82 



THE CONSTRUCTION OF LOG RULES 



TABLE XIV 



Conversion of Log Rules with J-inch Saw Kekf and No Shrinkage 

 Allowance to Otheb Widths of Saw Kerf 



* Rules made by first subtracting slabbing and edging may evidently be altered for different 

 widths of saw kerf, as these deductions are directly proportional to volume, and are applied to the 

 reduced cylinder only. Where, as with the International rule, the deduction for saw kerf is made 

 before subtracting AD for slabs and edging, this rule still holds good, since the per cent of cor- 

 rection is not applied to the entire log, but to the values in the rule, which already exclude AD. 

 If worked out for the log, independent of the rule, the sawdust in the slabs is deducted before 

 the factor AD is found, and for larger saw kerfs this factor AD would be proportionally smaller, 

 so that the total net product in lumber is the same as if computed by the above correction. 



TABLE XV 



Per Cent of Increase in Sawed Lumber Caused by Sawing 

 Lumber of Different Thicknesses f 



t In preparing tables of volume for Connecticut hardwoods (Bui. 96, Forest. Service), Frothing- 

 ham used the International rule, reduced for a J-inch saw kerf by subtracting the required 9.5 

 per cent of volume from-values for J-inch saw kerf. Complaint was later made that in applying 

 these tables to logs sawed in mills using i-inch saw kerf, the output over-ran the tables. This 

 was due not to error in the tables, but to the production of a large proportion of thick planks, 

 thus reducing the sawdust waste. 



These per cents are applied to the scale of 1-inch lumber. When 50 per cent of 

 the output is in 2-inch plank, the correction would be 50 per cent of 11.1 per cent 



