Predicting board strength by X-ray scanning of logs: The impact of different measurement concepts

The objective of this study was to compare the individual board strength predictions from an X-ray log scanner by using either two or four X-ray directions. The benefit of applying traceability between log and board was also studied. In total, 119 Norway spruce [Picea abies (L.) Karst.] sawlogs were scanned by an X-ray log scanner at the log sorting station of a sawmill and sawn into two centre pieces per log. Individual board traceability was enabled by following the rotational position of the log in the scanner and at the succeeding sawing. All boards were graded by a commercial strength grading machine before destructive testing was done. The resulting data were used to derive variables for building multivariate partial least squares strength prediction models. In the modelling a hierarchical modelling approach was used, where annual ring width, dry density and elasticity were also modelled. For all concepts studied the models’ fit was similar. Only minor benefits could be found when using four directions and traceability compared with two directions and no traceability. One conclusion is that the result for traceability, from four directions in particular, is more sensitive for the interior knot reconstruction result. The strength prediction was on the same R 2 level as for the strength grading machine.