MILL OVER-RUN. 123 



diameter breasthigh which contains four logs in the merchantable 

 length, three of which are of course smaller than the butt log, has, as a 

 whole, a larger per cent over-run than does the butt log alone. Mature 

 trees and butt logs from them show a lower per cent over-run than do 

 immature trees and butt logs from immature trees of corresponding 

 diameters. The fact that the Spaulding Log Rule is not a level one is 

 also indirectly the cause of this. Mature trees have a thinner bark than 

 the immature, therefore a 16' butt log from a mature tree of a given 

 diameter breasthigh has a greater diameter inside the bark than a butt 

 log of the same length coming from an immature tree of the same 

 diameter breasthigh. The larger the logs the lower the per cent over- 

 run ; hence, the difference between Figs. 204 and 206. 



The differences in Figs. 200 and 202 are brought about by thickness 

 of bark together with form of bole. Mature trees show a higher form 

 factor than the immature ; they are filled out more, the taper being very 

 slight in the first three or four 16' logs. The effect of high form factors, 

 or fullness of bole, tends to decrease the per cent of mill over-run. 



In Fig. 207 a comparison of per cent over-run for butt logs and whole 

 trees, of immature western yellow pine, is shown, while in Fig. 208 a 

 similar comparison is made for mature trees and 16' butt logs from 

 them. It will be observed that there is at least 23% over-run in all 

 cases, regardless of size of log or tree. This difference between actual 

 cut at the mill and the Spaulding Log Rule is easily accounted for, since 

 the Spaulding rule was constructed for a thick saw, and since some of 

 the lumber sawed was cut shy on dimensions, and that clear, straight 

 grained edgings were usually graded as moulding stock. 



NOTE. During the season of 1915 it was learned that the company had discon- 

 tinued the practice of cutting shy on dimensions. 



