Why is a floating tenon weaker than a tenon?

[Doug Garson]

While many of the tests give a reasonable comparison of the strength of the joints, the flaw is that the mode of failure in most cases is not a single overload but rather dozens, hundreds or perhaps thousands of cycles of loading and unloading combined with expansion and contraction due to seasonal humidity changes. Running a set of tests to mimic that type of cyclic failure would be extremely difficult.

[Carl Beckett]

I tend to make my mortise slot longer than my tenon is high. Had a couple that were tight, towards the end of a stile, where the tenon expanded and popped a section out of the end of the stile.

Less likely to happen with loose Domino style tenons.

Really not sure why, if apples and apples, one would be stronger than another other than dissimilar wood types. But I agree it would be nominal and most of the strength will be determined by geometry/size/thickness.

[Edwin Santos]

It's not. All those videos are flawed.

Agree, and I'd like to elaborate.
Every strength test video I have ever seen leaves out the single most important factor - the design of the project. In a properly designed assembly most elements are held in two different planes and load interdependent with other components. That's why it's called an assembly.
The difference between a properly made integral tenon M&T vs a properly made floating tenon M&T is splitting hairs, if there's even a meaningful difference. The difference between a well designed assembly and an open right angle is miles of difference.

The videos always involve an open corner or T joint completely exposed to worst kind of leverage, which they proceed to break apart and measure. How is this relevant in the real world?

There's also a question of whether stronger is better in a vacuum. Designing to a level of strength that's appropriate for normal use for the piece, plus maybe a little moving abuse, is reasonable. If the goal is to withstand thousands of pounds, a hurricane, or pack of rampaging gorillas, I'd say build out of concrete or steel.

Don't even get me started on gluing technique as a factor. Because it is.

[Edwin Santos]

I tend to make my mortise slot longer than my tenon is high. Had a couple that were tight, towards the end of a stile, where the tenon expanded and popped a section out of the end of the stile.

Less likely to happen with loose Domino style tenons.

Did the section pop out during assembly?
I may be thinking of a different issue, but I was taught to be careful about making a mortise and tenon joint too tight. Not only does it leave inadequate space for glue, but no way for air to escape. Think about a tight tenon entering a mortise like a plunger with nowhere for air to go. I believe the dominos have the crosshatch pattern on them for this reason. Same with fluted dowels. Some builders take a v groove gouge and cut a little relief in the tenon.

[Michael Rutman]

I agree that the Domino is plenty strong, I can’t imagine how much abuse I’d have to do to fail even with an undersized domino. I don’t do as much woodworking as the vast majority here but I’ve never had a domino actually fail and I’ve been known to use smaller than recommended dominos. Then again I don’t test my joints with car jacks .

I’m curious as to the reason those videos consistently show the domino fails first. Reading this I suspect their using a smaller domino than tenon. One other explanation was the end grain side started splitting, which pulled the domino out on the end grain side. My problem with that theory is the other videos that are common show the domino rip out of the side grain side pulling side grain with it.

It’s all theoretical anyway, the odds of my trying to cut another tenon when I own a domino is pretty slim.

[Prashun Patel]

Having one actually fail is one thing, but it does not take a lot of abuse to make one fail.

[Bryan Hall]

I can watch YouTube videos of it being tested and see it’s true, so I don’t doubt it’s true. I fully believe it’s true, I just can’t grasp why.

In every single test I see the wood on the mortise side rips apart before the glue. If the loose tenon pulled out I’d understand it, but that isn’t happening. If the glue failed, again, I’d understand it. I understand that the tenon side is going to be extremely strong, but again, even in a loose tenon that’s not the failure point.

For what reason is a loose tenon like a Domino weaker if it’s the wood itself that fails?

Just got home from an Egyptian exhibit at the Portland art museum. What joint held the sarcophagus together? Floating tenon and mortise. Looked a little loose after 3000 years but still functional.

[Warren Lake]

did they use a Domino?

got a photo, you mean it was a joint or just a spline to line a case up? this was posted not too long back and not a joint but a loose spline to line a case up. They did use mortise and tennon and dovetails I think the oldest I read of that stuff though were the Germans.

[Jim Becker]

Just got home from an Egyptian exhibit at the Portland art museum. What joint held the sarcophagus together? Floating tenon and mortise. Looked a little loose after 3000 years but still functional.

That actually doesn't surprise me...whether or not one has rudimentary or really nice tools, it's pretty easy and fast to make mortises on either side of a joint and fabricate a piece of material to fit in both simultaneously. For a container, this method works pretty well, IMHO.

There are so many ways to do jointery. Most methods, when done carefully, can yield more than acceptable strength, even if one might have an edge in extreme conditions.

[mike stenson]

By hand, it's faster to cut an integral tenon than a loose tenon. Easier too.