Resawing / lumber question - having trouble with W Oak

[JasonG]

Hello,

I am making a nightstand. I am working up some panels for the top / sides, out of white oak. I bought some S2S (top and bottom planed) 4/4 white oak from a good dealer. I've had good luck there in the past.

I'm having the worst time resawing this oak (1", resaw king blade, laguna 14" bandsaw), it keeps pinching my blade, and as soon as the wood is fully sliced through, it springs out into a potato chip. The wood itself is flat and pretty, before I resaw, no evidence of cupping or twist. But as soon as that blade gets through, the 1/2" slices instantly cup.

Did i Just end up with a bad batch or something? I've really never had this problem before.

Any advice?

Jason

 

[bob vaughan]

Internal stresses in the wood are often relieved when ripping edgeways (re-sawing). There's no way to predict it or avoid it by looking at the wood. The next piece from that same tree may behave perfectly.
A dull blade can heat things up and stress the wood.

 

[creasman]

Agree w/Bob. No way to know what stress is inside until you cut. These are some things you can do to minimize the chance of this happening.

• Use quarter-sawn or rift-sawn lumber. Of course, if you're looking for the cathedral grain pattern you get with flat-sawn, this isn't an option.
• Cut the boards to the rough length you need before re-sawing. It's easier to deal with shorter boards.
• Use the table saw to saw the first couple of inches on each edge before switching to the band saw. This means less the band saw has to cut through and you have a wider kerf left by the table saw, so less pinching.

The problem you can't avoid is that once you've resawn a board like this it's now cupped or warped and you have to flatten it again. This means you have to oversize it enough to allow for re-planing.

If you really like the grain pattern, consider resawing it into 1/16" thick sheets and then use it as veneer. You can use a less expensive substrate (e.g., MDF, plywood or poplar) and your nice (and presumably more expensive) wood goes a lot further.

 

[JasonG]

These are both great answers. All i wanted to hear was that it wasn't my fault (kidding). I'm pretty sure it's not my blade and further it was warm but not hot post a few resaws.

The good news is I can reflatten, i think i could get away with something as thin as 1/4" panels, since they are dado locked on 4 sides.

I was just so surprised at the instantaneous movement here.

After reading your answers, i actually resawed a different board of white oak, purchased at a different date - and it came out perfectly, and did not bend / bow / warp at all.

So, I'm blaming this batch of wood.


Thanks again

 

[bob vaughan]

Calling it a 'bad' batch of wood may be somewhat of a misnomer.
Look at the end grain. If the board is flat sawn with large arches, that cut is a whole lot more risky of warp than what Jim said about quarter or rift sawn.
It is more likely that the cut of wood was risky rather than 'bad'.

 

[bob vaughan]

Here's the best shot of flat sawn wood that I can come up with.

 

[ggoss]

If it's kiln dried, the potato chipping may be the result of case hardening (resawing the board creates 2 new boards, each with 3 faces with more internal stress than the 4th, causing them to warp). It may not help with any boards you have already resawn, but if you have any others that you suspect are case hardened and can spare some thickness, planing a little bit from each side before resawing (removing some of the 'case') may help to reduce the warping.

 

[jlwest]

If it's kiln dried, the potato chipping may be the result of case hardening (resawing the board creates 2 new boards, each with 3 faces with more internal stress than the 4th, causing them to warp). It may not help with any boards you have already resawn, but if you have any others that you suspect are case hardened and can spare some thickness, planing a little bit from each side before resawing (removing some of the 'case') may help to reduce the warping.

I agree that it might be case hardened from incorrect drying.

 

[golfdad]

Try a smaller blade. A 1in blade is much to large for a 14in saw. I dont go more than 1/2in 3TPI blade on mine

 

[tiswritten]

It sounds like the wood was not properly conditioned after kiln drying to relieve stress. This is the last step in kiln drying the lumber and is sometimes ignored or rushed...because time is money. When a kiln cycle is done, the core moisture in the lumber will always be higher than the shell. The right thing to do is add steam back to the charge in the end to bring the shell moisture back up as to be comparable to the core. This takes the stress out of the lumber which helps it stay flat when resawing. The lumber could have also been dried in a dehumidification kiln with no means to add steam in the end. This is why I prefer lumber dried properly in steam kilns. I believe 4/4 White Oak should condition with steam for 18-24 hours after drying to equalize the shell/core. I've seen a lot of case hardening in Walnut. It's difficult to case harden White Oak because it would typically develop severe surface checks to alleviate stress before actually case hardening.

I believe you got a bad batch that wasn't conditioned... and that it wasn't your fault.

 

[mkepke]

It sounds like the wood was not properly conditioned after kiln drying to relieve stress. This is the last step in kiln drying the lumber and is sometimes ignored or rushed...because time is money. When a kiln cycle is done, the core moisture in the lumber will always be higher than the shell. The right thing to do is add steam back to the charge in the end to bring the shell moisture back up as to be comparable to the core. This takes the stress out of the lumber which helps it stay flat when resawing. The lumber could have also been dried in a dehumidification kiln with no means to add steam in the end. This is why I prefer lumber dried properly in steam kilns. I believe 4/4 White Oak should condition with steam for 18-24 hours after drying to equalize the shell/core. I've seen a lot of case hardening in Walnut. It's difficult to case harden White Oak because it would typically develop severe surface checks to alleviate stress before actually case hardening.

I believe you got a bad batch that wasn't conditioned... and that it wasn't your fault.

Shouldn't case-hardening be easy to confirm by checking the mositure content on the 'old' face as well as the newly cut face? Assuming one has a moisture meter. Dunno what the MC differential needs to be tho.

Also, wouldn't letting the wood acclimate in one's shop for weeks (or months or years in my case ) resolve the case-hardening? Again, MC on the two faces should be nearly the same after a suitably long acclimation period.

-Mark

 

[tiswritten]

Shouldn't case-hardening be easy to confirm by checking the mositure content on the 'old' face as well as the newly cut face? Assuming one has a moisture meter. Dunno what the MC differential needs to be tho.

Also, wouldn't letting the wood acclimate in one's shop for weeks (or months or years in my case ) resolve the case-hardening? Again, MC on the two faces should be nearly the same after a suitably long acclimation period.

-Mark

Yes. you would see a fair amount of variance in the moisture content on the faces after resawing in the stressed lumber. I think if it is properly conditioned after drying, the core vs. shell MC should be within 5% of each other. Professor Gene Wengert from Woodweb says case hardening does not go away with time. In the lumber business, when we talk about case hardening, it is defined as a condition where the shell has been dried too rapidly in a low humidity setting in lumber that has not been given much air drying time prior to putting into a kiln. In this case, the degree of damage that has been done to the shell fibers on a cellular level creates a condition where it is nearly impossible to wick any moisture out of the core to complete the drying process. I once witnessed a company case harden 80,000 bft of 8/4 Walnut. The shell was around 10% MC. The core was around 40%. They had dehumidification kilns with no steam for conditioning. They tried everything but could not get that core MC to move because of the shell damage. That was an expensive lesson on how not to dry lumber.

I guess if it were me, I would find a meter to see what the core MC is and would probably use that batch for something that doesn't need resawn. It's true that the MC on the two faces (shell) would be nearly the same after a suitably long time, but the core MC has to be considered as well, especially if you are resawing the material.

 

[MTod]

There is a test you can conduct to determine whether the wood has been case hardened. Attached is the paper from Purdue University.

https://www.extension.purdue.edu/extmedia/FNR/FNR-132.pdf

 

[JasonG]

These are all great thoughts. I really appreciate the thinking here.

One follow up, the comment about a blade being too large. I wasn't aware that was possibly an issue. I'm obviously no expert, but how would one say what is the appropriate size blade for a bandsaw? Is there some formula? As mentioned, I've had no problems before. It's a Laguna 14SUV.

Given every board in the lot has bent the same way, and given the purdue paper picture of case hardening (the combined boards look like a cylinder almost, after being resawed), I think that's what has happened here.

As noted, i think i have some decent room left to flatten. Hopefully will all end Ok.

 

[JasonG]

I meant to add, as well, this is def flat sawn lumber. Plenty of cathedrals.

 

[Rwe2156]

Hey Jason, even if the saw says OK, really a 1" blade on a 14" bandsaw is WAY too big. 3/4 is probably pushing it, too. Personally, I resaw with a 1/2" blade, and that's on an 18" 3HP saw. I'd rather have overkill but I can tension the you know what out of the blade.

You are very likely right about case hardening. It's an issue plus flat sawn white oak is notorious for stress and going wonky on you. I've worked with some that drove me nuts. The one board you have with the pith is going to be the least stable. I would saw the middle out and have two quarter sawn strips, you can glue back together.

My suggestion to you is try 1/2" resaw blade. Timberwolf if good, I don't recommend Woodslicer they never hold up that good for me. A few years ago I got a couple Infinity rip blade and I'm totally sold on them. They outperform a Woodslicer by far.

I also suggest you not be too quick about surfacing. I would sticker them and clamp the stack between a couple beams or thick strong boards & let them sit around for a couple weeks. Don't be surprised if you have difficulty keep them flat. Wood with that much internal stress often end up in my burn pile. White oak can be frustrating to work with sometimes.