[ruevs]

Had to Google this one :-)

Since SolveSpace has a helix tool that can "extrude" any sketch along a helix it should be doable.

https://www.linkedin.com/pulse/dreaded-double-helix-tutorial...

[contingencies]

That's the right target in Solidworks, but I'm seeking open source solutions.

I think the very latest Blender can do it, I haven't got it working yet though.