A gear of infinite radius: teeth cut along a flat bar, with straight-sided flanks in the involute system. Meshed with a pinion, it converts rotary motion to linear or the reverse, as in steering gear, gantry drives and machine tool travel. The basic rack is also the reference profile that defines a whole gear tooth system, and generating cutters such as hobs are based on it.
Gantry rack joints need to be set with a pitch gauge or the pinion will bump every time it crosses one.
Also heard as
- gear rack
- toothed rack
Related terms
Pinion
The smaller of two meshing gears, usually the driver in a speed reducer.
Involute
The curve traced by the end of a taut string unwound from a circle, the shape of almost every gear tooth flank.
Hob
A gear cutter shaped like a worm with gashes across its threads, used on a hobbing machine.
Pressure angle
The angle between the line of tooth contact force and the tangent to the pitch circle, usually 20 degrees.