What causes FANUC alarm 055?

CHF or CNR command written without a value (e.g. CHF alone instead of CHF1.0). Zero value programmed for the CHF/CNR command. Address word missing from the chamfer or corner rounding block. Post-processor output omitted the chamfer value.

How do I fix FANUC alarm 055?

1. Locate the CHF or CNR command block where the alarm triggered. 2. Verify the chamfer value is specified (e.g., CHF2.0 for a 2mm chamfer). 3. Add the required distance or radius value to the command. 4. Check post-processor settings if the program was CAM-generated.

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FANUC Controller

Program/G-code · Basic · 5-15 minutes

Alarm 055

Fanuc Alarm 055 - MISSING MOVE VALUE IN CHF/CNR

Fanuc Alarm 055 indicates the tailstock is not properly positioned or the system cannot verify its position before executing a machining operation. This alarm occurs when the PMC ladder logic detects a mismatch between the commanded tailstock position and the actual position feedback from limit switches or proximity sensors, or when position confirmation signals fail to activate within the programmed time window.

FANUCProgram/G-codeBasic5-15 minutes

055

Fanuc Alarm 055 - MISSING MOVE VALUE IN CHF/CNR

MISSING MOVE VALUE IN CHF/CNR

Root Cause Summary

Fanuc Alarm 055 indicates the tailstock is not properly positioned or the system cannot verify its position before executing a machining operation. This alarm occurs when the PMC ladder logic detects a mismatch between the commanded tailstock position and the actual position feedback from limit switches or proximity sensors, or when position confirmation signals fail to activate within the programmed time window.

Safety

Operation blocked for safety

Causes and Fixes

1
Navigate to PMC DIAGNOSIS screen (SYSTEM > PMC > PMCDGN) and identify the tailstock position input signals (typically G addresses like G0.0-G0.7 or G1.0-G1.7). Verify which signals should be ON for forward/retract positions.
2
Manually move tailstock to forward position using MPG or manual mode. Observe the corresponding input signal on PMC DIAGNOSIS screen. Signal should change from OFF to ON. Repeat for retract position.
3
If signal does not change, physically inspect limit switches or proximity sensors at tailstock assembly. Check for proper target positioning (1-2mm gap for proximity sensors), contamination (chips, coolant), damaged wiring, and secure connector seating at sensor and I/O terminal block.
Ensure machine is in emergency stop before inspecting mechanical components.
4
Using multimeter, measure continuity at the limit switch terminals or proximity sensor output (typically 24VDC NPN/PNP). Replace faulty sensors and re-verify signal response on PMC DIAGNOSIS screen.
Disconnect power to I/O circuits before performing continuity tests to prevent damage to PMC input modules.

DIY Feasiblehigh confidence

Call a technician if:

·Parameter corruption suspected
·Repeated alarms after program corrections
·Machine geometry calculation errors persist

Prevention

Always verify chamfer and radius values against part geometry before programming
Use program simulation to catch geometric conflicts early
Establish programming standards for minimum segment lengths relative to chamfer/radius values

Common Mistakes

Copying chamfer values between different sized features without scaling
Ignoring the relationship between corner angle and maximum radius
Not accounting for tool nose radius in chamfer calculations

Related Alarms

010 020 056

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