Watch and Clock Escapements | Page 2

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, ¼" wide, 1½" 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 5½" 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;