FANUC codes
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FANUC Controller

Program/G-code · Intermediate · 30-60 minutes

Alarm 455

Fanuc Alarm 455 - ILLEGAL COMMAND IN GRINDING

Fanuc alarm 455 occurs exclusively during grinding canned cycle execution (G7501-G7509) when the directional signs of infeed commands I, J, and K are inconsistent with each other, or when the grinding axis total infeed amount is zero or not specified. This alarm protects against invalid grinding cycle geometry that would result in improper tool motion or potential collision.

FANUCProgram/G-codeIntermediate30-60 minutes

455

Fanuc Alarm 455 - ILLEGAL COMMAND IN GRINDING

Servo Alarm - Axis 7 Serial Data Error

Serial data communication error on Axis 7. The CNC cannot establish or maintain serial data communication with the servo amplifier or encoder on the 7th axis.

Root Cause Summary

Fanuc alarm 455 occurs exclusively during grinding canned cycle execution (G7501-G7509) when the directional signs of infeed commands I, J, and K are inconsistent with each other, or when the grinding axis total infeed amount is zero or not specified. This alarm protects against invalid grinding cycle geometry that would result in improper tool motion or potential collision.

Safety

  • Communication lost
  • Disconnect power to the CNC machine before inspecting or replacing any cables or components. Lockout/Tagout procedures should be followed.
  • Be aware of potential electrical hazards when working with electrical equipment. Use proper safety precautions and personal protective equipment (PPE).
  • Ensure the CNC machine is properly grounded to prevent electrical shock.
  • Refer to the CNC machine and servo amplifier manufacturer's documentation for specific safety instructions.
  • Be cautious of moving parts when the CNC machine is powered on. Keep hands and clothing away from moving parts.
  • Never attempt to repair or modify the CNC control or servo amplifier without proper training and authorization.
  • Risk of electrical shock: Always power down the equipment before inspecting or handling cables.
  • Communication loss may lead to unexpected machine behavior: Proceed with caution and isolate the axis if possible.

Causes and Fixes

  1. 1

    Review the grinding cycle program block that triggered the alarm. Identify which G75XX cycle is being used and verify all I, J, K values have consistent signs (all positive or all negative).

  2. 2

    Check grinding wheel position relative to workpiece. If grinding wheel approaches from positive direction, all infeed values (I, J, K) must be negative. If approaching from negative direction, all must be positive.

  3. 3

    Correct the program by changing signs: I__ (roughing stock per pass), J__ (finish allowance), K__ (number of sparkout passes or dwell). Ensure algebraic sum I+J provides correct total depth.

  4. 4

    Verify parameter 5301 (grinding cycle specification) matches your machine configuration. Check SYSTEM > PARAM > 5301 to confirm grinding axis assignment is correct.

DIY Feasiblemedium confidence

Call a technician if:

  • ·Servo amplifier replacement required
  • ·CNC main board suspected
  • ·Multiple axes affected
  • ·Safety systems compromised

Prevention

  • Regular FSSB cable inspection
  • Proper cable routing away from power lines
  • Periodic backup of servo parameters
  • Environmental control to prevent moisture/contamination

Common Mistakes

  • Ignoring loose cable connections
  • Not checking FSSB parameter consistency
  • Swapping amplifiers without parameter backup
  • Working on system without proper lockout procedures

Related Alarms

400401410450456

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Always verify with your machine manual or a certified technician before performing service procedures.