Shop-built Large Framing Clamp for Stretcher Bars and Frames
What you wind-up with is an easy clamp that makes good solid and “square” frames and stretcher bars up to about 48 X 48″
Make corner clamps slightly thicker than what you will be clamping. Drill (2) 1/4″ holes; one for carriage bolt, the other for corner relief.
Corner clamp re-sawed to a little thicker than frame or stretcher bar you’ll be using. I made two thicknesses; one for stretcher bars and one for gallery frames.
The clamp is made with (4) 36″ steel straps with holes, a turnbuckle for tightening, and bolts with wing nuts to hold the clamps (I used 1/4-20 carriage bolts). I got everything here from Home Depot.