[Part] Thickness with Tube object cannot be cut

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uwestoehr
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[Part] Thickness with Tube object cannot be cut

Post by uwestoehr » Sun Nov 22, 2020 1:50 am

I want to perform a cut operation on a tube on which I run a thickness operation.

This fails. I tried out other part primitives and they all work fine, only the tube object cannot be cut.
Here is my example file:
Boolean_tests.FCStd
example file
(26.96 KiB) Downloaded 13 times

Try to make a cut of the "ThicknessTube" with the Cube.
Cutting the tube alone works.

Werner, as implementer of tube maybe you have an idea why only tube is failing here? Do you think this is an OCC issue?
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TheMarkster
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Re: [Part] Thickness with Tube object cannot be cut

Post by TheMarkster » Sun Nov 22, 2020 4:48 am

CheckGeometry shows some self-intersections in the ThicknessTube object. Report view shows some other errors, too, but it might be I need to update FreeCAD.

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chrisb
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Re: [Part] Thickness with Tube object cannot be cut

Post by chrisb » Sun Nov 22, 2020 9:15 am

You used Face1 for the Thickness of the tube. That is here the outer face, perhaps due to different OCC versions. I don't know what thickness is supposed to do in such case. What do you expect?

You used a thickness of 1mm. That would make the inner circle vanish.

If I choose sensible parameters, i.e. the top face of the tube, and a thickness of <1mm, thickness succeeds.

Finally: please clean models before uploading from stuff not relevant to show the issue.


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tube_thickness_cb.FCStd
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uwestoehr
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Re: [Part] Thickness with Tube object cannot be cut

Post by uwestoehr » Sun Nov 22, 2020 2:41 pm

chrisb wrote:
Sun Nov 22, 2020 9:15 am
You used Face1 for the Thickness of the tube. That is here the outer face, perhaps due to different OCC versions. I don't know what thickness is supposed to do in such case. What do you expect?
The thickness operation is correct, the cut operation fails.
Here is a more simple file containing only the objects you need to reproduce:
Boolean_tests2.FCStd
simple testcase
(16.04 KiB) Downloaded 6 times
You used a thickness of 1mm. That would make the inner circle vanish.
No, the thickness feature ends correctly up with 1 mm thickness.
If I choose sensible parameters, i.e. the top face of the tube, and a thickness of <1mm, thickness succeeds.
But I don't want the top face. The thickness operation result is exactly what I want.

It seems OCC has problems because the tube is created already as boolean cut operation of 2 cylinders. After playing around it seems there is not much we can do to improve the situation.
drmacro
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Re: [Part] Thickness with Tube object cannot be cut

Post by drmacro » Sun Nov 22, 2020 3:25 pm

But, a geometry check on the thimble itself show it is bad to begin with :roll: :
Snip macro screenshot-f21110.png
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Re: [Part] Thickness with Tube object cannot be cut

Post by chrisb » Sun Nov 22, 2020 5:15 pm

I see now what you want to do.
uwestoehr wrote:
Sun Nov 22, 2020 2:41 pm
It seems OCC has problems because the tube is created already as boolean cut operation of 2 cylinders.
You are right with the interpretation of thickness in this case and with the cause coming from OCC, although I think the cause is a different one: The issue is not the tube being a cut, but rather that the end of the face touches the beginning, which causes the self intersections.
I created an additional slot in the tube and applied thickness to the slotted tube. Then it succeeds for small values of thickness. For bigger values we probably face the usual unsovable thickness issues with non rectangular shapes.

This object doesn't show errors and can be cut from the cube:
SnipScreenshot-f00574.png
SnipScreenshot-f00574.png (17.84 KiB) Viewed 62 times
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thickness_cb.FCStd
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