Multiple factors may be involved in the instability of workpieces processed by CNC vertical lathes. Here are some possible reasons why artifacts may be unstable:

1. Insufficient clamping: If the CNC vertical lathe workpiece is not clamped enough or unevenly, it will cause the workpiece to vibrate or shake during the processing, thus affecting the processing quality.

2. Tool selection and cutting parameters: Improper tool selection or cutting parameter settings for CNC vertical lathes may cause excessive cutting force during the cutting process, causing vibration or resonance phenomena.

3. Too fast processing speed: Too high processing speed of CNC vertical lathe may cause collision between the tool and the workpiece, causing vibration and instability.

4. Tool wear: Severe wear of CNC vertical lathe tools may lead to unbalanced cutting forces, which in turn affects the stability of the workpiece.

5. Tool path design: Unreasonable tool path design of CNC vertical lathe may cause uneven cutting force during the cutting process, affecting the stability of the workpiece.

6. Machine tool power system problems: Failure or imbalance of the power system of the CNC vertical lathe may also cause the workpiece to be unstable, requiring timely inspection and maintenance.

7. Material issues: The inhomogeneity or internal stress of the CNC vertical lathe workpiece material may cause deformation during processing, thus affecting the processing stability.

8. Insufficient cooling: Insufficient cooling of CNC vertical lathes may cause the workpiece or tool to overheat, affecting processing stability.

9. Machine tool foundation issues: The foundation stability of the CNC vertical lathe is also an important factor. An unstable machine tool foundation may cause vibration to be transmitted to the workpiece.

10. Environmental vibration: The vibration of the environment around the CNC vertical lathe, such as other machine tools, equipment or ground vibration, may also have an impact on the CNC vertical lathe processing process.

In order to solve the problem of unstable workpieces, it is recommended to check the above possible factors one by one and take corresponding measures to adjust and improve. This may include more reasonable clamping solutions, optimized cutting parameters, tool replacement, improved tool path design, machine tool maintenance, etc.