The old-style workman would take a round broach and calculate the size
of the cylinder by finding a place where the broach would just go
between the teeth, and the size of the broach at this point was supposed
to be the outer diameter of the cylinder. By our method we measure the
diameter of the escape wheel in thousandths of an inch, and from this
size calculate exactly what the diameter of the new cylinder should be
in thousandths of an inch. Suppose, to further carry out our comparison,
the escape wheel which is in the watch has teeth which have been stoned
off to permit the use of a cylinder which was too small inside, or, in
fact, of a cylinder too small for the watch: in this case the broach
system would only add to the trouble and give us a cylinder which would
permit too much inside drop.
DRAWING A CYLINDER.
We have already instructed the pupil how to delineate a cylinder escape
wheel tooth and we will next describe how to draw a cylinder. As already
stated, the center of the cylinder is placed to coincide with the center
of the chord of the arc which defines the impulse face of the tooth.
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