I can't offset this projected curve

[walawa25]

I attached a screen shot: I projected a curve from the edge of a 3D surface on to a 2D sketch.  I now want to offset this curve on this new plane a few mm forward, but I can't select the curve.  It will highlight blue when I hover over it, but I cannot select it.  I tried just extruding it as a surface as a workaround in order to offset the new surface, but it wouldn't let me extrude the curve--even though it's from a flat plane.  

The weird part is: I've actually performed this exact action in Fusion 360 in the past with other designs and it never failed before.  Does anyone know what is causing this issue/how to get around it?

[davebYYPCU]

 I now want to offset this curve on this new plane a few mm forward, 

Projecting the original articles to the new planes will work as expected, but offset a 3d curve? 

Don't know that you can do that. 

Might help.....

[walawa25]

The curve is no longer 3D.  I projected a 3D edge to a 2D curve using the "Project" sketch tool.  The curve is now 2D on a 2D plane.  It should act as a spline curve now that it has been translated.  

[TheCADWhisperer]

Can you File>Export your *.f3d file to your local drive and then Attach it here to a Reply?

[walawa25]

Yeah, I'll attach it here:

[davebYYPCU]

I agree with you, should work but does not.

One for @jeff_strater

[TrippyLighting]

Generally, in Fusion 360, projecting a 3D curve onto a plane will result in completely broken curvature.

Offsetting a "good" 2D spline in the same sketch often enough will result in broken curvature but offsetting a spline projected from a 3D curve will utterly kill it.

I cannot even get a curvature comb on this curve at all.

[jeff_strater · Accepted solution]

Thanks, @davebYYPCU for pinging me on this.

I believe that the result of this projection is a degenerate curve, and that is why the offset fails (and also why the curvature comb fails, @TrippyLighting ).  If you look at the edge that was projected, on both ends, the edge comes in perpendicular to the sketch plane:

and, I think that this creates an illegal last span at both ends (two sets of coincident control points).  You can see that in the screencast where I break the projection link (creating just a normal CV spline).  Even then, offset does not work, but if I delete that illegal last span, I can, indeed offset the curve.  I am not implying that this is a workaround, just a technique I used to try to figure out what is going on.

The bug here is not Offset, but instead is Project - Project should never create these kinds of degenerate curves - at the very least, it should fail, and if not, should create a valid curve in all cases.  I created bug FUS-96583 for this issue.

[walawa25]

Thanks @jeff_strater 

By following the process you showed in the screencast, I was able to get the curve that I wanted. 

I figured that the projected curve might have been bugged, because I've been able to do this successfully in the past with very similar bodies and sketches.  Thanks for looking into this, and hopefully bug FUS-96583 is resolved soon.

[TrippyLighting]

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@walawa25 wrote:

Thanks @jeff_strater 

By following the process you showed in the screencast, I was able to get the curve that I wanted. 

I figured that the projected curve might have been bugged, because I've been able to do this successfully in the past with very similar bodies and sketches.  Thanks for looking into this, and hopefully bug FUS-96583 is resolved soon.

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While this might be a bug, the real bug is in your workflow. In Fusion 360 ( I don't see this in other CAD software I use)  Projecting 3D curves or edges into other sketches almost always results in curves with degraded curvature. They are usually not as degraded as this one, but they are degraded.

That can result in continuing problems with modeling.