An Analysis of Shook Yields from Box Lumber

A sample of 2,000 bd. ft. of number 3, 4, and 5 Common ponderosa pine (Pinus ponderosa Laws.) was obtained from three different sources. The original boards were about 1-1/2 inches thick and 12 inches wide. The boards were ripped into 2-inch, 4-inch, 6-inch, and 8-inch widths and were then marked for flaws and photographed. The photographs were marked to simulate cut-off and band rip cuts that would be made to remove the defect not allowed in each of the high, medium, and low grades (A, B, and C). The yields of 6-, 12-, and 18-inch lengths of the grades for which each set of pictures was marked was then obtained by determining the number of pieces that were available in the length between defect cuts. Kerf losses were estimated by calculating them as the volume of wood that would be removed from the theoretical yields of any length and grade as determined from the photographs. The 2-, 4-, and 6-inch boards yielded about the same amount of grade A shook 6 inches long, while 8-inch boards yielded somewhat less. As shook length increased, yield fell off with wider boards. There was little difference in the yield of the different grades from 4-inch and 6-inch boards. However, the yields of grade A and B were lower from the 8-inch boards, while the grade C yield was higher. The effect of shook length on yields was much more marked that the effect of grade. When all the wood available as both long and short pieces was considered, shook grade had little effect on yield. However, yield decreased as shook length increased, and decreased more rapidly for higher-grade shook than for low. Kerf loss was not large compared to defect loss, except when thin or narrow pieces were sawn. The effect of kerf on the yield of thin and narrow pieces was high compared to other losses.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member