Jig Journal: Keyed Miter Jig

Keyed Miter JigThis shop-made table saw jig makes quick work of reinforcing miter joints.

By Matthew Teague
Pages 60-61

I love the clean look of a mitered box that has continuous grain wrapping around the corners. It’s an easy detail to create, but a sure sign that the maker is paying close attention to the details. The downside of a mitered box? Miter joints are notoriously weak because they have no real mechanical strength; glue is all that holds them together.

You can reinforce miter joints in a few different ways, but my favorite method is to use exposed keys. These hardwood keys are nothing more than thin lengths of wood glued into slots that span both sides of the joint to help hold everything together. To cut the slots for these keys at the table saw you need only a small jig that runs against the saw’s fence. The jig cradles the assembled box at a 45° angle and allows you to guide it through the cut.

Keys not only add great strength to miter joints, they also provide a decorative effect. Once the jig is made, you can arrange the keys in any number of ways, using either a matching or contrasting wood. For a slightly different look, you can cut wider key slots by simply adjusting the table saw fence to take two or more passes for each slot. For angled keys, which create joints that arguably are even stronger, simply angle the blade. You can even use this same jig at the router table to create dovetailed key slots – just be sure to hog out the bulk of the waste in the jig itself before you cut the actual box.

Making the Jig
This jig can be made from plywood, MDF or whatever scrap you have on hand. If you choose sheet goods or thinner stock, you’ll need to face-laminate a few thicknesses so that the cradle of the jig is wide enough to hold the full height of the box. I simply glue and screw through all the thicknesses to create one large chunk of material. It’s a good idea to glue up a longer length of stock than necessary, just so that it is easier to hold during the next step.

Once the glue dries I remove the screws so that there’s no risk of the saw blade catching a screw when the jig is in use. You can then cut both ends of the stock at 45° angles on the miter saw or use your miter gauge at the table saw. Instead of cutting the miters to a sharp point where they meet, I like to leave about 1⁄8″ or so flat on each piece; once the jig is assembled and in use, this raises the box off the saw table and allows the jig to move more smoothly across the table.

Blog: See more on building mitered boxes and a slide show on installing the keys.
Model: Download a 3D SketchUp model of the box seen here.
Articles: Find plans and instructions for making and using a wide variety of jigs.

From the August 2012 issue #198
Buy the issue now.
Popular Woodworking Magazine August 2012 Cover