(Choose PCBN tool finish turning hardened steel, the workpiece hardness is higher than 45HRC, the best effect. The cutting speed is usually 80-120m/min. The higher the hardness of the workpiece, the lower the cutting speed should be. For example, the cutting speed of a workpiece with a turning hardness of 70HRC should be 60-80m/min. The depth of cut of the finishing turning is 0.1~0.3mm, the feed rate is 0.05~0.025mm/r, the surface roughness of the workpiece after finishing turning is Ra0.3~0.6μm, and the dimensional accuracy can reach 0.013mm. like)