Rifling or helical vanes on non-straight funnel?

[B3nn]

I’m trying to figure out the best approach to create rifling inside a funnel.
If I make a rifling feature and rotate the base around the funnel axis, the path doesn’t maintain the contact to the funnel surface.

Any suggestions to accomplish this on my iPad

[TigerMike]

Here’s one way. It is rather quick and dirty but it may give you some ideas.