Effect of Drying Methods on Warp and Grade of 2 by 4’s From Small-Diameter Ponderosa Pine

Two studies were performed to characterize and control warp in nominal 2by 4-in. (standard 38by 89-mm) dimension lumber sawn from small-diameter ponderosa pine trees. One study was conducted at a commercial sawmill with trees harvested in central Arizona. The other study was conducted at the USDA Forest Service, Forest Products Laboratory, Madison, Wisconsin, in small experimental kilns with lumber from trees harvested in central Idaho. The three main variables in the studies were top loading, presteaming, and a high-temperature kiln schedule. A limited study of hot press drying was also included. The high-temperature kiln schedule in the experimental kilns reduced drying time to about half that of the conventional temperature schedule. Press drying time was slightly more than 3 h. Crook and bow caused most of the warp and the grade loss from warp. There was no evidence that presteaming affected warp or grade loss from warp. Top loading had a modest effect in reducing warp and grade loss from warp. High-temperature drying did not affect measured warp compared with the conventional temperature schedule. Grade loss from warp was less in high-temperature than in conventional temperature dried lumber. This might be explained by differences in moisture content change during storage. Press drying did not reduce warp or grade loss from warp.