What causes FANUC alarm 764?

Mechanical binding or obstruction in spindle 2 drive train or bearings. Excessive cutting forces from aggressive feed rates or depth of cut in the part program. Worn or damaged spindle bearings causing increased rotational resistance. Spindle drive belt slipping or broken causing erratic torque feedback. Incorrect spindle load parameters or torque limit settings in the drive amplifier.

How do I fix FANUC alarm 764?

1. Stop the machine and manually rotate spindle 2 by hand to check for rough spots, binding, or unusual resistance that would indicate a mechanical issue. 2. Review the part program for aggressive cutting conditions such as high feed rates, excessive depth of cut, or improper tooling that could cause spindle overload. 3. Check the spindle drive amplifier parameters for spindle 2 torque limit settings and compare against the machine builder specifications to ensure they are correct. 4. Inspect the spindle belt or coupling for wear, damage, or slippage and replace if necessary before running the spindle again. 5. Run spindle 2 at low RPM with no load and monitor the spindle load meter on the CNC screen to see if abnormal torque is present even without cutting. 6. If mechanical and program causes are ruled out, check spindle motor feedback cables and encoder connections for damage or loose connections that could cause false torque readings.

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FANUC Controller

Spindle · Intermediate · 30-90 minutes depending on root cause

Alarm 764

Fanuc Alarm 764 - SPINDLE-2 ABNORMAL TORQUE ALARM

Fanuc Alarm 764 indicates the spindle amplifier has detected torque exceeding the configured limit on the second spindle (SP2). This protection feature monitors spindle load via parameter settings and triggers when actual torque exceeds the threshold defined in parameters 4260-4265, typically due to mechanical binding, excessive cutting load, or amplifier/motor issues.

FANUCSpindleIntermediate30-90 minutes depending on root cause

764

Fanuc Alarm 764 - SPINDLE-2 ABNORMAL TORQUE ALARM

SPINDLE ALARM 764

Root Cause Summary

Fanuc Alarm 764 indicates the spindle amplifier has detected torque exceeding the configured limit on the second spindle (SP2). This protection feature monitors spindle load via parameter settings and triggers when actual torque exceeds the threshold defined in parameters 4260-4265, typically due to mechanical binding, excessive cutting load, or amplifier/motor issues.

Causes and Fixes

1
Navigate to DIAGNOSIS > SPINDLE screen (PMC or Spindle tab depending on control series). Monitor current load percentage for SP2 while manually jogging spindle at low RPM (M43 or direct MDI command). Normal load should be under 20% with no tool/workpiece.
2
Manually rotate spindle 2 by hand with E-stop pressed and spindle motor power OFF. Check for grinding, tight spots, or complete seizure. Inspect drawbar mechanism, tool holder interface, and collet closer for debris or damage.
Lock out main power and verify motor is de-energized before manual rotation
3
Remove tool holder and workpiece from SP2. Clear alarm and test spindle with M code command (M43 S500 for SP2 at 500 RPM). If alarm clears without load, inspect bearings, preload adjustment, and lubrication system. Check grease levels and automatic lubrication operation if equipped.
4
Check spindle orientation (C-axis) encoder feedback if equipped. Navigate to DIAGNOSIS > PARAMETER and verify SP2 position encoder signals are stable. Misaligned or failing encoder can cause orientation hunting and excessive torque during positioning.

DIY Feasiblemedium confidence

Call a technician if:

·Spindle bearing replacement required
·Amplifier module failure confirmed
·Parameter backup/restore needed
·Encoder replacement required

Prevention

Monitor spindle load regularly through servo diagnostics
Maintain proper spindle lubrication schedule
Use appropriate cutting parameters for material and tooling
Perform regular spindle runout checks

Common Mistakes

Ignoring gradual increase in spindle load over time
Setting torque limits too low for heavy cutting applications
Failing to verify tool condition before troubleshooting mechanical issues
Adjusting parameters without understanding spindle specifications

Related Alarms

AL-700 AL-701 AL-765 AL-766

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