I concur with tmcpeek: Do USE the center bit as you need it as a guide for the hole cutter.
I have used a standard hole cutter, with the center bit, to cut out the holes on my DIY
skimmer. I first drilled a smaller hole then used the hole cutter. Just go at it very slowly, as the metal will heat up and the acrylic will start to melt if you go to fast. You don't want to end up with the hole cutter fused to the tank. 8O HTH