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Thread: Devil in the details.
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25th December 2008, 05:59 PM #1SENIOR MEMBER
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Devil in the details.
The current Fine Woodworking has a comparison of the strength of 15 common framing joints. They were all tested to breaking point. The half lap and bridle joints came out strongest, with M&T and floating M&T very close behind.
That surprised me, but it makes sense as they explain that the glue faces of the half lap and bridle joints get clamped, whereas a M&T joint though squeezed up does not actually get any clamping on the glue faces.
But the detail that always worries me is how tight a M&T should be for optimal strength? If the side pressure of clamping a half lap or bridle is important, the side pressure created within a M&T by the tightness of fit must be highly relevant. I have varied between "tap in with a mallet" and "slide in neatly without it rattling" but I have never come across any actual test comparisons of goodness of fit.
Can anyone clue me in please?
(Note, dowels, dominos, and biscuits were okay for most applications but when they failed it was usually the stile that split down the grain at the point where the dowel or domino ended. The implication here is that for strength make your dowels, dominos, biscuits, and floating tenons as long as you can.
It is a good article and the author is careful to point out that there are criteria other than sheer strength, such as speed and esthetics that are considered in joint selection.
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26th December 2008, 06:42 AM #2SENIOR MEMBER
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It would have been interesting to see the results with the force applied the opposite way,as in practice both apply. But yes a good article. Sorry I can't help with tenon fit, a "neat, push fit" seems a bit vague even to me.
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26th December 2008, 09:18 AM #3
I belt my M&T joints together with a leather mallet and I make sure the friction is predominantly on the wider cheeks and not the narrow edges. Anything less and you're relying on glue alone for joint strength which is a fallacy.
With antique furniture that was built pre-glue (or just didn't employ glue), one usually needs to use considerable force to dissasemble M&T joints. Glue is the split pin of the M&T joint..
I know you believe you understand what you think I wrote, but I'm not sure you realize that what you just read is not what I meant.
Regards, Woodwould.
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27th December 2008, 04:12 PM #4SENIOR MEMBER
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Thanks Pommy and Woodwould for that info. When I make my M&T very tight I worry about starving the join of glue. My imagination of how the glue works is that it soaks between the fibres if both sides of the joint, swells the wood a bit, and then solidifies so that the wood fibres stay in the swollen positions. But in view of your experience I think I shall aim for a bit more tightness than I have been making in the past.
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