>A few weeks ago, I got a frosted glass 1/3 sphere from a friend.
>He was going to throw it out.  As a pack rat, I took it.  Found a
>use for it as a lampshade in my son's bedroom.  Just had to drill
>a 1/2" hole in it.
>
>I had a 1/4" tile & ceramic bit from some bathrooom work.  Great
>for tile.  It's a pointed ogive shaped flat cutter mounted on a
>shaft.  Package claimed it would do glass.  Cost about US$8.
>
>It does work.  Took about 10 minutes on the drill press.  Maybe I
>could have gone faster if I had pushed harder, but flexing of the
>glass surface made me nervous.  I then used a 1/4" bit on my wife's
>glass grinder (for stained glass) to enlarge the hole to 1/2".

My experience with doing this is that it works, but it does pay to half the
glass item under water to keep it cooled. It may be sufficient to have a
stream of water flowing over it, like lubricant in a machine shop. The
biggest problem seems to be localised heating from the drilling causing heat
stress in the glass and making it crack. The Ogee shaped bits seem to be
available at quite reasonable cost at local DIY stores here in the UK.

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