RADIAL SAWING: PREPARING FOR THE INTRODUCTION OF A NEW TIMBER INDUSTRY

Radial technology has been under development since  1988. Radial has worked with natural principles to develop sawmilling that works with the nature of the tree. This produces timber sections with consistent growth ring orientation and less residual stress. Radial technology is applicable to hardwood and softwood logs.

The present sawmilling industry is faced with a resource that is increasingly difficult to process. Average saw log diameters are decreasing as old growth forests are cut over or taken out of production for conservation purposes and there is an increased reliance on managed forests and plantations.

Economic forces and resource competition force the reduction of rotation cycles in many native and plantation forests. This results in the production of logs that in many cases are not suitable or ideal for economic processing by traditional or ordinary milling systems. The logs are smaller and have sawing and use characteristics that can be quite different from old growth and larger sized logs.

With older growth trees and timber that is highly stable it is not so important to produce timber sections with a particular growth ring alignment, but it has always been the general aim of the sawyer to produce timber that is either quartersawn, (growth rings at “right angles” to the broad face of the section) or backsawn (growth rings “parallel” to the broad face of the section). 

A high proportion of wastage occurs in ordinary sawmilling in the attempt to cut sections of timber with the correct growth ring alignment that will adequately meet end use requirements.

Processing logs containing growth stresses and timber with a high rate of drying distortion makes it increasingly important to produce timber as close as possible to true quartersawn or true backsawn.

Smaller log diameters makes it more difficult to isolate the band of “good” quality timber that occurs between the sapwood and the core of the tree. The geometrical problem of efficiently turning smaller round logs into rectangles is compounded by the effect of growth stresses and the distortion that occurs during the drying of the cut timber.

Growth stresses and drying distortion are related to the circular and radial nature of the log. The primary effects of spring, bow and cupping in a particular section of timber relate directly to the alignment of the growth rings.

Ordinary milling, which only saws at right angles and parallel to initial breaking down cuts, cuts at varying angles across the radial stress lines which relate to the annular growth rings of the tree. This “parallel and right angle cutting” produces a relatively high percentage of wide boards from close to the centre of the trees or the log. Wide boards cut near the heart of the tree (especially in quick growing and relatively young  hardwoods) contain high levels of residual stress and are prone to splitting and excessive cupping during drying. Cutting these wide boards to narrow boards to minimize the effect of cupping produces a high percentage of boards with “incorrect” growth ring alignment (i.e. neither quartersawn nor backsawn) which are prone to excessive “diamonding” during drying and contain both bow and  spring, which are difficult or wasteful to use and straighten.

 These wide boards also tend to cut across defective and lower quality core wood. This lower quality wood  contaminates the good wood at the edges of the boards and lowers the quality and value of the timber.

Lower percentages of sawn timber recovered from a log and lower quality timber produced results in lower profits and forces change on traditional sawmills that historically are small production units located close to the forest resource.

Current technology using ordinary sawing patterns attempts to address the problems presented by the changes in available log resource by maximizing recovery, and by maximizing throughput.

Maximizing recovery generally involves the increased turning of the log in ninety degree increments to produce as much timber as possible with the correct growth ring alignment. If this approach is not automated it is labour intensive and requires the sawyer to have a high level of skill. If it is automated the automation required is complex and expensive to install per unit of timber produced. Even though the method maximizes recovery of sawn timber and gross profit from the logs processed, capital or labour costs are high and production of quality timber is still limited by the geometry of the sawing pattern used and the nature of the log.

Radial sawing works with the nature of the tree.

Instead of making cuts parallel and at right angles to initial cuts, in the Radial process cuts are made in relation to a chosen centre. This effectively means that cuts are made at right angles and parallel to the growth rings and radial stress lines. This produces triangular timber sections that are quartersawn and trapezoidal sections that are backsawn. Growth and drying distortion stresses are evenly and consistently distributed into each section of timber.

Defective or lower quality core wood is efficiently isolated from better quality wood and better quality wood is efficiently produced   from the good wood zone. Core wood can be efficiently and cost effectively removed from production or allocated to manufacture of specific and suited product.

Radial is repetitive and highly suited to automation. It allows for quality timber production and recovery levels that previously could only be approached by highly skilled sawyers with the best and most appropriate equipment.

Radial brings options for the small mill and the large mill- all with the same result of highest possible quality output. Efficient manual, automated and robotic mills of all scales are on the way.