Effect of kiln-drying on the hardness and machining properties of tamarack wood for flooring Cecilia Bustos Roger E. Herna ´ndez S Yves Fortin S Abstract The hardness, planing, and moulding properties of tamarack wood from natural forests were evaluated on kiln-dried speci- mens following three types of drying schedules: high temperature, elevated temperature, and conventional. Hardness tests were conducted according to the ASTM D143 standard. Planing and moulding properties were evaluated according to the ASTM D1666-87 standard. Wood specimens were machined at 7 percent moisture content, and the resulting surface quality was visually graded on a scale of 1 to 5 (excellent or defect-free to very poor). The maximum depth of torn grain produced by planing was also measured for eight cutting conditions. Hardness was positively related to wood density. Machining and hardness properties appeared not to be affected differently by the drying process. Tamarack wood performed well in the planing and moulding processes. The best planing condition was obtained when using a 10° rake angle and 20 knife marks per 25.4 mm cutting length. The global analysis of properties indicated that tamarack wood is suitable for the fabrication of flooring products. Tamarack is a larch species (Larix laricina (Du Roi) K. Koch) that grows from Maine to Minnesota, throughout much of Canada, and in Alaska. This species can live on poorly drained sites as well as on cool, moist, well-drained soils. Tamarack is rarely found in pure stands. Black spruce, northern white cedar, balsam fir, paper birch, and red maple are common associates of tamarack in mixed stands (Mullins and McKnight 1981, Johnston and Carpenter 1985). Tamarack wood is moderately hard and heavy and yellow- ish to russet brown or occasionally reddish-brown in color. The sapwood is whitish and narrow. The wood ranks fairly high in bending and compressive strength but low in resis- tance to impact. In hardness, tamarack is second only to west- ern larch among the Canadian coniferous species (Jessome 2000). Traditionally, tamarack has been used primarily as lumber in building construction, for railroad ties, mine tim- bers, poles, posts and piling, and pulpwood (Panshin and de Zeeuw 1980, Mullins and McKnight 1981). Over the last decade, however, a new market niche developed throughout North America for tamarack: rustic and classic solid wood floors. This new utilization opportunity brought about a need for more research on the kiln-drying, hardness, and machining properties of tamarack wood. Hardness is a practical mechanical property used to assess the suitability of a wood species for use as residential and/or com- mercial flooring (Wiemann and Green 2007). Tamarack wood frequently contains spiral grain. To avoid warping during the drying process, the kiln operator must take special precautions, such as the application of top-load restraint and the use of a high- temperature schedule to take advantage of the plasticization effect of heat on wood. The presence of spiral grain combined with the hardness of the wood requires extra attention when machining. Torn or raised grain are two of the typical defects observed when planing dried lumber which result in a poor quality surface. Moulding or shaping performance, however, seems to be ranked high (Lihra and Ganev 1999, Anon. 2006). The authors are, respectively, Assistant Professor, Departamento de Ingenierı ´a en Maderas, Universidad del Bı ´o-Bı ´o, Concepcio ´n, Chile (cbustos@ubiobio.cl); and Professors, Centre de recherche sur le bois (CRB), De ´partement des sciences du bois et de la fore ˆt, Pavillon Gene Kruger, Universite ´ Laval, Quebec, Canada (roger. hernandez@sbf.ulaval.ca, yves.fortin@sbf.ulaval.ca). This paper was received for publication in February 2008. Article No. 10465. SForest Products Society Member. ÓForest Products Society 2009. Forest Prod. J. 59(1/2):71–76. FOREST PRODUCTS JOURNAL VOL. 59, NO. 1/2 71