Upgraded to P4 Yet No Reduction in Vibration?

At WD, a customer once asked us:

“We upgraded our bearing from P6 to P4. Why didn't the vibration decrease?”

It's a common assumption: Higher precision = better stability

But in engineering, that's not always true.

So what does bearing precision actually change?

Where is the real issue?

At first, the focus was on precision grade. But later it became clear:

The problem wasn't the bearing. It was whether the system was amplifying the error.

What does precision grade really affect?

Bearing precision（P0 / P6 / P5 / P4 / P2）mainly controls:

1. Dimensional accuracy– Affects fit, preload, and assembly consistency
2. Rotational accuracy (more critical)– Determines runout and rotational stability

In simple terms:

• Dimensional accuracy = how well it fits
• Rotational accuracy = how smoothly it runs

In this case, the issue was clearly about how stable the rotation was.

Why didn't switching to P4 solve the problem?

The system had structural flexibility and relatively high speed.

That means: Even small runout errors were amplified

Because eccentricity creates centrifugal force: F = m · r · ω²

At higher speeds, the effect grows quickly.

So even with higher precision, vibration didn't improve significantly.

A more practical way to think about it

After this project, we summarized a more effective approach:

Instead of asking: “Should we use higher precision (P4 / P2)?”

Ask first: “Will the system amplify the error?”

Because in reality: Vibration ≈ error × system amplification

And this amplification depends on: Speed, Structural stiffness, Resonance characteristics, Load conditions

When does higher precision really matter?

In some applications, precision grade is critical:

• High-speed spindles
• Robot joints
• Precision machines

But in many other applications—such as construction machinery, conveyors, or low-speed systems—

system-level factors often dominate.

In those situations, increasing precision may add cost, but not necessarily improve performance.

Conclusion

In this project, we didn't continue increasing precision.

Instead, we optimized structural stiffness and the support design.

The result:

• No need for higher precision bearings
• Vibration decreased significantly

We've seen many similar cases.

The key issue is often not whether the parameter is high enough,

but rather: whether the system is amplifying the error.

Bearing precision is not about “the higher, the better,” but about matching the system.

This is the engineering approach we follow at WD.