How I Cut a Through Tenon

thru1_9488Almost every task in woodworking comes down to cutting to a line. If you can cut to a line consistently and accurately, you can build anything. There are any number of ways to do it, and the more methods you know, the more options you have and the more problems you can solve. Making a tenon means eight precise cuts, four to define the shoulder, two for the tenon cheeks and two for the tenon ends. It all starts with the layout, and I begin by using a knife and a combination square to define the shoulder cuts.

Many woodworkers turn to a table saw to do this work, and while that tool is fast, there are a number of reasons you should  make tenons by hand. At the table saw, the surface being cut is down on the table and it’s better to see what’s going on. Setting up the saw can be fussy, especially if the blade height differs during the course of the project, which it almost always does.  But the main reason to cut by hand is the quality of the cut and the low risk of botching the joint. Even the best table saw  blade can leave some tear out on the cut line. The shoulder is the visible part of the joint and if you have to make an adjustment after the cut for appearance’s sake, you change the length. When you cut by hand, the knifed-in layout line that you make first is actually the finished edge you will see when you’re done. If you don’t lose that line, you’re in good shape.

thru2_9490You don’t need anything fancy to do this, a simple bench hook holds the piece steady. The knife line acts as a guide for the saw if you use a gentle touch to push the saw forward as you start the cut. Students are encouraged to try to push the saw across the board without scratching the surface – getting a good start is the key to making a good cut as the saw will want to follow the kerf. If you try to force it, the saw can jump all around and be hard to control. The layout line takes care of making the cut square, and a decent saw will be easy to balance vertically. If you’re new to this, or a bit rusty, make some practice cuts until you can cut plumb. In this piece the depth is only about 1/8″ and the cut only requires a few strokes if you use the entire length of the saw.

thru3_9502For the long cheek cuts, we prefer to use the band saw. On shorter, non-through tenons we suggest a jig that holds the piece vertically at the table saw, or cut the cheeks by hand. In this case the cheeks are about 3″ long. That’s more work than we care to do by hand and a lot of blade exposed on the table saw.

Set the fence so that the cut line on the outside of the cheek is lined up with the inside tooth of the saw blade. (Click on the photo for a larger version and you can see how things line up.) Because the shoulder is already cut, you don’t need a stop to keep from going to far. Slow your pace as you approach the shoulder line and most of the time the waste falls off.

thru4_9503Put the piece in a vise to make the second, longer shoulder cut. Start at the far side with the saw tilted down so that the plate of the saw is riding on the first shoulder cut. That keeps both shoulder cuts lined up. When the cut gets going lean the saw back, and stop when you reach the layout lines, which are drawn after the cheeks are cut. (The position of the lines is easily found from the layout lines on the end of the board, too.)

The end cuts are about 1/2″ from the edge of the board, so I can return to the bandsaw to make these cuts without readjusting the fence. Once again the shoulder cut leaves a margin of safety that allows you to stop the cut at the bandsaw to prevent nicking into the shoulder.

The idea is to get as close as possible with the saw cuts without going beyond the finished exposed edges. You usually have a little nub of waste left in the corner between the shoulder and the cheek. That can be removed with a chisel held flat on the tenon cheek. If the first chisel cut doesn’t get all of the waste, a second cut with the back of the chisel held against the shoulder line will. Fitting to the mortise is the next step, but before that, bevel the ends of the tenon with a block plane. That makes it easier to get the tenon started in the mortise, and it prevents the tenon from breaking out the edges of the mortise when it exits on the other side.


— 360 Woodworking


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