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​CNC spindle motors​ are one of the core power sources of CNC machine tools. Their main function is to provide cutting power for processing and realize the speed regulation and forward and reverse rotation of the spindle. The motor built into the spindle structure eliminates the mechanical loss of traditional belt/gear transmission, and the speed can reach tens of thousands of revolutions per minute, which significantly improves the processing efficiency and precision.

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The working principle of CNC spindle motors is based on the generation of electromagnetic induction and rotational torque. It is integrated through AC high-frequency motors, and the motor is directly built into the spindle, which reduces the driving process, has a more compact structure, lower noise, higher mechanical efficiency, better precision, and smaller vibration amplitude. In addition, the spindle motor usually uses a photoelectric encoder to detect the speed and rotor position, and the detection signal is used as a feedback signal for vector frequency conversion control for magnetic field oriented control.

1. Compact structure: CNC spindle motors integrate the motor directly into the spindle, eliminating the transmission components such as belts and gears required by traditional spindles, thereby simplifying the structure and reducing space occupancy. This design integrates the motor and the spindle, further improving the compactness of the overall structure.

‌2. High speed: CNC spindle motors eliminate the mechanical loss and inertia limitations of the intermediate transmission link, and the speed can reach tens of thousands of revolutions per minute, which is significantly higher than traditional spindles (usually thousands of revolutions per minute).

‌3. High precision: Direct drive reduces transmission errors, and through precision bearings or magnetic suspension technology, it can effectively control thermal deformation and vibration, thereby improving processing accuracy.

‌4. Fast dynamic response: The integrated design of the motor and the spindle makes the inertia small, the acceleration and deceleration time short, and can respond quickly to CNC instructions, improving the flexibility and processing efficiency of the machine tool.

‌5. High power density‌: Modern CNC spindle motors usually require active cooling, such as water cooling or air cooling systems, to keep the spindle temperature stable, extend service life and improve processing quality‌.

‌6. Advanced technology‌: CNC spindle motors are driven by synchronous motors or asynchronous motors. Asynchronous motors are standard due to their high reliability and ease of use, while synchronous motors use permanent magnet technology, which is more efficient and generates less heat‌.

‌1. Power and torque‌: The spindle motor needs to have sufficient power and torque to cope with the cutting resistance requirements during rough machining. Motors with different center heights have different power and torque output capabilities. Motors with larger center heights are suitable for heavy-load start-up and operation occasions, while motors with smaller center heights are suitable for light-load, high-speed applications‌.

‌2. Speed ​​range‌: The spindle motor needs to have a wide speed range, usually between 1000-15000rpm, to cover different process requirements such as drilling and fine milling. During the design phase of CNC machine tools, the technical indicators such as the output power and speed range of the spindle must be clearly defined to ensure that the spindle will not "stuck" due to insufficient power during cutting.

‌3. Dynamic response‌: The spindle motor needs to have fast dynamic response capabilities to ensure the smooth transition process. The dynamic response of vector control ensures that the transition process (Δv)/(Δt) is large enough to ensure the stability and accuracy of the processing process.

‌4. Servo characteristics‌: The spindle motor should have servo characteristics to achieve precise positioning and synchronization of the spindle, such as complex operations such as thread processing. The accuracy and stability of the servo system have a direct impact on the processing quality.

‌5. Vibration and thermal drift‌: The vibration value of the spindle motor should comply with ISO standards, and the vibration value is usually required to be less than 2.5mm/s. At the same time, it is necessary to have a thermal drift compensation function to ensure processing accuracy and stability.

‌6. Cooling system‌: The spindle motor should adopt an efficient cooling system, such as a heat pipe cooling system, to ensure that it can still maintain a good working condition under long-term operation or high temperature environment.

‌7. Magnetic circuit design‌: The magnetic circuit design of the motor should be optimized to reduce heat and improve efficiency. For example, the use of a unique additional magnetic pole design can reduce losses and improve motor efficiency‌.
Source:​https://steppermotor2.hatenablog.com/entry/2025/06/26/182601​