William Marsden - "The History of Sumatra"

Various - "The Nursery, No. 107, November, 1875, Vol. XVIII."

Ethel M. Dell - "The Safety Curtain, and Other Stories"

Edwin E. Slosson - "Creative Chemistry"

Anonymous - Watch and Clock Escapements

A >> Anonymous >> Watch and Clock Escapements



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WATCH AND CLOCK ESCAPEMENTS

A Complete Study in Theory and Practice of the Lever, Cylinder and
Chronometer Escapements, Together with a Brief Account of the Origin
and Evolution of the Escapement in Horology

Compiled from the well-known Escapement Serials
published in The Keystone

Nearly Two Hundred Original Illustrations







Published by
The Keystone
The Organ of the Jewelry and Optical Trades
19th & Brown Sts., Philadelphia, U.S.A.

1904

All Rights Reserved
Copyright, 1904, By B. Thorpe,
Publisher of the Keystone.




PREFACE


Especially notable among the achievements of The Keystone in the field
of horology were the three serials devoted to the lever, cylinder and
chronometer escapements. So highly valued were these serials when
published that on the completion of each we were importuned to republish
it in book form, but we deemed it advisable to postpone such publication
until the completion of all three, in order that the volume should be a
complete treatise on the several escapements in use in horology. The
recent completion of the third serial gave us the opportunity to
republish in book form, and the present volume is the result. We present
it to the trade and students of horology happy in the knowledge that its
contents have already received their approval. An interesting addition
to the book is the illustrated story of the escapements, from the first
crude conceptions to their present perfection.




CONTENTS


CHAPTER I.

THE DETACHED LEVER ESCAPEMENT 9


CHAPTER II.

THE CYLINDER ESCAPEMENT 111


CHAPTER III.

THE CHRONOMETER ESCAPEMENT 131


CHAPTER IV.

HISTORY OF ESCAPEMENTS 153


CHAPTER V.

PUTTING IN A NEW CYLINDER 169


INDEX 177






WATCH AND CLOCK ESCAPEMENTS




CHAPTER I.

THE DETACHED LEVER ESCAPEMENT.


In this treatise we do not propose to go into the history of this
escapement and give a long dissertation on its origin and evolution, but
shall confine ourselves strictly to the designing and construction as
employed in our best watches. By designing, we mean giving full
instructions for drawing an escapement of this kind to the best
proportions. The workman will need but few drawing instruments, and a
drawing-board about 15" by 18" will be quite large enough. The necessary
drawing-instruments are a T-square with 15" blade; a scale of inches
divided into decimal parts; two pairs dividers with pen and pencil
points--one pair of these dividers to be 5" and the other 6"; one ruling
pen. Other instruments can be added as the workman finds he needs them.
Those enumerated above, however, will be all that are absolutely
necessary.

[Illustration: Fig. 1]

We shall, in addition, need an arc of degrees, which we can best make
for ourselves. To construct one, we procure a piece of No. 24 brass,
about 51/2" long by 11/4" wide. We show such a piece of brass at _A_,
Fig. 1. On this piece of brass we sweep two arcs with a pair of dividers
set at precisely 5", as shown (reduced) at _a a_ and _b b_. On these
arcs we set off the space held in our dividers--that is 5"--as shown at
the short radial lines at each end of the two arcs. Now it is a
well-known fact that the space embraced by our dividers contains exactly
sixty degrees of the arcs _a a_ and _b b_, or one-sixth of the entire
circle; consequently, we divide the arcs _a a_ and _b b_ into sixty
equal parts, to represent degrees, and at one end of these arcs we
halve five spaces so we can get at half degrees.

[Illustration: Fig. 2]

Before we take up the details of drawing an escapement we will say a few
words about "degrees," as this seems to be something difficult to
understand by most pupils in horology when learning to draw parts of
watches to scale. At Fig. 2 we show several short arcs of fifteen
degrees, all having the common center _g_. Most learners seem to have an
idea that a degree must be a specific space, like an inch or a foot. Now
the first thing in learning to draw an escapement is to fix in our minds
the fact that the extent of a degree depends entirely on the radius of
the arc we employ. To aid in this explanation we refer to Fig. 2. Here
the arcs _c_, _d_, _e_ and _f_ are all fifteen degrees, although the
linear extent of the degree on the arc _c_ is twice that of the degree
on the arc _f_. When we speak of a degree in connection with a circle we
mean the one-three-hundred-and-sixtieth part of the periphery of such a
circle. In dividing the arcs _a a_ and _b b_ we first divide them into
six spaces, as shown, and each of these spaces into ten minor spaces, as
is also shown. We halve five of the degree spaces, as shown at _h_. We
should be very careful about making the degree arcs shown at Fig. 1, as
the accuracy of our drawings depends a great deal on the perfection of
the division on the scale _A_. In connection with such a fixed scale of
degrees as is shown at Fig. 1, a pair of small dividers, constantly set
to a degree space, is very convenient.


MAKING A PAIR OF DIVIDERS.

[Illustration: Fig. 3]

To make such a pair of small dividers, take a piece of hard sheet brass
about 1/20" thick, 1/4" wide, 11/2" long, and shape it as shown at Fig.
3. It should be explained, the part cut from the sheet brass is shown
below the dotted line _k_, the portion above (_C_) being a round handle
turned from hard wood or ivory. The slot _l_ is sawn in, and two holes
drilled in the end to insert the needle points _i i_. In making the slot
_l_ we arrange to have the needle points come a little too close
together to agree with the degree spaces on the arcs _a a_ and _b b_. We
then put the small screw _j_ through one of the legs _D''_, and by
turning _j_, set the needle points _i i_ to exactly agree with the
degree spaces. As soon as the points _i i_ are set correctly, _j_ should
be soft soldered fast.

The degree spaces on _A_ are set off with these dividers and the spaces
on _A_ very carefully marked. The upper and outer arc _a a_ should have
the spaces cut with a graver line, while the lower one, _b b_ is best
permanently marked with a carefully-made prick punch. After the arc _a a_
is divided, the brass plate _A_ is cut back to this arc so the
divisions we have just made are on the edge. The object of having two
arcs on the plate _A_ is, if we desire to get at the number of degrees
contained in any arc of a 5" radius we lay the scale _A_ so the edge
agrees with the arc _a a_, and read off the number of degrees from the
scale. In setting dividers we employ the dotted spaces on the arc _b b_.


DELINEATING AN ESCAPE WHEEL.

[Illustration: Fig. 4]

We will now proceed to delineate an escape wheel for a detached lever.
We place a piece of good drawing-paper on our drawing-board and provide
ourselves with a very hard (HHH) drawing-pencil and a bottle of liquid
India ink. After placing our paper on the board, we draw, with the aid
of our T-square, a line through the center of the paper, as shown at
_m m_, Fig. 4. At 51/2" from the lower margin of the paper we establish
the point _p_ and sweep the circle _n n_ with a radius of 5". We have
said nothing about stretching our paper on the drawing-board; still,
carefully-stretched paper is an important part of nice and correct
drawing. We shall subsequently give directions for properly stretching
paper, but for the present we will suppose the paper we are using is
nicely tacked to the face of the drawing-board with the smallest tacks
we can procure. The paper should not come quite to the edge of the
drawing-board, so as to interfere with the head of the T-square. We are
now ready to commence delineating our escape wheel and a set of pallets
to match.

The simplest form of the detached lever escapement in use is the one
known as the "ratchet-tooth lever escapement," and generally found in
English lever watches. This form of escapement gives excellent results
when well made; and we can only account for it not being in more general
use from the fact that the escape-wheel teeth are not so strong and
capable of resisting careless usage as the club-tooth escape wheel.

It will be our aim to convey broad ideas and inculcate general
principles, rather than to give specific instructions for doing "one
thing one way." The ratchet-tooth lever escapements of later dates
have almost invariably been constructed on the ten-degree
lever-and-pallet-action plan; that is, the fork and pallets were
intended to act through this arc. Some of the other specimens of this
escapement have larger arcs--some as high as twelve degrees.


PALLET-AND-FORK ACTION.

[Illustration: Fig. 5]

We illustrate at Fig. 5 what we mean by ten degrees of pallet-and-fork
action. If we draw a line through the center of the pallet staff, and
also through the center of the fork slot, as shown at _a b_, Fig. 5, and
allow the fork to vibrate five degrees each side of said lines _a b_, to
the lines _a c_ and _a c'_, the fork has what we term ten-degree pallet
action. If the fork and pallets vibrate six degrees on each side of the
line _a b_--that is, to the lines _a d_ and _a d'_--we have twelve
degrees pallet action. If we cut the arc down so the oscillation is only
four and one-quarter degrees on each side of _a b_, as indicated by the
lines _a s_ and _a s'_, we have a pallet-and-fork action of eight and
one-half degrees; which, by the way, is a very desirable arc for a
carefully-constructed escapement.

The controlling idea which would seem to rule in constructing a detached
lever escapement, would be to make it so the balance is free of the
fork; that is, detached, during as much of the arc of the vibration of
the balance as possible, and yet have the action thoroughly sound and
secure. Where a ratchet-tooth escapement is thoroughly well-made of
eight and one-half degrees of pallet-and-fork action, ten and one-half
degrees of escape-wheel action can be utilized, as will be explained
later on.

We will now resume the drawing of our escape wheel, as illustrated at
Fig. 4. In the drawing at Fig. 6 we show the circle _n n_, which
represents the periphery of our escape wheel; and in the drawing we are
supposed to be drawing it ten inches in diameter.

We produce the vertical line _m_ passing through the center _p_ of the
circle _n_. From the intersection of the circle _n_ with the line _m_
at _i_ we lay off thirty degrees on each side, and establish the points
_e f_; and from the center _p_, through these points, draw the radial
lines _p e'_ and _p f'_. The points _f e_, Fig. 6, are, of course, just
sixty degrees apart and represent the extent of two and one-half teeth
of the escape wheel. There are two systems on which pallets for lever
escapements are made, viz., equidistant lockings and circular pallets.
The advantages claimed for each system will be discussed subsequently.
For the first and present illustration we will assume we are to employ
circular pallets and one of the teeth of the escape wheel resting on the
pallet at the point _f_; and the escape wheel turning in the direction
of the arrow _j_. If we imagine a tooth as indicated at the dotted
outline at _D_, Fig. 6, pressing against a surface which coincides with
the radial line _p f_, the action would be in the direction of the line
_f h_ and at right angles to _p f_. If we reason on the action of the
tooth _D_, as it presses against a pallet placed at _f_, we see the
action is neutral.

[Illustration: Fig. 6]


ESTABLISHING THE CENTER OF PALLET STAFF.

[Illustration: Fig. 7]

With a fifteen-tooth escape wheel each tooth occupies twenty-four
degrees, and from the point _f_ to _e_ would be two and one-half
tooth-spaces. We show the dotted points of four teeth at _D D' D''D'''_.
To establish the center of the pallet staff we draw a line at
right angles to the line _p e'_ from the point _e_ so it intersects the
line _f h_ at _k_. For drawing a line at right angles to another line,
as we have just done, a hard-rubber triangle, shaped as shown at _C_,
Fig. 7, can be employed. To use such a triangle, we place it so the
right, or ninety-degrees angle, rests at _e_, as shown at the dotted
triangle _C_, Fig. 6, and the long side coincides with the radial line
_p e'_. If the short side of the hard-rubber triangle is too short, as
indicated, we place a short ruler so it rests against the edge, as shown
at the dotted line _g e_, Fig. 7, and while holding it securely down on
the drawing we remove the triangle, and with a fine-pointed pencil draw
the line _e g_, Fig. 6, by the short rule. Let us imagine a flat surface
placed at _e_ so its face was at right angles to the line _g e_, which
would arrest the tooth _D''_ after the tooth _D_ resting on _f_ had been
released and passed through an arc of twelve degrees. A tooth resting on
a flat surface, as imagined above, would also rest dead. As stated
previously, the pallets we are considering have equidistant locking
faces and correspond to the arc _l l_, Fig. 6.

In order to realize any power from our escape-wheel tooth, we must
provide an impulse face to the pallets faced at _f e_; and the problem
before us is to delineate these pallets so that the lever will be
propelled through an arc of eight and one-half degrees, while the escape
wheel is moving through an arc of ten and one-half degrees. We make the
arc of fork action eight and one-half degrees for two reasons--(1)
because most text-books have selected ten degrees of fork-and-pallet
action; (2) because most of the finer lever escapements of recent
construction have a lever action of less than ten degrees.


LAYING OUT ESCAPE-WHEEL TEETH.

To "lay out" or delineate our escape-wheel teeth, we continue our
drawing shown at Fig. 6, and reproduce this cut very nearly at Fig. 8.
With our dividers set at five inches, we sweep the short arc _a a'_ from
_f_ as a center. It is to be borne in mind that at the point _f_ is
located the extreme point of an escape-wheel tooth. On the arc _a a_ we
lay off from _p_ twenty-four degrees, and establish the point _b_; at
twelve degrees beyond _b_ we establish the point _c_. From _f_ we draw
the lines _f b_ and _f c_; these lines establishing the form and
thickness of the tooth _D_. To get the length of the tooth, we take in
our dividers one-half a tooth space, and on the radial line _p f_
establish the point _d_ and draw circle _d' d'_.

To facilitate the drawing of the other teeth, we draw the circles _d' c'_,
to which the lines _f b_ and _f c_ are tangent, as shown. We divide
the circle _n n_, representing the periphery of our escape wheel, into
fifteen spaces, to represent teeth, commencing at _f_ and continued as
shown at _o o_ until the entire wheel is divided. We only show four
teeth complete, but the same methods as produced these will produce them
all. To briefly recapitulate the instructions for drawing the teeth for
the ratchet-tooth lever escapement: We draw the face of the teeth at an
angle of twenty-four degrees to a radial line; the back of the tooth at
an angle of thirty-six degrees to the same radial line; and make teeth
half a tooth-space deep or long.

[Illustration: Fig. 8]

We now come to the consideration of the pallets and how to delineate
them. To this we shall add a careful analysis of their action. Let us,
before proceeding further, "think a little" over some of the factors
involved. To aid in this thinking or reasoning on the matter, let us
draw the heavy arc _l_ extending from a little inside of the circle _n_
at _f_ to the circle _n_ at _e_. If now we imagine our escape wheel to
be pressed forward in the direction of the arrow _j_, the tooth _D_
would press on the arc _l_ and be held. If, however, we should revolve
the arc _l_ on the center _k_ in the direction of the arrow _i_, the
tooth _D_ would _escape_ from the edge of _l_ and the tooth _D''_ would
pass through an arc (reckoning from the center _p_) of twelve degrees,
and be arrested by the inside of the arc _l_ at _e_. If we now should
reverse the motion and turn the arc _l_ backward, the tooth at _e_
would, in turn, be released and the tooth following after _D_ (but not
shown) would engage _l_ at _f_. By supplying motive to revolve the
escape wheel (_E_) represented by the circle _n_, and causing the arc
_l_ to oscillate back and forth in exact intervals of time, we should
have, in effect, a perfect escapement. To accomplish automatically such
oscillations is the problem we have now on hand.


HOW MOTION IS OBTAINED.

In clocks, the back-and-forth movement, or oscillating motion, is
obtained by employing a pendulum; in a movable timepiece we make use of
an equally-poised wheel of some weight on a pivoted axle, which device
we term a balance; the vibrations or oscillations being obtained by
applying a coiled spring, which was first called a "pendulum spring,"
then a "balance spring," and finally, from its diminutive size and coil
form, a "hairspring." We are all aware that for the motive power for
keeping up the oscillations of the escaping circle _l_ we must contrive
to employ power derived from the teeth _D_ of the escape wheel. About
the most available means of conveying power from the escape wheel to the
oscillating arc _l_ is to provide the lip of said arc with an inclined
plane, along which the tooth which is disengaged from _l_ at _f_ to
slide and move said arc _l_ through--in the present instance an arc of
eight and one-half degrees, during the time the tooth _D_ is passing
through ten and one-half degrees. This angular motion of the arc _l_ is
represented by the radial lines _k f'_ and _k r_, Fig. 8. We desire to
impress on the reader's mind the idea that each of these angular motions
is not only required to be made, but the motion of one mobile must
convey power to another mobile.

In this case the power conveyed from the mainspring to the escape wheel
is to be conveyed to the lever, and by the lever transmitted to the
balance. We know it is the usual plan adopted by text-books to lay down
a certain formula for drawing an escapement, leaving the pupil to work
and reason out the principles involved in the action. In the plan we
have adopted we propose to induct the reader into the why and how, and
point out to him the rules and methods of analysis of the problem, so
that he can, if required, calculate mathematically exactly how many
grains of force the fork exerts on the jewel pin, and also how much (or,
rather, what percentage) of the motive power is lost in various "power
leaks," like "drop" and lost motion. In the present case the mechanical
result we desire to obtain is to cause our lever pivoted at _k_ to
vibrate back and forth through an arc of eight and one-half degrees;
this lever not only to vibrate back and forth, but also to lock and hold
the escape wheel during a certain period of time; that is, through the
period of time the balance is performing its excursion and the jewel pin
free and detached from the fork.

We have spoken of paper being employed for drawings, but for very
accurate delineations we would recommend the horological student to make
drawings on a flat metal plate, after perfectly smoothing the surface
and blackening it by oxidizing.


PALLET-AND-FORK ACTION.

By adopting eight and one-half degrees pallet-and-fork action we can
utilize ten and one-half degrees of escape-wheel action. We show at _A A'_,
Fig. 9, two teeth of a ratchet-tooth escape wheel reduced one-half;
that is, the original drawing was made for an escape wheel ten inches in
diameter. We shall make a radical departure from the usual practice in
making cuts on an enlarged scale, for only such parts as we are talking
about. To explain, we show at Fig. 10 about one-half of an escape wheel
one eighth the size of our large drawing; and when we wish to show some
portion of such drawing on a larger scale we will designate such
enlargement by saying one-fourth, one-half or full size.

[Illustration: Fig. 9]

At Fig. 9 we show at half size that portion of our escapement embraced
by the dotted lines _d_, Fig. 10. This plan enables us to show very
minutely such parts as we have under consideration, and yet occupy but
little space. The arc _a_, Fig. 9, represents the periphery of the
escape wheel. On this line, ten and one-half degrees from the point of
the tooth _A_, we establish the point _c_ and draw the radial line
_c c'_. It is to be borne in mind that the arc embraced between the points
_b_ and _c_ represents the duration of contact between the tooth _A_ and
the entrance pallet of the lever. The space or short arc _c n_
represents the "drop" of the tooth.

This arc of one and one-half degrees of escape-wheel movement is a
complete loss of six and one-fourth per cent. of the entire power of the
mainspring, as brought down to the escapement; still, up to the present
time, no remedy has been devised to overcome it. All the other
escapements, including the chronometer, duplex and cylinder, are quite
as wasteful of power, if not more so. It is usual to construct
ratchet-tooth pallets so as to utilize but ten degrees of escape-wheel
action; but we shall show that half a degree more can be utilized by
adopting the eight and one-half degree fork action and employing a
double-roller safety action to prevent over-banking.

[Illustration: Fig. 10]

From the point _e_, which represents the center of the pallet staff, we
draw through _b_ the line _e f_. At one degree below _e f_ we draw the
line _e g_, and seven and one-half degrees below the line _e g_ we draw
the line _e h_. For delineating the lines _e g_, etc., correctly, we
employ a degree-arc; that is, on the large drawing we are making we
first draw the line _e b f_, Fig. 10, and then, with our dividers set at
five inches, sweep the short arc _i_, and on this lay off first one
degree from the intersection of _f e_ with the arc _i_, and through this
point draw the line _e g_.

From the intersection of the line _f e_ with the arc _i_ we lay off
eight and one-half degrees, and through this point draw the line _e h_.
Bear in mind that we are drawing the pallet at _B_ to represent one with
eight and one-half degrees fork-and-pallet action, and with equidistant
lockings. If we reason on the matter under consideration, we will see
the tooth _A_ and the pallet _B_, against which it acts, part or
separate when the tooth arrives at the point _c_; that is, after the
escape wheel has moved through ten and one-half degrees of angular
motion, the tooth drops from the impulse face of the pallet and falls
through one and one-half degrees of arc, when the tooth _A''_, Fig. 10,
is arrested by the exit pallet.

To locate the position of the inner angle of the pallet _B_, sweep the
short arc _l_ by setting the dividers so one point or leg rests at the
center _e_ and the other at the point _c_. Somewhere on this arc _l_ is
to be located the inner angle of our pallet. In delineating this angle,
Moritz Grossman, in his "Prize Essay on the Detached Lever Escapement,"
makes an error, in Plate III of large English edition, of more than his
entire lock, or about two degrees. We make no apologies for calling
attention to this mistake on the part of an authority holding so high a
position on such matters as Mr. Grossman, because a mistake is a
mistake, no matter who makes it.

We will say no more of this error at present, but will farther on show
drawings of Mr. Grossman's faulty method, and also the correct method of
drawing such a pallet. To delineate the locking face of our pallet, from
the point formed by the intersection of the lines _e g b b'_, Fig. 9, as
a center, we draw the line _j_ at an angle of twelve degrees to _b b''_.
In doing this we employ the same method of establishing the angle as we
made use of in drawing the lines _e g_ and _e h_, Fig. 10. The line _j_
establishes the locking face of the pallet _B_. Setting the locking face
of the pallet at twelve degrees has been found in practice to give a
safe "draw" to the pallet and keep the lever secure against the bank. It
will be remembered the face of the escape-wheel tooth was drawn at
twenty-four degrees to a radial line of the escape wheel, which, in this
instance, is the line _b b'_, Fig. 9. It will now be seen that the angle
of the pallet just halves this angle, and consequently the tooth _A_
only rests with its point on the locking face of the pallet. We do not
show the outlines of the pallet _B_, because we have not so far pointed
out the correct method of delineating it.


METHODS OF MAKING GOOD DRAWING INSTRUMENTS.

Perhaps we cannot do our readers a greater favor than to digress from
the study of the detached lever escapement long enough to say a few
words about drawing instruments and tablets or surfaces on which to
delineate, with due precision, mechanical designs or drawings. Ordinary
drawing instruments, even of the higher grades, and costing a good deal
of money, are far from being satisfactory to a man who has the proper
idea of accuracy to be rated as a first-class mechanic. Ordinary
compasses are obstinate when we try to set them to the hundredth of an
inch; usually the points are dull and ill-shapen; if they make a
puncture in the paper it is unsightly.

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