Solved! Go to Solution.
It's nearly impossible to provide an answer to this question without knowing more about your specific practices and intended objectves. For instance, are you working on class A surfaces, aerospace, or marine hull design? Then, in order to get the specific shapes, continuity, and editability you need, perhaps you do need more than just "blends".
Realize, of course, that by "blend" we're really just talking about a transition surface, usually conic in nature, between and having continuity with 2 or more adjacent surfaces. So what's the purpose of blends in your models? Perhaps more important, what are you finding to be problematic with blending?
It just sounds like you are looking to make things more difficult and time consuming than they should be. NX blending is very effective, generally speaking, and I find that almost all students I teach coming from another CAD system are impressed with its capabilities. For simpler machining shapes, Edge Blending would be the default with Face Blending used when Edge Blending fails or when you need to blend over non-adjacent faces. Then there are another half dozen blend commands in NX, all preserving their own uniqueness in shape control, editability, or surface type. I believe Siemens maintains all of these methodologies for very critical and specific customer needs. Some are rarely used but when needed, they are there for you.
Despite the simplistic rhetoric I state above, it is indeed worth clarifying that once you enter into the world of sheet and surface modeling approaches, the modeling task can go from minutes and hours to days and weeks. And it tends to break more when making subsequent changes. As the s/w has developed over the years, the blending functions incorporate a high level of "rounding and filleting" that capture the intent internally so that you shouldn't have to deal with intense modling effort and features breaking when changes must be implemented.
Then again, I've seen some customers that don't blend models at all and just leave it to the machinists to add those shapes as a result of their toolpaths and choice of cutters. But obviously, that violates the advantages and benefits of CAD such as pinpoint accuracy of volume, mass, and weight not to mention clearance and interferenece checking in assemblies.
For us, we use our 3D models to make the tooling from. We need every draft, edge blend, split line to be on our model per what the die caster needs to make the tool. This also helps with accurate FEA and other analysis,
So we usually model square corners, then add the fillets at the end of the history tree.
I think it depends on what you are modeling. This works for our Castings, plastic molds.... Most of our parts are parametric, very little surfacing, sketch, extrude, revolve....
I agree with @StevenVickers, @kochg and @sdeters however, opinons can change depending on what you're modeling and for some reason, your situation seems to be top secret. Your intitial steps of the model shouldn't be so difficult that you cannot apply blends later. Granted, as @kochg has already pointed out, not knowing what in the world you're modeling doesn't make giving you advice any easier. It's getting almost frustrating in some cases, but mostly because you won't just say with words what it is you're modeling.
In regards to surfacing, the advice of overbuilding surfaces is pretty much standard practice in most cases I've encountered. You build the larger areas first, confirm those surfaces are of the complexity (rather simplicity), shape, and quality that is required for the model then you work on the secondary surfaces, repeat the checks on the results. At this point, you should be very close to done and able to apply tertiary surfaces (usuallyblend and/or chamfer surfaces). Repeat with the checking. There is a reason for this and it's mostly because if the primary surfaces aren't good, it's much easier to change those at the beginning stages of the model rather than waiting until later and ending up having to change something way back at the beginning as well as the surfaces built on top of those. That's when you can end up having to start completely over or at least remodeling a large chunk that should have been done already.
If you model in smaller steps or pieces, it can be much easier to make changes. Once you build up your knowledge and command aresenal and mastery, then you can go back and possibly combine some of those smaller steps into larger ones, with one of the goals being to cut out features in the model tree while maintaining good practices and building models which just about any user can come after you and make changes without wondering just what in the heck you were thinking. At that point you might also have a better understanding of what value certain techniques have over others.
Finally, don't take this the wrong way, as these words aren't meant to hurt any feelings, but you're only making things harder on yourself by considering trying to reinvent the wheel in some cases. Too many people have been lurking around these boards for too long designing too many different products using too many different techniques for that to happen. Keep it simple, then when you've mastered the simple stuff, move onto refining things more towards your preferences or adding more layers of complexity or management.
I would make a conscious decision on what is a blend and what is a base surface, =<6-8mm blend is probably a blend for me, >12mm circular face is probably a construction surface. The grey area in the middle is part of your experience and assessed dependently. Of course all of that is fluid based on the type of surfacing task and product area. This is a good discussion that will benefit everyone.
the term 'Blend' indicates a connecting surface instead of a 'Blend' often.
Even a 'Draft' is sometimes build with ad hoc surfaces because the 'Draft' command failed or achieves a unespected result.
In the attached file there are some surfaces made with different methods. I did them quickly, just to give an idea.
Hi @TimF Thank you for your both posts!
At first I must say sorry for be unable to disclose information about products I work on. As you can understand nowadays companies don't want to see their employees discussing their work on public forum. I know this situation makes my questions abstract or sometimes even pointless and also add to big trouble for helping people.
Please don't say something like "hurt any feelings". I'm appreciative for both your guidance and your criticism. I know that some of my ways of doing design things are undermining my efforts to become a qualified surfacing worker. I'm happy that you are willing to point them out.
The workflow you decribed in the first post is very help. I would analyze it careful and make it my daily practice.
As to tutorial videos, in fact I have spent quite a lot of time searching YouTube. However most videos seem to focus on single commands. I think I can never learn from YouTube videos those important things I learnt from you, @Cesare, @StevenVickers and many other kindly people on this forum. One thing I observed is that YouTube has much more useful materials for SolidWorks or other design software than for NX. I don't know about Alias, but I did study many SW things. Although I don't have access to SW software, I did learn a lot from its tutorial materials. And the book "SolidWorks Surfacing and Complex Shape Modeling" is especially helpful, and it's a pitty NX doesn't have such a book on surfacing.
You just refered to concepts of primary, secondary, tertiary surfaces. They seem to be very helpful for making a reasonable overall plan for a design project. I would try to understand them better. Thanks!