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Here we go again.
She blinded me with "science"!!
Yep, here we go again. Sound scientific testing proves dogma wrong. Thousand of people claim this isn’t for the “real world” or it isn’t tried and true and fail to advance in their knowledge of woodworking. I wish some of the authors at fine woodworking would realize they continue to advance false information and stop pushing these myths, but it will never happen. I assume the regular experts will chime in as well.
This is a well-conducted study.
Everything he says in it is true.
The problem is that situations where this is remotely relevant are not appropriate for butt-joints. They fail not because end-grain glue joints are weak - as the author states, they are actually the strongest glue joint, but because the wood is so strong that it is able to apply sufficient leverage to break the glue before the wood itself breaks.
Isn’t it also a wood movement thing? I’m working on a blanket chest lid. It has molding around all four edges. The front and back (long grain) molding is attached with glue only, but the author has the molding on the side edges slide on dovetail keys, with glue only at the miters. I assumed it was because the direction of wood movement is such that glue-only on the side edges would ultimately fail. If that’s not the case, it would be good to know, lol. The molding has been the most challenging part of the project thus far.
Yes, the dovetail keys are so that the lid can move, while the cross grain moulding will not. It's an elegant detail, and you'll be glad you did.
The "study" falls into the category of "interesting but useless" and does not test the strength of glued wood joints. The comparison of a long "side grain" offcut and long grain butt joint broken under finger pressure proves nothing.
The only takeaway is that there may be some small value in adding glue to the shoulders of M&T joints. Build yourself a dining table & chairs with this "method" and let us know how it works out.
Agree - however it is really good evidence that end-grain glue-up is not in and of itself weak, it is simply that the situations in which it can be used are such that the glue is insufficiently strong to support the load.
If someone ever comes up with a glue that is stronger than long-grain wood in tension or flexion then I'm sure it will become relevant!
Should people stop saying 'end grain glue-up is weak'? It is untrue, but IMHO useful as it directs beginners away from making mistakes in construction. As you say, I doubt a butt-joint chair would support my 100Kg butt for very long!
When I first started learning about serious woodworking I was taught (by really fine woodworkers that I will never equal) two basic lessons. One is that end grain does not glue well. That turns out to be wrong. The second lesson was that the best joint is one that doesn’t need glue. That insight is true as ever. So you could build a picture frame or a jewelry box with unreinforced glued-up miter joints and not worry about it. (To be honest, I still spline my miters even though it seems silly now.) But no one would build a chair relying on glued butt joints, and the video doesn’t suggest that you do. The real strength of wood is in its long grain and that is a principle that you’d better understand if you build anything meant to hold a human being.
I would not stop splining the mitres.
All this shows is that end-grain joints are stronger than side-grain joints, but the force-per-unit-area bearing on a mitred corner can be enormous (say if the box is dropped) and this is often easily enough to break a joint.
End-grain glue-ups are inherently weak; not because the joint is weak, but because the joint is very small in proportion to the forces acting upon it and it is thus easy to fracture the glue. This is exacerbated by minor imperfections in the joint too - many mitre joints are not exact, and this further reduces the glue area in the joint.
Exactly, in fact we still do not know which glue joint is stronger since the wood fails first in the long grain glue up under a bending moment. The surface area is the real factor here and if we were to glue panels from wood with the grain running at 90 degrees from the long dimension, we would need to joint and plane end/side grain, quite unlikely. As for joining sticks, there is the scarf joint and a better comparison would be between the scarf and butt joints.
Of course movement over time is an issue, and, yes he didn't test actual butt joints in use, or mitered end grain joints. He pretty clearly wasn't testing any of those. It was strictly a test of the strength of glue + grain orientation. No recommendations or suggestions to change joinery. Just addressing something I've heard since the beginning - gluing endgrain to endgrain makes a weak joint. Now, apparently, not so weak. Changing anything I do, no.
https://www.youtube.com/watch?v=Fuvq0FDsUC0 - a very professional answer.
Well, there goes 4000 years of joinery ................
My two cents as I have posted already on other forums.
This is just bad science.
“The wood always splits before the glue fails”.
What this should tell you, is that the breaking strength of the glue joint is higher than the breaking strength of the wood in that orientation (side grain) which is x,
”On average, end to side joints were about 20% stronger than side to side."
X + 20%
“End grain joints were the strongest joints of all”
There is no way to know if end grain joints are strongest due to the fact that the side grain test and the end to side tests both failed before the actual joint strength could be measured. All you know for certain is that end grain joints fail at y. You can not claim to know or declare which is stronger, since in two of the three tests to be compared, the testing material routinely fails before a strength measurement of the glue joint could be taken. All you can prove, is that wood glue is stronger than x or x + 20%.
You could say end grain joints, y are stronger than x or x + 20% but that’s it. Anything else is pure speculation.
There is no myth