(1) The parallelism of the saddle movement relative to the spindle axis is out of tolerance.
(2) The guide rail surface of the bed is seriously worn.
(3) When the workpiece is clamped and processed between the two centers, the taper is generated because the tailstock line does not coincide with the spindle axis.
(4) The anchor bolts of the bed are loose, causing the level of the machine to change.
