All you have to do is create a thread profile using a helix and then using a spiral. Assuming the thread profile starts out in line with the axis, the isocurves of the helix based surface will remain oriented toward the central axis while the spiral will
twist. I’m not claiming this is wrong. I’m saying there is no automated way to do a proper radial sweep along a spiral in Rhino. Radial Sweep is a missing feature that other CAD programs have.
The sweep1 roadlike option produces a radial sweep when the path curve is circular when veiwed from the cplane plan direction. For any other curve that is not circular (when viewed from the cplane plan direction) the resulting surface will not have isoparms kept in line with the axis.
Rail revolve is another tool that behaves similar to a radial sweep. Rail revolve keeps the interpolated profiles oriented correctly to qualify as a radial sweep but it scales the profiles based on the distance from the defined axis instead of sweeping the profiles along a path.
Radial sweeps have been included in CAD programs for many years because they are important in defining the geometry of things like augers, centrifugal pumps and turbines.
Ultimately what we are talking about here is what rule is to be followed for orienting the intermediate profiles that are created before all the profiles are interpolated to create the result surface.