Spiral grain

Fortunately there is very considerable between-tree variation (Nicholls and Dadswell, 1965) with eorewood values ranging from 1 to 20° and the trait is strongly heritable, so there is the prospect of genetic selection to screen the worst material. Spiral grain is not sueh a problem in the South Island of New Zealand, supporting the belief that there are pronounced genotype x environment interactions. 

Spiral grain in combination with heart shake lowers both volume eonversion and grade reeovery of lumber where either by itself would not be signifieant. For example a eheck in a 5 m log will rotate through 96° as a result of spiral grain of only 2°, degrading the output from a whole quadrant. 

Finally both spiral and interlocked grain present diffieulties in finishing. The grain runs out of the surface in opposite directions on either faee of the board (spiral 

Until recently, for many plantation pines and spruces any interest in breeding has been to delay the onset of heartwood formation and to rely on preservative treatment to provide protection or in the short term to take advantage of the reduced amount of heartwood in fast grown, short rotation operations. Yet even today, heartwood of older southern pine is used for flooring in the US south. 

Cultural preferences and tradition are powerful influences. Hinoki, Chamaecyparis obtusa, is a highly desired plantation species in Japan. Its pinkish-yellow to pale 

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Spiral Grain and Wave Phenomena in Wood Formation (1989)... 

Spiral grain F igure/grain/texture Hardness movement in service ability to stain Newsprint - high speed printing,... 

Nicholls and Dadswell (1965) argued that the breeding of pine should be based on density, tracheid length and spiral grain. This strategy addressed the needs of that time as these characteristics could be measured without undue difficulty and so offered a pragmatic means of delivering improved wood and pulp properties. 

Despite - or as a eonsequenee of - the unpredictability between trees and aeross sites spiral grain is an important eause of degrade in sawn lumber of many speeies. For eonvenienee, the pattern in radiata pine is examined. Here the broad trends within-tree (Figure 6.15) are ... 

A rapid inerease in spiral grain angle in the corewood on ascending the stem (from the juvenile zone in the butt log to the mature zone in the upper logs) that is completed over the first 6 m. Spiral grain increases from about 3 to 6° and... 

A maximum spiral grain angle oceurs around ring 3, thereafter there is a steady decline on moving from corewood to outerwood. 

This arises simply because of the anisotropic shrinkage of wood (Figure 8.14). Spiral grain, cross-grain and reaction wood contribute, and warping is especially likely in corewood. Drying under heavy restraint (1000 kg m"" ) mitigates the problem. 

Twist is a spiral distortion along the length of a piece of wood. It is found in speeies with spiral grain. It arises because the angle of the grain varies with the position of the fibres within the tree, and this is reflected when sawn into lumber. It is also assoeiated with eross-grain. 

Spiral grain can result in buckling or cracking during veneer drying. Even where such material is dried successfully thin plywood, in particular, can warp if the plies are not properly balanced. 

ECS (2004) Structural timber determination of characteristic values of mechanical properties and density, EN 384. European Committee for Standardization Elliott GK (1958) Spiral grain in second-growth Douglas fir and western hemlock. Forest Products Journal, 8 1) 205-11... 

Harris JM (1973) The use of beta rays to examine wood density of tropical pines in Malaysia. In Burley J and Nikles DG (eds). Selection and tree breeding to improve some tropical conifers. Commonwealth Forestry Institute, Oxford, Vol. 2 86-94 Harris JM (1989) Spiral Grain and Wave Phenomena in Wood Formation. Springer-Verlag, Berlin... 

Fig. 6.19. A higher-resolution AFM image of one of the SrTiOs bicrystal YBCO junctions in Fig. 6.18 showing the 36.8° rotation of spiral grains across the junction.

Severe spiral grain in the first few growth rings, especially above butt log... 

Cross grain A pattern in which the fibers and other longitudinal elements deviate from a line parallel to the sides of the piece. Applies to either diagonal or spiral grain or a combination of the two. 

Spiral grain n. A form of cross grain in which the fibers extend spirally about instead of vertically along the bole of a tree or axis of a timber. 

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