1) Drum-shaped
That is, after turning, the diameter of both ends of the workpiece is small, and the middle diameter is large. The reason for this defect is due to the poor rigidity of the slender shaft, the contact between the support claw of the tool holder and the surface of the workpiece is not real, and the wear produces a gap. When turning to the middle part, due to the radial force, the turning tool will The center of rotation of the workpiece is pressed to the right of the center of rotation of the spindle, which reduces the cutting depth, while the rigidity of the two ends of the workpiece is better, and the cutting depth is basically unchanged. The slender shaft is bulged due to the "make knife" in the middle.
Elimination method: When you follow the claw of the tool holder, you must be careful so that the claw surface is in contact with the surface of the workpiece without gaps. The main declination of the turning tool should be selected from 75 ° to 90 ° to reduce the radial force. Cast iron with better wear resistance should be selected with the claw of the tool post.
2) Slub shape
The shape is bamboo-like, and its pitch is approximately equal to the distance between the supporting claw of the tool post and the tip of the turning tool, and it appears cyclically. The reason for this defect is that the gap between the large carriage and the middle carriage of the lathe is too large, and the centrifugal force is caused when the blank is bent and rotated, and the "knife" when the tool is connected is generated at the reference tool joint supported by the tool holder The diameter of the turning section is slightly larger than the reference section, and the tool continues to be turned, and the tool holder support claw contacts the section with the larger diameter of the workpiece, so that the center of rotation of the workpiece is pressed to the side of the turning tool, and the diameter of the turned workpiece is reduced. In this way, the tool holder is cyclically supported at different diameters of the workpiece, so that the workpiece leaves and approaches the turning tool, forming a regular slub shape. There is also too much force in the follower and the heel of the tool holder, so that the center of rotation of the workpiece is pressed against the side of the turning tool, which causes the diameter of the turning tool to become smaller. Continue to move the tool. This cycle also forms a slub.
Elimination method: adjust the gap of each part of the machine to enhance the rigidity of the machine. When contacting the tool holder claw, make sure that the claw surface is not only in contact with the workpiece, but also without excessive force. More cutting depth (0.05 ～ 0.1) mm at the tool joint to eliminate the "make knife" phenomenon when cutting the tool. The size of the cutting depth should be mastered by the rules of the machine tool and flexibly mastered.
