Home Chapter 15 Cams and linkages

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Cams and linkages

The cam below would trigger a movement of three valleys and peaks per rotation. As the roller surface goes along the edge of this three-lobed cam from peak to valley, there is a quick change of direction in the follower arm, which may also create a noise.


 Three lobed cam


The cam below would move the follower up and down five times per rotation.


5 lobed cam


Snail or drop cam


A snail (or drop) cam (above) has a slow rise and then a sudden drop. This is a one-event-per-turn cam with a slow buildup to the peak and a rapidly decreasing edge. This cam has one direction only, which is counter clockwise. You can think of this mechanism as a sound generating device with acoustics which are based on the physics of the materials you select.

In the image below the turning snail cam moves a rod with a shoulder bolt at the tip.


Snail Cam and a vertical follower with a roller shoulder bolt at the end that makes contact with the spinning cam


A shoulder bolt creates a rolling surface, so the follower arm will be able to roll against the cam with ease.


Shoulder bolt used to create rolling surface on rods or other objects coming into contact with the spinning cam.



Linkages are connections that can be levers (but aren’t always) and function to transfer motion from one component to another. The distance that the arm travels is determined by the size of the crank.1

The crank slider (below) is a type of linkage composed of three main components: the crank is the rotating circular disc, the slider slides inside the slot or tube, and the pushrod connects the slider to the crank.

The pushrod traces a curved line as a mirror of the circulating crank. By changing the length of the slider or the diameter of the crank you can change the shape of the circular line being traced.


Crank slider