Having a Boolean Difference problem

 From:  davidb45
I think I did everything you suggested. It did get rid of the mico-hole in the center of the wheel.
I went back to the basic shape of the slot cutter and did a new array, this time picking the center of the
wheel Revolve and not the slightly off center of the slot cutter. I then did an Extrude on one of the new
cutters, then a Boolean Difference. Unfortunately, it still did not cut holes in the wheel.

I have attached a new 3dm file. I could just use the corrected files you sent me, but I need to
understand my mistakes.

Thanks for you help.