64 THE CONSTRUCTION OF LOG RULES 



The deduction 2.12D was determined from tests of sawed logs, including all crook 

 of 4 inches or less. 



Since the log is divided into 4-foot lengths, the sum of which gives the scale, 

 the formula reads for each length, 



B.M. = (.66Z> ! -2'.12:D) T V 

 = .22Z) 2 -.71I>. 



A taper of |-inch in 4 feet is allowed. D is thus increased by |-inch for each succes- 

 sive section and the sum of the scale of the separate 4-foot cylinders gives the scale 

 of the log (§ 43). On account of the allowance for shrinkage the rule is based in 

 reality on the production of lyj-inch boards measured as inch boards. A minimum 

 width of 3 inches, and a minimum length of 2 feet are adopted as standard, no piece 

 to contain less than 2 board feet. Standard values were published, it being the inten- 

 tion of the author to furnish a commercial log rule that could be accepted as a com- 

 mon standard for the measurement of logs as sawed in modern mills using a band 

 saw cutting a 4-inch kerf. 



60. International Log Rule for \ -inch Kerf, Judson F. Clark, 1917. 



For general adoption as a standard commercial log rule, the £-inch rule 

 is open to the objection that it over-scales the product of most small 

 mills, since it is seldom that such mills use saws cutting less than J-inch 

 kerf, or make close use of the taper of the log. A log rule which gives 

 a safe margin, and which permits mills using thin band saws and up-to- 

 date equipment to secure an over-run of about 10 per cent is more 

 acceptable as a commercial standard than one which scales for the 

 closest possible standard of utilization. For this reason, Mr. Clark 

 has computed values for the International rule, for j-inch saw kerf. 

 This form of the rule is here published for the first time from values 

 furnished by its author (Appendix C, Table LXXX). To obtain this 

 rule, the original values for the |-inch rule were reduced by 9.5 per cent 

 and then rounded off to the nearest 5 or 10 board feet. The rule is 

 recommended as a standard for scientific measurements of volume and 

 growth in terms of board feet, for regions where the product is manufac- 

 tured by small mills using circular saws cutting a ;-inch kerf. 



61. British Columbia Log Rule, 1902. This is the only case of the 

 legal adoption and application in commercial scaling of a new log rule 

 based on sound scientific principles, as the direct result of a thorough 

 investigation. In 1902 a commission of three men prepared from dia- 

 grams a rule to suceed the Doyle Rule for the province, which was 

 adopted in 1909 as the Statute rule. 



Their results were embodied in a formula reading: 



"For logs up to 40 feet in length deduct 1J inches from the diameter of the small 

 end inside the bark; square the result and multiply by the decimal .7854; from 



