Movement No. 94 demonstrates an adjustable variable crank mechanism using two circular plates mounted on the same center. One plate has a spiral groove cut into its face, while the other has a series of radial slots extending outward from the center. A bolt passes through both the spiral groove and one of the radial slots simultaneously. When one plate is rotated relative to the other, the intersection point of the spiral groove and the radial slot shifts, forcing the bolt to move either inward toward the center or outward away from it. By adjusting the bolt’s radial distance from the center, the effective crank radius is changed, allowing the stroke length of the connected reciprocating mechanism to be continuously varied without disassembly. This elegant design enables on-the-fly stroke adjustment in machinery such as pumps and presses.
94. Variable crank, two circular plates revolving on the same center. In one a spiral groove is cut; in the other a series of slots radiating from the center. On turning one of these plates around its center, the bolt shown near the bottom of the figure, and which passes through the spiral groove and radial slots, is caused to move toward or from the center of the plates.