[speakerguy]

After getting a quote of $100 from the glass store to drill three 1.5" holes in my 50 gallon tank with no guarantee that they wouldn't crack it, I decided to do it myself.

I bought a 1.5" diamond hole saw off eBay for $13 + $3 shipping.

To prevent the bit from 'walking' during the initial drilling, I made an 'L' out of two pieces of poplar I had laying around. The poplar 'L' was placed on the inside bottom of the tank with one side against the back glass. The bit was positioned inside the corner of the 'L' so that when it turned it would want to walk into the poplar 'L', which being held by my own hand ensured the bit wouldn't walk. This seemed fairly successful.

The cutting was very easy, the only part you have to keep an eye on is keeping the bit square to the glass. The more of an angle you have, the more chip out you will have on the back of the glass. For this reason, drill from the INSIDE TO THE OUTSIDE. Bulkhead gaskets go on the inside of the tank, so you want the best edge there with no chipout. The backside is less important, so a little chip out is ok there.

Drill anywhere from 60 to 180 RPM, just by sight. Put a marking or something on one side of the bit so you can gauge how many times per second it is going around. 1-3 times per second is OK.

During the cutting, keep a stream of water from a garden hose flowing over the area to cool the bit and wash away glass dust. Remember, you are sanding - NOT cutting - the glass away.

When you get towards the end, speed the drill up and do not apply ANY pressure. This will also help reduce back side chip-out.


I have never, ever in my life drilled glass before. Not even tile, or anything remotely similar. Today, using the method above, I put three 1.5" holes in the bottom of a 50 gallon tank successfully and for 16% of the cost a glass shop would have charged me. It was very easy, took about an hour to an hour and a half to drill three holes, and looks pretty good IMO.

 

[Fortuna Wolf]

I fully agree. Drilling glass is very easy if you take it slow with plenty of water and very little pressure. The only problem I've had was with thin glass and small holes - I didn't temper the glass and a few weeks later they cracked, I guess because the holes changed the stresses in the glass.

 

[speakerguy]

I've read that it's actually easier with thicker glass, assuming you go slow. My initial experience would seem to bolster that too since I was doing 3/8" glass.

 

[JG06]

If you want to clean up the outer edge of the hole, try some 400 grit wet/dry sandpaper with a little water.

Just be careful where you put your fingers...it'll bite ya if you aren't careful!

 

[RestlessCrow]

I fully agree. Drilling glass is very easy if you take it slow with plenty of water and very little pressure. The only problem I've had was with thin glass and small holes - I didn't temper the glass and a few weeks later they cracked, I guess because the holes changed the stresses in the glass.

Since I work with glass I feel pretty confident commenting on this and wanted to share a little anectdote. Yes, Drilling glass is easy. I recently had a customer ask me to drill 47 holes around the outside, bottom rim of a lampshade to hang prism's on. The hardest part was marking out the holes to get them spaced evenly.

Glass DOES have internal stresses in it which is why the glass shop wouldn't guarantee. (I don't either, and in fact have all my customers sign a waiver.) With all that said, I have a 99.9% success rate. One time however, I had ground down the top of a Waterford Decanter for a woman to remove a big chip and it came out beautifully. The work was all done, the woman came to pick it up, I set it down in front of her. She picked it up, inspected, and was raving about how well it came out. She set it down and started to reach for the packing material, and we heard this "BING"

Well... the grinding had released some internal stresses. The decanter was sitting on the counter and just cracked. No one was touching it at that point. She looked at me, I looked at her.....

"If I hadn't been here, I wouldn't have believed it". She said.

Ya win some... ya lose some.... Glass is a funny substance.

 

[Burks]

Best place I've found to order: http://www.glass-holes.com/

Funny people, great products. I used one of their overflow kits and loved it.

 

[jestep]

But can you do this?

I wish I had the guts to pull this one off, because I need a 75 drilled, and I don't want to drain it...

 

[jestep]

Well... the grinding had released some internal stresses. The decanter was sitting on the counter and just cracked. No one was touching it at that point. She looked at me, I looked at her.....

"If I hadn't been here, I wouldn't have believed it". She said.

Ya win some... ya lose some.... Glass is a funny substance.

That's what you call brittle fracture. Imagine what the people were thinking when this happened, literally sitting in the harbor...

 

[Diana K]

In the link "Can you do this" see how the drill and hole saw is wandering around so much?
Avoid this by setting up some sort of jig as described by the original poster.