Hi Brian,
attached is a simplified drawing showing the variable pitch helix and the nod file so you can see it work.
( the full drawing of the Screws is 2g so otherwise I would have posted it)
I have added an entry and exit pieces to show the areas I would like to include in my nod file.
These areas will not have any Bottle rotation.
I haven't any particular requirements for a screw at the moment but with this facility it will be easy to test.
Cheers
Barry