When evaluating a CNC milling machine, you must prioritize the Spindle Speed (RPM) and Spindle Taper (e.g., BT40, SK40) to ensure compatibility with your tooling. Additionally, assess the Axis Travel (X, Y, Z dimensions) to match your largest workpiece requirements. For high-precision industries, look for Positioning Accuracy of ±0.005mm and Repeatability of ±0.003mm. The Control System (e.g., Fanuc, Siemens, or Mitsubishi) is critical as it determines the ease of programming and availability of local technical support.