To delineate the exit pallet, sweep the short arc u u (from g as a center) with the dividers set at five inches, and from the intersection of this arc with the line g j’ set off eight and one-half degrees and draw the line g l. At one degree below this line is drawn the line g m. The space on the arc f between these lines defines the locking face of the exit pallet. The point where the line g m intersects the arc f is named the point x. From the point x is erected the line x w, perpendicular to the line g m. From x as a center, and with the dividers set at five inches, the short arc y y is swept, and on this arc are laid off twelve degrees, and the line x z is drawn, which line defines the locking face of the exit pallet.
Next is taken ten and one-half degrees from the brass degree-scale, and from the point d on the arc n the space named is laid off, and thus is established the point v; and from g as a center is swept the arc v’ v’ through the point v. It will be evident on a little thought, that if the tooth A’ impelled the exit pallet to the position shown, the outer angle of the pallet must extend down to the point v, on the arc v’ v’; consequently, we define the impulse face of this pallet by drawing a line from point x to v. To define the outer face of the exit pallet, we draw the line v e parallel to the line x z.
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.
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’.