After reading all the posts about drilling, I find I have some
important things to add. I did an article about this for Lapidary
Journal a few years ago.
First, your drilling process will improve a great deal if you add a
soluble oil to the water. There is a brand called Tool Cool that
works well. This will also save your bit.
Second, when you first start, the bit will cut well. When it begins
to slow down, as it will, it is because the diamonds have been worn.
If you’re using smaller bits in the mm range, sharpen the diamonds and
clean the bit by running the tip of the bit over a grinding wheel,
preferably aluminum oxide while the bit is under water.
I use an old glass soap dish to hold the piece of stone in which also
has the oil and water, about 1/2 and 1/2. You should be able to tell
whether you’re drilling throught the stone by a swirl of dust that
comes out of thie hole. If there is no swirl, try sharpening. Also,
once you’re finished drilling, the solution can be left to separate
If you sharpen and it still doesn’t cut, use a fresh bit.
Finally, don’t be tempted to turn the piece over and try meeting the
holes from the other side. It won’t work.
Good luck. the drilling takes much longer than you expect,
especially when \you think you ought to be through by now.