Here is a couple of homemade cam clamps
I had an ugly, really bad quality big pump clamp from the far east, you know the kind of tool you want to through away every time you use it.
So I ended up hack sawing the bar (the only thing good in that clamp) in two pieces, and making these two rather large cam clamps, with firewood.
Firewood (ash or similar) is often not very dry, has often lots of cracks, but has the quality to be perfectly quater sawn (at least you arrange to use it that way).
So, not a piece of art, but pretty strong and quite efficient for reaching the middle of a plate for instance.
The design is pretty classic, but I did two things differently : there is no head, no foot, both pieces can slide along the bar and you can use it cam on top or cam under.
The axis for the cam is a 8mm round aluminium. It's always more precise and strong to use a large axis than simply a pin.