Straightening a bowed board

[Mel Fulks]

The method does indeed work; but before George's post I had only heard of it used on cups. Mostly table tops. It came to my atension in an article written by Bob Flexner. Your explanation of it is more complicated than Flexner's. I don't enough about it to say if it is essentially the same or not.The condition,( before the fix) is commonly called " compression ring set" for anyone trying to find more information.

[Jack Curtis]

...Kiln dried wood is sometimes given an extra "wet" cycle after it is dry to release the compression from the outside surfaces. When it is then re-dried it has almost no internal tension.

Steve, is this what steaming is all about?

And thanks to you, Dave Keller, and George, who've increased my knowledge appreciably.

[Steve Elliott]

Steve, is this what steaming is all about?

I've seen steamed cherry, which I believe is done to even out the color between the heartwood and sapwood. Other than that there's steam bending, which relies on the principle of increasing the moisture content to the point where the fibers will slide, then holding them in the desired position until they dry out again.

[george wilson]

Wetting the convex side was applied to a mahogany, VARNISHED table that had not been wetted with wiping over its life. The varnish was original and intact.

I missed where you said the wood had been GLUED UP. This technique might not work if you glued up the wood. It might also not work anyway. Depends upon conditions in the wood that caused it to bow. It was standard procedure on 18th. C. antiques in the furniture conservation lab in the museum,which was pretty much World class.

[Jack Curtis]

I've seen steamed cherry, which I believe is done to even out the color between the heartwood and sapwood. Other than that there's steam bending, which relies on the principle of increasing the moisture content to the point where the fibers will slide, then holding them in the desired position until they dry out again.

Yes, sure on the bending; but I wondered if steamed drying, even if it is to even out color and the like, also has some effect on keeping the boards straighter than plain kiln drying.

[Adam Cruea]

Well, I took Andrae's advice and flipped the board over and planed the bowed up ends. After about and hour of planing and checking for flat and square, I finally saw what was giving me so much grief. . .there was an abscess in the wood and a knot. I noticed right before I'd gotten to it that the grain was starting to go every which way and that my plane seemed to be getting stuck there near the end, or at least heavily dragging.

So, off to the trash pile that puppy went. I worked the second stretcher flat and pretty square (one end falls off, but since it's getting sacrificed as a tenon I don't really care much) and that took all of about 3, maybe 4 hours.

*sigh* Lesson learned. . .pay more attention to the grain and any possible knots. The guy at the lumber store even pointed it out to me. *shaking head* I just forgot it.

[Steve Elliott]

I wondered if steamed drying, even if it is to even out color and the like, also has some effect on keeping the boards straighter than plain kiln drying.

Most of my knowledge of kiln drying comes from Bruce Hoadley's book, Understanding Wood. On page 98 he describes a typical drying schedule and mentions the use of increased moisture near the end of the process to reduce casehardening, which is the type of tension I've described.

I don't have personal experience with a kiln but do think Hoadley's book is very good.

[Mel Fulks]

Different culture ,in Japan some practices are encouraged and even subsidized that would have you fired (or committed ) for suggesting them here. They have a commitment to continuing traditions that just does not exist in the West. We wait for old ways to disappear completely then pay for research to bring them back . Niether culture is going to change anytime soon.

[Jack Curtis]

Most of my knowledge of kiln drying comes from Bruce Hoadley's book, Understanding Wood. On page 98 he describes a typical drying schedule and mentions the use of increased moisture near the end of the process to reduce casehardening, which is the type of tension I've described.

I don't have personal experience with a kiln but do think Hoadley's book is very good.

Thanks, Steve, I've only scanned Hoadley; but I'll definitely study the drying schedule part.

[David Keller NC]

The original post referred to a board that was bowed rather than cupped. (Bow is curvature along the length of the board; cupping is curvature from edge to edge.) George's method of wetting the convex side could be effective for correcting the bowed condition.

Oops - maybe I should read the OP a bit more carefully next time. Your explanation makes more sense, though I've been told that fibers in wood won't actually slide past each other - the lignin binding and ray-cell structure prevents that. Instead, I've been told by a Forestry professor at my local University that branch-bending is more about stretching the fibers, which they will do when wet in a tree.

One interesting note - "Comp Wood" is a product that by nature of its processing has apparently broken the ray cell structure and lignin binding between the fibers, so it is highly flexible until dried out. I've never tried it, but it looks intriguing (and expensive).