INFLUENCE OF TANGENTIAL BREAK DOWN METHODS ON THE YIELD AND ON THE QUALITY OF Eucalyptus spp SAWN TIMBER

Abstract

This work evaluated the production and the quality of green sawn timber of ten clones of Eucalyptus hybrids. The logs were classified according to their defects and were sawn in a band saw, using three variations of the balanced tangential method: parallel to the centre of the log (M1), cutting slabs at 1/3 of the log ray (M2) and parallel to the bark (M3). Following the logs breakdown, the yield was calculated and the sawn timber was sorted in terms of warp and splits. All clones presented logs with small taper, low bowing and high circularity; the smaller end splits of the logs were presented by clones 280, 36 and 299; clones 62, 2 58 and 36 presented the smallest pith eccentricity. The average lumber recovery between clones, obtained in the three breakdown methods were 35.2 % for the method M1; 30.1 % for the method M2 and 37.2 % for the method M3. These figures were increased when the production of the central plank and rips, removed from the slabs were considered in the account. Clones 44a, 62 and 36 presented highest lumber recovery. Bowing was small in all clones (average = 3.0 mm/m) presenting small variation among the three tested breakdown methods; similar behaviour was  observed for lumber crook (average = 0.93 mm/m); the clone 44a presented the smallest lumber checks in the three tested breakdown methods (average = 5.7 %). Cluster Analysis, indicated to verify that clones 44a and 62 presented best sawn timber recovery and check performance.