Okuma Alarm A-8502 – Unable to Execute G21 Command

Okuma Alarm A-8502 indicates that the G21 command for axis movement to the tool change position cannot be executed because the required conditions are not satisfied. This command is also used during ATC macro operations such as G171 and M421.

Meaning of the Alarm

This alarm occurs when the control system detects that the G21 command is issued without meeting the necessary machine conditions. As a result, the axis cannot move to the tool change position.

Possible Causes

  • Machine not in the correct state for tool change

  • G21 command executed at the wrong time

  • Conditions for ATC macro (G171, M421) not fulfilled

  • Incorrect CNC program sequence

  • Safety or interlock conditions not satisfied

Recommended Checks

  • Verify machine status before executing G21

  • Ensure all tool change conditions are met

  • Review CNC program sequence

  • Check ATC macro commands (G171, M421)

  • Confirm that safety interlocks are properly engaged

When Professional Service Is Required

If the alarm persists after verifying machine conditions and program logic, the issue may be related to the automatic tool changer system or control configuration. In such cases, professional diagnostics are recommended.

Related Solutions

  • CNC diagnostics and troubleshooting

  • ATC system inspection and repair

  • Program sequence correction

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