The first thing to always remember is: Heat Is The Enemy. Diamond bits cut by abrasion, grinding away the unwanted material to make the hole. This process creates a lot of heat. Diamond bits "wear out" because the heat melts the metal and the diamonds fall off. There are several ways to get the most out of your drill bits.
Always use a lubricant. There are several water soluble lubricants on the market. Plain water is better than nothing, but metal is best protected with a lubricant. Drilling underwater – with the bit and stone submerged – is great for reducing heat, but it is messy. The best way to lubricate your bit is to use a water soluble additive and water in a squirt bottle. As you are drilling the waste material accumulates in the lubricant so a new squirt from the bottle pushes the dirty lubricant out of the way, thus helping to keep the bit cool and allowing you to see the drilling area better.
When purchasing a diamond drill bit be sure you get the speed recommendations for your bit. Different manufacture’s will have slightly different recommendations. Larger bits need a slower speed and smaller bits faster speeds. I have found that using the slowest recommended speed is best, (that heat factor). As an example, The Gem Shop, has a drill press with the top speed being 3600 RPM. The 2.1mm bits we use from Chrystallite recommend 5000 to 20,000 RPM for this bit. The top setting on the drill press works fine. Slower drilling is much better for controlling the heat. Larger drill bits that require slow settings should be used as close to the recommended speed as possible.
The actual drilling process should be slow and easy. Spray, press, release, press, release, spray, press, release, press, etc. One second for each process, just about as long as it takes you to say it out loud. The pressure on the drill bit should be minimal. The bit cuts by abrasion so it only needs to come in contact with the material. Too much pressure only causes more heat.
The stability of the bit is important while you are drilling. The bit should only extend out of the chuck a small amount further that the depth of the hole you are drilling. This allows for less vibration which lowers the level of heat. If you are drilling with a dremel, foredoom tool or other tool, your bits will last longer the better you can stabilize your drilling tool. Also, be sure the surface under the piece you are drilling is soft such as a piece of wood to protect your bit.
A stick of Dop Wax
When drilling pieces that are not flat, it is best to use something to hold them firmly so they do not move while drilling. You can use dop wax on a piece of wood. This works well as the stones are very still. You will need to heat the wax and the stone. Put a blob of heated wax on a small piece of wood. Position your stone in the wax. Push the wax around the stone and allow to cool well before drilling. Pry the wax and stone off the board, then put the wax and stone in the freezer. After an hour or so take it out and gently chip away to remove the wax. There are other clay or putty-like things that could be used but I have not tried them. I have also used other small pieces of wood and wooden clothes pins for holding stones still while drilling.
Be aware that when you drill a hole straight through, it will chip out the back of the hole so be sure to drill with the side you want to be the top or front facing up. When drilling flat pieces that are important to have a good hole on both sides, it is necessary to drill from both sides. I have made a holder from a piece of wood and some used drill bits for lining up the second half of the hole. Use a regular drill to drill a hole in your pieces of wood and then tap a "dead" drill bit of the same diameter bit into the wood. It is important when drilling this way that you do not press your bit into the metal of the bit underneath. To avoid this, drill the first part of the hole 2/3 to ¾ of the way through, and make sure your bit tapped into the wood sticks out only a very small amount.
I have also found from my drilling experience that Chrystallite makes the best drill bits for the money. They are more expensive but last longer by far, drilling more holes.You can purchase Chrystallite drill bits, Tool Cool lubricant, and dop wax on our Lapidary Equipment page.