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create circle on spline (sketch)

Valued Contributor
Valued Contributor
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!
 
Image.png
6 REPLIES

Re: create circle on spline (sketch)

Legend
Legend

I can get very similar circle but not exact.

1. Create 3 point on the Spline. [P, P', P'']
(Each distance of points [dP] is same.)
2. Create a Circle including the 3 points.

If dP value approach with 0, the radius of circle will be similar to curvature radius.

SmartSelectImage_2018-01-08-14-27-41.png

 Sunkap Ahn, Senior Support Engineer


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Re: create circle on spline (sketch)

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

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.

Ken Akerboom Sr CAx Systems Engr, Moog, Inc.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled


Re: create circle on spline (sketch)

Gears Esteemed Contributor Gears Esteemed Contributor
Gears Esteemed Contributor

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

Ken Akerboom Sr CAx Systems Engr, Moog, Inc.
Production: NX10.0.3.5 MP16/TC11.2
I'd rather be e-steamed than e-diseaseled


Re: create circle on spline (sketch)

Valued Contributor
Valued Contributor

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!

 

Re: create circle on spline (sketch)

Siemens Phenom Siemens Phenom
Siemens Phenom

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.

 

(view in My Videos)

 

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**

 

Re: create circle on spline (sketch)

Valued Contributor
Valued Contributor

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.