whenever i would mention my intent to drill holes in the glass and use bulkhead fitings to plumb from underneath, fellow fishkeepers eyebrows would go up, they would think that i would have to be crazy. "wont it leak?" "youre going to drill the glass by hand?" everybody seemed to think that it sounded like a bad idea, and they said that they would be afraid to try because of the risks of cracking the tank.
I talked to people at the lfs, they didnt know anybody who would drill glass for pay. then i called a local reef shop, they didnt know either.
One thing that i have noticed is that everyone seems to be afraid of this, but yet all over the net are pics of drilled tanks that have the super clean, no equipment look, and videos of people drilling tanks. So i did what i always do, forgot about the naysayers, bought a pair of 1 7/8" glass hole saws and got to work.
i drilled about 12 holes in a 10 gallon tank for practice. the first 3 came out very junky, i cracked the glass a few times, until after about 8 holes it just came natural. the next 4 were easy.
Then moving up to the 1/2" glass, custom built 125.
Drilled one hole for about 20 minutes and popped through, no snags, no chips, it was close to perfect. Then the second one was a bit harder.
I switched to the new bit at this point and it is much easier to snag a fresh and sharp new bit than a smoothed out dull one. the upside is that cutting goes a lot faster. so i started the second, it took probably 5 minutes less to do the second because the bit was so much sharper. I did not realize how far through i was already when the bit busted through the last bit of glass right as i was shifting my weight a little bit and was still putting a slight amount of pressure on the drill. so that hole has some minor chipping, which goes into the glass about 4 mm from the edge of the hole on one part. I think it will be fine, at least im hoping.
I plan to use gaskets on both sides of the glass anyway.
I think i could have both holes perfect, but this is acually really easy to do and i am glad that i did it and everything turned out good.
So i encourage anybody who has been thinking of doing this to take the plunge and order those hole saws. order an extra so that you can use one to practice, and grab a 10 gallon tank and punch about 10 or 15 holes through it. then you will be ready to tackle any tank, the thin 1/8" glass is probably the hardest thing you can try to drill because it is so brittle that even a minor snag will crack it. So it's just that once you get the drill started on cutting the hole, you keep going and dont stop until you sink the bit all the way through. there is definetly a technique, and the one i used is to start at a slight angle at a medium speed, about 1500 rpm if i had to guess and just stick it right into the glass. once it sarts cutting you can slowly start to level it out. then you just let it cruise along at a speed just high enough so that the drill wont snag. and use only the weight of the drill, plus a tiny bit. then, as you see water start to leak out into the other side, you know youre getting close, so you hold the drill steady, and you speed up the drill slightly, and just let it go and pretend that you are trying to keep the drill hovering, weightless until the glass drops out through the other side. That's all there is to it.
I used the hose and set it up to where it would keep a slow flow of water flowing over the area. I used both hands to keep the drill steady, and i used a great corded power drill. i think a cordless drill would suck for this purpose. I have one that i bought around 2000, it is skil brand, i think i paid 30 dollars at osh for it. it has keyed chuck and plugs into the wall. to me this is the best kind. and it has seen heavy, heavy use, polished lots and lots of aluminum parts with it using a buffing wheel and compound, where it is being ran at full speed, until it gets so hot that i cant hold the handle anymore. that takes a long time. i have drilled thousands of holes and mixed concrete with it. So you can see that i abused and beat the crap out of this thing for 8 years and it still works 100% perfect, and i only paid 30 dollars for it. That is a hell of a bargain to me and i love my drill.