End Grain Glueups


Coop
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Thanks for sharing.  The guy did a nice job of presenting a lot of data in a simple, clear manner.  In a couple of decades I have not run into many conversations about end glue grain joints being "worthless".  Maybe I live a sheltered life :)

I have certainly read and watched plenty of articles and videos where the comment is made in passing that for M&T joints (as one example) the long grain glue joint is what is focused on.  Maybe comments like this have spawned an illusory truth condition for some people where end grain = bad.  If so, I am glad since it urged the video to be made and I enjoyed it. 

I got a kick out of the well presented results since they were unexpected.  It does not inspire me to start using butt joints in the middle of stretchers on my furniture however and I do not think that was the authors intent. Information that contradicts common knee-jerk conclusions are always entertaining and educational.  Thanks again!

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I think for the basis of the myth he explained at the end, we often suggest a half lap or similar to increase glue area. I don’t think it is unwarranted, because there is a factor he did not include. What happens over time with humidity releasing behind that end grain glue? Just a thought, not an expert argument. 

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Sorry, I see it but still don't believe it.  He hasn't made some break through.  If what he's "discovered" is real, the whole world of ww'ing, cabinet and door manufacturing would be rendered obsolete.

IMO the test is flawed because he is pushing down with a narrow piece of steel parallel to the fibers, which is going to break soft wood very easily even if its not glued (think karate class).  Compared to that, sure the end glue joint is stronger.

If you disagree, then just butt blue those cabinet doors & aprons to legs:mellow:.

Sorry, but I don't see Kreg, biscuit joiners, dowellers, Dominoes or mortising machines becoming obsolete anytime soon.....

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I think the information that is missed here is that the end grain to side grain while somewhat strong isn't weak because of the end grain but because of the very limited long grain support. The board is glued to a small strip of long grain that is connected to the leg with lignin bonds. These lignin bonds are easily broken as apparent in the video. The other aspect not shown is that this bond is highly susceptible to end grain run out.

What a M&T, Bridle, Halflap, joint does is connects the beam (apron etc) to the leg in a manner that eliminate the reliance on the lignin bond between wood fibers of the leg. The beam is connect to fibers that run the length of the leg, or maximize the amount of lignin bonds before grain run out so that the lignin bonds are stronger than the wood adjacent to the joint.

This is good information as it illustrates to me for the first time that the length of a tenon is more important that the width. It also illustrates how important grain run out can be and is another nod in the favor of rift sawn material for legs.

Wood movement isn't mentioned either. Differential movement could easily break an end grain bond without any stress being applied to the joint. If he let the samples go through 2-3 seasonal moisture swings would the results be the same?

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All I know is that miter joints on large picture frames will come apart over time, unless splines or keys or dowels or half laps or something like that was used to reinforce the joint. I think we've all seen that happening. A butt joint is going to be weak regardless of grain direction.

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I think what his research comes down to is that glue is stronger than lignin, and wood fibers are stronger than glue.  That does not mean that an end to side or end to end joint is strong enough for a given application.  Joinery does have to consider wood movement, for example.  And what classic joinery, like M&T, seems to do is get the the wood fibers to cross the joint and provide the strength.  I'm thinking a well made M&T is probably just as strong without glue as with it, it's just more likely to get knocked apart.

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I do segmented turnings after gluing up the individual rings I have to send them through my 16/32 belt sander I've never had the rings break apart all the pieces are just glued end grain to end grain and aren't structured until the segments are glued to each other in a brick pattern

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I'm glad to know that end grain to end grain glue ups are stronger than I thought, I'm still going to baby the process anyway. Thanks for sharing.  

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The end result is something we should all be doing anyway...make the JOINTERY hold the piece together, and use glue to hold the joint in place. The only stress on the glue should be in the direction the joint slides together, which, in turn, should be the direction least likely to be under stress in normal use.

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Ironically, this came to me at a semi-opportune time. I am building a sitting bench that after dry fitting, it is 2” lower than I would like. I was planning on adding a 2” block to each leg, end grain to end grain, reinforcing the joints with 1/4” ss dowels with epoxy as an adhesive. Wondering now if the dowels are really needed? Maybe better safe than sorry? 

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A few thoughts on the video:

  1. If the test is to determine which type of "glue joint" is strongest, I'd say the test results favor the "conventional wisdom."  The only glue joint that fails is the end-to-end.  For the other types up glue ups, the wood fails before the glue joint.
  2. I mostly build furniture, and I'm having a hard time coming up with an example of a situation where an end-to-end glue up is an alternative to a side-side or side-end glue up.  So, it seems like the comparison this guy is doing is something that never comes up in my world.
  3. In a situation where I might need to glue stock end-to-end to get components longer than the solid stock I have available, I'm still not going to use just an end-to-end butt joint - it will be a finger joint or a bridle or half-lap.  Although these weren't tested in the video, I have a pretty good idea how it would turn out.
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@Coop, I agree.  Nothing has suddenly changed in the world of joinery.  Except perhaps for our understanding of why things are the way we have observed them to be.  

With your sitting bench the grain in the legs runs up and down and given the wood's strength in that orientation the crossections have been sized accordingly.   So if you add length to your vertically grained leg with an end to end butt joint you will have a strong joint, but one that is probably not strong enough.

It's not that the glue is stronger than the wood, the glue is stronger than the lignin.  The wood's fibers are stronger than the glue.  Which is why most strong joints have wood fibers crossing the joint.

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On 9/7/2021 at 11:47 PM, Coop said:

Ironically, this came to me at a semi-opportune time. I am building a sitting bench that after dry fitting, it is 2” lower than I would like. I was planning on adding a 2” block to each leg, end grain to end grain, reinforcing the joints with 1/4” ss dowels with epoxy as an adhesive. Wondering now if the dowels are really needed? Maybe better safe than sorry? 

Try this Japanese joint :ph34r:

 

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