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 Sawing Eucalypt

This lumber came fresh off the saw perfectly square. As it seasoned it has distorted and cracked. This is because of opposing stresses around the pith. The wood has been torn apart. Never include pith in sawn hardwood timber.
The cracks result from including the pith.

The basics

In order to mill eucalypt well, one has to understand stresses and how these influence how the timber is sawn and how it seasons.

Rules of thumb:
 
  • Never include the pith
    Caption text     in sawn boards or flitches;
  • Mill as soon as possible after felling to minimise end-splits;
  • If quartersawing pay attention to crook - if necessary oversize the width and undertake straightening cuts;
  • If flatsawing do not saw wide boards (these will cup) and season the timber slowly and carefully;
  • Where compression fractures and shakes are present the central core of wood must be excluded from boards. This compression core is larger in bigger diameter logs and is not necessarily visible to the naked eye;
  • Keep log lengths short if using straightening cuts to deal with movement (i.e. quartersawing). Suggested lengths are 3m for diameters up to 45 cm and 4m for larger diameters.

Case studies

Movement and distortion can be phenomenal on eucalypt. It is important that the sawmiller knows how to deal with this. Here the sawmiller is producing eight quarters - the next step is to cross-cut these four quarters into eight. The resulting shortened quarters will then be slabbed and straightened before edging. The long initial log length meant eight quarters could be produced with only two bandsaw cuts, thus greatly improving efficiency. By then shortening each quarter recovery is improved - this log yielded 50% nominal recovery!

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