Q. We bought some No.1 Common kiln-dried hardwood lumber and it is warped up and down along the length. This cannot be used to make our larger doors, as the pieces we cut will not be flat. The supplier says that warp is not covered in the grades. Is this correct?

A. It is incorrect. The NHLA rule states that for Common grades, like No. 1 Common, the clear areas, called cuttings, used to establish the grade, "shall be flat enough to surface two sides to standard surfaced thickness after [the cutting] has been removed from the board.” So, in practice, you will find that the clear cuttings will often be 4 or 5 feet long or longer in the No.1 Common grade, and so that region must be flat.

The rule goes on to state that "In the grades of Selects and Better the entire board must be flat enough to surface two sides to standard surfaced thickness." which is quite restrictive for flatness.

Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.

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