Does G2 Continuity exist on extended surfaces especially for tool paths?

[Anonymous]

Hi,

      Your recent video "Using Surfaces for Extended Toolpaths" leaves questions for those people who use CNC to make expensive parts. Are  extended surfaces G2 continuous?  Can I trust the cutting tool will not make a plunge with unexpected squiggle data point in extended 5th degree polynomial curve/surface. Could the developers comment on this?  I think your T-spline technology covers this g2 Continuity so these expensive accidents will rarely occur. ( my reference point is mid -1980's using Catia v2 where we had to make "multiple bread slice cuts" of extended surface tool paths to verify G2 continuity (no squiggles)and save $10K to $20K parts from a "oh sugar" moment🤐) My last question: Should  we still perform "bread slices cuts" as a precaution with Fusion 360?  I am plan to make some complex aero models and the answers to these questions are still pertinent to the premise of my request and budget.

Thanks,

John

[karina.harper]

Hi @Anonymous 

I'm going to get this conversation started but as a qualifier, I am not a dev. I can reach out internally to get you some more answers, however.

I'm not sure which video you're referencing (link?) but you might also be interested in this class from Fusion Academy. Marti and Dan did a great job explaining how to use surfaces, and how they relate back to your part. There are times they use Sculpt instead of patch in a really neat way to be certain it's G2. One of the biggest takeaways I got from that class though was how to view the UV diagnostic texture.

You can view that by right clicking a body and selecting 'texture map controls', then activating 'UV diagnostic texture as the display mode.

On this example, I took the top face and did an extend surface on it. You can see that the surface is G2 from where it was extended (the G1 edges are due to how the part was originally modeled). Fusion's surfacing toolpaths use this diagnostic texture to map out its results, so you can use this to really verify that Fusion is displaying what you want it to.

I'm not entirely sure what you mean by "bread slice cuts", but the method shown in Marti and Dan's video where they use sculpt may be something similar.

Does that answer your question? I'm happy to dig deeper if need be. @jeff_strater may have some good thoughts on this as well!

Cheers,

Karina

[TrippyLighting · Accepted solution]

I think the OP is referring to this quick tip released yesterday (?).

@Anonymous if you are working with external models then at this time you'll have to live with the geometry as is. The patch command also allows to set continuity conditions for the boundaries, but the patch command also creates a "draped surface" and that has it's limitations. 

We don't have an un-trim command (yet) that would allow you to use the original surface.

In some cases a loft might b a better option.

In general I think that you'll only have to resort to your bread-slice technique in extreme cases.

[Anonymous]

Hi karina,

               Bread slice cuts are section cuts. I used them when an extended and extrapolated surface was needed for a cutting tool path transition to start towards cutting the part. The section cuts were a check against potential failure Sometimes ( iN catia V2  1980's) the surface was an extended 5th degree polynomial curve set which can have a squiggle when extrapolating/extending  out beyond part boundaries.  The squiggle in tool path is what plunges the tool into edge  part. I was asking  to see if that heartache has been corrected with T splines. 

[TrippyLighting]

A T-Spline ins an intermediary between a quad mesh (mostly) and a NURBS surfaces. With the timeline enabled, once you leave the form environment the T-Spline is converted to a 3-degree NURBS surface.

This thread has a few interesting details about extended surfaces.