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1-Newbie

## Need Help with Spline Control

Is there a way to make a 2D spline tangent to some other entity, like a line or plane, at a point that is in the middle of the spline, rather than just an endpoint?  The attached picture shows an example of what I am trying to accomplish (easily achievable in SolidWorks).  I can make a line tangent to a spline referenced in a different sketch, but I can't make it work with a line and a spline that are in the same 2D sketch, nor can I make a 2D spline tangent to a line that is referenced from a different sketch.  The only workaround I've found is to use two splines, but that introduces some undesirable changes in curvature continuity that wouldn't be present if it were just one spline.

Note how the spline is tangent to the line in the middle where the red arrow is, and the curvature combs are nice and smooth.  It seems like there has to be a way to do this in Creo as well and I must be missing something; any help would be appreciated.

8 REPLIES 8
6-Contributor
(To:dw-2)

Sketch your spline with a point on the tangent line. Create an angle dimension by first selecting the spline, then select the point, then select the line. Change the value to 180

Thanks!  Although I now have to ask, is there another method that doesn't require adding in that additional spline point?  Or can it be done while using the control polygon to manipulate the spline rather than interpolation points?

17-Peridot
(To:dw-2)

I posted this idea as it would solve part of the issue.

please vote on it if you can.

Improve sketched spline manipulation

For those not able to access the Ideas section:

PTC Creo 3.0: Sketched Spline Manipulation - YouTube

6-Contributor
(To:dw-2)

With the polygon, if you make the middle span parallel to the line, then you can get close. Dimension the middle span to the reference line, dimension the end spans with angular dimensions. Tangency is still maintained while modifying the angles. The problem is if you have to move the endpoints. Then the spline moves off the line. I'm sure there's got to be some equation to relate the middle span dimension to the endpoints. If I have time I'll try to research it.

I've had to do that well. It kinda works as long as you don't make any changes down the road. It totally looks like it works, and that was enough for what I was doing.

17-Peridot
(To:dw-2)

I keep running into spline limitations in Creo.  This is an algorithm that's been around for ages and has never been optimized to more recent standard ways of manipulating them.  This is one area that needs some enhancement!

Had a similar issue when I tried offsetting a spline inside a sketch

17-Peridot
(To:TomD.inPDX)

Okay, yes, you can make the 2-point spline and fit the references around it using tangency.

When you go back and edit the spline, the references move.

1-Newbie
(To:TomD.inPDX)

Yes, I am able to do that.  The problem is that I was trying to (partially) drive the spline from the other references, not the other way around.

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