First,
placing a bit of bristol board on our drawing-board in which we can set
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.
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