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in some threads as
@StevenVickersgave you some very effective and good tips.
When I did my first works of this kind, the best definition of class A surfaces was given to me by a customer: it must be 'bella' (beautiful in english ).
More than a mathematical definition a class A surface is defined whit what you must NOT to do, never use three sides surface, for example.
Some customers require specifications such as never using Blend command for radii higher than 5 mm, an so on.
I design small parts, I don't work in the automotive industries, I try to work on the details. Below only the red one is a blend.
Class A, as Cesare states, are surfaces that look good.
Mathematically it is generally seen as a collection of surfaces were the reflection lines are clean, usually this means curvature continuous (G2) or higher continuity (G3) between surfaces and no odd indentations/bulges. But it is more an aesthetic evaluation.
Main commands to get to know are the surface analysis ones such as reflection lines and highlight lines.
Opinions will be divided on this so below is just that. An opinion.
this does not represent any official Siemens view and is purely my own.
Why is it called "A" = The visible product exterior
The other side is "B"
Before folks start throwing rocks: Below are some of my personal definitions.
Sufficiently good and acceptable visible exterior.
If needed: has the required required tangency and possibly curvature qualities.
Maybe: C2 and certainly higher continuity isnt appropriate.
Maybe: reasonable reflective quality.
Easy (easier) to NX create without too much option trial and erroring..
Surface order: Low (typically degree 3, maybe higher), Can have knots.
Some of the NX surface quality tools aren't appropriate
"True" A-Class for the main = big, primary surfaces: typical: automotive exterior
Low polynomial surfaces (degree ~typically 6 to 8) The user is constantly trying to get the lowest order.
No (= zero) knot lines
Has the required: very high quality G0,G1,G2,frequently G3 continuity to adjacent surfaces.
Good reflective qualities, means: unable to detect the surface boundary on a reflective plot.
Surfaces typically have single convexity and not "S" multi convexity type.
Much more labour intensive to create.
Mr User has to be aware of every pole, every surface order.
Many of the NX analysis tools are used extensively to give surface feedback.
Only a few NX features are suited (and using only some of the options)
Secondary surfaces: eg: joining the big primaries: Some blending features may not be approprate.
Results in: Very good Follow on NX modelling behaviour
For both the above:
Good curvature is better than bad flow continuity
Good tangency is better than poor curvature continuity
some NX features (although extremely useful) I do not consider A-Class. eg: Fill surface.
Your question: Where can you find more info?: I'd expect training to deliver on that one.