The reason why CNC vertical lathe workpiece processing is unstable may involve multiple factors. Here are some common reasons why workpiece machining may be unstable:

1. Insufficient or uneven clamping force: The fixture or device that clamps the workpiece may not provide enough clamping force, resulting in slight movement or vibration of the workpiece during cutting. In addition, if the clamping force is unevenly distributed, it will also cause the workpiece to deform or shift.
2. Insufficient stiffness of the workpiece: Insufficient stiffness of the workpiece itself may cause vibration and deformation during processing. Especially when processing workpieces with larger sizes or thinner plates, the stiffness problem is more obvious.
3. Improper cutting conditions: Improper selection of cutting parameters may lead to unstable workpiece processing. For example, cutting speed is too high, feed speed is too fast, cutting depth is too large, etc., which may lead to vibration, unbalanced cutting force or excessive tool wear.
4. Cutting tool problems: Using aging or poor quality cutting tools may lead to unstable cutting results. Problems such as wear, eccentricity, and imbalance of cutting tools may have an impact on processing quality.
5. Machine tool structure and power issues: The structural stability and rigidity of the machine tool are crucial to the processing stability. If the structure of the machine tool is unstable, the guide rail is loose, or the spindle is not running smoothly, it may cause vibration and instability during machining.
6. Numerical control system problems: CNC system errors, program errors or inaccurate control parameters may also lead to unstable workpiece processing. For example, incorrect settings such as tool radius compensation and feed axis control errors may lead to machining errors and instability.
7. Coolant problem: Incorrect use or supply of coolant may also affect the stability of workpiece processing. For example, improper coolant flow, concentration, and temperature may lead to overheating of the cutting zone or poor removal of chips, thereby affecting processing stability.

Any one or more of these factors can cause workpiece machining instability. In order to solve these problems, you can check one by one and take corresponding measures, such as improving the clamping device, adjusting cutting conditions, replacing cutting tools, overhauling machine tool structure, optimizing NC programs, etc. For complex instability problems, systematic analysis and adjustment may be required to achieve stable processing results.The reason why CNC vertical lathe workpiece processing is unstable may involve multiple factors.