G-code: The Standard CNC Programming Language

G-code provides a standardized, human-readable (to a degree) méthode for creating a set of instructions that a CNC machine controller can interpret and execute. Each line, or ‘block’, of a G-code program typically contains one or more commands that tell the machine what to do next. The structure is based on a word-address format, where a letter (the ‘address’) is followed by a numerical value. For example, the block ‘G01 X10.0 Y5.0 F150’ instructs the controller to perform a linear feed move (G01) to the coordinate position X=10.0, Y=5.0 at a feed rate (F) of 150 units per minute.

The ‘G’ commands are the most crucial, defining the type of motion. G00 is a rapid positioning move, used for non-cutting travel. G01 is a controlled linear feed for cutting straight lines. G02 and G03 command clockwise and counter-clockwise circular/arc movements, respectively. Other G-codes handle tasks like setting coordinate systems (G54-G59), selecting units (G20/G21 for inches/mm), and activating cutter compensation (G41/G42). ‘M’ codes, or miscellaneous functions, control non-geometric actions like starting or stopping the spindle (M03/M05), turning coolant on or off (M08/M09), and initiating tool changes (M06). While RS-274 provides a standard, most machine tool manufacturers have implemented their own specific dialects or extensions of G-code, requiring post-processors in CAM logiciel to translate a generic toolpath into the specific format required by a particular machine controller.