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I have been working with wood all my life. Since the 1960's. And I have always had in my head, when you look at the end grain of a board, by the way the circles are, you can determine if it was to warp, what direction it would.
But my latest batch of wood I have gotten has gone the other way. ODD! So my question to all the smart folk here when you see wood as in the image,
"N" if it was to warp what way would it most likely warp "A" or "B"?
I would expect B. The way to remember is the rings are trying to straighten out. That is if the wood is drying after milling. The opposite is true if the wood is gaining moisture.
That's what I always remembered thinking the grain circles want to flatten out so make a hill like "B" bit I got some that is behaving like "A" sooo odd.
Remember - wood only changes shape in response to changes in moisture in its environment.
While the terminology is anything but precise, where I am, the defect you describe is cupping. Warp has to do with curving along an edge.
It is possible that the lumber was surfaced or brought to the current thickness by removing more from one side than the other , now the moisture is not centered, maybe that is helping the cupping happen.
D Brown is right, but....
That is true only if the lumber is not dried properly. Hardwoods often have a final step in the drying schedule - called conditioning - that causes the wood to be a bit over dry on the surface, while the center comes right down to the right MC. Then the kiln operator adds some humidity to the load, putting back the water vapor that was taken in the short overdrying step.
Look up casehardening on this site and you can test some of your lumber in a few easy minutes.
Wood movement is entirely related to moisture loss or gain. Most moisture content related issues come from the lumber being too wet. But the thing to remember is lumber will swell if it's too dry.