I have to drill a 1/2" hole in a piece of flat glass. I have a diamond hollow bit. First two attempts on small pieces of sample glass failed with resultant cracked glass. Both pieces failed as the bit broke through. I am using right speed and water lube.

Any hints?

Thanks

Peter
UK

Pete,try a pc. of 1/2" diameter brass round stock and some valve lapping compound found in automotive supply houses.Put your round stock in your drill press and mix up a slurry of valve compound and clock oil.Apply the slurry on the glass underneath the round stock on a continuous basis while drilling.The valve compound acts as an abrasive and will slowly abrade the glass until the round stock cuts through.Slow and steady is the keyword here.Make sure you have a good solid support underneath the glass to prevent flexing.
Best of luck with your glass project.
Bob Fullerton

Bob, I'd heard of your solution using copper pipe, but thought i'd go for the easy solution with a diamond cutter!!
Actually made some progress. Your no flexing hint is key and I have found that cutting from both sides reduces breakout and stress too. Now have one sucessful hole. I think I will use my milling machine for ultimate stiffness, albeit when I 've thought through how to protect it, from diamond slurry.
Thanks Bob,

Peter

Make a dam around the hole with modeling clay, caulk or some like substance so the slurry isn't running all over the glass

Curly

Curly
Yes I have done that and one hole protection is fine, I have to drill 3 holes in close proximity so I'm not sure I can 'dam' them separately, maybe I duck tape the drilled hole. Well get there!
Thanks for your response.

Peter