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In Siemens HMI, navigate to Program > Block %2 and review CYCLE79 call parameters, specifically the RTP (safety clearance plane) value. Compare against actual workpiece Z-height and tool length offsets.

Document the exact RTP value that triggered the alarm

Check MD24090 (MAX_AXIS_SPEED_INCH/MM) and MD24080 (MAX_AXIS_ACCEL) to confirm rapid traverse envelope is properly configured. Verify tool offset table (Tool Offset Memory) via NCK > Offsets menu for correctness of tool length compensation (TL value).

Increase RTP parameter in CYCLE79 call by minimum 5-10mm above current workpiece surface. Re-enter program and verify alarm clears. If alarm persists, proceed to Cause Block 2.

Do not reduce RTP below machine geometry minimums defined in machine data

Confirm CYCLE79 syntax compliance: RTP must be absolute coordinate value (not incremental). Verify using Program > Edit > Syntax Check in HMI.

Access NCK Parameters via Diagnostics > Parameter > Machine Data. Navigate to MD20050 (axis software limits) and MD20070 (soft limits) for the affected axis. Document current boundary values and compare against actual machine travel limits and workpiece fixture envelope.

Request machine installation documentation to verify correct MD values for your specific machine model

In Program > Offset > Geometry, verify Tool Offset Table entries match physical tool lengths. Confirm Workpiece Offset (TRANS) coordinates reflect actual fixture position relative to machine zero. Use Diagnostics > Actual Position to validate current axis position.

If MD values are correct, recalculate CYCLE79 RTP using formula: RTP = Fixture_Top_Z + Tool_Length + 10mm (minimum safety margin). Update program and test.

Consult machine builder OEM specifications for minimum safe clearance distance on your model

If alarm persists after MD verification, check NC > DPL > $MCErr for detailed servo axis error code. Contact Siemens field support with error code and MD20050/20070 values.

In Diagnostics > Trace (or Siemens SCOUT if available), enable servo axis monitoring and run single-block test of CYCLE79. Observe actual Z-axis deceleration distance during rapid retract. Compare against safety clearance value in alarm message.

Use single-block mode to safely execute diagnostic test without full machining cycle

Verify MD24090 (max rapid speed) is set to machine-rated specification (typically 10-25 m/min for vertical mills). Check MD24080 (max acceleration) against servo drive nameplate rating. If values appear conservative, consult machine manual for axis performance specification.

If kinematic limits are correct, modify CYCLE79 to include explicit SBLK (single-block) call during retract phase, or insert intermediate clearance plane stop (G01 move) before rapid. This reduces required deceleration distance.

Adding intermediate moves increases cycle time; only use if geometry cannot be modified