Fanuc spindle alarm 36 means the spindle's error counter overflowed — in a position-control mode (rigid tapping, Cs contour control, spindle synchronization, orientation) the gap between commanded and actual spindle position grew beyond what the counter can hold. It is the spindle's cousin of the servo excess-error alarm (SV0410): the commanded position ran away from reality. Fanuc gives two cause families — parameters and sequence — and both are checkable without opening anything.
Cause 1 — Parameter settings
(a) Gear ratio set too large
The spindle-to-motor gear ratio parameters tell the drive how motor rotation maps to spindle rotation. An excessively large (or simply wrong) ratio makes every commanded spindle degree demand impossible motor motion — the error counter fills in moments. Check the gear ratio set:
- FS16i / FS0i-B/C and FS30i / FS0i-D: parameters 4056–4059 (FS15i: 3056–3059) — gear ratio between spindle and motor, one per gear stage.
- Verify against the machine's actual mechanical ratio (count the pulleys/gears or consult the builder's sheet) — after a belt/pulley change or a parameter restore from a different machine variant, these are prime suspects.
(b) Position gain set too low
If the gear ratio is genuinely correct, Fanuc's next instruction is to increase the position gain — too low a gain lets position error accumulate faster than the loop corrects it. The gains live per mode:
- 4060–4063 (15i: 3060–3063) — position gain at orientation
- 4065–4068 (15i: 3065–3068) — position gain in servo mode / spindle synchronization
- 4069–4072 (15i: 3069–3072) — position gain in Cs contour control
Note which mode was active when AL-36 tripped and adjust that mode's gain set — raising Cs gains will not fix a rigid-tap overflow. Change conservatively (steps of 10–20%), against the machine's documented values, with PWE handled per our write-protection guide.
Cause 2 — Sequence error: motor deactivated in a position mode
The subtle one, straight from Fanuc: check whether the ladder turns off SFR/SRV (the spindle forward/reverse run commands) while a position-control mode is still active — rigid tapping, Cs contour, or spindle synchronization. Dropping the run signal deactivates the motor while the CNC is still commanding position — the commanded position marches on, the spindle stands still, and the error counter overflows almost instantly.
- Typical fingerprints: AL-36 always at the same point in the program (end of a tap cycle, mode transitions), or after ladder modifications / retrofit work.
- Watch SFR/SRV and the position-mode signals together on the PMC diagnosis screen through the failing transition — the run signal must stay up until the mode is properly exited.
- Fix is in the sequence timing, not in gains — raising gains to mask a sequence fault just makes the failure more violent.
Diagnosis checklist (in order)
- Which mode was active, and where in the cycle did it trip — mid-motion or at a transition?
- Mid-motion → verify gear ratios 4056–4059 against the real mechanics.
- Ratios correct → raise the active mode's position gain set (4060–4072 family) conservatively.
- At transitions / after ladder work → watch SFR/SRV vs position-mode signals on the PMC screen; fix the sequence timing.
- After any fix: air-test rigid tapping / orientation before cutting — error-counter faults break taps first.
Related guides
- Fanuc SV0410 (servo excess error — the axis-side cousin)
- Fanuc spindle alarm 34 (parameter out of range)
- Fanuc spindle alarm 27 (position coder disconnected)
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained