Trying to square up a large cabinet or box during glue-up has always been difficult for me. Even if I own a clamp that’s long enough to handle the diagonal span, it gets in the way of the glue-up clamps. This simple, low-profile clamp bar solves the problem.

Start by dry-fitting the cabinet with all the required clamps in place, and then use the average of the two diagonal measurements to size your shopmade squaring jig. The jig is a long strip of wood with a fixed stop on one end and an adjustable stop placed along its length, at that exact dimension that represents the two equal diagonals. I made my strip 8 ft. long, so it can be used on carcases in a wide range of sizes.

Now remove the rear clamps and place your squaring jig across the long diagonal dimension—all box glue-ups tend to skew one way or the other— using it to pull the case back to square. Leave it there and mark it where the shelves cross the bar.

Before the real glue-up, drill a few clearance holes in the bar for screws to pass into the back of a couple of the shelves and/or the case itself. This will keep the jig in place without getting in the way of other clamps. Now you can apply glue to the joints, start clamping up the case, place your clamp bar across the long diagonal dimension as before, and drive a few short screws to hold it there while you finish clamping and wait for the glue to dry. You’ll get a perfectly square cabinet every time, without the stress.

—PETER GRAF, San Francisco, Calif.

Illustrations by Dan Thornton
From Fine Woodworking issue #285