In the turning process of shaft workpieces, issues such as inaccuracy and excessive surface roughness often occur. To address these problems, a detailed analysis of the turning process is essential. First, the reasons for inaccurate dimensions and their solutions must be understood. One common cause is operator error, such as incorrect use of measuring instruments or misreading the dial. It is crucial to ensure that operators are trained to use the dials correctly, as different lathes may have different types of dials. Each small dial can be calculated using the formula: Scale shift distance = tool travel distance = lead screw distance / total number of lines on the dial (in mm). Once the scale value per grid is known, careful handling is required. Due to the clearance between the screw and nut, the dial may rotate without the tool moving, so when adjusting, it's important to reverse one full rotation and then realign the dial rather than just a few divisions. Additionally, any errors in the measuring tool itself should be checked and corrected before use. Temperature changes during cutting can also affect the workpiece size, as heat generated from chip deformation and friction between the tool and workpiece causes thermal expansion. The majority of the heat (about 75%) comes from the chips, followed by the lathe (20%) and the workpiece (4%). When the workpiece heats up, its diameter increases, and after cooling, it contracts, leading to dimensional inaccuracies. Therefore, it is not advisable to measure the workpiece while it is still hot. To prevent temperature rise, sufficient coolant should be used during machining. Another issue is the uneven blank, which can result from an improperly straightened bar or misaligned center holes. This leads to geometric inaccuracies, such as ellipticity. Ellipticity in the spindle journal directly affects the workpiece. If the spindle uses a sliding bearing, under load, the main journal may press against a specific area of the bearing surface, causing the center position to change as the spindle rotates, resulting in elliptical deformation. The ellipticity of the bearing bore has no effect on the workpiece. Other factors include uneven blanks, clearance between the spindle and bearing, and misaligned center holes. These issues can cause axial wobbling and uneven wear, contributing to irregular shapes. The generatrix of the workpiece may become curved, convex, or saddle-shaped due to improper alignment of the lathe guide rails with the spindle centerline, especially in the horizontal direction. If the guide rails are bent, the workpiece may appear convex or concave, and if they are not parallel to the spindle centerline, a taper may form. Similarly, if the top centerline is not parallel to the bed rail, a taper will develop. As the workpiece heats up, it may bend, especially in long-axis machining, where thermal expansion is restricted by the fixed distance between the two centers, causing bending. To minimize this, it's important to control temperature and retract the tool periodically. Internal stresses within the workpiece can also lead to distortion once it is removed from the machine. This is typically resolved through aging treatment. Radial runout can occur due to pulsation, non-round center holes, or contamination like chips. A workpiece with elliptical shape will also contribute to radial runout. Regarding surface roughness, several factors may be responsible. A lack of rigidity in the lathe, such as loose tailstock or unbalanced drive components, can cause vibration, affecting surface quality. Improper installation of the machine can also introduce instability. Additionally, a flexible cutting tool or a workpiece with low rigidity can lead to vibrations. When turning slender shafts, it is essential to use a center rest or replace the tailstock with a clamp. The geometry of the cutting tool also plays a role; selecting the right cutting angles based on the material properties helps reduce roughness. Built-up edge formation can also impact surface finish, as it may cause scratching or grooving. This should be avoided during machining. In conclusion, addressing these issues early in the process is critical. By identifying and solving potential problems at their root, the accuracy and quality of the workpiece can be significantly improved, meeting the design specifications effectively.