Elliptical spur-gears are a fascinating type of non-circular gear pair used to produce a continuously variable rotational speed from a constant-speed input. Unlike standard circular gears, each gear in this pair is elliptical in shape, with both gears sharing the same elliptical profile and rotating about their respective focal points. As the gears mesh and rotate, the effective gear ratio changes continuously throughout each revolution — alternately speeding up and slowing down the output shaft. The degree of speed variation is determined by the ratio between the major axis (longer diameter) and the minor axis (shorter diameter) of the ellipses: a greater difference between the two axes results in a more dramatic speed fluctuation. This mechanism was widely used in textile machinery, printing presses, and other applications requiring periodic variations in rotational speed.
33. Elliptical spur-gears. These are used where a rotary motion of varying speed is required, and the variation of speed is determined by the relation between the lengths of the major and minor axes of the ellipses.