Current Literature 91 



A Discussion of Log Rules — Their Limitations and Suggestions 

 for Correction. By H. E. McKenzie. Bulletin 5, California 

 State Board of Forestry. Sacramento. 1915. Pp. 56. 



This is an important contribution to the literature of this 

 subject. The fimdamental principles of board foot log rules as 

 developed by Daniels and by Clark, and discussed in Graves' 

 Mensuration, are here again set forth in a still more complete and 

 convincing form. A formula is given for the calculation of an 

 elastic log rule which may be modified with change of widths of 

 saw, average width of timber sawed, and average thickness of 

 lumber. 



Diagrams and analyses are given of the Spaulding, Scribner, 

 and Doyle Rules, and the waste allowance shown in per cent of 

 the product for logs of different diameters. For the Doyle Rule 

 this varies from 191 per cent for 10" logs, to 23.6 per cent for 50" 

 logs. It is shown that in principle the Doyle Rule is mathe- 

 matically sound, but that it errs in providing too great an allowance 

 for slabbing, and too small a loss in sawdust. 



The author then develops a formula in which the slabbing 

 allowance is found by subtracting a constant from the diameter, 

 as in the Doyle Rule, and computing the board foot contents of 

 the resiiltant enclosed cylinder. The sawdust allowance is based 

 on the principle of saw kerf on the side as well as surface of each 

 board and reads : 



Volimie of saw kerf = width of kerf X area of kerf. 



The latter area amounts to width plus thickness of board plus 

 width of kerf itself as may be seen from a diagram. The volume 

 of the board plus kerf equals width of board plus kerf X thickness 

 of board plus kerf. From these expressions the per cent of volume 

 in sawdust is obtained, and the net per cent of product. 



The method is probably a slight improvement over previous 

 plans. Excessive taper in small logs, tending to increase the out- 

 put, is allowed for by adding a constant. 



In appljdng this rule, at Lassen, California, a saw kerf of >^" 

 width board of 12", and thickness of 5/4" was used. The constant 

 subtracted for slab was 1" from the diameter, instead of 4" as in the 



