Duration of contact
in inches. in seconds.
48 0.00008
36 0.00008
28 0.00008
17 0.00009
9-1/4 0.00010
4 0.00011
1 0.00013
0-1/4 0.00016
0-1/16 0.00018
0-1/32 0.00021
0-1/80 0.00030
From this it would appear that when the velocity of a blow is increased,
the duration is decreased within a certain limit; but that it reaches a
minimum. The velocity of impact in the first experiment was about sixty
times as great as in the last one; but the duration of the blow appears
to be reduced only to about one-fourth of the time. The blows given by
two hammers of different weights were compared. No. 1 weighed 4 ozs.,
No. 2 weighed only 2-1/4 ozs. The durations of the blows were as
follows:
+----------------+---------------------------+
| | Duration of contact. |
| Vertical fall. +-------------+-------------+
| | Ball No. 1. | Ball No. 2. |
+----------------+-------------+-------------+
| inch. | seconds. | seconds. |
| 1 | 0.000135 | 0.000098 |
| 4 | 0.000096 | 0.000083 |
+----------------+-------------+-------------+
It appears from this that a heavier hammer of the same material gives a
longer duration of blow.
In the course of these experiments it was observed that the ball after
striking the anvil rebounded irregularly, sometimes to a greater, at
others to a less height, and that some relation appeared to exist
between the heights to which the ball rebounded and the excursions of
the galvanometer needle due to the residue of the charge.
In the next series, therefore, the rebounds of the iron ball from the
iron anvil were measured and recorded, from which it appeared that when
the rebound was greater the duration of contact was shorter, and _vice
versâ_.
+----------------+-------------------+-------------------+
| Vertical fall. | Vertical rebound. | Duration of blow. |
+----------------+-------------------+-------------------+
| inch. | inch. | seconds. |
| 6 | 2 | 0.000120 |
| 6 | 2-1/2 | 0.000111 |
| 6 | 3-1/4 | 0.000101 |
| 6 | 3-1/2 | 0.000091 |
| 14-1/2 | 3-1/4 | 0.000106 |
| 14-1/2 | 4-1/2 | 0.000103 |
| 14-1/2 | 5-1/4 | 0.000095 |
| 14-1/2 | 6-1/2 | 0.000086 |
| 25 | 7-3/4 | 0.000096 |
| 25 | 8-1/4 | 0.000091 |
| 25 | 9-1/2 | 0.000086 |
| 25 | 12 | 0.000078 |
+----------------+-------------------+-------------------+
The explanation of this is probably that when the energy of the blow is
expended in bruising or permanently altering the form of the hammer or
anvil by which the contact of the two is prolonged, it has less energy
left to enable it to rebound, and _vice versâ_. Substituting a brass
anvil and brass ball, it was found that the blow was duller, the rebound
much less, and the duration contact nearly three times as great as when
the iron ball and anvil were used.
+----------------+-------------------+----------------------+
| Vertical fall. | Vertical rebound. | Duration of contact. |
+----------------+-------------------+----------------------+
| inch. | inch. | seconds. |
| 1-3/4 | 0-1/3 | 0.00036 |
| 6 | 1 | 0.00033 |
| 14-1/2 | 1-1/2 | 0.00026 |
| 25 | 2 | 0.00027 |
+----------------+-------------------+----------------------+
This series also shows the longer duration of the blow when its velocity
is small. Using a brass anvil and iron ball the duration of the blow was
greater than when both were of iron, but less than when both were of
brass.
+----------------+-------------------+----------------------+
| Vertical fall. | Vertical rebound. | Duration of contact. |
+----------------+-------------------+----------------------+
| inch. | inch. | seconds. |
| 1-3/4 | 0-1/8 | 0.00021 |
| 6 | 0-1/2 | 0.00018 |
| 14-1/2 | 1-1/3 | 0.00015 |
| 25 | 2 | 0.00014 |
+----------------+-------------------+----------------------+
Striking the brass anvil with a common hammer, the duration of the blow
appeared shorter when struck sharply.
Duration of contact.
seconds.
Moderate blow 0.00027
Harder blow 0.00019
Striking the blacksmith's anvil with a common carpenter's hammer, the
duration appeared to be nearly constant.
Duration of contact.
seconds.
Moderate blow 0.00011
Harder blow 0.00010
It was, of course, necessary to allow in each case the hammer to rebound
freely, and not to prevent it doing so by continuing to exert any
pressure at the instant of the blow. When this condition was observed,
it was invariably found that the harder and sharper the blow the shorter
was its duration. It was also noticed that whenever the anvil gave out a
sharp ringing sound, the duration of the blow was much shorter than when
the sound was dull.
A very slight error would be introduced by reason of thermo-currents set
up between the metals at the moment of the blow. By reversing the
direction of charge of the accumulator, however, the effect from this
cause was found to be quite inappreciable.
[Illustration: Fig. 2094.]
[Illustration: Fig. 2095.]
[Illustration: Fig. 2096.]
[Illustration: Fig. 2097.]
[Illustration: Fig. 2098.]
The machinists' hand hammer is usually made in one of the three forms
shown in Figs. 2094, 2095 and 2096, and varies in weight from about
1-3/4 lbs. for heavy chipping to about 1/2 lb. for light work, the
handle being about 15 inches long for the heavy, and about 10 or 12 for
the light business. The round face is usually somewhat convex on its
surface with its edge slightly rounded or beveled. The pane or pene A,
Fig. 2097, is usually made in European practice to stand at a right
angle to the axis of the handle as shown, while in the United States it
is usually made to stand parallel with the handle as in Fig. 2096. The
face end is sometimes given taper as in Figs. 2094 and 2095, and at
others parallel as in Figs. 2097 and 2098, or nearly so. The pene is
mostly used for riveting purposes, and it is obvious that with the pene
at a right angle to the handle axis as in Fig. 2097, it will not matter
whether the pene meets the work quite fair or not, especially as the
pene is made slightly curved in its length, and it is easier to hold the
hammer level sideways than it is to hold it so true lengthways that the
pene, when forward, as in Fig. 2096, will meet the work fair.
[Illustration: Fig. 2099.]
[Illustration: Fig. 2100.]
[Illustration: Fig. 2101.]
The proper shape for the eye of a hammer is that shown in Figs. 2099 and
2100, a representing the top of the hammer. The two sides of the eye are
rounded out from the centre towards each end, while the ends of the eye
are made parallel. The form of the eye as viewed from the top A is as
shown in Fig. 2102, while Fig. 2101 represents a view from the bottom B.
The handle is fitted a driving fit and is driven in from side B, and is
shaped as in Figs. 2103 and 2104 which are side and edge views.
From C to D the handle fills the eye, but from D to E it fills the eye
lengthways only of the oval. A saw-slot, to receive a wedge, is cut in
the handle, as shown in Fig. 2104. The wedge is best made of soft wood,
which will compress and conform itself to the shape of the slot. To
drive the handle into the eye, preparatory to wedging it permanently, it
should be placed in the eye held vertically, with the tool head hanging
downward, and the upper end struck with a mallet or hammer, which is
better than resting the tool head on a block. The wedge should be made
longer than will fill the slot, so that its upper end may project well,
and the protruding part, which may split or bulge in the driving, may be
cut off after the wedge is driven home.
[Illustration: Fig. 2102.]
[Illustration: Fig. 2103.]
The wedge should be driven first with a mallet and finally with a
hammer. After every few blows on the wedge, the tool should be suspended
by the handle and the end of the latter struck to keep the handle firmly
home in the eye. This is necessary, because driving the wedge in is apt
to drive the handle partly out of the eye.
[Illustration: Fig. 2104.]
[Illustration: Fig. 2105.]
The width of the wedge should equal the full length of the oval at the
top of the eye, so that one wedge will spread the handle out to
completely fill the eye, as shown in Fig. 2105. Metal wedges are not so
good as wooden ones, because they have less elasticity and do not so
readily conform to the shape of the saw-slot, for which reasons they are
more apt to get loose. The taper on the wedge should be regulated to
suit the amount of taper in the eye, while the thickness of the wedge
should be sufficiently in excess of the width of the saw-cut, added to
the taper in the eye, that there will be no danger of the end of the
wedge meeting the bottom of the saw-slot.
[Illustration: Fig. 2106.]
By this method, the tool handle is locked to the tool eye by being
spread at each end of the same. If the top end of the tool eye were
rounded out both ways of the oval, two wedges would be required to
spread the handle end to fit the eye, one wedge standing at a right
angle to the other. In this case, one wedge may be of wood and one of
metal, the one standing across the width of the oval usually being the
metal one. The thin edge of the metal wedge is by some twisted, as shown
by Fig. 2106, which causes the wedge to become somewhat locked when
driven in.
In fitting the handle, care must be taken that its oval is made to stand
true with the oval of the tool eye. Especially is this necessary in the
case of a hammer. Suppose, for example, that in Fig. 2107 the length of
the oval of the handle lies in the plane A B, while that of the eye lies
in the plane C D, then the face of the hammer will meet the work on one
side, and the hammer will wear on one side, as shown in figure at E. If,
however, the eye is not true in the hammer, the handle must be fitted
true to the body of the hammer; that is to say, to the line C D. The
reason for this is that the hand naturally grasps the handle in such a
manner that the length of the oval of the handle lies in the plane of
the line of motion when striking a blow, and it is obvious that to
strike a fair blow the length of the hammer should also stand in the
plane of motion.
[Illustration: Fig. 2107.]
The handle should also stand at a right angle to the plane of the length
of the hammer head, viewed from the side elevation, as shown in Fig.
2108, in which the dotted line is the plane of the hammer's length,
while B represents a line at a right angle to A, and should, therefore,
represent the axial line of the hammer handle. But suppose the handle
stood as denoted by the dotted line C, then the face of the hammer would
wear to one side, as shown in the figure at D.
In the operation of straightening iron or steel plates by hammer blows,
the process when correctly carried out is one of liberating the strains
(whose existence throws the plate out of a true plane) by stretching
those parts that are unduly contracted. Every hammer blow should,
therefore, be directed towards this end, for one misdirected blow
entails the delivery of many others to correct its evil influence;
hence, if several of such misdirected blows are given, the plate will
have upon it a great many more hammer marks, or "hammer sinks" or chops,
as they are sometimes termed, than are necessary. As a result, not only
will the painter (in fine work) be given extra trouble in stopping the
hollows to make a smooth surface, but the following evil will result:
Every blow struck by the hammer compresses and proportionately stiffens
the small surface upon which it is delivered, and creates a local
tension upon the surrounding metal. The misdirected blows then cause a
tension acting in opposition to the effect of the properly delivered
ones; and though the whole plate may be stiffened by the gross amount of
blows, yet there will be created local tensions in various parts of the
plate, rendering it very likely to spring or buckle out of truth again.
If, for example, we take a plate of iron and hammer it indiscriminately
all over its surface, we shall find it very difficult to straighten it
afterwards, not only on account of the foregoing reasons, but for the
additional and most important one that the effect of the straightening
blows will be less, on account of the hammered surface of the plate
offering increased resistance to the effects of each blow; and after the
plate is straightened, there will exist in it conflicting strains, an
equilibrium of which holds the plate straight, but the weakening of any
of which will cause the preponderance of the others to throw the plate
out of straight; for the effects of the blows cannot be permanent unless
the whole body of the iron is acted upon to an equal extent by the
hammer. Suppose, for example, that we take a flat plate, and deliver
upon it a series of blows round about its centre. The effect will be to
make it hollow on one side and rounding on the other, the effect of the
blows being, not only to indent the plate in the spots where they fell,
but to carry the whole body of the middle out of true; because, the area
of the iron being increased by the stretching effect of the blows, the
centre leaves the straight line to accommodate the increased area. Thus,
if we mark off a circle of, say, a foot in diameter, in the middle of a
plate, and hammer it so as to stretch it and increase its area 1/8 inch
each way, the form of the plate must alter to suit this added area, and
the form of a dish or curve is the only one it can assume.
[Illustration: Fig. 2108.]
The skilful workman, so soon as he has ascertained where the plate is
out of true, sets to work to stretch it, so as to draw the crooked place
straight, taking care that the shape and weight of the hammer and the
weight of the blows delivered shall bear a proper relation to the
thickness of the plate and the material of which it is composed. If it
is of consequence that the finished work shall bear no marks of the
hammering (as in the case of engravers' plates), an almost flat-faced
hammer is employed; but for other work the shapes, as well as the
weights, of the hammers vary.
[Illustration: Fig. 2109.]
[Illustration: Fig. 2110.]
[Illustration: Fig. 2111.]
Fig. 2109 represents what is called the long cross-face hammer, used in
saw straightening for the first part of the process which is called the
smithing. The face that is parallel to the handle is called the long
one, and the other is the cross-face. These faces are at a right angle
one to the other, so that without changing his position the operator may
strike blows that will be lengthways in one direction, as at A, in Fig.
2110, and by turning the other face towards the work he may strike a
second series standing as at B. Now, suppose we had a straight plate and
delivered these two series of blows upon it, and it will bend to the
shape shown in Fig. 2111, there being a straight wave at A, and another
across the plate at B, but rounded in its length, so that the plate will
be highest in the middle, or at C; if we turn the plate over and repeat
the blows against the same places, it will become flat again. Both faces
of this hammer are made alike, being rounded across the width and
slightly rounded in the length, the amount of this rounding in either
direction being important, because if the hammer leaves indentations, or
what are technically called "chops," they will appear after the saw has
been ground up, even though the marks themselves are ground out, because
in the grinding the hard skin of the plate is removed, and it goes back
to a certain, but minute, extent towards its original shape. This it
will do more in the spaces between the hammer blows than it will where
the blows actually fell, giving the surface a slightly waved appearance.
[Illustration: Fig. 2112.]
The amount of roundness across the face regulates the widths, and the
amount of roundness in the face length regulates the length of the
hammer marks under any given force of blow. As the thicker the plate the
more forcible the blow, therefore the larger the dimensions of the
hammer mark.
The twist hammer, shown in Fig. 2112, is used for precisely the same
purposes as the long cross-face, but on long and heavy saws or plates,
and for the following reasons, namely: When the operator is engaged in
straightening a short saw he can stand close to the spot he is
hammering, and the arm using the hammer may be well bent at the elbow,
which enables him to see the work plainly, and does not interfere with
the use of the hammer, while the shape of the smithing hammer enables
him to bend his elbow and still deliver the blows lengthways, in the
required direction. But when a long and heavy plate is to be
straightened, the end not on the anvil must be supported with the left
hand, and it stands so far away from the anvil that he could not bend
his elbow and still reach the anvil. With the twist hammer, however, he
can reach his arm out straight forward to the anvil, to reach the work
there, while still holding up the other end, which he could not do if
his elbow were bent. By turning the twist hammer over he can vary the
direction of the blow the same as with the long cross-face.
[Illustration: Fig. 2113.]
[Illustration: Fig. 2114.]
It is obvious that by slightly bending the elbow and turning either of
these hammers over the blows may be caused to be in any required
direction, as shown in Fig. 2113. These two hammers are used for the
straightening or smithing processes, and not to regulate the tension,
because the effects of their blows do not extend equally around the part
struck, but follow the form of the hammer marks, whose shapes are shown
in Fig. 2114, at A and B, the radiating lines denoting the directions in
which the effects extend; obviously the size of these marks depends upon
the shape of the hammer face and the force of the blow.
[Illustration: Fig. 2115.]
[Illustration: Fig. 2116.]
[Illustration: Fig. 2117.]
An inspection of hammered saw plates, however, will show that the marks
(which are scarcely visible, having a merely dulled surface), are
usually about one-half wider than the thickness of the plate, and about
four or five times as long as they are wide. Obviously, also, the
direction of the effects of a blow follow the direction in which the
hammer travels. If, for example, the long cross-face falls vertically
its effects will extend equally all around the hammer mark, as at A in
Fig. 2115, but if the hammer moved laterally to the left while falling
its blows would have more effect on the left-hand side of the mark as at
B, or if it moved away from the operator its effects would extend most
in front as at C, the amount increasing with the force of the blow, and
it may be remarked that quick blows are not used, because they would
produce indentations or chops; hence, the force of the blow is regulated
by the weight of the hammer rather than by the velocity it travels at.
On account of the oval shape of the blow delivered by the long
cross-face and by the twist hammers, the dog-head hammer, shown in Fig.
2116, is used to regulate the tension of the plate or saw, the effects
of its blow when delivered vertically being circular, as at A, in Fig.
2117; obviously, however, if in falling it moved vertically in the
direction of arrow C the effects would extend as at B. But while the
dog-head is used entirely for regulating the tension, it may also be
used for the same purposes as either the long cross-face or the twist
hammer, because the smith operates to equalize the tension at the same
time that he is taking down the lumps; hence he changes from one hammer
to the other in an instant, and if after regulating the tension with the
dog-head he should happen to require to do some smithing, before
regulating the tension in another, he would go right on with the
dog-head and do the intermediate smithing without changing to the
smithing hammer. Or, in some cases, he may use the long cross-face to
produce a similar effect to that of the dog-head, by letting the blows
cross each other, thus distributing the hammer's effects more equally
than if the blows all lay in one direction.
In circular saws, which usually run at high velocity, there is generated
a centrifugal force that is sufficient to actually stretch the saw and
make it of larger diameter. As the outer edge of the saw runs at a
greater velocity than the eye it stretches most, and therefore the
equality of tension throughout the saw is destroyed, the outer surface
becoming loose and causing the saw to wabble as it revolves, or to run
to one side if one side of the timber happens to be harder than the
other, as in the case of meeting the edge of a knot.
The amount of looseness obviously depends upon the amount the saw
expands from the centrifugal force, and this clearly depends upon the
speed the saw is to run at; so the saw straightener requires to know at
what speed the saw is to run, and, knowing this, he gives it more
tension at the outside than at the eye; or, in other words, while the
eye is the loosest, the tension gradually increases towards the
circumference, the amount of increase being such that when the saw is
running the centrifugal force, and consequent stretching of the saw,
will equalize the tension and cause the saw to run steadily.
If the eye of a circular saw is loose, or, in other words, if it is rim
bound when running, it will dish, as in Fig. 2118, and the rounded side
rubbing against the side of the saw slot or kerf, will cause the saw to
become heated and the eye to expand more than the outer edges, thus
increasing the dish. But if the saw strikes a knot on the hollow side it
may throw the dish over to the other side of the saw in an instant. The
remedy is to hammer the saw with the dog-head as shown in the figure,
not touching the eye, and letting the blows fall closer together
towards the circumference.
[Illustration: Fig. 2118.]
[Illustration: Fig. 2119.]
[Illustration: Fig. 2120.]
[Illustration: Fig. 2121.]
[Illustration: Fig. 2122.]
[Illustration: Fig. 2123.]
[Illustration: Fig. 2124.]
On the other hand, if the eye is tight and the circumference loose the
saw will flop from side to side as it runs, and the remedy is to stretch
it round about the eye, letting the blows fall wider apart as the outer
edge of the saw is approached. The combinations of tight and loose
places may be so numerous in circular saws that as the smith proceeds in
testing with the straight-edge he marks them, drawing a circular mark,
as at G, in Fig. 2119, to denote loose, and the zig-zag marks to
indicate tight places. To cite some practical examples of the principles
here laid down, suppose we have in Fig. 2120 a plate with a kink or bend
in the edge, and as this would stiffen the plate there, it would be
called a tight place. To take this out, the hammer marks would be
delivered on one side, radiating from the top of the convexity, as on
the left, and on the other as shown radiating from the other end of the
concavity, as on the right, the smithing hammer being used. This would
induce a tight place at A which would be removed by dog-head blows
delivered on both sides of the plate. Suppose we had a plate with a
loose place, as at G in Fig. 2121. We may take it out by long cross-face
blows, as at A and B, delivered on both sides of the plate, or we might
run the dog-head on both sides of the plate, both at A and at B, the
effect being in either case to stretch out the metal on both sides of
the loose place G, and pull it out. In doing this, however, we shall
have caused tight places at E and F, which we remove with dog-head
blows, as shown. If a plate had a simple bend in it, as in Fig. 2122,
hammer blows would first be delivered on one side, as at A, and on the
other side, as at B. A much more complicated case would be a loose place
at G, in Fig. 2123, with tight places at H, J, K, and L, for which the
hammer blows would be delivered as marked, and on both sides of the
plate. Another complicated case is given in Fig. 2124, G G being two
loose places, with tight places between them and on each side. In this
case, the hammering with the long cross-face would induce tight places
at D and E, requiring hammer blows as denoted by the marks.
[Illustration: Fig. 2125.]
[Illustration: _VOL. II._ =THE HAMMER AND ITS USES.= _PLATE VIII._
Fig. 2127.
Fig. 2128.
Fig. 2129.
Fig. 2130.
Fig. 2131.
Fig. 2132.
Fig. 2133.
Fig. 2134.]
The saw or plate straightener's anvil or block is about 12 by 18 inches
on its face, which must be very smooth and is slightly convex, because
it is necessary that the plate should be solid on the block, directly
beneath the part of its surface which is being hammered, otherwise the
effect of the blows will be entirely altered. If, for instance, A, in
Fig. 2125, represents the straightening block, and B a plate resting
thereon, then the blows struck upon the plate anywhere save over the
very edges of the anvil will have but little effect, because of the
spring and rebound of the plate; and the effect of the blow will be
distributed over a large area of the metal, tending to spring it rather
than give it a permanent set. If the blow is a quick one, it may indeed
indent the plate without having any straightening effect. On the other
hand, by stretching the skin on the upper side of the plate, it will
actually, under a succession of blows, become more bent. In fact, to use
a straightening block, so large in proportion to the size of the plate
that the latter cannot be adjusted so that the part of the plate struck
lies solid on the block, renders all the principles above explained
almost valueless, and is a process of pounding, in a promiscuous way,
productive of hammer marks, and altogether fatal to the production of
true work.
[Illustration: Fig. 2126.]
To straighten the plate shown in Fig. 2125, we place it upon the anvil,
as shown in Fig. 2126, striking blows as denoted at A, and placing but a
very small portion of the plate over the anvil at first; and as it is
straightened, we pass it gradually farther over the anvil, taking care
that it is not, at any part of the process, placed so far over the anvil
as to drum, which will always take place if the part of the plate struck
does not bed, under the force of the blow, well upon the anvil.
The methods employed to discover in what parts a plate requires
stretching, in order to straighten it and to equalize its tension, are
as follow: Suppose we have a plate, say 18 inches by 24, and having a
thickness of 19 gauge, and we rest one end of it upon the block and
support the other end in the left hand, as shown in Fig. 2127; then with
the right hand we exert a sudden pressure in the middle of the plate;
and quickly releasing this pressure, we watch where its bending movement
takes place. If it occurs most at the outer edges, it proves that the
plate is contracted in the middle; while, if the centre of the plate
moves the most, it demonstrates that it is expanded in the middle. And
the same rule applies to any part of the plate. This way of testing may
be implicitly relied upon for all plates or sheets thin enough to be
sprung by hand pressure.
Another plan, applicable for either thick or thin plates, and used
conjointly with the first named, is to stand the plate on edge with the
light in front, as in Fig. 2128; we then cast one eye along the face of
the plate upon which the light falls, and any unevenness will be made
plainly visible by the shadows upon the surface of the plate. The eye
should also be cast along the edges to note any twist or locate any
kinks.
We may take a thin piece of plate in the hands, and if it is loose in
the middle and we lay a straight-edge upon its upper surface, and try to
bend the middle of the plate downward with the fingers, it will go down
under the finger pressure, the straight-edge showing a hollow place in
the middle; and the same thing will occur if the straight-edge be tried
with either side of the plate uppermost. But if the piece be tight in
the middle and we test with the fingers and straight-edge in the same
way, the middle instead of bending downwards, appears to rise up, the
straight-edge showing it to be rounded. In the first case the middle
moves because it is loose, and in the second the edges move because they
are loose.
Fig. 2129 represents a plate for a circular saw that is loose in the
middle, and if we bend the middle down it will become concave on the
top, as shown in the figure. But if it were tight in the middle and
loose at the outer edge, it would become, under the same pressure,
convex on the top, as in Fig. 2130, and here again the part that is
loose moves the most.
In thin saws, such as hand saws, the workman takes the saw in his hands,
as in Fig. 2131, and bends it up and down so that by close observation
he may see where it moves the most, and then discover the loose places,
or he may watch for the tight places, since these are the places he must
attack.
[Illustration: Fig. 2135.]
The sledge hammer used by the machinist is usually made in one of the
two forms shown in Figs. 2132 and 2133, the latter being the most
serviceable because it has two faces which may be used for driving
purposes, which is the only use the machinist has for the sledge hammer.
The coppersmith varies the shape of his hammer faces to suit the nature
of the work, thus Fig. 2134 represents a coppersmith's hammer, its two
faces being of different sizes and of different curvature, and both
being used to form convex surfaces having different degrees of
curvature, it being noted that the curvature of the hammer face is
always less than that of the work. In other forms of coppersmith's
hammers there are two penes and no face, one being at a right angle to
the other, as in Fig. 2135, the penes being rounded as in the figure, or
sometimes square.
[Illustration: Fig. 2136.]
Fig. 2136 represents a coppersmith's hammer with a square nosed pene,
which is sometimes made to stand at a right angle to the handle as in
the figure, and at others parallel to it.
[Illustration: Fig. 2137.]
Fig. 2137 represents the file cutter's hammer, whose handle is at the
angle shown because the chisel is held at an angle, the point or cutting
edge being nearest to the workman; hence if the handle were at a right
angle to the hammer length his arm would require to be considerably
elevated in order to let the hammer face fall fair on the chisel head,
whereas by setting the handle at the angle shown the arm need not be
elevated, and the blow may be given by a movement of the wrist.
[Illustration: Fig. 2138.]
[Illustration: Fig. 2139.]
Figs. 2138 and 2139 represent hammers used by boiler-makers for riveting
boiler seams. The faces are made small so that if the blows are properly
directed the edge of the face will not meet the boiler plate and indent
it. These hammers are made long and narrow so that the weight may lie in
the same direction as the hammer travels in when delivering the blow,
and thus cause the effects of the hammer blows to penetrate deeper than
if the hammer was wider.
In the cooper's hammer, shown in Fig. 2140, the face extends flush up to
the head, thus enabling it to strike a hoop upon a barrel without
danger of the extreme end or top of the hammer meeting the barrel, and
preventing the hammer face from meeting the edge of the barrel hoop when
driving it on the barrel. The face is square and its front edge
therefore a straight line, which is necessary on account of the circular
shape of the hoop of the barrel.
[Illustration: Fig. 2140.]
[Illustration: Fig. 2141.]
The mallet is made in various forms to suit the nature of the work and
the tools it is to be used upon. Thus the carpenter's mallet is a
rectangular block, such as shown in Fig. 2141. It is composed of wood,
because the carpenter's tools are held in wooden handles, and a metal
hammer would split them in course of time. It is rectangular in shape so
that it may be applied to tools held in a corner of the work, where a
round mallet could not, if of sufficient diameter, give the necessary
weight. For such carpenters' or wood-workers' tools as are for heavy
duty, and the tools for which have ferrules at the head of their handles
to prevent them from splitting, the mallet is made cylindrical or round,
as it is termed, and has an iron band at each end to prevent the face
from spreading or splitting.
The stonemason's mallet is also of wood, and is disk-shaped, with the
handle in the centre, the circumferential surface forming the face. The
reason for this is that his tools are of steel and have no handles;
hence if the blow continually fell on the same part or spot of the
mallet face it would sink or indent holes in it, which is prevented by
utilising the whole circumference of the mallet for the face.
An excellent mallet for the machinist's use, for driving finished work
without damaging it, is formed of raw hide secured in a metal eye that
receives the handle. Or for the same purpose a lead hammer is used,
being especially serviceable for setting work in machines.
What is known as pening, or paning, consists of hammering the skin of
metal to stretch it on the side that is hammered. It may be employed
either to bend or to straighten. Suppose, for example, we have a piece
of metal that is bent to a half circle, and if we take a light hammer
and hammer it on the concave side and all over its surface the piece
will straighten out to an amount depending on the amount of pening. Or
if he hammers the convex side the piece will bend to a smaller circle.
The principle involved is, that if one side of a piece is elongated and
the other remains of its original length, the only shape it can assume
to accommodate or permit the elongation is that of a curve of which the
convex side is the longest. It follows, therefore, that the hammer blows
must in pening be sufficiently light to condense or stretch the metal on
one side only of the metal, and not forcible enough to effect it all
through.
In order to accomplish this stretching as rapidly as possible it is
necessary to use a light hammer, with sufficient force to be expended in
condensing the metal at its surface, and to so form the hammer that it
shall expend its force upon the work with a dead blow, that is, with as
little rebound as possible. These results are best accomplished with a
ball pened hammer, such as shown in Fig. 2108 and weighing about 1/2 lb.
The blows should fall dead; that is, the hammer should fall, to a great
extent, by its own weight, the number rather than the force of the blows
being depended upon; hence, the hammer marks will not be deep. This is
of especial importance when pening has to be performed upon finished
work, because, if the marks sink deeply, proportionately more grinding
or filing is required to efface them; and for this reason the force of
the blows should be as near equal as possible. Another and a more
important reason, however, is that the effect of the pening does not
penetrate deeply; and if much of the pened surface is removed, the
effects of the pening will be also removed. The work should not be
rested upon metal, but upon wood.
[Illustration: Fig. 2142.]
[Illustration: Fig. 2143.]
The following are examples of pening. Fig. 2142 represents a shaft bent
as shown, the arms being too wide at A, which may be corrected by pening
at B. If the error was in the arms themselves and not in the stem, the
side faces of the arms would require to be pened. Thus in Fig. 2143 the
distance A is too short, and the pening must be at B C.
[Illustration: Fig. 2144.]
Fig. 2144 represents a strap requiring to be closed across A, the pening
being at C or D. But as pening at D would bend the crown and unpair the
bed of the brasses, it is preferable to pene at C. In either case the
jaws will close as denoted by the dotted lines.
Fig. 2145 represents another common form of connecting rod strap, and in
this case the pening may be most quickly and effectively done at the
crown as denoted by the dots; and as this would alter the inside curve,
the brass or box fitting into it must be refitted. In case the pening
should be overdone it is better to modify it by filing away some of the
pened surface.
Cast iron is more rapidly affected by pening than either wrought iron or
steel. One of the most useful applications of pening is in the case of
moulding patterns, which in time may become warped from the rapping of
the pattern in the mould, and this warping may be corrected by judicious
pening, or suppose that a number of plates, such as represented in Fig.
2146, having been cast, it is found that the ends of the tongues A B
curl up when cooling in the mould, then the tongues may be pened as at C
D, throwing them down to the requisite amount, and thus moulding the
pattern to accommodate the curling in cooling.
[Illustration: Fig. 2145.]
[Illustration: Fig. 2146.]
The riveting usually performed by the machinist is generally upon cold
metal. The blows in this case should fall dead and the riveting be
performed with a view to stretching the metal uniformly and evenly over
the surface to be riveted.
[Illustration: Fig. 2147.]
[Illustration: Fig. 2148.]
An excellent example of cold riveting is given in the crank pin P in
Figs. 2147 and 2148. C is the crank (both being shown in section). The
end of the pin should be recessed as shown at A, so that it may be the
more readily riveted outward to fill the countersink shown in the crank
at B, B. The crank-pin is rested upon a piece of copper D interposed
between it and the iron block E to prevent damage to the finished face
of the crank-pin.
The riveting blows should be given with a ball-faced hammer, and
delivered with a view to stretch the whole end face of the crank-pin
evenly. Otherwise the riveted surface will be apt to split as shown.
This usually occurs from not riveting the area at and near the
circumference sufficiently, although it may occur from riveting that
part of the area too much. The line of travel of the hammer should not
be directly vertical, but somewhat lateral in a direction from the
centre towards the circumference. If the countersink is a deep one, it
is desirable to leave the crank-pin sufficiently too long, so that after
the riveting has proceeded some time the surface of the metal which has
become condensed and crystallized from the direct impact of the hammer
blows, may be chipped away, leaving a surface that is swollen by the
riveting without being so much condensed. This enables a much greater
spreading of the metal without splitting it.
If in this class of work the riveted piece (as the crank-pin) is not
driven in very tight before riveting, the riveting blows will be apt to
jar the pin back. Hence, it is necessary to occasionally drive the pin
home. The riveting should proceed equally all over, as if one side be
riveted in advance of the other it tends to throw the pin out of true.
When, however, the riveting begins to bed the pin, four equidistant
places may be riveted home in advance so as to bring the pin home and
hold it firmly.
[Illustration: Fig. 2149.]
[Illustration: Fig. 2150.]
[Illustration: Fig. 2151.]
THE CHISEL.--The machinist's cold chisel is made from the two forms of
steel shown in Figs. 2149, 2150, and 2151, and of these the former is
preferable because it has two broad flats diametrally opposite and these
form a guide to the eye in holding the chisel on the grindstone, and aid
in grinding the facets that form the cutting edge true. Furthermore, as
the cutting edge is in the same plane as these flats they serve as a
guide to denote when the chisel edge lies parallel to the work surface,
which is necessary to produce true and smooth chipping.
The width of the chisel may be made greater, as in Figs. 2152 and 2153,
for brass or cast-iron work than for wrought iron or steel for the
following reasons. On account of the toughness and hardness of wrought
iron and steel the full force of a 1-3/4 lb. hammer, having a handle 13
inches long, may be used on a chisel about 7/8 inch wide without danger
of causing the metal to break out below the chipping line, but if such a
chisel be used with full force blows upon cast iron or brass the metal
is apt to break out in front of the chisel, the line of fracture often
passing below the level it is intended to chip down to. Hence if a
narrow chisel is used lighter blows must be delivered. But by using a
broader chisel the force of the blow is distributed over a longer length
of cutting edge, and full force blows may be used without danger of
breaking out the metal.
[Illustration: Fig. 2152.]
[Illustration: Fig. 2153.]
[Illustration: Fig. 2154.]
[Illustration: Fig. 2155.]
[Illustration: Fig. 2156.]
[Illustration: Fig. 2157.]
[Illustration: Fig. 2158.]
The cutting end of the chisel should be kept thin, as in that case it
cuts both easier and smoother. The total length of a chisel should not
when new exceed 8 inches, for if made longer it is not suitable for
heavy or smooth chipping, as it will bend and spring under heavy blows,
and cannot be held steadily. The forged part should not exceed about
2-1/2 or 3 inches in length, as a long taper greatly conduces to
springiness, whereas solidity is of great importance both to rapid and
smooth work. The facets forming the cutting edge should be straight in
their widths, as at B in Fig. 2154, and not rounded as at A, so that the
face next to the work may form a guide in holding the chisel at the
proper angle to maintain the depth of the cut. This angle depends upon
the nature of the material to be cut; the facets forming an angle one to
the other of about 65° for cast steel and about 50° for gun metal or
brass. The more acute these angles the nearer the body of the chisel
lies parallel with the work and the more effective the hammer blows.
Thus in Fig. 2155 chisel C is the position of the chisel for wrought
iron, and position D is for steel. The angles should always be made,
therefore, as acute as the hardness of the material will permit. If they
are too acute the cutting edge will be apt to bend in its length, while
if not sufficiently acute they will not cut keen enough; hence the
object is to make them as acute as possible without causing the cutting
edge to bend in its length. For copper and other soft metals the angle
may be about 30° or 35°, the chisel end being kept thin so that it may
not become wedged between the work and the chipping, which will bend but
little, and is, therefore, apt to grip the wedge end of the chisel. The
cutting edge should be slightly rounded in its length, which will
strengthen it and also enable a fine finishing clip to be taken off, as
in Fig. 2156, the width of the chip not extending fully across the
chisel width so that the corners are not under duty and are not,
therefore, liable to break, or dig in and prevent smooth chipping. In
some practice the edge is made straight in its length, as shown in Fig.
2149, which is permissible in heavy chipping when a cape chisel has been
used, but in any event an edge rounded in its length is preferable. If
the edge is hollow in its length, as shown in Fig. 2157, and magnified
in Fig. 2158, the chip acts as a wedge to force the corners outwards as
denoted by the arrows, causing them to break under a heavy cut, and,
furthermore, a smooth cut cannot be taken when the corners of the chisel
meet the work surface.
If the facets are ground under on one side, those on the other, as in
Fig. 2159, the edge will not be parallel with the flats of the chisel,
so that in holding it the flats will not form a guide to determine when
the edge lies parallel to the work surface as it should do. The edge
should also be at a right angle to the length of chisel, as denoted by
the lines, as in Fig. 2160, for if not at a right angle the chisel will
be apt to move sideways after each blow, and cannot be held steadily.
[Illustration: Fig. 2159.]
[Illustration: Fig. 2160.]
The chisel should be held as close to its head as possible, so that the
hand will steady the head as much as possible, and should be pushed
forward firmly and steadily to its cut, which will greatly facilitate
rapid and smooth chipping, and for wrought iron and copper it is found
better to occasionally moisten the chisel with oil or water, the former
being preferable.
[Illustration: Fig. 2161.]
Messrs Tangye, of Birmingham, have introduced the employment of chisel
holders, such as shown in Fig. 2161, the object being to fit to each
holder a number of short pieces of steel for chisels so that a number
can be ground or forged at one time; obviously chisels of different
shapes require different forms of handle.
[Illustration: Fig. 2162.]
[Illustration: Fig. 2163.]
[Illustration: Fig. 2164.]
When a heavy cut is to be taken the cape (Fig. 2162) chisel is used,
first to carry through grooves or channels, such as shown in Fig. 2176
at A, B, and C, the distance apart of these grooves being slightly less
than the width of the flat chisel, whose cut is shown partly carried
across at D in the figure. The width of a cape chisel should gradually
decrease from A to B in Fig. 2163, so that its side will be free in the
groove it cuts, and the chisel head will be free to be moved sideways,
and the direction of the groove may be governed thereby. If the chisel
end be made parallel, as at C in Fig. 2164, it will have no play in the
groove and the head cannot be moved; hence if the groove is started out
of line, as it is apt to be, it will continue so.
[Illustration: Fig. 2165.]
[Illustration: Fig. 2166.]
[Illustration: Fig. 2167.]
[Illustration: Fig. 2168.]
The round-nosed chisel, Figs. 2165 and 2166, may be straight from H
nearly to the point G, but should be bevelled at and near G, so that the
chisel head may be raised or lowered to govern the depth of the cut. Its
round nose should also be wider than the metal higher up, so that the
chisel head may be moved sideways to govern the direction of the cut as
in the cape chisel. The cow mouth chisel, Figs. 2167 and 2168, should be
bevelled from G to the point to enable the governing of the depth of
the cut, and should be of greater curvature than the corner it is to cut
out, so that its corners cannot wedge in the work.
[Illustration: Fig. 2169.]
[Illustration: Fig. 2170.]
The oil groove chisel, Figs. 2169 and 2170, should be wider at the
cutting edge than at A for reasons already stated, and of less curvature
than the bore of the brass or bearing it is to cut the oil groove in.
[Illustration: Fig. 2171.]
[Illustration: Fig. 2172.]
[Illustration: Fig. 2173.]
[Illustration: Fig. 2174.]
[Illustration: Fig. 2175.]
[Illustration: Fig. 2176.]
The diamond point chisel, Figs. 2171 and 2172, may be made in two ways.
First, as in Figs. 2173 and 2174, for shallow holes, and as in Figs.
2171 and 2172 for deep ones. In shallow holes the chisel can be leaned
over, as in Fig. 2176 at _y_, whereas in deep ones it must be held
straight so that the chisel body may not meet the other side of the
hole, slot, or keyway. The form shown in Fig. 2172 is the strongest,
because its point is brought into line with the body of the steel, as
shown by the line Q. The side chisel, Fig. 2175, for cutting out the
sides of keyways or slots, should be bevelled from W to the cutting edge
for the reasons already given, and straight from W to V, the line V W
projecting slightly above or beyond the body U. An application of the
cow mouth chisel is shown at L, and one of the side chisel is shown at Z
in Fig. 2176. All these chisels are tempered to a blue color.
The chisel that is driven by hammer blows may be said to be to some
extent a connecting link between the hammer and the cutting tool, the
main difference being that the chisel moves to the work, while the work
generally moves to the cutting tool. In many stone-dressing tools the
chisel and hammer are combined, inasmuch as that the end of the hammer
is chisel shaped; an example of this kind of tool being given in the
pick that flour millers use to dress their grinding stones. On the other
hand we may show the connection between the chisel and the cutting tool
by the fact that the wood-worker uses the chisel by driving it with a
mallet, and also by using it for a cutting tool for work driven in the
lathe. Indeed, we may take one of these carpenter's chisels and fasten
it to the revolving shaft of a wood-planing machine, and it becomes a
planing knife; or we may put it into a carpenter's hand plane, and by
pushing it to the work it becomes a plane blade. In each case it is
simply a wedge whose end is made more or less acute so as to make it as
sharp as possible, while still retaining strength enough to sever the
material it is to operate upon.
[Illustration: Fig. 2177.]
In whatever form we may apply this wedge, there are certain well-defined
mechanical principles that govern its use. Thus when we employ it as a
hand tool its direction of motion, under hammer blows, is governed by
the inclination of the face which meets the strongest side of the work,
while it is the weakest side of the material that moves the most to
admit the wedge and therefore becomes the chip, cutting, or shaving. In
Fig. 2177, for example, we have the carpenter's chisel operating at A
and B to cut out a recess or mortise, and it is seen that so long as the
face of the chisel that is next to the work is placed level with the
straight surface of the work the depth of cut will be equal; or in other
words, the line of motion of the chisel is that of the chisel face that
lies against the work. At C and D is a chisel with, in the one instance,
the straight, and in the other the bevelled face toward the work
surface. In both cases the cut would gradually deepen because the lower
surface of the chisel is not parallel to the face of the work.
If now we consider the extreme cutting edge of chisel or wedge-shaped
tools it will readily occur that but for the metal behind this fine edge
the shaving or cutting would come off in a straight ribbon, and that the
bend or curl that the cutting assumes increases with the angle of the
face of the wedge that meets the cutting, shaving, or chip.
[Illustration: Fig. 2178.]
I may, for example, take a piece of lead, and with a penknife held as at
A, Fig. 2178, cut off a curl bent to a large curve, but if I hold the
same knife as at B it will cause the shaving to curl up more. Now it has
taken some power to effect this extra bending or curling, and it is
therefore desirable to avoid it as far as possible. For the purpose of
distinction we may call that face of the chisel which meets the shaving
the top face, and that which lies next to the main body of the work the
bottom face. Now at whatever angle either face of the chisel may be to
the other, and in whatever way we present the chisel to the work, the
strength of the cutting edge depends upon the angle of the bottom face
to the line of motion of the chisel, and this is a principle that
applies to all tools embodying the wedge principle, whether they are
moved by a machine or by hand.
[Illustration: Fig. 2179.]
Thus, in Fig. 2179 we have placed the bottom face at an angle of 80° to
the line of tool motion, which is denoted by the arrow, and we at once
perceive its weakness. If the angle of the top face to the line of tool
motion is determined upon, we may therefore obtain the strongest cutting
edge in a hand-moved tool by causing the bottom angle to lie flat upon
the work surface.
[Illustration: Fig. 2180.]
But in tools driven by power, and therefore accurately guided in their
line of motion, it is preferable to let the bottom face clear the work
surface, save at the extreme cutting edge. The front face of the wedge
or tool is that which mainly determines its keenness, as may be seen
from Fig. 2180, in which we have the wedge or tool differently placed
with relation to the work, that in position A obviously being the
keenest and less liable to break from the strain of the cutting process.
[Illustration: Fig. 2181.]
If we now turn our attention to that class of chisel or wedge-shaped
tools in which the cutting edge is not a straight line, but may be
stepped or curved--as, for example, the carpenter's plane blade--we
shall find that so long as the blade stands at a right angle to the
surface it is operating upon, as in Fig. 2183 at B, the shape of surface
it cuts will exactly correspond to the shape of its cutting edge; but so
soon as the tool is inclined to its line of motion its cutting edge
will, if curved, produce a different degree of curvature on the work.
[Illustration: Fig. 2182.]
[Illustration: Fig. 2183.]
Suppose, for instance, that we have in the figure a piece of moulding M
and a plane blade B, and the length of the cutting edge is denoted by A,
Fig. 2182; now suppose that the blade is inclined to its line of motion
(as in the case of carpenters' planes) and stands at C, Fig. 2183: we
then find that the cutting edge must extend to the length or depth D,
and it is plain that the depth of the curve on the moulding is less than
the depth of the cutting edge that produces it; the radius E being less
than of D, so that if we place the cutter C upright on the moulding it
will appear as shown in Fig. 2181. If, therefore, we are required to
make a blade that will produce a given depth of moulding when moved in a
straight line and presented at a given angle to the work, we must find
out what shape the blade must be to produce the given shape of moulding,
which we may do as follows:
In Fig. 2184 let A be a section of the moulding, and if the blade or
knife is to stand perpendicular, as shown at B, Fig. 2183, and if it is
moved in a straight line in the direction of the length of the work,
then its shape would necessarily be that shown at B, Fig. 2184, or
merely the reverse of A. In the position mentioned it could be used only
as a sweep applicable to some few uses, but not adapted to cutting. To
become a cutting tool it must be inclined and stand at some angle of
less than 90° to its line of motion.
[Illustration: Fig. 2184.]
[Illustration: Fig. 2185.]
Thus in Fig. 2185 D B E represents the bottom of the moulding and line
of motion of the cutter, and A B the cutter perpendicular to it, the
highest point of the cutting edge, as _c_ of Fig. 2184, being at _c_,
Fig. 2185. The height or thickness of the moulding cut would be the
space between the lines E B D and _e_ _c_ _f_, but the cutter assuming
the position B C at an angle of 30° from A B, the point _c_ is brought
to _d_; consequently the highest line of the moulding would now be _g_
_d_ _h_, and its thickness less. This is further exhibited in Fig. 2186,
where _a_ represents the original depth section of Fig. 2184 that would
be formed by knife B of Fig. 2184 when standing perpendicular; and G
shows the depth with the same knife when placed as B C, Fig. 2185, or at
30° inclination, and H shows the depth that would be cut with the same
knife or cutter at 45°. It is now evident that every change in the
inclination of the same cutter would effect a change in the shape of
moulding which it cuts, and to produce a given style of moulding the
shape of the cutter must be decided by its inclination, or the angle at
which it is used.
[Illustration: Fig. 2186.]
[Illustration: Fig. 2187.]
The method of projecting a given section of moulding in order to exhibit
the form that the curve of the opening should assume on the face of the
knife, is shown in Fig. 2187. Upon a horizontal line A B C D draw a
section of the required style of moulding, as shown at A E B. To the
right of this draw a line, as F C, to meet the base line A B C D, and as
F C represents the cutter, it must stand at the same angle that the
proposed cutter is to have--in this particular example 30° from the
perpendicular. From the highest point of the section A E B draw a
horizontal line E G, meeting F C in G. From points G and C draw lines,
as C J and G H, of any convenient length, at right angles to F C. At any
distance from G H draw K L parallel to G H, and upon K L trace the
section of moulding A E B, as K M L. Draw lines from the extreme edges K
and L of K M L, as K N, L J, perpendicular to K L, cutting G H and
meeting C J at N and J. E G being parallel to A B C D, G will be the
point on the cutter where the top E of the moulding will come on the
highest point of the cutting edge, and C G will be the entire length of
cutting edge or height of opening measured on the face of the cutter F
C. C J being drawn from the lowest point C of the cutter and G H being
drawn from G, the highest cutting point, both lines at right angles to G
C, then their distance from each other, as P O, must obviously represent
the extreme height of opening in the cutter in its new position or front
view, and K L, representing the width of moulding transferred to N J by
the parallel lines K N and L J, will show the width of opening in the
cutter. Having now the height and width, it only remains to project an
indefinite number of points and trace the curve through them. Divide A B
into a number of parts, and to avoid confusion mark the points of
division thus obtained upon A B--1, 2, 3, 4, &c. Divide K L in an
exactly similar manner and into the same number of parts, and mark the
divisions I., II., III., IV., &c. Erect perpendiculars from points 1, 2,
3, 4, &c., meeting the curve A E B, and from the points thus found on A
E B draw horizontal lines to F C; from the termini of these horizontals
on F C draw the remaining lines parallel to and between G H and C J.
From the divisions _i._, _ii._, _iii._, _iv._, &c., on K L, let drop the
perpendiculars, cutting the other series of lines at right angles. A
point of the curve will then be at the intersection of the line from 1
on A B, with line I on K L; another at the intersection of the line
originating at 2 with that from II, and so on, and the proper curve is
found by tracing from N through the intersections to P, and from P to J.
Then K N being one side of the cutter and L J the other, N P J is the
curve that the opening or cutting edges must have to cut the profile A E
B, with the cutter set at F C, or 30°.
[Illustration: Fig. 2188.]
The same method is shown in Fig. 2188, except that in this case, instead
of dividing A B and K L, the divisions are made directly on the
peripheries A 6 B and K VI. L by stepping round with the dividers. The
cutter F C is shown in this case at an angle of 45°, in order that the
change in form which the curve assumes with the cutter at different
angles may be clearly seen by comparing the curve N P J of Fig. 2187
with the same in Fig. 2188. The two figures are similar in other
respects, and as the lettering is the same on each, the description of
Fig. 2187 will apply equally to Fig. 2188.
[Illustration: Fig. 2189.]
There remains one more case of cutters moving in right lines, and that
is where, besides having an inclination backward, as at F C, Fig. 2187,
making a vertical angle to the line of motion, they are placed at an
angle across the guiding piece also, or "skewing," thus making an angle
to the line of motion on a horizontal plane as well as on a vertical
one. Thus, suppose an ordinary carpenter's plane to have the cutter or
"iron" turned partly round and placed so that the cutting edge, instead
of lying at a right angle across the body, crosses it at some other
angle. Fig. 2189 represents an ordinary carpenter's plane with the blade
so placed. Here the edge, or rather side, D B, of the blade inclines
back at an angle, as A B D, which is 45° in this case, to the
perpendicular line A B on the side of the plane. For convenience call A
B D the vertical angle. The lower or cutting edge E B of the blade also
crosses the bottom of the plane at an angle E B C--30° in this
instance--to a line B C, crossing the bottom at right angles. Now, it is
evident that this latter angle E B C will influence the form of the
cutter, if, instead of being a flat plane, as represented for clearness
in Fig. 2189, it had a cutting edge of curved outline for cutting
mouldings or similar work. But in either case the angle that D B or one
side of the blade makes to E B, or the cutting edge--that is, the angle
D B E--must be found in order to cut off the blank for the cutter or
knife at the right "slant."
[Illustration: Fig. 2190.]
The method given in Figs. 2187 and 2188 of determining the form of
cutter to produce a moulding of given profile now undergoes a
modification where there are two angles to be taken into consideration
instead of one. As an example, suppose a cutter is required that is to
be fixed in such a position in its carrier or block that the handle A B
D, or "vertical angle," of Fig. 2189 is, say, 45°, and the angle E B C,
or "horizontal angle," of Fig. 2189 shall be 30°. Required the angle at
which the bottom of the blank for the cutter must be cut off; or the
angle that the side D B and lower edge B E of Fig. 2189 would make to
each other, measured on the face of the cutter, and required the outline
of cutting edge to be traced on the face of cutter to cut the section of
moulding A E B, Fig. 2190: draw a horizontal line, as A B C D, and erect
a perpendicular, as C R. From C draw C F, making an angle to C R equal
to the "vertical angle," or angle A B D, Fig. 2189, which is 45° in this
case. Draw a profile of the required moulding, as A E B, with its back A
B coincident to the horizontal line A B C D. Draw a horizontal line from
the highest point of the profile, as E, to meet F C in G. Draw parallel
lines C J and G H, from C and G respectively, of any convenient length
and making right angles to F C. At right angles to G H and C J, and
parallel to F C, draw K H J to represent one side or edge of the cutter,
but the angle of the lower end or angle D B E of Fig. 2189 must now be
determined; to do this, draw an indefinite horizontal line, A B C, Fig.
2191, and from any point, as B, drop a perpendicular B D; now, from B
set off on A B C the distance C _b_ of Fig. 2190, obtaining point E, and
from E extend a perpendicular above and below A B C, as F E H. From E on
E F set off distance G _b_ of Fig. 2190, obtaining J on E F. From B draw
a line, making the same angle to B D that the angle E B C is in Fig.
2189, or 30° in this case, and cutting E H in K. Set off distance E K
from E on A C, obtaining L; draw L J. Now, on Fig. 2190, with centre at
H, and radius L J of Fig. 2191, describe arc _w_ _x_, and from J as
centre, on Fig. 2190, and B K of Fig. 2191 as radius, describe arc _y_
_z_. Through the intersection _v_ of arcs _y_ _z_ and _w_ _x_, J L M
must be drawn, making the proper angle to the side J H K of the cutter;
this angle is 69° in this case, as found by construction. From H draw H
N parallel to J L, and from H draw H O at the same angle to H N that B K
is to B D, Fig. 2191, or angle E B C, Fig. 2189. Place a duplicate of A
E B, with its base coincident to H O and corner A at H, as H P R. From R
draw R N at right angles to H R and cutting H N at N; through N draw S N
L parallel to K H J. Then while K H J represents one edge of the cutter,
S N L will be the other, and J L the cutting edge before the opening is
cut out. Divide the curves E B and P R similarly, obtaining points 1, 2,
3, &c., and I., II., III., &c., respectively. From points 1, 2, 3, &c.,
lines are to be drawn parallel to E G, meeting G C, continued from G C
parallel to G H, and meeting H J, and from H J parallel to H N, meeting
N L. From points I., II., III., &c., lines are to be drawn perpendicular
to H R, meeting H N and continued from H N, parallel to H J, to J L,
thus intersecting the first series. Lines from points 1, 2, 3, &c., then
determine the height of different points of the curve, and those from
I., II., III., &c., their location laterally; hence, by tracing through
the intersections of 1 with I., 2 with II., &c., the curve H T L is
obtained. The two outside lines K H J and S N L may now represent the
edges of a piece of steel of which the cutter is to be made, and H T L
will be the contour of cutting edge that must be given it in order that
when, fixed for use at the angles named, it will form the required
moulding A E B.
[Illustration: Fig. 2191.]
[Illustration: Fig. 2192.]
If the chisel, knife, or cutter revolves in a circle, instead of in a
right or straight line, the problem is again different, and the shape of
cutting edge necessary to produce a given shape of moulding is again
altered. Let Fig. 2192, for example, represent the bar or head of a wood
moulding machine, the bar or head revolving in the direction of the
arrow, and the moulding being moved beneath it in a straight line
endways as denoted by the arrow at N.
In order that the nut that holds the cutter to the head may clear the
top of the moulding the highest cutting point of the cutter must not
come nearer to the corner of the head than 1/4 inch. This is shown in
the end view of a 2-1/2 inch cutter head in Fig. 2193, the circle B
representing the path of revolution of the nut. In larger heads the nut
will clear better.
Now we may consider that the cutter simply revolves about a circle whose
diameter is the largest that can be described on the end of the square
bar that drives it.
If, for instance, we look at the end of the bar as it is presented in
Fig. 2195, we see that the circle just fills the square, and that if we
cut off all four corners, leaving the bar round, as denoted by the
circle, the chisel will revolve in the same path as before. Now suppose
we place beneath the revolving chisel a piece of square timber, and
raise this timber while holding it horizontally, as would be done by
raising the work table. It will cut the work to the shape shown in the
two views in the figure, enabling us to observe the important point that
the only part of the work that the chisel has cut to its finished shape
is that which lies on the line A A. This line passes through the axis on
which the bar and cutter revolve, and represents the line of motion of
the work in feeding upward to the chisel.
If now we were to move the work endways upon the table, we should simply
cause the moulding to be finished to shape as it passes the line A;
because all the cutting is done before and up to the time that the
chisel edge reaches this line; or in other words, each part of the
chisel edge begins to cut as soon as it meets the moulding, and ceases
to cut as soon as it reaches this line. We may now draw this circle and
put on it a chisel in two positions, one at the time its lowest cutting
point is crossing the line A and the other at the time the highest point
on its cutting edge is passing the line, these positions being marked 1
and 2 in Fig. 2196; the depth of moulding to be cut being shown at S.
Now, since the chisel revolves on the centre of the circle, the path of
motion on its highest cutting point C will be as shown by the circle B,
and that of the lowest point or end E of its cutting edge will be that
of the circle D, while the depth of moulding it will cut is the distance
between C and E, measured along the line A A, this depth corresponding
to depth shown at S.
[Illustration: Fig. 2193.]
[Illustration: Fig. 2194.]
Clearly when the chisel has arrived at position 2, the moulding will be
finished to shape, and it is therefore plain that it takes a length of
cutter-edge from C to F to cut a moulding whose depth is S, or what is
the same thing, C E.
But to solve the question in this way, we require for every different
depth of moulding to make such a sketch, and the square bar that drives
the chisel is made in various sizes, each different size again altering
the length or depth of chisel edge necessary for a given depth of
moulding.
[Illustration: Fig. 2195.]
[Illustration: Fig. 2196.]
But we may carry the solution forward to the greatest simplicity for
each size of square bar, and for any depth of moulding that can be
dressed on that size of bar, by the following means:--In Fig. 2197 we
have the circle and the line A as before; the depth from C to E being
the greatest depth of moulding to which the square bar is intended to
drive the chisels; while point C is the nearest point to the square bar
at which the top of the moulding must be placed. Line _a_ represents a
chisel cutting at its highest point; line _b_ a chisel cutting the
moulding to final shape at 1/4 inch below C, on the line A; line _c_ a
chisel cutting the moulding to final shape at a distance of 1/2 inch
below point C and measured on the line A; lines _d_, _e_, _f_, _g_, _h_,
and _i_ represent similar chisel positions, the last meeting the point
E, which is the lowest point at which the chisel will cut. Suppose, now,
we set a pair of compasses one point at the centre A of the circle, and
strike the arc _j_; this arc will represent the path of motion of that
part of the chisel edge that would finish the moulding to shape at C;
similarly arc _k_ represents the path of motion of that part of the
chisel edge that cuts the moulding to final shape on the line A, and at
a distance of 1/4 inch below C, and so on until we come to arc _r_,
which represents the path of motion of the end of the chisel. All these
arcs are carried to meet the first chisel position C _a_, and from these
points of intersection with this line C _a_ we mark lines representing
those on a common measuring rule. The first of these from C we mark 1/4,
the next 1/2, the next 3/4, and so on to 2, these denoting the
measurement or depth of chisel necessary to cut the corresponding depth
of moulding. If, for example, we are asked to set a pair of compasses to
the depth of cutting edge necessary to cut a moulding that is an inch
deep, all we do is to set one leg of the compasses at C, and the other
at line 1 on the line C _a_; or if the moulding is to be 2 inches deep,
we set the compasses from C to 2 on line C _a_. We have here, in fact,
constructed a graduated scale that is destined to be found among the
tools of every workman who forms moulding cutters, and if we examine it
we shall find that the line that is marked 1/4 inch from C is not 1/4
inch but about 5/16 inch; its distance from C being the depth of chisel
edge necessary to cut a moulding that is 1/4 inch deep.
[Illustration: Fig. 2197.]
Again, the line marked 1 measures 1-3/16 inch from C, because it
requires a chisel edge 1-3/16 deep to cut a moulding that is one inch
deep. But if we measure from _c_ to the line marked 2 we find that it is
2-1/4 inches from C, and since it represents a chisel that will cut a
moulding two inches deep, we observe that the deeper the moulding is the
nearer the depth of cutting edge is to the depth of moulding it will
produce. This occurs because the longer the chisel the more nearly it
stands parallel to the line A, at the time when its point is crossing
the line A. Thus, line _i_ is more nearly parallel to A than line _a_
is, and our scale has taken this into account, for it has no two lines
equally spaced; thus, while that marked 1/4 is 5/16 inch distant from C,
that marked 1/2 is less than 5/16 inch distant from that marked 1/4, and
this continues so that the line marked 2 is but very little more than
1/4 inch from that marked 1-3/4. Having constructed such a scale we may
rub out the circle, the arcs, the line A, and all the lines except the
line from C to _a_ and its graduations, and we have a permanent scale
for any kind of moulding that can be brought to us.
If, for example, the moulding has the four steps or members _s_, _t_,
_u_, _v_, in the figure, each 1/2 inch deep, then we get the depth of
cutter edge for the first member _s_ on our scale, by measuring from _c_
to the line 1/2 on line C _a_. Now the next member _t_ extends from 1/2
to 1 on the moulding, and we get length of cutter edge necessary to
produce it from 1/2 to 1 on the scale. Member _u_ on the moulding
extends from 1 to 1-3/4; that is to say, its highest point is 1 inch and
its lowest 1-3/4 inch from the top of the moulding, and we get the
length for this member on a scale from the 1 to the 1-3/4; and so on for
any number of members.
After the depth of cutting edge for each member has thus been found, it
remains to find the exact curve of cutting edge for each step, and, in
doing this, the same scale may be used, saving much labor in this part
also of the process, especially where a new piece of moulding must be
inserted to repair part of an old piece that needs renewal in places
only, as is often the case in railroad cars.
In Fig. 2197A we have a scale or rule constructed upon the foregoing
principles, but marked to sixteenths, and it may now be shown that the
same scale may be used in finding the actual curve as well as the depth
of cutter edge necessary to produce the moulding of any member of it.
Let the lower curves _s_, _t_, for example, represent the moulding to be
produced, and the upper outline represent the blank piece of steel of
which the cutter is to be made, the edges C, D being placed in line one
with the other. We may then draw across both the moulding and the steel,
lines such as E E, F F, G G, H H, I I, J J, all these lines being
parallel to the edges C, D. To get the total depth of cutter edge for
the moulding we measure with a common measuring rule the total height of
the moulding, and supposing it to measure an inch, we set a pair of
compasses to an inch on our cutter scale, and with them mark from the
base _m_ of the steel, the line P giving total depth of cutter edge. We
next measure with a common rule the depth of member _s_ of the moulding,
and as it measures 1/2 inch we set the compasses to the 1/2 on the
cutter scale, and with these compasses mark from line _m_ line B,
showing the depth of member _s_. In order to find the exact curve for
each member, we have first to find a number of points in the curve and
then mark in the curve by hand, and it is for the purpose of finding
these points that the lines E E, F F, G G, H H, I I, J J, have been
drawn. These lines, it may be remembered, need not be equally spaced,
but they must be parallel, and as many of them may be used as
convenient, because the greater their number the more correctly the
curve can be drawn.
[Illustration: Fig. 2197A.]
[Illustration: Fig. 2198.]
[Illustration: Fig. 2199.]
The upper edge or base line, _m_ _m_, both of the steel and of the
drawing, is that from which all measurements are to be taken in finding
the points in the curve, which is done as follows: With an ordinary
measuring rule we measure on the moulding and from line _m_ _m_ of the
moulding as a base the length of the line F F below _m_ _m_, to the
curve, which in this case measures say 5/16 inch; we then set a pair of
compasses or compass calipers to the 5/16 on the cutter scale, and from
base _m_ _m_ on the cutter steel, mark, on line F F, an arc, and where
the arc cuts F F is one point in the curve.
Similarly we measure on the moulding, or drawing of the moulding, the
length of line G G from line _m_ _m_ to the moulding curve, and find
that it measures, say 7/16 inch, hence we mark from base line _m_ _m_ of
the steel, on line G G, arc V, distant 7/16 according to the cutter
scale. Similar measurements are taken at each vertical line of the
drawing which represents the moulding, and by means of the corresponding
divisions of the cutter scale, arcs are marked on the vertical lines on
the cutter steel, and where the arcs cut the vertical lines are points
in the curve, and through these points the curve may be drawn by hand.
We may make a cutter scale from an ordinary parallel rule, marking one
end to correct inches and the other end for a cutter scale. Measurements
from the moulding may then be made on one end of the rule; measurements
for the cutter may be taken from the other end of the rule, and the rule
may be used at the same time to draw the parallel lines E E, &c. Or, as
each size of cutter head requires a different cutter scale, we may make
a rule out of a piece of box or other close-grained wood, say 3/4 inch
square, using one side for each size of cutter head. One end of each
face of this rule may be marked in correct inches and parts of an inch
(the divisions being thirty-seconds of an inch), and the other end may
be marked as a cutter scale, the divisions being found as described with
reference to Fig. 2197.
An instrument, patented by R. Drummond, for finding the depth of cutting
edge and also for finding the curves, is shown in Figs. 2198 and 2199.
It consists essentially of a bar G bent at a right angle, thus making
two arms. Upon one arm is a slide W (best seen in Fig. 2199) secured by
a set-screw B, and having at A a pivot to carry a second bar H, which is
slotted throughout its length to permit bar G to slide freely through
it. Upon the other arm of G is a slide P secured by a set-screw C, and
carrying a compass point E. The bar H carries an adjustable slide Z
secured by a set-screw D and carrying the compass point F.
[Illustration: Fig. 2200.]
In using the instrument but three very simple operations are necessary.
First, the two slides W and P are set to the numerals on the bar, which
correspond to the size of the head on the moulding machine the cutter is
to be used upon; thus in Fig. 2199 they are shown set to numeral 2, as
they would be for a 2-inch cutter head. The instrument is next opened,
its two bars occupying the position shown in Fig. 2199, and the two
compass points are set to the height of the moulding or to any desired
member of it, as the case may be. The bars are then opened out into the
position shown in Fig. 2200, and the compass points at once give the
depth of cutter edge necessary to produce the required depth of
moulding.
It will be noted that the pivot A represents the centre upon which the
cutter revolves, and that while the face of the bar H corresponds to the
line of moulding formation answering to line A A in Fig. 2196, the face
of bar G corresponds to the face C F of the cutter in Fig. 2196; hence
the instrument simply represents a skeleton head and cutter, having
motions corresponding to those of an actual cutter head and cutter.
[Illustration: Fig. 2201.]
[Illustration: Fig. 2202.]
THE FILE.--The file is a piece of hardened steel having teeth produced
upon its surface by means of rows of chisel cuts which run more or less
diagonally across its width at an angle that is varied to suit the
nature of the material the file is to be used upon. The vertical
inclination of the tooth depends upon the inclination of the face of the
chisel with which it is cut, the two being equal, as is shown in Fig.
2201, which is an enlarged view of a chisel and some file teeth. In
order that the tops of the teeth shall be sharp, and not rounded or
curved, as in Fig. 2202, it is necessary that the edge of the chisel be
kept sharp, an end that is greatly aided by the improved form of chisel
shown in Fig. 2203. When a file possesses curved points, or caps, as
they are technically termed, a few strokes upon a narrow surface will
cause them to break off, reducing the depth of the teeth and causing the
cuttings to clog in them. If, however, the file is used upon a broad
surface these caps will remain, obviously impairing the cutting
qualifications of the file, even when new, and as they soon get dulled
the file loses its grip upon the work and becomes comparatively
valueless.
[Illustration: Fig. 2203.]
Files were, until the past few years, cut entirely by hand--file cutting
by machinery having previously been a wide field of mechanical
experiment and failure. Among the most prominent causes of failure was
that the teeth produced by the earlier machines were cut too regular,
both as to their spacing and their height; hence the points of the rear
teeth fell into the same channels as those in advance of them, thus
giving the tooth points too little opportunity to grip the work. This
also gives too broad a length of cutting edge and causes the file to
vibrate on the forward or cutting stroke, an action that is technically
known as chattering, and that obviously impairs its cutting capacity.
The greatest amount of duty is obtained from a file when the rear tooth
cuts off the projection left by the preceding one, because in that case
the duty of the tooth is confined to cutting off a projection that is
already weakened and partly separated from the main body by having the
metal cut away around its base. Workmen always practically recognise
this fact, and cause the file marks to cross each other after every few
strokes. In the machine-cut files made by The Nicholson File Co., the
teeth are arranged to attain this object by the following means:--1. The
rows of teeth are spaced progressively wider apart from the point
towards the middle of the file length by regular increments of spacing,
and progressively narrower from the middle toward the heel. 2. This
general law of the spacing is modified by introducing as the teeth are
cut an element of controllable irregularity in the spacing, which
irregularity is confined within certain limits, so that neither the
increment nor decrement of spacing is entirely regular. 3. In arranging
the teeth so that the successive rows shall not be exactly parallel one
to the other, the angle of inclination being reversed as necessity
requires. The irregularity of spacing, while sufficient to accomplish
the intended object, is not enough to practically vary the cut of the
file, or, in other words, it is insufficient to vary its degree of
coarseness or fineness to any observable extent. But it enables the file
to grip the work with as little pressure as possible, and enables the
teeth to cut easily without producing deep file marks or furrows.
Files and rasps have three distinguishing features: 1. Their length,
which is always measured exclusively of their tangs. 2. Their cut, which
relates not only to the character, but also to the relative degree of
coarseness of the teeth. 3. Their kind or name, which has reference to
the shape or style. In general, the length of files bears no fixed
proportion to either their width or thickness, even though of the same
kind. The tang is the spiked-shaped portion of the file prepared for the
reception of a handle, and in size and shape should always be
proportioned to the size of the file and to the work to be performed.
The heel is that part of the file to which the tang is affixed.
Of the cut of files we may say that it consists of three distinct forms;
viz.: "single cut," "double cut" and "rasp," which have different
degrees of coarseness, designated by terms as follows viz.:--
Single-cut. Double-cut. Rasp.
Rough Coarse Coarse
Coarse Bastard Bastard
Bastard Second-cut Second-cut
Second-cut Smooth Smooth
Smooth Dead-smooth
[Illustration: Fig. 2204.]
The terms "rough," "coarse," "bastard," "second-cut," "smooth" and
"dead-smooth," have reference only to the coarseness of the teeth, while
the terms "single-cut," "double-cut" and "rasp" have special reference
to the character of the teeth. The single-cut files (the coarser grades
of which are sometimes called "floats") are those in which the teeth are
unbroken, the blanks having had a single course of chisel-cuts across
their surface, arranged parallel to each other, but with a horizontal
obliquity to the central line, varying from 5° to 20° in different
files, according to requirements. Its several gradations of coarseness
are designated by the terms "rough," "coarse," "bastard," "second-cut"
and "smooth." The rough and coarse are adapted to files used upon soft
metals, as lead, pewter, &c., and, to some extent, upon wood. The
bastard and second-cut are applied principally upon files used to
sharpen the thin edges of saw teeth, which from their nature are very
destructive to the delicate points of double-cut files. The smooth is
seldom applied upon other than the round files and the backs of the
half-rounds. Fig. 2204 represents the cut of single-cut rough files,
their lengths ranging from 16 inches down to 4 inches. Fig. 2205 shows
the cut of the coarse, bastard, and second-cut, whose lengths also range
from 16 to 4 inches, and whose cut is also finer as the length
decreases. The float is used to some extent upon bone, horn, and ivory,
but principally by plumbers and workers in lead, pewter, and similar
soft metals. It will be seen that the teeth are nearly straight across
the file and are very open, both of these features being essential
requirements for files to be used on the above-named metals.
Double-cut files are those having two courses of chisel cuts crossing
each other. The first course is called the over cut, and has a
horizontal obliquity with the central line of the file, ranging from 35°
to 55°. The second course, which crosses the first, and in most double
cuts is finer, is called the up-cut, and has a horizontal obliquity
varying from 5° to 15°. These two courses fill the surface of the file
with teeth inclined toward its point, the points of which resemble
somewhat, when magnified, those of the diamond-shaped cutting tools in
general use. This form of cut is made in several gradations of
coarseness, which are designated by the terms "coarse," "bastard,"
"second-cut," "smooth" and "dead-smooth." Fig. 2206 represents the cut
of double-cut bastard files, from the 16 inch down to the 4 inch, and
Fig. 2207 the cut of the coarse, second-cut, and smooth. For very fine
finishing a still finer cut, called the dead-smooth, is made, being like
the smooth, but considerably finer. It is a superior file for finishing
work in the lathe, or for draw-filing machine work that is to be highly
finished. The double-cut is applied to most of the files used by the
machinist, and, in fact, to most of the larger number in general use.
For unusually fine work, tool-makers and watch-makers use the Swiss or
Groubet files--so called from their being made by M. Groubet, of
Switzerland. These files are double-cut, and their degree of coarseness
is denoted by number; thus, the coarsest is a bastard and the finest
number 8. The prominent characteristics of these files are their
exceedingly even curvature and straightness, and, in the finer grades,
the unusual fineness of the cut, which feels soft and velvety to the
touch. They are made in sizes ranging from 2 to 10 inches, and are
always double-cut.
[Illustration: Fig. 2205.]
[Illustration: Fig. 2206.]
[Illustration: Fig. 2207.]
Rasps differ from the single or double-cut files in that the teeth are
disconnected from each other, each tooth being made by a single-pointed
tool, denominated by file-makers a punch, the essential requirement
being that the teeth thus formed shall be so irregularly intermingled
as to produce, when put in use, the smoothest possible work consistent
with the number of teeth contained in the surface of the rasp. Rasps,
like files, have different degrees of coarseness, designated as
"coarse," "bastard," "second-cut" and "smooth." The character and
general coarseness of these cuts, as found in the different sizes, are
shown in Figs. 2208 and 2209. Generally speaking, the coarse teeth are
applied to rasps used by horseshoers, the bastard to those used by
carriage makers and wheelwrights, the second-cut to shoe-rasps, and the
smooth to the rasps used by cabinet-makers.
[Illustration: Fig. 2208.]
[Illustration: Fig. 2209.]
[Illustration: Fig. 2210.]
[Illustration: Fig. 2211.]
[Illustration: Fig. 2212.]
Figs. 2210, 2211 and 2212 are respectively coarse, bastard, and
finishing second-cut files, the first two being for brass.
Fig. 2210 represents a file open in both its over and up-cut, which is
not, therefore, expected to file fine, but fast, and is adapted for very
rough work on the softer metals, as in filing off sprues from brass and
bronze castings, filing the ends of rods, and work of a similar nature.
It is also, to some extent, used upon wood. The essential difference
between the bastard file shown in Fig. 2211 and that just described is
the degree of fineness of the up-cut, which is nearly straight across
the tool. This form of teeth, which may be applied to any of the finer
cuts, and upon any of the shapes usually made double-cut, is especially
adapted to finishing brass, bronze, copper and similar soft metals, and
is not so well adapted to the rougher work upon these metals as the
coarse brass file previously described. Fig. 2212 is a finishing file.
The first or over-cut in this case is very fine, and, contrary to the
general rule, has the least obliquity, while the up-cut has an unusual
obliquity, and is the coarser of the two cuts. The advantages in this
arrangement of the teeth are that the file will finish finer, and by
freeing itself from the filings is less liable to clog or pin than files
cut for general use. This form of cut is especially useful when a
considerable quantity of finishing of a light nature is required upon
steel or iron. It is not recommended for brass or the softer metals, nor
should it be made of a coarser grade than the second-cut.
The names of files are sometimes derived from the purpose for which they
are to be used. Thus, we have saw files, slitting files, warding files,
and cotter files. The term "warding" implies that the file is suitable
for use on the wards of keys, while "cotter" implies that it is suitable
for filing the slots for that class of key which the machinist terms a
cotter. In other cases files are named from their sections, as in the
case of "square," "round," "half-round," and "triangular," or
"three-square" files, as they are often termed.
The term "flat" may be considered strictly as meaning any file of
rectangular section whose width exceeds the thickness. Hence, "mill
files," "hand files," and "pillar files" all come under the head of flat
files, although each has its own distinguishing features. The general
form of the flat file is shown in Fig. 2213, while the cross-sections of
various quadrangular files are shown in Figs. from 2214 to 2218. From
these views it will be seen that the thicknesses gradually increase from
the mill to the square file. Mill files are slightly tapered from the
middle to the point both in their width and thickness. They are
single-cut, and are usually either bastard or second-cut, although they
are sometimes double-cut. Mill files of both cuts are principally used
for sharpening mill saws, mowing-machine knives and ploughs, and in some
machine shops for rough lathe work, and, to some extent, in finishing
composition brasswork. Mill sections are occasionally made blunt--that
is to say, their sectional shape is alike from end to end--in which case
they are mostly double-cut, and seldom less than 8 inches in length.
They are suitable for filing out keyways, mortises, &c., and for these
purposes should have at least one safe edge. A safe edge is one having
no teeth upon it, which allows the file to be used in a corner without
cutting more than one of the work surfaces. When the corner requires to
be very sharp it is preferable to take a file that has teeth upon its
edge and grind the teeth off, so as to bring the corner of the file up
sharp, which it will not be from the cutting, because the teeth do not
come fully up to a sharp corner.
[Illustration: Fig. 2213.]
[Illustration: Fig. 2214.]
[Illustration: Fig. 2215.]
[Illustration: Fig. 2216.]
[Illustration: Fig. 2217.]
Hand-files are tapered in thickness from their middle towards both the
point and the tang, and are, therefore, well curved or bellied on each
side. This fits them for the most accurate of work, on which account
they are generally preferred by expert workmen. They are nearly parallel
in width and have one safe edge and one edge cut single, while the face
is cut double. Hand-files are also made equaling, the term equaling
meaning that, although apparently blunt or of even thickness throughout
the length, yet, in fact, there is a slight curvature, due to the file
being thickest in the middle of its length. An equaling hand-file is
especially suitable for such purposes as filing out long keyways, in
which a great part of the file length is in action, and it can,
therefore, be easily pushed in a straight line.
The flat file, Fig. 2213, when 10 inches and under in length, is made
taper on both its sides and edges, from the middle to the front of the
file, and when longer than 10 inches they should be made full
taper--that is to say, the taper should extend from the middle toward
the heel, as well as toward the point. Flat files are usually
double-cut, the coarse-cut being used upon leather, wood, and the soft
metals. The flat bastard is that most commonly used, the flat
second-cut, smooth, and dead-smooth being used by machinists for
finishing purposes, the latter preceding the polishing processes.
Pillar files are tapered in thickness from the middle to each end; the
width is nearly parallel, and one of the edges is left safe. They are
double-cut, and, although not in general use, are especially adapted to
narrow work, such as in making rifles, locks, &c. The square file
ranges from 3 to 16 inches in length, and is made for general purposes
with considerable taper. It is usually double-cut, the bastard being the
principal cut, the second-cut and smooth being mainly used by the
machinist.
Square blunt files range from 10 to 20 inches in length, of the same
sectional sizes as the square taper, and are cut double, usually
bastard. For machinists' use, however, they are used in the second-cut
also, and are provided with sometimes one and sometimes two safe sides.
Square equalling files are in every respect like the square blunt,
except in the care taken to prepare a slight curve or belly in the
length of the file, which greatly enhances their value in filing out the
edges of keyways, splines, or mortises. The fault of the square blunt,
when used for fine, or true work, is that the heel, having no belly, is
apt to come into too prominent action.
[Illustration: Fig. 2218.]
Warding files, Fig. 2218, are made parallel in thickness, but are
considerably tapered on their edges. They range in size from 3 to 8
inches in length, progressing by half-inches in the sizes below 6
inches. They are cut double, and usually on both edges, and are mainly
used by locksmiths and jewellers, and to but a limited extent by
machinists. Some of the warding files are provided with teeth upon their
edges only, which are made quite rounding, the cut usually being
second-cut, single.
[Illustration: Fig. 2219.]
[Illustration: Fig. 2220.]
[Illustration: Fig. 2221.]
Files deriving their sections from the circle are shown from Figs. 2219
to 2222. "Round files" are circular in section, as shown in Fig. 2219,
their lengths ranging from 2 to 16 inches, and are usually of
considerable taper. The small bastards are mostly single-cut and the
larger sizes double-cut. The second-cuts and smooths are rarely
double-cut, except in some of the very large sizes. In imitation of
double-cut, however, they are sometimes made with the first, or overcut,
very open, called "hopped," which adds, however, but very little to the
cutting capacity of the file. The very small sizes--as, say, those of
one-quarter inch and less in diameter--are often called "rat-tailed"
files. For some classes of work--as for instance, the circular edges of
deep keyways--round, blunt files are used, their sizes running up to 18
and 20 inches, their principal cut being bastard and double.
The gulleting file is a round, blunt saw file, and, like most other
files for this purpose, is single-cut (except for a small space at the
point, which is left uncut). Its principal use is for extending the
gullet of what are known as gullet-tooth and briar-toothed saws.
Half-round files are of the cross-section shown in Fig. 2220, and
although their name implies a semicircle, yet, as generally made, their
curvature does not exceed the third part of a circle. They are made
taper; the bastard is usually double cut on both its sides; the
second-cut and smooth is double-cut on their flat sides, and single-cut
on the curve side, except occasionally in the larger sizes, when it is
double-cut or hopped. Half-round files for wood usually range in size
from 10 to 14 inches, and are of the same shape and taper as the regular
half-rounds. They are cut coarse and double, and are used by
wood-workers generally. Half-round rasps are also like the regular
half-round in shape, the sizes usually called for being 10, 12, and
14-inch. They are used principally by wheelwrights and carriage
builders, but are to some extent used by plumbers and marble workers.
[Illustration: Fig. 2222.]
Cabinet files are of the section shown in Fig. 2222, being both wider
and thinner than the half-rounds, the sectional curvature being somewhat
less than the fifth part of a circle. They are made taper from near the
middle to the point, while both the files and the rasps are made from 6
to 14 inches in length; 8, 10, and 12 inches are the sizes in most
common use. As usually known, the cabinet file is a bastard double-cut.
The cabinet rasp is punched smooth, and both the cabinet rasp and file
are rarely made of any other degree of coarseness. They are used by
cabinet, saddle-tree, pattern, and shoe-last makers, and also by
gunstockers and wood-workers generally.
[Illustration: Fig. 2223.]
Three-square files are made with equilateral triangular sections, as in
Fig. 2223. They are tapered to a small point with considerable curve,
and are double-cut. The larger sizes--say, from 10 to 14 inches--are
usually bastard, and are used to a considerable extent in rolling mills.
The smaller sizes are not unfrequently smooth or dead-smooth, and are
used in machine shops quite generally for filing interval angles more
acute than the rectangle, clearing out square corners, sharpening
cutters, &c. Three-square blued files of sizes from 3 to 6 inches are
sometimes made. They are mostly second-cut, or smooth and double-cut,
and are principally used in machine shops for filing up cutters for
working metals.
[Illustration: Fig. 2224.]
[Illustration: Fig. 2225.]
Cant files, whose cross-sections are shown in Fig. 2224, are usually
made blunt and double-cut, mostly bastard, on all three sides. These
sizes are usually 6, 8, and 10 inches. Lightning files are of the
cross-section shown in Fig. 2225, the term lightning being known
principally by those using the saws of this name, and to some extent by
those using other cross-cut, [M]-shaped saw teeth. The obtuse angle of
this file is five-canted, while the regular cant is hexagon or
six-canted, and it is found to be too obtuse for the purposes required
of the saw file. They are made blunt, and range in length from 4 to 12
inches, and are cut (except for a short space near the point) single on
their three sides.
[Illustration: Fig. 2226.]
[Illustration: Fig. 2227.]
[Illustration: Fig. 2228.]
Knife files are of the section shown in Fig. 2226, and rarely exceed 10
inches in length, the principal sizes being 4, 5, and 6-inch. They are
tapered, resembling somewhat the blade of a knife, and are cut double.
The very acute angle of the sides of this file makes it especially
useful in filing the inner angles of the rear and main springs of a
rifle lock and work of similar shape. These files are also made blunt.
Cross files (sometimes called double half-round or crossing files) are
of the section shown in Fig. 2227. They are mostly made to order, either
blunt or tapered, and usually double-cut. "Feather-edge" files (Fig.
2227) are but little used by the mechanics of this day. They were
formerly used in filing feather springs (as the rear spring of a gun
lock is sometimes called), and also the niches in currycombs, which led
them to be called by some currycomb files. The few files of this kind
which are now made are usually blunt and double-cut. Half-round "shoe
rasps" as generally made are of the cross-section shown in Fig. 2228,
their sizes ranging from 6 to 12 inches, while 8, 9, and 10 inch are the
most common. They are made parallel in width, but with their sides
slightly tapered from the middle; the ends are rounded and cut single;
the edges are safe or uncut, or if cut are usually made half-file and
half-rasp reversed (1/4 rasp and 3/4 file, while sometimes made, are the
exception). The file quarters are bastard double-cut, and the rasp
quarters second-cut. This form of shoe rasp is the one in general use at
this time, having almost entirely superseded the flat and swaged rasps
formerly in use.
[Illustration: Fig. 2229.]
Reaper files (B, Fig. 2229), so called from their use in sharpening the
knives of reaping and mowing machines, are of the cross-section shown.
They range in length from 7 to 10 inches, are slightly tapered, and are
cut single and on their sides only.
Tumbler files, whose cross-section is shown at A, Fig. 2229, were
formerly much used to file the tumblers of gun locks, but are now rarely
called for. They are taper and cut double. It will be seen, however,
that unless for some special purpose, the pitsaw round or half-round
file will be found to answer the same purpose as the tumbler file.
It is obvious that in the use of files the coarser cuts are for use when
it is required to remove a maximum quantity of material, and the finer
to produce a more smooth and true surface, and also that the form of
file selected is that which will best conform to the shape of the work,
or can be best admitted upon or into the work.
In selecting the length of the file, the size of the work and the
delicacy of the same are the determining considerations; thus, a 14-inch
file would be a clumsy tool upon a small piece of work, as, say, one
having an area of 1/2 inch square. In selecting the shape of the file
there are, however, other considerations than the shape of the work.
Among these considerations may be enumerated that, in proportion as the
number of teeth on any given file, performing cutting duty
simultaneously, is increased, the less metal will be taken off, because
the pressure on each tooth is reduced, and the file does not bite or
take hold of the work so well; hence it cuts smoother.
To fit the handles to small files, as 6-inch or less, it is simply
necessary to bore suitable-sized holes in the handles, and force in the
tang of the file. In doing this care should be taken to bore the hole
axially true with the handle, so that the latter may stand true with the
file, which greatly assists the production of true and rapid filing.
For larger files the handle should have a small hole bored up it as
before, the file tang should be made red hot (a piece of wet rag or
cotton waste being wrapped around the heel of the file, so that it shall
not get hot and be softened), and forced into the handle by hand, the
file and handle being rotated during the operation, and sighted to
insure that the handle is kept true with the centre line of the file. So
soon as the tang of the file has entered three-quarters or thereabouts
of its length it should be removed and gradually cooled by dipping in
water.
[Illustration: Fig. 2230.]
[Illustration: Fig. 2231.]
When the surface of the work is so large that the file handle would meet
the work before the point had reached fully across it, the raised handle
shown in Fig. 2230 is employed. The square end of the handle has a
dovetail groove into which the tang of the file is fitted. In the figure
the file is shown applied to a connecting rod end, and in such broad
surfaces it is especially necessary to vary the line of motion of the
file after every few strokes, so as to cause the file marks to cross and
recross, as shown in Fig. 2231.
The height at which work should be held to file it to the best advantage
depends entirely upon its size, the amount of metal to be filed off, and
the precision to which the filing requires to be executed.
Under ordinary conditions the work should stand about level with the
operator's elbow when he stands in position to file the work. This is
desirable so that the joint of the arm from the elbow to the wrist may
be in the same plane as the line of motion of the file, which will give
the workman the least fatigue. But when the work surface is very broad
it should be lower down, so that the operator may reach over all parts
of its surface. On the other hand, on very small round work, or work so
small as to require but one hand to hold the file, the work may be so
high as to require the operator to stoop but very little, in which case
the fatigue will be less, while the work will be more in sight, and can
be better scrutinized.
[Illustration: Fig. 2232.]
When the file is pushed endways it is termed cross-filing, and the teeth
cut on the forward or pushing stroke only, and in this case the file
should be held as in Fig. 2232, the end of the file handle abutting
against the palm of the right hand. But when the file is held in one
hand only, the forefinger may be placed uppermost, and either on the
file handle or on the file itself, as may be found most convenient. In
cross-filing the file should be relieved of cutting duty on the return
or back stroke, but should not be removed from the work surface.
For heavy cross-filing on iron or brass, a 15-inch file is sufficiently
large for any of the ordinary duty required by the machinist, and will
require all the pressure one man can put on it to enable it to cut
freely, and move at a suitable speed.
The workman should for heavy cross-filing stand well off or away from
the work so as to require to bend the body well forward. His feet should
in this case be spread apart so that when the pressure of the hands is
placed upon the file it will relieve the forward foot of a great part of
the weight of the workman's body, which will be thrown upon the file.
The rear foot operates during the forward stroke as a fulcrum, wherefrom
to push the file.
At each forward stroke the workman's body should move somewhat in unison
with the file; his arms being less extended than would otherwise be the
case, and the file being under more pressure and better control.
During the backward stroke the forward foot should again take the
workman's weight, while he recovers the upright position.
For less heavy filing and for smooth filing, the workman should stand
more nearly upright and nearer to the work.
The heavier the pressure (either in cross-filing or draw-filing), the
coarser the file cuts, and the more liable it is to pin and scratch.
In the case, however, of slim files, the pressure is apt to bend the
file, causing it to cut at the edges or ends only of the work, as shown
at A, in Fig. 2233. This may be avoided by holding the file as in the
figure, the pressure of the fingers in the direction of the arrows
causing the file to bend, and produce more straight work.
From the nature of the processes employed to cut the teeth of files,
they are unequal in height, and as the file in addition to this varies
in its straightness or warps in the process of hardening, it becomes
necessary in many cases to choose for certain work files whose shape is
best suited for it. Suppose, however, that files were produced whose
teeth or tops or points were equal in height from end to end of the
file, and it would be necessary for the workman to move the file in a
true straight line in order to file a straight surface. This the most
expert filers cannot accomplish. It is for this reason that hand files
are made as in Fig. 2234, being thickest in the middle M, and of a
curved taper both towards the point P and the heel H, so that when
applied to the work the file will bear on the work at A, Fig. 2235, and
be clear of it at B and C, which allows the file motion to deviate from
a straight line without cutting away the work too much at B and C. The
file curvature also enables any part of the file length to be brought
into contact with the work or with any required part of the surface of
the same, so as to locate or limit its action to any desired part.
If a bellied file (as this shape of file is sometimes termed) be moved
in a straight line it will file flat so long as it is moved to have
contact clear across the work, but if the file is concave in its length
it can only cut at that part which is in contact with the edge of the
work, and the latter must be filed convex.
[Illustration: Fig. 2233.]
It becomes obvious then that for flat work a bellied file must be used,
and that the belly should preferably be of even sweep from end to end.
But files, whatever their shape, and however evenly formed when soft,
warp (as already remarked) in the hardening process, sometimes having
crooks or bends in them, such as at E and D, in Fig. 2236. In such a
file the teeth at E would perform no duty unless upon work narrower than
the length of the concavity at E, while on the other side D, the extra
convexity would give the file great value for work, in which particular
spots only required to be filed, because the teeth at D could be brought
to bear on the required spot without fear of cutting elsewhere.
[Illustration: Fig. 2234.]
If, however, we have a taper flat file, such as in Fig. 2234, the
thickness being equal from H to M, and a curved taper from M to P only,
then it would be impossible to file flat unless only that part from M to
P be used, because the heel H would meet the work at the same time as M,
and it could not be known where the file would cut, more than that the
most prominent teeth would cut the most.
[Illustration: Fig. 2235.]
[Illustration: Fig. 2236.]
[Illustration: Fig. 2237.]
An excellent method of testing the truth of a file, and of finding its
high spots is to chalk a piece of board, press the file firmly to it and
take several strokes and the chalk will be transferred to the highest
parts of the file, showing very distinctly every hill and hollow in the
teeth, even on the finest of Groubet files, and it will be found from
this test that but very few of the best-made files are true, and that
very great care is necessary in selecting a file for flat and true work.
[Illustration: Fig. 2238.]
The curvature or belly on a file not only enables but few teeth to be
brought into action at any one turn, and thus cause it to cut more
freely; but it also enables all parts of the file length to be used and
worn equally. Thus in Fig. 2238 are shown two positions of a file, one
cutting at A and the other at B, these different locations being due to
different levels of the file which may be given by elevating or
depressing it at the handle end.
[Illustration: Fig. 2239.]
If a file is hollow in one side of its width, and rounding on the other,
as in Fig. 2239, the hollow side is unfit for any but the roughest of
work, since it will not file any kind of work true; but the rounded side
is very effective for flat surfaces, since the number of teeth in action
is more limited and their grip is therefore greater, while by canting
the file any part of its width may be brought into action. The rounded
side is especially advantageous for draw-filing (a process to be
hereafter explained).
In all cross-filing, whether performed to clean up a surface, remove a
maximum of metal, or prepare the work for draw-filing, or for reducing
the work to shape, the file should be given a slight lateral as well as
a forward motion, and it will be found that this lateral motion is more
effective if made from right to left, leaving the file marks in the
direction of marks B, in Fig. 2240, because the workman has more control
over the file (especially if a large one) than when the lateral motion
is from left to right; but this latter motion must be given occasionally
to prevent the file from cutting deep scratches, and to keep the file
surface true.
[Illustration: Fig. 2240.]
[Illustration: Fig. 2241.]
A new file should be used at first on broad surfaces so that the teeth
may not grip or bite the work so firmly that the strain will cause their
fine sharp edges to break off, which is apt to occur unless their edges
are slightly worn off. As a file becomes worn it may be used on narrower
work, because the narrower the surface the more readily the file will
bite. When a file is much worn, or when it is desired to remove a
quantity of metal as quickly as possible, the file may be used at
different angles upon the work, as shown in Fig. 2241, which by reducing
the number of teeth in action facilitates the cutting, but if this be
done with a new file it will break off the points of the teeth.
Cast iron, brass, and copper require a sharper file than do either steel
or wrought iron, hence for the first named metals (especially brass and
copper) new files are used, and these should not be used upon wrought
iron or steel until worn out for the above metals.
In the case of unusually hard cast iron or tempered steel a second-cut
file will cut more freely than a coarser grade.
Work to be draw-filed should first be cross-filed with smooth or at the
coarsest with second-cut files, so as to remove the scratches of the
bastard or rough file before the draw-filing, which should not be done
with a rough or bastard file.
Draw-filing consists in moving the file in a line at a right angle to
its length, the file being grasped at each end independently of its
handle, which may be removed from the file if it be in the way, as in
the case of files used on broad surfaces.
Draw-filing is employed for two purposes: first and most important, to
fit work more accurately than can be done by cross-filing, and secondly
to finish surfaces more smoothly, and lay the grain of the finish
lengthwise of the work. The greater accuracy of draw-filing occurs
because the high parts of the file can be selected and the file so
balanced that this high part covers the place on the work requiring to
be filed, while the strokes may be made to suit the length of the spot
to be filed.
In draw-filing the file can be moved more steadily than in cross-filing,
and will, therefore, rock so much less that even the novice can with
care produce very true work.
[Illustration: Fig. 2242.]
Suppose, for example, that a piece of work requires filing in the middle
of its length and half way along its width and half along its length,
and a well bellied file may be balanced upon C, Fig. 2242, and grasped
at its two ends A and B, and used with strokes of a sufficient length to
file half the work length as required.
In draw-filing the file should be pressed to the cut on the pushing
stroke only, and not on the return or pulling stroke.
Draw-filing produces with a given cut of file a smoother surface than
cross-filing, but it will not remove so much metal in a given time.
In draw-filing short strokes will produce better work than long ones,
because with the latter the file cuttings are apt to become locked in
the teeth of the file, and cut scratches in the work. This is called
_pinning_, and the pins cutting deeper than the file teeth produce the
scratches.
To avoid this pinning the file surface may be well chalked, which will
at the same time cause the file to cut smoother although not quite so
freely. It is necessary, however, to clean the file after every ten or
twelve draw-filing strokes so as to remove the filings. This removes the
chalk also, hence it requires occasional renewal. For this purpose lumps
of chalk are employed, but great care is necessary in its selection,
because it sometimes contains small pieces of flint or other stones, and
these score and greatly damage the file teeth.
To dislodge the chalk and filings the file surface may be rubbed two or
three strokes with the hand, and the file lightly tapped on the vice
back. But it will also be found necessary to occasionally clean the file
with a file-brush or file-card. The file-card is brushed across the
width of the file so that the wire may reach the bottoms of the rows of
teeth and clean them out.
[Illustration: Fig. 2243.]
If the pins have lodged too firmly in the teeth to be removed, the
scorer shown in Fig. 2243 is employed. This scorer is a piece of copper
or brass wire flattened out thin at the end E, which end is pressed
firmly to the file teeth and pushed across the width of the file. By
this means the thin edge becomes serrated, and the points of the teeth
forming the serrations pass down the bottoms of the rows of file teeth
and force out the pins. Here it may be remarked that pinning takes place
in cross-filing as well as in draw-filing, and is at all times
destructive to either good or quick work.
Oil is sometimes used to prevent pinning and produce a dead finish,
which will hide scratches, but it is much more dirty than chalk and no
more effective. Neither of these substances, however, is employed upon
cast iron, brass, copper, or other than the fibrous metals.
In removing the cross-file marks it will be found that the file will cut
more freely if it be slightly canted so that it cuts most at and near
the edge, as shown in Fig. 2244, the edge A B meeting the work, the file
stroke having progressed from C as shown. This is especially
advantageous if the metal be somewhat hard or have a hard skin upon it,
or in case of a hard spot, because it will enable the file to bite when,
if pressed flat upon the work, it would slip over it.
[Illustration: Fig. 2244.]
When draw-filing is resorted to, to obtain a very fine surface, to be
finished with emery paper and crocus cloth, it is best to reverse the
direction of the file strokes so as to cause the file marks to cross and
recross as shown in Fig. 2244, where the marks C cross those previously
made, which will not only produce smoother work, but it will partly
prevent the file from pinning. It will also be found that the
draw-filing will be smoother and pinning less liable to occur when the
file strokes cross the fibres or grain of the metal than when they are
parallel to that grain; hence when the finishing marks are to be left in
a line with the grain and a very smooth surface is required, the
draw-filing marks should, just before the final finishing, be across the
grain, the final finishing being with the grain simply to reverse the
direction of the marks.
Half-round files should be well curved in their lengths on the
half-round side, so that when applied to the work any part of the file's
length may be brought to bear upon the required spot on the work, as was
explained for the flat file, and shown in Fig. 2238. If the flat side is
straight or hollow in its length it is of little consequence, because it
can be used upon convex or upon narrow surfaces. The sweep or curve of
the file should in its cross-section always be less than the curve of
the work it is to operate upon, and the teeth should be brought up sharp
on the edges, and over the whole area of the half-round side, which is
in inferior files not always the case, because the rows of chisel cuts
are too far apart in the width of the file; hence, there is along the
length of the file between the rows of full teeth, rows that are not
brought fully up, which impair the cutting qualifications of the file.
[Illustration: Fig. 2245.]
[Illustration: Fig. 2246.]
[Illustration: Fig. 2247.]
In using a half-round file to cross file it should at each stroke be
swept first from right to left, and after a few strokes from left to
right, so that the file marks appear first as in Fig. 2245, running
somewhat diagonal from right to left, and then, when the side sweep of
the file is reversed in direction, the file marks will cross after the
manner shown exaggerated in Fig. 2247. Unless this is done, the curve
will be apt to have a wave in it as in Fig. 2246, or in large curves
there may be several waves, and the same thing may occur if the
direction of side sweep is not reversed sufficiently often. The file
should also be partly swept around the curve, so that if at the
beginning of a stroke it meets the work at the upper position in Fig.
2247, then at the end of the stroke it should be as at the lower one,
which will also prevent the formation of waves. The larger the curve the
less the amount of this sweep can be, the operator giving as much as
convenient for the size of curve being filed.
In draw-filing the file should be slightly rotated, so that if at the
beginning of a stroke it stands as at A, Fig. 2247, at the end of that
stroke it should stand as at position B, and it should at the same time
be given sufficient end motion, so as to cause the file marks to cross
as shown.
A round file should always be a little smaller at its greatest diameter
than the hole in the work. Before inserting it in the hole it should be
rotated in the fingers, and the eye cast along it, to select the part
having the most belly, which may then be brought to bear on the required
spot in the work, without filing any other place, and without filing
away the edges at the ends of the hole. For very accurate work it is
sometimes desirable to grind on a round file, a flat place forming a
safe edge. So likewise a safe edge flat file requires grinding on its
safe edge, because in cutting the teeth a burr is thrown over on the
safe edge, rendering it capable of scoring the work when filing close up
to a shoulder.
The work should be held as near down to the surface of the jaws of the
vice as will allow the required amount of metal to be filed off without
danger of the file teeth coming into contact with those jaws, and should
be placed so that the filing operation when finished shall be as near as
possible parallel with the top of the vice jaws. These jaws then serve
somewhat as a guide to the filing operation, showing where the metal
requires filing away.
For cutting steel that contains hard spots or places, a second-cut file
is more effective than a rough or bastard file.
Rough files are more suitable for soft metals, the bastard cut being
usually employed upon wrought iron, cast iron, and steel by the
machinist. But in any case the edge of the file is employed to remove
small spots that are excessively hard. The file should be clean and dry
to cut hard places or spots, and used with short strokes under a heavy
pressure, with a slow movement.
When a file has been used until its cutting edges have become too dull
for use, it may be to some extent resharpened by immersion in acid
solutions; but the degree of resharpening thus obtained has not proved
sufficient to bring this process into general or ordinary application;
hence, the files are either considered useless, or the teeth are ground
off and new ones formed by recutting them.
A recut file is of course thinned by the process, but if properly done
is nearly, if not quite, as serviceable as a new one, providing that in
grinding out the old teeth the file be ground properly true to curve;
but, unfortunately, this is rarely found to be the case.
An excellent method of resharpening files, and also of increasing the
bite of new files (which is an especial advantage for brass work), is by
the means of the sand blast. The process consists of injecting fine sand
against the backs of the teeth by means of a steam jet, and is
applicable to all files, from the rasp to the finest of Groubet files.
The action of the sand is to cut away the backs of the file teeth, thus
forming a straight bevel on the teeth back, and giving a new cutting
edge, and the process occupies from three to five minutes.
[Illustration: Fig. 2248.]
Fig. 2248 represents a machine constructed for this purpose. Steam is
conveyed by the piping to the nozzles A, A, which connect by rubber hose
H, H to sand pipe K, so that the steam jets passing through A, A carry
with them the mixture of quartz, sand, and water in the sand box. By
means of the overhead guide frame at D, E the file clamp C is caused to
travel when moved by hand in a straight line between the nozzles A, A in
the steam box, from which the expended sand and water flow down back to
the sand box. Thus both sides of the file are sharpened simultaneously,
and from the fixed angles of the nozzles and true horizontal motion of
the file the angles of all the teeth are equal and uniform.
To distribute the sharpening effects of the sand equally across the
width of the file, the carriage has lateral or side motion, as well as
endwise, and on the apparatus represented adjustable rollers regulate
this side movement. Having the two motions, any part of the file can be
presented to the blast.
The following is from _Engineering_:--"A comparative trial of the
cutting power of the sharpened files was lately made with the following
results: A piece of soft wrought iron was filed clean and weighed; 1200
strokes were made by a skilled workman with one side of a new 10-inch
bastard file, the iron was again weighed, and the loss noted. The other
side of this file was then subjected to the sand blast for five seconds,
and 1200 strokes were made with this sand-blasted side on the same piece
of iron, great care being taken to give strokes of equal length and
pressure in both cases. The iron was then weighed, and the loss found to
be double as much as in the first case.
"These operations were repeated many times, counting the strokes and
weighing the metal each time, and the quantity cut was found to
gradually become less for both sides as these became worn. When the
weight of metal cut away by 1200 strokes of the sand-blasted side was
found to be no greater than had been cut by the first 1200 strokes of
the ordinary side when quite new, a second sand blasting was applied to
it for 10 seconds, and in the next 1200 strokes its rate of cutting rose
to nearly its first figure. When the cut made by the ordinary side of
the file fell to about four-tenths of its cut when new, it was
considered by the workman as worn out, and a new file of the same size
and maker was used to continue the comparison with the one sand-blasted
side; 83 sets of 1200 strokes each and 13 sand-blastings were made on
the same side of this file, and in that time it cut as much metal as six
ordinary sides. In 99,600 strokes it cut away 14 ozs. avoirdupois of
wrought iron, and 16.4 ozs. of steel.
"With an equal number of strokes its average rate of cutting was, on
wrought iron, 50 per cent. greater than the average of the ordinary
sides, and on steel 20 per cent. greater. As the teeth became more worn,
the time of the application of the sand blast was lengthened up to one
minute. After the thirteenth re-sharpening its rate of cutting was
nine-tenths that of the ordinary side when quite new.
"When the teeth become so much worn that the sand blast ceases to
sharpen them effectively, the file can be recut in the usual way, and
each set of teeth can be made to do six times as much work as an
ordinary file, and to do it with less time and labor, because it is done
with edges constantly kept sharp. The time required to sharpen a
worn-out 14-inch bastard file is about four minutes, or proportionately
less if sharpened before being entirely worn out. Smooth files require
much less time. About 4 horse power of 60 lb. steam used during four
minutes, and one pint per minute of sand (passed through a No. 120
sieve), and the time of a boy are the elements of cost of the
operation."
RED MARKING OR MARKING.--This is a paint used by machinists to try the
fit of one piece to another, or to try the work by a test piece or
surface plate. It should be composed of dry Venetian red, mixed with
lubricating oil of any kind.
Instead of Venetian red, red lead is sometimes used for marking, but it
is too heavy and separates from the oil, and furthermore will not spread
either evenly or sufficiently thin, and is therefore much inferior to
Venetian red.
It is applied to the surface of the test piece or piece of work, and the
latter is brought to bear on the surface to be tested, so that it leaves
paint marks disclosing where the surfaces had contact, and therefore
what parts of the surface require removing in order to make the surfaces
have the desired degree of contact.
When either the test piece or the work can be put in motion while
testing, one piece is rubbed upon the other or passed along the same in
order that the bearing marks may receive the marking more readily and
show the bearing spots more plainly, the operation coming under the head
of fitting. When neither piece can be given motion, one is made to mark
the other by being struck with a mallet or hammer, or to avoid damage to
the work from the hammer blows, a piece of wood or copper is interposed.
This operation is termed "bedding."
[Illustration: _VOL. II._ =SCRAPERS AND SCRAPING.= _PLATE IX._
Fig. 2252.
Fig. 2253.
Fig. 2254.
Fig. 2255.
Fig. 2256.
Fig. 2257.
Fig. 2258.
Fig. 2259.
Fig. 2260.]
The thickness of the coating of marking varies with the kind of work,
the finer fit the work requires to be, the thinner the coat of marking.
Thus in chipping a thick coat is applied, for rough filing a thinner,
for smooth filing a still thinner coat, and so on, until for the finest
of work the coat is so thin as to be barely perceptible to the naked
eye. When either the work or the testing piece can be given motion and
the surfaces rubbed together, a thinner coat of marking may be used.
Marking is usually applied with a piece of rag doubled over and over,
and bound round with a piece of twine so as to form a kind of
paint-brush. This will give the surface a lighter and more evenly spread
coat than would be possible with a brush of any kind. For very fine
work red marking may be spread the lightest and the most even with the
palm of the hand, which will readily detect any grit, dirt, or other
foreign substance which the marking may contain from being left exposed.
[Illustration: Fig. 2249.]
[Illustration: Fig. 2250.]
THE HACK-SAW.--The hack-saw is employed by the machinist for severing
purposes, and also for sawing slots in the heads of screws. The blade
should be tightly strained in the frame, which will prevent saw
breakage. The ordinary method of doing this is to provide the end of the
saw frame with a sliding stud threaded at its end to receive a thumb
nut. The studs at each end of the blade should be squared where they
pass through the frame, as at A, B in Fig. 2249, so that the blade shall
not be permitted to twist. An improved form is shown in Fig. 2250, in
which the end E has a saw slot to receive the blade F. At the handle end
of the blade it is held by a stud sliding through the frame, being
squared at B; at C is a nut let into and screwed in the handle, and into
or through the nut is threaded the end of the stud, so that by rotating
the handle the blade is strained. The curve in the back at A gives a
little elasticity to it, and therefore a better strain to the blade. A
hack-saw should always be used with oil, which preserves the cutting
edge of the teeth.
In sharpening a hack-saw it is best to rest the smooth edge of the blade
on a piece of hard wood or a piece of lead, and spread the tops of the
teeth by light hammer blows, which serves a two-fold purpose, first it
thickens them and enables them to cut a groove wide enough to let the
blade pass freely through, and secondly it enables the teeth to be filed
up to a sharp cutting edge with less filing.
[Illustration: Fig. 2251.]
The screw-driver to be used in saw slots should have its end shaped as
at A in Fig. 2251, which will tend to prevent it from slipping out of
the saw slot, as it will be apt to do if wedge-shaped as at B, because
in that case the action of the torsional pressure or twist is to lift
the screw-driver out of the slot.
SCRAPERS AND SCRAPING.--The process of scraping is used by the machinist
to true work, and to increase the bearing area of surfaces, while the
brass finisher employs it to prepare surfaces for polishing, applying it
mainly to hollow corners and sweeps.
For scraping work to fit it together the flat scraper is used, ordinary
forms being shown in Figs. 2252 and 2256.
That shown in Fig. 2252 may be made of a flat smooth file, of about an
inch wide, and 3/16-inch thick, which is large enough for any kind of
work. Two opposite faces, one of which is shown at A, are ground beveled
so as to leave the end face B about 1/16-inch thick. This end face is
then ground square as denoted by the dotted lines, producing two cutting
edges of equal angles, and therefore equally keen. If it were attempted
to grind face B at an angle as denoted by the dotted lines G, in Fig.
2253, the lower edge H would cut too keenly, causing the scraper to
chatter and cut roughly, while the upper one I would not cut
sufficiently easily.
For very smooth work the scraper may be formed as in Fig. 2256, the
front face E being ground slightly out of square as shown, and the
bottom face F being given considerable angle to the body of the scraper.
For very rapid cutting, however, the front face E may be at an angle of
less than 90° to the top of the scraper.
The only objection to this form is that the eye lends no assistance in
bringing the edge fair with the work surface. The scraper should not
exceed about 6 inches in length, exclusive of the handle, for if longer
it will not cut well or smoothly, and its end face should be slightly
rounded as in Fig. 2254. Its facets should be ground square or straight
and carefully oil-stoned after the grinding, the oil-stoning process
being repeated for two or three resharpenings, after which it must be
reground upon the grindstone.
The scraper should be grasped very firmly in the hands, and held as in
Fig. 2255. It requires to be pressed hard to the work during the cutting
and lightly during the backward stroke.
The strokes should not exceed for the roughing courses, say, half an
inch in length, the first course leaving the work as represented in Fig.
2257.
The second course should be at a right angle to the first, leaving the
work as in Fig. 2258, and after these two courses the work should be
tested by surface plate, or with the part to which it is to fit, as the
case may be. Previous to the testing, however, the work must be
carefully wiped clean with old rag, as new rag or waste is apt to leave
ravelings behind. The surface plate should be given a light coat of red
marking, and then moved backward, forward, and sideways over the work,
or, if the work is small, it may be taken from the vice and rubbed upon
the surface plate, and the high spots upon the work will be shown very
plainly by the marks left by the plate. The harder the plate bears upon
the work the darker the marks will appear, so that the darkest parts
should be scraped the heaviest.
After applying the plate, the scraper may again be applied, the marks
being at an angle to the previous operation, the testing and marking by
the plate and scraping process being continued until the job is
complete, appearing as shown in Fig. 2259.
It will be noted that the scraper marks are much smaller and finer at
and during the last few scrapings; and it may be here remarked that the
scrapings are very light during the last few finishing processes.
The strokes of the scraper being made of a length about equal to the
acting width of its edge cuts, makes the scraper mark approximately
square, on which account it is sometimes termed "block" scraping. It
gives an excellent finish, while not sacrificing the truth of the work
to obtain the finish.
The scraper will not remove a quantity of metal so quickly as a file,
and on this account it is always preferable to surface the work with a
file before using the scraper, even though the work be well and smoothly
planed. Not until the file has almost entirely removed the planer marks,
and the surface plate shows the surface to be level and true, should the
scraper be brought into requisition, the first courses being applied
vigorously to break down the surface.
It would appear that scraping might be more quickly done by taking long
scraper strokes promiscuously over the work, but in this case the
bearing marks are not well defined and do not show plainly, which leads
to confusion and causes indecision as to where the most or heaviest
scraping requires to be done, whereas in the block scraping the marks
are clearly defined and the high patches or spots on the work show very
plainly, and the workman is able to proceed intelligently and with
precision.
Fig. 2260 represents a three-cornered or "three-square" scraper, which
is used principally upon hollow or very small flat surfaces. The
half-round scraper is employed upon holes, bores, or large concave
surfaces, such as brasses. Both these tools are for vice work, used in
the same manner as described for flat scrapers, while all scrapers cut
smoother when the edge is kept wetted with water, as is essential when
used upon wrought iron, copper, and steel.
HAND REAMERS OR RYMERS.--The hand reamer is employed for two purposes,
first, to make holes of standard diameter and smooth their walls, and
second, to bring holes in line one with the other.
[Illustration: Fig. 2261.]
Fig. 2261 represents an ordinary solid hand reamer for parallel holes.
The teeth are ground so that their tops form a true circle, this
grinding being done after the reamer has been hardened and tempered,
because in these processes the reamer is apt to get both out of round
and out of straight.
[Illustration: Fig. 2262.]
In some practice the reamers are formed as shown in Fig. 2262, and are
made in sets of three for each size; the first is slightly taper from
end to end, the second is slightly tapered at the entering end for a
length about or nearly equal to the diameter, and the third is parallel
and rounded on the end like the second, and in many cases only three
teeth are employed.
[Illustration: Fig. 2263.]
[Illustration: Fig. 2264.]
Fig. 2263 represents a reamer in which the distance between the cutting
edges A B, Fig. 2264, is greater than between B C, and so on, the
spacing decreasing from tooth A to tooth _a_. The spacing of _a_, _b_,
&c. to _f_ on the other side is also irregular, so that if the reamer be
given half a revolution no two teeth will have arrived at similar
positions except A and _a_, the former arriving at the position occupied
by the latter.
Now suppose that a hole to be reamed has a hollow or spongy seam along
it, and if the reamer be regularly spaced, there will at this point
occur a lateral movement of the reamer that will impair the roundness of
the hole, and this lateral movement the irregular spacing tends to
prevent.
If a solid reamer is made to standard gauge diameter when new, and the
bolts or pins turned to standard diameter, then by reason of the wear of
the reamer the work will become gradually a tighter fit and finally will
not go together, hence the reamer must be restored to standard diameter,
which may be done by upsetting the teeth with a set chisel. Furthermore
the workman's measuring gauges are themselves subject to wear, those for
measuring the pins wearing larger and those for the holes wearing
smaller, and this again is in a direction to prevent the work from
fitting together. It is preferable, therefore, to employ adjustable
reamers.
Thus Fig. 2265 represents an adjustable reamer in which the teeth fit
tightly into dovetail grooves, that are deeper at the entering than at
the shank end of the reamer, so that by forcing the teeth up the grooves
towards the shank the diameter is increased.
Both castings and forgings are found to alter somewhat in shape in
proportion as their surfaces are removed by the machine tools, so that
the shape of the work undergoes continuous alteration.
Suppose, for example, that a piece of metal two inches square and four
inches long, has a hole cast in it of an inch in diameter, and when
finished it is to be 1-3/4 inches square, 3-3/4 inches long, and have a
hole 1-1/8 diameter. Let it be chucked in a lathe or shaping machine and
have its surfaces cut down to the required dimensions. Removing the
metal to true the first surface will reduce the strain on that side of
the casting and alter the shape of the whole body, but this alteration
of form will not occur to its full extent until the piece is removed
from the pressure of the chuck jaws, or other clamping device holding it
in the machine, because this pressure holds it; as a result the surface
will not be so true after leaving the machine as it was before. On
surfacing the second side of the piece, the internal strain is still
further reduced, and a second alteration of form ensues, and so on at
the surfacing of every side of the piece. Now let the piece be chucked
true to have the hole bored out, and the removal of the metal in the
hole will again reduce the internal strain and the form of the body will
again alter.
Suppose, however, that the piece after having its surfaces thus removed,
and its hole bored as true as may be, were again trued over each
surface, and in its bore there will still be at each surfacing and at
the boring an alteration of form, although it may be to a very minute
degree, and from these causes the use of the reamer for work requiring
to be very true becomes indispensable.
[Illustration: Fig. 2265.]
[Illustration: Fig. 2266.]
Fig. 2266 represents a taper hand reamer with straight flutes. It is
preferable, however, to give the flutes a left-hand spiral, as was
explained with reference to reamers for lathe work.
[Illustration: Fig. 2267.]
The frames of large machines are frequently composed of parts that are
bolted together after having the holes for shafts, &c. bored, and to
insure the alignment of these holes after the frames are put together a
hand reaming bar, such as in Fig. 2267, is employed, A and B being two
shell reamers fastened to the bar by a pin.
[Illustration: Fig. 2268.]
Reamers are sometimes employed to enlarge holes or bring them fair one
with another, without reference to their being precise to a designated
diameter; thus Fig. 2268 represents a half-round reamer of the form used
by boiler makers to bring rivet holes fair, and sometimes by machinists
to ream the holes for taper securing pins. The flat face is cut down to
below the centre line, so that the back requires no clearance ground
upon it.
[Illustration: Fig. 2269.]
The square reamer shown in Fig. 2269 is used for rough work generally,
although with careful grinding and use it will produce excellent results
upon work of small diameter. Brass finishers generally prefer a square
reamer to all others for reaming the bores of brass cocks, &c., and some
of them prefer that one edge only be sharpened to cut, the other three
being oilstoned off so as not to cut, but simply serve as guides. The
square reamer is very easily sharpened whether by grinding or
oil-stoning; the flat sides are operated on, taking care to keep them
straight and the thickness even on the two diameters, so that, the sides
being straight and the reamer square, it will cut taper holes whose
sides will be straight. If the reamer is not ground square, two only of
the edges will be liable to have contact with the work bore, causing the
reamer to wabble, and rendering it liable to break.
[Illustration: Fig. 2270.]
Another and very good form of reamer for the rapid removal of metal is
shown in Fig. 2270, having three teeth and a good deal of clearance,
which enables it to work steadily and cut freely.
CHAPTER XXVI.--VICE WORK--(_Continued_).
In most of the operations of the machine-shop, the work of the chisel is
followed by that of the file; hence, as an example in the use of the
chisel independent of that of the file, the cutting of the teeth upon
files may be given as follows:--
[Illustration: Fig. 2271.]
[Illustration: Fig. 2272.]
[Illustration: Fig. 2273.]
[Illustration: Fig. 2274.]
The largest and smallest chisels commonly used in cutting files are
represented in two views and half size in Figs. 2271 and 2272. The first
is a chisel for large rough files; the length is about 3 inches, the
width 2-1/2 inches, and the angle of the edge about 50°; the edge is
perfectly straight, but the one bevel is a little more inclined than the
other; this chisel requires a hammer of about 7 or 8 pounds weight. Fig.
2272 is the chisel used for small superfine files; its length is 2
inches, the width 1/2 inch; it is very thin, and sharpened at about the
angle of 35°; it is used with a hammer weighing only 1 or 2 ounces; as
it will be seen, the weight of the blow mainly determines the distance
between the teeth. Other chisels are made of intermediate proportions,
but the width of the edge always exceeds that of the file to be cut. The
first cut is made at the point of the file; the chisel is held in the
left hand, at a horizontal angle of about 55° with the central line of
the file, as at _a_ _a_, 2273, and with a vertical inclination of about
12° to 4° from the perpendicular, as represented in Fig. 2274, supposing
the tang of the file to be on the left-hand side. The following are
nearly the usual angles for the vertical inclination of the chisels,
namely: For rough rasps, 15° beyond the perpendicular; rough files, 12°;
bastard files, 10°; second-cut files 5°, and dead-smooth-cut files 4°.
The blow of the hammer upon the chisel causes the latter to indent and
slightly to drive forward the steel, thereby throwing up a trifling
ridge or burr; the chisel is immediately replaced on the blank, and slid
from the operator until it encounters the ridge previously thrown up,
which arrests the chisel or prevents it from slipping farther back, and
thereby determines the succeeding position of the chisel. The chisel
having been placed in its second position, is again struck with the
hammer, which is made to give the blows as nearly as possible of uniform
strength, and the process is repeated with considerable rapidity and
regularity, 60 to 80 cuts being made in one minute, until the entire
length of the file has been cut with inclined parallel and equidistant
ridges, which are collectively denominated the "first course." So far as
this one face is concerned, the file, if intended to be single-cut,
would be then ready for hardening, and when greatly enlarged its section
would be somewhat as in Fig. 2274.
The teeth of some single-cut files are much less inclined than 58°;
those of floats are in general square across the instrument. Most files,
however, are double-cut, and for these the surface of the file is now
smoothed by passing a smooth file once or twice along the face of the
teeth, to remove only so much of the roughness as would obstruct the
chisel from sliding along the face in receiving its successive
positions, and the file is again greased. The second course of teeth is
now cut, the chisel being inclined vertically as before, or at about
12°, but horizontally about 5° to 10° from the rectangle, as at _b_ _b_,
Fig. 2273. The blows are now given a little less strongly, so as barely
to penetrate to the bottom of the first cuts, and consequently the
second course of cuts is somewhat finer than the first. The two series
of courses fill the surface of the file with teeth which are inclined
toward the point of the file. If the file is flat and to be cut on two
faces, it is now turned over; but to protect the teeth from the hard
face of the anvil a thin plate of pewter is interposed. Triangular and
other files require blocks of lead having grooves of the appropriate
sections to support the blanks, so that the surface to be cut may be
placed horizontally. Taper files require the teeth to be somewhat finer
toward the point, to avoid the risk of the blank being weakened or
broken in the act of its being cut, which might occur if as much force
were used in cutting the teeth at the point of the file as in those at
its central and stronger part. Eight courses of cuts are required to
complete a double-cut rectangular file that is cut on all faces, but
eight, ten, or even more courses are required in cutting only the one
rounded face of a half-round file. There are various objections to
employing chisels with concave edges, and therefore, in cutting round
and half-round files, the ordinary straight chisel is used and applied
as a tangent to the curve. It will be found that in a smooth,
half-round file 1 inch in width, about twenty courses are required for
the convex side, and two courses alone serve for the flat side. In some
of the double-cut, gullet-tooth saw-files, as many as twenty-three
courses are sometimes used for the convex face, and but two for the
flat. The same difficulty occurs in a round file, and the surfaces of
curvilinear files do not therefore present, under ordinary
circumstances, the same uniformity as those of flat files.
[Illustration: Fig. 2275.]
The teeth of rasps are cut with a punch, which is represented in two
views, Fig. 2275. The punch for a fine cabinet rasp is about 3-1/2
inches long and 5/8 inch square at its widest part. Viewed in front, the
two sides of the point meet at an angle of about 60°; viewed edgewise,
or on profile, the edge forms an angle of about 50°, the one face being
only a little inclined to the body of the tool. In cutting rasps, the
punch is sloped rather more from the operator than the chisel in cutting
files, but the distance between the teeth of the rasp cannot be
determined, as in the file, by placing the punch in contact with the
burr of the tooth previously made. By dint of habit the workman
moves--or, technically, hops--the punch the required distance; to
facilitate this movement, he places a piece of woollen cloth under his
left hand, which prevents his hand from coming immediately in contact
with and adhering to the anvil.
As an example in the use of the chisel for chipping purposes, let it be
required to fasten a feather on a shaft.
There are four methods of inserting feathers: First, a shaft may have a
parallel recess sunk into it and a parallel feather may be driven in;
second, the feather may be made slightly taper and driven in; third, the
feather may be dovetailed on the sides and ends both, or on the ends
only, and as one or the other of these is the proper method, and the
process is the same for both, one only need be described.
[Illustration: Fig. 2276.]
[Illustration: Fig. 2277.]
[Illustration: Fig. 2278.]
In Fig. 2276 let S represent a shaft and F a feather, required by the
drawing to be permanently fixed therein. The drawing will not, in
ordinary shop practice, give any instructions as to how the feather is
to be fastened; hence the mechanic usually exercises his own judgment
about the matter, or is governed by the practice of the shop. If left to
his own judgment he may determine to so fix it that it may be locked on
all four sides, as in Fig. 2277, or he may simply set it in as in the
similar views shown in Fig. 2278.
The method shown in Fig. 2277 is the most secure and best job; but, on
the other hand, it is the most difficult and costly. The difficulty
consists in filing the parallel part above the surface of the shaft to a
line that shall be quite even with the surface of the shaft. This
difficulty may be overcome by leaving the sides parallel, and making the
length A equal to the length of the acting part of the key, and the
bottom B as much longer as may be required to get the required amount of
dovetail on the feather ends.
[Illustration: Fig. 2279.]
[Illustration: Fig. 2280.]
[Illustration: Fig. 2281.]
[Illustration: Fig. 2282.]
The first thing to do is to mark off the keyway by scribing lines on the
surface of the shaft, indicating the location for the feather seat; and
for this purpose nothing is better than the key seat rule shown in Fig.
2279, in which W is the key seat rule, and S the shaft. After the lines
are drawn they should be defined by centre-punch dots, as in Fig. 2280,
and then the metal should be cut out on the sides first, using a cape
chisel, and cutting close to the side lines, as in Fig. 2281, in which A
is a cape chisel cut taken along one side, D a second cape chisel cut,
being carried along the other side, C the cape chisel, C´ the cut taken
by the chisel, and B a piece of metal to be cut out after the cape
chisel has done its work. Suppose, now, the mass of the metal is
removed, then the dovetailing is performed as follows: Next the
_setting_ or _upsetting_ is proceeded with as shown in Fig. 2282, which
is a side sectional view. S is a set chisel driven by hammer blows
against the walls of the feather seat (as against the end _e_), causing
it to bulge up, as shown at _f_. This setting will enlarge the feather
seat or recess, so that the wide part of the dovetail on the feather
will just pass in (the dotted lines shown in Fig. 2281 having, of
course, been marked to the size of the feather, where it will, when
fixed, meet the surface of the shaft). The feather is then placed in its
seat and bedded properly by red marking applied to its bottom surface to
show the high spots on the seat of the recess, and when properly bedded
it is fastened, as in Fig. 2283, in which S is a set chisel, which, by
being struck with hammer blows, closes the bulged metal back again on
the dovetail of the feather, and firmly locks it in the shaft. And all
that remains is to file the shaft surface around the feather level with
the surrounding surface, there being usually a little surplus metal from
the upsetting.
[Illustration: Fig. 2283.]
[Illustration: Fig. 2284.]
[Illustration: Fig. 2285.]
[Illustration: Fig. 2286.]
[Illustration: Fig. 2287.]
As an example of chipping and filing let it be required to chip and file
to shape and to fit a knuckle joint (or a double and single eye, as it
may more properly be termed), such as in Fig. 2284. The eye being marked
out by lines, the first operation will be to remove the surplus metal
around the edges by chipping, which should be done (with the pin in
place, so that it may support the eye) before the joint faces are filed
at all, and should be carried in a direction around the eye, as shown in
Fig. 2285, in which _v_ is the vice jaw, E a lead clamp, C the cut, and
D the chisel. By chipping in this direction two ends are served: first,
the force of the chipping blows is less likely to bend the eye if it is
a light one, and, secondly, the chipping will not break out the metal at
the edge of the eye, which it would be apt to do if the chipping was
carried across. This is shown in Fig. 2286, where a chisel cut is
supposed to have been carried across from A to B and a piece has broken
out at B. If the width of the eye is too broad for one chisel cut, a
cape chisel should be run around it, as in Fig. 2287, A D showing the
cutting, the flat chisel cuts B, C being taken separately afterwards.
In order to illustrate the filing clearly, it will be necessary to show
more metal to be filed off than would be the case in practice, unless
the eye were very small, in which case it would not pay to chip.
[Illustration: Fig. 2288.]
Put the eyes together with the pin in and let the two lowest places on
the edges coincide. Then file a flat place clear across them, as shown
in Fig. 2288 at F, making it parallel to the pin, and, say, down to
within 1/100 of the finished depth. To test the parallelism of the flat
place, take out the pin and apply to the flat place a square, rested
against the radial face of the double eye, or measure its distance from
the hole of the eye on each side of the double eye, that is at each end
of the hole.
[Illustration: Fig. 2289.]
When it is true and down to the required size, put the eyes together and
let their relative positions be such that the flat places do not
coincide, and that on the double eye will serve as a guide to carry the
filing around the single eye, while that on the single eye will serve as
a guide to carry the filing around the double eye, as will be seen on
reference to Fig. 2289, in which the flat places A, B on the double eye
serve as a guide to file C down to, while the flat place on the single
eye at D is a guide to file the metal at E, F down to, and it is obvious
that by moving the eyes to different positions the eye may on that side
be filed true and to circle.
When the filing has thus been carried around as far as the movement of
the eyes permits on that side, turn the single eye over in the double
eye, and they will appear as shown in the end view, Fig. 2290, A being
the filed side of the single and E D that of the double eye; hence the
metal at C, B must be filed down level with A, and that at F down level
with E, D.
[Illustration: Fig. 2290.]
We have assumed that the edges only required finishing irrespective of
the joint faces; but let it be assumed that the whole of the eye has
been dressed up by machine tools, and that it requires fitting and
finishing by the file both on its joint faces and on its edges.
If the eye has been bored and faced in the lathe the faces will be about
true with the hole, but if it has had its faces trued in a machine, as a
planer or slotter, and the hole bored subsequently in a slotting
machine, the hole may not be true to the faces. This may occur from want
of truth in the chucking devices, from these devices having been held to
a table or carriage moving on slides, and having lost motion or play, in
which case from the leverage of the pressure of the boring tool-reamer
or bit, this table may have lifted to the extent of such play, in which
case the hole will not be at a right angle to the face or faces.
[Illustration: Fig. 2291.]
First, then, these faces must be tested for truth and smoothed by
filing. The best testing device is a pin and washer, the pin neatly
fitting the hole in the eye and the washer neatly fitting the pin. The
radial face of the pin head and of the washer should then be given a
light coat of marking, and be inserted in the eye, as shown in Fig.
2291, in which _a_ is the pin head and B the washer. If each be then
rotated under pressure against the eye, they will mark the high spots,
which may be filed and draw-filed until an even contact all around is
shown.
The single eye should be similarly faced and fitted, a somewhat tight
fit, into the double eye. In a job of this kind, where accuracy of fit
is essential, it is usual to bore the hole about 1/100 inch smaller than
its finished diameter, and after fitting the two eyes, to ream out the
eyes while bolted together.
For the reaming the two eyes should be clamped together. The single eye
is left somewhat too tight a fit to the double eye to permit of the
finishing being done after the holes are reamed, because the reaming may
slightly alter the axial line of the hole. The two bolts holding the
clamping plates should be brought just home on the plates, and then
tightened up gradually and alternately, so that the eyes may be gripped
fair, and not liable to move during the reaming. The bores of the eyes
should be set as true as possible one with the other before the plates
are tightened upon the eyes, for if it is attempted to set the eyes true
by hammer blows afterwards, the pressure of the plates would cause the
arm or hub of the double eye which received the hammer blow to move more
than the other, or, in other words, to spring out of its normal
position, and the eye will be distorted. But when released from the
pressure of the clamping plate the double eye will resume its normal
shape, and the holes will not be axially true in the two eyes.
After the holes are reamed the temporary pin and washer used for the
facing will be too loose, and the proper pin should be used for all
future operations. The eyes should be put together with a light coat of
marking on both faces of the single eye, and, with the pin in place, one
eye should be moved back and forth, when they may be taken apart again
and filed on the high spots. When by repetition of this process they fit
properly the outside edges may be filed up, as already described.
It is obvious, however, that the pin and washer shown in the figure may
be hardened and used to file the edges up before the reaming, in which
case, their diameters being equal, and equal to that of the required
finished diameter of the eye, it is easy to file the eye edges true and
to size; but even in this case the eyes should be finished by reversing
and moving as before described. There is, however, the objection to
filing the edges--first, that the joint will show plainer, because in
filing the side faces to fit the single into the double eye, that part
of each face near the edge is apt to be filed away slightly too much,
causing the joint to show; but if the circumferential edges of the eye
be filed last, the part so filed away is removed and the joint may be
made almost invisible.
The best plan of all is to first fit the eyes, then ream them out and
then provide a hardened pin and washer to fit the reamed hole, then file
down the circumferential edges nearly level with the pin and washer and
finish by reversing and moving the eyes as before described.
In the absence of any pin and washer, such as shown in Fig. 2291, the
inside faces of the jaws of the double eye must be filed parallel to the
outside radial faces of the single eye, the outside surfaces being trued
when the hole is bored. If none of the surfaces have been trued with the
hole, the outer ones should first be trued, using a [T]-square (if there
is no pin) to test the truth of the face with the hole, and the inside
jaw faces must be trued with the outside, measuring each jaw with
outside calipers, and the width between the jaws with inside calipers.
[Illustration: Fig. 2292.]
Let us now suppose that it were attempted to first fit the single to the
double eye a tight fit, then to ream the hole and then to make the joint
an easy working fit. In this case the finished hole in one eye may
become out of true with that in the other, that is, it may not be
parallel with that in the other, and for the following reasons:--The
holes of the two eyes will rarely come quite true with each other, even
though the radial faces of the eyes be turned in the lathe or faced in a
machine when the holes are bored, and it is the duty of the reamer to
true as well as smooth them in whatever direction they may be out of
true or face one with the other until they are put together. Now, if
they be put together a tight fit, the outside jaws are sprung open to
some extent. Again, they may be sprung slightly atwist, and if the hole
be reamed true and this twist taken out afterwards the hole will come
atwist or out of fair in proportion as the jaws lose their twist from
being fitted.
Again, reaming the hole slightly alters its axial line, and the radial
faces, if at a right angle to the hole before reaming, will not be so
after reaming, and it is not practicable to discover in just what
direction and to what degree reaming the hole will alter its axial
direction; hence, the single eye must be fitted as near as may be before
the holes are reamed, and finished afterwards as described.
Let it be required to reduce by filing, the diameter of a round pin or
to file it to fit a taper hole, and the diameter of the pin being small
it may be held by one end in the vice jaws or by means of the clamps,
shown in Fig. 2091 or those in Fig. 2092. But the filing can be more
truly and easily finished as in Fig. 2292, in which there is shown
fastened in the vice a filing block having [V]-grooves (of varying width
to suit varying diameters of work), in which the pin to be filed may be
rested.
The pin is held by the hand vice shown, and is rotated towards the
operator during the forward file stroke (one hand holding the hand vice
and the other the file), and in the opposite direction during the back
stroke. After every few file strokes the hand vice is partly rotated in
the hand so that the whole of the pin surface may be subjected to the
file. The hand vice enables the pin to be forced into its hole and
rotated, to show by the contact or bearing marks where it requires
filing to adjust the fit.
[Illustration: Fig. 2293.]
Fig. 2293 represents an excellent form of hand vice for holding pins,
&c., the jaws being pivoted to a cross piece and opened by a cone, the
handle threading to the stem of the cross piece, and being hollow so
that the work may pass through it. The work is thus very firmly gripped
and not liable to move in the jaws as it is when the hand vice is
fastened upon the work by a thumb nut.
Very thin pieces of metal cannot be well held in the vice jaws, and as
an example of this kind of work holding, let it be required to file up a
caliper leg, which being curved cannot well be held in any of the vice
fixtures heretofore shown.
[Illustration: Fig. 2294.]
In Fig. 2294 there is a block of wood having an extension at A that may
be gripped in the vice jaws. Upon the surface of the block the caliper
leg is held by brads or nails driven around its edge, as shown, or it is
obvious screws may be used.
[Illustration: Fig. 2295.]
An excellent example of filing is to file up a hexagon nut or a bolt
head. This is apparently a simple piece of work, but it is in fact a job
that requires a good deal of care and precision to properly accomplish.
The requirements are that the nut shall measure alike across the flats,
that each flat shall be parallel to the axial line of the bolt, and at a
proper and equal angle to both of its neighbors, and that the nut shall
be of equal thickness all round. The method of accomplishing this result
is as follows: Let Fig. 2295 represent a bolt head, after it has been
turned in the lathe. It will be observed that the end face of the bolt
head is rounded. Now a bolt head of this form gives a very neat
appearance, but it presents difficulties in the filing up, as we shall
see presently.
[Illustration: Fig. 2296.]
[Illustration: Fig. 2297.]
[Illustration: Fig. 2298.]
[Illustration: Fig. 2299.]
Suppose that one flat (which we will call flat A) of a nut, is nearest
to the bore, then to make the nut of equal thickness all around, the
other flats must be so filed down as to approach the bore as nearly as A
does, and it is assumed that there is metal enough to permit this. The
flat A will then be the first one to be filed up, taking off just
sufficient to make it true when tested by the nut gauge, applied as in
Fig. 2296, in which N is the nut, and G the gauge. The flat must also be
filed true when tested by the gauge, as in Figs. 2297 and 2298, the
gauge G being tried rested on A and applied to B, and then rested on A
and applied to C. A should be filed so that, if possible, it will be at
the proper angle to both B and C, but if, from errors in the angles of B
and C, this is impossible, the error should be divided between the two,
as shown, for example, in Figs. 2299 and 2300, where the gauge is shown
in the two positions necessary to test each respective flat, B and C;
the amount of error being equal at H and I.
The next flat to file will be E, Fig. 2299. Now, in a small nut, the
chamfer of the nut edge will be sufficient guide to the eye in filing E
to an equal thickness (that is, equal for distance from the bore to A).
In order that the finished nut shall be so true that the nut gauge shall
show that the flats or angles are true one with the other all around the
nut, it is necessary that the flat E shall stand parallel to A; hence it
should be made so by measurement with calipers, irrespective of its
angle to either D or F. After E is filed it will serve as a base from
which D and F may be filed to angle, while A will serve as a base from
which the flats D and C may be filed to angle; but, while testing the
angle with the gauge, C and D should be tried for parallelism, and F and
B for parallelism, while the diameters across these flats should be
equal on all sides.
[Illustration: Fig. 2300.]
If it were attempted to go all around the nut, filing to the gauge, as,
for example, filing C, Fig. 2300, from A, F from C, E from F, D from E,
and B from D, all the error in the angle of the gauge, or errors of
workmanship, will (supposing the latter to be always in the same
direction) be multiplied upon, or rather added to B when tested with A,
and these two will not be of correct angle. Again, any error made upon
one flat will be copied upon the one filed to gauge angle from it;
whereas, filing E parallel to A insures the correctness of these two,
and testing the parallelism of the others, as B, F, serves to discover
and correct any error of angle that may exist. It is obvious that in
filing each flat the gauge must be applied as in Fig. 2296, as well as
in Fig. 2298.
In filing the opposite flats to diameter to fit the wrench or gauge, if
one be used, it is best to leave them a tight fit until all are nearly
finished, so that any error that may be discovered may be corrected
while finishing them.
[Illustration: Fig. 2301.]
[Illustration: Fig. 2302.]
In small nuts, if two are to be filed, a better plan may be followed.
The two nuts may be put upon a short piece of screw, as shown in Fig.
2301, and screwed firmly together. In doing this, however, it may be
found that the nuts will not tighten against each other, with the flats
fair one with the other. This, however, may be accomplished by winding
around the piece of screw, and between the nuts, a piece of waste,
twine, or rag, and then screwing them together until they bind
sufficiently and the sides come fair; the nuts may then be put in the
vice, the jaws of the latter meeting the end A of the screw and the face
B of the nut in the figure. Select the thinnest flat on either of the
two nuts, and file it and the one coincident to it, but on the other
nut, at the same time taking care that both are filed equidistant from
the screw. To test this, apply the gauge as shown in Fig. 2296. File
these faces down a little above size, and then loose the nuts and put in
an addition of waste or twine, so that the same faces shall not
coincide, and the two filed faces will serve as guides, down to which
their new contiguous faces may be filed, the hexagon gauge being applied
as before. By adding waste or twine, this process may be repeated, the
original, or first-filed faces serving as guides down to which to file
all the others, which will insure equal thickness of all the flats.
After roughing out all the flats in this manner, reverse the nuts on the
screw, so that the two chamfered faces come together, as in Fig. 2302,
and any want of truth in the parallelism of the flats one with the
other, or with the axial line of the screw, will become at once
apparent, and will be corrected in the finishing, providing that an
equal amount be filed off the respective sides that are in the same
plane as are A and B in the figure. Of course nuts filed in this way
require the application of the calipers and gauges, the same as
described for a single nut; but uniformity will be assured and the
filing truer, because the filing in small nuts, as an inch or less, will
be more true on account of there being a larger area for the file to
rest and steady upon. It is obvious that a plain cylindrical piece,
instead of a piece of screw, may be used, in which case the waste or
twine will be unnecessary; but in this case the plug, or cylindrical
piece, should be shorter than the length of the two nuts, and should not
be so tight a fit to the bores as to damage the threads.
In small nuts it will not pay to chip off the surplus metal, because
they cannot be held sufficiently firmly in the vice without suffering
damage from the vice-jaws, or even from copper clamps, while lead ones
are too soft to hold them.
[Illustration: Fig. 2303.]
The finishing marks, if any, should be in a line with the bore of the
nut, which gives the neatest appearance. The process is the same for a
bolt head, such as shown in Fig. 2295, as for a single nut, with the
exception that the gauge must be applied as in Fig. 2303, when testing
the truth of the flats with the axial line of the bolt, this being
necessary because of the roundness of the end face A, in Fig. 2303. The
distances D and C will be equal when the flat is true in that direction.
A pair of outside calipers form an excellent example in vice work. The
material should be good cast steel of an even thickness, and therefore
(unless for very large ones) saw blade will answer the purpose. It
should be well softened by being made to a low red heat and buried in
fine cinder ashes or lime, and allowed to cool there; the proper width
of this piece of steel being sufficiently greater than the size of the
caliper washer, to allow room for a chisel cut and leave a little to
file off in truing up the joint. The length should be somewhat more than
that required to make the legs, because a piece will be required to be
cut off the narrow end to give substance enough for the points. The size
of the washer should be drawn at each end of the steel, the centre of
the washer should be centrepunch-marked, and a line should then be drawn
to set off the two legs. The steel is then severed along this line, thus
getting out the two rough legs. When shears are not at hand, or when it
is not designed to use them for this purpose, three methods of dividing
may be pursued: First, we may drill small holes along the line, and cut
between the holes with a chisel. The objection to this is that the blade
is sometimes very hard to drill. Secondly, we may make centrepunch
marks along the line, and then cut along the line with a chisel; and
thirdly, we may drill a few holes at each end, and cut the middle with
the centrepunch and chisel. The entire drilling is the safest, and the
centrepunching the most hazardous, but it can be accomplished if the
centrepunching is done lightly and gone over several times, with the
chisel applied between the centrepunch marks, which will be much the
quickest plan of the three.
The hole is next drilled for the rivet, care being taken to make it
about 1/32 inch smaller than the proper size, because the drill will not
make a sufficiently true and parallel hole, and the latter must be
reamed or trued out; and again because the legs have to go into the fire
to be bent, and hence the holes may become damaged. There is another
consideration, however, in determining the size to drill this hole,
which is that the two legs require to be riveted together to bend them,
and it is as well to drill the hole to suit the piece of metal intended
to be used for this temporary rivet, which should be of brass or copper,
so as to drive out easily after the bending is done. During the bending
process the points should be thickened, care being taken not to twist
them in the process. If the vice hand does the bending, the following
instructions are pertinent: Heat the steel slowly and turn it over and
over in the fire so that the points may not get burned before the wider
parts are sufficiently heated. Let the fire be a clean one, that is,
with no gaseous or blazing coal about it, or the coal will stick to the
sides of the calipers, and they will get cool while being cleaned of
adhering coal after being taken from the fire. Begin the bending from
the thick end, carrying it forward by degrees. Strike light but rapidly
succeeding blows, placing the steel upon the round point of the anvil.
The bending completed, and the points being thickened, the edges of the
legs are trimmed upon an emery wheel or with a file, using the latter
lengthwise of the edges if a new one, or crosswise if an old one. A full
1/32 inch may be left to trim off after the calipers are put together.
The temporary rivet may next be driven out, first, however, gripping the
legs firmly and near to the rivet end with a hand vice, putting a piece
of sheet brass between each jaw of the hand vice and the steel;
otherwise the teeth of the latter will mark the steel, entailing a great
deal of extra labor to file the marks out. The rivet hole is then reamed
out to the required size, the two legs being held together by the hand
vice to render the reaming more steady and true by making the hole
longer when the two are together.
The next operation is to turn the rivet and washers. It is a very common
practice to turn two separate washers and a rivet. On account, however,
of the small amount of bearing in the washer holes, such washers are apt
to rivet up out of fair one with the other, making an unsightly joint
and causing them to be out of round when the edges of the joint are
filed up. A better plan is to turn a pin and washer, taking care to make
the diameters of the two exactly equal and the flat faces of each quite
level. The pin should be turned about 1/64 inch taper, the small end
being made a neat fit to the holes in the caliper legs, and should be
made of cast steel properly annealed. When finished, the head of the pin
should be gripped by a pair of lead clamps in the vice, the end being
left protruding so that the legs can be put upon it and revolved back
and forth with a good supply of oil and under hard pressure, so that the
pin will be forced a good and rather tight fit into the holes. This
process will also smooth out the holes and condense the metal around
both the holes and the pin. It is well to leave the pin to fit about one
half as tight as the finished joint requires to be. The washer should be
countersunk about three-quarters of the way through the hole, the latter
being left a close working fit to the pin.
The legs should be rough filed, second-cut filed, and smooth filed
before being draw-filed, care being used to keep the files clean, so as
to avoid scratches. During this filing, however, the pin should be tried
in the hole to see if the head comes fair down upon the face; thus the
pin forms a guide and test in facing up the joint of the leg, and this
is one of its advantages over the two-washer plan. After carefully
draw-filing and polishing the sides of the legs the fitting of the joint
is finished as follows: Place the two legs upon the pin in their proper
position, and then put the washer into its place. Then behind the washer
place another temporary one that will protrude beyond the end of the
pin; then grip the whole tightly between a pair of lead clamps or pieces
of thick leather in the vice; this will bring all parts of the joint
home. Take hold of one leg in each hand and move them backward and
forward as far as the vice will let them go, repeating the operation
about a dozen times or more. This will mark the high spots upon the
legs, which may then be taken apart again and have the bright parts
removed by a scraper. It is also well to place the flat face of the
washer upon a smooth file and rub it backward and forward under finger
pressure, which will tend to correct any defect in its flatness. When
the faces of the joint bear all over, it may be put together with oil
and placed in the vice as before. Work it well back and forth, take it
apart again and cut off the rivet to the required length, taking care
very slightly to recess the end to assist the riveting. The whole joint
should then be wiped quite clean, freely oiled, and put together ready
to rivet. The head of the pin should be rested upon a block of lead, so
that it will not get damaged. The riveting should be done with a small
light ball-pened hammer, the blows being delivered very lightly and
evenly all round the edge. As the riveting continues it is necessary to
move the legs occasionally to see how the tightening proceeds, and when
the legs are sufficiently tight, one of them may be gripped between
pieces of leather in the vice, while the other is well worked and
lubricated with oil. Then the riveted end should be filed off to very
nearly its proper height and shape, and the joint well worked back and
forth and round and round in the hand until it gets quite warm, when it
may be cooled in water and tried for tightness. If too tight, it may be
either worked until easy, or the riveted end of the pin may be tapped
with a hammer to loosen it slightly. The riveting being completed, and
the end filed smooth, the rounded part of the washer and the pin head
should be draw-filed with a very fine file moved in varying directions,
and then the polishing may be done with emery paper.
FITTING KEYS.--Keys that have been planed or milled will still require
fitting with the file to insure that they bed properly. If the key to be
fitted is taper and intended to fit top and bottom, the sides should
first be filed true to a surface plate, and fitted into the keyway in
the shaft, so that it can be slid up and down a good working fit. While
fitting it, however, it is well to try it once or twice in the keyway in
the wheel, as well as in the shaft, so as to see by the marks whether
the keyways in the shaft and wheel require any fitting at all, either to
make them quite square with the outside face, supposing it to be turned
off, or to give them a good even bearing surface. The key being fitted
sideways we must give the two keyseats a coating of red marking just
sufficient to show that the surface is of a red tint, and then put the
wheel in its place on the shaft. Then we bevel off the edges of the key
at each end, leaving a chamfer of 1/16 inch, and after facing off the
top of the key with a bastard file, we place it in the keyway and tap it
very lightly to a gentle bearing. After driving the key lightly home and
taking it out again, we may file it on the top and bed it on the bottom,
according to the indication of the marking, and re-insert it, tapping it
up until it is home, top and bottom, without being a driven fit at all;
on taking it out we file it according to the marks again, and if we
continue this process until the key is a good fit, it will not spring
the wheel the least out of true, no matter how tight, reasonably, it is
finally driven. The key must never be driven in or out dry, for it will,
in that case, inevitably cut during the first part of the operation; the
marking put on the keyway is sufficient lubrication, but after two or
three insertions the key also should be itself given a light coat, which
will serve as lubrication, as well as denote the fit.
The bearing or contact marks upon a key driven home very lightly may
show at one end or on one side only, while if the key was driven farther
in those marks may show all over, making the key appear to fit much
better than it actually does. This occurs from the elasticity and
compression of the metal of the keyway and key, the metal giving most
where the contact is hardest; from this it is apparent that a wheel
truly bored and a good fit may be set out of true by the key.
In Fig. 2304, for example, is a wheel hub W, assumed to be a good fit to
the shaft S, while the key K fits at the end A only. If the key be
driven tightly home, the wheel will spring over, so that instead of the
plane of its diameter standing at a right angle to the axial line of the
shaft as at D in Fig. 2305, it will stand at an angle as at E, throwing
the wheel out of true in that direction. This would occur not only on
account of the elasticity and compression of the metal of the keyway,
but also because the surface of the bore of the wheel and of the shaft
is not, even under the best of turning, smooth enough to come into close
contact all over, but are covered with slight projections or
protuberances, which may occur in spirals because of the turning tool
marks, or in localities because of differences in the texture of the
metal. In driving the key home these protuberances give way, and they do
so most where the contact pressure is greatest, which would be at G in
Fig. 2305, causing the wheel to cant over. If the wheel is not a good
fit to the shaft it will not in this case touch the shaft at C, Fig.
2305.
[Illustration: Fig. 2304.]
[Illustration: Fig. 2305.]
[Illustration: Fig. 2306.]
Now suppose the key to bear at _a_ and _b_, Fig. 2306, only, then the
wheel would be thrown out of true in a direction at a right angle to the
length of the key as denoted by the line E, which should stand as at D.
A properly bedded key binds the opposite half of the circumference of
the wheel bore to the corresponding half circumference of the shaft; but
if the key binds at one end only, as in Fig. 2304, the contact will be
at the end H only; hence the surfaces will soon compress, on account of
all the strain of the key falling on a small area, and the key will get
loose.
It is obvious then that if a wheel has not been bored to run true the
error may be to some extent corrected in fitting the key, but in this
case the key must be driven well home, and the wheel rim tried for
running true during the fitting process, the key being so bedded as to
true the wheel as far as the elasticity and compression will permit; but
a key thus bedded will not hold so firmly.
The distance a key of a certain length, breadth, and thickness, and of a
given taper, will drive after being pushed home by hand or lightly
tapped in with a hand hammer depends upon how closely it fits to its
seat, and upon the elasticity of the metal, as well as upon the force
with which it is driven. The workman usually, while fitting the key,
drives it well home occasionally, to see how much of its length to allow
for the final driving, and while doing so, if the key is a small one, a
hand set chisel or a piece of copper should be interposed between the
key head and the hammer (a blacksmith's set chisel is used for large
keys) to prevent the hammer from damaging the key.
In fitting keys to old keyways the key is made too long, and cut off
after being driven home. A long key is apt to bend in the driving, hence
it is not unusual to support it by holding a second hammer beneath and
against it to support it while being driven. In driving a key out,
especially if it is fast home, a quick heavy blow is best, as it is less
likely to burr, swell, or bulge the end of the key. But after the key
has started lighter blows will answer.
To make a key for an old sunk keyway, it is as well to fit a piece of
wood thereto as a guide in forging and fitting the key. If a _fast_
running grindstone or emery wheel is at hand, many will forge the key a
trifle large and then grind it as near as possible, and finish by
filing. This, however, does not produce good work; it is better to plane
the key all over, leaving a little in size for fitting. In preparing the
piece of wood referred to, it should not in the fitting be driven or
even forced in and out to try the fit, for the wood will compress and
the marks mislead as to the actual fit. The proper way is to chalk the
piece of wood and push it up the keyway just tightly home, then withdraw
and fit it again.
In cases where the key is forged to very nearly the finished size, and
is finished by the file, as sometimes occurs when away from the shop, it
is best to forge the key with a gib head, as in Fig. 462, to assist in
extracting it, especially when it is difficult to drive the key out from
the back end, or when the keyway does not pass entirely through. The key
should be finished with a smooth file and with the file marks
lengthways; it is, in fact, better to use a small smooth file and
draw-file it, taking care to ease the high spots the most; and before
driving it home both it and the keyway should be oiled.
If a keyway is to be cut by hand through a bore, as in a pulley or
gear-wheel bore, its width should be marked with a [T]-square. If its
width does not exceed 1/2 inch a cape chisel a little less (say 1/32
inch less) than the finished width of keyway should be used, which will
leave a little metal for the sides to be filed true. If the keyway be an
inch wide it is better to take a cape chisel about 1/4 inch wide and cut
a groove along each side of the keyway (keeping close to the marked
line), and then cut out the middle with a flat chisel. The sides and
bottom of the keyway should be surfaced true with the file.
If a keyway is to be cut in a shaft the cape chisel should be used in
the same manner as above. But in both cases it is best, when filing, to
occasionally ease out the corners with the edge of a half-round file,
for reasons which will be explained presently.
In chipping a keyway in a bore the cut must not be carried entirely
through from one side, or the metal at the end of the cut will break
out, and even in wrought iron this is apt to occur, so that it is
necessary to cut the keyway from each end, or, at least, nick it in at
one and cut it from the other end. In long key ways it is handiest to
cut them half-way from each side, using, in the absence of anything
better, a piece of planed wood and red marking or chalk to try the
keyway with.
[Illustration: Fig. 2307.]
In cutting out through keyways by hand the location of the keyway is
marked off by lines on both sides of the stub end of the rod, and then
the mass of the metal is removed by drilling through as many holes as
can be got in the size of keyway required, as shown in Fig. 2307, in
which W is the work, B C D E the location of the keyway, and 1, 2, 3, 4
are the holes, taking care to have the drill rather smaller than the
width of requisite keyway. The holes are drilled half-way through from
each side, which is done to keep the keyway true; for if the drills were
to run a little to one side, as they are apt to do from a variety of
causes, a great deal of work would be required to correct the error.
If the keyway is of sufficient dimensions to admit of the use of a
chisel, the pieces left between the drilled holes are chipped out, and
for this purpose a side chisel is found very useful, not only to nick
the sides of the pieces left by the drilling, but also to take the
finishing chipping cuts on the sides of the keyway. To cut out the
square corners of the keyway, the diamond-point chisel shown in Fig.
2171 is employed.
[Illustration: Fig. 2308.]
If, however, the keyway is a very deep one, requiring long and slight
chisels, the chipping process may be greatly reduced, or in fact
entirely dispensed with, by plugging up the holes first drilled in the
stub end by driving pieces of round iron tightly into them, and then
drilling new holes, having their centres midway between the pieces so
driven in, as at A in Fig. 2308. After the latter drilling, the
remaining pieces of plugs are driven out, leaving the centre of the
keyway cut clear through and the sides with a series of flutes in them,
as shown at B, Fig. 2308 (in which 1 2 are the plugs and A is a centre
for the new hole at that end), which should be filed away with a file as
thick or strong as the clear space will allow. These plugs must be of
the same metal as that in which the keyway is cut, otherwise the drill
will be apt to run to one side.
To insure truth in the surfaces, a surface plate to test with is an
absolute necessity, while to test the parallelism, a small sheet iron
gauge is used, which gauge may afterwards be employed as a guide whereby
to plane the thickness of the gib and key.
In cases where a slotting machine is at hand, it is sometimes the
practice to cut out one end of the keyway to a sufficient length to
admit a slotting tool, and then to slot out the remainder. This plan is
often resorted to in getting out keyways of unusually large dimensions.
A much more usual method, however, is to employ slotting or keyway
drills.
It is obvious that the ends of the keyways cut by drills are half round;
hence, if square corners are required, they must be cut out square with
the chisel shown in Fig. 2176, and afterwards filed out true. As a
general rule, keyways cut with these drills require filing on the sides
to get proper smoothness and bearing for the keys; and here it may be
remarked that, in filing the corners of the keyway, a safe-edge file
must be used, so that the two faces forming the corner will not be
operated upon simultaneously, because that would require that the file
be used in a straight line laterally as well as horizontally, and this
is impracticable even in the hands of the most skilful.
Even the square file should have a safe edge upon it, and such an edge
is usually produced by grinding the teeth off one face of the file. In
selecting the face to have the teeth ground off, choose a face that is
hollow in its length, or, if none of the faces is hollow, then select a
face that is at a right angle to a good face of the file. It will be
noted that with one safe edge only the square file will require turning
over in order to operate upon both corners and maintain in each case a
safe edge of the file against the flat sides of the keyway. For this
reason many workmen select the two best parallel faces of the file and
grind off the two other faces, giving to the file two safe edges, one
opposite to the other. In this case either of the cutting faces of the
file may be used upon the whole end face of the keyway operating close
up to the corner, or if the file is much narrower than the keyway it may
be used with a side sweep that will prevent the file from pinning, and
produce much truer filing.
It is useless to attempt to cut out a square corner with a square file
unless one edge of the latter is ground safe, because the teeth of the
file itself do not form a square corner, and it is therefore only by
grinding the teeth off one side that the points of the file teeth can be
brought full up to a sharp angle. Here, however, it may be noted that
even if the filing is performed with the best of safe-edge files, and as
carefully as possible, it will still be necessary to square out the fine
corners with the edge of a fine smooth half-round file.
If the edges of the keyways are rounding, as they are sometimes made
where strength is required in the strap, it is better to take a file
nearly or about 1/8 inch larger in diameter than the width of the
keyway, and grind two safe edges on it, otherwise the round file is very
apt to go astray and cut the sides as well as the edge of the keyway.
An equaling file is much better for keyways than one actually parallel.
[Illustration: Fig. 2309.]
Another way employed to finish small keyways is by the aid of the tools
shown in Figs. 2309 and 2310, which are termed drifts, because they are
driven through with a hand hammer. That shown in Fig. 2309 is intended
for holes having but little depth and not requiring to be very true,
such, for instance, as those cut in the ends of keyways or bolts to
receive cotters; the thickness at A A is made greater than at B C to
give the cutting edge clearance.
The form shown in Fig. 2309 is for use by hand, the teeth being cut
diagonally instead of across, as at A A, to preserve the strength. This
end may also be attained by making the serrations round at the bottom,
as shown in the figure.
[Illustration: Fig. 2310.]
The slant of the teeth on one side of the drift should cross the slant
of the teeth on the diametrally opposite side, because if the teeth on
opposite sides were parallel one to the other the drift would have a
tendency to move over to one side, and crowd there during the process of
drifting.
In using these drifts the keyway should first be filed out to very
nearly the finished size, leaving very little duty for the drift to
perform, although the drift may be driven a short distance into the
keyway occasionally during the filing, so as to show where filing is
requisite. The work must lie flat and level upon a metal block, lead
being preferable, and oil freely supplied to the drift. "If the hole is
a deep one, and the cuttings clog in the teeth, or if the cut becomes
too great (which may be detected by the drift making but little
progress, or by the blows sounding solid) the drift must be driven out
again, the cuttings removed, and the surplus metal, if any, removed by
filing. The drift must again be freely oiled, and driven in as before,
and the operation continued until the drift is driven through the
keyway. After the drift has passed once through it should be reversed
(or, if a square one, turned a quarter revolution) and again driven
through, so that each side of the drift will have cut on each side of
the hole, which is done to correct any variation in the size of the
drift" ("Complete Practical Machinist").
The great desideratum in using these drifts is to drive them true, and
to strike fair blows, otherwise they will break. While the drift is
first used, it should be examined for straightness at almost every blow;
and if it requires drawing to one side, it should be done by altering
the direction in which the hammer travels, and not by tilting the hammer
face.
[Illustration: Fig. 2311.]
In Fig. 2311, suppose A to be a piece of wood and B and C drifts which
have entered the keyways out of plumb, as shown by the dotted lines D
and E. If, to right the drift C, it was struck by the hammer F in the
position shown, and travelling in the direction denoted by G, the drift
C would be almost sure to break; but if the drift B was struck by the
hammer H, as shown, and travelling in the direction denoted by I, it
would draw the drift B upright without breaking; or, in other words, the
hammer face should always strike the head of the drift level and true
with it, the drawing of the drift, if any is required, being done by the
direction in which the hammer travels. When it is desired to cut a very
smooth hole, two or more drifts should be used, each successive one
being a trifle larger in diameter than its predecessor. Drifts slight in
cross-section or slight in proportion to their lengths would be tempered
evenly all over to a blue, while those of stout proportions would be
tempered to a deep brown, bordering upon a bright purple.
For cutting out long narrow keyways, that are too narrow to admit of a
machine cutting tool, and for very true holes, not to be cut out in
quantities all of the same dimensions, it has no equal.
[Illustration: Fig. 2312.]
Hand drifts are sometimes used to cut keyways in small bores, as in
small hubs, the method being shown in Fig. 2312, in which A represents a
pulley with a keyway to be cut in the hub _b_; _c_ is a plug, and _d_
slips of iron placed between _c_ and the drift _e_ to press the latter
to its cut. It is obvious that in this case the keyway in the pulley
will be cut parallel, and the taper must be provided for in the key seat
in the shaft. Keyways cut in this way are more true than those filed
out. It is also obvious that the sides of the keyway, as well as its
depth, may be finished by a drift, and this is very desirable (on
account of insuring parallelism) when the key is to act as a feather
that is to have contact on the sides and not bind top and bottom.
The most improved form and method of using this class of tool, however,
is as follows:--If a keyway is to be cut out of solid metal, holes are
drilled as closely together as the length of the keyway will admit,
their diameter nearly equaling the required width of keyway, after these
holes are drilled through the metal remaining between them.
TEMPLATES.--Templates for vice work are used for two purposes: first to
serve as guides in filing work to shape and size, and secondly to test
the finished work. When used as guides to file the work they are mainly
used to work of irregular, curved, or angular form, to which the square
and other ordinary vice tools cannot be applied.
Fig. 2313 represents a template for filing out a square hole. The edges
A, B are at a right angle to each other, the wire simply serving as a
handle.
There are two methods of applying this template; the first is to file
out two opposite surfaces of the hole to the required diameter, making
them true and parallel one to the other, and to then employ the template
while filing out the remaining two sides; the other is to file out one
side and apply the template from that as a base for the other sides. The
first is preferable because the liability to error is a minimum.
When work is to be from a template, the latter obviously becomes the
original standard, and in many cases the best method of forming it so as
to insure correctness and enable its proper application to the work is a
matter of great consideration. The shape of the template must, of
course, be marked by lines which should be as fine and as deep as
possible. But it does not matter how closely the template may be filed
to these lines, it will still have some error, and this can in many
cases be discovered and corrected during its application to the work. In
the following examples there are principles which will be found of
general application:--
[Illustration: Fig. 2313.]
[Illustration: Fig. 2314.]
[Illustration: Fig. 2315.]
[Illustration: Fig. 2316.]
[Illustration: Fig. 2317.]
Let it be required to make or test a piece of work such as in Fig. 2314,
the teeth to be equally spaced, of the same angle, and of equal height.
A template must be made of one of the two forms shown in Fig. 2315. To
begin with, take a piece of sheet metal equal in width to at least two
teeth, and, assuming that the template is to have two teeth, file its
sides P Q, in Fig. 2316, parallel, and make the width equal to twice the
pitch of the teeth. We next divide its width into four equal parts by
lines, and mark the height, as shown in Fig. 2316. If we desire to make
the template such as at A, we cut out the shaded portion; or for the
template at B, the shaded portion. It will be observed, however, that in
template A there are two corners C and D to be filed out, while at B
there is but one E, the latter being the easier to make, since the
corners are the most difficult to file and keep true. The best method of
producing such a corner is to grind the teeth off the convex side and at
the edge of a half-round file, producing a sharper corner than the teeth
possess, while giving at the same time a safe edge on the rounded side
that will not cut one angle while the other is being filed. But when we
come to apply these templates to the work, we shall find that A is the
better of the two, because we can apply the square S, Fig. 2317, to the
outside of the template, and also to the edge F of the work, which
cannot be done to the edges G of the work and H of the template, because
the template edge overhangs. We can, however, apply a square S´ to the
other edge of B, but this is not so convenient unless the tops of the
teeth are level.
[Illustration: Fig. 2318.]
[Illustration: Fig. 2319.]
Assuming, therefore, that the template A is the one to be made, we
proceed to test its accuracy, bearing in mind that for this purpose the
same method is to be employed whatever shape the template may be.
Consequently, we make from the male template A, Fig. 2318, a female
template K, beginning at one end of K and filing it to fit A until the
edges of A and K are in line when tested by a straight-edge S. We then
move the template A one tooth to the right, and file another tooth in K,
and proceed in this way until a number of teeth have been made, applying
a square as at S, Fig. 2319, to see that the template A is kept upright
upon K. When K has been thus provided with several teeth that would fit
A in any position in which the latter may be placed, we must turn
template A around upon K to test the equality of the angles. Thus,
suppose at the first filing the edges _a_, _b_, _c_, _d_, upon A
accurately fit the template K, and the straight-edge shows the edges
fair; then if we simply turn the template A around, its angles, which
were before on the right, will now be on the left, as is shown at the
right of Fig. 2318. Thus in one position _a_ fits to _e_, in the other
it fits to _h_, or _b_ fits to _f_, and when turned around it fits to
_g_, and so on. Supposing that when thus turned around the angles do not
coincide, then half the error will be in the teeth of A and one-half in
those of K, and the best plan will be to correct them on A to the
necessary amount as near as judgment will dictate, and then to apply K
as before, continuing this process until A will fit anywhere in K, and
may be turned around without showing any error. But at each correction
the straight-edge must be applied, and finally should be tried to prove
if the teeth tops are level. We thus have two interchangeable templates,
of which A may be used on the work and K kept to correct A when the
latter becomes worn. It may be as well to add, however, that in first
applying A to K it is best to press the straight-edge S against the edge
of K, and hold it there, and then to place A against S, and slide it
down into K.
[Illustration: Fig. 2320.]
[Illustration: Fig. 2321.]
Fig. 2320 represents an example in which, the form being a curve, it
would be best to have the template touch more than two teeth, as shown
in the cut. By letting the side A, Fig. 2321, of the template T
terminate at the centre line of the two curves, and the end B terminate
at the top of a curve, turning the template around would cause end A to
envelop side C of the middle curve, thus increasing the scope of the
template. Suppose, however, that the base curve D required to be true
with the teeth, then a second template T´ must be used, its ends at E
and F measuring an equal length or height, so that when they are placed
even with the ends of the work, the distances G H being equal, the
corrugations will be true to the curve D D. Now let it be supposed that,
instead of making a template to test a piece of work such as in Fig.
2321, it is required to make a template for use in making another piece
of work that is to fit to piece W, then template T in Fig. 2321 will not
answer, because it is a female template, whereas a male one is required,
so that the edge of the template may coincide with that of the work. But
we may convert T, Fig. 2321, into a male template by simply cutting off
the edge A as far as the line J, and causing its right-hand edge to
coincide with the edge of the work so that the latter, after being
fitted to the template, may be turned upside down and fit upon the piece
of work.
[Illustration: Fig. 2322.]
[Illustration: Fig. 2323.]
[Illustration: Fig. 2324.]
In Fig. 2323 is an example in which the forms of both sides of a piece
require to be exactly alike, and the easiest method of accomplishing
this is as follows:--The face A should first be made true, and face B
made parallel to A. A centre line C may then be drawn, and from it the
lines E, E may be marked. The lines D are then drawn parallel to A A,
lines E being made square to D and to A. The sides E may be calipered to
width and parallelism, and all that will then remain is to file the
angles F, F and the ends G, G to their required lengths. For F, F all
that is necessary is a template formed as in Fig. 2324. The object of
dressing the ends G, G last is that if they were finished before, their
faces E would have to be made at exactly correct distances from them,
which would render the job considerably more difficult.
[Illustration: Fig. 2325.]
[Illustration: Fig. 2326.]
Fig. 2325 represents a sketch for a piece of work whose two sides are to
be shaped exactly alike, requiring a template of the form of the work,
as shown. From this a second template, Fig. 2326, is made, and to this
latter the work may be filed. To make the template in Fig. 2325, which
represents the work, the edge _x_ _x_ must be made straight, and the edge
D parallel to it at the proper height. A centre line S is then marked,
and the edges at E may be filed equidistant from S and square to D;
hence they will be parallel to each other. The side sections F should
then be filed equidistant from S and parallel to each other. They should
be the proper width apart and square to D, being tested in each of
these respects. The line joining E and F should be left full, as
denoted by the dotted line at A on the right. The edges at C, C should
then be filed, calipering them from the edge _x_ _x_. Edges G, G are
obviously equidistant from S and parallel to S, or, what is the same
thing, at a right angle to _x_ _x_, from which they may therefore be
tested with a square, and, finally, the edges B are made parallel to _x_
_x_, and the ends H made square to _x_ and equidistant from S. We have
now to file the angular groove at A, and to get this true after marking
its depth from the lines at A, we file it first to the lines as near as
may be by the eye and very nearly to the full depth. We then make a
small supplemental male template T, Fig. 2327, equal in width to the
distance E F, or, in other words, to the width of the step at A, and
having its edges quite parallel. Its end is then filed to fit the groove
at A, when its edge meets and coincides with edge E, as in Fig. 2327, T
representing the supplemental template. It is clear that when the
[V]-groove A is so filed that T will fit it with either of its edges
against E, the angles of the groove will be alike, and we may then make
a male gauge, as in Fig. 2326, that may be used to mark or line out the
work and to use as a template to file it to, its edge H being kept
parallel to face D, Fig. 2325, of the work.
[Illustration: Fig. 2327.]
CHAPTER XXVII.--VICE WORK--(_Continued_).
[Illustration: Fig. 2328.]
[Illustration: Fig. 2329.]
There are two principal kinds of connecting rods, first those in which
the brasses fit in spaces provided in the solid rod, and which are known
as solid-ended connecting rods, and second those in which the brasses
fit in a strap secured by bolts or keys to the end of the rod. In Fig.
2328 is shown the simplest form of solid-end connecting rod. It consists
of a rod enlarged at its end to receive a brass held up to the journal
by a set-screw as shown, one-half the bore being provided in the rod and
one-half in the brass. The objection to this kind of rod is that as the
bore wears the rod gets shorter and no means is provided to restore its
length, and that during the pulling stroke of the rod the whole of the
strain is concentrated on the end area of the set-screw, and this causes
it to imbed in the brass, giving play to the brass unless frequent
adjustment is made. It is, therefore, difficult to readily maintain a
very accurate adjustment of fit with a simple set-screw of this kind.
This may be to some extent remedied by the construction shown in Fig.
2329 in which the half brass A threads upon the stem of the rod, so that
when it wears shorter to the amount of half the pitch of the thread upon
the rod end, the brass may be unscrewed half a turn, and the original
length will be restored. The cap is held on by two screws, which may
have slotted heads as shown, or screws with check-nuts to prevent the
screws from slackening back, as all screws are apt to do that receive
alternating strains in reverse directions.
[Illustration: Fig. 2330.]
[Illustration: Fig. 2331.]
[Illustration: Fig. 2332.]
[Illustration: Fig. 2333.]
Yet another simple form of solid-end connecting rod is shown in Fig.
2330, there being two brasses with a key on one side and a set-screw on
the other. In this case, as soon as either brass is moved by the key it
can fit the rod at the top and at the bottom only; hence there is but
little to hold the brasses sideways in the rod, and furthermore the
brasses are damaged from the key and the set-screw acting directly upon
them, as will be explained with reference to strap-ended rods. In Fig.
2333 is shown a very substantial form of solid-ended rod, a sectional
view being shown in Fig. 2331. The bottom or back brass A has a flange,
as shown in Figs. 2331 and 2332 at A, which secures it to the rod end at
the back. The top or key brass B has the keyway partly sunk in it, and
the key binds against one side as well as on the bottom of the keyway,
and this draws that brass close down to the face of the rod, as shown in
Fig. 2331.
In this as in all other connecting rods in which one edge of the key
beds against the back of the brass, the taper for the key should be cut
in the rod so that the edge which meets the brass will stand square
across the opening for the brass; in this way the back of the brass will
also stand square across, which is easier to mark off and cut, plane,
and fit. If the taper for the key is cut on the brass, marking the
latter and fitting it become more difficult, as it must be put in and
out of its place to fit and bed the taper for the key edge, whereas, in
the other case, it can be squared with a square while planing and
fitting. As the bore of connecting-rod brasses wears, and the lost
motion incident thereto is taken up (by driving in the key) the location
of the brasses in the rod end is altered, making the rod longer or
shorter according to the location of the key. But when this wear has
been sufficient to let the key pass through the rod, slips of iron
termed liners are inserted between the backs or bedding faces of the
brasses and the end of the rod or crown of the strap, as the case may
be. In putting in these liners the location of the brasses in the rod
end may be adjusted so as to bring the brass back to its original
position and restore the rod to its proper length, and in doing so the
back brass, as distinguished from the key brass, is the one to be lined
first.
[Illustration: Fig. 2333.]
[Illustration: Fig. 2334.]
In the rod ends shown in Figs. 2333 and 2334 the joint faces (that is
the faces where the brasses meet) must be filed away to take up the
wear, hence the rods get shorter. In Fig. 2333 the liner may be placed
behind either brass, A or B, or behind both, the thickness of that
behind A adjusting the length of the rod (which is always measured from
centre to centre of the respective brass bores), while the thickness of
that placed behind B would simply act to prevent the key from passing so
far through the keyway. To prevent as far as possible the wear from
altering the length of the rod, the key at one end of the rod is placed
outside the crank pin or at the outer end of the rod, as in Fig. 2333,
while at the other end it is placed between the brasses and the stem of
the rod, as in Fig. 2334. In this latter case the thickness of liner
placed behind the key brass B (as the brass against which the key bears,
or the brass next to the key, is always termed) would adjust the length
of the rod, while the thickness of liner placed behind the back brass
(as the other brass is termed) would be the one to adjust the distance
the key would pass through the keyway.
[Illustration: Fig. 2335.]
In this form of rod end, as in many other solid-ended rods, the flange
or collar of the crank pin, if solid with the pin, requires to pass
through the opening in the rod end which receives the brasses. This may
be accomplished by making that opening large or wide enough to pass over
the crank-pin collar (which will increase the width of the brasses, and
hence that of the rod end); or else the crank-pin collar may have two
flat places filed on it, as in the end view shown in Fig. 2335. The
objection to this plan is that the rod can only be taken on and off in
one position of the engine; that is, when the two flat places A and B,
Fig. 2335, stand parallel with the length of the rod.
[Illustration: Fig. 2336.]
[Illustration: Fig. 2337.]
[Illustration: Fig. 2338.]
[Illustration: Fig. 2339.]
[Illustration: Fig. 2340.]
[Illustration: Fig. 2341.]
[Illustration: Fig. 2342.]
It will be noticed in Fig. 2331 that the brass B does not fill the space
in the rod. This is because that brass has to pass in over crank-pin
collar and push up into the journal after it is in the rod. To make this
space as small as possible, and to enable giving the crank pin as large
a collar as possible, the key brass is sometimes beveled off, as shown
in Fig. 2336 at A B. Another form of this rod end is shown in Fig. 2336,
in which there are two keys to the brasses, the object being to adjust
the keys to maintain the rod of its proper length. In order to
facilitate making this adjustment, there should always be upon the face
of the rod end centrepunch marks, as shown in Fig. 2338 at F and G, or
else two deep marks, as shown at C D in Fig. 2337. Then, in lining up
the brasses to set the key back, the rod may be restored to its original
length by putting behind the back brass a piece of metal of such
thickness as will bring the centre of the bore of the back brass B even
with the centrepunch or other marks. This being the case, it does not
matter about the exact thickness of the piece of metal put behind the
other brass, since a variation in that will only act to let the key come
more or less through the rod end without affecting the length of the
rod. In Fig. 2337 is shown a form of rod end sometimes used. The end
being open, the brasses pass through it. In this case the whole strain
of the pull of the rod falls upon the edge of the gib at top and bottom
of the strap, causing the gib to wear out very fast; furthermore, the
back brass condenses the metal at the back of the brass opening, acting
to pene it and throw the points of the rod end open, which it always
does, the jaws of the gib imbedding in the jaws of the rod. This opening
of the rod jaws makes the brasses loose in their places; hence this is a
weak and undesirable form of rod end, though very convenient to take on
and off. In Figs. 2338, 2339, 2340, and 2341 is shown a form of
solid-ended rod of more modern construction. In this case a wedge A is
used instead of a key, being adjusted by screws passing through the rod
at the top and bottom, it being obvious that the set-screws may have
check-nuts added. B is the back brass, and C the key brass. In this case
the flange of the brass goes next to the crank pin, and a plate D is
provided to serve as a flange on the front face of the brass. In Fig.
2338 this plate is removed to show the wedge A; but it is shown in the
plan view, 2339, and the end view, 2340, and by itself in Fig. 2341. A
groove is cut on each side of the two brasses and the plate spans the
brasses, passing up the groove being held in position by a screw at E.
The opening for the brass (in the rod end) is here shown wide enough for
the rod end to pass over the collar of the crank pin, but in many cases,
with this as well as with other forms of solid-ended rods, the crank pin
may be made plain--that is, without a flange--and have a washer secured
by a screw, so that by removing the washer the rod may be put on with
the brasses already in place, and made no thicker (at the joint face)
than is necessary for strength. In Fig. 2342 is shown what may be termed
a clip-end connecting rod, the screw closing the rod end (to take up the
wear) against the spring of the metal. It is obvious that in this case
the hole may receive a brass bush split as is the rod end and secured
from turning by a pin. Fig. 2343 presents another form of solid-end rod,
which admits of the use of a brass having a flange on both sides of the
strap, and will take on and off by removing the cap B. If the crank-pin
collar is solid, the brasses must be placed on the crank pin, and the
rod, with the wedge in place, lifted or lowered to the brasses; but if
the crank pin has a washer and bolt, the rod may be put together and
slipped on its place.
A compromise between the solid and the strap-rod end is shown in Fig.
2344, which represents a design used upon the fast engines of the
Pennsylvania Railway. The piece A takes out to enable putting on the
rod or taking it off, A being secured in position by the bolt and nuts
shown. This forms a solid and durable rod that is much less costly to
make than strap-ended rods.
[Illustration: Fig. 2343.]
[Illustration: Fig. 2344.]
[Illustration: Fig. 2345.]
[Illustration: Fig. 2346.]
[Illustration: Fig. 2347.]
[Illustration: Fig. 2348.]
The simplest form of strap-ended connecting rod is that shown in Fig.
2345; S is the strap, secured to the rod end by the key D and gib C. A
is the top, and B the bottom, or crown brass, and E the set-screw for
securing the key in its place. [When the rod ends are forged in separate
pieces, to be afterwards welded to the stem of the rod after the strap
brasses are fitted up (which is done for convenience in handling them
while fitting them up), they are termed stub ends.] This form of rod
affords great facility for connection with the journals as the strap is
easily removed. As the strap, however, is only secured to the rod by the
gib and key, and as these have a small amount of area on the sides, it
is not unusual to employ two gibs and one key, as in Fig. 2346, which
holds the strap more securely, and more effectually prevents its
movement sideways upon the rod end. In rods in which gibs and keys alone
are used to hold the strap to the rod, the strap moves along the rod as
the key passes farther through the strap, and the fit of the strap to
the rod must be easy enough to permit of this motion; hence it cannot be
locked to the rod. This, however, may be done by the employment of a
bolt as well as a gib and key, as is shown in Fig. 2347. The edge of the
gib here abuts against the back of the top brass, or key brass, as it is
sometimes termed, which is objectionable, inasmuch as that it is apt to
indent the brass, as shown in Fig. 2348 at B. This causes the bore to
close at A, and causes the journal to heat, while it makes the brass fit
loosely between the jaws of the strap, because it stretches the metal at
the back of the brass, which has the same effect as pening it with the
hammer.
In Fig. 2349 is shown an end of a connecting rod, such as is employed on
American locomotives, the use of a gib being dispensed with, and the
strap being held by two bolts. To prevent the edge of the key from
imbedding in the brass, a piece of hardened steel is sometimes placed
between the key and the brass, as shown in the figure.
In some designs this method is reversed, the gib being prolonged in a
screw-thread, as shown in Fig. 2350, and the key head is carried over as
shown. Two wing nuts are provided for adjusting the key, which enables
its adjustment without the employment of a wrench or hammer.
To prevent the end of the set-screw from raising a burr on the key,
which would prevent its easy motion through the keyway, a shallow groove
is sometimes cut along the key, as in Fig. 2351 at A, the end of the
set-screw binding on the bottom of that groove.
In other forms of rod a gib and key are used as well as two bolts. This
not only holds the strap very firmly, but it prevents to a certain
extent the pening of the back of the brass, explained with reference to
Fig. 2348. It is obvious that in the absence of a gib the key moving
under friction against the brass stretches the metal more than a gib
that presses against the brass, but has no motion endways.
[Illustration: Fig. 2350.]
[Illustration: Fig. 2351.]
[Illustration: Fig. 2352.]
In Fig. 2352 the strap is held by bolts having nuts at each end, instead
of a solid head at one end and nuts at the other. The single nuts at the
top serve to draw the bolts out when the rod is to be taken apart, thus
saving the use of the hammer for that purpose.
[Illustration: Fig. 2353.]
In Fig. 2353 is shown a form of rod in which the strap is held by two
dies A B, and a bolt which passes through the strap, the dies, and the
rod end.
[Illustration: Fig. 2354.]
In Fig. 2354 is a form of rod end in which the strap ends are keyed
against abutments on the rod by means of the key A. The abutments and
strap ends being bevelled, keying up the strap with A closes it down
upon the rod.
[Illustration: Fig. 2355.]
In Fig. 2355 is a form of rod end largely used upon marine engine work;
A is the end of the rod, B, B the brasses, and D, D bolts passing
through the brasses. Here we have no means of correcting the alteration
of length due to the wear, unless a line is marked on the rod end, as at
C, and the distance that line should stand from the centre of the brass
bore is marked beside it, as is denoted by the figure in the cut,
indicating that the line should stand 9 inches from the cuts of the
brass bore.
In general practice the inside jaw faces of connecting rod straps and
the faces of the rod are made parallel, which serves very well when the
duty and wear is not great; but when the wear and tear is great, as in
locomotive work, it is much better to make them taper; indeed, they are
in any event better taper, because in that case the brasses can be made
a tighter fit. The reason for making them parallel is because they can
be more readily planed so than taper; but a parallel strap is more
difficult to fit, and cannot be made so good a fit as a taper one, even
when new, while it is very much more difficult and expensive to repair.
[Illustration: Fig. 2356.]
When the faces of the stub end (or, more properly speaking, of the
block) are parallel one to the other, and the inside faces of the strap
are also parallel, the strap must be made a very easy fit to the block,
in order to be an equal fit from end to end; for if the strap fits as
tightly as it should to be a good job, it will, when put on the rod,
spring open, fitting across A, Fig. 2356, only; this because the strap
springs open from contact at A. The fit, then, can only be such as will
not have force enough to spring the strap open, and this is very small
indeed even in a very strong strap. It is within the mark to state that
in a strap measuring 4 inches between jaws, at A in Fig. 2356, it can be
forced by hand on the rod sufficiently tight to spring them open 1/16th
of an inch at B, B. When the brasses are fitted into the strap a second
difficulty arises, inasmuch as they must be made a very easy fit, or
else they will spring the strap open so that it will neither fit at A
nor at B, whereas it is desirable that the bottom brass drive home, and
the top brass, or one nearest the rod, just push home by hand.
When the rod requires repairing a more serious difficulty arises.
Suppose, for example, that the strap requires refitting to the rod, then
it must evidently be closed between the jaws, especially if the rod end
requires filing up, as it usually does. Now the jaws being parallel
cannot be closed without being taken to the blacksmith shop and closed
across the crown, as at A in Fig. 2357; for if the jaws are closed (as
they might be) by pening the corners B, C the jaws would close as
denoted by the dotted lines. The brasses will have to be made larger
than the diameter at D, in order to fill the space at A, and will be an
easier fit as they pass from D to A, whereas the opposite should be the
case. The strap must therefore be closed across A in the blacksmith's
fire; this will scale the crown end and render it necessary to file down
the whole of the surface on each of the side faces of the strap and rod
in order to make them parallel, as they must be to have the flanges of
the brasses fit when home in the strap.
[Illustration: Fig. 2357.]
The blacksmithing will in most cases render it necessary to file out the
keyways, and this again entails the making of a new gib and key. All
this extra work may be avoided by making the block and strap a little
taper. But before proving this it may be noted that when the rod is made
parallel the strap may be made to fit tightly by making the jaws taper,
as shown by dotted lines in Fig. 2357; so that when the strap is on the
rod, and the jaws spring open by reason of the close fit, the fitting
surfaces will be parallel. Such a construction would be faulty however,
for the brasses would fit too tight when entering the strap, and get
easier as they passed to their places, whereas, as already stated, the
exact opposite should be the case.
[Illustration: Fig. 2358.]
Let us now observe the advantages of a strap, whose inside faces are
made as in Fig. 2358; smaller at A than at B, and also at C than at D,
while the thickness from A to B is greater than that from C to D, while
the widths C D are less than the corresponding width of the rod.
First, as to fitting the strap to the rod. It may be made so tight to
the rod that it will only just pass on when pushed by the hand.
Second, this will render possible a tighter fit than would be possible
with a parallel strap and rod.
Third, the width B A being taper, the brasses may be easier made a good
fit, because there will be some metal to fit on after they enter at B.
Fourth, the brasses may be made a tighter fit, the bottom brass being
tight enough to spring the strap a trifle, easing but not destroying its
fit on the rod.
Fifth, the top brass may be made a handsliding fit to the strap without
springing the strap open, which being already under a tension because of
the spring due to the bottom brass, will be more rigid and permit of a
tighter degree of top brass fit, without springing open and away from
the rod.
Sixth, this will leave the bottom brass a tight driving fit, and the top
a hand sliding fit, which is desirable, because the top brass has to be
taken out to get the rod off while the bottom brass remains in its
place.
[Illustration: Fig. 2359.]
Seventh, what is of more consequence than all, the strap can be more
easily and cheaply refitted to repair it. Thus, in Fig. 2359, suppose
the strap to have been closed by pening at D; then whether the end D
will be narrowed will depend on the amount the strap was closed, and the
amount of taper it had before closing. Let us take, however, the most
unfavorable conditions, and suppose that the amount of taper was so
small, and the amount of closing by pening so great, that the jaws were
made taper and smallest at D. Then the amount to be filed off to bring
the width of jaw correct, and a fit to the strap, will be less than if
the strap jaws were formed as in Fig. 2357, as will be seen by comparing
Fig. 2357 with Fig. 2359, the amount to be filed away being that between
the dotted and the full lines in both figures; the amount of closure
being the same in the two figures.
But there is another great advantage, inasmuch as in pening, the strap
may be pened and tried on the rod, the strap being pened and tried
alternately until the required fit is obtained, which is not practicable
with upsetting in the blacksmith's shop.
Again, the keyways in the strap will not be set out of true with those
in the rod, as they are apt to be when upsetting is resorted to, nor
will the strap be scaled; hence the side faces will require but little
filing.
Furthermore the step may be located so as to come against the rod end
when the wear has let the key down, and this will prevent the strap from
passing too far upon the rod, and, therefore, tend to prevent the rod
length from being improperly altered from errors in the thickness of the
liners placed behind the brasses to take up the wear.
FITTING UP CONNECTING RODS.--The method of fitting up a connecting rod
depends entirely upon its size. Very small rods to be made in numbers
are usually got out by means of special devices which leave the fitter
but little to do; indeed, sometimes the machine work is so accurately
and finely fitted and finished as to finish the rod without the aid of
the vice hand, save to put it into its place upon the engine or machine.
As, however, the dimensions of the rod increase, this method of
manipulation is in practice departed from, and the filing, fitting, and
adjusting operations increase. In any event, however, the principles to
be observed in the manipulation are the same, because the points to be
observed in the fitting by hand work must be accomplished by the machine
if the rods are to be finished by machine work.
Let Fig. 2360 represent a connecting rod; A representing the centre line
in the side, and F the centre line in the edge view, and it is obvious
that the axial lines, B and C, of the brass bores must stand at a right
angle to line F, and be parallel to each other, because the journals on
which they fit will do so. Furthermore, the faces of the brasses, as E,
must stand their proper distance from the centre line F, this distance
being at each end respectively half the whole width D, and the faces E
must be in the same plane whatever their widths may be. The centre lines
A and F are imaginary lines not worked to (except it be in marking or
lining the rod out for the planing operations); but the method employed
to fit up the rod must be such as will make all parts true to those
lines if they were tested by them.
The process of fitting up a connecting rod may be tersely stated as
follows: 1st, the rod is planed; 2nd, the straps are planed; 3rd, the
straps are fitted to the rods; 4th, the straps are drilled and bolted to
the rod; 5th, the keyways are cut, and the keys and gibs fitted; 6th,
the side faces of the rod ends are again planed with the straps on; 7th,
the brasses are fitted and the rods marked off for length and the
brasses bored; and, 8th, the file finishing and polishing done.
[Illustration: Fig. 2360.]
[Illustration: Fig. 2361.]
[Illustration: Fig. 2362.]
[Illustration: Fig. 2363.]
[Illustration: Fig. 2364.]
In the case of very large rods the two ends are made and fitted up as
separate pieces, and are afterwards welded to the body or stem of the
rod, and the setting of the ends true one to the other after the welding
affords such an excellent insight into the alignment of rods that it may
be well to describe it. First, then, the rod being laid on its side, two
straight-edges, or rather winding strips, S and S´, Fig. 2361, are
placed on the side faces, and the rod will be set in this direction when
their ends A, B, C, D, appear parallel when sighted by the eye. If the
winding strips are adjusted to stand straight across the rod, and,
therefore, parallel one to the other, any twist or wind in the two rod
faces will be very plainly discernible by the sighting process. The rod
is then stood on edge, as in Fig. 2362, to test the alignment of the
side faces. A straight-edge S is pressed firmly against one of the
faces, as H in the figure, with the other end elevated as shown. The
elevated end is then lowered, the motion serving to keep the end fairly
bedded against face H. The distance, I J, Fig. 2363, is then measured.
The straight-edge is then used in the same manner on the other side of
the rod as at S in the figure, and the distance K L is measured, the
setting in this direction being correct when distances I J and J K are
equal. The straight-edge is then applied to the edge faces of end H of
the rod, as in Fig. 2364, at M and at N, the distances O, P, are made
equal. During these operations a straight-edge is applied along the body
of the rod to see where to set it to effect any required adjustment, and
if that body is straight the adjustment is made near the end at which
the straight-edge is pressed to the rod.
The setting of the small end I is effected in the same manner, but the
straight-edge will in this case fall over the face at the larger end, as
is shown in Fig. 2365; hence, instead of measuring, lines as G and T are
marked coincident with the edge of the straight-edge and the distances
T U, I G, are made equal. Winding strips are applied to the edge faces
as well as to the side faces, and as making one adjustment or alignment
may alter another, the whole process must be repeated until the whole of
the tests prove the setting to be true.
[Illustration: Fig. 2365.]
[Illustration: Fig. 2366.]
[Illustration: Fig. 2367.]
[Illustration: Fig. 2368.]
Now suppose the rod to have been forged solid and all these faces to
have been made true in the planing, and the first operation is to fit
the straps to the rod ends. The strap should be put in place on the rod
and moved laterally, when the centre of its motion where it moves the
least will be the place where it binds and therefore requires filing. If
its side faces come atwist with the side faces of the rod end, as shown
in section in Fig. 2366, either the faces of the rod end or the inside
faces of the jaw are out of square as denoted by the dotted lines. In
any event the face E, Fig. 2367, of the rod end should be surfaced true
and made at a right angle to the side face, and if to be made parallel
to M, also at a right angle to K, a square and a surface plate are used
to test them. If the diameter J is to be smaller than that at H, then
the angle of both face E, and its opposite, should be equal with
reference to K. These faces should be finished by draw-filing, with the
file marks lengthwise of the rod. To fit the strap, proceed as follows:
To find where it requires filing, place it on the rod (having previously
put red marking on the rod end), and move it endwise and sideways,
observing where the least motion takes place when the strap is moved
sideways by pressing its crown end, for this point of least motion is
always where it fits the tightest. To test the jaw faces for being
square apply a straight-edge S, and a square P, Fig. 2368, pressing S
against the strap, and P firmly against S.
[Illustration: Fig. 2369.]
When the strap shows to bed well on the rod and its motion is an ambling
one (and not a pivoted one), it fits properly, and if both rod and strap
have been filed square, their side faces will come fair or even. The
keyways being drilled, may then if necessary be filed out, for which
purpose it is necessary to bolt the strap to the rod, a process that
requires very skilful treatment, because if the tightening of the bolts
moves the strap on the rod, or if the strap be moved on the rod after
the clamp is tightened, the keyways will not come fair when the clamp is
taken off. In Fig. 2369 the strap is shown held to the rod by plates C
and bolts B, the rod being shown in position ready to file out the
keyway. It is better, however, to let the side face of the rod stand
vertical as the strap will stand steadier that way. The strap should be
set fair with the outside faces, which will bring the keyway fair if it
is properly located. The bolt nuts should be tightened gradually, first
one a little and then another, going over all four once or twice before
they are fully tightened, and if the strap is not fair when they are all
tight, all must be loosened before the strap is adjusted, or the clamp
pressure will cause the strap jaws to spring out of true, and the
keyways will not come fair when the clamp is removed.
Should the keyways not come fair when the strap sets fair on the rod the
strap may be set to accommodate the keyways, and thus save filing, but
this must be done before clamping it to the rod end. Care must, however,
be taken to see if cutting the strap out to suit the keyway may not
leave too little metal on one side of the keyway when the strap is
subsequently planed.
The sides of the keyway should be filed true to a surface plate, using a
well-bellied file and as stout a one as possible, so that it may not
bend under the pressure, and file away the edges of the keyway.
The keyway should be made parallel to the side face of the strap, so
that it may be fair with the centre line F in Fig. 2360. It should be
made of equal width throughout, a piece of iron being used as a gauge in
place of the key, and this same piece of sheet iron will serve as a
gauge to plane the keys to thickness.
The corners of the keyway, if to be made square, should be filed out
with the corner of a smooth half-round file, because the corners even of
safe-edge files do not come up sharp enough.
For filing out the end faces of rectangular keyways, a square file with
both edges safe must be used, the safe edges being on opposite sides of
the file. For roughing out, a taper square, but for finishing, a
parallel, or equalizing file is preferable.
The next operation is to fit the keys and gibs. The key should first be
fitted and should be filed true to a surface plate, for in no other way
can a really good reliable gib be obtained, no matter how well the keys
may have been planed or milled. It should be filed a tight fit to the
keyway so that it may be used (with a light coat of red marking) to show
tight places in the keyway, driving the key in for that purpose from
first one and then the other end of the keyway. If, however, it is
driven too forcibly, it may seize or cut, and it will be difficult to
get it out, besides damaging both it and the keyway. When the keys are
reduced so that they will drive lightly into the keyway, they should be
tried in the rod and in the strap separately, moving the key laterally
or edgeways, so that it may mark any high places in the keyway of either
of them.
The finished key and gib should be left tight enough, that they will
hold themselves in any position in the keyway of the strap or of the rod
when standing vertical.
[Illustration: Fig. 2370.]
The head of the gib should be chamfered as in Fig. 2370, so that it may
be driven in and out to fit without raising burrs which would prevent it
from passing into the keyway, and the key should be similarly chamfered
and rounded in its width.
[Illustration: Fig. 2371.]
The width of the key and gib should be such as to just fill the key
ways, leaving no draw when the key is down in the keyway so that its
head is level with the head of the gib, as in Fig. 2371, A equaling the
keyway width; and their edges should bed fairly one against the other,
and against the edges of the keyway. The strap must then be keyed upon
the rod, and the side faces of the rod and strap planed to thickness,
placing a bolt and nut in the rod end in place of the brasses, so that
the key may lock the strap and bind it in position. The rod end should
be planed to thickness for the brasses and of equal thickness on each
side of the keyway. The brasses should be planed after the rod end is
planed to thickness. The width for the brasses should be measured while
the strap is on the rod end, because the width between the jaws of the
strap is greater when the strap is in place on the rod end than when it
is off, because in order to make the strap jaws a tight fit to the rod
end it is made narrower between the jaws than the width of the rod end,
so that the jaws spring open when the strap is pushed on the rod end.
The sizes for the brasses to be planed to will then be the width of the
strap across its edge face, and the width of the strap between the jaws
_when it is on the rod_; and for these sizes a wire gauge should be
made; or an adjustable gauge may of course be set.
The method to be pursued in planing the brasses is an important
consideration. It is most convenient to plane both the brasses together,
by which means much time is saved. To obtain this end the brasses are
sometimes cast together, as in Fig. 2372, and after planing and before
boring are cut in two at the narrow section A. In this case the brasses
are cast sufficiently wide from crown to crown as denoted by B to allow
for the length cut away in separating them. In other practice the joint
faces of the brasses are faced first and then soldered together for the
planing; but very large brasses are planed separately. In either case
the joint face of the brass should be made at a right angle to the faces
of the brass that fit the strap.
[Illustration: Fig. 2372.]
The brasses should be fitted separately to the strap, and hence should,
if joined, be separated, being cut in two in a shaper, if of the form
shown in Fig. 2372, and split by driving a keen chisel between the
corners of the joint faces, if the latter have been soldered. The back
or crown brass, and not the key brass, should be fitted first. The
corners of the ways, in the brass, for the strap should be eased just
clear with the edge of a smooth half-round file, because otherwise they
will rub down the sharp edges of the strap, and make the strap jaws
appear to be a bad fit when on the rod. The brass should be driven in
and out of the strap to fit, using a block of wood to strike on,
otherwise the skin of the bore may become pened, and when the brasses
are bored they will close in at the sides and become loose in the strap.
[Illustration: Fig. 2373.]
As a guide when fitting the bottom brass in the strap, place the strap
on the rod as in Fig. 2373, and take the measure of the strap at A A,
the strap overlapping the rod to admit the calipers or gauge. Each time
the brass is driven in the strap to try the fit, the calipers so set
should be tried in the strap (the brass being in the strap), as in the
figure, and when the calipers very nearly touch the strap jaws, the
strap with the back brass still in should be tried on the rod end, or in
the case of a very heavy strap the caliper measurement minutely taken
may be relied on to show that the brass does not spring the strap jaws
too wide open. It is better, however, to leave the brasses a little too
tight in the strap as they close slightly in the boring, becoming easier
in the strap.
[Illustration: Fig. 2374.]
[Illustration: Fig. 2375.]
After the brass has been tried in the strap, and before it is filed
again, it should be tried with a square, using a straight-edge also if
the square back is too short to cross both faces of the brass. The
method of testing is shown in Fig. 2374, in which B represents the
brass, S the square, and T the straight-edge. The inside face of the
flange should also be tried as in Fig. 2375, in which P represents the
surface plate, S the square, and B the brass. This will insure that the
brass face joint is square as it should be, and is further necessary
because the bearing marks on the brass are not to be altogether relied
upon.
[Illustration: Fig. 2376.]
In Fig. 2376, for example, the brass is shown in section in the strap,
and the side A of the brass has a bearing against the jaw B of the
strap, and hence would show marks of contact. The succeeding blows in
driving the brass, however, may cause the brass to have contact on the
side C with the jaw D; hence the bearing marks would show the brass to
fit well when such was not the case. This may be detected by striking
the brass on its joint face, and then measuring from E and from F to the
end of the strap, and then striking the joint face at F and again
measuring both distances, when any canting of the brass will readily be
detected. It is better, however, to also apply the square, as shown in
Figs. 2374 and 2375, because by this means the joint faces E F being
parallel to the crown face G of the brass, the brass will be fitted so
that when G meets the crown face H of the strap, the two will be
parallel to each other and require but little filing to fit or bed
together.
The crown of the brass should be bedded very finely to the strap, or it
will spring the strap jaws away from the rod when the key is driven
home.
Suppose, for example, that the crown of the brass did not bed well at A
in Fig. 2377, then keying up the strap would spring its jaws away from
the rod end, as shown at B C, the least error in the bedding having this
effect notwithstanding the fit of the gib jaws.
[Illustration: Fig. 2377.]
The second brass must be made to just fit the strap when the back brass
is in its place, and is small enough when the calipers, set as shown in
Fig. 2373, and tried as shown in Fig. 2376, just fit the strap. This
will insure that both brasses fit the strap when it is in its place on
the rod.
When both pairs of brasses have been fitted to their straps, the latter
should (if held by bolts) be bolted to their places on the rod, and the
centre of the respective spaces for the brasses will be the location for
the marks G, G, Fig. 2360. A pair of trammels should, however, be set to
the proper length of the rod and these marks tested. If the strap is
held by gibs and keys, as in the small end in Fig. 2360, the strap
should be put on its place with the gibs in, and drawn up the rod by
slowly forcing the key in until the mark G at that end stands in its
proper distance from G at the other end, at which time the key should
come through its proper distance.
The thickness of the brasses must be measured from these marks G, G to
the crowns of the straps and the ends of the rod respectively. If the
rod is of its proper length and the straps are in their proper
positions, these marks will come in the centre of the space for the
brasses. If, however, there is any error, as there is apt sometimes to
be in very large rods, the course to be pursued depends upon the kind of
rod end. If both straps are bolted to the rod end, the error may be
divided equally at each end. If one end has a key and gib or gibs, but
no bolt, as at the small end in Fig. 2360, the key brass may be made of
such thickness as to butt against the end of the rod and meet the mark
G.
[Illustration: Fig. 2378.]
For the large end, the thickness of the key brass, or, in other words,
the distance D in Fig. 2378, must be taken after the face of the crown
brass has been squared up, as described with reference to Figs. 2374 and
2375, the connecting rod strap being placed in such position that the
key will be up in its proper place.
When the joint faces of brasses do not meet, but are left open to take
up the wear, it is a difficult matter to properly adjust the brass bore
to the journal. If the flanges of the brasses do not quite fit the
length of the journal, as is very commonly the case, it is customary to
tighten the key until the rod end can just be moved by hand so as to
force the brass flanges against first one and then the other end of the
journal. This is an approximate adjustment; and if the journal heats at
all, the key is slacked back a trifle; whereas if it pounds, the key is
set up a little. As a matter of fact, then, nothing is actually known of
the precise fit of the brass to the journal; and while looseness may be
detected by the pounding, the brass may be tight enough to cause undue
wear without very sensibly heating the journal, especially if the latter
is freely lubricated. If, however, the brasses fit the length of the
journal, and do not butt, it is usual to drive the key in till the
brasses bind the journal, and to then slack the key back to the
necessary amount. What that amount should be cannot be stated, because
it varies with the taper of the key and the force with which it is
driven home. As a result, then, the operation is left to the judgment,
or, in other words, to guess-work, of men, many of whom are not well
experienced in the operation; while under any circumstances the actual
fit is not positively known. A plan not infrequently adopted is to
insert a piece of lead wire of small diameter between the brasses, the
key is first driven tightly home, and then slacked back until the lead
wire is just freed. It is estimated that the adjustment will then be
correct; there is no actual certainty of the fit, however, even in this
case.
Another objection is that the oil is apt to flow out of the opening, and
the brass having communication with the oil cup is better lubricated
than the other brass.
In cases where the brasses are difficult to get out of the strap,
because of the location or of the size and weight of the parts, a piece
of sheet brass is sometimes placed between the joint faces, and this
piece is filed thinner to let the brasses together, the necessary
thickness for the piece being ascertained by the lead wire process
described. If the strap is held to the rod end by a gib and key only,
and the joint faces are left open, there is nothing to lock the strap to
the rod end save the jaws of the gib, whereas when the brasses butt, the
key binds the brasses to the end face of the rod and the strap to the
brasses, which if there is any wear sideways (as in locomotives),
prevents the keys from wearing the sides of the key ways and the brass
flanges from wearing the straps.
A method of overcoming this defect is shown in Fig. 2379, where the
joint faces are left open, and four set-screws S, S, two on each side of
the rod, pass through the flange of one brass and abut against the face
of the other, serving to adjust the fit of the brasses to the journal,
and lock them in their adjusted position, locking at the same time the
brasses to the strap and the strap to the rod end.
When the rods are finished so far as the fitting of its various parts
are concerned, the brasses should be marked so that the bore, when bored
out, will leave an equal thickness of metal between the brass and the
strap on each side of the bore, while the rod will be of proper length.
To accomplish this, mark on the outside face of the top brass two lines
level with the faces which fit against the inside jaws of the strap, as
shown in Fig. 2380, A, B being the lines referred to. We then key up the
brasses in their places in the rod and fasten a centre piece in the
brasses at each end of the rod. Upon these centre pieces we first mark a
line parallel with and central between the lines A, B, and then a line
across the joint of the brasses if the joint faces meet, and in the
centre of the space between them if they do not meet.
[Illustration: Fig. 2379.]
[Illustration: Fig. 2380.]
Before applying the trammels to test the rod length, the latter should
be stood or placed in the position in which it works when on the engine;
for all rods deflect by their weight, the amount of such deflection
depending upon the position in which the rod is suspended. The trammels
also deflect, it is true, but their deflection is allowed for in setting
them, whereas the deflection of the rod will not be accounted for unless
it is trammelled when standing or lying in the position in which it
works.
FITTING UP SOLID-ENDED CONNECTING RODS.--In fitting up solid-ended rods
the side faces require to be filed up first and the jaws to receive the
brasses next, taking care to file them out either square with the faces,
or if slightly taper, as they should be, then each inside face should be
an equal degree of taper to the side faces. This is necessary so that if
the brasses are bored true to their own faces, the bore of the brasses
at one end of the rod shall stand parallel to the bore of those at the
other end.
The fitting of the keys and brasses is performed as described for
strap-ended rods.
The reason that the jaws or box that receives the brasses is but a
trifle taper is that in that case they are easier made a good fit, as
they can be tried in their places while being fitted and before being
reduced to the finished size, and furthermore because they can be put in
and taken out easier.
FITTING UP A FORK-END CONNECTING ROD.--A fork-end connecting rod affords
as good an example of vice work as can be found, because any faulty
workmanship, either in the individual truth of the parts, or their
relative truth one part to another, will make itself very plainly
apparent.
[Illustration: Fig. 2381.]
[Illustration: Fig. 2382.]
Fig. 2381 represents a side and plan view of an ordinary form of
fork-end rod, and the requirements are that the centre line A of the
brass bores at the fork end shall be parallel with the centre line B of
the bore at the butt end; that the side faces of all the brasses shall
be parallel one to the other; that the side faces at the fork end shall
be equidistant, or at the required distance, from the side faces at the
butt end as denoted by C, D; that the bores of the brasses shall be at
the proper distance apart to make the length of the rod come right; that
the brasses at the fork end shall be the right distance apart, and that
they shall stand parallel to each other, as well as to the bore at the
butt end, as denoted by the line E in Fig. 2382.
If the rod were of a size that it could be conveniently handled and
planed, if forged solid, the fitting up would be much simplified,
because the setting of the rod for the machine operation would, to a
great extent, insure truth in the relative alignment of the parts. Thus
all the side faces of the rod ends could be planed at one chucking, in
which case they would necessarily be parallel, and their proper relative
distances apart, if the rod was properly marked out by lines and planed
to the lines. The jaws or ways to receive the brasses would be slotted
out together, and necessarily true, if the rod was chucked true on the
machine table. But even in this case the rod has to be marked out by
lines denoting where the metal is to be cut off to, and the principles
involved in the lining are just the same as those involved in the
fitting up.
[Illustration: Fig. 2383.]
[Illustration: Fig. 2384.]
If the rod be large, the ends may be, and usually are, forged and fitted
up separately, and subsequently welded to the body of the rod, which has
been forged separately. In this case, the alignment of the parts is a
part of the process in welding the rod, and setting it after welding.
All the principles involved in making the rod ends separate, and
afterwards welding them, or in marking out a small and complete forged
rod, are, however, involved in the process of refitting an old rod in
the jaws, and putting in new brasses; hence a description of that
process will cover the whole ground. The first thing to do is to file up
the side faces, as F, G, Fig. 2381, and, in doing this, all that is
necessary is to file F up true, when tested by a straight-edge applied
as in Fig. 2383, in which R is the fork and S a straight-edge, whose
edge should measure the same distance at H as it does at I from the side
face F, while the face C measures the same distance from face A of the
other fork end, or from the imaginary centre line X, Fig. 2381. Then
turning the rod on its side, a straight-edge should be placed across the
face F, and one across the face G, as in Fig. 2384, at S and S´; and the
edges of the two straight-edges should stand parallel, when sighted in
such a position that the edges are very nearly in line with the eye, as
shown in the figure.
The inside faces of the fork jaws may be filed to measurement from the
outside ones.
[Illustration: Fig. 2385.]
[Illustration: Fig. 2386.]
[Illustration: Fig. 2387.]
The ways for the brasses should be filed square with the outside faces,
as shown in Fig. 2385, in which S is a [T]-square; but if one jaw is
wider than the other, as sometimes occurs, it will not matter, providing
that, with the square applied, resting against the side and the face of
the ways on the narrow jaw, the ways of the other jaw are equidistant
from the square blade, as would be the case; for example, if the width
of the ways of the jaw J extended to the dotted lines at K, L, because
the line P would still form the centre line of both jaws, standing at a
right angle to the side faces of the fork end, and parallel to the bore
of the brasses at the butt end. Before filing up the side faces at the
butt end, the strap should be fitted on and keyed up, so that its side
faces may be filed up with those on the rod. To test the truth of the
side faces at the butt end, a straight-edge should be applied, as at S
and S´´, Fig. 2386, being pressed firmly to the side faces at the butt
B, the fork faces being measured from the edge of the straight-edge at
that end, and also with straight-edges, as in Fig. 2384. The brasses,
after being fitted into the ways of the jaws, should have their joint
faces squared, as in Fig. 2387, the top of each jaw being shown broken
away, so as to fully expose the brasses. S is a square held firmly
against the side face of a jaw, the brasses having their joint faces
true with the square blade, and true also when tested with a square,
applied as in Fig. 2388, in which B is the brass and S the square. The
brasses at the other end should be filed true to the side faces of the
strap in a similar manner, and, the fitting being completed, it simply
remains to mark off the brasses for boring. The joint faces of the
brasses should form the centre of their respective bores; hence, all
that is necessary, is to insure that the brasses be of equal thickness,
top and bottom, and this may be accomplished as follows: Mark across
each face a line even with the ways of the brass, as shown in Fig. 2389,
at A, C, and carry these lines around the side face, as shown in the
figure at B, D. Place the brasses in the strap, put in a piece of wood
whereon the compasses may be rested, as shown in Fig. 2390, which
represents one jaw, and mark on this piece of wood a line even with the
joint faces of the brasses, and on this line a centre-punch dot
equidistant between the lines B, D. From this dot, as a centre, strike
the circle shown, and define it by centre-punch dots, and if the
lathe-hand chucks the brasses true to the ways that fit the rod jaws,
and to the dotted circle, the bores will stand true in every respect.
[Illustration: Fig. 2388.]
[Illustration: Fig. 2389.]
[Illustration: Fig. 2390.]
REPAIRING CONNECTING RODS.--In repairing connecting rods the following
is the work usually required to be done, and in the order named:
Refitting straps, refitting gibs, and perhaps new gibs and keys, filing
up the side faces of rod ends and straps, lining up brasses to make them
fit the strap, lining up the rod to length and fitting the brasses
together so as to fit their journals.
[Illustration: Fig. 2391.]
If the strap is taper and can be closed by pening, the outside of the
back should be pened; but if the strap requires closing in the
blacksmith's shop, then it should be tested by winding strips as shown
in Fig. 2391, to insure that the faces are true, and thus save filing at
the key ways and on the side faces to make them come fair with the rod
ends. The rod ends should then be filed up and the straps fitted on.
[Illustration: Fig. 2392.]
[Illustration: Fig. 2393.]
[Illustration: Fig. 2394.]
Next comes putting in the new key and gib, or refitting the old gib. If
the jaw of the gib has cut into the strap, as it will do in some cases
(especially in marine and locomotive rods), this may be repaired as
follows: Cut out the recess shown in Fig. 2392 at A, making it
dovetail-shaped as shown, and with a set chisel set up its sides as
shown in Fig. 2393, which is a sectional side elevation through the line
of B. Cut out a piece of wrought iron and bevel its edges as shown in
Fig. 2394, filing it to fit into the recess cut at A, Fig. 2392, and
letting the bevelled edge be uppermost. Then take a set chisel and close
down again upon the bevelled edge of the piece the metal that was set
up, as shown in Fig. 2393, and the piece will be riveted, and it and the
gib jaw may be refitted to touch the piece thus let in.
[Illustration: Fig. 2395.]
The jaws of the gib are sometimes made slightly taper at A, Fig. 2395.
To refit the brasses to the jaws of the strap, the flanges which do not
as a rule wear much are usually tinned with a soldering iron, and given
a lining of babbitt metal. This must be done all around the flanges (of
both pairs of brasses) that come on the same side of the rod, so as to
keep the faces of the brasses leading fair.
[Illustration: Fig. 2396.]
The fit between the jaws is restored by riveting pieces of sheet brass
to that side of the brasses that has worn the most (usually the top
which carries the weight of the rod). Fig. 2396 shows this operation
carried out, A being the pieces of sheet brass which are sometimes
soldered as well as held by rivets. These rivets are screwed into the
brass, being composed of softened brass wire riveted after being screwed
in.
If these pieces, which are called liners, are placed on the top of the
brasses at one end, they should also be placed at the top of the brasses
at the other end of the rod. They should not be less than about the 1/24
inch thick, the body of the brass being cut off to admit them if
necessary.
In filing the joint faces of the brasses to let them together so as to
take up the lost motion due to the wear of the brass bore and of the
crank pin, the following considerations are met.
[Illustration: Fig. 2397.]
If the brass faces are to come "brass and brass," that is, butt
together, when their bore is of the diameter of the journal, file those
faces away until the bore appears just perceptibly too large for the
journal, when measured with calipers, as in Fig. 2397, the bore
measuring parallel all the way through. But, in doing this, it is
necessary to be careful to file each brass so that it shall embrace
one-half the journal diameter, which will be the case when the two
brasses measure correctly as above, and alike, when tested, as in Fig.
2398, in which P is a planed surface, C a pair of inside calipers, and B
a brass resting on P. When filing the joint faces, test them with a
square as in Fig. 2399, in which _s_ is a square and B a brass, and also
in Fig. 2400, in which _s_ is a square and B the brass shown in section,
thus making the faces quite square.
[Illustration: Fig. 2398.]
[Illustration: Fig. 2399.]
[Illustration: Fig. 2400.]
The necessity of having their faces quite square when the brasses come
brass and brass may be shown as follows:--
[Illustration: Fig. 2401.]
Suppose the joint to be at an angle as at A, A, Fig. 2401, instead of
square across, as denoted by the dotted lines B, B, then the respective
brasses will be forced by the key-pressure in the direction of the
respective arrows, and there will be a tendency to twist the brasses in
the strap. Or suppose the joint faces to be out of square as at C, C,
instead of square as at D, then there will be a tendency to twist the
respective brasses in the direction of E, F, and therefore to cause
these to move in the direction of G, H, and as a result the brasses will
spring the strap away from the rod, as shown at I, J.
[Illustration: Fig. 2402.]
To line up the brasses for length we proceed as follows: One of the
liners adjusts the length of the rod and the other simply serves to set
the key back to its proper height, so that it shall not pass too far
through the keyway, as the wear of the brasses lets it down. Which of
the liners will be the one by which to alter or adjust the length of the
rod depends upon the design of the rod itself; but, in the case of all
solid-ended rods, or those in which the position of the strap is fixed
by means of bolts, it is the liner behind the end brass, as D, in Fig.
2402, as stated in the opening of this discussion, and it is the first
one, therefore, to be fitted. The space at E is where the second liner
requires to be placed, its thickness being that necessary to lift up the
key from its bottom or lowest position, as shown in the cut, to the
highest position.
[Illustration: Fig. 2403.]
In strap-ended rods in which the strap is not bolted to the rod, but
moves farther upon the rod as the key passes farther through the keyway,
it is the brass next to the rod end, as B, in Fig. 2403, by which to
adjust the length of the rod, and its liner L is, therefore, the one to
be fitted first; the space E is, in this case, the one to be fitted with
a liner of sufficient thickness to lift the key up. It will now be noted
that the thickness of L in both figures requires to be exact, so that
the rod may be of correct length, which is necessary, so that there may
be the same amount of clearance or space between the piston head and the
cylinder cover when the piston is at the respective ends of the stroke.
But the liners to fill the respective spaces E need not necessarily be
of the exact thickness (although it is better that they should be),
because if too thin the only effect will be that the key will pass
farther through the keyway than otherwise. In considering in any form of
rod which is the liner to be put in first to bring the rod to length, we
have the general rule that the brass that moves in the strap or rod end
when the key is moved farther through the keyway is the one to be lined
last. The method of obtaining the proper thickness of the liners L,
Figs. 2402 and 2403, are as follows: If the rods have been correctly
made at first, the centre of the brass bores will be midway in the
spaces for the brasses (denoted by F in the two figures). If the
oil-holes in the strap or rod end (as the case may be) have been drilled
in the centre of this space F as they should be, then the line _g_ will
represent the centre of F and the centre of the oil-holes, and all that
will be necessary will be to place behind D and B respectively a liner
of sufficient thickness to bring the joint face of these brasses (D and
B) even with the line _g_. To ascertain the thickness of liner necessary
for this purpose, suppose the case of a rod end of the design shown in
Fig. 2402, then, with the strap off the rod, drive the brass D down
until its crown face beds fairly against the strap C, and with a scriber
mark on the inside face of the jaw of the strap a line coincident with
the joint face of the brass, then set the brass up the strap until its
joint face comes fair with the centre of the oil-hole or the central
line _g_, and then mark a second line so that on taking the brass out of
the strap there will appear two lines, and the distance between these
two lines is the necessary thickness of liner. In the case of the form
of rod end shown in Fig. 2403, the process would be as follows: Let the
strap have placed in it the brass B only, place it upon the rod, and set
it so that it binds the gib and key, when the key is lifted up to its
required position, then, with the brass B bedding fairly against the rod
end, mark on the strap a line coincident with the joint face of the
brass as before. Then move the brass in the strap until its face comes
fair with the centre of the oil-hole or line _g_, and mark another line,
and the thickness between these lines is the thickness of liner required
at L.
[Illustration: Fig. 2404.]
[Illustration: Fig. 2405.]
[Illustration: Fig. 2406.]
If the brass is to be lined sufficiently to merely bring the key up
without respect to the length of the rod we may drive the key home as in
Fig. 2404, and mark on it a line coincident with the edge A of the
strap. We then lift the key up to its proper height and mark a second
line, so that when removed from the keyway the key will have on it the
two lines shown in Fig. 2405, A being the first and B the second line;
and the difference between the width of the key at A and its width at B
will be the thickness of the liner necessary to be placed behind the
brass nearest to the key. To ascertain the precise amount of this
difference (because a very small error as to this amount causes a great
deal of extra labor), we set a pair of outside calipers to the width at
A; and then passing the caliper points down to B, we keep one of the
points even with the line B, and insert a wedge until it just fills the
space between the other point and the side of the key, as shown in Fig.
2406, C being the wedge, which should be chalked along its surface so
that, when inserted until it touches against the caliper point, the
latter will leave a mark on the wedge, denoting exactly how far the
wedge entered, and hence the exact required thickness of liner.
[Illustration: Fig. 2407.]
[Illustration: Fig. 2408.]
It has thus far been supposed that the joint faces of the brasses are
made to come brass and brass, that is to say, butt close together from
the key pressure, when the brass bores properly fit the journal.
Suppose, however, that the joint of the brass is left open as in Fig.
2407, and in that case a strip of metal F, whose diameter equals that of
the journal, may be inserted between the brasses as shown, and at its
centre should be provided a small centre-punch mark, denoting the centre
of the bore. A piece of this kind should be inserted in the brasses at
each end of the rod and placed in the middle of the length of the bore,
the centre-punch marks being to apply the trammels to. Or if the rod was
made of correct length when new, and the bore of the brasses, therefore,
requires to stand central in space F, Fig. 2403, then the pieces F, Fig.
2407, may be dispensed with by marking a line B, Fig. 2408, central to
space F, Fig. 2403. Then put the strap on the rod (with the brasses,
gib, and key in place), and pull the strap back to hold the key up to
its proper height.
[Illustration: Fig. 2409.]
The two brasses should then be placed as far apart as possible in the
strap, each bedding fairly against its back or crown. Then, using the
joint face of the back brass as a straight-edge or guide, a line should
be marked on the side face of the strap, this line representing the
position of that face when the brass is bedded fairly home, and being
shown in Fig. 2408 at A. This brass should then be moved forward until
the bore of the pair of brasses at D, Fig. 2408, measures equal to the
diameter of the journal (of the crank pin or of the cross-head pin as
the case may be) and a second line B, also coincident with the joint
face of the brass, should be marked upon the strap, and the strap will
then have marked on it the two lines shown in Fig. 2409, in which it is
shown removed from the rod; the distance apart of these two lines will
be the thickness of the two liners combined, hence half this thickness
will be the thickness necessary for each liner. Suppose, however, that
it is not known whether the rod has been correctly made, and therefore
it be unknown whether, in order to have the rod of the correct length,
the brass bore should stand in the centre of the space or not.
This is often the case in repairs, and sometimes on new rods, in which
slight inaccuracies of workmanship are apt to occur. In this case it is
best to mark a line, as G, in Fig. 2410, representing at each end of the
rod the centre of the space F in that figure. Then set a pair of
trammels to the correct length of the rod, and with one point of the
trammel resting on the point at the intersection of line C with line D
(the latter being the line G transferred to the centre of the bore) at
the small end of the rod, we mark a line at the other end. If the lines
D are too far apart, making the rod too long, the trammels will mark a
line R, and the distance between lines R and D at the large end will be
the amount the rod is too long, while half this distance will be the
thickness of liner to go behind each bottom brass if the error of length
is to be equally divided between the two ends of the rod, in which case
a line T, midway between D and R, must be marked, the trammel then being
rested on T, and the line S marked. These two lines, S and T, are then
the centre lines for the bores of the brasses.
[Illustration: Fig. 2410.]
If it is determined that one pair of brasses shall be central in its
space F, all the error being thrown on the other pair, this may be done
by lining one pair up so that its bore is true to line D, and putting
behind the back brass at the other end a liner whose thickness is equal
to the distance between D and R at the large end of the rod. It is
obvious that the measurement for rod length must be taken on the line C.
Having thus determined what thickness of liner is necessary to bring the
rod to its proper length, it remains to find the thickness of liner
necessary for the other half brass, to bring the key up to its proper
position, the process for which has already been explained. After,
however, the various liner thicknesses have been found, and the sheet
metal selected to cut them from, it is well to try if the thickness is
correct by cutting off a small piece of the metal, putting it in place
behind the brass, and then, after keying up the brasses, the rod length
may be trammelled.
As the liners placed behind connecting-rod brasses require to be very
finely bedded, the facility with which their forms permit them to be
fitted is an important consideration.
[Illustration: Fig. 2411.]
In Fig. 2411 is shown the forms commonly given, the requisite form of
liner being shown beneath each. Form 1 will bed very firmly to its seat,
but it will be observed that its liner is a difficult one to make, the
bottom section A being thicker than the sides or wings B. This is a
troublesome form of liner to fit as well as to make. If it be made of
wrought iron, the wings B must be either forged or filed to their
reduced thickness.
In the form at 2 in the figure we have the same defect, while in
addition the liner will not adjust itself so readily in position to its
bed.
This latter is an easier form to make in the moulding pattern, and
easier to mould, and somewhat easier to fit, but it is not so firm as
the first. To cause this form of brass to bed easily to its proper
position it is sometimes given a lug on the bottom, as at 3 in the
figure, the lug extending part of the width across only, because if it
extended fully across, the liner would require to be in two pieces,
causing trouble both in fitting them and in getting them into their
places. When the lug extends partly across, the liner must have a slot
to pass over and admit the lug, and this causes trouble in bending the
liner to the required curve.
In the form shown at 4 in the figure all these difficulties are avoided,
while, if the lower corners are made square instead of rounding, a
simple piece of sheet metal will serve as a liner requiring but little
fitting and bedding if it be of the proper thickness.
[Illustration: Fig. 2412.]
To fit up a link motion, assuming the machine work to be done, the first
thing to do is to face up the side faces of the links, making them
parallel, and true to a surface plate. The slot is then filed out square
to the side faces, its curve being filed to a template T, Fig. 2412,
which is provided with a piece of wire for a handle. It is supplied with
red marking, and is rubbed upon the slot to mark the high spots. The
same template may be used to prepare the link block or die; but as soon
as the block can be moved in the slot with slight hammer blows (using a
mallet or a block of wood) it should be used instead of the template,
the bearing marks serving to correct and finish the block as well as the
slot. In filing up the block care should be taken to make it of even
thickness on each side of its hole and with its sides parallel to the
hole, the latter being of great importance. When the block is a
sufficiently easy fit in the slot to permit it, a round stick of wood
may be put through it and used to move it up and down the link slot for
the marking process.
The next operation is to fit the eccentric rod eyes to the link, and to
then ream out the holes in both the link and the eyes while they are put
together. The block may then be placed in the link, and the rocker pin
passed through the block and into the rocker arm, so that the working
fit of these parts when put together may be tested and adjusted if
necessary. The link hanger may then be fitted to the saddle pin, when
the whole will be ready for the file finishing and polishing, after
which it may be case-hardened.
CASE-HARDENING.--Case-hardening consists in the conversion of the
surface of wrought iron into steel, or in converting the grade of a low
steel into a sufficiently high grade to render it capable of hardening.
The depth to which this conversion occurs depends upon the material used
to produce it, and the length of time the process is continued, varying
from 1/64 inch under the prussiate of potash process to 1/16 or 1/8 inch
in the case of long-continued box case-hardening.
Work that is thoroughly case-hardened has a dull white, frosted-looking
surface. If the surface of the work is mottled, or has patches of fancy
water-mark colors, it may be hard, but it is not so to the highest
attainable degree.
To thoroughly test this, take a new dead-smooth file and apply its
corner edge under heavy pressure to the work on an edge where the fancy
colours are, and then on an edge where the surface is white, and the
latter will be found to be the hardest as well as hardened the deepest.
The simplest method of case-hardening is by the prussiate of potash
process, for which it is essential that the prussiate of potash be
finely powdered, and contain no small lumps. The piece being heated may
then, if small, be dipped in the prussiate of potash, or if large have
the same spread upon it. In either case, however, the work must be hot
enough to cause the potash to fuse and run over the work surface, and
this action may be assisted by using a piece of iron wire, spoon-shaped
at the end, wherewith to apply potash to the work and rub it upon the
work surface.
After the potash has thoroughly fused and run over the entire surface of
the work it will usually have become somewhat cooled, and will require
reheating before quenching in the water.
If this reheating be done in the blacksmith's fire, it is not well to
put the blast on; it is better to let the blast on gently while applying
the potash to the work, so as to have a live clear fire to put the work
in, and reheat it with the blast turned off.
While the work is in the fire it should be constantly rotated, not only
to heat it evenly, but to let the adhering potash run over the entire
surface, and as soon as the required heat is attained the work should be
removed from the fire quickly and quenched in water.
It may be added, however, that if after the potash has been applied and
fused more potash be added, so that it will adhere to the work and not
fuse until the work is put into the fire a second time, then, after the
work is quenched and taken from the water, there will be found on it a
thick white and closely adhering fur of melted potash, and the work will
be a dead white, with no fancy colors on it, and as hard as it is
possible to make it.
The prussiate of potash process is, of course, from its expensiveness,
both in material and labor, too costly for work to be done in
quantities, and box-hardening is therefore resorted to.
In box case-hardening the work is case-hardened all over. It consists in
packing the work in an iron box containing the hardening material, and
subjecting the whole to a cherry-red heat for some hours.
A very common process is to fill a sheet-iron box with the work closely
packed about with bone-dust, the pieces of the work having at least a
thickness of 3/8ths of an inch of bone-dust around them. The seams of
the box are well luted with clay to prevent the gases from the consumed
bone-dust from escaping, and to exclude air.
Various ingredients are used to effect case-hardening. One process is as
follows: 20 lbs. of scrap leather and 15 lbs. of hoofs (cut into pieces
of about an inch square), 4 lbs. of salt, and one gallon of urine are
prepared, and a wrought iron box with a lid capable of being fastened on
is obtained. The fastenings must be capable of ready unfastening when
hot. A layer of leather and pieces of hoofs about 1-1/2 inches thick is
first laid in the box, then a layer of salt, and then a layer of work.
Leather and hoof are then packed closely around the work and above it
for a thickness of about an inch, and a second layer of work added, and
so on, the last layer being of leather, &c., completely filling the box;
the urine is then added, and the box well sealed with clay.
The box is placed in a furnace and kept at a red heat for about fourteen
hours, and is then taken to a deep tank, and the work quickly immersed,
so as not to be exposed to the air after the box is opened.
If the pieces are of solid proportions, so as not to be liable to bend
or warp in the cooling, the contents of the box are simply dumped into
the tank, the water being allowed to flow freely in the tank to keep up
a circulation and cool the work quickly; some work, however, requires
careful dipping to prevent it from warping. Thus a link or a double-eye
would be dipped endwise, a plate edgewise; but all pieces should be
immersed as quickly as possible after the box is opened.
Sheehan's patent process for box case-hardening, which is considered a
very good one, is thus described by the inventor:
DIRECTIONS TO MAKE AND USE SHEEHAN'S PATENT PROCESS FOR STEELIFYING
IRON.
No. 1 is common salt.
No. 2 is sal soda.
No. 3 is charcoal pulverized.
No. 4 is black oxide of manganese.
No. 5 is common black rosin.
No. 6 is raw limestone (not burned).
Take of No. 1, 45 lbs., and of No. 2, 12 lbs. Pulverize finely and
dissolve in as much water as will dissolve it and no more--say 14
gallons of water in a tight barrel; and let it be well dissolved before
using it.
Then take three bushels of No. 3, hardwood charcoal broken small and
sifted through a No. 4 sieve. Put the charcoal in a wooden or iron box
of suitable size made water-tight.
Next take of No. 4, 5 lbs., and of No. 5, 5 lbs., the rosin pulverized
very fine. Mix thoroughly No. 4 and No. 5 with the charcoal in your box.
Then take of the liquid made by dissolving No. 1 and No. 2 in a barrel
as stated, and thoroughly wet the charcoal with the whole of said
liquid, and mix well.
The charcoal compound is now ready for use.
A suitable box of wrought or cast iron (wrought iron is preferable)
should next be provided, large enough for the work intended to be
steelified.
Now take No. 6, raw limestone broken small (about the size of peas), and
put a layer of the broken limestone, about 1-1/2 inches thick, in the
bottom of the box. A plate of sheet iron, one-tenth of an inch in
thickness, is perforated with 1/4-inch holes one inch apart. Let this
plate drop loose on the limestone inside the box. Place a layer of the
charcoal compound, two inches thick, on the top of said perforated
plate. Then put a layer of the work intended to be steelified on the
layer of charcoal compound, and alternate layers of iron and of the
compound until the box is full, taking care to finish with a thick layer
of compound on the top of the box. Care should also be taken not to let
the work in the box come in contact with the sides or ends of the box.
Place a suitable cover on the box and lute it with fire-clay or yellow
mud. The cover should have a quarter-inch hole in it to permit the steam
to escape while heating.
The box should now be put in an open fire or furnace (furnace
preferred), and subjected to a strong heat for five to ten hours,
according to the size of the box, and the bulk of iron to be steelified.
Remove the pieces from the box one by one and clean with a broom, taking
care not to waste the residue, after which, chill in a sufficient body
of clear, cold water, and there will be a uniform coat of actual steel
on the entire surface of the work to the depth of 1/16 or 1/8 of an
inch, according to the time it is left in the fire. The longer it is
left in the fire the deeper will be the coat of steel.
Then remove the residue that remains in the box, and cool with the
liquid of No. 1 and No. 2, made for the purpose with 20 gallons of
water, instead of 14 gallons, as first used with the charcoal compound.
The residue must be cooled off while it is hot, on a piece of sheet iron
or an iron box made for the purpose. Turn the residue into the supply
box, and it will be ready for use again. The more it is used, the better
and stronger it will be for future work.
There is nothing to be renewed for each batch of work but the limestone,
and that, after each job, will be good burned lime.
A process used at the Elevated R.R. shops in New York city is as
follows: The materials used are: leather, 1 part; bone dust, 5 parts;
salt, 1 part. Heat for 48 hours to a red heat in a box sealed with fire
clay, and quench in a solution of 3 pounds of potash to 30 gallons of
water.
The wrought iron thus treated is impervious to a new smooth file at a
depth of 1/16 of an inch.
The potash water is said to prevent both warping and the formation of
blister marks on the work.
The durability of work case-hardened is greatly enhanced, but it is an
expensive process; not so much by reason of the cost of it, but because
it involves resetting and a refitting of the parts. The resetting is
necessary because the work warps under or during the process. This
warping can be prevented to some extent by placing the heaviest pieces
in the bottom of the box, and so packing the same that the weight of the
top pieces shall not tend to bend those beneath them when the hardening
material has burned away, and so placing the upper pieces that they
shall not be bent by their own weight. Thus both in packing and locating
the work in the box the utmost care is necessary.
SETTING WORK AFTER HARDENING IT.--Work that has been hardened or
case-hardened usually swells during the hardening process, and therefore
requires refitting afterwards. This swelling usually occurs in all
directions, thus holes and bores become of smaller dimensions, while the
outside dimensions also increase, bolts become of larger diameter and
sometimes increase in length.
In very exceptional cases, however, the dimensions of a piece of work
will not alter.
This renders it usually necessary to refit the work after it has been
hardened, thus holes which are ground out by laps or bolts may be ground
to diameter in a grinding lathe.
In some practice, however, the work to be hardened is made a somewhat
too easy fit, the holes tapped out and the bolts ground in by direct
application of the bolts to their holes in connection with flour emery
and oil. This latter plan is also adopted for forms not easily ground
out in a machine, as, for example, a die in a link of a link motion.
[Illustration: Fig. 2413.]
[Illustration: Fig. 2414.]
To prevent surfaces or forms of this class from altering their shape or
dimensions during the hardening process, slips of iron are sometimes
fitted to them before they are placed in the hardening box. Thus Fig.
2414 represents a double eye, and Fig. 2413 a link having thin pieces
fitted in as shown at A in both figures.
The heating for the hardening process is also apt to impair the
alignment of the work, causing it to require resetting by the aid of
parallel strips and straight-edges.
[Illustration: Fig. 2415.]
The faces of the link having been set, the width of the link slot must
be set, for it may open or close in places. If it opens it may be closed
by the jaws of a powerful vice, while if it closes it may be opened by a
pair of inverted keys, inserted as shown in Fig. 2415, and driven in by
the hammer. At each trial, however, a mark should be made on the driven
key, so that it may be known how far to drive it at the next trial.
[Illustration: Fig. 2416.]
[Illustration: Fig. 2417.]
Fig. 2416 represents a link that is supposed to have been case-hardened,
and to therefore require resetting. The stem from A to B should first be
straightened to a straight-edge on both its side and edge faces. It
should then be tested for winding with the winding strips, C, D, placed
as in Fig. 2416, and then as in Fig. 2417.
[Illustration: Fig. 2418.]
[Illustration: Fig. 2419.]
To test the alignment of end E, press a straight-edge S fair against its
side face, as in Fig. 2418, and measure the distance H. Then place the
straight-edge on the other side face of E and measure the distance I,
Fig. 2419, and these distances both measuring alike, E will be true
providing that the jaws at end F have not altered from their proper
width apart.
To test the alignment of the jaws at end F, press a straightedge against
the outside face of the hub and measure the distance J, Fig. 2420, then
apply it on the other side and measure distance K, Fig. 2421, and when
distances J and K are equal and the width L between the jaws is correct,
end F is in line in one direction. To test it in the other direction,
apply a pair of parallel strips, placing one on end E as in Fig. 2417,
and the other across the face of the hub of end F to see if there is any
twist.
[Illustration: Fig. 2420.]
[Illustration: Fig. 2421.]
Suppose, however, that distances J K are unequal, then if distance L is
too narrow (when tested by the piece that fits between the jaws) then
the jaw at F that gives the widest distance at E is the one that
requires correction, or if distance L is too wide, the jaw that shows
the least distance at end E is the one requiring correction.
The link should be warmed to about 300°, or nearly _black_ hot, and
pieces of sheet copper placed between the work and the anvil, and
between the blacksmith's tools and the work, so that the latter may not
be bruised by the blows delivered to effect the straightening.
After the process has been performed at each end individually the
testing should be repeated, because setting the end F may have impaired
the setting of end E, in the alignment to F.
It is obvious that the same setting or aligning process would be
required in the case of a large link, where the ends were forged
separately and welded to the body after the machine work and fitting had
been done to them.
[Illustration: Fig. 2422.]
[Illustration: Fig. 2423.]
[Illustration: Fig. 2424.]
[Illustration: Fig. 2425.]
[Illustration: Fig. 2426.]
FITTING BRASSES TO BOXES OR TO PILLAR BLOCKS.--In the operation of
fitting brasses to their boxes or to pillar blocks there are two things
to be especially guarded against: First, having the brass let down
one-sided, as shown in Fig. 2422; and next, aslant, as shown in Fig.
2423. The first depends on taking the proper amount off the two side
faces, and the second in cutting the inside of the flanges fair. To cut
the side faces fair, grip the brass in the vice, as shown in Fig. 2424
(the brass being shown in section), in which a is A block of wood. Take
the measure of the box, down where the brass will come when home, and,
if there be any taper to the box, set the inside calipers to the top of
the location for the brass, and after the brass is in the vice place a
square under one side-face, as at B in Fig. 2426, and see how much there
is to come off. This saves the use of outside calipers, and is better
because, not only is the trouble of setting the latter avoided, but the
inside calipers can be tried to the box and the work in an instant, and
a correction can at once be made if the calipers have got shifted. The
cape chisel, or cross-cut, as it is sometimes termed, should first be
used, taking a cut close to the flange, and making it half as deep as
the calipers (applied as shown in Fig. 2426) show there is metal to come
off. Then a similar cut should be taken close to the other flange,
especial care being taken to take both cuts equally deep, and leaving
as much to come off the other side face of the brass; otherwise, the
brass will come atwist. Then take a straight-edge, and, placing its edge
fair with the two chisel-grooves, while holding it firmly against the
joint face of the brass, mark a line running from one chisel groove to
the other; this line serving as a guide for the depth of all the other
cape-chisel grooves. Now cut off the intermediate spaces with the flat
chisel, using a straight-edge as a guide. If the box is taper, chip the
side face to a corresponding taper, using a bevel-square, or estimating
the amount by the eye if it is not too much. Now file the chipped
surface flat and true, and then turn the brass upside down, gripping it
with the wood as before, and dress the other side face (applying the
inside calipers as in Fig. 2426), and bring that face down to within
about 1/64 inch of the size to which the calipers are set. If the block
of wood is made a little shorter than the length of the brass, the
calipers can be applied without moving the brass from or in the vice.
The method of applying the square to these side faces is shown in Fig.
2425, in which A is the brass in section, B a straight-edge, and C a
square.
[Illustration: Fig. 2427.]
[Illustration: Fig. 2428.]
[Illustration: Fig. 2429.]
[Illustration: Fig. 2430.]
We now turn our attention to the flanges, and apply a square to the
crown of the box, bringing the edge of the blade fair with the edge of
the box, as shown in Fig. 2428, A representing the box in section, and B
the square. Supposing the crown of the box to stand square, as shown in
the engraving, and as it should do, we set the brass upon a
truly-surfaced iron plate and square up the joint face, as shown in Fig.
2427, in which A is the surfaced iron, B the brass, and C the square.
Since, however, the joint face of the brass may not be parallel with the
crown face, we may place the square so that its blade edge comes fair
with the crown face--that is, as shown at D in Fig. 2427--and set the
brass crown (by means of inserting a wooden wedge under its face) truly
perpendicular or parallel with the square blade edge. Now try the square
with the side face of the brass, setting the latter true with the square
blade, as in Fig. 2430; A being the iron plate and B the square; and,
supposing the box to be true, as it usually is, we may set a
scribing-block, as shown in Fig. 2427, and mark off how much is to come
off the flanges by scribing a line around the flange, sufficiently
depressing the scriber-point to allow an equal amount to come off each
of the flanges. Sometimes, however, the inside faces of the box are not
true with the outside face. To test this, we place a straight-edge
across the outside face, place a square on it, and apply it to the
inside face of the box, as in Fig. 2429, which is a plan view of the
box, A being the straight-edge and B the square. If the square thus
applied shows a want of truth in the box, we may set the brass over when
adjusting it (as in Fig. 2427) to a corresponding amount, and thus mark
off the flanges to suit the box.
[Illustration: Fig. 2431.]
To hold the brass while operating on the flanges, we resort to the
device shown in Fig. 2431, in which A is a bolt, B the brass, C a piece
of hard wood, and P a clamp fastened down by a nut D. To sustain the
plate P, so that it shall not fall down on the piece of wood every time
the brass is taken out to try it in the box, we may insert the spiral
spring S, shown in the separate view of the bolt, nut, and plate. One
such holding device will do for different sizes of brasses, by either
gripping the bolt lower down in the vice jaws or putting washers between
the nut and the plate. This will hold the brass very firmly, and at the
same time leave the whole of the flange easily got at. When the flanges
are dressed, we may try the brass in the box, putting red-lead marking
on the box to mark where the brass binds. While letting the brass down,
however, we must be careful to let it down fair, to avoid the state of
things shown in Figs. 2422 and 2423. A ready method of doing this is
(supposing the box to be true, as it should be, and making the necessary
allowance if it is not), to set a pair of inside calipers to the joint
face of the brass and the top of the box, as shown in Fig. 2432, trying
the calipers (in the two positions there shown) on both sides of the
box. This should be done every time the brass is tried in the box, until
such time as the brass begins to bed against the bottom of the box.
[Illustration: Fig. 2432.]
We now come to the bedding of the brass to its seat in the box. This
requires skillful treatment; for one mistake will involve a great deal
of extra work to rectify it.
In fitting the brass to the box care must be taken to leave it a rather
tighter fit to the box than it requires to be when finished, that is
after the bore has been made, because in the boring operation the sides
of the brass are apt to close and loosen the fit of the brass to the
box.
[Illustration: Fig. 2433.]
When the side faces and flanges are so far fitted as to render probable
the brass driving home at the next trial, the bed of the box should be
given a coat of red-lead marking, and small pellets of stiff red lead or
putty should be stuck on the bottom of the box, two at each end of each
bevel, and two at each end of the bottom, with one in the middle of the
bottom and each bevel, as shown at A, B, C, D, E, F, in Fig. 2433, by
the black spots. Then when the brass comes home, it will flatten these
pellets, and their thickness (when the brass is taken out) will show how
much the bevels are out, and how much to take off the brass to make it
bed. These pellets _must_ be restored to their original shape every time
the brass is tried; otherwise, they may mislead. To insure their
sticking to the box, and not coming out with the brass, the bottom of
the box must have red-lead marking kept upon it. The chipping should
continue until the pellets flatten out equally on the two bevels, but
are left a little thicker on the bottom. If this is not done, the bottom
will bed first, causing a great deal of extra filing, because filing the
side bevels will let the bottom down too far.
In driving the brass in and out of the box while fitting it, a piece of
wood must be used to strike on, otherwise the brass will stretch during
the fitting and come loose in the box during the boring.[33]
[33] See remarks on Pening, p. 162.
[Illustration: Fig. 2434.]
[Illustration: Fig. 2435.]
The patterns from which the castings for brasses are moulded should not
be made of the same angle or sweep on the bedding part or bottom as the
bottom of the box, pedestal, or pillar block, because the brass casting,
in cooling in the mould, contracts across the bore; thus if in Figs.
2434 and 2435 the full lines denote the shape of the pattern the dotted
lines denote the shape the casting will be.
[Illustration: Fig. 2436.]
[Illustration: Fig. 2437.]
The result of this is that when the brass is let down in the box it will
bed on the crown and not at the sides. Thus in Fig. 2436, A is a
pedestal, and B a brass which beds at C, but not at D or E. In Fig. 2437
is shown an example of a brass, with a circular bottom, which would bed
at the crown C, but not at the sides D E, until the metal was cut down
to the dotted circle F.
The amount to which this contraction in the mould occurs varies with the
size of the brass, the difference in the thickness at the crown and at
the face joint, the composition of the metal of which the casting is
made, and the temperature of the metal when poured into the mould. It
should always be allowed for, however, for the following reasons.
Referring again to Fig. 2436, it will be noted that it requires a heavy
cut off C to bring E, D to a bearing, while it is apparent that if the
brass met the box at E, D before it did at C, but little filing at E, D
would let the brass down a long way. It saves work, therefore, to so
make the pattern as to insure that the brass casting shall have bedding
contact at D and E before it does at C. As an example of the allowance
to be made for this purpose, it may be stated that in brasses of 6
inches bore and 9 inches long, the hexagon of the brass pattern at D, E,
Fig. 2436, would require about 1/16 inch put on them to compensate for
the contraction, supposing that the hexagon on the brass pattern were
made at first to fit the hexagon of the pedestal or axle box.
To originate a true flat surface we proceed as follows: In the absence
of a standard plate to go by, we must have three plates, and one of them
must be accepted as a provisional or temporary standard. This we will
call No. 1, and we fit Nos. 2 and 3 to it and then try them together,
and if they also fit it is proof that No. 1 was true, and that all three
are therefore true. It will very rarely happen, however, that this is
the case; but Nos. 2 and 3 merely serve to show how much No. 1 was out
of true.
Suppose, for example, that No. 1 is concave in its length, and we fit
No. 2 to it, as in Fig. 2438, and then fit No. 3 to it as in Fig. 2439,
and when we come to put Nos. 2 and 3 together, as in Fig. 2440, we find
that they are out of true to twice the amount that No. 1 is, and that
all the work that has been done to them to fit them to No. 1 has been
thrown away, and possibly to make them worse instead of better. It
becomes important therefore to select the most true plate for No. 1, and
this we may do as follows:--
[Illustration: Fig. 2438.]
[Illustration: Fig. 2439.]
[Illustration: Fig. 2440.]
[Illustration: Fig. 2441.]
[Illustration: Fig. 2442.]
If we have a straight-edge that is known to be true, we may lay it on
the face of a plate and move it laterally from each end alternately, and
if it swings from the centre the plate face is rounding, while if it
shuffles across moving first at one end and then at the other the face
is hollow; but if it glides as it were across, the surface is nearer
true. The straight-edge must not be pressed to the plate, but merely
touched laterally to make it move laterally, for if we take a true
straight-edge and press it vertically to a true surface while moving it,
it will show the marks of contact the most plainly immediately beneath
the parts where it is pressed. Selecting by this means the two plates
that appear to be the most true we proceed to test them further as
follows: We give to one of them which we will call No. 1 a light coat of
red marking, and placing it upon the other or No. 2, we move it about in
all directions and then take the two apart to examine the bearing marks.
Suppose then that No. 1 shows the bearing marks to be at the shaded
places, A and B, in Fig. 2441, while the bearing marks on No. 2 are as
at the shaded parts A and B in Fig. 2442, the two ends A having been
placed together; then we know that B is a high spot on No. 1, and A a
high spot on No. 1 for the following reasons. The marks at A, No. 2,
have been made by the marking at A on No. 1, and will extend across No.
2, a distance depending upon how much No. 1 has moved across No. 2, for
if corner A of No. 1 had only moved half-way across No. 2, it could only
have marked half-way across it. Similarly spot B on No. 1 has marked
spot B in No. 2, because it has been moved all the way across, it being
evident that the marking on B, No. 1, can only mark plate 2 as far
across its width as it is moved across it. From this it follows that the
higher or more prominent a spot is the less will be the area of the
bearing mark at that spot.
[Illustration: Fig. 2443.]
[Illustration: Fig. 2444.]
Now suppose that the two plates were curved to an equal degree as in
Fig. 2443, and the bearing marks would extend all over both surfaces;
but we may discover this error by turning one plate at a right angle, as
in Fig. 2444, in which case the bearing marks would show along the edges
of No. 1 and along the middle of No. 2, and we may correct each with the
file until both plates mark all across and from end to end when tried
together lengthways as in Fig. 2443, and one across the other as in Fig.
2444. But the plates may be curved to a different degree, as in Fig.
2445, and it then becomes necessary to know which to file the most in
correcting them and fitting them together, which we may discover as
follows:--
[Illustration: Fig. 2445.]
[Illustration: Fig. 2446.]
[Illustration: Fig. 2447.]
We give one plate a light coat of red marking and rub it upon the other
both sideways and lengthways. Suppose that on being separated and
examined the bearing marks, shown as at A A and B B, Fig. 2446, on one
plate, and at C C and D D, Fig. 2447, on the other, and as those at A A
and B B are the narrowest, or in other words extend the least distance
across the plate, it is proof that this plate is more concave than the
other plate is convex, and therefore needs the most correction. This is
plain because whatever part of a plate touches another, will, if the two
are merely pressed together, only leave a bearing mark equal in area to
itself, while this area will obviously be increased in proportion as one
plate is moved about upon the other.
[Illustration: Fig. 2448.]
When the object is to merely produce a flat surface, independent of the
thickness or parallelism of the plate, it is not always necessary to
file or scrape the whole of the area showing bearing marks. Suppose, for
example, that the marks appear as in Fig. 2448, and as the bearing marks
at A A show that edge of the plate to be straight already, all that is
necessary is to ease the surface at B in order to let that side of the
plate come up.
When we have fitted two of the three plates together we must accept one
of them as a true one and (calling it No. 1) fit Nos. 3 and also 2 to
it, and then try Nos. 2 and 3 together. If these require correcting the
amount of correction must be made equal on each, and when this is done
we must accept one of these two (say No. 3) as the standard, fit No. 1
to it, so that Nos. 1 and 2 both having been fitted to No. 3 may be
tried together and both corrected equally; nor will the surfaces of any
of them be true until all three will interchange in this manner and show
a perfect contact.
It is to be noted, however, that in this process we have not altogether
eliminated the error due to the deflection of each plate. Suppose, for
example, a plate to be resting on its feet and its middle will sag or
deflect to some extent (very minute though it may be in a small plate),
and when we place another plate upon it the latter will also sag or
deflect if its points of contact are far apart, and in any event the
truing is performed by the bearing-marks, which the operator knows show
the darkest and the brightest where the contact is greatest; hence by
the time the contact marks show equally strong all over, the top plate
will have been fitted to suit the deflection of the lower one. Since,
however, the nearer the points of contact (between the plates) are
together the less the degree of deflection, it is better in trying them
to place the test plate on the top of the one being operated on. If the
plates are long ones it will not answer to have more than three points
of rest for the lower plate, unless the foundation on which the plate
rests is made so true that each resting point of the plate will bear
with equal pressure on the foundation plate or stone.
To eliminate as far as possible the deflection, the three plates may be
got up by the process described, and then finished by trying them when
resting on their edges (the trued surfaces standing vertical),
interchanging the three plates as before.
In this case the surface will be true when standing vertical as
finished, but there will still be some untruth from deflection when the
plates are rested on their feet, though it will be less in amount than
if the plates were finished on their feet as first described.
In finishing surface plates with a hand scraper, we have a surface that
bears in fine spots only, these spots being the tops only of the scraper
marks. Now the depth of the scraper marks are unequal, because
immediately after the scraper is sharpened it cuts the easiest and the
deepest, the scraper cutting less deep as its edge dulls. The operator
regulates this to some extent by applying a greater pressure to the
scraper as it gets dull, but from differences in the texture of the
metal and from other causes it is impracticable to make the scraper cut
equally deep at each stroke, as a result the tops of the scraper marks,
which are the points of contact of the plates, wear away quickest, and
the plate soon loses, to some extent, its truth.
Again, work that is so small as to cover part of the plate surface only,
wears the part of the plate to which it is applied, and although the
careful workman usually applies small work at and near the outside edges
of the plate only, still these are all elements tending to produce
increased local wear and to throw the plate out of true.
To obviate this difficulty the surface should be got up to bear all
over, thus greatly increasing its bearing area and proportionately
decreasing its wear. To produce such a surface the following plan was
adopted by the author in 1876.
The filing process was continued with fine Groubet files, and testing
the plates, rubbing them together sufficiently to mark them without the
use of oil. Very short file strokes must be employed, and great care
taken to apply the file to the exact necessary spots and places.
Then instead of using the scraper, No. 0 French emery paper was used,
wrapped over the end of a flat file. The plates being interchanged and
trued with No. 0, No. 00 was used, and the testing and interchanging
repeated. These grades of emery paper were then wrapped or folded over
the curved end of a piece of wood, the plates interchanged and rubbed
together as before, and the emery paper used as described for the
scraper. Subsequently Nos. 000 and 0000 French emery paper were
similarly applied until the plates were finished. Much assistance to
this method may be rendered by taking a piece of Water of Ayr stone, and
truing its surfaces by rubbing them on the plates after the fine filing
and before the emery papering. Then while applying the finer grades of
emery paper the stone may be rubbed (with oil or water) in various
directions over the surface. This has the effect of wearing off the very
fine protuberances due to the emery paper cutting the metal most around
its pores, and furthermore it causes the marks made in testing to show
more plainly.
In skillful hands this process very far surpasses, both in the
superiority of its results and in rapidity of execution, the scraping
process, leaving a brilliant polished surface, so smooth that it feels
as soft as satin, and the contact becomes so complete that no bearing
marks can be distinguished.
In this process great care must be taken in cleaning the surfaces before
applying them together, as the finest particle of dust will cut
scratches, which though imperceptible on scraped surfaces, appear very
coarse and deep on these smooth ones.
The amount of metal taken off by the finer grades of emery paper is so
small as to be scarcely appreciable, save that it slightly discolors the
emery paper.
The finest test for plates finished in this way is to rest the lower one
quite level, clean it with alcohol, wipe it clean with old linen rag and
finally with the palm of the hand, which if quite dry is more effective
than anything else. The eye should carefully sight the plate surface
with the light reflecting on that surface, when particles too fine to be
felt may be observed and wiped off with the hand. In dry weather it is a
difficult matter to clean the plates perfectly, as while one is being
cleaned the fine particles of matter floating in the air rest upon the
other; but in rainy weather the cleaning is much easier.
The plates being cleaned one must be lowered vertically on the other
where it will float, there being a film of air between the two which it
is almost impossible to exclude by pressure even though the plates be
moved while pressed together.
If under these conditions the surfaces are not true and the top plate be
set in motion in various directions, by a light finger touch it will
swing round, the parts of the surface most in contact being the centre
of motion. Suppose then the top plate to swing from one end it should be
turned end for end on the bottom plate, and if the location of the
centre of motion is still at the same end of the top plate, that plate
is high there, while if the centre of motion in both cases is at the
same end of the bottom plate it is the one that contains the error.
If the top plate swings upon its own centre of motion it must be moved
farther off the bottom one, first on one side and then on the other, to
discover if it or the bottom plate is in error; while if the top plate
swings first from one end and then from the other, one or both of the
plates are hollow and the top one must again be moved farther off the
lower one, and the test by motion continued. The error discoverable in
this way is very much finer than can be discovered by the marks of
contact, since a plate showing quite even contact when quite dry and
clean, and tested as lightly and carefully as may be will show error by
this motion test. The error being so small in amount that it may be
corrected by rubbing the plate with rag and oil, applied under hand
pressure to the plate.
To cause the plates to bind together so that rubbing one on the other
will leave contact marks, the top plate must be placed about an inch
over the corner of the bottom one, pressed closely to it and forced
laterally over it. A pair of plates of the Whitworth pattern (such as
shown in Fig. 2449) placed by the author in the Centennial Exhibition,
required, when put together dry as above, 341-1/2 lbs to _slide_ the top
one over the other, which was due to the friction caused between the
surfaces by the atmospheric pressure acting on the back surface of the
plate, the latter having a superficial area of 12 by 8 inches.
Here it may be added that a plate of the same dimensions, and having its
surface finished simply by filing with a dead smooth file, which plate
was made for exhibition at a lecture on hand work, delivered before the
Spring Garden Institute of Philadelphia, required a force of 22 lbs. to
slide on the one on which it rested.
[Illustration: Fig. 2449.]
If two plates finished by the above method be placed together by sliding
one upon the other it will be found that with the hands applied as in
Fig. 2449, they can be separated or pulled apart with less force than it
requires to slide one upon the other, because the plates bend and unlap,
as would be the case if two sheets of paper were wetted and placed
together and then taken apart by pulling two edges in opposite
directions. But if the power to pull the plates apart be applied at the
middle of the plate it will require a much greater force to separate
them, although how much is problematical, no experiments having been
made upon the subject. Furthermore the friction between two such plates
will be greater if the surfaces be lubricated than if quite dry.
Thus, with the surfaces cleaned by alcohol, the top plate will move
comparatively easily, but if the surfaces be slightly oiled and then
wiped apparently quite clean with old dry rags, the friction will be a
maximum. If then a piece of rag, say of an area of an inch, have one
drop of oil upon it and be then applied to the surfaces of two plates
after they have been cleaned with alcohol, the friction will still be
about 3 lbs. per inch of area of one plate. With the surfaces well
lubricated it will still require more power to slide one plate upon the
other than would be the case were both plates quite dry.
The reason of this is that when quite dry it is impracticable to exclude
the air from between the surfaces, whereas with the lubrication the air
is more perfectly excluded and the atmospheric pressure forces the
plates together.
CHAPTER XXVIII.--ERECTING.
ERECTING.--The term erecting is applied in large work to the operations
involved in fitting the parts to their places on the engine or machine,
as well as to placing them upon their foundations and putting them
together ready to run.
In vice work or fitting, the various parts are put together ready to be
erected, each part being complete in itself, but not adjusted with
relation to the others. Thus, while a link motion may be complete in
itself, the length of its eccentric rods will usually require correcting
when placed upon the engine. Furthermore the position of the eccentric
is to be adjusted.
The boiler fittings may be complete in themselves, but will still
require to be fitted or erected upon or to their places.
Erecting requires the greatest of skill, care, and judgment, in order
that the work may be put together properly aligned and any defects of
construction corrected in the finished machine.
In erecting a machine, as in building a house--or, indeed, as in
everything that man constructs--the work must be begun at the
foundation.
In a machine in which the working parts are carried and contained upon
framework, such framework becomes the foundation so far as the erector
is concerned.
In a stationary steam engine the cylinder and bed plate form the
erector's foundation while the engine is in the shop, the mason's
foundation being an after consideration.
In a locomotive the boiler is the foundation to which all the other
parts are either directly or indirectly affixed.
The erector uses all the measuring tools used by the fitter or vice
hand, and in addition many others, as stretched lines, the spirit-level
and plumb-level. Either of these tools forms the readiest means of
testing whether surfaces that are widely removed and in different
positions about a machine are parallel one to the other, it being
evident that all surfaces standing vertical will be parallel, or all
those standing horizontal will also be parallel, one to the other.
Spirit-levels are often made of wood, which is very objectionable for
the erector's use, because the lower or testing surface is apt to catch
and hold particles of metal, and furthermore it is very susceptible to
abrasion, and wears rapidly. It is preferable, therefore, that it be of
iron or steel. The test of a spirit-level is its sensitiveness, and it
is found in a properly constructed one that the bubble will move to a
perceptible extent if a piece of gold leaf be inserted under one end. In
a spirit-level which came into the hands of the author of this work he
found the warmth of the finger when placed on its top sufficient to
cause the bubble to move nearly the full length of its tube, the body of
the level being a block of iron 1-1/4 inches square and 9 inches long.
The movement of the bulb was caused by the heat of the finger expanding
the top of the spirit-level and causing it to bend. To test the truth of
a spirit-level, it should be placed upon a true surface, as a surface
plate, and if the bubble comes to rest at the same spot in the length of
the spirit tube when the level is tried turned end for end, the level is
true. The test should be made several times.
[Illustration: Fig. 2450.]
The plumb-rule, though less used by machinists than formerly, is better
for machinists' use than the ordinary wooden-bodied spirit-level, since
it is more delicate if properly constructed. It should be formed as in
Fig. 2450, the sides A A and B B being straight and parallel one to the
other; C and D are two plugs of soft yellow brass let in so as to keep
the line _l_ _l_ clear of the face of the level, so that there shall be
no friction between them. At N are notches to secure the line, which
should be as fine and as closely spun as possible.
[Illustration: Fig. 2451.]
The plumb-level, Fig. 2451, is also preferable to the ordinary
spirit-level; its edges A, B must be straight and at a right angle one
to the other, C and D representing brass plugs as before. The edge A of
the rule or of the level should be laid upon a surface plate, and a fine
line drawn on the face of these plugs with a scribing block, the
coincidence of the line _l_ with these marked lines testing the truth of
the work.
FITTING OR MAKING JOINTS.--The best form of joint to withstand pressure
is the ground joint, and next to this, but more expensive, is the
scraped joint. The difference between the two is as follows:--
For a ground joint the fitting with files or scrapers is only carried
far enough to bring the fit sufficiently near that it may be finished by
grinding the surfaces by rotating one upon the other with oil and emery
interposed between them.
To grind a joint it is obvious that all the bolts or studs must be
removed.
In a scraped joint the scraping is carried to such a point of
correctness that the fit will be tight without grinding.
Joints in new work are easily ground, because the bolts or studs being
new have not become rusted in their places and may therefore be readily
removed; furthermore the joint may be ground before the studs are
inserted. But in the case of old joints the studs may have become so
rusted to their places as to render them liable to break off in the
effort to extract them, and in such case it is better in most cases to
make a scraped joint, which may be done with the studs left standing in
their places.
To make a ground joint, as say a cylinder cover joint, proceed as
follows:--
Put a thin coat of red marking upon the joint face of the cover, and
after it is coated lightly and smoothly all over, the hand should be
passed over the whole surface marked, because any grit left on the
surface will cut the faces of the joint when they are rubbed together to
fit them, and there is no wiping material that will so effectually clean
dust from the surface as the hand will; and furthermore, the sense of
touch will instantly detect any grit present. The cover may now be put
into its place on the cylinder and rotated back and forth a turn or so
to insure that it is properly seated; then we may strike it a light blow
in different places with a piece of wood or the end of the handle of
the chipping hammer; and if the cover does not fit pretty closely to its
seat, a sharp metallic sound will be distinctly heard when the blow is
struck over the parts of the face that are much out of true. Hence, by
striking the blows all around the flange, we can easily find not only
the high and low spots, but can determine, after a little practice, by
the degree of the sound, how much the faces are out of true. We next rub
the cover back and forth on its seat, so that the marking on the cover
will mark the high spots on the cylinder face. If, however, we make the
forward reciprocating movement of the cover a longer one than the
backward, we shall give to it a gradually rotary as well as a
reciprocating movement, and this will tell us if the face of the cover
is true or not, for if the marking is removed from the face of the cover
in two diametrically opposite places only, it shows that the cover
itself is not true; and if the cylinder face also marks on two
diametrically opposite places only, it is proof that both the faces are
a good deal out of true: but there is no knowing which one is the most
out, and so we must file off each an equal amount. If either face marks
in more than two places it is evidence that it is pretty nearly true,
and it follows that that face does not need much filing. Here it becomes
necessary to state why the movement of the cover must, when being tried
to its place, be back and forth, as well as rotated by the movement
already explained. If we revolve a radial surface of metal upon a
similar surface they are extremely liable to cut or abrade each other,
and the presence of the least grit will inevitably cause them to cut;
and if cutting once begins, the metal gathers upon the cutting part,
increasing its size so that the groove cut will get deeper until a
complete revolution has been made, and this rule applies to all
revolving surfaces, but more particularly to radial or conical ones.
By making the movement a partly reciprocating one we destroy this
tendency, and either imbed the grit into the iron or else work it out.
To proceed, however. If during our testing the blows induced a secondary
and metallic sound as above described, we take a rough file and ease the
high spots on both the cover and the cylinder face, filing a good deal
off the face that shows diametrically opposite bearing spots only, and
but very little off the face that shows three or more bearing spots. In
this latter case, indeed, it is better to use a second-cut than a rough
file. We next wipe both faces quite clean, apply the marking to the
cover as before, and try it to its seat again; rubbing it in the same
manner to its seat and testing it for the metallic sound as in the first
case. So soon as this sound ceases we may take a second-cut file and fit
the faces until they bear in at least four different places, when a
smooth file should be used and the fitting and trying continued, until a
very light coat of the red marking will show both the cover and the
cylinder face to mark in spots not more than an inch apart; and we may
then take a flat scraper, ease away the high spots, pressing the scraper
firmly to its work and making it cut fine scrapings, using the scraper
in strokes of about 1/2 inch for a large face and 1/4 inch for a small
one. When the two faces show about an even contact all over, the
grinding may be performed as follows:--
The two faces must be wiped quite clean, and then with an oil-can we can
run a line of oil around both the cylinder and cover faces, and then
with the fingers sprinkle on them some dry grain emery, of a grade of
about 50 for a cylinder whose diameter is, say, 14 inches or over, and
of a grade of about 60 to 65 for smaller diameters; if, however, only
coarser grades of emery are at hand it may be ground finer by abrasion
on an iron block, using a hammer face to grind it with. The emery and
oil being applied, we place the cover in its place upon the cylinder,
and give to it the reciprocative rotatory movement already described,
continuing the movement until the cover moves so smoothly and
noiselessly that it is evident that the emery has done its duty. We then
take the cover off and examine the faces.
If there are prominently bright spots upon either face, denoting that
the emery has not operated upon them, it will pay to take the scraper
again and ease away the dullest and most frosted-looking spots, which
denote that they have suffered most during the grinding operation. The
difference between the spots that have been the most and those the least
affected by the grinding will be very plainly visible if the faces are
wiped clean. We must continue the grinding operation with this grade of
emery until the marks show the grinding to have been performed pretty
evenly all over the faces, and we then apply a coating of oil and emery,
as in the previous operations, the latter being in this case of a grade
of about 70, moving the cover as before until it revolves so smoothly
and noiselessly as to indicate that the emery is no longer doing any
duty. Having continued this process, applying fresh emery and oil until
the face appears true, we may perform the finishing and testing process,
which is of the utmost importance, since it will detect the faintest
possible defect in the job. Wiping the faces quite clean, we put the
cover in place upon the cylinder again, and move it as before back and
forth, and yet slowly advancing; but it must be borne in mind that if
the cover makes the least jarring noise during the operation we must at
once remove it and wipe it clean again, or the faces will abrade and
become destroyed. There is no danger of this, however, if the cover be
at once removed when the jarring sound is heard. If it be not heard, we
continue the operation until the cover has made four or five
revolutions, and then remove it, and we shall find that the emery and
oil, which had impregnated the surfaces, have worked out. We again wipe
the faces clean and put them together and rub one upon the other as
before, bearing in mind that if the faces cling much one to the other,
we must wipe them clean again. Usually the finishing process requires
performing about three times, and then the faces will have become as
bright and clear as a mirror, magnifying the slightest defect in the
joint. Joints made in this way will stand any pressure without leaking
(unless the pressure be so great as to spring the metal of the cover).
It is well, however, when making the joint, to put a little oil or pure
tallow on it, and it is from this that it is called in England a grease
joint, while in the United States it is termed the ground joint. It is
common, however, in England to finish the whole joint by scraping; but
this is a much more tedious job, and not so good a one, after all. Here
it becomes necessary to remark, that in order to be able to handle the
cover readily, it is best to bolt to it a wooden lever overhanging both
sides of the cover, and to serve as a handle in moving it. And during
the grinding we may place a weight on the cover, which will greatly
expedite the process. It would appear that this is a long job, but such
is not the case; indeed, a 16-inch cylinder face and cover 1/32 inch out
of true one with the other can be got up in half an hour.
It is to be observed, however, that the cylinder cover that contains the
stuffing box for the piston rod often carries one end of the guide bars,
and in any event carries the gland whose bore requires to stand in line
with the cylinder bore. It must be remembered that if more is filed off
the top than off the bottom of the face, or _vice versâ_, the gland bore
may be thrown out of parallel with the cylinder bore, and the guide bar
seatings will be thrown out of parallel in the same direction.
To facilitate the making of ground and scraped joints it is preferable
that the surface of the joint, both on the cylinder and the cover,
project from the rest of the flange, from the bolt holes to the bore in
the one case, and from the bolt holes to the body in the cover in the
other, so that the bearing surface of the joint shall extend from the
inside edge of the bolt holes to the cylinder bore only. This provides
ample surface to make a joint, while reducing the surface to be operated
upon.
TO MAKE A SCRAPED JOINT.--Let us now suppose that the studs are in their
places, and it is decided, for fear of breaking them in taking them out,
to make a scraped joint, and the process is as follows:--
The testing and marking of the high spots or places must be made by
giving to one of the surfaces a light coat of red marking and then
bolting up the cover moderately tight, screwing up the nuts at first
until they just grip the work all around, and not letting one part of
the cover face bear at any time with greater pressure against the
cylinder face than there is on the diametrically opposite side of the
cover, for the side under most pressure will receive the marking most
readily. Especially is this the case when the two faces first meet,
because even a low part of the face will show most contact under such
circumstances, and then easing such marks away will make the cover a
worse fit than it was before. When the cover is bolted home, the marking
on the cylinder face may be made to transfer itself on to the high spots
of the cylinder cover face more plainly if a piece of wood be placed on
the cover and struck lightly with a hammer, moving the wood around and
between the studs. If the wood be struck heavily it will cause an almost
endless and assuredly a faulty job, because the force of the blow will
spring that part of the cover to its seat on the cylinder face, whether
it fits in that particular spot to its seat or not, and hence the filing
or scraping may be done in places where it is not required, because the
marking misleads. If the bolt holes are very close together, as in
English practice, lightly striking the cover will prove an assistance;
but where they are several inches apart, as in American practice, it is
better to omit it, for the bedding marks will show plainly and properly
if the marking be evenly distributed by the hand over the cylinder face,
and the cover is bolted at each trial tightly to its seat, providing of
course that the red marking is free from grit.
In a job of this kind it is difficult to know, when a leak occurs,
whether the defect is in the cylinder face or the cover, and it is very
desirable to perform the operation with a view to correct the defect
rather than bed one face to the incorrectness of the other.
If then the stud holes are equidistant apart and concentric (so as to
permit it), the cover may be tried on in one or two positions, and, if
the bearing marks occur on the cover at each trial in the same places it
is the cover that is out; or if this occurs on the cylinder face, it is
that face which is out. Since the studs are in their places the cylinder
face may be best operated on by a scraper, while for the first part of
the operation on the cylinder cover a file may be used. The corner at
the junction of the cylindrical part of the cover (where it fits into
the cylinder bore) should be scraped well clear, or it will be apt to
bind on the edge of the cylinder bore and prevent the cover from
screwing fairly home to the cylinder face. The joint should be made to
bed well inside of the bolt holes, and coated with oil or grease when
finally put together.
JOINTS FOR ROUGH OR UNTRUE SURFACES.--The most permanent form of joint
for a rough or untrue surface is, for steam pressure, a gauze, and for
water pressure, a pasteboard, or a duck or canvas joint.
A gauze joint is composed of copper wire gauze, having square meshes of
about 1/32 inch square; this gauze is cut out to fit over the joint
surfaces, a single, double, or treble thickness being used according to
the unevenness of the surfaces. A coating of red-lead putty is first
spread over the joint with a piece of smooth surfaced metal; the wire
gauze is then put on, and over it another coating of red lead; the cover
is then put on, and the nuts screwed lightly home so as to bring the
cover to bear against the red lead. Then any nut may be given a quarter
or a half-turn, and the diametrically opposite one also given a
half-turn, this process being continued until all the nuts have been
screwed home a half-turn, when the process may be continued until the
nuts are screwed firmly home. This is necessary, because if the nuts on
one side are screwed home in advance of those on the other, the red lead
on that side may be squeezed out too much and the joint will leak. In
joints of this class the surfaces being rough it is not unusual to cut
out the gauze wire as follows: Lay the sheet of gauze over the joint and
cut it to the size by lightly hammering it over the sharp edges of the
joint, which will cause the sharp edges to cut the copper wire. To cut
out the holes place the ball piece of a hand hammer on the wire and over
a hole and strike the hammer face several light blows, and the corners
of the hole will cut the wire through.
The gauze joint will answer equally well for hot water as for steam
joints, provided that it be given time to dry and become hard. If the
joint can have a week in which to dry the red-lead putty may have about
one-sixth of its bulk of white lead mixed with it, being made to a
consistency of soft dough so that it will spread easily; and the amount
being sufficient to fairly cover the gauze and no more, the soundness of
the joint may be known by the lead squeezing out all around the joint
edge as the bolts are screwed home. If the joint is to be used in a day
or so after being made, the white lead should be omitted. In either case
the lead should be mixed stiffly at first; the best lead should be used
and it should be well hammered on an iron block, after which it may be
thinned with boiled oil, or with a little varnish, which will cause it
to harden more quickly.
For water joints requiring to stand high pressure, and to be used as
soon as made, a paper, pasteboard, or a duck or canvas joint are best.
The joint is made by using, in place of the gauze wire, one or two
thicknesses of the pasteboard, duck, or canvas, cut out to the size of
the flange, and with the necessary holes to receive the standing bolts
and leave the bore of the pipe clear. If the flange of the joint is of
copper, brass, or wrought iron, or, if of cast iron, is of sufficient
strength to permit it, one disk may be made the full size of the flange,
and a second may be made to have an external diameter sufficiently large
to fit snugly inside of the bolt holes, which will form sufficient
thicknesses if the flange is a fair fit to its seat; if it is not,
however, three, or even four, thicknesses may be used, in which case at
least one of them should fit inside the diameter of the flange across
the bolt holes, as described. The disks being prepared, we spread on the
first one a thin coating of red-lead putty, and then lay another canvas
disk on, again adding the putty until the whole is completed. We then
spread a thin layer of the putty around the hole of the seat and that of
the flange, place the disk in position and screw the joint up,
tightening down the nuts until they bring the flange to an equal seating
all around and not sooner on one side than on another, for in that case
the red-lead putty will be squeezed unevenly, and too much on the side
screwed up to excess. The nuts should be screwed up very tight; the
joint wiped, the protruding canvas cut off, and the joint is complete.
For very rude and rough joints, whether used under pressure or not, we
may make, for either water or steam, a joint as follows: Taking four or
five strands of hemp, we saturate them with a coating of white lead
ground in oil, applying just sufficient to make the fibres of the hemp
cling well together. We then plait the strands and coat the whole rope
thus formed with red-lead putty, and place the strand around the hole of
the joint, taking care that the ends lap evenly, so that the joint shall
be of even thickness. It is better, however, to bend a piece of lead or
iron wire to suit the size and shape of the hole in the joint, and then
wind the hemp and red lead around the wire. And in cases where the
flanges of the joint are sufficiently strong to have no danger of their
breaking from the pressure due to screwing up the nuts, the piece of
lead wire, if given a neat butt joint or neatly lapped, may be employed
without any red-lead putty or hemp; this does not, however, make a good
permanent joint. In cases where a joint requires to be made thick to
accommodate the length of the pipe, pasteboard may be used in the place
of canvas, giving to it a thinly-spread coating of red-lead putty on
each side, and, if possible, leaving the pasteboard a trifle too thick
and springing open the flanges of the joint to get the pasteboard into
position without scraping off the red-lead putty.
Where it is required that a joint stand great heat or fire, asbestos
board, about 1/16 inch thick, makes a good and permanent joint. It is
coated with red lead mixed thinly with boiled oil, containing as much as
it will soak up, leaving a thin layer of the lead upon the surface of
the asbestos. The holes for the bolts to pass through in the duck,
canvas, pasteboard, or asbestos joint should be cut large enough to well
clear the bolts.
For cold water, where it is not subject to great variations of
temperature, common sheet lead makes a very good joint; but under
excessive changes of temperature the expansion of the pipes will soon
cause the sheet lead to squeeze out and the joint to leak.
Joints are frequently made with copper wire rings, made of a diameter to
pass around the hole of the joint and lie within the diameter of the
bolt holes, and brazed together at the ends; but if the joint be
rectangular instead of circular the wire must either lie in a recess, or
else a shoulder must be left for the wire to abut against, which will
prevent its blowing or becoming forced out by the pressure.
In some practice softened sheet copper about 1/32 inch thick is used to
make joints on surfaces that have been planed. Joints of this kind are
used for locomotive steam chests.
Rubber joints are used to make steam, water, and air-tight joints, and
are usually made from what is known as combination rubber--that is,
sheet rubber having a linen or other web running through it; with one
such web it is called single, and with two webs two-ply, and so on.
There is in many cases, however, an objection to this form of joint, in
that it compresses; and hence in the case of the steam chest, for
example, it affects the distance of the slide-spindle hole in the chest
from the seat, and throws it somewhat out of line with the eccentric. In
long eccentric rods the variation is of course minute; but still it
exists, and must exist, since it is impossible to tell exactly how much
the rubber will compress in making the joint. Furthermore, if it is
required to break such a joint, the rubber will very often cling so
tenaciously to the seat in one place and to the chest in the other, that
it will tear asunder in breaking the joint. To obviate this as much as
possible, however, we may chalk the rubber on one face and slightly oil
it on the other, so that the oil will aid the rubber in clinging to one
face, while the chalk will assist it in separating from the other face
of the joint.
Rubber joints slowly compress after being under pressure a day or so,
and also if subjected to heat; hence they should have their bolts
screwed up after becoming heated, or after having stood some time. It is
advisable also that the rubber be as thin as the truth of the surfaces
will admit. If it is necessary to use more than one thickness of rubber,
the thickness may be made up of rings, whose diameter will just pass
within the bolt holes.
The holes in a rubber gasket should be made larger than the bolt holes,
so that there shall be no danger of the bolt, when being inserted,
catching the gasket.
If the flanges should not come fair, and it is determined not to set
them fair, the rubber should be as thick as the widest part of the
opening between them, and shaved off to suit the thin side of the joint,
and in this case the bolts must be tightened very uniformly and
gradually around the joint to secure a tight one. If there is room to
shave the gasket to the amount of taper, and use in addition a ring
around the bolt holes, it will make a safer job.
When the gasket requires to be split to pass it around or over a rod, it
should be cut through to the canvas on one side, and a short distance
off cut through to the canvas on the other side; the rubber may then be
stripped carefully back from the canvas and the latter cut through and
passed over the rod, when the rubber may be put back and sewed to the
canvas again.
Sheet rubber with a gauze wire insertion instead of canvas makes an
excellent joint.
[Illustration: Fig. 2452.]
In Fig. 2452 is shown a method of making a steam-tight joint largely
employed in England, upon the steam chest joint where the cylinders of
crank shaft (inside cylinder) engines are bolted together. A is the
flange of one cylinder, which is bolted to the other by the bolt B. C is
a strip of copper let into a dovetail groove cut one half in one
cylinder, and the other half in the other. After the bolts B are all
firmly screwed home, hammer blows are delivered upon the top of the
copper strip as denoted by the arrow E, expanding the copper so that it
completely and closely fills the dovetail groove, and makes a
steam-tight groove.
In riveting the copper it is necessary to hammer it evenly all along
lightly, and only sufficiently to make it closely fill the groove,
otherwise it will spring the joint open, and cause it to leak,
notwithstanding the bolts B, which will give under the extreme strain.
Temporary joints are sometimes made by bending a piece of lead wire into
a ring or frame, of such a size as to well clear the inside of the bolt
holes. The ends are neatly joined, and the lead wire compressing and
accommodating itself to the inequalities of the surfaces forms a joint.
[Illustration: Fig. 2453.]
[Illustration: Fig. 2454.]
JOINTS FOR BOILER FITTINGS.--Let it be assumed that the casting shown in
Figs. 2453 and 2454 requires to be fitted to a boiler, both being new.
In this case, the holes for the studs or bolts should first be drilled
in the flange of the casting, which will reduce its weight and render it
easier to handle. The casting should then be held against the boiler in
its proper position and location; and, with a fork scriber whose width
of points is equal to the widest space between the face of the casting
flange and the boiler, pass the fork scriber around the fitting or
casting with one point against the boiler shell and the other pressed
against the edge of the casting, the result being to mark around the
flange of the latter a line exactly following the surface or contour of
the boiler, and at a distance from the boiler the nearest that will
suffice to properly bed the casting to the boiler surface, or, in other
words, the line that will exactly mark the amount of metal requiring to
be cut off the flange face to make it bed all over; and that face may,
therefore, be cut down to the line. In chipping and filing it, however,
the straight-edge may be used to advantage as follows:--
[Illustration: Fig. 2455.]
Suppose the casting flange to be gripped in the vice facing the
operator, as in Fig. 2455, and that L L represents the scribed line:
then the cape chisel cuts may be carried clear across the flange, coming
exactly down to the line on each side of the flange, while a
straight-edge S may be used as shown to show when the cut is carried
across level. Then, when the intermediate spaces are cut out with the
flat chisel the surface will be of correct shape, and the surface may be
rough filed. The casting should be cut clear down to the lines, and if
the job has been properly set, marked and faced, no further trying will
be necessary previous to marking the bolt or stud holes in the boiler.
It is well, however, if the operator is inexperienced in this kind of
work, to again set the casting in its proper position to correct the
fit. But, with proper care, all the holes in the boiler may be marked
without any second fitting of the flange, since the operation properly
performed is bound to give correct results. In doing a job of this kind
it must be borne in mind that it is very easy to consume more time in
trying and altering the job than is required under proper conditions to
do the entire job; hence, in setting the casting, preparatory to marking
it with the fork scriber, nothing is near enough that does not carry
with it a conviction of perfect reliability; and if any doubt exists it
is better to go through the process again. If the casting flange varies
much in shape from its seat, and rocks or is unsteady, wooden wedges may
be placed beneath it, or a few pellets of stiffly mixed red lead may be
placed on the boiler where there is most room between it and the
casting, the boiler surface being coated or painted with red marking, so
that the pellets shall adhere to it and not to the flange face. If the
casting is too heavy to be steadied by hand, one hole may be drilled in
the boiler and a temporary bolt inserted to hold the casting while
setting it in position, and marking with the fork scriber.
When the flange is approaching a fit, it must be placed in position on
the boiler and the stud holes marked on the boiler with an ordinary
scriber, its point being pressed against the boiler while it is pressed
against the side of the hole in the casting flange and traversed around
it, so as to scribe on the boiler surface circles corresponding to the
holes in the flange. From the centres of these circles others of the
proper size of the tapping holes may be struck and the tapping holes may
then be drilled, and the studs put in. The remainder of the fitting
operation consists in applying red marking on the boiler surface,
bolting the casting to its place and filing the high spots. The marking
is made to show plainly upon the flange by light hammer blows with a
piece of wood interposed between the hammer and the flange face to
prevent piercing the latter. These blows, however, should be lightly
delivered, or they will cause the marking to be deceptive.
[Illustration: Fig. 2456.]
The fit of the flange to the boiler, however, should vary according to
the kind of bolt used to hold the fitting to the boiler. If stud bolts
are used they are supposed to screw into the boiler steam-tight, hence
the flange may be fitted so that it has the closest contact with an
annular ring extending from the outside of the bolt holes to the central
hole of the flange, as shown in Fig. 2456, in which the area within the
dotted circle C encloses the area to be most closely bedded. This is a
highly important consideration in flange joints of every description,
for, if a joint is made there, that is all that is necessary, and the
fit outside of the bolt holes--that is to say from the bolt holes to the
perimeter of the flange--has nothing to do with making the joint, unless
the studs or bolts leak, and in that case the leak will find egress
beneath the nut, unless grummets are used. A grummet is a washer made of
twisted hemp, cotton, or other material, and coated with red-lead putty,
and is placed beneath the heads of bolts, or under washers placed
beneath nuts to stop leaks. It is not necessary to ease the flange from
the bolt holes outward much, but to merely make the flange, or fitting,
bed clearly and distinctly the most around the main hole, and outwards
to the inside of the bolt holes; for, if there was given too much
clearance, the flange would bend from the pressure of the nuts, and
would in consequence spring if made of brass, or perhaps break if made
of cast iron.
To make the joint, gauze wire, pasteboard, or asbestos board may be
used, or if the joint is to have ample time to set, a red-lead joint
without the gauze may be used; but in this case it is an advantage to
cut up into pieces about 3/8 inch long, and thoroughly shred some hemp,
and well mix it in the lead, well beating the same with a hammer.
To preserve red-lead putty from becoming hard and dry, as it will do if
exposed to the air, it should be kept covered with water.
In some cases joints of flanges to boilers are made by riveting the
flanges to the boiler and caulking or closing the edge of the flanges to
the boiler shell; but this possesses the disadvantage that the rivets
must be cut off to remove the fitting from the boiler when necessary,
and access to the interior of the boiler is necessary in order to attach
the fitting again by rivets.
[Illustration: Fig. 2457.]
Fig. 2457 (which is taken from _The American Machinist_), represents a
joint for boiler fittings, designed to facilitate the breaking and
re-making of the joint. C represents, say, a boiler plate, B a piece
having a ball joint seat in C ground steam tight, and A a flange, say,
for a feed pipe; the studs D thread permanently into C, and the joint is
bolted up by the stud nuts E. It is obvious that the ball joint between
B and C permits the flange A to set at an angle if necessary.
RUST JOINTS.--These are joints made by means of filling the space
between the flanges, or annular spaces, as the case may be, with
cast-iron turnings, and compacting them with a caulking tool. Any
interstices through which steam or water, &c., might leak become filled
by the subsequent rusting of the iron cuttings, the rust occupying
considerably more space than the iron from which it was formed.
[Illustration: Fig. 2458.]
Rust joints are employed upon very uneven surfaces, and for pipes for
mains to go under ground. In former times this class of joints was much
used in engine and boiler work, but of late years it has been to a great
extent abandoned. In Fig. 2458 is shown the method of construction for
a rust joint for what are known as spigot and socket joints for pipe
work. S is the spigot and P the socket. R R is a metal ring, bound over
with either dry hemp fibre or tarred twine or rope. The remainder of the
space between the pipes at A A being filled with a cement composed of
Sifted cast-iron borings 100 lbs.
Sal-ammoniac 1/2 lb.
Sulphur 1/2 lb.
but when required to set quickly, 1 lb. sal-ammoniac may be used. These
ingredients are thoroughly mixed with water immediately before being
used, and just covered with water when used intermittently. The cement
is put into the space A A, in quantities sufficient to fill up about 3/4
inch in length of the annular space A A, and then caulked by being
driven in with the tool shown in Fig. 2459. Cement is then again put in
and the caulking repeated, the process being continued until the whole
space is filled.
[Illustration: Fig. 2459.]
In some cases (as in gas mains) the space A A is filled with melted
lead, and when cold caulked with the tool described.
[Illustration: Fig. 2460.]
In Fig. 2460 is shown the method of making a rust flange joint; A A
being a ring covered with hemp twisted around it, the cast-iron cement
being caulked in as before.
The wire rings should be firmly gripped by the bolts to prevent them
from moving from the caulking blows, which should be at first delivered
lightly.
[Illustration: Fig. 2461.]
In some cases pipes are joined with rust joints, as in Fig. 2461 in
which A A is a sleeve, there being two rings of wire and hemp inserted
as shown.
When flanged joints are made with a scraper, or ground joint, or with
rubber, duck, or other similar material to make the joint, the length of
the pipe, from face to face of the joint, must be made accurate.
[Illustration: Fig. 2462.]
Fig. 2462 is a face, and Fig. 2463 (which are from _Mechanics_), a
sectional edge view of an expansion joint, being that used by the New
York Steam Supply Company for the steam pipes laid under the streets to
convey steam to buildings. The object is to provide a joint which shall
permit and accommodate the expansion and contraction of the pipe under
varying temperatures. P P are corrugated copper disks secured to the
faces of the pipe ends by flanges, as shown, and gripped at their edges
by the flanges of the cast-iron casing, and it is obvious that the ends
of the pipe may move longitudinally carrying the corrugated disks with
it. The cavity A is filled with steam, and to support the disks P
against the pressure segmental blocks B of cast iron are placed behind
them, the number of these blocks being as indicated by the dotted radial
lines in the figure. It may be added that this joint has been found to
answer its purpose to great perfection.
[Illustration: Fig. 2463.]
Pipe cutters, for cutting steam or gas pipe by hand, are usually
provided with either a rotary wheel which severs by rolling an
indentation, or else are provided with cutting tools. The rolling wheel
has the advantage that it makes no cuttings, cuts very readily and is
not apt to break; on the other hand it is apt to raise around the
severed end of the pipe a slight ridge, which with a worn cutter may be
sufficiently great as to require to be filed off before the threading
dies will grip the pipe. Cutting tools are apt to break and require
frequent grinding; hence, as a rule, the rolling wheel cutter is
generally preferred.
[Illustration: Fig. 2464.]
Fig. 2464 represents a cutter of this kind, the piece A carrying the
cutter B, which is operated in the stock C by means of the threaded
handle H.
[Illustration: Fig. 2465.]
Fig. 2465 represents a pipe cutter in which are a pair of anti-friction
rollers and a severing tool bevelled on one edge only so as to leave the
end of the pipe face cut square, and the piece cut off bevelled on its
face; or by turning the cutter round the reverse will be the case, the
piece cut off being flat on its end.
The action of this cutter is, as in the case of the wheel cutter, simply
that of a wedge, hence no cuttings are formed.
[Illustration: Fig. 2466.]
Fig. 2466 represents a pipe cutter in which a cutting tool is employed,
being fed to its cut by the handle which is threaded similar to the
handle shown in Fig. 2464. The end jaw is operated to suit different
diameters of pipe by means of the milled nut shown, which receives a
threaded stem on the adjustable jaw.
[Illustration: Fig. 2467.]
PIPE VICE.--The ordinary bench vice is sometimes provided with an
attachment to enable it to grip pipe at three points, and, therefore,
hold it sufficiently firmly without squeezing it oval, but it is
preferable to use a proper pipe vice, such as shown in Fig. 2467, which
consists of a base frame bolted to the work bench and receiving a
serrated die to grip the pipe. The upper die is carried to a frame
pivoted on both sides to the base, and is operated to grip or release
the pipes by means of the handled screw shown.
[Illustration: Fig. 2468.]
To change the dies one pivot is removed and the upper frame swung open,
as in Fig. 2468.
[Illustration: Fig. 2469.]
The proper shape for pipe tongs depends upon the number of sizes of pipe
the tongs are intended for, but in all cases the point at which the
gripping point should be is about as shown in Fig. 2469. This enables
the edge at A to enter the work and grip it. If this point of contact
were nearer to C it would be apt to slip upon the pipe, whereas, were it
farther towards B, it would present a less acute angle to the pipe,
which would be apt to jam in the tongs.
It is obvious that, if the tongs be moved in the direction of H, the
whole power applied to F acts to cause the edge at A to grip the pipe,
and that the length from A to G has an important bearing on the grip of
A to the pipe; because the nearer A is to G not only the greater the
leverage of the leg F, but also the less A, with a given amount of
movement of F on its pivot, endeavors to enter the pipe; hence the
movement of A in a direction to grip the pipe is less in proportion to
the movement of F, and has a corresponding increase of force. It follows
then that the nearer the grip of A is to C, the less, and the nearer the
grip to B the greater, its grip upon the pipe. But, by making the
length of A such as to grip the pipe in about the position shown in the
cut, there is latitude enough in the location at which it will grip the
pipe to permit of the tongs being used upon pipe of a somewhat greater
or less external diameter, increasing the availability of the tongs.
Furthermore, if A gripped the pipe at or too near to B, it would be apt
to indent it. The crown of the jaw D may be made to fit to the pipe or
to be clear of it; for thin pipe, as solid drawn brass pipe, it should
fit so that the pressure will not indent the pipe, but for strong iron
pipe it is better to let it clear, which will not only afford a firmer
grip, but will also better fit the tongs to take in different diameters
of pipe. In some cases, as in adjustable pipe tongs, the jaw surface D
is, for this purpose, considerably [V]-shaped, as will be seen
presently.
It is obvious that as A grips the pipe automatically, the tongs may be
moved through any portion of a rotation that the location may render
most desirable. Pipe tongs are designated for size by the diameter of
the pipe they are intended for; thus, a pair of inch tongs are suitable
for pipe an inch in diameter of bore, the handles or legs of the tongs
coming so close together that both can be readily grasped in one hand
applied at their extreme ends. If, however, the tongs be applied to pipe
of a larger diameter the legs will be wider apart, and one hand will be
required to be applied to each leg to force them together. A complete
set of pipe tongs, therefore, includes as many pairs as there are
diameters of pipe, unless adjustable tongs be used.
[Illustration: Fig. 2470.]
[Illustration: Fig. 2471.]
[Illustration: Fig. 2472.]
Adjustable tongs are made of various forms; thus a simple plan is shown
in Fig. 2470. The gripping surface of the jaw is shaped as at V, so as
to admit varying diameters of pipe, the smaller diameters passing
farther up the V, the distance of the end A of jaw, or leg F, being
regulated to grip the pipe in the proper place by operating the screw S,
which is tapped into the jaw F and pivoted in B, the slot C enabling F
to move along B. The capacity of tongs of this design is about three
diameters of pipe, as 1, 1-1/4, and 1-1/2 inches. There are various
other forms of adjustable pipe tongs, but most of them possess the
disadvantage that the adjustable jaw hangs loosely, involving some extra
trouble in placing them upon the pipe, because one hand must be employed
to guide the loose jaw and adjust its position on the pipe. Fig. 2471
represents tongs of this class, the gripping size being varied by moving
the jaw A upon B at the various notches. The end of B is serrated to
afford a firmer grip upon the pipe. Fig. 2472 represents another
adjustable pipe tongs, which is made in two parts, a straight lever A
and hooked lever B, the former passing through a slot in the latter. The
back of the straight lever is notched and a serrated fulcrum piece C is
pivoted in the slotted lever by a pin upon which the lever B receives
its support when the tongs are in operation. The fulcrum piece is
provided with a spring which retains the serrated edge in proper
position to engage the notches in the lever A. By means of the thumb
piece D, the piece C can be moved in either direction to increase or
diminish the gripping size of the tongs. When the tongs are open the
lever A can be moved within the slot and adjusted so that the tongs will
fit the pipe. The fulcrum piece C, being pivoted, allows the full length
of its serrated edge to come into contact with the corresponding portion
of the lever A, so that the parts always have a firm bearing and are
subjected to an equal wear.
A common form of pipe tongs of this class is shown in Fig. 2473, B being
pivoted to A by a pin, and changing to various holes in A to suit
different diameters of pipe.
ERECTING PIPE WORK.--In erecting pipe work care must be taken to have it
align as true as possible, as well as to have the joints tight enough to
stand the required pressure without leakage. If the elbows, tees, or
other fittings are not threaded true, a pipe whose thread is not true
with its axis may be selected or cut purposely to suit the error in the
fitting, so as not to leave an unsightly finish to the job.
[Illustration: Fig. 2471.]
[Illustration: Fig. 2474.]
Suppose, for example, that in Fig. 2474, _e_ is a pipe erected parallel
to the wall, but that the holes in its elbows are tapped at an acute
instead of at a right angle, then by cutting the thread on the end of
pipe _d_ untrue with its axis, its far end will rotate out of true as
denoted by the shaded and by the plain lines, and all that will be
necessary is to screw up the pipe sufficiently firm to make the joint,
but to leave it in the position shown in the plain lines.
If the pipe tightens sufficiently before it has reached that position it
may generally be eased by rotating it back and forth in the elbow with
the pipe tongs. If this does not suffice, the pipe must of course be
threaded sufficiently further along. To cut a pipe out of true to suit
an untrue elbow, a very good plan is to cut the end of the pipe at an
angle to its axis, which will cause the dies to cant over when starting
the thread, but little practice being required to educate the judgment
as to how much to do this to suit any given degree of error.
In erecting pipe it is best to begin at one end and screw each
successive piece firmly home to its place before attaching another, so
that the lengths of the pieces may be accurate and not vitiated by
screwing them up and causing them to enter farther into the fittings. If
it is probable that the piping may have to be taken down after erection,
it should be put up at first screwed together rather tighter than will
be necessary, as the thread fits become eased by being moved one within
the other. This is especially the case with brass fittings, upon which
it is best in cutting the lengths of pipe to have it of full length, as
the threads will conform to each other sufficiently to cause the pipe to
enter a thread or so farther if the pipe be rotated back and forth a few
times in the fitting.
The fit should in all cases be made by tightness of thread fit, and not
by the union or elbow face jambing against the end of the thread or the
pipe, as joints in which this is the case will usually leak if used
under pressure.
The thread of both the pipe and the fitting should be smeared with a
thick lead paint. If the pipe is to be used as soon as erected, plain
red lead and boiled oil should be used for the paint; but if it may
stand a few days it is better to mix white and red lead in about equal
quantities, as this, if given time to dry, makes a tighter job. The
quantity of this paint should not be more than will thinly cover the
threads, otherwise it will squeeze out when the pipes are screwed home,
and falling from the end of the pipe within the fitting be apt to be
carried by the steam or water to the valves, and getting between them
and their seats cause them to leak. The iron cuttings should be
carefully cleaned both from the pipe and the fitting for the same
reason.
In cases where the piping may require to be used under heavy pressure as
soon as erected, it is a good plan to use dry red lead in varnish,
thoroughly hammering it to mix it well, and thinning it after it has
been so hammered.
In case of emergency a loose pipe may be somewhat improved by wrapping
around its thread a piece of lamp wick saturated with this varnish lead,
beginning at the end of the pipe and wrapping the thread from end to
end.
It is preferable that the stem of the valve stand nearly horizontal, so
that any water of condensation may pass freely away with the steam and
not collect and lie in the pipe as it does when vertical. If it be quite
horizontal the water of condensation will drip through the stuffing box;
hence it is better that it stand 10 or 12 degrees from the horizontal.
It is better in all cases to purchase nipples than to make them by hand,
because when made in a machine the threads are more true to the axis
than those made by hand; especially is this the case in short nipples in
which there is not sufficient length to use the guide socket when
engaged in threading the nipple with the hand dies.
It is a very good plan in making such short nipples to cut them off the
end of a length of pipe that has been threaded by machine, and to screw
on the threaded end a coupling. Into this coupling a piece of pipe may
be threaded to afford a hold in the vice. If then the nipple is long
enough, a guide to suit the size of the nipple may be used in the
threading dies, or a guide socket to fit the diameter of the coupling
may be used.
A globe valve should be so placed on the pipe that the pressure will,
when the valve is closed, fall on the bottom face of the valve, so that
the steam may be shut off while the valve stem is being packed.
Cotton lamp wick plaited to fit the packing space, and well oiled, is as
good as anything to pack the stem with.
In taking old pipe down a refractory joint may be sometimes loosened by
striking it with a hammer while it is under full pipe tongs pressure; or
these means failing, the elbow or tee may be heated, which should be
done as quickly as possible, so that the fitting may be hotter than the
pipe. A very good method of doing this, where it is desired to save the
fitting, is to pour red-hot lead over the fitting.
If it is not important to save the fitting, it may be split by a flat
chisel, or by cutting a groove along it with a narrow cape chisel; or if
the pipe is free the elbow may be rested on an anvil and hammered around
its circumference, which will either free it or break it, if of cast
iron.
When pipes are to be taken down and re-erected elsewhere they should all
be marked to their fittings and places before being taken down, as this
will preserve their lengths as near as possible for re-erection. Black
japan is an excellent marking for this purpose because it dries quickly.
RE-FITTING THE LEAKY PLUGS AND BARRELS OF COCKS.--When a cock leaks, be
it large or small, it should be refitted as follows, which will take
less time than it would to ream or bore out the cock or to turn the
plug, unless the latter be very much worn indeed, while in either case
the plug will last much longer if refitted, as hereinafter directed,
because less metal will be taken off it in the re-fitting.
After removing the plug from the cock, remove the scale or dirt which
will sometimes be found on the larger end, and lightly draw-file, with a
smooth file, the plug all over from end to end. If there is a shoulder
worn by the cock at the large end of the plug, file the shoulder off
even and level. Then carefully clean out the inside of the cock, and
apply a very light coat of red marking to the plug, and putting it into
the cock press it firmly to its seat, moving it back and forth part of a
revolution; then, while it is firmly home to its seat, take hold of the
handle end of the plug, and pressing it back and forth at a right angle
to its length note if the front or back end moves in the cock; if it
moves at the front or large end, it shows that the plug is binding at
the small end, while if it moves at the back or small end, it
demonstrates that it binds at the front or large end. In either case the
amount of movement is a guide as to the quantity of metal to be taken
off the plug at the requisite end to make it fit the cock along the
whole length of its taper bore.
If the plug shows a good deal of movement when tested as above, it will
be economical to take it to a lathe, and, being careful to set the taper
as required, take a light cut over it. Supposing, however, there is no
lathe at hand, or that it is required to do the job by hand, which is,
in a majority of cases, the best method, the end of the cock bearing
against the plug must be smooth-filed, first moving the file round the
circumference, and then draw-filing; taking care to take most off at
that end of the plug, and less and less as the other end of the plug is
approached. The plug should then be tried in the cock again, according
to the instructions already given, and the filing and testing process
continued until the plug fits perfectly in the cock. In trying the plug
to the cock, it will not do to revolve the plug continuously in one
direction, for that would cut rings in both the cock and the plug, and
spoil the job; the proper plan is to move the plug back and forth at the
same time that it is being slowly revolved. As soon as the plug fits the
cock from end to end, we may test the cock to see if it is oval or out
of round. The manner of testing the cock is as follows:--
First give it a very light coat of red marking, just sufficient, in
fact, to well dull the surface, and then insert the plug, press it
firmly home, and revolve it as above directed, then remove the plug, and
where the plug has been bearing against the surface of the cock the
latter will appear bright. If, then, the bore of the cock appears to be
much oval, which will be the case if the amount of surface appearing
bright is small, and on opposite sides of the diameter of the bore,
those bright spots may be removed with a half-round scraper.
Having eased off the high spots as much as deemed sufficient, the cock
should be carefully cleaned out (for if any metal scrapings remain they
will cut grooves in the plug), and the red marking re-applied, after
which the plug may be again applied. If the plug has required much
scraping, it will pay to take a half-round smooth file that is well
rounding lengthwise of its half-round side, so that it will only bear
upon the particular teeth required to cut, and selecting the highest
spot on the file, by looking down its length, apply that spot to the
part of the bore of the cock that has been scraped, draw-filing it
sufficient to nearly efface the scraper marks. The process of scraping
and draw-filing should be continued until the cock shows that it bears
about evenly all over its bore, when both the plug and the cock will be
ready for grinding.
Here, however, it may be as well to remark that in the case of large
cocks we may save a little time and insure a good fit by pursuing the
following course, and for the given reasons. If a barrel bears all
around its water-way only for a distance equal to about 1/16th of the
circumference of the bore, and the plug is true, the cock will be tight,
the objection being that it has an insufficiency of wearing surface. It
will, however, in such case wear better as the wearing proceeds. Plug
and barrel being fitted as directed, we may take a smooth file and ease
away very lightly all parts of the barrel save and except to within,
say, 3/8 inch around the water or steam-way. The amount taken off must
be very small indeed, just sufficient, in fact to ease it from bearing
hard against the plug, and the result will be that the grinding will bed
the barrel all over to the plug, and insure that the metal around the
water or steam-way on the barrel shall be a good fit, and hence that the
cock be tight.
The best material to use for the grinding apparatus is the red burnt
sand from the core of a brass casting, which should be sifted through
fine gauze and riddled on the work from a box made of, say, a piece of
1-1/2 pipe 4 inches long, closed at one end and having fine gauze
instead of a lid.
A very good material, however, is Bath brick rubbed to a powder on a
piece of clean board. Neither emery nor ground glass is a good material,
because they cut too freely and coarsely, which is unnecessary if the
plug has been well fitted.
Both the barrel and the plug should be wiped clean and free from
filings, &c., before the sand is applied; the inside of the barrel
should be wetted in and the plug dipped in water, the sand being sifted
a light coat evenly over the barrel and the plug. The plug must then be
inserted in the barrel without being revolved at all till it is home to
its seat, when it should be pressed firmly home, and operated back and
forth while being slowly revolved. It should also be occasionally taken
a little way out from the barrel and immediately pressed back to its
seat and revolved as before, which will spread the sand evenly over the
surfaces and prevent it from cutting rings in either the barrel or the
plug. This process of grinding may be repeated, with fresh applications
of sand, several times, when the sand may be washed clean from the
barrel and the plug, both of them wiped comparatively dry and clean, and
the plug be re-inserted in the barrel, and revolved, as before, a few
revolutions; then take it out, wipe it dry, re-insert and revolve it
again, after which an examination of the barrel and plug will disclose
how closely they fit together, the parts that bind the hardest being of
the deepest colour. If, after the test made subsequent to the first
grinding operation, the plug does not show to be a good even fit, it
will pay to ease away the high parts with a smooth file, and repeat
afterwards the grinding and testing operation.
To finish the grinding, we proceed as follows: Give the plug a light
coat of sand and water, press it firmly to its seat and move it back and
forth while revolving it, lift it out a little to its seat at about
every fourth movement, and when the sand has ground down and worked out,
remove the plug, and smear over it evenly with the fingers, the ground
sand that has accumulated on the ends of the plug and barrel, then
replace it in the barrel and revolve as before until the plug moves
smoothly in the barrel, bearing in mind that if at any time the plug,
while being revolved in the barrel, makes a jarring or grating sound, it
is cutting or abrading from being too dry. Finally, wipe both the barrel
and the plug clean and dry, and revolve as before until the surfaces
assume a rich brown, smooth and glossy, showing very plainly the exact
nature of the fit. Then apply a little tallow, and the job is complete
and perfect.
In place of the tallow a soft paste of good beeswax and castor oil is an
excellent application, the two being heated in order to thoroughly mix
them.
The grinding material must be frequently changed to produce smooth work,
because if the grinding cuttings accumulate in it, they will scratch and
score the work. Indeed, it is a good plan when convenient, to hold the
cock and plug under water while grinding them, and to occasionally lift
the plug out, so as to wash out the cuttings.
The surface of a well-ground plug will be in all cases polished, and not
have that frosted appearance which exists so long as active grinding is
proceeding, and all that is necessary to produce this polish is to well
work the plug in its barrel while keeping it quite clean.
[Illustration: Fig. 2475.]
FITTING BRASSES TO THEIR JOURNALS.--Brass bores always require fitting
to their journals after having been bored, because the finished hole is
not a true circle, but too narrow across the joint face, as at F in Fig.
2475, in which the full lines represent the form of the brass before,
and the dotted line its form after being bored and released from the
pressure of the devices or chuck that held it while it was being bored.
This almost always occurs to a greater or less degree, and it arises
from local strains induced from the unequal cooling of the casting in
the mould, which strains are released as the metal is removed (in the
process of boring) from the surface of the bore. It would appear,
however, that if the finishing cut taken by the boring cutter be a very
fine one it should leave the hole true and round, but the pressure which
is placed upon the bearing to hold it against the force of the cut
prevents the bearing from assuming its natural form until released from
that pressure.
If a bearing be bored to very nearly its finished size and first
released altogether from the pressure of the holding chuck, or other
device, and then re-chucked, it is probable that the finished bore would
be practically quite round and true, but such re-chucking is not the
usual practice.
Suppose, however, that the bearing shown in Fig. 2475, be properly
fitted to a journal, still improper conditions arise from wear, because
the area of the surface D becomes from the weight and from vibration
condensed, and finally it stretches, causing the bore at F to close upon
the journal and bind it with undue friction.
[Illustration: Fig. 2476.]
If the shape of the bedding part of the brass, or bearing, be such as
shown in Fig. 2476, the surfaces A B and C will condense and stretch,
closing the diameter of the bore at E and making the sides G G fit
loosely in their places. It is to be observed that a similar
condensation of the metal occurs to some extent around the bore of the
bearing; but this surface is being continuously worn away by the
journal, and it is, therefore, at all times less stretched and condensed
than that on the bedding surface.
[Illustration: Fig. 2477.]
There is, therefore, a constant action causing the brass to bind unduly
hard at and near its joint face E, Fig. 2476, and thus to cause heating
and undue abrasion and wear. To prevent this it is necessary to ease
away that part of the brass bore, as is shown in Fig. 2477 from J to K,
clear of the journal.
But in the case of bearings receiving thrust, as in engine main
bearings, the line of pressure is in a horizontal direction; and hence
the most effective bore area to resist that pressure has been removed.
Furthermore, the bearing area of the brass bore has been reduced, thus
increasing the pressure per square inch on the remaining area.
[Illustration: Fig. 2478.]
The methods employed to avoid this evil are as follows:--In the form
shown in Fig. 2478 the joint faces are at an angle instead of being
horizontal and parallel to the line of the thrust, or the joint faces
may be made to stand at a right angle to the line of journal thrust, so
that the crown of the brass will receive the thrust. But the brasses
will still close across the joint faces (as already described) as the
wear proceeds, and the areas from J to K in Fig. 2477, must still be
eased away, requiring frequent attention and giving a reduced bearing
area. Furthermore, in proportion as the line of the joint faces of the
brasses is at an angle to the line of thrust, the strain on the top or
cap brass will fall on the bolts, so that if those joint faces be at a
right angle to the line of thrust, the whole strain of that thrust will
fall on the bolts that hold the cap and cap brass.
[Illustration: Fig. 2479.]
Another plan is to make the bearing in parts, as in Fig. 2479, in which
the top and bottom parts of the bearing extend to the joint face on one
side, but admit a chock or gib, A in the figure, which may be adjusted
by a set-screw as shown. By this means the bearing area may extend all
around the bore. In some cases two of such chocks and set-screws, one on
each side of the journal, are employed.
[Illustration: Fig. 2480.]
In place of the set-screws, whose ends, from receiving the pressure of
the thrust, are apt to imbed themselves into the chock and to thus
loosen the adjustment, wedges lifted by bolts passing up through the
cap, as shown in Fig. 2480, are employed, being preferable to the
screws.
In the Porter Allen engine the wedges pass clear through the bearing, as
in Fig. 2481, so that they may be pushed up after the manner of a key
and their pressure against the side chocks judged independently of the
nuts at the top.
In some designs the top and bottom parts of the bearing are free to move
in the line of the thrust, and the side chocks or blocks alone are
relied on to resist the thrust.
When the brasses are in two halves, they may be fitted so as to have a
known degree of bearing pressure upon the journal, and the fit may thus
be accurately adjusted, in which case they will wear a long time before
requiring re-adjustment. On the other hand when the side chocks are used
the wear in the line of the thrust may be taken up as it proceeds. In
one case the attending engineer cannot alter the fit of the bearing nor
the alignment of the shaft, while in the other he can do both. Thus the
facilities that enable him to make these adjustments properly also
enable him to make them improperly. But this would be of no consequence,
providing it could be determined whether the adjustment were improving
the conditions without first making it. With an engine at rest it is
easy to determine, by means of the connecting rod, whether the chock
adjustment is correct, so far as the adjustment of the shaft is
concerned, but it is not easy so to determine the pressure of the chock
on the journal; nor when each chock has two adjusting screws is it easy
to determine when they both bear alike.
[Illustration: Fig. 2481.]
When the bearing is in four pieces, and three of them have two screws
each, it is still more difficult to operate all so as to have the
bearing equal on the journal. The fit to the journal can only be
determined by the results: if too easy, the bearing pounds; if too
tight, the bearing heats and wears.
But undue wear may take place without heating, and this is one of the
greatest objections to this method of adjustment.
[Illustration: Fig. 2482.]
A design of bearing used in American locomotive practice is shown in
Fig. 2482. Here the joint faces C, B of the brass is bevelled, fitting
into a corresponding bevel in the box, which prevents the brass from
closing across the joint face; hence, the bearing on the journal may
extend all around the brass bore from the oil cavity A to the edges B C.
The brass is, in this case, forced to its place in the axle box under
hydraulic pressure, and this pressure springs the box open at H, making
it wider; but when the box is put to work the brass compresses somewhat,
and its surfaces conform more closely to the bedding surface of the box
than when first put in, and this causes the box to close slightly at H.
To prevent this closure from carrying the brass with it and close it
across the joint face (as in the case of the brass shown in Fig. 2476)
the following plan is adopted. The brasses, after having been turned in
the lathe, are filed along the entire surface (on each side) for a
distance of about 1-1/2 or 2 inches, so as to clear the bore of the box
near the bevels B, C. When the box is put into the hydraulic press, to
have the brass forced in, a centre-punch mark J is made, and part of a
circle L L is struck; when the brass is home in the box the arc of
circle K is made, the distance between K and L showing how much the box
has been sprung open by the brass; the amount allowed is about 1/32 of
an inch. If, as the brass is pressed in, it is found that this will be
exceeded, it is taken out and eased. When the engine is running and the
boxes spring to some extent they do not carry the brass with them,
because the sides being eased away gives liberty to the box to come and
go slightly; the bevels also tend to keep the brass bore open.
Here, then, the brasses may be fitted to align the axle perfectly, and
it is not permitted to the engineer to alter that alignment, while at
the same time the fit of the brass to the journal being made correct,
the engineer cannot alter it. Under these conditions the whole area of
the brass is effective in holding the journal, which increases the
durability of the brass by keeping the pressure per square inch on the
brass bore at a minimum.
If side chocks are used, however, it is better to set them up by wedges
than by screw bolts, because from the tightness of the fit of such
screws in the tapped holes, it is difficult to determine, with
precision, with what degree of pressure the chocks are forced against
the journal. Furthermore, the screws may not fit with an equal degree of
tightness; hence, when screwed up with an equal degree of pressure, one
end of the same chock may be set tighter to the journal than the other
end, and any undue pressure of fit at either end tends to throw the
shaft out of line as well as inducing undue wear. But when wedges are
used to set up the side chocks the nuts operating those wedges may be an
easy fit without fear of their becoming loosened (as set-screws in the
line of thrust are apt to do).
On the fast engines of the Pennsylvania Railroad solid bronze boxes,
without brasses, are used, and when the boxes require truing from having
cut or from having worn oval they close them under a steam hammer,
closing the bore across and enabling it to be trued out in the lathe
without taking much metal out of the crown of the bore. The wedges and
adjusting shoes are thickened when this becomes necessary by reason of
the box closure or width.
If a brass bore does not bed fully and equally over the entire intended
bearing area the part not fitting will at first perform no duty as
bearing area, and the whole strain will be thrown upon a less area than
is intended by the construction, causing undue abrasion until the brass
bore has what is termed worn down to a bearing. The amount of this
wearing down to a bearing may be so small as to be scarcely perceptible
to ordinary observation, but if the oil that has passed through the
journal be smeared upon stiff white paper, as writing paper, it will be
found to contain the particles of abraded metal, which will be plainly
distinguishable. Under these conditions the journal will have a dull,
though perhaps a smooth appearance, and will not have that mirror-like
surface which is characteristic of a properly fitted and smooth working
bearing, while under a magnifying glass the journal will show a series
of fine rings or wearing marks. It is necessary, therefore, that each
brass be properly fitted to its journal so that it shall bed fairly and
evenly over all the area of its bore that is intended to bear upon the
journal.
The most expeditious method of fitting a new bearing box or brass to its
journal is to first file the bore until it fits the journal when simply
placed thereon by hand, and without going to the trouble to put the
brass or the journal in position in the frame which holds them. So soon,
however, as the crown of the brass beds to the journal along its whole
length, the brass should be placed in its box, or in the frame, and the
journal adjusted in its place and rotated so as to leave its bearing
marks upon the brass bore, to assist which it may have a faint coat of
red marking on its surface. The fitting should be continued both with
file and scraper until the whole area of the part intended to bed fits
well and is smooth and polished. To produce this result the finishing
should be done with a very smooth half-round file, draw-filing so as to
leave the marks in a line with the circumference of the bore, and
finally with a half round scraper, which will remove the file marks. The
degree of contact should be such that, when the bearing is bolted up,
brass and brass, as it is termed (which means that the joint faces of
the brasses are held firmly together), the journal will rotate as freely
as when the top brass is removed, while the contact marks on the top
brass have been removed by scraping. By this means the fit will be just
sufficient to permit the lubricating oil to pass between the journal and
the bearing, and the journal will work freely and easily without any
play, knock, or pound. If, when the top brass or bearing is bolted home
and the shaft is rotated by hand, that brass on removal shows contact
marks on its bore, although it may rotate comparatively easily it will
be so tight a fit that the oil cannot pass, and as a result the wear,
instead of producing a glossy surface, will produce a dull one, and
undue abrasion will ensue even though no rings appear.
When brasses are held in rods that connect two journals together the
fitting of the brass bore must be conducted with a view to have the
brasses fit their journals all over the intended bearing area of their
bores, which can only be accomplished by trying the brass bores to their
journals while in the rod, in the manner to be hereafter described with
reference to connecting rods and to lining engines.
When a journal is worn in rings, or so rough as to cause destructive
abrasion and undue friction, it may be refitted as follows:--First, with
a smooth file draw-file the journal in the direction of its length,
taking off all the projecting rings. Then sweep a very smooth file that
is somewhat worn (which will cut smoother than a sharp file) around the
circumference of the journal so that the file marks will be in the plane
of revolution. Then wrap a piece of fine and somewhat worn emery paper
around the journal, and wrap around it (say twice around) a piece of
coarse string, leaving the two ends about two feet long. Take one end of
the string in each hand and pull first one end and then the other,
causing the emery paper to revolve around the journal and smooth it.
To refit the bearings, first with a smooth half-round file remove the
rings or rough surface, and then fit the surface with the file, so that
when in its place the journal is rotated the contact marks show a proper
bearing. Then draw-file the bore with a smooth half-round file and
finish with a half-round scraper, easing away the high spots until the
bore shows proper contact and is smooth. A piece of fine emery paper may
then be wrapped around a half-round file and the surface smoothed with
the emery paper moved across the bore and not in the direction of the
circumference of the same. The emery paper should be well worn for the
finishing and of a fine grade number, so as to leave a bright polish and
not dull marks.
In some practice the bores of brasses are left rough-filed, the file
marks being lengthways of the bearing of bore. If the journal requires
smoothing it is draw-filed lengthways of the journal. The philosophy of
this is, that the file marks will hold the oil and afford unusually free
lubrication while the bearing and journal are wearing down to a bearing.
But where the framework holding the bearings and journals are rigid,
these bearings and journals may, with care, be fitted to a polished and
equal bearing, leaving a smoother surface than that produced by wearing
down to a bearing. But if, as in the case of a locomotive, the framework
is subject to torsion, rough surfaces left to adjust themselves are
possibly better than those accurately fitted, because the whole
framework holding the bearings changes its form when the full load is
upon it and after put to work, and the fitting done when there was no
load upon the parts is no longer quite correct. The lubrication of the
bearing, however, should be very free, and the effort appears at present
to be to afford more ample oil ways than hitherto even at some sacrifice
of bearing area.
LEAD-LINED JOURNAL BEARINGS.--If a journal is worn in grooves or
undulations it becomes impracticable to properly fit the brass to it
without reducing its diameter to remove the rings, and to obviate the
cutting and heating which necessarily follow, as well as to obviate the
necessity of fitting the brasses at all, Mr. D. A. Hopkins introduced
lead-lined bearings; the lead lining being merely auxiliary to the
bearing proper, which is made preferably of hard bronze, and to which
the thin layer or facing of lead is firmly attached by a soldering
process, so that the two metals are virtually one piece. Into this lead
facing the journal, under the pressure of the car, moulds or imbeds
itself from the start, and afterwards gradually wears its way through it
into the hard metal. The perfect fit thus secured under all conditions
of the journal, aided with proper lubrication, not only prevents
heating, but secures the full wear of the brasses, and makes them at all
times perfect counterparts of the journal surfaces.
[Illustration: Fig. 2483.]
Fig. 2483 shows at the top an unfitted bearing without the lead lining,
resting upon a worn and badly-cut journal, the only points of contact
being near the ends. For obvious reasons such a journal is sure to run
hot.
The engraving below shows the application of the lead lining to the same
journal, the dark shading between the journal and bearing representing
the lead which has been pressed into the worn and hollow surface of the
journal, forming a complete bearing and distributing the weight equally
upon its surface.
[Illustration: Fig. 2484.]
Fig. 2484 represents an end view of an unfitted journal and the same
lead lined.
The lead compresses until the brass meets the journal and thus permits
between the two contact over the area that does fit or touch; while the
lead fills the remaining area of the brass bore, giving it a bearing on
the journal, thus relieving the touching points from receiving the whole
weight of the load, and preventing the cutting or abrasion that would
otherwise occur. As, however, the wear takes place the lead compresses,
permitting the journal and brass to come into bearing over its full
area, being obviously effective providing the bearing be kept free from
grit, which would imbed in the bearing and cause it to unduly wear the
journal.
If a brass is too tight a fit upon its journal, heating and abrasion, or
"cutting" as it is termed, ensues. But if a brass or box does not fit
close to its journal, lost motion and sometimes knocking or pounding
ensues. When the joint faces of brasses abut, or come brass and brass as
it is termed, they should be a proper fit to the journal when they are
keyed, or otherwise set up close together; hence there is no danger of
either having a pound in the brass, or of heating and cutting. The
objection to this plan is that the brasses must be removed from their
boxes and the joint faces filed away to let the brasses together, to
take up the wear; hence, in positions in which it is difficult to get
the brasses out, the joints should be left open, while in all cases
where they can be readily removed they should be made brass and brass.
It is to be observed that brasses that come brass and brass require less
adjusting and last longer than those left open, because the latter often
suffer from the abrasion due to an improper adjustment.
In brasses that are left open, it is not an uncommon practice to adjust
the fit as follows: Between the brass joint faces at each of the four
corners a piece of lead wire is inserted; the brasses are keyed as close
home as can be upon the journals, which compresses the lead wire; the
top brass is then released until the piece of lead wire can be moved
freely between the brass joints.
[Illustration: Fig. 2485.]
[Illustration: Fig. 2486.]
A compromise between the brass and brass and the open joint is sometimes
effected by the insertion of slips, as shown in Fig. 2485 at A, B. These
slips may be taken out by simply removing the top brass, while their
reduction of thickness lets the brasses together to take up the wear.
The thickness for these strips may be readily obtained by means of the
pieces of lead wire used as already described.
In the case of large brasses which come brass and brass, much of the
filing on the joint faces to let them together may be saved by reducing
their thickness and area by cutting away part of the metal, as at A A in
Fig. 2486.
[Illustration: Fig. 2487.]
To enable the removal of bearings for renewal, or to refit them without
taking the shaft out, various forms of construction are employed, of
which Fig. 2487, which shows a main bearing, is an example.
Thus, when the cap is removed the side chocks, or gibs as they are
sometimes called, can be lifted out by eye-bolts screwed into the holes
at _c_; the weight of the shaft can then be sustained while the bottom
piece D is removed.
A great deal of trouble in fitting journals and bearings may be avoided
if the best conditions are observed in their manufacture. If, for
example, the conditions of casting are uniform, and the diameter of the
bearing bore and journal bores are constant, that is to say, when a
great number of pieces are to be bored, the amount the bearings will
close across the joint being definitely determined, the conditions of
boring may be made such as to allow for the closure, and the fitting in
this respect may be facilitated; but this applies to small bores only,
as, say, three inches and less in diameter, because in larger diameters
there will be sufficient variation in the amounts of contraction across
the joint face to render it necessary to fit to some extent at least the
bores to their journals.
In some cases slips of paper are placed between the joint faces of the
bearings, or if the joint faces do not meet, slips of brass may be
placed between them; or again the conditions of chucking or holding the
bearings to bore them may be such as to hold them a certain amount
farther apart than they will require to be when on the journal. The bore
is then made sufficiently larger than the diameter of the journal that
it will be as nearly as possible round after being removed from the
boring machine, and will bed down fairly upon the journal without being
fitted with a file, which saves considerable labor. But unless the
bearings are so held as to be to some extent self-adjusting for
alignment, there is liability of the axis of the bore not being quite
true with the axis of the journal, the amount being so small as to
escape detection save by trial for fit with the shaft, and the bearings
in their respective positions. It is a difficult matter, in the absence
of special holding devices, to chuck a bearing, especially if a long
one, so true in a boring machine or lathe as to insure that its bore
shall stand in absolutely correct alignment with the journal when placed
in its position in the framing where it is to operate, and it is for
this reason that many bearings are bored while in their frames. In some
cases, however, this difficulty is overcome by so constructing the bores
and the pieces holding them that the boxes may swivel and adjust
themselves, as in the case of the bearings of line shafting.
Examples of the oil cavities for bearings are given as follows:--
For journals of small diameter oil cups screwing into the bearing cups,
with feed-regulating devices, are generally used, and the same are used
in the case of two half-brasses. But if the journals are of large
diameter, as, say, 5 inches or more, oil receptacles are often cast in
the caps.
In the absence of side chocks in the bearing all the oiling usually
proceeds from the top, save perhaps that an oil groove may be provided
in the crown of the bottom brass.
Fig. 2488 represents a bearing lubricated from the top and bottom; thus
in the cap is an oil cup or cavity from which passes nearly down to the
bearing a brass tube containing cotton wick, which slowly feeds the oil
to the bearing.
Fig. 2489 represents this tube and wick removed from the bearing. This
plan of feeding is largely used on marine engines and on locomotives.
When used upon stationary bearings the cotton wick need not fill the
tube, but if used on reciprocating parts it should fill so that the oil
may not spill over and pass too freely down the tube. In either case,
however, it is desirable to twist in the cotton a piece of fine copper
wire, and bend the ends over the top of the tube to keep the wick in
place in the tube.
[Illustration: Fig. 2488.]
The bottom of the bearing, Fig. 2488, is provided with an oil cavity and
a similar tube and wick. Usually, however, the oil is fed in at the top
only, except in the case of locomotives, because in them all the weight
falls on the top brass; hence, the bottom may be utilised as an oil
receptacle. In English locomotive practice this receptacle as a rule
merely catches the oil that has passed through the bearing box, but
sometimes a roller is inserted and forced against the journal by springs
so as to rotate, by friction, with the rotating journal.
[Illustration: Fig. 2489.]
The bottom of the roller runs in oil so that the roller feeds the
journal with oil, but ceases to feed when the journal ceases to rotate,
an advantage not possessed by self-feeding oil cups, or by the cotton
wick syphons shown in Fig. 2489.
The oil ways or oil grooves are usually provided in small journal
brasses as follows:--
[Illustration: Fig. 2490.]
[Illustration: Fig. 2491.]
[Illustration: Fig. 2492.]
It is obvious that if the joint faces of the brasses are left open and
oil be supplied to one brass only, a great part of the oil supplied will
pass out between the joint faces before reaching the other brass, and
one brass will therefore be better lubricated than the other, unless
each brass be lubricated independently. Even in this event, however, a
great part of the lubricating material will be lost from finding rapid
egress through the opening of the brasses. This may be to some extent
prevented in brasses whose joint faces lie horizontally by chamfering
the edges of the bore so as to form a trough extending nearly to the
ends of the brass, as shown in Fig. 2492. Now it is obvious that the oil
hole must always be above the journal or bearing bore; hence when the
joint faces stand horizontal, the oil hole should come through the crown
of the brass, and oil grooves are necessary to convey and distribute the
oil along the bore. A single groove, as in Fig. 2490, is sufficient for
light duty, but for heavy duty a double groove, such as shown in Fig.
2491, is necessary.
[Illustration: Fig. 2493.]
When, however, the joint faces stand vertically and come brass and
brass, the oil hole may be filed half in the joint face of each brass,
and the edges chamfered off as in Figs. 2492 and 2493, A B representing
the chamfers and C the oil hole, the two brasses put together appearing
as shown in section in Fig. 2493.
This plan has the advantage that the oil is confined within the journal,
except in so far as it may in time work through the ends of the journal
bore, while there are two oil grooves provided without reducing the
bearing or bedding area of the brass. When the oil grooves run
diagonally, as in Fig. 2491, there is the advantage that the length is
greater, and lying nearer to the plane of rotation the oil flows along
the grooves easier, being assisted by its frictional contact with the
journal, but on the other hand the bearing area of the brass on the
journal is so much the more reduced.
Oil holes that are not provided with oil cups should be provided with
small wooden plugs, which will serve to keep the dirt and dust out; they
should be made of as small diameter as the quantity and nature of the
lubricant to pass through them will admit of, and should be left plain
at the top and not countersunk, because the countersinking simply forms
a dish that will collect dust, &c., which the oil applied will carry
down into the bearing.
In some cases there is provided an oil dish around the oil hole, and
this dish is filled with tallow that will not melt under the normal
temperature at which the brass is supposed to operate. But if from
defective oil lubrication or other cause the bearing begins to heat, the
tallow will melt, and flowing through the oil hole afford the needed
lubrication.
It is to be observed that the lubrication of a bearing in which the
pressure is moved alternately from one half of the bearing to the other
is far easier to attain, and more perfect, than in one in which the
direction of the journal pressure is constant, because in the latter
case the journal pressure acts to squeeze out and exclude the oil
continuously, whereas when the pressure is relieved alternately on each
brass, the oil has an opportunity to pass back between the relieved
surfaces. Again the lubrication is more perfect when the direction of
the journal motion is periodically reversed, as the passage of the oil
through the bearing is retarded by the motion, and yet again the
abrasion is reduced because, as stated when referring to rotating radial
surfaces, the particles of metal abraded add themselves together and
form cutting pieces when the motion is continuous in one direction,
whereas in a reversing motion the particles are kept separated and flow
out more freely with the oil that passes through the journal.
If a shaft having a continuous direction of rotation be given end play
so that while rotating it may move endwise, the particles abraded are
again kept separated, and the conditions of lubrication are such as to
give a minimum of wear, because the formation of fine rings or serration
is avoided, the end motion serving to cause the wear to smooth the
surfaces.
[Illustration: Fig. 2494.]
When a shaft has a collar, that is subject to end pressure, the oil way
may be carried up the face of the collar as in Fig. 2494 at B. So also
where very free lubrication is required, an oil groove may also be cut
in the journal itself, as at C in the figure. This plan is adopted by
some American engineers upon the crank pins of steam engines, the
grooves being cut on diametrally opposite sides of the pin in a line
with the throw of the crank.
Referring now to the oil itself, it is generally conceded that a pure
sperm or lard oil is equal to any that can be used for general journal
lubrication, but the ordinary purchaser has no means of knowing if the
oil is pure. The requirements of an oil for lubricating purposes are
given in the following paper on testing the value of lubricants, which
was read by Mr. W. H. Bailey before the Manchester (England) Institution
of Employers, Foremen and Draughtsmen:--
"A fact in connection with oil and lubrication is probably about as
difficult a thing to describe as anything which agitates the minds of
engineers and mechanical men. We appear to have very little published
information on the subject, except that which describes the labors of
Morin, of France, about forty years ago, and that which has been given
to us by Professor Rankine more recently in this country. Those
investigators who preceded Morin do not appear to have published
information of very much value, or which can be used with profit for the
discussion of lubricants, for their researches have been more concerning
the proportions of bearings, and the value of different materials of
construction, rather than the value of different lubricants.
"At the present moment so little is known generally concerning the
performance of different oils, that the public are much at the mercy of
the vendors of these oils, who can make almost any assertion they like
without fear of contradiction.
"The valuable discoveries of our distinguished townsman, Dr. Joule, have
enabled us to look upon the cost of friction and the cash value of heat
as mere questions of arithmetic. Dr. Joule's investigations have been
put into such forcible and elegant English by Professor Tyndall, and
other students of the science of force, as to cause us to understand
that when friction is produced heat is lost, and that all energy thus
wasted passes away in this heat, which may be measured and valued with
nearly as much facility as any article of commerce. We may gather from
this knowledge, when we apply it to workshop economy, that if a pedestal
or bearing becomes so hot through friction as to cause 1 lb. of water to
be raised only one degree Fahrenheit in temperature in one minute, that
heat has been lost equal to that which would be created by a weight of
_one pound falling through a space of 772 feet_. We are told that if we
apply this conversely, that heat has been lost which would lift 1 lb.
weight 772 feet; and if we apply these illustrations still further, and
imagine forty-two pedestals or bearings losing heat by friction in a
similar manner, we may inform ourselves that we are losing nearly 1
horse-power, because they represent 32,424 foot-pounds of force; and if
we know from our books what our coal costs, it will take very little
trouble to give us the exact cash value of this friction and destructive
action.
"What is friction? It may be described as the effect produced by two
bodies sliding one upon the other, which have upon their opposing
surfaces minute asperities, which interlock with each other. The sliding
movement which forcibly removes these minute irregularities creates what
we call friction. Friction is reduced when these asperities are small,
and lubrication is resorted to to prevent that loss of power caused by
motion under these conditions. The chief lubricants used are oil and
tallow, which have a less coefficient of friction than the parts in
contact. It may be well now to state that the term 'coefficient of
friction' is an expression which indicates the proportion which
resistance to sliding bears to the force which presses the surfaces
together. There is little friction when this amounts to only
one-twentieth, it is moderate when it is one-tenth, and it is very high
when it is a quarter or twenty-five per cent. of the force which presses
the surfaces, together, as I before said.
"QUALITIES OF LUBRICANTS.--Good lubricants should have the following
qualities: (1) Sufficient body to keep the surfaces free from contact
under maximum pressure. (2) The greatest possible fluidity consistent
with the foregoing condition. (3) The lowest possible coefficient of
friction. (4) The greatest capacity for storing and carrying away heat.
(5) A high temperature of decomposition. (6) Power to resist oxidation;
or in other words, the influence of the atmosphere upon them. (7)
Freedom from corrosive action on the metals upon which they are used. It
will thus be seen that many conditions have to be carefully taken into
consideration; and further, it may be stated that an oil which may be
good for heavy bearings may not be desirable for use on light spindles,
and for delicate machinery like clocks and watches, where very little
power is required to be transmitted beyond that of overcoming their own
inertia; and also that oil which is good for small machinery running at
quick speeds is very often useless for heavy pressures and large
shafting. For very heavy bearings tallow and other solid lubricants are
used, such as mixtures of sulphur and tallow, asbestos, soapstone with
asbestos, graphite, caustic soda, beeswax, and other similar mixtures,
which find favor among locomotive engineers and those in charge of heavy
machinery. The pressure that can be borne by a good lubricant for a
useful length of time depends upon the nature of the bearings as well as
upon the lubricant itself. The velocity of the rubbing action also must
be taken into consideration. The maximum of pressure that solid
lubricants will bear without destruction is unknown. For steel surfaces,
lubricated with best sperm oil moving slowly, 1,200 lbs. pressure per
square inch of bearing surface has been found permissible. Under the
pivots of swinging bridges several thousand pounds per square inch have
been found to work, and for iron journals 800 lbs. per square inch
should not be exceeded.
"Lubricants in the market vary much in cost as well as in quality, and
very often it is found that the varying prices bear little or no
relation to the value of the article purchased. Probably the best test
of value is one with which I was familiar some years ago. It consisted
of a small engine very much overworked, which stopped and refused to
move or go at the proper speed if the shafting had not been lubricated
with good oil.
"TESTING BY DESTRUCTION.--The instrument here illustrated, in Figs. from
2495 to 2501, to which I call attention, consists of a bed-plate, having
upon it a piece of shafting upon which friction is created by means of
two brass steps, the speed at which it is driven being about 300
revolutions per minute. The friction is brought to bear by levers and
weights somewhat after the manner of a friction brake as shown in Figs.
2495 and 2500. In the top step is a thermometer for indicating any
increase of temperature caused by the friction. A small index indicates
the number of revolutions that the shaft makes for any given temperature
which the friction causes the thermometer to indicate. The machines used
for testing oil have the friction shaft where the oil is destroyed three
inches in diameter. Those for tallow are of larger dimensions. It will
be seen that on ascertaining the number of revolutions which may be
obtained without generating heat, or with the lowest possible increase
of heat, that the value of the oil can be obtained. That oil which
allows the greatest heat to accumulate with the fewest revolutions must
be a bad lubricant. This tabular method of keeping an account of
experiments has been found useful. The machine is stopped when the
thermometer indicates 200 degrees, as it is considered that an oil has
not much lubricating power left if it permits that heat.
------------+--------+--------------+--------------+------------------
Name of oil.| Price. |Revolutions to| Temperature |No. of revolutions
| |200 degrees F.|of atmosphere.| to each degree.
------------+--------+--------------+--------------+------------------
| | | |
------------+--------+--------------+--------------+------------------
"When testing with this machine a definite quantity of oil should be
placed on the friction roller, the top step being removed for that
purpose; the quantity should be about five drops. A glass tube or small
tin measure should be used, as drops vary in size according to the
temperature of the oil, and also differ with the specific gravity. The
inventor of this machine is Mr. Heinrich Stapfer. I believe he may be
considered the inventor of the first instrument for testing oils by
destroying them by friction under the actual conditions in which oils
are used as lubricants. In using this machine I found that, although it
was supposed to test lubricants in the way in which they are used in
manufactories, a slight difference existed, which prevented accurate
results.
[Illustration: Fig. 2495.]
[Illustration: Fig. 2496.]
[Illustration: Fig. 2497.]
"BEHAVIOR OF THIN OILS.--The first machines were made with the brass
steps lipped or recessed, to prevent the oil running away, (see Fig.
2496), which, when thus tested, gave results very much different to
those which are accepted by those who are familiar with the use of
lubricants. For instance, some thin mineral oils were found to be quite
as valuable as, and in some cases superior to, sperm; and this was
caused by the lips on the sides, which prevented the oil from running
off the bearing when an increased fluidity was caused by friction, and
by any slight elevation of temperature. This is a very important quality
in lubricating oils, probably next to the capacity to resist oxidation,
the most important to be criticised by those who wish to value a
lubricant. Although this experiment points out to us that it may be
advisable to make the journals of heavy bearings similar to these, if we
wish to obtain the best results from cheap thin oils, yet, as oil should
be criticised and prepared to be used on bearings with parallel necks,
such as are used in works, it was considered proper to alter the tester
to that shape to make the conditions similar. This illustration (see
Fig. 2497) permits the oil when tested to run away from the bearing if
its increased fluidity gives it a tendency to do so. It is this severe
test which has enabled sperm oil to rise superior to all rivals, because
it has these two apparently opposite attributes--body or thickness,
which keep it on its bearing, combined with sufficient fluidity for
lubricating purposes. Permit me further to illustrate what I mean in
another manner. Suppose we take an oil, good as a lubricant in all other
respects, and place it on a bearing, and that 40 per cent. works quickly
away because of its extra fluidity when subjected to an increase of
frictional temperature, and then compare it with another oil under
similar conditions which only wastes, say, 5 per cent. This latter will
be 35 per cent. superior as an oil having body, and even if slightly
inferior as a lubricant, it may be the most valuable, because strong in
this one great quality of remaining at its duty when placed in position.
Still another illustration will inform us that in the one case we
obtain, say, 60 gallons of lubricating material out of every 100
purchased, and in the other we obtain 95 gallons.
[Illustration: Fig. 2498.]
"THE BEST METHODS OF USING THIN OILS.--This will show us that oils which
are deficient in body, but which are good in other respects, may be used
with good results if doled out in small quantities, as required, by
automatic oil-cups like the Lieuvain needle lubricator, Fig. 2498, or
any other means. Journals which cannot be fed by means of automatic
oil-cups in positions difficult of access should be fed with oil which
has a good body. If time permitted, much might be said of the proper
shape for bearings of machinery--a subject which would lead to valuable
results if discussed by the members of this Society, many of whom must
have great experience of those designs which have produced the best
results, as well as of those mixtures of metals which are the most
durable for light high speed and heavy slow shafting. If any member will
take up this subject, or if several members will read short notes,
giving their actual experience of different sorts of footsteps,
pedestals, and spindles, as well as of the use of different sorts of
oil-cups and lubricators, it will be highly advantageous knowledge,
which must be of great value to all who use machinery.
[Illustration: _VOL. II._ =OIL-TESTING MACHINE.= _PLATE X._
Fig. 2501.
Fig. 2502.]
"FLUIDITY OF OILS.--Continuing my remarks on the thinness or fluidity of
oils, I wish to call attention to an ingenious arrangement for testing
the fluidity when subject to a slight increase of temperature, and also
for detecting any tendency which they may have for combining with the
oxygen of the atmosphere; this latter quality being advantageous in oils
which are used to mix with paint, but which is a great evil when used
for lubricating purposes. A piece of plate-glass placed at an angle is
made warm to 200° Fahr. A drop of oil when placed on the upper end of
this glass will flow down a few inches and thus indicate its fluidity
when subjected to increase of temperature. Fig. 2499 shows a ready
method I have designed for testing oil in this way. It consists of a tin
box in which is fixed the glass, through which can be seen a
thermometer. A graduated scale at the side of the box enables the track
of the oil to be measured. The box has a door at the back which enables
a copper vessel full of boiling water to be introduced; the box is lined
with felt to prevent rapid radiation, and when the door is closed it
will be seen that several experiments may be conducted before the
apparatus becomes too cool for use. I think this a cleaner way than
using a lamp for the purpose. The copper may also be used by itself for
indicating the behavior of oil on copper when slightly warm in making
it discolored or otherwise. As I have before stated, there are many oils
which are good lubricants, but which become too thin when exposed to
slight heat, and I do not hesitate to reiterate the statement, as I wish
to have some influence on the future designs of bearing in this
district. A correspondent writing to _Engineer_ from Queensland says
that for six months in the year oil runs off the machinery like water
and seems to have no lubricating power; he says that the thermometer
registers in the summer 140° in the sun, and 110° in the shade. Great
difficulty seems to have been experienced by him in keeping oil on the
bearings; his experiments on locomotives show that it costs for
lubricating a locomotive there about a halfpenny to three farthings a
mile, according to the mixture used.
[Illustration: Fig. 2499.]
"INFLUENCE OF THE ATMOSPHERE ON OILS.--There are some oils which are
excellent lubricants for the first few hours of use, but which have a
low capacity for resisting the influence of the oxygen of the atmosphere
upon them. The warm glass test may be used for indicating this weakness.
If after the test for fluidity the oil be permitted to remain on the
glass any exhibition of a resinous or varnish quality may be observed.
Another test for this resinous or gummy quality is one which has been
suggested to me by Mr. F. R. Wheeldon, of Bilston. He has made many
experiments. He found that by permitting oil to remain on a Stapfer
friction tester after one test which had been recorded, he tested again
on the following day, without adding any fresh oil. This is a severe
test, as the thermometer was made to indicate 200° Fahr. each time.
[Illustration: Fig. 2500.]
"LONGEVITY OF LUBRICANTS.--Supposing an oil to possess all the qualities
which we think a good lubricant should have--that it has fluidity in
season, and that it does not combine with the atmosphere and become
varnish, that it does not become like water in summer and like mutton
suet in winter, and is in most respects satisfactory. We then want to
know its powers of endurance, its capacity to resist wear and tear--in
other words, its longevity. A good test for longevity or durability of
oil when subject to either heavy or light frictional pressure is one
suggested by Mr. W. H. Hatcher, a very careful investigator, and chief
of the Laboratory of Price's Patent Candle Company, who are extensive
oil manufacturers. It consists in taking away the bottom step of the
Stapfer tester and placing a small dish containing oil underneath the
friction roller (as in Fig. 2500). This oil is carefully weighed before
and after several hours' frictional wear and tear. The drawing (Fig.
2501) shows the application of this mode, which I have designed, for
testing solid lubricants, such as lard and sulphur and other railway and
steamship mixtures. It will be seen that the material is kept to its
duty by the weighted lever, and its progress of diminution can be tested
in its place by the scale-beam arrangement. When it is used with the
pressure on the top step it is advisable to drive it at about 2,000
revolutions per minute; otherwise much time will be occupied in
destroying a weighable quantity of oil. The large Stapfer tester (Fig.
2502) was designed a few months ago for this purpose for the Government
railways of New South Wales, and it is also used by the Manchester,
Sheffield, and Lincolnshire, the Lancashire and Yorkshire, and other
railways. I have not been able to get any results of these tests in time
for our subject on this occasion, but hope to do so at some future time.
The frictional roller is 6 inches in diameter, the pressure amounts to 1
cwt. on each step. As it takes a considerable time to wear away half a
pound of solid lubricant, it may be advisable to measure by minutes
instead of using the speed index. The speed should be at least 1,500
revolutions per minute. The Stapfer tester should be used in a room of
equal temperature, and should not be subject to draughts of cold air, as
it will be obvious these will interfere with the indications of the
thermometer. A recent alteration in the Stapfer tester permits the
quantity of oil used for testing to be measured with greater accuracy
than before. A small oil-hole is made in the top step (see Fig. 2502 at
_a_ and at _c_) in which is placed a glass tube. This only holds a few
drops, and can be filled by simply dropping the oil in, holding the
finger at the bottom to prevent it running away, and then place it in
the hole. If a small needle lubricator be weighed and then filled with
oil of a definite weight, and placed in this hole (see Fig. 2502 at
_b_), oil may be tested for longevity and for its anti-frictional
properties for a longer period than with the small tube. If oil be
placed in this at the same time that oil is placed in the lubricators in
the works and the oil tester be driven from the same shafting,
permitting it to stop and start when the engine stops and starts, the
effect of a week's work upon the weight of the oil may be seen; notice
should be taken of the difference of the temperature between the
thermometer on the instrument and the temperature of the atmosphere of
the workshop.
"TESTING FOR SALTS AND ACIDS, ETC.--It will be obvious that however good
as a lubricant an oil is, and however valuable its properties may be
when examined, if it possesses any corrosive quality which will be
injurious to the metals upon which it is placed, it will soon become
detrimental to the machinery, and may also cease to be valuable as a
lubricant. Mr. William Thomson, analytical chemist, of Manchester, read
a paper on this subject at the British Association at Glasgow, and he
stated the results of elaborate experiments conducted by him to discover
the influence of various oils of commerce upon bright strips of copper.
He permitted the copper strips to remain entirely covered by oil. He
also conducted similar tests with half of the strip below the surface of
the oil, and the other half exposed to the atmosphere, in order to see
what influence the oil had, when the surface line touching the metal
would, of course, be acted on by the atmosphere. After noticing the
effect upon the brightness or dulness of the copper, he carefully tested
the oils in order to detect the quantity of metal which had been
dissolved. Mr. Thomson found the following oils dissolved the largest
proportions of copper, leaving the surfaces of the copper slips
bright--rape, linseed, sperm, raw cod-liver, Newfoundland cod, and
common seal oils; and that the following dissolved much smaller
proportions of copper, also leaving the slips bright--seal, whale, cod,
shark, and East Indian fish oils; and that mineral oils seem to have no
dissolving power on the copper, the only effect being a slight
discoloration on the copper slip of a greyish color.
"SWISS WATCHMAKERS' TEST FOR FLUIDITY AND CAPACITY TO RESIST COLD.--It
seems, according to the _Watchmaker and Jeweller_ (a monthly trade
journal), that the plan I have described, and what may be called the
warm glass test, seems to be looked upon with favor for testing oil in
Switzerland. The degree of heat used for testing the fluidity of oil is
200° Fahr., and if this causes the oil to become a varnish two or three
days after the test the oil is considered unfit for use. Another test is
one to which I have not alluded, and that is, capacity to resist low
temperatures. Oils are tried for their capability to withstand low
temperature in the following manner: Fifteen parts of Glauber salts are
put into a small glass vessel, a small bottle of oil to be tested is
immersed into this; this done, a mixture of five parts of muriatic acid
and five parts of cold water is placed over the salt. By means of a
thermometer the temperature is indicated, and when it shows a very low
temperature, the behavior of the oil, subject to this freezing mixture,
may be observed and noted. Mr. Thomson, however, considers that this
mixture is not so good or so cheap as ice alone, or a mixture of ice and
common salt.
"BLOTTING-PAPER TEST.--It seems it is considered that the blotting-paper
test for fluidity is more reliable, according to the writer of the
article, than the inclined plane experiment. In order to use this test
we must saturate the strip of blotting-paper with oil, and watch whether
the drops fall off in pearls or have an inclination to spread out. The
latter is a certain sign, the writer says, of a viscid oil. Although
this may be considered viscid oil, and may not be valuable for watches,
it may, however, be a good oil for heavier machinery."
The amount of friction between a journal and its bearing varies with the
kind of metal of which the journal and bearing are composed; on the area
of surface in contact in proportion to the load or pressure sustained by
the bearing surfaces; on the nature or degree of the lubrication
afforded; on the diameter of the journal in proportion to its length; on
the manner in which the journal fits or beds to its bearing, and on the
kind of motion, as whether the same be continuous, intermittent,
rotatory, or reciprocating.
Referring to the friction as influenced by the nature of the metals in
contact: the friction varies with the hardness of the metal; thus, with
hard cast iron, there will, under equal conditions, be less friction
than with soft cast iron. The friction is greater when the surfaces in
contact are both of the same metal than when they are of different
metals. Mr. Rankine summarizes General Morin's experiments on the
friction of various bodies not lubricated as follows:--
GENERAL MORIN'S EXPERIMENTS ON FRICTION.
--------------------------------------+----------------+------------
| Angle of |Friction in
Surfaces. | repose. |terms of the
| | weight.
--------------------------------------+----------------+------------
| degrees. |
Wood on wood, dry |14 to 26-1/2|.25 to .5
" " soaped |11-1/2 " 2 |.2 " .04
Metals on oak, dry |26-1/2 " 31 |.5 " .6
" " wet |13-1/2 " 14-1/2|.24 " .26
" " soapy |11-1/2 |.2
" elm, dry |11-1/2 " 14 |.2 " .25
Hemp on oak, dry |28 |.53
" " wet |18-1/2 |.33
Leather on oak |15 " 19-1/2|.27 " .38
" metals, dry |29-1/2 |.56
" " wet |20 |.36
" " greasy |13 |.23
" " oily | 8-1/2 |.15
Metals on metals, dry | 8-1/2 " 11-1/2|.15 " .2
" " wet |16-1/2 |.3
Smooth metal surfaces occasionally | 4 " 4-1/2|.07 " .08
greased | |
" " " continuously | 3 |.05
greased | |
" " " best results | 1-3/4 " 2 |.03 " .036
Bronze on lignum-vitæ, constantly wet | 3(?) |.05(?)
--------------------------------------+----------------+------------
"The 'angle of repose' given in the first column is the angle which a
flat surface will make with the horizon when a weight placed upon it
just ceases to move by gravity. The column of 'friction in terms of the
weight' means the proportion of the weight which must be employed to
draw the body by a string in order to overcome its friction, and the
proportionate weight is sometimes called the _coefficient of
friction_."[34]
[34] From Bourne's "Handbook of the Steam Engine."
In the following table are given some of the results obtained from
Morin's experiments with unguents interposed.
------------------------------+-----------------+---------------------
Nature of surfaces in contact.| Coefficient of |
| friction during | Kind of
| motion. | unguent.
------------------------------+-----------------+---------------------
Brass upon brass | .058 | Olive oil.
Cast iron upon brass | .078 | "
" " " cast iron | .314 | Water.
Steel upon cast iron | .079 | Olive oil.
" " brass | .056 | Tallow or olive oil.
Wrought iron upon brass | .103 | Tallow.
" " " cast iron | .066 | Olive oil.
" " " wrought iron| .136 | "
------------------------------+-----------------+---------------------
Morin's experiments demonstrated that friction is always proportional to
the pressure and independent of the area pressed in contact, providing
that the pressure is not so great as to cause the surfaces to abrade in
the manner or to the degree commonly known as cutting, which occurs when
the area of bearing surface in proportion to the pressure is so small as
to press out the lubricating material.
Now, between the degree of abrasion that is sufficient to cause a
bearing to heat and the minimum, possibly lies a wide range that is very
difficult of classification, and that influences the friction of the
bearing and journal. Under any given dimensions of journal area and any
given pressure of the same to its bearing, the abrasion, and, therefore,
the friction, will be less in proportion as the fit of the journal to
its bearing extends over its whole area and with an equal pressure of
contact. Under these conditions, and with a bearing area ample for the
given pressure, the surfaces of a journal and bearing have a smooth,
glossy appearance, with a surface as glossy as plate-glass.
This degree of perfection, however, is only occasionally reached in
practice, because of imperfections in the fitting and lubrication.
Now, between this condition of glossy smoothness and the degree of
abrasion known to practical men as _cutting_ lies, as already stated, a
wide range of degrees of abrasion, and each of these has its own
coefficient of friction. This may be readily proved by freely
lubricating the bearings of a number of journals working under the usual
conditions of practice and smearing the oil just as it passes through
the bearings upon a sheet of white note paper, when it will be found to
contain fine particles of metal, the number and size of particles in a
given quantity of the oil decreasing as the surfaces of the bearings are
glossy, and increasing as those surfaces appear dull.
The order of value to resist wear is generally considered in practice to
be as follows:--
1st in value, hardened steel running on hardened steel.
2nd (and by some considered equal to the first when the pressure per
square inch of area is light), cast iron either upon cast iron, hardened
wrought iron, or hardened steel.
3rd, under light duty cast iron upon wrought iron or steel not hardened.
4th, wrought iron upon hard composition or brass.
5th, wrought iron upon some anti-friction metal, as Babbitt metal.
Cast iron appears to be an exception to the general rule, that the
harder the metal the greater the resistance to wear, because cast iron
is softer in its texture and easier to cut with steel tools than steel
or wrought iron, but in some situations it is far more durable than
hardened steel; thus when surrounded by steam it will wear better than
will any other metal. Thus, for instance, experience has demonstrated
that piston-rings of cast iron will wear smoother, better, and equally
as long as those of steel, and longer than those of either wrought iron
or brass, whether the cylinder in which it works be composed of brass,
steel, wrought iron, or cast iron--the latter being the more noteworthy,
since two surfaces of the same metal do not, as a rule, wear or work
well together. So also slide-valves of brass are not found to wear so
long or so smoothly as those of cast iron, let the metal of which the
seating is composed be whatever it may; while, on the other hand, a
cast-iron slide-valve will wear longer of itself, and cause less wear to
its seat, if the latter is of cast iron, than if of steel, wrought iron,
or brass. The duty in each of these cases is light; the pressure on the
cast iron, in the first instance cited, probably never exceeding a
pressure of ten pounds per inch, while in the latter case two hundred
pounds per square inch of area is probably the extreme limit under which
slide-valves work; and what the result under much heavier pressures
would be is entirely problematical.
Cast iron in bearings or boxes is found to work exceedingly smoothly and
well under light duty, provided the lubrication is perfect and the
surfaces can be kept practically free from grit and dust. The reason of
this is that cast iron forms a hard surface skin when rubbed under a
light pressure, and so long as the pressure is not sufficient to abrade
this hard skin, it will wear bright and very smooth, becoming so hard
that a sharp file or a scraper made as hard as fire and water will make
it will scarcely cut the skin referred to. Thus in making cast-iron and
wrought-iron surface plates or planometers, we may rub two such plates
of cast iron together under moderate pressure for an indefinite length
of time, and the tops of the scraper marks will become bright and
smooth, but will not wear off; while if we rub one of cast iron and one
of wrought iron, or two of wrought iron, well together, the wrought-iron
surfaces will abrade so that the protruding scraper marks will entirely
disappear, while the slight amount of lubrication placed between such
surfaces to prevent them from cutting will become, in consequence of the
presence of the wrought iron, thick and of a dark blue color, and will
cling to the surfaces, so that after a time it becomes difficult to move
the one surface upon the other. If, however, the surfaces are pressed
together sufficiently to abrade the hard skin from the cast iron, a
rapid cutting immediately takes place, which is very difficult to
remove.
To obtain the best results from cast-iron bearings the bedding of the
journal to the bearing must be full and perfect, and the surfaces bright
and smooth, in which case it will wear better than hardened steel,
unless it be very heavily loaded.
Again, a cast-iron surface will hold the lubricating oil better than
either steel, wrought iron, or brass of any kind. Indeed, if a cast-iron
surface be made very true and smooth so that it is polished and no marks
are visible upon its surface, it will take _much patient_ rubbing and
cleaning with a _dry clean rag_ to remove the oil entirely, whereas
other metals will clean comparatively easy. In testing this matter upon
surface plates the author has found that the only safe method, and by
far the quickest, of removing the oil from cast iron is an application
of alcohol or spirits of turpentine, because the oil will enter and to
some extent soak into the pores of cast iron and gradually work out
again as it is continuously wiped, so that if apparently quite clean
(after having been oiled and wiped) a short period of rest will cause
oil to again be present to some extent upon the surface.
As a general rule motion in a continuous direction causes more wear
under equal conditions than does a reciprocating one, because when a
revolving surface commences to abrade, the particles of metal being cut
are forced into and add themselves, in a great measure, to the particles
performing the cutting, increasing its size and the strain of contact of
the surfaces, causing them to cut deeper and deeper until at least an
entire revolution has been made, when the severed particles of metal
release themselves, and are for the most part forced into the grooves
made by the cutting.
In reciprocating surfaces, when any part commences to cut, the edge of
the protruding cutting part is abraded by the return stroke; which fact
is clearly demonstrated in either fitting or grinding in the plugs of
cocks, in which operation it is found absolutely necessary to revolve
the plugs back and forth, to prevent the cutting which inevitably and
invariably takes place if the plug is revolved in a continuous
direction. Furthermore, when a surface revolves in a continuous
direction, any grit that may lodge in a speck, hollow spot, or soft
place in the metal, will cut a groove and not easily work its way out,
as is demonstrated in polishing work in a lathe; for be the polishing
material as fine as it may, it will not polish so smoothly unless kept
in rapid motion back and forth. Grain emery used upon a side face, such
as the radial face of a cylinder cover, will lodge in any small hollow
spots in the metal and cut grooves, unless the polishing stick be moved
rapidly back and forth between the centre and the outer diameter. If a
revolving surface abrades so much as to seize and come to a standstill,
it will be found very difficult to force it forward, while it will be
comparatively easy to move it backward, which will not only release the
particles of metal already severed from the main body, and permit them
to lodge in the grooves due to the cutting, but will also dislodge the
projecting particles which are performing the cutting, so that a few
reciprocating movements and ample lubrication will, in most cases, stop
the cutting and wash out the particles already cut from the surfaces of
the metal.
In determining the metals to be used for a journal and bearing it is
preferable to use the softer metal, or that which will wear the most, in
the position in which it can be the most easily and cheaply replaced,
which is usually in the bearing rather than in the journal; and since
two metals of a different kind run better together than two of the same
kind, the bearing is usually of a different kind of metal from that
composing the journal. It may be stated, however, that under _light
duty_ cast iron will wear upon cast iron better than wrought iron or
brass upon cast iron (for reasons which have already been stated),
especially if the bearing area be broad and the lubrication ample and
perfect.
To facilitate the removal of the bearings, brasses or boxes are
provided, but in the case of small journals, as, say, of about 3 inches
and less in diameter, the duty being light, the lubrication ample and
equally distributed, and the journals an easy working fit when new, it
is found that solid cast-iron boxes will last for a great length of time
without sensible wear.
In some cases cast-iron boxes are cast with a receptacle for some soft
metal, such as the various compound metals known under the general name
of Babbitt metal.
Babbitt metal is composed of tin, antimony, and copper, mixed in varying
proportions. A good mixture for general use where the duty is light is
composed of 50 parts tin, 5 parts antimony, and 1 part copper. A harder
composition, sometimes termed white metal, is composed of tin 96 parts,
copper 4 parts, and antimony 8 parts. This mixture is especially
suitable for journal boxes or bearings. It is mixed as follows: Twelve
parts of copper are first melted, and then 36 parts of tin are added; 24
parts of antimony are put in, and then 36 parts of tin, the temperature
being lowered as soon as the copper is melted in order not to oxidize
the tin and antimony; the surface of the bath being protected from
contact with the air. The alloy thus made is subsequently remelted in
the proportion of 50 parts of alloy to 100 tin.
For brass bearings or boxes a mixture of 64 parts copper, 8 parts tin,
and 1 part zinc is found to answer well; but for bearings not requiring
so hard a metal, the quantity of zinc is increased, and that of the tin
diminished.
[Illustration: Fig. 2503.]
Bearings or boxes that are to be babbitted are usually cast as in Fig.
2503, there being a rib at A, B, and C, forming a cavity at D, into
which the melted metal is poured. The ribs (in new boxes) are sometimes
bored out, or for rougher work may be chipped and filed out to fit the
shaft, and hold it in line; and to prevent the ribs A, B, &c., from
bearing and cutting the shaft, a piece of pasteboard is laid on ribs A
and B, thus confining the journal bearing to the babbitt. The best
method is to pour the bearing and then rivet the babbitt well into the
cavity D, which is made wider at the bottom, to prevent the babbitt from
coming loose, and then bore out the bearing in the usual manner.
The principal advantage of a babbitted bearing is the ease with which it
can be renewed, and the fact that the metal will soon bed itself to the
journal. This is of great advantage in the case of solid bearings in the
framing of fast-running machines, and in situations where it would be
awkward or difficult to take brasses or bushes out to fit them, or align
them to the shaft, which in many cases would also require to be taken
out to remove the brasses. On the other hand, any particles of grit that
may find ingress to babbitted boxes are apt to become bedded into the
babbitt metal and cut or grind away the journal.
Since the babbitt metal in a bearing is apt to close across the bore
when cooling after being poured, a mandrel of slightly larger diameter
than the diameter of the journal should be used in place of the working
journal to run the bearing on. Some effect the same purpose by wrapping
writing paper around the journal; but it is wrong to use the journal,
for the following reasons: To get a good, sound, well-fitting babbitt
metal box, the metal should be poured as cool as possible, for if made
red hot it contracts so much in cooling that it does not fit well in the
box or frame of the machine. On the other hand unless the metal be well
hot it is apt to cool and set too soon and be unsound. To remedy this
the journal, or whatever represents it, must be heated. The heating is
very apt to bend it. It is obvious then that instead of the journal a
temporary bar of iron of slightly larger diameter than the working
journal should be used, heating it to a good black hot heat, so that the
babbitt metal may be poured less hot than would otherwise be
permissible, and the contraction of the babbitt in the box reduced to a
minimum. A little powdered resin sprinkled in the box will help the
babbitt to flow easily and make a sound casting.
The temporary spindle, or journal, should also be oiled, and as soon as
the metal has well set, the temporary journal should be revolved to free
it. Babbitt bearings cast in two halves should be fitted to the journal
as already described for brasses, which will well repay the cost and
trouble.
To prevent the metal from running out of the bearing, its ends are
closed by means of either clay or putty closely packed against the
bearing ends and the shaft, and in pouring in the melted metal it is
best to pour it on the top of the shaft, and let it run down its sides
into the cavity of the bearing. This heats the shaft equally, and
prevents it bending from unequal expansion, as it would do if it met the
heated metal on its lower half only, it being obvious that if the shaft
bends the bore of the bearing will not be cast in line; hence, the shaft
will bear at the end only, and will require to wear the babbitt down to
a bearing.
Babbitting is sometimes employed to refit parts that have worn loose, or
to bush the bores of work. Suppose, for example, that in a case of
emergency a pulley of a certain diameter is required, and that the only
one at hand has too large a bore, then we may take a mandrel or arbor of
the diameter of the shaft the pulley is required for, and drive on it
two thin washers and turn them to fit the bore of the pulley, and cut a
recess in each to enable the metal to be poured through. We may then put
the arbor and washers in the pulley (the washers serving to hold the
arbor true), and fill in the bore with babbitt metal, leaving the pulley
set-screw in place and set to just touch the arbor, so as to cast the
thread in the babbitt bushing, and thus save drilling and tapping.
PROPORTIONS OF JOURNALS.--It follows from what has been already said
that under a given amount of duty the friction will be less and the
durability greater in proportion as the bearing area of a journal is
increased. But it is an important consideration whether such area shall
be obtained in the diameter or in the length of the journal, or, in
other words, what shall be the proportions between the diameter and
length of a journal. It is found in practice that a journal wears better
in proportion as its length exceeds its diameter, providing that the
stress is not sufficient to cause sensible flexure, because in that case
the pressure is reduced at that part of the journal where the most
flexure occurs, and increased where the journal is most rigid. As a
result, the abrasion increasing with the pressure becomes locally
excessive, the glossy smoothness is lost and increased friction ensues.
If, however, the length of a journal is limited by the exigencies of its
location or the design of the machine, the diameter of journal must be
increased if necessary in order to obtain sufficient bearing area to
withstand the stress without causing undue abrasion.
Referring to the bearing area in proportion to the load, Prof. R. H.
Thurston writes, in an article in the _Railroad Gazette_ of January
18th, 1878, as follows:--
"A pressure of 800 pounds to the square inch can rarely be attained on
wrought iron at even low speeds, while 1,200 pounds is not infrequently
adopted on the steel crank-pins of steamboat engines. I have known of
several thousand pounds pressure per inch being reached on the
slow-working and rarely moved pivots of swing bridges. In my own
practice, I never, if I can avoid it, use higher pressures than 600 and
1,000 on iron and on steel, and, for general practice, make the pressure
less as the speed is greater."
W. Sellers and Co. state that under a pressure of 50 lbs. per square
inch, and with oil well distributed over the surface of the box, the
metal of the journal will not touch that of the bearing box bore.
In practice bearings are made with a length varying from that equal to
the diameter of the journal to about four times that diameter, and but
few cases occur in which these limits are exceeded in either direction.
It is to be observed, however, that diminishing the length is apt to
increase the abrasion unless the duty is very light indeed, while
increasing it increases the durability while not affecting the friction,
unless the shaft bends.
There are special cases in which within certain limits the proportions
of journals are nearly uniform in practice; thus the length of engine
crank-pin bearings rarely exceeds once and a half times the diameter,
while the main shaft bearings are often similarly limited in width from
the exigencies of designing the engine so that the eccentric shall come
in line with the slide-valve spindle. In the case of crank-pins the pin
cannot be held sufficiently rigidly to prevent spring or flexure; hence
it is desirable to limit its length so that its pressure shall be as
short a leverage as possible to the crank. The solid bearings in the
framing of machines usually admit of room enough to make their lengths
three or four times the diameter. Again, in the case of line shafting,
boxes having a length equal to three or four times the diameter may be
employed, providing that the alignment be made correct, or that the
boxes are self-adjusting. But in all cases the longer the bearings the
greater the necessity for correct alignment, so that the axis of the
bearing bore may be in line with the axis of the shaft, the error
manifestly increasing with the length of the bearing.
PLACING TWO CRANKS ON A SHAFT SO THAT THEIR CENTRE LINES SHALL STAND AT
A RIGHT ANGLE.--It is obvious that the keyways in both the crank and the
shaft must be cut accurately in their proper positions, because it is a
tedious operation to file out the sides of the keyways when the cranks
are placed upon the shaft. To mark the keyways in the absence of any
tools or appliances specially designed for the purpose we proceed as
follows: Placing the shaft upon a marking-off table, we plug up the
centres upon which the shaft has been turned by driving a piece of lead
in them, leaving the surface level with those of the shaft; and then
from the perimeter of the shaft we carefully mark, upon the lead plugs,
the centres of the shaft. From this centre we describe a circle whose
diameter will be equal to the required widths of the keyway, and then
taking a square we place its stock upon the face of the marking-table,
and bringing the edge of the blade even with the edge of the circle, we
mark a perpendicular line upwards from the circle to the perimeter of
the shaft, and then draw a similar line on the other side of the circle,
as shown in Fig. 2504, in which A represents the shaft and B the circle,
C the perpendicular line struck on one side of the circle, and D the
square placed upon the marking-table E, in position to mark the line on
the other side of the circle, F and G being wedges to keep the shaft A
from moving its position upon the table. We next mark with a
scribing-block or surface gauge the depth of the keyway as denoted by
the line H, and the marking at that end of the shaft is completed.
Passing to the other end of the shaft we find the centre of the shaft,
and describe around it a circle equal in diameter to the required width
of keyway, and from the edges of the circle to the perimeter of the
shaft draw two lines with a scribing-block, as shown in Fig. 2505, A
representing the shaft, B the circle, C D the breadth of the keyway, E
the marking-off table, F and G the wedges, and H the depth of the
keyway, which must, in this case, be marked with a square resting on the
table.
[Illustration: Fig. 2504.]
[Illustration: Fig. 2505.]
If, however, the shaft is too heavy or large to be placed on a
marking-off table, we may proceed as follows: Strike as before the
circle B, Fig. 2504, equal in diameter to the required width of keyway,
and adjust a straight-edge held firmly against the end face of the
shaft, so that its upper edge is coincident with the perimeter of this
circle, while the straight is horizontally level-tested by a
spirit-level. Draw a line along the shaft face, using the straight-edge
as a guide. This will give us the line C in Fig. 2505. By a similar
process the line D, Fig. 2505, may be drawn. At the other end of the
shaft similar lines, but standing vertical, may be marked, which will
give the positions of the keyways.
[Illustration: Fig. 2506.]
We have now marked off on the end faces of the shaft a keyway at each
end, one standing at a right angle to the other; but it must be borne in
mind that we have paid no attention as to which crank shall lead; that
is to say, suppose in Fig. 2506 A and B represent cranks placed upon the
shaft C, and running in the direction indicated by arrow D, it is
evident that the crank B leads in the direction in which the engine is
to run, and hence the keyway E stands in advance of the keyway F; and
therefore, as shown in the figure, the right-hand crank leads. To have
made the left-hand crank lead, when the engine runs in the direction of
the arrow D, we should, supposing the keyway F to be already cut, have
to cut the keyway E on the directly opposite side of the shaft; or, what
is the same thing, supposing the keyway E to be already cut, the keyway
F would require to be cut on the diametrally opposite side of the shaft.
It is obvious that if the engine ran in the direction of the arrow G,
the left-hand crank would lead, supposing in each case the cylinders to
stand at H. Here it may be necessary to explain the manner of
determining which is the right-hand and which the left-hand crank.
Suppose then that the figure represents a locomotive crank, the
cylinders being at H, then as the engineer stands in the cab, facing his
engine, A will be the left-hand and B the right-hand crank. It is usual
in locomotives to make the left-hand crank lead when the engine is
running forward, the practical difference being, that if the workman
were by mistake to make the right-hand crank lead, the engine would run
forward when the reversing lever was placed to run backward, and _vice
versâ_. It makes no difference whether the shaft can be turned end for
end or not: if the right or left crank is required to lead when the
crank is required to revolve in a given direction the keyways in the
shaft must be marked off in the relative positions on the shaft
necessary to obtain that result.
The keyways may be carried along the circumference of the shaft by a
square applied to its end face, or if that face is not flat by the
ordinary keyway marking tool.
[Illustration: Fig. 2507.]
To mark off the keyways in the cranks, we place a centre-piece in the
bore of the crank, as shown in Fig. 2507, in which A represents a crank
having a centre-piece of sheet iron B placed in the bore. On the face of
this centre-piece we mark the centre of the hole into which it fits, and
from that centre we describe the circle C, which must be of exactly same
diameter as the crank-pin if it is in its place, or otherwise of the
crank-pin hole. We then draw the lines D and E, using as a guide a
straight-edge placed one end upon the crank-pin journal, or even with
the edge of the crank-pin hole, as the case may be, and the other end
(of the same edge of the straight-edge) exactly even with the
circumference of the circle C. From D and E we find the centre of the
circle F, which must be central between D and E, and whose diameter must
be exactly equal to the required width of keyway; and we then mark the
circle G, describing it from the centre of the hole, and therefore of
the circle C. By drawing the lines H and I, which must be even with the
circumference of the circles F and G, using a straight-edge as a guide,
we shall obtain the correct position for the keyway K, and the whole of
the keyways may be cut, care being taken to cut them quite true with the
lines, and of an exact equal width.
To put the cranks on the shaft, first provide a temporary key, a close
fit on the sides, but clear top and bottom, so that it will bind just
easily on the sides of the keyways in both the shaft and the crank. The
shaft must be placed and wedged with its keyway downwards, so that in
putting the crank on, the pin end may hang downwards, which will render
it more easy both to put on, handle, and adjust. As soon as the shaft
has entered the crank, say a quarter of an inch, we must insert the
temporary key (which may have its end edges well tapered off to assist
the operation of entering it) sufficiently far into the keyway of the
shaft that it will not fall out, and we may then proceed to put the
crank on the shaft to the necessary distance, keeping the temporary key
sufficiently far in the keyway to enable it to act as a guide--that is
to say, up to at least half the length of the keyway.
[Illustration: Fig. 2508.]
[Illustration: Fig. 2509.]
To put on the second crank, we first place the shaft so that the crank
already on stands exactly horizontal, setting it by placing a
spirit-level, as shown in Fig. 2508, in which A represents either the
crank-pin journal or the crank-pin hole in the crank, and B a circle
struck on the end face of the shaft and from its centre, the diameter of
the circle B being exactly the same as that of A. If then we so adjust
the position of the crank that a spirit-level applied to the exact
circumferences of the circles A and B stands level, the crank will stand
level, and we have only to put the second crank on with its centre-line
standing perpendicular, and the two cranks will be at a right angle one
to the other. We now proceed to put on the second crank, pursuing the
same method employed in putting on the first one, save that the
temporary key need not be inserted so far into the keyway, because, if
the keyways have been cut the least out of true, it will make a great
difference at the crank-pin, because of the increased distance of the
latter from the centre of the crank-shaft. As soon as the second crank
is placed to its position on the shaft we must ascertain if it stands
vertical, which we may do by applying the spirit-level as shown in Fig.
2509, bringing its edges exactly fair with the edges of the circles A
and B, and moving the crank until the bubble of the level stands true,
and taking out the temporary key if it is necessary to adjust the crank
at all.
If, however, the crank is to be forced on by hydraulic pressure, this
latter adjustment should be made when the crank is just sufficiently far
on the crank shaft to enable it to bind enough to well support its own
weight, to facilitate which the end of the shaft is sometimes slightly
tapered for a very short distance--a practice which is sometimes
rendered unnecessary by reason of there being attachments fitted to the
hydraulic presses which of themselves adjust the position of the cranks,
and insure their being at a right angle one to the other.
After the cranks are on their places the keys may be fitted, care being
taken that, if the crank last put on had to be moved to adjust it, the
sides of the keyways be filed even, otherwise driving the key will tend
to move the crank.
FITTING ENGINE CYLINDERS.[35]--When engine cylinders are made in
quantities, as in locomotive building shops, a great deal of the fitting
work is saved by the machine work; but when a single cylinder or a pair
of cylinders only are to be fitted up it will not pay to make jigs and
appliances; hence, they are usually fitted up entirely by hand. The
first thing to do is to mark off all the holes requiring to be drilled,
and have the drilling done.
[35] From the "Complete Practical Machinist."
In marking the holes in the cylinder covers it is to be noted whether
that part of the cylinder cover which fits into the cylinder has a
portion cut away to give room for the steam to enter (as is usually the
case), and if so, first mark a line across the inside flange of the
cover, parallel to the part cut away, and then scribe each end of the
line across the edge of the flange. Then mark a similar line across the
cylinder end, parallel to the steam port where it enters the cylinder,
and scribe each end of this line across the cylinder flange, so that,
when the cylinder cover is placed into the cylinder and the lines on the
flanges of the cylinder and the cover are placed parallel to each other,
the piece cut away on the cover will stand exactly opposite to the steam
port, as it is intended to do. The cover may then be clamped to the
cylinder, and holes of the requisite size for the tap (the tapping
holes, as they are commonly called) may be drilled through the cover and
the requisite depth into the cylinder at the same time.
[Illustration: Fig. 2510.]
The cylinder covers must, after being drilled, as above, be taken from
the cylinder, and the clearing drill put through the holes already
drilled so that they will admit the bolts or studs, the clearing holes
being made 1/16 inch larger than the diameter of the bolts or studs. The
steam chest may be either clamped to the cylinder, and tapping holes
drilled through it and the cylinder (the same as done in the case of the
covers), or it may have its clearing holes drilled in it while so
clamped, care being taken to let the point of the drill enter deep
enough to pass completely through the steam chest, and into the cylinder
deep enough to cut or drill a countersink nearly or quite equal to the
diameter of the drill. If, however, the steam chest is already drilled,
it may be set upon the cylinder, and the holes marked on the cylinder
face by a scriber or by the end of a piece of wood or of a bolt, which
end may be made either conical or flat for the purpose, marking being
placed upon it; so that, by putting it through the hole of the chest,
permitting it to rest upon the cylinder face (which may be chalked so as
to show the marks plainly), and then revolving it with the hand, it will
mark the cylinder face. This plan is generally resorted to when the
holes in the chest are too deep to permit of being scribed. To true the
back face, round a hole against which face the bolt head or the face of
the nut may bed, in cases where such facing cannot be done by a pin
countersink or a cutter used in a machine, the tool shown in Fig. 2510
may be employed, _a_ being a pin provided with a slot at one end to
admit the cutter B, which is held fast by the key C, and is also
provided with a square end _f_, by which it may be turned or revolved by
means of a wrench, and with a thread to receive the nut E, _d_ being a
washer; so that, by screwing up the nut E, the cutting-edges of the
cutter are forced against the cylinder _g_, and will, when revolved, cut
the face, against which they are forced, true with the hole in the
cylinder through which the pin _a_ is passed.
After the drilling the cylinder should be placed on end and all the
holes that can be got at should be tapped. Then the cover joint,
supposing it to be a ground joint, should be made according to the
directions given for making ground joints, when the cylinder may be
turned upside down and the other cover fitted. Then the holes for the
cylinder cocks and for the steam and exhaust pipe should be tapped, and
the faces for these pipe joints fitted as required.
The steam-chest holes should then be tapped and the ports marked out and
chipped and filed to the lines, such lines being marked as described in
the remarks on lining out work.
The face for the steam-chest seat and the steam-chest cover may then be
prepared by filing, scraping, or grinding, as may be required, and
simultaneously the valve seat and valve face may be fitted. If the
cylinders are to be bolted together as in a locomotive, the holes for
holding them together should be drilled about 1/64 inch smaller than the
bolts, so that they may be reamed out together after the cylinder bores
are aligned.
One cylinder face should be marked and drilled first, and the two
cylinder bores being set to align true the other cylinder should be
marked from the other, or if there is a saddle between the two cylinders
both cylinders may be marked and drilled, and also the holes on one side
of the saddle. Temporary bolts may then be put through the holes that
are drilled in the cylinder and saddle and clamps used to hold the
undrilled cylinder to the saddle, when the cylinder bores may be set
true one to the other, and the holes on the remaining side of the saddle
marked through those already drilled in the cylinder. These latter holes
being drilled, temporary bolts of smaller diameter than the holes (so as
to give room to move the cylinders to align their bores) may be used to
bolt the cylinders together while their bores are accurately aligned,
which alignment may be effected as follows:--
[Illustration: Fig. 2511.]
The bores should be set as near true as possible, tested by a
spirit-level rested on the bore and placed as near true as can be judged
with the length of the bore, and a plumb rule may be applied to the end
faces where the cover joint comes. Then a straight-edge should be
applied, as in Fig. 2511, in which S is the straight-edge, and C and D
the two cylinder ends.
The method of testing is shown in Fig. 2511, where the straight-edge S
is shown in three positions, marked respectively 1, 2, and 3 at one end,
and F, G, and H at the other.
[Illustration: Fig. 2512.]
[Illustration: Fig. 2513.]
The first test should be made by simply placing the straight-edge across
the two cylinder faces, as at G 3; and when the cylinders are set
apparently true and the spirit-level applied to the respective bores
shows them true, greater accuracy may be secured by placing the
straight-edge in position 1 H, being pressed firmly to its cylinder face
with end 1 above the other cylinder face. Then, while end H is held
firmly to its cylinder, let end 1 lower until it passes entirely over
the face of cylinder C, whose face it should just touch; if on meeting C
the straight-edge strikes it or does not meet it, further adjustment of
the cylinder positions is necessary. Next place the straight-edge in
position 2, pressing end F firmly against cylinder D, and passing the
other end entirely over the end of cylinder C, which it should just
touch, and no more. It will then be necessary to repeat this process,
pressing the straight-edge against cylinder C and testing the other end
with cylinder D, and the cylinders thus set will be (if the end faces
are true, as they should be, and usually are) more truly aligned than is
possible by the use of the spirit-level. This method also brings the end
faces of the cylinders in the same plane, so that each piston head will
travel central in the length of the cylinder bore, approaching the
cylinder covers equally, and therefore keeps the clearance equal.
Incidentally, also, this secures accuracy in the cross-head traverse on
the guide bars (supposing these bars to be bolted to the cylinder
cover). The holes for bolting the cylinders together may then be reamed
and the bolts driven in and screwed up.
To guide the tap when tapping the cylinder cover and steam-chest holes
the guide stand S, shown in Fig. 2512, should be employed. It is bolted
to the cylinder face by the bolt B, which passes through a slot in the
stand.
The tap T is inserted through the two arms of the stand and its end
inserted in the hole to be tapped when bolt B is tightened up.
The stem of the tap should be of slightly larger diameter than the tap
thread, so as to fit in the holes of the guide or stand.
When, however, one end of the guide bars is carried on the cylinder
cover, it is necessary when setting that cover to be marked for the
drilling, to so set it that the seats for the guide bar ends shall be
horizontally level when the cylinder is on the engine; and when setting
the bores of the cylinder in line to mark the holes for bolting the
cylinders together or to the saddle, this point should also be looked
to, as if these seats are not in line the faces of the guide bars will
not be in line, and will not, therefore, bed fair to the cross-head
guide unless the error is in some way corrected.
It is desirable that these seatings be quite true and in line one with
the other on both cylinders, so that if liners require to be made, or if
the ends of the bars require to be filed to let the bars together at any
time, the surfaces may be filed true to the face of the bar, and thus be
set true and to fit the cross-head guides without requiring to put the
bars on and off to fit them true by trial.
[Illustration: Fig. 2514.]
[Illustration: Fig. 2515.]
REBORING CYLINDERS IN THEIR PLACES ON THE ENGINE.--When a cylinder bore
becomes so worn out of cylindrical truth, or becomes grooved or cut, as
it is termed, as to require to be rebored, it may be done with the class
of boring bar shown in Fig. 2513. It consists of a bar having journal
bearing in castings which bolt on to the two ends of the cylinder in
place of the cylinder covers. On the bar is fitted a sliding head
carrying the cutting tool and fed by a screw passing within the bar. To
operate the bar and simultaneously the feed screw, the hand-wheel and
worm-wheel is employed, giving rotary motion to the worm-wheel which is
fast upon the bar. Fast also upon the bar is the inside one of the two
small gears shown, which operates the inner of the two small gears shown
above it. The outer of the upper gears engages with the outer of the
lower ones, the latter being fast upon the feed screw. In the inner pair
the lower is of largest diameter, but in the outer pair the upper is the
largest, and as a result the outer of the lower rotates the fastest, and
hence rotates the feed screw, causing the tool to feed to its cut.
The proportions of these wheels are, first or inside pair, lower wheel
36, upper 37; outside pair, upper 37, lower 36, so that the feed per bar
rotation is in amount that produced by moving the outer lower gear a
part of a rotation equal to twice the pitch of the teeth, the cutting
tool motion depending upon the pitch of the feed screw.
To enable the rapid traverse of the head from end to end of the bar, the
upper pair of gears are mounted on an eccentric stud, so that by
operating the small handle shown they may be disengaged from the lower
feed gears and the feed screw operated direct by means of the handle
shown.
[Illustration: Fig. 2516.]
[Illustration: Fig. 2517.]
In setting such a bar to a cylinder bore it is to be remembered that two
methods may be employed. First, the bar may be set to accommodate the
cylinder bore, truing it out with as light a cut as possible. In this
case the bore of the cylinder may be made out of line with the guide
bars and with the centre of the length of the crank-pin journal.
In the second the bar may be set with a view to bore it out in line with
the guide bars and crank pin, and then taking as much cut as will be
necessary to true the bore.
The latter plan is the preferable of the two, unless the repairs are so
extensive as to require the guide bars to be redressed and the main
bearing renewed, in which case those parts requiring to be re-aligned,
the cylinder may be rebored with a view to take out as little metal as
possible, and the other parts set to suit the new bore.
To set the bar true to the guide bars and crank pin, and thus retain the
axis of the new bore true with that of the original bore, the bar should
be set true with the recessed counterbore at each end of the cylinder,
which being unworn remains true.
If, however, only one cylinder cover can be conveniently taken off, the
piece of wood will require to fit in the counterbore at the open end,
and in the cylinder bore at the closed end of the cylinder; hence we
make it large enough for the counterbore, and after having removed the
ridge at that end we cut the length of the wood down to fit the cylinder
bore, whereas if we made our rest to fit the bore at first we should
require to use wedges to make it fit the counterbore. In some cases
holes might be bored near the ends of the rest or fulcrum to serve the
same purpose as the notches.
The method of using the scraper, Fig. 2516, is shown in Fig. 2514, which
latter represents an engine cylinder. At B is shown the wooden rest or
fulcrum; and at C the lever scraper operating on the ridge at the closed
end of the cylinder. The lever C is worked on the pulling stroke only,
and is so held that the edge presents a keen scraping tool which will
cut very freely. The fulcrum B should be adjusted as closely as
convenient to the work, so as to obtain good leverage for the scraper.
It should be moved in its position, so that during the roughing out only
the lower notches in the fulcrum are used.
A plan was lately resorted to on the White Star Line of steamships for
re-boring a cylinder. The cylinder heads and piston follower were taken
off; a groove was cut from the outer end of the cylinder along the bore
as far and as deep as the counterboring was required to be done. The
counterboring was then accomplished in the manner shown in Fig. 2515.
The junk ring was provided with a small tool holder, such as is used
upon boring bars. The tool was fastened in the holder while its cutting
edge was in the groove referred to, cut as deep and as far up the
cylinder as the counterboring was to be. To the junk ring was fastened,
by two long bolts, a wooden lever extending above and across the
cylinder. Two men walked around pushing the lever, and when the tool at
each revolution arrived at the groove, a fresh cut was taken by moving
the engine so as to raise the piston the necessary amount. It is obvious
that the piston head may be steadied and held true in the bore of the
cylinder by means of a few wooden wedges. Thus we see that in this
operation the junk ring was made to serve as a boring bar head, the men
furnishing the necessary rotative motion, the feed motion to the tool
being obtained by advancing the piston toward the end of the cylinder
where the work was being done.
The ridges which in time form at the two ends of a cylinder bore are
usually removed by the hand-boring bar shown in Fig. 2513, but they may,
in cylinders of from 12 to 24 or 30 inches in diameter, be readily cut
out by hand as follows:--
Take a bar of steel 9/16 inch square and 3 feet 6 inches long; forge it
at one end to the shape shown in Fig. 2516, in which from A to B is the
forged end. This end must then be heated along its entire length to a
cherry red, and dipped vertically into cold water to harden it; after
which it must be ground from A to B on all four faces square across, and
as nearly of an even curve as can be ascertained by the eye. Next take a
piece of hard wood--oak, for instance--about an inch thick and 3 inches
wide; cut it to such a length that when placed upright its ends will
wedge tightly into the counterbore of the cylinder. Into the edges of
this piece of wood saw out a series of notches, making its finished
appearance to be such as shown in Fig. 2517. The object of fitting its
length tightly into the counterbore of the cylinder is as follows: If
both cylinder covers are off or can be conveniently taken off, the ridge
can be operated upon at each end of the cylinder; hence our piece of
wood, which is merely an improvised rest to act as a fulcrum for the bar
scraper shown at the top of the figure, would require to fit into the
counterbore.
CHAPTER XXIX.--ERECTING ENGINES AND MACHINERY.
In engines having suspended guide bars, it is not uncommon to set those
bars by the working parts of the engine, instead of by lines. This is an
advantage when the parts of the engines are not taken down, and, if care
is taken, will make a true and smooth working job; but otherwise, it is
likely to introduce errors in the lining of the engine, which throw it
out of proper line, and cause a great deal of friction.
The proper method of setting the bars depends upon the condition of the
engine as to wear. Suppose, for example, that a new piston head has been
put in, then, if the gland is new also, or is a good fit to both the
piston rod and the bar of the stuffing box, the bars may be set as
follows:--
[Illustration: Fig. 2518.]
Place the piston at the back end of the cylinder, and put the cross head
and guide blocks in proper place on the rod. Put up the bottom guide
bars so that they just touch the cross-head guides. Now, in adjusting
these bottom bars there are two essential points: first, that the plane
of their upper surfaces shall stand parallel with the axial line of the
main shaft, and secondly, to place the upper surface parallel with the
axial line of the cylinder (it being of course assumed that the cylinder
and crank shaft are in proper line). The first of these essential points
will be attained when a spirit-level, placed truly along the bore of the
cylinder, shows the bubble to stand in the same position in the tube, as
it does when placed upon and along the bar. The second will be attained
when a spirit-level, placed across the bars, as in Fig. 2518, at A,
shows the bubble to stand the same as it does when the level is placed
on a parallel part of the shaft, as in the figure at B. When the bars
are thus temporarily set, the liners, or pieces of iron, may be fitted
to the proper thickness, so that the gland will pass in and out of the
stuffing box easily by hand, no matter in what position the piston may
be in the cylinder.
To get the thickness of these liners, take wedges made of iron, wood, or
lead, and insert the thin end between the faces of the bars and those of
the supports, forcing the wedges in sufficiently to leave a mark upon
them. By chalking the faces of the wedges they will exhibit the marks
more plainly. The wedges should be inserted at each end and on both
sides of the bar, for one bar at a time, the liners being got out a
trifle too thick so as to allow some for fitting.
If the liners require to be very thin and are difficult to hold in the
vice without springing, take a piece of soft wood faced true, and grip
it in the vice, and fasten the liner on it by means of brads driven in
around the edge of the liner.
When the four liners are ready place them in position between the bars
and their seatings. Bolt the bars firmly in position, wipe them clean
and test them lengthwise with the spirit-level to ascertain if they are
parallel with the cylinder bore, and place the level across the bars at
each end to test parallelism with the engine shaft, as in Fig. 2518,
and, having noted where further adjustment is necessary, put marking
upon the bars and move the cross head back and forth to ascertain how
much the respective liners require reducing. If the gland is a fit upon
the piston rod and in the stuffing box, moving the gland in and out of
the stuffing box will be an admirable test of the guide-bar adjustment.
[Illustration: Fig. 2519.]
The straight-edge should also be applied to test if the surfaces of the
bars lead true one to the other; thus, in Fig. 2519, A and B are the
bars and E the straight-edge, which by being pressed firmly to the
surface of A discloses that the surface of A is not in line with B,
because if it were so the straight-edge would meet the face of B as in
Fig. 2519, where the straight-edge F pressed to the surface of C leads
true to the surface of the bar D. All four of the bars require testing
in this manner. If the seatings for the bars or the liners are not made
flat and of equal thickness, or if from any other cause the bars do not
bed properly upon the liners, then bolting up the bars will spring them
as shown in Fig. 2520, in which, at A, is shown a bar sprung in the
bolting up, because the liners fit at the ends B C only; while at E is
shown a bar sprung or bent because the liners fit at the ends D D only.
In either case the cross head would be forced to travel in a curve,
bending the piston rod, and inducing much friction. The way to test the
bars in this respect is, after the above operations, and before
loosening the bolts, place a long straight-edge lengthwise along each
bar and move it laterally at one end. If it swings from the centre the
bar is rounding, while if it shuffles across first at one end and then
at the other the bar is hollow in its length and we must find at which
end of the bar this spring exists. To do this, slightly slacken the
bolt or bolts at one end and again apply the straight-edge, if the
spring is removed the error lies in the bedding of the liner at that
end. If not removed, retighten the bolts at that end and slacken those
or that at the other end, and again apply the straight-edge, and thus
may it be determined how much of the spring is due to each of the
liners, and this must be remembered and allowed for in filing the liner
to its final adjustment. Before putting the liners in a second time it
is better to give them a light coat of marking to show where they bear.
At each trial of the bars the spirit-level and straight-edge should be
applied and the cross head should be moved back and forth to show by the
bearing marks how the cross-head guides fit to the bars. These marks are
a great deal finer test than any spirit-level adjustment, hence the last
part of the fitting should be performed with strict reference to the
bearing marks upon both the bars and the cross-head guides as well as
upon the liner, the cross-head flanges being adjusted and fitted at the
same time as the face fitting.
[Illustration: Fig. 2520.]
To set the top bars place the cross head in the middle of its stroke,
and place them upon the cross-head guides. Then, with the wedges applied
as before, ascertain the required thickness of the respective liners one
at a time, leaving them, as previously, a trifle too thick, and testing
them while fitting by marking placed upon their faces. The top bars may
be entirely adjusted from the contact marks left by the cross-head
guides when moved along the bars, thus dispensing with the use of the
straight-edge and spirit-level.
As the bolts supporting the bottom bars often require to be loosened to
get the top bars off, pieces of wood may be placed beneath the bottom
bars to retain them in position when the bolts are loosened. These
pieces must be removed during the testing, for if left so as to wedge
the bars they may spring them, and thus mislead in the adjustment. After
the top bars are adjusted the whole bearing surfaces should be oiled,
and the cross head pulled back and forth by hand without the use of a
lever, providing the size of the piston does not exceed about eighteen
inches diameter. The bars when set true should be clamped to their
seatings and the holes reamed out to receive the proper bolts, and,
finally, mark each bolt, bar, and liner to its place.
When the bars, tested with the straight-edge and spirit-level as
described, show true, if the gland will pass freely in and out of the
stuffing box with the cross head at any part of its stroke, the guide
bars are set.
In this operation let it be noted that the close fit of the piston to
the cylinder bore and of the gland to the stuffing box is alone depended
upon as a guide whereby to so set the guide bars that the axial line of
the piston rod and its plane of motion shall be in line with the centre
of the crank shaft.
[Illustration: Fig. 2521.]
Suppose, however, that the piston head is a new one, and the gland is
worn a loose fit to the stuffing box, then setting the bar to the gland
would produce the result shown in Fig. 2521, in which the dotted line A
A is a line or cord stretched axially true with the cylinder bore, and
coincident with the centre of the pillow block at B. The gland being a
loose fit permits the piston rod to fall below its proper level, and the
surface of the bars, if set by the gland only, without using the
spirit-level, would be set true to the full line C C, and therefore out
of true line. If the bars are set by spirit-level true to the length of
the cylinder bore, the gland becomes useless as a guide to set the bars
by. It is a not uncommon practice, when the gland has play, to insert in
the stuffing-box bore, at the bottom, a piece of tin or sheet brass,
equal in thickness to one-half the amount to which the gland is too
small, or to insert a similar piece beneath the piston head if it is too
small. As a rule, however, there will be at least as much play between
the piston rod and the gland bore as between the gland and the
stuffing-box bore; hence, if there is any play, it is better to discard
the use of the gland altogether.
The proper method of setting guide bars by a stretched line is as
follows:--
[Illustration: Fig. 2522.]
The cord or line is set true to the cylinder bore, and coincident with
the centre of the pillow block, as at A A in Fig. 2521, and the two
bottom bars are put up in line horizontally with the axial line of the
crank shaft, and at a distance below the stretched line equal to
one-half the height of the guides for the cross head, as in Fig. 2522,
in which A represents the stretched line, B, B the bottom bars, C C a
straight-edge, and D a piece of wire whose length from point to point is
equal to one-half the height or thickness of the guide blocks. The width
apart of the bars is set to suit the width apart of the flanges of the
guide blocks on the cross head, by means of a square. The square is
applied in the following manner: On a straight-edge mark two lines A and
D, Fig. 2523, a distance apart equal to the distance between the flange
edges of the cross-head guides. Midway between A and D mark the line C;
place the straight-edge across the bars as shown, and when the edge of a
square, placed on the straight-edge, coincides with C and the stretched
line, and the marks A and D coincide with the edges of the bars, the
latter are set true, and will come right for distance apart, and
distance from the centre line, supposing the flange edges of the
cross-head guides to be equidistant from the centre of the length of the
cross-head journal. If, however, such is not the case, the width from A
to C and from C to D must be made to suit, C representing the centre of
the length of the cross head journal, D the flange on one guide and A
the flange on the other guide. Here it may also be remarked that, if the
thicknesses of the cross-head guides vary, or if they are not central to
the axial line of the cross-head journal, the bars must be set for
distance from A in Fig. 2523, to suit the error, because in that figure
the straight-edge is supposed to stand parallel to the axial line of the
shaft, as it is also in Fig. 2522, the aim in both cases being to so set
the bars that the cross-head journal shall stand parallel with the crank
shaft.
[Illustration: Fig. 2523.]
It is the liability of variation in the thickness of the guide blocks,
and of their not being central to the cross-head journal, that
constitutes the disadvantage of setting the bars by lines, it being
obvious that the bars must be either set to suit any errors in the
guides, or those errors must be eliminated before setting the bars. The
top bars must be set parallel to the bottom ones, at a distance from the
bottom ones equal to the thickness of the guide blocks, and parallel to
one another. It is preferable to set the top ones with the cross head
and guides in place, observing all the precautions as to springing them
given in the case of the bottom bars.
[Illustration: Fig. 2524.]
The bars thus set will be in line with the crank axle, but unless the
piston accurately fits the cylinder bore, they will not long remain in
line with the line of motion of the piston rod. For example, Fig. 2524
shows a piston head too small for the cylinder bore, the guides fitting
the bars properly, and the gland and stuffing box fitting the piston
rod; the piston will be suspended in the cylinder, its overhanging
weight being supported by the guides B, the gland, and packing ring.
This would cause friction and rapid wear of the gland bore and guide
surfaces in a direction parallel to the line C, which would gradually
let the piston fall to the bottom of the cylinder bore, touching at the
end of D first. In some engines provision is made to adjust the piston
to take up its wear, which is, it will be seen, a great advantage.
THE HEATING AND POUNDING, OR KNOCKING, OF ENGINES.--The heating of any
part of an engine occurs from one of two causes, viz., either the fit of
the parts is too close, inducing undue friction, or the parts are not in
line.
When the former is the cause the remedy is to ease the fit. If the parts
are not in line, the heating may also be remedied by loosening the fit
of the parts; but this will often induce a pound or knock, hence the
true remedy is to properly align the parts.
The location of a pound may be discovered by placing a piece of metal
wire between the teeth, and resting the other end of the wire upon each
end of the cylinder, guide bars, and bearings of the main shaft,
repeating the operation in each place, and the sense of feeling will
distinctly indicate the location of the knock, by imparting a more
severe shock to the teeth when the vicinity of the knock is approached.
The most prominent location of the causes of a pound are, first, in the
crank pin, from causes to be hereafter explained, and from its wearing
oval at the cross-head journal; and second, at the ends of the
cylinders, or the ends of the guide bars, because of a ridge forming
there as the wear proceeds.
A crank pin cannot wear oval if the brasses are kept adjusted to fit it,
because in that case the brass bore must wear it round; but if there is
any play it wears oval, because the pressure of contact between the
journal and the brass bores is least when the pin is at and near the
points of dead centre, and the most when it is at and near half stroke.
The cross-head pin wears oval because the pressure between the pin and
its bearing is in a line with the connecting rod, and there is but
little wear on the pin in a direction at right angles to the rod.
Ridges form at the ends of the cylinder bore and at the ends of the
guides for the following reasons:--
Referring to the cylinder, the location of the piston stroke in the
cylinder bore alters as the connecting-rod keys pass through the rod,
because that alters the length of the connecting rod, and therefore the
path of the cross-head guides on the guide bars, and also that of the
piston in the cylinder.
As the piston rod is shortened there is less wear at the extreme end of
the cylinder bore farthest from the crank, and the same remark applies
to the guide bars.
If the piston head travels past the end of the cylinder bore and into
the counterbore at each end, a distance equal to the amount of taper on
the connecting-rod keys, or equal to the amount the connecting-rod
length will alter while those keys are passed through the rod (to take
up the journal and brass wear), the piston head will (if the rod is kept
to its original length within that amount) always travel to the end of
the cylinder bore, and no ridge should form on account of the length of
the rod altering; but even then a slight ridge may form because the wear
is naturally less at the ends. Thus in the middle of the cylinder length
the whole thickness of the piston head, piston rings, and of the
follower passes over the bore, while at the ends only the flange of the
piston head at one end and the follower at the other passes over the
metal of the bore; hence the friction and wear are less.
The ordinary cause of pounding and heating is a want of truth in the
alignment of the crank pin, or in that of the cylinder, main shaft, or
guide bars.
[Illustration: Fig. 2525.]
The method to be employed to line an engine, or to discover if it is out
of line, depends upon the design of the engine and its condition; thus
an engine having a Corliss frame has the slides to receive the cross
head made at a true right angle to the end face which meets the cylinder
end; equidistant from the centre of the gland hole or axis of the piston
rod, and the end of the frame fitting either the bore of the piston or
the turned flange of the cylinder cover; hence the guide bars must be
true if the frame is got up true, the fit of the frame end to the
cylinder end insuring truth in the guide or cross-head slides, providing
that the centre line of the frame, during the turning and planing
operations, leads from the centre of the cylinder end of the frame to
the centre of the crank-shaft brass; or, in other words, the planing and
boring of the frame must be true with a line running from the centre of
the cylinder end of frame to the centre of location for the crank shaft.
This will not only cause the outside of the frame casting to stand at
its proper level when the cylinder bore stands horizontally level; but
it will insure that the crank-shaft bearing brasses both be of equal and
of a proper thickness through the crown.
The engine being properly lined at first will not be liable to get out
of line, excepting so far as affected by the wear of the crank-shaft
bearing, which will cause the crank shaft to drop, as shown in Fig.
2525, where A A represents the true centre line of the cylinder and
guide bars, which, when the crank is in the position shown in the cut,
should be coincident with the centre line of the connecting rod and the
crank, but the crank brass having worn below the centre line of the
connecting rod and crank, the crank will get out of line as denoted by
the line B B.
[Illustration: Fig. 2526.]
As a result, a portion of the piston movement and pressure which should
be exerted on the crank after leaving the dead centre, will be exerted
on it before it reaches the dead centre, thus causing a back pressure,
involving a loss of power. Furthermore, the relative position of the
eccentric to the valve gear will be altered, impairing the proper set of
the valves; hence it follows that the wear of the crank bearing in this
direction should be taken up (by raising the lower brass) before it
becomes excessive. To find how much the bottom brass requires raising,
or whether it requires raising or not, find the centre of the crank
shaft, and from this centre strike the circle B, in Fig. 2526, whose
diameter must equal that of the crank pin A, and place the edge of a
spirit-level coincident with the perimeters of the crank pin and circle,
as shown in the cut. When the bubble of the spirit-level stands in the
same position as it does when the level is placed upon the bore of the
cylinder or along the piston rod, the crank will be in line with the
cylinder bore.
As a rule, the cylinder bore of a horizontal engine stands horizontally
true, and the crank centre line should also stand so when the crank is
on its dead centre, but if such is not the case the crank centre line
must nevertheless stand true with the axial line of the cylinder, when
the crank is on the dead centre.
[Illustration: Fig. 2527.]
If, instead of having a Corliss frame and fixed guide bars, the engine
has a flat bed and adjustable guide bars, as shown in Fig. 2527, the
operation is as follows:--
In setting up a new engine it is obvious that if the flanges of the
cylinder are planed parallel with its bore and at the proper distance
from its axial line, and the pillow block is made of the proper height,
a line stretched axially true with the cylinder bore will pass through
the centre of bore of pillow-block brasses, or be equal in height from
the engine bed; but the length of the cylinder being only about
one-fifth of the distance from the cylinder to the centre of pillow
block, any error in the planing of the cylinder flange true to the
cylinder bore becomes magnified five times at the pillow block; hence it
is necessary to stretch a line through the cylinder bore and set the
cylinder so that the line, being axially true with its bore, will pass
the pillow block at the centre of the bore of its brasses. This is
sometimes done by inserting thin pieces of sheet tin, metal, or even
paper beneath the cylinder flanges and the bed, and in the requisite
positions. The method of stretching the line is shown in Fig. 2527. F is
a device for holding the line at that end. It consists of a frame in the
form of a cross, with adjusting screws at the end of each arm, and a
small hole at its centre to receive the line. The other end of the line
A must be secured, under as much tension as the line will safely bear,
to a piece of wood clamped to the engine frame at R. The adjustment of
the line is made by measuring its distance from the walls of the bore of
the cylinder at one end and of the bore of the gland hole at the other
end, using a pair of inside calipers or a wire gauge. The latter should
be bent in its length to admit of adjusting the same by straightening to
increase, or still further bending to diminish, its length to suit the
requirements.
The wire, when applied, should only just meet or touch the line and not
bear the least hard, or it will spring the line, causing an error of
adjustment that will be serious when multiplied by the length of the
line to the pillow block as compared with the length of the cylinder
bore.
If the pillow block is planed on its bottom face and has its brasses
fitted, the latter may be marked off for boring from the line A, Fig.
2527, when stretched to set the cylinder, thus avoiding a second
adjustment of the line A A.
Suppose now that it is required to line the brasses in the pillow blocks
true to be bored (the pillow blocks being bolted in position). The
distance of the face P, of the brass from the stretched line A, in Fig.
2527, must equal the distance from the centre of the length of the
crank-pin journal, to the face of the large crank hub, and this distance
may be shown by a line marked on the edge of the brass flange.
Place a straight-edge C, Fig. 2527, having a line D parallel with its
edge E, so that this line will be in the centre of the width of the
pillow-block jaws, and at a right angle to the line A. The line D will
then represent the axial line of the crank shaft, and may be used as the
centre from which to mark the lines on the brasses used to set them by
for boring. To test if A and D are at a right angle, or to set D to A, a
large square should be used. If the side face P P of the pillow block
stands parallel to A, as it should do when it is true, it will serve to
chuck the pillow block by, thus boring the brasses in their places in
the pillow block, with the centre line of the bore at a right angle to
P. If otherwise, two flat places should be filed on the brasses, as
shown in Fig. 2528, in which C is the straight-edge, and A the
stretched line as before, H and I representing the flat places whose
distance from A, as shown at J J, may be made to represent the thickness
of the crank from its large hub face to the centre of length of
crank-pin journal; hence the depth of the flat places will show how much
to take off the face of the brass to leave it of the proper thickness.
[Illustration: Fig. 2528.]
A straight-edge placed across these flat places, or true to the lines H
I, must stand at a right angle to the line D, so that by setting the
brasses by the flat places they will be bored to stand at a right angle
to A. To set the brasses the other way a circle is struck from D, as a
centre, upon the faces of the brasses as in the end view, Fig. 2528, in
which the straight-edge C is shown wedged in the bore of the brasses,
which is the most convenient way when it can be done.
The line D is carried down on the end face of the straight-edge, and the
latter is used as a support for the compass points while striking the
circle M, which is defined more clearly by indenting it with fine
centre-punch marks. The height of the centre for bore of brasses may be
carried from the centre line of the cylinder A A to the end of the
straight-edge C, by placing another straight-edge across the engine bed
and measuring from the end of C to A.
Suppose now that the brasses are bored, and the position of the pillow
block is to be set, and the process is the same, the line D being marked
true from the bore of the brasses, and the pillow blocks adjusted until
D is at a right angle to line A A.
Though in a new engine every part may be made as true as possible in the
details of manufacture, yet when the parts come to be put together
errors of alignment will generally be found to exist. These errors may
be too minute for discovery in the separate piece, and yet form
important defects in the finished engine.
In rough practice these defects are left to remove themselves by
abrasion and wear, the process being to allow the parts to be somewhat
loose (wherever possible) in their adjustment, and adjust them closer as
the abrasion proceeds.
This is termed letting the parts _wear down to a bearing_. But the very
process of wearing _down to a bearing_ attests that the parts have not
been properly fitted to a bearing, whereas to attain the best possible
results the parts should be fitted to a bearing, because in wearing down
to a bearing, undue abrasion, and to some extent or in some degree,
roughness of the wearing surfaces, must ensue, because the strain
intended to be distributed over the whole _intended_ bearing area is
limited to the _actual_ bearing area. It is necessary, therefore, that,
in putting an engine together, each part be properly fitted to its
place, and that it be subsequently adjusted in its fit and position with
relation to the other parts to which it is connected.
The fitting of the single piece is a test of its individual or
disconnected truth; the subsequent or second adjustment is a test of its
truth with relation to the others. Thus a pair of brasses may fit a
journal perfectly, but that is no assurance that the brasses are so
bored as to bring the rod holding them in proper line to enable
connection at the other end without springing or bending the rod.
Furthermore, it often happens that the frame work of an engine does not
form a base for the whole of the parts, thus in a large stationary
engine, the end of the main shaft or crank shaft farthest from the crank
(generally called the _outboard_ bearing) is generally supported by a
bearing having an independent foundation, and as this foundation does
not exist until the engine comes to be permanently fixed for operation,
its alignment must be performed when setting the engine. In an old
engine this foundation may settle, or the wear itself may throw the
engine out of line, so that the lining of an engine becomes periodically
a necessity.
As a general rule a want of alignment induced by wear or incurred from
repairs to the parts principally affects the main shaft, the cross head
remaining more nearly true; and, with the exception of the crank pin,
the same holds good with reference to a new engine.
Now while an error of alignment may exist in any direction, it is true,
nevertheless, that an error in any direction will be discoverable if the
parts be tested at four equidistant parts of the stroke or revolution,
as, for instance, on the two dead centres of the crank and at the
highest and lowest points of the path of rotation of the crank pin;
hence attention may be confined to those four points.
Suppose then an engine already put together requires to be tested for
being in line, and we have to test--
1st. The alignment of the main or crank shaft vertically.
2nd. The alignment of the main shaft horizontally.
3rd. The axial truth of the crank pin with the main or crank shaft.
4th. The adjustment of the crank shaft for vertical height, with
relation to the cross-head journal.
Referring to this last, it may be necessary to remark that the axial
line of the main shaft may be parallel when viewed either vertically or
horizontally with the cross-head journal, and yet if a line be passed
through the centre of the cylinder bore, and prolonged past the crank
centre, the latter may fall above or below that line, but it will
generally be below, because from the weight of the crank shaft its
bottom bearings wear the most; and, further, to whatever extent those
bearings wear after being in proper line, the crank shaft will fall too
low.
We may now subdivide the errors of alignment of a crank shaft thus:--
1st. Its axial line, when viewed vertically, may form an acute angle to
the axial line of the cross-head journal.
2nd. It may form an obtuse angle with the cross-head journal when so
viewed.
3rd. It may, when viewed from the crank-pin end of the engine on about a
horizontal position, be too high or too low at the crank-pin end only.
4th. It may be too high or too low at the outboard end only.
5th. It may be too high or too low at both ends, although parallel to
the cross-head journals.
It will be found on consideration that with the exception of the
last-named case, the connecting rod forms the best test whereby to
discover an error in any of these directions, because it magnifies the
error and makes it more plainly discernible. It will further be found
upon careful observation, that although a combination of these errors
may exist, the connecting rod will serve to discover each error
separately, as well as the collective error, because, although in some
respects two distinct errors may have the same general result, yet the
result will be different if taken in detail, and it follows, therefore,
that the testing must be taken or made in detail first.
[Illustration: Fig. 2529.]
To test the parallelism of the axial line of the crank shaft with that
of the cross-head journal, when viewed vertically: In Fig. 2529, let A A
represent a line true axially with the bore of the cylinder, and B B a
line at a right angle to A A, and passing through the centre of the
pillow block or bearing spaces. If the engine were in line, B B would be
coincident with the axial line of the crank. Suppose, however, that line
B C represents the actual centre line of the crank, not then being at
right angles to A, the end E of the connecting rod, if connected to the
crank pin as shown, and made a good working fit so that there is no play
of the pin in the brasses, will not come fair laterally with the bearing
in the cross head. The amount of the error is the amount it is out of
true in the length of the crank-pin journal, multiplied by the product
of the length of the connecting rod (from centre to centre of the bores
of the brasses) divided by the length of the crank-pin journal. It is
apparent, however, that if the crank shaft be set to have its axial line
at B B instead of at B C, the error at E D will be corrected, and thus
we may employ the connecting rod to set the crank shaft in line.
It is, however, not sufficient to try the crank on one dead centre only
(as will be seen presently), hence we place it on the other, and move
the cross head to the other end of its stroke, and again try the end E
of the connecting rod with the cross-head journal, and if it falls to
one side, and _on the same side as before, but to a less amount_, it
demonstrates that the axial line of the crank forms with the line A A an
acute angle. If, however, instead of falling too much laterally towards
the side F of the cross head, it fell too much towards D, but more so
when tried with the crank on the dead centre nearest to the cylinder
than when tried with the crank on the other dead centre, then it is
proof that the axial line of the crank shaft forms with A A an obtuse
angle.
[Illustration: Fig. 2530.]
The reason that the error will be more plainly shown with the crank on
one dead centre than when on the other is shown in Fig. 2530, in which A
A is a line coincident with the axial line of the cylinder bore, and B B
the axial line of the crank shaft, from C to D is the plane of
revolution of the crank pin, while G represents the crank centre. The
points at C and F denote points central to the length and diameter of
the crank-pin journal. Now, the centre line of the connecting rod for
one dead centre is represented by E D, and for the other by F C, and it
will be seen that the point at E is farther from A than is the point at
F. It will be observed that the point D falls _outside_, while the point
C falls _inside_ of A A, and yet the centre line of the connecting rod
stands, in both cases, at the same angle to the centre line A A of the
engine, and in both cases throwing the end of the connecting rod,
represented by the points at E F, _outside_ the line A A.
If the connecting rod does not, when connected to the engine, as in Fig.
2529, fall true into the cross-head bearing, the error is the same _in
amount_ and comes on the outside of the cross-head journal with the
crank placed on each respective dead centre, it is proof that either the
flange of the crank-shaft brass (which is between the crank face and the
frame) is too thick, or the inside flange of the connecting-rod on the
crank pin is too thick, or else the crank is too thick, measured from
the crank-pin journal to its inside hub face, the error being in the new
crank or new brass, if one has been put in.
[Illustration: Fig. 2531.]
It may here be remarked that if the bore of the crank-pin brasses of the
connecting rod is not at right angles to the centre line of the rod
itself, the end E, Fig. 2529, might fall either inside or outside,
laterally, of the cross-head bearing, but in this case the error will
show more at one end of the stroke than at the other, for reasons which
are explained with reference to Fig. 2530; hence it follows that the
connecting-rod brasses should be properly fitted to their journals, and
made to lead true before using the rod to line the engine by. In some
cases it is more convenient to connect the rod at the cross-head end,
and try the other end with the crank-pin journal, as shown in Fig. 2531.
In this case, however, the connecting rod will (whenever the axial line
of the crank shaft is out of square, forming an acute angle with the
centre line A A, as in Figs. 2529 and 2530), fall laterally inside the
crank-pin journal when on one dead centre, as in Fig. 2531, and outside
when on the other dead centre, as in Fig. 2532, the respective amounts
of error being in this case equal for the two positions. The reason for
this is that the plane of revolution of the crank pin falls outside of
the centre line in one case, and inside for the other, as shown in Fig.
2530 at D C.
[Illustration: Fig. 2532.]
[Illustration: Fig. 2533.]
[Illustration: Fig. 2534.]
[Illustration: Fig. 2535.]
If the axis of the crank axle formed an obtuse angle to the engine
centre line A A in Fig. 2529, the connecting-rod end tried with the
crank pin, as shown in Fig. 2531, would fall outside of the crank-pin
journal when the latter was on the dead centre nearest to the cylinder,
as shown in Fig. 2534, and inside of the crank-pin journal when on the
other dead centre, as in Fig. 2535.
Now, suppose either of the errors to exist, and the alignment be
neglected, then if the brasses at each end be keyed up to fit their
respective journals, then the body of the rod must be bent into a bow
shape, and the strain of forcing or springing it into this shape will
fall upon the journals, which will heat and pound in consequence.
It is now to be explained how to test if the axial line of the crank
shaft is at a right angle to that of the cross-head journal, when viewed
from the crank-shaft end and horizontally.
From a want of parallelism in this direction, heating of the crank pin
and cross-head journals is _sure_, and a pound or thump is, to some
extent, liable to occur, and the cause, if the error is slight, is
difficult to discover, save by using the connecting rod to test it with.
When a thump occurs at the end of the stroke (when the crank is on a
dead centre), it may arise from a ridge at the cylinder, or at the
guide-bar end, or from the connecting-rod brasses being insufficiently
keyed up; but when it occurs while the crank is at half stroke these
causes are eliminated, and the cause must be looked for in either a
crank pin not parallel to the crank shaft, or, as in the case now under
consideration, because of one or the other of the crank-shaft journals
being too low.
Assuming the crank pin and crank shaft to be axially true, one with the
other, we may proceed to show separately the cause of the heating and
that of the pounding, if the crank journal is too low at either end.
[Illustration: Fig. 2536.]
In Fig. 2536, let A represent the cross-head journal, and B B a line
parallel to it. Let B C represent the axial line of the crank shaft
(being out of parallel because the crank end is too high or the other
end too low). Let F F represent the centre line of the crank pin when at
the top, and G G when at the bottom of its path of rotation, and it will
be observed that the vertical distance between the crank pin and the
axial line of the cross-head journal is less on one side than on the
other; thus in the figure distance D is less than E. We have in this
case measured these distances on a plane at a right angle to the
cross-head journal, but it will make no difference if we measure them on
a plane with the path of rotation of the crank pin, as will be seen in
Fig. 2537, in which the distance from the centre of the crank pin at two
opposite points in its path is represented by dots shown at E F, and
from E to H measures less than from F to H, H representing the centre of
the cross-head journal.
[Illustration: Fig. 2537.]
In Fig. 2537, let A represent the axial line of the cross-head journal,
B a vertical line at a right angle to A; C representing the crank shaft
extended by a dotted line, so as to enable comparison with A; D the
crank, E and F the centre of the crank-pin journal, and G G a line at a
right angle to cross-head journal A.
Now G, being at a right angle to A, represents what should be the plane
of rotation of the crank pin, whereas C, being out of parallel with A,
causes the path of rotation to be in the path from E to F, or as D
compared to B; supposing then that the bores of the connecting-rod
brasses to be axially parallel one to the other, and keyed up properly,
and when at E one bore of those brasses will stand parallel to E while
the other is parallel to A, or when at the bottom of the crank rotation,
one bore will be parallel to F and the other parallel to A. Thus the rod
will be twisted, and the strain due to this twist will cause the
bearings to heat. That this twisting is continuous throughout the whole
revolution may be seen by the want of parallelism of the dotted line
(representing the crank pin when on the dead centre) with A
(representing the cross-head journal).
It is now to be observed that if the plane of the crank rotation were at
a right angle to the axis of the cross head, as it should be, the path
of the centre of the crank-pin journal would be in the plane of G G,
whereas it falls outside as at E, and inside as at F, while at H it is
coincident; hence it appears that starting from a dead centre H, the rod
bends, passing at that end outward to E (when the crank has made a
quarter revolution), where it attains its maximum bend, thence
diminishing until finally ceasing, when the crank reaches the other dead
centre. As soon, however, as it passes the last dead centre a bend in
the opposite direction takes place, attaining its maximum at F, and
ceasing at H. This bending also causes undue friction and the consequent
heating of the journals; furthermore, if there be any _end_ play between
the brasses and the journals, there will be a pound, as the brasses jump
from one end of the journal to the other at different parts of the
stroke. It is obvious that if the crank end of the crank shaft was too
high instead of too low, as in our example, then the effects would be
the same, but E would fall on the inside instead of the outside of G,
while F would fall outside instead of inside.
[Illustration: Fig. 2538.]
[Illustration: Fig. 2539.]
[Illustration: Fig. 2540.]
To discover if the crank shaft is out of parallel in the direction here
referred to, connect the connecting rod to the cross-head journal,
setting the brasses up to a close working fit. At the other end of the
connecting rod put the strap keys and brasses in their places, but not
on the crank-pin journal. Place the crank in its highest position, and
lower the end of the rod down to the crank-pin journal, as shown in Fig.
2538, and if the crank shaft is parallel (in the respect here referred
to) to the cross-head journal, the brass flanges will just meet the
faces of the crank-pin journal, as shown in Fig. 2539. If, however, the
crank end of the crank shaft is too low, as in our example, the flanges
of the brasses will fall to one side of the crank-pin journal, and that
side will be toward B, Fig. 2540, when the crank pin is at the top, and
toward C, Fig. 2541, when it is at the bottom of its path of rotation.
The effects will be precisely the same, and in the same direction with
relation to the various parts of the crank's revolution, if the
crank-pin end of the shaft was of correct height; but the other end was
too high, hence, in correcting the error, it is desirable to place the
engine on the dead centre, so as to determine which end of the shaft to
operate on--that is to say, whether to raise the crank-pin end or lower
the other end. But suppose the error to be that the crank-pin end of the
shaft was too high instead of too low, then, the testing being continued
as before, the effects will be of the same general character, but
altered with relation to the specific parts of the revolution. Thus,
when the crank is at the bottom, the rod would fall towards A, Fig.
2542, and when at the top, it would fall in the opposite direction--that
is, towards D, Fig. 2542.
[Illustration: Fig. 2541.]
[Illustration: Fig. 2542.]
We now come to one of the most common errors in the alignment of the
parts of an engine, and to the one that it is the most difficult to
locate or discover, namely, a want of parallelism between the axial line
of the crank pin and that of the crank shaft.
This generally arises from improper methods in the chucking of the crank
to bore it, or from errors induced in fastening the crank to its shaft.
The results are precisely alike in both cases, supposing, of course, the
errors to exist in the same direction in the two cases.
The error in chucking usually consists in planing one surface of the
crank, and bolting the planed surface against the chuck to bore both
crank holes. In this case the crank holes will be out of true to twice
the amount the lathe face plate may be out of true, and to whatever
amount the crank may alter its form from having its surface metal
removed.
To avoid these errors the large bore and its hub face should be turned
at one chucking, and this hub face should be bolted to the face plate
for the second chucking, the small end swinging free, except in so far
as the ends of the plates may touch against it to steady it.
[Illustration: Fig. 2543.]
The error in putting the crank on may occur from the key springing the
crank out of true, and if the crank is shrunk on from too great an
allowance for shrinkage or improper heating for the shrinkage or
contraction, as it is sometimes termed. Referring to the error in
keying, it is more liable to occur when the crank bore and its seat upon
the shaft are made taper, than when made parallel, because it is a
difficult matter to insure accuracy in the fit of the taper, and the key
pressure will spring the crank over on the side at which it is the
easiest fit. In Fig. 2543 let A represent the end of the crank shaft; B
the key, and C the crank shown partly in section: suppose the crank bore
(whether made taper or parallel) has a slightly easier fit on the side D
than on the side E, and the pressure of the key (supposing it to fit
properly top and bottom) would spring the crank over in the direction
shown in the figure, the axial line of the crank pin standing at the
angle denoted by the line F, instead of parallel to the axial line of
the shaft. Suppose the crank to be put on by hydraulic pressure, and the
key to fit on the sides and not on the top and bottom, then its fit to
its seat on the shaft would depend on the truth and smoothness of its
bore and seat on the shaft, the amount allowed for the forcing fit and
the amount of the error. If the latter amount was so small that the
crank would fit at both ends, but simply fit tighter at E E than at D,
the crank would remain true, but might possibly get loose in time. This
would be especially liable to occur if the tool marks on the bore and
seat were so deep that the contact was mainly at the tops of those marks
or ridges which would be apt to compress. But if the surfaces were
cylindrically true and smooth, and the amount allowed for forcing was
sufficient as stated to give the bore and seat contact at D, with a key
fitting sideways, the crank would probably remain tight and true.
Were the bore and its seat parallel the crank would remain true, no
matter whether the key fitted on the sides or at the top and bottom,
providing the key fitting top and bottom were bedded fairly from end to
end.
When the surfaces are not smooth, but contain tool marks or ridges, an
unequal pressure of the key at one end, as compared to the other, sets
the crank over, as shown in the figure, because the key pressure
compresses the ridges and lets the crank move over.
[Illustration: Fig. 2544.]
Supposing the strain of the key, or keys, to be depended upon to hold
the crank, they must fit top and bottom, and their accurate fit becomes
of the first importance; because not only is it necessary that they fit
equally at each end, but they must also fit equally across the width of
the key at each end. For example, in Fig. 2544 is a key binding most at
the opposite corners, as denoted by the dotted surfaces A B, and the
result will be that the key pressure would tend to twist the crank in
the direction of D E, having C as a centre of motion, providing that the
error was equal at A and B; but in proportion as the error was greatest
and the fit tightest at A, or at B, would the centre of motion be moved
nearer to either point.
Supposing now that the crank is to be shrunk, or contracted on, then the
points of consideration are (supposing the crank to fit properly to its
seat, whether the same be either parallel or taper) that the hub of the
crank opposite to the throw is the weakest and is likely to give most
in the process of contraction, so that if one part (as F) of the crank
be made hotter than another (as G) it will give way more, and this will
twist the crank. This is specially liable to occur if an excessive
amount of difference in the bore and seat diameters has been allowed for
contraction.
[Illustration: Fig. 2545.]
It may not happen that a crank pin is out of truth in a direction in
which the error will show plainest when the crank is on its dead
centres, or at half-stroke; but if a crank pin, tested in those four
positions, fails to show any error when tested by the connecting rod, it
will be true enough for all practical purposes, and true enough to avoid
heating and pounding, both of which evils accompany an untrue crank pin.
Suppose, now, that a crank pin stands out of true in the direction shown
in Fig. 2545, in which A A represents the axial line of the cylinder
bore prolonged, and B B the axial line of the crank shaft (the two being
parallel or in proper line). Let E E represent the centre line of the
connecting rod when the crank is on one dead centre, the axial line of
the crank pin being at C C. Then the brasses being keyed up to fit the
crank pin, the centre or axial line of the connecting rod would stand as
denoted by E E. But the brasses at the other end of the rod being keyed
up to fit the cross-head journal, and their lines being at a right angle
to the line A A, we have that the rod is at that end endeavored to be
held parallel to A A; hence, keying up the connecting-rod brasses on the
crank pin would tend to bind the rod, one end standing parallel to A A,
and the other parallel to E E.
This would place great strain on the outer radial face of the cross-head
journal, as well as on the cylindrical body of the journal.
When, however, the crank pin arrives at the opposite dead centre, as
denoted by the dotted lines in Fig. 2545 (G G representing its axial
line, and F F the centre line of the connecting rod at a right angle to
G G), the want of truth in the pin throws the cross-head end of the
connecting rod against the inside face of the cross-head journal. Hence,
twice in each revolution is the connecting rod bent, and twice does it
jam from side to side of the cross-head journal.
It may now be pointed out that if we take either dead centre singly, and
connecting the rod at the crank-pin end, try it at the cross-head end,
and it will be a difficult matter to determine whether any want of truth
at the latter end is caused by the crank pin being out of axial truth,
or whether it is the crank shaft itself that is out of line. But there
is this difference between the two cases. When the error is due to want
of alignment in the crank shaft, the connecting rod will show the error
_on the same side_ of the cross head, no matter on which dead centre the
crank pin stands; but when it is due to the crank pin, the rod will fall
inside the cross head on one dead centre, and outside when tried on the
other dead centre, as is shown by the respective lines E and F, in Fig.
2545; E being at a right angle to C, and F at a right angle to G.
[Illustration: Fig. 2546.]
Again, it has been shown that when the shaft was out of line, a point on
the crank-pin journal passed outside of the cylinder centre line at one
dead centre and inside at the other; but when the pin is axially out of
parallel, the path of a point on its journal will remain in the true
plane, as is shown in Fig. 2546, the point being taken at the
intersection of E and C C. A A represents the path of rotation of the
same, which is parallel to the true face B of the crank.
From the angle of the axial line of the pin being in opposite
directions, when on opposite dead centres to the axial line of the crank
shaft, the bore of the brasses cannot wear to suit the error, which,
therefore, only diminishes by the wear of the crank pin. Suppose the
error to be 1/64 inch in a crank-pin journal 3 inches long, and that the
connecting rod is 6 feet long, the error at the cross-head end of the
rod will amount to 3/8 inch.
[Illustration: Fig. 2547.]
In Fig. 2546 the error is shown to exist in an opposite direction,
throwing the rod to the other side of the cross-head journal. But, in
this case, the crank, when on the dead centre nearest to the engine
cylinder, throws the connecting-rod end against the inside face of the
cross-head journal, as denoted by the line E, which is on the opposite
side of A A to what it is in Fig. 2545. Again, when on the other dead
centre, the line F F, in Fig. 2546, falls _outside_, while F F, in Fig.
2545, falls _inside_ of A A, and it is by this difference that we are
enabled to know in which direction the crank pin is out of true. To find
the amount to which it is out of true in the length of its journal,
place the crank on one dead centre, and with the connecting-rod brasses
keyed up firmly home on the crank pin, and the other end of the
connecting rod entirely disconnected from the cross head, mark on the
latter a line coincident with the side face of the rod end, as at D,
Fig. 2547. Then, with the crank pin placed on the other dead centre,
mark another line on the cross head, coincident with the other side face
of the rod, at C, Fig. 2547. Now, suppose that the line D shows the rod
to fall 3/8 too much on that side, and line C shows it to fall (when on
the other dead centre) 3/8 too much on the other side of the journal,
and that the length of the rod is 6 feet, while that of the crank-pin
journal is 3 inches, then the latter, divided into the former, gives 24,
and this sum divided into the 3/8, the rod end falling out of true at C
and D, Fig. 2547, gives us 1/64-inch as the amount the crank pin stands
out of true in its length; hence, to correct the error, we may file on
the crank pin a flat place at each end, as shown in Fig. 2548 by the
lines C D, and then file on the top and the bottom of the crank pin a
flat place B, 1/128-inch deep, and of equal depth all along the journal;
by then filing the crank pin round and bringing the flat places just up
to a circle, we shall have reduced the diameter of the crank pin by 1/64
inch, and have made it axially true with the cross-head journal. It is
important, however, to bear in mind that, in this case, the crank pin is
supposed to be out of true in the direction shown in Fig. 2545, and to
stand axially true with the cross-head journal, when the crank is placed
at half stroke, top and bottom, the crank shaft being in proper line.
[Illustration: Fig. 2548.]
If the axial line of the cross-head journal stands truly horizontal, the
flat places on the crank pin may be filed horizontally level, with the
crank placed on the corresponding and respective dead centres. But as
the length of the cross-head journal is so short, it is difficult to
gauge, if it does stand axially exactly horizontal, hence it is better
to try the rod, or follow the above directions; especially as the
cross-head journal and crank shaft may be in line without being axially
horizontal.
Suppose now that the axial line of the crank pin stands true with that
of the cross-head journal when the crank is on either dead centre, but
out of true when at the top and bottom half stroke. The connecting rod,
connected as before, and tried with the cross head, will fall first to
one and then to the other side of the cross-head journal, and the
direction in which the crank is out of true may be known from the
position of the crank pin when the error shows itself.
[Illustration: Fig. 2549.]
[Illustration: Fig. 2550.]
If the error exists to an extent that is practically measurable, a pound
in the journals, as well as their heating, is the inevitable result. In
Fig. 2549, for example, the rod end is shown in section, and it will be
noted that the error being in the direction there shown, and the crank
pin in the respective positions there shown, the brass bore only
contacts with the journal at each end, and that the diameter of the bore
of the brasses is greater than the diameter of the crank pin journal to
_twice_ the amount the crank pin is out of line. Now let us place the
crank at the top of its revolution, as in Fig. 2550, and as its axial
line then stands parallel to that of the cross-head journal, the brass
bore is too large to fit the crank pin journal and there is lost motion.
From the time the crank pin passes the dead centre this lost motion
increases in amount until it becomes sufficiently great to slam the rod
over against the side of the cross-head journal, while at the same
instant the crank pin pounds in the connecting-rod brasses. At what
precise part of each quarter crank revolution this action will occur,
depends upon the amount the crank pin is out of line; but the more it is
out the nearer to the dead centre it will be, and, conversely, the
nearer true it is the nearer the crank will approach its highest and
lowest positions before the pound takes place. If it is attempted to key
up the brasses so as to spring the rod and let them close along the
journal, the brasses will heat in proportion to the amount of error;
hence when the crank pin pounds with the brass properly adjusted, and
heats while keyed up enough to stop the pound, the crank pin is out of
true.
To test the alignment of an engine with stretched lines take out the
piston and rod, and take off the connecting rod, then fasten a piece of
iron at the open end of the cylinder so that it will hold a stretched
line true with the axis of the cylinder bore. Provide at the crank end
of the engine bed a fixed piece of wood to hold the other end of the
line, and then with a piece of wire as a gauge set this line (tightly
stretched) true with the cylinder bore. Then place the crank pin at the
top of its path of rotation and drop a plumb line from the centre of its
journal length, and this line should, if the crank shaft is horizontally
level, just meet the stretched line. If it does not do so place a spirit
level on a parallel part of the crank shaft, and if the shaft is not
level it should be made so, and so adjusted that the line from the
centre of the length of the crank pin journal just meets the stretched
line from the cylinder bore.
To test if the axial line of the crank shaft is at a right angle to the
cylinder bore axis move the crank pin nearly to its dead centre, and
measure the distance from the middle of its length to the stretched
line. Then move the crank pin over to nearly the opposite dead centre,
and (by means of the plumb line) measure the distance of the plumb line
from the stretched line. To be correct the plumb line from the crank pin
will during this movement just touch the stretched line.
To test if the stretched line is fair with the centre of the crank shaft
place a square on the end of that shaft and even with its centre, and
the blade should then just meet the stretched line.
The edges of the guide bars may also be tested with the stretched line,
and the top and bottom of the guide-bar flanges may be tested to prove
if the bars are of the correct height.
To further test the bars place a spirit-level across them and lengthwise
on them.
If the piston rod and connecting rod are in place the alignment may be
tested as follows; Let the piston rod be as far out of the cylinder as
possible, and stretch a line to one side of it, just far enough off to
clear the guide bars, &c. Set this line as follows: Let it be in line
with the rod as sighted by the eye when standing some few feet away from
it but horizontally level with the centre of the rod, set it parallel to
the rod with a rule or its equivalent. Then the centre of the crank-pin
journal should measure from the stretched line, the distance of the line
from the piston rod added to half the diameter of that rod. This test,
however, is not very accurate on account of the difficulty in setting
the line, and because the piston rod may not have worn equally on each
side.
SETTING SLIDE-VALVES--An engine slide-valve may be so set as to
accomplish either one of three objects. First, to give equal lead for
each stroke; second, to cause the live steam to be cut off and expansion
to begin at an equal point in each stroke; and third, for the exhaust to
begin at an equal point in each stroke.
If we, set the eccentric so that the exhaust will begin at corresponding
points for the two strokes, the valve lead will not be equal, and the
exhaust opening will be greater when the piston is at one end of the
cylinder than it will be when the piston is at the other end.
If the eccentric be set to cut off the steam at corresponding points for
the two strokes, then the lead, the admission, and the exhaust of the
steam at one port will differ (with relation to the piston movement)
from that at the other. It is generally preferred to set the eccentric
so as to give equal lead for the two ports when the piston is at the
respective ends of its stroke, which gives an equal amount of exhaust
opening when the piston is at the respective ends of its stroke.
The only operations properly belonging to the setting of a slide-valve
are those of finding the true dead centres of the crank pin, and setting
the eccentric to give the valve the desired amount of lead. It is
generally found, however, that the length of the eccentric rod requires
a little correction, and as this must be done before the eccentric can
be set, the setting operations should be conducted with a view to making
the correction as early as possible.
In many of the instructions given by various writers it is directed to
first square the valve, which is to attach the parts and move the engine
crank, or fly-wheel, through one revolution, to ascertain if the valve
moves an equal distance on each side of the centre of the cylinder
ports, correcting the length of the eccentric rod until this is the
case. This is an error, because on account of the angle of the eccentric
rod the valve does not, when set to have equal lead at each end of the
stroke, move an equal distance on each side of the cylinder ports, but
travels farther over the port nearest than it does over that farthest
from the crank.
When the travel of the valve is equal to twice the width of the steam
port, added to twice the amount of steam lap, the valve does not fully
open the farthest port from the crank. When the valve-travel is more
than this amount both ports may open fully, but the error due to the
unequal valve-travel from the angularity of the eccentric rod is
increased. That the amount of error induced by squaring the valve is
appreciable, may be seen from the fact that with 1-1/4 inch steam ports,
3/4 inch steam lap, and 4-1/2 inches of valve-travel, it amounts to
about 1/8 inch with an eccentric rod 4 feet long. As the eccentric rod
has (if a solid one, as in the case of a locomotive) to be operated upon
by the blacksmith to alter its length, and requires some accurate
setting for alignment after having its length corrected, it is obviously
preferable to obtain its exact length at once. This may be done with
less work than by the squaring process, which is entirely superfluous.
[Illustration: Fig. 2551.]
Assuming, then, that all the parts are properly connected and oiled, the
valve is set as follows: Upon the face or edge of the fly-wheel an arc,
true with the centre of the wheel, should be drawn, as at A B, in Fig.
2551, marking it on opposite sides of its diameter and opposite to the
crank pin P. The engine should then be moved in the opposite direction
to that in which it is to run, until the guide block I is very near its
full travel. A straight-edge must then be placed to bear against, or be
coincident with, the end face of block I, and held firmly while a line
is drawn across the edge of the guide bars, as shown at C. There should
then be fastened to the floor (which must be firm, and not give under
the engineer's weight), a piece of iron W, having a deep centre-punch
mark, or its equivalent. A steel tram-rod T, pointed at each end, is
then set in the centre-punch mark at W, and with the upper end D a line
made across the wheel edge or face. The fly-wheel must then be moved so
that the crank passes the dead centre, the guide block moves back and
away from the line C, and then approaches it again. When the end of the
guide block is again coincident with the line C, the tram should be set
as before and a second line, F, marked on the fly-wheel rim, and from
these two lines, D and F, the crank may be placed upon its true dead
centre as follows:--
[Illustration: Fig. 2552.]
In Fig. 2552 a section of the fly-wheel rim is shown (enlarged for
clearness of illustration); from the lines D, F the centre E is found,
and marked with a centre punch dot to define it. It will be obvious,
then, that if the fly-wheel be moved until this line and dot come fair
with the upper edge of the tram T, the guide block will be at the exact
end of its travel, and the crank, therefore, on its dead centre. By a
similar operation performed with the guide block at the other end of the
guide bars, and with lines on the other side of the wheel rim (as shown
at B, J, K), the other centre L may be found. In obtaining these
centres, however, a question arises as to the direction in which the
wheel should be moved for bringing the guide block up to the lines at C,
and for marking the lines D F and J K, or for bringing E or L true with
the tram point. If the fly-wheel be moved in the opposite direction to
that in which the engine is to run, the cross-head journal and crank pin
will bear against the boxes of their brasses in the direction in which
they will have contact when the engine is running. Suppose, for example,
that the top of the fly-wheel when the engine is in motion moves from
the cylinder, then the cross-head and crank-pin journals, driven by the
piston, will bear against the half-brass nearest to the cylinder, which,
_when the force-producing motion is applied to the fly-wheel instead of
to the piston_ will be the case when the fly-wheel is moved in the
opposite direction. By moving the fly-wheel in an opposite direction to
that in which the engine is to run, the lost motion in the journals and
bearings is therefore taken up in the proper direction so far as the
connecting-rod brasses are concerned, and any lost motion between them
and their journals will not impair the set of the valve, as would be the
case were the fly-wheel moved in the direction in which it is to run.
But by moving the fly-wheel backwards the play in the eccentric and in
all the joints between it and the valve spindle is up in the wrong
direction, because the power to move the rods is being applied in the
opposite direction to that in which it will be applied when the engine
is running, and, therefore, the play motion of the jointed or working
parts will cause a lost motion impairing the set of the valve.
Now there are generally more working parts between the eccentric and the
valve than between the crank pin and the piston, and hence more
liability for lost motion to exist, and it follows that in such case it
is better to move the engine in the direction in which it is to run.
It may be remarked, however, that the play may be taken up in the proper
direction in both cases, and the engine be brought upon its dead centre,
by moving it in the opposite direction to that in which it is to run,
and that in setting the eccentrics they be moved on the shaft in the
direction in which the engine is to run, as forward for the forward
eccentric, and backward for the backward one (assuming the engine to
have a link motion, and, therefore, two eccentrics).
It is obvious that any other resting place may be used instead of the
floor for the tram; thus in a locomotive the wheel guard may be used,
the tram T being used to mark lines on the upper part of the wheel rim,
instead of opposite the crank. To set the valve, place the fly-wheel on
its dead centre, moving the fly-wheel as directed until one of the
points (E or L, say E) comes fair with the point of the tram; then move
the eccentric on the shaft until the steam port is open to the required
amount of lead, and fasten the eccentric to the main shaft. Next move
the fly-wheel around until on the opposite dead centre, and if the lead
is the same in amount for both ports the valve is set. Suppose, however,
that in this last case the lead is too great; then it shows that the
eccentric rod is too long, and it must be shortened to an amount equal
to half the difference in the lead. Or suppose that the lead when the
wheel was tried on the last dead centre L, was less than for the other
port; then the eccentric rod must be lengthened to half the amount of
the difference. Assuming that the rod was too long by 1/32 of an inch,
then it may very often be shortened by simply heating about six inches
of its length to a low red heat, and quenching it in water. If the rod
has a foot which bolts on a corresponding foot on the eccentric, then to
lengthen it a liner of the requisite thickness may be placed between the
two feet.
[Illustration: Fig. 2553.]
Suppose there is an equal amount of lead at each end but the amount is
not sufficient or is too great: then the eccentric must be moved on the
shaft until the proper amount of lead appears at the port. The lead must
then be again tried at the other dead centre. In moving the eccentric,
however, it must, under all conditions, be moved in the direction in
which it will rotate, for reasons already given. The best method of
measuring the lead where the lines on a rule cannot be seen is with a
lead wedge P, as shown in Fig. 2553; this, if slightly forced in, will
mark itself, showing how far it entered.
[Illustration: Fig. 2554.]
In some practice the position of the valve is transferred to the valve
stem outside of the stuffing box or gland, as shown in Fig. 2554,
sectional view. The valve stem being disconnected from the rod or arm
that drives it, the valve is moved by hand to have the proper lead, as
at A; a centre-punch mark is then made outside the stuffing box and a
tram B rested thereon; with the other end of the tram a mark C is made
on the valve stem. A similar mark is made on the stem when the crank is
on the other dead centre, and the tram and marks, applied as shown, are
employed instead of measuring the lead at the ports themselves. This
involves extra work, but gives no more correct results. It involves
marking lines on the valve stem, which is objectionable. If several
trials have to be made there is a confusion of lines on the valve stem,
and the wrong one is apt to be taken. On the other hand it affords a
facility for setting the valve without having the steam chest open,
which may in some cases be desirable. If this plan be adopted the lines
on the valve rod should not be defined by centre-punch marks, for they
will cut the packing in the stuffing box.
When the eccentrics are secured to the shaft by a set-screw only, and
not by a feather, it is an excellent plan, after they are finally set,
to mark their positions on the shaft, so that if they should move they
may be set to these marks without moving the engine around.
For this purpose take a chisel with the cutting end ground to the form
of a fiddle drill, one cutting edge being at a right angle to the other.
The chisel must be held so that while one edge rests upon the axle, the
other edge will bear against the radial face of the eccentric. A sharp
blow with a hammer upon the chisel head will make a clean indented cut
upon the axle and the eccentric, the two cuts exactly meeting in a point
where the eccentric bore meets the axle circumference, so that when they
coincide the eccentric is in its proper position.
If the eccentrics of a locomotive should slip when the engine is upon
the road, and there are no marks whereby to readjust them, it may be
done approximately as follows:--Put the reverse lever in the end notch
of the forward gear, then place the crank as nearly on a dead centre as
the eye will direct, and open both the cylinder cocks, then disconnect
the slide-valve spindle from the rocker arm, and move the valve spindle
until the opening of the port corresponding to the dead centre on which
the crank stands will be shown by steam blowing through the cylinder
cock, the throttle valve being opened a trifle. The position of the
valve being thus determined, the eccentric must be moved upon the shaft
until the valve spindle will connect with the rocker arm without being
moved at all. The throttle valve should be very slightly opened,
otherwise so much steam will be admitted into the cylinder that it will
pass through any leak in the piston and blow through both cylinder cocks
before there is time to ascertain which cock first gives exit to the
steam.
Instead of finding when the crank pin is on the dead centre by means of
the process shown in Fig. 2551, it may be found as in Fig. 2555, which
is for a vertical engine. On the face of the crank and from the centre
of the crank shaft as a centre, draw a circle B equal in diameter to the
diameter of the crank pin. Then take a spirit-level C and apply it to
the cylinder bore and note where its bubble stands. Then apply the
spirit-level to the perimeter of the crank pin A and circle B, and move
the crank until the spirit-level bubble stands in the same position as
it occupies when applied to the cylinder bore. If the cylinder bore
stands truly vertical the bubble will in both cases stand in the middle
of the spirit tube; but in any event, the bubble must stand in the same
position when applied to the crank as when applied to the cylinder
bore, in which case the crank will be on its dead centre whether the
cylinder bore be horizontal, vertical, or at an angle, the dotted line E
passing through the centre of the crank and the axis of the cylinder
bore.
[Illustration: Fig. 2555.]
When an engine has two eccentrics, so as to enable the engine to run in
either direction, as in the case of a locomotive, it is necessary to
consider which eccentric is to be set for the forward, and which for the
backward motion. In American locomotive practice it is usual to let the
eccentric nearest to the wheel, and, therefore, the most difficult to
get at, be for the backward motion, which is the least used, and
therefore the least liable to get loose upon the axle.
The eccentric that connects to the top of the link is usually that for
the forward motion, and hence that which connects with the eccentric
farthest from the wheel.
In testing the lengths of the eccentric rods, work may be saved after
the engine is first placed on its dead centre by putting the
reverse-lever in the forward notch of the link, and adjusting the
forward eccentric until the valve has the proper lead. Then set the
reverse-lever in the back notch and move the backing eccentric (in both
cases moving them in the direction in which they will run), until the
proper amount of lead appears. The engine may then be placed on the
other dead centre, and the lead both for forward and backward gear
measured, so that if there are any errors both the rods may be corrected
for length; but for the final trial the crank pin must be set on its
dead centre for each direction of motion separately, so as to take up
any lost motion in the connecting-rod brasses.
[Illustration: Fig. 2556.]
In the case of large marine engines it is not practicable to move or
rotate the engines to set the valves, and the eccentrics are therefore
adjusted to their positions on the crank shaft by lines before the crank
shaft is put into its place or bearings. First, the throw of the crank
is set to stand horizontally true by the following method: From the
centre of the crank shaft strike a circle of the diameter of the crank
pin, as shown in Fig. 2556, at A, and draw upon the face of the crank a
line that shall just meet the two circles as denoted by the line B,
using a straight-edge, one end of which rests upon the crank pin, while
the other end is coincident with the perimeter of the circle A.
[Illustration: Fig. 2557.]
By means of the wedges shown at C D adjust the crank until the line B
stands horizontally level, tested by a spirit-level. A straight-edge
having straight and parallel edges is set horizontally level, beneath
the eccentric, so that its edges will stand parallel with the throw line
of the crank. On this straight-edge, and parallel to the edges, is
marked the line A A, Fig. 2557. The first process is to mark on A A the
centre of the crank shaft K, which is done as follows: Over K is placed
the fine line B B, suspending the weights or plumb bobs at B B;
coincident with this line and across A A, are marked two lines C D;
midway between C D is marked E, which therefore stands directly beneath
the shaft centre. From E the line F is drawn distant from E to the
amount of lap added to the lead the valve is to have. From F as a centre
two lines are drawn across A, their distance apart equalling the full
diameter of the eccentric; the plumb line is then placed over the
eccentric, and the latter is rotated on the shaft until the plumb lines
come exactly fair with the lines G H.
[Illustration: Fig. 2558.]
It is obvious that instead of using plumb lines a square may be employed
to mark the lines C D, and to set the eccentric to the lines G H, the
square being applied as at S and S´, in Fig. 2558.
[Illustration: Fig. 2559.]
In this example it has been assumed that the direction of crank rotation
was to be as denoted by the arrow; but, suppose the crank rotation
required to be in the opposite direction, then the marks on the
straight-edge would require to be located precisely the same, but the
position of the eccentric throw-line would require to be as in Fig.
2559, the perimeter of the eccentric being set to the lines G H as
before. The eccentric rod being supposed to connect direct to the valve
spindle, without the intervention of a rock shaft, for if there is no
rock shaft the eccentric leads in the direction of rotation, while if
the engine has a rock shaft the eccentric follows the crank-pin in the
direction of rotation, and F must be marked on the crank-pin side of E,
as in Fig. 2560.
[Illustration: Fig. 2560.]
[Illustration: Fig. 2561.]
If two eccentrics are used, as in a link motion, the lines for setting
one eccentric are equally applicable to both; the lap and lead line F
being located on the crank-pin side of E when there is a rock shaft, as
is supposed to be the case in Fig. 2561; and on the other side of E when
there is no rock shaft; and in this case the eccentric that is to
operate the valve to make the engine run forward must have its
throw-line following the crank pin, as at J, in Fig. 2561; the eccentric
K operating the valve for running backward. Conversely, in the absence
of a rock shaft, the throw-line of the forward eccentric leads, while
that of the backward eccentric follows the crank pin.
When the line of connection of the eccentric rod is not parallel to the
axial line of the cylinder bore, the crank must be placed horizontally
level (or if it be a vertical engine, on the dead centre), but instead
of the straight-edge being placed parallel to the throw-line of the
crank, it must be placed at a right angle to the line of connection of
the eccentric rod.
[Illustration: Fig. 2562.]
Thus in Fig. 2562 the engine is supposed to be a vertical one, and the
crank is, therefore, placed on its dead centre, its throw-line being
vertical instead of horizontal as in our previous examples (which were
supposed to be for a horizontal engine). It is also supposed to have a
rock shaft A; hence the straight-edge is set at a right angle to the
line of connection of the eccentric rod which is denoted by B.
It is obvious that to set the crank throw-line vertical the circle B in
Fig. 2509 may be used, the spirit-level being resorted to to discover
when the crank stands vertical.
[Illustration: Fig. 2563.]
An example in the erection or setting of framed work is shown in Fig.
2563, which represents a side elevation of a frame put together in four
parts, two side and two end frames. A and B are journal bearings
requiring to stand parallel and true one to the other, B being capable
for adjustment in distance from A by means of the adjusting screws G, H.
The bearings C, D, E, F, are to be parallel one to the other and to A,
B. Their proper relative distances apart, and the axes of all the
shafts, are to stand at a right angle to the side frames.
[Illustration: Fig. 2564.]
Fig. 2564 represents an end view of the frame, the ends T being bolted
to the side frames S and S´ at I, J, K, and L.
Now it is obvious that the ways for the bearings A, B, C, &c., may be
trued out, ready to have the brasses fitted before the framework is put
together, and that from their positions they would have to be planed out
at separate chuckings; supposing, of course, the frame to be too large
to be within the capacity of the machine table. It would be difficult to
cut all the surfaces of the bearing ways to stand in the same plane,
unless there were some true plane to which all might be made common for
parallelism.
Furthermore, unless the surfaces where T is fastened to S and S´ are
properly bedded to fit each other, bolting them up would spring and bend
the frames out of their normal planes. To meet these requirements, there
are given to the side frames a slightly projecting surface where the
feet of T meet them, and furthermore, the feet of T themselves project
beyond the sides of T as shown. These projecting pieces may therefore be
planed to a common plane without planing the sides of the respective
frames; and this plane should be as nearly as can be parallel with the
body of each frame surface. The surfaces of the bearing ways may then be
planed parallel to those of the projections, and the jaw surfaces true
to the side surfaces, and all the bearing ways will stand true if the
frames be properly set--when put together with the bolts. But unless the
bedding surfaces at I, J, K, L, be made to bed and fit properly, the
whole truth of the bearing ways and their distances apart across the
framework may be altered. Thus, supposing the feet of T at I and J to
meet S as denoted by the dotted lines O R, and whether the fault lie
with the feet of T or with the projections on S the result will be that
the pressure of the bolts holding I J to S will bend S so that its plane
will be a curve as denoted by the dotted line P P, and the distances
apart of the journal ways B B and D D respectively will be wrong, being
too wide on account of the bend outward of S.
But the feet may touch on the opposite corners, the surfaces of S´ or of
T being out of true or out of full contact, as denoted by the dotted
lines V W on K, L; in this case the frame S´ would be bent to the curve
Q Q, and the journal ways would be too close together.
On the other hand, the want of fit between these surfaces may be in the
direction of the length of the frame instead of the direction of its
height, as has been supposed; or it may be in one direction on one foot
and in another direction on another foot. But in whatever direction it
does exist, it will inevitably bend and twist the frame.
It must not be taken for granted, that because these surfaces have been
planed or milled, that therefore they are true; because frames of this
class cannot, if large, be held without springing them to some extent
from the pressure of the bolts or other devices necessary to hold them
to be cut.
It is not uncommon to plane the surfaces as true as may be, and put the
frames together, bolting them up tight, and then applying the
straight-edge trammel and rule to test the truth, correcting any error
that may be found by inserting pieces of paper, sheet tin or material of
requisite thickness on one side of the surfaces, so as to offset the
error in their fit and bring the framing true; but this is not the
proper way, because it reduces the area of contact, and furthermore
renders a new testing and adjustment necessary whenever the frames are
taken apart. It is better therefore to apply a straight-edge to the
surfaces and true them to it, testing them vertically as by placing the
straight-edge across K L, and longitudinally across S´, at K and the
corresponding projection at the other end of the frame, filing them
until they appear true.
The holes through the frame may be drilled before filing these surfaces,
so as to reduce the area to be filed. Since the end frames T do not in
this example carry any journals or mechanism, the position of T is not
so particular as it otherwise would be; hence, the holes in its feet may
be marked off and drilled independently of the frame, the holes being
drilled a little too small to allow for reaming with the holes in the
frame. The framing will then be ready to put together (all machine work
upon them being supposed to be done). The feet of all such frames should
be planed true, so that the frame, when put together, may stand true and
steady when placed upon a level floor or foundation, and in this case
the distance and parallelism of the feet surfaces will be true with the
ways or bearings, affording much assistance in holding the frame while
putting it together. The height of the holes may be measured and marked
from the feet surface, thus insuring truth as far as height is
concerned. Lines may be drawn or marked on each side frame, at the
proper distance from and parallel with the jaws of the ways A, B, thus
completing on the side frames the marking of the location of the centres
of the holes for bolting the end frames on.
If the frames were of a size to be sufficiently easily handled, the end
frames might be put in their places, and the whole framework set true,
so as to mark the holes in the end frames from those already drilled in
the side frame. But if the use of a crane were necessary to lift them,
it would be better to mark the holes on the end frames, and drill them
before putting the framework together at all, leaving sufficient to ream
out of the holes to bring them fair, notwithstanding any slight error in
drilling them. In this case, a line denoted by the dotted line X in Fig.
2564, should be drawn across the frame, and the holes at I and J be made
equidistant on each side of it, as well as the proper distance apart. X
must be at a right angle to the trued foot surfaces at I J, so as to
cause the side frames to stand vertical while their feet are horizontal.
Supposing now the holes to be drilled and the frames are to be bolted
together, the whole frame may be held temporarily together by bolts
passing through the side frames at each end, or a bolt may be passed
through the holes F to steady it. Indeed, if these holes F have been
accurately bored, a neatly fitting mandrel passed through them should
hold the side frames true. The end frames T having been set to stand at
a right angle to the side frames, and with their holes at I J, &c., as
near fair as may be with the holes in the side frames, two feet, as I J,
may have their holes reamed fair with the holes in the side frames, and
tightly fitting bolts be driven in and screwed firmly home. Before
reaming the other holes (as K L) of each end frame, the jaws to receive
the bearing boxes should be tested for alignment one with the other.
Truth, in this respect, being of the utmost consequence for the
following reasons:
Suppose the bearing ways on one side frame to stand higher than those on
the other, then, the shafts will not stand level in the frame unless
(except in the case of the brasses or boxes in B) the lower brasses are
made of unequal thickness through the crown, to an amount equal to that
of the error. In the case of the brasses in A, C, D, E, the joint faces
of all the brasses of one side frame would require to be made thinner
beneath the journal than above it on the high frame, and thicker beneath
than above on the low frame, This would entail much extra work in
planing, marking, and boring the bearing boxes or brasses, and be an
inferior job when done.
Again, the bores of all the brasses would not be parallel to the crown
or bedding faces, and this error would entail the following extra work:
1. Ascertaining the amount of the error, and allowing for it in marking
the brasses; 2. The setting of the ways of the brasses out of true with
the ways when clinking them for boring; and, finally, extra fitting or
filing the brass bores when fitted with the shafts in place. This extra
fitting would be necessary for the following reasons:
When the surfaces of work are to be parallel, they can be measured with
calipers. Surfaces to be at a right angle can be tested with a square;
those to be in line can be tried with a straight-edge, and in each case
the truth or alignment of the surfaces is tested by contact of the
testing tool. But in the cases where surfaces at an angle are tested or
measured the tools must be set to a line or lines, and the work must be
measured or cut to lines, thus: Suppose it were found that the bedding
surface of the brass B was a certain amount out of alignment with the
corresponding bedding surface on the other side frame, and, by
measurement, this amount determined to be 1/64 inch, then there is a
liability to error in measuring this 1/64. The brasses must be marked
(for boring the same 1/64 out of square, inducing another liability of
error in marking that amount); this marking being done by lines, there
is a liability to error in setting the work to the lines. From these
liabilities to error, it is generally found that work not true in
alignment requires, when it comes to be put together, to have each piece
fitted to its place and corrected for alignment.
But, suppose the ways are made true and in proper alignment, then the
brass bores are simply made of equal thickness at the crown, and on the
sides at a right angle to the inside faces of the ways; and truth, in
these respects, may be measured by actual contact, with the square or
calipers, eliminating the chance of error.
In repairing the machine, or putting in new bearings or brasses; the
measurement and transferring of the error in the ways to the brasses has
all to be gone through with again, and the parts fitted for alignment;
whereas, if the ways are true, the brasses can be made true, and to go
together, with but little, if any, adjustment when tried in their
places.
[Illustration: Fig. 2565.]
The most accurate method of testing the adjustment of the ways is as
follows: Fig. 2565 represents a plan view of the frame; N represents a
straight-edge applied to the surfaces of the jaws _a_ _b_. The method of
applying this straight-edge is to place one end across a jaw, as _a_,
while the other end is elevated above _b_; then, while pressing the end
firmly against _a_, lower the other end to the face of _b_; if its edge
at that end falls fair with _b_, so as just to touch it, the process may
be reversed--one end being pressed to _b_, and the other lowered upon
_a_. By this means, it will not only be discovered whether the jaws _a_
and _b_ stand square across the frame, but also whether the frame on
either side is sprung. A square _c_ may also be rested against N, and
its blade _d_ tested with the side face of the way, as shown. The same
process of testing should be applied to the other jaw faces _e_, _f_.
Suppose, however, that the width between the jaws _a_, _f_ was less than
that between _e_, _b_, then the straight-edge, when pressed to _a_,
would show a space between its edge and _b_; and also a space between
its edge and _e_, when its other end was pressed to _f_; and, when these
spaces were equal in amount, the frames would be set true in one
direction. To test the truth in the other direction, the straight-edge
should be applied after the same manner to the bottom surfaces _g_, _h_.
It will not answer to rest the straight-edge against the two surfaces
and observe their coincidence with its edge, because any error cannot be
sufficiently, readily, or accurately tested by this means. Nor will it
answer to test by the bearing marks of a straight-edge applied with
marking, unless the coat of marking be very fine and the straight-edge
be moved without any vertical pressure on it; because, under such
pressure, the straight-edge will bend.
The ways for all the bearings should be tested in this manner; so that,
if from any error in the machine work, some of them will not come fair,
the frames may be set to align those that it is of most importance to
align truly; or if there is no choice in this respect, then those
carrying the largest bearing should be set true; because, if it be
decided to correct the error on the other bearing or bearings, there
will be less area to file or operate upon. The setting being complete
the holes may be reamed and the remaining bolts put in, the testing
being repeated after the frame is finally bolted together. If this final
test shows that bolting the frame up has altered the alignment by
springing the frame, the bolts in one foot, as say I, Fig. 2564, may be
slackened and the test repeated; and, if the frame is then found true,
it is the bolting at I that causes the spring, on account of the bedding
surfaces not fitting properly. If I is not found to be at fault, it may
be bolted up again and J tested by loosening its bolts, and so on, until
the location of the error is detected. Furthermore, when the frame is
bolted up, the width of the bearings, as from _a_ to _b_, should be
tested; for in a job of this kind, it will pay to have the framework so
true to the drawing that, if the other parts, as the shafts, bearing
parts, &c., be also made to the drawings, the parts will go together,
thus avoiding the necessity of varying all the other parts from the
drawing to accommodate errors in the framework.
[Illustration: Fig. 2566.]
Among the jobs that the erector is often called upon to perform is that
of patching or repairing pieces that have cracked or broken. Fig. 2566
represents a case of this kind, the fracture being at D. The principle
to be observed in work of this kind is to cause the bolts to force the
fractured pieces together, so that the irregularity or crookedness of
the crack, as at D in the figure, may serve to lock the pieces together.
[Illustration: Fig. 2567.]
Suppose, for example, we were to put on a patch P, Fig. 2567, and there
would be but little to prevent the crack from opening under severe
strain, and the patch would stretch, permitting the crack to open and
finally causing the bolts to break or sheer off. A preferable plan,
therefore, is to put two patches on the sides in the following manner:--
The holes should be drilled through the beam and the plates held against
the beam so that their holes may be marked by a scriber passed through
the holes in the beam. The holes in the plates should be drilled closer
together than those in the beam, so that when driven in they will serve
as keys to close the two sides of the crack together, as shown in Fig.
2568, where it is seen that one side of the bolt bears against the holes
in the patch and the other against the holes in the beam. To facilitate
getting the bolts in place the plates may be heated so as to expand
them.
In cases in which it would not be permissible to drill so many holes
through the beam on account of weakening it, we may use patch bolts with
countersunk heads, as in Fig. 2569. Two only of the bolts pass entirely
through, and it is best to let them be taper, as at A in the figure, the
head not meeting the patch. The hole in the beam, after being reamed
taper, should be filed out on the side B, and that in the patch plates
on the other side, as at C and D, so that the bolts will serve as keys.
After these two bolts are in place and their nuts firmly screwed home,
the holes for the patch bolts may be drilled through the plates and into
the beam. When the countersunk head bolts are fitted they should be
turned down behind the head, so as to leave a part weaker than the bolt,
and then screwed in until the required end breaks off. The taper bolts
should be of steel, but those with countersunk heads may be of iron.
[Illustration: Fig. 2568.]
[Illustration: Fig. 2569.]
ERECTING AN IRON PLANER.--If an iron planer be properly fitted and
erected, the table will be quite solid in the [V]-ways in the bed, and
will not rock or move even though a heavy vertical cut be taken at the
extreme sides of the table, but any error of truth of alignment or fit
either in the bed-ways or the table [V]'s will cause the table to lie
improperly in the [V]'s and to be apt to rock as it traverses. The
author has had planed upon a planer thirty years old, at the Freeland
Tool Works, in New York City, a cast-iron surface 12 × 20 inches, the
metal weighing about 60 lbs., and the surfaces were so truly planed that
one would lift the other by reason of a partial vacuum between the two.
These planed surfaces were exhibited by the author at the American
Institute Exhibition in 1877, and were awarded a medal of superiority.
The manner in which this planer was fitted and erected, and the
principles involved in such fitting and erecting, are as follows:
While it is essential that the foot or resting surface of a planer bed
(whether it stands on legs or rests direct upon its foundation) be as
true as it is practicable to plane it, still it is more essential that
the [V]'s or ways be true, and as the casting will be apt to alter its
form from having the surface metal removed, it is best to plane the side
on which the ways are the last.
When the bed is placed upon the machine to have its resting surface
planed, the casting being uneven, it will be necessary to place packing
pieces of suitable thickness beneath the places where the clamping
plates hold it, so that the pressure of those plates may not spring or
bend the casting.
These packing pieces require to fill up solidly (without lifting the
bed) the hollow places, and it is a good plan to place among them a
piece of strong writing paper for reasons which will appear presently.
In planing the bed all the surfaces should be roughed out before any are
finished. Before any finishing cuts are taken all the clamping bolts
should be loosened and the pieces of paper tried by pulling them, so
that if the casting has altered its form it will be made apparent by
some one of the pieces of paper becoming loose.
In this case the packing must be readjusted, clamping both as lightly as
will hold the work, and all as equally as possible, when the finishing
cuts may be taken.
[Illustration: Fig. 2570.]
The best form of template to plane the ways to is that shown in Fig.
2570, in which B is a side and A an end view. A corresponding female
template being shown at D to be used in planing the table [V]'s.
The length C of the [V] of the template must not be longer than from 4
to 6 inches, or it will be liable to spring or twist from its own
weight. This template is not intended to be used in any sense as a
straight-edge to test the truth of the length of the ways, but rather as
one to test their width apart, and the correctness of the angles. The
top surface A B should be quite true with the [V]'s, being equidistant
from them, so that by testing that surface with a spirit-level it may be
known whether the ways are level either crosswise or lengthwise.
The [V]'s of the template require to have red marking on them so as to
mark the ways when the template is moved, and show that the ways
accurately fit to the template, which is highly important.
In planing the table or platen it is essential to bear in mind that the
area to be planed on the [V] side is always small in comparison with
that to be planed on the other or work-holding side of the table, and as
the planing of this latter surface is sure to cause the casting to alter
its form, it is necessary to plane it first, so that the alteration of
form may occur before and not after the [V]'s have been planed.
In chucking the table to plane its work-holding surface, the packing
pieces must be used as described for the bed, and the bolts placed as
there described.
Both bed and table being planed they require to be fitted together (no
matter how expertly the planing has been done) if a really first-class
job is to be made of them. In doing this it is essential that the bed be
supported at the same points as it will be when the machine is put to
work, for in large or long casting the deflection or bending from its
own weight is sufficient to have an important practical effect. The same
fact will also apply to the table and even to the cross slide, even
though the latter be heavily ribbed and but, say, 5 feet long.
If, therefore, the bed is to be supported by legs, its guideways or
[V]'s should be fitted after the legs are attached. The bed must be
carefully levelled so that the ways may stand horizontally true, which
may be tested by placing the template A B in Fig. 2570 in place and
applying a spirit-level first across and then lengthwise of the upper
surface of the template.
If the bed rests upon a foundation at several points in its length it
should be rested at those points while being fitted and carefully
levelled as before, the template and spirit-level being tried at every
two or three feet of the bed length.
To test the width of the [V]'s and their widths apart in the fitting,
the template A B, Fig. 2570, must be used in connection with red
marking, but to true the lengths of the ways a surface plate about 4
feet long and slightly wider than the width of one side of the ways must
be used, and if the template and the surface plate show the ways true
they will be of the correct width, of correct angle and true planes. But
this does not insure that the two ways are in line one with the other,
and for this purpose separate test blocks are necessary, because the
template is too narrow in width to give a good test, and cannot be made
wider, because in that case its own weight would cause it to spring or
deflect to suit any error in the work.
[Illustration: Fig. 2571.]
These test blocks are simply two pieces of metal, such as shown in Fig.
2571. The lengths of these blocks should be about 8 inches, and the best
way to obtain them true and exactly alike is to make one block and then
cut it into two. They possess an advantage not possessed by a template
that spans both ways, inasmuch as they may be turned end for end in each
way and thus test the accuracy of the angles of each way.
Again, both may be placed in one way, and by various applications in
connection with straight-edge, surface plate, and level they will test
the truth of the ways, both individually and one with the other in a
better manner than by any other method.
Fig. 2572 represents the various positions of the [V] blocks for the
testing, A, B, C, D, E, F, G, H, representing the blocks; straight-edges
may be placed as at I, at J, and at K, and if the ways are true the
straight-edge, lightly coated with marking, should have contact clear
across the upper surface of both [V]-blocks, and a spirit-level placed
on the straight-edge (in each position of the same) should show them to
be level.
The surface P, on which uprights or standards on that side of the plane,
rest, being planed with the [V]-ways will be true with them, and the
uprights may be erected thereon, their base surfaces being fitted to P
until the standards stand truly vertical and parallel in their widths
apart. In testing these uprights they should be bolted home as firmly as
they will be when finally erected, as they will be liable to alter their
set if bolted up more firmly than when tested. These front surfaces
should be at a right angle to the length of the bed [V]-ways, and this
may be tested by placing a straight-edge across their surfaces and
testing it with a square rested against the edge of the planer table.
The method of erecting planers at the Pratt and Whitney Company's shops
is as follows:--
To test the [V]'s, a plate P, Fig. 2573, is applied as shown, its lugs
_a_, _a_^{1} fitting to corresponding sides of the two [V]s; as B, B. In
Fig. 2573 the test is made by inserting thin pieces of tissue paper
between _a_, _a_^{1} and the [V]-sides, the friction with which the
paper is held showing the nature of the fit. Thus, if the paper will
move easily at one end and is tight at the other end of either of the
lugs _a_, _a_^{1} the fit is shown to be defective. When the fit on
these sides is corrected, the plate P is turned around, as in Fig. 2574,
and from a similar tissue-paper test, the other sides are corrected.
Thus the outside angles of the two [V]s are fitted to the same angle;
inside angles are also fitted to the same angle. But it will be observed
that it does not follow that the inside angles of the [V]s are of the
same degree of angle as are the outside halves or angles, unless the two
lugs _a_, _a_^{1} of the plate P have equal angles. It is on this
account that the test is made by tissue paper, rather than by the
bearing marks produced by rubbing P along the [V]s, since that might in
time wear the angles _a_, _a_^{1} out of true. The same plate P may be
used to true the male [V]s on the work-holding table of the machine, as
is shown in Figs. 2575 and 2576, where the table is seen upside down, as
is necessary in order to apply the plate. Here, again, the outside
angles or halves of the [V]s are fitted from the same [V] (_a_^{1}) of
the plate, so that the fit of the table will be true to the bed, even
though the angle on one side of the [V]-ways were not precisely correct,
and there is less liability to error than would be the case were a male
and female plate used instead of a single plate. The alignment next in
importance is that of the uprights, standards, or side frames of a
planing machine, and to enable the correct erection of these, the device
A, Fig. 2577, is employed. It consists of a solid plate fitting into the
[V]-ways of the planer-bed and having two steps, B and C, which receive
the side frames to be erected. The width D is the width apart of the
side frames, and the side surfaces of the steps (as G) are vertical to
the centre line of the [V]-ways of the bed, so that the side frames may
be rested against G on one side, and the corresponding surface on the
other step. The surfaces E, F are at a right angle to the [V]-ways of
the bed, so that when the side frames are against E, F they will be set
square across the machine. The top face of the plate A is planed
parallel to the [V]s of the plate, so that in addition to resting each
side frame against the surfaces (as F G) a square may be rested on plate
A and applied to their trued surfaces, and thus may these side frames be
set true and square, both one with the other, and with the ways in the
bed, without the use of stretched lines and straight-edges, which
secures greater accuracy and saves considerable labor.
[Illustration: Fig. 2578.]
All the smaller parts of the machine may then be erected true to the bed
or the side frames, as may be required, and if it be a small planer, in
which the bed rests upon feet, all that will be necessary in setting the
machine in position to work is to set the surface of the work-table
level. But in the case of a large heavy planer a solid foundation must
be built for the bed, because it will spring, bend, and deflect from its
own weight, and thus the side frames, as well as the bed, may be thrown
out of true and alignment. Fig. 2578 is a side and plan view of the
foundations for a planer, showing the bed-plate in position upon the
same.
[Illustration: _VOL. II._ =TESTING PLANER BEDS AND TABLES.= _PLATE XI._
Fig. 2572.
Fig. 2573.
Fig. 2574.
Fig. 2575.
Fig. 2576.
Fig. 2577.]
The stone blocks forming the base of the foundation require themselves
to rest upon a solid base, and not upon a soil or gravel that is liable
to sink beneath them. The brickwork above them is best laid in cement,
which should be properly set before the planer bed is placed in
position. Near the centre of the bed, and directly beneath the
cross-slide, is shown a screw jack, to take up any sag of the bed, and
cause the [V]s to have a good bearing directly beneath the cutting tool,
which is essential to prevent the table from springing from the pressure
of the tool cut.
FITTING UP AND ERECTING A LATHE.--The first operation will be to true
the bed or shears. If the lathe has raised [V]s on the bed it will be
sufficient to true them only, without truing the flat surfaces. The bed
should during the fitting be supported at the same points as it will be
when in use.
[Illustration: Fig. 2579.]
The method of aligning the lathe heads at the Pratt and Whitney
Company's workshops is as follows: Fig. 2579 is a side and an end view
of a part of a lathe shears A, with the tailstock B thereon. To the bore
of the tailstock there is closely fitted an arbor C, accurately turned
in the lathe, and having at the end D and at E two short sections of
enlarged diameter. A plate F is fitted to the inside [V]s of the shears
(upon which [V]s the tailstock sits). This plate carries a stand G, and
a second gauge or stand G. Stand G fits at its foot into a [V] provided
in F, as shown, the object of which is to so hold G to F that its (G's)
face will stand parallel to arbor C. The stand is so adjusted that a
piece I may be placed between C and G and just have contact with both,
and it is obvious that if this is found to be the case with the
tailstock and the stand placed at any position along the bed, the arbor
C, and, therefore, the bore of the tailstock, must be true, sideways, to
the inside [V]s of the lathe shears. The testing, however, is made at
the enlarged sections D and E, G of course being firmly bolted to F. To
test the height of the arbor C from the [V]s, and the parallelism in
that direction, stand H is provided. It carries a pointer or feeler K,
whose end is adjusted to just touch the enlarged sections D and E of C,
it being obvious that when the degree of contact is equal at these two
sections, with the tailstock and the plate F moved to various positions
along the bed, the adjustment or alignment in that direction is also
correct. The adjustment and corrections may then be made with the
headstock of the lathe in place of the tailstock, the arbor fitting into
the bored boxes of the lathe and extending from it, and having two
sections of the same diameter, as sections E in the figure. Now, suppose
that in the test thus made the bar C proves to stand true in some
locations, but not in others, upon the bed; then it is proof that it is
the [V]s that require correction, while the tailstock is in error in all
cases in which the error is constant, with the tailblock moved in
various positions along the shears.
In some practice the heads are bored after being fitted to the ways, and
in this case the boring bar may be supported by standards fitting to the
lathe bed, running in bearings, and not on centres. There should be
three of these bearings, one at one end of the head, and as close to it
as convenient, another at the other end, as close as will permit the
insertion of the cutters, and the third as far from the second as will
permit the insertion on the bar and between them of a pulley to drive
the bar, which must be splined to receive a feather in the pulley, so
that the bar may be fed through its bearings and through the pulley to
the cut. After the live head has been bored the tailstock or back-head
may be bored from the other end of the bar, so that the standards will
not require to be moved on the bed until the boring is completed. The
bar may be fed by hand, or an automatic feed motion may be affixed to
one of the standards. The heads being secured to the bed while being
bored, there is no liability of error in their alignment, because, even
if the holding bolts spring the heads in clamping them to the bed, the
holes will be true when the heads are firmly home upon the bed, as they
will be when in use, whereas under this condition such will not be the
case if the holes for the spindles are bored before the seats are planed
and fitted.
The feed screw must be placed quite parallel to the [V]s or guides of
the bed, or otherwise the pitches of threads cut in the lathe will be
finer than they should be, and the screw will bind in the feed nut,
causing undue wear to both.
The method employed to test the truth of lathe shears and heads in the
David W. Pond Works, at Worcester, Massachusetts, is as follows:--
[Illustration: Fig. 2580.]
The planing, both of the lathe shears and of the heads, being done as
accurately as possible, the heads are provided with a mandrel or arbor,
to the end of which is secured the device shown in Fig. 2580, in which A
is a hollow cylindrical piece having a threaded and split end, so that
by means of a nut the bore may be closed to tightly fit the arbor
referred to; B, B are two arms, a sliding fit in A, to enable their
adjustment for the width of lathe [V]s, and having a flat place on one
side, as at C C, to receive the pressure of a locking device D, by means
of which B, B may be fastened in their adjusted positions; E, E are
cylindrical arms, a sliding fit in B, B, also having flat sides, and
capable of being secured in their adjusted positions by means of
locking devices F, F.
[Illustration: Fig. 2581.]
[Illustration: Fig. 2582.]
Fig. 2581 is an end view of the device in position on a lathe tail
stock, and Fig. 2582 is an enlarged view (being half full size) of the
devices at the lower end of arms or rods E, E.
At the lower ends of E, E are provided two pieces G, G, which are
capable of adjustment to fit the [V]s H, H of the lathe, as follows:--
The middle pins I are fast in the arms J, but are pivoted in G, the end
pins, as K, are pivoted in G, are flat where they pass through J, and
threaded to receive the nuts, L, of which there are four, two to each
piece G. By operating these nuts, G may be adjusted to bed fair on the
angles on the lathe [V]s H. At M are two fixed pins which afford a
fulcrum, at N and O respectively, to four index needle arms. Two of
these index arms only are seen in the cut, marked respectively P and Q,
which are pivoted at N. Two similar pointer or needle arms are on the
other side of M, being behind P and Q, these two being pivoted
respectively at O. At the lower end of P is a point resting in the
centre of the nut, and similarly the end of Q rests in the centre of the
nut on that side. Similarly the two needles not seen have pointed ends
resting in the centre of the nuts marked respectively L. Between G and J
are two springs placed back to back, which act to hold G away from J.
But it will be seen that if either end of G be forced towards J, as by
passing over a projection on the [V] H, then the pin K, will push nut L,
and this will raise the end of the pointer or needle to a corresponding
degree, and the pointer being pivoted (as at N), its upper end will move
and denote on the graduated index R that there is an error in the lathe
[V], the amount of the error being shown multiplied on account of the
leverage of the needle arms from the pivots.
The pieces G being adjusted to bed fairly on the lathe [V]s, the heads
of the lathe are moved along the lathe shears, and if the [V]s are true
to angle the upper ends of the needles will remain stationary, a
projecting part of a [V] will, however, cause the needle point to move
toward E, while a depression on a [V] would cause the springs K to move
G in, keeping it in contact with the [V], while the needle point would
move away from E. To maintain the needle arms in contact with the nut
heads L, springs S are employed. Variations in the widths apart of the
[V]s on either side of the shears would obviously be shown in the same
manner, the defect being located by the needle movement. The corrections
are made from the contact marks of the heads, caused by moving the heads
along the [V]s and by careful scraping.
Notwithstanding that every care and attention may be taken to make a
lathe true in the process of manufacture, yet when the whole of the
parts are assembled it is found essential to test the truth of the
finished lathe, because, by the multiplication of minute errors the
alignment of the lathe, as a whole, may be found to need correction. A
special inspector is therefore employed to test finished machines before
they leave the works, and in Fig. 2583 is represented the device
employed for testing the alignment of the line of centres of lathes.
Upon the face of the face plate and near its perimeter there are turned
up two steps, as denoted by B and C. The tail-spindle is provided with a
stud S, which fits in the place of the dead centre, and carries what may
be termed a double socket, one-half of which (as F) envelops the stud S,
while the other half (A) envelops and carries a rod R. These two halves
are in reality split sleeves, with set screws to close them and adjust
the fit. By means of the screws E, the sleeve F may be made a tight
working fit upon S, while, by means of screws G, sleeve A may be made to
firmly grip the rod R, which may thus be securely held while still
capable of being swung upon stud S. Upon the outer end of the rod R is
another sleeve I, which is also split and secured to the rod R by means
of screws corresponding to those shown at G. It also carries a pin, upon
which a disk K is pivoted, and a lug through which the adjusting screw V
is threaded. Upon K is a lug which has on one side of it the end of a
spring T, and it is obvious that by operating V the disk K will be
rotated upon its central pin. K carries two lugs, L and M, the latter
being threaded and split. These two lugs receive a sleeve N, threaded
into M, and a close plain fit in L. The small end of this sleeve is
split and is threaded slightly taper, and is provided with the nut P.
Through this sleeve passes a needle Q Q, one end of which is bent as
shown, and it is obvious that by screwing nut P upon N the sleeve will
be closed and will tightly grip the needle Q Q. Now, suppose that the
head of N is operated, and it will move endwise through L and M,
carrying with it the needle Q Q, which will remain firmly clasped in the
sleeve; or suppose that screw V is operated, and K will revolve,
carrying with it the needle Q Q, which will still remain firmly gripped,
and it follows that there is thus obtained a simple means of adjusting
the needle without releasing it.
[Illustration: Fig. 2583.]
The application of the instrument is as follows: To test if the head and
tailstocks are of equal height from the bed, the instrument is set and
adjusted exactly as shown in the engraving, the needle being adjusted to
just touch the diameter of the step at B. The rod R is then swung around
so that the needle comes opposite to the same step B at the bottom of
the face plate, and if the needle just touches there also the adjustment
for tailstock height is correct. Similarly for testing if the tailstock
is set true sideways the needle may be tried in the same manner and upon
the same step, but upon the two opposite sides of the face plate,
instead of at the top and bottom. It now remains to test if the
tailstock is in line in a horizontal direction with the live spindle,
and this is done by reversing the needle end for end in the sleeve N,
and setting it to just touch the face C of the turned step on the face
plate, and if it just touches at the top and bottom as well as at the
two sides the tail-spindle is obviously in line. It may be observed,
however, that if an error in any one direction is found, it is necessary
to go through the whole series of tests in order to precisely locate the
error. Suppose, for example, that the needle, being adjusted as in the
engraving to just touch the step at B, does not touch it when tried at
the bottom of the plate, then the error may be caused in three
ways--thus, in the first place, the whole tailstock may be lower than
the headstock; in the second place, the front end of the tailstock may
be too low; or, in the third place, the back end of the tailstock may be
too high. If the first was the cause, the test with the needle point
tried with face C would show correct. If the second or third was the
cause of the error, the needle point when tried to face C would touch
when applied at the top, but would not touch when tried at the bottom of
the face plate. Another case may be cited. For example, suppose the
needle applied as shown touched at the bottom but not at the top of the
step B, then the test with the needle reversed would show whether the
whole tailstock was too high, or whether the front end only was too
high, or the back end too low. There is one excellent feature in this
device to which attention may be called, which is that the tests are
made on as large a diameter of face plate as possible, which shows the
errors magnified as much as possible.
The same device is used to test if the cross slide of the carriage or
saddle is at a right angle to the lathe shears, the method of its
application being as shown in Fig. 2584. The split sleeve A receives in
this case a rod R, which is laid in the slideway S of the carriage or
saddle, and a long rod H carries the needle-holding devices. The rod R
is held fair against the slideway, and the face of the sleeve A is held
against the edge of the carriage or saddle. The needle Q is then
adjusted to just touch the edge D of the lathe bed. When this adjustment
is made the rod H is swung over to the right and the coincidence of the
needle point again tried with the edge of the lathe bed, the cross
slideway being at a right angle when the needle point touches the edge D
of the lathe bed when tried on the left hand, and also on the right
hand, of the carriage. The stiffening rod U is brought under tension by
a nut operated against a lug on X. To counterbalance the overhanging
weight of the rod H and its attachments, a rod carrying a weight W is
employed. It is obvious that the truth of the operation depends wholly
upon the straightness and parallelism of the enlarged sections P of the
rod R, upon keeping the end face of A in contact with the carriage at Z,
and upon the correct adjustment of the needle to the edge of the lathe
bed.
[Illustration: Fig. 2584.]
SETTING LINE SHAFTING IN LINE.--The following method of adjusting line
shafting or setting it in line, as it is termed, is that generally
adopted in the best practice.
[Illustration: Fig. 2585.]
[Illustration: Fig. 2586.]
[Illustration: Fig. 2587.]
First prepare a number of rude wooden frames, such as shown in Fig.
2585. They are called targets, and are pieces of wood nailed together,
with the outer edge face A planed true, and having a line marked
parallel with the planed edge and about three-quarters of an inch inside
of it. Upon this frame we hang a line suspending a weight and forming a
plumb-line, and it follows that when the target is so held that the
plumb-line falls exactly over and even all the way down with the scribed
line, the planed face A, Fig. 2586, will stand vertical. To facilitate
this adjustment, we cut a small [V] notch at the top of the scribed
line, the bottom of the [V] falling exactly even with the scribed line,
so that it will guide the top of the plumb-line even with the scribed
line at the top; hence the eye need only be directed to causing the two
lines to coincide at the bottom. To insure accuracy, the planed edge A
should not be less than a foot in length. Then tightly stretch a strong
closely-twisted and fine line of cord beside the line of shafting, as
shown in Fig. 2587, placing it say six inches below and four inches on
one side of the line of shafting, and equidistant at each end from the
axial line of the same, adjusting it at the same time as nearly
horizontally level as the eye will direct when standing on the floor at
some little distance off and sighting it with the line shaft.
In stretching and adjusting this line, however, we have the following
considerations:--It must clear the largest pulley hub on the line of
shafting, those pulleys having set-screws being moved to allow it to
pass. If the whole line of shafting is parallel in diameter, we set the
line equidistant from the shafting at each end. If one end of the
shafting is of larger diameter, we set the line farther from the surface
of the shafting, at the small end, to an amount equal to one-half of the
difference in the two diameters; and since the line is sufficiently far
from the shafting to clear the largest hub thereon, it makes, so far as
stretching the line is concerned, no difference of what diameter the
middle sections of shafting may be. The line should, however, be set
true as indicated by a spirit-level.
We may now proceed to erect the targets as follows: The planed edge A in
Fig. 2585 is brought true with the stretched line, and is adjusted so
that the plumb-line B in Fig. 2586 will stand true with the line or mark
B. When so adjusted, the target is nailed to the post carrying the
shafting hanger. In performing this nailing, two nails may be slightly
inserted so as to sustain the target, and the adjustment being made by
tapping the target with the hammer, the nails may be driven home, the
operator taking care that driving the nails does not alter the
adjustment.
[Illustration: Fig. 2588.]
In Fig. 2588 A A represents the line of shafting, B, B two of the hanger
posts, and C, C two of the adjusted targets.
[Illustration: Fig. 2589.]
We have now in the planed edges A of the targets a rigid substitute for
the stretched line, forming a guide for the horizontal adjustment, and
to provide a guide for the vertical adjustment we take a wooden
straight-edge long enough to reach from one post to another. Then
beginning at one end of the shafting, we place the flat side of the
straight-edge against the planed edge of two targets at a distance of
about 15 inches below the top of the shafting; and after levelling the
straight-edge with a spirit-level, we mark (even with the edge of the
straight-edge) a line on the planed edge of each target, and we then
move the straight-edge to the next pair of targets, and place the edge
even with the mark already made on the second target. We then level the
straightedge with a spirit-level, and mark a line on the third target,
continuing the process until we have marked a straight and horizontally
level line across all the targets, the operation being shown in Fig.
2589, in which A represents the line of shafting, B the hangers, and C
the targets. D represents the line on the first target, and E the line
on second. F is the straightedge, levelled ready to form a guide whereby
the line D may be carried forward, as at E, level and straight, to the
third target, and so on across all the targets.
[Illustration: Fig. 2590.]
[Illustration: Fig. 2591.]
The line thus marked is the standard whereby the shafting is to be
adjusted vertically; and for the purpose of this adjustment, we must
take a piece of wood, or a square, such as is shown in Fig. 2590, the
edges A and B being true and at a right angle to each other. The line D,
in Fig. 2589, marked across the targets being 15 inches below the centre
line of the shaft at the end from which it was started, we mark upon our
piece of wood the line C in Fig. 2590, 15 inches from the edge A (as
denoted by the dotted line); and it is evident that we have only to
adjust our shaft for vertical height so that, the gauge being applied at
each target in the manner shown in Fig. 2591, the shaft will be set
exactly true, when the mark C on the piece of wood comes exactly fair
with the lines D marked on the targets.
[Illustration: Fig. 2592.]
For horizontal adjustment, all we have to do is to place a straight-edge
along the planed face of the target, and adjust the shaft equidistant
from the straight-edge, as shown in Fig. 2592, in which A is the shaft,
B the target, C the straight-edge referred to, and D a gauge or distance
piece. If, then, we apply the straight-edge and wood gauge to every
target, and to the adjustment, the whole line of shafting will be
complete.
There are several points, however, during the latter part of the process
at which consideration is required. Thus, after the horizontal line,
marked on the targets by the straight-edge and used for the vertical
adjustment, has been struck on all the targets, the distance from the
centre of the shafting to that line should be measured at each end of
the shafting, and if it is found to be equal, we may proceed with the
adjustment; but if, on the other hand, it is not found to be equal, we
must determine whether it will be well to lift one end of the shaft and
lower the other, or make the whole adjustment at one end by lifting or
lowering it, as the case may be. In coming to this determination we must
bear in mind what effect it will have on the various belts, in making
them too long or too short; and when a decision is reached, we must mark
the line C, in Fig. 2590, on the gauge accordingly, and not at the
distance represented in our example by the 15 inches.
The method of adjustment thus pursued possesses the advantage that it
shows how much the whole line of shafting is out of true before any
adjustment is made, and that without entailing any great trouble in
ascertaining it; so that, in making the adjustment, the operator acts
intelligently and does not commence at one end utterly ignorant of where
the adjustment is going to lead him to when he arrives at the other.
Then, again, it is a very correct method, nor does it make any
difference if the shafting has sections of different diameters or not,
for in that case we have but to measure the diameter of the shafting,
and mark the adjusting line, represented in our example by C, in Fig.
2590, accordingly, and when the adjustment is complete, the centre line
of the whole length of the line of shafting will be true and level. This
is not necessarily the case, if the diameter of the shafting varies and
a spirit-level is used directly upon the shafting itself.
In further explanation, however, it may be well to illustrate the method
of applying the gauge shown in Fig. 2590, and the straight-edge C and
gauge D shown in Fig. 2592, in cases where there are in the same line
sections of shaftings of different diameters. Suppose, then, that the
line of shafting in our example has a mid-section of 2-1/4 inches
diameter, and is 2 inches at one, and 2-1/2 inches in diameter at the
other end: all we have to do is to mark on the gauge, shown in Fig.
2590, two extra lines, denoted in figure by D and F. If the line C was
at the proper distance from a for the section of 2-1/4 inches in
diameter, then the line D will be at the proper distance for the section
of 2 inches, and E at the proper distance for the section of 2-1/2
inches in diameter; the distance between C and D, and also between C and
F, being 1/8 inch, in other words, half the amount of the difference in
diameters.
In like manner for the horizontal adjustment, the gauge piece shown at D
in Fig. 2592 would require when measuring the 2-1/4 inch section to be
1/8 inch shorter than for the 2 inch section, while for the 2-1/2 inch
section would require to be 1/8 inch shorter than that used for the
2-1/4 inch section, the difference again being one-half the amount of
the variation in the respective diameters. Thus the whole process is
simple, easy of accomplishment, and very accurate.
If the line of shafting is suspended from the joists of a ceiling
instead of from uprights, the method of procedure is the same, the forms
of the targets being varied to suit the conditions. The process only
requires that the faced edges of the targets shall all stand plumb and
true with the stretched line. It will be noted that it is of no
consequence how long the stretched line is, since its sag does not in
any manner disturb the correct adjustment, but in cases where it is a
very long one it may be necessary to place pins that will prevent it
from swaying by reason of air currents or from jarring.
The same system may be employed for setting the shafting hangers, the
bores of the boxes being used instead of the shafting itself.
CHAPTER XXX.--LINE SHAFTING.
LINE SHAFTING.--A line of shafting is one continuous run or length
composed of lengths joined together by couplings. The main line of
shafting is that which receives the power from the engine or other
motor, and distributes it to other lines of shafting, or to the various
machines to be driven. In some practice each line of shafting is driven
by a separate engine or motor, so that it may be stopped without
stopping the others. This same object may be obtained by providing a
clutch for each line. It is obvious that in each line of shafting the
length nearest to the driving motor transmits the whole of the power
transmitted by the line, and that the diameter of the shafting may,
therefore, be reduced as it proceeds from the engine in a proportion
depending upon the degree to which the power it is required to transmit
is reduced. It is desirable, therefore, so far as the shafting is
concerned, to place the machines requiring the most power to drive as
near as possible to that end of the shafting that receives power from
the motor. Line shafting is supported in bearings provided in what are
termed hangers, which are brackets to be bolted to either suitable
framing, to walls, posts, or to the ceiling or floor of the building.
The short lengths of shafting that are provided to effect changes of
speed, and to enable the machine to be stopped or started at pleasure,
are termed countershafts. When there is interposed a countershaft
between the motor and the main line of shafting, it is sometimes termed
a jack shaft.
Shafting is usually made cylindrically true either by special rolling
processes as in what is known as "cold-rolled," or "hot-rolled"
shafting, or else it is turned up in the lathe. In either case it is
termed bright shafting. What is known as black shafting is simply bars
of iron rolled by the ordinary process and made cylindrically true only
where it receives its couplings, and for its journal bearings, &c. The
diameter of black shafting varies by a quarter of an inch, and is
usually above its designated diameter by about 1/32 inch.
The main body of the shafting not being turned cylindrically true and
parallel, the positions of the pulleys cannot be altered upon the
shafts, nor can pulleys be added to the shaft as occasion may require
without the sections being taken down and seatings turned for the
required pulleys to be added. Furthermore black shafting does not run
true, and is in this respect also objectionable. Nevertheless, black
shafting is used for some special cases where extra pulleys are not
likely to be required and the shafting is exposed to the weather, as in
the case of yards for the manufacture of building bricks.
The diameters of bright or turned shafting (which is the ordinary form
in which shafting is made, unless otherwise specified) vary by 1/4 inch
up to about 3-1/2 inches in diameter; but the actual diameter is 1/16
inch less than the denominated commercial diameter, which is designated
from the diameter of the round bar iron from which the shafting is
turned; thus a length of what is known as 2-inch shafting will have an
actual diameter of 1-15/16 inches, being parallel, or as nearly parallel
as it is practicable to turn it in the ordinary lathe.
Cold-rolled shafting has its actual diameter agreeing with its
designated or commercial diameter, and is parallel throughout its
length.
In England the diameters of shafting vary by eighths of inches for
diameters of an inch and less, and by quarters of an inch for diameters
above an inch, the commercial and the actual diameters being alike.
The strains to which a line of shafting is subject are as follows: The
torsional strain due to rotating the line of shafting, independent of
the power transmitted; the torsional strain due to the amount of the
power transmitted; and the transverse strain due to the unequal belt
pressures and distances from the bearings of the driving or transmitting
pulleys. The first and the last are, however, so intimately connected in
practice that they may be considered as one: hence we have, 1st, the
torsional strain due to driving the whole load, and, 2nd, the transverse
strain due to the belt pressures being exerted more on one side than on
another of the shaft, and to the belt pulleys being at unequal distances
from the hanger bearings.
The first may be reduced to a minimum by so proportioning the strength
of the line of shafting that it shall be capable of transmitting the
required amount of power at the various sections of its length without
suffering distortion of straightness beyond certain limits, and shall be
at the same time as light as is consistent with this duty and a certain
factor of safety.
Referring for a moment to the above limitation, the weight of the shaft
itself will cause it to deflect between the hanger bearings, and the
amount of this deflection will depend upon the distance apart of the
points of support, or, in other words, of the distance apart of the
hanger bearings.
The second may be reduced to a minimum by so regulating the distance
apart of the hanger bearings that the deflection of the shaft from the
belt pressures shall not be sufficient to produce sensible
irregularities in the axis of rotation of the shaft; by so connecting
the bearings to the hangers that they shall be rigidly held, and yet
capable as far as possible of automatically adjusting their bores to be
true with the shaft axis, notwithstanding its deflection from any cause;
by placing the pulleys transmitting the most power as near to the hanger
bearings as practicable; by so disposing the driving belts as to deliver
the power as near as possible equally on all sides of the shaft; and by
having the shafting and the pulleys balanced so as to run true, so that
the strains on the pulleys shall be equal at each point in the shaft
rotation. From this it appears that the distance apart of the shafting
hangers may vary according to the amount of power transmitted by a shaft
of a given diameter. The following table (given by Francis) gives the
greatest admissible distances between the bearings of continuous shafts
subject to no transverse strain except from their own weight, as would
be the case were the power given off from the shaft equally on all
sides, and at an equal distance from the hanger bearing.
+----------------+------------------------------------+
| Diameter of | Distance between bearings, in feet.|
|shaft in inches.+--------------------+---------------+
| |Wrought-iron shafts.| Steel shafts. |
+----------------+--------------------+---------------+
| 2 | 15.46 | 15.89 |
| 3 | 17.70 | 18.19 |
| 4 | 19.48 | 20.02 |
| 5 | 20.99 | 21.57 |
| 6 | 22.30 | 22.92 |
| 7 | 23.48 | 24.13 |
| 8 | 24.55 | 25.23 |
| 9 | 25.53 | 26.24 |
+----------------+--------------------+---------------+
These conditions, however, do not usually obtain in the transmission of
power by belts and pulleys, and the varying circumstances of each case
render it impracticable to give any rule which would be of value for
universal application.
For example, the theoretical requirements would demand that the bearings
be nearer together on those sections of shafting where most power is
delivered from the shaft, while considerations as to the location and
desired contiguity of the driven machines may render it impracticable to
separate the driving pulleys by the intervention of a hanger at the
theoretically required location. The nearer together the bearings the
less the deflection either from the shaft's weight or from the belt
stress, and since the friction of the shaft in its bearings is
theoretically independent of the journal-bearing area, the closer the
bearings the more perfect the theoretical conditions; but since it is
impracticable to maintain the true alignment of the shaft, and as the
friction due to an error in alignment would increase with the nearer
proximity of the bearings, they are usually placed from about 7 to 12
feet apart, according to the facilities afforded in the location in
which they are to be erected.
It is to be observed, however, that the nearer together the bearings are
the less the diameter, and, therefore, the lighter the shafting may be
to transmit a given amount of power, and hence the less the amount of
power consumed in rotating the shafting in its bearings.
COLD-ROLLED SHAFTING--This is shafting made cylindrically round and
parallel by means of cold rolling, which leaves a smooth and bright
surface. The effects of cold rolling upon the metal have been determined
by Major Wm. Wade, U.S.A., Sir William Fairbairn, C.E., and Professor
Thurston, of the Stevens Institute, as follows:--
The experiments were made upon samples of cold-rolled shafting submitted
by Messrs. Jones and Laughlins, of Pittsburgh, Pennsylvania.
SUMMARY OF THE RESULTS OBTAINED BY MAJOR WADE FROM NUMEROUS EXPERIMENTS
WITH ORDINARY HOT-ROLLED BAR IRON, COMPARED WITH THE RESULTS OBTAINED
FROM THE SAME KINDS OF IRON ROLLED AND POLISHED WHILE COLD BY LAUTH'S
PATENT PROCESS.
------------------------------------------+-------------+---------+---------
| Iron rolled | Ratio of|Average
| while | increase|rate per
+------+------+ by cold |cent. of
| Hot. | Cold.| rolling.|increase.
------------------------------------------+------+------+---------+---------
TRANSVERSE.--Bars supported at both | | | |
ends; load applied in the middle; distance| | | |
between the supports, 30 inches. Weight | | | |
which gives a permanent set of one-tenth | | | |
of an inch, viz. | | | |
} 1-1/2 inch square bars | 3,100|10,700| 3.451 |}
} Round bars, 2 inch diameter| 5,200|11,100| 2.134 |} 162-1/2
} Round bars, 2-1/4 " " | 6,800|15,600| 2.294 |}
| | | |
TORSION.--Weight which gives a permanent| | | |
set of one degree, applied at 25 inches | | | |
from centre of bars. Round bars, 1-3/4 | | | |
inch diameter, and 9 inches between the | | | |
clamps | 750| 1,725| 2.300 | 130
| | | |
COMPRESSION.--Weight which gives a | | | |
depression, and a permanent set of | | | |
one-hundredth of an inch to columns 1-1/2 | | | |
inches long and 5/8 inch diameter |13,000|34,000| 2.615 | 161-1/2
Weight which bends and gives a permanent | | | |
set to columns 8 inches long and 3/4 inch | | | |
diameter, viz. | | | |
} Puddled iron |21,000|31,000| 1.476 |}
} Charcoal bloom iron |20,500|37,000| 1.804 |} 64
| | | |
TENSION.--Weight per square inch, which | | | |
caused rods 3/4 inch diameter to stretch | | | |
and take a permanent set, viz. | | | |
} Puddled iron |37,250|68,427| 1.837 |}
} Charcoal bloom iron |42,439|87,396| 2.059 |} 95
Weight per square inch, at which the same | | | |
rods broke, viz. | | | |
} Puddled iron |55,760|83,156| 1.491 |}
} Charcoal bloom iron |50,927|99,293| 1.950 |} 72
| | | |
HARDNESS.--Weight required to produce | | | |
equal indentations | 5,000| 7,500| 1.500 | 50
------------------------------------------+------+------+---------+---------
NOTE.--Indentations made by equal weights, in the centre, and near the
edges of the fresh cut ends of the bars, were equal; showing that the
iron was as hard in the centre of the bars as elsewhere.
GENERAL SUMMARY OF THE RESULTS OBTAINED BY SIR WILLIAM FAIRBAIRN'S
EXPERIMENTS.
--+-------------------+-----------+-------------------+------------
| | Breaking | | Strength,
| Condition of bar. | weight of |Breaking weight per| the un-
| |bar in lbs.| square inch. |touched bar
| | | |being unity.
--+-------------------+-----------+-------------------+------------
| | | In lbs. In tons. |
1| Untouched (black) | 50,346 | 58.628 26.173 | 1.000
3| Rolled cold | 69,295 | 88.230 39.388 | 1.505
4| Turned | 47,710 | 60.746 27.119 | 1.036
--+-------------------+-----------+-------------------+------------
NOTE.--In the above summary it will be observed that the effect of
consolidation by the process of cold rolling is to increase the tensile
powers of resistance from 26.17 tons per square inch, to 39.38 tons,
being in the ratio of 1:1.5, one-half increase of strength gained by the
new process of cold rolling.
Extract from the general conclusions arrived at by Professor R. Thurston
from experiments.
"The process of cold rolling produces a very marked change in the
physical properties of the iron thus treated.
"It increases the tenacity from 25 to 40 per cent., and the resistance
to transverse stress from 50 to 80 per cent.
"It elevates the elastic limit under torsional as well as tensile and
transverse stresses, from 80 to 125 per cent....
"It gives the iron a smooth bright surface, absolutely free from the
scale of black oxide unavoidably left when hot rolled.
"It is made exactly to gauge diameter, and for many purposes requires no
further preparation.
"The cold-rolled metal resists stresses much more uniformly than does
the untreated metal. Irregularities of resistance exhibited by the
latter do not appear in the former; this is more particularly true for
transverse stress.
"This treatment of iron produces a very important improvement in
uniformity of structure, the cold-rolled iron excelling common iron in
density from surface to centre, as well as in its uniformity of strength
from outside to the middle of the bar.
"This great increase of strength, stiffness, elasticity, and resilience
is obtained at the expense of some ductility, which diminishes as the
tenacity increases. The modulus of ultimate resilience of the
cold-rolled iron is, however, above 50 per cent. of that of the
untreated iron.
"Cold-rolled iron thus greatly excels common iron in all cases where the
metal is to sustain maximum loads without permanent set or distortion."
From this it appears that cold-rolled iron is peculiarly adapted for
line shafting. Suppose, for example, a given quantity of power to
transmit, and that a length of cold-rolled and a length of hot-rolled
iron be connected together to form the line. Then the diameters of the
two being such as to have equal torsional strength, we have--
1st. That the weight of the cold rolled will be the least, and it will,
therefore, produce less friction in the hanger bearings.
2nd. That the cold rolled will be harder, and will therefore suffer less
from abrasion of the journals.
3rd. That being of smaller diameter the journals are more easily and
perfectly lubricated.
The resistance to transverse stress (say) 50 per cent.; but the elastic
limit under transverse stress is increased from 80 to 125 per cent.,
accepting the lesser amount we have in the case of the two shafts.
4th. That the resistance to permanent set or bend will be 30 per cent.
more in the cold rolled.
5th. The accuracy to gauge diameter enables the employment of a coupling
having a continuous sleeve, and gives an equal bearing along the entire
coupling bore.
6th. The reduction of shaft diameter enables the employment of a smaller
and lighter coupling; and
7th. The hubs of the pulleys may be made smaller and lighter, are easier
to bore, and may be bored to gauge diameter with the assurance that they
will fit the shaft.
The friction between the journals of a line shafting and its bearings
depends so intimately upon the distance apart of the bearings, upon the
alignment of the same, upon the accurate bedding of the shaft journals
to the bearings, and upon the amount of transverse strain; and this
latter is so influenced by the amount of power that may be delivered
from one side of the shaft more than from another, that the application
of rules for determining the said friction under conditions of perfect
alignment rigidity would be practically useless. The conditions found in
actual practice are so widely divergent and so rarely alike, or even
nearly alike, that the consideration of this part of the subject would,
in the opinion of the author, be of no practical value. The reader,
however, is referred to the remarks made with reference to the friction
of journals.
To prevent end motion to a line of shafting it is necessary that there
be fixed at some part of the line two shoulders, or collars, on
relatively different sides of a bearing, or of the bearings, these
collars meeting the side faces of the bearing. If shoulders are produced
by reducing the diameter of the journal bearing of the shaft, the
strength of the shafting is reduced to that at the reduced bearing,
because the strength of the whole can be no greater than its strength at
the weakest part. If collars are placed one on each end of the line of
shafting, the difficulty is met that the collars will permit end motion
to the shaft whenever the temperature of the shaft is greater than that
which obtained at the time at which the collars were adjusted, which
occurs on account of the increased expansion of the shaft. On the other
hand the collars will bind against the side faces of the bearing boxes
whenever the shaft is at a lower temperature than it was at the time of
setting the shaft, because of the contraction of the shaft's length, and
this would cause undue friction, abrasion, and wear.
It is preferable, therefore, to place such collars one on each side of
one bearing, so that the difference in contraction and expansion from
varying temperatures shall be confined to the difference in expansion
between the metal of which the bearing and shaft respectively are
composed in the length of the bearing only, instead of being extended to
the difference in expansion between the shaft throughout its whole
length and that of the framework to which the hangers, or bearings, are
bolted.
[Illustration: Fig. 2593.]
The collars may be shrunk on to the shaft so as to avoid the necessity
of set-screws, or if set-screws are used they should be as short as is
practicable so as to avoid the liability to catch against the lacings,
&c., of belts, which, on slipping off the pulley may come into contact
with the set-screw head. The Lane and Bodley Co., of Cincinnati, employ
a collar (for loose pulleys, &c.) in which the radius of the collar for
a width equal to the diameter of the set-screw head, is equal to that of
the set-screw head thus projecting from the centre of the collar
circumference, a slot in the ring affording access to the set-screw
head, as shown in Fig. 2593. By this means the head of the set-screw is
protected from contact with a belt, in case the latter should be off the
pulley and resting upon the shaft.
As a rule it is preferable that the collars, to prevent end motion to
the shaft, be placed at the bearing nearest to the engine or motor; and
this is especially desirable where bevel-wheels are employed to drive
the shaft, because in that case the pitch lines of the wheels are kept
to coincide as nearly as practicable, and the teeth are prevented from
getting too far into or out of gear.
DIAMETERS OF LINE SHAFTING.--The necessary diameters of the various
length of the shafts composing a line of shafting, should be
proportioned to the quantity of power delivered by each respective
length, and in this connection the position of the various pulleys upon
the length and the amount of power given off by the pulley is an
important consideration. Suppose, for example, that a piece of shafting
delivers a certain amount of power, then it is obvious that the shaft
will deflect or bend less if the pulley transmitting that power be
placed close to a hanger or bearing than if it be placed midway between
the two hangers or bearings.
The strength of a shaft to resist torsion is the cube of its diameter in
inches, multiplied by the strength of the material of which the shaft is
composed, per square inch of cross-sectional area, giving the strength
in statical foot-pounds. The application of this rule is to find the
necessary strength of the shaft to convey power irrespective of the
distance from its centre at which it delivers such power.
But since the point at which the power to produce torsion is applied is
at the rim of the pulley, the amount of torsion produced upon a shaft by
a given stress must be obtained by multiplying the given amount of
stress by the radius of the pulley in inches and parts of an inch.
Example: the static stress upon a pulley, 24 inches diameter, is 100
lbs., what static torsion does it exert upon the shaft?
Here, stress 100 × 12 (radius of the pulley) = 1200 = static torsional
stress.
In the following rules for finding the necessary diameters and strengths
of shafts, the margin of extra diameter for strength necessary for
safety is included, so that the given sizes are working diameters.
To find the necessary diameter of shaft from a given torsional
stress.--Rule, divide the torsional stress expressed in statical foot
lbs., by 57.2 for steel, by 27.7 for wrought iron, or by 18.5 for cast
iron, and the cube root of the quotient is the required working diameter
of shaft expressed in inches.
To find the maximum amount of horse-power capable, within good working
limits, of being transmitted by a _shaft_ of a given diameter.--Rule,
multiply the cube of the diameter of the shaft, in inches, by its
revolutions per minute and divide by 92 for steel, by 190 for
wrought-iron, or by 285 for cast-iron shafts, and the quotient is the
amount of horse-power.
Since, in this rule, the horse-power is a given quantity, the diameter
of the pulley is of no consequence, since with a given stress it must
have been taken into account in obtaining the horse-power.
To find the revolutions per minute a shaft will require to make to
transmit a given amount of horse-power.--Rule, multiply the given amount
of horse-power by 92 for steel, by 190 for wrought-iron, or by 285 for
cast-iron shafts, and divide the product by the cube of the diameter of
the shaft expressed in inches, and the quotient is the required
revolutions per minute for the shaft.
The rule adopted by William Sellers and Co. to determine the size of
shafts to transmit a given horse-power is:--Rule, divide the cube root
of the horse-power by the revolutions per minute and multiply the
quotient by 125, the product is the diameter of shaft required.
This gives a shaft strong enough to resist flexure, if the bearings are
not too far apart. The distance apart that the bearings should be placed
is an important consideration. Modern millwrights differ slightly in
opinion in this respect: some construct their mills with beams 9 feet 6
inches apart, and put one hanger under each of the beams; others say 8
feet apart gives a better result. We are clearly of opinion that with 8
feet distance, and shafting lighter in proportion, the best result is
obtained.
The following table (from "Machine Tools," by Wm. Sellers and Co.) gives
the strength of round wrought iron as given by Clark:--
TABLE SHOWING STRENGTH OF ROUND WROUGHT-IRON SHAFTING.
+--------+---------------------------------------------------------+
| | TORSIONAL ACTION. |
| +----------+------------+-----------+----------+----------+
| Dia- | Ultimate | Working | Work for | Horse | Speed in |
| meter | resist- | stress. | one turn | Power at | turns |
| of | ance. | | per | the rate | per |
| shaft. | | | minute. | of one | minute |
| | | | | turn per | for |
| | | | | minute. | one- |
| | | | | | horse |
| | | | | | power. |
+--------+----------+------------+-----------+----------+----------+
| =1= | =2= | =3= | =4= | =5= | =6= |
+--------+----------+------------+-----------+----------+----------+
| Inches.| Stat'l. | Stat'l ft. | Ft. lbs. | H. P. | Turns. |
| |ft. tons. | lbs. | | | |
| 1 | .42 | 27.7 | 174 | .00526 | 190 |
| 1-1/4 | .82 | 54.1 | 340 | .01028 | 97.3 |
| 1-1/2 | 1.42 | 93.5 | 587 | .01779 | 56.2 |
| 1-5/8 | 1.80 | 118.9 | 746 | .02259 | 44.3 |
| 1-3/4 | 2.25 | 148.4 | 932 | .02820 | 35.4 |
| 1-7/8 | 2.77 | 182.6 | 1,147 | .03469 | 28.8 |
| 2 | 3.36 | 221.6 | 1,391 | .04211 | 23.7 |
| 2-1/8 | 4.00 | 265.8 | 1,669 | .05062 | 19.8 |
| 2-1/4 | 4.80 | 315.5 | 1,981 | .05995 | 16.7 |
| 2-3/8 | 5.62 | 371.1 | 2,330 | .07051 | 14.2 |
| 2-1/2 | 6.56 | 432.8 | 2,718 | .08224 | 12.2 |
| 2-3/4 | 8.73 | 576.1 | 3,618 | .1094 | 9.14 |
| 3 | 11.3 | 747.9 | 4,697 | .1421 | 7.04 |
| 3-1/4 | 14.4 | 951.0 | 5,972 | .1807 | 5.54 |
| 3-1/2 | 18.0 | 1,188 | 7,458 | .2257 | 4.43 |
| 3-3/4 | 22.1 | 1,461 | 9,173 | .2775 | 3.60 |
| 4 | 26.9 | 1,773 | 11,136 | .3368 | 2.97 |
| 4-1/4 | 32.2 | 2,127 | 13,345 | .4040 | 2.48 |
| 4-1/2 | 38.2 | 2,524 | 15,851 | .4796 | 2.09 |
| 4-3/4 | 45.0 | 2,969 | 18,635 | .5642 | 1.77 |
| 5 | 52.5 | 3,463 | 21,750 | .6579 | 1.52 |
| 5-1/4 | 60.7 | 4,008 | 25,177 | .7616 | 1.31 |
| 5-1/2 | 69.8 | 4,609 | 28,936 | .8758 | 1.14 |
| 5-3/4 | 79.8 | 5,266 | 33,077 | 1.000 | 1.00 |
| 6 | 90.6 | 5,983 | 37,584 | 1.137 | .880 |
| 6-1/2 | 117 | 7,606 | 47,780 | 1.445 | .692 |
| 7 | 144 | 9,501 | 59,682 | 1.805 | .554 |
| 7-1/2 | 177 | 11,680 | 73,254 | 2.220 | .450 |
| 8 | 215 | 14,180 | 89,088 | 2.694 | .371 |
| 8-1/2 | 258 | 17,010 | 106,836 | 3.232 | .309 |
| 9 | 306 | 20,190 | 126,846 | 3.837 | .261 |
| 9-1/2 | 360 | 23,750 | 149,118 | 4.512 | .222 |
| 10 | 420 | 27,700 | 174,000 | 5.260 | .190 |
| 11 | 559 | 36,870 | 231,594 | 7.005 | .143 |
| 12 | 725 | 47,860 | 300,672 | 9.095 | .110 |
| 13 | 922 | 60,860 | 382,278 | 11.83 | .0865 |
| 14 | 1,152 | 76,010 | 477,456 | 14.44 | .0693 |
| 15 | 1,417 | 93,490 | 587,250 | 17.76 | .0563 |
| 16 | 1,720 | 113,500 | 712,704 | 21.56 | .0464 |
| 17 | 2,062 | 136,100 | 854,862 | 25.86 | .0387 |
| 18 | 2,447 | 161,500 | 1,014,768 | 30.69 | .0326 |
| 19 | 2,880 | 190,000 | 1,193,466 | 36.10 | .0277 |
| 20 | 3,360 | 221,600 | 1,392,000 | 42.11 | .0237 |
| |
| NOTE.--To find the corresponding values for shafts of cast iron |
| or steel, multiply the tabular values by the following |
| multipliers: |
| |
| Cast | | | | | |
| iron | 2/5 | 2/3 | 2/3 | 2/3 | 1.5 |
| Steel | 1.2 | 2.06 | 2.06 | 2.06 | .48 |
+--------+----------+------------+-----------+----------+----------+
+--------+---------------------------+
| | TRANSVERSE ACTION. |
| +-----------------+---------+
| | Under | Under |
| | the gross | the net |
| | distributed |weight of|
| Dia- | weight. | shaft. |
| meter |-----------------+---------+
| of |Distance| Gross |Distance |
| shaft. |of bear-| weight |of bear- |
| |ings for| for |ings for |
| | the | the | the |
| |limiting| span. |limiting |
| |deflec- | |deflec- |
| | tion. | | tion. |
+--------+--------+--------+---------+
| =1= | =7= | =8= | =9= |
+--------+--------+--------+---------+
| Inches.| Feet. | Lbs. | Feet. |
| | | | |
| 1 | 6.6 | 30 | 7.9 |
| 1-1/4 | 7.7 | 55 | 9.2 |
| 1-1/2 | 8.6 | 89 | 10.3 |
| 1-5/8 | 9.2 | 112 | 11.0 |
| 1-3/4 | 9.6 | 134 | 11.5 |
| 1-7/8 | 10.1 | 163 | 12.1 |
| 2 | 10.5 | 193 | 12.7 |
| 2-1/8 | 11.0 | 227 | 13.2 |
| 2-1/4 | 11.4 | 264 | 13.7 |
| 2-3/8 | 11.8 | 305 | 14.2 |
| 2-1/2 | 12.5 | 359 | 15.0 |
| 2-3/4 | 13.0 | 450 | 15.6 |
| 3 | 13.7 | 566 | 16.5 |
| 3-1/4 | 14.5 | 701 | 17.4 |
| 3-1/2 | 15.2 | 854 | 18.3 |
| 3-3/4 | 16.0 | 1,029 | 19.2 |
| 4 | 16.7 | 1,225 | 20.1 |
| 4-1/4 | 17.4 | 1,439 | 20.9 |
| 4-1/2 | 18.1 | 1,679 | 21.7 |
| 4-3/4 | 18.8 | 1,943 | 22.6 |
| 5 | 19.4 | 2,220 | 23.3 |
| 5-1/4 | 20.0 | 2,525 | 24.0 |
| 5-1/2 | 20.6 | 2,854 | 24.7 |
| 5-3/4 | 21.2 | 3,210 | 25.4 |
| 6 | 21.6 | 3,600 | 26.2 |
| 6-1/2 | 22.9 | 4,421 | 27.5 |
| 7 | 24.2 | 5,426 | 29.0 |
| 7-1/2 | 25.3 | 6,518 | 30.4 |
| 8 | 26.5 | 7,774 | 31.8 |
| 8-1/2 | 27.6 | 9,133 | 33.1 |
| 9 | 28.7 | 10,650 | 34.4 |
| 9-1/2 | 29.8 | 12,320 | 35.7 |
| 10 | 30.8 | 14,100 | 36.9 |
| 11 | 32.8 | 18,180 | 39.4 |
| 12 | 34.7 | 22,880 | 41.7 |
| 13 | 36.6 | 28,330 | 44.0 |
| 14 | 38.5 | 34,560 | 46.2 |
| 15 | 40.3 | 41,530 | 48.4 |
| 16 | 42.1 | 49,330 | 50.5 |
| 17 | 43.3 | 57,970 | 52.6 |
| 18 | 45.5 | 67,490 | 54.6 |
| 19 | 47.2 | 78,040 | 56.6 |
| 20 | 48.8 | 80,660 | 58.5 |
| |
| NOTE.--To find the corresponding |
| values for shafts of cast iron or |
| steel, multiply the tabular values |
| by the following multipliers: |
| |
| Cast | | | |
| iron | .86 | .81 | .86 |
| Steel | 1.05 | 1.07 | 1.05 |
+--------+--------+--------+---------+
"It is advantageous that the diameter of line shaft be kept as small as
is possible with due regard to the duty, so as to avoid extra weight in
the shafting hangers, pulley hubs and couplings, whose weights
necessarily increase with the diameter of the shafting.
"SPEEDS FOR SHAFTING.--The speed at which shafting should run is
determined within certain limits by the kind of machinery it is employed
to drive. Shafting to drive wood-working machines may, for example, be
made to rotate much faster than that employed to run metal-cutting
machines, because the motions in the wood-working machines themselves
are faster than those in metal-cutting machines. In a general sense, the
rotation of shafting is greater in proportion as the movements of the
machines driven require to run faster.
"This occurs because in proportion as the driving pulleys of the
machines require to rotate faster than the line shaft, the diameters of
the pulleys on the line shaft must be larger than the diameters of those
on the machines; hence a great variation in speed would demand a
corresponding increase of diameter of pulley on the line shaft, and the
extra weight of this pulley would be so much added to the weight causing
friction, as well as so much added to the cost. If small pulleys were
used and countershafts employed to multiply the speed the cost would be
increased, extra room would be taken up; indeed, this is so obvious as
to require no discussion, further than to remark that the faster the
shafting rotates the smaller may be its diameter to transmit a given
horse-power. From deflection and weakness to resist transverse strains
and other obvious causes it is not found in practice desirable to employ
line shafts of less than about 1-1/4 inches in diameter, and the
diameters of shafting employed are usually arrived at from a calculated
speed of about 120 revolutions per minute for metal-cutting machines
such as used in machine shops, 250 revolutions per minute for
wood-working machines, and from 300 to 400 revolutions per minute for
cotton and woollen mills, and the countershafts for the machines usually
have pulleys of the requisite diameters to convert this speed of
rotation into that required to run each respective machine. Tubular or
hollow shafting has been made to run at 600 revolutions per minute, but
this kind of shafting has been of very limited application because of
its expensiveness.
"It is obvious that since the speed of a line shaft is used as a
multiplier in the calculation of the horse-powers of shafts, a given
diameter of shaft will transmit more power in proportion as its speed is
increased. Thus a shaft capable of transmitting 20 horse-power when
making 120 revolutions per minute will transmit 40 horse-power if making
240 revolutions per minute.
"There are now running in some factories lines of shafting 1,000 feet
long each. The power is generally applied to the shaft in the centre of
the mill and the line extended each way from this. The head shaft being,
say, 5 inches in diameter, the shafts extending each way are made
smaller in proportion to the rate of distribution, so that from 5 inches
they often taper down to 1-3/4.
"When very long lines of shafting are constructed of small or
comparatively small diameter, such lines are liable to some
irregularities in speed, owing to the torsion or twisting of the shaft
as power is taken from it in more or less irregular manner. Shafts
driving looms may at one time be under the strain of driving all the
looms belted from them, but as some looms are stopped the strain on the
shaft becomes relaxed, and the torsional strain drives some part of the
line ahead, and again retards it when the looms are started up. This
irregularity is in some cases a matter of serious consideration, as in
the instance of driving weaving machinery. The looms are provided with
delicate stop motion, whereby the breaking of a thread knocks off the
belt shifter and stops the loom. An irregular driving motion is apt to
cause the looms to knock off, as it is called, and hence the stopping of
one or more may cause others near to them to stop also. This may in a
measure be arrested by providing fly-wheels at intervals on the line
shaft, so heavy in their rim as to act as a constant retardant and
storer of power, which power is given back upon any reaction on the
shaft, and thus the strain is equalized. We mention this, as at the
present time it is occupying the thoughts of prominent millwrights, and
the relative advantage and disadvantage of light and heavy fly-wheels
are being discussed, and is influencing the proportions of shafting in
mill construction.[36]"
[36] From "Machine Tools," by William Sellers and Co.
Countershafts are separate sections of shafting (usually a short
section) employed to increase or diminish belt speed, to alter the
direction of belt motion, to carry a loose as well as a fast pulley (so
that by moving the belt on to the loose pulley it may cease to
communicate motion to the machine driven), and for all these purposes
combined.
[Illustration: Fig. 2594.]
[Illustration: Fig. 2595.]
An excellent form of countershaft hanger is shown in Fig. 2594, the
guide for the slide being adjustable along the arm, and fixed in its
adjusted position by means of the set-screws. The bearing is
self-adjusting horizontally for alignment. The countershaft is shown in
Fig. 2595, _a_ _b_ being the bearings, _c_ the cone pulley, _d_ the fast
and _e_ the loose pulley, which is placed next to the bearing, so that
it may be oiled without having to reach past the belt and fast pulley.
By reducing the journal for the loose pulley no collar is needed, the
shaft shoulder and the face of the bearing serving instead.
[Illustration: Fig. 2596.]
When the direction of rotation of the cone pulley on the countershaft
requires to be occasionally reversed, there are two belts, an open one
and a crossed one, from the line shaft to the countershaft, and there
are three pulleys on the countershaft, their arrangement being as shown
in Fig. 2596. L L´ are two loose pulleys, one receiving the open and the
other the crossed belt, both these pulleys being a little more than
twice the width of the belt; F is a fast pulley. By operating the belt
skipper or shifter in the requisite direction either the open or the
crossed belt is brought upon the fast pulley, the other belt merely
moving across the width of its loose pulley, which must be twice that of
the fast one. In the position of the belt shifter shown in the cut, both
belts would be upon the loose pulleys L L´, hence the countershaft would
remain at rest. If the direction of rotation of one pulley is required
to be quicker than the other, two fast pulleys, each slightly more than
twice the width of the belt, may be placed upon the line shaft, one of
them being of enlarged diameter, to give the requisite increased
velocity.
[Illustration: Fig. 2597.]
In Fig. 2597 Pratt's patent friction clutch is shown applied to a
countershaft requiring to rotate in both directions, but quicker in one
direction than in the other; hence, one of the pulleys is of smaller
diameter than the other. The pulleys are free to rotate upon the
countershaft unless engaged by the clutch, which is constructed as
follows:--
The inside surface of the pulley rim is bored and the end surface of the
shoes is turned to correspond. The shoes are in the form of a bell
crank, upon the exposed end of which is provided a small lug, clearly
shown in the cut. To prevent end motion of the pulley a collar is placed
on one side of it and secured to the countershaft, while, on the other,
the sleeve to which the shoes are pivoted is also secured to the
countershaft; upon the shaft between the two pulleys there is a sleeve,
having at each end a conical hub. When this sleeve is moved to the
right, its right-hand coned hub passes between the lugs on the exposed
ends of the shoes, forcing these lugs apart and causing the shoes to
grip the bore of the large pulley, which thereupon rotates the shaft
through the medium of the sleeve upon which the shoes are pivoted.
Similarly, if the engaging (and disengaging) sleeve be moved to the left
it will pass between the lugs of the shoes on the left-hand pulley,
which will, therefore, be caused to drive the shaft. In the position
shown in the cut the engaging sleeve is clear of the ends of all the
shoes, hence the pulleys would be caused to rotate (by their belts), but
the shafts, &c., would remain stationary.
In yet another form the inner face of the pulley rim is coned, and in
place of shoes a disk, whose circumference is coned to fit the pulley
rim, is fast upon the shaft. The shaft is provided with a fixed collar,
and from this collar, as a fulcrum, the pulley and disk are (by means of
short levers attached to a sleeve upon the countershaft) brought into
contact, the thrust on the other side of the pulley being sustained by a
conical surface on the sleeve, fitting to a similar cone on the hub of
the pulley. Thus the pulley is gripped between two coned surfaces, one
on each side, and is released by moving the sleeve laterally so as to
relieve the grip, which it does noiselessly.
By this means motion to the shaft is communicated from the pulley
without the sudden shock incidental to the impact of two fixed pieces,
because the grip of the cones is gradual, and a certain amount of slip
may occur until such time as the grip of the surfaces is sufficient to
drive by friction.
[Illustration: Fig. 2598.]
Fig. 2598[37] represents a cone friction clutch pulley. The outer half
is a working fit upon the shaft, but is secured against end motion by
the collar D. The sliding half is coned and covered with leather as
shown at C C, the outer half being coned to correspond. The sliding half
is driven by a feather fast in its bore, and sliding in a feather-way or
spline in the shaft.
[37] From _The American Machinist_.
The driving power of the device is obtained by means of the friction of
the coned surfaces. The less the angle _x_ of the cones the more power
transmitted with a given pressure of the internal to the external cone.
On the other hand, however, this angle may be so little that the
external cone will not release the internal one when the end pressure on
the latter is removed.
The object is, therefore, to so proportion the angle _x_ of the cones
that their friction will be a maximum, while the internal cone may be
moved endwise and unlocked from the external without undue effort or
strain at the moving clutch bar E. If the angle be 30 degrees, the
clutch will release itself when the lateral pressure is removed. If the
angle be 25 degrees the internal cone will require a slight lateral
pressure to release it. If the angle be 20 degrees, the internal cone
cannot be released by end pressure applied by hand.
The transmitting capacity of the clutch depends upon the pressure
applied to maintain the cones in contact, and therefore upon the
leverage of the clutch bar, whose fork end is shown in section at E.
It is desirable that the end pressure be as small as possible, because
of the friction between E and the hub of the sliding half of the pulley.
The hangers which carry the bearing boxes supporting shafting may be
divided into four principal classes:--Those in which the bearing boxes
are permitted to swivel, and to a certain extent to adjust themselves,
to the axial line of the shafting, and having means to adjust the
vertical height of the bolts.
Those in which the bearings are incapable of such adjustments.
Those in which the bearing boxes are supported on each side; and those
in which the bearing is supported on one side only, so that the shafting
may be taken down without disturbing the couplings.
The first named are desirable in that they eliminate to a certain extent
the strains due to the extra journal bearing friction which occurs when
the shafting is sprung out of its true alignment, and obviate to a great
extent the labor involved in fitting the bore of the bearing boxes to
the journals of the shafting, so as to hold the same with its axis in a
straight line, while they permit of vertical movement to attain vertical
alignment.
[Illustration: Fig. 2599.]
Fig. 2599 represents Wm. Sellers & Co.'s ball-and-socket hanger which
has come into extensive use throughout the United States: _a_ represents
the frame of the hanger threaded to receive the cylindrical threaded
plungers _d_ _e_, which therefore by rotation advance or recede
respectively from the centre of the bearing boxes _b_ _c_.
The ends of these plungers are concave, and the top and bottom halves of
the bearing boxes are provided with a spheroidal section fitting into
the concaves of the plungers, so that when the plungers are adjusted to
fit (a working fit) against the boxes, the latter are held in a
ball-and-socket or universal joint, which permits motion in any
direction, the centre of such motion being central to the spherical
concaves on the ends of plungers _e_ _d_.
To adjust the vertical height of the bearings or boxes, it is simply
necessary to rotate the plungers _d_ _e_, in the threaded holes in the
frame. F is simply a dish to catch the lubricating oil after it has
passed through the bearing.
It is obvious that if a shaft be aligned axially true, and held in a box
of this design, the centre of a length of shaft on either side of the
box may be sprung or deflected out of alignment, and that the box will
adjust itself so that its bore will be parallel with the axis of the
shaft thus deflected, hence the friction between the shaft journal and
the bearing box will be at all times a minimum.
This feature of self-adjustment permits of the employment of longer
bearings, which reduces the wear, as well as the friction, and by
providing sufficient bearing and wearing area, enables the bearings to
be composed of cast iron, which is the cheapest as well as the very best
material of which a bearing can be made, provided that its area of bore
is sufficiently large in proportion to the duty, or load, to have a
pressure of not more than about 60 lbs. per square inch of area.
Again, if the alignment of the shaft should require readjustment from
the warping or sinking of beams, as is a very common occurrence where
hangers are fixed to the joists of ceilings, the adjustment is readily
and easily effected by means of the plungers, nor need the boxes be
fitted to the shaft more than to see that when free from the hangers
they bed firmly down until the crowns of their bore have contact with
the shaft. The hangers themselves require no refinement of alignment,
because that may be secured by means of the plungers, and the boxes
require no fitting to the shafts after the hangers are erected.
In hangers in which the self-adjusting ball-and-socket feature is
omitted, the bottom hangers must not only be accurately aligned, but the
boxes must, to avoid friction and undue wear, all be fitted to the
shaft, and the latter must, during such fitting, be tried in the boxes;
the operation, if properly performed, costing far more in labor than is
equivalent to the difference in the first cost of the ball-and-socket
adjustable hangers and those solid or not self-adjustable, especially if
the boxes be long ones, as about, or not less than, three times the
diameter of the shaft, as they should be.
[Illustration: Fig. 2600.]
An external side elevation of this hanger is shown in Fig. 2600, it
being obvious that the hanger is designed for bolting to timbers, or
framing overhead.
[Illustration: Fig. 2601.]
Fig. 2601 represents a hanger of this class. In this the lower part
carrying the bottom bearing is held to the upper by two bolts, as shown,
the object being to enable the same to be placed in position on a line
of shafting without disturbing the pulleys or the couplings. The lower
section with the bottom bearing is removed and again put on after the
hanger is set over the shaft.
[Illustration: Fig. 2602.]
Fig. 2602 represents an open-sided ball-and-socket hanger in which the
plungers can be retired, the bearings removed, and the hanger erected on
an existing line of shafting without removing the pulleys or couplings,
or disturbing the line of shafting.
[Illustration: Fig. 2603.]
When the face of the framing to which the hangers are to be bolted
stands vertical, the hangers are formed as in Fig. 2603, in which the
ball-and-socket or swivelling feature is maintained as before.
Fig. 2604 represents a wall hanger, which is open in front similar to
the hanger shown in Fig. 2602, and for the same purpose.
[Illustration: Fig. 2604.]
The section of shafting receiving power from the engine or prime mover
is usually supported in bearings or pillow blocks. Pillow blocks are
also used for vertical shafts, and in cases where the foundation or
framing is not liable to lose correct horizontal adjustment.
[Illustration: Fig. 2605.]
Fig. 2605 represents a pillow block, in which the ball-and-socket
principle shown in Fig. 2602 is embodied. The bearings have each a ball
section fitting into spherical recesses or cups provided in the body of
the block, and in the cap, so that the bearings are capable of
swivelling as already described with reference to the hanger Fig. 2599.
[Illustration: Fig. 2606.]
[Illustration: Fig. 2607.]
A sectional view of a pillow block having this adjustable feature is
shown in Fig. 2606. To provide increased seating bearing, and also means
of side adjustment to pillow blocks, they are sometimes bolted to base
plates as in Fig. 2607, room being left in the bolt holes to permit of
their being moved and adjusted upon the plate. The adjustment may be
made by means of wedges, as at A, B in Fig. 2607. These base plates are
usually employed when the pillow block is to be held against a wall.
[Illustration: Fig. 2608.]
An inverted pillow block of similar construction, but designed for the
head line (as the length receiving power from the engine or motor is
termed) of the shafting, is shown in Fig. 2608, but an improved form of
the same has plungers so as to effect a vertical adjustment of the
bearings.
[Illustration: Fig. 2609.]
When a pillow block requires to be enveloped by a wall it is provided
with a wall box as shown in Fig. 2609, and within this box is set the
pillow block as shown, space being sometimes left to adjust the pillow
block laterally within the box by means of a wedge as shown.
In cases where the shafting requires to stand off from a wall to allow
room for the pulleys, brackets or knees, such as shown in Fig. 2610, are
employed.
COUPLINGS FOR LINE OR DRIVING SHAFTS.--The couplings for connecting the
ends of line shafts should accomplish the following objects:--
1. To hold the two shaft ends axially true one with the other.
2. To have an equal grip along the entire length of shaft enveloped by
the coupling.
3. To have a fastening or locking device of such a nature that it will
not be liable to work loose from the torsional strains due to the
flexure of the shaft, which is caused by the belts springing or
straining the axial line of shafting out of the straight line.
[Illustration: Fig. 2610.]
4. To be capable of easy application and removal, so as to permit the
erection or disconnection of the lengths of shafting with as little
disarrangement of the hangers and bearings as possible, and to be light,
run true, and be balanced.
To these requirements, however, may be added that, since it is well-nigh
impracticable to obtain lengths of lathe-turned shafting of exactly
equal diameter, couplings for such shafting require to fill the
following further requirements:
5. The piece or pieces gripping the shaft ends must be capable of
concentric and parallel closure along the entire area, enveloping the
end of each shaft, and must do this at each end independently of the
other, and the piece or pieces exerting the closing or compressing
pressure must grip the closing piece or pieces, enveloping the shafting
over the entire area.
[Illustration: Fig. 2611.]
[Illustration: Fig. 2612.]
[Illustration: Fig. 2613.]
If, for example, a sleeve be split at four equidistant parts of its
circumference, and from each end nearly to the middle of its length, as
in Fig. 2611, any pressure that may be applied to its circumference to
cause it to grip the shaft it envelops will cause it to grip the shaft
with greater force at one part than at another, according to the
diameter of the shaft and the location of the external pressure. Thus,
if the pressure be applied equally along the length A B, the weaker end
B will close most readily, while at A the support afforded by the
unsplit section offers a resistance to closure at the ends A of the
split, hence the shaft, even though a working fit to the sleeve bore,
will be gripped with least force at the end A. If the shaft were simply
a close fit, as, say, just movable by hand on the sleeve bore, the form
of the coupling bore would, when compressed upon the shaft, be as shown
in Fig. 2612, the bend on the necks _a_, _b_, _c_, _d_, being magnified
for clearness of illustration. If the compressing piece covered the
compressed sleeve for a lesser distance, the grip would be more uniform,
because there would be a greater length of the sleeve to afford the
curves _a_, _b_, _c_, _d_, as shown in Fig. 2613. The grip may be more
equalised by boring the sleeve of slightly smaller diameter than the
shaft.
[Illustration: Fig. 2614.]
Fig. 2614 represents a sleeve carrying out this principle. It is
composed of two halves, as shown, bored slightly smaller than the shaft
diameter, and is to be compressed on the shaft, which, acting as a
wedge, would spring open the sides of the bore until the crown of the
bore bedded against the shaft. This, in the case of parallel shaft ends
of equal diameter, would hold them with great force axially true, and
with equal force and bearing, thus meeting all the requirements. If,
however, the end of one shaft were of larger diameter than the end of
the other (as has hitherto been supposed to be the case), the end
accomplished by boring the sleeve of smaller diameter than the shaft is,
that the end of the sleeve is afforded the extra elasticity due to the
transverse spring of the sleeve, which permits the edges of each half of
the sleeve to bear along a greater length of the shaft end than would
otherwise be the case; but the bearing is in this case mainly at and
near the edges of the split.
It will be perceived, then, that under this principle of construction,
when applied to shaft ends of varying diameters, the metal is left to
spring and conform itself to the shape of the parts to be connected, and
that there is nothing outside of the condition of relative diameter of
shaft to sleeve bore to determine what the direction of the spring or
closure of sleeve shall be; but, on the other hand, the principle
possesses excellence in that the sleeve being cylindrical and its
closure taking place equally at similar points of contact the shafts
will be held axially true, one with the other; or in other words, the
movements of the metal while sleeve closure is progressing are equally
radial to the axis of the sleeve, and there is no element tending to
throw the shaft axis out of line one with the other.
If a sleeve have a single split, the manner in which it will grip a
shaft smaller than the sleeve's bore depends upon the manner in which
the compression is effected.
In Fig. 2615, for example, is a ring supposed to be compressed by a
pressure applied at A and at B, causing the ring to assume the form
shown by the dotted lines. The centre of the ring bore would therefore
be moved from C to D. Now, suppose that the end of one section of
shafting were to fit the sleeve bore, then compressing the sleeve upon
it would not practically move the centre of the bore; but if the shaft
at the other end of the sleeve were smaller than the sleeve bore, the
compression of the sleeve to grip the shaft would move the centre of the
bore, and, therefore, of the shaft towards D, hence the axial lines of
the shafts would not be held true one with the other. To accomplish this
latter object, the compression must be equal all round the sleeve, or it
may be applied at the points E and F, Fig. 2616, although it is better
to have the compression area embrace all the circumferential area
possible of the sleeve, and to have the movement that effects the
compression simultaneous and equal at all points on the circumference of
the ring or sleeve, because if these movements are independent, more
movement or compression may be given at one point than at another, and
this alters the centre of the bore; thus, if more pressure were exerted
at E than at F, in figure, the centre of the bore would be thrown
towards F, or _vice versâ_. If the pressure be concentric, the single
split ring or sleeve grips the shaft all round its circumference; hence
it is only necessary in this case to maintain the circumference of the
sleeve in line to insure that the shaft ends be held axially true one
with the other; and if the pressure on the ring be applied equally from
end to end its closure will also be parallel and equal, and the shaft
will be held with equal force along that part of its length enveloped by
the coupling. It is obvious, however, that the piece or sleeve gripping
the end of one shaft must be independent of that gripping the other, so
as to avoid the evils shown in Fig. 2612, while at the same time the
casing or guide enveloping the two independent rings or sleeves must
guide and hold them axially true, one with the other.
[Illustration: Fig. 2615.]
[Illustration: Fig. 2616.]
[Illustration: Fig. 2617.]
In Fig. 2617 is shown an excellent form of _plate coupling_, in which
most of the requirements are obtained. A and B are the ends of the two
lengths of shafting to be connected, C and D are the two halves of the
coupling driven or forced on the ends of the shafting, and further
secured by keys. The end of one half fits into a recess provided on the
other half, so as to act as a guide to keep the shafts axially true one
with the other, and also to keep the two halves true one with the other,
while drilling the holes to receive the bolts E which bolt the coupling
together. The objections to this form are, that it is costly to make,
inasmuch as truth cannot be assured unless each half coupling is fitted
and keyed to the shaft, and turned on the radial or joint faces
afterwards. Furthermore, if the coupling were taken off in order to get
a solid pulley on the shaft, the coupling is apt to be out of true when
put together again, and, therefore, to spring the shaft out of true.
Also, that the bearing, support, or hanger must be open-sided to admit
the shaft, and that each coupling, being fitted and turned to its place,
would be apt to run out of true if removed and applied to another shaft,
whether the same be of equal diameter or not; but if each half coupling
be provided with a feather instead of the usual key, the coupling may be
readily removed and will remain true when put on again.
[Illustration: Fig. 2618.]
Fig. 2618 represents a plate coupling, in which one end of the shaft
passes into the bore of the half coupling on the other length of shaft,
which serves to keep the shafts in line one with the other.
[Illustration: Fig. 2619.]
Fig. 2619 represents a single cone coupling composed of an external
sleeve having a conical bore and a split internal sleeve bored to
receive the shaft, and turned on its outer diameter to the same cone as
the bore of the outer or encasing sleeve. The bolts pass through the
inner sleeve, the bolt head meeting the radial face of the inner sleeve
while the nut meets the radial face of the outer sleeve, so that
screwing up the nut forces the inner sleeve into the outer and closes
the bore of the former upon the shaft. This coupling is open to the
objection that it cannot grip the ends of the shafts equally unless both
shafts be of exactly equal diameter, and the bearing on the smaller
shaft will be mainly at the outer end only, as explained in Fig. 2611.
As a result, the transverse strains on the shaft will cause the
couplings to come loose in time.
[Illustration: Fig. 2620.]
Fig. 2620 represents a coupling composed of a cylindrical sleeve split
longitudinally on one side, as at _d_; the bolts _c_ pass through the
split. Diametrally opposite is another split passing partly through as
at _b_. A key is employed at right angles to the two splits as shown.
Here, again, the pressure on a shaft that is smaller than the other, of
the two shafts coupled, will be mainly at one end, but separation of the
shaft ends is provided against by means of two cylindrical pins on the
ends of the key fitting into corresponding holes drilled in the shaft,
as shown in the side elevation in the figure.
[Illustration: Fig. 2621.]
[Illustration: Fig. 2622.]
In Fig. 2621 is shown a coupling whose parts are shown in Fig. 2622. It
consists of a cylindrical ring turned true on the outside and bored
conical from each end to the middle of its length, as shown. The split
cones are bored to receive the shaft and contain a keyway to receive a
spline provided in the shaft ends, and are turned on the external
diameter to fit the conical borings in the sleeve. Three square bolts
pass through the split cones, which, being square, are prevented from
rotating while their nuts are being screwed up.
To put the coupling together one split cone is passed over the end of
one shaft and the other over that of the other. The sleeve is then put
between the ends of the shaft, the position of the shaft adjusted for
length and the split cones pushed up into the sleeve; the bolts are then
passed through and screwed up. The forcing of the split cones into the
conical borings of the sleeve causes the former (from being split) to
close upon the shaft ends and grip them equally tight, notwithstanding
any slight difference in the diameters of the shaft, there being left
between the ends of the split cones sufficient space to allow them to
pass through the conical borings sufficiently to close upon the
respective ends of the shafts; the pressure being parallel and equal on
each shaft end, because when the cone has gripped the largest shaft the
whole movement due to screwing up the nuts is transferred to the cone
enveloping the smaller shaft, and by reason of the cones fitting, the
closure of the holes in the cones is parallel, giving an even grip along
the shaft end and an equal amount of grip to each shaft end.
To remove the coupling the bolts are removed, and the sleeve being moved
endways the cones open from their spring and relieve the grip upon the
shaft.
It is evident that in their passage through the sleeve casing the cones
will move with their axial lines true with the axial line of the casing;
and it is equally evident that the taper on the cone accurately fitting
the taper in the sleeve bore, the closure of the cone bores must be
equal; while at the same time the pressure on the two cones upon the
respective shaft ends must be equal, because it is the friction of the
cone bores upon the shaft ends which equally resists the motion of both,
while the pressure applied to the respective cones is derived from the
same bolts, and hence is equal and simultaneous in its action.
To loosen this coupling for removal the bolts must be stacked back and a
few blows on the exterior of the outer shell with a billet of wood may
loosen the coupling; but if not, a wedge or a cold chisel may be driven
in the splits of the cones to loosen them, but such wedge or chisel
should not have contact with the sides of the split, either near the
bore or near the perimeter, for fear of raising a burr.
[Illustration: Fig. 2623.]
[Illustration: Fig. 2624.]
In Fig. 2623 is shown a patent internal clamp coupling. It is formed of
a cylindrical piece containing a pair of separate clamps, and between
these clamps and the outer casing are four screws, two to each clamp;
these screws are tapered so as to close the clamp when screwed up and
release it when screwed outwards. The holes to receive the shaft ends
are bored somewhat smaller than the shafts they are to fit, and the
clamps opened to permit the easy insertion of the shaft ends by means of
wedges A driven in the split B of each clamp, as shown in Fig. 2624.
The lower edge of the wedges should be slightly above the bore of the
clamp to prevent the formation of a burr or projection of metal when the
wedge is driven in. When placed upon the shaft ends and in proper
position the wedges are removed and the clamp bore will have contact at
and near the edges of the longitudinal split and on the opposite sides
of the bore where the keyway is shown, but the pressure of the tape
screws will spring the clamps on the side of the longitudinal splits,
and increase the bearing area at those points.
The main features of this device are that though the bore be made a
driving fit to the shaft, it can, by the employment of the wedges, be
put on the shaft with the same ease as if it were an easy fit, while the
clamps being separated by a transverse groove may open and close upon
the shaft independently of each other, so as to conform separately to
any variation in the diameters of the two shaft ends it couples. But it
may be noted that since the circumference of each shaft end has a
bearing along the line of the coupling bore diametrally opposite to the
longitudinal splits, the shafts will not be held quite axially true one
with the other unless there be as much difference in the diameters of
the separate clamp bores as there is in the diameters of the shaft ends;
because to hold two shafts of different diameters axially true one with
the other the longitudinal planes of the two circumferences must not at
any part of the circumferences form a straight line, as would be the
case at that part of the coupling bore at and near the keyway.
It is to be noted, however, that this coupling is formed of one solid
piece, and that the strain on the tightening bolts or screws is one of
compression only, which tends to hold them firmly and prevent their
coming loose.
If the workmanship of a plate coupling, such as in Fig. 2617, be
accurately and well done, and the proportions of the same are of correct
design, so that the strain placed on the same in keying and coupling it
up does not distort it, the coupling and the shaft will run true,
because the strain due to the key pressure will not be (if properly
driven) sufficient to throw the coupling out of true. But the degree of
accuracy in workmanship necessary to attain this end is greater than can
be given to the work and compete in the market with work less accurately
made, because the difference in the quality of the workmanship will not
be discernible save to the most expert and experienced mechanic, and not
to him even unless the pieces be taken apart for examination. If the
bore of the coupling be true and smooth and of proper fit to the shaft
the key pressure, if the key fits on its top and bottom, will not, as
stated, be sufficient to throw the coupling out of true. It is true,
however, that such pressure is exerted on one half the bore _of the
coupling_ only, being the half bore opposite to the key. On the other
diametral side of the coupling the strain due to the key is exerted on
the top face of the key.
If, therefore, the key seats in the shaft and in the couplings are in
line or parallel, and both therefore in the same plane, the strain due
to the key may throw the coupling out of true to the amount that the key
pressure may relieve the bore of the coupling (on the half circumference
of the shaft of which the key is the centre) from contact or pressure
with the shaft. As a result, the coupling may run to that extent out of
true, but the shaft would run true nevertheless so long as the nature of
the surfaces on the shaft and on the coupling bore was such that the key
pressure caused no more compression or closer contact in the case of one
half coupling than in the case of the other.
It is obvious that a plate coupling will require at least as much force
to remove it from the shaft as it took to put it on, and sometimes, from
rusting of the keys, &c., it requires more. If it be removed by blows it
becomes damaged, and damage is likely to be also caused to the shaft,
while the surfaces having to slide in contact under the pressure of the
fit the surfaces abrade and compress, and the fit becomes impaired. But
in couplings such as shown in Fig. 2621, the gripping pieces are
relieved of pressure on the shaft by the removal of the bolts, and the
removal of the coupling becomes comparatively easy.
The interchangeability of plate couplings is further destroyed by the
fact already stated, that turned shafting is not, as a rule, of accurate
gauge diameter, and the least variation in the pressure or fit of the
coupling to its shaft is apt to cause a want of truth when the key bears
on its top and bottom. The fit of the coupling to its shaft may be, it
is true, relied on to do the main part of the driving duty, and the key
fitting on the sides only may be a secondary consideration, but in
proportion as the fit is relied on to drive, that fit must be tighter,
and the difficulty of application and removal is increased.
Another and important disadvantage of the plate coupling in any form is
that it necessitates the use of hangers open on one side to admit the
shaft, because the couplings must be fitted upon the shaft before the
same is erected and should not be removed after being fitted, as would
be necessary to slide the end of the shaft through the bearing.
When plate couplings are constructed as in Fig. 2617, the removal of a
section involves either the driving back of one-half of the coupling so
that the other half will clear it, or else the moving endwise of the
whole line to effect the same object.
With a plate coupling the half coupling on one end of the shaft must be
removed when it is required to put an additional pulley on the shaft,
unless, indeed, a split pulley be used, whereas with a clamp coupling,
such as shown in Fig. 2621, the half coupling at each end may be slacked
and moved back, one end of the shaft released, a solid pulley placed on
the shaft and the coupling replaced, when it will run as true as before,
and the pulley may be adjusted to its required position on the length of
shafting.
It is to be remarked, however, that a well-made plate coupling, such as
in Fig. 2618, makes a good and reliable permanent job that will not come
loose under any ordinary or proper conditions.
[Illustration: Fig. 2625.]
[Illustration: Fig. 2626.]
In Fig. 2625 is shown a patent self-adjusting compression clamp, which
is peculiarly adapted to connect shafting that is of proper gauge
diameter. It consists of a sleeve A made in two halves, each embracing
nearly one-half of the shaft circumference and being bored parallel and
slightly smaller than the diameter of the shaft ends. Over this sleeve
passes at each end a ring D E, bored conical and fitting a similar cone
on the external diameter of the sleeve. On each end of the sleeve is the
nut F G, which by forcing the cone ring up the taper of the sleeve
causes the two halves of the latter to close upon and grip the shaft.
For shafts less than two inches in diameter there are provided in the
sleeve two pins to enter holes in the shaft ends in place of keys, but
for sizes above that keys are employed. All parts of this coupling being
cylindrical it is balanced. The separate parts of this coupling are
shown in Fig. 2626.
[Illustration: Fig. 2627.]
[Illustration: Fig. 2628.]
[Illustration: Fig. 2629.]
[Illustration: Fig. 2630.]
In Figs. 2627 to 2630 are shown a side elevation and sectional view of
another form of shaft coupling. A is the sleeve, B B nuts on the ends of
the sleeve, and C C cones fitting taper holes in the sleeve. These cones
are split, as shown in Fig. 2629, to permit them to close upon the shaft
ends. The shaft ends themselves are matched with a half dovetail, as in
Fig. 2630, which dispenses with the employment of a key.
In coupling shafts of different diameters it is usual to reduce the
diameter of the end of the larger to that of the smaller shaft, and to
employ a size of coupling suitable for the smaller shaft; but in this
case it is necessary that the coupling be placed on the same side of the
hanger or bearing as the smaller shaft, otherwise it is obvious that the
strength of the larger would, between its bearings, be reduced to that
of the smaller shaft.
The couplings for line shafting are usually placed as near to the
bearings or hangers as will leave room for the removal of the couplings
by sliding them along the shaft.
The couplings on the length of shaft receiving power from the motor are
placed outside the bearings, hence on the succeeding lengths there will
be one coupling between each pair of bearings, the couplings being in
each case as close to each bearing as will allow the coupling to be
moved towards the bearing sufficiently to permit the length to be
removed without disconnecting the adjacent length from its bearings.
[Illustration: Fig. 2631.]
Fig. 2631 represents a very superior form of coupling for line shafts.
The ends of the line shaft are reduced to half diameters as shown, and
lapped with a horizontal joint at an angle to the axis of the shaft as
denoted by the dotted line, which prevents end motion; the ends of the
shaft and their abutting surfaces are dovetailed, as shown A and B, and,
therefore, perform driving duty. A sleeve envelops the whole joint and
is secured by a key. This coupling accomplishes all that can be desired,
but requires very accurate workmanship, and on this account is expensive
to make.
[Illustration: Fig. 2632.]
Fig. 2632 represents a form of coupling suitable for light shafting. It
consists of two halves A A, of cast iron, which are drawn together by
the bolt C; the centre of the coupling is recessed to enable the
coupling to take a better hold on the shaft, which is prevented turning
by the pins D D. This coupling has no projections to catch clothes or
belts, and is quickly applied or removed.
[Illustration: Fig. 2633.]
Fig. 2633[38] represents a form of coupling for heavy duty, the
transmitting capacity only being limited by the strength of the
projections A. If the shafts are not axially in line, this form of
coupling accommodates the error, since the projections A may slide in
their recesses, while if the axial lines of the shafts should vary from
flexure of the bearings or foundations, as in steamships, clearance
between the ends of A and the bottom of the recesses may be allowed, as
shown at B.
[38] From Rankine's "Machinery and Millwork."
[Illustration: Fig. 2634.]
In Fig. 2634 is shown a coupling (commonly known as the universal joint
coupling) which will transmit motion either in a straight line, or at
any angle up to 45°.
It is formed of two double eyes, such as A, connected to a yoke or
crosspiece B as shown at C. It is mainly used for connecting shafts or
arms carrying tools of some kind, such as rubbers for polishing stone,
tools for boring, or other similar purposes in which the tool requires
to be rotated at varying angles with the driving shaft.
CHAPTER XXXI.--PULLEYS.
Pulleys for the transmission of power by belt may be divided into two
principal classes, the solid and the split pulley. The former is either
cast in one entire piece, or the hub and arms are in one casting, and
the rim a wrought-iron band riveted on. The latter is cast in two halves
so that they may be the more readily placed upon or removed from the
shaft.
On account of the shrinkage strains in large pulley castings rendering
them liable to break, it is usual to cast pulleys of more than about 6
feet in halves or parts which are bolted together to form the full
pulley. On account of these same shrinkage strains it was formerly
considered necessary to cast even small pulleys with curved arms, so
that the strains might be accommodated or expended in bending or
straightening the curves of the respective arms. It is found, however,
that by properly proportioning the amount of metal in the hub, arms, and
rim of the pulley, straight arm pulleys may be cast to be as strong as
those with curved arms, and being lighter they are preferable, as
causing less friction on the shafting journals, and, therefore, being
easier to drive.
It is obvious that a pulley for a double belt requires to be stronger
than is necessary for a single one, but the difference is not
sufficiently great to give any practical advantage by making separate
pulleys for single and double belts; hence all pulleys are made strong
enough for double belts.
Pulleys are weaker in proportion to their duty as the speed at which
they rotate is increased, because the centrifugal force generated by the
rotation acts in a direction to burst the pulley asunder, so that if the
speed of rotation be continuously increased a point will ultimately be
reached at which the centrifugal force generated will be sufficient to
cause the wheel to burst asunder. But the speed at which pulleys are
usually run is so far within the limits of the pulley's strength, that
the element of centrifugal force is of no practical importance except in
the case of very large pulleys, and even then may be disregarded
provided that the pulleys be made in a sufficient number of pieces to
avoid undue shrinkage strains in the castings, but if solid pulleys are
rotated at high velocities the internal strains due to unequal cooling
in the mould has been known to cause the wheels to fly asunder when
under high speeds.
Fig. 2635 represents a solid pulley, the tapered arms meeting the rim in
a slightly rounded corner or fillet, and the rim being thickened at and
towards its centre. When the width of rim is excessive in proportion to
one set of arms a double set is employed as in Fig. 2636.
In some forms of pulley the arms and hub are cast in one piece and the
rim is formed of a band of wrought iron riveted to the arms. By this
means shrinkage strains are eliminated and a strong and light pulley is
obtained.
Fig. 2637 represents a split pulley in which the two halves are bolted
together after being placed on the shaft.
Variable motion may be transmitted by means of an oval driving pulley,
as in Fig. 2638, it being obvious that the belt velocity will vary
according to the position of the major axis of the oval. Arrangements of
this kind, however, are rarely met with in practice.
In Fig. 2639 is shown an expanding pulley largely employed on the drying
cylinders of paper machinery, and in other similar situations where
frequent small changes of revolution speed is required. Each arm of the
wheel carries a segment of the rim, and is moved radially to increase or
diminish the rim diameter by sliding in slots provided in the hub of the
wheel, a radial screw operated by bevel gears receiving motion from the
hand wheel and gear-wheels shown in the engraving. It is obvious that in
this case the driving belt must be made long enough to embrace the
pulley when expanded to its maximum diameter, the slack of the belt due
to reduction of diameter being taken up by a belt tightener.
[Illustration: Fig. 2640.]
[Illustration: Fig. 2641.]
[Illustration: Fig. 2642.]
In Fig. 2640 is shown a wooden pulley having a continuous web or disk
instead of arms. It is built up of segments, the web being secured to
the shaft as follows. In Figs. 2641 and 2642 A, B are clamping plates,
and C a split sleeve fitting easily to the shaft and passing through A,
B, while receiving the nut E on the other side. The web of the pulley
fits on the shoulder J, and the flange B fits on the shoulder K, so as
to keep these parts true or concentric to A. The bore of A is taper to
fit the taper of C; hence the nut E in drawing C through A, causes C to
close upon and grip the shaft, while the flanges A, B grip the pulley
and hold it to C.
In Figs. 2643 and 2644 are represented the Otis self-oiling loose
pulley, designed to automatically oil itself upon its starting or
stopping.
[Illustration: _VOL. II._ =EXAMPLES OF PULLEYS.= _PLATE XII._
Fig. 2635.
Fig. 2636.
Fig. 2637.
Fig. 2638.
Fig. 2639.]
[Illustration: Fig. 2643.]
[Illustration: Fig. 2644.]
The hub D is cored out in such manner as to form within it an annular
chamber or cavity B B, entirely surrounding the bore, and serving as a
reservoir to contain oil or other lubricating liquid.
This chamber or reservoir has no direct communication with the bore of
the hub, but a communication is formed between it and the bore through
one or more chambers C C, which are termed supply chambers, and which
are partitioned off within the bore from the reservoir B, by coring the
hub in a suitable manner.
These supply chambers have openings N N in their sides or ends
communicating with the reservoir B, and also openings C C communicating
with the bore of the pulley. These supply chambers are filled with wick
or other fibrous or capillary material, which is also inserted into the
openings N N, to draw the oil from the reservoir by capillary attraction
and supply it in moderate quantities between the bore of the pulley and
the shaft on which it runs. Three or more openings are provided in the
outer shell of the hub for the introduction of oil into the reservoir B,
which openings are closed by thumb-screws, plugs, or other stoppers E E.
There being three of these openings, one will always be at or near the
top when the pulley is at rest, and through this the oil may be
introduced without difficulty. It is not intended that the reservoir
should at any time contain more than one-third its capacity of oil, so
that whenever the pulley is at rest the surface of the oil will be below
the lowest point of the bore, thus preventing any waste of oil at such
times.
When the pulley is in motion, the centrifugal force imparted to the oil
in the reservoir throws it outwardly, causing it to be distributed in an
even layer against the inner surface of the shell which encloses and
forms the reservoir, thus preventing any possible waste when the pulley
is in motion.
But when the pulley is either stopped or started, the oil is caused to
change its position, and in so doing is brought into contact with the
wicks protruding from the small openings N N, by which it is conveyed
into the supply chamber, and thence to the shaft. By thus taking
advantage of what is a necessity in all business establishments in which
machinery is employed--to wit, the stopping and starting of the
machinery at regular intervals--to insure the supplying, at such times,
of a small quantity of oil to the bearings of the loose pulleys, the
makers claim that a perfect and reliable means is obtained for guarding
against any needless waste of the lubricant.
[Illustration: Fig. 2645.]
A crowning or crowned pulley is of largest diameter in the middle of its
width or face, the object being to cause the belt to run on the middle
of the pulley width. It would appear that this crowning would give to
the belt a greater degree of tension at its centre than at its edges,
but it is shown by experiment that if a piece of belt be clamped square
across its width at each end and stretched, the centre as section _b_,
in Fig. 2645, will stretch the most, and that if the piece be divided
along its centre lengthwise, and both halves again stretched, they will
again do so the most in the middle of their widths.
From this it appears that the crowning serves to produce a tension equal
across the pulley width, because it will stretch the belt the most in
the middle of its width, where it has the greatest capacity to stretch.
The amount of crowning employed in practice varies from about 3/16 to
3/8 inch per foot of width of pulley face, the minimum being employed
where the belt requires to be moved or slipped laterally from one pulley
to another of equal diameter, as from a fast to a loose pulley and _vice
versâ_. To relieve the belt of strain when on a loose pulley the loose
pulley is sometimes made of smallest diameter, and has a coned step up
which the belt moves when pressed against it. During this passage of the
belt, however, one edge is stretched more than the other, while in
passing from the large to the smaller pulley the same edge is under
tension, while the other is released from tension; hence, with the belt
passing either to or from the large pulley there is a tendency to unduly
stretch one of its edges. On the other hand, however, in cases where the
belt requires to run for long periods on the loose pulley relieving it
from tension is a great advantage.
In fixing pulleys so that they shall run true upon their shafts several
difficulties are met with. First, it is difficult to turn the shafts
quite parallel and to exact standard gauge diameter. Second, the bore of
the pulley must be made a sufficiently easy fit to enable their being
moved by hand along the shaft to the required location. As a result the
set-screw pressure throws the pulley out of true, unless the mandrel on
which the pulley is turned in the lathe be the same diameter as the
pulley shaft, and the pulley be held upon the mandrel by the set-screw
pressure, and not by driving the mandrel into the pulley bore. In this
case two set-screws must be used one on each end of the pulley hub, so
as to steady the pulley on the mandrel. A pulley thus trued will still
run out of true when on its shaft unless the shaft be of the same
diameter as the mandrel.
One means of obviating this difficulty is to reduce the diameter of the
shaft between the pulley seats sufficiently to allow the pulley to pass
easily, and to make the pulley bores a driving fit to their seats. This,
however, is only practicable in cases where the locations of the pulleys
are permanently fixed, and no occasion arises for the addition of new
pulleys.
[Illustration: Fig. 2646.]
To obviate this difficulty what is termed an internal clamp pulley has
been constructed. This pulley is shown in Fig. 2646. The bore is made
sufficiently smaller than the shaft diameter to be a forcing fit. A slot
in the form of an arc of a circle is formed in the hub as shown, and a
split runs from this arc into the bore. As a result a wedge driven
between the walls of the split will spring open the bore and permit its
easy passage along the shaft to its required location, when the removal
of the wedge will permit the bore to close upon the shaft. To secure the
pulley to the shaft four set-screws are employed, two of them being
shown in the cut, and the other two being similarly located on the other
side of the pulley.
By this means there will be less difference between the diameters of the
pulley bore and of the shaft should the latter be slightly less than its
standard diameter, and as a result the pulley will run more true.
Split pulleys are bored a tight fit to the shaft when the two halves are
bolted firmly together. They may, however, be made to grip the shaft in
two ways; first, if bored when bolted together the edges of the bore
will meet the shaft and clip it so firmly as to require each half bore
to spring open to permit it to pass on the shaft, but by inserting
between the two halves of the hub two thicknesses of writing paper, and
boring out the hole the thicknesses of the paper too large (which may be
done by placing two pieces of the same paper beneath the calipers or
gauge) the bore will be slightly oval when the paper is removed, and
will grip the shaft at the crown of each half bore, but the grip thus
obtained will not be so firm.
Pulleys of small diameter, as three feet or less in diameter, are
usually held to their shafts by set-screws, the consideration of their
shapes and position having been already treated of when referring to the
applications of keys and set-screws. Pulleys of large diameters, and
those which act as fly-wheels as well as pulleys, are usually held by
keys.
BALANCING PULLEYS.--A pulley (more especially those running at high
speed) should be balanced or in balance when rotating at the greatest
speed at which it is intended to run. This is necessary, because if the
centrifugal force generated by the pulley's rotation be greater on one
side than on another of the pulley, it will cause the pulley shaft to
vibrate and shake whenever the amount of unbalanced centrifugal force
becomes, on account of the speed of rotation, sufficient to bend the
shaft or deflect the framing holding the shaft.
The balancing of a pulley will not be correct unless the centrifugal
force is equal at all points on the perimeter in the same plane, as will
appear presently. In practice two methods of testing the balance of a
pulley are employed: first, the standing; and second, the running
balance. A standing balance does not in any sense balance a pulley, but
merely corrects the want of balance to a limited degree. A running
balance correctly balances a pulley when running up to the speed at
which the balance was made, but does not balance for greater speeds.
[Illustration: Fig. 2647.]
[Illustration: Fig. 2648.]
A standing balance is effected when the shaft being supported
horizontally and with as little friction as possible, the pulley will
remain at rest in any position in which it can be placed. Thus, in Fig.
2647 let C C represent the two centres of a lathe adjusted in their
distance apart so as to sustain the shaft S with just sufficient force
to prevent end movement or play of the shaft, and if the pulley P
remains motionless when arrested at any point of rotation it is in
standing balance. A common method of balancing is to set the pulley in
slow rotation several times in succession, and if the same part of the
pulley's circumference comes to rest in each case at the bottom as at B
then it is heaviest and its weight must be reduced, or weight must be
added on the diametrically opposite side of the pulley. Another method
is to rest the shaft horizontally on a pair of metallic strips as B B in
Fig. 2648, the strips resting on a flat horizontal surface D, the
testing being applied as before. Sometimes, however, cylindrical pieces
are used in place of the strips or pieces B B.
[Illustration: Fig. 2649.]
A pulley that is in balance thus tested, may not, however, be in balance
when rotated, or, as already stated, a standing balance may not be a
running balance, for the following reasons: In Fig. 2649 is a pulley
that if turned true inside and out would be of correct standing balance,
because the weight is equal on each side of the shaft; thus the point A,
though farther from the axis than B, would be counterbalanced by C,
while B would be counterbalanced by D, but as soon as the pulley was put
in rotation there would be more centrifugal force generated at A than
at B, and more at C than at D, because, though the weights would be
equal, the velocities of A and C would be greatest.
Now, suppose that instead of a continuous wide pulley several pulleys
were used, being out of true so as to be practically equal in shape to
Fig. 2649, and it is apparent that the fact of pulley A B being out of
balance is not removed by pulley C D being out in an opposite direction,
and that each pulley will tend to bend the shaft in the direction of its
excessive centrifugal force.
[Illustration: Fig. 2650.]
The effect of this inequality of centrifugal force will depend, in each
case, upon the strength of the shaft in comparison with the amount of
unbalanced centrifugal force. Suppose, for example, that the centrifugal
force at a point A in Fig. 2650 were 10 lbs. greater than at B at a
given velocity, and that the strength of the shaft be such that it will
bend 1/32 inch under a weight of 10 lbs., then the effort of the point A
will be to swing in a circle 1/16 inch larger than that due to its
diameter. Suppose, then, the stand be so firmly fixed at C as to be
motionless in a vertical direction under this effort, then the point A
will swing in an oval, as denoted by the dotted lines, the shaft
vibrating as denoted by the arrows.
[Illustration: Fig. 2651.]
Thus vibrations of the shaft, bearing, &c., occur whenever the excess of
centrifugal motion on one side of a pulley is sufficient to spring the
shaft, bearings, standard or foundation, as the case may be, and will
occur most in the direction in which those parts will most easily
succumb. From this it is evident that a pulley practically in balance,
so far as being free from vibration at a certain speed, may be
considerably out of balance at an increased speed. Thus, suppose a
pulley P, in Fig. 2651, has a rim of equal thickness, but the distance
of A from the axis of rotation is 6 inches, while the distance of B is 8
inches; then the centrifugal force at B will, at any speed of rotation,
be one-quarter more than that at A, because the distance is one-quarter
greater. Suppose, then, that its shaft, bearings, and foundation be
capable of resisting 100 lbs. without sensible flexure, but that
sensible flexure of those parts will occur under any pressure over 100
lbs.
The centrifugal force of 1 lb. at A and at B, respectively, may be
calculated by the following rule:--
_Rule._--Multiply the square of the number of revolutions per minute by
the diameter of the circle of rotation in feet, and divide the product
by 5,870. The quotient is the centrifugal force in terms of the weight
of the body.
In the case of A the pulley making, say, 200 revolutions per minute, we
have by the rule:
200^{2} × 1
----------- = 6.81 = the centrifugal force.
5,870
Likewise, centrifugal force at B = (200^{2} × 1.25)/5,870 = 8.51 = the
centrifugal force, 1 and 1.25 being diameters of circle of rotation of A
and B in feet.
Now, suppose the revolutions to be 2,000 per minute, we have in the case
of A 2,000 × 2,000 × 1 (= 4,000,000) ÷ 5,870 = 681 lbs. centrifugal
force. Add one-quarter more, or 170 lbs., to obtain the centrifugal
force at B = 851 lbs.; the unbalanced centrifugal force = 170 lbs.; and
this being 70 lbs. more than the shaft, bearings, &c., are capable of
resisting without flexure, a corresponding vibration will occur, whereas
at 200 revolutions the unbalanced centrifugal force was: Centrifugal
force at B = 8.51 lbs. less that at A = 6.81 = 1.70 lbs. unbalanced
centrifugal force, and it becomes apparent that while at 200 revolutions
the pulley would rotate without sensible vibration, at 2,000 revolutions
(in the same time), sensible vibration would occur; hence, the sensible
vibration of a pulley is in the proportion as the unbalanced centrifugal
motion is to the resistance of the shaft, bearings, &c., to flexure, and
further, as the unbalanced centrifugal motion increases with the
velocity, so also does the sensible vibration increase with the
velocity.
But there are two ways of increasing the velocity of a pulley: 1st, by
increasing the revolutions of a given pulley; 2nd, by employing a pulley
of a larger diameter, but making the same number of revolutions. In our
example we increased the speed tenfold (from 200 revolutions to 2,000)
but the centrifugal force was increased one hundredfold, according with
the law that the centrifugal force increases with the square of the
revolutions, and 10 × 10 = 100. But if the velocity had been increased
by augmenting the diameter of the pulley, the centrifugal force would
have increased in the same ratio as the pulley diameter was increased;
hence it appears that under equal velocities larger pulleys generate
less centrifugal force per unit of unbalanced weight than do smaller
ones.
[Illustration: Fig. 2652.]
A device for testing the balance of pulleys is shown in Fig. 2652; it
consists of a frame carrying a vertical spindle, which may be rotated by
suitable bevel-wheels, and the hand wheel shown. In this case it would
be preferable to balance the pulley at the greatest speed at which it
would be convenient to run it by hand with the wheel shown, because a
pulley balanced at any given speed will be balanced at any lesser speed,
although not at a greater one. But the pulley should not be driven by
the arms, because the pressure against the same will affect the balance.
It would be better therefore to let the spindle of the machine be small
enough in diameter to fit the smallest bore of pulley to be balanced, to
employ sleeves fitting the spindle and the bores of all larger bored
pulleys, and to obtain the most correct results the pulley should be
fastened to the sleeve by its set-screws, or keys of the pulley, as the
case might be, so that whatever error there might be induced by
tightening the same will be accounted for in the balancing. It is
obvious also that the pulley bore should fit the sleeve with the same
degree of tightness as it will fit the shaft to which it is to be fixed.
The heaviest side of the pulley will rotate through a circle of larger
diameter, and may be marked by a point, as a tool point moved up to it
by a slide rest, or roughly by a piece of chalk steadily moved up to it
by hand until it just touches the high side of the pulley.
[Illustration: Fig. 2653.]
The methods of correcting the balance are as follows: The heavy side of
the pulley having been found, a weight is attached to the diametrically
opposite side of the pulley; a convenient form of light weight for this
purpose is shown in Fig. 2653; it consists of what may be termed a
spring clamp, since it holds to the edge of the pulley rim, on which it
is forced by hand, by reason of the spring of the jaws. There are
numerous clamps of this form, each having a definite weight, as 2 ozs.,
3 ozs., 4 ozs., &c.; but for weights above about 1-1/2 lb. a clamp with
a set-screw is employed. For a running balance a set-screw is
indispensable. It is obvious that pulleys will be more easily and
correctly balanced when the inner side of their rim is turned up, as far
as the arms will permit, in the lathe; but on account of the expense
this is not usually done, except in the case of large pulleys.
In the best practice, however, the pulley is set in the lathe, so that
the inside of the rim runs as true as possible. Remarks on this subject
are given under the head of chucking pulleys.
When the balance is to be effected by adding weight to the pulley
mushroom-shaped pieces of metal are made for the purpose, their weights
varying by ounces; the stems are driven through holes drilled through
the rim to receive them, and riveted on the face side. The stems are of
wrought iron, while the heads may be of cast iron, but are better of
lead, because in that case they may be set with a hammer to fit the
inner surface of the pulley rim.
In some practice, protuberances, or a web in the middle of the pulley,
are cast on the pulley, and the balance is effected by cutting this away
to reduce the weight on the heavy side.
When pulleys are to revolve at very high speeds, as in the case of those
for emery-wheel spindles, the shafts themselves require to be balanced,
especially if of cast iron, because that part of the shaft uppermost in
the mould will be of less density and weight than that at the bottom of
the mould. The pulley should be balanced separately, and the whole again
balanced after being put together, because the weight of the key or
set-screw will be sufficient to destroy the balance under a sufficiently
high speed of rotation.
The edges of pulley rims should be trued up in the lathe when the rim is
turned so that the pulleys to receive a belt may be set in line by
pressing a straight-edge, or setting a line to have contact with (as
near as possible) diametrically opposite points of the edge of one
pulley, and setting the other to have its corresponding edge in line.
Pulleys should run true so that the strain or tension of the belt shall
be equal at all parts of the revolution, and the transmitting power
shall be equal. The smoother and more polished the surface of the pulley
the greater its driving power.
The transmitting power of a pulley may be increased by covering the
pulley face with leather or rubber bands, but the thickness of these
should be equal both across the width and all around the circumference
so as to run true.
The amount of increase of driving power due to this covering is
variously stated, but may be taken at about 20 to 30 per cent. A cement
for fastening such pulley coverings may be made as follows: Take one
ounce of caoutchouc (pure or native rubber) and cut it into thin slices,
place it in a tinned sheet-iron vessel with six or seven ounces of
sulphide of carbon; the vessel is then to be placed in a water tank
previously heated to about 86° Fahr. To prevent the solution from
becoming thick and unmanageable, mix with a solution consisting of
spirits of turpentine, in which half an ounce of caoutchouc in shreds
has been dissolved over a slow fire, and then a quarter of an ounce of
powdered resin; from an ounce and a half to two ounces of turpentine
being afterwards stirred in, to be added in small quantities. This
cement must be kept in a large-mouthed bottle well corked, and in using
clean the parts to be united thoroughly with benzine; apply two coats of
cement, allowing each to dry before applying the next; when applying the
last coat allow the cement to dry so as to become very sticky, then
press the surfaces firmly together and allow to thoroughly dry. This is
waterproof.
A pulley that imparts motion to the belt enveloping or partly enveloping
it is termed a driving pulley or driver. A driven pulley is one that
receives motion from, or is driven by, the belt; hence in every pair of
pulleys connected by belt, one is termed the driver and the other the
driven. The revolutions of two pulleys connected by belt will vary in
the same proportion as their diameters, although their rim velocity will
be equal.
Suppose, for example, that a pulley of 7 in. diameter drives one of 14
in. diameter, then if there is no slip on either pulley both pulleys
will run at the same velocity as the belt, and this velocity must be
equal to the velocity of the driver, because the belt is moved by the
driver. Now, suppose the driver which is of 7 in. diameter makes one
revolution in a minute, and as it is only one-half the diameter of the
driven wheel, its circumference will also be half that of the driven, so
that it must make two revolutions to carry around length of belt enough
to pass once around the driven pulley. The revolutions of the two are,
therefore, in the same proportions as are their diameters, which in this
case is two to one. As the driven pulley is the largest diameter, it
will make one revolution in the same time that the driver makes two. But
suppose the driving pulley was 14 and the driven was 7 inches in
diameter, then the proportion would still be two to one, and the driven
would make two revolutions to every revolution of the driver.
[Illustration: Fig. 2654.]
If we are given the number of revolutions a driving pulley makes and the
diameter or circumference of both pulleys, and require to find the
number of revolutions the driven pulley will make to one or to any given
number of the driver, we may consider as follows: Suppose the
circumference of the driver to be 24 inches and that of the driven to be
18 inches, then in Fig. 2654 let circle A represent the driver, and
circle B the driven pulley. If we divide the circumference of A into
four equal divisions, as at 1, 2, 3, and 4, each of these divisions will
equal 6 inches, because the whole circumference being 24 inches, one
quarter of it will be 6. If we divide the circumference of B into
six-inch divisions there will be but three of them as marked, because
one-third of 18 (its circumference) is 6. Now three of the divisions at
A will move A a full revolution, and the remaining division on A will
move B through another one-third of a revolution, hence, each revolution
of A equals 1-1/3 revolutions on B. The proportions of the circumference
are, therefore, as 1-1/3 to 1, or as 133 is to 100, taking A as the
driver, and, therefore, as the basis of the proportion. But suppose we
take B as the basis of the proportion, and one revolution of B will
cause A to make three quarters of a revolution, or during 100
revolutions of B, A will make 75. But nevertheless during the period
that A is making 100 revolutions B will have made one-third more, or
133-1/3, because B makes 1-1/3 revolutions to cause A to make one
revolution. From this it will be seen that the proportion is as the
greater is to the lesser, and not as the lesser is to the greater, or,
in other words, it is in this case as 24 is to 18, which is one and
one-third times, for one-third of 18 is 6, and 18 + 6 = 24.
Suppose, now, we take the four divisions on A and the three on B to
consider their proportions, and we may say 4 is 1-1/3 times 3, or we may
with equal propriety say 3 is 3/4 of 4, hence 4 is not in the same
proportion to 3 that 3 is to 4. Let it now be supposed that a driven
pulley B is 18 inches in diameter, and requires to be driven one quarter
faster than the driver, what then must be the diameter of that driver?
As the revolutions require to be increased one-fourth the pulley
diameter must be increased one-fourth. Thus one quarter of 18 = 4-1/2,
and this added to 18 is 22-1/2, which is therefore the diameter of the
driving pulley, as may be proved as follows: Suppose the circumferences
instead of the pulley diameters to be 22-1/2 and 18 respectively, and
that the largest pulley makes 100 revolutions, then it will pass 2,250
(22-1/2 × 100 = 2,250) inches of belt over its circumference, and every
18 inches of this belt will cause the small pulley to make one
revolution; hence we divide 2,250 by 18, which gives us 125 as the
revolutions made by the small pulley, while the large one makes 100.
Thus it appears that we obtain the same result whether we take the
circumferences or the diameters of the pulleys, because it is their
relative proportions or relative revolutions that we are considering,
and their actual diameters do not affect their proportions one to the
other. Thus, if a 10-inch pulley drives a 30-inch one, the proportions
being three to one, the revolutions will be three to one, and the driven
being three times the largest, will make one revolution to every three
of the driver. If the driver was 3 inches in diameter and the driven 9,
the revolutions would be precisely the same as before, but with equal
revolutions the velocities would be different, because in each
revolution of the driver it will move a length of belt equal to its
circumference; hence, the greater the circumference the greater length
of belt it will move per revolution. To take the velocity into account,
we must take into consideration the number of revolutions made in a
given time by the driver. Suppose, for example, that the driver being 3
inches in diameter makes one revolution in a minute, then it will move
in that minute a length of belt equal to its circumference, so that the
circumference of the driver, multiplied by the number of its revolutions
per minute, gives its velocity per minute. Thus, if a pulley has a
circumference of 50 inches, and makes 120 revolutions per minute, then
its velocity will be 6,000 inches per minute, because 50 × 120 = 6,000.
The velocity of the belt, and therefore that of the driven wheel, will
also be 6,000 inches per minute, as has already been shown. From this
train of reasoning the following rules will be obvious:--
To find the diameter of the driving pulley when the diameter of the
driven pulley and the revolutions per minute of each are given:
_Rule._--Multiply the diameter of the driven by the number of its
revolutions, and divide the product by the number of revolutions of the
driver, and the quotient will be the diameter of the driver.
The diameter and revolutions of the driver in a given time being known,
to find the diameter of a driven wheel that shall make a given number of
revolutions in the same time:
_Rule._--Multiply the diameter of the driver by its number of
revolutions, and divide the product by the number of revolutions of the
driven. The quotient will be the diameter of the driven.
To find the number of revolutions of a driven pulley in a given time,
its diameter and the diameter and revolutions of the driver being given:
_Rule._--Multiply the diameter of the driver by the number of its
revolutions in the given time, and divide by the diameter of the driven,
and the quotient will be the number of revolutions of the driven in the
given time.
Suppose, however, that the speed of the shaft only is given, and we
require to find the diameter of both pulleys, as, for example, suppose a
shaft makes 150 revolutions per minute, and we require to drive the
pulley on a machine 600 revolutions per minute. Here we have two
considerations: first, the relative diameters of the two pulleys, and
secondly, the diameter of pulley and width of belt necessary to transmit
the amount of power necessary to drive the machine at the speed
required. Leaving the second to be discussed hereafter in connection
with the driving power of belts, we may proceed to determine the first
as follows: The pulley on the machine must be as much smaller than that
on the main shaft, as the speed of the pulley on the machine requires to
run faster than does the main shaft, hence we divide the 600 by 150 and
get four, which is the number of times smaller than the driver that the
driven pulley must be. Suppose then the driver is made a 24-inch pulley,
then the driven must be a 6-inch one, because 24 ÷ 4 = 6; or we may make
the driver 36, and the driven 9, because 36 ÷ 4 = 9; or the driver being
48 inches in diameter, the driven must be 12, because 48 ÷ 4 = 12. To
reverse the case, suppose the shaft to make 200 revolutions per minute,
and the machine pulley to make 50, then since 200 ÷ 50 = 4, the driven
(or machine pulley) must have a diameter four times that of the driver,
and any two pulleys of which one is four times the diameter of the other
may be used, as say: Pulley on line shaft 10 inches in diameter, pulley
on machine 40 inches in diameter; or, pulley on line shaft 20 inches in
diameter, pulley on machine 80 inches in diameter.
Now, in nearly all cases that are met with in practice, it would be
inconvenient to have so large a pulley as 80 inches in diameter to drive
a machine, and again in most cases a driving pulley of 10 inches in
diameter would be too small. So likewise in cases where the machine
pulley requires to run faster than the line shaft, a single pair of
pulleys will be found to give, where great changes of revolution are
required, too great a disproportion in the diameter of the pulleys; thus
in the case of a shaft making 150, and the machine requiring to make
600, we may use the following pairs of pulleys:--
On Main Shaft. On Machine Shaft.
First 32 inch diameter 8 inch diameter.
Second 40 " " 10 " "
Third 48 " " 12 " "
Fourth 60 " " 15 " "
But the machine may require so much power to drive it, that with the
width of belt it is desired to employ, a pulley larger than either of
these is necessary, as, say, one 20 inches in diameter. Now, with a
20-inch driven pulley, the driver would require to be 80 inches in
diameter, because 20 × 4 = 80. But there may not be room between the
shaft and the ceiling for a pulley of so large a diameter, or such a
large pulley may be too heavy to place on the shaft, or it may be too
costly, and to avoid these evils, countershafts are used.
By the employment of a countershaft we simply obtain--with two pairs of
pulleys and by means of small pulleys--that which could be obtained in a
single pair, providing the great difference in their diameters
(necessary to obtain great changes of rotation), were not objectionable;
all that is necessary, therefore, is to accomplish part of the required
change of rotation in one pair, and the remainder in the other. In
doing this, however, while the velocity of each driver and driven
will be equal (as was explained with reference to a single pair),
notwithstanding the difference in their diameters, yet the velocity of
one pair will necessarily differ from that of the other, so that the
pulley on the machine will vary in its velocity as well as in its
rotation from that of the first driver. The first driver is that on the
main or driving shaft, and the pulley it drives is the first driven. The
second driver is the second pulley on the countershaft, and the second
driven is the one it drives or that on the machine. Suppose, then, a
driving shaft makes 100 revolutions per minute, and the machine requires
to make 600, then the speed of rotation requires to be increased six
times. Now we may effect this change of six times in several ways; thus:
Suppose we increase the rotations three times in the first pair, then
the second pulley will make 300 rotations, or three times those of the
main shaft, and all we have to do is to make the second driven one-half
the diameter of the second driver, and its rotations will be double
those of the second driver, which will give the required speed of 600
revolutions. Suppose, however, we change the speed four times in the
first pair, and the 100 of the shaft becomes 400 on the countershaft,
and to increase this to 600 on the second driven, all that is required
is to make its diameter one-half less than that of the second driver,
because 600 is one-half more than 400. From this it will be perceived
that the number of changes or amount of increase or decrease of speed
being given, the proportion of diameters for both pairs of pulleys will
be represented by any two numbers which, multiplied together, will give
a sum equal to the number of increased revolutions required. Having
found the proportions for each pair, it remains to determine their
actual diameters, and they will be found to vary under different
conditions.
Suppose, for example, we have the following conditions: Main shaft runs
100; machine must run 600. The pulley on the line shaft is 36 inches in
diameter; required, the diameters for the other three pulleys.
To make three changes in the first pair, the first driven must be 1/3
the diameter of the first driver, which is 12 inches. Now the second
pair we may make any diameters that are two to one; and since the second
driver is to be the smallest, we may select as small a pulley as will
answer for the machine, and make its driver twice its diameter.
But suppose it is the diameter of the pulley on the machine that is
fixed, and the diameter of the other three require to be found. Let the
diameter of the second driven be 12; then its driver on the countershaft
must be 24. The other two must have diameters 3 to 1 as before, any
suitable wheels being selected.
Yet another condition may occur. Thus, suppose the countershaft is on
hand, and that it has on it two pulleys, as a 12 and a 24-inch; then a
36 on the inner shaft will be three times as large as the 12, and a
12-inch on the machine will be twice as small; or, what is the same, one
half as large as the 24.
When the principle is clearly understood the calculations can be
performed mentally with ease so far as the required diameters to attain
the necessary speed is concerned, but there are other considerations
that claim attention.
Thus, for example, to multiply the rotations 6 times we may proportion
the first pair as follows: Driver 48, driven 16; second pair, driver 30,
driven 15 inches in diameter.
Or we may proportion them as follows: First pair: driver 36, driven 12;
second pair: driver 28, driven 14 inches in diameter.
In the second arrangement of diameters the drivers are each 2 inches,
and the driven each 1 inch less in diameter than in the first; hence
their cost would be diminished, as would also be the wear of the
journals, on account of the reduced weight of the pulleys; hence, if the
driving capacity of each pulley is equal to the requirements the second
arrangement would be preferable.
In considering this part of the subject, first let it be shown that
although the horse-power transmitted by the two belts is equal whatever
be the proportions of the pulleys (provided, of course, that the belts
do not slip), yet the strain or wear and tear of the belts varies, and
the requirements for one belt are therefore different from those for the
other.
[Illustration: Fig. 2655.]
In Fig. 2655 let A represent a 36-inch pulley on the driving shaft, B a
12-inch, and C a 24-inch pulley on a countershaft, and D a 12-inch
pulley on a machine shaft. Let the main shaft make 100 revolutions per
minute, and the machine requires a force to move it equal to 50 pounds
applied to the perimeter of D. Now the rotations of D will, with these
pulleys, be six to one of the main shaft or A, which gives D 600
revolutions per minute, thus: 100 × 6 = 600. The circumference of D is
about 37.69 inches, which, multiplied by 600 (the number of its
revolutions), gives 22,614 inches, or 1,884.5 feet as its speed per
minute. This multiplied by the 50 pounds it takes to move the machine at
the perimeter of D, gives 94,225 as the foot pounds per minute required
to drive the machine 600 revolutions per minute, and this, therefore, is
the amount of power transmitted by each belt. On the second belt this is
shown to be composed of 50 pounds moving 1,884-1/2 feet per minute,
hence we may now find how it is composed on the first belt, as
follows:--
The diameter of the first driver is 36 inches, and its circumference
113.09 inches, or 9.42 feet; this, multiplied by its revolutions per
minute, will give its speed, thus: 9.42 × 100 = 942 feet per minute. To
obtain the necessary amount of pull for this first belt, we must divide
this speed into the number of foot pounds it takes to drive the machine,
thus: 94,225 ÷ 942 = 100.02. The duties of the two belts are therefore
as follows:--
First belt, weight of pull 100.02
" speed per minute 942 feet.
Second belt, weight of pull 50.00
" speed per minute 1884.5 feet.
The duty in foot pounds being equal, as may be shown by multiplying the
feet per minute by the force or weight of the pull, leaving out the
fractions, thus:--
942 × 100 = 94,200.
1884 × 50 = 94,200.
The difference in the requirements is, then, that the first belt must
have as much more weight or force of pull than the second as its speed
is less than that of the second.
It is obvious that in determining the proportions of the pulleys this
difference in the requirements should be considered, and the manner in
which this should be done depends entirely upon the conditions.
Thus, in the case we have considered, the speed was increased, but the
object of the countershaft may be to decrease the speed, and in that
case the conditions would be reversed, inasmuch as though the foot
pounds transmitted by both belts would still be equal, yet the speed
would be greatest and the strain or pull the most on the second belt
instead of on the first.
It is obvious, then, that the proportions of the pulleys being
determined the actual diameters must be large enough to transmit the
required amount of power without unduly straining the belt.
CHAPTER XXXII.--Leather Belting.
The names of the various parts of a hide of leather as known to commerce
are as follows:--
[Illustration: Fig. 2656.]
In Fig. 2656 the oblong portion between the two belly parts marked G G
is known as the "butt," and when split down the ridge, as shown by the
dotted line down the centre, the two pieces are known as "bends;" the
two pieces marked Y are "belly offal;" D is known as "cheeks and faces."
The butt within the dotted line may extend in length from A to B, or
from A to C; if cut off between B and C that portion is called the
"range" or the whole from B to X may be cut in one piece and termed a
"shoulder."
Sometimes the range is cut off and the rest would be called a shoulder
with "cheeks and faces" on; or, again, the range and shoulder may be in
one nearly square piece. The manner of cutting this part depends upon
the spread and size of the hide.
[Illustration: Fig. 2657.]
The part of the hide that is used to manufacture the best belting is
shown in Fig. 2657, on which the characteristics of the various parts
are marked. The piece enclosed by the dotted lines is that employed in
the manufacture of the commonest belting, while that enclosed by the
full lines B, C, D is that used for the best belting. The former
includes the shoulder, which is more soft and spongy, while it contains
numerous creases, as shown. These creases are plainly discernible in the
belt when made up, and may be looked for near the belt points.
[Illustration: Fig. 2658.]
The centre of the length of the hide will stretch the least, and the
outer edges on each side of the length of the hide the most. Hence it
follows that the only strip of leather in the whole hide that will have
an equal amount of stretch on each edge is that cut parallel to line A,
and having that line as a centre of its width. All the remaining strips
will have more stretch on one edge than on the other, and it follows
that, to obtain the best results the leather should be stretched after
it is cut into strips, and not as a whole in the hide, or in that part
of it employed for the belt strips. It is found, indeed, that, even
though stretched in strips, the leather is apt in time to curve. Thus a
belt that is straight when rolled in the coil will, on being unrolled,
be found to be curved. It is to be observed, also, that each time the
width of the strips is reduced, this curving will subsequently take
place; thus, if a belt 8 inches wide and quite straight, be cut into two
belts of 4 inches wide, the latter will curve after a short time. The
reason of this is almost obvious, because it is plain that the edge that
was nearest the centre line of the hide offers the greatest resistance
to stretching; hence, when the strip is stretched straight, and an
equilibrium of tension is induced, reducing the width destroys to some
extent this equilibrium, and the leather resumes, to some extent, its
natural conformation. This, however, is not found to be of great
practical importance, so long as the outer curve of one piece is on the
same side as the outer curve of its neighbor, as shown on the left view
in Fig. 2658, in which case the belt will run straight, notwithstanding
its curve; but if the curves are reversed, as on the right in Fig. 2658,
the belt will run crooked, wabbling from side to side on the pulley. To
avoid this, small belts may be made continuous by cutting them from the
hide, as shown in Fig. 2659; but in this case it is better that the belt
be cut from the centre strip of the hide.
[Illustration: Fig. 2659.]
If the leather is stretched in strips after being cut from the hide, the
amount of the stretch is about 6 inches in a length of 4-1/2 feet of a
belt, say, 4 inches wide, but the stretch will be greater in proportion
as the width of the strip is reduced. But if stretched as a whole, the
amount of stretch will be about 1 inch per foot of length, the shoulder
end stretching one-third more.
If the leather has been properly stretched in strips the length of the
belt may be cut to the length of an ordinary tape line drawn tightly
over the pulleys, which allows the same stretch for the belt as there is
on the tape line, added to the degree of tension due to cutting the belt
too short to an amount equalling its thickness (as would be the case if
the belt is cut of the same length as the tape line); or if the belt is
a double one, the belt thus cut to length would be too short to an
amount equal to twice the thickness of the strips of leather of which it
is composed.
When the amount to which the leather has been stretched is an unknown
quantity (as is commonly the case), the workman cuts the belt too short,
to an amount dictated solely by judgment, following no fixed rule. If,
as in the case of narrow belts, the stretching be done by hand, the belt
is placed around the pulleys, stretched by hand, and cut too short to an
amount dictated by judgment, but which may be stated as about 2-1/2 per
cent. of its length.
But the stretch of a belt after it is put to work proceeds very much
more rapidly if it has been stretched in the piece and not in the strip,
hence it gets slack in the course of a few hours, or of a day or more,
according to how much it has been stretched; whereas one properly
stretched in the strip will last for weeks, and sometimes for months,
without getting too slack.
[Illustration: Fig. 2660.
+----------------+----------------+-----------------+----------------+
|2,000 1/4 3. |2,050 3/16 3.1|2,150 3/16 3.2 |2,175 1/4 3.3 |
+----------------+----------------+-----------------+----------------+
|1,400 9/32 2.12|2,000 1/8 3. |2,625 3/16 3.4 |2,325 7/32 3.4 |
+----------------+----------------+-----------------+----------------+
|2,000 1/4 2.11|2,075 3/16 3.1|2,375 7/32 3.4 |2,175 7/32 3.5 |
+----------------+----------------+-----------------+----------------+
|2,075 1/4 2.12|2,700 7/32 3.3|2,600 7/32 3.4 |2,275 5/32 3.7 |
+----------------+----------------+-----------------+----------------+
|2,450 1/4 2.13|3,025 9/32 3.7|2,575 11/32 3.8 |2,225 7/32 3.10|
+----------------+----------------+-----------------+----------------+
|2,475 1/4 3. |2,975 5/16 3.6|3,200 9/32 3.10|2,175 3/8 3.10|
+----------------+----------------+-----------------+----------------+
|2,575 11/32 3.2 |2,875 9/32 3.7|3,475 11/32 3.13|1,850 11/32 3.11|
+----------------+----------------+-----------------+----------------+
|2,675 11/32 3.2 |3,075 11/32 3.8|3,450 9/32 4. |1,950 1/4 3.11|
+----------------+----------------+-----------------+----------------+
|2,650 3/8 3.2 |2,900 9/32 3.6|3,150 3/16 3.15|2,225 1/4 3.10|
+----------------+----------------+-----------------+----------------+
|2,800 1/4 3.1 |3,050 5/16 3.6|2,850 1/4 3.13|2,275 3/16 3.7 |
+----------------+----------------+-----------------+----------------+
|2,700 1/4 3. |3,150 7/32 3.5|3,000 3/16 3.10|2,600 1/4 3.5 |
+----------------+----------------+-----------------+----------------+
|2,650 1/4 2.13|3,000 7/32 3.4|3,400 1/8 3.6 |2,550 1/4 3.4 |
+----------------+----------------+-----------------+----------------+]
The results of some experiments made by Messrs. J. B. Hoyt & Co. on the
strength of the various parts of a hide are given in Fig. 2660. One side
of the part of the hide used for leather belting was divided off into 48
equal divisions, each piece being 11-3/4 inches long, and two inches
wide, the results of each test being marked on the respective pieces.
The first column is the strain under which the piece broke; the second
column is the amount in parts of an inch that the piece stretched
previous to breaking; and the third column is the weight of the piece in
ounces and drachms.
From the table it appears that the centre of the hide which has the most
equal stretch has the least textile strength, while in general that
which has the most stretch has the greatest textile strength, but at the
same time the variations are in many cases abrupt.
A single belt is one composed of a single thickness of leather put
together, to form the necessary length, in pieces, riveted and cemented
together at the joint, or sewed or pegged as hereafter described.
A double belt is similarly constructed, but is composed of two
thicknesses of leather cemented and riveted, pegged, or sewed together
throughout its whole length, as hereafter described. The object of a
double belt is to increase the strength without increasing the width of
the belt. Belts are usually made in long lengths coiled up for ease of
transportation, the length of belt required being cut from the coil.
To find the length in a given coil that is closely rolled--Rule: the sum
of the diameter of the roll and the eye in inches, multiplied by the
number of turns made by the belt, and this product multiplied by the
decimal .1309, will equal length of the belt in feet.
[Illustration: Fig. 2661.]
The grain or smooth side of the leather is the weakest, as may be
readily found by chamfering it to a thin edge, when it will tear like
paper, and a great deal more easily than will the flesh side under
similar treatment. Again, it will crack much more readily: thus, take a
piece of leather and double it close with the grain side outward, and it
will crack, as shown in Fig. 2661 at C, whereas if doubled, however
closely, on the flesh side no cracks will appear. If the edge of a
clean-cut piece of leather be examined, there will be found extending
from the grain side inward a layer of lighter color than the remainder
of the belt; and this whole layer is less fibrous and much weaker than
the body of the belt, the strongest part of which is on the flesh side.
If the grain side is shaved off thin and stretched slightly with the
fingers it will exhibit a perfect network of small holes showing where
the hair had root. Here, then, we have weakness and excessive liability
to crack on the grain side of the leather, and it is obvious that if
this side is the outside of the belt, as in Fig. 2662, at A, the
tendency is to stretch and crack it, especially in the case of small
pulleys, whereas if the grain side were next to the pulley the tendency
would be to compress it, and therefore, rather to prevent either
cracking or tearing. Furthermore, very little of the belt's strength is
lost by wearing away its weakest side.
[Illustration: Fig. 2662.]
Another and important consideration is, that the grain side will lie
closest and have most contact over a given area with the pulley surface.
In making double belts of extra good quality, it is not uncommon to cut
away or shave off the grain side of both belts, and place those surfaces
together in making up the belts.
If the grain side of a belt is the outside when on the pulleys, and a
crack should consequently start, the destruction of the belt proceeds
rapidly, because the line of crack is the weakest part of the belt, and
the belt has less elasticity as a continuous body, and more at the line
of crack. Cracking may, to some extent, be provided against by oiling
the belt, and for this purpose nothing is better than castor oil. In the
manufacture of belts, extra pliability is induced by an application of
fish oil and tallow, applied when the belt (after having been wetted),
is in a certain stage of progress toward drying. The oil and tallow are
supposed to enter the pores of the leather and supply the place of the
evaporated water.
LENGTH OF BELTS.--Since the stretch of a belt is variable in different
belts of the same length, no rule can be given for the amount to which a
belt should be cut shorter than the measured length around the pulleys,
and it follows, therefore, that the length of a belt cannot be obtained
precisely by calculation. In practice the necessary length for a belt to
pass around pulleys already in their places upon the shaft is usually
obtained by passing a tape line or cord around the pulleys, the stretch
of the tape line being allowed as that necessary for the belt. Then when
the belt is placed around the pulleys it is shortened if it should
appear to require more tension. If, however, the belt length for pulleys
not in position is required, it may be obtained as follows, the error
being so slight as to be within the margin of difference of stretch in
different belts, and therefore of no practical moment:--
[Illustration: Fig. 2663.]
For open belts let the distance between the shaft centres, as _a_ _b_ in
Fig. 2663, be the base of a right angle triangle, and the difference
between the semi-diameters, as _b_ _c_, the perpendicular. Square the
base and the perpendicular, and the square root of the sum of the two
will give the hypothenuse, and this multiplied by 2 and added to
one-half the circumference of each pulley is the required length for the
belt. This will give a belt too long to the amount to be cut out of the
belt to give it the necessary tension when on the pulleys.
_Example._--Let the distance between centres in Fig. 2663 be 48 inches;
diameter of large pulley 24 inches; diameter of small pulley 4 inches--
Here distance between centres 48
" " " 48
---
384
192
----
2304
Square of perpendicular 100
----
2404 Square root of 2404 = 49.03
Multiply by 2 2
-----
98.06
Half circumference of large pulley 37.699
-------
135.759
Half circumference of small pulley 6.283
-------
Length of belt 142.042
A simpler rule which gives results sufficiently accurate for practical
purposes is as follows:--
_Rule._--Add the diameter of the two pulleys together, divide the result
by 2, and multiply the quotient by 3-1/4, then add this product to twice
the distance between the centres of the shafts, and you have the length
required.
When the length of a crossed belt is required, and the pulleys are not
erected upon the shafts, it is, on account of the abstruseness of a
calculation for the purpose, preferred in workshop practice to mark off
by lines the pulleys set at their proper distance apart (either full
size or to scale), and measure the length of the side of the belt,
supposing the belt to envelop one-half the circumference only of each
pulley, and to add to this one-half the circumference of each pulley; or
if there is a great difference between the relative diameters of the
pulleys and the distance apart of the shafts is unusually small, the
lengths of the straight sides of the belt are measured and the arcs of
contact around the pulleys are stepped around by compasses, the set of
the compasses being not more than about one-tenth the circumference of
the pulleys. This gives a more near result than that obtained by
calculation, because although it will give a belt shorter than by
calculation, yet the belt will be too long on account of the stretch
necessary to the tension required for ordinary conditions.
[Illustration: Fig. 2664.]
In narrow belts, as, say, three inches and less in width, the belt may
be cut to the length of a tape line passed over the pulleys, and when
placed over the pulleys it may be strained under a hand pull and cut as
much shorter as the tension under hand pressure indicates as being
necessary.
But if the belt is a wide one a stretching clamp, such as shown in Fig.
2664, is employed, the screws being right hand at one end and left hand
at the other, so that operating them draws the clamps, and therefore the
ends of the belt, together.
The stretch of a belt not stretched in the piece proceeds slowly when
the belt is at work, hence if laced at first to a proper degree of
tension it will get slacker in a few hours or in a day or so, and must
be tightened, or taken up as it is termed, by cutting a piece out. For
this purpose a butt joint possesses the advantage that the piece to be
taken out may be less, and still leave the end clear for new holes to be
punched, than is the case with a lap joint, which occurs because the
butt joint occupies a shorter length of the belt than is the case with a
lap joint.
[Illustration: Fig. 2665.]
[Illustration: Fig. 2666.]
When a belt is under tension upon two pulleys and at rest, the friction
or grip of the belt upon the respective pulleys (supposing them to be of
the same diameter and therefore to have the same arc and area of
contact) will depend upon the relative positions of the pulleys; thus
suppose one pulley to be above the other as in Fig. 2665, the upper
pulley P will have the grip due to the tension of the belt added to that
due to the weight of the belt, whereas if placed horizontally, as in
Fig. 2666, the weight of the belt will fall equally on the two pulleys,
and for this reason vertical belts of a given width require to have a
greater tension to transmit the same amount of power as the same belt
would if placed horizontally. But as soon as motion was transmitted, by
the belt, from one pulley to the other, the belt on one side of the
pulley would be under greater tension then that on the other.
[Illustration: Fig. 2667.]
Suppose, for example, a belt to transmit motion and power from pulley A
in Fig. 2667, to pulley B, then the side C of the belt is that which
drives or pulls B, and it is therefore called the driving side of the
belt, the resistance to rotation offered by B causing the driving side
of the belt to be the most strained; and hence the straightest, whereas
the side D will be free of the tension due to the resistance of B.
[Illustration: Fig. 2668.]
But if the direction of motion be reversed as in Fig. 2668, A still
being the driving pulley, the side D will be the one most tightly
strained, and therefore, the driving side of the belt; or, in other
words, the driving side of a belt is always that side which approaches
the driving pulley, and the slack side is always that which recedes from
the driving pulley. In horizontal belts, however, the driving side of
the belt is not a straight line, because of the belt sagging from its
own weight no matter how tightly it may be strained, but the shorter the
belt the less the sag.
[Illustration: Fig. 2669.]
It is always, therefore, desirable, so far as the driving power of the
belt is concerned, to have the lower half (of belts running
horizontally) the driving side, because in that case the sag of the belt
causes it to envelop a greater arc of the pulley, which increases its
driving power. If the circumstances will not permit this and the sag of
the belt operates to practically incapacitate the belt for its duty,
what is termed an idle wheel or idler may be employed as shown in Fig.
2669 at E, serving to prevent the sag and to cause the belt on the
driving side to envelop a greater portion of the pulley's circumference,
and hence increase its friction on the pulley and therefore its driving
power. In the example the two pulleys A and B are of equal diameters;
hence the idle wheel is placed midway between them, but when such is not
the case the idle wheel should be located according to the circumstances
and the following considerations. The idle wheel requires a certain
amount of power to drive it, and this amount will be greater as the idle
wheel is nearer to the smallest wheel of the pair connected; but on the
other hand, the closer the idle wheel to the small pulley (all other
factors being equal) the greater the arc of small pulley surface
enveloped by the belt, and hence the greater the belt's driving power.
When therefore a maximum increase of driving power is required, the
idler must be placed near to the smallest pulley, the desired effect
being paid for in the increased amount of motive power required to
rotate the driving pulley.
But under equal conditions the larger the diameter of the idle wheel the
less the power required to drive it, because the less its friction on
its journal bearing. A belt tightener should whenever practicable be
placed on the slack side of the belt.
Belt tighteners are sometimes used to give intermittent motion, as in
the case of trip hammers; the belt being vertical is made long enough to
run loose, until the tightening pulley closes the belt upon the pulley,
taking up its slack and increasing the arc of contact.
[Illustration: Fig. 2670.]
When the direction of rotation of the driven pulley requires to be
reversed from that of the driving pulley, the belt is crossed as in Fig.
2670. A crossed belt has a greater transmitting power than one uncrossed
(or, as it is termed, than an "open belt") because it envelops a greater
arc of both pulleys' circumference. This is often of great advantage
where the two pulleys are of widely varying diameter, especially if the
small pulley requires to transmit much power, and be of very small
diameter.
But a crossed belt is open to the objection that the surfaces of the
belt rub against each other at the point of crossing, which tends to
rapidly wear out the laced joint of the belt. By crossing a vertical
belt the lower pulley receives part of the weight of the belt.
When a belt connects two pulleys whose respective planes of revolution
are at an angle one to the other, it is necessary that the centre line
of the length of the belt shall approach the pulley in the plane of the
pulley's revolution, which is sufficient irrespective of the line of
motion of the belt when receding from the pulley. This is shown in Fig.
2671, which represents what is known as a quarter twist; A, B are two
pulleys having their planes of revolution at a right angle, the belt
travelling as denoted by the arrows, then the centre line C of the belt
being in the plane of rotation of A on the side on which it advances to
A, the belt will continue to run upon the same section of A. If the
pulley positions be reversed, as in Fig. 2672, the same rule applies,
and the side D in the figure being that which advances upon B must
travel to B in the plane of B´s rotation, otherwise the belt would run
off the pulley; hence it is obvious that the belt motion must occur in
the one direction only.
[Illustration: Fig. 2671.]
[Illustration: Fig. 2672.]
[Illustration: Fig. 2673.]
Shafts at any angle one to another may have motion communicated from one
to the other by a similar belt connection, providing that a line at a
right angle to the axis of one shaft forms also a right angle with the
axis of the other. Thus in Fig. 2673 the axis of shaft A may be set at
any required angle to the plane of rotation of pulley B, provided that
the axial line of A be made to lie at a right angle to the imaginary
line _l_, which is at a right angle to the axis of the shaft of B, and
that the side of the driving pulley which delivers the belt (as C, Fig.
2671) is in line with the centre line of the driven pulley, as denoted
by the dotted line C.
[Illustration: Fig. 2674.]
But when this provision cannot be carried out, pulleys to guide the
direction of motion of the belt must be employed; thus in Fig. 2674 are
an elevation and plan[39] of an arrangement of these guide or mule
pulleys; A B is the intersection of the middle planes E E and F F of the
pulleys P and P´ to be connected by belt. Select any two points, A and
B, on this line and draw tangents A C, B D to the principal pulleys.
Then C A C and D B D are suitable directions for the belt. The guide
pulleys must be placed with their middle planes coinciding with the
planes C A C, D B D, and the belt will then run in either direction.
[39] From Unwin's "Elements of Machine Design."
[Illustration: Fig. 2675.]
In Fig. 2675 is an arrangement of guide pulleys by which two pulleys not
in the same plane are connected, while the arc of contact of the smaller
pulley C is increased by the idlers or guide pulleys A B, while either C
or D may be driven running in either direction.
[Illustration: Fig. 2676.]
In Fig. 2676 is shown Cresson's adjustable mule pulley stand, which is a
device for carrying guide pulleys, and admitting of their adjustment in
any direction. Thus the vertical post being cylindrical, the brackets
can be swung around upon it and fastened in the required position by the
set-screws shown. The brackets carrying the pulleys are also capable of
being swung in a plane at a right angle to the axis of the guide
pulleys, and between these two movements any desired pulley angle may be
obtained. It is obvious that by moving the brackets along the
cylindrical post their distance apart may be regulated.
When a belt is stretched upon two pulleys and remains at rest there will
be an equal tension on all parts of the belt (that is to say,
independent of its weight, which would cause increased tension as the
points of support on the pulleys are approached from the centre of the
belt between the two pulley shafts); but so soon as motion begins and
power is transmitted this equality ceases, for the following reasons:--
[Illustration: Fig. 2677.]
In the accompanying illustration, Fig. 2677, A is the driving and B the
driven pulley, rotating as denoted by the arrows; hence C is the driving
and D the slack side of the belt. Now let us examine how this slackness
is induced. It is obvious that pulley A rotates pulley B through the
medium of the side C only of the belt, and from the resistance offered
by the load on B, the belt stretches on the side C. The elongation of
the belt due to this stretch, pulley A takes up and transfers to side D,
relieving it of tension and inducing its slackness. The belt therefore
meets pulley B at the point of first contact, E, slack and unstretched,
and leaves it at F, under the maximum of tension due to driving B.
While, therefore, a point in the belt is travelling from E to F, it
passes from a state of minimum to one of maximum tension. This tension
proceeds by a regular increment, whose amount at any given point upon B
is governed by the distance of that point from E. The increase of
tension is, of course, accompanied by a corresponding degree of belt
stretch, and therefore of belt length; and as a result, the velocity of
that part of the belt on pulley B is greater than the velocity of any
part on the slack side of the belt; hence the velocity of the pulley is
also greater than that of the slack side of the belt. In the case of
pulley A the belt meets it at G under a maximum of tension, and
therefore of stretch, but leaves it at H under a minimum of tension and
stretch, so that while passing from G to H the belt contracts, creeping
or slipping back on the pulley, and therefore effecting a reduction of
belt velocity below that of the pulley. To summarize, then, the velocity
of the part of the belt enveloping A is less than that of A to the
amount of the creep; hence the velocity of the slack side of the belt is
that of A minus the belt creep on A. The velocity of the part of the
belt on B is equal to that of the slack side of the belt plus the
stretch of the belt while passing over B; and it follows that if the
belt or slip creep on one pulley is equal in amount to the belt stretch
on the other, the velocities of the two pulleys will be equal.
[Illustration: Fig. 2678.]
Now (supposing the elasticity of the belt to remain constant, so that no
permanent stretch takes place) it is obvious that the belt-shortening
which accompanies its release from tension can only equal the amount of
elongation which occurs from the tension; hence, no matter what the size
of the pulleys, the creep is always equal in amount to the stretch, and
the velocity ratio of the driven pulley will (after the increase of belt
length due to the stretch is once transferred to the slack side of the
belt) always be equal to that of the driving pulley, no matter what the
relative diameters of the pulleys may be. In Fig. 2678, for example, are
two pulleys, A and B, the circumference of A being 10 inches, while that
of B is 20; and suppose that the stretch of the belt is an inch in a
revolution of A (A being the driving pulley). Suppose the revolutions of
a to be one per minute, then the velocity of the belt where it envelops
A and B, and on the sides C and D, will be as respectively marked.
Thus the creep being an inch per revolution of A, the belt velocity on
the side C will be nine inches per minute, and its stretch on B being an
inch, the velocity of B will be ten inches per minute, which is equal to
the velocity of the driving pulley.
It is to be observed, however, that since A receives its motion
independently of the belt, its motion is independent of the creep, which
affects the belt velocity only: but in the case of B, which receives its
motion from the belt, it remains to be seen if stretch is uniform in
amount from the moment it meets this pulley until it leaves it, for
unless this be the case, the belt will be moving faster than the pulley
at some part of the arc of contact.
[Illustration: Fig. 2679.]
Thus suppose P, Fig. 2679, represents a driven pulley, whose load is
1,000 pounds, and that from A to B, from B to C, from C to D, and from D
to E, represent equal arcs of contact between belt and pulley, then arc
A B will have on it the amount of stretch due to a pull of 250 pounds at
B, diminishing to nothing at A. Arc C B will have on it the amount of
stretch due to a pull of 500 pounds at C and 250 at B; arc D C will have
on it the amount of stretch due to a load of 750 at D, and 500 at C; and
arc D E will have the tension due to a load of 1,000 pounds at E, and
750 pounds at D. Suppose, then, that the amount of belt stretch is
greater between B and C than it is between D and E, then the belt will
travel faster between B C than between D E to an amount equal to the
difference in stretch, and will at B C slip over the pulley to that
amount; or if the friction of the belt at B C is sufficient to move the
pulley in accordance with the stretch, then the belt must move the
pulley at a greater velocity than the belt motion from D to E.
But since the friction of the belt is greatest at D E, it will hold the
pulley with the greatest force, and hence the velocity of the belt and
pulley will be uniform, or at least the most uniform, at D E.
Here arises another consideration, in that the stretch of the leather is
not uniform, and the section of belt at C B may stretch more or less
under its load than section C D does under its load, in which event the
velocities of the respective belt sections cannot be uniform, and to
whatever amount belt slip ensues the velocity of the driven wheel will
be less than that of the driver.
Attention has thus far been directed to the relative velocities of the
pulleys while under continuous motion. But let us now examine the
relative velocities when the two pulleys are first put in motion.
Suppose, then, the belt and pulley to be at rest with an equal degree of
tension (independently of the weight of the belt, as before) on both
sides of the belt. On motion being imparted to the driving pulley, the
amount of belt elongation due to the stress of the load on the driving
pulley has first to be taken up and transferred to the slack side of the
belt, and during such transfer a creep is taking place on the arc of
belt contact on the driving pulley.
[Illustration: Fig. 2680.]
Furthermore, let it be noted that while under continuous motion the belt
first receives full stress at point F, Fig. 2677; at starting it first
receives it at point E, and there will be a period of time during which
the belt stretch will proceed from E towards F, the pulley remaining
motionless. The length of duration of this period will, in a belt of a
given width, and having a given arc of contact on the driven pulley,
depend on the amount of the load. Thus, referring to Fig. 2680, if the
amount of the load is such that the arc of contact between the top and
the point B is sufficient to drive the pulley, the pulley will receive
motion when the belt stretch has proceeded from A to B; but if the load
on the pulley be increased the belt stretch will require to proceed
farther towards C.
At the top the stretch will proceed simultaneously with that of the
driving side of the belt, between the points F G, Fig. 2677; but from
the friction between the belt and pulley, the stretch of the part
enveloping the pulley will be subsequent and progressive from F towards
E, Fig. 2677.
It follows, then, that the velocity of the driven wheel will be less
than that of the driver at first starting than when in continuous
motion.
As the length of the belt is increased, the gross amount of stretch,
under any given condition, increases, and hence the longer the belt, the
greater the variation of velocity at first starting between the driven
pulley and the driver.
From what has been said, it follows that when a mathematically equal
velocity ratio is essential, belts cannot be employed, but the
elasticity that disturbs the velocity ratio possesses the quality of
acting as a cushion, modifying on one pulley any shocks, sudden strains,
or jars existing on the other, while the longer the belt and less
strained within the limit of elasticity, the greater this power of
modification; furthermore in case of a sudden or violent increase of
load, the belt will slide on the pulley, and in most cases slip off it,
thus preventing the breakage of parts of the driving gear or of the
machine driven that would otherwise probably ensue. Furthermore, belt
connections are lighter and cheaper than gear-wheel or other rigid and
positive connections, and hence the wide application of leather belts
for the transmission of power, notwithstanding the slight variations of
pulley velocity ratio due to the unequal elasticity of the various parts
of the leather composing the belt.
[Illustration: Fig. 2681.]
The ends of belts are joined by two principal methods, the butt and the
lap joint. In butt joints the holes are pierced near the ends of the
belts, and the ends of the belt are brought together by means of a
leather lace threaded through these holes. If the duty is light a single
row of holes is all that is necessary. An example of this kind is shown
in Fig. 2681, in which there are five holes on one side, and four on the
other of the joint, the extra hole coming in the middle of its end of
the belt. The lace is drawn half-way through this extra hole, and laced
each way to the side and back again to the middle, the ends being tied
on the outside of the belt, which does not come in contact with the
pulley surface. By this means the lacing is double through all the
holes, and if the knot should slip the slackness will begin at the
middle of the belt and extend gradually towards the edges; whereas, if
the lacing terminated at one side, and the knot or fastening should
slip, all the tension would be thrown on one edge of the belt, unduly
stretching it, and rendering it liable to tear. By this method of lacing
the lace is not crossed on either side of the belt, which is desirable,
because it is found in practice that a crossed lace does not operate so
well as an uncrossed one.
[Illustration: Fig. 2682.]
If the power to be transmitted is so much as to render it desirable to
have the strength of the laced joint more nearly approach that of the
solid belt than is obtainable with a single row of holes, a double row
is provided, as shown in Fig. 2682.
For belts of about 3 inches wide and over, these holes are made as
follows: A, B, and C, D, E, about an inch apart and 5/8 inch from the
line of joint; F, G, H, and I, J, being about 1/2 inch behind A, B, and
C, D, E, respectively.
For thinner belts the holes may be closer together, and to the edges of
the belt the exact distances permissible being closer together as the
duty is lighter; but however narrow the width of the belt, it should
contain at least two holes on each side of the joint. The sizes of these
holes are an important element, since the larger the hole the more the
belt is weakened. The following are the sizes of holes employed in the
best practice:--
Width of Belt. Size of Punched Hole.
Up to 4 inches 1/4 inch.
From 4 to 8 inches 5/16 "
From 8 inches upwards 3/8 "
[Illustration: Fig. 2683.]
The holes are usually made round, but from the pliability of the lace,
which enables it to adapt itself to the form of the hole to a remarkable
degree, it is not unusual to preserve the strength of a belt by making
an oblong hole, as in Fig. 2683 at A, or a mere slit, as at B, which,
from removing less material from the belt, leaves it to that extent
stronger.
[Illustration: Fig. 2684.]
[Illustration: Fig. 2685.]
The ends of the belt should be cut quite square, and at a right angle to
the edges, so that when the two ends are drawn together by the lace the
edges of the belt will remain straight, and not curved, as they would do
if either end of the belt were not cut at a right angle. Suppose, for
example, that the ends of a belt were cut aslant, as in Fig. 2684, when
laced up the edge of the belt would come as in Fig. 2685.
[Illustration: Fig. 2686.]
The holes must be punched exactly opposite to each other, or lacing the
belt will bring the edges out of fair, as shown in Fig. 2686, the
tension of the lace drawing the holes opposite to each other,
irrespective of where the edges of the belt will come. If some of the
holes are opposite and others are not, the latter will throw the edges
of the belt out of line to some extent, especially if the lace is first
entered in the holes that are not opposite, because, in that case,
drawing the lace tight at once throws the belt edges out, and the
subsequent lacing has but a limited effect in correcting the error,
unless, indeed, the majority of the holes are opposite, and but one or
two are out of line.
The lace should be drawn sufficiently tight to bring the ends of the
belt firmly together, and should be laced with an even tension
throughout, and for a belt doing heavy duty should have its ends tied in
a knot at the back, and in the middle of the belt.
The width of the lace is usually about as follows:--
Width of Belt. Width of Lace.
24 inches and over 1/2 inch
6 to 24 inches 3/8 "
2 to 4 inches 5/16 "
2 inches and less 1/4 "
Since belts are tightened by cutting a piece off one end (preferably the
end which shows the holes most stretched), it is obvious that a
butt-joint possesses an advantage, because as less of the belt length is
occupied by the holes they may be cut quite out and new ones punched,
whereas, in some cases, the length of the belt occupied by the holes in
a lap-joint is more than the length of belt required to be cut out to
tighten it.
[Illustration: Fig. 2687.]
[Illustration: Fig. 2688.]
[Illustration: Fig. 2689.]
There are many different methods of lacing a belt, but those here
described are generally preferred. Thus referring to Fig. 2687 the lace
is first passed through holes G and D, the ends being of equal length
from the belt and emerging on the side that is to be the outside of the
belt, thence each end of the lace is laced towards the edge of the belt,
the dotted lines in the cut showing the path of the lace. It is then
laced back to the middle of the belt, the second inside lacing exactly
overlaying the first, the laces never crossing; the outside appearing as
in Fig. 2688. The ends are in some cases tied in a knot on the outside,
and in others fastened as shown in Fig. 2689, in which case the ends are
merely held by friction, which will serve very well unless for a belt
that is tightly strained.
By this method of lacing all the crossing of the lace is on the outside
of the belt, which is an advantage, because from the creep of the belt
the lace undergoes considerable friction, which is apt to rapidly wear
out the lace, especially if it be crossed on the side of the bed that
meets the pulley surface.
[Illustration: Fig. 2690.]
Fig. 2690 shows a method of lacing in which the crossing of the lace is
entirely avoided, the knot being on the outside at _a_ _a_. The path of
the lace on one side of the belt is shown in full lines, and on the
other side in dotted lines.
The objections to lacing are that the lace lifts the belt from the
pulley surface, which throws all the wear on the lace, causing it
eventually to break, and which also reduces the area of belt (at the
joint) in contact with the pulley surface and reduces the driving power
of the belt at the time the joint is passing over the pulley. In fact,
in running belts this reduction of transmitting capacity is not great,
because of the rapidity with which the joint passes over the pulley,
but in slow moving belts slip is very apt to occur when the lace meets
the pulley, especially if the power transmitted is great in proportion
to the width of the belt.
[Illustration: Fig. 2691.]
[Illustration: Fig. 2692.]
There are considerable movement and friction between the lace and the
belt, more especially when the latter passes over a pulley of small
diameter, and this with the friction due to whatever amount of slip the
belt may experience, wears away the lace so that in time it breaks.
Sometimes a cover is employed as shown in Fig. 2691 at A, to protect the
lace, the cover being riveted or cemented to the belt on the side that
is to meet the pulley surface. A similar means is also sometimes
employed to make a butt joint. Thus in Fig. 2692 A is the cover riveted
or cemented to the two ends B C, of the belt so as to dispense with
lacing.
[Illustration: Fig. 2693.]
Fig. 2693 represents an excellent method of joining very thin belts, the
operation being as follows:--
Place the two ends of the belt together with the edges fair one with the
other, and with an awl make a row of holes at _a_, through both ends;
then take about half a yard of strong twine (in some cases a lace or gut
is better) and draw half the length through the first hole, then pass
each end of the twine through the second hole, one end to the right and
the other to the left, and draw both tight at the same time, and so on
until the last hole is reached, when one end only of the twine is passed
through; the two ends of the twine are then knotted tight together and
the excess cut off.
The middle sketch shows the joint when the belt is stretched. The lower
sketch shows it passing over a small pulley, where it will be seen that
in the act of bending over the curve there is no friction between the
lace and the belt, and this is the reason of its superiority over other
methods, where there is always more or less friction between the lace
and the belt when bending over a curve. Another advantage is, that in
this system the lace does not come into contact with the pulley, so that
whatever friction or slipping may take place between the belt and the
pulley, the lacing is perfectly unaffected by it.
[Illustration: Fig. 2694.]
A lap joint is one in which the two ends of the belt overlap, as in Fig.
2694. The overlap is cut down to a plain bevel so as to reduce the joint
to nearly or quite the same thickness as the main body of the belt. The
lap joint is employed to join together the strips of leather forming the
belt, and to fasten the ends of the finished belt together. In making
the belt the overlap is cemented and riveted, while in joining the ends
it may be cemented, or riveted, or laced.
The advantage of rivets lies simply in that they are easily applied.
Their disadvantages are that they grip but a small area of the belt,
namely, that portion beneath the rivet head and washer surface; hence,
when rivets are used the joint should always be cemented also. A more
important defect is, however, that the heat generated by the compression
of the rivet while riveting it is sufficiently great to _burn the
leather_ beneath the rivet-head. The reason that the leather under the
head and not under the washer or burr at the riveted end of the rivet
burns is, that although the heat due to riveting is most at the burr end
of the rivet, its passage from the rivet to the washer is less rapid
than it is through the body of the rivet, because in the one case it has
to be transferred from one body to another (from the rivet to the burr),
while in the other its passage is uninterrupted and continuous.
[Illustration: Fig. 2695.]
Rivets for lap joints are usually placed about, as in Fig. 2695, the
rows A and C being about 1/2 inch from the edges B and D respectively,
and the row F about 3/8 inch from the edge F of the lap, while the
rivets are about 5/8 inch apart in the rows.
For comparatively narrow belts as, say, four inches wide, a single row G
would be placed in the middle, additional middle rows should for wider
belts be about 1-1/4 inches apart.
The rivet holes should be a close fit to the rivets, the latter being
left just long enough to hold the washer or burr and sink with it, in
the riveting, to the level surface of the belt.
The heads of the rivets should be on the side of the belt that is to run
next to the pulley.
The strongest method of forming a belt is by means of small taper wooden
pegs, such as are used in boot and shoe manufacture, the joint being
cemented, and the pegs inserted. In this case the belt is merely pierced
with an awl, hence none of the leather is removed.
[Illustration: Fig. 2696.]
The arrangement of wooden pegs should be as in Fig. 2696, the rows A and
B being respectively about 5/8 inch from the edges C D, the row E being
about 1/4 inch from the edge of the joint, and H about 3/4 inch from
that edge. The pegs are placed about 1/2 inch apart in the rows.
A cemented and pegged joint is the strongest made, and it preserves a
more equal tension throughout the belt than any other, while the belt is
strong, since the hole for the pegs may be pierced with an awl, which
does not remove any leather from the belt, as is the case with punched
holes.
The length of the lap in some of the best practice is as follows:
When the strips of leather are cut from the hide in such lengths that
the part termed the shoulder of the hide is utilised, a uniform lap of 8
inches is employed for all widths of belt. When the strips do not
contain the shoulder of the hide, the following are the respective
lengths of lap:--
Width of single belt. Length of lap.
1 to 4-1/2 inches 4-1/4 inches.
5 inches 5 "
6 to 8 inches 6 "
9 inches 6-1/2 "
10 to 14 inches 7 "
15 to 24 " 8 "
All double belts are given a 6 inch lap.
[Illustration: Fig. 2697.]
Another and excellent method of joining a belt, or of fastening two
thicknesses together to form a double belt, is to sew it together with
lace leather, as shown in Fig. 2697. The lace is in this case about 1/4
inch wide, the holes being pierced so as to have the lace diagonal, as
shown in the cut. Sometimes four rivets are added at the joint as shown
in the cut.
[Illustration: Fig. 2698.]
Other methods of fastening the ends of leather belts are by means of
metal hooks of various forms. Fig. 2698 represents a fastening of this
kind, the appearance of both sides of the joint being shown in the
figure. In this case considerable leather is removed from the belt, but
this is to some extent compensated for, because the hook holds each end
of the belt in two places; that is to say, in the crook of the hook as
well as at the end. This, however, while it has the effect of increasing
the grip of the hook on the belt, still leaves the belt as a whole
weaker, by reason of the removal of leather to form the holes.
[Illustration: Fig. 2699.]
[Illustration: Fig. 2700.]
In Figs. 2699 and 2700 is shown a belt screw, intended to take the place
of rivets, and thus avoid the burning of the leather which accompanies
the use of rivets. It consists of two screws, one having a right and the
other a left-hand thread. The former is of bronze, and has a coarse
exterior thread cut conically, while it is hollow with a fine thread
tapped inside. The latter is of steel, and has a conical shoulder
underneath. The heads of both screws are slightly rounded and formed
with circular grooves on the under side, to give them a firm grip on the
leather. The conical screw is first run into the leather, and the steel
screw is then introduced. The belt is run with the head of the latter on
the inner side.
If the body of a narrow belt is riveted it contains two rows only of
rivets; but as the width of the belt increases, other rows are
introduced, all the rows running the entire length of the belt. In some
cases two separate single belts running one over or outside the other
are employed in place of an ordinary double belt, and the arrangement
works well.
Two single belts applied in this manner are especially preferable to a
double belt when used upon a small pulley, because they will bend to the
curvature of the pulley more readily, being more pliable; whereas a
double belt will from its resistance to bending not envelop as much of
the circumference of the belt as is due to the relative sizes of the
pulleys, and the distance apart of their axes.
Round leather belts are made in two forms, the solid and the twisted.
The first consists of a simple leather cord, hence its diameter cannot
exceed the thickness of the leather. The second consists of a strip of
leather twisted into cylindrical form, the grain side of the leather
being outside.
The ends of round belts are usually joined by means of cylindrical hooks
and eyes, which are threaded so as to screw on to the end of the belt,
but for twisted round belts it is better to place in the centre of the
belt a small core of soft wood. The ends of the belt should be slightly
tapered, and the hook and eye screwed firmly home. Sometimes from the
smallness of the pulleys the inflexibility of the hook and eye becomes
objectionable, and a simple hook is employed on solid round belting.
The length of twisted round belting may be altered by twisting or
untwisting it, which renders it unnecessary to cut the belt for a small
amount of shortening.
Round belts should bear upon the sides, and not on the bottom of the
pulley-groove, which increases their transmitting power. Thus, if the
groove is a semicircle of the same radius as is the belt when new, the
stretch of the belt as it wears decreasing its diameter, it will then
touch only on the bottom of the groove. Furthermore, when the belt bears
on the sides only of the groove it becomes wedged to a certain extent in
the sides of the pulley groove.
[Illustration: Fig. 2701.]
[Illustration: Fig. 2702.]
[V]-belting is formed of strips of leather welted together, as shown in
Figs. 2701 and 2702, the latter showing the joint or splice of the belt.
The pulleys are [V]-grooved as shown. The tension of the belt causes it
to grip the sides of the groove on the wedge principle, and the belt is
flat at the apex of the [V] so that it shall not bottom in the groove,
which would impair its wedging action. This class of belt is largely
employed for connecting shafts at an angle, especially in cases where
the distance between the shafts is small, in which case it will last
much longer than a flat belt.
From the construction, the rivets joining the pieces forming the belt do
not come into contact with the surfaces of the pulley, and from the
tension of the belt causing it to wedge into the sides of the pulley
groove, the driving power is greater than that simply due to the area of
contact and the tension of the belt.
[Illustration: Fig. 2703.]
A belt will run to the largest diameter of a pulley, thus in Fig. 2703,
the belt would, unless guided, gradually creep up to the side A of
pulley P, and following this action would move to side C of pulley D.
[Illustration: Fig. 2704.]
If the pulleys are parallel, but the axis of their shafts are not in
line, then the belt will run towards that side on which the axes are
closest; thus in Fig. 2704 the belt would run towards the side P of the
large pulley, because the belt B will meet the pulley surface at _a_,
and if a point on the belt at _b_ travelled coincident with the point on
the pulley with which it took contact, its plane of rotation, while on
the pulley, would be as denoted by the dotted line _b_.
But to follow this plane of rotation, the belt would require to bend
edgeways, as denoted by the dotted line _b_, which it does to some
extent, carrying the belt with it.
CHANGING OR SLIPPING BELTS ON PULLEYS.--To change a belt on a stepped
cone, proceed as follows:--
Suppose the belt to be on the small step of the driving cone, and to
require to run on the largest step. Throw the belt on the smallest step
of the lower cone and place the palm of the hand on the inside face of
the belt on the side on which it approaches that cone. Draw the belt
tight enough (with the palm of the right hand) to take up the slack and
cause the lower cone to rotate. When it is in full motion place the palm
of the left hand against the inside face of the other side of the belt
(while still keeping the pressure of the right hand against the slack
side of the belt).
Release suddenly the pressure of the right hand and immediately with a
quick and forcible lateral motion of the left hand force the belt
towards the larger step of the upper cone, which will cause it to mount
the next step, when the operation may be repeated for each succeeding
step.
If the steps of the cone are too steep, or the belt is too long for this
method, a wooden rod may be used, its end being applied to the side of
the belt that runs on the upper cone and close to the cone. Then lift
the belt with the rod, while the lower end of the rod is inclined away
from the step the belt is to mount, when the belt will mount the step of
the rotating cone.
In the case of broad heavy belts it is best to stop the running pulley
and place the belt on it, then lift the belt edge on the stationary
pulley at the point where the belt will first meet it when in motion,
forcing the belt on by hand as far as possible. Take a strong cord, as,
say 3/8 inch diameter, and double it, pass the loop between the pulley
arms around the belt and over the pulley face. Pass the two free ends of
the cord through the loop (formed by doubling the cord) and pull the
free ends as tight as possible by hand. While standing on the side of
the pulley opposite to that of the belt, communicate slow motion to the
driving pulley and release the ends of the cords as soon as the belt is
on. The belt, in travelling from the pulley, will then undo the cord of
itself.
A belt may be taken off a pulley, either by pressing it in the required
direction and as close to the pulley as possible, or by holding the two
sides of the belt together, which should be done as far from the running
pulley as possible, or as far from the pulley the belt is required to
come off as possible.
[Illustration: Fig. 2705.]
In Fig. 2705 is shown a device for automatically replacing a belt that
has slipped off a pulley. A is the pulley and B the device, which has a
curved projection which is of the full width of the device at one end,
where it comes even with the perimeter of A, and tapers laterally
towards the outside edge of the device. As a result the belt will easily
pass on the broad end and cause the device to rotate, the belt running
up the curved projection and therefore lifting clear of the pulley A,
but on account of the taper of the projection the belt finally has
contact with the projection on one edge only, and therefore tips over to
the other side, and as a result falls on A, because it is under tension
and naturally adjusts itself to be in line with the pulley at the other
end of the belt. It would appear that the belt, if running, would move
on the pulley, driving it, and this would be the case if sufficient time
were allowed for it to do so, but the action of the device is too quick,
and furthermore, when the belt is off one pulley and therefore loose its
motion is apt to become greatly reduced, which retards its moving
laterally on the pulley driving it.
It is obvious that the device must be applied to that side of the pulley
on which the belt is found to run off, but it may be noted that belts
are not apt to run off the loose pulley, but off the driving one, and
only at times when from excessive resistance or duty the velocity of the
pulley is reduced below that of the belt, or the velocity of the belt is
less than that of the pulley driving it; hence the device must be
applied on the outside of the fast or tight pulley.
The driving power of a belt is determined principally by the amount of
its pull upon the pulley, and the speed at which it travels.
The amount of pull is determined by its tension, or in other words, the
degree with which it grips the pulley and the closeness with which it
lies to the pulley surface. The amount of tension a single belt is
capable of withstanding with a due regard to its durability has been
fixed by various experimenters at 66-2/3 lbs. per inch of its width. The
pull of the belt under this degree of tension will vary as follows:--
It will be more with the grain or smooth side than it will with the
flesh or fibrous side of the belt in contact with the pulley face, some
authorities stating the amount of difference to be about 20 per cent. It
will be more with a smooth and polished surface on the pulley than with
one less smooth and polished. At high speeds it will be diminished by
the interposition of air between the belt and pulley surface, and from
the centrifugal force generated by the passage of the belt around the
pulley. It will be more when the pulley is covered with leather rubber
or other cushioning substance than when the pulley is bare, even though
it be highly polished, some authorities stating this difference to be
about 20 per cent.
It will be increased in proportion as the belt envelops a greater
proportion of the pulley circumference, the part of the pulley enveloped
by the belt when the pulley is at rest (or what is the same thing, at
any point of time when it is in motion) being termed the arc of contact.
It is obvious that the arc of contact taken to calculate the belt power
must be the least that exists on either the driving or the driven
pulley, because when the belt slips it ceases to transmit the full
amount of the power it receives, the remainder being expended in the
friction caused by the belt slipping over the pulley.
The speed at which a belt may run is limited only by reason of the
centrifugal force generated during its passage around the pulley, this
force tending to diminish its pressure upon the pulley. The maximum of
speed at which it is considered advisable to run a belt is about 6,000
feet per minute; but the amount of centrifugal force generated at this
speed depends upon the diameter of the pulley, because the centrifugal
force increases in direct proportion as the number of revolutions is
increased, or in other words it increases in the same proportion as the
velocity; but in a given circle it increases as the square of the
velocity. Suppose, then, that it be required to double the velocity of a
belt, and that the same pulley be used running at twice the velocity,
this will increase fourfold the centrifugal force generated; but if the
diameter of the pulley be doubled the centrifugal force generated will
be simply doubled; hence it appears that the larger the pulley the less
the centrifugal force of the belt in proportion to its velocity. This
will be apparent when it is considered that the larger the pulley the
nearer will the curve of its circumference approach to a straight line.
The following experiments on the transmission of power by belting were
made Messrs. Wm. Sellers & Co.
[40]These experiments were undertaken with a view to determine, under
actual working conditions, the internal resistances to be overcome, the
percentage of slip, and the coefficient of friction on belt surface.
They were conducted, during the spring of 1885, under the direction of
Mr. J. Sellers Bancroft.
[40] From a paper read before the American Society of Mechanical
Engineers by Wilfred Lewis.
These experiments seemed to show that the principal resistance to
straight belts was journal friction, except at very high speeds, when
the resistance of the air began to be felt. The resistance from
stiffness of belt was not apparent, and no marked difference could be
detected in the power required to run a wide double belt or a narrow
light one for the same tension at moderate speeds. With crossed and
quarter-twist belts the friction of the belt upon itself or upon the
pulley in leaving it was frequently an item of more importance, as was
shown by special experiments for that purpose.
In connection with the experiments upon internal resistances, some
interesting points were noted. Changes in tension were made while the
belt was running, commencing with a very slack belt and increasing by
definite amounts to the working strength. As this point was approached,
it was found necessary, to maintain a constant tension, that the
tightening bolt should be constantly operated on account of stretch in
the belt. Then, again, as the tension was reduced from this limit, it
was found that at lower tensions the belt would begin to shrink and
tighten for a fixed position of the sliding frame. This stretching and
tightening would continue for a long time, the tightening being, of
course, limited, but the stretching indefinite and unlimited.
The first series of experiments was made upon paper-coated pulleys 20"
diameter, which carried an old 5-1/2" open belt 3/16" to 1/4" thick and
34 ft. long, weighing 16 lbs. The arc of contact on the pulleys has been
calculated approximately from the tension on slack side, and for this
purpose the width and length of the belt were taken. The percentage of
slip must be considered as equally divided between the two pulleys, and
from observations made it is easy to calculate the velocity of sliding
when the speed is given.
Some of the most important results obtained with this belt are given in
Table I. in which the experiments have been selected to avoid
unnecessary repetition. In all cases the coefficient of friction is
shown to increase with the percentage of slip. The adhesion on the
paper-covered pulleys appears to be greater than on the cast-iron
surfaces, but this difference may possibly have been due to some change
in the condition of the belt surfaces.
After a fresh application of the belt dressing known as "Beltilene," the
results obtained are even higher on cast iron than on paper surfaces,
but after a time it was found that the adhesive property of this
substance became sensibly less and less. Flakes of a tarry nature rolled
up from the belt surface and deposited, themselves on the pulleys, or
scaled off.
So much was found to depend upon the condition of the belt surface and
the nature of the dressing used, that the necessity was felt for
experiments upon some standard condition which could be easily realized
and maintained. For this purpose a belt was taken from a planing machine
when it had become perfectly dried by friction. The results of
experiments upon this belt are given in Table II. When dry, as used on
the planer, the coefficients for any given percentage of slip were much
smaller than those given in Table I. This was naturally to be expected,
and the experiments were continued to note the effect of a belt dressing
in common use, known as "Sankey's Life of Leather," which was applied to
the belt while running. At first, the adhesion was very much diminished,
but it gradually increased as the lubricant became absorbed by the
leather, and in a short time the coefficient of friction had reached the
unprecedented figures of 1.44 and 1.37.
TABLE I.
STRAIGHT OPEN BELT 5-1/2" WIDE BY 7/32" THICK AND 34 FT. LONG, WEIGHING
16 LBS., IN GOOD PLIABLE CONDITION, WITH HAIR SIDE ON PULLEYS 20 IN.
DIAM. RUNNING AT 160 R. P. M., OR ABOUT 800 FT. PER MINUTE.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.[41]
[F] = _T_[41]
[G] = _t_[41]
[H] = _T_/_t_[41]
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Remarks.
---+---+---+---+---+-----+-----+-----+----+----+----+----+---
[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J]| [K]|[L] |[M]
---+---+---+---+---+-----+-----+-----+----+----+----+----+---
17|200|210| |100|155 | 55 | 2.82| .4| 1.6|177°|.336|[A]
19| |220| |140|180 | 40 | 4.50| .6| 2.4|176 |.490|
21| |246| |180|213 | 33 | 6.45| 1.2| 4.8|175 |.610|
22| |260| |200|230 | 30 | 7.67| 2.6|10.4|174 |.671|
23| |270|180|220|245 | 25 | 9.80| 7.9|31.6|173 |.756|
---+---+---+---+---+-----+-----+-----+----+----+----+----+
24|300|316| |200|258 | 58 | 4.45| .7| 2.8|177 |.483|
27| |344| |260|302 | 42 | 7.20| 1.0| 4 |176 |.643|
28| |350| |280|315 | 35 | 9 | 1.8| 7.2|175 |.719|
29| |364| |300|332 | 32 |10.4 | 2.8|11.2|175 |.784|
30| |380|260|320|350 | 30 |11.7 | 5.5|22 |175 |.805|
---+---+---+---+---+-----+-----+-----+----+----+----+----+
31|400|422| |200|211 |111 | 1.90| .5| 2 |179 |.205|
33| |440| |280|360 | 80 | 4.50| .8| 3.2|178 |.484|
35| |470| |360|415 | 55 | 7.54| 1.1| 4.4|177 |.654|
36| |506| |400|453 | 53 | 8.54| 2.1| 8.4|177 |.694|
37| |520|380|420|470 | 50 | 9.40| 5 |20 |177 |.725|
---+---+---+---+---+-----+-----+-----+----+----+----+----+---
60|200|205| | 80|147.5| 67.5| 2.18| .5| 2 |178 |.251|[B]
61| |210| |100|155 | 55 | 2.82| .9| 3.6|177 |.336|
62| |215| |120|167.5| 47.5| 3.52| 1.7| 6.8|177 |.407|
63| |220| |140|180 | 40 | 4.50| 3 |12 |176 |.490|
65| |246|180|180|213 | 33 | 6.45|12 |48 |175 |.610|
---+---+---+---+---+-----+-----+-----+----+----+----+----+
66|300|300| |120|210 | 90 | 2.33| .5| 2 |179 |.270|
68| |310| |160|235 | 75 | 3.13| .8| 3.2|179 |.365|
69| |315| |180|247.5| 67.5| 3.67| 1 | 4 |178 |.418|
70| |320| |200|260 | 60 | 4.33| 1.7| 6.8|178 |.472|
71| |325| |220|272.5| 52.5| 5.19| 2.6|10.4|177 |.545|
72| |340| |240|290 | 50 | 5.80| 3.8|15.2|177 |.569|
73| |350| |260|305 | 45 | 6.77| 5.5|22 |176 |.623|
74| |360| |280|320 | 40 | 8 | 8.6|34.4|176 |.677|
75| |375| |300|337.5| 37.5| 9 |15.2|60.8|175 |.719|
---+---+---+---+---+-----+-----+-----+----+----+----+----+---
76|400|420| |200|310 |110 | 2.82| .6| 2.4|179 |.336|[C]
78| |460| |280|370 | 90 | 4.11| 1 | 4 |179 |.452|
81| |480| |340|410 | 70 | 5.86| 1.5| 6 |178 |.569|
84| |510| |400|455 | 55 | 8.27| 2.2| 8.8|177 |.684|
86| |535| |440|487.5| 47.5|10.2 | 4.5|18 |177 |.760|
88| |560|385|480|520 | 40 |13 | 8.4|33.6|176 |.834|
---+---+---+---+---+-----+-----+-----+----+----+----+----+
89|300|320| |120|220 |100 | 2.20| .4| 1.6|179 |.252|
93| |350| |200|275 | 75 | 3.67| .8| 3.2|178 |.418|
97| |390| |280|335 | 55 | 6 | 1.6| 6.4|177 |.580|
101| |440| |360|400 | 40 |10 | 3.1|12.4|176 |.750|
104| |470|310|420|445 | 25 |17.8 | 8.6|34.4|173 |.953|
---+---+---+---+---+-----+-----+-----+----+----+----+----+---
Legend Remarks: [A] = Paper-covered pulleys.
[B] = Cast-iron surfaces.
[C] = Belt dressed with "Beltilene."
[41] _T_ represents the tension on the tight part, and _t_ on the sag
part of the belt.
An interesting feature of these and subsequent experiments is the
progressive increase in the sum of the belt tensions during an increase
in load. This is contrary to the generally accepted theory that the sum
of the tensions is constant, but it may be accounted for to a large
extent by the horizontal position of the belt, which permitted the
tension on the slack side to be kept up by the sag. That this is only a
partial explanation of the phenomenon, and that the sum of the tensions
actually increases as their difference increases for even a vertical
position of the belt, will be shown by a special set of experiments. If
a belt be suspended vertically, and stretched by uniformly increasing
weights, it will also be found that the extension is not uniform, but
diminishes as the load is increased, or, as already stated, the stress
increases faster than the extension. A little reflection will show that
when this is the case the tensions must necessarily increase with the
load transmitted.
TABLE II.
DOUBLE BELT 2-1/4" WIDE BY 5/16" THICK, AND 32 FT. LONG, WEIGHING 9-1/2
LBS., ON 20" CAST-IRON PULLEYS. THIS BELT HAD BEEN USED ON A PLANING
MACHINE, WAS QUITE PLIABLE, DRY, AND CLEAN. 160 R. P. M.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Remarks.
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J]| [K]| [L] |[M]
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
105|100|104| | 40| 72 | 32 | 2.25| .3| 1.2|177°| .263|
106| |110| | 60| 85 | 25 | 3.40| .8| 3.2|177 | .395|
107| |122| | 80| 101 | 21 | 4.81| 1.7| 6.8|176 | .511|
108| |138| |100| 119 | 19 | 6.26| 4.3|17.2|175 | .600|
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
109|200|208| | 80| 144 | 64 | 2.25| .4| 1.6|179 | .260|
110| |212| |100| 156 | 56 | 2.81| .7| 2.8|179 | .331|
111| |216| |120| 168 | 48 | 3.50| 1 | 4 |179 | .401|
112| |220| |140| 180 | 40 | 4.50| 1.8| 7.2|178 | .484|
113| |230| |160| 195 | 35 | 5.57| 4.4|17.6|178 | .553|
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
114|300|308| |120| 214 | 94 | 2.28| .4| 1.6|180 | .262|
116| |316| |160| 238 | 78 | 3.05| .8| 3.2|180 | .355|
118| |322| |200| 261 | 61 | 4.28| 1.6| 6.4|179 | .465|
119| |330|285|220| 275 | 55 | 5 | 2.6|10.4|179 | .516|
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
121|400|404| |160| 282 |122 | 2.31| .7| 2.8|180 | .267|
124| |410| |220| 315 | 95 | 3.37| 1.5| 6 |180 | .387|
125| |412| |240| 326 | 86 | 3.79| 2.3| 9.2|180 | .424|
126| |414| |260| 338 | 78 | 4.33| 3.7|14.8|179 | .469|
127| |416|370|280| 348 | 68 | 5.12|10.1|40.4|179 | .523|[A]
---+---+---+---+---+-----+-----+-----+----+----+----+-----+
128|500|516| |200|358 |158 | 2.27| .5| 2 |180 | .261|
131| |520| |260|390 |130 | 3 | 1.1| 4.4|180 | .350|
133| |525| |300|412.5|112.5| 3.67| 1.8| 7.2|180 | .414|
134| |525| |320|422.5|102.5| 4.11| 2.7|10.8|180 | .450|
135| |525|460|340|432.5| 92.5| 4.67| 5.1|20.4|180 | .490|
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
136|100|105| | 40| 72.5| 32.5| 2.02| .2| .8|177 | .228|[B]
137| |110| | 60| 85 | 25 | 3.40| .4| 1.6|177 | .396|
138| |125| | 80|102.5| 22.5| 4.56| .6| 2.4|176 | .494|
140| |150| |120|135 | 15 | 9 | 1.8| 7.2|174 | .723|
141| |164| |140|152 | 12 |12.7 | 2.8|10.8|172 | .779|
142| |180| |160|170 | 10 |17 | 5 |20 |170 | .954|
144| |215| |200|207.5| 7.5|27.7 | 7.3|29.2|166 |1.15 |
146| |250| |240|245 | 5 |49 |10.6|42.4|158 |1.41 |
147| |270| 90|260|265 | 5 |53 |17.7|70.8|158 |1.44 |
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
149|100|105| | 40| 72.5| 32.5| 2.02| .2| .8|177 | .228|[C]
150| |110| | 60| 85 | 25 | 3.40| .3| 1.2|177 | .396|
151| |120| | 80|100 | 20 | 5 | .4| 1.6|176 | .524|
153| |150| |120|135 | 15 | 9 | .7| 2.8|174 | .723|
155| |182| |160|171 | 11 |15.5 | 1.2| 4.8|172 | .913|
156| |202| |180|191 | 11 |17.3 | 3 |12 |172 | .950|
157| |216| |200|208 | 8 |26 | 5.8|23.2|167 |1.12 |
158| |232| |220|226 | 6 |37.3 | 7 |28 |161 |1.29 |
159| |252| |240|246 | 6 |41 | 9.8|39.2|161 |1.32 |
161| |292| |280|286 | 6 |47.7 |13.7|54.8|161 |1.37 |
---+---+---+---+---+-----+-----+-----+----+----+----+-----+---
Legend Remarks: [A] = Belt almost slipped off.
[B] = Here the belt was coated with "Sankey's Life of
Leather," and run until in good working
condition before noting experiments.
[C] = Three days later without any additional
dressing.
A piece of belting 1 sq. in. in section and 92 ins. long was found by
experiment to elongate 1/4 in. when the load was increased from 100 to
150 lbs., and only 1/8 in. when the load was increased from 450 to 500
lbs. The total elongation from 50 to 500 lbs. was 1-11/16", but this
would vary with the time of suspension, and the measurements here given
were taken as soon as possible after applying the loads. In a running
belt the load is applied and removed alternately for short intervals of
time, depending upon the length and speed of the belt, and the time for
stretching would seldom be as great as that consumed in making the
experiments just mentioned.
The differences between the initial and final tensions unloaded, as
given in the tables, show the effect of extension or contraction during
the course of the experiments made at a fixed position of the pulleys.
The percentage of elongation which a belt undergoes in passing from its
loose to its tight side, is the measure of the slip which must
necessarily take place in the transmission of power. This is a direct
loss, and within the assumed working strength of 500 lbs. per sq. in.
for cemented belts without lacings, experiment indicates that it should
not exceed 1-1/2 or 2 per cent. When, therefore, an experiment shows
less than 2 per cent. of slip, the amount may be considered as allowable
and proper, and the belt may be relied upon to work continuously at the
figures given.
Table III. gives the results of experiments upon a soft and pliable
rawhide belt made by the Springfield Glue and Emery Co. This belt had
been used by the Midvale Steel Co. for a period of seven months, at its
full capacity, and was sent in its usual working condition to be tested.
It had been cleaned and dressed with castor oil at intervals of three
months, and was received three weeks after the last dressing. Commencing
with the light initial tension of 50 lbs. on a side, it was found
impossible with the power at command to reach a limit to the pulling
power of the belt, and in order to do so the experiment was made of
supporting the slack side of the belt upon a board to prevent sagging.
TABLE III.
RAWHIDE BELT 4" WIDE BY 9/32" THICK AND 31 FT. LONG, WEIGHING 15 LBS.
160 R. P. M. ON 20" CAST-IRON PULLEYS.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Duration of run at time of experiment.
[N] = Remarks.
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J] | [K]| [L] | [M] |[N]
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
171|100|118| | 40| 79 | 39 | 2.03| .2| .8 |177°| .229| |
173| |140| | 80|110 | 30 | 3.67| .4| 1.6 |176 | .423| |
175| |168| |120|144 | 24 | 6 | .6| 2.4 |174 | .590| |
177| |202| |160|181 | 21 | 8.62| .8| 3.2 |172 | .661| |
179| |232| |200|216 | 16 | 13.5 | 1 | 4 |170 | .897| |
181| |268| |240|254 | 14 | 18.1 | 1.2| 4.8 |167 | .993| |
183| |302| |280|291 | 11 | 26.5 | 1.4| 5.6 |163 | 1.15 | |
184| |318|110|300|309 | 9 | 34.3 | 1.6| 6.4 |160 | 1.27 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
185|100|150|115|140|145 | 5 | 29 | 1.6| 6.4 |180 | 1.02 | |[A]
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+
186|200|258| |240|249 | 9 | 27.4 | 1.2| 4.8 |180 | 1.05 | |
188| |290| |280|285 | 5 | 57 | 2.2| 8.8 |180 | 1.29 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
189|300|412| |400|406 | 6 | 67.7 | 1.7| 6.8 |180 | 1.34 | |
190| |428| |420|424 | 4 |106 | 1.8| 7.2 |180 | 1.48 | |
191| |446|275|440|443 | 3 |148 | 3.3|13.2 |180 | 1.59 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+
192|400|570|360|560|565 | 5 |113 | 2 | 8 |180 | 1.47 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
329|100|110| | 40| 75 | 35 | 2.14| .3| .6 |177 | .246| |[B]
330| |135| | 80|107.5| 27.5| 3.90| .6| 1.2 |175 | .446| |
331| |198| |160|179 | 19 | 9.42| 1 | 2 |171 | .751| |
332| |275| |240|257.5| 17.5| 14.7 | 1.5| 3 |169 | .911| |
334| |345| |320|232.5| 12.5| 18.6 | 2 | 4 |165 | 1.01 | |
336| |420|110|400|410 | 10 | 41 | 3.2| 6.4 |162 | 1.31 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
339|200|230| |160|195 | 35 | 5.86| .8| 1.6 |176 | .576| |
340| |360| |320|340 | 20 | 17 | 1.6| 3.2 |171 | .949| |
341| |435| |400|417.5| 17.5| 23.8 | 2 | 4 |169 | 1.07 | |
342| |505| |480|492.5| 12.5| 39.4 | 2.7| 5.4 |165 | 1.28 | |
343| |590|200|560|575 | 15 | 38.3 | 5 |10 |168 | 1.24 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
344|300|400| |320|360 | 40 | 9 | 1.4| 2.8 |175 | .719| |
345| |450| |400|425 | 25 | 17 | 1.7| 3.4 |173 | .938| |
346| |520| |480|500 | 20 | 25 | 2.1| 4.2 |171 | 1.08 | |
347| |600| |560|570 | 10 | 57 | 3 | 6 |162 | 1.43 | 1 min.|
348| |600|280|560|570 | 10 | 57 | 3.4| 6.8 |162 | 1.43 | 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
350|400|500| |400|450 | 50 | 9 | 1.6| 3.2 |176 | .715| |
352| |605| |560|577.5| 17.5| 21.3 | 2.3| 4.6 |169 | 1.04 | |
353| |680| |640|660 | 20 | 33 | 3.2| 6.4 |171 | 1.17 | 1 min.|
354| |680| |640|660 | 20 | 33 | 3.7| 7.4 |171 | 1.17 | 5 min.|
355| |680| |640|660 | 20 | 33 | 4.1| 8.2 |171 | 1.17 |10 min.|
356| |680| |640|660 | 20 | 33 | 6.1|12.2 |171 | 1.17 |15 min.|[C]
357| |600| |560|580 | 20 | 29 |10 |20 |171 | 1.13 |20 min.|[D]
358| |600| |560|580 | 20 | 29 |17.2|34.4 |171 | 1.13 |25 min.|
359| |530| |480|505 | 25 | 20.2 | 5.2|10.4 |173 | .955|30 min.|
360| |530|350|480|505 | 25 | 20.2 | 2.8| 5.6 |173 | .955|35 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
361|500|570| |400|485 | 85 | 5.71| 1.3| 2.6 |178 | .561| |
364| |700| |640|670 | 30 | 22.3 | 2.3| 4.6 |174 | 1.02 | |
365| |755| |720|637.5| 17.5| 36.4 | 3.2| 6.4 |169 | 1.22 | |
366| |820| |800|810 | 10 | 81 | 6.6|13.2 |162 | 1.55 +-------+[E]
367| |750| |720|735 | 15 | 49 | 5.1|10.2 |168 | 1.32 | 1 min.|
368| |750| |720|735 | 15 | 49 |11 |22 |168 | 1.32 | 5 min.|
369| |690| |640|665 | 25 | 26.6 |12 |24 |173 | 1.09 +-------+[F]
370| |610| |560|585 | 25 | 23.4 |14.4|28.8 |173 | 1.05 | 1 min.|
371| |610| |560|585 | 25 | 23.4 |20 |40 |173 | 1.05 | 4 min.|
372| |550| |480|515 | 35 | 14.7 | 7.4| 14.8|175 | .880| 1 min.|
373| |550|410|480|515 | 35 | 14.7 | 2.3| 4.6|175 | .880| 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
374|600|680| |480|580 |100 | 5.8 | 1.5| 3 |178 | .566| |
376| |755| |640|697.5| 57.5| 12.1 | 2.1| 4.2 |177 | .807| |
378| |850| |800|825 | 25 | 33 | 2.8| 5.6 |173 | 1.16 | 1 min.|
379| |850| |800|825 | 25 | 33 | 3.5| 7 |173 | 1.16 | 5 min.|[G]
380| |780| |720|750 | 30 | 25 | 8.8|17.6 |174 | 1.06 | 1 min.|
381| |680| |560|620 | 60 | 10.3 |11.2|22.4 |177 | .755| 5 min.|
382| |680| |560|620 | 60 | 10.3 | 2 | 4 |177 | .755+-------+[H]
383| |730| |640|685 | 45 | 15.2 | 2.5| 5 |176 | .886| 1 min.|
384| |730| |640|685 | 45 | 15.2 | 2.4| 4.8 |176 | .886| 5 min.|
385| |780| |720|750 | 30 | 25 | 4.6| 9.2 |174 | 1.06 | 1 min.|
388| |780|550|720|750 | 30 | 25 | 8.8|17.6 |174 | 1.06 | 5 min.|
389| |780| |720|750 | 30 | 25 | 4 | 8 |174 | 1.06 | 1 min.|[I]
390| |780| |720|750 | 30 | 25 | 6.4|12.8 |174 | 1.06 | 5 min.|[E]
391| |730| |640|685 | 45 | 15.2 | 3.7| 7.4 |176 | .886| 1 min.|
392| |730|550|640|685 | 45 | 15.2 | 3.9| 7.8 |176 | .886| 5 min.|
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
396|600|680| |400|540 |140 | 3.86| 2 | .45|170 | .432| |[J]
397| |820| |720|770 | 50 | 15.4 |17.2| 3.87|176 | .890| |
398| |750| |640|695 | 55 | 12.6 |15 | 3.37|177 | .874| |
399| |700| |560|630 | 70 | 9 | 9.4| 2.17|177 | .711| |
400| |670| |480|575 | 95 | 6.05| 4.5| 1.12|178 | .579| |
401| |630|550|400|515 |115 | 4.48| 3.5| .75|178 | .483| |
402| |830| |720|775 | 55 | 14.1 |26 | 5.85|177 | .856| |
403| |630| |320|475 |155 | 3.06| 1.5| .30|179 | .358| |
404| |610| | 60|335 |275 | 1.22| .7| .16|180 | .063| |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
408|600|610| |120|365 |245 | 1.49| .2| .09|180 | .127| |[K]
413| |660| |400|530 |130 | 4.08| 1 | .45|179 | .450| |
415| |710| |560|635 | 75 | 8.46| 1.9| .86|177 | .691| |
416| |750| |640|695 | 55 | 12.6 | 3.2| 1.44|177 | .820| |
417| |800| |720|760 | 40 | 19 | 3.8| 1.71|175 | .964| |
418| |340| |200|274 | 70 | 3.91| .6| .27|177 | .441| |
419|300|380| |280|330 | 50 | 6.6 | 1.2| .54|176 | .614| |
421| |450| |400|425 | 25 | 17 | 3.2| 1.44|173 | .938| |
423| |515| |480|497.5| 17.5| 28.4 | 4 | 1.8 |169 | 1.13 | |
425| |580| |560|570 | 10 | 57 | 5 | 2.25|162 | 1.43 | |
427| |695| |680|687.5| 7.5| 91.7 | 7 | 3.15|155 | 1.67 | |
---+---+---+---+---+-----+-----+------+----+-----+----+------+-------+---
Legend Remarks: [A] = Slack side of belt running on a board to prevent
sagging.
[B] = 10" cast-iron pulleys.
[C] = Belt slipped off 4 m. later.
[D] = Continuing.
[E] = Belt slipped off 2 m. later.
[F] = Belt slipped off 3 m. later.
[G] = Belt slipped off 5 m. later.
[H] = After running 5 minutes at _T_ - _t_ = 560.
[I] = Belt scraped.
[J] = 18 r. p. m. 10" cast-iron pulleys.
[K] = 20" cast-iron pulleys. 18 r. p. m.
These experiments, however, are subject to an error arising from the
friction of the belt upon the board, the amount of which was not
determined. All of the experiments, in fact, are subject to slight
errors which were extremely difficult to eliminate or properly allow
for, but an effort has been made throughout to obtain results which
should approximate as closely as possible to the truth. The sum of the
tensions, as determined by measuring scales, was subject only to errors
in observation. This part of the apparatus was carefully tested by a
horizontal pull of known amount and made to register correctly.
The difference of the tensions _T_ - _t_, as computed from the reading
of the scales, was measured by the force of an equivalent moment at 20"
radius. This moment, divided by the radius of the pulley was taken to be
the difference _T_ - _t_.
In this calculation, it will be noticed that two slight corrections have
been omitted which are opposite in effect and about equal in degree. One
is the friction of the brake shaft in its bearings, which of course was
not recorded on the scales, and the other is the thickness of the belt
which naturally increases the effective radius of the pulley. Both of
these errors are somewhat indefinite, but the correctness of the results
obtained was tested in a number of cases by the sag of the belt, and the
tension _t_, as calculated from the sag, was found to agree closely with
the tension calculated by the adopted method.
As the limiting capacity of the belt was reached, the difficulty of
obtaining simultaneous and accurate observations was increased by the
vibrations of the scale beams. This was apparently due to irregularity
in the slip, and it was only by the use of heavily loaded beams and a
dash-pot that readings could then be taken at all. The dash-pot
consisted of a large flat plate suspended freely in a bucket of water by
a fine wire from the scale beam. This provision, however, was applied
only to the scales on which the vibrations were more pronounced.
TABLE IV.
DOUBLE OAK-TANNED LEATHER BELT 4" WIDE BY 5/16" THICK AND 30 FT. LONG,
WEIGHING 17 LBS., ON 10" CAST-IRON PULLEYS. 160 R. P. M.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Duration of run at time of experiment.
[N] = Remarks.
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
[A]|[B]|[C]|[D]|[E]| [F] | [G] | [H] | [I]| [J] | [K]| [L] | [M] |[N]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
209|120|120| | 48| 84 | 36 | 2.33| .4| .8 |176°| .275| |
210| |140| | 80|110 | 30 | 3.67| .6| 1.2 |175 | .426| |
211| |168| |120|144 | 24 | 6 | .9| 1.8 |174 | .590| |
212| |198| |160|179 | 19 | 9.42| 1.6| 3.2 |170 | .756| |
213| |235| |200|217.5| 17.5|12.4 | 2.3| 4.6 |174 | .829| |
214| |270| |240|255 | 15 |17 | 3.2| 6.4 |168 | .966| |
215| |310| |280|295 | 15 |19.7 | 5.1|10.2 |168 |1.02 | |[A]
216| |345|122|320|332.5| 12.5|25.8 | 9.4|18.8 |164 |1.13 | |[B]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
217|200|200| | 48|124 | 76 | 1.63| .4| .8 |179 | .156| |
219| |240| |160|200 | 40 | 5 | 1 | 2 |176 | .524| |
220| |360| |320|340 | 20 |17 | 2.7| 5.4 |170 | .954| |
221| |430| |400|415 | 5 |27.7 |15 |30 |167 |1.13 | |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
222|300|318| |160|239 | 79 | 3.03| .8| 1.6 |179 | .354| |
223| |350| |240|295 | 55 | 5.36| 1.2| 2.4 |177 | .543| |
224| |400| |320|360 | 40 | 9 | 2 | 4 |175 | .719| |
225| |470| |440|455 | 15 |30.3 | 8 | 1.6 |167 |1.17 | |[C]
226| |450| |400|425 | 25 |17 | 4 | 8 |172 | .943| 1 m.|
227| |450| |400|425 | 25 |17 | 8 |16 |172 | .943| 5 m.|
228| |450| |400|425 | 25 |17 |17.3|34.6 |172 | .943| 10 m.|[D]
229| |418| |360|389 | 29 |13.4 | 3 | 6 |173 | .859| 15 m.|[E]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
230|400|405| |160|282.5|122.5| 2.30| .8| 1.6 |179 | .267| |
232| |455| |320|387.5| 67.5| 5.74| 1.4| 2.8 |177 | .566| |
233| |495| |400|447.5| 47.5| 9.42| 1.9| 3.8 |176 | .730| 1 m.|
234| |495|370|400|447.5| 47.5| 9.42| 2.1| 4.2 |176 | .730| 5 m.|
235| |560| |480|520 | 40 |13 | 2.7| 5.4 |175 | .859|Start.|
236| |560| |480|520 | 40 |13 | 4.5| 9 |175 | .859| 5 m.|
237| |560| |480|520 | 40 |13 | 7.5|15 |175 | .859| 10 m.|
238| |550|380|480|465 | 85 | 5.47|20 |40 |178 | .547| 15 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
239|400|560| |480|520 | 40 |13 | 3.4| 6.8 |175 | .859| 1 m.|[F]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
240|500|610| |480|545 | 65 | 8.38| 2.1| 4.2 |177 | .688| 1 m.|
241| |610| |480|545 | 65 | 8.38| 2.5| 5 |177 | .688| 5 m.|
242| |660| |560|610 | 50 |12.2 | 3.2| 6.4 |176 | .814| 1 m.|
243| |655| |560|607.5| 47.5|12.8 | 8.4|16.8 |176 | .830| 5 m.|[G]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
244|600|700| |560|630 | 70 | 9 | 1.9| 3.8 |177 | .711| 1 m.|
245| |700| |560|630 | 70 | 9 | 2.1| 4.2 |177 | .711| 5 m.|
246| |690|550|560|625 | 65 | 9.69| 2.3| 4.6 |177 | .735| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
247|600|750| |600|675 | 75 | 9 | 2.2| 4.4 |177 | .771| 1 m.|
248| |740|585|600|670 | 70 | 9.57| 2.4| 4.8 |177 | .731| 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
249|600|770| |640|705 | 65 |10.8 | 2.5| 5 |177 | .770| 1 m.|
250| |765| |640|702.5| 62.5|11.2 | 3.5| 7 |177 | .782| 5 m.|
251| |770|600|640|685 | 85 | 8.06| 4.2| 8.4 |178 | .672| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
252|600|790| |680|735 | 55 |13.4 | 4.3| 8.6 |176 | .845| 1 m.|
253| |790| |680|735 | 55 |13.4 | 6.3|12.6 |176 | .845| 5 m.|[H]
---+---+---+---+---+-----+-----+-----+-----+-----+----+-----+------+---
254|100|100| | 44| 72 | 28 | 2.57| .6| 1.2 |176 | .307| |[I]
256| |160| |120|140 | 20 | 7 | 2.1| 4.2 |172 | .648| |
257| |200| |160|180 | 20 | 9 | 4 | 8 |171 | .736| |
258| |230| |200|215 | 15 |14.3 | 6.6|13.2 |168 | .907| 1 m.|
259| |230|100|200|215 | 15 |14.3 | 7.2|14.4 |168 | .907| 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
261|100|100| | 44| 72 | 28 | 2.57| .6| 1.2 |176 | .307| |[J]
263| |160| |120|140 | 20 | 7 | 2.8| 5.6 |172 | .648| |
264| |200| |160|180 | 20 | 9 | 5.1|10.2 |171 | .736| |
265| |230| |200|215 | 15 |14.3 | 7.3|14.6 |168 | .907| 1 m.|
266| |230| |200|215 | 15 |14.3 | 7.9|15.8 |168 | .907| 5 m.|
267| |270| |240|255 | 15 |17 |10.7|21.4 |168 | .966| 1 m.|[K]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
268|300|350| |240|295 | 55 | 5.36| 1.4| 2.8 |177 | .544| |
269| |400| |320|360 | 40 | 9 | 3 | 6 |175 | .719| |
270| |450| |400|425 | 25 | 17 | 6.8|13.6 |172 | .943| 1 m.|[K]
271| |418| |360|389 | 29 |13.4 | 8.8|17.6 |173 | .859| 1 m.|
272| |418| |360|389 | 29 |13.4 |15.6|31.2 |173 | .859| 5 m.|[G]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
273|600|700| |560|630 | 70 | 9 | 6.3|12.6 |177 | .711| |
274| |650| |480|565 | 85 | 6.65| 3.1| 6.2 |178 | .610| 1 m.|
275| |650| |480|565 | 85 | 6.65| 3.9| 7.8 |178 | .610| 5 m.|
276| |650| |480|565 | 85 | 6.65| 4.4| 8.8 |178 | .610| 10 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
277|600|652| |400|526 |126 | 4.17| 1.4| 2.8 |178 | .460| |[L]
279| |715| |560|637.5| 77.5| 8.23| 2.4| 4.8 |177 | .682| |
280| |705| |560|632.5| 72.5| 8.72| 2.8| 5.6 |177 | .701| |
281| |700|560|560|630 | 70 | 9 | 3 | 6 |177 | .711| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
282|560|750| |640|695 | 55 |12.6 | 4.1| 8.2 |176 | .824| 1 m.|
283| |735|535|640|682.5| 47.5|14.3 |22 |44 |176 | .866| 5 m.|[M]
284| |770| |640|705 | 65 |10.7 | 5.4|10.8 |177 | .767| 1 m.|[N]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
285|300|350| |240|295 | 55 | 5.36| 1.2| 2.4 |177 | .543| |[O]
286| |400| |320|360 | 40 | 9 | 1.8| 3.6 |175 | .719| |
287| |430| |360|395 | 35 |11.3 | 2.7| 5.4 |174 | .798| |
289| |465| |400|432.5| 32.5|13.3 | 5.3|10.6 |174 | .852| |
290| |455| |400|427.5| 27.5|15.5 | 7.3|14.6 |173 | .907| |
291| |460| |400|430 | 30 |14.3 |11.6|23.2 |173 | .881| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
292|100|100| | 44| 72 | 28 | 2.57| .5| 1 |176 | .307| |
293| |125| | 80|102.5| 22.5| 4.55| .8| 1.6 |173 | .502| |
294| |165| |120|142.5| 22.5| 6.33| 1.2| 2.4 |173 | .611| |
295| |200| |160|180 | 20 | 9 | 2.1| 4.2 |171 | .736| |
296| |230| |200|215 | 15 |14.3 | 3.4| 6.8 |168 | .907| |
297| |230| |200|215 | 15 |14.3 | 3.9| 7.8 |168 | .907| |
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
298|100|270| |240|225 | 15 |17 | 5.7|11.4 |168 | .966| 1 m.|
299| |270| |240|255 | 15 |17 | 7.6|15.2 |168 | .966| 5 m.|
300| |270| |240|255 | 15 |17 | 9.3|18.6 |168 | .966| 10 m.|[P]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
303|100|110| | 40| 75 | 35 | 2.14| .1| .4 |177 | .246| |[Q]
304| |132| | 80|106 | 26 | 4.08| .4| 1.6 |174 | .463| |
305| |160| |120|140 | 20 | 7 | 1 | 4 |172 | .648| |
306| |195| |160|177.5| 17.5|10.1 | 1.9| 7.6 |169 | .814| |
307| |230| |200|215 | 15 |14.3 | 3 |12 |168 | .907| 1 m.|
308| |230| 90|200|215 | 15 |14.3 | 3.5|14 |168 | .907| 5 m.|
309| |270| |240|255 | 15 |17 | 4.5|18 |168 | .966| 1 m.|
310| |270| |240|255 | 15 |17 | 5.8|23.2 |168 | .966| 5 m.|
311| |270| |240|255 | 15 |17 | 6.2|24.8 |168 | .966| 10 m.|
312| |270| |240|255 | 15 |17 | 6.2|24.8 |168 | .966| 15 m.|[R]
313| |270| |240|255 | 15 |17 | 2 | 8 |168 | .966| 1 m.|
314| |270| |240|255 | 15 |17 | 2.1| 8.4 |168 | .966| 5 m.|[S]
315| |305| |280|292.5| 12.5|23.4 | 3.4|13.6 |165 |1.09 | 1 m.|
316| |305|100|280|292.5| 12.5|23.4 | 3.5|14 |165 |1.09 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
317|100|335| |320|327.5| 7.5|43.7 | 5.2|20.8 |152 |1.42 | 1 m.|
318| |335| |320|327.5| 7.5|43.7 | 6.5|26 |152 |1.42 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
319|300|380| |320|350 | 30 |11.7 | 1.3| 5.2 |173 | .814| 1 m.|
320| |380| |320|350 | 30 |11.7 | 1.4| 5.6 |173 | .814| 5 m.|
321| |440| |400|420 | 20 |21 | 2.1| 8.4 |170 |1.03 | 1 m.|
322| |440|260|400|420 | 20 |21 | 2.4| 9.6 |170 |1.03 | 5 m.|
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
323|300|480| |440|460 | 20 |23 | 2.8|11.2 |170 |1.06 | 1 m.|[T]
324| |480|285|440|460 | 20 |23 | 3 |12 |170 |1.06 | 5 m.|
325| |510| |480|495 | 15 |33 | 3.2|12.8 |167 |1.20 | 1 m.|
326| |510| |480|495 | 15 |33 | 5 |20 |167 |1.20 | 5 m.|[U]
---+---+---+---+---+-----+-----+-----+----+-----+----+-----+------+---
Legend Remarks: [A] = Sag 10" at middle of belt.
[B] = Finally slipped off.
[C] = Belt finally slipped off.
[D] = Belt slip'd off.
[E] = Continuing.
[F] = After running 5 m. without load.
[G] = Belt slipped off 2 m. later.
[H] = Belt sl. off 2 m. lat. Pul. warm.
[I] = Belt scraped.
[J] = Belt dres'd with preparation recommend'd by
maker.
[K] = Belt slipped off 3 m. later.
[L] = One day later.
[M] = Belt slipp'd off.
[N] = After 3 min. intermission.
[O] = Temp. 52°.
[P] = Belt slipped off 4 m. later.
[Q] = 20 in. pulleys.
[R] = Temp. 56°.
[S] = Temp. 42°.
[T] = Temp. 46°.
[U] = Belt sl. off 5 m. lat. Pul. warm.
A peculiar and important feature of Tables III. and IV. is the effect of
time upon the percentage of slip. In previous experiments the percentage
of slip was measured at once after the load was applied, but it was
accidentally discovered that repeated measurements seldom agreed, and
investigation showed that these discrepancies were principally due to
the duration of the experiment. The continual slipping of the belt was
found to cause a deposit of a thick black substance upon the surface of
the pulley, which, acting as a lubricant, continued to increase the slip
still further.
Upon removing the load on brake-wheel, this deposit would be again
absorbed by the belt, and the original adhesion would be restored. The
temperature was also found to affect the slipping, and, in general, the
colder the weather the slower would this deposit take place.
Experiments 353 to 360 inclusive were made to determine the limit at
which the belt would run continuously without increasing its percentage
of slip. After the pulleys had become well coated and the slip had
reached a high per cent., the load on the brake-wheel was gradually
removed until a marked improvement was reached, as shown by experiments
359 and 360. The highest allowable coefficient of friction for this belt
is therefore estimated to be somewhere between 1.13 and .995, or we may
safely say 1. The highest coefficient obtained was 1.67, but, of course,
this was temporary. The diameter of the pulley also appears to affect
the coefficient of friction to some extent. This is especially to be
noticed at the very slow speed of 18 revolutions per minute on 10 in.
and 20 in. pulleys, where the adhesion on the 20 in. pulleys is
decidedly greater; but, on the other hand, at 160 revolutions per minute
the adhesion on the 10 in. pulleys is often as good, and sometimes
better, than appears for the 20 in. at the same velocity of sliding.
It might be possible to determine the effect of pulley diameter upon
adhesion for a perfectly dry belt, where the condition of its surface
remains uniform, but for belts as ordinarily used it would be very
difficult, on account of the ever-changing condition of surface produced
by slip and temperature. It is generally admitted that the larger the
diameter the greater the adhesion for any given tension, but no definite
relation has ever been established, nor, indeed, does it seem possible
to do so except by the most elaborate and extensive experiments.
It should be observed, however, that such a variation, if true, implies
a corresponding variation in the coefficients of friction for different
intensities of pressure upon the same pulleys, and that, consequently,
our experiments should show higher coefficients under the lighter loads
for the same velocity of sliding. Referring to Table II., where the
condition of the belt is dry and uniform for a large range of tensions,
we find that this inference is generally sustained, although there are
some few exceptions.
Experiment 106 may be compared with 116, and 112 with 133, also 108,
113, and 135, all showing great reductions in the coefficients of
friction for increments in tension. The exceptions are all to be found
under the smallest velocities of sliding, and appear only in the third
decimal place, so that the weight of their record against the
probability of such a law is light. By a similar inference it should
also follow that a wide belt would drive a little more at a given
tension than a narrow one, on account of the reduction in pressure per
square inch against the pulley. The mean intensity of pressure of a belt
against its pulley may be considered as proportional to the sum of the
tensions divided by the product of pulley diameter and width of belt,
and an analysis of the experiments referred to will show the relation
there existing between intensity of pressure and coefficient of
friction.
If we let [Iota] = intensity of pressure, and [phi] = coefficient of
friction, we shall find that [phi] is approximately proportional to
[Iota]^{-.15}, or, in other words that doubling the width of belt or
diameter of pulley would apparently increase the coefficient of friction
about 10 per cent. of its original value. This relation is not proved,
of course, and it is given only as a suggestion toward the solution of
the question. If the coefficient of friction does vary with the
intensity of pressure, the problem of determining the driving power of a
belt on strictly mathematical principles will indeed be complicated.
The coefficient of friction in the tables has been calculated by a
well-known formula, developed upon the assumption of a uniform
coefficient around the arc of contact, but this could no longer be
considered as correct if the coefficient is known to vary with the
pressure. Referring from Table II. to Table III., we shall find at once
the proof and contradiction of the inferences drawn from Table II., and
we are left as much in the dark as ever respecting the value of pressure
intensity.
Practical millwrights all know, or think they know, that an increase of
pulley diameter increases the drive, and it is a matter of common
observation that when large and small pulleys are connected by a crossed
belt, the smaller pulley will invariably slip first.
On one side a great deal of testimony can be adduced to show that
pressure intensity should be an important factor in the theory of belt
transmission, and, on the other hand, we have strong evidence to the
contrary. I may refer, in this connection, to the experiments of Mr.
Holman in _Journal of Franklin Institute_ for September, 1885, in which
there is no indication that the coefficient of friction varies at all
with the pressure. The coefficients obtained by Mr. Holman follow the
variations in slip like our own, and it gives us pleasure to observe
that our general results and conclusions are so strongly corroborative
of each other. There is at the same time a great difference in the
methods pursued in arriving at the same results. In his experiments, the
velocity of sliding was the fixed condition upon which the coefficient
of friction was determined, while, in ours, the conditions were those of
actual practice in which the percentage of slip was measured. Our least
amount of slip, with a dry belt running at the extremely slow speed of
90 feet per minute, was 1.08 inches, and ten times this would be
perfectly proper and allowable. A great many of Mr. Holman's experiments
are taken at rates below 1" per minute, and the coefficients obtained
are very much below the average practice, as himself seems to believe.
The velocity of sliding which may be assumed in selecting a proper
coefficient is directly proportional to the belt speed, and may safely
be estimated at .01 of that speed. For a pair of pulleys we should have
.01 on each pulley, and therefore .02 for slip. Few belts run slower
than 200 or 300 ft. per minute, and consequently a slip of less than 2
or 3 ft. per minute need seldom be considered. Another point of
difference which may possibly affect the coefficients obtained, is that,
in Mr. Holman's case the same portion of belt surface was subject to
continuous friction, while in ours, the friction was spread over the
belt at successive portions as in actual work. This we consider a new
and important feature of our experiments. As a matter of practical
importance, care was taken to observe, as nearly as possible, the
maximum slip which might safely take place before a belt would be thrown
from its pulley. A number of observations taken throughout the
experiments led to the final conclusion that 20 per cent. of slip was as
much as could safely be admitted. This information has been found of
value in cases where work is done intermittently by a fly-wheel and the
belt has to restore the speed of the wheel. It cannot be said in regard
to a maximum value of [phi] that any was determined or even indicated,
although it is certain that the increase at high rates of slip becomes
less rapid.
We have now seen that the driving power of a leather belt depends upon
such a variety of conditions, that it would be manifestly impracticable
if not impossible to correlate them all, and it is thought better to
admit the difficulties at once than to involve the subject in a
labyrinth of formulæ which life is too short to solve.
The relative value of pulley diameters may vary with different belts,
and all that can be expected or desired is some general expression
covering roughly the greatest number of cases. Our apparatus did not
admit of extensive variations in this respect, and our attention was
given principally to the question of slip.
The coefficients given in Table III. are remarkably high, and show a
great superiority for the rawhide over tanned leather in point of
adhesion. The belt in question was very soft and pliable, but a little
twisted from use on a cone pulley where it had rubbed against one side.
It is not desirable, on account of its soft and adhesive nature, to use
this kind of belt where frequent shifting is required, and when used on
cone pulleys it is liable to climb and stretch against the side of the
cone; but for a plain straight connection, there seems to be little room
for improvement. Table IV. contains the results of similar experiments
upon an oak-tanned leather belt made by Chas. A. Shieren & Co. Here the
coefficients are much smaller than those given in Table III., and there
is quite a marked difference between the coefficients for 10 in. and 20
in. pulleys.
As before noticed, the outside temperature has its effect, and it is
probable that much lower results would have been obtained had the
experiments been made in the heat of midsummer. The high coefficients
obtained, together with the rapid increase of tension, show that the
pulling power of a long horizontal belt must, in many cases, be limited
by its strength rather than by its adhesion.
Table V. gives the results of experiments upon a light planer belt at
very slow and very high speeds. As would naturally be expected, much
higher coefficients were found at the high speed on account of the
greater velocity of sliding.
TABLE V.
OAK-TANNED LEATHER BELT 2" WIDE BY 3-16" THICK AND 30' 4" LONG, WEIGHING
4 LBS., ON 20" CAST-IRON PULLEYS. DRY AND SMOOTH, TAKEN FROM SERVICE ON
PLANER.
Legend column headings: [A] = No. of Experi'nt.
[B] = Sum of Tensions. _T_ + _t_ Initial.
[C] = Sum of Tensions. _T_ + _t_ Working.
[D] = Sum of Tensions. _T_ + _t_ Final.
[E] = _T_ - _t_ Working.
[F] = _T_
[G] = _t_
[H] = _T_/_t_
[I] = Percentage of Slip.
[J] = Velocity of Slip in ft. per min.
[K] = Arc of contact.
[L] = Coefficient of Friction.
[M] = Duration of run at time of experiment.
[N] = Remarks.
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
[A]|[B]|[C]|[D]|[E]| [F] | [G]|[H] | [I]| [J] | [K]| [L]| [M] |[N]
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
429|100|110| | 40| 75 |35 |2.14| 1.2| .54|179°|.243| |18
430| |115| | 60| 87.5|27.5|3.18| 6.1| 2.75|178 |.372| |r.
431| |118| | 70| 94 |24 |3.92|16.5| 7.42|178 |.440| |p.
432| |105| | 20| 62.5|42.5|1.47| .3| .14|179 |.123| |m.
433| |112| | 50| 81 |31 |2.61| 3.5| 1.57|178 |.309| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
435|200|204| | 40|132 |82 |1.61| .2| .09|180 |.152| |
436| |206| | 60|133 |73 |1.82| .7| .32|180 |.191| |
437| |208| | 80|144 |64 |2.25| 1.8| .81|179 |.260| |
438| |210| |100|155 |55 |2.82| 3.7| 1.66|179 |.332| |
439| |212| |120|166 |40 |3.61| 7.7| 3.47|179 |.411| |
440| |215| |140|177.5|37.5|4.73|18.4| 8.28|179 |.497| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
442|100|110| | 60| 85 |25 |3.40| .3| 7.12|178 |.394| |950
443| |120| | 80|100 |20 |5 | .7| 16.62|178 |.518| |r.
445| |125| | 90|107.5|17.5|6.14| 3 | 71.25|177 |.587|Start.|p.
446| |125| | 90|107.5|17.5|6.14|25 |593.7 |177 |.587|min. |m.
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
448|200|200| | 80|140 |60 |2.33| .4| 9.5 |179 |.271| |
449| |200| |100|150 |50 |3 | .5| 11.87|179 |.352| |
450| |195|175|120|157.5|37.5|4.20| .8| 19 |179 |.459| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
451|150|175| |120|147.5|27.5|5.36| .9| 21.38|178 |.540| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
452|135|160| |120|140 |20 |7 |20 |475 |178 |.626| |
---+---+---+---+---+-----+----+----+----+------+----+----+------+---
It may here be mentioned that the sum of the tensions was the horizontal
pressure of the belt against the pulleys, and that no allowance was
necessary for the effect of the centrifugal force. At the speed here
used, the tension indicated in the belt at rest was about 50 lbs.
greater than when in motion.
TABLE VI.
SHOWING THE AVERAGE COEFFICIENT OF FRICTION AND VELOCITY OF SLIP FOR A
NUMBER OF EXPERIMENTS IN WHICH THE SLIP APPROXIMATED 2 PER CENT.
-------------------------------------+--------------+-----------------
No. exper'ts in av'ge. | |
|Percentage of Slip. | |
| |Veloc. of Sl. in ft. per m. | |
| | |Coefficient of Fric- | |
| | |tion. | |
| | | | Belt. | Pulleys. | Remarks.
--+----+-----+-----+-----------------+--------------+-----------------
3|1.4 | 5.6 | .661|5-1/2" old belt. |20" diam. |Belt in nor.
| | | |Table I |pap. cov'd |w'k'g con.
--+----+-----+-----+-----------------+--------------+
2|1.7 | 6.8 | .44 |5-1/2" old belt. |20" di. | " "
| | | |Table I |cast-iron sur.|
--+----+-----+-----+-----------------+--------------+-----------------
2|1.55| 6.2 | .575|5-1/2" old belt. |20" di. |Belt dressed
| | | |Table I |cast-iron sur.|with "Beltiline."
--+----+-----+-----+-----------------+--------------+-----------------
5|1.7 | 6.8 | .452|2-1/4" dbl. belt.|20" di. |B't dry as us.
| | | |Table II |cast-iron sur.|on plan'r.
--+----+-----+-----+-----------------+--------------+-----------------
2|1.5 | 6 | .818|2-1/4" dbl. belt.|20" di. |Belt dressed
| | | |Table II |cast-iron sur.|with "Sankey's
| | | | | |Life of Leather."
--+----+-----+-----+-----------------+--------------+-----------------
2|1.7 | 6.8 |1.38 |4" r´hide b. |20" di. |Belt in nor.
| | | |Table III |cast-iron sur.|w'k'g con.
--+----+-----+-----+-----------------+--------------+
11|1.8 | 3.6 | .861|4" r´hide b. |10" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
1|2 | .45| .432|4" r´hide b. |10" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
1|1.9 | .86| .691|4" r´hide b. |20" diameter. | " "
| | | |Table III | |
--+----+-----+-----+-----------------+--------------+
7|1.94| 3.88| .617|4" o.tan'd b. |10" diameter. | " "
| | | |Table IV | |
--+----+-----+-----+-----------------+--------------+
4|1.85| 7.40| .906|4" o.tan'd b. |20" diameter. | " "
| | | |Table IV | |
--+----+-----+-----+-----------------+--------------+-----------------
2|1.5 | .67| .251|2" o.tan'd b. |20" diameter. |B't dry as us. on
| | | |Table V | |plan'r.
--+----+-----+-----+-----------------+--------------+
2| .8 |38 | .529|2" o.tan'd b. |20" diameter. | " "
| | | |Table V | |
--+----+-----+-----+-----------------+--------------+-----------------
The conclusion to be drawn from this series of experiments is the great
importance of high speed in the economy of belt transmission. The
friction of belts on pulleys is evidently dependent on the velocity of
sliding, and, as a general rule, the greater the velocity the greater
the friction. There are but few apparent exceptions to this rule, and
investigation of them has led to the inference that in all such cases,
the condition of the belt or pulley surface had undergone a change
either by heating or by deposit from the belt on the pulley. The
percentage of slip is the measure of the power lost in transmission by
the belt itself, and the higher the speed the less this becomes. There
is a limit, however, to the power which may be transmitted as the speed
is increased, and this limit is caused by the reduction in pressure
against the pulley arising from the action of centrifugal force.
This point has been clearly demonstrated in a paper read before this
Society by Mr. A. F. Nagle on the "Horse Power of Leather belts,"[43]
and the formula there developed is written thus:
_HP_ = _CVtw_(_S_ - .012_V_^{2}) ÷ 550, (1.)
in which _C_ is a constant to be determined from the arc of contact and
coefficient of friction as expressed in the equation:
_C_ = 1 - 10^{-.00758_f[alpha]_}, (2.)
_V_ = velocity of belt in feet per second.
_t_ = thickness of the belt in inches.
_w_ = width " "
_S_ = working strength of leather in lbs. per square inch.
_f_ = coefficient of friction.
_[alpha]_ = arc of contact in degrees.
[43] Transactions A. S. M. E., Vol. II., page 91. See also Mr. Nagle's
Tables I., II., and III., in Appendix VI. to this paper for values of
_C_ and _H.P._
The velocity at which the maximum amount of power can be transmitted by
any given belt is independent of its arc of contact and coefficient of
friction, and depends only upon the working strength of the material and
its specific gravity.
From equation (1.) we obtain for the maximum power of leather belts the
condition:
_____
_V_ = \/28_S_, (3.)
and for any other material whose specific gravity is _y_, we find
____
/_S_
_V_ = \ / ---
\/ _y_
The coefficient of friction .40, adopted by Mr. Nagle, appears from
these experiments to be on the safe side for all working requirements,
except in cases where dry belts are run at slow speeds.
If we assume 2 per cent. as the greatest allowable slip, and select
within this limit the coefficient corresponding to the nearest
approximations to it, we can form some idea of the coefficients which
can be relied upon at different speeds.
Table VI. gives the average results obtained for this maximum allowance
of slip, and shows an extreme variation in the coefficient of friction
from .251 for a dry oak-tanned belt at the slow speed of 90 feet per
minute to 1.38 for a rawhide belt at the moderate speed of 800 feet per
minute.
For continuous working, it is probable that the coefficient 1.38 is too
high, but still it is certain that a coefficient of 1.00 can be steadily
maintained for an indefinite length of time, and we may say that in
actual practice the coefficient of friction may vary from .25 to 1.00
under good working conditions. This extreme variation in the coefficient
of friction does not give rise, as might at first be supposed, to such a
great difference in the transmission of power. It will be seen by
reference to formula (1.) that the power transmitted for any given
working strength and speed is limited only by the value of _C_, which
depends upon the arc of contact and the coefficient of friction.
For the usual arc of contact, 180°, the power transmitted when _f_ = .25
is about 24 per cent. less than when _f_ = .40, and when _f_ = 1.00, the
power transmitted is about 33 per cent. more, from which it appears that
in extreme cases the power transmitted may be 1/4 less or 1/3 more than
will be found from the use of Mr. Nagle's coefficient of .40.
TABLE VII.
SHOWING THE TORSIONAL MOMENT IN LBS. REQUIRED TO OVERCOME JOURNAL
FRICTION AND OTHER INTERNAL RESISTANCES, FOR BELTS AT VARIOUS SPEEDS AND
TENSIONS ON DIFFERENT ARRANGEMENTS OF PULLEYS.
------+-----+-------+-----+-----+-----+------+-------------+--------------
No. of|Ten- |Moment |Dia- |Revo-|Width|Thick-| |
exper-|sion.|in inch|meter|lut's| of | ness | Manner of |
im'nt.|_T_ +| lbs. | of |per |Belt.| of | Driving. | Remarks.
| _t_ | |pul- |min. | |Belt. | |
| | |leys.| | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
1 | 100| 20 | 20" | 160 | 6" |7/32" |Straight open|
3 | 300| 25 | | | | |belt. |
5 | 500| 30 | | | | | |
7 | 700| 35 | | | | | |
10 | 1000| 45 | | | | | |
45 | 100| 15 | | | | | |
47 | 300| 22.5 | | | | | |
49 | 500| 27.5 | | | | | |
51 | 700| 35 | | | | | |
54 | 1000| 50 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
163 | 100| 17.5 | 20" | 160 | 4" |9/32" |Straight open|
165 | 300| 25 | | | | |belt. |
167 | 500| 30 | | | | | |
169 | 700| 35 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
194 | 100| 17.5 | 10" | 160 | 4" |5/16" |Straight open|
196 | 300| 27.5 | | | | |belt. |
198 | 500| 40 | | | | | |
200 | 700| 55 | | | | | |
202 | 900| 70 | | | | | |
203 | 1000| 80 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
327 | 100| 20 | 10" | 18 | 4" |5/16" |Straight open|
328 | 1000| 80 | | | | |belt. |
393 | 100| 20 | | | | | |
394 | 1000| 100 | | | | | |
395 | 600| 60 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
405 | 100| 20 | 20" | 18 | 4" |9/32" |Straight open|
406 | 1000| 160 | | | | |belt. |
407 | 600| 100 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
428 | 100| 20 | 20" | 18 | 2" |9/32" |Straight open|
434 | 200| 25 | | | | |belt. |
------+-----+-------+-----+-----+-----+------+-------------+--------------
441 | 100| 25 | 20" | 950 | 2" |3/16" |Straight open|
447 | 200| 30 | | | | |belt. |
------+-----+-------+-----+-----+-----+------+-------------+--------------
453 | 100| 25 | 20" | 160 | 6" |7/32" |Crossed belt.|14' 6" between
454 | 500| 60 | | | | | |pulleys.
455 | 1000| 110 | | | | | |14' 6" bet.
| | | | | | | |pul'ys.
------+-----+-------+-----+-----+-----+------+-------------+--------------
459 | 100| 15 | 20" | 160 | 6" |7/32" |Straight open|14' 6" between
460 | 500| 25 | | | | |belt. |pulleys.
461 | 1000| 65 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
462 | 100| 25 | 20" | 160 | 6" |7/32" |Straight open|With 8"
463 | 500| 60 | | | | |belt. |tightener.
464 | 1000| 110 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
465 | 100| 45 | 20" | 160 | 6" |7/32" |Crossed belt.|8 feet between
466 | 500| 105 | | | | | |pulleys.
467 | 1000| 180 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
470 | 100| 25 | 20" | 160 | 6" |7/32" |Quarter turn |
471 | 500| 80 | | | | |belt on 16" |
472 | 750| 145 | | | | |diameter mule|
473 | 1000| 250 | | | | |pulleys. |
474 | 750| 170 | | | | | |
475 | 500| 110 | | | | | |
476 | 1000| 220 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
477 | 1000| 140 | 20" | 160 | 6" |7/32" |Quarter turn |Freshly oiled.
478 | 750| 100 | | | | |belt on 16" |
479 | 500| 70 | | | | |diameter mule|
480 | 100| 20 | | | | |pulleys. |
481 | 50| 60 | 20" | 160 | 6" |7/32" |Quarter turn |Belt rub.
482 | 25| 120 | | | | |on 16" mule |against low.
| | | | | | |pulleys. |guide m. pul.
------+-----+-------+-----+-----+-----+------+-------------+--------------
483 | 100| 20 | 20" | 160 | 6" |7/32" |Quarter turn |Well oiled,
484 | 500| 50 | | | | |on 16" mule |after a run of
485 | 750| 70 | | | | |pulleys. |2 hrs. at _T_
486 | 1000| 105 | | | | | |+ _t_ = 100.
------+-----+-------+-----+-----+-----+------+-------------+--------------
495 | 250| 30 | 20" | 160 | 6" |7/32" |Half turn |
496 | 500| 50 | | | | |belt on 16" |
497 | 750| 90 | | | | |mule pulleys.|
498 | 1000| 170 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
503 | 1000| 260 | 20" | 160 | 6" |7/32" |Quarter |10 feet
504 | 750| 190 | | | | |twist. |between
505 | 500| 130 | | | | | |pulleys.
506 | 250| 80 | | | | | |
507 | 100| 30 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
513 | 100| 50 | 20" | 160 | 6" |7/32" |Quarter |7' 6" between
514 | 250| 105 | | | | |twist. |pulleys.
515 | 500| 200 | | | | | |
516 | 750| 290 | | | | | |
517 | 1000| 380 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
523 | 100| 25 | 20" | 160 | 4" | 1/4" |Quarter |10 feet
524 | 250| 50 | | | | |twist. |between
525 | 500| 95 | | | | | |pulleys.
526 | 750| 145 | | | | | |
527 | 1000| 210 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
528 | 100| 65 | 20" | 160 | 4" | 1/4" |Quarter |6 feet between
529 | 250| 135 | | | | |twist. |pulleys.
530 | 500| 245 | | | | | |
531 | 750| 380 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
533 | 100| 25 | 20" | 160 | 6" |7/32" |Quarter |16' 6" between
534 | 250| 40 | | | | |twist. |pulleys.
535 | 500| 75 | | | | | |
536 | 750| 105 | | | | | |
537 | 1000| 165 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
539 | 1000| 130 | 20" | 160 | 6" |7/32" |Quarter twist|7' 6" between
540 | 750| 110 | | | | |with 16" |pulleys.
541 | 500| 90 | | | | |diameter |
542 | 250| 60 | | | | |carrying |
543 | 100| 40 | | | | |pulley. |
544 | 100| 30 | | | | | |
545 | 250| 55 | | | | | |
546 | 500| 90 | | | | | |
547 | 750| 120 | | | | | |
548 | 1000| 170 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
569 | 100| 25 | 20" | 160 | 6" |7/32" |Straight open|
571 | 500| 55 | | | | |belt. |
572 | 750| 70 | | | | | |
573 | 1000| 90 | | | | | |
------+-----+-------+-----+-----+-----+------+-------------+--------------
The percentage of slip is the most important factor affecting the
efficiency of belt transmission, but in addition to this we have journal
friction, the resistance of the air, and with crossed belts the friction
of the belt upon itself. These have been termed internal resistances,
and their values for some of the most common arrangements of pulleys are
given in Table VII. From this table it appears that the moment required
to run a straight belt varies from 15 to 25 inch lbs. at 100 lbs.
tension for all speeds. At 160 revolutions per minute and 1,000 lbs.
tension, the required moment varied from 45 to 90 inch lbs., and at 18
revolutions per minute and at the same tension it varied from 80 to 150
inch lbs.
From the average of these quantities we find the moment of resistance to
be expressed by the following formulæ for straight open belts between 2"
journals:
At 160 r. p. m.:
_M_ = .053_S_ + 14.7, (5.)
At 18 r. p. m.:
_M_ = .11_S_ + 9, (6.)
in which
_M_ = moment of resistance in inch lbs.
_S_ = sum of tensions.
When a crossed belt does not rub upon itself, the resistance is the same
as for an open belt.
The resistance offered by the introduction of carrying pulleys and
tighteners is appreciable, and depends upon the pressure brought to bear
against their journals. If the belt rubs against the flanges of the
carrying pulleys, the resistance is very much increased, and this is
often liable to occur in horizontal belts from a change of load. The
friction on journals of carrying pulleys may be estimated by the formulæ
already given if we substitute for _S_ the pressure against their
journals. In the experiments which were made upon internal resistances,
the greatest resistance was offered by a quarter-twist belt 6 feet
between journals on 20-inch pulleys.
The equation for this belt may be written:
_M_ = .35_S_ + 58, (7.)
but the introduction of a carrying pulley reduced the resistance to no
more than what might be expected from the same number of journals with a
straight belt.
With quarter-twist belts the resistance lies chiefly in slip, which
occurs as the belt leaves the pulleys, and this naturally depends upon
the distance between journals in terms of the diameters of the pulleys.
The effect of time upon the tension of the belt used in Table VIII. is
plainly shown by experiments 588 to 613 inclusive, between which the
pulleys remained at a fixed distance apart, and the belt slowly
stretched from a tension of 380 to 280 lbs.
To estimate the efficiency of belt transmission for an average case, we
may assume 40 in. lbs. as the moment of internal resistance for a belt
whose tension is 500 lbs. and 40 in. lbs. statical moment = about 20 ft.
lbs. per revolution. If the belt is transmitting 400 lbs. with two per
cent. of slip on 20 in. pulleys, then .02 × 400 × 5 = 40 ft lbs. are
lost per revolution in slip, making a total loss of 60 ft. lbs. per
revolution.
TABLE VIII.
SHOWING THE INCREASE IN THE SUM OF THE TENSIONS ON A VERTICAL BELT 4"
WIDE BY 1/4" THICK, AND 24 FT. LONG, ON 20" CAST-IRON PULLEYS, AT 120 R.
P. M.
------+---------+-----------+-----+-----+--------+---------+----------
No. of| Scales | Tension | | | Incre- |Percen'e |
exper-+----+----+-----+-----+ | | m´nt |of Incre-| Date.
im'nt.| A. | B. |_T_ +|_T_ -| _T_ | _t_ |of _T_ +| ment. |
|[44]|[44]| _t_ | _t_ | | | _t_ | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
578 | 93 | 101| 194 | 16 |105 | 89 | 0 | |5-15-1885.
579 | 70 | 142| 212 | 144 |178 | 34 | 18 | |
580 | 67 | 170| 237 | 206 |221.5| 15.5| 43 | |
581 | 66 | 180| 246 | 228 |237 | 9 | 52 | |
582 | 66 | 188| 254 | 244 |249 | 5 | 60 | .323 |
583 | 91 | 101| 192 | 20 |106 | 86 | -2 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
584 |202 | 210| 412 | 16 |214 |214 | 0 | |5-15-1885.
585 |167 | 250| 417 | 166 |292.5|292.5| 5 | |
586 |145 | 300| 445 | 310 |376.5|376.5| 33 | .171 |
587 |185 | 195| 380 | 20 |200 |200 | -32 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
588 |190 | 199| 380 | 0 |190 |190 | 0 | |5-18-1885.
589 |133 | 250| 393 | 214 |303.5| 89.5| 13 | .033 |
------+----+----+-----+-----+-----+-----+--------+---------+----------
590 |177 | 177| 354 | 0 |177 |177 | 0 | |5-19-1885.
591 |156 | 203| 359 | 94 |226.5|132.5| 5 | |
592 |138 | 235| 373 | 194 |283.5| 89.5| 19 | |
593 |135 | 250| 385 | 230 |307.5| 77.5| 31 | |
594 |128 | 275| 403 | 294 |348.5| 34.5| 49 | |
595 |125 | 300| 425 | 350 |387.5| 37.5| 71 | |
596 |123 | 325| 448 | 404 |426 | 22 | 94 | .333 |
597 |168 | 168| 336 | 0 |168 |168 | -18 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
598 |143 | 143| 286 | 0 |143 |143 | 0 | |5-25-1885.
599 |140 | 148| 288 | 16 |152 |136 | 2 | |
600 |130 | 160| 290 | 60 |175 |115 | 4 | |
601 |122 | 170| 292 | 196 |194 | 98 | 6 | |
602 |116 | 180| 296 | 28 |212 | 84 | 10 | |
603 |112 | 190| 302 | 156 |229 | 73 | 16 | |
604 |108 | 200| 308 | 184 |246 | 62 | 22 | |
605 |105 | 210| 315 | 210 |262.5| 52.5| 29 | |
606 |102 | 220| 322 | 236 |279 | 43 | 36 | |
607 |100 | 230| 330 | 260 |295 | 35 | 44 | |
608 | 99 | 240| 339 | 282 |310.5| 28.5| 53 | |
609 | 98 | 250| 348 | 304 |326 | 22 | 62 | |
610 | 98 | 260| 358 | 316 |337 | 21 | 72 | |
611 | 99 | 270| 369 | 342 |355.5| 13.5| 83 | |
612 |100 | 280| 380 | 360 |370 | 10 | 94 | .357 |
613 |140 | 140| 280 | 0 |140 |140 | -6 | |
------+----+----+-----+-----+-----+-----+--------+---------+----------
[44] Scales A recorded the reduction of the load on the testing device
for _vertical_ belts by the tension of the loose part of the belt
(_t_). Scales B, by that of the tight side of the belt (_T_).
The total power expended per revolution is about 2,000 ft. lbs.,
therefore .03 is lost.
Under light loads, the internal resistance, which is nearly constant in
amount, may be a large percentage of the power transmitted, while under
heavy loads the percentage of slip may become the principal loss.
It would be difficult to work out, or even to use, a general expression
for the efficiency of belt transmission, but, from the foregoing, it
would seem safe to assume that 97 per cent. can be obtained under good
working conditions.
When a belt is too tight, there is a constant waste in journal friction,
and when too loose, there may be a much greater loss in efficiency from
slip. The allowance recommended of 2 per cent. for slip is rather more
than experiment would indicate for any possible crawl or creep due to
the elasticity of the belt, but in connection with this, there is
probably always more or less actual slip, and we are inclined to think
that in most cases this allowance may be divided into equal parts
representing creep and slip proper. Under good working conditions, a
belt is probably stretched about 1 per cent. on the tight side, which
naturally gives 1 per cent. of creep, and to this we have added another
per cent. for actual slip in fixing the limit proposed.
The indications and conclusions to be drawn from these experiments are:
1. That the coefficient of friction may vary under practical working
conditions from 25 per cent. to 100 per cent.
2. That its value depends upon the nature and condition of the leather,
the velocity of sliding, temperature, and pressure.
3. That an excessive amount of slip has a tendency to become greater and
greater, until the belt finally leaves the pulley.
4. That a belt will seldom remain upon a pulley when the slip exceeds 20
per cent.
5. That excessive slipping dries out the leather and leads toward the
condition of minimum adhesion.
6. That rawhide has much greater adhesion than tanned leather, giving a
coefficient of 100 per cent. at the moderate slip of 5 ft. per minute.
7. That a velocity of sliding equal to .01 of the belt speed is not
excessive.
8. That the coefficients in general use are rather below the average
results obtained.
9. That when suddenly forced to slip, the coefficient of friction
becomes momentarily very high, but that it gradually decreases as the
slip continues.
10. That the sum of the tensions is not constant, but increases with the
load to the maximum extent of about 33 per cent. with vertical belts.
11. That, with horizontal belts, the sum of the tensions may increase
indefinitely as far as the breaking strength of the belt.
12. That the economy of belt transmission depends principally upon
journal friction and slip.
13. That it is important on this account to make the belt speed as high
as possible within the limits of 5,000 or 6,000 ft. per minute.
14. That quarter-twist belts should be avoided.
15. That it is preferable in all cases, from considerations of economy
in wear on belt and power consumed, to use an intermediate guide pulley,
so placed that the belt may be run in either direction.
16. That the introduction of guide and carrying pulleys adds to the
internal resistances an amount proportional to the friction of their
journals.
17. That there is still need of more light on the subject.
CHAPTER XXXIII.--FORGING.
FORGING.--The operation of forging consists in beating or compressing
metal into shape, and may be divided into five classes, viz.,
hand-forging, drop-forging, machine-forging, forging under trip or steam
hammers, and hydraulic forging. In purely hand forging much work is
shaped entirely by hand tools, but in large shops much work is roughed
out under trip or steam hammers, and finished by hand, while some work
is finished under these hammers. In drop forging the work is pressed
into shape by dead blows, which compress it into shape in dies or
moulds. In machine forging the work is either formed by successive quick
blows rather than by a few heavy ones, or in some machines it is
compressed by rolling. In hydraulic forging the metal is treated as a
plastic material, and is forced into shape by means of great and
continuous pressure.
In all forging the nature or quality of the iron is of primary
importance; hence the following (which is taken from _The English
Mechanic_), upon testing iron, may not be out of place.
"The English Admiralty and Lloyds' surveyor's tests for iron and steel
are as follows:--
"Two strips are to be taken from each thickness of plate used for the
internal parts of a boiler. One-half of these strips are to be bent cold
over a bar, the diameter of which is equal to twice the thickness of the
plate. The other half of the strips are to be heated to a cherry-red and
cooled in water, and, when cold, bent over a bar with a diameter equal
to three times the thickness of the plate--the angle to which they bend
without fracture to be noted by the surveyor. Lloyds' Circular on steel
tests states that strips cut from the plate or beam are to be heated to
a low cherry-red, and cooled in water at 82° Fahr. The pieces thus
treated must stand bending double to a curve equal to not more than
three times the thickness of the plate tested. This is severe treatment,
and a plate containing a high enough percentage of carbon to cause any
tempering is very unlikely to successfully stand the ordeal. Lloyds'
test is a copy of the Admiralty test, and in the Admiralty Circular it
is stated that the strips are to be one and a half inches wide, cut in a
planing machine with the sharp edges taken off. One and a half inches
will generally be found a convenient width for the samples, and the
length may be from six to ten inches, according to the thickness of the
plate. If possible, the strips, and indeed all specimens for any kind of
experimenting, should be planed from the plates, instead of being
sheared or punched off. When, however, it is necessary to shear or
punch, the piece should be cut large and dressed down to the desired
size, so as to remove the injured edges. Strips with rounded edges will
bend further without breaking than similar strips with sharp edges, the
round edges preventing the appearance of the small initial cracks which
generally exhibit themselves when bars with sharp edges are bent cold
through any considerable angle. In a homogeneous material like steel
these initial cracks are apt to extend and cause sudden fracture, hence
the advantage of slightly rounding the corners of bending specimens.
[Illustration: Fig. 2824.]
"In heating the sample for tempering it is better to use a plate or bar
furnace than a smith's fire, and care should be taken to prevent unequal
heating or burning. Any number of pieces may be placed together in a
suitable furnace, and when at a proper heat plunged into a vessel
containing water at the required temperature. When quite cold the
specimens may be bent at the steam-hammer, or otherwise, and the results
noted. The operation of bending may be performed in many different ways;
perhaps the best plan, in the absence of any special apparatus for the
purpose, is to employ the ordinary smithy steam-hammer. About half the
length of the specimen is placed upon the anvil and the hammer-head
pressed firmly down upon it, as in Fig. 2824. The exposed half may then
be bent down by repeated blows from a fore-hammer, and if this is done
with an ordinary amount of care it is quite possible to avoid producing
a sharp corner.
[Illustration: Fig. 2825.]
"An improvement upon this is to place a cress on the anvil, as shown at
Fig. 2825. The sample is laid upon the cress, and a round bar of a
diameter to produce the required curve is pressed down upon it by the
hammer-head.
[Illustration: Fig. 2826.]
"The further bending of the pieces thus treated is accomplished by
placing them endwise upon the anvil-block, as shown in Fig. 2826. If the
hammer is heavy enough to do it, the samples should be closed down by
simple pressure, without any striking.
[Illustration: Fig. 2827.]
"Fig. 2827 is a sketch of a simple contrivance, by means of which a
common punching machine may be converted temporarily into an efficient
test-bending apparatus. The punch and bolster are removed, and the
stepped cast-iron block A fixed in place of the bolster. When a sample
is placed endwise upon one of the lower steps of the block A the
descending stroke of the machine will bend the specimen sufficiently to
allow of its being advanced to the next higher step, while the machine
is at the top of its stroke. The next descent will effect still further
bending, and so on till the desired curvature is attained. It would seem
an easy matter, and well worth attention, to design some form of machine
specially for making bending experiments; but with the exception of a
small hydraulic machine, the use of which has, I believe, been abandoned
on account of its slowness, nothing of the kind has come under the
writer's notice.
"The shape of a sample after it has been bent to pass Lloyds' or the
Admiralty test is that of a simple bend, the sides being brought
parallel. While being bent the external surface becomes greatly
elongated, especially at and about the point of the convex side, where
the extension is as much even as fifty per cent. This extreme elongation
corresponds to the breaking elongation of a tensile sample, and can only
take place with a very ductile material. While the stretching is going
on at the external surface, the interior surface of the bend is being
compressed, and the two strains extend into pieces till they meet in a
neutral line, which will be nearer to the concave than to the convex
curve with a soft specimen. When a sample breaks, the difference between
the portions of the fracture which have been subject to tensile and
compressive strains can easily be seen.
[Illustration: Fig. 2828.]
"Fig. 2828 shows a piece of plate folded close together; and this can
generally be done with mild steel plates, when the thickness does not
exceed half an inch.
"Common iron plates will not, of course, stand anything like the
foregoing treatment. Lloyds' test for iron mast-plates 1/2 inch thick,
requires the plates to bend cold through an angle of 30° with the grain,
and 8° across the grain; the plates to be bent over a slab, the corner
of which should be rounded with a radius of 1/2 inch.
[Illustration: Fig. 2829.]
"When the sample of metal to be tested is of considerable thickness, as
in the case of bars, it is often turned down in a lathe to the shape
shown in Fig. 2829, so as to reduce its strength within the capacity of
the machine. The part to be tested has usually a length between the
shoulders of 8, 10, or 12 inches, and must be made exactly parallel with
a cross-sectional area apportioned to the power of the machine and the
strength of the material to be tested. When it is desired to investigate
the elastic properties of materials, it is desirable to have the
specimens of as great a length as the testing apparatus will
accommodate.
[Illustration: Fig. 2830.]
[Illustration: Fig. 2831.]
"Many of the early experiments on the tensile strength of wrought iron
were made with very short specimens, such as in Fig. 2830, which is a
sketch of that used formerly in the royal arsenal at Woolwich. This had
no parallel length for extension at all, its smallest diameter occurring
at one only point. Mr. Kirkaldy, to whom is due in a great measure the
honour of having raised 'testing' to an exact science, discovered that
this form of specimen gave incorrect results. He found that experiments
with such specimens, more especially when the metals were ductile, gave
higher breaking strains than were obtained with specimens of equal
cross-sectional area having the smallest diameter parallel for some
inches of length. This was due to the form of the specimen resisting to
some extent the 'flow' or alteration of shape which occurs in soft
ductile materials previous to fracture. He accordingly commenced to use
a specimen of the form shown in Fig. 2831, with a parallel portion for
extension of several inches in length, and specimens like that in Fig.
2830 became a thing of the past.
"The specimens shown in the figures admit of being secured in the
testing machine in many different ways. But whatever description of
holder be employed, two absolute requirements must be kept in view. The
holders must be stronger than the sample, and they must transmit the
stress in a direction parallel to the axis of the sample without any
bending or twisting tendency.
[Illustration: Fig. 2832.]
"Fig. 2832 gives two views of a very effective method of holding round
specimens, used by Mr. Kirkaldy in his earlier experiments carried out
for Messrs. Napier & Sons, of Glasgow. The enlarged ends of the samples
are clasped in split sockets provided with eye-holes for attaching them
to the shackles of the testing machine, the halves of the sockets being
held together during the experiment by small bolts passing through the
projecting lugs.
[Illustration: Fig. 2833.]
"Fig. 2833 explains the plan adopted for testing the strength of bolts
and nuts in the same series of experiments.
[Illustration: Fig. 2834.]
"A good holder for lathe-turned samples is shown in Fig. 2834. Close
fitting socket-pieces _b_ _b_ embrace each end of the specimen, and also
the turned collar at the extremity of the shackle _a_. The halves of the
socket are held together by a collar _c_, the interior of which and
exterior of the socket rings are turned to an equal taper, so that the
socket-pieces are held quite firmly when the collar _c_ is simply
slipped over them by hand. When the experiment is over, a few taps with
the hammer will remove the collar _c_.
[Illustration: Fig. 2835.]
"Samples of plates for tensile testing are usually shaped like Fig.
2835. The parallel portion B is generally 8, 10, or 12 inches long, as
in the case of the turned specimens. Two minor points in the preparation
of specimens may be here alluded to. In the first place the holes _a_
_a_ must be made large enough to obviate any danger of the pins which
are placed in these holes to secure the specimen being sheared in two
before the specimen breaks. In the second place, enough material must be
left around these pin or bolt holes to prevent the probability of the
metal tearing away between the hole and the edge of the plate. The pin
holes must be placed exactly in a line with the axis of the specimen,
and the part B must be quite parallel in width, so that the strength
(and the elongation during the testing) may be, as nearly as possible,
equal throughout the length of B. The shoulders, as _c_, should be easy
curves, so that sharp corners may be avoided. When a number of such
specimens are required at the same time, the strips of plate may be
clamped together and planed or slotted to the desired width as one
piece, but the tool marks should be afterwards removed by careful
draw-filing.
"When the plates are thin, small side pieces are riveted on the sides of
the ends to be clamped, as shown in Fig. 2836. These stiffen those ends
and afford a larger bearing for the securing pins. The connection with
the shackles is made by means of steel pins passing through the end
holes, and when specimens like 2835 are properly prepared, the direction
of the stress on them must be in a line with their axis. Fig. 2837 shows
another form of plate specimen in which the holes are dispensed with,
the ends being held in the machine by friction clips, as shown. These
specimens are more easily prepared, and from the absence of holes may be
made of a very narrow strip of plate.
[Illustration: Fig. 2836.]
[Illustration: Fig. 2837.]
"In Fig. 2837 the jaws or forked arms of the shackle are closed to form
a rectangular ring, as shown in section in the figure. Two of the
interior faces are tapered inwards to the same angle as the back of the
wedges or clips _a a´_, which are perfectly smooth and free to slide
upon the inclined or tapered surfaces of the shackles. The faces of the
wedges, however, which come in contact with and grip the specimen to be
tested, as _b_, are fluted or grooved, so that the friction of the edges
against the specimen is much greater than against the inside surfaces of
the shackles. The result of the arrangement is, that when the shackles
are pulled, the wedges _a a´_ are tightened against the specimen with a
degree of force proportionate to the load on the specimen, which is
prevented from slipping through the clips by the 'bite' of their fluted
faces. The grooves on the faces of the clips need not be deep--a depth
of a little more than 1/16, with about the same distance apart,
answering well for ordinary loads. With deep grooves and a wider pitch
apart, the danger of the specimen breaking in the clips is increased.
The inclination of the backs of the wedges _a a´_ to the faces may be at
an angle of 5 or 6 degrees. When the taper is too small, the removal of
the halves of the specimen after breaking is sometimes difficult, while
on the other hand, when too great, the specimen is apt to slip between
the wedges while being tested. The wedges exert a very considerable
outward pressure, and the jaws of the shackles must be made strong
enough to resist any strain likely, under extreme conditions, to fall on
them, otherwise they will speedily become unfit for use. In securing a
specimen care must be taken that its axis is in the direct line of
strain, and the opposite clips should be driven in equally so that the
stress may act fairly upon it. Parallel planed strips of metal, without
any enlargement at the ends, may be tested in these friction clips,
though, of course, there is a chance of the specimen breaking within
them. Turned specimens may also be held by such clips; as also may
rough, unturned round and square bars, an advantage when it is desired
to immediately ascertain approximately the strength of metal samples."
Open fires for hand forging purposes are mainly of two classes, those
having a side and those with a bottom or vertical blast.
[Illustration: Fig. 2838.]
Fig. 2838 represents a side draft forge. F is the fireplace, usually
from 3 to 5 feet long, T is the tuyère through which the blast enters
the fire, B being the blast pipe. To prevent T from being burned away it
is hollow as at S, and two pipes P and P´ connect to the water-tank W,
thus maintaining a circulation of water through S; V is simply a valve
or damper to shut off the supply of air from the tuyère; D is the
opening to the chimney C.
The side blast, though not so much used as in former years, is still
preferred by many skilful mechanics, on the ground that it will give a
cleaner fire with less trouble. The method of accomplishing this is to
dig out a hole in the fire bed and fill it in with coked coal, which
will form a drain through which the slag or clinker may sink, instead of
remaining in the active fire and obstructing the blast.
In cases where the fire requires to be built farther out from the
chimney wall than the location of the tuyère permits, it may be built
out as follows:--
[Illustration: Fig. 2839.]
[Illustration: Fig. 2840.]
A bar B, Fig. 2839, is placed in the tuyère hole and supported at the
other end at P. The coal is well wetted and packed around and above the
bar, which is then pulled out endwise, leaving a blast hole through the
coal, as is shown in the end view Fig. 2840.
[Illustration: Fig. 2841.]
Fig. 2841 represents a patent tuyère of vertical or bottom draft, in
which the blast passes through pipe A and circulates around B, finding
egress at C into the fire. C is hollow and receives water from the tank
F by the pipe D. The steam generated in the nozzle C is conveyed to the
tanks by the pipe E.
Figs. 2842 and 2843 represent a blacksmith's forge, for work up to and
about 4 inches in diameter. It consists of a wind-box A, supported on
brickwork which forms an ash-pit G beneath it. To this box is bolted the
wind-pipe B, and at its bottom is the slide E. In an orifice at the top
of A is a triangular and oval breaker D, connected to a rod operated by
the handle C. This rod is protected from the filling which is placed
between the brickwork and the shell F of the forge by being encased in
an iron pipe I. The blast passes up around the triangular oval piece D.
The operation is as follows: when D is rotated, it breaks up the fire
and the dirt falls down into the wind-box, cleaning the fire while the
heat is on. At any time after a heat the slide E may be pulled out,
letting the slag and dirt fall into the ash-pit beneath. It is a great
advantage to be able to clean the fire while a heat is on without
disturbing the heat.
[Illustration: Fig. 2842.]
[Illustration: Fig. 2843.]
Blacksmiths' anvils are either of wrought iron steel faced, or of cast
iron steel faced, the faces being hardened. It is sometimes fastened to
the block by spikes driven in around the edges. A better plan, however,
is to make the block the same size as the anvil, and secure the latter
by two bands of iron and straps, as shown in Fig. 2844, because in this
way the block will not come in the way of arms or projecting pieces that
hang below the anvil. The square hole is for receiving the stems of
swages, fullers, &c., and for placing work over to punch holes through
it, and the round is used for punching small holes.
The proper shape for blacksmiths' tongs depends upon whether they are to
be used upon work of a uniform size and shape, or upon general work. In
the first case, the tongs may be formed to exactly suit the special
work. In the second case, they must be formed to suit as wide a range of
work as convenient.
Suppose, for example, the tongs are for use on a special size and shape
of metal only; then they should be formed so that the jaws will grip the
work evenly all along, and therefore be straight along the gripping
surface. It will be readily perceived, however, that if such tongs were
put upon a piece of work of greater thickness, they would grip it at the
inner end only, and it would be impossible to hold the work steady. The
end of the work would act as a pivot, and the part on the anvil would
move about. It is better, therefore, for general work to curve the jaws,
putting the work sufficiently within the jaws to meet them at the back
of the jaw, when the end will also grip the work. By putting the work
more or less within the tongs, according to its thickness, contact at
the end of the work and at the point of the tongs may be secured in one
pair of tongs over a wider range of thickness of work than would
otherwise be the case. This applies to tongs for round or other work
equally as well as to flat or square work.
To maintain the jaw pressure of the tongs upon the work, a ring is
employed, the tong ends being curved to prevent the ring from slipping
off.
After a piece of work has left the fire it should, if there are scales
adhering upon it, have them cleaned off before being forged, for which
purpose the hammer head or an old file is used, otherwise the forging
will not be smooth, and the scale will be hammered into the surface.
This will render the forging very hard to operate upon by steel cutting
tools, and cause them to dull rapidly. For the same reason it is proper
to heat a finished forging to a low red heat and pass a file over its
surface, which will leave the forging soft as well as free from scale. A
forging should not be finally finished by being swaged or forged after
it has become black hot, because it produces a surface tension that
throws the work out of true as the metal is cut away in finishing it.
Work to be drawn out is treated according to the amount of elongation
and reduction of diameter required. Thus, suppose a piece of square work
to require to be drawn out, then it is hammered on its respective sides,
being turned upon the anvil so that each successive side shall receive
the hammer blows. It is essential, however, that the piece be forged
square, or in other words, that during the forging the sides be kept at
a right angle one to the other, or else the work will hammer hollow, as
it is termed; that is to say, the iron will split at the centre of the
bar, which occurs from its being forged diamond-shaped instead of
square. If a piece required to be forged diamond-shaped, it must be
forged square until reduced to such dimensions as will leave sufficient
to draw out while altering its form from the square to the
diamond-shape.
In very small work, which is more apt to hammer hollow than large work,
the end of the piece is left of enlarged size, as shown in the figure,
the strength of the enlarged end serving to prevent the hammering
hollow, which usually begins at the end of the piece; the end is in this
case forged last. In the case of round work the same rule holds good,
inasmuch as that a round bar may be forged smaller to some extent,
either by hammer blows or by swaging, but if the forging by hammer blows
be excessive, hammering hollow is liable to ensue.
The blacksmith's set of chisels consists of a hot chisel for cutting off
hot iron, a cold chisel for cutting cold metal, a hardy, which sets in
the square hole in the anvil, [C]-chisels, which are curved somewhat
like the carpenter's gouge, and a cornering or [V]-chisel, in which the
cutting edges are at a right angle one to the other.
[Illustration: Fig. 2844.]
The hot chisel has its edge well curved in its length, and is kept cool
by lifting it from the work after each hammer blow, and by occasionally
dipping it in water. Lifting it also prevents it from wedging in the
work. The cold chisel is tempered to a blue, and answers virtually to
the machinist's chisel. The hardy is used for small work, which is laid
upon it and struck with the hammer. The [C]-chisel is used, not only in
curved corners, but also to cut off deep cuts, answering, like the cape
or cross-cut chisel of the machinist, to relieve the corners of the hot
chisel. The cornering chisel is used for square corners, situated so
that the hot chisel cannot be used. The blacksmith's punch is made well
taper, so that it shall not wedge in the hole it produces.
For large holes a small punch is first used, and the hole enlarged in
diameter by driving in punches of larger diameter. If this swells the
work at the sides, it is forged down while the punch is in the hole.
The first blow given to the punch is a light one, so as to leave an
indentation that will mark the location, and enable its easy correction
if necessary. The blows delivered after the correct location is indented
are quick and heavy; but a piece of soft coal is inserted and the punch
placed on top of it, the gases formed by the combustion of the coal
serving to prevent the punch from binding in the hole. Between the blows
the blacksmith lifts the punch and moves the handle part of a lateral
rotation, which prevents it from becoming fast in the hole. The punch
should not be suffered to get red hot, but must be removed and cooled, a
fresh piece of green soft coal being inserted in the hole just previous
to the punch. If the punch is allowed to become as heated as the work,
the end will "upset" or swell and become firmly locked. Should the punch
lock in the hole a few blows will usually loosen it, but in extreme
cases it is sometimes necessary to employ another punch from the
opposite side of the work. Unless in very thin work, the hole is punched
half way from each side, because by that means a short stout punch may
be used.
It is obvious that when the hole requires to be bell-mouthed or of any
other form, the punch must be made to correspond.
The tools employed by the blacksmith, other than tongs, hammers,
chisels, and punches, are composed mainly of "fullers" and "swages" of
various kinds. The fuller is essentially a spreading tool, while the
swage may be termed essentially a shaping one.
[Illustration: Fig. 2845.]
In Fig. 2845, for example, let A represent an end view of an anvil, B
the bottom, and C the top fuller, and the effects of blows upon C will
be mainly to stretch the piece in the direction of its length without
swelling it out sideways.
[Illustration: Fig. 2846.]
[Illustration: Fig. 2847.]
[Illustration: Fig. 2848.]
[Illustration: Fig. 2849.]
If the work requires to be swelled sideways we turn the fuller the other
way around, as in Fig. 2846, in which it is supposed that one side of
the work is to be kept flat, hence no bottom fuller is employed. The
action of a fuller may be increased in the required direction by leaning
in the direction in which we desire to drive the iron; thus, suppose we
require to spread the end of a rectangular bar from the full lines to
the dotted ones in Fig. 2847 and the first fuller across the piece as at
A, Fig. 2848, and then spread out the end by fullering, as in Fig. 2849,
inclining the fuller in the direction in which we desire to forge the
iron.
[Illustration: Fig. 2850.]
It is the roundness of the face of the fuller that serves to control the
direction in which it will drive the iron, since the curve acts somewhat
on the principle of a wedge. Suppose, for example, that the faces were
flat, as in Fig. 2850, and the iron would spread in both directions, the
same as though the hammer were used direct, and if the work were
intended to be kept parallel it would frequently require to be turned on
edge to forge down the bulge that would form on the edge.
[Illustration: Fig. 2851.]
Fullers are, however, also used as finishing tools for curves or
corners, an example being given in Fig. 2851, which represents a fuller
applied to finish the round corner of a collar.
[Illustration: Fig. 2852.]
[Illustration: Fig. 2853.]
[Illustration: Fig. 2854.]
For finishing plane surfaces the flatter shown in Fig. 2852 is employed,
W representing the work. For inside surfaces the flatter requires to be
offset, as in Fig. 2853, in which L represents a link whose face A may
be flattened by the flatter F. There is a tendency in this case for the
flatter to tip or cant; and to avoid this and regulate the flatter upon
the work, a side foot is sometimes added, as at A in Fig. 2854.
Swages are shaped according to the kind of work they are to be used for.
[Illustration: Fig. 2855.]
[Illustration: Fig. 2856.]
Fig. 2855, for example, represents a top and bottom swage for rounding
up iron. For general work the recesses or seats of such swages would be
made considerably oval, as in Fig. 2856, the work being revolved
slightly after each blow. This capacitates one swage for different sizes
of iron. When, however, a swage is to be used for one particular size
only, its cavity may be made more nearly a true half circle and may
envelop one half the diameter of the work, so that when the top and
bottom swages meet, the work will be known to be of the required
diameter without measuring it. If the seat were made a true half circle
it would lock upon the work, preventing the smith from revolving it and
making it difficult to remove the swage.
[Illustration: Fig. 2857.]
If the conditions are such that a swage must be used to perform forging
rather than finishing, its seat should be [V]-shaped and not curved.
Suppose, for example, that a piece of iron, say, 6 inches in diameter,
required a short section to be forged down to a diameter of 3 inches,
then the swages should be formed as in Fig. 2857, because otherwise the
effects of the blow will act to a certain extent to force the iron out
sideways, for reasons which will be explained presently.
[Illustration: Fig. 2858.]
[Illustration: Fig. 2859.]
[Illustration: Fig. 2860.]
In some cases, for small work, the upper swage is guided by the lower
one: thus, in Fig. 2858 is a swage for a cross piece, and the outside of
its base is squared and fits easily within the upper part of the lower
one shown in Fig. 2859. For very small work, on which the hand hammer
is sufficiently heavy to perform the swaging, a spring swage may be use:
thus, in Fig. 2860 is a swage for pieces of 3/8, 5/16, and 1/4 inch in
diameter, and having a square stem fitting into the square hole in the
anvil. Fig. 2861 represents a spring swage for a pin having a collar,
and it may be observed that the recess to form the collar must be
tapered narrowest at the bottom, so that the top swage will readily
release itself by the force of the spring, and so that the work may
easily be revolved in the lower one. A similar tool is shown in Fig.
2862, designed for punching sheet metal cold, the die D being changeable
for different sizes of punches P.
[Illustration: Fig. 2861.]
[Illustration: Fig. 2862.]
[Illustration: Fig. 2863.]
For large hand-made forgings the swage block, such as in Fig. 2863, is
employed, S representing a stand for the block, whose dimensions are
larger than the block, so that the latter may be rested on its face in
the stand when the holes are to be used.
[Illustration: Fig. 2864.]
Fig. 2864 represents a swage block mounted on bearers, so that it may be
revolved to bring the necessary cavity uppermost.
[Illustration: Fig. 2865.]
[Illustration: Fig. 2866.]
[Illustration: Fig. 2867.]
Swages for trip hammers or for small steam hammers are for work not
exceeding about 4 inches in diameter, made as in Fig. 2865, the weight
of the top swage being sufficient to keep the two closed as in the
figure; for larger sizes the bottom swage fits to the anvil, and the top
one is provided with a handle, as in Fig. 2866, B representing the anvil
block, S´ the bottom, and S the top swage, having a handle H. The flange
of the bottom swage is placed as in Fig. 2867, so as to prevent the
swage from moving off the anvil block when the work is pushed through it
endways. Obviously such swages are employed when the part to be swaged
is less in length than the width of the hammer or of the anvil face.
If the hammer and anvil face is rounded as in Fig. 2868, or if dies thus
shaped are placed in them, their action will be the same as that of the
fuller, drawing the work out lengthways, with a minimum of effect in
spreading it out sideways.
Detached fullers, such as shown in Figs. 2869 and 2870, are, however,
used when the section to be acted upon is less in length than the hammer
face.
In the case of trip hammers, steam hammers, &c., blocks fitted to the
hammer and anvil block may take the place of detached swages and
fullers. Thus, in Fig. 2871 is represented the hammer and anvil block
for flat work, the corners being made rounded, because if left sharp
they would leave marks on the work. The blocks or dies A and B are
dovetailed into their places, and secured by keys K; hence they may be
removed, and dies of other shapes substituted.
When the work is parallel it may be forged to its finished dimensions by
forming in the lower die recesses whose depth equals the required
dimensions. Thus, in Fig. 2872 the recess A in the lower die equals in
depth the depth A of the work, while the depth of the recess B in the
die equals the thickness of the bar; hence by passing the work
successively from A to B, and turning it over a quarter turn, it will be
made to finished size, when the faces C D of the dies meet.
For this class of work the recesses must obviously be made in the lower
die, because it would be difficult to hold the work upon the lower die
in the proper position to meet a recess cut in the upper one: and,
furthermore, the recesses in the die should be wider than the work, to
avoid the necessity of holding the work exactly straight in the recess,
and keeping it against the shoulder or vertical face of the recess. If,
however, the work is to be made taper, we may obviously make the recess
taper, so as to produce smooth work, the die recess being made to be of
the correct depth for the smallest end of the work.
[Illustration: _VOL. II._ =EXAMPLES IN STEAM HAMMER WORK.= _PLATE XV._
Fig. 2868.
Fig. 2869.
Fig. 2870.
Fig. 2871.
Fig. 2872.
Fig. 2873.
Fig. 2874.
Fig. 2875.
Fig. 2876.
Fig. 2877.
Fig. 2878.]
When the shape of the work is such that it cannot be moved upon the die
during the forging, the operation is termed stamping, or if the hammer
or upper die falls of its own weight it is termed drop forging, and in
this case the finishing dies are made the exact shape of the work, care
being taken to let the work be enveloped as much as possible by the
bottom die, so that the top one shall not lift it out on its up stroke.
In forging large pieces from square to round we have several important
considerations. In order to keep the middle of the work sound, it must
be drawn square to as near as possible the required diameter before the
finishing is begun. During this drawing-down process the blows are heavy
and the tendency of the work is to spread out at the sides, as in Fig.
2873.
When the work is ready to be rounded up it is first drawn to an octagon,
as shown in Fig. 2874, so as to bring it nearer the work, nearer to
cylindrical form. The corners are then again hammered down, giving the
work sixteen sides, the work during this part of the process being moved
endways, as each corner is hammered down. The blows are during this part
of the forging lighter, but still the tendency is to spread the work out
sideways. The final finishing to cylindrical form is done with light
blows, the work being revolved upon the anvil without being moved
endways, so that a length equal to the width of the anvil is finished
before the work is moved endways to finish a further part of the length.
The tendency to spread sideways is here unchecked, because the iron is
squeezed top and bottom only. We may check it to some extent, however,
by employing a bottom swage block, as in Fig. 2875, in which case the
contact of the swage and the work will extend further around the work
circumference than would be the case with a flat anvil. If we were to
use a top and a bottom swage, as in Fig. 2876, the circumferential
surface receiving the force of the blow will be still further increased,
but there will still be a tendency to spread at the sides, as at A B, in
Fig. 2876. A better plan, therefore, is to use a [V]-block with the
hammer, as in Fig. 2877, in which case the effects of the blow are felt
at A, B, and C, and the points A B of resistance being brought higher up
on the work, its tendency to spread is obviously diminished. By using a
top and bottom [V]-block, as shown in Fig. 2878, the effect will be to
drive the metal towards the centre, and, therefore, to keep it sound at
the centre, it being found that if the metal is swaged much without
means being taken to prevent spreading, it "hammers hollow," as it is
termed, or in other words, splits at its centre.
[Illustration: Fig. 2879.]
The points A B of resistance to the blow at C are higher and the
tendency to spread sideways is better resisted. For cutting off under
the steam hammer, the hack shown in Fig. 2879 is used, being simply a
wedge with an iron handle.
WELDING.--In the welding operations of the blacksmith there are points
demanding special attention: first, to raise the temperature of the
metal to a proper heat; second, to let the temperature be as nearly
equal as practicable all through the mass; third, to have the surfaces
to be welded as clean and free from oxidation as possible; fourth, have
the parts to be welded of sufficient diameter or dimensions to permit of
the welded joint being well forged.
The following remarks on the theory of welding are from a paper read by
Alexander L. Holley before the American Institute of Mining Engineers:--
"The generally received theory of welding is that it is merely pressing
the molecules of metal into contact, or rather into such proximity as
they have in the other parts of the bar. Up to this point there can
hardly be any difference of opinion, but here uncertainty begins. What
impairs or prevents welding? Is it merely the interposition of foreign
substances between the molecules of iron, or of iron and any other
substance which will enter into molecular relations or vibrations with
iron? Is it merely the mechanical preventing of contact between
molecules, by the interposition of substances? This theory is based on
such facts as the following:
"1. Not only iron but steel has been so perfectly united that the seam
could not be discovered, and that the strength was as great as it was at
any point, by accurately planing and thoroughly smoothing and cleaning
the surfaces, binding the two pieces together, subjecting them to a
welding heat, and pressing them together by a very few hammer blows. But
when a thin film of oxide of iron was placed between similar smooth
surfaces, a weld could not be effected.
"2. Heterogeneous steel scrap, having a much larger variation in
composition than these irons have, when placed in a box composed of
wrought-iron side and end pieces laid together, is (on a commercial
scale) heated to the high temperature which the wrought-iron will stand,
and then rolled into bars which are more homogeneous than ordinary
wrought iron. The wrought-iron box so settles together as the heat
increases that it nearly excludes the oxidizing atmosphere of the
furnace, and no film of oxide of iron is interposed between the
surfaces. At the same time the enclosed and more fusible steel is
partially melted, so that the impurities are partly forced out and
partly diffused throughout the mass by the rolling.
"The other theory is that the molecular motions of the iron are changed
by the presence of certain impurities, such as copper and carbon, in
such a manner that welding cannot occur, or is greatly impaired. In
favor of this theory it may be claimed that, say, 2 per cent. of copper
will almost prevent a weld, while, if the interposition theory were
true, this copper could only weaken the weld 2 per cent., as it could
only cover 2 per cent. of the surfaces of the molecules to be united. It
is also stated that 1 per cent. of carbon greatly impairs welding power,
while the mere interposition of carbon should only reduce it 1 per cent.
On the other hand, it may be claimed that in the perfect welding due to
the fusion of cast iron, the interposition of 10 or even 20 per cent. of
impurities, such as carbon, silicon, and copper, does not affect the
strength of the mass as much as 1 or 2 per cent. of carbon or copper
affects the strength of a weld made at a plastic instead of a fluid
heat. It is also true that high tool steel, containing 1-1/2 per cent.
of carbon is much stronger throughout its mass, all of which has been
welded by fusion, than it would be if it had less carbon. Hence copper
and carbon cannot impair the welding power of iron in any greater degree
than by their interposition, provided the welding has the benefit of
that perfect mobility which is due to the fusion. The similar effect of
partial fusion of steel in a wrought-iron box has already been
mentioned. The inference is, that imperfect welding is not the result of
a change in molecular motions due to impurities, but of imperfect
mobility of the mass--of not giving the molecules a chance to get
together.
"Should it be suggested that the temperature of fusion, as compared with
that of plasticity, may so change chemical affinities as to account for
the different degrees of welding power, it may be answered that the
temperature of fusion in one kind of iron is lower than that of
plasticity in another, and that as the welding and melting points of
iron are largely due to the carbon they contain, such an impurity as
copper, for instance, ought, on this theory, to impair welding in some
cases and not to affect it in others.
"The obvious conclusions are: 1st. That any wrought iron, of whatever
ordinary composition, may be welded to itself in an oxidizing atmosphere
at a certain temperature, which may differ very largely from that one
which is vaguely known as 'a welding heat.' 2nd. That in a non-oxidizing
atmosphere heterogeneous irons, however impure, may be soundly welded at
indefinitely high temperatures.
"The next inference would be that by increasing temperature we chiefly
improve the quality of welding. If temperature is increased to fusion,
welding is practically perfect; if to plasticity and mobility of
surfaces, welding should be nearly perfect. Then how does it sometimes
occur that the more irons are heated the worse they weld?
"1. Not by reason of mere temperature, for a heat almost to dissociation
will fuse wrought iron into a homogeneous mass.
"2. Probably by reason of oxidation, which, in a smith's fire
especially, necessarily increases as the temperature increases. Even in
a gas furnace a very hot flame is usually an oxidizing flame. The oxide
of iron forms a dividing film between the surfaces to be joined, while
the slight interposition of the same oxide, when diffused throughout the
mass by fusion or partial fusion, hardly affects welding. It is true
that the contained slag, or the artificial flux, becomes more fluid as
the temperature rises, and thus tends to wash away the oxide from the
surfaces; but inasmuch as any iron with any welding flux can be oxidized
till it scintillates, the value of a high heat in liquefying the slag is
more than balanced by its damage in burning the iron.
"But it still remains to be explained why some irons weld at a higher
temperature than others; notably, white irons high in carbon, or in some
other impurities, can only be welded soundly by ordinary processes at
low heats. It can only be said that these impurities, as far as we are
aware, increase the fusibility of iron, and that in an oxidizing flame
oxidation becomes more excessive as the point of fusion approaches.
Welding demands a certain condition of plasticity of surface; if this
condition is not reached, welding fails for want of contact due to
mobility; if it is exceeded, welding fails for want of contact due to
excessive oxidation. The temperature of this certain condition of
plasticity varies with all the different compositions of irons. Hence,
while it may be true that heterogeneous irons, which have different
welding points, cannot be soundly welded to one another in an oxidizing
flame, it is not yet proved, nor is it probable, that homogeneous irons
cannot be welded together, whatever their composition, even in an
oxidizing flame. A collateral proof of this is, that one smith can weld
irons and steels which another smith cannot weld at all, by means of a
skilful selection of fluxes and a nice variation of temperatures.
"To recapitulate. It is certain that perfect welds are made by means of
perfect contact due to fusion, and that nearly perfect welds are made by
means of such contact as may be got by partial fusion in a non-oxidizing
atmosphere or by the mechanical fitting of surfaces, whatever the
composition of the iron may be within all known limits. While high
temperature is thus the first cause of that mobility which promotes
welding, it is also the cause, in an oxidizing atmosphere, of that
'burning' which injures both the weld and the iron. Hence, welding in an
oxidizing atmosphere must be done at a heat which gives a compromise
between imperfect contact due to want of mobility on the one hand, and
imperfect contact due to oxidation on the other hand. This heat varies
with each different composition of irons. It varies because these
compositions change the fusing points of irons, and hence their points
of excessive oxidation. Hence, while ingredients such as carbon,
phosphorus, copper, &c., positively do not prevent welding under fusion,
or in a non-oxidizing atmosphere, it is probable that they impair it in
an oxidizing atmosphere, not directly, but only by changing the
susceptibility of the iron to oxidation."
In welding steel to iron both are heated to as high a temperature as
possible without burning, and a welding compound or flux of some kind is
used.
In welding steel to steel the greatest care is necessary to obtain as
great a heat as possible without burning, and to keep the surfaces
clean.
An excellent welding compound is composed as follows: Copperas 2 ozs.,
salt 4 ozs., white sand 4 lbs., the whole to be mixed and thrown upon
the heat, as is done when using white sand as described for welding
iron. An equally good compound is made up of equal quantities of borax
and pulverized glass, well wetted with alcohol, and heated to a red heat
in a crucible. Pulverize when cool, and apply as in the case of sand
only.
A welding compound for cast steel given by Mr. Rust in the _Revue
Industrielle_ is made up as follows: 61 parts of borax, 20 parts of
sal-ammoniac, 16-3/4 parts of ferrocyanide, and 5 parts of colophonium.
He states that with the acid of this compound cast steel may be welded
at a yellow red heat, or at a temperature between the yellow, red, and
white heats. The borax and sal-ammoniac are powdered, mixed, and slowly
heated until they melt. The heating is continued until the strong odor
of ammonia ceases almost entirely, a small quantity of water being added
to make up for that lost by evaporation. The powdered ferrocyanide is
then added, together with the colophonium, and the heating is continued
until a slight smell of cyanogen is noticed. The mixture is allowed to
cool by spreading it out in a thin layer.
[Illustration: Fig. 2880.]
[Illustration: Fig. 2881.]
The lap weld is formed as follows: Suppose it is required to weld
together the ends of two cylindrical pieces, and the first operation is
to pump or upset the ends to enlarge them, as shown in Fig. 2880, so as
to allow some metal to be hammered down in making the weld without
reducing the bar below its proper diameter. The next operation is to
scarf the ends forming them, as shown in Fig. 2881, and in doing this it
is necessary to make the scarf face somewhat rounding, so that when put
together as in the figure contact will occur at the middle, and the weld
will begin there and proceed as the joint comes together under the blows
towards the outside edges. This squeezes out scale or dirt, and excludes
the air, it being obvious that if the scarf touched at the edges first,
air would be enclosed that would have to find its escape before the
interior surfaces could come together.
It is obvious, that if the two pieces require to weld up to an exact
length and be left parallel in diameter when finished an allowance for
waste of iron must be made; and a good method of welding under these
conditions is as follows:--
[Illustration: Fig. 2882.]
[Illustration: Fig. 2883.]
Let the length of the two pieces be longer than the finished length to
an amount equal to the diameter. Then cut out a piece as at A, in Fig.
2882, the step measuring half the diameter of the bar as shown. The
shoulder A is then thrown back with the hammer, and the piece denoted by
the dotted line B is cut off, leaving the shaft as shown in Fig. 2883.
The faces of the scarf should be somewhat rounding, so that when the
weld is put together contact will take place in the centre of the
lapping areas. Then, as the surfaces come together, the air and any
foreign substances will be forced out, whereas, were the surfaces hollow
the air and any cinder or other foreign substances would be closed in
the weld, impairing its soundness.
The lap of the two pieces, when scarfed in this manner, is shown in Fig.
2884.
[Illustration: Fig. 2884.]
To take the welding heat the fire should be cleaned out and clear coked
coal, and not gaseous coal, used. The main points in a welding heat are,
to heat the iron equally all through, to obtain the proper degree of
heat, and to keep the scarfed surfaces as free from oxidation, and at
the same time as clean, as possible.
To accomplish these ends the iron must not be heated too quickly after
it is at a good red heat, and the fire must be so made that the blast
cannot meet it at any point until it has passed through the bed of the
fire.
When the iron is getting near the welding heat it may be sprinkled with
white sand, which will melt over it and form a flux that will prevent
oxidation and cool the exterior, giving time to the interior to become
equally heated. The sand should be thrown on the work while in the fire,
as removing the work from the fire causes it to oxidize or scale
rapidly. The work should be turned over and over in the fire, the scarf
face being kept uppermost until the very last part of the heating, when
the blast must be put on full, the bed of the fire kept full and clear
so that there shall be sufficient bed to prevent the blast from meeting
the heat until it has passed through the glowing coals.
When the heat is taken from the fire it should meet the anvil with a
blow, the scarfed face being downwards, to jar off any dirt, cinder,
&c., and the scarf should be cleaned by a stroke or two of a wire brush.
But as every instant the iron is in the air it is both cooling and
oxidizing, these operations must be performed as quickly as possible.
The two scarfs being laid together as shown in Fig. 2884, the first
blows must be delivered lightly, so as not to cause the upper piece to
move, and as quickly as possible, the force of the blows being increased
regularly and gradually until the weld is sufficiently firm to hold well
together, when it may be turned on edge and the edges of the scarf
hammered to close and weld the seam. If this turning is done too soon,
however, it may cause the two halves to separate. When the weld is
firmly and completely made the enlarged diameter due to the scarfing may
be forged down, working the iron as thoroughly as possible.
[Illustration: Fig. 2885.]
[Illustration: Fig. 2886.]
To form the scarf of a ring or collar, one end is bevelled, as at B in
Fig. 2885 and after the piece is bent to a circle it is cut off and
bevelled as at A. When a slight band is to be welded, and it is
difficult to steady the ends to bring them together, a clamp may be used
to hold them as in Fig. 2886.
[Illustration: Fig. 2887.]
Fig. 2887 represents a tongue weld, and it is obvious that to insure
soundness the wedge piece should fit in the bottom of the split, which
may be well closed upon it by the hammer blows.
[Illustration: Fig. 2888.]
Fig. 2888 represents an example of a [V]-weld applied to welding up a
band that is to be square when finished, and as the lengths of the sides
must be equal when finished, the side on which the weld is made should
be made shorter, so that in stretching under the welding blows it will
be brought to its proper length. The [V] form of weld is employed
because it stretches less in welding than the lap weld. The [V]-piece to
be welded in should bear at the bottom of the [V], and the weld made by
fullering.
[Illustration: Fig. 2889.]
[Illustration: Fig. 2890.]
Welds of this kind are obviously most suitable for cases in which the
weld is required to influence the shape of the piece as little as
possible. The figures above, which are taken from _Mechanics_,
illustrate as an example the repairing of a broken strap for the beam of
a river steamboat. The crack is at A, Fig. 2889, and is held together by
a clamp as shown; a [V]-recess is cut out as in Fig. 2890, and this
recess is fullered larger, as in Fig. 2891. A [V]-block is then welded
in. The strap is then turned over a second [V]-groove, cut out and
fullered out, and a second [V]-piece welded in. By thus welding one side
at a time the welding is taken in detail as it were, and the blows can
be less heavy than if a larger weld were made at one heat, as would be
the case if but one [V] block were used. A similar form of weld may be
employed to form a square corner, as is shown in Fig. 2892, which is
taken from "The Blacksmith and Wheelwright." In this example the inside
corner is shown to have a fillet, which greatly increases the difficulty
of the job. The weld is made by first fullering the [V]-piece on the
sides and on the rounded corner and then laying the piece on the anvil
to forge down, the fullering leaving the finished job as in Fig. 2893.
[Illustration: Fig. 2891.]
[Illustration: Fig. 2892.]
[Illustration: Fig. 2893.]
[Illustration: Fig. 2894.]
[Illustration: Fig. 2895.]
When one piece has to be driven on to the other, the weld is called a
pump-weld, for which the ends should be rounded as in Fig. 2894, so that
they will meet at their centres, and will, when struck endways to make
the weld, come to the shape shown in Fig. 2895.
[Illustration: Fig. 2896.]
It is obvious that in this case the interior of the iron comes together
and is welded, and that dirt, &c., is effectually excluded; hence if the
iron is properly heated the weld may be as sound as a lap weld, and is
preferred by many as the sounder weld of the two. When a stem requires
to be welded to a large flat surface, the pump weld is the only one
possible, being formed as in Fig. 2896, in which the stem is supposed to
be welded to a frame. The plate is cupped as shown, and the metal being
driven up on the sides as much as possible, the stem overlaps well at C
B, so that it may be fullered there. The stem should first meet its seat
at A, so that dirt, &c., may squeeze out as the welding proceeds.
[Illustration: Fig. 2897.]
[Illustration: Fig. 2898.]
Figs. 2897 and 2898 represent an example of welding a collar on round
iron. The bar is upset so as to enlarge it at A, where the collar is to
be. The collar is left open at the joint, and while it is cold it is
placed on the red-hot bar and swaged until the ends are closed. The
welding of the whole may then be done at one heat, swaging the outside
of the collar first. Unless the bar is upset there would be a crack in
the neck B of the collar on both sides.
WELDING ANGLE IRON.--Let it be required to form a piece of straight
angle iron to a right angle.
[Illustration: Fig. 2899.]
The first operation is to cut out the frog, leaving the piece as shown
in Fig. 2899; the width at the mouth A of the frog being 3/4 inch to
every inch of breadth measured inside the flange as at B.
The edges of the frog are then scarfed and the piece bent to an acute
angle; but in this operation it is necessary to keep the scarfs quite
clean and not to bend them into position to weld until they are ready
for the welding heat; otherwise scale will form where the scarfs overlap
and the weld will not be sound.
The heat should be confined as closely as possible to the parts to be
welded; otherwise the iron will scale and become reduced below its
proper thickness.
The iron is then bent to the shape shown in Fig. 2900; and the angle to
which it is bent is an important consideration. The object is to leave
the overlapping scarf thicker than the rest of the metal, and then the
stretching which accompanies the welding will bring the two arms or
wings to a right angle.
[Illustration: Fig. 2900.]
It is obvious, then, that the thickness of the metal at the weld
determines the angle to which the arms must be bent before welding. The
thicker the iron the more acute the angle. If the angle be made too
acute for the thickness of the iron at the weld there is no alternative
but to swage the flange down and thin it enough to bring the arms to a
right angle. Hence it is advisable to leave the scarf too thick rather
than too thin, because while it is easy to cut away the extra metal, if
necessary, it is not so easy to weld a piece in to give more metal. In
very thin angle irons, in which the wastage in the heating is greater in
proportion to the whole body of metal, the width of the frog at A in
Fig. 2901 may be less, as, say, 9/16 inch for every inch of angle-iron
width measured as at B in the figure. For angles other than a right
angle the process is the same, allowance being made in the scarf-joint
and bend before welding for the stretching that will accompany the
welding operation.
The welding blows should be light and quick, while during the scarfing
the scale should be cleaned off as soon as the heat leaves the fire, so
that it will not drive into the metal and prevent proper welding. The
outside corner should not receive any blows at its apex; and as it will
stretch on the outside and compress on the inside, the forging to bring
the corner up square should be done after the welding.
[Illustration: Fig. 2901.]
The welding is done on the corner of an angle block, as in Fig. 2901, in
which A is the angle iron and B the angle block.
[Illustration: Fig. 2902.]
To bend an angle iron into a circle, with the flange at the extreme
diameter, the block and pins shown in Fig. 2902 are employed. The block
is provided with the numerous holes shown for the reception of the pins.
The pins marked 1 and 2 are first inserted and the iron bent by placing
it between them and placed under strain in the necessary direction. Pins
3 and 4 are then added and the iron again bent, and so on; but when the
holes do not fall in the right position, the length of the pin-heads
vary in length to suit various curves.
To straighten the iron it is flattened on the surface A and swaged on
the edge of the flange B, the bending and straightening being performed
alternately.
[Illustration: Fig. 2903.]
When the flange of the angle iron is to be inside the circle, as in Fig.
2903, a special iron made thicker on the flange A is employed. The
bending is accomplished, partly by the pins as before, and partly by
forging thinner, and thus stretching the flange A while reducing it to
its proper thickness.
TO FORGE A BOLT BY HAND.--The blanks for bolts must be cut off
sufficiently long to admit of one end being upset to form the head, the
amount of this allowance, obviously, being determined by the size of the
head.
[Illustration: Fig. 2904.]
[Illustration: Fig. 2905.]
Fig. 2904 is a side view, partly in section, and Fig. 2905 a top view of
an anvil block for upsetting the ends of blanks to form the heads of
bolts. The stem fits into the square hole of the anvil. The tongue is
pivoted as shown in the top view to two lugs provided on the block; upon
the tongue rests a steel pin whose length determines the height to which
the blank will project above the top of the block, and, therefore, the
amount or length of blank that will be upset to form the head, this
amount being three times the diameter of the bolt for _black heads_.
[Illustration: Fig. 2906.]
[Illustration: Fig. 2907.]
The hole for the blank is made about 1/64 inch larger in diameter than
the designated size of the bolt, to permit of the easy extraction of the
blank after it is upset, this extraction being accomplished by striking
the end of the tongue with the hammer. If the block is made of cast iron
the upper end of the hole will become worn after forging five hundred or
six hundred bolts, leaving the bolts with a rounded neck, as at C C in
Fig. 2906; a steel block, however, will forge several thousand bolts
without becoming enlarged.
An excellent plan is to provide the block with removable dies, such as
at _d_ _d_ in Fig. 2907, which are easily renewed, a number of such dies
having different diameters of bore fitted to the same block.
When the bolt end is sufficiently reset or enlarged to form the head it
is laid in a bottom swage, containing three of the six sides of the
hexagon, and a hammer blow on the uppermost part of the end forges a
flat side. After each blow the work is revolved one-sixth of a
revolution, and as the angles of the swage are true they obviously true
the angles of the bolt head. After the head has been roughed down it is
necessary to flatten it again under the head and on the end, for which
purpose it may be placed in the heading block shown in Fig. 2904, after
which the sides of the head may be finished and the cupping tool for
chamfering the head applied.
The bolt may require passing from the heading tool to the swage several
times, as forging it in one direction spreads it in another.
[Illustration: Fig. 2908.]
In shops where bolt-making is of frequent occurrence a special
bolt-making device is usually employed. It consists of an oliver or foot
hammer, having two hammers and an anvil; in the square hole at one end
of the anvil fits a hardy or bottom chisel, such as shown in Fig. 2908,
for cutting up the bar or rod iron into bolt blanks; A is the anvil, H
the hardy, and G a gauge to determine the length cut off the rod R to
form a blank. An upsetting or heading device corresponding to that in
Fig. 2907 is provided, and at the other end of the anvil is the swage
for forming the bolt head.
The object of having two hammers is that one may be used for the
upsetting of the blank and the other for the swage. The swaging hammer
is provided with a hole and set-screw to receive top swages, and bolt
hammers are adjustable for height so that they may be set so that their
faces will meet the work fair.
[Illustration: Fig. 2909.]
[Illustration: Fig. 2910.]
[Illustration: Fig. 2911.]
Figs. 2909 to 2911 represent front, side, and top views of Pratt &
Whitney's portable bolt-forging device. It is provided with an elevating
screw that permits the employment of a single bolster-pin for all
lengths of bolt for a given diameter, instead of requiring a separate
pin for each different length of bolt. In the figures, A is a frame
carried upon wheels, and to which is pivoted at C C the jaw D. The
bolt-gripping dies are shown at E F. A treadle G is pivoted at H, and
acts upon the lower end of D, causing the die F to grip or release the
bolts, as may be required. The bolster-pin rests upon the end of the
screw I, which enters at its foot a split nut J, which is caused to grip
and lock the screw by operating the nut of the bolt K that passes
through the split of the nut. L is a spring that lifts the treadle when
it is relieved of the pressure of the operator's foot.
At M is a leather washer to protect the nut J from the scale that falls
from the forging. The operation is as follows:--
The nut K is released and the screw I operated to suit the length of
bolt required. Then J is caused to clamp the screw by operating the nut
K. The blank for the bolt is placed in the dies resting on the
bolster-pin, which in turn rests upon the end of the screw I. The
treadle G is depressed, and the bolt blank clamped between E and F. The
helper then with the sledge upsets the blank end to form the bolt head,
and the blacksmith forges it to shape in the former bar B, which is
provided with impressions for the form of head required, these
impressions being of varying sizes, as shown. The device is so strongly
proportioned as to be very solid, and is found to be a most useful
addition to the blacksmith's shop.
[Illustration: _VOL. II._ =EXAMPLES IN HAND FORGING.= _PLATE XVI._
Fig. 2917.
Fig. 2918.
Fig. 2919.
Fig. 2920.
Fig. 2921.
Fig. 2922.
Fig. 2923.
Fig. 2924.
Fig. 2925.
Fig. 2926.]
[Illustration: Fig. 2912.]
[Illustration: Fig. 2913.]
[Illustration: Fig. 2914.]
[Illustration: Fig. 2915.]
[Illustration: Fig. 2916.]
To forge a turn buckle, such as in Fig. 2912, we bend two rings, such as
in Fig. 2913, and weld into the open ends a piece as shown in Fig. 2914,
on the opposite side a recess A, Fig. 2915, is cut out to receive a
second piece, which being welded in the work appears as in Fig. 2916,
and the end may be drawn taper. Two such pieces welded together
obviously complete the job.
Fig. 2917 represents a yoke for the slide valve of a steam engine or a
locomotive, which may be forged by either of the following methods:
Fig. 2918 represents a stem A welded into the bar B, which may be bent
to the required rectangle and welded at the ends.
A second method is to jump the stem D and split it open as in the side
view in Fig. 2919. The bar E is forged with a projecting piece to go in
the split of D, and after the weld is made, bar E is drawn to size as
shown, leaving the two projections _x_ where the corners are to come,
which is necessary in order to have sufficient stock to bring the
corners up square. The ends of E are split open as in the end view at F,
and a piece G is then welded to F.
In a third method the end of the stem is rounded for the weld, as shown
in Fig. 2920. The ends of the bar J are then split open and piece K
welded on.
It is to be observed with reference to the two last methods that in
hammering to forge the weld the frame is closed, so that after welding
the swaging to finish may be carried on until the frame is brought to
square, and any superfluous metal may be cut away; whereas if the kind
of weld is such as to stretch the sides, it may happen that to get a
sound weld will stretch the side welded too long and throw the frame out
of shape.
Suppose, for example, that a scarf weld were made on the side of the
yoke opposite to the stem, and if, in welding, the scarf is hammered too
much, it would draw it out too much and throw the whole frame out of
shape, as in Fig. 2921, so that the welded side would require to be
jumped to bring it back to the proper length again.
A fourth method is to take a piece of iron and punch a hole in it, and
then split it open up to the hole, as in Fig. 2922, and by opening out
the split form the stem and part of the frame out of the solid, forging
the remainder of the frame by the plan described for either the second
or third methods.
A fifth method is to make the weld of the stem as in Fig. 2923, then
forge out the bar B, leaving projections _x_ _x_ to bring the corners
_y_ _y_ up square, and after bending to shape and squaring up to weld in
a piece C.
A sixth method is to form the band first as in Fig. 2924, form the stem
as in Fig. 2925, and weld as in Fig. 2926.
[Illustration: Fig. 2927.]
[Illustration: Fig. 2928.]
[Illustration: Fig. 2929.]
Figs. 2927, 2928, and 2929 represent a method of forging a fifth wheel
for a vehicle. A rectangular piece of Norway iron is fullered to form
the recess at C in Fig. 2927. Holes are then punched at _h_ and splits
are made to the dotted lines shown in the figure. The ends are then
opened out, forming a piece such as in Fig. 2928. The letter A
represents the same face of the work in all the figures, being the edge
in Fig. 2927, and the top face after the ends are opened out. The four
arms may then be dressed to shape, the two lower ones being drawn out
and threaded before being finally closed to shape. A piece may then be
welded on one end, as at B, to complete the circle.
[Illustration: Fig. 2930.]
[Illustration: Fig. 2931.]
[Illustration: Fig. 2932.]
To forge a double eye, such as in Fig. 2930, we may take a piece of
sufficient size and fuller at _a_ _a_, Fig. 2931; a hole is then punched
at _b_, and it is then split through to the dotted line in Fig. 2931,
and opened out as in Fig. 2932, and then forged to shape.
[Illustration: Fig. 2933.]
BENDING.--Fig. 2933 represents a tool for bending pieces of small
diameter to a short curve, either when cold or heated. In bending hot
iron it is advantageous to confine the heat as closely as possible to
the part to be bent, as a more true bend may then be obtained.
[Illustration: Fig. 2934.]
[Illustration: Fig. 2935.]
[Illustration: Fig. 2936.]
As an example in bending, let it be required to bend a straight shaft
into a crank shaft, and the following method (from "The Blacksmith and
Wheelwright") is pursued. The shaft is first bent as in Fig. 2934. The
piece is next bent as in Fig. 2935, and finally as in Fig. 2936, the
corners A A and B B corresponding in all the figures.
[Illustration: Fig. 2937.]
BLACKSMITH'S BENDING BLOCKS.--In cases where a great number of pieces of
the same size and shape are required to be bent during the forging
process, a great deal of time may be saved and greater accuracy secured
in the work by the employment of bending devices. Thus, in Fig. 2937 is
shown at A a clip requiring to be bent to the shape at B. A pair of
tongs is provided with a hole at C to receive the stem of the clip, and
the jaw D is made of the necessary width to close the ends of the
forging upon. It is obvious that the hole C being in the middle of the
width of the tong jaw, the wings will be equidistant from the pin.
Figs. from 2938 to 2943 represent bending devices.
[Illustration: Fig. 2938.]
[Illustration: Fig. 2939.]
[Illustration: Fig. 2940.]
[Illustration: Fig. 2941.]
Figs. 2938, 2939, and 2940, represent a "former" for a stake pocket for
freight cars. A is a cast-iron plate having a projection B, around which
the stake pocket C is bent. D is fast upon A, and affords a pivoted
joint for the bending levers E F. The work is placed in the former as
shown in Fig. 2939, and levers E F are swung around to the position
shown in Fig. 2938. To enable the work to be put in and taken out
rapidly and yet keep it firmly against the end of B, a hand-piece G is
used as in Fig. 2940, its form being more clearly shown in the enlarged
Fig. 2941. Sufficient room is allowed between B and D to admit the work,
and the end of the piece G, which is pressed in the direction denoted by
the arrow in Fig. 2940, forcing the work against B. A number of the
pieces are piled on the fire so as to heat them sufficiently fast to
keep the former at work, and the bottom piece is the one taken out.
The corners of the work are by this process brought up square and the
faces are kept out of wind. The surface A forms a level bed. These
advantages will be readily appreciated by all smiths who have had
comparatively thin work to bend to a right angle in the ordinary way.
[Illustration: Fig. 2942.]
[Illustration: Fig. 2943.]
Figs. 2942 and 2943 represent a similar former for the step irons of
freight cars. In Fig. 2942 the piece is thrown in place ready to be
bent, its ends being fair with the lines J K on the bending levers E F.
In Fig. 2943 the levers are shown closed and the work C therefore bent
to shape. The bed plates A are mounted on a suitable frame to raise them
to a convenient height for the blacksmith.
FORGING A STABLE-FORK.--In the manufactories where stable and hay forks
are made, the whole process of forging is done under the trip hammer,
and is conducted as follows:--
[Illustration: Fig. 2944.]
[Illustration: Fig. 2945.]
[Illustration: Fig. 2946.]
[Illustration: Fig. 2947.]
[Illustration: Fig. 2948.]
To forge a four-tined fork, such as in Fig. 2944, a blank piece of steel
is employed, its dimensions being 5-3/4 inches long, 7-3/4 inches wide,
and 1/2 inch thick. The first operation is to swage down one end, as at
A in Fig. 2945. A split is then cut down as at B in Fig. 2946. The split
is then opened out as in Fig. 2947, and is fullered and drawn out at C.
Two more splits are then made at D D, and the ends are bent open as in
Fig. 2948, when the four tines E E and F F are drawn out and shaped out.
The stem, A, Fig. 2945, is then finished for the handle.
[Illustration: Fig. 2949.]
The following example of forging under the hammer is derived from _The
Engineer_, of London, England. Fig. 2950 shows the piece to be forged.
A block of iron, Fig. 2951, is drawn out as in the figure, the
dimensions of A and B being considerably above the finished ones. A
forked tool T, Fig. 2952, may be used to nick the two grooves shown in
Fig. 2953, which marks the locations for the hub and forms a starting
guide for the two fullering tools shown in Fig. 2954, one of which is
held by the blacksmith and the other by the helper. After this fullering
the forging will appear as in Fig. 2955. The ends E, F may then be drawn
out, having the shape as in Fig. 2956. To shape the curve between the
side of the hub and the body of the stem, grooves are formed as in Figs.
2957 and 2958, Y and B being top and bottom half-round fullers, and
these two grooves are subsequently made into one by means of larger
half-round fullers, as in Fig. 2959. The object of making two small
fullered grooves and then making them into one is to prevent the
fullering from spreading the body of the stem by lessening the strain
due to using a large fuller at once. The piece now appears as in Fig.
2960.
[Illustration: Fig. 2950.]
[Illustration: Fig. 2951.]
[Illustration: Fig. 2952.]
[Illustration: Fig. 2953.]
[Illustration: Fig. 2954.]
[Illustration: Fig. 2955.]
[Illustration: Fig. 2956.]
[Illustration: Fig. 2957.]
[Illustration: Fig. 2958.]
[Illustration: Fig. 2959.]
[Illustration: Fig. 2960.]
The next operation is to cut or punch away the metal between the ends of
the hub and the body of the piece, which is accomplished as follows:
[Illustration: Fig. 2961.]
A top and bottom die and block are made to contain the work, as in Fig.
2961, A and B being the work ends. Through these dies are two holes for
two punches which are driven through together as marked; the dies are
held fair, one with the other, by four holes in the lower and four pins
in the upper one, a section and top view of the dies being shown in Fig.
2962.
The piece is at this stage roughed out to shape all over, and may be
finished between the pair of finishing dies shown in Fig. 2963, which
also represents a plan and sectional view, _a_, _b_, _c_, _d_ being the
holes to receive guide pins in the upper die.
An excellent example of forgings in Siemens Martin steel is given in
the following figures, being the rope sockets for the Brooklyn Bridge.
[Illustration: Fig. 2962.]
[Illustration: Fig. 2963.]
[Illustration: Fig. 2964.]
[Illustration: Fig. 2965.]
Fig. 2964 represents two views of the forgings, and it will be readily
perceived that they are very difficult to make on account of the taper
hole, which is shown in dotted lines. The first operation was to take a
bar of steel 6-1/2 inches square and punch a hole, as at A Fig. 2965.
[Illustration: Fig. 2966.]
[Illustration: Fig. 2967.]
[Illustration: Fig. 2968.]
Next the piece was fullered at B, C by the fuller A, Fig. 2966, and cut
partly off as at D. The fullering at B was then extended by a spreading
fuller, shaped as at B, and the end E was drawn out. Then the piece was
cut off at D. Next the spreading fuller was applied to C, and the
forging appeared as in Fig. 2967. The end F was then drawn out, and the
appearance was as in Fig. 2968.
[Illustration: Fig. 2969.]
The next operation was to enlarge the hole A, Fig. 2965, by drawing
taper mandrels through it, the mandrels being about 7 in. long, having
1/2-in. tapes on them, and being successively larger. With the last of
these mandrels in the hole the hub was drawn out to length and diameter,
leaving the forging roughly shaped, but having the form shown in Fig.
2969.
[Illustration: Fig. 2970.]
To finish the hole the forging was then placed in a block such as shown
at G, in Fig. 2970, a finishing punch being shown at H in the figure.
[Illustration: Fig. 2971.]
The next operation was to let the steam hammer down upon the face of the
punch and bring up the wings E F parallel, but not more than parallel,
as then the mandrel could not be got out; the forging then appearing as
in Fig. 2971.
The next process was to put in a bar mandrel such as shown in Fig. 2972
at I, the pieces J, K fitting on their sides to the mandrel and being
curved outside to the circular and taper shape of the hole. The wings E
F may then be closed on the mandrel to their proper width and the whole
hub end being trimmed by hand, all the previous work having been done
under the steam hammer. The hub being finished the key M may be taken
out and the washer L taken off, when I can be pulled out, leaving J K to
be taken out separately. A pair of tongs are then put through the
finished hub end, while the wings are punched and trimmed under the
steam hammer, and subsequently finished by hand.
[Illustration: Fig. 2972.]
[Illustration: Fig. 2973.]
[Illustration: Fig. 2974.]
The forging of wrought-iron wheels for locomotives is an excellent
example. The spokes are first forged in two pieces, as 1 and 2 in Fig.
2973, and then welded to form the complete spoke. Piece 1 is first
forged in dies under the steam hammer to the form shown in Fig. 2974,
the dimensions being correct when the faces of the dies meet. The stud C
D is then drawn out to the required length and dimensions.
[Illustration: Fig. 2975.]
[Illustration: Fig. 2976.]
[Illustration: Fig. 2977.]
[Illustration: Fig. 2978.]
The upper half of the spoke is first blocked out under dies to the shape
shown in Fig. 2975, and the block B spread so as to form a section of
the wheel rim, as shown in Fig. 2976, in which D is a die, L a movable
piece wedged up by the wedges W W, and removable to enable the
extraction of the forging, and F is an end view of the fuller, the use
of which is necessary to cause the metal to spread sufficiently in the
direction of the dotted lines. The corners of the rim are then cut off,
as shown in Fig. 2973, and the rim is bent in a block having its top
face of the necessary curve, as in Fig. 2977, A being the block, and B a
piece movable, to allow the extraction of the work, and fastened in
place by the key or keys C. The two pieces are then welded together,
their lengths, &c., being gauged by a sheet-iron template, formed as in
Fig. 2978. The welding is usually performed with sledge-hammers, but as
soon as the pieces will hold well together, the drawing down is done
under a steam hammer.
[Illustration: Fig. 2979.]
The spokes thus forged are then put together, as in Fig. 2979, B
representing a wrought-iron band, encircling the rim of the wheel and
closed upon the same by the bolt and nut at N.
[Illustration: Fig. 2980.]
Two washers are then forged, to be placed and welded in as at W W, in
Fig. 2980.
The welding together of the spokes and of the washers to the spokes
proceeds simultaneously. The washers are heated to come to a welding
heat at the same time as the wheel hub is at a welding heat, and the two
are welded together under a steam hammer. During the heating of the
wheel hub, however, the band B, Fig. 2979, is tightened up with the
screw to bring the spokes into closer contact when heated to the welding
point.
[Illustration: Fig. 2981.]
[Illustration: Fig. 2982.]
The seams between the spokes at the circumference of the hub are welded
with bars as shown in Fig. 2981, in which R R are two bars of iron which
are operated by hand as rams. The wedge shape of the washers on their
inside faces performs important duty in spreading the metal as well as
simply compressing it, giving a much more sound weld than a flat washer
or plain dish would.
The rim of the wheel is welded up as follows:
In Fig. 2982 are shown four spokes of the rim as they appear after the
hub is welded. Into the [V] spaces, as _a_, _b_, _c_, _d_; wedges of
metal, of the form shown at E, are welded, after which the surplus metal
of E is cut away, and the rim is solid as at F. In this process,
however, it is necessary to weld all the pieces on one side of the
wheel, as at _a_ _b_, &c., except one, which must be left unwelded until
all the pieces save one on the other side are welded, and the wheel must
be allowed to become quite cool before these last two pieces are welded.
Otherwise the strain induced by the contraction of the wheel rim while
cooling will often cause the rim to break with a report as loud as that
of a rifle. In those cases in which this breakage does not occur the
wheel will be very apt to break at some part of the rim, when subjected
to heavy shocks or jars.
The Figs. 2983 to 2999 (which are taken from _Mechanics_), illustrate
the method employed to forge the rudder frame of the steamship
_Pilgrim_.
[Illustration: Fig. 2983.]
A side elevation of the rudder frame is shown in Fig. 2983.
The forging is made in eight separate pieces, which are so united as to
make three pieces. These three pieces are finally joined by five welds.
The whole length being 29 feet 11-3/4 inches, and the weight 6,500
pounds.
[Illustration: Fig. 2984.]
[Illustration: Fig. 2985.]
[Illustration: Fig. 2986.]
[Illustration: Fig. 2987.]
[Illustration: Fig. 2988.]
[Illustration: Fig. 2989.]
The work is commenced by piling and welding on the porter-bar at the
point in the shaft marked A. The stubs B and C having been previously
prepared, the pile on the porter-bar is heated and welded up and drawn,
shown in Fig. 2984, and scarfed as shown in Fig. 2985; the piece, shown
in Fig. 2986, is then laid in the scarf and welded; then the part from B
to A is finished to size, the finished forging of the post being shown
in Fig. 2984. The surplus stock to the right of B, Fig. 2984, is worked
down into the post E, and the distance from B to F is thus made correct
without loss of stock or time. The curve at D, Fig. 2983, was worked
down somewhere near, and then another pile and weld carries the job to
G. Here the same operations as at first are repeated, and the arm C is
welded in. There is left a good lump of stock in front of C, and by
another pile and weld enough is added to make the job to I, as shown in
Fig. 2987. Holes are then punched at J and L, and the piece of stock M
cut entirely out. A cut is made to L with a hack opening out the piece N
from the shaft. A taper punch, with a 3-inch point and a 4-inch head, is
then driven at L; to throw the piece N out into the position shown at
N^{1}, Fig. 2983; N^{1} is then finished, and the post from L to J
brought to forging size; then, by the ordinary process of piling,
welding and drawing, the shaft is finished from I to O. Next the
porter-bar is cut off, so as to leave stock enough to make the lower
part of the shaft, as shown in Fig. 2988. A hole was punched at Q, and
the stubs drawn out, as shown in Fig. 2989, which gives the post
complete.
[Illustration: Fig. 2990.]
The pieces S and T, and the tiller V, having been forged, as shown in
Fig. 2991, the upper member of the frame is started on the porter-bar at
W, Fig. 2983, and filed, welded and drawn to make the job as far as
X^{1}. Wooden templates, such as in Fig. 2992, are provided for the
pieces of the frame, the first extending from W to X^{1} and X, and the
second including the part from X^{1} to X^{2} and X^{3}. After W, X^{1}
has been drawn out with lumps left where the tiller and the arm S are to
be joined, the scarf is made for the tiller and that is welded in, and
the job finished to piece S. The scarf for S is then made, and S welded
in. This makes the upper member of the frame. The lower member is made
in the same way, starting at X^{3}. These two members are shown complete
in Fig. 2993. The post, Fig. 2989, was sent to the machine shop, and was
turned, planed, bored, and slotted, as shown in Fig. 2990. The frame was
now ready to be pieced up, by welds at W, X, X^{1}, X^{2}, and X^{3},
Fig. 2983.
[Illustration: Fig. 2991.]
[Illustration: Fig. 2992.]
[Illustration: Fig. 2993.]
[Illustration: Fig. 2994.]
[Illustration: Fig. 2995.]
[Illustration: Fig. 2996.]
[Illustration: Fig. 2997.]
[Illustration: Fig. 2998.]
[Illustration: Fig. 2999.]
The several sections are now ready to be welded together for the
complete frame, these welds being made as follows: The ends are upset as
in Fig. 2994 to receive on each side a [V]-piece such as in Fig. 2995,
which is heated on a porter-bar, and is of a more acute wedge than the
ends to be welded, so that when laid in as in Fig. 2996 it will touch at
the bottom first, and thus allow the air and whatever dirt there may be
on the surfaces to squeeze out as the welding proceeds. The method of
heating the frame for these welds is as follows: The [V]-block (which
has the grain of the iron running in the same direction as that of the
frame) being heated in the blacksmith's forge, the frame is clamped
together and counterbalanced by means of weights, so that it may be laid
over a fire pot, constructed as in Fig. 2997. This fire pot is lined
with brick, and has its blast supplied through a piece of flexible tube.
The anvil is of cast iron, shaped as in Fig. 2998, and placed on the
other side of the frame and opposite to the fire pot or portable forge,
as shown in Fig. 2997, so that the frame, when the heat is ready, may be
turned over upon the blocks on which it rests, and the part to be welded
will come upon the anvil. After one side is welded the anvil and the
portable forge change places, and the second side of the weld is made.
In the following figures (which are taken from _Mechanics_) is
illustrated the method employed to build up the shaft shown in Fig.
3001, which was for the steamer _Pilgrim_. Forgings of such large
dimensions are built up of pieces or slabs, called blooms, which are
themselves forged from scrap iron, which is piled as in Fig. 3000. For
the forging in question this scrap iron consisted of old horseshoes,
boiler-plate clippings, boiler rivets and old bolts, and the first step
in the manufacture is to form this scrap into piles ready for the
furnace.
[Illustration: Fig. 3000.]
[Illustration: Fig. 3001.]
[Illustration: Fig. 3002.]
[Illustration: Fig. 3003.]
These piles are made upon pieces of pine board 1/2 inch thick by 16
inches long by 10 inches wide. On these the scrap is piled about 14
inches high, each pile weighing about 270 pounds. After piling, the
scrap goes into the furnace and is raised to a welding heat, the board
retaining its form as a glowing coal almost to the last. The pile of
scrap is heated so nearly to melting as to stick together enough so that
it can be picked up in a long pair of tongs with peculiarly-shaped jaws,
and, as these tongs are suspended by a chain from an overhead traveller
running on an iron track, the bloom is easily transferred to the anvil
of the steam hammer, where, after one or two blows, a small porter-bar
with a crank end, such as shown in Fig. 3003, is welded on, and the pile
is rapidly drawn out into a square bar. When completed the porter-bar is
cut off, and the bar is laid aside to cool. The pile of scrap has now
become a "bloom," such as shown in Fig. 3002, and has been reduced in
weight from 270 lbs. to 240 lbs. The bloom is about 30 inches by 5
inches by 5 inches in dimensions, and has rounded, ragged ends, and a
surface full of lines marking welding of the individual pieces, and at
the ends looking as though the scrap had united by melting rather than
by any welding process.
[Illustration: Fig. 3004.]
These blooms are then taken to the large steam hammer and furnace by
which the shaft is to be built up. The porter-bar, although merely a
tool whereby to handle the mass, forms practically a base wherefrom to
build up the shaft. The construction of the furnace is shown in Fig.
3004, the heat, after passing the work being used for the steam boiler
that supplies steam to the steam hammer.
The porter-bar is held by a crane, the chain being placed in such
position in the length of the porter-bar as to balance it. On the end of
the porter-bar is a clamp, having arms by which the bar may be turned in
the furnace and when under the hammer.
Fig. 3005 represents the bar in position in the furnace, the aperture
through which it was admitted having been closed up by bricks luted with
clay, one brick only being left loose, so that it may be removed to
examine the heat of the bar. The end of the bar is flattened somewhat,
and a slab is laid upon it as in Fig. 3006, the appearance after the
first weld being shown in Fig. 3007. It is then turned upside down, and
blooms are piled upon it as in Fig. 3008. After these are welded the end
is shaped up round and to size. The extreme end is again flattened, or
"broken down," as it is termed, and first a slab, and after reheating,
blooms are added, as already explained; when these are welded and forged
enough to consolidate the mass the mass is rounded up again, thus
increasing the length of finished shaft. The end is again broken down
and a slab added, and so on, the shaft thus being forged continuously
from one end, and being composed of alternating slabs and blooms.
To forge this shaft 118,000 lbs. of blooms, 185 tons of coal, and 360
days of labor were required, the time occupied being 34 working days.
The slabs are simply forged pieces of larger dimensions than the blooms,
and more thoroughly worked, the difference between slabs and blooms
being that there is more waste with the blooms than with slabs, because
the blooms heat quicker than the forged part of the crank.
Between both the slabs and the blooms there are placed rectangular
pieces to hold them apart, and let the furnace heat pass between them,
the arrangement of these pieces being shown in Figs. 3009 and 3010.
Figs. 3011 to 3024 (which are taken from _Mechanics_), represent the
method employed to forge the crank shaft of the United States steamship
Alert.
[Illustration: Fig. 3005.]
[Illustration: Fig. 3006.]
[Illustration: Fig. 3007.]
[Illustration: Fig. 3008.]
[Illustration: Fig. 3009.]
[Illustration: Fig. 3010.]
[Illustration: Fig. 3025.]
[Illustration: Fig. 3026.]
[Illustration: Fig. 3027.]
[Illustration: _VOL. II._ =FORGING UNDER THE HAMMER.= _PLATE XVII._
Fig. 3011.
Fig. 3012.
Fig. 3013.
Fig. 3014.
Fig. 3015.
Fig. 3016.
Fig. 3017.
Fig. 3018.
Fig. 3019.
Fig. 3020.
Fig. 3021.
Fig. 3022.
Fig. 3023.
Fig. 3024.]
Fig. 3011 represents the crank shaft, and Fig. 3012 an end sectional
view, showing how the throws were built up. The first operation was to
forge the saddles shown in Fig. 3013, these being the pieces that are
shown between the cap and the wrist.
These saddles were made in halves, each half appearing as in Fig. 3014.
From a pile and weld of blooms on the porter-bar, enough to make the two
halves, one half was cut off. The other half was then drawn down on the
porter-bar, and the first half was then piled on the latter, as shown in
Fig. 3015. The square cross bar goes clear across and projects about an
inch at each side. The back pieces were short bits. The square cross bar
makes the saddle less liable to split in welding it on to the square
shaft. Two "caps" were also made before the forging of the shaft itself
began. These are shown in Fig. 3016, and their position in the finished
work is shown in Fig. 3012.
The shaft itself was piled, welded, and drawn on the porter-bar in the
usual manner, until the location of a crank was reached. Then a part of
the work some distance from the new end was squared, as shown in Fig.
3017, and on this square the saddle was piled to heat and weld, as shown
in Fig. 3018. As will be seen, the saddle rested upon the outer lines of
the angle. The first blow was struck square on the top of the saddle,
and after three or four blows the job presented the appearance shown in
Fig. 3019. The piece was now turned so as to lie as shown in Fig. 3020,
and worked with blows on the sides to the shape shown in Fig. 3021. This
opened the top of the juncture of the saddle and squared the shaft down
to the point where the weld was good. The piece was then turned back to
the position shown in Fig. 3019, and worked with blows which again
closed the angle on top, and made the weld good all through. The piece
was then returned to the furnace, and at the next heat the saddle was
squared up and finished, and the cap was piled on top of the saddle, as
shown in Fig. 3022. The cap was welded on at the next heat, and two
cheeks, like that shown in Fig. 3023, were laid upon one flat of the
crank and pinned with 1-5/8-inch round pins. One of these pins is shown
in the figure. Bits of iron were put under these cheek pieces in the
usual manner. As the cheeks were very much smaller in section than the
crank body, it was necessary to turn them over away from the fire, or
else the cheeks would be burned before the crank body was hot enough to
weld. To prevent the cheeks from falling off in the furnace the pins
were put in as described before heating. After two cheek pieces had been
welded on one side, two more were added on the opposite side, and then
the crank was finished, as shown in Fig. 3024.
As will be seen by inspection of Fig. 3012, the weld between the cap and
the saddle comes about the middle of the wrist, and the cheek pieces
support the cap sideways. By means of the piles and welds described, the
grain of the iron was so disposed as to offer the most resistance to
working strains. This method was devised by Mr. Farrell Dorrity, of the
Morgan Iron Works.
FORGING LARGE CRANK SHAFTS.[45]--The following paper describes the
method of forging marine crank shafts adopted at the Lancefield Forge,
Glasgow. It will be better understood if a short account is first given
of the ordinary methods in use for the same purpose.
[45] From a paper read at the Glasgow meeting of the Institution of
Mechanical Engineers, by W. L. E. MacLean.
"_First Method._--The most common method is technically termed by the
forgeman, 'finishing the piece before him.' He begins with a staff or
stave, as shown in Fig. 3025, suspended by a chain from the crane, and
made round for the convenience of manipulating under the steam hammer;
this stave is used over and over again for many forgings, as it is
merely the "porter" to carry the piece and enable it to be worked. The
forging is begun by two or three slabs being placed on the stave as at S
S S, and then inserted in the furnace. These slabs are flat blocks made
up of pieces of scrap iron, which have been piled and heated, and then
welded together. After being brought to a welding heat in the furnace,
the slabs are withdrawn, placed under the steam hammer, and beaten down
solid. The piece is then turned upside down, and two or three similar
slabs placed on the opposite side, as shown at S S. When sufficient iron
has been thus added to form the collar of the shaft (assuming it is to
have a collar), it is rounded under the hammer, as at C, Fig. 3026, and
the body of the shaft next to the collar is roughly formed, as at D.
More slabs, S S S, are added to bring out the body, and afterwards the
crank itself is proceeded with, on the same plan. The piece will begin
to assume the appearance of A, Fig. 3026. Then more slabs are welded on
the top, as at S S S, till the depth of the crank is obtained, after
which the forgeman proceeds to finish the collar and body of the shaft,
as shown. The collar on being finished is cut all round, as shown at C
D, Fig. 3027, so that it may be more easily detached from the stave when
the shaft is completed, leaving only sufficient connection to carry it
till then. The forgeman then cuts the gable of the crank as at E G, and
rounds up the body and neck as at B N, Fig. 3027.
"This, it will be observed, is a speedy process, and would invariably be
adopted if it were not attended with a very serious drawback; it is very
hazardous to the solidity of the forging. For it will be easily
understood that not above a third of the crank itself can be thus
formed, because the iron at the neck N would not carry a greater mass;
if the whole mass of the crank, or even the half of it, was formed
before the body and neck of the shaft were finished, a proper heat could
not be taken on the body and neck for finishing, without the neck giving
way or rupturing. Indeed, as it is, the undue proportion often causes
the shaft to be strained at this part, where most strength should be, so
that it is rendered weak, and a flaw is developed which by-and-by causes
it to be removed from the steamer as dangerous and useless, if indeed it
does not break outright; so that the forgeman, if he adopts this method,
must be very careful to proportion the amount of iron he has massed in
the furnace to the size of the body he is finishing, otherwise the
weakening above mentioned will take place. All marine engineers will
easily recognise this defect, which frequently occurs, but the cause of
which is probably not well understood. Such a flaw will present a
similar appearance to that shown at F, Fig. 3033, taken from an actual
example.
[Illustration: Fig. 3028.]
[Illustration: Fig. 3029.]
"This difficulty of proportioning the part of the crank first forged to
the size of the neck, will be still better understood by the appearance
of it in the furnace, as shown in Fig. 3028. Having reached this stage,
with one end of the shaft completed, as also that portion of the crank
itself which of necessity was completed before the collar was cut, in
order that the neck might be finished, no more iron can be added on the
top edge, as it is up to the full depth already; it must therefore be
added on the flat, as in Fig. 3029, where the piece is shown on its flat
side in the furnace, the finished portion being outside the furnace
door. A number of slabs S S S are then placed side by side to bring out
the width of the crank further; these being welded down, the piece is
turned upside down, and the process repeated on the other side.
Afterwards other slabs are similarly placed on both sides, as shown in
Fig. 3030, of which one is the flat, and the other is the edge view of
the crank at this stage; and this is continued until sufficient iron
has been massed to allow of the other gable of the crank being cut down,
as at A, Fig. 3031, and sufficient also to allow of the other part of
the body B being rounded and prepared for further piecing out.
[Illustration: Fig. 3030.]
[Illustration: Fig. 3031.]
[Illustration: Fig. 3032.]
"Now it will be observed that the first gable finished has the slabs all
welded on the edge of the crank, and the hammering has all been on the
edge; hence the subsequent hammering on the flat has a tendency to open
up the weldings, if they have not been thoroughly made. A section taken
at A B, Figs. 3028 and 3029, will show as in Fig. 3032, on the left, the
weldings being across the web of the crank; the circle indicates the
section which the crank pin would present if cut through there. But when
the slabs are placed on the flat afterwards, some of the joinings of the
ends of the slabs, or "scarf ends," are certain to fall within the crank
pin, as seen in Figs. 3028 and 3029; therefore the section through C D,
Fig. 3030, will show somewhat like Fig. 3032 on the right, and the crank
pin necessarily includes some of these flaws. The flaw thus produced,
called 'a scarf end in the pin,' is readily recognizable by all marine
engineers; at F, Fig. 3033, is a sketch from an actual occurrence.
"When the second gable is cut, and the other end is rounded, there is
only the other collar to be put on (if a double-collared shaft), and the
forging is completed.
[Illustration: Fig. 3033.]
This method is so speedy, compared with any other, that it is often
resorted to even at the risk of making a bad forging; and too many
broken shafts testify to the fact. Besides, it may be observed that in
making a double crank shaft, while the one crank may be made in this
way, the other must; for, the first crank, A, Fig. 3033, being
completed, and the body, B, between the two cranks, also completed, the
second crank, C, must of necessity be pieced off this body, even at the
risk of the neck N being strained. This may account for the many
instances in which one of the cranks of a double crank shaft gives way,
rendering the shaft useless; and also for the plan, now almost
universal, of making the two cranks separately and coupling them
together; a further object being, no doubt, to have the means of
replacing a defective half, if need be, without losing the whole shaft.
"At Lancefield, when a double crank shaft is to be made, the after
crank, A, is first made by the method afterwards described, so as to
insure that this crank, through which, as being next the propeller, all
the power of the engine passes, is perfectly sound; and in piecing the
other crank off the body, it is worked with slabs on the flat instead of
on the edge, as afterwards described.
"The writer's own opinion is that the crank is the most important part
of the shaft, and, therefore, at all costs, should be made first.
Others, no doubt, may take the same view, and, to avoid the risks just
mentioned, may adopt the process described in the second method.
[Illustration: Fig. 3034.]
[Illustration: Fig. 3035.]
"_Second Method._--This method builds the middle first, and is called
"turning the shaft end for end." The shaft is begun from a stave, by the
addition of slabs, as shown in Figs. 3034 and 3035; Fig. 3034 shows it
with iron added in slabs, till a butt is formed, as at B, to form the
nucleus of the crank; slabs S S S are then piled on it to bring the
crank up to the height.
[Illustration: Fig. 3036.]
"These are beaten down and welded, and more are added, as at S S S, Fig.
3035, till the full height of the crank is reached. Should the web (or
edgeway of the crank) be thick, two slabs are frequently used to make up
the breadth, placed edge to edge, as shown in Fig. 3035 on the right
hand of the figure; the widths of these slabs are limited by that at
which the shinglers can conveniently work and turn them under the steam
hammer. The crank, however, is completed without any "side slabs," for
the beating down of the slabs on the edge will broaden out the mass, and
give sufficient material to forge out the crank to the proper height by
hammering on the flat. The crank is afterwards cut at the off gable at
G, Fig. 3036, the body B pieced out and rounded, the collar welded on,
and then a small stave S is drawn upon the end, to enable the forgeman
to handle the piece when he "turns it end for end" to complete the other
end of the shaft.
[Illustration: Fig. 3037.]
"This method, though better than the last, is also objectionable; for
though there is not equal risk of 'scarf ends' in the pin, yet the
weldings are all on the edge, as in the lower view, in Fig. 3036, where
the section of the crank pin is shown by the dotted circle; and the
cheeks of the crank, O O, are thus liable to give way if a heavy strain
comes on the crank when at work. The defects arising from this cause are
shown in Fig. 3037, and will be readily recognised by all engineers.
"_Third Method._--Considerations such as these have led to the adoption
of the third or Lancefield method.
[Illustration: Figs. 3038 and 3039.]
"Fig. 3038 shows the piece begun from the stave in the usual way, with
the slabs all welded, however, on the flat, till a basis is formed for
the building up of the crank. A portion A is roughly rounded to form the
one end of the shaft, and the butt of the crank will present the
appearance of a slightly elongated square, as shown at B, Fig. 3039. The
workman then "scarfs" or hollows it down at one edge all along the side,
as indicated in the end view by the dotted line from C to D; it will
then present the appearance shown by the end view, Fig. 3040, being
somewhat bulged outward at the points E and F. Three long thin slabs,
Fig. 3042, shaped for the purpose, are then placed on the hollowed part,
the piece lying flat in the furnace. These slabs are tapered a little
the broad way, not on the length, and little pieces of iron are
interposed between them, to keep the surfaces apart, and allow the flame
free access between them. The object of making them thin is that they
may be all equally heated, which is not so readily achieved when the
slabs are thick; and the object of the tapering is to allow the slag to
flow out freely when the uppermost slab is struck by the steam hammer.
The surfaces thus get solidly welded.
[Illustration: Figs. 3040 and 3041.]
[Illustration: Fig. 3042.]
"Fig. 3041 represents the slabs thus placed in elevation, and the figure
on the right, in section. The slabs are forged long enough to go right
across the whole width of the crank, excepting about 6 inches; this
margin is necessary to allow of the lengthening out of the slabs to the
whole width under the process of forging. After these slabs are
perfectly welded, the piece is turned upside down, and the process is
repeated on the other side, as shown in Fig. 3042. When welded down the
mass has increased in depth as well. Another scarfing takes place on the
first side, and then another on the second side, as shown in the figure,
and so on, till the full size is obtained; and it will be seen, as in
the right-hand view in Fig. 3042, that by this process of "scarfing"
equally from, both sides, the iron from the very middle of the body of
the shaft is drawn up quite to the crank pin. The location of the pin is
indicated by A A, and it will be seen that by no possibility can there
be a "scarf end" in the crank pin, as the slabs in all cases go right
across the crank, and also that the cheeks of the cranks have no edge
weldings crossing them, as in the previous cases; for the tail of a slab
may be at R, Fig. 3042, while the other end may be at S. The fibre is
also developed by the continuous drawing up of the iron consequent upon
the repeated flat scarfings across the whole width of the crank. When
the crank has been thus massed sufficiently large, it is cut at the
gable, with sufficient material left to piece out the other body of the
shaft. This is now done, the coupling welded on, and a small stave drawn
on the end to enable the forgeman to manipulate it, when it is turned
end for end, to complete the other end.
"These proceedings occupy longer time than either of the other two
methods, and consequently costs a little more; but the advantage is well
worth all the difference, as greater confidence can be entertained that
the forging is every way satisfactory. In brief, by making the crank
first, is avoided the liability to weakness at the neck, characteristic
of the forgeman's making the shaft before him, as in the first method;
by the repeated 'side scarfing' is avoided the liability to fracture
across the cheeks, consequent upon the edge weldings of both first and
second methods; while by having the slabs the whole length of the width
of the crank, any 'scarf end' in the length way of the crank pin is
impossible (such as may occur in the first method); and the welding of
the mass of the crank being wholly on the flat must tend to form a more
solid forging than if hammered otherwise. Thus, if the forging is well
heated and properly hammered, the system promises to insure that no weak
part will be found in the shaft after it is finished and put to work.
The writer believes, from the success which has already followed in
every case the adoption of this method, that it will eventually be found
that almost more depends on the mode in which a crank shaft forging is
constructed than on the material of which it is made.
"This leads him to some observations regarding the material for such
shafts. It is of course well known that in the early days of
engineering, before the time when steam navigation had received a great
impetus by the invention of the screw propeller, the connecting rods,
cranks, shafts, &c., of land engines were all formed of cast iron;
except, indeed, where the connecting rods were made of wood, strapped
with plates of wrought iron, as frequently was the case with pumping,
winding and blowing engines. In fact, all the parts that could be made
of cast iron were so made, and the piston rods, bolts, keys, straps, and
other smaller parts were alone made of malleable iron, the smaller
pieces being made from rolled bars direct, as at present, and the larger
made of similar bars, but placed side by side and bound together or
'fagoted,' as they were called, from their resemblance to a bundle of
fagots. These bars, thus fagoted, were either brought to a welding heat
in a smith's hearth and welded under the sledge-hammers of the men
called 'strikers,' or hammermen; or else heated in a furnace, and welded
under the tilt hammer worked by a steam engine. By-and-by it was found
necessary to adopt the stronger material, wrought iron, for parts
hitherto confined to cast iron, because the latter was found too
deficient in cohesion to stand the strains due to the power of
high-pressure steam, which was now almost universally superseding the
use of low-pressure steam in the condensing engine. The system of
fagoting, however, was still carried out, even far into the history of
marine engineering; but when the rapid increase in the dimensions of
engines, both stationary and marine, called forth the steam hammer, and
so rendered the forging of heavy masses comparatively easy, the system
of fagoting fell into disuse, for the following reason: In making up a
fagot, say, of 18 inches or 20 inches square, it was found, that in the
furnace the outside bars would reach a welding heat much sooner than
those in the middle; consequently on welding this fagot under the steam
hammer, though the blow might reach to the centre, yet the interior
would not be welded, while the surface was; hence the shaft or other
forging would not be welded throughout, and it was no uncommon thing for
a shaft to break and expose the internal bars quite loose and separate
from each other.
"When it was seen that malleable was so much superior to cast iron, and
that the system of fagoting was so imperfect, the adoption of 'scrap
iron,' which was then composed principally of parings of boiler plates,
pieces of cuttings from smiths' shops, old bolts, horseshoes, angle
iron, &c., became general. These being piled together in suitable
pieces, and in a pile of suitable size, for the convenience of working,
were brought to a welding heat, and beaten out into a slab, or
oblong-shaped piece, ready for the forgeman; who would build two or
three together, adding more when required, and so bring out his piece to
a sufficient size to enable him to shape his forging out of it. Then it
was that engineers, seeing what an increase of strength they obtained by
these means, invariably specified on their drawings (as many of them
still do), 'These forgings are to be made of carefully selected scrap
iron, free from flaws and defects.'
"To meet the requirements of their customers, therefore, forge-masters
had now nothing to do but to select and use the best available scrap
iron; but the universal adoption of iron hulls in place of wooden ones,
conjoined with the rapid and unprecedented increase in steam navigation,
soon introduced a class of scrap iron which did not possess the
qualifications of good scrap, and also called for a very much greater
supply of forgings than could be obtained in superior scrap iron. The
consequence was that shafts of scrap iron, when turned and finished,
became liable to exhibit streaks and seams, not due alone to imperfect
welding in the forging, but likewise to the laminations and
imperfections of the original scrap iron, which the process of piling
and shingling into the slab was not sufficient to obliterate. So
constantly does this yet occur that it causes a strong temptation to
make such forgings of new iron puddled direct from the pig and then
shingled into slabs or blooms, under the idea that these streaks and
seams will thus be avoided, and that the iron will be improved almost to
the condition of scrap iron, while being forged under the steam hammer.
This, however, is found not to be the case. The forging is certainly
free from the streaks of the scrap iron, but this is obtained at the
expense of strength; for the material is too raw; it wants cohesion, and
has not had the proper kind or amount of working to bring it to the
condition of superior wrought iron. This method is still further
tempting, inasmuch as it is far cheaper than the other; the material
costs less than scrap iron, and, as it welds at a lower temperature, a
forging can be much more quickly and easily made. Still, for whatever
class of machinery it may be fitted, it should certainly be renewed in
every case for a crank shaft or propeller shaft.
"From these considerations it has been the custom at Lancefield, in the
preparation of the iron for crank shafts, to improve upon the ordinary
condition of the scrap iron in the following manner: The pile is made up
of carefully cleaned and selected scrap; it is brought to a welding
heat, and then hammered under the steam hammer. But instead of being
beaten into a flat slab for the forgeman, it is beaten into a square
billet, which is afterwards rolled in the rolling-mill into a flat bar,
as if for 'best best' merchant iron. By this additional heating,
hammering and rolling, all the different qualities of the scrap iron
composing the pile are merged into one homogeneous material, having the
fibre given to it that was lost in the separated portions of the scrap
iron; and this, when cut up into proper lengths, and again piled and
shingled into the slab, results in a material possessing somewhat the
closeness and density of steel, while retaining all the toughness and
tenacity of superior malleable iron. The improved method of constructing
the forging, previously detailed, is worthy the use of this superior
material; and both having been adopted at Lancefield with results which
have commended themselves so unmistakably to many engineers, that they
now not only specify the material, but stipulate for the mode of
manufacture, it is thought the system has only to be more widely known
in order to be universally adopted. It is certain to give greater
confidence in the endurance of such important parts of the machinery,
although this confidence may have to be obtained by a small increase in
the cost, due to the extra workmanship both on the material and on the
forging.
"When we take into consideration the vastly accelerated speed of the
marine engine in late years, and the many disastrous effects which
follow the breaking of a shaft at sea--also that the tendency of the age
is still towards much higher pressures, and further lengthening of
stroke it is not surprising that improvement in such an important part
as the crank shaft should be eagerly sought after; but it has hitherto
been sought in the direction of the material alone. Cast steel has been
advocated, and brought to some extent into use; but its expense renders
such shafts costly out of all proportion to the other parts of the
engine; while, in the event of their heating when at work (a very
frequent casualty), and having the water-hose directed upon the crank
pin or journals, it cannot be expected that the material will behave any
better, or even so well, as tough wrought iron. What is termed puddled
steel is liable to the same objection, and probably, from its mode of
manufacture, in a still greater degree. The so-called mild steel is no
doubt proving itself a superior material, and yielding good results when
rolled into ship or boiler plates. But thus prepared it is more costly
than 'rolled scrap bar;' and if not rolled, but cast into an ingot, then
it possesses some of the crystalline characteristics of steel, with all
the disadvantages attending its manipulation into a forging.
"For extra large crank shafts, the fear of unsoundness, arising from the
ordinary mode of forging, has led some engineers to consider the
propriety of building the shafts and cranks in separate pieces. This,
with engineers generally, has not hitherto been looked upon with favor;
as the fewer the pieces the more rigid the shaft. Moreover, the
increased weight necessitated by this separate building is viewed as a
disadvantage, even although it were not attended with greater cost, as
undoubtedly it is.
"The material and mode of manufacture advocated in this paper may tend
to dissipate some of these apprehensions. They will not obviate
defective construction in the engines themselves, or faulty proportion
of their parts, or neglectful supervision of their working, but they
will reduce to a minimum the risk of breakage in such untoward
circumstances. If any objection be taken on the score of extra size, the
enterprise which a quarter of a century ago engaged in the making of the
unusually large shafts necessary for the 'Great Eastern' may still be
trusted to meet the advancing requirements of the present day."
Fig. 3043 represents a foot-power hammer or Oliver. The hammer is upon a
shaft in bearings, and is held in the position shown by an open coiled
spring. On the shaft is a chain pulley, the other end of the chain being
connected through a leather strap to the treadle. Means are provided to
adjust the height to which the hammer will lift to bring the hammer face
fair with the work and to give the required degree of tension to the
spring.
Fig. 3044 represents a Standish's foot-power hammer, in which the hammer
and the anvil are provided with dovetail seats for receiving dies,
swages, &c. The force of the blow is regulated by the height to which
the hammer is raised, which may be adjusted by the nuts beneath the
spiral springs. The handle on the hammer is for pulling the hammer down
by hand when adjusting the lower die fair with the upper one.
What are known as power hammers are those driven by belt and pulley;
while those known as trip hammers have their helve lifted through the
medium of revolving lugs or cams. Steam hammers are those in which the
hammer is lifted by a piston in a steam cylinder; while in hydraulic
hammers, the hammer is moved by water pressure.
Fig. 3045 represents a Justice's power hammer, in which the hammer is
guided in a slideway and is operated by leather straps attached to the
ends of a spring, at the crown of which is attached a connecting rod
driven by a crank disk. The stroke is altered by means of placing the
crank pin in the required position in the slot in the crank disk. By
means of gibs the hammer may be set to match the dies. The pulley is
provided with a friction clutch operated by the treadle, shown.
Fig. 3046 represents a Bradley's Cushioned Hammer, in which motion is
obtained by a belt passing over a pulley on a crank shaft, whose
connecting rod R is capable of adjustment for length, so as to govern
the distance to which the hammer shall fall, which obviously varies with
different sizes of work. The hammer is lifted through the medium of a
rubber cushion A, seated in a casting to one end of which is connected
the rod R, while the other end is pivoted. The lever to which the hammer
is affixed is raised against the compression of the rubber cushion B,
and at the top of its stroke also meets the rubber cushion C; hence
these two cushions accelerate its motion after the crank has passed its
highest point of revolution. The cushion D prevents the rebound of the
hammer after the blow is struck; hence as a result of these cushions,
heavy or light blows may be struck with great rapidity and regularity.
The weight W is on a lever that actuates a break upon the wheel shown at
the side, so as to enable the stopping of the hammer quickly. The
machine is put in motion by pressing the foot upon the treadle T, which
operates a belt tightener, the belt running loose when the treadle is
released.
[Illustration: Fig. 3043.]
[Illustration: Fig. 3044.]
[Illustration: Fig. 3045.]
[Illustration: Fig. 3046.]
The hammer lever or helve is adjustable for height by means of the screw
G and hand-wheel H, which raise or lower the bearings in which the helve
journals are carried. This is necessary, because as the helve moves in
the arc of a circle the faces of the upper and lower die, or of the
hammer and the anvil, as the case may be, can only come fair at one
particular point in the path of the hammer; hence in proportion as the
blow terminates (by meeting the work surface) farther from the anvil
face, the pivot or journal of the helve must be raised, so that the
journal will be horizontally level (or as nearly so as possible) with
the hammer face at the moment the blow is delivered.
By giving motion to the helve through the medium of cushions, a direct
mechanical connection, and the destructive concussion that would
accompany the same, is avoided; hence a high speed may be obtained
without the frequent breakage that would otherwise ensue.
[Illustration: Fig. 3047.]
Fig. 3047 represents Corr's power hammer, the construction being as
follows: The semi-elliptic springs, shown on top and bottom of the beam,
serve to balance the stroke, so that the hammer may run from 350 to 450
strokes per minute, with safety to the machinery. The hammer is adapted
to almost any form or kind of forging. Large dies may be inserted for
various kinds of forming and welding, such as making plough-shares and
other articles, which require that the operation be commenced with a
light tap, and increased to a heavy blow at the will of the operator.
The whole structure is mounted on a substantial iron bed V, 18 inches
deep, 22 inches wide and 5-1/2 feet long. Attached to this bed V are two
circular arms L; between them is pivoted near their top, at K, an
oscillating frame H, having a longitudinal opening, in which is attached
two semi-elliptic springs G G, and two plates I, with trunnions
projecting laterally through the oscillating frame at K; the hammer beam
F is inserted between the springs G G, and the trunnion plates I, which
are bolted firmly to beam F at I; the ends of the trunnions and outsides
of the oscillating frame H rest evenly against the inside of the
circular arms L; at K a shaft is passed through the trunnions and beam
F, and made rigid in them with its ends resting in boxing at K. Caps are
provided to cover the ends of the boxing and shaft with set-screws
projecting against the ends of the shaft, which secures it against end
play.
By these mechanical arrangements the beam F and oscillator H are
securely attached independently, vibrating on one common centre,
allowing no side play of the hammer E, admitting F to the free action of
the springs G G; in the lower end of the oscillating frame at N is a
lateral opening 10 inches vertically by 6 inches longitudinally and 4
inches laterally, with flanges projecting longitudinally one inch into
this opening from both sides. This makes the opening two inches smaller
on the outside than the internal cavity; the rear and front internal
walls are provided with steel plates, 4 by 10 inches, 1/4 thick, resting
against the inner ends of four set-screws, not shown, provided to adjust
these plates to or from the sliding box at N, to compensate for wear and
prevent lost motion. These plates and flanges form slides and guides
between which a loose box and eccentric is provided with shaft
projecting laterally through boxing at N, which project upwards from an
adjustable frame immediately under the oscillator H; this permanently
locates the eccentric and shaft in the lateral opening in the oscillator
H, at N. The adjustable frame mentioned rests on suitable bearings on
the inside of the circular arms L, and is fastened down by four bolts
passing through suitable slots in the adjustable frame, entering the
bearings on the arms L. This frame is adjusted back or forth by
set-screws S S; this adjustment is for the purpose of giving a greater
or less distance between the anvil and hammer at D, as may be desired
for large or small work, long or short dies, &c.
The anvil B, weighing about 500 lbs., sits down in the bed at R and
rests on circular bearings (between R and B), which radiate to the
centre of the top of the anvil at D, and is held rigidly in any position
longitudinally desired by set-screws Q Q, with their inner ends resting
on shoulders on the sides of the anvil B, which projects down about ten
inches; between this lower projection and the internal wall of the bed
is sufficient space to admit of any adjustment desired. This lateral
adjustment is accomplished by set-screws R, passing through the sides of
the bed V, with their inner ends resting against the anvil which holds
it rigid at any lateral adjustment. By this arrangement the anvil is
accommodated to all and any class of work or shape of dies.
The anvil is constructed in two parts. Four inches of the top C may be
taken off, leaving a suitable place to insert large dies for various
purposes, such as dies for welding plough-shares and dies for forging
journals on large shafts. A counter-shaft, provided with suitable
pulleys, is attached on the rear end of the bed; this shaft is kept
constantly in speed and power by the vertical belt in the direction
indicated by the arrow; the other end of the shaft is provided with a
flanged pulley, corresponding to a flanged pulley M, on the eccentric
shaft; around these pulleys is placed a loose belt, as shown; in contact
with this is a press pulley T, adjustably attached by two arms to the
projecting end of the treadle P at O. If the foot be placed on the
treadle at U and it be pressed down, the break on the opposite side
breaks contact with the balance wheel (not shown); the press pulley will
at the same time tighten the loose belt on the flanged pulleys. This
gives motion to the pulley M, in the direction indicated by the arrow.
Its motion is increased by a heavier pressure until it attains the same
speed as the other flanged pulley; this would be the full speed, which
may be diminished to any speed desired by lessening the pressure on the
loose belt. By this means motion and power is given to the eccentric,
which carries back and forth the lower end of the oscillating frame H;
this gives vertical motion to the springs G G, and this imparts
corresponding motion to the beam F. These springs accomplish a threefold
object:
1st. They carry the hammer E up and down.
2nd. They cushion the hammer at the returning points and give off that
power which was stored in them while cushioning.
3rd. By the power exerted in the machinery they follow up and impart
still greater force to the blow.
It is found by this arrangement of eccentric loose box and oscillator
that when the machinery is moved in the direction indicated by the
arrow, that the downward stroke is one-sixth quicker than the up stroke;
this is a natural result, for the down stroke is performed while the
eccentric is revolving above the centre of its shaft and nearest the
fulcrum of the operator H. With the present arrangement the downward
stroke is performed with 5/12 of the revolution and the up stroke is
performed with 7/12; the difference is 2/12, which equals one-sixth. The
up stroke is performed while the eccentric is revolving below the centre
of its shaft and in that part farthest from the fulcrum of the
oscillator H, so if the machinery were reversed the quick stroke would
be up and the slow stroke would be down.
[Illustration: Fig. 3048.]
In Fig. 3048 is shown a Kingsley's trip hammer. The main bed or
foundation plate A carries the bed plate or frame B, at one end of which
are the pillar blocks C, which afford journal bearing to the casting
carrying the hammer shaft E, being fastened thereto by the clamp D.
These journals are the centre of motion of the hammer helve E.
At the other end of the bed plate B, are the pillar blocks F, affording
journal bearing to the cam and fly-wheel shaft, _a´´_ is the tripping
cam, which is provided with two toes or cam arms, which meet the
tripping piece _b´´_, and this gives the hammer two strokes in a
revolution of the fly-wheel shaft or cam shaft G. The stroke of the
hammer may be altered by means of the set-screws _c´´_, which move the
pillar blocks F, so that the cam toes _a´´_ have contact with the
tripping piece _b´´_ through more or less of the revolution of _a´´_;
the pillar blocks F being retained in their adjusted position by means
of the set-screws shown below them in the bed piece B.
By the following means provision is made whereby the face of the hammer
may be set out of parallel with that of the anvil block or lower die
_d´_.
[Illustration: Fig. 3049.]
Fig. 3049 is a sectional view through the pillar blocks C, and casting
and clamp D. The pillar blocks C C are carried in a semicircular frame
_a´_, hence by unscrewing the bolts _b´_ and screwing up the pillar
block on the other side, the journals are thrown out of parallel, and
the plane of motion of the hammershaft is altered so that the face of
the upper die does not meet that of the anvil die fair to an amount
which may be varied at will by operating the screws _b´_. The object of
this is to enable the forging taper (as in sword blades) with common
dies, and thus to save the making of special dies for each degree of
taper required.
Similar provision is made in the anvil block which is easier to set,
providing the degree of taper is within the limit of its range, of
movement, otherwise the hammer also may be set.
Fig. 3050 represents a drop hammer, and Fig. 3051 is a sectional view of
the lifting mechanism.
This machine consists of a base or anvil, a hammer which moves up and
down between two uprights, and a lifting device, which is secured to the
top of the uprights.
A board secured to the hammer passes up between two friction rolls,
which revolve in opposite directions. When the two rolls are moved
towards each other, the friction on the board causes the hammer to rise;
and when again separated the hammer will fall. The _back_ roll is keyed
to a shaft, on each end of which is a driving-pulley; and thus by the
use of two pulleys on the same shaft, equal wear comes on the bearings
in which it revolves. The _front_ roll turns freely on its shaft, and is
driven by the back roll being geared to it. To secure to the gears both
strength and durability, they are made with wide faces, are geared at
both ends, and the teeth are of peculiar shape.
The bearings to the shaft, on which the front roll revolves freely, are
eccentric to the roll, and a partial revolution of the shaft moves the
_front_ towards the _back_ roll, pinching the board. To an arm which is
secured to the front shaft is fastened the upright rod, the _upward_
movement of which _opens_ the rolls, and whose downward movement closes
the same; the weight of the rod being sufficient to cause the hammer to
rise. This arrangement, simple and yet substantial, dispenses with the
two eccentric-armed bushings, and the spreading of the upright rod at
the top to reach both bushings, which caused so much trouble in the old
way. In place of the dog which is usually used to hold up the hammer,
(which is limited in adjustment to holes located at fixed distances in
one of the uprights, necessitating not only the removal of the dog to
another hole, and connecting and disconnecting the same to the treadle,
but also the most accurate adjustment of the collar on the upright rod
to the dog holding the hammer), we use a pair of clamps, located on the
lifter, under the rolls. These clamps, holding the hammer centrally,
prevent the side blow against the upright, the inevitable result of the
contact of hammer and dog, when the former is only held on one side, as
it must be, by the use of the dog. The opening of the clamps by the
foot-treadle allows the hammer to fall; and the clamps are so made that
the hammer will ascend freely, whether the foot is on the treadle or
not, and if the foot is off the treadle, will hold up the hammer at any
point where it may be arrested in its upward movement. It will be
readily seen that the only adjustment required is that of the collar on
the upright rod, to any height of blow desired.
[Illustration: Fig. 3050.]
This machine has two treadles, one connected to the clamps, and the
other to a lever which operates the upright rod.
[Illustration: Fig. 3051.]
To obtain repeated blows with one motion of the foot, place the foot
upon the treadle connected to the clamps. If variable blows are wanted,
place the foot upon the _other_ treadle, and the hammer will follow the
motion of the foot. This extra treadle is a late improvement, and is not
shown in the cut. The operation required to obtain automatically any
number of blows of the same height is described as follows:--
[Illustration: Fig. 3052.]
Pressure upon the treadle opens the clamps and allows the hammer to
fall; just before the dies come together, the trip at the bottom which
holds up the upright rod is released, and allows the rod to drop; this
closes the rolls, causing the hammer to ascend. The hammer continues to
rise until it strikes the collar on the upright rod, and, lifting the
rod, opens the rolls, removing the pressure upon the board, and allows
the trip at the bottom to go under to hold the rod up, and the hammer
remains suspended, provided the foot is off the treadle. So long as
pressure is kept on the treadle, the blows of the hammer will be
continuous; but upon removal of the pressure, the hammer will assume its
original position.
[Illustration: Fig. 3053.]
[Illustration: Fig. 3054.]
[Illustration: Fig. 3055.]
To procure variable blows, the operation is as follows:--
Pressure upon the treadle connected to the lever which operates the
upright rod communicates itself to the treadle that opens the clamps,
and the hammer falls; a locking device (not shown in cut) keeps this
treadle down, and on completion of the variable blows wanted, removal of
the foot from the treadle disconnects the locking device, and the hammer
goes up to its original position, and is there held by the clamps.
When the work is such that the operator requires an assistant, variable
blows may be obtained by the use of the hand lever by this assistant.
A gentle pressure upon the treadle will allow the hammer to go down
slowly, but it will stop and remain suspended at any point as soon as
the pressure is removed. The hammer can also be arrested at any point on
its way up, by bringing into action the hand lever, so that the next
blow can be given from a state of rest at a less height than the collar
is set for. The clamps in holding up the hammer keep the board from
touching either roll, and prevent the same from being worn uneven when
not in use.
The back roll is made adjustable to different thicknesses of lifting
board, as are also the clamps.
[Illustration: Fig. 3056.]
Figures from 3052 to 3056 represent a steam hammer. The head A is set at
an angle in the frame. The anvil or die C is oblong, as is also the
anvil die D. The object of this arrangement is to enable the workman,
after drawing out his work across the short way of the die, to turn it
and finish it lengthwise without being inconvenienced by the frame. By
this means skew and [T]-shaped dies can be dispensed with, and the full
service of the ram utilised. The latter is moved between the guides E E,
and held in place by the steel plate F, bolted through the frame B. The
valve G is a plain cylinder of cast iron, enlarged at each end to work
in the cylindrical seats H H, in which the ports I I are placed. Steam
is admitted through the valve J, and circulates round the valve G,
between the seats. The exhaust chamber K is below the cylinder, which
therefore drains condensed steam into it at each stroke through the
lower steam port. The exhaust above the piston passes down through the
interior of the valve, as shown by the arrow on the drawing. The valve
stem L is connected with the valves in the exhaust chamber. No stuffing
box is therefore required, there being only atmospheric pressure on each
side of it. This combination enables the valve to be so perfectly
balanced that it will drop by its own weight while under steam.
[Illustration: Fig. 3057.]
[Illustration: Fig. 3058.]
The automatic motion is obtained by an inclined plane M upon the ram A,
which actuates the rocker N, the outer arm of which is connected by a
link to the valve stem, and thus gives motion to the valve. The valve is
caused to rise in the up-stroke by means of the rocker N and its
connections, through the inclined plane. The steam is thus admitted to
the top, which drives down the piston, while the valve and its
connections follow by gravity, thus reducing considerably the friction
and wear upon the valves. In very quick work the fall of the valves may
be accelerated by the aid of a spring; or it may be retarded in heavy
work by friction springs, so as to obtain a heavier blow by a fuller
admission of steam. For general work, however, the arrangement shown is
perfectly effective, and as the rocker N is hung upon the adjustment
lever P, any required variation can be obtained by the movement of the
lever. Single blows can be struck with any degree of force, or a rapid
succession of constant or variable strokes may be given.
The anvil O rests upon a separate foundation, in order to reduce the
effect of concussion upon the frame. The drawing illustrates the
arrangement. The bed is long, extending beyond the hammer on each side
so as to give plenty of area, and the ends are left open for convenient
access in case the anvil should settle and require re-adjustment.
Other forms of hammers having the same general principles of
construction are as follows:--
Fig. 3057 represents a double frame hammer, the weight of the hammer
being supplemented by steam pressure. The spiral springs shown beneath
the cylinder are to prevent the hammer from striking the cylinder and
causing breakage from careless handling by the operator. The valve gear
is arranged for operation either automatically or by hand.
Fig. 3058 represents a double frame steam drop hammer for stamping work
out in formers or dies. The frames are bolted to the anvil base and the
ram for the top die is guided by vertical slides on the inner face of
the frame. Shoes are provided, whereby the wear of the ram and of the
slides may be taken up, and the upper die kept properly matched with the
lower one.
[Illustration: Fig. 3059.]
[Illustration: Fig. 3060.]
[Illustration: Fig. 3061.]
[Illustration: Fig. 3062.]
[Illustration: Fig. 3063.]
Fig. 3059 represents a double frame steam drop hammer for locomotive and
car axles and truck bars. The frame is spread at the base to admit wide
work, and the upper surface of the base is provided with rollers
supported by springs, these rollers supporting the work. The same may be
operated automatically or by hand.
The hydraulic forging press at the Edgemore Iron Works of Wilmington,
Delaware, consists of a piston operating in a cylinder, and having at
its lower end a head guided by four cylindrical columns that secure the
base plate, or anvil, as it may be termed, to the cylinder. To the
above-mentioned head is secured the upper die, the lower one being
secured to the base plate.
Fig. 3060 represents a female die, and Fig. 3061 plan of another female
die, and Fig. 3062 plan of male die used in connection with the press to
forge the eye bars for the Brooklyn Bridge, five pieces each an inch
thick being welded to the bar and pressed into shape at one operation.
[Illustration: Fig. 3064.]
[Illustration: Fig. 3065.]
[Illustration: Fig. 3066.]
Figures from 3063 to 3066 represent a locomotive driving wheel ready to
have its hub welded by hydraulic pressure. The spokes having been forged
are held together by a band or hoop, as shown. The thickness of the hub
or boss is made up by the rings or washers shown in the sectional view.
The dies under which the welding is done are shown in Figs. 3064 and
3066.
[Illustration: Fig. 3067.]
Thin forgings are often made by compression between two rollers, the
form of the surface of the rollers, or projections or depressions upon
the same, pressing the forging to shape.
Thus, in Fig. 3068 are shown a pair of rolls A B, P representing a piece
of work, and C D two cam pieces fast upon the roll surfaces; S is a
fixed stop.
Suppose the work to be pushed through the rolls and to rest against the
stop S, then when the cams C D meet it they will pull it through and
reduce its thickness by compression towards the workman. The rollers are
obviously rotated by gear wheels; but they are sometimes provided with a
certain amount of give or elasticity at their bearings, so that the
reduction of work diameter may be obtained by several passages of the
work through the rolls.
[Illustration: Fig. 3068.]
[Illustration: Fig. 3069.]
The shape of the cams, as C D, determines that of the work; thus in Fig.
3069 is shown a pair of rolls for forming knife blades, each cam having
sunk in it a die equal in depth to half the thickness of the knife.
If the work is very short in comparison with the circumference of the
rolls, two, three, or more cams may be arranged around the
circumference, making an equal number of forgings or impressions, as the
case may be, at each revolution of the rolls.
In Fig. 3067 is shown a nail-forging machine for producing, from strip
iron, nails similar to hand-made, at rates varying from two to three
hundred per minute, and lengths of from six to one inch, two nails being
completed at each revolution of the driving shaft of the machine. The
framing consists chiefly of a main casting, to which are fixed an upper
frame, carriages for the driving shaft, and other details. The principal
moving part is a heavy steel slide, deriving its motion from a crank pin
with adjustable throw; this slide carries two shears, two gripping dies,
and sundry indispensable appendages, to some of which it imparts motions
for guiding the nails between the stages of cutting off and finishing.
The successive operations by which each nail is perfected are as
follows:--
A piece of iron about six inches long, and of a width and thickness
respectively of the finished nail, is inserted at a red heat to the
feeder of the machine; a narrow strip is immediately cut off the lower
side of the heated iron, and by the motion of the steel slide is carried
to and pressed against a fixed die; while in this position another die
rises at right angles and presses the partially formed nail against
another fixed die. Thus the headless nail is firmly held on its four
sides, and while in this position a lever, moved by a cam, and carrying
a suitable tool, advances and forms the head, thus completing the nail.
The return motion of the steel slide releases the nail, leaving it free
to fall, but as its weight is not sufficient to insure this happening, a
"knocker off" is provided, which at the right moment forcibly ejects the
nail by way of a guiding shoot into a receptacle placed outside the
machine. It is to be noted that the tools for shearing and gripping, and
which have to be changed with each different size of nail, are made of a
special mixture of cast iron. They are thus easy of preparation and
renewal, while at the same time answering their intended purpose as well
as or better than the finest cast steel, at less than half the cost. The
whole of the machine is carried upon an open-top cast-iron water tank,
serving as a receptacle for the tongs and tools heated in withdrawing
the iron from the furnace.
[Illustration: Fig. 3070.]
Figs. 3070 and 3071 represent a machine for forging threads on rods and
screws. As forgings, the threads are beautifully clean, and for the
general work of coach screws much stronger than the cut threads. A
perspective view of the machine is given in Fig. 3070, and a vertical of
it shown in Fig. 3071. In the former figure, _a_ _b_ are the screw dies.
The rod or bolt to be threaded is placed upon the lower die _b_, and fed
forward while screwing it. The upper die is mounted on a slide _c_,
which is actuated in the downward direction by an eccentric _e_ on the
main shaft and the toggle-bar _d_, the upward motion being obtained by
an internal spiral spring _f_. The lower die _b_ is carried in a slide
_g_, and is adjusted at the proper distance from the upper die by means
of wedge _h_, and the inclined plate _i_, beneath the slide _g_. The
wedge _h_ is operated by a pedal _l_, and secured in its highest
position by a bolt _j_, received in a mortice made in the plate _i_, the
bolt being operated by a pedal _m_. In order to release the wedge and
return it to its lowest position, the bolt is raised by pressing down
the pedal _m_, whereby the wedge is free to be returned by the
counterweights _k_, in connection with pedal _l_; slide _g_, carrying
the lower die, then descends by its own gravity, and so separates the
two dies sufficiently to allow of the removal of the screw-bolt or rod
therefrom. To compensate for the wear of the dies, and admit of their
adjustment, another wedge _o_, with screw adjustment, is disposed below
the inclined plate _i_.
Fig. 3072 represents a lag screw forged by the machine.
[Illustration: Fig. 3071.]
[Illustration: Fig. 3072.]
[Illustration: Fig. 3073.]
Fig. 3073 represents a finishing machine for horseshoes. The bars of
iron are rolled with the creases (for the nail heads of the finished
shoe) in them. The blanks for the shoes are then cut to length and bent,
and the nail holes punched. The shoes then pass to a machine, Fig. 3073,
which consists of a frame A B, carrying the roll C, above the table D,
and a second roll, not shown in the cut, but being directly beneath C,
there being between these two rolls sufficient space to let the dies
(which press the shoes into shape) pass.
These dies rest upon the table D, and are carried around upon it in a
direction from left to right of the chain H, to the links of which the
dies are attached. This chain is operated by the vertical shaft J,
having a pulley for belt power at K.
As each die approaches the rollers, a shoe (cut to length, creased, and
punched as already described) is placed on it, and on reaching the rolls
the shoe is pressed into form on the die by the rolls, the bottom roll
serving as a rolling bed so as to reduce the friction that would be due
to a sliding motion on the bottom of the die. The top roll C, which
presses the shoe into the die is driven by power.
[Illustration: Fig. 3074.]
[Illustration: Fig. 3075.]
A plan view of the machine is shown in Fig. 3074, and a view showing the
shape of the dies is given in Fig. 3075.
[Illustration: Fig. 3076.]
The surface _h_ forms the frog. To give the required concavity to the
toe and sides of the shoe, the surface _i_ is made convex, and tapered
or inclined towards _h_. The tread _e_ is deepest at the heel on both
sides, and highest at the toe. It is obvious that by suitably shaping
the surfaces _h_, _i_, and _e_, any required form may be given to the
shoe. Fig. 3076 represents a shoe creased, punched, and bent ready to be
passed to the machine.
[Illustration: Fig. 3077.]
Fig. 3077 represents a circular saw for cutting off hot iron; A is the
frame of the machine, the arm B pivoted at C carrying the saw D; F is a
spring bolted to the frame and serving to hold the saw in the position
shown. The work E is gripped by the lever L, which is pushed over by
hand. The lever L is adjusted to suit different sizes of work by the
screw G, which raises or lowers the piece H, to which L is pivoted. The
saw is brought into contact with the work, and fed to it by applying the
foot to the lever or arm B at I, the screw J being made to contact with
the foot of the machine by the time the saw has passed through the work,
thus preventing the saw from moving too far forward after passing
through the work.
CHAPTER XXXIV.--WOOD-WORKING.
PATTERN-MAKING.--Of the different kinds of wood serviceable to the
pattern-maker, pine is, for many reasons, usually employed. It should be
of the best quality, straight-grained, and free from knots; it is then
easy to work in any direction, possessing at the same time sufficient
strength for all but the most delicate kinds of work, and having besides
the quality of cheapness to recommend it. Care taken in its selection at
the lumber-yard will be amply repaid in the workshop. When it is
straight-grained, the marks left by the saw will show an even roughness
throughout the whole length of the plank; and the rougher the
appearance, the softer the plank. That which is sawn comparatively
smooth will be found hard and troublesome to work. If the plank has an
uneven appearance--that is to say, if it is rough in some parts and
smooth in others--the grain is crooked. Such timber is known to the
trade as cat-faced. In planing it the grain tears up, and a nice smooth
surface cannot be obtained. Before purchasing timber, it is well to note
what convenience the yard possesses for storing. Lumber on the pile,
though it be out in all weathers, does not deteriorate, but becomes
seasoned; nevertheless its value is much increased if it has an
extemporised roof to protect it from the sun and rain. But as it is not
convenient to visit the pile for every customer, quantities are usually
taken down to await sale, and for such a shelter must be provided,
otherwise it will be impossible to insure that the lumber is dry, sound,
and fit for pattern-making. It is obvious that the foregoing remarks on
the storage of lumber apply to all woods.
The superiority of pine for pattern-making is not, however, maintained
when we come to fine delicate patterns or patterns requiring great
durability. When patterns for fine work, from which a great many
castings are to be made, are required, a fine pattern wherefrom to cast
an iron pattern is improvised, because, if pine were employed, it would
not only become rapidly worn out, but would soon warp and become
useless. It is true that a pine pattern will straighten more easily than
one made of a hard wood; but its sphere of usefulness in fine patterns
is, for the above reasons, somewhat limited. Iron patterns are very
desirable on account of their durability, and because they leave the
sand easily and cleanly, and because they not only do not warp but are
also less liable than wooden ones to give way to the sand, while the
latter is being rammed around them by the moulder, a defect that is
often experienced with light patterns, especially if they are made of
pine. Iron patterns, however, are expensive things to make, and
therefore it is that mahogany is extensively employed for fine or
durable pattern work. Other woods are sometimes employed, because they
stand the rough usage of the moulding shop better and retain the sharp
corners, which, if pine be used, in time become rounded impairing the
appearance of the casting. Mahogany is not liable to warp, nor subject
to decay; and it is exceedingly durable, and is for these reasons the
most desirable of all woods employed in pattern-making, providing that
first cost is not a primary consideration. There are various kinds of
this beautiful wood: that known as South American mahogany is chiefly
used for patterns.
Next to mahogany we may rank cherry, which is a very durable wood, but
more liable to twist or warp than mahogany, and it is a little more
harsh to the tool edge. If, however, it is stored in the workshop for a
length of time before being used, reliable patterns may be made from it.
In addition to these woods, walnut, beech, and teak are sometimes
employed in pattern-making.
The one property in all timber to be specially guarded against is its
tendency to warp, bend, expand, and contract, according to the amount of
humidity in the atmosphere. Under ordinary conditions, we shall be right
in supposing a moisture to be constantly given off from all the exposed
surfaces of timber; therefore planks stored in the shop should be placed
in a rack so contrived that they do not touch one another, so that the
air may circulate between the planks, and dry all surfaces as nearly
alike as possible. If a plank newly planed be lying on the bench on its
flat side, the moisture will be given off freely from the upper surface,
but will, on the under surface, be confined between the bench and the
plank: the result being that a plank, planed straight, and left lying as
described, will be found, even in an hour, to be curved, from the
contraction of the upper surface due to its extra exposure; therefore it
is obvious that lumber newly planed should be stored on end or placed on
edge. Lumber expands and contracts with considerable force across the
grain; hence if a piece, even of a dry plank, be rigidly held and
confined at the edges, it will shrink and break in two, often with a
loud report. There is no appreciable alteration lengthwise in timber
from the above causes; and if two pieces be glued together so that the
grain of one crosses that of the other, they can never safely be relied
upon to hold. Hence they had better be screwed so that there will be a
little liberty for the operation or play of the above forces, while the
screws retain their hold. The shrinkage, expansion, and warping of
timber may perhaps be better understood by the following considerations:
The pores of wood run lengthwise, or with its grain, and hence the
moisture contained in these passes off more readily endwise or from any
surface on which the pores terminate.
THE SHRINKAGE OF TIMBER.--The direction in which timber shrinks in
seasoning or drying is shown in the following figures, which are
extracted from a lecture delivered by Dr. Anderson before the Society of
Arts in London, England. The shrinkage of timber lengthwise of the grain
is very slight, its shrinkage in a direction across or at a right angle
to the length of the grain being much greater and depending upon the
part of the log from which it is cut.
[Illustration: Fig. 2706.]
The shrinkage is greater on the outside than near the heart of the tree;
thus if a log be cut into four quarters it will shrink as in Fig. 2706,
from the full block outside to the inside or white outline; or if we cut
out a square as in figure, one corner extending to the heart, it will
shrink to the form shown in the figure. If we sever the log by the four
parallel saw cuts it will shrink as shown by the black outline, the
shrinkage of the middle piece being more clearly shown in Fig. 2707.
[Illustration: Fig. 2707.]
[Illustration: Fig. 2708.]
It is evident, therefore, that to obtain a uniform degree of shrinkage
throughout the length of a piece of timber, it should be sawn as near as
possible parallel with the grain of the log. Thus in Figs. 2708 and 2709
we have a side and an end view of a log, the saw cuts at A being from
logs that have been squared, the upper slab B being waste material, and
the planks being parallel to the squared sides of the log.
[Illustration: Fig. 2709.]
The lines from A to C on the lower half of Fig. 2709 represent planks
that are what is termed flitched, the saw cuts following the taper of
the tree, and it is plain that the shrinkage would be more uniform; thus
the outside plank is near the bark from end to end, while at the top of
the figure the outside plank is near the outside at the small end only
of the log, and would therefore shrink most at the right hand end.
Furthermore as the planks at A cross the grain of the log at its large
end, they are therefore weaker and more liable to split at that end.
BENDING TIMBER.--By bending a piece of timber to bring it as near as
possible the required shape the strength of the work is increased,
because the grain of the wood runs parallel with the shape of the work,
and, furthermore, the cutting tools act on this account to better
advantage. In bending a piece of timber it is obvious that either the
convex side must stretch, or the concave one compress, or if no
extraneous pressure is brought to bear upon the piece, both of these
actions may occur, and as the side of the piece that was nearest to the
heart of the tree is the hardest and strongest, it will stretch less if
made the convex side, or compress less if made the concave side of the
timber, but the bent piece will maintain its shape better if the heart
is the convex or outside of the curve.
The modern method of bending wood is to fasten on the outside, or convex
side of the piece, a strap that will prevent it from stretching. And it
is found that wood thus bent is stronger, stiffer, and heavier than
before it was bent, because the fibres become interwoven, and it is
found that the wood is harder to split than before.
[Illustration: Fig. 2710.]
[Illustration: Fig. 2711.]
[Illustration: Fig. 2712.]
Suppose we require to bend a piece to a half circle, and after it has
been boiled, steamed, or heated with a dry heat it is placed in an iron
strap, such as shown in Fig. 2710, having an eye at each end in which a
hook may be inserted to hold the piece in shape (after it is bent) until
it is dry again. The piece with this strap on its outside or uppermost
surface is laid on the _former_ or forming piece shown in Fig. 2711,
which has a projection at A, fitting into the recess A of the bending
block in Fig. 2712. On the outside of the piece is then placed the
strap, shown in Fig. 2713, its blocks of wood fitting to the ends of the
piece to be bent.
The winch of the bending block is provided with a rope, whose ends have
two hooks which are engaged in the eyes of the straps, shown in Fig.
2714, and by operating the winch the piece is bent to shape, as shown in
Fig. 2714. While in this position a hook is placed through the eyes of
the band that is around the bent piece of work, so that when removed
from the forming block or stand it appears as in Fig. 2715.
[Illustration: Fig. 2713.]
[Illustration: Fig. 2714.]
[Illustration: Fig. 2715.]
[Illustration: Fig. 2716.]
[Illustration: Fig. 2717.]
[Illustration: Fig. 2718.]
When, however, the piece requires to be bent to more than one sweep or
bend, the process requires to be changed somewhat. Thus, suppose the
middle is to be bent circular and the two ends left straight, and the
strap on the piece to be bent is provided with a piece, such as in Fig.
2716, the ends B engaging in eyes in the strap, and the screw A abutting
against the end of the piece to bind the strap firmly upon the ends, as
in Fig. 2717, in which the piece is shown within the strap. After it has
been bent to the former it is held there by straps and wedges, as shown
in Fig. 2718.
[Illustration: Fig. 2719.]
The next operation is to lock the curve, as shown in Fig. 2719, between
an inside and outside former by means of straps A A and wedges C, when
the ends D of the piece may be bent up to the dotted lines and locked to
the ends of the top former by straps and wedges.
The length of time a piece should be boiled or steamed for the bending
process depends upon the size of the piece and the kind of wood, hard
wood requiring longer boiling or steaming. A piece of ash, say 2 by 4
inches in cross section, would require about six hours' steaming with a
low pressure of moist or wet steam, but it would not suffer damage if it
were steamed for a day. Pieces not over half an inch thick may be bent
after steaming them about half an hour.
If the wood is steamed too much it loses its elasticity and will pucker
on the inside surface of the bend when in the former or bending block.
The period during which the piece should be held to its bent shape
before being released varies from twelve hours for thin pieces to
twenty-four hours for thick ones, and it is found that pieces which have
been bent in a strap so as to prevent the outside from stretching, will,
in drying, increase their bend or curvature, while those not confined at
their ends straighten out.
[Illustration: Fig. 2720.]
[Illustration: Fig. 2721.]
[Illustration: Fig. 2722.]
The cracks that are found in timber are termed _shakes_; thus in Fig.
2720 the black lines represent what are called heart shakes, while those
in Fig. 2721, being wider, are termed star shakes. When the shakes are
circular, as in Fig. 2722, they are called cup shakes.
Many of the tools used by the pattern-maker have been described in
connection with hand turning, hand boring tools, lathe tools, &c., and
therefore need no further reference.
PLANES.--For roughing out the work the jack plane is employed, varying
in size from 14 inches long with a cutter knife or blade 2 inches wide,
to 27 long with a blade 2-1/4 inches wide, and as its purpose is to make
a flat surface, it is preferable that it be as long as the work will
conveniently permit. The jack plane is followed by the fore plane, the
truing, or trying plane, which varies in size from about 18 inches long
with a blade 2-1/8 inches wide, to 20 inches long with a cutter or blade
2-3/8 inches wide. When the fore plane is made longer, as for planing
long joints, it is termed a jointer plane, the length being as much as
30 inches and the blade 2-5/8 inches wide.
The smoothing plane varies from about 5 inches long with a blade 1-1/2
inches wide, to 10 inches long with a blade 2-3/8 inches wide. Smoothing
planes are, as the name implies, used to simply smoothen the work
surface after it has been trued.
The angle of the plane blade to the sole of the plane is for ordinarily
soft wood 45°, but 50° or 55° may be used for very hard woods.
[Illustration: Fig. 2723.]
[Illustration: Fig. 2724.]
To break the shaving the blade is attached to what is termed a cover,
which is shown in Fig. 2723, B representing the blade and A the cover.
The cover is curved to insure that it shall bed against the blade at its
very end, and, therefore, as near to the cutting edge as a maximum
distance 1/16 inch for rough and 1/32 inch for finishing cuts. The blade
of a jack plane is most efficient when it is ground well away towards
the corners, as at A B in Fig. 2724, thus producing an edge curved in
its length.
When the blade is in position in the stock for cutting off the maximum
of stuff, its blade should project nearly 1/16 through the sole of the
stock, while the corners A B are about level with the face of the stock.
The bevelled face should stand at about an angle of 25° to the flat
face. In grinding it care should be taken to grind it as level as
possible, rounding off the corners as shown above. The grindstone should
be kept true and liberally supplied with water; the straight face should
not be ground away, nor indeed touched upon the stone, except to remove
the burr which will sometimes turn over. The pressure with which the
blade is held against the grindstone should be slight at and toward the
finishing part of the grinding process, so as not to leave a long ragged
burr on the end of the blade, as is sure to be the case if much pressure
is applied, and it will occur to a slight extent even with the greatest
of care. The blade should not be held still upon the grindstone, no
matter how true, flat, or smooth the latter may be; but it should be
moved back and forth across the width of the stone, which will not only
grind the blade bevel even and level, but will also tend to keep the
grindstone in good order.
In oilstoning a plane blade, the straight face should be held quite
level with the face of the oilstone, so that the cutting edge may not be
bevelled off. Not much application to the oilstone is necessary to the
straight face, because that face is not ground upon the grindstone, and
it only requires to have the wire edge or burr removed, leaving an
oilstone polish all along the cutting edge. The oilstoning should be
performed alternately on the flat and bevelled faces, the blade being
pressed very lightly on the oilstone toward the last part of the
operation, so as to leave as fine a wire edge as possible. The wire is
the edge or burr which bends or turns over at the extreme edge of the
tool, in consequence of that extreme edge giving way to the pressure of
the abrading tool, be it a grindstone or an oilstone. This wire edge is
reduced to a minimum by the oilstone, and is then so fine that it is
practically of but little account; to remove it, however, the plane
blade or iron may be buffed backwards and forwards on the palm of the
hand.
The blade being sharpened, we may screw the cover on, adjusting it so
that its edge stands a shade below the corners of the iron, and then
screwing it tight; the blade or iron and the cover must now be placed in
the mouth of the plane stock, and adjusted in the following manner:--
The plane iron should be passed through the mouth of the stock until as
much in depth of it is seen to protrude from the bottom face of the
stock as is equal to the thickness of shaving it is intended to cut: to
estimate which, place the back end of the plane upon the bench, holding
the stock in the left hand with the thumb in the plane mouth, so as to
retain the iron and wedge in position, the wedge being turned towards
the workman. A glance down the face of the stock will be sufficient to
inform the operator how much or how little the cutting edge of the iron
protrudes from the face of the plane stock, and hence how thick his
shaving will be. When the distance is adjusted as nearly as possible,
the wedge may then be tightened by a few light hammer blows. If, after
tightening the wedge, the blade is found to protrude too much, a light
blow on the fore end on the top face of the plane will cause it to
retire; while a similar blow upon the back end will cause it to advance.
In either case the wedge should be tightened by a light blow after it is
finally adjusted.
In using a jack plane we commence each stroke by exerting a pressure
mostly on the fore part of the plane, commencing at the end and towards
the edge of the board, and taking off a shaving as long as the arms can
conveniently reach. If the board is longer than can be reached without
moving, we pass across the board, planing it all across at one standing;
then we step sufficiently forward, and carry the planing forward,
repeating this until the jack planing is completed. To try the level of
the board, the edge or corner of the plane may be employed; and if the
plane is moved back and forth on the corner or edge, it will indent and
so point out the high places.
The fore plane (or truing plane, as it is sometimes called) is made
large, so as to cover more surface, and therefore to cut more truly. It
is ground and set in the same manner as the jack plane, with the
exception that the corners of the iron or blade, for about one-eighth
inch only, should be ground to a very little below the level of the rest
of the cutting edge, the latter being made perfectly straight (or as
near so as practically attainable) and square with the edge of the iron.
If the end edge of the cover is made square with the side edge, and the
iron is ground with the cover on, the latter will form a guide whereby
to grind the iron edge true and square; but in such case the cover
should be set back so that there will be no danger of the grindstone
touching it. The oilstoning should be performed in the manner described
for the jack plane, bearing in mind that the object to be aimed at is to
be able to take as broad and fine a shaving as possible without the
corners of the plane iron digging into the work. The plane iron should
be so set that its cutting edge can only just be seen projecting evenly
through the stock. In using the fore or truing plane, it is usual, on
the back stroke, to twist the body of the plane so that it will slide
along the board on its edge, there being no contact between the cutting
edge of the plane iron and the face of the board, which is done to
preserve the cutting edge of the plane iron from abrasion by the wood:
as it is obvious that such abrasion would be much more destructive to
the edge than the cutting duty performed during the front stroke would
be, because the strain during the latter tends mainly to compress the
metal, but, during the former, the whole action tends to abrade the
cutting edge. The face of the fore plane must be kept perfectly flat on
the underside, which should be square with the sides of the plane. If
the under side be hollow, the plane iron edge will have to protrude
farther through the plane face to compensate for the hollowness of the
latter; and in that case it will be impossible to take fine shavings off
thin stuff, because the blade or iron will protrude too much, and as a
consequence there will be an unnecessary amount of labor incurred in
setting and resetting the plane iron. The reason that the under surface
should be square, that is to say, at a right angle to the sides of the
body of the plane, is because the plane is sometimes used on its side on
a shooting board.
When the under surface of the plane is worn out of true, let the iron be
wedged in the plane mouth, but let the cutting edge of the iron be well
below the surface of the plane stock. Then, with another fore plane,
freshly sharpened and set very fine, true up the surface, and be sure
the surface does not wind, which may be ascertained by the application
of a pair of winding strips, the manner of applying which will be
explained hereafter. If the mouth of a fore plane wears too wide, as it
is apt in time to do, short little shavings, tightly curled up, will
fall half in and half out of the mouth, and prevent the iron from
cutting, and will cause it to leave scores in the work, entailing a
great loss of time in removing them at every few strokes. The smoothing
plane is used for smoothing rather than truing work, and is made shorter
than the truing plane so as to be handier in using. It is sometimes
impracticable to make a surface as smooth as desirable with a truing
plane, because of the direction of the grain of the wood.
[Illustration: Fig. 2725.]
Fig. 2725 represents an ordinary compass plane, which is a necessary and
very useful tool for planing the surfaces of hollow sweeps. This tool is
sometimes made adjustable by means of a piece dovetailed in the front
end of the plane, which, by being lowered, alters the sweep and finally
converts it from a convex to a concave.
[Illustration: Fig. 2726.]
In Fig. 2726 is shown a much superior form of circular or compass plane.
Its sole consists of a flexible steel blade, whose ends are attached to
levers that are connected together by toothed segments. By means of the
large hand-screw the levers are operated, causing the sole to bend to
the required curvature, and by reason of the toothed segments the levers
move equally, and therefore give the sole a uniform curve throughout its
length.
[Illustration: Fig. 2727.]
[Illustration: Fig. 2728.]
Planes are also made with the sole and the cutting edge of the blade
made to conform to the shape of the work. Thus Fig. 2727 represents a
rabbeting plane, and Fig. 2728 a side rabbet plane. The latter is,
however, very seldom used, but is especially useful in planing hard wood
cogs fitted to iron wheels, or the teeth of wheel patterns or other
similar work. For ordinary use, it is sufficient to have two, a 3/4 and
a 1-1/4 inch, and two or three having a flat sole for flat bottom
grooves.
What is known as a core box plane has its sole at an angle of 90°, or a
right angle; the principle of its action is that in a semicircle the
angle is that of 90°.
[Illustration: Fig. 2729.]
[Illustration: Fig. 2730.]
In Fig. 2729, for example, it is seen that if a right angle be laid in a
semicircle so that its sides meet the corners of the same when revolved,
its corner will describe a true circle; hence at each plane stroke the
plane may be slightly revolved, to put on the cut, which must be very
light, as the core box plane is only suitable for finishing purposes.
For planing across the end grain of wood, what are termed block planes
are used, the angle of the blade to the sole being from 65 to 85
degrees, as shown in Fig. 2730, which represents the Stanley iron frame
block plane. In block planes the bevel that is ground to sharpen the
blade is placed in front and therefore meets the shaving instead of the
flat face as in other planes.
[Illustration: Fig. 2731.]
[Illustration: Fig. 2732.]
Fig. 2731 represents the Stanley bull-nose rabbet plane for getting
close into corners, and Fig. 2732, a block plane, in which the blade may
be set in the usual position or at one end of the stock as denoted by
the dotted lines.
[Illustration: Fig. 2733.]
[Illustration: Fig. 2734.]
For fine work planes having an iron body are much preferable to the
wooden ones, and in the improved form of planes there is provided a
screw mechanism, whereby the blade may be set much more accurately and
easily than by hammer blows, such as are necessary with ordinary
wedge-fastened blades. Thus Fig. 2733 represents Bailey's patent
adjustable planes, the handles only being of wood. The blade is secured
by a simple lever movement, and is set by means of the thumb screw shown
beneath and behind the blade. The metal stock possesses several
advantages, such as that the sole keeps true, the mouth does not wear
too large, as is the case with wooden planes. Planes are also made
having a wooden body and an iron top, the latter containing the
mechanism for locking the blade and setting it quickly. Fig. 2734
represents one of these planes.
[Illustration: Fig. 2735.]
Figs. 2735 to 2744 represent a combination plane. Fig. 2735 is a side,
and Fig. 2736 a top view of the tool as a whole.
Pieces A and B form the body of the plane, between which the bits or all
the tools are carried except the slitting knife, which is carried by A
alone.
In the figures T is a beading tool shown in position, having a bearing
or seat in both A and B so as to support it on both sides, and being
locked in position by the thumb-screw C. At G is a depth gauge which is
moved over into the hole at D, when that position is most suitable for
the kind of work in hand. Piece B is made adjustable in its distance
from A so as to accommodate different widths of bits by sliding it on
the arms M, securing it in its adjusted position by the set-screws S.
Similarly the fence F slides on arms M, and is secured in its adjusted
position by the set-screws H, thus enabling it to regulate the distance
from the edge of the board at which the bits shall operate, and also
guiding the bits true to the edge of the board or work. F is provided
with an upper pair Q, and a lower pair R of holes (as seen in Fig. 2737)
so that it may be set on the arms M at two different heights as may best
suit the nature of the work. In Fig. 2736 it is shown with arms M
passing through the lower pair of holes. The points of the set-screws H
meet the bores of both pairs of holes and therefore lock F to the arms,
whether the upper or lower holes are upon the arms. For rabbeting and
fillister work the upper holes Q are used, while using ploughs the lower
ones are brought into requisition.
[Illustration: Fig. 2736.]
[Illustration: Fig. 2737.]
[Illustration: Fig. 2738.]
[Illustration: Fig. 2739.]
[Illustration: Fig. 2740.]
At W, Fig. 2735, is a spur for cutting the end grain of the wood in
advance of the bit, as is necessary in dado and other across grain work,
the construction of the spur is seen more clearly in Fig. 2738. The
pieces A and B are provided with a recess having four arms or branches,
while the spur itself has but three, so that the spur may be set as in
Fig. 2735 and be out of action, or its screw being loosened it may be
given a half-turn, so that one of its arms will come below B as at X in
Fig. 2738. The cutting edges of the spur come exactly flush with the
outside faces of A and B, and the bits are so held in their seats that
their edges also come flush with these outside faces, which therefore
act as guide to the bit; thus Fig. 2739, shows a beading bit in
position, and Fig. 2740 a section of work finished, A and B being in
section. Fig. 2741 shows a plough in position on the work, A and B being
shown in section. It is seen that their inner edges being bevelled, will
in using a beading tool, act as a gauge regulating the thickness of
shaving taken at each plane stroke, which will equal the depth to which
the bit edge projects beyond the bevels of A and B. Similarly in
grooving or ploughing the amount to which the bits project below the
lowest edges of A and B regulates the thickness of the shaving, and as A
and B follow the bit into the work, the blade being once set requires no
further attention, the depth gauge regulating the total depth of tool
action.
[Illustration: Fig. 2741.]
[Illustration: Fig. 2742.]
[Illustration: Fig. 2743.]
[Illustration: Fig. 2744.]
This principle of the side pieces entering the work with the bits and
being adjustable to suit various widths of bits, gives to the tool a
wide range of capacity. Fig. 2742 represents the tool arranged for
slitting thin stuff into parallel slips, the piece B being removed. The
depth gauge is not shown in figure, because it would hide the slitting
knife from view, but it is obvious that it would rest on the surface of
the work and thus steady the plane. Fig. 2743 is an example of a number
of operations performed by this one tool. For tonguing, the bit shown in
Fig. 2744 is employed, the depth gauge _g_ being adjustable in the
groove by means of the slot shown.
CHISELS.--The principal kinds of chisels are the paring chisel which is
used entirely by hand, and the firmer chisel which is used with the
mallet. The difference between the two lies in the shapes of their
handles, and that the paring chisel is longest. A paring chisel worn to
half its original length will serve for a firmer chisel, because when so
worn it is long enough for the duty. A chisel should not, however, be
used alternately as a paring and a firmer chisel, because the paring
chisel requires to be kept in much better condition than the firmer
chisel does. Mortice chisels are made thicker than either the paring or
the firmer because of their being longer and requiring rougher usage. It
is necessary to have several sizes of chisels, varying in width from an
eighth of an inch to one and a half inches.
[Illustration: Fig. 2745.]
[Illustration: Fig. 2745_a_.]
[Illustration: Fig. 2746.]
Fig. 2745 represents the form of handle for a paring chisel, its total
length being 6 inches, and from A to B being 1-1/2 inches. The diameter
at C is 1-1/2 inches, the hollow below D of 3/8 of an inch radius, the
diameter at D 1 inch, and the length from B to E 1-1/2 inches. This form
affords a firm grip to the hand, the end E being applied to the
operator's shoulder. The shape of handle for a firmer chisel is shown in
Fig. 2746.
Chisels require great care both in grinding and oilstoning them, being
held very lightly upon the grindstone when finishing the grinding so as
to avoid as far as possible the formation of a long feather edge. The
flat face of the chisel should never be ground, as that would make it
rounding in its length, hence there would be nothing to guide it in
cutting straight and the value of the tool would be almost destroyed.
In oilstoning the chisel, great care is necessary in order to avoid
forming a second facet at a different angle to that at which it was
ground, because such a facet is too narrow to form any guide whereby to
move the chisel in a straight line, and the consequence is that the edge
is oilstoned rounding and cannot do good service. The whole length of
the ground facet or bevel should rest on the oilstone, but the pressure
should be directed mainly to the cutting end so that at that edge the
oilstone will entirely remove the grinding marks, which will, however,
remain at the back. If there is at hand a grindstone of sufficiently
small diameter, the chisel may be made hollow on the bevel, as shown in
Fig. 2745_a_, so that when laid on the oilstone the bevel will touch at
the back and at the end only, and this will enable the chisel to be
pressed evenly down on the stone, thus producing a very even and flat
edge, while leaving but a small area to be oilstoned.
The motion of the hands should not for the oilstoning be simply back and
forth, parallel with the oilstone length, but partly diagonal, which
will assist in keeping the chisel level. The back of the chisel should
be laid flat upon the oilstone and moved diagonally, under a light
pressure, which will remove the wire edge, which may be further removed
by lapping the chisel on the operator's hand.
[Illustration: Fig. 2747.]
Chisels for turning work in the lathe are best if made short, and to
enable the cutting edge to get up into a corner, the chisel is sometimes
given two cutting edges, as at A, in Fig. 2747, the edges forming an
angle, one to the other, of less than 90°. For finishing curves in the
lathe the chisel shown at B in the figure is employed, or for deeper
work, as in the bores of holes, handles are dispensed with, chisels
being formed as at C and D in the figure.
Gouges, like chisels, are made "firmer and paring," the distinction
being precisely the same as in the case of chisels.
When the bevel is on the outside or convex side of the gouge it is
termed an outside, while when the bevel is on the inside or concave side
it is termed an inside gouge.
[Illustration: Fig. 2748.]
Fig. 2748 represents an outside firmer gouge. The inside gouge may be
ground a little keener than the chisel, and requires great care in
grinding, because it must be held on the corner of the grindstone, which
is rarely of the desired curve. In oilstoning the concave side of a
gouge an oilstone slip is employed, the gouge being held in the left
hand and the slip in the right, the latter being supplied with clean
oil.
The convex side of an outside gouge should be made level on the face of
the oilstone, and while the gouge is moved to and fro its handle must be
revolved so as to bring all parts of the curve in contact with the
oilstone. The small amount of surface on the gouge in contact with the
grindstone makes it very liable to have a long feather edge, hence it
must be very lightly pressed to the stone, and the same remark applies
to the oilstoning in order to reduce the wire edge.
[Illustration: Fig. 2749.]
Fig. 2749 represents a gouge for lathe work, its handle being made long
enough to be held in both hands and used as described with reference to
turning with hand tools.
Another tool, very useful to the pattern-maker, is the skew chisel,
which is also described in connection with hand turning.
SAWS.--There are two principal kinds of saws, the rip saw for cutting
lengthwise of the grain of the wood, and the cross-cut saw for cutting
across the grain. In shaping these saws the end to be obtained is to
enable them to sever the fibre of the wood in advance of the effort to
remove it from the main body.
[Illustration: Fig. 2750.]
[Illustration: _VOL. II._ =THE ACTION OF SAW TEETH.= _PLATE XIII._
Fig. 2751.
Fig. 2752.
Fig. 2753.
Fig. 2754.
Fig. 2755.
Fig. 2756.]
In Fig. 2750, for example, the grain of the wood runs lengthwise and the
throat, or front face of each tooth, is hooking or hooked, so that the
cutting edge will cut through the fibres at their ends before it is
attempted to remove them from the main body of the wood. Suppose, for
example, that the saw shown in Fig. 2750 was put into a piece of timber
and a tooth pressed hard enough on the wood to leave a mark, and this
mark would appear as in Fig. 2751 at E, extending across a width equal
to the full width of the saw tooth. It would do this because the front
face or throat B and the back face A are both at a right angle to the
saw length as is denoted by the dotted lines. As the grain is supposed
in Fig. 2751 to run lengthways of the timber, clearly the fibre between
the indentation E and the saw slot is severed and would be removed as
the tooth passed farther down through the wood, the action of first
severing the fibre at its end and then removing it being carried on by
each tooth.
In Fig. 2752 is shown a cross-cut saw in action upon a piece of wood in
which the grain or fibre runs across the timber, and in this case the
teeth require to be shaped to cut on each side of the saw instead of
directly in front of it, because in that way only can the ends of the
wood fibre be severed before it is dislodged from its place.
To enable the cross-cut saw to accomplish this, one tooth cuts on one
side of the saw slot and the next tooth on the other, as at A and B in
Fig. 2751, from which it will be seen that as the grain runs lengthways
of the timber, the fibres between the lines A and B will be severed at
their ends by the extreme edges of the teeth before the thicker part of
the tooth reaches them to remove them.
The necessity for this action may be plainly perceived if we apply the
rip saw for cross-cutting and the cross-cut saw for ripping. Suppose,
for example, we place the saw shown in Fig. 2750 to cut across the grain
of the piece of timber, and as its tooth met the wood it would indent it
as at G, Fig. 2751, and as this is in line with the grain, the tooth
would wedge in the piece and the piece cut could not be dislodged
without first tearing the fibres apart at each end. Or suppose we take
the cross-cut saw and apply it for ripping (as cutting lengthways of the
grain is called) and if we indented the surface with a single tooth it
would leave a mark as at F, Fig. 2751, which is lengthways of the fibre,
so that the tooth would here again wedge between the fibres and not cut
them. The next tooth would make a mark parallel to F, but on the other
side of the saw slot or kerf as it is called, still leaving the fibre
unsevered at its ends where it should be severed first.
In order that the saw may not rub against the sides of the slot or kerf,
and thus be hard to move or drive, it is necessary that the kerf be
wider than the thickness of the saw blade, and to accomplish this the
teeth are bent sideways, each alternate tooth being bent in an opposite
direction, as shown in the front view of the teeth in Fig. 2753. This
bending is called the set of the saw, and should be sufficient to make
the kerf about two-thirds wider than the thickness of the saw blade.
While preserving the feature of severing the fibre before attempting to
dislodge it from its place, we may at the same time give the teeth of
rip saws more or less sharpness by fleaming their faces.
In Fig. 2754, for example, the throat face is filed square across or at
a right angle to the length of the saw, but the back face A is at an
angle, making the points of the teeth sharper, and therefore enabling
them to cut more freely. The result of this fleam would be that the
tooth, instead of cutting equal and level all the way across as in Fig.
2751 at E, would cut at the corner first and only across its full width
as it entered deeper into the wood; we have, in fact, placed the leading
part of the cutting edge more at the extreme point and less in front of
the tooth.
In Fig. 2755 the throat or front face of the saw is given fleam, as
shown by the line B, which is not at a right angle to the saw length,
and as a result the cutting edge is carried still more advanced at the
point and more towards the side of the tooth and we have, therefore, to
a certain extent, qualified it as a cross-cut saw.
We might give the face B so much angle as to carry the leading part of
the cutting edge to the side of the saw, thus giving it the
characteristics of a cross cut.
In Fig. 2756, both the throat face B and the back face A are given
fleam, making the points extremely sharp, and showing the leading part
of the cutting edge towards the side, the corner leading still more.
[Illustration: Fig. 2757.]
In Fig. 2757 we have two saws R and S, the latter having fleam on the
front and the former on the back face of the tooth, the amount or degree
of fleam being equal.
[Illustration: Fig. 2758.]
In Fig. 2758 we have indentations of their teeth. The teeth of S would
leave a mark as at E F, and R would leave a mark as at G H. The side cut
F being more than the side cut G, and the front cut E being at a less
angle to F than the front cut H to G, it follows that the saw S would be
the best, provided the grain of the wood ran diagonally as shown, not
only because it has more side and less front cut, but also because its
cutting edge is keener on the side, as is seen on comparing the lines P
and A in Fig. 2757.
[Illustration: Fig. 2759.]
If we give fleam to both faces we alter the indentation, as denoted in
Fig. 2759, in which E F represents the line of tooth cut when one face
has fleam, and G H the line of tooth cut when both faces are fleamed,
the shape of the actual saw cut being shown at J.
Obviously the fleam makes the points weak, but this in coarse saws may
be partially remedied by shaping the teeth as in Fig. 2760. Fleam on the
front face or throat of the tooth has the effect of preserving its set,
the pressure of the cut being as shown by the arrows in Fig. 2753.
It is evident that the finer the point of the tooth the sooner it will
become dulled, and that the harder the timber the more quickly the tooth
will become dull. So soon as this occurs the teeth refuse to cut freely,
and the extra pressure on them acts to spring them upward and to take
off the set. It is obvious that for soft wood the teeth may be given
fleam on both faces, and that the front face should have some fleam,
even for the hardest of wood, whether the back face has fleam or not.
Also, that in proportion as the grain of the wood runs more across the
saw kerf than in line with it the teeth should be filed to cut on the
side, and the hook of the front face may be lessened, while
_vice-versâ_, in proportion as the grain of the wood runs parallel with
the kerf, the tooth may have hook and fleam on the back face with a
slight fleam on the front one.
[Illustration: Fig. 2760.]
[Illustration: Fig. 2761.]
GAUGES.--Of gauges for marking on the work lines parallel to its edges
there are several kinds, a common form being represented in Fig. 2761,
in which the block that slides against the edge of the work is secured
by a set-screw.
A better method, however, is to use a key set at a right angle to the
stem, so that the head may be tightened or loosened by striking it, as
if it were a hammer, against anything that may happen to lie on the
bench, hence the gauge may be set and adjusted with one hand while the
other is holding the work, as is often necessary when marking small
work. The marking point should be a piece of steel wire fitted tightly
in the stem, the protruding part being ground or tiled to a wedge, with
the two facets slightly rounding, and whose broad faces stand at a right
angle to the stem of the gauge, the point or edge only projecting
sufficiently to produce a line clear enough to work by; otherwise it
will not be suitable for accurate work.
[Illustration: Fig. 2762.]
The mortice gauge, Fig. 2762, is similar to the above as regards the
stem and sliding piece, but it is provided with two marking points,
their distance apart being adjustable. The head screw works in brass
nuts.
[Illustration: Fig. 2763.]
For lines that are to be marked more than about ten inches from the edge
of the work a broader base is necessary to the head or block, which may
be shaped as shown in Fig. 2763.
[Illustration: Fig. 2764.]
The lines drawn upon pattern work require to be very fine, and for this
purpose the cutting scriber, Fig. 2764, is employed. The end A is
bevelled off on both sides like a skew chisel. The end B is ground to a
fine point and both ends are oilstoned. The point end is for drawing
lines with the grain, and the knife end for lines across the grain of
the wood. The wooden handle is to afford a firm grip.
[Illustration: Fig. 2765.]
In Fig. 2765 we have the cutting gauge, in which a steel cutter takes
the place of the marking point, being wedged in position. It is employed
to cut thin strips of wood, that is to say, of thicknesses up to about a
quarter of an inch. The cutter point should be tempered to a dark straw
color.
The principal forms of joints employed by the pattern-maker are as
follows:--
[Illustration: Fig. 2766.]
Fig. 2766 represents the mortice and tenon, the thickness of the tenon
being one-third that at C, which leaves a thickness at E and D equal to
that of the tenon. When the mortice is away from the end of the work the
breadth B of the tenon is made less than the breadth F of the work so as
to leave stuff at A to strengthen the mortised piece. To make this joint
the two pieces, having been planed or otherwise made to size as
required, are marked for the position and length of the mortice in one
case, and for the length of the tenon in the other; both pieces are now
gauged with a mortice gauge, both being marked alike; and then from the
face side we mark a tenon or mortice of the dimensions required.
[Illustration: Fig. 2767.]
If the stuff is broad two or more tenons and mortices may be given, as
shown in Fig. 2767.
[Illustration: Fig. 2768.]
To lock the tenon in the mortice two methods may be employed. In the
first and preferable one the mortice is tapered, as in Fig. 2768, and
the two wedges are inserted and driven home. In the second the tenon is
provided with saw cuts to receive the wedges.
[Illustration: Fig. 2769.]
A very superior method of jointing is the dovetail, shown in Fig. 2769,
which is serviceable for connecting the ends and sides of a box, or any
article in that form. The strength of the corner formed in this way is
only limited by that of the material itself; therefore it should be
preferred when available in making standard patterns, or for work too
thin to admit nails or screws; the corner formed by this joint is not
limited to 90° or a square, so called, but may form any angle. Nor is it
imperative that the sides or ends of the box or other article be
parallel. They may incline towards one another like a pyramid; a mill
hopper is a familiar example of this. If it be required to dovetail a
box together, get out four pieces for the sides and ends, to be of the
full length and width respectively of the box outside. They are to be
planed all over, not omitting the ends. The gauge, that is already set
to the thickness of the stuff, must now be run along the ends, marking a
line on both sides of each piece. Then mark and cut out the pins as on
the piece A; the dovetail openings in B are traced from the pins in A.
The pieces having been tried and found to go together are finally
brought into contact and held in their places with glue.
[Illustration: Fig. 2770.]
Fig. 2770 is a mitre joint, the only one serviceable to mouldings,
pipes, and other curved pieces. It is not a strong form of joint, and is
only used where the preceding kinds are inapplicable. It is made with
glue, the pieces having been previously sized; and as an additional
precaution, if the work will admit, nails, brads, or screws are inserted
at right angles to one another.
[Illustration: Fig. 2771.]
Fig. 2771 represents the half check joint, and it is obvious that the
thickness at A must equal that at H, and be half that at B, which will
give each half equal strength.
A gland for an engine piston rod forms a simple example of the different
ways in which a pattern may be formed. Fig. 2772 represents the drawing
for the gland.[46]
[46] From the "Pattern Maker's Assistant."
"Let us suppose the pattern-maker to be uninformed of the purpose the
casting is to serve, or how it is to be treated: in such a case he is
guided partly by his knowledge of the use of such patterns, and a
consideration of being on the safe side. The form shown in Fig. 2773
would suggest itself as being a very ready method of making the pattern;
by coring out the hole, it can be made parallel, which the drawing seems
to require. The advantage of leaving the hole parallel is that less
metal will require to be left for boring in case it should be necessary;
because, if the hole is made taper, the largest end of the bore will
require to have the proper amount of allowance to leave metal sufficient
to allow the hole to be bored out true, and the smaller end would,
therefore, have more than the necessary amount; while just the least
taper given to the exterior would enable the moulder to withdraw the
pattern from the mould. Made in this way, it would be moulded as shown
in Fig. 2774, with the flange uppermost, because almost the whole of the
pattern would be imbedded in the lower part of the flask, the top core
print being all that would be contained in the cope; and even this may
be omitted if the hole requires to be bored, since the lower core print
will hold the core sufficiently secure in small work, unless the core is
required to be very true. The parting of the mould (at C D, Fig. 2774)
being level with the top face of the flange, much taper should be given
to the top print (as shown in Fig. 2773), so that the cope may be lifted
off easily. Were this, however, the only reason, we might make the top
print like the bottom one, providing we left it on loose, or made it
part from the pattern and adjust to its place on the pattern by a taper
pin; but another advantage is gained by well tapering the top print, in
that it necessitates the tapering of the core print at that end; so
that, when the two parts of the mould are being put together, that is to
say, when the cope is being put in place, if the core has not been
placed quite upright, its tapered end may still arrive and adjust itself
in the conical impression, and thus correct any slight error of position
of the core. The size of the core print should be, at the part next the
pattern, the size of the core required; for if the extremities are made
of the size of the core, and the taper or draft is in excess, there will
be left a useless space around the core print, as shown at A B in Fig.
2774, into which space the metal will flow, producing on the casting,
around the hole and projecting from the end face, a useless web, which
is called a fin, which will of course require to be dressed off the
casting.
[Illustration: Fig. 2772.]
"We will now suppose that our piece, when cast, is to be turned under
the flange and along the outside of the hub or body, and that the hole
also is to be bored. In this case the pattern made as above would still
be good, but could be much more easily made and moulded if it has to
leave its own core, its shape being as shown in Fig. 2775; because the
trouble of making a core is obviated, and the core is sure to be in the
centre of the casting, which it seldom is when a core is used. We must,
however, allow more taper or draft to a hole in a pattern than is
necessary on the outside; about one-sixteenth inch on the diameter for
every inch of height on work of moderate size is sufficient. The
allowance for boring should be one-sixteenth inch at the large end of
the hole, provided the diameter of the hole is not more than five or six
inches, slightly exceeding this amount as the diameter increases;
whereas, if the pattern had been made with core prints, an allowance of
one-eighth inch for small, and three-sixteenths inch for larger work
would be required. These are the advantages due to making the pattern
leave its own core. We have still to bear in mind, however, that, if the
casting require a parallel hole, a core must be used; and furthermore,
if the hole is a long one, we have the following considerations: The
separate dry sand core is stronger, and therefore better adapted to
cases where the length of the hole greatly exceeds the diameter. Then
again, if the hole require to be bored parallel, it can be more readily
done if the hole is cast parallel, because there will be less metal to
cut out. The casting also will be lighter, entailing less cost, provided
it has to be paid for by the pound, as is usually the case. The moulder
is given more work by making the core; but the saving in metal, and in
turning, more than compensates for this, provided the length of the hole
is greater than the diameter of the bore.
"Let it now be required that the casting is to be finished all over. It
would, in that case, be preferred that if the casting should contain any
blow or air holes, they should not be on the outside face of the flange,
and this will necessitate that the piece be moulded the reverse way to
that shown in Fig. 2773: that is to say, it must be moulded as shown in
Fig. 2776, with the flange downwards; for it may be here noted that the
soundest part of a casting is always that at the bottom of the mould;
and furthermore, the metal there is more dense, heavier, and stronger
than it is at the top, for the reason that the air or gas, which does
not escape from the mould, leaves holes in the top of the casting or as
near to the top as they can, by reason of the shape of the casting,
rise. The bottom metal also has the weight of the metal above it,
compressing it, and making an appreciable difference in its density. It
must, therefore, be remembered that faces requiring to be particularly
sound should be cast downwards, or at least as near the bottom of the
mould as they conveniently can. Following this principle, our gland will
require to be moulded as shown in Fig. 2777, P P representing the line
of the parting of the mould; so that, when the cope is lifted off, the
loose hub A will rise with it, leaving the flange imbedded in the lower
half of the mould. It is evident that in this case the pattern must be
made, as shown in Fig. 2776, the body and core prints being in one piece
and the flange in another, fitting easily on to a parallel part on one
end, and adjoining the core print, as shown at A. For glands of moderate
size, this method is usually adopted, and it answers very well for short
pieces; but in cases where the length of the body approaches, say, three
diameters, the horizontal position is the best, and the pattern should
be made as shown in Figs. 2778, 2779, or 2780. Even in short pieces,
when the internal diameter approaches that of the external, this plan is
the best, because it is difficult for the moulder to tell when his core
is accurately set in position.
[Illustration: Fig. 2780.]
"For a pattern to be moulded horizontally, Fig. 2780 shows the best
style in which it can be made. Its diameters are turned parallel; the
required draft is given by making the rim of the flange a little thinner
than at the hub, and by making the end faces of the hub and the core
prints slightly rounding. If the hub is very small, as, say, a half-inch
or less, and the flange does not much exceed it, the pattern may be made
solid, as shown in Fig. 2778; but if the hub be small and the flange
large, it should be made as shown in Fig. 2776.
[Illustration: _VOL. II._ =EXAMPLE IN PATTERN WORK.= _PLATE XIV._
Fig. 2773.
Fig. 2774.
Fig. 2775.
Fig. 2776.
Fig. 2777.
Fig. 2778.
Fig. 2779.]
"To construct the pattern shown in Fig. 2773, we proceed as follows:
From a piece of plank we saw off a piece of wood a little larger and
thicker than the required flange, and turn it up between the lathe
centres, using a pattern makers' contraction rule, which has its
measurements larger than the actual standard ones in the proportion of
one-eighth inch per foot: so that a foot on the contraction rule is
12-1/8 standard inches, and an inch is 1-1/96 standard inches. The
reason for this is, that when the metal is poured into the mould, it is
expanded by heat; and as it cools it contracts, and a casting is,
therefore, when cold, always smaller than the size of the mould in which
it was made. Brass castings are generally said to be smaller than the
patterns in the proportion of one-eighth inch per foot, and cast-iron
castings one-tenth inch per foot; and so, to avoid frequent calculations
and possible errors, the contraction rule has the necessary allowance in
every division of the foot and of the inch. It is not, however, to be
supposed that the possession of such a rule renders it possible for the
pattern-maker to discard all further considerations upon the contraction
of the casting; because there are others continually stepping in. Such,
for example, is the fact that the contraction will not be equal all
over, but will be the greatest in those parts where the casting contains
the greatest body of metal.
"In the smaller sizes of patterns, such as those of 6 inches and less in
diameter, there is another and a more important matter requiring
attention, which is, that after a moulder has imbedded the pattern in
the sand, and has rammed the sand closely around it, it is held firmly
by the sand and must be loosened before it can be extracted from the
mould. To loosen it, the moulder drives into the exposed surface of the
pattern a pointed piece of steel wire, which he then strikes on all
sides, causing the pattern to compress the sand away from the sides of
the pattern in all directions; and as a result, the mould is larger than
the pattern. In many kinds of work, this fact may be and is disregarded,
but where accuracy is concerned, it is of great importance, especially
in the matter of our example (brasses for journals), for they can be
chipped and filed to fit their places much more rapidly than they can be
planed, and it is necessary to have the castings as nearly of the
correct conformation as possible. In cases where it is necessary to have
the castings of the correct size without any work done to them, the
shake of the pattern in the sand is of the utmost importance. If it is
required to cast a piece of iron 3 inches long and 1 inch square,
supposing the pattern were made to correct measure by the contraction
rule, the moulder, by rapping the pattern (as the loosening it in the
mould is termed) would, by increasing the size of the mould above that
of the pattern, cause the casting to be larger than the pattern; that is
to say, it would be longer and broader, and therefore, in those two
directions, considerably above the proper size, since even the pattern
was too large to the amount allowed for contraction. The depth, however,
would be of correct size, because the loosening process or rapping does
not drive the pattern any deeper in the mould. It follows that, to
obtain a casting of as nearly the correct size as possible, the pattern
must be made less in width and in length than the proper size, to the
amount of the rapping; and to insure that the moulder shall always put
the pattern in the sand with the same side uppermost, the word "top"
should be painted on the face intended to lie uppermost in the mould.
The amount to be allowed for the rapping depends upon the size of the
pattern, and somewhat upon the moulder, since some moulders rap the
patterns more than others; hence, where a great number of castings of
accurate size are required, it is best to have two or three castings
made, and alter the pattern as the average casting indicates. For
castings of about 1 inch in size, the patterns may be made 1/32 inch too
narrow and the same amount too short; but for sizes above 6 inches,
allowance for rapping may be disregarded.
"In patterns for small cast gears, the rapping is of the utmost
consequence. Suppose, for instance, we have six rollers of 2 inches
diameter requiring to be connected together by pinions, and to have
contact one with the other all along the rollers; if we disregard the
allowance for rapping, the pinions will be too thick, and we shall
require to file them down, entailing a great deal of labor and time,
besides the rapid destruction of files.
[Illustration: Fig. 2781.]
[Illustration: Fig. 2782.]
"Let it be required to cast a pillow block to contain a babbitt-metal
bearing. In this case there requires to be a cavity to receive and hold
the babbitt metal. This is provided by casting ridges of metal around
the edges of the bearing, as shown in Fig. 2781, at D E and on each side
at F, the pieces D E may be made solid with the pattern, but those for
the sides must be removable, having dovetails as at _c_ _c_ to hold them
in position while being moulded, or in place of the dovetails, wires as
at F F may be employed, in either case the pattern would be extracted
from the mould, leaving the side strips to be removed afterwards. If,
instead of a pillow block, a bracket or frame, such as in Fig. 2782,
were required, it must be moulded in the direction of the arrow, and in
that event it would be desirable to core out the journal bearing. This
would be accomplished by providing a core print to block up the whole
opening B. A suitable core box for the bearing would be as in Fig. 2783.
The core print must project below the casting so as to form in the
mould a core print for the core, and it is obvious that the core itself
must be made of increased depth to the amount allowed for core print;
hence the end piece B, Fig. 2783, is increased in thickness to the
amount allowed for core print."
[Illustration: Fig. 2783.]
Patterns for cylindrical bodies, especially those that are hollow and
thin, are constructed in pieces by a process termed "building up." The
pieces are usually segments of circles, and the manner of marking them
is as follows:--
[Illustration: Fig. 2784.]
[Illustration: Fig. 2785.]
[Illustration: Fig. 2786.]
[Illustration: Fig. 2787.]
Let it be required to make a pattern for a flanged pulley, such as shown
in section in Fig. 2784. It would be constructed in two halves composed
of a number of courses as from 1 to 8, and each course would be composed
of segments of the form shown in Fig. 2785. The length of the arc of
these segments must be such that it will require a certain number of
these to complete the circle of that part of the cylinder which the
segment is to form; and the manner of accomplishing this is shown in
Fig. 2786, in which the circle C is of the diameter of the outside,
while circle D is that of the outside of the pulley proper, circle E is
of the diameter of the inside of the pulley rim. These circles are
divided into as many equal divisions as there are to be segments in the
circumference; hence the number of divisions determines the length of
arc of the segments. Thus A would be a segment for the body of the
pulley, and F a segment for the rim. A template is then made of each one
of these segments, as at A and F. This template must be made slightly
larger in every direction than the respective divisions, to allow for
the stuff that will be turned off in truing the pattern in the lathe and
in jointing the segments to one another during the building. The
templates are employed to mark out on the board which should first be
planed to the required thickness. This will be a trifle thicker than the
course so as to allow for truing the surface of each finished course in
the lathe. The courses are best built up on the chuck of the lathe on
which they are to be turned, and a saving in time will be effected if
there are two chucks, so that a course on one half of the pattern may be
built up while the glue of another course on the other half is drying.
On the lathe chuck, and directly beneath, where the joints of the
segments will come, pieces of paper as at _a_, _c_, _e_, _g_, Fig. 2787,
and if the segments are long ones, intermediate pieces of paper, as _b_,
_d_, _f_, _h_, will be necessary. The radial edges of the segments are
trimmed on what is termed a shooting board, which is a device such as
shown in Fig. 2788, in which A is a piece of board on which is fastened
the piece B. S is a piece projecting above B, and is provided to rest
the segment S´ against, the flat surface of the latter lying on the
board B. It is thus held in a fixed position, ready to have its edges E
planed, the whole being laid upon the bench against the bench stop G.
If, however, it is more convenient to rest the shooting board across the
bench, a piece C may be fastened beneath A, so as to come against the
edge of the bench as in Fig. 2789, in which T is the bench. The plane is
laid with its side on A as in Fig. 2790, so that the surface of A acts
as a guide, keeping the edge of the plane vertical, and thus planing the
edges of the segment square. The plane is operated by hand in the usual
manner (save that it lies on its side), taking its cut most off the
outside or inside of the edge of the segment S´, according as the
position of the latter is varied. In some of the shooting boards
manufactured by tool makers, the height of B from A is adjustable, so
that all parts of the plane blade edge may be used, which saves
grinding, since only that part of the edge that is used dulls. Also
there is provided means whereby the required lateral position of the
segment may be adjusted; such a device is shown at P, Fig. 2788, which
is a plate having a slot through it, through which passes the thumb
screw V, which screws into S. Hence the plate may be adjusted so that
when one end of the segment rests against the end of S, and the other
against the end of P, its edge E will be in the proper position to be
planed to correct angle by the plane, whose line of action is in this
case rendered positive by means of a slide on the plane, acting in a
groove in the base A.
[Illustration: Fig. 2788.]
[Illustration: Fig. 2789.]
[Illustration: Fig. 2790.]
The first segment is glued to the pieces of paper on the chuck, as shown
in Fig. 2787, S´ representing the segment. A second segment is then
added, being set fair to the pencil circle O, and jointed and glued both
to the chuck and to the ends of the first segments. Successive segments
are added until the whole circle or course is completed, and when dry
the radial face of this course is turned in the lathe so as to be true,
flat, and of the required thickness, and the diameter is trued. The
second course may then be added, but the joints at the ends of the
segments should not come over those of the first course, but in the
middle as shown by the dotted line. The ends of the segments should be
made to bed properly against each other, and glue should be applied to
the joint between the two courses and at the ends. By adding the
successive courses the whole may be built up on the chuck ready to
receive the arms. As each segment is added it should be clamped or
weighted to press it firmly to its seat and press out the excess of
glue.
If the pattern consists of two, or say three, courses, the glue will be
sufficient to hold it to the chuck while turning, but if there are more
courses a screw should be inserted through the chuck and into each
segment of the first course. The cylinder must then be turned inside and
out ready to receive the spokes. These are made of pieces equal in
length to the internal diameter of the rim, or a trifle longer, so that
the ends may be let into the rim. A line is then marked along the edge
of the rim, dividing its thickness into two divisions, and in the centre
of the length a recess should be cut out from the face to the line, the
width of the recess equalling the width of the arm, so that one arm will
let into the other, forming a cross, of which the flat surfaces lie in
the same plane. This cross is let into the rim of the wheel and fixed
temporarily with brads. The lathe may then be started and the centre of
the arms (and therefore that of the cylinder or pulley) be found by a
pencil point moved until it marks a point and not a circle when the
lathe revolves. The arms may then be marked to shape and a recess turned
at their centre to receive the hub. The arms being marked to their
respective places and their outside faces being marked with a pencil so
that they may be replaced in the same position in the wheel, they may be
removed and shaped to the required dimensions and form, and then
replaced and glued to the rim.
If the wheel is to have six arms they may be constructed as follows:--
Instead of taking two pieces of the diameter of the rim, as in the case
of four arms, three pieces are necessary, and in this case the thickness
of the edge of each piece is divided by two marked lines which will
divide the thickness of the edge into three equal divisions, as shown by
the dotted lines 1 and 2 in Fig. 2791, which will divide the thickness
of the edge into three equal divisions of thickness. From the centre of
the lengths of each of the three pieces we mark on the flat face a
circle whose diameter will equal the width on the flat face of the
pieces themselves.
With an angle square having its adjustable blade set to an angle of 60°,
and set so that the back is fair with the edge of the piece, and one
edge coincident with the perimeter of the circle, lines tangent to the
circle and crossing each other are drawn on the pieces A C. On the piece
B four of such tangent lines (two on each side) must be drawn. The piece
A is recessed between one pair of tangent lines to the depth of the
second lines on its edge, or, in other words, to a depth of two-thirds
its thickness, and between the other pair to a depth of one-third, as
shown, the two-thirds at D, the one-third at E. The piece D must be
recessed between its tangents on each side to a depth of one-third its
thickness, as denoted at F F, while on C the whole space between the
tangent lines must be recessed to a depth equal to two-thirds its
thickness, as shown at G. The pieces may then be put together so that
the two diametrically opposite arms will be in one piece. If an odd
number of arms is employed this form of construction cannot be followed;
hence each spoke will be a separate piece, extending from the rim to the
centre and jointed at the latter, as in Fig. 2792, which is for five
arms.
For this construction draw a circle _c_, Fig. 2792, and divide it into
as many equal points of division as there are to be arms in the wheel.
From these points of division draw lines to the centre, and these lines
will show the required bevel at the end of each spoke, as shown in the
figure. The ends should be verified for bevel by striking from the
common centre a second circle, as D; and measuring if the arms are
equidistant, measured at the circle and from the edge of the arm to that
of the next, finished along the full length. When fitted, corrected,
glued and dry, the spokes may be let into the wheel and a recess turned
into the centre to receive the hub.
The rim and all parts that can be got at may then be turned in the
lathe, the pattern then being reversed in the lathe to turn the inside
of the rim, or the other side of the spokes, when the job will be
complete. When, however, the rim is to be a very thin one, it may be
necessary to fasten the segments together at the ends by other means as
well as glue, hence a saw-cut may be made in each end, and a tongue
inserted.
[Illustration: Fig. 2791.]
[Illustration: Fig. 2792.]
It is obvious that each half of the pattern is constructed by similar
segments, the line of parting being through the centre of the arms, as
at A B, in Fig. 2791. To keep the two halves coincident when in the
mould, pins are inserted in the rim and arms of one half, fitting
closely into holes provided in the other half.
To construct a pattern for a pipe, the pattern would be made in two
halves, and constructed of what are termed staves, that is, pieces of
wood running lengthways of the pipe. The number of these staves is
optional, save that it must be even, so that each half pattern will
contain an equal number.
[Illustration: Fig. 2793.]
Let it be required to make a pattern for a pipe 18 inches in diameter,
and to be 1 inch thick. Draw the line A B, Fig. 2793, and from a point
on it, as C, draw a semicircle A B, equal in diameter to the diameter of
the outside of the pipe. Also the circle D E F, equal to the diameter of
the inside of the pipe, and these will represent an end view of the
pipe. Divide these semicircles into as many equal divisions as it is
decided to have staves in the half pattern--as 1, 2, 3, 4, 5, 6; and
from one of these divisions make a template as denoted by the oblique
lines at 2, leaving it slightly larger than the division, to allow stuff
to work on in fitting the staves, &c.
[Illustration: Fig. 2794.]
Now, when the staves are cut out it is necessary to have some kind of a
frame or support to hold them while jointing them; hence, draw also from
the points of division, as D, E, F, the lines _a_, _b_, _c_, _d_, _e_,
_f_, and these will form the sides of a half-disk polygon, whose
diameter is from D to F. A sufficient number of these polygonal
half-disks are cut out to stand about two feet apart along the whole
length of the pipe, as in Fig. 2794, and on these, temporarily fastened
to the board B, the staves are jointed and fastened together by glue
while each stave is held to its place on each half-disk by a screw. The
top stave may be put on first, as it will act as a stay to the
half-disks. If the pipe is so long that it is composed of more than two
pieces, the end pieces should be put on first, and the intervening space
filled up last, which enables the ends to abut firmly. The second half
may be added to the first one, putting a piece of paper between the
edges of the two to prevent their sticking together.
If the pipe has a bend, it is built up separately, instead of being
formed of staves, the process being as follows:--
[Illustration: Fig. 2795.]
[Illustration: Fig. 2796.]
In Fig. 2795 let B represent the centre of the bend curve, the line C
representing one end, G the other end, H the inner and J the outer arc
of the bend. Let it be determined to build up the bend in five pieces,
as shown at 1, 2, 3, 4, 5, which represents an end view of the half
pattern. Templates are then made for each of the pieces 1, 2, &c., being
formed as denoted by the oblique lines, whose dimensions slightly exceed
the half circle E of the pattern, to allow wood for dressing up. To find
the curve for these pieces, set the compasses to a radius from B to the
outer corner of piece 1, and draw the arc K. Set the compasses to the
radius from B to the inner corner of piece 1, and draw the arc L, and
the space between these two arcs, which space is marked 1 T, is a
template for the curve of piece 1. By a similar process applied to
pieces 2, 3, 4 and 5 similar templates for their respective curves are
obtained; and selecting timber of a proper thickness, we mark out the
respective curves from these templates, which may be of thin board or of
stiff paper. In putting these pieces together the lower ones are set to
lines forming a plan of the bend, being set a little outside the lines
to allow wood for truing the pieces to shape after they are put
together. The lower pieces are temporarily fixed to the board on which
the plan is marked, and the upper ones fastened to the lower by glue,
the joint surfaces of each line being planed true previous to being
glued. It is a great assistance, however, to cut out two half circles,
representing the ends of the pipe, and to place them on the board to
build upon. When a bend of this kind occurs in a covering for a pipe
that is exposed to view, it is necessary, for the sake of appearance, to
have the pieces composing the bend to correspond with those on the
straight part of the pipe, as shown in Fig. 2796. The part A would be
got out in staves, as described for the pattern of a pipe. The bend B
would be also got out as described for that figure for a bend, save that
the number of staves for the bend would equal the number on the pipe.
But in this case each stave should be fitted to its fellow by pins, or
its edge fitting into dowels on the edge of its fellow; thus one edge of
a stave would have the dowels and the other the pins; the whole, when
finished, being bound together by metal bands, as shown in the figure.
[Illustration: Fig. 2797.]
The patterns for a globe valve, such as shown in section in Fig. 2797,
would be made as follows (which is taken from "The Pattern Makers'
Assistant"):--
[Illustration: Fig. 2798.]
[Illustration: Fig. 2799.]
"The flanges vary in shape; but as a rule small valves are provided with
hexagons and large ones with round flanges suitable for bolting to
similar flanges to make joints. For small valves, say up to 2 inches,
the pattern is usually made with the hexagons cut out of the solid, but
for sizes above that, they should be made in separate pieces, as shown
in Fig. 2798, and screwed to the pattern, so that in case of necessity
they may be removed, and flanges substituted in their stead. In Fig.
2799, we have a perspective view of the finished pattern; and Fig. 2800
represents the pattern as prepared, ready to receive a flange or hexagon
as may be required. A globe valve pattern should be made in halves, as
shown in Fig. 2801, the parting line of the two halves being denoted by
A B. To make this pattern, we first prepare two pieces of wood so large
that, when pegged together, the ball or body of the pattern can be
turned out of them, and long enough not only to reach from P to P, in
Fig. 2799, but also to allow an excess by means of which the two pieces
may be glued or otherwise fixed together. These two pieces we plane to
an equal thickness, and then peg them to retain them in a fixed
position, taking care, however, that the pegs do not occur where the
screws to hold the flanges will require to be. We also place two pegs
within a short distance of what will be the ends of the pattern when the
excess in length referred to is turned off. We next prepare, in the same
way, two more pieces, to form the two halves of the branch, shown at B,
in Fig. 2801, for which, however, one peg only will be necessary. These
pieces must be somewhat wider than the size of the required hexagon
across the corners, that is, supposing the hexagon is to be solid with
the branch; otherwise we must make them a little wider than the diameter
of the hub of the flange, or of the round part of the hexagonal pieces.
Their lengths must be such as to afford a good portion to be let into
the ball or body of the pattern (as shown by the dotted lines in Fig.
2800), which is necessary to give sufficient strength. The two pieces
must be firmly fixed together, and then turned in the lathe.
[Illustration: Fig. 2800.]
[Illustration: Fig. 2801.]
[Illustration: Fig. 2802.]
"During the early stages of the turning, or, in other words, during the
roughing out, we must occasionally stop the lathe and examine the flat
places on the body; for unless these places disappear evenly, the work
is not true, and one half will be thicker than the other, so that the
joint of the pattern will not be in the middle. It was to insure this
that the pieces were directed to be planed of equal thickness, since, if
such is the case, and the flat sides disappear equally and
simultaneously during the turning, the joint or parting of the pattern
is sure to be central. If the lathe centres are not exactly true in the
joint of the two pieces, they may be made so by tapping the work on the
side having the narrowest flat place, the process being continued and
the work being trued with the turning tool at each trial until the flat
places become equal. By this means, we insure, without much trouble, two
exact halves in the pattern, which is very important in a globe valve
pattern on account of the branch and other parts, not to mention the
moulding. Having turned the body of the pattern to the requisite
outline, and made, while in the lathe, a fine line around the centre of
the ball where the centre of the branch is to come, as shown in Fig.
2800 by the line A, we make a prick point (with a scriber) at each
crossing of the line A and the joint or parting of the pattern. We then
mount the body upon a lathe chuck, in the manner shown in Fig. 2802. A
point centre should be placed in the lathe and should come exactly even
with the line A. In Fig. 2802, V V are two [V]-blocks made to receive
the core prints. These [V]s are screwed to the lathe chuck, and the
pattern is held to them by two thin straps of iron, placed over the core
prints and fastened to the [V]s by screws. If the chuck and centre point
run true, the [V]-blocks are of equal height, and the core prints are
equal in diameter, the prick point opposite to the one placed to the
centre point will run quite true; and we may face off the ball or body
to the required diameter of branch, and bore the recess to receive the
same. We make the holes in the flanges of the same size as the core
prints; but we should not check in the print, because, if a flange with
a different length of hub were substituted, it would be a disadvantage.
To obtain the half flanges, we take a chuck and face it off true in the
lathe; then, with a fine scriber point, we mark the centre while the
chuck is revolving. We then stop the lathe, and, placing a straight-edge
to intersect the chuck centre, we draw a straight line across the chuck
face. We then take two pieces suitable for the half flanges, and plane
up one flat side and one edge of each piece. If the flanges are not
large ones, they may be planed all at once in a long strip. We place the
pieces in pairs, and mark on each pair a circle a little larger than the
required finished size of flange. We then fix each pair to the chuck,
with the planed faces against the chuck, and the planed edges placed in
contact, their joint coming exactly even with the straight line marked
on the chuck face, and we may then turn them as though they were made in
one piece and to the requisite size.
[Illustration: Fig. 2803.]
"In Fig. 2803 we have a representation of one half of a suitable core
box, the other half being exactly the same, with the exception that the
position of the internal partition is reversed. To get out this core
box, we plane up two pieces of exactly the same size and length as the
pattern, and of such width and thickness as will give sufficient
strength around the sphere, allowing space for the third opening. After
pegging these two pieces together, we gauge, on the joint face of each,
lines representing the centres of the openings and the centre of the
sphere. We then chuck them (separately) in the lathe, and turn out the
half sphere. We next place the two halves together, and chuck the block
so formed in the three positions necessary to bore out the openings; or
if preferred, we may pare them out. The partition (A, in Fig. 2803)
follows the roundness of the centre hole, and is on that account more
difficult to extract from the core than if it were straight and
vertical. When, however, the partitions are of this curved form, the
pieces of which they are formed are composed of metal, brass being
generally preferred. Patterns have in this case to be made wherefrom to
cast these pieces, and they may be made as follows: First, two half
pieces are turned; each is then cut away so as to leave the shape as
shown at A in the same figure, and is then fitted into the spherical
recess in the core box, letting each down until both are nearly but not
quite level. The two wing pieces are then fastened on, and this pattern
is complete. When the pieces are cast, they must be filed to fit the
core box, and finished off level with its joint face, a small hole being
drilled in the centre, and a pin being driven through the piece and into
the box to steady the corners. We then saw the pieces in halves with a
very fine saw.
[Illustration: Fig. 2804.]
"If the partition, instead of following the roundness of the valve seat,
is made straight, the construction of the core box is much more simple.
In this case, a zigzag mortice is made clear through each half of the
box, its size and shape being that of the required partition. Fig. 2804
represents a half-core box of this kind. A piece of wood A is fixed, as
shown, to the partition, to enable the core maker to draw it out before
removing the core from the box. The mortice for the partition should be
turned out before the half-spherical recess, the mortice being
temporarily plugged with wood to render easy the operation of turning.
[Illustration: Fig. 2805.]
"In very large valves (say 10 or 12 inches) a half-core box is generally
made to serve by fitting the two half partitions, shown at A, in Fig.
2803, to a half-core box, and keeping them in position by means of pegs,
a half-core being made first with one and then one with the other in the
core box. It is often necessary to form a raised seat in the body of an
angle valve, such as shown in Fig. 2805, which represents a section of
such a body. It is shown with flanged openings, though in small valves
hexagons to receive a wrench would be substituted.
[Illustration: Fig. 2806.]
[Illustration: Fig. 2807.]
"Fig. 2806 is a plan of half the core box necessary for forming the
raised seat. From this construction, it will be seen that the large
core, though solid with the branch core, is not solid with that forming
the hole in the seat and the part below it; therefore the core prints on
the body pattern must be left extra long to give sufficient support in
the mould for the overhanging cores. The loose round plug P, is made of
the size of the outside of the seat and fitted to the box. The part
outside the box is a roughly shaped handle to draw it out by. The
diminished part D is a print, and into the impression left by it is
inserted the core made in box shown in Fig. 2807. The print D is of the
same diameter as the hole in the seat; and the print on the pattern is
of the size of the increased diameter below the seat. Large angle valves
are made with half a core box by making a branch opening in the box
right and left, a semicircular plug being provided. Two half-cores are
made with the plug, first in one and then in the other branch opening.
The plug P should be in this case only half round."
[Illustration: Fig. 2808.]
For finding the lengths of the sides of regular polygons, scales, such
as shown in Figs. 2808 and 2809, may be used, the construction being as
follows:--
[Illustration: Fig. 2809.]
Draw a horizontal line O P, Fig. 2809, and at a right angle to it the
line O B. Divide these two into inches and eighths of an inch, and draw
lines meeting the corresponding divisions on O P, O B. From the point O
draw the following lines: A line at 55-1/2 degrees from line O P, which
is to serve for polygons having 9 sides; a line at 52-1/2 degrees to
serve for polygons having 8 sides; a line at 49 degrees for polygons
having 7 sides; a line at 45 degrees for 6 sides; a line at 40 degrees
for polygons having 5 sides. It may be added, however, that additional
lines may be drawn at the requisite angle for any other number of sides.
The application of the scale is as follows:--
The point O represents the centre of the polygon; hence from O to the
requisite line of division on O B represents the radius of the work.
From the line O B to the diagonal line (measured along the necessary
horizontal line of division) is shown the length of a side of the
polygon. From the point O, measured along the line having the requisite
degrees of angle, to the horizontal line denoting the radius of the
work, gives the diameter across corners of the polygon. The diameter
across the flats of a square being given, its diameter across corners
will be represented by the length of a line drawn from the necessary
line of division on O B to the corresponding line of division on O P. A
cylindrical body is to have six sides, its diameter being 2 inches, what
will be the length of each side? Now, the radius of the 2-inch circle of
the body is 1 inch; hence, find the figure 1 on line O B and measure
along the corresponding horizontal line the distance from the 1 to the
line of 45 degrees, as denoted by the thickened line.
A body has six sides, each side measuring an inch in length, what is its
diameter across corners? Find a horizontal line that measures an inch
from its intersection of the line O B to the line of 45 degrees, and
along this latter to the point O is one-half the diameter across
corners.
_Example 3._--It is desired to find the diameter across corners of a
square whose side is to measure 3 inches. Measure the distance from the
3 on line O P to the 3 on line O B, which will give the required
diameter across corners.
This scale lacks, however, one element, in that the diameter across the
flats of a regular polygon being given, it will not give the diameter
across the corners. This, however, we may obtain by a somewhat similar
construction. Thus, in Fig. 2808, draw the line O B, and divide it into
inches and parts of an inch. From these points of division draw
horizontal lines; from the point O draw the following lines and at the
following angles from the horizontal line O P:--
A line at 75° for polygons having 12 sides.
" 72° " 10 "
" 67-1/2° " 8 "
" 60° " 6 "
From the point O to the numerals denoting the radius of the polygon is
the radius across the flats, while from point O to the horizontal line
drawn from those numerals is the radius across corners of the polygon.
A hexagon measures 2 inches across the flats, what is its diameter
measured across the corners? Now, from point O to the horizontal line
marked 1 inch, measured along the line of 60 degrees, is 1-5/32 inches;
hence the hexagon measures twice that, or 2-5/16 inches across corners.
The proof of the construction is shown in the figure, the hexagon and
other polygons being marked for clearness of illustration.
[Illustration: Fig. 2810.]
[Illustration: Fig. 2811.]
Let it be required to make a pattern for a section of pipe such as shown
in section and in plan in Fig. 2810, which is from "The Pattern Maker's
Assistant." This pattern would be made to mould, as shown in the
section, lying horizontally, and must therefore be made in two halves,
the line of joint for the two halves being along A B in Fig. 2811.
"The body A and the branch B would be made separate from the flanges,
and would be reduced in diameter at the ends to receive them. To form A,
take two pieces of timber, say three inches longer than the length of A,
including the core prints, and measuring a little more than half the
diameter of the pipe one way, and a little larger than the full diameter
of the pipe the other way, and glue them together at the ends for a
distance of 1-1/2 inches, which will serve to hold them while turning
them in the lathe.
"The pieces may then be turned in the lathe to the required diameter.
During this turning, however, it is essential to insure that the joint
of the two pieces be exactly in the centre, otherwise one half of the
pattern will be (when the halves are separated) thicker than the other.
"The ends are then turned down to receive the flanges, the reduced
diameter being necessary so as to leave a shoulder for the flanges to
abut against to keep them true, or at a right angle to the axial line of
the body. The branch is turned up in the same way, and the flanges are
then turned and put on.
"The end of the branch may be cut to fit the circumference of the body
as follows:--
"Set a bevel square to an angle of 45°. Take the halves of the branch
apart, and rest the stock or back of the bevel against the end face, and
let the blade lie on the joint face, and mark two lines A B in Fig.
2812, which lines must just meet in the centre of the branch at the end.
Cut away the angular pieces C and D down to the lines A B. This
performed on each half will leave them when given a quarter turn as
shown in Fig. 2812, and the curve shown by the junction of the
horizontal with the vertical shading lines is the curve for the end;
hence the surface covered with the horizontal lines requires to be cut
away.
[Illustration: Fig. 2812.]
"When this is done on both halves the branch will fit to the body, as
shown in Fig. 2813, in which A is the body and B C the two half
branches. For a temporary pattern the branch may be fastened to the body
with a few screws; but for a permanent pattern it should be glued also,
which is done as follows:--
[Illustration: Fig. 2813.]
[Illustration: Fig. 2814.]
[Illustration: Fig. 2815.]
"Lay one half of the body A, Fig. 2813, on a board, with the flange
overhanging to be out of the way, and clamp it there; lay the branch
also on the board, and draw it firmly up to the body by clamps, while
also clamping it flat down to the board, as shown in Fig. 2814. This
will insure that the joint faces are true with one another, that is, lie
in the same plane. Paper should, however, be placed between the joint
faces and the board to prevent them from becoming glued to the board,
and the edges, therefore, from breaking away. The second half can be put
together as the first one, paper being put between the two to prevent
them from being glued together; and to further strengthen the joint, let
into each half a piece of hard wood P, Fig. 2815, and put in the screw
shown at A.
"Suppose now that the diameter of the branch had been smaller than that
of the body of the pattern, then the length of curve necessary on the
branch end to let it abut fairly against the cylindrical pattern body
may be found as follows:--
[Illustration: Fig. 2816.]
[Illustration: Fig. 2817.]
[Illustration: Fig. 2818.]
"Draw on a piece of board the line A B, Fig. 2816, and from any point C
mark a semicircle equal in radius to that of the radius of the body of
the pattern, draw the line E parallel to A B, and distant from it to an
amount equal to the radius of the branch, then from the junction of E
with the semicircle as at D, mark the line F at a right angle to A B.
Let it now be noted that the semicircle A G represents half the pattern
body, and E D F B the branch; hence from F to G is the length of the
branch end that will require to be curved to fit the circumference of
the body, while it is also the length to be added to the distance the
branch requires to stand out from the body. To draw the curve on the end
D F G of the branch the gauge or marking instrument, shown in Fig. 2817,
is employed. The branch P is placed in [V]-blocks (Fig. 2818), resting
upon a plane surface. The gauge consists of a stand E carrying a
vertical bar A; upon A is the closely fitting cross-tube carrying the
arm C, which in turn carries the marking pointer D, which is set distant
from the centre of the bar A to the amount of the radius of the piece of
work or the cylinder is to fit against.
[Illustration: Fig. 2819.]
"If the branch required to stand at an angle to the body, as in Fig.
2819, the marking may be performed by the same gauge and in the same
manner, but the axial line of the branch must be set, when marking one
side, at an acute angle to the axial line of A, and at an obtuse angle
to A when turned over to mark the other side, which may be done in each
case by raising one of the [V]-blocks until the branch lies in either
case at the same angle to A as it will require to stand to the body on
which it is to fit.
"When the body is much larger in diameter than the branch, a hole may be
bored in the former to receive the end of the latter, by giving to the
branch end a stem, as in Fig. 2820, and then cutting in the body a
recess for the branch end and its additional stem. This recess may be
cut out in the lathe, chucking the body as in Fig. 2821.
[Illustration: Fig. 2820.]
[Illustration: Fig. 2821.]
"Should it occur that one end of the [T] is of larger diameter than the
other, one chucking [V] must be deeper than the other, and we may find
their respective depths by the following process:--
[Illustration: Fig. 2822.]
"Draw line A B, Fig. 2822, which line represents the chuck face. Let
point C represent the centre of the lathe. Mark line C E and set a pair
of compasses to the radius of the body of the pattern at the centre of
the branch location. Then take a radius from C and about 1/16 inch up
from line A B, and with this radius we mark on the line C E the point E.
From this centre we mark the two arcs having radii corresponding to the
unequal diameters of the pattern at the location where the chucking
[V]'s are to be placed. We then draw tangent lines to each of these
arcs, and thus obtain the correct depth of [V] necessary to hold the
axial line of the pattern parallel to the lathe chuck.
[Illustration: Fig. 2823.]
"The core box would, unless the pattern were a small one, be built up in
courses, as shown in Fig. 2823. The box would be drawn in plan, and end
and side views drawn as shown, so as to draw in the half circle
representing the bore of the half-core box and mark off the courses as
from 1 to 6. These courses need not be of equal or of any particular
thickness, but may suit that of any suitable timber at hand. Courses 1
and 2 should extend over the whole outline of the box, while the pieces
3 and 4 are made in width to suit the curvature of the core as shown,
and to extend the full length of the box. The pieces 7, 8, 9, and 10 are
of the length of the branch, and are made in width to suit the curvature
of the branch core. If the branch core were a short one it could be cut
out of the solid; but in any event, the grain of the wood should be as
shown, and the holding pieces at G and H should be employed."
CHAPTER XXXV.--WOOD WORKING MACHINERY.
The machines employed in wood working may be divided into 7 classes as
follows:
1. Those driving circular saws.
2. Those driving ribbon or band saws.
3. Those driving boring or piercing tools.
4. Those employing knives having straight edges for surfacing purposes
and cutting the work to thickness.
5. Those employing knives or cutters for producing irregular surfaces
upon the edges of the work.
6. Those employed to produce irregular surfaces on the broad surface of
work.
7. Those employed to finish surfaces after they have been acted upon by
the ordinary steel cutting tools.
CIRCULAR SAWS.
[Illustration: Fig. 3078.]
The thicknesses of circular saws is designated in terms of the
Birmingham wire gauge, whose numbers and thicknesses are shown in Fig.
3078, where a Birmingham wire gauge is shown lying upon two circular
saws, which show the various shapes of teeth employed upon saws used for
different purposes.
The teeth numbered 1 are for large saws, as 36 inches in diameter, to be
used on hard wood. Numbers 2 and 5 are for soft wood and a quick feed.
Numbers 3 and 4 are for slabbing or converting round logs into square
timber. Number 6 is for quick feeds in large log sawing. Numbers 7, 8, 9
and 10 are for bench saws, or, in other words, saws fed by hand or
self-feeding saws. Number 8 is known as the "London Tooth," because of
being used in London, England, on hard and expensive woods. Number 9 is
the regular rip-saw tooth for soft woods. Number 10 is the Scotch gullet
tooth. Number 11 is for either cross-cutting or rip sawing by circular
saws used on soft woods. Number 12, is for large cross-cut saws; the
flat place at the bottom of the tooth prevents the teeth from being
unnecessarily deep and weak. Number 13 is for cross-cutting purposes
generally. Number 14 is for rip sawing on saws of small diameter. It is
also used for tortoise-shell, having in that case a bevel or fleam on
the front face, and no set to the teeth.
The following table gives the ordinary diameters and thicknesses of
circular saws and the diameters of the mandrel hole:
---------+------------+-------------------
Diameter.| Thickness. | Size Mandrel Hole.
---------+------------+-------------------
4 inch.| 19 gauge. | 3/4
5 " | 19 " | 3/4
6 " | 18 " | 3/4
7 " | 18 " | 3/4
8 " | 18 " | 7/8
9 " | 17 " | 7/8
10 " | 16 " | 1
12 " | 15 " | 1
14 " | 14 " | 1-1/8
16 " | 14 " | 1-1/8
18 " | 13 " | 1-1/4
20 " | 13 " | 1-5/16
22 " | 12 " | 1-5/16
24 " | 11 " | 1-3/8
26 " | 11 " | 1-3/8
28 " | 10 " | 1-1/2
30 " | 10 " | 1-1/2
32 " | 10 " | 1-5/8
34 " | 9 " | 1-5/8
36 " | 9 " | 1-5/8
38 " | 8 " | 1-5/8
40 " | 8 " | 2
42 " | 8 " | 2
44 " | 7 " | 2
46 " | 7 " | 2
48 " | 7 " | 2
50 " | 7 " | 2
52 " | 6 " | 2
54 " | 6 " | 2
56 " | 6 " | 2
58 " | 6 " | 2
60 " | 5 " | 2
62 " | 5 " | 2
64 " | 5 " | 2
66 " | 5 " | 2
68 " | 5 " | 2
70 " | 4 " | 2
72 " | 4 " | 2
---------+------------+-------------------
Circular saws are sometimes hollow ground or ground thinner at the eye
than at the rim, to make them clear in the saw kerf or slot with as
little set as possible, and therefore produce smooth work while
diminishing the liability of the saw to become heated, which would
impair its tension. They are also made thicker for a certain portion of
the diameter and then bevelled off to the rim.
This is permissible when the work is thin enough to be easily opened
from the log by means of a spreader or piece that opens out the sawn
piece and prevents it binding against the saw.
The shingle saw, shown in Fig. 3079, is an example of this kind, the saw
bolting to a disc or flange by means of countersink screws.
The concave saw shown in Fig. 3080, is employed for barrel heads. The
three pieces for a barrel head are clamped together and fed in a
circular path, so that the saw cuts out the head at the same time that
it bevels the edge.
The advantage of the circular saw lies mainly in the rapidity of its
action, whether used for ripping or cross-cutting purposes. In order,
however, that it may perform a maximum of duty, it is necessary that the
teeth be of the proper shape for the work, that they have the proper
amount of set, that they be kept sharp, and that the tension of the saw
is uniform throughout when running at its working speed.
[Illustration: Fig. 3079.]
[Illustration: Fig. 3080.]
The centrifugal force created by the great speed of a circular saw is
found to be sufficient to cause it to stretch and expand in diameter.
This causes the saw to run unsteadily unless it is hammered in such a
way as to have it rim bound when at rest, leaving the stretching caused
by the centrifugal force to expand the saw and make its tension equal
throughout. The saw obviously stretches least at the eye, and the most
at its circumference, because the velocity of the circumference is the
greatest, and the amount of stretch from the centrifugal force is
therefore the greatest.
It is obvious that the amount of centrifugal force created will depend
upon the speed of the saw, and it therefore follows that the hammering
must be regulated to suit the speed at which the saw is to run when
doing cutting duty, and in this the saw hammerer is guided solely by
experience.
A circular saw may have its tension altered and impaired from several
causes as follows:
1. From the saw becoming heated, which may occur from the arbor running
hot in its bearings, or from the work not being fed in proper line with
the saw.
2. From the reduction in diameter of the saw by frequent resharpening of
the saw, this reduction diminishing the amount of centrifugal force
generated by the saw, and therefore acting to cause the saw to become
loose at the eye.
3. From the saw teeth being allowed to get too dull before being
sharpened, which may cause the saw teeth to heat, and thus destroy the
tension.
4. From stiffening the plate at the throats of the teeth when gumming
the saw, an effect that is aggravated by using a dull punch.
5. From the saw teeth having insufficient set, and thus causing the saw
to heat.
The methods of discovering the errors of tension in a saw, and the
process of hammering to correct them, have already been explained with
reference to the use of the hammer on pages from 68 to 70 of volume 2 of
this work.
Before hanging a saw on a mandrel, it is necessary to know that the
mandrel itself runs true in its bearings or boxes. In a new machine this
may be assumed to be the case, but it is better to know that it is so,
because if the mandrel does not run true several very improper
conditions are set up. First, the saw will run out of true
circumferentially, and therefore out of balance, and the high side of
the saw will be called upon to do more cutting duty than the low side.
Second, the centrifugal force will be greatest on the high side, and the
saw will be stiffer, thus setting up an unequal degree of tension.
Third, the saw will run out of true sideways, cutting a wider kerf than
it should, thus wasting timber while requiring more power to drive.
The collar on the saw arbor should be slightly hollow, so that the saw
will be gripped around the outer edge of the collar, and the arbor or
mandrel should be level so that the saw will stand plumb. The boxes or
bearings of the arbor should be an easy working fit to the journals, and
there should be little, or what is better, no end play of the arbor in
its bearings.
If a saw arbor becomes heated enough to impair the tension of the saw,
it has been hot enough to impair its own truth, and should be examined
and trued if necessary.
The most important point in this respect is that the face of the collar
against which the saw is clamped should run true, bearing in mind that
if it is one hundredth of an inch out of true in a diameter of, say 3
inches, it becomes twenty hundredths or one-fifth of an inch at the
circumference of a saw that is 60 inches in diameter.
In cases of necessity, a saw that wabbles from the collar face of the
mandrel running out of true, may be set true by means of the insertion
of pieces of paper placed between the saw and the face of the collar.
The first thing to do in testing the saw is to take up the end motion of
the saw arbor, or if this cannot be done, then a pointed piece of iron
or wood should be pressed on the end of the mandrel so as to keep it
from moving endways while the saw is being tested.
The saw should be revolved slowly, and a piece of chalk held in the
cleft of a piece of wood should be slowly advanced until it meets some
part of the face of the saw just below the bottom of the saw teeth.
As soon as the chalk has touched and the saw has made one or two
revolutions the chalk should be moved a trifle farther on from the
teeth, and another mark made, and then moved on again, and so on, care
being taken to notice how much space there is between the high and low
sides of the saw. It will be found, however, that the shorter the chalk
marks are the more the saw is out of true.
A more correct method is to chalk the face of the saw and use a pointed
piece of iron wire of about one-quarter inch in diameter, but in any
case the saw should only be touched lightly.
The pieces of paper should be portions of rings or segments, and should
extend an equal distance below the circumference of the collar, because
the same thickness of paper will alter the saw more in proportion, as it
is inserted farther in toward the eye of the saw.
If it should happen that two thicknesses of paper are necessary to true
the saw, one should be made about half the length of the other, and the
long one may extend farther in toward the eye of the saw. Thus one ring
of paper may be an inch deep and the other one-half inch deep.
If but one piece of thin paper is needed, it may be simply a straight
piece inserted half way down the collar and trimmed off level with the
collar. In placing the paper, the middle of its length should be on that
side of the saw that is diametrically opposite to the marks left by the
chalk on the face of the saw.
When the saw is trued and is started it will be loose on the outside,
but as its speed increases it should stiffen up so as to run true and
steadily when running at its working speed.
If the saw is to be tried by actual work, it must be borne in mind that
the tension of the saw must be right for its speed when in actual use,
and not when running idle. If the machine has belt power enough to
maintain the same speed whether the saw is cutting at its usual rate of
feed, or whether it is running idle, the tension will not be altered by
putting on the feed, but if the saw has been hammered to run at the full
speed of the machine when not cutting and the feed is heavy enough to
slacken the speed, then the tension of the saw will not be correct for
its working speed.
[Illustration: Fig. 3081.]
The eyes of small saws are either made to fit the mandrel an easy
sliding fit, or else the mandrel is provided with cones to accommodate
various sizes of holes, an ordinary construction being shown in Fig.
3081, in which A is the saw arbor, fast on which is the collar B, S
representing a section of the saw, W a washer or loose collar, and N the
nut for tightening up W. The cone _c_ is screwed upon A and passed
through the saw until it just fills the hole, and thus holds the saw
true.
In putting on the saw, it should be passed up to the collar, and _c_
screwed home until it binds in the saw eye with enough force to bring
the threads of _c_ fairly in contact with those on the mandrel A, but if
screwed home too tightly it may spring the saw, especially if the saw is
a very thin one.
As _c_ must be removed from the arbor or mandrel every time the saw is
changed, the wear on its thread is great, and in time it becomes loose,
which impairs its accuracy.
[Illustration: Fig. 3082.]
This objection is overcome in the construction shown in Fig. 3082, which
is that employed by the S. A. Woods Machine Company. It is seen in the
figure that the cone _c_ fits externally in a recess in the collar B,
and at the coned end also upon the plain part _e_ of the arbor. The cone
is hollow and receives a spiral spring _s_, S. When the saw is put on it
first meets _c_, and as nut N is screwed up, the saw S and cone are
forced along arbor _e_ until the saw meets the face of B, and the
clamping takes place. The strength of the spring _s_ is sufficient to
hold the saw true, and as the motion of cone _c_ is in this case but a
very little, therefore its wear is but little, which makes this a
durable and handy device, while the saw cannot be sprung from
over-pressure of the cone. Circular saws of large diameter, as from 40
inches upwards, are made a fair sliding fit upon their arbors or
mandrels, and are provided with two diametrically opposite pins that are
fast in the arbor collar.
The pins should be on diametrically opposite sides of the arbor, and an
easy sliding fit to the holes in the saw, but they should not bind
tight. Both pins should bear against the holes in the saw, and if both
the pins and the holes in the saw are properly located, the saw will
pass up to the collar with either side against the arbor collar, or in
other words, the saw may be turned around upon the arbor.
If the pins, or either of them, bind in the holes of the saw, and the
latter is forced on the arbor, it will spring the saw out of true, and
when this is the case care should be taken in making the correction to
discover whether it is the pins or the holes in the saw that are wrongly
located. If it is the pins, the error will show the same whichever side
of the saw is placed next to the arbor collar, while if the error is in
the holes, the error will show differently when the saw is reversed on
the arbor.
When a saw becomes worn, and its teeth require sharpening, the first
thing to do is to _joint_ it, that is to say, bring down all its teeth
to the same height, which may be done by holding an emery block or file
against it while the saw is running, care being taken to hold the block
or file firmly, and to continue the process until the tops of the teeth
run true.
The next operation is to gum and sharpen the teeth. Gumming a saw is
cutting out the throats, or gullets between the teeth, so as to maintain
the height of the tooth, and it follows that on saws that have sharp
gullets (or in other words, saws in which the back of one tooth and the
face of the next tooth join in a sharp corner), the sharpening process
with the file may be made to also perform the gumming.
In the case of teeth of coarse pitch, however, this would entail too
much labor in filing, and furthermore, as the height of the teeth
increases with the pitch or distance apart of the teeth of circular
saws, and as the higher the tooth the weaker it is, therefore coarse
pitched teeth are given round gullets so as to strengthen them as much
as possible. The gumming of a saw should always be performed before the
sharpening, and the sharpening before the setting.
When the sharpening is to be done with the file, the cutting strokes of
the file should be in the same direction as the teeth lean for the set,
as this leaves a sharper cutting edge, and it follows that the proper
plan is to file every other tooth first, going all around the saw, and
to then turn the saw around in the vise, and file the remaining teeth.
The height of the teeth and the diameter of the saw will be best
maintained by filing the front face of the tooth to bring it up to an
edge, but in filing the front face the spacing of the teeth should be
kept as even as possible.
If the front face has been filed until a tooth is as widely spaced as
those already filed, and the edge is not brought up sharp, then the edge
may be brought up by filing the back of the tooth.
[Illustration: Fig. 3083.]
A saw gumming, gulleting or chambering machine to be operated by hand,
and constructed by Henry Disston & Sons, is illustrated in Fig. 3083. It
consists of a frame spanning the saw, and having screws B B, B B, to
adjust to the saw thickness; 4 and 5 are two saw teeth, and 6 the
cutter, K is a wheel for the feed screw G, and C and D gauges for
regulating position and depth of the gulleting.
The cutter 6 is driven or revolved by means of the handles H H, but an
important point in the construction is, that a pawl and ratchet wheel is
used to drive the cutter, so that if the handles H H were revolved in
the wrong direction, the cutter would not be revolved. This saves the
cutter teeth from breakage. The machine is operated as follows:
Run the cutter back by means of screw G as far as necessary, then place
the machine on the saw, with the cutter close up in the chamber of the
tooth to be gummed.
If the teeth are regular and the same distance apart, start the cutter
in any chamber; but if they are irregular, make them even by commencing
in the smallest space. After gumming the saw a few times the teeth must
become regular. F is a set-screw to regulate the depth of gullet. Fasten
the machine to the saw by means of the screws B B, and proceed to gum
the first tooth, one of the points of the star being struck at each
revolution by a projection on the handle, steadily feeding the cutter
until arrested by set-screw F. Remove the machine to the next tooth
towards you, after having run the cutter back, and proceed as before
until the whole of the teeth are gummed.
The cutter is so arranged as to slide on its axis, and when one portion
becomes dull, remove a washer from back to front, and thus present a new
sharp cutting surface; and so continue changing the washers until the
whole face of the cutter becomes dull.
Set is given to saw teeth in two ways: first, by what is called _spring
set_, which is applied to thin saws and to cross-cut saws; and second,
_swage set_, which is given to thick saws and to inserted teeth. Spring
set consists of bending the teeth sideways so as to cause the saw to cut
a passageway or _kerf_, as it is termed, wide enough to permit the saw
to pass through the timber without rubbing on its sides.
Swage set consists of upsetting the point of the tooth with a swage,
thus spreading it out equally on both sides of the body of the saw
plate, as shown at A, Fig. 3084.
The set of the teeth, whether given by swaging or upsetting, or by
spring set, should be equal throughout the saw, so that each tooth may
have its proper share, and no more, of duty to perform.
If spring set is employed, it should not extend down more than half the
depth of the teeth, and this point is one of considerable importance for
the following reasons. The harder the saw is left in the tempering the
easier the teeth will break, but the longer they will keep sharp. Now a
tooth that is hard enough to break if it is attempted to carry the set
down to the root or bottom, will set safely if the set is given to it
for one-half its depth only.
If a saw is to be sharpened by filing, it should be made as hard as it
can be to file properly, even at the expense of rapidly wearing out the
file, because the difference in the amount of work the saw will do
without getting dull enough to require resharpening is far more than
enough to pay the extra cost of files.
Circular saws with inserted teeth are made of thicker plate than solid
saws of corresponding diameters, which is necessary in order that they
may securely hold the teeth. The principal difference in the various
forms of inserted teeth lies in the method of locking or securing the
teeth in the saw.
Figs. 3084 and 3085 represent the chisel tooth saws of R. Hoe and
Company. The No. 2 tooth is that used on gang edging machines and for
bench work. No. 3 tooth is that used in miscellaneous sawing, for hard
woods and for frozen lumber. No. 4 is the shape used in the soft and
pitchy woods of southern and tropical countries.
The method of inserting the teeth is shown in Fig. 3084 on the left, the
pin wrench being shown in position to move the socket whose projection
at C carries the tooth D home to its seat and locks it there.
The sockets for the numbers 3 and 4 tooth are, it is seen, provided with
a split, which gives to them a certain amount of elasticity that
prevents the sockets from getting loose.
Swing-frame saws are made in various forms, generally for cross-cutting
purposes or cutting pieces to length.
[Illustration: Fig. 3084.]
[Illustration: Fig. 3085.]
[Illustration: Fig. 3086.]
Fig. 3086 represents a swing-frame saw that is mounted over a work
bench, and can therefore be used without necessitating carrying the work
from the bench. It consists essentially of a frame pivoted at the upper
end to the pulley shaft and carrying below a circular saw driven by
belt over pulleys on the upper shaft and the saw arbor. In this machine
the iron hubs carrying the frame have sockets fitting over the outer
diameter of the hanger hubs, so that the frame hangs upon those hubs and
not upon the pulley shaft. The advantage of this plan is that the frame
joint is relieved of the wear which would ensue were it hung upon the
revolving spindle, while at the same time the movement of the joint is
so small as to induce a minimum of abrasion. To counterbalance the frame
while it is placed out of the perpendicular, there is provided a
compensating weight as shown in the engraving.
[Illustration: Fig. 3087.]
Fig. 3087 represents an example of that class of cutting-off saw bench
in which the length of the work is determined by the width apart of the
saws.
This machine is constructed by Trevor and Company, and is designed for
cutting barrel staves to exact and uniform lengths.
[Illustration: Fig. 3088.]
The stave is laid upon the bars of the upright swing-frame (which is
pivoted at its lower end), and the latter is vibrated by hand, which may
obviously be done both easily and quickly on account of the lightness of
the swing-frame and its vertical position. A dimension sawing machine,
by G. Richards and Company, is shown in Fig. 3088. This machine is
designed for general fine work, such as pattern making, and its general
features are as follows:
It carries two saws (a cross-cut and a rip-saw), mounted on a frame that
can be quickly revolved by a worm and worm wheel to bring either saw
into position as may be required.
There is a fixed table and adjustable fence on one side of the saw, and
a movable table and fence on the other.
The saws are ground thin at the centre, as shown in Fig. 3089, so that
but little or no set need be given to the saw teeth; hence the cutting
edges of the teeth are more substantial and true, and as a result the
work is cut very smoothly, and if the machine is kept in thoroughly good
order, the sandpaper may follow the saw.
In Fig. 3088, A is a substantial box frame, to which is bolted the fixed
table T. T´ is the movable table which runs on rollers, and is guided by
the [/\] slideway at _e_. This table the workman pushes to and fro by
hand, the work being adjusted upon the table or to the fence, as the
case may be. At W is the wheel for swinging the frame to bring the
required saw into position.
[Illustration: _VOL. II._ =DIMENSION SAWING MACHINE.= _PLATE XVIII._
Fig. 3089.]
In Fig. 3089 the worm gear for swinging the saws into position is shown,
and also a sectional view of one saw arbor and of the movable table. A
is the main frame, and _f_ the disc frame carrying the two saw arbors.
The disc _d_ is turned to fit a seating formed in the base, while the
other end of the disc frame fits through a substantial bearing B; W´ is
the worm wheel, and W´´ the worm for swinging the disc frame. The worm
teeth fit closely to the worm wheel teeth, and backlash or play is
prevented by means of the spring bearing shown at D, the spiral springs
forcing the worm teeth into the worm wheel teeth. Thus _a_ is the
bearing for the worm carried in the box _c_, upon which is the spiral
spring whose tension is regulated by the screw _g_.
The end of the worm is therefore held in a swivel joint that causes it
to operate very easily.
[Illustration: Fig. 3090.]
Fence F, Fig. 3088 is for slitting, and is made to swing back for bevel
cutting, while F´ is for cross cutting, and is adjustable for angle
cutting. Fence F is fitted to a plate P, Fig. 3090, which rests on the
table top, and also rests on the long slide _g_. This slide fits in a
beveled way _h_, and contains a [_|_] groove. A tongue likewise beveled
fits in the top of this groove, the tongue being permanently fast to the
fence plate. The [_|_] bolt passes through the tongue and fence plate,
having at its upper end a milled or knurled thumb wheel R, which when
tightened up fastens the fence plate and the slide together.
Upon slacking the thumb wheel R, the fence plate and [_|_] bolt may be
readily shifted, setting the fence as near to gauge as possible by hand,
and the thumb wheel is then tightened, and the slide (which carries the
fence bodily with it) is adjusted by means of the hand wheel H and its
screw which threads into a lug from the table.
The fence F is pivoted to plate P at _p_, and the angling link which
holds it in position is secured by a hand nut M.
The front journal of the saw arbor has a double cone, and by means of
the nuts _n n´_, Fig. 3089, can be regulated for fit independently of
the back bearing and journal, the latter being also coned and capable of
independent adjustment by means of the adjustment nuts _m m´_.
The countershaft for driving the saw arbors is below the machine, so
that the saw that is not in use remains stationary.
[Illustration: Fig. 3091.]
Examples of the work done on this machine are shown in Fig. 3091, the
various sections shown being produced by the vertical movement of the
saw through the table and the cross movement of the fence. For example,
for cutting out a core box, such as shown at 6, small grooves are cut
through to remove the bulk of the wood, and the saw marks at the bottom
of each saw cut serve as gauge lines for the workman in finishing the
circular bore with the gouge, etc.
An example in which the table is fixed to the frame and the saw is
adjusted for height above the table is shown in Fig. 3092. The saw arbor
is here carried in a frame that is pivoted at one end to the main frame,
while at the other end is a handle through which passes a locking screw
for securing that end of the saw arbor frame to the arc slot shown on
the main frame.
[Illustration: Fig. 3092.]
In a more expensive form of this machine an adjusting screw is used for
regulating the height of the saw, and an iron table is employed instead
of a wooden one.
[Illustration: Fig. 3093.]
A double saw machine constructed by P. Pryibil is shown in Fig. 3093. In
this machine each saw is carried in separate frames, that are pivoted at
one end to the main frame and secured at the other to segments, so that
either saw may be elevated to the required distance above the work
table.
One saw is for ripping and the other for cross cutting, and the arbor of
the latter is provided with an adjusting screw operated by the hand
wheel shown on the right hand of the machine.
As the saws are on independent arbors, they can be speeded differently
to suit different saw diameters, which is an advantage because, as
machines of this class are for the lighter classes of work, the ripping
saw will rarely be required for work of more than about 3 or 4 inches
thick, and a rip saw of large diameter is not therefore necessary.
The cross cut saw however requires to be of larger diameter, as its work
includes cross cutting up to 8 or 10 inches diameter, and the saw being
larger does not require so high a speed of revolution.
Both saws are provided with ripping gauges and with right and left hand
mitre fences, adapted to the application of either short or long work,
and provided with length gauges.
[Illustration: Fig. 3094.]
Fig. 3094 illustrates the various gauges in place upon the table of a
machine. The table is provided with a slideway, or slot, on each side of
the saw, and parallel with it, and also with a slideway at one side of
the table. In the figure, the mitre gauge, or gauge for sawing at an
angle, is shown in two positions.
The gauge A A A is for cutting work to length, and for cropping the ends
at the same time, an extension frame being used, as shown for unusually
long work.
[Illustration: Fig. 3095.]
[Illustration: Fig. 3096.]
Fig. 3095 illustrates the method of employment of the mitre gauge. The
pointer is set to the degree of angle the work is to be cut to, and is
fastened to its adjusted position by the set screw H. The stop is set to
the required length, and the work is held by hand against the face of
the gauge, and at the same time endways against the stop, and the gauge
is then moved along the slot, feeding the work to the saw. When the work
is sawn and is to be withdrawn, care must be taken to keep the work
fair, both against the gauge and against the stop.
[Illustration: Fig. 3097.]
Figs. 3096 and 3097 show the application of the gauges for cropping off
the ends of work and cutting it to exact length. There are two stops, S
and T, each of which is secured in position by a set screw, and has a
tongue that may be thrown over, as occasion may require--thus, suppose
it is desired to merely crop off the end of the work--and both stops may
be set for the work to rest against as in Fig. 3096, and the end of the
work may be cut off or cropped to square it or remove a defective part.
Stop S may then be thrown over as in Fig. 3097, and the squared or
cropped end of the work rested against stop T, to gauge the length to
which the work will be cut. This is a simple and convenient method of
cropping and gauging.
[Illustration: Fig. 3098.]
Fig. 3098 represents a circular saw machine, constructed by the Egan
Company, in which the table is carried on a vertical slide, and may be
raised or lowered by means of the hand-wheel, bevel gears, and screw
shown, and may be set at any required angle to the saw for cutting
bevels.
The saw arbor or mandrel is carried by the main frame, and is therefore
rigidly held.
The fences can be used on either side of the saw, which is very
convenient when the table sets out of the level.
BEVEL SAWING MACHINE OR COMBINATION MITRE SAWING MACHINE.
In this machine, which is shown in Figs. 3099, 3100, and 3101, the
construction permits of the saw being set so as to revolve at other than
a right angle to the work table, which is rigidly secured to the frame
of the machine.
This machine is constructed by J. S. Graham & Company, and its action
may be understood from the following:
Fig. 3099 is a general view, while Figs. 3100 and 3101, are sectional
views of the machine.
The table is firmly bolted to the frame, and is fitted with the
necessary groove slides and fences for rip sawing and cross cutting. It
is also provided with a removable piece, which allows the use of
wabbling saws, dado heads, etc.
[Illustration: Fig. 3099.]
[Illustration: Fig. 3100.]
The sides of this machine A, A, Fig. 3099, are cast with an extension
for countershaft. Referring now to Figs. 3100 and 3101, the upright
piece I, I, with arms B B, and G, G, is bolted to the frame as shown.
The arbor frame M, M, is gibbed to T, T, by the circular piece U, and is
moved to any angle by the hand wheel Z, which operates the worm W, which
in turn moves the arbor frame M, M. This arrangement does not require
any locking device to hold the saw in position. As the centre upon which
the arbor swings is in the intersection of the planes of the saw and
table top, the opening in the table needs not be larger than for the
ordinary saw. When cutting a mitre the saw takes the position J, Fig.
3101. When cutting at a right angle the saw takes the position J´ and
the arbor takes the position P´ N´.
[Illustration: Fig. 3101.]
The saw arbor can be raised and lowered by the use of the hand wheel
which operates the screw _b_ (Fig. 3100.)
There is an accurate index located in front of the machine in sight of
the operator, marked from 0 to 45°.
The iron table is of one piece 4 feet by 3 feet and fitted with the
necessary groove slides for ripping and cross cutting gauges. It is also
provided with removable piece E, Fig. 3101, allowing the use of dado
head, etc. The table is provided with a bevel slitting gauge S´, and
cross cut or mitering gauge X´, Fig. 3099, which in connection with the
angular adjustment of the saw enables the operator to get every
conceivable plain or double mitre ever required. The pulleys A´, B´, are
made wide to allow the belt to travel as the saw is inclined. The pulley
B´ takes up the slack of the belt. The countershaft and tightener are a
part of the machine and can be run wherever a belt can be brought to
them.
ROLL FEED CIRCULAR SAWS.
Figs. from 3102 to 3105 represent a roll feed circular saw, by J.
Richards.
Fig. 3102 is a side elevation, Fig. 3103 a plan, and Fig. 3104 a
cross-sectional view through the rolls.
In Fig. 3102, P is the saw-driving pulley, T a stand for carrying the
saw guides _a_, _b_, _c_, _d_, which are adjustable for height by means
of the arm whose set screw is shown at U; at W is the spreader for
opening out the board after it has been cut by the saw, and thus prevent
its binding against the saw and heating it.
The construction of the feed motion is shown in Figs. 3103, 3104, and
3105.
On the saw arbor is the feed cone C, Fig. 3103 having four steps so as
to give four rates of feed. This cone connects by belt to feed cone D,
whose shaft drives feed pulley E, which drives F by belt connection. F
drives two worms shown by dotted lines at H and I, and these drive the
worm wheels which drive the feed rolls, one of these worm wheels being
shown at K, in the side view, Fig. 3102.
The feed roll L (Fig. 3103) is supplemented by a fence or gauge face P,
which guides the work closer up to the saw than would be possible with a
roll, and a supplemental roll is provided at M, thus affording a guiding
surface for the work from M to the end of P. The stand for guide roll L
fits in a slideway, and is adjustable along it by means of the screw S.
Similarly the stand for roll N is fed along its slideway by screw R.
There are three separate sets of saw guides, all of which are shown in
the plan view Fig. 3103, and of these the top ones, _a_, _b_, _c_, _d_,
_e_, _f_, _g_, and _h_ are adjustable by nuts. The front ones, _l_, _m_,
_n_, _o_, _p_, _q_, and the back ones, _i_, _j_, _k_, and _r_, _s_, _t_,
are adjustable by means of the wedges _w_. At Z is a wedge for adjusting
the spreader W so as to keep it close to the saw whatever the diameter
of the latter may be.
[Illustration: Fig. 3102.]
[Illustration: Fig. 3103.]
Fig. 3105 is an end view of the machine showing the feed worms H and I,
and the belt tightener V, which is carried on the arm _u_ on whose shaft
is the weight _y_, attached to which is the handle X.
[Illustration: Fig. 3104.]
[Illustration: Fig. 3105.]
SEGMENTAL CIRCULAR SAWS.
[Illustration: Fig. 3106.]
A segmental circular saw is one in which the saw is composed of segments
secured by screws to a disc, the construction being such as shown in
Fig. 3106, in which A is the saw arbor, D the disc, and E, F, G, H, I,
J, etc., the segments.
The segments are made of varying thicknesses at the cutting edge, and
are tapered for a distance for from 6 to 8 inches inwards from the teeth
points. Thus in the figure there is shown at P an edge view of a
segment, from _a_ to _b_ being parallel, and from _b_ to _c_ being
ground off taper.
The segments are held to the disc by the two sets of screws, R, S, and
are further secured at their edges by pieces of copper, as shown at W.
Between the edges of the segments there is left a space or opening of
about 1/16 inch, which is necessary to insure that the segments shall
not bind together edgeways, as that might prevent their seating fairly
against the face of the disc D.
The seats for these pieces of copper are shaped as shown in the face
views at W, and in the edge views at W´, the mouth of the slot being
widened on each side, so that riveting up the pieces of copper will
prevent the segments from moving sideways.
In fitting in these pieces of copper, it is essential to take care that
they do not completely fill the slots, but leave a small opening at each
end of the slot, as at _f_ and _g_ in the figure, and in order to do
this the copper must be left about 1/8 inch narrower than the width of
the slot.
If the copper is, in riveting up, brought to bear against the end of the
slot, it will twist the segments out of line one with the other, causing
the saw to drag, cut roughly and produce bad work.
[Illustration: Fig. 3107.]
[Illustration: Fig. 3108.]
Figs. 3107 and 3108 represent portions of segmental saws for cutting
veneering. In some of these saws the screw holes are so arranged that
the segments can be moved out to maintain the diameter of the saw as it
wears.
GANG EDGING MACHINES.
For dressing the edges of planks parallel and to width what are called
gang edgers or gang edging machines are employed.
A gang edger consists of an arbor driving two or more circular saws,
through which the boards to be edged are fed. Means are provided whereby
the distance apart of the saws may be rapidly adjusted while the saws
are in motion, so that if a board will not true up to a given width, the
saws may be set to cut it to a less one without delay.
[Illustration: Fig. 3109.]
Fig. 3109 represents a self-feeding gang edger, constructed by J. A. Fay
& Company, and in which the left-hand saw may be fixed at any required
position on the left-hand half of the saw arbor, while the two
right-hand ones may be adjusted independently along the arbor, while the
machine is running.
At the back of the saw is a feed roll, and above it a pressure roll,
whose pressure may be regulated by means of the weight and bar shown at
the back of the machine. The object of placing the feed and pressure
rolls at the back of the saws, is, that if a board is found to be too
narrow for the adjustment of the saws, it may be withdrawn without
stopping or reversing the machine, and the saws may be drawn together
sufficiently to suit the case.
Fig. 3110 is a plan and Fig. 3111 an edge view of the work table, and
show the means of adjusting the saws. A is the saw arbor, and 1, 2, 3,
the circular saws. Saw 1 is carried by the sleeve B, which is secured in
its adjusted position by the set screw C.
The mechanism for traversing saws 2 and 3 corresponds in design, and may
be described as follows:
The arbor A has a spline S to drive the sleeves D, D´, which hold the
saws and are carried by arms E, E´, which operate in slideways and have
racks F, F´, into which gear pinions whose shafts G, G´, are operated by
the hand wheels H, J.
It is obvious that by means of the hand wheels H, J, saws 2 and 3 may be
regulated both in their distances apart or in their distances from saw
1, while the machine is in full motion, the bushes or sleeves D and D´
being carried by and revolving in the slide pieces or sliding bearings E
and E´ respectively. Now suppose that E´ be moved to the left by hand
wheel J, until it abuts against the end of D, at the slide end, and a
further movement of D´ will also move D, causing it to operate its
pinion and revolve the hand wheel H, hence D and D´ may be
simultaneously moved without disturbing their distances apart by
operating hand wheel J. On the yoke above the saws is a coarse-figured
register plate to enable the setting of the saws to accurate widths
apart.
RACK FEED SAW BENCH.
This machine is employed for the purpose of reducing balks or logs into
planks of any thickness required. The machine is fixed on the floor of
the saw mill, all the gearing being underneath the floor, so that the
table may be set level with the floor, which is a great convenience when
heavy logs are to be operated upon. The machine consists of a
substantial bed plate or frame A, Fig. 3112, carrying the saw and the
feed works. The carriage runs on rollers, some of which are fixed to the
frame A, and others to the framing timbers B, which are long enough to
support the carriage throughout its full length, when the carriage is at
either end of its traverse.
[Illustration: Fig. 3110.]
[Illustration: Fig. 3111.]
The driving pulley for the saw arbor is shown at C, Fig. 3112, in dotted
lines and in Fig. 3113 in full lines. Upon the saw arbor is a cone
pulley D, Fig. 3113, for operating the carriage to the feed, the
construction being as follows:
Referring to Figs. 3112 and 3113, cone pulley D connects by a crossed
belt to cone pulley E, on whose shaft is a pulley _e_ which drives the
pulley F, on whose shaft is the pinion _f_, which drives the gear G. On
the same shaft as G is a pinion _g_, which drives the gear wheel H,
which engages the rack J, on the carriage, and feeds the carriage to the
cut. The diameters of pulleys E, F, and of _f_, G, and _g_, are
proportioned so as to reduce the speed of the cone pulley D, down to
that desirable for the carriage feed. But, as there are four steps on
the cones D, E, therefore there are four rates of cutting feed or
forward carriage traverse, which varies from 15 to 30 feet per minute.
The speed of the saw varies in practice, some running it as slow as
9,000 feet per minute at the periphery of the saw, and others running it
as high as 16,000 feet per minute. The latter speed however, is usually
obtained when the saws are packed with fibrous packing, which will be
explained presently.
The quick return motion for the carriage is obtained as follows:
Referring to Figs. 3113, and 3114, K is a fast and K´ a loose pulley on
the shaft _k_, and receiving motion by belt from a countershaft.
[Illustration: _VOL. II._ =RACK-FEED SAW BENCH.= _PLATE XIX._
Fig. 3112.]
The speed of the fast pulley K is such as to give a return motion to
the carriage of about 50 or 60 feet per minute, being about twice as
fast as the carriage feed motion.
We have now to explain the methods of putting the respective carriage
feed motions into and out of operation, and insuring that both shall not
be in gear at the same time.
[Illustration: Fig. 3113.]
Referring therefore to Figs. 3113 and 3114, suppose the carriage to have
completed a feed or cutting traverse, and the operator pushes with his
knee the lever or handle _h_, Fig. 3114, which revolves shaft _m_, on
which is an arm that moves the belt-shifting rod _n_, thus moving the
belt from fast pulley F to loose pulley F´, thus throwing the feed gear
out of engagement and causing the carriage to stop. He then presses down
the foot lever L, Fig. 3113, which operates the belt-shifting rod _p_,
Fig. 3114, and moves the belt from loose pulley K´, to fast pulley K,
which having a crossed belt, operates the pulley F in the reverse
direction and traverses the carriage backwards, or on the return motion.
Upon releasing the foot from the lever L, the weight W operates the foot
lever L, and the belt is re-shifted from fast pulley K to loose pulley
K´, and the carriage stops.
The carriage is formed of iron plates with an open space of about 1/2
inch between them, as shown in Fig. 3114, this space forming a race to
permit the carriage to travel past the saw. The only connection between
the two sections or parts of the table, is a wide plate at the rear end
which secures them together, and causes the lighter portion of the
table, which is merely driven by the friction of the rollers C, to
always travel with the lower or under portion, which is driven by the
rack J. In larger machines for the heaviest work, both sections are
driven by a rack motion.
The guide motion for the carriage is constructed as follows:
_a_, _a_, are brackets placed at intervals along the whole frame work.
These brackets support rollers _c_, which have flanges on them to
prevent any side motion of the carriage, the construction being most
clearly seen in Fig. 3113; _b_ being a bearing for the shaft _v_ of the
rollers. Each section of the carriage, it will be seen, has two ribs or
ways which rest on the rollers, which are arranged four on each shaft
_v_ (_i.e._ two for each section of the carriage).
The fence or gauge against which the face of the work runs is very
simply arranged as is shown in Figs. 3113, and 3114, being secured to
the shaft _q_, by a long bolt _t_, threaded into the top of the fence,
and at its lower end abutting against a shoe fitting partly around the
top of the shaft _q_. It is squared at the top to receive a wrench or
handle _u_, and it is obvious that unscrewing the handle releases the
fence from shaft _q_, so that the fence may be moved rapidly by hand
across the table to approximate the adjustment of the fence from the
saw. The fence having been thus approximately adjusted, and locked to
the shaft by means of the handle _u_, the final adjustment is made by
means of the hexagon nut _w_, on the bed of the shaft nut _x_, serving
as a lock nut, to hold _q_ in its adjusted position.
FIBROUS PACKING.--The fibrous packing before referred to is composed of
hemp, plaited in a four strand plait and inserted in an open-top trough,
along the sides of the saw for a distance about two inches less than the
radius of the smallest saw the machine uses.
[Illustration: Fig. 3114.]
This packing steadies and stiffens the saw, and also affords a means of
adjusting its tension, while the saw is running.
Suppose for example, that the saw is rim bound,[47] and the fibrous
packing may be rammed tightly to the saw, as near to the saw rim as
possible, and less tight as centre of the saw is approached.
[47] For the principles involved in hammering saws to equalize the
tension see page 69 (Vol. II.) _et seq._
This warms the saw, but makes it warmer at the circumference than at the
centre, expanding the circumference, and by equalizing the tension,
enables the saw to run straight.
[Illustration: Fig. 3115.]
When the packing is to be adjusted, the carriage is run out of the way,
and the packing operation is performed by hand, with a caulking tool.
The packing and its box, as applied to a rack saw bench is shown in Fig.
3115, by the dark rectangles. By thus packing the saw to guide it and
keep it straight, thinner saws may be used, saws 52 inches in diameter,
and having a thickness of but 7 or 8 gauge being commonly employed, and
in some cases of 9 gauge.
Saws that are thus packed, produce much smoother work.
The packing, it may be observed, is kept well lubricated with oil, and
the following is the method of adjusting it.
[Illustration: _VOL. II._ =PLANTATION SAW MILL.= _PLATE XX._
Fig. 3117.]
The side of the saw on which the operator stands is the last to be
packed, the packing on the other side being inserted so as bed fairly
but lightly against the saw, so as not to spring it, which may be tried
with a straight-edge. The packing on the other side is then inserted to
also bed fairly against the saw, without springing it, and the saw is
run until it gets as warm as it may, from the friction of the packing.
If, then, the saw flops from side to side, the outside (circumference)
is _loose_, and the packing is rammed together on both sides of the saw
and near the saw arbor or mandrel, care being taken that in ramming the
packing the saw is not unduly pressed on either side.
Expert sawyers generally change the packing when the saw is changed, and
thus keep for each saw its own packing. The slot or pocket in which the
packing lies is about 1-1/4 inches deep, and 1/2 inch wide.
[Illustration: Fig. 3116.]
In ordinary circular saw benches or machines the packing comes about up
to the level of the table, as shown in Fig. 3116, in which A is a hand
hole for putting in and lifting out the plate B, so as to put in or
remove the wooden pieces C, D, upon which the packing rests.
Fig. 3117 represents a saw mill constructed by the Lane & Bodley
Company. In this machine two circular saws are employed, the upper one
being of small diameter and revolving in the same direction as the log
feed. A is the driving pulley for the main saw arbor _a_, and B the
driving pulley for the upper saw arbor _b_. The carriage feed is
obtained by belt from cone pulley C to cone pulley D, on whose shaft is
a friction pulley _e_, which, for the feed motion, is moved by lever E
into driving contact with pulley F, whose shaft drives the pinion G,
which gears with the rack of the carriage. The three steps on the cones
C, D, give three rates of feed, and a quick return motion is given to
the carriage by engaging the friction pulley with a wheel not shown in
the engraving.
The log to be sawn rests upon the slideway S S´, and is secured thereon
by the dogs J, J, which are capable of sliding up or down upon the heads
H, H´. When the handles K are raised the slides carrying dogs J are free
to be moved up and down H, H´, whereas when handles K are depressed the
dogs J are locked and hold the log. The operation is to raise the dog
slides to the top of H, H´, set the log up to the faces of H, H´, and
then by raising handles K, let the dog slides fall, their weight forcing
the dogs into the log, and the depression of K locks the dog slides upon
H, H´, respectively.
The log feed is obtained from the lever L, which operates the ratchet
wheel T, which drives bevel gears V and W, which operate the screws that
slide the heads H, and H´, along the slideways S and S´.
Three rates of log feed are obtained by regulating the amount of motion
that can be given to the lever L, the construction being as follows:
In the lever L is a slot in which a stop _r_ can be secured at different
heights, and the piece M has four notches. The limit to which L can be
moved to the left is until it comes against the stop _x_, but the limit
to which it can be moved to the right is governed by the height of the
stop _r_ in the slot in L. If stop _r_ is set at its highest position in
the slot, L can be moved to the right until the stop _r_ meets the right
hand step on the circumference of M, and a maximum of log feed is given.
TUBULAR SAW MACHINE.
[Illustration: Fig. 3118.]
Fig. 3118 represents a tubular saw machine. The saw runs in fixed
bearings, the work feeding on the table B, running on ways on A. The
work is here obviously sawn to a curve corresponding to that of the
circumference of the saw.
CROSS CUTTING OR GAINING MACHINE.
In Figs. 3119 and 3120 is represented a machine constructed for either
cross cutting or gaining, the gaining head shown on the machine being
replaced by a cross-cut saw when cutting off is to be done.
[Illustration: Fig. 3119.]
It consists of a vertical column or standard, upon the face of which a
slideway A for the arm B, on which is a slideway C, along which the head
for carrying the saw arbor traverses.
When the saw is to be used, the carriage or work table must be locked in
position and adjusted so that the saw will come fair in the groove,
provided in the table, but it is not necessary to dog or fasten the work
to the table, because the saw itself draws the work over fair against
the fence.
When the machine is used for gaining, the work must be dogged fast to
the table, so that the work and table may be moved accurately together
and the widths apart of the gains kept accurate.
Joshua Oldham's combination saw for grooving or gaining is shown in Fig.
3121. It consists of two outside saws, such as shown at the top of the
figure, and having spur teeth between the ordinary cutting teeth. The
tops of the spur or cross-cutting teeth are a little higher than the
other teeth, so that they sever the fiber before the ordinary teeth
attempt to remove it, and thus produce very smooth work. The inside
pieces, shown at the bottom of the figure, go between the two outside
saws, if necessary, to make up the required width of gain. They are made
1/8 inch thick, with an odd one 1/16 inch thick, and will thus make
gains advancing in widths by sixteenths of an inch.
SCROLL SAWING MACHINES.
The scroll sawing machine derives its name from the fact that it is
particularly fitted for sawing scroll or curved work by reason of the
saw (which is a ribbon of steel with the teeth cut on one edge) being
very narrow.
The principal points in a scroll sawing machine are to have the saw held
under as nearly equal tension as possible throughout the whole of the
stroke; to render the machine readily adjustable for different lengths
or sizes of saws, to provide it with means of taking up lost motion, and
to avoid vibration when the machine is at work.
A scroll sawing machine constructed by the Egan Company is shown in Fig.
3122, a sectional view of the saw straining mechanism being shown in
Fig. 3123. A, A, is a casting having slides for the head B, which is
adjustable upon A to suit different lengths of saws, and is secured in
its adjusted position by the bolt C and nut D. To the ends of the
springs S, a strip or band of leather is secured, the other end passing
around the small step F of a roller R, and being secured thereto. The
roller R is so supported that it may rise and fall with the strokes of
the saw. A second leather band G is secured at T, passes over the large
step of R, and at its lower end hooks to the saw, which is strained by
the springs S. This reduces the motion of the springs, and thus serves
to equalize their pressure throughout the saw stroke.
The lower end of the saw is gripped in a slide or cross-head that is
driven by the connecting rod and crank motion shown in the general view
Fig. 3122. The lever shown at the foot of the machine moves the belt to
the fast or loose pulley to start or stop the machine, and operates a
brake to stop the machine quickly.
[Illustration: _VOL. II._ =GAINING OR GROOVING MACHINE.= _PLATE XXI._
Fig. 3120.
Fig. 3121.]
Fig. 3124 represents a scroll saw constructed by H. L. Beach. This
machine is provided with a tilting table, which can be set at any angle
up to 39 degrees, either to the right or left, the exact angle being
indicated by a graduated arc.
[Illustration: Fig. 3122.]
[Illustration: Fig. 3123.]
[Illustration: Fig. 3124.]
The straining device, including the springs, air pump, guide-ways,
cross-head and steel bearing, are all attached to the vertical tubular
shaft, which is secured to the heavy cast back support by the box E and
eccentric lever F. By raising the lever F, the shaft, being balanced, is
free to move up or down to suit any length of saw.
At the same time, the steel bearing L forms a support for the back and
sides of the saw, and can be raised or lowered to suit any thickness of
work.
The under guide-ways are so constructed that their expansion by
tightening does not tighten the cross-head. Instead of the ordinary
tight and loose pulleys, the crank shaft carries a friction pulley and
combination brake by which the saw is stopped or started instantly, by a
single motion of the foot.
This leaves the hands entirely free, and saves considerable time in
stopping and starting.
The lower end of the saw is held by a steel clamp; when the saw breaks
it can be used again by filing a notch. Both ends of the saw are
arranged to take up lost motion and wear.
Any desired strain from 10 to 75 pounds can be given to the saw, and the
strain is equal at all points of the stroke.
BAND SAWING MACHINES.
[Illustration: Fig. 3125.]
The simplest form of band sawing machine is that in which the work is
fed to the saw by hand, a machine of this class, constructed by J. A.
Fay & Co., being shown in Fig. 3125. It consists of a standard or frame
A, carrying the saw-driving wheel B, and the upper wheel C, the saw
being strained upon these two wheels. The lower wheel runs in fixed
bearings, while the bearing of the upper wheel is carried in a slide
provided in the frame, being operated in the slide by a screw, whose
hand wheel is shown at E, so that it may be suited for different lengths
of saws.
The bearing of the upper wheel is so arranged that the tension placed on
the saw may be governed by a weighted lever F, which enables the upper
bearing to lower slightly, so that if a chip should fall between the saw
and the lower wheel, it may not overstrain, and therefore break the saw.
At J, is a bar carrying a guide G, which sustains the saw against the
pressure of the cut, a similar guide being placed below the table T, at
G´. This latter guide is fixed in position, whereas the upper one, G, is
adjustable for height from the work table, so that it may be set close
to the top of the work, let the height of the latter be what it may. G´´
is a guide and shield for the saw at the back of the machine, and H is a
shield to prevent accident to the workman, in case the saw should break.
Band saws are ribbons of steel, brazed together at their ends and having
their teeth provided on one edge. The widths of band saws vary from 1/16
inch to 8 inches, and their thicknesses from gauge 18 to 22 gauge,
according to width.
The advantage of the band saw lies in that it may be run at high
velocity, may be made thin, and its cutting action is continuous.
As a band saw is weak, it is desirable to have the teeth as short as
possible and leave enough room for the sawdust, so that it shall not
pack in the teeth.
[Illustration: Fig. 3126.]
In a circular saw, the centrifugal force acts to throw the sawdust out,
while in a frame saw, the backward motion of the saw acts to clear the
teeth of the dust, whereas in a band saw the dust is apt to pack in the
teeth while they are passing through the work. The remedy is to space
the teeth widely, thus giving room for the dust without having a deep
tooth, an ordinary form of tooth being shown in Fig. 3126.
[Illustration: Fig. 3127.]
A stronger form of tooth is shown in Fig. 3127, the tooth gullets being
well rounded out, and the teeth shallow at the back, while having ample
room in front for the dust.
In determining the shapes of the teeth of band saws, we have the
following considerations:
[Illustration: Fig. 3128.]
One of the principal objects is to have the back edge of the saw bear as
little as possible upon the saw guide, and as the feed tends to force
that edge against the guide, we must so shape the teeth as to relieve
the back guide as much as the circumstances will permit. This may be
done by giving to the front faces of the teeth as much rake as the
nature of the work will permit. Thus, in Fig. 3128, it will be seen that
from the front rake, or _hook_ of the teeth, as it is commonly called,
there is a tendency for the cut to pull the saw forward, this tendency
being caused by the pressure, on the teeth in the direction of the
arrows, and obviously acting to prevent the saw from being forced
against the back guide.
For sawing soft woods, such as pine, the teeth may be given a maximum of
front rake or hook, whereas for hard woods, the front faces must be made
to stand at very nearly a right angle to the length of the blade, and
the feed must therefore be lighter, in order to relieve the back edge of
the saw from excessive contact with the back guide, which would not
only rapidly wear the guide, but acts to crystallize the edge of the saw
and cause it to break.
[Illustration: Fig. 3129.]
The set of the teeth of band saws is given in two ways, _i. e._ by
spring set, which consists of bending each alternate tooth sideways, as
in Fig. 3129, or by swage set (upsetting or spreading the points of all
the teeth), a plan that may be followed with advantage for all saws
thicker than about 20 gauge.
Spring set is given either by bending, or by hammer blows, and swage set
either by blows or by compression. In spring set, each tooth cuts on one
side, and there is consequently a pressure tending to bend the tooth
sideways, and break it at the root, whereas in spread set, the tooth
cuts on both sides equally. As the front faces of band saw teeth are
filed straight across, as in Fig. 3129, and are not given any fleam for
any kind of woodwork, the set, whether spring or a spread, should be
equal in amount for every tooth, and the pitch and depth of the teeth
should be exactly alike, so that no one tooth will take more than its
proper share of the cut.
The bend or set of the tooth in spring set saws, should not extend more
than half way down the depth of the tooth, which will make the set more
uniform and save tooth breakage, it being borne in mind, that a tooth
hard enough to break if the set extends down to the root, will set
easily if it extends half way down only, and that a saw may be soft
enough to file, and of a proper temper, and yet break if the spring set
is attempted to be carried too far down the tooth.
[Illustration: Fig. 3130.]
If as in the case of fine pitched teeth, the teeth are filed with a
triangular or _three_ square file but little front rake or hook can be
given, without pitching the teeth widely. This is shown in Fig. 3130, in
which S, is the section of a saw, and F, a section of a three square
file. The front faces have no rake, and the file is shown as acting on
both faces.
[Illustration: Fig. 3131.]
In Fig. 3131, we have the same pitch of teeth, but as the file is canted
over, so as to give front rake or hook to the tooth, the tooth depth is
reduced, and there is insufficient room for the sawdust. In order,
therefore, to give to the teeth front rake, and maintain their depth
while keeping the pitch fine, some other than a three square file must
be used.
The principal defect of the band saw is its liability to break,
especially in band saws of much width, as say 3 inches and over. A saw
that is 6 inches wide will ordinarily break by the time it has worn down
to a width of 4 inches. Now for heavy sawing it is necessary that wide
saws be used, in order to get sufficient driving power without
over-straining the saw.
[Illustration: Fig. 3132.]
The causes of this saw breakage are as follows:
In order that the saw may be regulated to run on the required part of
the upper wheel, and lead true to the lower wheel, it is necessary that
the upper wheel be canted out of the vertical, and band sawing machines
are provided with means by which this may be done. If the upper wheel
were set level, as in Fig. 3132, the saw itself would be held out of
level, and the toothed edge would be more tightly strained than the back
edge. Furthermore the middle of the saw cannot bed itself perfectly to
the wheel. Furthermore, the velocity of the toothed edge would be
greater than that of the back edge because of its running in a circle of
larger diameter when passing over the wheels.
[Illustration: Fig. 3133.]
This is to some extent remedied by setting the wheel out of the
vertical, as in Fig. 3133, in which case the two edges will be more
equally strained, and have a more equal velocity while passing over the
wheels.
[Illustration: Fig. 3134.]
There will still however, be an unequal strain or tension across the
saw width, and it is found that unless the saw is made what is known as
loose,[48] it is liable to break, and will not produce good work. It is
to be observed however, that the above may be to a great extent, and
possibly altogether, overcome by means of having the rim face of the
wheel, or of both wheels, curved or crowned in their widths, so that the
saw will be in contact with the face of the wheel, nearly equally across
the full saw width. This would also cause the saw to run in the middle
of the wheel width, and thus enable the alignment of the saw to be made
without requiring the upper wheel to be set out of level.
[48] See page 69, Vol. II., for what is technically known as looseness
in a saw.
RE-SAWING BAND SAW MACHINE.
A re-sawing machine is one used to cut lumber (that has already been
sawn) into thinner boards. Fig. 3134 represents a band saw machine,
constructed by P. Pryibil, having a self-acting feed motion, consisting
of four feed rolls, all of which are driven, and two small idle rolls,
which are so arranged as to guide the last end of the stuff or work
after it has left the driven rolls.
Four rates of feed are provided, and the upper wheel can be set at the
required angle from a perpendicular while the machine is in motion.
The upper guide wheel, and the mechanism by which it is carried, is
counterbalanced by a weight that hangs within the column or main frame,
and is therefore out of sight.
[Illustration: Fig. 3135.]
The construction of the parts by means of which the upper wheel is
adjusted in height to regulate the tension of the saw, and which also
cants the wheel out of the vertical, is shown in Fig. 3135, which
represents a portion of the main frame or column, on which is a slideway
B, for the slide C, which carries the bearing for the upper wheel.
The method of moving the slide C for moving the upper wheel to adjust
the saw tension is as follows:
By means of the handle H and the worm and worm wheel at W, the shaft S
is revolved. The upper end of S is threaded into the nut N, which is
capable of end motion in its bearing at _e_, and which abuts against the
lever L, the latter abutting against the end of the screw M, and acting
at its other end on the rubber cushion P. Now suppose that S be revolved
in the direction denoted by the arrow, and the effect will be to raise
the nut N. This effect will be transferred through the screw M to the
slide C, which will rise up on B, carrying with it the upper wheel
bearing and wheel.
When the upper wheel receives the strain of the saw, then the continued
revolution of shaft S will cause the nut N to lift endways in its
bearing _e_, the screw M acting as a fulcrum to cause the lever L to
compress the rubber cushion P. The amount of tension on the saw is
tested by springing it sideways with the hands. Now suppose the saw to
be properly strained, and that a piece or chip of wood accidentally gets
between the saw and the lower wheel, and the result will be that the
slide C will (from the extra strain caused by the chip) move down on its
slideway B, which it is capable of doing, because the long arm of the
lever L can move down, compressing P, and this will prevent the saw from
breaking.
To cant the wheel for leading the saw true to the lower wheel, the
following means are provided:
The upper wheel bearing rests on the fulcrum at _a_, and is guided
sideways by the screws _c_ and _d_. At _f_ is a stud threaded into the
bottom half of the upper wheel bearing, the wheels _g_ and _h_ threading
upon _f_. The weight of the upper saw wheel endeavors to lift the end J
of the wheel bearing, and wheel _h_ determines how much it shall do so,
while wheel _g_ acts as a check nut to lock the adjustment.
[Illustration: _VOL. II._ =BAND SAW WITH ADJUSTABLE FRAME.= _PLATE
XXII._
Fig. 3139.]
[Illustration: _VOL. II._ =BAND SAW MILL.= _PLATE XXIII._
Fig. 3140.
Fig. 3141.
Fig. 3142.]
The feed rolls are carried in slides which are operated in slideways by
means of screws, and the two back rolls, or those nearest to the column
are maintained vertical. The two front ones, however, are provided with
means by which they may adjust themselves to bear along the full depth
of the work, notwithstanding that it may be taper. The construction by
means of which this is accomplished is shown in Figs. 3136 and 3137, in
which A is front and B a back feed roll. The bearings of feed roll A
abut against rubber cushions C, C, whose amount of compression is
regulated by the set screws D, D.
[Illustration: Fig. 3136.]
[Illustration: Fig. 3137.]
[Illustration: Fig. 3138.]
The construction of the saw guides is shown in Fig. 3138, which is a
plan view partly in section. S S are hardened steel plates set up to the
saw by means of studs whose nuts are shown at N N. W is a friction wheel
which supports the saw against the thrust caused by the work feeding to
the saw. The adjustment of the wheel W to the saw is obtained by means
of the wheel H.
The hand wheel H operates the screw _r_ _r_, that adjusts the wheel W to
the saw, the wheel J serving to lock the screw in its adjusted position.
Fig. 3139 represents Worssam's band saw machine, in which the standard
may be set at any required angle for cutting bevels.
When the work is heavy and not easily handled it is preferable to set
the standard and saw at the required angle, rather than to set the table
at an angle and have the saw remain vertical. In Worssam's machine this
is accomplished as follows:
A is the main frame carrying the work table T, and having circular
guideways B, B´, which carry the standard C having guide C´ for working
in the circular guideways B, B´.
The saw-driving wheel D, is carried in bearings provided in C, and,
therefore moves when the standard C is moved.
At the upper end of C, is the slide E, which carries the bearing for the
upper wheel F, this slide being adjusted to regulate the saw tension by
the hand wheel O, whose screw threads into a nut in the slide E. H
carries the front guide G, for the saw, the back guide G´ being carried
by a bracket bolted to C. The back guide is fixed in position, but the
front one is adjustable to suit the height of the work by raising or
lowering it.
The means for setting the saw at the required angle to the work table
are as follows:
At the back of the standard C is a rack J, whose pitch line is an arc of
a circle of which the axis of the guideway C´ is the centre.
Into the rack J fits the worm wheel K, at the bottom of the shaft of
which is a pair of bevel gear wheels L, which are operated by the hand
wheel M.
A band saw machine constructed by Messrs. London, Berry & Orton, is
shown by Figs. 3140, 3141 and 3142, in plate XXIII. The saw-driving
wheel D, has wrought iron arms turned true and screwed into the wheel
hub. The wooden segments have their grain lengthways of the rim, and
between them are placed pieces of soft wood with the grain across the
rim. This acts to keep the joints tight, notwithstanding the expansion
and contraction of the wood.
The upper wheel is adjusted for straining the saw, and for leading the
saw true, by the following construction. It is carried in a U-shaped
frame F, which is pivoted at _y_ to a slide that is gibbed to the main
frame, and by operating the screw shown at X, the frame F is set to the
required level.
To regulate the tension of the saw, the hand wheel K is operated, which
drives the pair of bevel gears J and I, the latter of which operates the
threaded shaft H, whose upper end G connects with the slide which
carries F. Within G is a spring to act as a cushion to the slide, and
thus prevent saw breakage should a chip pass between the saw and its
driving wheel.
The saw guide frame is secured to the main frame at _m´_, _m´_. Upon the
face of _m_, is a slideway for the saw guide arm _n_, which may thus be
adjusted as closely to the upper face of the work as possible.
The weight of arm _n_ is counterbalanced by a rope passing over the
pulley V, and supporting the counterbalance weight _w_. The feed motion
is constructed as follows:
On the same shaft as the main fast and loose pulleys A, B, is the feed
pulley L, which by belt connection drives pulley M, which is on the
shaft W, upon which is a friction disc N, by means of which the rate of
feed is regulated. The feed disc N drives the wheel O; the degree of
contact between these two (N and O) is regulated by means of the weight
T, on the lever U.
On the same shaft as the friction wheel O, is a pinion driving the gear
X, which is on the same shaft as the pinion Y, which drives the two
gears Y´ and Y´´.
Referring now to Fig. 3142, gear Y´ drives the pair of bevel gears Z and
Z´, for the feed roll _e_, and the pair of bevel gears shown at Z´´, the
feed roll _f_. The gear Y´´ drives similar gearing for the feed rolls
_e´_ and _f´_, seen in the plan Fig. 3140.
Referring now to the plan Fig. 3140, and the side elevation, Fig. 3142,
the feed roll _f_ is carried in a frame _g_, which is fitted on the
slideway _d_, _d_, and receives a screw _i_, upon which is a hand wheel
_h_; at the back of this wheel is the lever _j_, which is weighted as
shown, so that the force with which feed roll _f_ grips the work is
determined by the weighted lever _j_, and may be varied to suit the
nature of the work by moving the weight along _j_.
The construction of the gear for feed roll _f´_ is similar, as may be
seen in the plan Fig. 3140, _f´_ being in a slide _g´_, which has a
screw _i´_, and hand wheel _h´_, a weighted lever corresponding to _j_
acting against wheel _h´_. In proportion as _f_ and _f´_ are opened out
to admit thick stuff or work, the hand wheels _h_ and _h´_,
respectively are used to screw the screws _i_ and _i´_ into their
respective slides _g_ and _g´_, and thus maintain the weighted levers in
their requisite horizontal positions. The feed rolls _e_ and _e´_ are
carried in slides _c_ and _c´_, and are adjusted to suit the thickness
of the stuff or work by a hand gearing, which consists of the hand wheel
_a_, seen in the plan and in the front elevation, Fig. 3141, which
drives the pinions _b_ and _b´_, which operate screws for the slides _c_
and _c´_, the latter being a left hand screw. The front rolls _e_ and
_e´_ are therefore held in a fixed position, whereas the back ones _f_
and _f´_ may open out under the pressure of the weighted levers _j_, and
thus accommodate any variation in the thickness of the work.
The rate of feed is varied to suit the nature of the work by the
following construction: The friction wheel O and the hand wheel R are
connected by a yoke _q_, Fig. 3142, at the ends of which are the joints
P, Q, seen in the plan, Fig. 3140. Hand wheel R is threaded to receive
the screw S, and it follows that by revolving R, the friction wheel O
may be moved towards the centre of the friction disc N, which would
reduce the velocity with which N would drive O, and therefore reduce the
rate of feed. If the friction wheel O be moved from the position it
occupies in the plan Fig. 3140, to any point on the other side of the
centre of the friction disc N, the direction of feed motion would be
reversed.
A band saw machine for the conversion of logs into timber, and
constructed by Messrs. London, Berry & Orton, is shown in Fig. 3143. The
logs are fixed to the carriage by dogs and the carriage traverses the
log to the feed.
RECIPROCATING CROSS CUTTING SAW FOR LOGS.--The machine shown in Figs.
3144 and 3145 is designed for the purpose of cutting heavy and long logs
into convenient lengths preparatory to cutting the logs up in other
machines, and it is usually therefore placed at the entrance to the
mill, where it is of immediate service as the lumber comes into the
building.
The machine here shown is intended for logs up to 36 inches in diameter,
is simple in construction, requires very little foundation, is easy to
handle, and occupies but very little room.
The saw is here fed mechanically to its cut, whereas in some machines it
is fed by its own weight, and therefore requires great care to be taken,
when the saw is finishing its cut, in order to prevent it from falling
after it has passed through the log.
Fig. 3145 is a side elevation and Fig. 3144 a plan of the machine, in
which A is the frame of the machine on which are the bearings for the
shaft B carrying the fast pulley C, loose pulley D and fly-wheel E at
one end, and at the other, a crank disc F, whose pin is shown at G. This
drives the saw K through the medium of the connecting rod H.
The saw is fast at the butt end to along slide J, J, which works in a
long guide formed on the face of the swinging frame L, which pivots at
one end on the shaft B and at the other is carried by a slide P, on the
vertical slideway M, and is fed down the same to give the saw its cut by
the screw whose hand wheel is shown at N.
V is a second guide for the saw, and being connected to the slide feeds
down with the saw until it meets the log.
A counterweight W balances the weight of the slides and saw, so that
there being a pit beneath the balance weight the saw and its guides may
be raised so that the saw stands out of the way when not in use. Y is a
dog for holding the log, which is also blocked by the wedges Z Z´.
[Illustration: Fig. 3146.]
The construction of the main bearing is shown in Fig. 3146, in which it
is seen that the hub or boss of the loose pulley is much longer than
that of the fast one, thus providing a large amount of bearing surface,
which is advantageous because the belt will remain longer at the loose
pulley than it will on the tight one. The sleeves or bushes in which the
shaft runs afford a simple means of renewal to restore the fit when the
shaft has worn loose in its bearings.
It is obvious that as the guide frame L is pivoted to the shaft B, it
carries the end of the saw (as it is fed down) in an arc of a circle of
which the axis of B is the centre, whereas the slideway M is straight,
and slide P therefore moves in a straight line instead of in the
required arc. Provision however is made to accommodate these two motions
as follows:
[Illustration: Fig. 3147.]
[Illustration: Fig. 3148.]
Fig. 3147 is a sectional view of the slides on the slideway M and Fig.
3148 a plan of the same. The hand wheel N corresponds to N in Fig. 3145.
Upon the vertical slideway (in Fig. 3145) of the standard fits the slide
P, which has a horizontal slideway for the slide R, which is free to
slide automatically, having no screw or other device to restrain it,
save the guide frame L, and therefore as this frame is lowered to feed
the saw the slide R moves automatically to accommodate the arc of a
circle in which the guide moves on account of being pivoted at B.
HORIZONTAL SAW FRAME.--This machine is designed for the more expensive
woods, such as mahogany, and is finding much favor because it will cut
at a very high speed, the saw travelling about 150 feet per minute.
[Illustration: _VOL. II._ =LOG CROSS-CUTTING MACHINE.= _PLATE XXIV._
Fig. 3144.
Fig. 3145.]
[Illustration: Fig. 3143.]
The roughest shaped trunk may be easily fixed on the travelling table,
and a thin saw may be used as it may be very tightly strained. This
machine is used either for breaking down timber, or for converting it
from the log to any desired thickness, the thickness of the boards being
very readily and easily varied.
The machine consists essentially of a framework carrying either one or
two very thin and tightly strained saws operating horizontally and
cutting on both strokes, so that the feed is continuous, the
construction being as follows:
[Illustration: Fig. 3150.]
Referring to Figs. 3149 and 3150, A is a base plate or bed carrying two
uprights or standards B, B, having guideways C, C, for the cross-head D,
which has slideways E, E´, for carrying the frame F, F, which carries
the saw G, which is guided on each side of the work by the guides H, H´.
The frame F, F is connected to the slides J, J´, and has the rod K, to
which the connecting rod pin L is attached, and the rod M, which acts as
a stretcher. A connecting rod P, connects the pin L to the crank pin Q,
on the crank Q´, which is driven by belt from the pulley T, a fly-wheel
being provided at S.
It is obvious that as the crank revolves the saw reciprocates, its line
of motion being determined by the guideways E, E´.
The construction of the saw is shown in Fig. 3151, and it is seen that
for half its length, the teeth are formed to cut when the saw moves in
one direction, while for the other half the teeth slope in the opposite
direction, and are therefore arranged to cut when the saw is on the
opposite or return stroke, and the construction whereby the saw is
enabled to cut on both strokes is obtained as follows:
[Illustration: _VOL. II._ =HORIZONTAL SAW FRAME.= _PLATE XXV._
Fig. 3149.]
Referring to Fig. 3149, the two slides E, E´, on which the saw-carrying
frame F F slides, are not in line or parallel one with the other, but
each slide is at an angle of about 85 degrees to the line of feed, so
that as frame F is reciprocated at each stroke, one end of the saw
advances towards the cut, and the other recedes from it, thus causing
the saw to cut first on one half and then on the other of its length,
one half cutting on the forward, and the other on the return stroke.
[Illustration: Fig. 3151.]
The studs or saw-buckles for attaching the saw to the frame are shown in
Fig. 3151, in place on the ends of the saw, the part I, that fits in the
frame F, Fig. 3149, being squared so that the saw cannot be twisted in
tightening up the nuts of the saw-buckle.
The belt works for driving the saw are arranged as follows: at T are the
fast and loose pulleys for driving pulley R, the belt passing from T
over two pulleys (shown dotted in, Fig. 3149), U, U´, whence it
stretches to the crank driving pulley R, whose bearing is provided on
the cross-head, so that the two move together when the cross-head is
altered in height from the work-table or carriage, to accommodate
different thicknesses or diameters of logs.
It is obvious that in proportion as the cross-head is set nearer to the
carriage, the belt from T to U, U´ would become slack; provision is made
however, to prevent this as follows:
Pulley U, is carried on a frame or swing lever X, to which is attached
by rope V the weight W, which therefore regulates the tension of the
belt.
The cross-head D may be raised or lowered by belt power or by hand, as
occasion may require, the usual course being to move it to nearly the
required position by belt power, and then complete the adjustment by
hand, a graduated scale being provided as shown, whereby the rack can be
set to cut the required thickness of plank without measuring the timber.
The belt motion for raising or lowering the cross-head is obtained by
the pulleys at Y, the wheel for the hand adjustment being shown at Y´.
In either case the bevel gear wheels Z, Z´ operate, respectively, a
vertical screw engaging a nut on the cross-head.
The log feed is obtained by a motion separate from the return motion,
there being three rates of feed and a quick return motion, the
construction being as follows:
Referring to Figs. 3149 and 3150, a is a belt pulley fast on the crank
shaft, and driving pulley _b_, which is also shown dotted in. Pulley _b_
drives the vertical shaft _c_, on which is the cone pulley _d_, having
three steps, and which drives (by means of belt _d´_) cone pulley _e_,
on which is a worm _f_, driving the worm wheel _g_, which runs idle on
its shaft unless engaged therewith by means of the clutch _h_. The shaft
of worm wheel _g_ is omitted in Fig. 3149, so as to leave the
belt-shifting mechanism for pulleys _q_, _q´_ exposed to view. On this
shaft however is a pinion driving the gear wheel _k_, on whose shaft is
a pinion _l_, driving the gear _m_, which engages the rack _n_, on the
under side of the carriage.
The clutch _h_ is engaged by the lever _i_, to the upper arm of which is
attached the rod _j_, _j_, from the lever _p_, hence operating _p_
(which is done by hand), back and forth, throws clutch _h_ into and out
of gear with the worm wheel _g_, and puts the carriage feed on or throws
it out, according to the direction in which _p_ is moved.
The upper end of shaft _c_ is carried in a bearing on the cross-head,
and is provided with a featherway or spline, so that as the cross-head
is raised or lowered the upper end of _c_ passes through its upper
bearing, and the pulley _b_ travels with the cross-head. The three rates
of carriage feed are obviously obtained by means of the three steps on
the cone pulleys _d_ and _e_.
We have now to explain the construction of the mechanism for traversing
the table back, and giving it a quick return motion, or in other words a
quicker motion on the back than on the feed traverse, and this is
arranged as follows:
_q_, is a fast and _q´_, _q´´_, are loose pulleys, one driven by an open
belt _r_, Fig. 3150, and the other by a crossed belt _r´_, from a
countershaft. The belt-shifting forks are operated by lever _s_, whose
upper end engages with the rod _t_, which is operated by the lever _u_.
The loose pulleys _q´_ and _q´´_ are twice as wide as the fast pulley
_q_.
Now suppose that lever _u_ is moved to the right, and the belt would be
moved from the loose pulley _q´´_ to the fast pulley _q_, while the
other belt would merely be moved or shifted from one to the other side
of loose pulley _q´_.
Similarly if lever _u_, be moved to the left, the belt on the loose
pulley _q´_ will be moved on to the fast pulley _q_, and the belt on
pulley _q´´_ would simply be moved across the face of the pulley, and as
the countershaft pulleys for the two pulleys are of different diameters,
therefore two rates of motion are obtained.
The shaft _v_, on which pulley _q_ is fast, drives the pinion _l_, which
drives _m_, the latter gearing with the rack beneath the carriage.
The carriage is guided by the wheels _z_, which are secured to it, and
run on the iron guideways _z´_, the flanges of the wheels preventing
side play, and causing the carriage traverse to be in a straight line.
WOOD-PLANING MACHINES.
[Illustration: Fig. 3152.]
The simplest form of planing machine for wood work, is the hand planer
or buzz planer, as it is termed, an example of this class of machine
being shown in Fig. 3152, which has been designed and constructed by
George Richards, for the use of pattern-makers.
It consists of a frame carrying a revolving shaft, which is by some
called the _cutter head_, and by others the cutter bar, and to which the
cutters or knives are attached.
The work is rested upon the work table, or else pressed against a guide
or _fence_, and fed by hand over the revolving knives, whose cutting
edges protrude above the surface of the table, to the amount of the
depth of cut it is intended to take.
[Illustration: Fig. 3153.]
In this example, however, the table is made in two sections, the front
one of which is below the cutter edges to an amount equal to the depth
of the cut, and the back one level with the cutter edge, when the latter
is at its highest point in its path of revolution, the construction
being shown in Fig. 3153, in which J, J, represents the top part of the
main frame of the machine, C the cutter head, B the front or feed table,
A the back or delivery table, and W a piece of work being fed in the
direction of the arrow.
Upon the upper surface of the frame J, J, and on the feed side of the
cutter head is the carriage G, to which are pivoted two links L, L,
which support the feed table B. At D is a hand wheel whose screw has
journal bearing in a lug from the table, while the screw threads into a
nut provided in the carriage. Obviously then by operating the hand wheel
D, carriage G is moved along the top of the frame J, and the height of
table B is adjusted. Thus if the carriage G is traversed to the left,
the link L would fall more nearly to a horizontal position, and table B
would lower. Or if G were moved to the right, links L would stand more
nearly vertical, and table B would be raised, it being understood that
table B is not permitted to move endways. Similarly by means of hand
wheel C, carriage H may be moved to adjust the height of table A.
By this construction, the work can bed fairly on the delivery side, as
well as on the feeding side of the cutter head, which is not the case
when a single table is used.
It is obvious that the work must be fed in opposition to the pressure of
the cut, which endeavors to push the work back from the cutter, and this
limits the size of work that the machine can operate upon.
[Illustration: Fig. 3154.]
The work can be fed easier however, with a cutter skewed or set out of
line with the axis of the cutter head. Thus in Fig. 3154, is the common
form of cutter head, carrying two knives placed diametrally opposite, so
that the weight of one counterbalances that of the other, and the head
will therefore run steadily and smoothly. The knives K, K´ are here set
parallel with the axis of the cutter head, hence the whole length of the
cutting edge meets the work at the same instant, and a certain amount of
time must pass after one cutting edge has left the work before the other
cutter edge meets it.
[Illustration: Fig. 3155.]
This is remedied by the construction of cutter head shown in Fig. 3155,
in which three cutters are used, and each cutter is set askew, or out of
parallel with the axis of cutter head, so that the knife begins to cut
at one end, and the cutting action gradually extends to the other, hence
the cutting action is more continuous and uniform, and better work is
produced, while less power is required to drive and feed the machine.
[Illustration: Fig. 3156.]
Fig. 3156 shows a cutter head with two skew cutters.
The cutter head is provided with a cover or guard, which is arranged as
follows: In the table is cut a groove or slideway, in which a slide
fits, and to this is attached a thin sheet-iron guard. To the slide is
attached a weight, which draws the guard back to the fence after the
work has passed over the cutter head. By this means the guard covers all
the knife edge that protrudes beyond the work, no matter what the width
or thickness of the work may be; the guard can however be fixed in
position when a number of pieces of the same size are to be planed.
The fence provides a guide surface for the work, and its face may be set
at any required angle to the surface of the work table. Suppose, for
example, that the sides or edges of a piece of work require to be at an
angle of 100 degrees to the top and bottom surfaces, then the top
surface may be planed first, and the fence being set at an angle of too
degrees to the table surface, the top of the work may be pressed to the
surface of the fence while fed across the cutter, and as a result, the
side or edge will be planed at 100 degrees to the top.
ROLL FEED WOOD PLANING MACHINE.
[Illustration: Fig. 3157.]
Fig. 3157 represents a roll feed wood planing machine, designed and
constructed by George Richards & Co., of Broadheath, near Manchester,
England, the construction being more fully shown in the detailed figures
following. The machine consists essentially of a framework, carrying a
cutter head with two knives, and having a pair of feed rolls, in front
and a pair behind it. The front pair feed the timber to the cutter head
and the back pair deliver it from the cutter head.
[Illustration: Figs. 3158, 3159.]
Each pair of rolls is geared together, so that both the top and bottom
rolls act to give a positive feed. Immediately in front of the cutter
head and between it and the feed rolls (_i. e._ the front pair of
rolls), is a pressure bar extending across the full width of the
machine, and having at its lower extremity a steel spring which presses
the work down to the table, and thus causes it to be planed of an equal
thickness throughout its length. Immediately behind the cutter head and
between it and the delivery rolls (_i. e._ the back pair of rolls), is a
pressure bar that also extends across the machine and prevents the
timber from rising up from the table after it has passed the cutters,
all timber being found to have a tendency to rise after having been
acted upon by the cutters. The arrangement of the feed rolls, delivery
rolls and pressure bars is shown in Fig. 3158, in which T, T, T,
represents three sections of the work table and W, W, a piece of work
passing through the machine in the direction of the arrow. Feed roller F
is fluted to increase its grip upon the work and insure a positive feed.
The lower feed roller F´, and the lower delivery roller D´, are fixed in
position, their upper surface projecting above the work table to about
1/100 inch. This is necessary to take the thrust of the upper rolls (F,
D) and prevent them from forcing the work down upon the surface of the
table with an undue amount of pressure, which would induce friction and
consume an unnecessary amount of power in driving the rolls. The method
of adjusting the lower rolls will be explained presently.
Between the cutter head C and the feed roll F is the pressure bar P, and
behind the cutter head is the pressure bar B, both these bars being more
clearly seen in Fig. 3159, in which the work W is shown entering the
machine, and the lower rolls and work table are removed.
Pressure bar P has at its lower end a steel spring J, Fig. 3159, and is
supported at each end by circular links Y, projecting into grooves
provided in the main frame of the machine, as shown in Figs. 3160 and
3161, in which C is the cutter spindle, Y the circular link at the end
of pressure bar P, and _y_ the circular link at the end of pressure bar
B, the two fitting into the one stepped groove.
[Illustration: Fig. 3160.]
[Illustration: Fig. 3161.]
This groove is concentric with the cutter spindle C, so that the
pressure bars keep at a positive or equal distance from the edges of the
cutter, no matter what the thickness of the work or the depth of the cut
may be.
[Illustration: Fig. 3162.]
In Fig. 3162, the work is shown passing beneath the two upper rollers,
and the spring J (which extends the whole length of the pressure bar),
is depressed from the weight of the bar. By this construction, the work
is pressed to the table at a point as close as possible to the cutters.
The pressure bar P cannot drop beyond a certain point, because of its
tail piece _y´_, Fig. 3160, which rests on the top of the frame at _y´´_
when the bar P has fallen to its required limit.
The feed pressure bar P is bolted to its circular links, as shown in
Fig. 3162, in which Y is a part of the circular link which is bolted to
the pressure bar P.
The delivery pressure bar B (Fig. 3160) is riveted to and forms part of
its links _y_. It acts through the medium of spiral springs _s_, which
are carried in cases or boxes _s´_, which overhang the end of the bar B.
A set screw _s´´_ regulates the pressure of the spring, and a screw _a_
(Fig. 3162) regulates the height of the pressure bar.
The adjustments of the feed and delivery rollers are made as follows:
The feed pressure is obtained through the medium of weights, shown at W,
W´, in Fig. 3163, upon the bars A, A´, whose ends are pivoted to the
lower ends of links _m_, _n_, the upper ends of which are pivoted to the
side frame of the machine.
Bar A engages or rests at _e_, on a lug or projection on the link I,
which fits in a recess provided in the side of the frame. This link I,
extends up and has a bearing to receive the feed roller (F, Fig. 3160),
whose driving gear is shown at O.
It is obvious therefore, that the amount of pressure on the feed roller
F may be varied by moving the weight W along the bar A.
Similarly for the delivery pressure roller, the weight W´ is adjustable
along the bar A´, which is pivoted to link _n_, and rests upon I at
_e´_. The link I´ is guided in ways in the side frame of the machine,
and at its upper end carries the delivery roller D, whose driving gear
is shown at O´ (Fig. 3163).
It is obvious that there are bars A, A´, and links I, I´, on both sides
of the machine, so as to adjust the feed rollers at both ends.
The work table and the two lower rollers are adjusted for different
thicknesses of work as follows:
Between the two main side frames M and M´, Fig. 3164, are two frames
having corresponding inclines or slideways, of which the upper carries
the work table and the lower rolls.
[Illustration: Fig. 3163.]
The lower incline sits on ways K, K, Fig. 3164, cast on the side frame,
and is capable of being moved endwise by means of the hand wheel R,
Figs. 3163 and 3164, which operates a screw threaded into the lower
incline. When the lower incline is moved endways, the upper one, which
carries the work table, is moved vertically, and as the lower feed rolls
are carried by the upper incline, and the upper rolls are guided to move
vertically only, the lower rolls maintain their position beneath the
upper ones, or in other words, the table and lower rolls move together
in a vertical direction only, when the lower incline is operated.
The lower rollers run in bearings formed in the links Q, Q, Fig. 3160,
which are pivoted at their other ends to the upper incline. On the sides
of the incline are lugs through which pass adjustment screws _z_, which
by operating beneath the outer ends of the links Q, Q, adjust the
heights, bearings of the lower rollers so that the uppermost point on
the circumference stands about 1/100 inch above the level of the work
table surface.
The upper surface of the lower incline is shown by the dotted line _f_,
_f_, _f_, in Fig. 3163.
We may now consider the means employed to drive the rolls, first
remarking that the upper rolls F and D, are given a motion slightly
quicker than the lower ones, so as to cause them to clean themselves
(from particles of wood that might otherwise cling to them), by a sort
of rubbing action which is due to their velocity being greater than the
lower rolls and the work. This rubbing action is due to the fact that
the work has the slower motion of the lower rollers, resisting the
quicker motion of the upper ones, and as a result there is a certain
amount of slip between the upper rollers and the work.
Another and important feature, is that the upper delivery roller (D,
Fig. 3260), is placed from 1/4 to 1/2 inch nearer to the cutter head
than the bottom delivery roll, which assists in keeping the work down
upon the table.
The mechanism for driving the feed rolls is shown in Figs. 3163, 3164
and 3165, in which L, L are the pulleys which receive motion from a
countershaft, and drive the cutter head, being fast upon its shaft, as
is also the pulley S, which connects by belt and drives pulley T, on
whose shaft is the stepped pulley U, which connects by a crossed belt to
pulley V, which drives the feed gear through the medium of the pinion
_a_. The two steps on pulleys U and V, obviously give two rates of feed.
The pinions O and O´, both receive motion from the gear wheel E, this
part of the gearing consisting of gears _a_, _b_, _c_, _d_ and E, and as
both pinions receive motion from the same gear, their revolutions are
equal. The lower feed roll is driven by the pinion _p_, which gears with
and is driven by wheel _d_, whose face is broad enough to meet _p_,
which sits nearer to the frame than pinion O does, so that the teeth of
_p_ may escape those of O.
Now the velocities of all the wheels O, O´, E, _d_ and _p_, will be
equal at the pitch circles, because they constitute a simple train of
gearing. Thus if _d_ moves through a part of a revolution equal to the
pitch E, then O and O´ will move through the same distance, because the
wheels are in continuous gear. Now as _d_ drives _p_, therefore the
velocity of _p_ must at the pitch circle be the same as _d_, let the
numbers of teeth in the respective wheels be what it may, and it follows
that the velocities of O, E, _d_ and _p_ are at the pitch circles equal.
But by making the diameter of the upper roll greater than the pitch
circle of its gear O, and the diameter of the lower roll correspondingly
less than the diameter of the pitch circle of its pinion _p_, the
velocity of the circumference of the upper roll will be greater than
that of the lower roll, and the rubbing action before referred to with
reference to the upper roll will thus be induced.
[Illustration: Fig. 3164.]
Referring now to the lower delivery roll, its pinion _x_ receives motion
through gear _w_, which is also driven by gear E, which has a broad face
so as to gear with _x_, which is behind and below gear O´. In this case
the circumstances are the same, as will be seen from the following.
An inch of motion of the pitch circle of E will produce an inch of
motion at the pitch circles of O´ and of _w_ and _x_, hence the
velocities of the pitch circles will be equal, and if the diameters of
the upper and lower rolls are equal, or the same as the pitch circles,
the velocities of the circumferences of the respective rolls will be
equal, but by making the diameter of the upper delivery roll greater
than that of the pitch circle of its pinion, and that of the lower roll
less, a rubbing action is induced between the roll and the work, and
this rubbing action will keep the roll clear of any dust, etc., that
might otherwise cling to it.
The cutter head is formed triangular, as in Fig. 3166, carrying three
knives. The knives are set at an angle to the axis of the cutter bar or
cutter head. When the knives are at an angle, they take their cut
gradually, and the cutting action is more continuous, which diminishes
the vibration of the machine, and causes the finished surface to be
smoother. Furthermore, the knives take a shearing cut, and therefore cut
more easily and freely.
In some practice the knives are made spiral, but spiral knives are
difficult to bed properly to the cutter head, and also difficult to
grind. The cutter head is made of a solid mild centre steel forging, and
runs in phosphor bronze journals, in which it has about 1/8 inch end
play, which tends to distribute the oil along the bearing. It is driven
by a pulley at each end, the pulleys seating on a cone.
The amount of skew is about 3/4 inch for a cutter head carrying a knife
30 inches long, and about 3/8 inch for a cutter head whose knives are 10
or 12 inches long.
[Illustration: Fig. 3165.]
[Illustration: Fig. 3166.]
[Illustration: Fig. 3167.]
Figs. 3167 and 3168 represent a machine in which there are three feed
rolls and one delivery roll, all being driven.
First there is the pair of feed rolls the bottom roll of which is set
sufficiently above the surface of the table to relieve the work of
friction upon the table.
The work next meets an upper feed roll that acts to force the work down
to the table surface (there being in this case no lower feed roll).
After passing the knives, the work is carried out by a delivery roll
that also acts to keep the work down to the table face.
All three upper rolls are provided with rubber springs in the casings H,
H´.
P, P, are the pulleys for the cutter head and B, those for the feed
works, which have two speeds. The feed is thrown in and out by the lever
_d_, which moves the pinion D endways and engages or disengages it from
its gear wheel.
[Illustration: Fig. 3168.]
[Illustration: Fig. 3169.]
Figs. 3169, 3170, 3171 and 3172 represent a pony planer, by P. Pryibil.
[Illustration: Fig. 3170.]
Referring to the sectional view Fig. 3170, the work table slides in
vertical slideways S, in the side frames, the elevating screw being
operated by the bevel gears at G, which receive motion from the hand
wheel M in Figs. 3170 and 3171. There are four upper rolls, marked 1, 2,
3 and 4 respectively, and of these the first two are fluted in the usual
way. There are two lower rolls, marked respectively 5 and 6. The fluted
feed rolls 1 and 2 are weighted, the weight lever acting on the rod R,
which at its upper end connects to the cap Y, which covers the bearings
of feed rolls 1 and 2. By this construction the two rolls are acted upon
by the same weights and levers, the rolls being of course weighted at
each end, or in other words on both sides of the machine.
The delivery rolls 3 and 4 receive their pressure by the construction
shown in Fig. 3172, the bearings of the rolls being held down by rubber
cushions receiving pressure from the cap E, screwed down by the bolt and
nut.
The rolls 5 and 6 are idle rolls, and are set to just relieve the work
from undue pressure on the work table.
By this construction of feed mechanism the following ends are attained.
First, sufficient feed power for heavy cuts is obtained without driving
the lower rolls. Second the work is held to the table on both sides of
the cutter head, hence there will not be left on the end of the work the
step that is left when but two upper and two lower rolls are used, and
which occurs because the work falls after leaving the feed rolls,
whereas, in this machine the work is held to the table by rolls 2 and 3.
The cutter head H, Fig. 3170, has in front of it the pressure bar P,
whose lever is shown at L and the weight at W. On the delivery side of
the cutter head is a pressure bar _r_, which is acted upon by a spiral
spring in the box C. In the engraving to the right of Fig. 3170 the
knife K is shown in action on a piece of work, and it is seen that the
end of the pressure bar P coming close to the edge of the knife prevents
the pressure of the cut from splitting or splintering off the end of the
work at _a_, and therefore acts as what is termed a _chip break_.
Furthermore, the sides of the cutter head between the knives being
hollowed out gives the shavings _s_ room to curl in and prevent the work
from splintering at the end when the cut is terminating.
BALANCING CUTTER HEADS AND KNIVES.--Planer knives must be balanced as
accurately as possible, in order that they may run steadily and
smoothly, and therefore produce smooth work.
The first requisite for proper balancing is that the cutter head itself
be properly balanced, and in order that this may be the case the faces
forming the knife seats must be equidistant from the axis of the cutter
head, and the journals must run true, being best tested on dead centres.
The holes for the cutter bolts should all be drilled to the same depth,
and tapped equally deep. The faces or seats for the knives should be
parallel one to the other, and this may be tested by a pair of straight
edges, one pressed to each face and the width between them measured at
each end, or if a long surface plate is at hand, one face of the head
may be rested on the surface plate, and the straight edge ruled on the
other face, and its distance measured from the surface plate at each
end, with a pair of inside callipers delicately adjusted.
A straight edge rested lengthways along the knife seat of the head and
projecting over the journal will show whether each knife seat is
equidistant from the journal as it should be, the measurement being
taken with a pair of inside callipers adjusted to just sensibly touch
the journal and the straight edge. This measurement should be taken at
each end of the head.
In all tests made with straight edges, the straight edge should be
turned end for end and each measurement repeated, because, if the
straight edge is true, turning it end for end will make no difference to
the measurement, while if the straight edge is not true the measurement
will vary when the straight edge is reversed.
If the cutter head is square, the straight edge tests may be applied to
all four of its faces, and they may then be tested with a square, and if
the head shows no error under these tests, and the bolt holes or slots
are of equal diameter and depths, the head will be correct as far as it
can be tested without running it.
[Illustration: Fig. 3171.]
[Illustration: Fig. 3172.]
A cutter head may be roughly tested by placing it between the lathe
centres, both centres being oiled and delicately adjusted so as to just
prevent end motion of the head without perceptible friction when the
head is revolved by hand.
The first thing to test is whether the journals run true, which may be
tested by a pointer fastened in the slide seat, and moved up to just
touch the journal. The pointer should be soft, and not a cutting tool,
unless indeed it be set so high in the slide rest that it cannot cut.
If the journals do not run true, the next thing to test is whether the
body of the head runs true to the centres, which may be done by first
setting a pointer to just touch the extreme corners of the head at each
end and in the middle of its length, and if there is an error in the
same direction as the test at the journal shows, then the centres of the
head are out of true, and must be corrected before a test of this kind
can be proceeded with.
But the body of the head may show true at the corners while the journals
do not run true, and if this is the case we may further test the body of
the head as follows:
With the lathe slide rest at one end of the head we may set a pointer so
that it will just pass on the flat of the cutter seat and make a mark
when the slide rest is traversed along the lathe bed. We then move the
slide rest so as to bring the pointer to the journal end of the head;
give the head a half a revolution on the centres and try the pointer on
the flat of the cutter seat, and if it makes a mark of equal strength,
then two faces of the head are equidistant from the axis of the head.
The next thing to do is to make the same test at the other end of the
head, and in order to do this without moving the pointer, and therefore
without altering its adjustment, we must move the slide rest so as to
bring the pointer opposite to the lathe centre, and out of the way of
the body of the head, and take the cutter head out of the lathe and turn
it end for end, and then repeat the test with the pointer, which will
show whether both ends of those two flats are alike.
This test we repeat on the other two faces of the head, and if they show
true, then the head is true, except the journal, which must be made true
with the head.
This testing will clearly show any want of truth in either the head or
the journals, and in what direction correction needs to be made.
Now suppose the above tests do not disclose any error, either in the
journals or in the head, and we may continue the tests by revolving the
head by hand between the dead centres, and apply the pointer to the
journals while the head is revolved as quickly as possible; as, however,
the head cannot be revolved very fast in this way, we may adjust the
lathe centres as before described, and revolve the head as rapidly as
possible by hand, and letting it come to rest mark which side is at the
bottom, and if on several tests the same side comes to the bottom of the
plane of revolution at each test, that side is the heaviest and must be
corrected. If it is found to be a flat side or cutter seat that comes to
rest at the bottom, the correction can be made by deepening the bolt
holes on that side, measuring to see which bolt hole is the shallowest,
and making all as nearly as possible equally deep.
If the head has T slots instead of bolt holes, the slots may be cut or
filed out to effect the balance, care being taken to make the slot equal
in distance from the edges of the cutter seat face.
The next essential in order to have a properly balanced cutter head is
that the bolts and nuts all weigh alike, and that the bolts be of the
same length. The bolts should be turned to an equal diameter of equal
length and threaded for an equal distance along the body of the bolt,
and the nuts should be of equal depth and all fit accurately to the same
wrench, and the weight of the bolts and nuts when put together may then
be equalized by reducing the heads of the heavy ones.
We now come to the balancing of the knives, which must be made of equal
thickness and width throughout, with the slots for the bolts of equal
widths and depths.
The knives require to be as accurately balanced as it is possible to
make them, for otherwise they will cause the head to jar and vibrate
violently, thus producing rough work. The knives weighed individually
may be of the same weight, and yet the head may run out of balance by
reason of one end of a knife being heavier than the other end.
[Illustration: Fig. 3173.]
Fig. 3173 represents a machine constructed by J. A. Graham & Co., for
balancing planer knives, moulding knives, cap screws, and knives in
rotary cutter heads of all kinds.
Let it be supposed that the knives are the same specific weight, but
that there is an excess of weight at one end; when revolving on the
head, a violent jarring or throwing will be caused by reason of the
excess. The knives could be reduced to the same specific weight by the
aid of common grocers' scales, but the ends could not be made the same
proportional weight as on such balance.
In the cut S S is the base of the scale; L, M the standards for the
support of the scale beams B B and K K.
_d_, _d´_ are two pivots of the scale beams.
D is the loop on which the pivot _d_ works.
E is a joint in the loop.
D´, E´, and F show the loop and connection.
_c_ is the sliding table which has the stop _c´_, and is adjustable for
different lengths of knives.
_a_ _a_ is a knife in position for balancing endwise.
G is a slotted piece, and is held to the scale beam by the screw _v_.
The slot in G is shown at G´, and limits the travel of the scale beams.
H is an angular piece fastened to the lower scale beam, and receives the
screw J.
I is a small weight used for fine adjustment.
O, O are weights which slide along the scale beam K K, and are held in
place by the thumb screws P, P.
N shows side view of weight, which is so constructed as to allow it to
be easily removed. In using the machine the lightest cutter or knife of
the set is first found and its two ends balanced, by turning it end for
end on the scales, and reducing the weight of the heavier end. The other
knife or knives are then balanced without disturbing the adjustment of
the machine as made for the first knife.
ENDLESS BED OR "FARRAR" WOOD SURFACING MACHINE.
This class of machine has a bed composed of slats which are connected
together and driven by a chain.
Fig. 3174 represents an endless bed double surfacer constructed by the
Egan Company. The upper cylinder may be raised or lowered to suit the
thickness of the work. The front feed roll is in two sections, enabling
two boards of unequal thickness to be planed simultaneously to an equal
thickness. These rolls are held to the work by a leaf spring, as shown
in the cut, the tension on the spring being adjusted by the screw at D,
_d_ serving as a check-nut.
A longitudinal section through the centre of the machine is shown in
Fig. 3175. The spring S bears at each end on a block T, which carries
the bearings for the feed roll. Feed roll M is held down by the screws
E, E, acting on a rubber cushion or spring, and is provided with a
scraper to clean it from dirt, etc.
The travelling bed is composed of slats S connected together by the
chain shown, and resting upon slides A, A, supported by the girts B, B.
The chain is operated by the spur or sprocket wheel W, and is therefore
pulled and not pushed, which tends to keep it under tension, and
therefore rigid upon the top side.
The ends of the slide A, A are depressed so that the slats shall not
tilt up at one corner above the level of the slide when in the positions
denoted by S´.
The lower cutter head is carried in a sliding head or frame J, adjusted
for height by the gears at H, which operate screw _h_, while the bed
above it is adjusted by the gears at F. It is obvious that the bottom
surface of this bed is set at the same height as the lowest point in the
path of revolution of the cutting edges of the knives of the front
cutter head or cylinder. The upper delivery roll N is provided with a
scraper.
PLANING AND MATCHING MACHINE.
Planing and matching machines that are made narrow to suit the planing
and matching of boards for flooring are sometimes called _flooring_
machines, the distinctive feature of a flooring machine being that it is
(unless in the case of a double machine) made narrow (because flooring
boards are narrow), and this makes the machine very stiff and capable
therefore of a high rate of feed and speed.
[Illustration: Fig. 3174.]
[Illustration: Fig. 3175.]
[Illustration: Fig. 3176.]
[Illustration: Fig. 3177.]
Fig. 3176 is a general view, and 3177 a longitudinal section through a
standard planing and matching machine of recent design, constructed by
Messrs. J. S. Graham & Company. The plank passes through two pairs of
rollers before meeting the front cutter head. The side heads then come
into operation cutting (in the case of flooring) the tongue on one side
of the plank and the groove on the other, the under side of the plank
being dressed last.
The machine is built in three widths viz., 8", 14" and 26", each planing
to 6" thick and matching as wide as it planes.
In place of matching heads, heads for beading, rabbeting, or fancy
siding may then be used.
The board R (Fig. 3177) is fed in over the grate _m´_ until it reaches
the rolls E and F´, which are held in place by the boxes fitted to the
roll stand _n´_, and brought to bear on the lumber by means of the screw
_a´_, equalizing bar _m_ and nuts _p_, _p_, together with the lever Y Y
and the weight _x_.
[Illustration: Fig. 3178.]
After the lumber leaves the second pair of rolls, it runs over the bed
plate W (Fig. 3178) and under the shoe L, the duty of which is to hold
the board firmly against the bed plate, and also to break the chips on a
heavy cut. After leaving the shoe it is operated on by the upper cutter
head H, then it passes beneath the pressure bar _g_, which holds the
lumber firmly while it is acted on by the matcher _c_.
[Illustration: Fig. 3179.]
It then passes beneath the cleaner E´´ (Fig. 3177) and under the
delivering roll, which is held down by the weight U in connection with
the lever V and screw _a´_, the top which is shown at C (Fig. 3179). The
board then passes underneath the pressure bar Q (Figs. 3177, 3180) and
over the under cutter S, from which it passes finished.
The pressure bar Q is moved up and down by turning the shaft _a´´_, the
motion of which is given to the screw _h´_ by means of a pair of bevel
gears. _k´_ is also a scraper that cleans the board before it passes
under the pressure bar Q. The under cutter is adjusted for depth of cut
by turning hand wheel A´, which moves the screw U´. The rolls are raised
and lowered by turning the shaft at P (Fig. 3176).
In feeding two boards through the machine, one thicker than the other,
that end of the roll that passes over the thick board can raise up
without taking the pressure off the thin one at the other end of the
roll. This raising mechanism is shown in Fig. 3179. The bevel gear C
works over a ball joint Q´. The shoulder B´ on the screw _a´_ works on
the under side of the ball Q´. The shaft _a_ passes through the tubular
shell B to the opposite end of the roll. The cross tie J is bolted to
the roll box K´´.
C, Fig. 3178, shows matcher hanger in position. It is gibbed to the bed
plate Z by the gib _f_, which is so constructed as to be free from dirt.
The sliding gib _f_ is adjustable for wear. One matcher hanger is moved
by the screw _e_, the other by _e´_. The left hand matcher hanger is
moved by the shaft _l´_ (Fig. 3177), which passes along the side of the
machine until it reaches the shaft _e_, where its motion is imparted to
the screw by means of a pair of spiral gears. An index at the rear of
the machine enables the operator to set the matcher heads to any desired
width. The right hand matcher hanger, together with the guide, can be
moved across the machine by turning the screw _e´_ at the side of the
machine (Fig. 3176).
The upright D which carries the pulley which drives the top cutter head,
or cylinder as it is sometimes termed, is set at an angle so that the
cylinder belt will always be of the same tension.
The top cylinder is raised by the shaft _d_ (Fig. 3176) and screw _b_.
It is held in place by the nut M (Fig. 3177). The bar I ties the
cylinder boxes together. K is held down by the weight I, and yields with
the pressure bar L.
The spindle of the matcher _c´_ (Fig. 3177) is driven by a belt which
comes from the pulley _h_ and passes over the guide pulley _k_, and then
to the pulley _b´_.
The lower end of the matcher is held in place by being gibbed to the
cross tie _p´_, Fig. 3177, which is adjusted and kept in position by the
screw _o´_.
S´ sustains the matcher spindle by means of an adjustable step.
Y´, Fig. 3176, is the feed shaft which drives the gearing that operates
the rolls. The pulley that drives the feed shaft is shown at L´ (Fig.
3176). The belt passes over this pulley and under and over the tightener
pulleys _w´_, _w´_, then to the pulley U´ which is on the feed shaft Y´.
[Illustration: Fig. 3180.]
The apron M´ in front of the under cutter S (Fig. 3180) is easily
dropped to M´´ by loosening the nut R´ and releasing the bolt T´ so as
to allow the apron M´ to drop.
This enables the operator to have free access to the under cutter for
sharpening knives, etc. _z´_ is the bed plate over which the lumber
passes before it reaches the under cutter.
[Illustration: Fig. 3181.]
[Illustration: Fig. 3182.]
A planing and matching machine designed and constructed by Messrs.
London, Berry and Orton is represented in Fig. 3181. In this machine the
upper surface of the board is surfaced first, and the matching second,
the under surface being operated upon the last. The method of suspending
the upper feed rolls of this machine is shown in Fig. 3182, in which A
is an upper and B a lower feed roll. The upper roll A is suspended by
the link C, which is supported by the link D, and also by link E, these
three links forming a parallel motion which guides A in a vertical line.
At F (which is fast to E) is a bearing for the screw G, and the pair of
bevel gears _g_ that drives it. This screw threads into the nut H on the
rod I, which receives the pressure of the bar J and weight K.
The lower feed rolls being larger in diameter gives them increased grip
on the work, and gives it a better base, and also makes it enter and
leave the rolls easier.
Each matcher bracket is fitted with a screw by which it can be moved at
will across the machine, and by turning one other screw with the same
wrench that moves the others, both brackets are firmly set to the slide
and all screws held firmly. There are three changes of feed. The top
cutter head is provided with improved pressure bars, which are set to or
from the head by means of a double eccentric, which, while they can be
set at any desired distance from the knives, limits their movement when
moved towards them, rendering it impossible to get them into the
cutters.
TIMBER PLANER.
The term timber planer implies that plain knives only are used in the
machine, which is therefore intended for producing plane surfaces. It
also implies that the machine is designed for heavy or large work, such
as is found in ship yards, bridge construction or car works, etc., etc.
In such work the cuts taken by the machine are sometimes very heavy, and
as a result the feed works of the machine require to be very powerful
and positive.
Fig. 3183 represents a timber planer designed and constructed by J. S.
Graham & Co., to plane all four sides of the timber at one passage
through the machine.
The timber passes through three pairs of feed rolls before reaching the
first cutter head, which planes the bottom surface.
It then passes to the side heads, which dress both sides simultaneously,
and then passes beneath the cutter head that finishes the upper surface,
and is finally delivered from the machine by a pair of delivery rolls.
The work is passed over roller B, the fence or gauge being shown at B´.
1 and 2 are the first pair of feed rollers, _a_ and _b_ being merely
adjustable intermediate wheels, which by means of the pieces _c´_, _b´_,
may be set so as to connect rollers 1 and 2 together, whatever their
distance apart may be, or in other words whatever the thickness of the
work may be.
[Illustration: Fig. 3183.]
From 1 and 2 the work passes to the second pair of feed rolls 3 and 4,
_c_ and _d_ being the intermediates.
Similarly 5, 6, 7 and 8 are feed rolls, and _e_, _f_, _g_, _h_
intermediates. The first head is shown at K´, the side heads at H, and
the last head at I´, the latter being carried on a sliding head J, which
is secured in its adjusted position by nuts I. On the side of the frame
D on which J slides is a graduated index to denote the adjustment of the
head I´.
[Illustration: Fig. 3184.]
The construction of the parts in immediate connection with the front
cutter head is shown in Fig. 3184. N is the frame corresponding to N in
Fig. 3183, the rolls 5 and 6 also corresponding in the two figures.
Upon N is a slide S having an arm G, carrying the roll G´, which holds
the timber down to the cut of the cutter head K´. The pressure of roll
G´ to the work is given through the medium of the rod _a´_, which
receives the pressure of the equalizing bar _x_, Fig. 3183.
The bottom surface of the timber passes over the bed plate U, Fig. 3185,
which raises and lowers with the lower feed rolls, being connected by
the screw _i_, Fig. 3184, to the bearing box of feed roll 6.
All the lower feed rolls are operated simultaneously by means of the rod
_l_, having for each lower feed roll a worm, driving a worm wheel _l´_
on a screw threaded into a hub _m_ in each feed roll bearing; the crank
for operating _l_ is seen at P, Fig. 3183.
[Illustration: Fig. 3185.]
The passage of the timber through the machine is continued in Fig. 3185,
in which it is seen that after the lower surface of the timber has been
planed it passes from the cutter head K´ to a bed plate V and is thus
supported by a flat and true surface while the side cutter heads plane
the two sides, one of these side heads being shown at H. The side heads
are carried in hangers, one of which is shown at _p´_. It is gibbed to
the under cutter frame U´ by the sliding gib _x_, the left hand head H
being moved across the frame by the screw _f´_. The hanger is held at
the bottom by the gib _t_ and the cross tie _t´_. _p_ is the pulley for
the side head H, the end wear of whose shaft is taken up by the
adjusting screw _s´_, _r´_ being a leather washer, and _r_ the end of
the shaft.
[Illustration: Fig. 3186.]
The top box H´ moves across the machine in the slideway _b´´_, Figs.
3186, _a´´_ being a part of the box H´.
Upon leaving the side heads the timber will have been planed on three
sides and the side surfaces dressed to a right angle with the bottom
surface.
It is then guided to the upper cylinder as follows:
The friction rolls K, K are to relieve the bed A´´ from the pressure due
to the feed roll Z´ and the roll J´, which holds the timber after it has
left the cutter I´, and thus prevents it from vibrating. After leaving
the pressure roll J´, the timber passes under the scraper _d´_, Fig.
3183, and thence to the delivery roll 7, which is held down by the
weight L, in connection with the lever L´.
By means of this construction all the cutter heads act upon the timber
within the short distance of 22-1/2 inches, while the side heads act
within 8-1/2 inches of the under cutter. This is desirable, being
conducive to the production of true work, which it is more difficult to
produce in proportion as the cutter heads are wider apart. This machine
will joint as narrow as 2 inches, and plane as thin as 3/4 inch.
The upper cylinder I´, Fig. 3183, is adjusted for height or thickness of
cut by means of the screw _f_, and is locked in its adjusted position on
D by the nut I.
The feed is started or stopped by operating the hand wheel _o´_.
The upper rolls are raised or lowered simultaneously by power, by means
of the shaft _s_, and the bevel gears _r_, which operate the screw _a´_.
The upper cylinder is driven by belt from the pulley Q, the under
cylinder from Q´ (both these cylinders being driven from both ends). P´
is the driving pulley for the feed belt, which passes to N´, which,
through K´´ and Y´, drives Y, which drives the feed rolls.
The machine will feed from 25 to 60 feet per minute.
PANEL PLANING AND TRYING-UP MACHINE.
This class of machine is employed for the production of true surfaces,
and is now used upon much of the work that was formerly assigned to the
Daniels class of planing machine. In this machine, as in the case of the
Daniels planing machine, the work is secured to the table, which travels
to carry the work to the feed.
Fig. 3187 represents a machine by J. Richards, in which a cutter head
with skew cutters is employed, and a pressure roll is placed in front
and at the back of the cutter head, the construction being as follows:
Upon the main frame are the slideways _t_, _t´_, upon which the
cross-head or cutter head frame Z is carried, the elevating screw S
raising or lowering the frame Z, to suit the thickness of the work. The
cutter head C, whose driving pulleys are shown at P, P, is carried in
frame Z, which also carries the pressure roll in front of the cutter
(the bearing for this roll being shown at R), and a similar roll behind
the cutter. To the frame Z are pivoted the pressure bars B, B´, weighted
with weights W. These bars rest on the cross-heads Y, whose pins _p_ act
on the bearing boxes of the pressure rolls.
The cutter head frame may be raised or lowered, for varying thicknesses
of work, either by hand or by power. The hand movement is obtained from
the hand wheel W, Fig. 3188, which operates bevel gears _b´´_ and _b´_,
the latter being threaded to receive the elevating screw.
[Illustration: _VOL. II._ =TRYING-UP MACHINE.= _PLATE XXVI._
Fig. 3187.]
The power or belt motion for raising or lowering the cutter head frame
is obtained from rope wheel _w´_, which receives motion from the guide
pulleys shown in Fig. 3187. The wheel _w´_ drives its shaft by the
friction cone of its bore, which is forced against the corresponding
cone on the shaft by the hand nut L. The handle _v_, Fig. 3187, is for
operating the upper guide pulley _q_, which acts as a belt-tightening
pulley as well as a guide pulley, and the hand wheel _t_ holds _v_ in
its adjusted position. When _v_ is pushed downwards the rope (E) is
loosened upon the pulleys, and both rope and pulleys remain idle.
[Illustration: Fig. 3188.]
The pulley that drives rope E is shown in Fig. 3189 at R.
The feed motions for the work table are shown in Fig. 3189, and the
construction is such that for ordinary work the table has a quick return
motion, while for heavy work the feed and return motions of the table
are speeded alike.
The driving pulley B, Fig. 3189, for operating the feed mechanism,
receives motion by belt connection from the countershaft, and drives the
shaft on which are the bevel gears _b_ and _d_, and from these gears the
feed motion and quick return are derived, while from gear _e_ and pulley
R the cutter head may be raised and lowered by belt power as occasion
may require. Beginning with the feed motion, the gear _d_ drives gears
_e_ and _f_, which are a working fit on the shaft S. Between these two
gears is the clutch _r_, _r_, which is operated by the handle shown in
the perspective view, Fig. 3187, at _v_.
To operate the feed, clutch _r_ is operated to engage gear _e_ with the
shaft S, upon which is the friction wheel _m_, which engages with the
internal surface of the wheel or drum _g_, which drives the rope wheel
A, which drives the rope for the work table traverse--wheel A and the
rope being seen in the perspective view, Fig. 3187. The shaft N has
bearing in a piece that is virtually a sleeve eccentric, because its
bore is eccentric to its circumference; to this sleeve is attached a lug
_h´_ to which the handle _h_, Fig. 3187, is bolted. Now suppose that
handle _h_ is depressed, and then G will partly revolve wheel _g_ and
cause it to engage with the friction wheel _m_, which will drive _g_,
and therefore A.
Diametrally opposite to _m_ is a friction wheel _n_, which is driven by
the bevel gear _c_, and which is brought into or out of action with _g_
by the eccentric action of sleeve G, it being obvious that when the
sleeve G moves _g_ in the direction of _n_, _m_ is engaged and _n_
disengaged from contact with _g_. Raising the handle _h_ therefore
places _n_ in gear with _g_, which revolves it in the direction
necessary to draw the work table on the back or return stroke.
The return motion of the table is more rapid than the feed motion
because gear _c_ is of smaller diameter than _b_, and _n_ is larger than
_c_ and than _m_.
In the case of heavy work, however, the return motion may be made to
have the same speed as the feed motion by simply moving the clutch _r_
so as to engage wheel _f_ with the shaft S.
The rope groove in the pulley A is waved as denoted by the dotted lines,
and this prevents the rope from slipping, notwithstanding that the rope
envelops but half the circumference of A. The wire rope from A operates
a drum, in which are waved grooves for the table traversing rope which
winds around this drum, and attaches to pins (K, Fig. 3187) carried in
brackets at the ends of the table, and one of which is shown in Fig.
3187, at _z_.
The slack of the rope is readily taken up (as occasion may require) as
follows:
[Illustration: Fig. 3189.]
The pin _k_, to which the rope is fastened, has at one end a squared
head to receive a wrench to revolve the pin and wind up the rope, set
screw _l_ locking the pin after the rope tension is adjusted.
We have now to explain the method of holding the work, which is as
follows:
The side frames forming the bed are bolted to the main frame and form
the ways on which the work table travels. The table frame J, Fig. 3187,
is provided with rollers, which rest on the upper surface of the bed and
reduce the friction.
The table is made in convenient sections bolted to the table frame J,
and at their points of junction the work-holding dogs are placed, the
construction being shown in Fig. 3190, in which T´ is the end of one,
and T´´ the end of another section of the table. Referring now to Figs.
3187 and 3190, upon the edge of the table are the abutment pieces _a´_,
_a´´_, against which the work is pulled by the dog, which is operated by
the screw, which is squared at its outer end to receive the handle M,
Fig. 3187.
The rate of work feed is 30 feet per minute and the quick return motion
is 60 feet per minute.
MOULDING MACHINES.
In moulding machines for light work the feed rolls and cutter head
overhang the frame, such machines being designated as outside moulding
machines.
Fig. 3191 represents a machine of this class constructed by J. A. Fay &
Company.
The table T slides on vertical ways on the main frame, being adjusted
for height by the hand wheel W.
The work while fed over table T is pressed against the vertical face A
by the four springs shown, whose pins swing to suit the width of the
work.
[Illustration: Fig. 3190.]
[Illustration: Fig. 3191.]
The two feed rolls are made up in sections or discs and the pressure bar
is pivoted and has the weight shown to adjust its pressure to suit the
work, and is combined with the bonnet whose shape throws the shavings
outwards from the side of the machine. The particular machine here shown
is constructed substantially enough to permit of its being used for
light planing or work not exceeding 6 inches in width, a head with
planing knives being shown in place on the machine. In a machine of this
kind it is essential that the cutter head spindle and its bearings be
rigid, and with ample journal bearings and free lubrication to prevent
wear, and for these reasons the arbor is of steel running in self-oiling
bearings of large diameter. The arbor frame is capable of lateral
movement to enable an accurate adjustment of the cutters to the work.
The term _sticker_, as applied to a machine of this class, means that it
is suitable for light work such as window sash and door stiles, blind
slats, etc., etc.
Fig. 3192 represents a machine termed by its manufactures (the Egan
Company) a "double head panel raiser and double sticker combined." The
term panel raiser means that the edges of the work may be dressed down
so as to leave a raised panel. To fit the machine for such work the bed
or table T is made wide.
The upper feed rolls are in sections, and the lower one extends nearly
across the bed. The upper feed rolls are held down by a spring, whose
tension may be regulated by a hand wheel with an adjustment at the back
end to give a lead to both rolls. By this is meant that the plane of
revolution of the feed rolls inclines toward the cutter head so that as
the rolls feed they exert a pressure on the work, holding it securely
against the face A.
A long spring extends from the front of the feed rolls past the back or
bottom cutter head, passing as shown beneath the pressure bar, and is
adjustable for height from the bed or table face T by having its ends
pass through two studs in which they may be secured by set screws. This
serves to keep the work down to the surface of T.
The cutter heads for panelling have three cutters set askew or at an
angle to their plane of revolution so as to give a more continuous and a
shearing cut, which is conducive to smooth work.
The bed above the lower cylinder is adjustable for height by means of
the screw at H.
MOULDING CUTTERS.
[Illustration: Fig. 3192.]
In the ordinary or common form of moulding cutter, the front face is
flat and the lower end is bevelled off and filed to shape so as to give
the required shape and keenness to the cutting edges, Fig. 3193 giving
examples of such cutters.
[Illustration: Fig. 3193.]
Cutters of this class must be sharpened by filing the bevelled edge,
which requires considerable skill in order to preserve the exact shape
of the moulding.
SOLID MILLED CUTTERS.
[Illustration: Fig. 3194.]
[Illustration: Fig. 3195.]
In the solid milled cutter the bevelled surface at the cutting end of
the cutter is a plane, and a curved, stepped or other shape is given to
the cutting edge by cutting or milling suitably shaped recesses on the
front face of the cutter as shown in Figs. 3194 and 3195, the former
being a tongue cutter for cutting a groove, and the latter a grooved
cutter for cutting a tongue.
[Illustration: Fig. 3196.]
[Illustration: Fig. 3197.]
Other examples for such cutters are given as follows:
Fig. 3196 represents a cove cutter and Fig. 3197 an ogee. Fig. 3198, a
double beading, and Fig. 3199 a bevel cutter, and it is obvious that by
a suitable arrangement and shape of groove cutting edges of any of the
ordinary forms may be produced.
[Illustration: Fig. 3198.]
[Illustration: Fig. 3199.]
The advantages of such cutters are that the plain bevelled face or facet
of the cutter may be ground (to sharpen the cutter) on an ordinary emery
wheel or grindstone, and the shape of the cutting edge will remain
unaltered, providing that the cutter is always held to the grinding
wheel or stone at the same angle, so that the length of the bevel
remains the same.
A common practice is when making the cutter to so regulate the depth of
the grooves or recesses in its face that the cutting edge will be of the
required shape when the length of the bevelled facet is equal to three
times the thickness of the cutter.
The method of finding the shape of cutter necessary to produce a given
shape of moulding has been fully explained on pages 80 to 85, Vol. II.
[Illustration: Fig. 3200.]
[Illustration: Fig. 3201.]
Various forms of side heads are shown in the figures from 3200, to 3207.
Fig. 3200 is a two-sided plain head, or in other words two diametrally
opposite sides of the head are provided with bolt holes, for cutter
fastening bolts. Fig. 3201 represents a four-sided slotted head, each
side having T grooves, so that the cutter may be adjusted endways on the
head. This enables the use of four narrow cutters, thus taking the cut
in detail as it were.
[Illustration: Fig. 3202.]
[Illustration: Fig. 3203.]
The two-sided head shown in Fig. 3202 is provided with a set screw, by
means of which a delicate adjustment of the height of the cutter may be
made. Fig. 3203 represents a three-sided slotted head, or in other words
T-shaped grooves, and not bolt holes are used.
CUTTER HEADS WITH CIRCULAR CUTTERS.
[Illustration: Fig. 3204.]
This form of cutter head was invented by S. J. Shimer, and are generally
known as Shimer cutter heads. The principle of construction is shown in
Fig. 3204, which is for an ogee door pattern.
The cutters are circular in form and are seated at an angle to the
flange to which they are bolted, this angle giving side clearance to the
cutting edges.
[Illustration: Fig. 3205.]
[Illustration: Fig. 3206.]
The full amount of cut is taken in successive stages or increments; thus
in the figure, the two upper cutters would produce one half the
moulding, and the two lower ones the lower half. As the cutters are
sharpened by grinding the front face, therefore they will maintain
correct shape until they are worn out. Fig. 3205 represents a Shimer
head for producing the tongue, and Fig. 3206 a similar head for
producing the groove of matched boards.
[Illustration: Fig. 3207.]
Fig. 3207 shows the action of the groove head, the cutter or bit D being
shown in full lines and the second cutter being shown in dotted lines.
Cutter D, it will be seen, operates on one half of the groove, and
cutter C on the other half, each cutter having side clearance, because
of being seated on a seat whose plane is not at a right angle to the
axis of revolution of the head.
By thus taking the cut in detail, the head works steadily, while the
side clearance makes the cutters cut clean and clear.
JOINTING MACHINE.
"Jointing" a piece of wood or timber, means producing a surface, so that
the joint between two pieces that are to come together or be glued shall
be close. In order to produce surfaces that shall be true enough for
this purpose, it is necessary that the work be held in such a way that
it is not sprung or deflected by the holding devices or feeding
apparatus.
[Illustration: Fig. 3208.]
Fig. 3208, for example, represents a jointing machine, in which the work
abuts against an inclined plate P at one end, while the other end is
clamped down to the table, which is traversed past the revolving head H,
to which are secured two gouge-shaped cutting tools, one of which is
seen at T. By using tools of this class, the amount of cutting edge in
action is small, and will not therefore spring the work, and if the
cutter spindle is adjusted to have no end motion, the work will be true,
notwithstanding any slight vibration of the head, because its plane of
revolution coincides with the plane of the surface being surfaced or
jointed.
[Illustration: Fig. 3209.]
In some jointing machines, knives are set on the face of a revolving
disc, an example of this class of machine being shown in Fig. 3209,
which is for facing the spokes of wheels and for finishing the mitre
joint on them.
Three cutters are used, each being set at an angle to a radial line, so
that the inner edge of the knife will meet the work first. This gives
the knives a shearing cut, and prevents the whole of the cutting edge
from striking the work at once. The spokes are placed against a stop on
the table, and brought into contact with the cutters by the foot
treadle.
The table has beneath it a spiral spring at each end, which returns the
table as soon as the foot pressure is released from the treadle. The
cutter head or disc is 10 inches in diameter, and should make 2,000
revolutions per minute.
Stroke jointers are machines (such as shown in Fig. 3210) in which a
long plane _e_ of the ordinary hand plane type is worked along a slide
by a connecting rod C, operated by a crank motion. A machine of this
class will do very accurate work, but is obviously suitable for thin
work only.
A machine constructed by J. J. Spilker, for cutting mitre joints by
hand, is shown in Fig. 3211. The frame A carries a slideway for the
slide to which the mitre cutting knife K is secured. The handle G
operates a pinion gearing into a rack, which gives vertical motion to
the slide and knife. At _c_ is a fence or gauge against which the work
is rested, and which is capable of a horizontal motion, so as to bring
the work more or less under the knife. For heavy work, the fence _c_ is
set back, so that the first cut of the knife will leave the moulding, as
shown at H, partly severed, and a second cut is necessary to sever it;
for very fine work, a fine shaving may be taken off by a cut taken on
the end of each piece separately, after the piece is severed. At D is a
graduated scale or rule for cutting the work to exact dimensions, and as
its lines are ruled parallel to the right hand edge of the knife K, the
inside measurements of a mitre joint may be taken at the outer edge, and
outside measurements at the inner end of each line, a set stop at E
serving to gauge the pieces for length.
[Illustration: Fig. 3210.]
[Illustration: Fig. 3211.]
MOULDING OR FRIEZING MACHINES.
These are machines that cut mouldings on the edges of the work. The term
friezing is applied by some, when the machine has but one cutter
spindle, while by others these machines, whether having one or two
spindles, are termed edge moulding machines. Still another term applied
to this class of machine is that of variety moulders or variety moulding
machines.
In machines of this class, it is of primary importance that lost motion
or play in the bearings be avoided, because the cutter end of the
spindle overhangs its bearings, and any side play of the spindle in its
bearings is multiplied at the cutting edges of the cutters. Perfect
lubrication of the spindle bearings, and ample bearing surface on the
journals and bearings, are therefore of the first importance.
The work is rested on the upper surface of the table, and is fed to the
cutters by hand.
[Illustration: Fig. 3212.]
[Illustration: Fig. 3213.]
[Illustration: Fig. 3214.]
[Illustration: Fig. 3215.]
[Illustration: Fig. 3216.]
Figs. 3212 to 3215 represent a machine by J. S. Graham. The frame B, B,
Fig. 3213, of this machine is cast in one piece cored out, and the base
is wide, so as to give necessary solidity. The hollow column is fitted
with a door W, and shelves V, V, forming a very complete case for the
reception of tools, cutters, etc. The spindle boxes and slides C are one
casting. They are planed on centres and held in the frame B´, Fig. 3215,
by large gibs L, and sliding surfaces shown in C´, Fig. 3214. They are
adjustable vertically by hand wheels K, in front of frame in connection
with nut O, as shown in Fig. 3214, and require no lock to hold them at
the proper height.
The cap O´ (Fig. 3213) has an oil chamber J and wick which feeds the oil
to the upper bearing. The lower box is fitted with a patent self-oiling
and adjustable step shown at _a_, _b_, _c_. The cap _a_, upon which the
spindle D rests, has a small opening in the centre. The circular block
_b_, under it, also has a hole in the centre. The bolt _d_ has two holes
in it, one horizontal and the other vertical.
The chamber surrounding this step and cup is filled with oil. The motion
of the spindle D on the cap _a_ causes the oil to flow from the chamber
through the openings to the spindle. Thus the oil is kept in constant
circulation. The end of this spindle D is by this arrangement kept
always lubricated.
The spindles D are of 1-7/8 hammered tool steel accurately turned and
fitted in the boxes, which are of extra length, and lined with the best
genuine Babbitt metal. They are 30" from centre to centre, and have
independent screw tops, as shown at S, enabling the operator to use
various sizes for large or small work, or clear the table of either
spindle for special work.
H is the threaded part of the screw top, G is the nut, and F the fill-up
collars.
The iron table A, A is 5 feet by 4 feet, planed and fitted with
concentric rings E, E around the spindle, to suit the various sizes of
heads and cutters. A heavy wooden table, made of narrow glued-up strips
of hard wood, can be used if preferred.
This machine has been run up to 6,000 revolutions per minute, without
perceptible jar, and cutter heads as large as 8" diameter may be used on
it for heavy work.
Fig. 3216 represents an edge moulding machine by J. H. Blaisdell. In
this machine the table is raised or lowered by the hand wheel upon the
central column. The construction of the spindle and its bearings is
shown in the sectional view, which also shows the square threaded screw
by means of which the table is raised. The spindle has a coned hole for
receiving the cutter sockets, which are therefore readily removable.
[Illustration: Fig. 3217.]
Figs. 3217 to 3220 represent examples of the shapes of cutters for use
on edge moulding or friezing machines. Fig. 3217 represents a cutter for
bevelling the edge of the work, the cutting edges being at A, B, or at
C, D, according to the direction in which the cutter is revolved.
[Illustration: Fig. 3218.]
Fig. 3218 represents an ogee cutter, in position on the cutter spindle.
As these cutters are made solid and accurately turned in the lathe, they
are balanced so long as the cutting edges are kept diametrally opposite.
The front faces only being ground to sharpen the cutting edges, the
cutter always produces work of the same shape.
[Illustration: Fig. 3219.]
[Illustration: Fig. 3220.]
Fig. 3219 represents a cutter (in a chuck) for cutting a dove-tailed
groove, and Fig. 3220 one for rounding an edge, it being obvious that a
wide range of shapes may be given to such cutters, and that, as they may
be sharpened on an emery wheel, they may be left comparatively hard,
thus enhancing their durability.
To regulate the depth to which a cutter such as shown in Fig. 3220 will
cut, a collar or washer is placed beneath it to act as a guide to the
edge of the work.
[Illustration: Fig. 3221.]
Fig. 3221 represents a machine in which rotary cutters are used to
produce all kinds of panel work, as well as edge moulding or friezing.
In this case the cutter is above the table, the latter being adjustable
for height to suit the thickness of the work. Examples of some of the
work are shown at the foot of the machine.
WOOD BORING MACHINES.
The rapidity with which holes may be bored in wood enables the feed to
be most expeditiously performed by hand or by foot motion. A foot motion
leaves both the workman's hands free to adjust and change the work, and
is therefore suitable for light work or work having holes of a moderate
depth.
The work tables of wood boring machines are provided with suitable
fences for adjusting the work in position, and in some cases with stops
to adjust the depth of hole.
Any of the augers or bits that are used in boring by hand may be used in
a boring machine, but it is obvious that, as the bit or auger is forced
to its feed by hand or foot, and as its revolution is very rapid, the
screw point, which is intended as an aid in feeding when the bit is used
by hand, is not necessary. On this account most augers for use in
machines are provided with triangular points instead of screw points.
[Illustration: Fig. 3222.]
In Fig. 3222 is shown a wood boring machine by J. A. Fay & Co. The table
is gibbed to a vertical slide on the face of the column, and is
adjustable for height by the hand wheel A, which, through the medium of
its shaft and a pair of bevel gears, operates the elevating screw B. The
spindle C feeds through its bearings, the supporting rod D being pivoted
at its lower end to permit C to feed in a straight line vertically. The
feeding is done by the treadle F, which operates the rod E.
The table may be set at an angle of 30 degrees from the horizontal
position.
The weight W counterbalances the treadle and brings it to its highest
position when the workman's foot pressure is removed.
The holes may all be gauged to an equal depth (when they are not to pass
through the work) by so adjusting the height of the table that the hole
is of the required depth when the treadle is depressed to its lowest
point, or limit.
[Illustration: Fig. 3223.]
Fig. 3223 represents a horizontal boring machine such as used in
furniture and piano factories. The spindle feeds through the driving
cone, being operated by the treadle shown. The work table is adjustable
for height by the hand wheel and elevating screw. The usual fences,
stops, and clamping devices may be applied to the table, which is on
compound slides to facilitate the adjustment of the work.
Fig. 3223_a_ shows a double spindle horizontal boring machine, in which
the table and work are fed up to the boring tools by hand. The spindles
are adjustable in their widths apart, and may also be set at an angle.
The work table is adjustable for height, and the spindle carrying head
is adjustable across the machine.
[Illustration: Fig. 3223_a_.]
[Illustration: Fig. 3224.]
Fig. 3224 represents a machine by J. A. Fay & Co., for heavy work,
rollers taking the place of the work table. The drill spindles are fed
by hand from the stirrup handles shown, which are weighted to raise up
the spindles as soon as they are released.
MORTISING MACHINES.
The mortising machine for wood work consists essentially of an ordinary
auger, which bores the holes, and a chisel for cutting the corners so as
to produce the square or rectangular mortise that is usually employed in
wood work.
The chisel is reciprocated and its driving spindle is provided with
means whereby the chisel may be reversed so as to cut on either the
sides or the ends of the mortise. The chisel is fed gradually to its
cut.
[Illustration: Fig. 3225.]
Fig. 3225 represents a mortising machine for the hubs of wheels.
The auger spindle is here fed vertically by a hand lever, the depth
bored being regulated by a rod against which the hand lever comes when
the hole is bored to the required depth.
Fig. 3226 represents a mortising machine in which the mortising tool
consists of a hollow square chisel containing an auger, and having at
its sides openings through which the cuttings escape.
The chisel is rectangular in cross section, but its cutting edges are
highest at the corners, as may be clearly seen in the figure.
The work is firmly clamped to the work table and simultaneously to the
fence, the upper hand wheel being operated to bring the work-holding
clamp down to the work, and the lower one to clamp it so as to press it
to both the table and the fence at the same time.
The chisel bar is mounted horizontally in a slide way on a substantial
bed that is mounted on a vertical slideway, which enables the chisel bar
to be set for height from the work table. It has a horizontal traverse
motion or feed, the amount of this motion being governed by the
horizontal rod with its nuts and check nuts as shown.
The auger runs continuously, and works slightly in advance of the
cutting edge of the chisel, which is passive except when making the
mortise.
The chisel bar and auger have a slow, reciprocating motion, and will
complete a hole the size of the chisel used. An inch chisel will cut an
inch-square hole, consequently a mortise 1" × 4" would only require four
strokes forward to complete it. It has a capacity to work mortises from
3/4" to 3" square, and 5" in depth, and any length desired. The boring
spindle is driven by an idler pulley, direct from the countershaft.
The bed upon which the timber is placed to be mortised is gibbed to a
sliding frame, which allows it to be set to any position, with the
chisel straight or at an angle. It is adjustable to and from the chisel
bar, to suit the size of material, the under side of which always
remains at one height. Adjustments are provided for moving the carriage
forward, for regulating the depth of the mortise, the position of the
chisel from the face of the material, and the adjustment of the chisel
bar, controlling the mortises to be made in the timber.
Two treadles are used upon the side of the machine; the pressure upon
one carrying the chisel bar attachment forward, completing the mortise,
while the other will instantly force it back when it is desired to
withdraw it from the wood, without allowing it to cut its full depth.
Provision is made by stops for regulating the length of the stroke as
well as the depth of the mortise.
TENONING MACHINES.
In tenoning machines, the lengths of the pieces usually operated upon
render it necessary that the work should lie horizontally upon the
table, while the shortness of the tenon makes an automatic feed
unnecessary.
The revolving heads carrying the cutters in tenoning machines are so
constructed that the cutting edges of the cutters are askew to the sides
of the heads, but so set as to produce work parallel to the axis of the
cutter shaft.
This causes the cutting action to begin at one end of the cutter edge,
and pass along it to the other, which enables a steady hand feed, and
reduces the amount of power required to feed the work.
Fig. 3227 represents a cutter head for a tenoning machine, _a_, _a_ and
_b_, _b_ being the cutters and _c_, _c_, _d_, _d_ spurs which stand a
little farther out than the cutter edges, so as to sever the fibre of
the wood in advance of the cutter edges coming into action, and thus
preserve a sharp shoulder to the tenon, and prevent the splitting out at
the shoulder that would otherwise occur.
To bring the outer edge of the shoulder in very close contact with the
mortised timber, the cutters are for some work followed by what is
termed a cope head, which is a head carrying two cutters bent forward as
in Fig. 3228, to make them cut very keenly, as is necessary in cutting
the end grain of wood.
The cope head undercuts the shoulder, as shown at _a_, _a_, in Fig.
3229, which is a sectional view of a mortise and tenon.
[Illustration: Fig. 3226.]
[Illustration: Fig. 3227.]
[Illustration: Fig. 3228.]
[Illustration: Fig. 3229.]
[Illustration: Fig. 3230.]
Fig. 3230 represents a tenoning machine for heavy work, constructed by
J. A. Fay & Co., adjusted for cutting a double tenon, the upper and
lower heads revolving in a vertical plane, and the middle head in a
horizontal plane.
A is a vertical slideway for the heads C, D, carrying the shafts for the
cutter heads _a_, _b_. At B is the hand wheel for adjusting D, and at E
that for adjusting C. The pulley _d_ is for driving the cope heads, one
of whose cutters is seen at _c_. The work carriage H is provided with
rollers which run on the slide on K, and is supported by the arm I,
which rises and falls to suit the cross motion of H. The fence G, for
the work, is adjustable by means of the thumb nuts.
[Illustration: Fig. 3231.]
SAND-PAPERING MACHINES.
Sand-papering machines are of comparatively recent introduction in wood
working establishments, but are found very efficient in finishing
surfaces that were formerly finished by hand labor.
Fig. 3231 represents a sand-papering machine, by P. Pryibil, in which a
spindle has three stepped cones on one end, and a parallel roller or
cylinder at the other. The steps on the spindle are covered with a
rubber sleeve, and the sand paper is cut to a template, and the edges
brought together and joined by gluing a strip of tough paper under them.
When this has become dry the paper is slightly dampened everywhere
except at the joint, and is then slipped on the taper drums. In drying
it shrinks and becomes tight and smooth upon the rubber covering with
which the drums are provided. These are of different sizes to fit
different curves in the work.
Flat work is done upon the table, which is hinged and provided with an
adjusting screw to regulate its height, and it can be raised to give
access to the drum.
When sand paper is applied in this way, every grain is brought into
contact with the work, whereas at first only the larger grains cut when
it is used on the faces of revolving discs, as in some machines of this
class. Furthermore, when used on drums it is offered ample opportunity
to clear itself of dust; it therefore does not become clogged, and, as a
consequence, it lasts longer and does more and better work than when
used on discs.
[Illustration: Fig. 3232.]
Fig. 3232 represents a similar machine, but having a spindle vertical
also, so that one face of the work can be laid on the table, which acts
as a guide to keep the work square, the table surface being at a right
angle to the vertical spindle.
The vertical cylinder or drum is split on one side, and provided with
internal cones, so, that by screwing down the nut shown the drum can be
expanded to tightly grip the sand paper, which is glued and put on as
already described.
Besides these rotary motions, these drums receive a slow vertical
motion, the amount of which is variable at the operator's pleasure. This
provides for using the full face of the drum on narrow work, while it
prevents the formation of ridges or grooves in the work.
For sand-papering true flat surfaces the flat table is provided, there
being beneath it a parallel revolving drum, whose perimeter just
protrudes through the upper surface of the table. The surface of the
table thus serves as a guide to steady the work while the sand-papering
is proceeding.
By using sand paper in this manner, every grain of the sand is brought
into contact with the work; furthermore, a small area of sand paper is
brought into contact with the work, and the wood fibre can fly off and
not lodge in the sand paper; while at the same time the angles of the
grains of sand or glass are presented more acutely to the work, and
therefore cut more freely and easily. Hence the sand paper lasts much
longer, because a given pressure is less liable to detach the sand from
the paper.
The machine is constructed entirely of iron, and the drum is intended to
revolve at about 800 revolutions per minute.
[Illustration: Fig. 3233.]
Fig. 3233 represents a sand-papering machine in which a long parallel
cylinder is employed, the work resting on the surface of the table and
being fed by hand. In using a machine of this class the work should be
distributed as evenly as possible along all parts of cylinder, or one
end of the cylinder may become worn out while the other is yet sharp;
this would incapacitate the machine for wide work unless a new covering
of sand paper were applied.
Fig. 3234 represents a sand-papering machine constructed by J. A. Fay &
Co., for finishing doors and similar work. The frame constitutes a
universal joint enabling the sand paper disc to be moved anywhere about
the door by hand. An exhaust fan on the top of the main column removes
the dust from the work surface. The head carrying the disc is moved
vertically in a slideway to suit different thicknesses of work.
Fig. 3235 represents a self-feeding sand-papering machine constructed by
J. A. Fay & Co. It is made in three sizes, to work material either 24",
30", or 36" wide by 4" thick and under; it has a powerful and continuous
feed, and gives to the lumber a perfect surface by once passing it
through the machine.
The feeding mechanism consists of six rollers, in three pairs, driven by
a strong train of gearing. The upper feeding rollers, with the pressure
rollers over the drum are lifted together in a perfect plane by the
movement of four raising screws, operated by a chain and hand wheel. The
lower feeding rollers always remain in perfect line with the drums.
It is supplied with two polishing cylinders, placed in the body of the
machine, on which the upper frame rests, both having a vibratory lateral
motion for removing lines made by irregularities in the sand paper. The
finishing cylinder is placed so that the discharging rollers carry the
lumber from it, thus running through and finishing one board, if
desired, without another following, and these rollers are arranged for a
vertical adjustment to suit the dressed reduction on the material to be
worked. The roughing cylinder carries a coarse grade of sand paper, and
the finishing one a finer grade. They may be driven in opposite or in
the same direction, as may be necessary. The lower frame is hinged at
each end to the upper frame, so that by removing a pin, either cylinder
can be reached by raising the frame with the screw and worm gear,
operated by a hand wheel at the end of the machine.
A brush attachment (not shown in the cut) is now placed at the end of
the machine just beyond the finishing cylinder, which is a most complete
device for brushing the material clean after it leaves the sand-papering
cylinders.
Fig. 3236 represents a double wheel sanding machine by J. A. Fay & Co.
This machine is intended for accurately finishing the tread of the wheel
ready for the tire, and is one of the most useful and labor-saving
machines that can be placed in a wheel shop.
The frame is built entirely of iron, and has a heavy steel arbor running
in long bearings, with tight and loose pulleys in the centre. On each
end of the arbor is a large sand paper disc for polishing the tread of
the rim.
The wheel to be finished is laid on a rotating carrying frame, having
two upright drivers. These are attached to a jointed swinging frame,
with flexible connections, adjustable to suit wheels of varying
diameters.
The first section of the jointed frame is driven by a shaft and bevel
gears, and swings upon it. The second one has the wheel-carrying frame,
and swings upon the extreme end of the first one, and is driven from it
by a chain connection.
[Illustration: _VOL. II._ SANDING MACHINES. _Plate XXVII._
Fig. 3235.
Fig. 3236.]
A roller wheel is secured at the bottom of the leg, affording a floor
support; also a chain to regulate the proper distance of the wheel from
the discs.
A wrought iron supporting frame is attached upon each side of the sand
paper discs, adjustable for different sizes.
[Illustration: Fig. 3234.]
The wheel when placed in the machine is carried by the gearing against
the sand paper discs, which finishes the tread in the most accurate and
perfect manner.
Machines are made both single and double. The latter are the most
desirable, as the operator has only to place a wheel in position on one
side, when it feeds and takes care of itself.
By the time this is done, the wheel on the opposite side will be
finished and ready to be removed, when a fresh one is put in, and the
operation continued, the only care required being to put in and remove
them. Its capacity is 150 set of wheels per day, and it will do the work
better than can be done by hand.
CHAPTER XXXVI.--BOILERS FOR STATIONARY STEAM ENGINES.
The boiler for a steam engine requires the most careful usage and
inspection, in the first case because a good boiler may be destroyed
very rapidly by careless usage, and in the second case because the
durability of a boiler depends to a great extent upon matters that are
beyond ordinary control, and that in many cases do not make themselves
known except in their results, which can only be discovered by careful
and intelligent inspection. All that the working engineer is called upon
to do is, to use the boiler properly, keep it clean, and examine it at
such intervals as the nature of the conditions under which it is used
may render necessary.
The periods at which a boiler should be cleaned and inspected depend
upon the quality of the water, whether the feed water is purified or
not, and to a certain extent upon the design of the boiler; hence these
periods are variable under different circumstances.
The horse power of a boiler is estimated in various ways, and there is
no uniform practice in this respect. Some makers estimate a boiler to
have a horse power for every fifteen square feet of heating surface it
possesses, while others allow but 12 square feet.
The heating surface of a boiler of any kind is the surface that is
exposed to the action of the fire on one side, and has water on the
other; hence the surface of the steam space is not reckoned as heating
surface, even though it may be exposed to the action of the heat. The
effectiveness of the heating surface of a boiler obviously, however,
depends upon the efficiency of the fire, and this depends upon the
amount of draught, hence the estimation of horse power from the amount
of its heating surface, while affording to a certain extent a standard
of measurement or comparison while the boiler is not in use, has no
definite value when the boiler is erected and at work.
Thus whatever amount of steam a boiler may produce under a poor or
moderate draught, it will obviously produce more under an increased
draught; hence the efficiency of the same boiler depends to a certain
extent upon the draught, or in other words upon the quantity of fuel
that can be consumed upon its fire bars.
The amount of water required in steam boilers varies from 16 lbs. to 40
lbs., per horse power per hour, and it has been proposed to compute the
horse power of boilers from the water evaporation, taking as a standard
30 lbs. of feed water at a temperature of 70 degrees, evaporated into
steam at a temperature of 212 degrees, at which temperature the steam is
assumed to equal the pressure of the atmosphere.
[49]"The strength of the shell of a cylindrical boiler to resist a
pressure within it, is inversely proportional to its diameter and
directly, to the thickness of the plate of which it is formed.
[49] From "_Steam Boilers_."
"For instance, take three cylindrical boilers each made of 1/2 inch
plate, the first one 2 feet 6 inches in diameter; the second twice that,
or 5 feet in diameter; and the third twice that again, or 10 feet in
diameter; and if the 2 foot 6 inch boiler is fit for a safe working
pressure of 180 lbs. per square inch, then the 5 foot boiler will be fit
for exactly one-half that amount, or 90 lbs. per square inch; and the
ten foot boiler will be fit for half the working pressure of the five
foot boiler, hence we have:
-----------------+------------+--------------------------
Diameter of | Thickness |Relative working pressure.
boiler shell. | of plate. |
-----------------+------------+--------------------------
2 feet 6 inches.| 1/2 inch. | 180 lbs. per square inch.
5 " | " " | 90 " " " "
10 " | " " | 45 " " " "
-----------------+------------+--------------------------
"The reverse applies to the thickness of the plate. For instance, if we
take two cylindrical boiler shells, each 5 feet in diameter, the first
one made of plate 1/2 inch thick, and the second twice that, or 1 inch
thick, and if the first is equal to a safe working pressure of 90 lbs.
per square inch, then the second is equal to a safe working pressure of
twice as much, or 180 lbs. per square inch, providing, of course, that
the riveted seams are of equal strength in each case, and that both
boilers are allowed the same margin for safety; hence we have:
----------------+------------+--------------------------
Diameter of | Thickness | Safe working pressure.
boiler. | of shell. |
----------------+------------+--------------------------
5 feet. | 1/2 inch. | 90 lbs. per square inch.
5 " | 1 " | 180 " " " "
----------------+------------+--------------------------
[Illustration: Fig. 3237.]
[Illustration: Fig. 3238.]
"These principles (namely, that the strength of a boiler is, all other
things or elements being equal, inversely proportional to its diameter,
and directly proportional to its thickness) afford us a groundwork upon
which we may lay down rules for determining by calculation the strength
of the solid part[50] of any boiler shell, and the bases of these
calculations are as follows:
[50] In the case of the riveted joints or seams other considerations
come in, as will be shown hereafter.
"If the shell plate of a cylindrical boiler is 1/2 inch thick, there is
one inch section of metal to be broken before the boiler can be divided
into two pieces, that is to say there is 1/2 inch on each side of the
shell, as shown in Fig. 3237, and the two together will make 1 inch. If
we take a ring an inch broad, as, say, at A in Fig. 3238, we shall
obviously have a section of 1 square inch of metal to break before the
ring can be broken into two pieces.
"The next consideration is, what is the average strength of a plate of
boiler iron? Now suppose we have a strip of boiler iron 2 inches wide
and 1/2 inch thick, or, what is the same thing, a bar of boiler iron 1
inch square, and that we lay it horizontally and pull its ends apart
until it breaks, how many lbs. will it bear before breaking? Now for our
present purpose we may assume this to be 47,040 lbs., and if this number
of lbs. be divided by the diameter of the boiler in inches, it will give
the bursting pressure in lbs. for any square inch in the ring, or any
other square inch in the cylindrical shell of the boiler.
"The reason for dividing by the diameter of the boiler is as follows:
[Illustration: Fig. 3239.]
"Of course the steam pressure presses equally on all parts of the
interior surface of the shell, and may be taken as radiating from the
centre of the boiler, as in Fig. 3239, which represents an end view of a
strip an inch wide, of one half of a boiler. Now leaving the riveted
seam out of the question, and supposing the shell to be truly
cylindrical, and the metal to be of equal quality throughout, it will
take just as much pressure to burst the shell apart in one direction as
it will in another, hence we may suppose that the boiler is to be burst
in the direction of arrow _a_, and it is the section of metal at _b_ _b_
that is resisting rupture in that direction.
"Now suppose we divide the surface against which the steam presses into
six divisions, by lines radiating from the centre C, and to find the
amount of area acting on each division to burst the shell in the
direction of arrow _a_, we drop perpendicular lines, as line _e_, from
the lines of division to the line _b_ _b_, and the length of the line
divided off (by the perpendicular) on the diameter represents the
effectiveness of the area of that division to burst the boiler in the
direction of arrow _a_; thus for that part of the boiler surface situate
in the first division, or from _b_ to line _e_, the area acting to burst
the boiler in the direction of _a_ is represented by the length of the
line _k_, while the general direction of the pressure on this part of
the shell is represented by arrow _m_.
"Similarly, for that part of the shell situate between vertical line _e_
and vertical line _f_, the general direction of the steam pressure is
denoted by the arrow _l_, while the proportion of this part that is
acting to sever the boiler in the direction of _a_ is represented by the
distance _n_, or from the line _e_ to line _f_ measured on the line _b_
_b_.
[Illustration: Fig. 3240.]
"By carrying out this process we shall perceive that, although the
pressure acts upon the whole circumference, yet its effectiveness in
bursting the boiler in any one direction is equal to the boiler
diameter. Thus in Fig. 3240, the pressure acting in the direction of the
arrows _a_ (and to burst the boiler apart at _b_ _b_) is represented by
the diametral line _b_ _b_, while the pressure actually exerted upon the
whole boiler shell is represented by the circumference of the boiler.
"To proceed, then, it will now be clear that the ultimate strength of
the boiler material, multiplied by twice the thickness of the boiler
shell plate in inches or decimal parts of an inch, and this sum divided
by the internal diameter of the boiler, in inches, gives the pressure
(in lbs. per square inch) at which the boiler shell will burst."
We have here only considered the strength of the solid plate of the
shell, and may now consider the strength of the riveted joints, because,
as the boiler cannot be any stronger as a whole than its weakest part
is, and as the riveted joints are the weakest parts of a cylindrical
boiler,[51] therefore the strength of the riveted joint determines the
strength of the boiler.
[51] It may be here noted that the riveted joint of a flat plate is
stronger than the flat surface of the plate, because at the joint the
plate is doubled, or one plate overlaps the other.
[52]"The strains to which a riveted joint is subjected are as follows:
That acting to shear the rivet across its diameter is called the
_shearing_ strain. But the same strain acts to tear the plate apart;
hence, when spoken of with reference to the action on the plate, it is
called the _tearing_ strain.
[52] From "_Steam Boilers_."
"The same strain also acts to crush and rupture the plate between the
rivet hole and the edge of the plate, and in this connection it is
called the _crushing_ strain.
[Illustration: Fig. 3241.]
"Thus, Fig. 3241 represents a single riveted lap joint, in which the
joint at rivets A, B, and C is intact, the metal outside of D has
crushed, the rivets E, F have sheared, and the plate has torn at H,
leaving a piece J on the rivets K L.
"It is obvious that, since it is the same strain that has caused these
different kinds of rupture, the joint has, at each location, simply
given way where it was the weakest.
[Illustration: Fig. 3242.]
"If a riveted joint was to give way by tearing only, the indication
would be that the proportion of strength was greatest in the rivets,
which might occur from the plate being of inferior metal to the rivets,
or from the rivets being too closely spaced. If the rivets were to shear
and the plate remain intact, it would indicate insufficient strength in
the rivets, which might occur from faulty material in the rivets, from
smallness of rivet diameter, or from the rivets being too widely spaced.
"The object then, in designing a riveted joint is to have its
resistance to tearing and shearing proportionately equal, whatever form
of joint be employed."
The English Board of Trade recommends that the rivet section should
always be in excess of the plate section, whereas, in ordinary American
practice, for stationary engine boilers, the plate and rivet percentages
are made equal.
The forms of riveted joints employed in boiler work are as follows:
[Illustration: Fig. 3243.]
[Illustration: Fig. 3244.]
Fig. 3242 represents a single riveted lap joint. Fig. 3243 represents a
double riveted lap joint, chain riveted; and Fig. 3244, a double riveted
lap joint, with the rivets arranged zigzag.
[Illustration: Fig. 3245.]
[Illustration: Fig. 3246.]
Fig. 3245 represents a single and Fig. 3246 a double riveted butt joint,
so called because the ends of the boiler plate abut together. The plates
on each side of joint are called butt straps.
The advantages of the butt joint are, first, that the boiler shell is
kept more truly cylindrical, and the joint is not liable to bend as it
does in the lap joints, in the attempt of the boiler (when under
pressure) to assume the form of a true circle, and second that the
rivets are placed in double shear. That is to say, if in a lap joint the
rivet was to shear between the plates, the joint would come apart,
whereas, in a butt joint, the rivet must shear on each side of the
plate, and therefore in two places.
[Illustration: Fig. 3247.]
Fig. 3247 represents a form of joint much used in locomotive practice in
the United States. It is a lap joint, with a covering plate on the
inside of the joint; rivets E and F are in single and rivets D in double
shear.
[53]"When we have to deal with comparatively thin boiler plates, there
is no difficulty in obtaining a sufficiently high percentage of strength
in the joints, by using the ordinary double riveted joint, but when we
have to deal with thick plates, as in the case of large marine boilers,
as 1 inch or upwards, a more costly form of joint must be employed, in
order to obtain the required percentage of strength at the joint; hence
the ordinary double riveted joint is replaced by various other forms as
follows:
[53] From "_Steam Boilers_."
[Illustration: Fig. 3248.]
"First, a triple zigzag riveted lap joint, such as shown in Fig. 3248,
or a chain riveted joint as in Fig. 3249, in both of which the third row
of rivets enables the rivet pitch to be increased, thus increasing the
plate percentage, while the third row of rivets also increases the rivet
percentage.
"Second, by employing butt joints with butt straps, either double or
treble riveted.
[Illustration: Fig. 3249.]
[Illustration: Fig. 3250.]
[Illustration: Fig. 3251.]
[Illustration: Fig. 3252.]
"A double riveted butt joint with double straps is shown in Fig. 3250,
and a treble with double straps in Figs. 3251 and 3252.
"Third. By various arrangements of the rivets in conjunction with butt
joints and double straps, with which it is not necessary, at this point,
to deal.
"One of the great advantages obtained by the use of the double strap is
that of bringing the rivet into double shear (or in other words, the
rivet must shear on each side of the plate, or in two places, instead of
between the plates only, before the joint can give way by shearing), and
thus obtaining an increased calculated strength of 1-3/4 times the
ordinary or single shear, the rule being to find the rivet strength in
the ordinary way (as before explained), and then multiply the result by
1.75.
"The Board of Trade rules for spacing the rivets of these joints are as
follows:
"Dimension E is the distance from the edge of the plate to the centre of
the rivet hole. Dimension V is the distance between the rows of rivets,
dimension _p_ is the pitch of the rivets, which is always measured from
centre to centre of the rivets, and dimension _pd_ is the diagonal pitch
of the rivets.
"The rule for finding dimension E, whether the plates and rivets are
either of steel or iron, is as follows:
"Multiply the diameter of the rivet by 3 and divide by 2, the formula
being as follows:
3 × _d_
------- = E.
2
"To find the distance V between the rows of rivets in chain riveted
joints. This distance must not be less than twice the rivet diameter,
and a more desirable rule is four times the rivet diameter plus 1
divided by 2, thus:
4_d_ + 1
-------- = V.
2
"To find the distance between the rows of zigzag riveted joints:
_____________________________
\/(11_p_ + 4_d_) × (_p_ + 4_d_)
------------------------------- = V,
10
that is, multiply 11 times the pitch plus 4 times the rivet diameter, by
the pitch plus 4 times the rivet diameter, then extract the square root
and divide by 10.
"To find diagonal pitch _pd_, multiply the pitch _p_ by 6, then add 4
and divide by 10, thus:
6_p_ + 4
-------- = _pd_."
10
[Illustration: Fig. 3253.]
Fig. 3253 represents a form of high percentage joint, used upon marine
boilers of 10 to 14 feet diameter, and carrying from 100 to 190 lbs.
pressure of steam. The rivets are what are termed unevenly pitched, or,
that is to say, on each side of the joint, there are three rows of
rivets, of which the inner and outer rows are wider pitched than the
middle row.
[54]"The advantage gained by this spacing is that the shear of the outer
row of rivets is added to the plate section at the narrow pitch, that is
to say, if the plate section broke through the line of rivet holes at
the narrow pitch, it has yet to shear the outer row of rivets before the
plate can separate."
[54] From "_Steam Boilers_."
[Illustration: Fig. 3254.]
Fig. 3254 represents a second example of joint with rivets unevenly
pitched, this form finding much favor in recent practice. The four inner
rows of rivets are spaced at narrow pitch and the two outer rows are
wide pitched.
[55]"The strength percentage of this joint is calculated from three
points of view, as follows:
[55] From "_Steam Boilers_."
"First. The plate section at the wide pitched rivets.
"Second. The rivet section in one pitch.
"Third. The plate section at the narrow pitch plus half the double shear
of the outer or wide pitched rivet."
The steam pressures generally employed in the boilers of stationary
engines range from about 60 to 100 lbs. per square inch, and as a result
of these comparatively low pressures less perfect forms of construction
are employed than would be permissible if higher pressures were used.
The strength of the shell plate of boilers of small diameter is always
largely in excess of the requirements, and as a result the strength of
the joints may bear a very low percentage to that of the solid plate,
and yet give a sufficient factor of safety for the working pressure.
Take, for example, a boiler shell of 36 inches internal diameter with a
shell plate 1/4 inch thick, and allowing the strength of the material to
be 48,000 lbs. per inch of section, and with a factor of safety of 4,
the working pressure will be 166 lbs. per square inch, thus:
Strength Plate thickness
of the material. × 2.
48000 × (.25 × 2)
--------------------------------- = 666-2/3 lbs. = bursting pressure.
36
Diameter of boiler.
By dividing this 666 by the factor of safety 4 we get 166-2/3 lbs. as
the working pressure of the shell plate independent of the riveted
joint. Usually, however, such a boiler would not be used for a pressure
above about 60 lbs. per inch, and this leaves a wide margin for the
reduction of strength caused by the riveted joints.
Suppose, for example, that a single riveted lap joint is used, and the
strength of this joint is but 50 per cent. of that of the solid plate,
and we have as follows:
Strength of % strength Twice
material. of riveted the plate
joint. thickness.
48000 × .50 × (.25 × 2)
---------------------------------- = 83-1/3 lbs. = W.P.
36 × 4
Internal diam. Factor of
of boiler. safety.
Here then we find that the working pressure of the solid plate is double
that of the riveted joint, and that the working pressure of the boiler
is 83 lbs. per square inch, notwithstanding that the strength of the
riveted joints is but 50 per cent. of that of the solid plate. Such a
boiler would not, however, be used for a pressure of over 60 lbs. per
square inch.
If the above-named boiler was double riveted so as to bring the
percentage of joint strength up to say 70 per cent, of that of the solid
plate, its working pressure would be 116 lbs. per square inch, thus:
Strength of % strength Twice
material of riveted the plate
joint. thickness.
48000 × .70 × (.25 × 2)
---------------------------------- = 116-2/3 lbs. = W.P.
36 × 4
Internal diam. Factor of
of boiler. safety.
But in practice such a boiler would not be used for pressures above
about 75 lbs. per square inch, hence the shell plate thickness is still
largely in excess of the requirements, and it may be remarked that
plates less than 1/4 inch thick are not used on account of the
difficulty of caulking them and keeping them steam tight.
On account therefore of the excessive strength of the shell plates in
boilers of small diameter, butt straps are rarely used in stationary
boilers, while punching the rivet holes and other inferior modes of
construction are employed. We may now consider the circumferential seams
of the boilers for stationary engines, such boilers sometimes being of
great length in proportion to the diameter.
In proportion as the length of a boiler (in proportion to its diameter)
is increased, the construction of the circumferential or transverse
seams, as they are sometimes called, becomes of more importance.
The strength of the circumferential seams is so much greater than that
of the longitudinal seams that it is often taken for granted that they
are sufficiently strong if made with a lap joint and single riveted, but
that such is not always the case will be shown presently.
[Illustration: Fig. 3255.]
In Fig. 3255 is represented a boiler composed of three strakes (_i. e._,
three rings or sections), and it is clear that as the thickness of the
shell is doubled at the circumferential seams where the ends of the
middle strake pass within the end strakes, therefore the strength of the
lapped joint of the shell to resist rupture in a transverse direction,
as denoted by the arrows A, B, is actually increased by reason of the
lap of the riveted joint. But suppose this boiler to be supported at the
ends only, and the weight of the shell and of the water within it will
be in a direction to cause the middle of the boiler to sag down, and
therefore places a shearing strain on the rivets of the circumferential
seams.
Moreover, the temperature of the outside of the boiler cannot be made or
maintained uniform, because the fire passing beneath the bottom of the
boiler first will keep it hotter, causing it to expand more, and this
expansion acts to shear the rivets of the circumferential seams. In
proportion as the heat of the fire varies in intensity, the amount of
the expansion will vary, and the consequence is that the circumferential
seams may get leaky or the joint may work, especially in boilers that
are long in proportion to their diameters. It is clear, therefore, that
for the very best construction at least a double riveted circumferential
joint should be employed.
Leaving these considerations out of the question, however, we may find
the amount of stress on the circumferential seams by multiplying the
area of the end of the boiler by the working pressure, and dividing by
the cross-sectional area of all the rivets in one circumferential seam.
Suppose, for example, that the diameter of the boiler is 36 inches, the
working pressure 60 lbs. per square inch, and that there are in each
circumferential seam 50 rivets, each 3/4 inch in diameter, and we
proceed as follows:
The area of a circle 36 inches in diameter = 1017.87 square inches.
The area of a rivet 3/4 inches in diameter = .4417 square inch.
Then
Area of Working
boiler end. pressure.
1017.87 × 60
------------------ = 2765 lbs. per cross-sectional square inch of rivet.
50 × .4417
Number Area of
of rivets. each rivet.
By multiplying the area of the boiler end by the working pressure, we
get the total steam pressure acting to shear the rivets, and by
multiplying the number of rivets by the area of one rivet, we get the
total area resisting the steam pressure, and then by dividing the one
quantity into the other, we get the shearing stress per square inch of
rivet section.
In the case of longitudinal seams, we have as follows, the pitch being
say 2-1/8 and the rivets 3/4.
Diameter Steam Pitch.
of boiler pressure.
in inches.
36 × 60 × 2.125
------------------------------ = 5196 lbs. per square inch of rivet
2 × .4417 area.
Rivets in Area of
one pitch. rivet.
It is seen, therefore, that the stress placed by the steam pressure on
the transverse seam is about one-half of that it places on the
longitudinal seam. But, as before remarked, the transverse seam is
subject to racking strains, from which the longitudinal seams are
exempt; thus, for example, the expansion of the boiler diameter, whether
uniform or not, does not strain the longitudinal seam, whereas it may
severely strain the transverse seam.
The English Board of Trade rules, in assigning values to the various
constructions and qualities of workmanship, assign a certain value, in
the form of an addition to the factor of safety, which takes into
account the difference in the stress upon the transverse and
longitudinal seams, the quantities in each case having been determined
both from experiment and from experience. A comparison of the different
values may be made as follows:
The rules take a boiler shell made of the best material, with all the
rivet holes drilled after the strakes are rolled into shape and put
together, with all the seams (both longitudinal and transverse) fitted
with double butt straps each at least five-eighths of the thickness of
the shell plates they cover, and with all the seams at least double
riveted, with rivets having an allowance of not more than 75 per cent.
over the single shear, and provided that the boilers have been open to
the inspection of their surveyors during the whole period of
construction, and say that such a boiler shell shall be allowed a factor
of safety (divisor of seam strength) of 5.
But for every departure from this, which they deem the best mode of
construction, a penalty in the shape of an addition to the factor of
safety is made. These additions to the factors of safety with reference
to the longitudinal as compared to the transverse seams, are given in
the following table:
-------------------------------------+----------------+---------------
|Addition to the |Addition to the
|factor 5 if the |factor 5 if the
Nature of the deviation in the |deviation is in |deviation is in
construction or workmanship. |the longitudinal|the transverse
| seam. | seam.
-------------------------------------+----------------+---------------
The holes not fair and good | .75 | .2
Holes drilled out of place after | |
bending | .15 | .1
Holes drilled before bending | .3 | .15
Holes punched after bending | .3 | .15
Holes punched before bending | .5 | .2
Joints lapped and double riveted | |
instead of having double butt straps | .2 | .1
Joints double riveted but have single| |
butt straps | .3 | .1
Joints single riveted and have a | |
single butt strap | 1.0 | .2
Joints lapped and single riveted | 1.0 | .2
-------------------------------------+----------------+---------------
[Illustration: Fig. 3256.]
An addition of .25 is also made to the factor of safety, when the
strakes are not entirely under or over. In Fig. 3256 for example, strake
_b_ is within or under strake _a_ at one end and strake _c_ at the other
end, hence _b_ is entirely under; strake _c_ is over _b_ and _d_, and
therefore entirely over; while strake _d_ is under _c_, and over _e_,
and therefore not entirely under nor entirely over.
When the rivet holes are punched they do not match properly, and unless
the holes are punched somewhat smaller than the required size and reamed
out afterwards, some rivets receive more stress than others, and may
consequently shear in detail. It is customary, however, to punch the
holes for ordinary stationary boilers, and it is with seams having
punched holes therefore that we have at present to deal.
In the United States the rivet diameter and plate percentages are, in
the boilers of stationary engines, usually made equal, and the reasons
advanced both for and against this are as follows:
First, in favor of a greater plate percentage than rivet section, it is
advanced that the plate gets thinner by wear, whereas the rivet does
not, hence the wear reduces the plate section; that the plate is
weakened by the punching process, and requires a greater percentage to
make up its strength as compared to the rivet; that the rivets are
usually of better material than the plates.
In favor of a greater rivet section than plate section, it is advanced
that the shearing strength of iron is but about four-fifths of the
tensile strength, and that with equal plate and rivet sections the rivet
is therefore the weakest; that with punched holes the rivets may be
sheared in detail, and that the rivets may be sheared gradually by the
working of the joint from varying expansion and contraction.
From these premises the assumption is drawn that the weakening of the
plate from being punched and from corrosion about offsets the excess of
the tensile over the shearing strength, and that it is best therefore to
employ such a pitch that the area of the rivet and of the metal left
between the rivet holes shall be equal.
In order to do this the diameter of the rivet must be determined, and
the following are the proportions given by the various authorities
named:
TABLE OF THE DIAMETERS OF RIVETS FOR VARIOUS THICKNESSES OF PLATES WITH
SINGLE RIVETED LAP JOINT.
---------+-------------------------------------------------------
| DIAMETER OF RIVETS.
+-------+---------+----------+----------+-------+-------
Thickness|Lloyds'|Liverpool| English |Fairbairn.| Unwin.|Wilson.
of Plate.|Rules. | Rules. |Dockyards.| | |
---------+-------+---------+----------+----------+-------+-------
in. | in. | in. | in. | in. | in. | in.
5/16 | 5/8 | 5/8 | 1/2 | 5/8 | 11/16 | 5/8
3/8 | 5/8 | 5/8 | 5/8 | 3/4 | 3/4 | 11/16
7/16 | 5/8 | 3/4 | 3/4 | 21/32 | 13/16 | 3/4
1/2 | 3/4 | 13/16 | 3/4 | 3/4 | 7/8 | 3/4
---------+-------+---------+----------+----------+-------+-------
9/16 | 3/4 | 13/16 | 7/8 | 27/32 | 7/8 | 7/8
5/8 | 3/4 | 7/8 | 7/8 | 15/16 | 15/16 | 7/8
11/16 | 7/8 | 7/8 | 7/8 | 1-1/32 |1 | 7/8
3/4 | 7/8 | 15/16 | 1 | 1-1/8 |1-1/16 | 1
---------+-------+---------+----------+----------+-------+-------
13/16 | 7/8 | 1 | 1 | 1-7/32 |1-3/32 | 1
7/8 |1 | 1-1/8 | 1-1/8 | ... |1-1/8 | 1
15/16 |1 | 1-3/16 | 1-1/8 | ... |1-3/16 | 1-1/8
1 |1 | 1-1/4 | 1-1/8 | ... |1-1/4 | 1-1/8
---------+-------+---------+----------+----------+-------+-------
From the above it is seen that with thin plates the diameter of rivet
employed is about twice the thickness of the plate, whereas as the
thickness of plate increases the proportion of rivet diameter decreases,
and the reasons for this are, first, that with rivets twice the
thickness of thick plates and pitched so as to equalize the rivet and
plate sections the pitch would be too great to permit of the seams being
caulked steam tight.
The diameter of the rivet having been determined, the rivet area and
area of plate left between the rivet holes may be made equal by
determining the pitch by the following rule:
_Rule._--To the area of the rivet divided by the plate thickness add the
diameter of the rivet, and the sum so obtained is the pitch. The
correctness of this rule may be shown as follows:
Suppose the rivet diameter to be 7/8 inch = decimal equivalent .875, and
its area will be .6013 square inch. Suppose the thickness of the plate
to be 9/16 = decimal equivalent .5625, then by the rule:
Rivet area.
Plate thickness = .5625 ) .6013 ( 1.0689
5625
----
38800
33750
-----
50500
45000
-----
55000
50625
To this 1.0689 we are to add the rivet diameter, thus:
1.0689
.8750 = rivet diameter.
------
1.9439 = pitch of the rivets.
We have thus found the required pitch to be 1.9439 inches, and as the
joint is single riveted there are two half rivets or one whole one to
one pitch, and if we subtract the diameter of the rivet from the pitch
we shall get the width of the metal or plate left between the rivets,
thus:
1.9439 = pitch of rivets.
.8750 = diameter of rivet.
------
1.0689 = distance in inches between the rivets.
If now we multiply this distance between the rivets by the thickness of
the plate, we shall get the area of the plate that is left between the
rivet holes, thus:
1.0689 = width of plate between rivets.
.5625 = thickness of plate.
------
53445
21378
64134
53445
---------
Area of plate = .60125625
between rivets
Here then we find the area of plate left between the rivet holes to be
6.01 square inches, and as the area of the rivet is 6.01 square inches,
the two are shown to be equal.
We may now place the various rivet diameters and the pitches that will
make the rivet area and plate area in a single riveted joint equal in a
table as follows:
TABLE OF RIVET DIAMETERS AND PITCHES FOR SINGLE RIVETED LAP JOINTS.
-------------------+------------------+--------
Thickness of Plate.|Diameter of Rivet.| Pitch.
-------------------+------------------+--------
1/4 | 1/2 | 1-1/4
5/16 | 5/8 | 1-5/8
3/8 | 11/16 | 1-11/16
7/16 | 3/4 | 1-3/4
1/2 | 3/4 | 1-5/8
9/16 | 7/8 | 2
5/8 | 7/8 | 1-7/8
11/16 | 7/8 | 1-3/4
3/4 | 1 | ..
13/16 | 1 | 2
7/8 | 1 | 1-1/8
15/16 | 1-1/8 | 2-1/8
1 | 1-1/8 | 2-1/8
1-1/16 | 1-1/8 | 2-1/8
1-1/8 | 1-3/16 | 2-1/4
1-1/4 | 1-3/16 | 2-1/8
-------------------+------------------+--------
The rivets in double riveted lap joints, and in butt strap joints having
a single cover, are spaced alike, because in both cases there are two
rivets in one pitch, and the rivets are in single shear.
As there are two rivets in one pitch (instead of only one as in a single
riveted joint), therefore the percentage of rivet section is doubled,
and the plate section must therefore be doubled if the plate and rivet
sections are to be made equal, and the rule for finding the required
pitch is as follows:
_Rule._--To the amount of rivet area in one pitch, divided by the
thickness of the plate, add the diameter of the rivet.
_Example._--Let the plate thickness be as in the last example 9/16,
decimal equivalent = .5625, and the rivet diameter be 7/8 inch = decimal
equivalent .875, the area of one rivet being .6013 square inch, and the
pitch is calculated as follows:
.6013 = area of one rivet.
2 = the rivets in one pitch.
------
Plate thickness = .5625 ) 1.2026 ( 2.1377
1.1250
------
7760 2.137
5625 .875 = rivet diameter.
---- -----
21350 3.012 = pitch.
16875
-----
43750
39375
-----
43750
39375
-----
4375
We find, therefore, that the pitch is 3.012, or 3 inches (which is near
enough for practical purposes), and we may now make it clear that this
is correct.
[Illustration: Fig. 3257.]
In Fig. 3257 the joint is shown drawn one-half full size, and the length
a of plate left between the rivet holes measures (as nearly as it is
necessary to measure it) 2-5/32 inches, or 2.156, and if we multiply
this by the thickness of the plate = .5625 inch, we get 1.2 square
inches as the area of the plate left between the rivet holes.
Now there are two rivets in a pitch (as one-half of B, one-half of C,
and the whole of F), and as the area of each rivet is .6, therefore the
area of the two will be 1.2, and the plate section and rivet section are
shown to be equal.
The area at _a_ is obviously the same as that at A, because the pitches
of both rows of rivets are equal, this being an ordinary zigzag riveted
joint.
We may now consider the diagonal pitch of the rivets, using the rule
below.
The pitch × 6, + 4 times the rivet diameter
------------------------------------------- = the diagonal
divided by 10 pitch _p__{D}.
In this example the pitch has been found to be 3 inches, hence we have
.875 = diameter of rivet.
4 = constant.
-----
3.500
3 = pitch of the rivets.
6 = constant.
--
18
3.5 = rivet diameter multiplied by 4.
----
10 ) 21.5 (2.15 = the diagonal pitch.
20
--
15
10
--
50
The diagonal pitch, that is, the distance _p__{D}, Fig. 3257, is
therefore found to be 2.15, or 2-1/8 inch full.
The amount of metal left between the rivets, measured on the diagonal
pitch, is twice the dimension H multiplied by the thickness of the
plate, and as this (with the diagonal pitch determined as above) always
exceeds the pitch A or _a_, therefore if the plate fails, it will be
along the line _a_, and not through the diagonal pitch.
We may now consider the total amount that the plates overlap in a double
riveted lap joint zigzag riveted, this amount being twice the distance
E, added to the distance V between the rows of rivets.
The distance E, Fig. 3257, is usually made one and a half times the
diameter of the rivet, this being found to give sufficient strength to
prevent the edge of the plate from tearing out and to prevent the rivet
from shearing the plate out to the edge, rupture not being found to
occur in either of these directions.
The rule for finding the distance V, when the diagonal pitch has been
determined by the rules already explained, is as follows:
_Rule._--To the pitch multiplied by 11, add 4 times the rivet diameter,
then multiply by the pitch, plus 4 times the rivet diameter. Then
extract the square root and divide by 10.
Placed in formula, the rule appears as follows, _d_ representing the
rivet diameter, and _p_ the pitch.
__________________________
\/(11_p_ + 4_d_)(_p_ + 4_d_)
---------------------------- = distance V between the rows of rivets.
10
As this rule involves the extraction of the square root of the sum of
quantities above the line, and as in determining the diagonal pitch, we
have already determined the distance V, it is unnecessary to our purpose
to carry out this latter calculation, as it is easier to find the
diagonal pitch, and then, after drawing the joint, the distance between
the rows of rivets can be measured if it is required, as it might be in
finding the length of plate required to roll into a strake for a boiler
of a given diameter and having a double riveted lap joint.
We may now consider chain riveted joints in comparison with zigzag
riveted joints, which is especially necessary, because it has been
assumed by some that the second row of rivets in a chain riveted joint
added nothing to the strength of the joint.
[Illustration: Fig. 3258.]
Fig. 3258 represents a chain riveted joint, having the same thickness of
plate, rivet diameter and pitch as the zigzag riveted joint in Fig.
3257, and it will be seen that the plate sections at a and at _a_ are
the same in the two figures, and as there are four half rivets, which
are equal to two rivets, in one pitch, therefore the strength of the two
joints is equal.
Each joint can be as efficiently caulked as the other, as the rivet
spacing is the same and the edge of the plate is the same distance from
the rivets in both cases.
The pitch of the rivets is obtained by the same rule as for zigzag
riveted joints, and all we have now to consider is the distance apart of
the two rows of rivets or distance V in the Fig. 3258, and for this
there are two rules, the first being that it shall not be less than
twice the diameter of the rivet, which would leave a dimension at H in
the figure equal to the diameter of the rivet. The second rule is that a
better proportion than the above is to multiply the diameter of the
rivet by 3. This makes the dimension at H equal to twice the rivet
diameter.
When the joints have double buttstraps, the rivets may be spaced as wide
as the necessity for tight caulking will admit, because, on account of
the rivets being in double shear, the rivet percentage exceeds the plate
percentage.
[Illustration: Fig. 3259.]
The allowance for the rivets being in double shear is 75 per cent., or
in other words, a rivet in double shear is allowed 1.75 times the area
of the same size rivet in single shear.
STATIONARY ENGINE BOILERS.
The simplest form of horizontal boiler is the plain cylinder boiler, an
example of which is given in Fig. 3259, and which is largely used in
iron works and coal mines.
Boilers of this class are easily cleaned, because the whole interior can
be readily got at to clean.
As the bottom of this boiler gets thinned from wear, the boiler is
turned upside down, thus prolonging its life.
[Illustration: Fig. 3260.]
Fig. 3260 represents an internally fired flue boiler, known as the
Cornish or Lancashire boiler. The furnace is at one end of the flues,
the fire passing through them to the chimney. There is here obviously
more heating surface than in the plain cylinder boiler, but somewhat
less facility for cleaning.
The Galloway boiler is of this class, but has vertical water tubes
placed at intervals in the flues. These water tubes are wider at the top
than at the bottom. They serve to break up the body of heat that passes
through the flues, and increase the heating surface while extracting
more of the heat and promoting the circulation of the water in the
boiler.
A water tube is one in which the water is inside and the fire outside,
as distinguished from a fire tube, in which the fire passes through the
tube and the water is outside. A water tube is stronger than a fire
tube, because the former is subject to bursting pressure and the latter
to collapsing pressure.
Vertical boilers are internally fired, and in the ordinary forms have no
return tubes or flues, examples of those used for small stationary
engines being given as follows.
[Illustration: Fig. 3261.]
Fig. 3261 represents an ordinary form with vertical tubes. The upper
ends of the tubes here pass through the steam space--a condition that
under the moderate pressures and firing that this class of boiler is
subjected to is of less importance than it is in boilers having higher
chimneys and therefore a more rapid draught, and using higher pressures
of steam. Furthermore, the small diameters and lengths or heights in
which these boilers are made give them ample strength with shells and
tubes of less thickness, while the condition of tube ends with steam on
one side and fire on the other is permissible without the injurious
effects that ensue under rapid combustion and high pressures.
[Illustration: Fig. 3262.]
The crown sheet of the fire boxes or furnaces of this class of boiler is
very effective heating surface, first, because of the great depth (and
therefore weight) of water resting upon it insuring constant contact
between the water and the plate, while there is no danger of the crown
sheet burning from shortness of water.
A similar boiler, but with the upper ends of the tubes below the water
level, is shown in Fig. 3262.
From the small diameters of these boilers, the flat surfaces are not
stayed except to the extent that the holding power of the tubes serves
that end.
[Illustration: Fig. 3263.]
[Illustration: Fig. 3264.]
A return flue vertical boiler is shown in Figs. 3263 and 3264. The whole
of the surfaces having contact with the fire also have contact with the
water, and the height of the crown sheet removes it from the intense
heat of the fire. It is stayed to the top of the boiler. The fire box or
combustion chamber being taper increases the effectiveness of its sides
as heating surface, since the heat in its vertical passage impinges
against it.
The products of combustion pass from the top of the combustion chamber
through short horizontal flues, which enter an annular space surrounding
the lower section of the boiler, and from this space vertical flues pass
to a corresponding space at the bottom of the boiler.
The passage of the steam generated at the sides of the combustion
chamber is facilitated by the taper of the chamber, which gives
increased room for the steam as it gathers in ascending.
Vertical boilers for high pressures, as from 60 to 120 lbs. per inch,
are represented in the figures from 3265 to 3269.
In boilers of this class, a majority contain water tubes, which, when
properly arranged, promote rapid evaporation and circulation.
A boiler with _Field_ tubes is shown in Fig. 3265. It consists of an
outer shell and a cylindrical fire box, from the crown sheet of which a
number of Field tubes are suspended in the fire box or combustion
chamber.
Fig. 3266 is a sectional view of a Field tube, the construction being as
follows:
The outer tube, which is expanded into the tube plate, is enclosed at
its lower end, and has at its upper end in the water space of the boiler
a perforated mouth piece, from which is suspended an inner tube that
extends nearly to the bottom of the outer tube.
As the outer tube is bathed in the fire, steam is generated very
rapidly, and a thorough and rapid circulation is kept up, the water
passing down the inner and up the outer tubes, as denoted by the arrows.
The outer tube is spread out at the upper end to a slight cone, so that
it cannot be forced out of the tube sheet by the pressure, and as it
hangs free, there is no liability for it to loosen or get leaky from
expansion and contraction.
From the great amount of heating surface obtained with these tubes, the
fire box may be kept at a minimum diameter for the duty, while still
leaving a wide space for the water leg, which facilitates the
circulation.
[Illustration: Fig. 3265.]
[Illustration: Fig. 3266.]
The damper, which is suspended in the uptake, spreads the fire sideways.
[Illustration: Fig. 3267.]
Fig. 3267 represents the arrangement of Field tubes in a boiler.
A boiler of this form may for a given capacity be made lighter and
smaller than in any other of the ordinary forms, while the rapid
circulation acts to keep the tubes clean.
The inner tubes may be thin, because they are under pressure both inside
and out, while the outer tubes may be thin, because they are under a
bursting strain, whereas a fire tube is under collapsing pressure.
[Illustration: Fig. 3268.]
A design of high rate boilers, in which the uptake does not come into
contact with the water, and water tubes are employed, is shown in Fig.
3268. In the fire box is an inclined tube which promotes the
circulation, and is very effective heating surface, and in the
combustion chamber are a number of vertical water tubes.
Two manholes give access for cleaning purposes.
The efficiency of the heating surface in this class of boiler is
increased from the fact that, as the heat does not pass direct through
the boiler, it impinges against the surface. In Fig. 3269, for example,
the exit from the spherical fire box is on one side of the boiler, and
the uptake on the other, the heat passing from the fire box into a
combustion chamber, and thence through the horizontal fire tubes to the
uptake.
The crown sheet is here stayed by gusset stays, but if made spherical,
as in Fig. 3270, the stays may be omitted.
[Illustration: _VOL. II._ =BOILER FOR STATIONARY ENGINES.= _PLATE
XXVIII._
Fig. 3271.]
Figs. 3271, 3272, and 3273 illustrate a 60-inch horizontal return
tubular boiler constructed by the Hartford Steam Boiler Inspection and
Insurance Company. This class of boiler has found much favor in the
United States. It is an externally fired, return tube boiler, the fire
passing beneath the boiler and returning through the tubes to the front
end of the boiler, whence it passes through the drum to the chimney.
[Illustration: Fig. 3269.]
[Illustration: Fig. 3270.]
[Illustration: Fig. 3272.]
The boiler is supported on the brackets B, B´, the front one, B, resting
on an iron plate imbedded in the brickwork, and the back ones on rollers
which rest on the plates P´ imbedded in the brickwork. This allows the
boiler to expand and contract endways under variations of temperature
without racking the brickwork.
[Illustration: Fig. 3273.]
A, A, etc., are for holding the brickwork together. The blow-off pipe C
is for emptying or blowing down the boiler. The feed-pipe F enters the
front end of the boiler, passes along it, and then crosses over. A pipe
H from the steam space of the boiler supplies steam to the steam gauge
G, and to the upper end of the gauge glass, which is on the casting K.
The lower end of the gauge glass receives water from a pipe which passes
into the water space of the boiler; at J are the three gauge cocks for
testing the height of the water in the boiler.
The manhole affords ingress into the boiler for inspecting and for
scaling or cleaning it, the nozzles being for a safety valve. At E is a
hand-hole for washing out and cleaning the boiler. P is a damper in the
fire door for admitting air above the fire bars, and R is a damper for
regulating the draught.
In the brick walls that support the boiler there are air spaces to
prevent the conduction of the heat through and prevent cracking of the
brickwork. The tubes are arranged in vertical and horizontal rows and
are equally spaced throughout.
Fig. 3274 represents the front end, and Fig. 3275 a longitudinal
sectional view of the front end of a boiler of this class. In this case,
however, the pipes for the water gauge pass direct into the boiler.
In some practice the tubes are arranged as in Fig. 3276, being wider
pitched or spaced in the middle of the boiler to increase the
circulation of the water in the boiler.
Another arrangement is shown in Fig. 3277, the tubes being _staggered_
or arranged zigzag. This permits of the employment of a greater number
of tubes, but does not afford such free circulation of the water.
Fig. 3278 represents an arrangement where the tubes are in rows both
vertically and horizontally.
Fig. 3279 represents a boiler by the Erie Iron Works, the details of the
setting being as follows:
[Illustration: Fig. 3274.]
[Illustration: Fig. 3275.]
[Illustration: Fig. 3276.]
[Illustration: Fig. 3277.]
[Illustration: Fig. 3278.]
[Illustration: Fig. 3279.]
[Illustration: Fig. 3280.]
[Illustration: Fig. 3281.]
Fig. 3280 is an end view of the setting with the brickwork in section.
Fig. 3281 side view of the boiler and setting.
[Illustration: Fig. 3282.]
[Illustration: Fig. 3283.]
Fig. 3282 a front end view of the boiler, and Fig. 3283 a ground plan of
the brickwork. When the front plate of the boiler setting extends above
the middle of the boiler, as in Fig. 3279, it is said to have a "full
arch front." Whereas when this plate or casting extends to the middle
only of the boiler, it is said to have a half arch front.
[Illustration: Figs. 3284, 3285, 3286, 3287.]
Figs. 3284, 3285, 3286, and 3287 show the setting for a half arch front
boiler, the dimensions of the settings of both these boilers being given
in the following tables:
MEASUREMENTS FOR SETTING TUBULAR STATIONARY BOILERS WITH FULL ARCH
FRONTS.
REFERENCE LETTERS ON DIAGRAMS.
------+---+----+----+----+----+----+------+----+----+----+----+----
No. | A | B | C | D | E | F | G | H | I | J | K | L
------+---+----+----+----+----+----+------+----+----+----+----+----
|Ft.|Ins.|Ins.|Ins.|Ins.|Ins.| Ins. |Ins.|Ins.|Ins.|Ins.|Ins.
1 | 7| 32 | 12 | 20 | 16 | 45 |44 | 7 | 32 | 64 | 85 | 26
2 | 7| 34 | 12 | 20 | 16 | 48 |47 | 8 | 34 | 66 | 90 | 26
3 | 8| 36 | 12 | 20 | 16 | 48 |47 | 8 | 36 | 68 | 92 | 26
3-1/2| 10| 36 | 12 | 20 | 16 | 48 |47 | 8 | 36 | 68 | 92 | 26
4 | 8| 42 | 14 | 20 | 16 | 48 |47 | 8 | 42 | 74 | 98 | 27
5 | 10| 42 | 14 | 20 | 16 | 48 |47 | 8 | 42 | 74 | 98 | 27
6 | 10| 44 | 14 | 24 | 16 | 48 |47 | 10 | 44 | 76 |100 | 27
7 | 12| 44 | 14 | 24 | 16 | 48 |46-1/2| 10 | 44 | 76 |100 | 27
7-1/2| 14| 44 | 14 | 24 | 16 | 47 |45-1/2| 10 | 44 | 76 | 99 | 26
8 | 12| 48 | 16 | 24 | 16 | 47 |45-1/2| 10 | 48 | 88 |103 | 26
9 | 14| 48 | 16 | 24 | 16 | 47 |45-1/2| 10 | 48 | 88 |103 | 26
10 | 12| 54 | 16 | 24 | 20 | 50 |48-1/2| 10 | 54 | 94 |112 | 26
10-1/2| 15| 54 | 16 | 24 | 20 | 50 |48-1/2| 10 | 54 | 94 |112 | 26
11 | 12| 60 | 18 | 24 | 20 | 50 |48-1/2| 12 | 60 |108 |118 | 26
12 | 14| 60 | 18 | 24 | 20 | 50 |48-1/2| 12 | 60 |108 |118 | 26
13 | 16| 60 | 18 | 26 | 20 | 50 |48 | 12 | 60 |108 |118 | 26
14 | 15| 66 | 18 | 28 | 20 | 50 |48-1/2| 12 | 66 |114 |124 | 26
15 | 16| 66 | 18 | 28 | 20 | 50 |48 | 12 | 66 |114 |124 | 26
16 | 16| 72 | 20 | 30 | 20 | 50 |48 | 12 | 72 |120 |130 | 26
------+---+----+----+----+----+----+------+----+----+----+----+----
------+----+-------+----+----+----+----+----+----+----+------+------
| | | | | | | | | | | NO.
| | | | | | | | | | |COMMON
| | | | | | | | | | |BRICK
| | | | | | | | | |NO. OF|ABOVE
No. | M | N | O | P | Q | R | S | T | U | FIRE |FLOOR
| | | | | | | | | |BRICK.|LEVEL.
------+----+-------+----+----+----+----+----+----+----+------+------
|Ins.|Ft.Ins.|Ins.|Ins.|Ins.|Ins.|Ins.|Ins.|Ins.| |
1 | 19 | 11-6 | 20 | 40 | 12 | 16 | 36 | 34 | 4 | 600 | 6800
2 | 22 | 11-6 | 20 | 40 | 12 | 16 | 36 | 34 | 4 | 600 | 7500
3 | 22 | 12-6 | 24 | 40 | 12 | 16 | 36 | 34 | 4 | 650 | 7700
3-1/2| 22 | 14-6 | 28 | 46 | 12 | 16 | 42 | 42 | 4 | 720 | 8500
4 | 21 | 12-8 | 24 | 40 | 12 | 16 | 36 | 34 | 4 | 730 | 8500
5 | 21 | 14-8 | 28 | 46 | 12 | 16 | 42 | 42 | 4 | 770 | 9600
6 | 21 | 15-0 | 28 | 46 | 12 | 16 | 42 | 42 | 4 | 880 | 10500
7 | 21 | 17-0 | 32 | 52 | 12 | 16 | 48 | 49 | 4 | 940 | 10800
7-1/2| 21 | 19-0 | 36 | 58 | 12 | 16 | 54 | 84 | 4 | 1120 | 11500
8 | 21 | 17-2 | 32 | 52 | 12 | 20 | 48 | 49 | 4 | 1120 | 13600
9 | 21 | 19-2 | 36 | 58 | 12 | 20 | 54 | 84 | 4 | 1140 | 15700
10 | 24 | 17-6 | 32 | 52 | 12 | 20 | 48 | 49 | 4 | 1160 | 16200
10-1/2| 24 | 20-8 | 36 | 56 | 16 | 20 | 54 | 90 | 4 | 1270 | 17500
11 | 24 | 17-10 | 32 | 50 | 16 | 24 | 48 | 49 | 4 | 1400 | 20500
12 | 24 | 19-10 | 36 | 56 | 16 | 24 | 54 | 84 | 4 | 1500 | 23000
13 | 24 | 22-0 | 40 | 56 | 16 | 24 | 54 | 96 | 4 | 1540 | 25300
14 | 24 | 21-2 | 36 | 56 | 16 | 24 | 54 | 90 | 4 | 1590 | 26000
15 | 24 | 22-2 | 40 | 56 | 16 | 24 | 54 | 96 | 4 | 1620 | 27000
16 | 24 | 22-6 | 40 | 56 | 16 | 24 | 54 | 96 | 4 | 1750 | 30000
------+----+-------+----+----+----+----+----+----+----+------+------
NOTE.--In setting "Standard" boilers, the side walls should be so built
that the longitudinal seams of the shell will be protected from the
fire.
MEASUREMENTS FOR SETTING TUBULAR STATIONARY BOILERS WITH HALF ARCH
FRONTS.
REFERENCE LETTERS ON DIAGRAMS.
------+---+----+----+----+----+------+------+----+----+----+-------
No. | A | B | C | D | E | F | G | H | I | J | K
------+---+----+----+----+----+------+------+----+----+----+-------
|Ft.|Ins.|Ins.|Ins.|Ins.|Ins. | Ins. |Ins.|Ins.|Ins.| Ins.
1 | 7 | 32 | 14 | 20 | 16 |46 |45 | 7 | 32 | 64 | 73
2 | 7 | 34 | 14 | 20 | 16 |46 |45 | 8 | 34 | 66 | 75
3 | 8 | 36 | 14 | 20 | 16 |46 |45 | 8 | 36 | 68 | 77
3-1/2|10 | 36 | 14 | 20 | 16 |46 |45 | 8 | 36 | 68 | 77
4 | 8 | 42 | 18 | 20 | 16 |46 |45 | 8 | 42 | 74 | 83
5 |10 | 42 | 18 | 20 | 16 |46 |45 | 8 | 42 | 74 | 83
6 |10 | 44 | 18 | 24 | 16 |46 |45 | 10 | 44 | 76 | 85
7 |12 | 44 | 18 | 24 | 16 |46 |44-1/2| 10 | 44 | 76 | 85
7-1/2|14 | 44 | 18 | 24 | 16 |46 |44-1/2| 10 | 44 | 76 | 85
8 |12 | 48 | 19 | 24 | 16 |50 |48-1/2| 10 | 48 | 88 | 93
9 |14 | 48 | 19 | 24 | 16 |50 |48-1/2| 10 | 48 | 88 | 93
10 |12 | 54 | 19 | 24 | 20 |50 |48-1/2| 10 | 54 | 94 | 99
10-1/2|15 | 54 | 19 | 24 | 20 |50 |48-1/2| 10 | 54 | 94 | 99
11 |12 | 60 | 21 | 24 | 20 |46-3/4|45-1/2| 12 | 60 |108 |101-3/4
12 |14 | 60 | 21 | 24 | 20 |46-3/4|45 | 12 | 60 |108 |101-3/4
13 |16 | 60 | 21 | 26 | 20 |46-3/4|45 | 12 | 60 |108 |101-3/4
14 |15 | 66 | 24 | 28 | 20 |47 |45-1/2| 12 | 66 |114 |108
15 |16 | 66 | 24 | 28 | 20 |47 |45-1/2| 12 | 66 |114 |108
16 |16 | 72 | 24 | 30 | 20 |48 |46-1/2| 12 | 72 |120 |115
------+---+----+----+----+----+------+------+----+----+----+-------
------+------+------+--------+----+------+----+----+----+----+----
No. | L | M | N | O | P | Q | R | S | T | U
------+------+------+--------+----+------+----+----+----+----+----
| Ins. | Ins. |Ft. Ins.|Ins.| Ins. |Ins.|Ins.|Ins.|Ins.|Ins.
1 |26 |20 | 10-3 | 20 |33 | 12 | 16 | 36 | 34 | 4
2 |26 |20 | 10-3 | 20 |33 | 12 | 16 | 36 | 34 | 4
3 |26 |20 | 11-3 | 24 |33 | 12 | 16 | 36 | 34 | 4
3-1/2|26 |20 | 13-3 | 28 |39 | 12 | 16 | 42 | 42 | 4
4 |27 |19 | 11-3 | 24 |32-1/2| 12 | 16 | 36 | 34 | 4
5 |27 |19 | 13-3 | 28 |38-1/2| 12 | 16 | 42 | 42 | 4
6 |27 |19 | 13-7 | 28 |38-1/2| 12 | 16 | 42 | 42 | 4
7 |27 |19 | 15-7 | 32 |44-1/2| 12 | 16 | 48 | 49 | 4
7-1/2|27 |19 | 17-7 | 36 |50-1/2| 12 | 16 | 54 | 84 | 4
8 |26 |24 | 15-7 | 32 |48 | 12 | 20 | 48 | 49 | 4
9 |26 |24 | 17-7 | 36 |54 | 12 | 20 | 54 | 84 | 4
10 |26 |24 | 15-11 | 32 |48-1/2| 12 | 20 | 48 | 49 | 4
10-1/2|26 |24 | 19-1 | 36 |52-1/2| 16 | 20 | 54 | 90 | 4
11 |26 |20-3/4| 16-1 | 32 |47 | 16 | 24 | 48 | 49 | 4
12 |26 |20-3/4| 18-1 | 36 |53 | 16 | 24 | 54 | 84 | 4
13 |26 |20-3/4| 20-3 | 40 |53 | 16 | 24 | 54 | 96 | 4
14 |26 |21 | 19-5 | 36 |52-1/2| 16 | 24 | 54 | 90 | 4
15 |26 |21 | 20-5 | 40 |52-1/2| 16 | 24 | 54 | 96 | 4
16 |28-1/4|19-3/4| 20-7 | 40 |52-1/2| 16 | 24 | 54 | 96 | 4
------+------+------+--------+----+------+----+----+----+----+----
------+------+------+----+----+----+------+------
| | | | | | | NO.
| | | | | | |COMMON
| | | | | | |BRICK
| | | | | |NO. OF|ABOVE
No. | V | W | X | Y | Z | FIRE |FLOOR
| | | | | |BRICK.|LEVEL.
------+------+------+----+----+----+------+------
| Ins. | Ins. |Ins.|Ins.|Ins.| |
1 |36 | 9 | 24 | 12 | 7 | 600 | 6150
2 |36 | 9 | 28 | 12 | 7 | 600 | 6200
3 |36 | 9 | 28 | 12 | 15 | 650 | 6700
3-1/2|36 | 9 | 28 | 12 | 25 | 720 | 7050
4 |32-3/4|12-1/4| 32 | 16 | 11 | 730 | 7700
5 |32-3/4|12-1/4| 32 | 16 | 25 | 770 | 8700
6 |32-3/4|12-1/4| 36 | 16 | 25 | 880 | 8800
7 |32-1/4|12-1/4| 36 | 20 | 35 | 940 | 9300
7-1/2|32-1/4|12-1/4| 36 | 24 | 45 | 1120 | 9500
8 |36-1/4|12-1/4| 36 | 20 | 35 | 1120 | 11100
9 |36-1/4|12-1/4| 36 | 24 | 45 | 1140 | 12900
10 |34 |14-1/2| 42 | 20 | 35 | 1160 | 13200
10-1/2|34 |14-1/2| 42 | 24 | 57 | 1270 | 14200
11 |31 |14-1/2| 48 | 20 | 37 | 1400 | 16700
12 |30-1/2|14-1/2| 48 | 24 | 45 | 1500 | 19200
13 |30-1/2|14-1/2| 48 | 24 | 65 | 1540 | 21500
14 |31 |14-1/2| 54 | 24 | 57 | 1590 | 22100
15 |31 |14-1/2| 54 | 24 | 65 | 1620 | 23100
16 |27-1/2|19 | 54 | 24 | 65 | 1750 | 26000
------+------+------+----+----+----+------+------
NOTE.--In setting "Standard" boilers, the side walls should be so built
that the longitudinal seams of the shell will be protected from the
fire.
THE EVAPORATIVE EFFICIENCIES OF BOILERS.
[56]"Many tests have been undertaken to ascertain the evaporative power
of different classes of boilers in actual work; but few of these are of
any value, owing to the unreliable means usually employed to measure the
quantity of water evaporated. The easiest method, and consequently the
one most frequently adopted, is to measure the quantity by the
difference of its height in the water-gauge glass at the beginning and
end of the trial, and also at intermediate stages. This method is very
rude and uncertain, since there can be little doubt that in many boilers
at work the surface of the water is not level, but is usually higher
over the furnace, or where the greatest ebullition occurs. The
difference in height at any moment will greatly depend upon the
intensity of the ebullition, which is ever varying during the intervals
between firing. With mechanical firing the difference of height is
probably reduced to a minimum.
[56] From "_A Treatise on Steam Boilers_," by Robert Wilson.
"The meters employed for measuring the water are sometimes not
trustworthy. The only sure method of ascertaining the quantity of water
evaporated is by actual measurement with a cistern or vessel whose cubic
contents are accurately known. The quantity of water in the boiler
before and after the trial should be measured at the same temperature,
which should not exceed 212° to insure accuracy. But even when the
amount of water introduced and the quantity passed off from the boiler
are accurately ascertained, there yet remains a doubt as to how much has
been actually evaporated, and how much may have passed off in priming,
unless the trial has been conducted with the boiler open to the
atmosphere, which appears to be the only condition under which accuracy
can be insured, unless a suitable apparatus can be provided for
accurately measuring the weight and temperature of all the steam and
water given off, when the boiler is working above atmospheric pressure.
"There are very few boilers that do not prime more or less, and the
quantity of water passed off in this manner is sometimes very
considerable, and has led to the impossible results of 16 and 17 lbs. of
water evaporated per lb. of ordinary coal in locomotive and water-tube
boilers being seriously recorded. Externally fired boilers, that have
given the moderate result of 5 lbs. of water per lb. of coal at
atmospheric pressure, have shown the unexpected result of 10 and 12 lbs.
of water evaporated at 40 lbs. pressure. In fact, unless the amount of
water passed over with the steam by priming or foaming, when working
under pressure, can be accurately ascertained, the evaporative results
are not to be relied upon, however careful in other respects the trial
may have been conducted. It is customary to give the quantity of water
evaporated from and at a temperature of 212°, or the boiling point at
atmospheric pressure, to which the results of evaporation are reduced."
The quantity corresponding to any temperature of feed water and working
pressure can readily be found with the aid of the annexed table, taken
from _The Encyclopædia Britannica_, wherein are presented the relations
of the properties of steam, as now accepted by the best authorities.
TABLE GIVING THE PRESSURE, TEMPERATURE, AND VOLUME OF STEAM.
-----------+-----------+-----------+----------+---------+-------------
Total pres-| | | | |Relative vol-
sure per |Gauge pres-| Sensible |Total heat|Weight of| ume of steam
square inch| sure or |temperature|in degrees|one cubic|compared with
measured | pressure | in |from zero |foot of | the water
from a | above | Fahrenheit| of | steam. |from which it
vacuum. |atmosphere.| degrees. | Fahren- | lbs. | was
lbs. | lbs. | | heit. | | evaporated.
-----------+-----------+-----------+----------+---------+-------------
1 | --- | 102.1 | 1144.5 | .0030 | 20582
2 | --- | 126.3 | 1151.7 | .0058 | 10721
3 | --- | 141.6 | 1156.6 | .0085 | 7322
4 | --- | 153.1 | 1160.1 | .0112 | 5583
5 | --- | 162.3 | 1162.9 | .0138 | 4527
6 | --- | 170.2 | 1165.3 | .0163 | 3813
7 | --- | 176.9 | 1167.3 | .0189 | 3298
8 | --- | 182.9 | 1169.2 | .0214 | 2909
9 | --- | 188.3 | 1170.8 | .0239 | 2604
10 | --- | 193.3 | 1172.3 | .0264 | 2358
11 | --- | 197.8 | 1173.7 | .0289 | 2157
12 | --- | 202.0 | 1175.0 | .0314 | 1986
13 | --- | 205.9 | 1176.2 | .0338 | 1842
14 | --- | 209.6 | 1177.3 | .0362 | 1720
14.7 | 0 | 212.0 | 1178.1 | .0380 | 1642
15 | .3 | 213.1 | 1178.4 | .0387 | 1610
16 | 1.3 | 216.3 | 1179.4 | .0411 | 1515
17 | 2.3 | 219.6 | 1180.3 | .0435 | 1431
18 | 3.3 | 222.4 | 1181.2 | .0459 | 1357
19 | 4.3 | 225.3 | 1182.1 | .0483 | 1290
20 | 5.3 | 228.0 | 1182.9 | .0507 | 1229
21 | 6.3 | 230.6 | 1183.7 | .0531 | 1174
22 | 7.3 | 233.1 | 1184.5 | .0555 | 1123
23 | 8.3 | 235.3 | 1185.2 | .0580 | 1075
24 | 9.3 | 237.8 | 1185.9 | .0601 | 1036
25 | 10.3 | 240.1 | 1186.6 | .0625 | 996
26 | 11.3 | 242.3 | 1187.3 | .0650 | 958
27 | 12.3 | 244.4 | 1187.8 | .0673 | 926
28 | 13.3 | 246.4 | 1188.4 | .0696 | 895
29 | 14.3 | 248.4 | 1189.1 | .0719 | 866
30 | 15.3 | 250.4 | 1189.8 | .0743 | 838
31 | 16.3 | 252.2 | 1190.4 | .0766 | 813
32 | 17.3 | 254.1 | 1190.9 | .0779 | 789
33 | 18.3 | 255.9 | 1191.5 | .0812 | 767
34 | 19.3 | 257.6 | 1192.0 | .0835 | 746
35 | 20.3 | 259.3 | 1192.5 | .0858 | 726
36 | 21.3 | 260.9 | 1193.0 | .0881 | 707
37 | 22.3 | 262.6 | 1193.5 | .0905 | 688
38 | 23.3 | 264.2 | 1194.0 | .0929 | 671
39 | 24.3 | 265.8 | 1194.5 | .0952 | 655
40 | 25.3 | 267.3 | 1194.9 | .0974 | 640
41 | 26.3 | 268.7 | 1195.4 | .0996 | 625
42 | 27.3 | 270.2 | 1195.8 | .1020 | 611
43 | 28.3 | 271.6 | 1196.2 | .1042 | 598
44 | 29.3 | 273.0 | 1196.6 | .1065 | 595
45 | 30.3 | 274.4 | 1197.1 | .1089 | 572
46 | 31.3 | 275.8 | 1197.5 | .1111 | 561
47 | 32.3 | 277.1 | 1197.9 | .1133 | 550
48 | 33.3 | 278.4 | 1198.3 | .1156 | 539
49 | 34.3 | 279.7 | 1198.7 | .1179 | 529
50 | 35.3 | 281.0 | 1199.1 | .1202 | 518
51 | 36.3 | 282.3 | 1199.5 | .1224 | 509
52 | 37.3 | 283.5 | 1199.9 | .1246 | 500
53 | 38.3 | 284.7 | 1200.3 | .1269 | 491
54 | 39.3 | 285.9 | 1200.6 | .1291 | 482
55 | 40.3 | 287.1 | 1201.0 | .1314 | 474
56 | 41.3 | 288.2 | 1201.3 | .1336 | 466
57 | 42.3 | 289.3 | 1201.7 | .1364 | 458
58 | 43.3 | 290.4 | 1202.0 | .1380 | 451
59 | 44.3 | 291.6 | 1202.4 | .1403 | 444
60 | 45.3 | 292.7 | 1202.7 | .1425 | 437
61 | 46.3 | 293.8 | 1203.1 | .1447 | 403
62 | 47.3 | 294.8 | 1203.4 | .1469 | 424
63 | 48.3 | 295.9 | 1203.7 | .1493 | 417
64 | 49.3 | 296.9 | 1204.0 | .1516 | 411
65 | 50.3 | 298.0 | 1204.3 | .1538 | 405
66 | 51.3 | 299.0 | 1204.6 | .1560 | 399
67 | 52.3 | 300.0 | 1204.9 | .1583 | 393
68 | 53.3 | 300.9 | 1205.2 | .1605 | 388
69 | 54.3 | 301.9 | 1205.5 | .1627 | 383
70 | 55.3 | 302.9 | 1205.8 | .1648 | 378
71 | 56.3 | 303.9 | 1206.1 | .1670 | 373
72 | 57.3 | 304.8 | 1206.3 | .1692 | 368
73 | 58.3 | 305.7 | 1206.6 | .1714 | 363
74 | 59.3 | 306.6 | 1206.9 | .1736 | 359
75 | 60.3 | 307.5 | 1207.2 | .1759 | 353
76 | 61.3 | 308.4 | 1207.4 | .1782 | 349
77 | 62.3 | 309.3 | 1207.7 | .1804 | 345
78 | 63.3 | 310.2 | 1208.0 | .1826 | 341
79 | 64.3 | 311.1 | 1208.3 | .1848 | 337
80 | 65.3 | 312.0 | 1208.5 | .1869 | 333
81 | 66.3 | 312.8 | 1208.8 | .1891 | 329
82 | 67.3 | 313.6 | 1209.1 | .1913 | 325
83 | 68.3 | 314.5 | 1209.4 | .1935 | 321
84 | 69.3 | 315.3 | 1209.6 | .1957 | 318
85 | 70.3 | 316.1 | 1209.9 | .1980 | 314
86 | 71.3 | 316.9 | 1210.1 | .2002 | 311
87 | 72.3 | 317.8 | 1210.4 | .2024 | 308
88 | 73.3 | 318.6 | 1210.6 | .2044 | 305
89 | 74.3 | 319.4 | 1210.9 | .2067 | 301
90 | 75.3 | 320.2 | 1211.1 | .2089 | 298
91 | 76.3 | 321.0 | 1211.3 | .2111 | 295
92 | 77.3 | 321.7 | 1211.5 | .2133 | 292
93 | 78.3 | 322.5 | 1211.8 | .2155 | 289
94 | 79.3 | 323.3 | 1212.0 | .2176 | 286
95 | 80.3 | 324.1 | 1212.3 | .2198 | 283
96 | 81.3 | 324.8 | 1212.5 | .2219 | 281
97 | 82.3 | 325.6 | 1212.8 | .2241 | 278
98 | 83.3 | 326.3 | 1213.0 | .2263 | 275
99 | 84.3 | 327.1 | 1213.2 | .2285 | 272
100 | 85.3 | 327.9 | 1213.4 | .2307 | 270
101 | 86.3 | 328.5 | 1213.6 | .2329 | 267
102 | 87.3 | 329.1 | 1213.8 | .2351 | 265
103 | 88.3 | 329.9 | 1214.0 | .2373 | 262
104 | 89.3 | 330.6 | 1214.2 | .2393 | 260
105 | 90.3 | 331.3 | 1214.4 | .2414 | 257
106 | 91.3 | 331.9 | 1214.6 | .2435 | 255
107 | 92.3 | 332.6 | 1214.8 | .2456 | 253
108 | 93.3 | 333.3 | 1215.0 | .2477 | 251
109 | 94.3 | 334.0 | 1215.3 | .2499 | 249
110 | 95.3 | 334.6 | 1215.5 | .2521 | 247
111 | 96.3 | 335.3 | 1215.7 | .2543 | 245
112 | 97.3 | 336.0 | 1215.9 | .2564 | 243
113 | 98.3 | 336.7 | 1216.1 | .2586 | 241
114 | 99.3 | 337.4 | 1216.3 | .2607 | 239
115 | 100.3 | 338.0 | 1216.5 | .2628 | 237
116 | 101.3 | 338.6 | 1216.7 | .2649 | 235
117 | 102.3 | 339.3 | 1216.9 | .2674 | 233
118 | 103.3 | 339.9 | 1217.1 | .2696 | 231
119 | 104.3 | 340.5 | 1217.3 | .2738 | 229
120 | 105.3 | 341.1 | 1217.4 | .2759 | 227
121 | 106.3 | 341.8 | 1217.6 | .2780 | 225
122 | 107.3 | 342.4 | 1217.8 | .2801 | 224
123 | 108.3 | 343.0 | 1218.0 | .2822 | 222
124 | 109.3 | 343.6 | 1218.2 | .2845 | 221
125 | 110.3 | 344.2 | 1218.4 | .2867 | 219
126 | 111.3 | 344.8 | 1218.6 | .2889 | 217
127 | 112.3 | 345.4 | 1218.8 | .2911 | 215
128 | 113.3 | 346.0 | 1218.9 | .2933 | 214
129 | 114.3 | 346.6 | 1219.1 | .2955 | 212
130 | 115.3 | 347.2 | 1219.3 | .2977 | 211
131 | 116.3 | 347.8 | 1219.5 | .2999 | 209
132 | 117.3 | 348.3 | 1219.6 | .3020 | 208
133 | 118.3 | 348.9 | 1219.8 | .3040 | 206
134 | 119.3 | 349.5 | 1220.0 | .3060 | 205
135 | 120.3 | 350.1 | 1220.2 | .3080 | 203
136 | 121.3 | 350.6 | 1220.3 | .3101 | 202
137 | 122.3 | 351.2 | 1220.5 | .3121 | 200
138 | 123.3 | 351.8 | 1220.7 | .3142 | 199
139 | 124.3 | 352.4 | 1220.9 | .3162 | 198
140 | 125.3 | 352.9 | 1221.0 | .3184 | 197
141 | 126.3 | 353.5 | 1221.2 | .3206 | 195
142 | 127.3 | 354.0 | 1221.4 | .3228 | 194
143 | 128.3 | 354.5 | 1221.6 | .3250 | 193
144 | 129.3 | 355.0 | 1221.7 | .3273 | 192
145 | 130.3 | 355.6 | 1221.9 | .3294 | 190
146 | 131.3 | 356.1 | 1222.0 | .3315 | 189
147 | 132.3 | 356.7 | 1222.2 | .3336 | 188
148 | 133.3 | 357.2 | 1222.3 | .3357 | 187
149 | 134.3 | 357.8 | 1222.5 | .3377 | 186
150 | 135.3 | 358.3 | 1222.7 | .3397 | 184
155 | 140.3 | 361.0 | 1223.5 | .3500 | 179
160 | 145.3 | 363.4 | 1224.2 | .3607 | 174
165 | 150.3 | 366.0 | 1224.9 | .3714 | 169
170 | 155.3 | 368.2 | 1225.7 | .3821 | 164
175 | 160.3 | 370.8 | 1226.4 | .3928 | 159
180 | 165.3 | 372.9 | 1227.1 | .4035 | 155
185 | 170.3 | 375.3 | 1227.8 | .4142 | 151
190 | 175.3 | 377.5 | 1228.5 | .4250 | 148
195 | 180.3 | 379.7 | 1229.2 | .4357 | 144
200 | 185.3 | 381.7 | 1229.8 | .4464 | 141
210 | 195.3 | 386.0 | 1231.1 | .4668 | 135
220 | 205.3 | 389.9 | 1232.3 | .4872 | 129
230 | 215.3 | 393.8 | 1233.5 | .5072 | 123
240 | 225.3 | 397.5 | 1234.6 | .5270 | 119
250 | 235.3 | 401.1 | 1235.7 | .5471 | 114
260 | 245.3 | 404.5 | 1236.8 | .5670 | 110
270 | 255.3 | 407.9 | 1237.8 | .5871 | 106
280 | 265.3 | 411.2 | 1238.8 | .6070 | 102
290 | 275.3 | 414.4 | 1239.8 | .6268 | 99
300 | 285.3 | 417.5 | 1240.7 | .6469 | 96
-----------+-----------+-----------+----------+---------+-------------
Here we see that at 212° the total quantity of heat in the steam is
1178.1°, which gives a difference of 966.1°. This heat, usually termed
latent, is absorbed in performing the work of expanding the particles of
water from the liquid to the gaseous state. Now, suppose the water is
evaporated at 60 lbs. pressure, the steam will have a temperature of
307°, and a total heat of 1207°. If the feed has been introduced at 60°,
it is evident that 1147° of heat have been imparted. As the amount
evaporated is inversely proportional to the quantity of heat required,
we have 1147 ÷ 966 = 1.2. Multiplying by this factor, the quantity
evaporated at 60 lbs. pressure from 60°, we obtain the amount that would
be evaporated at 212° by the same quantity of fuel.
By the same table can be ascertained the comparatively small increase of
heat required to evaporate water at higher pressures. Suppose we take
water evaporated at 45 lbs. pressure from a feed temperature of 60°,
then each lb. of water will require 1202.7-60 = 1142.7 for its
conversion into steam. If we take the pressure at 100 lbs., we shall
have 1216.9-60 = 1156.9° as the quantity required. The difference
between these two total quantities is only 14.2°, and is so small as to
be scarcely worth considering. Leaving out of account the loss due to
the slight reduction of the conducting power of the material, the
increased amount of heat required for the higher pressure will be only
1/36 of the total heat required at 60 lbs. With an evaporation of 7 lbs.
of water from 1 lb. of coal, it will be obtained by using 1/563 more
fuel, or about 1 lb. in about 556 lbs., a quantity not appreciable to
the ordinary modes of weighing coal. The economy is then manifest of
using steam of high pressures when at the same time advantage is taken
of the facilities it offers for working the steam more expansively to
the engine cylinders.
The saving that may be effected by heating the feed water may be shown
as follows:
If we take the normal temperature of the feed water at 60°, the
temperature of the heated water at 212°, and the boiler pressure at 20
lbs., the total heat imparted to the steam in one case is
1192.5° - 60° = 1132.5°
and in the other case 1192.5° - 212° = 980.5°
152°
the difference being 152°, or a saving of -------
1132.5°
which is 13.4 per cent. If the pressure be taken at 120 lbs., instead of
20 lbs., the saving will be 13.1 per cent, showing a slight diminution
in the economy effected by heating the feed water when a high boiler
pressure is employed.
THE CARE AND MANAGEMENT OF STATIONARY ENGINE BOILERS.
The first thing to do in taking charge of a stationary engine boiler is
to know from personal inspection that the safety fittings and the
boiler-feeding apparatus are in good order.
The safety valve is the first thing to inspect, as it is liable to stick
in its seat, especially in cases in which it is set at a greater
pressure than is got up in the boiler, because in that case it is not
lifted from the seat and in time sticks fast there.
In such cases it is proper to lift the valve at least once a day while
steam is on. For this purpose a cord may be attached to the lever,
passing over a pulley directly above the lever, and thence to some
convenient place near the boiler, but where it is not liable to get
caught and pulled accidentally.
Before lighting the fire, see that there is sufficient water in the
boiler. If there is a gauge glass on the boiler, it should show
three-quarters full, or three-quarters of a glass, as it is called.
The gauge glass may show a false water level, and to be sure that such
is not the case, open the top gauge cock and the cock at the bottom of
the gauge glass, letting the water run through the gauge glass. Open and
close the cock below the gauge glass two or three times to see that the
water comes to the same level each time.
If the steam pressure has been allowed to fall in the boiler without any
of the cocks being opened, there will be a partial vacuum in the boiler,
and air must be let in before the true water level will be shown either
by the gauge glass or by the gauge cocks.
Opening the upper gauge cock will let in the air, and it should not be
closed again until enough steam has been got up in the boiler to expel
the air again, or in other words, until steam begins to issue from it.
The grate bars and ash pit should be cleaned of clinker, ashes, etc.,
and it should be seen that the tubes are clear of ashes, etc., before
the fire is laid; if the grate is a shaking one, the lever should be
applied to see that the grate will shake properly.
TO LIGHT THE FIRE--In the case of anthracite or hard coal, as it is
sometimes termed, first cover the bars with a thin layer of coal and
then put in pieces of lighted greasy waste (if it is at hand)
distributed about the furnace, taking especial care to light the fire at
the fire-door end and in the corners, because the fire will spread from
the front end towards the back easier than it will from the back end
towards the front.
The fire should light from the bottom and not from the top, hence the
thinnest pieces of the wood should be put in first.
If there is any soft coal at hand, a small quantity of it will
accelerate lighting the fire, as it burns easier and quicker than hard
coal.
Before putting on the coal the wood should be well lighted, the bottom
portion of it having ceased flaming.
This causes the lighted wood to spread over the bars and the fire to
light evenly.
Charge the coal lightly, first covering the places that have burned up
the most.
FIRING.--The fire door should be kept open as little as possible, as it
admits cold air that is detrimental to the combustion, as well as to the
draught, hence firing should be done quickly.
A good fireman will maintain as even a temperature as possible in the
fire box by charging the coal lightly and quickly.
Some firemen will, after the fire is at its proper depth all over the
grates, charge the fire in the front end, that is, at the fire-door end,
and push it back as it burns up, to keep up the thickness of the fire at
the back.
The thickness of the fire depends upon the size and kind of coal.
With small coal a fire from 4 to 6 inches deep will answer, while, if
the lumps are five or six inches in diameter, a fire from a foot to 15
inches deep may be maintained, as is done in some locomotives.
The object is to have the fire thick enough to prevent it from burning
through in spots or letting cold draughts of air pass through it.
The sides of the furnace require particular attention, not only because
cold air is more likely to get through there, but also in boilers
having fire boxes the cool sides of the box keep the temperature of the
fuel down, hence a thicker fire is necessary around the sides than in
the middle of the furnace or fire box.
Three things are to be considered in cleaning a fire--first, that the
boiler pressure will fall during, and for a short time after, the
cleaning; second, that the depth of fire will be diminished by the
cleaning; and third, that the temperature of the fire will fall during
the cleaning.
SHAKING GRATE BARS.
When a furnace has shaking grate bars, the cleaning of the fire is
greatly facilitated, and with bars that shake singly (and good coal) the
fire is often not disturbed during the day, except to shake the bars
occasionally, passing the poker through it and using the hoe to keep it
evenly spread.
If the grate shakes in sections, more cleaning will be required to break
up the clinker, while, if the bars do not shake, the cleaning assumes
greater importance.
Before cleaning, therefore, see that there is sufficient water in the
boiler, that it need not be fed while cleaning, nor just after cleaning
the fire.
Prepare for cleaning by having a thick fire on the grate, so that after
cleaning it will burn up quickly, and let the cleaning be done as
quickly as possible.
[Illustration: Fig. 3288.]
The tools used for cleaning the fire are the slice bar, Fig. 3288, which
is pushed along the top of the fire bars to loosen up the fire, and let
the ashes fall through the bars.
[Illustration: Fig. 3289.]
[Illustration: Fig. 3290.]
The hoe, Fig. 3289, which is used to push the fire to the back of the
furnace and to pull it forward. The poker, Fig. 3290, which dislodges
any clinker that may be between the bars, and lets the ashes fall
through.
[Illustration: Fig. 3291.]
[Illustration: Fig. 3292.]
The clinker hook or devil's claw, Fig. 3291, which is used to haul
clinker out of the fire, and the rake, Fig. 3292, which is used to
spread the fire evenly over the bars after it is cleaned.
In cleaning a fire, first use the slice bar to loosen up the fire and
let the ashes fall through, and also dislodge clinkers from the surface
of the bars. Then push the fire to the back of the furnace. Next use the
poker to clean out clinker from between the exposed part of the bars.
Then with the hoe pull a part of the fire forward and pull out the
clinker that may be in this part, doing so with the hoe as far as
possible, as that will save time, but if it should be necessary, use the
clinker hook.
Then pull forward a second portion of the fire, and spread it on the
bars, removing the clinker as before. When all the fire has thus been
cleaned, use the rake to spread it evenly over the bars, and put on a
light charge of coal, covering the brightest parts of the fire first,
and taking care that no part of the fire bars is left uncovered.
The cleaning should be done quickly.
DRAUGHT.--The draught should be decreased while the fire is being
cleaned, but the damper should never be entirely closed, as this might
cause an explosion in the fire box and tubes.
During a temporary interruption, as in the case of the engine stopping,
partly close all the dampers, as it is wasteful to make steam and blow
it off through the safety valve.
COMBUSTION.--A blue flame is evidence of incomplete combustion, but
there may be a blue flame and imperfect combustion at the back end of
the furnace, and a white flame and perfect combustion at the other end.
This is likely to occur with heavy firing near the fire door, and a thin
fire at the tube sheet end of the fire box. In this case the unconsumed
gases produced near the fire door (as evidenced by the blue flame) are
consumed in passing over the bright fire at the tube plate end of the
furnace.
AT NIGHT.--Always leave plenty of water in the boiler when leaving it
for the night, not only to allow for any leak, but also because it gives
a fair start in the morning and more time to remedy any defect in the
feed pump if it arise.
By plenty of water, very nearly a full gauge is meant, or if there is no
gauge glass to the boiler, let the water stand above the second or
middle cock.
The usual method of leaving the fire for the night is to bank it. There
is an element of danger, however, in banking a fire, unless it is done
to suit the circumstances, because steam may generate very rapidly, and
perhaps more rapidly than the safety valve can carry it off.
A safe method is to clean the fire, leaving the clinker and ashes
covering the front half of the grate and the fire piled up on the back
half.
The damper and ash pit door should be closed tight, the fire door open,
and the fire well covered with fresh coal, choosing small rather than
large coal.
If this method is found not to keep up the fire sufficiently, the same
plan may be employed, except that the ashes and clinker may be removed,
and if this still leaves too cold a boiler, and too poor a fire in the
morning, the fire may be left spread over the grate, but heavily covered
with fresh coal, the draught being stopped as much as possible by
closing the dampers and opening the furnace door.
To further insure safety, the weight on the safety valve lever should be
pushed towards the valve, so as to cause the safety valve to blow off at
a less pressure than during the day.
IN THE MORNING.--In starting up a banked fire in the morning, first
close the fire door and open the damper, so as to give the fire all the
draught possible, and let it burn up a little; then, if it has been
piled up at the back of the furnace, clean out the ashes by passing the
T bar beneath the fire, and spread it over the grate, letting it burn up
a little before making up a fire.
BOILER-FEED.--The fireman should endeavor, if possible, to so regulate
the boiler feed that it is kept going as nearly continuously as possible
while maintaining a uniform quantity of water in the boiler, and this,
with uniform firing, will give the greatest economy.
When pumps are used to feed with, the amount of the lift of the valves
can be regulated by a screw, so as to vary the amount of water the pump
will deliver, and in this case it is comparatively easy to set them so
that the pump may be kept going without putting too much water in the
boiler.
When injectors are used, however, the feed will be intermittent, and a
uniform quantity of water in the boiler is best obtained by feeding at
short intervals, stopping the feed when the fire door is opened much, as
when cleaning the fire.
If the feed water is dirty, the gauge glass should be kept clean by
first shutting off the upper cock and opening the lower one, so as to
let the water blow through the lower cock, and then shutting off the
lower cock from the boiler, and opening the upper one, which will let
the steam blow all the water out of the glass. This should be done two
or three times a day, so as to keep the holes in the boiler and those in
the cocks from closing up with fur or scale.
If the water falls in the glass, or if the gauge cocks show the water to
be falling, notwithstanding that the feed pump has been started, it is
evident that the pump is not working.
This may occur from a stuck valve, a leak in the suction pipe, from the
feed water being too hot, or from the pump failing to start in action
from leaky or choked valves.
A stuck valve may generally be relieved by striking a few blows on the
outside of the pump with a hammer and a block of wood, or if this does
not answer, with the hammer only. Check valves are the ones most likely
to stick.
If a pump fails to work by reason of the feed water being too hot, the
remedy is to open the pet cock to let the steam out of the pump, but if
this does not succeed, cold water may be poured on the outside of the
pump, which will start it, after which, in most cases, the pump will
keep going and the pet cock may be closed.
If the suction pipe has a joint, a leak there will impair the action of
the pump, and, if the leak is great enough, will stop it; the remedy is
to make the joint tight.
Plunger pumps sometimes fail to act because the plunger has worn so
small in diameter that there is sufficient air between the plunger and
the pump barrel to expand and compress without lifting the valve; the
remedy is obviously a new plunger of as large diameter as the pump gland
will admit of, boring the gland out to admit the new plunger.
All the impurities in the water are left in the boiler when the water
has evaporated, and it is obvious these impurities must be blown off or
they will form scale on the internal surface of the boiler and the
external surface of the tubes or flues.
This scale obstructs the passage of the heat from the iron to the water,
and if let get thick enough will cause the iron to rapidly burn out.
To prevent the formation of scale, two principal methods are employed,
one being to purify the feed water, and the other to occasionally blow
the impurities out of the boiler.
Feed-water heaters generally serve also as purifiers, and their
effectiveness is increased in proportion as the water can pass quietly
through them, and has a large area on which the impurities can settle.
Horizontal heaters have the advantage that they have a large settling
area, and a less distance for the impurities to fall through. The
water-gauge glass and the lower gauge cock are usually set so as to have
a margin of about three inches of water above the tubes or crown sheet
of the fire box, hence if it is known that the water is but just below
the bottom of the gauge glass or gauge cock, there is no positive
danger, although it is improper to let it get so low.
If the water is out of sight, and it is not known exactly how low it is,
then it is dangerously low, and every minute is of vital importance.
Should the water get dangerously low in the boiler, the most dangerous
thing to do is to lift the safety valve or pump in cold water,
especially if it is not known how much water there is in the boiler.
As quickly as possible cover the fire with ashes, coal, earth, sand, or
anything that is at hand that will smother the fire, then close the
draught to the fire, leaving the fire door and the chimney damper open.
Leave all the steam outlets just as they are, and also the feed.
PRIMING.--Priming, which is also called "foaming," is that the steam
carries up water into the steam space. This may arise from several
causes, but it is well known that what will stop priming in some cases
will cause it in others.
The known causes of priming are--first, too little room for the steam in
the boiler, and it follows that a high water level may cause priming;
second, it may be caused by a difference of temperature between the
water and the steam in the boiler. Suppose, for example, that the
pressure of the steam and water in the boiler is 160 lbs. by gauge, and
its sensible temperature will be 370 degrees. Suppose then that enough
steam is permitted to escape from the boiler to reduce the steam
pressure to 140 lbs., and its temperature will be reduced to 361
degrees. But the water will remain at 270 degrees, and the result will
be that it will pass into steam so rapidly that it will carry up the
water and hold it in suspension among the steam. The water will pass
with the steam into the engine cylinder, and the boiler will be said to
"prime," "foam," or "work water." The same thing may happen if the water
is heated very rapidly.
Priming is wasteful because it rapidly empties the boiler of its water,
and dangerous because it may cause the piston to knock out the cylinder
head or cover.
When the safety valve blows off, priming may be induced, especially if
the engine is at work, because in this case the boiler is being forced,
or, in other words, is making steam more rapidly than it is designed to
do, and the passage of so large a body of steam through the water is apt
to lift it.
Muddy water will sometimes cause foaming or priming, as will also
insufficient circulation of the water in the boiler or sometimes the
presence of grease or oil.
Priming may be detected from the discharge of water with the steam when
the gauge cock is opened, the steam looking white and fluttering as it
escapes, and also by violent motion of the water in the gauge glass, or
by a thump or pound at the ends of the piston stroke.
To stop priming, the steam from the boiler should be decreased by
slackening the speed of the engine, or if necessary, by stopping it. The
true water level can then be seen, and if there is too much water in the
boiler some of it may be blown off, while if the quantity of water in
the boiler will permit it, the feed may be put on.
If the boiler has a surface blow-off cock, or a mechanical boiler
cleaner, it is best to blow off from that, as it carries off the scum at
the same time as relieving the boiler.
To prevent priming, a steady and uniform rate of boiler feed, the use of
pure water, a clean boiler, and steady firing are the best means,
turning on the steam slowly so as not to violently disturb the water in
the boiler.
The engine as well as the boiler requires attention when the boiler
primes. Thus the cylinder cocks should be opened to let out the water
from the cylinder and prevent breakage of the cylinder cover.
SCALE IN BOILERS.--The steam leaves behind it all the impurities that
the water contained, and these impurities deposit in form of mud and
scale, which must be got rid of because it causes a loss of fuel, and if
allowed to get thick enough will cause the boiler to burn.
The use of boiler compounds or scale preventatives may be resorted to
with advantage, providing they are of a nature to suit the water, but
mechanical cleaning must also be resorted to at periods determined by
the nature of water.
Boilers are cleaned in two ways--first, by blowing off the impurities
before they have formed into scale; and second, by removing at certain
intervals whatever scale has formed.
Blowing down may be done in two ways--first, from the surface of the
water by means of mechanical cleaners; and second, by blowing out from
the bottom of the boiler.
The first draws off the impurities as they are thrown to the surface,
the second draws them off after they have become more condensed and sink
to the bottom.
How often a boiler should be blown down depends upon the kind of water
fed to the boiler; where purifiers are used, less blowing down is
obviously needed.
It is best to blow off from the bottom of the boiler when no steam is
being used, as during dinner time, letting the water blow down about a
quarter of the glass, or from the upper to the middle gauge cock.
As no steam is being used, the feed can then be put on to restore the
quantity of water without reducing the temperature of the boiler so
much. The feed should be gradual and the fire regulated to keep the
steam pressure even.
How often a boiler should be washed out and cleaned depends upon the
quality of the water it uses, and varies from about once a week to once
a month, according to whether bad and unpurified water or purified water
is used.
The first thing to do is to draw the fire, leaving the chimney damper
open and closing all the other dampers so that as little cold air as
possible can get into the boiler, while the heat can pass away up the
chimney.
Let the steam and water all remain in the boiler until there is a gauge
pressure of about 5 lbs. in the boiler.
Then open the blow-off cock and let out the water. If the water is blown
off under a high pressure, then after the waste is all out the iron is
hot enough to dry up the scale, making it hard and very difficult to
remove.
After all the water is blown off, take out all the mud plugs and the
man-hole and hand-hole covers, and wash out the boiler under as much
water pressure as can be had, directing the hose so to reach all parts
of the boiler and tubes, and continuing the washing until the water
leaves the boiler clean.
Then with a wooden hoe on a piece of gas-pipe of small diameter for a
handle, and small enough to pass through the hand-hole, draw all the
loose scale to the hand-hole and remove it, letting the water run
slowly, so as to carry the small pieces of scale towards the hand-hole
as fast as the hoe disturbs it.
Then get inside the boiler, and a few blows with a light ball-pened
hammer will loosen the scale, and a steel scraper will remove more,
which must be washed down and drawn out with a hoe.
After the cleaning and scaling are complete, the engineer, with lamp in
hand, should carefully examine the interior of the boiler and of the
fire box, paying especial attention to the stays to see that they are
not broken.
The hammer test should also be applied. It consists of sounding the
boiler by light blows given by a light ball-pened hand hammer, the sound
indicating defective places.
CHAPTER XXXVII.--THE STEAM ENGINE.
The high pressure steam engine, in whatever form it exists, consists of
a frame or bed plate carrying two distinct mechanisms, first, the
driving or power-transmitting mechanism, and second, the valve gear or
valve motion, and to these are added such other mechanisms as the nature
of the duty the engine is to perform may require.
The most prominent of these additional mechanisms is a governor for
regulating the speed at which the engine is to run; nearly all steam
engines require a governor in some form or other, while for electric
lighting and some other purposes it constitutes the main feature in the
design of the engine.
In a locomotive the air brake and the sand box are elements not found in
other engines.
In a jet condensing engine, the condenser and injection water, or
condensing water mechanism, is a part of the engine.
In a surface condensing engine, the air pumps and circulating pumps are
a part of the engine.
In marine engines there are mechanisms for turning the engine around
when no steam is up; for moving the reversing gear quickly, and for
varying the point of cut off, and therefore the amount of expansion, and
various other and minor mechanisms.
[Illustration: Fig. 3293.]
Referring now to the simplest form of high pressure stationary steam
engine, such as represented in Figs. 3293, 3294, and 3295, its valve
gear or valve motion consists of the eccentric and its strap, the
eccentric rod, the valve rod guide A, the valve rod or valve spindle,
and the valve _v_, these parts controlling the admission of steam to one
side of the piston, and the exhaust from the other.
The piston, piston rod, cross head, connecting rod, crank, crank shaft,
main shaft or driving shaft, and the fly wheel constitute the driving or
power-transmitting mechanism.
The steam side of the piston is that against which the steam is
pressing, as side S in Fig. 3295. The exhaust side, E, of the piston is
that on which the steam is passing out or exhausting.
The governor for a common D valve engine regulates the engine speed by
varying the opening in the bore of the pipe through which the steam
passes from the boiler to the steam chest, leaving a wider opening in
proportion as the engine runs slower, and reducing the opening when the
engine runs faster. Assuming the engine to be running at its slowest, or
its load to be so great that a full supply of steam is required in order
to keep the engine up to its proper speed, and the governor will be open
at its widest, so that all the further action the governor can have is
to reduce the steam pipe opening, and thus cause the pressure in the
steam chest to be less than that in the steam pipe.
This action is called wire-drawing the steam, and the governor is called
a throttling governor.
An engine bed or bed plate is a frame that is seated or bedded to its
foundation along its whole length.
An engine frame is seated to its foundations at two or more places, but
not continuously throughout its length.
THE CYLINDER.
Cylinders are secured to the engine frames in three principal ways, as
follows: by bolting them down to the bed plate; by bolting them to one
end of the bed plate, so that they may expand and contract without
springing the bed plate; and in vertical engines, by bolting them to the
top of the frames.
The bores of cylinders require to be parallel, so that the piston rings
may fit to the bore without requiring to expand and contract in diameter
at different parts of the stroke.
Cylinders are designated for size by the diameter of the cylinder bore
and the length of the stroke; thus, a 10 × 12 cylinder has a piston of
ten inches diameter and 12 inches stroke.
The wear of a cylinder bore is (if the engine is kept in proper line and
the piston rings, or packing rings as they are sometimes termed, fit to
the bore with an equal pressure throughout the stroke) greatest near the
middle of the length and least at the ends of the stroke. But when the
piston rings are set out by the steam pressure, and the point of cut off
occurs early in the stroke, the wear may be greatest at the ends of the
cylinder bore, because of the pressure of the steam diminishing during
the expansion.
The counterbore of a cylinder is a short length at each end of the
cylinder, that is made of larger diameter than the rest of the bore, so
that the piston head may travel completely over the working bore, and
thus prevent the formation of a shoulder at each end of the cylinder.
Such a shoulder forms when there is a part of the bore over which the
piston does not pass. The length of the counterbore should exceed the
amount of the taper on the connecting rod key, so that as the connecting
rod length alters from the wear, the piston shall not strike the
cylinder head.
The clearance of a cylinder is the amount of space that exists between
the face of the piston when it is at the end of its stroke and that of
the valve when it covers the port, the piston being at the end of the
stroke, and as this space exists at each end of the cylinder, the total
clearance for a revolution is twice the above amount.
The clearance at the crank end of the cylinder is reduced by the piston
rod passing through it.
The amount of clearance may be measured by the following method, which
has been given by Professor John E. Sweet:
[Illustration: Fig. 3294.]
[Illustration: Fig. 3295.]
See that the piston and valves are made tight, and the valves
disconnected; arrange to fill the clearance spaces with water through
the indicator holes, or holes drilled for the purpose. Turn the engine
on the dead centre; make marks on the cross-head and guide that
correspond; weigh a pail of water, and from it fill all the clearance
space. Weigh the remaining water, so as to determine how much is used.
Then weigh out exactly the same amount of water, turn the engine off the
centre, pour in the second charge of water, and turn back until the
water comes to the same point that it did in the first case. Make
another mark on the cross-head, and the distance between these marks is
exactly what you really wish to know; that is, it is just what piston
travel equals the clearance. This gives the proportion that the
clearance space bears to the space in the cylinder occupied by the steam
at the end of the piston stroke. Thus, if it takes one pound of water to
fill this space, and to admit the one pound of water the piston must be
moved one inch, then the clearance bears the same relation to the
capacity of the engine as one inch bears to the stroke of the piston.
Thus, under these circumstances, in an engine of ten-inch stroke, it
would be said the engine had ten per cent. clearance.
When a cylinder is to be rebored, the boring bar should be set true or
central to the circumference of the counterbore, so that the bore of the
cylinder may be brought to its original position with reference to the
bore of the stuffing box.
Cylinders require lubricating, both to avoid friction and wear of the
cylinder bore, as well as of the valve and valve seat. The amount of
lubrication required depends upon the degree of tightness of the piston
rings, upon the speed of the piston, upon the amount of pressure of the
valve to its seat, and upon the method of operating the side valve.
Cylinders with releasing valve gears require freely lubricating, because
the closure of the valve depends upon the dash pot, and undue friction
retards the closing motion.
The less the movement of the valve at the moment of its release, the
easier it is to move it, because the friction is less, and less
lubrication is required.
Cylinders are lubricated by automatic oilers placed on the steam pipe of
the engine, the oil being distributed over the surfaces by the steam.
Cylinder oilers sometimes have a pump to force the oil in, and in others
the steam in the oiler condenses, and the water thus formed floats the
oil over the top of a tube, or up to an orifice through which the oil
gradually feeds as the condensation proceeds.
In other oil feeders, the feed is regulated by increasing or diminishing
the opening through which the steam passes from the cup to the steam
pipe.
Sight oil feeders are those in which there is a glass tube or body, in
which the passage of the oil can be seen as it drops.
Cylinder cocks are employed at each end of the cylinder to let out the
water that condenses from the steam when admitted to a cold or partly
cooled cylinder. The two cocks are usually connected together by a rod,
so that both may operate together.
Cylinder relief valves are valves at each end of the cylinder to relieve
the cylinder from the charges of water that sometimes enter from the
boiler with the live steam.
Steam ports give a quicker admission in proportion as their length is
increased, and this reduces the amount of valve travel, and are
sometimes given a length equal to the diameter of the cylinder bore.
The bottoms of the steam ports are sometimes so placed as to be below
the level of the cylinder bore, so as to drain off the water of
condensation of the steam.
Rule to find the required area of steam port.
Multiply the area in square inches of the piston, by the number opposite
to the given piston speed in the following table:
Speed of piston in Number by which to
feet per minute. multiply the piston area.
100 0.02
200 0.04
300 0.06
400 0.07
500 0.09
600 0.1
700 0.12
800 0.14
900 0.15
1,000 0.17
The cylinder exhaust port must be open when the valve is at the end of
its travel, to an amount equal to the width of the steam port, but what
this width will be in any given case depends upon the width of the
bridges, the amount of the steam lap and the travel of the valve, as
will be explained with reference to the slide valve.
Jacketed cylinders are those in which there is a space around the
cylinder that is filled with live steam.
The object of jacketing is to prevent the loss of heat from the steam
within the cylinder by radiation. The steam in the jacket should be
received direct from the boiler, and should not be drawn from the jacket
into the steam chest because the jacket reduces its temperature and
condenses it.
The water of condensation of a steam jacket should not be allowed to
accumulate in any part of the jacket, but should drain off and pass back
to the boiler. To render the jacket as effective as possible, it should
extend from end to end of the cylinder, the exhaust steam pipe leading
directly away, so as to have as little communication with both the
cylinder and the jacket as possible.
The jacket should have open communication with the boiler at all times,
so as to have the pressure in the jacket at the same pressure as that in
the steam chest, while the cylinder being kept hot, it will be
unnecessary to blow steam through in order to warm the cylinder when
starting the engine. The steam should enter the jacket at the highest
point, so as to prevent the accumulation of air in the jacket. Or, if
the steam is admitted at some other point, it should be so arranged as
to permit its thorough circulation in the jacket. When a jacket is used,
the metal of the cylinder body should be as thin as possible, because
the transmission of heat through the metal is, both in time and
quantity, inversely as the distance or thickness passed through.
The steam in the jacket should be as dry as possible, so that all wet
steam admitted during the live steam period may be evaporated by the
heat received from the steam in the jacket. The outside of the jacket
should be thoroughly protected from cooling by being lagged or clothed
with felt or some other material that is a non-conductor of heat.
From experiments made by Mr. Charles A. Smith, of St. Louis, it was
found that the amount of variation of temperature that occurred during
the stroke in a locomotive cylinder was inversely proportional to the
speed of engine revolution, which shows the advantages of jacketing
cylinders and of lagging them, as well as the advantage of a high
rotative speed.
A lagged cylinder is one clothed, which is sometimes done with wood or
metal strips, leaving an air space around the cylinder, while in others
this space is filled with felt or some non-conducting material.
Experiments made by Charles E. Emery gave the following general results:
The thickness of the pipes and of the non-conducting materials was kept
constant.
Hair felt was the best non-conducting material of all those tested, and
the value of a thickness of two inches of hair felt was taken as unity
and the maximum.
The value of two inches of mineral wool as a non-conductor was 0.832 of
hair felt; two inches of mineral wool and tar was 0.715. Two inches of
sawdust, 0.68; two inches of a cheaper grade of mineral wool, 0.676;
charcoal, 0.632; two inches of pine wood, across the grain, 0.553; two
inches of loam, 0.55. This was from the Jersey flats, and almost all
vegetable fibre not yet become compact. Slaked lime from the gas works,
expressed decimally, with hair felt as unity, 0.48; coal ashes, 0.345;
coke, only 0.277, the same as used for fuel; two inches of air space,
only 0.136, which dashes a great many people's hopes, and is as
interesting as any part of the data; two inches of asbestos, 0.363; two
inches of Western coke, about the same as the other coke; two inches of
gas house charcoal, 0.47.
These are very interesting, particularly so this matter of an air space.
It has been supposed that an air space around a pipe is as good as
anything we can have. The fact is, convection or circulation takes
place; the air is cooled on one side of the space, descends, and rises
on the other, and it is necessary to break up the air space, and that
undoubtedly accounts for the efficiency of these different materials. It
is the air probably that is the non-conductor; but it should be kept
quiescent instead of being allowed to circulate. The air space itself is
of very little value until the circulation is prevented.
THE PISTON.
In calculating the power of an engine it is the piston speed that is
taken into account, and not the length of the stroke, the latter being
used merely in order to obtain the piston speed.
Long strokes are usually employed upon engines running at moderate
piston speeds, as from 300 to 500 feet per minute, and short strokes for
piston speeds from 400 to 800 feet per minute.
The Porter Allen engine has been run noiselessly at 1,100 feet per
minute.
In determining the stroke of an engine the nature of the valve-operating
mechanism is taken into account.
In releasing mechanisms, or those in which connection between the
eccentric rod and valve spindle is broken in order to permit the valve
to close quickly, too high a speed of revolution may cause the tripping
mechanism to fail to act, hence a high piston speed is obtained by means
of employing a comparatively long stroke.
In positive valve gears, or those in which the valve is controlled
throughout the whole of its movement by the eccentric, the valve
mechanism may operate quicker without danger of missing, hence the
piston speed may be greater.
When the stroke equals the diameter of the cylinder bore, the cylinder
presents the least amount of exposed surface in proportion to its
cubical contents.
To obtain the same amount of expansion in a short as in a long stroke
engine, the steam must be expanded through an equal proportion of the
stroke; thus, if the steam is cut off at half stroke in both cases, the
amount of this expansion will be equal.
Pistons are made an easy fit to the cylinder bore, a steam-tight fit
between the two being obtained by means of the piston rings.
Solid pistons are provided with snap piston rings.
A snap piston ring is one that is larger in diameter than the cylinder
bore, and is closed in to get it into the cylinder, while it depends on
its own spring outwards for its fit to the cylinder bore, having no
supplementary rings or springs to force it out.
Piston rings that are expanded by supplementary springs should be
tapering in thickness, the thickest part being opposite to the split,
and the thinnest at the split. This causes the ring to conform itself to
the cylinder bore, and makes it sit more evenly around its whole
circumference. These rings are made larger in diameter than the cylinder
bore, in proportion of about 1/8 inch per foot of diameter, the split
being closed when the ring is sprung into place in the cylinder. But if
made of brass, the split must be left open enough to allow for the
expansion, or otherwise the ring expanding more than the cylinder will
seize and cut single.
The split of a piston ring should be placed on the bottom of the piston
(in a horizontal engine), so that the piston head, in resting on the
cylinder bore, will cover up the opening of the ring.
When two or more rings are employed, the splits may be placed on the
lower half of the cylinder, so as to cover up their splits as much as
possible.
The follower of a piston is a plate or cover that is employed to hold
the piston rings in place, and the piston rings should be so fitted that
the follower should be bolted firmly up, or otherwise the bolts may come
loose and work out, and getting between the piston and the cylinder
cover, may cause the piston to knock the cylinder cover out.
Piston followers are necessary when the rings are set out by springs or
other parts adjustable within the piston head. Snap piston rings,
however, permit the use of a solid piston, dispensing with the need for
a follower.
The effectiveness of a piston ring may be tested, when the construction
of the engine will permit it, by disconnecting the valve for the head
end, setting it so that it covers the port, and then taking off the
cylinder cover at the head end and admitting steam through the crank
end steam port, when any leak in the piston rings will be seen by the
escape of the steam.
THE PISTON ROD.
Piston rods should be of slightly diminishing diameter at the ends, so
that the wear shall not leave a shoulder at each end of the rod.
In determining the diameter of the piston rod, allowance is made for
turning it occasionally in the lathe to restore its parallelism, the
wear reducing its diameter more in the middle than at the ends. The
diameter of a piston rod is found in practice to range between one-sixth
and one-tenth the diameter of the cylinder bore.
Steel piston rods wear better than those of wrought iron, being free
from scaly seams which are apt to cut the packing and cause the rod to
wear in grooves.
The best method of securing a piston rod to a piston head and to the
cross head is by a taper seat and a key, so that no nut is needed, and
the cylinder cover need not have a recess to receive the nut when the
piston is at the end of the stroke, and the amount of clearance is
correspondingly reduced.
Piston head key ways are sometimes given so little clearance that the
key completely fills the keyway when driven fully home. This prevents
the edges of the keys from bulging into the clearance space in the
keyway, which action is apt to cause the key to loosen in time. The key
should have a safety pin at its small end.
When piston rods are threaded into the cross head, or into the piston,
the threads are made an easy fit, and taper seats or split hubs secured
by clamping screws are relied upon to keep the rod true to the cross
head or piston, it being found that the screw alone cannot be relied
upon for this purpose.
PISTON ROD PACKING.
Piston rod packing, of fibrous or similar material, should be cut in
rings that will not quite fully envelop the piston rod, and the first
ring should be placed with its split upwards. After two or three rings
have been inserted, each having its split at a different part of the
bore, so as to "break joints," the gland should be screwed up enough so
as to carry the packing home to the back of the stuffing box. This
process should be continued until the stuffing box is filled for about
two-thirds of its depth, when the gland may be screwed home.
The gland should be screwed up quite evenly, so that the packing in the
stuffing box shall be compressed equally all around the rod, and will
not cause the gland to bind on the rod or in the stuffing box bore.
The wrench should be applied first to one nut, giving it a turn or two,
and then to the other, and after the gland is firmly home the nuts
should be eased back about two turns.
When a gland requires packing, it is proper to take out all the old
packing that has become hard and set.
A leak in piston rod packing may sometimes be remedied by taking out
three or four rings of the packing and reversing it.
If the packing is tightened up while the engine is running, it should be
done very gently and evenly, as a very little screwing up may stop the
leak, while excessive screwing produces undue friction.
Piston rods are in some of the most advanced practice packed with
metallic packing, or packing composed of soft metal. In some forms of
metallic packing the construction is such that the gland and packing do
not attempt to restrain the line of motion of the piston rod, this duty
being left to the guide blocks and guide bars, where it properly
belongs.
THE CROSS HEAD.
In engines having Corliss frames, the cross head is provided with shoes
and adjusting screws, to take up the wear.
When guide bars are shaped thus __|¯¯ the cross head is provided with
gibs (usually of brass composition) to take up the wear.
In either case care must be taken to make the adjustment correct, and
thus keep the piston rod in line. The shoes or gibs should not bear hard
upon the guides, but be an easy sliding fit without lost motion.
Cross head pins should be kept eased away on the two parts of their
circumference which are within the connecting rod brasses or boxes and
near the joint faces of the same. This is necessary because the wear is
greatest on the crowns of the boxes, and the pins are apt to wear oval.
In some engines, the surface of the pin is cut away, but if it is not,
and the pin can be revolved in the cross head, it is a good plan to give
it half a turn occasionally, which will keep it round.
THE GUIDE BARS.
The guide bars of an engine require to be set exactly in line with the
axis of the cylinder bore, so that they may guide the piston to travel
in a straight line. They should be an easy sliding fit to the cross-head
guide.
The top bar is more difficult to lubricate than the bottom one,
especially when it receives the most pressure, as is the case when the
top of the fly-wheel runs towards the cylinder.
Cast iron guide bars wear better than either brass, iron, or steel ones,
so long as they are properly lubricated. The face of each guide bar
should be cut away, so that the ends of the cross head guides will
travel past it. This will prevent a shoulder forming at the ends of the
bar as the face wears away. Such shoulders are apt to cause a knock as
the connecting rods are lined up, because in the lining the connecting
rod is restored to its original length, and the path of the cross-head
guides along the bars may be altered.
THE CONNECTING ROD.
There are two principal kinds of connecting rods, the "strap ended" and
the "solid ended." The solid ended wear the best, but are more difficult
to get on and off the engine.
Connecting rod straps are secured to the stub ends (as the ends of the
rod are called), either by bolts or by one or two gibs, and the brasses
are set up by a taper key or wedge.
The taper for connecting rod keys is about an inch per foot.
The angularity of a connecting rod is a term that applies to its path of
motion, which is (during all parts of the stroke except on the dead
centre) at an angle to the line of engine centres. The effect of this
angularity is to cause the piston motion to be accelerated at one part
of the stroke and retarded at another, thus causing the point of cut-off
to occur at different points of the two strokes.
The direction of the variation is to cause the point of cut-off to occur
later on the stroke when the piston is moving from the head end of the
cylinder towards the crank.
The amount of variation caused in the two points of cut off by the
connecting rod depends upon the proportion that exists between the
length of the crank and that of the connecting rod, and is less in
proportion as the length of the connecting rod is greater than that of
the crank.
An ordinary length of connecting rod is six times the length of the
crank, or _six cranks_, as it is commonly termed.
Fig. 3296 represents a cylinder, piston and rod, cross head, connecting
rod, and crank.
The piston _b_ is shown in the middle of the cylinder, the cross head at
E, and the crank pin at B, instead of being at G´, as it would but for
the connecting rod, or if the connecting rod was infinitely long.
Now take a pair of compasses and set it from _b_ to E, and then try it
from _a_ to D, and from _c_ to F, and it will be seen that the three
cross head positions D, E, and F correspond correctly to the three
piston positions _a_, _b_, _c_. Then take a pair of compasses and set
them to the length of the connecting rod (from E to B) and try them from
D to A, from B to E, and from C to F, and it will be seen that crank pin
positions A, B, and C correspond to cross head positions D, E and F, and
therefore that the crank is not at half stroke when the piston is in
the middle of the cylinder. Take these same compasses, and resting one
point at (G´) mark the arc H, and that is where the cross head would be
when the crank was at (G´). Now then we see that the connecting rod
causes the piston to move slower while running from _a_ to _b_ than it
does while running from _b_ to _c_.
[Illustration: Fig. 3296.]
THE D SLIDE VALVE.
The various events which are governed by the D slide valve of a steam
engine are as follows:
The live steam period is that during which the steam is admitted from
the steam chest into the cylinder and the steam admitted during this
period is termed _live_ steam.
The point of cut off is that at which the valve closes the steam port,
and the admission of steam into the cylinder is stopped, hence the point
of cut off is at the end of the live steam period.
The period of expansion is that during which the steam is allowed to
expand in the cylinder, and therefore begins at the point of cut off,
and ends at the point of release.
The point of release is that at which the valve opens the port and
permits the steam to escape.
The point of compression is that at which the exhaust port is closed,
which occurs before the piston has reached the end of its stroke; the
steam that has not passed out of the cylinder is therefore compressed,
the compression continuing until the valve opens for the lead.
The lead of the valve is the amount the port is open to the live steam
when the crank is on the dead centre.
The point of admission is that at which the port opens for the live
steam to enter, and it follows that the lead and compression both act as
a cushion, arresting the motion of the piston when it reaches the end of
the stroke.
Cushioning begins, however, at the time the exhaust port is closed
enough to arrest the escape of the steam, while compression begins when
the valve has closed the exhaust port.
[Illustration: Fig. 3297.]
The construction of a common slide valve is shown in Fig. 3297, in which
the valve is shown in its mid-position. P P are the cylinder steam ports
(as the openings through which the steam passes from the steam chest to
the cylinder are termed), and at X is the cylinder exhaust port, through
which the steam escapes from the cylinder. Z is the valve exhaust port
or exhaust cavity.
The lip of a valve is the width of its flange face, or the distance L,
which is measured from the steam edge A to the exhaust cavity Z. At the
other end of the valve, H is the lip extending from the steam edge B to
the exhaust cavity.
Steam lap is the distance the steam ends (or the steam edges as they are
called) A, B overlap the steam ports, this distance being shown on the
ends of the valve at _a_ C. If the valve had no steam lap, its steam
edges would just cover the ports, as denoted by the dimension W.
Exhaust lap is the amount the exhaust cavity Z overlaps the bridges _q
q´_, as at _p_, _r_.
Unequal steam lap is given to cause the point of cut off to occur at
equal points in the piston stroke; thus in the figure there is more
steam lap at the head end than at the crank end of the valve. But
unequal lap could also be given in order to greatly vary the points of
cut off for the two piston strokes, if such was desired.
Unequal exhaust lap may be given to equalize the point of release, or to
equalize the points of compression.
The head end of the valve (or of the cylinder) is that which is furthest
from the crank shaft, the other end, or that nearest to the crank shaft,
being termed the crank end.
THE ACTION OF A COMMON SLIDE VALVE.
The action of a common slide valve may be traced as follows:
[Illustration: Fig. 3298.
Port _a_, open to the amount of the lead.]
[Illustration: Fig. 3299.
Port _a_, full open for the admission.]
[Illustration: Fig. 3300.
Port _a_, closed off for cut.]
[Illustration: Fig. 3301.
Valve opening port _a_, for the exhaust.]
[Illustration: Fig. 3302.
Port _a_, full open for the exhaust.]
Suppose the port _a_ to be at the head end of the cylinder and open to
the amount of the lead with the crank on the corresponding dead centre,
and if the valve travel be made equal to twice the lap and the lead, the
various positions of the valve will be as marked in Figs. from 3298 to
3302; the event corresponding to each valve position being stated in the
figures.
DOUBLE PORTED VALVES.
The term _port_ applies strictly to the area of opening of the steam
passage where it emerges upon the valve seat. The term _steam passage_
includes the full length of the opening from the cylinder bore to the
face upon which the valve is seated.
A double ported steam port is one in which there are _two_ openings or
steam ports, leading into _one steam passage_.
A double ported valve is one in which there are two ports _at each end_
of the valve. These two ports in some cases admit steam to a single
cylinder port, and in others to two steam ports, terminating in one
steam passage.
A griddle valve is one that has two or more ports at each end upon a
seat that has two or more ports for each steam passage.
Double ported valves are employed in some cases to increase the
admission of live steam to the cylinder, and in others to increase the
exhaust openings also. The effectiveness of a double ported valve is
mainly valuable at the beginning of the stroke, and is especially
valuable in cases when the travel of the valve is diminished to hasten
the point of cut off, because in such cases the outer edges of the valve
do not open the steam port to its full width, and a single port is apt
to wire draw the steam. By the employment of more than one port, or
several ports, a sufficient admission may be obtained with less valve
travel.
[Illustration: Fig. 3303.]
The Allen double ported valve is one in which the second port increases
the port opening for the admission only, as shown in Fig. 3303, in which
the valve is moving in the direction of the arrow; the port K will
receive steam through the opening at _g_, and from a port passing
through the valve, the steam entering it as shown by the arrow. The
second port forms part of the lap of the valve, and enables the travel
to be short enough to be cut off at early points in the stroke, without
employing so much steam lap as to widely distort the points of cut off,
this latter being a defect of the D valve.
Webb's patent slide valve is circular, and is so arranged as to be free
to revolve in the hoop of the valve rod, the effect being that the valve
moves around, or to and fro in the hoop, without any special mechanism
to produce such movement, and the result is, that the valve and port
facings wear smooth and even without any tendency to become grooved.
BALANCED VALVES.
A balanced valve is one in which means are employed to relieve the back
of the valve of the steam pressure, and thus prevent its being forced to
its seat with unnecessary pressure.
In some of the most successful balanced valves this is accomplished by
providing a cover plate, which may be set up to exclude the steam from
the back of the valve which works (a sliding fit) between the valve face
and the face of the cover plate. Such a method of balancing is
sufficiently effective for all practical purposes, if the following
conditions are observed: The valve rod must be accurately guided so as
to avoid side strains; the valve must fit accurately to its seat and to
the cover plate, and the adjustment so made that the valve slides freely
at first, being steam tight, and yet allowing room for lubrication to
enter. When the travel of a valve, balanced by a cover plate, is varied
to alter the point of cut off, the construction must be such that the
ends of the valve at the shortest stroke pass over the ends of the seat
and cover plate faces, or otherwise the middle of the seat and cover
plate faces will wear hollow.
The Buckeye, Porter-Allen, and Straight-Line Engines are examples of
practically balanced valves. The first of these has a balancing device
that follows up the wear; the second has an adjustment whereby the cover
plate may be set up to take up the wear; and in the third the wear is
reduced to a minimum, by accurately fitting and guiding the parts.
[Illustration: Fig. 3304.]
The construction of the valve in the Straight-Line Engine is shown in
Fig. 3304, in which B represents the cylinder bore; the valve _v_ rests
on a parallel strip _n_, and on its top rests the parallel strip _m_,
the pressure relieving plate P is set up firmly against the pieces _m_
_n_, whose thicknesses are such as to leave the valve a working fit
between the faces of R R and of P.
[Illustration: Fig. 3304 _a_.]
Instead of the valve sliding on a flat face, it may work upon a shaft or
spindle as a centre, its face moving in an arc of a circle, and its
action will be the same as a flat valve having the same proportions.
Fig. 3304_a_ represents a valve V of this construction, whose shaft is
at S, A being an arm fast on S, and driven by the eccentric rod R. To
find the necessary amount of travel for such a valve, we draw lines, as
_f_, _g_, from the inner edges of the steam ports, through the centre of
the shaft S, and also draw an arc through the centre of the eye of arm
A, and where lines _f_ _g_ cut the arc, as at _d_ and _e_, are the
extremes of motion of A.
PISTON VALVES.
[Illustration: Fig. 3305.]
A piston valve acts the same as a flat or plain (D) valve, having the
same amount of lap lead and travel. In Fig. 3305 we have a cylinder with
a flat valve on one side and a piston valve on the other, the head end
ports being about to take steam, and it is seen that the eccentrics
occupy the same positions for the two valves. The steam ports are, for
the piston valve, annular grooves provided in the bore in which the
valve fits. The piston valve is balanced because it receives its steam
pressure on the ends, but it will not follow up its wear as the flat
valve does, hence it is liable to leak.
SEPARATE CUT OFF VALVES.
[Illustration: Fig. 3306.]
Meyer's cut off valve is constructed as shown in Fig. 3306, M being the
main valve, and _v_ _v_ the two cut off valves, whose sole duty is to
cut off the steam at an earlier point than the main valve would do. If
the engine is to have a fixed point of cut off, or, in other words, if
the cut off is always to occur at some one particular point in the
stroke, the valves may be set to do so, and equalize the points of cut
off.
Variable points of cut off with the Meyer's valve may be obtained by
shifting the position of the eccentric that operates the cut off valve,
but it is usually done by means of moving the valve by a right and left
hand screw, such as shown in Fig. 3306. The cut off eccentric is set
ahead of the main eccentric, so that the cut off valve will close the
ports before the main valve would do so; thus, in the figure the cut off
valve is shown to have effected the cut off for port _a_ by the time the
main valve has fully opened port _a_, and is reversing its motion. If
the engine requires to reverse its motion, the cut off eccentric is set
exactly opposite to the crank, but otherwise, it may be set 8 or 10
degrees either ahead of or behind the crank, but if set too little ahead
of the crank, the port may reopen after the cut off has been effected.
[Illustration: Fig. 3307.]
Gonzenback's cut off valve is constructed as in Fig. 3307, the steam
chest having two compartments. A, A are the cylinder steam ports, C the
main valve, and E the cut off valve, whose ports (as G) are made wider
than the ports F.
Reducing the travel delays the point of cut off in the Gonzenback valve,
whereas in the common slide valve it gives an earlier cut off.
THE ECCENTRIC.
When a single eccentric is used, it is simply termed _the_ eccentric. If
a cut off valve (or two cut off valves) are used upon the engine, then
the eccentric that works the main valve is called the main eccentric,
while that which works the cut off valve or valves is called the cut off
eccentric. The main valve is that which works on the cylinder face; the
cut off valve is that which effects the cut off.
A shifting eccentric is one that is _moved across_ the shaft so as to
alter its amount of throw, and, therefore, the amount of valve travel,
the effect being to vary the point of cut off.
In engines where a constant amount of lead is given, or in other words,
when the eccentric position is intended to be fixed, the eccentric
should be secured to the crank shaft by a feather or key sunk into the
crank shaft so as to prevent the eccentric from moving, while enabling
it to be taken off and replaced without requiring any operations to
adjust its position with relation to the crank.
The feather should fit tight on the sides, as well as on the top and
bottom, and may have a slight taper on the sides, which will make it
easier to fit the featherway or keyway to the feather, and easier to put
the eccentric on or take it off.
By this means the eccentric cannot shift, and may be replaced after
being taken off without having to set the whole valve motion over again.
When the amount of valve lead or of compression is varied to suit the
speed at which the engine is to run, or to aid the counterbalancing of
the engine, a feather cannot be used because it will not permit the
eccentric to be moved to effect the adjustment.
Set screws possess disadvantages, inasmuch as that the point of the set
screw may leave an indentation, which, if the eccentric is moved a
trifle, may cause the set screw point to fall back into the old
indentation, thus rendering it difficult to make a small adjustment of
eccentric position.
[Illustration: Fig. 3308.]
An eccentric is the exact equivalent of a crank having the same amount
of throw, as may be seen from Fig. 3308, in which the outer dotted
circle represents the path of the crank and the inner one the path of
the centre of the eccentric. A small crank is marked in, having the same
throw as the eccentric has, and the motion given by this small crank is
precisely the same as that given by the eccentric whose outer
circumference is denoted by the full circle.
Considering the motion of both the crank and the eccentric, therefore,
we may treat them precisely the same as two levers, placed a certain
distance apart, revolving upon the same centre (the centre of the crank
shaft), and represented by their throw-lines.
[Illustration: Fig. 3309.]
In Fig. 3309, let the full circle E E represent an eccentric upon a
shaft whose centre is at C, and let the centre of the eccentric be at
_e_. The path of revolution of the eccentric centre will be that of the
dotted circle whose diameter is B, D. As the eccentric is in
mid-position (_e_ being equidistant from B and D), the valve will be in
mid-position as denoted by the full lines at the bottom of the figure.
Now suppose the eccentric to be revolved on the centre C, until its
centre moves from _e_ to V, its circumference being denoted by the
dotted circle A A, and if we draw from V a vertical line cutting the
line B, D at _f_, then from C to _f_ will be the distance the eccentric
would move the valve, which would then be in the position denoted by the
dotted lines at the bottom of the figure. It becomes clear then that if
we suppose the eccentric to have moved from mid-position to any other
position, we may find how much it will have moved the valve by first
drawing a circle representing the path of the centre of the eccentric,
next drawing a line (as B D) through its centre, and then drawing a
vertical line as (C _e_) through its mid-position and also a vertical
line from the eccentric centre in its new position, the distance between
these two vertical lines (as distance C _f_ in the figure) being the
amount the eccentric will have moved the valve.
It may have been noticed that the diameter of the eccentric does not
affect the case, the distance B D, or the diameter of the circle
described by the centre of the eccentric, being that which determines
the amount of valve motion in all cases. This being the case, we may use
the circle representing the path of the eccentric centre for tracing out
the valve movement without drawing the full eccentric, and the diameter
of that circle will of course equal the full travel of the valve.
[Illustration: Fig. 3310.]
The position of an eccentric upon a shaft is often given in degrees of
angle, which is very convenient in some cases. If a valve has no lap or
lead, the eccentric will stand at a right angle or angle of 90 degrees
when the crank is on the dead centre.
The division of a circle into degrees may be explained as follows:
Suppose we take a circle of any diameter whatever and divide its
circumference into 360 equal divisions, then each of these divisions
will be one degree. The number 360 has been taken as the standard, and
this being the case, there are 360 degrees in a circle, in a quarter of
a circle there will therefore be 90 degrees, because 90 is one quarter
of 360. By means of dividing a circle in degrees therefore we have a
means of measuring or defining any required portion of it.
In Fig. 3310 the degrees of a circle are applied for defining the
relative positions of a crank and an eccentric. As the zero position of
the crank is on a dead centre, it is so placed in the figure, while as
the zero position of the eccentric (which is for a valve having no steam
lap) is at 90 degrees from the crank, therefore the dotted circle
representing the path of the eccentric centre has its O or zero point at
90 degrees from the crank. Now suppose the eccentric centre stood at _v_
and the eccentric throw line at _c_ _v_, and it will stand at 30 degrees
from O, hence the angular advance of the eccentric is in this case 30
degrees, or in other words, it is 30 degrees in advance of its zero
position, or the position it would occupy when the crank is on the dead
centre and the valve has no lap and no lead.
If we measure the distance apart of the crank and the eccentric in
degrees, we find it is 120 degrees, hence place the crank where we may,
we can find the corresponding eccentric position because it is 120
degrees ahead of the crank. The sign for degrees is a small ° placed at
the right hand of the figures and slightly above them; thus, thirty
degrees would be written 30°.
FINDING THE WORKING RESULTS GIVEN BY A D SLIDE VALVE.
Although not strictly within the line of duty of an engineer or engine
driver, he is nevertheless sometimes called upon to find out how a valve
of given proportions will dispose of the steam, or what proportions to
give to a valve to accomplish certain results.
This is easy enough when either the travel of the valve or the amount of
the lap and the width of the port are given, but if the width of the
port alone is given, and all the other elements are to be found, it
becomes a more difficult problem.
An engineer, however, is rarely called upon to solve the question from
this stand-point, which properly belongs to the draughtsman or engine
designer.
If the amount of valve travel is given, however, all the other elements
may readily be found by the following construction:
[Illustration: Fig. 3311.]
Suppose that in Fig. 3311 a D valve is to be designed to cut off the
steam when the piston has travelled from position B´ to R´, or at
three-quarters of its stroke. Then to find the position the crank pin
will be in when the cut off occurs, we draw a circle, B D, representing
the path of the crank on the same scale that the length of the piston
stroke is represented. The straight line from B to D will, therefore,
represent the piston stroke without drawing the piston or cylinder at
all (this being done in the figure to make the explanation clear). When
the crank is on its dead centre, B, the piston, will be at B´, and the
valve in the position shown (supposing it to have no lead). As soon as
the crank and valves begin to move, the steam will enter steam port _a_,
and to find where the crank will be when the piston is at three-quarters
stroke, and is, therefore, in position R´, we mark a point at R
three-quarters of the distance from B to D. Then, taking no account of
the length of the connecting rod, we draw a vertical line Y from R to
the circle, and this line gives at H the position the crank will be in
when the piston is at R. We have so far, therefore, that while the
piston travels from B´ to R´, the crank will travel from B to H. Now, it
will be found that if we set a pair of compasses from B to F, which is
half-way from B to H, and then rest the compasses at D, and mark an arc
V, then a line from V to the centre of the crank will give us the proper
position of the eccentric. As the centre of the crank pin and also the
centre of the eccentric both travel in a circle, we may, therefore, take
a circle having a diameter equal to twice the throw of the eccentric,
(or, what is the same thing, equal to the full travel of the valve), and
let it represent the paths of both the eccentric centre and the crank
pin centre, the latter being drawn to a scale that is found by dividing
the length of the piston stroke by the travel of the valve; thus, if the
travel is 3 inches and the stroke 30 inches, the diameter of a 3 inch
circle will represent the valve travel full size, and the piston stroke
one-tenth full size, because 30 ÷ 3 = 10. It has been shown on page 376
that the length of the connecting rod affects the motion of the piston
by distorting it, and it is necessary to take this into account in
constructing the actual diagram, which may be done as follows:
The valve travel and point of cut off being given, to find the required
amount of lap, there being no lead, draw a circle equal in diameter to
the travel of the valve, and draw the line of centres B D, Fig. 3312;
mark on the line of centres a point R, representing the position the
piston is to be in at the time the cut off is to take place.
Set a pair of compasses to represent the length of the connecting rod on
the same scale as the circle B D represents the path of the crank; thus,
if the connecting rod is three times the length of the stroke, the
compasses would be set to three times the diameter of the circle B D.
[Illustration: Fig. 3312.]
A straight line from B to D and passing through the centre C of the
crank will represent the line of centres of the engine, which must be
prolonged to the right sufficiently to rest the compasses on it and draw
the arc Y, which will give at H the position of the crank when the
piston is at R, and the cut off is to occur.
We have thus found that the amount of circular path the crank will move
through from the dead centre to the point of cut off is from B to H, and
as the eccentric is fast upon the same shaft, it will, in the same time,
of course, move through the same part of a circle.
One half of its motion will be to open and one half to close the port,
so that we may by means of the arcs at F get the point F, which is
midway between B and H, and with the compasses set from B to F, mark
from D the two arcs V and V´ whose distance apart will obviously be the
same as from B to H.
Then from V to V´ draw the line P, and from this line to the centre C of
the crank shaft is the amount of steam lap necessary for the valve,
while from this line (P) to D is the width of the steam port.
The proof of the diagram is as follows:
When the crank is on the dead centre, the centre of the eccentric is at
V, its throw line being represented by the line from V to C, and the
valve is about to open the port as shown in the figure.
While the eccentric is moving from V to D, the valve will move in the
direction of the arrow and will fully open the port, while the crank pin
will move from B to F.
Then, while the crank moves from F to H, the eccentric will have moved
the valve to the position it occupies in the figure, having closed the
port and effected the cut off.
We have here found the amount of lap and the position of the eccentric
necessary for a given point of cut off when the latter is given in terms
of the piston stroke. If, however, the point of cut off had been given
in terms of the crank pin position, we might find the required amount of
lap at once, by simply drawing a line from the centre B, the point to H
where the crank pin is to be when the cut off occurs.
From this line we could then draw the dotted circle G, and just meeting
the line P, which would give the eccentric position.
To find the piston position, the arc Y would require to be drawn by the
same means as before.
[Illustration: Fig. 3313.]
[Illustration: Fig. 3314.]
If the valve is to have lead, the diagram may be constructed as in Fig.
3313, in which the circle has a diameter equal to the travel of the
valve and the cut off is to occur when the piston is at R and the crank
at H.
When the valve is at the end of its travel and has fully opened the
port, the eccentric will be at D, hence from D we mark an arc G distant
from D to an amount equal to the width of the steam port, drop the
vertical _m_ from G, and at its lower end V´ is the position of the
eccentric centre at the point of cut off. Then draw a line P, distant
from _m_ equal to the lead, which will give at V the position of the
eccentric when the crank is on the dead centre, and the valve is open to
the amount of the lead. The lap is obviously the distance from the
centre C of the crank shaft to the arc G.
We have here found all the points necessary except the point at which
the valve will open the port for the lead, and this we may find by
setting a pair of compasses to the radius B H (or to radius V V´, as
both these radii are equal), and from V as a centre, mark at A an arc,
which will give the crank pin position at the time the port first opens
for the lead, or in other words it will give the position. The proof of
the construction is, that if we set the compasses to the distance
between the crank pin position on the dead centre and the point of cut
off (or from B to H), we may apply the compasses to the points V, V´,
which represent the eccentric position when the port is opened to the
amount of the lead, and when the cut off occurs.
If the point of cut off only is to be found, we mark from C, Fig. 3314,
an arc G representing the amount of valve lap and arc S representing the
lead. A vertical P gives the eccentric position V when the crank is on
the dead centre at B, and a vertical _m_ from G gives at V´ the
eccentric position at the point of cut off. Then with the compasses set
to the points V V´, we may mark from B an arc, locating at H the
position of the crank at the point of cut off, and from this with
compasses set to represent the length of the connecting rod on the same
scale as the circle represents the path of the crank, we may, from a
point on the line of centres, mark an arc Y giving at R the piston
position at the point of cut off.
When, therefore, the lap is given, we mark it from the center C of the
crank shaft, and find the other elements from it, whereas, when the lap
is to be found, we mark the width of the port from the end D of the
valve travel, and find the other elements from that.
A proof of all the constructions is given in Fig. 3314, in which the
letters of reference correspond to those in the previous figures, and
the positions of the parts are marked in degrees of angle.
To find the piston position at the point of cut off, measured in inches,
of the piston stroke it must be borne in mind that as the circle B D
represents the full travel of the valve, the diagram gives all the
positions of the eccentric and valve full size, but that as it
represents the crank path on a reduced scale, therefore we must multiply
the measurement on the diagram by that scale.
Suppose, for example, that the piston stroke is 10 inches, and the valve
travel 2-1/2 inches, and the circle being 2-1/2 inches in diameter, is,
when considered with relation to the eccentric motion, full size, but
when considered with relation to the piston or crank motion, it is only
1/4 the size, hence to find the piston position at the time of cut off,
we must multiply the distance from B to R by 4.
[Illustration: Fig. 3315.]
LINK MOTION FOR STATIONARY ENGINES.
The ordinary mechanism employed to enable a stationary engine to be
reversed or run in either direction is the Stephenson link motion. Other
forms of link motion have been devised, but the Stephenson form has
become almost universal.
[Illustration: Fig. 3316.]
Fig. 3315 represents this link motion or reversing gear with the parts
in position for the full gear of the forward motion, and Fig. 3316
represents it in full gear for the backward motion.
The meaning of the term full gear is that the parts are in the position
in which the steam follows the piston throughout the longest or greatest
part of the stroke. When in full gear the link motion operates the valve
almost precisely the same as if the eccentric rod was attached direct to
the valve spindle and no link motion was used.
Besides enabling the engine to run in both directions, however, the link
motion provides a means of reducing the amount of valve travel and thus
causes the live steam to be cut off earlier in the piston stroke, thus
using the steam more expansively. This is done by moving the reversing
lever more upright, the earliest point of cut off being obtained when it
is upright and the latch is in the notch marked O on the sector in Fig.
3315. If with the engine standing still we move the link motion from
full gear forward to full gear backward and watch the valve, we shall
find that the valve lead increases as the reversing lever approaches the
upright position, or mid gear as it is termed, and that after passing
that point it gradually diminishes again, the valve being so set that
the lead is the same for full gear forward as it is for full gear
backward.
The reversing lever is used to move the link into the required position
and to hold it there (the end of the latch fitting into the notches in
the sector being the detaining or locking device); as the link is
suspended by its saddle pin S and the link hanger, therefore its motion
is to swing or partly rotate on the pin S, and at the same time ending
in the arc of a circle whose centre of motion is in the pin at the upper
end of the link hanger which is pivoted to the lower arm of the lifting
shaft (which is sometimes termed the tumbling shaft). It will clearly be
seen that with the position the parts occupy in Fig. 3315, and the crank
motion being in the direction of the arrow, the forward eccentric will
move the top of the link to the right and therefore the valve will move
to the right, while the backward eccentric will move the bottom end of
the link to the left.
In full gear, however, the bottom eccentric rod has but a very slight
effect indeed on the motion of the valve because both the link hanger
and the link block will permit the link to swing on centre of the link
block pin as a pivot. If now we turn to Fig. 3316 for the full gear
backward, we shall see that these conditions are reversed and the
backward eccentric becomes the effective one, being in line with the
valve spindle. By shifting the link from one gear to the other,
therefore, we have merely changed the direction in which the link will
move the valve, and, therefore, the direction in which the engine would
run.
In Fig. 3315 for the full gear the parts are shown in position, with the
piston at the crank end of the cylinder, and the crank pin on the dead
centre, and the eccentrics must be set as shown in the cut, the
eccentric rods being open and not crossed. When, however, the crank is
on the other dead centre and the piston at the head end of the cylinder,
the rods will cross each other, and it is necessary to remember that the
rods should be open when the piston is at the crank end of the cylinder.
If, however, the running gear contains a rock shaft, or rocker (as is
the case in American locomotives), then these conditions are reversed,
and the eccentric rods will cross when the piston is at the crank end of
the cylinder.
In setting the slide valve of an engine having a link motion, there are
two distinct operations. First, to put the crank on the respective dead
centres, which will be fully described on page 394 and need not be
repeated; and second, to set the eccentrics in their proper positions on
the shaft, and correct, if necessary, the lengths of the eccentric rods.
The crank being on the dead centre, with the piston at crank end of the
cylinder, the eccentric should be moved around on the shaft by hand
until there is the desired amount of lead at the crank end port, and
temporarily fastened there, a set screw usually being provided (in the
eccentric) for this purpose. The lead is best measured with a wedge, W,
Fig. 3315. The crank is then put on its other dead centre, and the lead
for the head end port is measured. If the lead is to be made equal for
the two ports (as is usually the case in horizontal engines) and it is
found to come so, the valve setting for the forward gear is complete. If
the lead is not equal, the forward eccentric rod or else the valve
spindle must be altered so as to make the lead equal. In some engines
adjusting screws are provided for the purpose of regulating the length
of either the eccentric rod or else of the slide spindle; it does not
matter which is altered. The link motion is then put in full gear for
the backward motion, and, with the crank on the dead centre (it does
not matter which dead centre), the eccentric is moved by hand upon the
crank shaft until there is the required amount of valve lead. The
eccentric is then fastened on the shaft and the crank put on the other
dead centre, and the lead tried for the other port, and made equal by
lengthening or shortening the backward eccentric rod. It is to be noted
that altering the length of the eccentric rod or of the valve spindle
makes it necessary to reset the eccentric, as it affects the amount of
lead at both ports; hence, if any alteration of rod length is made, the
whole process here described must be repeated after each alteration of
rod length.
FLY BALL OR THROTTLING GOVERNORS.
An isochronal governor is one in which the two opposing forces are equal
throughout the whole range of governor action, or, in other words,
equal, let the vertical height of the plane in which the balls revolve
or swing be what it may.
A dancing governor is one that acts spasmodically. Such an action may
occur from undue friction in the parts of the governor or of its
throttle valve.
The friction offers a greater resistance to starting the parts in motion
than it does to keep them in motion after being started; hence, the
parts are apt to remain at rest too long, and to move too far after
being put in motion.
Rule to find the number of revolutions a governor should make. Divide
the constant number 375.36 by twice the square root of the height of the
cone in inches. The quotient is the proper number of revolutions per
minute.
_Example._--A governor with arms 30-1/2 inches long, measuring from the
centre of suspension to the centre of the ball, revolves, in the mean
position of the arms, at an angle of about thirty degrees with a
vertical spindle forming a cone of about 26-1/2 inches high. At what
number of revolutions per minute should this governor be driven? Here
the height of the cone being 26.5 inches, the square root of which is
5.14 and twice the square root 10.28, we divide 375.36 by 10.28, which
give us 36.5 as the proper number of revolutions per minute at which the
governor should be driven.
The construction of the Pickering governor is as follows:
[Illustration: Figs. 3317, 3318.]
In Fig. 3317 it is shown in its simplest form, and in Fig. 3318 with the
driving pulley and speeder (or engine speed regulating device) attached.
This speeder consists of a spiral spring whose tension may be adjusted
to more or less resist the rise of the governor balls, and thus enable
the engine to run at a greater speed for a given amount of rise of the
governor balls, hence by increasing the tension the engine speed is
increased.
THE SPRING ADJUSTMENT.
The adjustment of the spring tension is made by a worm actuating a worm
wheel on a rod passing through the spring, and to which one end of the
spring is attached, the other acting on an arm that projects into a slot
in the governor spindle. It is obvious that the speeder can be adjusted
while the engine is running.
[Illustration: Fig. 3319.]
In Fig. 3319 the governor is shown with the speeder and Sawyer's valve,
the latter enabling the governor valve to be opened or closed without
affecting the rise and fall of the governor balls, which is done by
operating the arm shown on the right, whose ends are provided with
loops, so that a cord may be attached, enabling the engineer to operate
the governor from a distance.
The safety stop or stop motion is shown on the right, Fig. 3320.
It acts to close the governor valve and stop the engine in case the belt
that drives the governor should get off the pulley or break. This stop
motion consists of a pulley suspended by a rod, and riding on the belt
which supports its weight. Should the governor belt break, this pulley
falls and severs the connection between the valve and the governor,
closing the valve, and holding it closed. Fig. 3321 shows the governor
in section to expose the construction of the valve. The valve V is what
is termed a poppet or poppet valve, which is balanced, because the steam
entering at I, and taking the course denoted by the arrows, acts equally
on both ends of the valve and does not press it in either direction,
while as the steam surrounds the valve it is not pressed sideways.
At B is a gland or stuffing box to keep the spindle or rod steam-tight.
At A is the slot for receiving the arm from the speeder and from the
stop motion.
P is obviously the driving pulley, imparting motion to the bevel wheels
G, which drive the outer spindle S, the inner spindle _s´_ being
connected to A. The balls are upon ribbon springs D, which are secured
at their lower ends to a link fast to the spindle S.
The centrifugal force generated by the balls causes them to move
outwards, their upper ends pulling down the cap to which they are
secured, and this cap operates the valve.
Governors of this class are sometimes termed _fly-ball_ governors.
STARTING A PLAIN SLIDE-VALVE ENGINE.
The method to be pursued before starting a plain slide-valve engine
depends upon what the engineer knows about the condition of the engine.
If he knows the engine is in proper running order, all that is necessary
is to first attend to the oil cups and start them feeding.
Then, if it is necessary, move the crank into the required position to
start it easily; open the waste water cocks to relieve the cylinder of
the water that will be condensed from the steam when it enters a cool
cylinder, and turn on the steam; giving the throttle valve enough
opening to start the engine slowly.
The best position for the crank pin to be in to enable its starting
easily is midway between the horizontal and vertical position (or, in
other words, at an angle of 45° to the line of centres) and inclining
toward the cylinder, so that when the engine moves the piston will
travel toward the crank shaft.
There are two reasons why this is the best position for starting. The
first applies to all engines because there is a greater piston area for
the steam to act on when the piston is moving toward the crank than
there is when it is moving away from it. This occurs because the piston
rod excludes the steam from a part of the face of the piston. The second
applies to all plain slide-valve engines whose slide valves have equal
laps and both steam ports of equal widths, because the live steam
follows further on the stroke when the piston is moving toward the crank
than it does when it is moving away from it, and it follows that more
piston power is developed, and the engine is less likely to stop when
passing the dead centre.
[Illustration: Fig. 3320.]
[Illustration: Fig. 3321.]
When first taking charge of an engine, it is proper, before starting it,
to ascertain that it is in fair working order.
A complete examination of an engine should include a test of the fit of
the piston to the cylinder bore, of the cross head to the guide bars, of
the connecting rod brasses to the crank pin and cross head journals, and
of the crank shaft to its bearings. It would also include a testing of
the alignment of the crank shaft and of the guide bars, as well as the
set of the valves and the adjustment of the governor.
The least examination permissible with a due regard to safety would be
to move the engine throughout at least one full revolution by hand, and
to see that the connecting rod brasses and the main bearings do not fit
too tight to their respective journals, and to then start the engine
slowly by giving it only enough steam to move it, keeping the hand on
the throttle valve so as to be able to shut off steam instantly should
it become necessary.
A thorough examination should be made in the following order:
First, slightly loosen the nuts on the crank shaft bearings and also the
connecting rod keys.
Then move the fly wheel around until the crank points straight to the
cylinder, which will bring the piston up to the outer end of the
cylinder bore.
Take off the cylinder cover and also the follower from the piston head,
and see that the piston rings are set out to fit the cylinder bore but
not to bind it tight. Then bolt the follower up firmly in place again.
Take off the connecting rod and move the piston until it touches the
cylinder cover at the other or crank end of the cylinder, and then draw
a line across the side face of the cross head guide and on the guide
itself.
Put on the cylinder cover and push the piston back until it abuts
against it, and then make another line on the cross head guide and the
guide bar, and these two lines will show the extreme positions to which
the piston can be moved when the connecting rod is disconnected.
Next put on the connecting rod, carefully adjust the keys or wedges, so
that the bores of the brasses fit easily to the crank pin and cross head
pin, seeing that the oil holes are clear, and that oil will feed
properly to the journals.
In making this adjustment it is a good plan, if there is any end play of
the brasses on the crank pin, to set up the key or wedge until the rod
can just be moved by hand on the pin, by first pulling the rod to one
end of the pin, and then pushing it to the other.
In putting on the rod, it will be necessary to move the piston a trifle
towards the crank.
In making the adjustment of the crank pin fit to the rod brasses, it is
a good plan to drive the key home until the brasses are known to bind
the crank pin, and then mark a line across the side face of the key and
fair with the top face of the connecting rod strap, to then slacken back
the key enough to ease back the brasses to a proper fit, and then mark
another line on the key.
The first line will form a guide as to how much to slacken back the
brasses to adjust the fit, and the second one will form a guide as to
how much the key is moved when making a second adjustment, if one
should be found necessary after the engine has been running.
Similarly in adjusting the main bearing boxes to the crank shaft, either
the nuts, or what are called leads, may be taken to adjust the fit.
Leads are necessary when the joint faces of the brasses do not meet, but
are left open so that the wear can be taken up while the engine is
running.
It is better, however, to let the brasses abut together, so that it may
be known that the fit is correct when the nut is screwed firmly home.
The method of taking a lead is as follows: The top brass is loosened,
and between the joint faces of the brasses or boxes on each side of the
shaft a piece of lead wire is inserted. For a shaft of, say, four inches
in diameter, the lead wire will be about 7/16 inch in diameter, or for a
10 inch shaft the wire should be 1/8 inch in diameter, and should be as
long as the brass. The nuts are then screwed firmly home, and the wire
will be squeezed between the brasses and thus flattened on two opposite
sides, the thickness showing how far the joint faces of the brasses are
apart when the bore grips the journal.
A liner, fit strip, distance piece, or shim (all these names meaning the
same thing) is a strip of metal placed between the joint faces of the
brasses to hold them the proper distance apart to make a working fit of
the journal and brasses, when the latter are firmly bolted up.
The fit of the top brass therefore depends upon the fit strip being of
the proper thickness from end to end.
Now the lead wire is the gauge for the thickness of the fit strip, the
latter being made a trifle thicker than the flattened sides of the lead.
If the lead is thicker one end than the other, or if one lead is thicker
than the other, the fit strips must be made so, and the leads must be
marked so that it may be known which way they were placed between the
brasses so that the proper fit strip may be on the proper side of the
brass, and the proper end towards the crank.
Another method that is adopted in the case of large brasses is to screw
down the nuts until the brasses bind the journal, and then make a mark
on the nut and on the bolt thread. The nut is then slackened back as
much as the judgment dictates, and a note made of how much this is, the
marks forming a guide.
As the wear takes place, and the nuts screw farther down, a new mark is
made on the nut, so that it may always be known how much to screw up or
unscrew the nut, to make a light adjustment.
To avoid heating, it is a good plan to press some tallow into the bottom
or in one corner of the oil cup, and then pour in the oil used for
ordinary lubrication. So long as the bearing remains cool, the oil will
feed and the tallow remain.
If the bearing heats, the tallow will melt, and, having a heavier body,
will give a more suitable lubrication.
To find if the connecting rod is of the right length to give, as it
should do, an equal amount of clearance (or space between the piston and
the cylinder cover) at each end of the stroke, move the fly wheel a
trifle in either direction, and then move it back until the crank is on
the dead centre, and draw a line across the cross head guide and guide
bar, and the distance between this line and that drawn when the
connecting rod was disconnected, shows the amount of clearance at that
end of the cylinder. Then move the crank pin over to its other dead
centre, and mark a line across the cross head guide and the guide bar,
and the distance between this line and that drawn before the connecting
rod was put on will show the clearance at this end of the cylinder.
If the clearance is not equal for the two ends, it should be made so by
putting liners behind the connecting rod brasses so as to lengthen or
shorten the connecting rod (according as the case may require), and
equalize the clearance, while at the same time bringing the connecting
rod keys up to their proper heights.
To test the set of the valve, the steam-chest cover must be taken off,
the crank placed alternately on each dead centre, and the lead measured
for each port.
An unequal or an equal degree of valve lead may be given by suitably
altering the length of the eccentric rod, but when the lead is equal for
the two ports, its amount must be regulated by moving the position of
the eccentric upon the crank shaft.
SQUARING A VALVE.--A method not uncommonly pursued in setting a valve is
to what is called _square it_ before trying it.
This squaring process consists in so adjusting the length of the
eccentric rod that the valve travels an equal distance over or past the
steam edge of each steam port; but since the valve does not, when set to
give equal lead, travel equally past each port, therefore the work done
in squaring a valve is all thrown away, and may result in altering the
eccentric rod from its proper length to an improper one, necessitating
that it be altered back again in order to set the lead right.
The proper method is to adjust both the length of the rod and the
position of the eccentric, by testing the lead at once, lengthening the
eccentric rod to increase the lead at the crank end, or vice versa.
Each alteration of eccentric position may render necessary an alteration
of rod length, or vice versa, each alteration of rod length may render
it necessary to alter the eccentric position, hence the lead should be
tried at both ends of the cylinder after each alteration of either rod
length or eccentric position.
In vertical engines the weight of the crank shaft causes it to wear the
bottom brass or part of the bearing box the most, thus lowering its
position, while the eccentric straps and pins wear most in the same
direction; hence the wear increases the lead at the head end of the
cylinder when the latter is above the crank, and at the crank end when
the crank is above the cylinder.
When the cylinder is above the crank, the weight of the piston, cross
head and connecting rod is counterbalanced at the end of the downward
piston stroke by giving the crank end port more lead; but when the
cylinder is below the crank, it is the head end port that must be given
increased lead to prevent a pound or knock, or to allow for the wear
downwards of the parts.
After an engine is started, the pet cocks should (if they are not
automatic) be closed as soon as dry steam issues, and if this cannot be
seen, it may be assumed to occur after the engine has made about 20
revolutions.
The parts that will then require particular attention are the crank pin,
main bearings, cross head guides and the pump, if there is one. The
former must be kept properly lubricated, so that they may not get hot
and the cylinder lubricator (which is usually placed on the steam pipe)
must be set to self feed properly.
If the crank shaft bearings should begin to heat, loosen the cap bolts
and lubricate more freely, or, if it is at hand, some melted tallow may
be applied with the oil, as a heavier lubricant may stop the heating.
The crank pin requires the most attention and is the most difficult to
keep cool and to examine, because of its circular path rendering it
difficult to feel it. This may be done, however, in two ways, first by
standing at the end of the engine bed and gradually extending the hand,
until the end of the rod meets it as it passes, and, second, by placing
the hand on the connecting rod as near to the end of the guide bar as
possible where its motion is diminished and moving the hand towards the
crank pin, by which means the end of the crank pin may be approached
gradually.
If the end of the rod is hot, the engine speed should be reduced or the
engine should be stopped so that the connecting rod key or wedge may be
eased back and the oil feed made more copious. Then, after the engine
has been stopped for the night, the brasses should be taken out and any
rough surface, either on the brasses or on the pin, smoothed down with a
file.
Hot crank pins may occur from several causes, but by far the most common
ones are from improper oiling, or from the engine being out of line.
A heavier oil will often stop, or at least modify, the heating, but its
cause should always be discovered and remedied.
Engines that are used out of doors or are exposed to temperatures below
the freezing point must be left so that steam leaks may not condense in
any of the parts or pipes and burst them.
Leaky throttle valves may, for example, cause water to accumulate in
the steam chest and freeze, perhaps bursting the steam-chest cover.
To prevent this let the engine stand with the crank just past the dead
centre, so that the steam port will be open, and open the waste water
cocks on the cylinder, and also on the steam chest if there is any.
If the cylinder is jacketed all the drain cocks for the jacket should
also be opened.
A leaky check valve may cause the steam to condense in the pump and
freeze it up solid or burst it or the pipes. To avoid this, open the
pump pet cock.
Open all the drain cocks on the heater and water pipes.
If the water is left in the boiler all night it is liable to freeze.
To prevent this leave a well banked fire.
In extreme weather remember that on exposed engines the oil, if of such
quality as sperm or lard oil, may freeze and prevent feeding until the
bearings get hot and melt the oil.
To prevent this use a lighter oil, as, for example, a mineral oil. Or,
in case of freezing, melt the oil in the cups with a piece of wire made
red hot while getting up steam in the morning.
A good plan to prevent oil from freezing and yet have a good quality of
oil is to mix two parts of lard oil with one part of kerosene.
Portable engines should stand as nearly level as possible, so that the
water will stand level above the tubes and crown sheet of the fire box.
When feed water is drawn from a natural supply, as from a stream, the
strainer at the end of the suction pipe should be clear of the bottom of
the stream, where it is liable to be choked.
When the exhaust steam is used to feed the boiler, do not open the valve
that lets the exhaust steam into the feed-water tank until a little
while after the engine has started, because the oil fed to the cylinder
will otherwise pass into the feed tank and may cause priming.
In engines having plunger pumps for feeding the boiler it is essential
to keep the plunger properly packed, as a leak there impairs or stops
the pump from acting.
A gauge glass may be cleaned when the engine is cold by shutting off the
cocks leading from the boiler and filling the glass with benzine,
allowing it to stand two hours; the benzine must be let out at the
bottom of the glass tube, and not allowed to enter the boiler.
In starting a new engine be careful to let the bearings be slightly
loose.
At first give only enough steam to just keep the engine going, and keep
the hand on the throttle valve ready to shut off steam instantly if
occasion should require.
PUMPS.
Pumps are divided into the following classes:
Lift pumps, in which the water flows freely away from the pump, which
performs lifting duty only.
Force pumps, which deliver the water under pressure.
Plunger pumps, in which a "plunger," or "ram," as it is sometimes
termed, is used.
Piston pumps have a piston instead of a plunger.
A double acting pump is one in which water enters into and is delivered
from the pump at each stroke of its piston or plunger, or, in other
words, one in which, while water is being drawn in at one end of the
pump, it is also being forced out at the other.
A single acting pump is one in which the water enters the pump barrel
during one piston or plunger stroke, and is expelled from the pump
during the next stroke, hence the action of the suction and of the
delivery is intermittent, although the pump is in continuous action.
For very heavy pressures plunger pumps are generally used, the plunger
being termed a _ram_.
The advantage of the plunger or ram is that it gives a positive
displacement, whereas in a piston pump a leaky piston permits the water
from the suction side to pass through the leak in the piston, to the
delivery side.
Piston pumps possess the advantage that there is less difference between
the contents of the pump and the displacement than is the case in
plunger pumps.
The displacement of a piston pump is found by multiplying the area of
the pump bore by the length of the piston stroke.
The displacement of a plunger pump is less than the above, by reason of
there being a certain amount of clearance or space between the
circumference of the plunger and that of the cylinder bore.
It is desirable to keep the clearance space in all pumps as small as the
conditions will allow, especially if the pump is liable to lose its
water.
Losing the water means the falling of the suction water back into the
source of supply, which may occur when the engine has to stop
temporarily, and there is a leak in the suction valves.
[Illustration: Fig. 3322.]
Rotary pumps are those in which the piston revolves, an example of the
most successful form of rotary pump being shown in Fig. 3322, which is
that used by the Silsby fire engine.
The advantage possessed by a rotary pump is that it keeps the water
passing through the suction in a continuous and uniform stream, as it
has no valves.
It may therefore be run at a high velocity or attached direct to the
engine shaft.
If a rotary pump leaks, the efficiency is not impaired so much as in a
piston or plunger pump, all that is necessary being to run the pump at a
high speed.
[Illustration: Fig. 3323.]
The principles of action of a pump may be understood from Fig. 3323,
which represents a single acting plunger pump shown in section, and with
the suction pipe in a tank of water, the pump being empty.
The surface of the water in the tank has the pressure of the atmosphere
resting upon it, and as the pump is filled with air, the surface of the
water within the pipe is also under atmospheric pressure.
Now suppose the plunger to move to the right, and as no more air can get
into the pump, that already within it will expand, and will therefore
become lighter, hence there will be less pressure on the surface of the
water within the suction pipe than there is on the outside of it, and as
a result the water will rise up the pipe, not because the plunger draws
it, but because the air outside the pipe presses it up within the pipe.
[Illustration: Fig. 3324.]
The water inside the pipe will rise above that outside in proportion to
the amount to which it is relieved of the pressure of the air, so that
if the first outward stroke of the plunger reduces the pressure within
the pump from 15 lbs. to 14 lbs. per square inch (15 lbs. per square
inch being assumed to be its normal pressure), the water will be forced
up the suction pipe to a distance of about 2-1/4 feet, because a column
of water an inch square and 2-1/4 feet high is equal to 1 lb. in weight.
In Fig. 3324 the pump plunger is shown to have moved enough to have
permitted the water to rise above the suction valve, and it will
continue to rise and enter the pump barrel as long as the plunger moves
to the right.
When the plunger stops, the suction valve will fall back to its seat and
enclose the water in the pump; but as soon as the plunger moves back to
the left hand and enters the barrel pump further, the delivery valve
will rise, and the plunger will expel from the pump a body of air or
water equal in volume to the cubical contents of the plunger, or rather
of that part of it that is within the barrel, and displaces water.
If the plunger was at the end of its first stroke to the right and the
pump half filled with air, then this air will be expelled from the pump
before any water is; whereas if the pump was filled with water, the
latter only will be delivered.
Now suppose the first plunger stroke reduces the air pressure from 15 to
14 lbs., and that the second drawing stroke of the plunger reduces the
air pressure in the pipe to 13 pounds per inch, the water will rise up
it another 2-1/4 feet, and so on until such time as the rise of a column
of water within the pipe is sufficient to be equal in weight to the
pressure of the air upon the surface of the water without; hence it is
only necessary to determine the height of a column of water that will
weigh 15 lbs. per square inch of area at the base of the column to
ascertain how far a suction pump will cause water to rise, and this is
found by calculation or measurement to be a column nearly 34 feet high.
It is clear then, that however high the pump may be above the level of
the water, the water cannot rise more than 34 feet up the suction pipe,
even though all the air be excluded from it and a perfect vacuum formed,
because the propelling force, that is, the atmospheric pressure, can
only raise a column of water equal in weight to itself, and it is found
in practice to be an unusually good pump that will lift water thirty
feet.
[Illustration: Fig. 3325.]
Fig. 3325 shows the plunger making a delivery stroke, the suction valve
being closed, and the delivery valve open where it will remain until the
plunger stops.
To regulate the quantity of water the pump will deliver in cases where
it is necessary to restrict its capacity, as in the case of maintaining
a constant boiler feed without pumping too much water in the boiler, the
height to which the suction valves can lift must be restricted, so as to
limit the amount of water that can enter the pump at each drawing
stroke.
The delivery valve should lift no more than necessary to give a free
discharge without causing the valve to seat with a blow; but if the pump
has a positive motion, the delivery valve must open wide enough to let
the water out, or pressure enough may be got up in the pump to break it.
A check valve is merely a second delivery valve placed close to the
boiler and serving to enable the pump to be taken apart if occasion
should arise, without letting the water out of the boiler.
The lift and fall of both valves act to impair the capacity of the pump.
Thus, while the suction valve is falling to its seat, the water already
in the pump passes back into the suction pipe, and similarly, while the
delivery valve is closing, the delivery water passes back.
A foot valve is virtually a second suction valve placed at the bottom or
foot of the suction pipe.
The capacity of a pump is from 70 to 85 per cent. of the displacement of
the plunger or piston, and varies with the speed at which the plunger or
piston runs.
If a pump runs too fast, the water has not sufficient time to follow the
piston or plunger, especially if the suction pipe has bends in it, as
these bends increase the friction of the water against the bore of the
pipe.
The speed of the piston or plunger should not exceed such as will
require the water to pass through the suction pipe at a speed not
greater than 500 feet per minute, and better results will be obtained at
350 feet per minute.
An air chamber placed above the suction pipe of any pump causes a better
supply of water to the pump by holding a body of water close to it, and
by making the supply of water up the suction pipe more uniform and
continuous. Air chambers should be made as long in the neck as
convenient, so that the water in passing through the pump barrel to the
delivery pipe could not be forced up into the chamber, as, if such be
the case, the air in the chamber is soon absorbed by the water.
Belt pumps are more economical than independent steam pumps, because the
power they utilize is more nearly the equivalent of the power it takes
to drive them, whereas in steam pumps there is a certain amount of
steam, and therefore of power, expended in tripping the valves and in
filling the clearance spaces in the cylinder. Furthermore, the main
engine uses the steam expansively, whereas the steam pump does not.
[Illustration: _VOL. II._ =AMERICAN FREIGHT LOCOMOTIVE.= _PLATE XXIX._
Fig. 3326.]
CHAPTER XXXVIII.--THE LOCOMOTIVE.
In Fig. 3326 is shown a modern freight locomotive, the construction
being as follows:
For generating the steam we have the boiler, which at the front end is
firmly bolted to the engine cylinders, which are in turn bolted to the
frames, while at the back end the boiler is suspended by the links B
(one at each end of the fire box on each side of the engine).
The starting bar is shown in position to start the engine, and it is
seen that the rod _a_ and bell crank _b_ are in such a position as to
open the valve T, and thus admit steam from the dome to the pipe _e_,
whence it passes through pipes _f_, _g_ and _r_ into the steam chest
_i_, the slide valve V distributing the steam to the cylinder. The
exhaust occurs through the exhaust port _d_, whence it passes up the
exhaust pipe and out at the smoke stack.
The boiler is fed with water as follows:
The _feed pipe from the tender_ supplies water to the injector, which is
forced by the injector through the _feed pipe to boiler_ and into the
latter.
In the figure the parts are shown in position for the engine to go
ahead, hence the reversing gear is in the extreme forward notch of the
sector, and the valve gear is in full gear for the forward motion.
The lever _m_ is for opening and closing the cylinder cocks, which are
necessary to let the water of condensation out of the cylinder when the
engine is first started and the cold cylinder condenses the steam.
To supply steam to the injectors (of which there are two, one on each
side of the engine) and to the steam cylinder of the pump, there is a
steam pipe leading from the dome to the steam drum, the pipe K supplying
steam to the injector, and pipe J supplying steam to the steam cylinder
of the air pump. The pipe for supplying oil to the slide valve and
cylinder is furnished with a sight feed oil cup, the oil being carried
by steam from the steam drum.
This pipe passes beneath the lagging until it reaches the smoke box,
which is done to keep it warm and prevent the oil from freezing, while
the steam pressure enables the oil to feed against the steam pressure in
the steam chest.
The slide valve is balanced by means of strips let into its back, and
bearing against a plate fixed to the steam chest cover.
The frame on the side of the engine shown in the engraving is shown
broken away from the yoke A to the fire box, so as to expose the link
motion to full view, the shaded portion of the frame being that on the
other side of the engine.
The yoke or brace A carries one end of the guide bars. The safety valve
S may be raised to see that it is in working order, or to regulate the
steam pressure, by the lever O, which has a ratchet tongue engaging with
the notches at _l_.
[Illustration: Fig. 3326_a_.]
[Illustration: Fig. 3326_b_.]
In addition to the safety valve with spring balance, however, a pop
safety valve is employed on the part of the dome that is shown broken
away, the construction of this pop valve being shown in the outside
view, Fig. 3326_a_, and a sectional view, Fig. 3326_b_, the casing being
removed from the latter. In the valve seat B is a recess _a_, and upon
the circumference of the valve is a threaded ring C´. When the valve
lifts, the steam is somewhat confined in the annular recess of the
valve, and the extra valve area thus receiving pressure causes the valve
to lift promptly and the steam to escape freely. The degree of this
action is governed as follows:
The sleeve C´ is threaded upon the upper part of the valve, so that by
screwing it up or down upon the valve the amount of opening between the
annular recess _a_ _a_, and the lower edge of the sleeve C´ C´, is
increased or diminished at will; the less this opening, the more
promptly the valve will rise after lifting from its seat.
To secure the sleeve or ring in its adjusted position, the ends of the
screws L, L seat in notches cut in the upper edge of the sleeve. In many
engines pop valves alone are used, and in some cases levers are provided
by means of which the pop valve can be raised from its seat to test if
it is in working order.
Referring again to Fig. 3326, H is the handle for operating the
injector, and _w_ a rod for opening the injector overflow.
We now come to the automatic air brake; steam for the steam cylinder of
which, is received from the steam drum through the pipe J, passing
through the pump governor, or regulator G. The exhaust pipe for the
steam cylinder of the air pump passes into the smoke box. The air
cylinder receives its supply of air through the small holes at _k_, _k_,
and delivers it through the pipe C into the air reservoir or tank, from
which it passes through the tank pipe up to the threeway cock or
engineer's brake valve, whose handle is shown at M. The brakes are kept
free from the wheels and out of action so long as there is air pressure
in the air reservoir and in the train pipe, hence the normal position of
the handle M is such as to let the air pass from the air reservoir up
the pipe _x_ and into the train pipe. When the brakes are to be applied,
handle M is moved so that there is an open connection made between the
train pipe and the _pipe to open_ air, which releases the air pressure
and then puts on the brakes not only on each car, but also on the
engine, because the engine brake cylinders receive their air pressure
from the pipe shown leading to the train pipe. From the tank pipe _x_ a
pipe _h_ leads to the top of the pump governor G, whose action is to
shut off the steam from the steam cylinder of the air pump whenever the
pressure in the air reservoir or tank exceeds 70 lbs. per square inch. A
small pipe leads up from pipe _h_ to the air pressure gauge.
For regulating the draught of the fire there is a damper door at each
end of the ash pan, and to increase the draught, a pipe leads from the
steam drum into the smoke box, where it passes up alongside of the
exhaust pipe, its end being shown at Z. This is called the _blower_, and
its pipe is on the other side of the engine. The plate shown at P, P in
the smoke box checks the draught in the upper tubes, and therefore
distributes it more through the lower ones.
[Illustration: Fig. 3327.]
There are two sand valves, both of which are operated by one rod, the
construction being shown in Fig. 3327, which is a plan showing the
bottom of the sand box broken away to expose the gear for moving the
valves. The two valves _v_, _v_ for the sand pipes are on raised seats
_e_, _e_, and are fast on the same shafts as the segments _s_, _s_, but
the valves are obviously above, while the segments are beneath the
bottom of the sand box. The gear wheel W is pivoted to the under side of
the bottom of the sand box, and the arm L is fixed to the wheel. At _t_
are pieces of wire, which, being fast in the spindle, revolve with it
and stir up the sand when the valves are moved. As shown in the figure,
the two sand pipes _a_, _a_ are open, but suppose the rod is moved
endways and L will revolve W, which will move _s_, _s_ and the valves
_v_, _v_, causing the latter to move over and cover the pipes _a_, _a_,
and shut off the sand from the pipes.
Fig. 3328 represents an American passenger locomotive with a steam
reversing gear, or in other words, a reversing gear that is operated by
steam.
The link motion is substantially the same as that shown in Fig. 3326 for
a freight locomotive, the eccentric rods in this case being straight, as
there is no wheel axle in the way.
The injector for feeding the boiler is the same as that shown on the
freight locomotive.
The ash pan is provided with two dampers, one at each end, and the front
one is operated by the bell crank _a_ _c_.
The sand boxes are here fastened to the frame, both sand valves being
operated by the lever _m_, which at its lower end connects to a rod,
_u_, which at its back end connects to an arm, _p_, on a shaft that
extends across the fire box and connects to a rod corresponding to rod
_u_, but situated on the other side of the engine and connecting with
the other sand valve.
The steam pump for the automatic air brake is on the other side of the
engine, and the air reservoirs, of which there are two, are horizontal
and situated beneath the front end of the boiler. The air pipe to the
triple valve here connects to the front pipe of the three beneath the
triple valve, the middle pipe being that which is open to the
atmosphere, which is the usual construction. The engine brake receives
its air from a pipe on the other side of the engine which feeds the
pipes G, V, for the brake cylinder shown in the figure. When the engine
is running backwards, the train brakes are operated through the medium
of the "pipe to air brake and to front end of engine" which is shown
broken off.
The construction of the steam reversing gear is shown in Fig. 3328_a_. A
is a steam cylinder and B a cylinder filled with oil or other liquid.
Each of these cylinders has a piston, the two being connected together
by their piston-rods C C´. These rods are also connected to a lever D E
F, which works on a fulcrum E. The lower end of the lever is connected
to the reverse rod F G, the front end of which is attached to the
vertical arm of the lifting or reverse shaft. It will readily be seen
that if the piston in B is free to move and steam is then admitted to
either end of the steam cylinder A, the two pistons will be moved in a
corresponding direction, and with them the lever D E F, and the other
parts of the reversing gear. A valve, H, is provided, by which
communication is opened between the cylinder A and the steam inlet pipe.
Another valve, I, is placed between H and the cylinder A, by which the
steam may be admitted either into the front or back end of the cylinder.
It will be apparent, though, that if the piston in A is thus moved, and
the reverse gear placed in any required position, some provision must be
made to hold it there securely. This is accomplished by the oil cylinder
and piston B. To it a valve, J, is provided, by which communication
between the front and back ends of the cylinder may be opened or closed.
It is evident that if the piston B is in any given position, and both
ends of the cylinder are filled with liquid, the former will be held
securely in that position if the liquid in one end cannot flow into the
other. If, however, communication is opened between the two ends, then,
if a pressure is exerted on the piston B, it will cause the liquid to
flow from one end of the cylinder to the other, and thus permit B to
move in whichever direction the pressure is exerted.
[Illustration: _VOL. II._ =AMERICAN PASSENGER LOCOMOTIVE.= _PLATE XXX._
Fig. 3328.]
[Illustration: Fig. 3328_a_.]
R is the reverse lever, made in the form of a bell crank, the short end
of which works in a slot _c_, in the upper end of a shaft or spindle
_d_. This shaft is inclosed by a tubular shaft S, to which the fulcrum
of R is fastened. The tubular shaft has an arm _b_. The reverse lever
has two movements, the one to raise the end up, and the other to turn on
the axis of the tubular shaft. The arm _b_ on the latter is connected by
a rod, _f_, with the valves J and H. The lower end of the shaft _d_ is
connected with a bell crank, _f´_, which, in turn, is connected by a
rod, _k_ _l_, with the valve I. Therefore, by turning the lever R so as
to partly revolve the shaft S, the valves J and H may be opened or
closed, and by moving the lever R up or down, the valve I is moved to
admit steam to the front or back end of A. To reverse the engine,
therefore, the lever R is turned so as to open the valves J and H. This
opens communication between the opposite ends of B, and H admits steam
to I. Now, by reversing the end of the reverse lever R, the valve I is
moved so as to admit steam to either end of A, the pressure in which
will move the reverse gear to the desired position. When this is done,
the valves J and H are closed. This prevents the fluid in B from flowing
from one end of the cylinder to the other, and thus securely locks the
piston B in the position it may happen to be in, and at the same time
the valve H shuts off steam from the cylinder A.
The bar K is graduated, as shown in the plan of R, K, to indicate to the
locomotive runner the position of the reversing gear.
This apparatus enables the reversing gear to be handled with the utmost
facility, and with almost no exertion on the part of the engineer. The
engine can be reversed almost instantly, and it can be graduated with
the most minute precision.
THE LINK MOTION AND REVERSING GEAR.
The link motion of an American locomotive is shown in Figs. 3329 and
3330. In Fig. 3329 it is shown in full gear for the forward gear, or in
other words, so as to place the engine in full power for going ahead.
The meaning of the term full power is that, with the link motion in full
gear, the steam follows the piston throughout very nearly the full
stroke.
[Illustration: Fig. 3331.]
[Illustration: Fig. 3332.]
In Fig. 3331 the link motion is shown in mid gear, in which position the
engine is at its least power, the cut off occurring at its earliest
point, and in Fig. 3332 it is shown in full gear for the backward
motion.
[Illustration: _VOL. II._ =LOCOMOTIVE LINK MOTION.= _PLATE XXXI._
Fig. 3329.
Fig. 3330.]
Referring to Fig. 3329 for the full gear forward, the reversing gear
proper consists of the reversing lever, the segment, the reach rod, the
tumbling shaft, and its counterbalance rod and spring; while the link
motion proper consists of the eccentrics and their rods, the link, the
link block or die, the suspension link S, the rock shaft and the rod P
P. These, however, are terms applied for shop purposes, so as to
distribute the work in sections to different men, it being obvious that
a _complete_ link motion includes the reversing gear, the eccentrics,
the link and its block, the rock shaft, the rod P P, and the valve and
its spindle or stem. This mechanism, as a whole, may also be called, and
is sometimes called, the valve gear, because it is the mechanism or gear
that operates the slide valve.
The link motion may be moved from full gear forward to full gear
backward or to any intermediate position, whether the engine is running
or at rest, but is, when the engine is running, harder to move from full
gear forward toward back gear, and easier to move from full gear
backward toward mid and forward gears, which occurs because of the
friction of the eccentrics in the straps, and it follows that this will
be the case to a greater extent in proportion as the revolutions of the
eccentrics are increased.
If in a properly constructed link motion we move the link from full gear
forward to mid gear when the engine is standing still, and watch the
valve, we shall find that the lead or opening at _f_ gradually
increases; and if we then move it from mid gear to full gear backward,
the lead will gradually decrease and finally become the same as it was
in full gear forward. The construction of the parts is as follows:
Referring to Fig. 3329 (full gear forward), the segment is fixed in
position and the reversing lever is pivoted at its lower end. _r_ _r_ is
a bell crank, which is pivoted to the reversing lever and to which the
latch rod is pivoted at its upper end. The spring acts on the end of _r_
_r_, and thus forces the tongue of the latch into the notches on the
sector as soon as the tongue comes fair with the notch and _r_ _r_ is
released from the hand pressure. As the reversing lever is moved over
from full gear forward, the reach rod moves the tumbling shaft, whose
lower arm _i_ (through the medium of the suspension link S) lifts the
link and brings the centre of the saddle pin nearer to the centre of the
pin in the link block, which reduces the amount of motion given to the
lower arm (B, Fig. 3331) of the rock shaft, and therefore reduces the
amount of valve travel, thus causing the point of cut-off to occur
earlier in the piston stroke.
The weight of the eccentric rods, the link, suspension link S, and the
tumbling shaft arm _i_, is counterbalanced by the counterbalance spring
in the box _s_ _s_, whose rod attaches to the lug _g_ on the tumbling
shaft. To regulate the proper amount of counterbalancing, the nuts at
_m_ are provided, these nuts regulating the amount of tension on the
spring _s_ _s_.
The forward eccentric E is that which operates the valve when the link
motion is in full gear forward, as in Fig. 3329, and the backward
eccentric is that which moves the valve when the link motion is in back
gear, as in Fig. 3332.
This occurs because it is the eccentric rod that is in line or nearest
in line with the link block that has the most effect in moving the
valve. When the link is in full gear, the motion of the valve is almost
the same as though there was no link motion and the eccentric rod was
attached direct to the rod P P, the difference being so slight as to
have no practical importance. This will be seen by supposing that we
were to loosen the backward eccentric F upon the shaft and revolve it
around the shaft by hand, in which case it would swing the lower end of
the link backward and forward with the centre of the link block as a
pivot or centre of motion, the forward eccentric rod rising and falling
a trifle only, and therefore moving the rock shaft to a very slight
amount.
Let it now be noted that the suspension link not only sustains the
weight of the link and eccentric rods, but also compels the centre of
the saddle pin to swing (as the link is moved by the eccentrics) in an
arc of a circle of which the centre is the upper end of the suspension
link. Suppose, therefore, that the backward eccentric rod was to break,
or was taken off and the engine could still run forward, but no motion
would be given to the valve, if the link was placed in mid gear, because
in that case the forward eccentric rod would simply swing the link on
the centre of the link block as a pivot. Now, suppose the forward
eccentric rod was to break or be taken off, and the engine may be made
to go ahead by setting the backward eccentric fair with the forward
eccentric and connecting its rod to the upper end of the link.
Similarly, if the engine was running with the smoke stack toward the
train and the link motion in backward gear, and the backward eccentric
rod was to break, we may take it off, shift the forward eccentric so
that it comes fair or stands in line with the backward eccentric and
connect its rod to the lower end of the eccentric and with the link
motion in backward gear, the engine would still haul the train.
If the reach rod was to break, the tumbling shaft could be held in
position by loosening the cap bolts of the tumbling shaft journal and
putting between the cap and the tumbling shaft journal a piece of metal,
which, on bolting up the cap screws again, would firmly grip the shaft
and prevent it from moving.
[Illustration: Fig. 3333.]
SETTING THE SLIDE VALVES OF A LOCOMOTIVE.--The principles of designing,
and the action of D valves, such as are used upon locomotives, have been
so thoroughly explained with reference to stationary engines, that there
is no need to repeat them in connection with the locomotive, and we may
proceed to explain how to set the valves of a locomotive. In doing this,
there are two distinct operations, one of which is to place the crank
alternately exactly on its respective dead centres, and the other is to
set the position of the eccentrics, and get the eccentric rod of the
proper length. These two operations comprise all that require to be done
to set the valves, under ordinary and workmanlike conditions; hence we
may proceed at once to explain the operation.
The first thing to be done is to put the crank pin on a dead centre, and
it does not matter which one.
In Fig. 3333 it is supposed that the piston is to be at the head end of
the cylinder when the crank is on its corresponding dead centre.
The first thing to do is to put the reversing gear in full gear forward,
so as to set the forward eccentric, and see if its rod is of proper
length.
The next thing to do is to move the wheel so that the crank pin is
nearly on the dead centre, and then take a tram (such as shown in the
figure), pointed at each end, and mark on the splash plate, or any other
convenient place, a centre punch dot in which the point _b_ of the tram
can rest. Next, from the centre of the axle as a centre, mark arcs or
portions of circles _a_, _a_. This being done, point _b_ of the tram is
rested in the centre punch dot before referred to, and with the other
end a line _c_ is marked, a straight edge is then rested against the
ends _e_ _e_ of the cross head, and a line _d_ is marked on the guide
bar, this line being exactly even or fair with the end _e_ _e_ of the
cross head.
We then move the wheel in the direction of the arrow, and as soon as we
begin to do so, the cross head will move to the left and away from the
line _d_ on the guide bar. But as soon as the crank pin has passed its
dead centre, the cross head will begin to move to the right, and as soon
as the end _e_ _e_ comes again exactly in line with the line _d_ marked
on the guide bar, we must stop moving the wheel, and again resting the
point _b_ of the tram in the centre punch mark before mentioned, we move
its other end so as to mark a second line, which will be the line or arc
_f_.
The next thing to do is to mark a fine centre punch dot, where _c_ and
_f_ cross the arc or line _a_, and then find the point _g_ midway
between _f_ and _c_, and mark a fine centre punch mark there. This being
done, we must move the wheel back into the position it occupies in the
figure, and then slowly move it in the direction of the arrow, until
with the end _b_ of the tram resting in the centre punch dot, the other
end of the tram will fall dead into the centre punch dot at _g_, at
which time the crank pin will be exactly on the dead centre.
During this part of the process we have nothing to do with anything
except getting the crank pin on the dead centre, but there is one point
that requires further explanation, as follows:
In this operation we have first put the crank on one side of the dead
centre and then put it to the same amount on the other side of the dead
centre, both being improper positions; but by finding the mean or mid
position between the two, we have found the proper position. In doing
so, however, we have moved the wheel, the wheel has moved the connecting
rod, and the connecting rod has moved the piston. But in the actual
running of the engine, this order of things will be reversed; for the
steam will move the piston, the piston will move the connecting rod, and
the connecting rod will move the crank and therefore the wheel.
The difference between the two operations is this: Suppose there is lost
motion or play between the connecting rod brasses and the crank pin, or
between the connecting rod brasses and the cross head pin, and then if
we move the wheel in the direction denoted by the arrow, we take up this
lost motion, so that if the tram was fair with the centre punch at _g_
and steam was admitted to the piston, then there would be no lost motion
to take up, and as soon as the piston moved the crank pin would move.
But if we moved the wheel in the opposite direction to that denoted by
the arrow, then we are placing any lost motion there may be in the
opposite direction, and if steam were turned on, the piston and
connecting rod might move before the crank and wheel moved.
In which direction the wheel should be moved while placing the crank on
the dead centre depends upon the condition of the engine, as will be
explained presently, the assumption being at present that the engine is
in thorough good order, in which case the wheel should (while placing
the crank on the dead centre) be moved in the direction of the arrow in
the figure.
The object is under all conditions to bring the working surfaces to bear
(while setting the valve) in the same way as they will bear when the
engine is actually at work.
Having placed the crank on the dead centre, and thus completed the first
operation in valve setting, we may turn our attention to the second,
viz., correcting the lengths of the eccentric rods and setting the valve
lead. Almost all writers who have dealt with this part of the subject
have fallen into a very serious error, inasmuch as they began the
operation by what they call _squaring_ the valve. This means so
adjusting the length of the eccentric rod that the valve will travel an
equal distance each way from its mid position, so that if the engine
wheel is revolved and the extreme positions of the valve marked by a
line, these lines will measure equally from the edges of the steam
ports, or, what is the same thing, from the centre of the cylinder
exhaust port. This procedure is entirely erroneous, because, on account
of the angularity[57] of the eccentric rod, the valve cannot, if equal
lead is to be given to the valve, travel equally beyond the two steam
ports, and if the eccentric rods are so adjusted for length as to
_square the valve_, they are made wrong.
[57] See page 376, Vol. II., for the meaning of angularity.
The valve lead, and the lead only, it is that determines the length of
the eccentric rods. Suppose that, as is generally the case, the lead is
to be equal, or, in other words, that there is to be as much valve lead
when the piston is at one end of the cylinder as there is when it is at
the other, and if we make the eccentric rods of such a length that the
valve travels equally on each side of the steam port, there will be less
lead at the head end port than there is at the crank end port. The
proper method, therefore, is (as soon as the crank is on the dead centre
and the link in full gear, as in Fig. 3334) to set the eccentric so as
to give the desired amount of lead, and then give the wheel a half
revolution, the lower end of the tram falling into the centre punch dot
at _s_, when the crank pin will be on its other dead centre and ready
for the lead to be measured again. If the lead is equal at each end, one
eccentric rod is of the right length, and all we have to do is to set
the eccentric so that the right amount of lead is given.
We now turn our attention to the backward eccentric and its rod, putting
the reversing lever in full gear for the backward motion, and putting
the crank on the respective dead centres, and testing the lead for both
ports as before, and when the required amount of valve lead is given the
valve setting is complete.
In some practice the wheel is blocked up on the pedestal guides while
setting the valves, but a more correct method is to let the engine rest
on the rails and push it back and forth with a crowbar to revolve the
wheels when putting the crank pin on the dead centre. The best thing to
measure the lead with is a wooden or leaden wedge having but a slight
degree of taper, as say 3/16 or 1/4 inch in a length of four inches. We
have in this example of valve setting supposed the parts to be of the
proper dimensions, as they would be in a new engine or in an engine that
had been running and merely had a new valve or a new eccentric put in.
But suppose the notches were not cut in the sector, and we have then to
mark them off while setting the valves. All the difference that this
makes to the operation is that we must clamp the reversing lever to the
sector while setting the valve, taking care to so clamp it that there is
the same space between the top end of the link block and the end of the
link slot in the full forward gear as there is between the bottom end of
the link block and the end of the link slot when the engine is in full
backward gear. In this connection it is, however, to be remarked that
when the link is in full gear, either forward or backward, and the crank
is on the dead centre, the link block is not at the end of its motion
toward the end of the link slot; hence it is a good plan to move the
wheels around and to so regulate the length of the reach rod and the
position of the reversing lever on the sector, that when the link block
is at the highest point in the link slot for the forward gear and at the
lowest point in the link slot for the backward gear, it comes an equal
distance from the end of the link slot.
[Illustration: _VOL. II._ =INJECTOR AS APPLIED TO A LOCOMOTIVE.= _PLATE
XXXII._
Fig. 3337.
Fig. 3338.]
[Illustration: Fig. 3334.]
The setting for an Allen valve is the same as that for an ordinary one,
but in determining the amount of the lead it is to be borne in mind that
it is virtually twice as much as it measures at the port because there
are two openings for the steam. This will be seen from Fig. 3335, in
which the valve is open to the amount of the lead at _f_. But the steam
also enters at _e_, and passes through the port in the valve and into
steam port _a_.
We have now to call attention to the fact, that the eccentric rods, when
properly connected, are, in an American locomotive, crossed when the
piston is at the crank end of the cylinder. In Fig. 3334, the piston is
at the head end of the cylinder, and the rods are open. In Fig. 3336,
however, the crank pin is supposed to be at B, and the eccentric rods
are crossed, F being the forward and E the backward eccentric.
THE INJECTOR.
The injector shown in the general view of a freight locomotive, Fig.
3326, is that constructed by William Sellers & Co., and there are two,
one on each side of the engine. The details of its construction are as
follows:
Fig. 3337 is a side elevation, Fig. 3338 a section on a vertical plane,
Fig. 3339 a section on a horizontal plane, Fig. 3340 an end view of the
injector at the right-hand side of the engine, and Fig. 3341 a plan of
the injector on the left-hand side of the engine.
This injector is self-contained, or in other words, it has both steam
and check valves, so that it can be connected directly without other
fittings, although, of course, it is generally desirable to place
another stop valve in the steam pipe, and a check valve in the delivery
pipe, so that the injector can be taken to pieces or disconnected at any
time. Another important feature of this injector is, that it is operated
by a single handle, and that the waste valve is only open at the instant
of starting.
Referring to Fig. 3338, A is the receiving tube, which can be closed to
the admission of steam by the valve X. A hollow spindle passing through
the receiving tube into the combining tube is secured to the rod B, and
the valve X is fitted to this spindle in such a way that the latter can
be moved a slight distance (until the stop shown in the figure engages
with valve X) without raising the valve X from its seat. A second valve
W, secured to the rod B, has its seat in the upper side of the valve X,
so that it can be opened (thus admitting the steam to the centre of the
spindle) without raising the valve X from its seat, if the rod B is not
drawn out any farther, after the stop on the hollow spindle comes in
contact with the valve X. D is the delivery tube, O an overflow opening
into space C, V the check valve in delivery pipe, and Z the waste valve.
The upper end of the combining tube has a piston N N attached to it,
capable of moving freely in a cylindrical portion of the shell M, M, and
the lower end of the combining tube slides in a cylindrical guide formed
in the upper end of the delivery tube.
The rod B is connected to a cross head which is fitted over the guide
rod J, and a lever H is secured to the cross head. A rod W, attached to
a lever on the top end of the screw waste valve, passes through an eye
that is secured to the lever H; and stops T, Q control the motion of
this rod, so that the waste valve is closed when the lever H has its
extreme outward throw, and is opened when the lever is thrown in so as
to close the steam valve X, while the lever can be moved between the
positions of the stops T, Q without affecting the waste valve. A latch F
is thrown into action with teeth cut in the upper side of the guide rod
J, when the lever H is drawn out to its full extent and then moved back;
and this click is raised out of action as soon as it has been moved in
far enough to pass the last tooth on the rod J. An air vessel is
arranged in the body of the instrument, as shown in the figure, for the
purpose of securing a continuous jet when the injector and its
connection are exposed to shocks, especially such as occur in the use of
the instrument on locomotives.
[Illustration: Fig. 3335.]
[Illustration: Fig. 3336.]
The manipulation required to start the injector is exceedingly
simple--much more so in practice, indeed, than it can be rendered in
description. Moving the lever H until contact takes place between valve
X and stop on hollow spindle, which can be felt by the hand upon the
lever, steam is admitted to the centre of the spindle, and, expanding as
it passes into the delivery tube D and waste orifice P, lifts the water
through the supply pipe into the combining tube around the hollow
spindle, acting after the manner of an ejector or steam siphon. As soon
as solid water issues through the waste orifice P, the handle H may be
drawn out to its full extent, opening the steam valve X and closing the
waste valve, when the action of the injector will be continuous as long
as steam and water are supplied to it.
To regulate the amount of water delivered, it is necessary only to
move in the lever H until the click engages any of the teeth on the
rod J, thus diminishing the steam supply, as the water supply is
self-regulating. If too much water is delivered, some of it will escape
through O into C, and, pressing on the piston N N, will move the
combining tube away from the delivery tube, thus throttling the water
supply; and, if sufficient water is not admitted, a partial vacuum will
be formed in C, and the unbalanced pressure on the upper side of the
piston N N will move the combining tube toward the delivery tube, thus
enlarging the orifice for the admission of water. From this it is
evident that the injector, once started, will continue to work without
any further adjustment, delivering all its water to the boiler, the
waste valve being kept shut. By placing the hand on the starting lever,
it is easy to tell whether or not the injector is working; and, if
desired, the waste valve can be opened momentarily by pushing the rod W,
a knob on the end being provided for the purpose.
[Illustration: Fig. 3339.]
[Illustration: Fig. 3340.]
[Illustration: Fig. 3341.]
THE WESTINGHOUSE AUTOMATIC AIR BRAKE.
Figs. 3342, 3343 and 3344 represent the Westinghouse automatic air brake
applied to an engine and tender, and in the following figures details of
the construction of various parts are shown.
[Illustration: Fig. 3345.]
The pump governor, which is shown at G in Fig. 3326, of a modern freight
locomotive, is shown in section in Fig. 3345.
The pump governor is employed for the purpose of cutting off the supply
of steam to the pump when the air pressure in the train pipe exceeds a
certain limit, say 70 lbs. per square inch.
Its operation is as follows:
When valve 10 is (by means of hand wheel 8) screwed home to its seat the
steam is entirely shut off from the steam cylinder, but by operating
wheel 8 to unscrew spindle 9, valve 10 is permitted to open and let the
steam pass through A and B to the steam cylinder which operates, forcing
air into the reservoir and thence into the train pipe. A pipe from the
train pipe connects to the upper end of the pump governor, hence air
from the train pipe passes around the stem 14 to the upper side of the
thin diaphragm 18, which is held in its position by the spring 12 with a
force sufficient to enable it to resist, without moving, a pressure of
70 lbs. per square inch. But when the pressure exceeds 70 lbs. per
square inch it forces the diaphragm down, pushing down valve 13 and
allowing the steam in A to pass up through valve 13 and out of the
exhaust pipe 6. The steam pressure in A being thus reduced, that in B
acts on the under side of the valve, causing it to rise and seat itself
and thus cut off the supply of steam to the pump.
[Illustration: _VOL. II._ =LOCOMOTIVE AIR BRAKES.= _PLATE XXXIII._
Fig. 3342.
Fig. 3343.
Fig. 3344.]
When the pressure in the train pipe is diminished by the brakes being
applied, the diaphragm is restored to the position it occupies in the
figure by the action of the spring 16. Then valve 13 is seated by the
spring 12, and the steam pressure accumulates on the upper end of valve
10, forcing it down and letting the steam from A into B and thence into
the steam cylinder, starting it into action, which continues until the
pressure in the train pipe exceeds 70 lbs. per square inch.
The use of this governor not only prevents the carrying of an excessive
air pressure in the train pipe, which may result in entirely preventing
the wheels from revolving and causing a flat place to wear on the wheel
tire, but it also causes the accumulation of a surplus of air pressure
in the main reservoir, while the brakes are applied, which insures the
release of the brakes without delay. It also obviates the unnecessary
working of the pump when the desired air pressure has been obtained.
[Illustration: Fig. 3346.]
A sectional view of the steam and air cylinders is shown in Fig. 3346,
the construction being as follows:
Steam is distributed to the steam cylinder by means of a piston valve,
composed of three pistons, marked 16, 14, and 20 respectively, the steam
entering between pistons 16 and 14, and, in the positions in which the
parts occupy in the figure, steam can pass through the bushing 18 and
beneath the steam piston 7, propelling it upwards until the bottom of
the hole in its piston rod strikes the end of rod 12, and raises it and
valve 13. The chamber 23, in which valve 13 works, receives steam
through a suitable port from the steam space between valves 14 and 16;
and the steam from chamber 23, it is that (in the positions the parts
occupy in the figure), acting on the area of the large valve piston 20,
holds the valve down against the pressure on the bottom face of piston
14 of the valve. As soon, however, as the piston rod 7 strikes and
raises rod 12 and valve 13, the steam is exhausted from the top of
piston 20 of the valve, and the steam beneath piston 14 of the valve
raises the valve, opening the lower port in the sleeve 18 for the
exhaust, and piston 14 admits steam to the upper side of the steam
piston 7. The construction of the air cylinder differs somewhat from
that shown in the freight locomotive, Fig. 3326, this air pump
corresponding with that shown on the engine and tender, Fig. 3342. A
detail list of the parts may be given as follows:
No.
2. Steam cylinder head (with reversing cylinder, piston, and valve
bushes).
3. Steam cylinder (with main valve and bushes).
4. Centre piece.
5. Air cylinder (with lower discharge valve).
6. Air cylinder head.
7. Steam piston and rod.
8. Air piston.
9. Piston rings.
10. Steam piston plate.
11. Steam piston bolt.
12. Reversing rod.
13. Reversing valve.
14. Piston valve.
15. Piston valve rings.
16. Piston valve rings.
17. Upper valve bushing.
18. Lower valve bushing.
19. Reversing piston casing.
20. Reversing piston.
21. Piston rings.
22. Reversing cylinder cap.
23. Reversing valve bush.
24. Reversing valve cap.
25. Piston rod nut.
26. Piston packing gland.
27. Piston packing nuts.
28. Packing glands.
29. Right Chamber cap.
30. Left chamber cap.
31. Air valve bushing.
32. Air valve.
33. Air valve.
34. Air valve.
35. Delivery union.
36. Exhaust steam outlet.
40. Steam cylinder gasket.
42. Top air-pump gasket.
43. Bottom air-pump gasket.
44. Waste water pipe.
46. Exhaust union stud.
49. Air exhaust union stud.
A side view of the driving wheel brakes is shown in Fig. 3347 and an end
view in Fig. 3348. The brakes are, it is seen, suspended by links so
that their weight tends to keep them from the wheels. The brake piston
rod carries at its end two links which attach to the arms attached to
the brakes. The ends of these arms being curved roll together, the
arrangement forming in effect a rolling toggle joint. The construction
of the piston of the driving wheel brake is shown in Fig. 3349. The
piston is made air tight by leather packing indicated by 11, held out by
a spring 12. The piston rod packing, 7, is leather held in place by the
cap 6 and the spring 8. The air for operating the brake enters below the
piston.
[Illustration: Fig. 3347.]
[Illustration: Fig. 3348.]
LOCOMOTIVE RUNNING.
The engineer's duty in running a locomotive is more arduous and requires
more watchfulness than any other engine running, because of the
peculiarities attending it. In the first place, the jolts and jars to
which the engine is subject are liable to cause nuts, pins, etc., to
come loose, and some of the parts to become disconnected and cause a
breakdown of the engine.
This renders necessary a careful examination of the engine, which should
be made both before and after each trip.
In the second place, we have that the amount of load the engine has to
pull varies with every varying grade in the railroad track, and the
variation is so great that on some descending grades the engine may
require no steam whatever, while on ascending grades the utmost power
attainable from the engine may be required. In firing, feeding the
pumps, oiling the parts, and determining the depth of water in the
boiler, the grade and the length of each grade has an important bearing,
and so has the weather, since it is clear that between the heat of
summer and the blizzards of winter there is a wide range of the
conditions under which the engine runs.
In former times, from the less perfect construction of locomotives, the
engineer's duties were greatly enhanced from breakdowns, which are
comparatively rare with modern locomotives, and there is promise that
from improved construction and safeguards they will become less frequent
in the future.
It is as important for the locomotive engineer to be familiar with the
track as it is to be with the engine, and there is no field of engine
driving or running in which more scope is permitted to the engineer to
exercise judgment and skill in his management, so as to effect economy
in fuel consumption.
The quality and size of the coal is another element that requires
attention and observation on the part of the engineer, in order that his
train may keep its time and the fuel consumption be kept down.
GETTING THE ENGINE READY.
The first thing to be done in getting ready for a trip is to see that
there is sufficient water in the boiler, so that if there is not, there
is time to supply the deficiency.
If the boiler is cold it may be that the condensation of the steam in
cooling may have left a partial vacuum in the boiler, and it will be
necessary in that case to open the top gauge cock and let in air so that
the water will come to its proper level in the gauge glass. Similarly,
in filling the boiler, it may be necessary to open a gauge cock to let
the air out.
The lower cock of the gauge glass should be opened to let the steam blow
through if there is pressure on the boiler, or to let a little water out
if there is not.
The safety valve should next be examined and moved to see that it works
properly and does not stick to its seat.
Before laying the fire the fire bars and ash pan should be cleared of
ashes and clinkers, and the grate bars tried with the shaking levers to
see that the grates will shake properly. It should be seen that the
tubes, etc., are clear of ashes.
In laying a new fire an ample supply of lighting material should be
used, disposing it so that the fire will light evenly and not in spots,
and a good layer of wood should be evenly distributed over the bars, the
thinnest pieces being at the bottom as they will light easiest, and it
is necessary to light the fire at the bottom, so that the heat from the
wood that is first lighted shall pass through that to be lighted.
The wood should be kept burning without coal until the lower stratum
has ceased to blaze and covers the bars, while there is an even layer of
blazing wood above it.
[Illustration: Fig. 3349.]
The quantity of coal to be fed at a time, and the depth of fire to be
kept, depends upon the size of the coal, because the larger the coal the
less it obstructs the draught, and the thicker the layer required in
order to prevent currents of air from passing through without entering
into combination with the gases from the coal.
If the coal is mixed, containing large lumps, they should be broken.
The first layer of coal should be enough to cover the fire to a depth of
about two inches, which will permit of a good draught. This will get
well alight while the wood is still serviceable, and a second layer may
be applied of another two inches. The third feeding should be given with
a view to have a greater depth of fire at the sides than at the middle
of the fire box, because the cool sides of the box prevent perfect
combustion, and currents of cold air are more apt to find their way
through the sides than in the middle of the fire box.
Banking a fire consists of piling it up at the back half of the fire box
and covering it up with green coal, so that it may keep alight and keep
the boiler hot without increasing the steam pressure.
The air passing through the uncovered half of the fire bars prevents
rapid combustion and a dead fire is maintained.
In starting up a banked fire, the first thing to do is to clean it of
ashes, clinker, etc., shaking up the bars to see that they will work
properly. The fire is then spread evenly over the bars, and wood fed to
enliven the fire and promote the draught.
The blower or blast pipe is then set going, and coal gradually fed a
little at a time, evenly distributed, covering those parts the most
where the fire burns through the most brightly.
A steady fire is better than one that is forced, because the combustion
is more perfect and less clinker is formed, hence less cleaning will be
necessary, and the fire door will not be kept open so long to let in
cold air. This is important because a steady temperature in the fire box
promotes its durability, as well as giving a uniform boiler pressure.
The strains placed upon a fire box by a fierce fire suddenly cooled by a
heavy charge of coal or of cold air from an open fire door are highly
destructive.
Furthermore, the greatest economy of fuel is attained by keeping the
boiler pressure up, and using the steam expansively by hooking up the
links to shorten the point of cut-off.
A safety valve steadily blowing off steam, whether the engine is running
or not, is a sign of bad firing and wastefulness.
It is the fireman's duty to attend to the fire, but nevertheless a
careful engineer will be as much interested in proper firing as in his
own duties, and as the engineer has more experience than the fireman, he
is warranted in exercising an ordinary supervision on the firing, which
will be welcome to an earnest or ambitious fireman.
The engineer should examine, with a wrench in hand, the bolts and nuts
about the trucks and axle boxes, as these are apt to become loose and
come off on the road. A proper construction would remedy this defect
almost entirely, and by a proper construction is meant the more frequent
employment of split pins, cotters, and other similar safety appliances
now omitted for the sake of economy of manufacture.
Nothing in the future of the locomotive is more certain than improvement
in this respect, and nothing is more urgently needed, as any engineer
will become satisfied if he will gather up along a mile of ordinary
railroad the nuts and washers that lay along the track.
The eccentric straps and the pins in the link motion require an
examination, which may be done while oiling the parts of the engine.
The oiling requires careful attention; first the cups themselves
sometimes become loose, an argument in favor of having, wherever
possible, the cups solid on the parts, as done in European practice.
Oil holes are apt to get choked by gumming, which is that the oil in
time forms into a brown gummy substance that fills the oil hole. Perfect
lubrication does not imply wasteful lubrication by any means, but a
wasteful use of oil is probably less expensive than insufficient
lubrication.
A thorough engineer will use no more oil than is necessary; he will
leave nothing to conjecture or chance, but know from personal inspection
that his engine is in complete working order, and to this end the
lubrication of the working parts is a vital element.
After having oiled the eccentric straps, the link motion and the
reversing gear beneath the engine, the reversing lever and the parts
above the frame must be oiled, and the reversing lever moved back and
forth several times, from end to end of the sector or quadrant, so as to
distribute the oil throughout the joints and working surfaces.
The axle boxes require careful attention in oiling. In English practice,
tallow is packed in the corners of the cavities of the top of the box,
so that if the box should begin to heat the tallow will melt, and afford
extra lubrication with a heavier lubricant than usual, which will often
stop the heating.
The connecting and coupling rods then require attention, the cups being
filled and the lubrication adjusted.
When steam is up the gauge glass should be blown through again, and it
will be found that the water stands higher in the glass than it did
before the boiler was under pressure.
The packing of the piston and of the pump glands, if the engine has
pumps, should be known to be properly set up, bearing in mind that a
leaky pump gland lets air into the pump and impairs its action.
The sand box should contain dry sand, as wet sand will not feed
properly.
If steam is raising too rapidly, close the lower damper to reduce the
consumption of fuel and save blowing off steam through the safety valve,
which should always be avoided as much as possible.
Before starting the engine, open the cylinder cocks and keep them open
until the sound discloses that dry steam, and not steam and water, is
issuing.
Open the throttle enough to start the engine easily and not with a jump,
and be prepared to shut off steam instantly if a blow in any part of the
engine should indicate an obstruction to its working.
In starting a train, the reversing lever is put in the end forward notch
and the cylinder cocks opened. Then the throttle is opened a little at
first, so as to avoid starting with a violent shock that might break the
couplings.
If in starting (or in ascending gradients) the wheels are forced to
slip, the sand lever should be operated, a slight sprinkling of sand
serving better than a heavy one. If the sand is damp, it will fall in
lumps and not distribute evenly as it should do, while at the same time
a great deal more sand will be found necessary.
When the train is fairly under way, the aim should be to maintain full
boiler pressure, so as to keep up the required speed with the links
hooked up to work the steam as expansively as possible, bearing in mind
that the higher up the links are hooked the more expansively the steam
is used, and that therefore less steam is used to do the work and the
boiler pressure can be kept up easier.
To understand this clearly, let it be supposed that the steam pressure
in the boiler is 90 lbs. per square inch, and that the piston area is
400 inches, and the total pressure impelling the piston will be 36,000
lbs.; if this follows the piston for 22 inches, the power becomes
792,000 inch lbs. per stroke.
Now suppose the pressure is 150 lbs. per square inch, and this
multiplied by the piston area (400) gives 60,000 lbs. impelling the
piston, and this would require to follow the piston but 13.2 inches in
order to give 792,000 inch lbs. In the one case we have 22 inches, and
in the other 13.2 inches of the cylinder to fill with steam. Of course
it will take more fuel under the heat of firing to keep the pressure up
to the 150 lbs.; but on the other hand, when the steam is cut off in the
cylinder there will be 160 lbs. per square inch in it, and all the work
that this does in expanding is gained during the rest of the stroke, so
that the required amount of power would be obtained by cutting off
earlier than at 13 inches.
The water should, under ordinary conditions, be kept at an uniform level
in the boiler. Steam can of course be made quicker with a small than
with a large quantity of water, but the smaller the quantity of water
the more the steam pressure is liable to fluctuate, and the closer the
firing must be attended to.
Furthermore, the more water there is in the boiler, the greater the
safety, because the longer the boiler can go without feeding, and, if
the pumps or injectors, as the case may be, should act imperfectly,
there is more time to get them working properly.
In testing the water level, the gauge glass alone is not to be entirely
depended upon, hence the gauge cocks should be opened. The water should
not be allowed to go below the middle gauge cock.
It is obvious that when the water is below a certain gauge cock, the
gauge glass only can give any information as to how far it is below it,
hence it must be used for this purpose.
When using it, it should be blown through by opening its lower cock, and
if there is any doubt about its showing the proper water level it should
be blown through two or three times, watching the level of the water in
the glass at each trial.
A constant boiler feeding is the best, as it is more conducive to a
uniform boiler pressure and temperature.
The fire should be fed in small charges, the fire door being kept open
as little as possible, because a high temperature in the firebox is
necessary to perfect combustion. If heavy charges of coal are given at
once, then for some time the fire box will be cooled, and then, as the
fire burns through, a fierce heat will be generated. This alternate
heating and cooling is very destructive to the fire box and the tubes,
as it causes an expansion and contraction that rack the joints and
seams.
There are several ways of firing, each having its advocate. Upon the
following points, however, there is no dispute. First, a slow combustion
is the most perfect, because it produces less clinker, which saves fuel
and also saves a large amount of fire cleaning and therefore of
admission of cold air to the fire box. A high temperature is necessary
to combustion, and the temperature of the fuel is most difficult to keep
up at the sides of the fire box.
By light and frequent firing the bright fire will never be covered up,
hence the temperature will be maintained. This favors an even
distribution over a large surface of the fire of each shovelful of coal.
But if at any point the draught is lifting the fire, and small bright
pieces of fire are lifting up, it is an evidence that the fire is
thinnest there or else that the bars are cleanest there. In either case,
an extra amount of coal is required at that spot.
Some engineers will charge one side of the fire box lightly and then the
other, this being done so as to keep up the temperature in the fire box.
Others will fire first the front and then the back of the box, which
answers the same purpose, but in no case should the charge be heavy.
A fireman may become so accustomed to the road and his engine, that
under some conditions he may fire when he reaches certain points on the
road, regulating it like clockwork.
On a trip from Philadelphia to Reading, on an engine having a Wooten
fire box (whose special feature is a large fire box, which enables slow
combustion), the firing was conducted as follows:
The fire was was not fed or touched until just before reaching
Bridgeport, 18 miles from Philadelphia, when a thin layer of coal Was
spread evenly on the fire. Eleven miles were then made without opening
the fire door, the next firing taking place just before reaching
Phoenixville.
Ten miles were run before the next firing, which occurred just before
arriving at Pottstown.
The next firing occurred at Bordenboro', three miles from Pottstown. The
remaining 8 miles were made without firing. The steam pressure did not
vary more than 10 lbs. per square inch during the trip.
On a trip from New York to Philadelphia by the lightning express train
the firing was conducted as follows:
The coal was anthracite and in lumps from 5 to 7 inches in diameter; at
one end it reached up to the level of the fire door, while at the tube
plate end of the fire box it was about 6 inches deep.
The grate bars were constructed to shake in three sections, and shaking
the bars to clear out the fire caused it to feed forward of itself, and
the combustion of the coal caused it to break up into lumps about 2
inches in diameter at the tube plate, where the fire was much brighter
than at the fire door end. The steam pressure varied about 10 lbs.
during the trip.
We now come to the best times to fire, to feed, and to oil the valves,
and this depends on the level of the road.
On a level road these matters could be attended to with regularity, but
as the engine has most work to do in ascending inclines, it is necessary
to prepare for such emergencies: First, by having a good fire prepared,
so that the fire door may be kept closed as much as possible while the
engine is ascending; second, by having plenty of water in the boiler, so
as to keep steam, without feeding any more than possible when the engine
is calling for more steam, by reason of the reversing lever being put
over towards full gear.
The speed is kept well up before reaching the incline, and the reversing
lever moved forward a notch or two at a time to maintain the speed,
while at the same time moving the sand lever to feed the sand as soon as
the engine speed shows signs of reducing.
ACCIDENTS ON THE ROAD.
The accidents to which the locomotive is most liable when running upon
the road, and the course to be pursued by the engineer to enable him to
take the engine to the depot or complete the trip, are as follows:
KNOCKING OUT THE FRONT CYLINDER HEAD OR COVER.--This arises from various
causes, such as a breakage of a connecting rod strap, or of a piston rod
or cross head. It is the practice of some locomotive builders to cut in
the cylinder cover flange a small groove close to the part that fits the
cylinder bore, so that the cover shall break out in the form of a disc,
leaving the cover, flange, bolts, and nuts intact, and diminishing the
liability to break the cylinder itself as well as the cover.
The provisional remedy for this accident is to take off the connecting
rod (on the side of the broken cover) and also the valve motion, either
at the rock shaft arm or by taking down the eccentric rod straps. Then
place the valve in the centre of its travel so that it shall cover and
enclose both the cylinder steam ports and leave the exhaust port open.
Then block the cross head firmly on the forward centre, and go ahead
with the other cylinder.
HEATING OF PISTON RODS.--This the engineer can often discover by sight,
or by smelling it from the cab. The remedy is to stop the engine and
slack back the gland until the steam from the engine cylinder leaks
freely through the packing. Then apply a little extra lubrication or
water while _running slowly_.
BREAKING OF A PISTON ROD.--If the piston rod breaks, but does not knock
out the cylinder head or cover, pursue the same course as directed for
breaking the cylinder cover, taking the additional precaution to block
the piston, which may be done by fitting pieces of wood between the
guide bars, making the pieces long enough to fit between the cross head
and guide yoke.
The cylinder or waste water cocks on the side of the accident must also
be opened, to prevent any leakage of steam past the slide valve from
getting into the cylinder and driving the piston against the cylinder
cover, and breaking the cylinder cover or even the cylinder itself.
If the piston rod breaks from the cross head, it is safest to remove it
from the cylinder, though this is unnecessary, if it be securely blocked
against the cylinder head so that it cannot move, though steam may leak
in on either side of it.
BREAKING A CRANK PIN.--This is a somewhat frequent accident, but seldom
takes place on both sides of the engine at once.
The remedy is to take off all the parallel or coupling rods, and if it
is the crank pin on the driving wheels which breaks, take off the
connecting rod also, and securely block the cross head, disconnecting
the valve motion as before directed, and opening the cylinder waste
water cocks. In the case of this accident occurring, it is absolutely
essential to take off the parallel rods on both sides of the engine, or
otherwise the crank pins on the other side are apt to break.
THROWING OFF A WHEEL TIRE.--In this case the best plan is to block the
tireless wheel entirely clear of the track, which may be done by putting
a block of wood into the oil cellar of the driving box, and then tow the
engine to the repair shop; for if the engine is run to the shop, and the
wheel touches the rail, it will impair its diameter for the proper size
of tire.
THROWING OFF A DRIVING WHEEL.--This is not a common accident, but
nevertheless it sometimes occurs; they break usually just outside of the
driving axle box. In this case take out the driving box and fit in its
place a block of wood affording journal bearing for the axle. Let this
block rest on the pedestal cap, holding the axle up in the centre of the
pedestal. Then secure the piston and disconnect the valve gearing and
open the cylinder cocks as before, and the engine can be run _slowly_ to
the repair shop without danger of further accident, or, if convenient,
it can be towed by another engine.
BREAKING A SPRING OR SPRING HANGER.--Lift the engine with the jacks
until the driving wheel axle box is about in the centre of the pedestal,
and put any convenient piece of iron across the top of the driving axle
box and between it and the engine frame, thus taking the weight of the
engine on the frame instead of on the spring. Place also a block of iron
between the end of the equalizing bar and the top of the engine frame,
so as to prevent the movement of the equalizing bar, and to allow the
spring at the other end of the equalizing bar to operate without moving
the said bar. Every engineer should carry in his tool box pieces of
metal suitable for this purpose, because this is a frequent accident. It
does not, however, materially affect the working of the engine, and
should not delay a train more than a few minutes.
BURSTED FLUES AND TUBES.--These are usually plugged by tapering a piece
of pine wood and driving it into the bursted tube by means of an iron
bar. Taper iron plugs are often carried, and then driven into the end of
the tube after the wooden one has been driven in. To enable this job to
be done, it is necessary to thickly cover the fire with green coal,
which operates to cool the tubes and prevent the loss of the water in
the boiler. Sometimes careful engineers prepare for use pine plugs
turned slightly taper, and a little slack, for the inside of the tube.
In case of leak, this plug is inserted in the flue, and driven along it
until it covers the fracture, the expansion due to its saturation
causing it to become locked in the tube.
SLIPPING OF ECCENTRICS.--Place the reverse lever in the forward notch of
the sector. Place the crank on its forward dead centre, as near as can
be judged by the eye, and loosen the set screw of the forward eccentric,
that is to say, the eccentric which connects to the upper end of the
link. Move that eccentric round upon the axle until the slide valve
leaves the steam port at the front end of the cylinder open to the
amount of required valve lead. In moving the eccentric round upon the
shaft, move it in the direction in which it will rotate when the engine
is running forward, so as to allow for and take up any lost motion there
may be in the eccentric straps, in the eccentric rod eyes and bolts, and
in the other working parts of the valve gear; for if the eccentric was
moved backward, all such lost motion would operate to vitiate the set of
the valve. The eccentric being placed as directed fastens its set screw
securely.
If the backward eccentric is the loose one, throw the reverse lever to
the backward notch of the sector, lifting the link up so that the
eccentric connected to the lower end of the link may be approximately
adjusted by moving it around upon the axle in the direction in which it
will rotate when the engine is running backward, until the back cylinder
port is open to the amount of the valve lead. Another very ready plan of
temporarily adjusting the eccentrics is as follows: Place the reverse
lever in the end notch forward, and place the engine crank or driving
crank pin as near on a dead centre as the eye will direct, and open both
the cylinder waste water cocks. Then disconnect the slide valve spindle
from the rocker arm, and move the slide valve spindle until the opening
of the cylinder steam port corresponding to the end of the cylinder at
which the piston stands will be shown by steam blowing through the waste
water cock at that end of the cylinder; the throttle valve being opened
but a trifle, to allow a small steam supply to enter the steam chest and
cylinder, for if much steam is admitted, it may pass through a leak in
the piston and blow through both the waste water cylinder cocks.
The position of the valve being thus determined, the eccentric must be
moved upon the driving axle until the valve spindle will connect with
the rocker arm without being moved, or moving the valve at all.
HOT AXLE BOXES.--If not convenient to reduce the speed of the engine, or
if that and free lubrication do not cool the box, a plentiful supply of
cold water should be administered, it being well to have at hand a small
hose pipe, by means of which water from the tender tank can be used. If
the brasses have Babbitt metal in them and it should melt, it is better,
if possible, to cool the axle box while the engine is moving, which will
injure the journal less than if the journal is stopped to cool the box,
because in the latter case the brass or box is apt to become soldered to
the journal of the axle, and when the engine is again started, the
cutting or abrasion will recommence with extreme violence.
BREAKING A LIFTING LINK OR THE SADDLE PIN THAT CONNECTS THE SLOT LINK TO
THE REVERSE SHAFT.--Cut a piece of wood and tie it into the slot of the
link, over the link block or die, making it of a length to keep the link
in the position for hauling the train. Then fasten another piece of wood
in the link slot beneath the sliding block or die, thus securing that
die in the proper position for the engine to go ahead. In this case, the
engineer must be careful in stopping, as he cannot reverse the engine on
the crippled side.
Secondary accidents are almost sure to occur if a disconnected piston is
not securely blocked in the cylinder, or from blocking the piston aright
and attempting to let the slide valve run, or from attempting to run
with the parallel rods on one side only disconnected. There are numerous
accidents, which only common sense and a familiarity with the locomotive
can provide a temporary remedy for, but those here enumerated are by far
the most common.
ADJUSTING THE PARTS OF A LOCOMOTIVE.
When the wedges of the axle boxes are to be adjusted for fit to the
pedestal shoes, the engine should be moved until the coupling rods on
one side of the engine are in line with the piston rod, because in this
position the rod will, to a certain extent, act as a guide in keeping
the axles parallel to each other, and at a right angle to the line of
engine centres.
Bear in mind that the distance from the centre to centre of axle boxes
must be the same as the distance from centre to centre of the crank
pins, and that when the coupling or side rods are in line with the
piston rod, they act to resist the axle boxes from being set up too
close together.
[Illustration: Fig. 3350.]
The importance of a proper adjustment of the axle boxes, coupling boxes,
and connecting rods cannot be overestimated, and it is necessary
therefore to explain it thoroughly. In Fig. 3350, then, _s_, _s_
represent two wheel axles, whose boxes are between their wedges. At S,
S´ are the screws for setting up the shoes or wedges W and W´
respectively. The axles are shown on the line of centres C, C of the
engine, the piston being at the head end of the cylinder, and the crank
pins on the line of centres as denoted by the small black circles. The
wedges W and W´ are shorter than the leg of the pedestal, so that they
may be set up by the set screws S and S´, and take up the wear.
In some engines the wedges V and V´ are also shorter for the same
purpose. Now it is clear that setting up the screws S and S´ will move
the axles _s_, _s´_ to the left, and this will alter the clearance
between the piston when it is at the end of the stroke and the cylinder
cover.
It is clear that the distance between the centres of the two axles must
be the same as the distance between the centres of the two crank pins,
or else the frame will be subjected to a great strain, tending to break
the crank pins and the side rods.
In order to keep the clearance equal and to know when it is equal, it is
necessary, at some time when the cylinder cover at the head end is off,
to disconnect the connecting rod and push the piston clear up against
the left hand cylinder cover, and from the cross head as a guide, make
on the side of the guide a line L´. Then put on the cylinder cover at
the head end and push the piston up against it and mark a line L. Then
when the connecting rod is put on again, the wheels may be moved around
if the engine is jacked up, or, if not, the engine may be moved along
the rails with a pinch bar, and the clearance will be equal when the
cross head (at the ends of the stroke) comes within an equal distance of
the respective lines L´, L when the crank is on the dead centres, and it
is well to adjust the wedges W W´ so that the cross head does travel
within an equal distance, and mark on the guide bar two more lines, one
at each end of the bar.
These lines are a permanent guide in setting up the shoes or wedges, and
lining up the connecting rods, and coupling or side rods, because it is
clear that from the method employed in marking them the distance between
the end of the cross head, when at the end of its stroke, and the line
L, and that between the face of the piston and the cylinder cover, will
be equal.
A proper adjustment, therefore, should be made as follows: The piston
should be at the end of its stroke, the crank pins being on the line of
centres.
Screw S should be operated to set up the wedge W, taking up the wear of
the sides of the box, and bringing the edge of the cross head the proper
distance from the line L. The connecting rod brasses should then be set
up to fit the pins, and the screw S´ operated to set up wedge W´ to have
easy contact with the side of its axle box. If, however, there has been
so much wear on the axle boxes that they are still too loose between the
wedges, both wedges may be set up to take up this wear, since it is more
important to have the axle boxes a proper fit between the wedges than it
is to maintain an exactly equal amount of clearance at each end of the
cylinder.
The engine will then be in proper tram on this side, or, in other words,
the distance from the centre to centre of the crank pins will be the
same as that from centre to centre of the axles.
On the other side of the engine the process is the same, the engine
being moved until the crank pins are on the line of centres C C and the
wedges set up according to the lines.
CHAPTER XXXIX.--THE MECHANICAL POWERS. LEVERS, PULLEYS, GEAR WHEELS,
ETC.
Power is distinguishable from force or pressure in that the term power
means force or pressure in motion, and since this motion cannot occur
without the expenditure of the force or pressure, power may, with
propriety, be termed the expenditure of force or pressure.
If we suppose a piston to stand in a vertical cylinder sustaining a
weight upon its surface and compressing the air within the cylinder, so
long as there is no motion no work is done, as the term "work" is
understood in a mechanical sense, and the weight merely produces a
pressure. If, however, the weight be removed, the compressed air will
force the piston upward, performing a certain quantity of work which may
best be measured by the amount of power exercised or expended.
The mechanical value of a given amount of power cannot be either
increased, diminished or destroyed by means of any mechanical device or
appliance whatsoever through which it may be transmitted.
It may be concentrated, as it were, by decreasing the amount of its
motion. It may be distended, as it were, by increasing the distance
through which it moves, or it may be expended in giving or producing
motion, but in either case the amount of duty or work done is the exact
equivalent of the amount of power applied.
A gain or increase in speed is not, therefore, a loss of power, but
merely a variation in the mode of using or utilizing such power.
For instance, 1 lb. moving through a distance of 12 inches in a given
time represents an amount of power which may be employed either as 1 lb.
moving a foot, 2 lbs. moving six inches, or 1/2 lb. moving through 24
inches, in the same space of time, the amount of the power or duty
remaining the same in each case, the method of utilization merely having
differed.
It is an inexorable law of nature that power is concentrated in
proportion as the amount of its motion is diminished, or distended in
precise proportion as such motion is increased.
[Illustration: Fig. 3351.]
Suppose, for example, that in Fig. 3351 L is a lever having its fulcrum
at F, which is 4 inches from end A, and 8 inches from end B, and
(leaving the weight of the lever out of the question) if we place an 8
lb. weight on a it will just balance 4 lbs. at B.
If the lever is moved, the amount of motion will be twice as much at end
B as it is at end A.
If we apply the power at A, the lever has become a means of converting 8
lbs. moving a certain distance into 4 lbs. moving twice that distance,
and nothing has been either gained or lost.
If we apply the power at B, the lever has merely been used as a means of
converting 4 lbs. moving a certain distance into 8 lbs. moving one half
that distance, and nothing has been gained or lost.
Suppose that end A was moved an inch, and the power at that end will be
8 inch pounds or 8 lbs. moving an inch, whereas at the end B the power
is 4 lbs. moving 2 inches; we have, therefore, reduced the weight in the
same proportion that we have increased the distance moved through.
Suppose now that the lever is moved to the position denoted by the
dotted line M M, and the leverages will be altered; that at end A
becoming that denoted by the distance from F to the vertical C, and that
for end B being denoted by the distance from F to the vertical D.
This occurs because we are dealing with gravity, which always acts in a
vertical line.
[Illustration: Fig. 3352.]
A crow bar is an excellent example of the application of the lever. In
Fig. 3352, for example, we have a 1 lb. weight on the long end of the
lever, and as we are dealing with a weight, the effective length of the
long end of the lever is from the fulcrum _f_ to _w_, which is divided
into 10 equal divisions. The short end of the lever is from _f_ to _p_,
which is equal to one division, hence the 1 lb. is balanced by the 10
lbs.
[Illustration: Fig. 3353.]
A simple method of distending power is by means of pulleys or gear
wheels. Suppose, for example, that in Fig. 3353, we have a weight of 12
lbs. suspended from a shaft or drum, whose radius _a_ is 10 inches, and
that on the same shaft there is a pulley, whose radius _b_ is 20 inches,
and the two weights will balance each other.
In this case the falling of either weight would not effect the leverage,
because the distance of both weights would remain the same from the
centre of the shaft. The leverage of the 12 lbs. is denoted by the line
_a_, and that of the 6 lbs. by _b_.
So far as the transmission of power is concerned, therefore, pulleys are
in effect revolving levers, which may be employed to concentrate or to
distend power, but do not vary its amount.
[Illustration: Fig. 3354.]
Suppose we have two shafts, on the first of which are two pulleys, B and
C, Fig. 3354, while upon the second there are two pulleys D and E. A
belt H, connecting C to D. Let the pulleys have the following
dimensions:
If we take the first pair of wheels B and C, we have that the velocity
will vary in the same ratio or degree as their diameters vary,
notwithstanding that their revolutions are equal.
Radius. Diameter. Circumference.
B = 5-1/8 inches. 10-1/4 inches. 32.2 inches.
C = 10-1/4 " 20-1/2 " 64.4 "
D = 7-5/8 " 15-1/4 " 47.9 "
E = 15-1/4 " 30-1/2 " 95.8 "
The velocity is the space moved through in a unit of time, and as it is
the circumference of the pulley that is considered, the velocity of the
circumference is that taken; thus, if we make a mark on the
circumferences of the two pulleys, B and C, Fig. 3354, the velocity of
that on C will be twice that upon B, or in the same proportion as the
diameters.
Let there be suspended from the circumference of B 10 lbs. weight, and
let us see the degree to which this power will be distended by this
arrangement of pulleys, supposing the weight to rotate B, and making no
allowance for the friction of the shaft.
Suppose the weight to have fallen 32.2 inches, and we have 10 lbs.
moving through 32.2 inches, this power it will have transmitted to
pulley B.
To find what this becomes at the perimeter of C, we must reduce the
number of lbs. in the same proportion that the perimeter of C moves
faster than does that of B; hence we divide the circumference of one
into the other, and with the sum so obtained divide the amount of the
weight; thus, 64.4 (circumference of C) ÷ 32.2 (circumference of B), =
2; and 10 lbs. ÷ 2 = 5 lbs., which, as the circumference of C is twice
that of B, will move twice as fast as the 10 lbs. at B, hence for C we
have 5 lbs. moving through 64.4 inches.
Now C communicates this to D by means of the belt H, hence we have at D
the same 5 lbs. moving through 64.4 inches.
Now E moves twice as fast as D, because its circumference is twice as
great, and both are fast upon the same shaft, hence the 5 lbs. at D
becomes 2-1/2 lbs. at E, but moves through a distance equal to twice
64.4, which is 128.8 inches. To recapitulate, then, we have as follows:
The weight gives 10 lbs. moving through 32.2 inches.
Pulley B " 10 " " " 32.2 "
" C " 5 " " " 64.4 "
" D " 5 " " " 64.4 "
" E " 2-1/2 " " " 128.8 "
That the amount of power is equal in each case, may be shown as follows:
For C, 5 lbs. moving through 64.4 inches is an equal amount of power to
10 lbs. moving through 32.2 inches, because if we suppose the first pair
of pulleys to be revolving levers, whose fulcrum is the centre of the
shaft, it will be plain that one end of the lever being twice as long as
the other, its motion will be twice as great, and the 5 at 10-1/4 inches
just balances 10, at 5-1/8 inches from the fulcrum, as in the common
lever.
In the case of D we have the same figures both for weight and motion as
we have at C, because D simply receives the weight or force and the
motion of C. In the case of E, we have the motion of the weight
multiplied four times; for the distance E moves is 128.8 inches, which,
divided by 4, gives 32.2 inches, which is the amount of motion of the
weight, hence the 10 lbs. of the weight is decreased four times, thus 10
lbs. ÷ 4 = 2-1/2 lbs., hence the 2-1/2 lbs. moving through 128.8 inches
is the same amount of power as 10 lbs. moving 32.2 inches, and we may
concentrate or convert the one into the other, by dividing 128.8 by 4,
and multiplying the 2-1/2 lbs. by 4, giving 10 lbs. moving 32.2 inches.
If, therefore, we make no allowance for friction, nothing has been lost
and nothing gained.
Thus far, we have taken no account of the time in which the work was
done, more than as one wheel is caused to move by the other, and all of
them by the motion of the weight, they must all have begun and also have
to move at the same time. Suppose, then, that the time occupied by the
weight in falling the 32.2 inches was one minute, and the amount of
power obtained may be found by multiplying the lbs. of the weight by the
distance it moved through in the minute, thus 10 lbs. moving 32.2 inches
in a minute gives 32.2 inch lbs. per minute, being the amount of power
developed by the 10 lb. weight in falling the 32.2 inches.
We may now convert the power at each pulley perimeter or circumference
into inch pounds by multiplying the respective lbs. by the distance
moved through in inches, as per the following table:
Distance moved.
Lbs. Inches. Inch lbs. of power.
Weight at B 10 × 32.2 = 322
" " C 5 × 64.4 = 322
" " D 5 × 64.4 = 322
" " E 2-1/2 × 128.8 = 322
If we require to find the power in foot lbs. per minute, we divide by 12
(because there are 12 inches in a foot), thus 322 inch lbs. ÷ 12 = 26.83
foot lbs. per minute.
Now suppose that B was moved by a belt, with a pull of 10 lbs. at its
perimeter, and made 100 revolutions in a minute instead of one, then the
pull at the perimeters of C, D, and E would remain the same, but the
motion would be 100 times as great, and the work done would therefore be
increased one hundred fold. It will be apparent, then, that the time is
as important an element as the weight.
The velocity and power of gear wheels are calculated at the pitch
circle.
Now suppose the gear A in Fig. 3355 has 30, gear B 60, gear C 10 and
gear E 80 teeth, and that 5 lbs. be applied at the pitch circle of A; to
find what this 5 lbs. would become at the pitch circle of E, we multiply
it by the number of teeth in B and divide it by the number of teeth in
C, thus:
Lbs.
At pitch of circle A 5
Number of teeth in B 60
---
Number of teeth in C 10 ) 300
---
30
--
Answer, 30 lbs. at the pitch circle of E.
Now suppose that on the shaft of A there is a pulley 20 inches in
diameter, and that on this pulley there is a belt exerting a pull of 5
lbs., while on the shaft of E there is a pulley 16 inches in diameter,
and to find how much this latter pulley would pull its belt, we proceed
as follows:
2 ) 20 = Diameter of pulley on A.
--
10 = Radius of pulley on A.
5 = Pull on pulley A.
--
Number of teeth in A = 30 ) 50 = Pull at centre of shaft
----- of A.
1.666
60 = Number of teeth on B.
------
Number of teeth on C = 10 ) 99.960 = Pull at axis of shaft
------ of B.
9.996
80 = Number of teeth on E.
-------
Radius of pulley on shaft of E 8 ) 799.680 Pull at axis of shaft E.
-------
99.96 Pull at perimeter of last
pulley.
We have in this case treated each pulley as a lever whose length
equalled the radius of the pulley, while in the case of the wheel we
have multiplied by the number of teeth when the power was transmitted
from the circumference to the shaft, and divided by the number of teeth
(the number of teeth representing the circumference) when the power was
transmitted from the shaft to the teeth.
We thus find that power is composed of three things, first, the amount
of impelling force; second, the distance that force moves through; and
third, the time it takes to move that distance.
If we take a number of pulleys, say four, and arrange them one after
another so that they drive by the friction of their circumferences, then
the amount of power transmitted by each will be equal and the velocities
will be equal, whereas, if we arrange them as in Fig. 3354, the power
will be equal for each, but the velocities or space moved through in a
given time will vary.
What is known as the unit of power is the foot lb., being the amount of
power exerted in raising or lifting one lb. one foot, and from what has
already been said, it will be perceived that this is the same amount of
power as 12 lbs. moving a distance of one inch.
Watt determined that the power of a horse was equal to that necessary to
raise 33,000 lbs. one foot high in a minute, and this is accepted, in
English speaking countries, as being a horse power.
An engine or machine has as much horse power as it has capacity to lift
33,000 lbs. a foot high in a minute.
CALCULATING THE HORSE POWER OF AN ENGINE.
The horse-power of an engine may be calculated as follows:
_Rule._--Multiply the area of the piston by the average steam pressure
upon the piston throughout the stroke, and by the length of the stroke
in inches, which gives the number of inch pounds received by the piston
from the steam during one stroke.
As there are two piston strokes to one revolution of the engine, we
multiply by two, and thus get the number of inch pounds received by the
piston in one revolution.
By multiplying this by the number of revolutions the engine makes in a
minute, we get the number of inch pounds of power received by the piston
in a minute.
By dividing this by 12, we get the number of foot pounds the piston
receives per minute, and dividing this by 33,000 lbs. we get the
horse-power of the engine.
It has already been stated that Watt determined that a horse was capable
of exerting a power equal to the raising of 33,000 lbs. one foot high in
a minute, hence, having foot pounds of the engine per minute, dividing
them by 33,000 gives the horse power.
This gives the amount of power received by the piston, but it is evident
that the engine cannot exert so much power, because part of it is
expended in overcoming the friction of the moving parts of the engine.
The amount of the piston power expended in overcoming the friction
depends upon the fit of the parts, upon the lubrication and the amount
of the load.
Thus, the friction of the cross head guides, of the cross head pin, of
the crank pin and of the crank shaft bearings will increase with the
amount of resistance offered to the piston motion.
The average pressure on the piston is a difficult thing to find,
however, for several reasons.
First, because the pressure in the cylinder may, during the live steam
period, vary from that in the steam chest because of the ports being too
small or from the passages being choked from a defective casting.
Second, because the steam is wire drawn during the time that the slide
valve is closing the port to effect the cut off.
Third, because the live steam in the port and passage at the time the
cut off occurs gives out some power during the period of expansion.
Fourth, because there is some condensation of the steam in the cylinder
after the point of cut off, and there is no means of finding by
calculation how much loss there may be from this cause.
During the live steam period there is also loss from condensation in the
cylinder, but this is made up for by steam from the steam chest.
Fifth, the loss from condensation after the cut off has occurred will
vary with the speed of the engine, and is greater in proportion as the
piston speed is less, because there is more time for the condensation to
occur in.
Sixth, there is some pressure on the piston between the time that the
exhaust begins and the piston ends its stroke.
Seventh, because the compression absorbs some of the piston power.
Assuming the average pressure on the piston to be known, however, we may
calculate the horse power as follows:
_Example._--What is the horse power of an engine whose piston is 20
inches in diameter, and stroke 30, the revolutions per minute being 120,
and the average pressure on the piston 60 lbs. per square inch?
Diameter of piston 20
Diameter of piston 20
---
Diameter of piston squared 400
---
.7854
400
------------
Area of piston = 314.1600 ([<--] these two ciphers neglected.)
60 average steam pressure.
--------
lbs. pressure on piston 18849.60 ([<--] this cipher neglected.)
30 length of stroke in inches.
--------
565488.0 inch lbs. per stroke.
2 two piston strokes per revolution.
-------
12 ) 1130976 inch lbs. per revolution.
-------
94248 foot lbs. per revolution.
120 revolutions per minute.
-------
1884960
94248
--------
11309760 foot lbs. per minute.
33000 ) 11309760 ( 342.72 = horse power of engine.
99000
140976
132000
------
89760
66000
-----
237600
231000
------
66000
66000
-----
In working out the calculation, the ciphers that are decimals and are on
the right hand are neglected or taken no account of, because they
represent no value and may therefore be discarded.
[Illustration: Fig. 3355.]
Thus the area of the piston is 314.1600 inches, the two right hand
ciphers having no value. Again the lbs. pressure on the piston is
18849.60 lbs., and the right hand cipher, having no value, is discarded.
The inch lbs. per stroke is 565488.0, and the decimal cipher,
representing nothing, is discarded when multiplying by the 2.
We have in this case taken no account of the fact that the piston rod
prevents the steam from acting against a part of the piston area during
one stroke; hence for correct results we must subtract from the area of
the piston one half the area of the piston rod.
The horse power thus obtained is that which the engine receives from the
steam, and is more than the engine is capable of exerting to drive
machinery, because a part of this power is consumed in overcoming the
friction of the working parts of the engine.
TESTING THE HORSE POWER OF AN ENGINE.
[Illustration: Fig. 3356.]
The useful horse power of a stationary engine may be readily and
accurately obtained by means of a pair of scales, and a brake, as shown
in Fig. 3356, which is constructed and used as follows:
On the crank shaft of the engine is a pulley enveloped by a friction
brake, which consists of an iron band, to which wooden blocks are
fastened.
The ends of the iron band do not meet, but are secured together by a
bolt as shown.
By screwing up the bolt the wood blocks are brought to press against the
circumference of the wheel.
This forms a friction brake that would revolve with the wheel, were it
not for two arms that are secured to the brake, and rest at the other
end upon a block placed upon a pair of scales.
The principle of action of this device is that the amount of friction
between the brake and the wheel is weighed upon the scales, and this
amount, multiplied by the velocity of the wheel at its circumference and
divided by 33,000, is the horse-power of the engine.
It is necessary, in arranging this brake, to have its end rest upon the
scale at the same height from the floor as the centre of the crank
shaft, so that the line marked 5' 3" (5 feet 3 inches), which represents
the length of the lever, shall stand parallel with the surface of the
platform of the scale.
To test the horse-power, we proceed as follows:
Suppose the pressure of the end of the lever on the scale is found by
the weight on the scale beam to be 540 lbs., the diameter on which the
brake blocks act being 3 feet, the length of the leverage being 5 feet 3
inches, as marked, and the engine making 150 revolutions per minute, and
the calculation is as follows:
540 lbs. on scale.
5.25 leverage in feet.
-----
2700
1080
2700
------
radius of pulley in feet 1.5 ) 2835.00 ( 1890 lbs. at pulley perimeter.
15
---
133
120
---
135
135
----
...0
====
Then
3.1416
3 diameter of pulley in feet.
------
9.4248 circumference of pulley in feet.
150 revolutions per minute.
-------
4712400
94248
---------
1413.7200 velocity of pulley perimeter.
1890 pounds at pulley perimeter.
---------
12723480
1130976
141372
----------
2671930.80 foot lbs. per minute.
==========
Then
33000 ) 2671930.80 ( 80.9
264000
------
319308
297000
------
223080
======
Answer, 80-9/10 horse power.
In this calculation we have nothing to do with the size of the cylinder
or the steam pressure, because the scale beam tells us how many lbs. the
brake exerts on the scale, and we treat the brake and brake pulley as
levers. Thus by multiplying the lbs. on the scale by the leverage of the
brake arm we get the number of lbs. exerted at the centre of the crank
shaft, and by dividing this by the radius of the brake pulley we get the
number of lbs. on the circumference, or, what is the same thing, the
perimeter of the brake pulley.
By multiplying the circumference of the pulley in feet by the
revolutions per minute, we get the speed at which the pounds travel, and
by multiplying this speed by the number of lbs. we get the foot lbs.
per minute, which, divided by 33,000, gives us the effective horse power
of the engine.
This effective horse power is correct, because in loading the engine by
the brake the crank pin, the cross head guides, etc., are all placed
under the same friction as they would be if it was a circular saw, or
some other piece of machinery or machine that the engine was driving.
SAFETY VALVE CALCULATIONS.
Among the most frequent questions asked in an engineer's examination are
those relating to the safety valves of boilers.
These questions may be easily answered from a study of the following:
The safety valve is a device for relieving the boiler of steam after it
has reached a certain pressure.
This it accomplishes by letting the steam escape after it has reached
the required pressure.
At what pressure the safety valve will blow off depends upon the
position of the weight on the safety valve lever.
The calculations referring to this part of the subject are, finding how
much weight will be required to be placed at a given point on the lever,
in order, with a given sized valve, to blow off at a given pressure.
Finding the position on the lever of a given amount of weight, in order
to blow off at a certain pressure.
Finding, with a given sized valve and a given weight, how to mark off
the lever and where the notches must be cut for given pressures.
In each of these calculations there are three elements: first, the area
of the valve and the steam pressure, which constitute the effect of
acting to lift the valve; second, the amount of the weight and its
position upon the lever, which acts to keep the valve closed; and third,
the weight of the lever and of the valve, which act to keep the valve
closed.
[Illustration: Fig. 3357.]
In Fig. 3357 we have a drawing of a safety valve shown in section, and
if there was no weight upon the lever, the pressure of steam the valve
would hold in the boiler would be that due to the weight of the valve
and of the lever upon the valve.
To find out how much this would be, we would have to put the valve
itself and the pin _a_ on a pair of scales and weigh them.
Then put a piece of string through the hole at _a_ in the lever, and see
how much it weighed when suspended from that point.
Suppose the valve and pin to weigh 2 lbs. and the lever (suspended by
the string) 10, and the total will be 12 lbs.
Next we find the area of the valve, and suppose this to be 8 square
inches; then we may find how much pressure the valve would keep in the
boiler, by dividing the area of the valve into the weight holding the
valve down, thus:
Lbs.
Weight of valve and pin, 2
" " lever, 10
--
Area of valve, 8 ) 12
---
Pressure the valve would hold, 1.5 lbs.
The area of the valve is that part of its face receiving the steam
pressure when the valve is seated, so that if the smallest part of the
valve diameter is equal to the diameter of the seat bore, the diameter
from which the valve area is to be calculated will be that denoted by D
in the figure, and cannot in any case be less than this. But if the
smallest end of the valve cone is of larger diameter than the smallest
end of the seat cone (which should not, but might be the case), then it
is the smallest diameter of valve cone that must be taken in calculating
the area, because that is the area the steam will press against.
Now suppose we rest a 20 lb. weight on the top of the valve that is on
the point denoted by I, and there will be 32 lbs. holding the valve
down, thus, weight of valve 2 lbs., of lever 10, and weight added, 20
lbs., and to find how much pressure this would hold in the boiler, we
divide it by the valve area, thus:
Weight on valve.
Valve area = 8 ) 32
--
4 = pressure valve will hold.
But suppose we put the weight on the lever, in the position shown in the
figure, which is six times as far from the fulcrum F of the lever as the
valve is, and its effect on the valve will be six times as great as it
would if placed directly upon the valve, so that leaving the weight of
the valve and of the lever out of the question (as is commonly done in
engineers' examinations), we may find out what pressure the valve will
hold, as follows:
_Rule._--Divide the length of the lever by the distance from the centre
of the valve to the centre of the fulcrum. Multiply by the amount of the
weight in lbs., and divide by the area of the valve.
_Example._--The area of the valve is 8 inches, the distance from the
centre of the fulcrum to the centre of the valve is 4 inches, and the
distance from the fulcrum to the point of suspension of the weight 24
inches, the weight is 40 lbs., what pressure will the valve hold?
Length of lever.
From fulcrum to valve, 4 ) 24
--
6
40 amount of weight.
---
Area of valve, 8 ) 240
---
30
Lbs. per square inch the valve will hold = 30.
The philosophy of this is clear enough when we consider that as the
weight is six times as far from the fulcrum as the valve is, and each 1
lb. of weight will press with a force of 6 lbs. on the valve, hence the
40 lbs. will press 240 lbs. on the valve, and as the valve has 8 square
inches, the 240 becomes 30 lbs. for each inch of area.
_Example._--The area of a safety valve is 8 inches, the distance from
the fulcrum to the valve is 4 inches, and the weight is 40 lbs., how far
must the weight be from the fulcrum to hold in the boiler a pressure of
30 lbs. per square inch?
In lbs.
From fulcrum to valve, 4 ) 40 amount of weight.
--
10
Area of valve, 8 square inches.
Pressure required, 30
---
10 ) 240
---
24
Answer = 24 inches from the fulcrum.
_Example._--The diameter of a safety valve is 4 inches, the distance
from the centre of the fulcrum to the valve is 3 inches, a 50 lb. weight
is 30 inches from the fulcrum, what pressure will the valve hold?
3 diameter of valve.
3
--
9
.7854
-----
36
45
72
63
------
7.0686 = area of valve.
======
3 ) 30
--
10
50 = weight
10 = leverage of weight.
-------
Area of valve, 7.068 ) 500.000 ( 70.7 = lbs. pressure per sq. in.
49476
-------
52400
49476
-----
2924
HEAT.
The heat unit, or the unit whereby heat is measured, is the quantity of
heat that is necessary to raise 1 lb. of water from its freezing
temperature (which is 32° Fahrenheit) 1°, and this unit is sometimes
termed a _thermal unit_.
The reason that some specific temperature, as 32° Fahrenheit, is taken,
is because the quantity of heat required to heat a given quantity of
water 1° increases with the temperature of the water; thus, it takes
more heat to raise 1 lb. of water from 240° to 245° than it does to
raise it from 235 to 240, although the temperature has been raised 5° in
each case.
The whole quantity of heat in water or steam is not, however, sensible
to the thermometer, or, in other words, is not shown by that instrument.
The heat not so shown or indicated is termed _latent_ heat.
Water obtains latent heat while passing from a solid to a liquid state,
as from ice into water, and while passing from a liquid to a gaseous
state, as while passing from water into steam, and the existence of
latent heat in steam may be shown as follows:
If we take a body of water at a temperature above freezing, and insert
therein a thermometer, the decrease in the temperature as the water
becomes frozen will be shown by the thermometer. If, then, its
temperature being say at zero, heat be continuously imparted to the ice,
the thermometer will mark the rise in temperature until the ice begins
to melt, when it will remain stationary at 32° so long as any ice
remains unmelted, and it is obvious that all the heat that entered the
water from the time the ice began to melt until it was all melted became
latent, and neither sensible to the sense of feeling nor to the
thermometer. Similarly, if the water, after the ice is all melted, be
heated in the open air, the thermometer will mark the rise of
temperature until the water boils, after which it will show no further
rise of temperature, although the water still receives heat. The heat
that enters the water from boiling until it is evaporated away is the
latent heat of steam. The latent heat of water is 143° Fahrenheit, and
that of steam when exposed to the pressure of the atmosphere, or under
an atmospheric pressure of 15 lbs. (nearly), is 960°, which may be shown
as follows:
If a given quantity of water, as say 1 lb., has imparted to it a
continuously uniform degree of heat sufficient to cause it to boil in
one hour, then it will take about 5-1/3 more hours to evaporate it all
away, hence we find the latent heat by taking the difference in the
amount of heat received by the water, and that shown by the thermometer
thus:
Degrees.
Temperature by thermometer at boiling point 212
Less the temperature of the water at first 32
---
Heat that entered the water in the first hour 180
Hours that the water was subsequently heated 5-1/3
-------
900
One-third of 180 = 60
---
Heat that entered the water during the 5-1/3 hours 960 degrees.
This, however, is not quite correct, as it would take slightly more than
5-1/3 hours to boil the water away, and the heat that entered the water
after it commenced to boil would be about 966 degrees.
If the steam that arose from the water while it was boiling were
preserved without increasing the pressure under which it boiled, and
without losing any of its heat, it will have a temperature the same as
that of the water from which it was boiled, which is a temperature of
212°, so that neither the steam nor the water account, by the
thermometer, for the 966° of heat that entered the water after it
boiled, hence the 966° became latent, constituting the latent heat of
the steam when boiled from and at a temperature of 212°.
The total heat of steam is the sensible heat, or that shown by the
thermometer, added to the latent heat; hence the heat necessary to
evaporate water into steam at a temperature of 212° (which corresponds
to a pressure of 14.7 lbs. per square inch) is 212° + 966°, which is
1178°, and these, therefore, are the number of degrees that must be
imparted by the coal to the water, in order to form steam at a
temperature of 212°.
WATER.
Water is at its greatest density when at a temperature of 39.1°
Fahrenheit, that is to say, it occupies its least space and weighs the
most per given quantity (as per cubic inch) when at that temperature.
At a lower temperature water expands, its freezing point being 32°
Fahrenheit, below which it forms ice. The weight of a cubic foot of
water when at its maximum density (39.1) is 62.382 lbs. Water also
expands as its temperature is increased above 39.1°; thus, while it is
heated from 39.1 to 212°, its volume increases from 1 to 1.04332. The
expansion for each degree of heat added to its temperature increases
from 0 at 40° Fahrenheit to .0043 at 212°.
The rate of expansion of water at a temperature above 212° is unknown.
STEAM.
At every temperature above freezing point water passes from the liquid
into a gaseous state, the gas being termed steam. While water is below
its boiling point its evaporation occurs at its surface only; but when
its mass is heated to boiling point, and additional heat is imparted to
it, evaporation occurs from the water lying against the surface from
which it receives the heat, and an ebullition is caused by the vaporized
water passing through the mass, the ebullition being what is known as
boiling.
The temperature at which water boils depends upon the pressure acting
upon its surface, the boiling point being at a lower temperature in
proportion as the pressure is reduced; thus water at the top of a
mountain, where the pressure of the atmosphere is less than at the sea
level, would boil at a lower temperature than 212°, which is the boiling
point when the atmospheric pressure is 14.7 lbs., which it is assumed to
be at the sea level. Conversely, the boiling point is raised in
proportion as the pressure upon its surface is raised, whether that
pressure consists of air or of steam. As, however, the pressure is
increased, the boiling point is at a higher temperature. So long as the
steam is in contact with the water both are at the same temperature, as
denoted by the thermometer (although they do not contain the same
quantity of heat, as will be show presently), and the steam is termed
_saturated_ steam.
The pressure of saturated steam cannot be either increased or diminished
without either increasing or diminishing its temperature, hence there is
a definite relation of pressure to temperature, which enables the
pressure to be known from the temperature, or conversely, the
temperature to be known from the pressure. But if the steam be separated
from the water and heated, it may be what is termed _superheated_, which
is that it may be surcharged with heat or contain more heat than
saturated steam at the same pressure. Such additional heat, however, is
latent.
The pressure of steam is the lbs. of force it exerts upon a given area,
as upon a square inch. In non-condensing engines the effective pressure
of the steam is its pressure above that of the atmosphere, because the
exhaust side of the piston being exposed to the atmosphere receives the
atmospheric pressure, which must be overcome by a corresponding
pressure of steam on the steam side of the piston, and this pressure is
not, therefore, available for producing work or power in the engine.
In condensing engines, however, the exhaust side of the piston is (as
nearly as practicable), relieved of the atmospheric pressure, and
assuming a perfect vacuum to be formed, the whole of the steam pressure
is exerted to propel the piston, in which case the steam pressure is
termed the _absolute_ pressure.
In considering the weight or density or the expansion of steam, its
_absolute_ and not its effective pressure must obviously be taken.
What is termed dry steam is _saturated_ steam that does not contain what
may be termed entrained water, which is water held in suspension in the
steam, which may be caused by the surface of the water through which the
steam is allowed to rise being too small in proportion to the volume of
steam formed, in which case the rapid passage of the steam through the
water causes it to carry up water with it and hold it in suspension,
this action being termed _foaming_ or _priming_.
Suppose, for example, that a boiler be filled with water up to the
bottom of the steam dome, then all the steam formed would require to
find exit from the water within the area of the dome, and the violence
of the ebullition would cause foaming. Obviously, then, to obtain dry
steam there must be provided a sufficient area of water surface for the
steam to pass through.
But water so entrained is evaporated into steam, if the steam is wire
drawn, that is, allowed to expand and reduce in pressure.
THE EXPANSION OF STEAM.
A cubic inch of water, when evaporated into steam at a pressure of 14.7
lbs. per square inch, occupies as steam a space or volume of 1644 cubic
inches, and its weight will be equal to that of the water from which it
was evaporated.
If additional heat be imparted (after its evaporation into steam), such
additional heat becomes latent and does not cause an increase of
sensible temperature or of pressure.
The weight of a given volume of steam, therefore, bears a definite and
constant relation to the pressure and sensible temperature of the steam,
so that the pressure or the sensible temperature being known, the weight
of a given volume, as say a cubic foot, may be known therefrom. Or the
weight of a cubic foot of steam being known, its sensible temperature
and pressure may be known therefrom.
This would not be the case if steam expanded by heat. Suppose, for
example, we have a cubic foot of steam at any absolute pressure, as say
15 pounds per square inch, a cubic foot weighing .0387 of a lb., and its
sensible temperature will be 213°. Now it is evident that the weight
will remain the same whatever the amount of heat that may be imparted to
the steam. Now if the steam were maintained within the cubic foot of
space, and was capable of expansion by the absorption of additional
heat, its pressure would increase and its weight remaining the same,
there would be no definite relation between the weight and the
temperature and pressure.
But if the cubic foot of steam were allowed to expand so as to occupy
more space, then additional heat is necessary to prevent its
condensation.
The relation between the temperature, pressure, and weight of steam is
not quite proportional to the volume, because steam is not a perfect
gas, and does not, therefore, strictly follow Mariotte's law.
A perfect gas is one that during expansion or compression follows the
law laid down by Boyle and Mariotte, this law being that, if maintained
at a constant temperature, the volume is inversely proportional to the
pressure.
For example, the quantity of gas that, if confined in a cubic inch of
space, would give a pressure of 80 lbs. per square inch, would give a
pressure twice as great (or 160 lbs. per inch of area), if confined in
one-half the space, that is, if compressed into one-half of a cubic
inch. Conversely, if the cubic inch was allowed to expand until its
pressure was 40 lbs., it would occupy 2 cubic inches of space, assuming,
of course, that the temperature remains the same. Since, however, if a
gas be compressed, its temperature is increased by reason of the
friction of the particles moving one upon the other, the law of Mariotte
may be better explained as follows:
Suppose we have three vessels, A, B, and C, filled with a fluid which is
a perfect gas, the temperatures being equal. Let the pressure be: A 40,
B 80, and C 160 lbs. per square inch, then 2 cubic inches of the fluid
in B will weigh the same as 4 cubic inches in A, because that in B is at
twice the pressure of that in A, and the 2 cubic inches in B will weigh
the same as 1 cubic inch in C, because its pressure is one-half that of
C, or, what is the same thing, whatever number of cubic inches of the
fluid in C it takes to weigh a pound, it will take twice as many in B,
and four times as many in A to weigh one pound.
But steam is not a perfect gas, as is evidenced by the fact that its
volume does not increase in a ratio inverse to its pressure. For
example, if a cubic inch of water be evaporated into steam at a pressure
of 14.7 lbs. per square inch, its volume will be 1644 cubic inches, and
its temperature 212° Fahrenheit.
But if the cubic inch of water be evaporated into steam at twice the
pressure, which is 29.4 lbs per square inch, its volume will be 838
inches.
The volume then is not inversely as the pressure, although the actual
quantity and weight remain the same, as is proven by the fact that if
the steam at either pressure were condensed it would pass back into the
cubic inch of water from which it was generated.
This may be accounted for in the difference in the boiling point of the
water in the two pressures, or in other words, by the difference in the
temperatures; thus the boiling point of the water at a pressure of 14.7
lbs. is 212°, while that for the pressure of 29.4 is increased about
38.4 degrees, and the steam is at the higher pressure expanded by these
38.4 degrees of heat, which adds to its pressure, although not affecting
its actual quantity or weight.
The amount of this expansion may be estimated as follows:
Taking the 1644 cubic inches, and supposing the steam to be a perfect
gas, we divide it by 2 to obtain half the volume, 1644 ÷ 2 = 822.
If then we subtract this 822, which is the volume of the steam if it
acted as a perfect gas from the 838 it actually occupies, we get 16
(838-822 = 16), which is the number of cubic inches of expansion due to
the increase in the boiling temperature.
THE CONVERSION OF HEAT INTO WORK.
When steam performs work a certain portion of the heat it contains is
converted into work, the steam simply being a medium of conveying the
heat into the cylinder in which the motion of the piston converts this
proportion of heat into work. It has been proven that a given quantity
of heat will pass into a given quantity of work, and conversely that a
given quantity of work is convertible into a given quantity of heat, and
it has also been proven that so much heat is convertible into so much
work, independent of the temperature of the heat during its conversion
into work, power, or energy, all three of these words being used to
imply pressure, force, or weight in motion.
The accepted measurement of the conversion of heat into work is known as
_Joule's equivalent_; _Joule_ having determined that the amount of power
exerted in raising 772 lbs. one foot is the equivalent of the amount of
heat that is required to raise the temperature of 1 lb. of water when at
or near its freezing point (that is, at a temperature of 32°) one
degree.
This is called the _mechanical equivalent of heat_, being merely the
quantity of heat necessary to do a certain amount of work, but having no
relation to the time in which that work was done.
The conversion of heat into work and of work into heat may be
demonstrated as follows: Suppose a cylinder to be so situated that heat
can neither be transferred to it or from it, and that saturated steam be
admitted under the piston so as to fill one-half of the cylinder at a
pressure of 50 lbs.
Suppose then that we raise the piston from an independent application of
power, the steam simply expanding to fill the space given by the piston,
but not exerting its force to move the piston.
Now suppose the experiment is repeated, permitting the force of the
steam to lift the piston, and the temperature of the steam will be less
in the second than it was in the first, proving that in the second
experiment a certain portion of the heat in the steam was converted into
the work of raising the piston.
If we desire to reconvert the work into heat, we may force the piston
back again to its original position, and its temperature will be
restored to what it was before we allowed it to raise the piston. It is
here, of course, assumed that there is no friction in moving the piston
in the cylinder.
The apparent or external work performed by steam in expanding and moving
a piston against a given resistance is measurable by multiplying the
amount of the resistance against which the piston moved by the distance
it moved through, thus:
Suppose a piston weighs 100 lbs. and had resting upon it a weight of 50
lbs., and that it be raised by the expansive action of steam a distance
of a foot, then, since the total resistance it moved against would be
(supposing it to move frictionless in the cylinder) 150 lbs., and since
the amount of motion was 1 foot, the external or apparent amount of work
performed by the steam will be 150 foot lbs., or 150 lbs. moved 1 foot.
But in expanding, the steam has performed a certain amount of what is
called _internal_ work, that is to say, its particles or atoms have done
work in expanding, and this work has been done at the expense of some of
the heat in the steam, so that the loss of heat due to the motion of the
piston is the amount of heat converted into work in moving the piston
against the piston resistance, added to that converted into the internal
work due to the expansion of the steam.
It is because of this internal work that the steam in expanding does not
strictly follow Mariotte's law.
The mechanical theory of heat is, that the atoms of which bodies are
composed are at absolute rest when at a temperature of 461.2° below the
zero of Fahrenheit, which is supposed to be absolute cold, and at any
degree of temperature above this the atoms are in motion; the extent and
force of their motion determines what we know as the temperature of the
body.
Atoms are capable of transmitting their motion to adjoining atoms of the
same or of other bodies, losing, of course, the amount of motion they
transmit, and it is in this way that heat is conveyed from one to
another part of the same body, or from one body to another, this being
known as the heat of _conduction_.
But heat may be conveyed by means of what is known as _radiation_, and
also by _convection_.
Thus, the air surrounding a heated body becomes heated, and by reason of
its expansion it then becomes lighter and rises, a fresh supply of
cooler air taking its place, becoming in turn heated, and again giving
place to cooler air; the heat thus conveyed away by the fluid or air is
conveyed by what is termed _convection_.
Heat also passes from a body in straight lines or rays, which do not
heat the air through which they pass to their own temperature, but do
impart that temperature to a solid body, as iron or water; the heat that
passes from a body in this manner is termed radiant heat, or the heat of
_radiation_.
In the cylinder of a steam engine, therefore, the heat contained in the
steam is disposed of as follows:
A certain portion of it is converted into work through the medium of the
piston.
Another portion is conveyed away by the walls of the cylinder, this
portion including the heat of convection and that of radiation.
Yet another portion is converted into internal work. Referring to the
latter, suppose that steam is permitted to expand and its atoms will be
in motion, which motion has been derived at the expense of or from the
conversion of a certain quantity of heat.
The amount of the heat so converted obviously depends upon the amount of
the motion. Suppose, for example, that steam is generated in a closed
vessel as in a steam boiler, and that a certain pressure having been
attained, the steam is permitted to pass off as fast as it is formed
from the boiler, then the amount of atomic motion will remain constant,
because the pressure remains constant; but suppose instead of the steam
passing off, it be confined within the boiler, then the pressure will
increase and there will be a greater resistance to the motion of the
atoms, hence their motion will be less, and less of their heat will
therefore be converted into atomic motion, and, as a consequence, more
of it will exist in the form of sensible heat; hence while the pressure
of steam continues to increase, its heat is increased, not only by
reason of the heat it receives from the furnace, but also by reason of
that abandoned by the steam, because it is prevented by the pressure,
from expending it in atomic motion.
CHAPTER XL.--THE INDICATOR.
The indicator is an instrument which marks or draws a figure, or diagram
as it is called, which shows the pressure there is in the cylinder at
every point in the piston stroke, while it also shows the resistance
offered by the same body of steam to the piston on its return stroke.
From the form of this figure or diagram, the engineer is enabled to
discover whether those parts of the engine whose operation regulates the
admission of the steam to and its exhaust from the cylinder are
correctly adjusted.
From the diagram the engineer may find the average or mean effective
pressure of steam on the piston throughout the stroke, for use in
calculating the power of the engine.
He may also locate the point of cut off, of release, the amount of back
pressure, the degree of perfection of the vacuum in a condensing engine,
and the amount of compression.
From the area of the diagram the engineer may also estimate the quantity
of steam that is used, and supposing it to be dry steam, he may
calculate the amount of water used to make the steam, and assuming one
pound of coal to evaporate so much water, he may calculate the amount of
coal used to produce the steam.
The indicators commonly used upon steam cylinders contain two principal
mechanical movements; first, a drum revolving the piece of paper upon
which the diagram is to be marked, and second, a piston and parallel
motion for moving the pencil to mark the diagram upon the revolving
paper.
The drum is given a motion that, to insure a correct diagram, is exactly
timed with the piston motion.
The pencil is given a vertical movement; this movement must bear a
constant and uniform relation to the pressure of the steam in the engine
cylinder.
[Illustration: Fig. 3358.]
An indicator may be attached to each end of the cylinder or in the
middle, with a pipe passing to each end of the cylinder, as in Fig.
3358, but an indicator of the usual construction and such as here
referred to, can take a diagram, or _card_ as it is sometimes called,
from but one end of the cylinder at a time. The stop valves A and B are
used, so that the communication between the indicator and one end of the
cylinder may be shut off while a diagram is being taken from the other
end, while both ends may be shut off when the indicator is not being
used.
In the figure a piece of paper (or card, as it is commonly called) is
shown in place upon the drum with a diagram upon it.
[Illustration: Fig. 3359.]
[Illustration: Fig. 3360.]
The Thompson Indicator is shown in Fig. 3359, and in section in Fig.
3360.
The Tabor Indicator is shown in Fig. 3361, and in section in Fig. 3362.
Both are made with the piston and parallel motion as light as possible,
in order to enable the taking of diagrams at as high a speed of engine
revolution as possible.
Each consists of a cylinder and piston, the bottom surface of the latter
being in communication with the bore of the engine cylinder, so as to
receive whatever steam pressure there may be in the cylinder.
This indicator piston receives, on its upper surface, the pressure of a
spiral spring, which acts to resist the steam pressure.
The indicator piston rod actuates an arm or line on the end of which is
a pencil, which, by means of a parallel motion, is caused to move in a
straight line.
The paper or _card_ being in place upon the drum, and steam let into
the indicator, the pencil lever is moved until the pencil touches the
paper as lightly as possible, and as a result of the combined movements
of the pencil and drum, the diagram is marked, its form being
illustrated in Fig. 3363, which represents a diagram placed above a
cylinder, and the engine piston in three positions; first at the
beginning of the stroke; second, at the point of cut off (which is
supposed to be at one-third of the stroke); and third, at the point of
release where the valve first opens the port for the exhaust. For
convenience, the diagram is shown as long as the cylinder, but the
actual diagram usually measures about 2-1/2 inches high and 4-1/4 inches
long.
[Illustration: Fig. 3361.]
[Illustration: Fig. 3362.]
[Illustration: Fig. 3363.]
Supposing the cylinder to be filled with air, and the engine piston in
position 1, and the indicator piston would be at the corner A of the
diagram; but if steam were admitted, the pencil would rise vertically,
marking the line from A to B, which is therefore called the _admission
line_, or by some, the _induction line_.
If on reaching B the pressure was enough to move the engine piston, that
piston and the indicator drum would move simultaneously, and as long as
live steam was admitted the line from B to C would be drawn, hence this
is called the _steam line_, its length denoting the live steam period.
The cut off occurs when the engine piston is in position 2, and the
indicator pencil at C.
From this point the pencil will fall, in proportion as the steam
pressure falls from expansion until the exhaust begins, the piston then
being in position 3, and the pencil at D.
The line from C to D is therefore called the _expansion line_ or
_expansion curve_, and the point D the _point of release_ or _point of
exhaust_.
We have now to explain that in reality the whole of the remainder of the
line of the diagram is, in reality, the exhaust line, yet there is a
difference between the part of the line from point D to the end E of the
diagram, and that part from E to A, inasmuch as that during the period
of exhaust from D to E, the pressure is helping to propel the piston,
while after E is reached, whatever steam pressure there may remain in
the cylinder acts to retard the piston.
The line from D to E is therefore the exhaust line, and that from E to A
is the _back pressure line_ or _counter pressure line_.
In this example it has been supposed that while the piston was moving
from position 3 to the end of its stroke, and the pencil from D to E,
the indicator piston would have a steam pressure on it equal to
atmospheric pressure, hence the line from E to A, in this case,
represents the atmospheric line, and also the back pressure line.
The atmospheric line is a line drawn when there is no steam admitted to
the indicator, and represents a pressure above a perfect vacuum equal to
the pressure of the atmosphere. Its use is to show the amount of back
pressure, and in a condensing engine to show the degree of vacuum
obtained.
It also forms a line wherefrom the line of perfect vacuum, or that of
full boiler pressure, may be marked.
The steam pressure at any point in the stroke is denoted by the height
of the diagram above the atmospheric line, but the steam pressure thus
taken is obviously above atmospheric, and is thus the same as the
pressure of a steam gauge, which is also above the atmospheric pressure,
and therefore represents the pressure that produces useful effect in a
non-condensing engine.
This is what may be called a theoretical diagram, because, first, it
supposes the steam not to be admitted to the cylinder until the piston
was at the end of its stroke, and to attain its full pressure in the
cylinder before the piston lead begins to move, whereas, in order to
attain a full steam pressure at the beginning of the stroke, the valve
must have lead.
Second, it supposes the cut off to be effected simultaneously, whereas
the valve must have time to move and close the port, and during this
time the steam pressure will fall, and the curve C of the diagram will
therefore be rounded more or less according to the rapidity with which
the valve closed.
Third, it supposes the steam to have exhausted down to atmospheric
pressure by the time the piston had reached the end of the stroke,
whereas the piston will have moved some part of the back or return
stroke before the steam will have had time to exhaust down to
atmospheric pressure; and,
Fourth, it supposes the steam to remain at atmospheric pressure until
the piston arrives at the end of its return stroke, whereas the valve
will begin to close the port and cause the steam remaining in the
cylinder to compress before the piston has completed its return stroke.
In practice the diagram will, under favorable conditions, accord nearer
to the shape shown in the lower part of Fig. 3363, in which the closure
of the port for the cut off is shown by the curve at F. At the point
denoted by _g_ the valve began to close, and at the point denoted by _h_
the cut off was completely effected, and the expansion curve began.
The curve beginning at D is caused by the gradual opening of the exhaust
port.
The height of the line of back pressure above the atmospheric line shows
the amount of back pressure.
At the point _m_, where the back pressure line rises into a curve, the
valve had closed, shutting in the cylinder a portion of the exhaust
steam, which is afterwards compressed by the piston.
This curve is therefore called the _compression line_ or _compression
curve_. The point at which it begins cannot be clearly seen when the
exhaust port is closed slowly.
The compression curve ends at _p_, where it merges into the admission
line, but the exact point where the compression ends and the admission
begins cannot always be located, this being the case when the port is
opened slowly or the compression extends through a large portion of the
stroke.
The admission line is, however, in most cases nearly vertical when the
valve has lead, because the valve opens the port quickly while the
engine piston is moving at its slowest.
A diagram as drawn by the indicator does not account for all the steam
that is used in the cylinder, however, as will be seen from Fig. 3363,
because, as the paper drum of the indicator receives its motion from the
engine cross head, its length represents the length of the piston
stroke, whereas, there is a part of the cylinder bore between the piston
(when it is at the end of the stroke) and the cylinder cover that is
filled with steam as is also the steam passage.
This steam performs no useful work during the live steam period, but
obviously expands during the expansion period, and therefore affects the
expansion curve, and must be taken account of in calculating the
consumption of steam, of water, or of coal from the diagram, or in
marking in the true expansion curve.
In calculating the horse power, however, it may be neglected, as it does
not enter into that subject.
But in any calculation involving the amount of steam used, the clearance
must be marked in by a line at a right angle to the admission line and
distant from the nearest point of the admission line to an amount that
bears the same proportion to the whole length of the diagram as the
clearance does to the whole contents of the cylinder.
The clearance line is shown at L, L´, in Fig. 3363, its distance from
the admission line representing the amount of clearance which includes
the contents of the steam port and passage, as well as that of the
cylinder bore that is between the cylinder cover and the piston, when
the latter is at the end of the stroke.
A method of measuring the amount of clearance has already been given
with reference to stationary steam engines.
[Illustration: Fig. 3364.]
A diagram for a condensing engine is shown in Fig. 3364, which
corresponds to Fig. 3363, except that the line of perfect vacuum or no
pressure is marked in.
It represents a perfect vacuum, and must be marked on all diagrams from
which the consumption of steam is to be calculated, because the quantity
of steam used obviously includes that which is used in counter balancing
the pressure of the atmosphere.
Learners often get confused on this point, hence it may be more fully
explained as follows:
Suppose the engine piston to be blocked, in the middle of the cylinder,
and has on one side of it a pressure of 20 lbs. of steam by steam gauge,
and on the other the pressure of the atmosphere, and we might pump out
the steam, thus leaving the cylinder empty on that side of the piston.
The atmosphere would then exert a pressure of about 14-1/2 lbs. per
square inch on one side of the piston, and if we slowly admitted steam
again, it would have to get up a pressure of 14-1/2 lbs. per square inch
before the atmospheric pressure would be counterbalanced and the piston
be in equilibrium.
But the steam gauge would at this time stand at zero, and not show that
there was any steam in the cylinder, because the zero of the steam gauge
is atmospheric pressure.
When, therefore, the steam gauge showed a pressure of 20 lbs. of steam
in the cylinder, there would actually be a pressure of 34-1/2 lbs. of
steam per square inch.
The clearance line and the vacuum line must both, therefore, be marked
on the diagram when the quantity of steam used is to be computed from
the diagram, and also when the proper or theoretical expansion curve is
to be marked on the diagram.
This is clear, because in finding the expansion curve for a given volume
of steam the whole of its volume must be taken into account, and this
whole volume is represented by the area inclosed within the clearance
line, the steam line, the expansion curve, the exhaust line, and the
line of perfect vacuum, or line of no pressure.
The atmospheric line should be drawn after the diagram has been taken,
and while the indicator is hot, as the expansion of the indicator
affects the position of this line. It is drawn with the steam shut
entirely off from the indicator, whose piston therefore has atmospheric
pressure on both sides of it.
Whether the engine is condensing or non-condensing, the same amount of
steam (all other things being equal) is used, the only difference being
that in a condensing engine a greater portion of the steam is available
for driving the piston.
If the condenser produced a perfect vacuum, the whole of the steam would
be utilized in propelling the piston.
The "line of no pressure," or of perfect vacuum, is marked as far below
the atmospheric line as will represent the pressure of the atmosphere,
which is, at the sea level, about 14.7 lbs. per square inch when the
barometer stands at 29.99 inches.
THE BAROMETER.
A barometer is an instrument for denoting the pressure or weight of the
atmosphere, which it does by means of a column of mercury inclosed in a
tube, in which there is a vacuum, which may be produced as follows:
A tube having a parallel bore and closed at one end is filled with
mercury and while the finger is placed over the open end of the tube, it
is turned upside down and inverted in a cup of mercury that is open to
receive the pressure of the atmosphere.
The finger is then removed from the end of the tube and the mercury will
fall, leaving a vacuum at its upper end.
The pressure of the atmosphere on the surface of the mercury in the cup
forces the mercury up the tube, because the surface of the mercury in
the tube has no atmospheric pressure on it, the action being the same as
that already described with reference to the principles of action of a
pump.
The weight of the atmosphere is equal to the weight of that part of the
column of mercury that is above the surface of the mercury in the cup,
hence lines may be drawn at different heights representing the weight of
the atmosphere, or of any other gas, when the column of mercury stands
at the heights denoted by the respective lines.
But as mercury expands by heat, a definite degree of temperature must be
taken in marking a column, to represent the weight, this temperature
being 32° Fahrenheit.
Similarly, as the weight of the atmosphere varies, according to the
height at which it is taken from the surface of the earth, a definite
height must be taken.
The sea level is that usually taken, the mean or average atmosphere (at
that level) being 14.7 lbs. per square inch.
For higher altitudes, the mean atmospheric pressure in lbs. per square
inch may be found by multiplying the altitude or height above sea level
by .00053, and subtracting the product from 14.7.
Each pound on the square inch is represented by a height of 2.036 inches
of mercury, hence the height of a column of mercury at a temperature of
32° that will balance the mean weight of the atmosphere is 29.92 inches,
and to avoid fractions, it is usual (for purposes not requiring to be
very exact) to say that the atmospheric pressure at sea level is
represented by 30 inches of mercury.
The atmospheric pressure is also, to avoid using fractions, taken
roughly at 15 lbs. per square inch at sea level.
Each 2 inches of mercury will, under these conditions, represent 1 lb.
of pressure.
Vacuum gauges are based upon the same principles and subject to the same
variations as to altitude as mercury gauges or the barometer.
To find the absolute pressure, or pressure above zero, or a perfect
vacuum, we may add the pressure of the boiler steam gauge to that shown
by the mercury gauge or barometer.
In Fig. 3364 the line of no pressure is marked at 15 lbs. per square
inch below the atmospheric line of the diagram, the atmospheric pressure
being for convenience taken as 15 lbs. above a perfect vacuum.
The line of no pressure serves as a guide in showing the effectiveness
of the condenser, as well as for computing the volume of steam used, but
is not necessary in computing the horse power of a non-condensing
engine, because the gauge pressure has its zero marked to correspond
with the atmospheric pressure.
In computing the consumption of steam or water from the diagram,
therefore, both the clearance line and the line of no pressure must be
marked on the diagram, and lines of the diagram extended so as to
include them, thus accounting for all the steam that leaves the steam
chest from the piston stroke.
Indicator springs are varied in strength to suit the pressure of steam
they are to be used for.
The scale of the spring is the number of lbs. pressure per square inch
represented by a vertical motion of the pencil; thus, a 40 lb. spring is
one in which a pressure of steam of 40 lbs. per square inch would cause
the piston to rise an inch above the atmospheric line of the diagram.
The strength or tension of the spring is so adjusted as to cause the
diagram to be about 2-1/2 inches high, let the steam pressure be what it
may. The following are the scales of springs of the Thompson and Tabor
indicator.
THOMPSON INDICATOR.
Scale of Used for pressure above atmosphere
spring. if not more than
15 lbs. 21 lbs. per square inch.
20 " 38 " " " "
30 " 94 " " " "
40 " 90 " " " "
60 " 143 " " " "
TABOR INDICATOR.
10 lbs. 14 " " " "
12 " 20 " " " "
16 " 30 " " " "
20 " 40 " " " "
24 " 48 " " " "
30 " 60 " " " "
32 " 64 " " " "
40 " 80 " " " "
48 " 96 " " " "
50 " 100 " " " "
60 " 120 " " " "
64 " 128 " " " "
80 " 160 " " " "
A spring that is strong enough for a given pressure may be used for any
less pressure.
The height of the diagram will, however, be less, and accuracy is best
secured by having the diagram up to the limit of about 2-1/2 inches,
using a spring that is light enough to secure this result.
Diagrams of high speed engines, however, will have their lines
more regular in proportion as a stronger spring is used.
This occurs because the spring, being under more tension, is less liable
to vibration.
An indicator requires careful cleaning and oiling with the best of oil,
as the slightest undue friction seriously impairs the working of the
instrument.
Instructions upon the care of the instrument, and how to take it apart,
etc., are usually given by the makers of the indicator.
There are various methods of giving to the paper drum of the indicator a
motion coincident with that of the engine piston, but few of them give
correct results.
Reducing levers, such as shown in Fig. 3365, are constructed as follows:
[Illustration: Fig. 3365.]
Fig. 3365 represents a reducing lever with the indicators attached. A C
is a strip of pine board three or four inches wide and about one and
one-half times as long as the stroke of the engine. It is hung by a
screw or small bolt to a wooden frame attached overhead. A link C
one-third as long as the stroke is attached at one end to the lever, and
at the other end to a stud screwed into the cross head, or to an iron
clamped to the cross head by one of the nuts that adjust the gibs, or to
any part of the cross head that may be conveniently used. The lever
should stand in a vertical position when the piston is at the middle of
the stroke. The connecting link C, when at that point, should be as far
below a horizontal position as it is above it at either end of the
stroke. The cords which drive the paper drums may be attached to a screw
inserted in the lever near the point of suspension; but a better plan is
to provide a segment, A, B, the centre of which coincides with the point
of suspension, and allow the cord to pass around the circular edge. The
distance from edge to centre should bear the same proportion to the
length of the reducing lever as the desired length of diagram bears to
the length of the stroke. On an engine having a stroke of 48 inches, the
lever should be 72 inches, and the link C 16 inches in length, in which
case, to obtain a diagram 4 inches long, the radius of the segment would
be 6 inches. It is immaterial what the actual length of the diagram is,
except as it suits the operator's fancy, but 4 inches is a length that
is usually satisfactory. It may be reduced to advantage to 3 inches at
very high speeds. The cords should leave the segment in a line parallel
with the axis of the engine cylinder.
The pulleys over which they pass should incline from a vertical plane
and point to the indicators wherever they may be located. If the
indicators and the reducing lever can be placed so as to be in line with
each other, the pulleys may be dispensed with and the cords carried
directly from the segment to the instruments, a longer arc being
provided for this purpose. The arm which holds the carrier pulleys on
each indicator should be adjusted so as to point in the direction in
which the cord is received.
In all arrangements of this kind the reduced motion is not
mathematically exact, because the leverage is not constant at all points
of the stroke.
Pantagraph motions have been devised for overcoming these defects. Two
forms have been successfully used, which, if well made, well cared for,
and properly handled, reproduce the motion on the reduced scale with
perfect accuracy. They are shown in working position in Figs. 3366 and
3367.
[Illustration: Fig. 3366.]
Fig. 3366 represents the manner of attaching the pantagraph motion, or
_lazy tongs_, as it is sometimes called, when the indicators are applied
to the side of the cylinder. It works in a horizontal plane, the pivot
end being supported by a post B erected in front of the guides, and the
working end receiving motion from an iron attached to the cross head.
By adjusting the post to the proper height and at a proper distance in
front of the cross head, the cords may be carried from the cord pin C to
the indicators, without the intervention of carrier pulleys.
[Illustration: Fig. 3367.]
If the indicators are attached to the side of the cylinder, the simplest
form of pantagraph shown in Fig. 3367 may be used. The working end A
receives motion from the cross head, and the front piece B is attached
to the floor. The cord pin D is fixed in line between the pivot and the
working end, and the pulleys E, attached to the block C, guide the cords
to the indicators.
The indicator rigging that gives the best results at high speeds is a
plain reducing lever like that first described, provided at the lower
end with a slot that receives a stud, screwed into the cross head. The
length of the lever should be one and one-half times the engine stroke,
as given on the preceding page.
Whatever plan is followed, it is desirable to avoid the use of long
stretches of cord. If the motion must be carried a long distance, strips
of wood may often be arranged in their place and operated with direct
connections. Braided linen cord, a little in excess of one-sixteenth of
an inch in diameter, is a suitable material for indicator work.
To take a diagram, a blank card is stretched smoothly upon the paper
drum, the ends being held by the spring clips. The driving cord is
attached and so adjusted that the motion of the drum is central.
For convenience two diagrams, one from each end of the cylinder, may be
made on the same card, as shown in Fig. 3368.
[Illustration: Fig. 3368.]
TESTING THE EXPANSION CURVE.
The usual manner of testing the expansion curve of a diagram is to
compare it with a curve representing Mariotte's law for the expansion of
a perfect gas.
A theoretic expansion curve that will accord with Mariotte's law may be
constructed on the diagram by the following method:
The diagram, as drawn by the indicator, will have the atmospheric line
upon it, and from this as a basis we may mark in the line of no pressure
or line of perfect vacuum.
To do this we draw, beneath the atmospheric line, a line as far beneath
it as will represent the atmospheric line, on the same scale as the
spring used, in the indicator, to draw the diagram.
Suppose, for example, that a 30 lb. spring was used, and assuming the
atmospheric pressure to be 15 lbs. per inch, then the line of no
pressure would be drawn half an inch below the atmospheric line, because
15 lbs. pull on the spring would cause it to distend half an inch.
The clearance line must then be drawn in, according to directions that
have already been given.
The next thing to do is to divide the length of the diagram into any
convenient number of equal parts, by vertical lines parallel to, and
beginning at, the clearance line, as shown in Fig. 3369. These lines are
numbered as shown, ten of them being used because that is a convenient
number, but any other number would do.
We next decide at which part of the diagram its expansion curve and the
test curve shall touch, and in this example we have chosen that it shall
be at line 10.
We have now to find what pressure the length of line 10 represents on
the scale of the indicator spring, which in this case we will suppose to
be 25 lbs., the line measuring 25/30 of an inch, and a 30 lb. spring
having been used to draw the diagram. Next multiply the pressure (25
lbs.) by the number of the line (10), and divide the product (250) by
the number of each of the other lines in succession, and the quotient
will be the pressures to be represented by the lines.
For example, for line 9 we have that 250 divided by 9 gives 27.7, hence
line 9 must be long or high enough to represent a pressure of 27.7 lbs.
above a perfect vacuum, or in this case 27.7/30 of an inch.
For line 8 we have that 250 divided by 8 gives 31.25 lbs., hence line 8
must be high enough to represent a pressure of 31.25 lbs. above a
perfect vacuum.
The atmospheric line is, in this case, of no other service than to form
a guide wherefrom to mark in the line of no pressure, or of perfect
vacuum.
[Illustration: Fig. 3369.]
Now take the case of line 5, and 250 divided by 5 gives 50, hence the
height of line 5 must represent a pressure above vacuum of 50 lbs.
Having carried this out for all the lines from line 10 to line 1, we
draw in the true expansion curve, which will touch the tops of all the
lines.
[Illustration: Fig. 3370.]
Another method of drawing this curve is shown in Fig. 3370. Having drawn
the clearance line B C, and vacuum line D C, as before and chosen where
the curves shall touch (as at _a_), then draw from _a_ a perpendicular
_a_ A.
Draw line A B, parallel to the vacuum line, and at any convenient height
above or near the top of the diagram.
From A draw A C, and from _a_ draw _a_ _b_ parallel to D C, then from
its intersection with A C, erect the perpendicular _b_ _c_, locating on
A B, the theoretical point (_c_) of cut-off.
From a number of points on A B (which may be located without regard to
equally spacing them), such as E, F, G and H, draw lines to C, and also
drop perpendicular lines, as E _e_, F _f_, G _g_, H _h_.
From the intersection of E C with _b_ _c_, draw a horizontal line to
_e_. From the intersection of F C with _b_ _c_, draw a horizontal line,
and so on; and where these horizontals cut the verticals (as at _e_,
_f_, _g_, _h_) are points in the curve, which begins at _c_, and passes
through _e_, _f_, _g_, _h_, to _a_.
But this curve does not correctly represent the expansion of steam. It
would do so if the steam remained or was maintained at a uniform
temperature; hence it is called the isothermal curve, or curve of same
temperature. But in fact steam and all other elastic fluids fall in
temperature during their expansion, and rise during compression, and
this change of temperature slightly affects the pressure.
A curve in which the combined effects of volume and resulting
temperatures is represented is called the _adiabatic_ curve, or curve of
no transmission; since, if no heat is transmitted to or from the fluid
during change of volume, its sensible temperature will change according
to a fixed ratio, which will be the same for the same fluid in all
cases.
A sufficiently close approximation to the adiabatic curve to enable the
non-professional engineer to form an idea of the difference between the
two may be produced by the following process:
Taking a similar diagram to that used for the foregoing illustrations,
as in Fig. 3371. Fix on a point A near the terminal, where the total
pressure is 25 pounds. As before, this point is chosen in order that the
two curves may coincide there.
Any other point might have been chosen for the point of coincidence; but
a point in that vicinity is generally chosen, so that the result will
show the amount of power that should be obtained from the existing
terminal. This point is 3.3 inches from the clearance line, and the
volume of 25 pounds 996, that is, steam of that pressure has 996 times
the bulk of water.
Now if we divide the distance of A from the clearance line by 996, and
multiply the quotient by each of the volumes of the other pressures
indicated by similar lines, the products will be the respective lengths
of the lines measured from the clearance line; the desired curve passing
through their other ends. Thus, the quotient of the first or 25 lb.
pressure line divided by 996 is .003313; this, multiplied by 726, the
volume of 35 lbs. pressure, gives 2.4, the length of the 35 lb. pressure
line; and so on for all the rest.
The application of either of the above curves will show that some
diagrams are much more accurate than others, even though taken from
engines of the same design and quality of workmanship.
As a general rule, those from large engines will be more correct than
from small ones, and those from high more correct than from low speeds,
and in either case efficiently covering the steam pipes and jacketing
the cylinder, to prevent condensation, will improve the diagram.
The character of the imperfection in the expansion curve, shown by the
application of a test curve, is generally too high a terminal pressure
for the point of cut off, the first part of the curve being generally
the most correct, and nearly all the inaccuracy appearing in the last
half.
The usual explanation of this is, that the steam admitted during the
live steam period condenses because of having to heat the cylinder, and
that this water of condensation re-evaporates during the latter part of
the stroke when this water of condensation is at a higher temperature
than the expanded steam, and thus increases the pressure.
A leaky admission valve may generally, however, be looked for (or else
wet steam), if the expansion curve rises much during its lower half.
TO CALCULATE THE HORSE POWER FROM A DIAGRAM.
In calculating the horse power of an engine, the only assistance given
by the indicator is, that it provides a means of obtaining the average
pressure of the steam throughout the piston stroke.
There are two methods of doing this, one by means of a planimeter or
averaging instrument, and the other by means of lines called
_ordinates_.
The ordinates or lines are drawn at a right angle to the atmospheric
line, as shown in Fig. 3372, and each line is taken to represent the
average height or length of one-half of the space between itself and the
next lines.
[Illustration: Fig. 3371.]
Suppose, for example, that we require to get the area of that part of
the diagram that lies between the dotted lines in the figure, and it is
clear that the average height of this part of the diagram is represented
by the height of the full line between them.
Any number of ordinates may be used, and the greater their number the
greater the accuracy obtained. It is, however, usual to draw 10.
[Illustration: Fig. 3372.]
The end ordinates A and D, in the figure, should be only half the
distance from the ends of the diagram that they are from the next
ordinate, as will be seen when it is considered that the ordinate is in
the middle of the space it represents.
The ordinates being drawn their lengths, are added together, and the sum
so obtained is divided by the number of ordinates, which gives the
average height of the ordinates.
Suppose, then, that the average height of the ordinate is two inches,
and that the scale of the spring of the indicator that took the diagram
was 30 lbs., then the average pressure, shown by the diagram, will be 60
lbs. per square inch. Or in other words, each inch in the height of the
ordinate represents 30 lbs. pressure per square inch.
The mean effective pressure having been found, the indicated horse power
(or I. H. P. as it is given in brief) is found by multiplying together
the area of the piston (minus half the area of the piston rod when great
accuracy is required) and the travel of the piston in feet per minute,
and dividing the product by 33,000, an example having been already
explained.
It is to be observed, however, that when great accuracy is required a
diagram should be taken from each end of the cylinder, as the mean
effective pressure at one end of the cylinder may vary considerably from
that at the other.
This will be the case when a single valve is used with equal lap,
because, in this case, the point of cut off will vary on one stroke as
compared with the other, which occurs by reason of the angularity of the
connecting rod.
When cut off valves or two admission valves are used, it may occur from
improper adjustment of the valves. It occurs in all engines, because on
one side of the piston the piston rod excludes the steam from the
piston face, unless, indeed, the piston rod passes through both covers,
in which case the rod area must be subtracted from the piston area.
If the expansion curve in a diagram from a non-condensing engine should
pass below the atmospheric line, then the mean effective pressure of
that part of the card that is below the atmospheric line must be
subtracted from the mean effective pressure of that part that is above
the atmospheric line, because the part below represents back pressure or
pressure resisting the piston motion.
The planimeter affords a much quicker and more accurate method of
obtaining the average steam pressure from a diagram.
[Illustration: Fig. 3373.]
Coffin's averaging instrument or planimeter is shown in Fig. 3373. The
diagram is traced by the point O, and the register wheel gives the area
of the diagram.
A quick method of approximating the mean effective pressure (or M. E. P.
as it is called) of a diagram is to draw a line _a_ _b_, in Fig. 3374,
touching the expansion curve at _a_, and so inclined that the space _e_
is, as near as the eye can judge, equal to the space _d_. Then the line
_f_ drawn in the middle of the diagram, and measured on the scale of the
spring that was used to take the diagram, represents the mean effective
pressure, or M. E. P. of the diagram.
CALCULATING THE AMOUNT OF STEAM OR WATER USED.
The amount of water evaporated in the boiler is not accounted for by an
indicator diagram or card, and the full reasons for this are not known.
It is obvious, however, that the loss, from the steam being unduly wet
or containing water held in suspension, is not shown by the diagram, and
this amount of loss will vary with the conditions.
Thus the loss from this cause will be less in proportion as the point of
cut off occurs earlier in the stroke, because, as the water is at the
same temperature as the steam, it will, as the temperature of the steam
reduces from the expansion, evaporate more during the expansion period,
doing so to a greater extent in proportion as the cut off is early, on
account of there being a wider variation between the temperature of the
steam at the point of cut off and at the end of the stroke. On the other
hand, however, in proportion as the cut off is earlier, the
proportionate loss from condensation during the live steam period is
greater, because a greater length of the cylinder bore is cooled during
the expansion period, and it has more time to cool in.
Whatever steam is saved by the compression, from the exhaust, must be
credited to the engine in calculating the water consumption from the
indicator card or diagram, since it fills, or partly fills, the
clearance space.
In engines which vary the point of cut off, by varying the travel of the
induction or admission valve, the amount of compression is variable with
the point of cut off, and increases in proportion as the live steam
period diminishes; hence to find the actual water or steam consumption
per horse power per hour, diagrams would require to be taken
continuously from both ends of the cylinder during the hour; assuming,
however, that the point of cut off remains the same, that the amount of
compression is constant, that the steam is saturated, and neither wet
nor superheated, steam and the water consumption may be computed from
the diagram as follows:
WATER CONSUMPTION CALCULATIONS.--An engine driven by water instead of
steam, at a pressure of 1 lb. per square inch, would require 859.375
lbs. per horse power per hour; the water being of such temperature and
density that 1 cubic foot would weigh 62-1/2 lbs. If the mean pressure
were more than 1 lb., the consumption would be proportionately less;
and, if steam were used, the consumption would be as much less as the
volume of steam used was greater than an equal weight of water. Hence,
if we divide the number 859.375 by the mean effective pressure and by
the volume of the terminal pressure, the result will be the theoretical
rate of water consumption in pounds per I. H. P. per hour.
[Illustration: Fig. 3374.]
For the terminal pressure we may take the pressure at any convenient
point in the expansion curve near the terminal, as at A, Fig. 3375, in
which case the result found must be diminished in the proportion that
the portion of stroke remaining to be made, A _a_, bears to the whole
length of the stroke _a_ _b_; and it may also be diminished by the
proportion of stroke remaining to be made after the pressure at A has
been reached in the compression curve at B. In other words, A B is the
portion of the stroke A B, during which steam at the pressure at A is
being consumed. Hence the result obtained by the above rule is
multiplied by A B, and the product divided by _a_ _b_.
To illustrate, suppose the mean effective pressure of the diagram to be
37.6 lbs., and the pressure at A, 25 lbs., of which the volume is 996.
Then 859.375/(37.6 × 996) = 22.94 pounds water per I. H. P. per hour,
the rate that would be due to using an entire cylinder full of steam at
25 pounds pressure every stroke. But as the period of consumption is
represented by B A (_b_ _a_ being the stroke), the following correction
is required:
(22.94 × 3.03)/3.45" = 20.15; 3.03 inches being the portion B A, and
3.45 inches being the whole length _b_, _a_. This correction allows for
the effects of clearance as well as compression, since, if more
clearance had existed, the pressure at A would not have been reached
till later in the stroke, and the consumption line B A would have been
longer.
[Illustration: Fig. 3375.]
But such a rate can never be realized in practice. Under the best
attainable conditions, such as about the load indicated on the diagram,
or more on a large engine with steam tight valves and piston, and well
protected cylinder and pipes, the unindicated loss will seldom be less
than 10 per cent., and it will be increased by departure from any of the
above conditions to almost any extent. It will increase at an
accelerating ratio as the load is diminished, so that such calculations
applied to light load diagrams would be deceptive and misleading; in
fact, they have but little practical value, except when made for
comparison with tests of actual consumption for the purpose of
determining the amount of loss under certain given conditions.
DEFECTIVE DIAGRAMS.
In seeking the causes that may produce a defective diagram, the
following points should be remembered:
The indicator must be kept in perfect order, thoroughly clean and well
lubricated, so that its parts will move freely. It should always be
cleaned throughout after using.
The motion of the indicator drum should be an exact copy, on a reduced
scale, of that of the piston at every point in the stroke.
The steam pipes from the cylinder to the indicator, if any are used,
must be large enough to give a free and full pressure of steam, and care
must be taken that the water of condensation does not obstruct them or
enter the indicator.
The cord should be as strong as possible, or if long, fine wire should
be substituted.
The pencil should be held to the card with just sufficient force to make
a fine line with a sharp pencil.
The diagram should be as long as the atmospheric line, any difference in
this respect showing unequal tension of the cord, probably from unequal
pressure of the pencil to the paper or card.
A fall in the steam line could arise from too small a steam pipe, and
this could be tested by a diagram taken from the steam chest. It could
also occur from too small a steam port or an obstructed steam passage as
well as from a leaky piston.
An expansion curve that is higher than it should be may arise from a
leaky valve, letting in steam after the cut off had occurred, or if at
the later point of expansion curve, it may be caused by the steam being
wet or containing water, which evaporates as the temperature falls from
the expansion.
An expansion curve that is lower than it should be may be caused by a
leaky piston, by a valve that leaks on the exhaust side but not on the
steam side, or if the exhaust valve is separate from the steam valve, it
may leak while the steam valve is tight.
It may also be caused by the cylinder being unduly cooled, as from water
accumulating in a steam jacket.
There are many defects in the adjustment of the valve gear, or of
improper proportion in the parts, that may be clearly shown by a
diagram, while there are defects which might exist and that would not be
shown on the diagram.
It is possible, for example, that a steam valve and the engine piston
may both leak to the same amount, and as a result the expansion curve
may appear correct and not show the leak.
Insufficient valve lead would be shown by the piston moving a certain
portion of its stroke before the steam line attained its greatest height
in Fig. 3376, in which from A upwards, the admission line, instead of
rising vertically, is at an angle to the right, showing that the piston
had moved a certain portion of its stroke before full pressure of steam
was admitted.
That too small a steam port or steam pipe did not cause this defect may
be known from the following reasoning:
The port opened when the pencil was at A, which shows that the valve had
lead. At this time the piston was near the dead centre and moving slower
than it was when the pressure reached its highest point on the diagram,
and since the steam line is fairly parallel with the atmospheric line,
it shows that the port was large enough to maintain the pressure when
the piston was travelling fast, and therefore ample when the piston was
moving slow.
The remedy in this case is to set the eccentric back.
With less compression the point A would be lower.
Excessive lead is shown in Fig. 3377 by the loop at A, where the
compression curve extends up to the steam line, and the lead carries the
admission line above it, because of the piston moving against the
incoming steam.
To mark in the theoretical compression curve, the vacuum line and the
clearance line must be drawn in as in the figure, and ordinates must be
drawn.
According to the diagram, in Fig. 3377, the compression is clearly
defined to have begun at C, and at that time the space filled by steam
is represented by the distance from C to the clearance line. The
pressure above vacuum (or total pressure) of the steam in the cylinder
when the compression began is represented by the length or height of the
dotted line 1.
Now suppose the piston to have moved from the point C, where compression
began, to line 2 (which is midway between line 1 and the clearance
line), and as the compressed steam occupies one-half the space it did
when the piston was at C, therefore the steam pressure will be doubled,
and line 2 may be drawn making it twice as high as line 1.
[Illustration: Fig. 3376.]
[Illustration: Fig. 3377.]
Line 2 is now the starting point for getting the next ordinate, and line
3, must be marked midway between line 2 and the clearance line, and
twice as high as line 2, because at line 3 the steam will occupy half
the space it did at line 2. Line 4 is obviously midway between line 3
and the clearance line.
Through the tops of these lines we may draw the theoretical compression
curve, which is shown dotted in.
To find the amount of steam actually saved by the compression, we have
to consider the compression curve only, beginning at the point of the
diagram where it is considered that the compression actually began, and
ending where the compression line joins the admission line, and the
horizontal distance between these two points represents the length of
the cylinder bore filled by the compression.
To find the average amount to which the steam is compressed, we must
draw within this length of the diagram, and within the boundaries of the
compression curve, and the line of no pressure ordinates corresponds to
those given for finding the average shown pressure of a diagram, as
explained with reference to that subject, taking care to have the end
ordinates spaced half as wide as the intermediate ones, as explained
with reference to Fig. 3372.
CHAPTER XLI.--AUTOMATIC CUT OFF ENGINES.
An automatic cut off engine is one in which the valve gear is so acted
upon by the governor as to keep the speed of the engine uniform under
variations of the load the engine drives, and notwithstanding variations
in the boiler pressure. This it accomplishes by varying the point in the
piston stroke at which the live steam is cut off. This is economical
because it enables the engine to use the steam more expansively than is
possible with engines having throttling governors, which govern the
engine speed by wire drawing the steam.
There are two principal forms of automatic cut off engines, first, those
in which the steam valve spindle or rod is released from the parts that
move it to open for admission, while dash pots, weights, or springs
close the valve to effect the cut off; and second, those in which the
travel of the valve is varied so as to alter the point of cut off.
The first usually employ fly ball governors which actuate cams or stops
to trip the valves for the steam cylinders. The second usually employ
wheel governors or speed regulators, as they are sometimes termed.
The distinctive features in the action of the first, of which the
Corliss engine is the most important, is that as two admission and two
exhaust valves are used, therefore the amount of the valve lead, the
point of exhaust and amount of the compression remain the same at
whatever point in the piston stroke the cut off may occur; whereas in
the second, the lead increases, the cut off occurs earlier, and the
compression increases in proportion as the cut off occurs earlier in the
piston stroke. In this class of engine the steam valve travels as
quickly when opening the steam port for a short and early period of cut
off as it does for a late one, hence the amount of steam port opening is
as full, with reference to the piston motion, for an early as it is for
a late point of cut off. In other words, there is the same amount of
steam port opening for the first, second, third, and fourth inch of
piston motion, let the point of cut off occur at whatever point in the
piston motion it may. In engines which vary the point of cut off by
reducing the travel of the slide valve, this is accomplished by using
double ported valves or griddle valves.
[Illustration: Fig. 3378.]
Fig. 3378 represents the arrangement of the valves in a Corliss engine,
V and V^{1} being the steam valves and V^{2} and V^{3} the exhaust
valves. These valves, it will be seen, extend crossways of the cylinder
and are circular. In the figure the valves are shown in the position
they would occupy when the piston was at the crank end of the cylinder,
as in the figure.
The principles of a Corliss valve gear will be understood from the
following, which is derived from a book by the author of this work, and
entitled _Modern Steam Engines_.
In 3379 and 3380 the valve gear (which is the distinctive feature of the
engine) is represented with the parts in the position they occupy when
the cut off occurs at half stroke, the piston having moved from the head
end of the cylinder. In Figs. 3381 and 3382 the parts are shown in
position with the crank on the dead centre and the piston at the crank
end of the cylinder, valve _v_ having opened its port to the amount of
the lead.
Referring to Fig. 3379, motion from the eccentric is imparted by the rod
M to the wrist plate Y, to which are connected the rods C, C´, for
operating the admission valves, whose shafts are seen at S, S´, and the
rods F, F´, for operating the exhaust valves, whose shafts are seen at
T, T´.
The mechanism for the steam or admission valves may be divided into
three elements: first, that for operating the valve to open the port for
admission; second, that for closing the valve to effect the cut off; and
third, that which determines the point in the stroke at which the cut
off shall occur.
The first consists of the rod M, wrist plate Y, and the rods C and C´,
which operate the bell cranks _r_ _r_, _r´_ _r´_ which are fast on the
valve shafts S, S´. Upon the ends of bell cranks _r_ _r_, _r´_ _r´_, are
pivoted latch links _u_, _u´_, which have in them a recess for the latch
blocks, of which one is seen at _e_ (the rod R´ and its connection with
the valve stem being shown broken away to expose _e_ to view). During
the admission the latch block abuts against the end _y_ of the recess
_w_ and is tripped therefrom by the cam _n´_. The ends of arms _g_ of
the latch links abut against the hub of the arms _d_, _d´_ upon which
are cams _n_, _n´_, and at _a_, _a´_ are springs for keeping the ends
_g_ of latch links _u_, _u´_ against the hubs and cams of _d_, _d´_.
Referring now to the valve mechanism at the head end only, suppose the
piston to be at the head end of the cylinder, and latch block _e_ will
be seated in the recess provided in _a_ to receive it, and as the bell
crank moves, the latch block will be raised by the latch link, which is
carried by a crank arm corresponding to that seen at _x_ at the crank
end of the cylinder, and as this crank arm is fast upon the valve
spindle, the lifting of _e_ will open the valve for admission. As soon,
however, as the end _g_ of the latch link meets the cam _n´_, the latch
link will be moved so that the end _y_ of its recess will leave contact
with the latch block _e_ and the dash pot will cause rod R´ to descend
instantaneously and close the valve, thus effecting the cut off.
The period of admission, therefore, is determined by the amount of
motion the latch link _u´_ is permitted to have before its end _g_ meets
the cam _n´_, which trips the latch link, and therefore frees _e_ from
the latch link recess.
[Illustration: Fig. 3379.]
The point at which the cut off will occur, therefore, is determined by
the position of the cam _n´_, because if _n´_ is out of the way, the end
_g_ of the latch link will not meet it, the latch link will not
disengage from the latch block _e_, and the cut off would be effected by
the lap of the valve, and independently of the dash pot. As in Fig. 3379
the parts are shown in the positions they occupy at the instant the cut
off is to occur, therefore the cam _n´_ has just tripped the latch link,
and the end of _e_ has just left contact with the end _y_ of the recess
_w_ in the latch link _u´_.
The point in the stroke at which the tripping of _u´_ from _e_ will
occur and effect the cut off is determined by the governor, because _d´_
is connected to the governor through the rod G´. In proportion as the
governor balls rise, _d´_ is moved from left to right, and the end of
cam _n´_ meets _g_ earlier, or, vice versa, in proportion as the
governor balls fall, the arm _d´_ is moved to the left, _g_ will meet
the end of cam _n´_ later, and the point of cut off will be prolonged.
[Illustration: _VOL. II._ =THE CORLISS VALVE GEAR.= _PLATE XXXIV._
Fig. 3381.]
We now come to the means employed to close the valve quickly and without
shock when the latch block is released from the latch link. Referring
then to the crank end of the cylinder, the latch block for that valve is
carried upon arm _x_, to which is attached the rod R from the dash pot
piston (the arm corresponding to _x_, but at the head end being shown
removed to expose the latch block to view). We may now turn again to the
head end of the cylinder, rod R´ corresponding to rod R at the other
end, and it is seen that R´ connects to a dash pot piston _p´_ having a
stepped diameter, the lower half fitting into bore H´, and the upper
half fitting into a bore H. The piston _p´_ fits the bore H´ and fills
it when the rod R´ is at the bottom of the stroke, hence as _p´_ is
raised there is a vacuum in H that acts to cause _p´_, and therefore R´
and _x_, to fall quickly and close the valve the instant the latch block
is released from the latch link. To prevent the descent of rod R´ and
piston _p´_ from ending in a blow, a cushion of air is given in H by the
following construction:
[Illustration: Fig. 3380.]
At S and S´ are valves, threaded to screw and unscrew, the ends forming
a valve for a seat entering H.
As the rod R´ and its piston _p´_ descend, the air in H finds exit
through a hole at _h_ until that hole is closed by the piston _p´_
covering it, after which the remaining air in H can only find exit
through the opening left by the end of the valve S´, and this amount of
opening is so regulated by the adjustment of S´ that a certain amount of
air cushion is given, which prevents _p´_ from coming to rest with a
blow. The head of valve S´ is milled or knurled, and a spring _t´_ fits,
at its end, into the milled indentation, thus holding it in its adjusted
position. The under surface of the upper part of _p´_ is covered by a
leather disc, while the part that fits in H´ is kept air-tight by a
leather-cupped packing.
The connection of the cam arms _d_ and _d´_ with the governor is shown
in Figs. 3381 and 3382, in which the parts are shown in the position
they would occupy when the crank is on the dead centre and the piston at
the crank end of the cylinder. The rod G´ connects the cam arm _d´_
with the upper end of lever A, which is connected to the governor and
vibrates on its centre as the governor acts upon it.
[Illustration: Fig. 3382.]
Now suppose the speed to begin to diminish, and the governor balls to
fall, and the direction in which A will move will be for its lower end
to move to the right, thus moving _d_ to the right and carrying its cam
away from the end of the latch link, which will therefore continue to
open the port for a longer period of admission. Or, referring to Fig.
3381, it is plain that, if the governor balls were to lower from a
reduced governor speed, G´ would move to the left and cam _n´_ would be
moved away from contact with the end _g_ of the catch link, which, not
being tripped, the admission would continue. On the other hand, suppose
the governor balls to rise from an increase of governor speed, and _d´_
(Fig. 3379) would be moved to the right, and the cam _n´_ meeting _g_
earlier, correspondingly hastening the cut off.
The governor is driven by a belt from a pulley on the crank shaft to the
pulley W, Fig. 3381, whose shaft conveys motion to the governor spindle
through the medium of a pair of bevel pinions in which _v_ represents
(referring again to Fig. 3378) the steam or admission valve for the
crank end port, and _v_^{1} that for the head end port, while _v_^{2} is
the exhaust valve for the crank end, and _v_^{2} that for the head end
of the cylinder. All four valves are shown in the positions they would
occupy when the crank was on the dead centre and the piston at the crank
end of the cylinder, hence the valve positions shown correspond to the
positions the parts of the valve motion occupy in Fig. 3381.
The faces of the valves are obviously arcs of circles of which the axes
of the shafts _s_, _s´_ are the respective centres. Valve _v_ has opened
its port to the amount of the lead, which in this class of engine varies
usually from 1/32 to about 1/16 inch. As separate exhaust valves are
employed, the point of release, and (as the same valve edge that effects
the release also effects the compression) therefore that of the
compression, may be regulated at will by adjusting the lengths of the
rods F, F´, Fig. 3379, which have at one end a right and at the other a
left hand screw, so that by turning back the check nuts and then
revolving the rods their lengths will be altered.
Similarly the amount of admission lead may be adjusted by an adjustment
of the lengths of rods C, C´, which also have right and left hand
screws. Referring now to the admission valve _v_, it is seen that its
operating rod C is at a right angle to bell crank _r_, _r_, hence the
amount of valve motion will not be diminished to any appreciable extent
by reason of the wrist plate end of rod C moving in an arc of a circle,
and the point of attachment of rod C to the wrist plate is such that,
during the admission, the valve practically gives as quick an opening as
though rod C continued at a right angle to _r_. But, if we turn to valve
_v´_, which has closed its port and covers it to the amount of the lap,
we find that bell crank _r´_ and its operating rod C´ are in such
positions with relation to the wrist plate, that the motion of the
latter will have but little effect in moving the bell crank _r´_. This
is an especial feature of the Corliss valve motion and is of importance
for the following reasons:
The lap of the valve (which corresponds to the lap of a plain D slide
valve) is usually, in this class of engine, such as to cut off the steam
at about 7/8 stroke, but the adjustment of the cam position is usually
so made that, from the action of the governor, the latest point of cut
off will occur when the piston has made 5/8 of its stroke, the range of
cut off being from this to an admission equal to the amount of the lead.
As the eccentric is fixed upon the shaft, the speed at which the valve
opens the port for the admission is the same for all corresponding
piston positions. Thus suppose the piston has moved an inch from the end
of the stroke, and the valve speed will be the same, whether the cut off
in that stroke is to occur at quarter stroke or half stroke, and as the
valve continues to open the port until it is tripped, therefore, at the
moment it is tripped, the direction of valve motion must be suddenly
reversed.
As the duty of its reversal falls upon the dash pot, it is desirable to
make this duty as light as possible, which is accomplished by the wrist
motion, which acts to reduce the valve motion after the port is opened a
certain amount for the admission.
We have, therefore, that during the earlier part of the admission, the
port opening is quick because of the eccentric throw being a maximum,
while during the later part of the port opening, this rapid motion is
offset or modified by the wrist motion, thus lessening the duty of the
dash pot and enabling it to promptly close the valve.
The range of governor action, so far as the governor itself is
concerned, is obviously a constant amount, because a certain amount of
rise and fall of the governor balls will move the cams a given amount.
But the range of cut off may be varied as follows: At Z, Z´, are
adjustment nuts, by means of which the lengths of rods G, G´ may be
varied.
Lengthening rod G obviously moves arm _d_ and its cam _n_ further from
the end of the latch link _u_, and therefore prolongs the admission
period.
Shortening the rod G´ causes cam _n´_ to move around and away from the
leg _g_ of the latch link, and prolongs the admission.
The adjustment of the lengths of G and G´ may therefore be employed for
two purposes; first, to prolong the point of cut off, and maintain the
speed when the engine is overloaded, or to hasten the point of cut off
for a given engine speed, and thus adjust the engine for a lighter load.
HIGH SPEED AUTOMATIC CUT OFF ENGINES.
What are termed high speed engines are those whose pistons run at a
velocity of more than about 600 feet per minute, some making as high as
800 or 900 feet in regular work. High speed engines are usually provided
with an automatic cut off, and a majority of them vary the point of cut
off, by means of shifting the eccentric across the shaft, so as to
reduce the eccentric throw, and therefore the valve travel. This causes
the valve to cut off the steam earlier.
The eccentric, instead of being fixed upon the crank shaft, has an
elongated bore, and is hung on an arm that is pivoted at its other end
after the manner of a pendulum. This arm is called the eccentric hanger.
A wheel governor is usually employed to shift the eccentric across the
shaft. In some cases, however, two valves are employed, one effecting
the admission, the release, and the compression, and the other the cut
off.
When two valves are employed, the lead, the point of cut off, the point
of release, and the point of compression may be maintained equal for all
points of cut off; whereas, when a single valve is employed, the lead,
the point of release, and the compression will vary with the point of
cut off, or, in other words, will be different for every different point
of cut off.
The general principles upon which a wheel governor is constructed is,
that two weights or weighted levers in moving outwards from the engine
shaft, from the action of centrifugal force, move or rather shift the
eccentric across the shaft, reducing its throw, and therefore by
reducing the travel of the valve hasten the point of cut off and reduce
the power of the engine.
In the governor of the Buckeye engine, the centrifugal force may be
varied by increasing or diminishing the distance of the weights from the
pivots of the arms on which they swing.
[Illustration: Fig. 3382_a_.]
This is shown in Fig. 3382_a_, in which it is seen that the weights A
are adjustable along the arms _a_, _a_. The points of attachment _d_,
_d_ of the springs to the weight arms are also adjustable.
When reversing is done, by shifting the eccentric across the shaft, the
lead cannot be kept equal, but will, if the eccentric is swung from a
pivot that is on the line of centres, when the crank is on a dead
centre, be greater at the head end than at the crank end of the
cylinder. The discrepancy may, however, be equalized by swinging the
eccentric from a pivot that is not on the line of centres at a time the
crank is on a dead centre.
But this equalization will only exist at some one point in the
eccentric position, or in other words, if the eccentric is shifted
across the crank shaft, simply to reverse the engine, and not to vary
the point of cut-off, it will naturally be moved, in reversing the
engine across the shaft, to a given and constant amount, and in this
case, the pivot on which its hanger is hung may be so located with
reference to the line of centres and the crank (the latter being on a
dead centre when the point of suspension of the eccentric hanger is
found) that the lead is equal for both the backward and forward gears.
But if the eccentric is shifted across the shaft to vary the point of
cut off as well as to reverse the direction of engine revolution, the
lead cannot be kept equal.
It is better, in this case, to so locate the point of eccentric hanger
suspension as to let the lead be the most at the head end cylinder port,
because the piston travels fastest at that end of the cylinder, and
therefore requires more lead, in order to cushion the piston.
[Illustration: Fig. 3383.]
A construction for shifting the eccentric across the shaft is shown in
Fig. 3383, in which D, D is a disc, having at _b_ a pivot for the
eccentric hanger. The amount the throw line of the eccentric must be
shifted to reverse from full gear forwards to full gear backwards is
from the line _b_ _x_ to line _b_ _x´_, and the shifting is done by two
racks F and J, having teeth at an angle of 45° to their lengths. F is
fast to the eccentric, and J is carried in a sleeve that slides along
the shaft, and sliding it moves the eccentric across the shaft by reason
of the teeth of one rack being at a right angle to those of the other.
It is obvious that the eccentric may be moved around the shaft in place
of across it, the distance its throw line requires to be moved being the
same in either case.
To shift an eccentric so as to reverse the direction of engine
revolution, all that is necessary is to place the crank on either dead
centre and measure the amount of valve lead. Then loosen the eccentric
from the crank shaft, and while the crank is stationary, move it around
upon the shaft until it has opened the port full, and nearly closed it
again, leaving it open to the same amount as it was before the eccentric
was moved, or in other words, open to the amount of the lead.
[Illustration: Fig. 3384.]
Fig. 3384 represents a side elevation of a high speed wheel governor
engine, designed and constructed by the Straight Line Engine Company of
Syracuse, New York, the construction of the governor being shown in Fig.
3385, in which R is the eccentric rod, the eccentric being carried in a
lever strap pivoted at A, and connected at B to two links C and D, the
former of which connects to the spring E, and the latter to the weighted
lever F. The centrifugal force generated by the weighted end of F
endeavors to move the eccentric inwards, and thus reduce its throw,
which reduces the valve travel and hastens the point of cut off.
On the other hand, the tension of the spring E acts to move the
eccentric in the opposite direction, and maintain the full throw of the
eccentric and maximum point of cut off. These two forces are so
calculated in the design and proportion of the parts that under a
maximum load the engine will run at its proper speed, while, if the
load decreases, the action of F will hasten the point of cut off enough
to allow for the decreased engine load, and thus keep the engine still
going at the same speed.
[Illustration: Fig. 3385.]
Other novel and interesting details in the construction of this engine
are as follows:
The two arms forming the frame are cast with and run in straight lines
from the cylinder to the two main bearings, and rest upon these
self-adjusting points of support.
There are two fly wheels, both between the main bearings, and one of
which carries the governor so that the centre of the valve is brought in
line with the centre of the eccentric.
[Illustration: Fig. 3386.]
In order to simplify the explanation, the mechanism has been separated
into three separate sections. Figs. 3386 and 3387 show such of the
details of the parts between the cylinder and crank as are peculiar to
this engine. The cross head is of the slipper guide style, and the
illustration, Fig. 3386, shows the simple method adopted for adjusting
the guide to the proper height to maintain the alignment. Another
feature peculiar to the straight line not mentioned above, that of
making the cross head pin fast in the connecting rod, is used in this
engine also, but in a somewhat different form. As will be seen by Fig.
3387, the pin is made much larger, and this allows of its being made of
"steel casting" and cast hollow with cross bars at each end for
centring. These pins are held in the rod by a binding screw which
catches in a groove that is milled around one-fourth of its
circumference. After the pin is placed in the rod and the binding bolt
is inserted, the pin is prevented from working out endwise, and the
binding bolt prevents it from turning; but when the binding bolt is
slackened, the pin can be rotated one-fourth of a revolution. The scheme
is as follows: After running the engine for a while, the engineer is
instructed to slack the binding bolt, give the pin a quarter turn and
bind it fast. By repeating this, the pin can be kept more nearly round,
probably, than by any other plan. By referring again to Fig. 3386, it
will be seen that the plan for taking up the wear in the cross head pin
bearings is simply that of setting up the common half box, and the
endurance of the arrangement, with the hardened and ground steel pin
running in babbitt lined boxes of double the ordinary size and length,
must be satisfactory.
[Illustration: Fig. 3387.]
The drop oil cups for lubricating the cross head pin are located so as
to have the drop "picked" off just as the cross head completes its
stroke at the cylinder end, and while it is travelling at its slowest
speed. The oil, as it leaves the wearing surfaces of the pin, is
conveyed to the lower slide.
[Illustration: Fig. 3388.]
[Illustration: Fig. 3389.]
Figs. 3388 and 3389 show the parts that connect the eccentric with the
valve. The method of connecting the rod to the eccentric strap is
convenient. The lower joint in the eccentric strap is set up tight,
metal to metal, and the upper joint left open 1/8 of an inch.
STEAM FIRE ENGINE.
In a steam fire engine the prime requisites are rapidity of getting up
steam and efficiency with lightness, economy of fuel being a secondary
consideration.
Fig. 3390 is a general view of a steam fire engine constructed by the
Clapp & Jones Manufacturing Company.
Fig. 3390_a_ is a longitudinal section through the boiler and one steam
cylinder and pump.
The construction of the boiler is shown in Figs. 3390_a_ and 3391, the
former being a vertical section of the engine and boiler bearing the
steam pipe and exhaust pipe shown in place, and one of the draught tubes
shown in section, and the latter a vertical central section.
The outside shell is represented at _a´´_, _a´´_. This shell extends the
whole length of the boiler. The fire box sheet _b´´_, _b_ is less in
length, extending only to the lower tube sheet.
The lower tube sheet C´´ is perforated by all the tubes; the heavy lines
showing the coil tubes in fire box, the others are smoke tubes. The
upper tube sheet _d_ has holes only for the smoke tubes. The smoke or
draught tubes are shown at _e´´_, _e´´_, _e´´_; these also answer the
important purposes of drying and superheating the steam.
F´´, F´´, F´´ are the sectional coil tubes, the main feature of this
boiler. They are in the form of a spiral coil, the spiral bend being
enough to leave room for five others of the same size between, so that
there are six of these coils in each circular row. The number of rows is
determined by the size of the boiler and the amount of steam required.
Each coil is connected with the lower tube sheet by screw joints, all
right hand, that require no fibrous or elastic packing, an angle elbow
being used to get the short bend at the end. The tubes then make about
one turn around the fire box, and are joined to the side sheet of the
same, with the same union used at its upper end, which makes a joint
that never gets loose from any kind of work it may be subjected to.
These unions or couplings are made of different kinds of metal, and put
together so that no two pieces of iron come in contact to corrode and
stick together; and should it, from any cause whatever, become necessary
to take these coils out, it can be done, and the same tubes replaced
without destroying any part of them, or damaging any piece so that it
could not be used again.
G´´, G´´ is the ornamental dome or covering for the upper end; _g´´_,
_g´´_ is the smoke bonnet and pipes for concentrating the hot escaping
products of combustion for the purpose of making a draught of air
through the fuel. H´´ are grate bars, and I´´ fire door. J´´, J´´ is the
water line. The height has been determined by experiment, yet should be
varied a little to get the best drying effect of the coal. A coal that
makes a flame would call for a higher range of the water line, while
coal that produces heat without the flame would call for a lower range;
this the engineer will soon find. The working of the boiler is as
follows: The fire being started in the fire box, as soon as the water in
the coils begins to heat circulation commences from natural causes (nor
is it at any time necessary to use a hand pump or any other artificial
means for keeping it up), the heated water passing up in the steam drum,
and the colder water from the leg and drum taking its place, as is shown
by the arrows in the leg, till the whole is heated to the steam making
temperature. At this point steam pressure begins to show, which goes up
very fast, as the water is all so near the steam temperature. Of course,
it is better to carry the water at about the height shown, as a uniform
pressure of steam is easier maintained, which is always desirable; yet
the limit of safety is not reached till the water is nearly all out, or
so long as it is not below the connection of the coils in the leg; and
even at this point the only danger is in the damage to the coils from
the heat when there is no water to protect them.
[Illustration: _VOL. II._ =STEAM FIRE ENGINE.= _PLATE XXXV._
Fig. 3390_a_.]
[Illustration: Fig. 3390.]
[Illustration: Fig. 3391.]
In Fig. 3391_a_, one engine and pump is shown in side elevation, and the
other in section, the cranks being at a right angle, one to the other. A
yoke from the piston rod spans the crank, so that the steam and pump
pistons are in line and directly connected. From the lower end of this
yoke, a rod connects to the crank shaft upon which are the two fly
wheels and the eccentrics for the steam valves.
It will be seen in the longitudinal section, Fig. 3390_a_, that the
steam valve face is a segment of a circle and therefore answers, so far
as the distribution of the steam is concerned, to a simple D slide
valve, which exhausts through the pipes _m_, _p_. The steam pipe _n_
enters the bottom of the steam chest at _n´_.
The two main pumps _a_ are made in one piece, entirely of composition;
one of them is shown in section. The piston is a solid piece of brass,
as well as the cylinder in which it works, but are made of different
composition, one hard, the other soft, to prevent cutting. The valves
are of India rubber; the discharge valve is a ring, one for each end of
the pump, as shown at _b_, Fig. 3391_a_. One is shown open, while the
other is closed. They are held in place by grooved rings of brass; these
rings fit in grooves in the rubber, which, when they are put in the
pump, and their set screws are in, with their points in the grooves in
the brass rings spoken of above, the discharge valves are complete for
work.
The suction valves are shown at K on Fig. 3391_a_, and will be easily
understood. They are of a design for this special use and place, which
is around the pump cylinder in a circular chamber. The water ways
covered by these valves are long and narrow, one valve covering two of
these openings, they being held in place by two studs that go through
the centre part of the valve, a wire going through these studs, and
close to the back of the valve which keeps it up to the seat, the only
spring to either of these valves being the elasticity of the rubber. The
opening and connection D, D is the inlet to the pump, and where the
suction hose goes on, there being a pipe or chamber with branches for
the two air chambers, and at each end is a discharge gate and a
connection for the leading hose. The part _d_ is the feed pump for the
boiler supply, _e_ is the air chamber on the pipe that leads to the
boiler to ease off the shocks caused by the plunger striking the water,
when the pump does not fill. It is drawn broken off to show the upper
part of the pump barrel and stuffing box. The pipe _f_ is the feed water
pipe from the pump to boiler, shown from different points in Figs.
3390_a_ and 3391_a_. _g_ is what we call the suction pipe to the feed
pump. It connects to the main pump in the discharge part of it.
A piece of hose pipe connects to the boiler at a point just above the
water line, so that hot water or steam (according to the height of the
water in the boiler) may be applied to any part that may have become
frozen.
[Illustration: Fig. 3391_a_.]
Heaters are almost universally used in connection with steam fire
engines to keep the water hot, and in many cases to keep a few pounds
pressure to shorten the time of going to work should the fire be close
at hand. This boiler has an advantage for this kind of heating; the
circulation is so perfect and free that all the water in it is heated
alike; so when the fire is lighted the steam starts immediately up,
instead of having to wait till some cold water has been heated that had
not been reached by the very limited circulation in them, there being
some parts that the circulation produced by the heater does not reach,
leaving, of course, this water cold.
The arrows K´´ (Fig. 3391), show the direction of the circulation when
working with fire in the fire box; those marked L´´ show the direction
of it when on the heater which is directly opposite.
The outside pipe connected at about the water line is the outlet from
the heater, and the inlet to the boiler, which carries the heated water
over the crown sheet, where, as it gets cooler, it enters the coils,
descends into the leg, and from there to the pipe near the bottom of the
boiler; this pipe leads to the heater, so that the water is kept moving
just in proportion to the heat given it; any kind of a heater can be
used with the same result.
CHAPTER XLII.--MARINE ENGINES.
Marine engines are made in the following forms:
1. With a single or with two cylinders receiving live steam from the
boilers, and exhausting into the atmosphere. These are termed high
pressure engines, let the steam pressure be what it may. They are also,
and more properly, termed non-condensing engines.
[Illustration: Fig. 3392.]
In the small sizes, such as are used for launch engines, it is simply a
non-condensing engine, with a link motion for varying the point of cut
off as well as for reversing purposes. Fig. 3392 represents an engine of
this class constructed by Chas. P. Willard & Co.
The cylinder is what is called "inverted," meaning that it is above the
crank shaft.
The slide spindle or valve rod passes through a guide and connects
direct to the link block or die, as it is sometimes called.
The thrust block is provided in the bearing of the crank shaft, and
consists, as seen in the sectional view, of a series of collars on the
crank shaft bearing.
2. The addition to each high pressure cylinder of a low pressure
cylinder constitutes a compound engine, and if the engine has also a
condenser, it is a compound condensing engine, an example being shown in
Fig. 3392_a_, which represents an engine in which the link motions are
employed to vary the points of cut off of both cylinders, as well as to
reverse the engine. The engine being small, the power required to move
the links is small enough to permit of their operation by hand, by means
of the hand lever L, which is secured to its adjusted position on the
sector T by the small lever nut shown on the side of the lever. The
lever L operates a shaft D which shifts both link motions. The air and
circulating pumps are at the back of the condenser, being operated from
the beams B, B, each beam connecting to rods J which connect to rod _c_,
which drives the air and circulating pumps.
The steam from the high pressure cylinder exhausts into a receiver or
chamber between the two cylinders, and from which the low pressure
cylinder receives its steam.
[Illustration: Fig. 3392_a_.]
[Illustration: Fig. 3395.]
[Illustration: Fig. 3396.]
The exhaust from the low pressure cylinder passes into the condenser,
where it is condensed, leaving a partial vacuum on the exhaust side of
the low pressure piston.
Figs. 3393 and 3394 show the arrangement of the pumps on a pair of
compound engines for a dredger. The steam from the low pressure cylinder
passes into the body of the condenser with which the air pump is in
communication, as shown in the end elevation. At _a_ is the foot valve
of the condenser. The piston of the air pump has a similar valve, and at
_e_ is the delivery valve.
The circulating pump is shown in the back elevation (Fig. 3394), being a
piston pump which forces the water through the tubes of the condenser.
There are two principal methods of compounding, in one of which the two
cylinders are placed one above the other, with their axes in line, and
both pistons connecting to the same crank, while in the other the
cylinders are side by side, and each connects to its own crank, the two
cranks usually being at a right angle.
When one cylinder is placed above the other, as in Fig. 3395, R being
the high pressure and S the low pressure piston, no receiver is
employed, the steam passing direct from the high pressure cylinder
through the pipe P to the low pressure steam chest _c_. The high
pressure steam valve V and the low pressure valve V are on the same
stem, a cut off valve V´ being provided for the high pressure cylinder.
3. Triple expansion engines have three cylinders, a high pressure, an
intermediate, and a low pressure cylinder.
In a triple expansion engine the intermediate cylinder receives the
steam that is exhausted from the high pressure cylinder, and expands it
further. The low pressure cylinder receives its steam from the exhaust
of the intermediate cylinder, and exhausts into the condenser.
[Illustration: Fig. 3397.]
[Illustration: Fig. 3398.]
In the illustrations from Fig. 3396 to Fig. 3406 are represented the
triple expansion engines of the steamship _Matabele_, constructed by
Messrs. Hall, Russell & Company, of Aberdeen, Scotland. Fig. 3396 is a
cross sectional view of the vessel showing the engine and its
connections, and Fig. 3397 a similar view, showing the boilers. Fig.
3398 is a back elevation of the engine, showing the boilers also, and
Fig. 3399 a plan of the same. Fig. 3400 is a sectional view, and Fig.
3401 an end view of the boilers. Fig. 3402 is a plan, Fig. 3403 an end
elevation, and Fig. 3404 a front elevation, partly in section, of the
engines. H P is the high pressure cylinder, I C the intermediate
cylinder, and L P the low pressure cylinder. The high pressure cylinder
has a piston valve, the steam chest being shown at A. The intermediate
cylinder is provided with a double ported flat valve as shown at B, and
the low pressure cylinder is provided with a similar valve whose weight
is counterbalanced by the small piston at E; at F are the relief valves
for relieving the cylinders of water.
[Illustration: _VOL. II._ =COMPOUND MARINE ENGINE.= _PLATE XXXVI._
Fig. 3393.
Fig. 3394.]
[Illustration: Fig. 3399.]
[Illustration: Fig. 3400.]
[Illustration: Fig. 3401.]
[Illustration: Fig. 3402.]
Each steam valve is provided with a link motion that may be used for
varying the point of cut off (and therefore the expansion) as well as
for reversing purposes.
The link motions are all shifted from one shaft, which may be operated
by hand or by steam, the construction being as follows:
For shifting by hand, the wheel W is operated, its shaft having a worm
driving the worm wheel G, Fig. 3403, which operates rod H, and through
the lever J and rod K shifts the link L, one pair of eccentric rods
being shown at N and P.
The shaft of the wheel W is, however, a crank shaft, and at M is a small
engine, which may be connected or disconnected at will to shaft W. The
lever J operates a shaft R in Fig. 3404, which connects (by a rod
corresponding to rod K in Fig. 3403) to each link motion; hence all the
links reverse together, and the ratio expansion of one cylinder to the
other cannot be varied, or in other words, the point of cut off will be
alike for each cylinder, let the link motion be shifted to whatever
position it may.
The beam S, Fig. 3403, for working the air, circulating and feed pumps,
is driven from the cross head of the intermediate cylinder.
The boilers are of the Scotch pattern that is usually employed for high
pressures, as 160 or more lbs. per square inch, and have Fox corrugated
furnaces and stay tubes.
Each cylinder requires a starting valve (which is sometimes called an
auxiliary valve or a bye pass valve), which is used to warm the cylinder
before starting the engine, and also (when there is no vacuum in the
condenser) to admit high pressure steam when the high pressure piston is
on the dead centre, in which case, there being no vacuum and no
admission of steam to the low pressure cylinder, the engine would not
have sufficient power to start.
[Illustration: Fig. 3403.]
In some cases the high pressure cylinder has no starting valve, the
reversing gear being used to admit steam to one end or the other of the
high pressure piston, and the starting valve being used to admit enough
live steam to the low pressure cylinder to compensate for the absence of
the vacuum.
When the vacuum in the low pressure cylinder is maintained while the
engine is standing still, its starting valve obviously need not be used,
except for warming purposes, before starting the engine; as soon,
however, as the engine has started, the starting valve must be closed.
Each cylinder is provided with a relief valve, both at the top and at
the bottom, to relieve the cylinder from a heavy charge of water, such
as may occur if the boiler primes heavily.
Each cylinder is also provided with drain cocks, to permit of the escape
of the ordinary water of condensation in the cylinders when the engine
is started, and also for use if the boiler primes.
The low pressure relief valve also prevents the accumulation of too
great a pressure in the low pressure cylinder, which, from its large
diameter, is not strong enough to withstand high pressure.
The oiling apparatus for the cylinders is arranged as follows:
In some cases pumps, and in others automatic or self-feeding devices are
used. Oil is fed to the steam pipe of the high pressure cylinder, and
this lubricates both the valves and the cylinders, but in many cases it
is also fed to the steam chest, so as to afford more perfect lubrication
to the valve.
For the low pressure cylinder the oil is fed into the receiver, and
usually at a point near the slide valves.
Large marine cylinders are usually constructed with a separate lining,
which may be replaced when worn or otherwise required.
A surface condenser consists of a cast iron shell or chamber forming the
back of the engine frame. At each end of this chamber is a short
partition, so that the condenser is divided lengthways into what may be
called three compartments, of which the middle one is the longest and
contains a number of thin brass tubes about 5/8 or 3/4 inch in diameter,
the ends of these tubes being held in the plates or tube sheets forming
the partitions. The object of providing tubes of small diameter is to
obtain a large area of cooling surface.
The exhaust steam from the engine generally passes into the shell or
body of the condenser, filling the middle partition and surrounding the
tubes.
The condensing or circulating water passes through the tubes, and by
keeping them cool condenses the steam and forms a vacuum or partial
vacuum in the condenser, which, having open communication with the low
pressure cylinder, therefore gives a corresponding degree of vacuum on
the exhaust side of the low pressure piston.
In some designs, however, the steam passes through the tubes and the
circulating water fills the middle compartment of the condenser. As,
however, there is no pressure to counterbalance the weight of the water,
it is preferable to have the water inside the tubes, so that they are
subjected to a bursting pressure, in which case they may, for a given
strength, be made thinner, because the strength of the tube to resist
bursting is greater than its strength to resist collapsing, hence the
circulating water usually passes through the tubes. The chamber at the
ends of the condenser permits the water to distribute through all the
tubes.
In some cases the chamber at one end is divided horizontally into two
compartments, so that the water is compelled to pass through one half
and return through the other half of the tubes.
The water of condensation falls to the bottom of the condenser, from
which it is removed by the air pump, which delivers it to the hot well.
The hot well is situated on the side of, and extends above, the pump,
whose upper end it covers, thus water sealing the top of the air pump
and preventing air from passing into it through a leaky valve or bucket.
The top of the hot well is provided with a _vapor pipe_, which permits
the air and gases to pass overboard. This pipe emerges through the side
of the ship above the water line, and as there is no valve between the
hot well and the sea, no pressure can possibly accumulate in the hot
well.
The boiler feed is taken from the hot well either by the feed pump or by
injectors, as the case may be.
In case the boiler feed should stop working, however, the hot well is
provided with a pipe of large diameter, and called the overboard
discharge pipe, so that the water of condensation may not accumulate a
pressure in the hot well if the boiler feed ceases.
This overboard discharge pipe is provided with a weighted valve (placed
at the side of the ship), which is constructed after the manner of a
safety valve, relieving the hot well of pressure if the water
accumulates, and preventing the sea water from entering the hot well.
To prevent loss of fresh water, the exhaust steam from the various
engines and pumps (if any) about the ship passes to the condenser and is
pumped into the hot well.
In some cases, however, a separate and independent condenser is used for
the smaller engines about the ship.
An independent condenser is one whose air pump and circulating pump are
not worked from the main engine, and can therefore be operated when the
main engine is standing still.
If the main condenser is independent, it may be started so as to form a
vacuum before the main engine is started, and thus obviate the use of
the starting valve on the low pressure cylinder except to warm the
cylinder before starting.
Feed water for the boilers when the engine is standing is obtained by a
pipe from the bottom of the condenser, so that the water of condensation
of steam blown through the engine cylinders, and from the exhausts from
the smaller engines about the ship, may be pumped or forced direct from
the bottom of the condenser to the boiler.
This feed from the bottom of the condenser is necessary when the air
pump is not working, and the water of condensation is not pumped into
the hot well.
If the water thus obtained is not enough to keep the boilers supplied,
an auxiliary or salt water feed admits extra water from the circulating
water to the inside of the condenser to supply the deficiency.
This secondary suction pipe is provided with a valve because it must be
shut off before the engine is started.
All the drain pipes from the cylinder pass into the condenser so as to
save the fresh water.
The air pump is usually worked by a beam, receiving motion from the
cross head of the low pressure cylinder.
The circulating pump is usually worked by the same beam as the air pump,
or receives its motion from some other part of the main engine. In some
cases, however, an independent circulating pump is employed.
It receives its water from a pipe leading to the sea, which is provided
with an injection cock or Kingston valve, placed close to the side of
the ship and well below the sea level. This valve is used to shut off
the circulating water and prevent its flooding the ship in case of
accident to the condenser or circulating pump.
The circulating water, after passing through the condenser, discharges
overboard through the circulator discharge pipe.
This pipe is also provided with a valve placed close to the ship's side,
at or above the water level, so that the opening at the ship's side may
be closed, and sea water prevented from entering the ship in case of
breakage to the condenser, etc.
To enable a surface condenser to be used as a jet condenser in case of
accident to the circulating pump, a pipe leads from the injection cock
of the circulating supply pump into the bottom of the exhaust pipe or
column, where it enters the condenser.
This pipe is supplied with a spray or rose nozzle, which divides up the
injection water and causes it to condense the steam as it enters the
condenser.
An additional pipe is sometimes added to the suction side of the
circulating pump, for use in pumping out the bilge by means of the
circulating pump in case of emergency, and also for pumping out ballast
tanks when the vessel is provided with such tanks.
An air valve is sometimes fitted to a reciprocating double acting
circulating pump. It admits air to the water during the up stroke of the
pump, and closes on the down stroke. The air thus admitted acts as a
cushion to soften the shock of the water.
A snifting (or snifter valve, as it is sometimes called) is a valve
fitted to the condenser and that opens upwards to permit of the
discharge of the air and gases before the engine is started. It also
serves to prevent any water from leaky condenser tubes from filling the
condenser and flooding the engine cylinders. It is so loaded with dead
weight that it opens automatically when the water in the condenser has
reached a certain height and must be placed as low down on the condenser
as possible, so as to receive the weight of the full height of the water
in the condenser.
Condenser tubes are made water tight in the tube plates of the condenser
by wooden or sometimes paper ferrules, which fit the tube and drive into
the tube plate. In other cases, however, the tube ends project through
the plates, and a rubber washer is placed on the end of each tube. A
covering plate is then bolted over the whole of the tube ends, the holes
in the covering plate being parallel for a short distance, and then
reduced in diameter so as to form a shoulder. The rubber rings compress
and make a joint, and the shoulders prevent the condenser tubes from
working out endways from expansion and contraction. The tubes are
usually about 3/64 inch thick.
[Illustration: _VOL. II._ =TRIPLE EXPANSION MARINE ENGINE.= _PLATE
XXXVII._
Fig. 3404.]
A blow through valve is a valve attached to the casing or steam chest,
and connecting by a pipe to condenser to blow out the air and gases that
may have collected there when the engine is standing still, and that
also connects to the exhaust port of the high pressure cylinder, so as
to supply live steam to the low pressure cylinder in case the high
pressure cylinder should get disabled.
A bucket air pump is one in which there is a valve or valves in the pump
piston, hence the pump is single acting, drawing on the lower side of
the piston and delivering on the upper, hence the capacity of the pump
per engine revolution is equal to the diameter of the bucket multiplied
by the length of its stroke. The suction or foot valve is at the foot of
the pump, and the delivery valve at the head.
A piston air pump is double acting, since it draws on each side
alternately of the piston, one side delivering while the other is
drawing, hence two suction and two delivery valves are required.
A plunger air pump is one in which a plunger is used in place of a
piston, the delivery being due to the displacement of the plunger.
An air pump trunk is a hollow brass cylinder attached to or in one piece
with the piston or bucket of the air pump. The rod which drives the
piston passes through the trunk, and connects to a single eye at the
bottom of the trunk.
A trunk air pump is necessary when the pump rod is driven direct from
the crank shaft, and therefore has sufficient lateral motion to push the
pump piston sideways, which would cause friction and excessive wear to
the gland that keeps the trunk tight. The delivery capacity of the pump
is obviously diminished to an amount equal to the displacement of that
part of the plunger that passes through the gland and within the pump
bore, whereas in a piston pump the delivery capacity is only diminished
to an amount corresponding to the displacement of the pump piston rod.
A bucket pump may in some cases be worked without either a foot or a
head valve, since the bucket valve will answer for both in cases when
the delivery water cannot pass back into the pump on the down stroke of
the bucket.
It will, however, be more efficient with the addition of either of them,
and most efficient with both.
A bucket pump with a foot valve and no discharge valve would, however,
suffer more from a leaky gland than if it had a discharge valve and no
foot valve, because the air would, on the ascent of the bucket and the
closing of the bucket valve, pass to the suction side of the bucket and
impair the vacuum.
Let the delivery valves be where they may, the foot valve will always
have some water above it, and the pump bucket will dip into this water,
and on lifting produce a vacuum that will cause the pump to fill with
water. Notwithstanding that the gland may leak air on the other side of
the bucket, this air will in a single acting pump be expelled with the
water, but in a double acting pump it will impair the vacuum, and
therefore the suction, on the gland side of the piston.
Bucket air pumps are provided with a valve or pet cock on the top or
delivery side of the bucket and above the bucket, when the latter is at
the highest point of its stroke. This valve opens on the descent of the
bucket, admitting air to act as a cushion between the surface of the
water and the delivery valve, when the water is about to meet the
latter. It obviously reduces the effectiveness of the pump, and in a
double acting pump is inadmissible, because of its impairing the vacuum
and the suction.
This valve also enables the engineer to know whether the air pump is
working properly.
A pet cock is also supplied to the feed pumps for this same purpose.
A bilge injection is one in which the injection water is taken from the
bilge, which may be done when the ship makes more water than the bilge
pumps can get rid of.
The fittings necessary for a bilge injection are a cock or globe valve
placed on the side of the condenser, and at or near the foot of the
exhaust pipe, with a spray or rose inside that pipe. From the cock a
pipe, usually lead, leads to the bilge, having at its end a strainer or
strum, and care must be taken that this strum does not get choked and
let the condenser get hot from the exhaust steam not being condensed.
The water in the hot well of a surface condenser is usually kept at a
temperature of about 100° Fahrenheit. A higher temperature than 100°
Fahrenheit injures the rubber valves of the air pump, while lower
temperatures cool the engine cylinders too much and cause waste from
cylinder condensation. Moreover, it is obvious that, since the boiler
feed is taken from the hot well, it is desirable to keep it as hot as
the valves and as the desired degree of vacuum will permit.
An air vessel or air chamber is a vessel fitted to the delivery and
sometimes also to the suction side of a pump. Its office is to maintain
a steady flow of water through the pipes.
Thus, in the case of the delivery air chamber, when the pump piston is
travelling at a speed above its average for the stroke, the water
accumulates in the air chamber, and the air is more compressed, while,
when the pump is on the dead centre, or at the end of its stroke and the
delivery valve closes, the air compressed in the air chamber continues
the delivery or discharge, thus maintaining a more uniform flow.
Pumps sometimes have an air or vacuum chamber on the suction side, from
which the air is exhausted when the pump starts, leaving a vacuum which
causes a steady flow of water up the suction pipe.
Both these chambers are more effective as the speed of the pump
increases. The chamber on the delivery side is apt to lose its air,
which is gradually absorbed by the water, which should be let out when
the pump is standing still.
Feed escape valves or feed relief valves are fitted to the feed pumps,
so that in case all the feed water cannot pass into the boiler it may
pass back to the hot well.
The construction of a feed escape valve is as follows:
It is an ordinary mitre valve held to its seat by the compression of a
spiral spring, whose pressure upon the valve may be regulated by an
adjusting screw, whose end abuts upon a stem provided for the purpose.
In proportion as the valve is relieved of the pressure of this spring, a
greater proportion of the water delivered by the feed pump will pass
back into the hot well, hence the amount of boiler feed may be regulated
by the feed escape valve, which also acts as a safety valve, preventing
undue pressure in the feed pipe.
When no feed escape valve is employed, the delivery water from the feed
pump must pass unobstructed to the boiler, or the feed pipes may burst
from over pressure, and it follows that the feed check valve on the side
of the boiler must not be restrained in its amount of lift, hence it
must not have a lift adjusting screw.
The amount of the boiler feed must, in this case, be regulated from the
suction side of the pump, the suction pipe being fitted with a cock or
valve whose amount of opening may be adjusted so as to regulate the
amount of water drawn per pump stroke from the hot well.
If the feed valve on the suction side, or the escape valve on the
delivery side of the pump, as the case may be, is adjusted to permit of
a proper amount of boiler feed, and yet the feed is insufficient or
ceases altogether, it may occur from the following causes:
1st. From the suction valve sticking or being choked, or from the
delivery valve being choked and not seating itself, thus either letting
the suction water pass back into the hot well, or the delivery water
pass back into the pump.
2d. Through leaks in the joints of the pump or of the suction pipe.
3d. From the water in the hot well being too hot.
4th. Through the spring of the escape valve having become disarranged.
5th. If two or more boilers are connected, and one has less pressure in
it than the other, it may take most of the feed water, or the water of
the other may empty itself into it.
Bilge Injection. The injection water for a common or jet condenser may
be obtained in one of two ways: first, direct from the sea, which is
that for ordinary use; and secondly from the bilge, which is resorted to
to assist the bilge pump in cases of emergency.
The necessary fittings for a bilge injection are, a pipe leading from
the condenser to the bilge, with a cock at the condenser end and a
strainer at the bilge end.
This pipe should be fitted with a check valve, which opens by lifting
upwards so that no water can pass down it into the bilge, or otherwise,
if the main and bilge injections should happen to be left open
together, the water from the main injection might pass down into the
bilge. This check valve should be so constructed that its amount of lift
can be regulated and as much of the bilge water used for injection as
the circumstances may require.
In the case of surface condensers, the bilge water is drawn off by the
circulating pump and used to supplement the main circulating water. The
pipe from the bilge in this case leads to the suction side of the
circulating pump, and requires a strainer at the bilge end, a cock at
the circulating pump, and a check valve.
A ship's side air pump discharge valve is an ordinary dead weight mitre
valve that opens to let the water pass out into the sea, but seats
itself and closes if the water attempts to pass inwards. It differs from
a common stop valve in being weighted, and therefore self-acting. It
requires to be lifted before starting the engine, as such valves are
liable to stick in their seats.
The course of the main injection water of a jet condenser is as follows:
From the rose plate or strainer, through the injection valve and pipe to
the condenser, where it mingles with the exhaust steam and from which it
is pumped with the products of condensation into the hot well. From the
hot well it passes mainly overboard through the Kingston valve, but that
part of it used for the boiler feed passes through the suction pipe and
valve into the pump, and thence through the delivery valve, pipe and
check valve into the boiler.
The course of the main circulating water of a surface condenser is
through the Kingston valve (on the ship's side or bottom), and the
circulator inlet pipe, either direct to the condenser, from which it is
_drawn_ by the circulating pump, or else it passes through it, and is
_forced_ through the condenser. It circulates through the condenser
twice or thrice according to the construction, and is forced overboard
by the action of the circulating pump, passing through a valve on the
ship's side or bottom.
The advantages of surface condensation are, first, that the feed water
is obtained at a higher temperature than if injection water was fed to
the boiler. Second, the feed water is purer, and therefore less water
requires to be blown out of the boiler in order to keep it clean. Third,
the boiler does not scale so much, hence its heating surface is
maintained more efficient; and fourth, the boiler suffers less from
expansion and expansion strains when hot feed water is used.
Surface condensers foul from the grease with which the cylinders are
lubricated and from the salt in the injection water. The condenser is
cleaned by the admission of soda with the exhaust steam and by washing
out.
A condensing engine has the following cocks and valves on the skin of
the ship in the engine room: The main Kingston valve for the injection,
or circulating water, the main delivery valve from the condenser, the
bilge delivery valves, and the water service cocks for keeping the main
bearings of the engine cool with streams of cold water.
A donkey engine is a small engine used to feed the boiler, and has the
following connections: A steam pipe from the boiler to drive the donkey
engine; and exhaust pipe into the condenser; a suction pipe from the hot
well or from the sea, as the case may be; and a delivery pipe to the
boiler; a suction pipe from the bilge, so that the donkey pump can
assist in pumping the bilge out; a suction pipe to the condenser, to
circulate the water when the main engines are stopped, and thus maintain
the vacuum; and a suction pipe from the water ballast tanks, to pump
them out when necessary.
The pipes that lead from, or go to, the sea are: Boiler blow off pipe,
sea injection or circulator pipe, condenser discharge pipe, and, in some
cases, donkey feed suction pipe.
The parts of an engine that are generally made of wrought iron are those
in which strength with a minimum of weight and size is desired; for
example, the piston rod, cross head, connecting rod, crank shaft, crank,
eccentric rods, link motion, valve spindle pump rods, and all studs,
bolts, and nuts.
The parts generally made of cast iron are those where strength and
rigidity are required, and which are difficult to forge, while weight or
size is of lesser importance, such as the bed plate, cylinders, pistons,
condensers, and pumps.
The parts sometimes made of steel are those subject to great wear, and
for which strength with a minimum of size is necessary, as piston
springs, piston rods, connecting rods, cranks, crank pins, and valve
rods.
The parts generally made of brass are those subject to abrasion or
corrosion, as the connecting rod brasses, the bearings for the crank
shaft, the pump plungers or pistons, and their rods, linings for the
pump barrels or bores, the bores of the glands, the condenser tubes, and
all cocks and valves.
White metal or babbitt metal is sometimes used in place of, or in
connection with, brasses, serving as an anti-abrasion surface. It is
easily renewed, as it is cast into its place, but will melt and run out
at a temperature of about 600° Fahrenheit.
Muntz metal is used where iron or steel would suffer greatly from
corrosion when in contact with salt water. It can be forged.
The difference in the composition of cast iron and steel has never been
determined; the difference lies in the percentage of carbon they contain
and the structure of the metal. Cast iron will not weld.
Cast iron is brittle, of granular structure, and always breaks short,
having a very low elastic limit.
Wrought iron is tough and fibrous, will weld but will not harden, and is
stronger than cast iron.
Steel is stronger than wrought iron, and will weld and harden and
temper. The breaking strain of wrought iron varies from about 42,000 to
60,000 lbs. per square inch of section.
Steel is tempered by first being heated red hot and suddenly cooled
(usually by plunging it into cold water), which hardens it. The surface
is then brightened, and on being reheated the tempering colors appear,
beginning at a pale yellow, and deepening into red, brown, purple, and
blue, the latter gradually fading away as the metal is re-heated to a
red heat. The higher the temperature to which the hardened steel is
reheated the softer or lower it is tempered.
These colors merely indicate the temperature to which the piece is
reheated, since they will appear on steel not hardened and upon iron.
Case hardening is a process that converts the surface of wrought iron
into steel, which is accomplished by placing them in a box filled with
bone dust, animal charcoal, or leather hoofs, etc. The box is sealed
with clay, heated red hot for about 12 hours, and the pieces are
quenched in water.
The parts usually case hardened are the link motion, and other light
working parts that are of wrought iron.
The forgeable metals used in engine work are wrought iron, steel,
copper, and Muntz metal. The brittle or short metals are cast iron and
brass.
Welding is the joining of two pieces solidly together. Wrought iron,
steel, and Muntz metal can be welded.
All the metals used in the construction of marine engines expand by
heat, and this is allowed for in adjusting the lengths of the eccentric
rods, or of the valve spindles when setting the valve lead. In the case
of two marine boilers being connected together, the steam pipe is fitted
with an expansion joint, one pipe end having an enlarged bore to receive
the other. The joint is made by packing, which is squeezed up by a
gland, whose bore fits on the outside of the pipe which moves through
the gland bore, from the expansion and contraction.
The piston of a marine engine steam cylinder is a disc of cast iron,
into which the piston rod is secured. Its body is cored out to lighten
it. Around its circumference is a recess to receive the packing ring or
rings, each of which is split across so that it may be expanded (to fit
the bore of the cylinder) by means of the packing or of the springs. The
split is closed in the centre by a tongue piece let into the ring, and
fastened to one end of the ring.
To hold the piston rings or ring in place, a junk ring is employed,
being an annular ring bolted to the piston. The piston rings are set out
to fit the cylinder bore by suitable springs. The round plugs seen on
the piston face merely fill the holes used to support the core in the
mould and to extract it from the finished casting.
Cylinder drain cocks sometimes have a check valve upon them, so that
while the water may pass out of the cylinder the air cannot pass in and
destroy or impair the vacuum.
Cylinder escape or relief valves are provided at the top and at the
bottom of the cylinders, and consist of a spring loaded valve with an
adjusting screw to regulate the pressure at which they shall act. They
are most needed when the boiler primes heavily, and the water might
knock out the cylinder heads or covers. They should be enclosed in a
case with a pipe to lead the water away, thus preventing it from flying
out and scalding the engineer.
A link motion is a valve gear by which the engine may be reversed
(caused to run in either direction), or which may be used to vary the
point of cut off. The advantage of the link motion is its simplicity and
durability.
A link motion for a marine engine is usually of the Stephenson type, and
consists of two eccentrics or eccentric sheaves fixed upon the crank
shaft, and so set as to give more lead at the bottom than the top ports,
because the wear of the journals, brasses, and pins gradually increases
the lead at the upper, and correspondingly diminishes that at the lower
port. In addition to this, however, more lead is required at the bottom
port, to counterbalance the weight of the piston at the end of its
descending stroke. The eccentric hoops or straps drive the rods which
connect to the ends of the link.
The link may be a curved, solid, or a slotted bar, and in either case
has fitted to it a block or die which connects to the valve spindle.
The link is pivoted at its centre to a swinging arm or suspension
link,[58] and by this arm may be moved endways to bring the required end
of the link beneath the valve rod or spindle. From the positions in
which the eccentrics are set, one end of the link operates the valve to
go ahead, while the other end operates it to go astern; hence all that
is necessary (so far as the link motion is concerned) to reverse the
engine is to move the link endwise to the requisite amount, which, for
full gear, is so that the block is at or near the end of the link.
[58] See page 383 for the construction of a link motion.
In proportion as the link block is (by moving the link endways) brought
nearer to the middle of the link, the valve travel is reduced and the
point of cut off is hastened, thus increasing the expansion.
When the link block is in the middle of the link, the latter is in mid
gear, and the valve only opens the ports to the amount of the lead, and
the link action is the same, whether the engine moves backwards or
forwards.
The motion of the link is as follows:
The two ends are vibrated by the eccentrics from the central pin of the
link hanger (or suspension link) as a centre of motion, while at the
same time this end of the link hanger swings in an arc of which its
other end is the centre of motion.
In small engines the link is sometimes used for varying the expansion as
well as for reversing the direction of engine revolution.
In large engines it is used for reversing only, a separate expansion
valve being used for varying the point of cut off.
In small engines the link is moved endwise for forward or backward gear
by a simple arrangement of hand levers. In large engines these levers
are supplemented by a worm and worm gear, and in still larger engines a
steam reversing gear is used for shifting the links from forward to
backward gear, or vice versa.
When there is no link motion, a Joy valve gear, a Marshall valve gear,
or a loose eccentric may be used. A loose eccentric is one that can be
moved around the shaft to reverse the engine. It may be moved around the
shaft by mechanical means, or the eccentric rods may be disconnected,
and the valve worked by hand, to cause the engine to run in the required
direction, until a pin fast in the shaft meets a lug on the eccentric
and drives it, there being two such lugs or shoulders spaced the
requisite distance apart on the eccentric. This plan is obviously only
suitable for small engines.
A separate expansion valve is a valve employed to effect the cut off and
vary the expansion. It does not affect either the admission or exhaust
of the steam to the cylinder.
It is used because by its means an early point of cut off and high rate
of expansion may be obtained with a fixed point of exhaust, a fixed
amount of compression, and a fixed amount of lead, whereas with the link
motion alone the exhaust occurs earlier in the stroke, and the
compression and the lead increase as the link is moved from full gear
towards mid gear. The expansion valve should, when the engine is to be
started, be set for the latest point of cut off. The eccentric for the
expansion valve is set opposite to the crank, in order that its action
may be the same, whether the engine runs backward or forward.
The small cylinders on top of the steam chests are for the purpose of
guiding the upper ends of the valve spindles, and are fitted with
pistons having steam beneath, the space above being in communication
with the condenser. The steam pressure on the piston supports the weight
of the valves and valve gear.
The friction of a slide valve may be relieved or reduced by excluding
the steam from its back, which is done by various means, such as by a
ring cast on its back and working steam tight against a plate held
independently of the valve. The interior of the ring should be open to
the exhaust.
The friction of a slide valve is caused by the steam pressing it to its
seat, the amount of this pressure varying with the fit of the valve to
its seat, and its position over the ports, or, in other words, upon how
much of the valve area has steam pressing on one side only.
The travel of the eccentric rod is the distance it moves measured on a
straight line. It is equal to twice the throw of the eccentric.
The throw of an eccentric is the distance between the axis of its bore
and the centre or axis from which its circumference was turned in the
lathe.
Double beat valves are composed of two discs or mitre valves, one above
the other on the same stem, so that as the steam presses on the opposite
faces of the two discs the valve is balanced. The objection to their use
as safety valves is, that they are balanced and would not lift unless
the area of the upper disc was made larger than that of the lower one,
in which the objection would remain that the two discs do not expand
equally, hence they are apt to leak. They are sometimes used instead of
slide valves, but are objectionable because a separate admission and
exhaust valve is required at each end of the cylinder, and because at
quick speeds of revolution they fall to their seats with a shock or blow
which wears out both the valve and the seat. When a high piston speed is
obtained by great length of piston stroke, and not by high rotative
speed, their use is less objectionable.
Expansion joints are joints which permit the parts they connect to
expand and contract without straining them. They are necessary on the
steam pipe connecting one boiler to another, and on the main steam pipe
from the boilers to the engine. The working surfaces require to be of
brass, so that they will not corrode.
They require the collar on the internal pipe of the joint (on which the
gland fits) to be permanently fixed by soldering or brazing, and check
nuts on the studs, so that the internal pipe shall not be blown out from
the steam pressure.
This pipe is also sometimes fitted with chains or stops, in case the
studs should break, or the nuts or collar strip.
An oil cup is either a cavity cast in the piece or a cup shaped vessel
or hollow cylinder screwed in. It contains a pipe extending up about
three-fourths of its height, and through this pipe the oil is fed to the
surface required to be lubricated. A hinged lid or, in some cases, a
screwed cap covers the oil cup to exclude dust, etc.
The syphon or worsted consists of a number of threads of worsted or lamp
wick of equal lengths; a piece of lead or copper wire is laid across the
middle of the worsted, the copper wire is doubled and twisted and is
then pushed down the tube, carrying the doubled end of the worsted with
it. The upper ends of the wire are bent over the end of the tube so as
to hold the worsted, whose lower end should pass down below the level of
the bottom of the oil cup. The oil feeds (on the syphon principle)
through the medium of the wick or worsted, which should not fit the tube
tight but quite easily, its upper ends hanging over the top of the tube
to the bottom of the cup.
The worsted may be cleaned with scalding water, or by water thrown upon
it from the boiler.
Tallow cups for high pressure cylinders must have two cocks, so that
after the cup is filled the top cock may be closed and the bottom one
then opened. The top cock prevents the tallow or oil from being blown
out of the cock by the steam. For the low pressure cylinder a cup with a
single cock will answer, as the cock may be opened when the vacuum is at
that end of the cylinder, and the air will force the oil or tallow in.
A steam lubricator or impermeator is an automatic oil feeding device
placed on the steam pipe of the high pressure cylinder. Steam
lubricators are made in various forms, some having a positive feed by a
pumping arrangement, while in others the oil floats upon water in the
body of the lubricator to which steam is admitted; the condensation of
the steam increases the quantity of water and causes the floating oil to
overflow and feed through a pipe leading into the steam pipe or steam
chest, as the case may be. Cooling the impermeator causes more rapid
condensation, and increases the amount of oil fed to the steam.
Cylinder escape or relief valves do not let all the water out of the
cylinder because of the clearance,[59] hence the amount of water left in
will equal the amount of clearance.
[59] See page 372, on clearance.
The small cylinders on top of the steam chest are for the purpose of
guiding the upper ends of the valve spindles, and are fitted with
pistons having steam beneath, the upper end being in communication with
the condenser.
The effort of the piston to rise supports the weight of the valves and
valve gear.
The valves of a marine engine that are worked by hand are, the stop
valves for letting on steam from the boiler, the safety valve, which is
lifted to see that it is in proper working order, the Kingston valve for
letting in the circulating water, the blow through or starting valve for
warming the cylinders and starting the engines. The valve for adjusting
the rate of boiler feed has its lift adjusting screw operated by hand.
The slide valve may also be operated by hand before the engine is
started, or it may be operated by a steam reversing gear. The expansion
valves are also set by hand to regulate the point of cut off or amount
of expansion. The valves that are operated automatically, or from the
motion of the parts, are the slide and expansion valves, the suction and
delivery and check valves of all pumps, the air pump bucket valves, the
snifting valves, and the ship's side overboard discharge valves. When
the engine is stopped and the steam shut off, close the dampers to check
the draught and open the drain cocks on the high pressure cylinders.
If the engine is soon to start and the pressure in the boiler is at the
blowing off point, start the boiler feed, if the height of the water in
the boiler will permit it, and this is a good time to clean the fires.
If the engine is to stop for any length of time, shut off the
impermeator and the injection supply.
A vacuum gauge is an instrument for measuring the total or absolute
pressure, or pressure above a perfect vacuum, and it is used to indicate
the degree of vacuum that exists in the condenser, which, when the
various joints about the cylinder and condenser are tight, averages
about 27 inches of mercury when the temperature in the hot well is about
100° Fahrenheit.
In round numbers a column of mercury 32 inches high equals the weight of
the atmosphere,[60] hence taking the weight of the atmosphere at sea
level to be 15 lbs. per square inch, then each two inches of mercury
represents an atmospheric pressure of 2 lbs. Suppose then that a bent U
shaped tube, each leg of which is 30 inches high, is half filled with
mercury, and that one end is in communication with the condenser, and
the other end is open to the atmosphere, and if there was a perfect
vacuum in the condenser, the pressure of the atmosphere in the open leg
would force all the mercury into the leg that communicated with the
condenser, hence there would be a column of 30 inches of mercury in one
leg, and air in the other.
[60] See "Barometer," Chapter XL.
If there was in the condenser a pressure of 1-1/2 pounds per square inch
above a perfect vacuum, the mercury would stand 27 inches high in one
leg, and 3 inches in the other, and so on, hence from the height of the
column of mercury above its natural level the degree of vacuum in the
condenser may be known. But the pressure of the atmosphere varies with
its temperature, and the weight of mercury also varies with its
temperature.
To find the total pressure in the condenser, therefore, we subtract
height of the column of mercury given by the condenser from the height
of the column in the barometer, and divide the remainder by 2.
_Examples._--The barometer stands at 29.5 and the vacuum gauge at 26,
what is the absolute pressure in the condenser?
Here,
29.5 - 26 = 3.5 ÷ 2 = 1.75
Answer, 1-75/100 lbs. per square inch.
A dial vacuum gauge of the Bourdon construction is similar to the
Bourdon steam gauge, that is used upon the boiler, except that the
inside of the elliptical tube is in communication with the condenser and
the atmospheric pressure bends the tube into a curve of smaller radius
(instead of to a larger one, as in the case of the steam gauge).
Obviously, therefore, the zero of the dial vacuum gauge is atmospheric
pressure.
Suppose the dial vacuum gauge shows 10 lbs., the steam gauge 120 lbs.,
and the barometer 15 lbs., and we may find the total pressure or
pressure above vacuum of the steam in the boiler is as follows:
One-half Pressure by steam gauge = 60 lbs.
A perfect vacuum = 15 lbs.
--
Total pressure supposing condenser had a perfect vacuum = 75 lbs.
To make the correction necessary because there is not a perfect vacuum
in the condenser, we then proceed as follows:
Barometer 30 inches of mercury = 15 lbs. per sq. in.
Dial vacuum gauge = 10 " " " "
--
Actual pressure in condenser = 5 " " " "
Then
Total pressure supposing condenser had a perfect vacuum = 75
Actual pressure in condenser = 5
--
Actual pressure of the steam = 70
Racing means a sudden acceleration of the engine speed, and occurs when
the propeller is not fully immersed in the sea, as by reason of the
pitching of the ship. Racing augments the strain on the working gear of
the pumps, and is likely to lead to accident. It is obviated by the use
of a governor or by partly shutting off the steam by hand.
A marine governor is a device for controlling the engine speed, by
reducing the supply of steam to the engine cylinder whenever the engine
begins to race. The governor is driven by band or rope on the crank
shaft. Governors are made in various forms; thus, in one the shaft has a
fly wheel and a friction clutch, one half of which is fast on the
governor shaft, while between it and the other is a spiral spring which
connects the two halves. If the speed accelerates, the sliding half of
the clutch is moved along the governor shaft, and by means of links it
closes the throttle valve of the main steam pipe, thus wire drawing the
steam, reducing its pressure and thereby controlling the engine speed.
A common paddle wheel has a cast iron centre into which the wrought iron
arms are set and secured by wrought iron bolts and nuts.
The bolts have hook heads to grip the back of the arm, and receive a nut
and plate to secure the paddles.
Paddle wheels are sometimes provided with cast iron floats to act as
counterweights to some unbalanced part of the engine. They are mostly
required on side lever engines having a single crank; they are placed
nearly opposite to the crank, but not quite, so that they may prevent it
from stopping on the centre, and be difficult to start again.
Paddle wheels for engines having a single crank sometimes have their
floats of varying breadths, so as to keep the speed of revolution as
uniform as possible. This is accomplished by making some of the floats
wider than the others. The broadest floats are in action when the crank
is at its points of greatest power, and the narrowest at the time the
engine is on a dead centre, hence there are four general graduations of
breadth in the circumference of the wheel.
A radial paddle wheel is one in which the floats are fixed to the paddle
arms, and their ends are in a line radiating from the centre of the
paddle shaft.
A feathering paddle float is pivoted at the centre of its ends, and so
arranged that by a mechanical movement it will remain vertical when in
the water, notwithstanding the circular path it revolves in.
The object of feathering is to cause the thrust of the float to be as
nearly as possible in a horizontal line, and therefore more nearly
parallel to the line of the ship's motion, and thus utilize more of the
paddle power to drive the ship.
The eccentric for feathering the floats is fixed to the ship's side, and
sometimes carries a plummer block or pillow block for the paddle shaft
bearing. The centre of the eccentric sheave or wheel is placed ahead of
and level with the paddle shaft axis. The working surfaces of a
feathering wheel are of brass, and the bushes of the paddle arms of
lignum vitæ.
The surfaces are lubricated by the water, but sometimes oil lubrication
is provided for the eccentric sheave.
A disconnecting paddle engine is one in which the paddles may be driven
separately or together. This is effected at the inner port bearing by a
clutch wheel, which slides endways on the shaft and is driven by
feathers seated in the shaft. This clutch wheel is operated by a lever
so as to engage or disengage with the crank pin, which is fast in the
outer crank.
Disconnecting paddle engines are always fitted with loose eccentrics,
such engines being used for steam tugs and ferry boats, where quickness
of turning and of reversing is of great importance.
The thread of a screw propeller is its length measured along the outer
edge of the blade.
The angle of the thread is its angle to the axial line of the propeller
shaft.
The length of the thread is the length of the outer or circumferential
edge of the blade.
The area is the surface of one side of the blade.
The diameter is the distance apart of the two points on the edges that
are diametrically opposite and furthest apart.
The pitch of a propeller is its degree of spirality, and is represented
by the distance it would move forward if the water was a solid. It is
measured by drawing a line representing the axis of the propeller shaft,
and at a right angle to it a line representing in its length the
circumference of the circle described by the tips of the blades; from
the point of intersection of these two right angle lines a diagonal line
is drawn representing the angle the blade at its outer edge stands at
the propeller shaft axis. The greatest distance between the diagonal
line and the line representing the propeller circumference is the pitch
of the propeller.
A left handed propeller has a left hand thread or spiral, and revolves
from left to right to move the ship ahead.
A right hand propeller has its blades inclined in the opposite
direction, and of course revolves in the opposite direction to a left
hand one.
The slip of a propeller is the difference between the distance the ship
is moved by the propeller and the distance it would move if the water
was solid. Slip is usually expressed in the percentage that the distance
the ship actually travels bears to the distance she would have travelled
if there had been no slip. From 10 to 20 per cent. is lost in slip.
A screw of increasing pitch is one in which the angle of the face of the
propeller blade to the axis of the shaft increases as the thread recedes
from the shaft, or from the centre to the circumference of the blade, or
in both directions.
In a uniform pitch the angle of the blade to the propeller axis is the
same at all distances from the axis.
An example of a screw of uniform pitch would be a piece of angle iron
wound around a parallel shaft. If wound on a tape shaft, the largest
diameter being nearest to the ship's stern, it would have an increasing
pitch. If wound around a parabola, the pitch would vary at every point
in its diameter and thread.
A thrust bearing is a journal bearing provided with a number of
corrugations or collars fitting with corresponding corrugations or
recesses in the thrust block, the area thus provided serving to resist
the end thrust placed by the propeller upon the shaft.
It must be freely lubricated by ways leading to each collar or
corrugation, and so situated that it is accessible for examination. It
is sometimes at the end of the first length of shaft aft of the engine.
A stern tube is a sleeve enveloping the aft end of the propeller shaft
to protect it from the sea water, which would corrode it. At the aft end
of the stern tube is a gland and stuffing box. At the inner end, which
extends to the aft bulkhead, it has a flange which is bolted to the
bulkhead.
The bearing area of the shaft and stern tube are lined with brass (about
half an inch thick) to prevent their oxidation from the action of the
sea water.
A lignum vitæ bearing is a wooden bearing generally fitted to the outer
end of the stern tube in propeller engines, or to the outer ends of the
paddle shaft of paddle engines. It consists of strips of lignum vitæ
dovetailed into the bearing or bush, and running lengthways of it. These
strips are prevented from working out by a check plate at each end of
the bearing.
Screw propellers may be fastened to their shafts in several ways, as by
a key or feather sunk in the shaft, and projecting into a keyway in the
propeller bore, and a nut on the end of the shaft with a safety pin
outside the nut, or by a key passing through the boss of the propeller,
and a safety pin or plate upon the key.
The principal pipes of a marine engine and boiler, and the parts they
connect, are, the main steam pipe, connecting the stop valve on the
superheater to the steam chest of the engine cylinders; the waste steam
pipe from the safety valve to the open air; the blow-off pipe,
connecting the blow-off cocks on the bottom of the boiler with the
blow-off Kingston cock on the ship's side; cylinder jacket pipe from the
stop cock on the boiler to the steam jacket.
The circulating suction pipe, connecting the main Kingston valve with
the bottom of the circulating pump; the circulating delivery pipe,
connecting the discharge compartment of the condenser with the main
delivery valve on the ship's skin; the air pump suction, connecting the
body of the condenser with the suction side or bottom of the air pump;
the main exhaust pipe, connecting the exhaust passage of the low
pressure cylinder with the condenser; the feed water suction pipe,
connecting the donkey feed pipe with the hot well; the feed water
delivery pipe, connecting the donkey feed pump with the check valve on
the boiler; the bilge suction pipe, connecting a strum box in the bilge
with the bilge pump; a suction pipe from the strum in the bilge to the
donkey pump; the bilge pump delivery pipe, connecting the bilge pumps
with bilge delivery valves on the ship's side.
A mud box is a rectangular box usually placed in the engine room, and
serving to clear the bilge water from foreign substances, as small
pieces of wood, coal, etc.; the construction is as follows: It is on the
suction side of the bilge pumps, and is provided with a hinged lid that
affords access to clean it out, and that must obviously close air tight,
or the bilge pumps will not draw. The box is divided into two
compartments by a loose division plate that stands vertical, and is
perforated so as to act as a strainer.
The steam from the boiler passes through the superheater, main stop cock
or valve, main steam pipe, separator, regulating and throttle valve,
steam chest, steam port, steam passage into cylinder, returns through
steam passage and port, exhaust cavity of valve into either the
condenser or the low pressure cylinder, as the case may be, finally
exhausting into condenser, whence the water of condensation is pumped by
the air pump into the hot well. In the case of a jet condenser part only
of the condensed steam goes back to the boiler, the rest going into the
sea through the injection discharge pipe.
A steam jacket[61] is an outer casing to a steam cylinder, the space
between it and the cylinder being filled with steam direct from the
boiler, with the object of preventing condensation of the steam in the
engine cylinder.
[61] See page 374 on steam jackets.
A drain cock is supplied to the bottom of the jacket to pass off
condensed water. Steam jackets should be lagged or felted to prevent
condensation.
The parts of an engine that require to be felted or lagged are the
cylinders and the steam pipes; the boilers also should be felted or
otherwise covered to prevent loss of heat by radiation, and the uptake
protected by means of thin plates, kept, by means of distance pieces and
bolts, at a distance of two or three inches from the plates of the
uptake.
Various non conducting substances are employed to prevent radiation, as,
for example, felt, mineral wool, asbestos, and various kinds of cement.
The pieces of the engine through which the steam pressure is received
and transmitted are as follows:
The piston, piston rod, cross head, cross head gudgeon, connecting rod,
crank pin, crank shaft and couplings to the propeller shaft.
Trunk engines are generally used in war vessels where it is required to
have the engines below the water line. The trunk passes through the
cylinder and the piston is upon the trunk, the connecting rod passes
down into the trunk and connects direct to the piston. A stuffing box
and gland in each cylinder cover keeps the trunk steam tight. The trunk
forms a guide to the piston in place of the ordinary cross head and
guides, and thus saves the room required by those parts.
The cylinders for a right handed propeller should be on the starboard
side of the vessel, so that the pressure on the piston, when the engine
is going ahead, shall be in a direction to lift the trunk in the
cylinder, and thus act to relieve the gland and cylinder bore of the
weight of the trunk and piston.
An oscillating engine is one in which the cylinder is mounted on
bearings called trunnions, so that the cylinder can swing and keep its
bore and the piston pointing to the crank at all parts of the engine
revolution. This enables the connecting rod and slide bars to be
dispensed with. The trunnions are hollow, one containing the steam and
the other the exhaust passage.
Oscillating engines are used for paddle steamers, because their
construction permits of a good length of piston stroke, while still
keeping the engine low down in the vessel.
The valve motion for an oscillating engine consists of an ordinary
eccentric gear or motion, with the addition of various mechanical
arrangements to accommodate the valve gear to the vibrating motion of
the valve chest.
The stuffing box of an oscillating engine is made deeper than usual
because the gland bore has more strain on it, and extra wearing surface
is therefore required to prevent its wearing oval.
Geared engines are those with gear wheels to increase the revolutions of
the shaft above those of the engine, and thus obtain a high propeller
speed without a high piston speed.
The pressure that propels a vessel is taken by the thrust block in a
screw propeller engine.
The pressure that drives a paddle steamer is applied to the hull at the
shaft bearings and their holding beams, and to the bed plates. The
amount of fuel required per horse power per hour, by modern compound
engines, is from about 1-1/2 to 3 lbs., and by common condensing engines
from 3 to 5 lbs. per horse power per hour.
The unit or measure of a horse power is the amount of power required to
lift 33,000 lbs. one foot high in a minute.[62]
[62] See page 407, Vol. II.
Nominal horse power is a term used to represent the commercial rating or
power of an engine, and is usually based upon the area of the piston. It
gives no measure of the engine power, however, because it does not take
the piston speed into account.[63]
[63] See page 374, Vol. II.
In a surface condensing engine the duty of the air pump is to merely
pump the condensed steam and vapor from the condenser to the hot well,
whereas in a jet condensing engine it has to also take the condensing
water from the condenser, hence an air pump for a surface condenser may
be made smaller than that for a jet condenser. As the air pump works
against the pressure of the atmosphere, therefore the smaller it is the
less of the engine power is absorbed in working it.
The injection cocks are regulated for opening by rods having handles
attached. If the injection cocks are not open wide enough, the condenser
will get hot and impair the vacuum, while if opened too wide, the water
in the hot well will be cold and the boiler feed will be cold. These
cocks should be so regulated as to keep the temperature in the hot well
at about 100° Fahrenheit.
The parts of a marine engine that are exposed to danger in a cold
climate are all pipes through which cold water circulates, and are
liable to freeze.
The precautions necessary to prevent freezing in cold climates are to
cover all pipes liable to freeze, to keep the water circulating through
them, or to let it out of them if necessary, as in the case of the
engine standing.
A marine engine may fail to start, or may be prevented from starting by
the following causes:
1st. The H. P. slide valve may be off, or away from its seat, thus
admitting the steam to both sides of the piston at the same time.
2d. The engineer may have forgotten to disengage the hand turning gear
from the crank shaft.
3d. The propeller may be fouled with a piece of timber, or by a chain or
rope (these causes sometimes occurring when the ship is in port), or
there may be something wrong with the outer bearing of the propeller
shaft.
4th. In the case of a propeller fitted with a banjo frame (for the
purpose of raising the propeller) the propeller may be locked.
5th. An obstruction, as a block of wood, in the crank pit may prevent
the crank from turning.
6th. The slide valve nut may have slackened back, thus loosening the
slide valve.
7th. The slide valve spindle may have broken.
8th. When an engine has no auxiliary or starting, but an _impulse_ valve
that merely lets a puff of steam into the receiver, this impulse valve
may leak, and if the escape or relief valve on the receiver is too much
loaded, it may gag the H. P. piston by giving it high pressure steam on
both sides, and this may throw the valve off its seat. Similarly, if the
engine has an auxiliary or starting valve, and it leaks, high pressure
steam may be admitted to both sides of the L. P. piston, thus gagging it
and causing its slide valve to throw back and away from its seat.
9th. The cylinders may be choked with water, and the drain cocks choked
up.
10th. The crank shaft bearings may be screwed up too tightly.
11th. The air or the circulating pump may be choked with water, either
the air pump overflow valve or the circulating discharge valve being
secured down.[64]
[64] The air pump overflow valve should never be permanently fastened
down. More engines have been broken down from this than from almost
any other neglectful cause, because, from great leaks in the condenser
tubes and engines standing for a length of time, a larger quantity of
water may require to be got rid of during the first few strokes of the
pump than can pass through the small air or vapor pipe, which is
usually fitted from the hot well either into the bilge or else
overboard. Unless the valve in this overflow pipe is heavy enough of
itself (which is very rarely the case), it should be loaded by a
spring or weight, so that when the puff of the air pump causes it to
lift, and the vessel is rolling, sea water may not pass into the hot
well. To avoid this, some engineers erroneously fasten this valve
down. An experienced engineer states that in his experience five
engines have been broken down from this cause alone.
12th. From the engines being allowed to stand a long time in one
position, and the glands being too tightly packed. An engine should be
turned a little daily when not in use.
13th. From the piston rings being set out too tight to the cylinder
bore.
14th. From the throttle or stop valve being shut, as from its spindle
being broken.
15th. From the eccentric sheave, or wheel, having shifted on the shaft,
some eccentrics having a key that is not sunk in the sheave, which is
done so that the eccentric may shift rather than break if it should
seize in its strap.
16th. From the H. P. piston leaking badly, or its ring being broken,
which will permit the cylinder to fill with steam and the slide valve to
unseat.
17th. If the engine has been overhauled, the forward eccentric may have
been connected to the wrong end of the link, thus giving an improper
motion to the slide valve.
18th. The expansion may be set to cut off too early in the stroke.
19th. From the air pump rod, or from the circulating pump rod being
broken, or from the valves being broken.
20th. From the cylinder casing or the receiver being cracked so as to
admit steam to both sides of the piston at the same time.
A defective vacuum, or loss of vacuum, may occur from the following
causes:
1st. From the glands of the low pressure cylinder leaking.
2d. From the pet cock of the air pump being left open.
3d. From the joints of the connections about the condenser leaking.[65]
[65] To discover a leak about a condenser, pass an exposed light, as a
candle, about the joints, etc., and where there is a leak the flame
will be drawn in towards the condenser.
4th. From the condenser being cracked, and therefore leaky.
5th. From the injection cock or valve being closed.
6th. From the condenser tubes being foul for lack of being cleaned. From
the L. P. cylinder escape valves or cylinder cocks being leaky, and
therefore letting in air.
7th. From the slide valve and piston of the L. P. cylinder leaking.
8th. From the air pump valve being leaky or broken. From the circulating
pump being defective, as from having leaky valves.
9th. From the Kingston injection valve not being properly opened, or
from its outside orifice being choked.
10th. The bilge injection may be so connected with the air pump or
condenser as to impair the vacuum when its valve is accidentally stuck
and its stop cock is left open.[66]
[66] It is obvious that a defective vacuum may or may not prevent an
engine from starting, according to the degree of defectiveness.
The principal causes of heating are:
1st. The bearing caps being screwed down too tight.
2d. The bearings being left uncovered, thus allowing the brick dust used
for cleaning the machinery, the dirt from coaling the ship, or the sand
used for cleaning the decks, to get into the bearing.
3d. The oil grooves in the brasses being worn out or too shallow, or the
brasses not being cleared at the sides.
4th. Improper fitting of the distance pieces or fit strips between the
brasses.
5th. Bad oil or too light an oil.
6th. If the brasses are too slack and thump or pound, the back of the
brass may be stretched by pening, causing the sides of the brass to
close in upon and bind the crank journal or crank pin, and this will
cause heating.
For other information concerning the engine see as follows:
Page.
Angularity of connecting rod 375
The slide valve 376
Double ported and griddle valves 377
Balanced valves 377
Piston valves 378
Separate cut off valves 378
Reversing gears 383
Finding the working results of a slide valve 376
Condensing engines 442, 444
Calculations on the mechanical powers 405
The unit of power 407
Calculating horse power 407
Calculations of safety valves 409
Heat, water, and steam 410
The expansion of steam 411
The conversion of heat into work 411
The indicator 413
Indicator diagrams 414, 421
The barometer 415
Calculating the horse power from indicator diagrams 419
Finding the steam of water consumption from an indicator 421
Figs. 3405 and 3406 represent a triple expansion marine engine, the
construction being as follows:
The high pressure cylinder has a piston valve and the intermediate and
low pressure cylinders flat valves. Each cylinder has a link motion, and
all three link motions are shifted from the same shaft, which is moved
by a steam reversing gear. At _a_, Fig. 3405, are the eccentrics for the
link B, for the high pressure cylinder; _b´_, _b´_ are those for link
B´, for the intermediate cylinder; and _c´_ _c´_ are those for the link
C´, for the low pressure cylinder. From each link are rods E, Fig. 3406,
connected to arms on the shaft F _f_, to an arm on which is connected
the rod G, from the worm wheel H, whose actuating worm I is on a crank
shaft operated by the small steam cylinder J. The slide spindles D work
in guides, and their cross heads C span the edges of the links, gibs
being provided to take up the wear.
The gear for turning the engine when there is no steam in the main
boilers is constructed as follows:
On the shaft of the wheel _m_, Fig. 3405, is a worm _n_ operating a worm
wheel _p_, on whose shaft is a worm which operates the large worm wheel
shown on the main crank shaft.
Figs. 3407 and 3408 represent the compound engines of the steamship
_Poplar_, concerning which _The Engineer_ (from which the engravings are
taken) says:
"Both the cylinders of these engines are fitted with piston valves,
placed at the back of the cylinders and worked by the single eccentric
valve gear, which has been so largely adopted and so successfully
carried out by this firm in triple expansion as well as compound
engines. It will be noticed that whilst this valve gear permits of the
cylinders being close together, it allows of the crank shaft being made
in two similar pieces, and affords exceptionally long main and crank pin
bearings, of the former of which there are only three, instead of the
usual four. In the case of the _Poplar_ the cylinders are 29 in. and 55
in. in diameter and 33 in. stroke, and the crank pins are 11 in. long,
whilst the centre main bearing, which does duty for both the engines, is
23-3/4 in. in length, each of the outer bearings being 18 in. in length,
the diameter of the crank shaft being 9-1/2 in. Another very interesting
feature about these compact little engines is the design of the front
framework. Instead of the ordinary upright columns in front of each
engine there is an arrangement which gives exceptional stiffness to the
whole structure whilst affording the fullest possible accessibility to
the main working parts, and which has the appearance of an arch, from
the shoulders of which there are branches worked up to receive the feet
of the cylinders, thus accommodating the close centres and providing for
the support of the reversing wheel without in the least obstructing the
gear below. The condenser is divided horizontally through the centre on
a plan strongly advocated by the builders, the whole of the base of the
engines being cast in one piece and made level on the under side, so as
to enable it to receive support from, and be bolted to, the engine
seating immediately beneath the crank shaft, as well as round the
margin."
[Illustration: Fig. 3405.]
[Illustration: Fig. 3406.]
[Illustration: Fig. 3407.]
[Illustration: Fig. 3408.]
CHAPTER XLIII.--MARINE BOILERS.
Boilers for marine engines are, in England, made of special qualities of
plate, the best being termed Yorkshire, and a nearly equal grade,
Staffordshire. The plates for the shell, the furnace bottoms and the
gusset stays are made of Staffordshire, while the tube plates, furnace
tops, and such parts as require to be flanged and are subject to more
intense heat, are made of Yorkshire plate, which has more ductility.
In the United States the grades of iron used for boilers are C H No. 1
S, or charcoal hammered No. 1 shell iron, for the shell, and C H No. 1
F, or charcoal No. 1 flange iron, which is used for the furnaces and
such parts as require flanging.
In both countries steel is also used for boilers, except for the tubes,
for which it is not entirely reliable if very high pressures are to be
used.
Both the iron and steel plates are tested for tensile strength and
ductility.
The breaking strain is that which is sufficient to cause rupture, while
the _proof strain_ is that which the metal is required to withstand with
safety.
The safe working strain, or working pressure, W P, is the strain under
which it is considered safe to work the boiler.
The strength of a boiler of a given diameter and thickness of plate
varies according to the construction of the riveted seams or joints.
Boiler stays or braces are rods, ribs, or plates for supporting the
weaker parts of the boiler. Thus the tube plates may be stayed by rods
passing through both plates and screwed into them, or nuts and washers
may be used on the stays one on each side of each tube plate.
Gusset stays are iron plates which are riveted to [T] irons or in some
cases to [L] irons, which are riveted on the surfaces to be stayed.
Stay tubes are thick tubes (usually about 3/16 inch thick), which screw
into the tube sheets and are riveted over at the ends. A superior
construction, however, is to provide nuts and washers to the ends of the
stay tubes, one on each side of each tube plate.
Boiler stays are usually made of such diameters that when new they will
sustain a tensile strain of not more than 5,000 lbs. per square inch of
cross section, this being the rule of the Board of Trade.
Stays are sometimes screwed into the tube plates and then riveted over
at the outside ends. A better method, however, is to let the ends of the
stays receive a nut on each side of each tube plate.
Boiler tubes are secured in their tube plates by being _expanded_ in.
This may be done by driving in a taper steel mandrel, and then clinching
them over, or by using a tube expander. There are two principal kinds of
tube expanders, in one of which small rolls travel around the bore of
the tube and expand it, while in the other a number of segments, held
together by a spring, are forced outwards by a mandrel driven in by
hammer blows.
Too much expanding is apt to weaken the tube close to the inside face of
the tube sheet.
Boiler tubes leak first at the end which receives the greatest heat from
the fire, the leakage being caused by the expansion and contraction of
the tube, which is obviously hotter than the water which causes the tube
to expand more than the boiler shell. The remedy is to re-mandrel or
expand the tube.
The scale that forms on the face of the tube sheet keeps the water away
from contact with the plate, which with an undue thickness of scale will
crack between the tube holes.
A tube that is split or that cannot be made steam tight by being
re-mandrelled or expanded is plugged up at each end by means of either
wooden or iron plugs. The best plan, however, is to use iron discs
having a stepped diameter, so that one end will fit the bore of the
tube, and the other will form a shoulder that will cover the end of the
tube.
[Illustration: Fig. 3409.]
Each disc has a hole through its centre, so that a wrought iron rod or
bolt may be passed through the hole and receive a nut at each end.
Beneath the flange of each disc, a grummet of spun yarn and white lead
is placed, so as to make a steam tight joint when the nuts are screwed
home. This stays the tube plates as well as stopping the leaky tube.
If wooden plugs are used, they are made a driving fit in the tube bore,
and driven through until they have passed the split, and a second wooden
plug is driven tightly from the same end of the tube.
The up take of a marine boiler is the casing or passage way through
which the heat and gases pass after leaving the boiler. A dry up take is
one which is outside of the boiler, as in Fig. 3409, which represents an
outside view of a boiler such as shown in Figs. 3410 and 3411.
A wet up take is one which passes through the boiler, and therefore has
fire on one side and steam on the other. It is therefore under a
collapsing pressure.
The furnace of a marine boiler extends from the fire door to the
combustion chamber (_i. e._, the box in which the heat of the furnace
passes before returning through the tubes).
The superheater of a marine boiler is a cylindrical vessel receiving the
steam from the boiler, and delivering it to the main steam pipe, whence
the steam is delivered to the engines, etc. When it has no connection
with the up take, it may, however, be more properly termed a steam
driver, since it serves to separate the steam from entrained water, and
does not superheat the steam.
In some cases, however, the superheater takes the form of a spherical
ended cylinder standing in the up take.
The receiver of a marine boiler is a drum or cylinder that receives the
steam from the boiler and from which the steam passes through the steam
pipe to the engine. The receiver is by some called the _steam chest_ of
the boiler.
The fittings essential for a marine boiler are: The safety valves; the
test cocks (or gauge cocks, as they are sometimes termed); the water
gauge glass; the stop valves; the check valve for the boiler feed pipe,
and the valves for letting on steam to the main engine and such other
engine or engines as may take steam from the main boiler; the scum
cocks; the blow off cocks; and a small cock to enable the drawing of
water from the boiler to test its degree of saltness.
There are two kinds of safety valves, the dead weight and the spring
loaded.
A dead weight safety valve is one in which the valve is held to its seat
by dead weight, the objection to which is, that when the vessel rolls
the effect of the weight or weights upon the valve is diminished; hence
under heavy rolling the steam may blow off at a less pressure than the
valve is set for.
A lock up safety valve is a dead weight safety valve, the top of whose
spindle is provided with a cast iron cap or bonnet with two handles on.
This cap is keyed to the spindle, and the keyway is so disposed that no
extra weight can be added to the valve, while at the same time the valve
can be lifted from its seat and turned around.
A spring loaded safety valve is one in which the valve is held down by
the pressure of a spiral spring, and this pressure will obviously not
vary, no matter how much the ship rolls.
In proportion as the valve lifts and the spring compresses, its
resistance increases, and this tends to impair the accuracy of the
valve. This, however, is offset from the fact that when the valve rises
from its seat it presents a greater area for the steam to act against.
The area of safety valve required by the English Board of Trade is about
1/2 square inch of valve area per square foot of fire grate area.[67]
[67] See page 409, Vol. II., for safety valve calculations.
There are three test cocks, which are sometimes placed in a diagonal row
on the front of the boiler, and sometimes on the fitting for the gauge
glass. The top test cock shows highest level to which the water should
rise in the boiler, and the lowest one the lowest level, the middle cock
indicating the average. There is usually a vertical distance of about 4
inches between the test cocks, which gives a permissible range of 8
inches in the level of the water in the boiler.
Test cocks are prevented from choking with scale by passing a wire
through the cock and clear into the boiler, a plug being provided,
which, when removed by unscrewing, permits the insertion of the wire.
This cleaning must obviously be performed when there is no steam on the
boiler.
A gauge glass is a glass tube whose bore is open to the boiler. It is
fitted at each end to a brass socket that is screwed into the boiler,
each socket having a cock that permits communication between the gauge
glass and the boiler to be shut off in case the glass should break. The
bottom socket is also fitted with a cock, which, on being opened,
permits the water and steam to blow through the gauge glass and clean it
of scum or dirt.
The gauge glass must be plainly in sight, and placed at such a height
that when the desired quantity of water is in the boiler it will half
fill the gauge glass.
Glass water gauges, instead of attaching to the boiler, are sometimes
fitted to a fitting that connects to the top and bottom of the boiler,
with the object of attaining, for the gauge glass, water free from the
scum and impurities which collect at and near the surface of the water
in the boiler. This fitting should have cocks in each pipe leading to
the boiler, so that in case the gauge glass breaks, steam can be shut
off from the boiler.
In some cases the test cocks are also attached to this fitting, and in
this case the construction should be such that shutting off
communication between the gauge glass and the boiler will not at the
same time shut off communication between the test cocks and the boiler.
When the boiler is priming or steaming very fast, the gauge glass may
show a false water level, hence reading should be compared with that of
the test cocks.
If the water gets too low, the first parts of the boiler to be injured
will be the top of the flame box, or the combustion chamber, and the top
row of tubes, because they are the first surfaces that the water will
fall below and leave exposed to the heat without having water on the
other side.[68]
[68] See page 370, Vol. II., on low water in boilers.
The pressure in the boiler is shown by a steam gauge, pressure gauge, or
dial gauge as it is promiscuously called.
A Bourdon dial gauge or pressure gauge consists of a dial casing,
containing a hollow thin brass hoop, oval in cross section, which
receives steam from the boiler.
This hoop is fixed at one end, while the other end is closed and free to
move. The free end is connected by a small link to a toothed sector,
which gears or engages with a small pinion fast upon the spindle of the
pointer or needle. When the steam is admitted into the hoop, it
straightens out or expands in diameter to an amount that is
proportionate to the amount of the pressure within the hoop, and thus
causes the needle or index pointer to revolve, and denote from the
markings or readings of a dial plate the amount of pressure within the
hoop.
If the pressure within the hoop is released, it will move to its normal
or zero position. In the course of time, however, the hoop is apt to get
a slight permanent set and not indicate correctly. It may, however, be
approximately tested for accuracy by testing its readings with that of
the safety valve.
The working parts of the gauge, and its casings also, are made of brass,
so that they shall not corrode, and to prevent the heat of the steam
from permeating the gauge and impairing the action from expanding the
parts, a small quantity of water interposes between the gauge and the
steam, the construction being as follows:
Outside the gauge casing the steam pipe is bent into a loop forming an
inverted syphon which is to contain the water.
At the lowest point in the bend of the syphon a small cock is inserted,
which lets the water out of the leg of the syphon nearest to the boiler,
because water in that leg would, from its weight, cause the gauge to
show a pressure higher than that in the boiler.
The pressure shown by a steam gauge is that above atmosphere,[69] and
not that above vacuum.
[69] See page 367, Vol. II., for remarks on total pressure and
pressure by gauge.
The stop valve of a marine boiler is a valve that is opened to let the
steam into the main steam pipe.
A blow off cock is a cock employed to blow off, or let all, or a part
of, the water out of a boiler. There are generally two, one on the
bottom of the boiler, and the other at the ship's side, so that if the
pipe was to break or get damaged, the cock at the vessel's side can be
closed to keep the sea water out, while that on the boiler may be closed
to keep the water and steam in the boiler. These two ends cannot
obviously be obtained if one blow off cock only was used.
Blow off cocks are opened and closed by a spanner or key that is
removable from the cock, and to prevent the possibility of taking off
the spanner or key, before the blow off cock is closed, a spanner guard
is employed.
A spanner guard is a cap having a lug or tongue, which projects into the
hole in the spanner guard, through which the spanner or key must pass
before it can fit on the head of the blow off cock, and the key or
spanner has a corresponding recess, so that the spanner or key can only
be put on or taken off when the cock is closed.
Blowing off a boiler is emptying it entirely, as for examining the whole
interior of the boiler.
Blowing down a boiler is letting out a portion of the water, so as to
carry off the loose scale, mud, or sludge that may accumulate on the
bottom of the boiler. The mud or sludge would form into scale if allowed
to remain.
A scum cock is a cock employed to blow off a portion of the surface
water in a boiler, and thus remove the scum, salt, and impurities which
float or are thrown up to the surface.
Two scum cocks are employed, one on the side of the boiler, and one on
the side of the ship. These two cocks are connected by a pipe. That on
the boiler is placed a little below the working level, which is supposed
to be (and is kept as nearly as possible) about 9 inches above the top
row of tubes.
Sluice valves are doors sliding, water tight, in ways at the entrance to
the bulkheads on both sides of the ship. They should be worked from
above, in order that they may be shut when the depth of water in the
bulk heads might prevent them from being worked from below. These valves
should be operated occasionally to ensure that they slide easily and are
in working order.
Scale in marine boilers using salt water is composed of sulphate of
lime. It is most objectionable on the furnace tops, on the sides and
tops of the combustion chamber, on the tubes and on the tube plates. It
may be prevented to some extent from forming by a rapid circulation of
the water in the boiler, by blowing down the boiler through the scum
cocks, by the suspension in the boiler of zinc plates in contact with
iron ones, by impregnating the water with chemical antidotes, which
maintain the impurities in the form of mud or sludge, and by purifying
the feed water. If surface condensers are used, scaling is obviously
diminished by feeding as little salt water as possible, which may be
done by not getting up a steam pressure high enough to cause the safety
valve to blow off, and by preserving the water from the exhausts of the
donkey or other engines about the ship.
A thin coating of scale, as say 1/32 inch thick, may serve as a
protection against the chemical action of water that would act to
corrode the surfaces, as in the case of harbors receiving the waste
waters from chemical works or other impure waters. A thick coating of
scale causes the plates to burn on the side receiving the furnace heat,
and causes blisters to rise, while at the same time it decreases the
value of the heating surface.
Scale on the tubes causes them to expand more, and therefore leak in the
tube sheets.
This extra expansion sometimes breaks away the scale at the neck of the
tube in the tube sheet and gives access to the water there, and the
chemical action of water will in some cases cause the tube to be eaten
through close to the tube plate.
Scale is removed mechanically by chisels, scrapers and chipping hammers,
which are applied to all the surfaces that can be got at from the inside
of the boiler (the man hole affording access to the boiler). After the
scale has thus as far as possible been removed, it is washed out of the
boiler. The efficiency with which scale may be removed from the tube
sheets and tubes depends, to a great extent, upon the facilities the
arrangement of the rows of tubes affords in giving access to the scaling
chisels.
The salinometer. Salt water is heavier than fresh water, hence the
amount of saltiness of water may be known from its density or weight. A
salinometer is an instrument that determines from the density of the
water the amount of salt contained in the water. It consists of a
graduated stem at whose extremity is a weighted bulb which partially
sinks the tube in the water; the depth to which the bulb sinks shows the
density of the water.
The reading of a salinometer is taken at the water level, and is read on
the tube, which is graduated as follows: The mark furthest from the bulb
or highest up the stem is marked O, and if the zero line is level with
the surface of the valve in which the salinometer floats, it indicates
fresh water. If salt be added to the fresh water, the salinometer will
rise in the water, and when the water contains 1 lb. of salt to 32 lbs.
of water (which is the average degree of saltiness of sea water), the
line marked 1/32 on the salinometer tube will be level with the surface
of the water. If the saltiness of the water be increased, the
salinometer will rise in the water until, at 2 lbs. of salt to 32 lbs.
of water, a line (on the tube) marked 2/32 will be level with the
surface of the water. The space between the 1/32 and 2/32 is divided
into halves and quarters.
As the density of the water varies with its temperature, therefore the
readings on the salinometer must agree with some specific temperature,
which is usually 200° Fahrenheit, and the reading of the salinometer is
correct only when the water is at that temperature. If, however, the
water varies a few degrees from the standard of temperature for which
the salinometer is marked, a correction of the reading may be made by
adding 1/8 of 1/32 for each 10 degrees, that the water is hotter, or
subtracting the same for each 10 degrees that it is cooler than the
temperature at which the salinometer is correct.
The density or specific gravity of ordinary sea water is 1.027 (that of
distilled water being unity or 1), and it contains about 4 oz. of salt
per imperial gallon.
Tallow is sometimes forced into a boiler fed with salt water to stop
priming, by means of a syringe that is screwed into a tallow cock
provided upon the boiler below the water level. If the boiler is fed
with fresh water, tallow is apt to cause priming.
Angle irons are used in boiler construction to be riveted to plates that
require supporting or strengthening, or for gusset stays to be riveted
to. Flanged plates are used in the construction of the furnaces, flame,
boxes or combustion chambers, boiler ends and tube plates or tube
sheets.
Division plates are fitted in some boilers to prevent the water from
passing from one side of the boiler to the other when the vessel rolls
heavily. This prevents some of the tubes from being left uncovered by
water, and thereby getting injured from undue heat.
These division plates are neither steam nor water tight, and stand fore
and aft of the ship. Similar division plates are sometimes used,
however, to prevent the tops of the combustion boxes from getting
overheated from the motion of the ship leaving them uncovered with
water, their location being subserved to this end and varying with the
position of the boiler.
The superheater of a marine boiler is provided with a safety valve, and
sometimes with a pressure gauge to enable the comparing of the steam
pressure with that in the boiler, and should also be provided with a
gauge glass, to show when heavy priming is going on.
The main stop valve is upon the superheater, as is also the blast pipe.
Priming is a lifting, into the steam space of the boiler, of a part of
the water, and may arise from heavy firing, from the safety valve
blowing off, from too little steam space, and from other causes.
Priming[70] often occurs when the boiler feed is changed from salt water
to fresh water, or from fresh to salt water.
[70] See page 370 Vol. II., on priming.
A separator or interceptor is a device fitted to either the superheater
or to the steam receiver, for separating entrained water from the steam.
It consists of a rectangular box or chamber with a partition plate
extending from the top half down into the box.
The entering steam strikes the face of the partition plate against which
the water collects, and from which it drops to the bottom of the box,
while the steam passes under the partition and out at the other side to
the engine.
The draught of a boiler is caused by the heat expanding the air and
lightening it, thus causing it to ascend. It can be checked by stopping
the exit of heated air up the funnel by means of a damper, by checking
the flow of cold air into the furnace, by closing the dampers, by
opening the furnace doors and letting cold air in the furnaces above the
fires.[71]
[71] See page 368, Vol. II.
A blast pipe is a small pipe leading from the superheater to the funnel,
and provided with a stop cock.
It is used for letting a jet of steam up the funnel to promote the
draught.
Flame seen at the top of the funnel is caused by the combustion of gases
that would have been consumed in the furnace had there been sufficient
air or sufficient room for complete combustion. It may be caused in a
variety of ways, as insufficient openings between the fire bars, too
narrow a space between the bridge wall and the boiler, or too deep a
fire upon the bars. It is detrimental, because it obviously wastes fuel.
Dampers are used to regulate the draught in the furnace; they are fitted
to the ash-pits or to the funnel, and should be fitted to both, because
closing a damper in the funnel sets up a certain amount of pressure in
the furnace by holding the heat, whereas dampers at the ash pit doors
and none in the funnel lets the heat out and prevents cold air from
getting in to promote combustion.
When there are no dampers the furnace doors are open instead, to check
the draught; this is, however, highly injurious to the boilers.
The most rapid wasting of the plates of a marine boiler occurs alongside
the fire bars, on the furnace tops, at the back of the flame box or
combustion chamber, and in those plates generally that receive the most
intense heat, and especially when they are heavily coated with scale and
are not covered with water.
The scale that forms on the face of the tube sheet keeps the water away
from contact with the plate, which, with an undue thickness of scale,
will crack between the tube holes.
A tube that is split or that cannot be made steam tight by being
re-mandrelled or expanded is plugged up at each end by means of either
wooden or iron plugs. The best plan, however, is to use iron discs
having a stepped diameter, so that one end will fit the bore of the
tube, and the other will form a shoulder that will cover the end of the
tube.
Each disc has a hole through its centre, so that a wrought iron rod or
bolt may be passed through the hole and receive a nut at each end.
Beneath the flange of each disc, a grummet of spun yarn and white lead
is placed, so as to make a steam tight joint when the nuts are screwed
home. This stays the tube plates as well as stopping the leaky tube.
If wooden plugs are used, they are made a driving fit in the tube bore,
and driven through until they have passed the split, and a second wooden
plug is driven tightly from the same end of the tube.
Black smoke is an evidence of incomplete or imperfect combustion, and
may be, to a great extent, prevented by careful firing, as by feeding
gradually and evenly, by the admission of the proper quantity of air, or
by a jet of steam admitted above the dead plates.
The furnace bars are ordinarily of cast iron about 1-1/4 inches thick at
the top, tapered towards the bottom, and with an air space of from 1/2
to 3/4 inch between them.
They require less air space for Welsh than for Newcastle coal, as the
latter is the flaming or gaseous coal, and burns the fastest.
The quantity of coal burned in marine boiler furnaces is about 15 lbs.
per square foot of fire grate area per hour; hence the quantity burnt
per day with common average engines with 4 furnaces, 3 feet wide and 5
feet long, may be found by multiplying the area of the 4 furnaces (60
feet) by the number of lbs. (15) burned per foot of grate per hour,
which will give the total lbs. weight burned per hour, which, divided by
112 lbs., will give the hundredweight burned per hour, and this,
multiplied by the number of hours reckoned as constituting a day, gives
the fuel consumption per day, based upon 15 lbs. coal per square foot of
fire grate area.
The number of tons of steam coal burnt per day to drive an ordinary
steamer of 40 feet beam 10 knots an hour by steam alone (or without
sail), will depend upon the kind of engine used. Experience teaches us
that with average vessels, the beam squared equals the consumption of
coal for 40 days, in the case of an ordinary jet condenser engine; 50
days with a surface condensing engine; and 60 days with a compound
engine; hence, in the present example, assuming the engine to be jet
condensing, we may calculate the fuel consumption per day, for a vessel
40 feet beam giving 10 knots an hour, as follows:
The beam squared gives 1600 (40 × 40 = 1600), which divided by 40 (40
days) gives 40 tons per day. For surface condensing the 1600 would be
divided by 50, giving 32 tons per day; and for a compound engine the
1600 would be divided by 60, giving 26 tons 13-1/3 cwt. per day.
It is obvious, however, that calculations of this kind, in which the
ratio of expansion is not stated, are the merest approximations.
The number of tons of steam coal that will be burnt per day with a pair
of average surface condensing engines having cylinders 50 inches in
diameter will be, under average conditions, 16 tons per day, the
calculations being based upon the common assumption that the diameter of
one cylinder squared and divided by 100 gives the consumption of fuel in
tons per day for condensing engines not compounded; thus, 40 × 40 = 1600
÷ 100 = 16 tons of coal burned per day.
Here again, the ratio of expansion not being specified, the calculation
has no real practical value.
If at sea and short of coal, bear in mind that the consumption of fuel
per mile run is greater for fast than for slow speeds; hence the
following points should be attended to:
Reduce the speed of the ship to say half the usual. Regulate the fire so
as to keep up full boiler pressure without blowing off. This will allow
the expansion or cut off valve to be set to cut off early in the stroke,
and thus save steam. If, under these conditions, the steam should
sometimes blow off at the safety valve, cover up part of the fire grate
area.
Use a thin, rather than a thick, fire, but be careful that it is not so
thin as to let currents of cold air pass through.
TO RELIEVE THE BOILER IN CASE OF EMERGENCY.--Suppose an engine breaks
down at a time when the fires are heavy and going full, that the steam
gauge shows blowing off pressure, but that the safety valve is stuck, or
from some cause or other is prevented from blowing off, and cannot be
eased or lifted, and the following is the course to be pursued:
1st. Close the ash pit dampers and open the smoke box door and fire
door. If there are no ash pit doors, close the damper in the up take and
open the fire and smoke box doors.
2d. Start the donkey engine to feed cold water into the boilers.
3d. Start the steam winches, and any other small engines that take steam
from the main boilers.
4th. Slacken the escape valves, and open the drain cocks of the
cylinders and receivers, and steam will blow through the H.P. cylinder
escape valve and drain cock at once. The H. P. slide valve may then be
worked by hand, back and forth, to let steam pass into the receiver and
blow through its escape valves and drain cock.
5th. Open the scum or brine cocks and keep them open, also open all
gauge or test cocks, etc., about the boiler.[72]
[72] It is not safe to draw the fire at a time when the pressure is at
a dangerous point, especially if heavy, as disturbing it may
temporarily increase the combustion and the danger of explosion.
[Illustration: Fig. 3410.]
Figs. 3410 and 3411 represent an example of a steel marine boiler,
designed for a working pressure of 160 lbs. per square inch, with a
margin of safety of 5.
The dimensions are as follows:
Diameter of shell 12 feet 6 inches.
Shell plate 1-1/8 " thick.
Front and back upper plates 31/32 " "
Back rivet plates 7/8 " "
Back lower plates 7/8 " "
Front tube plate 15/16 " "
Front lower plate 13/16 " "
Furnaces 17/32 " "
Inner tube plate 3/4 " "
Combustion chamber back 17/32 " "
Combustion chamber sides 17/32 " "
Outer sides of wing combustion chambers 9/16 " "
And bottom of centre one to be 9/16 " "
Shell of receiver 7/16 " "
Beds of receiver 5/8 " "
Receiver connecting pipe 3/4 " "
The riveted joints have all holes drilled. The longitudinal seams are
made with butt joints treble riveted, and with double butt straps.
The circumferential seams are lapped and treble riveted.
Fig. 3412 represents the "Martin" boiler for marine engines. In the
return flue there are a number of vertical water tubes which are very
effective in promoting circulation as well as in generating steam. These
boilers are used largely in the United States navy for moderate
pressures.
The following upon the testing and examining of a boiler of this class
is from _Modern Steam Boilers_:
"Every new boiler should, when complete, be tested by water pressure to
double the amount of the intended working pressure; for while the wisdom
of applying as high a pressure as three times the working pressure,
which is sometimes done, may be questionable, experience has shown that
a test by hydraulic pressure will reveal defects that would otherwise be
apt to pass unnoticed.
"For instance, when the top plate of a combustion box is stayed against
the pressure by girder stays that are not stayed to the boiler shell,
the girder stay merely acts to stiffen the top plate, and as a result
the whole pressure on the area of the top plate falls on the walls of
the combustion box. The back tube plate therefore springs down and
transfers part of this pressure to the furnace, causing it to become
elliptical, as may generally be found by the application of rod gauges
fitted to it before testing and tried while the pressure is on.
[Illustration: Fig. 3411.]
[Illustration: Fig. 3412.]
"This flattening under test naturally drew attention to the
defectiveness of girder stays. Another instance may be given with
reference to gusset stays, which, if fitted so as to support too large
an area of back plate, in proportion to the area of combustion box it
supports, may cause the combustion box to distort from its natural
shape, pulling the tube sheet back and flattening the furnace. The
amount of distortion may be only 1/16 inch in some cases, but that is
sufficient to show the existence of unequal strains which require
attention in boiler designing.
"This brings us to the important fact that in almost every instance
where the furnaces of marine boilers collapse, they come down at the
sides, notwithstanding that when collapse occurs from overheating, the
crown of the furnace must have been left bare of water first, and
should therefore come down first, flattening the furnace at the top.
This points to the conclusion, that the top of the furnace received some
extraneous support.
"When a furnace collapses from corrosion, it naturally gives way at the
most corroded part. An hydraulic test to twice the working pressures is
recommended for new boilers only, unless it be small vertical
cylindrical and steam launch boilers, which may always be subjected to
the same test as new main boilers.
"In the case of old main boilers, however, and particularly rectangular
ones, an hydraulic test of less than twice the working pressure may be
employed, the amount being governed by the circumstances of the case.
If, for instance, a boiler has undergone a thorough repair and received
new furnaces, then every part of the boiler should have received
proportionate consideration and an hydraulic test depending upon the
judgment of the responsible engineer, but not less than one and one-half
times the working pressure should be made, while one of one and
three-quarter times could scarcely be objected to. This, however, is a
subject upon which there is some controversy, especially in the case of
old boilers having a good foundation of strength, but patched or local
weak spots, such as combustion chamber backs and sides, these patches
having been, perhaps, made with a view to a more extensive repair in the
near future.
"In such a case as this an hydraulic test sufficient to prove the
tightness of the seams and joints may, perhaps, be all that is
absolutely essential.
"After a boiler has been tested by hydraulic pressure it should be
examined internally, as it sometimes occurs that a stay may break under
the test (especially if gusset stays are employed), and the extra strain
thrown on the adjacent parts may cause them to fail, and thus cause the
destruction of the boiler when under strain.
"When an examination is to be made inside and outside of a boiler, the
boiler must be properly prepared for the same, which may be done as
follows:
"The tubes should be swept; the furnace cleaned out; the fire bars
should be taken out; the bridges in the furnace should be taken down;
the up take smoke box and combustion box should be cleaned out and
swept; every man hole and hand hole or peep hole door should be removed;
the bottom of the boiler should be cleaned out and dried (in damp
weather a little heat may be necessary for this purpose); all
impediments, if any, should be removed in order to allow the bottom
outside to be inspected; at the time of inspection a few mats, good
lights, a hand hammer and small chipping hammer should be at hand. In
the case of a boiler having any plates weakened by corrosion, a 5/8 inch
tapping drill with a drilling brace should also be provided to test the
thickness of such plates if considered necessary.
"The safety valves should invariably be taken out for examination, and
it is a commendable feature sometimes followed to take out the feed
valves, stop valves, blow off and brine cocks; at the same time, all the
deposits that would prevent a thorough examination of the boiler should
be removed. In some cases, however, there may not be time for the
scaling before it is necessary for the repairs to be gone on with, and,
in that case, a good examination may with care be made by an experienced
man.
"To proceed, then, with the examination, the boiler should be entered
through the man hole door beneath the furnaces, examining the boiler
bottom and the bottom and sides of the furnaces all the way along, and
on arriving at the end of the boiler the water space and stays at the
backs of the combustion boxes can be examined as well as the midship
combustion box stays and plates. In an old and corroded boiler it may be
found necessary to use a chipping hammer very freely about the furnaces,
particularly below the lap of the furnace.
"The most corroded part of a furnace will generally be found about on a
line with the fire bars, but the furnaces may have suffered from some
other cause than the corrosion due to ordinary wear, as, for example,
from chemical or galvanic action, and in that case they may be found
comparatively good at the sides but with the extreme bottoms in a
_dangerously_ corroded state, perhaps in the form of pit holes extending
half through the plate and _hidden by a coating of red scale, which
requires to be chipped away before the pit holes are brought to light_.
"Corrosion by galvanic action may have produced honey combing or a
general attack over the surfaces, which have a dark or _dark and
sparkling appearance_, the latter more particularly when corrosive
action has been very active.
"Of these various classes of corrosion that which is the most deceiving
is that which attacks the plates over the largest surface of the plate,
leaving at the same time an apparently smooth exterior surface, for in
this case the extent of the waste cannot be so clearly detected by the
eye, and the only reliable way of testing the thickness is by drilling a
hole through the plate.
"The flanges of the furnaces should always be examined in the bends, for
flaws, for such defects, although not very common, do at times
unexpectedly make their appearance, and might, if not detected, be the
means of breaking the boiler down at sea. This part of the inspection
being made, any drilling that is to be done to ascertain the thickness
of suspected plates may be proceeded with before the rest of the
inspection is made.
"It may, however, be well to remark that a very common defect is the
wasting away of the combustion box plates around the necks of the stays
or the internal surface of the plates, and it is a usual thing for
deposits to accumulate around these necks, hence, unless these deposits
have been removed (particularly in the case of boilers about three years
old), the true condition of the boiler may not be known.
"The plate around the man hole door should next be examined, a great
defect from waste at the surface that makes the water tight joint. Next
comes the man hole door itself, which should have the rubber or other
material used to make the joint cleaned off, for cases have occurred
where the surface beneath was found apparently sound, whereas the
application of a chisel showed that the iron was so corroded that but
little iron was left in the flange, causing great surprise that the
whole door had not blown out. This defect may generally be looked for in
old boilers, and serves to emphasize the necessity for strong wrought
iron doors.
"The outside surfaces of the end plate in the vicinity of the furnace
fronts are a great source of trouble in some boilers, particularly where
plane furnaces are fitted and flush rivets used for connecting them to
the end shell plates.
"The insides of the furnaces and combustion boxes next require
attention. The most common defects here are lamination of the furnace
plate (if of iron), slight collapsing of furnaces, wasting of the
furnace plates (particularly when anthracite coal has been used), and
wasting when the fire bar bearers or bridges have rested against the
plate.
"In the combustion box the buckling of flat plates may have occurred;
plates may have wasted from leaks, distortion of the crown sheet from
shortness of water may have occurred, or tubes may leak, and whenever,
after sounding with the hammer, doubt exists as to the strength of the
plate, a hole should be drilled through to test the thickness.
"The wing sides of the furnace may next be examined (through the usual
peep holes or by having a boiler mounting taken off for the purpose),
and the shell plating on the sides of the boiler, paying special
attention to the plates where the feed water enters.
"We may next examine the outside of the bottom of the boiler, which
should never be totally inaccessible to the eye, and should always be
capable of being reached by a long-handled paint brush, for if kept well
painted, the bottom of the boiler is, so far as the exterior is
concerned, as durable as the other parts of the shell.
"If, however, the bottom is not kept painted and gets damp, and more
particularly from bilge water, it will corrode rapidly, and the boiler
must be lifted for examination. Under these circumstances a new boiler
_must_ at five years, at the very most, be lifted for examination, and
if found comparatively good it should not be taken as an indication of
the probable condition of any other boiler working under similar
conditions, for the only means of avoiding a great risk in this matter
is to rigidly inspect.
"In the case of flat bottomed boilers in small vessels a good result has
obtained by placing them on a bed of cement, which if properly done
excludes the bilge water from approaching the plate; but even this
precaution would scarcely be sufficient to justify an engineer in
neglecting to lift the boiler at reasonable periods for examination of
the bottom.
"The internal examination of the boiler is continued from the top by
examining the stays in the steam space, the tube and tube plates,
getting down between the nests of tubes and reaching the crowns of the
furnaces. The surface of the shell plates should also be examined, more
particularly if the boiler contains plates subject to heat on the
outside and steam on the other (as in the case of wet up take boilers),
for under these conditions a steel plate may become as weak and
unreliable as a piece of cast iron.
"If the boiler is fitted with the superheater, the examination of the
latter is of the utmost importance, as rapid destruction is here a
common occurrence. In the case of a circular marine boiler of any size,
nothing need be taken for granted, even though an hydraulic test be made
up to twice the working pressure, because there is room for a thorough
internal inspection which may disclose defects that would not be shown
from the hydraulic test. The proper proportions of fire grate surface,
heating surface, steam space, etc., in a marine boiler differ with the
type of boiler and engine, and the steam pressure and degree of
expansion employed.
"Upon the question of steam space, for example, it is asserted by many
that marine boilers are not so liable to prime under the higher
pressures, and as a result of this asserted fact the steam receiver is
in some cases being dispensed with.
"It may be observed, however, that priming to any extent is so costly
and detrimental that much consideration needs to be exercised before
dispensing with the provisions ordinarily made to prevent it.
"For circular tubular boilers, having a working pressure of from 60 to
80 lbs. per square inch and to be used for compound engines, the
following proportions represent current practice.
"1st. One square foot of fire grate area to every indicated horse power
of the engine.
"2d. 28 square feet of heating surface[73] to 1 square foot of fire
grate area.
[73] The heating surface here referred to includes the total interior
surface of the tubes, the sides, backs, crowns and tube plates of the
combustion boxes, and that part of the furnace that is above the level
of the fire bars, but does not include the front tube plate (_i. e._,
the tube plate in the smoke box).
"3d. 6-1/2 to 8 cubic feet of steam space to each square foot of fire
grate area.
"4th. 8 to 10 square feet of tube surface to the total heating surface
in single ended boilers.
"5th. 8-1/2 to 10 is about the ratio of tube surface to the total
heating surface in double ended boilers.
"6th. The diameters of boiler tubes should be about one-half inch for
each foot of length of tube. If less, the tube is liable to choke. About
14 cubic feet of steam (of from 60 to 80 lbs. pressure) should be made
for each square foot of fire grate area.
"Each square foot of fire grate will burn from 13 to 18 lbs. of steam
coal per hour. About 1-1/2 cubic feet of live steam (of the above
pressure) is required for each indicated horse power."
CHAPTER XLIV.--HARDENING AND TEMPERING.
Hardening and tempering processes are performed upon steel for three
purposes:
1st. To enable it to resist abrasion and wear.
2nd. To increase its elasticity.
3rd. To enable it to cut hard substances and increase the durability of
the cutting edge.
Of these, the first is the simplest, because the precise degree of
hardness imparted is not of vital importance.
The second is more difficult, because the quality of the steel employed
for such purposes is variable, and hence the tempering process must be
varied to suit the steel. The third is of the greatest importance,
because the articles to be tempered are the most expensive to make, the
duty obtained is of the greatest consequence to manufacturing pursuits,
and the fine grade of steel employed renders it more liable to crack in
the hardening process.
In those mechanical parts of machines which are hardened to resist
abrasion and wear, the quality or grade of the steel is very often
selected with a view to obtain strength in the parts and ease of
mechanical manipulation in cutting them to the required shape, rather
than to the capacity of the steel to harden. Hence, tougher and more
fibrous grades of soft steel termed "Machine" steel, are employed,
meaning that the steel is especially suitable for the working parts of
machines. This class of steel is of a lower grade than that known as
"tool" steel. It is softer, works, both on the anvil and in the lathe,
more easily, and will bear heating to a higher temperature without
deteriorating. It approaches more nearly to wrought iron, and is
sometimes made of so low a grade as to be scarcely distinguishable
therefrom.
The kinds of steel used where elasticity is desired are known as spring
steel, blister steel, and shear or double-shear steel, although, for
small springs, steel of the tool-steel class is often employed.
The word _temper_, as used by the manufacturer of steel, means the
percentage of carbon it contains, the following being the most useful
tempers of cast steel.
_Razor Temper_ (1-1/2 per cent. carbon).--This steel is so easily burnt
by being overheated that it can only be placed in the hands of a very
skilful workman. When properly treated it will do twice the work of
ordinary tool steel for turning chilled rolls, &c.
_Saw-file Temper_ (1-3/8 per cent. carbon).--This steel requires careful
treatment, and although it will stand more fire than the preceding
temper should not be heated above a cherry red.
_Tool Temper_ (1-1/4 per cent. carbon).--The most useful temper for
turning tools, drills, and planing-machine tools in the hands of
ordinary workmen. It is possible to weld cast steel of this temper, but
not without care and skill.
_Spindle Temper_ (1-1/8 per cent. carbon).--A very useful temper for
mill picks, circular cutters, very large turning tools, taps, screwing
dies, &c. This temper requires considerable care in welding.
_Chisel Temper_ (1 per cent. carbon).--An extremely useful temper,
combining, as it does, great toughness in the unhardened state, with the
capacity of hardening at a low heat. It may also be welded without much
difficulty. It is, consequently, well adapted for tools, where the
unhardened part is required to stand the blow of a hammer without
snipping, and where a hard cutting edge is required, such as cold
chisels, hot salts, &c.
_Set Temper_ (7/8 per cent. carbon).--This temper is adapted for tools
where the chief punishment is on the unhardened part, such as cold sets,
which have to stand the blows of a very heavy hammer.
_Die Temper_ (3/4 per cent. carbon).--The most suitable temper for tools
where the surface only is required to be hard, and where the capacity to
withstand great pressure is of importance, such as stamping or pressing
dies, boiler cups, &c. Both the last two tempers may be easily welded by
a mechanic accustomed to weld cast steel.
The preference of an expert temperer for a particular brand of steel is,
by no means, to be taken as proof of the superiority of that steel for
the specific purpose. It may be that, under his conditions of
manipulation, it is the best, but it may also be that, under a slight
variation of treatment, other brands would be equal or even superior. It
may be accepted as a rule that the reputation of a steel for a
particular purpose is a sufficient guarantee of its adaptability to that
purpose, and all that is necessary to a practical man is to be guided by
the reputation of the brand of steel, and only change when he finds
defects in the results, or ascertains that others are using a different
steel with superior results.
Where large quantities of steel are used the steel manufacturers in many
cases request customers to state for what particular purposes the steel
is required, their experience teaching them what special grade of their
make of steel is most suitable.
To harden steel it is heated to what is termed a "cherry red" and then
dipped into water and held there until its temperature is reduced to
that of the water.
_Tempering_ steel as the blacksmith practises it consists in modifying,
lowering, or tempering the degree of hardness obtained by hardening. The
hardening of steel makes it brittle and weak in proportion as it is
hardened, but this brittleness and weakness are removed and the steel
recovers the strength and toughness due to its soft state in proportion
as it is lowered or tempered.
When therefore a tool requires more strength than it possesses when
hardened, it is strengthened by tempering it. Tempering proceeds in
precise proportion as the temperature of the hardened steel is raised.
When the steel is heated to redness the effects of the hardening are
entirely removed, and the steel, if allowed to cool slowly, is softened
or annealed. To distinguish maximum hardness from any lesser degree the
terms to give the steel "all the water," or to harden it "right out" are
employed, both signifying that the steel was heated to at least a clear
red, was cooled off in the water before being removed from the same, and
was not subsequently tempered or modified in its hardness. If a piece of
steel has its surface bright and is slowly heated, that surface will
assume various colors, beginning with a pale straw color (which begins
when the steel is heated to about 430°) and proceeds as in the following
table:--
Fahr.
Very pale yellow 430°
Straw yellow 460
Brown yellow 500
Light purple 530
Dark purple 550
Clear blue 570
Pale blue 610
Blue tinged with green 630
It happens that between the degree of hardness of hardened steel and the
temper due to reheating it up to about 600° Fahr. lie all the degrees of
hardness which experience has taught us are necessary for all
steel-cutting tools. Hence we may use the appearance of colors as
equivalent to a thermometer, and this is called color-tempering. The
presence of these colors or of any one of the tints of color, however,
is no guarantee that the steel has been tempered or possesses any degree
of hardness above the normal condition, because they appear upon steel
that is soft or has not been hardened. To obtain exact results by color
tempering, therefore, the steel must first be thoroughly hardened, and
this is known in practice by the whiteness of the hardened surface.
Any number of pieces hardened so as to have a white surface may be
tempered to an equal degree of color, or heated to an equal
thermometrical temperature, with the assurance that they will possess a
degree of hardness sufficiently uniform for all practical purposes; but
if their hardened surfaces have dark patches, tempering to an equal tint
of color is no guide as to their degree of temper. Successful tempering,
therefore, must be preceded by proper hardening.
The muffle should therefore bear such a proportion in size that when
heated to a blood red, and taken from the fire, its temperature will be
reduced to nearly that of the steel when it has acquired its proper
degree of temper.
The shape of the bore of the muffle should always conform to that of the
article tempered; for round work, a round muffle; for square work, a
square one; and so on. The muffle should be shorter than the work, so
that the tempering of either end of the work may be retarded, if it is
proceeding too fast, by allowing that end to protrude through the
muffle.
Color tempering, it will be observed, gives us no guide or idea of any
of the degrees of temper which occur while the hardened steel is being
heated up to about 430° Fahr.; and thus it leaves us in the dark as to
all the ranges of hardness existing in steel thoroughly hardened and
tempered to any degree less than that due to about 430° degrees of
reheating. How wide this range may be can be appreciated when it is
remembered that in the color test there are only 200° of heat between
the hardness known as straw color, which is hard enough for almost all
cutting purposes, and blue, tinged with green, which is almost normal
softness.
It is for this reason (among others) that where very exact results are
to be obtained and a large number of pieces are to be tempered, fluxes,
heated to the required temperature, are very often employed.
Color tempering is conducted in different ways. In a muffle, in heated
sand, with hot pieces of flat iron, and in boxes heated to the requisite
temperature in an oven, the temperature being indicated by a pyrometer
or heat-gauge. The articles to be tempered remain in the oven a length
of time determined by experiment or experience, these being influenced
by the size and substance, or thickness, of the pieces.
A muffle is a tube or cylinder receiving its heat from the outside and
open at the end or ends to receive the steel. Where tempering is carried
on continuously the muffle is kept in the fire, although it is claimed
by many that better results are obtained by removing it from the fire
when heated. It is obvious that if the muffle is heated evenly the steel
will temper most evenly by being held in the centre of the muffle, or
the piece may be revolved and moved endways in the muffle in order that
the steel may heat evenly. The tempering should always proceed slowly,
otherwise the heat may not have time to penetrate the steel to the
centre, the outside tempering more quickly, thus the tool will be weak
because of the undue hardness of the interior metal. Furthermore,
protruding edges, or slight sections of the steel, may reduce to the
required temper before the main body of the steel, which induces either
serious weakness of the insufficiently tempered part, or softness in the
thin sections, providing that the steel is kept long enough in the
muffle to temper the main body to the proper degree.
In heating steel to harden it, especial care is necessary, particularly
when the tool is one finished to size, if its form is slight or
irregular, or if it is a very long one, because unless the conditions
both of heating and cooling be such that the temperature is raised and
lowered uniformly throughout the mass, a change of form known as
_warping_ will ensue. If one part gets hotter than another it expands
more, and the form of the steel undergoes the change necessary to
accommodate this local expansion, and this alteration of shape becomes
permanent. In work finished and fitted this is of very great
consideration, and, in the case of tools, it often assumes sufficient
importance to entirely destroy their value. If, then, an article has a
thin side, it requires to be so manipulated in the fire that such side
shall not become heated in advance of the rest of the body of the metal,
or it will become locally distorted or warped, because, though there may
exist but little difference in the temperature of the various parts, the
more solid parts are too strong to give way to permit the expansion:
hence the latter is accommodated at the expense of the form of the
weakest part of the article.
Pieces, such as long taps, are very apt to warp both in the fire and in
the water. In heating, they should rest upon an even bed of coked coal,
and be revolved almost continuously while moved endways in the fire; or
when the length is excessive, they may be rested in a heated tube, so
that they may not bend of their own weight. So, likewise, spirals may be
heated upon cylindrical pieces of iron or tubes to prevent their own
weight from bending or disarranging the coils.
Experiments have demonstrated that the greater part of the hardness of
steel depends upon the quickness with which its temperature is reduced
from about 500° to a few degrees below 500°, and metal heated to 500°
must be surrounded by a temperature which renders the existence of water
under atmospheric pressure impossible; hence, so long as this
temperature exists the steel cannot be in contact with the water, or, in
other words, the heat from the steel vaporizes the immediately
surrounding water. The vapour thus formed penetrates the surrounding
water and is condensed, and from this action there is surrounding the
steel a film of vapour separating the water from the steel, which
continues so long as the heat from the steel is sufficiently great to
maintain the film against the pressure of the water and the power of the
water which rushes toward the steel to fill the spaces left vacant by
the condensation of the vapour as it meets a cooler temperature and
condenses. The thickness of the vapour film depends mainly upon the
temperature of the steel; but here another consideration claims
attention. As the heated steel enters the water the underneath side is
constantly meeting water at its normal temperature, while the upper side
is surrounded by water that the steel has passed by, and, to a certain
extent, raised the temperature of. Hence, the vapour on the underneath
side is the thinnest, because it is attacked with colder water and with
greater force, because of the motion of the steel in dipping. For these
reasons it is desirable, especially with thick pieces of steel, to
inject the water in a full stream upon the article, as is done in the
Brown & Sharpe hardening tanks.
In cases where a great many pieces are to be hardened and tempered to an
even degree, the steel is heated for the hardening in a flue with the
advantage that contact between the heated steel and the impurities (as
sulphur or silicon) of ordinary fuels is avoided, and also that all the
pieces may be heated, and therefore hardened, to a uniform degree. The
capacity of this system is great, because a number of pieces can be
heated without fear of any of them becoming overheated if not attended
to immediately. Thus the Waltham Watch Co. heat their mainsprings for
the hardening in a flux composed of melted salt and cyanide of potash,
the latter serving to clean the surface of the steel; but as the latter
wastes it requires to be added occasionally.
The Watch Company, however, find this mixture will not do for the hair
springs, as it alters (to a very small degree, however) the nature of
the steel; hence these springs are heated for hardening in melted glass.
The Pratt and Whitney Co. heat their taps, &c., for hardening in a
composition of equal quantities of salt and cyanide of potash, adding
the latter as it wastes, and temper them by the cold test.
The Morse Twist Drill Co. use a similar compound for heating to harden,
and the following apparatus for dipping. In a large tank having a free
water circulation, stand two pots of a capacity of about five gallons
each, one of these contains cyanide of potash and salt, and another
sperm oil. The heated work is dipped for an instant into the pot
containing the potash and salt, which clean the surface of the steel,
and then cooled in the main water tank; but if the work is, from its
shape, liable to crack, it is at the final cooling dipped in the pot of
sperm oil instead of in the water.
Before heating the steel it is dipped in soft soap to prevent oxidation,
and on dipping it into the potash and salt pot it causes a cracking
sound, the operator knowing from the sound if the mixture is proper, and
how long to hold the steel therein.
This company first fill the heating pot with salt, and then add cyanide
of potash until a trial of the tool gives quite satisfactory results,
adding cyanide of potash as the work proceeds to make up for the
evaporation and keep the mixture of the compound correct.
In many cases it is considered an advantage to harden the outside of an
article, keeping the inside as soft as possible so as to increase the
strength. In such case the article may be heated in red-hot lead, the
surface of which may be covered with charcoal. Under these conditions
the outside of the article, especially if thick, will get red hot in
advance of the inside.
Articles having thick and thin sections may be heated in fluxes to great
advantage, the thick side being immersed first, and the article being
lowered very slowly into the pot of lead. If the shape of the article is
such as to render it liable to crack in the water because of containing
holes or sharp corners in weak parts, these holes and sharp corners may
be filled with fire-clay, the dipping water may be heated to about 50°,
and salt (1 lb. per gallon of water) added to it.
The Monitor Sewing Machine Company harden and temper their spiral
springs at one operation, by heating them to a blood-red heat and
quenching them in a mixture of milk and water, which will give an
excellent result, providing that the springs are heated to precise
uniformity and the mixture of milk and water is correct. For a process
of this kind (which is very expeditious, because the hardening and
tempering is performed at one operation), the steel should be heated to
a very uniform temperature, and a mixture of, say, two-thirds milk and
one-third water tried at first, more milk being added to lower the
temper, or more water to increase it if necessary.
Saws are hardened in compositions of animal oil, such as whale-oil, with
which resin, pitch, and tallow are sometimes mixed.
Resin hardens but somewhat crystallises the metal, but it is used
because, on common saws, the scale will not strike properly without it.
Tallow gives body to the liquid and causes it to extract the heat
quickly from the steel (and the hardening is solely due to the rapid
extraction of the heat). In addition to this, the saws hardened in oil
and tallow show a very fine grain if fractured, and are tough. The
effect of pitch is much the same as that of resin. In place of tallow,
bees-wax is sometimes used, giving an excellent result. A very little
spirits of turpentine mixed with the oil every time it is used (that is,
for every batch) is an excellent ingredient to cause the scale to
strike, but being very inflammable, it is somewhat dangerous. If none of
these ingredients are used, and the scale does not strike, it acts as a
fine separating lining, preventing the contact between the metal and the
liquid, and hence retarding the cooling, and therefore the hardening.
Let us suppose some thin saws of the finest grade of steel are to be
tempered. The liquid would be about half a barrel of tallow to a barrel
of whale-oil (which will harden as hard as glass). After the temperature
of the saw is reduced to that of the bath, it is removed, the adhering
oil is removed, and the surface dried by an application of sawdust, and
the tempering process may be proceeded with.
There are three methods of drawing the temper. One is with the saw lying
in the open furnace; a second, an English plan, is with the saw
stretched in a frame, so as to prevent its warping, and in fact, to
cause the tempering to aid in straightening the saw; and the third is to
temper between flat dies.
In the first, the temper is determined by the appearance of the saw in
the furnace. The saw absorbs some of the liquid in which it was quenched
to harden it; and as it is reheated to temper it, this oil passes off as
a cloud, or rather as a breath passes off the surface of a window-pane.
This action takes place first on the lower surface of the saw, nearest
to the furnace bottom, the oil exuding in a mist-like form. The length
of time the saw must remain in the furnace after the cloud has passed
off is determined by the thickness of the saw and the heat of the
furnace, the operator being guided entirely by experience; but when the
saw is taken from the furnace, it will have a very dark-red glimmer, and
must be laid flat and allowed to cool off in the air, for if again
dipped it would be too hard. When cool, the saw thus tempered will be of
a sky-blue color, and will spring from point to butt without bend or
break. This process requires skilful management and good judgment, but
will give most excellent results. The main objection to it is, that it
is expensive, since it gives no aid to the straightening processes.
The straightening frame, or English tempering system, is as follows: The
plates of steel are made of a size that will cut into four saws. The
furnace front is provided with a tramway extending to the floor of the
furnace, and on this runs the stretcher-frame. The plates are stretched
in the frame, which is run into the furnace so that the plate is heated
under a tension, which operates to straighten them. As the temper
lowers, the screws of the stretcher are turned, increasing the tension;
when the tempering is done, the screws are made to stretch the plates
very tight just previous to taking it from the fire, and the plates are
allowed partly to cool off while kept in the frame. In this process the
indications of the temper are determined as in the first process. In the
third process, the saws are placed between a stationary and a movable
die provided in the body of the furnace, the movable one descending and
pressing the saw to the other die; thus the tempering is accompanied by
a flattening process (the dies being operated by pressure). The degree
of temper is regulated by the temperature to which the saws are heated,
which is ascertained by a pyrometer. The furnace is kept at a constant
temperature, and the length of time the saw remains between the dies is
varied to suit the thickness of the saw. The gain due to this system is,
that less straightening is required and a determinate temperature is
secured. Some makers claim that in this system the vapour of oil that
exudes from the saw has no means of escape, and that a chemical effect
injurious to the steel ensues; and furthermore that the temperature of
the dies will be greatest at or near their circumference, and hence the
teeth and back and the ends of the saw will be softer than the middle of
the width and length of the saw, and that if two saws, one above the
other, be placed on the dies at once, the contacting surfaces of the
saws will be the hardest, and those surfaces will be black by reason of
the oil burning into the steel, instead of exuding, as in the open
furnace process.
The floor of the tempering furnace should be flat and even; for if any
part of the saw-plate lies suspended, it will sag when heated, greatly
increasing the amount of straightening required. The furnace must be so
constructed as to heat evenly all over, otherwise the temper of the saw
will not be even. The air must be carefully excluded to prevent the
steel from decarbonizing, which being thin, it is very apt to do. Thin
saws warp proportionally as they are heated more, and if they are
allowed to remain longer in the furnace and not heated too quickly,
existing buckles or bends will partly straighten themselves in the
furnace. Care must be taken to keep the tongs clear of the teeth, and in
taking the saws from the furnace the length of the saw must stand at a
right angle to the operator (two pairs of tongs being used), so that the
saw's own weight shall not cause it to bend. The saw must be transferred
from the furnace to the bath very quickly, to prevent, as much as
possible, its cooling in the air; for such cooling would take place
unequally, causing the saw to warp, as well as impairing the temper. It
should be dipped with the length horizontal, the teeth downward and the
side faces vertical, and plunged quickly into the bath. On being dipped
in the hardening liquid, they warp again, but the dipping may be
manipulated to partly regulate the warping. From the moment the cold air
strikes the plate a warping process sets in, hence quickness in
transferring from the furnace to the bath is a great point. When the saw
is hot enough to temper, the scale will begin to rise upon its surface,
and if the furnace is unequally heated, the scale will arise first at
the hottest part, instantly notifying the operator of the defect.
From the appearance of the surface of the saw after it comes from the
hardening bath, the operator can see if it is properly hardened. If so,
the scale will be what is termed "struck," that is, it has come off,
leaving the surface from a grey to a white color; while if the scale
remains in dark patches, the saw is too soft in those parts.
After the saws are tempered they are allowed to cool in the open air,
and then require to be straightened by the hammer, and in this process
the tempering has been interfered with, inasmuch as that the elasticity
due to the tempering has been counterbalanced to some extent by the
local condensation of the metal induced by the immediate effects of the
hammer blows. The condensation of the metal has impaired the natural
grain or fibre of the metal, and stiffens it so that if the saw be bent
these stiffened hammer marks will cause it to remain set instead of
springing back straight, as it should do. To remove this defect the saws
are what is termed _stiffened_, that is, they are heated until the
surface assumes a yellow color, when they are removed and allowed to
cool. This causes the metal condensed by the hammer to assume its
natural structural condition, and permits the tempering to spring the
saw back straight, even though it be bent until the two ends touch, and
the bend carried half way along the blade by carrying one end forward
along the blade surface. The yellow color is subsequently removed by an
application of a solution of muriatic acid.
The method employed by the Tomlinson Carriage Spring Company for
carriage springs is as follows:--
The spring plates are heated to bend them to the _former_, which is a
plate serving as a gauge whereby to bend the plate to its proper curve,
which operation is performed quickly enough to leave the steel
sufficiently hot for the hardening; hence the plates after bending are
dipped edgeways and level into a tank of linseed oil which sets in a
tank of circulating water, the latter serving to keep the oil at about a
temperature of 70° when in constant use. About 3 inches from the bottom
of the oil tank is a screw to prevent the plates from falling to the
bottom among the refuse.
To draw the temper the hardened springs are placed in the furnace, which
has the air-blast turned off, and when the scale begins to rise, showing
that the adhering oil is about to take fire, they are turned end for end
in the furnace so as to heat them equally all over. When the oil blazes
and is freely blazed off, the springs are removed and allowed to cool in
the open air, but if the heat of a plate, when dipped in the oil to
harden is rather low, it is cooled, after blazing, in water. The cooling
after blazing thus being employed to equalize any slight difference in
the heat of the spring when hardened.
The furnace is about 10 inches wide and about 4 inches longer than the
longest spring. The grate bars are arranged _across_ the furnace with a
distance of 3/8 inch between them. The coal used is egg anthracite. It
is first placed at the back of the furnace, and raked forward as it
becomes ignited and burns clearly. For shorter springs the coal is kept
banked at the back of the furnace, so that the full length of the
furnace is not operative, which, of course, saves fuel. By feeding the
fire at the back end of the furnace, the gases formed before the coal
burns clearly pass up the chimney without passing over the plates, which
heat over a clear fire.
For commoner brands of steel, what is termed a water-chill temper is
given. This process is not as good as oil-tempering, but serves
excellently for the quality of steel on which it is employed. The
process is as follows: The springs are heated and bent to shape on the
_former_ plate as before said; while at a clear red heat, and still held
firmly to the _former_ plate, water is poured from a dipper passed along
the plate. The dipper is filled four or five times, according to the
heat of the plate, which is cooled down to a low or very deep red. The
cooling process on a plate 1-1/2 × 1/4 inches occupies about 6 seconds
on an average, but longer if the steel was not at a clear red, and less
if of a brighter red, when the cooling began. Some brands of steel of
the _Swede steel_ class will not temper by the water-chill process while
yet other brands will not harden in oil, in which case water is used to
dip the plates in for hardening, the tempering being blazing in oil as
described. In all cases, however, steel that will not harden in oil will
not temper by the water-chill process.
The Columbia Car Spring Company temper their springs as follows:--Using
"Gregory crucible steel," heating is performed in a furnace consuming
gas coke, but the furnace has a number of return enclosed flues, and
between these flues (one over the other), are ovens, the heat passing
through the brick-work forming the flues into the ovens. To facilitate
renewing the ovens (which of course also renews the flues), the floor of
each oven (which forms the ceiling of the oven below), is built on iron
supports, protected by the brick-work and suitable fire clay, the bricks
all being made to pattern, thus involving very little labor in building.
The furnace doors are at the ends, and are kept closed as much as
possible. In this way the steel has no contact with the products of
combustion of the fuel, and the air is excluded as far as practicable
(two valuable features). The furnaces are long and narrow, and not being
connected with the flue there is but little disposition for the cold air
to rush in when the furnace doors are opened.
The hardening and tempering of springs whose coils are of thick
cross-section is performed at one operation as follows: The springs are
heated in the furnace or oven described, and are first immersed for a
certain period in a tank containing fish oil (obtained from the fish
"_Moss Bunker_," and termed "_straights_"), and are then removed and
cooled in a tank of water. The period of immersion in the oil is
governed solely by the operator's judgment, depending upon the thickness
of the cross-section of the spring coil, or, in other words, the
diameter of the round steel of which the spring is made.
The table below gives examples of the hardening and tempering in this
way of springs of the following dimensions:--
Number of coils in spring 5-3/4
Length of the spring 6 inches.
Outside diameter of coils 4-3/4
Diameter of steel 1
+-----------+-----------+-----------+
| | Time of | Number of |
| Examples. | Immersion | Swings in |
| | in Oil. | Oil. |
+-----------+-----------+-----------+
| | Seconds. | |
|First | 28 | 35 |
|Second | 36 | 46 |
|Third | 27 | 36 |
|Fourth | 38 | 40 |
+-----------+-----------+-----------+
As will be seen, the spring in the first example was immersed in the oil
and slowly swung back and forth for 28 seconds, having been given 35
swings during that time. Upon removal from the oil the spring took fire,
was redipped for one second, and then put in the cold water tank to cool
off.
The following are examples in hardening and tempering springs of the
following dimensions:--
Number of coils in the springs 6
Length of the springs 9 inches.
Inside diameter of coils 3-1/4
Size of steel 1 × 1-1/2 square.
+-----------+-----------+-----------+
| | Time of | Number of |
| Examples. | Immersion | Swings in |
| | in Oil. | Oil. |
+-----------+-----------+-----------+
| | Seconds. | |
|First | 9 | 12 |
|Second | 8 | 12 |
|Third | 8 | 12 |
|Fourth | 9 | 12 |
|Fifth | 9 | 12 |
|Sixth | 9 | 12 |
+-----------+-----------+-----------+
To keep the tempering oil cool and at an even temperature, the tank of
fish oil was in a second or outer tank containing water, a circulation
of the latter being maintained by a pump. The swinging of the coils
causes a circulation of the oil, while at the same time it hastens the
cooling of the spring. The water tank was kept cool by a constant stream
and overflow. If a spring, upon being taken from the oil, took fire, it
was again immersed as in the first example. Resin and pitch are
sometimes added to the oil to increase its hardening capacity, if
necessary.
The test to which these springs were subjected was to compress them
until the coils touched each other, measuring the height of the spring
after each test, and continuing the operation until at two consecutive
tests the spring came back to its height before the two respective
compressions. The amount of set under these conditions is found to vary
from 3/8 inch, in comparatively weak, to 7/8 inch for large stiff ones.
The New Haven Clock Company heat their springs in a furnace burning
wood, the springs being _kept in the flames only_, and quenched in a
composition of the following proportions:--"To a barrel of oil 10 quarts
of resin and 12 quarts of tallow are added."
If the springs "fly," that is, break, more tallow is added, but if the
fracture indicates brittleness or granulation of the steel, rather than
excessive hardness, a ball of yellow beeswax, of about 6 inches in
diameter, is added to the above.
These springs are tempered, singly, to a reddish purple by being placed
on a frame having horizontally radiating arms like a "star," which is
attached at the end of a vertical rod. The spring is laid on the "star"
and lowered into a pot of melted lead, being held there a length of time
dictated by the judgment of the operator.
The star-shaped frame is termed a sinker, and if upon being lifted from
the lead the colour of the spring is too high, a second immersion is
given.
APPENDICES
APPENDIX--PART I.
TEST QUESTIONS FOR ENGINEERS.
An efficient engineer must certainly be able to determine any practical
question that may arise in the management, not only of his engine and
boiler, but also in that of such shafting, pulleys, gear wheels, etc.,
as may constitute the driving gear connected with the engine.
A very moderate examination of an engineer (whether to test his
suitability for employment or for promotion) should therefore include
questions tending to determine his capability to give such directions as
may be necessary when the engine or shafting breaks down, or when
alterations are to be made and he is consulted with reference to them.
The following questions have been framed with a view to include such
information as a first-class engineer, and even an assistant or night
engineer, may be expected to possess, and a large proportion of these
questions have been taken from actual engineers' examinations in various
parts of the country.
In many cases engineers of manufactories are required to make, as far as
possible, their own repairs and sometimes indeed also the repairs to the
machinery the engine drives, but to give questions covering this ground
would be to refer the reader to nearly every page in the two volumes,
which is manifestly impracticable.
=Matching gear wheels.=--Suppose you were running a hoisting engine
whose pinion had 15 teeth, driving a wheel with 150 teeth in it; if the
pinion had teeth with radial flanks, what orders would you send to get
another wheel that would work with the pair?--For answer, see Volume I.,
page 15.
=Radial flanks.=--If a pinion has radial flanks what information does
that give to the engineer if at any time he requires to order another
wheel to work with it? I. 15.
=Teeth of gear wheels.=--What is the difference between an epicycloidal
tooth and an involute tooth of a gear wheel? I. 8, 13.
=Ordering bevel gears.=--Two lines of shafting are to be connected by a
pair of bevel gears and one is to run twice as fast as the other; how
would you find the bevel of the wheels so as to be able to tell the
maker what was wanted, and what dimensions would you give, leaving the
pitch and the shape of the teeth out of the question? I. 22.
=Ordering taps.=--Suppose you were ordering a set of taps for use in the
engine room, what precautions would you be obliged to take as to the
shape of the thread in order to get proper taps? I. 85.
=Fitting a nut.=--Will a nut having a United States standard thread fit
a bolt having a common V thread, both threads having the same pitch and
diameter, and how could you tell one bolt from the other? I. 85.
=Curing a pounding cam.=--Suppose some part of the machinery driven by
an engine had a cam motion with a small roller which hammered and
pounded on the cam, how would you cure the defect? I. 83.
=Ordering a new spur wheel.=--Suppose a spur wheel broke and you wanted
to give the diameter for a new one, where would you measure the diameter
of the old one? I. 1.
=Comparing screw threads.=--What is the difference between the common V
thread and the United States standard thread? I. 85.
=Using two set screws.=--When two set screws are placed in a hub how
should they be located? I. 127.
=Best lathe tool.=--What is the most useful turning tool for a hand
lathe, such as is sometimes provided for an engineer to make repairs
with? I. 331.
=Fitting a crank pin.=--How would you proceed to put in by a contraction
fit a crank pin, the crank being on the engine? I. 366.
=Increasing strength of teeth.=--Suppose you had to order a new pair of
wheels to replace a pair whose teeth frequently broke, what alterations
in the dimensions of the wheels would you make so as to get stronger
teeth in wheels of the same diameter? I. 65.
=Wear of a cam roller.=--If an engine had a valve motion worked by a
parallel roller in a parallel cam groove, would the roller wear out
quick, and why? I. 84.
=Altering the speed of a shaft.=--Do a pair of mitre wheels alter the
speeds of the shaft they drive or not? I. 1.
=Driving out a key.=--In driving out a key is a quick or a slow hammer
blow the most effective? II. 65.
=Riveting a crank pin.=--For riveting a crank pin what shape should the
pene or pane of the hammer be? II. 73.
=Face of a cold chisel.=--What is the proper shape for the face of a
cold chisel? II. 73.
=Key bearing.=--What is the effect upon a wheel if its key bears upon
opposite corners? II. 107.
=Fitting a key.=--Should a key be driven lightly or not when fitting it,
and why? II. 106.
=Angle Of wrench jaws.=--What angle should the jaws of a wrench be to
its body in order to enable it to turn a nut in a corner with greatest
advantage? I. 123.
=Chucking a crank.=--How should a crank be chucked in order to prevent
the crank pin from being out of true, and the engine from beating and
pounding? I. 247.
=Chucking a cross-head.=--How should a cross-head be chucked so as to
have its piston rod and wrist pin at a true right angle? I. 252.
=Length of drill edges.=--Why should both edges of a drill be exactly
equal in length and of equal angle? I. 277.
=Boring bar edges.=--Should a boring bar for an engine cylinder have
one, two, three or four cutters? I. 289.
=Spiral spring.=--Give a method of making a spiral spring. I. 329.
=Expansion fit.=--What is meant by an expansion or a contraction fit,
say for an engine crank pin? I. 366.
=Fitting brasses.=--Suppose the joint faces of a pair of brasses are not
square with the sides of the box or strap in which the brasses fit, what
will the effect be when the brasses are locked tight together by the
key? II. 125.
=Wear of brasses.=--When an engineer is taking up the wear of connecting
rod brasses, what must he do to keep the rod of the proper length? II.
124-127.
=Case hardening.=--Describe the simplest method of case hardening. II.
128.
=Fitting pillar block brasses.=--State the proper order of procedure in
fitting in a new pair of main bearing or pillar block brasses for an
engine. II. 130.
=Driving brasses.=--What will be the effect of driving a brass in and
out with a hammer and without a block of wood to strike on? II. 72 and
132.
=Originating a true plane.=--How is a true plane or flat surface
originated? II. 133.
=Cover joint.=--What is the best form of joint for an engine cylinder
cover? II. 137.
=Grinding a cover.=--How must a cylinder cover be moved when grinding
it? II. 137.
=Appearance Of a joint.=--What is the appearance of a finished ground
joint? II. 137.
=Grade of emery.=--About what grade of emery would you use to make a
ground joint? II. 137.
=Best heat joint.=--What is the best kind of joint to withstand great
heat or flame? II. 138.
=Best water joint.=--What are the best kinds of joints for withstanding
water pressure? II. 138.
=Fitting a flange.=--In fitting a flange to a boiler what part of the
flange face should bed most? II. 140.
=Rust joint.=--How are rust joints made? II. 140.
=Leaky plug.=--How would you test the fit of a leaky plug in a cock? II.
144.
=Well-ground plug.=--What is the appearance of a well-ground plug? II.
145.
=Quick brass fitting.=--Describe the quickest method of fitting a new
brass or bearing box to its journal. II. 147.
=Babbitt bearing.=--What is the principal advantage of a Babbitted
bearing? II. 156.
=Adjusting guide bars.=--What two essential points are there in
adjusting the bottom guide bars of an engine? II. 162.
=Setting guide bars.=--Describe roughly the method employed to set guide
bars by means of a stretched line or cord? II. 163.
=Pounding journals.=--What are the two principal causes of the beating
or pounding of the journals of an engine? II. 164.
=Locating a pound.=--How may the location of a pound be discovered? II.
164.
=Cause of pounding.=--What is the ordinary cause of beating and pounding
in an engine? II. 164.
=Wearing down.=--What is the defect induced by letting the parts of an
engine wear down to a bearing? II. 166.
=Testing alignment.=--What are the tests that should be made to find out
what part of an engine is out of line? II. 166.
=Best test for alignment.=--What part of an engine can be used to form
the best test of alignment to cure pounding? II. 167.
=Connecting rod alignment.=--State in a general way the method of using
the connecting rod to place the engine in line, and thus prevent beating
and pounding. II. 167 to 172.
=Difficult alignment.=--What error in the alignment of the parts of an
engine is the most difficult to discover? II. 170.
=Alignment of crank pin.=--What is the general cause of a crank pin
being out of line with the crank shaft? II. 170.
=Pound at quarter stroke.=--When a pound occurs in an engine at the time
the crank pin is at quarter stroke, or thereabouts, where would you look
for the cause? II. 170 to 172.
=Setting a slide valve.=--What are the three objects, either of which a
slide valve may be so set as to accomplish? II. 173.
=Essentials of slide valve setting.=--What are the two operations
essential to the setting of a slide valve? II. 173.
=Squaring a valve.=--Why is the common process of squaring the valve an
improper proceeding? II. 173, 394.
=Crank pin on dead centre.=--How would you proceed to put an engine
crank pin exactly on the dead centre for setting the valve? II. 173,
394.
=Direction of movement.=--What are the considerations that determine in
which direction the engine should be moved when setting the valve? II.
173, 174, 394.
=Setting eccentrics.=--What tools are used to set eccentrics upon shafts
before the shafts are upon the engine? II. 175.
=Patching a break.=--In patching a broken beam or frame, how may the
bolts be made to serve to act as keys closing the crack? II. 178.
=Erecting shafting.=--Give a general or rough description of the method
of adjusting or aligning or erecting shafting. II. 184 to 186.
=Kinds of shafting.=--What is the difference between bright and black
shafting? II. 187.
=Fitting a pulley.=--If you had a pulley whose bore was 1-15/16 inches,
what diameter of bright shafting would you order for it? II. 187.
=Locating collars.=--What is the best location for the collars that
prevent end motion on a line shaft? II. 189.
=Ball and socket hangers.=--What are the advantages of hangers having a
ball and socket adjustment? II. 192.
=Shaft couplings.=--What four objects should the couplings for line
shafts accomplish? II. 194.
=Universal joint.=--What object does a universal joint accomplish? II.
199.
=Crowning a pulley.=--What is the object of crowning a pulley? II. 201.
=Pulley balance.=--Why should a pulley be balanced? What is a running
and what a standing balance for a pulley? At what speed should a running
balance be made? II. 202.
=Size of pulleys.=--If a shaft makes 150 revolutions per minute, and it
is required to drive a pulley on a machine at 600 revolutions, what
proportions must the diameter of the two pulleys have, and what
determines the diameters of the pulleys? II. 205, 206.
=Testing belts.=--What appearance in leather belting indicates that it
was cut from the spongy shoulder? II. 208.
=Stronger side of belts.=--Which is the stronger side of leather, the
smooth or grain side or the rough or flesh side? II. 208.
=Placing a belt tightener.=--Should a belt tightener be placed on the
tight or slack side of a belt? II. 210.
=Crossed vs. open belt.=--Which will transmit more power, an open or a
crossed belt, and why? II. 210.
=Crossed belt.=--What are the objections to a crossed belt? II. 210.
=Shortening a round belt.=--Can a round twisted belt be shortened
without removing either the hook or the eye and how? II. 216.
=Wide belt.=--How would you get a very wide belt on a pulley? II. 217.
=Mending an eccentric rod.=--Suppose an eccentric rod broke, and you
were required to weld it again, what shape could you make the scarf for
the weld? II. 234.
=Butt weld.=--What is a butt or pump weld? II. 236.
=Scarf weld.=--Describe roughly the means you would employ to make a
scarf weld. II. 235.
=Tongue weld.=--What are the shapes of the two pieces that come together
in a tongue weld? II. 235.
=Strain on boiler joint.=--How would you calculate the amount of stress
there is upon the riveted joint of a boiler? II. 350.
=Shearing strain.=--What is meant by the terms, shearing, tearing and
crushing strains of a steam boiler? II. 351.
=Lapped and butt joints.=--How does a lapped joint differ from a butt
joint or seam in a boiler? II. 352.
=Chain and zigzag riveting.=--How does a chain riveted joint differ from
a zigzag riveted joint? II. 352.
=Butt joint.=--What are the advantages of the butt joint? II. 352-353.
=Margin for holes.=--How would you find the proper distance the rivet
holes should be from the edge of the plate in a boiler seam? II. 353.
=Spacing rows Of rivets.=--How would you find the distance apart for the
rows of rivet holes in a double riveted joint? II. 353.
=High percentage joint.=--What is meant by a "high percentage" riveted
joint? II. 353.
=Single and double shear.=--What is meant by a rivet being in single
shear or double shear? II. 353.
=Allowance for shear.=--How much additional allowance is made in the
shearing strength of a rivet in double shear over that of the same rivet
if in single shear? II. 358.
=Taking charge of a boiler.=--What is the first thing you would do in
taking charge of a boiler? II. 368, 400.
=First inspection.=--What part of the boiler would you inspect first?
II. 368.
Safety valve defect.--To what defect is a safety valve most liable? II.
368, 400.
=Water supply.=--How much water should there be in the boiler when the
fire is lit? II. 368.
=Reliability of gauge glass.=--Is a gauge glass always reliable for
showing the height of the water in the boiler? II. 368, 402.
=Testing gauge glass.=--What would you do to find out if the gauge glass
was showing the correct water level? II. 368.
=Condensation in boiler.=--What is likely to happen if the steam
condenses in the boiler without any of the cocks being open? II. 368,
400.
=Cleaning a boiler.=--What parts of the boiler would you clean before
lighting the fire? II. 368.
=Laying a fire.=--How would you lay the fire? II. 368.
=Quick combustion.=--Does bituminous (soft) or anthracite (hard) coal
light more easily? II. 368.
=First coal.=--How soon would you put coal on after the fire is lit? How
deep would you make the first layer of coal? II. 368, 401.
=Amount of coal.=--How much coal would you put on the fire at a time?
II. 368, 401.
=Even heat.=--How can an even temperature be kept up in the fire box?
Why is it necessary to keep an even temperature in the fire box? II.
368, 370.
=Shaking grate.=--What is the advantage possessed by shaking grate bars?
II. 369.
=Before cleaning a fire.=--What preparations would you make before
cleaning the fire? II. 369.
=Fire tools and their uses.=--What tools are used in cleaning a fire?
And what is the use of each? II. 369.
=Draught while firing.=--How should the draught be regulated while the
fire is being cleaned? II. 369.
=Temporary interruption.=--What should be done to prevent blowing off
through the safety valve when the engine is stopped and no steam is
being taken from the boiler? II. 369.
=Blue flame.=--What does blue flame in the fire box indicate? II. 369.
=Water supply at night.=--How much water would you have in a boiler when
leaving it for all night? II. 369.
=Fire at night.=--How would you leave the fire for the night? II. 369.
=Banking.=--What is banking a fire? Give a safe method of banking a
fire. II. 369, 401.
=Dampers at night.=--How should the dampers be left when the fire is
banked? II. 369.
=Safety valve at night.=--How would you set the safety valve for a
banked fire? II. 369.
=Opening a banked fire.=--What is the first thing to do in starting up a
banked fire? II. 369, 401.
=Regulating boiler feed.=--How would you regulate the boiler feed? II.
369.
=Regulating a pump.=--How can a pump be regulated so as to be kept
pumping without surcharging the boiler? II. 369.
=Even boiler injection.=--Can a continuous feed be maintained if
injectors are used? II. 370.
=Stuck valve.=--How may a stuck valve or a check valve be released? II.
370.
=Hot feed water.=--What would you do if the feed water got so hot that
the pump worked imperfectly or not at all? II. 370.
=Scale.=--What causes scale to form in the boiler and what effect does
scale have on the boiler? II. 370.
=Preventing scale.=--What are the principal methods employed to prevent
the formation of scale in the boiler? II. 370.
=Horizontal heater.=--What advantage does a horizontal heater possess?
II. 370.
=Dirty gauge glass.=--What should be done to the gauge glass if the feed
water is dirty? How many times a day should the gauge be blown out? II.
370.
=Priming.=--What is the priming or foaming of the water in a boiler?
What are the known causes of priming? Why is priming wasteful? Can
blowing off at the safety valve cause priming? What are other causes of
priming? How can priming be detected? What would you do to stop priming?
What would you do to prevent priming? What parts of the engine would you
attend to if the boiler primes? II. 370.
=Low water.=--What would you do if the water got dangerously low in the
boiler? In such a case how would you regulate the dampers? What do you
consider dangerously low? What is blowing down a boiler? II. 370.
=Cleaning a boiler.=--How often would you clean a boiler? II. 371.
=Water falling.=--What would you suppose was going wrong if the pump was
kept going and the water still fell in the boiler? II. 370.
=Empty pump.=--What causes a pump to fail? II. 370.
=Blowing down.=--How much would you blow down a boiler? How low should
the pressure get before the water is let out? What would be the result
if the boiler was blown off under a high pressure? What would you do
after the water is all out of the boiler? II. 371.
=Special examination.=--What parts would you pay special attention to in
examining the boiler after cleaning it? II. 371.
=Hammer test.=--What does the "hammer test" consist of? II. 371.
=Washing and scaling.=--What determines the periods at which a boiler
should be washed out and scaled? II. 371.
=Regulating dampers.=--How would you regulate the dampers when letting
the fire out? II. 371.
=Naming the parts.=--Name all the parts of a simple or plain D
slide-valve engine, beginning with the cylinder. II. 372.
=Dividing the parts.=--Into what three divisions may the parts of a
plain slide-valve engine be divided? II. 372.
=Defining clearance.=--What is the meaning of the word "clearance" as
applied to an engine cylinder? II. 372.
=Finding equal clearance.=--How would you proceed to find if the
clearance in the cylinder was equal at each end? II. 372, 404.
=Parts of valve motion.=--What parts constitute the valve motion or
valve gear? II. 372.
=The driving parts.=--What parts constitute the driving or
power-transmitting mechanism? II. 372.
=Lubricating attachments.=--Name the attachments used upon an engine
cylinder to lubricate the piston and valves. II. 373.
=Pet cock.=--What is the difference between a cylinder pet cock and a
cylinder relief valve? II. 373.
=Relief valves.=--What are cylinder relief valves used for? II. 373.
=Quick steam admission.=--Which gives the quickest steam admission, a
long and narrow or a wide and short steam port, both having the same
area? II. 373.
=Placing the piston-ring split.=--At what part of the cylinder bore
should the split of a piston ring be placed? II. 374.
=Fitting a piston ring.=--How tight should a piston ring fit to the
cylinder bore? II. 374.
=Testing steam tightness.=--How would you test the steam tightness of a
piston? II. 374.
=Jacketed.=--What is a jacketed cylinder? II. 374.
=Valve gear.=--What is a releasing valve gear? What is a positive valve
gear? II. 374.
=Packing a stuffing box.=--About how full of packing would you fill a
stuffing box for a piston gland? II. 375.
=Connecting rods.=--What are the two principal kinds of connecting rods?
What is meant by the angularity of a connecting rod? II. 375.
=Oiling guide bars.=--Which guide-bar is the most difficult to oil, the
top or the bottom one? II. 375.
=Effect of angularity.=--What effect does the angularity of the
connecting rod have on the piston motion? Is this effect increased or
diminished by shortening the connecting rod? II. 375.
=Crank at full power.=--When the crank is at its point of full power, is
the piston in the middle of the cylinder? Is it nearer to the crank-end
or the head-end of the cylinder? II. 375.
=Piston motion irregular.=--What causes the piston to have irregular
motion? II. 375.
=Live steam period.=--What constitutes the live steam period of a
position? II. 376.
=Cut-off.=--What is the point of cut-off? II. 375.--What is a separate
cut-off valve, and what event does it control in the supply of the steam
to the cylinder? How is the point of cut-off varied when a cut-off valve
is used? II. 378.
=Working expansively.=--What causes the steam to be worked expansively
in an engine cylinder? II. 402.
=Follower.=--What is a piston follower? II. 374.
=Valve lead.=--What is the lead of valve? II. 376.
=Valve lap.=--What is the lap of a valve? II. 376.
=Admission.=--What is the point of admission? II. 376.
=Cushioning.=--At what point in the valve travel does cushioning begin?
II. 376.
=Release and compression.=--What are the points of release and of
compression? II. 376.
=Double-ported valve.=--What is a double-ported valve? II. 377.
=Valves.=--What is a griddle valve? What is a balanced valve? II.
377.--What is a piston valve? II. 378.
=Slide and piston valves.=--Is there any difference between the action
of a plain slide valve and a piston valve if both have the same amount
of lap, lead, and travel? II. 378.
=Cut-off diagram.=--Make a diagram to give the dimensions of a slide
valve, to cut off at 3/4 stroke, the valve travel being 4 inches. II.
380.
=Reversing an engine.=--What is the ordinary means provided for
reversing an engine? II. 383.
=Full gear.=--What is the meaning of the term full gear, with regard to
a link motion? II. 383.
=Third use Of link motion.=--What does a link motion accomplish besides
enabling the engine to run in either direction? II. 383.
=Slide valve for link motion.=--What are the two operations to be
performed in setting the slide valve of an engine having a link motion?
Describe these two operations. II. 383.
=Governors.=--What is a throttling governor? What is an isochronal
governor? What is a dancing governor? II. 384.
=Forward.=--What is full gear forward? II. 383.
=Backward.=--What is full gear backward? II. 383.
=Starting.=--How would you proceed to start a plain slide valve? II.
384, 400.
=Crank position.=--What is the best position for the crank to be in to
start the engine, and why is it the best position? II. 384.
=Taking charge.=--What is the first thing you would do in taking charge
of an engine? II. 385.
=Length of connecting rod.=--How would you find out if the connecting
rod was the right length to give an equal amount of clearance at each
end of the cylinder? II. 385, 404.
=Order of examination.=--In what order should a thorough examination of
the engine be made? II. 385.
=Least examination.=--What would constitute the least permissible
examination of an engine, with a due regard to safety? II. 385.
=Thorough examination.=--What would constitute a complete examination of
a plain slide-valve engine? In what order should such an examination be
made? II. 385.
=Quick examination.=--What examination should an engineer make of a
plain slide-valve engine, if called upon to start it as quickly as
possible without knowing its condition? II. 385.
=Taking a lead.=--How would you take a lead for adjusting the fit of a
bearing to its journal? II. 386.
=Set of slide valve.=--How would you test whether the slide valve was
set properly? II. 386.
=Squaring a valve.=--Is it proper to square a plain slide valve? II.
386.
=Lead affected by wear.=--How does the wear of the parts affect the lead
in vertical engines? II. 386.
=Heating of crank-shaft.=--What would you do if the crank-shaft bearings
began to heat? II. 386.
=Hot crank-pins.=--What are the principal causes of hot crank-pins? II.
386.
=Heating.=--What part of the engine is the most likely to get hot from
the friction of the fit? II. 386.
=Use of lead.=--What is a lead used for in adjusting the fit of a brass
to its journal? II. 386.
=Fit of top brass.=--When a liner is used between the two brasses, what
does the fit of the top brass depend upon? II. 386.
=Oiling.=--In oiling the engine, what precaution would you take to
prevent the journals from heating? II. 401.
=Cold weather.=--What is liable to happen to an engine that is used out
of doors in cold weather? II. 386.
=Leaky throttle valve.=--What damage might a leaky throttle valve do,
and how would you prevent it? II. 386.
=Leaky check valve.=--What damage may a leaky check valve do, and how
would you prevent it? II. 387.
=Freezing in the pump.=--How would you prevent the water from freezing
in the pump? II. 387.
=Freezing oil.=--How would you prevent the oil from freezing? II. 387.
=Thawing oil.=--How would you thaw frozen oil? II. 387.
=Setting a portable engine.=--How should a portable engine stand when it
is at work, and why should it stand so? II. 387.
=Natural supply of water.=--What precaution would you take when feed
water is drawn from a stream, or other natural source of supply? II.
387.
=Pumps.=--Into what classes may pumps be divided? What is a force pump?
What is a piston pump? What is a single-acting pump? What is a
double-acting pump? II. 387.
="Suction."=--What causes the flow of water up the suction pipe of a
pump? How high can a pump lift water, or cause it to lift or rise? II.
388.
=Regulating a pump.=--How can the quantity of water a pump will deliver
be regulated? II. 388.
=Pump valves.=--What is the check valve of a pump? What is the foot
valve of a pump? II. 388.
=Speed of pumping.=--What is the highest speed at which a pump should
run? What is the consequence if a pump runs too fast? II. 388.
=Locating the air chamber.=--When should the air chamber be placed on a
pump, and what is its use? II. 388.
=Belt pump.=--What is the advantage possessed by a belt pump? II. 388.
=Starting bar.=--What is a starting bar, and what is it used for? II.
389.
=Link sketch.=--Make a rough sketch of a locomotive link motion. II.
392.
=Link gear and eccentric.=--Does a link motion when in full gear operate
the valve much different to what a simple eccentric motion would do? II.
393.
=Exchanging eccentric rods.=--If the forward eccentric rod was to break,
could the backward eccentric be utilized to run the engine forward? If
so, how? II. 393.
=Broken reach rod.=--How would you hold the tumbling shaft if the reach
rod broke? II. 393.
=Eccentric and crank motions.=--Does the acting eccentric lead or follow
the crank when the link is in full gear? II. 393.
=Setting a slide valve.=--In what position would you place the link
motion when the slide valve is to be set? II. 394.
=Length of eccentric rod.=--What determines the length of the eccentric
rods when setting the slide valve? II. 394.
=Setting an Allen valve.=--What difference is there between setting a
common slide valve and another (an Allen) valve? II. 395.
=Injector.=--What is an injector? II. 395.
=Before firing.=--What should be done before laying the fire? II. 400.
=Kindling the fire.=--How long should the wood burn before putting on
coal? II. 400.
=Oiling.=--What points require examination when oiling the engine? II.
401.
=After oiling.=--What points would you move after having oiled the
engine? II. 401.
=Using tallow.=--Where would you place tallow in oiling the engine, and
for what purpose would you use it? II. 401.
=Fire too hot.=--What would you do if steam was rising too rapidly? II.
401.
=Link position.=--Where should the link be when starting the engine? II.
402.
=Even steam pressure.=--Why should the steam pressure be kept up, and
what difference does it make in the consumption of the fuel? II. 402.
=Quick steaming.=--Can steam be made quickest with a large or with a
small quantity of water in the boiler? II. 402.
=Best boiler feed.=--Which is better, a constant or an intermittent
boiler feed? II. 402.
=Best firing.=--Which is better, heavy firing at long intervals or light
and frequent firing, and why? II. 402.
=Broken cylinder cover.=--What would you do if the cylinder cover got
knocked out while on the road? II. 402.
=Hot piston rod.=--What would you do if the piston rod got hot? II. 403.
=Broken piston rod.=--What if the piston rod broke? II. 403.
=Broken crank-pin.=--What if the crank-pin broke? II. 403.
=Tire off.=--What if a wheel tire came off? II. 403.
=Driving wheel off.=--What if a driving wheel came off? II. 403.
=Broken lifting link.=--What if a lifting link or saddle-pin broke? II.
403.
=Slipping eccentric.=--What if an eccentric slipped? II. 403.
=Hot axle-box.=--What if an axle-box got hot? II. 403.
=Broken spring hanger.=--What if a spring or spring hanger broke? II.
403.
=Bursted tube.=--What if a tube bursted? II. 403.
=Fitting axle-box wedges.=--In what position should the engine be placed
when the axle-box wedges are to be adjusted for fit to the pedestals?
II. 404.
=Changing clearance.=--What is it that, as the engine wears, tends to
alter the amount of clearance? II. 404.
=Crank-pin centres.=--How would you get the distance from centre to
centre of the crank-pins when adjusting the axle-boxes and the side
rods, parallel rods, or coupling rods, as they are promiscuously termed?
II. 404.
=Adjusting Shoes.=--In what position would you place the crank when
adjusting the shoes or wedges of the axle-boxes? Why is this adjustment
important? II. 404.
=Force, pressure, and power.=--What is the difference between force or
pressure and power? II. 405.
=Increase of power.=--Can we increase a given amount of power by means
of mechanical appliances? II. 405, 406.
=Speed vs. power.=--Is a gain in speed a loss in power? II. 405.
=Lever.=--Explain the principle of the lever. II. 405.
=Elements of power.=--What are the three elements composing power? II.
407.
=Horse-power.=--What is a horse-power as applied to steam-engine
calculations? How would you calculate the horse-power of a steam engine?
II. 407.--Give a method of testing the effective horse-power of an
engine. II. 408.
=Safety-valve problem.=--A safety valve is three inches in diameter; the
lever is twenty-eight inches long from the point of suspension of the
weight to the pivoted end of the lever; the valve pin is four inches
from the pivot; the weight is twenty pounds. What is the greatest
pressure of steam the valve will hold, leaving the weight of the valve
and of the lever out of the question? II. 409.
=Thermal unit.=--What is the heat unit or thermal unit? II. 410.
=Latent heat.=--Is all the heat in steam or water shown by a
thermometer? What is the latent heat of water? What is the latent heat
of steam? II. 410.
=Sensible heat.=--What is the sensible heat of steam? II. 410.
=Total heat.=--What is the total heat of steam? II. 410.
=Heaviest water.=--At what temperature is water at its greatest density?
What is the weight of a cubic foot of water when at its maximum density?
II. 410.
=Heat of boiling water.=--What determines the temperature at which water
will boil? II. 410.
=Heat of steam.=--Can steam be made hotter than the water while they are
in contact? What is superheated steam? II. 410.
=Absolute pressure.=--What is meant by the absolute pressure of steam?
II. 411, 416.
=Dry steam.=--What is meant by dry steam? II. 411.
=Weight of steam.=--Is there any difference between the weight of water
and that of the steam it will evaporate into? II. 411.
=A perfect gas.=--What is Marriotte's law, or Boyle's law? Is steam a
perfect gas? II. 411.
=Joule's equivalent.=--What is meant by the conversion of heat into
work? What is Joule's equivalent? What is the mechanical equivalent of
heat? II. 411.
=Indicator.=--What is a steam-engine indicator? II. 413.--How are
indicators attached to an engine? II. 416.
=Indicator diagram.=--What are the names of the lines of a diagram? Why
is a theoretical diagram not correct? II. 414.--What difference is there
between the lines of a diagram of a condensing and those of a
non-condensing engine? II. 415.--How is the expansion curve of a diagram
tested? II. 417.
=Barometer.=--What is a barometer, and for what purpose is it used in
connection with engine diagrams? II. 415.
=Horse-power by diagram.=--How do you calculate the horse-power of a
steam engine from an indicator diagram? II. 418.
=Diagram vs. diagram.=--What difference is there between the diagram
taken from one end and that taken from the other? II. 419.
=Consumption of steam by diagram.=--How would you calculate the
consumption of steam or water of an engine from an indicator diagram?
II. 420.
=Steam line.=--What would a fall in the steam line of a diagram
indicate? II. 421.
=Expansion curve.=--If the expansion curve is above the true expansion
curve, what defect in the engine does that indicate? If the expansion
curve falls too low, what does it indicate? II. 421.
=Valve lead by diagram.=--How would insufficient valve lead be shown on
a diagram? II. 421.
=Excessive lead.=--How is excessive lead shown on a diagram? II. 421.
=Automatic cut-off.=--What is an automatic cut-off engine? What are the
principal forms of automatic cut-off engines? II. 423.
=Releasing valve governor.=--What kinds of governors do engines with
releasing valves have? II. 423.
=Corliss engine valves.=--How many valves does a Corliss engine have?
Explain the action of a Corliss valve gear. II. 423.
=Crab claw.=--What duty does the latch-link or crab-claw of a Corliss
valve gear perform? II. 423.
=Valve trip.=--What means are employed in a Corliss engine to trip the
admission valve? II. 423, 424.
=Point of cut-off.=--What determines the point of cut-off in a Corliss
engine, and how does it do so? II. 424.
=Valve closing.=--What closes the valve in a Corliss engine? II. 424.
=Dash-pot.=--What is a dash-pot? What enables the dash-pot of a Corliss
engine to work noiselessly? II. 424.--How is the amount of air cushion
in the Corliss dash-pot regulated? II. 425.
=Shape of Corliss valve.=--What shape is a Corliss valve, and how far
would its lap, as ordinarily constructed, carry the live steam period,
leaving the cut-off mechanism out of the question? II. 426.
=High-speed engines.=--What is meant by the term high-speed engines? II.
427.
=Adjusting for load.=--What adjustments would you make if the engine had
been running a very light load, and required to be adjusted for a heavy
load? II. 427.
=High-speed governor.=--What class of governor is generally used upon
high-speed engines? II. 427.
=Varying the cut-off.=--What is the usual method of varying the point of
cut-off on high-speed engines? II. 427.
=Wheel governor.=--State, in a general way, what a wheel governor
consists of. II. 427.
=Even valve lead.=--Can the valve lead be kept equal when the point of
cut-off is varied by shifting the eccentric across the shaft or
crank-axle? II. 427.
=Marine engine.=--What forms of engine are used for marine purposes? II.
434.
=Inverted cylinder.=--What is an inverted cylinder engine? II. 434.
=Receiver.=--What is a receiver? II. 434, 453.
=Triple expansion.=--What is a triple-expansion engine? II. 436.
=Condensing engine.=--What is a condensing engine? II. 434.
=Compound engine.=--What is a compound engine? II. 434.
=Arranging compound cylinders.=--What are the two methods of arranging
compound cylinders? II. 436.
=Condenser.=--What is a surface condenser? II. 440.
=Hot well.=--What is a hot well? II. 440.
=Steam condensation.=--Describe the means by which the steam is
condensed after it is exhausted from the cylinder in a surface
condensing engine, and state what becomes of the water of condensation
and the injection, circulating, or condensing water. II. 440.
=Condenser tubes.=--How are condenser tubes made tight? II. 440.
=Blow-through valve.=--What is a blow-through valve? II. 440.
=Air pumps.=--What is a bucket air pump, and is it single or double
acting? What is a piston air pump? What is a plunger air pump? What is a
trunk air pump? When is a trunk air pump necessary? II. 441.
=Air-pump valves.=--Are a foot valve and a head valve always necessary
to an air pump? II. 441.
=Pet cock.=--Why are bucket pumps provided with a valve or pet cock? II.
441.
=Bilge injection.=--What is a bilge injection? What fittings are
necessary for a bilge injection? II. 441.
=Hot-well temperature.=--At what temperature is the water in the hot
well usually kept? II. 441.
=Use of air chamber.=--What is an air vessel or air chamber used on a
pump for? II. 441.
=Feed escape.=--What is a feed relief, or feed escape valve? II. 441.
=Checked boiler feed.=--What causes may act to stop the boiler feed? II.
441.
=Admitting the exhaust.=--When the exhaust steam is condensed for
boiler-feeding purposes, how soon after the engine has started would you
let the exhaust into the feed tank? II. 441.
=Ship's side discharge.=--What is a ship's side air pump discharge
valve? II. 442.
=Course of water.=--What is the course of the main injection water of a
jet condenser? What is the course of the main circulating water of a
surface condenser? II. 442.
=Surface condensing.=--What are the advantages of surface condensing?
How are surface condensers cleaned out? II. 442.
=Engine-room cocks and valves.=--What cocks and valves are there in the
engine room of a condensing engine? II. 442.
=Donkey engine.=--What is a donkey engine? What pipes connect to a
donkey engine, and what are their uses? II. 442.
=Pipes to the sea.=--What are the pipes that lead from or go to the sea?
II. 442.
=Parts classified.=--What parts of a marine engine are generally made of
wrought iron, of cast iron, of brass, and what of steel? II. 442.
=Use of Babbitt.=--What is Babbitt metal or white metal used for? II.
442.
=Use of Muntz.=--What is Muntz metal used for? II. 442.
=Breaking strain.=--About what is the breaking strain of wrought iron
per square inch of section? II. 442.
=Tempering.=--How is steel tempered? II. 442, 460-463.
=Case-hardening.=--What is case-hardening? What parts of an engine are
usually case-hardened? II. 442.
=Forging.=--What are the forgeable metals used in engine construction?
II. 442.
=Welding.=--What is welding? II. 442.
=Metal expansion.=--What metals used in engine construction expand by
heat, and what allowances are made in the construction on this account?
II. 442.
=Composition of iron and steel.=--What is the difference in the
composition of cast iron and steel? II. 442.
=Marine piston.=--Describe a marine engine piston. II. 442.
=Drain cocks.=--What are cylinder drain cocks? II. 442.
=Link motion.=--What is a link motion? What is a link motion used for?
II. 443.
=Expansion valve.=--What is a separate expansion valve? II. 443.
=Top cylinders.=--What are the small cylinders on top of the steam
chests used for? II. 443.
=The throw.=--What is the throw of an eccentric? II. 443.
=Double beat.=--What is a double-beat valve? II. 443.
=Expansion joint.=--What is an expansion joint? II. 141, 443.
=Oil cup.=--What is an oil cup? II. 443.
=Siphon.=--What is a siphon or worsted? II. 443.
=Impermeator.=--What is a steam lubricator or impermeator? II. 444.
=Hand-worked valves.=--What are the valves of a marine engine that are
worked by hand? II. 444.
=Vacuum gauge.=--What is a vacuum gauge? What is a mercury vacuum gauge?
II. 444.
=Total condenser pressure.=--How would you find the total pressure in a
condenser? II. 444.
=Racing.=--What is meant by the racing of an engine? II. 444.
=Uniform paddle-wheel revolution.=--How may the speed of revolution of
single crank paddle-wheels be made uniform? II. 444.
=Paddle-wheel construction.=--What is the construction of a common
paddle wheel? What is a radial paddle wheel? What is a feathering paddle
wheel? II. 445.
=Disconnecting engine.=--What is a disconnecting paddle engine? II. 445.
=Propeller thread.=--Where is the thread of a screw propeller measured?
II. 445.
=Propeller pitch.=--What is the pitch of a propeller? II. 445.
=L. H. propeller.=--What is a left-hand propeller? II. 445.
=Thrust bearing.=--What is a thrust bearing? II. 445.
=Propeller fastening.=--How are screw propellers fastened to their
shafts? II. 445.
=Marine engine pipes.=--What are the principal pipes of a marine engine
and boiler? II. 445.
=Mud box.=--What is a mud box? II. 445.
=Course of steam.=--Describe the course of the steam from the boiler to
the hot well. II. 445.
=Exposure to cold.=--What parts of an engine are exposed to danger in a
cold climate? II. 446.
=Preventing freezing.=--What precautions are necessary to prevent the
engine from freezing in cold climates? II. 446.
=Failure to start.=--Name all the reasons that may cause a marine engine
to fail to start when it is expected to do so. II. 446.
=Pressure pieces.=--Name all the pieces of an engine through which the
steam pressure is received and transmitted. II. 446.
=Horse-power.=--What is the unit or measure of horse-power? What is the
meaning of nominal horse-power? II. 446.
=Lost vacuum.=--Name all the causes from which the vacuum may become
defective or lost. II. 447.
=Hot journals.=--What are the principal causes of the heating of engine
journals? II. 447.
=Stays.=--What is a boiler stay? What is a gusset stay? What is a tube
stay or a stay tube? II. 452.
=Stress per square inch.=--How much stress is usually allowed per
sectional square inch of boiler stay? II. 452.
=Breaking of tubes.=--What is the commonest cause of boiler tubes
breaking? II. 452.
=Split tube.=--How is a split tube stopped up? II. 452.
=Uptake.=--What is the uptake of a marine boiler? What is a wet uptake?
II. 453.
=Superheater.=--What is the superheater of a marine boiler? II. 453.
=Fittings.=--What fittings are essential to a marine boiler? II. 453.
=Safety valves.=--What is a dead-weight safety valve? What is a
spring-loaded safety valve? What is a lock-up safety valve? II. 453.
=Test cocks.=--What do the three boiler test cocks show? How are boiler
test cocks cleaned? II. 453.
=Steam gauges.=--What is a gauge glass or water-gauge glass? What is a
Bourdon dial gauge? What pressure is shown by a boiler steam gauge? II.
453.
=Scum cocks.=--How many scum cocks are used in a marine boiler? II. 454.
=Sluice valves.=--What are sluice valves in steamships? II. 454.
=Removing scale.=--How is scale removed in boilers? II. 454.
=Salinometer.=--What is a salinometer? II. 455.
=Salt in sea water.=--About how much salt does sea water contain? II.
454.
=Division plates.=--What are division plates in boilers? II. 455.
=Intercepter.=--What is the separator or intercepter of a marine boiler?
II. 455.
=Boiler draft.=--What causes the draft in a boiler? II. 455.
=Rapid wasting.=--Where does the most rapid wasting occur in marine
boilers? II. 455.
=Coal consumption.=--About how much coal is consumed per square foot of
grate in marine boilers? II. 455.
=Short of coal at sea.=--If at sea and short of coal, what course would
you pursue in order to save coal and get into port? II. 455.
=Boiler relief in extreme danger.=--How would you relieve a marine
boiler in case of the safety valve being locked down from some
accidental cause, the engine also being disabled? II. 455.
=Pressure test.=--At what pressure should a new boiler be tested? II.
456.
=Boiler examination.=--State what you would consider a proper
examination, inside and out, of a marine boiler that had been in
sufficient service to require examining. II. 458.
APPENDIX--PART II.
DICTIONARY OF WORKSHOP TERMS.
A
=Addendum.= That part of a gear wheel tooth that extends beyond or
outwards from the pitch line.
=Addendum-circle.= The circle representing the full or greatest
circumference of a gear wheel.
=Adjustable reamer.= A reamer whose teeth may be adjusted to the
required diameter.
=Angle-iron.= A shape of wrought iron or steel having two flanges at a
right angle; thus, [L]
=Angle-plate.= A plate having surfaces at a right angle, one to bolt to
the machine work-table, the work being bolted to the other.
=Angle-tooth.= A gear wheel tooth that runs across the face of the wheel
in a line that envelops part of the wheel circumference.
=Angular cutters.= Cutters, whose teeth are on a circumferential
surface, that is, at an angle to the cutter axis, such angle not being
that of 90° to either the side face nor to the axis of the cutter.
=Angular-velocity.= Velocity measured in degrees of angle.
=Annular.= In the form of a ring.
=Apron.= 1. The piece that carries the tool port or clamp on an iron
planing machine. 2. The front plate of a lathe carriage.
=Arbor.= 1. A mandrel used to drive work upon. 2. A spindle or shaft of
a machine.
=Arc.= A portion of a circle.
=Archimedean drill= (är-k[)i]-m-[e.]-d[=e]'an) A drilling device in
which a nut moved endwise on a stock or handle causes the drill to
revolve back and forth.
=Arc of approach.= That part in the revolution of a pair of gear wheels
in which the teeth in contact approach the line of centres of the two
wheels.
=Arc of recess.= That part in the revolution of a pair of gear wheels in
which the teeth in contact recede from the line of centres of the two
wheels.
=Arc-pitch.= The pitch of gear wheel teeth when measured around the
pitch circle.
=Attachment.= A work-holding device that may be attached to a machine.
=Auger.= A wood-boring tool having two spiral plates and a pointed screw
to feed it, the cutting edge being at the end of the tool.
=Axle-box.= The bearing in which an axle revolves.
B
=Back-gear.= The toothed wheels on the spindle of a lathe and at the
back of the lathe-head, by means of which the speed of the lathe is
reduced.
=Back-geared lathe.= A lathe having a back gear to reduce its motion.
=Back-knife gauge-lathe.= A lathe in which the work is finished and cut
to size and shape by a knife at the back of the lathe.
=Balanced pulley.= A pulley whose weight is so equally distributed that
it will run steadily and smoothly at the speed for which it is balanced.
=Balanced valve.= A valve so constructed as to move with equal force in
either direction.
=Ball and socket joint.= A universal joint consisting of a ball on the
end of a shaft and in a casing that envelops it and yet permits it to be
moved in its casing.
=Ball-cutter.= A tool for finishing metal balls.
=Ball-pene.= A spherical pene of a hammer.
=Band-saw.= A continuous ribbon of steel having saw teeth on one of its
edges.
=Band-saw machine.= A machine for operating a band-saw.
=Bastard file.= A file whose teeth are one degree or grade coarser than
a _second_ cut file and one degree finer than a _coarse_ cut file.
=Belt.= A leather band employed to drive pulleys, for transmitting
motion.
=Belt-clamp.= A clamp for pulling the ends of a belt together, to lace
it, while the belt is upon the pulleys.
=Belt-hook.= A hook employed to fasten the ends of belts together.
=Belt-pulley.= A wheel that drives or is driven by a belt.
=Belt-shipper.= A device for moving a belt from one pulley to another.
=Belt-tightener.= A pulley employed to cause a belt to tighten upon
another pulley to enable it to transmit motion periodically instead of
continuously.
=Bevel-sawing machine.= A wood-working machine in which the saw or the
work table may be set to cut a surface at other than a right angle to
the face of the work that rests against the work table or the fence as
the case may be.
=Bevel-square.= A square whose blade may be set to any required angle to
the stock that holds it.
=Bevel-wheel=, _or_ =bevel-gear.= A gear wheel with its teeth at an
angle to its shaft.
=Bit.= 1. A boring tool. 2. A tool that is carried in a holder.
=Blank.= A piece of material roughly formed and ready to be formed into
some definite shape.
=Blast-pipe.= 1. The pipe conveying the blast or air to a fire furnace
or cupola. 2. A small pipe through which steam escapes up a locomotive
chimney to increase the draught of the fires.
=Blob.= An extremely loose place in a plate or saw blade.
=Block-plane.= A short plane.
=Boiler-shell.= The outer casing of a steam-boiler.
=Bolt.= 1. A holding device having a head at one end and at the other a
threaded stem to receive a nut. 2. A short piece of a round log.
=Bolt-cutter.= A machine for cutting screw threads upon bolts or similar
work.
=Boring-bar.= A bar that carries boring tools.
=Boring-machine.= A machine for boring holes in metal or wood.
=Boring-mill.= A form of lathe used mainly for boring.
=Boring-tool.= A tool for cutting out and enlarging a bore or hole.
=Boss.= An enveloping piece on an axle or shaft and having upon it an
arm, arms, or spokes.
=Bottoming-tap.= A tap having a full thread up to its very end so that
it will cut a full thread to the bottom of a hole.
=Box-chuck.= A rectangular two-jawed chuck used by brass finishers.
=Box-tool.= A tool used in screw machines and turret heads, and which
guides the work while it is being operated upon. A box tool in many
cases carries more than one cutting tool.
=Box-wrench.= A wrench which fits over the head of the bolt and passes
endways upon it.
=Brace.= 1. A rod, bar, or beam that braces or supports. 2. A device for
revolving cutting tools.
=Bracket.= A projecting frame that is bolted to its supporting pieces or
frame.
=Brad-awl.= An awl for piercing small holes in wood and having a
wedge-shaped end.
=Branch-pipe.= A pipe leading out of another.
=Brass-and-brass.= A term used to denote that the two brasses or boxes
of a bearing are locked together by the key, cap, or set-screw.
=Brasses.= Pieces fitted into a frame and intended to afford a bearing
for a journal.
=Break-lathe= _or_ =gap-lathe.= A lathe having a break or gap in the bed
and beneath the face plate to let chucked work of large diameter pass.
=Broach.= A toothed tool for cutting the walls of a hole.
=Broaching-press.= A machine that forces a broach to its cut.
=Bunter-dog.= A work-gripping device for a planing machine, and
consisting of a piece having a hook end to engage in the T-slot of the
table, and a set-screw to bind the work.
=Butt-joint.= A riveted joint in which the ends of the plate abut fair,
one against the other.
=Butt-strap.= A strip or band of iron employed to hold the joint
together in a butt-joint.
=Butt-weld.= A weld in which the end of one piece merely abuts against
the other when the two pieces are put together to weld.
=Buzz-planer.= A wood-planing machine in which the work is fed by hand.
C
=Calender-roll.= A roll for calendering paper.
=Caliper-gauge.= A gauge in the form of a solid caliper.
=Calipers.= A hinged tool for measuring work.
=Cam.= A revolving disc whose actuating surface is not a true circle.
=Cam-motor.= A cam together with the rod it actuates.
=Cap.= The plate or upper part of a bearing that holds the top half of
the box or brasses in place.
=Cape-chisel.= A narrow machinist's chisel.
=Caps.= The backward curves on the points of file teeth.
=Cap-screw.= A screw with a collar and a square head.
=Carrier.= A device for driving lathe work.
=Case hardening.= A process of hardening the surface of wrought iron,
the hardening usually extending about 1/32 inch in depth.
=Cat-head.= A sleeve fastened by set-screws to slender lathe work and
running in a bearing so as to steady the work.
=Caulking-tool.= A tool used for caulking riveted joints and in making
rust-joints.
=Centre-bit.= A bit having a triangular conical point with its cutting
edge on one-half of the end and a spur on the other half.
=Centre-punch.= A tool having a coned point for marking the centres to
work.
=Chamfer.= A facet that removes the corner of a right angle.
=Change-gears= _or_ =change-wheels.= The gear wheels employed to change
the revolutions of a lead screw or feed motion.
=Chaser.= A toothed tool for cutting threads by hand in a lathe.
=Check.= A crack.
=Check nut.= A second nut screwed against the first to check it from
slackening back.
=Chip-break.= A piece that rests upon the work of a wood-working machine
and prevents the cutter from splitting out the wood as the cut leaves
the surface.
=Chipping-hammer.= A machinist's hand hammer.
=Chips.= 1. The cutting from a metal cutting machine tool. 2. The thick
cuttings from a wedge-shaped wood-working tool, as from an axe or adz.
=Chisel.= A wedge-shaped tool.
=Chisel-tooth saw.= A saw having inserted teeth with a maximum of front
rake.
=Chop= _or_ =hammer-sink.= A mark left on a plate by a sawmaker's or
plate straightener's hammer.
=Chord-pitch.= The pitch of gear wheel teeth measured in a straight
line.
=Chuck.= A work-holding or tool-holding device.
=Chucked.= Held in a chuck.
=Chucking-lathe.= A lathe having a large face plate for chucking
purposes, and usually a short bed.
=Chuck-plate.= A large face plate on which work may be chucked.
=Circular saw.= A saw having its teeth arranged around its
circumference.
=Clamp.= A device for fastening or holding work together or to some
other part.
=Clearance.= 1. The amount to which one piece clears or escapes another.
2. On a lathe tool, clearance is the amount to which the back face of
the tool escapes the metal it is cutting.
=Clements driver.= A device for driving work in a lathe, and that places
an equal strain on each end of the lathe dog or carrier.
=Clutch.= A device for engaging or disengaging so as to cause the motion
of one piece to be communicated to another, or to stop such
communication.
=Cock.= A device for opening or closing the bore of a pipe.
=Cog.= A wooden tooth for a gear wheel.
=Collapsing-taps.= A tap that is so formed that its teeth close inwards
when the thread is cut so that the tap can be withdrawn without winding
it backwards.
=Collar.= 1. A disc-shaped enlargement on a cylindrical piece. 2. A
hollow cylindrical piece containing a set screw, to prevent a shaft from
end motion.
=Collet.= A casing for holding tools or drawers in position.
=Combination-chuck.= A chuck in which the jaws may be moved
simultaneously or independently.
=Comparator.= A machine for comparing measurements, for testing them and
originating sub-divisions.
=Compass-calipers.= A pair of calipers having one bent leg and one leg
with compass joint.
=Compasses.= A tool answering the same purpose as dividers, but with
longer legs and a set screw to secure the position of the legs.
=Compass-plane.= A plane whose sole or bottom is curved in its length.
=Compound gears.= A train of gear wheels in which there are two wheels
fixed on the same shaft but of different diameters so as to vary the
velocity.
=Compound slide-rest.= A slide-rest having two slides, one above the
other.
=Cone-bearing.= A bearing (for a journal) that contains a coned sleeve
that may be moved endways to take up wear.
=Cone-mandrel.= A mandrel that holds hollow work by means of two cones.
=Cone-plate.= A device for steadying work in the lathe by supporting one
end in a coned mouth.
=Cone-pulley.= A pulley having steps of different diameters.
=Cone-shaft.= The shaft for a cone-pulley.
=Cook's auger.= An auger rounded at the end for cutting end-grain wood.
=Cope-cutter.= A cutter for under-cutting the shoulder of a tenon on
wood-work.
=Cope-head.= A head for a cope-cutter in a tenoning machine.
=Core.= A body of sand that produces a hole or cavity in a casting.
=Core-box.= The box in which a core is made.
=Cored.= Containing a hole or recess.
=Cotter= _or_ =cottar.= A term applied to small keys that are very broad
in proportion to their thickness.
=Cotter-drill.= A drill used in cutting out keyways in a machine.
=Cotter-file.= A file thin in proportion to its length, for filing out
keyways or slots.
=Counterbore.= 1. A parallel recess at the mouth of a hole. 2. A tool
for producing such a recess.
=Countershaft.= A shaft with pulleys upon it, employed to permit a
machine to be started and stopped without stopping and starting the line
shaft, also, to afford means for varying the speed of a machine.
=Countersink.= A tool for cutting a coned mouth to a hole.
=Countersunk.= Having a coned mouth.
=Coupling.= A piece used to connect two pieces together.
=Covering-plate.= A plate used to cover the seams of a boiler.
=Cow-mouth chisel.= A machinist's chisel shaped at the cutting end like
a carpenter's gouge.
=Crank.= An arm that is fast to a shaft and is used as a lever wherewith
to revolve the shaft.
=Crank-shaft.= A shaft having a crank.
=Cross-cut.= A narrow machinist's chisel.
=Cross-cut saw.= A saw whose teeth are shaped to cut across the fibre or
grain of wood.
=Cross-face.= A plate straightener's or saw maker's hammer, having one
face at a right angle to the other.
=Cross-feed.= That feed of a lathe which runs across the bed.
=Cross-filing.= That class of filing in which the file is pushed in the
line of its length.
=Cross-head.= That part of an engine that connects the piston rod to the
connecting rod.
=Cross-slide.= A slide that stands across a work-table.
=Crowning.= Highest in the middle when tested by a straight edge.
=Crown-wheel.= A gear wheel having its teeth upon its side face.
=Cup-chuck.= A chuck having a coned or cupped mouth.
=Cup-shape.= A crack of circular form in a piece of timber or a log.
=Cutter.= A tool that is held or carried in a stock bar or mandrel.
=Cutter-bar.= The bar or shaft that carries the cutting knives in a
wood-planing machine.
=Cutter-grinder.= A machine for grinding cutters.
=Cutter-head.= 1. A head that carries cutters. 2. The head that carries
the cutters in a wood-moulding machine.
=Cutting-off lathe.= A lathe used for cutting up rods into required
lengths, and having a hollow spindle through which the rod passes.
=Cutting-off saw.= A sawing machine designed for cropping the ends of
work and cutting it to length.
=Cutting-off tool.= A tool for cutting up rods or bars, and used in the
common lathe and in the cutting-off lathe.
=Cycloid= (si'kloid). A curve generated by a pencil fixed in the
perimeter of a circle that is rolled upon another circle.
=Cylinder.= 1. That part of a steam-engine in which the steam is
utilized to drive the piston. 2. The shaft that carries the knives in a
wood-planing machine.
=Cylinder-head=, _or_ =cylinder-cover.= A piece that encloses or seals
the end of a cylinder.
D
=Dead centre.= The stationary centre of a lathe.
=Dead-smooth file=, _or_ =superfine file.= The finest or smoothest cut
of file.
=Delivery-rolls.= Rolls that remove the work from a machine or from its
cutters or knives.
=Describing-circle.= The circle or cylinder containing the pencil for
rolling a curve.
=Diametral pitch.= A system of designating the pitches of gear wheels.
=Diamond-point.= A machinist's chisel, square in cross-section, having a
diamond-shaped face at the end, and two cutting edges, one at a right
angle to the other.
=Die.= 1. A tool for cutting threads upon external surfaces, such as
bolts. 2. A chumpy sliding piece.
=Differential screw.= A screw having a coarse and a fine thread, the
difference between the two pitches enabling a more powerful strain to be
endured by the thread.
=Dimension planer.= A wood-planing machine, for planing accurately to
size.
=Disk= _or_ =disc.= A cylinder whose length is very short in proportion
to its diameter.
=Dividers.= A tool having two legs with sharp points at their ends for
measuring distances or drawing circles.
=Dog.= A work holding device.
=Dog-chuck.= A chuck containing independent dogs or jaws.
=Dog-head.= A hammer used in plate or saw straightening.
=Double-eye= _or_ =knuckle-joint.= A joint in which one piece is forked
at its end, to receive the other, and a pin passes through both.
=Double-thread.= A screw thread, having two spirals in the same bolt or
body.
=Dovetail.= A groove that is wider at the bottom than at the top, or a
projection thicker at the top than at the bottom.
=Draw-filing.= That class of filing in which the line of file motion is
in the direction of the width of the file.
=Drawn-down.= Decreased in diameter, width or thickness, by forging or
swaging.
=Drawn-out.= Increased in length, by forging or swaging.
=Drift.= A tool that cuts the walls of a hole while it is driven through
by hammer blows.
=Drift-pin.= A taper pin that is used by boiler makers to drive through
holes that do not come fair, or match properly.
=Drill.= A tool to pierce holes.
=Drill-chuck.= A chuck used to hold drills.
=Drilling-machine.= A machine for drilling holes in metal.
=Driver.= 1. A device for driving work in the lathe and sometimes called
a dog or carrier. 2. A gear wheel which drives another.
=Drop-hammer.= A forging or stamping hammer which is lifted by power and
let fall of its own weight.
=Drunken thread.= A screw thread that is not a true spiral, but is waved
in its course.
=Duplex slide-rest.= A feed motion in which there are two slide-rests in
one slide-way.
=Dutchman.= A piece let in to restore a worn part, or to hide a defect.
E
=Edge-moulding machine.= A machine for dressing the edges of wood-work
to shape, and usually for forming a moulding thereon.
=Emery grinder=, _or_ =emery-grinding machine.= A machine in which emery
wheels are used to grind the work.
=Emery wheel.= A wheel composed of emery cemented together under
pressure.
=Endless screw.= A short length of screw formed to drive the teeth of a
worm wheel.
=End-mill.= A milling-machine cutter, having teeth on its end face.
=Engine-lathe.= A lathe having a feed motor for the cutting tool.
=Epicycloid= ([)e]p-i-s[=i]'-kloid). A cycloidal curve in which the
rolling circle is rolled outside the fixed or base circle.
=Equalizing-file.= A file that is slightly thicker in the middle than it
is at either end.
=Expanding-chuck.= A chuck that is capable of expanding to accommodate a
slight variation of work-diameter and usually holding the work from its
bore.
=Expanding-mandrel.= A mandrel whose diameter may be varied, usually by
means of moving jaws or pieces.
=Expansion-joint.= A joint capable of permitting the parts it connects
to expand and contract under variations of temperature.
=Extension-bit.= A bit in which a cutter can be set so as to bore
different sizes of holes.
=Extension-lathe.= A lathe whose bed is in two longitudinal divisions so
that the upper one may be moved endways and thus form a gap to let
chucked work of large diameter pass.
F
=Face.= 1. The broadest surface of a piece, or that having the largest
area. 2. The circumferential surface of a wheel or pulley. 3. A surface
on a gear-wheel tooth.
=Face-cam.= A cam in which the actuating surface is on its side or
sides.
=Face-cutter.= A milling cutter having its teeth upon its
circumferential surface.
=Face-plate.= A plate or table having a plain or flat surface for
holding work.
=Facing-cutter.= A cutter for levelling a face or surface.
=Farrar planer.= A wood-planing machine in which a travelling bed is
used to feed the work to the cutter head.
=Feather.= A key that is fast in one piece of the work, and an easy fit
to the other, so that the latter may be moved along the feather.
=Feed-motor.= That part of a machine that feeds either the work or the
tool, so as to put on the cut.
=Feed-rolls.= Rolls that move the work to machines or to cutting tools.
=Feed-screw.= A screw that is used to feed the cutting tool in a
machine.
=Fence.= A plate in a wood-working machine, against which the work is
set or moved to hold it in proper position for the cutting operations.
=Fiddle-drill.= A drill that is revolved back and forth by a device
similar to a fiddle-bow.
=Fifth wheel.= The circular slideway that enables the front axle of a
vehicle to turn horizontally.
=File.= A hand tool for cutting metal, wood, ivory, bone and all other
hard substances except stone.
=File-card.= A wire-brush for cleaning files.
=Fillet.= A curved piece for filling in a corner.
=Fillister-head.= A screw-head that is cylindrical and contains a screw
slot.
=Firmer-chisel.= A stout carpenter's chisel that is used for cutting out
mortises and similar heavy work.
=Fit-strip.= A projection usually about an inch wide that is intended to
be fitted to bed the piece properly and save bedding the whole surface
of the piece.
=Fixture.= A device for holding work in an exact position, true with
some one face, hole, or pin, as the case may be.
=Flat-chisel.= A wedge-shaped machinist's chisel.
=Flat-drill.= A drill whose body is rectangular in cross-section.
=Flatter.= A swage for flat surfaces.
=Fleam.= Acuteness given to saw teeth by filing their front faces at an
acute angle to the plane of the saw blade.
=Flexible shaft.= A shaft composed of wire, similar to a wire rope, for
transmitting rotary motion, notwithstanding that the shaft may be an arc
of a circle.
=Flooring-machine.= A machine for planing and matching at the same time,
and generally used for floor boards.
=Flute.= A groove.
=Fly-cutter.= A cutting tool fastened in an arbor or spindle, and used
for producing irregular shapes.
=Follower.= A gear wheel that receives motion from another gear wheel.
=Follower-rest.= A rest that steadies work on the lathe and travels with
the slide rest.
=Foot-block.= A work-holding device containing a dead centre, used upon
a milling machine.
=Foot-lathe.= A lathe operated by foot-power.
=Fore-plane= _or_ =jack-plane.= A roughing out plane.
=Forging.= A piece or part that has been forged into shape.
=Fork-centre.= A centre used to drive woodwork in the lathe.
=Fork-scriber.= A double pointed tool used by boiler-makers to mark
small circles.
=Former.= 1. A piece that acts as a guide to control the movement of a
cutting tool. 2. A template or block on which a piece is bent or shaped.
=Fox-lathe.= A brass finisher's lathe, having a turret head and spiral
thread-cutting devices that obviate the use of a lead screw or change
gears.
=Friction-clutch.= A clutch that operates by frictional contact.
=Friction-gearing.= Wheels that transmit motion by the frictional
contact of their circumferences.
=Friction-rollers.= Rollers employed to reduce the friction of the
parts.
=Friction-wheel.= A wheel that drives by the frictional contact of its
surface.
=Friezing-machine= _or_ =edge-moulding-machine.= A machine for cutting
mouldings on the edge of wood work.
=Front-tool.= A tool having its cutting edge in front, and used for
plain surfacing work.
=Fuller.= A blacksmith's tool for spreading the metal in any particular
direction.
G
=Gang-drill.= A drilling machine on which a number of drills may be used
simultaneously.
=Gang-edger= _or_ =gang-edging machine.= A machine in which a gang of
saws are employed to trim the edges of boards or cut them to width.
=Gang-mills.= Milling machine cutters that are placed in gangs and side
by side on the same arbor.
=Gap-lathe= _or_ =break-lathe.= A lathe having a gap in its bed to
enable the chucking of work that would not otherwise pass over the bed.
=Gauge.= 1. A standard of measurement. 2. A standard of shape.
=Gear.= A term applied to a piece of mechanism that accomplishes a
single object: thus a valve-gear operates a valve; a steering-gear
steers the vessel.
=Geared.= Placed in gear or connected together.
=Gear-wheel.= A wheel provided with teeth to engage with similar teeth
upon another wheel.
=Generating-circle.= The circle that is supposed to move in the
construction of cycloidal curves.
=Gib.= 1. A piece that may be set up to take up the wear. 2. A piece for
holding a strap, and forming an abutting piece for a key.
=Gimlet.= A wood-boring hand tool, having a threaded conical end to pull
it to its cut.
=Gimlet-bit.= A fluted gimlet having no thread at its end, but a spiral
flute so shaped as to pull the bit forward to its cut.
=Gland.= A piece enveloping a stem and used to make a tight working
joint.
=Globe-valve.= A valve, having a spherical body, used in pipe-work.
=Goose-neck.= A frame affording a fulcrum for a ratchet brace.
=Gouge.= A wood-cutting hand tool that is curved in its cross-section.
=Gravis.= A hand tool, rectangular in cross-section and having cutting
edges at its end that are formed by grinding the end face at an acute
angle to the body of the tool.
=Groove-cam.= A cam in which the actuating surface is in the form of a
groove.
=Ground joint.= A joint that is finished by grinding the parts together,
usually with oil and emery.
=Guide-bar= _or_ =slide-bar.= A bar that forms a guide for the crosshead
of an engine or other moving piece.
=Gum.= 1. The bottom of the space between saw teeth. 2. A rubber-like
substance formed of oil that has dried.
H
=Hack.= A tool used for cutting iron in two under a steam hammer.
=Hack-saw.= A saw held in a frame and used by hand for cutting metal.
=Half-check joint.= A joint in which a piece is let into the other, so
that the surfaces come level.
=Half-round file.= A file that is half round in cross-section.
=Hand-file.= A superior class of file that is parallel in width and
thickest in the middle of its length.
=Hand-hammer.= A hammer that can be used in one hand.
=Hand-lathe.= A lathe with which hand cutting tools are used.
=Hand-nut.= A nut that may be screwed up by hand without the aid of a
wrench.
=Hand-planer.= A wood-planing machine in which the work is fed by hand.
=Hand-rest.= The rest on which hand-turning tools are supported in a
lathe.
=Hand-tap.= A tap that is used by hand.
=Hand-vise.= A small vise for use in the hand.
=Hanger.= A frame that is bolted to another frame or part, and carries
another piece, usually a shaft of some kind.
=Hardened.= Hardened steel is that which has been made hard by heating
to a cherry red and suddenly cooling it, usually by quenching it in
water.
=Hardy.= A blacksmith's chisel that fits into the anvil.
=Heading-block.= A block used in upsetting the heads of bolts or pins.
=Heart-shake.= A split radiating from the centre of a log.
=Heating-surface.= That part of the surface of a steam-boiler that
receives heat on one side and has water on the other.
=Heel-tool.= A hand turning tool having a projecting heel to cross the
tool rest, and usually held in a wooden stock or handle.
=Herring-bone tooth.= A form of gear wheel tooth in which the tooth,
instead of passing direct across the wheel face, curves partly around
the circumference and then back again, so that the two ends of the tooth
only are opposite to each other.
=Hindley's-screw.= A short length of screw used to drive a worm wheel,
and sometimes termed an endless screw.
=Hob= _or_ =hub.= A tool for cutting the threads on screw cutting tools,
such as chaser dies.
=Hour-glass screw.= A worm or tangent screw which is formed to envelop
part of the arc of circumference of a worm wheel, and therefore assumes
in outline the form of a sand hour-glass.
=Hunting-tooth.= An extra tooth put into a pair of gear wheels that
would otherwise contain the same number of teeth, the object being to
prevent the same teeth from always falling together.
=Hypocycloid= (h[=i]-po-s[=i]'kloid). A cycloidal curve in which the
rolling circle is rolled within the fixed or base circle.
I
=Idle pulley= _or_ =guide pulley.= A pulley employed to guide a belt.
=Independent chuck.= A chuck in which each jaw is operated separately.
=Index-plate.= A plate having holes or notches accurately dividing a
circle into equal divisions.
=Inserted-tooth cutter.= A cutter in which the teeth are inserted in a
disc or head.
=Inside calipers.= Calipers used to measure inside dimensions, as boxes,
recesses, etc.
=Intermediates.= The wheels that are between the front driver and last
follower of a train of gear wheels.
=Involute.= A curve generated by the path of a given point in a straight
line, as the line is rolled upon a circle. (Vol. I. p. 31.)
J
=Jack-plane.= A plane employed to rough out the work.
=Jig.= A device for holding work and guiding the operating tool.
=Jointing-machine.= A machine for truing the surfaces of wood-work that
are to form a joint.
=Journal.= That part of a shaft that runs in a bearing which guides or
limits the motion of the shaft.
=Jump= _or_ =upset.= To enlarge at the end by a forging process.
K
=Kerf.= The passageway or slot cut by a saw.
=Key.= A rectangular wedge for locking two pieces together.
=Knife.= The cutting tool used on a wood-planing or wood-splitting
machine.
=Knurling-tool= _or_ =milling-tool.= A tool used to press indentations
into the edges or upon the surface of metal, in order to increase the
hand grip of it.
L
=Land.= That part of a tap or a reamer that lies between its plates and
carries the cutting edges or teeth.
=Lantern.= A primitive form of gear in which rungs are used instead of
teeth.
=Lap.= A grinding device consisting of a lead or other soft metal
surface, on which emery and oil is used.
=Lap-joint.= A joint in which one piece overlaps the other.
=Lap-weld.= A weld in which both pieces are beveled at the ends and one
end overlaps the other where the two are put together to weld.
=Lathe.= A machine that revolves work to be operated by cutting tools.
=Lathe-bed.= The frame that carries the head and tail stock of a lathe,
and that rests upon a solid foundation.
=Lathe-carriage.= The sliding piece that carries the tool rest of a
lathe.
=Lathe-centre.= The piece or part of a lathe that enters the coned
recess of lathe work that is held between centres.
=Lathe-saddle.= The sliding piece that carries the tool rest of a lathe.
=Lathe-shears.= The frame of a lathe that carries the head and tail
stocks, and that rests on legs.
=Lead-screw.= A screw for a lathe that is used for screw cutting only.
=Left-hand thread.= A screw thread in which the nut must be revolved in
a direction opposite to that in which the hands of a watch move, in
order that the nut may screw upon the bolt.
=Leg-vise.= A machinist's or blacksmith's vise having legs.
=Line of centres.= A line, real or imaginary, passing from one centre to
another.
=Line out.= To mark on work lines denoting the depth of surface that is
to be cut away.
=Liner.= A piece of iron put behind or upon a piece to take up its wear.
Line-shaft. A shaft employed to transmit motion from an engine or motor
to distant points.
=Link.= A piece having holes or pins at its end to connect two other
pieces together.
=Live centre.= The centre of the live spindle of a lathe.
=Live spindle.= The revolving spindle of a lathe.
=Loose.= A term used to denote a part of a plate or saw that is not
under tension.
=Lost motion.= Motion that is not transmitted on account of the
looseness of the parts.
=Lug.= A small projection.
M
=Machine-bolt.= A bolt and nut of the sizes kept in stock by machinery
dealers, the bolt usually being black or unturned.
=Machine-screw.= A small screw made to the Birmingham wire gauge.
=Machine-tap.= A long taper tap used in threading nuts in a machine.
=Machine-tool.= A machine that performs work by means of cutting tools.
=Mandrel.= 1. A cylindrical piece which is driven into hollow work and
holds it while it is turned in the lathe. 2. A piece or bar on which
work is driven or forced. 3. A shaft running in bearings.
=Mangle-wheel.= A gear wheel whose teeth are so arranged that the wheel
is reciprocated back and forth on its centre, and does not make a full
revolution.
=Marking-gauge.= A tool used by wood-workers to draw a line upon work.
=Master-tap.= A standard tap used for producing thread-cutting tools, or
kept as a standard of size.
=Matched.= A board that has a tongue on one edge and a groove on the
other so that the edges of the boards will match or be fitted together.
=Matching-machine= _or_ =matcher.= A wood-working machine which cuts a
groove on one edge and a tongue on the other edge of a board or piece of
work.
=Measuring-machine.= A machine for determining the measurement of a
piece.
=Micrometer.= (m[=i]-kr[)o]m'e-ter). A tool for measuring to minute
fractions of an inch.
=Mill-file.= A single cut file used for filing sheet steel, saw teeth,
etc.
=Milling-cutter= _or_ =mill.= The cutter or cutting tool used in a
milling-machine.
=Milling-machine.= A machine in which revolving cutters are used to
dress the surfaces of metal and cut them to size and shape.
=Mitre-cutting machine.= A machine for cutting mitre joints.
=Mitre-joint.= A joint at an angle of 45 degrees to the plane of the
pieces it joins.
=Mitre-wheel.= A bevel gear having its teeth at an angle of 45 degrees
to its shaft.
=Mortise.= A recess slot usually square or rectangular, and employed to
receive a tenon from another piece.
=Moulding-cutters.= The cutters employed to produce mouldings on wood.
=Multiple-drilling machine.= A drilling-machine in which more than one
drilling-tool may be used, and separate and successive operations may be
performed upon the work, carrying it from one drill-spindle to another.
=Mute-pulley.= A belt-guiding pulley that can be adjusted to various
positions upon its stand.
N
=Nail-bit.= A boring tool for wood, used for cutting across the grain of
wood.
=Nut.= A threaded piece for receiving a screw.
O
=Odontograph= ([=o]-d[)o]n'-to-gr[)a]f). An instrument employed in
making or drawing gear-wheel teeth.
=Oliver.= A foot-power hammer used by blacksmiths, mainly for forging
bolts or studs.
=Outside-calipers.= Calipers used to measure external surfaces.
P
=Panelling-machine.= A machine for cutting mouldings upon panels.
=Parallel-file.= A file whose thickness is equal from end to end.
=Parallel-vise.= A vise in which the gripping face of the movable jaw is
maintained parallel to that of the fixed jaw.
=Paring-chisel.= A wood-worker's chisel that is pushed to its cut by
hand pressure.
=Pattern-lathe.= A lathe designed for the use of pattern-makers.
=Pawl.= A tongue that engages with a ratchet.
=Pene= (p[=e]n) _or_ =pane.= The lightest end of a hammer.
=Pening= (p[=e]n'ing). The hammering of the surface of metal in order to
stretch it and alter the shape of the piece.
=Pillow-block=, =pillar-block= _or_ =plumber-block.= A piece that
affords a bearing for a shaft and is bolted to a pillar or frame.
=Pin-block.= A wooden block used to steady small pins when filed in the
vise.
=Pinion.= The smallest wheel in a pair of wheels or in a train of
gearing.
=Pin-wrench.= A wrench having a pin to enter holes in the nut.
=Pipe-cutter.= A hand tool for cutting pipe into lengths.
=Pipe-die.= A tool for cutting threads on pipes.
=Pipe-tongs.= A hand tool for gripping pipes.
=Piston.= 1. That part of a steam-engine that moves under steam
pressure. 2. A disc that fits a bore and slides therein.
=Pitch.= The distance apart of two pieces.
=Pitch-circle.= A circle drawn through these parts in a gear wheel where
the face of the tooth meets the flank, this circle representing the
diameter of the wheel for calculations involving its velocity.
=Pitch-line.= A part of a pitch circle.
=Pitman.= A name sometimes given to a connecting rod.
=Planer-shaper.= A metal-cutting machine in which the ram or slide
carrying the tool is moved after the manner of a planing machine.
=Planimeter= (pla-n[)i]m'-e-ter). An instrument for finding the area of
irregularly shaped plane surfaces.
=Planing-machine.= 1. For iron. A machine having a travelling work-table
sliding in guideways, the tool being carried in a slideway that spans
the table, two or more slide-rests are used in the larger-sized
machines. 2. Wood-planing machine. A machine in which the work is fed to
a revolving shaft or head carrying long planing knives.
=Platen.= 1. A work-holding table. 2. The plane surfaced plate which
presses on the type in printing.
=Play.= Looseness of fit.
=Plug.= The interior piece of a cock.
=Plug-and-collar gauge.= A pair of gauges for the same size, the plug
being sometimes termed the male and the collar the female gauge.
=Plug-tap.= A tap that follows the taper taps and has but two or three
of its teeth eased off at the end.
=Plumb-level.= A levelling tool depending for its accuracy on a weighted
line and an edge that is straight.
=Plumb-rule.= A straight edge containing a plumb-bob.
=Pod-bit= _or_ =nose-bit.= A wood-boring tool, having a cutting lip at
its end.
=Point.= The surface or the extremity of a gear-wheel tooth.
=Polishing-lathe.= A lathe that is used for polishing and therefore
requires no tool-carrying devices.
=Poppet-head.= The main head of a lathe.
=Porter-bar.= A bar for handling heavy forgings, which is welded to the
forging and afterwards cut off.
=Pressure-bar.= A bar or piece that presses the work to the table in a
wood-planing machine.
=Protractor.= A tool having a blade which may be set to the degrees of a
circle which are marked upon the back or stock of the protractor.
=Pulley.= A wheel that receives or drives a band, belt or rope.
=Pulley= _or_ =belt-pulley.= A wheel that drives or is driven by a belt.
Q
=Quadrant.= 1. A piece forming one-fourth of a circle. 2. A piece
forming the segment of a circle.
=Quick return.= A motion by means of which a head ram or work-table is
moved faster during its return traverse than during its cutting
traverse.
R
=Rabbet.= A step at the end of a piece of wood.
=Rabbeting-plane.= A plane for rabbeting.
=Rack.= A straight body, having on it, (1) teeth corresponding to the
teeth in the wheel that drives it or that it drives; (2) notches to
engage a pawl or ratchet.
=Rack-feed.= A feed motor in which the work-table has a rack driven by a
gear-wheel.
=Rake.= The inclination of the front face of a cutting tool to the body
of the steel of which it is made.
=Ratchet.= A pawl or tongue one end of which engages in notches in a
rack or wheel.
=Ratchet-brace.= A hand-drilling device, in which a lever carries a pawl
that engages with a ratchet-wheel, which drives the drill.
=Rat-tail file.= A taper round file of small diameter or less than
one-fourth of an inch.
=Reamer=, =rymer=, _or_ =rimer.= A tool for smoothing and enlarging
bores or holes.
=Recut-file.= A file whose original teeth have been ground off and new
teeth have been cut.
=Red-marking.= A mixture of Venetian red and common oil, used to put on
a piece of work when trying its fit, and serving to denote the fit.
=Return-cam.= A secondary cam used to move a piece back, after the main
cam has moved it forward.
=Reverse-keys.= An arrangement of keys or wedges, that releases two
pieces that have been keyed together.
=Rib.= A projecting strip usually employed to strengthen a piece, as the
arm of a wheel.
=Right-hand thread.= A screw thread in which, with the end of the bolt
towards you, the top of the nut must revolve from left to right like the
hands of a watch in order to cause it to screw upon the bolt.
=Rip-saw.= A saw whose teeth are shaped to cut lengthways of the grain
of the wood.
=Rod-feed.= A feed motion that is operated by a rod.
=Roll-feed.= A feed motion in which the work is fed to the cutting tool
by revolving rolls.
=Rope-socket.= A socket in which the ends of a wire rope are secured.
=Rose-bit.= A reamer that cuts at the end only.
=Rotary planer.= An iron planing machine in which a number of cutters
are set in a revolving face plate that is fed to the cut by a head on a
slide.
=Round-nosed chisel.= A machinist's chisel whose cutting edge is shaped
so as to cut a groove circular in cross-section.
=Round-nosed tool.= A tool whose cutting edge is circular in its course
or length.
=Routing-machine.= A machine using a revolving cutter to cut away some
parts of a surface and leave the rest in relief.
=Rust-joint.= A joint that is made by being filled with cast-iron
cuttings mixed with sal-ammoniac and sulphur to cause the cuttings to
rust and form a solid body.
S
=Safe-edge file.= A file having no teeth upon one of its edges.
=Sanding= _or_ =sand-papering machine.= A machine in which
sand-paper-covered rollers or wheels are used for finishing wood-work.
=Saw-arbor.= The arbor or mandrel on which a circular saw is driven.
=Saw-bench.= A circular saw machine.
=Saw-gummer.= A machine for deepening the spaces between saw teeth.
=Saw-packing.= Plaited hemp that is packed on both sides of a circular
saw to warm it and equalize its tension when it is running.
=Scale.= 1. A rule or measuring device having lines of division upon it.
2. Proportion of size.
=Scarf.= The bevel of a piece of metal that is to be lap welded.
=Scraper.= A hand tool that scrapes rather than cuts the metal.
=Screw-cutting lathe.= A lathe that has a screw feed with change gears
to enable it to cut threads or screws upon the work.
=Screw-cutting lathe with independent feed.= A lathe that has a lead
screw for cutting threads and a separate feed motion for ordinary tool
traverse.
=Screwing-machine.= A machine used to cut screw threads.
=Screw-machine.= A form of lathe in which the spindle is hollow and a
revolving head or turret is employed to carry the cutting tools.
=Screw-plate.= A tool for cutting external threads on small work.
=Screw-thread.= The thread upon a screw or other piece of work.
=Screw-tool.= Another name for a chaser.
=Scribing-block= _or_ =surface-gauge.= A tool that carries a needle or
scriber for marking on work lines denoting its finished size or the
amount of metal that is to be cut off, and that is also used for setting
work.
=Second-cut file.= A file whose teeth are coarser than a _smooth_ file
and finer than a bastard file.
=Sector.= A device used in connection with an index plate to denote the
holes to be used in any particular division of a circle.
=Segment.= A piece having the shape of a segment of a circle, used for
building up a hollow cylinder.
=Segmental saw.= A saw that is composed of parts secured to a frame or
disc.
=Self-acting lathe.= A lathe having an automatic feed motion for the
cutting tool.
=Set.= 1. The bend to one side of the body of the blade of the teeth of
saws. 2. Adjustment or alignment. 3. Binding two pieces together.
=Set-screw.= A screw that binds or secures two pieces together by being
screwed through one piece and against the other.
=Shafting-rest.= A slide rest carrying several cutting tools and usually
employed for turning shafting in the lathe.
=Shake.= A crack in timber.
=Shank-mill.= A milling machine cutter that is provided with a shank or
stem.
=Shaper-centres.= A chuck in which the work is held between centres.
=Shaper= _or_ =shaping-machine.= 1. A machine for cutting such surfaces
on iron work as can be cut by a tool travelling in a straight line. 2. A
woodworking machine in which cutting tools are revolved on an upright
spindle projecting above a work table.
=Shavings.= The cuttings from a paring tool.
=Shell.= 1. The body of a steam-boiler. 2. An outer casing.
=Shell-reamer.= A short reamer that is driven by fitting to a coned
mandrel.
=Shimer-heads.= A form of cutter head for woodworking machines, in which
circular cutters are used.
=Shingle saw.= A saw thick in the body and beveled off for about two or
three inches of its outer diameter.
=Shooting-board.= A device upon which pieces are held when required to
have their ends dressed to exact shape or angle.
=Shrinkage-fit= _or_ =contraction-fit.= A means of securing two pieces
together by leaving the hole of one too small to receive the other, and
then expanding the piece containing the hole so that it will go on and
bind fast as it cools and contracts.
=Side-chisel.= A machinist's chisel shaped to cut on the sides of slots
or keyways, and having its cutting edge on one side of the end facet.
=Side-tool.= A tool used to cut the ends of lathe work that is held
between the lathe centres.
=Single-geared lathe.= A lathe in which there is no back gear.
=Single-riveted joint.= A joint having but one row of rivets in a lap
joint and one row of rivets on each side of the plate joint in a butt
joint.
=Single-thread.= A screw thread having a single spiral.
=Skew-bevel.= A bevel gear wheel in which the teeth sides do not form
lines radiating from the wheel centre, but point to one side of it.
=Skew-chisel.= A carpenter's chisel in which the cutting edge is not at
a right angle to the body of the tool.
=Skew-cutter.= A cutter in which the cutting edge does not stand
parallel to the axis of the shaft that drives it.
=Slab.= 1. A rough square piece of iron forged from scrap. 2. The first
piece cut from the side of a log of wood.
=Sleeve.= An enveloping piece that is usually cylindrical and too long
to be termed a ring.
=Slide-valve.= The valve that governs the admission of steam into and
its exhaust out of a cylinder.
=Slot.= A rectangular passage or hole passing entirely through the
material.
=Slotting-machine.= A machine having a vertical bar or ram that carries
the cutting tool on its lower end and has a vertical reciprocating
motion.
=Smooth-file.= The finest cut of file that is made for ordinary use.
=Smoothing-plane.= A carpenter's short plane for producing a smooth
surface.
=Socket.= A piece that is hollow and receives another.
=Socket-wrench.= A wrench that envelops the whole of the head of a bolt.
=Solid milled cutters.= Cutters for woodwork, in which an irregular
shaped cutting edge is obtained by recesses cut in the flat face of the
cutter.
=Space= _or_ =spaces.= The opening between the teeth of gear wheels.
=Spanner.= A form of wrench.
=Spindle.= A shaft that is used to transmit purely rotary motion, and
that is usually of small diameter in proportion to its length.
=Spiral cutter.= A milling cutter having its teeth cut spirally and not
parallel to the axis of its bore.
=Spiral head.= A device for holding work and revolving it in a milling
machine.
=Spirit-level.= An instrument in which an air-space or bubble is
utilized to disclose whether the surface upon which the spirit level is
laid is horizontal.
=Spline.= A long feather-way.
=Split-pin.= A pin that is split so that its end can be opened out to
prevent its coming out of place.
=Spoke.= The arm that connects the hub of a wheel to its rim or felloe.
=Spoon-bit.= A wood-boring tool that is shaped somewhat like a gouge.
=Spring.= 1. A piece of elastic metal. 2. The movement or deflection of
a piece of metal on a tool, by its own weight or from the strain placed
on it.
=Spring-tool.= A tool so formed as to have a slight give or spring to
it.
=Spur.= A sharp cutting edge placed on some kind of wood-cutting tools
to sever the fibre before the cutting edge removes the wood cuttings.
=Spur-wheel.= A gear-wheel having its teeth upon its circumferential
surface.
=Square-centre.= A lathe centre having four cutting edges at its coned
end.
=Square thread.= A screw-thread that is rectangular in cross-section.
=Stanchion= (st[)a]n'shun). A vertical frame.
=Standard.= An upright piece.
=Standing-bolt.= A bolt that screws into the work, and does not
therefore require a nut.
=Stave.= 1. A piece that forms part of a hollow wooden casing. 2. A pin
on a gear-wheel that has pins instead of teeth.
=Steady-rest= _or_ =back-rest.= A device for steadying work in the
lathe.
=Steam-boiler.= A boiler used to generate steam and hold it at a
pressure above that of the atmosphere.
=Steam-hammer.= A forging machine in which the hammer is raised or
lifted by steam, and is sometimes also forced downwards by steam.
=Steam-space.= That part of the boiler that is above the level of the
water.
=Sticker.= A machine that operates on wood of small cross-sectional area
in proportion to its length, such as picture frame moulding.
=Stock.= Material.
=Stocks-and-dies.= Tools for cutting external threads by hand.
=Stop.= 1. A piece that arrests the motion of another piece. 2. A part
of a gauge, against which the work abuts.
=Stop-motion.= A device for preventing the overwinding of clocks and
watches.
=Straddle-mills.= Milling-machine cutters that are used in pairs and
straddle the work, both cutters being of the same diameter.
=Straight edge.= A piece or strip having one or both edges made straight
to use as a guide in testing work.
=Stub end.= The end of a connecting rod.
=Stud.= 1. A bolt that screws into the work at one end and receives a
nut at the other. 2. A piece that screws into the work at one end.
=Stuffing-box.= The box in which a gland fits.
=Surface-plate.= A plate having a true flat surface to test the flatness
of work by.
=Swage.= A blacksmith's tool for smoothing and shaping surfaces.
=Swing-frame.= A frame having a movable stud for carrying the change
gears of a lathe.
=Swing-saw.= A saw that is suspended in a swinging frame.
=Swivel-vise.= A vise that may be swiveled or revolved upon its base
plate.
T
=[T]= or =tee=. A pipe fitting having two bores at a right angle, one to
the other.
=Tailstock= _or_ =tailblock.= That part of a lathe that carries the dead
centre.
=Tangent-wheel.= A wheel whose teeth are formed to work with a screw or
worm.
=Tap.= 1. A tool for cutting threads in holes or bores. 2. A device for
shutting off or turning on the flow of water through a pipe.
=Taper-tap.= A tap that has part of the thread turned off in order that
it may enter the hole easily and start to cut the thread. It is
sometimes termed the first tap.
=Tapped.= 1. Threaded internally. 2. Having a connection that branches
from the main pipe or flow.
=Target.= A frame used in setting shafting in line.
=Temper.= 1. The degree of hardness that has been imparted to steel by
heating and suddenly cooling it. 2. A term employed by steel makers with
reference to the percentage of carbon contained in steel.
=Tempering.= Tempering consists in reheating hardened steel and thus
modifying or reducing its degree of hardness.
=Template= _or_ =Templet.= A piece of metal made to shape, to serve as a
pattern for one or more of the work surfaces.
=Thread-gauge.= A threaded cylinder or bore that serves as a standard of
reference for the shape and diameter of a screw thread.
=Threading-tool.= A tool for cutting screws in the lathe.
=Throw-line.= The travel of a piece, moved by an eccentric.
=Thumb-nut.= A nut so shaped that it may be screwed up or unscrewed by
hand.
=Tight.= A term used to denote those parts of a plate or saw that are
under undue tension, and prevent the other parts of the plate from lying
flat.
=Timber-planer.= A wood-planing machine for thick work, usually having
side heads as well as cutter bars.
=Tire.= The iron band surrounding a wheel rim.
=Tit-drill.= A drill having a point or teat, and employed to cut
flat-bottomed holes.
=Tool-post.= The device employed in a slide-rest to grip the cutting
tool.
=Train.= An arrangement of gear wheels in which there are more than two
gear wheels employed.
=Trammels= _or_ =tram.= A device for measuring distances too great to be
measured by ordinary compasses.
=Trip-hammer.= A forging machine in which the helve or hammer holding
beam is tripped by a revolving cam.
=Trundle.= A gear-wheel having rungs in place of teeth.
=Trying-up.= A term usually employed to indicate that the work is
accurately done or fitted.
=Try-square.= A tool having a rectangular back, and a blade whose edges
are a right angle to the edges of the back.
=[T] Slot.= A slot or groove, shaped to receive a bolt head and prevent
it from turning when the nut is screwed up.
=Turnbuckle.= A socket that receives and holds the ends of two rods and
permits either to be revolved independently of the other or the socket
to be revolved without revolving either rod.
=Turret-lathe.= A lathe in which a revolving head or turret carries the
cutting tools.
=Tuyère= (tw[=e]'ar). The nozzle through which air is forced into a
blacksmith's fire, a furnace or a cupola.
=Twin-mills.= Milling cutters that are used in pairs, and have teeth on
their side faces as well as upon the circumference.
=Twist-drill.= A drill having a spiral flute along it.
=Twist-hammer.= A sawmaker's hammer having its two faces parallel, so
that by turning it over in the hand its marks will be in opposite
directions.
=Two-jawed chuck.= A chuck having two jaws.
U
=Universal chuck.= A chuck in which the jaws move simultaneously.
=Universal joint.= A joint or connection that permits a piece to be
moved about in any required direction.
=Universal milling-machine.= A milling-machine that is capable of
cutting spirals, and is provided with an index head.
=Upright.= A vertical post or frame.
=U. S. standard thread.= A V-shaped thread having a flat place at the
top and bottom.
V
=Vernier= (vër'ni-er). A measuring device in which two sets of lines of
division are employed, one set being narrower spaced than the other, but
so spaced that in a certain number of divisions the two end lines of
each piece measure exactly alike: this provides a means of making a
minute measurement.
=Vise.= A work-holding device in which one jaw is movable and the other
stationary.
=Vise-clamp.= A piece of metal placed on the vise jaw and passing
between it and the work to prevent the jaw teeth from indenting the
work.
=[V]-thread.= A V-shaped thread, sharp at the top and bottom.
W
=Warding file.= A thin file suitable for filing out the wards of the
keys of door locks, etc.
=Washer.= A perforated disc of metal, usually forming a seating for some
other piece as a rest or a pin.
=Wheel lathe.= A lathe for turning wheels.
=Whitworth's quick-return motion.= A mechanism employed to move a
cutting tool faster on its return than on its cutting stroke.
=Whitworth's thread.= A screw thread designed by Sir Joseph Whitworth,
and having a rounded top and bottom.
=Winding strips.= A pair of straight edges, used to detect any wind or
twist in surfaces that ought to be parallel.
=Wing-nut.= A nut having wings so that it may be screwed up with the
fingers.
=Wire-gauge.= A gauge having notches in it that are standards of size
for wire, for the thickness of sheet metal, for screws, etc., etc.
=Worm-wheel.= A wheel whose teeth are formed to work with a worm or
screw.
=Wrench.= A tool for turning nuts, etc.
Y
=Yoke.= A piece that embraces two other pieces to hold them together, or
adjust their distance apart.
INDEX TO THE TWO VOLUMES.
A
Absolute steam pressure, ii, 411.
Accidents to locomotives, ii, 402.
Accurate standards, i, 341.
Admission of steam to indicator, ii, 414.
point of, ii, 376.
Adjustable centre rest, ii, 14.
chucks for true work, i, 235.
cutters, i, 448.
with half-round bit, i, 281.
die stock, i, 448.
drivers for bolt-heads, i, 224.
end measurement gauges, i, 377.
or jamb dies, i, 98.
planes, ii, 269.
reamers, i, 189, 284, ii, 99.
shell reamers, i, 284.
tap wrenches, i, 110.
taps, i, 104.
wrenches, various forms of, i, 125.
Adjusting connecting rod brasses, ii, 385.
length of connecting rods, ii, 126.
main bearings, ii, 386.
parts of a locomotive, ii, 404.
Adjustment of band saws, ii, 309.
by differential screw, i, 119.
Advantages of face cutters, i, 108.
of involute gear teeth, i, 34.
Air brake for locomotives, ii, 398.
Air chambers, ii, 388, 441.
Air pumps, ii, 441.
Aligning connecting rods, ii, 119, 124.
Alignment in crank pins, errors, ii, 169.
of cranks, testing the, ii, 167.
of lathe tail stocks, i, 145.
Allen valve, ii, 377.
Allowance, for contraction fits, i, 366.
for hydraulic fits, i, 365.
Alteration of shape of threads from the wear of tools, i, 89.
Angle irons, welding of, ii, 236.
of clearance in lathe tools, i, 257.
plate chucking, examples of, i, 251.
plates for planer tables, i, 418.
valve patterns, ii, 283, 284.
Angles for the facets of scrapers, ii, 97.
of cutting edges of chisels, ii, 74.
of thread cutting tools, i, 91.
Angular advance of eccentrics, ii, 380.
cutters, ii, 19.
cutters for groove cutting, ii, 27.
of helical teeth, i, 69.
teeth, and thrust of, i, 69.
herring-bone, i, 69.
velocity of gear-wheels, i, 6.
Angularity of connecting rods, ii, 375.
Annular emery wheels, ii, 47.
wheels, i, 1.
compared with spur, i, 32.
Anvils, ii, 230.
Apparatus for oiling, ii, 439, 440.
Appliances for bending timber, ii, 265.
for tapping standard work, i, 111.
Aprons, lathe, feed motion for, i, 168.
Apron tools for planers, i, 411.
Arbors, adjustable, i, 227.
cutter, ii, 25.
emery wheel, construction of, i, 198.
expanding, i, 227.
for eccentric work, i, 229.
shell reamers, i, 283.
threaded work, i, 228.
lathe, i, 227.
Arc of approach of gear-wheels, i, 13, 16.
of contact of gear-wheels, i, 17, 25.
of recess of gear-wheels, i, 13, 16, 20.
Area of the indicator diagram, ii, 419.
Arms for pulleys, ii, 279.
pivoted, for tooth templates, i, 44.
Atmosphere, influence of, on oils, ii, 153.
Auger bit, i, 453.
Augers for end-grain wood, i, 454.
Augers for wood boring, ii, 342.
Automatic air brake, ii, 398.
cut-off engines, ii, 423.
engine, high speed, ii, 427.
engine, straight line, ii, 428.
wheel governors, ii, 427.
feed motions, i, 408; ii, 8.
gear cutter, ii, 54.
nut tapping machine socket, ii, 475.
grindstone traversing device, ii, 53.
Auxiliary valve, ii, 438, 439.
Ax handle lathes, i, 210.
Axle boxes, hot, ii, 403.
locomotive, ii, 148.
brasses, testing, i, 366.
Axles, crank, lathes for turning, i, 152.
forging, ii, 259.
B
Babbitting boxes, methods of, ii, 155.
Babbitt metal-lined boxes, ii, 155.
Back-gear of lathe, i, 135, 145.
throwing in and out, i, 165.
treble, i, 143.
Back-knife gauge lathe, i, 211.
Back rest, i, 233.
Balanced valves, ii, 377.
Balancing cutter heads, ii, 324, 326.
emery wheels, ii, 39.
pulleys, ii, 202.
Ball turning, i, 325.
Banking fires, ii, 401.
Band saw machines, ii, 308, 311, 312.
Band saw guides, ii, 311.
teeth, ii, 308-310.
pitch of, ii, 309.
tension, ii, 310, 311.
Bar cutters, boring, i, 289.
the shapes of, i, 291.
Bar iron, straightening, i, 305.
Barometer, graduation of, ii, 416.
construction of, ii, 415.
Bars, boring, i, 289.
boring, with fixed heads, i, 290.
Bar steel, forms of, for chisels, ii, 73.
Beading bits, ii, 270, 271.
Bearings, adjusting, ii, 386.
for lead screw, i, 139.
of engine lathes, i, 134.
of line shafting, ii, 166.
surfaces of keys, i, 126.
thrust of, ii, 445.
various forms of, ii, 147.
wear of, i, 158.
Beating and pounding, causes of, ii, 168.
Bedding brasses in their boxes, ii, 132.
Beds, planer, flat guideways for, i, 414.
planer, oiling devices for, i, 415.
Belt stretching clamps, ii, 210.
lacings, covers for, ii, 215.
forms of, ii, 214.
Belt pumps, ii, 388.
shifting mechanism, i, 406, 407.
Belts, bevelled joints for, ii, 215.
changing or shipping, ii, 217.
driving power of, ii, 208-225.
friction, coefficient of, ii, 222.
grain side, weak, ii, 208.
to pulley, ii, 209.
guide pulleys for, ii, 211.
lap joints for, ii, 215.
length of, ii, 209.
line of motion of, ii, 217.
parts of hide used for, ii, 207.
pegged, ii, 215.
single and double, ii, 208.
stretch of, parts of hide, ii, 208.
the creep of, ii, 222.
length of, ii, 209.
sag of, ii, 210.
tension of, ii, 211, 224.
torsional moment, ii, 223.
[V] or angular, ii, 217.
Bench lathes, i, 130.
Bending appliances, ii, 226, 265.
block for wood, ii, 265, 266.
iron, ii, 226, 240.
timber, ii, 265, 266.
wood, modern methods, ii, 265.
Bent files, use of, ii, 93.
Bevel gear teeth, originating, i, 22.
pinion, drawings for, i, 59.
protractors, i, 380.
squares, i, 380.
wheel, body pattern, i, 59.
Bevel wheels, i, 1, 21, 61.
formation of the teeth of, i, 22.
testing the angle of, i, 60.
Bilge injection marine engines, ii, 441.
Billiard cues, steady rest for, i, 233.
Birmingham wire gauge for gold and silver, i, 387.
Bit, half round, i, 281.
Bits for wood working, ii, 342.
Blacksmith's anvils, ii, 230.
drilling levers, i, 456.
fire, side blast for, ii, 228.
forges, ii, 228, 229.
swages, ii, 230, 231.
temper, ii, 460.
tools, ii, 229, 230.
work, swaging, ii, 232.
Blade, form of, necessary to produce a given shape of moulding, ii, 77.
Block planes, ii, 269.
Blocks for filing pins, ii, 104.
pillow for shafting, ii, 194.
or pillar, patterns for, ii, 277.
swage, ii, 232.
Blotting paper, oil test, ii, 154.
Blowing down boilers, ii, 370.
Blows upon plates, effects of, ii, 69.
Blow through valve, ii, 440.
Boiler fitting joints, ii, 140.
Boilermakers, drilling machine, i, 435.
drilling machine, feed motion, i, 436.
Boilermakers' turning machine, i, 435.
Boiler, blowing down, ii, 370.
cleaning, ii, 370.
evaporative efficiency of, ii, 366.
examining, ii, 458.
factors of safety of, ii, 355.
feed water, ii, 370.
feeding, instruction upon, ii, 370.
fire cleaning, ii, 369.
cleaning tools, ii, 369.
for stationary engine, ii, 350.
gauge cocks, ii, 368.
grate bars, ii, 369.
bars, shaking, ii, 369.
horizontal, return tubes, ii, 361.
lighting the fire under, ii, 368.
internally fired, ii, 358.
plate, the strength of, ii, 351.
settings, ii, 364-366.
seams, diameter of rivets, ii, 356.
treble riveted, ii, 353.
shells, drilling machines for, i, 436.
the strains on, ii, 351.
the strength of, ii, 350.
strains on, ii, 355.
the care and management of, ii, 368.
tubes, for fire engines, ii, 431.
vertical, ii, 359.
external uptakes, ii, 361.
water gauge glass of, ii, 368.
with Field tubes, ii, 359.
Boilers, low water in, ii, 370.
of marine engines, ii, 436, 437.
of steam fire engines, ii, 431.
priming in, ii, 370.
Bolt-cutting machine, head of, i, 466.
dies, i, 473.
rapid, i, 467.
the construction of dies for, i, 473.
with automatic stop motion, i, 466.
back gear, i, 467.
Bolt-forging, ii, 238.
Bolt-threading machinery, i, 468.
capacity of, i, 471.
construction of, i, 468-472.
Bolted connecting-rod straps, ii, 116.
Bolt-heads, adjustable drivers for, i, 224.
bedding, i, 117.
filing, ii, 105.
Bolt-holes, classification of, i, 112.
Bolts and nuts, table for, i, 114.
Bolts, classification of, i, 112.
countersunk, i, 112.
devices for forging, ii, 238.
for foundations, forms of, i, 113.
planer tables, forms of, i, 417.
quick removal, i, 116.
forms of drivers for, i, 224.
hook, i, 113.
not passing through the work, i, 117.
rapid construction of, i, 468.
removing corroded, i, 122.
self-locking, i, 117.
Bore gauge, i, 387.
Boring and turning mill or lathe, i, 211.
bar, centres for, i, 293.
cutters, i, 289.
cutters, shapes of, i, 291.
bars, i, 289.
for taper work, forms of, i, 292.
three or four cutters for, i, 290.
with fixed heads, i, 290.
with sliding heads, i, 290.
double-coned work, i, 293.
end grain wood, augers for, i, 453.
head with nut feed, i, 291.
heads, i, 288.
lathe for engine cylinders, i, 219.
with double heads, i, 220.
with traversing spindle, i, 218.
mill, i, 211.
purposes, chucking lathe for, i, 152.
tool holders, i, 287.
tools for brass, lathe, and small work, i, 285-287.
octagon, holders for, i, 175.
the spring of, i, 286.
Boring-machine, i, 431.
for car wheels, i, 438.
wood, ii, 342.
horizontal, i, 433.
pulley, i, 438.
the feed motion of, i, 432.
Box wrenches, i, 124.
body chucks, i, 237.
tools for screw machines, i, 208.
Brace drill, i, 455.
with multiplying gear, i, 456.
ratchet motion, i, 456.
Brad awl, i, 452.
Brake for lathe pulley, i, 149.
for pattern lathe, i, 149.
lathe, i, 151.
Branch pipe core boxes, ii, 286.
Brasses, fitting to their journals, ii, 145.
Brasses, for connecting rods, adjusting, ii, 120-127, 130-132.
lead lined, ii, 148.
oil cavities for, ii, 150.
open, ii, 149.
various forms of, ii, 127, 147.
Brass work, boring tools for, i, 286.
front tools for, i, 264.
hand tool for roughing out, i, 332.
side tools for, i, 264.
special lathes for, i, 217.
Breast drill with double gear, i, 456.
Broaches, construction of, i, 479.
Broaching press, i, 478.
Broken frames, repairing, ii, 178.
Brush wheels, for polishing, ii, 50.
speed of, ii, 50.
Built-up gearwheels, i, 61.
Burnishing lathe work, i, 311.
Butt joints, boiler, ii, 352.
Butt welds, ii, 236.
Buzz planer, ii, 315.
By-pass valve, ii, 438.
C
Calculating the horse power of engines, ii, 407, 419.
revolutions of, and power transmitted by, gear wheels, i, 5.
speeds of pulleys, ii, 204.
strength of gear teeth, i, 65.
strength of riveted seams, ii, 354.
horse power by indicator diagrams, ii, 418, 419.
Calculations, safety-valve, ii, 409.
Calendar roll lathe, i, 195, 215.
Caliper, the micrometer, i, 354.
Calipers, compass, i, 378.
holding and using, i, 361, 362.
inside, i, 360.
spring, i, 360.
with locking devices, i, 360.
Cam chuck for irregular work, i, 328.
motion for an engine slide-valve without steam lap, i, 83.
motions, applications of, i, 327.
for engines, i, 83.
return or backing, i, 82.
Cams, finding the pitch line of, i, 80.
finding the working face of, i, 80.
originating in the lathe, i, 326.
return, finding the shapes of, i, 82.
Capacity of pumps, ii, 388.
of thread cutting machine, i, 471.
Cape chisels or cross-cut chisels, ii, 74.
Car axle lathe, i, 147.
the feed motions of, i, 148.
Carpenter's chisel, ii, 77.
Carriages, lathe, testing, ii, 182.
for lathes, i, 137, 145.
Carriers, lathe, i, 222.
Car wheels, boring machine for, i, 438.
Case-hardening, ii, 128, 442.
finished work, ii, 129.
preparing work for, ii, 129.
Casting pillow blocks, ii, 277.
Cast gear, contact of the teeth of, i, 67.
iron, internal strains, i, 306.
teeth, contact of, i, 67.
scale for curves of, i, 51.
side clearance, i, 53.
Cat head, i, 233.
steady rest, i, 233.
Caulking tools, ii, 141.
Cement chuck, i, 242.
Cements used in the manufacture of emery wheels, ii, 38.
Centre bit, i, 454.
dead, methods of removing, i, 159.
drill and countersink, i, 300.
chuck, i, 302.
drilling lathe attachment, i, 300.
chucks for, i, 303.
machine, i, 300.
live, removing, i, 159.
of rough work, i, 301.
planer, i, 408.
punch, i, 300.
guide, i, 301.
Centres for boring bars, i, 293.
for hollow work, i, 226.
lathe, i, 296.
shaping machines, i, 397.
taper work, i, 226.
live, tapers for, i, 159.
Centring devices for crank axles, i, 230.
square, i, 300.
work with the scribing block, i, 301.
Chain riveted joints, ii, 352.
Chambering or gumming, ii, 290.
Change gears, arrangement of, i, 319.
gears, compounded, i, 321.
table for finding, for screw cutting, i, 180.
hanging, i, 158.
wheels, pitches of teeth, i, 182, 321.
Changing or slipping belts, ii, 217.
Chasers, errors in applying, i, 336.
forms of, i, 268.
holders, i, 268.
improved form of, i, 90.
outside and inside, i, 335.
setting, i, 268.
Check valves, ii, 388.
Chisels, angle of presentation, ii, 77.
angles of cutting edges, ii, 74.
blacksmith's, ii, 230.
cape or cross-cut, ii, 74.
carpenter's, ii, 77.
cow-mouthed, ii, 75.
curved or oil groove, ii, 76.
cutting ends of, ii, 74.
diamond point, ii, 76.
dimensions of, ii, 74.
for wood, ii, 271.
handles for, ii, 271.
holders, ii, 74.
machinist's application of, ii, 76.
round-nosed, ii, 76.
shapes of cutting edges, ii, 74.
the use of, ii, 76.
Chucking device for pulleys, i, 318.
devices for planer tables, i, 408.
errors in, i, 250.
lathe for boring purposes, i, 152.
machine beds, on a planer, i, 421.
on angle plates, i, 251.
reamers, for true work, i, 283.
the halves of large pulleys on a planer, i, 422.
Chucks and chucking, i, 234.
Chucks, box body, i, 237.
cement, i, 242.
combination, i, 237.
cone, i, 232.
contracting, for lathes, i, 188.
drill, i, 446.
drill-holding, construction of, ii, 41.
expanding, i, 188.
for centre-drilling and countersinking, i, 303.
large planing machines, i, 422.
milling machines, ii, 31.
screw machine, i, 205.
straightening wire, i, 305.
true work, adjustable, i, 235.
wood-working lathes, i, 242.
independent, i, 238.
planer, for curved work, i, 420.
planer, for grooved work, i, 419.
reversible jawed, i, 237.
special forms of, i, 234-241.
swivelling, i, 395.
tailstock for drilled work, i, 279.
the wear of, i, 240.
three and four-jawed, i, 237.
two-jawed, i, 236.
universal, i, 238.
various forms of, i, 394.
vise, for vise work, i, 396.
vise, holding taper work in, i, 394.
vise, rapid motion, i, 396.
Circle, dividing the, i, 348.
rolling, for change gears, i, 16.
Circular cutters, i, 272; ii, 22.
cutters, tool holders for, i, 272.
cutting tools, i, 267.
plane, ii, 268.
saw gauges, ii, 287.
inserting teeth, ii, 290, 291.
machine, roll feed, ii, 298, 300.
mandrel hole, size of, ii, 287.
segmental, ii, 300.
stretching by heat, ii, 288.
tension, ii, 288.
Circular slide valves, ii, 377.
Circulating pumps, ii, 440.
Circumferential seam strength, ii, 356.
grindstone speed, ii, 52.
Clamp couplings, ii, 197.
Clamping work on face plates, i, 245.
Clamps, belt, ii, 210.
chucking, i, 245.
for steady rests, i, 233.
polishing for lathe-work, i, 311.
steady rest, i, 233.
vise, various forms of, ii, 64.
Classification of bolts, i, 112.
of bolt heads, i, 112.
of lathes, i, 129.
of measuring tools, i, 354.
Cleaning boilers, ii, 370.
files, ii, 94.
Clearance in cast gear teeth, i, 53.
of front tools, i, 254.
of planer tools, i, 424.
of taps, i, 102.
of tools for square threads, i, 269.
of twist drills, i, 274, 275.
on cutter, ii, 35.
Clements driver, i, 223.
Clinker hook, ii, 369.
Clip-ended connecting-rod, ii, 115.
Clock wheels, i, 21.
Clutches, friction, ii, 192.
Cocks and plugs, grinding, ii, 144.
leaky, ii, 145.
Cogged gear-wheels, i, 63.
Cogs, durability of, i, 66.
strength of, i, 66.
thickness of, i, 66.
methods of fastening, i, 63.
Cold-rolled shafting, ii, 187.
Collapsing tap, screw machine, i, 107.
taps, tapping machine, i, 107.
Collar gauges and standard plug, i, 356.
for threads, i, 91.
testing, i, 356.
Collars for shafting, ii, 189.
Color tempering, ii, 460.
Combination chucks, i, 237.
Combination planes, ii, 269, 270.
Combined centre-drill and countersink, i, 300.
cutting off tools and holders, i, 273.
drilling machine and lathe, i, 433.
Compass planes, ii, 268, 269.
Compasses, i, 377.
Compound engines, ii, 434, 435.
slide rest, i, 140.
tool holders for, i, 174.
Compounded gears, i, 320.
Compounds for welding, ii, 234.
Compression curve of engines, ii, 422.
Compression curve, ii, 415.
line, ii, 415.
the point of, ii, 376.
Concave saw, ii, 287, 288.
Condenser, total pressure in, ii, 444.
Condensing engine diagram, ii, 415.
Cone chuck, i, 232.
Connecting-rods, adjusting the length of, ii, 126.
angularity of, ii, 375.
brasses, adjusting, ii, 385.
joint faces of, ii, 122.
lining up, ii, 126.
double gibbed, ii, 116.
ends, tapered, ii, 117.
fitting up, ii, 118.
keys, ii, 375.
keyways, filing out, ii, 120.
locomotive, ii, 115.
length of, ii, 123.
marine engine, ii, 116.
marking length of, ii, 123.
repairing, ii, 125.
setting up keys of, ii, 126.
solid-ended, ii, 114.
strap-ended, ii, 115.
straps, ii, 120.
bolted, ii, 116.
stepped, ii, 117.
trammelling the length of, ii, 122.
various forms of, ii, 117.
welding up stub ends of, ii, 119.
Construction of gland patterns, ii, 276.
of groove cams, i, 84.
of lathe carriages, i, 137.
of emery wheel arbors, i, 198.
of tailstock of engine lathe, i, 135.
of reciprocating cross-cut saw, ii, 312.
of scroll sawing machines, ii, 306, 307.
of the barometer, ii, 415.
Contact of cast teeth, i, 67.
Contracting chucks for lathes, i, 188.
Contraction or shrinking fits, i, 366.
Convection, ii, 412.
Conversion of heat into work, ii, 411.
Cope cutters, ii, 344.
Core boxes for branch pipes, ii, 286.
Core box plane, i, 269.
Cored work, drivers for, i, 225.
Corliss engine, ii, 423, 424.
valve, lap of, ii, 426, 427.
valve gear, ii, 424, 425.
Correcting the errors of thread pitch caused by hardening, i, 109.
Corroded bolts, removing, i, 122.
nuts, removing, i, 122.
Cotter or keyway drilling machine, i, 438.
drills, i, 446.
Counterbore and drill, i, 449.
Countershafts, ii, 191.
Countersink cutters, i, 449.
Countersink, for hardened work, i, 303.
for lathe work, i, 302.
with adjustable drill, i, 300.
Countersinking, chucks for, i, 303.
Countersinks, i, 285.
Countersunk bolt heads, i, 112.
Coupling for light shafting, ii, 198.
plate, ii, 196.
universal, ii, 199.
Couplings, clamp, ii, 197.
for line shafting, ii, 194.
for split sleeves, ii, 195.
self-adjusting, ii, 196.
Covers for belt lacings, ii, 215.
Cow mouthed chisel, ii, 75.
Crank, application of slide-rest, i, 152.
axles, centring devices, i, 230.
axles, lathe for turning, i, 152.
drill, i, 457.
lathe for turning, i, 154.
motion for shaping machines, i, 401.
simple, i, 13.
placing at right angles, ii, 156.
Crank-pin aligning, errors, ii, 158, 170.
remedying errors of, ii, 171.
riveting, ii, 73.
Crank-pins, hot, ii, 386.
Crank position, engine starting, ii, 384.
Crank-shaft, forging, ii, 248, 249.
setting eccentrics on, ii, 174.
Cranks, placing at right angles, ii, 156.
special lathe chuck for, i, 248.
testing the alignment of, ii, 167.
Creep of belts, ii, 211.
Cropping gauge, ii, 296.
Cross-bar, construction of, i, 409.
Cross-cut, or cape chisels, ii, 74.
saws, ii, 272, 273, 312.
Cross-cutting or gaining machine, ii, 305.
Cross-feed motion, construction of, i, 138.
Cross-files, ii, 91.
Crossfiling, ii, 92, 93.
Cross-head chucking, i, 251, 253.
Cross-heads of steam engines, ii, 375.
Crowding of cutters, to avoid, ii, 27.
Crowned pulleys, ii, 200.
Crowns of brasses, shapes of, ii, 127.
Crown wheels, i, 1.
Curve of expansion of indicator diagrams, ii, 414.
of gear wheel teeth, variation of, i, 12.
Curved or oil groove chisel, ii, 76.
work, planer chuck for, i, 410.
work, turning, i, 314, 315.
Curves, compression, ii, 415.
marking, by hand, i, 45.
of gear teeth for bevel gear, i, 22.
templates for, i, 384.
Cushioned hammers, ii, 252, 253.
Cut, and kinds of rasps, ii, 87.
of files, ii, 86.
gear-wheel teeth, strength of, i, 65.
Cut-off engines, ii, 423.
the point of, ii, 376.
valves, ii, 378.
Cutter, adjustable, i, 448.
adjustable on half-round bit, i, 281.
angle for worm wheels, i, 43.
angle of, for spiral grooves, ii, 29.
arbors, ii, 25.
boring-bar, the shapes of, i, 291.
clearance of, ii, 35.
grinding taper, thin edge, ii, 33.
heads, ii, 337.
heads for planing machines, ii, 320.
revolving, for gear teeth, i, 37.
Cutters, angular, ii, 18.
angular, grooving, setting of, ii, 28.
circular, ii, 22.
countersink, i, 449.
crowding, to avoid, ii, 27.
face, ii, 17.
fly, ii, 21.
for drilling machines, i, 442.
edge moulding, ii, 341.
friezing machines, ii, 340.
moulding machines, ii, 340.
mouldings, ii, 336, 337.
standard shapes, i, 111.
gang or composite, ii, 23.
holders for fly, ii, 22.
matched, ii, 73.
milling, ii, 16.
milling, errors in grinding, ii, 32.
parallel, fixture for grinding, ii, 32.
right and left-hand, ii, 18.
rotary, for all kinds of work, ii, 341.
shank, ii, 19.
sizes of, ii, 17.
slide of gear-cutter, operating, ii, 55.
spiral, grinding teeth of, ii, 36.
tube-plate, i, 448.
twin, ii, 18.
with inserted teeth, ii, 24.
with spiral teeth, ii, 17.
Cutting cams in the lathe, i, 326.
coarse pitch square threads, i, 269.
double threads, i, 322.
edge of chisels, angles of, ii, 74.
of chisels, shapes of, ii, 74.
on drills, clearance, ii, 43, 44.
edges for dies, number of, i, 471.
for taps, number of, i, 105.
ends of chisels, ii, 74.
feeds for wrought iron, i, 294.
files, ii, 101.
gauge, ii, 274.
grooves in cylindrical work, ii, 27.
helical teeth in the lathe, i, 69.
iron when hot, ii, 263.
keyways by hand, ii, 108.
left-hand threads, i, 322.
out keyways by drifts, ii, 109.
steam ports, jigs for, i, 441.
right and left-hand grooves, ii, 29.
right or left-hand thread, single, double, or treble, with same
dies, i, 99.
screws by the metric system, i, 322.
screw thread by hand, i, 62.
speeds, examples of, i, 295.
for threading dies, i, 474.
for wrought iron, i, 294.
taper threads, i, 338.
threads, multiple, i, 322.
on taper work, i, 324.
tools, circular, i, 267.
producing gauges for, i, 92.
power required to drive, i, 273.
the utmost duty of, i, 258.
wheels, angle of cutter for, i, 43.
wood slips, ii, 271.
worm-wheel teeth in the lathe, i, 42.
Cutting-off machine, i, 193.
tool for screw machines, i, 208.
tools, i, 262, 273.
Cycloidal curves for gear teeth, i, 8.
Cylinder boring lathe with facing slide rests, i, 219.
cover joints, ii, 137.
cover, turning a, i, 318.
ends, scraping out, ii, 161.
Cylinder heads, knocking out, ii, 402.
Cylinders, bores of, ii, 372.
clearance in, ii, 372.
counterbore of, ii, 372.
for steam engines, ii, 372.
jacketed, ii, 374.
lagging, ii, 374.
lubricating, ii, 373.
reboring in place, ii, 160.
relief valves for, ii, 373.
steam, ports of, ii, 373.
waste water cocks of, ii, 373.
wear of, ii, 372.
Cylindrical work, cutting grooves, ii, 27.
D
Dancing governors, ii, 384.
Dead-centre, finding the, ii, 174.
methods of removing, i, 159.
of the crank, finding the, ii, 172.
Deflection of surface plates, ii, 135.
Depth of gear wheel teeth, i, 42.
Designing slide valves, ii, 380.
Detachable slide rest, i, 143.
Determining the pitches of the teeth for change wheels, i, 182.
Diagram, theoretical, ii, 414.
the uses of, ii, 413.
Diagrams for condensing engine, ii, 415.
indicator, ii, 414.
defective, ii, 421.
Diameter at the roots of threads, i, 269.
of circle for generating curves of gear teeth, i, 10.
of the pitch circle of wheels, i, 1.
Diameters of line shafting, ii, 189.
Diametral clearance of twist drills, i, 274.
Diamond point chisel, ii, 76.
Diamond pointed tool for lathe work, i, 254.
Dictionary of work-shop terms, ii, 473.
Die stock for pipe-threading by hand, i, 463.
by power, i, 463.
Dies, adjustable, i, 98.
for finishing square threads, i, 269.
for forging eye-bars, ii, 260.
for gas and steam pipes, i, 101.
or chasers in the heads of bolt-cutting machines, i, 463.
the wear of, i, 89.
with four cutting edges, i, 100.
Differential threads for locking, i, 119.
Displacement of pumps, ii, 387.
Distance between bearings of line-shafting, ii, 186.
Dividers, i, 377.
Dividing device for circle, i, 352.
engine, i, 349.
mechanism for gear cutting, ii, 57.
Division of the circle, i, 348.
Dog-head hammer, ii, 69.
Dogs, lathe, various kinds of, i, 222.
movable for face-plate work, i, 250.
Donkey engines, ii, 442.
Double beat valves, ii, 443.
eye, filing up a, ii, 103.
forging of, ii, 240.
eyes, fitting pins in, i, 121.
gibbed connecting rod, ii, 115.
head panel raiser and sticker, ii, 335.
heads for planing machines, i, 404.
ported side valves, ii, 377.
rapid bolt threading machine, i, 467.
riveted lap joint, ii, 352.
saw machine, ii, 294, 295.
spindle milling machine, ii, 16.
threads, cutting, i, 322.
tool holder for slide rest, i, 169.
wheel sanding machines, ii, 348.
Double-coned work, boring, i, 293.
Dovetail joint, ii, 275.
Draught of keys, i, 127.
Draw filing, ii, 93.
Drawing the temper, ii, 462.
Drawings for bevel pinion, i, 59.
for gear wheels, i, 59.
Drifts, forms of, ii, 109.
methods of using, ii, 160.
Drill, and counter-bore, i, 449.
brace, i, 445.
universal joint for, i, 456.
with multiplying gear, i, 456.
with ratchet motion, i, 456.
chucks, i, 446; ii, 41.
cranks, i, 457.
for stone, i, 454.
for wood work, i, 449.
grinding, varied for diameter, ii, 41.
conditions for all diameters, ii, 41.
holders, flat, for lathe work, i, 281.
holders, twist, i, 274.
machine, grinding, ii, 41.
position, for all drills, ii, 41.
shanks, i, 445.
shank, improved form of, i, 446.
sockets, i, 445.
with cord, i, 455.
with spring motion, i, 455.
Drilled work, tailstock chucks for, i, 279.
Drilling and boring machine, i, 431.
feed motion of, i, 432.
device for lock work, i, 459.
engine cylinders, jigs for, i, 440, 441.
hard metal, i, 445.
Drilling holes true to location with flat drills, i, 442.
levers for blacksmith, i, 457.
square holes, device for, i, 450.
taper holes, i, 451.
and turning machine for boiler makers, i, 435.
machine, and lathe combined, i, 433.
cotter or keyway, i, 438.
feed motion of, i, 432.
feed motions of, i, 436.
for boiler shells, i, 436.
four-spindle, i, 434.
hand, i, 459.
lever feed, i, 428.
power, i, 428.
three-spindle, i, 434.
with automatic motions, i, 428.
with quick return, i, 428.
machines, counterbores for, i, 449.
cutters for, i, 447.
drills for, i, 442.
fixtures for, i, 439.
flat drills for, i, 442.
jigs for, i, 439.
radial, i, 430, 431.
stocks for, i, 447.
Drills and cutters, i, 442, 447.
cotter or keyway, i, 446.
flat, errors in grinding, i, 443.
flat, for drilling machines, i, 442.
flat, for lathe work, i, 280.
for wood work, i, 279.
square-shanked, i, 446.
disadvantages of, i, 446.
stock, with spiral grooves, i, 445.
twist, diametral clearance of, i, 274.
fluting, ii, 29.
front rake of, i, 275; ii, 44.
grinding by hand, i, 279.
large, grinding, ii, 41.
speeds and feeds for, i, 277.
Driver, and face plate, i, 223.
Drivers, equalizing, i, 223.
for bolt heads, i, 224.
coned work, i, 225.
lathe mandrels or arbors, i, 227.
steady rest work, i, 22.
threaded work, i, 225.
wood, i, 225.
lathe, i, 222.
the elements, i, 223.
Driving cones, steps of, i, 159-164.
drills, flexible shaft for, i, 458.
gear of universal milling machine, ii, 15.
gear table, i, 404.
Drop hammers, ii, 255, 256.
Duration of a hammer blow, experiments on, ii, 65, 66.
Duplex slide-rests, i, 143.
E
Eccentrics, fixed and shifting, ii, 378.
slipping, ii, 403.
turning in the lathe, i, 317.
Eccentric work, lathe mandrels for, i, 229.
Edge tools, oilstoning, ii, 54.
Effects of hammer blows, ii, 69.
of speed of a hammer blow, ii, 65.
Elevating slide rests, i, 168.
Elliptical gears, tooth curves of, i, 73.
gear wheels, i, 70.
gears, the pitch lines of, i, 70.
taps, in cross section, i, 109.
Emery belt grinding machine, ii, 47.
grinder for car axle boxes, ii, 45.
for engine guide bars, ii, 45.
machine knives, ii, 46.
rough work, ii, 46.
true surfaces, ii, 45.
with revolving emery wheel, ii, 40.
machines, grinding, ii, 40.
charging, polishing wheels, ii, 50.
paper, use on lathe work, i, 308.
wheel arbors, i, 198.
arbors, positions of, ii, 35.
swing frame for dressing large castings, ii, 46.
wheels, annular, ii, 48.
balancing, ii, 39.
cements used in the manufacture of, ii, 38.
clearance of, ii, 39.
coarseness and fineness of, ii, 38.
positions of, i, 282; ii, 36, 37.
presenting to work, ii, 47.
qualifications of, ii, 38.
recessed, ii, 47.
speeds of, ii, 39.
wear of, ii, 48.
End, face and twin milling, ii, 25.
grain wood boring, i, 453.
measurements of lathe work, i, 376.
milling, advantages of, ii, 25.
thrust of angular teeth, i, 69.
Endless screw thread, cutting, i, 62.
Engine, alignment, errors in, ii, 166.
calculating the power of, ii, 407.
connecting rods, ii, 375.
crank turning, i, 247.
crossheads, ii, 375.
crosshead turning, i, 252.
cylinder covers, turning, i, 318.
cylinders, bores of, ii, 372.
boring lathe for, i, 219.
clearance in, ii, 372-404.
counterbore of, ii, 372.
fitting, ii, 158.
jacketed, ii, 374.
lagging, ii, 374.
lubricating, ii, 373.
relief valves for, ii, 373.
steam ports, ii, 373.
waste water cocks of, ii, 373.
wear of, ii, 372.
eccentrics, ii, 378.
turning a cover, i, 318.
gear cutting, ii, 56.
glands, turning, i, 316.
guide bars, ii, 375.
setting, ii, 162.
spring of, ii, 162.
testing, ii, 163.
lathe, i, 129, 147.
construction of carriage, i, 137.
of the back gear, i, 135.
of the bearings, i, 134.
of the head stock, i, 134.
general construction of, i, 133.
lead screw and change wheels of, i, 139.
shears of, i, 134.
link motion, designing, ii, 389.
plain slide valve, starting, ii, 384.
valves, ii, 376-378.
balanced, ii, 377.
circular, ii, 377.
cut-off, ii, 378.
double ported, ii, 377.
exhaust lap of, ii, 376.
lead of, ii, 376.
point of admission, ii, 376.
slide and piston, ii, 378.
slide, designing, ii, 380.
testing horse power of, ii, 408.
the Allen, ii, 377.
the D, ii, 376.
tracing the action of, ii, 376.
Webb's, ii, 377.
Engines, compound, ii, 434, 435.
donkey, ii, 442.
heating and knocking of, ii, 164.
subject to freezing, ii, 386.
Engineers, test questions for, ii, 467.
Engraver's plates, polishing, ii, 51.
Epicycloidal gear teeth, curves, i, 8.
teeth, the strength of, i, 64.
filleting the roots of, i, 53.
Equalizing drivers for lathe work, i, 223.
Erecting, ii, 137.
a lathe, ii, 181.
an iron planer, ii, 179.
pipe-work, ii, 143.
the framework of machinery, ii, 176.
Errors in alignment, determining, ii, 158-167.
in chucking, i, 250.
crank pin alignment, ii, 169.
cutting threads on taper work, i, 324.
cutting up inside chasers, i, 337.
drill-grinding machines, ii, 41.
grinding flat drills, i, 443.
grinding milling cutters, ii, 32.
jigs, limits of, i, 439.
shafting couplings, ii, 196.
Evaporative efficiency of boilers, ii, 366.
Examining a boiler, ii, 368.
a locomotive, ii, 401.
Excessive lead of engines, ii, 421.
Exhaust lap, ii, 376.
Expanding bit, i, 454.
chucks for lathes, i, 188.
for ring work, i, 241.
for large work, i, 228.
laps, i, 311.
mandrels, i, 227.
taps, i, 107.
Expansion, ii, 376.
curve of indicator, ii, 417, 418.
testing of indicator, ii, 417, 418.
joint, ii, 141.
line of diagrams, ii, 414, 415.
of steam, ii, 411.
pulleys, ii, 200.
valves, separate, ii, 443.
Experiments on duration of a blow, ii, 65, 66.
on the strength of the parts of a hide, ii, 208.
Extension lathe, i, 151.
Eye-bar dyes, ii, 260.
Eyes, hammer, shapes of, ii, 66.
F
Face and taper cutters, fixture, ii, 34.
cutters, ii, 17.
advantages of, ii, 18.
disadvantages of, ii, 18.
fixtures for, ii, 34.
milling, advantages of, ii, 26.
length of feed, ii, 26.
plate, clamping work on, i, 245.
clamps, i, 245.
errors in, and their effects, i, 243.
for wood-work, i, 247.
work, examples of, i, 249.
work, movable dogs for, i, 250.
Facets of scrapers, angles for, ii, 97.
Facing and countersink cutters, i, 449.
cutters, i, 449.
rests, boring lathe with, i, 220.
tool with reamer-pin, i, 449.
Facing tools or knife tools, i, 262.
Factors of safety, boiler seams, ii, 355.
Fastening cogs, i, 63.
pulleys to their shafts, ii, 201.
Feather-edge, removing, ii, 54.
Feathers and their applications, i, 127.
methods of securing, ii, 102.
sinking into shafts, ii, 101.
Feed, direction, for shank cutters, ii, 20.
for spiral grooves, ii, 27.
escape valve, ii, 441.
gear, i, 197.
for screw machine, i, 205.
in cutting spiral grooves, ii, 28.
length, in face milling, ii, 26.
motions, automatic, i, 408.
construction of, i, 390.
examples of, i, 170.
for boiler-maker's drilling and turning machine, i, 436.
for boring machine, i, 432.
boring mills, i, 215.
cam turning, i, 326.
car-axle lathe, i, 148.
carriage or saddle, i, 137.
chucking lathe, i, 150.
drilling machine, i, 432.
grinding lathe, i, 200.
lathe aprons, i, 168.
milling machine, ii, 13.
planer heads, i, 413.
reversing traverse, i, 168.
special lathe, i, 146.
weighted slide rest, i, 168.
wood-working, i, 209.
friction wheels for, i, 78.
nut, position of, i, 177.
ratchet, i, 173.
regulators for screw cutting, i, 171.
spindle bearings, i, 139.
spindle for lathe, i, 139.
spindle, giving motion to, i, 135.
water, heating, ii, 370.
Feeds, cutting, for wrought iron, i, 294.
for roughing cuts, i, 306.
for twist drills, i, 277.
Feed-water, ii, 370.
from natural supply, ii, 387.
Fiddle drill with feeding device, i, 455.
Field tube for boilers, ii, 359.
Fifth wheel, forging of, ii, 239.
File cutters' hammers, ii, 71.
cutting, ii, 101.
teeth, shapes of, ii, 85.
Files, ii, 85.
bent, using, ii, 93.
cleaning of, ii, 94.
cross, ii, 91.
cut of, ii, 86.
flat sizes and kinds, ii, 86, 87.
for soft metals, ii, 95.
Groubet, ii, 87.
half-round, ii, 90.
instruction on holding, ii, 92.
knife, ii, 91.
names of, ii, 88.
putting handles on, ii, 92.
reaper, ii, 91.
resharpening, ii, 95.
round, ii, 90.
selection of, ii, 91.
thin, ii, 93.
three square, ii, 90.
tumbler, ii, 91.
warping, ii, 93.
Filing bolt heads, ii, 105.
cross, ii, 93.
draw, ii, 93.
fixture for lathes, i, 189.
lathe work, i, 308.
nuts, ii, 105.
out connecting rod keyways, ii, 120.
out round corners, ii, 95.
pins, ii, 105.
pins, blocks for, ii, 104.
the link slot, template for, ii, 127.
the teeth of band saws, ii, 309.
Filleting the roots of gear teeth, i, 53.
Finishing cast iron with water, i, 307.
cast iron work, specks in, i, 307.
cuts, rates of feeds for, i, 307.
horseshoes, machines for, ii, 262.
internal work, laps for, i, 311.
lathe work, scrapers for, i, 307.
Fire cleaning, ii, 369.
cleaning tools, ii, 369.
engine boiler tubes, ii, 431.
engine heaters, ii, 432, 433.
engines, steering gear for, i, 75.
Firing boilers, ii, 368.
methods of, ii, 402.
Firmer chisels, ii, 272.
Fits, shrinkage or contraction, i, 366.
Fitting brasses to connecting rod straps, ii, 121.
brasses to journals, ii, 146.
engine cylinders, ii, 158.
keys, ii, 107.
keys, examples of, ii, 107.
straps, ii, 120.
taper pins, i, 122.
taper work, i, 313.
the keys and gibs, ii, 120.
up connecting rods, ii, 118.
a double eye, ii, 103.
a fork end connecting rod, ii, 123.
a lathe, ii, 181.
a link motion, ii, 127.
Fixed pins, i, 122.
Fixture for grinding cutters, ii, 32, 33.
for grinding taper work, ii, 33.
Fixtures for drilling machines, ii, 439.
Flank contact of gear teeth, i, 28.
Flat drill holders, i, 281.
drills, drilling with, i, 444.
errors in grinding, i, 443, 444.
for lathe work, i, 280.
files, sizes and kinds, ii, 86, 87.
guideways for planer beds, i, 414.
side lathe shears, i, 183.
Flexible shaft for driving drills, i, 458.
Flue boiler, ii, 358.
Flutes, shapes of taps, i, 105.
the number of, i, 107.
Fluting twist drills, ii, 29.
Fluxes, heating in, ii, 462.
Fly ball governors, ii, 384.
cutters, ii, 21.
holders for, ii, 22.
making, ii, 21.
methods of originating, ii, 21.
Follower rests, i, 234.
Foot lathe, i, 130.
Foot-power hammers, ii, 252, 253.
Foot valves, ii, 388.
Forges for blacksmiths, ii, 228, 229.
side blast for, ii, 228.
Forging bolts, ii, 238.
crank shafts, ii, 248, 249.
hydraulic, ii, 260.
machine thread, ii, 261.
nails by machinery, ii, 261.
of bolts, ii, 238.
press, ii, 260.
rope sockets, ii, 243, 244.
rudder frames, ii, 245, 246.
steel forks, ii, 241.
threads on rods, ii, 261, 262.
turn buckles, ii, 239, 240.
under the hammer, ii, 242, 243.
under a steam hammer, ii, 241.
wheels, ii, 244, 245.
Fork end connecting rod, fitting, ii, 123.
aligning, ii, 124.
Fork forging, ii, 241.
Former of Corliss bevel gear-wheel engine, i, 45.
Form of lead screw threads, i, 177.
worm to give a period of rest, i, 74.
Forms of lathe shears, i, 183.
of outside calipers, i, 360.
pin wrenches, i, 126.
riveted joint, ii, 352.
taps, i, 102.
templates for gear teeth, i, 44.
wrenches, i, 125.
Foundations for an iron planer, ii, 179.
Four-jawed chucks, i, 237.
Four-spindle drilling machine, i, 434.
Fractional pitch change gears, i, 34.
Frames for rudders, forging, ii, 245, 246.
of machinery, erecting, ii, 176.
Freezing, preventing an engine from, ii, 386.
French gear-cutting machine, ii, 56-61.
Friction clutches, ii, 192.
experiments on, ii, 154.
of jamb dies, i, 98.
plane surfaces, ii, 135.
slide valves, ii, 443.
taper taps, i, 103.
tap threads, i, 108.
wheels, i, 77.
for feed motion, i, 78.
materials for, i, 77.
paper, i, 78.
to reduce journal strain, i, 79.
Friezing machines, cutters for, ii, 340.
or moulding machines, ii, 334, 339.
Front rake of twist drills, ii, 44.
tools for brass work, i, 264.
rake and clearance of, i, 254.
Fullers, blacksmith's, ii, 230.
Furnaces for scrap iron, ii, 247.
G
Galvanized iron, gauge for, i, 387.
Gang edging machines, ii, 301.
Gang or composite cutters, ii, 23.
Gap, or break lathe, i, 151.
Gas pipe, dies for, i, 101.
Gauge cocks for boiler, ii, 368.
Gauges, i, 356-359.
adjustable, i, 377.
cropping, use of, ii, 296.
cutting, ii, 274.
for American sheet zinc, i, 387.
circular saws, ii, 287.
cutting tools, i, 92.
galvanized iron, i, 387.
lathe work, i, 359.
marking wood, ii, 274.
music wire, i, 386.
planer tools, i, 423.
planing V-guideways, i, 421.
Russian sheet iron, i, 387.
setting over taper work, i, 313.
shrinkage fits, i, 367.
threading tools, i, 266.
woodworking machine, ii, 295.
forms of laps for, i, 310.
hexagon, i, 381.
instrument, standard, i, 96.
mitre, use of, ii, 294.
mortise, ii, 274.
notch wire, i, 384.
plug and collar, comparing, i, 356.
screw thread, producing, i, 92.
standard for taper work, i, 316.
standard, comparing, i, 356.
surface, i, 378.
vacuum, i, 444.
wire, i, 387.
Gauging the pitch of threads, after hardening, i, 108.
Gear cutter, automatic, ii, 55.
cutting engine, vertical spindle, ii, 56.
machine, half-automatic, ii, 56.
machine, French, ii, 56-61.
table of index holes for, i, 417.
racks, i, 77.
Gear-teeth, i, 73.
arc of approaching contact, i, 16.
of receding contact, i, 16.
pitch of, i, 2.
calculating strength of, i, 65.
chord pitch of, i, 2.
curve of, for bevel gear, i, 22.
curves, templates for rolling, i, 43.
cutting by hand, i, 62.
cutting templates for, i, 35.
elliptical, i, 70.
depth or height of, i, 1.
errors produced by wear, i, 18.
faces of, i, 1.
factors of safety for, i, 64.
flank contact of, i, 18.
depth or height, i, 1.
flanks of, i, 1.
forms of template for, i, 44.
generating involute curves, i, 31.
helical, i, 69.
line of centres of, i, 2.
pitch line of, i, 2.
point of, i, 2.
requirements of curves, i, 7.
revolving cutters for, i, 37.
rolling and sliding motion of, i, 16.
curves for, i, 43.
strength of, i, 65.
table of cutters for, i, 41.
variation of curve, i, 12.
of shape, i, 16.
Gear-wheels, i, 1.
angular velocity of, i, 6.
bevel, i, 21.
drawing for built-up, i, 61.
pinion, drawings for, i, 59.
calculating revolutions of, i, 5.
chord pitch, i, 3.
cogged, i, 63.
cogs, i, 67.
durability of, i, 66.
diameters of pitch circles of, i, 4.
drawings for, i, 59.
driver and follower, i, 3.
for rapid increase of motion, i, 75.
reciprocating motion, i, 77.
reversing motion, i, 75.
steering steam fire engines, i, 75.
variable motion, i, 74.
generating curves for, i, 11.
hunting tooth in, i, 7.
interchangeable gearing, i, 16.
internal, compared with spur, i, 25.
or annular, i, 23 to 27.
making cogs for, i, 63.
mortised, i, 63.
motion at a right angle, i, 69.
patterns, i, 54-61.
power of, ii, 406.
transmitted by, i, 5.
skew bevel, i, 61.
spacing teeth on, i, 58.
stop motion of, i, 7.
strength of, i, 66.
table of pitches, i, 3.
table giving strength of, i, 67.
thickness of, i, 66.
tracing path of contact, i, 13.
value of cutters, table, i, 41.
various applications of, i, 74.
velocity of, uniform, i, 16.
with dovetail teeth, i, 60.
involute teeth, i, 31-34.
stepped teeth, i, 69.
Gear-worm or endless screw, i, 62.
Gears, for screw cutting, i, 320.
Generating the involute curve, i, 31.
German bit, i, 452.
Gibbed elevating slide-rest, i, 169.
Gimlet bit, i, 452.
Gland patterns, ii, 275.
Globe valve patterns, ii, 281, 282.
Gonzenback's cut-off valve, ii, 378.
Gouge for wood, ii, 272.
use of, i, 338.
Governors, dancing, ii, 384.
fly ball or throttling, ii, 384.
for automatic engines, ii, 427, 428.
for stationary engines, ii, 425, 426.
isochronal, ii, 384.
Sawyer's valve for, ii, 384.
speed of, ii, 384.
speeders for, ii, 384.
spring, adjustment of, ii, 386.
Grate bars, cleaning, ii, 368.
Grades of emery wheels, ii, 38.
Graduations of planer heads, i, 412.
Grain side of leather, weakness of, ii, 208.
Graver, i, 330.
Grinder, emery, for axle boxes, ii, 45.
for engine guide bars, ii, 45.
Grinder for planing machine cutters, ii, 46.
for rough work, ii, 46.
for true surfaces, ii, 45.
Grinding clamps for lathe work, i, 311.
cocks and plugs, ii, 145.
operations, ii, 38.
taper cutters, ii, 33.
taper work, i, 313.
teeth of reamers, i, 282.
teeth of spiral cutters, ii, 36.
thin cutters, ii, 33.
twist drills by hand, i, 279.
universal, i, 195.
with elevating rest, i, 194.
with traversing wheel, ii, 46.
Grinding-lathes, i, 193.
for calendar rolls, i, 199.
construction of tailstock, i, 200.
special chuck for, i, 196.
Grinding-machine, drill, ii, 41.
emery belt, ii, 47.
for milling cutters, ii, 32.
errors in construction, ii, 41.
Grindstones and tool grinding, ii, 51.
application of work to, ii, 53.
for saws or iron plates, ii, 52.
wood-working tools, ii, 52.
hacking, ii, 53.
speeds of, ii, 52.
traversing device for, ii, 53.
truing device for, ii, 53.
various kinds of, ii, 51, 52.
Gripping devices, ii, 227.
Groove cams, i, 84.
proper construction of, i, 84.
wear of, i, 84.
with double roller, i, 84.
Groove cutting, angular cutters, ii, 27.
Grooved friction wheels, wear of, i, 79.
Grooves, producing different shapes with same cutter, ii, 29, 30.
right and left-hand, ii, 29.
Groubet files, ii, 87.
Ground joint, ii, 137.
Guide-bars, ii, 375.
setting by stretched lines, ii, 163.
Guide pulleys for belts, ii, 211.
Guide for centre punches, i, 301.
Guide-ways, flat, i, 414.
planing, i, 422.
Guides for band saws, ii, 311.
Gumming or gulleting, ii, 290.
H
Hacking grindstones, ii, 53.
Hack saw, ii, 97.
Half-round bit for true work, i, 281.
for wrought iron or steel, i, 281.
or pod auger, i, 281.
reamers, ii, 99.
with adjustable cutter, i, 281.
Hammer, ii, 64.
blow, effects of, ii, 65, 69.
coopers', ii, 71, 72.
cushioned, ii, 252.
dog-head, ii, 69.
drop, ii, 255.
eyes, shapes of, ii, 66.
foot power, ii, 252.
forging, methods, ii, 242.
file cutters', ii, 71.
handles, putting in, ii, 67.
machinists' hand, ii, 66.
paning or pening, ii, 68.
plate and saw makers', ii, 68.
power, ii, 252.
riveters', ii, 71.
sledge, machinists', ii, 71.
steam, ii, 256-259.
trip, ii, 254.
Hand bolt threading machine, i, 97.
device to straighten lathe work, i, 305.
drilling machine, i, 459.
finishing tool, i, 331.
hammers, machinists', ii, 66.
lathe, i, 130.
watch manufacturers', i, 191.
milling machine, ii, 1.
planer, i, 391.
reamers, ii, 98.
shaping machine, i, 392.
side tools, i, 331.
tools for brass-work, i, 332.
round nosed, for iron, i, 331.
screw cutting, i, 96.
threading machine, head, i, 465.
turning, i, 330.
vise, ii, 104.
work, swages for, ii, 230.
Handles for chisels, ii, 271.
of files, putting on, ii, 92.
of hammers, putting in, ii, 67.
Hangers, shafting, forms of, ii, 192.
wall, ii, 194.
Hardening, case, ii, 128, 442.
outside, ii, 462.
saws, ii, 462.
to resist wear, ii, 460.
increase elasticity, ii, 460.
provide a cutting edge, ii, 460.
Hard metal, drilling, i, 444.
Head boring, i, 288.
with nut feed, i, 291.
Heads, construction of, i, 408.
double for planing machines, i, 404.
Heads for match board grooves, ii, 337, 338.
for tenoning machines, ii, 345.
of the rapid machines, i, 468.
planer, feed motions for, i, 414.
safety devices for, i, 413.
V-guideways for, i, 414.
Headstock lathe, construction, i, 153.
of engine lathes, i, 134.
grinding lathes, i, 200.
special lathe, i, 144.
Heat, ii, 410.
conversion of, into work, ii, 411.
latent, ii, 410.
radiation of, ii, 412.
Heaters for fire engines, ii, 432, 433.
Heating and knocking, ii, 164.
feed-water, ii, 370.
showing the causes of, ii, 168.
Heavy oil for hot bearings, ii, 386.
Heel tool, i, 330.
Height of lathe tools, ii, 260.
of vise jaws, i, 62.
Helical teeth, cutting in the lathe, i, 69.
Herring-bone gear-teeth, i, 69.
Hexagon gauge, i, 381.
Hide, parts of, used for belting, ii, 208.
High pressure steam engine, ii, 372.
High speed automatic engines, ii, 427.
Hobbing dies, methods of, i, 473.
Hob for threading dies, i, 474.
Hobs and their uses, i, 335.
for cutting up dies, i, 99.
threading dies, i, 474.
Hoe, ii, 369.
Holders, for chasers, i, 268.
for fly cutters, ii, 22.
octagon boring tools, i, 175.
Holding chisels, ii, 74.
Hollow work, centres for, i, 226.
Hook bolts, i, 113.
Hooks, belt, ii, 216.
Horizontal boring machine, i, 433.
Horse-power, from diagram, ii, 418.
of an engine, calculating, ii, 407, 419.
testing, ii, 408.
Horseshoes, finishing, machine for, ii, 262, 263.
Horizontal tubular boiler, ii, 361-366.
saw frame, ii, 312.
Hydraulic fits, allowance for, i, 365.
parallel holes and taper plugs for, i, 365.
forging, ii, 260.
press, ii, 260.
pressure, i, 366.
Hypocycloidal curves, i, 8.
I
Inclination of skew bevel teeth, i, 61.
Index plate of milling machine, ii, 7.
Index wheel, originating, i, 342, 353.
Indicator, ii, 413.
attachment of, to engine, ii, 416.
diagram, area of the, ii, 419.
diagrams, ii, 414.
defective, ii, 421.
expansion curve, ii, 417, 418.
springs, ii, 416.
vacuum line, ii, 415.
Injector, feed, ii, 370.
for locomotives, ii, 395.
Inside calipers, i, 360.
chasers, i, 335.
errors in cutting up, i, 337.
Interchangeable gearing, i, 16.
Intermediate gears, i, 3.
wheels, i, 319.
rolling circle, i, 24.
Internal gear wheels, i, 23-27.
strains in cast iron work, i, 306.
threading tools, i, 264.
wheels, i, 23.
Involute curves for gear teeth, i, 8.
teeth, advantages of, i, 34.
Iron and steel welding, ii, 234.
bending, ii, 240.
devices, ii, 240.
galvanized, gauge for, i, 387.
planer, erecting an, ii, 179.
foundation for, ii, 180.
plates, grindstones for, ii, 52.
testing, ii, 226.
Irregular forms, lathes for, i, 210.
motion, cams for, i, 80.
work, turning, i, 326.
Isochronal governors, ii, 384.
J
Jacketed cylinders, ii, 374.
Jam dies, i, 98.
nuts, i, 119.
Jeweller's rests for lathes, i, 189.
Jigs, designing, i, 440.
errors in, limit of, i, 439.
for cutting out steam ports, i, 441.
drilling engine cylinders, i, 440.
drilling machines, i, 439.
simple work, i, 440.
Jointing machines, ii, 338.
Joints, boiler fitting, ii, 140.
butt, boiler, ii, 352.
cylinder cover, ii, 137.
dovetail, ii, 275.
easily removable, ii, 141.
expansion, ii, 140.
for boiler work, ii, 352.
rough surfaces, ii, 138.
gauze, ii, 138.
ground, ii, 137.
half check, ii, 275.
lap, boiler, ii, 352.
mitre, ii, 275.
mortise, ii, 274.
open, for wear, ii, 121.
riveted, proportioning, ii, 355, 356.
rubber, ii, 139.
rust or caulked, ii, 141.
scraped, ii, 137.
tenon, ii, 274.
thimble, ii, 141.
to withstand great heat, ii, 138.
water, ii, 138.
Joule's equivalent, ii, 411.
K
Key seats, cutting, ii, 101.
Keys and gibs, fitting, ii, 120.
bearing surfaces of, i, 126.
draught of, i, 127.
forms of, i, 126.
for parallel rods, i, 128.
seating rule, i, 378; ii, 101.
with set-screws, i, 127.
Keyway calipers, i, 363.
Keyways, cutting by hand, ii, 101, 108.
cutting out by drifts, ii, 109.
Knife blade rolls, ii, 261.
files, ii, 91.
Knives for balanced heads, ii, 324-326.
for jointing machines, ii, 338.
moulding machines, ii, 336-340.
moulding, scale for shapes of, ii, 83.
Knurling tool, improved forms of, i, 328.
L
Lap joint, boiler, ii, 352.
of Corliss engine valve, ii, 426.
Latent heat, ii, 410.
Lathe, advantages of, i, 129.
apron, i, 138.
feed motion for, i, 168.
back gear, i, 144.
bench, i, 130.
boring devices for, i, 288.
tools, shapes of, i, 285.
break, i, 151.
capacity, i, 130.
carriage, i, 145.
feed motion for, i, 37.
testing, ii, 182.
carriers, i, 222.
centre drilling attachment, i, 300.
centres, i, 290.
removing, i, 159.
shapes of, i, 299.
testing, i, 298.
change wheels for, i, 139.
chucks for, i, 188.
chucking for boring purposes, i, 152.
clamps, i, 223.
classification of, i, 129.
cutting fractional threads on, i, 181.
helical teeth in the, i, 69.
screws in the, i, 319.
cutting-off machine, i, 193.
cylinder boring, i, 219.
dogs, various kinds of simple, i, 222.
drivers, i, 222.
English chucking, i, 149, 150.
erecting a, ii, 180.
extension, i, 151.
face-plates, i, 243.
chucking, i, 246.
clamps for, i, 245.
errors in, i, 143.
for wood work, i, 247.
feed-motions, i, 144.
feed-screw, i, 175.
feed, spindle for, i, 139.
filing, fixtures for, i, 189.
fit of the live spindle of a, i, 157.
fitting up, ii, 180.
foot, i, 130.
for axe handles, i, 210.
engine cylinders, i, 219.
irregular forms, i, 210.
taper turning, i, 142.
turning crank shafts, i, 152, 154.
turning wheel hubs, i, 221.
gap, i, 151.
grinding, i, 193.
universal, i, 195.
with elevating rest, i, 194.
hand, i, 130.
headstock, construction of, i, 153.
importance and advantages of, i, 129.
jewellers', rest for, i, 189.
locking spindles of, i, 186.
lead-screw, i, 175.
bearings for, i, 139.
nuts for, i, 140.
supporting long, i, 176.
mandrels, drivers for, i, 227.
expanding, i, 227.
for eccentric work, i, 229.
nuts, i, 229.
threaded work, i, 228.
tubular work, i, 227.
forms of, i, 229.
with expanding cones, i, 278.
with expanding pieces, i, 228.
motions for turning cams, i, 326.
open spindle, tailstocks for, i, 189.
pattern makers', i, 148.
pulley, i, 150.
screws, errors of pitch, i, 79.
screw slotting, i, 192.
self-acting, English, i, 148.
shears, the legs of, i, 184.
various forms of, i, 183.
methods of ribbing, i, 184.
or beds, i, 182.
with flat slides, i, 183.
[V] and flat slides, i, 183.
[V] slides, i, 183.
sizes of, i, 130.
slide-rest for, i, 131, 145.
lost motion of, i, 133.
special chucks for, i, 190.
swing frames, i, 158.
tailblock, i, 185.
setting over, for tapers, i, 136.
various methods of testing, i, 187.
wear of the spindles of, i, 185.
with rapid spindle motion, i, 185.
releasing devices, i, 185.
testing, i, 186.
instruments for, ii, 182.
tool-holders for outside work, i, 270.
with clamp, i, 271.
tools, angle of clearance of, i, 257.
height of, i, 260.
shapes of, i, 254.
watchmakers', i, 188.
with compound slide-rest, i, 140-143.
elevating rest, i, 194.
flat chucking surface, i, 143.
rapid spindle motion, i, 185.
sliding heads, i, 290.
variable speed, i, 192.
wooden bed, i, 149.
work, boring tools for, i, 285.
burnishing, i, 311.
chisels for, i, 339.
countersinks for, i, 302.
end measurements of, i, 376.
filing, i, 308.
flat drills for, i, 280.
holders for, i, 281.
forms of countersink for, i, 302.
gauge for, i, 359.
grinding clamps for, i, 311.
holding straps for, i, 244.
mandrels or arbors for, i, 227.
method of polishing, i, 308.
polishing clamps for, i, 311.
side tools for, i, 261.
technical terms used in, i, 296.
use of emery paper on, i, 308.
Lead-lined brasses, ii, 149, 386.
Lead of a valve, adjusting the, ii, 386.
Lead of slide valves, ii, 376.
Lead-screw, bearings for, i, 139.
conveying motion to the, i, 147.
nuts, i, 180.
for lathes, i, 175.
forms of threads of, i, 177.
long supporting, i, 176.
swing frame for, i, 139.
with three threads per inch, i, 177.
five threads per inch, i, 178.
Leather, grain side, weak, ii, 208.
Left-hand threads, cutting, i, 322.
Leg vise with parallel motion, ii, 63.
Lever feed drilling machine, i, 428.
drilling, for blacksmiths, i, 457.
principles of, ii, 405.
Lift and force pumps, ii, 387.
Line of contact of skew bevel gear wheels, i, 61.
Line shafts, couplings for, ii, 194.
Line shafting, diameters of, ii, 189.
ordinary, ii, 186.
setting in line, ii, 184, 185.
sizes of, ii, 186.
the strength of, ii, 189.
Lined boxes, babbitt metal, ii, 155.
Lining connecting rod brasses, ii, 126.
Link-motion, gear, ii, 383.
fitting up, ii, 127.
for expansion engines, ii, 438.
for marine engines, ii, 443.
quick return shaper, i, 399.
setting the valves for, ii, 383.
the action of, ii, 383.
Link slot, templates for filing, ii, 127.
Lip drill, i, 443.
Live centres, tapers for, i, 159.
spindle, end adjustment of, i, 158.
wear of bearings, i, 158.
with coned journals, i, 157.
Locking, differential threads for, i, 119.
Lock work, drilling device for, i, 459.
Locomotive ash pan, ii, 390.
automatic air brake, ii, 390, 398.
axle boxes, ii, 147.
blower, ii, 390.
boiler and frames, ii, 389.
connecting-rod, ii, 116.
freight engine, ii, 389-404.
injector, ii, 395.
link motion, ii, 391-393.
passenger engine, ii, 390.
reversing gear, ii, 391.
sand valves, ii, 390.
safety and pop valves, ii, 389.
Locomotive wheel forging, ii, 244.
yoke and guide bars, ii, 389.
Longevity of lubricants, ii, 153.
Lost motion in valve setting, ii, 174.
Low water in boilers, ii, 370.
Lubricants, longevity of, ii, 153.
qualities of, ii, 152.
testing, ii, 152.
Lubricators, steam, ii, 444.
M
Machine centre drilling, i, 300.
cross cutting or gaining, ii, 305, 306.
for cutting mitre joint, ii, 338.
finishing horseshoes, ii, 262.
forging threads, ii, 261, 262.
gang edging, ii, 301.
gumming or gulleting, ii, 290.
horizontal saw frame, ii, 313.
moulding, ii, 334.
scroll sawing, ii, 306.
Machinery for wood working, ii, 287.
Machinists' chisels, applications, ii, 76.
hand hammers, ii, 66.
sledge hammer, ii, 71.
Main bearings, adjusting, ii, 386.
Mallet, ii, 72.
Mandrels, expanding, i, 227.
for threaded work, i, 228.
lathe, i, 227.
expanding, i, 228.
for eccentric work, i, 229.
for nuts, forms of, i, 229.
with expanding cones, i, 228.
with expanding pieces, i, 228.
or arbors for lathe work, i, 227.
Mangle gearing, various forms of, i, 76.
Manufacturers' temper, ii, 460.
Marine-engine boilers, ii, 436, 437.
connecting-rod, ii, 116.
link motion, ii, 443.
pumps, ii, 436.
valves, ii, 444.
Marine engines, pipes of, ii, 445.
various, ii, 434.
Marriotte's law, ii, 411.
Matched cutters, ii, 23.
Matching and planing machines, ii, 326.
Mean effective steam pressure, ii, 420.
Measurements, the standards of, in various countries, i, 341.
Measuring by sight, and feeling, i, 341.
machine for sheet metal, i, 348.
special, i, 342-346.
tools, classification of, i, 354.
valve lead, ii, 173.
Mechanical equivalent of heat, ii, 411.
powers, ii, 405.
Metal, soft, files for, ii, 95.
Metric pitch screws, i, 322.
Meyer's cut-off valve, ii, 378.
Micrometer caliper, i, 354.
gauge for thread angles, i, 91.
Mill boring, i, 211.
turning, i, 211.
Milling-cutters, grinding, ii, 32.
or mills, ii, 16.
with inserted teeth, ii, 24.
Milling-machine, ii, 1-16.
advantages of, ii, 1.
chucks for, ii, 31.
cam cutting attachment, ii, 12.
cutters, ii, 17-31.
double-spindle, ii, 16.
fixtures for, ii, 10.
hand, i, 410.
head for spiral cutting, ii, 12.
holding work on, ii, 30.
power, ii, 2.
rotary vise for, ii, 10.
universal, ii, 2, 4, 12, 15.
head and back centre, ii, 10.
head for gear cutting, ii, 11.
vertical, ii, 31.
Milling or knurling tools, i, 328.
Milling taper work, ii, 30.
Mitre gauge, use of, ii, 295.
joint, ii, 275.
machine, ii, 338.
wheels, i, 1.
Monkey wrench, i, 125.
Mortise gauge, ii, 274.
Mortised gear-wheels, i, 63.
Mortising machines, ii, 344.
Moulding knives, scale for marking out the necessary shapes of, ii, 83.
Moulding-machines, ii, 334, 339.
cutters for, ii, 336, 337, 341.
Muffle, ii, 461.
Mule pulleys for belts, ii, 211.
Music wire, gauge for, i, 386.
N
Nail bit, i, 452.
Nail forging machines, ii, 261.
Non-condensing engine, ii, 372.
Nose bit, i, 453.
Notch wire gauges, i, 384.
Number of cutters used for a train of wheels, i, 41.
of cutters on boring bars, i, 290.
of cutting edges on taps, i, 105.
of cutting edges on reamers, i, 282.
Nut-tapping-machine, i, 475.
automatic socket for, i, 475.
rotary, i, 475.
three-spindle, i, 475.
Nuts, filing, ii, 105.
jam, i, 119.
lock, i, 119.
lost motion in, i, 120.
removing corroded, i, 122.
securing by cotters, i, 121.
by notched plates, i, 121.
by taper pins, i, 121.
devices, i, 120.
steam tight, the forms of, i, 118.
taking up the wear of, i, 120.
O
Odontograph, using, i, 47, 49.
Oil and lubrication, ii, 151.
cavities for brasses, ii, 150.
groove or curved chisel, ii, 76.
for brasses, ii, 150.
heavy, for hot bearings, ii, 386.
stones, truing, ii, 54.
various kinds of, ii, 54.
test, Swiss, ii, 153.
Oiling apparatus, ii, 439, 440.
devices for planer beds, i, 416.
true surfaces, ii, 135.
Oils, testing for acids, ii, 153.
testing for salts, ii, 153.
Oilstoning edge tools, ii, 54.
Olivers, ii, 252, 253.
Open brasses, ii, 149.
sided shafting hangers, ii, 193.
spindle lathes, tailstocks for, i, 187.
Originating angles for screw threads, i, 92.
cams, i, 326.
fly cutters, ii, 21.
gear teeth, i, chaps. I, II, III.
index wheels, i, 345.
surface plates, ii, 135.
templates for screw threads, i, 92.
Outside and inside chasers, i, 335.
calipers, making, ii, 105.
the various forms of, i, 360.
threads, starting, i, 338.
P
Paddle wheels, ii, 444, 445.
Panel planing, ii, 332, 333.
Paning or pening, ii, 72.
hammers, ii, 68.
Pantagraph engine for dressing the cutters for gear teeth, i, 38.
motions, ii, 417.
Paper friction wheel, i, 78.
Parallel cutters, grinding, ii, 32.
holes and taper plugs for hydraulic fits, i, 365.
rods, keys for, i, 128.
Paring chisels, ii, 271.
Patching broken frames, ii, 178.
Path of gear tooth contact, i, 13, 16.
Pattern lathe, brake for, i, 149.
slide-rest for, i, 149.
with wooden bed, i, 149.
Pattern-makers' lathe, i, 148.
pipe gauge, i, 379.
Pattern-making, woods for, ii, 264.
Patterns, building up, ii, 278.
brasses, proper shape for, ii, 132.
choice of wood for, ii, 264, 265.
for angle pipe, ii, 284, 285.
glands, ii, 275.
globe valves, ii, 281, 282.
pillow blocks, ii, 277.
pipes, ii, 280, 281.
pulleys, ii, 278, 279.
spacing gear-wheel teeth on, i, 58.
Pattern-wheel scale, i, 51.
Pening or paning, ii, 72.
Piat's gear cutting machine, ii, 56-61.
Pillow-block casting, ii, 277.
fitting brasses to, ii, 131.
for shafting, ii, 194.
patterns, ii, 277.
Pinion bevel, drawings for, i, 59.
with dovetail teeth, i, 60.
Pins, securing, for adjustment, i, 121.
filing, ii, 103.
fitting in double eyes, i, 121.
fixed, i, 122.
taper, i, 128.
working, i, 122.
wrench, i, 126.
Pipe cutters, ii, 142.
gauge, pattern-makers', i, 379.
patterns, ii, 280, 281.
threads, taper for, i, 95.
tongs, ii, 143.
vises, ii, 142.
work, erecting, ii, 144.
Pipe-threading by hand, i, 463.
by power, i, 463.
machine, i, 475-477.
machines, construction of, i, 463.
Piston valves, ii, 378.
Pitch, alteration in hardening, i, 108.
circle, the diameter of, i, 1.
correcting the errors of, i, 109.
gauging the, after hardening, i, 108.
line of cams, i, 80.
lines of elliptical gear-teeth, i, 70.
number of teeth, and pitch diameter, i, 68.
of screw threads, i, 85.
Pitch of teeth for band saws, ii, 305.
Pivoted arms for tooth templates, i, 44.
Plane blades, ii, 77.
blades, finding shapes of, for mouldings, ii, 78-83.
Planer beds, flat guideways for, i, 414.
beds, oiling devices for, i, 416.
centres, i, 408.
chuck, for curved work, i, 420.
chucking halves of pulleys on, i, 423.
chucks, i, 419.
for spiral grooved work, i, 419.
for timber, ii, 330, 331.
head slides, wear of, i, 410.
or iron planing machine, i, 402.
shapers, reversing, i, 398, 399.
swivel heads for, i, 411.
swivelling tool holder, i, 411.
tool, aprons for, i, 411.
heads, feed motions for, i, 414.
graduations of, i, 390.
safety devices for, i, 413.
[V]-guideways for, i, 414.
tables, angle plates for, i, 418.
chucking devices for, i, 422.
chucking machine beds on, i, 421.
forms of bolts for, i, 417.
supplementary tables for, i, 417.
tool-holder, applications of, i, 425.
with tool post, i, 425.
examples of application of, i, 426.
simple form of, i, 426.
tools for coarse finishing feeds, i, 423.
for slotted work, i, 424.
clearance of, i, 424.
shapes of, i, 423.
gauge for, i, 423.
Planes, ii, 267-270.
circular, ii, 268.
combination, ii, 269.
compass, ii, 268.
core-box, ii, 269.
for pattern making, ii, 268, 269.
fore, ii, 268.
grinding of, ii, 267.
jack, ii, 267.
oilstoning of, ii, 267.
rabbeting, ii, 268.
Plane surfaces, friction of, ii, 135.
Planet motion, i, 75.
Planimeter, ii, 420.
Planing and matching machine, ii, 326.
curved work, i, 420.
guideways, i, 421.
Planing-machine, i, 406-426.
gear, ii, 56.
large, chucks for, i, 423.
motions of, i, 402, 403.
tables, i, 414.
tables, slots and holes in, i, 415.
with double heads, i, 404.
wood, ii, 326.
Plate couplings, ii, 196.
straightener's hammers, ii, 68.
Plates, angle, for planer tables, i, 418.
iron, grindstones for, ii, 52.
saw, grindstones for, ii, 52.
straightening, ii, 69.
Plug and collar gauges, i, 357.
Plug gauges for threads, i, 91.
Plumb level, ii, 136.
rule, ii, 136.
Plunger pumps, ii, 370, 387.
Point of compression, ii, 376.
cut off, ii, 376.
release, ii, 376.
Poker, ii, 369.
Polishing clamps, i, 311.
device for engraver's plates, ii, 51.
materials, for brush wheels, ii, 50.
for polishing wheels, ii, 50.
for rag wheels, ii, 51.
wheels, ii, 49-51.
construction of, ii, 49.
emery charging, ii, 50.
for brass work, ii, 50.
lapping leather on, ii, 49.
large, keeping true, ii, 50.
materials for, ii, 50.
rag, ii, 51.
speed of, ii, 50.
Polygons, measuring sides, ii, 283.
Pony planer, ii, 323.
Position of emery wheel, ii, 35-37.
of dies in bolt cutting, i, 473.
of taper pins for locking, i, 128.
Positive feed, gear cutter, ii, 55.
Pounding, the causes of, ii, 168.
Power drilling machine, i, 428.
hammer, ii, 252.
lathes, i, 130.
milling machine, i, 470.
of an engine, testing, ii, 408.
threading machine, i, 465.
Powers, mechanical, ii, 405.
Preserving wood, ii, 264.
Press for forging, ii, 260.
Pressure and volume of steam, ii, 411.
Priming, its causes and prevention, ii, 370.
Profiling machine, ii, 31, 32.
Protractors, bevel, i, 380.
Propeller, screw, ii, 445.
Pulley arms, ii, 280.
Pulley balancing, device for, ii, 203.
boring machine, i, 438.
considered as a lever, ii, 405.
diameter, change for grindstone speed, ii, 52.
crowned, ii, 201.
expansion, ii, 200.
lathe, i, 150.
patterns for, ii, 278.
self-oiling, ii, 200.
solid and split, ii, 200.
calculating speeds of, ii, 204.
transmitting power of, ii, 204.
turning, i, 318.
turning, special lathe for, i, 211.
wood, ii, 200.
Pump air chambers, ii, 388.
capacity of, ii, 388.
displacement, ii, 387.
plunger, ii, 387.
principles of action of, ii, 387.
Pumps belt, ii, 388.
for circulating, ii, 440.
double acting, ii, 387.
lift and force, ii, 387.
for marine engines, ii, 436.
regulating, ii, 388.
rotary, ii, 387.
single acting, ii, 387.
Q
Quartering machine, i, 434.
Questions for Engineers, ii, 467.
Quick removal, bolts for, i, 116.
Quick-return motion, Whitworth's, i, 401.
shapers, link motion for, i, 399.
R
Rabbet planes, ii, 269.
Rack and pinion wheel, i, 1.
Rack feed saw bench, ii, 301.
Radial drilling machines, i, 430, 431.
Radiation of heat, ii, 412.
Rag polishing wheels, ii, 51.
wheel, polishing materials for, ii, 51.
Raised [V]-guideways, lathes with, i, 182.
Rake, ii, 369.
Ramsden's dividing engine, i, 349.
Rasps, kinds and cut of, ii, 87.
Ratchet brace, i, 457.
feeds, i, 173.
Rates of feed for finishing cuts, i, 307.
Reamers, adjustable, ii, 99.
chucking, i, 280.
chucking for true work, i, 283.
for framing, ii, 99.
grinding the teeth of, i, 282.
half-round, ii, 99.
hand, ii, 98.
number of teeth for, i, 282.
rose-bit or rose, i, 283.
shell, i, 283.
shell rose, i, 284.
spacing the teeth of, i, 282.
spiral teeth for, i, 282.
square, ii, 99.
taper, ii, 99.
Reamer-pin, with facing tool, i, 449.
Reamer-teeth, odd or even, i, 282.
spacing of, i, 282.
Reaper-files, ii, 91.
Reboring cylinders in place, ii, 160.
Recentring turned work, i, 304.
Recessed emery wheels, ii, 47.
Reciprocating motion, gear for, i, 77.
Red marking for vise work, ii, 96.
Reducing knife, i, 209.
Reduction of temper, ii, 461.
Refitting leaky cocks and plugs, ii, 144.
Regulating pumps, ii, 388.
Release, the point of, ii, 376.
Releasing devices, tailblock with, i, 185.
Relief feed valve, ii, 441.
Removing corroded bolts, i, 122.
corroded nuts, i, 122.
feather-edge, ii, 54.
Repairing broken frames, ii, 178.
connecting rods, ii, 124.
Resharpening files, ii, 95.
Rests, follower, i, 234.
Return cams, designing, i, 82.
motions compared, i, 401.
Reversible jawed chucks, i, 237.
Revolving cutters for gear teeth, i, 37.
Ribbing lathe shears, i, 184.
Right and left angular cutters, ii, 18.
and left hand cutters, ii, 18.
Ring work, expanding chucks for, i, 241.
Rings, welding, ii, 235.
Rip saws, ii, 272, 273.
Rivet diameters, ii, 356.
Riveter's hammer, ii, 71.
Riveting crank pins, ii, 73.
Riveted-joints, forms of, ii, 352.
proportioning, ii, 354-356.
strength of, ii, 354.
unevenly spaced rivets, ii, 353.
Rivets, diagonal pitch of, ii, 353.
spacing of, ii, 353.
Rod-feed for screw machines, i, 206.
Roll-feed circular saw, ii, 298-300.
wood planing machine, ii, 317.
Rolling motion of gear teeth, i, 16, 27.
Rolling-circles, by using two, the pinion may contain but one tooth
less than the wheel, i, 26.
circles for internal gearing, i, 25.
curves for gear teeth, i, 43.
Roll-turning lathe, i, 215.
lathe, tools for, i, 216.
calender, method of driving, i, 200.
Rolls for knife blades, ii, 261.
Rope socket, forging, ii, 243.
Rose-bit or rose reamers, i, 283.
Rotary nut tapping machine, i, 475.
planing machine, i, 395.
pumps, ii, 387.
Roughing cuts, feeds for, i, 306.
Rough surfaces, joints for, ii, 138.
Round corners, filing out, ii, 95.
files, using of, ii, 95.
half-round, three-square files, ii, 90.
Round-nosed chisels, ii, 75.
tools, i, 258.
Rudder frame, forging, ii, 245.
Rule for finding horse-power, ii, 418.
for locating pitch line of worm, i, 29.
for finding the chord pitch, diametral pitch, and arc pitch, i, 3.
for proportioning the steps of the driving cone, i, 159, 161.
Russian sheet iron, gauge for, i, 387.
Rust or caulked joints, ii, 140.
S
Safety devices for planer heads, i, 413.
Safety-valve, the inspection of, ii, 368.
calculations for, ii, 409.
Sag of belts, ii, 210.
Salts and acids, testing oils for, ii, 153.
Sand blast process, ii, 96.
Sand-papering machines, ii, 347-349.
Saturated steam, ii, 410.
Saw bench, rack feed, ii, 301.
frame, horizontal, ii, 312.
hack, ii, 97.
hammering, ii, 70, 71.
machine, tubular, ii, 305.
machines, re-sawing band, ii, 310.
maker's hammer, ii, 68.
plates, grindstones for, ii, 52.
straightening, ii, 70, 71.
teeth, shapes of, ii, 273, 287.
Sawing hot iron, ii, 263.
Saws, chisel teeth for, ii, 290.
concave, ii, 287, 288.
cross-cut, ii, 272, 273.
for swing frame, ii, 292.
grindstones for, ii, 52.
hardening, ii, 462.
heating of circular, ii, 288.
insertion of teeth in, ii, 290.
rip, ii, 272, 273.
sharpening the teeth of, ii, 290.
shingle, ii, 287, 288.
stiffening, ii, 463.
tension of, ii, 288.
truth of circular, ii, 288.
Sawyer's valve for governors, ii, 384.
Scale for moulding knives, ii, 83.
of tooth proportions, i, 54.
Scraped joint making, ii, 137.
Scrapers, angles for facets of, ii, 97.
applications of, i, 332.
for finishing, i, 307.
for true surfaces, ii, 97.
various forms of, ii, 97.
Scraping out cylinder heads, ii, 160.
Scrap iron, furnaces, ii, 247.
welding, ii, 247.
Screw-cutting, driver for, i, 223.
face plate for, i, 223.
feed regulators for, i, 171.
hand tools, i, 96.
pitches, metric system, i, 322.
reversing tool traverse in, i, 168.
with hand tools, i, 334.
Screw-driver, and shape, ii, 97.
Screw-machine, box tools for, i, 208.
chuck for, i, 205.
cross-slide for, i, 205.
feed gear for, i, 205.
cutting off tool for, i, 208.
examples of use of, i, 203.
for heavy work, i, 201.
light work, i, 203, 204.
or screw making lathe, i, 200.
stop motion for, i, 206.
threading tool for, i, 208.
tool holders and tools for, i, 202.
turret of, i, 205.
with special wire feed, i, 206.
Screw-propeller, ii, 445.
Screw-slotting lathe, i, 192.
Screw-thread angles, gauge for, i, 91.
cutting tools, the wear of, i, 89.
standard forms of, i, 85, 86.
Screw-threads, alteration of shape, i, 89.
pitch of, i, 85.
requirements of, i, 86.
self-locking, i, 85.
tools for cutting, i, 87.
variation of pitch, i, 87.
Screws, i, 115.
belt, ii, 216.
set, i, 127.
variation of pitch, i, 87.
Scroll chucks, i, 238.
chuck threads, wear of, i, 238.
sawing machine, ii, 306.
Seams for boilers, forms of, ii, 352.
Securing feathers, methods of, i, 120.
devices, nut, i, 120.
pins for exact adjustments, i, 121.
Segmental circular saws, ii, 300.
Segments, for patterns, ii, 278, 279.
saw, fastening to discs, ii, 301.
Self-acting lathe, English form of, i, 148.
locking bolts, i, 117.
nuts, i, 85.
screw threads, i, 85.
Self-adjusting couplings, ii, 198.
Self-oiling pulleys, ii, 201.
Set-screws, i, 115.
application to hubs, i, 127.
Setting angular grooving cutters, ii, 28.
brasses to pillow-blocks or axle-boxes, ii, 131.
double eccentric by lines, ii, 175.
connecting-rod brasses, ii, 125.
eccentrics on crank shafts, ii, 174.
engine cylinders, ii, 159.
engine guide bars, ii, 162.
guide-bars by stretched line, ii, 163.
line shafting in line, ii, 184, 185.
locomotive slide valves, ii, 394.
numbers and tabular values for odontograph, i, 50.
over tailstock to turn tapers, i, 312.
slide valves, ii, 173.
threading tools, i, 266.
up or aligning new engines, ii, 165.
up axle box wedges, ii, 404.
up keys of connecting rods, ii, 127.
work after case hardening, ii, 129.
Settings for boilers, ii, 364.
Shaft, flexible, for driving drills, i, 459.
forging, ii, 249-252.
Shafting, collars for, ii, 189.
couplings, errors in, ii, 196.
pillow blocks for, ii, 194.
speeds for, ii, 190.
tests of, ii, 188.
turning, three-tool slide-rest, i, 143.
hangers, open-sided, ii, 193.
various forms of, ii, 192.
Shafts, sinking feathers in, ii, 101.
welding to exact lengths, ii, 234.
Shaking grate bars, ii, 369.
Shank cutters, ii, 19.
cutters, applications of, ii, 20.
feed for, ii, 20.
sizes of, ii, 21.
drill, improved form of, i, 446.
Shanks, drill, i, 445.
Shapes of boring bar cutters, i, 291.
of centres for large work, i, 299.
crowns of brasses, ii, 127.
cutting edges of chisels, ii, 74.
file teeth, ii, 85.
hammer eyes, ii, 66.
lathe boring tools, i, 285.
lathe tools, i, 254.
planer tools, i, 423.
Shaping-machine, centres for, i, 397.
crank motions for, i, 401.
general description of, i, 389.
or planer shaper, with tappet motion for reversing, i, 399.
quick return link motion, i, 399.
with traveling head, i, 397.
Shears, lathe, i, 182.
Sheet iron, gauge for, i, 387.
metal, measuring, machine for, i, 348.
zinc, gauge for, i, 387.
Shell reamers, i, 283.
reamers, arbor for, i, 283.
rose reamers, i, 284.
Shimer heads, ii, 337.
Shingle saw, ii, 287, 288.
Shrinkage fits, i, 366.
gauge for, i, 367.
of iron, i, 368, 374.
system at the royal gun factory at Woolwich, i, 367.
Shrinking work, to refit it, i, 374.
Side rake in lathe tools, i, 256.
tools for lathe work, i, 261.
Siphon, ii, 443.
Size of mandrel holes for saws, ii, 287.
Sizes of lathes, i, 130.
Skew bevel gear-wheels, i, 61.
cutters, ii, 316.
knives, ii, 316.
Sledge hammer, machinist's, ii, 71.
Slice bar, ii, 369.
Slide, construction of, i, 390.
Slide-rest, American form of, i, 132.
application of, to a crank, i, 155.
compound tool-holder for, i, 174.
detachable, i, 143.
double tool-holder for, i, 169.
English form of, i, 132.
for lathe crank turning, i, 154.
lathes, i, 131.
pattern lathe, i, 149.
special lathe, i, 145.
spherical-work, i, 133.
gibbed, elevating, i, 169.
various forms of, i, 132.
Slides of planers, construction of, i, 410.
of planer heads, wear of, i, 410.
Sliding motion of gear teeth, i, 16, 27.
motion of worm-wheel teeth, i, 28.
Slide-valve, exhaust lap of, ii, 376.
lead adjusting, ii, 386.
setting a, ii, 386, 394.
squaring, ii, 386.
the Allen, ii, 377.
the D, ii, 376.
Webb's, ii, 377.
Slide-valves, balanced, ii, 377.
circular, ii, 377.
designing, ii, 380.
double ported, ii, 377.
Slide-valves, steam lap of, ii, 376.
the lead of, ii, 376.
Slots and holes in planing-machine tables, i, 417.
Slotted work, tools for, i, 424.
Slotting-machine, i, 459.
sectional view of, i, 460.
tool-holders, i, 460, 461.
tools, i, 461.
Snifting valve, ii, 440.
Socket forging, ii, 243, 244.
wrench, i, 125.
Sockets, drill, i, 445.
Solid and split pulleys, ii, 200.
ended connecting rods, ii, 114.
leather wheels, ii, 51.
tap wrenches, i, 110.
Spacing gear-wheel teeth, i, 57, 58.
reamer teeth, i, 282, ii, 98.
rivets in boiler seams, ii, 353.
Special chucks for watchmakers' lathes, i, 190.
index plate for gear cutting, ii, 7.
forms of chucks, i, 241.
lathe for pulley turning, i, 211.
for wood working, i, 208.
for brass work, i, 216.
Specks in cast-iron work, i, 307.
Speeders for governors, ii, 384.
Speed of a hammer blow, effects of, ii, 65.
of automatic engines, ii, 427.
brush-wheels, ii, 50.
cutter heads or discs, ii, 338.
emery-wheels, ii, 39.
governors, ii, 384.
grindstones, ii, 52.
pulleys, calculating, ii, 204.
polishing wheels, ii, 50.
shafting, ii, 190.
Speeds and feeds for twist drills, i, 277.
for cutting wrought iron, i, 294.
Spherical work, slide-rest for, i, 133.
Spindles live, with coned journals, i, 157.
various methods of locking, i, 186.
Spiral cutters, grinding teeth of, ii, 36.
feed in cutting, ii, 27.
grooves, drill stock with, i, 445.
planer chucks for, i, 419.
springs, winding in the lathe, i, 329.
teeth for reamers, i, 282.
Spirit levels, ii, 136.
Spoon bit, i, 452.
Spring adjustment of governors, ii, 384.
calipers, i, 360.
of engine guide-bars, ii, 162.
swages for blacksmiths, ii, 231.
tools, i, 263.
Springs for indicators, ii, 416.
Spur-wheel, annular, i, 23.
compared with annular, i, 32.
construction of pattern for, i, 54.
Square work, steady rest for, i, 233.
centre, advantage of, i, 303.
various forms of, i, 303.
centring, i, 300.
holes, device for drilling, i, 450.
reamers, ii, 99.
bevel, i, 380.
shanked drills, i, 446.
the T, i, 379.
the try, i, 379.
Squaring a valve, ii, 386.
Square-threads, clearance of tools, i, 269.
cutting, i, 269.
dies for finishing, i, 270.
worms to work with, i, 29.
Stable fork, forging of, ii, 241.
Standard-cutters, ii, 17.
Standard bar for the United States standard of measurement, i, 341.
gauges, diameter of work limits the application of, i, 363.
for taper work, i, 316.
for wire, etc., i, 384.
plug and collar gauges, i, 91.
screw threads, i, 91.
sizes of washers, i, 123.
taps, i, 104.
variations in, i, 341.
Starting a slide valve engine, ii, 384.
a locomotive, ii, 400.
Stationary engine boilers, ii, 350-371.
Steady-rest, cat-head, i, 233.
clamps, i, 233.
for square and taper work, i, 232.
improved form of, i, 233.
or back rest, i, 231.
work, drivers for, i, 225.
Steam, ii, 410.
admitted to indicator, ii, 414.
amount of, used in engines, ii, 420.
engine high pressure, ii, 372.
expansion of, ii, 411.
fire engine, ii, 430, 431.
hammer forging, examples in, ii, 241.
hammers, ii, 252-259.
laps of slide valves, ii, 376.
lubricators, ii, 444.
pipe thread, tapping machine, i, 477.
pipes, dies for, i, 101.
ports, jigs for cutting out, i, 431.
pressure absolute, ii, 411.
reversing gear, locomotive, ii, 390.
saturated, ii, 410.
superheated, ii, 410.
tight nuts, i, 118.
volume and pressure of, ii, 411.
weight of, ii, 411.
Steaming, wood for bending, ii, 266, 267.
Steel and iron welding, ii, 233, 234.
plates, engraver's, polishing, ii, 51.
Steering gear for fire engines, i, 75.
Stepped connecting-rod straps, ii, 117.
reamers for taper work, i, 285.
Stiffening saws, ii, 463.
Stock, adjustable, i, 448.
Stocks and dies, i, 97, 101.
for drilling machines, i, 449.
forms of, i, 101.
Stone drill, i, 454.
Stop motion for gear-wheels, i, 7.
for screw machines, i, 206.
Straight-edge and applications, i, 381.
Straightening saws, ii, 70, 71.
lathe work, device for, i, 305.
machine for bar iron, i, 304.
plates, ii, 69.
wire, check for, i, 305.
work by pening, ii, 72.
Straight-line-engine, automatic, ii, 428.
important details of, ii, 429, 430.
Strains on boiler shells, ii, 351.
Strap ended connecting rod, ii, 116.
Straps, connecting rod, ii, 115.
connecting rod, fitting, ii, 120.
Strength of boiler plate, ii, 350.
boiler shells, ii, 350.
gear-wheel cogs, i, 66.
gear-wheel teeth, i, 64.
line shafting, ii, 190.
wire, experiments on the, i, 387.
Stroke jointers, ii, 338, 339.
Studs, i, 115.
Sun-and-planet motion, i, 75.
Superheated steam, ii, 410.
Supplementary planer tables, i, 417.
Surface condensers, ii, 440, 442.
condensing engine valves, ii, 442.
Surface gauge, i, 378.
Surface plates, originating, i, 383; ii, 132.
Surfaces, rough, joints for, ii, 138.
true, scrapers for, ii, 97.
Swage blocks, ii, 232.
Swages, spring, ii, 232.
for blacksmiths, ii, 230, 231.
Swaging, blacksmiths' work, ii, 232, 233.
Swing-frame, i, 158.
attaching, i, 166.
for lead screw, i, 139.
saws, ii, 290, 291.
Swing machine with fixed table, ii, 294.
Swing machine bevel or mitre, ii, 296.
Swiveled tool-holding devices, i, 411.
Swiveling vise chucks, i, 395.
vises, ii, 63.
Swivel-heads, construction of, i, 389.
for planers, i, 411.
Swiveling tool-rest, i, 174.
T
Table of arc and diametral pitches, i, 3.
change wheels, screw cutting, i, 180.
circular saw diameters, ii, 287.
feeds for twist-drills, i, 277.
index holes for gear cutting, ii, 7.
natural sines, i, 3.
of wrought iron tubes, i, 95.
pitch-diameter, pitch, and number of teeth in gear-wheels, i, 68.
pressure, temperature and volume of steam, ii, 367.
screw threads, i, 95, 96, 107.
sizes of, bolts and nuts, i, 114.
milling-machine cutters, ii, 17.
tapping drills, i, 445.
twist drills and shanks, i, 442.
speeds for twist drills, i, 277.
spring for indicators, ii, 416.
standard for the V-thread, i, 95.
Tabular values and setting numbers for odontograph, i, 51.
Tail-block lathe, i, 185.
Tailstock, adjustments of, i, 245.
chucks, i, 135, 145.
construction of, i, 209.
for drilled work, i, 279.
engine lathe, i, 135.
open spindle lathes, i, 189.
securing and releasing, i, 136.
Tangent screw, i, 1.
Tap-wrenches, adjustable, i, 110.
Taper bolts, standards, i, 359.
cutters, fixtures for, ii, 34.
for pipe threads, i, 95.
grinding, ii, 33.
holes, device for drilling, i, 451.
milling, ii, 30.
pins, fitting, i, 128.
position for locking, i, 128.
plugs for hydraulic fits, i, 365.
reamers, ii, 99.
taps for blacksmiths, i, 106.
threads, cutting, i, 338.
turning attachments, i, 143.
lathe, i, 142.
Tapered connecting-rod ends, ii, 117.
Taper-work, centres for, i, 226.
chucking, i, 394.
fitting, i, 313.
fixture for grinding, ii, 33.
gauge for setting over, i, 313.
grinding, i, 313.
plug and collar gauges for, i, 357.
standard gauges for, i, 316.
Taper-work, steady rest for, i, 233.
stepped reamers for, i, 285.
turning, i, 312, 313.
wear of lathe centres in, i, 312.
Tapers for live centres, i, 159.
Tapping, i, 111.
drills, table of sizes of, i, 445.
machine for steam pipe thread, i, 477.
Taps, clearance on, i, 102.
collapsing, machine, i, 107.
for lead, i, 109.
for very straight holes, i, 109.
form of, i, 103, 104.
improved forms of, i, 103.
number of cutting edges, i, 106, 471.
taper, for blacksmiths, i, 106.
taper, the friction of, i, 102.
wear of, i, 89.
Technical terms in lathe work, i, 296.
Tees, patterns for, ii, 284.
Teeth, angular, end thrust of, i, 69.
angular or herring bone, i, 69.
band saw, ii, 308, 309.
cast, the contact of, i, 67.
curves of elliptical, i, 73.
file, shapes of, ii, 85.
gear-wheel, factors of safety, i, 64.
for variable motion, i, 74.
requirements of curves, i, 7.
helical, i, 69.
reamer, number of, i, 282.
spacing of, ii, 98.
saw, ii, 273, 287.
Temper, blacksmiths', ii, 460.
drawing, the, ii, 462.
manufacturers', ii, 460.
reduction of, ii, 461.
Tempering, ii, 460-464.
color, ii, 460.
heating in fluxes, ii, 462.
methods of, special, ii, 461-464.
outside, ii, 462.
using a muffle, ii, 461.
warping in, ii, 461.
Template, ii, 110-112.
of Corliss bevel-gear-engine, i, 45.
for curves, i, 384.
marking division lines on the face of a gear wheel, i, 59.
filing a link slot, ii, 129.
gear-teeth, i, 43, 44.
involute curves, i, 32.
planing teeth to shape, i, 54.
rolling gear-tooth curves, i, 43.
gauges for end measurements, i, 376.
Tenoning machines, ii, 344.
Tenon joints, ii, 274.
Tension of band saws, ii, 310, 311.
belts, ii, 211.
circular saws, ii, 288.
Testing angle of bevel wheels while in the lathe, i, 60.
boilers, strength of, ii, 456.
engine alignment, ii, 166-172.
engine guide-bars, ii, 163.
indicator expansion curves, ii, 417.
iron, ii, 226-228.
lathe carriages, ii, 182.
lathe tailblock, i, 187.
lathes, i, 180, 181.
lubricants, ii, 152.
machines for iron, ii, 227, 228.
oils, ii, 153, 154.
shafting, ii, 188.
squares, various methods of, i, 379.
the power of an engine, ii, 408.
various methods of, i, 187.
Theoretical compression curve, ii, 421.
diagram, ii, 415.
expansion curve, ii, 417, 418.
Thimble joints, ii, 141.
Thinning twist-drill points, ii, 44.
Thread angles, gauge for, i, 91.
cutting, i, 111.
avoiding friction in, i, 474.
dies, i, 97.
taps, i, 102.
tools, angles of, i, 91.
wear of, i, 88.
pitch varied by hardening, i, 87.
screw, forms of, i, 85.
Threaded work, drivers for, i, 225.
Threading dies, cutting speeds for, i, 474.
dies, hob for, i, 474.
machine, hand bolt, i, 464.
hand, revolving head, i, 465.
pipe, i, 463, 475-477.
power, i, 466.
tools, circular, i, 264, 267.
for gauges, i, 266.
screw machine, i, 203.
holders, i, 267.
internal, i, 264.
setting, i, 266.
the level of, i, 265.
Threads, diameter at the roots of, i, 269.
left-hand cutting, i, 322.
square, clearance of tools for, i, 269.
Three and four-jawed chucks, i, 237.
Three-spindle drilling machine, i, 434.
nut tapping machine, i, 475.
Three-tool slide-rest for shafting, i, 143.
Three or four boring bar cutters, i, 290.
Throttle valves leaky, ii, 386.
Throttling governors, ii, 384.
Thrust bearings, ii, 445.
Thrust on wheel shafts, i, 16.
Timber, bending, ii, 265, 266.
Timber, shakes or cracks in, ii, 264.
shrinkage of, ii, 264.
steaming to bend it, ii, 266.
Timber-planer, ii, 330, 331.
Tit drill, i, 443.
Tongs, blacksmith's, ii, 229.
Tool aprons for planers, i, 411.
edge, oilstoning, ii, 54.
front for lathe work, i, 254.
facing with reamer pin, i, 449.
grinding and grindstones, ii, 51.
holders, boring, i, 287.
combined, i, 273.
for compound slide-rests, i, 174.
circular cutters, i, 272.
octagon boring tools, i, 175.
screw machine, i, 202.
lathe for outside work, i, 270.
planer, i, 426.
slotting machine, i, 460, 461.
swiveled, i, 273.
threading, i, 267.
holding devices, i, 173.
swiveled for planers, i, 411.
rest, swiveling, i, 174.
taps, improved, i, 103.
Tools, caulking, ii, 141.
bolt heading, ii, 237.
box for screw machine, i, 208.
circular cutting, i, 267.
cutting-off or grooving, i, 262.
cutting, the utmost duty of, i, 258.
diamond-pointed, i, 254.
facing or knife, i, 262.
for blacksmiths, ii, 229, 230.
cutting rods in pieces, i, 305.
screw threads, i, 87.
wood slips, ii, 271.
a worm in a lathe, i, 62.
mortising machines, ii, 344.
roll turning, i, 215.
screw machine, i, 202.
standard shapes, i, 111.
testing lathe centres, i, 298.
planer, clearance of, i, 424.
for coarse finishing feeds, i, 423.
slotted work, i, 424.
gauge for, i, 423.
shapes of, i, 423.
round-nosed, i, 258.
spring, i, 263.
square-nosed, i, 260.
thread-cutting, i, 97.
threading for screw machine, i, 264.
wood working, grindstones for, ii, 52.
with side rake, i, 256.
Tooth form, variation of, i, 15.
proportions, scale of, i, 54.
templates, pivoted arms for, i, 44.
Trammeling connecting rods, ii, 122.
Trams or trammels, i, 377.
Traversing grindstones, automatic, ii, 53.
spindle lathe, i, 218.
Triple riveted joints, ii, 353.
Triple-expansion-engine, ii, 436.
link motions of, ii, 438.
valves of, ii, 438, 439.
Trip-hammers, ii, 254.
swages for, ii, 231.
Trying-up machines, ii, 332.
Try-squares, i, 379.
True surfaces, scrapers for, ii, 97.
surfaces, oiling, ii, 135.
plane, originating, ii, 132.
Truing grindstones, ii, 53.
lathe centres, devices for, i, 297.
oilstones, ii, 54.
Trundle-wheels, i, 1.
T-squares, i, 379.
Tube plate cutters, i, 448.
Tubular saw machine, ii, 305.
Tubular work, lathe mandrels for, i, 227.
Tubes, boiler, arrangement of, ii, 364.
bursted, ii, 403.
Tumbler-files, ii, 91.
Turn-buckle, forging, ii, 239.
Turned work, recentring, i, 304.
Turning a cylinder cover, i, 318.
calendar rolls, i, 215.
crank axles, lathe for, i, 152.
crank, lathe for, i, 154.
irregular shapes, i, 210.
machine, feed motions of, i, 436.
for boiler makers, i, 435.
mill, i, 211.
outside threads, i, 338.
pulleys, i, 318.
shafting, three tool slide rest, i, 143.
tapers, i, 136, 312.
Turret for screw machine, i, 205.
Twin cutters, ii, 18.
milling, advantages, ii, 25.
Twist-drills, i, 274.
clearance of, i, 274; ii, 41-44.
effect of improper grinding, i, 276.
fluting, ii, 29.
feeds and speeds for, i, 277.
front rake of, i, 275; ii, 44.
grinding, i, 276.
large, thinning the points of, ii, 44.
table of sizes of, i, 442.
Two-jawed chucks, i, 236.
U
United States standard for gas pipe, i, 93.
for finished bolts and nuts, i, 113.
rough bolts and nuts, i, 114.
United States standard for screw thread, i, 86.
Universal chucks, i, 238.
coupling, ii, 199.
grinding lathes, i, 195.
joint for drill brace, i, 456.
milling-machines, ii, 2-15.
for heavy work, ii, 15.
V
Vacuum gauge, ii, 444.
line of indicator diagram, ii, 415.
Valve, cut off, ii, 378.
expansion, ii, 443.
for marine engines, ii, 444.
for triple expansion engines, ii, 439.
gear, principles of the Corliss, ii, 424.
globe, pattern for, ii, 281.
Kingston, ii, 440.
lead adjusting, ii, 386.
measuring, ii, 173.
motion, designing, ii, 381.
of surface condensing engines, ii, 442.
snifting, ii, 440.
squaring a, ii, 386.
throttle freezing, ii, 386, 387.
Velocity, uniform for gear wheels, i, 16.
Vertical boilers, ii, 359, 361.
milling machine, ii, 31.
water tube boiler, ii, 360.
V-guideways for planer heads, i, 414.
Vise, ii, 62, 63.
chucks for vise work, i, 396.
construction of, i, 393.
chucking work in, i, 393.
holding taper work in, i, 394.
rapid motion, i, 396.
swiveling, i, 395.
various forms of, i, 394.
clamps, various forms of, ii, 64.
hand, ii, 104.
jaws, heights of, ii, 62.
leg, with parallel motion, ii, 63.
wood workers', ii, 62.
work, classification of, ii, 62.
examples in, ii, 102-135.
red marking for, ii, 96.
Vises, swiveling, ii, 63.
Volume and pressure of steam, ii, 411.
V-slide lathe shears, i, 182.
V-thread standard, i, 93.
V-tool for starting threads, i, 337.
W
Wall hangers, ii, 193.
Warping, ii, 461.
Warping of files, ii, 93.
Washers, i, 123.
standard sizes of, i, 123.
Watchmakers' lathes, i, 188.
Watch manufacturers' hand lathe, i, 191.
lathe, details of, i, 190.
Water, ii, 410.
evaporation, calculation of, ii, 420.
gauge glass, ii, 368.
joints, ii, 139.
tube boiler, vertical, ii, 360.
Wear of dies, i, 89.
of back bearings, i, 158.
emery wheels, ii, 48.
groove cams, i, 84.
nuts, i, 120.
planer head slides, i, 410.
scroll chuck threads, i, 238.
spindles of lathe tailblock, i, 185.
taps, i, 89.
worm and worm-wheel, i, 28.
upon grooved friction wheels, i, 79.
Weight of steam, ii, 411.
Weighted elevated slide rest, i, 168.
slide-rest, feed motion for, i, 168.
Weld, butt, ii, 234.
lap, ii, 234.
split, ii, 235.
Welded connecting rods, aligning, ii, 118.
Welding iron and steel, ii, 233, 234.
scrap iron, ii, 247.
stub ends of connecting rods, ii, 118.
theory of, ii, 233.
Wheel, emery, position of, ii, 35.
forging of fifth, ii, 239.
hubs, lathe for turning, i, 221.
lathe, i, 151.
rack and pinion, i, 1.
rim, spacing the teeth on, i, 56, 58.
shafts thrust on, i, 16.
tire, throwing off, ii, 403.
worm, i, 1.
Wheels, bevel line of faces, i, 22.
brush, for polishing, ii, 50.
speed of, ii, 50.
clock, i, 21.
considered as levers, ii, 405.
emery, annular, ii, 47.
balancing, ii, 39.
grades of, ii, 39.
presenting, to work, ii, 47.
qualifications of, ii, 38.
recessed, ii, 47.
swing frame, large work, ii, 46.
speeds of, ii, 39.
wear of, ii, 48.
work suitable for, ii, 39.
friction, i, 77.
material for, i, 77.
for transmitting motion, i, 21.
gear drawings for, i, 59.
intermediate, i, 319.
locomotive, forging, ii, 244.
number of cutters for a train of, i, 39.
paddle, ii, 444.
polishing, construction of, ii, 49.
charging with emery, ii, 50.
for brass work, ii, 50.
large, method of truing, ii, 50.
polishing materials for, ii, 50.
rag, ii, 51.
speed of, ii, 50.
solid leather, ii, 51.
trundle, i, 1.
White-metal lined boxes, ii, 155.
Width and thickness of chisels, ii, 74.
Winding spiral springs, i, 329.
strips and their use, i, 382.
Wire-feed for screw machines, i, 206.
gauge, i, 387.
Wire, strength of, experiments on, i, 387.
Wood bending block, ii, 265, 266.
boring machines, ii, 343.
for patterns, ii, 264.
gouges, ii, 272.
moulding machines, knives of, ii, 84.
planing machine, ii, 317-341.
pulleys, ii, 200.
steaming, ii, 266.
turning, hand tools for, i, 338.
work, chisels for, ii, 271.
counterbore for, i, 449.
drill for, i, 449.
drivers for, i, 225.
forms of joints for, ii, 275.
lathe, face plates for, i, 247.
on swing frame machine, ii, 292.
twist drills for, i, 279.
worker's vise, ii, 62.
Wood-working, circular-saw gauges for, ii, 295.
lathes, chucks for, i, 242.
machinery, ii, 287-349.
special lathe for, i, 208.
tools, grindstones for, ii, 52.
Woods for patterns, ii, 264.
Work, cored, drivers for, i, 225.
face plate, examples of, i, 249.
holding straps, i, 244.
hollow centres for, i, 226.
shrinking, to refit, i, 374.
Worm and worm-wheel, i, 28.
gears, i, 62.
wheel, application of, i, 30.
cutting teeth of, i, 42.
enveloping teeth, i, 28.
number of teeth in, i, 29.
teeth, sliding motion of, i, 28.
Worm to work with a square thread, i, 29.
Wrench, adjustable, i, 125.
for carriage bolts, i, 125.
jaws, angle for, i, 123.
monkey, i, 125.
pin, i, 126.
sockets, i, 125.
various forms of, i, 125.
Wrought iron, cutting speeds for, i, 294.
Y
Yoke and guide-bars, ii, 389.
Z
Zigzag riveted seams, ii, 352.
Zinc gauge, the American sheet, i, 387.
gauge, the Belgian sheet, i, 387.
THE END.
+------------------------------------------------------------------+
| TRANSCRIBER'S NOTES |
| Text: |
| * Minor obvious typographical errors (including punctuation) have|
| been corrected silently. |
| * Footnotes have been moved to directly under the paragraph or |
| table they belong to. |
| * Mid-dots (·, inconsistently used as decimal points) have been |
| replaced with periods (.). |
| * Calculations and rounding of results have not been changed, |
| except when they contained obvious errors (see below). |
| * Inconsistent spelling has not been changed, except as mentioned|
| below (see "Changes made"). Inconsistencies that occur in the |
| original work include variants such as vice/vise, colour/color,|
| gray/grey, ...er/...re (center/centre, fiber/fibre, etc.) adze/|
| adz, axe/ax, draft/draught, cotter/cottar, ...ise/...ize |
| (crystallise/crystallize, equalize/equalise, etc.), mould/mold,|
| intercepter/interceptor, mandrel/mandril, planimeter/ |
| planometer, l/ll inconsistencies (jeweller/jeweler, travelling/|
| traveling, etc.), Beltiline/Beltilene, Stubb/Stub, and Swasey/ |
| Swayzey. The plural of [V] is sometimes written [V]s, sometimes|
| [V]'s. |
| * Inconsistent hyphenation has not been changed either, except as|
| listed below under "Changes made". Many compound words are |
| variously spelled hyphenated, spaced or as a single word. |
| * Volume I, Page 61: let the Fig. 166 ...: part of sentence |
| appears to be missing. |
| * Volume I, Page 369: heading PART I. There does not appear to |
| be a PART II (or further). |
| * Volume I, Page 370, Fig. 1430: 995 and 598 should probably be |
| .995 and .598. |
| |
| Illustrations: |
| * Illustrations and plates are given in the order in which they |
| are found in the original work. In some cases, the plates |
| contain illustrations that are out of their numerical order. |
| * In Volume II the numbering of illustrations is as expected up |
| to Fig. 2705, after which follow Figs. 2824 through 3077, |
| followed by Figs. 2706-2823, after which the numbering |
| continues as expected. This has been maintained in this e-text.|
| * Similarly in Volume II, plates are numbered I-XII, followed by |
| Plates XV-XVII, then XIII-XIV, followed by Plate XVIII et seq. |
| This has not been changed either. |
| |
| Tables: |
| * Many tables have been split or otherwise re-arranged. In |
| several tables the headings have been changed to legends [A], |
| [B], etc.; these are explained directly above the table. In |
| other tables, remarks have been changed to [A], [B], etc.; |
| these are explained directly underneath the tables. |
| |
| Changes made to the text: |
| |
| Volume I: |
| Page number Original work Changed to |
| ----------- -------------------------- ------------------------- |
| page xi Machine 309 Machine 300 |
| page 7 under wear undue wear |
| page 30 Hindleys' Hindley's |
| page 37 Fig. 106 Fig. 109 |
| page 40: (for 97 bears... (for 96 bears... |
| page 47, table in fig. 135: row 16 teeth, 2nd last value: |
| 191 119 |
| page 49: 1/2 = 500 1/2 = .500 |
| page 67: After very few blows After every few blows |
| page 84: maintained a close fit maintained in a close fit |
| page 87: second reference to Fig. Fig. 259 (description |
| 258 clearly refers to 259) |
| page 95: apt to have a waver apt to have a wave |
| page 95: closing " added (after 'a single operation.') |
| page 96: Whitworth table, Hydraulic Piping, 1" ID, row 2: |
| 1-3/8 1-5/8 |
| page 107, table: |
| 5-12/16 5-13/16 |
| page 127: .937/1000 937/1000 |
| page 136: in figure : in Fig. 498: |
| page 162, column 1, row ending in 0.00: |
| unclear .0594 |
| column 1: column 2 moved to between columns 1 and 3 |
| column 33, row ending in 0.72: |
| 1.22 0 1.2200 |
| column 31, row ending in 0.96: |
| .8 94 .8994 |
| page 186: gibbs gibs |
| page 234: out if true out of true |
| page 274, table, first row: |
| 1/6 1/8 |
| page 307: Fig. 1029 Fig. 1209 |
| page 312: smoothes smooths |
| page 321: 66 ÷ 36 = 2-3/4 99 ÷ 36 = 2-3/4 |
| page 322: as at J in Fig. 1241 as at I in Fig. 1241 |
| page 335: Fig. 1334 Fig. 1324 |
| page 344: Fig. 1532 Fig. 1352 |
| page 356: Lloyd's Lloyds' (as elsewhere) |
| page 366: if it is found possible if it is found impossible |
| page 367: will expend will expand |
| page 370, Fig. 1430: |
| smart quotes " (inches) |
| x × |
| page 373, third table: |
| 0.2 .02 (twice) |
| page 388: reamless seamless |
| page 388, table, row 2" column 3: |
| 1/5 1/8 |
| page 406: Fig. 1669 Fig. 1569 |
| page 442 first table, row 11/16, column 2: |
| 8-1/4 9-1/4 |
| |
| Volume II: |
| page x: Mariotte's law Marriotte's law (as in |
| text) |
| page 7, table, row 25 teeth, column 3: |
| 12/0 12/20 |
| page 7/8, table: rearranged to become continuous, repeat headings|
| removed |
| page 17: a length of 3 inches a length of 3 feet |
| page 88: Figs. 2211, 2212 and 2213 Figs. 2210, 2211 and 2212 |
| page 132, footnote [33]: |
| p. 162 p. 68 |
| page 151: Figs. 2405 and 2500 Figs. 2495 and 2500 |
| page 154, first table, row Smooth metal surfaces, occasionally |
| greased, second column: |
| 4 to 1-1/2 4 to 4-1/2 (as in Bourne's|
| book (Rose's source) at |
| archive.org) |
| page 208, table in illustration, row 7, column 5: |
| 9.32 9/32 |
| all fractions transcribed as x/y for consistency |
| within table |
| page 224, second formula: |
| 11. .11 |
| page 311: Ortow Orton (as elsewhere) |
| page 319: Fig. 3260 Fig. 3160 |
| page 348: 4' 4" (thickness) |
| page 354, first formula: |
| by 2 2 |
| page 354: formula resulting in 116-2/3 lbs.: |
| + × |
| page 356: found the required pitch found the required pitch |
to to be |
| page 367, table row Total pressure 33, column 3: |
| 225.2 252.2 |
| table row Total pressure 44, column 6: |
| 595 585 |
| table row Total pressure 61, column 6: |
| 403 430 |
| page 401: colters cotters |
| page 407, first calculation: |
| line added under 5 (third row) |
| page 471: Marriott's Marriotte's |
| page 476: Tuyere Tuyère (as in text) |
| Verneer Vernier (as in text) |
| page 479: featheredge feather-edge (as in text) |
| page 480: Gimblet Gimlet (as in text) |
| doghead dog-head (as in text) |
| Guideways Guide-ways (as in text) |
| page 481: Marriott's Mariotte's |
| rabbetting rabetting (as in text) |
| Piaté Piat's as in Table of |
| Contents (word does not |
| occur in text) |
| page 482: featheredge feather-edge (as in text) |
+------------------------------------------------------------------+
*** End of this LibraryBlog Digital Book "Modern Machine-Shop Practice, Volumes I and II" ***
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