B-Surface best practices?

[skanskan]

Hello

Where can I find more information on B-Surfaces with NX?
I don't mean the general definition of B-Surface but using B-Surfaces with NX instead.
When is advisable to use a B-Sruface (for example when I want to align an edge) and when not. And what's the best way to work with them.

 

[JohnRBaker]

Have you looked at the NX User Documentation/Help Files?

John R. Baker, P.E.
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[skanskan]

If I search for "B-surface" I get several commands where that word appear but I don't know where to find more in depth information

 

[Toost]

Don't know if this helps or not.
In principle all freeform faces and sheets in NX are B-surfaces. And since Bezier more or less is a special case of B-surface, it's counted under the same "umbrella".
Can you elaborate on cases where there is a choice to make ?

Regards,
Tomas

 

[skanskan]

I just want to know in general.
Sometimes is advised to transform from or to B-Surface.
How is it called when it's not B-surface?
And sometimes is faceted.

 

[Toost]

The non freeform are analytic shapes such as Planar, cylindrical, spherical, conical and probably a few other well known shapes.
There are also common shapes which i think in "Nurbs language" are called procedural, such as a extruded or revolved spline, whose shape in the curve plane is freeform but in the extrusion / revolve direction is "Extruded" or "revolved". ( The NX term is "Extruded" or "Revolved".)
As always, the simpler the better, an analytic surface is described by exact math whilst freeform is more complex, and needs / might need tolerances / approximation.

Regards,
Tomas

 

[Toost]

and... If you bump into something faceted, it's not a true surface but a "representation" consisting of triangular planar areas.

Regards,
Tomas

 

[skanskan]

Toost, Do you mean that B-surface is the same than freeform?

 

[Toost]

Yes. NX Freeform = B-surface.
There might be some surfaces which are not B- Surfaces. Many years ago the then Unigraphics had some other underlying math for some surface types but i would expect all today to be Nurbs. ( -For those who have been around long enough, one of these was called "Sculptured Surface".)

Regards,
Tomas

 

[skanskan]

OK, thanks

 

[JohnRBaker]

Canonical forms, such as Cylindical, Toroidal, Spherical, Conical and Planar faces/surfaces are NOT defined as NURBS but rather by using their exact mathamatical form.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

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

 

[Toost]

I think i said approximately that in my post dated 16 Nov 12 11:53.
-Or ?



Regards,
Tomas

 

[skanskan]

OK, but now I would like to find somewhere explaining what things need to be done using B-surfaces. For example why do I need to convert a surface to B-surface in order to "match surface edges"?

 

[skanskan]

B-splines are more generic than canonical forms, that's why sometimes we can use B-splines to fit complex shapes. But I would like see a document describing tips and tricks about when and how to use them.

regards

 

[JohnRBaker]

The type of surface 'needed' is pretty much determined by which function you use. There is NO explicitly named B-Surface or NURB function per se, but rather a set of functional types depending on what sort of data you have to start with, be it curves, faces, bodies, points or simply a desired size and shape. Also note that rolling-ball blends are also a special surface type which are generally not stored as B-Surface.

My advice is to NOT worry about what math-forms are being used to define any specific surface or face but rather to just become familiar with how the different types and methods can be used to create geometric shapes. As far as virtually ALL of the downstream applications are concerned, there is really NO difference when it comes to what those applications are tasked to do, it will be able to handle any math-form, be it when defining toolpaths, finite element meshes, high quality rendering, creating Drawing views, exporting/interfacing data for other 3rd party applications, etc.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

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

 

[Xwheelguy]

skanskan,

One reason might be the type of surface of the "tool" edge (edge to which you want to match). If it's a B-surface, then it's possible that to meet whatever settings you're using in Match Edge, the only solution possible is to convert the target sheet/surface into a B-surface. More often than not, this will probably occur any time you're going to Match Edge and try to achieve G2 continuity or higher - at least that's what I would expect, given the number of poles that would have to be "locked" on the surface in order to achieve that level of continuity.

Tim Flater
NX Designer
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