In India many years ago the cutters cut lot of sapphire from there, the form was the same what they found in the river but well polished by hend. We call it Free form cabochons. They made lot of silver things with these sapphire for the Maharadsas..After the cutters had best toosl for cutting and they make nice stones, half side round half side flat like in this time.
Now you can buy very good tolls for cutting, like concave diamond wheel ( 1. photo) But many cutter use cabbing machines with 6 or 8 cutting wheel.
How can you cut cabochon? Firt you need a stone slab, if yoi have cutting machine you can cut, if not, you can buy. You need template with round and oval form, these are same size like the stone settings , after you finish your stone you can put the stone to the settings and the jewellery is ready.
Next step, make marks to the slad with pencil or aluminium stick, they are semi waterproof. ( 2. Photo)Now you can cut it with a thin cutting disc. If it is ready gluing the stone to dte dop stick with lapidary wax.( 3 photo) Next step sending the oval with 80 grit diamond wheel, i use a Diamond Pacific wheel for it.
If the oval is calibrated cut the top, first 45 degres to the side and afrte finish the arc.
I use after it a 80 grit dics an othet type of diamond disc from Diamond Pacific, it is a NOVA wheel
this is soft, i can push the stone into the wheel, this give me a perfect form, i start it with 220 grit and after 600 and 1200 grit.