Looking for a detailed G code primer.

[maspeir]

I've written computer programs since I was 8 in many different languages, so I do not expect that I'll have any difficulty learning g code. However, Google really doesn't turn up much. I can find lists of varying lengths of the various g code commands, but I can find very little in the way of a tutorial. I would like to not only see the complete list of commands, but also an example of each command.

Maybe I'm using the wrong search terms. Can someone direct me to such a tutorial, if it exists?

[Geof]

This is a very comprehensive course thst covers everything.

MFET 275 - CNC Applications

A thing to be aware of with G and M codes is that there are some differences in code interpretation between different manufacturers. Most codes do mean the same on just about every machine but codes that call up canned routines are often different.

[Al_The_Man]

The difference also applies to Machine application types, for e.g. the G codes will vary between Mill, Lathe,Gantry (router,plasma,oxy/gas), EDM, Punch press etc, to suit the difference in machine peculiarities.
Also as Geoff points out M codes although often follow traditional practice, are written at the discretion of the MTB, so these can vary between identical controllers.
Get a hold of a copy of CNC Programming Handbook by Peter Smid.
Al.

[maspeir]

That's good, but I'm hoping for more of a book format. Not necessarily a book, but in the format of a book.

Also, how would one write a g code program to machine a curve path? Let's say, for example, that I want to mill the letter "S" out of wood and I use a drawing program to define the character out of Bezier curves. How do I machine the profile? My guess would be to write a program (not g code) that converts the curves into a series of line segments and then outputs the correct g code. Is there a better way?

Originally Posted by Al_The_Man The difference also applies to Machine application types, for e.g. the G codes will vary between Mill, Lathe,Gantry (router,plasma,oxy/gas), EDM, Punch press etc, to suit the difference in machine peculiarities.

In my case, strictly mill.

Originally Posted by Al_The_Man Also as Geoff points out M codes although often follow traditional practice, are written at the discretion of the MTB, so these can vary between identical controllers.

So, if I am using Mach3, I need to write the g code for Mach3's interpretation?

Originally Posted by Al_The_Man Get a hold of a copy of CNC Programming Handbook by Peter Smid.

Will do, although I'd like an online reference as well. It has been my experience, from a game programming perspective, that technical books pretty much are out of date at the moment of printing. Maybe not so much in this case, but the internet is far more dynamic.

[Al_The_Man]

You need a CAM system, this follows the CAD operation, Mach has a built in CAM called Lazycam where you can import different CAD or drawing file types.
It also has a Customizable M code application.
Even complicated shapes end up as G code, if not simple arcs or circles then smaller segments are generated.
Al.

[maspeir]

Originally Posted by Al_The_Man You need a CAM system, this follows the CAD operation, Mach has a built in CAM called Lazycam where you can import different CAD or drawing file types. It also has a Customizable M code application. Even complicated shapes end up as G code, if not simple arcs or circles then smaller segments are generated. Al.

I don't have the money for "professional" CAM software and I am aware of LazyCAM. I'll probably use it for a while after my machine is built, but I would like to write my own simple CAM application. Other than that, I would really like to know what my machine is doing or about to do and that requires understanding g code in depth.

[MrWild]

You don't need a CAM program, it just makes things easier. I went to a community college and bought a G-code programming book (used) at the book store. It came with a 100 line G-code interpreter (Predator CNC) to show the moves from a written G-code program.

A book from a college book store will teach you how to interpret a blue print, offset your cutter (cutter comp) and do lead in's to your work. Ebay might be a good place to look for a used college book that's cheaper than a college bookstore would be. My book used Fanuc G-code language as the G-code it taught. Fanuc is about as generic a G-code as it comes.

[ger21]

Also, how would one write a g code program to machine a curve path? Let's say, for example, that I want to mill the letter "S" out of wood and I use a drawing program to define the character out of Bezier curves. How do I machine the profile? My guess would be to write a program (not g code) that converts the curves into a series of line segments and then outputs the correct g code. Is there a better way?

That's pretty much it. Some CAD programs can export the Bezier curves (spines) as line segments.

[Al_The_Man]

Originally Posted by maspeir but I would like to write my own simple CAM application. Other than that, I would really like to know what my machine is doing or about to do and that requires understanding g code in depth.

If you run a program through Lazycam, you can see the resultant G code to get an example of what you require for programming purposes.
Al.

[johnohara]

As a developer, my guess is you'll appreciate this document.

http://citeseerx.ist.psu.edu/viewdoc...=rep1&type=pdf

G-Code files are text, so understanding what the interpreter is looking for is a good place to start.

Another good resource is the EMC2 Project. The source code is available as a free download.

~John

[maspeir]

Originally Posted by ger21 That's pretty much it. Some CAD programs can export the Bezier curves (spines) as line segments.

I was really expecting it to be more involved than that. CNC is all about precision and accuracy and representing a curve with line segments is, in the graphics programming world at least, considered to be the least precise and accurate representation of a curve. No matter how finely you subdivide the curve, part of the line segment will always be off of the curve.

Originally Posted by johnohara As a developer, my guess is you'll appreciate this document.

That is EXACTLY the kind of thing I was looking for! Thanks!

I'll look up the EMC2 project. Sounds interesting.

[judleroy]

I agree that breaking things up into line segments detracts from accuracy...but... You can decide the standard deviation from the actual curve. That means basicly you can let the path deviate by as much as you want to shorten program length by using longer and fewer line segments. You can also specify better accuracy standards which just means more smaller segments that better apporximate the actual geometry. This can give you accuracy to as close a tolerance as your machine tool can hold. (.01-.001 for a decent cnc router or .001-.0002 for a mill from my experiance).
Judleroy