62 



THE CONSTRUCTION OF LOG RULES 



TABLE IX 



Deductions for Slabbing and fob Saw Kerf, for 12-inch Logs, in Ten Log 

 Rules Based on Formulae. The Basis Used in the Rule is Shown in 

 Heavt Type. 



* Diagram rule. 



Of the rules above cited, the British Columbia and Doyle are the only ones used 

 extensively at present. The table is instructive as an indication of the proper allow- 

 ances to make for slabbing. The test of a formula is actual comparison with sawed 

 output. The deductions in the International rule were determined by careful 

 measurement on logs actually sawed. The Champlain rule is known to be too 

 close a rule, with too small an allowance for slabs. The British Columbia rule 

 neglects shrinkage and is a good standard. The Click rule was carefully checked 

 by sawed output. These results indicate that for 1-inch lumber sawed to exact 

 dimensions, an allowance for slabbing of 1.5 to 1.75 inches subtracted from diameter, 

 or one-half this deduction as the single thickness of the collar, is a fair allowance 

 for slabbing. This allowance would be too small for lumber of greater average 

 thickness than 1 inch or for very small logs. 



When the deduction is made in the form of a plank whose width equals the 

 diameter, D, of the log, the thickness of plank required to make it equivalent to the 

 collar deduction is from 1.75 to 2 inches for 12-inch logs, slightly more for larger 

 logs, and decreasing in thickness for smaller logs. But where the deduction is made 

 in this form, as in the International and Champlain rules, it is used as a constant 

 for all dimensions (§ 59 and § 62) with results corresponding more closely to actual 

 waste than by the first method. 



The allowance for saw kerf, on all log rules in commercial use, is 1-inch or over. 

 The International rule in its original form gives values for a i-inch saw kerf, which, 

 with the other allowances, gives a rule intended to measure the output of modern 

 band mills. 



