"Joe AutoDrill" fired this volley in
news:z78Ni.28281$Ww5.16972@trnddc03:

I was reviewing some charts I have on tapping speeds, etc. and noticed
that the creator of the cart included information for tapping ceramics
and glass.

I can see tapping macninable ceramic or especially "green" ceramic
items, but glass? I suppose it could be done while the glass is
semi-molten, but how else could you tap a hole in glass?!?

It's actually not difficult. The secret is in how _little_ material gets
removed on each revolution. It's easy, for instance, to smoothly contour
a glass edge with an abrasive belt. There's "cutting" going on there,
too. The material is removed in such small amounts per "pass" that it
doesn't break.

There are some special, very-slow-taper, taps for brittle/hard materials
like glass. They progress from minor to major diameter at only a few
thousanths per inch.

Fine threads are a bitch, though. That's more a job for an abrasive
process.

LLoyd