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##### create circle on spline (sketch)

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01-07-2018 06:56 AM - edited 01-07-2018 07:02 AM

I have a fully constrained spline in sketch as shown below.

Now I want to create a circle which is:

- tangent to the spline at the sketch origin and
- of the
**radius equal to the curvature radius**of the spline at the sketch origin.

Is it possible by certain constraining trick in sketch? Thanks!

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6 REPLIES

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01-08-2018 12:49 AM - edited 01-08-2018 12:53 AM

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01-08-2018 09:57 AM

Is there a measurement expression to get the curvature of a spline at a point?

If not, you will probably need to create a UDO or Custom Feature object to parse thespline at the end point, get curve params, and either set an expression (with the radius you need) or create the circle directly.

There might be other ways.

Production:NX10.0.3.5 MP16/TC11.2

I'd rather be e-steamed than e-diseaseled

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01-08-2018 09:58 AM

OTOH, does the curvature of a spline (by definition) go to 0 (radius = infinite) at the end of the spline?

Production:NX10.0.3.5 MP16/TC11.2

I'd rather be e-steamed than e-diseaseled

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01-08-2018 10:42 AM - edited 01-08-2018 10:44 AM

Hi @Ken_A Thanks for your comments!

@Ken_A wrote:OTOH, does the curvature of a spline (by definition) go to 0 (radius = infinite) at the end of the spline?

No. At the point where the circle is to be created, the curvature is not 0 (radius <> infitite).

@Ken_A wrote:Is there a measurement expression to get the curvature of a spline at a point?

The spline and the circle to be created are in the same active sketch, and therefore no measurement expression can be built to get the curvature.

And it's beyond my knowledge to customize a feature to measure the curvature radius at a point on a spline. If possible, could you give some clues? Thanks!

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01-09-2018 03:55 AM - edited 01-09-2018 04:00 AM

Hi,

You can try applying a G2 constraint. In order to make it work you will have to trim the circle to become an arc so the spline connects to an open end. Connect the spline to the arc and infer G2. See movie.

Please note how the poles move at the end of the movie. I did this to show you that the uniform scale constraint would conflict with the size of the arc changing while the end point of the spline is fixed.

Regards, **bleep**

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01-09-2018 08:51 AM

Hi @DickBaardse Thanks for your reply and video!

In my situation, I have an existing spline in my current model, and later I want to add a circle to the spline. In other words, the spline is earlier than the circle.

In another thread, @Yamada gives a solution to this issue.

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