What is G-code, and how does it affect CNC machining processes? This plain-text computing language directs and guides CNC machines throughout the machining process, ensuring adhesion to design parameters.
Understanding G-code is no longer a prerequisite for machinists’ knowledge base. Today, CNC machines implement CMA and CAD software with all G or M codes ready-encoded for the CNC process.
However, some machinists or CNC enthusiasts may want to understand G code and how the commands control the device and cutting process. The layman won’t have any idea what they’re looking at when reviewing a G-code command list.
However, applying a reference key to the command review can assist with interpreting the command schedule and the machine’s programming for the CNC process. G-code is a standardized computing language for CNC machining, but variations exist between manufacturers regarding their use.
Different CNC manufacturers produce controllers operating off CAM or CAD software. The controller’s programming determines how the CNC machine determines the commands. CNC programs utilize commands combined with lettered instructions directing the operation of the CNC machine.
G-codes provide CNC machines with a set of instructions to perform lathe or milling functions. M-codes are commands with prefixes, including S for spindle speed and F for feed rate. G-codes are typically self-explanatory.
Programs define the start and end of the process using a percentage symbol. The program formatting features classification using the numbers O0001 to O9999.
The modal nature of G-codes means commands remain active until reset or canceled by a replacement command. The CNC tools mobilize according to the interpolation of changes in the Y & X coordinates throughout the CNC machining process.
CNC machining commands typically feature linear or circular interpolation, allowing CNC tools to simultaneously move along the X & Y axes.
Here are a few examples of G-code commands used in CNC machining processes.
G-Code List (Milling)
- G code Description
- G00 Rapid traverse
- G01 Linear interpolation
- G02 Circular interpolation CW
- G03 Circular interpolation CCW
G-Code List (Lathe)
- G code Description
- G00 Rapid traverse
- G01 Linear interpolation
- G02 Circular interpolation CW
- G03 Circular interpolation CCW
The Importance of Macros and Subprograms in Programming CNC Machines
M98 commands call up subprograms followed by numbers to indicate the repetitions of each subprogram. A M-code, M99, ends the execution of the subprogram. The M98 P53000 uses the letter P to indicate the program number O3000. The number 5 is the repetitions the subprogram repeats during the CNC machining process.
There are other versions of subprograms following the form of M98 P3000 L5. Like our prior example, using M98 indicates the subprogram, with the P3000 being the subprogram O3000 and L5 indicating the repetitions in the CNC process.
Subprograms feature in several CNC operations, such as indexing the CNC Z-axis between repetitions. In either situation, the M98 returns the CNC controller to its main program or prior subroutine if nested.
Another practical subcode program resets all modal statuses before or after tool changes. This procedure is a safety strategy followed on all SOPs.
The M97 subprogram will reference line numbers in the program. The line number represents the machine program line number. M97 codes don’t require independent programming, instructing the chosen line to repeat.
Like M98 subprograms, M97 codes end with M99. All CNC machines feature a set of conveniently preprogrammed functions to enhance the user experience. These onboard programs are also subprograms called up in the G-code commands.
Instructions for CNC machining describe the function of pre-existing codes. Macro programming presents a methodology of shortening codes, allowing for fast repetitions in the CNC process. Speeds, feeds, and material applications are all adjustable with macro programming.
Macro programming changes the parameter settings and coordinates data to adjust the G-codes. It enables the same program to cut parts in several sizes as they appear in the schematics. These variations receive independent addresses in the program.
For instance, G00 X#123 instructs the CNC machine to shift to the stored locations in the variable address 123. Operators should use macros carefully because changes create unexpected crashes, motions, and malfunctions.
Commanding the CNC machine to execute functions too fast may damage the machine, tools, or cutting piece. It’s required for CNC programmers to include checks in the programming to avoid these types of disasters.
Top-Rated G-code Simulators
Several organizations produce “G-code simulators.” Let’s unpack the characteristics, features, and abilities of these simulators and the OEMs.
G Code Viewer by 3D Printing Canada
The G Code Viewer by Printing Canada offers a web-based G-code simulator, allowing users to analyze and visualize G-code programming directly in their browser. It provides a 3D representation of toolpaths while supporting interactive model manipulation.
Users can pan, rotate, and zoom, allowing full inspection of the machining simulation. G Code Viewer provides basic analytic features, like G-code line highlighting, visualization, and cross-sectional viewing.
NC Viewer by Machinist Web
This web-based G-code simulator supports several CNC machine models. It offers a simplistic but effective user interface for visualizing G-code commands and simulating tool movements during the CNC process.
NC Viewer provides toolpath rendering in real-time, with dynamic viewing of the machining process available to operators. The simulator includes other impressive features like panning, zooming, and line highlighting for optimal analysis.
Ice SL Web Printer by Autodesk
Autodesk is the creator of the legendary “AutoCAD” software used in the design process of CNC machined parts. Autodesk has its Ice SL Web Printer, a G-code simulator designed for Stereolithography (SLA) 3D printing processes using Ice SL slicer software.
This program features a web interface for previewing and simulating printing processes before printing the G-code physically. Ice SL Web Printer provides a layer-by-layer visualization feature with support structures, allowing users to optimize and analyze printing parameters. It assists users with identifying issues while ensuring the accuracy of SLA 3D printing.
Key Takeaways
G-codes and M-codes are essential for programming CNC instructions. Previously, programmers would have to understand G-code commands, but implementing CAM and CAD systems ended this requirement.
However, programmers, operators, and engineers can benefit from understanding basic G-code language to better understand G-codes’ role and how they define the CNC machining process.