Detection of Spiral Grain Prior to Debarking 



No reliable way has been found to date for detecting presence or absence of spiral grain 

 in a tree or pole before debarking. A practical method for doing this could effect considerable 

 savings for pole producers because buyers could use greater selectivity in purchasing poles, 

 and the expenses of producing and processing unsuitable material could be avoided. 



To determine the feasibility of detecting spiral grain, two methods were tried in 1952 at 

 pole yards in Newport, Washington. In the first, the outer bark surface of 29 poles was exam- 

 ined and an attempt was made to determine the direction of the bark furrows with reference to 

 the longitudinal axis of the pole. The direction was then translated into terms of spiral ratio. 

 The direction and degree of spiral were recorded. After machine peeling, the actual direction 

 and slope of grain were determined by scribing the surface with a TECO slope of grain detec- 

 tor.^ Measurements were made at the top, middle, and butt of each pole, and were averaged. 



In the second method, the outer bark was removed with a drawknife at various places 

 along the pole's length. At each debarked area, a narrow strip of the thin inner skinlike bark 

 was peeled off and the direction of peel noted. These directions were then translated into spiral 

 ratios and averaged to give a predicted direction and degree of spiral for each pole . After the 

 pole was peeled, the actual slope of grain was determined as for the first method- -using a 

 TECO slope of grain detector. The 28 poles examined in this manner made a total of 57 poles 

 included in the study. 



Results of this study showed that it was impossible to predict occurrence of severe spiral 

 grain (i.e., 1:20^ or more severe) with any consistent degree of success. In the first method 

 (visual examination of the bark), one pole having severe spiral grain was not detected prior to 

 peeling, while another pole, believed to have severe spiral grain, did not fall into this category. 

 With the second method (peeling of the inner bark), five poles actually had severe spiral grain 

 and five poles were predicted to have this characteristic. However, only two of the poles that 

 had severe spiral grain were properly identified. 



Somewhat better success was attained in predicting the direction of spiral without refer- 

 ence to the degree of grain slope. This was particularly true for the inner bark examination 

 method, by which direction of spiral was correctly predicted in 86 percent of the poles. The 

 comparable percentage for outer bark examination was 55 percent. 



^ Product of Timber Engineering Co. , Wash. , D.C. Use of trade name herein does not 

 imply endorsement by the U.S. Forest Service. 



® One inch of grain deviation in 20 inches measured along the longitudinal axis of the pole. 



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