Mats Bengtsson More Advanced Wood Working and Do It Yourself

How to do mortise and tenon joinery in a small frame using routing

Mats Bengtsson mib over the years

Doing mortise and tenon joinery using a router

A very nice way of joining wood is if you can do it without screws or nails, using only wood and glue. The different types of mortise and tenon joints are the perfect solution for this:

  • The tenon fits in the mortise, providing a strong joint
  • The tenons placement in the mortise assures the joint does not move during glue up (sometimes side movement is allowed through a wider mortise than tenon)
  • The tenons placement int the mortise assures the two pieces are placed in the same way during glue up as during construction

A number of pine wood frames with routed tenonsAll of the above is good. But it requires that the mortise and tenon are cut out in the right spot with the right measurements so the two pieces come together with a good fit, and at the right height. Thus the major feat will be to assure that the fit is right. It can be achieved quite easily by first knowing and using a few basic but very essential tips and tricks for all home improvement and wood working, namely base the work on the principle to relate to a flat, a square and the middle.

I will assume you have already achieved the first two objectives (flat and square piece, normally achieved by buying a flat planed piece of wood, or by jointing or planing it yourself). The next step is to do the actual mortise and tenon joint. The tenon is the easiest to make. Using a router table, it is an easy and quick process. The mortises are harder to do, and should also be done first to assure the tenons get the right size.

Mortise and tenons are best created in a specific order

The best setup method is a three step process:

  • First do a test mortise. If it is not centered, then place it as correctly as you can, but on a test piece.
  • Next do the tenon, it can be done on a test piece, but due to the way they are made, it could be done on the final piece as well
  • Finally if the mortise is not centered, adjust the placement of the mortise on the test piece until the mortise and tenon joint gives a good even joinery between the two boards.

Ideal is if you have two work stations for this, so the setup can be done for mortises in one place and tenons in another, assuring that all settings remain in place after tested on a test piece. However, even if it can not be done like that, the process would be the same. The difference would be the need to first do a number of mortises (one for each size if you have different sizes which should ideally be avoided if you do not have to stations). Then do a set of corresponding test tenons, and finally return to doing the final mortises, tested using the test tenons. When all mortises are done, do all tenons.

Tools used to create mortises

The most difficult thing is actually to cut the mortise joint. As long as the mortise is to be centered along an edge, it is easy to do in many different ways, but there is a number of safety things to keep in mind. There are a number of possible tools to use to do it, all with their advantages and disadvantages. But when the mortise is not centered, rather placed square to the long edge, it becomes more difficult. Such mortise can be done on the router table. But the way I find easiest is to do it on the Leigh D4R jig.

Tools used to cut the tenon

When the mortise is cut, the tenon is to be produced. I almost always make it dead center from the sides (by routing it equally from both sides). I more or less always use the router table for it (route it against the fence, turn it on the other side and route again so the tenon is in middle. Test the fit. Keep increasing the router height and routing from both sides to keep the tenon in the middle until the tenon fits the mortise).

Since the router removes the same distance form the side each time, the tenon will get to be exactly in the middle. Since the router height is not changed after that, the thickness will be exactly the same each time (possibly not the originally wanted thickness, but still the same each time). This also explains why the boards need to be absolutley flat. If they are not, the tenon is still going to be flat, but the bend of the board will result in a thicker tenon.

There is not much more to it, unlike a non centered mortise, it is a thing likely to come out right without much effort.




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