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Building a Finger or Box Joint Jig

Attach a long 1 by 2 extension on your table saw miter fence. It will be used to support the finger joint indexing panel.

Clamp an indexing panel, which is about 8" high and 24" long, to the extension board on your miter fence. This tall indexing panel will help support large boards as they are pushed through the dado blade. Once secured, cut through the indexing panel. I am setting up, and testing this jig, with a 1/2" wide dado blade.

Cut a wood indexing pin, which equals the cut width, and glue it in the notch on the panel.

Use a loose indexing pin, which also is the same width as the notch, to set the fixed indexing pin 1/2" away from the dado blade. Clamp the indexing board securely to the miter fence extension.

Cut the two boards to be joined together. The rear board is held tight to the fixed indexing pin and the front board is set away from the fixed pin using the loose spacer block as a guide. Remove the loose index pin and make the first cut.

The second cut is made with the rear board notch over the index pin and the front board tight to the pin. Make the remaining cuts by moving the notches over the pin until all fingers and slots have been formed.

If the test joint is loose, move the indexing panel so the fixed pin is slightly farther away from the blade. If the fingers are too wide for the notches, move the fixed indexing pin towards the blade. Be careful moving the index board because it doesn't take very much pin movement toward or away from the blade to dramatically change the finger and slot width.