Causes of Ovality
The ovality of the main shaft journal is directly reflected on the workpiece. If it is a sliding bearing, when the magnitude and direction of the load remain unchanged, the main journal is pressed on a certain position on the bearing surface under the action of the load (due to the difference between the main shaft and the bearing). there is a gap). When the spindle rotates through 90°, the center position of the spindle changes, so that the spindle has two center positions during one rotation, and the amount of the turning tool's back engagement changes, which makes the workpiece ovality. The ovality of the bearing hole has no effect on the workpiece.
The blank allowance is not uniform, and there is a gap between the spindle and the bearing, and the amount of back-feeding knife changes during the cutting process.
The front and rear center holes do not match (the two center holes form an angle with the center of the workpiece), the center hole and the center only touch one side, and the uneven wear causes axial movement to form an ellipse T9 p/ g$ y2 y$ c9 C8 \
Front tip swing.
Causes of non-straightness (curvature, convexity, saddle) and taper of the busbar
As the workpiece temperature rises, the shaft will bend. For example, when machining a long shaft on a heavy-duty lathe, when the temperature rises to a certain level, the workpiece will stretch, but since the distance between the two centers does not change, the workpiece will bend because it cannot stretch in the length direction. Therefore, when the axle is long, the temperature should be reduced as much as possible, and at the same time, the rear tip must be retreated frequently.
The influence of the internal stress of the workpiece. There is often internal stress inside the workpiece. During the cutting process, due to the plastic deformation of the surface layer, internal stress will also be generated. This internal stress is in a balanced state inside the workpiece, so that the workpiece maintains a certain shape. However, when the workpiece is unloaded from the fixture or lathe When it goes down, it will produce deformation. To solve this problem, the aging treatment method is generally used.
Causes of radial runout
The front tip pulsates; the center hole is not round or there are dirt such as chips; of course, the surface of the workpiece with ovality will also cause radial runout.