Why 3D offset cannot be applied on a Ruled surface?

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amuzeshi
Posts: 13
Joined: Tue Jan 14, 2020 7:08 pm

Why 3D offset cannot be applied on a Ruled surface?

Post by amuzeshi »

Hi
Here is my geometry (the file is attached):

Image
I can easily create an offset for the shell called "Root" as shown with a highlighted color in the images below:

Image
Image

Problem
When I create a solid from a shell which incliudes all faces, 3D offset ends up with this error:

Code: Select all

BRepOffsetAPI_MakeOffsetShape not done
Image
Image

How I can create 3D offset for the faces included in the compound called "Leaflet"?

Thanks

File URL: https://ufile.io/iji9u78d
Last edited by amuzeshi on Fri Jul 23, 2021 5:56 pm, edited 2 times in total.
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Shalmeneser
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by Shalmeneser »

No file, no image, no answer
emills2
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by emills2 »

amuzeshi wrote: Fri Jul 23, 2021 2:20 pm Hi
Here is my geometry (the file is attached):
...

Thanks
i don't see a file attached. also cannot see the pictures, except by manually going to the links, which i can manually copy/paste from the quoted text of the reply (cumbersome). Actually, i can right click, open in new tab on the broken image icon, much easier. Usually, it if it displays correctly in the post preview, it'll work, but if it doesn't display the image in the post preview, then it'll never work.

i think the relevant error message is here, in https://postimg.cc/xcv2Th20:
"cannot convert leaflets, because shape is not a shell"

that would seem to indicate perhaps you skipped a step? or you did the step, but it did not return a valid shell?

something else to note, offset typically fails if it requires a change in topology, i.e. a surface shrinks so much it wants to disappear. in those cases, it can help to make a tiny offset first, because it is more likely to succeed. This at least helps narrow the problem
amuzeshi
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Joined: Tue Jan 14, 2020 7:08 pm

Re: Why 3D offset cannot be applied on a Ruled surface?

Post by amuzeshi »

Shalmeneser wrote: Fri Jul 23, 2021 2:22 pm No file, no image, no answer
Thanks. I corrected the problem of images and added a URL for downloading the model.
amuzeshi
Posts: 13
Joined: Tue Jan 14, 2020 7:08 pm

Re: Why 3D offset cannot be applied on a Ruled surface?

Post by amuzeshi »

emills2 wrote: Fri Jul 23, 2021 2:32 pm
amuzeshi wrote: Fri Jul 23, 2021 2:20 pm Hi
Here is my geometry (the file is attached):
...

Thanks
i don't see a file attached. also cannot see the pictures, except by manually going to the links, which i can manually copy/paste from the quoted text of the reply (cumbersome). Actually, i can right click, open in new tab on the broken image icon, much easier. Usually, it if it displays correctly in the post preview, it'll work, but if it doesn't display the image in the post preview, then it'll never work.

i think the relevant error message is here, in https://postimg.cc/xcv2Th20:
"cannot convert leaflets, because shape is not a shell"

that would seem to indicate perhaps you skipped a step? or you did the step, but it did not return a valid shell?

something else to note, offset typically fails if it requires a change in topology, i.e. a surface shrinks so much it wants to disappear. in those cases, it can help to make a tiny offset first, because it is more likely to succeed. This at least helps narrow the problem
Thanks.
Actually I've already created the shell. Also the magnitude of offset is not so much that the problem of shrinking comes in. There is another difficulty with this model which I'm trying to find out.
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Vincent B
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by Vincent B »

Sorry but, the surfaces seems pretty trickky :? make crash my freecad many times here.
Do you have any blueprint drawing to redraw the part?
Attachments
Capture.JPG
Capture.JPG (28.38 KiB) Viewed 1273 times
emills2
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by emills2 »

amuzeshi wrote: Fri Jul 23, 2021 6:01 pm Actually I've already created the shell
i believe you, and there may be an object in your document that came from this shell creation operation, but the visible error in the report view in your pictures says:

"class 'Part.OCCError'>: Shape is not a shell
18:38:13 Cannot convert Leaflets because Shape is not a shell."

so to some degree, and whatever you may see in your model tab of the combo view, it appears you do not have a "good" shell. I point this out because if this is the case, then the problem doesn't lie directly with 3D offset, but the previous operation
GlouGlou wrote: Fri Jul 23, 2021 7:23 pm Sorry but, the surfaces seems pretty trickky make crash my freecad many times here.
as glouglou highlighted in his screenshot, a surface with 2381X2 Poles is very unusual, for what looks like a cylindrical section. this could in principle be very hard to 'stitch' to the next surface when forming the shell. so maybe the shell operation did its best, but returned an 'unstitched' shell along this seam
emills2
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by emills2 »

amuzeshi wrote: Fri Jul 23, 2021 6:01 pm I've already created the shell
i tried to make a new shell from the contents of 'leaflet' and i can't do it with shape builder.
aorticValveAndRoot-cannot make shell from components.png
aorticValveAndRoot-cannot make shell from components.png (287.72 KiB) Viewed 1159 times

Code: Select all

16:58:05  Traceback (most recent call last):
  File "<string>", line 1, in <module>
<class 'Part.OCCError'>: Shape is not a shell
16:58:05  Shape is not a shell
and now i see that "leaflet" at the bottom of the tree looks like a compound object, which is not a shell.
emills2
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by emills2 »

i was able to create an actual shell object from the two original half leaflets
aorticValveAndRoot-can make shell from 2 halfs.png
aorticValveAndRoot-can make shell from 2 halfs.png (292.26 KiB) Viewed 1153 times
emills2
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Re: Why 3D offset cannot be applied on a Ruled surface?

Post by emills2 »

but creating a shell from two halves across the creased seam fails to produce a shell
aorticValveAndRoot-cannot make shell across creased seam.png
aorticValveAndRoot-cannot make shell across creased seam.png (278.7 KiB) Viewed 1142 times
So the shell building tool, part of "PArt>Shape Builder" (official menu command name), with tooltip "advanced utility to create shapes"

does not accept your rotated copies. the match along the seam is not good enough. this comes from your building strategy (clone rotate etc, not obvious to me what you did)
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