et
one leg of our dividers or compasses when we sweep the peripheral arc
which we use in our delineations; second, making three arcs in brass or
other sheet metal, viz.: the periphery of the escape wheel, the arc
passing through the center of the chord of the arc of the impulse face
of the tooth, and the arc passing through the point of the escape-wheel
tooth. Of these plans we favor the one of sticking a bit of cardboard on
the drawing board outside of the paper on which we are making our
drawing.

[Illustration: Fig. 132]

At Fig. 132 we show the position and relation of the several parts just
as the tooth passes into the shell of the cylinder, leaving the lip of
the cylinder just as the tooth parted with it. The half shell of the
cylinder as shown occupies 196 degrees or the larger arc embraced
between the radial lines _k_ and _l_. In drawing the entrance lip the
acting face is made almost identical with a radial line except to round
the corners for about one-third the thickness of the cylinder shell. No
portion, however, of the lip can be considered as a straight line, but
might be described as a flattened curve.

[Illustration: Fig. 133]

A little study of what would be required to get the best results after
making such a drawing will aid the pupil in arriving at the proper
shape, especially when he remembers that the thickness of the cylinder
shell of a twelve-line watch is only about five one-thousandths of an
inch. But because the parts are small we should not shirk the problem of
getting the most we possibly can out of a cylinder watch.

The extent of arc between the radial lines _k f_, as shown in Fig. 132,
is four degrees. Although in former drawings we showed the angular
extent added as six degrees, as we show the lip _m_ in Fig. 132, two
degrees are lost in rounding. The space _k f_ on the egress or exit side
is intended to be about four degrees, which shows the extent of lock. We
show at Fig. 133 the tooth _D_ just having passed out of the cylinder,
having parted with the exit lip _p_.

In making this drawing we proceed as with Fig. 132 by establishing a
center for our radius of 10" outside of our drawing paper and drawing
the line _A A_ to such center and sweeping the arcs _a b c_. We
establish the point _e_, which represents the center of our cylinder, as
before. We take the space to represent the radial extent of the outside
of our cylinder in our dividers and from _e_ as a center sweep a fine
p