Attaching a sketch to an Additive Helix

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chrisb
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Joined: Tue Mar 17, 2015 9:14 am

Re: Attaching a sketch to an Additive Helix

Post by chrisb »

It seems to be an issue with the PartDesign helix, perhaps with its concept. Using a Part helix, it is possible to attach the section with FrenetNB to the helix which means that it is appropriately tilted.
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user1234
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Re: Attaching a sketch to an Additive Helix

Post by user1234 »

Workshop_Notes wrote: Mon Feb 12, 2024 12:34 pm If you want the pipe to come out straight, would you not need to put a small circular arc cross section between the end of the helix and the start of the straight piece?
That is true. I meant, that there is a difference between normal to main axis as the sketches or normal to the curve of the helix. This was not explicit enough from my side.

For example when you cut the helix normal to the curve, yours is a circle, that from the op is not a circle (the b-spline near form OCCT aside). Just said, your model have a very good data quality (precision).



Workshop_Notes wrote: Mon Feb 12, 2024 12:34 pm I would be grateful if you could explain how I might join the three individual sweep paths together in the attached. It seems wrong to have to make three sweeps and then union them together.
That depends extremely on your preferred workflow and more on the usecase. For example i edited a little bit yours for PartDesign. But there are also much other ways in (like in Part) to execute it.

2024-02-12_14-33.png
2024-02-12_14-33.png (194.09 KiB) Viewed 240 times
Helical pipe extended_edit.FCStd
(43.43 KiB) Downloaded 5 times



chrisb wrote: Mon Feb 12, 2024 12:40 pm It seems to be an issue with the PartDesign helix, perhaps with its concept. Using a Part helix, it is possible to attach the section with FrenetNB to the helix which means that it is appropriately tilted.
Maybe. But also there seems an issue, how the helix is generated. Note: i am not a programmer, my C++ skills are very very limited. But when i read the FeatureHelix.cpp, the Helix::generateHelixPath i do not see, that the derivative or curvature is respected in the spline generation at start point and/or end point. Maybe with this it works much better, since the curve starts with a wrong inclination. Maybe i am totally wrong. Maybe a developer can share more insights.



Greetings
user1234
domad
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Re: Attaching a sketch to an Additive Helix

Post by domad »

Greetings to the Community!
A quick test (obviously flow can be optimised) to model the helical tube, in which the junction point of the circumferences, which create the annular section of the tube, have been rotated upwards in order to limit the appearance of artefacts in the rendering of the helix .
I would like to point out a strange behavior of the "Create additive helix" function:
- it is not clear why the "sweep-helix" does not start exactly from where the sketch/section is positioned, but a pitch lower;
- if you set the "Map reversed" parameter to "true", it works, obviously starting from the opposite side;
- if it moves along the "Offset Z" direction by a length equal to the external radius of the tube section, plus 2 hundredths of a millimeter then it works.
Attached is the helical tube complete with terminals and the tube without the terminals to be able to test the strange behaviors described above. To replicate the strange behavior, move the "Offset Z" mapping of the Sketch002 to a value lower than 4.02, in particular if you bring it to "0" then the "sweep-helix" starts one pitch lower.

Code: Select all

OS: Linux Mint 20.3 (X-Cinnamon/cinnamon)
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.35858 (Git) AppImage
Build type: Release
Branch: main
Hash: 3a73f916ddab6a0af75265acef7cc87e44e4664a
Python 3.10.13, Qt 5.15.8, Coin 4.0.2, Vtk 9.2.6, OCC 7.6.3
Attachments
Helix Test_no_terminal_domad.FCStd
(246.04 KiB) Downloaded 4 times
Helix Test_domad.FCStd
(461.38 KiB) Downloaded 4 times
Helix Test_domad.gif
Helix Test_domad.gif (867.03 KiB) Viewed 208 times
casterle
Posts: 37
Joined: Tue Nov 08, 2022 7:49 pm

Re: Attaching a sketch to an Additive Helix

Post by casterle »

user1234 wrote: Mon Feb 12, 2024 9:21 am
There are few things coming together.
Thank you for your detailed explanation.
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