In high-precision mechanical systems—especially those found in CNC machines, robotics, electric motors, and precision gearboxes—rolling bearing preload plays a critical role in ensuring consistent performance, stability, and longevity. For equipment manufacturers and bearing wholesalers, understanding preload and its correct application is essential for delivering products that meet modern performance expectations and minimize failure risks.
This article explains why preload is necessary, its main benefits, and the correct methods to apply preload in real-world industrial applications.
What Is Bearing Preload?
Preload refers to the intentional application of internal axial or radial force to a rolling bearing before it starts operating under external loads. It removes internal clearances and ensures all rolling elements are in continuous contact with the raceways.
Why Do Rolling Bearings Need to Be Preloaded?
Here are the primary reasons why preload is critical in rolling bearing applications:
1. Improved Rotational Accuracy
Preloading eliminates internal clearances and minimizes shaft displacement, which enhances the positional and rotational precision of equipment—critical for applications like CNC spindles and robotic arms.
2. Higher Rigidity
A preloaded bearing resists deformation more effectively under load, increasing system stiffness, which is particularly important in high-speed cutting, automation, and servo systems.
3. Reduced Vibration and Noise
By eliminating gaps between rolling elements and raceways, preload helps reduce vibration, mechanical noise, and micro-movements, thereby improving performance and comfort in high-speed or sensitive applications.
4. Increased Operating Speed
Proper preload allows for higher permissible rotation speeds by maintaining optimal rolling contact and reducing slippage.
5. Extended Bearing Life
When correctly applied, preload ensures even load distribution, minimizing localized stress and wear that lead to premature bearing failure.
6. Prevention of Bearing Loosening
Preload creates a stable internal contact pressure that helps prevent bearing components from loosening under alternating or vibratory loads. This is especially important in high-speed or high-shock applications where relative motion between bearing parts can lead to fretting, noise, or even structural failure.
Note: Insufficient or excessive preload can both cause problems. Poor preload may lead to vibration, while excessive preload generates heat and stress, shortening bearing life.
Types of Preload
Preload can be applied in two general ways:
Fixed (Constant) Preload
Applied during assembly and remains constant.
Achieved using rigid spacers, shims, or fixed-position spring systems.
Common in machine tool spindles and high-speed gearboxes.
Spring (Adjustable) Preload
Maintained via coil springs, wave springs, or Belleville washers.
Allows for flexibility and compensation for thermal expansion or slight misalignment.
Used in applications with variable loads or thermal growth.
Correct Preload Operation Methods
The correct preload operation method depends on the bearing type, application requirements, and operational environment. Below are standard industrial methods:
1. Preload by Axial Adjustment
Typically used for angular contact ball bearings arranged face-to-face or back-to-back.
Adjust axial positioning of bearings using shims or threaded sleeves to remove clearance.
Requires precise axial displacement measurement using dial indicators or micrometers.
2. Preload Using Springs
Install springs to provide a constant axial force to the bearing, ensuring continuous contact.
Ideal for applications with thermal expansion or fluctuating loads.
Must carefully calculate spring force based on bearing size and operating load.
3. Preload by Spacer Grinding
A fixed-size spacer is ground to a precision thickness that creates the desired preload.
Used in matched bearing sets for high-speed spindle applications.
Offers high repeatability and excellent rigidity.
4. Preload Using Preload Bearings
Purchase preloaded matched pairs of bearings directly from the manufacturer.
These are factory-set to specific preload values and are ready for installation.
Eliminates manual adjustment and guarantees preload consistency.
Warning: Always follow bearing manufacturer preload recommendations. Over-preloading can cause excessive heat, energy loss, and early fatigue.
Common Mistakes to Avoid
| Mistake | Consequence |
| Applying too much preload | Excessive heat, increased friction, bearing fatigue |
| No preload or too little preload | Vibration, reduced stiffness, noise, uneven load distribution |
| Using incorrect adjustment tools | Misalignment, inconsistent preload |
| Ignoring thermal expansion in design | Loss of preload over time or bearing seizure |
Practical Example: CNC Spindle Bearing Preload
Problem: A customer using angular contact bearings in a CNC spindle experiences high vibration and spindle runout.
Solution: The supplier recommends a matched bearing pair with medium preload and guides the end-user to install using precision-ground spacers. After preload is correctly applied, vibration levels drop significantly, and spindle accuracy improves by 40%.
Conclusion
For terminal equipment users and B2B bearing wholesalers, understanding and applying the correct preload is essential to unlocking the full performance of rolling bearings. Preload improves accuracy, rigidity, lifespan, and noise control—but only when applied correctly.
Whether you’re a manufacturer seeking to optimize product performance or a distributor advising your customers, correct preload methods add significant value and reduce failure risks in critical mechanical systems.
Please click on the link below to read another article of mine for more technical knowledge on rolling bearings.
