Rack and Pinion 101
A rack and pinion is a device which converts rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack". As the pinion rotates it causes the rack to move relative to it, thereby translating the rotational motion of the pinion into linear motion of the rack.
As woodworkers we will be most familiar with their use in machinery, however they are widely used in other industries as well, automotive steering, pneumatic actuators, and railways.
Rack railways are particularily interesting as they are used to help a train up a steep incline but just importantly as a brake on decent.
Probably the best example to illustrate a rack and pinion is an arbor press.
A rack and pinion is utilized in the mechanisms that raise and lower the chuck and often the table as well.
In this case the rack is a cylinder with the teeth milled into it.
Here the rack is exposed.
When the handle "d" is rotated a pinion moves the carriage by engaging in the rack "K".
Colt "Peacemaker" 1875
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