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Vertex on revolve axis

Hi Onshape community,

My project has a sketch with a point on the axis I'm trying to revolve around, but the revolve feature says it's self intersecting. I don't see anything self intersecting when I check the sketch.

https://cad.onshape.com/documents/a398f96ab77e7c2712b2088c/w/96b1384b7b0609deda5c3695/e/a8d9d3102e601e013ad41a0b

The model in question ^^^

Answers

  • Member Posts: 395 PRO

    did you make it public? I couldn't get in

  • Member Posts: 3

    Hi,

    Also beginner here. I am experiencing the same problem and it seems to be a bug. When point is on revolving axis full revolve cannot be created. I move point outside revolving axis just tiny bit and is OK.

  • Member Posts: 561 ✭✭✭

    Seems like this should work. I retraced the sketch image. Fully defined sketch with upper right vertex coincident with revolve axis. Full revolve fails. Revolve of 359.9 degrees is successful. - Scotty

  • Member Posts: 230 PRO

    This shouldn't need to work. Why are you trying to create infinitely thin geometry? What's your overall goal?

    Something infinitely thin is not possible to manufacture.

  • Member Posts: 561 ✭✭✭

    What resulted in the revolve is a solid with a very small wedge gap in it. Thus, I don't understand the reference to 'create infinitely thin geometry'. - Scotty

    Document (part studio 2)

  • Member, Onshape Employees Posts: 428

    If the vertex is right on the revolve line, the revolve would be infinitely thin at that point. This is called "nonmanifold geometry", and our geometry kernel disallows that.

  • Member Posts: 230 PRO

    A full revolve would create two faces which touch in their centres, where there is no edge.

    In real life if you tried to do this you would break through the material.

    By doing an incomplete revolve you are creating edges at that point, which necessarily has to be allowed. The two cases are topologically very different

  • Member Posts: 561 ✭✭✭

    Thanks for responding. So, intersecting a point with the axis results in no thickness i.e. no geometry at that point?

    . - Scotty

  • Member Posts: 3,256 PRO

    Bingo. That point results in non-manifold geometry, which the Parasolid kernel can't handle. There's a vertex which is both inside and outside at the same time, which isn't allowed.

  • Member Posts: 695 ✭✭✭

    Although technically not self intersecting. It's kind like asking a computer or calculator to divide by zero. Error

  • Member Posts: 561 ✭✭✭

    Good analogy. Thanks All. - Scotty

  • Member, Developers Posts: 1,314 ✭✭✭✭✭

    Also called a knife-edge. Something most CAD doesn't handle well.

  • Member Posts: 3

    Got it. Thanks for all answers.

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