A Primer on Joinery – The Mortise & Tenon
When making furniture or woodworking projects, you often need to get pieces of wood to join together. This can certainly be done with screws and glue, but a more time tested (and honored) method is to use Joinery. Joinery is the process of making interlocking parts with the pieces of wood and fitting them together like a puzzle.
Joints fall into two categories:
- Glue Only Joints -where the wood pieces are held together with just glue
- Mechanical + Glue Joints where the parts are held together with both glue and some mechanical locking mechanism – check out dovetails as a great example of this type of joint.
Let’s take a look at one of the most useful joints – the Mortise and Tenon Joint.
Mortise & Tenon 101
A mortise and tenon joint falls into the category of housed joints – where one piece slots or fits into another. Once you have mastered the lap joint, making a mortise and tenon is relatively easy, so you may want to take a look at Lap Joints 101 before you tackle this. Think of mortise and tenon as ‘square peg/square hole.’
Mortise and tenons can be used to help reduce racking and twisting in a project and will make your piece of furniture last for years. As with most joints, there are variations, but all of them rely on the long grain glue surface area for their glue strength, the fit of the side of the tenon – known as the “cheeks” for snugness and the depth of mortise for strength.
Let’s start by looking at the names of the different parts of the mortise and tenon joint and some of the guidelines you can use.
General Guidelines when laying out a Tenon for a Mortise & Tenon Joint
There are two general guidelines when planning for your tenons (you’ll cut your mortise first). Not following them could interfere with the structural soundness of the joint.
- Length of cheek should not be more than the width of the wood
- Width of the cheek should not be more than half the thickness of the wood – preferably a third.
Regardless of how you cut your mortise and tenons, clean layout is the key to accuracy.
Tools To Layout a Joint
There are various tools you can use to lay out a mortise and tenon – a pencil and a square, a mortise marking gauge, or marking knife can all be used. The goal is to have clean, thin, easy to see marks.
The mortise is the cavity into which the tenon is placed.
Generally speaking, the width of the mortise should be one-third of the thickness of the stock, but you do have some latitude. If you are going to use a router to cut your mortises, you’ll need to find out what router bit you have that is the closest to that thickness.
Note: If you are planning on buying a router bit for your project, make sure you invest in a good quality bit. Look for carbide blades and a reputable manufacturer.
You don’t want your mortise to too wide as then your cheeks will be weak, nor do you want them to be too narrow as it will make your tenons weak. A third is just right.
Layout and cut your mortises first and then cut your tenons.
Mortise can be cut using a plunge router, fixed table router, or with a sharp chisel and mallet.
They can also be cut using a drill press using either regular drill bit and then chiseling out the cheeks, or using a mortising drill bit (although these are a pain as they dull fast and get clogged easily).
There are lots of different kinds of tenons, but two of the most common are:
- Blind or stub – which stop inside of the receiving part and cannot be seen
- Through – where they go all the way through to the other side and sometimes protrude beyond the surface (you’ll see this in Arts and Crafts furniture a lot)
How To Cut Tenons
You can cut tenons with a wide variety of tools such as the table saw, bandsaw, handsaw or chisels, but the most critical aspect is that they are cut accurately.
Just like mortises, they should be laid out on the wood surface before cutting.
Different Types of Mortise and Tenon Joints
There are lots of different types of mortise and tenon joints, but they all rely on having the two parts fitting snugly together. A great book by has this page that gives just a few examples.
Where Can You Use Mortise and Tenon Joints?
Mortise and tenon joints are very versatile.
You can use them to join the legs on chairs,
You can use them to make a door,
or create case pieces
If you are new to woodworking or joinery, this versatile joint is a great one to learn how to cut and if you need a bit more help, consider taking a JOINERY CLASS at the Florida School of Woodwork in Tampa Florida.