Measurement of spiral grain with computed tomography

Spiral grain is a feature of wood that affects the shape of the sawn timber . Boards sawn from logs with a large spiral grain have a tendency to twist when the moisture content changes. In sawmills the spiral grain in logs is judged manually. For research purposes the spiral grain in stems and logs i s normally measured by destructive methods. In this study the spiral grain of the stems was measured nondestructively with a computed tomography (CT) scanner. Twelve Norway spruce (Picea abies) stems from two stands in Sweden were scanned with a CT scanner with one cross-sectional scan every 10 mm a long the stem. Concentric surfaces at various distances from the pith were reconstructed from the stack of CT images. In these concentric-surface imag es, which show various internal features of the log, the spiral grain angle was measured at different distances from the pith and at different heights in the stem. The destructive measurements of the spiral grain were carried out on disks from the top ends of the logs. On these disks the spiral grai n was measured at different distances from the pith with a protractor. Fina lly, the results from the destructive method were compared with the results from analysis of the CT images. The nondestructive and destructive measure ments were compared in pairs with the same radial and approximately the sam e height position in each pair. The correlations (r) between the two method s were 0.81 and 0.71, respectively, for the two stands. It was concluded th at it is possible to measure the spiral grain angle nondestructively with a CT scanner.