Linking visual and stress wave grading of beech wood from the log to the sawmill product

The quality potential and possibilities of using beech logs and sawn wood has been investigated. Thirty beech logs, having 48 cm mean diameter, were cut from 10 trees from a Hacquetio epipactidis-Fagetum SE-site in Slovenia. Trees, with 28.2 m mean height, were pre-selected according to the national 5-grade quality scale of assessing forest stands. Beech logs were classified according to the EN 1316-1 and sawn afterwards into unedged boards of 35 mm nominal thickness. Altogether 250 boards were visually graded according to the EN 975-1 and European Organisation of the Sawmill Industry (EOS) rules. Longitudinal vibration of logs and boards with the determination of stress wave velocity and dynamic modulus of elasticity by MTG timber grader was additionally included into the quality assessment. This machine grading was used on logs and sawn timber – in the latter in green and air dried state. In the case of logs, we confirmed significance of the relationship between visually assessed log quality and stress wave velocity. The stress wave velocity in logs was also related to the stress wave velocity in boards, where it varied considerably, especially at low graded material. In the case of sawn wood, the relationship between sawn wood grade and stress wave velocity was insignificant. The research confirmed the possibility of determining the stiffness of air-dried sawn wood and its strength grade already in the green state.