Definition of Pinion Gear
Generally, when meshing pair of gears, the smaller gear is called a pinion gear. Also, it refers to the cylindrical gear that meshes with a rack in a rack-and-pinion mechanism which transforms rotational motion to linear motion.
Regarding undercut
Undercut occurs during gear cutting when, for example, the number of teeth on the pinion is less than 17 (with 20-degree pressure angle), the root of the gear teeth are gouged. Generally, in these cases, the undercut can be avoided by profile shifting the gear in the positive direction.
Regarding rack and pinion
The pinion side of the rack and pinion combination has a higher frequency of the gear mesh. Therefore, in selecting the material and heat treating method, the pinion should have a higher hardness than the rack to lessen the tendency to wear faster.
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小齿轮
Rack and Pinion