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Keeping sharp edges on imported Rhino model


patternmaker
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I am trying to make more polygons in surface mode (voxel room) on the sharp - edged object shown so I can blend it in with other sculpted objects that are merged with it. I can't seem to find a way that doesn't collapse the edge polygons as shown. Is there a recommended brush or settings that will let me do this?  Right now, if I get too close to the sharp object with any smoothing brush, it "melts" the edges badly.

 

The sharp object was modeled in NURBS, then exported as an obj. I imported it into 3DCoat with "merge without voxelizing" checked. It is a fairly complex object and was over 500,000 polycount, even at the resolution you see.  I have been successfully merging other sculpted surface objects to it without damaging the sharp edges. Just need to be able to work on the intersections.

 

Many Thanks!

 

Dave

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I can get closer by voxelizing, but then must sharpen all the edges again manually (with pinch or crease?). It stays sharp if I merge it as a surface model. Do I need to export a much finer mesh from Rhino in order to be able to work with the edges? I was hoping there was some command in 3DCoat that would let me break up the large polygons in the surface model without damaging the sharp edges. Is there nothing that does that?

 

Many thanks for your replies!

 

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One should indeed always export at a very high polygon count from Rhino as 3DCoat only deals with the mesh.

The program therefore can only convert to Voxel what gets captured by the exported rendermesh.

 

For best results I would suggest to go to the advanced interface in the Rhino mesher and enter 0 in all fields

(also uncheck simple planes): Only enter a number of at least 256 in one field: Initial Quads. 

That setting gives you a reasonably dense mesh quickly. Also it makes sense to convert extrusions to polysurfaces

before meshing as Rhino's mesher wants to keep extrusions Low Poly by all means - this might answer your "break up

large polygons" comment.

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Don't voxelize ? Problem solved.

 

I would rather not say so..

Meshes converted from Nurbs often are too irregular for direct editing in Surface mode, especially when exported with default settings.

Subdividing at Import time often makes no sense too, as there's no loops. Bringing these quad dominant meshes with lots of triangles

into the Voxels room first yields an even surface-mesh to start with.

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Thanks for the advice! I did get a more usable surface by meshing finer in Rhino, but I also found that I could improve my original mesh by scaling up a bit less than I was, then subdividing when merging. Subdividing twice generally crashed the program. Having a lot of trouble now getting objects to merge with this one in surface mode. Looks like I will need to switch everything to voxels after all, merge all the parts, then clean up the whole assembly back in surface mode. Needs to be one unit for 3d printing. 

 

In surface mode, I had quite a few places where lots of triangles meet at a point, and they sometimes had messy little bunches of triangles hiding inside at those points. Got rid of them by smoothing, decimating, reducing, reconstructing using "clean clay", but it was not easy. Reconstruct would often cause a crash. Is there a better way to do that? I'm guessing those types of bad triangles were what was making my objects not want to boolean sometimes.

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It's hard to comment without seeing pictures, so just a few comments. It's surprisingly little known that for 3D printing your object

does not need to be a single volume. One can just stick a sphere into a cube and export a triangulated mesh from the result - it will

print ok. The only pre-condition is: The printer needs a closed outline in sections to understand what it's supposed to do.

You will only need to merge everything to just one physical volume if you want to hollow your model out - which will greatly cut cost.

 

If you see all sorts mesh errors when bringing your Rhino model into surface mode it's very likely that your Nurbs model had problems

too -stuff that doesn't boolean can be indicators for open polysurfaces where Rhino can not determine Normals direction or you could

also have invalid geometry in your model. Simply select the item in question and type "what" into the promt and the program will tell.

Edited by polyxo
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Thanks! I knew you could print discrete objects inside each others, like a ball in a cage, but didn't know objects could touch or overlap. 

 

I check my polysurfaces in Rhino pretty carefully. Took quite a while to clean this one up. The picture shows a place where in 3DCoat surface mode passing over it with a smooth or build tool would cause a really long, spiky eruption to occur. Looking at it in wireframe showed little folded up surfaces bunched together. Could this be a tolerance issue? I try not to build at a tighter tolerance than the printer will work to; in this case, I used .003". Any suggestions for how to fix these things when they do occur? There were about five or six places where this happened on this model. 

 

Sorry not to show the full model - that would violate my customer's confidentiality.

post-6575-0-04516300-1383407142_thumb.jp

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That's a singularity - a place with stacked controlpoints - one should avoid such surfaces.

I see two options: Redo the surface in question, maybe as a Sweep2Rail - this also will give you a better mesh export.

The simplest hack is to create a tiny sphere at the singularity and to trim hole which you then close again with a patch.

Or merge to Voxels with the option "make mesh closed", then you should be able to fix that defect in 3DCoat.

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All you need to do is increase the resolution in your layer before you import.  In some cases, you can increase the resolution of the model before committing it to the scene in the dialogue box that comes up, by subdividing, but I don't find that useful.  I almost never check 'merge without voxelizing,' but others have had trouble with this.  The reason to merge without voxelizing is so that you can work in Surface mode.  You can still voxelize it afterwards, but, again, the resolution of your layer might need to increase.

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