Movement No. 37 presents an inventive and visually striking mechanism for converting uniform rotary motion into variable rotary motion — using a bevel pinion whose full-face teeth mesh with a spirally arranged series of studs mounted on a conical wheel. The driver is a bevel-cut pinion or small gear with teeth cut across the entire width of its face, giving it maximum engagement capacity. Rather than meshing with conventional gear teeth on the driven side, this pinion engages with a series of cylindrical studs or pins arranged in a spiral pattern across the surface of a large conical wheel. As the pinion rotates at a constant speed, it successively contacts each stud in the spiral sequence. Because the studs are arranged in a spiral — meaning they are positioned at continuously varying radial distances from the axis of the conical wheel — the effective lever arm through which each stud pushes the conical wheel changes progressively with each engagement. When the pinion contacts studs near the large-diameter end of the cone, the effective radius is large and the conical wheel turns slowly with high torque; when it contacts studs near the small-diameter end, the effective radius is small and the wheel turns more quickly with less torque. This produces a smoothly varying, cyclically changing output speed from a perfectly uniform input — an elegant alternative to elliptical gears for applications requiring periodic speed variation. The spiral arrangement of the studs ensures a smooth and continuous sequence of engagements throughout each revolution, avoiding the abrupt speed changes that would result from a non-spiral stud layout.
37. Uniform into variable rotary motion. The bevel-wheel or pinion to the left has teeth cut through the whole width of its face. Its teeth work with a spirally arranged series of studs on a conical wheel.