There are no set rules for drawing the general form of the pallet arms,
only to be governed by and conforming to about what we would deem
appropriate, and to accord with a sense of proportion and mechanical
elegance. Ratchet-tooth pallets are usually made in what is termed
"close pallets"; that is, the pallet jewel is set in a slot sawed in the
steel pallet arm, which is undoubtedly the strongest and most
serviceable form of pallet made. We shall next consider the
ratchet-tooth lever escapement with circular pallets and ten degrees of
pallet action.


DELINEATING CIRCULAR PALLETS.

To delineate "circular pallets" for a ratchet-tooth lever escapement, we
proceed very much as in the former drawing, by locating the point _A_,
which represents the center of the escape wheel, at some convenient
point, and with the dividers set at five inches, sweep the arc _m_, to
represent the periphery of the escape wheel, and then draw the vertical
line _A B'_, Fig. 19. We (as before) lay off thirty degrees on the arc
_m_ each side of the intersection of said arc with the line _A B'_, and
thus establish on the arc _m_ the points _a b_, and from _A_ as a center
draw through the points so established the radial lines _A a'_ and _A b'_.

We erect from the point _a_ a perpendicular to the line _A a_, and, as
previously explained, establish the pallet center at _B_. Inasmuch as we
are to employ circular pallets, we lay off to the left on the arc _m_,
from the point _a_, five degrees, said five degrees being half of the
angular motion of the escape wheel utilized in the present drawing, and
thus establish the point _c_, and from _A_ as a center draw through this