How to Cut a Mortise

The mortise and tenon joint has been a woodworking staple for thousands of years.

Not only is it strong, effective, and attractive, but it also requires minimal tools – you can even create this joint with simple woodworking hand tools.

Whether you choose to keep things simple with old school hand tools or capitalize on the latest technology with power tools, cutting a mortise is a project anyone can accomplish.

After you’re done reading through this detailed guide, you’ll feel more than confident in your abilities to create this age-old cut.

Here’s how to cut a mortise (and tenon) joint the right way.

What You’ll Need

The tools you need for this project depend on the method you choose.

You’ll need one of the following:

  • Mortise Chisel & Mallet
  • Drill Press & Brad Point Bit (or Mortise Attachment)
  • Plunge Router & Straight Bit

You will also need:

Method I: Chisel

Cutting a mortise with a chisel is slightly time consuming, but it’s not at all difficult. It’s among the most affordable methods too.

Step I: Measure and Mark

Start by making measurements and marking where each mortise will go. It’s helpful to also mark where the tenon will go in the corresponding piece of wood.

Step II: Set a Depth Measurement

It’s important to cut the right depth for your mortise. So, mark each chisel you’ll use with masking tape at the desired depth. This will enable you to more accurately mark each cut.

Step III: Make the Cut

Clamp the piece of wood to the workbench, so you can drive the chisel straight down to make the mortise cut.

Use the mallet and chisel to dig into the marked off area. Make sure that each blow drives the chisel straight down.

Start by making cuts around the marked off area. Then, begin to use the chisels to remove wood from the center of the mortise cut.

Method II: Drill Press

A drill press is a much more efficient, but also more expensive, way to cut a mortise compared to a hand woodworking chisel.

Step I: Measure and Mark

Use the measuring tape and carpenter’s pencil to mark where the mortise will go on the piece of wood. It’s typically best to make the corresponding tenon marks at this time.

Step II: Drill a Hole

Clamp the piece of wood solidly on the workbench underneath the drill press. Use the drill press (never use a hand drill) to drill the first hole into the mortise area. A brad point bit or Forstner bit works the best.

Step III: Finish the Cut

Move the piece of wood along the workbench, securely clamping it each time, until you’ve drilled out the entire mortise cut.

Method III: Router

If you have a router at home, then you’ve just discovered perhaps the easiest way to cut a mortise for your woodworking project.

Step I: Measure and Mark

Begin by making any necessary measurements and marking the block of wood where the mortise will go.

Step II: Use a Guide Block

Clamp the piece of wood firmly to your worktable. Set up the router with a straight bit that will cut the width of the mortise. Set the proper plunge depth on the router.

Use a guide block clamped to the router to guide the router with the markings you made for your mortise cut.

Step III: Make the Cut

Begin the cut using the router. Ensure the guide block guides the router cut in a straight line across the mortise for the duration of the cut.

Even More Options

Though the three methods above are the easiest and most common ways of cutting a mortise, there’s quite a few others you can use.

The most popular alternatives are to use a mortising machine or a Festool Domino.

Both of these alternative methods/tools are best for professionals and serious hobbyist carpenters that mortise on a regular basis.

A mortising machine is a benchtop tool that’s specifically designed to cut mortise holes and smooth them at the same time.

The Festool Domino is basically a sort of combination between a standard mortiser and biscuit joiner. Like a mortising machine, it’s a specialized tool that’s probably too expensive for most hobbyists and DIYers.

Clean Up with a Chisel

No matter which method you choose to cut your mortise, you’ll almost always need to clean it out with a hand chisel.

Start with a chisel roughly as wide as the ends of the mortise hole. Use this chisel to smooth out these ends and square the edges.

Move on to a chisel roughly as wide as the long sides of the mortise hole. Now, use the chisel to smooth out and square these sides.

Make sure to keep the face of the chisel flat against the sides of the mortise hole as you work to ensure that you’re only smoothing the hole and not making it any larger. 

Final Thoughts

Learning how to cut a mortise and tenon might seem difficult at first.

But, I’m confident that with the knowledge gained from reading this guide, the project will seem like a piece of cake for you.

So, why not put your new woodworking skills to use with these top DIY projects for the home? 

Gus Donaldson
About Gus Donaldson

I built houses for over 30 years and recently retired. I've made lots of mistakes and hopefully teach you not to make the same ones. I still love to build and have a garage workshop that I use for hobby projects like the walnut bookshelf I made for my wife. I like to write and let people know that working with your hands and tools does not need to be intimidating.

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