Causes for warpage after planing

Why boards may warp after surfacing. January 16, 2001

Question
I’ve had some warping after jointing a board dead flat and running it through the planer. This has occurred with oak, maple and pine. Any thoughts?

Forum Responses
You may not be letting the lumber acclimate to your shop long enough--at least a week, two if possible. Also, try planing off opposite faces more equally.

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Maybe the wood wasn’t dried thoroughly. Cut a wood block 1.5" x 1.5" and weight it on a scale. Dry it for 24 hours. Weigh it again. Then use the equation MC= (MassWet-MassDry)/MassDry * 100. This will give you the moisture content.

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The cause is drying stress (casehardening), which should be relieved in the kiln by a process called conditioning. Sometimes the process is not done correctly or at all.

You can check for stress by cutting a clothespin-shaped sample from the lumber--many texts illustrate how to do this. Wood with drying stress should be returned to the seller.

If it were a moisture problem, then you would see warp developing after jointing and before planing.

Gene Wengert, forum technical advisor