Conical knob

Added a conical top to the knob, with a raised ridge on the side of the cone. Also made the hole in the center round instead of 'D' shaped.

I had to use a raft, or it would not stick. Also, used supports, since I made it flat side down. I could have inverted it, but then the cone part would have had supports, and, while easier to remove, would have not left a smooth finish on the cone.