Luthier cam clamp fail

[Daniel Rode]

So I attempted to make a set of luthier cam clamps. Despite a few stumbles, I was able to get 4 clamps that all look right. However, I'm having one major failure. The cam doesn't stay put. It tightens up nicely and the moving head does not slip at all but as soon as I let go of the cam lever, it slips back releasing the pressure :(

I'm sure I have made some mistake with the shape of the cam (lobe?). I took the shape directly from the drawing on http://woodshopmike.com/diy-woodworking-cam-clamps-free-plans/. I tested a few variations in the lobe shape with no improvement but it was pretty haphazard.

Anyone know where I can get some information on how to properly make the cam so it will stick in place?

[Steve Pippins]

Dan, I have not made these clamps and suggest posting the question to Wood Shop Mike.

[george wilson]

Don't make the hole in the cam too far off center. That is probably what you did wrong. Doing that doesn't give the cam enough "grip" to stay put. The jaw of these sliding clamps doesn't have to move very far to tighten after being slid up snugly to the part you're clamping.Hope this makes sense.

[Daniel Rode]

Thanks! I think I know what you mean. I'll give it a try this weekend.

[george wilson]

It's been so many years I can't recall how far off center I drilled the working surfaces of the cams. The cams I made are just perfectly circular in shape,though. They have always worked perfectly on all 48 clamps. I might have had to experiment on the first few cams to get them to work. Can't recall. At that time I had never seen a cam clamp in person. I think I saw them in a book somewhere.

By the way,I did glue thin cork on the clamping faces to prevent marring on soft spruce guitar tops. I think I used a thin cork roll made for putting on bulletin boards.

[Daniel Rode]

I have a roll of cork for just that purpose :) While I do not make instruments, this style will be useful for many things. I do a lot of things with soft pine, so light duty and non-marring jaws are handy. The long reach is also nice. If I can get the first 4 to work, I'll make some more :)

[Jim Tremain]

If the cam is sanded too smooth it can slip. Rough up the end of the cam where it touches the jaw. I used 80 grit.

Jim

[Chris Fournier]

My cam pins are offset 0.125" and they work every time. Do not refine the cam face with too much sanding, if you have then pop them out and drag them over 50 to 80 grit and retry. You need friction so rough surfaces should help.