I have a couple and they are surprisingly effective while looking simple to copy.
Basically the top jaw is held by to roll pins through a metal bar
the lower jaw has a couple of roll opins placed through the wood of the jaw with enough clearance to allow the jaw to slide up and down.
It also has a slit approx 3/8" down parallel to the clamping action. At 90 degrees to this slit you insert your cam lever on an eccentric so that when its turned it raises the slit part of the jaw to grip whatever
Hope this is of help.
BTW the jaws are covered with a thin cork pad.
As for a pattern I suggest buying one unless you design your own from the description I've given
Note: the first two pictures, top to bottom, show the sample woods I bought to match: mahogany, walnut, oak, the bottom is the side of the table. The remaining 3 pictures are of the wood in question...