Watch and Clock Escapements | Page 5

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