Tangent Sketch Constraint Problem

[Anonymous]

I'm unable to apply a tangent constraint to the circle and construction arc as seen in the screencast.  The problem doesn't seem to be related to the number of constraints, as I can add the third tangent constraint to the circle and straight construction line to the right, but it won't work when I try to apply to the construction arc on the left.  Am I doing something wrong?

Thanks!

[Beyondforce]

Hi @Anonymous,

Have you tried first to create a tangent  to the construction circle and then to the other two circles?

Cheers / Ben
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[Anonymous]

Ben,

I have, with the same result.

[Beyondforce]

If you could please attach the file, I'll take a look at it.

[Anonymous]

Thanks @Beyondforce. Here's the link to the file.  Let me know if this isn't the correct way to share.  The issue is within the sketch named "Speedholes 2" under component Top Plate.

[TrippyLighting]

Very simple. the Dashed line you are attempting to make the tangent constraint to is in another sketch. 

The first two solid line circles are in "Speedhole 2", the dashed circle is in sketch "Speedhole 1"

You need to project the dashed circle from the one sketch into the other to be able to make a tangent constraint to it. 

[Anonymous]

@TrippyLighting, thanks for looking at it.  I'm certain that all the sketch lines/circles/arcs I'm trying to use are in Speedholes 2, though.  

[TrippyLighting]

You are correct. I've got to dig a little deeper 😉

[TrippyLighting]

The dashed arc is not really a circular arc but seems to be offset from a projection that is not perfectly circular.

This might either be a bug ( @jeff_strater ?) , or limitation of the tangent constraints. Tangents to "real" arcs and circles are no problem

[Anonymous]

>not perfectly circular

That's correct.  This seems to be the problem.  If I sketch a 3 point circle on top of the dashed arc (parabola?), I can use it for the tangent constraint and it works fine.  I'm curious to hear if it's a bug or known limitation.  Thanks for the help!

[jeff_strater]

Yes, this is correct.  Those dashed lines are not circles.  They are actually splines.  I haven't tracked down why that it, but my guess is the underlying model edge in the solid model is also not a perfect circle.  So, yes, this is a "limitation", not a bug.

Jeff

[jeff_strater · Accepted solution]

I understand now.  This hole was made by subtracting an angled tube from the plate:

So the edge is elliptical.

Then, later, the construction geometry in that sketch was made by offsetting the projection of the elliptical edge, and the offset of an ellipse in Fusion is a spline curve:

And Fusion does not support tangency to a spline curve (except at the ends of the spline)

Jeff

[Anonymous]

@jeff_strater, thanks for the info on tangency to splines.

[mroek]

@jeff_strater:

This is a limitiation that is quite annoying. Not being able to use tangency to splines (except for at the ends) is quite limiting. It seems that projecting geometry to a sketch often also makes the projected curve a spline (depending on what it was projected from), and thus tangency can't be used.

Are there any plans to improve on this?