Glass drilling (again)

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coralnerd

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May 11, 2006
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I'm thinking about building a sump for my 4 ft glass aquarium. The plan is use it for a freshwater setup for now, with scope to add a skimmer and convert to marine in the future. My problem is finding a way to shift the water from the tank to the sump. I have more or less decided that a wier or standpipe in the corner with drilled hole at the bottom with a fitted PVC bulkhead is the way to go. I prefer the aesthetics and simplicty of this setup compared to an overflow box setup.

I rang around most of the local glass workers, and almost all of them refused to drill an aquarium, because they're afraid of cracking it. So I'm starting to lean towards doing it myself. Can anyone give me some advice? I read another old thread on this forum that discussed this issue, but there wasn't much detail. I gather that it's not too hard as long as your glass isn't tempered. The question is, how can you tell if it is tempered or not?
 
I did this same thing last weekend, only I wanted to drill a side overflow into my sump tank for automatic water changes. I too could not find a glass place willing to drill a glass aquarium even though I called many of them. The best they would tell me is that they would drill the glass if I could seperate it from the tank. If you've tried this you found as I did, it's asking the impossible.

I went to home depot and bought the largest glass bit they had which was (1/2") and bought a cheap 10gal tank to try it on. I did some searching on the internet for how to drill glass and found a number of links, which I'll add to the end of this.

Anyway I managed to drill the 10gal tank no problem, however, with the hole only being 1/2" in diameter I figured I'd need at least 6 to 8 of them to get an outgoing flow rate that exceeded the incomming flow rate. I abandoned this idea figuring it would be a chore to get a water tight seal on that many holes.

I found a cheap 40mm diamond coated glass drill bit on ebay, seller was lautszyan0@netvigator.com from Hong Kong. I bought some bulkheads from Big Al's online that would fit in a 1.5" hole (close to 40mm).

I have a small cheap benchtop drill press in my garage. I mounted in on the edge of my workbench with the table over hanging. I clamped some scrap wood to the bench to support the tank, and mounted the tank on it's side with the drill press table inside the tank. I also attached a small piece of wood to the metal drill press table to protect the table and the glass that would be in contact with it.

After marking my holes with magic marker I used my daughter's play dough to form a bowl around where I was drilling to fill with water. I set the drill press to the slowest speed (500rpm).

For the drilling, it is a little different than drilling through wood. You dont drive the drill bit through the glass, you allow it to just come into contact and rub it's way though very slowly. It took me about 30 mins to grind my way though 1/8" glass and about 45 mins to grind my way through 1/4" glass.

The sites I found strongly recommend that you drill part way through on one side then flip the glass over and finish from the other side. I did not do this because the top of my drill press would not fit inside the tank. As a result when the bit came out the other side on the 40mm holes, it was not a nice clean sharp edge, but instead had some tiny minor chips around the inside corner of the hole. Not a big problem since the bulkheads I bought have a large rubber gasket that completly covers all the chips, however, I'd imagine that if the bulk heads ever experience a good strike from something that is where a crack will form.

The best tips I can give you are, start cheap, that way if you screw up your not out much, and wear hearing protection. Some of the squeeks that were produced while drilling would resonate in the tank and get loud enough to get your ears ringing. At no time durring drilling should the drill bit get hot to the touch.

As promised here are some of the links I found:

http://www.drillglass.com/drillingglass.html

http://www.uhh.hawaii.edu/~pacrc/bigisaquapg/Drilling.htm
http://www.wetdryfilter.com/drilling_holes.htm
 
Thanks a lot. That's a big help. Especially the playdough idea to keep the area wet. I'd already been shopping around on ebay for drill bits, and now I'm thinking that this the best way to go.

I would have to use a hand held drill, since I'm talking about a 4' tank, and its too big to get under a drill press from any angle. It probably would be possible to go halfway then turn the tank over, but I'd be worried that the bit would not line up exactly with the groove I'd already made on the other side. I have visions of the bit catching on the glass when it breaks through and sending enourmous cracks across the base of my tank. Should I be worried, or is it really as easy as it looks in the pictures I've seen on the web?
 
I would strongly recommend the drill press if you have access to one, it gives you much better control while drilling and allows you to stop and restart with everything staying in position. The only draw back is you loose the sense of feel for the amount of force you are appling, so you have to be very careful.

I just had a thought on how you could drill the bottom with a drill press. You would mount the drill press so that the top is overhanging a work bench edge and turn both the base and the table around backwards out of the way so that they are not under the drill bit. I suggest clamping or bolting the drill press in place. Then mount the tank upside down under the drill bit. I would recommend that you support the area under the glass you are drilling with a block of wood. I suppose this would also work with a hand drill.

The only limitation with using a drill press would be how far in from any edge of the tank you can drill. You'd be limited to a maximum of the distance between the drill bit and the center support column of the drill press. I don't think this would be an issue though, because I can't think of a reason anyone would want to drill the center of the glass on any aquarium side.
 
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Oh, one more thing I found. The small glass drill bits look like a rod with a flat metal spade shaped tip. The larger glass drill bits look more like a hole saw with like diamond sand paper around the edge instead of teeth.

I also saw references somewhere to using a piece of pipe as the drill bit and using and abrasive material between the pipe and the glass. I didn't really look into this much, but it is probably much cheaper than buying a glass bit. I bought the bit, to keep things simple for my level of inexperience.
 
If you drill the side of a tank, chances are it is not tempered glass, and therefore can be drilled.

Larger tanks usually have a tempered glass bottom. Any holes desired must be drilled before the tempering process. In my younger days I tried to drill tempered plate to achieve a small hole using the same type of spade style bit. The result I got was an instant explosion of glass shards from end to end with total destruction of the plate. There were no salvageable pieces left.

In short, before you drill the bottom of your tank, contact the people who made your tank and find out if the bottom is tempered glass plate. Some makers are now using tempered plate for the backs of their tanks, as well.

Here is a link to a pic of what happens when one tries to drill or re-shape glass plate after the tempering process:

Tempered Glass Fragmentation

v/r, N-A
 
After reading that article posted by vidiots, I suspect that the bottom pane of my tank isn't tempered, as it is quite thick (about 7 or 8 mm), and feels like it has some give in it when I tap on it. Ie. it vibrates and seems to flex slightly in response to pressure.

I doubt that I'll be able to find out from the manufacturer, because I have no idea who the manufacturer is. I've had the tank for over ten years. I'll try calling the shop I bought it from (if they still exist) and ask them if they can help me.
 
Before I can get this hole drilled, the question I need to sort out is what size bulkhead fitting I should use.

The only ones I can find that are available through Asutralian suppliers are a 25 mm or a 40 mm fitting. I'm planning to use a 2500 lph powerhead to pump the water from the sump back into the tank. It will be lifting the water about 1.2 m (4' for the americans), which according to the manufacturer will produce about 2000 lph at the outlet. Does a 25mm (1") bulkhead fitting sound big enough to accomodate that kind of flow rate? Or should I play it safe and go for the slightly more expensive 40mm fitting (which will require a larger and more expensive drill bit for the hole)
 
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