Gluing a miter joint is a challenge . There just isn't an easy way to clamp it. The store-bought clamps I've tried in the past didn't always pull the joint together. So I came up with a shop-built corner clamp that uses wedges to push (or press) the mitered pieces in place.



Looking at the photo at the right and drawing below, you can see that this corner clamp uses a piece of plywood as a base. Then a square block and two cleats are glued and screwed on top.



What's important here is that the inside corner of the square block is exactly 90°. Then align the inside edge of each cleat parallel with the inside edges of the block.



A pair of wedges sized to fit between the workpiece and the cleat does all the work. They apply pressure in two directions at the same time. When the inside wedge (the one contacting the mitered piece) is tapped forward, it pushes the joint tighter together and firmly holds the pieces in place while the glue dries.