IA 12-in. dia. log yields mostly I ANo. 2 common or Ho. 3 common stock. Larger trees generally contain more FAS lumber.
Lumber grader* »¡»end an average of 15 mtoihI* grading a hounl, uning u lumber rule like (life one to gauge (lie uiiiuIm'I' of hoard feel and a practiced eye to define defects.
Wood grading is part art, part science for the pros, but mostly confusion for novices. Not only is the grading system complex, but also the rules applied to hardwoods differ from those applied to softwoods. Plus, each species is likely to be eligible for several exceptions to the general guidelines.
Fortunately, you can take advantage of the grading system without actually knowing much about how a lumber grader does his work. You just have to understand a few basic terms. (Sec wood-grading chart.)
When a grader evaluates a board, in a way he Is actually doing some of the preliminar}' work for you by gauging the number of defect-free areas, how large they are, and what percentage of the board they make up. ()f course, he's not evaluating beauty, figure, and other design variables.
Graders judge liardwoods using standards the National Hardwood Lumber Association (NHLA) has administered since 1897. The grader checks each board with a lumber rule (see photo) to gauge the number of board feet, then uses several fairly complicated systems to determine how many clear cutting units the sawyer can obtain. Typical diagrams for firsts and seconds (FAS) and No. 1 common boards are shown in Fig. 2. The fewer the defects, the higher the grade ;uid value of the board.
Wide boards are much more expensive than those less than 9 in. but are more prone to cupping and cracking in the drying process, so the sawyer must rip them apart for the maximum yield of liiglvquality
Quality of lumber decreases as you move closer to heartwood.
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