Q. We manufacture moulding and buy FAS grade lumber that sometimes is cupped edge to edge so much that it gives us problems. Can you please clarify the NHLA Rules, especially paragraphs 14 and 61? Our supplier hides behind these rules. I think we might have improperly graded lumber.
A. It is my experience that the seller of dried hardwood lumber almost always tries to deliver the quality that the customer needs, rather than use the rules as an excuse for lumber that the customer cannot use efficiently. So, I do suggest considering another lumber supplier that cares more about your needs.
When grading FAS lumber, the rule concerning cup is that the grader is allowed to consider that the lumber is going to be planed down to "standard surfaced thickness."
Using an imaginary, perfect planer, if the cup will surface out for the entire piece of lumber, then cup is not a grading defect. For 4/4 lumber, after kiln drying, standard surfaced thickness is 13/16 inch, which means that FAS lumber can be somewhat cupped.
Also, pieces 12 inches and wider can be ripped with the grader's imaginary rip saw, and then the two pieces measured for cup separately? This ripping will automatically reduce cupping to one-quarter of the original value. Again, FAS wide lumber can be somewhat cupped.
Note that the piece of lumber must be flat and not bowed. Also, with side bend warp, the clear cuttings must all be in the same axis, and cannot curve around with the warp. Even a small amount of side bend will lower the grade to No.1 or lower; likewise, a small amount of side bend will greatly impact your yield and cost. Twist warp is also a big loser.
For No.1 Common grade and lower, flatness applies to the clear areas used for grading and not the entire piece of lumber.
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