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I have these 9”-wide, 3/4”-thick pine panels from the bigbox store that i would like to make into a carcass with dovetails.

Such panels commonly exhibit some cupping, but have some spring into them, and can typically be flattened with clamp pressure.

Would they stay flat once joined with dovetails? or does stock need to be absolutely flat from the start?

three panels with edge grain up

Photo shows three panels with varying amounts of cupping. A second clamp, if placed in the center, makes them flat again.

  • I think this is a subjective thing unfortunately, because obviously some people are going to be all, no-you-can't-use-them-you-have-to-use-stock-that's-absolutely-flat. So, judgement call, I think you should be fine using it, although it would be best if you can remove the cupping prior to use if poss (even if this would be temporary if the boards were susequently left unused). BTW ever checked, does the cupping ever go away on its own with better storage? – Graphus Mar 26 at 6:26
  • I tried sprinkling water on the belly-side of the boards, and clamping them against thicker material in storage, but the boards have a mind of their own and spring back. Even when I select flat boards at the store, the stresses shift when I cut them to length and it's hard to predict how they'll react. It's a crapshoot with these panels. I've tried planing the warp/cup out before, but these panels are a bit more stable with more thickness. – ww_init_js Mar 26 at 6:47
  • Sprinkling with water isn't enough for this kind of thing, the entire face needs to be wetted for the effect to work. It's a bit of a "gulp" moment the first time you do this (because, like, you're not supposed to wet wood!) but it can work, albeit temporarily in some cases! – Graphus Mar 26 at 7:07
  • i also realized after writing this that I may have sprinkled the wrong side of the board! (how to fix warped cutting boards). – ww_init_js Mar 26 at 16:40
  • <doh> I read you'd done the bellied side and it didn't even register. I used to get confused which side to dampen and finally got it firmly in my head — the water seeks to expand the shrunk side, and as it's fairly easy to visualise which side of the board has shrunk I don't make the mistake any more. Unless I'm tired. Or not paying attention. Er, I mostly don't make the mistake any more. – Graphus Mar 27 at 6:08
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My rule is to use it if it can be flattened with no more than moderate hand pressure. Dovetails in particular are forgiving, because the joinery forces pieces into contact along the entire joint line. The wood will continue to move over time anyway. Also, just by looking at the ring orientation, these pieces are going to bend that way.

You'll want to be careful with layout - best to clamp the boards flat, so that when you mark across the thickness (ie, on the end grain for tails, presuming tails-first) you are marking square across. If you're using a machine jig, make sure they are clamped in with enough pressure to stay flat during machining.

Finally, perhaps most importantly, orient the boards in the joint so that the ends will tend to cup into the joint. Oriented the other way, the ends will eventually show gaps. As i mentioned above, the joinery itself will keep the middle part tight. This means that heart side should face out of your box/drawer/assembly.

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