Control point spline internal symmetry bug

[Benlorimore]

Hi all,

I was hoping for some help on an issue I cannot seem to solve. 

I am modeling a control point spline that has internal symmetry. I have it co-linearly constrained to a line for continuity and then have applied symmetry constraints to every control point of the spline across the centerline, which should ensure internal symmetry.  Yet when I pull up the curvature comb the curve is clearly not symmetric. I have triple checked and measured every point's coordinates and they are all perfectly symmetrical across the centerline, yet the curve is not... Any thoughts? is this a bug?

Screen recording attached

Thanks so much,

Ben

[jhackney1972]

Please attach your model because it will help the forum users troubleshoot your issue a lot better than a video.  If you do not know how to attach your model, open it in Fusion360, select the File menu and then choose Export and save the .F3D file to your hard drive. Then use the Attachments section of a reply forum post to attach it.

[TrippyLighting]

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@Benlorimore wrote:

Hi all,

I am modeling a control point spline that has internal symmetry. 

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Why would you do that ? 

[Benlorimore]

I am doing a revolve of the spline and I want the curve leading up to the center point of the revolve to have g3 continuity across the center line. Also for the curvature comb to be smooth throughout. When I make the control spline lock to a line or an arc on the other side of the centerline to ensure g3, I get massive peaks/valleys in the comb. I figured making a single smooth symmetric spline and then just revolving half of it would be the best way to get a smooth curve/curvature comb on the entire revolve. 

[Benlorimore]

Here is the file, thank you!

[TrippyLighting]

It does indeed look like a bug. @jeff_strater can you comment on this ?

@Benlorimore 

Use a fit point spline. There is no good reason to use the control point spline in its case. You used 10 control points for a 5-degree spline, which results in a multi-span spline, just as a fit point spline. No reason to overcomplicate things.

[jeff_strater]

interesting.  That does seem odd.  I tried to create another case, even in the same file, and was unable to do it.  Was there anything interesting about how it was created?

[Benlorimore]

Not that I can remember, maybe the order I constrained things? (I don't remember unfortunately)  I've made a few other control point splines with internal symmetry including the same one since and have not had the bug repeat. 

[jeff_strater]

OK, thanks.  We'll take a look at this model.  Maybe something will reveal itself...