M04

For CNC machines equipped with a remote activated spindle, the M04 M-Command will activate the spindle in the counter clock-wise direction, also known as Spindle Reverse. For CNC machines with a pulse width modulated (PWM) spindle, an additional parameter will set the speed, typically calculated in RPM.

It is very important to issue a spindle stop command M05 prior to activating the spindle reverse code. An appropriate G04 dwell command should be used to allow a previously running spindle enough time to slow down and come to a stop. Likewise it is important to issue a dwell command after the spindle has been turned on, to ensure it has enough time to get up to full speed.

Standard Format:
M04 S00000

The S parameter represents the desired speed.

Code Examples

In this example, the spindle will be turned on clockwise, run for 10 seconds and then turn off with command M05. After a 5 second wait, we will activate the spindle reverse run for 5 seconds and then come to a stop.

M03
G04 P10.000
M05
G04 P5.000
M04
G04 P5
M05

For spindles with a PWM speed control, this example will turn the spindle on and set the speed to 12000 rpm. A G04 dwell command is added to ensure it gets up to speed.

M04 S12000
G04 P5.000