Half-lap joint jig
Cutting on-the-money rabbets for half-lap joints with a portable circular saw and handheld router is a breeze with this two-in-one jig.
Build the jig
You can make a simple half-lap joint on your tablesaw with a dado blade, miter-gauge extension, and a workpiece stop. But when working with very long parts, cutting them on a tablesaw proves awkward at best, and maybe unsafe. And what if you don't own a tablesaw? Here's how to form the rabbets that make up a half-lap joint with portable tools. With this jig, you'll save time by cutting several parts with one setup.
To make the jig base, measure from the motor edge of your circular-saw base to the blade, and add 1/8". Then chuck a 1/2" straight bit into your router, measure from the edge of the router subbase to the bit, and add 1/8". To these two dimensions, add 1 1/2" for the guide, and cut an 18"-long piece of 1/2" medium-density fiberboard to this width.
Cut the guide to the size shown right. Glue and clamp it to the base. Then, with the glue dry, clamp the base to your workbench with the saw side overhanging. With the saw base against the guide, trim the saw side to width. Now with the router side overhanging the workbench, use your router with the 1/2" bit to trim the router side to width.
Measure the trimmed width of the base, and cut two cleats to this length. Then glue and clamp the cleats to the bottom of the base, flush at the ends and edges.