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Title: The Modern Clock - A Study of Time Keeping Mechanism; Its Construction, Regulation and Repair
Author: Goodrich, Ward L.
Language: English
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The Modern Clock
A Study of Time Keeping Mechanism;
Its Construction, Regulation and Repair.
by
WARD L. GOODRICH
Author of the Watchmaker’s Lathe, Its Use and Abuse.
With Numerous Illustrations and Diagrams
CHICAGO
Hazlitt & Walker, Publishers
1905
Copyrighted
1905
by Hazlitt & Walker.
TABLE OF CONTENTS
CHAP. PAGE
I. THE NECESSITY FOR BETTER SKILL AMONG CLOCKMAKERS. 3
II. THE NATURAL LAWS GOVERNING PENDULUMS. 10
III. COMPENSATING PENDULUMS. 23
IV. THE CONSTRUCTION OF MERCURIAL PENDULUMS. 53
V. REGULATIONS, SUSPENSIONS, CRUTCHES AND MINOR POINTS. 79
VI. TORSION PENDULUMS FOR FOUR-HUNDRED DAY CLOCKS. 91
VII. PECULIARITIES OF ANGULAR MEASUREMENT—
HOW TO READ DRAWINGS. 98
VIII. THE GRAHAM OR DEAD BEAT ESCAPEMENT. 109
IX. LE PAUTE’S PIN WHEEL ESCAPEMENT. 135
X. THE RECOIL OR ANCHOR ESCAPEMENT. 141
XI. THE DENNISON OR GRAVITY ESCAPEMENT. 150
XII. THE CYLINDER ESCAPEMENT AS APPLIED TO CLOCKS. 163
XIII. THE DETACHED LEVER ESCAPEMENT AS APPLIED TO CLOCKS. 184
XIV. PLATES, PIVOTS AND TIME TRAINS. 198
XV. SPRINGS, WEIGHTS AND POWER. 264
XVI. MOTION WORK AND STRIKING TRAINS. 293
XVII. CLEANING AND REPAIRING CUCKOO CLOCKS. 319
XVIII. SNAIL STRIKING WORK, ENGLISH, FRENCH AND AMERICAN. 330
XIX. THE CONSTRUCTION OF SIMPLE AND PERPETUAL CALENDARS. 347
XX. HAMMERS, GONGS AND BELLS. 367
XXI. ELECTRIC CLOCKS AND BATTERIES. 376
XXII. THE CONSTRUCTION AND REPAIR OF DIALS. 426
XXIII. CLOCK CASING AND CASE REPAIRS. 446
XXIV. SOME HINTS ON MAKING A REGULATOR. 463
LIST OF ILLUSTRATIONS 495
INDEX 497
CHAPTER I.
THE NECESSITY FOR BETTER SKILL AMONG CLOCKMAKERS.
The need for information of an exact and reliable character in regard
to the hard worked and much abused clock has, we presume, been felt by
every one who entered the trade. This information exists, of course,
but it is scattered through such a wide range of publications and is
found in them in such a fragmentary form that by the time a workman
is sufficiently acquainted with the literature of the trade to know
where to look for such information he no longer feels the necessity of
acquiring it.
The continuous decrease in the prices of watches and the consequent
rapid increase in their use has caused the neglect of the pendulum
timekeepers to such an extent that good clock men are very scarce,
while botches are universal. When we reflect that the average ‘life’ of
a worker at the bench is rarely more than twenty years, we can readily
see that information by verbal instruction is rapidly being lost, as
each apprentice rushes through clock work as hastily as possible in
order to do watch work and consequently each “watchmaker” knows less of
clocks than his predecessor and is therefore less fitted to instruct
apprentices in his turn.
The striking clock will always continue to be the timekeeper of the
household and we are still dependent upon the compensating pendulum,
in conjunction with the fixed stars, for the basis of our timekeeping
system, upon which our commercial and legal calendars and the movements
of our ships and railroad trains depend, so that an accurate knowledge
of its construction and behavior forms the essential basis of the
largest part of our business and social systems, while the watches
for which it is slighted are themselves regulated and adjusted at the
factories by the compensated pendulum.
The rapid increase in the dissemination of “standard time” and the
compulsory use of watches having a maximum variation of five seconds
a week by railway employees has so increased the standard of accuracy
demanded by the general public that it is no longer possible to make
careless work “go” with them, and, if they accept it at all, they are
apt to make serious deductions from their estimate of the watchmaker’s
skill and immediately transfer their custom to some one who is more
thorough.
The apprentice, when he first gets an opportunity to examine a clock
movement, usually considers it a very mysterious machine. Later on,
if he handles many clocks of the simple order, he becomes tolerably
familiar with the time train; but he seldom becomes confident of his
ability regarding the striking part, the alarm and the escapement,
chiefly because the employer and the older workmen get tired of telling
him the same things repeatedly, or because they were similarly treated
in their youth, and consider clocks a nuisance, any how, never having
learned clock work thoroughly, and therefore being unable to appreciate
it. In consequence of such treatment the boy makes a few spasmodic
efforts to learn the portions of the business that puzzle him, and then
gives it up, and thereafter does as little as possible to clocks, but
begs continually to be put on watch work.
We know of a shop where two and sometimes three workmen (the best
in the shop, too) are constantly employed upon clocks which country
jewelers have failed to repair. If clock work is dull they will go upon
watch work (and they do good work, too), but they enjoy the clocks and
will do them in preference to watches, claiming that there is greater
variety and more interest in the work than can be found in fitting
factory made material into watches, which consist of a time train only.
Two of these men have become famous, and are frequently sent for to
take care of complicated clocks, with musical and mechanical figure
attachments, tower, chimes, etc. The third is much younger, but is
rapidly perfecting himself, and is already competent to rebuild minute
repeaters and other sorts of the finer kinds of French clocks. He now
totally neglects watch work, saying that the clocks give him more money
and more fun.
We are confident that this would be also the case with many another
American youth if he could find some one to patiently instruct him in
the few indispensable facts which lie at the bottom of so much that is
mysterious and from which he now turns in disgust. The object of these
articles is to explain to the apprentice the mysteries of pendulums,
escapements, gearing of trains, and the whole technical scheme of these
measurers of time, in such a way that hereafter he may be able to
answer his own questions, because he will be familiar with the facts on
which they depend.
Many workmen in the trade are already incompetent to teach clockwork
to anybody, owing to the slighting process above referred to; and the
frequent demands for a book on clocks have therefore induced the writer
to undertake its compilation. Works on the subject—nominally so, at
least—are in existence, but it will generally be found on examination
that they are written by outsiders, not by workmen, and that they
treat the subject historically, or from the standpoint of the artistic
or the curious. Any information regarding the mechanical movements
is fragmentary, if found in them at all, and they are better fitted
for the amusement of the general public than for the youth or man who
wants to know “how and why.” These facts have impelled the writer to
ignore history and art in considering the subject; to treat the clock
as an existing mechanism which must be understood and made to perform
its functions correctly; and to consider cases merely as housings of
mechanism, regardless of how beautiful, strange or commonplace those
housings may be.
We have used the word “compile” advisedly. The writer has no new ideas
or theories to put forth, for the reason that the mechanism we are
considering has during the last six hundred years had its mathematics
reduced to an exact science; its variable factors of material and
mechanical movements developed according to the laws of geometry and
trigonometry; its defects observed and pointed out; its performances
checked and recorded. To gather these facts, illustrate and explain
them, arrange them in their proper order, and point out their relative
importance in the whole sum of what we call a clock, is therefore all
that will be attempted. In doing this free use has been made of the
observations of Saunier, Reid, Glasgow, Ferguson, Britten, Riefler and
others in Europe and of Jerome, Playtner, Finn, Learned, Ferson, Howard
and various other Americans. The work is therefore presented as a
compilation, which it is hoped will be of service in the trade.
In thus studying the modern American clocks, we use the word American
in the sense of ownership rather than origin, the clocks which come to
the American workmen to-day have been made in Germany, France, England
and America.
The German clocks are generally those of the Schwartzwald (or Black
Forest) district, and differ from others in their structure, chiefly in
the following particulars: The movement is supported by a horizontal
seatboard in the upper portion of the case. The wooden trains of many
of the older type instead of being supported by plates are held in
position by pillars, and these pillars are held in position by top
and bottom boards. In the better class of wooden clocks the pivot
holes in the pillars are bushed with brass tubing, while the movement
has a brass ’scape wheel, steel wire pivots and lantern pinions of
wood, with steel trundles. In all these clocks the front pillars are
friction-tight, and are the ones to be removed when taking down the
trains. Both these and the modern Swartzwald brass movements use a
sprocket wheel and chain for the weights and have exposed pendulums and
weights.
The French clocks are of two classes, pendules and carriage clocks,
and both are liable to develop more hidden crankiness and apparently
causeless refusals to go than ever occurred to all the English, German
and American clocks ever put together. There are many causes for this,
and unless a man is very new at the business he can tell stories of
perversity, that would make a timid apprentice want to quit. Yet the
French clocks, when they do go, are excellent timekeepers, finely
finished, and so artistically designed that they make their neighbors
seem very clumsy by comparison. They are found in great variety, time,
half-hour and quarter-hour strike, musical and repeating clocks being
a few of the general varieties. The pendulums are very short, to
accommodate themselves to the artistic needs of the cases, and nearly
all have the snail strike instead of the count wheel. The carriage
clocks have watch escapements of cylinder or lever form, and the
escapement is frequently turned at right angle by means of bevel gears,
or contrate wheel and pinion, and placed on top of the movement.
The English clocks found in America are generally of the “Hall”
variety, having heavy, well finished movements, with seconds pendulum
and frequently with calendar and chime movements. They, like the
German, are generally fitted with weights instead of springs. There are
a few English carriage clocks, fitted with springs and fuzees, though
most of them, like the French, have springs fitted in going barrels.
The American clocks, with which the apprentice will naturally have
most to do, may be roughly divided into time, time alarm, time
strike, time strike alarm, time calendar and electric winding. The
American factories generally each make about forty sizes and styles of
movements, and case them in many hundreds of different ways, so that
the workman will frequently find the same movement in a large number of
clocks, and he will soon be able to determine from the characteristics
of the movement what factory made the clock, and thus be able to at
once turn to the proper catalogue if the name of the maker be erased,
as frequently happens.
This comparative study of the practice of different factories will
prove very interesting, as the movement comes to the student after a
period of prolonged and generally severe use, which is calculated to
bring out any existing defects in construction or workmanship; and
having all makes of clocks constantly passing through his hands, each
exhibiting a characteristic defect more frequently than any other, he
is in a much better position to ascertain the merits and defects of
each maker than he would be in any factory.
Having thus briefly outlined the kinds of machinery used in measuring
time, we will now turn our attention to the examination of the
theoretical and mechanical construction of the various parts.
The man who starts out to design and build a clock will find himself
limited in three particulars: It must run a specified time; the arbor
carrying the minute hand must turn once in each hour; the pendulum
must be short enough to go in the case. Two of these particulars are
changeable according to circumstances; the length of time run may be
thirty hours, eight, thirty, sixty or ninety days. The pendulum may be
anywhere from four inches to fourteen feet, and the shorter it is the
faster it will go. The one definite point in the time train is that the
minute hand must turn once in each hour. We build or alter our train
from this point both ways, back through changeable intermediate wheels
and pinions to the spring or weight forming the source of power, and
forward from it through another changeable series of wheels and pinions
to the pendulum. Now as the pendulum governs the rate of the clock we
will commence with that and consider it independently.
CHAPTER II.
THE NATURAL LAWS GOVERNING PENDULUMS.
LENGTH OF PENDULUM.—A pendulum is a falling body and as such is subject
to the laws which govern falling bodies. This statement may not be
clear at first, as the pendulum generally moves through such a small
arc that it does not appear to be falling. Yet if we take a pendulum
and raise the ball by swinging it up until the ball is level with the
point of suspension, as in Fig. 1, and then let it go, we shall see it
fall rapidly until it reaches its lowest point, and then rise until it
exhausts the momentum it acquired in falling, when it will again fall
and rise again on the other side; this process will be repeated through
constantly smaller arcs until the resistance of the air and that of
the pendulum spring shall overcome the other forces which operate to
keep it in motion and it finally assumes a position of rest at the
lowest point (nearest the earth) which the pendulum rod will allow
it to assume. When it stops, it will be in line between the center of
the earth (center of gravity) and the fixed point from which it is
suspended. True, the pendulum bob, when it falls, falls under control
of the pendulum rod and has its actions modified by the rod; but it
falls just the same, no matter how small its arc of motion may be, and
it is this influence of gravity—that force which makes any free body
move toward the earth’s center—which keeps the pendulum constantly
returning to its lowest point and which governs very largely the time
taken in moving. Hence, in estimating the length of a pendulum, we must
consider gravity as being the prime mover of our pendulum.
[Illustration: Fig. 1. Dotted lines show path of pendulum.]
The next forces to consider are mass and weight, which, when put in
motion, tend to continue that motion indefinitely unless brought to
rest by other forces opposing it. This is known as momentum. A heavy
bob will swing longer than a light one, because the momentum stored up
during its fall will be greater in proportion to the resistance which
it encounters from the air and the suspension spring.
As the length of the rod governs the distance through which our bob
is allowed to fall, and also controls the direction of its motion, we
must consider this motion. Referring again to Fig. 1, we see that the
bob moves along the circumference of a circle, with the rod acting
as the radius of that circle; this opens up another series of facts.
The circumference of a circle equals 3.1416 times its diameter, and
the radius is half the diameter (the radius in this case being the
pendulum rod). The areas of circles are proportional to the _squares_
of their diameters and the circumferences are also proportional to
their areas. Hence, the lengths of the paths of bobs moving along these
circumferences are in proportion to the _squares_ of the lengths of the
pendulum rods. This is why a pendulum of half the length will oscillate
four times as fast.
Now we will apply these figures to our pendulum. A body falling in
vacuo, in London, moves 32.2 feet in one second. This distance has
by common consent among mathematicians been designated as _g_. The
circumference of a circle equals 3.1416 times its diameter. This is
represented as π. Now, if we call the time _t_, we shall have the
formula:
———————
t = π √ (1/_g_)
Substituting the time, one second, for _t_, and doing the same with the
others, we shall have:
(32.2 ft.)
1 = ——————————— = 3.2616 feet.
(3.1416)²
Turning this into its equivalent in inches by multiplying by 12, we
shall have 39.1393 inches as the length of a one-second pendulum at
London.
Now, as the force of gravity varies somewhat with its distance from
the center of the earth, we shall find the value of _g_ in the above
formula varying slightly, and this will give us slightly different
lengths of pendulum at different places. These values have been found
to be as follows:
Inches.
The Equator is 39
Rio de Janeiro 39.01
Madras 39.02
New York 39.1012
Paris 39.13
London 39.14
Edinburgh 39.15
Greenland 39.20
North and South Pole 39.206
Now, taking another look at our formula, we shall see that we may get
the length of any pendulum by multiplying π (which is 3.1416) by the
_square_ of the _time_ required: To find the length of a pendulum to
beat three seconds:
3² = 9. 39.1393 × 9 = 352.2537 inches = 29.3544 feet.
A pendulum beating two-thirds of a second, or 90 beats:
(⅔)² = ⁴/₉
39.1393 × 4
———————————— = 17.3952 inches.
9
A pendulum beating half-seconds or 120 beats:
(½)² = ¼
39.1393 × 1
——————————— = 9.7848 inches.
4
CENTER OF OSCILLATION.--Having now briefly considered the basic facts
governing the time of oscillation of the pendulum, let us examine it
still further. The pendulum shown in Fig. 1 has all its weight in a
mass at its end, but we cannot make a pendulum that way to run a clock,
because of physical limitations. We shall have to use a rod stiff
enough to transmit power from the clock movement to the pendulum bob
and that rod will weigh something. If we use a compensated rod, so as
to keep it the same length in varying temperature, it may weigh a good
deal in proportion to the bob. How will this affect the pendulum?
If we suspend a rod from its upper end and place along-side of it our
ideal pendulum, as in Fig. 2, we shall find that they will not vibrate
in equal times if they are of equal lengths. Why not? Because when
the rod is swinging (being stiff) a part of its weight rests upon the
fixed point of suspension and that part of the rod is consequently not
entirely subject to the force of gravity. Now, as the time in which
our pendulum will swing depends upon the distance of the _effective_
center of its mass from the point of suspension, and as, owing to the
difference in construction, the center of mass of one of our pendulums
is at the center of its ball, while that of the other is somewhere
along the rod, they will naturally swing in different times.
[Illustration: Fig. 2. Two pendulums of equal length but unequal
vibration. B, center of oscillation for both pendulums.]
[Illustration: Fig. 3.]
Our other pendulum (the rod) is of the same size all the way up and
the center of its _effective_ mass would be the center of its weight
(gravity) if it were not for the fact which we stated a moment ago that
part of the weight is upheld and rendered ineffective by the fixed
support of the pendulum rod, all the while the pendulum is not in a
vertical position. If we support the rod in a horizontal position, as
in Fig. 3, by holding up the lower end, the point of suspension, A,
will support half the weight of the rod; if we hold it at 45 degrees
the point of suspension will hold less than half the weight of the
rod and more of the rod will be affected by gravity; and so on down
until we reach the vertical or up and down position. Thus we see that
the force of gravity pulling on our pendulum varies in its effects
according to the position of the rod and consequently the _effective_
center of its mass also varies with its position and we can only
calculate what this mean (or average) position is by a long series of
calculations and then taking an average of these results.
We shall find it simpler to measure the time of swing of the rod which
we will do by shortening our ball and cord until it will swing in the
same time as the rod. This will be at about two-thirds of the length of
the rod, so that the _effective_ length of our rod is about two-thirds
of its real length. This _effective_ length, which governs the time of
vibration, is called the _theoretical_ length of the pendulum and the
point at which it is located is called its _center of oscillation_. The
distance from the _center_ of oscillation to the point of suspension
is called the _theoretical_ length of the pendulum and is _always_ the
distance which is given in all tables of lengths of pendulums. This
length is the one given for two reasons: First, because, it is the
timekeeping length, which is what we are after, and second, because,
as we have just seen in Fig. 3, the _real_ length of the pendulum
increases as more of the weight of the instrument is put into the rod.
This explains why the heavy gridiron compensation pendulum beating
seconds so common in regulators and which measures from 56 to 60 inches
over all, beats in the same time as the wood rod and lead bob measuring
45 inches over all, while one is apparently a third longer than the
other.
Table Showing the Length of a Simple Pendulum
That performs in one hour any given number of oscillations, from 1
to 20,000, and the variation in this length that will occasion a
difference of 1 minute in 24 hours.
_Calculated by E. Gourdin._
============================================================
| Length | Variation in Length
Number of | in | for One Minute in 24
Oscillations per Hour. |Millimeters. | Hours in Millimeters.
-----------------------+-------------+----------------------
20,000 | 32.2 | 0.04
19,000 | 35.7 | 0.05
18,000 | 39.8 | 0.05
17,900 | 40.2 | 0.06
17,800 | 40.7 | 0.06
17,700 | 41.1 | 0.06
17,600 | 41.6 | 0.06
17,500 | 42.1 | 0.06
17,400 | 42.4 | 0.06
17,300 | 43.0 | 0.06
17,200 | 43.5 | 0.06
17,100 | 44.0 | 0.06
17,000 | 44.6 | 0.06
16,900 | 45.1 | 0.06
16,800 | 45.7 | 0.06
16,700 | 46.3 | 0.06
16,600 | 46.7 | 0.07
16,500 | 47.3 | 0.07
16,400 | 47.9 | 0.07
16,300 | 48.5 | 0.07
16,200 | 49.1 | 0.07
16,100 | 49.7 | 0.07
16,000 | 50.0 | 0.07
15,900 | 51.0 | 0.07
15,800 | 51.6 | 0.07
15,700 | 52.3 | 0.07
15,600 | 52.9 | 0.07
15,500 | 53.6 | 0.07
15,400 | 54.3 | 0.08
15,300 | 55.0 | 0.08
15,200 | 55.7 | 0.08
15,100 | 56.5 | 0.08
15,000 | 57.3 | 0.08
14,900 | 58.0 | 0.08
14,800 | 58.8 | 0.08
14,700 | 59.6 | 0.08
14,600 | 60.4 | 0.08
14,500 | 61.3 | 0.08
14,400 | 62.1 | 0.09
14,300 | 63.0 | 0.09
14,200 | 63.9 | 0.09
14,100 | 64.8 | 0.09
14,000 | 65.7 | 0.09
13,900 | 66.7 | 0.09
13,800 | 67.6 | 0.09
13,700 | 68.6 | 0.09
13,600 | 69.6 | 0.09
13,500 | 70.7 | 0.09
13,400 | 71.7 | 0.10
13,300 | 72.8 | 0.10
13,200 | 73.9 | 0.10
13,100 | 75.1 | 0.10
13,000 | 76.2 | 0.10
12,900 | 77.4 | 0.11
12,800 | 78.6 | 0.11
12,700 | 79.9 | 0.11
12,600 | 81.1 | 0.11
12,500 | 82.4 | 0.11
12,400 | 83.8 | 0.11
12,300 | 85.1 | 0.12
12,200 | 86.5 | 0.12
12,100 | 88.0 | 0.12
12,000 | 89.5 | 0.12
11,900 | 91.0 | 0.12
11,800 | 92.5 | 0.13
11,700 | 94.1 | 0.13
11,600 | 95.7 | 0.13
11,500 | 97.4 | 0.13
11,400 | 99.1 | 0.13
11,300 | 100.9 | 0.14
11,200 | 102.7 | 0.14
11,100 | 104.5 | 0.14
11,000 | 106.5 | 0.14
10,900 | 108.4 | 0.15
10,800 | 110.5 | 0.15
10,700 | 112.5 | 0.15
10,600 | 114.6 | 0.16
10,500 | 116.8 | 0.16
10,400 | 119.1 | 0.16
10,300 | 121.4 | 0.17
10,200 | 123.8 | 0.17
10,100 | 126.3 | 0.17
10,000 | 128.8 | 0.18
9,900 | 131.4 | 0.18
9,800 | 134.1 | 0.18
9,700 | 136.9 | 0.19
9,600 | 139.8 | 0.19
9,500 | 142.7 | 0.19
9,400 | 145.8 | 0.20
9,300 | 148.9 | 0.20
9,200 | 152.2 | 0.21
9,100 | 155.5 | 0.21
9,000 | 159.0 | 0.22
8,900 | 162.6 | 0.22
8,800 | 166.3 | 0.23
8,700 | 170.2 | 0.23
8,600 | 173.7 | 0.24
8,500 | 178.3 | 0.24
8,400 | 182.5 | 0.25
8,300 | 187.0 | 0.25
8,200 | 191.5 | 0.26
8,100 | 196.3 | 0.27
8,000 | 201.3 | 0.27
7,900 | 206.4 | 0.28
7,800 | 211.7 | 0.29
7,700 | 217.2 | 0.30
7,600 | 223.0 | 0.30
7,500 | 229.0 | 0.31
7,400 | 235.2 | 0.32
7,300 | 241.7 | 0.33
7,200 | 248.5 | 0.34
7,100 | 255.7 | 0.35
7,000 | 262.9 | 0.36
6,900 | 270.5 | 0.37
6,800 | 278.6 | 0.38
6,700 | 286.9 | 0.39
6,600 | 295.7 | 0.40
6,500 | 304.9 | 0.41
6,400 | 314.5 | 0.43
6,300 | 324.5 | 0.44
6,200 | 335.1 | 0.46
6,100 | 346.2 | 0.47
6,000 | 357.8 | 0.48
5,900 | 370.0 | 0.50
5,800 | 382.9 | 0.52
5,700 | 396.4 | 0.54
5,600 | 410.7 | 0.56
5,500 | 425.8 | 0.58
5,400 | 440.1 | 0.60
5,300 | 458.5 | 0.62
5,200 | 476.3 | 0.65
5,100 | 495.2 | 0.67
5,000 | 515.2 | 0.70
4,900 | 536.5 | 0.73
4,800 | 559.1 | 0.76
4,700 | 583.1 | 0.79
4,600 | 608.7 | 0.83
4,500 | 636.1 | 0.86
4,400 | 665.3 | 0.90
4,300 | 696.7 | 0.95
4,200 | 730.2 | 0.99
4,100 | 766.3 | 1.04
4,000 | 805.0 | 1.09
3,950 | 825.5 | 1.12
3,900 | 846.8 | 1.15
3,850 | 869.0 | 1.16
3,800 | 892.0 | 1.21
3,750 | 915.9 | 1.25
3,700 | 940.1 | 1.28
3,650 | 966.8 | 1.31
-----------------------+-------------+----------------------
Table of the Length of a Simple Pendulum, (CONTINUED.)
------------+----------------+----------------------------
| | To Produce in 24 Hours
| | 1 Minute.
| +----------------------------
Number of | Length | Loss, | Gain,
Oscillations | in | Lengthen by | Shorten by
per Hour. | Meters. | Millimeters.| Millimeters.
------------+----------------+-------------+--------------
3,600 | 0.9939 | 1.38 | 1.32
3,550 | 1.0221 | 1.42 | 1.36
3,500 | 1.0515 | 1.46 | 1.40
3,450 | 1.0822 | 1.50 | 1.44
3,400 | 1.1143 | 1.55 | 1.48
3,350 | 1.1477 | 1.60 | 1.53
3,300 | 1.1828 | 1.64 | 1.57
3,250 | 1.2194 | 1.69 | 1.62
3,200 | 1.2578 | 1.75 | 1.67
3,150 | 1.2981 | 1.80 | 1.73
3,100 | 1.3403 | 1.86 | 1.78
3,050 | 1.3846 | 1.93 | 1.84
3,000 | 1.4312 | 1.99 | 1.90
2,900 | 1.5316 | 2.13 | 2.04
2,800 | 1.6429 | 2.28 | 2.18
2,700 | 1.7669 | 2.46 | 2.35
2,600 | 1.9054 | 2.65 | 2.53
2,500 | 2.0609 | 2.87 | 2.74
2,400 | 2.2362 | 3.11 | 2.97
2,300 | 2.4349 | 3.38 | 3.24
2,200 | 2.6612 | 3.70 | 3.54
2,100 | 2.9207 | 4.06 | 3.88
2,000 | 3.2201 | 4.48 | 4.28
1,900 | 3.568 | 0.0050 | 0.0048
1,800 | 3.975 | 0.0055 | 0.0053
1,700 | 4.457 | 0.0062 | 0.0059
1,600 | 5.031 | 0.0070 | 0.0067
1,500 | 5.725 | 0.0080 | 0.0076
1,400 | 6.572 | 0.0091 | 0.0087
1,300 | 7.622 | 0.0106 | 0.0101
1,200 | 8.945 | 0.0124 | 0.0119
1,100 | 10.645 | 0.0148 | 0.0142
1,000 | 12.880 | 0.0179 | 0.0171
900 | 15.902 | 0.0221 | 0.0211
800 | 20.126 | 0.0280 | 0.0268
700 | 26.287 | 0.0365 | 0.0350
600 | 35.779 | 0.0497 | 0.0476
500 | 51.521 | 0.0716 | 0.0685
400 | 80.502 | 0.1119 | 0.1071
300 | 143.115 | 0.1989 | 0.1903
200 | 322.008 | 0.4476 | 0.4282
100 | 1,288.034 | 1.7904 | 1.7131
60 | 3,577.871 | 4.9732 | 4.7586
50 | 5,152.135 | 7.1613 | 6.8521
1 |12,880,337.930 | 17,903.6700 | 17,130.8500
------------+----------------+-------------+--------------
In the foregoing tables all dimensions are given in meters and
millimeters. If it is desirable to express them in feet and inches,
the necessary conversion can be at once effected in any given case
by employing the following conversion table, which will prove of
considerable value to the watchmaker for various purposes:
Conversion Table of Inches, Millimeters and French Lines.
===============================
Inches expressed in
Millimeters and French Lines.
-------------------------------
| Equal to
+-----------------------
Inches. |Millimeters.| French
| | Lines.
-------+------------+----------
1 | 25.39954 | 11.25951
2 | 50.79908 | 22.51903
3 | 76.19862 | 33.77854
4 | 101.59816 | 45.03806
5 | 126.99771 | 56.29757
6 | 152.39725 | 67.55709
7 | 177.79679 | 78.81660
8 | 203.19633 | 90.07612
9 | 228.59587 | 101.33563
10 | 253.99541 | 112.59516
-------------------------------
================================
Millimeters expressed in
Inches and French Lines.
--------------------------------
| Equal to
+--------------------
Millimeters.| Inches. | French
| | Lines.
-----------+-----------+--------
1 | 0.0393708 | 0.44329
2 | 0.0787416 | 0.88659
3 | 0.1181124 | 1.32989
4 | 0.1574832 | 1.77318
5 | 0.1968539 | 2.21648
6 | 0.2362247 | 2.65978
7 | 0.2755955 | 3.10307
8 | 0.3149664 | 3.54637
9 | 0.3543371 | 3.98966
10 | 0.3937079 | 4.43296
--------------------------------
==============================
French Lines expressed in
Inches and Millimeters.
------------------------------
| Equal to
+-----------------------
French| Inches. |Millimeters.
Lines.| |
------+----------+------------
1 | 0.088414 | 2.25583
2 | 0.177628 | 4.51166
3 | 0.266441 | 6.76749
4 | 0.355255 | 9.02332
5 | 0.444069 | 11.27915
6 | 0.532883 | 13.53497
7 | 0.621697 | 15.79080
8 | 0.710510 | 18.04663
9 | 0.799324 | 20.30246
10 | 0.888138 | 22.55829
11 | 0.976952 | 24.81412
12 | 1.065766 | 27.06995
------------------------------
CENTER OF GRAVITY.—The watchmaker is concerned only with the
theoretical or timekeeping lengths of pendulums, as his pendulum comes
to him ready for use; but the clock maker who has to _build_ the
pendulum to fit not only the movement, but also the case, needs to know
more about it, as he must so distribute the weight along its length
that it may be given a length of 60 inches or of 44 inches, or anything
between them, and still beat seconds, in the case of a regulator. He
must also do the same thing in other clocks having pendulums which
beat other numbers than 60. Therefore he must know the center of his
weights; this is called the center of gravity. This center of gravity
is often confused by many with the center of oscillation as its real
purpose is not understood. It is simply used as a starting point in
_building_ pendulums, because there must be a starting point, and
this point is chosen because it is always present in every pendulum
and it is convenient to work both ways from the center of weight or
gravity. In Fig. 2 we have two pendulums, in one of which (the ball and
string) the center of gravity is the center of the ball and the center
of oscillation is also at the center (practically) of the ball. Such
a pendulum is about as short as it can be constructed for any given
number of oscillations. The other (the rod) has its center of gravity
manifestly at the center of the rod, as the rod is of the same size
throughout; yet we found by comparison with the other that its center
of oscillation was at two-thirds the length of the rod, measured from
the point of suspension, and the _real_ length of the pendulum was
consequently one-half longer than its _timekeeping_ length, which is
at the center of oscillation. This is farther apart than the center
of gravity and oscillation will ever get in actual practice, the most
extreme distance in practice being that of the gridiron pendulum
previously mentioned. The center of gravity of a pendulum is found at
that point at which the pendulum can be balanced horizontally on a
knife edge and is marked to measure from when cutting off the rod.
The center of oscillation of a compound pendulum must always be below
its center of gravity an amount depending upon the proportions of
weight between the rod and the bob. Where the rod is kept as light as
it should be in proportion to the bob this difference should come well
within the limits of the adjusting screw. In an ordinary plain seconds
pendulum, without compensation, with a bob of eighteen or twenty pounds
and a rod of six ounces, the difference in the two points is of no
practical account, and adjustments for seconds are within the screw of
any ordinary pendulum, if the screw is the right length for safety, and
the adjusting nut is placed in the middle of the length of the screw
threads when the top of the rod is cut off, to place the suspension
spring by measurement from the center of gravity as has been already
described; also a zinc and iron compensation is within range of the
screw if the compensating rods are not made in undue weight to the
bob. The whole weight of the compensating parts of a pendulum can be
safely made within one and a half pounds or lighter, and carry a bob
of twenty-five pounds or over without buckling the rods, and the two
points, the center of gravity and the center of oscillation, will be
within the range of the screw.
There are still some other forces to be considered as affecting the
performance of our pendulum. These are the resistance to its momentum
offered by the air and the resistance of the suspension spring.
BAROMETRIC ERROR.—If we adjust a pendulum in a clock with an air-tight
case so that the pendulum swings a certain number of degrees of arc,
as noted on the degree plate in the case at the foot of the pendulum,
and then start to pump out the air from the case while the clock is
running, we shall find the pendulum swinging over longer arcs as the
air becomes less until we reach as perfect a vacuum as we can produce.
If we note this point and slowly admit air to the case again we shall
find that the arcs of the pendulum’s swing will be slowly shortened
until the pressure in the case equals that of the surrounding air, when
they will be the same as when our experiment was started. If we now
pump air into our clock case, the vibrations will become still shorter
as the pressure of the air increases, proving conclusively that the
resistance of the air has an effect on the swinging of the pendulum.
We are accustomed to measure the pressure of the air as it changes
in varying weather by means of the barometer and hence we call the
changes in the swing of the pendulum due to varying air pressure
the “barometric error.” The barometric error of pendulums is only
considered in the very finest of clocks for astronomical observatories,
master clocks for watch factories, etc., but the resistance of the air
is closely considered when we come to shape our bob. This is why bobs
are either double-convex or cylindrical in shape, as these two forms
offer the least resistance to the air and (which is more important)
they offer equal resistance on both sides of the center of the bob and
thus tend to keep the pendulum swinging in a straight line back and
forth.
[Illustration: Fig. 4. A, arc of circle. B, cycloid path of pendulum,
exaggerated.]
THE CIRCULAR ERROR.—As the pendulum swings over a greater arc it
will occupy more time in doing it and thus the rate of the clock
will be affected, if the barometric changes are very great. This is
called the circular error. In ancient times, when it was customary to
make pendulums vibrate at least fifteen degrees, this error was of
importance and clock makers tried to make the bob take a cycloidal
path, as is shown in Fig. 4, greatly exaggerated. This was accomplished
by suspending the pendulum by a cord which swung between cycloidal
checks, but it created so much friction that it was abandoned in favor
of the spring as used to-day. It has since been proved that the long
and short arcs of the pendulum’s vibration are practically isochronous
(with a spring of proper length and thickness) up to about six degrees
of arc (three degrees each side of zero on the degree plate at the foot
of the pendulum) and hence small variations of power in spring operated
clocks and also the barometric error are taken care of, except for
greatly increased variations of power, or for too great arcs of
vibration. Here we see the reasons for and the amount of swing we can
properly give to our pendulum.
TEMPERATURE ERROR.—The temperature error is the greatest which we
shall have to consider. It is this which makes the compound pendulum
necessary for accurate time, and we shall consequently give it a great
amount of space, as the methods of overcoming it should be fully
understood.
EXPANSION OF METALS.—The materials commonly used in making pendulums
are wood (deal, pine and mahogany), steel, cast iron, zinc, brass
and mercury. Wood expands .0004 of its length between 32° and 212°
F.; lead, .0028; steel, .0011; mercury, .0180; zinc, .0028; cast
iron, .0011; brass, .0020. Now the length of a seconds pendulum,
by our tables (3600 beats per hour) is 0.9939 meter; if the rod is
brass it will lengthen .002 with such a range of temperature. As this
is practically two-thousandths of a meter, this is a gain of two
millimeters, which would produce a variation of one minute and forty
seconds every twenty-four hours; consequently a brass rod would be a
very bad one.
If we take two of these materials, with as wide a difference in
expansion ratios as possible, and use the least variable for the rod
and the other for the bob, supporting it at the bottom, we can make the
expansion of the rod counterbalance the expansion of the bob and thus
keep the effective length of our pendulum constant, or nearly so. This
is the theory of the compensating pendulum.
CHAPTER III.
COMPENSATING PENDULUMS.
As the pendulum is the means of regulating the time consumed in
unwinding the spring or weight cord by means of the escapement, passing
one tooth of the escape wheel at each end of its swing, it will readily
be seen that lengthening or shortening the pendulum constitutes the
means of regulating the clock; this would make the whole subject a very
simple affair, were it not that the reverse proposition is also true;
viz.; Changing the length of the pendulum will change the rate of the
clock and after a proper rate has been obtained further changes are
extremely undesirable. This is what makes the temperature error spoken
of in the preceding chapter so vexatious where close timing is desired
and why as a rule, a well compensated pendulum costs more than the rest
of the clock. The sole reason for the business existence of watch and
clockmakers lies in the necessity of measuring time, and the accuracy
with which it may be done decides in large measure the value of any
watchmaker in his community. Hence it is of the utmost importance that
he shall provide himself with an accurate means of measuring time, as
all his work must be judged finally by it, not only while he is working
upon time-measuring devices, but also after they have passed into the
possession of the general public.
A good clock is one of the very necessary foundation elements,
contributing very largely to equip the skilled mechanic and verify
his work. Without some reliable means to get accurate mean time a
watchmaker is always at sea—without a compass—and has to trust to
his faith and a large amount of guessing, and this is always an
embarrassment, no matter how skilled he may be in his craft, or adept
in guessing. What I want to call particular attention to is the
unreliable and worthless character of the average regulator of the
present day. A good clock is not necessarily a high priced instrument
and it is within the reach of most watchmakers. A thoroughly good and
reliable timekeeper of American make is to be had now in the market for
less than one hundred dollars, and the only serious charge that can
be made against these clocks is that they cost the consumer too much
money. Any of them are thirty-three and a third per cent higher than
they should be. About seventy-five dollars will furnish a thoroughly
good clock. The average clock to be met with in the watchmakers’ shops
is the Swiss imitation gridiron pendulum, pin escapement, and these
are of the low grades as a rule; the best grades of them rarely ever
get into the American market. Almost without exception, the Swiss
regulator, as described, is wholly worthless as a standard, as the
pendulums are only an imitation of the real compensated pendulum. They
are an imitation all through, the bob being hollow and filled with
scrap iron, and the brass and steel rods composing the compensating
element, along with the cross-pieces or binders, are all of the
cheapest and poorest description. If one of these pendulums was taken
away from the movement and a plain iron bob and wooden rod put to
the movement, in its place, the possessor of any such clock would
be surprised to find how much better average rate the clock would
have the year through, although there would then be no compensating
mechanism, or its semblance, in the make-up of the pendulum. In brief,
the average imitation compensation pendulum of this particular variety
is far poorer than the simplest plain pendulum, such as the old style,
grandfather clocks were equipped with. A wood rod would be far superior
to a steel one, or any metal rod, as may be seen by consulting the
expansion data given in the previous chapter.
Many other pendulums that are sold as compensating are a delusion
in part, as they do not thoroughly compensate, because the elements
composing them are not in equilibrium or in due proportion to one
another and to the general mechanism.
To all workmen who have a Swiss regulator, I would say that the
movement, if put into good condition, will answer very well to maintain
the motion of a good pendulum, and that it will pay to overhaul these
movements and put to them good pendulums that will pretty nearly
compensate. At least a well constructed pendulum will give a very
useful and reliable rate with such a motor, and be a great help and
satisfaction to any man repairing and rating good watches.
The facts are, that one of the good grade of American adjusted watch
movements will keep a much steadier rate when maintained in one
position than the average regulator. Without a reliable standard to
regulate by, there is very little satisfaction in handling a good
movement and then not be able to ascertain its capabilities as to rate.
Very many watch carriers are better up in the capabilities of good
watches than many of our American repairers are, because a large per
cent of such persons have bought a watch of high grade with a published
rate, and naturally when it is made to appear to entirely lack a
constant rate when compared with the average regulator, they draw
the conclusion that the clock is at fault, or that the cleaning and
repairing are. Many a fair workman has lost his watch trade, largely
on account of a lack of any kind of reliable standard of time in his
establishment. There are very few things that a repairer can do in the
way of advertising and holding his customers more than to keep a good
clock, and furnish good watch owners a means of comparison and thus to
confirm their good opinions of their watches.
We have along our railroads throughout the country a standard time
system of synchronized clocks, which are an improvement over no
standard of comparison; but they cannot be depended upon as a reliable
standard, because they are subject to all the uncertainties that affect
the telegraph lines—bad service, lack of skill, storms, etc. The clocks
furnished by these systems are not reliable in themselves and they
are therefore corrected once in twenty-four hours by telegraph, being
automatically set to mean time by the mechanism for that purpose, which
is operated by a standard or master clock at some designated point in
the system.
Now all this is good in a general way; but as a means to regulate a
fine watch and use as a standard from day to day, it is not adequate. A
standard clock, to be thoroughly serviceable, must always, all through
the twenty-four hours, have its seconds hand at the correct point at
each minute and hour, or it is unreliable as a standard. The reason is
that owing to train defects watches may vary back and forth and these
errors cannot be detected with a standard that is right but once a
day. No man can compare to a certainty unless his standard is without
variation, substantially; and I do not know of any way that this can
be obtained so well and satisfactorily as through the means of a
thoroughly good pendulum.
Compensating seconds pendulums are, it might be said, the standard time
measure. Mechanically such a pendulum is not in any way difficult of
execution, yet by far the greater portion of pendulums beating seconds
are not at all accurate time measures, as independently of their slight
variations in length, any defects in the construction or fitting of
their parts are bound to have a direct effect upon the performance of
the clock. The average watchmaker as a mechanic has the ability to do
the work properly, but he does not fully understand or realize what is
necessary, nor appreciate the fact that little things not attended to
will render useless all his efforts.
The first consideration in a compensated pendulum is to maintain the
center of oscillation at a fixed distance from the point of suspension
and it does not matter how this is accomplished.
So, also, the details of construction are of little consequence, so
long as the main points are well looked after—the perfect solidity
of all parts, with very few of them, and the free movement of all
working surfaces without play, so that the compensating action may
be constantly maintained at all times. Where this is not the case
the sticking, rattling, binding or cramping of certain parts will
give different rates at different times under the same variations of
temperature, according as the parts work smoothly and evenly or move
only by jerks.
The necessary and useful parts of a pendulum are all that are really
admissible in thoroughly good construction. Any and all pieces attached
by way of ornament merely are apt to act to the prejudice of the
necessary parts and should be avoided. In this chapter we shall give
measurements and details of construction for a number of compensated
pendulums of various kinds, as that will be the best means of arriving
at a thorough understanding of the subject, even if the reader does not
desire to construct such a pendulum for his own use.
PRINCIPLES OF CONSTRUCTION.—Compensation pendulums are constructed upon
two distinct principles. First, those in which the bob is supported by
the bottom, resting on the adjusting screw with its entire height free
to expand upward as the rod expands downward from its fixed point of
suspension. In this class of pendulums the error of the bob is used
to counteract that of the rod and if the bob is made of sufficiently
expansible metal it only remains to make the bob of sufficient height
in proportion to its expansibility for one error to offset the other.
In the second class the attempt is made to leave out of consideration
any errors caused by expansion of the bob, by suspending it from
the center, so that its expansion downward will exactly balance its
expansion upward and hence they will balance each other and may be
neglected. Having eliminated the bob from consideration by this means
we must necessarily confine our attempt at compensation to the rod in
the second method.
The wood rod and lead bob and the mercurial pendulums are examples of
the first-class and the wood rod with brass sleeve having a nut at
the bottom and reaching to the center of the iron bob and the common
gridiron, or compound tubular rod, or compound bar of steel and brass,
or steel and zinc, are examples of the second class.
WOOD ROD AND ZINC BOB.—We will suppose that we have one of the Swiss
imitation gridiron pendulums which we want to discard, while retaining
the case and movement. As these cases are wide and generally fitted
with twelve-inch dials, we shall have about twenty inches inside our
case and we may therefore use a large bob, lens-shaped, made of cast
zinc, polished and lacquered to look like brass.
The bobs in such imitation gridiron pendulums are generally about
thirteen inches in diameter and swing about five inches (two and a half
inches each side). The pendulums are generally light, convex in front
and flattened at the rear, and the entire pendulum measures about 56
inches from the point of suspension to the lower end of the adjusting
screw. We will also suppose that we desire to change the appearance of
the clock as little as possible, while improving its rate. This will
mean that we desire to retain a lens-shaped bob of about the same size
as the one we are going to remove.
We shall first need to know the total length of our pendulum, so that
we can calculate the expansion of the rod. A seconds pendulum measures
39.2 inches from the point in the suspension spring at the lower edge
of the chops to the center of oscillation. With a lens-shaped bob the
center of gravity will be practically at the center of the bob, if
we use a light wooden rod and a steel adjusting screw and brass nut,
as these metal parts, although short, will be heavy enough to nearly
balance the suspension spring and that portion of the rod which is
above the center. We shall also gain a little in balance if we leave
the steel screw long enough to act as an index over the degree plate,
in the case, at the bottom of the pendulum, by stripping the thread and
turning the end to a taper an inch or so in length.
We shall only be able to use one-half of the expansion upwards of our
bob, because the centers of gravity and oscillation will be practically
together at the center of the bob. We shall find the center of gravity
easily by balancing the pendulum on a knife edge and thus we will be
able to make an exceedingly close guess at the center of oscillation.
Now, looking over our data, we find that we have a suspension spring
of steel, then some wood and steel again at the other end. We shall
need about one inch of suspension spring. The spring will, of course,
be longer than one inch, but we shall hold it in iron chops and the
expansion of the chops will equal that of the spring between them, so
that only the free part of the spring need be considered. Now from the
adjusting screw, where it leaves the last pin through the wood, to the
middle position of the rating nut will be about one inch, so we shall
have two inches of steel to consider in our figures of expansion.
Now to get the length of the rod. We want to keep our bob about the
size of the other, so we will try 14 inches diameter, as half of this
is an even number and makes easy figuring in our trials. 39.2 inches,
plus 7 (half the diameter of the bob) gives us 46.2 inches; now we
have an inch of adjustment in our screw, so we can discard the .2;
this leaves us 46 inches of wood and steel for which we must get the
expansion.
Wood expands .0004 of its length between 32° and 212° F.
Steel expands .0011 of its length between 32° and 212° F.
Lead expands .0028 of its length between 32° and 212° F.
Brass expands .0020 of its length between 32° and 212° F.
Zinc expands .0028 of its length between 32° and 212° F.
Tin expands .0021 of its length between 32° and 212° F.
Antimony expands .0011 of its length between 32° and 212° F.
Total length of pendulum to adjusting nut 46 inches.
Total length of steel to adjusting nut 2 inches.
Total length of wood to adjusting nut 44 inches.
.0011 × 2 = .0022 inch, expansion of our steel.
.0004 × 44 = .0176 inch, expansion of our wood.
————
.0198 total expansion of rod.
We have 7 inches as half the diameter of our bob .0198 ÷ 7 = .0028,
²/₇, which we find from our tables is very close to the expansion of
zinc, so we will make the bob of that metal. Now let us check back; the
upward expansion of 7 inches of zinc equals .0028 × 7 = .0196 inch, as
against .0198 inch downward expansion of the rod. This gives us a total
difference of .0002 inch between 32° and 212° or a range of 180° F.
This is a difference of .0001 inch for 90° of temperature and is closer
than most pendulums ever get.
The above figures are for dry, clear white pine, well baked and
shellacked, with steel of average expansion, and zinc of new metal,
melted and cast without the admixtures of other metals or the formation
of oxide. The presence of tin, lead, antimony and other admixtures
in the zinc would of course change the results secured; so also will
there be a slight difference in the expansion of the rod if other
woods are used. Still the jeweler can from the above get a very close
approximation.
[Illustration: Fig. 5. Zinc bob and wood rod to replace imitation
gridiron pendulum.]
Such a bob, 14 inches diameter and 1.5 inches thick, alike on both
sides, with an oval hole 1 × .5 inches through its center, see Fig. 5,
would weigh about 30 to 32 pounds, and would have to be hung from a
cast iron bracket, Fig. 6, bolted through the clock case to the wall
behind it, so as to get a steady rate. It would be nearly constant, as
the metal is spread out so as to be quickly affected by temperature;
and the shape would hold it well in its plane of oscillation, if both
sides were of exactly the same curvature, while the weight would
overcome minor disturbances due to vibration of the building. It would
require a little heavier suspension spring, in order to be isochronous
in the long and short arcs and this thickening of the spring would
need the addition of from one and a half to two pounds more of driving
weight.
[Illustration: Fig. 6. Cast iron bracket for heavy pendulums and
movements.]
If so heavy a pendulum is deemed undesirable, the bob would have to
be made of cylindrical form, retaining the height, as necessary to
compensation, and varying the diameter of the cylinder to suit the
weight desired.
[Illustration: Fig. 7. Wood rod and lead bob.
Fig. 8. Bob of metal casing filled with shot.]
WOOD ROD AND LEAD BOB.—The wood should be clear, straight-grained and
thoroughly dried, then given several coats of shellac varnish, well
baked on. It may be either flat, oval or round in section, but is
generally made round because the brass cap at the upper end, the lining
for the crutch, and the ferrule for the adjusting screw at the lower
end may then be readily made from tubing. For pendulums smaller than
one second, the wood is generally hard, as it gives a firmer attachment
of the metal parts.
Inches.
Length, top of suspension spring to bottom of bob 44.5
Length to bottom of nut 45.25
Diameter of bob 2.0
Length of bob 10.5
Weight of bob, 8 lbs.
Acting length of suspension spring 1.0
Width of spring .45
Thickness .008
Diameter of rod .5
The top of the rod should have a brass collar fixed on it by riveting
through the rod and it should extend down the rod about three inches,
so as to make a firm support for the slit to receive the lower clip of
the suspension spring. The lower end should have a slit or a round hole
drilled longitudinally three inches up the rod to receive the upper
end of the adjusting screw and this should also fit snugly and be well
pinned or riveted in place. See Fig. 7. A piece of thin brass tube
about one inch in length is fitted over the rod where the crutch works.
In casting zinc and lead bobs, especially those of lens-shapes, the
jeweler should not attempt to do the work himself, but should go to
a pattern maker, explain carefully just what is wanted and have a
pattern made, as such patterns must be larger than the casting in
order to take care of the shrinkage due to cooling the molten metal.
It will also be better to use an iron core, well coated with graphite
when casting, as the core can be made smooth throughout and the exact
shape of the pendulum rod, and there will then be no work to be done
on the hole when the casting is made. The natural shrinkage of the
metal on cooling will free the core, which can be easily driven out
when the metal is cold and it will then leave a smooth, well shaped
hole to which the rod can be fitted to work easily, but without shake.
Lens-shaped bobs, particularly, should be cast flat, with register
pins on the flask, so as to get both sides central with the hole, and
be cast with a deep riser large enough to put considerable pressure of
melted metal on the casting until it is chilled, so as to get a sound
casting; it should be allowed to remain in the sand until thoroughly
cold, for the same reason, as if cooled quickly the bob will have
internal stresses which are liable to adjust themselves sometime
after the pendulum is in the clock and thus upset the rate until such
interior disturbances have ceased. Cylinders may be cast in a length of
steel tubing, using a round steel core and driven out when cold.
If using oval or flat rods of wood, the adjusting screw should be
flattened for about three inches at its upper end, wide enough to
conform to the width of the rod; then saw a slot in the center of the
rod, wide and deep enough to just fit the flattened part of the screw;
heat the screw and apply shellac or lathe wax and press it firmly
into the slot with the center of the screw in line with the center of
the rod; after the wax is cold select a drill of the same size as the
rivet wire; drill and rivet snugly through the rod, smooth everything
carefully and the job is complete.
If by accident you have got the rod too small for the hole, so that
there is any play, give the rod another coat of shellac varnish and
after drying thoroughly, sand paper it down until it will fit properly.
Round rods may be treated in the same manner, but it is usual to drill
a round hole in such a rod to just fit the wire, then insert and rivet
as before after the wax is cold, finishing with a ferrule or cap of
brass at the end of the rod.
The slot for the suspension spring is fitted to the upper end of the
rod in the same manner.
PENDULUM WITH SHOT.—Still another method of making a compensating
pendulum, which gives a lighter pendulum, is to make a case of light
brass or steel tubing of about three inches diameter. Fig. 8, with a
bottom and top of equal weight, so as to keep the center of oscillation
about the center of gravity, for convenience in working. The bottom may
be turned to a close fit, and soldered, pinned, or riveted into the
tube. It is pierced at its center and another tube of the same material
as the outer tube, with an internal diameter which closely fits the
pendulum rod is soldered or riveted into the center of the bottom, both
bottom and top being pierced for its admission and the other parts
fitted as previously described.
The length of the case or canister should be about 11.5 inches so as to
give room for a column of shot of 10.5 inches (the normal compensating
height for lead) and still leave room for correction. Make a tubular
case for the driving weight also and then we have a flexible system.
If it is necessary to add or subtract weight to obtain the proper arcs
of oscillation of the pendulum, it can be readily done by adding to or
taking from the shot in the weight case.
Fill the pendulum to 10.5 inches with ordinary sportsmen’s shot
and try it for rate. If it gains in heat and loses in cold it is
over-compensated and shot must be taken from it. If it loses in heat
and gains in cold it is under-compensated and shot should be added.
The methods of calculation were given in full in describing the zinc
pendulum and hence need not be repeated here, but attention should
be called to the fact that there are three materials here, wood,
steel or brass and lead and each should be figured separately so that
the last two may just counterbalance the first. If the case is made
light throughout the effect upon the center of oscillation will be
inappreciable as compared with that of the lead, but if made heavier
than need be, it will exert a marked influence, particularly if its
highest portion (the cover) be heavy, as we then have the effect of
a shifting weight high up on the pendulum rod. If made of thin steel
throughout and nickel plated, we shall have a light and handsome case
for our bob. If this is not practicable, or if the color of brass be
preferred, it may be made of that material.
The following table of weights will be of use in making calculations
for a pendulum or for clock weights.
Weight of Lead, Zinc and Cast Iron Cylinders One-Half Inch Long.
-----------+------------------------
| Weight in Pounds.
Diameter +--------+-------+-------
in Inches. | Lead | Zinc | Iron
-----------+--------+-------+-------
.25 | .020 | .012 | .012
.5 | .080 | .049 | .050
.75 | .180 | .111 | .114
1. | .321 | .198 | .204
1.25 | .503 | .310 | .319
1.5 | .724 | .447 | .459
1.75 | .984 | .607 | .624
2. | 1.287 | .794 | .816
2.25 | 1.630 | 1.005 | 1.033
2.5 | 2.009 | 2.239 | 1.274
2.75 | 2.434 | 1.502 | 1.544
3. | 2.897 | 1.788 | 1.837
3.25 | 3.400 | 2.098 | 2.156
3.5 | 3.944 | 2.434 | 2.491
3.75 | 4.51 | 2.783 | 2.865
4. | 5.149 | 3.177 | 3.265
4.25 | 5.813 | 3.587 | 3.686
4.5 | 6.519 | 3.922 | 4.134
4.75 | 7.265 | 4.483 | 4.607
5. | 8.048 | 4.966 | 5.103
5.25 | 8.872 | 5.474 | 5.626
5.5 | 9.737 | 6.008 | 5.175
5.75 | 10.643 | 6.567 | 6.749
6. | 11.590 | 7.152 | 7.350
-----------+--------+-------+-------
Example:—Required, the weight of a lead pendulum
bob, 3 inches diameter, 9 inches long, which has a
hole through it .75 inch in diameter. The weight of
a lead cylinder 3 inches diameter in the table is
2.897, which multiplied by 9 (the length given) =
26.07 lbs. Then the weight in the table of a cylinder
.75 inch diameter is .18 and .18 × 9 = 1.62 lbs. And
26.07 - 1.62 = 24.45, the weight required in lbs.
AUXILIARY WEIGHTS.—If for any reason our pendulum does not turn out
with a rating as calculated and we find after getting it to time that
it is over-compensated, it is a comparatively simple matter to turn off
a portion from the bottom of a solid bob. By doing this in very small
portions at a time and then testing carefully for heat and cold every
time any amount has been removed, we shall in the course of a few weeks
arrive at a close approximation to compensation, at least as close as
the ordinary standards available to the jeweler will permit. This is a
matter of weeks, because if the pendulum is being rated by the standard
time which is telegraphed over the country daily at noon, the jeweler,
as soon as he gets his pendulum nearly right, will begin to discover
variations in the noon signal of from .2 to 5 seconds on successive
days. Then it becomes a matter of averages and reasoning, thus: If the
pendulum beats to time on the first, second, third, fifth and seventh
days, it follows that the signal was incorrect—slow or fast—on the
fourth and sixth days.
If the pendulum shows a gain of one second a week on the majority
of the days, the observation must be continued without changing the
pendulum for another week. If the pendulum shows two seconds gain at
the end of this time, we have two things to consider. Is the length
right, or is the pendulum not fully compensated? We cannot answer the
second query without a record of the temperature variations during the
period of observations.
To get the temperature record we shall require a set of maximum and
minimum thermometers in our clock case. They consist of mercurial
thermometer tubes on the ordinary Fahrenheit scales, but with a marker
of colored wood or metal resting on the upper end of the column of
mercury in the tube. The tube is not hung vertically, but is placed in
an inclined position so that the mark will stay where it is pushed by
the column of mercury. Thus if the temperature rises during the day to
84 degrees the mark in the maximum thermometer will be found resting in
the tube at 84° whether the mercury is there when the reading is taken
or not. Similarly, if the temperature has dropped during the night to
40°, the mark in the minimum thermometer will be found at 40°, although
the temperature may be 70° when the reading is taken. After reading,
the thermometers are shaken to bring the marks back to the top of the
column of mercury and the thermometers are then restored to their
positions, ready for another reading on the following day.
These records should be set down on a sheet every day at noon in
columns giving date, rate, plus or minus, maximum, minimum, average
temperature and remarks as to regulation, etc., and with these data to
guide us we shall be in a position to determine whether to move the
rating nut or not. If the temperature has been fairly constant we can
get a closer rate by moving the nut and continuing the observations. If
the temperature has been increasing steadily and our pendulum has been
gaining steadily it is probably over-compensated and the bob should be
shortened a trifle and the observations renewed.
It is best to “make haste slowly” in such a matter. First bring the
pendulum to time in a constant temperature; that will take care of its
proper length. Then allow the temperature to vary naturally and note
the results.
If the pendulum is under-compensated, so that the bob is too short to
take care of the expansion of the rod, auxiliary weights of zinc in the
shape of washers (or short cylinders) are placed between the bottom
of the bob and the rating nut. This of course makes necessary a new
adjustment and another course of observations all around, but it will
readily be seen that it places a length of expansible metal between the
nut and the center of oscillation and thus makes up for the deficiency
of expansion of the bob. Zinc is generally chosen on account of its
high rate of expansion, but brass, aluminum and other metals are also
used. It is best to use one thick washer, rather than a number of
thinner ones, as it is important to keep the construction as solid at
this point as possible.
TOP WEIGHTS.—After bringing the pendulum as close as possible by the
compensation and the rating nuts, astronomers and others requiring
exact time get a trifle closer rating by the use of top weights. These
are generally U-shaped pieces of thin metal which are slipped on the
rod above the bob without stopping the pendulum. They raise the center
of oscillation by adding to the height of the bob when they are put
on, or lower it when they are removed, but they are never resorted to
until long after the pendulum is closer to time than the jeweler can
get with his limited standards of comparison. They are mentioned here
simply that their use may be understood when they may be encountered in
cleaning siderial clocks.
Mercurial pendulums also belong to the class of compensation by
expansion of the bobs, but they are so numerous and so different that
they will be considered separately, later on.
COMPENSATED PENDULUM RODS.—We will now consider the second class, that
in which an attempt is made to obtain a pendulum rod of unvarying
length.
The oldest form of compensated rod is undoubtedly the gridiron of
either nine, five or three rods. As originally made it was an accurate
but expensive proposition, as the coefficients of expansion of the
brass or zinc and iron or steel had all to be determined individually
for each pendulum. Each rod had to be sized accurately, or if this was
not done, then each rod had to be fitted carefully to each hole in the
cross bars so as to move freely, without shake. The rods were spread
out for two purposes, to impress the public and to secure uniform and
speedy action in changes of temperature. The weight, which increased
rapidly with the increase of diameter of the rod, made a long and large
seconds pendulum, some of them measuring as much as sixty-two inches in
length, and needing a large bob to look in proportion. Various attempts
were made to ornament the great expanse of the gridiron, harps, wreaths
and other forms in pierced metal being screwed to the bars. The next
advance was in substituting tubes for rods in the gridiron, securing an
apparently large rod that was at the same time stiff and light. Then
came the era of imitation, in which the rods were made of all brass,
the imitation steel portion being nickel plated. With the development
of plating they were still further cheapened by being made of steel,
with the supposedly brass rods plated with brass and the steel ones
with nickel. Thousands of such pendulums are in use to-day; they
have the rods riveted to the cross-pieces and are simply steel rods,
subject to change of length with every change in temperature. It does
no harm to ornament such pendulums, as the rods themselves are merely
ornaments, usually all of one metal, plated to change the color.
As three rods were all that were necessary, the clockmaker who
desired a pendulum that was compensated soon found his most easily
made rod consisted of a zinc bar, wide, thin and flat, placed between
two steel parts, like the meat and bread of a sandwich. This gives
a flat and apparently solid rod of metal which if polished gives a
pleasing appearance, and combines accurate performance with cheapness
of construction, so that any watchmaker may make it himself, without
expensive tools.
[Illustration: Fig. 9. Pendulum with compensated rod of steel and zinc.]
A, the lens-shaped bob; T P, the total length of the compensating part.
R, the upper round part of rod.
The side showing the heads of the screws is the face side and is
finished. The screws 1, 2, 3, 4 hold the three pieces from separating,
but do not confine the front and middle sections in their lengthwise
expansion along the rod, but are screwed into the back iron section,
while the holes in the other two sections are slotted smaller than the
screw heads.
The holes at the lower extreme of combination 5, 6, 7, 8, 9 are for
adjustments in effecting a compensation.
The pin at 10 is the steel adjusting pin, and is only tight in the
front bar and zinc bars, being loose in the back bar.
O and P show the angles in the back rod, T shows the angle in the rod
at the top, m shows the pin as placed in the iron and zinc sections
where they have been soldered as described.
h shows the regulating nut carried by the tube, as described, and
terminating in the nut D.
l and i show the screw of 36 threads.
The nut D is to be divided on its edge into 30 divisions.
n is the angle of the back bar to which zinc is soldered.
FLAT COMPENSATED ROD.—One of the most easily made zinc and iron
compensating pendulums, shown in detail in Fig. 9, is as follows: A
lead or iron bob, lens-shaped, that is, convex equally on each side,
9 inches diameter and an inch and one-quarter thick at the center. A
hole to be made straight through its diameter ½ inch. One-half through
the diameter this hole is to be enlarged to ⅝ inch diameter. This will
make the hole for half of its length ½ inch and the remaining half ⅝
inch diameter. The ⅝ hole must have a thin tube, just fitting it, and
5 inches long. At one end of this tube is soldered in a nut, with a
hole tapped with a tap of thirty-six threads to the inch, and ¼ inch
diameter, and at the other end of the tube is soldered a collar or
disc one inch diameter, which is to be divided into thirty divisions,
for regulating purposes, as will be described later on. The whole
forms a nut into which the rod screws, and the tube allows the nut to
be pushed up to the center of the diameter of the bob, through the
large hole, and the nut can be operated then by means of the disc at
its lower end. The rod, of flat iron, is in two sections, as follows:
That section which enters the bob and terminates in the regulating
screw is flat for twenty-six inches, and then rounded to ½ inch for
six inches, and a screw cut on its end for two inches, to fit the
thread in the nut. The upper end of this section is then to be bent at
a right angle, flatwise. This angle piece will be long enough if only
³/₁₆ inch long, so that it covers the thickness of the zinc center
rod. The zinc center rod is a bar of the metal, hammered or rolled, 25
inches long, ³/₁₆ inch thick, and ¾ inch wide, and comes up against the
angle piece bent on the flat part of the lower section of the rod. Now
the upper section of the rod may be an exact duplicate of the lower
section, with the flat part only a little longer than the zinc bar,
say ½ inch, and the angle turned on the end, as previously described.
The balance of the bar may be forged into a rod of ⁵/₁₆ inch diameter.
As has been stated, the zinc bar is placed against the angle piece
bent on the upper end of the lower section of the rod, P, n, Fig. 9,
and pins must be put through this angle piece into the end of the zinc
bar, to hold it in close contact with the iron bar. The upper section
of the rod is now to be laid on the opposite side of the zinc bar,
with its angle at the other end of the zinc, but not in contact with
it, say ¹/₁₆ inch left between the angle and the zinc bar. Now all is
ready to clamp together—the two flat iron bars with the zinc between
them. After clamping, taking care to have the pinned end of the zinc
in contact with the angle and the free, or lower end, removed from the
other angle about ¹/₁₆ inch, three screws should be put through all
three bars, with their heads all on the side selected for the front,
and one screw may be an inch from the top, another 3 inches from the
bottom, and one-half way between the two first mentioned. Now the rod
is complete in its composite form, and there is left only the little
detail to attend to. Two flat bars, with their ends angled in one case
and rounded in the other into rods of given diameter, confining between
them, as described, a flat bar of wrought zinc of stated length and of
the same thickness and width as the iron bars, comprises the active
or compensating elements of the pendulum’s rod. The screws that are
put through the three bars are each to pass through the front iron
bar, without threads in the bar, and only the back iron bar is to have
the holes tapped, fitting the screws. All the corresponding holes in
the zinc are to be reamed a little larger than the diameter of the
screws, and to be freed lengthwise of the bar, to allow of the bar’s
contracting and expanding without being confined in this action by
the screws. At the lower or free end of the zinc bar are to be holes
carried clear through all three bars, while the combination is held
firmly together by the screws. These holes are to start at ½ inch from
the end of the zinc, and each carried straight through all three bars,
and then broached true and a steel pin made to accurately fit them
from the front side. These holes may be from three to five in number,
extending up to a safe distance from the lower screw. The holes in
the back bar, after boring, are to be reamed larger than those in the
front bar and zinc bar. These holes and the pin serve for adjusting
the compensation. The pin holds the front bar and zinc from slipping,
or moving past one another at the point pinned, and also allows the
back bar to be free of the pin, and not under the influence of the two
front bars. The upper end of the second iron section is, as has been
mentioned, forged into a round rod about ⁵/₁₆ inch diameter, and this
rod or upper end is to receive the pendulum suspension spring, which
may be one single spring, or a compound spring, as preferred.
Now that the pendulum is all ready to balance on the knife edge,
proceed as in the case of the simple pendulum, and ascertain at what
point up the rod the spring must be placed. In this pendulum the rod
will be heavier in proportion than the wood rod was to its bob, and
the center of gravity of the whole will be found higher up in the bob.
However, wherever in the bob the center of gravity is found, that is
the starting point to measure from to find the total length of the rod,
and the point for the spring. The heavier the rod is in relation to the
bob, the higher will the center of gravity of the whole rise in the
bob, and the greater will be the total length of the entire pendulum.
In getting up a rod of the kind just described, the main item is to
get the parts all so arranged that there will be very little settling
of the joints in contact, particularly those which sustain the weight
of the bob and the whole dead weight of the pendulum. The nut in the
center of the pendulum holds the weight of the bob only, but it should
fit against the shoulder formed for the purpose by the juncture of the
two holes, and the face of the nut should be turned true and flat, so
that there may not be any uneven motion, and only the one imparted
by the progressive one of the threads. When this nut is put to its
place for the last time, and after all is finished, there should be a
little tallow put on to the face of the nut just where it comes to a
seat against the shoulder of the bob, as this shoulder being not very
well finished, the two surfaces coming in contact, if left dry, might
cut and tear each other, and help to make the nut’s action slightly
unsteady and unreliable. A finished washer can be driven into this
lower hole up to the center, friction-tight, and serve as a reliable
and finished seat for the nut.
In reality, the zinc at the point of contact, where pinned to the
angle piece at the top of the lower section, is the point of greatest
importance in the whole combination, and if the joint between the
angle and the end of the zinc bar is soldered with soft solder, the
result will be that of greater certainty in the maintenance of a steady
rate. This joint just mentioned can be soldered as follows: File the
end of the zinc and the inside surface of the angle until they fit so
that no appreciable space is left between them. Then, with a soldering
iron, tin the end of the zinc thoroughly and evenly, and then put into
the holes already made the two steady pins. Now tin in the same manner
the surface of the angle, and see that the holes are free of solder, so
that the zinc bar will go to its place easily; then between the zinc
and the iron, place a piece of thin writing paper, so that the flat
surfaces of the zinc and iron may not become soldered. Set the iron
bar upright on a piece of charcoal, and secure it in this position
from any danger of falling, and then put the zinc to its place and see
that the pins enter and that the paper is between the surfaces, as
described. Put the screws into their places, and screw down on the zinc
just enough to hold it in contact with the iron bar, but not so tight
that the zinc will not readily move down and rest firmly on the angle.
Put a little soldering fluid on the tinned joint, and blow with a blow
pipe against the iron bar (not touching the zinc with the flame). When
the solder in the joint begins to flow, press the zinc down in close
contact with the angle, and then cool gradually, and if all the points
described have been attended to the joint will be solidly soldered, and
the two bars will be as one solid bar bent against itself. The tinning
leaves surplus solder on the surfaces sufficient to make a solid joint,
and to allow some to flow into the pin holes and also solder the pin
to avoid any danger of getting loose in after time, and helps make
a much stronger joint. At the time the solder is melted the zinc is
sufficiently heated to become quite malleable, and care must be taken
not to force it down against the angle in making the joint, or it may
be distorted and ruined at the joint. If carefully done the result
will be perfect. The paper between the surfaces burns, and is got
rid of in washing to remove the soldering fluid. Soda or ammonia will
help to remove all traces of the fluid. However, it is best, as a last
operation, to put the joint in alcohol for a minute.
This soldering makes the lower section and the zinc practically one
piece and without loose joint, and the next joint is that made by the
pin pinning the outside bar and the zinc together. This is necessarily
formed this way, as in this stage of the operation we do not know
just what length the zinc bar will be to exactly compensate for the
expansion and contraction of the balance of the pendulum. By the
changing of the pin into the different holes, 5, 6, 7, 8, 9, 10, Fig.
9, the zinc is made relatively longer or shorter, and so a compensation
is arrived at in time after the clock has been running. After it is
definitely settled where the pin will remain to secure the compensation
of the rod, then that hole can have a screw put in to match the three
upper ones. This screw must be tapped into the front bar and the zinc,
and be very free in the back bar to allow of its expansion. It is
supposed that in this example given of a zinc and steel compensation
seconds pendulum that there has been due allowance made in the lengths
of the several bars to allow for adjustment to temperature by the
movements of the pin along the course of the several holes described,
but the zinc is a very uncertain element, and its ultimate action is
largely influenced by its treatment after being cast. Differences of
working cast zinc under the hammer or rolls produce wide differences
practically, and therefore materially change the results in its
combination with iron in their relative expansive action. Wrought zinc
can be obtained of any of the brass plate factories, of any dimensions
required, and will be found to be satisfactory for the purpose in hand.
The adjusting pin should be well fitted to the holes in the front iron
bar, and also fit the corresponding ones in the zinc bar closely, and
if the holes are reamed smooth and true with an English clock broach,
then the pin will be slightly tapering and fit the iron hole perfectly
solid. After one pair of these holes have been reamed, fit the pin
and drive it in place perfectly firm, and then with the broach ream
all the remaining holes to just the same diameter, and then the pin
will move along from one set of holes to another with mechanically
accurate results. Otherwise, if poorly fitted, the full effect would
not be obtained from the compensating action in making changes in the
pin from one set of holes to another. This pin, if made of cast steel,
hardened and drawn to a blue, will on the whole be a very good device
mechanically.
Many means are used to effect the adjustments for compensation, of more
or less value, but whatever the means used, it must be kept in mind
that extra care must be taken to have the mechanical execution first
class, as on this very much depends the steady rate of the pendulum in
after time.
TUBULAR COMPENSATED RODS.—There are tubular pendulums in the market
which have a screw sleeve at the top of the zinc element, and by this
means the adjustments are effected, and this is thought to be a very
accurate mechanism. The most common form of zinc and iron compensation
is where the zinc is a tube combined with one iron tube and a central
rod, as shown in Figs. 10, 11, 12. The rod is the center piece, the
zinc tube next, followed by the iron tube enveloping both. The relative
lengths may be the same as those just given in the foregoing example
with the compensating elements flat. The relative lengths of the
several members will be virtually the same in both combinations.
TUBULAR COMPENSATION WITH ALUMINUM.—The pendulum as seen by an observer
appears to him as being a simple single rod pendulum. Figs. 10 and 12
are front and side views; Fig. 11 is an enlarged view of its parts,
the upper being a sectional view. Its principal features are: The steel
rod S, Fig. 11, 4 mm. in diameter, having at its upper end a hook for
fastening to the suspension spring in the usual way; the lower end has
a pivot carrying the bushing, T, which solidly connects the steel rod,
S, with the aluminum tube, A, the latter being 10 mm. in diameter and
its sides 1.5 mm. in thickness of the wall.
The upper end of the aluminum tube is very close to the pendulum hook
and is also provided with a bushing, P, Fig. 11. This bushing is
permanently connected at the upper end of the aluminum tube with a
steel tube, R, 16 mm. in diameter and 1 mm. in thickness. The outer
steel tube is the only one that is visible and it supports the bob, the
lower part being furnished with a fine thread on which the regulating
nut, O, is movable, at the center of the bob.
For securing a central alignment of the steel rod, S, at its lowest
part, where it is pivoted, a bushing, M, Fig. 11, is screwed into
the steel tube, R. The lower end of the steel tube, R, projects
considerably below the lenticular bob (compare Figs. 10 and 12); and is
also provided with a thread and regulating weight, G (Figs. 10 and 12),
of 100 grammes in weight, which is only used in the fine regulation of
small variations from correct time.
The steel tube is open at the bottom and the index at its lower end is
fastened to a bridge. Furthermore all three of the bushings, P, T and
M, have each three radial cuts, which will permit the surrounding air
to act equally and at the same time on the steel rod, S, the aluminum
tube. A, and the steel tube, R, and as the steel tube, R, is open at
its lower end, and as there is also a certain amount of space between
the tubes, the steel rod, and the radial openings in the bushings,
there will be a draught of air passing through them, which will allow
the thin-walled tubes and thin steel rod to promptly and equally adapt
themselves to the temperature of the air.
[Illustration: Fig. 10. Fig. 11. Fig. 12.]
The lenticular pendulum bob has a diameter of 24 cm., and is made
of red brass. The bob is supported at its center by the regulating
nut, O, Figs. 10 and 12. That the bob may not turn on the cylindrical
pendulum rod, the latter is provided with a longitudinal groove and
working therein are the ends of two shoulder screws which are placed
on the back of the bob above and below the regulating nut, O; and thus
properly controlling its movements.
From the foregoing description the action of the compensation is
readily explained. For the purpose of illustration of its action we
will accept the fact that there has been a sudden rise in temperature.
The steel rod, S, and the tube, R, will lengthen in a downward
direction (including the suspension spring and the pendulum hook),
conversely the aluminum tube, A, which is fastened to the steel rod at
one end and the steel tube at the other, will lengthen in an upward
direction and thus equalize the expansion of the tube, R, and rod, S.
As the coefficients of expansion of steel and aluminum are
approximately at the ratio of 1:2.0313 we find that with such a
pendulum construction—accurate calculations presumed—we shall have a
complete and exact coincidence in its compensation; in other words, the
center of oscillation of the pendulum will be under all conditions at
the same distance from the bending point of the suspension spring.
This style of pendulum is made for astronomical clocks in Europe and
is furnished in two qualities. In the best quality, the tubes, steel
rod, and the bob are all separately and carefully tested as to their
expansion, and their coefficients of expansion fully determined in
a laboratory; the bushings, P and M, are jeweled, all parts being
accurately and finely finished. In the second quality the pendulum is
constructed on a general calculation and finished in a more simple
manner without impairing its ultimate efficiency.
At the upper part of the steel tube, R, there is a funnel-shaped piece
(omitted in the drawing) in which are placed small lead and aluminum
balls for the final regulation of the pendulum without stopping it.
The regulation of this pendulum is effected in three ways:
1. The preliminary or coarse regulation by turning the
regulating nut, O, and so raising or lowering the bob.
2. The finer regulation by turning the 100 grammes
weight, g, having the shape of a nut and turning on
the threaded part of the tube, R. 3. The precision
regulation is effected by placing small lead or
aluminum balls in a small funnel-shaped receptacle
attached to the upper part of the tube, R, or by
removing them therefrom.
It will readily be seen that this form of pendulum can be used with
zinc or brass instead of aluminum, by altering the lengths of the inner
rod and the compensating tube to suit the expansion of the metal it is
decided to use; also that alterations in length may be made by screwing
the bushings in or out, provided that the tube be long enough in the
first place. After securing the right position the bushings should have
pins driven into them through the tube, in order to prevent further
shifting.
CHAPTER IV.
THE CONSTRUCTION OF MERCURIAL PENDULUMS.
Owing to the difficulty of calculating the expansive ratios of metal
which (particularly with brass and zinc) vary slightly with differences
of manufacture, the manufacture of compensated pendulums from metal
rods cannot be reduced to cutting up so many pieces and assembling them
from calculations made previously, so that each must be separately
built and tested. While this is not a great draw-back to the jeweler
who wants to make himself a pendulum, it becomes a serious difficulty
to a manufacturer, and hence a cheaper combination had to be devised to
prevent the cost of compensated pendulums from seriously interfering
with their use. The result was the pendulum composed of a steel rod and
a quantity of mercury, the latter forming the principal weight for the
bob and being contained in steel or glass jars, or jars of cast iron
for the heavier pendulums. Other metals will not serve the purpose, as
they are corroded by the mercury, become rotten and lose their contents.
Mercury has one deficiency which, however, is not serious, except for
the severe conditions of astronomical observatories. It will oxidize
after long exposure to the air, when it must be strained and a fresh
quantity of metal added and the compensation freshly adjusted. To an
astronomer this is a serious objection, as it may interfere with his
work for a month, but to the jeweler this is of little moment as the
rates he demands will not be seriously affected for about ten years, if
the jars are tightly covered.
To construct a reliable gridiron pendulum would cost about fifty
dollars while a mercurial pendulum can be well made and compensated for
about twenty-five dollars, hence the popularity of the latter form.
Zinc will lengthen under severe variations of temperature as the
following will show: Zinc has a decided objectionable quality in its
crystalline structure that with temperature changes there is very
unequal expansion and contraction, and furthermore, that these changes
occur suddenly; this often results in the blending of the zinc rod,
causing a binding to take place, which naturally enough prevents the
correct working of the compensation.
It is probably not very well known that zinc can change its length
at one and the same temperature, and that this peculiar quality must
not be overlooked. The U. S. Lake Survey, which has under its charge
the triangulation of the great lakes of the United States, has in its
possession a steel meter measure, R, 1876; a metallic thermometer
composed, of a steel and zinc rod, each being one meter in length,
marked M. T., 1876s, and M. T. 1876z; and four metallic thermometers,
used in connection with the base apparatus, which likewise are made of
steel and zinc rods, each of these being four meters in length. All
of these rods were made by Repsold, of Hamburg. Comparisons between
these different rods show peculiar variations, and which point to the
fact that their lengths at the same degree of temperature are not
constant. For the purpose of determining these variations accurate
investigations were undertaken. The metallic thermometer M. T. 1876
was removed from an observatory room having an equal temperature
of about 2° C. and placed for one day in a temperature of +24° C.,
and also for the same period of time in one of -20° C; it was then
replaced in the observatory room, where it remained for twenty-four
hours, and comparisons were made during the following three days
with the steel thermometer 1876, which had been left in the room.
From these observations and comparisons the following results were
tabulated, which give the mean lengths of the zinc rods of the metallic
thermometer. The slight variations of temperature in the observatory
room were also taken into consideration in the calculations:
M. T. 1876s. M. T. 1876z.
mm. mm.
February 16-24 - 0.0006 + 0.0152, previous 7 days at + 24°C
February 25-27 - 0.0017 - 0.0011, previous 1 day at - 20°C.
March 2-4 + 0.0005 + 0.0154, previous 1 day at + 24°C.
March 5-8 - 0.0058 - 0.0022, previous 1 day at - 20°C.
These investigations clearly indicate, without doubt, that the zinc rod
at one and the same temperature of about 2° C., is 0.018 mm. longer
after having been previously heated to 24° C. than when cooled before
to -20° C.
A similar but less complete examination was made with the metallic
thermometer four meters in length. These trials were made by that
efficient officer, General Comstock, gave the same results, and
completely prove that in zinc there are considerable thermal
after-effects at work.
To prove that zinc is not an efficient metal for compensation pendulums
when employed for the exact measurement of time, a short calculation
may be made—using the above conclusions—that a zinc rod one meter in
length, after being subjected to a difference of temperature of 44°
C. will alter its length 0.018 mm. after having been brought back to
its initial degree. For a seconds pendulum with zinc compensation
each of the zinc rods would require a length of 64.9 cm. With the
above computations we get a difference in length of 0.0117 mm. at
the same degree of temperature. Since a lengthening of the zinc rods
without a suitable and contemporaneous expansion of the steel rods is
synonymous with a shortening of the effectual pendulum length, we have,
notwithstanding the compensation, a shortening of the pendulum length
of 0.017 mm., which corresponds to a change in the daily rate of about
0.5 seconds.
This will sufficiently prove that zinc is unquestionably not suitable
for extremely accurate compensation pendulums, and as neither is
permanent under extremes of temperature the advantages of first cost
and of correction of error appear to lie with the mercurial form.
The average mercurial compensation pendulums, on sale in the trade
are often only partially compensated, as the mercury is nearly always
deficient in quantity relatively, and not high enough in the jar to
neutralize the action of the rigid metallic elements, composing the
structure. The trouble generally is that the mercury forms too small
a proportion of the total weight of the pendulum bob. There is a
fundamental principle governing these compensating pendulums that has
to be kept in mind, and that is that one of the compensating elements
is expected to just undo what the other does and so establish through
the medium of physical things the condition of the ideal pendulum,
without weight or elements outside of the bob. As iron and mercury,
for instance, have a pretty fixed relative expansive ratio, then
whatever these ratios are after being found, must be maintained in the
construction of the pendulum, or the results cannot be satisfactory.
First, there are 39.2 inches of rod of steel to hold the bob between
the point of suspension and the center of oscillation, and it has
been found that, constructively, in all the ordinary forms of these
pendulums, the height of mercury in the bob cannot usually be less
than 7.5 inches. Second, that in all seconds pendulums the length of
the metal is fixed substantially, while the height of the mercury is a
varying one, due to the differing weights of the jars, straps, etc.
Third, the mercury, at its minimum, cannot with jars of ordinary
weight be less in height in the jar than 7.5 inches, to effectually
counteract what the 39.2 inches of iron does in the way of expanding
and contracting under the same exposure.
Whoever observes the great mass of pendulums of this description on
sale and in use will find that the height of the mercury in the jar
is not up to the amount given above for the least quantity that will
serve under the most favorable circumstances of construction. The less
weight there is in the rod, jar and frame, the less is the height
of mercury which is required; but with most of the pendulums made in
the present day for the market, the height given cannot be cut short
without impairing the quality and efficiency of the compensation. Any
amount less will have the effect of leaving the rigid metal in the
ascendancy; or, in other words, the pendulum will be under compensated
and leave the pendulum to feel heat and cold by raising and lowering
the center of oscillation of the pendulum and hence only partly
compensating. A jar with only six inches in height of mercury will in
round numbers only correct the temperature error about six-sevenths.
CALCULATIONS OF WEIGHTS.—As to how to calculate the amount of mercury
required to compensate a seconds pendulum, the following explanation
should make the matter clear to anyone having a fair knowledge of
arithmetic only, though there are several points to be considered which
render it a rather more complicated process than would appear at first
sight.
1st. The expansion in length of steel and cast iron, as given in
the tables (these tables differ somewhat in the various books), is
respectively .0064 and .0066, while mercury expands .1 in bulk for
the same increase of temperature. If the mercury were contained in a
jar which itself had no expansion in diameter, then all its expansion
would take place in height, and in round numbers it would expand
sixteen times more than steel, and we should only require (neglecting
at present the allowance to be explained under head 3) to make the
height of the mercury—reckoned from the bottom of the jar (inside) to
the middle of the column of mercury contained therein—one-sixteenth of
the total length of the pendulum measured from the point of suspension
to the bottom of the jar, assuming that the rod and the jar are both
of steel, and that the center of oscillation is coincident with the
center of the column of mercury. Practically in these pendulums, the
center of oscillation is almost identical with the center of the bob.
2d. As we cannot obtain a jar having no expansion in diameter, we must
allow for such expansion as follows, and as cast iron or steel jars
of cylindrical shape are undoubtedly the best, we will consider that
material and form only.
As above stated, cast iron expands .0066, so that if the original
diameter of the jar be represented by 1, its expanded diameter will
be 1.0066. Now the area of any circle varies as the square of its
diameter, so that before and after its expansion the areas of the jar
will be in the ratio of 1² to 1.0066²; that is, in the proportion
of 1 to 1.013243; or in round numbers it will be one-seventy-sixth
larger in area after expansion than before. It is evident that the
mercury will then expand sideways, and that its vertical rise will be
diminished to the same extent. Deduct, therefore, the one-seventy-sixth
from its expansion in bulk (one-tenth) and we get one-eleventh (or more
exactly .086757) remaining. This, then, is the actual vertical rise
in the jar, and when compared with the expansion of steel in length
it will be found to be about thirteen and a half times greater (more
exactly 13.556).
The mercury, therefore (still neglecting head No. 3), must be thirteen
and a half times shorter than the length of the pendulum, both being
measured as explained above. The pendulum will probably be 43.5 inches
long to the bottom of the jar; but as about nine inches of it is cast
iron, which has a slightly greater rate of expansion than steel, we
will call the length 44 inches, as the half inch added will make it
about equivalent to a pendulum entirely of steel. If the height of the
mercury be obtained by dividing 44 by 13.5, it will be 3.25 inches high
to its center, or 6.5 inches high altogether; and were it not for the
following circumstance, the pendulum would be perfectly compensated.
3d. The mercury is the only part of the bob which expands upwards;
the jar does not rise, its lower end being carried downward by the
expansion of the rod, which supports it. In a well-designed pendulum,
the jar, straps, etc., will be from one-fourth to one-third the weight
of the mercury. Assume them to be seven pounds and twenty-eight pounds
respectively; therefore, the total weight of the bob is thirty-five
pounds; but as it is only the mercury (four-fifths) of this total that
rises with an increase of temperature, we must increase the weight of
the mercury in the proportion of five to four, thus 6.5 × 5 ÷ 4 = 8⅛
inches. Or, what is the same thing, we add one-fourth to the amount of
mercury, because the weight of the jar is one-fourth of that of the
mercury. Eight and one-eighth inches is, therefore, the ultimate height
of the mercury required to compensate the pendulum with that weight
of jar. If the jar had been heavier, say one-third the weight of the
mercury, then the latter would have to be nearly 8.75 inches high.
If the jar be required to be of glass, then we substitute the expansion
of that material in No. 2 and its weight in No. 3.
In the above method of calculating, there are two slight elements
of uncertainty: 1st. In assuming that the center of oscillation is
coincident with the center of the bob; however, I should suppose that
they would never be more than .25 inch apart, and generally much
nearer. 2d. The weight of the jar cannot well be exactly known until
after it is finished (i. e., bored smooth and parallel inside, and
turned outside true with the interior), so that the exact height of the
mercury cannot be easily ascertained till then.
I may explain that the reason (in Nos. 1 and 2) we measure the mercury
from the bottom to the center of the column, is that it is its center
which we wish to raise when an increase of temperature occurs, so that
the center may always be exactly the same distance from the point of
suspension; and we have seen that 3.25 inches is the necessary quantity
to raise it sufficiently. Now that center could not be the center
without it had as much mercury over it as it has under it; hence we
double the 3.25 and get the 6.5 inches stated.
From the foregoing it will be seen that the average mercury pendulums
are better than a plain rod, from the fact that the mercury is free to
obey the law of expansion, and so, to a certain degree, does counteract
the action of the balance of the metal of the pendulum, and this
with a degree of certainty that is not found in the gridiron form,
provided always that the height and amount of the mercury are correctly
proportional to the total weight of the pendulum.
COMPENSATING MERCURIAL PENDULUMS.—To compensate a pendulum of this
kind takes time and study. The first thing to do is to place maximum
and minimum thermometers in the clock case, so that you can tell the
temperature.
Then get the rate of the clock at a given temperature. For example,
say the clock gains two seconds in twenty-four hours, the temperature
being at 70°. Then see how much it gains when the temperature is at
80°. We will say it gains two seconds more at 80° than it does when the
temperature is at 70°.
In that case we must remove some of the mercury in order to compensate
the pendulum. To do this take a syringe and soak the cotton or whatever
makes the suction in the syringe with vaseline. The reason for doing
this is that mercury is very heavy and the syringe must be air-tight
before you can take any of the mercury up into it.
You want to remove about two pennyweights of mercury to every second
the clock gains in twenty-four hours. Now, after removing the mercury
the clock will lose time, because the pendulum is lighter. You must
then raise the ball to bring it to time. You then repeat the same
operation by getting the rate at 70° and 80° again and see if it gains.
When the temperature rises, if the pendulum still gains, you must
remove more mercury; but if it should lose time when the temperature
rises you have taken out too much mercury and you must replace some.
Continue this operation until the pendulum has the same rate, whether
the temperature is high or low, raising the bob when you take out
mercury to bring it to time, and lowering the bob when you put mercury
in to bring it to time.
To compensate a pendulum takes time and study of the clock, but if you
follow out these instructions you will succeed in getting the clock to
run regularly in both summer and winter.
Besides the oxidation, which is an admitted fault, there are two
theoretical questions which have to do with construction in deciding
between the metallic and mercurial forms of compensation. We will
present the claims of each side, therefore, with the preliminary
statement that (for all except the severest conditions of accuracy)
either form, if well made will answer every purpose and that therefore,
except in special circumstances, these objections are more theoretical
than real.
The advocates of metallic compensation claim that where there are great
differences of temperature, the compensated rod, with its long bars
will answer more quickly to temperature changes as follows:
The mercurial pendulum, when in an unheated room and not subjected to
sudden temperature changes, gives very excellent results, but should
the opposite case occur there will then be observed an irregularity
in the rate of the clock. The causes which produce these effects
are various. As a principal reason for such a condition it may be
stated that the compensating mercury occupies only about one-fifth
the pendulum length, and it inevitably follows that when the upper
strata of the air is warmer than the lower, in which the mercury
is placed, the steel pendulum rod will expand at a different ratio
than the mercury, as the latter is influenced by a different degree
of temperature than the upper part of the pendulum rod. The natural
effect will be a lengthening of the pendulum rod, notwithstanding the
compensation, and therefore, a loss of time by the clock.
Two thermometers, agreeing perfectly, were placed in the case of a
clock, one near the point of suspension, and the other near the middle
of the ball, and repeated experiments, showed a difference between
these two thermometers of 7° to 10½° F., the lower one indicating less
than the higher one. The thermometers were then hung in the room, one
at twenty-two inches above the floor, and the other three feet higher,
when they showed a difference of 7° between them. The difference of
2.5° more which was found inside the case proceeds from the heat
striking the upper part of the case; and the wood, though a bad
conductor, gradually increases in temperature, while, on the contrary,
the cold rises from the floor and acts on the lower part of the case.
The same thermometers at the same height and distance in an unused
room, which was never warmed, showed no difference between them; and it
would be the same, doubtless, in an observatory.
From the preceding it is very evident that the decrease of rate of
the clock since December 13 proceeded from the rod of the pendulum
experiencing 7° to 10.5° F. greater heat than the mercury in the bob,
thus showing the impossibility of making a mercurial pendulum perfectly
compensating in an artificially heated room which varies greatly in
temperature. I should remark here that during the entire winter the
temperature in the case is never more than 68° F., and during the
summer, when the rate of the clock was regular, the thermometer in the
case has often indicated 72° to 77° F.
The gridiron pendulum in this case would seem preferable, for if the
temperature is higher at the top than at the lower part, the nine
compensating rods are equally affected by it. But in its compensating
action it is not nearly as regular, and it is very difficult to
regulate it, for in any room (artificially heated) it is impossible to
obtain a uniform temperature throughout its entire length, and without
that all proofs are necessarily inexact.
These facts can also be applied to pendulums situated in heated rooms.
In the case of a rapid change in temperature taking place in the
observatory rooms, under the domes of observatories, especially during
the winter months, and which are of frequent occurrence, a mercurial
compensation pendulum, as generally made, is not apt to give a reliable
rate. Let us accept the fact, as an example, of a considerable fall
in the temperature of the surrounding air; the thin pendulum rod
will quickly accept the same temperature, but with the great mass of
mercury to be acted upon the responsive effects will only occur after
a considerable lapse of time. The result will be a shortening of the
pendulum length and a gain in the rate until the mercury has had time
to respond, notwithstanding the compensation.
Others who have expressed their views in writing seem to favor the
idea that this inequality in the temperature of the atmosphere
is unfavorable to the accurate action of the mercurial form of
compensation; and however plausible and reasonable this idea may seem
at first notice, it will not take a great amount of investigation
to show that, instead of being a disadvantage, its existence is
beneficial, and an important element in the success of mercurial
pendulums.
It appears that the majority of those who have proposed, or have tried
to improve Graham’s pendulum have overlooked the fact that different
substances require different quantities of heat to raise them to the
same temperature. In order to warm a certain weight of water, for
instance, to the same degree of heat as an equal weight of oil, or
an equal weight of mercury, twice as much heat must be given to the
water as to the oil, and thirty times as much as to the mercury;
while in cooling down again to a given temperature, the oil will cool
twice as quick as the water, and the mercury thirty times quicker
than the water. This phenomenon is accounted for by the difference in
the amount of latent heat that exists in various substances. On the
authority of Sir Humphrey Davy, zinc is heated and cooled again ten and
three-quarters times quicker than water, brass ten and a half times
quicker, steel nine times, glass eight and a half times, and mercury is
heated and cooled again thirty times quicker than water.
From the above it will be noticed that the difference in the time steel
and mercury takes to rise and fall to a given temperature is as nine to
thirty, and also that the difference in the quantity of heat that it
takes to raise steel and mercury to a given temperature is in the ratio
of nine to thirty.
Now, without entering into minute details on the properties which
different substances possess for absorbing or reflecting heat, it is
plain that mercury should move in a proportionally different atmosphere
from steel in order to be expanded or contracted a given distance
in the same length of time; and to obtain this result the amount of
difference in the temperature of the atmosphere at the opposite ends of
the pendulum must vary a little more or less according to the nature of
the material the mercury jars are constructed from.
Differences in the temperature of the atmosphere of a room will
generally vary according to its size, the height of the ceiling, and
the ventilation of the apartment; and if the difference must continue
to exist, it is of importance that the difference should be uniformly
regular. We must not lose sight of the fact, however, that clocks
having these pendulums, and placed in apartments every way favorable
to an equal temperature, and in some instances, the clocks and their
pendulums encased in double casing in order to more effectually obtain
this result, still the rates of the clock show the same eccentricities
as those placed in less favorable position. This clearly shows that
many changes in the rates of fine clocks are due to other causes than
a change in the temperature of the surrounding atmosphere. Still it
must be admitted that any change in the condition of the atmosphere
that surrounds a pendulum is a most formidable obstacle to be overcome
by those who seek to improve compensated pendulums, and it would be of
service to them to know all that can possibly be known on the subject.
The differences spoken of above have resulted in some practical
improvements, which are: 1st, the division of the mercury into two,
three or four jars in order to expose as much surface as possible to
the action of the air, so that the expansion of the mercury should not
lag behind that of the rod, which it will do if too large amounts of
it are kept in one jar. 2nd, the use of very thin steel jars made from
tubing, so that the transmission of heat from the air to the mercury
may be hastened as much as possible. 3rd, the increase in the number
of jars makes a thinner bob than a single jar of the same total weight
and hence gives an advantage in decreasing the resistant effect of air
friction in dense air, thereby decreasing somewhat the barometric error
of the pendulum.
The original form of mercurial pendulums, as made by Graham, and still
used in tower and other clocks where extraordinary accuracy is not
required, was a single jar which formed the bob and had the pendulum
rod extending into the mercury to assist in conducting heat to the
variable element of the pendulum. It is shown in section in Fig. 13,
which is taken from a working drawing for a tower clock.
The pendulum, Fig. 13, is suspended from the head or cock shown in the
figure, and supported by the clock frame itself, instead of being hung
on a wall, since the intention is to set the clock in the center of the
clockroom, and also because the weight, forty pounds, is not too much
for the clock frame to carry. The head, A, forms a revolving thumb-nut,
which is divided into sixty parts around the circumference of its
lower edge, and the regulating screw, B, is threaded ten to the inch.
A very fine adjustment is thus obtained for regulating the time of the
pendulum. The lower end of the regulating screw, B, holds the end of
the pendulum spring, E, which is riveted between two pieces of steel,
C, and a pin, C′, is put through them and the end of the regulating
screw, by which to suspend the pendulum.
The cheeks or chops are the pieces D, the lower edges of which form the
theoretical point of suspension of the pendulum. These pieces must be
perfectly square at their lower edges, otherwise the center of gravity
would describe a cylindrical curve. The chops are clamped tightly in
place by the setscrews, D′, after the pendulum has been hung.
The lower end of the regulating screw is squared to fit the ways and
slotted on one side, sliding on a pin to prevent its turning and
therefore twisting the suspension spring when it is raised or lowered.
The spring is three inches long between its points of suspension, one
and three-eighths inches wide, and one-sixtieth of an inch thick.
Its lower end is riveted between two small blocks of steel, F, and
suspended from a pin, F′, in the upper end of the cap, G, of the
pendulum rod.
The tubular steel portion of the pendulum rod is seven-eighths of an
inch in diameter and one-thirty-second of an inch thickness of the
wall. It is enclosed at each end by the solid ends, G and L, and is
made as nearly air-tight as possible.
[Illustration: Fig. 13.]
The compensation is by mercury inclosed in a cast iron bob. The
mercury, the bob and the rod together weigh forty pounds. The bob of
the pendulum is a cast iron jar, K, three inches in diameter inside,
one-quarter inch thick at the sides, and five-sixteenths thick at the
bottom, with the cap, J, screwed into its upper end. The cap, J, forms
also the socket for the lower end of the pendulum rod, H. The rod, L,
one-quarter inch in diameter, screws into the cap, J, and its large
end at the same time forms a plug for the lower end of the pendulum
tube, H. The pin, J′, holds all these parts together. The rod, L,
extends nearly to the bottom of the jar, and forms a medium for the
transmission of the changes in temperature from the pendulum tube to
the mercury. The screw in the cap, J, is for filling or emptying the
jar. The jar is finished as smoothly as possible, outside and inside,
and should be coated with at least three coats of shellac inside. Of
course if one was building an astronomical clock, it would be necessary
to boil the mercury in the jar in order to drive off the layer of air
between the mercury and the walls of the jar, but with the smooth
finish the shellac will give, in addition to the good work of the
machinist, the amount of air held by the jar can be ignored.
The cast iron jar was decided upon because it was safer to handle, can
be attached more firmly to the rod with less multiplication of parts,
and also on account of the weight as compared with glass, which is the
only other thing that should be used, the glass requiring a greater
height of jar for equal weight. In making cast iron jars, they should
always be carefully turned inside and out in order that the walls of
the jar may be of equal thickness throughout; then they will not throw
the pendulum out of balance when they are screwed up or down on the
pendulum rod in making the coarse regulation before timing by the upper
screw. The thread on the rod should have the cover of the jar at about
the center of the thread when nearly to time and that portion which
extends into the jar should be short enough to permit this.
Ignoring the rod and its parts for the present, and calling the jar
one-third of the weight of the mercury, we shall find that thirty
pounds of mercury, at .49 pounds per cubic inch, will fill a cylinder
which is three inches inside diameter to a height of 8.816 inches,
after deducting for the mass of the rod L, when the temperature of the
mercury is 60 degrees F. Mercury expands one-tenth in bulk, while cast
iron expands .0066 in diameter: so the sectional area increases as
1.0066² or 1.0132 to 1, therefore the mercury will rise .1-.013243, or
.086757; then the mercury in our jar will rise .767 of an inch in the
ordinary changes of temperature, making a total height of 9.58 inches
to provide for; so the jar was made ten inches long.
Pendulums of this pattern as used in the high grade English clocks, are
substantially as follows: Rod of steel ⁵/₁₆ inch diameter; jar about
2.1 inches diameter inside and 8¾ inches deep inside. The jar may be
wrought or cast iron and about ⅜ of an inch thick with the cover to
screw on with fine thread, making a tight joint. The cover of the jar
is to act as a nut to turn on the rod for regulation. The thread cut on
the rod should be thirty-six to the inch, and fit into the jar cover
easily, so that it may turn without binding. With a thirty-six thread
one turn of the jar on the rod changes the rate thirty seconds per day
and by laying off on the edge of the cover 30 divisions, a scale is
made by which movements for one second per day are obtained.
We will now describe (Fig. 14) the method of making a mercurial
pendulum to replace an imitation gridiron pendulum for a Swiss, pin
escapement regulator, such as is commonly found in the jewelry stores
of the United States, that is, a clock in which the pendulum is
supported by the plates of the movement and swings between the front
plate and the dial of the movement. In thus changing our pendulum,
we shall desire to retain the upper portion of the old rod, as the
fittings are already in place and we shall save considerable time and
labor by this course. As the pendulum is suspended from the movement,
it must be lighter in weight than if it were independently supported
by a cast iron bracket, as shown in Fig. 6, so we will make the weight
about that of the one we have removed, or about twelve pounds. If it
is desired to make the pendulum heavier, four jars of the dimensions
given would make it weigh about twenty pounds, or four jars of one
inch diameter would make a thinner bob and one weighing about fourteen
pounds. As the substitution of a different number or different sizes of
jars merely involves changing the lengths of the upper and lower bars
of the frame, further drawings will be unnecessary, the jeweler having
sufficient mechanical capacity to be able to make them for himself.
I might add, however, that the late Edward Howard, in building his
astronomical clocks, used four jars containing twenty-eight pounds of
mercury for such movements, and the perfection of his trains was such
that a seven-ounce driving weight was sufficient to propel the thirty
pound pendulum.
The two jars are filled with mercury to a height of 7⅝ inches, are
1⅜ inches in diameter outside and 8⅜ inches in height outside. The
caps and foot pieces are screwed on and when the foot pieces are
screwed on for the last time the screw threads should be covered with
a thick shellac varnish which, when dry, makes the joint perfectly
air-tight. The jars are best made of the fine, thin tubing, used in
bicycles, which can be purchased from any factory, of various sizes and
thickness. In the pendulum shown in the illustration, the jar stock is
close to 14 wire gauge, or about 2 mm. in thickness. In cutting the
threads at the ends of the jars they should be about 36 threads to the
inch, the same number as the threads on the lower end of the rod used
to carry the regulating nut. A fine thread makes the best job and the
tightest joints. The caps to the jars are turned up from cold rolled
shafting, it being generally good stock and finishes well. The threads
need not be over ³/₁₆ inch, which is ample. Cut the square shoulder
so the caps and foot pieces come full up and do not show any thread
when screwed home. These jars will hold ten pounds of mercury and this
weight is about right for this particular style of pendulum. The jars
complete will weigh about seven ounces each.
[Illustration: Fig. 14.]
The frame is also made of steel and square finished stock is used as
far as possible and of the quality used in the caps. The lower bar
of the frame is six inches long and ⅝ inch square at the center and
tapered, as shown in the illustration. It is made light by being planed
away on the under side, an end view being shown at 3. The top bar of
the frame, shown at 4, is planed away also and is one-half inch square
the whole length and is six inches long. The two side rods are to bind
the two bars together, and with the four thumb nuts at the top and
bottom make a strong light frame.
The pendulum described is nickel plated and polished, except the jars,
which are left half dead; that is, they are frosted with a sand blast
and scratch brushed a little. The effect is good and makes a good
contrast to the polished parts. The side rods are five inches apart,
which leaves one-half inch at the ends outside.
The rod is ⁵/₁₆ of an inch in diameter and 33 inches long from the
bottom of the frame at a point where the regulating nut rests against
it to the lower end of the piece of the usual gridiron pendulum shown
in Fig. 14 at 10. This piece shown is the usual style and size of
those in the majority of these clocks and is the standard adopted by
the makers. This piece is 11⅛ inches long from the upper leaf of the
suspension spring, which is shown at 12, to the lower end marked 10. By
cutting out the lower end of this piece, as shown at 10, and squaring
the upper end of the rod, pinning it into the piece as shown, the union
can be made easily and any little adjustments for length can be made by
drilling another set of holes in the rod and raising the pendulum by
so doing to the correct point. A rod whose total length is 37 inches
will leave 2 inches for the prolongation below the frame carrying the
regulating nut, 9, and for the portion squared at the top, and will
then be so long that the rate of the clock will be slow and leave a
surplus to be cut off either at the top or bottom, as may seem best.
The screw at the lower end carrying the nut should have 36 threads to
the inch and the nut graduated to 30 divisions, each of which is equal
in turning the nut to one minute in 24 hours, fast or slow, as the case
may be.
The rod should pass through the frame bars snugly and not rattle or
bind. It also should have a slot cut so that a pin can be put through
the upper bar of the frame to keep the frame from turning on the rod
and yet allow it to move up and down about an inch. The thread at the
lower end of the rod should be cut about two inches in length and when
cutting off the rod for a final length, put the nut in the middle of
the run of the thread and shorten the rod at the top. This will be
found the most satisfactory method, for when all is adjusted the nut
will stand in the middle of its scope and have an equal run for fast
or slow adjustment. With the rod of the full length as given, this
pendulum had to be cut at the top about one inch to bring to a minute
or two in twenty-four hours, and this left all other points below
corrected. The pin in the rod should be adjusted the last thing, as
this allows the rod to slide on the pin equal distances each way. One
inch in the raising or lowering of the frame on the rod will alter the
rate for twenty-four hours about eighteen minutes.
Many attempts have been made to combine the good qualities of the
various forms of pendulums and thus produce an instrument which would
do better work under the severe exactions of astronomical observatories
and master clocks controlling large systems. The reader should
understand that, just as in watch work, the difficulties increase
enormously the nearer we get towards absolute accuracy, and while
anybody can make a pendulum which will stay within a minute a month,
it takes a very good one to stay within five seconds per month, under
the conditions usually found in a store, and such a performance makes
it totally unfit for astronomical work, where variations of not over
five-thousandths of a second per day are demanded. In order to secure
such accuracy every possible aid is given to the pendulum. Barometric
errors are avoided by enclosing it in an air-tight case, provided with
an air pump; the temperature is carefully maintained as nearly constant
as possible and its performance is carefully checked against the
revolutions of the fixed stars, while various astronomers check their
observations against each other by correspondence, so that each can get
the rate of his clock by calculations of observations and the law of
averages, eliminating personal errors.
One of the successful attempts at such a combination of mercury and
metallic pendulums is that of Riefler, as shown in Fig. 15, which
illustrates a seconds pendulum one-thirtieth of the actual size.
It consists of a Mannesmann steel tube (rod), bore 16 mm., thickness
of metal 1 mm., filled with mercury to about two-thirds of its length,
the expansion of the mercury in the tube changing the center of
weight an amount sufficient to compensate for the lengthening of the
tube by heat, or vice versa. The pendulum, has further, a metal bob
weighing several kilograms, and shaped to cut the air. Below the bob
are disc shaped weights, attached by screw threads, for correcting the
compensation, the number of which may be increased or diminished as
appears necessary.
Whereas in the Graham pendulum regulation for temperature is effected
by altering the height of the column of mercury, in this pendulum it
is effected by changing the position of the center of weight of the
pendulum by moving the regulating weights referred to, and thus the
height of the column of mercury always remains the same, except as it
is influenced by the temperature.
[Illustration: COLUMN OF MERCURY Fig. 15.]
A correction of the compensation should be effected, however, only in
case the pendulum is to show sidereal time, instead of mean solar time,
for which latter it is calculated. In this case a weight of 110 to 120
grams should be screwed on to correct the compensation.
In order to calculate the effect of the compensation, it is necessary
to know precisely the coefficients of the expansion by heat of the
steel rod, the mercury, and the material of which the bob is made.
The last two of these coefficients of expansion are of subordinate
importance, the two adjusting screws for shifting the bob up and
down being fixed in the middle of the latter. A slight deviation
is, therefore, of no consequence. In the calculation for all these
pendulums the co-efficient for the bob is, therefore, fixed at
0.000018, and for the mercury at 0.00018136, being the closest
approximation hitherto found for chemically pure mercury, such as that
used in these pendulums.
The co-efficient of the expansion of the steel rod is, however, of
greater importance. It is therefore, ascertained for every pendulum
constructed in Mr. Riefler’s factory, by the _physikalisch-technische
Reichsanstalt_ at Charlottenburg, examinations showing, in the case
of a large number of similar steel rods, that the co-efficient of
expansion lies between 0.00001034 and 0.00001162.
The precision with which the measurements are carried out is so great
that the error in compensation resulting from a possible deviation from
the true value of the co-efficient of expansion, as ascertained by the
Reichsanstalt, does not amount to over ± 0.0017; and, as the precision
with which the compensation for each pendulum may be calculated
absolutely precludes any error of consequence, Mr. Riefler is in a
position to guarantee _that the probable error of compensation in these
pendulums will not exceed ± 0.005 seconds per diem and ± 1° variation
in temperature_.
A subsequent correction of the compensation is, therefore, superfluous,
whereas, with all other pendulums it is necessary, partly because
the coefficients of expansion of the materials used are arbitrarily
assumed; and partly because none of the formulæ hitherto employed for
calculating the compensation can yield an exact result, for the reason
that they neglect to notice certain important influences, in particular
that of the weight of the several parts of the pendulum. Such formulæ
are based on the assumption that this problem can be solved by simple
geometrical calculation, whereas, its exact solution can be arrived at
only with the aid of physics.
This is hardly the proper place for details concerning the lengthy and
rather complicated calculations required by the method employed. It is
intended to publish them later, either in some mathematical journal or
in a separate pamphlet. Here I will only say that the object of the
whole calculation is to find the allowable or requisite weight of the
bob, _i. e._, the weight proportionate to the coefficients of expansion
of the steel rod, dimensions and weight of the rod and the column of
mercury being given in each separate case. To this end the relations
of all the parts of the pendulum, both in regard to statics and
inertia, have to be ascertained, and for various temperatures.
A considerable number of these pendulums have already been constructed,
and are now running in astronomical observatories. One of them is
in the observatory of the University of Chicago, and others are in
Europe. The precision of this compensation which was discovered by
purely theoretical computations, has been thoroughly established by the
ascertained records of their running at different temperatures.
The adjustment of the pendulums, which is, of course, almost wholly
without influence on the compensation, can be effected in three
different ways;
(1.) The rough adjustment, by screwing the bob up or down.
(2.) A finer adjustment, by screwing the correction discs up or down.
(3.) The finest adjustment, by putting on additional weights.
These weights are to be placed on a cup attached to a special part of
the rod of the pendulum. Their shape and size is such that they can
be readily put on or taken off while the pendulum is swinging. Their
weight bears a fixed proportion to the static momentum of the pendulum,
so that each additional weight imparts to the pendulum, for twenty-four
hours, an acceleration expressed in even seconds and parts of seconds,
and marked on each weight.
Each pendulum is accompanied with additional weights of German silver,
for a daily acceleration of 1 second each, and ditto of aluminum for an
acceleration of 0.5 and 0.1 second respectively.
A metal clasp attached on the rear side of the clock case, may be
pushed up to hold the pendulum in such a way that it can receive no
twisting motion during adjustment.
Further, a pointer is attached to the lower end of the pendulum, for
reading off the arc of oscillation.
The essential advantages of this pendulum over the mercurial
compensation pendulums are the following:
(1.) It follows the changes of temperature more
rapidly, because a small amount of mercury is divided
over a greater length of pendulum, whereas, in the
older ones the entire (and decidedly larger) mass of
mercury is situated in a vessel at the lower end of
the pendulum rod.
(2.) For this reason differences in the temperature
of the air at different levels have no such
disturbing influence on this pendulum as on the
others.
(3.) This pendulum is not so strongly influenced as
the others by changes in the atmospheric pressure,
because the principal mass of the pendulum has the
shape of a lens, and therefore cuts the air easily.
CHAPTER V.
REGULATIONS, SUSPENSIONS, CRUTCHES AND MINOR POINTS.
REGULATION.—The reader will have noticed that in describing the various
forms of seconds pendulums we have specified either eighteen or
thirty-six threads to the inch; this is because a revolution of the nut
with such a thread gives us a definite proportion of the length of the
rod, so that it means an even number of seconds in twenty-four hours.
Moving the bob up or down ¹/₁₈ inch makes the clock having a
seconds pendulum gain or lose in twenty-four hours one minute,
hence the selecting definite numbers of threads has for its reason
a philosophical standpoint, and is not a matter of convenience and
chance, as seems to be the practice with many clockmakers. With a screw
of eighteen threads, we shall get one minute change of the clock’s
rate in twenty-four hours for every turn of the nut, and if the nut is
divided into sixty parts at its edge, each of these divisions will make
a change of the clock’s rate of one second in twenty-four hours. Thus
by using a thread having a definite relation to the length of the rod
regulating is made comparatively easy, and a clock can be brought to
time without delay. Suppose, after comparing your clock for three or
four days with some standard, you find it gains twelve seconds per day,
then, turning the nut down twelve divisions will bring the rate down
to within one second a day in one operation, if the screw is eighteen
threads. With the screw thirty-six threads the nut will require moving
just the same number of divisions, only the divisions are twice as long
as those with the screw of eighteen threads.
The next thing is the size and weight of the nut. If it is to be
placed in the middle of the bob as in Figs. 10, 12 and 15, it should
project slightly beyond the surface and its diameter will be governed
by the thickness of the bob. If it is an internal nut, worked by means
of a sleeve and disc, as in Fig. 9, the disc should be of sufficient
diameter to make the divisions long enough to be easily read. If the
nut is of the class shown in Fig. 5, 6, 7, a nut is most convenient, 1
inch in diameter, and cut on its edge into thirty equal divisions, each
of which is equal to one second in change of rate in twenty-four hours,
if the screw has thirty-six threads to the inch. This gives 3.1416
inches of circumference for the thirty divisions, which makes them long
enough to be subdivided if we choose, each division being a little over
one-tenth of an inch in length, so that quarter-seconds may be measured
or estimated.
With some pendulums, Fig. 13, the bob rotates on the rod, and is in
the form of a cylinder, say 8½ inches long by 2½ inches in diameter,
and the bob then acts on its rod as the nut does, and moves up and
down when turned, and in this form of bob the divisions are cut on the
outside edge of the cover of the bob, and are so long that each one is
subdivided into five or ten smaller divisions, each altering the clock
.2 or .1 second per day.
On the top of the bob turn two deep lines, close to the edge, about
⅛-inch apart, and divide the whole diameter into thirty equal
divisions, and subdivide each of the thirty into five, and this will
give seconds and fifths of seconds for twenty-four hours. Each even
seconds division should be marked heavier than the fraction, and should
be marked from one to thirty with figures. Just above the cover on the
rod should slide a short tube, friction-tight, and to this a light
index or hand should be fastened, the point of which just reaches the
seconds circle on the bob cover, and thus indicates the division, its
number and fraction. The tube slides on the rod because the exact
place of the hand cannot be settled until it has been settled by
experiment. After this it can be fastened permanently, if thought best,
though as described it will be all sufficient. While the bob is being
raised or lowered to bring the clock to its rate, the bob might get too
far away or too near to the index and necessitate its being shifted,
and if friction-tight this can be readily accomplished, and the hand
be brought to just coincide with the divisions and look well and be a
means of accomplishing very accurate minute adjustments.
SUSPENSIONS.—Suspensions are of four kinds, cord, wire loop, knife
edges and springs. Cords are generally of loosely twisted silk and
are seldom found except in the older clocks of French or Swiss
construction. They have been entirely displaced in the later makes of
European manufactures by a double wire loop, in which the pendulum
swings from a central eye in the loop, while the loop rocks upon a
round stud by means of an eye at each end of the loop. The eyes should
all be in planes parallel to the plane of oscillation of the pendulum,
otherwise the bob will take an elliptical path instead of oscillating
in a plane. They should also be large enough to roll without friction
upon the stud and center of the loop, as any slipping or sliding of
either will cause them to soon wear out, besides affecting the rate
of the pendulum. Properly constructed loops will give practically no
friction and make a very free suspension that will last as long as the
clock is capable of keeping time, although it seems to be a very weak
and flimsy method of construction at first sight. Care should be taken
in such cases to keep the bob from turning when regulating the clock,
or the effect upon the pendulum will be the same as if the eyes were
not parallel.
Knife edge suspensions are also rare now, having been displaced by
the spring, as it was found the vibrations were too free and any
change in power introduced a circular error (See Fig. 4) by making the
long swings in longer time. They are still to be found, however, and
in repairing clocks containing them the following points should be
observed: The upper surface of the stud on which the pendulum swings
should carry the knife edge at its highest point, exactly central
with the line of centers of the stud, so that when the pendulum hangs
at rest the stud shall taper equally on both sides of the center,
thus giving equal freedom to both sides of the swing. Care should be
taken that the stud is firmly fixed, with the knife edge exactly at
right angles to the movement, and also to the back of the case. The
suspension stud and the block on the rod should be long enough to hold
the pendulum firmly in line, as the angle in the top of the rod must be
the sole means of keeping the pendulum swinging in plane. The student
will also perceive the necessity of making the angle occupy the proper
position on the rod, especially if the latter be flat. In repairing
this suspension it is usual to make the plate, fasten it in place and
then drill and file out the hole, as it is easier to get the angles
exactly in this way than to complete the plate and then attempt to
fasten it in the exact position in which it should be. After fastening
the plates in position on the rod, two holes should be drilled, a small
one at the apex of the angle (which must be exactly square and true
with the rod), and a larger one below it large enough to pass the files
easily. The larger hole can then be enlarged to the proper size, filing
the angle at the top in such a way that the small hole first drilled
forms the groove at the apex of the angle in which the knife edge of
the stud shall work when it is completed. Knife edge suspensions are
unfitted for heavy pendulums, as the weight causes the knife edge to
work into the groove and cut it, even if the latter be jeweled. Both
the edge and groove should be hardened and polished.
PENDULUM SUSPENSION SPRINGS.—Next in importance to the pendulum is
its suspension spring. This spring should be just stiff enough to make
the pendulum swing in all its vibrations in the same time; that is,
if the pendulum at one time swung at the bottom of the jar 1¼ inch
each side of the center, and at another time it swung only 1 inch each
side, that the two should be made in exactly one second. The suspension
springs are a point in the construction of a fine pendulum, that there
has been very much theorizing on, but the experiments have never thus
far exactly corroborated the theories and there are no definite rules
to go by, but every maker holds to that plan and construction that
gives his particular works the best results. A spring of sufficient
strength to materially influence the swing of the pendulum is of
course bad, as it necessitates more power to give the pendulum its
proper motion and hence there is unnecessary wear on the pallets and
escape wheel teeth, and too weak a spring is also bad, as it would not
correct any inequalities in the time of swing and would in time break
from overloading, as its granular structure would finally change,
and rupture of the spring would follow. The office of a spring is to
sustain the weight without detriment to strength and elasticity, and
if so proportioned to the weight as to be just right, it will make
the long and short swings of the pendulum of equal duration. When a
pendulum hung by a cord or knife edge instead of a spring is regulated
to mean time and swings just two inches at the bottom, any change
in the power that swings the pendulum will increase its movement or
decrease it, and in either case the rate will change, but with a proper
spring the rate will be constant under like conditions. The action of
the spring is this: In the long swings the spring, as it bends, lifts
the pendulum bob up a little more than the arc of the normal circle in
which it swings, and consequently when the bob descends, in going to
the center of its swing, it falls a little quicker than it does when
held by a cord, and this extra quick drop can be made to neutralize the
extra time taken by the bob in making extra long swings. See Fig. 4.
This action is the isochronal action of the spring, the same that is
attained in isochronal hair springs in watches.
As with the hairspring, it is quite necessary that the pendulum spring
be accurately adjusted to isochronism and my advice to every jeweler
is to thoroughly test his regulator, which can easily be done by
changing the weight or motive power. If the test should prove the lack
of isochronism he can adjust it by following these simple rules. Fig.
16 is the pendulum spring or leaf. If the short arcs should prove the
slowest, make the spring a trifle thinner at B; if fastest, reduce the
thickness of the spring at A. Continue the test until the long and
short arcs are equal. In doing this care must be taken to thin each
spring equally, if it is a double spring, and each edge equally, if
a single spring, as if one side be left thicker than the other the
pendulum will wabble.
[Illustration: Fig. 16.]
The cause of a pendulum wobbling is that there must be something wrong
with the suspension spring, or the bridge that holds the spring. If
the suspension spring is bent or kinked, the pendulum will wabble; or
if the spring should be of an unequal thickness it will have the same
effect on the pendulum; but the main cause of the pendulum wobbling in
American clocks is that the slot in the bridge that holds the spring,
or the slot in the slide that works up and down on the spring (which
is used to regulate the clock) is not parallel. When this slot is not
parallel it pinches the spring, front or back, and allows it to vibrate
more where it is the freest, causing the pendulum to wabble. We have
found that by making these slots parallel the wobbling of the pendulum
has ceased in most all cases. If the pallet staff is not at right
angles to the crutch, wobbling may be caused by the oblique action of
the crutch. This often happens when the movement is not set square in
the case.
It occasionally happens in mantel clocks that the pendulum when brought
to time is just too long for the case when too thick a spring is used.
In such a case thinning the spring will require the bob to be raised a
little and also give a better motion. If compelled to make a spring use
a piece of mainspring about .007 thick and ⅜ wide for small pendulums
and the same spring doubled for heavier pendulums, making the acting
part of the spring about 1.5 inches long.
The suspension spring for a rather heavy pendulum is better divided,
that is, two springs, held by two sets of clamps, and jointly acting as
one spring. The length will be the same as to the acting part, and that
part held at each end by the clamps may be ¾ inch long; total length,
1.5 inches with ⅜ inch at each end held in the clamps. These clamps are
best soldered on to the spring with very low flowing solder so as not
to draw the temper of the spring, and then two rivets put through the
whole, near the lower edge of the clamps. The object of securing the
clamps so firmly is so that the spring may not bend beyond the edge of
the clamps, as if this should take place the clock will be thrown off
of its rate. After a time the rate would settle and become steady, but
it only causes an extra period of regulating that does not occur when
the clamps hold the spring immovable at this point. About in the center
of each of the clamps, when soldered and riveted, is to be a hole bored
for a pin, which pins the clamp into the bracket and holds the weight
of the pendulum.
The width of this compound spring for a seconds’ pendulum of average
weight may be .60 inch, from outside to outside, each spring .15 inch
wide. This will separate the springs .30 inch in the center. With this
form of spring, the lower end of each spring being held in a pair of
clamps, the clamps will have to be let into the top of the rod, and
held in by a stout pin, or the pendulum finished with a hook which will
fit the clamp. In letting the clamp into the rod, the clamp should just
go into the mortise and be without side shake, but tilt each way from
the center a little on the pin, so that when the pendulum is hung it
may hang perpendicular, directly in the center of both springs. Also,
the top pair of clamps should fit into a bracket without shake, and
tilt a little on a pin, the same as the lower clamps. These two points,
each moving a little, helps to take any side twist away, and allows
the whole mechanism to swing in line with the center of gravity of the
mass from end to end. With the parts well made, as described, the bob
will swing in a straight line from side to side, and its path will be
without any other motion except the one of slight curvature, due to
being suspended by a fixed point at the upper clamp.
PENDULUM SUPPORTS.—Stability in the movement and in the suspension of
the pendulum is very necessary in all forms of clocks for accurate
timekeeping. The pendulum should be hung on a bracket attached to
the back of the case (see Fig. 6), and not be subject to disturbance
when the movement is cleaned. Also the movement should rest on two
brackets attached to the bracket holding the pendulum and the whole be
very firmly secured to the back board of the case. Screws should go
through the foot pieces of the brackets and into a stone or brick wall
and be very firmly held against the wall just back of the brackets.
Any instability in this part of a clock is very productive of poor
rates. The bracket, to be in its best form, is made of cast iron, with
a large foot carrying all three separate brackets, well screwed to a
strong back board and the whole secured to the masonry by bolts. Too
much firmness cannot be attained, as a lack of it is a very great
fault, and many a good clock is a very poor timekeeper, due to a lack
of firmness in its supports and fastenings. The late Edward Howard
used to make his astronomical clocks with a heavy cast iron back, to
which the rest of the case was screwed, so that the pendulum should
not swing the case. Any external influence that vibrates a wall or
foundation on which a clock is placed, is a disturbing influence, but
an instability in a clock’s attachment to such supports is a greater
one. Many pendulums swing the case in which they hang (from unstable
setting up) and never get down to or maintain a satisfactory rate from
that cause. This is also aggravated by the habit of placing grandfather
clocks on stair landings or other places subject to jarring. The writer
knows of several clocks which, after being cleaned, kept stopping
until raised off the floor and bolted to the wall, when they at once
took an excellent rate. The appearance of resting on the floor may be
preserved, if desirable, by raising the clock only half an inch or so,
just enough to free it from the floor.
CRUTCHES.—The impulse is transmitted to the pendulum from the pallet
staff by means of a wire, or slender rod, fastened at its upper end
to the pallet staff and having its lower end terminating in a fork
(crutch), loop, or bent at right angles so as to work freely in a slot
in the rod. It is also called the verge wire, owing to the fact that
older writers and many of the older workmen called the pallet fork the
verge, thus continuing the older nomenclature, although of necessity
the verge disappeared when the crown wheel was discarded.
In order to avoid friction at this very important point, the centers
of both axes of oscillation, that of the pallet arbor and that of the
pendulum spring, where it bends, should be in a straight horizontal
line. If, for instance, the center of suspension of the pendulum be
higher, then the fork and the pendulum describe two different arcs of
circles; that of the pendulum will be greater than that of the fork
at their meeting point. If, however, the center of suspension of the
pendulum be lower than that of the fork, they will also describe two
different arcs, and that of the pendulum will be smaller than that of
the fork at their point of meeting. This, as can be readily understood,
will cause friction in the fork, the pendulum going up and down in it.
This is prevented when, as stated before, the center of suspension
of the pendulum is in the prolonged straight imaginary line going
through the center of the pivots of the fork, which will cause the
arcs described by the fork and the pendulum to be the same. It will be
well understood from the foregoing that the pendulum should neither be
suspended higher nor lower, nor to the left, nor to the right of the
fork.
If the centers of motion do not coincide, as is often the case with
cheap clocks with recoil escapements, any roughness of the pendulum
rod where it slides on the crutch will stop the clock, and repairers
should always see to it that this point is made as smooth as possible
and be very slightly oiled when setting up. If putting in a new verge
wire, the workman can always tell where to bend it to form the loop by
noticing where the rod is worn and forming the loop so that it will
reach the center of that old crutch or loop mark on the pendulum rod.
If the verge wire is too long, it will give too great an arc to the
pendulum if the latter is hung below the pallet arbor, as is generally
the case with recoil escapements of the cheap clocks, and if it is too
short there will not be sufficient power applied to the pendulum when
the clock gets dirty and the oil dries, in which case the clock will
stop before the spring runs down.
An important thing to look after when repairing is in the verge wire
and loop (the slot the pendulum rod goes through). After the clock is
set up and oiled, put it on a level shelf; have a special adjusted
shelf for this level adjusting, one that is absolutely correct. Have
the dial off. If the beat is off on one side, so that it bangs up
heavily on one side of the escape wheel, bend the verge wire the
same way. That will reverse the action and put it in beat. So far so
good—but don’t stop now. Just notice whether if that shelf were tipped
forward or back, as perhaps your customer’s may, that the pendulum
should still hang plumb and free. Now if the top of your clock tips
forward, the pendulum ball inclines to hang out toward the front. We
will suppose you put two small wedges under the back of the case. Now
notice in its hanging out whether the pendulum rod pinches or bears in
the throat of the verge; or if it tips back, see if the rod hits the
other end of the slot. This verge slot should be long enough, with the
rod hanging in the middle when adjusted to beat on a level, to admit of
the clock pitching forward or back a little without creating a friction
on the ends of the slot. This little loop should be open just enough
to be nice and free; if open too much, you will notice the pallet fork
will make a little jump when carrying the ball over by hand. This is
lost motion. If this little bend of wire is not parallel it may be
opened enough inside, but if pitched forward a little it will bind in
the narrowest part of the V and then the clock will stop. The clock
beat and the tipping out or in of the clock case, causing a binding or
bearing of the pendulum rod in this verge throat, does more towards
stopping clocks just repaired than all other causes.
PUTTING IN BEAT.—To put a clock in beat, hang the clock in such a
position that when the pendulum is at rest one tooth of the escape
wheel will rest on the center of a pallet stone. Screwed on the case
of the clock at the bottom of the pendulum there is, or should be, an
index marked with degrees. Now, while the escape wheel tooth is resting
on the pallet, as explained above, the index of the pendulum should
point to zero on the index. Move the pendulum until the tooth just
escapes and note how many degrees beyond zero the pendulum point is.
Say it escapes 2° to the left; now move the pendulum until the next
tooth escapes—it should escape 2° to the right. But let us suppose it
does not escape until the index of the pendulum registers 5° to the
right of zero. In this case the rod attached to the pallets must be
bent until the escape wheel teeth escape when the pendulum is moved an
even number of degrees to the right and left of zero, when the clock
will be in beat.
CLOSE RATING WITH SHOT.—Very close rating of a seconds’ pendulum,
accompanied by records in the book, may be got with the nut alone, but
there is the inconvenience of stopping the clock to make an alteration.
This may be avoided by having a small cup the size of a thimble or
small pill box on the pendulum top. This can be lifted off and put back
without disturbing the motion of the pendulum. In using it a number of
small shot, selected of equal size, are put in, say 60, and the clock
brought as nearly as possible to time by the nut. After a few days
the cup may be emptied and put back, when on further trial the value
of the 60 shot in seconds a day will be found. This value divided by
60 will give the value of a single shot, by knowing which very small
alterations of rate may be made with a definite approach towards
accuracy, and in much less time than by putting in or taking out one or
more shot at random.
CHAPTER VI.
TORSION PENDULUMS FOR FOUR-HUNDRED DAY CLOCKS.
As this pendulum is only found in the 400-day, or annual wind, or
anniversary clocks (they are known by all of these names), it is best
to describe the pendulum and movement together, as its relations to the
work to be done may be more easily perceived.
Rotating pendulums of this kind—that is, in which the bob rotates by
the twisting of the suspension rod or spring—will not bear comparison
with vibrating pendulums for accurate timekeeping. They are only used
when a long period between windings is required. Small clocks to go for
twelve months with one winding have the torsion pendulum ribbons of
flat steel about six inches long, making 15 beats per minute. The time
occupied in the beat of such a pendulum depends on the power of the
suspending ribbon to resist twisting, and the weight and distance from
the center of motion of the bob. In fact, the action of the bob and
suspending ribbon is very analogous to that of a balance and balance
spring.
[Illustration: Fig. 17.]
In order to get good time from a clock of this character, it should
be made with a dead-beat escapement. With such an escapement there is
no motion of the escape wheel, after the tooth drops on the locking
face of the pallet; the escape wheel is dead and does not move again
until it starts to give the pallet impulse. This style of an escapement
allows the pendulum as much freedom to vibrate as possible, as the fork
in one form of this escapement may leave the pallet pin as soon as the
latter strikes the guard pins, as in the ordinary lever escapement of
a watch, and it will remain in that position until the return of the
fork unlocks the escapement to receive another impulse. B, Fig. 17,
represents the escape wheel; C, the pallet; E, pallet staff; D, the
pallet pin rivetted on to the pallet staff E, which works in the slot
or fork H; this fork is screwed fast to the spring. The spring G is
made of a piece of flat steel wire and looks like a clock hairspring
straightened out. G is fast to the collar I and rests on a seat
screwed to the plate of the clock, as shown at P; the spring is also
fastened to the pendulum ball O with screws; the ball makes about one
and one-half revolutions each beat, which causes the spring to twist.
It twists more at the point S than it does at L; as it twists at L it
carries the fork with it, so that the latter vibrates from one side to
the other, similar to a fork in a watch. This fork H carries the pin D,
which is fast to the pallet staff E, far enough to allow the teeth to
escape.
[Illustration: Fig. 18.]
In the most common form of this escapement, see Fig. 18, the fork does
not allow the pin D to leave the slot H, and the beat pins are absent,
the pendulum not being as highly detached as in the form previously
mentioned. In this case great care must be taken to have the edges of
the slot, which slide on the pallet pin, smooth, parallel and properly
beveled, so as not to bind on the pin. The pendulum ball makes from
eight to sixteen vibrations a minute. Of course the number depends upon
the train of the clock.
In suspending the pendulum it is necessary to verify the drop of the
teeth of the escape wheel as follows: The pendulum is suspended and
the locking position of the pallets marked, taking as a guiding
point the long, regulating screw, which, fixed transversely in the
support, serves for adjusting the small suspension block. An impulse of
about a third of a turn is given to the pendulum while observing the
escapement. If the oscillations of the pendulum, measured on the two
sides, taking the locking point as the base, are symmetrical, the drop
is also equal, and the rate of the clock regular and exact; but if the
teeth of the escape wheel are unlocked sooner on one side than on the
other, so that the pendulum in its swing passes beyond the symmetrical
point on one of the pallets and does not reach it on the other, it is
necessary to correct the unequal drop.
[Illustration: Fig. 19.]
The suspension block B, Fig. 18, between the jaws of which the steel
ribbon is pressed by two screws, has a lower cylindrical portion,
which is fitted in a hole made in the seat, and is kept immovable by
the screw A. If the vibration of the pendulum passes beyond the proper
point on the left side, it is necessary to loosen A and turn the
suspension block slightly to the right. If the deviation is produced
in the opposite direction, it is necessary to turn it to the left.
These corrections should be repeated until the drop of the escape wheel
teeth on the pallets is exactly equal on the two sides. As the drop is
often disturbed by the fact that the long thin steel ribbon has been
twisted in cleaning, taking apart or handling by unskilled persons
before coming to the watchmaker, it is desirable to test the escapement
again, when the clock is put into position on the premises of the buyer.
[Illustration: Fig. 20.]
The timing adjustment of the pendulum is effected with the aid of
regulating weights, placed on the ball. By moving these away from
the center by means of a right and left hand screw on the center
of the disk (see Fig. 19), the centrifugal force is augmented, the
oscillations of the pendulum slackened, and the clock goes slower.
The contrary effect is produced if the weights are brought nearer the
center. In one form of ball the shifting of the regulating weights is
accomplished by a compensating spring of steel and brass like the rim
of a watch balance, Fig. 20.
If necessary to replace the pendulum spring, the adjustment is
commenced by shortening or lengthening the steel ribbon to a certain
extent. For this purpose the end of the spring is allowed to project
above the suspension block as a reserve until adjustment has been
completed, when it may be cut off. If the space between the ball and
the bottom of the case, or the bottom of the movement plates, does not
allow of attaining this end, it is necessary to increase or decrease
the weight of the disk, adding one or several plates of metal in a
depression made in the under side of the ball, and removing the plates
screwed to it, which are too light.
There are some peculiarities of the trains of these clocks. The cannon
pinion is provided with a re-enforcing spring, serving as guide to
the dial work, on which it exercises a sufficient pressure to assure
precise working. The pressure of this spring is important, because if
the dial work presses too hard on the pinion of the minute wheel, the
latter engaging directly with the escape wheel, would transmit to the
latter all the force employed in setting the hands. The teeth of the
escape wheel would incur damage and the consequent irregularity or even
stopping of the clock would naturally follow.
In order that it may run for so long a time, the motive force
is transmitted through the train by the intervention of three
supplementary wheels between the minute wheel and the barrel, in order
to avoid the employment of too large a barrel; the third wheel is
omitted; the motion work is geared immediately with the arbor of the
escape wheel. It is evident that the system of the three intermediate
wheels, of which we have spoken, requires for the motive force a barrel
spring much stronger than that of ordinary clocks.
The points which we have noticed are of the most importance with
reference to the repair and keeping in order of an annual clock.
It very often happens that when the repairer does not understand
these clocks, irregularities are sought for where they do not exist.
The pivot holes are bushed and the depthings altered, when a more
intelligent examination would show that the stopping, or the irregular
rate of the clock, proceeds only from the condition of the escapement.
Unless, however, they are perfectly adjusted, a variation of five
minutes a week is a close rate for them, and most of those in use will
vary still more.
Annual clocks are enjoying an increased favor with the public; their
good qualities allow confidence, the rate being quite regular when
in proper order. They are suitable for offices; their silent running
recommends them for the sick chamber, and the subdued elegance of their
decoration causes the best of them to be valued ornaments in the home.
CHAPTER VII.
PECULIARITIES OF ANGULAR MEASUREMENT—HOW TO READ DRAWINGS.
We now come to a point at which, if we are to keep our pendulum
vibrating, we must apply power to it, evenly, accurately and in small
doses. In order to do this conveniently we must store up energy by
raising a weight or winding a spring and allow the weight to fall or
the spring to unwind very slowly, say in thirty hours or in eight
days. This brings about the necessity of changing rotary motion to
reciprocating motion, and the several devices for doing this are called
“escapements” in horology, each being further designated by the names
of their inventors, or by some peculiarity of the devices themselves;
thus, the Graham is also called the dead beat escapement; Le Paute’s is
the pin wheel; Dennison’s in its various forms is called the gravity;
Hooke’s is known as the recoil; Brocot’s as the visible escapement, etc.
THE MECHANICAL ELEMENTS.—We shall understand this subject more clearly,
perhaps, if we first separate these mechanical devices into their
component parts and consider them, not as parts of clocks, but as
various forms of levers, which they really are. This is perhaps the
best place to consider the levers we are using to transmit the energy
to the pendulum, as at this point we shall find a greater variety of
forms of the lever than in any other place in the clock, and we shall
have less difficulty in understanding the methods of calculating for
time and power by a thorough preliminary understanding of leverage and
the peculiarities of angular or circular motion.
If we take a bar, A, Fig. 21, and place under it a fulcrum, B, then by
applying at C a given force, we shall be able to lift at D a weight
whose amount will be governed by the relative distances of C and D from
the fulcrum B. If the distance CB is four times that of BD, then a
force of 10 pounds at C will lift 40 pounds at D, for one-fourth of the
distance through which C moves, minus the power lost by friction. The
reverse of this is also true; that is, it will take 40 pounds at D to
exert a force of 10 pounds at C and the 10 pounds would be lifted four
times as far as the 40 pound weight was depressed.
[Illustration: Fig. 21.]
[Illustration: Fig. 22.]
If instead of a weight we substitute other levers, Fig. 22, the result
would be the same, except that we should move the other levers until
the ends which were in contact slipped apart.
[Illustration: Fig. 23.]
If we divide our lever and attach the long end to one portion of an
axle, as at A, Fig. 23, and the short end to another part of it at B,
the result will be the same as long as the proportions of the lever are
not changed. It will still transmit power or impart motion according
to the relative lengths of the two parts of the lever. The capacity of
our levers, Fig. 22, will be limited by that point at which the ends
of the levers will separate, because they are held at the points of
the fulcrums and constrained to move in circles by the fulcrums. If
we put more levers on the same axles, so spaced that another set will
come into action as the first pair are disengaged, we can continue
our transmission of power, Fig. 24; and if we follow this with still
others until we can add no more for want of room we shall have wheels
and pinions, the collection of short levers forming the pinion and
the group of long levers forming the wheel, Fig. 25. Thus every wheel
and pinion mounted together on an arbor are simply a collection of
levers, each wheel tooth and its corresponding pinion leaf forming one
lever. This explains why the force decreases and the motion increases
in proportion to the relative lengths of the radii of the wheels and
pinions, so that eight or ten turns of the barrel of a clock will run
the escape wheel all day.
[Illustration: Fig. 24.]
We now come to the verge or anchor, and here we have the same sort
of lever in a different form; the verge wire, which presses on the
pendulum rod and keeps it going is the long arm of our lever, but
instead of many there is only one. The short arm of our lever is the
pallet, and there are two of these. Therefore we have a form of lever
in which there is one long arm and two short ones; but as the two are
never acting at the same time they do not interfere with each other.
[Illustration: Fig. 25.]
These systems of levers have another advantage, which is that one arm
need not be on the opposite side of the fulcrum from the other. It
may be on the same side as in the verge or at any other convenient
point. This enables us to save space in arranging our trains, as such
a collection of wheels and pinions is called, by placing them in any
position which, on account of other facts, may seem desirable.
PECULIARITIES OF ANGULAR MOTION.—Now our collections of levers must
move in certain directions in order to be serviceable and in order to
describe these things properly, we must have names for these movements
so that we can convey our thoughts to each other. Let us see how they
move. They will not move vertically (up or down) or horizontally
(sidewise), because we have taken great pains to prevent them from
doing so by confining the central bars of our levers in a fixed
position by making pivots on their ends and fitting them carefully into
pivot holes in the plates, so that they can move only in one plane, and
that movement must be in a circular direction in that predetermined
plane. Consequently we must designate any movement in terms of the
portions of a circle, _because that is the only way they can move_.
These portions of a circle are called angles, which is a general term
meaning always a portion of a circle, measured from its center; this
will perhaps be plainer if we consider that whenever we want to be
specific in mentioning any particular size of angle we must speak of it
in degrees, minutes and seconds, which are the names of the standard
parts into which a circle is divided. Now in every circle, large or
small, there are 360 degrees, because a degree is ¹/₃₆₀th part of a
circle, and this measurement is always _from its center_. Consequently
a degree, or any angle composed of a number of degrees, is always the
same, because, being _measured from its center_, such measurements
of any two circles will coincide as far as they go. If we draw two
circles having their centers over each other at A, Fig. 26, and take
a tenth part of each, we shall have 360° ÷ 10 = 36°, which we shall
mark out by drawing radial lines to the circumference of each circle,
and we shall find this to be true; the radii of the smaller circle AB
and AC will coincide with the radii AD and AE as far as they go. This
is because each is the tenth part of its circle, _measured from its
center_. Now that portion of the circumference of the circle BC will be
smaller than the same portion DE of the larger circle, but each will be
a _tenth part of its own circle_, although they are not the same size
when measured by a rule on the circumference. This is a point which has
bothered so many people when taking up the study of angular measurement
that we have tried to make it absurdly clear. An angle _never_ means
so many feet, inches or millimeters; it _always_ means a _portion of a
circle, measured from the center_.
[Illustration: Fig. 26.]
There is one feature about these angular (or circular) measurements
that is of great convenience, which is that as no definite size is
mentioned, but only proportionate sizes, the description of the machine
described need not be changed for any size desired, as it will fit all
sizes. It thus becomes a flexible term, like the fraction “one-half,”
changing its size to suit the occasion. Thus, one-half of 300,000
bushels of wheat is 150,000 bushels; one-half of 10 bushels is 5
bushels; one-half of one bushel is two pecks; yet each is _one-half_.
It is so with our angles.
There are some other terms which we shall do well to investigate
before we leave the subject of angular measurements, which are the
relations between the straight and curved lines we shall need to study
in our drawings of the various escapements. A radius (plural radii) is
a straight line drawn from the center of a circle to its circumference.
A tangent is a straight line drawn outside the circumference, touching
(but not cutting) it _at right angles_ (90 degrees) to a radius drawn
to the point of tangency (point where it touches the circumference).
A general misunderstanding of this term (tangent) has done much to
hinder a proper comprehension of the writers who have attempted to make
clear the mysteries of the escapements. Its importance will be seen
when we recollect that about the first thing we do in laying out an
escapement is to draw tangents to the pitch circle of the escape wheel
and plant our pallet center where these tangents intersect on the line
of centers. They should always be drawn at _right angles_ to the radii
which mark the angles we choose for the working portion of our escape
wheel. If properly drawn we shall find that the pallet arbor will then
_locate itself_ at the correct distance from the escape wheel center
for any desired angle of escapement. We shall also discover that it
will take a different center distance for every different angle and yet
each different position will be the correct one for its angle, Fig. 27.
Because an angle is always the same, no matter how far from the center
the radii defining it are carried, we are able to work conveniently
with large drawing instruments on small drawings. Thus we can use an
eight or ten inch protractor in laying off our angles, so as to get
the degrees large enough to measure accurately, mark the degrees with
dots on our paper and then draw our lines with a straight edge from the
center towards the dots, as far as we wish to go. Thus we can lay off
the angles on a one-inch escape wheel with a ten inch protractor more
easily and correctly than if we were using a smaller instrument.
[Illustration: Fig. 27.]
Another thing which will help us in understanding these drawings is
that the _effective_ length of a lever is its distance from the center
to the working point, _measured in a straight line_. Thus in a pallet
of a clock the distance of the pallets from the center of the pallet
arbor is the _effective length_ of that arm of the lever, no matter how
it may be curved for ornament or for other reasons.
The lines and circles drawn to enable us to take the necessary
measurements of angles and center distances are called “construction
lines” and are generally dotted on the paper to enable us to
distinguish them as lines for measurement only, while the lines which
are intended to define the actual shapes of the pieces thus drawn are
solid lines. By observing this distinction we are enabled to show the
actual shapes of the objects and all their angular measurements clearly
on the one drawing.
With these explanations the student should be able to read clearly
and correctly the many drawings which follow, and we will now turn
our attention to the escapements. In doing this we shall meet with a
constant use of certain terms which have a peculiar and special meaning
when applied to escapements.
THE LIFT is the amount of angular motion imparted to the verge or
anchor by the teeth of the escape wheel pressing against the pallets
and pushing first one and then the other out of the way, so that the
escape wheel teeth may pass. According as the angular motion is more
or less the “lift” is said to be greater or less; as this motion is
circular, it must be expressed in degrees. The lifting planes are
those surfaces which produce this motion; in clocks with pendulums
the lifting planes are generally on the pallets, being those hard and
smoothly polished surfaces over which the points of the escape wheel
teeth slide in escaping. In lever escapements the lifting planes are
frequently on the escape wheel, the pallets being merely round pins.
Such an escape wheel is said to have club teeth, as distinguished from
the pointed teeth used when the lifting planes are on the pallets. In
the cylinder escapement the lifting planes are on the escape wheel;
they are curved instead of being straight; and there is but one pallet,
which is on the lip of the cylinder. In the forms of lever escapement
used in watches and some clocks the lift is divided, part of the
lifting planes being also on the pallets; in this case both sets of
planes are shorter than if they were entirely on one or the other,
but they must be long enough so that combined they will produce the
requisite amount of angular motion of the pallets, so as to give the
requisite impulse to the pendulum or balance.
THE DROP is the amount of circular motion, measured in degrees, which
the escape wheel has from the instant the tooth escapes from one pallet
to that point at which it is stopped by the other pallet catching
another tooth. During this period the train is running down without
imparting any power to the pendulum or balance, hence the drop is
entirely lost motion. We must have it, however, as it requires some
time for the other pallet to move far enough within the pitch circle
of the escape wheel to safely catch and stop the next tooth under all
circumstances. It is the freedom and safety of the working plan of
our escapement, but it is advisable to keep the drop as small as is
possible with safe locking.
THE LOCK is also angular motion and is measured in degrees from the
center of the pallet arbor. It is the distance which the pallet has
moved inside of the pitch circle of the escape wheel before being
struck by the escape wheel tooth. It is measured from the edge of the
lifting plane to the point of the tooth where it rests on the locking
face of the pallet. A safe lock is necessary in order to prevent the
points of the escape wheel teeth butting against the lifting planes,
stopping the clock and injuring the teeth. We want to point out that
from the instant of escaping to the instant of locking we have the two
parts of our escapement propelled by different and entirely separate
forces and moving at different speeds. The pallets, after having given
impulse to the pendulum, are controlled by the pendulum and moved by
it; in the case of a heavy pendulum ball at the end of a 40-inch lever,
this control is very steady, powerful and quite slow. The escape wheel,
the lightest and fastest in the train, is driven by the weight or
spring and moves independently of the pallets during the drop, so that
safe locking is important. It should never be too deep, as it would
increase the swing of the pendulum too much; this is especially true
with short and light pendulums and strong mainsprings.
THE RUN.—After locking the pallet continues to move inward towards
the escape wheel center as the pendulum continues its course, and the
amount of this motion, measured in degrees from the center of the
pallet arbor, is called the run.
When the escapement is properly adjusted the lifting planes are of
the same length on both pallets, when they are measured in degrees
of motion given to the pallet arbor. They may or may not be equal in
_length_ when measured by a rule on the faces of the pallets. There
should also be an equal and safe lock on each pallet, as measured in
degrees of movement of the pallet arbor. The run should also be equal.
The reason why one lifting plane may be longer than the other and still
give the same amount of lift is that some escapements are constructed
with unequal lockings, so that one radius is longer than the other, and
this, as we explained at length in treating of angles, Fig. 26, would
make a difference in the length of arc traversed by the longer arm for
the same angle of motion.
CHAPTER VIII.
THE GRAHAM OR DEAD BEAT ESCAPEMENT.
This escapement is so-called because the escape wheel remains “dead”
(motionless) during the periods between the impulses given to the
pendulum. It is the original or predecessor of the well known detached
lever escapement so common in watches, and it is surprising how many
watchmakers who are fairly well posted on the latter form exhibit a
surprising ignorance of this escapement as used in clocks. It has like
the latter a “lock,” “lift” and “run”; the only difference being that
it has no “draw,” the control by the verge wire rendering the draw
unnecessary.
It may be made to embrace any number of teeth of the escape wheel,
but, owing to the peculiarities of angular motion referred to in the
last chapter, see Fig. 26, B C, D E, the increased arcs traveled
as the pallet arms lengthen introduce elements of friction which
counterbalance and in some cases exceed the advantage gained by
increasing the length of the lever used to propel the pendulum.
Similarly, the too short armed escapements were found to cause
increased difficulty from faulty fitting of the pivots and their holes,
and other errors of workmanship, which errors could not be reduced in
the same proportion as the arms were shortened, so that it has been
determined by practice that a pallet embracing ninety degrees, or
one-fourth of the circumference of the escape wheel, offers perhaps
the best escapement of this nature that can be made. Therefore the
factories generally now make them in this way. But as many clocks are
coming in for repair with greater or less arcs of escapement and the
repairers must fix them satisfactorily, we will begin at the beginning
by explaining how to make the escapement of any angle whatever, from
one tooth up to 140 degrees, or nearly half of the escape wheel.
It is quite a common thing for some workmen to imagine that in making
an escapement, the pallets ought to take in a given number of teeth,
and that the number which they suppose to be right must not be departed
from; but there seems to be no rule that necessarily prescribes any
number of teeth to be used arbitrarily. The nearer that the center of
motion of the pallets is to the center of the escape wheel, the less
will be the number of teeth that will be embraced by the pallets. Fig.
28 is an illustration of the distances between the center of motion of
the pallets and the center of the wheel required for 3, 5, 7, 9 and
11 teeth in a wheel of the same size as the circle; but although we
have adopted these numbers so as to make a symmetrical diagram, any
other numbers that may be desirable can be used with equal propriety.
All that is necessary to be done to find the proper center of motion
of the pallets is first to determine the number of teeth that are to
be embraced, and draw lines (radii) from the points of the outside
ones of the number to the center of the wheel, and at right angles
to these lines draw other two lines (tangents), and the point where
they intersect each other on the line of centers will be the center of
motion of the pallets.
[Illustration: Fig. 28.]
[Illustration: Fig. 29. Note the difference in length of arc for the
same angle.]
It will be seen by the diagram, Fig. 28, that by this method the
distance between the centers of motion of the pallets and that of the
scape wheel _takes care of itself_ for a given number of teeth and that
it is greater when eleven and one-half teeth are to be embraced than
for eight or for a less number. These short pallet arms are imagined
by some workmen to be objectionable, on the supposition that it will
take a heavier weight to drive the clock; but it can easily be shown
that this objection is altogether imaginary. Now, bearing in mind
the principles of leverage, if the distance between the pallets and
escape wheel centers is very long, as in Graham’s plan, in which the
pallets embraced 138° of the escape wheel, the value of the impulse
received from the scape wheel and communicated through the pallets to
the pendulum is no doubt greater with a proper length of verge wire,
for, the lifting planes being longer, the leverage is applied to the
pendulum for a longer arc of its vibration, yet we must not suppose
that from this fact the clock will go with less weight, for it is
easy to see that the longer the pallet arms are the greater will be
the distance the teeth of the escape wheel will have to move (run) on
the circular part of the pallets. See Fig. 29. The extra amount of
friction, and the consequent extra amount of resistance offered to the
pendulum, caused by the extra distance the points of the teeth run on
the circular locking planes of the pallets and back again, destroys
all the value of the extra amount of impulse given to the pendulum
in the first instance by means of the long arms of the pallets. The
escape wheel tooth resting on the locking plane of the pallet is quite
variable in its effective action, and since it rests on the pallet
during a part of each swing of the pendulum and the pendulum is called
on to move the pallet back and forth under the tooth, any change in the
friction between the tooth and pallet is felt by the pendulum and when
the clock gets dirty and the friction between the tooth and pallet is
increased, the rate of the clock gets slow, as the friction holds the
pendulum from moving as fast as it would without friction. Now, as
this friction increases by dirt and thickening of the oil, all these
forms of escapements are subject to changes and so change the clock’s
rate. An increase of the driving weight, or force of the mainspring, of
clocks with dead-beat escapements always tends to make their rate slow,
from the action mentioned.
It is for this reason that moderately short arms are used in clocks
having dead-beat escapements of modern construction. Most of the
first-class modern makers of astronomical clocks only embrace seven
and one-half teeth, on a 30-tooth wheel, with the centers of motion
of the pallets and scape wheel proportionately nearer, as it can be
mathematically demonstrated that with the pallets embracing an arc of
90° the application of the power to the pendulum is at right angles to
the rod and therefore is most effective.
TO DRAW THE ESCAPEMENT.—In order to make the matter clearer we show
in Fig. 30 the successive stages of drawing an escapement and also the
completed work in Figs. 32 and 33 embracing different numbers of teeth.
Draw a line, A B, Fig. 30, to serve as a basis for measurements. With
a compass draw from some point C on this line a circle to represent
the diameter of our escape wheel. Now we shall require to know how
many teeth there will be in our escape wheel. There may be 60, 40, 33,
32, 30, or any other number we desire to give it; seconds pendulums
generally have 30 teeth in this wheel, because this allows the second
hand to be mounted directly on the escape wheel arbor and thus avoids
complications. We divide the number of degrees in a circle (360) by the
number of teeth we have selected, say 30. 360 ÷ 30 = 12° for each tooth
and space. One-fourth of 360° equals 90° and one-fourth of 30 teeth
equals seven and one-half teeth; each tooth equaling 12 degrees, we
have 12 × 7 = 84°, which gives us six degrees for drop, to ensure the
safety of our actions.
[Illustration: Fig. 30.]
We now take 90° and, dividing it, set off 45° each side of our center
line and draw radii, R, from the center to the circumference of our
circle; this marks the beginnings of our pallets. Now to find our
pallet center distance we draw tangents, T (at right angles), from the
ends of these radii toward the line of centers. The point where they
intersect on the line of centers is the pallet center.
Now we must determine how much motion we are going to give our
pendulum, so that we can give the proper lift to our pallets. Four
degrees of swing is usual for a seconds pendulum, so we will take four
degrees and, dividing it, give two degrees of lift to each pallet. To
do this we draw a line two degrees _inside_ the tangent, T (towards the
escape wheel center), from our pallet center on the entering pallet
side and another line from the pallet center two degrees _outside_
of the tangent, T, on the exit pallet side. Next, from the pallet
center we draw arcs of circles cutting the tangents, T, and the radii,
R, where they intersect; this gives us the locking planes on which
the teeth of the escape wheel “run” (slide) during the excursions of
the pendulum, if the escapement is to have unequal lockings; if the
lockings are to be equidistant (if the pallet arms are to be of equal
length) the arc for the entering pallet is drawn three degrees below
(outside) the radius, R, while that on the exit pallet is drawn three
degrees _above_ (inside) the exit radius. Finally the lifting planes
are drawn from the intersection of the arcs of circles struck from
the pallet center with their tangents, T, to the lines, marking the
limits of the lift, two degrees away. These lifting planes should be
at an angle of 60° from the radii, R, and as a tangent is always at
right angles (90°) to its radius, they are consequently at 30° to the
tangents running to the pallet center. Thus we can measure these angles
from either the escape wheel or the pallet center, as may be most
convenient.
When making a new pallet fork, it is most convenient to mark out the
lifting planes on the steel at 30° from the tangents, T, as we then do
not have to bother with the escape wheel further than to get its center
distance and the degrees of arc the lifting planes are to embrace. The
workman who is not familiar with this rule is apt to have his ideas
upset at first by the angles of inclination toward the center line
which the lifting planes will take for different center distances,
as owing to the fact that the tangents meet on the center line at
different angles for different distances, the lifting planes assume
different positions with regard to the center line and he may think
that they do not “look right.” They are right, however, when drawn at
30° to their tangents. Fig. 31 shows several pallets with different
arcs arranged in line for purposes of comparison, each being drawn
according to the above rule, as measurements with a protractor will
show.
[Illustration: Fig. 31.]
We have now arrived at the complete escapement, having finished our
pallets. We have, however, nothing to hold them in position; they must
be rigidly held in position with regard to each other and the escape
wheel, consequently we will make a yoke to connect them to the pallet
arbor out of the same steel, giving it any desired shape that will not
interfere with the working of the clock. Two of the most usual forms
are shown at Figs. 32 and 33.
[Illustration: Fig. 32.]
[Illustration: Fig. 33.]
Let us see how this rule will work in repairs. Suppose we have a clock
brought in with the pallet fork missing, and that the movement is one
of those in which the pallet arbor is held by adjustable cocks which
have been misplaced or lost, so that we don’t know the center distance
of the pallet arbor and escape wheel. We shall have to make a new part.
Measure the escape wheel, getting its diameter carefully, take half
of this as a radius, and mark out the circle with a fine needle point
on some copper, brass or sheet steel, drawing the escapement as
detailed in Figs. 30 and 32. Then measure carefully the angles made
by the tangents with the center line; take the steel which is to be
used in making the pallets and fork; draw on it a center line; lay
off the tangents and the lift lines; draw the locking arcs and the
lifting planes carefully from the tangents and give the rest of the
fork a symmetrical shape. Use needle points to draw with and have your
protractor large enough to measure your angles accurately. Then drill
or saw out and file to your lines, except on the locking and lifting
planes; leave these large enough to stand grinding or polishing after
hardening. Harden; draw to a straw color and polish the planes. Your
verge will fit if it has not warped in hardening. If this is the case,
soften the center, keeping the heat away from the pallets, and bend or
twist the arms until the verge will fit the drawing, when laid on top
of it. In grinding the pallets the fork should be mounted on its arbor
and the latter held between the centers of a rounding-up tool while the
grinding is done by a lap in the lathe. This insures that the planes
will be parallel to the pallet arbor and hence square with the escape
wheel teeth, so that they will not create an end thrust on either
escape or pallet arbor. It is also the quickest, easiest and most
reliable way of doing the job. When clocks come in with the pallets
badly cut; soften the center of the fork, place the ends between the
jaws of a vise, squeeze enough to bring them closer, mount in the
rounding-up tool and lap off the cut planes until they are smooth and
stand at the proper angle; then polish. This is done quickly.
[Illustration: Fig. 34. Drawing escape wheel to fit a tracing from a
pallet fork.]
Can we work the rule backwards? Suppose we get a clock in which we
have the pallet arbor adjustable as before, and we have the pallet
fork all in good shape, but we have lost the escape wheel, or it has
been butchered by somebody before coming to us, so that a new one is
required.
Take off the pallet fork; lay it on a sheet of brass and trace around
it carefully with a needle point. Fig. 34. Mark the center carefully
at the pallet arbor hole and measure carefully the distance between
the pallets and mark that center. Draw a center line cutting these
centers and extending beyond. Now draw the tangent from the beginning
of the entering pallet (as shown by the tracing on our brass) to the
pallet center; do the same with the exit pallet. Now take a metal
square and place it on one of the tangents exactly, with the end at
the beginning of the entering pallet; trace a line cutting the line
of centers and we have the radius of our escape wheel. Trace a circle
from the intersection of the radius and the center line and we have
the circumference of our escape wheel. This circle should also cut
the intersection of the tangent and radius on the other side if it is
drawn correctly; if it does not do this an error has been made in the
drawing.
[Illustration: Fig. 35. Drawing an escape wheel to cut. The last
drawing shows the complete wheel.]
Having found the diameter and circumference of our escape wheel it may
be sawed out and mounted for wheel cutting; or, if we have no wheel
cutter and must make the wheel, we must draw it on the brass by hand
with a fine needle point before proceeding to saw it out by hand, Fig.
35. Say that the wheel is to have thirty-two teeth, which is a common
number; then 360° ÷ 32 = 11¼° as the space between the points of our
teeth. Take a large protractor, one with the degrees large enough
to be divided (I use a ten inch); place its center on the center of
our escape wheel, set off 11¼° and mark them on the brass with the
needle point, at the edge of the protractor. Then take a straight edge
and draw a radius from the center to the circumference; change the
straight edge to the other mark and mark the point where it crosses
the circumference; set your dividers accurately by this mark and
space off the teeth on your circumference. If they are set at eleven
degrees and fifteen minutes they will come out exactly at the end.
Now take your protractor and with its center at the junction of the
radius and circumference set off ten degrees and draw a line past the
center of the wheel; set off twenty degrees and draw another line the
same way. From the center of the escape wheel draw two circles just
touching these lines. Outside of these draw two circles defining the
inner and outer edges of the rim of the wheel. With the straight edge
just touching the inner circle draw in the fronts of the teeth; these
will all be set at ten degrees from a radius, so that only the extreme
points will touch the locking planes of the pallets and thus reduce the
friction during the run. The backs of the teeth are marked out in the
same way from the twenty-degree circle. The hub is made to coincide
with the ten-degree circle; the spokes are traced in and we are ready
to begin sawing out.
If the workman has a wheel cutter the job is much simpler. A piece
of brass is mounted on a cement brass with soft solder, faced off,
centered and the pitch circle, inner and outer edges of the rim and
the hub are traced with the T-rest and graver. The extra metal is then
cut away and a suitable index placed on the spindle and locked. The
wheel cutter is set up with a fine-toothed, smooth cutting saw on the
spindle, horizontal, with its upper edge at the line of centers of the
lathe. It is then run out to the circumference of the wheel, turned
upwards ten degrees and the wheel cut around, Fig. 36. This makes the
fronts of the teeth. Turn the saw ten degrees more and cut the backs
of the teeth. Then turn the saw so that it will reach from the front
of one tooth to the root of the back of the next one, without touching
either tooth, and cut round again; this cuts out a triangular piece of
waste metal between the teeth. Turn the saw again so that it reaches
from the bottom of the front of a tooth to the top of the back of the
next one and cut around again, thus removing another portion of the
waste metal, and leaving only a small triangle between the teeth. Lower
the saw its own thickness and cut around the wheel again, repeating the
operation until the waste metal is all removed and you have a smooth
circular rim between the teeth, Fig. 36.
[Illustration: Fig. 36. Making an escape wheel with a saw, showing the
successive cuts.]
Set the saw horizontally at the lathe center; raise it one-half the
thickness of the spokes; set the index pin of the lathe head firmly at
O; feed in the saw the thickness of the wheel and make straight cuts
across from the circle of the inner rim to the circle marking the hub,
but not cutting either; set the index pin at 30 and repeat; next lower
your saw and cut the other side of the spokes the same way.
Next you can mount a lap in place of the saw and smooth the fronts and
backs of the teeth and if you have a rather thick disc the outer edge
of the rim, between the teeth, may also be smoothed.
If you have a good strong pivot polisher, mount a triangular end mill
in the spindle, lock the yoke, and cut the arcs of circles of the hub
and rim from edge to edge of the spokes, feeding carefully against the
mill with the hand on the lathe pulley.
Put on your jeweling tailstock and open the wheel to fit the pinion,
collet, or arbor, if there is no collet.
You now have the wheel all done, except facing the side that was
soldered to the cement brass and trimming up the corners of the spokes
at the rim and hub, and you have got it round, true and correct in much
less time than you could have done in any other way, while an immense
amount of work with the file and eye-glass has been avoided. It is true
because it was soldered in position at the beginning and has not been
removed until finished.
Sometimes what are known from their appearance as club-shaped teeth are
used in the wheels of Graham’s escapements. Pendulums receive their
impulse from escapements made in this manner partly from the lifting
planes on the pallets, and partly from the planes on the scape wheel.
The advantage gained by this method is, that wheels made in this
way will work with the least possible drop, and consequently, power
is saved; but the power saved is thrown away again in the increased
friction of the planes of the wheel against those of the pallets, which
is considerably more than when plain-pointed teeth are used on the
escape wheel.
Clock pallets are usually made of steel, and on the finer classes of
work jewels are often set into them to prevent the oil from drying,
after the same fashion as jewels are placed in steel pallets in a
lever watch; but it is obvious that stone pallets made in this way
have to be finished with polishers held in the hand, and that, except
in factories, they cannot be made so perfectly regular, especially
that pallet that is struck downwards, as the particular action of a
fine Graham escapement requires. When great accuracy is required, the
pallets are usually made of separate pieces, and the acting circles
ground and polished on laps, running in a lathe. This method of
constructing pallets also allows a means of adjustment which in some
particular instances is very convenient.
There is also a plan of making jeweled pallets adjustable, which is
practiced on fine work, such as astronomical and master clocks. The
pallet fork consists of two pieces of thin, hard, sheet brass, cut out
in the usual form and two mounted on one arbor. Circular grooves are
cut in the sides of both plates, at the proper distance, and of the
proper size to receive the jewels which are the acting parts of the
pallets. When jewels cannot be made of the desired size, pallets of
steel are made, and the jewels are then set into the steel large enough
for the teeth of the wheel to act upon. The two parts of the fork are
fastened at a given distance apart, and the jewels, or pieces of steel,
go in between them, and, after they have been adjusted to the proper
position, are fastened by screws that pull the frames close together
and press against the edges of the jewels. Pallets made in this manner
have a very elegant appearance. Another method is to have only one
frame, and to have it thick enough, where the jewels have to be set in,
to allow a groove to be cut in its side as deep as the jewels (or the
pieces of steel that hold the jewels) are broad, and which are held in
their proper position by screws. This system of jeweling pallets is
frequently adopted by the makers of fine mantel clocks.
[Illustration: Fig. 37. Brocot’s visible escapement, escaping over 120°
with pointed teeth. Dotted lines on pallets show where they are cut to
avoid stopping.]
BROCOT’S VISIBLE ESCAPEMENT.—Fig. 37 represents a system of making
and jeweling pallets much used by the French in their small work,
especially in visible escapements. The acting parts of the pallets
are simply cylinders, generally of colored stones, usually garnets,
one-half of each cylinder being cut away. These cylinders extend some
distance from the front of the pallet frame, and work into the escape
wheel the same as the pallets of a Graham escapement—the round parts
of the pallets serving as impulse planes. The neck of the brass pallet
frame is cut up in the center, and the width between the pallets is
sometimes adjusted by a screw, sometimes by bending the arms.
Clock movements with this escapement, of a careful construction, will
frequently come for repairs, accompanied by the complaint of constant
stopping and that no attempt at closely regulating can succeed with
them, although they appear to have no visible disturbing cause. In such
cases the depthing of the escapement is generally wrong. With proper
depthing the point of the escape wheel tooth should drop on the center
or a little beyond the center of the pallet stone. If it is set in
this way the clock will stop when wound, especially if it has a strong
spring, as the light pendulum will not then have momentum enough to
unlock it against the full power of the spring. If the pallets are set
shallow, in order to avoid this difficulty, then, the pendulum will
take too short a swing and thus the clock will have a gaining rate.
Generally the pendulum ball cannot be made enough heavier to correct
the defect.
[Illustration: Fig. 38. Brocot’s visible escapement escaping over 90°
with a small lift on the escape wheel teeth.]
In these movements, in which the length of the pendulum does not
exceed 4 inches, the pallet fork embraces, generally about 120°, or
the one-third part of the wheel; it will be seen that unless there are
stop works on the barrel of the main spring no manner of regulating
is possible with these conditions, in view of the considerable
influence exercised by the mainspring through the train on the very
light pendulum, and by replacing this unduly high anchor by a lower
one, I have always been able to produce a very satisfactory rate with
movements having pendulums of three and a half to four inches. Fig. 38
shows a 90° escapement with a small lift on the escape wheel teeth.
In spite of its incontestable qualities, the visible escapement
possesses one inherent fault. I refer to the formation of its pallets,
the semi-circular shape of which renders unequal the action of the
train in giving impulse to the pendulum exceeding 50 centimeters (20
inches), since to make it to describe arcs of from one to two degrees
only, with pendulums of from 60 centimeters to one meter in length,
it became necessary to make the anchor arms extremely long, which
considerably impeded the freedom of action, especially when the oil
became thick, and this disposition would, therefore, stand in direct
contradiction with the principles of modern horology. Both stopping and
the irregularity of rate can be obviated by changing the semi-circular
form of the pallets for one of an inclined plane, either by grinding a
new plane or turning the stones in such manner as to offer an inclined
plane to the action of the wheel, analogous to that of the Graham
escapement. See Fig. 37, the dotted lines on the pallets showing the
portion to be ground away.
The importance of this transformation will readily be understood; it
suffices to give to these planes a more or less large inclination in
order to obtain a greater regularity of lifting, and, at desire, a
lifting arc more or less considerable without being compelled to modify
the proportions of the fork or to exaggerate the center distance of
wheel and pallet arbor.
In adjusting an escapement, perhaps it may be advisable to mention that
moving the pallets closer together, or opening them wider, will only
adjust the drop on one side, while the other drop can only be affected
by altering the distance between the centers of the pallets and scape
wheel. This is accomplished in various ways. The French method consists
of an eccentric bush, riveted in the frame just tight enough to be
turned by a screwdriver. Another plan, common in America, is simply
pieces of brass (cocks) fastened on the sides of the frames. The pivots
of the pallet axis are hung in holes in these cocks, and an adjustment
of great accuracy may be quickly obtained by loosening the clamping
screws. Lock, drop and run should be of the same amount on each pallet.
However, we do not approve of adjustments of any kind, except in the
very highest class of clocks, where they are always likely to be under
the care of skillful people, who understand how to use the adjustments
to obtain nicety of action in the various parts.
In making escapements, lightness of all the parts ought to be an object
always in view in the mind of the workman, and such materials should be
used as will best serve that purpose. The scape wheel, and the pallets
and fork, should have no more metal in them than is necessary for
stiffness. The pallet arbor, and also the escape wheel arbor, should be
left pretty thick when the wheel and pallets are placed in the center
between the plates, to prevent their springing when giving impulse to
the pendulum. We have often been puzzled to find out the necessity or
the utility of placing them in the center between the plates, as they
are so generally done in English clockwork. The escapement acts much
more firmly when it is placed near one of the plates, and it is just as
easy to make it in this way as in the other.
It is often assumed that the friction of the teeth on the circular
part of the pallets of a dead-beat escapement is small in amount and
unimportant in its value. With respect to its amount, we believe it
is often not far short of being equal to one-half of the combined
retarding forces presented to the pendulum; and with respect to its
being unimportant, this assumption is founded on the supposition that
it is always a uniform force, when it is easy to show that it is not
a uniform force. It is very well known that the force transmitted in
clock trains, from each wheel to the next, is very far from being
constant. Small defects in the forms of the teeth of the wheels and
of the leaves of the pinions, and also in the depths to which they
are set into each other, cause irregularities in the amount of power
transmitted from each wheel to the next; and the accidental combination
of these irregularities in a train of four or five wheels, makes the
force transmitted from the first to the last exceedingly variable.
The wearing of the parts and the change in the state of the oil, are
causes of further irregularities; and, from these causes, it must be
admitted that the propelling power of the scape wheel on the pallets is
of a variable amount, and a more important question for consideration
than it is usually supposed to be. To avoid the consequences of this
irregular pressure of the scape wheel on the pallets being communicated
to the pendulum, is a problem that has puzzled skillful mechanicians
for many years; for, although we find the Graham escapement to be
pronounced both theoretically and mechanically correct, and by
some authorities little short of perfection, we find some of these
same authorities—both theoretically and practically—testify their
dissatisfaction with it by endeavoring to improve on it. In Europe the
experience of generations and the expenditure of small fortunes, in
pursuit of this improvement, through the agency of the gravity, and
other forms of escapements, proves this fact; while of late years,
in the United States, much time and money has been spent on the same
subject, and results have been reached which have raised questions
that ten years ago were little dreamed of by those clockmakers who are
generally engaged on the highest class of work.
While considering this class of escapements, we would say a few words
in regard to the sizes of escape wheels generally used. Small wheels
can now be cut as accurately as larger ones and there is now no reason
or necessity for continuing the use of a wheel of the size Graham and
Le Paute used, and which has been the size generally adopted by most
European makers who use these escapements. The Germans and Swiss make
wheels much smaller for Graham escapements than the English makers do;
and the American factories make them smaller still. On the continent
of Europe the wheels of Le Paute’s escapement are made much larger
than they are made in England and in the United States. No wheel, and
more especially a scape wheel, should be larger than will just give
sufficient strength for the number of teeth it has to contain, in
proportion to the amount of work that it has to perform. The amount
of work a scape wheel has to perform in giving motion to the pendulum
is of the lightest description, and not more than one-tenth of what
it is popularly supposed to be, which is shown by its variation under
slight increase of friction; therefore we do not consider that we take
extreme ground in recommending wheels for these escapements to be made
nearly half the size their originators made them, and the pallets
drawn off in proportion to the reduced size of the wheel. It is plain
that by reducing the size of the wheel its inertia will be reduced.
When the teeth begin to act on the inclined planes of the pallets, the
wheel will be set in motion with greater ease, as it has a shorter
leverage, and the amount of the dead friction of the scape wheel teeth
on the inclined planes and circular part of the pallets will also be
proportionately reduced by making the wheel smaller. Factory experience
and examination of a large number of clocks in repair shops have also
shown that smaller and thicker escape wheels will wear much longer than
larger and thinner ones, as all the wear is at the points of the teeth
and this is the portion to be protected.
CHAPTER IX.
LE PAUTE’S PIN WHEEL ESCAPEMENT.
Probably in no other escapement, except the lever, has there been so
many modifications as in the pin wheel; this is so to such an extent
that it will be found by the student that nearly every escapement of
this kind which he will examine will differ from its fellows if it
has been made by a different maker. They will be found to vary in the
lengths of the pallet arms from three-fourths to one and a half times
the diameter of the escape wheel; some of them will have the longer
arm of the pallets outside and some inside; some will have the lift
for both pallets laid out on one side of the perpendicular P, Fig.
39, while others will have the lift divided, with the perpendicular
in the center. Very old escapements have the pallet center directly
over the escape wheel center, while the pallet arms work at an angle
of 45°, while others have them with the pallet center planted on a
perpendicular, tangent to the pitch line of the escape wheel. Some have
the circular rest or locking faces of the pallets rounded slightly to
hold the oil in position while others have them flat and still others
have them made of hard stone, polished. More than half have the pins in
the escape wheel cut away for one-half of their diameters, leaving the
bottoms round, as shown in Fig. 39, while others use a wider pin and
trim away the bottoms also, as in Fig. 40, leaving the lifting surface
on the pins not more than one-fourth the arc of the circle. This is
especially true of the larger escapements used in tower clocks, though
they are also found in regulators.
[Illustration: Fig. 39. Pin Wheel Escapement.]
[Illustration: Fig. 40. Pin Wheel With Flattened Teeth.]
In view of the wide variation in practice, therefore, we have
endeavored to present in Fig. 39 a conservative statement of the
general practice as found in existing clocks. We say existing, because
very few of these escapements are made now—none at all in America—and
those in use are generally in imported regulators, which have come from
Switzerland or Germany. The Waterbury Clock Co. at one time made this
escapement for its regulators and the Seth Thomas Clock Company made a
number of its early tower clocks with it, but both have discontinued
it for some years, and it is safe to say that any movement coming into
the watchmaker’s hands which has this escapement is imported; or if
American, it is out of the market. Le Paute claimed as an advantage
the fact that the impact of the escape wheel teeth is downward on both
pallets, whereas in the gravity and recoil escapements one blow is
struck upwards and the other downwards. He claimed that by this means
a better action was secured after the pivot holes began to wear, as
there was less lost motion with both blows in the same direction and
any shake would not affect the amount of impulse given to the pendulum.
The difference is more theoretical than practical, however, and the
escapement possesses one serious fault, which is that the pins forming
the escape wheel teeth conduct the oil away from the pallets, so that
the clock changes its rate in from eight months to one year after being
oiled and cleaned. The most effective means of counteracting this is
to round the locking planes of the pallets slightly, so that the oil
will be held on them by capillary attraction. Another method is to turn
the pins so that they are thicker in diameter at the point of contact
with the pallets, but this is seldom tried. The best plan is to keep
the pallets as close as they can be to the face of the wheel without
touching.
TO DRAW THE ESCAPEMENT.—In laying out this escapement the first thing
to consider is the arc of swing of the pendulum, because one-half
of the lift is on the pin and consequently one-half the lift must
equal one-half the diameter of the pin, as shown in Fig. 39. If the
pendulum swings four degrees, then the diameter of each pin must
equal four degrees of the pallet movement. This establishes the size
of our pin; it is measured from the pallet staff hole. There are 30
of these pins for a second’s pendulum, and unless it is a very large
escapement the pins cannot be made less in diameter than one-fourth the
distance between the pins, or they will be too weak and will spring;
consequently 360 ÷ 30 = 12° and 12° ÷ 4 = 3°, so that three degrees of
the pitch line of the escape wheel equals the swing of the pallet fork.
This establishes the relation as to size between the escape wheel and
the opening, or swing of the pallet fork. Draw a perpendicular, P, from
the pallet center and on one side of it lay out the lift lines L, L;
draw a line at right angles to the perpendicular and where it crosses
the inner lift line draw a circle touching the outer lift line. The
diameter of this circle equals three degrees of the circumference of
the wheel, on its pitch line, and this multiplied by 120 gives 360° or
the pitch circumference of the escape wheel. Dividing the sum so found
by 3.1416 gives the diameter of the escape wheel and half of this is
the radius. After finding the radius draw the pitch circle and set out
the other twenty-nine teeth spaced twelve degrees apart, and drawn in
half circles as shown in Fig. 39.
Now to get the thickness of the pallet arms. When the pin shown in
action in Fig. 39 has just cleared the lower edge of the inner pallet,
the succeeding pin should fall safely on the upper corner of the outer
pallet; consequently the thickness of these two arms, the pin between
them, and the drop (clearance between the pin and the lower edge of the
upper pallet) should just equal the distance between two pins, from
center to center, or 12° of the escape wheel. With the first or inner
lift line as a starting point, draw the lower arcs of the pallets and
draw the upper or locking planes from the perpendicular and the outer
lift line. Then draw the lifting planes of the pallets by connecting
the ends of these arcs. The enlarged view above the escape wheel in
Fig. 39 will show how this is done more clearly than the main drawing.
It is best to make the pallet fork of steel, in two pieces, screwed to
a collet on the pallet arbor, as the inner arm must be bent, or offset,
so that it will clear the pins of the escape wheel, and the pallets
should lie in the same plane, as close to the wheel as is possible
without touching it. The pallets are hardened.
In tower clocks the escapement is so large that a pin having a diameter
of three degrees of the escape wheel gives a half pin of greater
strength than is necessary for the work to be done and such pins are
cut away on the bottom, as in Fig. 40. In making the wheel it should be
drilled in the lathe with the proper index to divide the wheel and the
pins riveted in; then the pins are cut with a wheel cutter as if they
were teeth of a wheel. Pins should be of hard brass.
Care should be used in handling clocks with this escapement while the
pendulum is connected with the pallet fork, as, if the motion of the
fork should be reversed while a pin was on one of the lifting planes,
it would bend or break the pin.
CHAPTER X.
THE RECOIL OR ANCHOR ESCAPEMENT.
This escapement, always a favorite with clockmakers, has had a long and
interesting history and development. Because it started with a suddenly
achieved reputation, and because it is adapted to obtain fair results
with the cheapest and consequently most unfavorable working conditions,
it has won its way into almost universal use in the cheaper classes of
clock work; that is to say, it is used in about ninety per cent of the
pendulum clocks which are manufactured to-day.
It achieved a sudden reputation at its birth, because it was designed
to replace the old verge, which, with its ninety degree pallets close
to the arbor, and working into the crown wheel, required a very large
swing of the pendulum. This necessitated a light ball, a short rod,
required a great force to drive it, and made it impossible to do
away with the circular error, while leaving the clock sensitive to
variations in power. The recoil escapement was therefore the first
considerable advance in accuracy, as its use involved a longer and
heavier pendulum, shorter arcs of vibration and less motive power than
was practicable with the verge; and as the pendulum was less controlled
by the escapement, it was less influenced by variations of power.
In the early escapements the entrance pallet was convex and the exit
pallet concave. Escapements of this description may still be met with
among the antiquities that occasionally drift into the repair shop.
Later on both pallets were made straight, as shown in Fig. 41. It will
be seen by studying the direction of the forces that the effect is to
wear off the points of the teeth very rapidly, and for this reason the
pallets were both made convex (See Fig. 42), so as to bring the rubbing
action of the recoil more on the sides of the teeth and do away to a
large extent with the butting on the points which destroyed them so
rapidly.
[Illustration: Fig. 41. Recoil Escapement with Straight Lifting Planes.]
The rather empirical methods of laying out the recoil escapement, which
have gained general circulation in works on horology, have had much
to do with bad depthings of this escapement and the consequent undue
wear of the escape wheel teeth and great variation in timekeeping of
the movements in which such faulty depthings occur, particularly in
eight-day movements with short and light pendulums. The escapement
will invariably drive the clock faster for an increase of power and
slower for a decrease; an unduly great depthing will greatly increase
the arc of vibration of the pendulum, as the train exerts pressure on
the pendulum for a longer period during the vibration; the consequence
is that instead of the pendulum being as highly detached as possible,
we have the opposite state of affairs and a combination of a strong
spring, light pendulum and excessive depthing will easily make a
variation of five minutes a week in an eight-day clock.
The generally accepted method of laying out this escapement is shown
in Figs. 41 and 42, as follows: “Draw a circle representing the escape
wheel; multiply the radius of the escape wheel by 1.4 and set off this
as the center distance between the pallet and escape wheel centers.
From the pallet staff center describe a circle with a radius equal to
half the distance between escape wheel and pallet centers. Set off
on each side of the center line one-half the number of teeth to be
embraced by the pallets and from the points of the outside teeth draw
lines tangent to the circle described from the pallet center. These
lines would then form the faces of the pallets if they were left flat.”
We wonder how much information this description and the drawing conveys
to the average reader. How long should the pallets be? What is the
drop? How much will the escape wheel recoil with such a depthing? What
arc will the pallets give the pendulum? Why should the center distance
always be the same (seven tenths of the diameter of the wheel) whether
the escapement embraces eight, or ten, or six teeth? As a matter of
fact it should not be the same. We could ask a few more questions as
to other details of this formula, but it will be seen that such a
description is practically useless to all but those who are already so
skilled that they do not need it.
[Illustration: Fig. 42. Recoil Escapement with Curved Lifting Planes.]
[Illustration: Fig. 43. Drawing the Lock Lift and Recoil of the Usual
Form.]
Let us analyze these drawings. A little study of Figs. 41, 42 and 43
will show that there is really only one point of difference between
them and Fig. 32, which shows the elements of the Graham, or dead
beat. The sole difference is in the fact that there are no separate
locking planes in the recoil, the locking and run taking place on an
extension of the lifting planes. Otherwise we have the same elements in
our problem and it may therefore be laid out and handled in the same
manner; indeed, if we were to set off on Fig. 32, the amount of angular
motion of the pallet fork which is taken up by the run of the escape
wheel teeth on the locking planes, by drawing dotted lines above the
tangents, T, we should then have measured all the angles necessary to
intelligently set out the recoil escapement. We should have the lock
at the tangent, T, the lift and the run (or recoil) being defined
by the lines on either side of it, and the length of our running and
lifting planes would be found for the entering pallet by drawing a
straight line between the points of the two acting teeth of the escape
wheel and noting where this line cut the lines of recoil and lift.
A similar line traced at right angles to this would in the same way
define the limits of run and lift on the exit pallet. It will therefore
be seen that our center distances for any desired angle of escapement
may be found in the same way (Fig. 28), for either escapement, and
thus the method of making the pallets for the ordinary American clock,
Fig. 43, becomes readily intelligible. The sole object of curving the
pallets, as explained previously, was to decrease the butting effect of
the run on the points of the teeth. This is accomplished in Fig. 43 by
straight planes on the pallets and straight sides to the teeth with 20°
teeth on the escape wheel; merely inclining the plane of the entering
pallet about six degrees toward the escape wheel center, thus serving
all purposes, while the gain in the cost of manufacture by using
straight instead of curved pallets and wheel teeth is very great.
[Illustration: Fig. 44. Recoil with Curved Planes.]
[Illustration: Fig. 45. Showing the Usual Position in Cheap Clocks and
the Verge Wire.]
One factory in the United States is turning out 2,000,000 annually of
two movements, or about 1,000,000 of each movement; there are four
other larger factories and several with a less product; so it will
readily be seen that any decrease in cost, however small it may be on
a single movement, will run up enormously on a year’s output. Suppose
the factory mentioned were enabled to save only one-eighth of a cent on
one of its million movements manufactured last year, this would amount
to $1,250 per year, a little over $100 per month. Thus it will be seen
that close figuring on costs of production is a necessity.
[Illustration: Fig. 46. Drum Escapement.]
Fig. 44 shows the method of drawing the escapement according to the
common sense deductions given above. As the methods of laying out the
angle of escapement, lock, lift, and run, were given in detail in Figs.
28 to 32, they need not be repeated here.
Fig. 46 shows the escapement frequently used in French “drum” clocks
and hence called the “Drum” escapement. These are clocks fitted to
go in any hole of the diameter of the dial and hence they have very
short, light pendulums. An attempt is made to gain control over the
pendulum by decreasing the arc of escapement to not more than two and
sometimes to only one tooth. This gives an impulse to the pendulum
only on one-half of the vibrations, the escape wheel teeth resting and
running on the long circular locking pallet during alternate swings
of the pendulum. The idea is that the friction of the long lock will
tend to reduce the effect of the extra force of the mainspring when
the clock is freshly wound. Such clocks often stop when the clock is
nearly run down, from deficiency of power, and stop when wound, because
the friction of the escape wheel teeth on the locking plane is such as
to destroy the momentum of the light pendulum. All that can be done in
such cases is to alter the locking planes as shown by the dotted lines,
so that the “drum” becomes virtually a recoil escapement of two teeth.
CHAPTER XI.
THE DENNISON OR GRAVITY ESCAPEMENT.
The distinguishing feature of this escapement lies in the fact that
it aims to drive the pendulum by applying to it a falling weight at
each excursion on each side. As the weight is lifted by the train and
applied to the pendulum on its return stroke and there is no other
connection, it follows that the pendulum is more highly detached than
in any other form of pendulum escapement. This should make it a better
timekeeper, as the application of the weight should give a constant
impulse and hence errors and variations in the power which drives the
train may be neglected.
On tower clocks this is undoubtedly true, as these clocks are
interfered with by every wind that blows against the hands, so that
a detached pendulum enables a surplus of power to be applied to the
train to meet all emergencies. With a watchmaker’s regulator, however,
the case is different. Here every effort is made to favor the clock,
vibrations, variations of temperature, variations of power, dirt, dust,
wind pressure and irregularities of the mechanism are all carefully
excluded and the consequence is that the special advantages of the
gravity escapement are not apparent, for the reason that there are
practically no variations for the escapement to take care of. Added to
this we must consider that the double three-legged form, which is the
usual one, is practically an escape wheel of but six teeth, so that
another wheel and pinion must be added to the train and this, with the
added complications of the fan and the heavier driving weight required,
counterbalance its advantages and bring it back to an equality of
performance with the simpler mechanism of the well made and properly
adjusted dead beat escapement. Theoretically it should work far better
than the dead beat, as it is more detached; but theory is always
modified by working conditions and if the variations are lacking there
is no special advantage in constructing a mechanism to take care of
them. This is the reason why so many watchmakers have constructed for
themselves a regulator with this escapement, used in the making all the
care and skill of which they were capable and then been disappointed
to find that it gave no better results with the same pendulum than the
dead beat it was to replace. They had eliminated all the conditions
under which the detached escapement would have shown superiority.
[Illustration: Fig. 47.]
Although the gravity escapement will not give a superior performance
under the most favorable conditions for timekeeping, it is distinctly
superior when these conditions are unfavorable and therefore fully
merits its high place in the estimation of the horological fraternity.
We have instanced its value in tower clock work; it has another
advantage in running cheap and poorly made (home made) regulators with
rough and poor trains; therefore, it is a favorite escapement with
watchmakers who build their own regulators while they are still working
at the bench, before entering into business for themselves. As the
price of a first-class clock for this purpose is about $300 and the
cheapest that is at all reliable is about $75, it will be seen that the
temptation to build a clock is very strong and many of them are built
annually.
Regulators with the gravity escapement are built by the Seth Thomas
Clock Co., the Howard, and one or two others in this country, but they
are furnished simply to supply the demand and sales are never pushed
for the reasons given previously. Clocks with this escapement are quite
common in England and many of them have found their way to America. It
is one of the anomalies of trade that our clockmakers are supplying
Europe with cheap clocks, while we are importing practically all the
high priced clocks sold in the United States and among them are a few
having the three-legged and four-legged gravity escapements, therefore
the chances are that when a repairer finds such a clock it is likely
to be either of English origin or homemade, unless it be a German
regulator.
Figs. 47 and 48 show plans and side views of the three-legged
escapement. Fig. 48 also shows an enlarged view of the escape wheel,
showing how the three-leaved pinion between the two escape wheels,
is made where it is worked out of the solid. A, B and C and a, b and
c show the escape wheel which is made up of two three-armed wheels,
one on each side of a three-leaved pinion marked D¹ and D² in the
enlarged view of Fig. 48. The pallets in this escapement consist of the
two arms of metal suspended from points opposite the point of bending
of the pendulum spring and the lifting planes are found on the ends of
the center arms in these pallets, which press against the three leaves
of the pinion, while the impulse pins e¹ and e², Fig. 47 and 48 act
directly upon the pendulum in place of the verge wire. The pallets act
between the wheels in the same plane as each other. The lifting pins
or pinion leaves act on the lifting planes after the line of centers
when the long teeth or legs of the escape wheels have been released
from the stops, F and G, Figs. 47 and 48, which are placed one on each
side of the pallets and act alternately on the wheels. These pallets
are pivoted one on each side of the bending point of the suspension
spring. To lay out the escapement, draw a circle representing the
escape wheel diameter, then draw the line of centers and set off on the
diameter of the escape wheel from each side of the line of centers 60°
of its circumference, thus marking the positions for the pallet stops
120° apart. Draw radii from the center of the escape wheel to these
positions and draw tangents from the ends of these radii toward the
center line. The point where these meet will be the bending point of
the pendulum spring.
[Illustration: Fig. 48.]
This is clearly shown at H, Fig. 47. The points of suspension for the
pallets are planted on the line of these tangents and a little below
the point H, where the tangents meet on the line of centers. This is
done to avoid the mechanical difficulty of having the studs for the
two pallets occupy the same place at the same time. The arms of the
pallets below the stops may be of any length, but they are generally
constructed of the same angle as the upper arms and will be all right
if drawn parallel to these upper arms. They are in some instances
continued further down, but this is largely a matter of taste and
the lower portion of the escapement is generally drawn so as to be
symmetrical.
The impulse of the pendulum is given by having pins projecting from
the pallet arms and bearing upon the pendulum rod, which pins may be
of brass, steel or ivory. In the heavier escapements they are made of
ivory in order to avoid any chatter from contact with the pendulum rod
of a heavy pendulum. These pallets should be as light as it is possible
to make them without having them chatter under the impact of the escape
wheel arms on the stops. They have only to counteract the force of the
pendulum spring and the resistance of the air and for light pendulums
this force is much less than is generally understood. Two ounces of
impulse will maintain a 250-pound pendulum, but two pennyweights is
more than sufficient for a fifty-pound pendulum. The reader can see
that in the case of a pendulum weighing but eight to fourteen pounds,
there will be a still greater proportionate drop, as the spring itself
is thinner, the rod is thinner, the pendulum ball offers little
resistance to the air and the consequence is that it is difficult to
get the pallet arms light enough for an ordinary clock.
Watchmakers who make this escapement for themselves, to drive an
eight to fourteen pound pendulum, generally make the escape wheel
three inches diameter and make the escape wheel and pallet arms all
from the steel obtained by buying an ordinary carpenter’s saw. The
lifting planes should not be more than one-eighth its diameter from
the center of the escape wheel, as where this is the case the circular
motion of the center pins will be so great that the pallet in action
will be thrown out too rapidly and will chatter when striking the
pendulum rod. On the other hand it should not be less than one-twelfth
of the diameter of the escape wheel, or the pendulum will not be given
sufficiently free swing and the motion will be so slow that while such
a clock will work under favorable conditions, jarring, shaking in wind
storms, etc., will have a tendency to make the pendulum wabble and stop
the clock. From what has been said above, it will also be seen that the
necessity for slow motion of the pallet arms unfits this escapement for
use with short pendulums.
The action of the escapement is as follows: The pendulum traveling to
the right, when it has thrown the right pallet arm sufficiently far,
will liberate the escape wheel tooth from the stop G and the pinion,
acting on the lifting plane, will raise the pallet arm, allowing the
pendulum to continue its course without doing any further work until
it has reached nearly its extreme point of excursion, when the weight
of the pallet will be dropped upon the pendulum rod and remain there,
acting upon the pendulum until it has passed the center when the pallet
arm will be stopped by the banking pin M¹; exactly the same procedure
takes place on the left side of the escapement during the swing of the
pendulum to the left. The beat pins M and M¹ should be set so that
the impulse pins e¹ and e² will just touch the pendulum when the
latter is hanging at rest and the escapement will then be in beat.
The stops should be cut from sheet steel and the locking faces of the
escape wheel arms, stops on the pallets, lifting planes of the pallets
and the lifting pins should all be hardened. In some of the very fine
escapements the faces of the blocks are jeweled. The arms of the inner
part of the escape wheel are usually set at equal angular distances
between those of the outer, although this is not absolutely necessary,
and the lifting pins are set on radii to the acting faces of the
arms of one of the wheels, so as to cross the line of centers at the
distance from the center, not exceeding one-eighth of the radius of the
wheel, for the reasons explained above.
[Illustration: Fig. 49.]
From the comparatively great angle at which the arms are placed, the
distance through which they have to be lifted to give sufficient
impulse is less in this escapement than in one with a larger number of
teeth acting in the same plane, as the pallets would then hang more
nearly upright. This is a great advantage, as the contact is shorter.
The unlocking is also easier for the same reason, and from the greater
diameter of the wheel in proportion to other parts of the escapement,
the pressure on the stops is considerably less. The two wheels must be
squared on the arbor, so there will be no possibility of slipping. The
lifting pins D are shouldered between them like a three-tooth lantern
pinion. In small escapements the lifting pins are not worked out of
the solid arbor, but are made as hardened screws to connect the two
portions of the wheel. In tower clocks the pinion is generally made
solid on the shaft J, Fig. 48. The wheel, A, B, C, is made to pass
over the pinion D and is fitted to a triangular seat, the size of the
triangle of the leaves, D, against the collar on the shaft. The other
wheel, a, b, c, is fitted to the inside triangle of the pinion, so that
the leaves, D, form a shoulder against which it fits. The pallets, E
and E¹, also lie in one plane between the wheels, but one stop, F,
points forward to receive the A, B, C, teeth and the other, G, points
backward to receive the a, b, c teeth alternately. The distance of
the pendulum top, H, or cheeks from the center of the escape wheel, J
equals the diameter of the escape wheel. The lifting pins should be so
placed that the one which is holding up a pallet and the one which is
to lift next will be vertical over each other, on the line of centers,
the third pin being on the level with the center, and to one side of
it, see Fig. 48, enlarged view.
The fly is a very essential part of this escapement, as the angular
motion of the escape wheel is such that unless it were checked it would
be apt to rebound and unlock; consequently, a large fly is always a
feature of this escapement and is mounted upon the scape wheel arbor
with spring friction in such a way that the fly can continue motion
after the scape wheel has been stopped. This is provided for by a
spring pressure, either like the ordinary spring attachment of the fly
of striking trains of small clocks, or as shown in Fig. 49 for tower
clocks. This fly is effective in proportion to its length and hence a
long narrow fly will be better than a shorter and wider one, as the
resistance of the air striking against the ends of the fly is much
greater the further you get from the center.
[Illustration: Fig. 50.]
The pallet stud pins and the impulse pins should on no account
be touched with oil or other grease of any kind, but be left dry
whatever they are made of, because the slightest adhesion between the
impulse pins and the pendulum rod is fatal to the whole action of the
escapement. Care must also be taken that one pallet begins to lift
simultaneously with the resting of the other, neither before nor after.
The gravity escapement requires a heavier weight or force to operate
the train than a dead beat escapement, because it must be strong enough
to be sure of lifting the pallets quickly and firmly, and also because
the escape wheel having but six teeth necessitates the use of another
wheel and pinion between the escape and center and consequently the
train is geared back more than it would be for a dead beat escapement,
with the seconds hand mounted on the escape wheel arbor. But with this
form of escapement the superfluous force does not work the pendulum
and it does no harm if the train is good enough not to waste power in
getting over rough places left in cutting the teeth of the wheels or
any jamming from those which have unequal widths or spaces. For this
reason a high numbered train is better than a low numbered one, as
these defects are greater on the teeth of a low numbered train and any
defect in such cases will show itself.
In the gravity escapement the escape wheel must have a little run at
the pallets before it begins to lift them and in order to do this the
banking pins, M, M¹ for the pallet arms to rest on, should hold them
just clear of the lifting pins or leaves of the escape wheel. The
escape wheel should be as light as possible, for every blow heard in
the machine means a loss of power and wear of parts. Of course, in an
escapement a sudden stop is expected, but the light wheel will reduce
it to a minimum if the fan is large enough. Particular attention should
therefore be given to the length of this fan and if the stop of the
escape wheel seems too abrupt, the fan should be lengthened.
[Illustration: Fig. 51.]
Figs. 50 and 51 show the same escapement with a four-legged wheel
instead of the double three-legged. In this case, where there is but
one wheel, the pallets must of necessity work on opposite sides of the
wheel and hence they are not planted in the same plane with each other,
but are placed as close to each side of the wheel as is practicable.
To lay out this escapement, draw the circle of the escape wheel as
before, make your line of centers and mark off on the circle 67½° on
each side of the line of centers and draw radii to these points, which
will indicate the approximate position of the stops. Tangents to these
radii, meeting above the wheel on the line of centers will give the
theoretical point of the suspension. One set of the lifting pins is
planted on radii to the acting faces of the teeth of the escape wheel.
The opposite set, on the other side of the wheel, is placed midway
between the first set. This secures the lifting at the line of centers.
The wheel turns 45° at each beat and its arbor likewise carries a fly.
In case the locking is not secure, the stops may be shifted a little
up or down, care being taken to keep them 135° apart. In this way a
draw may be given to the locking of the scape wheel arms similar to the
draw of the pallets in a detached lever escapement and thus any desired
resistance to unlocking may be secured. The stops in either escapement
are generally made of steel and it is of the utmost importance that the
arms of the escape wheel should leave them without imparting the least
suspension of an impulse. Therefore, the stops and the ends of the
arms should be cut away (backed off) to rather a sharp angle to insure
clearance when the arms are leaving the stops. It is also of equal
importance that the legs of the wheels should fall on the stops dead
true. The fit of each of the legs should be examined on both stops with
a powerful eye-glass, so that they should be correct and also see that
when the unlocking takes place the wheel is absolutely free to turn.
CHAPTER XII.
THE CYLINDER ESCAPEMENT AS APPLIED TO CLOCKS.
We remarked in a previous chapter that the lifting planes were
sometimes on the wheel and sometimes on the anchor. In another chapter
we pointed out clearly that the run on the locking surface of the
pallets had an important bearing on the freedom of the escapement and
hence on the rate of the dead beat escapement. In considering the
cylinder escapement, so common in carriage clocks, we shall find that
the lift is almost entirely on the curved planes of the escape wheel,
and that the locking planes are greatly extended, so that they form the
outer and inner surfaces of the cylinder walls. Thus we have here a
form of the dead beat escapement, which embraces but one tooth of the
escape wheel and is adapted to operate a balance instead of a pendulum.
Therefore the points for us to consider are as before, the amount of
lift, lock, drop and run, and the shapes of our escape wheel teeth to
secure the least friction, as our locking surfaces (the run) being so
greatly extended this matter becomes important.
ACTION OF THE ESCAPEMENT.—Fig. 52 is a plan of the cylinder escapement,
in which the point of a tooth of the escape wheel is pressing against
the outside of the shell of the cylinder. As the cylinder, on which
the balance is mounted, is moved around in the direction of the arrow,
the wedge-shaped tooth of the escape wheel pushes into the cylinder,
thereby giving it impulse. The tooth cannot escape at the other side
of the cylinder, for the shell of the cylinder at this point is rather
more than half a circle; but its point locks against the inner side
of the shell and runs there till the balance completes its vibration
and returns, when the tooth which was inside the cylinder escapes,
giving an impulse as it does so, and the point of the succeeding tooth
is caught on the outside of the shell. The teeth rise on stalks from
the body of the escape wheel, and the cylinder is cut away just below
the acting part of the exit side, leaving for support of the balance
only one-fourth of a circle, in order to allow as much vibration as
possible. This will be seen very plainly on examining Fig. 53, which is
an elevation of the cylinder to an enlarged scale.
[Illustration: Fig. 52. a, wheel; b, cylinder; f, stalk on which teeth
are mounted.]
PROPORTION OF THE ESCAPEMENT.—The escape wheel has fifteen teeth,
formed to give impulse to the cylinder during from 20° to 40° of its
vibration each way. Lower angles are as a rule used with large than
with small-sized escapements; but to secure the best result either
extreme must be avoided. In the escapement with very slight inclines
to the wheel teeth, the first part of the tooth does no work, as the
tooth drops on to the lip of the cylinder some distance up the plane.
On the other hand, a very steep tooth is almost sure to set in action
as the oil thickens. The diameter of the cylinder, its thickness and
the length of the wheel teeth are all co-related. The size of the
cylinder with relation to the wheel also varies somewhat with the angle
of impulse, a very high angle requiring a slightly larger cylinder
than a low one. If a cylinder of average thickness is desired for an
escapement with medium impulse, its external diameter may be made equal
to the extreme diameter of the escape wheel multiplied by 0.115.
[Illustration: Fig. 53.]
[Illustration: Fig. 54.]
Then to set out the escapement, if a lift of say 30° be decided on, a
circle on which the points of the teeth will fall is drawn within one
representing the extreme diameter of the escape wheel, at a distance
from it equal to 30° of the circumference of the cylinder. Midway
between these two circles the cylinder is planted (see Fig. 54). If
the point of one tooth is shown resting on the cylinder, a space of
half a degree should be allowed for freedom between the opposite side
of the cylinder and the heel of the next tooth. From the heel of one
tooth to the heel of the next equal 24° of the circumference of the
wheel, 360 ÷ 15 = 24°, and from the point of one tooth to the point
of the next also equals 24° so that the teeth may now be drawn. They
are extended within the innermost dotted circle to give them a little
more strength, and their tips are rounded a little, having the points
of the impulse planes on the inner or basing circle. The backs of the
teeth diverge from a radial line from 12° to 30°, in order to give the
cylinder clearance, a high angled tooth requiring to be cut back more
than a low one. A curve whose radius is about two-thirds that of the
wheel is suitable for rounding the impulse planes of the teeth. The
internal diameter of the cylinder should be such as to allow a little
freedom for the tooth. The rule in fitting cylinders is to have equal
clearance inside and outside, so as to equalize the drop. The acting
part of the shell of the cylinder (where the lips are placed) should be
a trifle less than seven-twelfths of a whole circle, with the entering
and exit lips which are really the pallets, rounded as shown in the
enlarged plan, Fig. 55, the entering lip or pallet rounded both ways
and the exit pallet rounded from the inside only. This rounding of the
lips of the cylinder adds a little to the impulse beyond what would be
given by the angle on the wheel teeth alone. The diameter of the escape
wheel is usually half that of the balance, rather under than over.
SIZE OF CYLINDER PIVOT.—To establish the size of the pivot with
relation to its hole is apparently an easy thing to do correctly, but
to an inexperienced workman it is not so. The side shake in cylinder
pivot holes should be greater than that for ordinary train holes;
one-sixth is the amount prescribed by Saunier; the size of the pivot
relatively to the cylinder about one-eighth the diameter of the body
of the cylinder. It is very necessary that this amount of side shake
should be correctly recognized; if less than the amount stated, the
escapement, though performing well while the oil is fresh, fails to do
so when it commences to thicken.
[Illustration: Fig. 55.]
When the balance spring is at rest, the balance should have to be moved
an equal amount each way before a tooth escapes. By gently pressing
against the fourth wheel with a peg this may be tried. There is
generally a dot on the balance and three dots on the plate to assist
in estimating the amount of lift. When the balance spring is at rest,
the dot on the balance should be opposite to the center dot on the
plate. The escapement will then be in beat, that is, provided the dots
are properly placed, which should be tested. Turn the balance from
its point of rest till a tooth just drops, and note the position of
the dot on the balance with reference to one of the outer dots on the
plate. Turn the balance in the opposite direction till a tooth drops
again, and if the dot on the balance is then in the same position with
reference to the other outer dot, the escapement will be in beat. The
two outer dots should mark the extent of the lifting, and the dot on
the balance would then be coincident with them as the teeth dropped
when tried in this way; but the dots may be a little too wide or too
close, and it will therefore be sufficient if the dot on the balance
bears the same _relative_ position to them as just explained; but if it
is found that the lift is unequal from the point of rest, the balance
spring collet must be shifted in the direction of the least lift till
the lift is equal. A new mark should then be made on the balance
opposite to the central dot on the plate.
When the balance is at rest, the banking pin in the balance should be
opposite to the banking stud in the cock, so as to give equal vibration
on both sides. This is important for the following reason. The banking
pin allows nearly a turn of vibration and the shell of the cylinder
is but little over half a turn, so that as the outside of the shell
gets round towards the center of the escape wheel, the point of a
tooth may escape and jam the cylinder unless the vibration is pretty
equally divided. When the banking is properly adjusted, bring the
balance round till the banking pin is against the stud; there should
then be perceptible shake between the cylinder and the plane of the
escape wheel. Try this with the banking pin, first against one and then
against the other side of the stud. If there is no shake, the wheel
may be freed by taking a little off the edge of the passage of the
cylinder where it fouls the wheel, by means of a sapphire file, or a
larger banking pin may be substituted at the judgment of the operator.
See that the banking pin and stud are perfectly dry and clean before
leaving them: a sticky banking often stops a clock when nearly run
down. Cylinder timepieces, after going for a few months, sometimes
increase their vibration so much as to persistently bank. To meet this
fault a weaker mainspring may be used, or a larger balance, or a wheel
with a smaller angle of impulse. By far the quickest and best way is
to _very slightly_ lap the wheel by holding a piece of Arkansas stone
against the teeth, afterwards polishing with boxwood and red stuff. So
little taken off the wheel in this way as to be hardly perceptible will
have great effect.
Sometimes the escape wheel has too much end shake. We must notice in
the first place how the teeth are acting in the cylinder slot. Suppose,
when the escape wheel is resting upon its bottom shoulder, the cylinder
will ride upon the plane of the wheel, which will cause it to kick or
give the wheel a trembling motion, then we know that the cylinder is
too low for the wheel; therefore, we have not only to lower the escape
top cock in order to correct the end shake, but we must also drive
the bottom cylinder plug out a little in order to raise the cylinder
sufficient to free it from the plane of the wheel. Now, if the end
shake of the cylinder is correct previous to this, we shall now either
have to raise the cock or drive the top plug in a little. But suppose
the end shake of the escape pinion is excessive, and is, when the
bottom shoulder is resting on the jewel, a little too low so that the
bottom of the escape wheel runs foul of the cylinder shell; in this
case we simply drive out the steady pins from the bottom escape wheel
cock and file a piece off the cock, leaving it perfectly flat when we
have enough off. We then insert the steady pins again, screw it down,
and if the end shake is right, the escapement is mostly free and right
also.
Now let us consider the frictions; there is the resistance of the
pivots, which depends on their radius, on the weight of the balance,
the balance spring, the collet, and the weight of the cylinder; these
are called locking frictions. Then there are those of the planes, of
the teeth of the wheel, of the lips of the cylinder. It is on these
that the change and destruction of the cylinder are produced. To
prevent this destruction, it is necessary to render the working parts
of the cylinder very hard and well polished, as well as the teeth of
the escape wheel.
The oil introduced in the cylinder is also a cause as in the dead beat.
It may thicken; the dust proceeding from the impact of the escapement
forms with the oil an amalgam which wears the cylinder. The firmness
and constancy of the cylinder depend on the preservation and fluidity
of the oil.
Then there are the accidental frictions; the too close opening of the
cylinder, the play of the balance and of the wheel, with the thickening
of the oil, changes the arc of vibration a good deal; the teeth of
the wheel may not be sufficiently hollowed, so that the cylinder can
revolve in the remaining space, for the oil with the dust forms a
thickness which also changes the vibration. The drop should not be too
great, for it is increased by the thickening of the oil and impedes the
vibration.
EXAMINATION OF CLOCKS.—In this particular escapement, when used for
larger timepieces than watches, it is astonishing the variety of
methods which are employed, yet the same results are expected. In
examining such clocks we will first notice that the chariot, cock,
etc., are so placed, many of them, that the last wheel in the train is
a crown wheel, hence it is made to work at 90° with the escape wheel
pinion which is set at right angles with the crown wheel pinion, and,
as a matter of course, the cylinder is also set the same way. Now,
this arrangement needs especial care, for it is quite natural that
when the entire friction of the cylinder is only on the bottom part of
the bottom pivot, the clock is sure to go faster than when the whole
length of both pivots are more in contact with their jewel holes,
which is always the case when the cylinder is parallel with all the
pinions, instead of standing upon one pivot only. Now, although there
must of necessity be a very great difference in timing the clock in
the two different positions, yet we find no difference in the strength
of mainspring or any part of the train, which is a mistake, for the
result is simply this: the clock will gain time for the first few days
after winding, and will then gradually go slower and slower until the
mainspring is entirely exhausted. It is not very difficult to ascertain
why it goes so fast after winding, for then the whole tension of the
spring is on, and as there is not sufficient friction on the point of
one pivot to counteract this, the banking pin is almost sure to knock,
and will continue to knock for the first few days until a part of the
spring’s pressure is exhausted. Now, in this case the knocking of the
banking pin alone would cause the clock to gain time, even if the extra
tension of the mainspring did not assist it to do so. Hence, on the
whole, the result is anything but satisfactory, for such a clock can
never be properly brought to time.
Having said this much about the fault (which is entirely through the
want of a little forethought with the manufacturer), I will give as
good a remedy as I can suggest to give the reader an idea of how these
faults may be put to right, if he is willing to spend the time upon
them. In the first place take out the cylinder and make the bottom
pivot perfectly flat instead of leaving it with a round end, as they
are mostly left, which only allows just one part of the pivot to be in
contact with the endstone. By leaving this pivot flat on the bottom,
there is more surface in contact; hence, in a sense, more friction.
In some cases the whole pivot left flat would not be sufficient to
retard the mainspring’s force; then we must resort to other methods to
effect a cure.
Well, our next method in order to try and get the clock to be a uniform
timekeeper, is to change the mainspring for one well finished and not
quite so strong as the original one. Perhaps some will say “why not do
this before we go to the trouble of flattening the bottom pivot?” Just
this; when a pivot is working only upon the bottom it is best to have
a flat surface to work upon, as the balance is then oscillated with
more uniformity, even when the mainspring is not exactly uniform in its
pressure; therefore we do no harm—but good—by making the bottom pivot
flat, and this alone will sometimes be sufficient to cure the fault of
the banking knocking if nothing else.
To my mind, when such strong mainsprings are used as we generally
see in this class of timepiece, neither of the jewel holes or pivots
should be so small as they usually are. Fancy such small pivots as
are mostly seen upon the escape wheel pinion being driven by such a
strong mainspring. If we allow the clock to run down while the escape
wheel is in place, we are very liable to find one or both pivots broken
off before it gets run down. I think all such pivots ought to be
sufficiently strong to stand the pressure of the mainspring through the
train of wheels without coming to grief. But there is another reason
why these pivots are liable to get broken off while letting the train
run down: that is, the badly pitched depth we often find in the crown
wheel and escape wheel pinion. We frequently find too much end shake to
the crown wheel which, while resting one shoulder of the arbor against
the plate puts the depth too deep, and on the other shoulder the depth
is too shallow. Now, when the train is running rapidly this crown wheel
is jumping about in the escape wheel pinion, so that the roughness
of the running all helps to break off the escape wheel pivots. The
best way to correct this depth is to notice how the screws fit in the
cylinder plate—for these screws have to act as steady pins as well. If
the holes where the screws go through are at all large, we then notice
which would be the most convenient side to screw it securely in order
to put a collet upon the shoulder of the crown wheel so that the depth
will be right by making the end shake right with only fixing a collet
to one shoulder. This depth, when correct, will also cause a more
uniform pressure upon the escapement, and help to make the clock keep
better time. We are supposing that this crown wheel is perfectly true,
or it is not much use trying to correct the depth as mentioned above,
for even if the end shake be ever so exact and the wheel teeth are out
of true, we shall never get the depth to act as it ought, neither can
the clock be depended upon for keeping going, regardless of keeping
time. When this crown wheel is out of true it is best to rivet it true,
not do as I have seen it done, placed in the lathe and topped true, and
then the teeth rounded-up by hand. This method simply means a faulty
depth after all, for in topping the teeth, those teeth which require
the most topping will, when they are finished, be shorter from the top
to the base than those which do not get topped so much; therefore,
some of the teeth are longer than the others, while the shorter ones
are thicker; for when the wheel was originally cut the teeth were all
cut alike. These remarks will apply to several kinds of wheels; for
whenever a wheel is topped to put it true, we may depend we are making
a very faulty wheel of it unless we have a proper wheel cutting machine.
The crown wheel must not be too thick because we will find the tooth
to act with the inner edge, and what is left outside only endangers
touching the pinion leaf which is next to come into action. Make sure
the escape pinion is not too large, which sometimes happens. If it is,
it must be reduced in size, or better, put in a new one. The crown
wheel holes must fit nicely and the end shake be well adjusted. Do
not spare any trouble in making this depth as perfect as you are able,
as most stoppages happen through the faults in this place. It would
be advisable, when sure the depth is correct, to drill two steady pin
holes through the escapement plateau into the edge of the plates. When
steady pins are inserted this will always ensure the depth being right
when put together.
In some of these clocks it is not only the crown wheel, but frequently
the escape wheel has too much end shake. The former, as I have said,
can be corrected by making a small collet that will just fit over
pivot, fasten it on friction-tight, place the wheel in the lathe and
turn the collet down until it is the same size as the other part of the
arbor, then run off the end to the exact place for the end shake to
be right. If it is properly done and a steel collet is used, it will
not be detected that a collet has been put on. Now, when the escape
wheel end shake is wrong we have to proceed differently under different
circumstances for we must notice in the first place how the teeth are
acting in the cylinder slot.
See that the cylinder and wheel are perfectly upright. Suppose, when
the escape wheel is resting upon its bottom shoulder, the cylinder will
ride upon the plane of the wheel, which will cause it to kick or give
the wheel a trembling motion, then we know that the cylinder is too low
for the wheel; therefore, we have not only to lower the escape top cock
in order to correct the end shake, but we must also drive the bottom
cylinder plug out a little in order to raise the cylinder sufficient
to free it from the plane of the wheel. Now, if the end shake of the
cylinder is correct previous to this, we shall either have to raise
the cock or drive the top plug in a little. But suppose the end shake
of the escape pinion is excessive, and is, when the bottom shoulder
is resting on the jewel, a little too low so that the bottom of the
escape wheel runs foul of the cylinder shell; in this case we simply
drive out the steady pins from bottom escape wheel cock and file a
piece off the cock, leaving it perfectly flat when we have got enough
off. We then insert the steady pins again, screw it down, and, if the
end shake is right, the escapement is mostly free and right also. It
sometimes happens that the wheel is free of neither the top nor bottom
plug, but should this be the case, sufficient clearance may be obtained
by deepening the opening with a steel polisher and oilstone dust or
with a sapphire file. A cylinder with too high an opening is bad, for
the oil is drawn away from the teeth by the escape wheel.
If a cylinder pivot is bent, it may very readily be straightened by
placing a bushing of a proper size over it.
These clocks are very good for the novice to exercise his skill
in order to thoroughly understand the workings of the horizontal
escapement. He is better able to see how the different parts act with
each other than he is in the small watch. When the escape is correct
he will find that the plane of the escape wheel will work just in the
center of the small slot in the cylinder.
If he will notice how the teeth stand in the cylinder when the banking
pin is held firmly upon the fixed banking pin, it will give him an idea
of how this should be. At one side the lip of the cylinder is just
about to touch the inside of the escape tooth, but the banking pin just
prevents it from doing so, while on the other side the cylinder goes
round just far enough to let the point of the next tooth just get on
the edge of the slot, but it cannot get in owing to the intervention
of the banking pin. If this is allowed to get in the slot just here,
we then have what is called “a locking,” which is, in reality, an
overturned banking. If the other side is so that the banking pin
does not stop it soon enough, the edge of the slot knocks upon the
inside of the teeth and causes a trembling of the escape wheel, and
the clock left in this form will never keep very good time. We may
easily remedy this by taking off the hair spring collet; holding the
cylinder firmly in the plyers, and with the left hand turn the balance
a little outwards; this will bring the banking pins in contact before
the cylinder touches the inside of the wheel teeth, and all is right,
providing we are careful in not doing it too much; if so, we shall find
the banking knock—a fault which is quite as bad, if not worse, than the
one we are trying to remedy. Those particulars are the most important
of anything in connection with the cylinder escapement. Yet, as this
kind of clock is now being made up at such a low price, these seeming
little items are frequently overlooked; hence, when they get into the
hands of the inexperienced, there is often more trouble with them than
there need be if they knew where to look for some of the faults which I
have been endeavoring to bring to light. There are several other things
in connection with this particular clock, but we will not comment
further just now, but take them up when we are considering the trains,
etc.
[Illustration: Fig. 56.]
In the meantime we will resume our study of the cylinder escapement
with particular reference to badly worn or otherwise ill fitting escape
wheels, as many times, the other points being right, the wheel and
cylinder may be such as to give either too great or too small a balance
vibration.
A poor motion can also be due to a rough or a badly polished cylinder,
but such a cylinder we rarely find. That with a wrong shape of the
cylinder lips the motion is not much lessened can be seen in quite
ordinary movements, where the quality is certainly not of the best
neither are the lips correctly formed, nevertheless they have rather
an excessive motion. To cover up these defects in such movements the
cylinder wheel teeth are purposely given the shape as shown at B in
Fig. 56, and to give sufficient power a strong mainspring is inserted.
With an excessive balance vibration we can usually conclude that it
is an intentional deception on the part of the manufacturer, while a
poor motion can generally be ascribed to careless methods in making.
The continued efforts in making improvements to quicken and cheapen
manufacturing processes very frequently result in the introduction
of defects which are only found by the experienced and practical
watchmaker.
As to the causes which induce excessive balance vibrations? As
this defect is generally found in the cheaper grades of cylinder
escapements, having usually rather small, heavy, and often clumsy
balances, those which have balances whose weight is probably less
than they ought to be, need not here be further considered, and it
only remains for us to look to the cylinder or the escape wheel for
the causes which produce these excessive vibrations. It will be found
that the cylinder is smaller in diameter than usually employed in such
a size of clock; the escape wheel is naturally also smaller, and its
teeth generally resemble B, Fig. 56, while A shows the correct shape of
a tooth for a wheel of that diameter.
In using small cylinders we can give the escape wheel teeth a somewhat
greater angle of inclination than generally used, but that the proper
amount of incline is exceeded is proved by the fact that the balance
vibrates more than two-thirds of a turn. It can also be readily seen
that with a tooth like B a greater impulse must be imparted than one
with an easy curve like A, and the impulse is still further increased
as the working width of the tooth B (the lift) is greater, indicated by
line _b_, while the same line in a correct width of tooth, as shown at
_a_, is considerably shorter.
In addition to what has been said of these escapements, we also find
them provided with very strong mainsprings to give the necessary power
to a tooth like B with its steeply inclined lifting face or impulse
angle.
To decrease the great amplitude of the balance vibrations many
watchmakers simply replace the strong mainspring with a weaker one.
But this procedure is not advantageous as the power of the escape
wheel tooth is insufficient to start the balance going and this is due
to two causes. First, the great angle of the escape wheel tooth, and
secondly, the inertia of the balance. It is only by violently shaking
such a clock that, we are enabled to start it going. And the owner soon
becomes dissatisfied from its frequent stoppage due to setting of the
hands and other causes so that he will be often obliged to shake it
until it starts going once more.
[Illustration: Fig. 57. Fig. 58.]
For properly correcting these defects the best method to pursue is to
replace the cylinder wheel with another one, whose teeth are of the
shape as shown at Fig. 55 and without question a good workman will
always replace the escape wheel if the clock is of fair quality. But if
a low grade one, we would hardly be justified in going to the expense
of putting in new wheels, as the low prices for which these clocks are
sold preclude such an alteration. As we must improve the wheel some
way to get a fair escapement action we can place it in a lathe and
while turning, hold an oil stone slip against it, we can remove the
point S, Fig. 56. After removing the point the tooth will now have
the form as shown at tooth C, Fig. 57. We now take a thin and rather
broad watch mainspring, bending a part straight and holding it in the
line _f f_, and revolving the wheel in the direction as shown by the
arrow, its action being indicated by figures 1 to 8; beginning at the
point of the tooth at 1, at 2 it comes in contact with the whole of the
lifting face, and from 3 to 8 only on the projecting corner which was
left by the oil stone slip in removing the heel of the tooth. In this
way all the teeth are acted upon until the corner is entirely removed.
Of course oil stone dust and oil is first used upon the spring for
grinding, after which the teeth are polished with diamantine. Care must
be observed in using the spring so as not to get the end _f_ too far
into the tooth circle, as it would catch on the heel of the preceding
tooth.
After the foregoing operation has been completed any feather edge
remaining on the points of the teeth must be removed with a sapphire
file and polished; we will now have a tooth as indicated by D, Fig. 57.
This shape of tooth can hardly be said to be theoretically correct,
nevertheless it is a close approximation of the proper form of tooth,
which is shown by the dotted lines, and will then perform its functions
much better than in its original condition.
Fig. 58 also shows how the spring must be moved from side to
side—indicated by dotted lines—so that the lifting face will have a
gentle curve instead of being flat; R represents the tooth.
After the wheel has been finished, as described, and again placed in
the clock, it will be found that the balance makes only two-thirds of
a turn, and as a result the movement can be easier brought to time and
closely regulated.
In the above I have described the cause of excessive balance vibration,
the method by which it can be corrected, and in what follows I shall
endeavor to make clear the reasons for a diminished balance vibration
or poor motion. It has been probably the experience of most watchmakers
to repair small cylinders of a low grade, having a poor motion or no
motion at all, and it would hardly be profitable to expend much time
in repairing them. But considerable time is often wasted in improving
the motion by polishing pivots and escape wheel teeth, possibly
replacing the cap jewels, or even the hole jewels, increasing the
escapement depth or making it shallower, examining the cylinder and
finding nothing defective, and as a last effort putting in a stronger
mainspring. But all in vain, the balance seems tired and with a slight
pressure upon an arm of the center wheel it stops entirely.
[Illustration: Fig. 59.]
In this case, as in a former one, in fact, it is necessary at all
times to carefully examine the cylinder wheel. My reason for not
considering the cylinder itself so much as the wheel is that the
makers of them have made a considerable advance in their methods of
manufacture, so we find the cylinders fairly well made and generally
of the correct size. Even if the cylinder is incorrectly sized,
either too large or small, it does not necessarily follow that the
watch would have a bad motion, as I have frequently had old movements
where the cylinder was incorrectly proportioned and yet the motion
was often a good, satisfactory one. Generally speaking, the cylinder
escapement is one which admits of the worst possible constructive
proportions and treatment, as we have often examined such clocks when
left for repairs, that, notwithstanding their being full of dirt, worn
cylinder, broken jewel holes, etc., they have been running until one of
the cylinder pivots has been completely worn away.
It only remains to look for the source of the trouble in the escape
wheel. If we examine the wheel teeth carefully, we shall find them
resembling those in Fig. 59, the dotted lines representing the correct
shape of the teeth for a wheel of that diameter.
Why do we find wheels having such defective teeth? This is probably due
to their rapid manufacture, as they very likely had the correct shape
when first cut, but by careless grinding and polishing they were given
improper forms, careless treatment being very evident at tooth F, which
we find on examination has a feather edge at the point as well as at
the heel of the tooth. If we grind these edges of the tooth with a ruby
file, by placing it in the position as indicated by dotted lines _h_
and _h¹_, and afterwards polishing the tooth point, we will find that
the balance makes a better vibration. A wheel, having teeth like E,
can still be used, but the balance will have a very poor motion, due
to the fact that the impulse angle of the wheel tooth is too small;
the impulse faces of the teeth having so small an angle, are nearly
incapable of any action. With a tooth like G, if we should remove its
bent point at the dotted line _d_, then the tooth would be too short,
and as the inclination of the impulse face is incapable to produce a
proper action, a new wheel must be used, having teeth as shown at Fig.
55.
The reasons why a tooth, having the shape as shown at F and G (Fig.
59), will cause a bad action of the escapement and also why in such
cases with a greater force acting on the wheel, causes a stopping of
the clock, I will endeavor to explain with the aid of the illustration
Fig. 60. Here we clearly see the curved points of the teeth resting
against the outer and inner walls of the cylinder while the escapement
is in action.
Teeth H and H¹ represent the defective tooth, while K and K¹ shows a
correctly formed tooth for a wheel of the same size, the correct depth
and positions where the tooth strikes the inner and outer walls of the
cylinder. It will be readily seen that the position of the tooth point
upon the cylinder (at _c_) is most favorable in reducing the resistance
to the least possible amount. But in the case of the teeth H and H¹
the condition is entirely different. We find that it was necessary
to set the escapement very deeply in order that it could perform its
functions at all, and, as a consequence, we have a false proportion;
the effects being considerably increased by the worst possible
position of the teeth H and H¹, where they touch the cylinder. While
the cylinder _c_ is turning in the direction shown by the arrows _i_
_i¹_, the tooth does not affect the cylinder to any extent; but during
the reverse movement of the cylinder, in the direction of _o o¹_, an
excessive amount of engaging friction must take place. A close
inspection of the drawing will enable us to see that there is a great
tendency of the cylinder to drag the tooth along with it during each
of these motions. It is evident that in such a case the friction will
eventually become so great as to lock the escapement, and if greater
pressure is applied by any means to teeth H and H¹, it is easily seen
that this effect will take place much more rapidly. Replacing the
escape wheel with one of correctly formed teeth and size is the best
means at our disposal.
[Illustration: Fig. 60.]
CHAPTER XIII.
THE DETACHED LEVER ESCAPEMENT AS APPLIED TO CLOCKS.
As the clock repairer is almost of necessity a watchmaker, or hopes to
become one, and as he must enter deeply into the study of all questions
pertaining to the detached lever in its various forms before he can
make any progress at all in watchmaking, it would seem unnecessary to
repeat in these pages that which has already been so well said and
so perfectly drawn, described and illustrated by such authorities as
Moritz Grossman, Britten, Playtner and the various teachers in the
horological schools, to say nothing of an equally brilliant and more
numerous coterie of writers among the French, Germans and Swiss, so
that the reader is referred to these writers for the mathematics and
drawings which already so fully cover the technical and theoretical
properties of the detached lever escapement. A few words as to its
adaptation to clocks may, however, not be out of place.
Anyone who sees the clocks of to-day would be inclined to suppose
that the first clocks were constructed with pendulums, because this
is evidently the most simple and reliable system for clocks, and that
the employment of the balance has been suggested by the necessity for
portable time pieces. This is, however, not the case, for the first
clocks had a verge escapement with a crude balance consisting of two
arms, carrying shifting weights for regulation. The pendulum was not
used until about three hundred years after the invention of the first
clock.
After the invention of the dead beat escapement, with its great gain
in accuracy by the reduction of the arc of pendulum oscillation,
attempts were made to combine its many virtues with the necessarily
large vibrations of a balance and thus get all the advantages of
both systems. By placing the lever on the arbor of the anchor, it
was possible to multiply the small angle of impulse on the pallets
very considerably at the balance, and to make all connection between
them cease immediately after the impulse had been given. The dead
beat escapement was thus converted into the detached lever escapement
and the latter made available for both watches and clocks. Another
important feature of this escapement is that when properly proportioned
it will not set on the locking or lifting, but will start to go as soon
as power is applied to the escape wheel through the train. This cannot
be said of the cylinder, duplex, or detent escapements, and it will
be seen at once that this has an important influence upon the cost of
construction, which must always be considered in the manufacture of
cheap clocks in enormous quantities.
[Illustration: Fig. 61. Pin Escapement for Clocks.]
The lever escapement with pins for pallets and the lifting planes
on the teeth of the escape wheel, which is the one usually put into
cheap clocks, is from the theoretical point of view a very perfect
form, because its lifting and locking take place at exactly the same
center distance and at the same angles, which again allows for greater
latitude in cheap construction, while still maintaining a reasonably
accurate rate of performance. These are the main reasons why the pin
anchor has such universal use in cheap clocks.
As this escapement is generally centered between the plates, banking
pins are dispensed with by extending the counterpoise end of the lever
far enough so that its crescent shaped sides will perform that office
by banking against the scape wheel arbor; see Fig. 61. The fork end of
the lever engages with an impulse pin carried in the balance and the
balance arbor is cut away to pass the guard point or dart, thus doing
away with the roller table. In other constructions the roller table is
supplied in the shape of a small brass collet which carries the pin and
has a notch for the guard point, thus making a single roller escapement.
The diameter of the lifting pins is generally made equal to 2½ degrees
of the scape wheel, which gives a lift of 2 degrees on the pallet arms,
and the remainder of the lift, 6½ degrees, must be performed by the
lifting planes of the wheel teeth. The front sides of the wheel teeth
are generally made with 15 degrees of draw and the lever should bank
when the center of the pin is just a little past the locking corner of
the tooth. Other details of the pin anchor escapement coincide with the
ordinary pallet form, as used in watches, and the reader is referred
for them to the works of the various authors mentioned previously.
The trouble with the majority of these clocks is in the escapement and
balance pivots, and to these parts are we going to direct particular
attention, for often, be it ever so clean, the balance gets up a sort
of “caterpillar motion” that is truly distressing, and if no more is
done we may expect a “come back” job in a very short time. In taking
down the movement the face wheels are left in place, but sometimes
it may be necessary to remove the “set wheel” of the alarm in order
to proceed as we do. Remove the screws or pins that hold the plates
together in the vicinity of the escapement, leaving the others, though
if screws they may be loosened slightly; pry up the corner of the
plate over the lever to loosen one pivot of same and let it drop away
from the scape wheel sufficiently to let the wheel revolve until it is
locked by a wire or pegwood previously inserted in the train, after
which the plates can be pried apart more conveniently to permit the
lever being removed entirely, also the scape wheel and the one next
following. As nickel clocks differ in make-up, the operator must, of
course, exercise judgment as to the work in hand to accomplish this.
Have ready a straight-sided tin pail, with cover, that will hold at
least one-half gallon of gasoline and of diameter large enough to
receive the largest brass clock; remove the wire or pegwood and immerse
the clock into the fluid and allow it to run down; this will loosen
all the dirt and gummy oil and clean the clock very effectually. Let
it remain long enough for all the dirt to settle to the bottom of the
pail; then remove and wipe as dry as possible with a soft rag; by
having no binder on the spring it is permitted to uncoil to its full,
and thereby remove all gummy oil between its coils. Now peg out the
holes of the wheels removed and of the lever and that portion of our
work is complete.
Polish or burnish the pivots of wheels either in a split chuck in the
lathe, or by holding in a pin vise, resting the pivot on a filing block
(an ivory one is best), and revolving between the fingers, using a
smooth back file for burnishing, after the manner of pointing up a pin
tongue, only let the file be held flat, so as to maintain a cylindrical
pivot as nearly as possible. The scape wheel is now polished, i.
e., the teeth, with a revolving bristle wheel on a polishing lathe,
charged with kerosene oil and tripoli. This will smooth up the teeth
in fine form, especially those wheels that work into a lever with pin
pallets. Clean the scape wheel by dipping into gasoline to remove all
the oil and tripoli. The other wheel may simply be brushed in the
gasoline or dipped and then brushed dry.
We now turn our attention to the lever and closely examine the pallets
with a glass; if there are the least signs of wear upon them they must
be removed. Of the lever with pin pallets it is better to remove the
steel pins and insert new ones. See if the holes in the anchor where
they are inserted will admit a punch to drive them out from the back;
if not, open these holes with a drill until the ends of the pins are
reached. Put a hollow stump with a sufficiently large hole in the
staking tool, and by placing the pins in the stump they can be driven
out successively, being sure that the driving punch is no larger than
the pins; drive or insert into their places a couple of needles of the
proper size, and then break off at correct lengths; this completes the
job in this particular style of lever.
With the other style the job is not quite so easy; with a pair of
small round-nose pliers grasp the brass fork close up to the staff and
bend it back from the pallets till it lays parallel with the staff;
treat the counter poise of the fork in like manner; place a thin zinc
lap into the lathe, charged with flour of emery, and with the fingers
holding the pallets grind off all wheel teeth marks on both the
impulse and locking faces of the pallets. Then polish with a boxwood
lap charged with diamantine. It is surprising how speedily this can
be done if laps are at hand. The only care necessary is not to round
off the corners of the pallets, and as they are so large they can be
easily held flat against the laps with the thumb and finger as before
stated. Bend back the fork and counterpoise to their original position.
The fork must now be attended to; see that no notches are worn in the
horns of the fork by the steel impulse pin in the balance; if they
appear they must be dressed out and polished, also examine and smooth
if necessary the ends of the horns that bank against the balance staff.
These may seem small matters, but they are often what cause all the
trouble.
We now come to the balance staff and the hardened screws in which the
staff vibrates; their irregularities are often the source of much
vexation, and there is only one way to go at it and that is with a will
and determination to make it right. Examine the points of the staff
and see if they are in their normal shapes and are sharp and bright;
if so they will probably do their work. But we will suppose we have a
bad case in hand and will therefore treat it thoroughly according to
our method. We find the staff is large in diameter and the ends are
very blunt; the notch in the center has a burr on each side as hard as
glass, making an admirable cause for catching the horns of the fork in
some of the vibrations or in a certain position; also the round part of
the staff back of the notch is rough and looks as if it never had been
finished, and, in fact, it has not, for it truly appears as if half, if
not all, the nickel clocks are made to be finished by the watchmaker.
Remove the hairspring and place the staff between the jaws of your
bench vise, with the jaws close up to the staff, but not gripping it,
the balance “hub” resting on the jaws with the impulse pin also down
between the jaws. Have a block of brass about one-fourth inch square;
rest it on top of the staff, or on its pivot end, if it may so be
called, holding it with the thumb and finger of the left hand. Strike
this block with a hammer and drive out the staff; a hollow punch is apt
to be split in doing this, and as the pivot is to be re-pointed no harm
will be done to the pivot or to the end of the staff. Draw the temper
so it will work easily, insert into a split chuck and turn up new
points; have them long and tapering, that is, turn the points to a long
slant from the end of the staff to the body of same, or at least twice
as much taper as they generally have; polish off the back of the notch
or round part of the staff with an oil stone slip. Remove from the
chuck, smear all over with powdered boracic acid by first wetting the
staff in water, and then heat to a bright red and plunge straight into
water; it will now be white and hard; draw the temper from the staff
in the vicinity of the notch, leaving the pivot points hard as before;
re-insert into the chuck and with diamantine polish the points and
also around the staff in the vicinity of the notch. The drawing of the
temper from the center of the staff to a spring temper is to make it
less liable to breakage while driving on the balance. Fasten the staff
tight in the vise and with a rather stout brass tube, large enough
to step over the largest staff, drive on the balance to its former
position.
If the workman has a pivot polisher with a large lap, the job may be
done, without softening the staff or removing the balance, by grinding
the pivots. In turning the staff we often find it almost impossible to
hold true. We straighten the best we can and then turn up our pivots,
and as long as the untruth of the staff will not cause the balance to
wabble to such an extent as to give us a headache or cause us to look
cross-eyed it will do. We do not wish to be misunderstood or to give
the impression that we go on the principle of “good enough”; but as
gold dollars cannot be bought for seventy-five cents, neither can a
workman devote the time to have everything perfect for fifty cents; and
for this very reason do they come in such an unfinished state from the
manufacturers.
Next see if the two screws in which the balance vibrates have properly
cut countersinks; if rough or irregular, better at once draw the
temper, re-drill with a sharp-angled drill and again harden.
Occasionally a bunch of these clocks will come in with both pivots and
cones badly rusted. This has generally been caused by acid pickling,
or some sort of chemical hardening at the factory; the acid or alkali
gets into the pores of the steel and comes out after the clock has
been shipped. They are generally made in such quantities that fifty
or a hundred thousand of them have been distributed before finding out
that they were not right and then it is a matter of two or three years
before the factory hears the last of it. The trouble is attributed
to bad oil, or to anything else but the hardening, which is the real
cause, and the expense of taking back and refitting the balance
arbors and cones, paying freight both ways and standing the abuse of
disgruntled jewelers, goes on until life becomes anything but a bed of
roses. Every jeweler should warn the factory immediately on finding
rust in the cones of a shipment of new clocks and not attempt to fix
them himself, as such a fault cannot be discovered at the factory and
every day it continues means more thousands of clocks distributed that
will give trouble.
Our clock is now ready to be put together. Wind up the spring and
slip on the binder; then put in the wheels and lever; then adjust
the balance and hairspring to their proper places, slightly wind the
mainspring and then see (by bringing either horn against the staff)
whether it sticks and holds the balance; if so, shorten the fork
slightly by bending; try this until the balance and fork act perfectly
free and safe. Slightly oil the balance pivots; an excess will only
gather dust and prove detrimental, as the countersinks form an
admirable place for holding the dust. Now oil the remaining parts and
we are sadly mistaken if our clock does not make a motion that will be
gratifying.
The foregoing process may seem tedious and uncalled for and too close
mention made of the lesser portions of the work, but we must not
“despise the day of small things,” and as we are watchmakers, we are
expected to do this work, even though troublesome and the pay small; we
should also bear in mind that if we only make a nickel clock run and
keep fair time, it will be a large advertisement, and possibly repay
tenfold. It takes only an hour to do this job complete, while in many
cases only the balance staff needs attention.
Sometimes such a clock will be apparently all right mechanically but
will continue to lose time; then it is probable that the balance does
not make the proper number of vibrations, which causes the clock to
lose time. There is one way to tell this, which will soon locate the
trouble: count the train to ascertain the number of vibrations the
balance should make in one minute. You do this by counting the number
of teeth in the center wheel, which we will say is 48; third wheel
48; fourth wheel, 45; escape, 15. Multiply all teeth together, which
give us 48 × 48 × 45 × 15 = 1,555,200. Now count the leaves in the
third wheel pinion, which is 6; fourth, 6; escape, 6. Multiply these
together, 6 × 6 × 6 = 216; now divide the leaves into the teeth,
1,555,200 ÷ 216 = 7,200, which is the number of whole vibrations some
Ansonia alarm clocks make in one hour. Dividing 7,200 by 60 gives us
120, the number of vibrations per minute. Now the balance must make 120
vibrations in one minute, counting the balance going one way. If the
balance only vibrates 118, the clock will lose time and the hairspring
must be taken up or made shorter, until it makes the required number
of vibrations. If it should vibrate 122 the clock would gain and the
hairspring should be let out.
Find out the number of vibrations your balance should make and work
accordingly; and if you find that the balance makes the proper number
of vibrations in one minute, then the trouble must lie in the center
post, which has not enough friction to carry the hands and dial wheels,
or the wheel that gears into the hour wheel and regulates the alarm
hand is too tight and holds back the hands. You should find some
trouble about these wheels or center post, for where a balance makes
the proper number of vibrations in one minute, the minute hand cannot
help going around if everything else is correct.
Fig. 62 illustrates the escapement of the Western Clock Manufacturing
Company for their cheap levers. It has hardened steel pallets placed
in a mould and the fork cast around them, thus insuring exact placing
of the pallets, and the company claim that they thus secure a detached
lever escapement with all the advantages of hardened and polished
pallets at a minimum cost.
[Illustration: Fig. 62.]
Mr. F. Dauphin, of Cassel, Germany, on page 387 of Der Deutsche
Uhrmacher Zeitung, 1905, has described a serious fault of some of the
cheap American alarm clocks in the depthings of the escapements and
how he remedied it by changing the position of the pins. It is to be
regretted that Mr. Dauphin did not state the measurements of the parts
as nearly as possible in this article and also give the manufacturer’s
name, simply to enable others not as skilled as he is to do what I
would do in such a case; namely, to return it to the jobber and get a
new and correct movement in its stead _free of charge_. The American
clock manufacturers are very liberal in this respect and never hesitate
to take back a movement that was not correct when it left the factory,
even when the customer, in the attempt to correct it, has spoiled it;
spoiled or not, it goes to the waste pile anyway, when it reaches the
factory. I seriously doubt the ability of the average watch repairer to
correctly change the position of the pins as suggested; and to change
the center of action of the lever is certainly a desperate job. I
herewith give a correct drawing of an escape wheel and lever, such as
are used in the above cited clocks, made from measurements of the parts
of a clock. The drawing is, of course, enlarged. The measurements are:
Escape wheel, actual diameter, 18.11 mm.; original diameter, 17 mm.;
lever, from pin to pin, outside, 9.3 mm.; distance of centers of wheel
and lever, 10.0 mm. I found that all these measurements almost exactly
agree with Grossmann’s tables, and I do not doubt at all that they were
taken from them. There is only one mistake visible, which is in the
shape of the escape teeth, and I fail to see why this was overlooked by
those in charge at the factory; _the draw is insufficient_. It is only
from seven to eight degrees, when it should be fifteen degrees. I show
this at tooth A, in the drawing, where you can see both dotted lines,
measuring the angle of draw; line C as it is and line B as it should be.
[Illustration: Fig. 63.]
Notwithstanding the deficient draw, this escapement will work safely
as long as the pivot holes are not too large, or worn sideways; but if
you want to make it safe you should file the locking faces of teeth
slightly under; even if you do not make a model job, you have remedied
the fault. Make a disk of 18.11 mm. diameter, put it on the arbor of
the wheel and lay a straight edge from the point of the tooth to the
center of the disk, so as to see how much it needs to be filed away.
Even if this undercutting is not very true it will go.
TO MEASURE WHEELS WITH ODD NUMBERS OF TEETH.—This is a job that so
frequently comes to the watchmaker who has to replace wheels or pinions
that the following simple method should be generally appreciated. It
depends upon the fact that the radius of a circle, R, Fig. 64, equals
the versed sine E (dotted) plus the cosine B. If we stand such a wheel
on the points of the teeth, A C, and measure it we shall get the
length of the line T B only, when what we really need is the length
of the lines T B E, to give us the real diameter for our wheel, and E
we find has been cut away, so that we cannot measure it. Say it is a
15-tooth escape wheel, then by standing the old wheel up on the anvil
of a vertical micrometer, resting it on two of its teeth, as shown in
Fig. 64, the measuring screw can be brought in contact with the tooth
diametrically opposite the space between the two teeth on the anvil,
and a measurement taken, which will be less than the full diameter by
the versed sine of 12 degrees (half the angle included between two
adjoining teeth). By bringing each tooth in succession to the top, such
a wheel could be measured in fifteen different directions, which would
vary slightly, owing to the fact that some of the teeth may be bent a
little, but the mean of these measures should be what the wheel would
measure were the teeth in their original shape. If a tooth was badly
bent the three measures in which it was involved could be rejected,
and the mean of the other twelve measures taken as the correct value
and found to be, we will say, 0.732 inch. Consulting a table of
natural sines the cosine of 12 degrees is found to be 0.97815, which
subtracted from 1 gives 0.02185 as the versed sine. Multiplying this
by 0.36 inch (practically one-half of our measured 0.732) to get the
approximate radius of the wheel, we get 0.008 inch, the amount to be
added to the micrometer measurement in order to get the diameter of the
blank.
At first sight it may appear like a vicious principle that we must
know the radius of the wheel before we can determine the value of
the correction in question, but we only need to know the radius
approximately in order to determine the correction very closely, an
error of ¹/₂₀ inch in the assumed value of the radius producing an
error of only 0.001 inch in the value of the correction.
[Illustration: Fig. 64. Getting the full diameter.]
This method can of course be applied to all wheels and pinions to get
the size of the blank; with other wheels than escape wheels, where the
pitch line and the full diameter do not coincide, the addendum may be
subtracted from the full diameter to get the pitch line.
CUTTERS FOR CLOCK TRAINS.—In cutting escape wheels or others with wide
space between the teeth, it is a matter of some difficulty with many
people to enable them to set the cutter properly.
Mr. E. A. Sweet calls attention to the fact that if a cutter be set so
that its center touches the circumference of the wheel to be cut, said
cutter will be in the proper position for work. For instance, if an
escape wheel is to be cut, it is sufficient to set the cutter in such
a manner that that portion of the cutter forming the bottom of the cut
touch the circumference of the blank at the center of the cutter. It
may then be backed off and fed in with the certainty of being properly
placed.
CHAPTER XIV.
PLATES, PIVOTS AND TIME TRAINS.
Before going further with the mechanism of our clocks we will now
consider the means by which the various members are held in their
positions, namely, the plates. Like most other parts of the clock these
have undergone various changes. They have been made of wood, iron and
brass and have varied in shapes and sizes so much that a great deal may
be told concerning the age of a clock by examining the plates.
Most of the wooden clocks had wooden plates. The English and American
movements were simply boards of oak, maple or pear with the holes
drilled and bushed with brass tubes—full plates. The Schwarzwald
movements were generally made with top and bottom boards and
stanchions, mortised in between them to carry the trains, which were
always straight-line trains. The rear stanchions were glued in position
and the front ones fitted friction-tight, so that they could be removed
in taking down the clock. This gave a certain convenience in repairing,
as, for instance, the center (time) train could be taken down without
disturbing the hour or quarter trains, or vice versa. Various attempts
have been made since to retain their convenience with brass plates, but
it has always added so much to the cost of manufacture that it had to
be abandoned.
The older plates were cast, smoothed and then hammered to compact the
metal. The modern plate is rolled much harder and stiffer and it may
consequently be much thinner than was formerly necessary. The proper
thickness of a plate depends entirely upon its use. Where the movement
rests upon a seat board in the case and carries the weight of a heavy
pendulum attached to one of the plates they must be made stiff enough
to furnish a rigid support for the pendulum, and we find them thick,
heavy and with large pillars, well supported at the corners, so as to
be very stiff and solid. An example of this may be seen in that class
of regulators which carry the pendulum on the movement. Where the
pendulum is light the plates may therefore be thin, as the only other
reason necessary for thickness is that they may provide a proper length
of bearing for the pivots, plus the necessary countersinking to retain
the oil.
In heavy machinery it is unusual to provide a length of box or journal
bearing of more than three times the diameter of the journal. In most
cases a length of twice the diameter is more than sufficient; in clock
and other light work a “square” bearing is enough; that is one in
which the length is equal to the diameter. In clocks the pivots are of
various sizes and so an average must be found. This is accomplished
by using a plate thick enough to furnish a proper bearing for the
larger pivots and countersinking the pivot holes for the smaller pivots
until a square bearing is obtained. This countersinking is shaped in
such a manner as to retain the oil and as more of it is done on the
smaller and faster moving pivots, where there is the greatest need of
lubrication, the arrangement works out very nicely, and it will be seen
that with all the lighter clocks very thin plates may be employed while
still retaining a proper length of bearing in the pivot holes.
The side shake for pivots should be from .002 to .004 of an inch; the
latter figure is seldom exceeded except in cuckoos and other clocks
having exposed weights and pendulums. Here much greater freedom is
necessary as the movement is exposed to dust which enters freely at the
holes for pendulum and weight chains, so that such a clock would stop
if given the ordinary amount of side shake.
We are afraid that many manufacturers of the ordinary American clock
aim to use as thin brass as possible for plates without paying too much
attention to the length of bearing. If a hole is countersunk it will
retain the oil when a flat surface will not. The idea of countersinking
to obtain a shorter bearing will apply better to the fine clocks than
to the ordinary. In ordinary clocks the pivots must be longer than
the thickness of the plates for the reason that freight is handled so
roughly that short pivots will pop out of the plates and cause a lot of
damage, provided the springs are wound when the rough handling occurs.
It will be seen by reference to Chapter VII (the mechanical elements
of gearing), Figs. 21 to 25, that a wheel and pinion are merely a
collection of levers adapted to continuous work, that the teeth may
be regarded as separate levers coming into contact with each other in
succession; this brings up two points. The first is necessarily the
relative proportions of those levers, as upon these will depend the
power and speed of the motion produced by their action. The second
is the shapes and sizes of the ends of our levers so that they shall
perform their work with as little friction and loss of power as
possible.
TO GET CENTER DISTANCES.—As the radii and circumferences of circles are
proportional, it follows that the lengths of our radii are merely the
lengths of our levers (See Fig. 24), and that the two combined (the
radius of the wheel, plus that of the pinion) will be the distance at
which we must pivot our levers (our staffs or arbors of our wheels)
in order to maintain the desired proportions of their revolution.
Consequently we can work this rule backwards or forwards.
For instance if we have a wheel and pinion which must work together in
the proportion of 7½ to 1; then 7½ + 1 = 8½ and if we divide the space
between centers into 8½ spaces we will have one of these spaces for
the radius of the _pitch circle_ of the pinion and 7½ for the _pitch
circle_ of the wheel, Fig. 65. This is independent of the number of
teeth so long as the _proportions_ be observed; thus our pinion may
have eight teeth and the wheel sixty, 60 ÷ 8 = 7.5, or 75 ÷ 10 = 7.5,
or 90 ÷ 12 = 7.5, or any other combination of teeth which will make the
correct proportion between them and the center distances. The reason is
that the teeth are added to the wheel to prevent slipping, and if they
did not agree with each other and also with the proportionate distance
between centers there would be trouble, because the desired proportion
could not be maintained.
Now we can also work this rule backwards. Say we have a wheel of 80
teeth and the pinion has 10 leaves but they do not work together
well in the clock. Tried in the depthing tool they work smoothly.
80 ÷ 10 = 8, consequently our center distance must be as 8 and 1.
8 + 1 = 9; the wheel must have 8 parts and the pinion 1 part of the
radius of the pitch circle of the wheel. Measure carefully the diameter
of the pitch circle of the wheel; half of that is the pitch radius, and
nine-eighths of the pitch radius is the proper center distance for that
wheel and pinion.
Say we have lost a wheel; the pinion has 12 teeth and we know the arbor
should go seven and one-half times to one of the missing wheel; we
have our center distances established by the pivot holes which are not
worn; what size should the wheel be and how many teeth should it have?
12 × 7.5 = 90, the number of teeth necessary to contain the teeth of
the pinion 7.5 times. 7.5 + 1 = 8.5, the sum of the center distances;
the pitch radius of the pinion can be closely measured; then 7.5 times
that is the pitch radius of the missing wheel of 90 teeth. Other
illustrations with other proportions could be added indefinitely but we
have, we think, said enough to make this point clear.
[Illustration: Fig. 65. Spacing off center distances; c, center of
wheel; e, pitch circle; d, dedendum; b, addendum; a, center of pinion.]
CONVERSION OF NUMBERS.—There is one other point which sometimes
troubles the student who attempts to follow the expositions of this
subject by learned writers and that is the fact that a mathematician
will take a totally different set of numbers for his examples, without
explaining why. If you don’t know why you get confused and fail to
follow him. It is done to avoid the use of cumbersome fractions. To use
a homely illustration: Say we have one foot, six inches for our wheel
radius and 4.5 inches for our pinion radius. If we turn the foot into
inches we have 18 inches. 18 ÷ 4.5 = 4, which is simpler to work with.
Now the same thing can be done with fractions. In the above instance
we got rid of our larger unit (the foot) by turning it into smaller
units (inches) so that we had only one kind of units to work with. The
same thing can be done with fractions; for instance, in the previous
example we can get rid of our mixed numbers by turning everything
into fractions. Eighteen inches equals 36 halves and 4.5 equals 9
halves; then 36 ÷ 9 = 4. This is called the conversion of numbers and
is done to simplify operations. For instance in watch work we may find
it convenient to turn all our figures into thousands of a millimeter, if
we are using a millimeter gauge. Say we have the proportions of 7.5 to
1 to maintain, then turning all into halves, 7½ × 2 = 15 and 1 × 2 = 2.
15 + 2 = 17 parts for our center distance, of which the pitch radius of
the pinion takes 2 parts and that of the wheel 15.
THE SHAPES OF THE TEETH.—The second part of our problem, as stated
above, is the shapes of the ends of our levers or the teeth of our
wheels, and here the first consideration which strikes us is that the
teeth of the wheels approach each other until they meet; roll or slide
upon each other until they pass the line of centers and then are drawn
apart. A moment’s consideration will show that as the teeth are longer
than the distance between centers and are securely held from slipping
at their centers, the outer ends _must_ either roll or slide after they
come in contact and that this action will be much more severe while
they are being driven towards each other than when they are being drawn
apart after passing the line of centers. This is why the _engaging_
friction is more damaging than the _disengaging_ friction and it is
this _butting_ action which uses up the power if our teeth are not
properly shaped or the center distances not right. Generally speaking
this butting causes serious loss of power and cutting of the teeth when
the pivot holes are worn or the pivots cut, so that there is a side
shake of half the diameter of the pivots, and bushing or closing the
holes, or new and larger pivots are then necessary. This is for common
work. For fine work the center distances should be restored long before
the wear has reached this point.
If we take two circular pieces of any material of different diameters
and arrange them so that each can revolve around its center with their
edges in contact, then apply power to the larger of the two, we find
that as it revolves its motion is imparted to the other, which revolves
in the opposite direction, and, if there is no slipping between the
two surfaces, with a velocity as much greater than that of the larger
disc as its diameter is exceeded by that of the larger one. We have,
then, an illustration of the action of a wheel and pinion as used in
timepieces and other mechanisms. It would be impossible, however, to
prevent slipping of these smooth surfaces on each other so that power
(or motion) would be transmitted by them very irregularly. They simply
represent the “pitch” circles or circles of contact of these two
mobiles. If now we divide these two discs into teeth so spaced that
the teeth of one will pass freely into the spaces of the other and add
such an amount to the diameter of the larger that the points of its
teeth extend inside the pitch circle of the smaller, a distance equal
to about 1⅛ times the width of one of its teeth, and to the smaller so
that its teeth extend inside the larger one-half the width of a tooth,
the ends of the teeth being rounded so as not to catch on each other
and the centers of revolution being kept the same distance apart, on
applying power to the larger of the two it will be set in motion and
this motion will be imparted to the smaller one. Both will continue to
move with the same relative velocity as long as sufficient power is
applied. Other pairs of mobiles may be added to these to infinity, each
addition requiring the application of increased power to keep it in
motion.
These pairs of mobiles as applied to the construction of timepieces are
usually very unequal in size and the larger is designated as a “wheel”
while the smaller, if having less than 20 teeth, is called a “pinion”
and its teeth “leaves.” Now while we have established the principle of
a train of wheels as used in various mechanisms, our gearing is very
defective, for while continuous motion may be transmitted through such
a train, we will find that to do so requires the application of an
impelling force far in excess of what should be required to overcome
the inertia of the mobiles, and the amount of friction unavoidable in a
mechanism where some of the parts move in contact with others.
This excess of power is used in overcoming a friction caused by
improperly shaped teeth, or when formed thus the teeth of the wheel
come in contact with those of the pinion and begin driving at a point
in front of what is known as the “line of centers,” i. e., a line drawn
through the centers of revolution of both mobiles, and as their motion
continues the driven tooth slides on the one impelling it toward the
center of the wheel. When this line is reached the action is reversed
and the point of the driving tooth begins sliding on the pinion leaf
in a direction away from the center of the pinion, which action is
continued until a point is reached where the straight face of the leaf
is on a line tangential to the circumference of the wheel at the point
of the tooth. It then slips off the tooth, and the driving is taken up
on another leaf by the next succeeding tooth. The sliding action which
takes place in front of the line of centers is called “engaging,” that
after this line has been passed “disengaging” friction.
Now we know that in the construction of timepieces, friction and
excessive motive power are two of the most potent factors in producing
disturbances in the rate, and that, while some friction is unavoidable
in any mechanism, that which we have just described may be almost
entirely done away with. Let us examine carefully the action of a
wheel and pinion, and we will see that only that part of the wheel
tooth is used, which is outside the pitch circle, while the portion
of the pinion leaf on which it acts is the straight face lying inside
this circle, therefore it is to giving a correct shape to these parts
we must devote our attention. If we form our pinion leaves so that
the portion of the leaf inside the pitch circle is a straight line
pointing to the center, and give that portion of the wheel tooth lying
outside the pitch circle (called the addenda, or ogive of the tooth)
such a degree of curvature that during its entire action the straight
face of the leaf will form a tangent to that point of the curve which
it touches, no sliding action whatever will take place after the line
of centers is passed, and if our pinion has ten or more leaves, the
“addenda” of the wheel is of proper height, and the leaves of the
pinion are not too thick, there will be no contact in front of the line
of centers. With such a depth the only friction would be from a slight
adhesion of the surfaces in contact, a factor too small to be taken
into consideration.
[Illustration: Showing that a hypocycloid of half the pitch circle is a
straight line.]
[Illustration: Generating an epicycloid curve for a cut pinion. D,
generating circle. Dotted line epicycloid curve. Note how the shape
varies with the thickness of the tooth.]
Here, then, we have an ideal depth. How shall we obtain the same
results in practice? It is comparatively an easy matter to so shape
our cutters that the straight faces of our pinion leaves will be
straight lines pointing to the center, but to secure just the proper
curve for the addenda of our wheel teeth requires rather a more
complicated manipulation. This curve does not form a segment of a
circle, for it has no two radii of equal length, and if continued
would form, not a circle, but a spiral. To generate this curve, we
will cut from cardboard, wood, or sheet metal, a segment of a circle
having a _radius_ equal to that of our _wheel_, on the pitch circle,
and a smaller circle whose _diameter_ is equal to the _radius_ of the
_pinion_, on the pitch circle. To the edge of the small circle we will
attach a pencil or metal point so that it will trace a fine mark. Now
we lay our segment flat on a piece of drawing paper, or sheet metal and
cause the small circle to revolve around its edge without slipping. We
find that the point in the edge of the small circle has traced a series
of curves around the edge of the segment.
These curves are called “epicycloids,” and have the peculiar property
that if a line be drawn through the generating point and the point of
contact of the two circles, this will always be at right angles to a
tangent of the curve at its point of intersection. It is this property
to which it owes its value as a shape for the acting surface of a wheel
tooth, for it is owing to this that a tooth whose acting surface is
bounded by such a curve can impel a pinion leaf through the entire lead
with little sliding action between the two surfaces. This, then, is the
curve on which we will form the addenda of our wheel teeth.
In Fig. 66, the wheel has a radius of fifteen inches and the pinion
a radius of one and one-half, and these two measurements are to be
added together to find the distance apart of the two wheels; 16.5
inches is then the distance that the centers of revolution are apart
of the wheels. Now, the teeth and leaves jointly act on one another to
maintain a sure and equable relative revolution of the pair.
In Fig. 66, the pinion has its leaves radial to the center, inside of
the pitch line D, and the ends of the leaves, or those parts outside
of the pitch line, are a half circle, and serve no purpose until the
depthings are changed by wear, as they never come in contact with the
wheel; the wheel teeth only touch the radial part of the pinion and
that occurs wholly within the pitch line. So in all pinions above 10
leaves in number the addendum or curve is a thing of no moment, except
as it may be too large or too long. In many large pieces of machinery
the pinions, or small driven wheels, have no addendum or extension
beyond their pitch diameter and they serve every end just as well. In
watches there is so much space or shake allowed between the teeth and
pinions that the end of a leaf becomes a necessity to guard against the
pinion’s recoiling out of time and striking its sharp corner against
the wheel teeth and so marring or cutting them. In a similar pair
of wheels in machinery there are very close fits used and the shake
between teeth is very slight and does not allow of recoil, butting, or
“running out of time.”
Running out of time is the sudden stopping and setting back of a pinion
against the opposite tooth from the one just in contact or propelling.
This, with pinions of suppressed ends, is a fault and it is averted by
maintaining the ends.
The wheel tooth drives the pinion by coming in contact with the
straight flank of the leaf at the line of centers, that is a line drawn
through the centers of the two wheels; centers of revolution.
The curve or end of the wheel tooth outside of the pitch line is the
only part of the tooth that ever touches the pinion and it is the
part under friction from pressure and slipping. At the first point of
contact the tooth drives the pinion with the greatest force, as it is
then using the shortest leverage it has and is pressing on the longest
lever of the leaf. As this action proceeds, the tooth is acted on by
the pinion leaf farther out on the curve of the wheel tooth, thus
lengthening the lever of the wheel and at the same time the tooth thus
acts nearer to the center of the pinion by touching the leaf nearer its
center of revolution.
By these joint actions it will appear that the wheel first drives with
the greatest force and then as its own leverage lengthens and its force
consequently decreases, it acts on a shorter leverage of the pinion,
as the end of a tooth is nearer to the center of the pinion, or on the
shortest pinion leverage, just as the tooth is about ceasing to act.
The action is thus shown from the above to be a variable one, which
starts with a maximum of force and ends with a minimum. Practically
the variable force in a train is not recognized in the escapement, as
the other wheels and pinions making up the train are also in the same
relations of maximum and minimum forces at the same time, and thus this
theoretical and virtual variability of train force is to a great extent
neutralized at the active or escaping end of the movement.
There is another action between the tooth and leaf that is not easy
to explain without somewhat elaborate sketches of the acting parts,
and as this is not consistent with such an article, we may dismiss
it, and merely state that it is the one of maintaining the relative
angular velocities of the two wheels at all times during their joint
revolutions.
In Fig. 66 will be seen the teeth of the wheel, their heights, widths
and spacing, and the epicycloidal curves. Also the same features of
the pinion’s construction. The curve on the end of the wheel teeth is
the only curve in action during the rotation between wheel and pinion.
Each flank (both teeth and leaves) is a straight line to the center
of each. A tooth is composed of two members—the pillar or body of the
tooth inside of the pitch line and the cycloid or curve, wholly outside
of this line. The pinion also has two members, the radial flank wholly
inside of the pitch line, and its addendum or circle outside of this
line.
[Illustration: Fig. 66.]
In Fig. 66 will be seen a tooth on the line of centers A B, just coming
in action against the pinion’s flank and also one just ceasing action.
It will be seen that the tooth just entering is in contact at the joint
pitches, or radii, of the two wheels, and that when the tooth has run
its course and ceased to act, that it will be represented by tooth 2.
Then the exit contact will be at the dotted line _o o_. From this may
be seen just how far the tooth has, in its excursion, shoved along
the leaf of the pinion and by the distance the line _o o_, is from
the wheel’s pitch line G, at this tooth. No. 2, is shown the extent
of contact of the wheel tooth. By these dotted lines, then, it may
be seen that the tooth has been under friction for nearly its whole
curve’s length, while the pinion’s flank will have been under friction
contact for less than half this distance. In brief, the tooth has moved
about ⁸⁰/₁₀₀ of its curved surface along the straight flank .35 of
the surface of the pinion leaf. From this relative frictional surface
may be seen the reason why a pinion is apt to be pitted by the wheel
teeth and cut away. In any case it shows the relation between the two
friction surfaces. In part a wheel tooth rolls as well as slides along
the leaf, but whatever rolling there may be, the pinion is also equally
favored by the same action, which leaves the proportions of individual
friction still the same.
In Fig. 66 may be seen the spaces of the teeth and pinion. The teeth
are apart, equal to their own width and the depths of the spaces are
the same measurement of their width—that is, the tooth (inside of the
pitch line) is a pillar as wide as it is high and a space between two
teeth is of like proportions and extent of surface. The depth of a
space between two teeth is only for clearance and may be made much
less, as may be seen by the pinion leaf, as the end of the circle does
not come half way to the bottom of a space.
The dotted line, _o o_, shows the point at which the tooth comes out
of action and the pointed end outside of this line might be cut off
without interfering with any function of the tooth. They generally are
rounded off in common clock work.
The pinion is 3 inches diameter and is divided into twelve spaces
and twelve leaves; each leaf is two-fifths of the width of a space
and tooth. That is one-twelfth of the circumference of the pinion is
divided into five equal parts and the leaf occupies two and a space
three of these parts. The space must be greater than the width of a
leaf, or the end of a leaf would come in contact with a tooth before
the line of centers and cause a jamming and butting action. Also the
space is needed for dirt clearance. As watch trains actuated by a
spring do not have any reserve force there must be allowance made for
obstructions between the teeth of a train and so a large latitude is
allowed in this respect, more than in any machinery of large caliber.
As will be seen by Fig. 66, the spans between the leaves are deep, much
more so than is really necessary, and a space at O C shows the bottom
of a space, cut on a circle which strengthens a leaf at its root and is
the best practice.
Having determined the form of our curve, our next step will be to get
the proper proportions. Saunier recommends that in all cases tooth
and space should be of equal width, but a more modern practice is
to make the space slightly wider, say one-tenth where the curve is
epicycloidal. When the teeth are cut with the ordinary Swiss cutters,
which, of course, cannot be epicycloidal, it is best to make the
spaces one-seventh wider than the tooth. This proportion will be
correct except in the case of a ten-leaf pinion, when, if we wish to
be sure the driving will begin on the line of centers, the teeth must
be as wide as the spaces; but in this case the pinion leaf is made
proportionately thinner, so that the requisite freedom is thus obtained.
The height of the addenda of the wheel teeth above the pitch circle is
usually given as one and one-eighth times the width of a tooth. While
this is approximately correct, it is not entirely so, for the reason
that as we use a circle whose diameter is equal to the pitch radius of
the pinion for generating the curve, the height of the addenda would be
different on the same wheel for each different numbered pinion. So that
if a wheel of 60 were cut to drive a pinion of 8, the curve of this
tooth would be found too flat if used to drive a pinion of 10. Now,
since the pitch diameter of the pinion is to the pitch diameter of the
wheel as the number of leaves in the pinion are to the number of teeth
in the wheel, in order to secure perfect teeth: we must adopt for the
height of the addenda a certain proportion of the radius or diameter of
the pinion it is to drive, this proportion depending on the number of
leaves in the pinion.
A careful study of the experiments on this subject with models of
depths constructed on a large scale, shows that the proportions given
below come the nearest to perfection.
When the pinion has six leaves the spaces should be twice the width
of the leaves and the depth of the space a little more than one-half
the total radius of the pinion. The addenda of the pinion should be
rounded, and should extend outside the pitch circle a distance equal
to about one-half the width of a leaf. The addenda of the wheel teeth
should be epicycloidal in form and should extend outside the pitch
circle a distance equal to five-twelfths of the pitch radius of the
pinion.
With these proportions, the tooth will begin driving when one-half
the thickness of a leaf is in front of the line of centers, and there
will be engaging friction from this point until the line of centers is
reached.
This cannot be avoided with low numbered pinions without introducing
a train of evils more productive of faulty action than the one we are
trying to overcome. There will be no disengaging friction.
When a pinion of seven is used, the spaces of the pinion should
be twice the width of the leaves, and the depth of a space about
three-fifths of the total radius of the pinion. The addenda of the
pinion leaves should be rounded, and should extend outside the pitch
circle about one-half the width of a leaf. The addenda of the wheel
teeth should be epicycloidal, and the height of each tooth above the
pitch circle equal to two-fifths of the pitch radius of the pinion.
There is less engaging friction when a pinion of seven is used than
with one of six, as the driving does not begin until two-thirds of the
leaf is past the line of centers. There is no disengaging friction.
With an eight-leaf pinion the space should be twice as wide as the
leaf, and the depth of a space about one-half the total radius of the
pinion. The addenda of the pinion leaves should be rounded and about
one-half the width of a leaf outside the pitch circle. The addenda of
the wheel teeth should be epicycloidal, and the height of each tooth
above the pitch circle equal to seven-twentieths of the pitch radius of
the pinion.
With a pinion of eight there is still less engaging friction than with
one of seven, as three-quarters of the width of a leaf is past the
line of centers when the driving begins. As there is no disengaging
friction, a pinion of this number makes a very satisfactory depth.
A pinion with nine leaves is sometimes, though seldom, used. It should
have the spaces twice the width of the leaves, and the depth of a space
one-half the total radius. The addenda should be rounded, and its
height above the pitch circle equal to one-half the width of the leaf.
The addenda of the wheel teeth should be epicycloidal, and the height
of each tooth above the pitch circle equal to three-sevenths of the
total radius of the pinion. With this pinion the driving begins very
near the line of centers, only about one-fifth of the width of a leaf
being in front of the line.
A pinion of ten leaves is the lowest number with which we can entirely
eliminate engaging friction, and to do so in this case the proper
proportions must be rigidly adhered to. The spaces on the pinion must
be a little more than twice as wide as a leaf; a leaf and space will
occupy 36° of arc; of this 11° should be taken for the leaf and 25°
for the space. The addenda should be rounded and should extend about
half the width of a leaf outside the pitch circle. The depth of a space
should be equal to about one-half the total radius. For the wheel, the
teeth should be equal in width to the spaces, the addenda epicycloidal
in form, and the height of each tooth above the pitch circle, equal to
two-fifths the pitch radius of the pinion.
A pinion having eleven leaves would give a better depth, theoretically,
than one of ten, as the leaves need not be made quite so thin to ensure
its not coming in action in front of the line of centers. It is seldom
seen in watch or clock work, but if needed the same proportions should
be used as with one of ten, except that the leaves may be made a little
thicker in proportion to the spaces.
A pinion having twelve leaves is the lowest number with which we can
secure a theoretically perfect action, without sacrificing the strength
of the leaves or the requisite freedom in the depths. In this pinion,
the leaf should be to the space as two to three, that is, we divide the
arc of the circumference needed for a leaf and space into five equal
parts, and take two of these parts for the leaf, and three for the
space; depth of the space should be about one-half the total radius.
The addenda of the wheel teeth should be epicycloidal, and the height
of each tooth above the pitch line equal to two-sevenths the pitch
radius of the pinion.
As the number of leaves is increased up to twenty, the width of the
space should be decreased, until when this number is reached the space
should be one-seventh wider than the leaf. As these numbers are used
chiefly for winding wheels in watches, where considerable strength is
required, the bottoms of the spaces of both mobiles should be rounded.
CIRCULAR PITCH. DIAMETRAL PITCH.—In large machinery it is usual to take
the circumference and divide by the number of teeth; this is called
the _circular pitch_, or distance from point to point of the teeth, and
is useful for describing teeth to be cut out as patterns for casting.
But for all small wheels it is more convenient to take the diameter
and divide by the number of teeth. This is called the _diametral
pitch_, and when the diameter of a wheel or pinion which is intended
to work into it is desired, such diameter bears the same ratio or
proportion as the number required. Both diameters are for their pitch
circles. As the teeth of each wheel project from the pitch circle and
enter into the other, an addition of corresponding amount is made to
each wheel; this is called the _addendum_. As the size of a tooth of
the wheel and of a tooth of the pinion are the same, the amount of
the addendum is equal for both; consequently the outside diameter of
the smaller wheel or pinion will be greater than the arithmetical
proportion between the pitch circles. As the diameters are measured
presumably in inches or parts of an inch, the number of a wheel of
given size is divided by the diameter, which gives the number of teeth
to each inch of diameter, and is called the _diametral pitch_. In all
newly-designed machinery a whole number is used and the sizes of the
wheels calculated accordingly, but when, as in repairing, a wheel of
any size has any number of teeth, the diametral number may have an
additional fraction, which does not affect the principle but gives a
little more trouble in calculation. Take for example a clock main wheel
and center pinion: Assuming the wheel to be exactly three inches in
diameter at the pitch line, and to have ninety-six teeth, the result
will be 96 ÷ 3 = 32, or 32 teeth to each inch of diameter, and would
be called _32 pitch_. A pinion of 8 to gear with this wheel would
have a diameter at the pitch line of 8 of these thirty-seconds of an
inch or ⁸/₃₂ of an inch. But possibly the wheel might not be of such
an easily manageable size. It might, say, be 3.25 inches, in which
case, 96 being the number of the wheel and 8 of the pinion, the ratio
is ⁸/₉₆ or ¹/₁₂, so ¹/₁₂ of 3.25 = 0.270, the pitch diameter of the
pinion. These two examples are given to indicate alternative methods,
the most convenient of which may be used. After arriving at the true
pitch diameters the matter of the addendum arises, and it is for this
that the diametral number is specially useful, as in every case when
figuring by this system, whatever the number of a wheel or pinion,
two of the pitch numbers are to be added. Thus with the 32 pitch, the
outside diameter of the wheel will be 3 in. + ²/₃₂, and if the pinion
⁸/₃₂ + ²/₃₂ = ¹⁰/₃₂. With the other method the same exactness is more
difficult of attainment, but for practical purposes it will be near
enough if we use ²/₃₀ of an inch for the addendum, when the result
will be 3.25 + ²/₃₀ or 3¼ + ²/₃₀ = 3⅓; in. nearly and the pinion
0.270 + ²/₃₀ = 0.270 + .0666 = 0.3366; or to work by ⅓ of an inch is
near enough, giving the outside diameter of the pinion a small amount
less than the theoretical, which is always advisable for pinions which
are to be driven.
We represent by Figs. 67 to 71 a wheel of sixty teeth gearing with a
pinion of six leaves. The wheel, whose pitch diameter is represented
by the line mm is the same in each figure. The pinion, which has for
its pitch diameter the line kk, is in Fig. 67, of a size proportioned
to that of the wheel, and its center is placed at the proper distance;
that is to say, the two pitch diameters are tangential.
In Fig. 68 the same pinion, of the proper size, has its center too far
off; the depthing is too shallow. In Fig. 69 it is too deep. Figs. 70
and 71 represent gearing in which the pitch circles are in contact, as
the theory requires, but the size of the pinions is incorrect. If the
wheels and pinion actuated each other by simple contact the velocity of
the pinion with reference to that of the wheel would not be absolutely
the same; but the ratio of the teeth being the same, the same ratio of
motion obtains in practice, and there is necessarily bad working of the
teeth with the leaves.
We will observe what passes in each of these cases, and refer to the
suitable remedies for obtaining a passable depthing and a comparatively
good rate, without the necessity of repairs at a cost out of all
proportion with the value of the article repaired.
[Illustration: Fig. 67.]
Fig. 67 represents gearing of which the wheel and pinion are well
proportioned and at the proper distance from each other. Its movement
is smooth, but it has little drop or none at all. By examining the
teeth h, h′, of the wheel, it is seen that they are larger than the
interval between them. With a cutter FF, introduced between the teeth,
they are reduced at d, d′, which gives the necessary drop without
changing the functions, since the pitch circles mm and kk have not been
modified. The drop, the play between the tooth d′ and the leaf a, is
sufficiently increased for the working of the gearing with safety.
We have the same pair in Fig. 68, but here their pitch circles do not
touch; the depthing is too shallow. The drop is too great and butting
is produced between the tooth h and the leaf r, which can be readily
felt. The remedy is in changing the center distance, by closing the
holes, if worn, or moving one nearer the other. But in an ordinary
clock this wheel may be replaced with a larger one, whose pitch circle
reaches to e. The proportions of the pair are modified, but not
sufficiently to produce inconvenience.
[Illustration: Fig. 68.]
It may also answer to stretch the wheel, if it is thick enough to be
sufficiently increased in size. A cutter should then be selected for
rounding-up which will allow the full width to the tooth as at p;
but if it is not possible to enlarge the wheel enough, a little of
the width of the teeth may be taken off, as is seen at h, which will
diminish the butting with the leaf r.
Too great depthing, Fig. 69, can generally be recognized by the lack
of drop. When the teeth of the wheel are narrow, the drop may appear
to be sufficient. When the train is put in action the depthing that is
too great produces scratching or butting and the ’scape wheel trembles.
This results from the fact that the points of the teeth of the wheel
touch the core of the pinion and cause it to butt against the leaf
following the one engaged, as is visible at r in Fig. 69. It should be
noticed that in this figure the pitch circles mm and kk overlap each
other, instead of being tangential.
[Illustration: Fig. 69.]
[Illustration: Fig. 70.]
To correct this gearing, the cutter should act only on the addenda of
the teeth of the wheel, so as to diminish them and bring the pitch
circle mm to n. The dots in the teeth d, d′, show the corrected
gearing. It is seen that there will be, after this change, the
necessary drop, and that the end of the tooth d′ will not touch the
leaf r.
In the two preceding cases we have considered wheels and pinions of
accurate proportion, and the defects of the gearing proceeding from
the wrong center distances. We will not speak of the gearing in which
the pinion is too small. The only theoretic remedy in this case, as in
that of too large a pinion, is to replace the defective piece; but in
practice, when time and money are to be saved, advantage must be taken,
one way or another, of what is in existence.
The buzzing produced when the train runs in a gearing with too small a
pinion proceeds from the fact that each tooth has a slight drop before
engaging with the corresponding leaf. If we examine Fig. 70, it will
be easy to see how this drop is produced. The wheel revolving in the
direction indicated by the arrow, it can be seen that when the tooth
h leaves the leaf r, the following tooth, p, does not engage with
the corresponding leaf, s; this tooth will therefore have some drop
before reaching the leaf. A friction may even be produced at the end or
addendum of the tooth p against the following leaf v.
To obtain a fair depthing without replacing the pinion, the wheels can
be passed to the rounding-up machine, having a cutter which will take
off only the points of the teeth, as is indicated in the figure; the
result may be observed by the dotted lines. The tooth h being shorter,
it will leave the leaf r of the pinion when the latter is in the dotted
position; that is to say, a little sooner. At this moment the tooth p
is in contact with the leaf s, and there is no risk of friction against
the leaf v. Care must be taken to touch only the addendum of the
tooth so as not to weaken the teeth. The circumference i will be that
of a pinion of accurate size, and if the pinion is replaced, it will
be necessary to diminish the wheel so that its pitch circle shall be
tangential with i.
[Illustration: Fig. 71.]
With too small a pinion a passable gearing can generally be produced.
In any case stoppage can be prevented. This is not so easy when the
pinion is too large. In Fig. 71, the pinion has as its pitch circle the
line k, instead of i, which would be nearer the size with reference to
that of the wheel. This is purposely drawn a little small for clearness
of illustration. The essential defect of such a gearing can be seen;
the butting produced between the tooth p and the leaf s will cause
stoppage. How shall this defect be corrected without replacing the
pinion?
To remedy the butting as far as possible, some watchmakers slope
the teeth of the wheel by decentering the cutter on the rounding-up
machine. At FF the cutter is seen working between the teeth d and d′.
It is evident that when the wheel becomes smaller it is necessary to
stretch it out, and to make use of the cutter afterwards. However,
the most rational method is to leave the teeth straight, and to give
them the slenderest form possible, after having enlarged the wheel or
having replaced it with another. The motive force of the wheel being
sufficiently weak, the size of the teeth may be reduced without fear.
The essential thing is to suppress the butting. Success will be the
easiest when the teeth are thinner.
In conclusion, we recommend verification of all suspected gearings by
the depthing tool, which is easier and surer than by the clock itself.
One can see better by the tool the working of the teeth with the
leaves, and can form a better idea of the defect to be corrected. With
the aid of the illustrations that have been given it can be readily
noticed whether the depthing is too deep or too shallow, or the pinion
too large or too small.
The defects mentioned are of less consequence in a pinion of seven
leaves, and they are corrected more readily. With pinions of higher
numbers the depthings will be smoother, provided sufficient care has
been taken in the choice of the rounding-up cutters.
ROUNDING-UP WHEELS.—It is frequently observed that young watchmakers,
and (regretfully be it said) some of the older and more experienced
ones, are rather careless when fitting wheels on pinions. In many cases
the wheel is simply held in the fingers and the hole opened with a
broach, and in doing this no special care is taken to keep the hole
truly central and of correct size to fit the pinion snugly, and should
it be opened a little too large it is riveted on the pinion whether
concentric or not. Many suppose the rounding-up tool will then make it
correct without further trouble and without sufficient thought of the
irregularities ensuing when using the tool.
To make the subject perfectly clear the subjoined but rather
exaggerated sketch is shown, Fig. 72. Of course, it is seldom required
to round-up a wheel of twelve teeth, and the eccentricity of the wheel
would be hardly as great as shown; nevertheless, assuming such a case
to occur the drawing will exactly indicate the imperfections arising
from the use of a rounding-up tool.
[Illustration: Fig. 72.]
Presuming from the drawing that the wheel, as shown by dotted lines,
had originally been cut with its center at m, but through careless
fitting had been placed on the pinion at o, and consequently is
very much out of round when tested in the calipers, and to correct
this defect it is put in the rounding-up tool. The cutter commences
to remove the metal from tooth 7, it being the highest, next the
neighboring teeth 6 and 8, then 5 and 9, and so on until tooth 1 comes
in contact with the cutter. The wheel is now round. But how about the
size of the teeth and the pitch? The result of the action of the cutter
is shown by the sectionally lined wheel. Many will ask how such, a
result is possible, as the cutter has acted equally upon all the teeth.
Nevertheless, a little study of the action of the rounding-up cutter
will soon make it plain why such faults arise. Naturally the spaces
between the teeth through the action of the cutter will be equal, but
as the cutter is compelled to remove considerable metal from the point
of greatest eccentricity, i. e., at tooth 7 and the adjoining teeth,
to make the wheel round, and the pitch circle being smaller the teeth
become thinner, as the space between the teeth remains the same. At
tooth 1 no metal was removed, consequently it remains in its original
condition. The pitch from each side of tooth 1 becomes less and less to
tooth 7, and the teeth thinner, and the thickest tooth is always found
opposite the thinnest.
In the case of a wheel having a large number of teeth and the
eccentricity of which is small, such faults as described cannot be
readily seen, from the fact that there are many teeth and the slight
change in each is so gradual that the only way to detect the difference
is by comparing opposite teeth. And this eccentricity becomes a serious
matter when there are but few teeth, as before explained, especially
when reducing an escape wheel. The only proper course to pursue is
to cement the wheel on a chuck, by putting it in a step chuck or in
any suitable manner so that it can be trued by its periphery and then
opening the hole truly. This method is followed by all expert workmen.
A closer examination of the drawing teaches us that an eccentric wheel
with pointed teeth—as cycloidal teeth are mostly left in this condition
when placed in the rounding-up tool, will not be made round, because
when the cutter has just pointed the correct tooth (tooth No. 1 in the
drawing) it will necessarily shorten the thinner teeth. Nos. 6, 7, 8,
i. e., the pitch circle will be smaller in diameter. We can, therefore,
understand why the rounding-up tool does not make the wheel round.
As we have before observed, when rounding-up an eccentrically riveted
wheel, the thickest tooth is always opposite the thinnest, but with
a wheel which has been stretched the case is somewhat different.
Most wheels when stretched become angular, as the arcs between the
arms move outward in a greater or less degree, which can be improved
to some extent by carefully hammering the wheel near the arms, but
some inequalities will still remain. In stretching a wheel with five
arms we therefore have five high and as many depressed parts on its
periphery. If this wheel is now rounded-up the five high parts will
contain thinner teeth than the depressed portions. Notwithstanding that
the stretching of wheels, though objectionable, is often unavoidable
on account of the low price of repairs, it certainly ought not to be
overdone. Before placing the wheel in the rounding-up tool it should be
tested in the calipers and the low places carefully stretched so that
the wheel is as nearly round as can be made before the cutter acts upon
it.
It is hardly necessary to mention that the rounding-up tool will not
equalize the teeth of a badly cut wheel, and further should there be a
burr on some of the teeth which has not been removed, the action of the
guide and cutter in entering a space will not move the wheel the same
distance at each tooth, thus producing thick and thin teeth. From what
has been said it would be wrong to conclude that the rounding-up tool
is a useless one; on the contrary, it is a practical and indispensable
tool, but to render good service it must be correctly used.
In the use of the rounding-up tool the following rules are to be
observed:
1. In a new wheel enlarge the hole after truing the
wheel from the outside and stake it concentrically on
its pinion.
2. In a rivetted but untrue wheel, stretch the
deeper portions until it runs true, then reduce it
in the rounding-up tool. The better method is to
remove the wheel from its pinion, bush the hole,
open concentrically with the outside and rivet, as
previously mentioned in a preceding paragraph. But
if the old riveting cannot be turned so that it can
be used again it is best to turn it entirely away,
making the pinion shaft conical towards the pivot,
and after having bushed the wheel, drill a hole the
proper size and drive it on the pinion. The wheel
will be then just as secure as when rivetted, as in
doing the latter the wheel is often distorted. With a
very thin wheel allow the bush to project somewhat,
so that it has a secure hold on the pinion shaft and
cannot work loose.
3. Should there be a feather edge on the teeth,
this should be removed with a scratch brush before
rounding it up, but if for some reason this cannot
well be done, then place the wheel upon the rest
with the feather edge nearest the latter so that the
cutter does not come immediately in contact with
it. If the feather edge is only on one side of the
tooth—which is often the case—place the wheel in
the tool so that the guide will turn it from the
opposite side of the tooth; the guide will now move
the wheel the correct distance for the cutter to act
uniformly. Of course, in every case the guide, cutter
and wheel, must be in correct position to ensure good
work.
4. To obtain a smooth surface on the face of the
teeth a high cutter speed is required, and for this
reason it is advantageous to drive the cutter spindle
by a foot wheel.
MAKING SINGLE PINIONS.—There are two ways of making clock pinions; one
is to take a solid piece of steel of the length and diameter needed
and turn away the surplus material to leave the arbor and the pinion
head of suitable dimensions; the other way is to make the head and
the arbor of separate pieces; the head drilled and fixed on the arbor
by friction. The latter plan saves a lot of work, and the cutting of
the teeth may be easier. One method is as good as the other, as the
force on the train is very slight and the pinion head may be driven
so tightly on the arbor as to be perfectly safe without any other
fastening, provided the arbor is given a very small taper, .001 inch in
four inches. The steel for the arbor may be chosen of such a size as
to require very little turning, and hardened and tempered to a full or
pale blue before commencing turning it, but the piece intended for the
pinion head must be thoroughly annealed, or it may be found impossible
to cut the teeth without destroying a cutter, which, being valuable, is
worth taking care of.
Pinions for ordinary work are not hardened; as they are left soft by
the manufacturers it would be nonsense for the repairer to put in one
hardened pinion in a clock where all the others were soft. Pinions on
fine work are hardened. Turning is done between centers to insure truth.
Before commencing work on the pinion blanks it is advisable to try
the cutters on brass rod, turned to the exact size, and if the rod
is soft enough it will be found that the cutter will make the spaces
before it is hardened, which is a very important advantage, admitting
of correction in the form of the cutter if required; only two or
three teeth need be cut in the brass to enable one to see if they are
suitable, and if found so, or after an alteration of the cutter, the
entire number may be cut round and the brass pinion made use of for
testing its accuracy as to size and shape by laying the wheel along
with it on a flat plate, having studs placed at the proper center
distance. By this means the utmost refinement may be made in the
diameter of the brass pinion, which will then serve as a gauge for the
diameter of the steel pinions, it being recollected, as mentioned in a
previous paragraph, that a slight variation in the diameter of a pinion
may be made to counterbalance a slight deviation from mathematical
accuracy in the form of the wheel teeth, such as is liable to occur
owing to the smallness of the teeth making it impracticable to actually
draw the true curves, the only way of getting them being to draw them
to an enlarged scale on paper, and copy them on the cutter as truly as
possible by the eye.
Supposing the cutter has been properly shaped, hardened and completed
and the steel pinion heads all turned to the diameter of the brass
gauge, the cutting may be proceeded with without fear of spoiling, or
further loss of time which might be spent in cutting the long pinion
leaves; and even what is of more importance in work which does not
allow of any imperfection, removing the temptation, which might be
strong, to let a pinion go, knowing it to be less perfect than it
should be.
Assuming the pinion teeth to be satisfactorily cut, the next operation
will be hardening and tempering. A good way of doing this is to enclose
one at a time in a piece of gas pipe, filling up the space around the
pinion with something to keep the air off the work and prevent any of
the products of combustion attacking the steel and so injuring the
surface. Common soap alone answers the purpose very well, or it may
have powdered charcoal mixed with it; also the addition of common salt
helps to keep the steel clean and white. The heating should be slow,
giving time for the pinion and the outside of the tube to both acquire
the same heat. Over-heating should be carefully avoided, or there will
be scaling of the surfaces, injurious to the steel, and requiring time
and labor to polish off. There is no better way of hardening than by
dipping the pipe with the pinion enclosed in plain cold water, or
if the pinion should drop out of the tube into the water it will do
all the same. To be sure the hardening is satisfactory it will be as
well not to trust to the clean white color likely to result from this
treatment, but try both ends and the center with a file. After all this
has been successfully accomplished the pinions will require tempering,
the long arbors straightening, and the teeth polishing.
The drilled pinion heads, if hardened at all by the method last
mentioned, will, on account of their short lengths, be equally hardened
all over, but if the pinion and arbor should be all in one piece care
will be needed to ensure equal heating all over, or one part may
be burnt and another soft. Also, to guard against bending the long
arbors, the packing in the tube will need to be carefully done, so as
to produce equal pressure all over; otherwise, while the steel is red
hot, and consequently soft enough to bend, even by its own weight, it
may get distorted before dropping in the water. A long thin rod like
this almost invariably bends if heated on an open fire unless equally
supported all along; if hardened so, a little tin tray may be bent up,
filled with powdered charcoal, and the pinion bedded evenly in it.
Either this way or with a tube the long arbor may get bent before being
quenched; but if the arbor, though kept straight up to this point,
should happen to be dropped sideways into the water the side cooled
first would contract most. To avoid this, the arbor should be dropped
endways, as vertically as possible.
TEMPERING THE PINIONS.—For common cheap work the usual and quickest
way is what is called “blazing off.” That is done either by dipping
each piece singly in thick oil and setting the oil on fire, allowing
it to burn away, or placing a number of pieces in a suitably sized
pan, covering with oil, and burning it. The result is the same either
way, the method being simply a matter of convenience regulated by the
number of pieces to be tempered at one time. As the result of blazing
off is to some extent uncertain, and the pinions apt to be too soft,
it will be advisable to adopt the process of bluing, by which the
temper desired may be produced with more accuracy. The first thing
to do will be to clean the surface of the arbor all along on one
side; the pinion head may be left alone. As the pinion head would get
overheated before the arbor had reached the blue color, if the piece
were simply placed on a bluing pan or a lump of hot iron, it will be
necessary to provide a layer of some soft substance to bed the pinion
on; iron, steel or brass filings answer well because the heat is soon
uniformly distributed through the mass, and by judiciously moving the
lamp an equable temper may be got all along, as determined by the
color. There is another and very sure way of getting a uniform temper,
in using which there is no need to polish the arbors. The heat of lead
_at the point of fusion_ happens to be just about the same as that
required for the tempering of this work; so if a ladle full of lead is
available each pinion may be buried in it for a few seconds, holding it
down beneath the molten surface with hot pliers. The temper suitable is
indicated by a pale blue, a little softer than for springs, and a piece
of polished steel set floating on the lead will indicate whether the
heat is suitable; if found too great some tin may be added, which will
cause the metal to melt at a lower temperature. Over-heating the metal
must be avoided: it should go no higher than the bare melting point.
STRAIGHTENING BENT ARBORS.—When all care has been taken in the
hardening, the long pieces of wire are still apt to become bent more
or less, and this is especially the case with solid pinions; so before
proceeding further the pieces must be got true, or as nearly so as
possible, and it will be found impracticable to do this by simple
bending when the steel is tempered. If the piece is placed between
centers in the lathe and rotated slowly, the hollow side will be found;
this side must be kept uppermost while the steel is held on a smooth
anvil, and the pene, or chisel-shaped, end of a small hammer applied
crossways with gentle blows, stepping evenly along so that each portion
of the steel is struck all along the part which is hollow; this will
stretch the hollow side, and, by careful working, trying the truth
from time to time, the piece can be got as true as may be wished, and
probably keep so during the subsequent turning and finishing, though
it is advisable to keep watch on it, and if it shows any tendency to
spring out of truth again, repeat the striking process, which should
always be done gently and in such a way as to show no hammer marks.
Having got the pieces sufficiently true in this way, each arbor may
have a collet of suitable size driven on to it for permanency, and as
the collets will probably be a little out of truth they may have a
finishing cut taken all over them and receive a final polish.
POLISHING.—To polish the steel arbors after turning, a flat metal
polisher, iron or steel, is used; this with emery or oilstone dust and
oil produces a true surface, with a sharp corner at the shoulder; the
polisher will require frequent filing on the flat and the edge to keep
it in shape with a sharp corner, and a grain crossing like the cuts
on a file to hold the grinding material. The polishing of arbors is
not done with the object of making them shine, but to get them smooth
and true, so there is no need of using any finer stuff than emery or
oilstone dust.
An old way to polish the leaves was to use a simple metal polisher of
a suitable thickness, placing the pinion on a cork or piece of wood,
or even holding it in the fingers; working away at a tooth at a time
until a good enough polish was obtained; but this method, while being
satisfactory as to results, was also tedious and very slow. It was in
some cases assisted by having guide pinions fitted tight on one or
both ends of the arbors to prevent rounding of the teeth, the polisher
resting in the guide and the tooth to be polished. On the American
lathes an accessory is provided called a “wig wag.” This is a rod
fastened at one end to a pulley by a crank pin near its circumference;
the pulley being rotated by a belt from the counter shaft pulleys
causes the rod to move rapidly backwards and forwards. On the other
end of the rod a long narrow piece of lead or tin is fixed, the pinion
being fitted by its centres into a simple frame held in the slide rest
so that it can be rotated tooth by tooth; the lead soon gets cut to the
form of the teeth, and the polishing is quickly effected. Another way
is to take soft pine or basswood, shape it roughly to about the form
of space between two teeth and use it as a file, with emery and oil or
oilstone dust. The wood is soon cut to the exact shape of the teeth,
and then makes a quick and perfect job. The pinion is held in the jaws
of the vise and the wooden polisher used as a file with both hands.
Where there is much polishing to do a simple tool, which a workman can
form for himself, produces a result which is all that can be desired.
It consists of an arbor to work between the lathe centres, or a screw
chuck for wood, with a round block of soft wood, of a good diameter,
fixed on it, and turned true and square across; this will get a spiral
groove cut in it by the corners of the pinion leaves. The pinion is
set between centres in a holder in the slide rest, with the holder set
at a slight angle, so that, instead of circular grooves being cut in
the wood a screw will be formed, the angle being found by trial. On
the wood block being rotated and supplied with fine emery the pinion
will be found to rotate, and, being drawn backwards and forwards by the
slide rest, can be polished straight, while the circular action of the
polisher will cause the sides of the pinion leaves to be made quite
smooth and entirely free from ridges.
If it should be desired to face the pinions, like watch pinions, it
may be done in the same way, by cutting hollows so as to leave only a
fine ring round the bottoms of the teeth, and using a hollow polisher
with a flat end held in the fingers while the pinion is rotating. A
common cartridge shell with a hole larger than the arbor drilled in the
center of the head makes a fine polisher for square facing on the ends
of pinions, while a stick of soft wood will readily adapt itself to
moulded ends.
The pinion heads being finished and got quite true, the arbors may
be turned true and polished. It is not advisable to turn the arbors
small; they will be better left thick so as to be stiff and solid, as
the weight so near the center is of no importance, the velocity on the
small circumference in starting and stopping being also inappreciable.
The thickness of the arbors when the pinion heads are drilled is
determined by the necessity of having sufficient body inside the
bottoms of the teeth; but when solid they may with advantage be left
thicker; however, there is no absolute size. The ends on which the
collets for holding the wheels are to be fixed may be turned to the
same taper as the broach which will be used for opening the collet
holes, while the other ends may be straight.
None of the wheels in a fine clock should be riveted to the pinion
heads; even the center wheel, which goes quite up to the pinion head,
is generally fixed on a collet. The collets are made from brass cut
off a round rod, the outside diameters being just inside the edges
of the wheel hubs, and a shoulder turned to fit accurately into the
center hole of each wheel. These collets should first have their holes
broached to fit their arbors, allowing a little for driving on, as they
may be made tight enough in this way without soldering. Be careful to
keep the broach oiled to prevent sticking if you want a smooth round
hole.
The holes in the wheels being made, each collet may be turned to a
little over its final size all over, and then driven on to its place
on the pinion, so that a final turning may be made to ensure exact
truth from the arbors’ own centers. When the collets are thus finished
in their places on the arbors, and the wheels fitted to them, if it
is a fine clock, such as a regulator, a hole may be drilled through
each wheel and its collet to take a screw, the holes in the collet
tapped, the holes in the wheels enlarged to allow the screw to pass
freely through, and a countersink made to each, so that the screws,
when finished, may be flush with the wheels. One hole having been thus
made and the wheel fixed with a screw, the other two holes can be made
so as to be true, which would not be so well accomplished if all the
holes were attempted at once. The spacing of the three screws will be
accurate enough if the wheel arms be taken as a guide. If all this has
been correctly done, the wheels will go to their places quite true,
both in the round and the flat, and may be taken off for polishing, and
replaced true with certainty, any number of times.
The polishing of the pivots should be as fine as possible; all should
be well burnished, to harden them and make them as smooth as possible
if it is a common job; if a fine one with hardened arbors the pivots
may be ground and polished as in watch work; if the workman has a pivot
polisher and some thin square edged laps this is a short job and should
be done before cutting off the centers and rounding the ends of the
pivots. During all this work the wheels, as a matter of course, will be
removed from the pinions, and may now be again temporarily screwed on,
the polishing of them being deferred till the last, as otherwise they
would be liable to be scratched.
LANTERN PINIONS.—The lantern pinion is little understood outside of
clock factories and hence it is generally underrated, especially by
watchmakers and those working generally in the finer branches of
mechanics. It will never be displaced in clock work, however, on
account of the following specific advantages:
1. It offers the greatest possible freedom from
stoppage owing to dirt getting into the pinions, as
if a piece large enough to jam and stop a clock with
cut pinions, gets into the lantern pinion, it will
either fall through at once or be pushed through
between the rounds of the pinion by the tooth of
the wheel and hence will not interfere with its
operation. It is therefore excellently adapted to run
under adverse circumstances, such as the majority of
common clocks are subjected to.
2. Without giving the reasons it is demonstrable
that as smooth a motion may be got by a lantern
pinion as by a solid radial pinion of twice the
number, and that the force required to overcome the
friction of the lantern is therefore much less than
with the other. It follows that such pinions can be
used with advantage in the construction of all cheap
and roughly constructed clocks which are daily turned
out in thousands to sell at a low price.
3. We have before pointed out the enormous
advantages of small savings per movement in clock
factories which are turning out an annual product of
millions of clocks, and without going into details,
it is sufficient to refer to the fact that where
eight or ten millions of clocks are to be made
annually the difference in the cost of keeping up the
drills and other tools for lantern pinions over the
cost of similar work on the cutters for solid pinions
is sufficient to have a marked influence upon the
cost of the goods. Then the rapidity with which they
can be made and the consequent smallness of the plant
as compared with that which must be provided for
turning out an equal number of cut pinions is also a
factor. There are other features, but the above will
be sufficient to show that it is unlikely that the
lantern pinion will ever be displaced in the majority
of common clocks. From seventy-five to ninety per
cent of the clocks now made have lantern pinions.
The main difference between lantern and cut pinions mechanically is
that as there is no radial flank for the curve of the wheel tooth to
press against in the lantern pinion the driving is all done on or after
the line of centers, except in the smaller numbers, and hence the
engaging or butting friction is entirely eliminated when the pinion
is driven, as is always the case in clock work. Where the pinion is
the driver, however, this condition is reversed and the driving is all
before the line of centers, so that it makes a very bad driver and
this is the reason why it is never used as a driving pinion. This, of
course, bars it from use in a large class of machinery.
The actual making of lantern pinions will be found to offer no
difficulties to those who possess a lathe with dividing arrangements,
a slide rest, and a drill holder or pivot polisher to be fixed on it.
The pitch circle, being through the centers of the pins, can be got
with great accuracy by setting the drill point first to the center of
the lathe, reading the division on the graduated head of the slide
rest screw, and moving the drill point outwards to the exact amount
of the semi-diameter of the pitch circle. This presupposes the slide
rest screw being cut to a definite standard, as the inch or the meter,
and all measurements of wheels and pinions being worked out to the same
standard, the choice of the standard being immaterial. If the slide
rest screw is not standardized the pitch circle may be traced with a
graver and the drill set to center on the line so traced.
The heads of the pinions may be made either of two separate discs, each
drilled separately, and carefully fitted on the arbor so that the pins
may be exactly parallel with the arbor; or, of one solid piece bored
through the center, turned down deep enough in the middle, and the
drill sent right through the pin holes for both sides at one operation.
The former way will be necessary when the number of pins is small,
but the latter is better when the numbers are large enough to allow
of considerable body in the center. In either case it is advisable to
drill only part way through one shroud and to close the holes in the
other with a thin brass washer pressed on the arbor and turned up to
look like part of the shroud after the pins are fitted in the holes.
This makes a much neater way of closing the holes than riveting and
takes but a moment where only one or two pinions are being made.
There is no essential proportion for the thickness of the pins or
rounds. In mathematical investigations these are always taken at
first as mere points of no thickness at all; then the diameters are
increased to workable proportions, and the width of the wheel tooth
correspondingly reduced until there is a freedom or a little shake. If
much power has to be transmitted, the pins, or “staves,” as they are
called in large work, have to be strong enough to stand the strain,
but, as the strain in clockwork is very small, the pins need not be
nearly as thick as the breadth of a wheel tooth. In modern factory
practice the custom is to have the diameter of the rounds equal to the
thickness of the leaf of a cut pinion of similar size, the measurement
being taken at the pitch circle of the cut pinion. As we have already
given the proportions observed in good practice on cut pinions they
need not be repeated here. Another practice is to have wheel teeth and
spaces equal; when this is done the spacing of all pinions above six
leaf is to have the rounds occupy three parts and the space five parts.
In some old church clocks, lantern pinions were much used, in many
cases with the pins pivoted and working freely in the ends, or, as they
called them, “shrouds,” but this was a mistake, and they are never
made so now. A simple way for clock repair work is to get some of the
tempered steel drill rod of exactly the thickness desired, hold one end
by a split chuck in the lathe, let the other end run free, and polish
with a bit of fine emery paper clipped round it with the fingers,
when the wire will be ready for driving through the pinion heads, the
holes being made small enough to provide for the rounds being firmly
held. The drill may be made of the same wire. The shrouds may be made
either of brass or steel; the latter need not be hardened, and, when
the rounds are all in place and cut off, the ends may be polished as
desired. In the case of a center wheel, where the pinion is close up to
the wheel, and space cannot be spared, the collet on which the wheel is
mounted may form one end of the pinion head.
[Illustration: Fig. 73. Lantern pinion showing pitch circle.]
[Illustration: Fig. 74. Generating epicycloid curve for lantern pinion
above; compare with curve for cut pinion of same size pitch circle,
page 206.]
THE WHEEL TEETH.—The same principles of calculation belong to these
and solid-cut pinions, the only difference being that the round pins
require wheel teeth of a different shape from those suited to pinion
leaves with radial sides. Both are derived from epicycloidal curves;
the curve used for lantern pinions is derived from a circle of the
_same size_ as the pitch circle of the pinion, while the curve for
wheel teeth to drive radial-sided leaves is derived from a circle of
_half_ that diameter, so that the wheel teeth in the former are more
pointed than in the latter. There also is a farther difference; as was
explained in detail when treating of cut pinions, the curve of the
wheel tooth presses upon the radial flank of the leaf inside its pitch
circle. Now there is no radial flank in the lantern and the curve is
generated from a circle of twice the diameter, so that it is twice as
long—long enough to interfere—so it is cut off (rounded) just beyond
the useful portion of the working curve of the wheel tooth.
Pillars and arbors are simple parts, yet much costly machinery is used
in making them. The wire from which they are made is brought to the
factories in large coils, and is straightened and cut into lengths by
machines. The principle on which wire is straightened in a machine is
exactly the same as a slightly curved piece of wire is made straight in
the lathe by holding the side of a turning tool between the revolving
wire and the lathe rest, which is an operation most of our readers must
have practiced. The rapid revolution of the wire against the turning
tool causes its highest side to yield, till finally it presses on the
turning tool equally all round, and is consequently straight. However,
in straightening wire by machines the wire is not made to revolve, but
remains stationary while the straightening apparatus revolves around
it. Wire-straightening machines are usually made in the form of a
hollow cylinder, having arms projecting from the inside towards the
center. The cylinder is open at both ends, and the arms are adjustable
to suit the different thicknesses of wire. The wire is passed through
the ends of the cylinder, and comes in contact with the arms inside. A
rapid rotary motion is then given to the cylinder, which straightens
the wire in the most perfect manner, as it is drawn through, without
leaving any marks on it when the machine is properly adjusted. The long
spiral lines that are sometimes seen on the wire work of clocks is
caused by this want of adjustment; and they are produced in the same
way as broad circular marks would be made in soft iron wire if the side
of the turning tool was held too hard against it when straightening it
in the lathe.
[Illustration: Fig. 75. A Slide Gauge Lathe.]
After the wire has been straightened it is cut off into the required
lengths, and this operation is worthy of notice. If the thick sizes of
wire that are used were to be cut by the aid of a file or a chisel, the
ends would not be square, and some time and material would be lost in
the operation of squaring them; and as economy of material as well as
economy of labor is a feature in American clock manufacture, wire of
all sizes is sheared or broken off into lengths, by being fed through
round holes in the shears, which act the same as when a steady pin is
broken when a cock or bridge gets a sudden blow on the side, or in
the same manner as patent cutting plyers work. The wire is not bent
in the operation, and both ends of it are smooth and flat. The wire
for the pillars is then taken to a machine to have the points made and
the shoulders formed for the frames to rest against. This machine is
constructed like a machinist’s bench lathe, with two headstocks. There
is a live spindle running in both heads. In the ends of these spindles,
that point towards the center of the lathe, cutters are fastened,
and the one is shaped so that it will form the end and shoulder of
the pillar that is to be riveted, while the other is shaped so as to
form the shoulder and point that is to be pinned. Between these two
revolving cutters there is an arrangement, worked by a screw in the
end of a handle, for holding the wire from which the pillar is to be
made, in a firm and suitable position. The cutters are then made to
act simultaneously on the ends of the wire by a lever acting on the
spindles, and the points and shoulders are in this way formed in a very
rapid manner, all of the same length and diameter. These machines are
in some points automatic. The pieces of wire are arranged in quantities
in a long narrow feed box that inclines towards the lathe, and the
mechanism for holding the wire is so arranged that when its hold is
loosened on the newly made pillar, the pillar drops out into a box
beneath, and a fresh piece of wire drops in and occupies its place.
In many of the factories, some clocks are manufactured having screws
in place of pins to keep the frames together, and the pillars of
these clocks are made in a different manner than that we have just
described. The wire that is used is not cut into short lengths, but
a turret lathe with a hollow spindle is used, through which the wire
passes, and is held by a chuck, when a little more than just the length
that is necessary to make the pillar projects through the chuck. The
revolving turret head of the lathe has cutting tools projecting from it
at several points. One tool is adapted to bore the hole for the screw,
and when it is bored the next tool taps the hole to receive the screw,
while another forms the point and shoulder; and after that end of the
pillar is completed another tool attached to the slide of the lathe
forms the other shoulder, prepares that end for riveting, and cuts it
off at the same time. One thousand of these pillars are in this manner
made in a day on each machine. The screws that screw into them are made
on automatic screw machines. The latest improvements in this direction
being to first turn the blanks and then roll the threads on thread
rolling machines.
[Illustration: Fig. 76. Slide Gauge Tools and Rack.]
The pinion arbors, after they have been cut to length, are centered
on one end by a milling machine having a conical cutter made for the
purpose. The collets for the pinion heads, and the one to fasten the
wheel by, are punched out of sheet brass, and a hole is drilled in
their centers a little smaller than the wire; and to drive them on,
in most instances, is all that is necessary to hold them. At one time
it was the practice to drive these collets by hand. One was placed
on the point of the arbor, and the point was then placed over a
piece of steel, with a series of holes in it of such depths that the
collets would be in their proper position on the arbor when the point
was driven to the bottom of the hole, but this method has now been
superseded by automatic machinery, which will be described later. It
is impossible to give an intelligible description of these machines
without drawings. All we can say at present is that they perform their
work in a very rapid and effective manner, and are in use by all the
larger clock factories.
The barrels of weight clocks are mostly made from brass castings,
and slight projections are raised on the surface of their arbors by
swedging, so as to prevent the arbors from getting loose in the barrels
after repeated winding of the clock. This swedging and all the other
operations in making arbors used to be done on separate machines; but
the largest companies now use a powerful and comprehensive machine that
works automatically, and straightens any size of wire necessary to be
used in a clock, cuts it to the length, centers it, and also swedges
the projections on the barrel arbors, or any of the other arbors that
may be necessary. A roll of wire is placed on a reel at one end of
the machine, first passing through a straightening apparatus, and
afterwards to that portion of the machine where the cutting, swedging
and centering are executed, and the finished arbors drop into a box
placed ready to receive them. The saving effected by the use of this
machine is very great, and in some instances amounts to a thousand per
cent over the method of straightening, cutting, swedging and centering
on different machines, at different operations.
Boring the holes in the arbors of the locking work, to receive the
smaller wires, and the pin holes in the points of the pillars, is done
by small twist-drills, run by small vertical drill presses. The work
is held in adjustable frames under the drill, and when more than one
hole has to be bored this frame is moved backward or forward between
horizontal slides to the desired distance, which is regulated by an
adjustable stop, so that every hole in each piece is exactly in the
same position. In arbors where holes have to be bored at right angles
to each other, the arbor is turned round to the desired position by
means of an index. The holes in the locking work arbors are bored just
the size to fit the wire that is to go into them, and these small wires
are easily and rapidly fastened in place by holding them in a clamp
made for the purpose, and riveting them either with a hammer or with a
hammer and punch.
[Illustration: Fig. 77. Automatic Pinion Making Machine of the
Davenport Machine Company.]
THE SLIDE GAUGE LATHE.—The system of turning with the slide gauge
lathe, formerly adopted for lantern pinions in the clock factories,
would seem to the watchmaker of a peculiarly novel nature. The turning
tools are not held in the hand, in the manner generally practiced,
neither are they held in the ordinary slide rest, but are used by a
combination of both methods, which secures the steadiness of the one
plan and the rapidity of the other. Adjustable knees are fastened to
the head and tail stocks of the lathe, Figs. 75 and 76, which answer
the purpose of a rest; both the perpendicular and horizontal parts
of these knees being fastened perfectly parallel with the centers of
the lathe. A straight, round piece of iron, of equal thickness, and
having a few inches in the center of a square shape, mortised for the
reception of cutters, is laid on these knees, and answers the purpose
of a handle to hold the cutting tools. Two handles will thus hold
eight tools, one set for brass and one for steel. On every side of the
square part of this iron bar, or what we will now call the turning tool
handle, a number of cutting tools are fastened by set screws, and the
method of using them is as follows: The operator holds the tool handle
with both hands on to the knees that are fastened to the head and tail
stocks of the lathe, with the turning tool that is desired to be used
pointing towards the center, and it is allowed to come in contact with
the work running in the lathe in the usual manner practiced in turning.
Fig. 76 is from a photo furnished by Mr. H. E. Smith of the Smith
Novelty Co., Hopewell, N. J., and shows the tools in the rack, which
is wound with leather so that the tools may be rapidly thrown in place
without injury.
[Illustration]
[Illustration: Fig. 78. Showing Successive Steps in Turning on
Automatic Pinion Making Machine.
Stock advanced.
First collet driven.
Second collet driven.
Third collet driven.
Shoulder turned.
First sides faced.
Second sides faced.
Pivots turned.
Pivots burnished.
Cut off.]
If a plain, straight piece of work is to be turned, the tool is
adjusted in the handle so that the work will be of the proper
diameter when the round parts of the handle come in contact with the
perpendicular part of the knees or rest; and while the handle is thus
held and moved gently along in the corners of the knees, with the tool
sliding on the T-rest, the work is easily turned perfectly parallel,
smooth and true. Sometimes a roughing cut is taken by holding the bar
loosely and then a finishing cut is made with the same tool by holding
it firmly in place. In turning a pinion arbor, for instance, the wire
having been previously straightened and cut to length and centered, and
the brass collets to make the pinion and to fasten the wheel having
been driven on, one end is held in the lathe by a spring chuck fastened
to the spindle of the lathe, while the other end works in a center in
the other head. One turning tool is shaped and adjusted in the handle
for the purpose of turning the brass collets for the pinion to the
proper diameter, another turns the sides of the brass work, while
others are adapted for the arbors, pivots, and so on, pins being placed
in holes in the T-rest to act as stops for the tools. After the brass
work has been turned, the positions of the shoulders of the pivots are
marked with a steel gauge, and by simply turning round the handle of
the turning tool till the proper shaped point presents itself, each
operation is accomplished rapidly, and the cutting is so smooth that
even for the pivots all that is necessary to finish them is simply to
bring them in contact with a small burnisher. The article is not taken
from the lathe during the whole process of turning, and when completed
the centers are broken off, having been previously marked pretty deep
at the proper place with a cutting point. Five hundred to 1,200 arbors
per day, per man, is the usual output. All the pinions, arbors, and
barrels—in fact every part of an American clock movement that requires
turning—were formerly done in this manner, at long rows of lathes
in rooms, and by workmen set apart for the purpose. But perhaps it
may be well to mention that in the machine shops of these factories,
where they make the tools, the ordinary methods of turning with the
common hand tool, and by the aid of ordinary and special slide rests,
are practiced the same as it is among other machinists. In the large
factories automatic turret machines are now coming into use and these
are shown in Figs. 77, 78 and 79.
[Illustration: Fig. 79. Automatic Pinion Drill of the Davenport Machine
Company.]
The lantern pinions of an American clock have long been a mystery to
those unacquainted with the method of their manufacture, and the usual
accuracy in the position of the small wires or “rounds,” combined
with great cheapness, has often been a subject of remark. The holes
for the wires in these pinions are drilled in a machine constructed
as follows: An iron bed with two heads on it, Fig. 80, one of which
is so constructed that by pulling a lever the spindle has a motion
lengthwise as well as the usual circular motion, and on the point of
this spindle, which is driven at 22,000 revolutions, the drill is
fastened that is to bore the holes in the pinions; the other head has
an arbor passing through it with an index plate attached, having holes
in the plate, and an index finger attached to a strong spring going
into the holes, the same as in a wheel cutting engine; on this head,
and on the end of it that faces the drill, there is a frame fastened
in which the pinion that is to be bored is placed between centers, and
is carried round with the arbor of the index plate, in the same manner
as a piece of work is carried round in an ordinary lathe by means of
a dog, or carrier; only in the pinion drilling machine the carrier is
so constructed that there is no shake in any way between the pinion
and the index arbor. This head is carried on a slide having a motion
at right angles to the spindle of the other head, by which means the
pitch diameter of the proposed pinion is adjusted. The head is moved
in the slide by an accurately cut screw, to which a micrometer is
attached that enables the workman to make an alteration in the diameter
of a pinion as small as the one-thousandth part of an inch. The drill
that bores the holes is the ordinary flat-pointed drill, and has a
shoulder on its stem that stops the progress of the drill when it has
gone through the first part of the pinion head and nearly through the
other. All operators make their own drills and the limits of error are
for pitch diameter .0005 inch; error of size of drills .0001. The reader
can see that these men must know something of drill making.
[Illustration: Fig. 80. Pinion Drilling Machine.]
The action of the machine is simple. The pinion, after it has been
turned, pivoted and dogged, is placed in its position in the machine,
and by pulling a lever, the drill, which is running at a speed of about
22,000 revolutions a minute, comes in contact with the brass heads of
the pinion and bores the one through and the other nearly through. The
lever is then let go, and a spring pulls the drill back; the index is
turned round a hole, and another hole bored in the pinion, and so on
till all the holes are bored. An ordinary expert workman, with a good
machine, will bore about fourteen hundred of medium-sized pinions in
a day. The wires or “rounds” are cut from drill rod and are put into
the holes by hand by girls who become very expert at it. This is called
“filling.” We have already stated that the holes are only bored partly
through one of the pieces of the brass, and after the wire has been
put in, the holes are riveted over, and in this manner the wires are
fastened so that they cannot come out. Some factories close the holes
by a thin brass washer forced on the arbor, instead of riveting.
Figs. 77, 78 and 79 show the automatic pinion turning machine and its
processes in successive operations. These machines are used by most
of the large clock manufacturers of the United States and some of the
European concerns also. They are entirely automatic, will make 1,500
pinions per day, as an average, and one man can run four machines.
Fig. 79 shows an automatic pinion drilling machine, which takes up the
work where it is left by the machine shown in Fig. 77. This machine
will drill 4,000 to 5,000 pinions per day according to the size hole
and the number of holes. The operator places the pinions in the special
chain shown in the front of the machine, from which the transport arms
carry them to the spindle, where they are drilled and when completed
drop out. One operator can feed three of these machines.
MAKING SOLID PINIONS.—The solid steel pinions are not hardened, but
are made of Bessemer steel, which could only be case hardened—a thing
hardly ever done. The process of making these pinions is as follows:
Rods of Bessemer steel are cut into suitable lengths. The pieces
obtained are pointed or centered on both ends. The stock not needed for
the pinion head is cut away, leaving the arbors slightly tapering, for
the purpose of fastening them by this means in a hole on the cutting
machine. On the end of the arbor of the index plate are two deep cuts
across its center, and at right angles to each other. These cuts are
of the same shape that would be made by a knife edged file. The effect
of these cuts is to produce a taper hole in the end of the arbor, with
four sharp corners. Into this hole the end of the arbor of the pinion
or ratchet that is to be cut is placed, and a spring center presses on
the other end, and the sharp corners in the hole hold the work firm
enough to prevent it from turning round when the teeth are being cut.
The marks that are to be seen on the shoulder of the back pivot of the
arbor that carries the minute hand of a Yankee clock is an illustration
of this method of holding the pinion when the leaves are being cut, and
no injurious effects arise from it. The convenience the plan affords
for fastening work in the engine enables twenty-five hundred of these
pinions to be cut in a day, one at a time. The pinion head is cut
subject to the proper dividing plate by a splitting circular saw, and
by a milling tool (running in oil) for forming the shape of the leaves,
both of which tools are generally carried on the same arbor, both being
shifted into their proper places by an adjusting attachment. Pinion
leaves of the better class are generally shaped by two succeeding
milling cutters, the second one of which does the finishing, obviating
any other smoothing. For very cheap work the arbors receive no further
finish. The shaping of the pivots, done by an automatic lathe, finishes
the job.
Figure 81 shows an automatic pinion cutting machine which has extensive
use in clock factories for cutting pinions up to one-half inch diameter
and also the smaller wheels. For wheels the work is handled in stacks
suited to the traverse of the machine, the work being treated as if the
stacks were long brass pinions.
[Illustration: Fig. 81. Automatic Wheel and Pinion Cutters.]
Wheels are cut in two ways, on automatic wheel cutters as just
described and on engines containing parallel spindles for the cutters,
carried in a yoke which rises and falls, so that it clears the work
while the carriage is returning to the starting point on each trip and
engages it on the outward trip. The cutters are about three inches in
diameter and rapidly driven; the first is a saw, the second a roughing
cutter, and the third a finishing cutter. The carriage is driven by a
rack and pinion operated by a crank in the hands of the workman and
streams of soda water are used on the cutters and work to carry away
the heat, as brass expands rapidly under heat, and if the stack were
cut dry the cut would get deeper as the cutting proceeded, owing to the
expansion of the brass, and hence the finished wheel would not be round
when cold, if many teeth were being cut. The stacks of wheels are about
four inches in length and the slide thus travels about twenty inches
in order to clear the three arbors and engage with the shifter for the
index. The last wheel of the stack has a very large burr formed by the
cutters as they leave the brass and this wheel is removed from the
stack when the arbor is taken out and placed aside to have the burrs
removed by rubbing on emery paper.
[Illustration: Fig. 82. Wheel Cutting Engine.]
This is one of the few instances in which automatic machinery has been
unable to displace hand labor, as the work is done so quickly that
the time of the attendant would be nearly all taken up in placing and
removing the stacks, and so the feeding is done by him as well. About
35,000 wheels per day can be thus cut by one man, with girls to stack
the blanks on the arbors, and an automatic feed would not release the
man from attendance on the machine, so that the majority of clock
wheels are cut to-day as they were forty years ago. Still, some of
the factories are adding an automatic feed to the carriage in the
belief that the increased evenness of feed will give a more accurately
cut wheel, a proposition which the men most vigorously deny. Such a
machine, they say, to be truly automatic, must take its stacks of
wheels from a magazine and discharge the work when done, so that one
attendant could look after a number of machines. This would result in
economy, as well as accuracy, but has not been done owing to the great
variations in sizes of wheels and numbers of teeth required in clock
work.
Figure 82 shows one of these machines, a photograph of which was taken
especially for us by the courtesy of the Seth Thomas Clock Company at
their factory in Thomaston, Conn.
About every ten years some factory decides to try stamping out the
teeth of wheels at the same time they are being blanked; this can, of
course, be done by simply using a more expensive punch and die, and
at first it looks very attractive; but it is soon found that the cost
of keeping up such expensive dies makes the wheels cost more than if
regularly cut and for reasons of economy the return is made to the
older and better looking cut wheels.
After an acid dip to remove the scale on the sheet brass, followed by a
dip in lacquer, to prevent further tarnish, the wheels are riveted on
the pinions in a specially constructed jig which keeps them central
during the riveting and when finished the truth of every wheel and its
pinions and pivots are all tested before they are put into the clocks.
The total waste on all processes in making wheels and pinions is from
two to five per cent, so that it will readily be seen that accuracy is
demanded by the inspectors. European writers have often found fault
with nearly everything else about the Yankee clock, but they all unite
in agreeing that the cutting and centering of wheels, pinions and
pivots (and the depthing) are perfect, while the clocks of Germany,
France, Switzerland and England (particularly France) leave much to be
desired in this respect; and much of the reputation of the Yankee clock
in Europe comes from the fact that it will run under conditions which
would stop those of European make.
We give herewith a table of clock trains as usually manufactured, from
which lost wheels and pinions may be easily identified by counting the
teeth of wheels and pinions which remain in the movement and referring
to the table. It will also assist in getting the lengths of missing
pendulums by counting the trains and referring to the corresponding
length of pendulums. Thus, with 84 teeth in the center wheel, 70 in the
third, 30 in the escape and 7-leaf pinions, the clock is 120 beat and
requires a pendulum 9.78 inches from the bottom of suspension to the
center of the bob.
TO CALCULATE CLOCK TRAINS.—Britten gives the following rule: Divide the
number of pendulum vibrations per hour by twice the number of escape
wheel teeth; the quotient will be the number of turns of escape wheel
per hour. Multiply this quotient by the number of escape pinion teeth,
and divide the product by the number of third wheel. This quotient
will be the number of times the teeth of third wheel pinion must be
contained in center wheel.
Clock Trains and Lengths of Pendulums.
===========+=========+========+==============+==========
| | | Vibrations | Length of
| | Escape | of Pendulum | Pendulum
Wheels | Pinions | Wheel | —Min. | in Inches
-----------+---------+--------+--------------+----------
120 90 75| 10 10 9| Double | *30 | 156.56
| |3 legged| |
120 90 90| 10 9 9 | Do. | *40 | 88.07
128 120| 16 | 30 | 60 | 39.14
112 105| 14 | 30 | 60 | 39.14
96 90| 12 | 30 | 60 | 39.14
80 75| 10 | 30 | 60 | 39.14
64 60| 8 | 30 | 60 | 39.14
68 64| 8 | 30 | 68 | 30.49
70 64| 8 | 30 | 70 | 28.75
72 64| 8 | 30 | 72 | 27.17
75 60| 8 | 32 | 75 | 25.05
72 65| 8 | 32 | 78 | 23.15
75 64| 8 | 32 | 80 | 22.01
84 64| 8 | 30 | 84 | 19.97
86 64| 8 | 30 | 86 | 19.06
88 64| 8 | 30 | 88 | 18.19
84 78| 7 | 20 | 89.1 | 17.72
80 72| 8 | 30 | 90 | 17.39
84 78| 7 | 21 | 93.6 | 16.08
94 64| 8 | 30 | 94 | 15.94
84 78| 8 | 28 | 95.5 | 15.45
108 100| 12 & 10 | 32 | 96 | 15.28
84 84| 9 & 8 | 30 | 98 | 14.66
84 78| 7 | 22 | 98 | 14.66
84 78| 8 | 29 | 98.9 | 14.41
80 80| 8 | 30 | 100 | 14.09
85 72| 8 | 32 | 102 | 13.54
84 78| 8 | 30 | 102.4 | 13.44
84 78| 7 | 23 | 102.5 | 13.4
105 100| 10 | 30 | 105 | 12.78
84 78| 8 | 31 | 105.8 | 12.59
84 78| 7 | 24 | 107 | 12.3
96 72| 8 | 30 | 108 | 12.08
84 78| 8 | 32 | 109.2 | 11.82
88 80| 8 | 30 | 110 | 11.64
84 77| 7 | 25 | 110 | 11.64
84 78| 7 | 25 | 111.4 | 11.35
84 80| 8 | 32 | 112 | 11.22
84 78| 8 | 33 | 112.6 | 11.11
96 76| 8 | 30 | 114 | 10.82
115 100| 10 | 30 | 115 | 10.65
84 78| 7 | 26 | 115.9 | 10.49
96 80| 8 | 30 | 120 | 9.78
84 70| 7 | 30 | 120 | 9.78
84 78| 7 | 27 | 120.3 | 9.73
90 84| 8 | 31 | 122 | 9.46
84 78| 7 | 28 | 124.8 | 9.02
100 80| 8 | 30 | 125 | 9.01
90 84| 8 | 32 | 126 | 8.87
100 96| 10 | 40 | 128 | 8.59
84 78| 7 | 29 | 129.3 | 8.42
100 78| 8 | 32 | 130 | 8.34
84 77| 7 | 30 | 132 | 8.08
84 78| 7 | 30 | 133.7 | 7.9
90 90| 8 | 32 | 135 | 7.73
84 78| 7 | 31 | 138.2 | 7.38
84 80| 8 | 40 | 140 | 7.18
120 71| 8 | 32 | 142 | 6.99
84 78| 7 | 32 | 142.6 | 6.93
100 87| 8 | 32 | 145 | 6.69
84 78| 7 | 33 | 147.1 | 6.5
100 96| 8 | 30 | 150 | 6.26
84 78| 7 | 34 | 151.6 | 6.1
96 95| 8 | 32 | 152 | 6.09
84 77| 7 | 35 | 154 | 5.94
104 96| 8 | 30 | 156 | 5.78
84 78| 7 | 35 | 156 | 5.78
120 96| 9 & 8 | 30 | 160 | 5.5
84 78| 7 | 36 | 160.5 | 5.47
84 78| 7 | 37 | 164.9 | 5.15
132 100| 9 & 8 | 27 | 165 | 5.17
84 78| 7 | 38 | 169.4 | 4.88
128 102| 8 | 25 | 170 | 4.87
84 78| 7 | 39 | 173.8 | 4.65
36 36 35| 6 | 25 | 175 | 4.6
84 77| 7 | 40 | 176 | 4.55
84 78| 7 | 40 | 178.3 | 4.43
45 36 36| 6 | 20 | 180 | 4.35
47 36 36| 6 | 20 | 188 | 3.99
===========+=========+========+==============+==========
* These are good examples of turret clock trains; the great
wheel (120 teeth) makes in both instances a rotation in
three hours. From this wheel the hands are to be driven.
This may be done by means of a pinion of 40 gearing with
the great wheel, or a pair of bevel wheels bearing the
same proportion to each other (three to one) may be used,
the larger one being fixed to the great wheel arbor. The
arrangement would in each case depend upon the number and
position of the dials. The double three-legged gravity
escape wheel moves through 60° at each beat, and therefore
to apply the rule given for calculating clock trains it must
be treated as an escape wheel of three teeth.
Take a pendulum vibrating 5,400 times an hour, escape wheel of 30,
pinions of 8, and third wheel of 72. Then 5,400 ÷ 60 = 90. And
90 × 8 ÷ 72 = 10. That is, the center wheel must have ten times as many
teeth as the third wheel pinion, or ten times 8 = 80.
The center pinion and great wheel need not be considered in connection
with the rest of the train, but only in relation to the fall of the
weight, or turns of mainspring, as the case may be. Divide the fall
of the weight (or twice the fall, if double cord and pulley are used)
by the circumference of the barrel (taken at the center of the cord);
the quotient will be the number of turns the barrel must make. Take
this number as a divisor, and the number of turns made by the center
wheel during the period from winding to winding as the dividend;
the quotient will be the number of times the center pinion must be
contained in the great wheel. Or if the numbers of the great wheel
and center pinion and the fall of the weight are fixed, to find the
circumference of the barrel, divide the number of turns of the center
wheel by the proportion between the center pinion and the great wheel;
take the quotient obtained as a divisor, and the fall of the weight as
a dividend (or twice the fall if the pulley is used), and the quotient
will be the circumference of the barrel. To take an ordinary regulator
or 8-day clock as an example—192 (number of turns of center pinion in
8 days) ÷ 12 (proportion between center pinion and barrel wheel) = 16
(number of turns of barrel). Then if the fall of the cord = 40 inches,
40 × 2 ÷ 16 = 5, which would be circumference of barrel at the center
of the cord.
If the numbers of the wheels are given, the vibrations per hour of the
pendulum may be obtained by dividing the product of the wheel teeth
multiplied together by the product of the pinions multiplied together,
and dividing the quotient by twice the number of escape wheel teeth.
The numbers generally used by clock makers for clocks with less than
half-second pendulum are center wheel 84, gearing with a pinion of 7;
third wheel 78, gearing with a pinion of 7.
The product obtained by multiplying together the center and third wheels
= 84 × 78 = 6,552. The two pinions multiplied together = 7 × 7 = 49.
Then 6,552 ÷ 49 = 133.7. So that for every turn of the center wheel the
escape pinion turns 133.7 times. Or 133.7 ÷ 60 = 2.229, which is the
number of turns in a minute of the escape pinion.
The length of the pendulum, and therefore the number of escape wheel
teeth, in clocks of this class is generally decided with reference to
the room to be had in the clock case, with this restriction, the escape
wheel should not have less than 20 nor more than 40 teeth, or the
performance will not be satisfactory. The length of the pendulum for
all escape wheels within this limit is given in the preceding table.
The length there stated is of course the theoretical length, and the
ready rule adopted by clockmakers is to measure from the center arbor
to the bottom of the inside of the case, in order to ascertain the
greatest length of pendulum which can be used. For instance, if from
the center arbor to the bottom of the case is 10 inches, they would
decide to use a 10-inch pendulum, and cut the escape wheel accordingly
with the number of teeth required as shown in the table. But they would
make the pendulum rod of such a length as just to clear the bottom of
the case when the pendulum was fixed in the clock.
In the clocks just referred to the barrel or first wheel has 96 teeth,
and gears with a pinion of eight.
Month clocks have an intermediate wheel and pinion between the great
and center wheels. This extra wheel and pinion must have a proportion
to each other of 4 to 1 to enable the 8-day clock to go 32 days from
winding to winding. The weight will have to be four times as heavy,
plus the extra friction, or if the same weight is used there must be a
proportionately longer fall.
Six-months clock have two extra wheels and pinions between the great
and center wheels, one pair having a proportion of 4½ to 1 and the
other of 6 to 1. But there is an enormous amount of extra friction
generated in these clocks, and they are not to be recommended.
The pivot holes and all the other holes in the frames, are punched at
one operation after the frames have been blanked and flattened. They
are placed in the press, and a large die having punches in it of the
proper size and in the right position for the holes, comes down on the
frame and makes the holes with great rapidity and accuracy. These holes
are finished afterwards by a broach. In some kinds of clocks, where
some of the pivot holes are very small, the small holes are simply
marked with a sharp point in the die, and afterwards drilled by small
vertical drills. These machines are very convenient for boring a number
of holes rapidly. The drill is rotated with great speed, and a jig or
plate on which the work rests is moved upwards towards the drill by
a movement of the operator’s foot. All the boring, countersinking,
etc., in American clocks, is done through the agency of these drills.
Bending the small wires for the locking work, the pendulum ball, etc.,
is rapidly effected by forming. As no objectionable marks have been
made on the surface of either the thick or smaller wires during any
process of construction, all that is necessary to finish the iron work
is simply to clean it well, which is done in a very effective manner by
placing a quantity of work in a revolving tumbling box, which is simply
a barrel containing a quantity of sawdust.
Milling the winding squares on barrel arbors is an ingenious operation.
The machine for milling squares and similar work is made on the
principle of a wheel cutting engine. The work is held in a frame,
attached to which is a small index plate, like that of a cutting
engine. In the machine two large mills or cutters, with teeth in them
like a file, are running, and the part to be squared is moved in
between the revolving cutters, which operation immediately forms two
sides of the square. The work is then drawn back, and the index turned
round, and in a like manner the other two sides of the square are
formed. The cutting sides of the mills are a little bevelled, so that
they will produce a slight taper on the squares.
Winding keys have shown great improvements. Some manufacturers
originally used cast iron ones, but the squares were never good in
them, and brass ones were adopted. At first the squares were made by
first drilling a hole and driving a square punch in with a hammer;
and to make the squares in eighteen hundred keys by this method was
considered a good day’s work. Restless Yankee ingenuity, however, has
contrived a device by which twenty or twenty-five thousand squares can
be made in a day, while at the same time they are better and straighter
squares than those by the old method; but we are not at liberty to
describe the process at present, but only to state that it is done by
what machinists call drilling a square hole.
Pendulum rods are made from soft iron wire, and the springs on the
ends rolled out by rollers. Two operations are necessary. The first
roughs the spring out on rollers of eccentric shape, and the spring
is afterwards finished on plain smooth rollers. The pendulum balls in
the best clocks are made of lead, on account of its weight, and cast
in an iron mold in the same manner as lead bullets, at the rate of
about eighteen hundred a day. A movable mandrel is placed in the mold
to produce the hole that is in the center of the ball. The balls are
afterwards covered with a shell of brass, polished with a bloodstone
burnisher. The various cocks used in these clocks are all struck up
from sheet brass, and the pins in the wheels in the striking part are
all swedged into their shape from plain wire. The hands are die struck
out of sheet steel, and afterwards polished on emery belts, and blued
in a furnace.
All the little pieces of these clocks are riveted together by hand, and
the different parts of the movement, when complete, are put together by
workmen continually employed in that department. Although the greatest
vigilance is used in constructing the different parts to see that they
are perfect, when they come to be put together they are subjected to
another examination, and after the movements are put in the case the
clocks are put to the test by actual trial before they are packed ready
for the market. As a general rule, all the different operations are
done by workmen employed only at one particular branch; and in the
largest factories from thirty to fifty thousand clocks of all classes
may be seen in the various stages of construction.
Such is a description of the main points in which the manufacture of
American clock movements differs from those manufactured by other
systems. All admit that these clocks perform the duties for which they
are designed in an admirable manner, while they require but little
care to manage, and when out of order but little skill is necessary
to repair them. Of late years there has been a growing demand for
ornamental mantel-piece clocks in metallic cases of superior quality,
and large numbers of these cases of both bronze and gold finish are
being manufactured, which, for beauty of design and fine execution,
in many instances rival those of French production. The shapes of the
ordinary American movements were, however, unsuitable for some patterns
of the highest class of cases, and the full plate, round movements of
the same size as the French, but with improvements in them that in some
respects render them more simple than the French, are now manufactured.
Exactly the same system is employed in the manufacture of the different
parts of these clocks that is practiced in making the ordinary American
movements.
CHAPTER XV.
SPRINGS, WEIGHTS AND POWER.
We see by the preceding calculations that there is one definite point
in the time train of a clock; the center arbor, which carries the
minute hand, must revolve once in one hour; from this point we may
vary the train both ways, toward the escape wheel to suit the length
of pendulum which we desire to use, and toward the barrel to suit the
length of time we want the clock to run. The center arbor is therefore
generally used as the point at which to begin calculations, and it
is also for this reason that the number of teeth in the center wheel
is the starting point in train calculations toward the escape wheel,
while the center pinion is the starting point in calculations of the
length of time the weight or spring is to drive the clock. Most writers
on horology ignore this point, because it seems self-evident, but its
omission has been the cause of much mystification to so many students
that it is better to state it in plain terms, so that even temporary
confusion may be avoided.
Sometimes there is a second fixed point in a time train; this occurs
only when there is a seconds hand to be provided for; when this is
the case the seconds hand must revolve once every minute. If it is a
seconds pendulum the hand is generally carried on the escape wheel and
the relation of revolutions between the hour and seconds wheels must
then be as one is to sixty. This might be accomplished with a single
wheel having sixty times as many teeth as the pinion on the seconds
arbor; but the wheel would take up so much room, on account of its
large circumference, that the movement would become unwieldy because
there would be no room left for the other wheels; so it is cheaper to
make more wheels and pinions and thereby get a smaller clock. Now the
best practical method of dividing this motion is by giving the wheels
and pinions a relative velocity of seven and a half and eight, because
7.5 × 8 = 60.
Thus if the center wheel has 80 teeth, gearing into a pinion of 10, the
pinion will be driven eight times for each revolution of the center
wheel, while the third wheel, with 75 teeth, will drive its pinion of
10 leaves 7.5 times, so that this arbor will go 7.5 times eight, or 60
times as fast as the center wheel.
If the clock has no seconds hand this second fixed point is not present
in the calculations and other considerations may then govern. These
are generally the securing of an even motion, with teeth of wheels
and pinions properly meshing into each other, without incurring undue
expense in manufacture by making too many teeth in the pinions and
consequently in the wheels. For these reasons pinions of less than
seven or more than ten leaves are rarely used in the common clocks,
although regulators and fine clocks, where the depthing is important,
frequently have 12, 14 or 16 leaves in the pinions, as is also the case
with tower clocks, where the increased size of the movement is not
as important as a smoothly running train. Clocks without pendulums,
carriage clocks, locomotive levers and nickel alarms, also have
different trains, many of which have the six leaf pinion, with its
attendant evils, in their trains.
WEIGHTS.--Weights have the great advantage of driving a train with
uniform power, which a spring does not accomplish: They are therefore
always used where exactness of time is of more importance than
compactness or portability of the clock. In making calculations for a
weight movement, the first consideration is that as the coils of the
cord must be side by side upon the barrel and each takes up a definite
amount of space, a thicker movement (with longer arbors) will be
necessary, as the barrel must give a sufficient number of turns of the
cord to run the clock the desired time and the length of the barrel,
with the wheel and maintaining power all mounted upon the one arbor,
will determine the thickness of the movement. If the clock is to have
striking trains their barrels will generally be of more turns and
consequently longer than the time barrel and in that case the distance
between the plates is governed by the length of the longest barrel and
its mechanism.
The center wheel, upon the arbor of which sits the canon pinion with
the minute hand, must, since the hand has to accomplish its revolution
in one hour, also revolve once in an hour. When, therefore, the pinion
of the center arbor has 8 leaves and the barrel wheel 144, then the
8 pinion leaves, which makes one revolution per hour, would require
the advancing of 8 teeth of the barrel wheel, which is equal to the
eighteenth part of its circumference. But when the eighteenth part
in its advancing consumes 1 hour, then the entire barrel wheel will
consume 18 hours to accomplish one revolution. If, now, 10 coils of
the weight cord were laid around the barrel, the clock would then run
10 × 18 = 180 hours, or 7½ days, before it is run down.
Referring to what was said in a previous chapter on wheels being merely
compound levers, it will be seen that as we gain motion we lose power
in the same ratio. We shall also see that by working the rule backwards
we may arrive at the amount of force exerted on the pendulum by the
pallets. If we multiply the circumference of the escape wheel in inches
by the number of its revolutions in one hour we will get the number of
inches of motion the escape wheel has in one hour. Now if we multiply
the weight by the distance the barrel wheel travels in one hour and
divide by the first number we shall have the force exerted on the
escape wheel. It will be simpler to turn the weight into grains before
starting, as the division is less cumbersome.
Another way is to find how many times the escape wheel revolves to one
turn of the barrel and divide the weight by that number, which will
give the proportion of weight at the escape wheel, or rather would do
so if there were no power lost by friction. It is usual to estimate
that three-quarters of the power is used up in frictions of teeth and
pivots, so that the amount actually used for propulsion of the pendulum
is very small, being merely sufficient to overcome the bending moment
of the suspension spring and the resistance of the air.
It is for this reason that clocks with finely cut trains and jeweled
pivots, thus having little train friction, will run with very small
weights. The writer knows of a Howard regulator with jeweled pivots
and pallets running a 14-pound pendulum with a five-ounce driving
weight. Of course this is an extreme instance and was the result of an
experiment by an expert watchmaker who wanted to see what he could do
in this direction.
Usually the method adopted to determine the amount of weight that is
necessary for a movement is to hang a small tin pail on the weight
cord and fill it with shot sufficient to barely make the clock keep
time. When this point has been determined, then weigh the pail of shot
and make your driving weight from eight to sixteen ounces heavier. In
doing this be sure the clock is in beat and that it is the lack of
power which stops the clock; the latter point can be readily determined
by adding or taking out shot from the pail until the amount of weight
is determined. The extra weight is then added as a reserve power, to
counteract the increase of friction produced by the thickening of the
oil.
Many clock barrels have spiral grooves turned in them to assist in
keeping the coils from riding on each other, as where such riding
occurs the riding coils are farther from the center of the barrel
than the others, which gives them a longer leverage and greater power
while they are unwinding, so that the power thus becomes irregular and
affects the rate of the clock, slowing it if the escapement is dead
beat and making it go faster if it is a recoil escapement.
Clock cords should be attached to the barrel at the end which is the
farthest from the pendulum, so that as they unwind the weight is
carried away from the pendulum. This is done to avoid sympathetic
vibrations of the weight as it passes the pendulum, which interfere
with the timekeeping when they occur. If the weight cannot be brought
far enough away to avoid vibrations a sheet of glass may be drilled
at its four corners and fixed with screws to posts placed in the back
of the case at the point where vibration occurs, so that the glass is
between the pendulum rod and the weight, but does not interfere with
either. This looks well and cures the trouble.
We have, heretofore, been speaking of weights which hang directly from
the barrel, as was the case with the older clocks with long cases, so
that the weight had plenty of room to fall. Where the cases are too
short to allow of this method, recourse is had to hanging the weight
on a pulley and fastening one end of the cord to the seat board. This
involves doubling the amount of weight and also taking care that the
end of the cord is fastened far enough from the slot through which it
unwinds so that the cords will not twist, as they are likely to do if
they are near together and the cord has been twisted too much while
putting it on the barrel. Twisting weight cords are a frequent source
of trouble when new cords have been put on a clock. The pulley is
another source of trouble, especially if wire cords (picture cords)
or cables are used. Wire cable should not be bent in a circle smaller
than forty times its diameter if flexibility is to be maintained, hence
pulleys which were all right for gut or silk frequently prove too
small when wire is substituted and kinks, twisted and broken cables
frequently result from this cause. This is especially the case with
the heavy weight of striking trains of hall and chiming clocks, where
double pulleys are used, and also leads to trouble by jamming and
cutting the cables and dropping of the weights in tower clocks where a
new cable of larger size is used to replace an old one which has become
unsafe from rust, or cut by the sheaves.
Weight cords on the striking side of a clock should always be left long
enough so that they will not run down and stop before the time train
has stopped. This is particularly the case with the old English hall
clocks, as many of them will drop or push their gathering racks free
of the gathering pinion under such conditions and then when the clock
is wound it will go on striking continuously until the dial is taken
off and the rack replaced in mesh with the gathering pinion. As clocks
are usually wound at night, the watchmaker can see the disturbance that
would be caused in a house in the “wee sma’ hours” by such a clock
going on a rampage and striking continuously.
OILING CABLES.--Clock cables, if of wire and small in size, should be
oiled by dipping in vaseline thinned with benzine of good quality.
Both benzine and vaseline must be free from acid, as if the latter
is present it will attack the cable. This thinning will permit the
vaseline to permeate the entire cable and when the benzine evaporates
it will leave a thin film of vaseline over every wire, thus preventing
rust. Tower clock cables should be oiled with a good mineral oil, well
soaked into them to prevent rusting. Gut clock cords, when dry and
hard, are best treated with clock oil, but olive oil or sperm oil will
also be found good to soften and preserve them. New cords should always
be oiled until they are soft and flexible. If the weight is under ten
pounds silk cords are preferable to gut or wire as they are very soft
and flexible.
In putting on a new cable or weight cord the course of the weight and
cord should be closely watched at all points, to see that they remain
free and do not chafe or bind anywhere and also that the coils run
evenly and freely, side by side; sometimes, especially with wire, a new
cable gets kinked by riding the first time of winding and is then very
difficult to cure of this serious fault. Another point to watch is to
see that the position of the cord when wound up will not cause an end
thrust upon the barrel, which will interfere with the timekeeping if it
is overwound, so that the weight is jammed against the seatboard; this
frequently happens with careless winding, if there is no stop work.
To determine the lengths of clock cords or weights, we may have to
approach the question from either end. If the clock be brought in
without the cords, we first count the number of turns we can get on
the barrel. This may be done by measuring the length of the barrel and
dividing it by the thickness of the cord, if the barrel is smooth, or
by counting the grooves if it be a grooved barrel. Next we caliper the
diameter and add the thickness of one cord, which gives us the diameter
of the barrel to the center of the cords, which is the real or working
diameter. Multiply the distance so found by 3.14156, which gives the
circumference of the barrel, or the length of cord for one turn of the
barrel. Multiply the length of one turn by the number of turns and we
have the length of cord on the barrel, when it is fully wound. If the
cord is to be attached to the weight, measure the distance from the
center of barrel to the bottom of the seat board and leave enough for
tying. If the weight is on a pulley it will generally require about
twelve inches to reach from the barrel through the slot of the seat
board, through the pulley to the point of fastening.
To get the fall of the weight, stand it on the bottom of the case and
measure the distance from the top of the point of attachment to the
bottom of the seat board. This will generally allow the weight to fall
within two inches of the bottom and thus keep the cable tight when
the clock runs down; thus avoiding kinks and over-riding when we wind
again after allowing the clock to run down. If the weight has a pulley
and double cord, measure from the top of the pulley to the seatboard,
with the weight on the bottom, and then double this measurement for
the length of the cord. This measure is multiplied by as many times as
there are pulleys in the case of additional sheaves. Striking trains
are frequently run with two coils or layers of cord, on the barrel,
time trains never have but one.
Now, having the greatest available length of cord determined according
either of the above conditions, we can determine the number of turns
for which we have room on our barrel and divide the length of cord
by the number of turns. This will give us the length of one turn of
the cord on our barrel and thus having found the circumference it is
easy to find the diameter which we must give our barrel in suiting a
movement to given dimensions of the case. This is frequently done where
the factory may want a movement to fit a particular style and size of
case which has proved popular, or when a watchmaker desires to make a
movement for which he has, or will buy, a case already made.
As to tower clock cables, getting the length of cable on the barrel is,
of course, the same as given above, but the rest of it is an individual
problem in every case, as cables are led so differently and the length
of fall varies so that only the professional tower clock men are fitted
to make the measurements for new work and they require no instruction
from me. It might be well to add, however, that in the tower clocks
by far the greater part of the cable is always outside the clock and
only the inner end coils and uncoils about the barrel. It is for this
reason that the outer ends of the cables are so generally neglected by
watchmakers in charge of tower clocks and allowed to cut and rust until
they drop their weights. Caretakers of tower clocks should remember
that the inner ends of cables are always the best ends; the parts that
need watching are those in the sheaves or leading to the sheaves.
Tower clocks should have the cables marked where to stop to prevent
overwinding.
In chain drives for the weights of cuckoo and other clocks with exposed
weights, we have generally a steel sprocket wheel with convex guiding
surfaces each side of the sprocket and projecting flanges each side of
the guides; one of these flanges is generally the ratchet wheel. The
ratchet wheel, guide, sprocket, guide and flange, form a built-up wheel
which is loose on the arbor and is pinned close to the great wheel,
which is driven by a click on the wheel working into the ratchet of
the drive. It must be loose on the arbor, because the clock is wound
by pulling the sprocket and ratchet backward by means of the chain
until the weight is raised clear up to the seat board. There are no
squares on the arbors, which have ordinary pivots at both ends, and the
great wheel is fast on the arbor. The diameter of the convex portion
of the wheel each side of the sprocket is the diameter of the barrel,
and the chain should fit so that alternate links will fit nicely in
the teeth of the sprocket; where this is not the case they will miss a
link occasionally and the weight will then fall until the chain catches
again, when it will stop with a jerk; bent or jammed links in the chain
will do the same thing. Sometimes a light chain on a heavy weight
will stretch or spread the links enough to make their action faulty.
If examination shows a tendency to open the links, they should be
soldered; if they are stretching, a heavier chain of correct lengths of
links should be substituted. Twisted chains are another characteristic
fault and are usually the result of bent or jammed links. A close
examination of such a chain will generally reveal several links in
succession which are not quite flat and careful straightening of these
links will generally cure the tendency to twist.
MAINSPRINGS FOR CLOCKS.--There are many points of difference between
mainsprings for clocks and those for watches. They differ in size,
strength, number of coils and in their effect on the rates of the clock.
Watch springs are practically all for 30-hour lever escapements, with
a few cylinder, duplex and chronometer escapements. If a fusee watch
happens into a shop nowadays it is so rare as to be a curiosity worth
stopping work to look at.
The clocks range all the way from 30 hours to 400 days in length of
time between windings and include lever, cylinder, duplex, dead beat,
half dead beat, recoil and other escapements. Furthermore some of
these, even of the same form of escapements, will vary so in weight
and the consequent influence of the spring that what will pass in one
case will give a wildly erratic rate in another instance. Many of the
small French clocks have such small and light pendulums that very nice
management of the stop works is necessary to prevent the clock from
gaining wildly when wound or stopping altogether when half run down.
Nothing will cause a clock with a cylinder escapement to vary in time
more than a set or gummy mainspring, for it will gain time when first
wound and lose when half run down, or when there is but little power
on the train. In such a case examine the mainspring and see that it is
neither gummy nor set. If it is set, put in a new spring and you can
probably bring it to time.
With a clock it depends entirely on the kind of escapement that it
contains, whether it runs faster or slower, with a stronger spring;
if you put a stronger mainspring in a clock that contains a recoil
escapement the clock will gain time, because the extra power,
transmitted to the pallets will cause the pendulum to take a shorter
arc, therefore gain time, where the reverse occurs in the dead-beat
escapement. A stronger spring will cause the dead-beat pendulum to take
a longer arc and therefore lose time.
If a pendulum is short and light these effects will be much greater
than with a long and heavy pendulum.
At all clock factories they test the mainsprings for power and to see
that they unwind evenly; those that do are marked No. 1, and those that
do not are called “seconds.” The seconds are used only for the striking
side of the clocks, while the perfect ones are used for the running,
or time side. Sometimes, however, a seconds’ spring will be put on the
time side and will cause the clock to vary in a most erratic way. This
changing of springs is very often done by careless or ignorant workmen
in cleaning and then they cannot locate the trouble.
All mainsprings for both clocks and watches should be smooth and well
polished. Proper attention to this one item will save many dollars’
worth of time in examining movements to try to detect the cause of
variations.
A rough mainspring (that is, an emery finished mainspring) will lose
one-third of its power from coil friction, and in certain instances
even one-half. The deceptive feature about this to the watchmaker
is that the clock will take a good motion with a rough spring fully
found, but will fall off when partly unwound, and the consequence is
that he finds a good motion when the spring is put in and wound, and
he afterward neglects to examine the spring when he examines the rate
as faulty. The best springs are cheap enough, so that only the best
quality should be used, as it is easy for a watchmaker to lose three or
four dollars’ worth of time looking for faults in the escapement, train
and everywhere else, except the barrel, when he has inserted a rough,
thick, poorly made spring. The most that he can save on the cheaper
qualities of springs is about five cents per spring and we will ask any
watchmaker how long it would take to lose five cents in examination of
a movement to see what is defective.
Here is something which you can try yourself at the bench. Take a
rough watch mainspring; coil it small enough to be grasped in the hand
and then press on the spring evenly and steadily. You will find it
difficult to make the coils slide on one another as the inner coils get
smaller; they will stick together and give way by jerks. Now open your
hand slowly and you will feel the spring uncoiling in an abrupt, jerky
way, sometimes exerting very little pressure on the hand, at other
times a great deal. A dirty, gummy spring will do the same thing. Now
take a clean, well polished spring and try it the same way; notice how
much more even and steady is the pressure required to move the coils
upon each other, either in compressing or expanding. Now oil the well
polished spring and try it again. You will find you now have something
that is instantly responding, evenly and smoothly, to every variation
of pressure. You can also compress the spring two or three turns
farther with the same force. This is what goes on in the barrel of
every clock or watch; you have merely been using your hand as a barrel
and _feeling_ the action of the springs.
Now a well finished mainspring that is gummy is as irregular in its
action as the worst of the springs described above, yet very few
watchmakers will take out the springs of a clock if they are in a
barrel. One of them once said to me, “Why, who ever takes out springs?
I’ll bet I clean a hundred clocks before I take out the springs of one
of them!” Yet this same man had then a clock which had come back to him
and which was the cause of the conversation.
There must be in this country over 25,000 fine French clocks in
expensive marble or onyx cases, which were given as wedding presents to
their owners, and which have never run properly and in many instances
cannot be made to run by the watchmakers to whom they were taken
when they stopped. Let me give the history of one of them. It was an
eight-day French marble clock which cost $25 (wholesale) in St. Louis
and was given as a wedding present. Three months later it stopped and
was taken to a watchmaker well known to be skillful and who had a fine
run of expensive watches constantly coming to him. He cleaned the
clock, took it home and it ran three hours! It came back to him three
times; during these periods he went over the movement repeatedly; every
wheel was tested in a depthing tool and found to be round: all the
teeth were examined separately under a glass and found to be perfect;
the pinions were subjected to the same careful scrutiny; the depthings
were tried with each wheel and pinion separately; the pivots were
tested and found to be right; the movement was put in its case and
examined there; it would run all right on the watchmaker’s bench, but
not in the home of its owner. It would stop every time it was moved in
dusting the mantel. He became disgusted and took the clock to another
watchmaker, a railroad time inspector; same results. In this way the
clock moved about for three years; whenever the owner heard of a man
who was accounted more than ordinarily skillful he took him the clock
and watched him “fall down” on it. Finally it came into the hands of an
ex-president of the American Horological Society. He made it run three
weeks. When he found the clock had stopped again he refused pay for
it. Three months later he called and got the clock, kept it for three
weeks, brought it back without explanation and lo, the clock ran! It
would even run considerably out of beat! When asked what he had done to
the clock, he merely laughed and said “Wait.”
A year later the clock was still going satisfactorily and he explained.
“That was the first time I ever got anything I couldn’t fix and it made
me ashamed. I kept thinking it over. Finally one night in bed I got to
considering why a clock wouldn’t run when there was nothing the matter
with it. The only reason I could see was lack of power. Next morning I
got the clock and put in new mainsprings, the best I could find. The
clock was cured! None of these other men who had the clock took out the
springs. They came to me all gummed up, while the rest of the clock was
clean, bright and in perfect order. I cleaned the springs and returned
the clock; it ran three weeks. When I took it back I put in stronger
springs, because I found them a little soft on testing them. If any of
your friends have French clocks that won’t go, send them to me.”
Three-quarters of the trouble with French clocks is in the spring box;
mainspring too weak, gummy or set; stop works not properly adjusted,
or left off by some numskull who thought he could make the clock keep
time without it when the maker couldn’t; mainspring rough, so that
it uncoils by jerks; spring too strong, so that the small and light
pendulum cannot control it. These will account for far more cases than
the “flat wheel” story that so often comes to the front to account for
a failure on the part of the workman. Of course he must say something
to his boss to account for his failure and the “wheels out of round”
and “the faulty depthing” have been standard excuses for French clocks
for a century. Of course they do occur, but not nearly as often as they
are credited with, and even then such a clock may be made to perform
creditably if the springs are right.
Another source of trouble is buckled springs, caused by some workman
taking them out or putting them in the barrel without a mainspring
winder. There are many men who will tell you that they never use a
winder; they can put any spring in without it. Perhaps they can, but
there comes a day when they get a soft spring that is too wide for this
treatment and they stretch one side of it, or bend, or kink it, and
then comes coil friction with its attendant evils. These may not show
with a heavy pendulum, but they are certain to do so if it happens to
be an eight-day movement with light pendulum or balance, and this is
particularly true of a cylinder.
All springs should be cleaned by soaking in benzine or gasoline and
rubbing with a rag until all the gum is off them before they are
oiled. Heavy springs may be wiped by wrapping one or two turns of a
rag around them and pushing it around the coils. The spring should be
well cleaned and dried before oiling. A quick way of cleaning is to
wind the springs clear up; stick a peg in the escape wheel; remove the
pallet fork; plunge the whole movement into a pail of gasoline large
enough to cover it; let it stand until the gasoline has soaked into the
barrels; remove the peg and let the trains run down. The coils of the
spring will scrub each other in unwinding; the pivots will clean the
pivot holes and the teeth of wheels and pinions will clean each other.
Then take the clock apart for repairs. Springs which are not in barrels
should be wound up and spring clamps put on them before taking down the
clock. About six sizes of these clamps (from 2½ inches to ¾ inch) are
sufficient for ordinary work.
Rancid oil is also the cause of many “come-backs.” Workmen will buy
a large bottle of good oil and leave it standing uncorked, or in the
sun, or too near a stove in winter time, until it spoils. Used in this
condition it will dry or gum in a month or two and the clock comes
back, if the owner is particular; if not, he simply tells his friends
that you can’t fix a clock and they had better go elsewhere with their
watches.
For clock mainsprings, clock oil, such as you buy from material
dealers, is recommended provided it is intended for French mainsprings.
If the lubricant is needed for coarse American springs, mix some
vaseline with refined benzine and put it on liberally. The benzine will
dissolve the vaseline and will help to convey the lubricant all over
the spring, leaving no part untouched. The liquid will then evaporate,
leaving a thin coating of vaseline on the spring.
It is best to let springs down, with a key made for the purpose. It
is a key with a large, round, wooden handle, which fills the hand of
the watchmaker when he grasps it. Placing the key on the arbor square,
with the movement held securely in a vise, wind the spring until you
can release the click of the ratchet with a screwdriver, wire or other
tool; hold the click free of the ratchet and let the handle of the key
turn slowly round in the hand until the spring is down. Be careful not
to release the pressure on the key too much, or it will get away from
you if the spring is strong, and will damage the movement. This is why
the handle is made so large, so that you can hold a strong spring.
It is of great importance, if we wish to avoid variable coil friction,
that the spring should wind, from the very starting, concentrically;
i. e., that the coils should commence to wind in regular spirals,
equidistant from each other, around the arbor. In very many cases we
find, when we commence to wind a spring, that the innermost coil bulges
out on one side, causing, from the very beginning, a greater friction
of the coils on that side, the outer ones pressing hard against it as
you continue to wind, while on the outer side of the arbor they are
separated from each other by quite a little space between them, and
that this bulge in the first coil is overcome and becomes concentric to
the arbor only after the spring is more than half way wound up. This
necessarily produces greater and more variable coil friction. When a
spring is put into the barrel the innermost coil should come to the
center around the arbor by a gradual sweep, starting from at least one
turn around away from the other coils. Instead of that, we more often
find it laying close to the outer coils to the very end, and ending
abruptly in the curl in the soft end that is to be next the arbor. When
this is the case in a spring of uniform thickness throughout, it is
mainly due to the manner of first winding it from its straight into a
spiral form. To obviate it, I generally wind the first coils, say two
or three, on a center in the winder, a trifle smaller than the regular
one, which is to be of the same diameter of the arbor center in the
barrel. You will find that the substitution of the regular center,
afterwards, will not undo the extra bending thus produced on the inner
coils, and that the spring will abut by a more gradual sweep at the
center, and wind more concentrically.
The form of spring formerly used with a fusee in English carriage
clocks and marine chronometers is a spring tapering slightly in
thickness from the inner end for a distance of two full coils, the
thickness increasing as we move away from the end, then continuing
of uniform thickness until within about a coil and a half from the
other end, when it again increases in thickness by a gradual taper.
The increase in the thickness towards the outer end will cause it to
cling more firmly to the wall of the barrel. The best substitute for
this taper on the outside is a brace added to some of the springs
immediately back of the hole. With this brace, and the core of the
winding arbor cut spirally, excellent results are obtained with a
spring of uniform thickness throughout its entire length. Something,
too, can be done to improve the action of a spring that has no brace,
by hooking it properly to the barrel. The hole in the spring on the
outside should never be made close to the end; on the contrary, there
should be from a half to three-quarters of an inch left beyond the
hole. This end portion will act as a brace.
When the spring is down, the innermost coil of it should form a gradual
spiral curve towards the center, so as to meet the arbor without
forcing it to one side or the other. This curve can be improved upon,
if not correct, with suitably shaped pliers; or it can be approximated
by winding the innermost coils first on an arbor a little smaller in
diameter than the barrel arbor itself.
Another and very important factor in the development of the force of
the spring is the proper length and thickness of it. For any diameter
of barrel there is but one length and one thickness of spring that will
give the maximum number of turns to wind. This is conditioned by the
fact that the volume which the spring occupies when it is down must
not be greater nor less than the volume of the empty space around the
arbor into which it is to be wound, so that the outermost coil of the
spring when fully wound will occupy the same place which the innermost
occupies when it is down. In a barrel, the diameter of whose arbor
is one-third that of the barrel, the condition is fulfilled when the
measure across the coils of the spring as it lays against the wall of
the barrel, is 0.39 of the empty space, or, taking the diameter of the
barrel as a comparison, 0.123 of the latter; in other words, nearly
one-eighth of the diameter of the barrel. This is the width that will
give the greatest number of turns to wind, whatever may be the length
or thickness of any spring. If now we desire a spring to wind a given
number of turns, there is but one thickness and one length of it that
will permit it to do so. The thickness remaining the same, if we make
the spring longer or shorter, we reduce the number of turns it will
wind; more rapidly by making it shorter, less so by making it longer.
It is therefore not only useless, but detrimental, to put into a barrel
a greater number of coils, or turns, than are necessary, not only
because it will reduce the number of turns the barrel will wind, but it
will produce greater coil friction by filling up the space with more
coils than are necessary.
A mainspring in the act of uncoiling in its barrel always gives a
number of turns equal to the difference between the number of coils in
the up and the down positions. Thus, if 17 be the number of coils when
the spring is run down, and 25 the number when against the arbor, the
number of turns in uncoiling will be 8, or the difference between 17
and 25.
The cause of breakage is usually, that the inner coils are put to the
greatest strain, and then the slightest flaw in the steel, a speck of
rust, grooves cut in the edges of the spring by allowing a screwdriver
to slip over them, or an unequal effect of change of temperature,
causes the fracture, and leaves the spring free to uncoil itself with
very great rapidity.
Now this sudden uncoiling means that the whole energy of the spring is
expended on the barrel in a very small fraction of a second. In reality
the spring strikes the inner side of the rim of the barrel, a violent
blow in the direction the spring is turning, that is, backwards; this
is due to the mainspring’s inertia and its very high mean velocity.
The velocity is nothing at the outer end, where the spring is fixed,
but rises to the maximum at the point of fracture, and the kinetic
energy at various points of the spring could no doubt be calculated
mathematically or otherwise.
For instance, take a going barrel spring of eight and a half turns,
breaking close up to the center while fully wound. A point in the
spring at the fracture makes eight turns in the opposite direction
to which it was wound, a point at the middle four turns, and a point
at the outer end nothing, an effect similar to the whole mass of the
spring making four turns backwards. At its greatest velocity it is
suddenly stopped by the barrel, wheel teeth engaging its pinion; this
stoppage or collision is what breaks center pinions, third pivots,
wheel teeth, etc., unless their elasticity, or some interposed
contrivance, can safely absorb the stored-up energy of the mainspring,
the spring being, as every one knows, the heaviest moving part in an
ordinary clock, except where the barrel is exceptionally massive.
STOP WORKS.--Stop works are devices that are but little understood by
the majority of workmen in the trade. They are added to a movement for
either one or both of two distinct purposes: First, as a safety device,
to prevent injury to the escape wheel from over winding, or to prevent
undue force coming on the pendulum by jamming the weight against the
top of the seat board and causing a variation in time in a fine clock;
or, second, to use as a compromise by utilizing only the middle portion
of a long and powerful spring, which varies too much in the amount of
its power in the up and down positions to get a good rate on the clock
if all the force of the spring were utilized in driving the movement.
With weight clocks, the stop work is a safety device and should always
be set so that it will stop the winding when the barrel is filled
by the cord; consequently the way to set them is to wind until the
barrel is barely full and set the stops with the fingers locked so as
to prevent any further action of the arbor in the direction of the
winding and the cord should then be long enough to permit the weight
to be free. Then unwind until within half a coil of the knot in the
cord where it is attached to the barrel and see that the weight is also
free at the bottom of the case, when the stops again come into action.
This will allow the full capacity of the barrel to be used.
When stop work is found on a spring barrel, it may be taken for granted
that the barrel contains more spring than is being wound and unwound
in the operation of the clock and it then becomes important to know
how many coils are thus held under tension, so that we may put it back
correctly after cleaning. Wind up the spring and then let it slowly
down with the key until the stop work is locked, counting the number
of turns, and writing it down. Then hold the spring with the letting
down key and take a screw driver and remove the stop from the plate;
then count the number of turns until the spring is down and also write
that down. Then take out the spring and clean it. You may find such a
spring will give seventeen turns in the barrel without the stop work
on, while it will give but ten with the stop work; also that the arbor
turned four revolutions after you removed the stop. Then the spring ran
the clock from the fourth to the fourteenth turns and there were four
coils unused around the arbor, ten to run the clock and three unused at
the outer end around the barrel. This would indicate a short and light
pendulum or balance, which is very apt to be erratic under variations
of power, and if the rate was complained of by the customer you can
look for trouble unless the best adjustment of the spring is secured.
Put the spring back by winding the four turns and putting on the stop
work in the locked position; then wind. If the clock gains when up and
loses when down, shift the stop works half a turn backwards or forwards
and note the result, making changes of the stop until you have found
the point at which there is the least variation of power in the up and
down positions. If the variation is still too great a thinner spring
must be substituted.
There are several kinds of stop work, the most common being what is
known as the Geneva stop, a Maltese cross and a finger such as is
commonly seen on watches. For watches they have five notches, but for
clocks they are made with a greater number of notches, according to the
number of turns desired for the arbor. The finger piece is mounted on a
square on the barrel arbor and the star wheel on the stud on the plate.
In setting them see that the finger is in line with the center of the
star wheel when the stop is locked, or they will not work smoothly.
There is another kind of stopwork which is used in some American
clocks, and as there is no friction with it, and no fear of sticking,
nor any doubt of the certainty of its action, it is perhaps the most
suitable for regulators and other fine clocks which have many turns of
the barrel in winding. This stop is simple and sure. It consists of a
pair of wheels of any numbers with the ratio of odd numbers as 7 and
6, 9 and 10, 15 and 16, 30 and 32, 45 and 48, etc.; the smaller wheel
is squared on the barrel arbor and the larger mounted on a stud on the
plate. These wheels are better if made with a larger number of teeth.
On each wheel a finger is planted, projecting a little beyond the
outsides of the wheel teeth, so that when the fingers meet they will
butt securely. The meeting of these fingers cannot take place at every
revolution because of the difference in the numbers of the teeth of
the wheels; they will pass without touching every time till the cycle
of turns is completed, as one wheel goes round say sixteen times while
the other goes fifteen, and when this occurs the fingers will engage
and so stop further winding. When the clock has run down sixteen turns
of the barrel the fingers will again meet on the opposite side, and so
the barrel will be allowed to turn backwards and forwards for sixteen
revolutions, being stopped by the fingers at each extreme. When in
action the fingers may butt either at a right or an obtuse angle, only
not too obtuse, as this would put a strain on, tending to force the
wheels apart. If preferred the fingers may be made of steel, but this
is not necessary.
[Illustration: Fig. 83.]
MAINTAINING POWERS.--Astronomical clocks, watchmaker’s regulators
and tower clocks are, or at least should be, fitted with maintaining
power. A good tower clock should not vary in its rate more than five
to ten seconds a week. Many of them, when favorably situated and
carefully tended, do not vary over five to ten seconds per month. It
requires from five to thirty minutes to wind the time trains of these
clocks and the reader can easily see where the rate would go if the
power were removed from the pendulum for that length of time; hence a
maintaining power that will keep nearly the same pressure on the escape
wheel as the weight does, is a necessity. Astronomical clocks and fine
regulators have so little train friction, especially if jeweled, that
when the barrel is turned backwards in winding the friction between
the barrel head and the great wheel is sufficient to stop the train,
or even run it backwards, injuring the escape wheel and, of course,
destroying the rate of the clock; therefore they are provided with a
device that will prevent such an occurrence. Ordinary clocks do not
have the maintaining power because only the barrel arbor is reversed
in winding, and that reversal is never for more than half a turn at a
time, as the power is thrown back on the train every time the winder
lets go of the key to turn his hand over for another grip.
[Illustration: Fig. 84.]
[Illustration: Fig. 85.]
Figs. 83, 84 and 85 show the various forms of maintaining powers, which
differ only in their mechanical details. In all of them the maintaining
power consists of two ratchet wheels, two clicks and either one or
two springs; the springs vary in shape according to whether the great
wheel is provided with spokes or left with a web. If the great wheel
has spokes the springs are attached on the outside of the large ratchet
wheel so that they will press on opposite spokes of the great wheel
and are either straight, curved or coiled, according to the taste of
the maker of the clock and the amount of room. If made with a web a
circular recess is cut in the great wheel, see Fig. 83, wide and deep
enough for a single coil of spring wire which has its ends bent at
right angles to the plane of the spring and one end slipped in a hole
of the ratchet and the other in a similar hole in the recess of the
great wheel. A circular slot is cut at some portion of the recess in
the great wheel where it will not interfere with the spring and a screw
in the ratchet works back and forth in this slot, limiting the action
of the spring. Stops are also provided for the spokes of the great
wheel in the case of straight, curved or coiled springs, Figs. 84 and
85. These stops are set so as to give an angular movement of two or
three teeth of the great wheel in the case of tower clocks and from
six to eight teeth in a regulator. The springs should exert a pressure
on the great wheel of just a little less than the pull of the weight
on the barrel; they will then be compressed all the time the weight is
in action, and the stops will then transmit the power from the large
ratchet to the great wheel, which drives the train. Both the great
wheel and the large ratchet wheel are loose on the arbor, being pinned
close to the barrel, but free to revolve. A smaller ratchet, having
its teeth cut in the reverse direction from those of the larger one,
is fast to the end of the barrel. A click, called the winding click,
on the larger ratchet acts in the teeth of the smaller one during
the winding, holding the two ratchets together at all other times. A
longer click, called the detent click, is pivoted to the clock plate,
and drags idly over the teeth of the larger ratchet while the clock is
being driven by the weight and the maintaining springs are compressed.
When the power is taken off by the reversal of the barrel in winding,
the friction between the sides of the two ratchets and great wheel
would cause them to also turn backward, if it were not for this detent
click, with its end fast to the plate, which drops into the teeth of
the large ratchet and prevents it from turning backward. We now have
the large ratchet held motionless by the detent click on the clock
plate and the compressed springs which are carried between the large
ratchet and the great wheel will then begin to expand, driving the
loose great wheel until their force has been expended, or until winding
is completed, when they will again be compressed by the pull of the
weight. In some tower clocks curved pins are fixed to opposite spokes
of the great wheel and coiled springs are wound around the pins, Fig.
85; eyes in the large ratchet engage the outer ends of the pins and
compress the springs.
[Illustration: Fig. 86.]
The clicks for maintaining powers should not be short, and the
planting should be done so that lines drawn from the barrel center to
the click points and from the click centers to the points, will form
an obtuse angle, like B, Fig. 86, giving a tendency for the ratchet
tooth to draw the click towards the barrel center. The clicks should
be nicely formed, hardened and tempered and polished all over with
emery. Long, thin springs will be needed to keep the winding clicks up
to the ratchet teeth. The ratchet wheel must run freely on the barrel
arbor, being carried round by the clicks while the clock is going, and
standing still while the weight is being wound up. It is retained at
this time by a long detent click mounted on an arbor having its pivots
fitted to holes in the clock frame. The same remark as to planting
applies to this click as well as the others, and to all clicks having
similar objects; but as this click has its own weight to cause it to
fall no spring is required. To prevent it lying heavily on the wheel,
causing wear, friction and a diminution of driving power, it is as
well to have it made light. There is no absolute utility in fixing the
click to its collet with screws, but if done, it can be taken off to
be polished, and the appearance will be more workmanlike. This click
should have its point hardened and tempered, as there is considerable
wear on it.
[Illustration: Fig. 87.]
If the great wheel has spokes the best form for the two springs for
keeping the train going whilst being wound is that of the letter U, as
shown to the left of Fig. 84, one end enlarged for the screw and steady
pin and the blade tapering all along towards the end which is free.
The springs may be made straight and bent to the form while soft, then
hardened and tempered to a full blue. They are best when as large as
the space between two arms of the main wheel will allow. When screwed
on the large ratchet the backs of both should bear exactly against the
respective arms of the mainwheel, and a pair of pins is put in the
ratchet, so that any opposite pair of the mainwheel arms may rest upon
them when the springs are set up by the clock weight. The strength of
the springs can be adjusted by trial, reducing them till the weight of
the clock sets them up easily to the banking pins.
There are two methods of keeping the loose wheels against the end of
the barrel, while allowing them to turn freely during winding; one is a
sliding plate with a keyhole slot, Fig. 87, to slip in a groove on the
arbor, as is generally adopted in such house clocks as have fuzees, as
well as on the barrels of old-fashioned weight clocks; the other is a
collet exactly the same as on watch fuzees. They are both sufficiently
effective, but perhaps the latter is the best of the two, because the
collet may be fitted on the arbor with a pipe, and being turned true
on the broad inside face, gives a larger and steadier surface for the
mainwheel to work against, whereas the former only has a small bearing
on the shoulder of the small groove in the arbor, which fitting is
liable to wear and allow the main and the other loose wheel to wobble
sideways, displacing the contact with the detent click and causing
the mainwheel to touch the collet of the center wheel if very near
together; so, on the whole, a collet, as on a watch fuzee, seems the
better arrangement, where there is plenty of room for it on the arbor.
There is an older form of maintaining power which is sometimes met with
in tower clocks and which is sometimes imitated on a small scale by
jewelers who are using a cheap regulator and wish to add a maintaining
power where there is no room between the barrel and plates for the
ratchets and great wheel.
The maintaining power, Fig. 88, consists of a shaft, A, a straight
lever, B, a segment of a pinion, C, a curved, double lever, D, a
weight, E. The shaft, A, slides endwise to engage the teeth of the
pinion segment with the teeth of the great wheel. No. 2, the straight
lever has a handle at both ends to assist in throwing the pinion out or
in and a shield at the outer end to cover the end of the winding shaft,
No. 3, when the key is not on it.
The curved lever is double, and the pinion segment turns loosely
between the halves and on the shaft, A; it is held up in its place by a
light spring, F; the weight, E, is also held between the two halves of
the double lever.
[Illustration: Fig. 88. Maintaining Power.]
The action is as follows: The end of the lever, B, covers the end of
the winding shaft so that it is necessary to raise it before putting
the key on the winding shaft; it is raised till it strikes a stop, and
then pushed in till the pinion segment engages with the going wheel of
the train, when the weight, E, acting through the levers, furnishes
power to drive the clock train while the going weight is being
wound up. Of course the weight on the maintaining power must be so
proportioned to the leverage that it will be equal to the power of the
going barrel and its weight, a simple proposition in mechanics.
The number of teeth on the pinion segment, C, is sufficient to maintain
power for fifteen minutes, at the end of which time the lever, B, will
come down and again cover the end of the winding shaft; or, it may
be pumped out of gear and dropped down. In case it is forgotten, the
spring, F, will allow the segment to pass out of gear of itself and
will simply allow it to give a click as it slips over each tooth in the
going wheel; if this were not provided for, it would stop the clock.
CHAPTER XVI.
MOTION WORK AND STRIKING TRAINS.
Motion work is the name given to the wheels and pinions used to make
the hour hand go once around the dial while the minute hand goes twelve
times. Here a few preliminary observations will do much toward clearing
up the operations of the trains. The reader will recollect that we
started at a fixed point in the time train, the center arbor which
must revolve once per hour, and increased this motion by making the
larger wheels drive the smaller (pinions) until we reached sixty or
more revolutions of the escape wheel to one of the center arbor. This
gearing to increase speed is called “gearing up” and in it the pinions
are always driven by the wheels. In the case of the hour hand we have
to obtain a slowing effect and we do so by making the smaller wheels
(pinions) drive the larger ones. This is called “gearing back” and it
is the only place in the clock where this method of gearing occurs.
We drew attention to a common usage in the gearing up of the time
trains—that of making the relations of the wheels and pinions 8 to one
and 7.5 to one; 7.5 × 8 = 60. So we find a like usage in our motion
work, viz., 3 to one and 4 to one; 3 × 4 = 12. Say the cannon pinion
has twelve teeth; then the minute wheel generally has 36, or three to
one, and if the minute wheel pinion has 10, the hour wheel will have
40, or four to one. Of course, any numbers of wheels and pinions may
be used to obtain the same result, so long as the teeth of the wheels
multiplied together give a product which is twelve times that of the
pinions multiplied together; but three and four to one have been
settled upon, just as the usage in the train became fixed, and for the
same reasons; that is, these proportions take up the least room and may
be made with the least material. Also, the pinion with the greatest
number of teeth, being the larger, is usually selected as the cannon
pinion, as it gives more room to be bored out to receive the cannon,
or pipe. If placed outside the clock plate, the minute wheel and
pinion revolve on a stud in the clock plate; but if placed between the
frames, they are mounted on arbors like the other wheels. The method of
mounting is merely a matter of convenience in the arrangement of the
train and is varied according to the amount of room in the movement, or
convenience in assembling the movement at the factory, little attention
being paid to other considerations.
[Illustration: Fig. 89. Fig. 90.]
The cannon pinion is loose on the center arbor and behind it is a
spring, called the center spring, or “friction,” Figs. 89 and 90, which
is a disc that is squared on the arbor at its center and presses at
three points on its outer edge against the side of the cannon pinion;
or it may be two or three coils of brass wire. This center spring thus
produces friction enough on the cannon to drive it and the hour hand,
while permitting the hands to be turned backward or forward without
interfering with the train. In French mantel clocks the center spring
is dispensed with and a portion of the pipe is thinned and pressed in
so as to produce a friction between the pipe and the center arbor which
is sufficient to drive the hands; this is similar to the friction of
the cannon pinion in a watch.
[Illustration: Fig. 91.]
In some old English house clocks with snail strike, the cannon pinion
and minute wheel have the same number of teeth for convenience in
letting off the striking work by means of the minute wheel, which thus
turns once in an hour. Where this is the case the hour wheel and its
pinion bear a proportion to each other of twelve to one; usually there
is a pinion of six leaves engaging a wheel of 72 teeth, or seven and
eighty-four are sometimes found.
In tower clocks, where the striking is not discharged by the motion
work, the cannon pinion is tight on its arbor and the motion work is
similar to that of watches. See Fig. 91.
The cannon pinion drives the minute wheel, which, together with its
pinion, revolves loosely on a stud in the clock plate, or on an arbor
between the frames. The meshing of the minute wheel and cannon pinion
should be as deep as is consistent with perfect freedom, as should also
that of the hour wheel and minute pinion in order to prevent the hour
hand from having too much shake, as the minute wheel and pinion are
loose on the stud and the hour wheel is loose on the cannon, so that
a shallow depthing here will give considerable back lash, which is
especially noticeable when winding.
The hour wheel has a short pipe and runs loosely on the cannon pinion
in ordinary clocks. In quarter-strike cuckoos a different train is
employed and the wheels for the hands are both on a long stud in the
plate and both have pipes; the minute wheel has 32 teeth and carries
four pins on its under side to let off the quarters. The hour wheel
has 64 teeth and works close to the minute wheel, its pipe surrounding
the minute wheel pipe, and held in position by a screw and nut on the
minute pipe. A wheel of 48 and a pinion of 8 teeth are mounted on the
sprocket arbor with a center spring for a friction, the wheel of 48
meshing with the minute wheel of 32 and the 8-leaf pinion with the hour
wheel of 64. It will be recollected that the sprocket wheel takes the
place of the barrel in this clock and there is no center arbor as it is
commonly understood. The sprocket arbor in this case turns once in an
hour and a half, hence it requires 48 teeth to drive the minute wheel
of 32 once in an hour, as it turns one-third of a revolution (or 16
teeth) every half hour. The sprocket arbor, turning once in an hour and
a half, makes eight revolutions in twelve hours and its pinion of eight
leaves working in the hour wheel of 64 teeth turns the hour hand once
in twelve hours.
In ordinary rack and snail striking work the snail is generally mounted
on the pipe of the hour wheel, so that it will always agree with the
position of the hour hand and the striking will thus be in harmony with
the position of the hands.
STRIKING TRAINS.--It is only natural, after finding certain fixed
relations in the calculations of time trains and motion work, that we
should look for a similar point in striking trains, well assured that
we shall find it here also. It is evident that the clock must strike
the sum of the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 78
blows of the hammer, in striking from noon to midnight; this will be
repeated from midnight to noon, making 156 blows in 24 hours, and if it
is a 30-hour clock, six hours more must be added; blows for these will
be 21 more, making a total of 177 blows of the hammer for a 30-hour
strike train. The hammer is raised by pins set in the edge of a wheel,
called the pin wheel, and as one pin must pass the hammer tail for
every blow, it is evident that the number of pins in this wheel will
govern the number of revolutions it must make for 177 blows, so that
here is the base or starting point in our striking train. If there are
13 pins in the pin wheel, it must revolve 13.5 times for 177 blows; if
there are 8 pins, then the wheel must revolve 22.125 times in giving
177 blows; consequently the pinions and wheels back to the spring or
barrel must be arranged to give the proper number of revolutions of the
pin wheel with a reasonable number of turns of the spring or weight
cord, and it is generally desirable to give the same, or nearly the
same, number of turns to both time and striking barrels.
If it is an eight-day clock the calculation is a little different.
There are 156 blows every 24 hours; then as the majority of “eight-day”
clocks are really calculated to keep time for seven and a half days,
although they will run eight, we have: 156 × 7.5 = 1,070 blows in 7.5
days. With 13 pins we have 1,070 ÷ 13 = 80 and ⁴/₁₃ths revolutions in
the 7.5 days. If now we put an 8-leaf pinion on the pin wheel arbor and
84 teeth in the great wheel or barrel, we will get 10.5 turns of the
pin wheel for every turn of the spring or barrel; consequently eight
turns of the spring will be enough to run the clock for the required
time, as such clocks are wound every seventh day.
Figuring forward from the pin wheel, we find that we shall have to lock
our striking train after a stated number of blows of the hammer each
hour; these periods increase by regular steps of one blow every hour,
so that we must have our locking mechanism in position to act after
the passage of each pin, whether it is then used or not; so the pinion
that meshes with the pin wheel, and carries the locking plate or pin
on its arbor must make one revolution every time it passes a pin. If
this is a 6-leaf pinion, the pins on the pin wheel must therefore be 6
teeth apart; or an 8-leaf pinion must have the pins 8 teeth apart; and
vice versa. For greater convenience in registering, the pins are set in
a radial line with the spaces of the teeth in the pin wheel, as this
allows us to measure from the center of the pinion leaf.
It will thus be seen that the calculation of an hour striking train
is a simple matter; but if half hours are also to be struck from the
train, it will change these calculations. For a 30-hour train 24 must
be added to the 156 blows for 24 hours, 180 blows being required to
strike hours and half hours for 24 hours. These blows may be provided
for by more turns of the spring, or different numbers of the wheels and
pinions, which would then also vary the spacing of the pins.
Half hours may also be struck directly from the center arbor, by
putting an extra hammer tail on the hammer arbor, further back,
where it will not interfere with the hammer tail for the pin wheel,
and putting a cam on the center arbor to operate this second hammer
tail. This simplifies the train, as it enables the use of a shorter
spring or smaller wheels while providing a cheap and certain means of
striking the half hours. Half-hour trains are frequently provided with
a separate bell of different tone for the half hours, as with only one
bell the clock strikes one blow at 12:30, 1 and 1:30, making the time
a matter of doubt to one who listens without looking, as frequently
happens in the night.
[Illustration: Fig. 92. Eight Day Hour and Half Hour Strike.]
Fig. 92 shows an eight-day, Seth Thomas movement, which strikes the
hours on a count wheel train and the half hours from the center arbor.
All the wheels, pinions, arbors, pins, levers and hooks are correctly
shown in proper position, but the front plate has been left off for
greater clearness. The reader will therefore be required to remember
that the escape wheel, pallets, crutch, pendulum and the stud for the
pendulum suspension are really fixed to the front plate, while in the
drawing they have no visible means of support, because the plate is
left off.
The time train occupies the right-hand side of the movement and the
striking train the left hand. Running up the right-hand from the
spring to the escape wheel, we find an extra wheel and pinion which is
provided to secure the eight days’ run. We also see that what would
ordinarily be the center arbor is up in the right corner and does not
carry the hands; further, the train is bent over at a right angle,
in order to save space and get the escape wheel in the center at the
top of the movement. The striking train is also crowded down out of
a straight line, the locking cam being to the right of the pin wheel
and the warning wheel and fly as close to the center as possible. This
leaves some space between the pin wheel and the intermediate wheel
of the time train and here we find our center arbor, driven from the
intermediate wheel by an extra pinion on the minute wheel arbor, the
minute wheel meshing with the cannon pinion on the center arbor. This
rearranging of trains to save space is frequently done and often shows
considerable ingenuity and skill; it also will many times serve to
identify the maker of a movement when its origin is a matter of doubt
and we need some material, so that the planting of trains is not only
a matter of interest, but should be studied, as familiarity with the
methods of various factories is frequently of service to the watchmaker.
Fig. 93 is the upper portion of the same striking train, drawn to a
larger scale for the sake of clearness. It also shows the center arbor,
both hammer tails and the stop on the hammer arbor, which strikes
against the bottom of the front plate to prevent the hammer-spring from
throwing the hammer out of reach of the pins. The pin wheel, R, and
count wheel, E, are mounted close together and are about the same size,
so that they are shown broken away for a part of their circumferences
for greater clearness in explaining the action of the locking hook, C,
and the locking cam, D.
Fig. 94 shows the same parts in the striking position, being shown as
just about to strike the last blow of 12. Similar parts have similar
letters in both figures.
The count wheel, E, is loose on a stud in the plate, concentric with
the arbor of the pin wheel, R. The pivot of R runs through this stud.
The sole office of the count wheel is to regulate the distance to which
the locking hook C, is allowed to fall. The count hook, A, and the
locking hook, C, are mounted on the same arbor, B, so that they move in
unison. If A is allowed to fall into a deep slot of the count wheel, C
will fall far enough to engage the locking face of the cam D and stop
the train, as in Fig. 93. If, on the contrary, A drops on the rim of
the wheel, C will be held out of the locking position as D comes around
(see Fig. 94), and the train will keep on running. It will be seen that
after passing the locking notch, D, Fig. 94, will in its turn raise the
hook C, which will ride on the edge of D, and hold A clear of the count
wheel until the locking notch of D is again reached, when a deep notch
in the wheel will allow C to catch, as in Fig. 93, unless C is stopped
by A falling on the rim of the wheel, as in Fig. 94.
[Illustration: Fig. 93. Upper Portion of Striking Train Locked.]
[Illustration: Fig. 94. Striking Train Unlocked and Running.]
One leaf, F, of the pinion of the locking arbor sticks out far enough
to engage with the count wheel teeth and rotate the wheel one tooth for
each revolution of D, so that F forms a one-leaf pinion similar to that
of a rack striking train. Here we have our counting mechanism; F and D
go around together; F moves E one tooth every revolution. A holds C out
of action (Fig. 94) until A reaches a deep slot, when C stops the train
by engaging D (Fig. 93).
The count wheel, E, must have friction enough on its stud so that it
will stay where the pin F leaves it, when F goes out of action and
thus it will be in the right position to suitably engage F on the next
revolution. Too much friction of the count wheel on its stud will use
too much power for F to move it and thus slow the train; if there is
too little friction here the count wheel may get in such a position
that F will get stalled on the top of a tooth and stop the train.
The count hook, A, must strike exactly in the middle of the deep slots,
without touching the sides of the slots in entering or leaving, as to
do this would shift the position of the count wheel if the rubbing were
sufficient, or it might prevent A from falling (as A and C are both
very light) and the clock would go on striking. If the hook A does not
strike the middle of the spaces between the teeth of the count wheel,
it will gradually encroach on a tooth and push the wheel forward or
back, thus disarranging the count. Many a clock has struck 13 for 12
in this way because the hook was a little out. This did not occur in
the smaller numbers because the action was not continued long enough to
allow the hook to reach a tooth. The pin, F, should also mesh fairly
and freely in the teeth of the count wheel, or a similar defect is
likely to occur.
When repairing or making new count hooks, A, Figs. 93 and 94, they must
be of such a length that they will enter the slots on a line radial
with the center of the wheel. The proper length and direction are shown
at A, Fig. 95, while B and C are wrong. With hooks like either B or C
you can set or bend the hook to strike right at one and as you turn
the clock ahead the hook does not fall in far enough and at twelve it
only strikes eleven. Then if you bend the same hook to strike right
at twelve it will strike two at one and as you turn the clock ahead
it will strike right at about five or seven. A, Fig. 95, being of the
proper length and shape will give no trouble. Many of the count wheels
of the older clocks were divided by hand and are not as accurate as
they should be; when a wheel of this kind is found and a new wheel
cannot be substituted (because the clock is an antique and must have
the original parts preserved) it will sometimes require nice management
of the hook A to obtain correct striking. A little manipulation of the
pinion, F, Fig. 93 is sometimes desirable also, if the count wheel is
very bad.
[Illustration: Fig. 95. The proper length of the count hook.]
The locking face of the cam, D, must also be on a line radial to its
center, or it will either unlock too easily and go off on the slightest
jar or movement of the clock, or the face will have too much draw and
the hook C will not be unlocked when the clock is fully wound, and the
spring pressure is greatest. In this case the clock will not strike
when fully wound, but will do so when partly run down, and as the count
wheel train strikes in rotation, without regard to the position of
the hands, you will have irregular striking of a most puzzling sort.
Repairs to this notch are sometimes required, when the corner has
become rounded, and the best way to make them is to cut a new face on
the cam with a sharp graver, being careful to keep the face radial with
its center.
Because the count wheel strikes the hours in rotation, regardless of
the position of the hands, if the hands are turned backwards past the
figure 12 on the dial the striking will be thrown out of harmony with
the hands. To remedy this the count hook, A, has an eye on its rear end
and a wire, shown in Fig. 92, hangs down to where it can be reached
with the hand when the dial is on. Pulling this wire will lift A and C
and cause the clock to strike; by this means the clock may be struck
around until the position of the striking train agrees with that of
the hands. Where this wire is not present the striking is corrected by
turning the hands back and forth between IX and XII until the proper
hour is struck.
Now we come to the releasing mechanism, which causes the clock to
strike at stated times. I, Figs. 93 and 94, is an arbor pivoted
between the plates and carrying three levers, H, K and J, in different
positions on the arbor. H is directly under the count hook, A, and
lifts A and C whenever J is pushed far enough to one side by L on the
center arbor, which revolves once an hour. Thus L, through J, H and A,
C, unlocks the train once every hour. When C is thus lifted the train
runs until the warning pin, O, Figs. 93 and 94, strikes against the
lever K, which is on the same arbor with H and J. This preliminary run
of the train makes a little noise and is called “warning,” as the noise
notifies us that the train is in position to commence striking. The
lever K and the warning pin, O, then hold the train until L has been
carried out of action with J and released it, when O will push K out of
its path at every revolution and the clock will strike.
The half hours are struck by L¹ pressing the short hammer tail, G¹,
and thus raising and releasing the hammer once an hour.
In setting up the striking train after cleaning, place the pin wheel
so that the hammer tail, G, may be about one-fourth of the distance
from the next pin, as shown in Fig. 93; this allows the train to get
well under way before meeting with any resistance and will insure its
striking when nearly run down. If the hammer tail is too close to the
pin, it might stop the train when there is but little power on.
Then place D in the locked position, with A in a deep slot of the count
wheel and C in the notch of D. Next place the warning wheel with its
pin, O, on the opposite side of its arbor from the lever K, see Fig.
93. This is done to make sure that when it is unlocked for “warning”
the train will run far enough to get the corner of the lock, D, safely,
past C, so that it will not allow C to fall into the notch again and
lock the train when J, K and H are released by L. This is the rule
followed in assembling these clocks at the factories and is simple,
correct and easily understood. A study of these points in Fig. 93 will
enable any one to set up a train correctly before putting the front
plate on.
If the workman gets a clock that has been butchered by some one who
did not understand it (and there are many such), he may find that when
correctly set up the clock does not strike on the 60th minute of the
hour; in such a case a little bending of J, in or out as the case may
be, will usually remedy the trouble. The same thing may have to be done
to the hammer tails, G and G¹, or the stop on the hammer arbor. If
both hammer tails are out of position, bend the stop; if one is right,
let the stop alone and bend the other tail.
A rough, set or gummy spring will cause irregular striking. In such
a case the clock will strike part of the blows and then stop and
finally go on again and complete the number. Much time has been lost
in examining the teeth of wheels and pinions in such cases when the
trouble lay in the spring. Too strong a spring will make the movement
strike too fast; too weak a spring will make it strike slow, especially
in the latter part of the day or week, when it has nearly run down.
Too small a fan, or a fan that is loose on its arbor, will allow the
clock to strike too fast. If this fan is badly out of balance it will
prevent the train from starting when there is but little power on.
There is a class of clocks which have the count wheel tight on the
arbor, outside the clock plate. Many of them are on much tighter than
they should be. In such a case take an alcohol lamp and heat the wheel
evenly, especially around the hub; the brass will expand twice as much
as the steel and the wheel may then be driven off without injury.
Fig. 96 shows another typical American eight-day train, made by the
Gilbert Clock Company, and striking the half hours from the train.
Here we notice, on comparing with Fig. 92, that there are many points
of difference. First the notches on the count wheel are twice as wide
as they are in Fig. 92. This means that half hours are struck on the
train; this will be explained later. Next there are two complete sets
of notches on the wheel, which shows that the wheel turns only once
in twenty-four hours, whereas the other makes two revolutions in that
time. There are no teeth on the count wheel, so that it must be fast
to its arbor, which is that of the great wheel and spring, while Fig.
92 has a separate stud and it is loose. The wheel being on the spring
arbor and going once in 24 hours, there must be one turn of spring for
each 24 hours which the train runs. There is no pin wheel in Fig. 96,
but instead of this two pins are cut out of the locking cam to raise
the hammer tail as they pass. There are also two locking notches in
the locking cam. The cams on the center arbor are stamped out of brass
sheet, while those of Fig. 92 were of wire.
[Illustration: Fig. 96. Half hours struck on the train.]
Turning to the enlarged view in Fig. 97 and comparing it with Fig. 93,
we find further differences. The levers K and J are here made of one
piece of brass, while the others were separate and of wire. The lifting
lever, H, is flattened at its outer end in Fig. 93, while in Fig. 97
it is bent at right angles and passed under the count hook, A. The
hook, C, Fig. 97, is added to the arbor, B, as a safety device, in case
the locking hook should fail to enter its slot in the cam, D. It is
shown as having just stopped the warning pin in Fig. 96. There is but
one hammer tail, G, and the hammer stop acts against the stud for the
hammer-spring, instead of against the bottom of the front plate, as in
Fig. 92.
The first important difference here is in the position of the count
hook, A. In Figs. 92 and 93 the hook must be exactly in the middle of
the slot, or there will be trouble. In trains striking half hours from
the train, we must never allow the hook to occupy the middle of the
slot, or we will have more trouble than we ever dreamed of. In this
instance the count hook must enter the slot close to (but not touching)
the side of the slot when the clock stops striking; then when the half
hour is struck the count wheel will move a little and the hook must
drop back into the same slot without touching; this brings it close to
the opposite side of the same slot and the next movement will land the
hook safely on top of the wheel for the strokes of the hour. Fig. 96
shows its position after striking the half hour and ready to strike the
hour of two. Fig. 97 shows it dropping back after striking two.
[Illustration: Fig. 97. Half hour strike on the count wheel.]
In setting up this train, see that the count hook. A, goes into the
slot of the count wheel close to, but not touching, one side of the
slot in the count wheel, and, after placing the intermediate, insert
the locking cam, D, so that it engages the locking hook; then put in
the warning wheel with the warning pin, O, safely to the left of the
hook C, Fig. 97, so that it cannot get past that hook after striking.
Placing the wheel with its warning pin six or eight teeth to the left
of the edge of the bottom plate is generally about right. The action of
the levers, H, J, K, the hammer tail, G, and the cam, L, in striking
the hours is the same as that already described in detail for Figs. 93
and 94, hence need not be repeated here. L¹ strikes the half hours by
being enough shorter than L to raise the hooks for one revolution, but
not quite so high as for the hours. The cams L, L¹ are friction-tight
on the center arbor and may be shifted on the arbor to register the
striking on the 60th minute, if desired. When the hands and strike do
not agree, turn the minute hand back and forward between IX and XII,
thus striking the clock around until it agrees with the hands.
Sometimes, if the warning pin is not far enough away, an eight-day
clock will strike all right for a number of days and then commence
to gain or lose on the striking side. It either does not strike at
some hours, or half hours, or it may strike sometimes both hour and
half hour before stopping. Take the movement out of the case and put
the hands on; then move the minute hand around slowly until the clock
warns. Look carefully and be sure there is no danger of the clock
striking when it warns. If this looks secure, then move the hand to
the hour, making it strike; say it is going to strike 9 o’clock; when
it has struck eight times, stop the train with your finger and let the
wheels run very slow while striking the last one, and when the rod
drops into the last notch stop the train again and hold it there.
For the striking part to be correct, the warning pin on the wheel wants
to be about one-fourth of a revolution away from the rod when the clock
has struck the last time, or as soon as this rod falls down far enough
to catch the pin. The object of this is so there is no chance of the
warning pin getting past the rod at the last stroke; this it is liable
to do if the pin is too close to the rod when the rod drops. If you
will examine the clock as above, not only when it strikes IX, but all
the hours from I to XII, you will generally find the fault. Of course,
if the pin is too close to the rod when the rod drops, you must lift
the plates apart and change the wheel so that the warning pin and the
rod will be as explained.
SHIP’S BELL STRIKING WORK.--Of all the count wheel striking work which
comes to the watchmaker, the ship’s bell is most apt to give him
trouble. This generally arises from ignorance as to what the system of
bells on shipboard consists of and how they should be struck. If he
goes to some nautical friend, he hears of long and short “watches” or
“full watches” and “dog watches.” If he insists on details, he gets the
information that a “watch” is not a horological mechanism, but a period
of duty for a part of the crew. Then he is told of the “morning watch,”
“first dog watch,” “afternoon watch,” “second dog watch,” “off watch,”
“on watch,” etc. Now the ship’s bell clock does not agree with these
“watches” and was never intended to do so. As a matter of fact, it is
simply a clock striking half hours from one to eight and then repeating
through the twenty-four hours.
The striking is peculiarly timed and is an imitation of the method in
which the hours are struck on the bell of the ship. As this bell is
also used for other purposes, such as tolling in fogs, fire alarms,
church services, etc., it will readily be seen that a different method
of striking for each purpose is desirable to avoid misunderstanding of
signals.
[Illustration: Fig. 98. Ships bell clock.]
The method of striking for time is to give the blows in couples, with a
short interval between the strokes of the couples and three times that
interval between the couples. Odd strokes are treated as a portion of
the next couple and separated accordingly, thus:
12:30 p. m. One Bell, O
1:00 p. m. Two Bells, O O
1:30 p. m. Three Bells, O O O
2:00 p. m. Four Bells, O O O O
2:30 p. m. Five Bells, O O O O O
3:00 p. m. Six Bells, O O O O O O
3:30 p. m. Seven Bells, O O O O O O O
4:00 p. m. Eight Bells, O O O O O O O O
After striking eight bells the clock repeats, although the ship’s bell
is generally struck in accordance with the two dog watches (which are
of two hours’ duration each) before commencing the evening watch (8 to
12 p. m.). It will thus be seen that the clock should strike eight at
12 m., 4 p. m., 8 p. m., 12 p. m., 4 a. m., and 8 a. m.
[Illustration: Fig. 100. The pins on the count wheel of the ships bell
clock.]
In order to strike the blows in pairs two hammers are necessary, see
Fig. 98; these hammers are placed close together, but not in the same
plane. The pin wheel has twenty pins, see Figs. 98, 99, 100; some of
these pins are shorter than the others, so that they do not operate one
of the hammer tails. These are shown graphically in Fig. 100; where
the two oblong marks at figure 1 represent the tops of the hammer
tails shown in Fig. 99. It will be seen by studying Fig. 100 that with
the wheel moving from left to right, the inside hammer tail will be
operated for one blow, while the outer hammer tail will not be operated
at all, thus giving but one blow, or “bell.” At the next movement of
the pin wheel, the outside hammer will be operated by the long pin
and the inside hammer by the short pin, thus giving one blow of each
hammer, or “two bells.”
[Illustration: Fig. 99. Enlarged view of striking work, ships bell
clock.]
We now have these hammer tails advanced along the wheel so that the
outside one is opposite the figure 3 in the drawing, while the other is
opposite the figure 2, with one pin between them. The next movement of
the pin wheel advances them so that the outside hammer will pass the
next short pin and consequently that hammer will miss one blow and the
pair will therefore strike three—one by the outside hammer and two by
the inside. It thus goes on until the cycle is completed, eight blows
being struck with the last four pins. The striking in pairs is effected
by having the two hammer tails close together, so that the pins will
operate both hammer tails quickly and there will then be an interval of
time while the wheel brings forward the next pins. This is so spaced
that the interval between pairs is three times that between the blows
of a pair and the hammer tails should not be bent out of this position,
or if found so they should immediately be restored to it. Tolling the
bells, instead of striking them properly, is very bad form at sea and
generally leads to punishment if persisted in, so that the jeweler will
readily perceive that his marine customers are very particular on this
point, and he should go any length to obtain the proper intervals in
striking.
The pin wheel moves forward one pin for each couple of blows or parts
of a couple, the odd blows being secured by the failure of the blow
when the hammer tail passes the short pin. Thus it moves as far for one
bell as for two bells; as far for three bells as for four, etc. The
result is that the count wheel has no odd numbers on it, but instead
two 2’s, two 4’s, two 6’s and two 8’s; the first two are counted on
the count wheel, but only one is struck on the pin wheel, owing to
the short pin; this is repeated at three, five and seven, when four,
six and eight are counted on the wheel, but the last blow fails of
delivery, owing to the short pin in the pin wheel at these positions.
The center arbor carries two pins, L and L¹, to unlock the train
through the lever J, as it is really a half hour striking clock. The
count hook, A; locking hook, C; count wheel, E; pins, P, and other
parts have similar letters for similar parts as in the preceding
figures and need not be further explained, as the mechanism is
otherwise similar to the Seth Thomas movement shown in Fig. 92.
CHAPTER XVII.
CLEANING AND REPAIRING CUCKOO CLOCKS.
The cuckoos are in a class by themselves for several reasons, all
of which have to do with their construction and should therefore be
understood by the watchmaker. They are bought as timepieces by but two
classes of people: those who were used to them in their former homes in
Europe and buy them for sentimental reasons; and those who admire fine
wood carvings as works of art and desire to possess a finely carved
cuckoo clock for the reasons which govern in the purchase of paintings
and statuary, bronzes, and other art objects. For this reason cuckoos
have never been a success when attempts have been made to cheapen their
production by the use of imitations of wood carving in composition
or metal. The use of cuckoos in plain cases, with springs instead of
weights, has also been attempted with the idea of thereby securing
an inclosed movement, as in ordinary clocks; but while it offers
advantages in cleanliness and protection of the movement, such clocks
have never become popular, as they have lost their character as works
of art by being enclosed in plain cases, or have become rather erratic
in rate by the substitution of springs for weights.
The use of exposed weights and pendulum necessitates openings in the
bottom of the case through which the dust enters freely and this makes
necessary unusual side shake, end shake and freedom of depthing of the
wheels and pinions and also the use of lantern pinions and an amount
of driving weight in excess of that necessary for protected movements,
as there must be enough weight to pull the cuckoo movement through
obstructions which would stop the ordinary movement.
Repairers therefore should not attempt to close worn holes as snugly
as in the ordinary movements, as when this is done the clock generally
stops about three weeks after it has left the shop and a “comeback” is
the result. Lightening the driving weights will have the same result,
as the movement must have sufficient power to pull it through when
dirty. As the plates and wheels are generally of cast metal, cutting
of pivots from running dry is frequent in old clocks, and where it is
necessary to close the holes care must be taken not to overdo it.
Another point where repairers fail is in not polishing the pivots.
Many watchmakers seem to think that any kind of a pivot will do for a
clock, although they take great care of them in their watchwork. Rough
and dry pivots will cut the holes in a clock plate deep enough to wedge
the pivots in the holes like a stuck reamer and stop a clock just after
it has been repaired, when if they had been properly polished the job
would not have come back.
The high prices of wood carving in America and the necessity for its
genuineness, as explained above, has resulted in making it necessary
to spend as little as possible for the movements; hence we ordinarily
find a total lack of finish on the movements, and this, with the great
freedom everywhere evident in its construction and the apparent excess
of angular motion of the levers, combine to give it an appearance of
roughness which surprises those who see them but rarely.
It has been frequently suggested by watchmakers that if the cases only
were imported and the movements were made by the American factories
better results should be obtained, in appearance at least. They forget
that the bellows, pipes and birds, with their wires, are parts of the
movements and the cost of having these portions made in this country
is prohibitive, so that the whole movement is imported. Arrangements
are now being made by at least one firm to have the frames and wheels
made of sheet metal by automatic machinery, instead of being cast and
finished in the usual way, and when this is done the appearance of the
movements will be greatly improved, so that American watchmakers will
regard them with a more kindly eye. So far as is known to the writer
all cuckoo movements are imported, although one firm is doing a large
and constantly growing trade in such clocks with cases made in America.
There are a number of importing firms who sell to jobbers, large
retailers and clock companies only, and as the large American clock
manufacturers all list and carry cuckoos the clocks find their way
to the consumer through many and devious channels. Probably more are
sold in other ways than through the retailers for the reason that the
average retailer does not understand the cuckoos and is reluctant to
stock them, thereby deliberately avoiding a large amount of business
from which he might make a handsome profit.
Under the general term Cuckoos are listed several kinds of movements,
all having bellows, pipes and moving figures, such as the cuckoo,
cuckoo and quail, trumpeter, etc., with or without the regular hammers
and gongs of the ordinary movements.
Figs. 101 and 102 show front and back views of a time train in the
center with quail strike train on the left and cuckoo strike train
at the right. The positions of arbors, levers, depthings of trains,
etc., are exact, but the movement plates have been left off for
greater clearness, so that the arbors appear to be without support.
The positions of the pillars are shown by the shaded circles above and
below the trains in Fig. 101. The parts have the same letters in both
Figs. 101 and 102, although as the movement is turned around to show
the rear in 102, the quail train appears on the right side.
[Illustration: Fig. 101. Front View of Quail and Cuckoo Strike
Movement.]
NAMES OF PARTS.
A—Quail count wheel.
B—Quail striking cam.
C—Minute wheel.
D—Quail lifting lever.
E—Quail count hook.
F—Quail locking arm.
G—Quail bird stick; also called bird holder.
H—Quail bellows arm.
I—Quail bellows lifting lever.
J—Quail gong hammer.
K—Quail warning lever.
L—Quail lifting pin.
M—Quail bird stick lever.
N—Quail hammer lever.
O—Quail Lifting pin wheel.
P—Cuckoo lifting lever.
Q—Cuckoo warning lever.
R—Cuckoo lifting pin.
S—Cuckoo locking arm.
T—Cuckoo count hook.
U—Cuckoo striking cam.
V—Cuckoo lifting pin wheel.
W—Cuckoo count wheel.
X—Cuckoo bellows lifting lever.
Y—Cuckoo hammer.
Z—Cuckoo bird stick; also called bird holder.
S¹—Cuckoo bird stick lever.
In examining a movement the student discovers a peculiarity of cuckoo
frames, which is that the pivot holes for several of the arbors of
the striking levers have slots filed into them, reaching to the edges
of the frames and narrower than the full diameter of the pivot holes.
This is because such arbors have levers riveted into them which must
function in front, between and at the rear of the plates and in setting
up the movement the slots are necessary to allow the end levers to pass
through the holes. Such arbors as have slots on the front plates are
inserted and placed in their proper positions before setting the train
wheels with which they function. The others are first inserted in the
back plate and turned to position while putting on that plate.
Both quail and cuckoo trains are set up very simply and surely by
observing the following points: In the quail train, when the quail
bellows lever, H, is just released from a pin in the pin wheel, O, the
locking lever, F, must just fall into the slot of the locking cam, B;
the warning pin should then be near the fly pinion and the count hook,
K, drop freely into the count wheel, A.
[Illustration: Fig. 102. Rear View of Quail and Cuckoo Movement.]
On the cuckoo side we find two levers, X; the upper one of these
operates the low note of the cuckoo call and the lower one the high
note. When this upper lever is released from a pin in the pin wheel,
the cuckoo locking lever, S, must drop into its locking cam, U, and the
count hook, T, drop into its count wheel, while the warning pin must be
near the fly pinion. After the run has stopped and the trains are fully
locked the warning pins will be as shown in Fig. 102; but at the moment
of locking they should be as described above.
The operation is as follows: Turning to Fig. 101, we find the minute
wheel, C, has four pins projecting from its rear surface. This revolves
once per hour and consequently the pins raise the lifting lever, D,
every fifteen minutes. Here is a point that frequently is productive of
trouble. The reader will readily see that if the hands of a cuckoo are
turned backward the pins in the minute wheel will bend this wire, D,
and derange the striking, as the warning lever is also attached to the
same arbor. _Never push the hands backward_ on a cuckoo clock; always
push them forward. If the striking and hands do not register the same
time, take off the weights of the striking trains; then push the hands
forward until they register the hour which the trains struck last. As
there is no power on the trains they will not be operated, the only
action being the rising and falling of the lever, D, as the pins pass.
When the hands point to the hour last struck by the trains, put on the
striking weights again and push the hands _forward_, allowing time for
each striking, until the clock has been set to the correct time.
Upon the lifting lever, D, being raised sufficiently the warning lever,
E, on the same arbor is lifted into the path of the warning pin and
at the same time unlocks the train by pressing against the lifting
pin, L, in the locking lever, F. The locking lever, F, count hook, K,
and the bird holder lever, M, are all on the same arbor and therefore
work in unison. When D drops, E releases the warning pin and the train
starts. The pin wheel has pins on both sides, the rear pins operate the
gong hammer, N, J; the front pins operate the quail bellows, I, H.
The rising, and falling of the unlocking lever, F, operates the bird
holder, G, through M and the wire in the bellows top tilts the tail
of the bird and flutters the wings. When the fourth quarter has been
struck, the pins shown in the quail count wheel, A, operate the hour
lifting lever, P, and the action of that train becomes similar to that
of the quarter train just described, with the difference that there
are two bellows levers, X, for the high and low notes of the cuckoo,
whereas there is but one for the quail.
There are several adjustments necessary to watch on these clocks. The
wires to operate the bellows from the levers X and H may be so long
that the bellows when stretched to its full capacity may not allow the
tails of X and H to clear the pins of the pin wheels and thus stop the
trains. The pins should clear safely with the bellows fully opened.
The levers M and S¹, which operate the bird holders, G and Z, may be
turned in their arbors so as to be farther from or closer to the bird
holder; this regulates the opening and closing of the doors and the
appearance of the birds; if there is too much movement the birds may
be sent so far out that they will not return, but will stay out and
stop the trains. Moving S¹ and M towards the bird holders, Z and G,
will lessen the amount of this motion and the contrary movement will
increase it.
Another important source of trouble—because generally unsuspected—is
the fly. The fly on a cuckoo train must be tight; a loose fly will
cause too rapid striking and allow the train to overrun, making wrong
striking, or in a very bad case it will not stop until run down. When
this happens turn your attention to the fly and make sure that it is
tight before doing any bending of the levers, and also see to the
position of the warning pin.
Sometimes the front of the case (which is also the dial) will warp and
cause pressure on the ends of the lever arbors and thus interfere with
their proper working. Be sure that the arbors are free at both ends.
When replacing worn pins in the striking trains, care should be taken
to get them the right length, as on account of the large amount of
end shake in these movements they may slip past the levers without
operation, if too short, or foul the other parts of the train if too
long. For the same reasons bending the levers should only be done after
exhausting the other sources of error and then be undertaken very
slowly and cautiously.
The notes of a cuckoo are A and F, just below middle C; these should
be sounded clearly and with considerable volume. If they are short and
husky in tone it may be due to holes in the bellows, too short stroke
of bellows, removal of the bellows weights, E, Fig. 103, dirt in the
orifices of the pipes, or cracks in the pipes. Holes in the bellows,
if small and not in the folds of the kid, may be mended by being glued
up with paper or kid, or a piece of court plaster which is thin enough
to not interfere with the operation of the bellows. If much worn a new
bellows should be substituted. Cracks in the pipes may be mended with
paper.
The orifice of the pipe, if dirty, may be cleaned with a piece of
mainspring filed very thin and smooth and carefully inserted, as any
widening or roughening of this slit will interfere with the tone.
Sometimes a clock comes in which has been spoiled in this regard, then
it becomes necessary to remove the outer portion or lip, A, Fig. 103,
of the slot (which is glued in position) and make a new inner lip, B,
or file the old one smooth again. The proper shape is shown in B, Fig.
103, while C and D show improper shapes which interfere with the tone.
[Illustration: Fig. 103. Cuckoo bellows and pipe. A, outer lip; B,
inner lip; C, D, incorrect forms of lip.]
Much time and money has been spent in trying to avoid the inherent
defects of this portion of the clock; sometimes the lips will swell
or warp and close the orifice; sometimes they will shrink and make
it too wide; in either case a loss of purity of tone is the result.
Brass tubes, if thin enough to be cheap, give a brassy tone to the
notes; compositions of lead, tin and antimony (organ pipe metal) are
readily cast, but give a softer, duller tone of less volume than the
wood. Celluloid lips to a wooden tube were at first thought to be a
great success, but were found to warp as they got older. Bone lips are
costly; so there is nothing at present that seems likely to displace
well seasoned wood, where discriminating lovers of music and art demand
purity and correctness of tone, reasonably accurate time, artistic
sculptural effects and durability, all in one article—a high class
cuckoo clock.
When sending a clock home after repairing, each of the chains should
be tied together with strings just outside the bottom of the case so
that they will not slip off the sprockets and the customer should be
instructed to hang the clock in its accustomed position before cutting
the strings and attaching the weights.
CHAPTER XVIII.
SNAIL STRIKING WORK, ENGLISH, FRENCH AND AMERICAN.
While the majority of snail striking movements made in America are on
the French system, because they are cheaper when made in that way,
still this system is so condensed and so difficult to illustrate, with
all its mechanism packed in a small space between the plates, that
the student will gain a much better idea of the rack and snail and
its principles by first making a study of an English snail striking
clock, which has the whole of the counting and releasing levers placed
outside the front plate, where they can occupy all the room that may be
necessary. The calculation and planting of the striking train do not
differ from those using the count wheel, up to and including the single
toothed pinion or gathering pallet. The stopping of the train after
striking is different and the counting is divided, being dependent upon
four pieces acting in conjunction in an hour strike of the simplest
order, which number may run to a dozen in a repeating clock.
As the count wheel system had the defect of getting out of harmony with
the hands when the latter are turned backward, so the snail system has
its defects, which are the displacement of the rack and failure to stop
the striking in some clocks if the striking train runs down before
the time side and is then rewound, and a most puzzling inaccuracy of
counting, resulting from slight wear and inaccuracy of adjustment.
We mention these things here because they have an influence on the
construction of the clock and an advance knowledge of them will serve
to make clearer some of the statements which follow.
HOUR AND HALF-HOUR SNAIL STRIKING WORK.—Fig. 104 is a view of the front
plate of an English fusee striking clock, on the rack principle. The
going train occupies the right and center and the striking train the
left hand. The position of the trains is indicated in dotted lines,
the trains having barrels and fusees as shown by the squared arbors,
all the dotted work being between the clock plates, and that in full
lines being placed on the outside of the front plate, under the dial.
The connection between the going train and the striking work is by
means of the motion wheel on the center arbor, and connection is made
between the striking train and the counting work by the gathering
pallet, F, which is fixed to the arbor of the last wheel but one of the
striking train, and also by the warning piece, which is shown in black
on the boss of the lifting piece, A. This warning piece goes through a
slotted hole in the plate, and during the interval between warning and
striking stands in the path of a warning pin in the last wheel of the
striking train. The motion wheel on the center arbor, turning once in
an hour, gears with the minute wheel, E, which has an equal number of
teeth. There are two pins opposite each other and equidistant from the
center of the minute wheel, which in passing raise the lifting piece,
A, every half hour. Except for a few minutes before the clock strikes,
the striking train is kept from running by the tail of the gathering
pallet; F, resting on a pin in the rack, C. Just before the hour, as
the boss of the lifting piece, A, lifts the rack hook B, the rack C,
impelled by a spring in its tail, falls back until the pin in the lower
arm of the rack is stopped by the snail, D. This occurs before the
lifting piece, A, is released by the pin in the minute wheel, E, and in
this position the warning piece stops the train. Exactly at the hour
the pin in the minute wheel, E, gets past the lifting piece, A, which
then falls, and the train is free. For every blow struck by the hammer
the gathering pallet, F, which is really a one-toothed pinion, gathers
up one tooth of the rack, C, which is then held, tooth by tooth, by
the point of the hook, B. After the pinion, F, has gathered up the last
tooth, its tail is caught by the pin in the rack, which stops and locks
the train, and the striking ceases.
The snail, O, is mounted on a twelve-toothed star wheel, placed on a
stud in the plate, so that a pin in the motion wheel on the center
arbor moves it one tooth for each revolution of the motion wheel, and
it is then held in position by the click and spring as shown. The pin,
in moving the star wheel, presses back the click, which not only keeps
the star wheel steady, but also completes its forward motion after the
pin has pushed the tooth past the projecting center of the click. The
steps of the snail are arranged so that at one o’clock it permits only
sufficient fall of the rack for one tooth to be gathered up, and at
every succeeding hour gives the rack an additional motion equal to one
extra tooth. It will be seen that where a star wheel is used a cord or
wire attached to A and run outside the case, so that A may be lifted,
will cause the clock to repeat the hour whenever desired.
The lower arm of the rack, C, and the lower arm of the lifting piece,
A, are made of brass, and thin, so as to yield when the hands of the
clock are turned back; the lower extremity of the lifting piece, A, is
a little wider, and bent to a slight angle with the plane of the arm,
so as not to butt as it comes into contact with the pin when this is
being done. If the clock is not required to repeat, the snail may be
placed upon the center arbor, instead of on a stud with a star wheel
as shown, and this is generally done with the cheaper class of hour
striking clocks; but the position of the snail is not then so definite,
owing to the backlash of the motion wheels, so that it will not repeat
correctly, as the pin of the rack may fall on a slope of the snail and,
besides, a smaller snail must be used, unless it is brought out to
clear the nose of the minute wheel cock, or bridge if one be used.
[Illustration: Fig. 104. Hour and half hour snail striking work with
fusee train.]
HALF-HOUR STRIKING.—The usual way of getting the clock to strike one
at the half-hour, is by making the first tooth of the rack, C, lower
than the rest, and placing the second pin in the minute wheel, E, a
little nearer the center than the hour pin, so that the rack hook,
B, is lifted free of the first tooth only at the half hour. But this
adjustment is too delicate after some wear has occurred and the action
is then liable to fail altogether or to strike the full hour, from the
pin getting bent or from uneven wear of the parts. The arrangement
shown in Fig. 104 is generally used in English work, as it is much
safer. One arm of a bell-crank lever rests on a cam fixed to the minute
wheel, E. This arm is shaped so that just before the half-hour the
other extremity of the bell-crank lever catches a pin placed in the
rack, C, and permits it to release the train and fall the distance
of but one tooth. This is the position shown in Fig. 104. After the
half-hour has struck, the cam carries the hook free from the pin in C.
[Illustration: Fig. 105. Rack, showing method of getting sizes of snail
steps according to distance from the rack center to the pin in the rack
tail.]
DIVISION OF THE HOUR SNAIL.—The length of the rack tail, from the
center of the stud hole in the rack to the center of the pin, should
be equal to the distance between the center of the stud hole and the
center of the snail. The difference between the radius of the top and
the radius of the bottom step of the snail may be obtained by getting
the angular distance of twelve teeth of the rack from center to pin.
See A B, C D, E F, Fig. 105, which show the total distances for twelve
steps of the snail for rack tails of different lengths. Divide the
circumference of a piece of brass into twelve parts and draw radial
lines as shown in Fig. 106. Each of these spaces is devoted to a step
of the snail. Draw circles representing the top and bottom step. Divide
the distance, A B or E F, Fig. 105, between these two circles, into
eleven equal parts, and at each division draw a circle which will
represent a step of the snail. The rise from one step to another should
be sloped as shown, so as to raise the pin in the rack arm if the
striking train has been allowed to run down, and it should be resting
on the snail when it is desired to turn the hands back. The rise from
the bottom to the top step is bevelled off, so as to push the pin in
the rack arm on one side, by springing the thin brass of the arm and
allow it to ride over the snail if it is in the way when the clock is
going. It should also be curved to avoid interference with the pin.
Clockmakers making new snails when repairing generally mark off the
snail on the clock itself after the rest of the striking work is in
position. A steel pointer is fixed in the hole of the lower rack arm,
and the star wheel jumped forward twelve teeth (one at a time) by means
of the pin in the motion wheel. After each jump a line is marked on the
blank snail with the pointer in the rack arm by moving the rack arm.
These twelve lines correspond to the twelve radial lines in Fig. 106.
The motion wheel is then turned sufficiently to carry the pin in it
free of the star wheel and leave the star wheel and blank snail quite
free on their stud. The rack hook is placed in the first tooth of the
rack, and while the pointer in the rack arm is pressed on the blank
snail, the latter is rotated a little, so that a curve is traced on
it. The rack hook is then placed in the second, and afterwards in the
succeeding teeth consecutively, and the operation repeated till the
twelve curves are marked. There is one advantage in marking off the
snail in this way. Should there be any inaccuracy in the division of
the teeth of the rack, the steps of the snail are thus varied to suit
it. This frequently occurs in old clocks which have had new racks filed
up by hand by some watchmaker.
Reference to the drawing, Fig. 105, will show that the rack is laid out
as a segment of a wheel with teeth occupying two degrees each, with a
few teeth added for safety. Fourteen to sixteen teeth are generally
provided, for the following reasons: If the first tooth is used to
strike the half hours, it may in time become worn so that it can no
longer be stretched to its proper length. In such cases moving the pin
two degrees nearer the rack teeth will allow us to use the teeth from
the second to the thirteenth in striking twelve, which makes a cheap
and easy repair, as compared to inserting a new tooth or making a new
rack.
Weight driven snail clocks should have the weight cords of the striking
side long enough so that the striking train will not run down before
the time train, as in such a case the rack tail is pushed to one side
by the progress of the snail (which is carried on the time train and
is still running); then the rack will drop clear out of reach of the
gathering pallet and when the striking train is wound that train will
continue striking until it runs down, or the dial is removed and the
rack replaced in mesh with the gathering pallet. This happens with
short racks and with large, old-fashioned snails. By leaving a few more
teeth in the rack the rack tail will strike the stud, or hour wheel
sleeve, before the rack teeth get out of reach of the gathering pallet.
Many watchmakers put a stud or pin in the plate to stop the rack from
falling beyond the twelfth step, to prevent troubles of this kind.
The rack tail is friction-tight on its arbor and should be adjusted so
that the proper tooth shall come in mesh with the gathering pallet for
each step of the snail, or irregular striking will result. Such a clock
may strike one, two, three and four correctly and then strike six for
five, or seven or nine for eight, or thirteen for twelve, or it may
strike one or two hours wrong and the rest correctly. This is because
the gathering pallet, F, Fig. 104, does not carry the rack teeth safely
past the edge of the rack hook, B, owing to the tail of the rack not
being properly adjusted. The teeth should all be carried safely past
the edge of the hook and then be dropped back a little as the hook
engages; this is the more necessary to watch with hand-made racks and
snails, or after putting in a new, and therefore larger, pin in the
rack tail to replace one which is badly worn.
[Illustration: Fig. 106. Laying out steps of snail.]
The snail should be put on so that the pin in the rack tail will strike
the center of each step, or there is danger of irregular striking, or
of failure to strike twelve, owing to the pin striking the surface of
the cam midway between one and twelve and thus preventing the rack
from falling the requisite number of teeth. When this occurs the clock
will jam and stop.
The rack hook, B, Fig. 104, should be lifted far enough so that the
rack will fall clear of the hook without the teeth catching and making
a rattling noise as they pass the hook. In many old hour strikes the
first tooth of the rack is left longer than the rest to ensure this
freedom of passage when the rack is released.
The gathering pallet, F, is the weakest member of the system and will
be very likely to be split or worn out in clocks brought in for repair.
It should be squared on its arbor, or pinned, but many are not. If
split, and the arbor is round, where the pallet is put on, it may cause
irregular striking by opening on the arbor and permitting the train
to run when the tail strikes the pin in the rack. A new one should be
made so as to lift one tooth and a very little of the next one at each
revolution. It is necessary to cause the gathering pallet to lift a
little more than one tooth of the rack, and let it fall back again, to
insure that one will always be lifted; because if such was not the case
the clock would strike irregularly, and would also be liable sometimes
to strike on continually till it ran down. If the striking part is
locked by the tail of the gathering pallet catching on a pin in the
rack, the tail should be of a shape that will best prevent the rack
from falling back when the clock warns for striking the next hour; and
of course the acting faces of the pallet must be perfectly smooth and
polished.
The teeth of the rack may require dressing up in some cases and to
allow this to be done the rack may be stretched a little at the stem,
with a smooth-faced hammer, on a smooth anvil; or, if it wants much
stretching, take the pene of the hammer and strike on the back, with
the front lying on the smooth anvil. The point of the rack hook, B,
will probably be much worn, and when dressing it up it will be safe
to keep to the original shape or angle. The point of the rack hook is
always broader than the rack, and the mark worn in it will be about
the middle of the thickness; so enough will be left to show what the
original shape or angle was.
After cleaning, particularly if it be French, look for dots on the
rims of the wheels, and for pinions with one end of one leaf filed off
slantingly. When putting it together, place the pin wheel (that is the
one with the pins) and the pinion it engages with so that the leaf of
the pinion (which you will find filed slanting at one extremity) enters
between the two teeth of the wheel, opposite which you will find a
countersunk mark, on the side of the wheel. See also that the gathering
pallet, F, which lifts the rack, does so at the same time that the gong
hammer falls. Then place the hour and minute wheels and cannon pinion
so that the countersunk marks on each line with each other. Neglect
of the marks on a marked train generally means that you will have to
take the clock down again and set it up properly before it will run;
therefore pay attention to these marks the first time.
QUARTER CHIMING SNAIL STRIKES.—Fig. 107 shows the counting mechanism
and trains of an English, fusee, quarter-strike work. The time train
occupies the center, the hour striking train the left and the chiming
train the right. All the train wheels are between the plates and are
dotted in as in Fig. 104, while the counting mechanism is on the front
plate, behind the dial and is drawn in full lines, to show that it is
outside.
GOING TRAIN.
Fusee Wheel 96
Pinion 8
Center Wheel 84
Pinion 7
Third Wheel 78
Pinion 7
STRIKING TRAIN.
Fusee Wheel 84
Pinion 8
Pin Wheel, 8 pins in Pin Wheel 64
Pinion 8
Pallet Wheel 70
Pinion 7
Warning Wheel 60
Fly Pinion 7
CHIMING TRAIN.
Fusee Wheel 100
Pinion 8
Second Wheel 80
Pinion 8
Pallet Wheel 64
Pinion 8
Chiming Wheel 40
Warning Wheel 50
Fly Pinion 8
The reader will see a marked resemblance between the hour and time
trains of Fig. 104 and the same trains of Fig. 107. The hour rack hook
in 107, however, is hung from the center and the hour warning lever is
raised by a spring instead of a lifting piece.
The minute wheel of Fig. 107 carries a snail of four steps,
corresponding to the four teeth of the quarter rack, and the tail of
the quarter rack is bent upwards towards the rack, to engage with the
quarter snail. The quarter rack carries a pin which projects on both
sides of the rack; one side of this pin stops the tail of the quarter
gathering pallet and therefore locks the train as fully described in
Fig. 104. The other side of the same pin acts on the tail of the hour
warning lever, so that whenever the quarter rack falls the hour warning
lever is released and its spring moves it into the path of the hour
warning pin. This goes on whether the hour rack hook is released or
not. Behind the quarter snail, there are four pins in the minute wheel;
these pins raise the quarter lifting piece, which raises the quarter
rack hook and the quarter warning lever at the same time, thus warning
and dropping the quarter rack; as soon as the lifting piece drops, the
warning lever and rack hook are released and the quarter train starts.
[Illustration: Fig. 107. Quarter chiming snail strike, English fusee
movement.]
[Illustration: Fig. 108. Eight day snail half hour strike, French
system, striking train locked.]
One, two, three, or four quarters are chimed according to the position
of the quarter snail, which turns with the minute wheel. At the time
for striking the hour (when the quarter rack is allowed to fall its
greatest distance), the pin in it falls against the bent arm of the
hour rack hook, and releases the hour rack and hour warning lever. As
the last tooth of the quarter rack is gathered up, the pin in the
quarter rack pulls over the hour warning lever, and lets off the hour
striking train. The position of the pieces in the drawing is as they
would be directly after the hour was struck.
Figs. 108, 109 and 110 are three views of the New Haven eight-day snail
strike, which is on the French system. As nearly all American strikes
utilize this system and the work is between the plates, this may be
considered a typical American snail strike.
As will be seen in Fig. 108, by the two pins at the center arbor,
immediately behind the snail, this is a half-hour strike; and as the
rack hook has for its lower step a little more than twice the depth of
the other steps in the snail, it will readily be perceived that this
rack hook may be pushed almost out and thus release the train without
dropping the rack. This is the method pursued in striking half hours.
Figs. 109 and 110 show the parts more clearly than in 108. They are
drawn a little larger than actual size and we will discover that the
rack is the only portion of this system that works by gravity, all the
others being spring operated. We see here the pins J K, which are used
to push out the lever M sufficiently far so that the upper portion,
which is bent at right angles to form a stop, will free the warning pin
O and allow the train to run. The rack hook and the locking lever L are
mounted on the same arbor and are kept in position by a coiled spring
on the arbor until they are pushed out by the lower projection at the
upper end of M for either the half-hour or hour strike.
As shown in Fig. 109, the lever M and the rack hook are pushed out by
J far enough to pass the warning pin O and to unlock the train, which
is normally locked by the pin N and the lever L. G is the gathering
pallet, which is a long pin in a lantern pinion as in the ordinary
count wheel strike. H is the hammer tail and P the pin wheel; R is the
rack and T the rack tail. The rack arm is curved to pass the center
arbor when dropping for twelve and the rack tail is bent toward the
teeth in order that it may admit of a longer rack in a small movement,
thus permitting of a large snail and consequently less liability of
disarrangement. The same necessity of the proper adjustment of the rack
tail T with the snail exists as has already been spoken of in regard to
the English form of the snail strike.
In Fig. 110 will be seen the rack dropped clear with the tail resting
clear of the snail at one stroke from the snail. In other words, the
train is now in position to give eleven more strokes, having struck the
first stroke of twelve. By comparison with Fig. 109, it will be seen
that the spring actuated arm M has been thrown forward so that its dog
is resting on the center arbor, after having been released from the
hour pin K. This holds M out of the way of the warning pin O and the
rack hook and allows the parts to operate as fully described with the
English rack.
The gathering pallet G must have as many teeth as there are teeth
between the pins in the pin wheel P. The train is locked by L coming in
contact with N, the locking pin on the wheel on the same arbor as the
gathering pallet. In setting this train up, it should stop so that the
warning pin O should be near the fly.
As all the parts are operated by springs on the arbor, as shown by the
hammer-spring H, it will be seen that this strike mechanism will work
in any position, while that which is operated by gravity must be kept
upright. A loose fly will cause the clock to strike too fast and may
cause it to strike wrong. Careless adjustment of the rack tail T with
the snail will also induce wrong counting, although this is somewhat
easier to adjust than the English form of strike. The hook should
safely clear the rack teeth just as the gathering pallet G lets go of
a tooth. If attention is paid to this point in adjusting the rack tail
there will generally be little trouble.
[Illustration: Fig. 109. Train about to strike the half hour; the hook
L free of the train, which is held by the warning pin O; one stroke
will be given when M drops.]
The cam bearing the pins J K on the center arbor may be shifted with
a pair of pliers to secure accurate register of hands and strike, as
is the case with most American strikes. In putting in the pin wheel it
should be set so that the pins may have a little run before striking
the hammer tail, as this hammer tail is very short, and if the spring
is strong the pins may not be able to lift the hammer tail without
sufficient run to get the train thoroughly under motion. The half-hour
strike should also be tested so that the pin J will release the warning
pin O from the lever M without releasing the rack hook from the rack,
as shown in Fig. 109. The parts of the train when at rest will be
readily discerned in Fig. 108, where the hook L has locked the train by
the pin N and the freedom between the pins and the hammer tail is about
what it should be.
[Illustration: Fig. 110. Train unlocked and running. Note position of L
and M.]
The relative position of the locking lever L and the rack hook is also
very clearly shown in Fig. 108; that is, when the rack hook is pressed
clear home at the lower notch of the rack, the lever L should safely
lock the train and the lever M be resting with its link against the
center arbor.
CHAPTER XIX.
THE CONSTRUCTION OF SIMPLE AND PERPETUAL CALENDARS.
In taking up the study of calendar work the first thing that the
student observes is the irregularity of motion of the various members.
Every other portion of a clock has for its main object the attainment
of the nicest regularity of motion, while the calendar must necessarily
have irregular motion. The hand of the day of the month proceeds around
its dial regularly from 1 to 28 and then jumps to 1 in February of
some years, while it continues to 29 in others; sometimes it revolves
regularly from 1 to 31 for several revolutions and then jumps from 30
to 1. What is the reason of this?
If the moon’s phases are shown they do not agree with the changes of
the month wheels, but keep gaining on them, while if an “equation of
time” is shown, we have a hand that moves irregularly back and forth
from the Figure XII at the center of its dial. What is the cause of
this gaining and losing?
In order to understand this mechanism properly we shall have to first
know what it is intended to show and this brings us to the study of the
various kinds of calendar.
The earth revolves about its axis with a circular motion; it revolves
about the sun with an elliptical motion. This means that the earth
will move through a greater angular distance, measured from the sun’s
center, in a given time at some portions of its journey than it will
do at others; at times the sun describes an arc of 57 minutes of the
ecliptic; at other times an arc of 61 minutes in a day; hence the sun
will be directly over a given meridian of the earth (noon) a little
sooner at some periods than at others. Now the time at which the sun
is directly over the given meridian is _apparent_ noon, or solar noon.
As before stated, this is irregular, while the motion of our clocks is
regular, consequently the sun crosses the meridian a little before or
a little after twelve by the clock each day, varying from 15 minutes
before twelve to 15 minutes after twelve by the clock. The best we can
do under these circumstances is to divide these differences of gaining
or losing, take the average or _mean_ of them and regulate the clock to
keep _mean_ time. Here then we have two times—the irregular _apparent_
time and the regular _mean apparent_ time. The amount to be added to or
subtracted from the mean in order to get the solar or actual apparent
time is called the _equation_ of time and this is shown by the equation
hand on an astronomical or perpetual calendar clock.
The moon revolves on its axis with a circular motion and it revolves
about the earth with an elliptical motion, the earth being at one focus
of the ellipse; as this course does not agree with that of the sun, but
is shorter, it keeps gaining so that the lunar months do not agree with
the solar.
Certain stars are so far away that they apparently have no motion of
their own and are called _fixed_; hence in observing them the only
motion we can discern is the circular motion of the earth. We can
set our clocks by watching such stars and a complete revolution of
the earth, measured by such a star, is called an _astronomical_ or
_sidereal_ day. This is the one used in computing all our time. It is
shorter than the _mean solar_ day by 3 minutes 56 seconds.
A _year_ is defined as the period of one complete revolution of the
earth about the sun, returning to the same starting point in the
heavens. By taking different starting points we are led to different
kinds of years. The point generally taken is the vernal equinoctial
point, and when measured thus it is called the _tropical_ year, which
gives us the seasons. It is 20 minutes shorter than the siderial year.
A _siderial year_ is the period of a complete revolution of the earth
about the sun. This period is very approximately 365 days, 6 hours, 9
minutes, 9.5 seconds of mean time. Here we see an important difference
between the siderial and the _civil_ year of 365 days, and it is this
difference, which must be accounted for somehow, that causes the
irregularities in our calendar work.
For ordinary and business purposes the public demands that the year
shall contain an exact number of days and that it should bear a simple
relation to the recurrence of the seasons. For this reason the _civil_
year has been introduced. The Roman emperor, Julius Caesar, ordered
that three successive years should have 365 days each and the fourth
year should have 366 days.
The fourth year, containing 366 days, is called a _leap_ year, because
it leaps over, or gains, the difference between the civil and siderial
time of the preceding three years. For convenience the leap year was
designated as any year whose number is exactly divisible by 4. This is
called the Julian calendar.
But as a siderial year is 365 days, 6 hours, 9 minutes, 9.5 seconds
of mean time, the addition of one day of twenty-four hours would not
exactly balance the two calendars; therefore Pope Gregory XIII., in
1582, ordered that every year whose number is a multiple of 100 shall
be a year of 365 days, unless the number of the year is divisible by
400, when it shall be a leap year of 366 days.
The calendar constructed in this way is called the Gregorian calendar,
and is the one in common use. Its error is very small and will amount
to only 1 day, 5 hours, 30 minutes in 4,000 years.
The revolution of the moon around the earth in relation to the _stars_,
takes place in 27 days, 7 hours and 43 minutes this is called a
_siderial_ month. But during this period the earth has advanced along
the plane of its path about the sun and the moon must make up this
distance in order to return to the same point in relation to the sun.
This period is called a _synodic_ month. Its average length is 29 days,
12 hours, 44 minutes, 2.9 seconds.
Having now understood these differences we shall be able to
intelligently examine the various calendar mechanisms on the market
and understand the reasons for their apparent departures from regular
mechanical progression, as the equation of time gives us the difference
between _real_ and _mean_ apparent, or solar time; we regulate our
clocks by means of siderial time; the irregular procession of 30 and 31
days makes the civil calendar agree with the seasons, or the tropical
year, and the remainder of the discrepancy between civil and siderial
time is made up in February at the period when it is of the least
consequence.
SIMPLE CALENDAR WORK.—Fig. 111 shows the American method of making a
simple calendar, the example shown being drawn from a movement of the
Waterbury Clock Company as a typical example. No attempt is made here
to show the day of the week or the month. The days of the month are
shown by a series of numbers from 1 to 31, arranged concentrically with
the time dial and the current day is indicated by a hand of different
color, carried on a pipe outside the pipe of the hour hand on the
center arbor.
[Illustration]
[Illustration: Fig. 111. Simple calendar on time train.]
[Illustration: Fig. 112. Calendar work for grandfather clocks.]
In order to accomplish this the motion work for the hands is mounted
inside the frames, the hour pipe and center arbor being suitably
lengthened. In the Figure A is the cannon pinion; B, the minute wheel;
C, the minute pinion; D, the hour wheel at the rear end of the hour
pipe; this pipe projects through the frame and forms a bearing in the
frame for the center arbor. Friction-tight on the hour pipe, in front
of the front plate, is the pinion E, which drives a wheel F of twice
as many teeth. This wheel F is mounted loosely on a stud and has a pin
which meshes with the teeth of a ratchet wheel G. G is carried at the
bottom end of a pipe which fits loosely on the hour pipe and carries
the calendar hand H under the hour hand and close to the dial. The
pinion on the hour pipe revolves once in twelve hours. The wheel E has
twice as many teeth and will therefore revolve once in twenty-four
hours. It moves the ratchet G one tooth at each revolution; therefore
the hand H moves one space every twenty-four hours. There are 31
teeth, so that the hand must be set forward every time it reaches the
28th and 29th of February and the 30th of April, June, September and
November. This is the simplest and cheapest of all the calendars,
occupies the least space and is frequently attached to nickel alarm
clocks for that reason.
A simple calendar work often met with in old clocks of European origin
is shown in Fig. 112. Gearing with the hour wheel is a wheel, A, having
twice its number of teeth, and turning therefore once in twenty-four
hours. A three-armed lever is planted just above this wheel; the lower
arm is slotted and the wheel carries a pin which works in this slot, so
that the lever vibrates to and fro once every twenty-four hours. The
three upper wheels, B, C and D in the drawing, represent three star
wheels. B has seven teeth, corresponding to the days of the week; C
has 31 teeth, for the days of the month; and D has 12 teeth, for the
months of the year. Each carries a hand in the center of a dial on the
other side of the plate. Every time the upper arms of the lever vibrate
they move forward the day of the week, B, and the day of the month,
C, wheels each one tooth. The extremities of the two upper levers are
jointed so as to yield on the return vibration, and are brought into
position again by a weak spring. There is a pin in the wheel, C, which,
by pressing on a lever once every revolution, actuates the month of
the year wheel, D. This last lever is also jointed, and is pressed on
by a spring so as to return to its original position. Each of the star
wheels has a click kept in contact by means of a spring. For months
with less than 31 days, the day of the month hand has to be shifted
forward.
PERPETUAL CALENDAR WORK.—Figs. 113, 114, 115, show a perpetual calendar
which gives the day of the week, day of the month and the month, making
all changes automatically at midnight, and showing the 31 days on a
dial beneath the time dial, by means of a hand, and the days of the
week and the month by means of cylinders operating behind slots in the
dial on each side of the center. This is also a Waterbury movement.
[Illustration: Fig. 113. Perpetual Calendar Movement.]
A pinion on the hour pipe engages a wheel, A, having twice the number
of teeth and mounted on an arbor which projects through both plates.
The rear end of this arbor carries a cam, B, on which rides the end of
a lever, C, which is pivoted to the rear frame. The lever is attached
to a wire, D, which operates a sliding piece, E, which is weighted at
its lower end. The cam, which, of course, revolves once in twenty-four
hours, drops its lever at midnight and the weight on E pulls it down.
E bears a spring pawl, F, which on its way down, raises the spring
actuated retaining click, H, and then moves the 31-toothed wheel G one
notch. This wheel is mounted on the arbor which carries the hand and,
of course, advances the hand.
Lying on top of the wheel, G, is a cam, I, pivoted to G near its
circumference and having an arm reaching toward the months cylinder
and another reaching towards the right leg of the pawl, H, while it is
cut away in the center, so as to clear the center arbor carrying the
hand. Trace this cam, I, carefully in Figs. 113 and 114, as its action
is vital. The lower arm of this cam is shown more clearly in Fig. 114.
It projects above the wheel and engages the long teeth, J, and the
cam, K, mounted on the year cylinder arbor; where the lower arm of I
strikes one of these teeth it shoves the upper arm outward, so that
it strikes the retaining end of the pawl, H, and holds it up, and the
descending pawl, F, may then push the wheel, G, forward for _more_ than
one tooth. The upper end of I is broad enough to cover three teeth of
the wheel, G, when pushed outward, and the slot in E is long enough so
that F may descend far enough to push G forward three teeth at once,
unless it is stopped by H falling into a tooth, so that the position of
I, when it is holding up H and the extra drop thus given to E serve to
operate the jumps of 30 to 1, 28 to 1 and 29 to 1 of the hand on the
dial. The teeth, J, Fig. 114, operate for two notches, thus making the
changes from 30 to 1. The wide tooth, M, and cam, K, acting together,
make the change for February from 28 to 31. The 29th day is added by
the movement of the cam, K, narrowing the acting surface once in four
years, as follows:
[Illustration: Fig. 114. The months change gear.]
Looking at Fig. 114 we see an ordinary stop works finger, mounted on
the months arbor and engaging a four-armed maltese cross on the wheel.
Behind the wheel is a circular cam (shown dotted in) with one-fourth of
its circumference cut away; the pivot holds the cam and cross rigidly
together while permitting them to revolve loosely in the wheel. The
cam, K, lies close to the wheel and is pressed against the cam on the
cross by a spring, so that ordinarily the full width of M and K act as
one piece on the end of the cam, I, which thus is pressed against the
retaining pawl, H, during the passage of three teeth, making the jump
from 28 to 1 each of these three years.
The fourth revolution of the maltese cross brings the cut portion of
its cam to operate on K and allows K to move behind M, thus narrowing
the acting surface so that I only covers two teeth (30 and 31) for
every fourth revolution of the month’s cylinder, thus making the leap
year every fourth year.
The months cylinder is kept in position by the two-armed pawl, N,
engaging the teeth, L, which stand at 90 degrees from the wheel, as
shown in Fig. 113. Attached to the bearing for the week cylinder (not
shown) is one revolution of a screw track, or worm, surrounding the
arbor for the hand. Attached to the arbor is a finger, O, held taut by
a spring and engaging the track, P. The revolution of the arbor raises
O on P until it slips off, when O, drawn downward by its spring, raises
the pawl, N, drops on one of the teeth, L, and revolves the cylinder
one notch.
Q is a shifter for raising the pawl, H, and allowing the hand to be
set.
[Illustration: Fig. 115. The weeks change gear.]
Fig. 115 shows the inner end of the cylinder for the days of the week.
There are two sets of these and fourteen teeth on the sprocket, R, so
as to get the two cylinders approximately the same size (there being
14 days and 12 months on the respective cylinders). S is a pawl whose
upper end is forked so as to embrace a tooth and hold the cylinder in
position. T is a hook, carried on the sliding piece, E, which swings
outward in its upward passage as E is raised and on its downward course
raises the pawl, S, and revolves the sprocket, R, one tooth, thus
changing the day of the week at the same time the hand is advanced.
To set the calendar, raise the pawl, N, and revolve the year cylinder
until M and K are at their narrowest width; that is, a leap year. Then
give the year cylinder as many additional turns as there are years
since the last leap year, stopping on the current month of the current
year. For instance, if it is two years and four months since the 29th
of February last occurred, give the cylinder 2 and ⁴/₁₂ turns which
should bring you to the current month, raise the shifter, Q, and set
the hand to the current day. Then raise the pawl, S, and set the week
cylinder to the current day. Place the hour hand on the movement so
that the cam will drop E at midnight.
Fig. 116 shows the dial of Brocot’s calendar work, which, with or
without the equation of time and the lunations, is to be met with in
many grandfather, hall and astronomical clocks. We will assume that
all of these features are present, in order to completely cover the
subject. It consists of two circular plates of which the front plate
is the dial and the rear plate carries the movement, arranged on both
sides of it. All centers are therefore concentric and we have marked
them all with the same letters for better identification in the various
views as the inner plate is turned about to show the reverse side, thus
reversing the position of right to left in one view of the inner plate.
Fig. 117 shows the wheel for the phases of the moon, which is mounted
on the outside of the inner plate immediately behind the opening in the
dial. The dark circles have the same color as the sky of the dial and
the rest is gilt, white or cream color to show the moon as in Fig. 116.
The position of this plate is also shown in Fig. 120. By the dotted
circles, about the center D.
[Illustration: Fig. 116. Dial of Brocot’s Calendar.]
The inner side containing the mechanism for indicating the days of the
week and the days of the month is shown in Fig. 118. The calendar is
actuated by means of a pin, C, fixed to a wheel of the movement which
turns once in twenty-four hours in the manner previously described
with Fig. 113. Two clicks, G and H, are pivoted to the lever, M. G,
by means of its weighted end, see Fig. 119, is kept in contact with a
ratchet wheel of 31 teeth, and H with a ratchet wheel of 7 teeth. As
a part of these clicks and wheels is concealed in Fig. 118, they are
shown separately in Fig. 119.
When the lever, M, is moved to the left as far as it will go by the
pin, e, the clicks, G and H, slip under the teeth; their beaks pass on
to the following tooth; when e has moved out of contact the lever, M,
falls quickly by its own weight, and makes each click leap a tooth of
the respective wheels, B of 7 and A of 31 teeth. The arbors of these
wheels pass through the dial (Fig. 116), and have each an index which,
at every leap of its own wheel, indicates on its special dial the
day of the week and the day of the month. A roll, or click, kept in
position by a sufficient spring, keeps each wheel in its place during
the interval of time which separates two consecutive leaps.
This motion clearly provides for the indication of the day of the week,
and would be also sufficient for the days of the month if the index
were shifted by hand at the end of the short months.
To secure the proper registration of the months of 30 days, for
February of 28 during three years, and of 29 in leap year, we have the
following provision: The arbor, A, of the day of the month wheel goes
through the circular plate, and on the other side is fixed (see Fig.
120) a pinion of 10 leaves. This pinion, by means of an intermediate
wheel, I, works another wheel (centered at C) of 120 teeth, and
consequently turning once in a year. The arbor of this last wheel bears
an index indicating the name of the month, G, Fig. 116. The arbor, C,
goes through the plate, and at the other end, C, Fig. 118, is fixed a
little wheel gearing with a wheel having four times as many teeth, and
which is centered on a stud in the plate at F. This wheel is partly
concealed in Fig. 118 by a disc V, which is fixed to it, and with
the wheel makes one turn in four years. On this disc, V, are made 20
notches, of which the 16 shallowest correspond to the months of 30
days; a deeper notch corresponds to the month of February of leap year,
and the last three deepest to the month of February common years in
each quarternary period. The uncut portions of the disc correspond to
the months of 31 days in the same period. The wheel, A, of 31 teeth,
has a pin (i) placed before the tooth which corresponds to the 28th of
the month. On the lever, M, is pivoted freely a bell-crank lever (N),
having at the extremity of the lower arm a pin (o) which leans its own
weight upon the edge of the disc, V, or upon the bottom of one of the
notches, according to the position of the month, and the upper arm of N
is therefore higher or lower according to the position of the pin, o,
upon the disc.
[Illustration: Fig. 117. Dial of Moon’s Phases.]
[Illustration: Fig. 118. Brocot’s Calendar; Rear View of Calendar Plate
showing Four Year Wheel and Change Mechanism.]
[Illustration: Fig. 119. Change Mechanism behind the Four Year Wheel in
Fig. 118]
It will be easy to see that when the pin, o, rests on the contour
of the disc the upper arm, N, of the bell-crank lever is as high as
possible, and out of contact with the pin as it is dotted in the
figure, and then the 31 teeth of the month wheel will each leap
successively one division by the action of the click, G, as the lever,
M, falls backward till the 31st day. But when the pin, o, is in one of
the shallow notches of the plate, V, corresponding to the months of
30 days, the upper arm, N, of the bell-crank lever will take a lower
position, and the inclination that it will have by the forward movement
of the lever, M, will on the 30th bring the pin, i, in contact with the
bottom of the notch, just as the lever, M, has accomplished two-thirds
of its forward movement, so the last third will be employed to make the
wheel 31 advance one tooth, and the hand of the dial by consequence
marks the 31st, the quick return of the lever, M, as it falls putting
this hand to the 1st by the action of the click, G. If we suppose the
pin, o, is placed in the shallowest of the four deep notches, that
one for February of leap year, the upper end of the arm, N, will take
a position lower still, and on the 29th the pin, i, will be met by
the bottom of the notch, just as the lever has made one-third of its
forward course, so the other two-thirds of the forward movement will
serve to make two teeth of the wheel of 31 jump. Then the hand of the
dial, A, Figs. 116 and 118, will indicate 31, and the ordinary quick
return of the lever, M, with its detent, G, will put it to the 1st.
Lastly, if, as it is represented in the figure, the pin, o, is in one
of the three deepest notches, corresponding to the months of February
in ordinary years, the pin will be in the bottom of the notch on the
28th just at the moment the lever begins its movement, and three teeth
will pass before the return of the lever makes the hand leap from the
31st to the 1st.
The pin, o, easily gets out of the shallow notches, which, as will be
seen, are sloped away to facilitate its doing so. To help it out of
the deeper notches there is a weighted finger (j) on the arbor of the
annual wheel. This finger, having an angular movement much larger than
the one of the disc, V, puts the pin, o, out of the notch before the
notch has sensibly changed its position.
PHASES OF THE MOON.—The phases of the moon are obtained by a pinion of
10, Fig. 120, on the arbor, B, which gears with the wheel of 84 teeth,
fixed on another of 75, which last gears with a wheel of 113, making
one revolution in three lunations. By this means there is an error
only of .00008 day per lunation. On the wheel of 113 is fixed a plate
on which are three discs colored blue, having between them a distance
equal to their diameter, as shown in Fig. 117, these discs slipping
under a circular aperture made in the dial, produce the successive
appearance of the phases of the moon.
EQUATION OF TIME.—On the arbor of the annual wheel, C, Figs. 116, 118,
120, is fixed a brass cam, Y, on the edge of which leans the pin, s,
fixed to a circular rack, R. This rack gears with the central wheel, K,
which carries the hand for the equation. That hand faces XII the 15th
of April, 14th of June, 1st of September and the 25th of December. At
those dates the pin, s, is in the position of the four dots marked on
the cam, Y. The shape of the cam, Y, must be such as will lead the hand
to indicate the difference between solar and mean time, as given in the
table of the Nautical almanac.
To set the calendar first see that the return of the lever, M, be made
at the moment of midnight. To adjust the hand of the days of the week,
B, look at an almanac and see what day before the actual date there
was a full or new moon. If it was new moon on Thursday, it would be
necessary, by means of a small button fixed at the back, on the arbor
of the hand of the wheel, B, of the week, to make as many returns as
requisite to obtain a new moon, this hand pointing to a Thursday;
afterward bring back the hand to the actual date, passing the number
of divisions corresponding to the days elapsed since the new moon. To
adjust the hand of the day of the month, A, see if the pin, o, is in
the proper notch. If for the leap year, it is in the month of February
in the shallowest of the four deep notches (o); if for the same month
of the first year after leap year, then the pin should be, of course,
in the notch, I, and so on.
[Illustration: Fig. 120. Brocot’s Calender: Wheels and Pinions under
the Dial with their Number of Teeth.]
CHAPTER XX.
HAMMERS, GONGS AND BELLS.
Just as the tone of a piano depends very largely upon the condition
of the felts on the hammers which strike the wires, so does the tone
of a clock gong or bell depend on its hammer action. The deep, soft,
resonant tone in either instance depends on the vibration being
produced by something softer than metal. Ordinarily this condition is
reached by facing the hammer with leather. The second essential is that
the hammer shall immediately rebound, clear of the bell, so as not
to interfere with the vibrations it has set up in the bell, wire or
tube. As the leather gets harder the tone becomes harsher and “tinny,”
sometimes changing to another much higher tone and entirely destroying
the harmony. The remedy is either to oil the leather on the hammers,
or if they are much worn to substitute new and thicker leathers until
the tone is sufficiently mellowed, so that a vigorous blow will still
produce a mellow tone of sufficient carrying power. A piece of round
leather belting will be found very convenient for this purpose.
The superiority of a chiming clock lies in its hammer action. If this
mechanism is not perfect, only inferior results can be obtained. The
perfect hammer is the one that acts with the smallest strain and is
operated with the least power. Heavy weights create a tremendous
strain on the mechanism and bring disastrous results when one of the
suspending cords break. The method of lifting the hammer is one of
importance, and the action of the hammer-spring is but seldom right on
old clocks brought in for repairs, especially if it be a spring bent
over to a right angle at its point. If there are two springs, one to
force the hammer down after the clock has raised it up, and another
shorter one, fastened on to the pillar, to act as a counter-spring and
prevent the hammer from jarring on the bell, there will seldom be any
difficulty in repairing it; and the only operation necessary to be
done is to file worn parts, polish the acting parts, set the springs a
little stronger, and the thing is done. But if there is only one spring
some further attention will be necessary, because the action of the
one spring answers the purpose of the two previously mentioned, and to
arrange it so that the hammer will be lifted with the greatest ease and
then strike on the bell with the greatest force, and without jarring,
requires some experience. That part of the hammer-stem which the spring
acts on should never be filed or bent beyond the center of the arbor,
as is sometimes done, because in such a case the hammer-spring has
a sliding motion when it is in action, and some of the force of the
spring is thereby lost. The point of the spring should also be made to
work as near to the center of the arbor as it is possible to get it,
and the flat end of the spring should be at a right angle with the edge
of the frame, and that part of the hammer-stem that strikes against the
flat end of the spring should be formed with a curve that will stop the
hammer in a particular position and prevent it jarring on the bell.
This curve can only be determined by experience; but a curve equal to a
circle six inches in diameter will be nearly right.
The action of the pin wheel on the hammer tail is also of importance.
The acting face of the hammer tail should be in a line with the center
of the pin wheel, or a very little above it, but never below it, for
then it becomes more difficult for the clock to lift the hammer, and
the hammer tail should be of such a length as to drop from the pins of
the pin wheel, and when it stops be about the distance of two teeth
of the wheel from the next pin. This allows the wheel-work to gain a
little force before lifting the hammer, which is sometimes desirable
when the clock is a little dirty or nearly run down. We might also
mention that in setting the hammer-spring to work with greater force
it is always well to try and stop the fly with your finger when the
clock is striking, and if this can be done it indicates that the hammer
spring is stronger than the striking power of the clock can bear, and
it ought to be weakened, because the striking part will be sure to stop
whenever the clock gets the least dirty.
Gong wires are also the cause of faulty tones. In the factories these
are made by coiling wires of suitable lengths and sections on arbors in
a lathe. They are then heated to a dull red and hardened by dipping in
water or oil. After cooling they are trued in the round and the flat
like a watch hairspring and then drawn to a blue temper. The tone comes
with the tempering, and if they are afterwards bent beyond the point
where they will spring back to shape the tone is interfered with. Many
repairers, not being aware of this fact, have ruined the tone of a gong
wire while trying to true it up by bending with pliers. When the owner
is particular about the tone of the clock, a new gong should always be
put in if the old one is badly bent.
The wires are soldered to their centers and if they are at all loose
they should be refastened in the same manner if it can be done without
drawing the temper of the wire. When this cannot be done a plug of
solder may be driven in between the wire and the side of the hole so as
to stop all vibration or the solder already in place may be driven down
so as to make all tight, as any vibration at this point will interfere
with the tone.
[Illustration: Fig. 121. The pins in the chiming barrels.]
TUNING THE BELLS.—Bells only very slightly out of tone offend the
musical ear, and they may easily be corrected to the extent of half
a tone. To sharpen the tone make the bell shorter by turning away
the edge of it if it be a shell, or by cutting off if it be a rod or
tube; to flatten the tone, thin the back basin-shaped part of the bell
by turning some off the outside. Bells which are cracked give a poor
sound because the edges of the crack interfere with each other when
vibrating. They may be repaired by sawing through the crack to the end
of it, so that the edges will not touch each other when vibrating. If
there is danger of the crack extending further into the bell, first
drill a round hole in the solid metal just beyond the end of the crack,
and then saw through into the hole; this will generally prevent any
further trouble.
MARKING THE CHIME BARREL.—The chime barrel in small clocks is of brass
and should be as large in diameter as can be conveniently got in. To
mark off the positions of the pins for the Cambridge chimes, first put
the barrel in the lathe and trace circles round the barrel at distances
apart corresponding to the positions of the hammer tails. There are
five chimes of four bells each for every rotation of the barrel, and a
rest equal to two or three notes between each chime. Assuming the rest
to be equal to three notes, divide the circumference of the barrel into
thirty-five equal parts by means of an index plate, and draw lines at
these points across the barrel with the point of the tool by moving it
with the slide rest screw. Call the hammer for the highest note D, and
that for the lowest note F. Then the first pin is to be inserted where
one of the lines across the barrel crosses the first circle; the second
pin where the next line crosses the second circle; the third pin where
the third line crosses the third circle and the fourth pin where the
fourth line crosses the four circle, because the notes of the first
chime are in the order, D, C, Bb, F. Then miss three lines for the
rest. The first note of the second chime is Bb and the pins for it will
consequently be inserted where the first line after the rest crosses
the third circle, and so on. Where two or more notes on the same bell
come so close as to make it difficult to strike them properly, it is
usual to put in another hammer, as it shown in Fig. 121, where there
are two Fs. In fine clocks the pins are of varying lengths so as to
strike the hammers on the bells with varying force and thus give more
expression to the music.
The following gives the Cambridge Chimes, which are used in the
Westminster Great Clock. They are founded on a phrase in the opening
symphony of Handel’s air, “I know that my Redeemer liveth,” and were
arranged by Dr. Crotch for the clock of Great St. Mary’s, Cambridge, in
1793.
[Illustration: Fig. 122. Westminster chimes.]
In Europe these chiming clocks are sometimes very elaborate, as the
following description of a set of bells in Belgium will show:
“So far as the experience of the writer goes the Belgian carillons are
invariably constructed on one prevailing plan, with the exception that
the metal used for the cylinder is generally brass; here, however, it
is of steel, and consists of a large barrel measuring 4 feet 2 inches
in width and 3 feet 6 inches in diameter, its surface being pierced
with horizontal lines of small square holes about ⅜ inch square. There
are lines of 60 of these in the width of the barrel, while there are
120 lines of them round the circumference, making a total of 7,200
holes. The drilling of these, of course, takes place when the cylinder
is made, and, so far as this part is concerned, the barrel is complete
before it is brought to the tower.
“Into these square holes are fixed the ‘pins,’ adjusted on the inside
of the cylinder by nuts.
“The pins are of steel of finely graduated sizes, corresponding with
the value of the notes of music. Some idea of the precision obtainable
may be gathered by the fact, as the carillonneur told the writer, that
there were no less than 24 grades of pins, so as to insure the greatest
accuracy of striking the bells.
“Over the cylinder are 60 steel levers with steel nibs; these are
lifted by the ‘pins’ and, connected by wires with the hammers, strike
the bells.
“The 35 bells are furnished with 72 hammers, which are fixed as
ordinary clock-hammers outside of the bells; three of the bells (in
the ring of eight) have a single hammer only, the limited space in the
‘cage’ making it impossible to put more, while others are supplied with
two or three apiece for use in rapidly repeating notes of the music. On
a visit some years ago to the carillon at Malines, the writer noticed
that some of the bells there had no less than five hammers apiece.
“Obviously, though there are 72 hammers in connection with the
carillon, only 60, corresponding with the number of levers, can be used
at one time; these are selected according to the requirement of the
tune; in case of new tunes, the wires can easily be adjusted so as to
bring other hammers and bells into use.
“The feature of the Belgian carillons is that instead of the single
notes of the air being struck as with the old familiar ‘chimes’
harmonized tunes of great intricacy are rendered with chords of three,
four or even five bells striking at one time.
“The cylinder here is capable of 120 ‘measures’ of music, but as, a
matter of fact it is subdivided so that half a revolution plays every
hour.
“A march is, as a rule, played at the odd hours, and the national air
at the even, but the bells are silent after 9 p. m. and start again at
8 a. m.
“The motive power is supplied by a weight of 8 cwt., and is controlled
by a powerful fly of four fans artistically formed to represent swans.
It may be mentioned that the keyboard for hand-playing consists of
thirty-five keys of wood and eleven pedals; these, as indeed the whole
apparatus of this part, are entirely separate from the automatic
carillon; in this instance the keys connect with the clappers of
the bells and have no association with the hammers. The pedals are
connected with the eleven largest bells and are supplementary to the
hour key.”
TUBULAR CHIMES are tubes of bell metal, cut to the proper lengths to
secure the desired tones and generally, but not always, nickel plated.
As they take up much room in the clock, they are generally suspended
from hooks at the top of the back board of the case, being attached to
the hooks by loops of silk or gut cords, passed through holes drilled
in the wall of the tubes near the top ends. The hour tube, being long
and large, generally extends nearly to the bottom of a six-foot case,
while the others range upwards, shortening according to the increase of
pitch of the notes which they represent.
This makes it necessary to place the movement on a seat board and
hang the pendulum from the front plate of the movement, so that such
clocks have, as a rule, comparatively light pendulums. On account of
the position and the great spread of the tubes, the chiming cylinder
and hammers are placed on top of the movement, parallel with the
plates, and operated from the striking train by means of bevel gears or
a contrate wheel. The hammers are placed vertically on spring hammer
stalks and connected with the chiming cylinder levers by silken cords.
This gives great freedom of hammer action and results in very perfect
tones. The hammers must of course be each opposite its own tube and
thus they are rather far apart, which necessitates a long cylinder.
This gives room for several sets of chimes on the same cylinder if
desired, as a very slight horizontal movement of the cylinder would
move the pins out of action with the levers and bring another set into
action or cause the chimes to remain silent.
Practically all of the manufacturers of “hall” or chiming clocks import
the movements and supply American cases, hammers and bells. The reason
is that there is so little sale for them (from a factory standpoint)
that one factory could supply the world with movements for this class
of clocks without working overtime, and therefore it would be useless
to make up the tools for them when they can be bought without incurring
that expense.
CHAPTER XXI.
ELECTRIC CLOCKS AND BATTERIES.
Electric clocks may be divided into three kinds, or principal
divisions. Of the first-class are those in which the pendulum is driven
directly from the armature by electric impulse, or by means of a weight
dropping on an arm projecting from the pendulum. In this case the
entire train of the clock consists of a ratchet wheel and the dial work.
The second class comprises the regular train from the center to the
arbor. This class has a spring on the center arbor, wound more or less
frequently by electricity. In this case the aim is to keep the spring
constantly wound, so that the tension is almost as evenly divided as
with the ordinary weight clock, such as is used in jewelers’ regulators.
The third system uses a weight on the end of a lever connected with
a ratchet wheel on the center arbor and does away with springs. One
type of each of these clocks will be described so that jewelers may
comprehend the principles on which the three types are built.
[Illustration: Fig. 123. Gillette Clock (Pendulum Driven).]
In the Gillette Electro-Automatic, which belongs to the class first
mentioned, the ordinary clock principle is reversed. Instead of the
works driving the pendulum, the pendulum drives the train, through
the medium of a pawl and ratchet mechanism on the center arbor. The
pendulum is kept swinging by means of an impulse given every beat by an
electromagnet. This impulse is caused by the weight of the armature as
it falls away from the magnet ends, the current being used solely to
pull back and re-set the armature for the next impulse. Any variation
in the current, therefore, does not affect the regulation of the clock,
as the power is obtained from gravity only, by means of the falling
weight. Referring to the drawings, Figs. 123 and 124, it is seen that
each time the pendulum swings the train is pushed one tooth forward.
A cam is carried by the ratchet (center) arbor in which a slot is
provided at a position equivalent to every fifth tooth of the ratchet.
Into this slot drops the end of a lever, releasing at its other end
the armature prop. Thus at the next beat of the pendulum the armature
is released and in its downward swing impulses the pendulum, giving it
sufficient momentum to carry it over the succeeding five swings.
The action of the life-giving armature is entirely disconnected and
independent of the clock mechanism. It acts on its own accord when
released every tenth beat and automatically gives its impulse and
re-sets itself. It is provided with a double-acting contact spring (see
Fig. 125) which “flips” a contact leaf from one adjustable contact
screw to the other as the action of the armature causes the spring to
pass over its dead center. Thus, when the armature reaches the lowest
point in its drop (Figs. 126 and 127) the leaf snaps against the right
contact screw, the circuit is completed, the magnet energized and
the armature drawn up. As the armature rises above a certain point,
the dead center of the flipper spring is again crossed and the leaf
snaps back against the post at the left. In the meantime, however, the
armature prop has slipped under the end of the armature and retains it
until the time comes for the next impulse.
[Illustration: Fig. 124. Side View.]
In adjusting the mechanism of this type of clock the increasing
pendulum swing should catch and push the ratchet before the buffer
strikes and lifts the armature from the prop. The adjustment of the
“flipper” contact screws (with ¹/₃₂ inch play) should be such that as
the armature falls the contact leaf will be thrown and the armature
drawn up at a point just beyond the half way position in the swing of
the pendulum. The power of the impulse can be regulated by turning the
adjusting post with pliers, thus varying the tension of the armature
spring, the pull of which reinforces the weight of the armature. Care
should be taken, however, that the tension is not beyond the “quick
action” power of the electromagnet. It is much better to ease up the
movement in other ways before putting too great a load on the life of
the battery.
The electrical contacts on the leaf and screw are platinum tipped to
prevent burning by the electric sparking at the “make” and “break.”
This sparking is also much reduced by means of a resistance coil placed
in series connection with the magnet coil, Fig. 127, to reduce the
amount of current used. If this coil is removed or disconnected the
constant sparking and heat would soon burn out the contact tips.
Care should be taken to see that the batteries are dated and the
battery connections are clean at the time of sliding in a new battery.
The brush which makes connection with the center or carbon post of the
battery is insulated with mica from the framework of the case. The
other connection is made from the contact of the uncovered zinc case
of the battery with the metal clock case surrounding it. The contact
points should be bright and smooth to insure good contacts.
These clocks need but little cleaning of the works as _no oil whatever
is used_, except at one place, viz., the armature pivot. Oil should
_never_ be used on the train bearings, or other parts. This clock ran
successfully on the elevated railway platforms of the loop in Chicago
where no other pendulum clock could be operated on account of the
constant shaking.
In considering the electrical systems of these clocks, let us commence
with the batteries. While undoubtedly great improvements have been made
in the present form of dry battery they are still very far from giving
entire satisfaction. Practically all of them are of one kind, which
is that which produces electricity at 1½ volts from zinc, carbon and
sal-ammoniac, with a depolarizer added to the elements to absorb the
hydrogen. The chemical action of such a battery is as follows:
[Illustration: Fig. 125.]
The water in the electrolite comes in contact with the zinc and is
decomposed thereby, the oxygen being taken from the water by the zinc,
forming oxide of zinc and leaving the hydrogen in the form of minute
bubbles attached to the zinc. As this, if allowed to stand, would shut
off the water from reaching the zinc, chemical action would therefore
soon cease and when this happens the battery is said to be polarized
and no current can be had from it.
[Illustration: Fig. 126. The Electric Contact.
Fig. 127. The Wiring System.]
In order to take care of the hydrogen and thus insure the constant
action of the battery, oxide of manganese is added to the contents of
the cell, generally as a mixture with the carbon element. Manganese
has the property of absorbing oxygen very rapidly and of giving it off
quite easily. Therefore while the hydrogen is being formed on the zinc,
it becomes an easy matter for it to leave the zinc and take its proper
quantity of oxygen from the manganese and again form water, which is
again decomposed by the zinc. As long as this cycle of chemical action
takes place the battery will continue to give good satisfaction,
and usually when a battery gives out it is because the depolarizer
is exhausted, for the reason that the carbon is not affected at all
and the zinc element forming the container is present in sufficient
quantity to outlast the chemical action of the total mass.
There are great differences in the various makes of batteries; also in
the methods of their construction. It would seem to be an easy matter
for a chemist to figure out exactly how much depolarizer would serve
the purpose for a given quantity of zinc and carbon and therefore to
make a battery which should give an exact performance that could be
anticipated. In reality, however, this is not the case, owing to the
various conditions. There are three qualities of manganese in the
market; the Japanese, which is the best and most costly; the German,
which comes second, and the American, which is the cheapest and varies
in quality so much as to be more or less a matter of guesswork. We
must remember that in making batteries for the price at which they are
now sold on the market we are obliged to take materials in commercial
quantities and commercial qualities and cannot depend upon the
chemically pure materials with which the chemists’ theories are always
formulated. This therefore introduces several elements of uncertainty.
In practice the Japanese manganese will stand up for a far longer
time than any other that is known and it is used in all special
batteries where quality and length of life are considered of more
importance than the price. The German manganese comes next. Then comes
a mixture of American and German manganese, and finally the American
manganese, which is used in making the cheaper batteries which are
sorted afterwards, as we shall explain farther on. These batteries are
sealed after having been made in large quantities, say five thousand
or ten thousand in the lot, and kept for thirty days, after which they
are tested. The batteries which are likely to give short-life will
show a local action and consequent reduction of output in thirty days.
They are, therefore, sorted out, much as eggs are candled on being
received in a storage warehouse, for the reason that after a cell has
been made and put together it would cost more to find out what was the
matter with it and remedy that than it would to make a new cell. Many
of the battery manufacturers, therefore, make up their batteries with
an attempt to reach the highest standard. They are sorted for grade in
thirty days and those which have attained the point desired are labeled
as the factories’ best battery and are sold at the highest prices.
The others have been graded down exclusively and labeled differently
until those which are positively known to be short-lived are run out
and disposed of as the factories’ cheapest product under still another
label.
When buying batteries always look to see that the tops are not cracked,
as if the seal on the cell is broken, chemical action induced from
contact with the air as the battery dries out, will rapidly deteriorate
the depolarizer and sulphate the zinc, both of which are of course
a constant draft on the life of the battery, which contains only a
stated quantity of energy in the beginning. Always examine the terminal
connections to see that they are tight and solid.
Batteries when made up are always dated by the factory, but this does
the purchaser little good, as the dates are in codes of letters,
figures, or letters and figures, and are constantly changed so that
even the dealers who are handling thousands of them are unable to read
the code. This is done because many people are prone to blame the
battery for other defects in the electrical system and many who are
using great quantities would find an incentive to switch the covers
on which the dates appear if they knew what it meant. This is perhaps
rather harsh language, but a good many men would be tempted to send
back a barrel of old batteries every now and then with the covers
showing that they had not lasted three months, if they could read these
signatures.
Practically the only means the jeweler has of obtaining a good cell,
with long life, is to buy them of a large electrical supply house,
paying a good price for them and making sure that that house has trade
enough in that battery to insure their being continuously supplied with
fresh stock.
The position of the battery also has to do with the length of life
or amount of its output. Thus a battery lying on its side will not
give more than seventy-five per cent of the output of a battery which
is standing with the zinc and carbon elements perpendicular. Square
batteries will not give the satisfaction that the round cell does. It
has been found in practice by trials of numerous shapes and proportions
that the ordinary size of 2½ × 6 inches will give better satisfaction
than one of a different shape—wider or shorter, or longer and thinner;
that is for the amount of material which it contains. The battery
which has proved most successful in gas engine ignition work is 3¾ × 8
inches. That maintains the same proportions as above, or very nearly
so, but owing to local action it will give on clock work only about
fifty per cent longer life than the smaller size.
It has been a more or less common experience with purchasers of
electric clocks to find that the batteries which came with the clock
from the factory ran for two or three years (three years not being at
all uncommon) and that they were then unable to obtain batteries which
would stand up to the work for more than three weeks, up to six months.
The difference is in the quality and freshness of the battery bought,
as outlined above.
[Illustration: Fig. 128. Fig. 129.]
In considering the rest of the electrical circuit, we find three
methods of wiring commonly used and also a fourth which is just now
coming into use. The majority of electric clocks are wound by a magnet
which varies in size from three to six ohms; bridged around the contact
points, there has generally been placed a resistance spool which
varies in size from ten to twenty-five times the number of ohms in the
armature magnets. See Fig. 128. This practically makes a closed circuit
on which we are using a battery designed for open circuit work.
If we use an electromagnet with a very soft iron core, we will need
a small amount of current, but every time we break the contact, we
will have a very high counter electro-motive force, leaping the
air gap made while breaking the contact and therefore burning the
contact points. If our magnet is constructed so as to use the least
current, by very careful winding and very soft iron cores, this counter
electro-motive force will be at its greatest while the draft on the
battery is at its smallest. If the magnet cores are made of harder
iron, the counter electro-motive force will be much less; but on the
other hand much more current will be needed to do a given quantity of
work with a magnet of the second description; and the consequence is
that while we save our contact points to some extent, we deplete the
battery more rapidly.
If we put in the highest possible resistance—that of air—in making
and breaking our contacts, we use current from the battery only to do
useful work; but we also have the spark from the counter electro-motive
force in a form which will destroy our contact points more quickly.
If we reduce the resistance by inserting a German silver wire coil of
say sixty ohms on a six-ohm magnet circuit, we have then with two dry
batteries (the usual number) three volts of current in a six-ohm magnet
during work and three volts of current in a sixty-six ohm circuit while
the contacts are broken, Fig. 128. Dividing the volts by the ohms, we
find that one twenty-second of an ampere is constantly flowing through
such a circuit. We are therefore using a dry battery (an open circuit
battery) on closed circuit work and we are drawing from the life of our
battery constantly in order to save our contact points.
It then becomes a question which we are going to sacrifice, or what
sort of a compromise may be made to obtain the necessary work from the
magnet and at the same time get the longest life of the contact points
and the batteries. Most of the earlier electric clocks manufactured
have finally arranged such a circuit as has been described above.
The Germans put in a second contact between the battery and the
resistance with a little larger angular motion than the first or
principal contact, so that the contact is then first made between the
battery and resistance spool, B, Fig. 129, then between the two contact
points of the shunt, A; Fig. 129, to the electromagnet, and after
the work is done they are broken in the reverse order, so that the
resistance is made first and broken after the principal contact. This
involves just twice as many contact points and it also involves more or
less burning of the second contact.
[Illustration: Fig. 130. Fig. 131.]
The American manufacturers seem to prefer to waste more or less current
rather than to introduce additional contact points, as they find that
these become corroded in time with even the best arrangements and they
desire as few of them as possible in their movements, preferring rather
to stand the draft on the battery.
One American manufacturer inserts a resistance spool of 60 ohms in
parallel with a magnet of seven ohms (3½ ohms for each magnet spool)
as in Fig. 130. He states that the counter electro-motive force is
thus dissipated in the resistance when the contact is broken, as the
resistance thus becomes a sort of condenser, and almost entirely does
away with heating and burning of the contacts, while keeping the
circuit open when the battery is doing no work.
It has been suggested to the writer by several engineers of high
attainments and large experience that what should be used in the
above combination is a condenser in place of a resistance spool, as
there would then be no expenditure of current except for work. One
of the clocks changed to this system just before the failure of its
manufacturers, but as less than four hundred clocks were made with the
condensers (Fig. 131), the point was not conclusively demonstrated.
It should also be borne in mind that the condenser has been vastly
improved within the last twelve months. With the condenser it will be
observed that there is an absolutely open circuit while the armature
is doing no work and that therefore the battery should last that much
longer, Figs. 130 and 131. As to the cost of the condensers as compared
with resistance spools, we are not informed, but imagine that with the
batteries lasting so much longer and the clock consequently giving so
much better satisfaction, a slight additional cost in manufacture by
changing from resistance to condensers would be welcomed, if it added
to the length of life and the surety of operation.
Electric clocks cost more to make than spring or weight clocks and sell
for a higher price and a few cents additional per movement would be a
very small premium to pay for an increase in efficiency.
The repairer who takes down and reassembles one of these clocks very
often ignorantly makes a lot of trouble for himself. Many of the older
clocks were built in such a way that the magnets could be shifted for
adjustment, instead of being put in with steady pins to hold them
accurately in place. The retail jeweler who repairs one of these
clocks is apt to get them out of position in assembling. The armature
should come down squarely to the magnets, but should not be allowed to
touch, as if the iron of the armature touches the poles of the magnet
it will freeze and retain its magnetism after the current is broken.
Some manufacturers avoid this by plating their armatures with copper or
brass and this has puzzled many retailers who found an electromagnet
apparently attracting a piece of metal which is generally understood to
be non-magnetic.
The method offers a good and permanent means of insulating the iron of
the armature from the magnet poles while allowing their close contact
and as the strength of a magnet increases in proportion to the square
of the distance between the poles and the armature, it will be seen
that allowing the armature to thus approach as closely as possible
to the poles greatly increases the pull of the magnet at its final
point. If when setting them up the magnet and armature do not approach
each other squarely, the armature will touch the poles on one side or
another and soon wear through the copper or brass plating designed
to maintain their separation and then we will have freezing with its
accompanying troubles.
A very good test to determine this is to place a piece of watch paper,
cigarette paper or other thin tissue on the poles of the magnet before
the naked iron armature is drawn down. Then make the connection, hold
the armature and see if the paper can be withdrawn. If it cannot the
armature and poles are touching and means should be taken to separate
them. This is sometimes done by driving a piece of brass into a hole
drilled in the center of the pole of the magnet; or by soldering a thin
foil of brass on the armature. As long as the separation is steadily
maintained the object sought is accomplished, no matter what means is
used to attain it.
Another point with clocks which have their armatures moved in a
circular direction is to see that the magnet is so placed as to give
the least possible freedom between the armatures and the circular poles
of the magnet, but that there must be an air-gap between the armature
and magnet poles.
In those clocks which wind a spring by means of a lever and ratchet
working into a fine-toothed ratchet wheel, or are driven by a weighted
lever, there is an additional point to guard against. If the weight
lever is thrown too far up, either one of two things will happen. The
weight lever may be thrown up to ninety degrees and become balanced if
the butting post is left off or wrongly replaced; the power will then
be taken off the clock, if it is driven directly by weight, so that a
butting post should meet the lever at the highest point and insure that
it will not go beyond this and thus lose the efficiency of the weight.
In the cases where a spring on the center arbor is interposed between
the arbor and the ratchet wheel, it should be determined just how many
teeth are necessary to be operated when winding, as if a clock is wound
once an hour and the aim is to wind a complete turn (which is the
amount the arbor has run down) if the lever is allowed to vibrate one
or two teeth beyond a complete turn, it will readily be seen that in
the course of time the spring will wind itself so tightly as to break
or become set. This was a frequent fault with the Dulaney clock and has
not been guarded against sufficiently in some others which use the fine
ratchet tooth for winding.
When such a clock is found the proper number of teeth should be
ascertained and the rest of the mechanism adjusted to see that just
that number of teeth will be wound. If less is wound there will come a
time when the spring will run down and the clock will stop. If too much
is wound the spring will eventually become set and the clock will stop.
Therefore such movements should be examined to see that the proper
amount of winding occurs at each operation. Of course where a spring is
wound and there are but four notches in the ratchet wheel and the screw
stop is accurately placed to stop the action of the armature, over
action will not harm the spring, provided it will not go to another
quarter, as if the armature carries the ratchet wheel further than it
should, the smooth circumference between the notches will let it drop
back to its proper notch.
There are a large number of clocks on the market which wind once per
hour. These differ from the others in that they do not depend upon a
single movement of the armature for an instantaneous winding. Thus
if the batteries are weak it may take twenty seconds to wind. If the
batteries are strong and new it may wind in six seconds. In this
respect the clock differs radically from the others, and while we have
not personally had them under test, we are informed that on account of
winding once per hour the batteries will last very much longer than
would be expected proportionately from those which wind at periods of
greater frequency. The reason assigned is that the longer period allows
the battery to dispose of its hydrogen on the zinc and thus to regain
its energy much more completely between the successive discharges
and hence can give a more effective quantity of current for hourly
discharge than those which are discharged several times a minute,
or even several times an hour. It is only proper to add that the
manufacturers of clocks winding every six or seven minutes dispute this
assertion.
Another point is undoubtedly in the increased length of life of the
contacts; but speaking generally the electric clock may be said now to
be waiting for further improvements in the batteries. Those who have
had the greatest experience with batteries, as the telephone companies,
telegraph companies and other public service corporations, have
generally discarded their use in favor of storage batteries and dynamos
wherever possible and where this is not possible they have inspected
them continuously and regularly.
In this respect one point will be found of great service. When putting
in a new set of batteries in any electrical piece of machinery, write
the date in pencil on the battery cover, so that you, or those who
come after you, some time later, will know the exact length of time
the battery has been in service. This is frequently of importance,
as it will determine very largely whether the battery is playing out
too soon, or whether faults are being charged to the battery which are
really due to other portions of the apparatus.
Never put together any piece of electrical apparatus without seeing
that all parts are solidly in position and are clean; always look
carefully to connections and see that the insulation is perfect so that
short circuits will be impossible.
All contacts must be kept smooth and bright and contact must be made
and broken without any wavering or uncertainty.
Fig. 132 shows the completely wired movement of the American Clock
Company’s weight driven movement, which may be accepted as a type of
this class of movements—weight driven, winding every seven minutes.
The train is a straight-line time train, from the center arbor to the
dead beat escapement, with the webs of the wheels not crossed out. It
is wired with the wire from the battery zinc screwed to the front plate
H and that from the battery carbon to an insulated block G.
Fig. 133 shows an enlarged view of the center arbor. Upon this arbor
are secured (friction-tight) two seven-notched steel ratchets, E, and
carried loosely between them are two weighted levers pivoted loosely
on the center arbor. Each lever is provided with a pawl engaging in
the notches of the nearest ratchet, as shown. The weighted lever has a
circular slot cut in it, concentric with the center hole and also has a
portion of its circumference at the arbor cut away, thus forming a cam.
Between these two levers is a connecting link D with a pin in its upper
end, which pin projects into the circular slots of the weight levers.
[Illustration: Fig. 132.]
[Illustration: Fig. 133.]
The lever F is pivoted to the front plate of the clock and carries at
right angles a beveled arm which projects over the ratchets E, but is
ordinarily prevented from dropping into the notches by riding on the
circumferences of the weighted levers. When one lever has dropped down
and the other has reached a horizontal position the cut portions of
the circumferences of these levers will be opposite the upper notch of
the ratchets and will allow the bar projecting from F to drop into the
notches. This allows F and G to connect and the magnet A is energized,
pulls the armature B, the arms C D, and thus lifts the lever through
the pin in D pulling at the end of the circular slot. As the lever
flies upward, the cam-shaped portion of its circumference raises the
arm out of the notches, thus separating F and G and breaking the
circuit. A spring placed above E keeps its arms pressed constantly upon
E in position to drop. The wiring of the magnets is shown in Fig. 130.
[Illustration: Fig. 134.]
The upper contact (carried in F) is a piece of platinum with its lower
edge cut at an angle of fifteen degrees and beveled to a knife edge.
The lower point of this bevel comes into contact first and is the
last to separate when breaking connection, so that any sparking which
may take place will be confined to one edge of the contacts while the
rest of the surface remains clean. (See Fig. 134.) Ordinarily there
is very little corrosion from burning and this is constantly rubbed
off by the sliding of the surfaces upon each other. The lower contact,
G, consists of a brass block mounted upon an insulating plate of hard
rubber. The block is in two pieces, screwed together, and each piece
carries a platinum tipped steel spring. These springs are so set as
to press their platinum tips against each other directly beneath the
upper contact. The upper and lower platinum tips engage each other
about one-sixteenth inch at the time of making contact. The lower block
being in two pieces, the springs may be taken apart for cleaning, or
to adjust their tension. The latter should be slight and should in
no case exceed that which is exerted by the spring in F, or the upper
knife edge will not be forced between the two lower springs. The pin
on which F is pivoted and that bearing on the spring above it must be
clean and bright and _never be oiled_, as it is through these that the
current passes to the upper contact in the end of F. The contacts are,
of course, never oiled.
The two weighted levers should be perfectly free on the center arbor
and their supporting pawls should be perfectly free on the shoulder
screws in the levers. Their springs should be strong enough to secure
quick action of the pawls. This freedom and speed of action are
important, as the levers are thrown upward very quickly and may rebound
from the butting post without engaging the ratchets if the pawls do not
work quickly.
The projecting arm, C, of the armature, B, has pivoted to it, a link,
D, which projects upward and supports at its upper end a cross pin.
The link should not be tight in the slot of C, but should fit closely
on the sides, in order to keep the cross pin at the top of D parallel
with the center staff of the clock. This cross pin projects through D
an equal distance on either side, each end respectively passing through
the slot of the corresponding lever, the total length of this pin being
nearly equal to the distance between the ratchets. When the electric
circuit is closed, and the magnets energized, B, C and D are drawn
downward; the weighted end of one of the levers which runs the clock,
being at this time at the limit of its downward movement, see Fig.
135, the opposite or slotted end of said lever, is then at its highest
point, and the downward pull in the slot by one end of the above
described crosspin which enters it will throw the weighted end of the
said lever upward. The direct action of the magnets raises the lever
nearly to the horizontal position, and the momentum acquired carries
it the remainder of the distance. By this arrangement of stopping
the downward pull of the pin when the ascending lever reaches the
horizontal, all danger of disturbing the other lever A is avoided. The
position is such that the top of the ascending lever weight is about
even with the center of the other weight when the direct pull ceases.
[Illustration: Fig. 135.]
Before starting the clock raise the lever weights so that one lever
is acting upon a higher notch of the ratchet than the other. They are
designed to remain about forty-five degrees apart, so as to raise only
one lever at each action of the magnet. This maintains an equal weight
on the train, which would not be the case if they were allowed to
rise and fall together; keeping the levers separated also reduces the
amount of lift or pull on the battery and uses less current, which is
an item when the battery is nearly run down. If these levers are found
together it indicates that the battery is weak, the contacts dirty,
making irregular winding, or the pawls are working improperly. See that
the levers rise promptly and with sufficient force. After one of them
has risen stop the pendulum and see that the butting post is correctly
placed, so that there is no danger of the lever wedging under the post
and sticking there, or causing the lever to rebound too much. The
butting post is set right when the clock leaves the factory and seldom
needs adjustment unless some one has tinkered with it.
The time train should be oiled as with the ordinary movements, also
the pawls on the levers. The lever bushings should be cleaned before
oiling and then well oiled in order to avoid friction on the center
arbor from the downward pull of the magnets when raising the levers. In
order to clean the levers drive out the taper pin in the center arbor
and remove the front ratchet, when the levers will slip off. In putting
them back care should be used to see that the notches of the ratchets
are opposite each other. Oil the edges of the ratchets and the armature
pins. Do not under any circumstances oil the contact points, the pins
or springs of the bar F, as this will destroy the path of the current
and thus stop the clock. These pins must be kept clean and bright.
HOURLY WINDING CLOCKS.—There are probably more of these in America
than of all other electric kinds put together (we believe the
present figures are something like 135,000), so that it will not be
unreasonable to give considerable space to this variety of clocks.
Practically all of them are made by the Self Winding Clock Company and
are connected with the Western Union wires, being wound by independent
batteries in or near the clock cases.
Three patterns of these clocks have been made and we will describe
all three. As they are all practically in the same system, it will
probably be better to first make a simple statement of the wiring,
which is rigidly adhered to by the clock company in putting out these
goods. All wires running from the battery to the winding magnets of the
movement are brown. All wires running from the synchronizing magnet to
the synchronizing line are blue. Master clocks and sub-master clocks
have white wires for receiving the Washington signal and the relay for
closing the synchronizing line will, have wires of blue and white plaid.
[Illustration: Fig. 136.]
By remembering this system it is comparatively easy for a man to know
what he is doing with the wires, either inside or outside of the case.
For calendar clocks there are, in addition, two white wires running
from the calendar to the extra cell of battery. There is also one other
peculiarity, in that these clocks are arranged to be wound by hand
whenever run down (or when starting up) by closing a switch key, shown
in Fig. 136, screwed to the inside of the case. This is practically an
open switch, held open by the spring in the brass plate, except when it
is pressed down to the lower button.
The earliest movement of which any considerable number were sent out
was that of the rotary winding from a three-pole motor, as shown in
Fig. 137. Each of these magnet spools is of two ohms, with twelve ohms
resistance, placed in parallel with the winding of each set of magnet
spools, thus making a total of nine spools for the three-pole motor.
[Illustration: Fig. 137.]
On the front end of the armature drum arbor is a commutator having six
points, corresponding to the six armatures in the drum. There are three
magnets marked O, P and X; each magnet has its own brush marked O′, P′
and X′. When an armature approaches a magnet (see Fig. 137) the brush
makes contact with a point of the commutator, and remains in contact
until the magnet has done its work and the next magnet has come into
action. When properly adjusted the brush O′ will make contact when
armatures 1 and 2 are in the position shown, with No. 2 a little nearer
the core of the magnet than No. 1; and it will break contact when the
armature has advanced into the position shown by armature No. 3, the
front edge of the armature being about one-sixteenth of an inch from
the corner of the core, armature No. 4 being entirely out of circuit,
as brush X′ is not touching the commutator.
The back stop spring, S, Fig. 137, must be adjusted so that the brush
O′ is in full contact with a point of the commutator when the motor is
at rest, with a tooth of the ratchet touching the end of the spring, S.
Sometimes the back stop spring, S, becomes broken or bent. When
this occurs it is usually from overwinding. It must be repaired by
a new spring, or by straightening the old one by burnishing with a
screwdriver. Set the spring so that it will catch about half way down
the last tooth.
Having explained the action of the motor we come now to the means of
temporarily closing the circuit and keeping it closed until such time
as the spring is wound a sufficient amount to run the clock for one
hour; as the spring is on the center arbor this requires one complete
turn.
This is the distinguishing feature of this system of clocks and is
not possessed by any of the others. It varies in construction in the
various movements, but in all its forms it maintains the essential
properties of holding the current on to the circuit until such time
as the spring has been wound a sufficient quantity, when it is again
forcibly broken by the action of the clock. This is termed the “knock
away,” and exists in all of these movements.
To start the motor the circuit is closed by a platinum tipped arm, A,
Fig. 138, loosely mounted on the center arbor, and carried around by a
pin projecting from the center wheel until the arm is upright, when it
makes contact with the insulated platinum tipped brush, B. A carries
in its front an ivory piece which projects a trifle above the platinum
top, so that when B drops off the ivory it will make contact with the
platinum on A firmly and suddenly. This contact then remains closed
until the spring barrel is turned a full revolution, when a pin in the
barrel cover brings up the “knock-away,” C, which moves the arm, A,
forward from under the brush, B, and breaks the circuit. The brush, B,
should lie firmly on its banking piece, and should be so adjusted that
when it leaves the arm, A, it will drop about one-thirty-second of an
inch. Adjusted in this way it insures a good, firm contact.
The angle at the top of the brush, B, must not be too abrupt, so as to
retard the action of the clock while the contact is being made. Wire
No. 8 connects the spring contact, B, to one of the binding plates at
the left hand side of the case; and wire No. 6 connects the motor, M,
to the other. To these binding plates are attached brown wires that
lead one to each end of the battery.
When the clock is quite run down, it is wound by pressing the switch
key, Fig. 136, from which a wire runs to the plate. The switch key
should _not_ be permanently connected to its contact screw, J. See that
all wires are in good condition and all connections tight and bright.
The main spring is wound by a pinion on the armature drum arbor,
through an intermediate wheel and pinion to the wheel on the spring
barrel.
At stated times—say once in eighteen months or two years—all clocks
should be thoroughly cleaned and oiled, and at the same time inspected
to be sure they are in good order.
Never let the self-winding clocks run down backward, as the arm, A,
Fig. 138, will be carried back against the brush, B, and bend it out of
adjustment.
[Illustration: Fig. 138.]
To clean the movement, take it from the case, take out the anchor and
allow it to run down gently, so as not to break the pins, then remove
the motor. Take off the _front_ plate and separate all the parts. Never
take off the back plate in these clocks. Wash the plates and all parts
in a good quality of benzine, pegging out the holes and letting them
dry thoroughly before reassembling. The motor must not be taken apart,
but may be washed in benzine, by using a small brush freely about the
bearings, commutator and brushes. Put oil in all the pivot holes, but
not so much that it will run. The motor bearings and the pallets of the
anchor should also be oiled.
Inspect carefully to see that the center winding contact is right and
that the motor is without any dead points. Dust out the case and put
the movement in place. Before putting on the dial try the winding by
means of the switch, Fig. 136, to be sure that it is right; also see
that the disc on the cannon socket is in the right position to open the
latch at the hour, and after the dial and hands are on move the minute
hand forward past the hour and then backward gently until it is stopped
by the latch. This will prove that the hand is on the square correctly.
On account of the liability of the motor to get out of adjustment and
fail to wind, from the shifting of the springs and brushes, under
careless adjustment, various attempts have been made to improve this
feature of these clocks and the company is now putting out nearly
altogether one of the two vibrating motors, shown in Figs. 139 and 140.
In Style C, Fig. 139, the hourly contact for winding is the same as in
the clock with the three-magnet motor, as shown in Fig. 138. The magnet
spools are twelve ohms and the resistance coil is eighty ohms, placed
in parallel, as described in Fig. 130.
The vibrating motor, Fig. 139, is made with a pair of magnets and
a vibrating armature. The main spring is wound by the forward and
backward motion of the armature, one end of the connecting rod, 8,
being attached to a lug of the armature, 2, and the other to the
winding lever, 10. This lever has spring ends, to avoid shock and
noise. As the winding lever is moved up and down, the pawl, 9, turns
the ratch wheel, 11, and a pinion on the ratch wheel arbor turns the
spring barrel until the winding is completed.
[Illustration: Fig. 139.]
The contact for operating the motor is made by the brass spiral spring,
3, which is attached to the insulated stud, 4, and the platinum pin,
5, which is carried on a spring attached to the clock plate. As the
armature moves forward the break pin, A, in the end of the armature
lifts the contact spring, 3, thus breaking the circuit. The acquired
momentum carries the armature forward until it strikes the upper
banking spring, 6, when it returns rapidly to its original position,
banking on spring 7, by which time contact is again made between
springs 3 and 5 and the vibration is repeated until the clock is wound
one turn of the barrel and the circuit is broken at the center winding
contact.
Fig. 140, Style F, is a similar motor so far as the vibrating armature
and the winding is concerned, but the winding lever is pivoted directly
on the arbor of the winding wheel and operates vertically from an arm
and stud on the armature shaft, working in a fork of the winding lever,
8, Fig. 140. It will be seen that the train and the motor winding
mechanism are combined in one set of plates. The motor is of the
oscillating type and its construction is such that all its parts may be
removed without dissembling the clock train.
CONSTRUCTION OF THE MOTOR.—The construction of the motor is very
simple, having only one pair of magnets, but _two sets_ of make and
break contacts, one set of which is placed on the front and the other
on the back plate of the movement, thus ensuring a more reliable
operation of the motor, and reducing by fifty per cent the possibility
of its failing to wind.
The center winding contact also differs from those used in the
three-magnet motors and former styles of vibrating motor movements.
The center winding contact piece, 13, has no ivory and no platinum.
The hourly circuit is not closed by the current passing through this
piece, but it acts by bringing the plate contact spring, 16, in
metallic connection with the insulated center winding contact spring,
17, both of which are platinum tipped. It will thus be seen that no
accumulation of dirt, oil or gum around the center arbor or the train
pivots will have any effect in preventing the current from passing from
the motor to the hourly circuit closer.
[Illustration: Fig. 140.]
The operation is as follows: As the train revolves, the pin, 12,
securely fastened to the center arbor, in its hourly revolution
engages a pin on the center winding contact piece, 13. This piece as
it revolves pushes the plate contact spring, 16, upward, bringing it
in metallic connection with the center winding contact spring, 17,
which is fastened to a stud on an insulated binding post, 18, thereby,
closing the hourly circuit. The current passes from the binding post,
18, through the battery (or any other source of current supply) to
binding post 19, to which is connected one end of the motor magnet
wire. The current passes through these magnets to the insulated stud,
4. To this stud the spiral contact spring, 3, is fastened and the
current passes from this spring to the plate contact spring, 5, thence
through the movement plate to plate contact spring, 16, and from there
through spring, 17, back to the battery.
The main spring is wound by the forward and backward motion of the
armature, 2. To this armature is connected the winding lever, 8. As
the winding lever is oscillated, the pawl, 9, turns the ratchet wheel,
11, and a pinion on the ratchet wheel arbor turns the winding wheel
until the pin, 15, connected to it engages the knock-away piece, 14,
revolving it until it strikes the pin on the center winding contact
piece, 13, and pushes it from under the plate contact spring, thereby
breaking the electric circuit and completing the hourly winding.
The proper position of the contact springs is clearly indicated in Fig.
140. The spring, 16, should always assume the position shown thereon.
When the center winding contact piece, 13, comes in metallic connection
with the plate contact spring, 16, the end of this spring should stand
about one-thirty-second of an inch from the edge of the incline. The
center winding contact spring, 17, should always clear the plate
contact spring one-thirty-second of an inch. When the two springs touch
they should be perfectly parallel to each other.
ADJUSTMENTS OF THE ARMATURE.—In styles C and F, when the armature,
2, rests on the banking spring, 7, its front edge should be in line
with the edge of the magnet core. The upper banking spring, 6, must be
adjusted so that the front edge of the armature will be one-sixteenth
of an inch from the corner of the magnet core when it touches the
spring.
When the contact spring, 3, rests on the platinum pin, 5, it should
point to about the center of the magnet core, with the platinum pin at
the middle of the platinum piece on the spring.
To adjust the tension of the spiral contact spring, 3, take hold of
the point with a light pair of tweezers and pull it gently forward,
letting it drop under the pin. It should take the position shown by the
dotted line, the top of the spring being about one-thirty-second of an
inch below the platinum pin. If from any cause it has been put out of
adjustment it can be corrected by carefully bending under the tweezers,
or the nut, 4, may be loosened and the spring removed. It may then be
bent in its proper shape and replaced.
The hole in the brass hub to which the spring is fastened has a flat
side to it, fitting a flat on the insulated contact stud. If the
contact spring is bent to the right position it may be taken off and
put back at any time without changing the adjustment, or a defective
spring may readily be replaced with a new one. When the armature
touches the upper banking spring the spiral contact spring, 3, should
clear the platinum pin, 5, about one-sixteenth of an inch. Both
contacts on front and back plates in style F are adjusted alike. The
circuit break pins “A” on the armature should raise both spiral contact
springs at the same instant.
If for any reason the motor magnets have become displaced they may
readily be readjusted by loosening the four yoke screws holding them
to the movement plates. Hold the armature against the upper banking
spring, move the magnets forward in the elongated slot, 20, until the
ends of the magnet cores clear the armature by one-sixty-fourth of an
inch, then tighten down the four yoke screws. Connect the motor to the
battery and see that the armature has a steady vibration and does not
touch the magnet core. The adjustment should be such that the armature
can swing past the magnet core one-eighth to three-sixteenths of an
inch.
DESCRIPTION OF SYNCHRONIZER.—At predetermined times a current is sent
through the synchronizer magnet, D′, Fig. 141, which actuates the
armature, E, to which are attached the levers, F and G, moving them
down until the points on the lever, G, engage with two projections, 4
and 5, on the minute disc; and lever F engages with the heart-shaped
cam or roll on the seconds arbor sleeve, causing both the minute and
second hands to point to XII. These magnet spools are wound to twelve
ohms, with an eighty-ohm resistance in parallel.
On the latch, L, is a pin, I, arranged to drop under the hook, H, and
prevent any action of the synchronizing levers, except at the hour.
A pin in the disc on the cannon socket unlocks the latch about two
minutes before the hour and closes it again about two minutes after the
signal. This is to prevent any accidental “cross” on the synchronizing
line from disturbing the hands during the hour.
M is a light spring attached to the synchronizing frame to help
start the armature back after the hands are set. The wires from the
synchronizing magnet are connected to binding plates at the right-hand
side of the clock and from these binding plates the blue wires, Nos. 9
and 10, pass out at the top of the case to the synchronizing line.
If the clock gets out of the synchronizing range it generally indicates
very careless regulation. The clock is regulated by the pendulum,
as in all others, but there is one peculiarity in that the pendulum
regulating nut has a check nut.
If the clock gains time turn the large regulating nut under the
pendulum bob slightly to the left.
If the clock loses time turn the nut slightly to the right.
Loosen the small check nut under the regulating nut before turning the
regulating nut, and be _sure to tighten_ the check nut after moving the
regulating nut.
[Illustration: Fig. 141.]
The friction of the seconds hand is very carefully adjusted at the
factory, being weighed by hanging a small standard weight on the point
of the hand. If it becomes too light and the hand drives or slips
backward, losing time, it can be made stronger by laying it on a
piece of wood and rubbing the inner sides of the points with a smooth
screw driver, and if too heavy and the clock will not set when the
synchronizing magnets are actuated, the points of the spring in the
friction may be straightened a little.
If the seconds hand sleeve does not hold on the seconds socket, pinch
it a little with pliers. If the seconds hand is loose on the sleeve put
on a new one or solder it on the under side.
In style F the synchronizing lever, heart-shaped seconds socket and
cams on the cannon sockets are the same as in the old style movements,
shown in Fig. 141. The difference is in the synchronizing magnets
and the way they operate the synchronizing lever. The magnet has a
flat ended core instead of being eccentric like the former ones. The
armature is also made of flat iron and is pivoted to a stud fastened to
the synchronizing frame. The armature is connected to the synchronizing
lever by a connecting rod and pitman screws. A sector has an oblong
slot, allowing the armature to be lowered or raised one-sixteenth of
an inch. The synchronizing lever is placed on a steel stud fastened to
the front plate and held in position by a brass nut. The synchronizing
magnets are 12 ohms with 80 ohms resistance and are fastened to a yoke
which is screwed to the synchronizing frame by four iron screws. The
holes in the synchronizing frame are made oblong, allowing the yoke
and magnets to be raised or lowered one-sixteenth of an inch. The
spring on top of the armature is used to throw it back quickly and also
acts as a diamagnetic, preventing the armature from freezing to the
magnets. A screw in the stud is used to screw up against the magnet
head, preventing any spring that might take place on the armature stud.
Binding posts are screwed to the synchronizing frame and the ends of
the magnet coils are fastened thereto with metal clips.
The blue wires in the clock case are coiled and have a metal clip
soldered to them. They connect direct by these clips to the binding
posts, thus making a firm connection, and are not liable to oxidize.
With the various points of adjustment a pair of magnets burned out or
otherwise defective may readily be replaced in from five to ten minutes.
When replacing a pair of synchronizing magnets proceed as follows:
Remove the old pair and then loosen all four screws in the yoke,
pushing it up against the tops of the oblong holes, then tighten down
lightly. Fasten the new pair of magnets to the yoke with the inner ends
of the coils showing at the outside of the movement. Press the armature
upward until the synchronizing lever locks tightly on the cannon socket
and the heart-shaped cams, then loosen the magnet yoke screws and press
the magnets down on the spring on top of the armature. Then tighten the
yoke screws on the front plate and see that the back of the magnets
clears the armature by one-hundredth of an inch (the thickness of a
watch paper), when the screws in the back of the yoke can be set down
firmly. The adjustment screw may then be turned up until it presses
lightly against the magnet head. When current is passed through the
magnets and held there the armature must clear the magnets without
touching. The magnet coils must then be connected to their respective
binding posts by slipping the metal clips soldered to them under the
rubber bushing, making a metallic connection with the binding plates.
Fasten these screws down tight to insure good connections.
[Illustration: Fig. 142.]
THE MASTER CLOCK.—Is a finely finished movement with mercurial pendulum
that beats seconds and a Gerry gravity escapement. At the left and near
the center of the movement is a device for closing the synchronizing
circuit once each hour. The device consists of a stud on which is an
insulator having two insulated spring fingers, C and D, one above the
other, as shown in Fig. 142, except at the points where they are cut
away to lie side by side on an insulated support. On these fingers, and
near the insulator, are two platinum pieces, E and F, so adjusted as
to be held apart, except at the time of synchronizing.
A projection, B, from the insulator rests on the edge of a disc on the
center arbor. At ten seconds before the hour, a notch in this disc
allows the spring to draw the support downward, leaving the points of
the fingers, C and D, resting on the raised part of the rubber cam on
the escape arbor. The end of the finger, C, is made shorter than that
of D, and at the fifty-ninth second, C drops and closes the circuit by
E striking F. At the next beat of the pendulum the long finger D drops
and opens the circuit again.
The winding is the same as in the regular self-winding clocks, the
motor wire and seconds contact being connected to the binding plates at
the left, from which brown wires lead up to the battery. Two wires from
the synchronizing device are connected to the binding plates at the
left, from which blue wires run out to the line.
Before connecting the clock to the line it must be run until it is well
regulated, and also to learn if the contacts are working correctly.
Regulate at first by the nut at the bottom of the rod until it runs
about one second slow in 24 hours (a full turn of the nut will change
the rate about one-half minute per day). The manufacturers send
with each clock a set of auxiliary pendulum weights, the largest
weighing one gram, the next in size five decigrams and the smallest
two decigrams; these weights are to make the fine regulations by
placing one or more of them on the little table that is fastened
about the middle of the pendulum rod. The five decigram weight will
make the clock gain about one second per day, and the other weights
in proportion. Care must be taken not to disturb the swing of the
pendulum, as a change of the arc changes the rate.
To start the clock after it is regulated, stop it, with the second hand
on the fiftieth second; move the hands forward to the hour at which
the signal comes from the observatory; then press the minute hand back
gently until it is stopped by the extension on the hour contact, Fig.
142, and beat the clock up to the hour. This ensures the hour contact
being in position to send the synchronizing signal.
A good way to start it with observatory time is with all the hands
pointing to the “signal” hour; hold the pendulum to one side and when
the signal comes let it go. With a little practice it can be started
very nearly correct.
Clocks not lettered in the bottom of the case must be wound before
starting the pendulum. To do this press the switch shown in Fig. 136,
which is on the left side of the case and under the dial.
Continue the pressure until the winding ceases. Then set the hands and
start the pendulum in the usual way. If the bell is not wanted to ring,
bend back the hammer.
SECONDARY DIALS.—One of the most deceptive branches of clock work
is the secondary dial, or “minute jumper.” Ten years ago it was the
rule for all manufacturers of electric clocks to put out one or more
patterns of secondary dials. Theoretically it was a perfect scheme,
as the secondary dial needed no train, could be cheaply installed and
could be operated without trouble from a master clock, so that all
dials would show exactly the same time. Practically, however, it proved
a very deceptive arrangement. The clocks were subject to two classes of
error. One was that it was extremely difficult to make any mechanical
arrangement in which the hands would not drive too far or slip backward
when the mechanism was released to advance the minute hand. The second
class of errors arose from faulty contacts at the master clock and
variation in either quantity or strength of current. Another and
probably the worst feature was that all such classes of apparatus
record their own errors and thereby themselves provide the strongest
evidence for condemnation of the system. Clocks could be wound once
an hour with one-sixtieth of the chance of error of those wound once
per minute, and they could be wound hourly and synchronized daily with
¹/₁₄₄₀th of the line troubles of a minute system.
The minute jumpers could not be synchronized without costing as much
to build and install as an ordinary self-winding clock, with pendulum
and time train, and after trying them for about ten years nearly all
the companies have substituted self-winding time train clocks with a
synchronizing system. They have apparently concluded that, since it
seems too much to expect of time apparatus that it will work perfectly
under all conditions, the next thing to do is to make the individual
units run as close to time as is commercially practicable and then
correct the errors of those units cheaply and quickly from a central
point.
It is for these reasons that the secondary dial has practically
disappeared from service, although it was at one time in extensive use
by such companies as the Western Union Telegraph Company, the Postal
Telegraph and the large buildings in which extensive clock systems have
been installed.
Fig. 143 shows one form of secondary dial which involves a screw and a
worm gear on the center arbor, which, it will be seen, is adapted to
be turned through one minute intervals without the center arbor ever
being released from its mechanism. This worm gear was described in the
AMERICAN JEWELER about fifteen years ago, when patented by the Standard
Electric Time Company in connection with their motor-driven tower
clocks, and modifications of it have been used at various times by
other companies.
The worm gear and screw system shown in Fig. 143 has the further
advantage that it is suitable for large dials, as the screw may be run
in a box of oil for dials above four feet and for tower clocks and
outside work. This will readily be seen to be an important advantage
in the case of large hands when they are loaded with snow and ice,
requiring more power to operate them.
[Illustration: Fig. 143. Minute jumper. A, armature; M, magnets;
W, worm gear on center arbor; B, oil box for worm; R, four toothed
ratchet.]
All secondaries operate by means of an electromagnet raising a weight,
the weight generally forming the armature; the fall of the weight then
operates the hands by gravity. Direct action of the current in such
cases is impracticable, as the speed of starting with an electric
current would cause the machine to tear itself to pieces.
This screw gear is the only combination known to us that will prevent
the hands from slipping or driving by and reduces the errors of the
secondary system to those of one class, namely, imperfections in the
contact of the master clock, insufficient quantity or strength of
current, or accidental “crosses” and burnings.
The series arrangement of wiring secondaries was formerly greatly
favored by all of the manufacturers, but it was found that if anything
happened to one clock it stopped the lot of them; and where more than
fifty were in series, the necessary voltage became so high that it
was impracticable to run the clocks with minute contacts. The modern
system, therefore, is to arrange them in multiples, very much after the
fashion of incandescent lamps, then if one clock goes wrong the others
are not affected. Or if the current is insufficient to operate all,
only those which are farthest away would go out of time.
Very much smaller electromagnets will do the work than are generally
used for it, and the economy of current in such cases is worth looking
after, as with sixty contacts per hour batteries rapidly play out if
the current used is at all excessive. Where dry batteries are used on
secondaries care should be taken to get those which are designed for
gas engine ignition or other heavy work. Wet batteries, with the zincs
well amalgamated, will give much better satisfaction as a rule and if
the plant is at all large it should be operated from storage cells
with an engineer to look after the battery and keep it charged, unless
current can be taken from a continuously charged lighting main. This
can be readily done in such instances as the specifications call for
in the new custom house in New York, namely, one master clock and 160
secondary dials.
ELECTRIC CHIMES.—There have lately come into the market several devices
for obtaining chimes which allow the separation of the chimes and the
timekeeping apparatus, connection being made by means of electricity.
In many respects this is a popular device. It allows, for instance, a
full set of powerful tubular chimes, six feet or more in length, to
be placed in front of a jewelry store, where they offer a constant
advertisement, not only of the store itself, but of the fact that
chiming clocks may be obtained there. It also allows of the completion
by striking of a street clock which is furnished with a time train
and serves at once as timepiece and sign. Many of these have tubular
chimes in which the hour bell is six feet in length and the others
correspondingly smaller. They have also been made with bells of the
usual shape, which are grouped on posts, or hung in racks and operated
electrically. It may also be used as a ship’s bell outfit by making a
few minor changes in the controller.
[Illustration: Fig. 144. Chimes of bells in rack.]
[Illustration: Fig. 145. Chimes of bells with resonators.]
Fig. 144 shows a peal of bells in which the rack is thirty-six inches
long and the height of the largest bell is eight inches, and the total
weight thirty pounds. This, as will readily be seen, can be placed
above a doorway or any other convenient position for operation; or it
may be enclosed in a lattice on the roof, if the building is not over
two stories in height. The lattice work will protect the bells from the
weather and at the same time let out the sound.
Fig. 145 shows the same apparatus with resonators attached. These are
hollow tubes which serve as sounding boards, largely increasing the
sound and giving the effect of much larger bells. Fig. 146 shows a
tubular chime and the electrical connections from the clock to the
controller and to the hammers, which are operated by electromagnets,
so that a heavy leaden hammer strikes a solid blow at the tops of the
tubes.
[Illustration: Fig. 146. Tubular electric chimes.]
The dials of such clocks contain electrical connections and the minute
hand carries a brush at its outer end. The contact is shown in enlarged
view in Fig. 147, by which it will be seen that the metal is insulated
from the dial by means of hard rubber or other insulating material, so
that the brush on the minute hand will drop suddenly and firmly from
the insulator to the metallic contact when the minute hand reaches
fifteen, thirty, forty-five or sixty minutes. There is a common return
wire, either screwed to the frame of the clock, or attached to the
dial, which serves to close the various circuits and to give four
strokes of the chimes at the quarter, eight at the half, twelve at the
three-quarter, and sixteen at the hour, followed by the hour strike.
The friction on the center arbor is of course adjusted so as to carry
the minute hand without slipping at the contacts.
[Illustration: Fig. 147. Enlarged view of connections on dial.]
By this means a full chime clock may be had at much less cost than
if the whole apparatus had to be self-contained and the facilities
of separation between the chimes and the timekeeping apparatus, as
hinted above, gives many advantages. For instance, the same clock and
controller may operate tubes inside the room and bells outside, or vice
versa. These are operated by wet or dry batteries purchased at local
electrical supply houses, and the wiring is done with plain covered
bell wire, or they may be operated by current from a lighting circuit,
suitably reduced, if the current is constantly on the mains. As a full
chime with sixteen notes at the hour strikes more than a thousand
times a day, considerable care should be taken to obtain only the
best batteries where these are used, as after the public gets used to
the chimes the dealer will be greatly annoyed by the number of people
asking for them if they are stopped temporarily.
There has lately developed a tendency to avoid the set tunes, such as
the Westminster and the Whittington chimes, and to sound the notes as
complete full notes, such as the first, third and fifth of the octave
for the first, second and third quarters, followed by the hour strike.
This allows them to be struck in any order and for a smaller chime
reduces the cost considerably. The tubes used are rolled of bell metal
and vary in pitch with the manufacture, so that the only way to obtain
satisfactory tones is to cut your tubes a little long and then tune
them by cutting off afterwards, the tone depending upon the thickness
of the wall of the tube and its length. The bells are tuned by turning
from the rim or from the upper portions as it is desired to raise or
lower the tone, and if the resonators are used they are tuned in unison
with the bells.
[Illustration: Fig. 148. Connections and contacts on front of clock
dial.]
Of the ordinary bells, Fig. 144, the dimensions run: First, height four
inches, diameter 5½; second, height four inches, diameter 5¼ inches;
third, height 4½ inches, diameter 5⅝ inches; fourth, height 4½ inches,
diameter 5⅝ inches; fifth, height 4⅝ inches, diameter 6½ inches. For
the tubes the approximate length is six feet for the longest tube and
the total weight of the chimes is 43 pounds. For the controller the
size is nine by eleven by six inches, with a weight of ten pounds. The
hour strike may be had separately from the chimes if desired.
[Illustration: Fig. 149. Connections and wiring on back of clock dial.]
This makes an easily divisible system and one that is becoming very
popular with retail jewelers and to some extent with their customers.
CHAPTER XXII.
THE CONSTRUCTION AND REPAIR OF DIALS.
Probably no portion of the clock is more important than the dial and
it is apparently for this reason that we find so little variation
in the marking. The public refuses to accept anything in the way of
ornamentation which interferes with legibility and about all that may
be attempted is a little flat ornament in light colors which will not
obscure the sight of the hands, as it is in reality the angle made by
the two hands which is read instead of the figures. In proof of this
may be cited the many advertising dials in which one letter takes
the place of each character upon the dial and of the tower clocks in
which the hours are indicated merely by blackened characters, being
nothing less than an oblong blotch on the dial. Thousands of people
will pass such a dial without ever noticing that the regular characters
do not appear. Various attempts have been made to change the colors
and the sizes and shapes of the characters but comparatively few are
successful. A black dial with gold characters and hands is generally
accepted, or a cream dial with black hands, but any further experiments
are dangerous except in the cases of tower clocks, which may have
gold hands on any light colored dial, or a glass dial. In all such
cases legibility is the main factor sought and the bright metal is far
plainer for hands and chapters than anything that may be substituted
for them.
In tower clocks the rule is to have one foot of diameter of the dial
for every ten feet of height. Thus a clock situated one hundred feet
above the ground level should have a ten foot dial. On very large dials
this rule is deviated from a little, but not much. All dials, except
those of tower clocks, should be fastened to the movement, rather than
to the case. This is particularly true where a seconds hand, with
the small opening for the seconds hand sleeve, makes any twisting or
warping of the case and consequent shifting of the dial liable to rub
the dial against the sleeve at the seconds hand and thus interfere with
the timekeeping.
The writer has in mind a case in which a large number of fine clocks
were installed in a new brick and stone building. They were finely
finished and no sooner had they been hung on the damp walls than the
cases commenced to swell and twist. It was necessary three times
to send a man to move the dials which had been attached to these
clocks. As there were about thirty clocks it will be seen that this
was expensive. After the walls had dried out the cases began to go
back to the positions in which they were originally, as the moisture
evaporated from the cases, and the dials had consequently to be moved
through another series. All told it took something like a week’s work
for one man to shift these dials half a dozen times during the first
nine months of their installation. If these dials had been fastened on
pillars on the movements, the shrinking and swelling of the cases would
not have affected them.
It is for this reason that dials are invariably fastened on the
movements of all high class clocks.
The characters on clock dials are still very largely Roman, the
numerals being known as chapters. Attempts have been recently made to
substitute Arabic figures and in such cases the Arabic figures remain
upright throughout the series, while the chapters invariably point the
foot of the Roman numeral toward the center of the dial. This makes
the Roman numerals from IIII to VIII upside down, while in the Arabic
numerals this inversion does not occur.
The proportions generally sanctioned by usage have been found, after
measuring clock dials, all the way from two to eighteen inches, and
may be given in the following terms: With a radius of 26 mm. the
minute circle is 1½ mm. The margin between minute circles and chapters
is 1 mm. The chapters are 8½ mm. The width of the thick stems of the
letters are ¾ mm. The width of an X is 4 mm. and the slanting of X’s
and V’s is twenty degrees from a radius of the dial. The letters should
be proportioned as follows: The breadth of an I and a space should
equal one-half the breadth of an X, that is, if the X is one-half inch
broad, the I will be three-sixteenths inch broad and the space between
letters one-sixteenth inch, thus making the I plus one space equal
to one-quarter inch or half the breadth of an X. The V’s should be
the same breadth as the X’s. After the letters have been laid off in
pencil, outline them with a ruling pen and fill in with a small camel’s
hair brush, using gloss black paint thinned to the proper consistency
to work well in the ruling pen. Using the ruling pen to outline the
letters gives sharp straight edges, which would be impossible with a
brush in the hands of an inexperienced person.
For tower clocks the chapters and minutes together will take up
one-third of the radius of the dial; the figures two-thirds of this, or
two-ninths of the radius, and the minutes two-thirds of the remaining
one-ninth of the radius, with every fifth minute more strongly marked
than the rest.
We often hear stories concerning the IIII in place of IV. The story
usually told is that Louis XIV of France was inspecting a clock made
for him by a celebrated watchmaker of that day and remarked that the IV
was an error. It should be IIII. There was no disputing the King and so
the watchmaker took away the dial and had the IIII engraved in place of
IV, and that it has thus remained in defiance of all tradition.
Mr. A. L. Gordon, of the Seth Thomas Clock Co., has the following
to say concerning this story and thus furnishes the only plausible
explanation we have ever seen for the continuance of this manifest
error in the Roman numeral of the dial:
“That the attempt has been made to use the IV for the fourth hour on
clock dials, any one making a study of them may observe. The dials on
the Big Ben clock in the tower of the Parliament buildings, London,
which may be said to be the most celebrated clock in the world, have
the IV mark, and the dial on the Herald building in New York City also
has it.
“That the IIII mark has come to stay all must admit, and if so there
must be a good and sufficient reason. Art writers tell us that pictures
must have a balance in the placing and prominence of the several
subjects. Most conventional forms are equally balanced about a center
line or a central point. Of the latter class the well known trefoil is
a common example.
“A clock or watch dial with Roman numerals has three points where the
numerals are heavier, at the IIII, VIII and XII. Fortunately these
heavier numerals come at points equally spaced about the center of
the dial and about a center line perpendicular to the dial. Of these
three heavy numerals the lighter of them comes at the top and it is
especially necessary that the other two, which are placed at opposite
points in relation to the center line, should be balanced as nearly
as possible. As the VIII is the heavier and cannot be changed, the
balancing figure must be made to correspond as nearly as possible, and
if marked as IV, it will not do so nearly as effectively as if the
usual IIII is used.”
It is comparatively an easy matter to make a metal dial either of
zinc, copper or brass, by laying out the dial as indicated above with
Roman chapters and numerals, after first varnishing the metal with
asphaltum. This may be drawn upon with needle points which cut through
the asphaltum and make a firmly defined line on the metal. It is best
to lay out your dial in lead pencil and then take a metal straight edge
and a needle point and trace through on the pencil marks. Mistakes may
be painted out with asphaltum, so that the job becomes easy. After
this has been done a comparatively dull graver may be used to cut or
scrape away the asphaltum where the metal is to be etched and then the
plate may be laid in a tray, a solution of chloride of iron poured on
and rocking the tray will rapidly eat away the metal, forming sunken
lines wherever the copper or brass is not protected by the asphaltum.
This furnishes a rough surface on the etched portions, which enables
the filling to stick much better than if it were smooth. In tracing the
circles a pair of heavy, stiff, carpenters’ compasses will serve where
the watchmaker has not a lathe large enough to swing the dial. In all
such cases it is best to start with a prick-punched center, tracing the
minute circles and the serifs of the chapters with the compasses and
then do your further division and marking by lead pencil, followed with
the needle and then by the acids. It should be done before the holes
are bored for the minute and seconds centers, as you then have an exact
center to mark from and can go back to it many times.
This will be necessary in dividing the minute or seconds circle by hand
(without an index on the lathe), as one of the tests of true division
consists in having all marks lined up with a straight edge placed
across the center. Thus IX and III should be in line with the center;
VI and XII; X and IIII; I and VII, etc. It will readily be seen that
for such purposes of reference the center should not be punched too
large.
If it is desirable to ornament the dial, the desired ornament may be
drawn on in the plain surface through the asphaltum and etched at the
same time as the chapters and degrees. Or chapters and ornament may
be drawn, pierced with a saw, engraved, filed up and backed up with a
plain plate of another color. Gold ornament and silver background looks
well.
Practically all the clocks having seconds hands carry that hand in
such a position as to partially obscure the XII, with the exception
of watchmakers’ regulators, and these, if they have separate hour,
minute and seconds circles, are made large enough to occupy the space
between the center and the minute circle, placing the hour circle
between the center and the thirtieth minute; the seconds between the
center and the sixtieth minute. The reason for this is that in the
watchmakers’ regulators the hours are almost a matter of indifference;
minutes are seldom referred to; the real comparison in watch regulation
comes on the seconds hand. For this reason the seconds hand is made as
large as possible and the chapters being placed on the hour circle by
themselves, the seconds circle may occupy almost the entire distance
between the center of the dial and the minute circle. They are placed
one above the other because in regulators the time train is nearly
always a straight-line train, which brings the seconds arbor vertically
over the center arbor, and consequently the centers of the dials must
be placed on a vertical line.
When the engraving has been properly done on a flat dial it is
desirable to fill it with black in order to make it legible. There are
several methods by which this may be done. The most durable is to make
a black enamel and if it is a valuable clock the movement is generally
worth a fine dial. The following formula will furnish a good black
enamel:
Siliceous sand 12 parts
Calcined borax 20 parts
Glass of antimony 4 parts
Saltpetre 1 part
Chalk 2 parts
Peroxide of Manganese 5½ parts
Fine Saxony Cobalt 2 parts
The enamel is ground into coarse particles like sand, and the incised
lines filled with it, after which the brass or copper plate is heated
red hot to fuse the enamel. Two or three firings may be necessary to
completely fill the lines; after filling they are stoned off level with
the surface of the dial. Jeweler’s enamel may be purchased of material
dealers and used for the dials.
Black asphaltum mixed with a little wax or pitch, or even watchmakers’
cement, used to fasten staffs and pinions into a lathe for turning, is
also used on these dials and with a sufficient proportion of wax or
pitch it prevents shrinking and forms a very satisfactory dial with the
single exception that it cannot be cleaned with benzine or hot potash,
which will dissolve the enamel. Shoemakers’ heel ball is also used
for repair jobs. In order to make either of these stick, the brass or
copper plate is heated up so as to “hiss” as will a laundry flat iron
when touched with a wetted finger, and a cement stick is rubbed over
the letters to fill them; the excess of filling can be scraped off
with an ivory scraper when at the right temperature—a little below the
boiling point of water. Such filled letters can be lacquered over by
going very quickly over the work so as not to dissolve the shellac in
the cement.
Another way is to fill the letters with black lacquer. For quick
repairs this is probably as good as any. Many of the old grandfather
clocks have been filled in with a putty made with copal varnish and
some black pigment. All putties shrink in drying and consequently
crack and finally fall out. The wax and pitch are not subject to these
disadvantages. If the plates are to be polished, polishing should
precede the filling in of the letters, else the work may have to be
done all over again. Black sealing wax and alcohol are also used,
applied as a paint with a fine brush.
If the dial is to be silvered or gilt the blacking should be done
first, and if to be electroplated the blacking should be what is known
as the “platers’ resist,” which is composed chiefly of asphaltum and
pitch dissolved in turpentine. It is also called “stopping-off”
varnish, and has large use in the plating establishments to prevent
deposition of metal where it is not desired.
The repairer who gets many grandfather clocks will often find that it
is necessary to repaint the dial, generally because of a too vigorous
scrubbing, or because of cracks or scaling, which the owner may
dislike. It is always best, however, to be cautious in such matters,
as many people value such a clock chiefly on account of its visible
evidences of age and such cracks form generally a large proportion of
such evidence. Therefore it is best never to touch an antique dial
unless the owner desires it.
Such dials are usually sheet-iron, and tolerably smooth, so the metal
will need but a few coats of paint to prepare it. For ground coats,
take good, ordinary white-lead or zinc white, ground with oil, and if
it has much oil mixed with it pour it off and add spirits of turpentine
and Japan dryer—a teaspoonful of dryer for every half pint of paint.
The test for the paint having the right amount of oil left in it is,
it should dry without any gloss. Rub every coat you apply with fine
sand paper, after it is perfectly dry, before applying the next coat
of paint. For the final coat, lay the dial flat and go over it with
French zinc white. This coat dries very slow, and for a person not
used to such work, is hard to manage. The next best (and for ordinary
clock or watch making _the best_) for the last pure white coat is to
take a double tube of Windsor & Newton’s Kremnitz white, thinned with a
little turpentine. Such tubes as artists use are the kind. Apply this
last white coat with a flat, camel’s hair brush. The tube-white should
have turpentine enough added to cause it to flow freely, and sink flat
and smooth after the brush. The letters or figures should be painted
with ivory-black, which is also a tube color. This black is mixed with
a little Japan, rubbing varnish and turpentine, and the lettering is
done with a small, sign writer’s pencil. Any flowers or ornaments are
painted on at the same time; and after they are dry the dial should be
varnished with Mastic or Damar varnish or white shellac. All kinds of
coach (Copal) varnish are too yellow.
Painted dials on zinc will blister and crack off if subjected to
extremes of heat and cold, unless they are painted with zinc white
instead of lead for all white coats. The reason is the great difference
in expansion between lead paint and metallic zinc. This case is similar
to that of using an iron oxide to paint iron work of bridges, ships,
etc., where other oxides will chip and scale off.
The metal dials on these old clocks were silvered by hand. When you get
such a dial, discolored and tarnished, it can be cleaned in cyanide and
resilvered, without sending it to an electroplater, by the following
formula:
Dissolve a stick of nitrate of silver in half a pint of rain water;
add two or three tablespoonfuls of common salt, which will at once
precipitate the silver in the form of a thick, white curd, called
chloride of silver. Let the chloride settle until the liquid is clear;
pour off the water, taking care not to lose any chloride; add more
water, thoroughly stir and again pour off, repeating till no trace of
salt or acid can be perceived by the taste. After draining off the
water add to the chloride about two heaped tablespoonfuls each of salt
and cream of tartar, and mix thoroughly into a paste, which, when
not in use, must not be exposed to the light. To silver a surface of
engraved brass, wash the surface clean with a stiff brush and soap.
Heat it enough to melt black sealing wax, which rub on with a stick of
wax until the engraving is entirely filled, care being taken not to
burn the wax. With a piece of flat pumice-stone, and some pulverized
pumice-stone and plenty of water, grind off the wax until the brass is
exposed in every part, the stoning being constantly in one direction.
Finish by laying an even and straight grain across the brass with blue
or water of Ayr stone. Take a small quantity of pulverized pumice-stone
on the hand, and slightly rub in the same direction, which tends to
make an even grain; the hands must be entirely free from soap or
grease. Rinse the brass thoroughly, and before it dries, lay it on a
clean board, and gently rub the surface with fine salt, using a small
wad of clean muslin. When the surface is thoroughly covered with salt,
put upon the wad of cloth, done up with a smooth surface, a sufficient
quantity of the paste, say to a dial three inches in diameter a piece
of the size of a marble, which rub evenly and quickly over the entire
surface. The brass will assume a greyish, streaked appearance; add
quickly to the cloth cream of tartar moistened with water into a thin
paste; continue rubbing until all is evenly whitened. Rinse quickly
under a copious stream of water; and in order to dry it rapidly, dip
into water as hot as can be borne by the hands, and when heated,
holding the brass by the edges, shake off as much of the water as
possible, and remove any remaining drops with clean, dry cloth. The
brass should then be heated gently over an alcohol lamp, until the wax
glistens without melting, when it may be covered with a thin coat of
spirit varnish, laid on with a broad camel’s hair brush. The varnish or
lacquer must be quite light colored—diluted to a pale straw color.
It is now possible to buy silver plating solutions which can be used
without battery and they will produce the same effect as the formula
just given. If they happen to be in stock for the repairing of jewelry
they may be used in cleaning the dials, but as this is liable to fall
into the hands of many who are far from such conveniences, we furnish
the original recipe, which can be executed anywhere the materials can
be obtained.
If the dial is of brass, very good effects have been produced by
stopping off portions of the dial in an ornamental pattern before
silvering, and then lacquering after removing the resist. But for a
plain black and brass dial a dip of strong sulphuric acid two parts,
red fuming nitrous acid one part, and water one part, mixed in the open
air and dipped or flowed over the dial, forms what is known as the
platers’ bright dip. After dipping the article should at once be rinsed
in hot water and dried, and lacquered at once with a lacquer of light
gold color. This makes a very neat and durable finish.
The satin effect may be obtained on a dial by prolonging the acid dip
and otherwise proceeding as before. Many of these dials were of zinc
and all that applies to brass or copper may be also executed in zinc,
but in plating it will be found necessary to plate two or three times,
as the single coating will apparently disappear into the zinc unless
it is given a heavy deposit of copper in a plating bath. Where it is
desired to obtain a bright gold color, the gold plating solutions
now sold for the coloring of jewelry may also be used on either of
these metals. For the reasons given above, however, they are not very
successful on a zinc base.
Many of the cheap clocks have paper dials glued on a zinc plate and
when the dial is soiled the repairer cleans them up by pasting another
dial on top of the original. These dials are made on what is known as
lithographic label paper; that is paper which is waterproof on one
side, so that it will not shrink or swell when dampened. In addition to
the lithograph coating they are generally given a varnish of celluloid
by the clock manufacturers, thus making them practically waterproof.
They are very cheap and the repairer will find that he will obtain in
prestige from such new dials far more than they cost.
Tarnished metal dials are best cleaned by a dip of cyanide of
potassium, of about the same strength as that used for cleaning silver.
If the tarnished parts have been gilded, however, the cyanide should be
excessively weak. Mining men use a cyanide solution for the recovery
of gold, which is only two-tenths of one per cent cyanide, and this
will collect all the gold from ore that runs from $10 to $15 to the
ton, the pulp in such cases being left in the solution from seventy to
ninety hours. The ordinary cyanide dip for the jeweler is one ounce
to thirty-two of water, while the miner’s solution is two-tenths of an
ounce to one hundred ounces of water. You can see that with the strong
cyanide solution the gilt surface will all be taken off unless very
rapid dipping is strictly followed by thorough washing.
A novelty which keeps periodically coming to the front, say about once
every ten years, is the luminous dial. This is done by painting the
dial with phosphorus or a phosphorescent powder. Then when it is placed
in the light it will absorb light and give it off in the dark until the
evaporation of the phosphorus.
The composition and manufacture of this phosphorescent powder is
effected in the following manner: Take 100 parts by weight of carbonate
of lime and phosphate of lime, produced by calcination of sea-shells,
especially those of the tridacna and cuttlefish bone, and 100 parts
by weight of lime, rendered chemically pure by calcination. These
ingredients are well mixed together, after which 25 parts of calcinated
sea salt are added thereto, sulphur being afterward incorporated
therewith to the extent of from 25 to 50 per cent of the entire mass,
and a coloring matter is applied to the composition, which coloring
matter consists of from 3 to 7 per cent of the entire mass of a powder
composed of a mono-sulphide of calcium, barium, strontium, magnesium
or other substance which has the property of becoming luminous in the
dark, after having been impregnated with light. After these ingredients
are well mixed, the composition is ready for use. Its application to
clock dials is made either by incorporating suitable varnish therewith,
such as copal, and applying the mixture with a brush to the surface
of the dial, or by the production of a dial which has a self-luminous
property, imparted to it during its manufacture. This is effected in
the following manner: From 5 to 20 per cent of the composition obtained
and formed as above described, is incorporated with the glass while
it is in a fused state, after which the glass so prepared is molded
or blown into the shape or article required. Another process consists
of sprinkling a quantity of the composition over the glass article
while hot, and in a semi-plastic state, by either of which processes a
self-luminous property will be imparted to the article so treated.
Where enamel dials are chipped the cracks may be hidden by first
pressing the cracks very slightly open and washing out. Then work in a
colorless cement to fill the crack, allow to dry and stone down. Where
holes have been left by the chipping, melt equal parts of scraped pure
white wax and zinc white and let it cool. Warm the dial slightly and
press the cold wax into the defective places and scrape off with a
sharp knife and it will leave a white and lustrous surface. If too hard
add wax; if too soft add some zinc white.
VARNISH FOR DIALS, ETC.—A handsome varnish for the dials of clocks,
watches, etc., may be prepared by dissolving bleached shellac in the
purest and best alcohol. It offers the same resistance to atmospheric
influence that common shellac does. In selecting bleached shellac for
this purpose be careful to get that which will dissolve in alcohol, as
some of it being bleached with strong alkalies, is thereby rendered
insoluble in alcohol. The shellac when dissolved should be of a clear
light amber color in the bottle and this will be invisible on white
paper when dry.
Colorless celluloid lacquer, known to jewelers as “silver lacquer”
on account of its being used to prevent tarnish on finished hollow
ware, also makes a good varnish to apply to dials, either metallic or
painted. It is best to have it thin, flow it on the dial and then level
the dial to dry.
Success in the repairing of a broken enameled clock dial will greatly
depend upon the practical skill of the operator, as well as of a
knowledge of the process. If it is only desired to repair a chipped
place on a dial, a fusible enamel of the right tint should be procured
from a dealer in watchmakers’ materials, which, with ordinary care,
may be fused on the chipped place on the dial so as to give it a
workmanlike appearance when finished off. The place to receive the
enamel should be well cleaned, and the moist enamel spread over the
place in a thin, even layer; and, after allowing it to dry, the dial
may be held over a spirit lamp until the new enamel begins to fuse,
when it may be smoothed down with a knife. The dial, after this
operation, is left to cool, when any excess of enamel may be removed by
means of a corundum file, and subsequently polished with putty powder
(oxide of tin). The ingredients of enamel, after being fused into a
mass, are allowed to cool, then crushed to powder and well washed to
get rid of impurities, and the resulting fine powder forms the raw
material for enameling. It is applied to the object to be enameled in a
plastic condition, and is reduced to enamel by the aid of heat, being
first thoroughly dried by gentle heat, and then fused by a stronger
one. The following is a good white enamel for dials:
Silver sand, 3 ounces; red lead, 3¾ ounces; oxide of tin, 2½ ounces;
saltpeter, ½ ounce; borax, 2 ounces, flint glass, 1 ounce; manganese
peroxide, 2 grains. The basis of nearly all enamels is an easily
fusible colorless glass, to which the required opacity and tints are
given by the addition of various metallic oxides, and these, on being
fused together, form the different kinds of vitreous substances used by
enamel workers as the raw material in the art of enameling.
The hands of timekeepers are worthy of more attention than is
frequently bestowed upon them by watch and clockmakers. Their shape
and general arrangement, and the neatness of their execution is often
taken by the general public as an index to the character of the entire
mechanism that moves them; and some are apt to suppose that when care
is not bestowed on the parts of the timepiece which are most seen,
much care cannot be expected to have been exercised on the parts of
the watch or clock which are invisible to the general view. Although
we are not prepared to fully endorse the opinion that when the hands
of timepieces are imperfect in their execution, or in their general
arrangement, all the mechanism must of necessity be imperfect also;
still we think that in many instances there is room for improving the
hands of timepieces, and we desire to direct more attention to this
subject by the workmen.
In the general arrangement of the hands of watches and clocks,
distinctness of observation should be the great point aimed at, and
everything that has a tendency to lead to confusion should be carefully
avoided. Clocks that have a number of hands radiating from one center,
and moving round one circle—as for instance, center seconds, days of
the month, equation of time, alarms and hands for other purposes—may
show a good deal of mechanical skill on the part of the designer and
maker of the timepiece; but so many hands moving together around one
circle, although they may be of different colors, causes confusion,
and requires considerable effort to make out what the different hands
point to in a dim light, and this confusion is frequently increased by
the necessity for a counterpoise being attached to some of the hands.
As a rule timekeepers should be so arranged that never more than the
hour and minute hand should move from one center on the dial. There
may be special occasions when it is necessary or convenient to have
center seconds to large dials; but these occasions are rare, and we are
talking about the hands of timekeepers in everyday use for the ordinary
purposes of life, and also for scientific uses. In astronomical clocks
and watchmakers’ regulators we find the hour, minute and second hands
moving on separate circles on the same dial; and the chief reason
for this arrangement is to prevent mistakes in reading the time. In
chronometers, especially those measuring sidereal time, the hour hand
is frequently suppressed, and the hours are indicated by a star wheel,
or ring, with figures engraved on it, that show through a hole in the
dial.
Hour and minute hands should be shaped so that the one can be easily
distinguished from the other without any effort on the part of the
observer. Probably a straight minute hand, a little swelled near the
point, and a spade hour hand, are the shapes best adapted for this
purpose, especially if the hands have to be looked at from a distance.
There are occasions, however, when a spade hand cannot be used with
propriety. In small watches and clocks having ornamental cases, hands
of other designs are desirable, but whatever be the pattern used, or
whatever color the hands may be made, it should ever be remembered that
while a design in harmony with the case is perfectly admissible, the
sole use of hands is to mark the time distinctly and readily.
The difference in the length of the hour and minute hands is also an
important point in rendering the one easily distinguished from the
other. The extreme point of the hour hand should extend so as to just
cover the edge of the inside end of the numerals and the extreme point
of the minute hand should cover about two-thirds of the length of the
minute divisions. Hands made of this length will be found to mark the
hours and minutes with great plainness, and the rule will be found to
work well in dials of all sizes. As a general rule, the extreme points
of the hands should be narrow. The point of the hour hand should never
be broader than the thickest stroke of any of the numerals, and the
extreme point of the minute hand never broader than the breadth of
the minute lines; and in small work it is well to file the ends of
the hands to a fine point. The ends of minute hands should in every
instance be bent into a short, graceful curve pointing toward the dial,
and as close to it as will just allow the point of the hand to be
free. The minute hands of marine chronometers are invariably bent in
this manner, and the hands of these instruments are usually models of
neatness and distinctness.
Balancing hands by means of a counterpoise is a subject which requires
some attention in order to effect the perfect poise of the hand without
detracting anything from its distinctness. In watch work, and even in
ordinary clock work, it seldom happens that any of the hands except
the seconds require to be balanced, and then there is only one hand
moving round the same circle, as is the case with seconds hands in
general. We have become so accustomed to looking at seconds hands with
projecting tails that we are apt to regard the appearance of the hands
to be incomplete without the usual tail; but we must remember that
the primary object in view in having a tail to a seconds hand is to
counterpoise it, not to improve the looks of the hand itself. Poising
becomes an actual necessity for a hand placed on so sensitive a part
as the fourth wheel of a watch, or on the scape wheel of a fine clock.
When only one hand moves in the same circle, like a seconds hand, the
counterpoise may be effected by means of a projecting tail without in
any way detracting from a distant reading of the hands, providing the
tail is not made too long, and it is made of such a pattern that the
one end can easily be distinguished from the other. In minute and hour
hands, however, it is different. These two hands move round the same
circle, and a counterpoise on the minute hand is liable at a distance
to be mistaken for the hour hand.
The minute hands of large timepieces frequently require to be balanced,
especially if the dial be large in comparison to the size of the
movement; and in very large or tower clocks, whatever may be the size
of the movement, it becomes an absolute necessity to balance the hands.
In our opinion, tails should never be made on minute hands, when they
can be avoided, and in cases where tails cannot be dispensed with,
they should invariably be colored the same as the ground of the dial.
In almost every instance, however, minute hands may be balanced in
the inside, as is usual with tower clocks. A great many clocks used
for railway and similar purposes in Europe have their minute hands
balanced in this manner, and the plan works admirably; for in addition
to rendering the hands more distinct, the clocks require less power to
keep them going than when the hands are balanced from the outside.
[Illustration: Fig. 150. Showing counterpoise on arbor of minute hand
in tower clock.]
Tower clock hands are generally made of copper, elliptical in section,
being made up of two circular segments brazed together at the edges,
with internal diaphragms to stiffen them. The minute hand is straight
and perfectly plain, with a blunt point. At the center of the dial the
width of the minute hand is one-thirteenth of its length, tapering to
about half as much at the point.
The hour hand is about the same width, ending just short of the
dial figure and terminating in a palm or ornament. The external
counterpoises are one-third the length of the minute hand, and of such
a shape that they will not be confounded with either of the hands; a
cylinder, painted the same color as the dial, and loaded with lead,
makes a good counterpoise. This counterpoise may be partly on the
inside of the dial if it is desired to keep it invisible, but it should
not be omitted, as it saves a good deal of power, prevents the twisting
of the arbors, and also assists in overcoming the action of the wind
on the hands. Two-thirds of the counterpoise weight may be inside, as
shown in Fig. 150.
TO BLUE A CLOCK HAND OR A SPRING.—To blue a piece of steel that is of
some length, a clock hand for example, clockmakers place it either
on ignited charcoal, with a hole in the center for the socket, and
whitened over its surface, as this indicates a degree of heat that is
approximately uniform, or on a curved bluing tray perforated with holes
large enough to admit the socket. The center will become violet or blue
sooner than the rest, and as soon as it assumes the requisite tint,
the hand must be removed, holding it with tweezers by the socket, or
by the aid of a large sized arbor passed through it; the lower side of
the hand is then placed on the edge of the charcoal or bluing tray,
and removed by gradually sliding it off toward the point, more or less
slowly, according to the progress made with the coloring; with a little
practice, the workman will soon be enabled to secure a uniform blue
throughout the length and even, if necessary, to retouch parts that
have not assumed a sufficiently deep tint.
Instead of a bluing tray, a small mass of iron, with a slightly rounded
surface and heated to a suitable temperature, can be employed; but the
color must not form too rapidly, and this is liable to occur if the
temperature of the mass is excessive. Nor should this temperature be
unevenly distributed.
A spring, after being whitened, can be blued in the same way. Having
fixed one end, it is stretched by a weight attached to the other end,
and the hot iron is then passed along it at such a speed that a uniform
color is secured. Of course, the hot iron might be fixed and the spring
passed over it. A lamp may be used, but its employment involves more
attention and dexterity.
CHAPTER XXIII.
CLOCK CASING AND CASE REPAIRS.
PRECISION CLOCK CASES.—The casing of a precision clock is only
secondary in importance to the compensation of its pendulum. The best
construction of an efficient case can be ascertained only by most
careful study of the conditions under which the clock is expected to
be a standard timekeeper, and often the entire high accuracy sought by
refined construction is sacrificed by an inefficient case and mounting.
The objects of casing a precision clock are as follows:
a. To protect the mechanism from the effects of dust
and dirt.
b. To avoid changes of temperature and barometric
pressure.
c. To provide an enclosed space in which the gas
medium in which the pendulum swings shall have any
chemical constitution, of any hygroscopic condition.
d. There must be provided ready means of seeing and
changing the condition of the pendulum, electric
apparatus, movement, etc., without disturbing the
case except locally.
Now if we hold the above considerations in view we can readily see that
cast iron, wood and glass, with joints of wash leather (which is kept
soft by a wax cement which does not become rancid with age), are the
preferable materials.
The advantages of using cast iron for the pillar or body of the case
are that it can be cast in such a shape as to require very little
finishing afterwards, and that only such as planing parallel surfaces
in iron planing machines. It makes a stiff column for mounting the
pendulum when it rests upon a masonry foundation from below. Plates
of glass can be clamped against the planed surfaces of iron piers (by
putting waxed wash leather between the glass and the iron) so as to
make air-tight joints without difficulty.
The mass of iron symmetrically surrounding the steel pendulum is
the safest protection the clock can have against casual magnetic
disturbances. In the language of electricians it “shields” the pendulum.
Suppose, then, we adopt as the first type of precision clock case which
our present knowledge suggests, that of an iron cylinder or rectangular
box resting on a masonry pier, and which has a table top to which the
massive pendulum bracket is firmly bolted. This type admits of the
weights being dropped in small cylinders outside of the cast iron
cylinder or box. These weight cylinders, of course, end in the table
top of the clock case above and in the projecting base of the flange of
the clock case below.
With this construction it is a simple matter to cover the movement
with a glass case, preferably made rectangular, with glass sides, ends
and top, with metal cemented joints. The metal bottom, edges of this
rectangular box can be ground to fit the plane surface of the top of
the clock case. Then, by covering the bottom edges with such a wax as
was used in making the glass plates fit the iron case in front or back,
we can secure an air-tight joint at the junction of the rectangular top
glass case with iron case. In practice the wax to be used may be made
by melting together and stirring equal parts of vaseline and beeswax.
The proportions may be varied to give a different consistency of wax,
and it may be painted on with a brush after warming over a small flame.
If the clock case will be exposed to a comparatively high temperature,
say 95° F., then the beeswax can be 3 parts to 1 of vaseline. The good
quality of this cement wax is that it does not change with age, or at
least for several years, is very clean, and can be wiped off completely
with kerosene, or turpentine, or benzine. In all joints meant to be
air-tight, the use of rubber packing is to be avoided. It answers well
enough at the start, but after several months it is sure to crack and
leak air.
By an air-tight joint I do not mean a joint which will not leak air
under any pressure which may be applied. It is not necessary that our
pendulum should vibrate in a vacuum; all we want is that the pressure
inside the clock case should be uniform; that it should not vary with
the barometer outside. In actual practice we find it best to have the
pressure inside the case as nearly as possible equal to the average
atmospheric pressure outside. Now, if the barometer in a given locality
never sinks below 27.5 inches, it is not necessary that the vacuum in
the clock case be less than that represented by 29.5 inches of mercury
pressure. So, too, if it were desirable to have the pressure inside the
case greater than that outside, owing to some special form of joint
which made the clock case less liable to leak out than to leak in,
it might be that an inside pressure would be efficient at 31 inches
of mercury. By not having the inside pressure vary but slightly from
the outside, the actual pressure of air will not exceed one inch of
mercury, or, say, pound pressure to the square inch. This is a pressure
which causes quite an insignificant strain upon any joint.
There are objections, however, to the use of air in an enclosed space
for precision clocks and so the attempt has been made to use hydrogen.
Air is, comparatively speaking, heavy. It is 14½ times as heavy as
hydrogen gas, for instance. The pendulum, therefore, in moving through
its arc has to push aside 14 times as much weight as it would have
to in case it were surrounded by hydrogen. Then what might be called
the “case friction” is greater than if we used hydrogen. By “case
friction” I mean resistance and a disturbance to the pendulum depending
on the effect of the currents of air produced by driving the air
before the pendulum against the sides and front of the case. It is
a well-established observation that small, cramped cases disturb the
clock’s rate more than large, roomy ones. This is because the air,
having no room to go before the pendulum, is cushioned up against the
side of the case at each pendulum swing, and acts as a resisting spring
against the swing of the pendulum. By the time the pendulum has reached
the end of its vibration the air has escaped upwards and downwards
perhaps so that it no longer has its spring power to restore the loss
of energy to the pendulum. This “case friction” is most pernicious in
its action when associated with free falling weights in the clock case.
Clock weights should always fall in separate compartments, and never
in such a manner that they can affect the space in which the pendulum
swings.
But this is a digression to explain the term “case friction” in its use
in horology.
Precision clocks, almost without exception, have electric break-circuit
attachments within the case. Most of these break-circuits are
constructed so that there is a small spark every time the circuit is
broken. The effect of such a spark in air is to convert a small portion
of the air in the immediate neighborhood of the spark into nitrous
acid gas. After several months there might be a considerable quantity
of this gas in the case, with the certain result of rusting the nicer
parts of the escapement.
Many attempts have been made to run a clock in an almost complete
vacuum of air; but the volume to be exhausted is so large, and the
leakage is so sure to occur after a time, that the attempt is now
pretty generally abandoned. It will be inferred from what has preceded
that a full atmosphere of hydrogen would only offer one-fourteenth the
resistance to the pendulum that air would, and all the disturbances
arising from the surrounding mediums would be only one-fourteenth for
hydrogen of that which we would expect for air. Every consideration,
therefore points to the use of hydrogen as the medium with which to
fill our clock cases. It is inert, it forms no compounds under the
influence of the electric spark, the case friction is no greater
than would exist if we made an air vacuum of only about 1 inch of
mercury, and hydrogen gas may be readily prepared. The method from
dilute sulphuric acid and scrap zinc is the handiest, and it will be
found described in almost any chemistry textbook or encyclopedia.
Should the horologist wish to know something of the chemistry of the
process, without previous study, he will find it described in very
simple language in any primary chemistry. The practical details of
filling a clock case with hydrogen gas I have not yet worked out. It
is evident that since hydrogen is 14½ times lighter than air, that by
attaching a small tube to the source of hydrogen and to the top of the
clock case, and another small outlet tube at the bottom of the clock
case, that by gravity alone the hydrogen would fill the upper part of
the case and drive the air before it out at the bottom. The hydrogen
should be dry. To insure this it should pass through a tube containing
quicklime, which, if it is a foot long and two inches in diameter,
will be sufficient. No burning light or electric spark must be put
into the case while filling, because the mixture of hydrogen with the
air is very explosive when ignited. Great care must be used in making
all joints when attempting to maintain an atmosphere of hydrogen as it
leaks readily through the pores of wood iron and all joints. It is,
therefore, better to treat the case friction as a constant element and
simply keep it constant.
The above discussion has not considered the temperature question. It
is important that the changes of temperature in a clock case should
be as slow as possible and as small as possible. Professor Rogers,
of the Harvard College Observatory, has shown that such bars as are
used in pendulum rods of clocks are often several hours in taking
up air temperatures many degrees different from that in which they
were swinging. We have at the top of the pendulum a thin spring for
suspension whose temperature decides its molecular friction; then we
have the pendulum rod, and lastly the large bob, all of which take up
any new temperature with different degrees of slowness. Now obviously
no compensation can be made to act unless the temperatures are the same
for all parts of the pendulum, and vary at the same rate. A number of
years ago, there was a long discussion as to the temperature at the top
and bottom of clock cases. It was shown that this regularly amounted to
several degrees in the best clocks. It was to lessen this difference
that at the Harvard College Observatory the Bonds built a deep well in
the cellar, purposing to put the clock at its bottom. The idea was a
good one, and were it not for the difficulty in getting at clocks in
wells, and keeping water out, it would doubtless find favor where the
utmost accuracy is desired.
A better plan is to run the clock at a high temperature, say 95° to
100° F. The oil is more liquid, the temperature can be more easily
maintained, it can all take place in lighted, dry rooms, and the means
for doing this we shall now consider.
[Illustration: Fig. 151. Section through clock room of the Waltham
Watch Company.]
Our iron case must now be housed in another outside case, which had
better be of wood, with glass windows for seeing the clock face. A
single thickness of wood would conduct heat too rapidly. It must
therefore be made of two thicknesses, with an air space between. If the
air space is left unfilled, the circulation of the air soon causes the
inner wooden layer to be of the same temperature as the outer. It is
necessary to prevent this circulation of air therefore by means of some
substance which is a non-conductor of heat and which will prevent the
air from circulating. The very best thing to be used in this connection
is cotton batting, which has been picked out until it is as light
and fibrous as possible. Then if the doors and windows of the wooden
case are made of two thicknesses of extra thick glass, and are firmly
clamped, by screws through their sashes or some other means, to the
frame of the case, we have the best form possible for our completed
case of the type I have described. It now remains to provide a layer
of hot water pipes inside the clock room, heated by circulating hot
water from the outside. The flame under the water tank outside, whether
of gas or kerosene, to be automatically raised or lowered by any such
thermostat arrangements as are in common use with chicken incubators,
when the temperature varies from the point desired. Experience teaches
that the volume of water had better be considerable, if there is
considerable difference in the annual variations of temperature
according to the seasons. Thus in Massachusetts or Illinois the
temperature is likely to vary from -30° F. to +110° F., and the heating
arrangements must be suitable to take care of this variation.
The Waltham Watch Company’s clock room is an excellent example of
the means taken to secure uniformity of temperature and absence of
vibration.
The clock room, which is located in the basement of one of the
buildings, is built with a double shell of hollow tile brick. The
outer shell rests upon the floor of the basement, and its ceiling is
within two or three inches of the basement ceiling. The inner shell is
10 feet square and 8 feet in height, measured from the level of the
cellar floor. There is an 18-inch space between the walls of the inner
and outer shell and a 9-inch space between the two ceilings. On the
front of the building the walls are three feet apart to accommodate the
various scientific instruments, such as the chronograph, barometer,
thermostat, level-tester, etc. The inner house is carried down four
feet below the floor of the basement, and rests upon a foundation of
gravel. The walls of the inner house below the floor level consist of
two thicknesses of brick with an air space between, and the whole of
the excavated portion is lined, sides and bottom, with sheet lead,
carefully soldered to render it watertight. At the bottom of the
excavation is a layer of 12 inches of sand, and upon this are built up
three solid brick piers, measuring 3 feet 6 inches square in plan by 3
feet in height, which form the foundation for the three pyramidal piers
that carry the three clocks. The interior walls and ceilings and the
piers for the clocks are finished in white glazed tiling. The object
of the lead lining, of course, is to thoroughly exclude moisture,
while the bed of sand serves to absorb all waves of vibration that
are communicated through the ground from the various moving machinery
throughout the works. At the level of the basement floor a light
grating provides a platform for the use of the clock attendants.
Although the placing of the clock room in the cellar and the provision
of a complete air space around the inner room would, in itself, afford
excellent insulation against external changes of temperature, the inner
room is further safeguarded by placing in the outer 18-inch space
between the two walls a lamp which is electrically connected to, and
controlled by, a thermostat. The thermostat consists of a composite
strip of rubber and metal, which is held by a clamp at its upper
end and curves to right or left under temperature changes, opening
or closing, by contact points at the lower end of the thermostat,
the electrical circuit which regulates the flame of the lamp. The
thermostat is set so as to maintain the space between the two shells at
a temperature which shall insure a constant temperature of 71 degrees
in the inner clock house. This it does with such success that there is
less than half a degree of daily variation.
The two clocks that stand side by side in the clock room serve to keep
civil time, that is to say, the local time at the works. The clock to
the right carries a twelve-hour dial and is known as the mean-time
clock. By means of electrical connections it sends time signals
throughout the whole works, so that each operative at his bench may
time his watch to seconds. The other clock, known as the astronomical
clock, carries a twenty-four-hour dial, and may be connected to the
works, if desired. These two clocks serve as a check one upon the
other. They were made at the works and they have run in periods of
over two months with a variation of less than 0.3 of a second, or
¹/₂₅₉₀₀₀ part of a day. The third clock, which stands to the rear of
the other two, is the sidereal clock. It is used in connection with the
observatory work, and serves to keep sidereal or star time.
The rate, as observed at the Waltham works, rarely exceeds one-tenth
of a second per day. That is to say, the sidereal clock will vary only
one second in ten days, or three seconds in a month. The variation, as
found, is corrected by adding or subtracting weights to or from the
pendulum, the weights used being small disks, generally of aluminum.
Summing up, then, we find that the great accuracy obtained in this
clock room is due to the careful elimination of the various elements
that would exercise a disturbing influence. Changes of temperature are
reduced to a minimum by insulation of the clock house within an air
space, in which the temperature is automatically maintained at an even
rate. Changes of humidity are controlled by the specially designed
walls, by the lead sheathing of the foundation pit, by the preservation
of an even temperature, and by placing boxes of hygroscopic material
within the inner chamber. Errors due to vibration are eliminated by
placing the clocks on massive masonry piers which stand upon a bed of
sand as a shock-absorbing medium.
The astronomical clock is inclosed in a barometric case, fitted with
an air pump, by which the air may be exhausted and the pendulum and
other moving parts relieved from barometric disturbances. For it must
be understood that variation in barometric pressure means a variation
in the density of the air, and that the speed of the pendulum must
necessarily be affected by such changes of density.
RESTORING OLD CASES.—Very often the watchmaker gets a clock which he
knows will be vastly improved by varnish, but not knowing how to take
off the old varnish he simply gives it a little sand paper or rubs it
off with oil and lets it go at that. Varnishing such a clock thinly
with equal parts of boiled oil and turpentine and allowing it to dry
will often restore the transparency of the varnish; if uneven results
are obtained a second coat may be necessary. Many of these old clocks
have not been varnished for so many years that the covering of the wood
looks like a cheap brown paint. To remove this in the ordinary way
means endless labor, and if the case is inlaid with colored patterns
of veneers, which are partly loosened by the glue drying out, the
repairer is afraid to touch it for fear he will only make matters worse
in the attempt to better them.
In the case of an old clock of inlaid marquetry, if the pieces of
veneer have become partly loosened, the first thing to do is to make
a thin, fresh glue. Work the glue under the veneer and then clamp it
down tightly with a piece of oiled paper, or waxed paper, laid between
the glue and the board used to clamp with and the whole firmly set
down tight with screws or screw clamps. To make waxed paper dissolve
parafine wax in benzine and flow or brush on the paper and let dry.
After the glue has hardened comes the work of removing the varnish. To
do this you will need some varnish remover, which can either be bought
at the paint store, or made as follows:
VARNISH REMOVER.—In doing such work the trick is to make sure that
nothing put on the case will injure it, as a clock one hundred years
old cannot be replaced. Therefore, if you are suspicious as to the
varnish removers you can purchase, and do not want to take chances, you
may make one of wood alcohol and benzole, or coal tar naphtha. Be sure
you do not get petroleum naphtha, which is common gasoline. The coal
tar naphtha is a wood product. The wood alcohol is also a wood product
and the varnishes used upon furniture are vegetable gums, so that
it will readily be seen that you are putting nothing on the antique
with which it was not associated in its natural state. Equal parts of
benzole and wood alcohol will dissolve gums instantaneously, so that
if the oil has dried out of the varnish so much that the varnish has
become opaque and only the rosins are left, the application of this
fluid with a brush will cause instant solution, making the gums boil
up and form a loose crust upon the surface of the wood, as the liquid
evaporates, which it does very rapidly.
Varnishes containing shellac and some other gums are rather hard to
dissolve and where an obstinate varnish is encountered it may be well
to use wax in the varnish remover. This is done by shaving or chopping
some parafine wax, dissolving it in the benzole, and when it is clear
and transparent, add the wood alcohol. Upon the addition of the alcohol
the wax immediately curdles so that the fluid becomes milky. In this
condition it is readily brushed upon any surface and when the wax
strikes the air it congeals and forms a crust which holds the liquid
underneath and enables it to do its work instead of evaporating.
The wax also serves the purpose of allowing the workman to see just
where he is putting his fluid and of holding it in position upon
vertical surfaces or ceilings, round moldings, carved work and other
places from which it will quickly run off. Only enough wax should be
added to make it spread readily with the brush and after soaking it
will be an easy matter to take a painter’s putty knife, a case knife,
or a scraper and laying it nearly flat on the wood remove all the
varnish at one operation, wiping off the knife as fast as it becomes
too full. After the bulk of the varnish is off some of the fluid,
without the wax, may be used upon a cloth to go over and smooth up by
removing the spots and stripes of varnish left by the knife, or in
moldings, etc., where the knife cannot be applied, and we have our bare
wood, which, after drying and sand papering, is ready for a fresh coat
of XXX coach varnish, which should dry in 24 hours and harden in a week.
A very little work and practice in this will enable the workman to
rapidly and cheaply clean up and repair antiques in such a way that it
will add greatly to his reputation.
To restore the gloss of polished wood it is not always the best plan to
employ true furniture polish. The majority of the so-called polishes
for wood are based on a mixture of boiled linseed oil and shellac
varnish, made by dissolving shellac in alcohol in the proportion of
four ounces of shellac to a pint of alcohol. A little of the dissolved
shellac is poured on to a canton-flannel rag, a few drops of the boiled
linseed oil are placed on the cloth, and the wood to be polished is
rubbed vigorously. About half an ounce of camphor gum dissolved with
the shellac in the alcohol will greatly facilitate the operation of
polishing.
A soft woolen rag, moistened with olive oil and vigorously rubbed
on dull varnished surfaces, like old clock cases, will brighten the
surface wonderfully. Some workmen add a few drops of a strong solution
of camphor gum in alcohol to the olive oil.
The polishing of cases is accomplished by applying several coats of the
best coach painters’ rubbing varnish, when, after perfect drying, the
surface is rubbed with a felt or a canton-flannel rag, folded flat,
using water and the finest pulverized pumice-stone. This operation
smooths the surfaces. The final polishing of such work is done by
rubbing with rotten stone and olive oil with the smooth side of canton
flannel. To remove the last traces of smear caused by the oil, an old,
soft linen cloth and rye flour is used. Of course, fine work like we
see on new cases of fine quality is not likely to be produced by one
who is unaccustomed to it; a man must serve a good, long apprenticeship
in the varnish finishing business before he is competent for it; and
even then some polishers fail to obtain the fine results achieved
by others. The great danger is that the rubber will cut through the
varnish and expose the bare wood on edges, corners and even in spots on
plane surfaces, before he has removed the lumps and streaks of varnish
on adjacent portions of the work. Whenever the varnish is flat and
smooth in any spot, you must stop rubbing there.
Black wood clocks which have become smoked and dull should have the
cases rubbed with boiled oil and turpentine on a piece of soft woolen
rag; afterwards polish off with a dry rag. If the gloss has been
destroyed it will have to be varnished. Flow the varnish well on and
use 1½-inch brush and be careful to get the varnish on even and so as
not to trickle. This is easy if you are careful to keep the varnish
thin and do not go over the varnish a second time after spreading it
on. Thin with turpentine and put very little on the case; it is already
smooth and a mere film will give the gloss. For white filling on the
engraving on black cases use Chinese white or get a good white enamel
at a paint store.
Gilding on wood cases is done by mixing a little yellow dry color with
thin glue and painting the cases with the mixture; the color lets you
see what you are doing. When the glue has dried until it is “tacky,”
lay gold leaf on the painted portions and smooth down with cotton.
If you have any holes do not attempt to patch them. It is easier and
quicker to put on another sheet of gold leaf over the first one. After
the gold is dry, it may be burnished with a bloodstone or smooth steel
burnisher, or it may be left dead. Finish with colorless lacquer, very
thin and smooth.
Imitation gold leaf, known to the trade as Dutch Metal, may be
substituted for the gold leaf, if the latter is thought to be too
expensive, but in such cases be sure to have the metal well covered
with the lacquer, as unless this is done it will blacken in two or
three years—sometimes in two or three months.
Bronze powder may be applied to the glue size with a tuft of cotton and
well rubbed in until flat and smooth; then lacquer and dry. Never put
on bronze paint, for the following reason: If we examine the bronze
under a microscope we shall find that it is composed of flat scales
like fish scales; if mixed as a paint they will be found lying at all
angles in the painted work—many standing on edge. Such scales reflect
the light away from the eye and make the work look dull and rough. If
we rub these dry scales in gently on the sticky size, we will lay them
all down flat and smooth, so that the work will glisten all over with
an even color. Always lacquer bronzed work—yellow lacquer being the
best—and put on plenty of lacquer.
Metal ornaments, when discolored, should be removed from the case,
dipped in boiling lye to remove the lacquer, scratch brushed, dipped
in ammonia to brighten, rinsed in hot water and dried in sawdust. They
may then be lacquered with a gold lacquer, or plated in one of the gold
plating solutions sold by dealers for plating without a battery and
then lacquered, if bright. If they are of oxidized finish cleaning and
lacquering is generally all that is necessary.
Oxidized metal cases, if badly discolored, should be sent to an
electroplater to be refinished, as the production of smooth and even
finishes on such cases, requires more skill than the clock repairer
possesses, and he therefore could not do a good job, even if he had the
necessary materials and formulæ.
Marble cases are made of slabs, cemented together. Many workmen use
plaster of paris by merely mixing it with water, though we rather think
it better to use glue in the mixing, as plaster so mixed will not set
as quickly as that mixed with water. After the case is cemented with
the plaster, the workman can go over the joint with a brush and water
colors, and with a little care should be able to turn out a job in
which the joint will not be noticeable. Another cement much used for
marble is composed of the white of an egg mixed with freshly slaked
lime, but it has the disadvantage of setting very quickly.
Marble case makers use a cement composed of tallow, brick dust, and
resin melted together, and it sets as hard as stone at ordinary
temperatures.
It often happens that the marble case of a mantel clock is injured by
some accident and its corners are generally the first to suffer. If
the break is not so great as to warrant a new case or a new part the
repairer may make the case a little smaller or file until the edges are
reproduced, after which the polish is restored. Proceed as follows:
Take off from the damaged part as much as is necessary by means of
a file, taking care however, not to alter the original shape of the
case. Now grind off the piece worked with the file with a suitable
piece of pumice-stone and water and continue the grinding next with a
water stone until all the scratches have disappeared, paying special
attention to the corners and contours. After this has been done take
a hard ball of linen, moisten it, and strew over it either tripoli
or fine emery and proceed to polish the case with this. Finish the
polishing with another linen ball, using on it still finer emery and
rouge. Now dry the case and finish the polishing with a mixture of
beeswax and oil of turpentine. This method may be employed for all
kinds of marble, or onyx and alabaster cases.
In cases where the fractures are very deep, so that the object cannot
be made much smaller without ruining the shape, the damaged parts may
be filled with a cement, prepared from finely powdered marble dust and
a little isinglass and water, or fish glue will answer very well. Stir
this into a thick paste, which fill into the deep places and permit to
dry; after drying, correct the shape and polish as described.
If the pieces which have been broken off are at hand they may be
cemented in place again. Wet the pieces with a solution of water
and silicate of potash, insert them in place and let them dry for
forty-eight hours. If the case is made of white marble use the white of
an egg and a little Vienna lime, or common lime will answer.
TO POLISH MARBLE CLOCK CASES.—It frequently becomes the duty of the
repairer to restore and polish marble clock cases, and we would
recommend him to make a thin paste of the best beeswax and spirits of
turpentine, clean the case well from dust, etc., then slightly cover
it with the paste, and with a handful of clean cotton, rub it well,
using abundant friction, finish off with a clean old linen rag, which
will produce a brilliant black polish. For light colored marble cases,
mix quicklime with strong soda water, and cover the marble with a thick
coating. Clean off after twenty-four hours, and polish well with fine
putty powder.
TO REMOVE OIL SPOTS FROM MARBLE.—Oil spots, if not too old, are easily
removed from marble by repeatedly covering them with a paste of
calcined magnesia and benzine, and brushing off the magnesia after the
dissipation of the oil; this may have to be repeated several times.
Another recipe reads as follows: Slaked lime is mixed with a strong
soap solution, to the consistency of cream; this is placed upon the oil
spot, and repeated until it has disappeared. In place of this mixture,
another one may be used, consisting of an ox gall, 125 grains of
soapmaker’s waste lye and 62½ grams of turpentine, with pipe clay, to
the consistency of dough.
CUTTING CLOCK GLASSES.—You will sometimes want a new glass for a clock.
I get a lot of old 5 × 7 negatives and scald the film off in plain
hot water, rinse well and dry. Now I lay my clock bezel on a piece of
paper and trace around with a pencil, inside measure. Now remove the
bezel and trace another circle around the outside of this circle about
one-eighth inch. Now, lay the paper on a good, solid, smooth surface,
glass on top, and with a common wheel glass-cutter follow around the
outside line, free handed, understand. The paper with marked circle on
is under the glass, and you can see right through the glass where to
follow with the cutter. Now cut the margins of glass so as to roughly
break out to one-half inch of your circle cut, running the cuts out on
the side, then carefully break out.
CHAPTER XXIV.
SOME HINTS ON MAKING A REGULATOR.
Of all the instruments used by a watchmaker in the prosecution of his
business, there is probably none more important than his regulator.
Its purpose is to divide time into seconds, and it is the standard by
which the practical results of his labors are tested; the guide which
all the other timekeepers in his possession are made to follow and the
arbitrator which settles all disputes regarding the performance of his
watches.
No regulator has yet been constructed that contains within itself
every element for producing absolutely accurate timekeeping. At
intervals they must all be corrected from some external source, such as
comparison with another timekeeper, the error of which is known, or by
the motion of the heavenly bodies, when instruments for that purpose
are available. Before beginning to make a regulator, the prudent
watchmaker will first reflect on the various plans of constructing all
the various details of an accurate timekeeper, and select the plan
which, in his opinion, or in the opinion of those whom he may consult
on the subject, will best accomplish the object he has in view.
In former years a regulator case was made with the sole object of
accommodating the requirements of the regulator, and every detail in
the construction of the case was made subservient to the necessities
of the clock. The plain, well made cases of former years are now
almost discarded for those of more pretentious design. If the general
change in the public taste demands so much display, there can be no
objection. It is perfectly harmless to the clock, if the designers and
makers of the cases would only remember that narrow waists or narrow
necks on a case, although part of an elegant design, do not afford the
necessary room for the weight and freedom of the pendulum; that the
doors and other openings in the case must be constructed with a view to
exclude dust; and that the back should be made of thick, well-seasoned
hardwood, such as oak or maple, so as to afford the means of obtaining
as firm a support for the pendulum as possible.
When a regulator case is known to have been made by an inexperienced
person, which sometimes happens, or when we already have a case, it
is always the safest course for those who make the clock to examine
the case personally and see the exact accommodation there is for the
clock. Sometimes, when we know beforehand, we can, without violating
any principle, vary the construction a little, so as to make the
weight clear the woodwork of the inside of the case, and in other
respects complete the regulator in a more workmanlike manner by
making the necessary alterations in the clock at the beginning of its
construction, instead of after it has been once finished agreeably to
some stereotyped arrangement.
The arrangement of the mechanism of an ordinary regulator is a simple
operation compared with some other horological instruments of a more
complex character. We are not limited in room to the same extent as
in a watch, and the parts being few in number a regulator is more
easily planned than timekeepers having striking or automatic mechanism
for other purposes combined with them; yet it often happens that
the inexperienced make serious blunders in planning a regulator,
and, as the clock approaches completion, many errors make themselves
visible, which might have been avoided by the exercise of a little
more forethought. It may be that, when the dial is being engraved, the
circles do not come in the right position, or the weight comes too
close to the pendulum, or the case, or the cord comes against a pillar,
or other faults of greater or less importance appear, all of which
might have been obviated by taking a more comprehensive view of the
subject before beginning to make the clock. The best way to do this is
to draw a plan and side and front elevations to a scale.
[Illustration: Fig. 152.]
The position which the barrel and great wheel should occupy is worthy
of serious consideration. In most of the cheap regulators, as well as
in a few of a more expensive order, the barrel is placed in a direct
line below the center wheel, as is shown in Fig. 152. This arrangement
admits of a very compact movement, and it also allows the weight to
hang exactly in the center of the case, which some think looks better
than when it hangs at the side, especially when there is a glass door
in the body of the case. But while a weight hanging in the center
of a case may be more pleasing to the eye than when it hangs at the
side, this is an instance where looks can, with great propriety, be
sacrificed for utility, because when the weight hangs in the center
it comes too close to the pendulum, and is very liable to disturb its
motion. In proof of this statement, let any reader who has a regulator
with a light pendulum and a comparatively large weight hanging in
front of it, closely watch the length of the arc the pendulum vibrates
when the weight is newly wound up and when it is down opposite the
pendulum ball, and he will observe that the length of vibration of
the pendulum varies from five to fifteen minutes of arc, according to
the position in which the weight is placed; that the pendulum will
vibrate larger arcs when the weight is above or below the ball than
when it is opposite it; and if the clock has a tendency to stop from
any cause, that it will generally do so more readily when the weight is
opposite the pendulum ball than when it is in any other position. For
this reason I would dispense with the symmetrical looks of the weight
hanging in the center of the case, which, after all, is only a matter
of taste, and construct the movement so that the weight will hang at
the side, and as, far away from the pendulum as possible.
Fig. 153 is intended to represent the effect which placing the barrel
at either side has on throwing the weight away from the pendulum. A is
the center wheel; B and C are the great wheels and barrels with weights
hanging from them; D is the pendulum. It will be noticed by the diagram
that the weight at the left of the pendulum is exactly the diameter of
the barrel farther away from the pendulum than the weight on the right.
On close inspection it will also be observed that on the barrel C the
force of the weight is applied between the axis of the barrel and the
teeth of the wheel, while on the barrel B the axis of the barrel lies
between the point where the force is applied and the point where the
teeth act on the pinion; consequently a little more of the effective
force of the weight is consumed by the extra amount of pressure and
friction on the pivots of the barrel B than there is in C.
[Illustration: Fig. 153.]
Notwithstanding this disadvantage, I would for a regulator recommend
the barrel to be placed at the left side of the center wheel, because
the weight may thereby be led a sufficient distance from the pendulum
in a simple manner. If we place the barrel at the right, and thereby
secure the greatest effective force of the weight, and then lead the
weight to the side by a pulley, we will lose a great deal more by the
friction of the pulley than we gain by the proper application of the
weight.
In a regulator with a Graham escapement but little force is required
to keep it going, and there is usually accommodation for an abundance
of power; therefore we cannot use a little of this superabundant
available force to better advantage than by placing the barrel at the
left side of the clock, and thereby throw the weight a sufficient
distance from the pendulum in the simplest manner.
The escapement we assume to be the old dead beat, as for timekeeping
it is equal to a gravity escapement while possessing advantages
undesirable to sacrifice for a doubtful improvement. The advantages it
possesses over any form of gravity escapement are: it has fewer pieces
and not so many wheels; it takes very much less power to drive; is not
liable to fail in action while winding, if the maintaining power should
be rather weak; while for counting, seconds and estimating fractions,
its clear, definite, and equable beat has great superiority over the
complication of noises made by a gravity escapement.
Full directions for making this and other escapements have already been
given, but in a regulator there are some considerations which will not
be encountered in connection with the escapements of ordinary clocks,
where fine timekeeping is not expected. We have previously stated that
the center of suspension of the pendulum should be exactly in line with
the axis of the escapement and we will now endeavor to state plainly
how important this is in a fine clock and the reasons for it. Mr.
Charles Frodsham, the noted English chronometer maker, has conducted a
series of careful experiments and the results were communicated in a
report to the British Horological Society, as follows:
When we talk of detached escapements, or any escapement applied to
a pendulum, it is necessary to bear in mind that there is always
one-third at the least of the pendulum’s vibration during which the
arc of escapement is intimately mixed up with the vibration, either
in locking, unlocking, or in giving impulse; therefore, whatever
inherent faults any escapement may possess are constantly mixed up in
the result; the words “detached escapement” can hardly be applied
when the entire arc of vibration is only two degrees; or, in other
words, what part of the vibration is left without the influence of the
escapement?—at most one degree. In chronometers the arc of vibration is
from ten to fifteen times greater than the arc of escapement.
The dead-beat escapement has been accused of interfering with the
natural isochronism of the pendulum by its extreme friction on the
circular rests, crutch, and difficulty of unlocking, etc., all of which
we shall show is only so when improperly made.
When the dead-beat escapement has been mathematically constructed, and
is strictly correct in all its bearings, its vibrations are found to
be isochronous for arcs of different extent from 0.75 of a degree to
2.50 degrees; injurious friction does not then exist; the run up on
the locking has no influence, nor is there any friction at the crutch;
oil is not absolutely necessary, except at the pivots; and there is no
unlocking resistance nor any inclination to repel or attract the wheel
at its lockings.
The general mode of making this escapement is very defective and
indefinite, and entirely destroys the naturally isochronous vibration
of the pendulum.
The following is the usual rate of the same pendulum’s performance
in the different arcs of vibration with an escapement as generally
constructed after empirical rules:
Arc of vibration 3° rate per diem 9.0 seconds.
Arc of vibration 2½° rate per diem 6.0 seconds.
Arc of vibration 2° rate per diem 3.5 seconds.
Arc of vibration 1½° rate per diem 1.5 seconds.
Arc of vibration 1° rate per diem 0.0 seconds.
Thus for a change of vibration of 1°, we have a daily error of 3.5.
No change of suspending spring will alter inherent mechanical errors
destructive of the laws of motion. With clocks made in the usual
manner, whether you apply a long or short spring, strong or weak,
broad or narrow, you will not remove one fraction of the error; so
the sooner the fallacy of relying upon the suspending spring to cure
mechanical errors is exploded the better.
That the suspending spring plays a most important part must be
admitted, since, when suspended by a spring, a pendulum is kept in
motion by a few grains only, whereas, if supported on ordinary pivots,
200 lbs. weight would not drive it 2′ beyond its arc of escapement, so
great would be the friction at the point of suspension.
The conditions on which alone the vibrations of the pendulum will be
isochronous are the following:
1. That the pendulum be at time with and without the
clock, in which state it is isochronous “suspended
by a spring.”
2. That the crutch and pallets shall each travel at
the same precise angular velocity as the pendulum,
which can only happen when the arc each is to
describe is in direct proportion to its distance
from the center of motion, that is, from the pallet
axis.
3. That the angular force communicated by the crutch
to the pendulum shall be equal on both sides of the
quiescent point; or, in other words, that the lead
of each pallet shall be of the same precise amount.
4. That any number of degrees marked by the crutch
or pallets shall correspond with the same number
of degrees shown by the lead of the pendulum, as
marked by the index on the degree plate.
5. That the various vibrations of the pendulum be
driven by a motive weight in strict accordance with
the theoretical law; that is, if a 5-lb. weight
cause the pendulum to double its arc of escapement
of 1°, and consequently drive it 2°, all the
intermediate arcs of vibration shall in practice
accord with the theory of increasing or diminishing
their arcs in the ratio of the square roots of the
motive weight.
To accomplish the foregoing conditions, there is but one fixed point
or line of distance between the axis of the escape wheel and that of
the pallet, and that depends upon the number of teeth embraced by the
pallets and only one point in which the pallet axis can be placed from
which the several lines of the escapement can be correctly traced
and properly constructed with equal angles, and equal rectangular
lockings on both sides, so that each part travels with the same degree
of angular velocity, which are the three essential points of the
escapement.
Much difference of opinion has been expressed upon the construction of
the pallets, as to whether the lockings or circular rests should be at
equal distances from the pallet axis, with arms and impulse planes of
unequal length, or at unequal distances from the pallet axis, with arms
and impulse planes of equal length. In the latter case the locking on
one side is three degrees above, and on the other three degrees below
the rectangle, whereas in the former the tooth on both sides reposes
at right angles to the line of pressure; but the length of the impulse
planes is unequal. When an escapement is correctly made upon either
plan, the results are very similar.
It is possible to obtain equal angles by a false center of motion or
pallet axis; but then the arcs of repose will not be equal. This,
however, is not of so much consequence as that of having destroyed the
conditions Nos. 2, 3, 4; for even at correct centers, if the angles are
not drawn off correctly by the protractor, and precisely equal to each
other, the isochronous vibrations of the pendulum will be destroyed,
and unequal arcs will no longer be performed in equal times; the
quiescent point is not the center of the vibration, except when the
driving forces are equal on both sides of the natural quiescent point
of the pendulum at rest.
Now this is the very pith of the subject, and which few would be
inclined to look for with any hope of finding in it the solution of
this important question, the isochronism of the pendulum.
One would naturally suppose that unequal arcs on the two sides of the
vertical lines would not seriously affect the rate of the clock, but
would be equal and contrary, and consequently a balance of errors, and
so they probably are for the same fixed vibration, but not for any
other; because different angles are driven with different velocities,
the short angle has a quicker rate of motion than the long. Five pounds
motive weight will multiply three times the pendulum’s vibration over
an arc of escapement of 0.75°; but the same pendulum, with an arc of
escapement of 1°, would require 11.20 lbs. to treble its vibration; the
times of the vibration vary in the same ratio as the sum of the squares
of the differences of the angles of each pallet, compared with the
spaces passed over.
From this it will be seen that the exact bending point of the pendulum
spring should be opposite the axis of the fork arbor when regulating
the clock and this may have to be determined by trial, raising or
lowering the plates by screws in the arms of the suspending brackets
until the proper position is found, when the movement may be clamped
firmly in position by the binding screws, see Fig. 158.
On common clocks the crutch is simply riveted on its collet and bent
as required to set the clock in beat, but for a first-class clock a
more refined arrangement is usually adopted. There are other plans,
but perhaps none so thoroughly sound and convenient as the following.
The crutch itself is made of a piece of flat steel cut away so as to
leave a round boss at the bottom for the fork, and a round boss at the
top to fit on a collet on the pallet arbor, a part projecting above to
be embraced between a pair of opposing screws. On the collet is fixed
a thin brass plate with two lugs projecting backwards from the frame,
these lugs being drilled and tapped to receive the opposing screws in
a line. The boss of the crutch lies flat against this plate, and is
held up to it by a removable collet. The collet may be pinned across
or fitted keyhole fashion, in either case so as to hold the crutch
firmly, allowing it to move with a little stiffness under the influence
of the screws. With this arrangement the adjustment to beat may be
made with the utmost delicacy by slacking one screw and advancing
the other, taking care that in the end they are well set home so as
to make the crutch practically all one piece with the arbor. Milled
heads are most convenient for these screws, and being placed at the
top they are easily got at. The crutch should always be fitted with a
fork to embrace the pendulum rod, as this ensures the impulse being
given directly through the center, and with the same object the acting
sides of the fork should be truly square to the frame. A slot in the
pendulum rod with a pin acting in it is never so sure of being correct,
as, although the surfaces may be rounded, it is very unlikely that the
points of contact will be truly in the plane of the axis of the rod.
The slightest error in this respect will tend to cause wobbling of
the bob, although, to avoid this, great attention must also be given
to the suspension spring, the pin on which it hangs, and the pin and
the hole at the top of the pendulum rod. All these points must be in
a true line, and the spring symmetrical on both sides of the line in
order that the impulse may be given exactly opposite the center of the
mass, otherwise wobbling must occur, although perhaps of an amount
so small as to be difficult of detection, and this is not a matter
of small importance, as it has an effect on the rate which could be
mathematically demonstrated.
The frames of many regulators are made too large and heavy. In some
cases there may be good reasons for making them large and heavy, but
in most instances, and especially when the pendulum is not suspended
from the movement, it would be much better to make the frames lighter
than we frequently find them. Very large frames present a massive
appearance, and convey an idea of strength altogether out of proportion
to the work a regulator is required to perform. They are more difficult
and more expensive to make than lighter ones, and after they are made
they are more troublesome to handle, and the pivots of the pinions are
in greater danger of being broken when the clock is being put together
than when they are moderately light.
In a clock such as we have under consideration, where the frame is
not to be used as a support for the pendulum, but simply to contain
the various parts which constitute the movement, the thickness of the
frames may with propriety be determined on the basis of the diameter
of the majority of the pivots which work into the holes of the frames.
The length of the bearing surface of a pivot will, according to
circumstances, vary from one to two and a half times the diameter of
the pivot. The majority of the pivots of our regulator will not be more
than .05 or .06 of an inch in diameter; consequently a frame 0.15 of an
inch thick will allow a sufficient length of bearing for the greater
portion of the pivots, and will also allow for countersinks to be made
for the purpose of holding the oil. If thin plates are used one or two
of the larger pivots should be run in bushes placed in the frame, as
described in Fig. 155.
The length and breadth of the frame, and also its shape, should be
determined solely on the basis of utility. There can be no better shape
for the purpose of a regulator than a plain oblong, without any attempt
whatever at ornament. For our regulator a frame nine inches long and
seven inches broad will allow ample accommodation for everything, as
may be seen on referring to Fig. 157.
[Illustration: Fig. 154.]
The plates are made of various alloys: cast-brass, nickel-silver, and
hard-rolled sheet brass. It is difficult to make plates of cast-brass
which would be even, free from specks, etc., but cast plates may very
well be made of ornamental patterns and bushings of brass rod inserted,
or they may be jeweled as shown in Figs. 154, 155, 156. Nickel, or
German silver, makes a fine plate, but it is difficult to drill the
small holes through plates of four-tenths of an inch in thickness, on
account of the peculiar toughness of the metal, so that bushings are
necessary. The best material where the holes are to be in the plates
is fine, hard-rolled sheet brass; it should have about 4 oz. of lead
to the 100 lbs., which will make it “chip free,” as clockmakers term
it, rendering it easy to drill; the metal is so fine and condensed to
that extent by rolling, that the holes can be made with the greatest
degree of perfection. The many improvements in tools and machinery
have effected great changes and improvements in clock-making. It once
was quite a difficult task to drill the small holes in the plates with
the ordinary drills and lathes; now we lay the plates after they are
soldered together at the edges (which is preferable to pinning), on the
table of an upright drill, and with one of the modern twist-drills the
task is rendered a very easy one. After the pivot holes are drilled,
we run through from each side a round broach, finished lengthwise and
hardened, which acts as a fine reamer, straightening and polishing the
holes exquisitely. A little oil should be used on the reamer to prevent
sticking. The method of fitting up the pivot holes invented by LeRoy, a
French clockmaker of some note, is shown in Fig. 154. It is a sectional
view of the plate at the pivot hole. It will be observed that, instead
of countersinking for the oil, the reverse is the case. A is a hardened
steel plate counterbored into the clock plate B, and held in its place
by the screws. There should be a small space between the steel plate
and the crown of the arch for the oil. After the clock has been put
together it is laid down on its face or side, a drop of oil is put to
the pivot end, and the steel plate immediately put on; and the oil will
at once assume the shape of the shaded spot in the drawing, being held
in the position at the center of the pivot by capillary attraction,
until it is exhausted by the pivots; the steel plates also govern the
end play of the pinions. The pivot ends being allowed to touch the
plates occasionally, the shoulders of the pinions are turned away into
a curve, and, of course, do not bear against the plate, as in most
clocks.
[Illustration: Fig. 155.]
Glass plates may be used instead of steel, or rose cut thin garnets,
or sapphires, with the flat sides smoothly polished, may be bought of
material dealers and set in bezels like a cap jewel. They are very hard
and smooth for the pivot ends, and the state of the oil at the pivots
can be seen at any time. Clocks fitted up in this manner have been
running many years without oiling.
[Illustration: Fig. 156.]
When fitted up in this way the plates may be thicker. We have made the
clock plates about four-tenths of an inch in thickness, which allows
of counterboring, and admits of long bearings for the barrel arbor,
which are so liable to be worn down in the holes by the weights; and
the pivots of the pinions, by being a little longer, do not materially
increase the friction.
In first-class clocks, when all the materials are as hard as possible,
the wheels and pinions high numbered, the teeth, pinions, pivots, and
holes smooth, true, and well polished, the amount of wear is very
slight, especially if the driving weight has no useless excess. Yet
there are advantages in having some parts jeweled, such as the pallets
and the four escapement holes. The cost of such jeweling is not an
objection, while the diminished friction of the smooth, hard surfaces
is worth the extra outlay. The holes can be set in the bushes described
in Fig. 156, the end stones being cheap semi-precious stones, either
rose cut or round.
For jeweling the pallets, dovetailed slots may be made so that the
stones will be of a wedge shape; there is no need for cutting the slots
right through as in lever watch pallets. The stones will be held more
firmly if shaped as wedges lying on a bed of the steel and exposing
only the circular resting curve and the driving face. The slots can
be filed out and the stones ground on a copper lap to fit, fixed with
shellac and pressed firmly home while warm. The grinding and polishing
of the acting surfaces are done exactly as described for hard steel,
only using diamond powder instead of emery. The best stones are pale
milky sapphires, such as are useless as gems, this kind of stone being
the hardest.
The holes may be much shorter when jeweled, as the amount of bearing
surface required with stones is less than with brass; this results in
less adhesion through the oil, and less variation of force through
its changes of consistency. The ’scape wheel may also be thinner with
similar results, and less weight to be moved besides. So the advantages
of jeweling are worth consideration.
It is important to finish the wheels and pinions before drilling any
holes in the plates and then to definitely locate the holes after trial
in the depthing tool.
For the clockmaker’s use the next in value to the wheel cutting
engine is a strong and rigid depthing tool, for it is by means of
this instrument that the proper center distances of wheels and pinions
can be ascertained, and all errors in sizes of wheels and pinions, and
shapes of teeth, are at once detected before the holes are drilled in
the plates. In fact, this tool becomes for the moment the clock itself;
and if the workman will consider that as the wheels and pinions perform
in the tool for the little time he is testing them, so they will
continue to run during the life of the clock, he will not be too hasty
in allowing wheels to go as correct when a hundredth of an inch larger
or smaller, and another test, would, perhaps, make the pitching perfect.
There are various kinds of depthing tools in use, but many of them are
objectionable for the reason that the centers are so long that the
marking points on their outer ends, are too far from the point where
the pitching or depthing is being tested, and the slightest error in
the parallelism of these centers is, of course, multiplied by the
distance, so that it may be a serious difference. Having experienced
some trouble from this cause, we made an instrument with very short
centers, on the principle that the marking points, or centers, should
be as near the testing place as possible. We succeeded in making one
with a difference of only three-fourths of an inch, which was so exact
that we had no further trouble. It was made on the Sector plan, but
upright, so that the work under inspection, whether wheels and pinions,
or escapements, could be observed closely, and with a glass, if
necessary.
It is very important that the posts or pillars and side-plates of
clocks should be made and put together in the most thorough manner; the
posts should be turned exact to length and have large shoulders, turned
true, so that the plates, when put together without screws should fit
accurately, for if they do not, when the screws are driven, some of the
pivots will be cramped. We prefer iron for the posts, it being stiffer,
and better retaining the screw threads in the ends, which in brass are
liable to strip unless long and deep holes are tapped. Steel pillars
should be blued after being finely finished, thus presenting a pleasing
contrast. The plate screws should also be of steel, with large flat
heads, turned up true, and having a washer next to the plate. Brass
pillars are favored by many and are easier turned in a small lathe, but
they should be much larger than the steel ones.
[Illustration: Fig. 157.]
[Illustration: Fig. 158.]
[Illustration: Fig. 159.]
When the pillars are made of brass round rod of proper diameter is
the best stock. If this cannot be procured, a pattern is turned from
wood, and a little larger in every respect than the pillar is desired
to be. If there is to be any ornament put on the pillar, it is never
made on the pattern, because it makes it more difficult to cast, and
besides, the ornamentation would all be spoiled in the hammering. The
pattern must be turned smooth, and the finer it is the better will be
the casting. After the casting is received the first thing to be done
is to hammer the brass, and then center the holes, because it will be
seen from Fig. 159 that there are holes for screws at each end of the
pillar. Holes of about .20 of an inch are then bored in the ends of the
pillars, and should be deep, because deep holes do no harm and greatly
facilitate the tapping for the screws. After the holes are tapped, run
in a bottoming tap and then countersink them a little, to prevent the
pillar from going out of truth in the turning. It will depend a great
deal on the conveniences which belong to the lathe the pillars are
turned in as to how they will be held in the lathe and turned. If the
holes in the ends of the pillars have been bored and tapped true, and
if the lathe has no kind of a chuck or face plate with dogs, suitable
for holding rods, the best way is to catch a piece of stout steel wire
in the chuck and turn it true, cut a true screw on it, and on this
screw one end of the pillar, and run the other end in a male center.
However, if the screws are not all perfectly true, and the centers of
the lathe not perfectly in line, this plan will not work well, and
it will be necessary to catch a carrier on to the pillar and turn it
between two male centers.
The dial feet are precisely the same as the pillars, only smaller.
These dial feet are intended to be fastened in the frame by a screw,
the same as the pillars; but it will be observed that the screw which
is intended to hold the dial on the pillar is smaller. The dial feet
will be turned in precisely the same manner as the pillars. For
finishing the plain surfaces of the pillars and dial feet, an old 6 or
7-inch smooth file makes a good tool. The end of the file is ground
flat, square or slightly rounded, and perfectly smooth. The smoother
the cutting surface the smoother the work done by it will be. It is
difficult to convey the idea to the inexperienced how to use this tool
successfully. In the first place, a good lathe is necessary, or at
least one that allows the work to run free without any shake. In the
second place, the tool must be ground perfectly square, that is, it
is not to be ground at an angle like an ordinary cutting tool. Then
the rest of the lathe must be smooth on the top, and the operator must
have confidence in himself, because if he thinks that he cannot turn
perfectly smooth, it will be a long time before he is able to do it. A
tool for turning the rounded part of the pillar, if a pattern of this
style is decided on, is made by boring a hole, the size of the desired
curve, in an old file, or in a piece of flat steel, and smoothing
the hole with a broach and then filing away the steel. The shoulders
should be smooth and flat, or a very little undercut, and the ends of
the pillars should be rounded as is shown in Fig. 159, because rounded
points assist greatly in making the frames go on to the pillars sure
and easy, and greatly lessen the danger of breaking a pivot when the
clock is being put together.
When a washer is used the points of the pillars project half the
thickness of the washer through the frames, the hole in the washer
being large enough to go on to the points of the pillars.
[Illustration: Fig. 160.]
Figure 160 is an outline of the cock required for the pallet arbor, and
the only cock that will be required for the regulator. It is customary,
in some instances, to use a cock for the scape wheel and also for the
hour wheel arbors, but for the scape wheel arbor I consider that a cock
should never be used when it can be avoided. The idea of using a cock
for the scape wheel arbor is to bring the shoulder of the pivot near to
the dial and thereby make the small pivot that carries the seconds hand
so much shorter; and so far this is good, but then the distance between
the shoulders of the arbor being greater, when a cock is used the
arbor is more liable to spring and cause the scape wheel to impart an
irregular force to the pendulum through the pallets. This is the reason
why I prefer not to use a cock except when the design of the case is
such that long dial feet are necessary, and renders the use of a cock
indispensable. In the present instance, however, the dial feet are no
longer than is just necessary to allow for a winding square on the
barrel arbor, and therefore a cock for the scape wheel is superfluous.
It is better to use a long light socket for the seconds hand than put
a cock on the scape wheel arbor in ordinary cases. Except for the
purpose of uniformity a cock on the hour wheel is always superfluous,
although its presence is comparatively harmless. The front pivot of
the hour wheel axis can always be left thick and strong enough should
the design of the case require the dial feet to be extra long.
For the pallet arbor, however, a cock is always necessary, and it
should always be made high enough to allow the back fork to be brought
as near to the pendulum as possible, so as to prevent any possibility
of its twisting when the power is being communicated from the pallets
to the pendulum. This cock should be made about the same thickness as
the frames, and about half an inch broad. Make the pattern out of a
piece of hard wood, either in one solid piece or by fastening a number
of pieces together. The pattern should be made a little heavier than
the cock is required to be when finished, and it should also be made
slightly bevelled to allow it to be easily drawn from the sand when
preparing the mould for casting. After it is cast the brass should be
hammered carefully, and then filed square, flat, and smooth.
Screws are better and cheaper when purchased, but they may be made of
steel or brass rod by any workman who is provided with a set of fine
taps and dies. If purchased they should be hardened, polished and blued
before using them in the regulator. The threads of screws vary in
proportion to the size of the screw and the material from which it is
made. A screw with from 32 to 40 turns to the inch, and a thread of the
same shape as the fine dies for sale in the tool shops make, is well
adapted for the large screws in a regulator. However, it is not threads
of the screws I desire to call attention to so much, although it must
be admitted that the threads are of primary importance. It is the shape
of the heads and the points which is too often neglected.
A thread, or a thread and a half, cut down on the point of a screw,
will allow it to enter easier than when the point is flat, round, or
shaped like a center. This is not a new idea for making the points
of screws, but the plan is either not known to many, or it is not
practiced to the extent it ought to be.
The shape of the head of a screw should also always be based on
utility, and the shape that will admit of a slit into it that will
wear well should be selected. A round head ought never to be used,
because a head of this shape does not present the same amount of
surface to the screwdriver that a square head does. It is the extreme
end of the slit that is most effective, and in round-headed screws this
part is cut away and the value of the head for wearing by the use of
the screwdriver is the same as if the head of the screw was so much
smaller. A chamfered head may suit the tastes of some people better
than a perfectly flat head, but in a head of this shape the slit must
be cut deeper than in a square head, because the chamfered part of the
head is of little or no use for the screwdriver to act against. The
slits should always be cut carefully in the center of the head and the
sides of the slit filed perfectly flat with a thin file and the slight
burr filed off the edge to prevent the top of the head getting bruised
by the action of the screwdriver. The shape of the slit which is best
adapted for wearing is one slightly tapered, with a round bottom. The
round bottom gives greater strength to the head, and prevents the heads
of small screws from splitting.
I have dwelt at some length on these little details because a proper
attention to them goes a long way in the making of a clock in a
workmanlike manner, and it is desirable that the practical details
should be as minute as possible.
The construction of the barrel is a subject which requires a greater
amount of consideration than is sometimes bestowed upon it. We often
meet with regulator barrels which have considerable more brass put into
them than is necessary. The value of this extra metal is of little or
no consequence. It is the unnecessary pressure the weight of it causes
on the barrel pivots, and the consequent increase of friction, which is
objectionable. For this reason the weight of the barrel, as well as the
weight of every other part of the clock that moves on pivots, should
be made no heavier than is absolutely necessary to secure the required
amount of strength. In every instance, except when the diameter is
required to be very small, the barrel should be made of a piece of thin
brass tubing with two ends of cast-brass fastened into it.
[Illustration: Fig. 161.]
Figure 161 is a sectional view of the ends of a barrel; the diagram
on the right is the end where the great wheels rest against, and the
one on the left is the other end. The insides of both these ends
are precisely the same, but the outsides differ a little. It will
be observed that there is a little projection near the hole on the
outside of the front end. This projection is left with the view of
making the hole in the center longer, and thereby causing this end to
take a firmer hold on the barrel arbor. The back end, or the end that
the great wheels rest against, and where the ratchet teeth are cut,
is shaped precisely like the diagram on the right of Fig. 161. If you
cannot get brass plate of sufficient thickness for the ends of the
barrel they must be cast.
The patterns for these barrel ends should be made without any hole
in the center, and in every way heavier and thicker than they are to
be when finished, because it is difficult to obtain good and solid
castings when the patterns are made thin, although it is by no means
impossible to make them so. Like all brass castings used for the
clockmaker’s purpose, they should be carefully hammered, and, although
these pieces are of an irregular shape, they can be easily hammered
regularly with the aid of narrow-faced hammers or punches, and with the
exercise of a little patience. After hammering, the castings should
be placed on a face plate in the lathe, and the tube which is to form
the top part of the barrel fitted easy and without shake on to the
flanges and the other parts of the castings turned down to the required
thickness, and a hole a little less than 0.3 of an inch diameter bored
in the center of each before it is removed from the face plate. The
tube which is to form the top of the barrel should be no heavier than
is just necessary to cut a groove for the cord, and for this regulator
it should be 1.5 inch diameter outside measurement, 1.5 inch long, and
turned perfectly true on the ends.
The hole in the front end of the barrel, which is the end nearest to
the dial, should be broached a little from the inside, and the other
end broached a little larger from the outside. The reason for broaching
the holes in this manner is to cause the thickest part of the barrel
arbor to be at the place where the great wheels work, because, in
making a barrel for a regulator, it will generally be found that the
arbor requires to be thickest in this particular place. The arbor
should be made from a piece of fine cast steel a little more than 0.3
of an inch thick, and not less than four inches long. It is always
well to have the steel long enough. This steel should be carefully
centered and turned true, and of the same size and taper as the holes
in the barrel ends. It is not necessary that the barrel arbor should be
hardened and tempered, except on special occasions. In most cases it
will last as long as any other part of the clock if it is left soft,
and it is much easier to make when soft. Before fitting the arbor
to the barrel ends it is well to place the ends into the tube that
is to form the top of the barrel, because a better fit can be made
in this way than when each is fitted separately. When the arbor has
been fitted, a good and convenient way of fastening it together is,
to use soft solder. It can be easily heated to the required degree of
heat with the blow-pipe. A very little solder is sufficient for the
purpose, and if the joints have been well fitted the solder will not
show when the work is finished. Care should be taken to notice that
the solder adheres to the arbors properly. Perhaps it would be well to
mention here that, should the clockmaker not have access to a cutting
engine with conveniences attached to it for cutting the barrel ratchet
after the barrel has been put together, the ratchet should be cut first.
When the different pieces which constitute a barrel have been fastened
together the brass work has next to be turned true, and the grooves cut
for the cord to run in. It is best not to turn anything off the arbor
till the grooves are cut, because they are usually cut smoother when
the arbor is strong. The most important points to notice when turning a
barrel is to be sure that the top is of equal diameter from the one end
to the other, and that the bearing where the great wheels rest against
are perfectly true, because, if the top of a barrel is of unequal
thickness, the weight will pull with unequal force as it runs down, and
if the bearing on the end be out of truth the great wheels will also
be very liable to get out of truth, as their position on the barrel is
altered by winding the clock up.
The shape of the outside of the barrel ends, as is represented in Fig.
161, will be found to be good and serviceable. AA is the bearing for
the great wheels to rest against; BB is where the ratchet teeth are to
be cut. There must be a little turned off the face of BB, as is shown
in the diagram, so as to prevent the great wheel from rubbing on the
teeth. The space between AA and the barrel arbor is turned smooth.
Although it is by no means an absolute necessity to have a groove cut
in the top of the barrel, yet it is extremely desirable that there
should be one, so that the cord may always be guided with certainty as
the clock is wound up. It has long been a disputed question whether
the cord should be fastened at the front end of the barrel and wind
towards the back, or whether it should be fastened at the back and
wind towards the front. I am not aware that there is any violation of
principle, so far as the regularity of the power is concerned, whether
the cord runs one way or the other. I understand it to be solely a
question of keeping the weight clear of the case and the pendulum
ball. In ordinary constructed regulator cases this object will be best
attained by cutting the screw so that the cord can be fastened at the
front of the barrel and wind towards the back; because in making it
in this way, the weight is the length of the barrel farther away from
the front of the case when it is wound up, and about the same distance
farther away from the pendulum ball when it is nearly run down, than if
the cord was fastened at the back end of the barrel and wound towards
the front. The cutting of the groove is usually done in an ordinary
screw cutting lathe.
In making the pivots on a barrel it is the usual custom to make the
back pivot smaller than the front one but, with all due respect for
this time-honored custom, I would direct a little attention to the
philosophy of continuing to make the barrel pivots of a regulator in
this manner. Friction varies with pressure; a large pivot has a greater
amount of friction than a smaller one, because the pressure on the
sliding surface of the revolving body is farther away from the center
of motion in one case than in the other. In regulators where the barrel
pivots are of a different size, the effective force of the weight will
vary slightly according as the weight is fully wound up or nearly run
down. In one instance the pressure of the weight is more directly
on the large pivot than it is on the smaller one; and in the other
instance the pressure is more directly on the small pivot than it is on
the larger one, and when the weight is half wound up, or half run down,
the pressure is equal on both pivots.
In the center pinion and in some of the other arbors of a clock, it
is sometimes necessary to make one pivot considerably larger than the
other; but in these cases the difference in the size of the pivots
does not affect the regularity of the transmission of the power,
because the pressure that turns the wheel is always at the same
point. In a regulator barrel, however, the pressure of the cord and
weight shifts gradually from one end of the barrel to the other, as
the clock runs down, and when the pivots are of unequal thickness the
power is transmitted nearly as irregular as if the top of the barrel
was slightly conical and both pivots of the same size. For the above
reason, I think, that it will be plain to all that in a fine clock
both of the barrel pivots should be made of an equal diameter. The
front pivot should be made no larger than is absolutely necessary for
a winding square, and when we take the fact into consideration that a
fine clock with a Graham escapement requires considerable less power
to keep it in motion than an eight-day marine chronometer does, we
may safely conclude that the winding squares of many regulators of
the Graham class might be made smaller. A pivot about 0.2 of an inch
will secure a sufficient amount of strength. For the reasons mentioned
above, the back pivot should be exactly the same diameter, and although
the effects of friction will be slightly greater when both pivots are
of an equal size, still the force of the weight will be transmitted
more regularly, which is the object aimed at. Where the plates are
bushed a length of two to three diameters is long enough for the pivot
holes.
The stop works, maintaining powers and general arrangement of the
great wheel, ratchets and clicks, have been so fully described and
illustrated on pages 282 to 290, Figs. 83 to 87, that it would be
useless duplication to repeat them here, and the reader is therefore
referred to those pages, for full particulars. This is also the case
with the purely mechanical operations of cutting the wheels and
pinions, hardening, polishing, staking, etc.; all have been fully
treated; but there are some further considerations which may be
mentioned here. The practical value of making pinions with very high
numbers is very much over-rated. I know of two clocks situated in the
same building that are compared every other day by transit observation.
They both have Graham escapements and mercurial pendulums, and are
equally well fitted up, and as far as the eye can detect, they are
about equally well made in all the essential points, with only this
difference: one clock has pinions of eight, and the other pinions of
sixteen leaves, yet for two years one clock ran about equally as well
as the other. In fact, if there was any difference, it was in favor of
the clock with the eight-leaved pinions. In giving this example, I must
not be understood to be placing little value on high numbered pinions.
I know that in some instances they can be used to advantage. The
idea that I want to illustrate at present is, that it is not in this
direction that we are to search for the means of improving the rates of
regulators.
A pinion as low as eleven leaves can be made so that the action of the
tooth will begin at or beyond the line of centers; but as eleven is an
inconvenient number to use in clockwork, we may with great propriety
decide upon twelve as being a sufficient number of leaves for all the
pinions used in a regulator having a Graham escapement.
In arranging the size of the wheels in a regulator, the diameters of
the center and third wheels are determined by the distance between
the center of the minute and the center of the seconds hand circle on
the dial. As the dials of regulators are usually engraved after the
dial plates have been fitted, and as the position of the holes in the
dial for the center and scape wheel pivots to come through determines
the size of the seconds circle, it may be well to mention here that,
for a twelve-inch dial, two and a half inches is a good distance for
the center of the minute circle to be from the center of the seconds
circle. Consequently the center and third wheels must be made of such
a diameter as will raise the scape wheel arbor two and a half inches
from the center arbor, and the other wheels must be made proportionally
larger, according to the number of teeth they contain.
We all know what a difficult matter it is to make a cutter that will
cut a tooth of the proper shape; but when the cutter is once made
and carefully used, we also know that it will cut or finish a great
number of wheels without injury. For this reason, those who are
contemplating making only one, or at most but a few regulators, will
find the work will be greatly simplified by making the wheels of a
diameter proportionate to the number of teeth they contain, and for all
practical purposes the cutter that cuts or finishes the teeth of one
wheel will be sufficiently accurate for the others. If we make all the
pinions with the same number of leaves they will also all be nearly of
the same diameter, and may be cut, or rather the cutting operation may
without any great impropriety be finished with one cutter.
An opinion prevails among a certain class of workmen that the teeth of
the great wheel and leaves of the center pinion should be made larger
and stronger than the other wheels and pinions, because there is a
greater strain upon them than on the other. However reasonable this
idea may seem, a little consideration will show that in the case of
a regulator, with a Graham escapement, where so little motive power
is required to keep it in motion, an arrangement of this nature is
altogether unnecessary. The smallest teeth ever used in any class of
regulators are strong enough for the great wheel; and if there be a
greater amount of strain on the teeth of the great wheel in comparison
with the teeth of the third wheel, for example, then make the great
wheel itself proportionately thicker, as is usually done, according to
the extra amount of strain that it is to bear. The teeth of wheels and
the leaves of pinions wear more from imperfect construction than from
any want of a sufficient amount of metal in them.
If we assume the distance between the center of the minute and the
center of the seconds circle to be 2½ inches, and also assume that the
clock will have a seconds pendulum, and all the pinions have 12 leaves,
and the barrel make one turn in 12 hours, then the following is the
diameter the wheels will require to be, so that the teeth may all be
cut with one cutter, and also the number of teeth for each wheel:
Great wheel 144 teeth.
Diameter 3.40 inches for the pitch circumference.
Hour wheel 144 teeth.
Diameter 3.40 inches for the pitch circumference.
Center wheel 96 teeth.
Diameter 2.26 inches for the pitch circumference.
Third wheel 90 teeth.
Diameter 2.11 inches for the pitch circumference.
Scape wheel 30 teeth.
Diameter 1.75 inches for the pitch circumference.
The number of arms or crosses to be put in a wheel is usually decided
by the taste of the person making the clock. There is, however, another
view of the subject, which I would like to mention. With the same
weight of metal a wheel will be stronger with six arms than with four
or five, and as lightness, combined with strength, should be the object
aimed at in making wheels, I prefer six arms to four or five for the
wheels of a regulator.
Figs. 157 and 158 are front and side elevations of the proposed
regulator movement, showing the size and position of the wheels, the
size of the frames, the positions of the pillars, dial feet, etc. The
dotted large circular lines on Fig. 157 show the position the hour,
minutes, and seconds circles will occupy on the dial. According to
the ordinary rules of drawing, the dotted lines would infer that the
movement is in front of the dial, and perhaps it may be necessary
to explain that in the present instance these lines are made dotted
solely with the view of making the diagram more distinct, and are not
intended to represent the dial to be at the back of the movement. A is
the barrel, B is the great wheel, which turns once in twelve hours; C
is the hour wheel, which works into the great wheel, and also turns
once in twelve hours; D is the center wheel, which turns once in an
hour, and carries the minute hand; E is the third wheel, and F is the
scape wheel, which turns once in a minute and carries the seconds
hand; G is the pallets; H the pillars, and I is the dial feet; J is
the maintaining power click, and K shows the position of the cord.
Neither the hour or great wheels project over the edge of the frame,
and it will be observed that a clock of this arrangement is remarkable
for its simplicity, having only four wheels and three pinions, with
the addition of the scape wheel and the barrel ratchets. There are no
motion or dial wheels, the wheel C turning once in 12 hours, carrying
the hour hand. The size and shape of the frames and the position of the
pillars, allows the dial feet to be placed so that the screws which
hold the dial will appear in symmetrical positions on the dial.
Formerly the term “astronomical” was applied to clocks which indicated
the motions and times of the earth, moon, and other celestial bodies,
but at present we may take it as indicating such as are used in
astronomical observatories. In all essential particulars they are
the same as first-class watchmakers’ regulators, the most obvious
departure being that the hour hand is made to revolve only once a day,
the dial being divided into twenty-four hours. This only requires an
intermediate wheel and pinion in the motion work, and, assuming the
hour hand to be driven from the center arbor, there will be the usual
hour and minute wheels and cannon pinion. The most suitable ratio for
these are ¼ and ⅙ = ¹/₂₄, and, as any numbers, being multiples, may be
used, they may as well be selected so as to be cut with the same tools
as the wheels of the train. Two pinions of 20 and wheels of 80 and 120
suit very well; 20 ÷ 80 and 20 ÷ 120 = ²⁰/₈₀ × ²⁰/₁₂₀ = ⁴⁰⁰/₉₆₀₀ =
¹/₂₄, and the hands will both go in the same direction.
Some astronomical clocks show mean solar, and others sidereal time;
this requires no structural alteration, merely a little shortening of
the pendulum in the latter case, which can be done with the regulating
nut.
LIST OF ILLUSTRATIONS.
A
Addendum, 202, 218, 220
Angular Motion, 103, 112
Automatic Pinion Cutter, 245, 247
“ “ Drill, 249
“ Wheel and Pinion Cutter, 254
C
Calendar, Simple, 351
“ Perpetual, 354, 356, 358
Center Distances, 105, 111, 202
Chimes, Laying out, 370, 421, 422, 423, 424, 425
Chimes Westminster, 372
Click, Position of, 288
Cock, 482
Compensated Rod, Steel and Zinc, 42
Counter-poising Hands, 443
Count hook, Position, of, 305
Count Wheel Striking Train, 302, 303, 311, 314, 315, 316, 322, 324
Cuckoo Bellows and Pipe, 328
D
Dedendum, 202
Dial Work, 295
Diameters of Wheels, Getting, 196
E
Eight-day Count Wheel, Time and Striking Trains, 299, 309
Eight-day Snail Strike, 342
Electric Chimes, 421, 422, 423, 424, 425
Electric Clocks, Pendulum Driven, 377, 379, 381, 382
Electric Clocks, Weight Driven, 394, 395, 396, 398
Epicycloid, 206, 219, 239
Escape Wheel, Cutting, 122, 124
“ “ Drawing to fit Pallets, 120
Escapement, Anchor, 142, 144, 145, 146, 147
“ Brocot’s Visible, 127, 129
“ Cylinder, 164, 165, 166, 167, 177, 179, 181, 183
“ Dead Beat, 117, 118
“ Drum, 148
“ Gravity, 152, 154, 157, 159, 161
“ Pin, 185, 194
“ Pin Wheel, 136, 137
“ Recoil, 142, 144, 145, 146, 147
“ to draw the, 114
F
Friction Springs, 294
G
Grandfather clocks, 352
H
Hypocycloid, 206
K
Keyhole Plates, 289
L
Lever Escapement for Clocks, 193
Levers, the Elements of, 99, 100, 101
M
Maintaining Powers, 285, 286, 287, 291
P
Pallets, Drawing, 116
Pendulum Brackets, 32
“ Mercurial, 67, 71, 75
“ Torsion, 92, 93, 94, 95
“ Oscillation of, 10, 14, 21
“ Rieffler, 50, 75
Perpetual Calendar Clocks, 354, 356, 358
“ Brocot, 360, 362, 363, 364, 366
Pinion Drill, 251
Pitch Diameter, 202, 218, 219, 220, 239
Plate, Jeweling, 475, 476
Posts, 480
Precision Clock Room, 452
Q
Quarter Chiming Snail Trains, 341
Quail and Cuckoo Train, 322, 324
R
Rack, Division of, 335
Regulator Trains, 465, 467, 479
Rounding-Up Wheels, 220, 224
S
Secondary Dials, 416
Self Winding Clocks, 400, 401, 404, 406, 408, 412
Ship’s Bell Train, 314, 315, 316
Slide Gauge Lathe, 241
“ “ Tools, 243
Snail, Laying Out, 337
“ Striking Trains, 333, 342, 345, 346
Suspension Springs, 84
Synchronizing Clocks, 412, 415
W
Wheel Cutting Engine, 255
Wiring Systems, 386, 388
Wood Rod and Lead Bob, 33
Z
Zinc Bob and Wood Rod, 331
INDEX.
A
Addendum, 202
Air, Pressure of, 20
Aluminum, Compensation with, 48
Anchor Escapement, 141
Angular Measurement, Peculiarities of, 102
Apparent Time, 348
Arbors, Polishing Steel, 232
“ Straightening Bent, 231
Arc of Escapement, 93, 109, 115, 127, 138, 145, 153, 164, 186, 469
Armatures, Adjustment of, 389, 409
Astronomical Clocks, 493
“ Day, 348
Auxiliary Weights, 37
B
Balance, Vibrations of, 180
Banking, 90, 156, 160, 170, 176
Barometric Error, 20
Barrels, 244, 267, 465, 485
“ Chiming, 370
Batteries, 380
“ Dating, 392
“ Grading, 384
“ Making, 383
“ Position of, 385
“ Wiring, Methods of, 385
Beat, to put a Clock in, 89
Bells, 369
“ Ships, 315
Brocot’s Calendar, 359
“ Visible Escapement, 127, 128
Bushing, 476
C
Cables, Clock, 269
“ Lengths of, 271
Calculations of Weights, 57
Calendars, 347
“ Brocot’s, 359
“ Gregorian, 349
“ Julian, 349
“ Perpetual, 353
“ Simple, 350
Carillons, 372
Case Friction, 448
“ Temperature, 450
Cases, 446
“ Gilding, 459
“ Marble, 460
“ “ to Polish, 461
“ Polishing, 457
“ Precision Clock, 447
“ Regulator, 463
“ Restoring old, 455
Cement for Marble, 460
“ for Dials, 438
Center Distances, 110, 200
“ of Gravity, 18
“ of Oscillation, 13
“ Springs, 96, 294
Chain Drives, 271
Cheap Clocks, to clean, 187
Chime Barrels, to mark, 371
Chimes, 339, 370
“ Cambridge, 372
“ Carillon, 372
“ Electric, 420
“ Tubular, 374, 422
Circle, Pitch, 202
Circular Error, 21
“ Pitch, 215
Cleaning Cheap Clocks, 187
Clocks, Astronomical, 493
“ Cuckoo, 319, 321
“ Designing, 8
“ Four-hundred day, 91
Clocks, Glass of, 462
“ Repeating, 332
“ Room, 452
Cock, 482
Collets, 234
Compensated Pendulum Rods, 40
“ Rod, Flat, 41
“ Rods, Tubular, 48
Compensation, 450
Compensating Pendulums, 23
“ “ Bracket for, 32
Compensating Pendulums, Principles of Construction, 27
Compensating Pendulums with shot, 36
Compensating Pendulums, Wood Rod and Lead Bob, 32
Compensation Pendulums, Wood Rod and Zinc Bob, 28
Compensation Pendulums, Aluminum, 48
Cones, Rusting of, 190
Construction of Dials, 426
Contacts, Dial, 423, 425
“ Electric, 396
Contrate Wheel, 171, 375
Conversion, Table of, 18
Cords, 268
“ Lengths of, 270
Count Hook, 301, 304, 310
“ Wheel, 301, 304, 315
“ “ Train, 300
Crown Wheel, 171
Crutches, 87, 472
Cuckoo, Adjustments of, 326
“ Bellows, 328
“ Clock, Names of Parts, 323
“ Motion Work, 296
“ Repairing, 327
Cutters for Clock Trains, 196
“ Setting, 197
Cycloid, 21
Cylinder Clocks, Examination of, 171
Cylinder, End Shake, 170
“ “ Proportion of, 149
“ Side Shake, 167
“ Teeth, Shape of, 183
Cylinders, Weight of, 37
D
Day, Astronomical, 348
“ Sidereal, 348
“ Solar, 348
Dedendum, 202
Dennison Escapement, 150
Depolarizers, 381
Depthing, 200
“ Tool, 477
Designing Clocks, 8
Detached Lever Escapement, 184
Dials, Construction of, 426
“ Contacts, 423, 425
“ Enamel for, 431
“ Phosphorescent, 437
“ Repairing, 432, 438
“ Secondary, 417
“ to Clean, 436
“ “ Silver, 434
“ Varnish for, 438
Distances, Center, 200
Drawings, to read, 98
Draw of Teeth, 194
Drill, Pinion, 249, 251
Drop, 107
E
Effect of Temperature, 62
Eight Day Trains, 299
Electric Chimes, 420
“ Clocks, 376
“ “ Synchronizing, 400, 413
“ Contacts, 396
Elements, Mechanical, 98
Enamel for Dials, 431
End Shake, of Cylinder, 170, 175
End Stones, 477
Epicycloid, 206
Equation of Time, 365
Error, Barometric, 20
“ Circular, 21
“ Temperature, 22
Escape Wheel, Sizes of, 109, 133, 155, 164
“ “ To make, 109, 120, 135, 138, 150, 155, 162, 164
Escapement, Brocot’s, 127, 128
“ Cylinder, 163
“ Dennison, 150
“ Detached Lever, 184
“ Drum, 148
“ Graham, 109
“ Gravity, 150, 161
“ Le Paute’s Pin Wheel, 135
“ Pin, 185, 193
“ Recoil, 141
“ To draw Graham, 113
“ “ Pin Wheel, 138
“ “ Gravity, 152
“ Western Clock Mfg. Co., 193
Examination of Cylinders, 171
Expansion of Metals, 22
F
Fan, 308, 326
Fly for Gravity Escapement, 158
Frames, Making, 261
“ Thickness of, 474
Four-hundred Day Clocks, 91
Friction, Disengaging, 203
“ Engaging, 203
“ of Teeth, 132
“ Springs, 294
G
Gathering Pallet, 338, 344
Gilding, 459
Gong Wires, 369
Graham Escapement, 109, 467
Gravity, Center of, 18
“ Escapement, 150
Gregorian Calendar, 349
H
Half Hour Striking Work, 334, 342, 345
Hammers, 367
“ Hardening, 198, 480, 482
“ Springs, 368
“ Tail, 298, 301
Hands, 439
“ Proportions of, 440
“ To Balance, 442
“ To Blue, 444
Hour Rack, 335
“ Snail, 296, 334
“ Strike, 342
“ Wheel, 96, 293, 296, 325
Hypocycloid Curves, 206
I
Iron, Expansion of, 57
Information, Need for, 3
Isochronism, 469
J
Jeweling, 475, 477
Jewels, Pallet, 126
Julian Calendar, 349
L
Lantern Pinions, 235
Lathe, Slide Gauge, 241, 243, 246
Laws of Pendulums, 11
Lead, 22, 32
Leap Year, 349
Length of Pivots, 199
Le Paute’s Escapement, 135
Leverage of Wheels, 99
Lift, 106
Lifting Cam, 301, 331
“ Piece, 331
“ Planes, 116
“ Pins, 186
Lock, 107
Locking Hook, 301
Losing Time, 192
Lunation, 365
M
Magnets, Arrangement of, 378, 386, 389, 395, 401, 406
Mainsprings, 272, 274, 277, 278, 279, 280, 281, 282
“ Breakage of, 281
“ Buckled, 277
“ Cleaning, 277
“ Clock, 288
“ Coil Friction, 277
“ Fusee, 279
“ Importance of Cleaning, 274
“ Length of, 280
“ Loss of Power, 274
“ Maintaining Power, 285, 291
“ Oiling, 278
“ Stop Works, 282
Maintaining Powers, 285
Mean Apparent Time, 348
Mean Time, 348
Measuring Wheels, 195
Measurement, Angular, 102
Mechanical Elements, 98
Mercurial Pendulums, 53, 60, 69
“ “ For Tower Clocks, 65
Mercury, 53, 56, 66, 70
Metals, Expansion of, 22
“ Weight of, 37
Millimeters Compared with Inches, 18
Minute Jumpers, 417
“ Wheels, 96, 293, 296, 325
Month Clocks, 260
“ Sidereal, 349
“ Synodic, 350
Moon, Phases of, 365
“ Train, 365
Motion Work, 96, 293, 296, 325
N
Need for Information, 3
Numbers, Conversion of, 201
Nut, Rating, 42, 50, 66
O
Oiling Cables, 269
Oscillation, Center of, 13
Overbanking, 90, 156, 160, 170, 176
P
Pallet Jewels, 126
Pallets, 106, 115, 121, 126, 130, 135, 139,
141, 144, 149, 153, 186, 193, 470
Pallets, To make, 119, 126
Pendulum, Isochronous, 470
“ Lengths, Table of, 10, 16
“ Rieffler, 49, 75
“ Rods, 262
“ “ Compensated, 40
“ Compensating, 23
“ Electric Driven, 376
“ Laws of, 11
“ Mercurial, 53, 60, 69
“ Sidereal, 493
“ Torsion, 91
Perpetual Calendar, 353
Phases of the Moon, 365
Pillars, Making, 240
Pinion Drill, Automatic, 249, 251
“ Making, 227, 252
“ “ Machine, Automatic, 245, 247
“ Canon, 293, 294, 295
“ Depthing, 206, 210, 217
“ Facing, 233
“ Hardening, 229
“ Lantern, 235
“ Tempering, 230
“ To Draw, 206
Pin Escapement, 185, 193
“ Wheels, 297, 301, 327
“ “ Escapement, 135
“ “ “ To Draw, 138
Pitch, Addendum, 216
“ Circle, 202
“ Circular, 215
“ Diametral, 216
Pivots, 488
“ Length of, 199
“ Proportions of, 167, 173, 199, 474
“ Side Shake, 199
Planes, Lifting, 116
Plates, Clock, 198
“ Thickness of, 474
Poising Balance Staffs, 189, 190
Polishing Steel Arbors, 232
Posts, Clock, 478
Power, 264, 265, 266, 267
“ Maintaining, 285
Putting in Beat, 89
R
Rack, Division of, 335
“ Striking Work, 331
Ratchet, 288
Rating Nut, 42, 50, 66
“ With Shot, 90
Reading Drawings, 98
Repeating Clocks, 332
Recoil Escapement, 141
Regulation, 79
Regulator Trains, 492
Regulators, Making, 463
Repairing Dials, 432, 438
Resistance Spools, 388
Rieffler Pendulum, 49, 75
Rounding-Up, 174, 221, 223
“ “ Rules for, 226
Run, 108
Rusting of Cones, 190
S
Screws, Clock, 483
Secondary Dials, 417
Self-winding Clocks, 376
Ship Bells, Striking, 313
Shot, Rating with, 90
Sidereal Day, 348
“ Month, 349
“ Pendulums, 493
“ Year, 349
Side Shake, Cylinder, 167
“ “ For Pivots, 199
Silvering Dials, 434
Simple Calendar, 350
Sizes of Teeth, 211, 213, 237
“ “ Wheels, 201
Slide Gauge Lathe, 241, 243, 244
Snail, 296, 336
“ Division of, 337
“ French System, 342
“ Quarter Striking Work, 339
“ Striking Work, 330, 340
Solar Day, 348
Sparking, to Prevent, 386
Springs, Center, 294
“ Clock, 273, 288, 307
“ Friction, 294
“ Hammer, 368
“ Main, 272, 273, 274, 277, 278, 279, 280, 282, 307
Squares, Milling, 261
Standards, Importance of, 26
Star Wheel, 332, 335
Steel, Expansion of, 57
Stop Works, 282
Straightening Bent Arbors, 231
Striking from Center Arbor, 298
“ To Correct, 306, 307
“ Trains, 297, 308, 313, 323, 330
“ “ Half Hour, 298, 308, 313
“ “ Setting Up, 307, 310, 339
“ “ To Calculate, 297
“ “ Rack, 331
“ Work, Repeating, 332
“ “ Snail, 330, 340
Supports, Pendulum, 86
Suspension, 81, 93
“ Springs, 82, 93
Synchronizing, 400, 413
Synodic Month, 350
T
Table, Lengths of Pendulum, 12, 16, 17, 34, 258
“ of Expansions, 30
“ Inches, Millimeters and French Lines, 18
“ “ Time Trains, 258, 339, 340, 492
“ “ Weights and Metals, 37
Tangent, 104
Teeth, Friction of, 132
“ Shape of Cylinder, 183
“ Shapes of, 203
“ Sizes of, 211, 213, 237
Temperature, Effect of, 62
“ Error, 22
Tempering, 229
Time, Apparent, 348
“ Equation of, 365
“ Losing, 192
“ Mean, 348
To Draw Anchor Escapement, 143, 145, 147
Top Weights, 39
Torsion Pendulums, 91
Tower Clock, Cables, 269
“ “ Dials, Sizes of, 426
“ “ Gravity Escapement for, 150
“ “ Hands, 442
“ “ Maintaining Powers, 285, 291
“ “ Motion Work, 295
“ “ Pendulums, 65
“ “ Stop Works, 287
“ “ Suspension, 65
“ “ Time Trains, 258
Trains, 330
“ Electric, 389
“ Regulator, 492
“ Table of, 258
“ To Calculate, 257, 264, 297
Tropical Year, 348
Tubular Chimes, 374, 422
Turning Tools, 481
V
Varnish for Dials, 438
“ Remover, 456
Vibrations of Balance, 180
W
Warning, 306, 312
“ Pin, 306, 312
“ Wheel, 306, 312
Weight Cords, 268
Weight of Lead, Zinc and Cast Iron Cylinders, 37
Weights, 265, 319
“ Auxiliary, 37
“ Calculations of, 27
“ Top, 39
Wheel Contrate, 171, 375
“ Crown, 171
“ Hour, 296
“ Cutting, 254
“ Leverage of, 99
“ Measuring, 195
“ Minute, 96, 293, 296, 325
“ Sizes of, 201, 490
“ Stamping, 256
“ Star, 332, 335
“ Stretching, 226
Wires, Gong, 369
Y
Year, 348
“ Leap, 349
“ Sidereal, 349
“ Tropical, 348
Z
Zinc, 54
Big Ben
[Illustration]
BIG BEN is the first and only alarm sold exclusively
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Western Clock Mfg. Co.
New York La Salle, Illinois Chicago
HOROLOGICAL DEPARTMENT—Bradley Polytechnic Institute
[Illustration]
THIS entire building used exclusively for instruction in
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[Illustration]
=MEYER= JEWELRY CO.
Kansas City :: Mo.
For
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=MEYER= JEWELRY CO.
Kansas City :: Mo.
[Illustration]
In 1854
Waltham Watches
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WALTHAM WATCHES= all representing the
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Howard Clocks
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The =E. Howard Clock Co.=
BOSTON, NEW YORK AND CHICAGO
Makers of Clocks but only of the highest grade
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THE GREAT
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[Illustration]
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[Illustration]
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=Heyworth Building, Chicago=
* * * * * *
Transcriber’s note:
Illustrations have been moved so they do not break up paragraphs.
Typographical errors have been silently corrected.
The “TABLE OF CONTENTS” was added by the transcriber. It was not part
of the original text.
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