Replies

1. 
   Andrew | Mar 14, 2003 06:58pm | #1

   Most times when you resaw a board your releasing some internal stress which can cause it to warp. The other possible cause is that the wood hasn't been dried evenly, which would cause it to warp. I've had this happen to me before, and the best thing to do is sticker the boards, put weight on top of them and let them sit for a little while before planing and jointing.

   hope this helps

   andrew

2. 
   StanleyNiemiec | Mar 14, 2003 07:22pm | #2

   There are two possibilites as to why this happened.

   The first probable cause is that the material is casehardened.  During final stages of the drying process, the wood was not properly conditioned and as such there are residual  drying stresses in the wood.  These stresses are entirely mechanical (ie as wood dries the surface takes on a compression set while the core assumes a tension set) and when you removed the restraining oppositional "other" side, these mechanical stresses equalize and the wood will distort.  (I explained casehardening in a thread in January.  If you do a keyword search on that term, you should be able to locate that discussion.)

   The second probable cause is that there was variation between the surface moisture content and the moisture content of the core.  If the core had a higher moisture content than the surface, when the core was exposed to ambient EMC conditions, it would dry and shrink, thus causing the wood to cup.

   If the material is casehardened, then you have to cut them oversize.  If the material has a different core/surface MC and you wish to cut it to a specific target size, then you need to equalize the overall moisture content to your shop's ambient conditions by allowing it to sit for several months before machining (assuming of course that you have controlled EMC conditions within your shop).

   My guess is that both conditions probably exist.  Casehardening is prevelant in thick oak as is variation between surface and core MC.  The fact that some bowing occurred indicates to me that the material is not perfectly straight grained and some grain angle exists in the piece you were resawing.

1. 
   AlanTurner | Mar 14, 2003 08:03pm | #3

   Stanley,

   Thanks.  I was hoping you might find time to respond.  This is what I was afraid of.  My normal sawmill does a great job, but they actually buy in their white oak.  Dried, I assume.  My shop is in my basement, which varies winter to summer, and when it rains (stone foundatin walls).  I'll leave it for a bit, and then reflatten by removing stock.  Wish it weren't so, but this is wood, after all.  Because the drawers are inset, which I prefer in terms of look, the fit is tighter than were I overlaping the front a bit. 

   I did read your thread on case hardening, and this is what I feared was happening.  My guess is that white oak esp. is subject to this condition since it is not ring porus, and is hard as a rock.  I find it quite challenging to work with, but this chest is a bit of a country piece, and I do not care for the appearance of red oak.  That is a purely personal preference of course - hard to argue taste.  I actually thought about using paulawinia (bad sp.!) for the appearance, but have never used it before, and it seemed a bit soft.  Huge slabs were at the mill when I was last there.  6/4 x 30" or better.  And, I didn't know how it would finish.  Have you ever worked with this wood?  Is it an east coast tree?  I've seen it on price lists before, but never seen it before a month or so ago.

   Alan

2. 
   BiotechBill | Mar 15, 2003 01:05am | #4

   Correct me if I'm wrong, but couldn't you eliminate some of the problem by using QS white oak? Plain or flat sawn seems to be just asking for cupping to occur after resawing. Not that this helps you now, I just wanted to learn from the situation presented.

   Dr. Bill

1. 
   johnhardy | Mar 15, 2003 01:32am | #5

   Nope. I bought some 8/4 quartersawn white oak for a Mission table project, and when it was resawn the two 4/4 boards bowed something fierce. It was majorly case hardened. Laying flat, the 8 foot boards probably bowed at least 4 inches in the middle.

   John

2. 
   StanleyNiemiec | Mar 15, 2003 02:52am | #6

   As I stated before, I felt that there were two probable causes of the problem manifestation  --  unequal moisture content within the board and/or casehardening. 

   If these conditions exist (both are drying problems) the actual orientation of the grain (eg flat sawn/tangential; quartersawn/radial) will not matter.  Both grain orientation patterns can still have these types of problems.

   Storing the board so that surface and core moisture content equalize could prevent one of the causes (providing one can wait 6-12 months).  This however will do nothing to minimize the drying defect casehardening unless of course sufficient moisture is adsorbed by the surface.  If this is the case, then the overall board MC will likely be too high and excessive shrinkage in situ would likely occur.

   The reality of this situation is that the lumber is of poor quality.  It may be of a particular grade but grade is different than quality.  It is possible that the kiln operator screwed up  --  they are human and do make mistakes.  Most often problems like this are more related to a company putting kiln throughput (production) ahead of quality by cutting corners (minimizing or eliminating the conditioning and equalization parts of a the kiln schedule) or the companies are not properly training the kiln operators in their employ.

   If an individual is purchasing thicker stock for resawing, then it is an essential purchase consideration (obtained in writing on the invoice or PO) that the material has attained an appropriate target MC and that it has been properly conditioned and equalized.

   Small quantities of 8/4 white oak are probably selling for about $7.00/bdft ($7000/M); the additional cost to a kiln operator to properly condition and equalize a charge is literally pennies per board foot yet the end result of not doing so can render the material unusable. 

3. 
   jjf | Mar 17, 2003 03:45pm | #8

   Quarter sawn lumber does not eliminate casehardening nor uneven moisture content through the lumber effects.  If one side is 5% (the side of a reswan board that corresponds to the outside of the original board) and the other side being 12% (the side that corrsponds to the inside of the original board), both quarter sawn and flatsawn will cup when the wet side dries out.  What it does help eleminate is cupping when the board changes moisture content.   Say from 6% to 10%.  There is less cupping in quartersawn than flatsawn lumber when the MC changes.

   If the cupped resawn board from a board that had casehardening was evenly dried very little can be done to flatten it out, even weights.  Best thing to do is rerip it into narrow strips and glue it up.

3. 
   DaveHeinlein | Mar 15, 2003 11:29pm | #7

   It is a good possibilty that if you stack the veneers flat with some weight on them, they will come back to a flat stage. I suspect the problem is most likely un-even moisture content.

4. 
   AlanTurner | Mar 17, 2003 04:54pm | #9

   Thanks for everyone's comments.  This weekend I reflattened, etc.  All I got from 8/4 white oak was two 5/8" boards, quite flat.  This is a bit disappointing.  I am sure it was the wood.  Does anyone know if white oak is particularly prone to this? 

   This weekend I resawed my drawer sides and bottoms from 8/4 maple, which I had bought from a yard that was no longer going to carry it (so got a very good price, 2.35/BF).  I suspect it had been there quite a while.  It was already surfaced two sides, and was at 1.75 light.  Got 3 boards, at .485 (replaned), and got 4 boards @ .3125, not yet resurfaced, but resurfaced between each cut.  It stayed quite flat and straight.