"Randy H." wrote in message
news:VtcTd.117917$0u.32003@fed1read04...
But ceramics vary widely in their properties, and this is one you could
only
learn from experience, unless you trip across someone else's account of
how
it's done -- from experience.


When I worked for Dow they brought in a ceramic they wanted me to try and
drill with the ultrasonic drill we used on glass. After 2 days drilling
and
wearing out 4 bits I was able to make a 3/16" wide dent about 1/8" deep in
it.

This stuff had a Rockwell rating of 97 for hardness!

Some of the engineering ceramics are unbelievable.

Back when GE had a division working on making injection-molded,
silicon-nitride turbocharger turbines (around 1980), they sent us editors a
sample of the material, which was a stick around 4" long, 1/4" wide, and a
little more than 3/16" thick. Silicon nitride is as hard as the hammers of
hell and I expected it to be brittle. So I closed the door to my office,
propped the stick up against the bottom of the door at a 45-deg. angle, and
stomped on it with the heel of my shoe.

It dug a 1/2" gouge in my door. But it didn't break the first time. I really
had to hit it very hard before it broke.

--
Ed Huntress