carbon frame (giant)

 From:  Michael Gibson
1012.6 In reply to 1012.1 
Hi Jack, it can be pretty tough to create smooth branching structures that have many junctures in them.

Here is one method that could work for your case here.

I started with your curve framework, mirroring a couple of pieces:

Next from the side view I drew the curve shown in yellow here:

That is now used as one of the rails for a 2 rail sweep:

That sweep now creates one major element of your shape. Next I mirrored and stretched out some of the curves on the right side, and then used Loft with the closed option to create this second shape on the right side:

That's the other major element. These pieces are running into each other, but that's ok, the next steps are about fixing that up. Next I went to the side view and drew this curve shown in yellow here, it will be used to cut the sweep:

Then the sweep is trimmed using that curve as the cutting object:

Another view of the trimmed sweep:

So that trimmed sweep is an interesting part. It would be quite difficult to try and create the above shape just using outline curves only (I mean like trying to sweep or loft that final shape directly instead of using trim). Sometimes it is easier to make pieces extend in larger swoops and then trim out the areas that you don't want.

Next I switched to the front view and drew an outline curve that generally followed the shape of the hole in the sweep:

I actually drew only half of that curve and then mirrored it to get symmetry, but then I also joined the 2 halves together, turned on control points and deleted the control point where each half touched, to fuse them together into a single segment. That just ensured that the curve would be smooth and would also end up being a single edge when it was used as a cutter for Trim.

Then I trimmed the right-side piece using that curve as the cutter:

Next I selected these 2 inside edges where the holes are at:

And then using Construct / Blend will fill in that area with a smooth surface:

The final result:

This one was done kind of quickly, you can tweak the shape quite a bit by making the width of the right-side piece match the width of the left sweep part a bit better, in this version the right-side tube is kind of bigger.

So the basic idea here is to try and build that thing in pieces, but actually not too many pieces. If you break things into a whole bunch of little pieces you will be able to surface all of them, but it will be difficult to maintain smoothness between each little piece. If you create fewer broader pieces, it can be easier to get a smooth result, like that sweep is able to generate a nice smooth curve for the whole left side of the shape.

Then combine the pieces together either using fillets or blends. In this case I tried filleting, but it was a bit bunched together since the lower tube is a bit narrow and kind of curves fairly tightly, it was easier to make a more gentle shape there by trimming it to my own drawn outline curve rather than the constant distance type trim that filleting generates.

I hope this helps, let me know if you have any questions on any of these stages or if you get stuck somewhere.

Model attached as .

- Michael