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How can a person drill a hole into glass?

Drilling holes in glass is a tricky matter, but of course there are ways to do it.

The first problem is that to cut glass you need something harder than it is -- usually a diamond. (That diamond can cut glass is the basis of an old test for the veracity of a diamond ring, which is to see if it will scratch glass).

Cutting always involves friction -- something rubbing against something else -- so heat is generated. Usually when one drills a hole one has a very hard material relative to what one drills, i.e. a steel drill bit to make a hole in wood, and the friction is small since the hole is made quickly. With drilling a hole in glass, the situation is different because glass, while quite brittle, has approximately the same hardness as steel.

Drilling in glass is also tricky because glass is so slippery that it's hard to get a drill to make a hole in a given place unless there's a little hole to get started with. This is not much of a problem with softer substances such as wood because just pushing with the drill bit will make a decent starting dent and you can get going with that.

A diamond-tipped drill will help you make a very small hole. For bigger holes, there are tricks, and they all involve having a diamond going around in a circle the size of the hole that you want. For very thin glass, you can have a rod with a diamond tip swing in a circle about a suction cup that you stick to the glass at the center. There are also specialized drill bits that are hollow, with the diamond cutting edge distributed around the edge of something like a piece of pipe.

It's important to go slowly, especially when almost through, to avoid cracking or chipping the glass. Of course (need I say it?) always remember to wear safety glasses and all other appropriate protection!

Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.