TechDraw - section view through a hole - problem in the center

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UR21
Posts: 39
Joined: Tue Nov 23, 2021 5:12 pm

TechDraw - section view through a hole - problem in the center

Post by UR21 »

Hello,

I modelled a simple pencil sharpener with WB PartDesign and try to represent it with WB TechDraw. (latest FC-Version)

My problem is a section view. It works fine, as long it's outside of the center of the two holes (cylindric made by pocket and conic by groove).
PencilSharpener - SectionView with Y3-Problem.PNG
PencilSharpener - SectionView with Y3-Problem.PNG (165.41 KiB) Viewed 1471 times
In the screenshot "Section - 001" is OK, but "Section -" shows the grooved grips, which are outside of the sharpener and shouldn't be shown in a section view.

"Section -" works correct, when I
- change Property - Section - Section Origin - Y = 2,9 or Y = 3,1 (instead Y = 3 in the center of the holes)
- disable the view of the grooved grips (see "Section - 001" in the screenshot).
- delete the cylindric hole (Pocket002)

When I delete the pocket for the blade on top of the sharpener (Pocket001) other negative effects take place and the inside parts of the section views change.

Do you know where the problem is?

Thank you!
---------------
OS: Windows 10 Version 2009
Word size of FreeCAD: 64-bit
Version: 0.20.26155 (Git)
Build type: Release
Branch: master
Hash: 0926a4148bcff11249fd4f56bc30256102ffe105
Python version: 3.8.6+
Qt version: 5.15.2
Coin version: 4.0.1
OCC version: 7.5.0
Locale: German/Germany (de_DE)
Attachments
PeniclSharpener - SectionView with Y3-Problem - reduced.FCStd
(183.47 KiB) Downloaded 28 times
Last edited by UR21 on Mon Dec 06, 2021 5:57 pm, edited 1 time in total.
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papyblaise
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Re: TechDraw - section view though a hole - problem in the center

Post by papyblaise »

you do Y = 2.7mm it's OK
Y = 3 it doesn't work: coplar problem :?:
Attachments
PencilSharpener.FCStd
(156.93 KiB) Downloaded 23 times
PencilSharpener.PNG
PencilSharpener.PNG (62.19 KiB) Viewed 1399 times
chrisb
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Re: TechDraw - section view though a hole - problem in the center

Post by chrisb »

UR21 wrote: Mon Dec 06, 2021 3:28 pm When I delete the pocket for the blade on top of the sharpener (Pocket001) other negative effects take place and the inside parts of the section views change.
TechDraw operates - of course - on the generated geometry and is thus affected by the topological naming problem.
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UR21
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Re: TechDraw - section view though a hole - problem in the center

Post by UR21 »

papyblaise wrote: Mon Dec 06, 2021 5:36 pm you do Y = 2.7mm it's OK
Y = 3 it doesn't work: coplar problem
Thank you for your answer!

Y=2,7 mm OK, Y=3 mm not OK, that's it.
But what is "coplar probleme"?
Last edited by UR21 on Mon Dec 06, 2021 6:03 pm, edited 1 time in total.
UR21
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Re: TechDraw - section view though a hole - problem in the center

Post by UR21 »

chrisb wrote: Mon Dec 06, 2021 5:52 pm TechDraw operates - of course - on the generated geometry and is thus affected by the topological naming problem.
TNP in TechDraw is no good news, but in my current question it's a minor problem.

Thank you for this information.
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papyblaise
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Re: TechDraw - section view through a hole - problem in the center

Post by papyblaise »

Sorry : coplanar problem
UR21
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Re: TechDraw - section view through a hole - problem in the center

Post by UR21 »

papyblaise wrote: Mon Dec 06, 2021 6:17 pm Sorry : coplanar problem
No problem, I thought, you did mean it.

But what is the problem?
chrisb wrote: Mon Dec 06, 2021 5:52 pm TechDraw ... is ... affected by the topological naming problem.
UR21 wrote: Mon Dec 06, 2021 6:02 pm in my current question it's a minor problem.
To be exact: In the moment this is NO problem for me.
My Problem is: How to get the Section View in the center of the holes?
Maybe without tricks 'n' cheats?
UR21
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Re: TechDraw - section view through a hole - problem in the center

Post by UR21 »

papyblaise wrote: Mon Dec 06, 2021 6:17 pm coplanar problem
OK, I found the explanation of the problem in "Round corner minus Cylinder inverts Body" (https://forum.freecadweb.org/viewtopic.php?f=3&t=64315).

As far as I understand: The case is, that the sketch of the cone is coplanar to the section line (section plane). The problem is, that the kernel of FreeCAD can not handle this case (always) correct. And the solution (for the user) is to move the section line a small distance.


Thank you for your notes!
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onekk
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Re: TechDraw - section view through a hole - problem in the center

Post by onekk »

In some case this is related to the "seam" of the shape.

FreeCAD has to compute some "lengths" at the intersection point, but as cylinder have 3 faces, top, bottom, and external "face" that is a sort of "rolled face" around the cylinder, there is the seam, in this point some "lengths" maybe related to tangents, or similar things, gave some "undefined" or "impossible" values (tangent has similar "non calculable" points).

Sometimes if this is the case, a simple rotation around axis, to move the seam away from this intersection points, will make things "work as expected".

But I think that this is not explained in documentation yet, or maybe if is cited is not very "visible".

Sadly I can't be more precise, but there were some discussion some time ago, and I'm using my "memory impaired" mind so reminding is not very precise.

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Carlo D.
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Shalmeneser
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Re: TechDraw - section view through a hole - problem in the center

Post by Shalmeneser »

In your example, a revolution of less than 360° erase the seam but the problem continues.
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