The following key factors need to be considered when purchasing a CNC vertical lathe:

1. Processing requirements: Define your own processing requirements, including workpiece type, size range, material, and processing accuracy. Knowing your needs can help determine the machine tool specifications and capabilities you need.
2. Machine tool performance and specifications: select the appropriate machine tool performance and specifications according to processing requirements. Consider the table size, maximum speed, processing stroke, feed speed, etc. to ensure that the machine tool can meet the expected processing requirements.
3. Accuracy and repeatability: The accuracy of CNC vertical lathe is crucial to the machining results. Understand the positioning accuracy, repeat positioning accuracy and cutting stability of the machine tool to ensure that the machine tool can meet the processing accuracy requirements.
4. Control system: Choose an advanced, flexible and easy-to-operate control system. It can provide a friendly user interface, rich functions, programmability and good compatibility. It is also important to understand the software support and upgradeability of the control system.
5. Tool system and cutting function: Consider the tool system and cutting function of the machine tool, including tool change method, tool magazine capacity, cutting force and feed system, etc. Choose the tool system and cutting function suitable for your own processing needs to improve production efficiency and processing quality.
6. Brand and supplier reputation: choose well-known brands and suppliers with good reputation. Understand the supplier's background, reputation, after-sales service and technical support. Consider the supplier's after-sales service, training support, and spare parts availability.
7. Budget and cost performance: choose the appropriate CNC vertical lathe according to the budget and resource constraints. Comprehensively consider the performance, quality, function and after-sales service of the machine tool, and compare with other suppliers to obtain a better cost performance.
8. Refer to user evaluations and cases: understand other user evaluations and use cases, and obtain valuable information and experience from practical applications. This information can be obtained through the Internet, trade exhibitions and visits to other factories.

Best practice is to communicate with multiple suppliers, ask for details of their products and services, request detailed specifications and quotes. Guided by the actual needs of the company, comprehensively consider various factors, and choose the most suitable CNC vertical lathe.