# Resawing dry wood without causing stress movements



## TopamaxSurvivor (May 2, 2008)

I have followed a lot of issues here on LJ the last couple of years where fellow JLs have experienced various stress changes in wood they have sawn. I have a piece of dry 9/4×9 x 28 inch blackline spalted maple I want to resaw on of these days. I am thinking the best time to saw it will be in the hot, dry days of the August summer. I believe it was air dried in western Oregon. I am also thinking I will sand a 1/16 off the side opposite the saw cut. I am hoping this should receive the board of the propensity to cup, warp bow, curl or otherwise decide to change shape. Any comments, suggestions or criticism of the plan? Better ideas??


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## patron (Apr 2, 2009)

spell *relieve*

wish i knew more about the milling and drying end of things
done allot of felling
and allot of using
but not much knowledge about the sawmill side of wood

only one way to find out

keep us posted
always ready to learn something

the proof is in the 
blackline spalted maple pudding


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## ScottN (Jan 24, 2011)

All stressed wood is a result from the moisture in the wood, it will absorb or desorb moisture until it is in equilibrium with its surroundings. The biggest factor is in the drying process. When wood is kihln dried, they'll dry the wood down
and shrink the cells in the wood and the condition the wood by slowly bring the moisture content back into the wood.
Each wood species is different and needs to be done so accordingly. And if its not done correctly and rushed through the process you'll get case hardening…which is "stressed wood".

The same thing applies to your wood shops. Most woodshops and millworks keep there shops around 40-45% humidity to prevent adding stress to the wood.I keep my shop between 40-50%. So if you keep your windows open or exhaust your dust collector outside I don't see how you you can control the humidity levels in your shop.If you don't control the humidity level you'll end up with more bowed, cupped and internal stressed boards…your call.

I was debating if I should post this or not. But I think its important.


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## ScottN (Jan 24, 2011)

I was searching for a video to further explain what I was getting at.


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## NBeener (Sep 16, 2009)

*ScottN*:

Darn.

My shop DOES stay at between 41% and 43% RH.

Meaning …. I have to find yet *another* excuse for my crappy woodworking ;-)

Good info. Thanks !


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## REK (Aug 30, 2009)

I work with exotic plastics, basicly we anneal the plastic and then machine it.

in dealing with movement and stress the best approach is to cut rough, let

the material spring. With wood it is the same. You can also insure a good out come

by doing several rough operations by making several rough cuts pulling the twisting

and cupping out as you go along. We use a lot of double sided tape turning on the

lathe. This way we can remove the high points with out puting any external force on

the material, after out first side is flat and stress free, it's just a matter of maching

the second side. My biggest problem is my jointer has only 6" of width, but I can

rely on the 6" and less boards to be dead flat. The big issue is removing the high

without stressing the material i.e. the rollers on your planer usually put to much

external force on the high spots…..Basicly it's a matter of building jigs, using hand tools,

to think your way thru the stressed material problem…..I think i had to much coffee

already!!!! Blah blah blah…LOL


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## stefang (Apr 9, 2009)

Scott knows what he is talking about. I live in a climate with high humidity as you yourself do. This climate is pretty ideal for woodworking as opposed to other areas which are much less humid and where there are big differences between summer and winter humidity. It's the differences that get you. However, I don't obsess on this. I just try to use my materials before they begin to warp, and I rarely have any warping problems once they are incorporated into my projects. So I guess I'm saying ignorance is bliss, but only because you live in a wet area like myself. I know my advice sounds a little stupid, but if you build with the warp problem in mind, you shouldn't have a lot of problems. Ok now I am in for it. Shoot away folks!


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## tenontim (Feb 24, 2008)

I will usually mill the board to a thickness more than I need. Let them acclimate to the shop for about a week, so I can see what they're going to do, then do the final milling to size. This will head off many of the problems.


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## TopamaxSurvivor (May 2, 2008)

Thanks guys, The board is flat now without any obvious signs of trouble. i have had it for about 6 months. i guess my concern is finding trouble a day or two after I resaw it. My thought was to expose new surface on both sides to reduce the risk of loss of equilibrium.


> ?


??? ;-)) Who knows until I do it eh? The shop is a garage with a double door that is opened frequently. Humidity control is out of the question. But, we never go to less than 30% and are usually in the 50 to 70% range. I'm not 10 % what I will do with it, but I have some ideas.

I'm afraid to resaw it thinner than an inch. Do you think I will be better off keeping it thicker than 3/8 to 1/2 inch?


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## TopamaxSurvivor (May 2, 2008)

Guess I'm trying to be proactive rather than sorry ;-)


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## Jack_T (Feb 6, 2010)

You could cut it into veneers and really stretch the spalt.


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## rance (Sep 30, 2009)

I mostly agree with tennontim. I might only extend the acclimation period. Imagine your board as a big sponge. The outer layers are drier than the inner layers because the inner layers are insulated by the outer layers. When you cut down the middle, you are exposing those moist inner layers. When they dry, they will likely affect the board because it is unbalanced.

If you resaw a board into thirds, then let the pieces dry, the middle third is mostly likely to remain straight since you have exposed equal parts on two opposite surfaces. The outer two boards are not quite as likely to remain straight since they now have a dry side and a moist side. They are unbalanced, moisture-wise, and as they reach equilibrium, they are likely to move.


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## TopamaxSurvivor (May 2, 2008)

That is why I was thinking of doing an aggressive sanding on the out side before the resaw. Will that make much difference or just stir up a lot of dust?


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## oldworld124 (Mar 2, 2008)

I would suggest you also plan your project to re-saw the spalted wood and work it and glue it in place the same day. This will insure that it stays straight. I have never had a problem with a board once it is in place. Most woods that tend to warp or move should be worked at once and secured. You will have much more movement if the processed board is left to "acclimate". Just my 2 cents worth.


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## rance (Sep 30, 2009)

Topo, 1/16" off one side and 1/2" or more on the other? Only doing it will really tell. I'm just telling you you have a better chance with equal on both sides. Sorry, I'm just not that much of a wood whisperer.


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## REK (Aug 30, 2009)

Resaw….be happy!!!!  Good luck, and may the warp be without you!!!!


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## upickhardwoods (Apr 6, 2011)

I have been a kiln operator for the last 10 years. We have 500,000' of Kiln capacity, drying Hardwood species.

Relieving drying stresses is very critical to our operation. Our Panelshop edgeglues thousands of sq ft of panels on a daily basis.
We resaw alot of material for Window blinds and shutter parts, shipping to the West Coast.

There are so many variables to look at when considering stress. Stress is what you have when your outer shell is dry or wetter than the Core. Casehardening is when the shell is dryer than the core, Reverse casehardeneing is when the Core is dryer than the shell.
Air drying any hardwoods in most parts of the country will only allow you to dry down to 12 - 15%. The core will be significantly higher in moisture than the shell. Although I'm sure that there might be someone out there who has resawn material like this and have been successful, the odds are against it. Even if you resaw the material and it comes off the saw flat it won't stay that way. The core that you have exposed will start drying "shrinking" and pull the shell side until it starts to curl up like a rocking chair part. 
Those longitudinal stresses are very hard to relieve and must be done in a controlled enviroment such as a dry kiln.
If the desired final moisture content is 7% for a kiln charge, we dry it down until the dryest sample reaches 5% then we setup an equalization step. Create conditions in the kiln that won't allow the lumber to dry less than 5% "Equalibrium Moisture Content" EMC, that way the lumber that is in the kiln at a higher moisture still drys but you don't over dry the rest. This process takes us about 4 days. 
Then "conditioning" begins thats where we put moisture back into the wood and bring it to the final moisture content of 7%. You want the core and shell to be less than 1% in diffence.
Ok lets say that you have done the perfect job of dying your material, then you have Growing stresses that you can't relieve with conditioning.
Where the pc was cut out of the log makes a difference.
The gentleman said Maintain RH of 40-50% I agree, our panelshop is controlled with those perameters.

I hope your pc works out for you

Sorry about the long message just thought I'd chime in.

You just can't imagine how much testing and studing we have done over the years on this subject. Dr. Gene Wengert "The Wood Dr." has helped me dial our Kiln drying in over the years.


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## ScottN (Jan 24, 2011)

Nice post wibles.

Sounds like your the man with the answers. 

I have a question for you…correct me if I'm wrong but isnt the purpose of drying down to 5% or down to a low percentage is to shrink the cells in the wood? damaging the cells to where they cant take on moisture or release it as fast as wood that hasn't been kiln dried? So in comparison non kiln dried wood would accumulate much faster to humidity changes.

Again…correct me if I'm wrong. I kinda remember reading something about it many years ago, and with my memory, it could have been something totally different.


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## upickhardwoods (Apr 6, 2011)

Scott, I don't know of any literature that says anything about Airdried or green lumber regaining moisture more rapidly than Kiln Dried. 
The purpose for drying down to 5% and equalizing is to get the Kiln Load down to a uniform Moisture. Even though the lumber is at 5% the moisture gradiant from the core to the shell is greater than 1% thats why we add moisture to the shell and relieveing the Stress.

Different species will take on Moisture or loose moistrue faster than others. Hickory for instance will not lose as fast as Basswood.

Kiln drying we try not to damage the wood cells, usually I think of "checking, honeycomb, collaps" as damaged cells.


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## woodism (Apr 2, 2010)

Ok…. just cause it hasn't been said. You can take a 1/2" cut off the end of the board, full width. Cut that in half . take note of where the middle of the board was. Go over to the bandsaw and make cuts from where the center was towards where the edge was but leave a 1/2 inch on the edge side. Cut the interior of the board , not the faces.You can make one of the pieces look like a "U, and make the other look like an "M". or a comb depending on how thick the plank is Severe stress ( case hardening) will show up almost immediately as the tines bend. Mild stress will show up overnight. Wood that has been well dried, will pretty much not react.

Jeeez,,, picture work a thousand words… So - 10" wide board, cut 1/2 " off end, cut in half to get 1/2" x 5" x thickness. Cut the middle out leaving both faces on 1" stock, or cut into a comb pattern ( remove every other "tooth" for thicker stock.

This is an easy way to figure out if your wood is stressed. It's on the cover of the federal Kiln operators handbook. great way to keep from getting screwed on badly dried wood.


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## Nomad62 (Apr 20, 2010)

Hi Topo, I would recommend slicing off a thin piece, maybe 1/8" thick and see what happens; you may be getting all worked up over a problem that may not be there. It sounds as if you are trying to think about the potential of case hardening… always a concern, but not so much with maple; and if it was only air dried, I would believe it to be a non-issue. Also, avoid cutting any questioned wood in extreme weather conditions, hot or cold, that would be the best way to cause a problem. The best time to cut, in my opinion, is when it is cool (65 deg or so) and dry.


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## TopamaxSurvivor (May 2, 2008)

Thanks for the replies. Yes I am just trying to anticipate potential issues and nip them in the bud. I have seen too many what happened posts on LJ;-(( My thought about sanding the present surfaces before cutting it into 2 or 3 pieces was to introduce a new surface to the atmosphere on both sides of the board rather than have one new and one old.


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## patron (Apr 2, 2009)

do it a tad thicker then
and turn and re-saw the 'old' side too
(just enough to clean it up)
that way they are both the same exposed
and can breath equally


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## a1Jim (Aug 9, 2008)

I think the subject of moisture and eternal stress has been well handled but what to do with your resawn wood after the jobs done. A simple way to have your wood equalize it's moisture content is to place it in a plastic bag until your ready to use it,if that can't be done make sure the wood is stickered so it has equal air circulation all the way around.


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## TopamaxSurvivor (May 2, 2008)

David, Would resawing a thin slice to expose the old side be different than an aggressive sanding?

I never thought about plastic bagging it, sounds like a good idea.


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