Saturday, April 7, 2012

Small Holes & Hard Rocks

So you want to drill a hole in a cabochon or other gemstone? Drilling gemstones has to be one of the most challenging and potentially frustrating lapidary techniques to master. The holes are usually small, the stone is harder than expected, diamond burrs wear out or break and it always requires more time than planned. Plus, there is always the problem of the gemstone chipping around the hole. Or even worse, the stone becomes a pile of worthless and sometimes very expensive fragments.

Sandy Craig at Orca Gems developed the following method. Admittingly, stone drilling is still an intimidating process, yet I've had a lot of luck with this method.

Get a plastic bowl, a piece of 1"x4" wood and a nail the same diameter as the drill.

Drill a hole in the 1"x4" the same diameter as the nail.

Insert the nail through the board and into the bottom of the plastic bowl. Epoxy everything in place and to seal up the hole in the bottom of the bowl.

Clip off the nail at about 2-3 mm.

Drill the first hole to a depth equal to the length of the nail or half the total speth of the hole.

Now clamp the board and entire drill in place so that the nail is centered directly under the drill.

If done properly, the nail will hold the cab in place. Drill the second portion of the hole.

No chipping. No blow-out. No mess. Just a nice little hole.

Add a pinch bail to complete the project. (This cab still needs to be polished. So a little water was added to show what is will look like when finished.)

If the hole is off-center, use a bead reamer to straighten it out. This method works great for stones up to a hardness of maybe six and for drilling side-to-side and front-to back. The maximum depth is about .375" to maybe .5".

If you need to drill something harder or deeper, then it's probably better to get something like this

Can't afford a $1800 tool to put some holes in rocks? Here's a gemstone drilling service. An average hole will run somewhere between $8 to $15 depending on the diameter and depth. The minimum order is $150. The holes from an ultrasonic drill are usually cleaner and don't require polishing. 

If drilling gets into to your blood, you can try to go crazy like Craigor Clark does at Slice of the Universe. 

Minnesota Lapidary Supply sells a few accessories for drilling that look very useful.

One additional tip.

If you need to core drill a stone, glue a thin piece of wood to the back of the stone. This will normally stop any blow out when the drill finishes the hole. Someone also mentioned using cardboard instead of wood.

Good luck!

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