# Question about warping of walnut/wood in general



## Dan9876 (Sep 12, 2007)

About a month ago, I made the small box in the pics below out of some scraps or mahogany, walnut and padauk. The box is about 8" x 5 7/8", and the top is 7/16" thick. The top is made of 3 jointed pieces of walnut. About 24 hours after jointing and gluing up the top, which was about 1/2" thick at that point, I planed it to the final 7/16 & while is was still a rectangle, I made a ~1/16" deep dado for the paduak insert in the middle. I then cut it into the final triangle shape, and glued in the paduak. This all happened in about 3 days. So far so good. After finishing with water based poly, the top slowly began to warp at the outer points of the triangle near the "handle", as shown in the final photo. The top sat nice and flat on the box right after finishing. The gap at the outer edge as shown in the pic is about 1/16". The walnut scrap I used had been in my dry shop for about 3 years, though I did have to resaw it to the 1/2" thickness used in the glue up. I have used the same wood for several tables over the last 3 years with no problems so far. What would have caused the top to warp this way, and what might I have done to prevent this? Should I have left the jointed glue up sit for some days prior to planing to the final thickness? Or should I have left the resawed pieces sit even before jointing/gluing up? Should a waiting period always be allowed prior to final jointing/gluing/planing to allow and panel to "settle"? I'm planning to remove the cleats on the underside of the top, and try jointing it flat, than fitting a smaller triangle to the flattened underside to replace the cleats. I hope all the above is clear! Any suggestions appreciated.

It may not be clear in the pics, but the top glue up is 3 pieces, 1 about 1 1/16" wide in the center where the dado is, and one on each side about 2 3/8" wide at their widest points.

Dan


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## bentwood (Jan 26, 2012)

My guess would be that the material was under stress because it came from a place on the tree where there was a crotch or other grain change. When you resawed it the apossing stress was relieved along with cut off piece. I rarly use water based materials with figured walnut. For stability oil rubbed on all sides is best on figured material.


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## TylerJones (Dec 4, 2011)

The resawing was the culprit. Anytime you resaw you need to sticker the wood for a week or so and then flatten and join. The moisture content on the inside of the board was different than the outside. A small kiln could speed this process and is what high end professional shops use.


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## MNsawyergp (Jan 31, 2012)

Here is the old technical lesson on panel glueing we were taught in woodshop back in the old days. Look at the end grain of each board to be glued into the panel. Most of the boards wil show a curve to the end grain. Every other board has the curve going the same way...so curve up, curve down, curve up, curve down...across the panel. This process evens out the stresses as the boards expand and contract with humidity changes. If you have a series of boards glued with the curve going the same direction, they will cup or "warp". Not much help for you now, but look at the end grain and see if it is going all one direction. Your wood can be bone dry and have dried for 100 years, but it can still cup if you don't glue it up properly. It is due to humidity differences to each surface. The amount of finish you apply to each side affects this a lot. I see it all the time on trim for houses like baseboard and crown molding. The painters varnish the front and leave the back unfinished. It lays on the jobsite until the finish carpenter comes and by then the back has swelled and none of the pieces are flat anymore...talk about a nightmare!


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## TylerJones (Dec 4, 2011)

Over the years the old rule of alternating grain has been found to be largely untrue. Once your lumber has dried to 6% then allowed to rest in a space, as long as your joints are perfectly square your panel shouldn't cup or twist. If it does the alternating method probably wouldn't have stopped it.


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## Dominick (May 2, 2011)

TylerJones said:


> Over the years the old rule of alternating grain has been found to be largely untrue. Once your lumber has dried to 6% then allowed to rest in a space, as long as your joints are perfectly square your panel shouldn't cup or twist. If it does the alternating method probably wouldn't have stopped it.


+1 agree. That's what I've read. Built my dining table walnut 3/4 x11"x 7' I didn't alternate the end grain.chose the best side, Built it about 3 years ago & no cupping. 
Maybe I got lucky.


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## Steve Neul (Sep 2, 2011)

I think the culprit was probably the water based poly. Warpage is usually caused by the moisture content of the wood being greater on one side than the other. If you got a little more on one side it would cause that side of the wood to swell making it warp. You can probably straighten it out by steaming the cup side but do it a little at a time or you might reverse the warp.


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## sawdustfactory (Jan 30, 2011)

> Once your lumber has dried to 6% then allowed to rest in a space


Here in the Pacific NW, our wood never even gets close to 6% :blink:
BTW, nice looking box.


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## TylerJones (Dec 4, 2011)

You guys don't have kilns there? Its not about keeping the wood at 6-8% its about getting it there once to get the free water out from between the cells. Once you do that the wood permenantly gains hardness and stability. After that just let it rest in your shop for a while and sticker it after rough machining.


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## MNsawyergp (Jan 31, 2012)

Just because wood has been kiln dried to 6 - 8% doesn't mean it will stay there. If that were true we wouldn't have all these warping problems. Unfinished wood is like a sponge and takes on humidity after a while and can end up back to 11 - 18% which is about where air dried wood is at. Once a good finish is put on, making sure the end grain is really saturated, this process of humidity transfer is greatly reduced, but not totally eliminated. Proper flip flopping of grain, as well as proper width of boards in a glued up panel does make a difference in my world, at least. If the other guys get by without doing it, lucky them.


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## TylerJones (Dec 4, 2011)

I'm not talking about the wood staying at that MC. Wood changes once it reaches that MC, it gains hardness and stability. These properties remain after the wood has taken in moisture. This is because the distribution of water within the wood fibers changes permenantly after reaching a certain MC.


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## TylerJones (Dec 4, 2011)

And as far as panel stability goes I don't see luck having anything to do with it. Alternating end grain doesn't even enter the equation when composing a panel for me. Its appearance, joint quality and hugely important is stock prep. I also don't pay attention to keeping boards a proper size for the most part. I very rarely make a tabletop with more than four boards. I worked on one a few months ago with Andy Rae who literally wrote the book on wood andthe two center pieces of the table were right around 18" each. That piece was being shipped from Asheville to Lake Tahoe and I can tell you, we weren't overly worried about warpage. Many of these so called rules came about because people weren't looking at what was happening to the wood on a molecular level. When you do that it expands your options endlessly.


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## MNsawyergp (Jan 31, 2012)

I would like to know what species of wood that table was made from and whether those wide boards were plain sawed or quarter sawed. All these things do matter. We are trying to solve a warping (cupping) problem here, not brag about how our projects haven't warped. I agree that warping doesn't happen often and that it can happen on a flip-flopped grained panel if not treated and handled properly, and many factors go into why a panel warps. I also agree that appearance takes priority over grain pattern. Here, we are trying to investigate which factors caused the warping problem so we need to go into the physics of water absorbtion in the wood. Most likely, not as many coats of finish were put on the back side which allows more moisture to be absorbed on that side, which swelled the cells and expanded that side or the opposite; the top side lost moisture and shrank, and it had nothing to do with grain orientation. That being said, if the panel has several boards which were plain sawed, and the bows of the end grain are going the same way, the chance of cupping increases considerably. You can't deny that boards cup and wider boards cup more. Plain sawed boards cup more than quarter sawed boards. Every species of wood differs in the tendancy to cup. Saying you were "lucky" was a loose phrase. When we are staring at a panel that has cupped and we are cussing because all our work has been wrecked I won't say we are unlucky, either. I just don't like to see anybody in that position. I've been there.


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## Dan9876 (Sep 12, 2007)

Thanks for the great replies. I finally did get around to reworking the top, as shown in the pic below. I removed the cleats (which were glued & nailed), and jointed the top flat, then fitted a triangular piece of walnut to replace the cleats. I think that should work much better. The triangle was more difficult to size as exactly for the fit I wanted then attaching the cleats was, but the end result fits the box quite well, and I think looks much nicer, too. 

When attaching the triangle to the bottom of the top, I ran the grain in the same direction as that of the top itself. As I write this, I'm wondering if stability would have been enhanced if I had run the grain of the insert 90 degrees to that of the top, plywood fashion?

What is meant by "sticker" the wood?

Thanks again,

Dan


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## rayking49 (Nov 6, 2011)

To sticker the wood is placing sticks of wood between stacks of lumber to let air flow between the wood allowing it to dry evenly. Like 1x1 pieces of wood between them.


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## Midlandbob (Sep 5, 2011)

To review, the board was resawed then finished with a water based finish. It warped within a few days.
Yes the resawing may have contributed. It is wise to let resawed wood rest and equilibrate for a period of time depending on its thickness. 1/2 inch wood would probably only take a few days. There can be tension in the wood from its growth or the interior may not have been as dry as the exterior. 
The water based finish may have contributed.
It appeared from the picture that the wood was tangentially cut with a fairly tight radius to the growth rings. This is the tell that the wood will change in shape when it's moisture content changes. The curves will flatten as they dry. Even coming from a normal basement in a centrally heated home to the upper floor will change the humidity enough to change the moisture content a bit. This property NEVER goes away. We manage it with structure that hold the slight cupping tension. Your original design has no such support. Breadboard or frame and panel construction are examples of such stabilising. Plywood is another way wood panels are kept flat. Veneering saves valuable wood but also prevents warping if the substrate is well chosen.
If there is no external stabiliser then using radial cut wood is vital.
It was written ( how do you get the quotes in the pretty blue boxes?)
"the wood staying at that MC. Wood changes once it reaches that MC, it gains hardness and stability. These properties remain after the wood has taken in moisture. This is because the distribution of water within the wood fibers changes permenantly after reaching a certain MC."
This in not accurate. There is no substantial permanent change.
Wood retains its movement forever. You can use centuries old tangentially cut wood as a humidity monitor as its movement is directly related to the surrounding humidity if it has time to equilibrate. It will cycle with the seasons. Drawers and doors that bind or stick in summer when humidity is high will be OK again next winter. Finishes can slow but none stop the movement. Check the graph in Bruce Hoadley's book Understanding wood for interest and confirmation. 
Another rant but the topic keeps coming up on one way or another. Especially with the current use of wood from small trees that have the small radius growth rings.
I hope your new box behaves.


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## TylerJones (Dec 4, 2011)

MidlandBob, I disagree with your statement that no permanent change occurs. Here is why: Within wood lies two types of water. There is free water and bound water. The free water is the first to go when drying and comes from the capillaries, the bound water is bound to the wood by a hydrogen bond. This is caused by free negatively charged Hydroxyl in the cellulose and lignin walls. Water is attracted and thus bound by a hydrogen bond. Once the mc of any given wood begins to dip below the FSP (fiber saturation point) of that wood the bound water begins to be released via evaporation and the wood gains strength and hardness. This is also when the bulk of shrinkage occurs as free water doesn't cause very much shrinkage or swelling. This doesn't mean that the wood never changes MC again. Far from it, but the wood is going to retain the hardness and stability because it will never again reach it's FSP. 

Can wood still move? Yes. But handled correctly you are able to negate most of these old rules of needing support or max board widths. Why? Because wood that is correctly dried and acclimated will take adjust to the changes in moisture slowly and fairly evenly. Shrinkage is about 5-10%max in the tangential plane and 2-6% in the radial. This is absolutely enough to bind a drawer or door but doing the math on those numbers shows that they aren't enough alone to warp a top or a board that badly if that board has an even MC throughout when it's introduced to its new area. This happens when the shrink or swell comes on suddenly because the wood wasn't acclimated well before it was opened or surfaced. Or if the wood is case hardened, which comes from basically the same thing. 

Also the observation that the growth rings want to straighten is problematic as a rule. They sometimes DO straighten some but this is caused by the variance in radial and tangential swelling and shrinking as well as the natural variance of bound water from heart to sapwood. Not from the direction of the growth rings, the rings are simply an indicator. This can be almost entirely negated by drying the wood more slowly after it is first sawn. If you have a three foot wide slab, yeah this is gonna happen some, but on an 8" wide board the effects are negligible if you handle the board and it's acclimatization correctly.

I'f I'm wrong on this last point I would love to be corrected, I just prefer science to age old rules or hearsay.


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## TylerJones (Dec 4, 2011)

Also the wide boards on the table I mentioned earlier were walnut. They were flitch cut slabs so they contained both planes.


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## Midlandbob (Sep 5, 2011)

Tyler 
You are wrong. Your understanding of the position of the bound vs the unbound water in wood seems flawed as is the role of tangential vs radial components of the wood. Reaction wood can also contribute to unwanted and asymmetrical wood movement
I don't want to get in a pissing match but if you do want to better understand the chemistry, I will be happy to try to be more specific.
Sorry if you are upset. I find it interesting to try to try inform other workers but the urge to be succinct is a challenge. The misunderstandings about wood movement come up often. Wood is an amazing product and the reasons are not often intuitive .
Knowledge can set us free. Now I'm sounding pompous and I'm not, I'm really shy.
Bob


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## TylerJones (Dec 4, 2011)

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.


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## Midlandbob (Sep 5, 2011)

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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## fixrite (Dec 1, 2010)

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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## WillemJM (Aug 18, 2011)

TylerJones said:


> 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


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## Midlandbob (Sep 5, 2011)

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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## wooddude (Jun 14, 2011)

very interesting debate now i am intriged and need to find out for myself (time to google)


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## MNsawyergp (Jan 31, 2012)

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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## WillemJM (Aug 18, 2011)

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.:laughing:


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## TylerJones (Dec 4, 2011)

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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## Midlandbob (Sep 5, 2011)

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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