Simplify surface for CNC

Hi there, I’ve been provided a model for CNC machining that in Rhino is classified as a closed polysurface but when exported as .iges appears as thousands of small surfaces in my CNC software. Is there a way to simplify the surface in Rhino into a single one?

Thank you!

This looks like a QuadRemesh on a mesh. What wa the original object? A 3D scan?

Hi @James_Smith can you share the 3D file?
It seems that you may need at least 4 surfaces to create this volume. 1 for the inside 1 for the outside, the hole and the border.
This can be remodeled with subd or nurbs, but depending on the tolerance can take some time to do the reverse engineering. The original models seems like a mesh converted to nurbs.

Yes, I believe it was a 3d scan of the original object

One simple step to reduce the surface count is to use the option “Packed” when converting to Nurbs.

Hi Joaquin, thanks for the suggestion, I’m struggling to upload as the file is 32mb and the forum seems to have a limit of 20mb…

Did you try save small option, and rar/zip?

Nice one, thanks Joaquin (2.7 MB)

Would the process be to convert to mesh and then from mesh to Nurbs? Please could you let me know the function names you’re suggesting?

I’m not sure how was the original model created, but it seems like a mesh converted to nurbs. That’s why it looks like many flat surfaces joined.
The process to get a clean single surface I would use, at least for a quick turnaround would be.

1 - convert the polysurface to mesh again. It’s not that important but it helps the next step.
2 - use quadremesher with a target edge length of about 4, and use subd and interpolate options.
3 - convert the result to NURBS with tonurbs command and use the packed option.

Hope this helps, it gives a good result, but as I mentioned before, it depends on the tolerance. (2.9 MB)

I see you are using Rhino 6 so there’s no use of diving into SubD.

While I don’t know the requirements, I’d suggest rebuiilding the object from scratch based on section curves. Attached is a quick Sweep2 with a maximum deviation to your sample object of about millimeter. The new surface is symmetric. The file attached doe not contain the original polysurface.

surfaceedit.3dm (490.1 KB)

Can your CNC handle meshes? Since that’s what this started out as?
And can you push it back to the customer to get you data appropriate for machining, since this is a bit absurd? Or charge them an extreme amount to do their job for them?

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Thanks very much Joaquin,

A couple of questions: I’m on Rhino6 and can’t open your file, it may also answer these if the features are only on rhino 7 :

There’s a function named ‘QuadrangulateMesh’ and it doesn’t have subd or interpolate options
likewise there’s a function named ‘MeshtoNurb’ but has no ‘packed’ option

Do you think I need the #7 upgrade to access these features

Apologies if I’m being slow and thanks for your time!

Thanks Martin, I guess if I create plenty of cross sectional curves then the accuracy will be improved

Well, @James_Smith I replaced my attachment with a V6 version now, it should have the SubD version I made. As @martinsiegrist mentioned you can do this without subd, at least for this simple form.
But if you need to do this kind of conversion frequently I wouldn’t doubt to getting V7, quadremesher is an impressive tool added in this version.
QuadrangulateMesh doesn’t help you in this case, it just divide the geometry to get all quads, and mesh to nurbs only converts planes to surfaces, but it doesn’t simplify anything.

That’s not the point. Less curves result in a cleaner shape and while I don’t know what 3D scanner was used to scan your shape, I must say that 3D scanning has some tolerances. Just imagine the scanner tolerance was larger than 1 mm. In that case you could rebuild the shape and make sure the shape is symmetric and the curves have a low control point count.

IGES doesn’t support joining of surfaces, but you should be able to CNC it none the less. Or make a mesh and machine that. That would be easier to do than to rebuild.

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Understood on all points, thank you for clarifying.

This is maybe cheeky to ask but I’ve attached below the full form, in two halves as I’ll be machining the two sides - if you could spare the time it would be so helpful if you could convert them into Nurbs as before? I’m not able to upgrade at this time and the tolerances are important so the rebuild isn’t viable - many thanks in advance if you can spare the time but also understand if I ask too much! (6.0 MB)

Much appreciated for your input Martin, very helpful, thank you. Unfortunately my client is quite particular about the organic form that they’ve provided and therefore I need to retain the asymmetry (and complexity) of the form. It looks like I need to get some extra work through to pay for the software upgrade!

Thanks again

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Thanks Holo, the issue seems to be that the CNC software can’t handle the sheer quantity of faces - I’ve successfully machined many .iges in the past. Thanks for your help.

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