Drilling hard stone

Help…I need to drill a post hole into a stone with a hardness of
7-7 1/2. Composition is hydrous iron, magnesium, andaluminum silicate.
What would be the fastest, eastiest and most efficient method of doing
this?? At present our method is to use a drill-press with a “triple
ripple” diamond bit, and drill it under water. Slow…tedious…and
the bits break…Heeeeeellllllppppp fellas!!!

Lisa,(fire in the woodstove, rain outside, the stupid bowl on the
tube today, and I’m off to a salsa lesson) Topanga, CA USA

Lisa, The tripple ripple may not be the problem, a more efficient
coolant such as a light oil and a gentle pulsating action. remember a
small diameter hole needs regular clearing to allow the coolant to
prevent the diamond surface overheating and stripping. David

Hi Lisa from Topanga -

I recently drilled more than 20 synthetic corundum (hardness 9)
faceted bottom, buff top stones - I used hollow core drills from
Stuller, while not a superb quality in my opinion, they did perform
well. I made a “holder” from Fimo clay, baked it, then epoxyied it to
a piece of steel . I used my CNC machine to “spot” the holes for
consistent centering, then used the drill press for the finish
drilling. I have diamond drilled stones for over 20 years, and yes,
plenty of water is the order of the day, but only in so far as you want
to keep a somewhat constant supply going to keep the drill from over
heating and remove the slurry which builds up. In order to eliminate
a messy “breakthrough” on the back side, I stop short and the come in
from the back by hand, using a smaller diameter drill or the angled
edge of the same drill to get the holes to connect. Fimo and stone may
be seen here Good Luck! P.S. I am writing a book about jigs and
fixtures for the bench jeweler, if you would like notice of its
progress e-mail me here

Where the Mountings Meet the Sea