Pre-twisting during sawing results in straight studs
Artikel i vetenskaplig tidskrift, 2006
Warp in lumber is a serious problem for the building industry. In particular, material from small-diameter logs experiences excessive twist. This paper presents a new sawing technique to minimize the problem of twist in material from small-diameter logs. Almost all the studs sawn from small-diameter logs twist in the same positive direction. By rotating the logs during sawing, it is possible to produce studs with a small negative pre-twist. The studs will twist as normal as a result of drying, but, due to the negative pre-twist, the studs will become straighter after drying. To test this new method of sawing, two studs (50 by 100 mm) were sawn from each log. One of the studs was sawn with a small negative pre-twist and the other was sawn to be straight. A total of 100 logs were sawn, resulting in 200 studs. Directly after sawing, the pre-twisted material had a mean twist of -6 mm/100 mm/2 m, while the material that was sawn straight had a twist of 0.1 mm/100 mm/2 m. After kiln-drying to 18 percent moisture content, the twist in the pre-twisted material was 3.4 mm/100 mm/2 m, while the material that had been sawn straight had a mean twist of 7.3 mm/100 mm/2 m. The percentage of studs passing the limit set for twist in wall studs (4 mm/100 mm/2 m) increased from 30 to 60 percent.