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MAINTENANCE / PROTOCOLS

SPINDLE TAPER RUNOUT

Step-by-step diagnostic procedure for isolating bearing wear vs. taper damage using a precision test bar.

PROTOCOL ID: M-SPD-041
REVISION: 2.4 (2024)
INTERVAL: 2,000 Hours
EQUIPMENT: Test Bar, 1-micron Indicator

1. Baseline Conditions

Runout checks performed on a cold spindle are invalid. The spindle must be run through a warm-up cycle (e.g., 500 RPM for 10 mins, 2000 RPM for 10 mins, 5000 RPM for 10 mins) to allow the bearings to reach steady-state thermal expansion and ensure the grease is evenly distributed.

2. Taper Cleanliness

Use a lint-free wipe and dedicated taper cleaner to wipe the internal taper. Inspect for fretting (black/brown marks) or raised burrs. A single chip flattened into the taper can induce 0.05mm of runout.

3. The Measurement Procedure

  1. Insert a certified precision ground test bar into the spindle. Do not use an endmill or standard toolholder.
  2. Mount a 1-micron (0.001mm) or 0.0001" dial test indicator to the machine table on a rigid magnetic base.
  3. Position the indicator tip against the test bar, exactly 1 inch (25.4mm) below the spindle face.
  4. Rotate the spindle by hand slowly. Record the Total Indicator Reading (TIR).
  5. Move the indicator down to 12 inches (300mm) below the spindle face and repeat the measurement.

Interpreting Results

  • High Runout at 1", High Runout at 12": Likely front bearing failure or a severely bent spindle shaft. Requires full spindle cartridge rebuild.
  • Low Runout at 1", High Runout at 12": Indicates angular runout, typically caused by a bell-mouthed taper or a chip caught between the taper and the test bar. Eject bar, reclean, retest. If persistent, taper grinding in-place may be viable.