Why Subtractive-Helix cannot revert back to functional ? (Solved)

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FredCailloux
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Why Subtractive-Helix cannot revert back to functional ? (Solved)

Post by FredCailloux »

OS: Windows 7 Version 6.1 (Build 7601: SP 1)
Word size of FreeCAD: 64-bit
Version: 0.20.29177 (Git)
Build type: Release
Branch: releases/FreeCAD-0-20
Hash: 68e337670e227889217652ddac593c93b5e8dc94
Python 3.8.10, Qt 5.15.2, Coin 4.0.1, Vtk 8.2.0, OCC 7.6.2
Locale: French/Canada (fr_CA)
________________________________________
A Bolt Body is created ( FreeCAD file below )
Among other objects in the body, a Rod is created with a sketch on the XY plane and padded.
On the XZ plane, an equilateral triangle is created for the thread.
The triangle position is set using some constants embedded in a spreadsheet.
Then, the Subtractive-Helix tool is utilized to thread the bolt.
Things go well until triangle position is changed on the XY plane.
The triangle position is augmented to a value significantly further than the Rod diameter.
The result is not functional.
Following this change the triangle position is set back to the functional original value.
The result is that the Subtractive-Helix is now an Additive-Helix, there is no more thread, instead the inside of the bolt rod is emptied and the thread include material which originally was removed by the Subtractive-Helix.
The Questions:
Why it has become impossible to revert back to the original Subtractive-Helix result ?
Even if the Triangle sketch and the Subtractive-Helix are deleted and rebuilt, the final result remain an Additive-Helix with an empty bolt rod.
Why is FreeCAD retain the error even after defective objects are deleted and re-created ?
Attachments
Bolt.zip
(872.63 KiB) Downloaded 11 times
Thread.png
Thread.png (67.03 KiB) Viewed 761 times
Last edited by FredCailloux on Fri Aug 12, 2022 4:35 pm, edited 2 times in total.
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Shalmeneser
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by Shalmeneser »

(your version presentation seems weird for a 0.20)
(please never .zip because it's too much work and .FCStd is yet a zip format file)

Helix should not self-intersect.
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Bolt_SHALM.FCStd
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chrisb
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by chrisb »

FredCailloux wrote: Wed Aug 10, 2022 6:18 pm Why is FreeCAD retain the error even after defective objects are deleted and re-created ?
If there is an error shown in the tree by a small overlay exclamation mark "!" in a red circle, then this object and all objects depending on it cannot be recomputed. Thus their shape is not updated and you still see the state before the error occurred.

As Shalmeneser said: Please leave the FreeCAD infos in the format created by FreeCAD itself. The forum regulars know this format and can recognize at a glance what they need to know.
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Shalmeneser
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by Shalmeneser »

Small message at the top of the +/-/Helix window :
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Capture d’écran 2022-08-11 024934.jpg
Capture d’écran 2022-08-11 024934.jpg (23.71 KiB) Viewed 637 times
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FredCailloux
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by FredCailloux »

Shalmeneser wrote: Wed Aug 10, 2022 7:15 pm (your version presentation seems weird for a 0.20)
(please never .zip because it's too much work and .FCStd is yet a zip format file)

Helix should not self-intersect.
Thanks for those tips. presentation corrected.
As for the zipping of .FCStd, I did try to upload the original file but there was an error and didn't work, so I resorted to zipping it.
I'll give is another try without zipping on my next post question.

Now, for the meat of the subject: I saw this warning or notice "Warning: helix might be self intersecting".
I just did not understand the meaning and what to do to correct the warning, hence the question:
" Why is FreeCAD retain the error even after defective objects are deleted and re-created ? "
So, I guess my question should have been: What is the meaning of "Warning: helix might be self intersecting" ?
And, How to avoid it ?

Notice there is only one(1) helix in the object. How could it intersect with itself ?
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Shalmeneser
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by Shalmeneser »

self-intersection : one turn touch the next one. Sometime it's not a problem, sometime it is.
To avoid it : pitch must be greater (0.01 mm ?) than the maximum height of the form.

+/-/Helix is a complex function. You should avoid self_intersection and coplanarity (same dimension/positionq).
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FredCailloux
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by FredCailloux »

Referring to this quote: https://forum.freecadweb.org/viewtopic.php?t=57128
papyblaise wrote: Sat Mar 27, 2021 9:56 am as Bance says, you have self-intersection in many ways
we have already dealt with it dozens of times here, so it has to be said again
the diameter of the cylinder and the diameter of the subtractive pipe must not be equal
the starting profile of the thread must not be tangent with the generator of the cylinder
the height of the thread must not be equal or greater than the pitch of the helix
Is it correct to understand that the error in my sketch is that "the height of the thread must not be equal or greater than the pitch of the helix" ?
Last edited by FredCailloux on Thu Aug 11, 2022 12:47 pm, edited 1 time in total.
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Shalmeneser
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by Shalmeneser »

Yes, it's what I've done in my file.
So if you want a specific pitch, you modify the thread maximum height.

Helix can be PITA.
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FredCailloux
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by FredCailloux »

Shalmeneser wrote: Thu Aug 11, 2022 11:30 am self-intersection : one turn touch the next one. Sometime it's not a problem, sometime it is.
To avoid it : pitch must be greater (0.01 mm ?) than the maximum height of the form.
+/-/Helix is a complex function. You should avoid self_intersection and coplanarity (same dimension/positionq).
I changed the thread profile so that one layer never touches the adjacent one and it worked great!
Thanks for the explanation. :)
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papyblaise
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Re: Why Subtractive-Helix cannot revert back to functional ?

Post by papyblaise »

I surprise myself, I already answered this question 1 year and 4 months before it was asked :lol: :lol:
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