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overview of joint

I am fixing a bench and came across the above mortise and tenon joint between the foot and the vertical support (2 actually, one on each support). Quite clearly, someone has messed with this joint in the past cutting down the tenon so that it is about 1-1/4” too short on its length and 1/2” too short on its depth (they also added a screw into the end grain of the tenon, presumably because the joint wasn’t strong enough after they cut down the tenon).

Obviously, I have to fix this in putting the bench back together, but I’m not sure if I should approach it as adding to the tenon or filling the mortise to make them match. Which is the better option, or is there some other way that I haven’t thought of?

mortise depth of mortise depth of tenon

Edit in response to comment asking about tenon thickness: The thickness of one tenon is what I’ve always thought is perfect: dry assembly requires no persuasion, the joint holds together by friction alone against gravity, and yet can be shaken apart with one good shake. The other tenon is 3 sheets of copy paper shy of that point (i.e., by placing three sheets of paper alongside the tenon I can get to the same degree of tightness).

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    Welcome to WSE. How snug is the fit between the mortise and tenon across the thickness of the tenon? IF it is snug you should have plenty of contact between the two pieces for a good glue job. – Ashlar Jul 5 at 3:20
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    Tenons shorter than the mortise are not just commonplace, they are the norm. It is far preferable to a mortise that fits the tenon exactly (no room for glue to be pushed into) or worse one that is even a tiny fraction too shallow of course. What matters for strength here is primarilyy the tightness of the tenon is its mortise. If the fit is tight enough that a good glue joint can form then you're fine really, just glue together with PVA. But reinstall the screw (and maybe add one more) for security if you like. – Graphus Jul 5 at 7:49
  • You can thicken the deficient tenon by gluing on a piece of wood veneer or two to get it to the correct thickness. – Ashlar Jul 5 at 23:53
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    *"One tenon is the perfect thickness (dry assembly without persuading, friction holds against gravity, and a single shake suffices to separate the two pieces)."8 That's not actually a perfect fit, that's loose — tenons should require being at least tapped home with the heel of a hand, but more commonly will require a mallet to seat them. For structural integrity I'd glue that with epoxy. The other one is way off obviously. You can add veneer or plane shavings to build out the tenon to thickness, but again you can use epoxy to glue it as it stands. Thicken the epoxy with wood dust if needed. – Graphus Jul 6 at 8:40
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    Many of these comments should just be Answers so we can kibitz about them in context. – jdv Jul 6 at 18:58

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