# Flattening boards with Heat?



## mochoa (Oct 9, 2009)

Hello Lumber Jocks,

I had a question for your all. I while back Mads posted some videos about Japanese woodworking. In the video these guys take rough boards, and before running them through jointer they heat them and forcefully bend most of the bow or twist out of the board. These board are air dried out in the sun, no shelter, so the heat turns the water into steam, you can see the steam coming off of the board. 
http://www.youtube.com/watch?feature=endscreen&v=AgNVCOpYojA&NR=1
Its around the 3.30 minute mark.

The question is: have any of you had success doing something similar? I've heard of the old "Lay the board on the damp grass in the sun" trick. But, what if I can't wake up that early? Or, the grass isn't very dewey this time of year.

I have an 8/4 red oak board that has some bow to it. I need to keep most of the thickness so I would like to remove some of the bend before jointing. The board is about 6' long and to flatten it might mean removing more wood than I want.

Here's what I've tired:
-Dampen one side of the board and hit the other side with a heat gun, then clamp it to my bench. I left it in the clamps for a few hours but that didn't work. Maybe because its air dried and the heat gun didn't generate enough heat. 
-Wet the grass, lay the concave side in the wet grass with the full mid-day sun hitting the convex side. I didn't notice a lot of movement but I put in the clamps again to see what happens. Here is a pic of it the clamps. I'm going to leave it in there for a while longer before removing. 








You can see that I have a board in the middle to help overbend it.

I'd be interested to know if any of you have tried anything similar with success.

Thanks,

Mauricio


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## apprentice (Jun 27, 2012)

Hi M

It looks like the grain is tighter underside and the top more open grain, if your trying to compress the lower edge which is closer grained, you can re-hydrate the incurve side so it swells, but it will still may want to move back again afterwards.

Try flexing it twice the distance than the bow so when it relaxes again it stays the opposite side of the bow slightly.

If your removing any width do so on the tightest grained edge/surface and it may even out the tensions slightly, do this first then encourage it in the direction you want it to go with clamps etc.


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## donwilwol (May 16, 2011)

you've got a 2" piece, so you've got some fibers to move. Clamping the way you have it will work, its just a matter of time, and it could be a long time. To speed up the processes, here's what may work.

First, a note that woods react different, kiln versus air dried, oak versus ash, thick versus thin, etc, so you just never know. Watch the woods reaction and adjust accordingly.

Soak the board in water for a day or so. THEN, clamp it like you have it. Ever two or three days, remove it and see what its doing. Each time add about an 1/8" shim. Watch it closely because you may wind up with a hump in the center. If you see that starting, use wider shim board. You'll want to over bend it a little, because it will probably settle back.

Heat will help speed the processes but it also make it more unpredictable. (heat the top of the board). I've heard that using boiling water can be used as well, but that's a big pot for your piece.

I'll be back later to watch the video. I've seen steam coming out of the end of boards, but never on purpose.


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## LukieB (Jan 8, 2012)

At the cabinet shop I used to work at we would do something similar with solid wood panels that bowed after glue-up. We would just set them on the floor overnight. The cool concrete floor combined with the heat from the shop heaters above would straighten them right out. You had to be careful, cause if you left them out too long they would cup/bow the other way. I don't really understand the science of it, but I do know it can work, hope that helps, Cheers!


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## mochoa (Oct 9, 2009)

Thanks apprentice, I'll take a look at the grain and if I can remove more from the tight grain side. I never would have thought of that. This board is weird because on one side there is a lot of runout, but on the other side there isn't, its pretty straight. Would it be better to take off of the side with a lot of runout?

Thanks Don, I think I'll keep wetting that one side, I like the idea of widening and heightening the shim.

There is another video where the guy is actually passing it through a bonfire.

Lukie I may just have to try that on the garage floor and a space heater.


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## DaleM (Feb 18, 2009)

Mauricio, this was discussed quite a while back. Here is the link to that post with a couple suggestions that might help, and a picture I posted similar to yours so I thought I would share. I do know for a fact that on some boards, the moisture and heat will straighten them, just like steam or or boiling will allow you to bend them.

http://lumberjocks.com/topics/9718


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## apprentice (Jun 27, 2012)

A lot of what happens to nice timber depends on where the section came from. Much of what you get on an outer fast growing stick is open grain on the side to weather, if the lumber comes from a branch, you get an underside which has compression and a top side of the branch with stretching, always go for the butt of the tree north side and the heaviest tightest grain.

The open side with run out will dry faster than the other side if the grain there is tighter, so its a try and see which method will work, I would opt for taking off the side with most compression so it can relax back.

If the timber is air dried and sticked well it has more time to settle, the quarters will be the steadiest and the top in the most air the one that will move the most.

I only use air dried and steer clear of kiln dried because most modern setup's don't cater for quality, just quantity and leach most of the natural sugars out from between the X Phloem or bast where the grain is open.


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## mochoa (Oct 9, 2009)

Dale, thanks for the link. I saved the picture you posted:









Your method (soaking and then using the hair dryer), and the way you clamp sounds good. It allows me to have the side I want to shrink facing up. This lets me hit it with the heat gun which will create steam and make it more effective at shaping the wood.

Wait I just reread it. That's only for extreme situations. I'll leave it in the clamps for now since I'm not planning on working on it tonight. If that doesn't work then I'll try your wet heating method.

I just need to be sure not warp my bench top with the heat! It's not totally dry yet.


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## donwilwol (May 16, 2011)

I just need to be sure not warp my bench top, cover it with newspaper, and just lightly dampen the top of the paper. Keep it damp if you use heat. Don't want to set it on fire either.


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## mochoa (Oct 9, 2009)

Hmm, so the news paper shields the bench and the water prevents the newspaper from burning?


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## donwilwol (May 16, 2011)

i wouldn't do it on my bench, and I'll do almost anything on my bench. I'd find something else to clamp it to or I'd cover the bench with heavy plastic first, then newpaper good and moist.


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## Bertha (Jan 10, 2011)

I wonder if you could pass a steam mop over it. I got one for like $100.


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## Sylvain (Jul 23, 2011)

Maybe you should look for "steam" and "steambox" in the search engine
like 
http://lumberjocks.com/shipwright/blog/29341
http://lumberjocks.com/topics/36709


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## mochoa (Oct 9, 2009)

Thanks Sylvain, the only problem is that the steam box would have to be so big to accommodate this board.

I do have an update though, I left the board in the clamps for a couple of days and it did remove most of the bow. I left it on the floor of the garage last night also to see if Lucas' trick would help but I think I needed the heat for it to work so it didnt seem to do anything.

There was still some bend in about 1/3 of the board. So now I'm clamping it at that spot like Dale suggested. 









I'm not really in a hurry so I'll leave it in until I'm ready to work on my tool well. By then it should be flat enough to joint. If I feel like it I may hit it with the Wet Heat per Dale.

I think its flat enough to joint now but since I'm not really in a hurry I'll leave it in the clamps for now.


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