Seeking advice on Mesh to CAD surface workflows

Replies to This Discussion

Permalink Reply by Nik Willmore on February 24, 2016 at 8:57pm

T-Splines models are inherently smooth and the ZBrush ZRemesher can create efficient quad meshes from any exported mesh that can then be imported back into Rhino to create a T-Splines model that in turn will become a Rhino NURBS model in one step.

I assume you are creating mesh geometry in Grasshopper for some reason, instead of using NURBS?

Sorry this is the short iPhone answer for now but an upload of a model would help for a desktop answer.

Permalink Reply by Hayes Urban on February 25, 2016 at 12:59pm

Thanks for the reply.

Id rather not incorporate additional software in the work flow for both efficiency purposes as well as the cost of another application license.

Yes I am using Grasshopper to generate geometry mesh geometry. The reason Im using meshes is that that is the techniques used in most of the tutorials I have watched. It seems almost everyone converts a surface to a mesh at some point. If there is a NURBs only workflow that achieves similar results, I'm not aware of it.

My question could be rephrased; Should I use NURBS and avoid using meshes at all so as to maintain manufacturable surfaces? By manufacturable, I mean curve based geometry rather than faceted.

Permalink Reply by martyn hogg on February 25, 2016 at 1:54pm

It depends on the CAM software and method of manufacture. If the surfaces you are going to produce are to be CNC machined for example, and you use CAM Works, integrated with Solid Works then it would be better to stick to surfaces that can be imported well into Solid Works so the workflow from Solid Works onwards goes smoothly. Although Solid Works can import a lot of geometry I have found it is MUCH better if you do everything with things that were either created by Solid Works or that Solid Works is happy importing.

Importing meshes into SW is not much fun! Even importing IGS or STP surfaces into Solid Works can make the SW experience frustrating with complex surfaces, especially if you plan to use mould making plugins within Solid Works.

Sometimes having faceted geometry doesn't matter because the facets become blurred by the tool radius used when machining them if the tool radius is bigger than the facets (Assuming you will CNC mill the surfaces). Also the CAM settings used when creating toolpaths can blend faceting so it is not noticeable on the finished part.

I'm sure there have been some discussions on here about converting meshes to NURBS surfaces but I don't think it is simple. Hopefully someone can chip in with some advice on this and what the limitations are (i.e. it might work better on some geometries than others)

Permalink Reply by Hayes Urban on February 25, 2016 at 2:18pm

Thanks for your input, Martyn.

I understand the option to cut directly from a mesh. However, since I am working for a client rather than directly with the manufacturer, I want to minimize the amount of re-interpretation on the manufacturers side, as I will have almost no direct communication with the factory. Therefore I think its best to export smooth accurate surface data that can easily be imported back into Solidworks or some other mainstream CAD package.

Im beginning to wonder if I need to just work with NURBs only and avoid meshes altogether.

Permalink Reply by martyn hogg on February 25, 2016 at 3:19pm

Then perhaps look at the different ways to generate surfaces from curve networks and understand what would  be the best way to create a surface with the effect in the image you posted.

I still think it would be good to understand the method of manufacture... 3D printing prefers meshes (currently) and for small batch production 3d printing can be used to produce moulds so a mesh might be better... the manufacturer could end up converting your lovely NURBS surface back to an STL mesh to print the moulds!

Permalink Reply by Nik Willmore on February 26, 2016 at 12:53am

Rhino, including Grasshopper, minus a few plug-ins, is a rather crappy mesh modeler anyway! There's a huge knowledgebase on this forum and a switch to NURBS sounds logical since you are just following tutorials into the wrong jungle rather than being an advanced user using meshes strategically.

Permalink Reply by Hayes Urban on February 26, 2016 at 6:43am

Thanks, Nik

I'll start focusing on generating NURBs curves and surfaces from scratch.

If you think of any good tutorials on the subject, please point them out.

Thanks again

Permalink Reply by Nik Willmore on February 27, 2016 at 12:13am

I find the forum itself much more useful than formal tutorials since there's so many different solutions from different people. YouTube is fantastic too, but Vimeo has a lot of collections too.

Google image searches on the forum are useful as well:

site:grasshopper3d.com +Boolean +union +fails

https://www.google.com/search?q=site+grasshopper3d+com+Boolean+unio...