Does the thickness of wood help stability?

[macdaddy]

Recently I let my son-in-law use my shop for a project and he planned a 1 by 12 board down to a little less than 3/8" thickness. I think he did this just because he liked the sound of my planner. I told him this was a mistake because the thinner board would cup and twist more with age than the inch thickness. Was I right in telling him this? My thought was that a 4 by 4 is used for a post because it twist less than a 2 by 4.

macdaddy

[DaveO]

A properly dried and handled thin board will not have a tendency to warp or cup any more than a thicker board. The problem arises when a thick board is planed down to a thin board often taking off different amounts from each side. This can result in an unbalance in the moisture content of each side of the thinner board leading to possible warping or cupping. That said, properly dried and acclimated wood should remain very stable and flat no matter the thickness.
Dave

[Larry Rose]

A piece of wood that shows twist warp or cup in excess, will likely do the same no matter what the thickness. Allways try to pick out the best looking rough stock. You can cut long pieces to get out of the twist or warp and a cupped piece can be ripped to help the situation.

[Kyle]

Most of the issues have to do with the drying of the wood and also the location from where the wood sawn in the log. If the wood was flat sawn close to the outside of the tree there is a string tendency to cup. If the tree grew in spiral pattern there is a tendency to twist. If the tree has a sweep to it there will be a tendency to bow. Not much to do about any of these defects as they are due to different gradients of fiber strength and density inherent in the tree itself. Good drying and stress relief will help mitigate these defects but wont eliminate them.