DISCUSSION OF LOG RULES. 55 



10,510,000 9,060,000 = 1,450,000 bd. ft. required for sawdust, 

 shrinkage and surfacing. 



= .138 fractional part of the logs, after slab allowance 

 10,510,000 



has been made, which becomes waste. 



(1 .138) = fractional part becoming lumber. 



Therefore the average value of (A) becomes (1 .138) for the above 

 milling conditions. 



(&) The determination of slab allowance or surface wastage: 



This allowance is provided for in the formula by the constant "a", 

 which represents twice the average thickness of the slabs and edgings 

 coming from the small end of logs, regardless of their length. The value 

 of " a " can be closely estimated at any mill by watching the logs being 

 sawed into lumber. If the character of the timber being sawed is such 

 that a waste allowance, additional to that made for slabs and edgings is 

 necessary, to correct for losses due to crook, such an allowance should be 

 made by increasing the value of the factor "a" to a sufficient amount 

 to offset losses caused by such defects. 



For the milling conditions under consideration here, the value of "a" 

 is assumed to be 5/8" X 2, or 1.25. Substituting this value and the aver- 

 age value of (A), already determined, in the general formula, we have 

 the following special form : 



for logs L feet long with no allowance made for taper. 

 For 8' sections this form becomes : 



or 



.407 (D 1.25) 2 + C = B.M. 



The constant C is included in the formula to counteract excessive 

 taper in small logs, and its value should never be over 10 board feet. It 

 can be definitely determined for a certain class of timber, by first ascer- 

 taining the mill overrun for small logs when C = o, and then making 

 the value of C great enough to correct for the overrun. Large logs will 

 be affected a negligible amount by the addition of this small quantity. 



"With C = 3 board feet, we have for the final reduction of the general 

 rule: 



.407 (D 1.25) 2 + 3 = B.M. 

 to be applied to 8' sections with a taper of 1/2" in each 8'. 



