In escapements not set
tangential, the detent is pushed forward in the direction of the arrow
_x_ about half a tooth space. Britten, in his "Hand-Book," gives a
drawing of such an escapement. We claim the chief advantage of
tangential locking to lie in the action of the escape-wheel teeth, both
on the impulse stone and also on the locking stone of the detent.
Saunier, in his "Modern Horology," gives the inclination of the front
fan of the escape-wheel teeth as being at an angle of twenty-seven
degrees to a radial line. Britten says twenty degrees, and also employs
a non-tangential locking.
Our drawing is on an angle of twenty-eight degrees, which is as low as
is safe, as we shall proceed to demonstrate. For establishing the angle
of an escape-wheel tooth we draw the line _C d_, from the point of the
escape-wheel tooth resting on the locking stone shown at _C_ at an angle
of twenty-eight degrees to radial line _C k_. We have already discussed
how to locate and plant the center of the balance staff.
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