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A Primer for Mortice-and-Tenon Joints

Part 1: The Blind Joint

The mortice and tenon is an extremely strong joint often used in cabinet and door frames, or in the construction of tables and chairs.

There are several different types of these joints, such as …

Reference: http://www.extremehowto.com/xh/article.asp?article_id=60169

The following tutorial follows the construction of a blind M&T joint that forms the frame within a cabinet presently under construction. Future tutorials will demonstrate variations of the mortice and tenon joint.

For reference, some of the terms used include:

Tools

Marking gauges

All joinery begins with accurate marking. Marking mortices requires a mortice gauge, and marking tenons is best with a cutting gauge.

Kinshiro morticing gauge, Colen Clenton cutting gauge.

Saws

Sawing a tenon involves three different saw cuts. Firstly, there is the rip cut to form the tenon cheek with a tenon saw, such as my 14” vintage Nurse (11 tpi ). The second saw cut is to define the tenon shoulder. Here I have used an 11” Eccentric Tools crosscut carcase saw (14 tpi). Lastly, there is a small rip cut to reduce the width of the tenon shoulder. This is can be done with any backsaw. In this tutorial, since the tenons were ¼” thick, I took advantage to test drive the new Veritas 20 tpi dovetail saw.

Above - Nurse tenon saw Below - Eccentric Tools carcase saw.

Tuning the tenon cheeks and shoulders…

… can be done with a chisel. One does not need more than this if you have terrific hand skills. Nevertheless, there are a few tools that make the job easier for the more ham-fisted, such as me. A router plane will level and ensure that the tenon cheek is parallel to the stretcher. A rabbet block plane can remove a lot of waste quickly. A joinery rasp fine tunes the thickness. And a shoulder plane trims and tunes the tenon shoulder.

Behind – Veritas Small Shoulder Plane, Lie-Nielsen Rabbet Block Plane, Lie-Nielsen Joinery Rasp

Front – Veritas Large Router Plane.

Chisels

My preference is for vintage oval (or English) bolstered mortice chisels. I have used Japanese mortice chisels, which are shorter. The extra length of the OB chisels makes it easier to determine if the chisel is being held vertically.

For reference, these are ground with a 20° primary bevel and honed with a 35° secondary bevel.

Vintage Ward and modern Ray Isles Oval Bolstered Mortice Chisels

The other tool I find useful is a bottom cleaning chisel I ground out of a hex wrench. This will pry out chips and smooth the bottom of the mortice.

Preliminaries

Step one is to transfer your dimensions to the boards, and leave an inch or two of ear beyond these marks. This is to prevent the mortices blowing out. The ears will be cut off later.

Make sure that the ends of the tenon boards are square.

Marking Out

I usually begin by marking out for the tenon cheeks. The “1/3 Rule” indicated a tenon length of 1 ¼”.

I laid out the 3 ¼” wide boards to create a tenon cheek 2 ¾” wide - that is, the length of the rail less a ¼” shoulder at each end.

Once the length of the tenon is marked, the width needs to be determined. Since we are using boards slightly under ¾” thick, the “1/3 Rule” indicates a tenon/mortice width of ¼”.

Use a rule to mark off a ¼” at roughly the centre of the board. It is not critical that this is exact, as long as all markings are made from the face side. Make sure that you have clear reference marks to avoid confusion.

Now mark across the width with the mortice chisel, as shown below.

This is going to aid in setting up the mortice gauge. Simply place the ends of the knives (or points) in the ends of the cut. This sets up the cutting width.

Now slide the head of the gauge against the work piece to set its depth. This completes setting up the mortice gauge.

Mark the mortice lines.

And then mark the tenons with the same settings.

The Mortice

First, here is an aid to holding the chisel vertical.

I prefer to hold the stile over a leg of the bench using a handscrew. The handscrew is clamped to the bench with a long F-clamp. The shaft forms a handy sight for the mortice chisel.

I stand directly behind the chisel and in line with the red handle (see lower image, above).

Time to begin chopping out the mortice.

The first incisions are made 1/8” – 1/4” in from the end of the mortice. Chopping to and levelling chips from the end of the marks will result in severe bruising. Rather work slightly inside the lines and leave the bruising there. The plan is to pare away these sections at the end and finish the mortice with clean, square ends.

I like to first pare out the surface of the mortice. This makes it easier to keep the first deep strikes in line with the edges.

There are a number of different ways to attack the mortice. Some choose to work from the centre outwards. Some choose to start on one side and work across to the other side. I choose to work halfway from the outside inward, then turn the work around and do this again.

The final step is to square the ends by paring out the last sections of waste.

The Tenon

I came across a great tip from Chris Schwartz awhile back. Chris suggested chiselling a tiny fence at the start of the saw cut. This is very helpful in sawing to the line.

I place the rail at 45° in my vise, which allows me to see the adjacent cut lines. Cutting along two lines simultaneously makes it easier to cut straight.

Being right-handed, I also prefer to cut on the right side as this allows me to site the lines as I saw. When I complete this cut, I turn the rail around and once again saw from the right side.

Some advocate sawing half the kerf from one side and half from the other. I find that when I do this I end up with an uneven kerf. Consequently, what works better for me is to straighten the board and finish the saw cut by levelling the saw blade.

Once the cheek cuts are made – stopping a hair short of the shoulder line – then it is time to make the shoulder cuts. These are kept clean and straight by creating a fence of the shoulder line.

Again saw until a whisper of waste remains, then alternately saw the cheek and the shoulder until the waste is freed.

Dimension the tenon cheek by marking the waste and sawing this off.

Finally you are left with a rough tenon, one that will likely reveal three areas for tuning:

A . There is waste remaining in the corner of the shoulder as a result of an incomplete saw cut.

B. The tenon is an uneven thickness, with one end thicker and out-of-parallel.

C. The end of the shoulder needed to be cleaned up.

I start with the cheeks. Put away the shoulder plane until you have planed the cheeks parallel to the rail. If you don't do this, then how can you know that you are planing the shoulders square?

If there is just a little waste to remove, I will immediately go for a router plane. If there is a lot of waste to remove (for example, if a repair is made), then I first use a rabbet block plane. After this I turn to the router plane.

It is not necessary to use an outrider for the router. It balances perfectly well on one half of the sole. This tenon here is 1 1/4" long.

For fine tuning the fit, I like using a rasp or, as here, a joinery float.

So what do you do if the tenon is too loose in the mortice?

Either glue back the cheek waste, or a veneer cut from it. Once dry, re-plane the tenon cheek.

Test fit the mortice and tenon. Is it a snug fit? Is the tenon shoulder flush all around, or are there high and low spots?

This combination could be a tighter fit. Close inspection reveals that the shoulders need to be tuned so that they are perpendicular. Now is the time to bring out a shoulder plane.

I push from one side …

… and pull from the other.

Once you are satisfied that the fit is flush all around, it is time to undo all the precise squaring by adding a little undercutting around the shoulders. This will ensure that the fit is tight, as well as provide a little space for glue to flow.

Finally …

… the joints are completed. Here is a sample …

And a few more …

In the following tutorials I shall show drawboring, haunched- and through-and-wedged tenons.

Regards from Perth

Derek

October 2009