Increasing Sawn Timber Yield in Cant Sawing

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Abstract

The log cutting theory accepts that the volumetric yield of edged sawn timber from the maximum volume cant will be maximal. According to current standards, edged sawn timber must have specified thickness and width. Some cants are not used for the production of centre yield because the widths of their faces are aliquant of the centre yield thickness. The volume of such cant in centre yield production is not taken into account in the log cutting theory and the conclusion that their volumetric yield from the maximum volume cant will be maximal is not obvious. The 1st stage of cant sawing is obtaining a two-edged cant from a log. At that, due to the deviation of the roundwood axis from the centre line of the sawing pattern, a narrow and a wide face are obtained. We consider the dimensioning of the narrow face of a two-edged cant, as its size determines the volumetric yield of centre yield. Within the narrow face of a two-edged cant 2 zones are allocated: unconditional and probabilistic. In the unconditional zone, an integer number of edged boards is obtained. In the range of roundwood diameters from 17 to 29 cm, only the roundwood with the diameters of 21 and 25 cm have provided the maximum volume two-edged cants, but the volumetric yield of the centre yield from the roundwood of these diameters has not been maximal. It follows from this that the maximum volume cant does not guarantee the maximal volumetric centre yield. The probability zone includes a non-integer number of edged boards. It is impossible to determine their number in an analytical way, so the methods of probability theory have been used. The distribution function of the narrow face of a two-edged cant has been derived. In order to use the distribution function to obtain a non-integer number of edged boards, the width of the probability zone has been calculated, as well as the size of the part of the probability zone decisive in obtaining a non-integer number of edged boards and the confidence interval. Further, the “Distribution function of the width of the narrow face of a two-edged cant” table was used to determine the non-integer number of edged boards. Obtaining the noninteger number of the edged boards from a two-edged cant can be implemented in practice using changeable or adjacent sawing patterns. The presented results can be applied when determining the number of sorting groups of roundwood before its feeding to the sawmill and when changing the technology of centre yield production.

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