Movement No. 70 presents an elegant refinement of the tappet-and-stud intermittent motion principle — introducing a rim on the driving wheel that serves double duty as both the locking device and the guide for the stud wheel, creating a fully integrated and self-contained intermittent indexing mechanism. The driving wheel C carries two key features: a tappet B projecting from its face, and a circular rim extending around its circumference, shown in dotted outline. The driven wheel A carries a series of studs projecting from its face at equal angular intervals. The rim of wheel C plays the central structural role: its exterior surface acts as a bearing and stop — when the tappet B is not in contact with any stud, the smooth exterior of the rim presses against and holds the studs of wheel A, preventing any rotation. The studs of wheel A are thus pinched and held stationary between the solid rim exterior and their circular path — positively locked in position. A single opening is cut through the rim. This opening is precisely sized to allow exactly one stud to enter and another to exit as wheel C rotates. The tappet B is positioned directly opposite the center of this opening. As wheel C rotates and the opening aligns with the studs of wheel A, two things happen simultaneously: one stud exits through the opening as the previous step’s lock is released, and tappet B — positioned at the opening’s center — engages the entering stud and pushes wheel A forward by one stud-space. As the opening rotates away, the rim’s solid exterior immediately re-engages the studs of A, locking it again. The result is a precisely controlled one-step advance with each revolution of driving wheel C, with smooth, robust locking provided entirely by the rim geometry.
70. The driving-wheel, C, has a rim, shown in dotted outline, the exterior of which serves as a bearing and stop for the studs on the other wheel, A, when the tappet, B, is out of contact with the studs. An opening in this rim serves to allow one stud to pass in and another to pass out. The tappet is opposite the middle of this opening.