Parts arriving warped

Q: We are purchasing a wood product made of beech that has an overall thickness of 1/4 inch and is 3 inches wide by 5 inches long. We have told the manufacturer that the wood must be dried to a 6 to 8 percent moisture content before making the part. However, the parts are arriving with a slight warp. The manufacturer insists that the wood is being properly dried to a 6-8 percent MC. Is there another possible explanation as to why the parts are warping? Thank you for your help.

A: Wood warps for only one reason and that is that the MC has changed. In your case, this means that if the wood is dried to 6 to 8 percent MC, then the air surrounding the wood is not at 6 to 8 percent EMC, which is equivalent to 30 to 42 percent RH.

There is one exception to this rule and that is that wood with internal stress, due to growth stress or drying stress, will warp immediately when it is machined, including sanding. Does your supplier state that the wood is flat when it leaves his facility? If so, then moisture change is indeed the problem.


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Gene Wengert

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 45 years. He is extension specialist emeritus at the University of Wisconsin-Madison.