Rack and Pinion Gears
Rack and pinion Gear are another variety of Spur gears. Actually a Rack is
defined as a straight bar that has teeth which are cut straight and across.
Basically, The Rack is considered as a spur gear that is unrolled and laid
flat. Pinion is the normal gear. A rack and pinion is really a very special
example of spur gearing. The rack-and-pinion has been found to be specially
useful in conversion of rotary motion into linear and vice versa. Rotating a
pinion produces a linear motion of the rack. Alternately moving a rack
causes rotation in the pinion.
Working of a Rack and Pinion Gear
To describe the working of a rack and pinion gears system is not very easy.
In fact the rack and pinion gear system looks a bit unusual. However you
will be amazed to know that it is composed of two gears. The pinion is what
you call a normal round gear while rack's shape is straight or flat. It is
the teeth of the rack which meshes with pinion gear's teeth.
Actually it is the pinion that rotates and is able to move the rack in a
straight line. In other words, rotary motion is converted into to linear
motion'. The perfect example to describe a Rack and pinion gear system is
the trains moving on the tracks, on steep inclines. The wheels of a train
are made up of steel and there is no way to grip the steel tracks. What
happens is that the heavy weight of the train is sufficient for allowing the
train to travel on the tracks. But consider a situation where a train has to
travel a steep incline or hill. It is quite likely that would slip
backwards.
Here comes the magnificent technology of rack and pinion system that
exactly provides solution to the trains to overcome this problem. As the
image shows a big gear wheel is added at the center of the train. While in
the track a Rack an extra track with teeth, is added. As the train moves
over an inclined hill or slope, the gear is lowered instantly to the track
where it meshes perfectly with the Rack. As a result there is no chance of
the Train slipping backwards and is carried along smoothly over the steep
slope.
Types of Rack and Pinion Gears
Basically there are three variations of Rack and Pinion Gears. They are
helical teeth modular pitch, straight teeth metric pitch and straight teeth
modular pitch. Rack and pinion gear variations are also made available in
various qualities. For example 9/10 milled teeth or hardened and milled
quality. 7/8 precision cut or precision cut and hardened quality and lastly
the quality of 5/6 teeth hardened and ground.
Application of Rack and Pinion Gears 
- Machine tools
- Heavy Machinery
- Scales for displaying weight
- The rack-and-pinion is used extensively. The following photograph
illustrates the rack and pinion gears used widely in a household scale.
Selecting the Right Rack and Pinion Gear System
For optimal efficiency it is very important to select the Rack and pinion
Gear System that comes with optimal features. For this keeping in mind the
following features would be really useful:
- Tooth Profile: If it is offers full depth
- Pressure Angle
- Material Used
- Heat treatment: This includes tempering, stress relief
annealing, induction hardening of tooth flanks
- Hardness: Hardness at the center, teeth
- Surface treatment
- Gear and Rack Precision
