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Sweep with Guide Rail Incapable of Making Flat Side Surfaces

Message 1 of 5
123 Views, 4 Replies

Sweep with Guide Rail Incapable of Making Flat Side Surfaces

Hi, I'm having trouble determining if what I just encountered is a bug or known limitation of the sweep command. I have produced the same behavior in a complicated design I have as well as a short example file. I'll show pictures of the latter.


If you Sweep a profile along a path and with a guide rail, the side surfaces that are created will never be made flat. In the example, the profile features four sides, all of which are flat. The path is a straight line attached at one of the corners of the profile, and it is normal to the profile. The guide rail is also a straight line normal to the profile, but it's attached at a different corner of the profile. No stretching or scaling of the profile is done and the sweep is not extended with the "full extents" option (though the issue can be reproduced regardless of these settings).







You can inspect the resulting body to see that all surfaces appear flat, but you will find that the sides created by the sweep cannot be selected by the Offset Plane, New Sketch, or any other command that requires you to select a flat face. You must remove the guide rail to make it a regular sweep in order for the sides to actually be flat.




It seems like there's no check to see if the path and guide rail is coplanar. Of course, a guide rail that isn't coplanar to the path should cause the profile to twist, but that's not the case in the example I'm describing. There are other ways to make non-flat surfaces even with coplanar guides/paths/profile lines but I would think that the input I've given in this example should produce flat sides.


Of course, this example doesn't really show much of a practical use of Sweep. In my aforementioned "complicated" design, the offending sweep uses the "stretch" and "full extents" options but the shape of the profile and positioning of the path/guide would have me expect to see flat sides. The profile and path are highlighted:




Furthermore, this issue can happen with both a 3D sketch defining everything or if the profile, guide rail, and path are defined in their own sketches. The attached file of this example is available, but really you can also just try this and see for yourself.


So, bug or known limitation?

Message 2 of 5
in reply to: arkenix

Are the path and rail coplanar?

Message 3 of 5
in reply to: Warmingup1953

He said they are.


Considering that extrude will give flat sides, Sweep is not ideal for this example, and the complicated version with stretch is unknown, Sweep and Loft give similar results to the complained behaviour so limitation is my view.


Might help….

Message 4 of 5
in reply to: Warmingup1953

Asking about the final picture? Sorry, forgot to mention that the path and guide there are also coplanar.

Message 5 of 5
in reply to: arkenix

This is just a limitation of Sweep with Rail (and Loft).  Some geometries that should create planes do not.

Jeff Strater
Engineering Director

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