Stress relief from bandsaw resawing

[Clay Fails]

I just resawed a beautiful piece of 8/4 Qsawn white oak in the hopes of producing bookmatched pieces for a tabletop. To my horror both pieces came off the saw really warped, which i assume is internal stresses being relieved. My questions for theose with more experience:

1) Could i have done anything to avoid this?
2) is there anything I can do to re-straighten the boards? Steaming?

If i try to joint and plane them i will never get the 3/4 thuckness i want. The warp is too severe.

thanks!

[Jim Finn]

I have had this issue resawing oak to 3/8" thickness and found that if I keep the ortiginal board in my shop a few days before re-sawing it , this issue goes away. Gives the wood a chance to warm up to the temp that I saw it in. At least it has worked for me.

[John TenEyck]

Temp. was not likely the cause, more likely it was the moisture content. When the center of the board has a higher MC than the outside faces the boards will spread apart as the original board is resawn. If it's lower in the center, the boards will try to pinch together. The solution is still the same - don't work wood until it's been in your shop long enough to come to the EMC of your shop. For the OP, all you can do now is wait; often the boards will straighten out again after the MC equilibrates within the cut board. Just leave it standing up or on edge on the bench and leave it for a few days. If it doesn't straighten out, not much you can do that will be permanent.

John

[Phil Thien]

I just resawed a beautiful piece of 8/4 Qsawn white oak in the hopes of producing bookmatched pieces for a tabletop. To my horror both pieces came off the saw really warped, which i assume is internal stresses being relieved. My questions for theose with more experience:

1) Could i have done anything to avoid this?
2) is there anything I can do to re-straighten the boards? Steaming?

If i try to joint and plane them i will never get the 3/4 thuckness i want. The warp is too severe.

thanks!

(1) Not if the movement was due to wood tension.

(2) Not if the movement was due to wood tension.

If, OTOH, the movement was due to a moisture imbalance, setting the pieces aside for a time may result in flatter stock.

BTW, I've seen so many times people note that movement after resawing is because of a moisture imbalance. But we've all had reactive wood that when ripped on the table saw (for example) pinches the splitter or riving knife. This is due to internal stresses of the wood being released. Well, resawing can release the same sort of internal stresses.

[Jim Matthews]

How much tension can their be in a quartersawn board?

[Steve Baumgartner]

How much tension can their be in a quartersawn board?

There can be tension in a board regardless of grain orientation. It results from imbalance between shrinkage in the outside and the inside of the board, not from grain orientation (i.e. the radial vs tangential shrinkage that makes qs more stable after drying).

[Clay Fails]

Temp. was not likely the cause, more likely it was the moisture content. When the center of the board has a higher MC than the outside faces the boards will spread apart as the original board is resawn. If it's lower in the center, the boards will try to pinch together. The solution is still the same - don't work wood until it's been in your shop long enough to come to the EMC of your shop. For the OP, all you can do now is wait; often the boards will straighten out again after the MC equilibrates within the cut board. Just leave it standing up or on edge on the bench and leave it for a few days. If it doesn't straighten out, not much you can do that will be permanent.

John

Thanks for the input. This board was in my shop for about a year and a half before yesterday. It may still be due to unequal moisture content between outside fibers and inside fibers. Hoping it will straighten itself, but not betting on it!

[Myk Rian]

Re-sawing is a crap shoot. Plain and simple. You never know what will happen.

[Reed Gray]

It can have a lot to do with how well the wood was dried in the first place. This is more of a problem with kiln dried wood where stress can be dried into the wood. Much less of a problem with air dried wood, solar kiln dried wood, and vacuum kiln dried woods. Production 'kill dried' wood can really spring a lot. With the other methods of drying, I often get no movement/spring at all.

robo hippy

[ernest dubois]

I disagree that there is risk in re-sawing but I can agree that kiln dried wood is probably more prone to a release reaction.

[John TenEyck]

Very true. The OP's result could just as easily have been caused by tension as moisture imbalance. Probably more likely seeing now that the wood had been in his shop for 18 months.

John

[Scott T Smith]

How much tension can their be in a quartersawn board?

Jim, there are several ways that tension can be present in a QS board. The most common way is if the log had an off-centered pith, which indicates internal stresses in the lumber (comes from a leaning tree). Other ways are if there is pith wood or sapwood present along the edges of the board.

8/4 white oak takes a long time to acclimate; however a year and a half is more than sufficient. Additionally, even if the board was improperly dried (case hardened) it would still most likely have equalized over the course of a year and a half.

Clay - can you post some photo's of the board? Show close-ups of the end grain (include as much of it across the width of the board as possible), as well as photo's that show the cup that developed (put the board halves back together for the photo).

[Steve Baumgartner]

Additionally, even if the board was improperly dried (case hardened) it would still most likely have equalized over the course of a year and a half.


It would have equalized MC, but if it was case-hardened during drying, that is permanent damage that won't be undone by equalizing moisture content.

Case hardening occurs when the outside and inside of the board are dried at rates that differ too much. The outside dries first, and tries to shrink. The still moist inner parts haven't shrunk yet, so the outer part comes to be in tension. It reacts to the tension by stretching horizontally and microfracturing. Drying "sets" the outer layer in this stretched state. Then when the inner part finally dries and shrinks, the outer part can't follow it and comes to be in compression.

[Clay Fails]

Jim, there are several ways that tension can be present in a QS board. The most common way is if the log had an off-centered pith, which indicates internal stresses in the lumber (comes from a leaning tree). Other ways are if there is pith wood or sapwood present along the edges of the board.

8/4 white oak takes a long time to acclimate; however a year and a half is more than sufficient. Additionally, even if the board was improperly dried (case hardened) it would still most likely have equalized over the course of a year and a half.

Clay - can you post some photo's of the board? Show close-ups of the end grain (include as much of it across the width of the board as possible), as well as photo's that show the cup that developed (put the board halves back together for the photo).

Will do Scott, as soon as I get them out of my last ditch clamping effort to straighten them! Probably tomorrow I can upload photos.

[Keith Hankins]

Hate that man, and I've been there. Not seeing the boards, I cant say it's a lost cause. However, I have tried a few things that have helped with cherry. Don't know it would work for you but ya never know. When I resaw a couple boards and see first sign of them getting funky, I'll put them back to back (wet faces to outside) tape them together, and put them in a black garbage bag wrap as tight as I can and put them under weight for a couple weeks. I've had them level out. Take them out of the bag and put them back under weight, and leave them another week and see how it goes. Like I said some times it works some times it was just not meant to be. If it happens a few times from the same mill that's doing the drying, I'd find another source they don't know what they are doing.

[Clay Fails]

Hate that man, and I've been there. Not seeing the boards, I cant say it's a lost cause. However, I have tried a few things that have helped with cherry. Don't know it would work for you but ya never know. When I resaw a couple boards and see first sign of them getting funky, I'll put them back to back (wet faces to outside) tape them together, and put them in a black garbage bag wrap as tight as I can and put them under weight for a couple weeks. I've had them level out. Take them out of the bag and put them back under weight, and leave them another week and see how it goes. Like I said some times it works some times it was just not meant to be. If it happens a few times from the same mill that's doing the drying, I'd find another source they don't know what they are doing.

Thanks for that idea. I may give it a try. This board was purchased in April 2013 from West Penn Hardwoods in Olean, NY. I've had good results with their lumber, but i dont know where they sourced this board.

[Scott T Smith]

It would have equalized MC, but if it was case-hardened during drying, that is permanent damage that won't be undone by equalizing moisture content.

Case hardening occurs when the outside and inside of the board are dried at rates that differ too much. The outside dries first, and tries to shrink. The still moist inner parts haven't shrunk yet, so the outer part comes to be in tension. It reacts to the tension by stretching horizontally and microfracturing. Drying "sets" the outer layer in this stretched state. Then when the inner part finally dries and shrinks, the outer part can't follow it and comes to be in compression.

Good explanation!

[Clay Fails]

It would have equalized MC, but if it was case-hardened during drying, that is permanent damage that won't be undone by equalizing moisture content.

Case hardening occurs when the outside and inside of the board are dried at rates that differ too much. The outside dries first, and tries to shrink. The still moist inner parts haven't shrunk yet, so the outer part comes to be in tension. It reacts to the tension by stretching horizontally and microfracturing. Drying "sets" the outer layer in this stretched state. Then when the inner part finally dries and shrinks, the outer part can't follow it and comes to be in compression.

This has been a really informative thread, and I hate to quarrel, but I don't see how the outer fibers (the "longer" side of the board) could be in compression when the inner side shrinks. Would the outer fibers not be in tension?

[Steve Baumgartner]

This has been a really informative thread, and I hate to quarrel, but I don't see how the outer fibers (the "longer" side of the board) could be in compression when the inner side shrinks. Would the outer fibers not be in tension?

The outer fibers take their "set" while stretched over the not-yet-shrunk inner. That is, their size is big enough to fit over the unshrunk inner. When the inner later shrinks, it becomes smaller and the outer fibers are compressed while trying to match this now smaller size.

[Clay Fails]

299042299043
Jim, there are several ways that tension can be present in a QS board. The most common way is if the log had an off-centered pith, which indicates internal stresses in the lumber (comes from a leaning tree). Other ways are if there is pith wood or sapwood present along the edges of the board.

8/4 white oak takes a long time to acclimate; however a year and a half is more than sufficient. Additionally, even if the board was improperly dried (case hardened) it would still most likely have equalized over the course of a year and a half.

Clay - can you post some photo's of the board? Show close-ups of the end grain (include as much of it across the width of the board as possible), as well as photo's that show the cup that developed (put the board halves back together for the photo).

For perspective,the gap between the two boards in the center is a little over 1/2 inch. It has to be stress relief as others have said.

[Scott T Smith]

299042299043

For perspective,the gap between the two boards in the center is a little over 1/2 inch. It has to be stress relief as others have said.

Clay, thanks for the photo's; they indeed do tell the story of what is happening and why. If you look at the view of the end grain, you can see where the board was pretty much perfectly quartersawn - at least in terms of the view from the end. If you look at the top of the board you can see where the grain on the right resawn side shows curvature, which also tells you that this was the pith side of the board.

Looking at the photo on the right that shows the bow in between the resawn boards, if you zoom in on the photo you can see where the cathedral edge grain is centered on the edge of the board where it is closest to the end of the board, but as you move up the board to where the bow is the worst the cathedral grain works its way to the right side of the board.

What this tells you is one of two things. First, the log may have had an off centered pith in one location, which would cause the edge grain to move relative to the face of the board. This will result in inconsistent stresses being present in the board. The other likely option is that the sawyer did not center the pith both way on the log when he/she made their opening cuts, which resulted in the board not having perfectly centered quartersawn grain on both ends.

Additionally, it is hard to see in the photo but it almost appears that there is a defect (knot) on the edge of the board adjacent to where you have your pencil marks on the edge in the center, or something that caused the grain to change directions. It also appears that there may be some edge checks due to the presence of pithwood along the edge of the board.

I would hazard a guess that if you study the medullary ray fleck on the board, it is much more pronounced on the end closest to where you took the photo of the end grain, and that it is much less pronounced on the opposite end of the board due to the lack of pith center in both dimensions.

[Brad Schafer]

stunning analysis. being unworthy, i will now put down the chisel and return to my lowly software career ...

[Scott T Smith]

stunning analysis. being unworthy, i will now put down the chisel and return to my lowly software career ...

<grin> Don't feel bad - I can't debug code so we're even! ;)

[Clay Fails]

Clay, thanks for the photo's; they indeed do tell the story of what is happening and why. If you look at the view of the end grain, you can see where the board was pretty much perfectly quartersawn - at least in terms of the view from the end. If you look at the top of the board you can see where the grain on the right resawn side shows curvature, which also tells you that this was the pith side of the board.

Looking at the photo on the right that shows the bow in between the resawn boards, if you zoom in on the photo you can see where the cathedral edge grain is centered on the edge of the board where it is closest to the end of the board, but as you move up the board to where the bow is the worst the cathedral grain works its way to the right side of the board.

What this tells you is one of two things. First, the log may have had an off centered pith in one location, which would cause the edge grain to move relative to the face of the board. This will result in inconsistent stresses being present in the board. The other likely option is that the sawyer did not center the pith both way on the log when he/she made their opening cuts, which resulted in the board not having perfectly centered quartersawn grain on both ends.

Additionally, it is hard to see in the photo but it almost appears that there is a defect (knot) on the edge of the board adjacent to where you have your pencil marks on the edge in the center, or something that caused the grain to change directions. It also appears that there may be some edge checks due to the presence of pithwood along the edge of the board.

I would hazard a guess that if you study the medullary ray fleck on the board, it is much more pronounced on the end closest to where you took the photo of the end grain, and that it is much less pronounced on the opposite end of the board due to the lack of pith center in both dimensions.


Thanks for the analysis Scott. Going forward, do you think there is any way to reliably predict if a board has these internal stresses by studying the grain patterns? That might save me from ruining another nice board!

[Scott T Smith]

Thanks for the analysis Scott. Going forward, do you think there is any way to reliably predict if a board has these internal stresses by studying the grain patterns? That might save me from ruining another nice board!


Sure.

If the lumber was quartersawn with a band mill, most likely the boards with the highest amount of ray fleck will experience pith wood checking along one edge. This is because a band mill usually includes the pith wood with the boards that are milled from the center of the log. Plan on removing around 15 years of growth rings along the edge of the board that was closest to the center of the log. Don't be afraid of buying these boards; what I typically do is start on the outside of the board with my edge jointing, and that way when I rip to width the part of the board that is discarded is the portion that has the edge checking.

Edge checking in quartersawn boards - when it is only present along one edge - is not an indicator of drying related defects (otherwise it would be checked on both sides, etc). It is an indicator of the presence of a small amount of pith wood.

Second, look for consistent cathedral grain running along the edges of the boards. Some variance is to be expected, but what you don't want to see is significant shifting of the grain from side to side along the full length of the board. If the amount of ray fleck is consistent from end to end on the board, that is also a sign that the log was both straight and properly aligned in all three dimensions when quartersawn.

I'll see if I can post some photo examples later.