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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.

Follow-up:

I gave it a go with the panels, based on feedback here. And it's totally fine, plus or minus some adjustments. This was my first attempt at dovetails. Here's a few things I'd not realized until I had to actually do it.

0) A bit more planning on my part would have revealed that the pin board (which was a glue-up panel) also had some cupping in it. So I had to clamp the two boards flat simultaneously while scribing my pin board on the tail board, which did complicate the clamping and marking situation. The tail board was clamped flat with a vise (a workmate), and I was holding the pin board vertically, with a 2x4 clamped on the piece to keep the pin board straight.

1) Depending on the level of cupping in the grain of the tail board, you end up with somewhat weak tail corners. I unfortunately didn't pay attention to that when I did the layout. I designed pins first, but didn't double check where the pins landed before committing to their final shape. I also should have pared more carefully around these fragile corners.

corner chips missing Photo shows two broken tail corners, right on the growth line. I tried glue, but it broke once more in a different spot, then I just accepted my mistake.

2) I put the heartside facing outwards of the box, as was recommended. But I still ended up with a minute gap. I've shone light through the gap here. There is some spring still in it and it won't rest at the bottom without pressure -- maybe my joint can be cleaned up a bit more. I feel it will probably vanish, with clamps and glue-up.

minute gap at the bottom of tail board Photo shows a minute gap at the bottom of the pin board.

And the overall look:

enter image description here Photo shows the overall look, before gluing and planing finished join. A few gaps which I'll try to fix using slivers (Full size).

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  • 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, 2019 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, 2019 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, 2019 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, 2019 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, 2019 at 6:08

1 Answer 1

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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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  • Thanks for this answer. I've given it a go and added follow up pictures. I've put the heart side out. I still have a small gap, but it looks more or less of the same thickness across, and the boards are flat. It needs tweaking now, but I think it worked!
    – ww_init_js
    Jun 2, 2019 at 2:13
  • nice work. yeah those gaps should go away upon clamp+glue. Looks like your chisels are nice and sharp :)
    – aaron
    Jun 3, 2019 at 12:33

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