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I resawed a 2x4 I've had in my garage for a couple years down to about 3/8th in strips to make the following:

finished

After gluing the panels togerther, I glued and screwed support strips to the back hoping to avoid what happened: back

It's been a few days now since I Stained it and it's now warped (and seems to be getting worse:

warped

The support strips just bent along with the rest of it.

Did I not wait long enough during various stages of the project (only about a week from start to staining) or was my decision to use garage 2x4 the problem?

  • Construction-grade 2x4s, even seasoned ones like yours, are cheap and nasty and not meant for this sort of thing, in my opinion. – HemiPoweredDrone Jul 27 '16 at 4:40
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The strips you secured to the bottom are the cause of the warping. The main boards can't expand and contract because they are fixed to the strips at a few points. If the boards were just glued to each other then it would expand/contract as a single panel. This is the same problem you face with tabletops, hence the need for connections that allow movement.

Also, not sure if you did in this case, but alternating the boards up/down/up/down will help prevent this type of warping as well.

At this point I would try removing the strips to see if it flattens out. If it does, and you wanted to keep the strips for support, the solution would be to cut keyways (or large holes) where the screws attach so that the panel can move relative to the strips.

Placing cauls across the panel while you glue and clamp it will also help keep it nice and flat as the glue dries.

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  • This seems to be the exactly correct answer. It took some work but I broke off the support strips and it instantly popped back to almost straight. Made 2 more supports and secured them only with a couple screws and washers so they have room to expand/contract. – kinar Jul 27 '16 at 3:49
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    @kinar, just to emphasise in case it's needed, the screws going into the underside of the panel need room to move with expansion or contraction of the panel. So if you haven't done this already the screw holes need to be enlarged, usually they're lengthened to short slots. – Graphus Jul 27 '16 at 5:56
  • @Graphus i dont have a plunge bit for my router so i couldnt easily make slots. However, the holes are now oversized for the screws and they have about a quarter inch of space to move in any direction due to the washers. I'm thinking/hoping that should be enough. – kinar Jul 27 '16 at 6:03
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    @kinar, 1/4" to move could easily prove enough so I think you should be fine. You'll find out empirically if it's not :-) When you don't have access to a router you can lengthen holes into short slots with a drill bit, by carefully leaning the drill side to side as it spins (assuming a power drill here). This is not recommended practice as you can imagine, but with care it usually works fine, esp. in softwoods. – Graphus Jul 27 '16 at 6:08
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The panel is curving because the support strips running perpendicular to the panel boards are flexible. The panel boards have dried and shrunk while the support strips remained unchanged in length. If the support strips were stiffer, the panel would not curve, but instead, the panel boards would be splitting. It the ambient moisture conditions were different (i.e. high humidity) the panel boards would have grown in width and the curvature would have been reversed.

This is indeed the classic table top problem.

If you had simply skipped the use of glue to make the panel, and had simply screwed the panel boards to the support strips (with a small space between boards) your panel would have remained relatively flat.

The panel might have remained relatively flat if you had simply omitted the strips, but you would have been challenged to have a flat panel just due to the vagaries of gluing up a panel.

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  • This makes perfect sense. I even just watched a YouTube video about this less than a month ago but didn't think about it when making the panel. I doubt (or at least hope) I never make this mistake again. Accepted the other answer simply because it was first. – kinar Jul 27 '16 at 3:52

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