The wood-grit interaction between an idealized steel grit and both dry and saturated ponderosa pine (Pinus ponderosa) is investigated for a range of grit rake angles. Regions of rubbing, ploughing and cutting are identified for machining both with the grain and cross grain by scanning electron microscope examination of the machined surfaces. Using data of the tangential force on the simulated grit the coefficient of friction for all test conditions was calculated and the effect of tool rake angle, grain direction and moisture content quantified. A model of the energy of deformation of wood fibers during rubbing and the initial stages of ploughing was postulated based upon the theoretical stress distribution in an elastic material beneath a moving indentor. This model was evaluated using the calculated friction coefficients and wood mechanical properties.

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