Q. I have been having problems with warp and twist in yellow-poplar, mostly in our S4S after it is in stock quite a while. Do not know that we have a problem when milling. To my knowledge wood will not change any after milling unless there is a moisture change. My question is will stressed lumber warp over a period of time? Also, will it warp more than non-stressed lumber when going thru MC change?

 

 A. Your preliminary comments are indeed correct.

 

 Further, drying stress will not show up later or affect warp when there is a MC change. Stress, whether it is growth stress or drying stress (also called casehardening) will show up only during machining. So, if wood moves after drying we are left with the fact that there is some MC change going on. (Most kilns do really well on final MC, but sometimes they only sample six to ten pieces out of the 510,000 pieces in a kiln load.) A wild guess is that better sampling when unloading the kiln is needed.

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