Question about warping of walnut/wood in general - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 29 Old 02-15-2012, 12:44 PM
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I will try to resolve. I re read your post carefully to try to figure out just what is the variance in you concepts.
The first paragraph is pretty much accurate. The FST and the bound water are important primarily in the first drying of wood. With the exceptions of a few underwater applications woodworkers never worry about the free water. If wood has water above the FSP it is considered Green even if it is being rehydrated.
I think the main misconception in some woodworkers is the degree of reversibility of the process. Wood can be rehydrated and even turned to mush with water, heat etc. below the FSP about 20% the water bonding to wood is still completely reversible.
You can chart the % moisture relative to the humidity as long as you give the wood time to equilibrate.
This equilibration concept causes a lot of the misunderstandings. Various finishes slow the process but none stop it. The only way to do that is outside our scope in this discussion. You can replace the water with other chemicals most often PEG or fairly long chain polyethylene glycol polymer. More complex chemical meddling with the glucose can create viscose or rayon but that is a whole topic. You can probably search Wikipedia on cellulose etc.
The water does come and go by making weak hydrogen bonds to the OH an O in the glucose molecules of the cellulose. This is Also completely reversible as long as there is cellulose and water.
Now you lauded to the changes in the properties of wood as it takes on mor or less water. First cellulose/wood gets softer and weaker as it takes on water or as you entwined harder as it loses water. We call it drying but below the FSP the wood is "dry" as the water is all bound. The wood also becomes a bit more elastic as it takes on water. These properties are used by woodworkers to shape wood and turners at least do a lot of their cutting when the wood is still 20% + or green as it easier on the tools. It also is done because of the other key property do wood and water.
Wood fibres, tracheids or vessels is the change in dimension with change in moisture content below the FSP. Fibres and boards change in width but not much in length. The organisation of the fibres in round structures called tree stems or logs accounts for the variability of the deformation in the wood as it "dries". Most of the cells go up and down the tree but some (eg the rays that are prominent in oak) go from the carter of the tree to the bark or phloem. Trees can carry the amount of cellulose in an area of the tree under compression so the density varies in various parts of poor quality logs. The wood around a knot is more dense and therefore different properties that the main wood.
Another variation in the cellulose structure can be best seen in a very ring porous wood like oak, elm ash, chestnut etc. the spring vs later season wood has markedly different properties.
These and a few more factors contribute to the dimensional change of wood as its moisture level changes. Where the wood is cut from the tree is the largest fact. You mentioned that most woods change in length almost twice as much tangentially as radially. This is the cause if simple cupping. The tighter the growth rings in radius the more the wood will cup for a given width. The rest of the ovemets are all variations on the theme. Different areas want to ove differently and they pull the board to a new shape.
Maybe enough . The most important statement for this discussion is that the water adsorption and loss is reversible forever. We find ways to work with it if we understand it.
Bob
I have a background in biochemistry and botany but that was long ago. I have tried to be clear but sorry if it's not.
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post #22 of 29 Old 02-15-2012, 02:08 PM
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Holy Crap......I mean that in a wow way. I thought I had a fair bit of knowledge on wood. But I must admit I feel very humbled by the depth of information here. Great discussion and glad to see that this has not diluted into some kind of a pissing contest you gentlemen are what these boards are for. Thankyou.
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post #23 of 29 Old 02-15-2012, 02:34 PM
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Quote:
Originally Posted by TylerJones View Post
Hey man if I'm wrong I will accept a correction. I truly hope that I didn't sound like someone who doesn't care about the truth. I would truly truly love to be corrected on the relationship and chemical bonds of water in wood. Elaborate as much as possible or PM me if you don't feel like posting in the thread. Dude I'm 26 years old, I have studied and trained under masters ONLY because I wish to be corrected. I certainly don't think I know it all. I just want to help others like I was helped when starting out. If I have misled others I apologize. To be great we must understand our medium more than everyone else.

I won't say that what I posted ease incorrect ...until you prove it to me. When you do that I will humbly withdraw. The moment we stop seeking a mentor or a master in the craft is the same moment we stagnate.
I enjoyed your post, you certainly understand this better than I do. It's OK to disagree with someone, but would have been nice if the other poster offered more information and entered value to the discussion.

Oh, I see he just re-posted, thx

Last edited by WillemJM; 02-15-2012 at 02:40 PM.
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post #24 of 29 Old 02-15-2012, 04:20 PM
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Sorry for the errors in spelling or words in the post. I didn't edit and the crazy iPad is always making small changes in its attemp to spellcheck.
Eg the word vary got changed to carry????
Bob
I hope I made most of the point of the reversibility of the processes.
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post #25 of 29 Old 02-15-2012, 08:33 PM
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very interesting debate now i am intriged and need to find out for myself (time to google)
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post #26 of 29 Old 02-16-2012, 12:03 PM
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Since I started following this debate, I have meant to check what the U. S. Forest Service Labs had on the subject. I just did and here is the link /http://www.fpl.fs.fed.us/documnts/pdf1994/winan94a.pdf It's a good read.
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post #27 of 29 Old 02-16-2012, 12:37 PM
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Find this very interesting.

I did a Bread Board table recently, from Maple which has been in my shop, which is an attached garage, for more than six years.

The top is 40" wide, finished with five coats of exterior WB Poly. Before installing in the house, we had warm weather and it expanded by about 1/4". Since installation in the house, it shrunk by more than 1/2" and what is interesting is that the shrinkage is not the same, once side almost 3/8" the other 1/4".

I can almost use it as a humidity meter.
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post #28 of 29 Old 02-16-2012, 05:17 PM
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Midland Bob, thanks for the in depth reply. This has definitely gotten me interested in studying this matter more deeply. I must say you had me pretty much convinced and then I read the forestry service doc and now I'm resting somewhere in the middle of my original position and yours. I suspect the reality may lie somewhere in between as well. I would love be be updated if anyone finds anything else on the subject.

I will however still state for the record that If handled correctly with regard to MC I see no reason to limit the width of boards used or to flip the rings. I have just done too many wide board tables and panels to buy it.

If wood wasn't a living and sometimes unpredictable material, however, I would certainly not enjoy it as much.
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post #29 of 29 Old 02-18-2012, 02:24 PM
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What did the forestry service have to say. There used to be a debate whether kiln drying causes any permanent change to the wood. Some believe that it does but I thought that had been put to rest. Link?
Let's hope the walnut boxes are staying flat.
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