Summary:
Today we’ll be answering a question from our member Mathieu, related to the practical usage of conics and spine curves. We’ll dive a little deeper and look at different ways of approaching this kind of geometry in NX.
Since you are using two guide curves and two tangent support, there’s noting holding it to the other sides, as opposed to let’s say a multi section surface.
So if you move, in this case, the bottom left edge, a gap is created…
Sometimes, the conic sweep/blend stops at one extremity of a surface if they are not stopping at the same place. I think it does none of that when one face has G1 continuous corner edge… Where a blend merges the end of the edges no matter what.
–Mathieu
topics:
Video One
- Studio Surface Tool
- Through Curves Tool
- Maintaining Control of Your Spine Curves
- Utilizing Curvature Cones to Analyze Surfaces
- Fillet Rho Surfacing
- Creating a Varied Rho Surface
Video Two
- Understanding Law Types and Surface Transitions
- Controlling Location of Surface Transitions
Video Three
- Fillet Bridge Surfacing
- Utilizing G3 Continuity Effectively
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Adam O'Hern is an industrial design consultant specializing in visual brand languages, and has designed products ranging from laptops to power tools, classroom toys to bathroom fixtures, and robots to lint rollers. He has published with 3DWorld Magazine, CGTuts+, and Luxology, and works with Josh Mings of SolidSmack.com on EngineerVsDesigner.com. |
Hey Adam,
May I ask what would be the proper way to generate that spine curve?
I’ve attached pictures of how I did it, which is :
1)an intersection of the top and bottom surfaces
2)a parallel curve offset on support to trim these
3)a connect/blend curve, in order to play with the tension (using intersection curves stopping at the bottom blend).
Then I did the same steps you did for the secondary & tertiary conic surfaces, but I am loosing continuity in the tertiary corner at that problematic, non-normal edge. You can clearly see the sharpness without the edges shaded, as shown in the last picture.
http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_01.jpg
http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_02.jpg
http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_03.jpg
http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_04.jpg
http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_05.jpg
Also, is there a specific reason why you chose a G2 blend curve instead of a G1 blend curve for the spine control?
One last thing that puzzles me…
Since conic sweeps (or fillet Rho) are G1/tangent continuous, I should count 4 CVs in the direction normal to the spine, where I have six… http://i1140.photobucket.com/albums/n567/mrthestig/CADSpineCurves/Spineconics_06.jpg
Thanks again
Mat
A couple of thoughts:
(1) Instead of ‘parallel on support’ I recommend offsetting the original surface and using an ‘intersect’ curve. This is a much cleaner approach in virtually any package, as it is much less likely to create the kinds of tolerancing issues you’re experiencing.
(2) As for the number of poles, I could be wrong here, but my understanding is that Catia doesn’t actually do pure analytical geometry the way NX does: every shape in Catia is actually a degree-5 NURBS surface. So even when you build a conic, it’s re-fitting the shape to a degree-5 surface. Fret ye not, it’s still everything we love about conics!
Adam
Thank you so much Adam, this is pure awesomeness :)
Since SolidWorks came on the subject; I was wondering if you can now define a spine curve in SW 2012? I think I remember you telling it was an omittance in that cad package.
Mat
You can create ‘spline’ curves, but I believe you may mean ‘spine’ curves? If so, you are correct: SolidWorks does not give the user any spine control at all (one of its biggest weaknesses, IMHO).
Yep, meant control over spine curve
Adam, could you define the terms ‘G2′ and ‘G3′ surface continuity?
I realize these videos are for NX users (looks like an awesome program, BTW), but it does raise some questions I’ve had about surfacing in SW. For instance, is there a way in SW to control the amount of influence a particular sketch has when creating a loft? For instance, say I’m doing a loft where the base is a square and the top is a circle. Normally, the part where the sketches blend together seems to occur roughly midway between the two ends. But suppose I wanted the loft to be 75% ‘circle’ and 25% ‘square’, so that the square sketch exerts far less influence over the shape of the loft than the circular sketch does. Is there any way to achieve this in SW without having to create a third sketch?
Hey Andrew!
“Adam, could you define the terms ‘G2? and ‘G3? surface continuity?”
http://cadjunkie.com/1113/tutorials_continuity-101/
The answer to your other question is a bit more nuanced, though unfortunately I think the short answer is ‘no’, or maybe ‘not without tangency supports’. If you have tangency supports, you can use the tangent tension value to push the shape one way or the other. Does that help?
Adam
Engineers often criticize architects for designing things that are difficult or impossible to build. While I think this criticism has merit, engineers themselves are not free of sin. Below is one example. Notice the extremely awkward collision of geometry on the triangular section at the base of the tail on the Soviet Mig 15:
[img]http://data3.primeportal.net/hangar/howard_mason/mig-15/images/mig-15_15_of_17.jpg[/img]
[img]http://data3.primeportal.net/hangar/bill_spidle4/mig-15uti_n9012/images/mig-15uti_n9012_14_of_15.jpg[/img]
[img]http://data3.primeportal.net/hangar/howard_mason/mig-15/images/mig-15_05_of_17.jpg[/img]
To get it to work, they had to cut out a section and patch it back together with another piece of metal. It took forever before I found a way to recreate it in SW, using a ton of spline curves, lofts, and surface fills. It’s interesting to find that in the Mig 17, which is virtually identical to the Mig 15, they avoided all this trouble by patching that area with a flat piece of metal:
[img]http://data.primeportal.net/hangar/clugston/mig-17_walk/Dennison%20126.jpg[/img]
Simplicity is more difficult to achieve than complexity. That’s true for every discipline, be it design, engineering, or romantic relationships :)
“Simplicity is more difficult to achieve than complexity.”
Truer words have never been spoken. It’s interesting to see how some aspects of the Mig 15′s construction seem to be more the result of extreme time constraints than sound engineering. There are all sorts of odd things about it that are noticeably absent in future designs. Notice for instance these strange fins on the wings:
[img]http://data3.primeportal.net/hangar/isaac_gershman/mig-15uti/images/mig-15uti_06_of_38.jpg[/img]
No other aircraft had them. Can you guess what they’re for? According to an article I read, the Mig 15 proved to be very unstable in testing. None of them could fly in a straight line without the pilot having to make constant course corrections. To fix that, the engineers would bend these fins to alter each plane’s flight characteristics until it would go straight! LOL
Andrew,
Those fences on the mig are designed to interupt the spanwise airflow that highly swept wings experience at at slow speeds. Without them the wing would stall toward the trailing edge at the tips causing the nose to pitch up further and induce further stalls.
Adam,
Once again a most useful set of videos, could I implore you to show NX a little more love and spread your wisdom. I realise there’s a much bigger audience for all things Solidworks but there’s a dearth of good NX tutorials. I’m trying to make the leap from Rhino and whilst I can truly appreciate the power and control NX brings it’s an uphill battle.
Thanks for the encouragement, Neil :) Comprehensive NX videos are definitely on the roadmap, but we’ve run into a snag–beyond our control–that’s been holding us up for six months now. Trust me: we want to release this stuff as soon as possible, and we will!
Cheers,
Adam