cam
A projection on a rotating part in machinery, designed to make sliding contact with another part while rotating, to impart reciprocal or variable motion to it.
A cam is a master of translation. It takes simple, continuous rotational motion and converts it into complex, reciprocating (back-and-forth) or irregular linear motion. The shape of the cam (its profile) determines the exact movement of the follower.
Word relationships
- eccentric wheel: An eccentric wheel is a specific type of circular cam mounted off-center, whereas a cam can be any irregular shape (like egg-shaped or pear-shaped).
- concentric wheel: A concentric wheel rotates perfectly about its center, producing no reciprocating motion in contacting parts.
Commonly confused with
- crank: A crank converts reciprocating motion into rotary motion (or vice versa) using a connecting rod, while a cam typically uses direct sliding contact with a follower.
Word family
- cammed (adjective): Equipped with or shaped like a cam.
Collocations
- camshaft
- cam lobe
- cam follower
- overhead cam
Example sentences
- "The egg-shaped cam on the rotating shaft pushes the engine valve open, while a spring forces it closed." An automotive engineering manual
- "Inside the mechanical doll, a series of brass cams controlled the lifelike writing motion of its hand." A description of an antique automaton
Memory hook
Think of a 'cam' as a 'camera' shutter mechanism. Inside older cameras, a tiny rotating 'cam' was used to open and close the shutter at lightning speed. A cam converts round-and-round into up-and-down.
When not to use
Do not use cam to describe a perfectly circular wheel centered on its shaft, as that does not produce reciprocating motion; a cam must be eccentric or non-circular.
Fun facts
- The camshaft in a modern car engine must be incredibly durable, as it rotates thousands of times per minute, constantly slamming valves open against stiff springs.
- Early automated musical instruments, like music boxes, use tiny pins on a cylinder that act as miniature cams to pluck specific metal tines.
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