DISCUSSION OF LOG RULES. 



19 



1O 12 14 16 18 2O 22 



AREA INSIDE BARK SMALL END SQ. FT 



FIG. 8. A graphic analysis of the McKenzie Log Rule, based upon area in square 



feet inside bark at small end of logs. This diagram shows the following: (a) Top 



curve, total contents in board feet of logs of different diameters 16' long with taper 



" in 8'. (&) Next lower curve, volume in board feet remaining after 



a allowance for slabs has been made, (c) The log rule curve for i" saw-kerf, show- 



ing volume in board feet after an allowance for slabs and sawdust has been made 



(The allowance for slabs in this rule varies directly as the "barked" area and that for 



sawdust directly as the volume minus slab allowance.) (d) Curve "k," position that 



the log rule curve takes when the saw-kerf is \" instead of |". (e) Curve "k"' shows 



position of the log rule curve for a |" saw-kerf. The formula for this rule is as follows : 



- 



k-= width of saw-kerf, in inches.. 

 MJ average width of lumber, sawed, in 



inches. 

 t average thickness of lumber sawed, 



in inches. 

 K = 3.1416. 



L + 



D average diameter inside bark, small 



end, in inches. 

 a = constant. 



L = length of log, in feet 

 C = constant included to compensate for 



excessive taper in small logs. 



The formula is : 



(not making any allowance for shrinkage and surfacing; the 

 complete formula with this allowance made is shown on page 52.) : 



(w + k) (t + 



TT(D a}' 

 48 



L + C = B.M. 



with a taper allowance of e" in /' to be applied when compiling a table. 

 The section used should not be taken over 16' long: 8' is better. 



