The Dale C. Maley Family Web Site

65. The left-hand disk or wheel, C, is the driv­ing-wheel, 
upon which is fixed the tappet, A. The other disk or wheel, D, 
has a series of equi­distant studs projecting from its face. Every 
ro­tation of the tappet acting upon one of the studs in the wheel, D, 
causes the latter wheel to move the distance of one stud. In- order 
that this may not be exceeded, a lever-like stop is arranged on a 
fixed center. This stop operates in a notch cut in wheel, C,- and at
the instant tappet, A, strikes a stud, said notch faces the lever. As 
wheel, D, rotates, the end between studs is thrust out, and the 
other extremity enters the notch ; but immediately on the tappet 
leaving stud, the lever is again forced up in front of next stud, 
and is there held by periphery of C pressing on its other end.

 And here is the finished model: