Using Path with external CAD

[bill.anderson]

I am a new user of FreeCad and I am trying to do something I would think would be quite normal. It probably is, but I haven't been able to figure it out. I can import or open various CAD files in MasterCAM, edit, create G-code and output a file to my controller software.

I have been able to import several different CAD files into FreeCAD . I have not been able to do much with them other than measure dimensions.
I have been able to create an object from scratch and generate toolpaths and output code within FreeCAD but nothing from external CAD.

What am I missing? Where can I find a procedure for importing and using external CAD?
I have searched existing tutorials and FAQ's. Can someone lead me in the right direction?

thanks
Bill Anderson

[chrisb]

Hi Bill, welcome to the forum.
Talking about "different CAD files" is not specific enough to give dedicated advice. In general there are two types of file formats:

• True geometry files, such as STEP format. A circle is a circle no matter how far you scale it. Don't let you distract by the fact, that if you zoom in far enough, FreeCAD will display a circle tesselated as well, but with these formats it is only a display issue depending on Preferences->Part Design->ShapeView.
  FreeCAD can use these just like solids made in FreeCAD. You can use them directly for GCode generation.
• Deteriorated file formats such as STL. These are mesh formats where the surface is modeled from (flat) triangles. This means a circle is no longer a circle, it is made of a certain number if straight lines.
  
  These formats are no solids, you can convert them in Part Workbench to a shape and the shape to a solid. There are several topics and videos around explaining this.

[bill.anderson]

I can import a .step file. I just can't change any dimension. I suspect that FreeCad doesn't support any parameterized import. Is that a true statement? If so that would mean that all one could do with the object available from GrabCad would be useless to me, that I would have to recreate the artwork from scratch for anything I wanted to machine. Why then have an import function if all I can do with imported files is to look at them.
I have looked through the tutorials and looked on the forums, which is why I asked you for some guidance to point me in the right direction. If I can't import a file created in another CAD program and modify it in FreeCad then I'll have to go back to Fusion 360 where I can. I would rather use a Linux based program offline.

Bill Anderson

[chrisb]

You are right, FreeCAD cannot change the parameters of an imported STEP file. But there is more you can do with it than just look at it. For one you can e.g. export it in another format, or create GCode paths for it. Furthermore you can use it as a base object and add additional features to it.
If you want to change the geometry of the object itself you have to stick to some other program. Please note, that Step does not contain any history, so no program can make parametric changes to previous development steps.

[Alexandr Parkhomenko]

STEP file

Why is internal format BREP?
How make Sketch like Épure (Monge's diagram) ?

[chrisb]

Why is internal format BREP?

The third party OCC graphic kernel uses it

How make Sketch like Épure (Monge's diagram) ?

I have no idea what this is about, so I'm unable to help.

[schnebeck]

Please note, that Step does not contain any history, so no program can make parametric changes to previous development steps.

O.T. - but maybe interesting:
Direct-Modelling CAD program do not have/need a history. For these programs STEP AP203/214 is enough to change every part of the model. Some history-based CAD programs now also have some kind of "auto-feature-reengineering" when loading STEP files. Here you can remove holes or change same basic dimensions. Parametric does not belong to history. Direct modeller also use parameters.

Loading IGS-file and change solid with a direct modeller:
https://www.youtube.com/watch?v=tuX8BNB9J8g

Bye

Thorsten

[chrisb]

Cannot watch the video now but it sounds like defeaturing.

[Alexandr Parkhomenko]

Guten Abend, chrisb
3th party OCC can work with Projections. It may use mouse event.

Code: Select all

DRAWEXE
Draw[1]> Draw[2]> source /usr/share/opencascade/samples/tcl/bottle.tcl
Constructing bottle body...
Constructing threading...
Putting together and writing "Open CASCADE"...
Showing result...
Draw[3]> mu4

I try build history now.

[Alexandr Parkhomenko]

Here answer about external geometry.
https://dev.opencascade.org/doc/overvie ... __xde.html