One giant try square
By adding blocks of wood as shown above, you can convert a framing square into an oversized try square for those big jobs. First, cut the blocks to size from 1⁄4 "3⁄4 " stock and clamp them in position on the square. Then, drill 1⁄8 " holes completely through the blocks and square blade. Remove the clamps and scuff the blade with 80-grit sandpaper. Then apply epoxy glue to the mating surfaces, and reassemble. Insert 1⁄8 " brass or steel pins of the appropriate length. Hold the assembly together with masking tape until the epoxy sets, then sand the pins flush with the surfaces of the blocks.
—Leslie Douette, Prince Edward Island, Canada