Drilling Established Tank

[2pts]

I've never done a tank with water in it but I have drilled 1 unsuccessful hole, then had the glass re cut and drilled 3 successfull holes.

I bought my glass hole saw from princess auto. The hole that cracked the glass... I drilled with the hole saw and the centre drill bit that came with the mandrell http://www.princessauto.com/workshop...ories/list-all

The drill bit was not turning perfectly level, once the centre bit broke through, the glass cracked.

Second time round I removed the centre drill bit, and used a piece of plywood with 3 pre-drilled holes the size and place i wanted to drill on the glass. I also had a piece of plywood on the inside to help prevent chipping and "busting" through on the other side. I clamped them together on either side of the glass (already siliconed in place in the aquarium) I drilled 3 holes in a row like this with no issue. I also had a cold water hose trickling on the spot I was drilling the whole time.