I've been trying to figure out how to cut the ribs inside the circle shown behind the glass.

I was able to cut the ribs if I just wanted to cut a round hole without the ribs.  But, I just wanted to cut the Ribs on the inside part since the surface round top and the bottom part is a green glass?  So that I can see through the glass without any ribs blocking the view.  Not sure whether I make any sense?  Any advise or suggestion?