Recently, I was gluing edging around a large table top, and my aluminum bar clamps just weren’t long enough to reach across the table. Rather than buying extra-long clamps that I’ll only occasionally use, I decided to make extensions for my clamps, like you see here.
What I did was cut a long strip of hardwood (I used hard maple) to match the size and shape of the bar of the clamp. This is important, because the rear clamp jaw has to travel along the extension. Next, I took the extension to my table saw and cut a groove down its length. This groove holds an aluminum strip that has been notched evenly along its length. These notches allow the adjustable jaw to lock in place. The notches in the aluminum strip can be made easily on your table saw by switching your standard blade to a non-ferrous saw blade.
Next, as the drawings show, a ”tenon” is cut on one end of each extension to fit inside the bar clamp. To hold the extension in place, holes are drilled in the end of the clamp through the tenon for bolts and locknuts. Now, whenever I need more clamping capacity, it takes just a few seconds to add these extensions to my bar clamps.