Rough turning is the most economical and effective method for the rough machining of external cylindrical surfaces. Since the primary objective of rough turning is to rapidly remove excess metal from the workpiece blank, maximizing productivity constitutes its principal task.
Rough turning typically employs the largest possible depth of cut and feed rate to enhance productivity. However, to ensure the necessary tool life, the cutting speed is generally not reduced. During rough turning, the turning tool should be selected with a large principal cutting edge angle to minimize the radial cutting force, thereby preventing bending deformation and vibration of the workpiece. Additionally, a smaller rake angle, relief angle, and a negative inclination angle are selected to reinforce the structural strength of the tool's cutting edge. The machining accuracy achievable through rough turning is IT11, with a surface roughness (Ra) ranging from 20 to 10 μm.
Finish Turning: The primary objective of finish turning is to ensure that the machined part meets the required dimensional accuracy and surface quality specifications. The finish turning of external cylindrical surfaces is generally performed using a relatively small depth of cut and feed rate, combined with a higher cutting speed. When finish turning the external surfaces of large shaft-type components, a wide-edge turning tool is often employed at a lower cutting speed. For finish turning, the tool should be selected with a larger rake angle, relief angle, and a positive inclination angle to enhance the quality of the machined surface. Finish turning can serve as the final machining operation for external cylindrical surfaces requiring higher precision, or as a preparatory step for subsequent precision machining processes. The machining accuracy achievable through finish turning ranges from IT8 to IT7, with a surface roughness (Ra) ranging from 1.6 to 0.8 μm.
Precision Turning: The defining characteristics of precision turning are the use of extremely small depths of cut and feed rates, combined with cutting speeds reaching as high as 150 to 2000 m/min. Precision turning is typically performed using tools made from super-hard materials-such as Cubic Boron Nitride (CBN) or diamond-and requires the use of high-precision or precision-grade machine tools featuring high spindle rotational speeds and exceptional structural rigidity. The machining accuracy and surface roughness achievable through precision turning are generally comparable to those obtained via standard external cylindrical grinding; machining accuracy can exceed IT6, while surface roughness (Ra) can reach values ranging from 0.4 to 0.005 μm. It is primarily employed for the precision machining of non-ferrous metal workpieces that exhibit poor grindability; for materials such as aluminum and aluminum alloys-which tend to clog the pores of grinding wheels-fine turning proves to be a more effective method. When machining large, precision external cylindrical surfaces, fine turning can serve as a substitute for grinding operations. High-speed fine turning performed on high-precision lathes using finely honed diamond cutting tools is known as "mirror turning"; this technique enables machining accuracies ranging from IT7 to IT5, with a surface roughness (Ra) of 0.04 to 0.01 μm, making it particularly well-suited for the ultra-precision machining of non-ferrous metal workpieces.
