drilling close to the edge/seam?

[Charney]

I am working on an above tank sump. It will be a 33g (glass) on top of my 120. I plan on using a 1.5 inch bulkhead to drain into the tank from the bottom panel. How close can the bulk head be to the silicone edge without risking the integrity of the glass? thanks

 

[deeda]

When I was drilling a bunch of 40B and 33L tanks for my fishroom, I found a link that recommended drilling the hole 1.5 X the diameter of the bulkhead fitting away from the edge of the glass. Unfortunately, I can't find the link now. Found it in the 2nd paragraph http://gmacreef.com/drilling-holes-bulkheads-glass-aquarium-tanks/

Another thing to consider is the flange on the bulkhead so both it and the gasket sits flat on the glass.

 

[duanes]

I usually allow at least 4 inches for the center of the drill bit, from the rim.
The overflow pipe here, is also 1.5"

the above sump/refugium I drilled is a 20 gal, I did slightly crack it toward the top. I find the smaller the tank (thinner glass) the easier it is to crack. Use plenty of cooling water while drilling and go slow.

 

[PYRU]

I usually allow at least 4 inches for the center of the drill bit, from the rim.
The overflow pipe here, is also 1.5"

the above sump/refugium I drilled is a 20 gal, I did slightly crack it toward the top. I find the smaller the tank (thinner glass) the easier it is to crack. Use plenty of cooling water while drilling and go slow.

I do the same