122 A MILL SCALE STUDY OF WESTERN YELLOW PINE. 



MILL OVER-RUN. 



"Mill over-run" is the difference between the total sawed out volume 

 in board feet and the volume in board feet as indicated by a given log 

 rule, when the former is greater than the latter. Should the total 

 sawed out volume be less than the volume indicated by the log rule, the 

 difference would then be called a "mill under-run." 



It is usually customary to express a mill over-run, or under-run, in 

 per cent of volume as indicated by the log rule used. For example: 

 If a log scales 800 board feet and saws out 1000 board feet, the mill 

 over-run is 25%. If it scales 1000 board feet and saws out 800 board 

 feet, the under-run is 20%. If it scales 800 and saws out 800, then it is 

 Said to "hold up the scale"; over-run in this case being 0%. 



The Spaulding Log Rule, which is the statute rule of California, was 

 used by the Red River Lumber Company in Lassen County, where the 

 field work of this study was conducted, and the following comparisons 

 of total sawed out and log scale are based upon volume indicated by 

 that rule. 



In Fig. 199 the average volume in board feet, sawed out at the mill 

 from immature trees of different diameters breasthigh, is shown by 

 Curve A; the average volume for the same trees, as indicated by the 

 Spaulding Log Rule, is shown by Curve As, and the difference between 

 these average curves, which is Curve O, is the average mill over-run 

 from immature trees of different sizes. (A As = 0) . 



Fig. 200 shows the mill over-run as indicated by Curve 0, expressed 

 in per cent of volume in board feet ; that is, 



lOO(A-As) 1000 



= Op = % Mill over-run. 



As As 



Figs. 201 and 202 show similar determinations made for mature 

 yellow pine. 



It will be observed that the per cent mill over-run for both immature 

 and mature trees is exceedingly high, and that it is higher for the 

 immature than for the mature, and higher for small trees than for large 

 ones. In Figs. 204 and 206 the same general tendencies will be seen 

 along with the striking feature that these determinations run lower 

 than the ones for whole trees. 



These differences are brought about by the log rule used and by local 

 practices in vogue at the mill. 



The Spaulding Log Rule, to begin with, has an enormous waste allow- 

 ance for small logs, which is over 130% of the volume allowed for 

 manufactured product. This allowance becomes smaller as the size of 

 the log in question becomes larger, and approaches 36.5% for very 

 large logs. Such a waste allowance is too large for small logs, even in 

 cases where 36.5% for large logs is about right. 



The wastage from small logs should, however, be greater than for 

 large ones, but not three or four times as great, as the Spaulding Log 

 Rule allows. This is why the per cent of mill over-run shown in 

 Figs. 199, 200, 204, and 206 is greater for small diameters than for large 

 ones. It also explains why the per cent over-run for whole trees is 

 much greater than for 16' but logs from the same trees. The smaller 

 the log the greater the per cent over-run; therefore, a tree 20" in 



