Warp in structural timber. Causes and control
AbstractOver a sample of 948 boards with dried dimensions of 150 X 50 X 3,000 mm, coming from 22 trees felled in 4 different areas of the National Park of «Cazorla y Segura» (Jaen, Spain), was studied the influence of site, tree and position of boards within the tree on bow, spring, twist and cupping of timber, measured according to the methodology of the Spanish standard UNE 56.544. The relationship between the percentage of rejected timber and the average twist in every log along the stem was studied, analysing the influence of site, tree and log on such a relation. The influence of every factor is studied, concluding that the main sources of variability are the intralog variability (> 50 %) and the intertree variability (>40 %). Site factor explain not more than the 2 % of the total observed variability in the percentage of rejected timber for excessive warp. Possible methods of control to increase industrial yield are discussed, concluding that an improvement of sawing and log grading methods are needed.
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