STANDARDIZATION OF VARIABLES IN LOG RULE 49 



Full and Scant Thicknesses of Boards. Boards not cut to exact 

 dimensions, if cut full lose the excess when measured, and if too scant 

 are either rejected, or reduced in grade. If cut scant but within pre- 

 scribed limits, they are scaled by superficial measure, and increase the 

 over-run (§20). 



In either case the sawyer to secure full scale of lumber must pro- 

 duce boards measuring within ^j-inch of the required thickness. This 

 is impossible without good machinery. In local custom mills, much 

 lumber is manufactured in uneven thicknesses causing a loss in scale 

 and reducing the over-run. 



49. Standardization of Variables in Construction of a Log Rule. 

 The over-run in sawing logs will depend for a given log rule upon thick- 

 ness of saw kerf, average dimensions of lumber, closeness of utilization 

 of slabs and of taper, and the exactness of manufactured dimensions. 

 All four of these factors are variables. 



For a given mill, the saw kerf alone is constant and even then the waste will vary 

 if two or more saws of different kerfs are used. The other factors are variable. 

 For different mills, one or more conditions are certain to differ radically, giving a 

 corresponding increase or decrease in over-run. Standardization of output and 

 methods, possible in mills of the same class serving the same markets, may secure a 

 similar degree of slab utilization and of efficiency in sawing to exact dimensions, 

 but this still leaves the fourth variable, differences in thickness of lumber sawed, to 

 affect the over-run. 



Where the sawed output is in thicknesses less than 1 inch, and expressed in 

 superficial feet, the product is not comparable with 1-inch lumber and must be 

 reduced to terms of 1-inch boards for a true comparison with the log scale. 



Arbitrary Standards. The essentials of any standard of measure 

 are fixed qualities and common acceptance. Even a poor or faulty 

 standard which is universally used would be better than a number of 

 different rules, or a rule which may be changed to suit conditions or 

 the preference of the user. These four variables must therefore be 

 arbitrarily fixed in adopting values for a standard or common log rule, 

 and in the case of most rules which have found wide use this was done. 

 The thickness of lumber was fixed at 1 inch, permitting an over-run 

 whenever thicker dimensions are sawed. The width of saw kerf adopted 

 by the rule was that used at the time and place of constructing the 

 rule, and was usually j-inch or larger. Local custom determined the 

 width of the narrowest 1-inch board sawed and this fixed the amount 

 of waste allowed for slabbing and edging. Taper was disregarded. 

 Boards were usually measured only to the nearest full inch of width 

 and fractional inches disregarded. Skill in manufacture was considered 

 by checking the results of the rule with the actual sawed output, by 

 means of mill tallies. 



