Solid Wood Products 2689 



STRUCTURAL LUMBER 



Two-by-4-inch, 8-foot studs for wall construction are a major lumber com- 

 modity in the United States and Canada. Also, 7- to 8-foot 2 by 6 's, 2 by 3 's, and 

 2 by 2's are much used. Traditionally these products have been cut from 

 softwoods. In the Midsouth and the Southeast studs made with chipping hea- 

 drigs from southern pine veneer cores and small logs are particularly competi- 

 tive. Most are dried at high temperatures (230°-240°F). If they are high- 

 temperature dried in narrow loads under heavy top load restraint to the moisture 

 content at which they will equilibrate in use, e.g., 9 percent, they can be 

 relatively crook-free (Koch 1969a, 1971a, 1974). Even greater freedom from 

 crook can be obtained if live-sawn oversized blanks are dried at high temperature 

 before they are edged and machined to final dimension, as demonstrated by 

 Koch (1966ab, 1967a, 1968, 1969b). 



Should demand require, some widely available hardwoods such as yellow- 

 poplar, sweetgum, black tupelo, red maple, and sweetbay can also be success- 

 fully manufactured into almost warp-free studs by edging and ripping live-sawn 

 flitches after they have been kiln-dried at high temperature. 



In West Virginia Koch and Rousis (1977) showed that more conventional 

 manufacture of yellow-poplar studs, i.e., sawing to usual dimensions and kiln- 

 drying at low temperatures without restraint, resulted in less than half of the 

 pieces meeting Stud grade requirements. Considering knots alone, 90 percent of 

 the pieces would have graded Stud or better at 19 percent moisture content; this 

 proportion was reduced to 34 percent, however, by consideration of crook as 

 well as knots. 



Hallock and Bulgrin (1978) eliminated most crook in yellow-poplar studs by 

 live sawing logs into 7/4 flitches which were dried and then ripped into studs. 

 This technique, which is similar in some ways to that Koch developed for 

 southern pine, has been termed SDR (Saw, Dry, and Rip; fig. 22-63). In their 

 experiment, they dried the studs on a mild schedule to a 15-percent moisture 

 content. 



Maeglin and Boone ^^ showed further benefits from high-temperature drying 

 in combination with the SDR process. They dried 7/4 yellow-poplar flitches cut 

 from trees 8 to 12 inches in dbh for 28 hours at 240°F dry-bulb temperature and 

 190°F wet-bulb temperature, followed by about 44 hours of equalizing at condi- 

 tions set for 10 percent equilibration moisture content — 200°F dry- and 188°F 

 wet-bulb temperatures. At the end of this schedule, stud moisture contents 

 averaged 12 percent with range from 9 to 15 percent. Flitches ripped to width 

 after drying, and planed to net dimensions of 1 .5 to 3.5 inches had average crook 

 of about 1/64-inch; none of the 417 studs were rejected from Stud grade for 

 exceeding y4-inch crook. Compared with conventionally sawn yellow-poplar 

 studs dried on a mild kiln schedule, the SDR studs dried at high temperature 

 averaged 86 percent less crook, 43 percent less twist, and 34 percent less bow. 



'^Maeglin, R. R. , and R. S. Boone. 1979. High quality studs from small hardwoods by the S-D-R 

 process. Paper presented at 33rd Annual Meeting, Forest Products Research Society, San Francisco, 

 July 8-13. See also Boone and Maeglin 1980. 



