Hey Michael,

Again, thank you for all the time you've taking to extensively answer all the inquiries in my walls of text.

1. Hi Larry, re: .3dm file from CAD Exchanger not working better - does CAD Exchanger have any option in it for what version of .3dm it will write out? If so can you try writing as a Rhino v2 .3dm file? That may avoid what seems to be the problematic area.

A: CAD Exchanger lets you choose which version of Rhino .3dm to export as. The first time I converted the .step file to .3dm with it I defaulted to exporting as a Rhino 6 .3dm but when I tried to open that in MOI nothing displayed at all. So I then exported again but as a Rhino 5 .3dm and that's the .3dm file I attached to my last reply.

I've now exported the .3dm as a Rhino 2 one :



and it appears to import better in MOI for the most part. But there still appear to be artefacts:



And the 5 different components in the original .step file are regarded by MOI as the same piece, when imported from the Rhino 2 .3dm file. So if I use this approach, I'll need to export each component to its own .step file and then its own .3dm file individually.

Moreover, when I exported an .obj file from the Rhino 2 .3dm of the model, with all the solids merged into one, there were tessellation issues with the obj model :



I thought maybe this is because all of the solids got wrongly merged together into one upon conversion from .step to Rhino 2 .3dm. So I then opened the original .step file in 123D Design again, deleted the 4 quarter mould pieces and kept just the cage and only exported that as a .step file. Then I converted that .step file to another Rhino 2 .3dm file and imported that into MOI. However, the tessellation issues were worse now :



These are the settings I used to export that .obj, from the Rhino 2 .3dm file of just the cage, without the 4 additional parts inside :



Unfortunately, it seems I deleted the original, native .123dx save of the model, from which I exported the original .step file containing all 5 components of the model. I only retained that one original .step file so I can't try to only export just the cage as its own .step file directly from the native .123dx save, to then convert that .step file of the one component to Rhino 2 .3dm and import that into MOI to see if it would make a difference. I don't think it's likely it would.

MOI does see both the Rhino 2 .3dm of all 5 pieces merged into one solid as a solid (not a Joined SRF) and the Rhino 2 .3dm of just the cage itself as a solid as well, not a joined SRF. So I don't think that the issues are due to the .step files I am converting from themselves being corrupted or faulty in some way. Also, I take care when modelling to never do things which might be ambiguous to the software 123D software I use and result in non-manifold edges or non-watertight solids.

I uploaded a 7z archive of :

a) The original .step file with all 5 components, converted to Rhino 2 .3dm instead of Rhino 5 .3dm (mould.quadlobe.toy.rhino.2.b.3dm).
b) .step file obtained by re-opening the original .step file with all 5 components in 123D Design, deleting the mould components and exporting just the cage (cage.only.stp).
c) .3dm file obtained by converting that new .step file to Rhino 2 .3dm (cage.only.3dm).

You can get the file at : https://drive.google.com/open?id=1N3Ebs5gmhwbd-oZst1bFXpTeiDRpT4Dq .

All conversions to .3dm were done with CAD Exchanger as that's the only other software I currently have that supports importing .step and exporting .3dm.

2. It's just a way you can reduce very skinny triangles if those are undesirable for what you're doing. They're kind of hard to reduce without using a different triangulation method which would be a lot more time consuming.

A: Thank you. However, the skinny triangles are non-issue for me, as long as they're not redundant cuts. My only concern is whether those additional seams shown by MeshMixer are false positives or they are indeed actual cuts / borders between islands in the mesh. If they aren't actual cuts or borders, it's a non issue and I'll stop using Meshmixer to check for this since it would mean it's generating false positives.

If they are actual cuts in the mesh, it would be nice if they can be prevented in 4.0 but it's not really an issue if they can't be helped. As long as the redundant cuts on the top/center/tip of curved surfaces don't result in the normals of vertices along those cuts being parallel to the face normals of the respective neighbouring triangles they belong to rather than divergent from those respective triangles' face normals.

For instance here :



there's additional cuts between each of the triangles which share that one vertex, right at the tip of the circular spherical cap. Even if those extra seams / cuts are indeed there, as long as the normals of the duplicated vertices are the same between the duplicated vertices rather than divergent from each other and parallel to their respective triangles' face normals, the extra cuts shouldn't matter when rendering.

This does indeed appear to be the case but can't say for sure due to the small size of the triangles in question it's hard to say for sure whether flat shading is going on or not. It doesn't seem to be resulting in flat shading, that I can tell.

Even if this results in flat shading, that's not an issue on flat faces :



3. Can you please upload the .obj file for this one here? :

A: Sure. I've uploaded a .7z of them here : https://drive.google.com/open?id=1xwWi19v1ORaR0eN-MtpjuVJ56ffxnh-z . You can also download the .obj files of just about any of my impeller models from grabCAD and they'll show the extra seams on the bottom plane and on the tips/tops/centers of bulging circular surfaces or sphere caps.

The ones here : https://grabcad.com/larry.v-1/models?page=4 . You can also download the .step model of any of them as well.

This one here : https://grabcad.com/library/impeller-design-02-2-1 doesn't appear to be a false positive due to skinny triangles. I've uploaded both its .step and .obj here :

https://drive.google.com/open?id=1VRlXPAT2w7gAgpBk9cftSscmdqZ5r-8I

It's not a bid deal if this can't be helped. I'm only asking about it because it's triggering my OCD :)

4. I can take a look at it to see whether there is any actual seam in there or if it's a really skinny triangle. It would be good for me to test with the same mesh settings that you used when generating it.

A: I checked with a different model and it doesn't appear to be due to skinny triangles. That's the model here :

https://drive.google.com/open?id=1VRlXPAT2w7gAgpBk9cftSscmdqZ5r-8I

Generally, I use the settings shown above or values close to them. Depending on the complexity of the model and the triangle count of the resulting mesh. For instance, for 'Divide larger than' I normally choose .1 and for avoid smaller than I choose '.01~.02' but that would result in way too high a poly count for the model of the cage.

Sorry to be taking so much of your time with this minutiae.

Best regards,

Larry.