loft with spline 3d sketch control curvature and tangency

[Raluca-CoffeBased]

Is there a way to better control the curvature of a 3d sketch in all 3 dimensions?

I made a surface loft using a 3d sketch and because I cannot control the curvature very well I obtain a wonky geometry that when offset or thickened results in errors. The tangency of the 3d sketch is hard to control in the "xy/flat dimesnion" but i think it's the "height/z" adjustment that makes this geometry so hard to resolve.. So I am wondering if I am missing some fundamental principle of curvature-control for this 3d sketch? Is there a way to control the curvature in all 3 dimensions or somehow ensure tangency to a vertical or horizontal line in such a way that when mirrored it would result in a smooth comb? I attach some images to try to explain what I mean.

 

 

[TrippyLighting]

Please share the model. Export as .f3d and attach to post.

[Raluca-CoffeBased]

Ah yes indeed would make more sense with a file 🙂

And yes, the loft can be created with just ONE loft not a sweep and a loft, I tried that too with simlilar results, I am almost 100% sure the problem lies in he tangency/curvature of the 3d sketch spline

[TrippyLighting]

I would use a different modeling approach that does not exhibit these problems:

[Raluca-CoffeBased]

Thank you Trippy for your alternative build-up!! Much appreciated! It's a bit harder to calculate the dimensions of the resulting geometry an the constant radius changes the design intent but yes, a good approach

BUT

that's not the point, the point is that I am trying to use this as an example to learn how to control the 3d sketch spline curvature/tangency in all 3 axes to ensure less errors. Yes in this case it was possible to replace the 3d sketch with 2d sketches and a different buildup but I'm mainly wondering in this article how to better control the curvature of the 3dsketch spline (and splines in general), not how to replace it with regular sketches 🙂 I hope you understand what I mean?

 

But yes, thank you for taking the time to build this!

[TrippyLighting]

this was created with a single closed spline defining the upper rim.

I created sketches for the rails with 5-degree control point splines, to ensure I'd have a single-surface loft. Probably not necessary.

Trying to get this curvature continuity by defining constraints between individual curve segments is going to fail. 

[davebYYPCU]

Your curvature comb is correct, 

take that the open end of your body is at 6 o’clock, then the most curvature in your spline is at 11 and 1 o’clock, and the comb reflects that as expected.

Might help.....

[TrippyLighting]

Fit point splines are 5-degree multi span spline and I would not use them if you model only half or in this case a quarter of the model and then mirror.

In my last example I used a single closed fit-point spline for the upper rim, which is why that works.

Trying to get true G3 curvature continuity across a symmetric surface - that's what you're really looking for -  not just an edge is not possible with this modeling technique in Fusion 360. 

[TrippyLighting]

---

@davebYYPCU wrote:

Your curvature comb is correct, 

The 2 combs in his screenshot show G2 curvature continuity. What he's really looking for, however, is G3!

With this modeling technique in Fusion 360 that can only be achieved by hand tuning the tangent handles, or as in my design below the 2 free control points of the 3-degree control point spline. 

[TrippyLighting · Accepted solution]

Ha, I'll eat my words!

Using a 3D  3-degree control point spline (single span, so with 4 control points) and some fine tuning by hand, I was successful. In essence, do not use fit-point splines for this if you want more precise control!

[Raluca-CoffeBased]

Trippy, you made my day man! Kudos and champagne! 🙂 🙂 🙂

 

Okay so that's done, thank you so much Trippy!

And ps: I am a woman 😉

 

[TrippyLighting]

For surface based workflows I very often refer to the Autodesk Alias Theory Builders. While Fusion 360 does not nearly have the tools and abilities to control surfaces Alias has,  the basic concepts are the same.

Another very good reference is this blog post written by Jake Fowler.

And if you are really interested in surfacing, I can hotly recommend is the Handlebar 3D YouTube channel. While he uses Alias, a lot of the concepts and also some of the techniques can be used in Fusion 360. It is generally very educational to see how a true professional works with the surfacing tools in Alias.