AN INGENIOUS new way to saw up logs produces stronger timber and reduces
wastage by a third, according to a Swedish logging company.
Using a technique patented by the Royal College of Technology in Stockholm,
the timber company SCA plans to 鈥渟tar-cut鈥� logs perpendicular to their growth
rings to produce six radial planks and six triangular sections
(see Diagram).
Normally, logs are cut to a 鈥渞ectilinear geometry鈥�. In traditional sawmills,
parallel cuts made along the length of a log produce planks of variable breadth,
which are then cut down to standard sizes. More sophisticated sawmills can make
both parallel and perpendicular cuts to produce the largest, most valuable
standard timber sizes from any given log.
Advertisement
But because logs have a circular profile, cutting them into rectangular
sections produces a lot of waste. Typically, only 50 per cent by volume of a log
emerges from the mill as timber. The remainder is sawdust and unusable parts
from the outside of the log, which are used as firewood or turned into paper or
chipboard.
By contrast, says Anders Ek, SCA鈥檚 head of marketing, 65 per cent of a
star-cut log is useful timber. Only the outside of the log and the low-quality
鈥減ith鈥� at its centre are wasted. 鈥淭his represents a significant increase in
efficiency of log usage,鈥� he says. However, the system is only suitable for
larger logs, 27 centimetres or more in diameter.
Another problem with standard cutting systems is that most boards are sliced
off the side of the log, so each face has a different number of growth rings
lying at different angles. This leads to warping, twisting and cracking as the
timber dries and with subsequent variations in temperature and humidity.
But the main faces of star-cut boards are perpendicular to the rings, and
their sides are parallel. So although the boards still expand and contract, they
don鈥檛 distort or crack. Such boards are ideal for high-quality products such as
musical instruments, window frames and furniture, and sell for between 50 and 75
per cent more than ordinary timber of the same dimensions.
The remaining triangular sections are then glued together using strong
industrial adhesives to make wood panels which, like the boards, do not distort
with changing temperature and humidity. By removing the knots and by
finger-jointing the ends of the triangular sections, it is possible to make
large, stable, defect-free panels that look like solid wood.
A star-cutting sawmill is due to open in Junsele in northern Sweden early
next year. The new plant will use adapted versions of existing sawmill
machinery. It will be operated by Nova Wood, a company that is part-owned by
SCA, and will process an estimated 14 000 cubic metres of pine a year. 鈥淲e
expect to generate two or three times the usual value from each log,鈥� says
Ek.
鈥淚n principle this sounds like a very good idea,鈥� says Lucinda Leech, an
award-winning furniture maker from Oxford. 鈥淭he main advantage of this approach
would be the stability of the timber because you get three times as many
vertical-grain boards out of each log. The system could also be applied to
hardwoods and produce similar benefits.鈥�