Mortise And Tenon Joint What Is It
Mortise And Tenon Joint What Is It
Mortise And Tenon Joint What Is It? Learning how to upgrade to a mortise and tenon joint can change your approach to all types of furniture. This durable and strong joint style can make everything from tables and chairs to beds and dressers sturdier and longer-lasting. And if you have the right tools, it can be easy to execute a perfect joint every time.
This article will guide you through how to make a mortise and tenon joint and explain how you can use it.
What Is a Mortise and Tenon Joint?
A mortise and tenon joint is an interlocking of two pieces of wood, where a tenon tongue on the end of a rail fits into a mortise hole on the side of another piece of wood.
The tenon is shaped to exactly match the size of the mortise hole, ensuring a tight, immovable hold. It fits into the hole up to the tenon shoulders, where the tongue ends on the rail. It’s similar to how a USB goes into its port.
This simple joint, like the dovetail joint, is one of the most widely used joints. Woodworkers across various cultures have been using variations of it for thousands of years to construct everything from clocks to household furniture and even ships.
Mortise and tenon joints are commonly used for decorative purposes in popular furniture styles as well. The tusk tenon joint, for example, is a defining feature of craftsman and mission-style furniture, a timeless touch of character and quality.
How to Make a Mortise and Tenon Joint
The strength of your mortise and tenon joint depends on your precision and several variables, including the shape, width, depth, and species of wood that you use. The strongest joints, and the subject of this how-to, are rectangular mortise and tenons. The standard version uses a closed mortise, where the mortise goes around the tenon on all four sides.
The deeper you make the joint, the stronger the hold. There will be a lower likelihood of splitting, and it can hold a higher static weight. You also benefit from a wider glue surface.
The most common type of mortise and tenon joint is the stub tenon, where the mortise stops partway through the depth of the wood, so there is only a hole on one side. You commonly see this on chair stretchers.
Other types of joints, like the tusk tenon joint, go all the way through the mortise piece. Depending on the project, this can sometimes be easier to make, as you need less accuracy with the tongue depth. You can also cut the protruding piece of tenon off to make it flush on the other side of the mortise.
Marking the Mortise and Tenon
It’s critical to lay out where the mortise and tenon will meet with your two pieces of wood to ensure you are working with the correct faces and making an appealing and practical joint.
Position the tenon piece of wood at the point on the mortise piece where you want them to interlock. Make two hash marks indicating where it will meet the tenon shoulder. Make a unique mark on the face of both the tenon and mortise so that you’ll know how to position the tenon when marking your cut lines.
Next, mark the depth of the tenon tongue by overlaying the tenon over the mortise. Leave it as deep as you want the mortise to run. If you want a through joint, overlay the tenon so that the end runs over the other side of the mortise, creating a “+” shape.
Use a square to run a line around each side of the tenon piece indicating the edge of the tenon shoulder.
Mark the Cut Lines
You’ll need to mark your cut lines for the tenon tongue and the mortise hole. The tongue should be between 1/3 – 1/2 the width of the rail.
Use a mortise gauge to set your cut lines. Measure the desired width of the tongue and set the gauge to that position. Run the gauge from the shoulder mark to the end of the rail so that it can score the wood.
Repeat the process going over the top of the end of the rail and down the other side.
If you have a single gauge, you’ll have to reset the width for the other side of the tongue. You can make it easy with a dual marking gauge, which has two markers that can be offset, so you can mark both sides of the tongue at once.
To make life easy if you’re using a chisel for the mortise, make the width of the tongue the same width as the chisel. This will save you time digging out the right mortise width later.
Make the First Tenon Cuts
Now that you have a scored line for two sides of your tenon tongue, you can cut those sides out. You can use a backsaw to do this, carefully cutting down to the shoulder line. To keep your backsaw steady when starting the cut, carve a notch with a chisel or utility knife for the backsaw to lock into.
With the backsaw method, you’ll also have to trim cut along the should line to separate the piece of wood and expose the bare side of the tongue. Chisel into the shoulder line for a crosscut saw to fit into, then carefully work the saw down to where the tongue begins. It’s important to try for a clean shoulder cut.
Repeat this process on the other side, so you end up with two sides of the tongue and two shoulders.
If you want a quicker cut, you can use your table router to trim back the shoulder.
Cut the Rest of the Shoulder
Once you have the two tongue sides cut, you can work on the two smaller sides. These may require more care and finesse, so it might be easier to work with a backsaw instead of a power tool.
Cut the remaining pieces off the tongue to make a shoulder that goes all the way around the tongue. Having a shoulder on all sides is better for cosmetics, and will cover any imperfection in the mortise size.
These tongue cuts don’t need to be a precise size, as they will be guides for the cut lines on the mortise.
Cut the Mortise Hole
You should already have two lines marked out from using the mortise gauge earlier. With your complete tenon tongue, you can overlay it onto your mortise, using it as a guide for making your width marks on the mortise.
You should now have a rectangular diagram for making the mortise hole.
The hole can be cut out by chopping it with a mortise chisel or with a plunge router. In either case, you’ll need to secure the mortise board in a clamp on your workbench.
When cutting with your mortise chisel, don’t start directly on the end, as the force will cause the wall to expand, thus widening the mortise hole. Instead, start roughly 1/4″ away from the end of the hole and hammer the chisel in, working back and forth to open and deepened the hole. Make sure you don’t go all the way to the edge of your guide lines on either side while getting to the right depth.
As you work, keep an eye on your mortise depth with a ruler until it equals the length of your tenon.
If you are doing a through tenon, make sure you don’t bore out the hole from only one side. Doing so will cause the wood on the other end to splinter and ruin the look. Instead, carve holes out on both sides until they meet in the middle.
The quicker way to drill the hole out is with a plunge router. Find the bit that matches your tenon tongue width and set the height to the tongue’s length. Then, plunge it into your outline on one side and carefully work to the other until you have a clean hole.
Fit the Pieces
Do a dry run fit with your tenon in place, trying not to force or hit it in too hard. If there’s too much resistance, try shaving wood off of the tenon to get it to fit. It should be snug and flush up to the tenon shoulder.
Once it’s trimmed to fit, you just need to apply glue and set it in place, being sure to wipe any excess glue.
You can also bolster the joint with dowels. Drill dowel holes through the joint when you do the dry run. Apply the glue, refit the joint, and insert the dowels for the strongest hole.
Try a Mortise and Tenon on Your Next Project
A mortise and tenon joint is attractive and stout, a detail that doesn’t go unnoticed by a knowledgeable furniture shopper. With this outline on how to make a mortise and tenon joint, you can start applying this high-end feature to countless projects.
Are you looking for your next big woodworking project? If you want to put your newfound knowledge to the test, check out our collection of 50 free woodworking plans.