Drilling glass for big bulkheads a few ?s

[Hustler]

I need to drill for 2 2" bulkheads in my sump.
It currently has a 1 1/2" bulkhead where i need to have a 2" :) can I drill over that hole seeing as its a larger diamond holesaw bit? Ide drilled plenty of larger holes in 1/2 and 5/8s glass but ive never re drilled in the same spot...
I may also have to drill in place so the glass will be verticle.... Im thinking ill use the putty with a half cut tupperware dish so its half submerged and I can pour water over the top aswell..... anyone ever tried this method? or have a better one lol
It always takes me a few beer to try and punch through glass..... this job will be worse on the nerves for sure

[ScubaSteve]

I need to drill for 2 2" bulkheads in my sump.
It currently has a 1 1/2" bulkhead where i need to have a 2" :) can I drill over that hole seeing as its a larger diamond holesaw bit? Ide drilled plenty of larger holes in 1/2 and 5/8s glass but ive never re drilled in the same spot...
I may also have to drill in place so the glass will be verticle.... Im thinking ill use the putty with a half cut tupperware dish so its half submerged and I can pour water over the top aswell..... anyone ever tried this method? or have a better one lol
It always takes me a few beer to try and punch through glass..... this job will be worse on the nerves for sure

You can re-drill over another hole. I did it recently and it was easy, though nerve-racking. If you can move the tank and lay it flat to drill, your life will be much easier. I recommend making a guide from a piece of plywood or MDF by drilling a hole the same size as your cutter and clamp it in place; that'll stop the diamond cutter from bouncing and chattering which is very important when re-drilling. Doesn't have to be clamped (got my roommate to hold the guide) but you don't want it moving around.

[jr999]

I've never drilled over an existing hole but using a 2x4 with a hole cut just bigger than the OD of the diamond bit helps me keep the bit from wandering. Do you have a piece of glass you could drill your holes sizes in as a test run.

http://i304.photobucket.com/albums/nn185/jr099/bit001.jpg

[The Grizz]

+1 on the above, you need to center the bigger hole over the small hole and clamp it good. Lots of water & take your time it is a breeze.

[Hustler]

Ok ill give it a shot with a 2x4 and clamps... first i have to try and dig out the sump......damn center braces and plumbing.... need a sawzall just to budge it