Cupping of compressed wood resulting from set recovery

Dimensional changes of compressed sugi (Criptomeria japonica D. Don) specim ens of a practical size R: 60, T: 100 mm) after water soaking and boiling w ere investigated. Not only set recovery in the compression direction but al so marked cupping, concave on the bark side, Mere observed. The degree of c urvature was proportional to the amount of compressive deformation. In the case of transverse compression of flat grained lumber of a practical size, the direction of compression gradually changes from the radial towar d the tangential direction as the edge is approached. When the specimen is divided into parts along the width, and the parts are compressed individual ly, they will deform into the shape of a parallelogram as the angle between the annual ring and the direction of compression decreases. When the divid ed specimens were matched again after compression, they suggested the cuppi ng deformation of the original specimen. Therefore, compressed wood appears to be essentially stabilized in the cupped state. Accordingly, it is inevi table that cupping will occur in compressed wood when the set is released b y water soaking. It was possible to decrease the set recovery in the compression direction a nd the curvature of cupping of compressed wood in practical sizes by heat t reatment after deformation. In addition, edge restraint during compression was more effective in reducing the curvature of cupping.