Mesh to T-spline Conversion failed

[Anonymous]

Hi all,

I'm trying to convert a quad mesh to T-spline, so that I may alter it in fusion before machining the model. I'm getting an error message of "Mesh to T-spline conversion failed" but no further information how to troubleshoot. My process is as follows:

- DICOM data from a CT scan is imported to Slicer to select the ROI, segment the bony anatomy and export an STL

- STL is imported into meshlab, where the polygon count is reduced to 9000 triangles by decimation

- model is converted to quad mesh by 4-8 subdivision in meshlab, and exported to obj-quad. 

- quad mesh obj is imported into new project in fusion 360

- "create new form" and select "convert" under utilities tab in the sculpt environment

- select the model and hit ok

- this is when I get the error. 

The model I'm trying to convert is here: 

If anyone can provide any insight, I'd greatly appreciate it!

Lee

[laughingcreek]

When people talk about a quad mesh, thisins't what they have in mind.  the mesh faces might each have 4 sides, but there is no edge flow or topology what so ever.  This isn't going to convert to a t-spline in this form.

[laughingcreek]

what type of edits do you want to make? there is probably a different work flow you can use.

[Anonymous]

Thanks for replying. There may well be a better workflow - I'm trying to teach myself all of this as I go. I have a couple of different things I'd like to do. 

1) make anatomical models. This involves taking CT scan data, making a 3D model of it, adding a pedestal and text labels directly on the anatomy, and machining from a solid using a cnc mill. 

2) similar to 1), but instead of engraving labels, I'd like to overlay a pattern of lines, something like a grid, on the imported model and machining that. Fusion360 is the only CAD/CAM software I've used and have access to.

I was able to get past the original error message by going back into meshmixer and adding a minimal thickness of 0.2mm in the "make solid" dialogue. That let me convert the mesh and enter the "edit form" environment.  I was really happy, but I found that it still won't let me finish the form due to multiple errors in the t-spline geometry. Autorepair doesn't do anything, and there are over a hundred errors - too many to go in and fix manually for the number of these I have to do. 

Definitely interested to hear about better workflows, or solutions to this. Thanks again!

Lee

[laughingcreek]

Rule of thumb, any workflow that involves converting a mesh to anything else in fusion is going to be tedious, problematic, and involve a lot of hacky approaches to get anywhere.  An in many cases you won't be able to get anywhere no matter what.   Your model is a good example of something that may be impossible to get into fusion in any workable form.  fusion just generally sucks at dealing with mesh models.

What I do in similar circumstances is bring in the mesh and use it as a visual reference only.  if I want to cut into it, for example put a hole in it, I place a brep cylinder representing my "hole" visually in the mesh.   export that as a mesh and bring it all into mesh mixer and do a boolean there.

[Anonymous]

Hi,

Thanks again. Yes, I'm finding that. This weekend has been an exercise in frustration - I assumed it was my lack of knowledge on this workflow, but it sounds like there are inherent limitations in what I'm trying to accomplish. 

Is there a better way of doing it? 

For example, I'd like to use a CT scan of an irregular object to create a model. I'd like to modify the object by milling it, which will require holding it in soft jaws in the vise. With a bRep model, I would just do a combine/cut procedure of the soft jaws using the model itself as the tool. I don't think I can use a mesh this way in Fusion, which is why I was trying to convert it to T-spline (and then bRep). 

I understand that working with mesh is easier in meshmixer or other dedicated mesh software. But, I need to be able to setup the CAM and mill these parts, and starting with the CT scan data is a prerequisite.  

I appreciate your help and suggestions! 

Thanks again

Lee

[TrippyLighting]

The way this object was remeshed (Voxel remesh in Blender for example) creates a quad mesh with very many poles (star points in Fusion 360). Such meshes generally don't lend themselves to conversion into T-Splines.

A different remeshing method is likely better such as the one offered by Instant meshes.

After conversion, such a mesh mesh might still need a some help ... 

[Anonymous]

Hi, 

Yes I was playing with instant meshes last night, and that's the obj I got furthest with. But, it does still create  many star points and many of those show as red error points. I'll need to play around with instant meshes options some more to see if that can be improved....

[laughingcreek]

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@Anonymous wrote:

...Is there a better way of doing it? ...

---

Yes.  do what I said in previous post.

1-clean up/repair mesh. insert into fusion

2-DON'T do any mesh conversion in fusion.

3-visually arrange the blocks you want to mill/print into soft jaws around the mesh.

4-export those bodies as meshes into mesh mixer (or some other mesh modeler)

5-boolean operations in the mesh modeler. 

6-fusion can do mill operations on meshes. so just bring your new meshes back into fusion for cam operations if that's how your going to do it. (we just 3d print the jaws on a sla printer)

[hfcandrew]

Why do you reduce the count to 9000?

Your attached model is already pretty low poly (low resolution) & blocky looking for what should be an organic shape. Plus fyi it is riddled with open boundaries and floating disconnected shells which its probably what is messing with fusion:

Just click auto repair all and then you won't have to 'make solid'.