Measures and yields of products and residues 



3283 



attributed to two factors: (1) fewer saw cuts and therefore less volume lost to saw 

 kerf, and (2) the log is turned only once so less volume is lost to slabbing. As 

 diameter increased, live-sawing was progressively better than grade-sawing in 

 terms of overrun (fig. 27-10). 



15 



i 



5 t 



y 



I 



10 



5 - 



8 9 10 II 12 13 14 15 

 LOG DIAMETER (INCHES) 



16 



Figure 27-1 0. — Percent overrun for grade 3 northern red oak saw logs related to diame- 

 ter at small end inside bark. (Drawing after Huyler 1974.) 



A study of white oak sawn at seven mills in Arkansas, Tennessee, and 

 Louisiana (Garver and Miller 1936) showed that quarter-sawing yielded about 

 12 percent less lumber per thousand board feet of logs than plain-sawing (table 

 27-111). One explanation was that quarter-sawn lumber is generally cut l'/4- 

 inches thick to yield a finished 1-inch board but plain-sawn lumber is cut 1 Vs- 

 inches thick for the same 1-inch board. 



Taper also has a marked effect on overrun. Board-foot log rules generally 

 ignore differences in taper since only log length and small-end diameter are 

 considered. Using a computer to simulate sawing for maximum yield from any 

 specific log, Hallock et al. (1979) investigated the effect of taper on yield. 

 Although he simulated softwood log breakdown, the trends he noted are perti- 

 nent to hardwoods too. In general, the greater the taper, the higher the overrun — 

 the more lumber the sawmill operator will get for his log investment (fig. 27- 11). 

 The percentage increased yield due to taper is less pronounced in large-diameter 

 logs than in small-diameter logs. 



Board feet log scale to cubic feet. — Table 27- 1 12 presents cubic foot volume 

 per Mbf by log scale for 8- and 16-foot southern pine logs. The Doyle scale 

 disregards taper, and requires more wood volume per Mbf for the longer logs. 



