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Common VFD, drive, UPS, and cabinet overheating failure point.
Fanuc Alarm 436 — What It Means
Fanuc Alarm 436 indicates a servo following error on the Z-axis — the actual Z-axis position lagged behind the commanded position by more than the allowable error tolerance. The Z-axis carries the spindle on most vertical machining centers, making this alarm particularly impactful: any Z-axis fault stops all cutting. Alarm 436 is the Z-axis equivalent of 414 (X) and 435 (Y).
Common Causes
- Z-axis counterbalance or weight issue — On VMCs, the Z-axis carries the spindle head. A failed counterbalance cylinder or compressed air system means the servo fights gravity constantly, causing following error under rapid moves.
- Z-axis servo amplifier degraded — Reduced drive torque output from a degraded amplifier can’t keep up with commanded Z moves under load.
- Ballscrew wear or contamination — A worn Z-axis ballscrew creates variable resistance through the stroke, causing following error at specific positions.
- Encoder feedback fault — An intermittent Z-axis encoder signal causes sudden position error jumps that trigger Alarm 436.
Step-by-Step Fix
- Check counterbalance pressure — On VMCs with pneumatic counterbalance, verify air pressure at the counterbalance cylinder. Low pressure forces the servo to carry full spindle head weight. Correct air pressure per machine specification.
- Test Z-axis servo amplifier — Check the amplifier display for its own fault indicators. Test DC bus voltage under load — sagging bus voltage reduces torque output.
- Inspect Z-axis ballscrew — Move Z to multiple positions and check for binding or rough spots. Clean and re-lubricate. Check ballscrew backlash compensation parameters.
- Check encoder cable — Inspect from motor to amplifier for damage. Substitute a known-good cable if you suspect intermittent signal loss.
- Reset and test with slow feed — Press RESET and jog Z slowly through full travel. If 436 appears only at speed, the torque or following error tolerance needs adjustment.
Parts Often Needed
| Part | Notes |
|---|---|
| Counterbalance cylinder / seals | If air pressure drops due to seal wear |
| Z-axis encoder cable | Most common cause of intermittent 436 |
| Z-axis servo motor | If motor winding test shows fault |
Technician Tips
CNC alarms should always be diagnosed by reading the full alarm text, not just the number. Modern Fanuc, Haas, and Mazak controls provide detailed alarm descriptions — press the help key while viewing the alarm for diagnostic suggestions. The alarm history screen stores the last 50-100 alarms with timestamps; review this before clearing to identify patterns. A servo alarm (SV series on Fanuc) that appears only during rapid traverse points to a different cause than one that appears during cutting.
Prevention: Back up your CNC parameters monthly. Battery-backed memory faults are much easier to recover when you have a current parameter, ladder, offset, and macro backup. Replace control batteries on a planned maintenance schedule before voltage drops far enough to risk data loss.
Need Replacement Parts?
Before ordering, match the machine-control part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Z-axis mechanical work on VMCs (ballscrew, guideway, counterbalance) requires precision re-leveling and accuracy verification. Fanuc-trained field service is recommended for any Z-axis mechanical repair.