Strengthen and simplify rail-and-stile framework with this easy variation on the classic mortise and tenon.
You can go a long way with the basic mortise-and-tenon joint, but sometimes a variation comes in handy. The curio cabinet, for example, features haunched tenons on the top and bottom rails. With a haunched tenon, you can cut a groove the length of each stile's inside edge, then automatically fill the exposed end of the groove with the haunch as you assemble the joint. A haunched tenon looks like a standard tenon, but adds a shoulder that extends to the edge of the rail, as shown in the drawing right.
Making the tenon is simple. All you need is a tablesaw and dado set, as shown here.
First, cut the rails and stiles to their final dimensions, with the rail length including the planned tenons. Plow a 1/4x1/4" centered groove along the inside edge of each part to receive a panel.
Now, lay out a mortise to be cut into the groove on the stile. Locate the mortise 1/4" from the end of the stile, and make its length 1/2" less than the width of the rail; our mortises measured 2 1/4" long. We made the curio cabinet mortises 1 13/16" deep to receive 1 3/4" tenons, allowing 1/16" of extra space for glue. Each mortise is 1/4" wide, matching the groove in the stile. Now, you're ready to form both parts of a haunched tenon joint following the steps shown above right.