3D Pretzel - how to do?

[WHolzwarth]

I came so far, but now I'm stuck.

Thanks for hints

Walter

[jeff_strater]

Hi Walter,

The problem is that your pretzel self-intersects, and you cannot then convert to BRep.  You can see when you exit Sculpt:

The red shows areas of intersection:

The fix is to edit the TSpline until these intersections no longer occur:

Then it will successfully convert to BRep:

The editing process is just to use Edit Form and tweaking it until it no longer intersects.  Here is a screencast showing how to do part of it:  http://autode.sk/1QyiD7E

Hope this helps,

Jeff Strater (Fusion development)

[WHolzwarth]

Thanks for your comments, Jeff. I know the issue.

But in real life, each and every pretzel is overlapping in these regions.

I think, modeling improvements are needed for cases like this. I've made an attempt with Inventor 2016 RC, but I've failed already with the initial sweep.

Walter

[jeff_strater]

true enough - real pretzels do self-intersect.

About the only way that I know of would be to separate the self-intersecting areas into different bodies, convert to BRep, and then use Combine to create a single body.

Jeff

[WHolzwarth]

I've thought about that too, but I didn't find a way for doing this.

[Anonymous]

Hi Walter, I'm putting together some screenshots now for a decent work around for this.

Jesse

[Anonymous]

First I took your spline and made a construction plane along its path that is before the intersection area, made a sketch on the plane, did intersection of spline, made circle from that center, and then in Create Form did a loft from one circle to other.

Finished that form, then created a new Form and a loft from the same circle to 3rd circle, being sure there are same circumferential faces as first loft, and enough longitudinal faces as well to follow spline well.

I finished the second Form, then went back to edit first and as you did with Edit Form, I moved the end of the first loft so has desired overlap with second loft, also with it having an added close hole as you did.

In my case I then made a surface patch at the end of the second loft, so that I could then do a boundary fill.

Giving a single solid Brep body.

I forgot to do more cool mesh editing to give the pretzel some more interesting shape.

Surprisingly I did not have any problems with boundry fill.  If you do have problems, some things to try are Stitching any patch to adjacent loft, or as last resort boundry filling each loft seperately.  For the latter, you would need to patch each loft section first.  The individual solid bodies could then be joined.  But I did not need to do any of this.

Interesting stuff, thanks for this challenge!

Jesse

[WHolzwarth]

Thanks a lot, Jesse.

Do you think, that you can get a solution like this for all overlaps?

[Anonymous]

Yeah, it seems to work good.

Since everything was done in top level/parent component, to make a new copy of the one half, I right clicked on parent component Brezel2 and chose "Save copy as".  I was then able from the data panel to insert this as a second component.  Also, instead of trying to mirror, I just rotated it 180 degrees and then Edited Form to move the "tail" to the correct side for second half.  To join the two halfs, I did a Component Move, using point to point, from the center of one circle end to center of other circle end. 

I was able to Edit Form very well for both halfs, and to my happy surprise, when editing one, other was always visible (in ghosted fashion), regardless of ordering in timeline 🙂

Here I'm editing the first half, and to make a more dramatic bend, I added several new Subdivisions.

I was able to get something I was happy with quite quickly.

In order to do Boundry Fill, I first had to do a Stitch of the two halfs, where they meet, which surprisingly to me worked fine.  The point to point component move must have been spot on. 

A tasty looking pretzel if I do say so myself 😉

Jesse

[jeff_strater]

Nice suggestions, Jesse.  The Boundary Fill command is a good idea, since it is more tolerant of intersecting bodies.  Thanks for providing a great answer!

Jeff

[WHolzwarth]

Thanks again, Jesse

I'll make a new attempt, following your workflow.

Walter

[Anonymous]

Glad to help 🙂  Let me know if you have any questions!

Jesse

[Anonymous]

Thanks Jeff!  Boundary Fill fascinated me ever since first trying it.  And it can take a little time to compute, but can always get to work, even if have to just make two surfaces overlap some to insure a closed volume.

Jesse

[WHolzwarth]

This is funny stuff. I've tried for several hours following Jesse's workflow without success. Trying out other attempts, suddenly I got a valid body.

I don't know what I did - but ended with a result.

Comments for enlightenment are welcome.

Walter

[Anonymous]

Hi Walter, sorry to hear the challenge, but I've found that definitely goes with the territory 😉

My previous description was quite sparse.  I've attached the pretzel/brepzel, cleaning up the timeline, so it should be instructional to scrub the timeline to the start and go through it one step at a time, perhaps repeating each step yourself (there are of course some direct modeling actions in Form that will not be captured in timeline).  If you run into a snag for any step, you can then just mention which step number in the timeline you ran into trouble with so I can look into it. 

Once you successfully build a brepzel with no confusion, you can then start attempting variations in the workflow, preferably one at a time, so that if something doesn't work, can easily identify what that something is.

Jesse

[WHolzwarth]

Thanks for all your help, Jesse. But I think, it's time for comments from Autodesk.

I've looked at the timeline of my last attachment, trying to reproduce my workflow. In the end, I got solid bodies. But I don't know, where I've been stepping in the right direction.

Perhaps it's been in connection with the Snapshot command. But I don't know, how to invoke it at all. Suddenly it appeared.

So, please F 360 development: You've seen, that it's possible somehow.

But show me a way for doing that in a straightforward way, without all these trials and errors.

Walter

[Anonymous]

And thank you Walter.  I learned a lot going through the timeline of that amazing water pitcher you did.  And with this challenge I learned a lot too. 

It's great that Autodesk has really great people and helpful manner.  But it's also good that we help each other out, creating a healthy community and learning a lot in the process. 

Snapshots are interesting, and as discussed in this thread, may get an update in a near release.  Look at the post by Jeff on the second page, which gives a very good explenation for snapshots:

http://forums.autodesk.com/t5/design-and-documentation/assembly-quot-some-components-have-been-moved...

Basically, any time a component move is performed, that new position for the component/compnent coordinate system can be captured in the timeline as a snapshot.  If an operation is performed that needs to know the desired component position, it will use the snapshot position that comes before the operation event in the timeline, or if a snapshot has not yet been taken for a new component move, then the question will then be asked to take snapshot of current position, or revert to old position.

Good luck!

Jesse

[jeff_strater]

Sorry for the delay.  To be honest, I am as confused as you as to how you got that solid body in there.  I've been scratching my head about it all day.  I cleaned things up a bit, and activated the component "Brezel v5 (1)".  This is what I'm left with:

one Form feature, and one Base Solid feature in the timeline for this component:

The Form feature shows errors.  If I edit it, it shows a TSpline that is exactly the same as the TSpline:

If I immediately finish the form, I get no error, even though the timeline item has an error indicator (yellow) that shows that it self-intersects.

So, I have no idea how this solid got created.  If you have any recollection at all, I would really like to know.  I will keep poking around, and see if I can find out how you did this.

Sorry not to be of more help explaining your success...

Jeff

[WHolzwarth]

Thanks a lot for your test, Jeff. It's good to know, that even skilled people don't see at first glance, how that happened.

Fusion sometimes is confusing ..

[WHolzwarth]

Life could be easy sometimes. I can imagine, having Boundary Fill both in Patch and Sculpt environment.

Having this option, working with overlapping shapes would be no problem. I've spent some additional time reproducing my mysterious workflow, but I couldn't get it.

Splitting up into separate parts is just a time-consuming workaround.

Walter