To investigate the characteristics of the surface in detail, the machined surfacewas observed using SEM. Fig. 8 shows the details of ductile machining region in region A of Fig. 6. Apart from the regular feed marks with an equal spacing, there are also regular parallel stripes on the finished surface in the cutting direction, which are formed by tool vibration in the thrust force direction. The spacing of the stripes is determined by the ratio of the cutting speed to the vibration frequency.