Router jig for easy 2x4 projects with dovetail tenons

This video is about cutting and assembling sliding dovetail joints in framing lumber. Sliding dovetails are common in woodworking and timber framing, but they are unlikely to show up on production framing jobsites anytime soon. 

The video is from the YouTube channel Appalachian Wood and seems to be about timber framing and homesteading. We will steer clear of the parsley-harvesting videos, but there are a few good carpentry videos worth promoting.

Transcript:

This is a sliding dovetail. This is also a sliding dovetail. These joints can be used for stairs, ladders, railings, any sort of 2-by material, furniture, even playhouses. Sliding dovetails are pretty popular in timber framing.

All the dovetails you see here are for a loft ladder we're installing in a timber-framed cabin. What we decided to do was make the same mortise and tenon connection using 2-by material. Here is a 2x4, and here is a 2x6.

Tools and setup

To make these tenons, I use this jig. It’s specially tuned for this exact router bit—a 1 1/8-inch dovetail router bit. I’ve linked the exact bit and bearing in the description. I had some trouble getting the bearing to stay on, but a dab of super glue at the base of the bearing solved that issue.

Let me show you exactly how this jig goes onto the piece of material. I’ve put the jig on its max setting—number 8—without a shim. The holes are perfectly lined up, and I’m drilling pilot holes.

Cutting the tenon

Now the tenon is done. Let’s take out the screws and check the result. You can see how long this tenon is—7 and 1/2 inches. That’s a good-sized tenon. Again, this is on the number 8 setting, which is the maximum.

The jig has two modes—with and without a shim. I’m using it without one, as shown by the small spacer difference.

Cutting the mortise

Now let’s do the mortise. We’ll cut it over here, and then join the two pieces together. I’m setting the jig the same way as before: number 8, no shim.

Fitting the joint

Now let’s cut the tenon so we can fit it into the mortise. I’ll be a little dramatic here; I don’t have to cut it exactly at the marked line—I can go a little below.

Next, I mark my cut lines using a speed square to make sure they’re parallel. I already marked the other side, so now I just need to rip cut.

Fine-tuning the tenon

There’s the tenon. I like to take just a quick shaving off the face. For long grain like this, a regular hand plane or jack plane works fine. But normally these tenons are on end grain, which makes using a hand plane difficult.

So I use an electric planer, being careful not to touch the clamp. One pass is usually enough.

Assembling the joint

This is the first time this joint is going together, so let’s test it. As you can see, it’s pretty tight. Let’s see what we need to do to persuade it—holy smokes! That is nice. A super strong joint with almost no wiggle. It’s not moving at all.

Adjusting for 2x4s

For the 2x4, I set the stop to number 3. You can see the numbered scale on the back. We’re going to do the other side next.

The jig just slides on and has two little prongs at the bottom that hold it onto the 2-by material. Just make sure it’s centered and running straight. These jigs are fully adjustable up to about 8 inches wide. If you have a 2x10, that’s probably the limit—but still an 8-inch tenon.

Testing the fit

Let me show you how these slide in. I’ve tested them already, so they slide easier now. There’s still a bit of tension, so we push it down—and yeah, I still need to hit it with a mallet.

You can see the 2x6 is now on there securely. I can’t pull it apart by hand. I really have to use a mallet. And there’s the tenon.

Addressing structural concerns

Of course, there’s the concern: aren’t you weakening the wood by taking off so much material? Yes, absolutely. The depth of the cut is 1 1/8 inches, so you are removing a lot.

If you’re using this as a joist, I suggest sistering it. But if that’s not a concern, go for it. You’re not limited to joists. Think about other applications: stairs, ladders, railings, furniture—chairs, tables, benches, even playhouses and beds.

The sky’s the limit with this technique, and it’s all made possible using this jig. Check the description for links to the exact product, router bit, and bearing combination I use.