Re: DXF v's IGS file formats / advice needed

Mike, Hi

IGES defines a curve, while DXF is a legacy format and will tend to
contain facetted data. What this means is that the IGES will have a
mathematical representation of your model, based on curves and be
much more accurate, while the STL/DXF will have taken this geometry
and broken it up into lots (ie hundreds/thousands) of little
triangles which approximate the shape!

The only downside of IGES is that different CAD systems sometimes
handle curves a little different and there can be discrepencies.

Formats (curves):
IGES
STEP
SLDPRT

Formates (triangles):
STL
DXF
3DS
OBJ

.. so going with IGES would be the best, however, it doesn't end just
here sadly. Many program which can read curves in, will actually just
parse the curves and create their own version of (triangle) geometry.
Usually CAD packages will have export options (STL/DXF) where you can
set the detail, so you may be able to bump this up and get better
results than the curves would give once the CAM program converted
them. This detail is sometimes called Chord Length, or angular
tolerance and you can set it in angles or spatial units. So if your
IGES import doesn't look too good, export it as DXF/STL with a chord-
length of 0.5mm. Of course, the file is going to be huge.

~Abby


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "junebrandy" <mike1@j...>
wrote:

> Hi all,
> I am trying to develope G code for a section of a boat,, the
> original design is in Rhino, and the sections will be cut using a 4
> axis wire machine
> I started using DXF file format but got a million pointsand lots of
> confusion on my part.
> I then switched to IGES or IGS and now have a nice easy to follow
> section ,
> I am looking for accuracy of about .5 mm but wonder how much
> accuracy , if any ,am I loosing.
> Can anyone explain the reason for the different formats , and how
> they'll effect the G code generated?
> thanks.
> Mike