We only show four
teeth complete, but the same methods as produced these will produce them
all. To briefly recapitulate the instructions for drawing the teeth for
the ratchet-tooth lever escapement: We draw the face of the teeth at an
angle of twenty-four degrees to a radial line; the back of the tooth at
an angle of thirty-six degrees to the same radial line; and make teeth
half a tooth-space deep or long.
[Illustration: Fig. 8]
We now come to the consideration of the pallets and how to delineate
them. To this we shall add a careful analysis of their action. Let us,
before proceeding further, "think a little" over some of the factors
involved. To aid in this thinking or reasoning on the matter, let us
draw the heavy arc _l_ extending from a little inside of the circle _n_
at _f_ to the circle _n_ at _e_. If now we imagine our escape wheel to
be pressed forward in the direction of the arrow _j_, the tooth _D_
would press on the arc _l_ and be held. If, however, we should revolve
the arc _l_ on the center _k_ in the direction of the arrow _i_, the
tooth _D_ would _escape_ from the edge of _l_ and the tooth _D''_ would
pass through an arc (reckoning from the center _p_) of twelve degrees,
and be arrested by the inside of the arc _l_ at _e_.
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