Comparison between automatic and manual quality grading of sawn softwood

An investigation has been performed to determine the repeatability and the accuracy of automatic and manual grading in a sawmill?s final grading station. In total, approximately 400 boards of pine (Pinus sylvestris L) and spruce (Picea abies) of different dimensions are included in the study. The most common automatic grading system for sawmills in the Nordic countries is studied. The study shows that in many cases it is possible to replace manual graders with an automatic system and, at the same time, make production more effective and improve grading, which results in higher value yield. The value yield produced by the automatic system is over 90 percent (91% to 98%) for both boards and planks for both species. The manual grader reached over 92 percent value yield for planks, but only 83 percent for boards. The quality yield for the automatic system is between 52 and 75 percent. The manual grader reached between 31 and 61 percent. The repeatability for the value yield varied between 85 and 96 percent for the manual grader and between 85 and 94 percent for the system. An overshadowing problem in this kind of study is how to obtain an irrefutably true grading result, as all grading of wood is subjective by nature.

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