An exploration of pre and post-stressed timber forms utilising plantation-grown eucalypt timber

An exploration of pre and post-stressed timber forms utilising plantation-grown eucalypt timber

This investigation concerns the behaviour of plantation-grown and natural forest eucalypt timber during secondary processing, from sawn and dried boards through to the production of fine furniture.

Tasmanian eucalypt plantations comprise only two species, Eucalyptus globulus (E. globulus) and E. nitens. Most Tasmanian plantations have been managed on short rotations to supply the pulpwood market. However a proportion of Tasmanian plantations have been pruned and thinned and are being grown on longer rotations to produce high quality sawlogs. The specific focus of this research is the timber produced from these sawlog plantations.

Preparatory to the testing phase, a review of previous research on growing and primary processing of plantation-grown eucalypt timber was undertaken in order to better understand how it might differ from native forest timber. It was evident that advances in growing, sawing and drying techniques developed in recent decades have improved primary processing outcomes.

For this study, sawn timber from a commercial sawing and drying trial on 22.5 year-old plantation sawlogs of E. globulus and E. nitens was obtained. Sawn timber from regrowth-age logs of the most widely available native forest species, Eucalyptus obliqua, provided a control for comparison.

The same sawmill produced all of the sawn and dried boards used in this investigation. This removed, as far as was possible, differences in primary processing as a confounding factor in the comparisons.

Research was conducted into secondary processing of the three types of timber. Wood is a complex material with a range of variable micro and macro-scale properties that affect processing outcomes, so this called for craft expertise to be applied. Each stage of processing was fully documented to enable evaluation of the suitability of these timbers for high-end, value-added manufacturing. Packs of timber for study were chosen to give representative samples of the sawn timber produced by the mill. Boards from the packs were randomly selected for evaluation so that the conclusions drawn would be representative of the sets of material under study.

This research encompassed a wide range of techniques required for flat panel construction and the production of more advanced steam bent and laminated forms. A number of modifications to existing techniques and innovative processes, particularly around steam bending, were introduced.

Findings by species:

• Plantation E. globulus demonstrated that it possessed exemplary working properties enabling it to be integrated into any form of high-end manufacture. The mid-range density of the material coupled with its strength enables it to be used in high stress applications.
• Plantation E.nitens proved to be better than expected in its qualities. The lighter weight coupled with excellent strength leadsto a robust material suitable for many high-end applications where these traits are particularly well suited.
• E. obliqua, performed as would be expected of a typical native forest eucalypt. The E. obliqua reacted to all of the process carried out in this project within normal furniture maker’s parameters for an available eucalypt.

Applying the methodologies detailed in the study, sawn timber from E. nitens and E. globulus plantation sawlogs was found to be ideally suited to the manufacture of fine furniture. The testing program revealed that for the manufacturing of fine furniture, plantation-grown timber of both species was superior to regrowth-age native-forest E. obliqua.

These conclusions are confirmed by a display of the step-by-step photo documentation, material samples from the full range of tests, processes and innovations, and the items of furniture produced in sets of three to demonstrate the practical outcomes for each species.