Hello guys!

I would have a question about CNC milling, laser cutting and 3d printers. Moi can export shapes into them by STL format. there is only one things make me confusing namely the resolution. STL as based on polygon format and how do the machines handle the resolution of the curved surfaces? I mean will the result be polygonal surface so I can see tiny polygons on their surfaces too ? So can someone explain it a bit ?

Your cnc/laser should accept NURBS data and cut that.. This will be correct curves only limited if you machine is making straight lines instead of true curves and then that resolution is controlled at the machine controller/CAM software. This would be the iges, sat, step, 3dm exports. STL data is polygons and only "looks" curved if they are small enough... For the 3d printing, the "facets" will be visible if they are big. The smaller you make them, the less noticable. If you dont want to see them, then mesh the facets very small in the stl output dialoue

Here is a sphere being meshed at a low polycount



Here I set the divide larger thasn value to .1



This would make all the little facets be .1 at it's largest.. This would be hard to see on a 3d print of a sphere. You can make them smaller.

Hi andras,

> I mean will the result be polygonal surface so I can see tiny
> polygons on their surfaces too ?

Yes - if you use STL format the resolution will be fixed at the time you export. Like Burr shows above the "Divide larger than" setting in MoI can be useful for forcing polygons to be more finely diced throughout the shape.

Once they are reasonably small enough, it becomes difficult to notice them in the final result.

But if the process permits like with CNC, you should transfer your NURBS data into the CAM program so that it will be able to have the highest fidelity model definition available for it to calculate toolpaths off of. Most CAM programs will accept NURBS data in IGES or STEP formats.

3D printing though is based off of STL. Usually though the resolution of the print process itself is more noticeable in the final result than the polygonization.

- Michael

I would check with the outfit first. I've been able to supply the 3DM files for my rapid prototyping. They then add a sprue for molding while it's still a 3DM and then they handle the conversion to STL.

STL might one day be replaced or improved.

http://en.wikipedia.org/wiki/Additive_Manufacturing_File_Format

hey, thank you! I just thought only STL is supported for CNC machine. (sorry I am not competent in manufacturing) and so...
in this basis Paracloud should not be a right choice for manufacturing, that is only for making models, I think. :(
So, Grasshopper or GC ?! So difficult and I am so lazyyy.

Hi andras,
Most CAM software will be NURBS based, and support loadfing STL's.. In a NURBS environment, an STL will be a "Dumb Solid" (not editable). Some may support the polygon data too and manipulate it.

Whether the output of Paracloud generates what you want/need or not, is the question... Paracloud will make stuff that would be very hard to do with NURBS tools. Same with Polygon software... For certain types of stuff though, a poly model will not be a good model to use due to it's inaccuracies or size.

Hi andras,

> in this basis Paracloud should not be a right choice for
> manufacturing, that is only for making models, I think. :(

Well I guess it depends on exactly what you're doing - if the objects you are building are all made up of planar faces then having polygons for them would work fine.

Also I'm not exactly sure how Paracloud works - it seems that it can be used to generate curves as well if you use it in combination with Rhino or something like that... I'm not exactly sure though, but it seems to be showing curved surface output in Rhino in some of its literature.

- Michael

Hi andras,

you mentioned different devices you would use to prototype models created by MoI.
Generally, depending if these devices uses an SRP or ARP approach (if they subtract or add material), the model could be handled as an analytic geometry (in case of SRP prototyping), or as a mesh (ARP prototyping).
I says "could be.." because in fact, most of the CAM used for subtraction prototyping (milling, turning, cutting etc.), even if they are capable to import NURBS based 3D geometries (.3DM, .Iges, .stp ...), they convert the imported model into a mesh just after importing it. This creates a chordal error (tolerance) that normally can be defined using the preferences of the application.
The only program I know that really calculates a toolpath based on NURBS geometry without triangolation is SprutCAM, but maybe there are other apps capable to do it.
In case of ARP systems, I do not thin that actually there is an alternative to mesh-based format. But increasing the number of polygons you can acheive good results. Do not worry about the big size of the files: normally they can be handled without problems even if very big.

- Pietro