smooth object from 2 curves (casted object)

[tsjaikdus]

Hi, I need to create a casting for a piece of an engine. The front and back sides are described by (rather complicated) curves. Though, when I try to make an object (using sweep/loft like functions in unigraphics) I get many creases in it. I've managed to create smooth objects between simple curves. So I know it works in principle. But the complex curves (many arcs and lines) of the front and backpiece apparently are too different to create a smooth object. Anyone knows if this is solvable?

 

[cowski]

Try the 'arclength' option rather than the 'parameter' option. If that doesn't work join the arcs/lines into a spline and use those. Just be sure to check the quality of the output spline first.

 

[tsjaikdus]

Arclength is a major improvement. Thank you

 

[Shadowspawn]

tsjaikdus,
Not sure if this will help, but try to have the same number of curves in each section. If you have 5 curves in the front section, make sure you have 5 in the rear.

SS

 

[tsjaikdus]

this gives similar results, converting into a spline too. However, I can't change the number of segments as they are specified. It's just a lot of trying to get it right. But it does work.

 

[cowski]

Let's say you are making a ruled surface in UG with 2 input 'curves' (top & bottom). If both curves are made of lines and arcs and you use the 'by parameters' option, UG will try to map each curve (lines/arcs) in the top input to each curve in the bottom input. If you have a different number of lines/arcs in the top and bottom, you may get strange twisting surfaces. The 'by arclength' option will look at the total length of the input string and will map the start/end of the top & bottom strings (it will ignore individual arc/line endpoints).

If you use 2 (relatively smooth) splines as inputs, the 'by parameter' and 'by arclength' options will give similar if not identical results. This is because you only have one entity for each input string. You don't need to change the number of segments. A spline in UG is one curve, no matter how many segments it may have.

 

[Xwheelguy]

While splines are a single curve, the number of segments in a spline does affect the resulting surface in both appearance and how "heavy" the surface is (how much data is required to create the surface, which affects the file size). Splines with fewer segments usually result in more desireable surfaces, both aesthetically and mathematically.

You can change just about anything having to do with a spline, including the number of segments, using Edit Curve. However, this can result in a shape change if you're not careful.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[tsjaikdus]

I mean same number of curves and arclength give similar results. Though best results were obtained by turning the curves into a spline, add curves in other direction. Then split splines by the curves in the other direction so the splines are more or less equal segments. Then using Through Curves. This is a bit of work, but gives near complete control over the surface. Many thanks for all the input!!!

 

[cowski]

Wow, that sounds... overly complicated.

 

[Xwheelguy]

Would be much easier to diagnose with a part on the screen. I have a hard time believing that this simple operation won't produce a smooth surface. Remember, if you give NX garbage curves, your resulting surfaces will likely be garbage as well. Keep the spline degree low and segments low if at all possible. This is an engine casting, not a Class A car body surface.

Also, if you want a surface to fly between 2 curves without regard for continuity to adjacent surfaces, Ruled surface is the way to go in my opinion.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[tsjaikdus]

OK, it isn't going to be a piece of styled design. Though, what made it so hard was that the curves were completely defined and I couldn't change them. Then they were all comprised of a different number of arcs and lines. And finally they were extremely curved, almost looping at some places, but then the next curve was completely different from the previous one. What happened was that the surface seemed to follow the curve to fast at some places and not fast enough at other places. This was improved by the Arclength option, but still showed. Only after I turned the curves into splines that I could split properly, it looked as good as it does now.