Non circular arcs in G-code
 

Hello all!

I am trying to learn how to use G-code more and I am making software for our team that will generate G-code for us (to put it simply). One thing that I am trying to do is make non circular arcs. I have figured how to make standard curves with G02 and G03 but I was wondering if it was possible to cut a non circular arc, such as an ellipse or a parabola.

Thanks, 3734

Re: Non circular arcs in G-code
 

I'm not familiar with any single G code to do this. Whatever CAM package you're using will likely approximate the curve with a series of a whole bunch of little tiny tangent fixed radius arcs when it goes to actually post the G code. So it would probably be a rather large file full of G02s or G03s.

Re: Non circular arcs in G-code
 

Although G-code itself isn't even fully standardized, there is no standard command for ellipse's, parabola's, etc. The closest thing you may find is NURBs interpolation, but this varies from controller to controller. NURB's commands work kind of like the spline tool in CAD programs, but again the exact implementation will vary, if it even exists on your machine. They are however, not very common in most basic machine work, and only really come into use in large die/mold work.

The most common way to do this is to use a CAM program (HSMworks is free) to output the curve. The CAM program will use either lines or arcs to approximate the curve. Sadly, if you're trying to write your own programs, you are pretty much out of luck when it comes to complex curves.

Re: Non circular arcs in G-code
 

And G01s. I can't think of a time you would want to do this anyway. It's much quicker to use CAM software for anything that isn't simple lines and arcs, which is still usually slower than CAM.

Re: Non circular arcs in G-code
 

Hey! I was part of a technical school for awhile and did precision machining, so along with manual machining I had started to learn CNC. For sheer programming in theory you could brute force it but that'd be a ton of lines in your code. (So literally putting in tons and tons of coordinates corresponding with the desired shape.) Or something along that train of thought. Depending on how much your team uses things needing g-code I would heavily recommend MasterCAM (This being if you use g-code A TON(I can't find an actual price anywhere but not cheap, and sadly student edition doesn't post. grrr. But it may give you the coordinates you need as effectively. But then you could use a few programs for that. Sigh why thou world cost so much of the money) I don't know about discounts but it's an investment.. not a free program but extrememly extrememly useful) though. It's got a very CAD like feel to it, however it also allows you to create a program and post G-Code all ready to go. It takes a bit to get used to and you still need to be careful about your program (Dry runs and single step) for the initial runs of it, but in all it's a VERY convenient software.

If you had any interest in it I would always be happy to help you understand the program or answer any questions you have about it at all! I'm a bit rusty on my g-code but I would love to refresh my memory and assist in any way I could if you'd like any help!

Re: Non circular arcs in G-code
 

Not sure that you'd want to reinvent that wheel. It is not a trivial task.

There is plenty of costware out there for this, from small hundreds to several thousands. MasterCAM is great, but check the price first. :ahh:

If you use SolidWorks or Inventor, get a copy of HSMExpress (it is free), that will do the job very well. It does have some minor drawbacks, but for the price...

Personally I recommend anything from Vectric, particularly Cut2D. Fast, simple and powerful. And $150.

Re: Non circular arcs in G-code
 

I had the same question when I was learning g&m code, the answer I found was don't worry about it lol. I applaud your effort to build an in house CAM software, my old boss did something similar with Autodesk so I know it is possible. As for an solution, you might want to check out linear approximation in calculus. I'm not sure if it would be applicable, but it does turn curves into tangent lines.