G-Code Restart, Mid-Program Start & Safe Block Skip Techniques

In CNC production, stopping a program midway and restarting from a specific point is common — after tool breakage, inspection, or a setup adjustment.

This guide explains safe ways to restart, use block skip (/), and resume programs without crashing or scrapping parts.

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📌 1. Why Mid-Program Restart Matters

• Avoid re-machining already finished areas.
• Save cycle time after tool changes or power loss.
• Reduce risk of tool gouging due to modal state mismatch.
• Essential for lights-out production recovery.

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📌 2. Key Modal States to Consider Before Restart

Before resuming, ensure:

• Work offset (G54–G59) is active.
• Tool length (G43 Hxx) is applied.
• Spindle is running at correct speed (M03/M04).
• Coolant is ON (M08 if needed).
• Correct plane is active (G17/G18/G19).
• Correct feedrate mode (G94/G95).

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📌 3. Fanuc Block Restart Procedure

1. Press RESET to clear alarm.
2. Select BLOCK RESTART on control.
3. Scroll to desired restart block.
4. Press CYCLE START — control re-reads modal states.

Example Program:

G17 G21 G40 G49 G80 G90
T05 M06
G00 G90 G54 X0 Y0
G43 H05 Z100.
S2500 M03
M08
/ G65 P9001   (BLOCK SKIPPED IF / ENABLED)
G01 Z-10. F200

Tip: Always include a safe start line before restart point.

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📌 4. Haas “Run From Here” Feature

• Press MEMORY → RECOVER → RUN FROM HERE.
• Haas prompts for tool, spindle, coolant state.
• Operator confirms → machine safely rapids to position.

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📌 5. Siemens Sinumerik Restart

• Use RESTART PROGRAM or Start from Block function.
• System restores active work offsets, spindle speed, feed, and TRAORI state.
• Always jog clear before resuming if last position was near stock.

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📌 6. Heidenhain Program Restart

• Select PROGRAM RESTART from menu.
• Choose block number visually.
• Control auto-restores modal conditions including PLANE and TCPM.

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📌 7. Using Block Skip (/) for Conditional Execution

Block skip allows you to selectively enable/disable lines without editing program.

/ M00 (OPTIONAL STOP FOR QC)
/ G65 P9002 (OPTIONAL PROBE MACRO)

Enable block skip switch to bypass those lines.

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📌 8. Safe Restart Tips

• Add Safe Start Lines before every operation:

G17 G90 G40 G49 G80

• Retract Z to a safe plane before restart.
• Re-probe or verify offsets if part has been removed.
• For tapping or drilling cycles, restart from retract plane to avoid double-cut.

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📌 9. Advanced Techniques

• Use macros to track last completed operation and jump automatically:

IF[#500EQ1]GOTO200 (RESUME FROM OP2)

• Log restart point using DPRINT or variable write for traceability.

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📌 10. Future of Program Restart (2025–2030)

• AI-based restart assistants suggest safest block automatically.
• Digital twin simulation verifies restart before running live.
• Cloud-logged machine states allow exact restoration after power loss.

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✅ Conclusion

Mid-program restart and block skip techniques are critical for efficient production.

By combining safe start lines, block restart functions, and careful modal state control, you can resume programs confidently and safely — protecting parts, tools, and your machine.