There are several important considerations to consider when using a CNC vertical lathe for workpiece positioning and setup:

1. Positioning method: choose the appropriate positioning method to ensure the accurate positioning of the workpiece. Common positioning methods include plane positioning, edge positioning, hole positioning, etc. According to the specific workpiece shape and size, choose the appropriate positioning method. Positioning accuracy is very important for process quality and dimensional control.
2. Clamping force and balance: Make sure that the clamping force is appropriate enough to maintain the stability of the workpiece, but avoid excessive clamping that causes deformation of the workpiece or distortion of shape due to stress release. At the same time, the distribution of the clamping force is balanced to avoid deflection or instability of the workpiece during processing.
3. Fixture design: According to the shape and size of the workpiece, design a suitable fixture to achieve stable and reliable clamping. Fixture design should consider the contact area of the workpiece, the location and number of clamping points to ensure that the workpiece is firmly fixed, while avoiding interference with the machining operation and cutting tool.
4. Avoid deformation: try to avoid deformation of the workpiece during the clamping process. Especially for flexible workpieces or long workpieces, appropriate clamping points and clamping methods should be selected to avoid shape changes or deformation during processing.
5. Clean the surface of the workpiece: Make sure the surface of the workpiece is clean, free from impurities, grease, dust, etc., so that the workpiece can be properly contacted and positioned. Dirty or uneven workpiece surfaces may affect positioning accuracy and clamping stability.
6. Machining allowance consideration: When clamping the workpiece, the influence of cutting pressure and thermal deformation on the workpiece during processing should be considered. In order to avoid that the size after processing does not meet the requirements, an appropriate machining allowance should be reserved when designing the fixture and workpiece clamping.

To sum up, workpiece positioning and clamping is a key link in CNC vertical lathe processing. By selecting the appropriate positioning method, fixture design and clamping force control, accurate positioning, stable clamping and high-precision machining of the workpiece can be achieved. At the same time, pay attention to the cleanliness of the workpiece surface and the consideration of the machining allowance, which can ensure the quality and dimensional accuracy of the machining.