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How to mate between a sphere ball and a rounded sphere groove in a cylinder

omri_romri_r Member Posts: 10
Hi!

I'm trying to mate between a sphere ball and a rounded sphere groove in a cylinder in a way such that the ball would slide only within the groove.

Both the ball and the groove have the same radius.

I tired to use the tangent mate, but it does not do the work (I'm not sure why).

It seems there is some overlap between the ball and the groove (see images below)

Any ideas how to accomplish that would be very appreciated.

https://cad.onshape.com/documents/c1fb23babb4668e97ce5a361/w/8cd120f13393056585a21bf4/e/74d56c1158535498da0cb145

Thanks!
Omri





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  • John_P_DesiletsJohn_P_Desilets Onshape Employees Posts: 51
    edited November 18
    @omri_r It might be easier to try and use a rack and pinion relation. Below is a quick gif of what I am referring to. 

    https://cad.onshape.com/documents/cefa2aff693213e49c73600e/w/c23e3a714b33eceace9f7ead/e/1a26b46dc5d55658f8df5884


    I created a revolute mate for the screw and mated it to the origin. 

    Next, I created a slider mate from the center of the ball to run parallel to the screw. The ball needed to be offset to the thread depth. 

    After I created a rack and pinion relation between the revolute mate of the screw and the slider mate of the ball. 

    Hope this helps!


  • omri_romri_r Member Posts: 10
    Thank you John.

    I'm newbie and tried to repeat what you did with minor tweaks to the depth of the groove and the pitch of the helix, and I don't succeed to achieve the same thing.

    See here...

    https://cad.onshape.com/documents/c1fb23babb4668e97ce5a361/w/8cd120f13393056585a21bf4/e/74d56c1158535498da0cb145

    The above is the first step of what I want to achieve in the end: This is three threads that revolve in a synchronous way and hold a ball between them like in the image attached below.

    Do you think the slider + rack and pinion mates done on all three threads would assist me achieve that?

    Thank you!
    Omri



    https://cad.onshape.com/documents/c1fb23babb4668e97ce5a361/v/345c1518ef86fd9edbcfbf07/e/74d56c1158535498da0cb145

    (the above link is done with the tangent mate but it does not work all the time and not accurate since there is minor overlap between the ball and the groove)
  • owen_sparksowen_sparks Member, Developers Posts: 2,484 PRO
    Nice :) ^^^
    Production Engineer
    HWM-Water Ltd
  • omri_romri_r Member Posts: 10
    Thank you @owen_sparks and @John_P_Desilets!

    I really appreciate your response and time you put to answer my question with much details!

    The timing is a big issue.

    I can "guess" what should be the timing for each screw. But it's a guess and it would never be accurate.

    Initially, when I tried the tangent mate, it (almost) solved for the right timing. And as you can see in the image below, the solution for the timing is some kind irrational phase between the screws.

    I want to be accurate since the next step would be fit a cogwheels on the shafts that would create this synchronized movement. 

    Do you have an idea how the timing or phase can be calculated from the assembly w/o guessing?

    Omri


  • owen_sparksowen_sparks Member, Developers Posts: 2,484 PRO
    There might be easier ways to calculate how to click the mates to bring the assembly into alignment but instead of that could to use the same ball profile  in the partstudio to sweep the profile of the shafts and build them with the correct initial orientation? Or at least build some sort of helper part that the shafts initialy mate to, to set the orientation, and then suppress that temporary mate?
    Production Engineer
    HWM-Water Ltd
  • omri_romri_r Member Posts: 10
    @John_P_Desilets, This is really amazing what you did here!

    Thank you very much! I really appreciate that non-trivial help.

    Can you share a link of the above so it would be easier to me to understand what you did? 
  • John_P_DesiletsJohn_P_Desilets Onshape Employees Posts: 51
    @omri_r   Here is the link to the document 
     https://cad.onshape.com/documents/a6e7be729c745ccfdc726535/w/640755938ea1d07b729e7d25/e/1b66f8404dc6f8d7b70bb968

    This is a rough mockup of what you are looking to do. Please let us know how you made out!


  • omri_romri_r Member Posts: 10
    This is really great!

    I followed it step by step. Currently just trying to understand what you did.

    Learning tons of new techniques and ideas how to accomplish things  :)  

    How did you calculate an offset value of 46.5mm? 
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