Offset twists the result

Is there a way to stop the offset twisting in this file?

offset.3dm (49.0 KB)


Have a look at the attached file - turn the layer on.

Depends how you want to offset it.

Opt 1. Offset in front view
Opt. 2 Patch to make surface, offset surface, duplicate the border, delete the surface


Andyoffset.3dm (379.5 KB)

Another way to do it is from the right view so that it looks correct in that plane but it gives you a very different result.

offset_02.3dm (455.5 KB)

Here’s my final hack.

Draw two circles, sweep and move the seam, or pipe and move the seam - copy the resulting edge.

offset_03.3dm (524.5 KB)

Looks like a fundamental bug in the Offset command.

Offset of nonplanar curves sometimes provides unexpecting results. I always avoid to make offset of nonplanar curves.

Yeah, could be. I was wondering what question it’s trying to answer… I find it really interesting to try to answer these questions. My first approach with project to plane I’ve just realised can be done by using offset normal to surface command, you learn something new everyday etc :slight_smile:

Following the pipe idea and seam as an offset solution I guess it could use the X and Y cross section of the pipe and place the seam at 45 degrees,or giving you an option of what direction and what angle?

Offset curve in 3D command?

I wonder if it could be approached like this as an option, assuming you could orient the plane perpendicular to the curve in question using the pipe curve solution above:

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After thinking about it some more, the definition of the offset of a non-planar curve is ambiguous without either linking it to a surface as done with OffsetCrvOnSrf and OffsetNormal, or other constraints. One possible constraint would be to make it a pseudo-2D offset. Project the curve to a plane, offset the projected curve. Then extrude the offset curve, and pull the original curve onto the the extrusion.

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Hi Kieth - rotate the curve so that it is in the WorldXY plane. I believe this is related to a Sweep1 and Pipe bug where things work ‘differently’ on non-planar curves.