IGES export for CNC: file size and resolution

[minisystem]

I'm using eMachineShop's CAD software to design machine parts. I export IGES and send it to the machinist for CNC machinist. There are some manipulations I can't do in the eMachineShop CAD software (make a hole on a non-90 degree axis), so I import the IGES into FreeCAD, make my hole and then export as IGES.

The .igs file I import is about 1MB. After cutting one hole in it in FreeCAD the .igs file I export is about 0.5MB. What's going on here? It looks fine in an IGES viewer, but am I losing resolution? Why is the exported .igs half the size of what I imported? I need to be able to send this .igs file for CNC machining, so I really want to make sure there's nothing wrong with it.

[NormandC]

Hello,

While you wait for an answer from the experts (i.e. wmayer)

To my best knowledge, an IGES file is made of surfaces calculated mathematically. This is not a resolution matter as you would find with STL files for example.

If the file size was reduced in half, maybe that's because some useless data was discarded? The IGES format can contain lots of data (such as technical drawings), and it's possible when imported into FreeCAD it was not retained. I think FreeCAD only retains the 3D model data.

Anyway, IGES files are text files. Maybe you can open then with a text editor such as Notepad to compare them.

[minisystem]

Thanks normandc, that is reassuring. This is mostly a problem of my ignorance about 3D file formats. The output of the eMachineShop CAD is kind of wacky. A smaller, simpler part, for instance, has an IGES file that is over 2.5MB!

[tanderson69]

Anyway, IGES files are text files. Maybe you can open then with a text editor such as Notepad to compare them.

Code: Select all

sudo apt-get install kompare

A great way to compare files and a very simple tool! check it out, you won't regret it.

[NormandC]

Thx tanderson69, nice to know! But the k must mean it's a KDE utility. I wonder if there's something similar for GNOME/Gtk... I'll check it out!

The output of the eMachineShop CAD is kind of wacky. A smaller, simpler part, for instance, has an IGES file that is over 2.5MB!

Then maybe FreeCAD simply outputs more efficient IGES files. I've noticed the same thing about some other CAD programs and CAD formats (STEP, Parasolid...). When you open the file as text, sometimes there's a lot of text not related to the actual 3D model, like info on what software it was produced in.

Just for fun, I converted as IGES an M6 x 10mm hex bolt I modeled in FreeCAD (with complete thread). The IGES file is 802KB. The original FCStd file is slightly bigger at 1.2MB.

[tanderson69]

But the k must mean it's a KDE utility. I wonder if there's something similar for GNOME/Gtk...

Oh! you are one of those gnome purists. Very telling

[NormandC]

Nah, not a purist. I used to have KDE apps such as digiKam (still the best), but getting the whole KDE desktop as a bargain/gun on your head is annoying as hell. (And if I was a Gnome purist, I wouldn't be on Unity  )

Plus, as I've said elsewhere, my brother's been bugging me to switch to KDE. That's just incentive to me to get really entrenched, and I mean REALLY, no matter what, even if the sky falls down (stubborn a bit? you bet).

On the other hand, I love Qt apps. They integrate quite well in any desktop environment or even OS, and they don't depend on a ton of KDE libraries.

[tanderson69]

On the other hand, I love Qt apps. They integrate quite well in any desktop environment or even OS, and they don't depend on a ton of KDE libraries.

I agree. hopefully http://razor-qt.org/ takes off. Might want to checkout http://meldmerge.org/ for text comparison

[NormandC]

Hey, didn't know about Razor-qt. Nice project. And thanks for the meldmerge link.

[shoogen]

Just for fun, I converted as IGES an M6 x 10mm hex bolt I modeled in FreeCAD (with complete thread). The IGES file is 802KB. The original FCStd file is slightly bigger at 1.2MB.

IGES is uncompressed while. FreeCAD doesn't employ 'solid compression'.
The uncompressed FreeCAD file structure would be 2.8 MiB. The uncompressed PartShape10 from that file is about 1.2 MiB. With zip (deflate) the whole file is 1.1 MiB. With LZMA, non solid (7zip) 680 KiB.
The same File would be 380kiB in 7zip (LZMA, with solid compression).
A FreeCAD file could be further compacted, in a way similar to the IGES File, by discarding unnecessary BREPs (Those which would be recomputed anyway).