Measures and yields of products and residues 32 o7 



from a stump height of 1 foot to a fixed top diameter limit of 8.0 inches outside 

 bark (Beck 1964). In 14-inch trees, the ratio varied from 4.16 to 5.16 bd ft 

 International !/4-inch scale, per cubic foot including bark. 



Cubic feet to board feet lumber scale. — The number of cubic feet required 

 to yield 1 ,000 bd ft of lumber varies widely; if pieces are sawn in large sizes from 

 large logs and if saw kerf is small, fewer than 125 cu ft will yield 1 ,000 bd ft of 

 timbers; if, however, 4/4 boards are innaccurately sawn from small logs with 

 saws taking a large kerf, more than 250 cu ft of logs are required to yield 1 ,000 

 bd ft of lumber. Table 27-1 12 shows the cubic footage of southern pine wood 

 required to yield 1,000 bd ft International !/4-inch log scale according to log 

 diameter and length; these values could also be used for lumber, as the Interna- 

 tional !/4-inch log scale yields close to zero overrun on a mill equipped with 

 handsaws cutting boards to exact nominal thickness. 



Lumber recovery factor (LRF) is the ratio of actual lumber volume produced 

 to the cubic volume of the piece processed; it is expressed as board feet/cubic 

 foot. In general, LRF is lower for hardwoods than for softwoods because 

 hardwoods are sawn thicker than nominal thickness but softwoods are sawn 

 thinner than nominal thickness. In addition, LRF varies with log size, product 

 sizes, type and condition of mill, and method of processing. Larger logs and 

 product sizes result in a larger LRF. Handsaws, with smaller kerfs than circular 

 saws, have a higher LRF. Sawing live usually produces a higher LRF than 

 sawing around, and careful and accurate edging and trimming can increase 

 lumber yield and LRF. 



In a study of 10 New York mills sawing hard maple logs (Burry 1976), LRF 

 averaged 6.7 for band mills and 6.4 for circle mills (table 27-109). The 1,030 

 sample logs averaged 13.4 inches in diameter and 11.5 inches in length. 



Similarly, an average lumber recovery of 6.7 bd ft/cu ft was reported for 

 yellow-poplar sawtimber trees bucked into 8- to 16-foot logs, debarked, and 

 sawn into 4/4 lumber on a handsaw in North Carolina (Clark et al. 1974). 

 However, the LRF was shown to vary with tree size, ranging from 5.2 for 12- 

 inch trees to 7.0 for 28-inch trees (table 27-100). LRF increased with tree size up 

 to 20 inches in dbh and then remained relatively constant. 



To determine the LRF for a specific small-log mill, Dobie and Warren (1974) 

 suggest a sample size of 60 to 100 logs per 2-inch diameter class. The average 

 LRF for a specific area can be obtained by weighting average LRF's of mills of a 

 product type according to their contribution to the area's total output. Three or 

 four mills of a product type should be an adequate sample. 



Cubic feet to log weight. — Data are available on the cubic foot content of 

 cord wood (tables 27-1 and 27-2), logs (tables 27-49 and 27-50), trees (tables 27- 

 51 through 27-66D), and tops (table 16-31). Weight per cubic foot of green 

 wood is extremely variable, however, because of variations in specific gravity 

 (see ch. 7) and moisture content (see sect. 8-1). Table 7-1 relates green wood 

 density to both specific gravity and moisture content. Tables 7-2, 7-2 A, and 7-3 

 give weights per cubic foot of green wood of important classes of southern 

 hardwoods. 



