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Help with Screw Relation

c_harshac_harsha Member Posts: 15 PRO

I have a linear rail assembly (with two rails, 1 motor) as shown in figure. The screw has revolute mate with motor (different subassembly in same document), the carriage has slider mate with the rail (different subassembly in same document). I have placed all remaining parts like nut (not visible in image) fastened to Part-A. Part-A is fastened to the carriage. the motor and rails are fixed to same part in main assembly.

Note: Part-A is the part that slides on two carriages.

Now I want to achieve screw relation between screw and nut. When I use cylindrical mate between them, I have it as over-constrained mate. So, I try Screw relation between revolute and slider mates of screw and carriage respectively, I have a message saying 'screw relation requires cylindrical mate'.

can someone please help me achieve this screw relation and figure out the problem I am facing?  


  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 3,792
    Hi @chandra_yerra is it possible to post a link to the document? If you can't make it public, you can share it with me (with edit permissions) and I will take a look for you (ncooke "at" onshape "dot" com).  POst the URL here when it is public and/or shared with me, thanks.

    Director, Technical Services, EMEAI
  • c_harshac_harsha Member Posts: 15 PRO
    hi @NeilCooke, I can't make the document public. I shared the document with you though share feature.

    here is the link

    Thank you
  • nicolas_duhamelnicolas_duhamel Member Posts: 7

    I believe I have a similar problem. I have three parts (A, B, C), two of them (A and B) have a screw relation with the third one (C) (different pitch and direction), and they also have a slider relation together (A and B). I get an "overdefined" error but I don't understand why.

    Here's a link to my assembly : https://cad.onshape.com/documents/a20d9e10264ee291b5ec3d7b/w/4dca1bea0b3bbfc9615b3e6d/e/fb2d639fa8acbd3151a082a0?configuration=default

    I have also added ncooke "at" onshape "dot" com to the editors of this assembly.

    Thanks for your help !
  • jakeramsleyjakeramsley Member, Moderator, Onshape Employees, Developers Posts: 628
    hi nicolas_duhamel,

    Glancing over at your document, I believe the issue is that cylindrical 3 and slider 2 mates serve the same purpose, causing it to be over defined when adding in the rotation of the screw mate relations.  The Carré and the Barillet bas can't feasibly rotate, offset, and stay in alignment all at the same time.
    Jake Ramsley

    Director of Quality Engineering & Release Manager              onshape.com
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 3,792
    edited June 2019
    @nicolas_duhamel the limits on Cylindrical 3 were preventing it from moving - I removed them and now it works.
    Director, Technical Services, EMEAI
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