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Drilling Holes in Agate Slices


You will need a sturdy drill press that will turn fast, about 10,000 rpm. Don't use the new Dremel drill press as they flex too much. The old metal ones are good, also the Foredom drill press is good, if you have their tool. I use an old Dunmore. Your drill press doesn't have to cost a lot. I purchased a metal drill stand at a yard sale for $2.00 and mounted my Black & Decker rotary tool in it, and that also works well. Do not buy the Covington gem drill to drill agate, as it goes too slow. It is meant for soft stones, not hard rock like agate.

Drill Bits:

I start with a small hole. If it needs to be bigger, I ream it out. It is much easier to drill a small hole than a big one. I start with a 1.4 diamond bit, then I ream it out with a 1.8 triple ripple diamond bit - this bit is fluted and tapered. I only use it as a reamer.


I use Kingsley Tool Cool to keep the bit cool. You will need a shallow container to hold the stone to be drilled and the coolant. I put a think wood backing under my stone so that the bit does not puncture my container as the bit comes through the back of the stone. Put just enough coolant in the container to cover the stone.

The Method:

Now, here is the secret: Use light pressure and a rapid up and down motion. This will keep the diamonds on the bit cool and lubricated. Too much pressure and you will fry your bit or break your stone. If you do not go up and down fast enough, you will burn the bit up. You will find there is a rhythm to it, and within a few slabs, you should be onto it.


I get 8 to 12 holes out of my 1.4 mm bits, and about 100 holes with the 1.8 mm triple ripple bit. Remember, this bit is just used as a reamer, not as a drill bit. I use the Kingsley North bits - their cheap ones - if you can call them cheap!

Tip by Steve - on LA-Rocks, May 2008 Via The Pegmatite, San Diego, CA, August 08