LOG ROTATION EFFECT ON CARRIAGE SAWING OF SWEPT LOGS

A computer sawing system, which simulated a multiple saw edger, was used to investigate the effect of log rotation on the timber conversions of swept logs of three sizeclasses. A sample of 100 logs was stratified with respect to both log size and sweep, and four sawing methods (half-taper live sawing, half-taper cant sawing, offset live sawing, and offset cant sawing) were applied with the computer sawing simulation system AUTOS AW to each log at 37 positions representing rotation at 10° intervals from 0° (equivalent to the "sweep up" position) to 360° inclusive. All 14 800 simulations used the same carriage configuration, saw kerfs, and target dimensions, and the timber conversion percentage was determined for each. The results suggest that, under the conditions selected for the simulations, any log rotation can be used with half-taper cant sawing without sacrifice of substantial volume, but rotation is more important with offset cant sawing. Increased conversions were obtained when the log rotation was approximately 145°, i.e., midway between the "sweep in" and "sweep down" positions. For every angle, half-taper sawing obtained conversions that were at least equal to, if not greater than, those obtained with offset sawing. Results were consistent with the general rule of thumb that each 0.1 increase in the sweep:diameter ratio (deviation : s.e.d.) leads to a 5% decrease in timber recovery.