The Family Handyman
Build this easy-to-make jig and cut dadoes accurately and quickly with a circular saw.
1. Cut a strip of plywood that’s precisely the width of the dado you need minus the thickness of your circular saw blade.
2. Clamp this strip to a 12-in. long piece of plywood that’s a little wider than your workpiece, then hinge them together with two 1-in. wide pin hinges. Once the hinges are screwed in place, remove the clamps. To use, first mark the dado locations on the workpiece. Then clamp on the jig square to the workpiece so the distance between the dado line and the jig equals the distance from the far edge of the blade to the left edge of the circular saw’s base. Set the blade to the desired depth and make the first cut. Flip the hinged strip and make the second cut. Make freehand passes with the saw between the sides of the dado, and clean out the remaining waste with a sharp chisel.
P.S. To work faster, cut a 1/4-in. plywood spacer the width from the far edge of the blade to the edge of the saw base and use it to align the jig with the marked dado line before clamping on the jig. Thanks to David Radtke for this tip.