When selecting a 3-axis CNC machine, prioritize the spindle power and speed (RPM), as these determine the types of materials (e.g., aluminum, wood, or steel) the machine can process efficiently. Ensure the positioning accuracy and repeatability are within ±0.01mm to ±0.03mm for industrial-grade precision. Additionally, verify the drive system type; while stepper motors are cost-effective for entry-level tasks, AC Servo motors are essential for high-speed, high-torque applications requiring closed-loop feedback.