I have two sections of 3x12" wood that have been out in the weather for a few years and are now bowed across the 12" width of the wood. The dip is pretty severe, maybe 1/2 an inch? It seems like sanding would take way too long.

What would be the easiest way to flatten them out again? Is there a tool designed to do something like this?

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    Make sure that the wood has the same level of moisture throughout the board before you use any method below. If not, it will probably just curve again when it dries. – Edwin May 8 '14 at 1:45

The power tool you would use to take the board down would be a thickness planer:

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It has an adjustable cutting head and you run the board through it in successive passes to shave off the surface.

However, unless you do a lot of rough lumbar milling or are into fine woodworking, it would probably be silly to buy one. Maybe you can rent / borrow?

Note that a thickness planer is good at making 2 faces parallel, but it won't be much help if the wood is also twisted or bent along its length. The twist will just follow through the planer and you will end up with a twisted board with 2 parallel (but not planar) faces.

Edit about the suitability of thickness planer:

Several people have pointed out that to use a thickness planer you are "supposed" to have one face flat already. I guess that's optimal but I have used a thickness planer many times to "save" cupped boards. If you have a great piece of wood, you might as well try something, right?

  • Start with the convex side up, so that the board is stable against the base and doesn't rock.
  • Work in small passes at the beginning. If you try to take too much off the planer will press down on the board and flatten it without really cutting.
  • Once you have flattened the convex side you can alternate faces.
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  • Do you have experience with getting a board flat with a thickness planer? If so can you detail technique? Everything I've read and done tells me that you have to have a flat side before passing through a thickness planer. Getting a flat side is usually done with a jointer. – Edwin May 8 '14 at 5:24
  • If the plank is cupped, you'll have to plane both sides, and you'll reduce the 3" plank to 2 1/2" at best. – Tester101 May 8 '14 at 13:10
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    @Edwin: Yes, I have a thickness planer and have used it many times to correct this exact problem. It's easiest if you start with the board convex so it sits flat on the bottom of the plane and doesn't rock. After you make a few passes it will be flat enough to proceed on either side. Of course, Tester101 is right, this will reduce the total thickness of the board. – Hank May 8 '14 at 21:07
  • Thanks. I can see how it is possible if the board is cupped. I read "bowed" and didn't fully comprehend that the OP was really meaning that the board was cupped. – Edwin May 8 '14 at 21:12
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    Make sure to run a metal detector over the surface of the wood before running it through a planer. Most sets of knives cost $50+, and can be ruined by a single nail. – Doresoom May 12 '14 at 20:35

You can use a tool called a Jointer to fix imperfections in lumber. The jointer has an infeed and outfeed table that are slightly different in height. The cutter removes a small amount of wood from one of the faces/edges of the board until the board is flat.

If you only have a planer and you don't want to buy a jointer you could try a planer sled.

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  • I think that you are thinking of a planner not a jointer for this lumber problem. A planner is used for flattening the wide face of lumber and a jointer is for truing the narrow edge. a planner takes the whole piece of lumber in under pressure and plains one wide surface. Depending on how cupped the lumber is, a planner may work after a few passes on each side, but the thickness of the board is going to be smaller. – shirlock homes May 28 '14 at 22:08
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    @shirlockhomes: Nope, making the edge OR face flat is a jointing operation. Planers are normally used just to bring an already-flat board to a specific constant thickness, though as noted above there are ways to make them function as jointers by stabilizing the board temporarily. (The presumes you're talking about power tools. Hand planes can certainly be used for both jointing and thicknessing, and can be quite a pleasant way to do so once you've got some skill... which I don't, yet, but I'm learning.) – keshlam May 28 '14 at 22:49

You can bend the boards over hot steam or fire until they are not warped anymore, then use a plane to flatten them. This requires some practicing, so if you have a shop nearby with heavy machinery, ask them to fix the boards (if they are worth it).

The distortions come from moisture and uneven drying, and can be fixed by using moisture, drying and physical force.

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I have a book called The Furniture Doctor which has been in print for a long time so your library is likely to have a copy. In it, the author describes treating this sort of warpage by laying the wood out on the grass in the early morning with some rocks or concrete blocks on it. Apparently the morning dew will moisten one side and allow some of the cupping to be alleviated.At that point you could plane it and lose less wood.

I have not tried it so I can't speak for its effectiveness.

The surface planer, BTW, is something that a serious woodworker might own and most woodworking clubs will have one.

I have however dealt with wood that has been in the weather as you describe and it has generally not been worth trying to plane and use for anything. The sun and rain cause a lot of deterioration. However that will depend on how long it's been outside and how thick the wood is and several other factors that i"m probably forgetting. If you like the weathered look than it's great.

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You would need to get them machined.

You could try to do it yourself with a electric planer. But would be a pain.

You could maybe turn them around, put them on 2 stands with some weight in the centre an leave them a few days.

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  • Oh interesting. Why is the planer a pain? – Brh May 7 '14 at 21:19
  • Just hard to get it heaps straight with a planer – Nathan May 7 '14 at 21:23
  • Reply to Henry Jackson. Are you kidding me? A thicknesser will not get a bow out of timber! An a small one at that. You have to have a straight edge on timber to use a thicknesser. – Nathan May 8 '14 at 4:34
  • I guess it's a little unclear exactly how the OP's wood is warped, but I think he means cupped. I've corrected that condition many times with a thickness planer, see the update to my answer. – Hank May 8 '14 at 23:59
  • @Nathan: See my comments above. A thickness planer can be persuaded to act as a face jointer by creating a "virtual" straight face via sled or runners. – keshlam May 28 '14 at 22:46

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