How To Make A Mortise And Tenon Joint With A Router

The mortise and tenon joint construction not only looks neat but it’s also one of the strongest joinery methods. It allows the furniture to stand the test of time because of its powerful grip.

There are several tools that you can use to make this construction including a router. A router is a versatile tool that allows you to control the depth of your cut accurately and offers clean and precise results.

Why Use a Router for Mortise and Tenon Joints?

Mortise and tenon joints are one of the most popular ways to join wood together. It is typically used in fine woodworking to join end grain to edge grain, and creates an incredibly strong bond. Because this style of joint is basically a large peg inserted into a hole, a router is a fantastic tool to use. 

The router makes the process simple and replicable. However, you can use other tools instead of a router. For the tenon joint, you could use a hand saw or a table saw with a dado blade. For the mortise, you can use a drill and chisel or a hollow chisel mortiser.

How To Make A Mortise And Tenon Joint With A Router

In this article, I’ll discuss a step-by-step method to make a mortise and tenon joint with a router.

A router is a versatile tool that allows you to carve different designs, make grooves and cutouts, construct mortise and tenon joints, and more. The following steps will help you complete the mortise and tenon joint construction efficiently and effectively.

Supplies You’ll Need

• Two wood pieces
• Plunge Rout
• Measuring tape or a try square
• Pencil
• Chisel

Step 1: Carry Out Layout Work

The first and probably the most important step is to take the right measurements to mark your wood pieces. Make sure that you double-check your measurements before marking your wood pieces in order to get a perfect cut and fit.

Marking the Mortise

First, you need to measure and mark a piece of wood to make the mortise. Regardless of the side of your wood piece, make sure that you leave at least 3/4″ inch space from the end while marking the edge side. Anything thinner will increase the risk of breaking the mortise walls.

Ideally, the mortise should be two inches long for a typical 3/4 X 3.5-inch wood piece. Use the following steps to mark out the mortise.

1. Mark a straight line (width-wise) on the edge of the wood piece at 3/4″ inch from the end using a pencil and measuring tool.
2. Measure 2″ inches from the first marked line and mark another straight line (again width-wise). This way, the total distance of the second line will be (2 3/4) 2.75″ inches from the end.
3. Join the two marked lines by drawing a straight line right in the middle of the edge. This line will represent the area where you’ll need to use your router (instead of a jointer).

Marking the Tenon

Use the following steps to mark out the tenon on the second wood piece of the same size.

1. Mark two 1″ inch-long lines starting from the edge on one end of the wood piece’s front face. Make sure that you leave 3/4″ inch shoulder space on either side. This way the length of the tenon will be 2″ inches.
2. Turn both one-inch-deep lines into two L-shaped lines facing away from each other.

Step 2: Set Up Router

After taking the measurements and marking your wood pieces, you need to set up your router. 

There are a variety of different kinds of routers, and you need to use a good plunge router for to make a mortise and tenon joint.

Using a router with a fence is very important for making a mortise and tenon joint to cut wood pieces precisely. The fence will help you move your router back and forth easily without deviating from the marked lines.

You’ll also need to choose the right router bit for this method. Make sure that you choose a straight router bit with a 1/4″ inch-wide cutting diameter. That’s because the thickness of your tenon and the distance between the two walls of the mortise will be 1/4″ inches.

Step 3: Make Mortise

Set your router bit to a one-inch depth and use the following steps to make the mortise.

1. Clamp your marked wooden piece (for mortise) vertically on a table. Make sure that you secure it properly so that it doesn’t move while you’re using the router.
2. Place your router on the first marked line on the edge (at 3/4-inch from the end). Make sure the router bit doesn’t go over the line towards the edge. The bit must also be perfectly aligned with the central line that you made to join the two spots.
3. Turn on your router and drive it all the way in without moving it. Once it has reached the depth you selected, turn the machine off.
4. Place the router on the second marked line on the edge (at 2.75 inches from the end). Make sure you don’t go over the line away from the edge. 
5. Turn the router on and move it slowly towards the first groove you made.

Using this technique will allow you to make mortises with accurate length. However, your mortise will have round edges and you’ll need to use a chisel to make them square.

Step 4: Make Tenon

Instead of cutting the wood inside the marked spots, you’ll need to cut it on the outside. You can use the same router bit for this step because the thickness of the wood that you need to cut is less than one inch.

1. Clamp the wood piece (for tenon) on the table horizontally.
2. Place the router on one of the L-shaped lines that you marked. Make sure the router bit doesn’t go over the line towards the outer side of the L-shaped line.
3. Turn on the router and cut the 3/4″ inch shoulder space that you left during the measurement.
4. Repeat the same process for the other end/L-shaped line.
5. Set the router bit depth to 1/4″ inches and run it on both the front and back sides of the tenon to reduce its thickness. This way, the thickness of the tenon will be 1/4″ inches (one-third of the wood piece).

Important Note: The thickness of the tenon should be at least 1/3 (one-third) of the thickness of the wood piece you’re using to make the mortise.

Step 5: Test Joint

After making both mortise and tenon, test the joint by inserting the tenon into the mortise to see if they fit. If you have followed the guidelines properly to take measurements, they’ll fit perfectly.

If they don’t fit due to some human error, use a chisel to adjust the mortise. Never try to make changes in your tenon because it can get damaged pretty easily. You’ll need to re-perform the entire process to make a new one.

Step 6: Attach Tenon and Mortise

Apply gorilla glue to your tenon on all sides and insert it into the mortise. Let the glue dry, which can that can take up to 24 hours. Your mortise and tenon joint will be ready.

You can use the same steps to make as many mortise and tenon joints as you want.

Tips to Use a Router to Make a Mortise and Tenon Joint

Taking safety measures before using a router is critically important. It’s a power tool and can lead to accidents if you don’t use it safely and carefully. Use the following tips to ensure your safety while using a router to make a mortise and tenon joint.

• Using a router on wood creates dust that can hurt your eyes and respiratory system. That’s why you should wear safety goggles and a dust mask or respirator to protect your eyes and nose. You can also install the dust collection system if you can’t or don’t need to wear a face mask.
• Use both hands to grab and move the router and make sure that you place your forearms on the table. It’ll provide you with better control to make accurate cuts.
• Disconnect your router from the power supply if you need to change the router bit or make adjustments to the current one.
• Make sure that your router bit is installed properly because a loose bit can damage your workpiece.
• Never use a dull router bit because it will create rough cuts and can also damage your wood boards.
• Feed the workpiece at a moderate speed to the router. Working too fast can lead to rough cuts and a very slow feed rate can burn the workpiece.

Final Words

Using a router to make a mortise and tenon joint is not a difficult task. The only tricky part of the entire process is taking the right measurements. I hope this guide will help you understand the right method to make a mortise and tenon joint with a router to build long-lasting woodworking items.