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

I forgot you wanted a bit of history of IGES. IGS is simply a suffix for
someone's IGES file. IGES was formulated under the umbrella of what is now
the US Gov National Institute of Standards maybe a about 25 years ago. The
major CAD and CAM companies wanted/needed to exchange drawing and modeling
data because of the problem your running into - multiple it by 100,000
issues if your dealing with a ship, a tank, or and aircraft. Most CAD
software at the time created models using their own proprietary modeling and
creation schemes. So IGES was created as a modeling and annotation
information (dimensions) exchange scheme. The IGES description or
specification evolved to about 600 page or more in size and it had to handle
rather complex items - points, lines, arcs, 2-D non-circular curves,
splines, non-reational B-splines, surfaces, dimensioning annotation,
standard drawing annotation, models, views, drawings the like. All
companies had to write a translator to and from the IGES specification, ie
the IGS file you used. Hence the reason, that I suggested you read the file
back in. Most IGES files contain the actual model you created or the
portions you selected to write out - very accurately. Some companies do it
better than others. Some CAD and CAM companies limit what IGES entities
(surfaces for example) they support - check their documentation - to and
from. Sometimes depending on your needs, you need to simply experiment by
passing files and corresponding limit what software methods you use to
create the model desired.

IGES is a National (ANSI) and International Standard (ISO).

IGES had its disadvantages hence the discontinuation of development of the
IGES model - moving to the STEP model and other subsequent methods that
allow the combination much more data to support part creation - this beyond
the scope of the issue at hand.

The dxf file is strictly a AUTOCAD definition containing the AUTOCAD
entities. Hence you need to use methods in that software that creates
geometry. What you see on the screen is not always geometry. Most CAD and
CAM companies support some forms of translation to and from that definition.
It is a defacto standard - great if it works - if it doesn't to bad.

Regards

----- Original Message -----
From: "junebrandy" <mike1@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Wednesday, September 08, 2004 5:41 AM
Subject: [CAD_CAM_EDM_DRO] DXF v's IGS file formats / advice needed


> 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
>
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