For all purposes of practical study the
delineation we show at Fig. 133 is to be preferred, because, if we carry
out all the details we have described, the lines would become confused.
We set our dividers at five of the spaces on the line _e f_ and from _g_
as a center sweep the circle _j_, which delineates the outer surface of
our cylinder shell.
Let us now, as we directed in our former instructions, draw a flattened
curve to represent the acting surface of the entrance lip of our
cylinder as if it were in direct contact with the impulse face of the
tooth. To delineate the exit lip we draw from the center _g_, Fig. 134,
to the radial line _g k_, said line passing through the point of contact
between the tooth and entrance lip of the cylinder. Let us next continue
this line on the opposite side of the point _g_, as shown at _g k'_, and
we thus bisect the cylinder shell into two equal parts of 180 degrees
each. As we previously explained, the entire extent of the cylinder half
shell is 196 degrees.
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