Bowing in kiln-dried pine

What causes warpage of kiln-dried pine boards? August 23, 2000

We receive our pine kiln dried from a usually reliable supplier. It seems that at certain times in the year we run across problems at our gangsaws with bow and crook.

I inspect the incoming loads for moisture, stress, and the temperature the pitch was set at, since some of our customers still bake-on their finishes. The samples generally turn out fine, except that the moisture content is drier than our target of 6 to 8 percent; it is closer to 5 to 6.5 percent.

Are there some other tests I can do along with the cross-sectional and longitudinal stress tests that I already perform, in order to determine the problem? Could this be moisture-related also, since our plant and warehouses are controlled enviroments with an equilibrium moisture content of 7 percent?

Immediate bowing and side bend at the gang is the result of either growth stress in the tree or longitudinal drying stress.

If there is no moisture gradient, then immediate cupping is the result of transverse casehardening (drying stress).

Delayed warp is always a moisture problem.
Gene Wengert, forum moderator