Watch and Clock Escapements | Page 4

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