Why the car tie roller vibration pattern

Problem 1, because the stick is not concentric (the so-called out-of-roundness), resulting in the front corner of the turning tool in the turning force is not uniform or caused by the vibration and the formation of vibration pattern!

Problem 2: The length of the stick at the end of the chuck exceeds the length of the turned part, causing the stick to chatter when the spindle is rotating, resulting in the formation of vibration patterns.

Problem two.