I have some 6' long 2"x12" planks of douglas fir that dried into a twist, I need to straighten it out but I don't want to plane this any thinner. So basically I'm trying to bend the board back into shape.
I was thinking of doing something like physically twisting the board the other way past its yield point, and hoping the board does not snap. Maybe I could try steam bending to straighten wood.
I am planning on making 6' long benches and shelves with this material, for indoor use.
Steam bending would be your only option. Wetting the fibers and allowing them to bend and twist. It might not work, but there is a chance. Not using a moister measure, you will just split the wood where the stresses get to great.
On top of that, you will have to redry the wood back to where you need it and you will need to keep a lot of weight on it so it will dry flat. Otherwise it will just rebend and twist.
Birch likes to bend and twist when it dries, but if you keep it flat with weight (like more drying wood on top) it will dry flat and stay that way (mostly).
Ultimately it will be a bit of work and it might be easier to just acquire new lumber for your project.
The other answers have covered how you can bend the wood, but one thing they left out relates to the length of the wood. The following applies to some other defects too like bows.
You mentioned you have 6ft boards, but you don't say what your final board length will be. If the length will be shorter than 6ft, then it would be advisable to cut them to approximate length before attempting to correct the defect. The twist might be noticeable over 6ft, but it won't be as severe over 2ft, you might even get a 2ft section with no noticeable twist.
Once you have a shorter board, you will have an easier time correcting it. In the case where you are removing material, you will end up removing a lot less wood than if you did the entire board at once. This applies to running wood through a jointer as well.
Bending using heat (usually steam) is one of the only ways to bend wood reliably. But, when a board twists as it dries that is usually not permanently fixable because the wood may have 'taken a set'. So while you could steam, bend back to perfectly flat and hold it there until it has cooled, and it may stay that way initially, it is likely to have a natural tendency towards warping back to the twisted shape again in time.
Because of this, generally, when a piece of wood does twist or bow when drying the usual way to get flat wood from it is to remove material until a flat board is revealed from within the bowed board. Obviously there can be a significant loss of thickness when doing this (and some loss in width) and sometimes it is so great that the board can't be used as originally intended.
I have tried to straighten a wood screen door with steam with very little improvement. I then forceably bent it well past straight, 1 1/2 inches in center of the 7 foot span. Then saturated it with linseed oil and carefully heated the board with a propane torch. It is holding it's shape after a week.
Little late but...I tought about how you straighten a door, using wood block on the 'to in' corner and close the door for a 36h, door is most time corrected. So, I put wood blocks under the two lowest corners, whem board lying flat on floor, then put heavy weight on middle on a high humidity day. Seems to work for now, will follow up.
I came across this question in search results, and I thought I'd give a little summary of possible solutions for this so that future visitors can benefit from it. If you don't want to remove any material from the wood, you can use:
1. Wet towels and an iron.
With this method, the warped wood is exposed to heat while covered with moist towels or blankets.
The towels should be damp but not soaked. The wood should be well covered and placed on a rigid iron bench.
Press a steam iron down onto the end of the wood piece moving systematically to the other end. Repeat the process while observing the results. This method is effective for wood that has mild to moderate warping.
2. Direct sun drying.
This method is ideal in instances when it's hot and the sun is shining.
The warped wood should be well-covered with a wet towel or blanket. The wood should be placed on a straight rigid surface or bench with the inward curve facing downward.
At this point, the wood is put in the sunlight and water is sprinkled on the wrapped towel for good measure. This process may take several days to have an effect. At night, the wood should be stored in a warm environment.
3. Pressure
For this method, pressure is applied to the wood on the curved area, and care is taken to avoid damage.
The warped wood should be covered with a wet paper towel on the concave side. Clamp the wood tightly and leave it for about a week while observing the results closely. If the bend is still there, increase the pressure on the curved area.
These are not complete instructions, but rather general summaries of the processes, which are readily found online. For more details, I recommend checking out the guide on Carve Your Creation.
In this case, as others have said, steam bending would likely be the best option.
For framing lumber it can be overpowered and fastened to prevent ends from moving back into the twisted position. Particularly southern yellow pine is a sappy warp prone species. I have even had to replace floor joists after they were securely fastened when the members actually warped UP in the center of the span, so powerfully as to separate plywood sheathing where the joint fell on that particular joist. Some trees just won't give up. Quite often a piece of lumber will bow apart when ripped down the middle - showing just how much interior stress is in the piece. I believe this is what causes the twist. I buy a lot of this twisted material for cheap and use it for short members such as truss chords and webs. The twist may still be there but much less of a problem. I've often thought of soaking lumber to "saturation" and trying to re-dry it to a straight configuration but suspect other irregularities would occur.
I have used this method to make a badly twisted board useable.
Rip the board into about three or four narrow pieces. Each piece will carry only a small part of the twist.
Joint and plane each piece
Joint the rip cuts so they come square to their new faces.
Glue up, keeping the pieces in their original order. With luck, the grain will match nicely.
Which way does the board twist? If you point your left thumb along the board and it twists the same way your left hand fingers curl you have discovered a secret about trees. Most trees are "right handed". About 10% of trees are left handed such that the branches spiral counter clockwise as you look up the tree. (Imagine a spiral staircase of branches that keep twisting to the left.) A left handed coniferous tree is almost always the problem when the sawn board twists. I bought a load of red pine from a plantation, had it sawn into 2" x 6", carefully stacked it to air dry, level and with uniform stickers. And every piece twisted to the left. A german Zimmerei (carpenter) told me that the seedlings for these pine trees must have all come from a single left handed tree because every board warped the same way and by the same amount. Rather than throw it all away I had to use glue, long screws on the tongues and clamps to force each board down to the joists in the new floor. Never again! It was three times more labour intensive. Pine and other softwoods do not steam bend like hardwoods do, so you will not have much choice about fixing this problem. Best to avoid the material in the first place especially if buying green ungraded lumber. Tom Muri Oakville, Ontario
