RTH Forum Tutorial

How to Drill Holes in Cabochons

By: RTH Member Zoran

Posted: Jan 3, 2007 at 6:29pm (lightly edited for readability)

I was asked to explain the way I am drilling my cabs, so here it is. Since a picture speaks a thousand words then I am going to tell you about 20,000 words. 🙂

My drilling tools. ;D I usually use a cable attachment with a handle at the end but since it is broken I am drilling directly with rotary tool.

These are electroplated diamond drill bits that I usually use for my holes. One to the right is 1.5mm and the other one is only 0.5mm at the very top.

Sometimes I use this vise to hold a cab (when drilling front of the cab). This is all I need.

And we must not forget the cabochons.

Now let’s drill some holes.

First I’ll drill plate like cab and I will be using a vise.

My first step is to always mark the position of the hole.

I use wooden plates and vise to fix the cab. Several wooden plates beneath the cab and one or two on top of the cab (depending on the thickness of the cab) so that last plate exceed the edge of the plastic box.

Pour the water just slightly over the top of the hole spot. Vise should not be tightened too much.

Drilling starts. The most important thing is to use just a slight pressure all the time.
It is also very important to “open” the hole. Since cab is polished and domed, drill bit very easily slips and leave very ugly scare on the surface of the cab. To avoid this to happen I use almost no pressure, just touching the marked spot. If the cab is domed I point the drill under 90 degree angle versus the spot of the hole. When I “open” the hole I am easily moving the drill to the vertical position (as can be seen on the next pic).

You need to pull out drill bit often and use extremely light pressure, in fact just hold the drill and diamonds on the drill bit are going to do all the job. If you are pressing too hard, cab is going to break and drill bit is going to last only very short period of time.

And there is the cab with a hole.

I, usually, don’t use vise. Sometimes, I even can’t use it because of the shape of the cab and position of the holes. In that case I hold the cab with my hand.
This is the cab that need to be side drilled.

Firstly mark the position of the hole

on the both sides.

You need to drill holes from both sides so they should meet somewhere in the middle of the cab. That way you are avoiding chipping and breaking. You must place and press your cab against the wooden plate and in no case cab should be lifted.

Hold drill under 90 degree angle against the edge of the cab, all the way of drilling. Very important is that your right hand have good support (hand that holds the drill).

Inspect holes frequently. You should be able to see when two holes approach each other (I hope that you can see that in the pic). Then you should be very careful and use virtually no pressure, frequently changing sides, allowing two holes to meet.

Sideways drilled cab.

Today’s drilling results. I drilled these 6 holes in about 90 minutes, but I lost lots of time photographing. Drilling a hole takes different time. Depending, of course, on hardness and thickness of material that you are drilling and complexity of drilling. Hard agate cab takes about 5-10 minutes (sometimes even 15 min) while malachite takes only 1-3 minutes.

Hope I was clear enough in spite of my bad English.
Zoran