Facets in Rhino --> VCarve Import

[joelschuman]

First time I've tried importing a Rhino 3D model into VCarve, a simple form for vacuum molding. In Rhino it's a completely smooth NURBS object. When I brought it into VCarve, it looked like it had facets, but I assumed those were due to simplified rendering. So I cut it. Big surprise! The cut part had facets, just like the preview.
I assume that VCarve meshes the NURBS object on import. The mesh was too big for the VCarve smoothing filter, so I went back to Rhino and exported as STL with very fine mesh setting. Smoother after import, and even better after using the smoothing filter.
It's workable as is, but as a VCarve 3D newbie I'm wondering if I missed something obvious. Is there a better way?

[Brady Watson]

Joel,
It's true WYSIWYG when it comes to the 3D view in VCP/Aspire. If it looks faceted, and the toolpath previewer shows it, it's 4 real dawg

Generally speaking in Rhino, outputting an STL (always use binary...it's smaller on disk) at .001" resolution is usually adequate. Only when you have small, highly detailed geometry like a relief, would you need to go finer than that. It's usually a set it & forget it thing.

You may want to review the Rhino Help covering STL I/O

The attached pic shows the export option screen asking you to pick the STL resolution when exporting. It essentially asks you how closely to the model you selected to export that you want the STL surface to follow. It has the effect of both how closely it follows the original model 'skin' as well as the size of the resulting triangles. The smaller the number, the more triangles and the finer the triangular mesh.

-B

[joelschuman]

Oh, no, another learning experience! Thanks, Brady.

Joel,
Generally speaking in Rhino, outputting an STL (always use binary...it's smaller on disk) at .001" resolution is usually adequate.
-B

Doesn't seem to be any penalty for setting the resolution even finer, AFAICT, other than a minor file size hit. At .0005" I don't think I need to use the filter smoothing function.

But it does have me scratching my head. Under what circumstances is importing a native Rhino .3DM 3D model workable? I guess only 2 or 2-1/2D. If any seriously sculpted curvy stuff has to be exported to .STL why is .3DM even an import format for VCarve?

[EricSchimel]

Do you have Rhino CAM? I've personally never used it, but perhaps it might be better to keep it all under the same program?

[Brady Watson]

Joel,
In many cases, no there isn't a hit for finer resolution. It is important to understand what's going on under the proverbial hood of each program in order for you to make an educated decision when it comes to file format.

In the case of Rhino, it is possible for the 3DM format to contain vectors, meshes, NURBS surfaces/solids, etc at the same time. 3DM import is a novelty and I would not recommend using this format as your goto file type. Instead, separate vectors - export vectors from Rhino as DXF and meshes as STL Binary. Same going the other way if the intention is to import into Rhino- export from Vectric, vectors as a DXF and 3D meshes as an STL.

Now the reason you didn't see much of a hit going to finer STL resolution into VCP/Aspire is because there comes a point where you reach diminishing return. Vectric works with 3D in a very different way than Rhino. Instead of working with the actual vertexes and triangles of the mesh, it transforms it into voxels, which can be thought of as 3D pixels. These voxels are like little cubes. IRC, you can't set the size of the voxels in VCP, but you certainly can in Aspire. This will let you gain additional resolution across a larger area than working with 3D files in VCP. When it comes to export, Vectric will take whatever 3D voxel based model you have created (in Aspire) and wrap it in an STL mesh, like a cloth where you again, specify the tolerance to the original model shape.

If you are really interested in working with 3D files, you should at the very least, consider upgrading to Aspire. It's the best value for a 3-axis router (and fun to use). Only in the past couple versions has VCP had the capability to machine 3D. This is a very small fraction of what is available in Aspire. I use Rhino and Aspire quite frequently. It is sometimes easier to create complex shapes in Rhino and then import them into Aspire for machining - or tweaking, like adding organic embellishment to it, etc.

-B

[joelschuman]

Brady,
Again I thank you for being so generous with your time and knowledge. This is exactly what I needed to know, boiled down to a couple of paragraphs. I spent hours rummaging around in the TSB and Vectric forums without stumbling across this info.
.3DM = novelty import format... huh! I've been a Rhino user since ver 2, so I've come to think of it as mainstream.
I had not heard of voxels. I'm curious about what advantages they might have over NURBS or meshes for CAD/CAM. Should make for some good late night reading.
I will check out Aspire. I haven't got a lot of time invested in VCarve, yet, so it might make sense to upgrade now.
Cheers,
Joel

[willnewton]

Woohoo, more Rhino users!

Here is a link to a short thread with three posts by me giving a bit of Rhino meshing tutorial with words and pictures and four part harmony. The original post is about edge length in STL files, but there is enough side info and pictures that I think you will find it useful, even though it is in a 3d printer forum.

I design the object and use Mesh>From NURBS object. You do need to watch out if you are working in mm or inches. If you are working to .001 inches and change units, you will be making meshes that are .001 mm and will bog down or crash Rhino if the model is large.

Brady's comments are spot on as well.

http://www.forum.makergear.com/viewt...it=+mesh+rhino

Here is a screenshot of my favorite mesh setting in inches. For mm I change the min. edge length to .1 or .01. That setting is the one that will make the most dramatic change in your mesh, taking it from extreme mesh to chunky blocks. You will have to get a feel for what is right for your project, but the link has a few tips to help find the sweet spot for you.

picsettings.jpg

[Brady Watson]

Will - thanks for the link. The pics tell the story.

Joel - You're welcome. Rhino is a fantastic program. I think of it as a Swiss-Army knife when it comes to CAD. It handles a lot of different types of formats and is brilliant for visualizing assemblies etc. I find its drawing tools do leave a lot to be desired having used either ArtCAM or Aspire over the past 17 years...So I do find myself doing artsy-fartsy shapes in Aspire and exporting them into Rhino for extrusions etc.

My comment about 3DM being a 'novelty format' requires some clarification. I said that within the confines of the work that we do - meaning CNC routing & I/O with Vectric CAD/CAM products. There are other software packages out there that can pull in a 3DM and parse out the vectors, meshes and solids/polysurfaces as distinct entities and have them laid out as you'd expect...but as far as the Vectric stuff goes, my recommendation is to just export as STL and DXF and pull them in as required. It just avoids agg...

Aspire (and newer versions of VCP) represent 3D as voxels...some refer to them as pixels, but they also have Z dimension = to the X&Y, so it becomes a voxel.

Go check out this thread. Follow the link to the Vectric page & download the PDF and read it. It's worth the read...

When users get beyond cutting out ready-made 3D clipart, these types of technical details can really influence the quality of the work that comes off the machine...We all run similar hardware, yet some people's stuff looks way better than others. (hint...)

-B

[srwtlc]

Along with all the good info previously, note that in Aspire and VCP, you can apply smoothing filter on selected components. I'll often use this after importing some .stl clipart that has noticeable facets to either greatly reduce or remove them. Sometimes a quick smoothing pass with the sculpting tools, with conservative settings, can take care of it too (Aspire only).

[Bobtail Farms]

I defer to the expertise expressed by others. However, for those of us with limited funds, or hobbyists (guilty on both counts) who (so far) choose not to justify the upgrade to Aspire (full disclosure: i am saving for that upgrade, however far in the future it might be): consider Blender, an open source 3D modeling program. It has, for me anyway a steep learning curve. But I have been able to use it to tweak existing 3d/2.5d models (not directly v3m), create simple models both imported into V-carve pro.