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If your CNC spindle motor is making a high-pitched squealing sound, don’t panic — in most cases, this is not a sign of failure, but rather a condition that can be diagnosed and resolved with a few steps.
This article explains the possible causes and what you should do next.
🔊 Common Cause: Uneven Grease Distribution
If your spindle is new or hasn’t been used in a while, the internal bearing grease may not have fully spread across the raceways. This is especially common in grease-lubricated Chinese spindles (1.5kW, 2.2kW, etc.).
Symptoms:
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Squealing or high-pitched noise at low RPMs
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Noise that lessens after warm-up
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No other signs of damage or overheating
What to do:
✅ Run-In Procedure
Let the spindle run at 8,000–12,000 RPM for 10–20 minutes continuously.
This helps redistribute the grease via centrifugal force and quiet the bearings.
In many cases, the squeal will disappear completely after this break-in period.
🔧 Other Possible Causes
If the noise persists after warm-up, or shows other symptoms (vibration, heat, etc.), consider the following possibilities:
1. Overloaded or Misaligned Bearings
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If the motor has excessive bearing preload or poor alignment, it may squeal due to internal friction.
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This is rare in new, properly assembled spindles but can occur after rough handling or improper servicing.
2. Dry or Contaminated Bearings
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If the spindle was stored improperly or used without maintenance, the grease may be contaminated or degraded.
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This can lead to a sharp, metallic squeal and eventual bearing failure.
🔥 Warning: Do not continue using the spindle if it squeals consistently and heats up rapidly — this may cause permanent bearing damage.
3. Electrical Noise (VFD Whine)
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Some spindle noises aren’t mechanical at all. VFD settings like PWM carrier frequency or ramp speeds can cause a high-pitched electronic whine.
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If the pitch changes with RPM and doesn't sound like friction, try adjusting your VFD’s switching frequency.
🧪 How to Diagnose the Squeal
| Step | What to Check |
|---|---|
| ✅ Run the spindle at 8,000–12,000 RPM for 20 minutes | Does the sound go away? |
| ✅ Touch the spindle body after 5–10 mins | Is it unusually hot to the touch? |
| ✅ Listen at various speeds (5k, 10k, 20k RPM) | Does the tone change, stay consistent, or worsen? |
| ✅ Check for vibration during spindle-on idle | Could indicate mechanical imbalance or wear |
🧠 Summary
A squealing spindle motor is often caused by unevenly distributed grease, especially in new or rarely used spindles. In most cases, a quick run-in at moderate RPM resolves the issue.
However, if squealing persists, check for heat, vibration, or worsening sound. This could indicate preload issues, bearing wear, or VFD-related resonance.
🆘 Need Help?
If you're unsure about the noise or suspect a more serious issue, contact our support team. We’ll help you determine whether the squeal is normal or whether your spindle needs service.
