Settings to CNC


I want to have the added 700mm long half model send to a CNC milling machine, but have not decided where to have it milled yet.
It seems that a STL file is good, but what settings in Rhino do I have to use?
I have found the Polygon Mesh Detail Options, but am not sure or I do have to use this one, and if so which settings and why.
And are there other settings in Rhino I also have to fill in?




Try playing with them… max angle of say 3, max edge length of say 9 for a 700mm model, and take a look at the preview to see if the mesh looks dense enough to get the detail you need. I usually reimport the stl and check in in Flat Shade mode to see if it’s smooth enough…

Hallo Cairn,

Thanks for your reply.
I’m using Rhino mostly for mechanical solutions, and have never done exporting to CNC milling nor printing before.
When surching on internet I find all kinds of partly suggestions, but a tutorial or something like that I can’t find.
I once had to exported curves to be used in a CAM machine, and John Brock of McNeel wrote a very good tutorial about the subject.
It is possible that I have to do the exporting to CNC and printing more in the future, so I want to know what and why settings have to be done the way they work best.
It seems that you have done this a lot, so maybe you could help me a bit more.
English is not my own language, I’m Dutch, so details in English/American are sometimes a bit hard for me to understand.
When we go back to the Polygon Mesh Detail Options, you say playing with the max angle and max edge length. But when I look in the Rhino Help it says that to refine the mesh, you have to fill in the maximum angle, minimum edge length, maximum edge length, and maximum distance edge to surface.
All these factors are scale related. But in what way? Is there a relation to the size of the model?
And what about the density and the grid quads?
And is there nothing else somewhere in Rhino that has a function as well to get a good STL file?

Thanks in advance,


Are you having it CNC’d or 3D printed? They’re totally different things, and a mesh format like STL is the WORST option for CNC. Send IGES or STEP, and the truth is sending to CNC is easier than 3D printing because models don’t actually need to be “wateright.”

Hallo Jim, (are you the one that wrote the “form vs shape” 1 and 3 I use?)
Do you mean that I cansimply export an IGES or STEP file without any settings?

Yes I am.

Yes, you want to send NURBS not meshes. Some flavor of IGES might work better than some other, that depends on the CAM software, I usually start with STEP and see if they like that.

Check to see if a native Rhino .3dm file is acceptable. If the CAM provider has Rhino then they may prefer a .3dm file to an IGES or STEP file. Starting with a .3dm file lets them export to their CAM software as they prefer.

Also important is to provide clean data without surperfluous information. Make sure there are no bad objects and surfaces or curves are not folded back on themselves.

Ah, now we are getting somewhere.
So the best thing to do would be to send them a .3dm, STP and IGES file so they can choose what works best for them.
After the milling I will probably have the same modell added with some details 3D printed. What filetype do I have to use then, or is it depending of the printer?
And if so, do I have to use meshes then?

Hi Dirk,
My experience is mostly in 3d-printong so far, for which STL is the only option (with its own particular set of requirements).
However, my colleague has just purchased a HeavyMill from 3DTEK so we are going to be learning a lot more about CNC soon, I guess starting Fusion 360 for the G-Code generation (unless anyone can recommend a better option?)

For example, this is news to me:

…so I obvs have a lot of work to do.

With STL for 3d printing it’s relatively easy: if your mesh is watertight (no naked edges) and looks ok in Flat Shade display mode in the Rhino viewport, then it will print fine. It took me some time to realise that you don’t need super-high density meshes to print ok- most of the detail gets smeared by the printer anyway…