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Split function causing unwanted geometry change

paul_berrypaul_berry Member Posts: 7 PRO
What is causing this <sweep> to lift off the path once I <split> it?....creating the gap...the white flat triangle between the blue part and the grey part.
I want to curve pattern a piece of the sweep along the same path, and use it for loft faces.  Later I want to duplicate the full sweep in order to <Boolean add> all the lofts together and have no facets popping up like this behavior causes. 

It seems to me that the sweep should stay attached to the path because it was completed higher in the tree and shouldn't "recalculate".

https://cad.onshape.com/documents/2fbd974e132e7ff733f3889b/w/84a46367be29d95f8a35bc80/e/a009762ff6d10f1993cde138



Best Answer

  • Alex_KempenAlex_Kempen Member Posts: 93 EDU
    Accepted Answer
    So, what you're seeing is actually a little bit different from what the model really is. The main reason for this is because circles and computers don't mix very well; accordingly, circles are generally rendered as multisided polygons, rather than as "perfect" circular bodies. This works pretty well under most circumstances, but can break down when parts are really small and/or when you zoom in really far.

    This effect can also be seen by zooming in on a point which is coincident to an arc in a sketch:

    The point is clearly not touching the arc, but this misrepresentation is purely visual, and Onshape internally understands that the point and the arc are touching, even if it renders them with a slight gap.

    Generally, the best way to tell if something is actually touching or not is to use the measuring tool. In your case, it shows that the rib is actually less than 0.000001" away from the inner part, so for all intents and purposes, they're touching. You can also see that the issue you're experiencing is visual in nature by manually turning up the tessellation of your parts, which you can change under appearances, but do note that even the best computers will still have weird visual things occur when you zoom in really close. I hope this clears up any confusion.

Answers

  • Alex_KempenAlex_Kempen Member Posts: 93 EDU
    Accepted Answer
    So, what you're seeing is actually a little bit different from what the model really is. The main reason for this is because circles and computers don't mix very well; accordingly, circles are generally rendered as multisided polygons, rather than as "perfect" circular bodies. This works pretty well under most circumstances, but can break down when parts are really small and/or when you zoom in really far.

    This effect can also be seen by zooming in on a point which is coincident to an arc in a sketch:

    The point is clearly not touching the arc, but this misrepresentation is purely visual, and Onshape internally understands that the point and the arc are touching, even if it renders them with a slight gap.

    Generally, the best way to tell if something is actually touching or not is to use the measuring tool. In your case, it shows that the rib is actually less than 0.000001" away from the inner part, so for all intents and purposes, they're touching. You can also see that the issue you're experiencing is visual in nature by manually turning up the tessellation of your parts, which you can change under appearances, but do note that even the best computers will still have weird visual things occur when you zoom in really close. I hope this clears up any confusion.
  • paul_berrypaul_berry Member Posts: 7 PRO
    I see what you are saying.  At one point I exported a part and it still looked rough, and acted as it appeared....but I can't reproduce it now, so I'll keep the curve appearance issue in mind and maybe never run into this again.  Thank you!
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