In this paper were evaluated multi-factor non-linear dependencies of main and normal cutting forces, from thickness of the cutting layer (chip thickness), rake angle and some mechanical properties, namely: bending strength, – compression strength parallel to grains, – tensile strength perpendicular to wood grains and sharing strength parallel to wood grains, for three wood species of Yellow Birch and Sugar Pine and White Ash, in very low speed, opened, flat, orthogonal longitudinal cutting were evaluated. In the analyzed relations there were evidenced several strong interactions, which were graphically illustrated and discussed. Although no wood density was taken into account, the fit obtained was very good. The lowest influence on the main and normal cutting forces was observed in case of the compression strength parallel to grains.