Wedged mortise & tenon
This wedged M&T joint on the other hand, is designed not only to be visible, but to be a design element as well. You can use it for knock-down furniture or glue it for a permanent joint.
The M&T joint is a very strong joint that is fairly easy to make. We won’t go through the process for making an M&T joint, since we covered that in a previous issue (Canadian Woodworking, Oct/Nov ’04, Issue #32). We will, however, show you how to adapt the M&T joint to make it a wedged joint.
The key to the wedged M&T is that the mortise goes all the way through the board, with the tenon having two shoulders on the sides. In addition, the tenon will extend out past the mortise to allow space for the wedge, with enough material at the end to prevent it from breaking when you hammer the wedge in.
The wedge keeps this joint tight
Mark the hole for the wedge
Chisel hole to match wedge angle
What You Need
The wedge can be cut on a bandsaw and then hand planed smooth. The hole for the wedge is made with a drill to remove waste, and a chisel to clean up the sides.
How To Make the Joint
Begin by cutting the mortise and the tenon. Then insert the tenon into the mortise and scribe a line along the outside edge of the tenon. Remove the tenon and make and scribe a new line across the tenon about 1/16″ to 3/32″ back of the first line. This marks the inside edge of the hole for the wedge, and should end up inside the mortise to ensure the wedge will pull the tenon snugly against the mortise.
The outside edge of the hole is angled to match the angle of the wedge itself. The length of the hole at the top will be more than the length of the hole at the bottom of the tenon, creating the angle for the wedge. Make a mark to indicate the length of the hole on the top surface of the tenon, and then make another mark approximately 1/8″ back (towards the shoulders) to indicate the necessary width at the bottom of the hole. Drill out the waste to the inside mark and clean up the hole with a chisel to make it square.
To make the matching angle on the hole, use a chisel to cut the waste from the top mark to the bottom edge of the hole you just chiselled out. Cut out a wedge with the same angle as the hole.
Assemble the mortise and tenon and insert the wedge into the hole. Hammer the wedge in place until it is tight.