The mechanics of the orthogonal cutting process are examined. Under an assumed streamline and shear plane curvilinear system, the Eulerian strain and strain rate tensor in the primary deformation zone are obtained analytically. When the material behavior is dependent on strain, strain rate and temperature, the temperature distribution in machining is numerically estimated using an iterative incremental method. The results obtained are compared with those from the classical shear plane theory. The shear angle as a function of undeformed chip thickness and cutting velocity, and cutting forces in orthogonal cutting are predicted by the total work minimization principle and are seem to agree with the experimental results from the literature.