Lay off one and a half
degrees on the arc _l_ below its intersection with the line _f'_, and
from _B_ as a center draw the line _B_ _i_ through said intersection.
From _B_ as a center, through the intersection of the radial line _A b_
and the arc _a_, sweep the arc _g_.
The space between the lines _B f'_ and _B i_ on the arc _g_ defines the
extent of the locking face of the entrance pallet _C_. The intersection
of the line _B f'_ with the arc _g_ we denominate the point _o_, and
from this point as a center sweep the short arc _p_ with a 5" radius;
and on this arc, from its intersection with the radial line _A b_, lay
off twelve degrees, and through the point so established, from _o_ as a
center, draw the radial line _o m_, said line defining the locking face
of the entrance pallet _C_.
[Illustration: Fig. 22]
It will be seen that this gives a positive "draw" of twelve degrees to
the entrance pallet; that is, counting to the line _B f'_. In this
escapement as delineated there is perfect tangential locking.
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