Artifact at start and end interface of subtractive sweep

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
kishore
Posts: 77
Joined: Sat Jun 11, 2016 6:09 am

Artifact at start and end interface of subtractive sweep

Postby kishore » Sat May 15, 2021 10:17 am

I was creating a worm gear and I'm getting an artifact that I think is the result of some rounding errors. My question is how do I fix it or work around it? I considered sweeping over the same edge (circle) twice to overpass the artifact but I cannot select the same circle to sweep again. I know i can create a second circle sketch and use that as the second edge in the sweep

I am unable to attach the file due to file size of 2.1MB.
WormGear.png
WormGear.png (62.37 KiB) Viewed 321 times
OS: KDE neon User Edition 5.21 (KDE/plasma)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.24276 (Git) AppImage
Build type: Release
Branch: (HEAD detached at 0.19.1)
Hash: a88db11e0a908f6e38f92bfc5187b13ebe470438
Python version: 3.8.8
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.4.0
Locale: English/India (en_IN)
chrisb
Posts: 35932
Joined: Tue Mar 17, 2015 9:14 am

Re: Artifact at start and end interface of subtractive sweep

Postby chrisb » Sat May 15, 2021 10:34 am

If you followed all the tipps in the Thread for Screw Tutorial and the issue persists, upload the file to a publicly available file service (without the need to register for others).
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
User avatar
Willem
Posts: 1536
Joined: Fri Aug 12, 2016 3:27 pm
Location: Lisse, The Netherlands

Re: Artifact at start and end interface of subtractive sweep

Postby Willem » Sat May 15, 2021 10:45 am

It is difficult to guess, how did you make this, in Partdesign or in Part workbench. Did you use a Part helix or a Partdesign subtractive helix.
A common mistake is that the sketch is on the same angle as the split of the cylinder. Here an example of how it works
Attachments
subtractiveSweep.FCStd
(526.31 KiB) Downloaded 8 times
chrisb
Posts: 35932
Joined: Tue Mar 17, 2015 9:14 am

Re: Artifact at start and end interface of subtractive sweep

Postby chrisb » Sat May 15, 2021 12:03 pm

Thinking about it: it could also be a misaligned sketch. It is best to attach the section with attachment mode FrenetNB without any further rotation.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
kishore
Posts: 77
Joined: Sat Jun 11, 2016 6:09 am

Re: Artifact at start and end interface of subtractive sweep

Postby kishore » Mon May 17, 2021 7:28 am

I have uploaded the file here.
Willem wrote: Sat May 15, 2021 10:45 am It is difficult to guess, how did you make this, in Partdesign or in Part workbench. Did you use a Part helix or a Partdesign subtractive helix.
A common mistake is that the sketch is on the same angle as the split of the cylinder. Here an example of how it works
It is made in partdesign with subtractive sweep where an internal involute gear is sweeping around a cylinder. The sweep path is a circle that is concentric with the cylinder but since I require the profile to twist along its axis by one tooth angle, a suitable aux path is constructed as a helix.