M03 starts the spindle turning clockwise at the speed set by the S word. Clockwise is the normal cutting direction for standard right-hand tooling. M04 runs it counterclockwise.
Format
How it works
- Set the speed with S, then start rotation with M03 (or M04 for counterclockwise).
- Let the spindle reach speed before feeding into the cut.
- M05 stops the spindle.
Example
FAQ
What’s the difference between M03 and M04? M03 starts the spindle rotating clockwise, as viewed from the spindle looking at the workpiece, while M04 starts it counterclockwise. Most right-hand cutting tools require M03; M04 is used for left-hand tooling or certain tapping and threading operations.
What happens if I command a feed move before the spindle reaches full speed? On most controls, the program simply proceeds without waiting for the spindle to reach commanded RPM, which can start a cut before the tool is up to speed. A dwell after M03 is common practice on larger spindles to avoid this.
Related: M05 Spindle Stop and the M-Code Reference.