Strange behavior when joining 2 bodies.

[cdotrodrigues]

Hi all,

Here is a small exercise I was making and when I tried to join these 2 bodies a strange body was created. 

a) I selected the sweep body as "target" and the scaled torus as "tool";

b) If I invert the selection (select the scaled torus as "target" and sweep body as "tool") the join is perfect;

c) @Anonymous did find that the problem had to do with the scaled torus and if we rotate the torus in a way that the "base circle" of the torus get out of the sweep body the problem ends.

Posted in: https://www.facebook.com/groups/fusion360users

In attach you find some pictures and the Fusion file.

Hope **** helps to improve this awesome software.

Carlos

[jhackney1972]

I do not see the issue, as described by your screen captures.  The Combine works fine using either body as the Target or Tool Bodies.  Of course the Appearance will be used from the one you select as the Target Body but that is normal.

[cdotrodrigues]

You need to delete the last operation in the timeline (that is the combine problem). Then try to combine the rings. The shpere will be a separate body.

[cdotrodrigues]

You need to delete the last operation in the timeline (that is the combine problem). Then try to combine the rings. The shpere will be a separate body.

[jhackney1972]

I can replicate what you are talking about but to me it is irrelevant to your design.  Normally you would Combine the two sections of the ring band first anyway.  If you get the proper results with a different workflow it seems you can finish your work with out any problems.

[TrippyLighting]

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@cdotrodrigues wrote:

Hope **** helps to improve this awesome software.

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What makes you feel that the software has a problem, but modeling techniques do not?

I can see that effect clearly:

But I am not surprised by it. Once you scale the small ring, it turns from an analytical BRep to a NURBS surface (contained in a BRep) and then has 2 seams. One seam is circumferential and the other one is where I marked the screenshot in red:

In my version I have rotated the inner ring 90 degrees so the seams of the two rings are aligned, and then that effect is not present, regardless what is the target and the tool body.

Rotating the inner ring, allows the geometric modeling kernel to better calculate the intersection between the two surfaces. I have experienced similar things in other CAD systems, much more costly than Fusion 360.

Intersecting surfaces at such shallow angels is tricky and sometimes requires a little inventiveness from the user 😉

[cdotrodrigues]

I did combine the 2 bodies without any problem. Just swap the target and tool and Fusion combines them. I´m not searching for a work around. I´m just presenting a problem that must be solved in the future by the autodesk team. I know that many problems need to be solved but my point was just to show this one. Perhaps this is not a big problem but it may bring some problem for other users or projects. Anyway thanks for your help.

[jeff_strater]

This is a faceting/graphics issue.  The geometry is fine, but the combined body is incorrectly split into triangles for display.  The usual methods for dealing with these issues (display detail control), however, did not fix the problem.  So, I had to resort to Split Faces.  Select the combined ring body:

and the XZ plane as splitting plane:

and the result is much better:

It probably doesn't matter what plane you choose, just something that forces the faceting algorithm to see the geometry differently will help.  Fixed model attached