Mesh to nurbs for milling


#1

Hi there,
I am trying to send out a landscape - mesh file for CNC milling.
The companies only seem to accept .stp files.
This means i need to convert my mesh landscape into nurbs surfaces - why ? and how? - if worst comes to worst i can simply “mesh to nurbs” all the triangle faces but it seems very stupid?
Any insight greatly appreciated
Nik


(John Brock) #2

Mesh to Nurbs won’t do what you want:
http://wiki.mcneel.com/rhino/meshtonurb


#3

yes it does - it will make them mill it … but it seems a very stupid solution! for most machine processes mesh files a the desired format …why not for CNC milling ?


#4

You can use mesh for milling. Architects do it all the time!
What CNC software do they use that can’t make toolpaths from a mesh?

Talk to the companies and tell them to double check, because mesh is jagged and not perfect, but normal to support.
I presume the reason they want STEP is because they are used to mill for the industry at really high tolerance and thus want to avoid the mesh angled edges.

Good luck!


#5

Classically most fabricators that deal with the mechanical industry are used to dealing with surface/volume models because they have the ability to produce geometrically precise objects like circular holes. A mesh model can only make a close approximation of a circle, for example. Personally, if I’m making geometrically precise parts, I much prefer a surface/volume model to a mesh. Surface/volume models are also MUCH easier to edit if editing is necessary.

In addition, many fabricators are actually running CAM software that is based on a solid modeling core like Parasolid or ACIS, perhaps even inside a solid modeler like Solidworks. None of those deal with meshes very well if at all. There are a number of CAM programs still out there that do not recognize meshes at all.

However, many CAM programs do accept meshes as input. If your fabricator cannot accept a mesh model, I suggest that you need to find a different one, as they are probably not going to like to mill a terrain model anyway. I don’t know where you’re located, but my first thought would be to find yourself a good architectural modelmaker. Most of them I know are quite competent in milling terrain models. If you are in the US, you can contact the APMM for a member listing of modelshops near you.

HTH, --Mitch


(John Brock) #6

Both VisualMill and DeskProto (plus many others), can generate toolpaths from meshes.
Even the free evaluation version of DeskProto will let you post and save the G-Code so you can actually cut the part with the free eval.

My guess is your CNC shop is using Mastercam, but that’s just a guess.


#7

I think MasterCAM can actually use meshes now… Surfcam on the other hand, still can’t… I also think most of the feature-based CAM software, designed to work with solid modeling kernels, won’t work well if at all with meshes.

As you said, RhinoCAM does mill on meshes, as does MadCAM (both Rhino plug-ins), plust a host of other stand-alone CAM programs, usually those aimed at desktop milling with small machines.

–Mitch