How to drill holes in glass without breakage
November 16, 2005 8:16 PM   Subscribe

Drilling holes in glass blocks without breakage: Looking for tips (and anecdotes about diamond drill bits) to stop burning (drilling?) through other people's money.

I'm drilling 1/2" holes in glass blocks (the kind used in showers) with a bit specially made for glass and tile. Previously (when the weather was warm) I drilled maybe 30 or 40, had about 15% break, now I'm drilling in cold weather (once with cold blocks, the other with them at room temp), and the breakage is doubled. It's to the point where I'm afraid to start another because I don't want to break someone's $4-5 block.

The bit gets dull really fast (seems to be 5-12 blocks), and I suspect a block breaks when the bit is too dull, but the bit is also $12-15.

I read a little about diamond bits, which are flat cylinders (the one I'm using is an arrowhead shape), and one was advertised to cause less breakage (if any) and to be usable for ~200 drillings.

The glass I'm drilling is about 1/2" thick, and the box usually seems to break about halfway through (i.e., the bit's tip hasn't broken through the surface yet; the speed picks up after that happens).
posted by artifarce to Home & Garden (10 answers total) 1 user marked this as a favorite
Best answer: Mineral oil, according to a glass artist friend of mine.
posted by piro at 9:06 PM on November 16, 2005

Are you running water over it as you drill? Both for the cooling and for bit life.

I do believe you'll find the cylinder-shaped bits last much, much longer. Guarantee it, in fact.

Use a drill press. You can find a cheap one for under $80, and resell it when you're done for $60. Well worth it.
posted by five fresh fish at 9:16 PM on November 16, 2005

Response by poster: I have a drill press and I'm intermittently spraying the bit with water (don't have a method to run water over it). Thanks for the tip about the cylinder bit though.
posted by artifarce at 9:31 PM on November 16, 2005

I haven't had good results with the spade bit drills. You might want to check out the diamond hole bits here.

The best results I've had are from using a drill press. Make a little clay dam around where you want the hole, and keep the bit in water.

Or, you could just use acrylic blocks instead of glass.
posted by Marky at 11:05 PM on November 16, 2005

Best answer: Or use clay to make a dam for the coolant ,
I use a section of copper pipe with a slot cut in the end, this slot feeds silicon carbide grit,(water souluble valvegrinding paste) 400 grit cuts fast, way cheaper than diamond ,even diamond needs constant cooling though. The trick is to let the abrasive do the work, don't push it .
posted by hortense at 1:14 AM on November 17, 2005

Used to be you could get a tungsten carbide drill bit. Dunno if they're still made, but they do not get dull on glass.
posted by ikkyu2 at 8:31 AM on November 17, 2005

Best answer: Whenever I've drilled glass, I used a standard masonry bit with valve grind compound, or lapping compound. Basically, the bit wasn't cutting the material, but spinning around a slurry of abrasive compound. It was very slow, but effective.

I don't know if it makes sense to use compound with a edged bit.
posted by Jack Karaoke at 9:43 AM on November 17, 2005

Missed hortenses post, yes.. that was my method, though I didn't have a choice of grits at the time.
posted by Jack Karaoke at 9:45 AM on November 17, 2005

Response by poster: Thank you for your responses. I have plenty of places to start now.
posted by artifarce at 11:05 AM on November 17, 2005

Best answer: Tungsten sucks on glass.because you have to push to hard to get it to cut. Silicon carbide /diamond cuts best with low pressure(no chips) coolant coolant coolant. If you use a twist drill with grit run it backwards as this feeds grit to the cut, and speeds things up.
posted by hortense at 11:16 AM on November 17, 2005 [1 favorite]

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