Which gears are used to change rotary motion to reciprocating motion?

Rack gears are specifically designed to convert rotary motion into linear or reciprocating motion. The rack gear consists of a flat bar with teeth that mesh with the teeth of a pinion gear, which is circular. When the pinion rotates, it moves along the teeth of the rack, causing the rack to slide back and forth in a linear manner. This process effectively transforms the circular motion of the pinion into straight-line movement of the rack.

The other types of gears mentioned serve different purposes. Hypoid gears are primarily used in applications requiring non-parallel shafts and facilitate the transfer of motion and torque between these shafts. Helical gears are designed to handle parallel shafts with smoother operation and higher load capacity due to their angled teeth, which engage more gradually. Herringbone gears, which are essentially two helical gears mounted side by side in a V shape, are used for high-load applications and reduce axial thrust, but they do not directly convert rotary motion into reciprocating motion like rack gears do.