What is the problem with CNC spindles?

Some common problems with CNC spindles include excessive noise, vibration, and heat, as well as issues with accuracy, tool runout, and bearing wear. Regular maintenance and proper use can help prevent and address these issues.

Computer numerical control (CNC) machine tools rely on spindles to rotate the cutting tools needed for milling, drilling, and other machining processes. CNC spindles must operate at high speeds and forces while maintaining accuracy. However, several common problems can impair CNC spindle performance and machine productivity. This article explores the causes and solutions to these problems.


Friction in spindle bearings can cause heat generation during operation, which can exceed 150°C in severe cases. Excessive heat reduces the performance of the lubricant and shortens the life of the bearings, as well as swelling precision parts and reducing machining accuracy.


During machining, cutting forces apply loads on the spindle. Spindle deflection under these loads causes vibrations and accuracy errors. The spindle must, therefore, have high static and dynamic stiffness to resist deflection. In addition, imbalances within the spindle motor components can generate vibrations during rotation. Vibration leaves a visible pattern on the machined surface. Balancing spindles, tool holders, gears, and pulleys can alleviate this problem.

Startup problem

When starting, low stability can lead to problems when restarting after an emergency stop. Therefore, the starting load must be kept below the level at which the drive motor stalls. Startability can be enhanced by using a variable frequency drive and optimizing the acceleration ramp speed.

Speed variation

Spindle drive systems rely on precise speed control to provide optimum cutting conditions. However, the load generated during cutting slows down the spindle speed. Excessive speed fluctuations can damage the surface finish.


Electric spindles are prone to problems such as overheating, vibration, and speed variation during operation. But through some design and adjustment, some of the problems can be overcome.

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