Gear rack knowledge

Writer： admin Time：2019-09-18 03:19:51 Browse：75℃

A rack can be seen as a part of a gear with an infinite number of teeth, where each circle of the gear becomes a straight line, and the involute as the tooth profile also becomes a straight line. Compared to a gear, a rack has the following characteristics: because the tooth profile of the rack is a straight line, the normals of each point on the tooth profile are parallel, and during transmission, the rack moves in a translational motion. The speed and direction of each point on the tooth profile are consistent, so the pressure angles at each point are equal, Its size is equal to the inclination angle of the tooth profile, which is called the tooth profile angle. As the tooth profiles on the same side of each tooth on the rack are parallel, the tooth pitch is equal regardless of whether it is on the indexing line, tooth crest line, or other parallel lines. The rack is also divided into straight and helical gears, which are paired with straight and helical cylindrical gears, respectively;

The tooth profile of the rack is a straight line rather than an involute (which is a plane for the tooth surface), equivalent to a cylindrical gear with an infinite radius of the indexing circle

The main characteristics of the rack and pinion

(1) Due to the straight tooth profile of the rack, each point on the tooth profile has the same pressure angle and is equal to the inclination angle of the tooth profile. This angle is called the tooth profile angle, with a standard value of 20 °.

(2) Any straight line parallel to the tooth crest has the same tooth pitch and modulus.

(3) The straight line parallel to the tooth crest line and with a tooth thickness equal to the width of the tooth groove is called the indexing line (centerline), which is the reference line for calculating the size of the gear rack. The main parameters of a rack include slot width, tooth top height, tooth root height, tooth height, tooth thickness, tooth root radius, etc