Tenon joints are among the strongest types of joints to be found, which is why they’re so common on furniture. Done well they’re also largely hidden from view and make the work look cleaner. The tenon and mortise can be made in different ways (there are specialized tools to create them, for instance), but the traditional way still works very well. It’s important that the tenon fits snugly into the mortise for stability.
Step 1 - Measurements
There are two basic types of tenon joint. It will either have a shoulder or be without a shoulder. The tenon itself as essentially a tongue at the end of a piece of wood that fits into a hole called a mortise on another piece of wood to make the joint. Where wood has been cut away from all sides of the tenon it has a shoulder. If the wood has just been cut away along the long sides from the tenon it has no shoulder.
The tenon should be no less than 1/16th thick, and thicker is better to give a stable joint. For an unshouldered tenon on a piece of 2-inch by 2-inch wood, measure in 1 ¼ inches from the end and mark all sides of the wood in pencil. For a tenon that is ½ inch thick, stand the wood on end with the marked end close to you. Across the end measure ¾ inch, then ½ inch and check that the remaining wood is ¾ inch Mark the lines across the top and then down the side of the mark you’ve made.
Step 2 - Cutting
You need to cut away the side pieces so that only the tongue, or tenon is left. Put on safety glasses and use a saw to very carefully make the cuts. Once you’ve pulled the wood away from the cuts, use the chisel lightly so that the angle where the tenon meets the wood is 90 degrees. Sand the edges smooth with sandpaper and set aside.
Step 3 - Mortise
To make the mortise, measure an area that’s ½ inch by 2 inches on the piece of wood that the tenon will join. Put a bit in your drill. Measure 1 ¼ inches on the drill bit and put masking tape on at the point to show you how deep to drill. Drill a hole to that depth in the center of the marked area. Drill further holes of the same depth on either side until you approach the edges of the mortise.
From her use your chisel to make the mortise, being sure the sides are straight and that the bottom is even. Finish by using sandpaper inside the mortise then clean out the hole.
Step 4 - Setting In Place
Dry fit the tenon into the mortise to ensure it’s a snug fit. If too tight, use a chisel to slightly widen the mortise. Apply glue to the tenon and push firmly into the mortise. Wipe off any excess glue and clamp the joint until dry.