I just came across this and found it fascinating. This really is a must-watch for DIY guitar builders and woodworkers in general. Audio quality isn't the best I'm afraid, the vocals are a bit muffled, but my tired old ears could still make it out.
Main results are
1) End grain-to-end grain glue joints are the strongest type of joint
2) The glue is not always stronger than the wood - it all depends on the grain direction at the joint.
Lots of 'but what if...' questions you can ask, so it's not fully a comprehensive result. The tests were all done with the wood under compression. No tests under tension (pulling the joint apart from the ends), or shear (twisting the joint). I wouldn't expect the results to be significantly different with regards to the glue strength, but the wood strength figures could change a bit.
Interesting video, although his conclusions from the test should be inconclusive for comparison of end grain glue joint versus side grain glue joints simply because he was unable to cause the side grain glue joint to fail.
Because the wood fails prematurely along the grain lines, the joint cannot be tested for comparison. The results should have been that glue joints are stronger than cross grain wood strength, but weaker than along the grain wood strength. But it was fun to watch.
It would be interesting to test under tension, so see if it is possible to test the joints without the wood failing in either direction and truly test glue joint strength.
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