Interesting video. But I think one should be very cautious while interpreting these results.
We all know that wood is very anisotropic with exceptional strength along the grain and relatively weak in the cross-grain direction. Furniture design takes that into account and wooden structures critically depend on the high strength along the grain. End grain glue joint may be stronger than a side grain glue joint but it’s still much much weaker than unbroken wood along the grain. And that’s the critical point relevant for design.
In other words, gluing sideways to make a wider board does not affect the integrity of the material — it may even enhance it as most glues are stronger than wood in the cross-grain direction. But pieces glued end to end is substantially weaker than a long single piece of same dimension. Whether its stronger than a side-to-side joint (as shown in the video) is more of an academic curiosity.
Thank you for your point of view. I concur with your conclusions. I knew that some glues are a stronger bonding agent than lignin, but I never envisioned the real meaning of it, until I saw the experiments in the video.
As you wrote it is mostly an academic curiosity, but sometime also from absurd experiments our minds are stimulated. It is something nice to know…
This video has engendered lots of interest in the blogosphere, and some YouTube stars have commented and done follow ups to translate the info into real woodworking, including Rob Cosman, Stumpy nubs, and others.
Cosman analyzed common woodworking joints to see how they might be done differently or better by making up joints and testing them
A couple results were pretty surprising.
Absolute novice’s opinion.
The tests proved that the glue and materials break at the weakest point. Something that we all new.
End grain to end grain breaks at the glue point because that is weakest point. So if you glue side grain to end grain and the other end grain (20 mm long) to another side grain and perform the test the side grain will break before either glue joints and the end grain piece will never break.
This means in certain joints we could take advantage of this as Rob Cossman proved with his rebate butt joint (??).
So never glue end grains together to extend the length of a board is still valid as the glue joint is much weaker than the wood in that application as we designed that pieces dimension for lateral/tensile/load carrying strength which is much higher than lignin and glue.
However when gluing joints together and saying you don’t need to put glue on the end grains because end grain gluing is weak and not worth doing should perhaps be reconsidered and glue them anyway as it will improve the overall minimum glue strength (not joint mechanical strength) and might just close the joint lines better due to swelling of the wood.
Don’t you just love wood working!!
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