Creating a body from a mesh

[greenwoods1462]

Hi all - I have posted similar questions before but struggling with importing a mesh.  Fusion 360 is brilliant but why does it make importing an STL and converting to a body so hard?   

I have attached my STL.   I have tried to smooth this using different mesh features but always end up with a mesh and not a body.

I am not looking for someone to just convert the file, I want to try and learn this properly so an overview of the approach you would take to convert would be useful.

The output I want to be able to treat as a body.

Many thanks in advance!

[TheCADWhisperer]

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@greenwoods1462 wrote:

... why does it make importing an STL and converting to a body so hard?   

I want to try and learn this properly so an overview of the approach you would take to convert would be useful.

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1. Why is the same geometry repeated twice?

2. Why is it not centered about the Origin?

3. What is the source of the stl file?

4. Have you closely examined the stl geometry? 

Did you notice that it is all faceted planar triangles and straight lines? Even planar faces are made up of multiple triangles.  

And there are no curves. Not one.  All straight lines and planes.

The way I would approach this might not be the proper way to create proper geometry - but,

I would use only as reference in creating proper geometry.

I would not use stl rubbish in my work.

Fortunately this geometry is pretty simple to recreate proper geometry from scratch.

Do you have Autodesk MeshMixer?

[TheCADWhisperer]

First thing I did was open in MeshMixer and delete duplicated geometry.

Export and then Open in Fusion 360 moving to center.

Then I did a Measure to get a sense of scale to check Units.

Because I don't know what I am looking at - I don't know what size I should expect.

Should it be 5mm or 5cm or 5inches?

Then I Generate Face Groups...

I then attempt to convert to solid and see anomalies.

Go back and go to Wireframe view and I see unexpected internal geometry...

Go to Section Analysis and what do I observe?

Start Deleting extraneous surfaces.

Uh oh, that's a problem...

[HughesTooling]

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@greenwoods1462 wrote:

Fusion 360 is brilliant but why does it make importing an STL and converting to a body so hard?   

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Are you trying to use the Prismatic option to convert this mesh? If you are the reason it doesn't work is because it's not a prismatic mesh. Fusion can only convert pretty simple meshes, fillets will tend to make conversions pretty much impossible. You can see in the image below how the fillets are making it hard for the face group calculation. It ends up with a single group rather than 4 faces, 8 fillets and 2 variable fillets. You could try create groups manually but from my experience you'll waste more time than it will take to model in Fusion from scratch.

[TheCADWhisperer]

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@greenwoods1462 wrote:

1.  but why does it make importing an STL and converting to a body so hard?   

2. I want to try and learn this properly so an overview of the approach you would take to convert would be useful.

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@greenwoods1462 wrote:

Hi all - I have posted similar questions before but struggling ...

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@greenwoods1462 

I would have expected an ongoing 2-way (or more) discussion based on the previous responses to your original post.

Where did you go?

1. It is hard because stl mesh is rubbish.  Even a cursory examination should reveal that it is all straight lines and faceted planar triangles.  No curves. Not one. Actually rather ugly geometry.  Most things in nature and man-made geometry are aesthetically pleasing forms. 

2. I am going to walk inexperienced new Fusion operator through reverse-engineering an stl for high quality fully parametric geometry in this thread (if the OP doesn't disappear). >>This discussion thread.<<

[greenwoods1462]

Hi CadWhisperer

Thank you for your help.   We had a holiday in UK/I so that kept me away from Fusion for a few days.

I have used this free utility to fix the STL https://www.formware.co/onlinestlrepair and it amplified the issues with regards to the original STL file.   

But I will read your attached link.   But your feedback did help.   In terms of using the colour coding for the mesh analysis, this is something I learnt from your response - thank you.

Why is it that Fusion does not give you the choice for a correctly formed STL to input as a mesh, body or component?  I understand the geometric arguement but given that so many people want to make changes or incorporate third party STLs, it may be a nice feature.

So the action is on me to read your link (that does still seem to work).

Once again thank you - you have helped me alot over the years.   For this particular model I will just redraw.

Michael 

[greenwoods1462]

Thanks Mark - I agree with your analysis - which in itself was very helpful.  I am going to redraw.

BTW I did find this free repair tool that seems to be able to fix STL that Meshmixer and Netfab struggles with.

It is freeware from some guys in Amsterdam.   Myabe useful to others.

https://www.formware.co/onlinestlrepair

[TheCADWhisperer]

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@greenwoods1462 wrote:

Why is it that Fusion does not give you the choice for a correctly formed STL to input...

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The issue isn't with Fusion (at least in this case).

Even the best stl is faceted rubbish, but most users that are creating this rubbish don't know what they are doing.

This particular stl isn't even clean geometry - as I have shown it has internal geometry that surely wasn't part of the design intent - the original designer simply missed this.  In my experience those who create stl are generally not very experienced.

Back in the last century we had a term GIGO for this.  Not sure that we are allowed to use that term now.