© 2002 by Institute of Chartered Foresters
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Spiral grain in Norway spruce: constant change rate in grain angle in Scandinavian sawlogs
1 Norwegian Forest Research Institute, Department of Economy, Technology and Processing, Høgskoleveien 12, N-1432 Ås, Norway 2 Växjö University, School of Industrial Engineering, SE-351 95 Växjö, Sweden 3 North-Trøndelag Research Institute, Bomveien 3, N-7729 Steinkjer, Norway
Any evident grain deviation will reduce strength and increase warp in sawn timber. To describe the magnitude and variance of grain angle in Norway spruce, specimens from 1046 Norwegian sawlogs and 380 logs from Sweden and Finland were examined. For individual specimens, grain angle outside the innermost zone closest to the pith might be expressed by a simple linear function of radial distance from the pith. The intercept and inclination of this function are close to bivariate normally distributed with mean values (SD) of 2.7° mm–1 (1.9) and –0.039° mm–1 (0.037), respectively. Inclination is less negative for wider annual rings (r = 0.3), and intercept and inclination are negatively correlated (r = –0.4). The constant rate of change indicates inherited property rather than influence of any dynamic, external stimulus. No predictor for grain angle pattern was found. The linear model leads to simplifications both when observing the grain angle in the forestry, and in calculations of strength properties and distortion in the timber industry.
Received 27 April 2001.