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Self-intersecting loft / sweep

Is it possible to create such a geometry using sweep / loft function in Onshape?

Using such a set of sketches:

I can't figure out how to do that.
Am I missing something or that is a big flaw in functionality?


Best Answer


  • paul_chastellpaul_chastell Onshape Employees Posts: 117
    The specific issue in this particular case is that Onshape is trying to make a single path and it is that which is crossing itself and Onshape doesn't like that but Onshape will be happy with the final result. As Neil says, by sweeping with two sweeps using two paths that are not crossing each other you can achieve that result. See https://cad.onshape.com/documents/b2724ca437fdb4b7ea41abb3/w/266674bfc17c15439f8fe4d7/e/d7b17eb691374acf4f80888b
    Paul Chastell / VP of R&D / Onshape Inc.
  • paul_chastellpaul_chastell Onshape Employees Posts: 117

    Paul Chastell / VP of R&D / Onshape Inc.
  • piotr_smektałapiotr_smektała Member Posts: 5
    Well, Neil's answer says everything :-(
    Just an inherited property of the geometry modeling kernel.

    Model presented by me was just an example of a problem.
    It is pretty easy to create such a geometry using two consecutive sweeps.

    What I was thinking to use OS for, was something like this (this is a simplified example also):

    And in this case I'll have to use 3 sweeps and 5 sketches (2 of them (circular intersections) with dimensions calculated in advance) to create one solid body, instead of just 3 sketches and start/end diameters.

    Well, it's just not as simple in OS as in other tools.

    P.S. Well, tried to create such 3s 5s trick in the meantime and no success so far ;-(

  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    Could that be use case for a featurescript that splits your sweep path into many "micro-paths", executes "micro-sweeps" on each in turn and then Booleans it together at the end?

    Could possibly test for fail condition and say double the number of segments as see if it passes then?

    Owen S. 
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • paul_chastellpaul_chastell Onshape Employees Posts: 117
    I threw this together at lunch but I'm not happy sharing the document yet. Still, it is possible. The key is that the body can self-intersect as long as the faces don't. Hence the two lofts, one for the 'left' and 'right' forming a single solid part.

    Paul Chastell / VP of R&D / Onshape Inc.
  • MBartlett21MBartlett21 Member, OS Professional, Developers Posts: 1,845 PRO
    edited March 2019
  • piotr_smektałapiotr_smektała Member Posts: 5
    Paul, ... I can see the light ahead.
    Tricky, smart, maybe not applicable to more complex models but really encouraging to experiment with.
    Thank you so much for this remark about  body/face difference.
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