My approach involves Deform > Twist - you can pick the original curve used to revolve the shape, and apply 2 different twist angles using the same centerline as the main object, then rotate one slightly to open one end. Then using a combination of project and trim you can extract two new profile curves to sweep along the two twisted/helix curves created earlier. This swept surface closely (but not exactly…) follows the surface of the dome shape. Next, you shell it (centerline, both-sided) and work from there. I cut off some parts using boolean diff with a straight line for example.

The technique of using Twist on a revolve profile works in most situations where you need a helix to follow such shapes exactly. I think it supersedes DannyT's technique in many cases now that Twist is available to us.

Turns out you can even use the twisted curve to directly Trim the surface, yielding an exact segment of the shape you can shell and work with as well. This is what I've done in the attached image.

I've attached an example below - if you watch the styles closely you should be able to figure it out. Let me know if you need some more detailed instructions!

/ Fabien

Cool approach Fabien!

And yeah if you project the curve onto the dome first, then when you twist it the twisted result will still hug directly along the surface if the surface is a surface of revolution and it has the same axis of rotation as the twist axis.

Because with an exact surface of revolution if you rotate any point that starts on the surface around the same axis, the ending point will also be on the surface too since it has that radial symmetry...

I'm still getting used to all the possibilities opened up by Twist and Flow myself! :) Definitely helix-ish stuff and Twist are friends.

- Michael

Wow thanks guys for your input I'll be trying these later on.

Lang

Hi Fabien

Would you mind giving me a more detailed description of what your doing with that twist method as I can't work it out.

I've tried the drawing the curve directly onto the dome that works well, thanks Michael, but I'm having all sorts of problems getting the sweep right. I see what you mean about how hard that may be to get right.

Thanks guys

Lang

Hi all

I've been playing around with the twist and sweep function and am getting there I think. Still not perfect but may be good enough for what I need. I sweeped the curve with 3 different circles as these work quite well around the tapering shape of the dome. No matter how I do it otherwise I can't seem to get say an oval to work how I want it so maybe one of you more experience guys out there can help me out on that one?

I have another issue going on here with the file attached. Basically I can't fillet the edges around the sweeped boolean shape to soften the edges and have come across this problem a few times. The object is unified and joined so don't know why it won't fillet. I've also tried using a very small fillet amount to begin with but that won't work either. I reckon its going to be something really simple no doubt that I'm missing here.

Thanks again for any advice here folks

Lang