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 above.
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 1⁄4 x1⁄4 " 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 21⁄4 " long. We made the curio cabinet mortises 1 13⁄16 " deep to receive 13⁄4 " 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 below.
Choose your method for forming mortises
Now, you're ready to form both parts of a haunched tenon joint following the steps shown.
Choose your method for forming mortises–a drill press equipped with a standard twist bit or a hollow chisel attachment, a plunge router and centering jig, or a mortising machine (our choice). When using this tool, bore at each end of the mortise layout with a 1⁄4 " hollow chisel bit, then bore a series of holes in between, leaving a wall between adjacent holes. Finally, bore out the walls.
Mount a dado set
Mount a dado set on your tablesaw and raise its height to 1⁄4 ". Make a test cut on both faces of a scrap piece, and test the fit in one of your mortises. Set your rip fence so that the distance from the fence to the left side of the dado set equals the depth of the mortise as measured from the stile edge, minus 1⁄16 ". With an auxiliary fence on your miter gauge, make passes on each face to form the tenon.
Move the rip fence
Move the rip fence 1⁄4 " closer to the dado set and lock it in place. Place the rail against the miter gauge with the grooved edge up. Make a series of passes to form the haunched shoulder of the tenon. You should be able to butt the end of the workpiece against the rip fence for the final pass, but test the fit before making that pass.
Test the joint's fit
Test the joint's fit by checking for gaps at the visible joint lines. Then, apply glue to all of the mating surfaces. Place the panel in the grooves as you slide the four joints of your frame together, and clamp the assembly.