A Practical Guide for Precision Spindle Assembly
Angular contact ball bearings are essential for high-speed, high-precision machine tool spindles. When used in matched pairs — such as back-to-back, face-to-face, or tandem configurations — they provide excellent rigidity and load-carrying capacity. However, their performance depends on one critical factor: correct preload.
And the key to setting preload? The spacer between the bearings.
This guide walks you through the step-by-step process of adjusting spacers to ensure optimal bearing performance, longer spindle life, and superior machining accuracy.
Why Spacer Adjustment Matters
The spacer, also known as a distance ring or gap ring, controls how tightly the two bearings are pressed together. This directly affects internal preload:
- Correct Preload: Removes internal clearance, increases stiffness, reduces vibration, and ensures smooth, quiet rotation.
- Too Much Preload: Causes high friction, rapid temperature rise, and can lead to early bearing failure.
- Too Little Preload: Results in axial play, noise, vibration, and poor machining quality.
Pro Tip: Never assume the spacer is ready to use out of the box. Most require fine grinding to match your specific application and achieve the ideal preload.
Step-by-Step: How to Adjust Spacers
Step 1: Choose Your Bearing Arrangement
The configuration determines which spacer controls the preload:
- Back-to-Back (DB): Best for handling moment loads. Preload is set by the outer ring spacer.
- Face-to-Face (DF): Better at accommodating minor misalignment. Preload is controlled by the inner ring spacer.
- Tandem (DT): Used when high axial load capacity in one direction is required. Both bearings share a common spacer.
Choose the right setup based on your machine’s load and precision needs.
Step 2: Measure All Components
Use a precision micrometer to measure:
- The width of each bearing’s inner and outer rings
- The initial thickness of the spacers
Even tiny differences — as small as 0.001 to 0.005 mm — can significantly impact preload. Accuracy is crucial.
Step 3: Adjust the Spacer Width
This is the most important step:
- To increase preload, make the spacer slightly thinner.
- To decrease preload, make the spacer slightly thicker (or replace it with a larger one).
Note: Spacer grinding requires precision equipment and experience. If you don’t have the tools, consider working with a bearing service center or using factory-preloaded matched sets.
Step 4: Clean Everything Thoroughly
Contamination is a major cause of incorrect preload and premature failure. Before assembly, clean:
- The spindle shaft and housing
- The bearings
- The spacers
Use a lint-free cloth and a pure solvent like isopropyl alcohol. Handle all parts with gloves to avoid fingerprints and oil transfer.
Step 5: Assemble Carefully
Follow these best practices:
- Place the spacer between the bearings, ensuring full and flat contact.
- Use a proper press tool — never use a hammer, as impact can damage raceways.
- Apply even, steady pressure during installation.
Misalignment or uneven force can ruin the adjustment and damage components.
Step 6: Test the Setup
After assembly, run a short test:
- Operate the spindle at low speed (20–30% of maximum RPM) for 10–15 minutes.
- Monitor bearing temperature — a quick temperature rise means preload is too high.
- Check for unusual noise or vibration — smooth operation is ideal.
- Use a dial indicator to measure axial play — any movement indicates insufficient preload.
If any issues arise, disassemble and re-adjust the spacer until the results are within specification.
Pro Tip: Save Time with Pre-Adjusted Bearing Sets
For consistent, reliable results, consider using factory-matched, preloaded bearing pairs. These sets come with precisely ground spacers and are tested for specific preload levels — eliminating trial and error and reducing setup time.
Conclusion: Precision Makes the Difference
Adjusting spacers is not just a mechanical step — it’s a precision process that directly affects spindle performance, accuracy, and bearing lifespan.
By measuring carefully, adjusting accurately, cleaning thoroughly, and testing before full operation, you can achieve maximum rigidity, stability, and reliability in your high-performance applications.
About Beining Technology
Beining Technology specializes in high-precision angular contact ball bearings for CNC spindles, grinding machines, electric motors, and industrial automation systems.
We offer:
- Matched bearing pairs in DB, DF, and DT configurations
- Custom preload options (light, medium, heavy)
- Technical support for installation, maintenance, and optimization
Contact us today for product specifications, free samples, or expert advice on selecting the right bearing solution for your machine.
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