The racks are also divided into straight racks and helical racks, which are paired with spur gears and helical gears respectively;

The tooth profile of the rack is a straight line instead of an involute (for the tooth surface, it is a flat surface), which is equivalent to an infinite cylindrical gear with a pitch circle radius

Main features of rack

(1) Since the rack tooth profile is a straight line, 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 and the standard value is 20°.

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

(3) The straight line parallel to the tooth top line and the tooth thickness equal to the tooth slot width is called the index line (center line), which is the reference line for calculating the rack size.

The main parameters of the rack

Tooth width, tooth tip height, tooth root height, tooth height, tooth thickness, tooth root radius, etc.