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INDEX
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Introduction to Cabochon Cutting and the Lapidary Hobby
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Introduction
This article is intended to be a guide for the beginner in the art of cabochon cutting and a brief overview of the lapidary hobby. No attempt is made to present all of the views on the various steps in the cutting, sanding, and polishing process. The
steps described here are those used by the author to instruct beginners in his shop and have been refined by 20 years of cutting for both the hobby and commercial fields.
The Equipment
There are five types of power equipment used in amateur cabochon (cab) making: slab saw, trim saw, grinder, sander, and polisher. There are, however, many different types or models of each.
Slab Saws
Slab saws are used for cutting rough rock into slabs for cabs. They are also used to cut rough rock into shape for bookends, intarsia, jewelry boxes, etc. Slab saws use a large (10" to 36") diamond blade in an oil or water bath to cut rock. The rock is
held in a vise and fed into the blade by lead screw or gravity. There is usually a cutoff switch at the end of cut. An easy way to clean the oil from slabs is by covering the slab with "kitty litter".
Trim Saws
Trim saws are used to cut the slabs into a rough outline of the final shape desired. They are similar to the slab saws but use a smaller diamond blade (4" to 10") and some have small clamps to allow slabbing of small rocks. The slabs are hand held and the
clamps are usually hand fed. Almost all older saws use oil as the cutting lubricant while the newer saws use water to which a wetting agent is frequently added. The blades are available in several different widths from .004" to .035" with the thinner
blades generally used on more valuable material such as opal.
Grinder
Grinders are used to shape the rough outline of the cab from the trim saw into the final shape and size desired for the cab. Grinders may be 4" to 8" drums or flat wheels and may be silicon carbide or diamond. The cab is hand held and almost all grinders
use water as the cooler and lubricant.
Sander
Sanders are used to remove the grinding scratches and to pre-polish the cab. Like grinders they may be 4" to 8" drums or flat wheels and may be silicon carbide or diamond. The most common sanders are 6" or 8" expandable drums that can use either silicon
carbide or diamond belts. There are also some inexpensive 6" or 8" flat wheel sanders that use adhesive backed diamond disks.
Polisher
Polishers are used to put the final shine or polish on the cab. They are usually 6" or 8" disks with a leather disk that has the polishing compound applied to it as the wheel turns. The compound is usually tin or cerium oxide, one of several commercial
polishing compounds, or diamond.
Other Equipment
There are a few other types of equipment that are in common use in the hobby. Flat sanders are used to sand large flats for use in book ends, display slabs, jewelry boxes, lamps, and intarsia. Wood sanders were popular at one time but are not used much
now. They used diamond compound applied to wooden drums. Tumblers are used to polish small stones. Rotary tumblers are relatively inexpensive and are frequently the first equipment used by the beginner. Vibrating tumblers are more expensive, but polish
stones much faster.
Diamond vs. Carborundum
The question always comes up: which is better diamond or carborundum (silicon carbide)? The answer is diamond is faster, silicon carbide is cheaper. If you can afford diamond you will like it better, but if you are cutting agate or softer stones (and that
is what most everyone cuts) there is nothing you can not grind, sand, and polish with silicon carbide. If you plan to cut sapphires or harder stones, the wear rate on silicon carbide is so high that diamond is the only practical answer. In addition to
speed, silicon carbide requires more care to get the same results. Silicon carbide belts wear enough that a used 400 grit may be finer than a newer 600. The life of the belts is enough shorter that most people are willing to pay the extra money. Diamond
grinding wheels require a true running arbor. Grinding cabs and especially larger rocks on a diamond wheel that has play in it can hammer the diamonds loose from the surface. Silicon carbide is more tolerant of a small amount of hammering and, since they
need to be trued up with a dressing tool to keep the surface flat anyway, the dressing process can remove a small amount of runout.
Safety
The lapidary hobby is relatively safe, but there are a few areas where accidents could happen. Always use safety glasses when cutting on the trim saw. The saw cuts fast enough to send chips flying. The heater to warm the cab to be dopped is an alcohol
lamp with an open flame; keep your fingers and flammable items away. Never grind or sand anything dry. Dry sanding is recommended for some stones, but until you know which stones are safe it is not worth the risk. Dry sanding raises a lot of dust. The
possibility of adverse affects from exposure to, or breathing this dust is too high to justify it. Wet sanding holds the dust in the water and it is not a health hazard. The grinding and sanding wheels are all smooth enough to present no hazard to your
fingers, however, sometimes the edges are sharp enough to give you a cut similar to a paper cut. Just keep your fingers away.
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Copyright, 1997 by Dick Friesen
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Dick Friesen writes, "I have been cutting cabs both as a hobby and as a commercial cutter for about 25 years. I teach lapidary for our local Gem and Mineral club and for
our local recreation department. I also do lost wax casting to keep my
sanity when all else fails. I am retired from Lawerence Livermore National
Laboratory where I ran one of their larger Physics ADP systems and did network
design."
The lessons will continue next month!
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