In CNC machining, precise timing control is just as important as accurate positioning. One essential command that helps achieve this control is the G04 Dwell command. Understanding how G04 works allows machinists and CNC programmers to improve accuracy, surface quality, and tool performance.
What Is the G04 Dwell Command?
The G04 Dwell command is a CNC instruction used to pause machine movement for a specified amount of time. During this dwell period, the machine holds its position without any axis movement.
This command is commonly used in:
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CNC milling
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CNC turning
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Drilling operations
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Automation sequences
The primary purpose of G04 dwell is to allow time for operations such as chip clearing, coolant flow stabilization, spindle settling, or precise depth finishing.
Basic G04 Syntax
or
Explanation:
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G04 → Activates the dwell command
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P → Time in milliseconds (commonly used)
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X → Time in seconds (machine-dependent)
Always check your CNC controller manual, as dwell units may vary between machines.
Example of G04 in a CNC Program
Explanation:
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The tool feeds down to Z-10.0
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G04 P3000 pauses the machine for 3 seconds
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The tool retracts after the dwell period
This technique is useful when drilling deep holes or ensuring clean bottom surfaces.
Why Use G04 Dwell in CNC Machining?
Using the G04 dwell command provides several benefits:
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Improves hole quality during drilling
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Allows spindle speed stabilization
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Enhances surface finish
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Reduces tool wear
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Supports precise automation timing
By applying dwell commands correctly, CNC programs become more reliable and repeatable.
Best Practices for Using G04
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Use the shortest dwell time necessary
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Avoid excessive dwell to prevent tool marks
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Test dwell values during program optimization
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Always verify controller-specific syntax
Strategic use of G04 dwell commands can significantly improve machining results.
Conclusion
The G04 Dwell command is a simple yet powerful CNC programming tool. By understanding its syntax and applications, machinists can enhance machining precision, improve part quality, and optimize CNC cycle performance. Mastering G04 is an important step toward professional-level CNC programming.
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