themselves. In the escapement shown at Fig. 20 we have
selected, as a very excellent example of this form of tooth, circular
pallets of ten degrees fork action and ten and a half degrees of
escape-wheel action.

It will be noticed that the pallets here are comparatively thin to those
in general use; this condition is accomplished by deriving the principal
part of the impulse from driving planes placed on the teeth. As relates
to the escape-wheel action of the ten and one-half degrees, which gives
impulse to the escapement, five and one-half degrees are utilized by the
driving planes on the teeth and five by the impulse face of the pallet.
Of the ten degrees of fork action, four and a half degrees relate to the
impulse face of the teeth, one and a half degrees to lock, and four
degrees to the driving plane of the pallets.

In delineating such a club-tooth escapement, we commence, as in former
examples, by first assuming the center of the escape wheel at _A_, and
with the dividers set at five inches sweeping the arc _a a_. Through _A_
we draw the vertical line _A B'_. On the arc _a a_, and each side of its
intersection with the line _A B'_, we lay off thirty degrees, as in
former drawings, and through the points so established on the arc _a a_
we draw the radial lines _A b_ and _A c_. From the intersection of the
radial line _A b_ with the arc _a_ we draw the line _h h_ at right
angles to _A b_. Where the line _h_ intersects the radial lines _A B'_
is located the center of the pallet staff, as shown at _B_. Inasmuch as
we decided to let the pallet utilize five degrees of escape-wheel
action, we take a space of two and a half degrees in the dividers, and
on the arc _a a_ lay off the said two and a half degrees to the left of
this intersection, and through the point so established draw the radial
line _A g_. From _B_ as a center we sweep the arc _d d_ so it passes
through the point of intersection of the arc _a_ with the line _A g_.

[Illustration: Fig. 20]

We again lay off two and a half degrees from the intersection of the
line _A b_ with the arc _a_, but this time to the right of said
intersection, and through the point so established, and from _B_ as a
center, we sweep the arc _e_. From the intersection of the radial line
_A g_ with the arc _a_ we lay off to the left five and a half degrees on
said arc, and through the point so established draw the radial line _A f_.
With the dividers set at five inches we sweep the