bent torus sometimes has seam, depending on dimensions -- mysterious

jim_wilson436 · September 2021

I'm trying to model O-rings wrapped around cylinders. Some sizes end up with a seam. Does anyone know why?

For example, this one is fine:

Image: https://us.v-cdn.net/5022071/uploads/editor/xy/23fiwqowu6mb.png

but this one has discontinuous surfaces:

Image: https://us.v-cdn.net/5022071/uploads/editor/og/akyx1s4t9y8u.png

I thought perhaps sometimes the sweep can't follow the path without the profile "kinking". But in the example shown, the continuous example curves more sharply than the seamed one. I'm baffled.

Here's a test document:

https://cad.onshape.com/documents/7ecf97ee54d24898e02e7e0d/w/f6879db4855cc174419ba6c8/e/3ea7af25d6e710920939a3cf

If you can shed light on this mystery -- or even better, suggest a way to prevent the seam, I'd be grateful.

Cheers!

Jim

NeilCooke · September 2021

The edge is caused by the Parasolid kernel. By default, we try to remove any edges between tangent surfaces but that is a kernel parameter we have little control over. The surface should still be tangent but the math behind the surface causes the edge. It might cause some downstream feature errors if you are dependent on one continuous surface but otherwise it should not matter.

steve_shubin · September 2021

@jim_wilson436

this works

https://cad.onshape.com/documents/ae087562bcfb633f6359f580/w/e7df5a33585ca6e7ea04846a/e/151861782e4b275ea4ef170b

NeilCooke · September 2021

The edge is caused by the Parasolid kernel. By default, we try to remove any edges between tangent surfaces but that is a kernel parameter we have little control over. The surface should still be tangent but the math behind the surface causes the edge. It might cause some downstream feature errors if you are dependent on one continuous surface but otherwise it should not matter.