This animation demonstrates Movement No. 74 from “507 Mechanical Movements” — an intermittent alternating rotation mechanism driven by a mutilated bevel gear. At the heart of this mechanism is the mutilated bevel gear C — a bevel gear from which teeth have been removed over a portion of its circumference, leaving alternating toothed and toothless segments. As gear C rotates continuously on its drive shaft, its toothed segment sequentially engages bevel-gear A and bevel-gear B, which are mounted on perpendicular axes on opposite sides of gear C. When the toothed portion of C meshes with gear A, gear A is driven in one rotational direction. As rotation continues and the toothless segment of C reaches gear A, the engagement is broken and gear A comes to a complete stop — it dwells motionless while the blank section passes. As C continues to rotate, the toothed segment then engages gear B on the opposite side, driving it in the reverse rotational direction. When the toothless segment reaches gear B, it too comes to rest. This cycle repeats with every full revolution of the driving gear C, producing a perfectly uniform intermittent rotation that alternates between gears A and B in opposite directions. The dwell periods are determined by the angular extent of the toothless segments on gear C, which can be designed to provide longer or shorter pauses as required by the application. This type of mechanism was historically used in textile machinery, indexing tables, and automatic feed systems where two alternating outputs needed to be driven from a single power source with precise timing and no additional control components.
74. A uniform intermittent rotary motion in opposite directions is given to the bevel-gears, A and B, by means of the mutilated bevel-gear, C.