Hi all,
I have two small pieces of white oak that have been exposed to the elements for some time. They both have unfortunately developed a slight bow to them. I have them both clamped together with their bow facing outward, sandwiched them between two pieces of wood and then clamped them together under lots of pressure to try straighten them out.
After a few days of this the second I take the clamps off they just go straight back to being bowed.
Am I approaching this wrong? Any advice or suggestions would be very much appreciated.
Regards,
Chris
Replies
Probably, they have taken on the shape they want based on the temperature and humidity of there surroundings. You won't be able to change it. All you can do is work around this by cutting and planing the planks into workable straight pieces for a suitable project.
That's been my experience as well. I am by no means an expert though.
If you are able to lay the concave side on grass and let the sun shine on the convex side, it will straighten them but usually goes back part way. If you can leave them til they are opposite, it may settle in the middle. I have used this for boards that will be attached immediately to solid uprights, where the curve would have made life miserable. Not for something that really mattered though, but it might be worth a try.
Mother Nature always wins. Prolly best to use them in their new natural shape.
My first taught was that you cannot and should not since we all work with the wood at hand and the way we straighten wood is by removing the curvature with hand planes or jointers. But then I taught, since we can bend wood with steam, we can straighten a curved piece using the same technique, so you could steam bend the wood straight with a soak in the steamer followed by drying on a form with just the right amount of spring back allowance.
Chuck 'em in the fire and hit the lumberyard. Sometimes the juice is not worth the squeeze.
Agree MJ, firewood
Something else to try... I knew a wood turner that hated when he encountered bowed turning blanks for the stair spindles he made. Even though it was less than 5% of the FAS oak stock he used it ticked him off to through otherwise perfectly good spindle stock away. The problem of course, was that at 3000 rpm a piece of 1"x1"x36" stock with even a minor bow would bend out enough to disengage with the center points and fly out of the lathe, usually taking a pair of fluorescent bulbs with it.
He ended up taking the bowed stock and putting it into his glue-press between blocks and stressing (or over-stressing) the bow in the opposite direction. After 24 hours of this he usually ended up with stock that was mostly straight, or straight enough to turn safely.
The stress in the board will not allow you to straighten a board simply by pressing it flat, at least not in any reasonable amount of time. The stress is built into the wood by the tree it is sliced from. Often this is due to "reaction wood" that the tree builds to counter long-term stresses it encounters in its lifetime. When the tree is cut down and sliced up these counter stresses remain in the wood and with the original stresses removed they end up bowing the wood. Unless you counter the built-in stress by applying an over-stress in the opposite direction for a reasonable period of time you are not going to get those boards straight. You can speed this process up if you have a steam box, but you still need counter pressure to move the wood in the direction you want.
The other approach is to understand that the stress that causes the bow is built-in to the wood. Start with oversized pieces, cut them to rough oversize dimensions, then let them sit in the shop you plan to make your project for a week or more until stresses resolve themselves into bows that you can see. Using a jointer get two flat faces that are perpendicular to each other, then run them through a planer to set the final dimension you want. This works, but plan to build your project quickly as the stresses may still be there and reappear after the wood has set for a few weeks or months.
Finally, you can to some extent, build projects with bowed lumber if you plan your design and use of wood such that the project itself compensates for the bend during assembly. All wood no mater how carefully you plan will end up with minor curves or even twists and some work must be done during dry-fit to make sure they are not significant enough to affect glue-up.
Good luck!
MJ, "the juice is not worth the squeeze." made me smile. I need to hang this phrase over my wood bin.
Ken