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 Profile: Full Precision Rebuild + Stator Rewind + Emergency Mechanical Machining

Executive Summary

An industrial CMS GR.6997-WC spindle was pulled from production and sent to our facility following sudden performance degradation. While initial diagnostics pointed directly to a dead stator, 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 completely rebuilt the spindle to OEM tolerances—saving the client from a costly full-machine replacement.

Technical Breakdown & Diagnostics

1. Electrical Failure Analysis

Initial incoming electrical diagnostics confirmed a critical defect in the motor assembly.

  • The Finding: The stator had completely failed, showing severe insulation breakdown.
  • The Culprit: Common causes include thermal overloading, electrical spikes, or localized contamination.
  • The Remedy: The stator was systematically extracted and sent out for a precision, high-spec rewind (P.O. 7528) to restore original motor integrity without the extreme cost of a brand-new 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 caused the end of the drawbar to friction-weld itself directly to the actuator piston rod, inflicting moderate to severe damage on both critical components.

The Recovery & Rebuild Process

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 actuator piston rod was precision-machined to skim away the friction-welded material, restoring 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 ensure perfect clamp/unclamp tolerances.

Advanced Component Upgrades

To ensure maximum longevity and resilience against future operational stress, the spindle was rebuilt with premium internal components:

  • Super-Precision Bearings: We upgraded the unit to P4-class, sealed ceramic hybrid bearings (HYKH60102RZCTAP4+DUL and HYKH60072RZCTAP4+DUL). These offer superior thermal stability, lower friction coefficient, and drastically improved contamination resistance compared to standard steel bearings.
  • Drawbar Spring System: Installed brand-new $50\text{mm} \times 25.4\text{mm} \times 2.25\text{mm}$ disc springs, treated with specialized MetalFlux lubricant to guarantee consistent tool retention force and prevent future fatigue.
[Incoming Diagnostic] ➔ [Stator Rewind] + [Piston Remachining] ➔ [P4 Ceramic Bearing Upgrade] ➔ [Class 10,000 Assembly]

Clean Room Assembly & Multi-Stage Balancing

  • Dynamic Balancing: Because the spindle suffered severe mechanical shock loading, single and multi-plane dynamic balancing was performed on all rotating parts both prior to 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 eliminate any risk of ambient particulate contamination during bearing seating.

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, which can bend shafts and destroy bearings instantly.

2. Electrical Failures Can Hide Mechanical Trauma

If we had simply swapped the stator without performing a rigorous, component-level mechanical teardown, the damaged drawbar mechanism would have caused immediate failure upon reinstallation.

3. Rewinding & Machining Equal Massive ROI

Full spindle replacement on a CMS machine carries an incredibly high price tag and lengthy lead times. Precision stator rewinding and localized component machining restored this unit to OEM standards at a fraction of the cost.

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.