chest top warping


Just built a pine blanket chest and for the top joined three boards together. The Pine was kiln dried and now it is warping, the top is approximately 4' x 3' , any ideas how I can undo the warping?
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Nuke wrote:

Have you recently started using air conditioning, opening windows, or have you put damp items in the chest?
I'm guessing that this is a flat lid and the warping is a large scale cupping of the top. I'm also guessing that the lid is only finished on the outside.
If so, then the warping is likely to have been caused by a change in ambient humidity that has caused moisture to enter or leave the wood faster through the unfinished side. If so, it will correct itself if it is expsoed to a prolonged period of stable humidity.
Or, if the unfinihsed side of the lid is concave you you can carefully moisten it by wiping once day or so with a damp rag. If it is convex, you can carefully dry it as with a hair drier. You have to go slowly to avoid splitting the wood. You can also take the top off and lay it convex side up in the sun or on cement. The idea here is that the moister face of the llid has expanded more than the other making that side convex, so that you need to dry it, or moisten the concave side to even it out, or both.
When the lid is flat again, finish the inside just like the outside is finished and it should remain fairly stable. Wood finishes do not stop moisture from diffusing into or out of wood, they slow the rate of diffusion through the surface. That way the higher diffusion rate thorugh the bulk of the wood prevents the formation of a moisure gradient which is what causes major warping.
It also helps, when edge gluing boards to make a wide panel, to alternate the orientation of the cupping of the grain so that as one board cups up the adjacent ones cup down. That is, arrange the boards so that what was the bark side of the tree is down on one board and up on the adjacent boards. Like this:
unu
That makes for a panel with better overall stablity but limits your options regarding matching for appearance and control of tearout should you wish to plane the panel after gluing.
--

FF


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Nuke wrote:

Have you recently started using air conditioning, opening windows, or have you put damp items in the chest?
I'm guessing that this is a flat lid and the warping is a large scale cupping of the top. I'm also guessing that the lid is only finished on the outside.
If so, then the warping is likely to have been caused by a change in ambient humidity that has caused moisture to enter or leave the wood faster through the unfinished side. If so, it will correct itself if it is expsoed to a prolonged period of stable humidity.
Or, if the unfinihsed side of the lid is concave you you can carefully moisten it by wiping once day or so with a damp rag. If it is convex, you can carefully dry it as with a hair drier. You have to go slowly to avoid splitting the wood. You can also take the top off and lay it convex side up in the sun or on cement. The idea here is that the moister face of the llid has expanded more than the other making that side convex, so that you need to dry it, or moisten the concave side to even it out, or both.
When the lid is flat again, finish the inside just like the outside is finished and it should remain fairly stable. Wood finishes do not stop moisture from diffusing into or out of wood, they slow the rate of diffusion through the surface. That way the higher diffusion rate thorugh the bulk of the wood prevents the formation of a moisure gradient which is what causes major warping.
It also helps, when edge gluing boards to make a wide panel, to alternate the orientation of the cupping of the grain so that as one board cups up the adjacent ones cup down. That is, arrange the boards so that what was the bark side of the tree is down on one board and up on the adjacent boards. Like this:
unu
That makes for a panel with better overall stablity but limits your options regarding matching for appearance and control of tearout should you wish to plane the panel after gluing.
--

FF


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Add hardwood cleats under the lid. - Elongated screw holes, glue only the center board. Dave
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If this is "new" pine you'd be hard pressed to keep a single one of those 3 foot-wide boards flat let alone all three flat as a unit. I'd be inclined to rip the top into at least six pieces, nine wouldn't be too many, and glue it back together. The ripping would relieve some of the stresses in the wood and may help keep the top flat. Additionally, cleats on the bottom side of the top would help--screwed through elongated holes or attached via a sliding dovetail across the width, unglued, would be two approaches.
John
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To stop that on my cabinet doors I put two pieces that go length wise then two that go across. the two that are going across are only 1 1/2 in thick but it has kept them from warping for 8 years. I live in the Portland Oregon area and it is wet here. :) Don;t know if that helps but try to put some wood under the top going across the grain to suck it down.
Al

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