Mastering CNC Control Codes: M-Codes & G-Codes Explained

In order to completely know how CNC machine work, there are some functional codes you need to know and memorize.  These codes include the M-code and the G-code

M-codes are miscellaneous machine commands that do not command axis motion. The format for an M-code is the letter M followed by two to three digits; for example:

• [M02 End of Program]
• [M03 Start Spindle – Clockwise]
• [M04 Start Spindle – Counter Clockwise]
• [M05 Stop Spindle]
• [M06 Tool Change]
• [M07 Coolant on mist coolant]
• [M08 Flood coolant on]
• [M09 Coolant off]
• [M10 Chuck open]
• [M11 Chuck close]
• [M13 BOTH M03&M08 Spindle clockwise rotation & flood coolant]
• [M14 BOTH M04&M08 Spindle counter clockwise rotation & flood coolant]
• [M16 Special tool call]
• [M19 Spindle orientate]
• [M29 DNC mode]
• [M30 Program reset & rewind]
• [M38 Door open]
• [M39 Door close]
• [M40 Spindle gear at middle]
• [M41 Low gear select]
• [M42 High gear select]
• [M53 Retract Spindle] (raises tool spindle above current position to allow operator to do whatever they would need to do)
• [M68 Hydraulic chuck close]
• [M69 Hydraulic chuck open]
• [M78 Tailstock advancing]
• [M79 Tailstock reversing]

Read: Everything you need to know about CNC machine

G-cold are used to command specific movements of the machine, such as machine moves or drilling functions. The format for a G-code is the letter G followed by two to three digits; for example, G01. G-codes differ slightly between a mill and lathe application, for example:

• [G00 Rapid Motion Positioning]
• [G01 Linear Interpolation Motion]
• [G02 Circular Interpolation Motion-Clockwise]
• [G03 Circular Interpolation Motion-Counter Clockwise]
• [G04 Dwell (Group 00) Mill]
• [G10 Set offsets (Group 00) Mill]
• [G12 Circular Pocketing-Clockwise]
• [G13 Circular Pocketing-Counter Clockwise]

Codes used in CNC programming