We
will, for the present, accept the thickness of the arms as being
equivalent to five degrees of angular extent of the pitch circle of the
escape wheel.
[Illustration: Fig. 87]
[Illustration: Fig. 88]
In making our drawings we commence, as on former occasions, by
establishing the center of our escape wheel at _A_, Fig. 87, and
sweeping the arc _a a_ to represent the pitch circle of such wheel.
Through the center _A_ we draw the vertical line _A B_, which is
supposed to also pass through the center of the pallet staff. The
intersection of the line _A B_ with the arc _a_ we term the point _d_,
and from this point we lay off on said arc _a_ thirty degrees each side
of said intersection, and thus establish the points _c b_. From _A_,
through the point _c_, we draw the line _A c c'_. On the arc _a a_ and
two and a half degrees to the left of the point _c_ we establish the
point _f_, which space represents half of the thickness of the entrance
pallet. From _A_ we draw through the point _f_ the line _A f f'_.
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