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Offset subtracted Threads

Ben_NiewoodBen_Niewood Member Posts: 9 PRO
I downloaded a model of a part with some large threads on it. I'm trying to make a mating 3D printed part that can screw into the threads. I'd like to subtract the threads from my part for 3D printing and offset them slightly so that when printed they aren't too tight. However, when I try to offset the threads (both inside the boolean and after I do the subtract) I'm unable to. Any advice on how to make that work?
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Comments

  • owen_sparksowen_sparks Member, Developers Posts: 2,308 PRO
    If you post a link to your doc I'm sure someone will have a look for you.
    Production Engineer
    HWM-Water Ltd
  • philip_thomasphilip_thomas Member, Moderator, Onshape Employees, Developers Posts: 1,299
    Philip Thomas - Onshape
  • Ben_NiewoodBen_Niewood Member Posts: 9 PRO
    I tried using the offset option in that, it didn't work.
  • philip_thomasphilip_thomas Member, Moderator, Onshape Employees, Developers Posts: 1,299
    @Ben_Niewood - please post a public link and someone here will fix it :)
    Philip Thomas - Onshape
  • Ben_NiewoodBen_Niewood Member Posts: 9 PRO
    Here's the link: https://cad.onshape.com/documents/e992f2209e18098bcd9a3cdd/w/0e5c7ec872896c6686cf7d97/e/4c5c53c2b627eecab94a34b4

    This is the part I imported:

    I'd like to try to make threads that fit into both the top and bottom inner threads on that part.

    Here's the subtract I tried on the bottom threads:

    When I tried offsetting in both the boolean and after it didn't work.

    Thank you all in advance for the help!


  • mahirmahir Member, Developers Posts: 857 ✭✭✭✭
    @Ben_Niewood, your link is view-only, so I can't make an editable copy. I do have several suggestions, though.

    1. Offset a simplified version of the threads by removing fillets first. Then add the fillets back after using Boolean and/or Offset Surface to create the basic thread form.
    2. Don't offset. It's a tapered pipe thread, so the whole point is for the parts to interfere.
    3. Find out the specific size femaile pipe thread on the imported part and model the matching male thread from scratch. There is a featurescript for creating threads, but I don't think it can do pipe threads.
    4. Import a vendor part with the correct male threads and modify it as necessary.
  • Ben_NiewoodBen_Niewood Member Posts: 9 PRO
    Sorry about that and thanks Mahir! Those are great suggestions, I'll try them out. I also think I just made it public correctly so you should be able to make a copy now.

  • Ben_NiewoodBen_Niewood Member Posts: 9 PRO
    @mahir Also, I tried not offsetting the threads since, like you, I thought there was a chance it would work fine as is. But when I printed the part it wouldn't screw in all the way.
  • mahirmahir Member, Developers Posts: 857 ✭✭✭✭
    edited November 2017
    Do you have a requirement for the parts to screw in all the way? Usually NPT threads aren't screwed in all the way. They're screwed in to a certain torque spec or until air tight. If you're bottoming out, you can't be sure you actually have a good seal. Straight pipe threads are bottomed out, but that only works because they incorporate an o-ring for sealing.

    Also, to ensure sealing, I would smooth the surface of the 3D printed part by exposing it to acetone vapor. This will create a better sealing surface and also make the threads slightly smaller.
  • mahirmahir Member, Developers Posts: 857 ✭✭✭✭
    Here you go. I found a mating part on McMaster and modified it. That will be closer to a real pipe thread than using a boolean subtract.

    https://cad.onshape.com/documents/a92da9dbcce4f30edcaafb9e/w/573739918210262dfe8f403a/e/059b8d5159706e1b7c69c7ea
  • philip_thomasphilip_thomas Member, Moderator, Onshape Employees, Developers Posts: 1,299
    edited November 2017
    Philip Thomas - Onshape
  • mahirmahir Member, Developers Posts: 857 ✭✭✭✭
    Ah! I didn't notice that it was the nut that needed threads. I thought it was the blank nipple inside the fitting.
  • Ben_NiewoodBen_Niewood Member Posts: 9 PRO
    I do need threads on the blank nipple inside the fitting, the nut doesn't need threads (or it does in real life but I don't need to worry about making them). Sorry that was unclear. Thank you both for the help!
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