If we then sweep the circle _h_ from the center of _g_ we define the
inner surface of the shell of our cylinder.
Strictly speaking, we have not assumed the position we stated, that is,
the impulse face of the tooth as passing half way into the cylinder. To
comply strictly with our statement, we divide the chord of the impulse
face of the tooth _A_ into eight equal spaces, as shown. Now as each of
these spaces represent the thickness of the cylinder, if we take in our
dividers four of these spaces and half of another, we have the radius of
a circle passing the center of the cylinder shell. Consequently, if with
this space in our dividers we set the leg at _d_, we establish on the
arc _b_ the point _i_. We locate the center of our cylinder when
one-half of an entering tooth has passed into the cylinder. If now from
the new center with our dividers set at four of the spaces into which we
have divided the line _e f_ we can sweep a circle representing the inner
surface of the cylinder shell, and by setting our dividers to five of
these spaces we can, from _i_ as a center, sweep an arc representing the
outside of the cylinder shell.
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