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We are working to design a lock mechanism and need to hold a square plunger out of a hole for extended periods of time (potentially years). The square plunger is under pressure from springs to return to the hole. Initial testing with a friction pawl has been positive, but we wonder about maintaining grip over a longer period of time. The pawl is lightly spring actuated to maintain forced contact with the plunger surface at all times. Does anyone have experience with friction pawls and in particular why these are not as commonly used as ratcheting pawls? They seem to grip quickly and if angled correctly seem to hold on. Are there pitfalls we are not aware of over the longer term? Thank you for any thoughts.

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Doesn't a boating cam cleat work in that fashion?

enter image description here

Image source: Schaefer Marine.

The harder the rope is pulled (to the left) the tighter the cleat bites it. If you can do the same with your friction pawl it too will lock onto the plunger even with wear over time.

The other device that comes to mind is the Sprague or one-way clutch.

enter image description here

Image source: SUMA Clutch and Bearing.

On this one the roller bearings will bite if the inner ring turns clockwise and will freewheel if the inner ring turns anti-clockwise. (Note the increased clearance on the anti-clockwise side of each roller bearing.)

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  • $\begingroup$ Thank you for the response. That is essentially how it works, though we are trying to keep a hard, flat metal plunger in place with a metal friction pawl. Those examples all work, but they also have teeth, whereas a friction pawl would not. I am mainly seeing these sort of solutions with teeth on them, and wonder if there is some sort of pitfall in a friction only (non-toothed) pawl that I need to worry about. Teeth would be hard for us. $\endgroup$ – HWandLocks Sep 24 '20 at 23:17
  • $\begingroup$ The Sprague clutch doesn't have teeth. The rollers never get as far as the hard stop before they bite. You, effectively, have one section of that clutch. $\endgroup$ – Transistor Sep 24 '20 at 23:24

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