Take the first step: Build the angled box-joint jig
1. Referring to the Box Joint Cutting Jig drawing, saw the parts for the jig to size. Assemble them as shown, except for the runners and guide block.
2. Install a 1/2" dado blade on your tablesaw, and adjust the cutting depth to 1/2".
3. To install the guide block, first mark a point on your saw table midway between the miter-gauge slots. Then, mark the midpoint of the jig's width on the face near the bottom edge. Place the jig on the saw table, the face toward the back of the saw. Offset the center mark on the jig 1" to the left of the center mark on the table.
Slide the saw's fence up against the right side of the jig. Holding the jig firmly against the fence, saw a dado 3" into the base. Install the guide block in the dado, extending 3/4" beyond the face.
4. Next, install the runners. To do this, slide the tablesaw fence exactly 1" to the right. Then, put a strip of double-faced cloth tape on top of each runner. Place the runners in the miter-gauge slots, taped side up, with a 1/16"-thick shim strip under each one. (Shimming brings the runner tops flush with the table's surface.)
Holding the jig against the fence to keep it square, press the base down to stick the runners to it. Lift the jig without disturbing the runners' positions on the base, and attach the runners with screws where shown.
5. Raise the blade to 3/4" cutting depth. Cut test joints in 3/4"-thick scrapwood to verify finger spacing. Cut at least eight fingers for a good test. When cutting with the jig, clamp the workpiece to the face. To keep the jig from tipping, which would cut an inaccurate joint, press down on the back of the jig as you push it forward.
If the joint doesn't fit together properly, adjust the jig position on the runners by tapping the jig with a hammer. To increase the distance between the fingers, tap the jig to the right; to reduce it, tap it to the left.
Download PDF of drawings