Curvy Stuff 301

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The thrust of this one is less of a 'how-to' and more of a 'how can I police
myself and use CAD without having it influence my design'. I was nervous
about it, but I got the reviews back from the session evaluation forms and
it looks like the point got communicated and was appreciated.
Example:
I have interacted with Industrial Designers who would not allow their
'vision' or 'creativity' to be compromised by manufacturing constraints...
"I don't see why we can't get away with an undercut here"."well, I guess you
have to redesign the circuit board to run cooler'."I guess you'll just have
to pull zero draft there".and the perennial favorite: "how about a
collapsing core...." These are the guys who make it hard to work in my
field because, after dealing with memorable prima-donnas, folks in industry
assume that all Industrial Designers are like that.
What is really ironic is that, though these Industrial Designers will not
compromise their 'vision' because of manufacturing constraints, they will
change direction on their designs if they can't figure out how to model the
shape in CAD.
Why does this bulge out here? 'Oh, I just couldn't model the leaner shape
without problems so this was the best I could get"
Why does it get thin and elongated? -"oh that is just what happens when you
flex a part."
That is f***ed up.
They won't change for constraints of the real world, but they cave-in to
constraints of the virtual one. The more I think about it, the more I hate
them for it.
I see it all the time - CAD-centric design is compromising design - or more
accurately, CAD-'feature'-centric design. I try to show that
'product-centric' design, literally forgetting the features while working
through how to construct your product, actually makes the modeling go more
smoothly.
After all, product are what pays eveyone's salaries. A product does not
care how it was modeled, nor does it care about the features that were used
to model it.
And that is the core of this session - not allowing CAD to do any designing
for you. You are smart, CAD is stupid, so lets let the smart party get back
in control
Best regards,
Ed
Reply to
Edward T Eaton
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Ed,
Your presentations are always intriguing and provocative, and very welcome, thanks!
We have been thinking a lot about the role Solidworks should take in our new product development. We are fortunate that our 'stylists' are also skilled at surfacing in Alias, so many of the ugly feature-based approaches you talk about are by-passed.
However, using one package or the other, we have three interesting problems:
1. Using a surfacing approach like the one shown for the 'check-out scanner' ultimately results in largely inflexible model. Granted, you never have to turn 'a Volkswagen into a toothbrush', but you often have to accommodate a larger LCD or new component. Looking at the complexity of your check-out scanner, the re-work would be similar using a straight surface modeller or SolidWorks.
2. We used to believe that generating native SolidWorks surfaces would make it easier for SolidWorks to shell the resulting solid body. By analysing our Solidworks surfaces back in Alias we can see that many of the surfaces Solidworks creates (using 'fill surface' etc) are unnecessarily heavy, compared to the equivalent surfaces you would create in a modeller like Alias - so the surfaces are worse quality, not better.
3. None of us want to start a production moulding (with all its associated ribs, bosses, partlines etc) with a feature tree full of surfaces. This is because rebuild takes longer (Solidworks insists on rebuilding everything occasionally), and may be less stable. The work-around is to develop the volume, save-out and re-import as a parasolid, then get to work.
It follows that we should use a dedicated surface modeller up front, with all its tools, and relegate Solidworks to the engineering detail.
Love to know your thoughts (and anyone else who's interested).
Regards,
Anthony
Reply to
Ant.
Ed,
Thanks for your reply, I have to admit that we have done the 'parasolid out - import in' approach, but only after the skin is essentially settled. Thanks for all your other tips, they are invaluable.
I can really only address one of the points immediately: heavy surfaces - will try to post on the others later.
I understand that Alias and Solidworks produce splines differently. In Alias the most basic curve is made up of an edit point at either end, and two control vertices. The control vertices lie off the curve. You can pull or push them to control the curve's shape. This is called a 3 degree curve (imagine one line from edit point 1 to CV1, one from CV1 to CV2, and one from CV2 to edit point 2). If you extrude this curve you get a beautiful, simple surface.
It is possible for a curve to have more than two edit points. For example, if you extrude a curve with 3 edit points, you will get a line down the middle of the surface called an isoparm.
When patching between edges of surfaces where the edit points of each surface don't match, you get multiple isoparms in the patched surface. In some cases, a patched surface can be incredibly dense with isoparms.
What's the problem with that? Sometimes very dense isoparms can result in surface rippling. What's more, offsetting (or shelling) dense surfaces can result in the offset surface 'folding over' on itself.
Poor automotive modellers must model an entire vehicle with A1 surfaces, ie no isoparms at all. Of course, they have expensive software to help them.
I hope to post an image from Alias to show the isoparms on a patched model - anyone able to host it?
Anthony
Reply to
Ant.

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