How to Make a Box Joint

Adding a box joint to a woodworking project is an easy way to enhance the project's strength and appearance. Once you build the box joint jig, making the joints themselves adds mere minutes to your project. The joint draws people's attention because of its signature checkerboard look, so make sure you take the time to fine-tune the jig for a perfect fit.

Difficulty: Moderate

Instructions

Things You'll Need:

• Table saw with miter gauge and dado stack
• 6 inch by 24 inch by 1/2 inch board for miter gauge extension
• Key for box joint jig
• Screws
• 2 boards of identical dimensions
• Wood glue and pin nails (optional)
• Sandpaper

1. Cut a straight, square board for a miter gauge extension. The board should measure approximately 6 inches wide, 24 inches long and at least 1/2 inch thick. You can vary the length to suit your particular needs, but make sure you have enough fence to fully support the width of your workpiece.

2. Install a dado stack in your table saw. The width of the dado should equal the thickness of the pieces you'll be putting the box joint in, and about 1/32 of an inch higher than this width.

3. Mark the board's center and attach it to the miter gauge so that the center point lines up with the center of the dado stack. Run the board through the dado once, then shut off the saw and adjust the board on the miter gauge for a second cut that is exactly as far removed from the first cut as the width of the dado. Run this dado and then shut off the saw again.

4. Mill a piece of hardwood lumber to the same width and height as the dado, and cut it down to about 6 inches in length. Remove the miter gauge extension from the miter gauge and insert the 6-inch piece, or "key," into the first dado slot you cut. Slide it forward so that only an inch of the wood is visible behind the gauge extension board. Attach it to the board with a countersunk screw through the bottom.

5. Put your miter gauge (extension piece unattached) into the "way" slot of the table saw and hold the extension in place on it, lining up the second dado slot with the dado stack. Reattach the extension to the miter gauge once you've got it lined up properly.

6. Make the first side of your box joint. Butt up with the key the edge of one of the 2 boards you'll be joining, then run this over the dado stack. Next, put this newly run dado over the key and run another dado. Do this until you run out of wood to run. Call this first board "A," and the second board "B." Note that "A" and "B" must be milled to the same dimensions for the joint to match perfectly.

7. Make the mating side of the box joint. Position board "A" backwards on the gauge, so that its first dado rests on the key and one full tenon extends past the key toward the dado stack. Now butt up board "B" against "A," so that the edge of "B" is perfectly lined up with the edge of the dado stack. Run this dado, then remove "A" and reposition "B" so that its first dado is on the key. Run this dado, and repeat this procedure until you run out of wood.

8. Test fit the box joint. If you're satisfied with it, glue it together and reinforce with pin nails, if desired. Finally, sand the joint flush on both sides.

Tips & Warnings

• Use hardwood for your miter gauge extension to minimize movement in the jig.
• Use a router table with a straight bit instead of a table saw for similar results without the expense of a dado stack.
• Always wear safety glasses when using power tools, and never get your fingers within 4 inches of a moving saw blade or router bit.

Resources

• See pictures of a box joint under construction at Lowes.