Having trouble understanding mesh conversion

[chrisQX8DX]

Hi all,

so i've been trying to reconstruct this stl file with the convert mesh function but i'm getting nowhere. Watched a couple tutorials, read the docs, tried out different settings ... always ends up in partial faces.

so i understood that you first have to generate face groups. i switched on the face group colors and it kinda looks like it's detecting the proper face groups judging by the colors:

but then on conversion i always end up sth like this:

i tried all different methods of conversion, simplifiying or cleaning up the mesh but haven't managed to produce a closed solid in any way.

what am i missing ?

[wersy]

Don't reduce mesh.

[TheCADWhisperer]

@chrisQX8DX 

Helical geometry is an issue between CAD conversions even when it it clean, and this is facted planar faces, so...

Are your intended units inch or mm?

What is the thread specification (appears to be non-standard)?

What is the source of the original geometry.

I would remodel from scratch using the stl only as reference.

[chrisQX8DX]

ah sorry forgot to mention i want it converted prismatic not faceted.

[TheCADWhisperer]

@chrisQX8DX 

Do you have the original stl file?

This would be easier to use if it was at the Origin (import will do that automatically).

[chrisQX8DX]

it's in mm but i have no idea what the thread is. it's a model from some 3d printing free models site. i don't really use STL at all but lately i've wanted to try using some of these free models to see if they can be converted and modded in fusion.

it seems like a pretty simple model so i was surprised to see i couldn't get any usable results.

[chrisQX8DX]

here is the original file

[TheCADWhisperer]

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@chrisQX8DX wrote:

1.    i don't really use STL at all but lately i've wanted to try using some of these free models to see if they can be converted and modded in fusion.

2.  it seems like a pretty simple model so i was surprised to see i couldn't get any usable results.

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1. To learn about converting stl models it might be best to start with your own models converted to stl and then back to solids.

That way you know the quality of the original model and what to expect in the conversion.

When I measure the dimensions of this geometry - none of the dimensions make logical sense (even allowing for conversion tolerances).

In my experience only about 10% if CAD users know what they are doing. That means you have a 90% chance of getting rubbish.  

For free stl - the ratio is much much worse (maybe I am only seeing the bad stuff posted here with issues.)

2. I have converted helical geometry from many different CAD softwares over the last 25 years.  To this day I see translators have trouble converting helical geometry. (And of course this issue is compounded with stl as there isn't ANY helical geometry - it is all coarsely faceted planar triangular surfaces.  No curves. Not one.)

Back in the last century we used to refer to the GIGO Principle.

I have had some stl files that convert beautifully, but it helps to start with high quality stl geometry.

[chrisQX8DX]

well it's just a random model, converting STLs is not really sth i'd do regularly, faceted poly models is so 90's, haven't used one in decades... but i think it's a pretty simple model: a box with a filet on the top edges sitting on a thread with a hole in the middle, despite the bad geometry the features are pretty well defined in most places for the conversion engine to approximate it i would have guessed. so to come back to my original question about the face groups and colors, when i play around with the values in the face groups panel it looks like fusion is picking up adjacent faces of those features. If you look at my first image, the colors of the different features are well defined, so i don't understand what i have to look for in the colors in order to generate geometry following each colors faces. Looks like it picks up all 3 helixes of the thread but only converts the green one but the red one looks pretty well defined.

@chrisQX8DX -  this post has been edited due to Community Rules & Etiquette violation.

[TrippyLighting]

The resolution of this mesh is not good enough to allow conversion into a solid. 

After the first round of creating face groups, you can clean that up by going into Modify->Direct edit:

Once in direct edit mode, you can make the brush smaller so that it allows you to select individual polygons. You can brush-select what needs to be in a face group and then assign the selection to a face group.

Even when all polygons are assigned to the proper face groups, the conversion fails to produce surfaces for the helical features.