<a href=showthread.php?s=&postid=14175908#post14175908 target=_blank>Originally posted</a> by DgenR8
I went the extra 9 yards and bought a drill press (Harbor Freight, about $100.00). It's great for keeping the hole saw exactly where you want it, with no chance of deviating from a 90* angle to the glass, but more importantly, can be set for a very slow rotation speed.
This is not an option on a tank with water in it, but if you want to be sure that you are doing everything you can to prevent breakage, it's the way to go.