I made this quick-release sanding block from four pieces of 1/2-in. -thick birch plywood. The top three pieces are glued together. Wrap a quarter sheet of sandpaper around the bottom piece and slip on the top assembly. The toggle clamp (www.rockler.com #20787, $9) locks the top assembly to the bottom.
All four pieces measure 2-1/2-in. wide by 7-in. long. The toggle clamp mounts on the bottom piece. The second piece has a hole just large enough for the toggle clamp’s base to fit through. This leaves a lip for the toggle to clamp onto. The third piece has a clearance hole for the entire clamp. The fourth piece is the same as the third, and builds up the block so the clamp sits inside. I glued on pieces of cork to cushion the sanding surface and fortify the toggle clamp’s grip.