How to Make a Box Joint on a Table Saw

Cut a piece of 3/4-inch hardwood, 6 inches wide by at least twice the width of the pieces to be joined. Position it on a table saw miter sled, centered, with the wide face against the fence and one long edge down. A miter sled is a thin, square metal rod that slides through the push grooves of the table saw. On the back end it has a push handle. Just in front of the handle is a perpendicular metal fence.

Drive two ¾-inch screws through the holes in the fence to anchor the hardwood to the sled so that its bottom edge will rest flush on the table. Install a 1/4-inch dado blade on your table saw to cut the notches for the joint. Set the depth of the blade to 3/4-inch.

Place the sled in the table slide groove to the right of the blade. Start the saw and run the hardwood, attached to the miter sled, over the blade to notch it. Stop the saw and wait for it to stop spinning before retrieving the piece.

Use a square and draw lines across its face vertically, every 1/4-inch, starting from both sides of the notch you cut. This will be your joint jig. Cut your joint pieces from ¾ inch thick hardwood to the size needed. Mark the ends of the pieces to be joined with the box joint every ¼ inch across their width at on end, with the lines perfectly matched between the two pieces. These are the members of your box joint.

Align the joint members, wide face to wide face, with the narrow ends flush and the long edges offset by 1/4-inch. Clamp the two pieces together with a c-clamp. Clamp the joint members to the miter sled, with one narrow edge against the table and the offset edge of the joint members on the left aligned squarely with the left side of the notch in the hardwood.

Start the saw and run the sled through the dado blade, cutting a 1/4-by-3/4-inch notch on the end of one joint member. Turn the saw off and allow the blade to stop spinning before retrieving the sled. Shift the joint members 1/2-inch to the left and re-clamp. Start the saw and cut again. Continue cutting, shifting left 1/2-inch each time until you reach the end of the board.

Fit the two jointed boards together, with the fingers of one piece fitted neatly into the notches of the other to form a solid 90-degree corner. Glue the joint with a small dot of wood glue in the bottom of each notch and clamp the boards together until the glue hardens for a permanent joint.