Mesh modelling VS Nurbs for CNC milling

In general, what workflow gives the best result?

Raw data is point cloud, CNC milling is out of wood.
3D scan software can save as point cloud or as a STL file.
What gives best result when modeling? working with Mesh or working with Nurbs?
Are there any advantages and disadvantages with either workflow?


Too broad a question… What is the object? Do you need smooth surfaces (typical manufactured object) or rough/textured (terrain model)?


Building off what Mitch said…

How your CAM package interacts with mesh models is key to determining your workflow

  • Open vs Closed mesh
  • Density of the triangles - excessive density and toolpathing takes forever, too few and you can read the triangulation in the final physical model (depending of course on tool dia. and stepover)

My suggestion is a hybrid approach: utilize NURBs surfaces as much as possible for your geometry (planar surfaces, easily swept curves etc.). When you get into more ornate details such as egg and dart or floral patterns utilize the scan data.

Truthfully, it really depends on the work you are trying to do, its detail and complexity, the quality you desire and if you are planning on re-tooling any of the milled wood post CNC to clean up/polish


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To clarify, it is wooden lasts made to create orthopedic shoes. all lasts have to be cleaned up by technicians before it is ready so hence the CNC milling is pretty rough. But this is the current workflow, maybe there is an alternative and that is to mill it very smooth so the technicians will do less work with sanding and grinding.

Mesh needs to be closed
at the moment you can see triangulation on the final milled product.

I think that a more smooth mesh would be just as good, but i have so little experience with NURBs surfaces so i do not know.

Thanks for your input, it does help me a lot getting input from you! :wink:


I would suggest retopologizing (TSplines, Blender, Modo…) o resurfacing the scanned STL-mesh (RhinoReverse, RhinoResurf) for best results. (It is fun too.)

Thanks i will give it a try :wink:

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I agree with 0netech. If you have the option make your mesh with quads! I personally use z-brush, its has its quirks and odd learning curve but its one of the best mesh editing softwares I’ve used. Only problem is everything is a relative scale.

My workflow for it is:
import the stl into Rhino, adjust scale if necessary, save the STL out, open it in ZBrush and perform the necessary modifications and retopo functions, save it out, Bring it back into Rhino to confirm dimensions (and adjust if necessary) and finally take my hybrid model into my CAM suite (mastecam)

The relative scale thing has to be fixed. I sure hope they do it for ZBrush v5! I’m sure I’m not alone in having suggested this to Pixologic, (and that was on version 1)

Are you are saying you can use a mesh in Mastercam?

I’ have had a few people tell me that Mastercam will not put an optimized toolpath to mesh geometry, and simply refuse to accept a mesh to produce any work.

Having worked with many CAM systems previosly, I was always puzzled by this. Even now, most CAM systems use a meshed version of nurbs surfaces to generate a toolpath, although there may be some spline interpolation when feeding the G1 moves to the machine.

Yep, I have used open meshes laid on top of NURBs geometry to route a few things. I haven’t had any issues with toolpathing the mesh - I’ve used rough parallel, 3D High Speed area clearance, finish parallel and scallop with success. Only problem with a mesh is the triangulation (or quad) density - the denser it is the more intense the toolpath is. When this occurs I generally loosen up my tolerance some to help it process faster.

I’ll be honest, I don’t route mesh daily. I have found it faster to mill a plaster backup of the hard geometry (NURBs) and allow the resident sculptors to put all the ornate details in. It is a much faster workflow for both parties and eliminates a lot of clean up that has to be preformed on the milled mesh i.e. the radius of the tool not allowing sharp inside corners.

You are absolutely right here - I think the reason people shy away from mesh is when its closed it can be harder to cut. However, Rhino has the split mesh function which makes it a breeze for me. Besides, you can also throw in some quick check surfaces and you don’t have to worry about the extreme plunges that wreck machines.

My fingers are crossed here but I am leery of it happening - CG artists don’t care about it as much as we do…

We’ll its nice to get confirmation from someone on milling meshes with Mastercam. I had a lengthy discussion with a shop manager about 2 years back who told me it could not be done in Mastercam, and I suspected they were wrong.

As far as the tolerances, the object was a relief to be cut in a machinable wax or plastic for a master. I told the shop guy the tolerance could be loose, but he did not seem to care. This particular shop actually cuts wood most of the time with 3 and 4 axis routers, which is why I thought they would not have any trouble with a mesh file.

Originally MasterCam only supported NURBS surfaces. It is only in the last few years that meshes have been allowed.

That should be a breeze! When I say loosen tolerance I mean going from .001 to .008 max. Nothing super crazy and a marginal error for my company. The overall finished product must be within 1/16" but of course I strive for ±.005"

Nick, mastercam tessellates the user’s surface/solid model to generate the toolpaths, the same way Rhino creates a mesh of your NURBs model for rendering purposes. Its been this way for forever. I know Mastercam has allowed STL toolpathing for at least 10 years and probably more -


Yeah, that’s what I thought.

I remember trying out and rejecting MasterCam for the educational shop I manage because it didn’t support meshes. There may have been a work around using .stl but they made it pretty inconvenient. As I recall they just kind of assumed that anyone using their product was coming from a solid modeling environment.
I thought that was less than 10 years ago but maybe time is moving faster than I realize.

Good old MadCam supports meshes, and they do not need to be closed either.
The polygons will be visible if the mesh is coarse of course. No way around that.
I recall David made a mesh subdivision plugin many years ago, but I can’t find it.

That I do believe, Mastercam does not always make things very intuitive/user friendly. Just getting NURBs in was pain in for a while since their .3dm translator always seemed to “forget” geometry. Thankfully that is now fixed and I don’t have to make an IGES tranfer file just for toolpathing