a bar or rod with gear teeth that engage a pinion or, less frequently, a worm gear, together with which it forms a drive for transforming rotary motion into transla-tory motion or vice versa (rack-and-gear drive). Gear racks are made with spur, helical, herringbone, or circular teeth. In the most frequently used gear drives with involute gearing, the shape of the teeth on the gear rack is rectilinear.
Gear racks are used in gear drives of metal-cutting machine tools and other machines. They are attached by screws and pins to the slide bars, tables, or stands of machine tools and machines. For example, in the drive of the main cutting motion in a planing machine, the gear rack is attached to the table that holds the part being worked; in the lengthwise feed mechanism of a lathe there is a stationary gear rack on the stand, and a pinion is mounted on the movable support with the cutting tool. Sometimes gear racks travel along guides, as in mechanisms for changing speeds on machine tools.