Inventor needs to be able to create a variable pitch helix, similar to the way Solidworks does it. I've used it in Solidworks to create variable pitch plastic injection screws with very complex double lead screw flights. It's as simple as entering in the starting diameter, starting pitch, height or distance, ending diameter and ending pitch. You can enter as many combinations as you want and it builds one continuous helix which can then be used as a path for a sweep. Here's an example of how Solidworks does it. Very easy to use. Much easier than using an equation curve in Inventor 3D sketch.
http://www.youtube.com/watch?v=aLQceqGgfh0
![Autodesk Design & Make Report](https://forums.autodesk.com/t5/image/serverpage/image-id/1350519iCB55845EBFC43016/image-size/large?v=v2&px=999" "Autodesk Design & Make Report")