Autodesk Alias Studio Tutorial – Large Surfaces G3 Continuity

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I am now putting some of my tutorials on YouTube, so whilst you’re there you may wish to check them out. There’s a full tutorial on how to create a Ball Corner to Class A Surfacing, Catia V5 spec.

 

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A BIG Surface. What’s That?

This is a typical comment from someone who has spent 3 years learning Alias as part of a Product Design Course. “I want to build an Automotive Exterior, but I don’t know how to control big surfs. Can you help me?”Ok! You’ve built say an electric drill, a micro wave and a cell phone and you have learned a lot, but nothing about surfacing a car and maintaining Catia V5 surf. boundary tolerances and critically INTERNAL surface Continuity i.e.G3.

“What’s that?”

Ok! Here goes: mastering building surfs. to close tolerances at boundaries is a great thrill, but we need eventually to learn a higher level of skill if we are going to make the center surfaces a car.
5_2The above pic. shows G3 curvature conditions between 2 surfs i.e. the hood top and the front surf.The 3 curvature CV rows are not close to the boundaries, but have been  SLID manually in towards the center of each surface and this means that the curvature is GENUINLY continuous through the entirety of both surfaces NOT JUST AT THE BOUNDARIES. This is the surface precision demanded in the Automotive Industry and it’s called G3. There is an even higher level called G4.

“Well how do you build it?”

First you must build curves that are as light as possible.Try to use deg 2-3 crvs, but if the surf has a lot going on you’ll have to go up to deg.5 and very occasionally higher, but in all cases try to use only 1 span, both in the U and V.

You can’t build to G3 without spending a lot of time getting elegant , light crvs

and you do this by matching CV’c on opposite boundaries an ALWAYS HAVE THE CURVATURE COMB SWITCHED ON.Move your CV’s with the CV Move tool (bottom of the Control Panel )Set the tool to either XYX or NUV mode and the step size to. o.o1 mm and to o.oo1 mm for fine tuning of the internal Cv’s of a surf.It’s usefull most of the time to constrian the movement of Cv’s to just 1 or max 2 axes.Before launching into hand modelling an internal surface:SAVE OUT YOUR WORK WITH A NEW FILE SUFFIX and then open the new file for the trial attempt.In Industry you are expected to follow file naming protocol, so that everybody who might handle your work will understand you file hierarchy at first glanceHere’s an exampleaudi_a5_hood_top_roof_graham_12c.wireaudi_a5_hood_top_roof_graham_12c1.wireaudi_a5_hood_top_roof_graham_12c2.wireaudi_a5_hood_top_roof_graham_12d.wireIf your files go to a parallel engineering dept, anyone can see how to find stuff in your file hierarchy.An Alias workstation is like a FLIGHT DECK,  and when someone else jumps in your chair, they should be able to understand your filing system straight away.

“Tell me more about G3 surf. Integrity?”

Ok! so now you know that changing the surfaces characteristics with Re-Invoke is very useful to lighten surfs. always do this with both surf. boundary indicators on and curv. comb, but to try and improve the interior of surfs. Re-Invoke is just going to load up your surf. with extra geo.

“So what do I do?”

You stat pulling CV’s manually.In conjunction with what I’ve already told you, switch the diag. Zebra stripe on, just on the 2-3 relevant surf. Select them and hit Zebra and then deselect them.TURN THE TRANPARENCY DOWN VERY LOW so that you can easily see the CV’sIf you have built single span surfs. you wont have too many CV’s to pull

Never pull the last 3 rows.

You may slide them toward the surf. int, but NEVER pull them.Watch the surf. bound. indicators all the time.

YOU CAN’T RESOLVE A G3 PROBLEM BY YANKING ON 1 CV,

you must look at 2 or 3 surfs. and see how the Zebra flows across them. Move each relevant CV just a touch and leave your work unsaved until you have improved your Zebra flows to some small degree and then save that change. If you really —- up, and Ctrl+Z fails to get you out of the hole you’ve just created, then just open the earlier version of the file.

Some Rules for G3 Crv. Cont.

To get G3 surfs, you must first build G3 ready curves(I try to use deg.3 crvs with 2 controllable CV’s for manual builds and when I’m using Align tools I use deg. 5 with 1 span, this leaves no controllable Cv’s once you have dual aligned, so if you want a controllable Cv you must use a deg.5 2 span curve)Try always to have CV’s opposite each of their counterparts on the opposite crvMake sure you have clean crvs. with no spurious edit pointsOnce you have your immaculately tangent aligned balanced 4 curve set build a quick simple Square and look at the internal structure of that Sq. any non-sym. isoparms/ diagonal spans that have appeared are telling you that you’ve —- Up! So go back to your curves and correct any dissimilarities between North and south or E&W.The flow of the Curv. comb should show progressive curvature acceleration towards both adjoining boundaries. The thin red line should be smooth with no breaks or HORRIBLE angles.

To Learn Alias Automotive to Industry entry level has been made easier. Why not visit my website and take a look for your self?

Info. on Courses:

“Course #1”.

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167 Euros (200 USD equivalent Nov.2011) per month. You get your .wire reviewed by me every 15 days and you will receive : feedback, instruction, tips and advice from me personally. Access to all videos including my ” Private Student Training Videos”. You will build at least 3 complete automotive exteriors. The course also includes an intensive Reverse Engineering section, which required by most employers.

“Course #3”.

Fast Track Full Pro. “One to One” Course with weekly reviews and coaching 250 Euros (USD. 300 approx. Nov. 2011) per month. One to One Private tuition. You will receive specific geometry and meshes and modeling from me personally where required, to help you to complete your exteriors quickly to an Industry entry level standard. This means a bigger investment, but once in an Alias modeling job you will get back what you invested many times over and be able to work anywhere in the world

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Regards

Graham Bullock B.Ed.(CNAA)Des.Tech.

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