I helped a neighbor put a 3/4" hole in the bottom of a decorative clay pot for her fish pond. She enlarged the fish pond and now needs the the hole enlarged for a greater amount of water throughput to 1 1/2". I have a 1 1/2" hole saw, but centering it over the already drilled hole is easier said than done. Suggestions? Put a thin piece of wood over the hole and go through that? Put the wood on the inside (I can adjust how far the drill bit sticks out)? I'm sure some of you have had this dilemma before. I'm sure after I've broken the pot when I get done, someone will tell me "Oh, you just.... Thanks for any ideas people.