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G4 means “pause for a given duration of time”.

Format

The command is used as such :

G4 S5

Which means : pause for 5 seconds.

This is useful for example to wait for spindles to ramp up to speed, or to wait for small layers to cool down on 3D printers.

Parameters

~ Parameter ~ Usage ~ Example
Shift Duration to wait in seconds G4 S10
P Duration to wait in milliseconds ( thousandth of a second ) G4 P100

Note that if grbl_mode is set to true then the P parameter is the duration to wait in seconds, not milliseconds, as a float value. This is to conform to G-Code standards.

Further reading

These resources are used as references for Gcode :