There are many reasons for the vibration of CNC vertical lathe, the following are some possible reasons:

1. Improper selection of cutting parameters: Incorrect selection of cutting parameters may cause oscillation. For example, tool feed rates that are too high, depths of cut that are too large, or cutting speeds that are too fast can cause oscillations in the cutting process.
2. Tool wear or damage: Wear or damage to the tool can result in unbalanced or unstable cutting forces, causing oscillations. If the tool wears unevenly or if the cutting edge is damaged, uneven cutting forces will be applied, which will cause oscillations.
3. Unstable workpiece clamping: If the workpiece is not clamped firmly or the clamping method is incorrect, oscillation will occur. An unstable workholding can cause the workpiece to vibrate during cutting, which is transmitted throughout the system.
4. Insufficient structural rigidity of the machine tool: If the structural rigidity of the machine tool is insufficient to effectively withstand the cutting force, it is easy to cause oscillation. The structure of the machine tool includes the rigidity of the bed, spindle, ball screw and other components.
5. Resonance effect during the cutting process: When the frequency of the cutting force during the cutting process matches the natural frequency of the machine tool structure or the workpiece itself, a resonance effect will occur, causing oscillation.
6. Cutting fluid or cooling system problems: Inadequate use of cutting fluid or cooling system failure may cause the tool to overheat or chip accumulation, which in turn can cause oscillation.

Methods to solve the oscillation problem usually include adjusting cutting parameters, changing tools, improving workpiece clamping methods, enhancing machine tool structural stiffness, avoiding resonant frequencies, etc. If the vibration problem is serious, it is recommended to consult a professional CNC mechanical engineer or technical support personnel for detailed analysis and solution formulation.