To make a nice corner clamp alllowing for various way of clamping it, I designed a router template to stick to a triangle cut on the table saw. I was a bit clumsy with my router so the picture aren't that nice but the clamp is really nice.

The pattern has a recess on one side, that is the side to stick to the wood piece (use double side tape). This recess is to give so leeway for the router bit to not hit the template while the router bearing will ride to the template.