2d spiral and swept cut issues

Hello there,

I seem to have run into a wall that I can't google my way out of, as most issues similar to this is regarding helixes.

I have a simple extruded base from a circular sketch. In this boss extrude I'd like to remove what essentially looks like an hourglass sketch along the path of a spiral on one surface.

I can make a simpler box shape work, but not an hourglass shape. No errors pop up, it just doesn't do anything though it thinks for 5 min like it does when it works. 
Would anyone have a clue as to what is wrong