# The rack and pinion drive

1, Rack

A flat or straight bar is called a rack when it has a series of equally spaced teeth.

Split straight rack and inclined rack

The rack can be regarded as a cylindrical gear whose number of teeth tends to infinity.

When the number of teeth of a cylindrical gear increases infinitely, its graduation circle, tooth top circle and tooth root circle are parallel lines, which are called graduation line, tooth top line and tooth root line respectively. The corresponding base circle increases infinitely.

Rack features:

Because the profile of the rack is a straight line, the normals of the points on the profile are parallel.

As the same side tooth profile of each point on the rack is parallel, the pitch is equal no matter on the graduation line, the tooth top line or other lines parallel to the graduation line.

Dimension calculation of each part of rack:

Top height of rack:

Root height of rack:

Rack height:

Rack tooth thickness:

Slot width of rack:

2. Rack and pinion drive

The kinematic pair consisting of straight rack (or helical rack) and straight (or helical) cylindrical gear is called rack pair.

The main purpose of the rack and pinion drive is to change the rotary motion of the gear into the reciprocating linear motion of the rack, or to change the linear reciprocating motion of the rack into the rotary motion of the gear.

Rack movement speed:

When the gear rotates for 1 revolution, the distance of rack movement:

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