Old Chips: Technique: Tenon and Mortise

Tenons and mortises is a type of joinery used since centuries. You need to master this technique because you will need this type of joint for many of your projects.

Here is my method. I will use Douglas fir boards that have been planed and are squares.

I will use Douglas fir boards that have been planed and are squares.

Those are all the tools that I will be using. I intentionally use regular chisels even if I own mortises chisels. A regular chisel is all you need for a mortise.

With a small ruler I mark the tenon's depth. The same ruler will be used for checking the mortise's depth.

With a knife and a square all the tenon perimeter is marked.

The marking gauge is set to centre the tenon. Typically a tenon is 1/3 of the width.

Marked with a pencil so you can see.

Sawing the tenon. I begin with a small cut on the far side.

Start another cut on the near side and slowly bring your saw back to horizontal and then complete the cut.

Completed cut. Watch your line, don't saw too far.

On the waste side, chisel to the knife wall.

The shoulders have been cut. Notice how thick the tenon is, I've sawn outside the lines on purpose. This tenon will now be flatten/straighten with a router plane.

The shoulders have been cut. Notice how thick the tenon is, I've sawn outside the lines on purpose. This tenon will be flatten/straighten with a router plane.

The mortise now. With my small ruler I find the center. That mark/spot will guide me to center the chisel and the marking gauge will register on the chisel side.

Now I locate where the tenon will fit.

With the length of the mortise already marked, I use a marking gauge for the final mortise width which is the same as the chisel to be used for chopping it.

When I chop a mortise, I'm always in a position where I can see the mortise lengthwise. That way it's much easier to keep your chisel vertical. Try that with the mortise parallel to your body...

I'm on the left side. I begin chopping on the far side with the chisel bevel facing me. The chisel angle will make for a vertical cut.

You chop deeper and deeper going toward yourself. I work from the top/left corner of the picture.

With the small ruler I check if I'm to depth. Just a little more to go.

When I am near the finish line, I then turn the chisel to have the back facing me and I complete this side of the mortise.

The mortise being completed I now need to trim the tenon. Here I mark where I want to cut it.

Using the router plane I slowly remove thin shavings at the same depth on both sides of the tenon. Before deepening the cut I verify if it fit in the mortise. I keep reducing the tenon thickness as required until I get a perfect fit.