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FANUC Controller
Spindle · Intermediate · 30-60 minutes
Fanuc Alarm 784 - SPINDLE-4 ABNORMAL TORQUE ALARM
Fanuc Alarm 784 indicates abnormal torque was detected on spindle 4, triggered when the spindle load monitoring function detects excessive torque deviation from commanded values. This typically occurs due to mechanical binding, incorrect load monitoring parameters (particularly parameters 4300-4399 series), or actual spindle amplifier feedback issues on the fourth spindle axis.
784
Fanuc Alarm 784 - SPINDLE-4 ABNORMAL TORQUE ALARM
SYSTEM ALARM 784
Fanuc spindle alarm 784: SYSTEM ALARM 784. A fault has been detected in the spindle system. Check the spindle amplifier for fault codes and the Fanuc alarm list for the specific SP alarm sub-code.
Root Cause Summary
Fanuc Alarm 784 indicates abnormal torque was detected on spindle 4, triggered when the spindle load monitoring function detects excessive torque deviation from commanded values. This typically occurs due to mechanical binding, incorrect load monitoring parameters (particularly parameters 4300-4399 series), or actual spindle amplifier feedback issues on the fourth spindle axis.
Causes and Fixes
- 1
Navigate to SYSTEM > PARAM and check parameter 4320#0 for spindle 4. Verify if spindle load detection is enabled (bit=1). Check parameter 4084 to confirm spindle 4 axis number assignment.
- 2
Check parameter 4324 (spindle load alarm time) and parameter 4326 (spindle load alarm level percentage). Typical values are 4324=500-2000ms and 4326=120-150%. If values are too aggressive, increase incrementally.
Record original parameter values before making changes. Parameter write enable (3202#0=1) must be active.
- 3
Navigate to DIAGNOSIS screen > spindle page and monitor diagnosis number 448-451 for spindle 4 load meter (actual torque %) during normal operation. Compare peak values against parameter 4326 setting.
- 4
If diagnosis shows load spikes near or exceeding parameter 4326 threshold during normal operation, increase parameter 4326 by 10-20% or increase parameter 4324 time delay to prevent nuisance alarms.
Do not disable load monitoring completely without investigating root mechanical cause first.
Call a technician if:
- ·Spindle bearing replacement required
- ·Amplifier hardware failure confirmed
- ·Encoder replacement needed
- ·Electrical power supply issues
Prevention
- Regular spindle load monitoring
- Proper cutting parameter selection
- Scheduled spindle bearing maintenance
- Tool condition monitoring
- Coolant system maintenance
Common Mistakes
- Ignoring gradual spindle load increases
- Setting torque monitoring parameters too high
- Operating with worn tooling
- Inadequate spindle warm-up procedures
- Neglecting coolant system maintenance
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