How to approach Rotary model in NURBS

[magicteddy]

Sorry in advance, this is again a long post…

@lander

Now, obviously this may have more to do with an inquiry for particular modeling techniques of NURBS in general

Yes, you are right. That was my first inquiry here.

Rotary tool

Hi Kyle, Great demo as always I do have one complaint though. On almost each model you present (at least, recently), you choose the SubD way. Don’t get me wrong, this is a perfectly valid workflow and there are great things to learn here. I also understand that you want to emphasize the most recent tools available in Rhino. But it feels to me as a cheat to quickly approximate shapes that are a nightmare to model in Nurbs for a beginner. I tried to reproduce this example starting fro…

@magicteddy

I would love to see some training material where you don’t necessarily go as deep in the model details, but rather spend more time analysing the shape, identifying where primary surfaces are, where do the blends start and stop, where do you need curvature or tangency…

And the answer was to post a specific file, which I perfectly understand as it’s the standard on the forum to solve specific issues. So I took this recent model as an example but really I have dozens of similar files with similar problems I can’t solve.

On another thread you said :

@lander

Maybe we should compile example geometry to demonstrate different scenarios where these issues arise, and design intent has to be compromised, etc.

And I couldn’t agree more. I’m in a desperate need of training material on how to approach modeling - that is, really, before even starting to draw a single curve in Rhino. I know the tools and their options. What I’m missing are more generic ‘skills’ that are in fact not Rhino-dependent.

Problem A
How do you “read” a picture or even a real object you want to reproduce ? How do you identify if the model is made of a single surface, a bunch of patches, where are the seams, how are you going to hide them : simple fillets, blends, more complex transitions ? What are the clues, the characteristics that can give an indication of how flat/bumpy/twisted/whatever a surface is, where it starts and where it ends ? This is especially hard when there are no “hard lines” on the model or there are disappearing edges.

And let’s clarify now that my job is not to design things. So I don’t care to copy existing designs, as bad as you may think they are, this is entirely for training purposes. I also think analysing how existing things were made is a necessary step anyway to get a deep understanding of the tools and methods that allow you to be creative. Maybe I’m wrong.

In the case of Rotary, yes, there is only a single picture. That’s often the case though and it’s not even always an orthographic one. The question is : how do I read this picture to get some information that I can use to build something that respects this front view, with some liberty in the perpendicular axis ?
In this case I think I can use the outer boundary and the inner boundary. Let’s say I want to respect those two front curves exactly - I like them, I need them, whatever.

Then in top view I can decide whatever shape I want - flat, curved inwards, outwards, whatever.

Now the question is : given these boundaries, how do I fill the gaps ? Is there something I miss ? If so, can I extract it from what I have ? Or is there nothing more to see, in which case I’ll have to invent it, fine, but still I would have to know what I’m missing. Because with only these curves, I have no idea how to patch this correctly.

Problem B
And then there is the topic of surfaces with more than 4 edges. I know, Nurbs doesn’t allow that, and yet I have at least one of those situations in every model I’m attempting. So again, the specific questions would be :
1/ am I doing something wrong repeatedly and can those be avoided ?
2/ if you decide to use a four-sided patch with a trimmed edge, how do you know which of the 5 edges in the trimmed one ? Is there a way to match a trimmed edge to an edge ? (I know refit or point editing until the shape looks close enough but both methods are not exact.)
3/ if you decide to break the patch in smaller 4-sided patches : what characteristics, what indicators can you use to choose where to divide the patch ?
4/ And then, what is the proper matching sequence, are there, again, rules that have to be followed so that the process is actually smart, and not an infinite random sequence of matchSrf - changeDegree - InsertKnot until miraculously everything is G1/2/whatever you need ?

See these other threads for examples.

Help to build a transition surface to a hole

Hello I (somehow) followed this tutorial. [getting started rhino for mac - designer kitchen knife] As an exercice I’d like to go a bit further by adding a nicer transition around the hole on the knife. FilletEdge or BlendEdge fail, no surprise here. [image] Before going on the main model I want to sketch the method on a simplified version, trying to blend between planar surfaces and a planar curve. [image] And I’m stuck filling those holes with G1 (already acknowledged G2 …

Class ring and network crvs

Could use some help. I need to make this ring from the line drawing. I laid out my crvs and got the basic shape using crv network. when I extrude the finger sz crv and booleon dif. the sides of the ring change as shown… I need it not to do that. .I’d like to make the ring by building surfaces but I think I need a few more crvs? any help is highly appreciated. I know I can turn on the srf. points and edit them over to the original crvs as seen in the ghosted view but it’s not easy nor does the ed…

This last one is an old thread but I encountered it again recently and tried many things… including doing it in Catia. I’m out of ideas.
SignetRing.3dm (2.4 MB)

So, summary

I’m looking for generic rules, checkpoints, pitfalls to avoid, options available, so I can at least have an indication I’m on the right path when modeling. Because it’s so easy to spend hours trying to build something that is anyway impossible and not realize it.