Abstract

Summary 20-year-old plantation-grown Eucalyptus nitens Maiden (shining gum) trees were examined for the production of structural and appearance products from sawn timber. Log characteristics were examined and measurements made of peripheral longitudinal strain. Basic density and mechanical strength characteristics of sawn timber were determined. Four commercial drying schedules were applied to 25 mm and 50 mm thick back—and quarter-sawn products. Measurements for twist spring, bow, width and thickness were made on the 50 mm boards before and after seasoning, and all boards were machined and graded to Australian Standard (AS) 2082 “Visually stress-graded hardwood for structural purposes”. The logs contained a high proportion of sapwood, and the basic density of the wood was lower than that reported for heartwood of mature E. nitens, though the moduli of rupture and elasticity, and crushing strength were comparable. The method of sawing only influenced the amount of bow in freshly sawn products. Drying reduced bow, significantly increased twist in quarter sawn boards and increased spring in quarter and backsawn boards. The different methods of drying had little effect on distortion, though progressive kiln drying induced more twist than any other treatment. Shrinkage, both radial and tangential was also independent of the drying method and was greater than in heartwood of mature E. nitens. Twist, spring and bow in the freshly sawn timber and in dried timber after reconditioning, were within the permissible limits prescribed in the Australian Standards. Knots were the most common cause for the downgrading of sawn structural and appearance products. Acceptance rates of 63% for structural products may be marginally acceptable to the manufacturing industry, the acceptance rate of less than 50% for appearance products indicates that this resource has little potential for appearance products unless the incidence of knots can be reduced or assessment criteria in the grading rules are altered.