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_.
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