Gear rack is a special gear whose teeth are distributed about the strip.
1. The basic concept:
The rack can be split into a spur gear rack and a helical gear rack, which are paired with a spur gear and a helical gear, respectively; the tooth profile of the rack is normally a straight line rather than an involute (planar for the tooth surface) , equivalent to the indexing circle radius is certainly infinite cylindrical gear.
2. The main features:
(1) Since the tooth profile of the rack is direct, each point about the tooth profile gets the same pressure angle and is add up to the inclination position of the tooth profile. This angle is named the tooth angle and the typical value is 20°.
(2) The same pitch and modulus are provided on the straight lines parallel to the top line.
(3) A line parallel to the top type of the tooth and having a tooth thickness add up to the width of the tooth groove is called a dividing line (middle line), which is a reference range for calculating how big is the rack.
3. The main parameters:
Groove width, high tooth tip, high root height, tooth elevation, tooth thickness, root radius, etc.
4. The choice of parameters:
(1) Whether the gear is beating, the entire tooth depth, the common normal series, the tooth direction is qualified, the tooth pitch is poor, and the circumferential section error is out of tolerance.
(2) Whether the installation distance following the gears and racks are installed is suitable.
(3) The rack and gear meshing clearance ought to be 0.25* modulus.
(4) Whether the full tooth depth, runout, and common 
normal type of the rack are skilled.
5. Processing methods:
Gear rack and pinion machining technique:
(1) hobbing
(2) gear shaping
(3) shaving
(4) grinding teeth
(5) molars
