Opal cutting using flat lap machines has many advantages. For many years I had cut and polished opal using the conventional grinding wheels. I started on a two wheel carborundum grinder as that was all I could afford. By being very careful and ensuring I used the full width of the wheel this produced reasonable results. I was then lucky to purchase a four diamond wheel grinding machine together with a home made polishing disc run off an old washing machine motor. I still use both of these items of equipment today and they work well. Photos of these two pieces of equipment are shown below.
4 Wheel Grinding Machine
The grinder set up now has 3 cutting wheels and a leather polishing wheel which I added.
Opal Polishing Disc
Flat Lap Machine
Another piece of equipment I purchased was a faceting machine made by a member of the Nunawading Lapidary Club. These machines are very robust and were made for club members to learn faceting. For years I used this machine to facet all sorts of stones. I still love faceting but have a greater passion for cutting opal. Several years ago I decided to switch to this machine to cut and sand opal and found it had a lot of advantages over the wheeled machine. A photo of the faceting machine is shown below.
Faceting Machine
The main advantages in using the flat lap machine are:
(1) You have a much wider area of wheel to cut on. The ordinary diamond wheel is fairly narrow and you have to be bit careful not to drag the stone onto the edge of the wheel. With the flat lap you have a much wider area to cut on and can use wider strokes making cutting that much easier.
(2) You can get your face a lot closer to the cutting surface thus getting a better view of what you are cutting. As I get older this is important as I can see a lot better just exactly what I am doing.
(3) Sitting down at a flat lap machine is much more comfortable. Usually I stand while using the conventional grinding wheels and this can get uncomfortable after a while. I find I can cut quite comfortably for several hours at a time whereas I could not do that on a wheeled machine.
(4) You can cut perfectly round or square stones using the faceting arm. It is extremely difficult to cut a perfectly round stone or ones with parallel sides such as a square or rectangle without using some sort of mechanical aid. The faceting machine has an arm with graduated wheels to allow you to cut these sort of shapes if you wish.
There are of course some disadvantages in using the flat lap machine. The main one is that you have to continually change the flat laps over rather than just moving to another wheel on the multi-wheeled grinder. I usually cut with a 400 mesh lap, then progress to a worn 600 mesh and then sand with a wooden lap with 1200 grit wet and dry glued to a thin rubber backing on the wooden lap. This means at least 3 lap changes per stone. In order to minimise the need to change laps I usually cut at least 12 stones at a time. This way I can coarsely shape the 12 stones before proceeding to the finer grinding stage. This works for me quite well.
The two opals shown below were cut and polished for a client this last week using the flat lap machine and polishing lap using cerium oxide as the polishing medium.
Gem Opal
Opal Potch
As you can see a really good cut and polish can be achieved using this equipment. You don't have to have the latest expensive pieces of machinery to cut opal or any gemstone for that matter. You do have to have patience, a light hand and a bit of experience. The only way to get that is to cut as many opals as you can and learn from your mistakes.
On this website there are quite a few posts to assist you with a few tips on what to do to ensure a good cut opal. If you have any queries please email me and I will reply as soon as possible.
Johno