Grading Problems That Challenge the Lumber Industry

Several important grading problems need to be solved by the lumber industry. In 1922, the American Lumber Standards standardized sizes and provided a general base grade classification for softwoods, but it did not provide standard grades. Twenty or more sets of regional grading rules still exist. Use of two principles in grade descriptions–description by example, and description by specification (defining permitted defects)–compounds the problem. USDA Circular 296 “Standard Grading Specifications for Yard Lumber” in 1923 presented a basis for standard grades, but regional lumber groups were unwilling to make changes in their grades. Stress grades are better standardized than yard grades. USDA Circular 295 proposed four basic grades, and American Lumber Standards adopted two of them as basic grades. Regional stress grades conform to principles used in defining these basic grades, so that numerical comparisons of the stress grades of different association can be made, though the stress grades differ both in description and assigned stress. Changes made in the 1923 stress grades designed to make them more efficient have also made them more complex. Simplification of grades means loss of efficiency. There is such a wide range in the strength of timbers of a single stress grade that many high-strength timbers are not used efficiently. A nondestructive test to replace present specification may solve the problem. A specific gravity test would improve selection, even though specific gravity has limitations as a criterion of quality. Industry has considered this method impractical. A hardness test would accomplish about the same improvement as a specific gravity test. The stiffness test is generally considered impracticable of application. A hardness test is being developed but is not yet perfected. Any of these three tests would improve selection of clear wood only. Sonic and supersonic methods may be developed to predict the quality of both clear wood and defects. Designers, architects, and engineers want what they call universal design values–a series of stress grades in 200-lb. steps from about 800 to 2,400 lbs. Region of growth is not a good indicator for segregating timber or lumber for strength; there is no way of telling from the wood where it grew, and when wood of the same species from different regions goes to the same distribution point, high and low strength material are mixed together. Also regions are seldom accurately defined–Appalachian oak, Arkansas soft pine, and North Carolina pine are indefinite terms. No visual method of identifying stronger timbers, using rings per inch, density, or combinations of these factors, has been successful. The solution to each of the problems considered lies with industry.

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