American Woodworker

Important Information >>


Q & A: Lock Miter Joint


Q & A: Lock Miter Joint



How do you set up a lock miter bit?





There are two critical adjustments (Fig. A). First, you set the bit’s height; second, you position the fence. Once that’s done, you can rout both sides of a lock miter joint without changing anything.

To get started, you must use a variablespeed router set at 10,000 rpm to slow down this large-diameter bit to a safe speed. Make some test pieces that are exactly the same thickness as the parts you’ll join together. Then adjust the bit’s height by eye until it looks like it’s centered on the workpiece. Position the fence by eye, too.

Make test cuts on two pieces (Photo 1). Put the pieces together and see whether their outside edges are flush. Raise or lower the bit as needed, without moving the fence, and make more test cuts until you’ve got the bit exactly centered on the thickness of your material.

Next, tweak the fence’s position in or out and make some more test cuts. Your goal is to make a sharp edge on top of the workpiece, leaving just a whisker of its original edge. If the fence is too far out, you’ll make a blunt edge on the workpiece, and the joint won’t have a sharp outside corner. If the fence is too far in, you’ll get a jog along the workpiece’s edge, and the board will snipe at the end of the cut.

Once you’ve set the fence, machine half of your pieces flat on the table. Cut the other half by holding them vertically against the fence (Photo 2).


Note: Product availability and prices are subject to change.

Woodcraft,, 800-225-1153, Whiteside Lock Miter Bit, 2” Dia. for 1/2”- to 3/4”-thick stock, 812508.

This story originally appeared in American Woodworker March 2008, issue #134.

March 2008, issue #134

Purchase this back issue.

Click any image to view a larger version.

Fig. A:

To make a lock miter joint, align the center of the bit with the center of your material. Then, position the fence to produce a knife edge.

1. To check the bit’s height, rout two test pieces and fit them together (see inset). If their outside edges are flush, you’re good to go.

2. Rout the mating piece of a lock miter joint by standing it upright. Pre-cut the ends of all your pieces on a tablesaw to make the job easier.