cabmaking2

How To Make a Cabochon, page 2
by Paul W. Cinnamon

STEP #4:     CABBING MACHINES
     You may use any of several types of machines to cut and polish cabs. They all perform the same basic functions, and all are capable of producing good quality work. Only the techniques used will vary slightly from one type machine to another.
     If you have an older type rotary machine, it may use one or more silicon carbide grinding wheels. If this is your type of machine, you should take care when first starting your machine because it is possible that as the machine begins rotation the lap wheel can break and the pieces become dangerous missiles. This is much more likely to occur if the last user of the machine didn't allow the wheels to spin dry before the machine was turned off. When this happens, the water which was absorbed by the porous silicon carbide wheels all gradually seeps downward accumulating on the bottom side of the wheels, seriously throwing the wheels out of balance. Occasionally, a wheel can get out of balance due to wear or some other factor. If you observe an out of balance condition, use with the machine with care, or replace the wheel or wheels. If you experience only a small persistent out of balance condition, you may need to true the wheel. Several companies make diamond bar lap wheel dressers that you can quickly use for this purpose. If, after truing all your silicon carbide wheels, you still have an out of balance condition; you may be able to minimize it by the following process. Loosen one of the wheels and rotate it about 1/4 turn at a time and then re-tighten it. Then turn the machine on and observe whether the rotation helped or made the condition worse. Continue the process one wheel at a time until you have the vibration minimized.
     The main drawbacks to using a machine with silicon carbide wheels is that it's messier, and has more of a tendency to undercut on materials having varying degrees of hardness.
     You may use a flat lap machine, including any faceting machine for cab production. The machine I usually recommend to a beginner is a variable speed, machine that uses 6 or 8-inch diamond laps. Hi Tech, and Ameritool are two manufacturers who are usually represented at our shows, and sell these machines new with all laps for around $250. - $350. They usually set up several of these machines to demonstrate, and if you ask early, you can often save substantially by purchasing one of their demonstrator units. Used machines of this type are also occasionally available.
     The most popular cabbing machines in use today are diamond rotary wheel units. Models are made using 4, 6, or 8-inch wheels. Diamond Pacific's Genie is a 6-inch wheel machine, and is probably the most used.
     A few notes regarding diamond laps and wheels. The diamond grits used on most commercial laps and wheels are imbedded in, or secured to a rigid backing of some type. They will cut quite efficiently for a long period of time if proper care and procedures are followed. One cutter may be able to produce 1,000 stones without wearing out a good quality diamond lap, while another inexperienced cutter can ruin the same lap or wheel on one stone. Although the diamonds are much harder than any material other than another diamond, they can be dislodged or fractured, or prematurely dulled by excessive pressure of the cab against the lap. On the rigid backed wheels, hold only sufficient pressure to keep the cab in constant contact with the lap. If the lap isn't cutting as rapidly as you would like, change to a lap with more coarse grit. After cutting quite a number of cabs you will notice that the lap doesn't cut quite as rapidly as it did when new. Remove the wheel, turn it half over and reinstall. It is now running in the opposite to its original direction, and a fresh leading cutting edge of the diamonds are now being used. You may greatly expand the cutting efficiency and useful life of wheel laps by this process. The same can be achieved with a flat lap if your machine is reversible.
     On the popular Nova type diamond wheels, there is a sponge type backing. You can place considerable pressure on this type of wheel as long as care is taken not to introduce a sharp edge into the wheel that cuts the surface.
     Laps can also be ruined by running dry or with too little water. I run more water on my laps than most cutters. I normally bind both fountains of my Genie together, thus doubling the water supply to the wheels. I don't ever operate the wheel in a condition where a dry streak is visible behind the point of contact with the material being cut. The water also assists in flushing the debris cut from the cab from the surface of the lap. Without this action, the lap would soon become clogged, much as a piece of sandpaper will become clogged when used on a heavily painted surface. Any clogging action will decrease the amount of cutting the diamonds achieve. I generally don't add anything to my water supply, but a drop or two of a liquid detergent such as Joy or Dawn will break the surface tension of the water and probably increase the efficiency slightly. Several companies make additives and coolants. My advice is not to waste your money. Just use clean water. If the water contains lots of minerals, empty and clean the machine each time you use it. The only exception to this advice is if your water supply contains minute particles of sand, as with some poorly filtered well water. In this case you may experience minute scratches because the quartz sand is contaminating your polishing laps. To eliminate this problem, you may need to purchase distilled water to use in the final sanding and polishing steps.