Any suggestions on fixing this? I cut the mortise about 1/16" too large in both dimensions. :(


Enlarge the tenon
Oh I wish I could leave it at just that one sentence ^_^ But it's not obvious how you'd do that.

Usually the error in an undersized tenon is quite small and you'd glue slips of veneer to each side that needs it (often it's the cheeks only that need attention). Here you'll need to use thin slips of wood that you cut yourself. When doing this ideally you're supposed to match the grain orientation of the tenon closely but it's not that vital at this scale unless you were using a completely different wood.

Glue the packing pieces to the tenon firmly and wait for the glue to harden, then check fit and adjust if necessary, then glue the M&T as normal.

Loose fit? No problem, glue with thickened epoxy
This sounds sketchy but actually it's a perfectly reasonable way to go. Epoxy is one of the few adhesives that can bridge gaps while still producing a strong joint and if you thicken the epoxy with a fine powder (wood dust is usually used but there are other options) you can get it to a consistency where it stays where you apply it and doesn't slump from the pull of gravity.

The usual aim point given for the consistency you'll need here is similar to peanut butter1..... and if you use wood dust as the filler the mixture often looks disturbingly close to peanut butter!

Next time
For next time the obvious reminder is to mark out more carefully but you may have had the problem where your marking out was on the money but the walls of the tenon moved back unintentionally as you cut due to how you're chiselling, which is a common enough error when starting out2.

Now the best thing is to try to avoid this as you work, by working more carefully and stopping to check your dimensions every now and then, but there's a good workaround and that is cut your mortises first and then size the tenon to match. This way you'll never end up with an undersized tenon again. And usually it's much easier to cut a tenon to match a mortise than to cut a mortise to match a tenon anyway.

1 What has peanut butter got to do with epoxy resin? on Epoxycraft.

2 Normally when a mortise is sized to the width of a chisel you only really need to worry about the two ends, not all four sides as here.

  • 5
    Thanks! For some odd reason I was cutting the tenon first, but it makes a lot more sense to do it the other way. And, yes, my chiseling skills are something of a work-in-progress. Oh, well - no one ever got good at anything by giving up or paying someone else to do it. – 3Dave Jan 24 '17 at 17:56
  • Welcome! Everyone's chiselling skills were a work in progress when they started, don't let them tell you any different. And like anything it's only practice, practice, practice that'll improve them. You might know this already but because you're working in softwood one of the odd things is that to get good results you actually need sharper chisels than if you were working in many hardwoods, even oak is more forgiving despite being so much harder. But you seem to be doing fine as far as honing goes, there's no obvious torn grain in the mortise that I can see. – Graphus Jan 24 '17 at 22:21
  • Thank you for the encouragement. I started the mortises with a router then went around and squared them up with the chisel. My Big Box special chisel isn't exactly the greatest - but I'm figuring it out gradually. It's not often I get to be a wanna-be artist, engineer and mechanic at the same time. :) It seems like working with a denser wood or something with smaller fibers would be easier, though obviously more expensive. Need to find a saw mill withing driving distance of North Dallas. – 3Dave Jan 24 '17 at 22:39
  • Also, I wish I could give you about 10k points for the peanut butter. Yet more tasty-looking toxic content in my shop... – 3Dave Jan 25 '17 at 0:22
  • Re. your big-box chisel, there's actually a decent chance the steel is quite reasonable these days. Many cheaper chisels are made from the same CrV steel alloy as much more expensive offerings but you're not paying a premium for nicer handles and the name printed on them! Sometimes they're not heat treated as well, but there's usually not a lot in it (Narex v. cheaper chisels for example, Narex will often lose in a value-for-money comparison because they're just not that good {despite their fanboys}, and many users don't care for their handles). – Graphus Jan 25 '17 at 9:01

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