Shop-Made Corner Clamp

Cut the plywood base with slots that let the fixed jaw sections flex inward under pressure.

Glue the angled hardwood jaw blocks to the base, making sure the counterbored bolt slot on each block faces down against the base, not up.

Drill through the base and jaw blocks for the carriage bolts.

Assemble the clamp with the carriage bolts, washers, and wing nuts.

Clamp a mitered corner by tightening the wing nuts, which draws the flexing jaw sections together across the miter.