Warped Top!

[Josh Bowman]

My nephew made us a flat screen tv cabinet....or at least almost did in his HS shop class. The cabinet still lacks doors and a few details, it also does not have a finish. It's made from white oak. It set in my shop for a month and the glued up top warped some. I decided to just let it sit and watch it. The top has gotten better since it's gotten cold out but it's still not flat. Now for the advice. It's about 3/4" x 60" x 20".
Should I saw it down the center of the warp and flip one side and reglue to reduce the warp.
Should I try planning and take a chance on making it to thin.
I saw an article that said put the cupped side down in the grass on a sunny day and that would correct it.

[Julian Nicks]

I would try putting a few cauls and clamps on it to straighten it out. I think your main problem it that it is too humid in the shop, and the moisture is making the top move on you.

[george wilson]

Wet the CONVEX top,counterintuitive as that sounds. Then,let it dry. Sometimes,for an extreme warp,wet the convex side,cover it with plastic for several days,periodically re wetting it,then finally take the plastic off and let it dry. This should be done INSIDE your house. ONLY wet the convex side.

HOWEVER,since you have had it in your shop,first do nothing except bring it into your house for a few weeks first,and see if it goes back flat first.

[harry strasil]

I was the one who made the grass post, but, in this case I am +1 with George, you do not specify your location so we are kinda in the dark a bit.
I am also curious as to the grain oriantation of the glued up boards in the top.

[Frank Drew]

Wet the CONVEX top,counterintuitive as that sounds. ONLY wet the convex side.

George, this is counterintuitive, and I don't think I've heard it suggested before; isn't the convex side convex (outwardly curved) because, at least in part, it already took in more moisture than the other (concave) side, causing the cells to expand thus creating the outward curve? I'm confused.

[David Keller NC]

Uh - Josh, you can definitely take the warp out by wetting the wood, but you want to do this on the concave side, then fix it with battens and clamps, or by screwing it down to the case of the piece.

This is essentially the "wet grass" method. With this technique, the high humidity from the ground/grass and the drying effect of the sun on the convex side will bring a board flat (or make it cup the other way if left too long). Essentially, what happens is that the wood cells expand on the concave side by absorbing moisture, while the cells on the convex side shrink from being dried by the sun.

I use this technique frequently because I regularly work with very wide boards, but it does require that you immediately stack/sticker the wood on a flat surface and weight it down heavily and leave it for a few days so that it will take the "set".

[harry strasil]

Note, after it straightens out seal it. both sides.

[Josh Bowman]

I'm located in good old east TN. My shop is heated and has AC (I only use it when it gets to hot, but keep the heat set at 60 degrees). I really meant to get the top finished when I picked it up last spring from his school, but got busy with honey do's and driving myself into the poor house buying old tools! Anyway the 3 or 4 boards making up the top do alternate rings. I looked at it closely last night and noted it's only warped now about 1/4 inch on one edge. The humidity has really dropped since the last rain and it's helping.
Thanks for all your comments. I'll get on the stick when I get the warp out and seal it on all sides.

[Frank Drew]

When and if the panel finally does come flat, do as Harry says and apply the same amount of finish to both sides; if you skimp on the underside it could make it more prone to take up moisture, which could lead to warping all over again. You don't have to polish the finish as well on the underside, just be sure to put the same (or pretty much the same) number of coats on.

[Brian Ashton]

George, this is counterintuitive, and I don't think I've heard it suggested before; isn't the convex side convex (outwardly curved) because, at least in part, it already took in more moisture than the other (concave) side, causing the cells to expand thus creating the outward curve? I'm confused.

I can see what George is saying about wetting the convex side. If you try to view what is going on a the cellular level it makes sense. But I think you would need to clamp cross pieces to the board to flatten it for the process to succeed.

If you force the board flat first with cross pieces and then introduce stress to the cells of the wood in the form of water (which will expand the cells) what would happen is the cell walls, in effect, would start to fail and or deform slightly as each cell "fights" with the surrounding ones for space during expansion. As the wood dries (to the touch) they would be more inclined to hold that shape as the cell wall has hardened again. If you then released the cross pieces, the side that was soaked would then shrink a slight bit more as the piece dried completely. Which should pull the board even more, so it should come out fairly flat.

Soaking the concave side works but it leaves the cells intact and it would be possible that the board could warp again. If you use the cross pieces to hold the shape after wetting, as the board dries the cells would tend to pull away from each other as they shrink during drying.

[Josh Bowman]

I can see what George is saying about wetting the convex side. If you try to view what is going on a the cellular level it makes sense. But I think you would need to clamp cross pieces to the board to flatten it for the process to succeed.

If you force the board flat first with cross pieces and then introduce stress to the cells of the wood in the form of water (which will expand the cells) what would happen is the cell walls, in effect, would start to fail and or deform slightly as each cell "fights.

Thanks for all the help. I've done it on the other side, but it does not hold the board flat after it redries. I've never tried it this way by putting water on the bowed side. It does make since, has anyone done this? Does it leave the surface rough or effect anything? I'm willing to try in the name of Neanderthal science! (can I do that?...do Neanderthals have science?)

[Ted Jay]

I can see what George is saying about wetting the convex side. If you try to view what is going on a the cellular level it makes sense. But I think you would need to clamp cross pieces to the board to flatten it for the process to succeed.

If you force the board flat first with cross pieces and then introduce stress to the cells of the wood in the form of water (which will expand the cells) what would happen is the cell walls, in effect, would start to fail and or deform slightly as each cell "fights" with the surrounding ones for space during expansion. As the wood dries (to the touch) they would be more inclined to hold that shape as the cell wall has hardened again. If you then released the cross pieces, the side that was soaked would then shrink a slight bit more as the piece dried completely. Which should pull the board even more, so it should come out fairly flat.

Soaking the concave side works but it leaves the cells intact and it would be possible that the board could warp again. If you use the cross pieces to hold the shape after wetting, as the board dries the cells would tend to pull away from each other as they shrink during drying.

Charles Neil addresses this issue in one of his videos to relieve the stress of the wood to make it lay flat by cutting kerfs and adding splines...
http://charlesneilwoodworking.com/ca...ideo=uncup.flv