Common Mistakes to Avoid When Using Shims

In mechanical assemblies, shims (or spacers) play a fundamental role in ensuring precise alignment, correct preload, and optimal performance of bearings and mechanical components. However, even small errors in the use or selection of shims can lead to premature wear, vibration, misalignment, or even machine failure. Understanding the most common mistakes and how to avoid them is essential for maintaining reliability and efficiency in industrial applications.

1. Using the Wrong Material

One of the most frequent errors is choosing shims made from incompatible materials. Each application requires specific physical and chemical properties:

• Stainless steel is ideal for high-load or corrosive environments.
• Brass or bronze are often used for low-friction applications.
• Plastic or composite materials are suitable for lightweight, non-conductive, or vibration-damping purposes.

❌ Mistake: Using low-grade or unsuitable materials that deform or corrode easily.
✅ Solution: Select materials based on the operating temperature, load, and environment.

2. Incorrect Thickness or Number of Layers

Precision in thickness is critical. Using too many shims to reach a desired dimension can cause instability or uneven load distribution.

❌ Mistake: Stacking multiple thin shims without verifying total uniformity.
✅ Solution: Use pre-calibrated shims or precision packs to achieve the correct dimension with minimal layering, maintaining flatness and parallelism.

3. Improper Installation

Even the best shims fail if installed incorrectly. Dirt, burrs, or misalignment during assembly can compromise accuracy.

❌ Mistake: Installing shims on unclean or uneven surfaces.
✅ Solution: Always clean and deburr contact surfaces and ensure perfect alignment before tightening.

4. Ignoring Thermal Expansion

In applications exposed to temperature variations, thermal expansion can alter the behavior of shims and components.

❌ Mistake: Using materials with different expansion coefficients in assemblies subject to heat.
✅ Solution: Choose materials with similar thermal properties to the mating components, especially in high-temperature environments such as motors or furnaces.

5. Reusing Damaged Shims

A common yet risky practice is reusing shims after disassembly. Once compressed or deformed, they lose their calibration and may cause uneven support.

❌ Mistake: Reinstalling shims with scratches, bends, or wear marks.
✅ Solution: Always replace shims when performing maintenance to ensure consistent performance and safety.

6. Neglecting Lubrication or Corrosion Protection

In high-humidity or corrosive environments, unprotected shims can rust and seize over time.

❌ Mistake: Installing bare metal shims in humid areas without protection.
✅ Solution: Use anti-corrosion coatings or stainless steel shims, and ensure proper lubrication where required.

7. Not Verifying Alignment After Assembly

After shimming, it’s crucial to check alignment and preload of the mechanical system.

❌ Mistake: Assuming the system is aligned once the shims are in place.
✅ Solution: Perform post-installation checks with dial gauges or laser alignment tools to confirm accuracy.

8. Overlooking Documentation and Traceability

In industrial maintenance, traceability is key. Not recording shim specifications or installation details can complicate future interventions.

❌ Mistake: Failing to log dimensions or materials used.
✅ Solution: Maintain a shim management log with size, material, and location data for each intervention.

Conclusion

Proper use of shims ensures precision, safety, and durability in every mechanical assembly. Avoiding these common mistakes means reducing downtime, improving bearing life, and guaranteeing consistent machine performance.

At Bearing Tools, we offer a wide range of precision shims and spacers made from stainless steel, brass, and high-performance plastics — ideal for the most demanding industrial environments. Our products are engineered to ensure maximum accuracy, reliability, and compliance with international quality standards.