Fixing invalid iges import - identifying faulty topology

stephen_allen

Morning all,

Overall, I'm trying to achieve something very simple here - make some holes bigger in a part called TGuardW2_v2 - however the part is invalid, and I think I'm missing something because the various "fix" tutorials are not helping.

I am working in this document. TGuardW2_v2 is an imported iges part which I created in FreeCad from an stl mesh (because OS can't generate a part from an stl mesh). There were no errors in FreeCad for either the mesh or the part.

I can see there are two surfaces of TGuardW2_v2 that OS doesn't like (faulty topology) - unfortunately, one of these is the main surface of the part (the imported TriggerW1_v2 has the same problem, but the main surface is not broken, so I can happily derive a part from that).

I've tried:

• Deriving a part avoiding the faulty surfaces - unfortunately the main surface has faulty topology.
• Using a boolean operation to "mould" the part (as per another "fix" thread) - cannot use a composite part.
• Using the inbuilt "highlight boundary edges"  - nothing shows up.
• Using the"find laminar edges" featurescript from another thread - nothing shows up.
• Looking through with section view - no red edges.

I think I may be fundamentally misunderstanding what I am trying to acheive with a "fix"?

stephen_allen

I saw Boolean Plus, but noted difficulties with edges of circles - in any event I've obtained a STEP file from the original designer - so this discussion is academic. Thanks again @NeilCooke for your help

NeilCooke

Hi @stephen_allen - there doesn't appear to be any holes in Surface1 - the faulty topology is probably overlapping edges/surfaces or inverted surface normals - this is kind of expected from IGES and/or STL. Can I ask what the purpose of this project is? Where did the original geometry come from? Mesh geometry in Onshape is only intended to be used as a modeling reference, not for making solids. Can you not achieve what you want to do in FreeCAD?

stephen_allen

@NeilCooke The project is remixing a community-source foam dart (nerf) blaster to use (mostly) printable hardware (I, and others are UK based so cannot easily access the US tubing and screws required). A tiny bit more info is here:

All the project now needs is me making the machine-screw holes in TGuardW2_v2 big enough to take a sturdy (4mm-ish) printed interference-fit hex plug. I've successfully done this (where applicable) for the other 10 parts which successfully imported as iges files.

Maybe "holes" is the incorrect technical terminology - what I mean are arrowed in the (crudely-made) picture.


Unfortunately I cannot achieve what I want in FreeCad without re-learning the package - this is because the UI in the latest version is unfathomable. I used to be quite proficient in FreeCad, but now cannot even do simple things like boolean operations / simple sketches pads and cuts, as there are multiple new preconditions (including an new entity called an object) which have been added the workflow that I don't yet understand. 

Perhaps it is easier for me to reverse engineer (trace) the part in OS, than (1) re-learn FreeCad; (2) fix the part; or (3) or contact the originator for a CAD version.

I am probably slightly hampered by being a hobbyist who only has access to a linux box, and no professional CAD packages.

NeilCooke

Nothing wrong with Linux - works perfectly with Onshape
Probably easier to try and model around it. There are other solutions you could possibly try, but the part looks simple enough to remodel and it’s probably faster. 

stephen_allen

NeilCooke said:

Nothing wrong with Linux - works perfectly with Onshape
Probably easier to try and model around it. There are other solutions you could possibly try, but the part looks simple enough to remodel and it’s probably faster. 

Linux for the win 

Thanks for your help - unless any other ideas come up, I'll either remodel, or edit the mesh directly in Blender - I understand that Blender has basic boolean functionality, which might help

NeilCooke

There is a custom feature called Boolean Plus (see + icon far right in Part Studio) that can Boolean meshes and solids. You could perhaps model the hole as a solid and subtract it from the mesh using that. 

stephen_allen

I saw Boolean Plus, but noted difficulties with edges of circles - in any event I've obtained a STEP file from the original designer - so this discussion is academic. Thanks again @NeilCooke for your help