Dimension from surface to sketch entity?

[fighterpilot]

In NX5, why am I not able to dimension from an existing surface to a sketch entity? In fact, I can't even make a constraint to constrain the sketch entity to the surface. My intent is to have the sketch always lie on the suface.

Thanks...

--
Fighter Pilot
Manufacturing Engineer

 

[JohnRBaker]

Is the 'surface' planar? If so, select the surface as the sketch plane. If the surface is NOT planar, you will need to position a sketch plane as close to parallel to the surface as you can and then project the resulting sketch curves onto the surface since sketches can ONLY be 2D.

John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[fighterpilot]

John,

I ended up projecting the edge of the surface into my sketch and then constraining to that. I'm assuming that edge will keep the relationship to its parent surface.

I know sketches are only 2D but in Pro/E you can dimension to an existing 3D surface in a sketch. Logic is surfaces usually stay, edges sometimes go away.

--
Fighter Pilot
Manufacturing Engineer

 

[JohnRBaker]

Using NX 5 I had no problems creating Sketch dimensions from a sketch curve to the end point (vertex) of a surface edge. Granted, due to the fact that a surface edge may not lay in the plane of the sketch nor that it would be a simple 2D shape, such as a line or an arc, it makes it difficult to create any meaningful geometric constraints between sketch curves and the edges of a surface, of course if you were to project those edges into the sketch, now you will have 2D geometry which will be more useful for this task, and yes, if you edit the shape or size of the surface, the projected edges inside the sketch will update as well.

Now there is one thing to remember, the surface that you wish to reference with the sketch must have been created BEFORE (in Timestamp Order) the sketch.

John R. Baker, P.E.
Product 'Evangelist'
NX Design
Siemens PLM Software Inc.
Cypress, CA

http://www.siemens.com/plm

http://www.plmworld.org/museum/

To an Engineer, the glass is twice as big as it needs to be.

 

[hudson888]

Try using some reverse logic.

With a surface you have a peice of gemoetry describing an infinite field with a defiened shape and bounded by edges. Now granted you can't just pick anywhere within the field of possilities that the surface describes and associate that with a sketch. Instead you would have to find a point somewhere on the surface and use that to associate with your sketch.

If that makes sense then the answer is clear becuase you can define a point on a surface many ways first and then anchor one end of you sketch dimension to that point. If you expect the point may vary because the surface will change then you should project the point or a curve ending at that point on to the surface and then you will increase the amount of associativity available to you.

Before you ask you won't be able to create a point in a single sketch, project it on to the surface and dimension from it back into the same sketch. That seems determined to create a circular reference error. But you can nevertheless achieve what you need with two sketches. And given that this appears to me from your brief description to be a relatively rare requirement I think this method is probably adequate.

If you aren't quite satisfied then please supply a detailed description of what you want to do and why before I could hope to provide a better explanation.

Cheers

Hudson