I want to know the best way to draw a spiral screw in Solidworks (see attached).  The attached file was imported from another drawing software.

I'll ultimately want it to start as a 12" wide, 6" pitch and transition to something like a 16" wide, 8" pitch.  But the exact numbers aren't real important to me right now... Just how to do it.

I'm running Solidworks Standard 2014.

Any input would be greatly appreciated.

Thanks