COMPARISON OF LOG RULES BASED ON FORMULAE 61 



The results, for certain diameters are shown below: 



TABLE VIII 



Thickness of Plank to be Deducted for Slab Waste to Coincide with a 

 Collar 1.5 Inches Thick. Sawdust Allowance 20 Per Cent 



The use of these ratios would give identical results by both methods. But in 

 application the second method usually stipulates that the thickness of plank shall 

 be constant for all logs. This results in a greater proportionate deduction for slabs 

 on small logs than by the first method. This deduction is more in accordance with 

 the actual results of sawing, owing to the increasing effect of minimum widths of 

 board on per cent of loss in slabbing (§ 51). The best application is to adopt a 

 ratio which applies to medium-sized logs, and use this for all logs, large and small. 



If a log rule is constructed to deduct the waste which actually occurs in sawing, 

 it must be based on one or the other of these two formulae. If the waste allowances 

 are correct for the conditions assumed, there will still be over-run when other condi- 

 tions apply, but the per cent of over-run will be practically the same for all sizes, 

 the rule is consistent, and the results are subject to correction by a fixed ratio or 

 per cent. 



If the waste allowance for either slabbing or sawing, or both, are incorrect for 

 the conditions assumed, the rule will not only give over- or under-run, but will also 

 be inconsistent, the per cent will differ with diameter, and the rule will not be subject 

 to correction by a fixed ratio, and will lack the basic requirements of a standard of 

 measure. 



57. Comparison of Log Rules Based on Formulae. In constructing 

 a formula log rule, the correct application of the deduction for saw kerf 

 presents no great difficulty. In the International rule, an extra deduc- 

 tion of yc-inch was made for shrinkage. Other rules neglect all factors 

 but the actual width of saw kerf (§53). 



The deduction for slabs, edging and normal crook requires determination not 

 only from diagrams but from practical tests. The following amounts are deducted 

 by the log rules given below, expressed both as a "collar" deduction from diameter, 

 (a), and as a thickness of plank (A), to correspond with the two methods descn'bpd 

 (§56). 



