Spiral Gadget, Involutes, and Cam Clamps

[jenordyke]

I'm trying to design some cam clamps for my inserts spoilboard using the spiral gadget. I've not had much luck as yet coming up with a shape that keeps the point of contact directly in line with the sideways clamping pressure...

I understand that an involute spiral should give me the correct geometry, but placing the central hub at the base circle's center point isn't working. For example, if I create a 5" wide involute spiral with center point at 0,0 and also place my hub at 0,0 the resulting cam doesn't maintain the point of contact in line with the direction of thrust.

Can anyone provide some pointers, please?

Thanks in advance

JN

[rink]

Good evening.
I think there are several plans available on the web. I studied the official cam geometry on several engineering sites. It was over my head. So I designed my own. I don’t know if they’re “involute”, but they worked well. Here’s how I approached it.

I first decided how much total deflection I wanted for one revolution. Then I drew line segments radiating out from a center point. Actually, I drew one line, then used the circular array function to copy it around every ten degrees. So then I had a point with 36 lines going outward from it all around.

Next I made each line slightly longer than the previous line. How much longer? Divide desired total deflection by 36. Add that much more to each line as you go around. By the time you get around the circle you will have achieved the desired total deflection.

Next, I connected all the line end points with a smooth curve. Draw in whatever handle/lever style you like. Now you have a cam.

I also milled a 0.25” hole at the original center point, glued in a short dowel. The dowel fits in holes in the spoil board.

I also have some cams with a hole and no dowel. I secure those with a nylon hex bolt after they’re good and wedged against the workpiece. Sometimes have to use spacers.

Of course, just tailor these details to your own situation.

Thx, rink.

[jenordyke]

Thank you Rink, that is an ingenious solution!