Need Help - Drilling 10 gallon

[jphong]

Hi guys,

I need some advice on drilling 10 gallon tanks. I tried on 2 of them already and just as it was about to punch through the glass cracks with the crack extending from the hole to the top edge and near side edge. I tried varying the speed and pressure but it doesnt seem to help. Im about 1" from each edge at the corner.

Any ideas? I tried my 15 gallon which had thicker glass and drilled two holes no problem.

From the looks of it is seems that when I am just about to punch through the thin layer of glass left shears off and in the process induces the cracking.

Thanks for any help I can get, John