3256 Chapter 27 



more than !/4-inch between its thickest and thinnest points or it is classified as a 

 miscut. Sawmills must cut hardwood lumber thicker to permit shrinkage during 

 drying. Circle sawmills must cut 1-inch lumber IVs inches thick to allow for 

 shrinkage and sawing inefficiencies. Band sawmills are generally more accu- 

 rate, and a good band mill can saw lumber 1-1/16 inches thick and still have a 

 full inch of lumber when dry. 



An industry survey (Hanks 1977) determined the following averages for the 

 actual thickness of green hardwood lumber: 



Nominal thickness Average thickness 



Inches Inches 



3/8 0.45 



2/4 .60 



5/8 .70 



3/4 .90 



4/4 1.15 



5/4 1.40 



6/4 1.65 



7/4 1.95 



8/4 2.20 



9/4 2.50 



10/4 2.70 



3 to 10 nominal 



In addition, Hanks reported that the industry practice for trimming hardwood 

 lumber is to leave 2 inches of trim beyond the nominal length. The actual width 

 of rough hardwood boards is random; this means that the industry average width 

 of boards in the 7-inch class is 7.0 inches. In commercial practice, boards are 

 scaled by area, rather than width. 



THE BOARD FOOT-LOG SCALE 



Numerous scaling procedures, i.e., log scales, have been developed to esti- 

 mate the board foot (lumber scale) yield of logs. Application of log scales can 

 only approximate lumber yield from logs because sawmills vary widely in 

 efficiency of lumber recovery. Schumacher and Jones (1940) discussed general 

 development of empirical log rules applicable to particular mills. Freese (1974) 

 summarized the major log rules (over 95 are in use in the United States and 

 Canada) and compared board-foot volumes attained by various rules. Fahey et 

 al. (1981) compared the precision of log scaling systems using the relationship 

 between lumber recovery and scaled volume, and compared the abilities of 

 scaling systems to adjust volume for defect. 



In the paragraphs that follow, specific formulae are presented for the log 

 scales most widely used in the South: Doyle, Scribner Decimal C, and Interna- 

 tional 1/4-inch. Log diameter, usually measured inside bark at the small end, and 

 log length are the primary determinants of log content. 



