I’d like to know what the below movement mechanisms are called so I can better research them and incorporate them into my own designs.

They are both quite similar, they are from rotary electrical isolator switches found on vehicles and industrial switch gear.

Type 1: Type 1 A pin on the internal shaft or key follows the path of the cut out therefore forcing it in.

Type 2: Type 2 Plunger Type 2 Rotary Shaft A linearly fixed T shaped shaft rotates and the internal plunger has a curved ramp. The plunger is sprung against the shaft. As the shaft rotates the T shaped runs up the ramp forcing the plunger down.

What are the two types of mechanism called?

I’ve tried searching for various terms but can only find basic cams etc. If there isn’t a specific terminology maybe someone could provide some search terms or some references

  • $\begingroup$ Good question. Good place to ask it. I sometimes think my life is spent trying to find the right search terms. $\endgroup$
    – stretch
    Commented Jun 7, 2020 at 0:52

3 Answers 3


This is a type of barrel cam, but also resembles a bayonet mount. Barrel cams consist of a cylindrical surface with a slot or raised ridge that wraps around the curved surface. As the cylinder rotates, the cam follower (in your case, the arms on the T-shaft) rides through the grooves, moving up and down along the length of the cylinder.

Barrel cams are commonly found in camera zoom lenses, as in the photo below. Notice how the three cam followers also ride in a slot, which is what enforces the linear motion and prevents the entirety of the lens from rotating.

Barrel cams inside of a parfocal zoom camera lens

As with many physical mechanisms, there are some barrel cams that work in reverse, where driving the cam follower in an a) linear, or b) rotary motion induces the cam to move in an a) rotary or b) linear motion. One example of type b is the reverse bayonet connector, where rotating the collar (which contains two or more followers) pulls the two connectors together.

Reverse bayonet connectors

Compare that to a bayonet connector, (such as BNC connectors), where the collar contains the cam slot:

BNC connectors are an example of bayonet connectors

  • $\begingroup$ Although the firs one is clearly a bartrel cam the second type may not be. ATleast doe snot appear to me as it is. $\endgroup$
    – joojaa
    Commented May 31, 2020 at 6:48
  • $\begingroup$ @joojaa It can be difficult to understand the movement of a (reverse) bayonet connector through a single stationary photo. They may not have a particularly interesting profile for a barrel cam, but I do think a barrel cam best describes the mechanism. $\endgroup$
    – Cowdozer
    Commented Jun 12, 2020 at 20:59

The mechanism that forces another mechanism to follow another shape is called a "cam mechanism". The movement generator is called a cam and the other part is called a follower. There are lots and lots of variations of this mechanism. As a general moniker in this case it's not super useful for searching since the possible space of what you could call a cam is incredibly large.

Although if you want to design a cam then you can find the general guidelines easy enough. Most literature concentrate on continuously moving cams.


Try an image search for "quarter-turn fasteners".

enter image description here


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