What is happening here with my surface sweep?

[u7120482]

I performed a surface sweep, sweeping a profile consisting of a single line around the edges of the other surface, and it's ended up with this strange clipping behaviour.

Normally I'd just go "weird graphical bug, huh" and move on, but it won't let me perform an extend on the edge, which I kinda need to do to tidy a few things up.

I tested it just sweeping along one edge, and it works fine -- no graphical clipping and the extend works as normal. It's only an issue when I select more than one edge for the path.

Does it have to do with the sharp corners?

[stiller.design]

Hard to say if you dont attach the model 

[u7120482]

How do I get the files to do that?

[laughingcreek]

export as an .f3d file and attach to post

[jeff_strater]

it looks to me like you have two surfaces that are overlapping.  It looks like "Z fighting" between two surfaces - one with the normal pointing outward (gray), and one with the normal pointing inward (yellow).  As @laughingcreek and @stiller.design requested, if you share the model here, it will probably be easy to diagnose it.

[u7120482]

Yup! That's what I was thinking as well, but I have no idea why two surfaces are being generated when it's just supposed to be one feature.

I've attached the .f3d file here. We're specifically looking at the surfaces generated by Sweep 7 in Component 4 (inside Component 1). Please excuse the messy model, this was meant to just be a lazy project for my spare time so I didn't bother with keeping it tidy.

[professor.secco]

Two or more surfaces coincidents...

[laughingcreek]

looks like a bug to me.  2 surfaces are being generated by the sweep.  maybe someone from AD will be along @jeff_strater ?

[jeff_strater]

I'm not sure yet what the problem is.  The projected curve that is the profile is listed as a type of spline.  If I replace that with just a line between the two projected end points, the sweep body is fine.  I'm wondering whether this spline somehow curves back around on itself, which could generate two faces in the same place.  But, that is just a theory at this point.  Do you happen to remember what you projected to make that curve?  Was it a single edge, or a face, or a whole body?

[u7120482 · Accepted solution]

It's a single edge from surface patch 11. I'm going to try doing it again, by only projecting the vertices of the edge, then drawing a line between the two resulting points. I didn't even know that that edge wasn't straight.

What it probably is, is a weird interaction between the spline, and the hard corners on the sweep path, as it only occurs after I select more than one edge along the path.

[u7120482]

Yup, that's fixed it! Still weird that it happened, though.

[jeff_strater]

there is definitely something weird about that profile curve.  If you do "break link" on it, it turns into an editable CV spline, but not one I'd seen before.  If you drag one of the CVs, you can make the curve do some weird stuff:

But, you are also right that the problem with the double faces only shows up if the path contains more than 2 segments.  I'm going to create a bug for this, and let the sketch/modeling team dig into it.  Definitely not something I've seen before...

[edit] created bug FUS-114818 for this issue

[u7120482]

Always an honour to find a bug! Although a little embarrassing to have my lazy halloween costume design enshrined in bug report form.

My bet is that the patch is creating a surface that is just subtly non-planar in a way that breaks some of the maths. There's a lot of freaky maths stacked on top of each other with this design.