Traditional Joinery

I decided to test the strength of some common joinery methods that you can do with the tools you already have in your shop so you don’t have to go out and buy an expensive domino or any other joinery system.

You can’t just use any joint for any situation. Unlike dominoes and dowels, you need to select a traditional joint based on the direction of the two pieces of wood you’re joining together. There are quite a few options to choose from, and they’re not all equal, but some of them are simpler to do than your favourite youtuber’s domino.

Miter

Like a miter! They’re a great joint if you’re looking for grain that flows around the joint and you don’t want to see any end grain on the edges. If your workpieces have a profile or detail of any kind, a miter can make that shape flow around the joint, like a picture frame.

Miters are a great looking solution for joints. But a good looking miter joint does not a miter gauge make. For that, you need a dedicated miter sled, like the one I was inspired to make after watching David Piccuito’s video. If made well, it’s a foolproof way to ensure your miters turn out as crispy as a kettle chip.

Gluing miters can be a pain if you’re not set up for success. Collins miter clamps are great if you can either hide or repair the indentations they leave. You can also opt for forty five degree clamping cauls. Both of these solutions will work if making a complete frame, but I also love band clamps for frames too–but they do take some practice.

But is a miter joint really that strong? Isn’t it just a bunch of end grain glued together? Conventional wisdom suggests that gluing end grain to long grain isn’t actually that strong, but there was a fellow named Patrick Sullivan who made a very convincing video that appears to disprove that line of thinking. I didn’t want to get that into the nitty gritty, but I decided to show how strong a joint is relative to other joints of the same size, in order to give a more practical guide for what joint to choose if strength is your number one priority.

Testing Strength

I used my testing jig that I got from Matthias Wandel, because he’s super smart.

I made five of each joint to break each one with the super scientific jig. The joint clamps and a bottle jack puts pressure on the end of the piece while putting pressure down on the scale to measure the force it takes to break it. I modified it to include a lever which divides the total load on the scale in half because I was worried that the joints were going to be so strong that they would exceed the scale’s limit. Because of that, I had to double the number on the scale to get the actual result. For each joint, I removed the highest and lowest values for a crude but consistent way to remove outliers, and then averaged out the middle three results. I also included a butt joint as a control because that seemed like the sciency thing to do.

The miter wasn’t much to write home about, but did score over twice the strength as the butt joint did at 187 pounds for the miter, and 79 pounds for the butt joint. So even though the miter seemed to be just a bunch of end-grain, it’s really not. There is clearly a better bond with the joint cut at a 45 degree over a straight-up butt joint, while it also slightly increases the amount of surface area for the glue to use. But is it strong enough?

Splined Miter

Enter the spline. You can put a spline in any miter with just your table saw, and if you’re making lots of picture frames, I highly recommend making a jig that rides on your fence, allowing you to repeatedly and accurately cut these slots. You can basically raise your blade up as high as it can go without going over.

If you don’t trust your planer to mill down the splines thin enough, you can double-stick tape your spline material down to a flat sheet of MDF, or you can sneak up to the perfect fit on a table saw using featherboards to keep things consistent.

A while back, Jason Hibbs of Bourbon Moth made a video about joint strength and his splined miters were the strongest in his test, so I was fully expecting this joint to blow my mind. It came in stronger than just regular miters at 271 pounds, sure, but it didn’t give a satisfying moment of destruction. It just kind of stretched apart. But I suppose that could be considered a good thing because there’s no sudden moment of failure, just a lot of warning that your table will fall apart if you keep using it as a stage for your at-home Fiddler on the Roof productions. Splined miter strength test Jason was using a splined miter in a different orientation, like if you were going to make a box or a case, so perhaps it’s still stronger for that scenario. So I decided to test that scenario too! Jason squeezed the joint together, as if you were closing a book, but the way I’m testing, I’m opening the metaphorical book. So that might be important to note. At any rate, this just confirms the limitations of any joint strength testing: there are a hundred and one ways that a joint can break and it’s really hard to account for them all. But these types of joints tend to be subjected to, and are weakest in a racking or rotational direction, so that’s why I tested them the way I did. I tried to maximize the size of the spline by raising my blade up as high as it would go.

All the same, the mitered spline is a great looking joint, particularly if you like to create accents with contrasting wood tones. If you want the clean look of the miter, but are doubting its strength for your application, then a spline fits the bill rather nicely.

Just be sure to double check the grain direction on your splines because it’s easy to mess this up. I’ve done it many many times. The grain needs to be perpendicular to the direction of the miter.

The Mortise and Tenon

The granddaddy of joints is the mortise and tenon. The thousands of years old joint is traditionally used in all walks of woodworking, like carcass construction, timber framing, chair making, et cetera because apparently it’s the strongest…or is it?

The great thing about modern machinery is that we do have a whole host of ways to accomplish this ancient joint. The most accessible way to create a mortise is with a plunge router, taking several shallow passes until you’re down to your desired depth. Clamp some extra boards to your workpiece to make your router more stable, and use a fence to guide you. There are fancier router base plate jigs you can make or buy to make things even more foolproof, but they’re not a necessity.

The matching tenon can be done with a hand held router, a router table, or my preferred way, a table saw. Better yet, a dado stack will make quick work if you’re batching out many of the same tenons. One tip I like to use is to size the width of the mortise so that your tenon’s shoulder height is the same on all four sides. Then, you don’t have to adjust the blade height when cutting the tenon sides. Sizing the width of a mortise The rule of thumb is to make the mortise and tenon’s thickness about one third the total thickness of your workpiece, but I have been known to go a bit thicker, up to one half the thickness of the piece…because for some reason I think I’m smarter than common wisdom.

I would love to test out the different thicknesses of tenons and how they perform, but that was outside the scope of this video. I could probably make a video about each joint and make a whole series of tests within each to determine the parameters that could potentially make the strongest version of that particular joint. But you might need to convince me to make that video if you want to see it.

I’m not gonna lie, it’s definitely more work to do a mortise and tenon over the miter or some other joints that you’ll see later, like the bridle joint. So what do you actually gain with all that extra effort? Strength?

Indeed! You do! It averaged out at 335 pounds! Not too shabby. And if you want a joint that looks about as innocuous as a butt joint, then the mortise and tenon is the way to make an extremely strong joint without anyone knowing that you put a considerable amount of effort into creating it. And since no one really knows how much effort woodworkers tend to put into anything we create, it’s really the ultimate woodworking joint.

The strength of each joint is interesting, and it’s cool to know some numbers behind the joints that we use. But realistically, the splined miter, the mortise and tenon, and the other joints are all more than strong enough for most furniture applications. I recommend trying all the joints just ‘cause, y’know, woodworking is fun.

Half Lap

The half lap is like the handshake of woodworking joints. When executed right, it’s strong, firm and instills confidence. But when it’s done wrong, it’s weak, clammy and a disappointment to your family name. Half lap joint There are so many ways to cut a half lap it’s bonkers, but I like doing it on a table saw. If I’m lazy, I’ll use a regular blade and nibble away. If I’m feeling fancy, I'll switch to a flat top grind blade for a smoother result (that no one will ever validate me for). But if I’m laying down legions of laps, then a dado stack is perfect.

Half laps are not just limited to joining two pieces together into an L shape, but they can also make an X and a T. And creating angled joints is easier with a half lap than many of the other joints I’ve talked about thus far. Therefore, the half lap is more versatile than many give it credit for.

One trick to nail the correct thickness for your half lap is to roughly put your blade to just under half the thickness of your workpiece. Take a scrap piece of the same thickness, then run it over your blade twice, flipping it to the opposite side so you’re just left with a thin bit. Then, raise your blade up a little, and make the same two passes. Keep repeating this until the thin little bit just about disappears. When that happens, that’s the right blade height.

When I snapped the half laps, it made a loud bang every time and felt like it took an enormous amount of pressure to break it. It averaged at 509 pounds of force to break it, which is insane. It’s one of the easiest joints to pull off and it beat the heavyweight champion of the world, the mortise and tenon? Keep in mind that the glue surface area of a half lap is about the same as a mortise and tenon that's half the depth of the workpiece.

Bridle Joint

Well cheese whiz! If a half lap is that good, then a whole lap must be even better!

In case you didn’t know, there’s no such thing as a whole lap, but there is the bridle joint. What is the bridle joint? It kind of looks like what the baby of a mortise and tenon and a half lap might look like if they consummated a marriage. And I would say it’s almost as easy to make as a half lap, and definitely easier than a mortise and tenon.

The trick is to use a sled similar to the one you used to make the splines for miters. In fact, I did use the same jig, but modified it to work, because I was too lazy to make another. The brilliant thing about the bridle joint is that you only need to set this up once to cut the joint for both pieces, unlike the mortise and tenon. Cutting bridle joint on table saw Just like the half lap, the bridle joint works well for angled joinery too. You just have to ensure you can safely angle the workpiece on your sled. They look great in a mid-century modern setting for those angled apron to leg situations.

So since this joint is like two half laps put together, and therefore twice the glue surface area, shouldn’t it be twice as strong as the half lap?

The bridle joint came in at 542 pounds. But compared to the half lap, it’s certainly not twice as strong, only just a little bit stronger. Compared to the mortise and tenon however, it’s quite a bit stronger, even though they do resemble each other. This shouldn’t be too surprising as there is about twice as much surface area in the bridle joint as there is in this mortise and tenon, but this was about as big as I could make it with a ¼” router bit.

Thoughts on Results and Conclusion

Of note, the test joints I used for this were all the same size as the joints I did for my previous test with pocket screws, biscuits, dominos and dowels. I used the same species of wood, the same glue, and I had the jack the same distance away from the joint. The splined miter, the mortise and tenon, the half lap, and the bridle joint are all stronger than any of the joinery systems from the last video.

You’re probably wondering about all the other types of joints out there: dovetails, rabbets, box joints, and the list goes on. I use these joints for situations like drawer boxes and wall-hung cases, so I actually made them and got started testing them, and then quickly found out that I couldn’t break them the way I wanted. I decided to break the video in half instead.

I’m sure there’s hundreds of other joints too, but I wanted to start testing some of the most popular ones for the average home hobbyist woodworker that can be done with either a table saw or a router.