Using a Sphere Machine
When buying a sphere machine, you also need to think about what accessories are necessary for using the machine. Covington Sphere Machines are designed for use with Cast Iron Cutter Cups and Silicon Carbide Abrasive. We recommend purchasing Old Miser binding compound along with your silicon carbide abrasives because it helps the grit stick to the sphere and promotes the grinding process.
Silicon Carbide is available in coarse, medium, and fine grades and we suggest beginning with a 60/90 grade for the initial grinds. From that point you can move through the 120/220, 400, and 600 grades to prepare your sphere for polishing. At this point it is important to again consider the type of material you are working with.
By consulting the Polishing Guide, you can decide which polishing compound will work best for your stone or glass. A good, low cost polish to begin with is the Covington Gold Polish #1. This polish is good for approximately 50% of stones.
If this doesn't polish your stone you can move up to a higher grade polish such as Covington Gold Polish #2 or Cerium Oxide. These are inexpensive polishes that will polish most stones. If these are still not polishing your pieces, consult the polishing guide and choose a polish such as Tin Oxide, Chrome Oxide, Linde ‘A’ Polish, etc., based on your stone and needs.
For the polishing stage, you will typically cover the clean cast iron cutter cups with a Leather Disc and attach using a wire wrap or some other form of sturdy material. The polish and leather combined with water and the motion of the unit will polish the stone.
It is important to remember that Sphere Machines need to be watched. Should the grit slurry or the polishing compound dry out, the motion becomes ineffective and can ruin the piece. Always keep the sphere in a slurry state. It may be handy to keep a small spray bottle close at hand to watch and spray as needed.
It is also important to keep fresh grit handy. Use your ears to listen for a cutting or grinding sound between the cups and the sphere (note: you will not hear a cutting sound during the polishing stages). If you do not hear the cutting sound you may need to add more grit. Keeping a close eye and ear on the machine will result in a faster grind.