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M3 means “start the spindle at a specific speed”.

A spindle is a controlled motor that turns a tool ( endmill ) at a given speed to allow it to remove material from the workpiece.

The M3 command must be accompanied by a s parameter which sets the speed of rotation.

M3's evil twin is the [M5] command which turns the spindle off ( it is equivalent to m3-s0 ).


The command is used as such :

code M3 S1000

Which means : start the spindle and make it turn at 1000 rotations per minute.


~ Parameter ~ Usage ~ Example
s The spindle must turn at this speed in rotations per minute M3 S1000


The spindle functionality of Smoothie is configured via the [/spindle-module Spindle] module

Further reading

These resources are used as references for Gcode :