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    Re: resawing QS white oak question

    Hate to sound difficult but with all the advice there is still a looming question I can't figure without a picture. What is the grain pattern?

    It seems like we're detectives looking for a missing person and we don't have a photo to reference. Just me.

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    Re: resawing QS white oak question

    Here's where we are today and Steve hasn't said much about what his cupped wood has done since then.

    I resawed a 5/4 board into two pieces and the following day it had cupped pretty badly. It was stored overnight with ample air to reach both sides of the boards. To re flatten it via jointer / planner / sander / handplane would have removed way too much material. It's been in my garage for almost 2 yrs and was bought kiln dried so I think it's just the nature of the wood releasing stresses rather than moisture content issues.
    2 quarter sawn pcs about 5/8"t each that cupped. Still cupped after about

    and....

    What most likely happened in Steve's situation was that the shell of the board regained moisture after kiln drying. This will occur if lumber has not been stored in a humidity controlled environment after coming out of the kiln. White oak can be problematic because the tyloses in the pores significantly deter the core from regaining moisture.
    I don't know if this is a general occurrence or just a few funny boards in Steve's stash. Why wasn't the original 5/4 board already cupped after 2 years in his garage?

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    Re: resawing QS white oak question

    I realize this is from a scroll saw related issue , but what so you have to lose?
    this is related to 1/4 wood so I wwould expect to wet it more, especially on the outer edges. I would also lightly weight it in the middle.

    Another trick is to wet one side of the board and set it in the sun. The theory is that the cupping is due to uneven drying. Place the board on a flat surface, cup side up. Lightly moisten the top surface and allow the sun to dry it. You could use a hair dryer or heat gun if you prefer. Theoretically this allows the wood cells on the top surface to shrink and compress, bringing the board back flat. If the cell compression has been permanently set in this board, the cup will likely eventually return, but it may be worth a try.

    Berta

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    Re: resawing QS white oak question

    Quote Originally Posted by Jeff View Post

    2 quarter sawn pcs about 5/8"t each that cupped. Still cupped after about

    and....

    I don't know if this is a general occurrence or just a few funny boards in Steve's stash. Why wasn't the original 5/4 board already cupped after 2 years in his garage?
    OK, let me elaborate on my original post. Sometimes this concept can be difficult to follow if you're not in the lumber drying business.

    For starters, Danmart the board in question is quartersawn, but both QS and FS lumber will cup after resawing if differences in MC% exist between the shell and the core of the board and the board is resawn into two equal thickness pieces. The direction of the cup will be based upon which part of the board had the higher MC% before resawing.

    Let's start off with a 5/4 thick quartersawn white oak board that has been kiln dried down to 6% MC throughout, and stored in a humidity controlled warehouse. Wally Woodworker purchases said board and takes it home and stores it in his non-humidity controlled garage shop. Being online, Wally has "learned" from the Internet that he should store his lumber stickered in his shop (which is not a good idea in this instance. I'll elaborate more below).

    Wally's shop is a garage, and it's not humidity controlled. For discussion purposes let's say that the relative humidity in Wally's shop averages around 53% relative humidity and the temperature averages around 75 degrees F. In this environment, the equilibrium moisture content for lumber will be 10%, so Wally's lumber starts to increase in moisture content from the shell inward.

    Jeff, in answer to your question Wally's boards didn't cup while being stored because each face is regaining the same amount of moisture in his shop. Moisture related cupping is caused by unequal MC% on each face of the board that subsequently equalize. In Wally's situation both faces have regained the same amount of MC% in his non climate controlled garage because they were stored stickered. This creates internal stresses on the board from core to shell that show up after resawing (or if not resawn but face jointed and planed they wood will move if you don't remove the same amount of thickness from each face of the board.)

    Because Wally's lumber is white oak, it is very resistant to changes in MC%. White oak is a close pored lumber, with the cellular openings filled with a product called Tyloses. Think of tyloses as similar to plaque in a human artery. They fill up the artery and block the flow of blood. In the case of wood, tyloses block the conveyance of moisture, which is one of the reasons that white oak is so difficult (and time consuming) to dry. Kiln operators typically have to really crank up the temperature in their kilns in order to help cook the moisture out of the wood. Tyloses are also why white oak is very rot and water resistant and used to build ships and whiskey barrels.

    So, after a few months in Wally's garage, stickered and exposed to ambient RH% on both faces of the board, a cross section of the MC% gradient in the board will look like this:



    Note that the outer portions of the board have equalized with their environment in Wally's garage and regained some moisture - up to 10%MC or so around the shell of the board. However, because of the tyloses the core of the board has not regained moisture and is still at 6% MC.

    Wally wants to use thinner boards in a project, so he resaws his 5/4 thick QSWO board through the center. When he does so, the two resawn pieces have unequal MC% on each face, with one face of the resawn pieces being 10% and the other (resawn) face being 6% MC. See this diagram:



    After resawing, the new, thinner boards spend some time stickered in Wally's garage. Because the shell of the original board had reached equilibrium with it's environment in Wally's garage, it's MC% is 10%. However, because the former core of the board is at 6%, it will gain moisture on that face in order to reach equlibrium with it's environment. In short, the resawn face gains 4 percentage points of moisture, while the opposite face remains the same. This causes the face to swell and cup the board. See this diagram:



    QSWO will move approximately .0018 per inch per 1% moisture change, so in our example above one face of the resawn boards will expand by about 1/16" per inch of width, while the other face remains the same. This 1/16" per inch expansion causes the resawn pieces to cup.

    Now in reality, based upon the average RH% in our part of the world lumber will typically equalize in the summer to around 12% - 14% MC. So that means that the amount of expansion on the former core of the board will be about 1/8" per inch on the resawn faces, causing noticeable cup.

    Certain species that are porous (red oak, pine, mahogany, poplar, etc) will tend to equalize across the entire board over time, thus they are not as prone to cupping after resawing unless they have not fully equalized with their environment.

    Now, if the board was not properly dried and the core had a MC% that was higher than the shell, the cupping would be in the opposite direction as the former core of the board lost MC% after resawing. This would cause the resawn boards to cup towards the center, instead of away from the center as the former core of the 5/4 board lost MC and shrunk while doing so..

    For this reason, it is best NOT to sticker kiln dried lumber in a non-climate controlled shop after purchasing. Instead wrap the stack in plastic to retard the regain of MC%, and this will help to keep the boards not on the perimeter of the stack from regaining moisture. Even better yet, store the lumber in a humidity controlled location or in a high temp/low RH% location (such as an uninsulated attic).

    Clear as mud?!

    Scott
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    Last edited by scsmith42; 07-09-2018 at 08:30 PM.

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    Re: resawing QS white oak question

    Good Summary Scott.

    My take away on this will be to continue using Air Dried stock and getting it close to the dimensions and then the wait. I have experienced cupping and surprises here and there .. I guess that's part of the wood business.

    I use a fair amount of thick sugar maple in the gun stock work I do. Kiln dried stock just doesn't work as well as the slow air dried maple.

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    Re: resawing QS white oak question

    +1 to a good explanation and thanks. It's clearer than mud now.

    Will the cupped boards eventually equalize and nearly flatten out in Wally's unconditioned garage or are those internal tyloses set and relatively impermeable to moisture so the cup is what it is forever after (you're last diagram with 10% EMC one each face suggests that is the fact).

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    Re: resawing QS white oak question

    Quote Originally Posted by Jeff View Post
    +1 to a good explanation and thanks. It's clearer than mud now.

    Will the cupped boards eventually equalize and nearly flatten out in Wally's unconditioned garage or are those internal tyloses set and relatively impermeable to moisture so the cup is what it is forever after (you're last diagram with 10% EMC one each face suggests that is the fact).
    The resaw cupped boards will most likely NOT flatten back out. What Wally should have done in this instance was to keep the board in a location where it would not pick up MC%, or if it had picked up some MC% put it in an area where it would dry back down before resaw it it in two.

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    Re: resawing QS white oak question

    Not so sound repetitive, but experience has proven what Scott said to be spot on. I found it all out by trial and error and just understanding the relationship between moisture and wood. I think stress is definitely a factor, but when a board goes bonky I find I'm blaming internal stress a lot less than I used to.

    IME once a board is cupped that's pretty much it. Selective wetting/drying one side or the other has never worked out for me. I'm usually looking at finding another board or ripping and re-jointing.

    So what has worked best for me is to clamp milled boards together in stickers (I alternate inside/outside surfaces if resawn) wrap the whole shebang in plastic. (I don't do this anymore explanation below). Then I clamp the stack, apply cargo straps (tried packing tape - doesn't work) & remove the clamps. Nowadays I move the clamped up pack into a climate controlled space. +1 on what Scott said about keeping panels, etc in plastic. With some lumber I'll do that even if I move it inside. Then I don't touch it for at least a week.

    So the absolute MC is not the issue, its the gradient of difference between the core and the surface. Like Scott said, in some areas there's no way you will get lumber under 12% so 8% KD lumber is drier on the inside than outside. But the principle is the same, that as soon as you start opening up lumber with surfacing, rip or resaw cuts, things start moving.

    When I remodeled my shop, I built an air conditioned space in the corner (I call it the "Bench Room") where I keep all my hand tools, workbench, etc. Its been the biggest boost to my ww'ing experience since I discovered what "sharp" is LOL.

    After an initial jointing/planing, I move project lumber in that room and let it acclimate for at least 1 month. I also keep the project + all the subassemblies in there. I've had many projects develop issues within even a week of being moved inside the house.

    Since I started doing that, ww'ing is much more pleasant an less stressful ;-D

    Shout out to Scott, I purchased some QS material from him last year for a dining table, and I have to say it was some of the straightest, flattest lumber I have ever bought. The man knows his stuff.
    Last edited by Rwe2156; 07-10-2018 at 02:31 PM.

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    Re: resawing QS white oak question

    Thanks Scott, a very clear explanation. Now lets get into the Mud. After kiln drying and stabilizing you've got the board at 6% throughout. lets say it's 10" wide. You re-saw it down the middle and you have two flat boards 10" wide. You let it sit and it becomes 10% mc over time and it's still flat, but now it's 10+x" wide. In your example of the cupped boards, after they sit and both sides are at 10% the concave side is not as wide as the convex side. I assume if you put the cupped board back in the kiln to equalize the mc throughout that it would still not flatten (correct?). My hypothesis is that before re sawing, when the outside of the board reached 10% mc, it couldn't expand (as much as it wanted to) because it was being restricted by the lower mc in the center. This would have the effect of crushing the cells (or Tyloses) - irreversible- which causes that side of the board to become permanently more dense and less than the 10 +x width it would have become if re-sawn out of the kiln.

    So my friend, is this why the same board, 1/2 cut with equalized mc and 1/2 cut with unequal mc will never look the same or can the second board be re-moisturized and re-dried to make it flat?

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    Re: resawing QS white oak question

    Quote Originally Posted by JohnnyR View Post
    Thanks Scott, a very clear explanation. Now lets get into the Mud. After kiln drying and stabilizing you've got the board at 6% throughout. lets say it's 10" wide. You re-saw it down the middle and you have two flat boards 10" wide. You let it sit and it becomes 10% mc over time and it's still flat, but now it's 10+x" wide. In your example of the cupped boards, after they sit and both sides are at 10% the concave side is not as wide as the convex side. I assume if you put the cupped board back in the kiln to equalize the mc throughout that it would still not flatten (correct?). My hypothesis is that before re sawing, when the outside of the board reached 10% mc, it couldn't expand (as much as it wanted to) because it was being restricted by the lower mc in the center. This would have the effect of crushing the cells (or Tyloses) - irreversible- which causes that side of the board to become permanently more dense and less than the 10 +x width it would have become if re-sawn out of the kiln.

    So my friend, is this why the same board, 1/2 cut with equalized mc and 1/2 cut with unequal mc will never look the same or can the second board be re-moisturized and re-dried to make it flat?
    Johnny, your hypothesis is correct. The problem with remoisturazation on a single face of a board is that it is not a precise science. I’ve done it before with mixed results.

    Boards such as this would be great candidates for some type of curved front cabinet or curved top chest.

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    Re: resawing QS white oak question

    wally here

    Guess it's too late for me to do anything with the boards I have other than to find a use them as close to their current thickness as possible and to join/plane from both sides equally. I like the QS grain look so it looks like I'll need to switch to red oak for thin panels or see how well I can cut veneer on my bandsaw. I just prefer the warmer tones of finished white oak over red oak and never had much luck with stains and dyes turning red to golden / brown.

    I also planned on laminating a few more planes with the white oak but looks like I'll have to switch to something else. Which of these would work best for a wood body plane? Ash, Sassafras, Sycamore, hard maple.

    Thanks....

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    Re: resawing QS white oak question

    Quote Originally Posted by scsmith42 View Post
    OK, let me elaborate on my original post. Sometimes this concept can be difficult to follow if you're not in the lumber drying business.

    For starters, Danmart the board in question is quartersawn, but both QS and FS lumber will cup after resawing if differences in MC% exist between the shell and the core of the board and the board is resawn into two equal thickness pieces. The direction of the cup will be based upon which part of the board had the higher MC% before resawing.

    Let's start off with a 5/4 thick quartersawn white oak board that has been kiln dried down to 6% MC throughout, and stored in a humidity controlled warehouse. Wally Woodworker purchases said board and takes it home and stores it in his non-humidity controlled garage shop. Being online, Wally has "learned" from the Internet that he should store his lumber stickered in his shop (which is not a good idea in this instance. I'll elaborate more below).

    Wally's shop is a garage, and it's not humidity controlled. For discussion purposes let's say that the relative humidity in Wally's shop averages around 53% relative humidity and the temperature averages around 75 degrees F. In this environment, the equilibrium moisture content for lumber will be 10%, so Wally's lumber starts to increase in moisture content from the shell inward.

    Jeff, in answer to your question Wally's boards didn't cup while being stored because each face is regaining the same amount of moisture in his shop. Moisture related cupping is caused by unequal MC% on each face of the board that subsequently equalize. In Wally's situation both faces have regained the same amount of MC% in his non climate controlled garage because they were stored stickered. This creates internal stresses on the board from core to shell that show up after resawing (or if not resawn but face jointed and planed they wood will move if you don't remove the same amount of thickness from each face of the board.)

    Because Wally's lumber is white oak, it is very resistant to changes in MC%. White oak is a close pored lumber, with the cellular openings filled with a product called Tyloses. Think of tyloses as similar to plaque in a human artery. They fill up the artery and block the flow of blood. In the case of wood, tyloses block the conveyance of moisture, which is one of the reasons that white oak is so difficult (and time consuming) to dry. Kiln operators typically have to really crank up the temperature in their kilns in order to help cook the moisture out of the wood. Tyloses are also why white oak is very rot and water resistant and used to build ships and whiskey barrels.

    So, after a few months in Wally's garage, stickered and exposed to ambient RH% on both faces of the board, a cross section of the MC% gradient in the board will look like this:



    Note that the outer portions of the board have equalized with their environment in Wally's garage and regained some moisture - up to 10%MC or so around the shell of the board. However, because of the tyloses the core of the board has not regained moisture and is still at 6% MC.

    Wally wants to use thinner boards in a project, so he resaws his 5/4 thick QSWO board through the center. When he does so, the two resawn pieces have unequal MC% on each face, with one face of the resawn pieces being 10% and the other (resawn) face being 6% MC. See this diagram:



    After resawing, the new, thinner boards spend some time stickered in Wally's garage. Because the shell of the original board had reached equilibrium with it's environment in Wally's garage, it's MC% is 10%. However, because the former core of the board is at 6%, it will gain moisture on that face in order to reach equlibrium with it's environment. In short, the resawn face gains 4 percentage points of moisture, while the opposite face remains the same. This causes the face to swell and cup the board. See this diagram:



    QSWO will move approximately .0018 per inch per 1% moisture change, so in our example above one face of the resawn boards will expand by about 1/16" per inch of width, while the other face remains the same. This 1/16" per inch expansion causes the resawn pieces to cup.

    Now in reality, based upon the average RH% in our part of the world lumber will typically equalize in the summer to around 12% - 14% MC. So that means that the amount of expansion on the former core of the board will be about 1/8" per inch on the resawn faces, causing noticeable cup.

    Certain species that are porous (red oak, pine, mahogany, poplar, etc) will tend to equalize across the entire board over time, thus they are not as prone to cupping after resawing unless they have not fully equalized with their environment.

    Now, if the board was not properly dried and the core had a MC% that was higher than the shell, the cupping would be in the opposite direction as the former core of the board lost MC% after resawing. This would cause the resawn boards to cup towards the center, instead of away from the center as the former core of the 5/4 board lost MC and shrunk while doing so..

    For this reason, it is best NOT to sticker kiln dried lumber in a non-climate controlled shop after purchasing. Instead wrap the stack in plastic to retard the regain of MC%, and this will help to keep the boards not on the perimeter of the stack from regaining moisture. Even better yet, store the lumber in a humidity controlled location or in a high temp/low RH% location (such as an uninsulated attic).

    Clear as mud?!

    Scott
    Just going to say Holy Cr@p I had no idea of how technical lumber drying is. Its definitely a science and explains why wood costs more when professionally dried. Thanks for helping to enlighten me.

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