G2 continuity issue

[merrelld29]

Hello I have Alias Auto Desk 2022 I have a problem constructing surface with G2 continuity I have tried all the construction options with different tolerances but nothing seems to work can you suggest something else I can try. 

[Fausto_Brevi]

Dear merrelld29,

I need the model or, at least, an image to answer your question because I don't understand what you have been done. Which tools are you using? waiting more info... have a good day

Fausto

[merrelld29]

I am sending an example file Alon with my preference sets.

[merrelld29]

Thank you for responding but I did not receive the Preference set file could you please resend.

David Merrell

Adjunct Professor Macomb Community Collage

[merrelld29]

I have imported the default preference sets and worked with a basic cube added some fillets and then tried to build a blend but the system refuses to give me G2 continuity

[merrelld29]

My blends are also G2

[BarryKimball]

What tool was used to make the curvature continuous fillet surfaces? How were the left and right fillet surfaces trimmed back to the vertical fillets boundaries? What tool did you use to create the fillet shape on the top surface? Why are you trying to create curvature continuous blends on planar sides of a box? There really is no valid point to the exercise in my opinion...based solely on the image you provided, open the continuity options and the colinear options and set those check boxes based on the attached image...

[merrelld29]

Hi Barry

Thanks for responding, just to let you know I started with a cube then added a 30mm G2 fillet, Trimmed the surface then added two 15mm G2 fillets with trim set to default then used Free Form blend set to G2 to create a blend then projected it to the surface and then trimmed the top surface back. Then I try and build the blend which I cannot get to achieve G2. I have just had 2022 installed on a new Elitebook computer and am many problems creating G2 blends so I built this one example just to prove to myself that its the system not me.

[robertsonldspj11]

G2 Continuity or Curvature continuity or Radial continuity implies two faces/surfaces meet along a common edge, are tangent, and the rate of curvature change at each point along the edge is equal for both faces/surfaces. The transition across the edge is therefore curvature continuous.

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[merrelld29]

For a surface to be curvature continuous G2 to another surface two rows of CV's must be in alignment, if only one row is in alignment the surface has G1 Tangency and therefore is not curvature continuous G2.

[BarryKimball]

I'd like to comment on the previous 2 replies regarding G2 continuity...First...matching the rate of change of curvature is G3 continuity, NOT G2...a G2 requirement means the curvature value at the boundary are equal, not the rate of change is equal. Second, please do not assume the number of CV's controls continuity...If you create 2 flat degree 1 X 1 Z oriented planar surfaces with a common boundary, those 2 surface will be curvature continuous. In your scenario they could not be because there are not enough CV's. Next, the shape of geometry determines if it is curvature continuous, not a specific number of CV's. No software checks the number of CV's to determine continuity. NURBS modelers can create non-planar surfaces that do not have enough CV's to fulfill your 1st=pos 2nd=tan 3rd=curv concept that are curvature continuous. I would just like to clarify that fundamentally shape determines curvature continuity, not strictly a number of CV's...I will concede that users in most cases need 3 CV's to achieve curvature continuity, but that is not a requirement.

[BarryKimball]

I calculated that someone might completely disagree with my previous comment, so I figured I would add an image to explain further...

[merrelld29]

I am grateful for all the input but unfortunately none of these comments solve my issue. I use Alias every day in design, I use 2021 which is fine but my other laptop which I use to teach Alias it has 2022 loaded and I just can't seem to get it to work building G2 surface.

[systembolaget]

Yeah, these edge blends are a good example to help understanding how G2 or G3 can be achieved.

[systembolaget]

There are many things that could make a thing fail or not, which is why it is essential to attach a zipped .wire file in forums, because only then other users can actually examine what you have in front of you, instead of looking at a static image that reveals nothing about the underlying geometry.

[BarryKimball]

This question has been answered already...on 01-20-2022 05:21 PM I (post 7 in this series) posted the answer and an image of the settings in square to achieve a curvature continuous blend in a corner constructed as you outlined. If you have a more specific file that you can share, as mentioned above, attach that and you will get an additional answer.

[systembolaget]

No help needed, wanted to point out that the image of that edge blend is a suitable exemplar why CV-counting ain't the thing.

[BarryKimball]

Hey systembolaget that post was not intended for you, it was for merrelld29

[merrelld29]

Hi 

I have attached a file with the issue.

[BarryKimball]

So this file is a completely different file from the original image that was attached...very confusing. This new example is not a simple ball corner where you are trying to build a square, as in the previous image you attached...this is a transitional surface that washes out 2 fillets, one convex and one concave fading to no radius. Ok...there are videos on Youtube to solve that exact scenario...that question cannot be answered here in text. The solution has nothing to do with preferences, tolerances or anything else specific to Alias or a tool in Alias...this is a modeling exercise that has multiple solution depending on how you want the surfaces to flow...