Splines/Polylines/DXF/G-Code

[Wolfspaw]

I am trying to understand how to approach shapes that require splines and/or polylines. If the shape is created in AutoCad (or some other CAD package) and then saved in DXF format, will a G-Code converter recognize this type of entity? Do you need to "explode" the spline/polyline into individual line segments to create the G-Code? If yes, then is a G-Code line created for each segment resulting in huge files and choppy final output at the machine?

Wolfspaw

[ger21]

If you look in the AutoCAD forum here, there are a couple of recent threads about converting splines to polylines. I don't know of any .dxf converters that recognize splines. If you use a controller with constant velocity, like Mach3, you probably won't even notice that it's made up of short straight segments.

[buscht]

Wolfspaw, I agree with Gerry on this. At work we use Alphacam which will allow you to machine a spline, but there is no such command in a G code file and the spline is changed over to line and arc segments when the G code is created. G01, G02, G03 commands.
The large files aren't as big a problem as they used to be, but if its a big deal for your machine you should use 3 point arcs and try and duplicate the spline as close as possible in your CAD program.
An old controller will give you choppy output as the CPU isn't fast enough to keep up with the code. Newer machines shouldn't have much problem.

[mxtras]

From what I gather, if the file is saved as an ACAD R-12 DXF, the spline data will be converted to polylines which can be accommodated by most G-code generators will correctly process. Whether or not it is choppy, I don't know as I have yet to try it, but I would imagine there will be some degradation of the data (choppy).

I learned this from one of the posts on this site a few months ago, but I have yet to try it as I try to stay away (and always find a way around using) splines. I think I will play a little....and it works - pretty well from what I can see. I wish I had known that stupid little trick about 4 years ago....

Please advise if this in inaccurate.


Scott

[ger21]

Scott, read this http://www.cnczone.com/forums/showthread.php?t=12148

[ger21]

One little thing. Scott mentioned ACAD v12 .dxf, but he didn't say if it was being saved from AutoCAD or not. Technically, it shouldn't matter. But just because someone says they're saving as v12, doesn't mean they are. So although this should work in any CAD program, a trial run may be necessary if not using AutoCAD.

[Wolfspaw]

Thanks guys...I understand it now.

Wolfspaw