Peeling, slicing, sawing, and chemically altering hardwoods and softwoods to form finished products such as boards or veneer; particles or chips for making paper, particle, or fiber products; and fuel. See also Paper; Veneer.
A high percentage of the weight of freshly cut or green wood is water. Green wood contains free water in the cell cavities and bound water in the cell walls. When all the free water has been extracted and before any of the bound water has been removed, the wood is said to be at the fiber saturation point. As the moisture content falls below the fiber saturation point, the bound water leaves the cell walls and the wood shrinks. During the drying process, differential shrinkage can cause internal stresses in the wood. If not controlled, this can result in defects such as cracks, splits, and warp. Below the fiber saturation point, wood takes on and gives off water molecules depending on the relative humidity of the air around it and swells and shrinks accordingly.
Wood is machined to bring it to a specific size and shape for fastening, gluing, or finishing. With the exception of lasers, which have a limited application at this time, all machining is based on a sharpened wedge that is used to sever wood fibers. Tools for sawing, boring holes, planing, and shaping, as well as the particles in sandpaper, use some version of the sharpened wedge.
Wood is ground to fibers for hardboard, medium-density fiberboard, and paper products. It is sliced and flaked for particle-board products, including wafer boards and oriented strand boards. Whether made from waste products (sawdust, planer shavings, slabs, edgings) or roundwood, the individual particles generally exhibit the anisotropy and hygroscopicity of larger pieces of wood. The negative effects of these properties are minimized to the degree that the three wood directions (longitudinal, tangential, and radial) are distributed more or less randomly. See also Wood products.
