Case Study: CMS GR.6997-WC Spindle Rebuild After Stator Failure & Drawbar Engagement Incident

Spindle Make: CMS
Model: GR.6997-WC
Serial Number: Co.039959-170
Service Type: Full Rebuild + Stator Rewind + Mechanical Repair

The Situation

This CMS GR.6997-WC spindle was sent in for evaluation after performance issues were reported.

Initial electrical testing immediately revealed a critical issue:
The stator had failed and required rewinding.

However, further disassembly uncovered an additional mechanical event that significantly increased the repair scope.

Initial Electrical Diagnosis

Upon arrival, the spindle underwent standard electrical testing.

🔹 Finding: Stator Failure

The stator tested defective and required a complete rewind.

A failed stator can result from:

  • Overheating
  • Insulation breakdown
  • Contamination
  • Voltage irregularities
  • Secondary mechanical events

The stator was removed and sent for precision rewind (P.O. 7528).

Mechanical Damage Discovered During Disassembly

During teardown, we identified a severe mechanical issue.

🔹 Drawbar Engaged While Spindle Was Running

Evidence showed that the drawbar actuator had been engaged while the spindle was rotating.

This caused:

  • The end of the drawbar to become friction welded to the actuator piston rod
  • Moderate damage to both components

Engaging the drawbar while the spindle is rotating can create instantaneous mechanical shock and extreme heat at the contact surfaces.

Corrective Mechanical Repairs

To restore the drawbar system:

✔ Damaged Actuator Piston Machined

The actuator piston rod was precision machined to remove damaged material and restore proper geometry.

✔ Drawbar Insert Replaced

The end of the drawbar insert was replaced to correct the friction weld damage.

✔ Full Actuator System Inspection

All actuator components were:

  • Disassembled
  • Cleaned
  • Inspected
  • Re-qualified or replaced as required

Component Restoration & Cleaning

Each remaining spindle component was:

  • Cleaned
  • Inspected
  • Reworked if necessary
  • Re-qualified or replaced

Precision cleaning is critical after a mechanical event of this nature.

Bearing Upgrade & Replacement

New sealed ceramic hybrid bearings were installed:

  • HYKH60102RZCTAP4+DUL
  • HYKH60072RZCTAP4+DUL

These P4-class sealed hybrid bearings provide:

  • High-speed capability
  • Improved contamination resistance
  • Reduced friction
  • Enhanced thermal stability

Replacing bearings was necessary due to stator failure and mechanical shock loading.

Stator Rewind & Reinstallation

The CMS GR.6997 stator was professionally rewound.

After rewind:

  • The stator was installed into the motor housing
  • Electrical testing was performed again
  • Motor integrity verified prior to final assembly

Rewinding restored motor performance without requiring full motor replacement.

Drawbar Spring System Service

New disc springs (50mm x 25.4mm x 2.25mm) were installed and coated with proper MetalFlux lubricant to ensure:

  • Correct tool retention force
  • Smooth clamp/unclamp function
  • Long-term reliability

Dynamic Balancing

All rotating components were dynamically balanced:

  • Prior to final assembly
  • After complete assembly

This is critical after mechanical shock events and stator replacement.

Clean Room Assembly

Final cleaning, preparation, and assembly were completed in our Class 10,000 clean room environment to ensure contamination-free precision assembly.

After assembly:

  • Spindle was run
  • Broken-in
  • Performance tested
  • Certified

The spindle was returned to the clean room for final verification prior to packaging.

Given the combination of electrical and mechanical damage, full replacement would have been significantly higher.

Root Cause Summary

Two primary failure events occurred:

1️⃣ Electrical stator failure
2️⃣ Drawbar engagement while spindle was rotating

The drawbar incident created mechanical damage requiring machining correction and component replacement.

Key Lessons

1️⃣ Never Engage the Drawbar While Spindle Is Rotating

This can cause immediate friction welding and mechanical shock damage.

2️⃣ Electrical Failures Often Hide Mechanical Damage

Full teardown inspection is essential.

3️⃣ Stator Rewind Is a Viable Alternative to Full Replacement

When handled properly, rewind restores motor integrity.

4️⃣ Mechanical Shock Requires Dynamic Rebalance

Shock loading affects rotational stability.

Final Takeaway

This CMS GR.6997-WC spindle experienced both electrical failure and mechanical shock damage. Through stator rewind, precision machining, bearing replacement, and clean-room assembly, full performance was restored.

Early diagnosis and proper corrective procedures prevented complete spindle replacement.