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Help creating a thread (nut and bolt essentially) that aligns both parts when tightened

morgin_blackmorgin_black Member Posts: 6
i understand the male thread but i don't quite understand how to do a top down design scenario of a female thread yet. i wish to have two parts screw together and align on a thread in the same place. multiple different ends will be screwed on and i wish them to all fit tight on the same axis.

i tried starting with a male thread and just extruding over to make the female but it wont work in the assembly




here is the workspace https://cad.onshape.com/documents/0636238f4d38df61fb6e3ee2/w/918435fe7a7d1af8c188b37b/e/aa98d01a0106f97e79164eb4
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  • morgin_blackmorgin_black Member Posts: 6
    im guessing if i want to model different ends to attach to the male i would have to recreate and entire thread for every situation and hopw the helix starts and stops in the same place, otherwise it could be fully up tight but still half a screw out.
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,801 PRO
    You should be able to use the same helix

    I would say boolean subtract them, but that would not be a proper thread.

    You can also use Thread Creator to reduce the workflow
    https://cad.onshape.com/documents/6b640a407d78066bd5e41c7a/v/845d049782179b9faee8b6e6/e/f8aea9e5c33e02eab0854a4f
  • konstantin_shiriazdanovkonstantin_shiriazdanov Member Posts: 1,002 ✭✭✭✭✭
    edited May 2019
    This is not a good idea from the constructive point, tolerances and backlashes of the thread are generally a lot wider then for the key slot and the simultaneous matching may happen only accidentally.
  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    edited May 2019
    Yes what @konstantin_shiriazdanov said.  :) Screw threads are done up to a certain torque setting, not to a position, for a reason. 

    Perhaps a method around that could be screw to a desired rotation and then use a separate lock nut to hold in place?

    Owen S.
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,801 PRO
    Yea, good point.
    We have never relied on threads being the same. So not used to the thought process of engineered thread position.


    I'm curious now, how is this handled when 3D printed threads or whatever get manufactured? is it a guess and check after it's made? Then tweak the rotation?
  • romeograhamromeograham Member Posts: 400 PRO
    The start position of the threads can (obviously) be set, and will not change between these two parts (if they're 3D printed).  Therefore you can expect that every time to put the parts together they will be about the same as last time ;)

    However, getting the tolerances of the printed parts just right would be tough - you'd need to design, print, check (adjust with files / sandpaper etc) and adjust to get the torque in the right range for your prototype application (hand-tight?). Each process has it's tolerance range, and for 3D printed threads the friction becomes the biggest issue (even if you have the dimensions correct). The "steps" created from the additive process usually need to be worked in some way to make the thread free-running. 

    Aside: (I had a good trick for a large custom thread I was prototyping on FDM: model with a little extra room in the thread - then drop in sandblasting medium and let the particles clear out the thread as I worked the parts together. Worked surprisingly well - without having to manually file smooth every inch of the male threads (can't really get in to mess with the female ones).


  • morgin_blackmorgin_black Member Posts: 6
    so everyone is saying it cant be done. it is impossible to have a thread alignment in onshape?
  • john_mcclaryjohn_mcclary Member, Developers Posts: 2,801 PRO
    no, they are  saying it is not a good practice in reality.
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