Spindle Diagnostic Guide

Before you decide to disassemble a spindle out of your machine tool, here are some fundamental checks you can perform:

1. Ensure any manufacturers’ safety recommendations are followed before working on any machine.
2. Spin test: spin by hand and listen/feel for any unexpected sounds or unevenness
3. High speed spin test, warm up your spindle, then run at 80% of maximum speed. Some machine controllers will provide a spindle motor load, it is worth logging this on a regular basis as it will be more obvious if it drifts away from what is normal.
4. Run-out
   1. First clean and inspect the tool holder
   2. Use a Dial Test Indicator to check both the tool taper and face
   3. Use a tool bar extension to check projected runout
5. Drawbar pull force gauge
6. Air cleaning (taper and face)
7. Electrical – switch position settings in machine software
8. Tool loading (carousel) position.

Fault finding list, Symptom > cause > checks

Symptom: Noise/Vibration

• Cause: Total Bearing Failure
• Check:
  • Verify if spindle spins
  • Test for resistance or noise during slow rotation
  • Monitor bearing temperatures after cooling and restarting
• Cause: Bearings Failing
• Check:
  • Measure motor load during idling, acceleration, and cutting
  • Document noise characteristics (high-pitched, rumbling, cutting-only)

Symptom: Noise During Tool Change

• Cause: Tool Changer to Spindle Alignment
• Check:
  • Inspect tool taper for uneven wear (egg-shaped runout)
  • Verify alignment of tool loading arm

Symptom: Tool Holding Problems

• Cause: Wear in Expanding mandrel/clamping jaws
• Check:
  • Clean components
  • Replace if possible
  • Verify tool clamp position and force
  • Inspect drawbar condition

Symptom: Tool Breakages or Poor Surface Finish

• Cause: Runout
• Check:
  • Replace tool holder/collet
  • Clean tool interface and air purge holes
  • Check for burrs or damage
  • Measure runout:
  • Radial (<5 µm good, >10 µm investigate)
  • Axial (tool taper face)
  • Projected (using gauge bar or known good tool)

Symptom: Burning Smell

• Cause: Friction Between Components
• Check:
  • Stop operation immediately
  • Test for resistance/noise during slow rotation
• Cause: Electrical Short
• Check:
  • Isolate electrically
  • Measure resistance between earth and motor phases

Symptom: Electrical and Feedback Faults

• Cause: Damaged Cabling/Wiring
• Check: Inspect cables for damage
• Cause: Damaged Plugs/Pins
• Check: Inspect plugs for contamination
• Cause: EMC Interference
• Check: Verify bonding and cabling of machine/motor/drives

Symptom: Fluid Leaks

• Cause: Cutting Fluid – Hydraulic Coupling
• Check: Inspect rotary coupling at spindle rear
• Cause: Hydraulic Oil – Tool Change Drawbar
• Check: Look for oil accumulation or seepage
• Cause: Cooling Fluid System
• Check:
  • Inspect water cooling jacket
  • Perform low-pressure air leak test

Symptom: Air Leaks

• Cause: O-ring Failure
• Check:
  • Conduct flow-through test
  • Verify purge flow rate
  • Clean purge holes if necessary

Symptom: Accelerated Wear

• Cause: Abrasive Material in Cutting Fluid
• Check:
  • Document cutting materials
  • Inspect cutting fluid and filtration
• Cause: Blocked Air Purge
• Check:
  • Clean and verify both air-purge systems:
  • Labyrinth seals
  • Tool taper/face cleaning holes

Symptom: Damage to Spindle Nose/Housing

• Cause: Machine Crash/Spindle Contact at Speed
• Check:
  • Assess potential bearing damage
  • Look for physical damage/dents/impact marks