The World’s Simplest Box Joint Jig

A box joint is a very strong way to join boards together because there is so much surface area for gluing. Plus it looks great on your projects. There are a lot of terrific adjustable jigs you can buy or build that will allow you to create box joints of all different sizes, and if you plan on making a LOT of projects with box joints, a dedicated machine makes sense. But chances are, you only need to make an occasional box joint. In this article and video, I’ll show you the absolute easiest way to make box joints without having to build a complicated jig. You can make this on the fly, in minutes, and get on with your project.

You will need a stack of dado blades for this method. This jig will allow you to make a fixed-width box joint. It could be a disposable jig, or save it if you think you might use it again. Box joints can be any width you like, but for this setup you will be limited by the width of your stack of dado blades. In general, I think a lot of small box joints looks nicer than a few large joints.

Avenger Stack Dado set

The critical part of making box joints, is the depth that you cut them. Their depths need to be exactly the thickness of the boards you are joining. If you cut them too deep, the ends will protrude and if you cut them too shallow, the ends won’t be flush.

Making the world’s simplest box joint jig

Start by setting up a stack of dado blades to whatever width you want the fingers of your joint to be.

Next, raise or lower the depth of the blades to match the thickness of the wood you are going to use for your project. I’m going to use regular ¾” lumber for this example.

Raise the blades flush with the thickness of your workpiece

Grab a scrap piece of ¾” or 18mm plywood to use as a fence. I prefer to use plywood because it its faces are perfectly flat without any twists or warps. Make it about twice as long as the width of your workpiece. Also, make it fairly tall to provide support for your workpiece.

Hold it tightly against your miter gauge and cut a notch near the center of the plywood.

You’ll need to make a small rod to match the size of that notch. I like to use a scrap of hardwood. Cut an extra one to use as a measuring gauge. Then glue one into the notch, making sure it doesn’t stick out on the back side of the fence.

This pin should protrude out on one side of the fence only.

Once that has dried for a few minutes, set your fence back against your miter gauge and slide it to one side of your dado stack, using that extra rod as a spacer to measure the distance between the pin and the edge of the blace.

Using a longer rod as a spacer to measure the distance from the pin to the edge of the blades.

Once you have that set, clamp your fence to your miter gauge to keep it from moving.

Screw the plywood fence to your miter gauge.

Start making box joints!

Begin by taking one end of your workpiece and butting it up against the pin and cutting a notch. This first cut will go all the way through the fence.

Then take the notch in your workpiece and drop it over the pin and make another cut.

Keep doing this all the way down the rest of the board. The final cut probably won’t be a full finger or notch, but that doesn’t matter. Here, it ended up being a thin sliver.

Cutting the joints in the mating board

You need to start your next board with a notch at the end rather than a finger. The easiest way to line that up is to flip your first board around, drop it onto the pin, and butt the new board next to its edge. Pull the first board away and cut the notch.

Continue all the way down the board. The last cut will leave a shallow notch to match the thin finger on the first board.

Flipping the first board around. (The thin finger is on the outside.)

Drop the first notch onto the pin.

Hold your workpiece steady to prevent it from slipping.

First notch on the edge of the second board.

A little glue in all the joints will hold it together.

It’s a good idea to run a couple tests before cutting your actual work pieces. If the fingers aren’t flush, you need to raise your dado blades a little. If the stick out, you are cutting too deep.

If the fingers only stick out a little, you can just sand them flush.

If you want to use this jig again, just set up the same dado blades and drop the notch over them and re-attach the fence to your miter gauge. You could save several of these for common sizes.

Well I hope you will try out some box joints in your next project. They don’t have to be complicated and this method is a simple way to step up your woodworking game.