Rack gears come in straight and helical varieties, respectively pairing with straight and helical cylindrical gears.

The teeth of the rack have a straight profile rather than a involute (for the tooth surface, it's a flat plane), which is equivalent to a cylindrical gear with an infinite radius of the pitch circle.

The main features of the rack

(1) Due to the linear tooth profile, each point on the tooth profile has the same pressure angle, which is equal to the inclination angle of the tooth profile. This angle is referred to as the tooth form angle, with a standard value of 20°.

(2) Any straight line parallel to the top land has the same pitch and modulus.

(3) The line parallel to the top of the gear and equal in thickness to the width of the gear slot is known as the pitch line (midline), which serves as the reference line for calculating the dimensions of the gear rack.

Main Parameters of the Rack

Gums wide, tooth top high, root height, tooth height, tooth thickness, root radius, etc.