Fanuc spindle alarm 29 means an excessive load was applied continuously — by the standard settings, a load-meter reading of 9 V (well over rated load) sustained for about 30 seconds. Where AL-22 is the amplifier's thermal time-rating protection, AL-29 is a blunter watchdog: the spindle has been pushed near its limit for half a minute straight — something is wrong. Fanuc's troubleshooting branches on what the spindle was doing when it tripped, and that branch structure is the diagnosis.
Case 1 — During cutting
Watch the load meter through the offending cut. Sustained readings at the top of the scale mean the process itself: worn/wrong tooling (the #1 reason a stable job starts tripping), a harder material batch, or cut parameters that have crept beyond the machine. Fresh inserts first; then review the cutting conditions honestly — the same logic as AL-22, Cause 1.
Case 2 — During a stop (the sneaky one)
The spindle is locked while the drive is being told to move it. Fanuc's specific scenario: the machine's sequence applies the spindle lock/brake while a very-slow-rotation command or an orientation command is active — the drive pushes against a clamped shaft at full current until the 30-second watchdog fires.
- Check the PMC sequence timing around spindle lock/clamp: is the lock engaged when orientation (M19) or a C-axis/slow-rotation command is issued? Watch the lock output and the rotation command together on the diagnosis screen.
- Typical trigger: recent ladder edits, a sticking lock solenoid/valve, or a lock-state switch reporting ‘released’ while the mechanism is still engaged.
Case 3 — Spindle rotates, but only very slowly
The drive is pushing, the shaft barely turns — the drive is fighting itself. Fanuc's four checks:
- Sensor parameters wrong — verify against B-65280EN (400x-range sensor settings); prime suspect after amplifier swaps or parameter restores.
- Motor power lead phase sequence wrong — U/V/W swapped after motor or cable work makes the motor fight its own commutation: it growls, crawls, and draws maximum current. Verify the phase order at both ends against the connection diagram.
- Feedback A/B phases crossed — a re-terminated feedback cable with A/B signal pairs swapped reverses the apparent rotation; the drive corrects endlessly against it. Check pin-to-pin against the manual, not by wire colour.
- Feedback cable faulty — Fanuc's field test is elegant: rotate the motor by hand and watch the motor-speed reading on the CNC diagnosis screen. Hand rotation with no speed indication = the speed signal is not arriving — replace the cable, then the sensor (or motor) if it persists.
Case 4 — Spindle does not rotate at all
- Power lead abnormal: check the motor power connections — and on machines with spindle switching or output (winding) switching, check that the switching magnetic contactor is actually ON: a dropped contactor leaves the motor disconnected while the drive pushes into an open circuit. (Contactor faults on switching machines have their own alarm too — see AL-15.)
- The amplifier itself — last suspect: output stage or control fault; bench repair or exchange.
Diagnosis checklist (in order)
- Note the spindle's state at the trip: cutting / stopped / crawling / dead.
- Cutting → fresh tooling, review conditions via the load meter.
- Stopped → watch lock output vs rotation command on the PMC screen; check the lock mechanism and its state switch.
- Crawling → verify sensor parameters → U/V/W phase order → A/B feedback pairs → hand-rotation speed test.
- Dead → power lead continuity and switching contactor state → then amplifier bench test.
Related guides
- Fanuc spindle alarm 22 (overload / time rating)
- Fanuc spindle alarm 31 (motor lock / speed detection)
- Fanuc spindle alarms 15–20 (switching sequence & board faults)
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained