Help with threading a cylinder

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Help with threading a cylinder

Postby garya » Thu Apr 11, 2019 9:53 pm

I'm having trouble cutting threads into a cylinder. I am trying to use method #3 in the Thread for Screw tutorial. But the resulting shape doesn't appear to be cut properly.

I defined the helix path and the shape to cut, then using part wb did:
Select Nozzle object
<Ctr>l-Select Sweep object
Click "Make a cut of two shapes" button

I'm using a 0.18 about two months old:
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.dace2f39cf
Build type: Release
Python version: 2.7.15
Qt version: 4.8.7
Coin version: 3.1.3
OCC version: 7.3.0
Locale: C/Default (C)

Thanks for any hints...
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Re: Help with threading a cylinder

Postby HarryGeier » Fri Apr 12, 2019 7:39 am


make the shape a little more away from the rotation center, then it does work:
2019-04-12 09_38_16-FreeCAD 0.18.png
2019-04-12 09_38_16-FreeCAD 0.18.png (13.07 KiB) Viewed 158 times
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Re: Help with threading a cylinder

Postby kisolre » Fri Apr 12, 2019 7:57 am

First, you should make the operation with the Body and not its feature. Now it gives "Link go out of scope"- see the red arrow:
LinkOutOfScope_01.JPG (139.94 KiB) Viewed 154 times
Your error is with the way OpenCascade kernel handles coplanar surfaces which sometimes gives errors like that. Increasing the outer diameter of the helix cut a tini amount will fix that. If you need the proper position of the cut you might want to dimension the inner point of the triangle to proper place which will make the proper cut
CoplanarFix.JPG (129.96 KiB) Viewed 154 times
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Re: Help with threading a cylinder

Postby garya » Fri Apr 12, 2019 8:14 pm

Thank you both. I read the bit about coincident edges causing problems but didn't recognize it as a problem since I was cutting and not fusing.
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Re: Help with threading a cylinder

Postby NormandC » Sat Apr 13, 2019 2:44 pm

Hi Gary,

You started with a PartDesign Body, you do not need to make a Part Sweep then a Part Cut: it's much more efficient to stay in the PartDesign workbench, you can simply use a Image PartDesign SubtractivePipe, so you do in one step what the Part tools take two, and you have a cleaner tree.

In the attached file, I recreated Sk_Thread because I could not move the existing sketch to the Body, and did not bother figure out what was preventing me from doing so, what with the expressions and all.
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