CNC Dwell & Timing Control: G04 Explained with Real Drilling, Tapping & Threading Examples
In CNC machining, G04 (Dwell) temporarily pauses machine motion for a specified amount of time.
It’s used to allow coolant penetration, spindle stabilization, chip evacuation, or synchronization between machine operations.
📌 1. What Is G04 (Dwell)?
G04 tells the CNC to stop motion for a programmed duration — usually in seconds or milliseconds depending on the control.
Basic Format:
G04 P(seconds)or (on some controls):
G04 X(seconds)📌 2. G04 Fanuc Example — Simple Dwell
G04 P2000Waits 2 seconds (P2000 = 2000 milliseconds).
📌 3. Haas Example — Seconds Mode
G04 P2.0Waits 2.0 seconds — Haas uses P in seconds, not milliseconds.
📌 4. Typical Use Cases for G04
| Use Case | Purpose |
|---|---|
| Drilling | Allow chips to evacuate |
| Tapping | Stabilize spindle speed |
| Threading | Ensure synchronized start |
| Coolant | Allow flow before cut |
| Probing | Stabilize measurement signal |
📌 5. Example: Drilling with Dwell
%
O7001 (G04 DRILL DWELL)
G90 G17 G21 G40 G80 G54
T05 M06
S1500 M03
G00 X50. Y50. Z5.
G81 X50. Y50. Z-20. R2. F200
G04 P1.5
G80
M30
%| Code | Description |
|---|---|
| G04 P1.5 | Wait 1.5 seconds after each hole |
| G81 | Drilling cycle |
| R2. | Retract plane 2 mm above surface |
Useful when drilling deep holes — gives coolant time to flush chips before retract.
📌 6. Example: Tapping with G04 Pause
%
O7002 (TAPPING WITH DWELL)
G90 G17 G21 G40 G80 G54
T06 M06
S500 M03
M29 S500
G00 X0 Y0 Z5
G84 Z-15. R2. F1.25
G04 P0.5
G80
M30
%Adds a short pause after tapping cycle — improves thread quality and spindle synchronization.
📌 7. Example: Threading Dwell (Lathe G76 + G04)
%
O7003 (THREAD DWELL EXAMPLE)
G97 S600 M03
T0101
G00 X30. Z2.
G76 P020060 Q100 R0.05
G76 X20. Z-30. P1024 Q200 F1.5
G04 P1.0
M30
%1-second dwell at the end of threading allows tool retract before next cycle start.
📌 8. Siemens Example
G04 F2.0Siemens uses F or P for dwell — both represent seconds.
📌 9. Heidenhain Example
CYCL DEF 32 DWELL TIME
Q210=2.0 ; DWELL FOR 2 SECONDSQ210 defines dwell time in seconds.
📌 10. G04 in Combined Operations
You can insert dwell between any motions to control timing:
G01 Z-10. F100
G04 P0.5
G01 Z-20.
G04 P0.25Short dwells improve coolant flow and chip evacuation during roughing.
📌 11. CNC Mill Example — Chip Break Drilling with G04
%
O7004 (CHIP BREAK DRILLING)
G90 G17 G21 G40 G80 G54
T05 M06
S1200 M03
G00 X25. Y25. Z5.
G01 Z-5. F150
G04 P0.25
G01 Z-10.
G04 P0.25
G01 Z-15.
G04 P0.25
G01 Z-20.
G00 Z100.
M30
%Uses multiple short dwell pauses to break long chips in deep hole drilling.
📌 12. Best Practices
- Always specify G04 dwell time clearly (milliseconds vs seconds).
- Avoid excessive dwell — can cause tool wear or heat buildup.
- Combine with M08 (coolant on) for better chip evacuation.
- Keep spindle running during dwell if coolant flow is required.
- Test short dwell times (0.2–0.5s) first before longer pauses.
📌 13. Common Mistakes
| Mistake | Result |
|---|---|
| Missing dwell unit (ms/sec confusion) | 10× longer pause |
| Too long dwell | Tool burns or chatter |
| No G04 before probing | Inaccurate measurement |
| Dwell during motion | Alarm or error |
| Using G04 after spindle stop | Unnecessary cycle delay |
📌 14. Advanced Application: Synchronizing CNC Robots or Automation
In automated CNC cells, G04 is used to synchronize robot handoffs and safety timing.
M09
M05
G04 P3.0 (WAIT FOR ROBOT PART UNLOAD)
M60 (ROBOT SIGNAL)Pauses 3 seconds for robot handshake before sending M60 “ready” signal.
📌 15. Future Trends (2025–2030)
- Adaptive dwell control: CNC dynamically adjusts pause based on spindle torque.
- AI-driven cycle timing: Smart dwell calculation from coolant pressure and chip load.
- Integrated I/O timing: G04 synchronizes directly with PLC automation signals.
✅ Conclusion
G04 dwell is more than just a pause — it’s a precise timing control tool.
Used correctly, it improves surface finish, chip removal, synchronization, and process stability in drilling, tapping, and automated machining cycles.
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