In considering the cylinder escapement we
shall pursue an analytical course and strive to build up from the
underlying principles. In the drawings for this purpose we shall
commence with one having an escape wheel of 10" radius, and our first
effort will be the primary drawing shown at Fig. 129. Here we establish
the point _A_ for the center of our escape wheel, and from this center
sweep the short arc _a a_ with a 10" radius, to represent the
circumference of our escape wheel. From _A_ we draw the vertical line
_A B_, and from the intersection of said line with the arc _a a_ we lay
off twelve degree spaces on each side of the line _A B_ on said arc _a_
and establish the points _b c_. From _A_ as a center we draw through
the points _b c_ the radial lines _b' c'_.
To define the face of the incline to the teeth we set our dividers to
the radius of any of the convenient arcs of sixty degrees which we have
provided, and sweep the arc _t t_. From the intersection of said arc
with the line _A b'_ we lay off on said arc sixty-four degrees and
establish the point _g_ and draw the line _b g_.
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