Slightly off from what you need, but I made these cam clamps on Sunday just to try out the idea. They are based on a design from Marius Hornberger on YouTube but I'll design my own if I decide to mass-produce them. To make sure they dont slip I fix them to the base with an M8 bolt, just loose enough to turn then lock them down once in place. Worked OK holding the test piece for surface skimming with a 22mm tool and being quick and easy to make from scraps of wood they can be treated as sacrificial.
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