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This boolean subtract with offset is not solving - help!

tom_augertom_auger Member Posts: 97 ✭✭
Hi friends, it's been a while but now I'm back and as always I have questions......

One of my most standard things for making 3D printed parts that fit into each other is to use Boolean Subtract with a small (eg: 0.3 mm) offset to create a bit of gap to account for the tolerances of FDM printing. Typically works a charm. I use it for things like threaded parts or even press-fit parts.

Well, here's my latest very simple threaded part - the inner part ("male") needs to subtract from the outer part to create the relief threading. However, if I apply a positive offset, even a tiny one, the boolean feature doesn't solve. Surprisingly, the opposite (negative offset) does work, but that's precisely the opposite of what I'm looking for.

Screen shot below and then a link to the doc if anyone wants to take a quick gander. As always, so greatly appreciated!



https://cad.onshape.com/documents/510bb745140070d8d7d5ce3a/w/83a9ab501d6696ead04ac9c6/e/4b95368fb7fda514f494f445?configuration=List_IWpyc5fQoT6y5H=Default
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Best Answer

  • tom_augertom_auger Member Posts: 97 ✭✭
    Accepted Answer


    I was able to solve the issue using three separate "Move Face" features - one for each "side" of the thread (upper and lower side of the "V") and then I had to offset the top face of the collar (in blue) as the inverse operation on the cap was not solving. Dimensionally I'm not pleased with that last piece but I like knowing that my approach is still more-or-less viable.

    But I'll probably remember that thread FS tool next time :)

Answers

  • alnisalnis Member, Developers Posts: 381 EDU
    I would take a look at the Thread Creator custom feature here: https://cad.onshape.com/documents/6b640a407d78066bd5e41c7a/

    It generally creates pretty well-behaved threads.

    Here's how you could modify your design to make use of it (reducing the feature count a lot:
    https://cad.onshape.com/documents/1c6c17d4576d0f7553bba4a6/

    General tips:
    • Fully define your sketches whenever possible--this helps a lot with complex geometry
    • Watch out for tiny sliver faces--these make offsets not work as well
    • There is generally a custom feature available to automate anything annoying
    Hope this helps!
    Onshape Intern | Get in touch: [email protected] | My personal site: https://alnis.dev
  • lougallolougallo Member, Moderator, Onshape Employees, Developers Posts: 1,955
    After a quick look it seems the valley in the thread when offset is disappearing and the overlap is causing the failure. You might consider using scale on the part but it might take some trial and wrror to match the gap you want. 
    Lou Gallo / PD/UX - Support - Community / Onshape, Inc.
  • tom_augertom_auger Member Posts: 97 ✭✭
    I would take a look at the Thread Creator custom feature here: https://cad.onshape.com/documents/6b640a407d78066bd5e41c7a/

    Thanks for the reminder Alnis! I have it installed but sometimes forget to use it. I also like doing things the "manual" way when I can because I always learn something new!

  • tom_augertom_auger Member Posts: 97 ✭✭
    Accepted Answer


    I was able to solve the issue using three separate "Move Face" features - one for each "side" of the thread (upper and lower side of the "V") and then I had to offset the top face of the collar (in blue) as the inverse operation on the cap was not solving. Dimensionally I'm not pleased with that last piece but I like knowing that my approach is still more-or-less viable.

    But I'll probably remember that thread FS tool next time :)

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