I've repaired a lot of commercial chairs (not antiques). Almost always, it's the joint at the back of the seat where the seat meets the upright of the back. And the reason for failure is not glue - it's wood failure. The joint is almost always two dowels. When you pull the joint apart, what you see is wood still stuck to the dowels. The glue on the dowels held just fine, but the wood in the back rail fractured because of the stress on the joint. There just wasn't enough glue surface area with two dowels.
The goal in repairing those chairs is not to make them last forever - it's to make them last until the owner decides to remodel and throw the old stuff away.
Because of the failure mode, the holes for the dowels will be too large - you can't just stick the joint back together. The easy way is to drill out the holes on both pieces of wood and put in a couple of larger dowels glued with epoxy.
A better approach is to put in a loose tenon, maybe using a Domino machine to make the mortises on both pieces. A proper sized tenon will have more long-grain-to-long-grain surface area and will be stronger.
But no matter which repair technique I used, I have not had one come back yet and that's a lot of years.
Mike
Last edited by Mike Henderson; 05-13-2024 at 12:36 AM.
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