I have some planks of air-dried (many years) maple. They are rough cut to about 1 1/4 inch thick. After removing the rough saw marks and cutting and planing to approximate size (3/4×3 x 80 inches), they have become bowed. This bow is too large to remove with a jointer - I would lose too much thickness, and my jointer is too short anyway.
So I wonder if I could remove the bow by steaming the boards and clamping them into a straight line. It seems like a no-brainer, but I have never done any steaming. Read about it, but never done it.
Does your project require 80" long parts? Cut to length before you try to straighten/flatten. Does the structure of the project help to pull the bow out? For instance, something like a dresser or bookcase has enough structure that you can pull things straight with adjoining members at right angles to it.
Oh, sorry, I should have asked, by bow do you mean cupping, where the boards curve across their width, or bow, where the boards curve along their length. I assumed you mean bow as they are only 3" wide.
Does your project require 80" long parts? Cut to length before you try to straighten/flatten. Does the structure of the project help to pull the bow out? For instance, something like a dresser or bookcase has enough structure that you can pull things straight with adjoining members at right angles to it.
Yes, in this case 80 inches is needed. There may be some help from the structure, but the degree of curvature makes me think I don't want to rely on structure to straighten it fully.
One article in one of the woodworking magazines I read awhile back the author said the best tool for bowed and twisted wood is the fire place. If you steam the wood what will keep it from twisting after it has dried again?
This comes from a Flexner article. I have used it successfully, but the board was about half as long as yours. It did work though.
The idea is to wet the wood thoroughly on the convex side of the bow. It seems counterintuitive since that will make the cells swell and increase the bow. However the trick is to then weight the board while set on supports at each end and let it dry while slightly bowed in the opposite direction. What happens is that the wood cells dry out and become rigid again, but have been slightly compressed by the bend and stay that way. It's a guessing game how much bend to have it dry with. I placed two 3/4" boards on my bench and set the bowed board with the bow up and that face very wet and then used some bricks I keep around that are wrapped in duct tape and placed them in the middle. I added enough weight so the middle of the board was resting on my bench and left it for several days so it was completely dry. It took the bow out. I would guess that if it wasn't perfect the first time you could keep trying with more or less bend.
One article in one of the woodworking magazines I read awhile back the author said the best tool for bowed and twisted wood is the fire place. If you steam the wood what will keep it from twisting after it has dried again?
That's a fair question, and I don't have a good answer. I have read, though, that people steam wood to introduce a permanent bend. They hold it in place while it is drying, and it seems to keep the shape when the clamps are removed.
This comes from a Flexner article. I have used it successfully, but the board was about half as long as yours. It did work though.
The idea is to wet the wood thoroughly on the convex side of the bow. It seems counterintuitive since that will make the cells swell and increase the bow. However the trick is to then weight the board while set on supports at each end and let it dry while slightly bowed in the opposite direction. What happens is that the wood cells dry out and become rigid again, but have been slightly compressed by the bend and stay that way. It s a guessing game how much bend to have it dry with. I placed two 3/4" boards on my bench and set the bowed board with the bow up and that face very wet and then used some bricks I keep around that are wrapped in duct tape and placed them in the middle. I added enough weight so the middle of the board was resting on my bench and left it for several days so it was completely dry. It took the bow out. I would guess that if it wasn t perfect the first time you could keep trying with more or less bend.
I had a 7' length of walnut with a 1" bow in it. I needed it straight.
I clamped it to a Ibeam with a 1" reverse curve and steamed it like that, repeatedly. After 1 year (yes, 365 days) I unclamped it and with went back immediately to how it originally.
I have some planks of air-dried (many years) maple. They are rough cut to about 1 1/4 inch thick. After removing the rough saw marks and cutting and planing to approximate size (3/4×3 x 80 inches), they have become bowed. This bow is too large to remove with a jointer - I would lose too much thickness, and my jointer is too short anyway.
So I wonder if I could remove the bow by steaming the boards and clamping them into a straight line. It seems like a no-brainer, but I have never done any steaming. Read about it, but never done it.
The answer to cut them into shorter lengths, and prep them 4square from there is the best I know of. But if you need the length, what ya gonna do???? If you are going to steam them please follow up, maybe with pics to let everyone know what happens.
In my head I don't think it will work, especially hearing it happened after you opened up a board, and then pooof they crooked on you. Typically that tells me these thicker boards were not as dry in the center as the outside. Cutting into them you exposed that wetter wood, and it did the presto chango thing. My belief is adding more water won't make them spring back. If somehow you could add more dryness, you might be on to something. I think they call that a kiln After the fact it probably wouldn't be worth the cost, but if you do need the length, some have reported a sort of kiln drying with putting the wood inside a black plastic bad, closed air tight. Allow the sun to heat it. Absolutely the wrong time of year for most of that though, unless you are real South.
I've tried the Flexner thing, way before I ever saw it in writing, it's an ages old idea. It incorporates SUN (heat) and dampness from the yard. Kinda like shooting dice, sometimes ya get a 6, sometimes you don't. If you're betting on the 6, it almost never happens. When you absolutely don't care, well lookit that it's flat again…
Yes, I am going to try it. My neighbour tells me that he and a buddy did the same thing about 15 years ago. I will get him to help me replicate their results.
I think it should work - no different from steam bending really. I've steam-straightened a few chair parts for post-and-rung chairs without problems (and Curtis Buchanan, master Windsor chairmaker talks about it a few times in his videos on youtube). Two potential issues. Normally with steam you have to overbend because if will spring back a bit once taken off the form. And maple is a very poor steam-bending species. But both of these potential issues may not be much of a problem given how gentle the bend (or unbend) is.
I ve tried the Flexner thing, way before I ever saw it in writing, it s an ages old idea. It incorporates SUN (heat) and dampness from the yard. Kinda like shooting dice, sometimes ya get a 6, sometimes you don t. If you re betting on the 6, it almost never happens. When you absolutely don t care, well lookit that it s flat again…
I'm not sure you are talking about the same technique. His (Flexner's) didn't involve the sun or wet ground. I shoot dice in Vegas often and am not sure where the notion of a winning 6 comes from.
But, you are the most brilliant, talented and knowledgeable person on this site and I will never dare to question your expertise. I'm sure Bob Flexner stole that tip from you since your vast experience predated the article I read. I bow to you, sir.
So, here's what I have learned so far.
First, hard maple really doesn't want to absorb moisture. i have steamed it for 3 hours, and never got the moisture content above 40%.
Second, it does work. So far I have removed a 1/2 inch bow from a piece of maple 4 feet long.
This first picture shows the general setup. I am using 6" diameter duct work for the steam chamber. I have taped it up and added some insulation (not shown).
The second picture shows the clamping arrangement. Yes, that is a humongous piece of angle iron I am using to define a straight edge for the steamed wood. The wood is a test piece I used. It has both a bow and a crook. As I said earlier, the steam has removed the bow, but it didn't touch the crook.
Because the maple is so reluctant to take in moisture, I am going to try soaking it first. Since I don't have a 7 foot trough, I will wrap it in wet cloth for a day or so before steaming it.
As I said above maple really doesn't want to absorb water. I soaked it for 48 hours (wet cloths repeatedly refreshed) then steamed it for 4 hours. Barely registered. It dried out almost immediately after I took it out of the steam.
Here's what did work for me.
I started with a piece of wood with a pronounced bow - sorry, I didn't measure it, but it was at least 1/2". I clamped it against a large piece of angle iron then I used the clothes steamer to heat the wood. I ran the head back and forth over the mid point of the bow (on the convex side), and some distance either side. After 20 minutes of this I stopped and waited for it to cool.
Much of the bow was gone! What I did next was a mistake. In an effort to remove the rest of the bow I turned the wood around and repeated the steaming on the concave side. After the wood cooled, I removed the clamps and the original bow had returned!
Do not steam the concave side.
I repeated the steaming on the convex side and the bow was mostly gone - about 1/8th inch was left.
I fixed two boards in this way. The other two boards had more complex faults, but I was able to fix them up with a jointer.
It will be interesting to see if the warping returns. Steam bending is more about the heat than the moisture. The heat softens the lignon allowing it to bend. Cooling while it is bent causes the lignon to reset leaving it bent, though it will usually spring back some.
Have you measured the moisture content of the wood now. After soaking it with water, I would be concerned that it needs to dry for a while. If the MC is still relatively high, you may want to leave it clamped to something straight so that the warp doesn't return as it dries while also ensuring that you get good airflow on all sides. Differential drying is often the cause of warping, especially after using a jointer and planer to straighten/flatten it. The idea of wetting one side while heating the other is about equalizing the MC on both sides to straighten and flatten it. The rule of thumb is that it will bow or cup towards the heat which seems to correlate with your results.
It will be interesting to see if the warping returns. Steam bending is more about the heat than the moisture. The heat softens the lignon allowing it to bend. Cooling while it is bent causes the lignon to reset leaving it bent, though it will usually spring back some.
Have you measured the moisture content of the wood now. After soaking it with water, I would be concerned that it needs to dry for a while. If the MC is still relatively high, you may want to leave it clamped to something straight so that the warp doesn t return as it dries while also ensuring that you get good airflow on all sides. Differential drying is often the cause of warping, especially after using a jointer and planer to straighten/flatten it. The idea of wetting one side while heating the other is about equalizing the MC on both sides to straighten and flatten it. The rule of thumb is that it will bow or cup towards the heat which seems to correlate with your results.
Lazyman - The wood never absorbed enough water to make a difference. The surface got wet but it dried almost instantly. MC before steaming read 0 on my meter. After drying it read 0 again.
I did plane the wood to thickness after straightening the bow, and it still seems OK. I haven't used it for its intended purpose yet - it will be one of the stiles of a door.
Hmm. You might need to check your moisture meter. It is next to impossible to get 0 MC, especially with air dried wood. Even after 20 years of air drying, it would have some moisture in it.
I've got a Wagner Orion Deep meter, and it stops at 4% because readings below just don't happen often enough to look for them. Plus if it is less than 6%, why bother, you won't do much better for woodworking use. I'd be leery of a meter that would even suggest a 0 reading.
Plus introduction of moisture to, or subtraction of it from wood doesn't really tell much about wood, and movement. Being a live thing it constantly will take in, and loose moisture. We know this, and that is the reason we try to build using that knowledge. It's so that we can hopefully control that movement. Failure to do so will give you a wreck, rather than a project.
So if adding moisture makes this board seem to behave. Does that mean that once it's back to it's desired resting equilibrium point that it will stay behaved? I don't think so. Not over a years time given that your environment is one where wood does truly move. Actually, I should say the environment where the finished piece is residing.
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