CNC vertical lathe is a high-precision machine tool equipment, and the selection and determination of its positioning benchmark is crucial to ensure processing accuracy and product quality.

 1. Principle of unified datum: In the mechanical processing process, using a unified positioning datum as much as possible can effectively improve processing accuracy and reduce errors. This is because the use of a unified positioning reference can reduce the number of tool changes and workpiece position adjustments, thereby reducing cumulative errors and improving machining accuracy.

2. Principle of datum coincidence: In order to avoid errors caused by non-coincidence of datums, the design datum and positioning datum should be coincident with each other as much as possible. This can ensure the accurate position of the workpiece, reduce adjustment and compensation work during the processing, and improve processing accuracy.

3. Mutual reference principle: In some cases, in order to achieve ideal processing results, two surfaces of the workpiece that require higher mutual position accuracy can be positioned as a reference to each other. This can improve processing accuracy and reduce processing errors.

4. Principle of easy installation: When selecting the positioning benchmark, the convenience of installation of the workpiece should be taken into consideration. The positioning datum should be compatible with the clamping device of the fixture or machine tool to facilitate the installation and fixation of the workpiece. This ensures that the workpiece remains stable during processing and prevents errors caused by workpiece movement.

5. Principle of convenient measurement: In order to facilitate the measurement and inspection of the size and position of the processed surface, the positioning datum should be selected at a location that is convenient for measurement and inspection. This can improve measurement accuracy and reduce the impact of measurement errors on processing accuracy.

The selection and determination of CNC vertical lathe positioning benchmarks are crucial to ensuring processing accuracy and product quality. Following the principles of unified datums, coincident datums, mutual datums, ease of installation and ease of measurement can effectively improve processing accuracy, reduce errors, and improve product quality.