The idea for this clamp, suitable for light-duty assemblages, like guitars, comes from Robert Wearing’s excellent book, “Woodwork Aids and Devices”.
I have had this book for many years. I have completed many of the projects in it, but not more than half ! (The annotations show the ones I HAVE done).
Here is a view of the cam, which is rosewood, showing how pressure is applied. I made the stocks in maple, which I retrieved from a colleague who had cut up some lengths for firewood, but it splits very readily, so a better alternative would be elm. The bars are mahogany, I think. At any rate, they needed handplaning parallel for fit. I made about two dozen, all by hand.