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What is a CNC Spindle and How Does it Function?

When we mention CNC machine tools, most people might think of precision machining processes, high production efficiency, and complex mechanical structures. However, few truly pay attention to an indispensable core component behind every CNC machine tool—the CNC spindle.

The CNC spindle, as the core component of a plastics and metal CNC machine, not only supports the machining tool but is also crucial for the high precision and high efficiency operation of the entire machine. Whether it’s a CNC milling machine, engraving machine, or lathe, their ability to precisely complete various complex machining tasks relies on the precise control and efficient operation of the CNC spindle.

So, what exactly is a CNC spindle? How does it work? Please continue reading to learn more about the spindle.

What is a CNC Spindle?

what is a cnc spindle

A CNC spindle refers to the shaft on a machine tool that drives the workpiece or the cutting tool to rotate. Except for machine tools like planers and broaching machines, which have linear main movements, most CNC machine tools are equipped with spindle components.

The motion precision and structural rigidity of spindle components are critical factors in determining machining quality and cutting efficiency. For CNC machine tools, spindle parts need to meet high precision requirements during fine machining, while also possessing the cutting capability necessary for rough machining. Additionally, CNC machine tool spindle components should have high dynamic and static rigidity and resistance to thermal deformation.

CNC spindles are designed to provide precise control over speed and torque to meet different machining requirements. They are typically driven by electric motors, which can be either AC (alternating current) motors or DC (direct current) motors, depending on the machine’s application needs and design.

How Do CNC Spindles Work?

The working principle of a CNC spindle is primarily based on the motor drive and the support of bearings, ensuring that the cutting tool can rotate at high speed and with stability.

Typically, a powerful motor drive (such as a servo motor or stepper motor) powers the spindle. This drive system accurately controls the spindle motor’s rotation according to the instructions sent by the CNC control system.

The spindle is supported by spindle bearings, which ensure its stability and precision during high-speed rotation. Cutting tools (such as drills, milling cutters, etc.) are mounted on the spindle through some form of clamping system (such as tool holders, tool posts, or collets).

The CNC control system acts as the “brain” of the entire process. Based on a pre-written machining program (usually G-code generated by CAD/CAM software), it precisely controls the spindle motor’s speed, rotational direction, and duration. This allows the CNC machine to automatically perform various complex machining operations such as cutting, milling, and drilling.

how does a cnc spindle work

Common CNC Spindle Drive Methods

The primary drive of CNC machine tools requires a wide speed range to ensure the use of reasonable cutting parameters during machining, thereby achieving optimal productivity, machining precision, and surface quality.

Gear Transmission

Gear transmission is commonly used in large and medium-sized CNC machine tools. This method uses pairs of gears to not only complete the transmission but also to achieve stepped variable speed or segmented stepless speed change for the spindle. It ensures that the spindle meets the torque characteristics required at low speeds. The shifting of sliding gears is mostly achieved by hydraulic forks or directly driven by hydraulic cylinders.

While this transmission method is effective, it adds complexity to the CNC machine tool’s hydraulic system. The electrical signals from the CNC device must first be converted into mechanical actions of solenoid valves, which then distribute hydraulic oil to the corresponding hydraulic cylinders, thus introducing intermediate steps in the speed change process.

Synchronous Belt Transmission

Synchronous belt transmission is primarily used in small CNC machine tools. It avoids the vibration and noise associated with gear transmission but is only suitable for spindles with low torque requirements.

Synchronous belt transmission combines the advantages of belt and chain transmission. The working surface of the belt and the outer circumference of the pulley are toothed, providing non-slip meshing transmission. The synchronous belt incorporates a high-strength layer that does not stretch elastically after bearing loads, maintaining the belt pitch, and enabling synchronous transmission without relative slippage between the driving and driven pulleys.

Motor-Driven Transmission

In motor-driven transmission, the motor is also known as an electric spindle. The stator of the motor is fixed, while the rotor and spindle are integrated into a single design. This greatly simplifies the structure of the spindle box and the spindle, effectively increasing the rigidity of the spindle components. However, this method has a smaller output torque, and the heat generated by the motor can significantly affect spindle precision. For instance, the spindle unit of a Japanese-developed vertical machining center, equipped with an internal motor spindle, can reach a maximum speed of 50,000 rpm.

How To Find The Right CNC Spindle?

The main spindle of CNC machine tools should meet the following requirements:

Durability of Precision

The durability of the spindle assembly’s precision refers to its ability to maintain its original manufacturing accuracy over a long period. CNC machines are expensive, and to accelerate their return on investment, they often operate at high utilization rates. To extend their service life and reduce maintenance frequency, CNC machine spindle components must have excellent precision durability.

Material and Power of the Spindle

Common spindle materials include carbon steel, alloy steel, stainless steel, and ceramics. Each material has different hardness, wear resistance, and thermal stability. For spindles that need to handle hard materials like steel, high-strength and high-hardness materials such as alloy steel or stainless steel are typically chosen.

The greater the power, the higher the torque and rotational speed the spindle can provide, allowing the use of larger drills at higher speeds. For example, if you plan to drill into steel with a 6mm drill bit at 2000 rpm, but your spindle can only provide a maximum power of 0.6 kW, it would be insufficient. You would need a higher-power spindle to ensure adequate torque and speed to complete the task.

High Rigidity

High-speed cutting operations in CNC machines require spindle assemblies with high rigidity. Otherwise, the spindle may undergo significant elastic deformation under external forces, leading to vibrations. These vibrations can affect the precision and surface roughness of machined parts.

Strong Thermal Stability

Spindle operation generates heat, causing the temperature of spindle components to rise. If the spindle lacks sufficient thermal stability, temperature changes can alter the shape and position of spindle components, affecting machining accuracy. Good thermal stability ensures that the spindle maintains stable performance despite temperature changes, reducing machining errors due to thermal deformation.

High Reversal Accuracy

Reversal accuracy refers to the positioning precision of the spindle’s front-end workpiece, fixture, or cutting tool during reversal. For CNC machines that frequently perform forward and reverse operations, high reversal accuracy ensures that the spindle maintains stable performance during reversals, reducing machining errors caused by reversal.

Excellent Anti-Vibration Capability

CNC machines are subject to various vibrations during machining, such as those induced by cutting forces and machine vibrations. These vibrations can affect machining accuracy and surface quality, and even damage the tools and spindle. Good anti-vibration capability ensures that the spindle maintains stable performance in vibrating environments, reducing machining errors and damage caused by vibrations.

How Exceptional CNC Machining Services Can Help You

In the pursuit of high precision and high efficiency in modern manufacturing, CNC machining technology has become an indispensable key. To meet your need for superior machining services, BOYI offers exceptional CNC machining services to help you easily tackle various complex machining challenges.

We have a professional technical team that is intimately familiar with every detail of CNC machine tools. They can provide you with the most suitable spindle configurations for your projects, the most precise programming setups, and the most considerate CNC machining services.

Contact us now to experience our exceptional CNC machining services!


In summary, the CNC spindle transmits rotational power to the cutting tool through a precise control system and efficient drive mechanism, enabling the precise machining of workpieces. It is one of the indispensable key components in CNC machine tools. If you are looking for efficient CNC machining services, please contact the professionals at BOYI. They always prioritize customer needs and are ready to answer any questions or concerns you may have.


How long do CNC spindles last?

The lifespan of a CNC spindle varies depending on several factors, including operating conditions, maintenance, cooling, and lubrication. Generally, a typical high-speed spindle can run for about 6000 hours on average before requiring a rebuild. However, factors such as overloading, collisions, and operating without proper cooling and lubrication can significantly reduce the spindle’s lifespan.

How to lock spindle on cnc lathe?

To lock the spindle on a CNC lathe, follow the manufacturer’s instructions and use the dedicated spindle lock function or engage a mechanical locking mechanism, if available, to prevent the spindle from rotating while performing operations like tool changes or maintenance.

Catalog: CNC Machining Guide

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