Box Joint Jig Video: How to Make a Box Joint Jig/Finger Joint Jig for a Tablesaw

Here's the box joint jig, as you can see, it cuts nice evenly spaced fingers for the box joints so that we can get a nice fit. Now I'll, ah, review some of the parts of the box joint. We'll come in a little bit closer, but keep in mind you can make this from any scraps that you have in your shop. You just need half inch and three quarter inch plywood, a piece of two by four, and some hardwood for a runner. Um, the runners fit into the miter slots.

It should fit tightly. You don't want any play. And, um, this fence is adjustable so that we can adjust the fingers. You'll notice that this one is a tad bit loose. I'll show you how to make the, ah, fingers a little bit fatter so they fit tighter.

So let's come in a little bit closer and take a look at how it's made. Okay, let's take a little bit closer look at this jig. Now I said that we had to make our finger joints. These are the ones that we just cut and they're a little bit loose. We wanted to tighten up the joint.

So, I'm going to move this fence in this direction. Now, if we turn this jig around you can see that there's some screws here. Now these screws are in to elongated holes in this sub fence. That means that if I loosen this I can move this adjustable fence, left and right, just an eighth inch, one way and an eighth inch the other way, which is more than enough. Remember that when we set up this space between the pin and the slot, it's exactly the same as the width of the dado blade.

So that's our reference point to start with. I put this tab, this hardwood tab on here, and I had cut this, these two surfaces flush, but I put a washer behind this, ah, tab. Now what that washer does is it gives me a distance, and that's a fixed distance to start with. And if I put my feeler gauge in there I've got about 40 thousandths of an inch. Now what I'd like to do is move this this way to kind of fatten up the fingers, and get a tighter fit.

So I'd reduce this by about three thousandths of an inch. So what I do loosen the screws. And then I'd select a blade configuration that gave me 37 thousandths. I had 40, and I tapped this until that was tight. And when that was tight then, so I could just tap this lightly, this fence, then go ahead and tighten it down.

And then I'd try another test fit. From experience I know that that would tighten it up just enough. So then you'd go ahead start a new blank, makes some new test cuts. And I've already done that with this one. And you'll notice that the joint holds together nicely.

It doesn't fall out due to its own weight. And you can see that the joint has protruding fingers. So they stick out past the surface which is exactly what I want. If, ah, the fingers were not protruding, and if they were actually below the surface then your blade would be too low. And if they're up too high, this is less than a 16th, which is ideal, then my blade is just right with this.

But if they were like an eighth inch out then I'd have to lower my blade. Now keep in mind that if you raise the blade too much on this jig, you tend to get some tear-out because this now is set for this height. And if I were to, ah, cut some thicker material like three quarters of an inch and then go back to cut half inch material, like we just cut, then I could get some tear-out in the back. Then I'd have to make a new, ah, fence here, a new adjustable fence, and then start over again. But pretty easy.

These are just plywood scraps. You've probably got plenty of them laying around the shop. So that is the basics of this jig. It's a great little jig. It'll last for many, many cuts.

Remember that you want it to fit nice and tightly but slide freely. If there's play left and right, like this, you're going to get sloppy joints and no amount of adjusting will make it right. So that's it. Make yours and enjoy the world of boxed right.