WARPED BOARDS

[Joe "Woody" Woodpecker]

I am told that warped boards are warped because they have too much moisture in one side of the board. Is this the concave side (the inside of the cup) or the convex side.

I am also told that you can dry out the side that has the moisture in it and it will straighten back out. Any truth to that?

-- Woody

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[Jock]

Joe, Cupping , bowing or warped? Warping is a twisting of the board lengthwise usually pre. use as a result of poor seasoning or unlevel / stacking or stripping out whereas cupping is where the board accepts moisture on the (usually) underside on fixed floors. If the flooring is sealed (poly / whatever) on top, the board will be flat only when the weather / moisture content of the board is close to what it was at the time it was sealed. The boards are unsealed underneath so they shrink and swell as moisture levels / seasons change. Cupping is where the edges are bowed upwards inside, bowing is where the centre of the board is raised due to lower moisture. Hope this helps. Jock

[Jim]

I don't try to unwarp or twist a board, as a general rule. My take on it is that a board is what it is & once it's settled in, it will likely stay that way. Incorrect storage can cause a board to warp during the drying process, otherwise, you just need to cut/mill the board up into smaller sections that are straight & flat. Even if you can pull a twist or cup out in the shop doesn't mean it won't come back in service.

We see a lot more of this now than we used to. Trees that wouldn't have hit the sawmill in years past are being used. A local sawyer told me he's getting a lot more 'stand alone' trees, not part of a stand, but ones that are off by themselves. These tend to have more limbs, so you don't get the clear lumber in the lengths you used to. Knots often mean warps & twists. Young trees mean cupping on wider boards as they use both sides of the tree in the same board, rather than pulling the entire board from one side. [ if an end grain looks like this ->

((((((o)))))) the board will tend to cup at the 'o' since the wood there is different than at the edges. It's best to get end grain that is from one side of the tree, if possible like this -> )))))) ]

All the above is very generalized, of course. I mostly deal with NE US wood & some readily available commercial lumber. Tropical, exotics & such are a whole different ballgame.

Jim

[George]

Posted a few places above, but if you want some good information, go to

and check out, as a minimum, chapter 3.

[Walt Cheever]

It has worked for me on occasion. "The Furniture Doctor" recommended putting them out in the yard, concave side down. Sun dries the convex side, moisture gets to the concave side. Doesn't say how to make the darn thing stay flat after you put it in the shop tho.

Walt C.

[Stephen M]

This is *one* way that a board can end up warped.

Is this the concave side (the inside

Wet side convex, dry side concave.

Some.

*if* that is the cause of your warpage, it will likely come back some or most of the way.

You can still have warping when there is completely even distribution of moisture. More dense wood reacts to moisture changes less to than less dense wood. Wood varies in density within a singe board. Generaly, the wood closer to the center of the tree is more dense. Around knots, all bets are off.

Consider this scenario:

A flatsawn board is dried to a certain moiture content and is brought to complete equalibrium with its envvironment. It this then milled flat and straight.

That board is then moved to a highly airconditioned environment (lower humidity level) and allowed to fully acclimate. This board will likely cup toward the outside of the tree. This is because the less dense wood from the outside of the tree will shrink more than the wood on the opposite face of the board when exposed to an equal decrease in moisture.

I hope that helps some.

Steve

[dadiOH]

Moisture expands wood. The convex side is wider than the concave. Therefore, the convex side is the damp one. _______________

Sometimes to usually. Depends on lots of things. Sometimes you can spritz the concave side lightly with water, weight or clamp the board flat, wait a week or two and they'll wind up perfect. Sometimes you can just wait. Sometimes they will wind up perfect, sometimes there will be some twist. One thing: don't try to dry them fast with heat (heat gun)...you will almost surely get a bad result.

It is really no different than resawing a thick board...they will almost always cup. Logical because unless they are ancient boards the inside has a higher moisture content. Ditto when thickness planing unless both sides are planed equally.

-- dadiOH ____________________________

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[fredfighter]

The definitions I have read are:

Cup -- curvature accross the face of the board, accross the grain

Bow -- curvature along the face of the board along the length of the board, that is, with the grain.

Crook -- curvature along the edge of the board, along the length of the board also with the grain.

Twist -- a combination of bow and crook with or without cup but once a board is that screwed up who cares. Aka kindling.

Wood swells as it absorbs moisture and shrinks as it dries. When a rectangular solid is curved (ignoring for the moment that it is no longer rectagular) the convex side of the curve is longer than the concave, so that if the curvature is due to a moisture gradient in the wood the convex side is moister.

Warp is typically used as a more generic term for any deformation of the wood, including or perhaps especially bending it in some way that the deformed shape is stable.