A mechanics of cutting analysis for orthogonal cutting with tool flank wear is presented based on an experimental investigation. It shows that tool flank wear does not statistically affect the basic cutting quantities such as the shear angle and shear stress, both qualitatively and quantitatively, but results in an additional rubbing or ploughing force on the wearland. Based on this finding, an orthogonal cutting force model is proposed which makes full use of the classical thin shear zone analysis for "sharp" tools. This model may form the basis for developing the predictive force models in practical operations. The study also shows that tool flank wear results in a substantial increase in the force components and that the thrust force is more sensitive to tool flank wear. These may be used as a primary basis for developing tool condition monitoring strategies.