Mortise and Tenon
The mortise and tenon joint offers exceptional strength, resisting racking and twisting forces better than most other joints while providing an ample glue surface.
The basic joint includes a mortise cut into one piece, which accepts a tenon cut in another piece. It’s used primarily in furniture construction and cabinet frames. Variations include Haunched Tenons, Loose Tenons, Multiple Tenons, Through Wedged Tenon, Pegged Tenons, and Mitred Tenons.
The mortise and tenon is easier to make than most woodworkers realize. Although it requires a little planning, you can make it by hand, with power tools, or a combination of the two.
You need to use accurate measurements so that the pieces line up and fit snugly. Marking your layout lines with a line with a sharp pencil or layout knife helps. Make sure your stock is milled square. Cut the mortise first, and then cut the tenon slightly larger, paring it down and test fitting until you get the perfect joint.
Left – Shop-made jig, Right – Routing with jig
Mortise & Tenon By Hand
The traditional way of making these joints uses hand tools. I also use a bandsaw and drill press to reduce production time.
Mark out the mortise on your stock, keeping the width about 1/3 the width of your stock.
Use a brad point or Forstner bit to drill out the waste. A depth stop keeps the depth consistent. Next, use a broad chisel to clean-up the inside face of the mortise, and a smaller chisel to cut the ends square.
Using a marking gauge, such as the Tite-Mark Gauge, measure the mortise depth and transfer the measurements to the tenon stock, scribing layout lines on all four sides of the tenon. Ensure that the width and depth of the tenon will be close to, but no smaller than the mortise. This gives you some leeway for the perfect fit.
Remove waste from tenon with a handsaw, router, table saw, or bandsaw. Cut shy of the shoulder, cleaning up with a sharp chisel or file.
Tenon should now fit snugly into the mortise. You may need to pare a little more off. If the joint is too loose, it won’t hold together, even with gluing. Fix this by gluing a thin piece of wood or veneer on the tenon, let it dry, then re-fit the tenon.
Loose Tenons With A Router
The Loose Tenon is easy to make with a router. Instead of cutting both a mortise and a tenon, you cut mortises on both pieces of stock and join them together with a shop-made tenon, much like dowelling two pieces of stock together. This method gives you the same sturdy construction as a traditional mortise and tenon, but in less time.
You will need a jig to use with your router. My jig is home-made from Plexiglas; you could also make one out of wood, or you could buy one. The hole in my jig is sized to accommodate a 1/2″ template guide bushing, and uses a 1/4″ router bit to make a 1″ by 1/4″ mortise.
Clamp your stock to the jig. With a plunge router and a 1/4″ spiral up-cut bit, rout the mortise to the required depth. Play it safe and rout the mortise in two or three passes, increasing the bit depth by 1/4″ each pass, rather than trying to do it all at once. Repeat on the matching stock, making sure that the pieces will line up when finished.
The mortises will have rounded edges, which is fine. Make the tenons from a piece of 1/4″ by 1″ stock about 12″ long. Using your router with a 1/8″ round over bit shape the edges. Glue and fit the loose tenon in place.