A Little on Faceting a Gemstone: A basic overview of the Step by Step Process
Step One: Selecting the Rough
The starting point for cutting a gem is, of course, the rough. The rough gem is then sawn and ground into a shape close to that of the finished stone. The "shaped" rough is called a preform. The Gem Bot actually has a preform form function that turns your stone into a basic shape selected based on the design. A big key at this first step is to identify and remove any remaining flaws and then find the shape of the rough that will yield the largest stone out of what remains.
Step Two: Making the Preform
The preform is cut with diamond grit saws and ground on coarse grinding wheels. One side of the stone is cut with a flat surface - this will eventually become the table or main flat facet on top of the stone. In the beginning, this main flat facet is used to orient the rest of the stone. This is where the dop stick will attach. At this stage the stone is called a preform, and you can see what the final shape will be. You can either preform the rough by hand or let the Gem Bot create the basic shape for you. The table will need to be made flat before centering and attaching the rough to the dop stick. The preform is ready to be "glued" to the dop stick. The flat tops of these dops are matched to the flat table facet on the stone. The glue that is used is actually a special high temperature wax or sometimes a superglue or epoxy resin.
Step Three: Dopping the Stone
The dopped rough will now be glued flat side down (the table) on to the dop stick. You want to try and get the dop stick directly in the center of your table. The rough end of the stone will be cut away to form the pointed base of the stone. Faceting is a process of grinding and polishing - this is true with both diamonds as well as colored stones. One or two and sometimes even three different grit flat lap wheels are used to grind in the facets and a polishing lap with a polishing compound is used to put a final polish on them. Diamonds are cut and polished on one lap.
Step Four: Cutting the Stone
The bottom part of the stone is cut first. The bottom part of the stone is called the pavilion and girdle. Each flat facet is cut on a series of grinding laps, and then the lap is changed and each facet is polished on a polishing lap with a series of different grit polishing compounds. The location of each facet is set by the toothed gear (index gear) and cut at specific angles. The Gem Bot makes this process very easy. You simply select a design. Calibrate, go through the preform function and go through the cut process.
Step Five: Cut and Polish the Cullet, Transfer
The bottom part (also called the cullet) of the stone has now been cut and polished - all the facets on the base are now polished and complete. Now it is time to cut the upper portion of the stone, known as the crown. In order to do that, the stone must be transferred to another dop. The new dop will hold the base of the stone so that the top portion is exposed for cutting and polishing. As the first dop had a flat surface to match the table facet, the second dop has a "V" shaped notch to match the "V" shaped bottom of the stone sometimes a cone shaped dop can also be used, even a flat dop. This all really depends on the design you have chosen. Transferring the stone should be done with precision to keep the stone aligned center and true also so the facets meet up as they should based on the selected design. A transfer jig can help keep this precision.
Here is a video going into detail of how to add a design and cut the girdle of the stone.
Here is a video of cutting and polishing the pavilion
Step Six: Polish the Table and the Crown
The stone has now been transferred from the first dop in order to turn it over for polishing the top side of the stone - called the crown. The first facet to be cut and polished on the crown side is the top flat or table facet. In order to do this, a special 45 degree dop holder is needed to allow us to reach the table. After all the crown facets are cut in and polished, the stone is removed from the dop stick and cleaned to remove any remaining wax or glue. The wax can be softened by gentile heat, and most of the wax removed. The rest of the wax used in this process washes off the stone when it is soaked in alcohol.
A detailed tutorial with videos for cutting a gemstone with Merlin's Gem Bot Automated Faceting Machine will be posted soon. Stay tuned!
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