Correcting case hardening

Correcting case hardening in processed lumber. July 11, 2000

Is there any way to correct reverse case hardening in 8/4 maple?

If you really have reverse case hardening, there is no way to cure it other than by heavy planing. However, how thick are the prongs? If too thin (under 1/4 inch) they will show reverse when there really is none.

Also, do you have any moisture gradients? A gradient will give you false readings -- reverse, intially.
Gene Wengert, forum moderator

I'm assuming it is reverse case hardening. When I resaw 8/4 to 4/4 it wants to close up and then blow apart when close to finishing the cut.

It is case hardening, not reverse case hardening, when it cups or bows together. Case hardening can be easily relieved, but reverse cannot. Reverse is very difficult to achieve, however -- I have seen it once or twice in production in 40 years.

Case hardening is removed by adding moisture quickly back to the lumber when it is very hot. Usually we steam the wood, attempting to achieve 180 degree F dry-bulb and 170 degree F wet-bulb (80 percent relative humidity, 18 percetn equilibrium moisture content). Some people use water sprays.

Once the wood is out of the kiln, it is next to impossible to remove the stress, especially when resawing.