NOTES FROM THE BENCH

Clock Repair Archive - -     How to drill glass ( flat, single strength ):

Please note: I have had many emails from persons having problems drilling glass. I must stress that my experience related here ONLY applies to flat, single strength, non-tempered, non-safety glass. Please read the note at the bottom of this page. This information is offered for free.
Your success at drilling glass is directly related to your experience and skill level. This information is intended for persons in the clock repair industry who are already master craftsmen and need some hints at how to drill glass. A person who does clock repair is most likely to have the skills required to successfully drill glass. It takes a lot of practice to get it right.

To drill a hole in a piece of flat glass with a diamond tipped drill bit ( use a "core bit" which has a hole in the center; its not a solid bit like a drill bit used for wood or metal ) use a leather washer with a bead of water in the center opening over where the hole is to be drilled ; this will allow for cooling and prevent the drill bit from wearing out prematurely. The washer does not necessarily have to be leather; it needs to be flexible enough to provide a means by which the water will stay long enough to get the work done. It is important to know that you are actually grinding the hole not drilling it. It is not like you would drill in a piece of wood or steel. Drill (grind) very very slowly with light pressure and only about halfway through the thickness of the glass ; ( use a drill press to do this at a fairly low rpm setting ( 300 - 400 rpm ). A standard drill press is what I have used set on the middle speed pulley) then turn the piece over and drill (grind) the rest of the way through on the other side. Use the - water in the middle - technique on the other side also of course. The holes on both sides must match up as closely as possible to prevent the glass from cracking. The glass must be supported by a surface that is absolutely FLAT AND LEVEL. By drilling (grinding) in this way you avoid cracking the glass when the drill bit breaks through on the other side. This works for flat glass.( I cannot tell you about jars, or plates,or decorative glass ornaments,etc. This technique may not be practical and I have not tried it on any of these. ) The pressure used to grind must be light pressure no more than 10 pounds at the point of contact of the working surfaces of the bit and the material being drilled; but this will vary and the most important part of the process is the feel of the drill grinding and moving very slowly through the glass. Don't try to drill it like wood or metal, you will break the glass for sure. More pressure will only wear out the bit faster and increase the likelyhood of cracking the glass. Be very patient and don't try to rush the job. Fifteen to twenty minutes of drilling on a 1/8 inch thick piece of glass is not uncommon. Try many scrap pieces first, if you have them, to get the feel of it. It took me many weeks to get to the point where I could drill holes in glass. I still have had it break occasionally. Don't expect to be able to drill glass as easily as wood or metal; that just does not happen; it is a very slow process and requires much practice. WEAR EYE PROTECTION. You can find more detailed information about diamond drills by following this link



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Copyright (c) 2002 David Tarsi. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being no invariant sections, with the Front-Cover Texts being no Front-Cover Texts, and with the Back-Cover Texts being no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

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