When it comes to understanding the NHLA grading standards for hardwoods, it’s helpful to understand a few key terms and exactly what they mean in regards to these specific standards. While the guidelines help standardize the wholesale lumber industry and help determine pricing, many woodworkers and craftsmen don’t completely understand the basis for the system.
The descriptions of the various grades as well as the steps to self-grading lumber are confusing to someone who doesn’t understand the jargon that’s part of those descriptions. While the grading of hardwood lumber is something even an amateur can do, it does require a thorough understanding of what is meant by the following terms.
Specific Types or Areas of Lumber for Grading
Board Foot: This unit of measurement describes a board that is 12 inches long, 12 inches wide, and 1 inch thick (or a cubic equivalent).
Parts: This term refers to the usable piece of wood into which hardwood lumber is cut.
Yield: Usually expressed in percentages, this term is used to refer to the ratio of the volume of parts to the volume of lumber. (Typically, higher grades of lumber have higher yields.)
Clear cuttings: These rectangular areas are parallel, rather than diagonal, to the edges of the lumber. By definition, they are “clear” of knots or other obvious blemishes on the grading face and free from wane, shake, pith, or rot throughout the entire cutting. (However, mineral stain is admissible.)
Sound cuttings: Similar to clear cuttings, these do allow for small holes, knots, and some discolorations.
Surface measure: Often abbreviated as “SM,” this refers to the number found by taking the following steps:
• Find the width of the lumber (in inches and fractions)
• Record the standard length in feet (with no fractions or rounding)
• Multiply those two numbers and divide by 12
• Round that number to the closest whole number
Cutting unit: This is measured as 1” wide by 1’ long
Types of Blemishes Considered in Lumber Grading
Shake: This kind of lengthwise separation appears between annual growth rings.
Pith: This dark central core of a tree shows the primary growth that formed when original branches elongated.
Wane: This term refers to a defect in a board caused by curvature of the log from which it has been cut
Pitch: Referring to a defect found in some boards, this refers to sticky residue that drains out of some logs.
There are certainly online sources for thorough listings of lumber-related terms as well as illustrated discussions of the NHLA grading system. However, there is no virtual equivalent for the kind of in-person, board-by-board, detailed quality control that a top lumber wholesaler/distributor such as the J. Gibson McIlvain Company exercises on every single board that comes their way.