The Measure^nent of Saw Logs 83 



inch log, and will, if they be similar in form, have ^the waste 

 in square-edging the lumber. But the area of the small end of 

 the 48-inch log is 16 times as large as that of the 12-inch log, and 

 if both be cut into inch boards by the same saw, there will be 16 

 times as much loss due to saw kerf in the larger log. To repeat 

 in other words, the 48-inch log hasyi?z/r times as much waste in 

 square-edging the boards as the 12-inch log, the increase being 

 in direct proportion to the increase in diameter. The 48-inch log 

 has sixteen times as much waste from saw kerf as the 12-inch log, 

 the increase being in proportion to the increase in the squares of 

 their diameters. If a rule is to be equally fair to large and small 

 logs, it is evident that the deductions to be made for waste due 

 to saw kerf and to square-edging the lumber, respectively, must be 

 kept absolutely separate and distinct in the computation of the 

 rule. In any rule where, as in the Doyle, but a single uniform 

 deduction is made, the rule can give correct values for any given 

 width of saw kerf at one point only, above and below which the 

 logs must be over and under-scaled, respectively, or vice-versa as 

 the case may be. 



The first log rule maker to recognize this fundamental principle 

 in the computation of a rule must have been a Mr. Baxter, for 

 the Baxter rule is the oldest of the four rules so computed. The 

 allowance for edging given by the Baxter rule is .5 inch beneath 

 the bark. The British Columbia rule followed with an edging 

 allowance of .75 inch beneath the bark. The only other log 

 rules similarly computed are the recently produced Universal 

 and Champlain rules in which the edging allowance is made 

 proportional to the top end diameter (or circumference). 



Allowance for Saw Kerf. The relation between the different 

 amounts of lumber which may be sawn from logs by saws cutting 

 different widths of kerf is a percental ow&. That is, if the product 

 that can be sawn out by a saw cutting any particular width of 

 kerf be known, the product that can be sawn out by saws cutting 

 narrower or wider kerfs may be got by simply adding or sub- 

 tracting the necessary percentage to or from the known scale. 

 This implies that the sum of a, b, and c as follows is practically 

 the same regardless of the diameters of the logs manufactured or 

 the width of the saw kerf cut by saws used in their manufacture. 



a = Waste due to square-edging the boards. 



(^= Allowance for shrinkage in width of boards. 



<:= Proportion of saw kerf waste which goes with a and b. 



