Case Study: CMS GR.6997-WC Spindle Rebuild After Stator Failure & Drawbar Engagement Incident
Case Study · CMS Spindle Rebuild
A CMS GR.6997-WC electrospindle arrived with a clear diagnosis — a dead stator. The teardown told a second, more important story: the drawbar had been engaged while the spindle was still spinning. Here’s how a full electrical restoration plus precision toolroom machining brought the unit back to OEM tolerances.
Case File
| Spindle Make | CMS |
| Model | GR.6997-WC |
| Serial Number | Co.039959-170 |
| Service Profile | Full Precision Rebuild + Stator Rewind + Emergency Mechanical Machining |
Overview
Executive Summary
An industrial CMS GR.6997-WC spindle was pulled from production and sent to our facility after sudden performance degradation. Incoming diagnostics pointed directly at a dead stator — but a comprehensive teardown revealed a secondary, high-impact mechanical event: the drawbar had been engaged while the spindle was still spinning. By combining advanced electrical restoration with precision toolroom machining, we rebuilt the spindle to OEM tolerances and returned it to service, sparing the client a full-machine replacement and its lead time.
The Hidden Failure
The stator was the obvious failure. The drawbar incident was not. Had we simply swapped the stator and shipped the unit, the damaged drawbar mechanism would have failed immediately on reinstallation. The whole case turns on the discipline of a full mechanical teardown — even when the electrical diagnosis looks complete.
Diagnostics
1. Electrical Failure Analysis
Incoming electrical diagnostics confirmed a critical defect in the motor assembly:
- The finding: the stator had completely failed, with severe insulation breakdown.
- The likely culprits: thermal overloading, electrical spikes, or localized contamination.
- The remedy: the stator was systematically extracted and sent for a precision, high-spec rewind (P.O. 7528) to restore original motor integrity without replacing the motor housing.
2. Mechanical Forensic Discovery: A Mid-Rotation Event
During deep mechanical disassembly, our technicians uncovered evidence of a catastrophic mechanical shock: the drawbar actuator had been engaged while the spindle was rotating at speed. The resulting kinetic energy and instantaneous thermal spike friction-welded the end of the drawbar directly to the actuator piston rod, inflicting moderate-to-severe damage on both critical components.
Recovery
Precision Machining & Mechanical Restoration
Rather than writing off the damaged mechanical components, our machine shop executed a precision salvage and repair strategy:
- Actuator piston reclamation: the damaged piston rod was precision-machined to skim away the friction-welded material and restore its exact original geometry.
- Drawbar insert replacement: the compromised end of the drawbar insert was removed and replaced with a fresh component to correct the mating surface.
- Actuator system re-qualification: the entire actuation assembly was stripped, ultrasonically cleaned, and systematically inspected to confirm correct clamp/unclamp tolerances.
Advanced Component Upgrades
To maximize longevity and resilience against future operational stress, the spindle was rebuilt with premium internal components:
Super-Precision Bearings
The unit was upgraded to P4-class, sealed ceramic hybrid bearings — HYKH60102RZCTAP4+DUL and HYKH60072RZCTAP4+DUL. Compared to standard steel bearings, these offer superior thermal stability, a lower friction coefficient, and markedly improved contamination resistance.
Drawbar Spring System
New 50 mm × 25.4 mm × 2.25 mm disc springs were installed and treated with specialized MetalFlux lubricant to guarantee consistent tool-retention force and prevent future fatigue.
Clean Room Assembly & Multi-Stage Balancing
- Dynamic balancing: because the spindle had taken severe mechanical shock loading, single- and multi-plane dynamic balancing was performed on all rotating parts both before and after final assembly to eliminate harmonic vibration.
- Class 10,000 clean room: final assembly was conducted in our strictly controlled Class 10,000 clean room to remove any risk of ambient particulate contamination during bearing seating.
Lessons
Root Cause & Key Lessons
1. Never Actuate a Spinning Drawbar
Engaging the drawbar during rotation creates an immediate friction-weld effect and severe mechanical shock. It can bend shafts and destroy bearings instantly — exactly the secondary damage uncovered on this unit.
2. Electrical Failures Can Hide Mechanical Trauma
A stator swap alone would have looked like a complete repair. Without a rigorous, component-level mechanical teardown, the damaged drawbar mechanism would have caused immediate failure on reinstallation.
3. Rewinding & Machining Restore OEM Standards
Full spindle replacement on a CMS machine carries lengthy lead times. Precision stator rewinding and localized component machining restored this unit to OEM standards and kept it out of the replacement queue entirely.
Outcome
Final Result
Following assembly, the CMS spindle underwent a rigorous test-stand run-in procedure, monitoring thermal signatures, vibration profiles, and drawbar pull-force. The spindle passed all quality gates, received full performance certification, and was securely packaged for return to the customer’s production floor.
What We Repair
Atlanta Precision Spindles rebuilds the spindle assembly only — including the motor stator, drawbar, and actuator system — not the CMS machine itself, its frame, controls, drives, or motion components. If the spindle assembly is the problem, that is exactly what we restore.
Stator Failure, Drawbar Damage, or Both?
We combine electrical restoration and precision toolroom machining under one roof — so a hidden mechanical fault doesn’t survive the rebuild. Tell us the make, model, and symptoms. Call (678) 225-7855 or send the details.
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