Re: cad to gcode and arcs

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Chris Brick" <cbrick@t...>
wrote:

> I got my plasma table up and running last night.
>
> I've been testing out some of the CAD/CAM packages for generating

gcode for letters and

> other intricate shapes. I've noticed that when I create circles

and arcs in autocad and

> then import them into CamExpert, the resulting gcode is many G01

moves as opposed to G02

> or G03. Circles created directly in CamExpert become G02 or G03.
> My question is, are there any packages that can do this conversion

to arc/circle from

> autocad or other drawings and which one would you recommend?
> Thanks,
>
> Chris

There in lies the dilemma of DXF. The format, on export, takes nice
bezier curves created in your CAD or illustration program and breaks
them into hundreds or even thousands of tiny line segments to make a
curve. Most CAM programs deal with what they are given and don't try
to change the line segments back into curves. Even if the post
processor for the CAM program will do G02 and G03's it never gets the
opportunity.

If you do your designs in a package that is integrated with a CAM
program (i.e. the CAM program will read the native CAD file format
that is stores its own files in) there is a possibility that true
curves are preserved. If you have a CAM program that will read the
native Autocad format (DWG ?) AND has a post processor that does G2
G3 then you are home free. Lastly there is one format for file xfr
that supports curves and that is EPS (encapsulated postscript). Most
CAM programs do not support EPS imports. Some of the more artsy ones
do (ArtCAM and SignLab to name two). There may be other solutions
like designing in Rhino3D and using STL or one of the other 3D file
formats to import into something like Dolphin or Visual Mill. Others
can answer this question.

The final thing I can offer is that several CAM programs will allow
you to deal with vector objects and change them so you can group
select a bunch of line segments, convert to curves, then edit and
delete all of the interpoints between cusps (where a curve has to
change direction). The ones I know about will let you import EPS so
it's a moot point!

Check with Fred Smith at IM Service and Bob Campbell at Campbell
Designs (both monitor this list) and get their advice. BTW even
ArtCam ($$$$) versions prior to 5.510 would import EPS, but their
post processor spit out G code with lots of tiny line segments for
curves. SignLab will do G2 G3 posts if you import files with curve
information intact.