Table 13. - -Distribution of poles selected for transverse sectioning 



by grain direction and seasoning 



Seasoning 





Grain classification 







' Straight 



: Left spiral : 



Right spiral 



: Moderate : Severe : 



Moderate 



: Severe 



Green 



^2-R 2.58 



5-L48.83 



7-R 8.58 





1 year 









20-R18.83 



2 years 



21-L18.17 



23-L32.83 



28-L12.50 





3 years 





34-L 5.58 36-L 8.83 





39-R 2.83 



The number before the dash is the pole number, and the letter and numbers 



after the dash are direction and degrees of maximum distortion in the standing pole. 



At the time the pole farm was terminated, these 10 sample poles were felled and sections 

 approximately 12 inches long were cut about 8 feet from each pole end,, and at the midpoint. 

 The sections were identified as to pole number and location within the pole, and referenced in 

 relation to the projecting pipe. The reference mark was also the longitudinal axis of the pole. 



In the laboratory, the sections were split on a line extending from the reference mark 

 through the pith, and the spirality on the split face was measured at 10 -year growth increments 

 using a device patterned after that developed by the Canadian Forest Products Laboratory (8, 11). 



The measurements showed a wide variation in the slope of grain for sections from any one 

 pole, as well as for sections from different poles. In general, the data conformed to those re- 

 ported by other investigators (4, 7, 11, 14) in that the grain spiraled to the left initially -when 

 the tree was yoiing, gradually decreased to zero, and then passed to an increasing right spiral. 

 In only four of the 30 sections split was there an initial zero or right spiral that remained 

 constant in direction. 



The measurements explain the stability of the right -spiraled poles. Poles containing left 

 spiral only are freer to respond to moisture content changes than are poles containing both left- 

 and right -spiraled grain. In the latter case, the tendency of the left -spiraled grain to twist to 

 the left is counterbalanced by the tendency of the right -spiraled grain to distort to the right. 

 Of course, any unevenness in the twisting forces compels the pole to move in the direction of 

 the dominant stress (fig. 2). 



The spirality measurements are shown graphically in figure 3. These graphs support 

 the cotinterbalance stress hypothesis. Those poles that contained both right- and left -spiraled 

 grain generally twisted less (pole numbers 2 and 39) or twisted in the direction of the dominant 

 stress (pole numbers 28, 7, 21, 20, and 23). In those poles having grain spiraled to the left 

 only (numbers 34, 36, and 5), the angle of spiral appeared to be the controlling twist factor. 

 The greater the slope-of -grain angle, the greater the amount of twist in the standing pole. 



12 



