146 A MANUAL FOR NORTHERN WOODSMEN 



Saw Kerf. This loss in logs of different sizes is pro- 

 portional to the area of their cross-section, or tp the square 

 of the diameter. It varies in proportion to the thickness 

 of saw kerf as well. As embodying an average of good 

 present practice, J inch was allowed. 



Loss in Edging Lumber. This includes not only that 

 portion of a log which is thrown away in the form of edg- 

 ings, but also the fractions of inches in the width of boards, 

 which in Dr. Clark's studies were uniformly thrown off. 

 It is counted to be in all logs proportional to the surface, 

 or, what amounts to the same thing, to the diameter. 

 Counting boards to be merchantable down to the size of 

 2 ft. B. M., Dr. Clark found that an allowance of .8 foot 

 board measure for each square foot of surface under the 

 bark, or, what amounts to much the same, a layer .8 inch 

 in thickness around the surface, would justly allow for 

 this waste. 



Formula for the Rule. The above elements being put 

 into mathemetical form with D representing top diameter 

 inside bark, there is obtained for 4-foot sections the formula 

 (D 2 X .22) - .71 D = contents B. M. 



Adaptation to Other Conditions. The product for other 

 widths of saw kerf than J inch may be obtained by apply- 

 ing the following per cents: 



For fa inch kerf add 1.3 per cent 



For -fs inch kerf subtract .5 per cent. 



For { inch kerf subtract 9.5 per cent. 



For J 5 inch kerf subtract 13.6 per cent. 



For | inch kerf subtract 17.4 per cent. 



For Js inch kerf subtract 20.8 per cent. 



Should the ^-inch allowance for shrinkage not be made 

 in the mill practice in question, this may be allowed for 

 in a similar way. According to Dr. Clark's assumptions, 

 each board with its saw kerf means l-fo inch in thickness 

 taken out of the log. 



If mill practice in other ways is not so economical as 

 the rule presupposes, that is to say, if logs are sawed 

 with more waste in slab and edging than has been assumed, 

 or if logs vary in taper and straightness from the standard, 

 that is considered by Dr. Clark to be proportional to the 



