Multijoint Routing Guide
Start with a plywood base
To make this jig, cut a 3⁄4 x8x18" plywood base, shown in the drawing. Then cut the remaining jig parts from a 2x48" blank that's a hair thicker than your workpieces. Drill countersunk pilot holes and screw the 18"-long fence to the base with the edges and ends flush. Place a workpiece against that fence and butt the edge of the 13"-long fence against the workpiece. Drill and screw the 13" fence in place.
Positioning the guides
Note: Before making the first routing pass, consult your router owner's manual and center the router baseplate around the collet. Or make a mark on top of the router base and hold that mark against the jig guide when making each pass. That way, the bit travels the same distance from the guides as you rout.
Chuck a 1⁄2 " straight bit in your router set to cut the rabbet or dado depth. Hold the router base against the guide and cut the first pass across both fences and the test scrap.
To position the second guide, hold your mating workpiece (or a scrap the same thickness) against the edge of the dado, as shown in photo. Use a craft knife to score its thickness on the edge of the fence. Then measure from the edge of the guide to the nearest edge of the dado. Measure that distance from your score mark to a point along the fence. Drill and screw the second guide there, 90° to the fences.
Now rout a second pass holding the router against the second guide and check the fit of the dado using the mating piece from your project. Adjust the second guide if necessary.
Two cuts rout a rabbet
For routing dadoes, rabbets, and half-laps, mark a joint edge and waste area on your workpiece, as shown in the photo, and set your bit depth. For dadoes, align the workpiece mark with the fence dadoes, clamp the workpiece in position, and rout one pass against each guide.
Rout rabbets, dadoes, and half laps with ease
For rabbets the same width as your dadoes, place the end of the workpiece just over the fence dado, as shown in the photo below, and rout against both guides. To make half-laps, unclamp the workpiece after each pair of passes and slide it along the jig. Repeat until you rout the full width of the half-lap.