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Remove tool holder and manually rotate spindle by hand to check for binding, rough spots, or excessive resistance. Spindle should rotate smoothly with consistent resistance.

Ensure spindle orientation is OFF and machine is in emergency stop before manual rotation.

Inspect spindle taper for damage, contamination, or debris. Clean thoroughly with solvent and check tool holder taper condition. Check draw bar operation for proper clamping force.

Check bearing condition by listening for abnormal noise during low-speed rotation (50-100 RPM in manual mode). Grinding, rumbling, or clicking indicates bearing failure.

Review cutting parameters in current program. Verify feeds, speeds, and depth of cut are within tool and material specifications. Reduce load and test incrementally.

Access spindle parameters and verify parameter 4001 (spindle motor serial number) matches the actual motor nameplate. Record motor rated current from nameplate.

Check parameter 4025 (maximum spindle motor current) and parameter 4026 (spindle current limit percentage). Verify these match motor specifications and are not set below 100% of rated current.

Do not exceed motor nameplate ratings. Incorrect settings can damage motor or drive.

Review spindle drive alarm history (SHIFT + ALARM) to identify if alarm occurs at specific speeds or loads. Note if alarm is immediate on start or during acceleration.

Perform spindle drive auto-tuning procedure from maintenance menu if parameter changes were made or motor was replaced. This recalibrates drive to motor characteristics.

Ensure spindle is unloaded with no tool holder installed during auto-tuning.

Perform spindle motor insulation resistance test using megger (500V DC). Test each phase (U, V, W) to ground and phase-to-phase. Readings should exceed 5 megohms. Values below 1 megohm indicate winding failure.

Disconnect motor cables from drive before megger test. High voltage test can damage drive electronics.

Measure motor winding resistance phase-to-phase (U-V, V-W, W-U) with multimeter. Readings should be balanced within 5%. Significant imbalance indicates shorted or open windings.

Inspect spindle motor power cables for damage, contamination, or overheating evidence. Check all connections at motor and drive for tightness and corrosion. Measure cable insulation resistance.

Monitor actual spindle current on drive diagnostic screen during low-speed test run (100-200 RPM, no load). Current should be steady and below 30% of rated. Erratic readings indicate drive current sensor failure.

If alarm repeats immediately, do not continue testing. Drive or motor replacement required.