[Illustration: Fig. 91]
We next desire to know where contact will take place between the
wheel-tooth _D_ and pallet _C_. To determine this we sweep, with our
dividers set so one leg rests at the escape-wheel center _A_ and the
other at the outer angle _t_ of the entrance pallet, the short arc _t' w_.
Where this arc intersects the line _w_ (which represents the impulse
face of the tooth) is where the outer angle _t_ of the entrance pallet
_C_ will touch the impulse face of the tooth. To prove this we draw the
radial line _A v_ through the point where the short arc _t t'_ passes
through the impulse face _w_ of the tooth _D_. Then we continue the line
_w_ to _n_, to represent the impulse face of the tooth, and then measure
the angle _A w n_ between the lines _w n_ and _v A_, and find it to be
approximately sixty-four degrees. We then, by a similar process, measure
the angle _A t s'_ and find it to be approximately sixty-six degrees.
When contact ensues between the tooth _D_ and pallet _C_ the tooth _D_
will attack the pallet at the point where the radial line _A v_ crosses
the tooth face.
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