Strength tests for different joinery systems

This video compares the strengths of popular wood joinery systems including pocket hole screws, biscuits, dominos, mortise and tenon and multiple dowels.

http://ca.video.yahoo.com/watch/5415338/14263959

I note that all bar one of the tests failed at the glue joint. Whereas the domino test was a clear timber failure which seemed to originate at the depth of the domino. Interesting!!!

Take a look at the quality of the wood being used for the test pieces, where the failures occur and which company seems to be sponsoring the tests. Why do the pieces used to test the joints made with the D******x seem to be 'clear' timber while the rest have visible knots & twist in the grain?

I have much the same problem with some of the recent tests done by FWW - the timber used for some joints was of noticeably inferior wood, and guess which joints failed at lower than expected pressures?

Next time an Elephant sits on one of my Domino joined tables I will be very worried.:)

Seems to me that the positioning of the piston will test for resistance to shearing more than torque/moment force on the joint. I guess it's taking leverage out of the equation, but is the method of testing used in this advertisement the only type of force these joints will face?

Regardless, even the weakest joint here would hold up fine to normal use I think... :)

I'd like to know how many ppl put 5 x 2 inch dowels of that size joint, I would have used maybe 2, max 3.
And strength test are irrelevant, joints of that size dont have that amount of force being applied to them in real world situations.

Every now and then a newish member puts up results like these trying to perform a public service. Heart in the right place and all that. :)

But it always turns into a bun fight over everyone's "pet joining technique." Older hands just shake their heads and wait for the inevitable squabble. :D

Go for your life. :wink:

Any test should be repeatable with similar results if it is to be considered valid. This would show up whether the mortice and tenon joint only failed due to the wood and not the joint. It would also show some consistancy for the tendency of some joints to fail at lower pressures. If the mortice and tenon joint continue to fail only because of the wood, maybe a stronger wood to do this test might be in order or it would show that the characteristics of the joint assist in the wood failure with this type of joint. My two bobs worth.:D:D

SB