Cutting toothless weirs in back of tanks with a Dremel for external overflows
 

I have a 90 gallon tank I'm putting two external Herbie overflows on. They will be 25cmX20cmX11cm. The tank glass is about 1cm thick but the overflow glass will be 6mm.

I was going to drill the tank and have 90-degree upturned PVC elbows to bring out the water to the overflow boxes, but they will not have as much surface skimming area as the weirs would, almost 2.5-times less, in fact. Not to mention, others have told me this could be noisy.

Then again, others have mentioned that cutting weirs in the back of tanks can weaken it and possibly cause cracks.

In any case, which is the better way to go? And if it's weirs, then how do I do it? I have a diamond bit to drill small glass holes, and I also have a tungsten carbide bit. Will these work or will I need a glass cutter? I'll also need to cut out chunks of the upper plastic rim, which I'm not crazy about.

Please help. Thanks. :)

well what you were going to do with having upright elbows is that your having 2 overflows and that i mean you have an internal and exterior overflow, one overflow to the exterior one then down to the sump, that is as least what it sounds like to me. cutting a weir can weaken the glass because people have done is at a 90 corners instead of rounding it, what i mean is that when you get to your corner of the weir instead of going round and then across then go straight down which with glass you cant do everything needs to be rounded on an inside cut. so you can do a wier yourself but drawing out your wier lines that need to be cut, START with drilling to holes on the corners so that the sides of the hole are touching both lines and then cut the glass down into those drilled holes, then sand or dremel it smooth so that they are perfectly inline incase you couldnt cut the lines straight. stick some eggcrate for a snail guard and there you go a wier cut, make sure you use alot of water as usual with drilling glass. if it doesnt work i can be to blame by the way. but that is how you can make a wier cut on your own. or take it to a store. that way you are only having one overflow or just go with an internal one. hope that helps a little.

Can u not drill the bottom of the tank?

No, it's tempered.

did that help at all??

Yes, it does. So instead of having perfect rectangles, make the edges sounded so as to keep the glass stronger. What I'm most worried about is cutting the plastic upper rim and keeping the lines straight. I'm picturing my lines not being straight at all. I really don't want to mess up an expensive tank. Do you think using a glass-cutter to score the straight lines then snapping it would be do-able for 1cm glass? Also, do you know if the Dremel comes with a jig to keep it straight? Thank you for your help. :)

Drill the back and have 90' elbows into the bulkheads?

Cutting the weir yourself sounds a bit risky.