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Thread: Why is a floating tenon weaker than a tenon?

  1. #16
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    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.

  2. #17
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    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.

  3. #18
    Quote Originally Posted by johnny means View Post
    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.

  4. #19
    Quote Originally Posted by Carl Beckett View Post
    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.

  5. #20
    I agree that the Domino is plenty strong, I canít imagine how much abuse Iíd have to do to fail even with an undersized domino. I donít do as much woodworking as the vast majority here but Iíve never had a domino actually fail and Iíve been known to use smaller than recommended dominos. Then again I donít test my joints with car jacks .

    Iím 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.

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

  6. #21
    Having one actually fail is one thing, but it does not take a lot of abuse to make one fail.

  7. #22
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    Quote Originally Posted by Michael Rutman View Post
    I can watch YouTube videos of it being tested and see itís true, so I donít doubt itís true. I fully believe itís true, I just canít 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 Iíd understand it, but that isnít happening. If the glue failed, again, Iíd understand it. I understand that the tenon side is going to be extremely strong, but again, even in a loose tenon thatís not the failure point.

    For what reason is a loose tenon like a Domino weaker if itís 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.

  8. #23
    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.

  9. #24
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    Quote Originally Posted by Bryan Hall View Post
    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.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  10. #25
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    By hand, it's faster to cut an integral tenon than a loose tenon. Easier too.
    ~mike

    life in a mud hut

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