Curves workbench weirdness?

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Olav
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Location: Netherlands

Curves workbench weirdness?

Post by Olav »

I'm just starting to explore the Curves workbench. In the example below I'm trying to make a transition between two solid objects (from Part Design, they are the blue bits in the picture) using the BlendSurface tool from Curves.

The goal is to create a solid from the curved surfaces, fuse it with the other bodies to create a single solid and then see if I can apply a thickness to it. But I haven't got that far yet.

FreeCAD 0.20_051.png
FreeCAD 0.20_051.png (229.65 KiB) Viewed 1418 times

As you can see one of the surfaces (Blend_Surface005 in the model) produces a lip or bulge near its top edge. Which seems weird to me because the surface above it doesn't do this and it should geometrically be the same, just mirrored.

What am I doing wrong?

Code: Select all

OS: Ubuntu 18.04.5 LTS (XFCE/xubuntu)
Word size of FreeCAD: 64-bit
Version: 0.20.
Build type: Release
Branch: unknown
Hash: d3800cc36b5271e59977b4a608cdc6ae6fa1cf65
Python version: 3.6.9
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.5.2
Locale: Dutch/Netherlands (nl_NL)
Attachments
curve_test.FCStd
(195.81 KiB) Downloaded 30 times
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Shalmeneser
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Re: Curves workbench weirdness?

Post by Shalmeneser »

It could be the orientation of some lines in sketches (clockwise or anti-...).
Olav
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Re: Curves workbench weirdness?

Post by Olav »

Sorry, obviously posted in the wrong subforum. Can I move this myself?
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Shalmeneser
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Re: Curves workbench weirdness?

Post by Shalmeneser »

Modifying the orientation of some lines give me another result. :o
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Corpus delicti 74.png
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chrisb
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Re: Curves workbench weirdness?

Post by chrisb »

Moved.
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Cekuhnen
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Re: Curves workbench weirdness?

Post by Cekuhnen »

I am close to say that the surface tools in FreeCAD are sadly very buggy

as you can see each command at one point creates a major issue
Screen Shot 2021-07-22 at 11.01.38 PM.png
Screen Shot 2021-07-22 at 11.01.38 PM.png (88.3 KiB) Viewed 1306 times
Screen Shot 2021-07-22 at 11.03.43 PM.png
Screen Shot 2021-07-22 at 11.03.43 PM.png (77.18 KiB) Viewed 1306 times

one tip: dont slice half rounds into quarter rounds
a circle in 4 edges is enough.
Screen Shot 2021-07-22 at 11.08.00 PM.png
Screen Shot 2021-07-22 at 11.08.00 PM.png (76.25 KiB) Viewed 1306 times
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zksmk
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Re: Curves workbench weirdness?

Post by zksmk »

I can't tell you what's specifically wrong with the blended surface other than that it's buggy, but I can suggest you a workaround if you need one. Here's the end result, looking as it should:
5.JPG
5.JPG (50.82 KiB) Viewed 1152 times
Here's how you do it. First delete the problematic surface. Then you have to select these two edges and use "create a ruled surface" from the Part workbench on them:
1.JPG
1.JPG (36.18 KiB) Viewed 1152 times
Then you select the edge on the left, use "discretize" on it, and then use "approximate points to NURBS curve or surface" on the discretized edge, all from the Curves workbench. If you just use the existing edge it will bug out, so this is how you create an identical copy. Repeat process on the edge on the right afterwards as well.
2.JPG
2.JPG (57.59 KiB) Viewed 1152 times
Now, you select your ruled surface and the two new edges, and use "sweep profiles on 2 rails" from the Curves workbench.
3.JPG
3.JPG (55.24 KiB) Viewed 1152 times
You'll get a point cloud called "sweep_2_rails" in the appropriate place. Now you just need to use "approximate points to NURBS curve or surface" on the cloud and the end result is the desired surface.
4.JPG
4.JPG (59.95 KiB) Viewed 1152 times
5.JPG
5.JPG (50.82 KiB) Viewed 1152 times
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Chris_G
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Re: Curves workbench weirdness?

Post by Chris_G »

Olav wrote: Thu Jul 22, 2021 2:54 pm As you can see one of the surfaces (Blend_Surface005 in the model) produces a lip or bulge near its top edge. Which seems weird to me because the surface above it doesn't do this and it should geometrically be the same, just mirrored.

What am I doing wrong?
Raise the number of Scale Samples from 3 to 6 or 7.
Then you can use all the visible faces to build a parametric solid.
Attachments
curve_test_fixed.FCStd
(315.96 KiB) Downloaded 27 times
Olav
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Re: Curves workbench weirdness?

Post by Olav »

chrisb wrote: Thu Jul 22, 2021 10:31 pmMoved.
Thank you.
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Re: Curves workbench weirdness?

Post by Olav »

Chris_G wrote: Fri Jul 23, 2021 6:00 am Raise the number of Scale Samples from 3 to 6 or 7.
Then you can use all the visible faces to build a parametric solid.
Thank you, that worked!

Would you know what "Scale Samples" actually means? Should I just always use higher values than the default 3? I can't find anything about this on the wiki page at https://wiki.freecadweb.org/Curves_Workbench.

Now of course the thickness tool fails on the solid because "BRep_API: command not done" and "Unknown OCC exception". But that's a different topic. Sigh.
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