How to strengthen mortise & tenon?


Wood Basher
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I kind of wonder how accurate the figures from that U of W paper really are. The material properties of wood, even a single species, vary considerably from tree to tree and board to board. Compared to a more consistent material, like steel or aluminum, wood structures must be 'over-built' to the point that minor variances, like pinning a tenon, make no appreciable difference. Aside from that, I see draw-boring as a replacement for glue, not a suppliment. Or 'belt and suspenders' insurance against glue failure.

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With suspicion rather than knowledge, I don’t see that a dowel/pin adds anymore support to a tenon, especially if the tenon/mortise are tight. If not, then it seems that the pin only allows for a pivot point. Maybe if the tenon were wide enough to allow for two pins? I’ll take my chances with tight fitting joints and a good adhesive and only add the dowel if it makes it look cooler! 

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There is no question pinning add tremendous strength to a tenon.

TMK, draw boring was prevalent during the hide glue days, and back then not all hide glue was created equally, so insurance was needed.  In fact, many pieces of furniture were built with no glue at all - just drawbored tenons.

The only instance I use them is for breadboards (which aren't glued).

I agree with Coop^.  Modern glues are simply not going to fail - the tenon will break off first.  Movement within the joint can be in issue, particularly if the joint is under stress.  IMO it goes more to the tenon design, making sure the fit is just right & there are good shoulders, etc.  That said, there were no vacuums bumping in to legs back then either, maybe the hide glue joints might have only lasted 5 years instead of 200 LOL.

In light of this, however, I will often pin tenons, truthfully more for show than anything.

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