Bug with STL export on revolved body

[Anonymous]

I created this body by revolving a sketch.

When attempting to export to STL, strange things happen.

See the attached screenshots.

[TheCADWhisperer]

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

Can you attach the resulting stl file here?

[Anonymous]

Sure. Here they are.

The forum software won't accept the stl file so I added a .doc extension.

[TheCADWhisperer · Accepted solution]

Well, it appears that you have a valid solid body - but I would model it very differently.

Not sure why you used a Loft and then Moved the face rather than simply doing a single Revolve feature.

I noticed that your Sketch3 had an overlap in the pattern and from that discovered that you had a void in the solid geometry.

[Anonymous]

I know its odd. I already had the smooth tapered cylinder.

I've tried it with a single sketch revolve as well, unfortunately got the same behavior.

[eellenburg]

I think the issue is the four small overlaps in Sketch 3.  You need to select them when creating the revolve.

[Anonymous]

Not sure how those overlaps for there, but that was the issue.

Thanks for the help.

[Anonymous]

It's definitely a bug. I can reproduce it on a simple profile: 2 squares touched in the corner.

 No gaps, etc. If I revolve it I get the same weird STL, But if I make a cut in that body, STL is correct. See the screencast.

P.S. I can get this body just extruded it from 2 circle profiles. And the behavior will remain the same. So, it;s unrelated to revolving. It depends on the body form.

[mroek]

@Anonymous

The reason for the odd behaviour is that you're creating what is known as "Zero thickness geometry". If you try to chamfer or fillet the inside corner edge of that revolved shape, it doesn't even work (but Fusion doesn't throw any errors either). Now, if you made the two sketched squares overlap by a tiny amount, it would work as you expect.

I think Fusion probably could improve in this area, at least by throwing some errors to let users know that they have created zero thickness geometry that may/probably will result in unexpected things to happen later. Not sure if they'd classify this as a bug, though.

[Anonymous]

Then f360 should interpret this case as 2 independent figures and still produce relevant STL. In any case f360 should not do that it does now.

[mroek]

I guess you could argue it should, but at the same time you are in essence creating invalid geometry, so I think the better action from F360 would be to actually tell you that, instead of silently trying to hide your mistakes.  🙂

In any case, it is easy to avoid this altogether (revolve each of the squares to independent bodies, for instance), so I'm not sure it should be a priority for the F360 team. They sure have a lot of other stuff that needs attention.