What is G-Code?

Nov 21 20:17 2007 Ivan Irons Print This Article

What is GCode? Maybe you have seen an example of GCode, but what exactly is it?

G-Code is the common name for the programming language of CNC Machines.  Somewhat of a generic,Guest Posting catch-all type of term for CNC programming language.  Very few machines adhere to this standard today.  There are as many varations as there are manufacturers.This is how I think of G-Code.  It is a simple language built off of the Cartesian Coordinate System for motion control.  That is a mouthful.

I don’t know if that is exactly right, but you will get my meaning in a second when we go through some code line by line.  You will remember your High School Geometry soon enough.  For the real pros out there, you know there is much more to G-Code then that, but it is a good place to start thinking about it.

You will see many variations of the G-Code name like:GcodegcodeG-Codeg-codeG CodeG-Code

Are there other “Codes?”In a word…Yes.  We will get to that in a moment.  G-code is also the name of any command in a CNC program that begins with the letter G.  G-Codes generally tell the machine to perform an action.  G-Codes can tell machines to move a certain distance in the X-Axis for example.  Or, make a rapid move to another location.  Or, move in an arcing fashion while milling.  An on and on and on.

Here are some examples of G-CodesRemember these codes change to a certain degree between CAM Software packages and CNC Machine Manufacturers.G00 Rapid positioning G01 Linear interpolation G02 CW circular interpolation G03 CCW circular interpolation G04 Dwell G20 Programming in inches G21 Programming in mm G28 Return to home position G40 Tool radius compensation off G41 Tool radius compensation left G42 Tool radius compensation right G43 Tool offset compensation positive G44 Tool offset compensation negative

Why does G-Code Change?We humans like flexibility.  We also like standards.  G-Codes are standardized in a certain sense.  Once you start to be able to read it, you can read just about any flavor of it.  That is the standardized part.All machines are not created alike.  Even identical machines are different to a certain degree.  They may not have the same tools loaded or they have been slightly modified to produce a certain type of part.  Interesting how people like to customize.

That is why G-Codes are not the same.  You need some flexibility in the programming to accommodate all situations.  Couple that with the fact that every manufacturer thinks their version is the best and you get a myriad of G-Codes out there.

Many manufacturers also try to force you to only use their code.  For example, they give you a design interface to make parts and a CAM interface to produce code.  They lock you into their “Black Box” so you can’t go elsewhere for service and support.  They lock you in their “Family.”  Sometimes they make up a completely different kind of G-Code language that no one can understand but them.  They do that to keep your hands tied up.

What is an M-Code?M-Codes are related to G-Codes.  M-Codes control different machine functions.  Some of these functions are turning the machine on and off.  Turning the spindle on or off.  Turning a plasma torch on or off.  Turning coolant on or off.  You get the idea.  When programming your CNC machine you may need to perform these functions.

Like G-Code, M-Codes vary from manufacturer to manufacturer and from machine to machine.  As you can imagine you would need an M-Code for turning a plasma torch on and off on a CNC Plasma Cutting Machine.  You wouldn’t need an M-Code to turn a spindle on and off though.  Hey, the machine doesn’t even have a spindle.  It’s a plasma cutter!

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Ivan Irons
Ivan Irons

Ivan is active in Gcode and CNC Programming. G-Code is one of his expertise.

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