The ultraprecision machining technology, one of the most successful development within precision engineering has been playing a rapidly increasing and important role in manufacturing. However, the physics of the micromachining process at very small depth of cut, which is typically 1μm or less, is not well understood. Shear along the shear plane and friction at the rake face dominate in conventional machining range. But sliding along the flank face of the tool due to the elastic recovery of the workpiece material and the effects of plowing due to the large effective negative rake angle resultant from the tool edge radius may become important in micromachining range. So the size effect, the increase in specific energy with decreased depth of cut, is unaccountable only by the conventional sharp edge model assuming that the total energy is consumed by shear along one shear plane and friction at the rake face. Shear energy must be modified to consider the effect of the tool edge radius and the effect of sliding along the flank face must be added to the total specific energy. This paper suggests an orthogonal cutting model considering the cutting edge radius and then quantifies the effect of plowing due to the large effective negative rake angle.