Marking Out The Tenon — How to Make a Mortise and Tenon

To mark the thickness of the tenon, take the stock of the gauge with your dominant hand and register against the face of your tenon. Start on one of the edges and run the pins so that they create two very superficial lines from the pencil line to the very end. Don’t forget that you’re mainly applying lateral pressure against the side of your tenon piece; the force exerted with the actual pins must be minimal.

Repeat on the end of the tenon and on the other side, using the vice to secure the piece if it helps.

Run the gauge along one edge, always applying firm lateral pressure to keep the stock registered flat

If necessary, go over the gauge lines with a sharp, pointed pencil for better visibility

Next, mark the defining shoulder lines with a sharp knife. Go right on the pencil line and apply light pressure at first, until you’re confident the knife won’t drift; then go a little deeper. Mark the shoulder lines on the other three sides in the exact same way, always registering your square against the marked face and edge.

Square the knifewall all around the four faces