Round corner minus Cylinder inverts Body

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Netaction
Posts: 2
Joined: Mon Dec 06, 2021 10:47 am

Round corner minus Cylinder inverts Body

Post by Netaction »

Hi!

I have a Body with simple rotated Shape. It is cut by a Pocket. As soon as the rounded corner (made with circle) touches the Pocket, the cylinder jacket (side of the cylinder) becomes missing.

If I add more structures to the Body, they vanish as soon as the Pocket appears. If I add more pockets, they are filled even if they are not in vicinity of the first pocket! So it seems the overlap between round corner and Pocket leads to inversion of larger Body parts.

Freecad version 0.19 Windows 10.

Is there any logic for this behaviour I should pay attention to? Or is this just a bug?

Thomas
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Screenshot 2021-12-06 120313.jpg
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Screenshot 2021-12-06 114636.jpg
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bugtest.FCStd
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jmaustpc
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Posts: 11207
Joined: Tue Jul 26, 2011 6:28 am
Location: Australia

Re: Round corner minus Cylinder inverts Body

Post by jmaustpc »

you have created an invalid solid, your "nut" has a tangent face with the hole in the rotation. Just try changing the radius in the Nut sketch and you will see that it becomes valid. You can't have wall that becomes infinitely thin at the tangent intersection, hence the solid is not valid.
chrisb
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Joined: Tue Mar 17, 2015 9:14 am

Re: Round corner minus Cylinder inverts Body

Post by chrisb »

Netaction wrote: Mon Dec 06, 2021 11:07 am Is there any logic for this behaviour I should pay attention to? Or is this just a bug?
Both. It is a sort of bug in the geometric kernel, to which the FreeCAD developers have not much influence. You should avoid such "coplanar" problems as they are called here according to their first occurrences in Part workbench. These issues can occur on coplanar faces, just touching seam lines or similar. You can avoid them by moving the seam to a non critical position (doesn't apply in your case) or by leaving a small distance or a small overlap.
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Rana
Posts: 31
Joined: Tue Oct 01, 2019 6:37 pm

Re: Round corner minus Cylinder inverts Body

Post by Rana »

You can achieve the acceptable visualization with part module, though the geometry report may show invalid solid.Please see picture.
BTW, do you really need such thin edge feature for your project considering it's manufacturing and structural strength ?
Thanks,
Rana
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Netaction
Posts: 2
Joined: Mon Dec 06, 2021 10:47 am

Re: Round corner minus Cylinder inverts Body

Post by Netaction »

Thanks very much for the detailed explanation. I will try to avoid touching surfaces in the future.
jmaustpc
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Posts: 11207
Joined: Tue Jul 26, 2011 6:28 am
Location: Australia

Re: Round corner minus Cylinder inverts Body

Post by jmaustpc »

Netaction wrote: Mon Dec 06, 2021 11:04 pm Thanks very much for the detailed explanation. I will try to avoid touching surfaces in the future.
it's not a bug, think about it, it is impossible for it to exist in the real world, I mean you can't have an infinitely thin wall in the real world, so it can't be a valid solid in FreeCAD. :)
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