A lot of wood cups when sawn, especially if it is in thin planks and kiln dried. That leads to a condition called case hardening. Case hardened wood when resawn will cup to the inner side. On the opposite side of the same board, it will cup the other way.
maple is a good example. Maple must be cared for before staining and spalting begins. To get pristine whites it is sometimes necessary to cut into smaller planks sticker and dry using fans or in many cases dehumidification kilns.
I read the earlier posts and agree with what was said. Here is another take on the problem. Spritz the inner cupped side, then wait. Within fifteen to twenty minutes, the cup will nearly vanish. Now go to work on the dry side, the case hardened side. Send it through the thickness sander and you are removing excess saw marks and also the case hard wood.
The wood will heat up as you work it in the sander driving much of the moisture out of the opposite side by the time you are done. stop way short of finish dimensions, sticker your wood, and you will be very happy once you come back to it. I've done this over and over with maple, so I know it works.
Another way to rid wood of case hardening is to soak the pieces overnight in water, relieving the cell damage to the outer hardened wood. It then must be stickered to re-dry the wood. That was shared with me recently by a respected wood man. I've yet to try it, but I totally believe this fellow.
What species are you dealing with? I have some cocobolo that falls in this same category with the maple. This is why air-drying is probably better for the long run. But suppliers like to move product, today.
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