WHAT ARE G CODES? (WITH EXAMPLE) - TECHNOLOGY - 2025

The G codes are encodings that correspond to the programming used to control equipment numerical control or CNC, machines that are running their jobs under the command of a computer. In this class of equipment are milling machines, lathes, 3D printers, cutters, etc.

G codes are also known as preparatory codes. The G stands for "geometric." They are codes that tell the machine which operation to carry out and are identified by starting with the letter "G".

Source: flickr.com Christopher Schmidt Attribution 2.0 Generic (CC BY 2.0)

They are made up of instructions or commands that tell the equipment to which position to move, at what speed, at what moment to use a tool, such as a laser, extruder, etc. For example, with 3D printing, G-codes contain commands to move parts within the printer.

There are several implementations of this language, but in each of them the commands and commands are similar. However, when generating the files, it will be required to know the appropriate version of the G codes that the equipment can interpret.

What is the G code?

G code is a programming language for numerical control equipment that directs machines on where and how to move. G codes vary depending on the type, make and model of the equipment.

It always follows some variant of the following alphanumeric pattern: N ## G ## X ## Y ## Z ## F ## S ## T ## M ##, where:

- N ##: Program line number.

- G ##: Defines the movement and the function.

- X ##: Declare the horizontal position.

- Y ##: Declare the vertical position.

- Z ##: Declare the depth.

- F ##: Feeding speed.

- S ##: Spindle speed.

- T ##: Selection of tools.

- M ##: Various functions, such as turning something on and off, such as coolant, indexing movement, axis lock, etc.

For example, G01 X2 Y3 F35 S450 T02 M04 would indicate a linear feed move (G01) to the given XY position and a feed speed of 35. The spindle speed is 450 and you are using tool 2.

The various functions vary from machine to machine. Therefore, to find out what the M code is, the machine's instruction manual should be referenced.

Machine movement

Everything that any machine can do is based primarily on three basic types of movement:

- Rapid movement: a linear movement to an XYZ position. It is done as quickly as possible.

- Feed movement: a linear movement to an XYZ position at a defined feed rate.

- Circular motion: a circular motion at a defined forward speed.

Each G code tells the team which variant of these basic movements to perform and also how to do it.

X, Y are the coordinates for the horizontal and vertical position, and Z corresponds to the depth of the machine. These numbers follow the motion or function command to express the position of the machine.

Next, F determines the feedrate (for feed or circular movements), while S determines the spindle speed. T is used to select a tool.

G code construction

If you open the G code in a text editor, you can see its content, but it is quite difficult to give it some meaning. With a tool like Repetier Host, you can better understand G codes.

This type of program allows you to open the G codes in order to see the paths that the head will take to produce a print. Repetier Host uses colors to indicate the function of the codes.

Generate G codes

Since, for example, a 3D print may have to carry out numerous movements, the G codes can take an immense number of pages. If this set of code were to be created by hand it would have to be done for a considerable amount of time.

Some special program, for example the Cura cutting program, is the one that technically composes all the G codes.

This program sections the STL files that contain all the information necessary to create a 3D print. Convert the STL file to G codes, thus automating the process.

Each G code is unique to the machine it was written for. The set of instructions is based specifically on each machine.

CNC vs 3D printing

Both CNC machines and 3D printers are controlled using the G codes, which is the group of commands that start with the letter "G", just as there are codes for many other letters.

G-code guidelines tell crews how to move and how to adjust their settings, such as cutting speed or nozzle temperature. Each order constitutes a step in the process of making the object.

However, although both 3D printers and CNC equipment use G codes, there are some important differences in these two applications.

CNC

Computer numerical control is a technique for controlling the instruments of a machine by means of a computer system.

CNC mills and lathes are generally used when very high precision or repeatability is needed. For example, these are useful for drilling hundreds of identical holes to create an optical plate.

This method of creating a part is classified as "subtractive manufacturing", as the part is created by gradually removing the material.

3d print

It is a manufacturing process that also produces parts using computer control. In fact, 3D printers are also CNC machines, but given their immense popularity, they are rarely known as such.

In 3D printing, a part is erected by adding material, until the complete part is created. 3D printing is very useful for creating custom parts and prototypes before reaching a final design.

Sample code

- 11: Indicates the code line number and is used as a reference. In this case it corresponds to line 11 of the program that is being executed.

- G / M: In blue color. Indicates that it is a command of the type indicated by the letter. In this case, the G1 code corresponds to the command: Coordinated movement at forward speed.

Next, each text that is in red defines certain parameters for the command and then the value for each parameter in question:

- F: Speed. In this case, the speed is indicated to be 900.

- X / Y / Z: They are the position coordinates.

- E: Feeder movement.

References

1. Educatibot (2019). G-Code. Taken from: educatibot.com.
2. Ultimaker (2019). What is g-code? Taken from: Ultimaker.com.
3. Benjamin Goldschmidt (2019). 3D Printer G-Code vs CNC G-Code - What's the Difference? All3dp. Taken from: all3dp.com.
4. Autodesk (2019). Getting Started with G-Code. Taken from: autodesk.com.
5. Wikipedia the free encyclopedia (2019). G-code. Taken from: en.wikipedia.org.